We-Hyo Soe

Yasuhiro Shirai

Corentin Durand

Yusuke Yonamine

Kosuke Minami

Xavier Bouju

Marek Kolmer

Katsuhiko Ariga

Christian Joachim

Waka Nakanishi

Conformation Manipulation and Motion of a Double Paddle Molecule on an Au(111) Surface

The molecular conformation of a bisbinaphthyldurene (BBD) molecule is manipulated using a lowtemperature ultrahigh-vacuum scanning tunneling microscope (LT-UHV STM) on an Au(111) surface.

BBD has two binaphthyl groups at both ends connected to a central durene leading to anti/syn/flat conformers. In solution, dynamic nuclear magnetic resonance indicated the fast interexchange between the anti and syn conformers as confirmed by density functional theory calculations. After deposition in a submonolayer on an Au(111) surface, only the syn conformers were observed forming small islands of self-assembled syn dimers. The syn dimers can be separated into syn monomers by STM molecular manipulations. A flat conformer can also be prepared by using a peculiar mechanical unfolding of a syn monomer by STM manipulations. The experimental STM dI/dV and theoretical elastic scattering quantum chemistry maps of the low-lying tunneling resonances confirmed the flat conformer BBD molecule STM production. The key BBD electronic states for a step-by-step STM inelastic excitation lateral motion on the Au(111) are presented requiring no mechanical interactions between the STM tip apex and the BBD. On the BBD molecular board, selected STM tip apex positions for this inelastic tunneling excitation enable the flat BBD to move controllably on Au(111) by a step of 0.29 nm per bias voltage ramp.

With the tip of a scanning tunneling microscope (STM), atomic-scale manipulation protocols are well-known since the pioneering work of D. Eigler, [START_REF] Frisch | Revision B.01[END_REF] and precise studies have described the various mechanisms of single atom (a small molecule) mechanical manipulations. [START_REF] Becke | Density-Functional Exchange-Energy Approximation with Correct Asymptotic Behavior[END_REF][START_REF] Becke | Density-Functional Thermochemistry. III. The Role of Exact Exchange[END_REF] Pushing a single large molecule on a surface with the tip of the STM [START_REF] Lee | Development of the Colle-Salvetti Correlation-Energy Formula into a Functional of the Electron Density[END_REF][START_REF] Ditchfield | Self-Consistent Molecular-Orbital Methods. IX. An Extended Gaussian-Type Basis for Molecular-Orbital Studies of Organic Molecules[END_REF] is now a standard procedure to position precisely functioning molecules on a surface for single molecule mechanics experiments [START_REF] Hehre | Self-Consistent Molecular Orbital Methods. XII. Further Extensions of Gaussian-Type Basis Sets for Use in Molecular Orbital Studies of Organic Molecules[END_REF] and also for single molecule electronic measurements. [START_REF] Hariharan | Accuracy of AH n Equilibrium Geometries by Single Determinant Molecular Orbital Theory[END_REF] To perform an atomically precise lateral manipulation of a molecule on a metallic surface with no mechanical interactions between the STM tip apex and the molecule, the bias tip must be able to feed up energy to the molecule with a few picometer lateral precision. [START_REF] Hariharan | The Influence of Polarization Functions on Molecular Orbital Hydrogenation Energies[END_REF] This excitation can be either inelastic from the tunneling current itself or originate from the enhanced electric field located in the biased tip/surface junction when the molecule carries a local dipolar moment. 9 For inelastic tunneling excitations, the energy entry port is generally the low-lying reduced electronic states of the molecule. [START_REF] Hariharan | Accuracy of AH n Equilibrium Geometries by Single Determinant Molecular Orbital Theory[END_REF]10 Here, a precise design of the molecule is required to avoid the energy provided by the tunneling current passing through the molecule from being equally distributed among the many mechanical degrees of freedom of this molecule. If not, a conformation change of the molecule may happen but with no lateral displacements. The molecule can also be broken in small chemical groups by the applied bias voltage pulse 11 instead of moving step-by-step on the supporting surface by steps, generally the commensurable surface atomic lattice constant. To also avoid energy redistribution toward the supporting surface, different leg and wheel molecular groups have been early identified. They can efficiently maintain a space (van der Waals distances) between the planar molecular chassis and the supporting surface. 12-14 Due, for example, to steric crowding, lateral chemical groups not having the shape of a leg or a wheel, mounted on the chassis in a symmetric way and holding it at van der Waals distances from the surface, are also interesting for molecular design as presented in this paper. [START_REF] Soe | Mapping the Excited States of Single Hexa-Peri-Benzocoronene Oligomers[END_REF] The light-driven molecular motor of the Feringa group the first switchable chemical group to be mounted by the Tour group on a chassis equipped with four wheels 16 in an attempt to leave space for this molecular group to change its conformation/configuration using an optical excitation. 17 A similar molecular switch was used by the Feringa group to obtain a molecule with four of those, used as switchable legs under a tunneling inelastic excitation. 18 Other switchable chemical groups are also available for equipping a molecular chassis. For example, molecules carrying a photoisomerizable double bond, such as stilbene, azobenzene, or diarylethene, have been used as molecular switches. 19 Their photoisomerization is usually studied in the gas phase or in solution. Conformation/configuration change triggered by tunneling electrons has also been observed in STM single molecule experiments, like with azobenzene. [20][21][22] Other molecules are also available which can twist around a single bond by photoirradiation. Twisted intramolecular charge transfer (TICT) molecules provide a nice example of such a light-activated conformation change. 23 Binaphthyl molecules or their derivatives (Scheme ) belong to another group of photosensitive compounds which are also known to change conformation under UV irradiation. 24,25 In this paper, we present the design and synthesis of a bisbinaphthyldurene (BBD) molecule (Scheme ) for STM imaging, single molecule manipulation, and step-by-step lateral motions. This molecule is equipped with two binaphthyl paddles mounted laterally on a very simple central phenyl chassis. On a planar BBD, we demonstrate here how to use the low amplitude vibration modes of its 1,1'-binaphthyl lateral paddles 26,27 for manipulating the BBD along a Au(111) surface using STM inelastic tunneling effects. Not existing in solution, this planar conformation is stabilized by the Au(111) surface. On Au(111), it enters in competition with its native in solution nonplanar conformation which can also be reached by the same excitation on a metallic surface as presented below.

In the initial subsections of the Results and Discussion, the design, the synthesis, and the structural analysis of the BBD molecules in solution are provided together with a detailed DFT theoretical study of the different possible conformations of a BBD molecule. In the following subsections, STM images of the BBD molecules on the Au(111) surface acquired at low-temperature (LT) and in ultrahigh-vacuum environment (UHV) are provided. We demonstrate how to prepare the BBD molecule in a planar conformation on the Au(111) surface using a very specific STM tip lateral molecular manipulation protocol. In this planar conformation, the BBD electronic probability density map of its electronic states around the Au(111) surface Fermi level can be recorded to prepare the BBD inelastic manipulation. In the final subsection, the entry ports for tunneling electron energy transfer to the BBD molecule are identified. It is shown how to STM manipulate step-by-step the BBD molecule by step of 0.29 nm on the Au(111) surface.

(TICT) molecules provide a nice example of such a lightactivated conformation change. 23 Binaphthyl molecules or their derivatives (Scheme 1) belong to another group of photosensitive compounds which are also known to change conformation under UV irradiation. 24,25 In this paper, we present the design and synthesis of a bisbinaphthyldurene (BBD) molecule (Scheme 1) for STM imaging, single molecule manipulation, and step-by-step lateral motions. This molecule is equipped with two binaphthyl paddles mounted laterally on a very simple central phenyl chassis. On a planar BBD, we demonstrate here how to use the low amplitude vibration modes of its 1,1′-binaphthyl lateral paddles 26,27 for manipulating the BBD along a Au(111) surface using STM inelastic tunneling effects. Not existing in solution, this planar conformation is stabilized by the Au(111) surface. On Au(111), it enters in competition with its native in solution nonplanar conformation which can also be reached by the same excitation on a metallic surface as presented below.

around this Coriginating from 360°naphthylbond. 24,25,[28][29][30] T are classified usin their absolute co binaphthyls and between -180° and those betw configurations, r and as a function conformation an mol of energy. conformation ch 90°saddle point at |θ| ∼ 70°and | chiral binaphthy (CD) spectra, co was demonstrate mechanical force binaphthyl relaxe singlet state con internal mechani the S 1 (θ) relativ curve minima. 26,[START_REF] Becke | Density-Functional Exchange-Energy Approximation with Correct Asymptotic Behavior[END_REF] (|θ| > 90°), the S discussion, and th BBD design. For theory (TD-DFT naphthol) molec synthesis; Sche conformation be that triggers an a optically from Information).

Entering now molecules are use reversal of the re and S 0 and bec Scheme 1. Synthetic Route of BBD 10358 Scheme 1. Synthetic Route of BBD.

RESULTS AND DISCUSSIONS

A. Design and Chemical Synthesis

A 1,1'-binaphthyl molecule consists of two naphthalene moieties with one single phenyl per moiety connected via a C-C single bond. The distinct characteristics of a 1,1'-binaphthyl are (1) its flexibility around this C-C bond 24,25,28-30 and (2) the axial chirality originating from the inhibition by steric crowding of a complete 360 • naphthyl-naphthyl rotation around its joint C-C bond. 24,25,[28][29][30] The enantiomers of axially chiral compounds are classified using the stereochemical labels R and S based on their absolute configuration around a stereocenter. Chiral 1,1'-binaphthyls and derivatives having a naphthyl torsion angle between -180 • < θ < 0 • correspond to the R configurations and those between 0 • < θ < 180 • correspond to the S configurations, respectively.

In its S 0 electronic ground state and as a function of the torsion angle |θ|, the 1,1'-binaphthyl conformation angle can vary from 60 • to 120 • within < 1 kcal/ mol of energy. The potential energy curve along this conformation change is a flat-bottomed well where the |θ| ∼ 90 • saddle point separates two shallow wells whose minima are at |θ| ∼ 70 • and |θ| ∼ 110 • . 24,25,[28][29][30] Since the conformation of chiral binaphthyls can be monitored by circular dichroism (CD) spectra, conformation controllability in this ground state was demonstrated at the air-water interface by applying a small mechanical force. 31,32 The difference between the S 0 1,1'-binaphthyl relaxed conformations and the S 1 lowest excited singlet state conformations 26,27 is at the origin of our BBD internal mechanical vibrations because of the reversal in θ of the S 1 (θ) relative to the S 0 (θ) double well potential energy curve minima. 26,27 Although for cisoid (|θ| < 90 • ) and transoid (|θ| > 90 • ), the S 1 and S 0 relaxed conformations are still under discussion, and this difference was important to preserve in the BBD design. For example, time-dependent density functional theory (TD-DFT) calculations show that the (R)-1,1'-bi (2-naphthol) molecule (the starting compound for the BBD synthesis; Scheme ) still preserves a different relaxed conformation between S 0 (θ = -91 • ) and S 1 (θ = -119 • ) that triggers an almost 30 • paddle effect going back and forth optically from S 0 to S 1 (Figure S16 in the Supporting Information).

Entering now in the design of our molecule, two binaphthyl molecules are used in the BBD as lateral paddles because of this reversal of the relative minimum energy |θ| value between S 1 and S 0 and because of the low 1 kcal/mol energy barrier between the two minima in the S 0 ground state. The two binaphthyls are connected laterally to a very small chassis made simply of a central phenyl (BBD in Scheme 1). This covalent binding of each binaphthyl via the methylene oxy bridges modifies the paddle switch ability with, for example, the suppression of the S 1 (θ = -119 • ) torsion angle energy minimum. What is important here is that S 0 keeps its awaited mechanical characteristics, that is, the possibility of its vibrational oscillations around its new (θ = -61 • ) ground-state minimum (TD-DFT calculated) reachable, for example, by optical excitation and relaxation via its new S 1 (θ = -58 • ) relaxed conformation for the (R,R) isomer (Figure S17 in the Supporting Information).

On a metallic surface and in a planar conformation, the two BBD binaphthyl groups permit to space the BBD chassis away from this surface at a distance compatible with a physisorption state. To drive the BBD molecule step-by-step along an fcc track of the Au(111) surface using the inelastic effect of the STM tunneling current, one has to first virtually prepare this molecule in its instantaneous virtual reduced electronic state well described for its mechanics by considering in first approximation the BBD S 1 excited state. Afterward, relaxation to the S 0 ground state will result in a small amplitude and noncoherent binaphthyl oscillations. As a function on the tip apex location on BBD, this will generate a surface lateral motion over the lateral diffusion barrier of the Au(111) fcc portion of the herringbone surface reconstruction.

The BBD molecule was synthesized by a one-pot reaction from commercially available (R)-1,1'-bi(2-naphthol) and α,α ,α ,α -tetrabromodurene (Scheme 1). Before its evaporation in the STM preparation chamber, it was further ultrapurified by sublimation to produce a colorless powder with no crystallinity. BBD UV-vis absorption spectrum is similar to the one of binaphthyl molecules 33 and shows an absorption peak maximum at 334 nm (Figure S1 in the Supporting Information), demonstrating a good electronic separation between the two BBD lateral paddles.

Recorded conventional CD spectra of chiral binaphthyls (Figure S2 in the Supporting Information) confirmed that the chirality of the binaphthyl groups remained after purification.

B. The Native BBD Molecule Conformation in Solution.

Variable-temperature (VT) analysis with NMR spectroscopy (Figure S13 in the Supporting Information) revealed the dynamic fluctuations between two BBD conformers with the same equilibrium population in solution. The two sets of 1 H NMR peaks that originate from those two conformers were also observed at low temperature from 218 to 223 K showing no sign of a favored conformer (Figure S13 in the Supporting Information). The analysis of those VT NMR spectra by a line-shape-fitting provides the experimental energetics for the interexchange processes between the two BBD conformers. Using an Eyring plot, the parameters of this interexchange were estimated to be ∆H = 9.8 kcal/mol and ∆S = -17 cal/(mol K) (Figures S14 and S15 in the Supporting Information), supporting the possibility of a fast interconversion of the two conformers at ambient temperature and in solution.

As presented in Figure 1, three BBD conformers were identified using DFT calculations (B3LYP/6-31G(d,p)) depending on the location of the two binaphthyl paddles relative to the central phenyl. They correspond to the flat, syn, and anti conformations of a BBD molecule.

The syn and anti conformers are expected to be the principal BBD isomers in solution since after molecular structure optimization, the flat, syn, and anti relative conformation energies are 20, 0.4, and 0.0 kcal/mol, respectively. Experimental ROESY peaks in NMR spectroscopy are also consistent with the existence of the anti-syn conformer in solution since a weak correlation was observed between the central aromatic CH and the side binaphthyl aromatic CH proton (Figures S10-S12 in the Supporting Information).

the S 0 ground state. The two rally to a very small chassis made BD in Scheme 1). This covalent via the methylene oxy bridges ability with, for example, the -119°) torsion angle energy here is that S 0 keeps its awaited that is, the possibility of its d its new (θ = -61°) groundlculated) reachable, for example, ation via its new S 1 (θ = -58°) (R,R) isomer (Figure S17 in the n a planar conformation, the two it to space the BBD chassis away compatible with a physisorption lecule step-by-step along an fcc using the inelastic effect of the has to first virtually prepare this virtual reduced electronic state hanics by considering in first cited state. Afterward, relaxation result in a small amplitude and lations. As a function on the tip will generate a surface lateral sion barrier of the Au(111) fcc rface reconstruction. nthesized by a one-pot reaction e (R)-1,1′-bi(2-naphthol) and (Scheme 1). Before its evapoation chamber, it was further to produce a colorless powder V-vis absorption spectrum is thyl molecules 33 and shows an at 334 nm (Figure S1 in the monstrating a good electronic BBD lateral paddles. Recorded iral binaphthyls (Figure S2 in the firmed that the chirality of the fter purification. le Conformation in Solution. nalysis with NMR spectroscopy ting Information) revealed the two BBD conformers with the in solution. The two sets of 1 H those two conformers were also from 218 to 223 K showing no (Figure S13 in the Supporting those VT NMR spectra by a linexperimental energetics for the een the two BBD conformers. meters of this interexchange were /mol and ΔS = -17 cal/(mol K) the Supporting Information), syn, and anti relative conformation energies are 20, 0.4, and 0.0 kcal/mol, respectively. Experimental ROESY peaks in NMR spectroscopy are also consistent with the existence of the antisyn conformer in solution since a weak correlation was observed between the central aromatic CH and the side binaphthyl aromatic CH proton (Figures S10-S12 in the Supporting Information).

A f lat BBD conformer is supposed by design to render accessible the different entry ports on its board for local STM excitations. In the following section, we will demonstrate how this f lat conformer can be produced molecule per molecule by STM single molecule mechanical manipulations. When obtained, this flat conformer turns out to be quite stable on the Au(111) surface.

Native BBD Conformation and 2D Organization on the Au(111) Surface. Two typical constant current STM images obtained after BBD molecules deposition on the Au(111) reconstructed surface are presented in Figure 2. They were mainly found self-assembled in small 2D islands (Figure 2a). In some place, single BBD molecule lines can also be observed. This pseudo-1D growth along the Au(111) herringbone track is usually stopped at both ends of the line by a different surface BBD molecular ordering (Figure 2b). In all those observed pseudo-1D and 2D surface molecular orderings, the BBD molecules appear having the shape of a curve letter Two typical constant current STM images obtained after BBD molecules deposition on the Au(111) reconstructed surface are presented in Figure 2. They were mainly found self-assembled in small 2D islands (Figure 2a). In some place, single BBD molecule lines can also be observed.

This pseudo-1D growth along the Au(111) herringbone track is usually stopped at both ends of the line by a different surface BBD molecular ordering (Figure 2b). In all those observed pseudo-1D and 2D surface molecular orderings, the BBD molecules appear having the shape of a curve letter " ". Those " " BBD molecules have three possible adsorption directions on the Au(111) surface (see the Figure 2a insert). As presented in Figure 2b, the observed single " " BBD lines confirm that the BBD molecules are sensitive to the lateral ridges of the herringbone reconstruction (in average 0.03 nm in height). [START_REF] Hehre | Self-Consistent Molecular Orbital Methods. XII. Further Extensions of Gaussian-Type Basis Sets for Use in Molecular Orbital Studies of Organic Molecules[END_REF] As certified experimentally by STM single molecule manipulations in the next subsection, each " " STM molecular feature is a BBD dimer consisting of two syn conformers oriented perpendicular to the surface plane. They are coupled by a pair along one of the three As discussed in the previous subsection, the BBD molecules are found equally in the syn and anti conformations in solution. Molecular dynamics (MD) simulations were performed to simulate a hot adsorption process of the BBD molecules on a Au(111) surface (see Supporting Information).

When the BBD molecules are annealed on the surface up to 500 K, the syn and anti conformers are deformed but remain on the surface with no transformation in the flat conformer. At this temperature and during their 2D diffusion around the Au(111) surface, the BBD molecules have enough kinetic energy to mutually transform between the syn and anti as they certainly performed in solution and at room temperature. Upon cooling down the surface to room temperature, the BBD molecules thermalize toward the syn conformers since syn is 9.0 kcal/mol lower in energy as compared to anti on the Au(111) surface. Furthermore, the syn thermalize with still their central phenyl perpendicular to the Au(111) surface because laterally stabilized by their two paddles.

During a slow thermalization process, the syn will also continue to diffuse on the surface. While in this perpendicular adsorption conformation, they can pair via a central phenyl π-stacking interactions as also confirmed by MD calculation (see Supporting Information). It results in the " " As discussed in the previous subsection, the BBD molecules are found equally in the syn and anti conformations in solution. Molecular dynamics (MD) simulations were performed to simulate a hot adsorption process of the BBD molecules on a Au( 111) surface (see Supporting Information). When the BBD molecules are annealed on the surface up to 500 K, the syn and anti conformers are deformed but remain on the surface with no transformation in the f lat conformer. At this temperature and during their 2D diffusion around the Au(111) surface, the confirmed by MD calcula It results in the "f " STM Figure 2 assembled in th islands.

According to MD calcul conformers would be mo surface syn and anti confor conformer from the nativ Au(111) surface would r about 1500 K. Therefore, the surface directly afterwa conformers. At such a h molecules will break and/ the gold melting point is l below, f lat conformers can on the Au( 111 According to MD calculations and if accessible, the flat BBD conformers would be more stable than the orthogonal to the surface syn and anti conformers. However, getting directly a flat conformer from the native syn and anti conformers on the Au(111) surface would require an annealing temperature of about 1500 K. Therefore, during deposition or by heating up the surface directly afterward, it will be difficult to produce flat conformers. At such a high temperature, most of the BBD molecules will break and/or desorb from the surface. Anyhow, the gold melting point is lower than 1500 K. As demonstrated below, flat conformers can be produced molecule per molecule on the Au(111) surface starting from the orthogonal to the surface syn conformers using a very specific STM single molecule mechanical manipulation protocol.

D. STM Single Molecule Mechanical Manipulation for Preparing flat BBD Conformers.

To produce a flat BBD conformer, a selected syn conformer dimer adsorbed perpendicular to the Au( 111) surface (one of the " " molecular units imaged in Figure 2) must be first separated into independent syn monomers. For this purpose and starting from a 2D island of the sort imaged in Figure 2a, STM lateral BBD molecule mechanical manipulation has been first performed as presented in Figure 3. Here, the threshold STM tunneling resistance for molecule manipulation is around R T = 270 MΩ. In most cases, a " " dimer can readily be separated out of the 2D island but only as a single " " dimer entity with no monomer separation as presented in the Figure 3a,b.

Then, a " " dimer can be step-by-step displaced over quite long distances over the surface in such STM manipulation conditions. When they are sometimes disassembled into two syn monomers during this process, one syn of the " " pair is generally transferred to the STM tip, and the other one remains in the island as shown in the sequence Figure 3b,c.

Notice also that after the breaking of a " " pair at the 2D island border and in its orthogonal to the surface adsorption configuration, the syn monomer left in the island (as obtained in Figure 3c) can be further extracted from this island byr a further lateral STM manipulation. In this case, it has also a high probability to be captured by the tip apex, confirming how this syn monomer orthogonal configuration is not very stable on an Au(111) surface. We have succeeded to manipulate a few of those syn monomers toward specific Au(111) surface areas like the herringbone kinks where generally the surface atomic order is not regular and can stabilize them. They can also be dragged e. They are coupled 11] crystallographic this surface (see the cation of this pairing the only molecular BDs molecular row. , the BBD molecules rmations in solution. were performed to BD molecules on a ion). When the BBD o 500 K, the syn and on the surface with At this temperature Au(111) surface, the energy to mutually certainly performed n cooling down the olecules thermalize 0 kcal/mol lower in Au( 111) surface. their central phenyl because laterally slow thermalization use on the surface. formation, they can nteractions as also conformers. At such a high temperature, most of the BBD molecules will break and/or desorb from the surface. Anyhow, the gold melting point is lower than 1500 K. As demonstrated below, f lat conformers can be produced molecule per molecule on the Au(111) surface starting from the orthogonal to the surface syn conformers using a very specific STM single molecule mechanical manipulation protocol.

STM Single Molecule Mechanical Manipulation for Preparing f lat BBD Conformers. To produce a f lat BBD conformer, a selected syn conformer dimer adsorbed perpendicular to the Au( 111) surface (one of the "f " molecular units imaged in Figure 2) must be first separated into independent syn monomers. For this purpose and starting from a 2D island of the sort imaged in Figure 2a, STM lateral BBD molecule mechanical manipulation has been first performed as presented in Figure 3. Here, the threshold STM tunneling resistance for molecule manipulation is around R T = 270 MΩ. In most cases, a "f " dimer can readily be separated out of the 2D island but only as a single "f " dimer entity with no monomer separation as presented in the Figure 3a,b. Then, a "f " dimer can be step-by-step displaced over quite long distances over the surface in such STM manipulation conditions. When they are sometimes disassembled into two syn monomers during this process, one syn of the "f " pair is generally transferred to the STM tip, and the other one remains in the island as shown in the sequence Figure 3b,c.

Notice also that after the breaking of a "f " pair at the 2D island border and in its orthogonal to the surface adsorption configuration, the syn monomer left in the island (as obtained in Figure 3c) can be further extracted from this island by a further lateral STM manipulation. In this case, it has also a high probability to be captured by the tip apex, confirming how this syn monomer orthogonal configuration is not very stable on an along the surface during standard imaging conditions, that is, for STM R T around 10 GΩ and a tunneling current below 10 pA.

At the border of a 2D-island and using R T ∼ 120 MΩ, a new specific BBD dimer molecule manipulation protocol can bring a different manipulation outcome. When in a " " pair located at the border of a 2D island, a syn BBD molecule is manipulated without trying to extract it directly from this island border; however, following the appropriate manipulation tip trajectory presented in Figure 4, a flat monomer can be produced with its two-fold paddles now fully open. Figure 4 presents an example of such an outcome with a reasonable 10% probability of success.

There are two essential conditions for this specific protocol to produce successfully a flat conformer and to open the BBD two paddles. First, the syn targeted BBD molecule must be paired with a syn BBD anchored at the edge of a 2D island but not at a corner. This anchoring will serve as a pivot for the opening following a classical molecular mechanical motion of the molecule, as if it was a solid and rigid body pivoting around a fix point. Second, the targeted syn BBD must be "rubbed" laterally on another " " dimer of the island during the manipulation, that is, the manipulation trajectory must maintain a lateral interaction with the other " " dimer for the flat flipping of the manipulated BBD molecule to be complete. As a consequence, the manipulated BBD molecule performs a 90 • flip down to the surface to reach a planar central phenyl configuration with the two paddles opened flat on the Au(111) surfacem as illustrated in Figure 4a,b (more examples in Supporting Information section 9). In this case, the lateral required interactions between the manipulated BBD and the border 2D island BBDs seem to be attractive according to the recorded manipulation signal, but this requires a more detailed interpretation in the future.

When produced, a flat conformer is very stable on the Au(111) surface as theoretically predicted by MD calculations. After its production, this is confirmed by the experimental RT threshold value for a flat conformer STM molecular manipulation in a pushing mode along the Au(111) surface, the lowest (∼ 66 MΩ) of all the R T values used for the different BBD molecule configurations met on this surface. A flat BBD monomer can be truly and reproducibly STM manipulated mechanically over long distances as presented in Figure 4b,c.

E. Tunneling Spectroscopy and States Mapping of the Flat BBD Conformer.

A flat BBD conformer on the Au(111) surface opens access to the detail STM dI/dV mapping of its low-lying molecular electronic states around the Au(111) surface Fermi energy. Such a the herringbone kinks where generally the surface atomic order is not regular and can stabilize them. They can also be dragged along the surface during standard imaging conditions, that is, for STM R T around 10 GΩ and a tunneling current below 10 pA.

At the border of a 2D-island and using R T ∼ 120 MΩ, a new specific BBD dimer molecule manipulation protocol can bring a different manipulation outcome. When in a "f " pair located at the border of a 2D island, a syn BBD molecule is manipulated without trying to extract it directly from this island border; however, following the appropriate manipulation tip trajectory presented in Figure 4, a f lat monomer can be produced with its two-fold paddles now fully open. Figure 4 presents an example of such an outcome with a reasonable 10% probability of success.

There are two essential conditions for this specific protocol to produce successfully a f lat conformer and to open the BBD two paddles. First, the syn targeted BBD molecule must be paired with a syn BBD anchored at the edge of a 2D island but not at a corner. This anchoring will serve as a pivot for the opening following a classical molecular mechanical motion of the molecule, as if it was a solid and rigid body pivoting around a fix point. Second, the targeted syn BBD must be "rubbed" laterally on another "f " dimer of the island during the manipulation, that is, the manipulation trajectory must maintain a lateral interaction with the other "f " dimer for the flat flipping of the manipulated BBD molecule to be complete. As a After its production, threshold value fo manipulation in a pu the lowest (∼66 MΩ) BBD molecule config monomer can be tru mechanically over lon Tunneling Spect Flat BBD Conforme surface opens access low-lying molecular surface Fermi energy confirm the f lat confo specific manipulation determining the loca weight of its reduced BBD molecular struct principal port for intra tunneling electrons in structure to move on push.

Figure 5a presents f lat BBD molecule ad STM tip apex was po lobes identified on the identifying the Au(11 V) in this spectrum, observed, one at -1. +2.7 V. This gives an for a f lat BBD mo compared to the 3.7 e the syn and anti conf Performed exactly precise dI/dV STM m molecular orbital el reduced and oxidized two tunneling resonan dV elastic scattering calculations were pe imental dI/dV maps. adapted to provide a molecules. 35,36 Thes contributor to theoccupied molecular unoccupied molecu resonance. Those im optimized f lat BBD co confirms how the B conformation by STM to Figure 5 images, electronically decoupl

Step-by-Step Ma mapping is of importance to confirm the flat conformation interpretation after the Figure 4 specific manipulation protocol. It is also very appropriate for determining the location of the maximum molecular orbital weight of its reduced and oxidized electronic states along the BBD molecular structure. Those maxima are known to be the principal port for intramolecular inelastic excitations induced by tunneling electrons in a way to bring energy to the molecular structure to move on a metallic surface with no mechanical push.

Figure 5a presents a typical dI/dV spectrum recorded on a flat BBD molecule adsorbed on the Au(111) surface. Here, the STM tip apex was positioned at the center of one of the two lobes identified on the topographic image (see Figure 4c). After identifying the Au(111) surface states energy location (∼ -0.5 V) in this spectrum, two differential conductance peaks are observed, one at -1.6 V and a small bump centered around +2.7 V. This gives an apparent electronic gap of about To manipulate a BBD molecule by inelastic electron tunneling effects along a fcc portion of the Au(111) surface, the single molecule must capture enough energy from the tunneling current to pass over the fcc surface lateral diffusion barrier. One way to trigger the inelastic energy release on the BBD vibronic mode is to increase the tunneling current intensity through the molecule reaching its first low-lying reduced states. According to the dI/dV spectrum in Figure 5a, this can be achieved with a bias voltage applied to the tunnel junction greater than about 2 V to reach at least the tail of the +2.7 V BBD tunneling electronic resonance. Notice here that the energy captured by the vibronic modes of the BBD molecule will be a small fraction of the 2 eV. 38 To maximize the tunneling inelastic excitations, it is also usually taken for granted to position the STM tip apex at the locations at the highest electron density of the targeted in energy molecular electronic states. This strategy also helps to minimize the STM bias voltage range in a way not to destroy the molecule. 11 The BBD dI/dV images presented in Figure 5 are mapping those maxima and minima in its flat surface conformation. This mapping results from the electronic coupling between the tip apex and the molecular orbitals entering in the composition of resonating BBD electronic states when considering that those electronic states can be well described by a superposition of Slater determinants constructed using a molecular orbital basis set. 37,39 The pixel-by-pixel construction of the Figure 5b,c maps results from the local measurement of the conductance of the BBD molecule at each pixel. In effect, this measurement projects the total BBD electronic probability density on a 2D plane. This is a very convenient way to identify where to position the tip for triggering a tunneling inelastic effect. For BBD, the highest electronic probability density (the highest dI/dV) sites are located on the BBD binaphthyl paddles as observed in Figure 5c.

ACS Nano

As indicated in Figure 5c, when positioning the tip apex at location 1 on the BBD molecule and then ramping up the bias voltage further than +2.3 V (but without reaching +2.7 V), the BBD changes its conformation with one naphthyl paddle going up the surface in a conformation similar to syn (syn/flat-like conformation, see Figure S21 in the Supporting Information). This conformational change occurs systematically opposite to the paddle been excited. On the corresponding reduced state potential energy surface, this indicates that the energy captured by the BBD molecule from the tunneling current is initiating a conformation change trajectory at the onset of the +2.7 V resonance. Starting from the flat ground-state conformation, this trajectory certainly reaches a minimum on this reduced state potential energy manifold corresponding to the rotating up of a paddle to form a "syn/flat-like" conformation. Then, the BBD molecule relaxes in its ground state in this new stable "syn/flat-like" conformation not observable natively event after an STM mechanical lateral manipulation procedure. Notice that in the first approximation, the reduced state potential energy manifold can be explored using the potential energy surface of the BBD S 1 vertically accessible excited electronic state.

After having tried to induce the paddle vibrations directly, we have selected the electronic probability density maximum 2 as indicated in Figure 5c. For this new excitation location and as presented in left column of Figure 6, when the bias voltage reaches about +2.3 V and the tunneling current several hundred pico-amperes, the current intensity through the BBD suddenly jumps up due to the molecule one step lateral translation. This very reproducible behavior shows how a BBD molecule can be step-by-step driven by steps of 0.29 nm on an fcc flat area on the Au(111) surface. To be more precise on the inelastic manipulation direction, an atomic resolved image of the Au(111) surface recorded using molecule terminated tip is inserted in Figure 6a to certify the accurate moving direction: exactly one of 110 orientations of the Au(111) surface inits fcc portion. The interatomic gold atom distance along those orientations is 0.288 nm, in complete agreement with the experimentally observed 0.29 nm long step motion per voltage ramp. As presented in Figure 6, a controllable inelastic motion is only possible when the molecule lies parallel to and in between two herringbones of the reconstruction. When the molecule sits on a herringbone (even when only one paddle end is laying on it), it is stuck and difficult to manipulate inelastically, as also recently observed with a windmill molecule. 40 For a BBD molecule laying parallel to the herringbones and located at the fcc portion of the Au(111) surface, the probability of a controllable stepwise motion is about 50% after a single shot bias voltage ramp. Incidentally, the probability of molecule motion regardless the adsorption site is around 5% and the probability of a breaking or a conformation changes is around 3%. As a consequence and after a three consecutive lateral step-by-step motions, the BBD molecule is stopped because of herringbone lateral diffusion barrier and must be reprepared for a new run like with the windmill molecule. 40 Here, the BBD molecule must be manipulated with care not to open a conformation change path on its reduced state potential energy surface nor a chemical reaction path breaking some of its chemical bonds leading to the final destruction of the molecule since a molecule is often very unstable under high positive STM bias voltage pulses. [START_REF] Hariharan | Accuracy of AH n Equilibrium Geometries by Single Determinant Molecular Orbital Theory[END_REF]41 While exciting the BBD molecule at two different spatial locations of the same resonance maxima, the difference of mechanical response is a nice indication of how the electronic coupling between the tip apex and the electronic states of a molecule can give rise to different mechanical responses. Here and during an STM excitation (or imaging), the effective lateral extension of the tunneling electrons inelastic excitation is much narrower than the BBD molecular orbitals spatial lateral extension. As a consequence, the electronic coupling between the tip apex and the BBD molecule is very local. For each tip positioning on the molecule, this brings out a very specific is often very unstable under high positive STM bias voltage pulses. [START_REF] Hariharan | Accuracy of AH n Equilibrium Geometries by Single Determinant Molecular Orbital Theory[END_REF]41 While exciting the BBD molecule at two different spatial locations of the same resonance maxima, the difference of mechanical response is a nice indication of how the electronic coupling between the tip apex and the electronic states of a molecule can give rise to different mechanical responses. Here and during an STM excitation (or imaging), the effective lateral extension of the tunneling electrons inelastic excitation is much narrower than the BBD molecular orbitals spatial lateral extension. As a consequence, the electronic coupling between the tip apex and the BBD molecule is very local. For each tip positioning on the molecule, this brings out a very specific superposition of BBD molecular orbitals to contribute to the motion as also observed for STM imaging in the case, for example, of an hexabenzocoronene (HBC) molecule. 42 This can trigger a large conformation of the paddle for one tip apex location or a gentle stepwise lateral motion for another location supposing that the effective potential energy surface built up from this superposition is different in the two cases.

For negative applied bias voltage, we have also tried the same strategy by locating the tip apex at one of the many maxima indicated in Figure 5b. No movement of the BBD molecule was observed down to a bias voltage ramp reaching a maximum of -2.0 V with several nA of tunneling current intensity. We do not yet have a detailed explanation of this observation.

CONCLUSION

A bisbinaphthyldurene (BBD) molecule was designed, synthesized, and deposited on an Au(111) surface, mechan- superposition of BBD molecular orbitals to contribute to the motion as also observed for STM imaging in the case, for example, of an hexabenzocoronene (HBC) molecule. 42 This can trigger a large conformation of the paddle for one tip apex location or a gentle stepwise lateral motion for another location supposing that the effective potential energy surface built up from this superposition is different in the two cases.

For negative applied bias voltage, we have also tried the same strategy by locating the tip apex at one of the many maxima indicated in Figure 5b. No movement of the BBD molecule was observed down to a bias voltage ramp reaching a maximum of -2.0 V with several nA of tunneling current intensity. We do not yet have a detailed explanation of this observation. 111) is a perpendicular dimer conformation. Once a BBD molecule was prepared in its flat conformation, dI/dV molecular orbital mapping was performed to determine the best tip apex location to free up this molecule inelastically for a manipulation on an Au(111) fcc flat terrace. The intuitive on-paddle excitation is not a good entry port for an inelastic tunnel manipulation since it leads to a drastic conformation change of the BBD molecule entering in competition with its step-by-step motion on the Au(111) surface. We have demonstrated that on the molecule and nearby the paddle location, there exists another energy entry port where the BBD molecule remains flat on the surface and can be laterally manipulated step-by-step with a step of about 0.29 nm per excitation. The BBD molecule was used by the MANA-NIMS Japanese team during the first international nanocar race in Toulouse. 43

MATERIALS AND METHODS

The synthetic procedure of BBD is described in the Supporting Information. The STM experiments were conducted as follows. The BBD molecules were deposited on a Au(111) single crystal surface previously cleaned by standard metal surface UHV preparation methods consisting of several cycles of ion sputtering and subsequent annealing. [START_REF] Hehre | Self-Consistent Molecular Orbital Methods. XII. Further Extensions of Gaussian-Type Basis Sets for Use in Molecular Orbital Studies of Organic Molecules[END_REF]10 The BBD molecules were sublimated from about 3 mg of the colorless BBD molecular powder by heating a Kentax quartz crucible at 563 K during 30 s. The gold substrate temperature was kept below 323 K during this deposition.

The evaporation parameters were selected in a way to deposit a minute amount of BBD molecules to produce a submonolayer coverage in order to leave enough large molecule-free areas on the clean Au(111) surface to be able to use the STM single molecule manipulation protocol. The Au(111) sample was then loaded on the STM sample stage kept at cryogenic temperature (LT) and rapidly cooled down to ∼ 5 K. All low-temperature ultrahigh-vacuum scanning tunneling microscopy (LT-UHV STM) experiments presented, that is, constant current imaging, molecule manipulations, tunneling spectroscopic measurements, and intramolecular dI/dV mapping were performed on one of the four STM heads of our new ScientaOmicron LT-UHV 4 independent STM instrument. 44 * E-mail: we-hyo.soe@cemes.fr † Present Address: Department of Chemical Engineering, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395, Japan. ‡ E-mail: Nakanishi.Waka@nims.go.jp.

Photophysical properties

See Fig. S1 and Fig. S2.

NMR spectra

See Fig. S3 to Fig. S15.

Theoretical calculations (DFT)

All calculations were performed using the Gaussian 09 program, 1 and the results were analyzed and visualized on GaussView 5.0.9. Calculations were performed at the density functional theory (DFT) level with the B3LYP functional, the gradient correction of the exchange functional by Table S16. Potential energy (S 0 and S 1 ) of (a) 1,1'-binaphthyl and (b) BINOL, which were modified from the reported one for 1,1'-binaphthyl. 9 As reported, two sets of optimized structure of 1,1'-binaphthyl were found both in S 0 and S 1 by DFT and TD-DFT (B3LYP/6-31G(d,p)) calculations. On the other hand, only one sets of optimized structure were found for BINOL by the same procedures.

Theoretical calculations (MD simulations)

Structures

The simulated systems consisted of one or two molecules on Au(111) ------------------------------------------------------------------- ------------------------------------------------------------------ ------------------------------------------------------------------- ------------------------------------------------------------------- ------------------------------------------------------------------ ------------------------------------------------------------------- ------------------------------------------------------------------- ------------------------------------------------------------------ ------------------------------------------------------------------- ------------------------------------------------------------------- ------------------------------------------------------------------ .661329 ---------------------------------------------------------------------Table S5. Cartesian coordinate anti-conformer SCF Done: E(RB3LYP) = -2226.74970717 A.U. after 14 cycles ---------------------------------------------------------------------Center Atomic Atomic Coordinates (Angstroms) Number Number Type X Y Z --------------------------------------------------------------------- 1.490691 ---------------------------------------------------------------------Table S5.

deformed. On the other hand, the stability of flat-conformer mainly originate from the large surface interaction energy (E surfaceinteraction_flat -E sur f aceinteraction_syn = -29.3 kcal/mol more favorable than syn-conformer) rather than molecular deformation energy (E flat -E syn = +6.9 kcal/mol higher than syn-conformer).

Total energy of syn-syn dimer on Au(111) surface (E total ) was -42 912.6 kcal/mol. The following energies were obtained as a single point energy calculation with the same force field. The energy of Au ( 111) (E surface ) was -43 945.7 kcal/mol, that of syn-syn dimer (E syn-syn-dimer ) is 1 438.2 kcal/mol, those of each syn-conformers (E syn-conformer-1 and E syn-conformer-2 ) are 724.3 kcal/mol and 724.3, respectively. The interaction energy between Au(111) and syn-syn dimers (E surfaceinteraction ) was calculated to be -405.1 kcal/mol and that between syn-syn dimers (E molecularinteraction ) was to be -10.4 kcal/mol based on the following equations:

E surfaceinteraction = E total -(E surface + E syn-syn-dimer ) E molecularinteraction = E syn-syn-dimer -(E syn-conformer-1 + E syn-conformer-2 )
The formation of syn-syn dimer is more favorable than being two syn-monomers, by the energy of E = (E total -E surface )/2 -(E total s yn -E surface m onomer ) = -2.8 kcal/mol. The formation of syn-syn dimer (in vacuum) is estimated to be E syn-syn-dimer /2 -Esyn = +4.8 kcal/mol more unfavorable compared with being monomers. On the other hand, surface interaction energy became E surfaceinteraction /2 -E surfaceinteraction s yn = -7.6 kcal/mol more favorable for formation of dimers. As a result, each syn-conformers are E = -7.6 + 4.8 = -2.8 kcal/mol more favorable as a dimer compared with being monomers.

Conformation transformations by forcible molecule manipulation

Here we provide more details and examples of lateral single molecule manipulation protocol in a mechanical mode to succeed to prepare one by one single planar BBD molecules are presented and used in the manuscript. See Fig. S20.

Inelastic electronic tunneling effect

After some of the inelastic electronic tunneling excitation of a BBD molecule by locating the STM tip apex on the highest electronic probability density site of a BBD molecule, we have S18 conformer on Au(111) surface was also obtained with higher energy cycle temperature was raised to 1500 K, flat-conformer was found wit compared with the syn-conformer. For calculations of a dimer on Au syn-conformers were used as initial structures, and syn-syn-dimer on A a stable conformer.

Figure 1 .Figure 1 .

 11 Figure 1. Various possible conformers of BBD molecule. (a) Flat, (b) syn, and (c) anti conformers obtained from DFT calculations (B3LYP/6-31G(d,p)) with relative energies of +20, +0.4, and 0.0 kcal/mol, respectively. Each structure was optimized with its D 2 , C 2 , and C 2 symmetry, respectively. The calculated torsion angles of the binaphthyl are θ = -61°, -64°and -64°, respectively. In solution, only the anti and syn conformers have been identified. Physisorbed on an Au(111) surface, STM molecular manipulations of BBD lead to the production of the flat conformer.

C

  . Native BBD Conformation and 2D Organization on the Au(111) Surface.

  [211] crystallographic orientations of the Au(111) fcc portion of this surface (see the Figure 2a insert). A first experimental indication of this pairing is evidenced in Figure 2a by analyzing the only molecular alignment defect at the top of the last left BBDs molecular row.

  oriented perpendicular to the surface plane. They are coupled by a pair along one of the three [211] crystallographic orientations of the Au(111) fcc portion of this surface (see the Figure 2a insert). A first experimental indication of this pairing is evidenced in Figure 2a by analyzing the only molecular alignment defect at the top of the last left BBDs molecular row.

  ) surface s surface syn conformers molecule mechanical man STM Single Molecul Preparing f lat BBD Co conformer, a selected perpendicular to the Au(1 units imaged in Figure independent syn monom from a 2D island of the so BBD molecule mechan performed as presented STM tunneling resistance R T = 270 MΩ. In most separated out of the 2D i entity with no monomer s 3a,b. Then, a "f " dimer can

Figure 2 .Figure 3 .Figure 2 .

 232 Figure 2. (a) A typical STM topographic image of BBD molecules forming a small 2D island on the Au(111) reconstructed surface.Each building block of the imaged island is a dimer of syn-syn conformers having the shape of a curved "f " letter. Insert a: the three possible adsorption orientations of the syn dimers. The atomic resolved image was also recorded using a molecule terminated STM tip to confirm the molecular orientation. (b) A good example of supramolecular assembly with a line of 10 BBD molecular dimers formed along an Au(111) herringbone whose growth was stopped at both ends of the BBD line by 2 "f " dimers of a different surface orientation. (All LT-UHV STM constant current image images were generally recorded at I = 20 pA, V = 0.5 V.)

Figure 3 .

 3 Figure 3. An example of the molecule manipulation experiments using the tunneling condition near the threshold R T = 270 MΩ. (a) 2D island of self-assembled syn-syn dimers on the Au(111) surface observed just after Au(111) sample preparation. (b) A "f " BBD molecule was step-by-step manipulated and extracted from its island while maintaining its dimer structure. (c) A monomer was detached from a down right corner "f " of the island and adsorbed to the tip apex and remains of the second syn of this dimer initially perpendicular to the surface conformation (same STM image conditions as in Figure 2. Image size: 15 nm × 15 nm).

Figure 3 .

 3 Figure 3. An example of the molecule manipulation experiments using the tunneling condition near the threshold R T = 270 MΩ. (a) 2D island of self-assembled syn-syn dimers on the Au(111) surface observed just after Au(111) sample preparation. (b) A " " BBD molecule was step-by-step manipulated and extracted from its island while maintaining its dimer structure. (c) A monomer was detached from a down right corner " " of the island and adsorbed to the tip apex and remains of the second syn of this dimer initially perpendicular to the surface conformation (same STM image conditions as in Figure 2. Image size: 15 nm × 15 nm).

Figure 4 .

 4 Figure 4. An example of the forcible molecule manipulation experiments using tunneling conditions less than 1/2 R T in Figure 3. Topographic images (a) before and (b) after R T = 120 MΩ manipulation. Using this condition, a structural transformation from syn to flat conformer occurs. (c) The so-produced flat conformer was manipulated with the STM tip away from its original four "f " dimer line with R T = 66 MΩ in order to isolate it to prevent the influence from other molecules during dI/dV STM spectroscopic measurements. The specific tip trajectories during the manipulation to produce a flat conformer are indicated by the arrows in (a) and (b). The tip location selected during the Figure 5 spectrum recording on this flat conformer is indicated by a dot in (c). Same STM image conditions as in Figure 2. Image size: 12 nm × 15 nm.Figure 4. An example of the forcible molecule manipulation experiments using tunneling

Figure 4 .

 4 Figure 4. An example of the forcible molecule manipulation experiments using tunneling conditions less than 1/2 R T in Figure 3. Topographic images (a) before and (b) after R T = 120 MΩ manipulation. Using this condition, a structural transformation from syn to flat conformer occurs. (c) The so-produced flat conformer was manipulated with the STM tip away from its original four "f " dimer line with R T = 66 MΩ in order to isolate it to prevent the influence from other molecules during dI/dV STM spectroscopic measurements. The specific tip trajectories during the manipulation to produce a flat conformer are indicated by the arrows in (a) and (b). The tip location selected during the Figure 5 spectrum recording on this flat conformer is indicated by a dot in (c). Same STM image conditions as in Figure 2. Image size: 12 nm × 15 nm.Figure 4. An example of the forcible molecule manipulation experiments using tunneling conditions less than 1/2 R T in Figure 3. Topographic images (a) before and (b) after R T = 120 MΩ manipulation. Using this condition, a structural transformation from syn to flat conformer occurs. (c) The so-produced flat conformer was manipulated with the STM tip away from its original four " " dimer line with R T = 66 MÎl' in order to isolate it to prevent the influence from other molecules during dI/dV STM spectroscopic mΩ. The specific tip trajectories during the manipulation to produce a flat conformer are indicated by the arrows in (a) and (b). The tip location selected during the Figure 5 spectrum recording on this flat conformer is indicated by a dot in (c). Same STM image conditions as in Figure 2. Image size: 12 nm × 15 nm. 14

4. 3

 3 eV for a flat BBD molecule on the Au(111) surface to be compared to the 3.7 eV (334 nm) UV optical gap observed for the syn and anti conformers in solution.Performed exactly at these resonances, the Figure5very precise dI/dV STM mapping permits to determine the spatial molecular orbital electronic distribution of the flat BBD reduced and oxidized electronic states at the origin of those two tunneling resonances. Monoelectronic constant current dI/dV elastic scattering quantum chemistry (ESQC) 34 image calculations were performed to compare with those experimental dI/dV maps. The ESQC calculation is particularly welladapted to provide accurate STM images for large adsorbed molecules.35,36 These calculations confirm that the main contributor to the -1.6 V resonance is the BBD highest occupied molecular orbital (HOMO) and the BBD lowest unoccupied molecular orbital (LUMO) to the +2.7 V resonance. Those images were calculated starting from an optimized flat BBD conformation on the Au(111) surface. This confirms how the BBD molecule can be prepared in a flat conformation by STM single molecule manipulation. According to Figure5images, the central phenyl chassis is relatively electronically decoupled for the Au(111) surface.

F

  . Step-by-Step Manipulation for Moving a flat BBD Conformer on the Au(111) Surface.

Figure 5 .

 5 Figure 5. (a) The dI/dV spectrum and (b and c) dI/dV maps recorded on flat BBD produced in Figure 4. The first tunneling resonances appear at -1.6 V and +2.7 V bias voltage (sample grounded on the LT-UHV 4-STM). A dI/dV map captures the spatial distribution of the electron density of the corresponding molecular electronic states contributing to the resonance. 37 (d and e) At energies corresponding to HOMO and LUMO of the flat BBD monomer, monoelectronic ESQC STM calculated images are also presented for comparison. Resonance at -1.6 V appears to be mainly coming from the HOMO component of the imaged ground state and at +2.7 V from the LUMO contribution of BBD reduced (image size: 3.6 nm × 2.4 nm).

Figure 5 .

 5 Figure 5. (a) The dI/dV spectrum and (b and c) dI/dV maps recorded on flat BBD produced in

Figure 4 .

 4 Figure 4. The first tunneling resonances appear at -1.6 V and +2.7 V bias voltage (sample grounded on the LT-UHV 4-STM). A dI/dV map captures the spatial distribution of the electron density of the corresponding molecular electronic states contributing to the resonance. 37 (d and e) At energies corresponding to HOMO and LUMO of the flat BBD monomer, monoelectronic ESQC STM calculated images are also presented for comparison. Resonance at -1.6 V appears to be mainly coming from the HOMO component of the imaged ground state and at +2.7 V from the LUMO contribution of BBD reduced (image size: 3.6 nm × 2.4 nm).

Figure 6 .

 6 Figure 6. Manipulation of a BBD molecule on the Au(111) surface using inelastic electrons tunneling excitations. (a-d) A series of images demonstrating the BBD molecule motion along the timeline. An atomic resolved image and its significant crystallographic orientation [101̅ ] is also presented. The red dots on each image indicate the tip apex location for applying the bias voltage ramp, resulting in the measured tunneling current. The moving direction, of a BBD molecule is always the [101̅ ] orientation and its average lateral motion per voltage ramping is around 0.29 nm, which perfectly matches with the 0.288 nm interatomic distance on Au(111) in the ⟨11̅ 0⟩ surface directions. The voltage ramp duration from +1.0 to +2.3 V was 20 s in each case. Left column shows I-V characteristics for each inelastic event. Right column: 12.0 nm × 5.6 nm constant current STM images recorded at V = +0.5 V and I = 10 pA. In each image, top left, two dimers and one BBD monomer in a syn conformation have been imaged at the same time to provide a clear measurement of the BBD molecule motion per excitation.

Figure 6 .

 6 Figure 6. Manipulation of a BBD molecule on the Au(111) surface using inelastic electrons tunneling excitations. (a-d) A series of images demonstrating the BBD molecule motion along the timeline. An atomic resolved image and its significant crystallographic orientation [101] is also presented. The red dots on each image indicate the tip apex location for applying the bias voltage ramp, resulting in the measured tunneling current. The moving direction, of a BBD molecule is always the [101] orientation and its average lateral motion per voltage ramping is around 0.29 nm, which perfectly matches with the 0.288 nm interatomic distance on Au(111) in the 110 surface directions. The voltage ramp duration from +1.0 to +2.3 V was 20 s in each case. Left column shows I -V characteristics for each inelastic event. Right column: 12.0 nm × 5.6 nm constant current STM images recorded at V = +0.5 V and I = 10 pA. In each image, top left, two dimers and one BBD monomer in a syn conformation have been imaged at the same time to provide a clear measurement of the BBD molecule motion per excitation.

  CONCLUSIONA bisbinaphthyldurene (BBD) molecule was designed, synthesized, and deposited on an Au(111) surface, mechanically manipulated with a STM tip, and then with the STM inelastic contribution of the tunneling current passing through this molecule. The BBD molecule is equipped with two lateral binaphthyl paddles mounted on a very simple central phenyl chassis to separate it from the supporting surface. Single molecule STM lateral mechanical manipulation must be first performed for this molecule to reach a flat conformation on the Au(111) surface since its native surface conformation on Au(

S3 4 .

 4 Figure S1. UV-vis absorption spectra of BBD in THF (5.6 × 10 -6 M).

Figure S2 .

 S2 Figure S2. CD spectra of BBD in THF (1.0 × 10 -5 M).

Figure S1 .

 S1 Figure S1. UV-vis absorption spectra of BBD in THF (5.6 × 10 -6 M).

S3Figure S1 .

 S1 Figure S1. UV-vis absorption spectra of BBD in THF (5.6 × 10 -6 M).

Figure S2 .Figure S2 .

 S2S2 Figure S2. CD spectra of BBD in THF (1.0 × 10 -5 M).

Becke 2 ,

 2 [START_REF] Becke | Density-Functional Thermochemistry. III. The Role of Exact Exchange[END_REF] and the correlation functional by Lee, Yang and Parr,[START_REF] Lee | Development of the Colle-Salvetti Correlation-Energy Formula into a Functional of the Electron Density[END_REF] and the 6-31G(d,p) split valence plus polarization basis set[START_REF] Ditchfield | Self-Consistent Molecular-Orbital Methods. IX. An Extended Gaussian-Type Basis for Molecular-Orbital Studies of Organic Molecules[END_REF][START_REF] Hehre | Self-Consistent Molecular Orbital Methods. XII. Further Extensions of Gaussian-Type Basis Sets for Use in Molecular Orbital Studies of Organic Molecules[END_REF][START_REF] Hariharan | Accuracy of AH n Equilibrium Geometries by Single Determinant Molecular Orbital Theory[END_REF][START_REF] Hariharan | The Influence of Polarization Functions on Molecular Orbital Hydrogenation Energies[END_REF] was used. Relaxed S 1 structures (= optimized structures in S 1 state) were calculated by time-dependent (TD) DFT.See Tab. S1, Tab. S2, Fig.S16, Fig.S17

Figure S5 .

 S5 Figure S5. DEPT 90 of BBD.

Figure S5 .S5Figure S5 .

 S5S5 Figure S5. DEPT 90 of BBD.

Figure S6 .

 S6 Figure S6. DEPT 135 of BBD.

Figure S6 .

 S6 Figure S6. DEPT 135 of BBD.

Figure S7 .

 S7 Figure S7. COSY of BBD.

Figure S7 .S6Figure S7 .

 S7S7 Figure S7. COSY of BBD.

Figure S8 .

 S8 Figure S8. HMQC of BBD.

Figure S8 .

 S8 Figure S8. HMQC of BBD.

Figure S9 .

 S9 Figure S9. HMBC of BBD.

Figure S9 .S7Figure S9 .

 S9S9 Figure S9. HMBC of BBD.

Figure S10 .

 S10 Figure S10. NOESY of BBD.

Figure S10 .

 S10 Figure S10. NOESY of BBD.

Figure S11 .Figure S12 .

 S11S12 Figure S11. ROESY of BBD.

Figure S11 .

 S11 Figure S11. ROESY of BBD.

Figure S11 .

 S11 Figure S11. ROESY of BBD.

Figure S12 .S9Figure S13 .

 S12S13 Figure S12. Selected correlation in NOESY (dashed lines) and

Figure S13 .S10Figure S14 .

 S13S14 Figure S13. Temperature dependent 1 H NMR (400 MHz, CDCl 3 ) spectra of BBD. The temperature was changed from 313 to 218 K. White and black dots at 218 and 223 K correspond to signals from two conformers. Proton resonances of aromatic region at the lower magnetic field were further analyzed for energetics, since they are comparably isolated. Two doublet peaks from one isomer and one overlapped doublet peaks from another isomer were observed at 218 K, which are merged to form two doublet peaks at 313 K.

Figure S15 .FigureFigure S15 .Figure S16 .

 S15S15S16 Figure S15. The Eyring plot for BBD. The energetics parameters are shown at the bottom of the plots. H = 9.8 kcal/mol, S = -17 cal/mol K.

Figure S18 .

 S18 Figure S18. (a, d) anti-, (b, e) syn-, (c, f) flat-BBD on Au(111) layers simu

Fig. S18 .

 S18 Fig. S18. (a, d) anti-, (b, e) syn-, (c, f) flat-BBD on Au(111) layers simulated by MD calculations.

  Bartels, L.; Meyer, G.; Rieder, K.-H. Basic Steps of Lateral Manipulation of Single Atoms and Diatomic Clusters with a Scanning Tunneling Microscope Tip. Phys. Rev. Lett. 1997, 79, 697-700. Bouju, X.; Joachim, C.; Girard, C.; Tang, H. Mechanics of (Xe) N Atomic Chains under STM Manipulation. Phys. Rev. B: Condens. Matter Mater. Phys. 2001, 63, 085415.

	1 Eigler, D. M.; Schweizer, E. K. Positioning Single Atoms with a Scanning Tunnelling Microscope. Nature
	1990, 344, 524-526.

2 3

  6-layer, with a vacuum layer. The size of unit cell for a single molecule on Au(111) was 19.9795 × 23.0703 × 51.7730 Å and that for two molecules was 29.9693 × 34.6055 × 61.7730 Å. All simulations were performed

	7. Cartesian coordinates
	Table S3. Cartesian coordinate flat-conformer
	SCF Done: E(RB3LYP) = -2226.71856349	A.U. after	14 cycles
	-
		S14

Table S4 .

 S4 -Cartesian coordinate syn-conformer

	SCF Done: E(RB3LYP) = -2226.74911677	A.U. after	7 cycles
	-

Table S4 .

 S4 -Cartesian coordinate syn-conformer

	SCF Done: E(RB3LYP) = -2226.74911677	A.U. after	7 cycles
	-

Table S5 .

 S5 -Cartesian coordinate anti-conformer

	SCF Done: E(RB3LYP) = -2226.74970717	A.U. after	14 cycles
	-

Jung, T. A.; Schlittler, R. R.; Gimzewski, J. K.; Tang, H.; Joachim, C. Controlled Room-Temperature Positioning of Individual Molecules: Molecular Flexure and Motion. Science 1996, 271, 181-184.

Hochstrasser, R. M. The Effect of Intramolecular Twisting on the Emission Spectra of Hindered Aromatic Molecules. Can. J.Chem. 1960, 39, 459-470.

ACKNOWLEDGMENTS

We thank Dr. Y. Okawa, Dr. T. Uchihashi, and Dr. K. Sagisaka in NIMS for prescreening of STM conditions and helpful discussions and Prof. M. Aono for its continuous support during this work.

Funding WPI MANA MEXT program and by JSPS KAKENHI (16H07436, JP16H06518, 26790003). M.K. acknowledges financial support received from the Foundation for Polish Science (FNP). We thank TOYOTA as an official sponsor for our NIMS MANA team in the nanocar race. 43 Notes The authors declare no competing financial interest.

SUPPORTING INFORMATION 1-General

Analytical thin-layer chromatography (TLC) was performed on a glass plate coated with silica gel (230-400 mesh, 0.25 mm thickness) containing a fluorescent indicator (silica gel 60F254, Merck). Flash silica gel column chromatography was performed on silica gel 60N (spherical and neutral gel, 40-50 µm, Kanto). Infrared (IR) spectra were recorded on Thermo Scientific Nicolet NEXUS 670 FT-IR and were reported as wavenumbers (ν) in cm -1 . Proton ( 1 H) and carbon ( 13 C) nuclear magnetic resonance (NMR) spectra were recorded on a JEOL JNM-ECA400 spectrometer.

Mass spectra were obtained on an Applied Biosystems Voyager DE STR SI-3 instrument (MALDI-TOF MS). UV-Vis absorption spectra were obtained on JASCO V-670. Circular dichroism (CD) spectra were obtained on JASCO, J-820.

Materials

Solvents and materials were purchased from Aldrich, Tokyo Kasei Chemical Co. or Wako Chemical Co., and were used without further purification.

Synthesis

To a mixture of (R)-(+)-1,1'-bi (2-naphthol) (1.00 g, 3.49 mmol) and CsCO 3 (2.84 g, 8.73 mmol) in dry acetone (100 mL) was added 1,2,4,5-tetrakis(bromomethyl)benzene (715 mg, 1.59 mmol) and the mixture was refluxed 48 h. The mixture was extracted with CH 2 Cl 2 (2 × 200 mL) and concentrated in vacuo. The crude material was purified by silica gel column chromatography (eluent: CH 2 Cl 2 /Hexane) to give pure desired compound, bisbinaphthyldurene (BBD) (410 mg, 37%).

The compound was further purified by sublimation (< 300 • C) for the STM experiments. Mp > 250 • C; FT-IR (KBr, cm 1 ) 3047, 2934, 2880, 1918, 1593, 1472, 1321, 1244, 1147, 1079, 1009, 893, 805, 749; 1 H NMR (400 MHz, CDCl 3 ) δ 5. 15 (d, J = 11.2 Hz, 4H), 5.21 (d, J = 11.2 Hz, 4H), 7.16 (ddd, J = 7.6, 7.6, 0.8 Hz, 4H), 7.18 (dd, J = 7.6, 7.2 Hz, 4H), 7.27 (ddd, J = 7.2, 7.2, 1.4 Hz, 4H), 7.32 (s, 2H), 7.46 (d, J = 9.0 Hz, 4H), 7.75 (d, J = 7.6 Hz, 4H), 7.80 (d, J = 9.0 Hz, 4H); 13 C NMR (400 MHz, CDCl 3 ): δ 71. 4, 117.0, 121.6, 123.9, 126.1, 126.3, 128.1, 129.3, 129.8, 133.4, 134.5, 136.6, 154.4

Theoretical calculations (DFT)

All calculations were performed using the Gaussian 09 program, 1 and the results were analyzed and visualized on GaussView 5.0.9. Calculations were performed at the density functional theory (DFT) level with the B3LYP functional, the gradient correction of the exchange functional by Becke 2,[START_REF] Becke | Density-Functional Thermochemistry. III. The Role of Exact Exchange[END_REF] and the correlation functional by Lee, Yang and Parr, [START_REF] Lee | Development of the Colle-Salvetti Correlation-Energy Formula into a Functional of the Electron Density[END_REF] and the 6-31G(d,p) split valence plus polarization basis set [START_REF] Ditchfield | Self-Consistent Molecular-Orbital Methods. IX. An Extended Gaussian-Type Basis for Molecular-Orbital Studies of Organic Molecules[END_REF][START_REF] Hehre | Self-Consistent Molecular Orbital Methods. XII. Further Extensions of Gaussian-Type Basis Sets for Use in Molecular Orbital Studies of Organic Molecules[END_REF][START_REF] Hariharan | Accuracy of AH n Equilibrium Geometries by Single Determinant Molecular Orbital Theory[END_REF][START_REF] Hariharan | The Influence of Polarization Functions on Molecular Orbital Hydrogenation Energies[END_REF] was used. Relaxed S1 structures (= optimized structures in S1 state) were calculated by time-dependent (TD) DFT.

Table S1. Torsion angle of flat-, syn-, and anti-BBD optimized by DFT (B3LYP/6-31G(d,p)).

Torsion angle

Flat Syn Anti C2-C1-C1'-C2' ( ) -60.5 -63.9 -63.9 C2'-C1'-C1''-C2'' ( ) -60.5 -63.9 -63.9 C2-O1-C3-C4 -158.9 -61.6 -61.7 C2'-O1'-C3'-C4' -158.9 -144.1 -144.6 C2''-O1''-C3''-C4'' -158.9 -144.1 -61.7 C2'''-O1'''-C3'''-C4'' ' -158.9 -61.6 -144.6 Table S2. Table S1. Table S1. Torsion angle of flat-, syn-, and anti-BBD optimized by DFT (B3LYP/6-31G(d,p)).

Torsion angle Flat Syn Anti

C2-C1-C1'-C2' ( ) -60.5 -63.9 -63.9 C2'-C1'-C1''-C2'' ( ) -60.5 -63.9 -63.9 C2-O1-C3-C4 -158.9 -61.6 -61.7 C2'-O1'-C3'-C4' -158.9 -144.1 -144.6 C2''-O1''-C3''-C4'' -158.9 -144.1 -61.7 C2'''-O1'''-C3'''-C4'' ' -158.9 -61.6 -144.6 Table S2. Table S2.

S13 in the NVT, and controlled using a NHL thermostat, with a decay constant of 1 ps.

To find several conformations of one or two molecules on Au(111) surface, anneal dynamics were used. Anneal dynamics consists of a dynamics simulation where the temperature is periodically increased from an initial temperature (4 K) to a mid-cycle temperature (500 K) and back again. All MD calculations were performed with Forcite in Materials Studio, and force field COMPASS was used. All the structures obtained were optimized with the same force field.

For calculations of a monomer on Au(111), the DFT optimized anti-structure was used as an initial structure, and syn-conformer on Au(111) surface was obtained as a stable conformer.

The anti-conformer on Au(111) surface was also obtained with higher energy (+9.0 kcal/mol).

When a mid-cycle temperature was raised to 1500 K, flat-conformer was found with lower energy, -22.5 kcal/mol compared with the syn-conformer. For calculations of a dimer on Au(111), the DFT optimized two syn-conformers were used as initial structures, and syn-syn-dimer on Au(111)

surface was obtained as a stable conformer.

See Fig. S18 and Fig. S19.

Interaction energies

Each total energies of syn-, anti-, and flat-conformers on Au( 111 The interaction energy between Au(111) and syn--conformer (E surfaceinteraction_syn ) was calculated to be -194.92 kcal/mol based on the following equation:

The interaction energy between Au(111) and anti-and flat-conformer (E surfaceinteraction_anti , E surfaceinteraction_flat ) was calculated with the same method to be -194.3 and -244.2 kcal/mol, respectively.

The surface interaction energy for syn-or anti-conformers were at the same level (E surfaceinteraction_syn = -194.9 kcal/mol, E surfaceinteraction_anti = -194.3 kcal/mol). The difference in stability of synand anti-conformers on Au(111) originates from the difference in molecular deformation energy (E anti -E syn = +8.4 kcal/mol higher than syn-conformer) rather than interaction energy (E surfaceinteraction_anti -E surfaceinteraction_syn = +0.6 kcal/mol more unfavorable for the anti-conformer).

In another words, to obtain similar interaction with Au(111) surface, anti-conformer needed to be

Interaction energies

Each total energies of syn-, anti


S Piazolo

M Montagnat

F Grennerat

H Moulinec

J Wheeler

Effect of local stress heterogeneities on dislocation fields: Examples from transient creep in polycrystalline ice

Keywords: stress heterogeneities, dislocation field, electron backscatter diffraction, full-field modeling, kink bands, viscoplastic anisotropy

This work presents a coupled experimental and modeling approach to better understand the role of stress field heterogeneities on deformation behavior in material with a high viscoplastic anisotropy e.g. polycrystalline ice. Full-field elasto-viscoplastic modeling is used to predict the local stress and strain field during transient creep in a polycrystalline ice sample. Modeling input includes the experimental starting microstructure and a validated slip system dependent flow law. EBSD measurements on selected areas are used to estimate the local dislocation field utilizing the Weighted Burgers Vector (WBV) analysis. Areas of local stress concentration correlate with triple junctions and grain boundaries, originating from strain incompatibilities between differently oriented grains. In these areas of highly heterogeneous stress patterns, (a) kink bands are formed and (b) WBV analysis shows a non-negligible c-axis component of the WBV. The correlation between this defect structure and presence of kink bands suggest that kink band formation is an efficient accommodation deformation mode.

Introduction

When polycrystalline material is plastically deforming, stress and strain heterogeneity fields are developing due to strain incompatibilities between grains of different crystallographic orientations. Depending on the level of viscoplastic anisotropy of the material, the heterogeneity amplitude can be high.

The viscoplastic anisotropy of ice is known to be very strong, with dislocations gliding mostly on the basal plane with three equivalent < 11 20 > Burgers vector directions [START_REF] Hondoh | Physics of Ice Core Records[END_REF]. This results in strong kinematic hardening at grain boundaries and triple junctions [START_REF] Duval | [END_REF].

As such ice is a good model for materials with high viscoplastic anisotropy, such as magnesium [3,4], quartz [START_REF] Hobbs | Preferred orientation in deformed metals and rocks, 405 chapter The geological significance of microfabric analyses[END_REF] and olivine [START_REF] Nicolas | Crystalline Plasticity and Solid State Flow 408 in Metamorphic Rocks[END_REF]. In ice, strong heterogeneity fields were measured by Digital Image Correlation on polycrystalline samples deformed by compression creep with local strain amplitude as high as ten times 18 the macroscopic strain [START_REF] Grennerat | [END_REF]. The strain heterogeneities 19 were also indirectly observed through lattice misori-20 entation measurements via EBSD [8,[START_REF] Montagnat | Lebensohn 414 RA[END_REF] and were 21 simulated using full-field viscoplastic approaches based 22 on Fast Fourier Transform formulation [10,[START_REF] Montagnat | Lebensohn 414 RA[END_REF][START_REF] Grennerat | [END_REF]. In [10,[START_REF] Montagnat | Lebensohn 414 RA[END_REF]. The same numerical constraint was derived for 34 polycrystalline Mg in conditions where twinning was not activated [11]. However, up to now there exists no unequivocal evidence for macroscopic strain resulting 37 from non-basal slip in ice [12,13].

38

The presence of heterogeneous dislocation fields in experimentally and naturally deformed ice was mostly 40 observed indirectly from substructures observations (Xray diffraction, optical analyses, EBSD...) [8,[START_REF] Montagnat | Lebensohn 414 RA[END_REF]14,[START_REF] Donges | Nuclear Instru-424 ments and Methods in Physics Research Section B: Beam Inter-425 actions with[END_REF].

42

In particular kink bands and double kink bands has been 43 commonly observed in polycrystalline ice deformed 44 in the laboratory. The origin of these kink bands was following [16,17]. Accuracy of EBSD data is within figures with both the sample coordinate system and the 125 crystal coordinate system (see Fig. 2).

83 0.3 • -0.4 • [18].
126 Table 1 presents the integral WBV calculated over se-127 lected areas in the analyzed samples (Fig. 2 and Fig. 3), 1 shows that the integral WBV values vary significantly depending on microstructure type and location. However, for each selected area, we obtained several WBV values and chose to present here values that are representative for the selected area.

The accuracy of the integral WBV is dependent on the angular resolution of the EBSD data. Using EBSD data with high angular resolution (here within 0.3 degrees), we consider an integral WBV ratio of one specific Burger vector over the maximum WBV value of 0.5 significant.

Local stress field estimation

Full-field numerical simulations were performed using the CraFT code as presented in [START_REF] Suquet | [END_REF]. The code is based on the FFT method initially proposed in [22,23], extended to elasto-viscoplastic composites using a step-by-step integration in time in [24] (see also the numerical details in [START_REF] Suquet | [END_REF]). The method used in the CraFT code finds a strain rate field associated with a kinematically admissible velocity field that minimizes the average local work rate under the compatibility and equilibrium constraints. An iterative scheme is used following a fixed point approach. It is numerically more efficient than the finite element method [25],

but is limited to simulations with microstructures with periodic boundary conditions. The exact experimental boundary conditions (stress free lateral surface) could not be reproduced due to the numerical periodicity constraint. therefore, Accordingly, stress and strain fields predicted close to the specimen edges are not expected to be very accurate, however Grennerat et al. [START_REF] Grennerat | [END_REF] showed a limited impact on the macroscopic response and estimated fields, especially in the center of the modeled microstructure, where the 185 areas of interest here are located.

186

The elasto-viscoplastic response of ice was modeled 187 following the law and hypothesis discussed in details in 188 [START_REF] Suquet | [END_REF]. To model ice, the used crystal plasticity formula- This is illustrated by the decomposition of the integral 261 WBV data (Table 1) and represented in the inverse pole 262 figure plots in Fig. 3 (see for instance mapG1-3 areas A 263 and B and mapG4-1-5 area B, Table 1).

264

As illustrated by the inverse pole figure of subarea D 265 from map G4-1-5, there is a systematic presence of a 266 minor but significant c-axis component close to triple 267 junctions. Such a c-axis component is considered as 268 non-negligible when the ratio K c /max(K ai ) is higher 269 than 0.5 (see Table 1). In contrast, most of the areas 270 analyzed in a grain interior show a c-axis component of 271 the WBV which is very close to the detection limit (see 272 Table 1). that cannot be resolved by the easy slip system i.e.

297

basal slip in ice [3,4,29]. In metals, kink bands 298 can occur at large deformation as strain localization 299 modes, as predicted by the bifurcation analysis of 300 [30], but also at the early stage of deformation in the 301 presence of obstacles [31]. Chang et al. [31] used

373

-The approach presented is applicable to materials 374 with significant viscoplastic anisotropy.

Analyses areas

Integral WBV (µm) - 2: Relative CRSS for the three slip system families at the beginning of the transient creep, τ iniR , and at the end, τ statR . n s is the stress exponent that was adjusted by [START_REF] Suquet | [END_REF] for each family. The absolute value of τ ini for the basal slip systems was fitted at 0.1 by [START_REF] Suquet | [END_REF], and the absolute value of τ stat for the basal slip systems was fitted at 0.022.

23 these

 23 modelling approaches, plasticity is simulated 24 by the activation of several slip systems (e.g. basal, 25 prismatic and pyramidal slip in the case of ice), where 26 each slip system is assigned a relative critical resolved 27 shear stress for slip activation. In this frame, these 28 last works have shown, among other results, that 29 observed high stress and strain heterogeneities could 30 only be correctly simulated providing a significant 31 amount of non-basal slip activity in the corresponding 32 areas, while the global non-basal activity remained low 33

3 .

 3 Fig. 1 presents selected EBSD maps 84 showing the local variations in orientations. 85 86 Weighted Burgers Vector analysis 87 To quantitatively analyze the EBSD point grid data 88 we utilized the Weighted Burgers Vector (WBV) analy-89 sis explained in details in [19]. The WBV is a recently 90 developed new quantity to constrain dislocation densi-91 ties and dislocation types using EBSD data on two di-92 mensional sections through crystalline materials. The 93 WBV is defined as the sum, over all dislocation types, 94 of [(density of intersections of dislocation lines with a 95 map) × (Burgers vector)] and as such can be calculated 96 from a planar set of orientation measurements such as 97 in an EBSD orientation map. There is no assumption 98 about the orientation gradient in the third dimension. 99 The magnitude of the WBV gives a lower bound of 100 the magnitude of the dislocation density tensor. The di-101 rection of the WBV can be used to constrain the types 102 of Burgers vectors of the geometrically necessary dis-103 locations present in the microstructure and their geo-104 metric relationship to intra-grain structures, for exam-105 ple subgrain walls. The WBV can then be decomposed 106 in terms of the 3 main lattice vectors [20]. In the case 107 of ice, the two a-axis lattice vectors are further decom-108 posed into the 3 equivalent a-axis lattice vectors. We 109 can calculate the net Burgers vector content of disloca-110 tions intersecting a given area of a map by an integra-111 tion around the edge of this area. This integral WBV 112 method is fast, complements point-by-point WBV cal-113 culations and, thanks to this integration, reduces the ef-114 fect of noise on the analysis. A lower bound of the 115 density of geometrically necessary dislocations can be 116 estimated from this calculation. This estimation is not 117 absolute but can be used for comparison purposes. It 118 should be noted that the net Burgers vector value de-119 rived using the integral WBV method is sensitive to the 120 chosen area both in terms of size and location. 121 WBV analysis data is represented in color coded maps 122 showing the WBV magnitude, WBV directions as pro-123 jected arrows onto the color coded maps and in pole 124

128

  decomposed into the three a-axes and the c-axis of the 129 ice crystallographic structure. Areas were selected to 130 represent the observed spectrum of different microstruc-131 tures present within the analyzed sample. Such mi-132 crostructures include triple junctions, grain boundaries 133 with or without asperities, areas in close vicinity or at distance to grain boundaries. Data from Table

  The specimen undeformed microstructure was discretized into 512 × 512 Fourier points with a single layer of Fourier points in the third (Z) direction, assuming thus infinite column length. To represent the microstructure, each Fourier point is allocated a c-axis orientation according to the measured orientation of the underformed experimental sample. Consequently grain boundary are not specifically defined as discrete objects with specific physical characteristics other than a change in crystal orientation. Throughout the numerical simulations, no crystallographic orientation changes are imposed, thus the microstructure (orientation, grain boundaries) does not evolve. Creep conditions equivalent to the experimental ones were applied (constant 0.5 MPa stress in the vertical direction, transient creep up to 1% macroscopic strain).

225

  189 tion accounts for three different families of slip systems, 190 namely the basal, prismatic and pyramidal systems, 191 the latter two being taken stiffer than basal slip. A 192 power law is considered for the evolution of the shear 193 strain rate as a function of the resolved shear stress on 194 each slip system that integrates kinematic hardening, 195 slip system interactions and their evolution with time 196 during transient creep. The material parameters of the 197 law were determined by adjusting them according to 198 experimental data available for single crystals as well 199 as for polycrystals, as detailed in [21]. The Critical 200 Resolved Shear Stress (CRSS) on each slip system 201 was allowed to evolve with strain between initial and 202 stationary values. Table 2 provides the relative CRSS 203 for each slip system family, and the value of the stress 204 exponent attributed to each family. It is worth noting 205 that the relative CRSS is much higher for the pyramidal 206 family, and that there is a relative softening of basal 207 systems during transient creep [21]. 208 The local heterogeneities of the strain and stress fields 209 are illustrated in Fig. 4a) and b) where the spatial 210 variation of the equivalent stress (σ eq = 3 2 σ i j σ i j ) 211 and equivalent strain (ε eq = 3 2 ε i j ε i j ) are repre-212 sented, respectively. For each simulated pixel of 213 the microstructure, the deviatoric part of the stress 214 tensor was decomposed into its eigenvector frame. 215 From this decomposition, we extracted the eigenvector 216 corresponding to the largest absolute eigenvalue. We 217 built a composite vector representation based on the 218 in-plane projection of a vector having the direction of 219 this eigenvector, and the amplitude of the associated 220 eigenvalue. This representation is given in Fig. 4c) for 221 the area of interest, superimposed on the equivalent 222 stress contour plot. Numerical modeling shows that local stress concen-226 trations and stress field heterogeneities occur close to 227 triple junctions and grain boundaries. The higher the 228 mismatch between crystallographic grain orientations, 229 the higher the concentration and heterogeneities (Fig.

  230

Fig. 3

 3 Fig.3where the heterogenous stress band crossing 253

  260

273

  Close to triple junctions, we observe near straight 274 subgrain boundaries. Their traces are parallel to the 275 c-axis, and the WBV are predominantly oriented along 276 the a-axis perpendicular to the subgrain boundary trace 277 (Fig. 1 and Fig.3). The other a-axis contribution is 278 related to a continuous crystal bending perpendicular to 279 the c-axis (see Fig.5with a sketch of the bending axis).

280

  Similar observations were made in[8,[START_REF] Montagnat | Lebensohn 414 RA[END_REF]. 281 These only slightly curved subgrain boundaries com-282 monly occur in parallel pairs with the main WBV 283 pointing in opposite directions (Fig. 3 mapG1-3 284 and mapG4-1-5, Table 1). The parallelism of the 285 subgrain boundary traces, their orientation relative to 286 the crystallographic axes of the host grain together 287 with the orientation of the main WBV a-axis compo-288 nent is consistent with a strongly crystallographically 289 determined boundary development. The opposing 290 directions of WBV in pairs of subgrain boundaries 291 (Fig. 3) is consistent with kink bands with alternating 292 opposing dislocation structures [26, 27, 28]. These 293 crystallographically well defined kink boundaries could 294 appear similar to the twinning modes in magnesium 295 in the way that they both accommodate shear stress 296

302

  Dislocation Dynamic simulation to illustrate the stable 303 position of an edge dislocation within the stress field 304 of an alignment of edge dislocations forming the kink 305 band. Consequently, in contrast to what was initially 306 thought [9], climb or cross-slip do not seem to be 307 necessary mechanisms to explain kink band formation. 308 In summary, observations suggest that kink bands form 309 in areas of very high local stress fields originating either 310 from strain incompatibilities developed in materials 311 with high viscoplastic anistropies or from high strain 312 rates. 313 It should be noted that the used numerical model does 314 not account for specific grain boundary properties. The 315 question of the strain continuity at an interface such as 316 grain boundary is therefore not addressed. In contrast, 317 recent work [32] showed that stress accumulation at 318 boundaries can explain grain boundary delamination 319 in alloys. In the case of ice deforming during tran-320 sient creep under low applied stress, no cracking was 321 observed at grain boundaries, but a better account for 322 continuity conditions of the plastic distortion at GB 323 might be necessary to evaluate the impact of strain 324 heterogeneities on recrystallization mechanisms for 325 instance. 326 Our data show that in high stress concentration areas, 327 close to triple junctions, a Burgers vector component 328 parallel to c-axis is present. Cross slip of dislocations 329 with Burgers vector lying in the basal plane cannot 330 explain this; instead it could be interpreted by a local 331 activity of a non-basal slip system. Conceptually, 332 such a non-basal slip activity is expected only in such 333 high stress areas, as non-basal activity requires high 334 level of local stress in order to overcome the high 335 critical resolved shear stress required for non-basal slip 336 dislocation activity in ice were performed in conditions 338 with very few dislocations activated, that could hardly 339 be extrapolated. Indeed, they were performed using 340 X-ray diffraction topography which enable individual 341 dislocation observation at the very early stage of 342 deformation [33, 34]. 343 The observed crystal bending parallel as well as per-344 pendicular to the kink bands which is accommodated 345 by the shown presence of Burgers vectors along not 346 one but two a-axes in high stress areas, may results in 347 the development of subgrain boundaries both parallel 348 and perpendicular to c-axis. This then will result in 349 the formation of a subgrain with near perpendicular 350 subgrain boundaries, one parallel to c-axis and one 351 perpendicular to c-axis. Such a developing subgrain is 352 shown in Fig. 5 and has been described in [8]. This 353 subgrain boundary formation represents one of the re-354 crystallization processes relaxing strain heterogeneities 355 at macroscopic strain exceeding the transient creep 356 regime [2, 35].

-

  Coupled full field elasto-viscoplastic modelling 360 and detailed EBSD analysis show the effect of 361 stress heterogeneities (magnitude and orientation) 362 on the dislocation field. 363 -The WBV c-axis component measured in high 364 stress areas could be consistent with local activa-365 tion of non-basal slip. 366 -At low strain, formation of kink bands with a well 367 defined crystallographic character appears as an ef-368 ficient accommodation deformation mode, similar 369 to twinning in Mg. 370 -Distinct misorientations across and perpendicular 371 to kink boundaries form substructures which act as 372 precursors for grain nucleation.

Figure 1 :Figure 2 :

 12 Figure1: Microstructure of a selected area of the columnar ice sample (in the plane perpendicular to the columns) after compressive strain of 10% along y direction. The central microstructure is color coded according to the measured c-axis orientation as represented by the color wheel (inset). EBSD maps of selected areas (marked by white rectangles) are shown with color code for change in orientation according to color scheme provided on the left side of the central microstructure. Insets of 3D crystal orientations (grey hexagons) are provided by EBSD analyses. Grains are given numbers for ease of reference (e.g. gr 1). Note labeling of the selected areas for which EBSD maps were obtained corresponds to the grain numbers of the grains present in the respective map.

Figure 3 :

 3 Figure 3: Comparison between stress field and dislocation field; deviatoric stress eigenvectors (left) zoomed in the areas selected for the WBV analyses (right maps). WBV analyses are shown with WBV magnitude (color range), WBV directions shown as white arrows on map (over a threshold value), and on inverse pole figures for selected areas (labeled A to D). Only upper limits are shown for these areas. Integral WBV of subareas are given in Table1. Black lines represent grain boundaries. Due to limitation in the simulation configuration (see text), the correspondence between modeled and observed microstructures such as the position of grain boundaries is approximate.

Figure 4 :

 4 Figure 4: Maps of equivalent stress (in MPa) (a) and of equivalent strain (b) predicted by the full-field simulation using CraFT on the area of interest after 0.01 macroscopic strain under compression creep. c) provides a map of the deviatoric stress eigenvectors projected on the plane, superimposed on the equivalent stress contour plot (same scale as in a)).Grain boundary traces are superimposed for clarity but they are not physical entities in the code.

Figure 5 :

 5 Figure 5: Planes of crystal bending (white stippled lines) for subgrain boundaries and associated rotation directions. The nearly horizontal subgrain boundaries are associated with abrupt misorientations, while the vertical ones correspond to more progressive misorientations. Both sub-structures were quantified in term of WBV, see Fig.3.

3

 3 Figure 5: Planes of crystal bending (white stippled lines) for subgrain boundaries and associated rotation directions. The nearly horizontal subgrain boundaries are associated with abrupt misorientations, while the vertical ones correspond to more progressive misorientations. Both sub-structures were quantified in term of WBV, see Fig.3.

  Figure 5: Planes of crystal bending (white stippled lines) for subgrain boundaries and associated rotation directions. The nearly horizontal subgrain boundaries are associated with abrupt misorientations, while the vertical ones correspond to more progressive misorientations. Both sub-structures were quantified in term of WBV, see Fig.3.

Table 1 :

 1 Integral WBV decomposed onto the three crystallographic axis of the ice crystal, for specific areas in EBSD maps shown in Figs.1, 2 and3. The two Ka vector directions are symmetrically equivalent, they were decomposed into the 3 a-directions following[START_REF] Wenk | Minerals: Their Constitution and Origin[END_REF]. The relative activity of K c /max(K ai ) is also given. ρ provides a lower bound estimate of the geometrically necessary dislocation density in the area. Step size is 15µm for all EBSD maps. * minimum value of the net Burgers vector magnitude. "gr" signifies grain number (cf. Fig.1) and "area", subarea as shown in Figs.2 and 3.

	2	ρ

Table

Table

Acknowledgments: Financial support by French ANR is

377

project DREAM #ANR-13-BS09-0001). Together with 378 support from institutes INSIS and INSU of CNRS, 379 France. The authors gratefully acknowledge the ESF support of the European Science 384 Foundation under the EUROCORES Programme, 385 EuroMinSci, MinSubStrDyn, No. ERAS-CT-2003-386 980409 of the European Commission, DG Research, 387 FP6. SP acknowledges additional funding from ARC 388 DP120102060 and FT1101100070. Funding by ARC 389 Centre of Excellence for Core to Crust Fluid Systems 390 (www.CCFS.mq.edu.au) allowed a Research visit of 391 M.M. to Macquarie University. This is contribution 392 534 from the ARC Centre of Excellence for Core to 393 Crust Fluid Systems (http://www.ccfs.mq.edu.au) and 394 975 in the GEMOC Key Centre. Funding from the 395 Australian Research Council (ARC) through the CCFS 396 Visiting Researcher scheme is gratefully acknowledged