Glenn Christopher

Otakandza Kandjani

Maxime Mikikian

Gautier Pascal Brault

Gautier Tetard

Armelle Michau

Jonathan Mougenot

Khaled Hassouni

Molecular Dynamics approach to volume and surface molecular reactivity in Ar/CH4 plasmas

de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Reactive plasmas or Complex Non-equilibrium Hydro-Carbon Plasmas (CNHCP) are weakly ionized gases containing solid particles of nanometric or micrometric size in addition to neutral species, electrons and ions. CNHCPs are governed by very different phenomena occurring on length-scales ranging from the molecule to the plasma size. Although the plasma chemistry in hydrocarbon discharges has been extensively studied during the last decades [1], many details remains poorly understood. This is especially the case for the precursors initiating the formation of nanoparticles in the plasma volume on one hand, and of the growth mechanisms of hydrogenated carbon thin films on the other hand. The aim of this work is to use molecular dynamics to study the reactivity of the main neutral species in the homogeneous and heterogeneous phases of an Ar/CH4 plasma. The mole fractions of the dominant initial species were determined using a fluid model detailed in [2,3]. For the homogeneous phase, the simulation is performed with 2683 molecules distributed approximately as follows: 54% H2, 24%CH4, 9%C2H4, 5% C2H, 4% C2H2 and 4% CH3 in a box of size 10x10x10nm 3 , in agreement with the fluid model [2,3]. Since argon is shown to only plays a thermostat role, it is thus replaced by a Nose-Hoover thermostat in the canonical ensemble. The inter-and intra-molecular interactions of the considered hydrocarbon molecules CH4, C2H2, C2H4, C2H, CH3 and H2 are modeled by the REBO potential [4]. The evolution of the gas composition is simulated during 40 ns with a time step of 0.1 fs. In this first study, we identified new species that result from this evolution. We have also determined their yield of formation (see Fig. 1 (a)) as a function of time for four temperature values. This yield rapidly saturates around 3% at all temperatures, indicating that volume reactivity is relatively small. The mass spectra were determined for each temperature and the species with every number of carbon atoms from C1, C2, C3, …, up to C14 are present at all temperatures. Other species with larger number of carbon atoms are also observed and the species with the highest carbon number (42) is identified at 500 K. For analysing reactivity, we consider the evolution coefficient (EC) of each initial species, i.e., the ratio between the concentration at time t and the initial concentration. This coefficient is determined for all temperatures considered. Figure 1 (b) shows the evolution coefficient at a temperature of 300 K for all initial species. As one can see, the EC of the C2H species is equal to 0 after 1 ns, which means that the species is completely consumed. This observation is valid for all temperatures, and at high temperatures a decrease of this EC is observed in the time interval [0, 1 ns]. These observations would indicate that C2H plays a major role in the initial reaction step involved in the generation of larger radicals. The EC of CH3 species decreases slowly with time, this is observed at all temperatures, with EC being lower at high temperatures. The EC of C2H2 is approximately around 0.9 over time, however, this EC increases with increasing temperature. It can be seen that the EC of Topic number 6 CH4, C2H4 and H2 molecules are approximately equal to 1 over time. This is observed at all temperatures for CH4 and C2H4 molecules, while for H2 molecules we observe a decrease of EC at high temperatures. We observed the formation of C2nH3 radicals (n=1, 2, 3) in the time interval [0, 5 ns]. This result is consistent with the fact that these radicals are known to play an important role in film growth [6].

For mimicking deposition on stainless steel surface, MD is performed at a rate of one molecule every 2000 time-steps dt (dt = 0.25 fs) onto an Fe67Cr17Ni14Mo2 substrate (40.18x40.18x1.4nm 3 ). The Me-C and Me-H interactions are modeled with Lennard-Jones potentials, while metal atom interactions are governed by Embedded Atom Method, and hydrogen and carbon ones again with REBO force field.

The sticking probability of each neutral molecule on the metallic substrate is calculated and was observed to decrease when the temperature increases (see Fig. 2 (a)). This is consistent with the fact that a larger temperature increases the surface mobility, which makes it more difficult to find a stable anchoring site on the metal surface. The observation of high values of sticking probability for the stable species CH4, C2H4 and C2H2 is due to the fact that the stainless steel is bare. However, the sticking probability of these three species are very low when the surface is covered with hydrocarbon layer. After this first series of simulations, the deposition of the film is simulated by sending all the molecules considered in the previous simulations of the homogeneous phase to the surface. The resulting global sticking probability (see Fig. 2 (b)) is decreasing as time and temperature increase. The contribution of each species to the growing film is followed by tagging each carbon atom with its corresponding radical. It allows to observe, as usually considered, that the C2H radical is the main contributor to the film growth. Moreover, the grown film is mainly populated by double C=C bonds.

Fig. 1

 1 Fig.1 Evolution of the new species % formed in the homogeneous phase (a), Evolution coefficient of each species at 300 K (b).

Fig. 2

 2 Fig.2 Sticking probability (a) of the main neutral species, and evolution of global sticking probability (b) of the Ar/CH4 plasma on stainless steel.

Molecular Dynamics approach to volume and surface molecular reactivity in Ar/CH4 plasmas

  . Otakandza Kandjani 1 , M. Mikikian 1 , P. Brault 1 , G. Tétard 2 , A. Michau 2 , J.Mougenot 2 , K. Hassouni 2 MD) is used to investigate the reactivity in volume and at surfaces of a low-pressure Ar/CH4 plasma. The initial plasma composition is determined using a 1D plasma model of a radio-frequency discharge. MD simulates the evolution of this composition showing the formation of new molecules in the homogeneous phase, and the molecular interactions with an exposed surface (sticking of plasma species and film growth). Simulations are performed for different temperatures, i.e., 300, 400, 500 and 1000 K.

	P	1 P	GREMI, UMR7344, CNRS -Université d'Orléans, BP6744 Orléans Cedex 2, France
			P	2 P	LSPM CNRS, Université Paris 13, 93430 Villetaneuse, France
				(*) pascal.brault@univ-orleans.fr
	Reactive Molecular Dynamics (

G

Acknowledgements

This work was partly supported by the French National Research Agency (ANR) through the MONA project (ANR-18-CE30-0016)


Christina Villeneuve-Faure

M Mitronika

Laurent Boudou

W Ravisy

M P Besland

Mireille Richard-Plouet

Antoine Goullet

Comparison of Ti x Si 1-x O 2 mixed oxide and TiO 2 in SiO 2 nanocomposite dielectric properties at nanoscale

Comparison of TiSi 1-x O 2 mixed oxide and TiO in SiO nanocomposite dielectric properties at nanoscale

I. INTRODUCTION

Concerning microelectronic applications, dielectric materials are used in a lot of passive or active devices. Among them, Metal-Insulator-Metal (MIM) capacitors are involved in a lot of applications such as analog-to-digital converters or dynamic random-access memory [START_REF] Jenkins | Review -beyond the highs and lows; a perspective on the future of dielectrics research for nanoelectronic devices[END_REF]. Considering MIM capacitor, SiO2 thin films have interesting characteristics regarding high energy storage, but are limited by their low relative dielectric permittivity (εr) [START_REF] Fan | Dielectric materials for high-temperature capacitors[END_REF]. To overcome this drawback, the International Roadmap for Devices and Systems (IRDS) 2026 projection indicates a target of an equivalent oxide thickness (EOT) close to 1 nm, εr of at least 40 and a leakage current lower than 10 -8 A.cm -². To reach the IRDS target, different approaches are developed. First, high-k materials, such as TiO2, BaTiO3 or Al2O3 appear interesting due to high relative dielectric permittivity but the main limitation is related to their high leakage current [START_REF] Jenkins | Review -beyond the highs and lows; a perspective on the future of dielectrics research for nanoelectronic devices[END_REF][START_REF] Jeon | Recent advances in the understanding of high-k dielectric materials deposited by atomic layer deposition for dynamic random-access memory capacitor applications[END_REF] and weak dielectric strength [START_REF] Yim | Novel high-k dielectrics for next-generation electronic devices screened by automated ab initio calculations[END_REF][START_REF] Khan | Layer-by-layer engineering of two-dimensional perovskite nanosheets for tailored microwave dielectrics[END_REF]. In this context, mixed oxides (MO) such as TixSi1-xO2 appear attractive to take advantage of both SiO2 low leakage current and of TiO2 high εr. However, the εr increasing remains limited [START_REF] Mitronika | TiO2-SiO2 mixed oxide deposited by low pressure PECVD: insights on optical and nanoscale electrical properties[END_REF]. Another way of improvement deals with nanocomposite (NC) materials. Considering in Organic fieldeffect transistor (OFET), the use of thin polymer nanocomposite films based on TiO2 or ZnO high-k nanoparticles (NPs) allows to improve performances in term of field-induced current [START_REF] Chen | Organic thin-film transistors with nanocomposite dielectric gate insulato[END_REF]. However, a fully-inorganic NC material for MIM capacitors thin films are scarcely reported in the literature. In this context, NC materials appear promising as they could combine advantages of each material. In this paper, we intend to compare TiO2/SiO2-based MO and NC films nanoscale dielectric properties in terms of leakage current and dielectric permittivity to identify the impact of nano-structuration.

II. EXPERIMENTS A. Materials

The mixed oxide TiO2-SiO2 thin films (50 nm thick), were obtained by low-pressure PECVD technique in a home-made reactor. Oxygen (24 sccm) is introduced at the top of the plasma source and Ti or Si organometallic precursors are introduced by a distribution ring located at 8 cm above the substrate. More experimental details can be found in previous papers [START_REF] Li | Structural and Optical Properties of PECVD TiO2-SiO2 Mixed Oxide Films for Optical Applications[END_REF]. Titanium Tetra-Isopropoxide (TTIP) and Hexamethyl-disiloxane (HMDSO) vapors were used as Ti and Si precursors respectively. During the deposition, the pressure value (before plasma ignition) was set at 3 mTorr. The variation of the TTIP and HMDSO flow rate was used to vary the Ti content in the deposited TiO2-SiO2 mixed oxide films. By this way, we intended to elaborate TixSi1-xO2 MO films with x = 0, 0.33, 0.49 and 0.54 [START_REF] Mitronika | TiO2-SiO2 mixed oxide deposited by low pressure PECVD: insights on optical and nanoscale electrical properties[END_REF]. The synthesis of TiO2 in SiO2 NC (50 nm thick) is based on the injection of a colloidal TiO2 NPs solution in the PECVD reactor described above. Concomitantly, the deposition of the SiO2 matrix is again ensured using HMDSO vapor and an O2based plasma. Prior injection, the colloidal solution dispersed in a propylene carbonate:propylene glycol (PC:PG) mixture needs to be diluted in a more volatile solvent in order to increase its volatility. Therefore, the final colloidal solution used was a mixture of PC:PG and methanol with a volume fraction of 20.25:54.75:25. The injection of the TiO2 colloidal solution was achieved through a separate industrial directliquid dispenser (Kemstream). The injection operating in a pulsed regime, at a frequency of 0.5 Hz, is controlled by a valve whose orifice includes 8 holes with a diameter of 70 μm each. For maintaining very-low pressure during the deposition (3 mTorr) and therefore obtaining a high-quality inorganic matrix, the pulsed sequence was adjusted in order to manage periods without injection to recover the nominal pressure. Thus for a sequence of 1 min, we defined N (= 1, 10, 15, 20 and Nmax=30) as the number of pulses lasting 1 ms that were triggered each 2s. Thus for N = 10 pulses, the dispenser valve is opened at a frequency of 0.5 Hz and after this first-time lapse of N × 2 s = 20 s (TON), the valve remains closed for 60-N × 2 s = 40 s (TOFF). Such sequence was repeated for 50 min. During this intermittent mode of injection, the oxygen mass flow rate of the working gas was set at 24 sccm (standard cubic centimeters per minute) while the continuous mass flow rate of HMDSO vapor was maintained at 0.11 sccm. The fraction between HMDSO and O2 was chosen in a way to produce a silica-like matrix with a very low carbon content. O2 was used to ensure the removal of solventbased organic moieties surrounding TiO2 NPs. In addition, in both cases, the films and NC growth was monitored with in situ ellipsometry with real-time fitting, allowing to stop deposition when the targeted thickness (50 nm) was reached. Thickness values were obtained thanks to a robust fitting model, fully validated for higher thicknesses [START_REF] Mitronika | TiO2-SiO2 mixed oxide deposited by low pressure PECVD: insights on optical and nanoscale electrical properties[END_REF]. We are thus confident that the targeted thicknesses were achieved.

B. Structural characterization

The chemical composition analysis at the very surface of the films were performed by X-Ray Photoelectron Spectroscopy (XPS) on a Kratos Nova spectrometer with Al Kα radiation at 1486.6 eV. After wide range spectra in the 1200 to -2 eV range in binding energy, high resolution spectra of relevant core level were recorded with charge neutralizer, i.e. O 1s, Ti 2p and Si 2p. The decomposition in elemental components and fitting of the measured peaks were carried out using CasaXPS software [START_REF] Fairley | Systematic and collaborative approach to problem solving using X-ray photoelectron spectroscopy[END_REF] and Gaussian-Lorentzian functions. The surface morphology of the thin films was assessed using SEM and AFM with JEOL JSM 7600F in a secondary electron mode operating at 5 kV and with a Bruker Multimode 8 setup in tapping mode, respectively. The Spectroscopic Ellipsometry (SE) measurements were conducted in the 245 nm to 1000 nm wavelength range at 71.7° incident angle using a rotating compensator ellipsometer (J.A. Woollam M-2000). The fitting was performed using CompleteEASE software using the Cauchy model for SiO2, the Tauc Lorentz (TL) model for TixSi1-xO2 and the Bruggeman effective medium approximation (BEMA) for NC (i.e. to model the TiO2 NPs dispersed in the SiO2 matrix).

C. Nanoscale dielectric properties characterization

Nanoscale electrical characterizations were performed on a Bruker Multimode 8 setup in Electrostatic Force Microscopy (EFM) mode for dielectric permittivity and Conductive AFM (C-AFM) for the current.

EFM phase shift ΔΦ measurements were done using 20 nm-lift and Pt-coated Si-tip with a quality factor Q of 293, a curvature radius Rc of 25 nm and a spring constant k of 2.81 N.m -1 . The phase shift parameter aΦ is deduced [START_REF] Riedel | Determination of the nanoscale dielectric constant by means of a double pass method using electrostatic force microscopy[END_REF]:

aΔΦ = [ΔΦ(V1) -ΔΦ(V2)]/[V1²-V2²]
(1) where ΔΦ(Vi) is the phase shift measured with a bias voltage Vi applied on the tip. (i.e. 0V or 5V).

A three steps methodology was developped to extract the εr cartography from the measured frequency or phase shift parameter 11]. First, a 2D-axisymmetric finite element model on COMSOL Multiphysics ® was used to compute in air and dielectric, the electric field distribution and the electrostatic force Fe on AFM-tip at various lift. Secondly, the second derivative of the capacitance between AFM-tip and dielectric sample d²C / dz² was deduced from Fe. And finaly related phase shift parameter aΦ was computed: aΔΦ = [Q/(k)] [d²C/dz²] (2) By this way the theoretical relationship between phase shift aΦ parameter and εr was obtained.

Current measurements at nanoscale were performed with a PtIr coated Si-tip (Rc = 27 nm and k = 0.4 N.m -1 ) using the Conductive AFM (C-AFM) mode with low noise amplifier modules and low contact force (30 nN). Different bias voltage was applied to the films as a function of film conductivity. The current collection surface Sc is estimated to 2 10 -3 µm².

III. RESULTS ANS DISCUSSION

A. Morphology and Structural characterization

To investigate the chemical composition of the TiO2 in SiO2 NC and of the TixSi1-xO2 MO thin films, at the very surface, XPS measurements were carried out. Concerning MO, the results confirm that we manage to elaborated TixSi1-xO2 films with a Ti atomic percentage of 0%, 33%, 49% and 54 % which correspond to x = 0, 0.33, 0.49 and 0.54 respectively [START_REF] Mitronika | TiO2-SiO2 mixed oxide deposited by low pressure PECVD: insights on optical and nanoscale electrical properties[END_REF]. Concerning NC, XPS results are reported in Table I and compare to those provided by the SE and the BEMA model concerning the volume fraction of TiO2 NPs [START_REF] Mitronika | TiO2 -SiO2 nanocomposite thin films deposited by direct liquid injection of colloidal solution in an O2 /HMDSO low-pressure plasma[END_REF]. Fig. 1 compares the surface topography of MO and NC materials. Concerning the TixSi1-xO2 films, the surface morphology is smooth and homogeneous (Fig. 1.a and 1.b) and weakly influenced by Ti contents. Indeed, the surface roughness remains constant around 0.45 ± 0.5 nm. Concerning NC films, the surface morphology depends strongly on the Ti contents. For low amount of TiO2 NP (N ≤ 10), the surface topography is flat, with few circle-like shape structures (Fig. 1.c) and surface roughness is close to SiO2 one (around 0.55 nm). For high amount of TiO2 NPs (N > 10), the surface topography presents a lot of circle-shape structures which could overlap (Fig. 1.d) which implies an increasing of the surface roughness of one order of magnitude (7.1 ± 0.5 nm). Such circle-shape structures are related to a coffee-ring effect, which could have occurred during the evaporation of aerosol droplet [START_REF] Mitronika | TiO2 -SiO2 nanocomposite thin films deposited by direct liquid injection of colloidal solution in an O2 /HMDSO low-pressure plasma[END_REF]. These results confirm the features that were already observed at the Scanning Electron Microscopy and Transmission Electron Microscopy scales as described in previous papers [START_REF] Mitronika | TiO2 -SiO2 nanocomposite thin films deposited by direct liquid injection of colloidal solution in an O2 /HMDSO low-pressure plasma[END_REF].

B. properties

Fig. 3 compares the surface topography and the εr map obtained by EFM on TixSi1-xO2 MO and TiO2 in SiO2 NC materials. Concerning the SiO2 layer, the surface topography is smooth (Fig. 3.a) and the εr map is homogeneous with a mean value of 3.7 which is closed to thermal silica one [START_REF] Robertson | High dielectric constant oxides[END_REF].

Concerning the TixSi1-xO2 films with x = 0.33, the surface topography (Fig. 3.b) is similar to SiO2 one. The εr map (Fig. 3.e) is homogeneous and the mean value is around 7 which is higher than SiO2. For NC with a number of pulses N ≤ 10 (i.e. Ti contents less than 2.8%), the surface topography is smooth (Fig. 3.c) and the εr map is homogeneous but with a mean value higher than SiO2 (results not shown). For N > 10, the surface topography presents a lot of grains (Fig. However, this increase is more important for NC than for MO. For a Ti content of around 30 at.%, the εr is equal to 7 for MO and to 29.5 for NC. This implies that the introduction of TiO2 NPs in SiO2 matrix is a more efficient process to increase εr. represents 15% of the surface and exhibits a current ranging from -100 pA to -600 pA. This area could be related to the presence of several TiO2 NPs (i.e. high εr area on Fig. 4.f), as TiO2 conductivity for electrons is important [START_REF] Mitronika | TiO2 -SiO2 nanocomposite thin films deposited by direct liquid injection of colloidal solution in an O2 /HMDSO low-pressure plasma[END_REF]. For NC with N = 20, only 10% of the surface is conductive (current around -20 pA for -28 V) and these areas should correspond to TiO2rich ones. For NC with N ≤ 20 no current was probed whatever the applied voltage value. Fig. 6 compares the evolution of the C-AFM mean current over 1 µm x 1 µm surface as a function of the bias for MO and NC films. For a Ti amount of 30 at.%, the NC film (N = 30) presents a mean current two order of magnitude higher than MO. Thus, for a same amount of Ti, NC films present higher εr but equally higher current than MO. Moreover, quite the same current is observed for N = 20 NC (i.e. 9.2% of Ti) and for Ti0.33Si0.67O2 whereas the εr is higher for NC. As a consequence, for similar current, NC films appear to achieve higher εr than MO.

In Table II are gathered the dielectric properties of MO and NC films which could be considered as high-k material (i.e. εr > 10) [START_REF] Robertson | High dielectric constant oxides[END_REF]. Results highlight that, for similar εr, NC films exhibits lower current density J than MO. In term of εr our films are similar to classical high-k material, however it is rather difficult to compare C-AFM current density to macroscale one as the surface collection in C-AFM is low, difficult to determine accurately [START_REF] Mortreuil | Influence of dielectric layer thickness on charge injection, accumulation and transport phenomena in thin silicon oxynitride layers: a nanoscale study[END_REF] and does not permit to reach very low current density (i.e. lower than 10 -2 -10 -3 A.cm -2 ). However, 60 nm-thick Y2O3 film processed by ALD exhibits a leakage current around 1 A.cm -2 which is close to the one of NC 9.16% of Ti with a comparable εr [START_REF] Xu | A Study on Solution-Processed Y2O3 Films Modified by Atomic Layer Deposition Al2O3 as Dielectrics in ZnO Thin Film Transistor[END_REF]. Similar conclusion could be done concerning the comparison of NC 29.8% of Ti and LaAlO3 [START_REF] Pelloquin | LaAlO3/Si capacitors: Comparison of different molecular beam deposition conditions and their impact on electrical properties[END_REF] which implies that TiO2 in SiO2 NC are competitive to replace high-k materials in MIMcapacitor. The next step is related to the improvement of TiO2 NPs dispersion in the SiO2 matrix to decrease the occurrence of TiO2-rich areas and consequently the current. IV. CONCLUSION This paper emphasizes the difference in term of morphology and dielectric properties between TiO2/SiO2-based MO and NC films. TixSi1-xO2 dielectric layers present homogeneous distribution of dielectric permittivity and current, whereas TiO2 in SiO2 NC films reveal heterogeneous dielectric properties mainly at high concentration in TiO2 NPs (upper than 6% in volume). Indeed, observed TiO2 rich areas exhibit high εr and current and correspond to gathering of TiO2 NPs (3 maximum). Moreover, the influence of the Ti content is really different for MO and NC films as the same Ti content induces higher εr in NC that in MO. For capacitance applications, the scope of high dielectric permittivity and low leakage current is reached for a Ti content of 6.2 % for NC and for 33% for MO. Therefore, NC films should be more suitable for MIM capacitance applications than MO and their properties are competitive to high-k materials. Managing the coffee ring effect that may lead to some agglomerations of NPs is currently under progress as it can be counterbalanced by adjusting the solvent composition of the TiO2 colloidal solution. Actually, this is also a way to tune the TiO2 NPs concentration in solution and in the NCs. Consequently, improvement in terms of dielectric properties are to be expected, in the future.

Fig. 1 .

 1 Fig. 1. Surface topography of (a) SiO2, (b) TixSi1-xO2 with x = 0.54, and TiO2 in SiO2 NC with number of pulses (c) N = 10 and (d) N = 30.

  Fig.3compares the surface topography and the εr map obtained by EFM on TixSi1-xO2 MO and TiO2 in SiO2 NC materials. Concerning the SiO2 layer, the surface topography is smooth (Fig.3.a) and the εr map is homogeneous with a mean value of 3.7 which is closed to thermal silica one[START_REF] Robertson | High dielectric constant oxides[END_REF]. Concerning the TixSi1-xO2 films with x = 0.33, the surface topography (Fig.3.b) is similar to SiO2 one. The εr map (Fig.3.e) is homogeneous and the mean value is around 7 which is higher than SiO2. For NC with a number of pulses N ≤ 10 (i.e. Ti contents less than 2.8%), the surface topography is smooth (Fig.3.c) and the εr map is homogeneous but with a mean value higher than SiO2 (results not shown). For N > 10, the surface topography presents a lot of grains (Fig.3.c) which is consistent with the increase of the surface roughness. The corresponding εr map (Fig.4.f) is no more homogeneous and presents high εr area (orange/red) and low εr area (dark blue) which corresponds respectively to TiO2-rich (εr ≈ 60-80) and SiO2-rich (εr ≈ 3.8) zones. As the lateral dimension of the TiO2 NPs is around 4nm, the TiO2-rich area corresponds to gathering of NPs . The main value of εr is around 29.5 for N = 30 (i.e. Ti contents of 29.8%). Fig.4compares the evolution of the εr as function of the Ti contents provided by XPS for TixSi1-xO2 MO and TiO2 in SiO2 NC. For both materials the εr increases with the Ti content. However, this increase is more important for NC than for MO. For a Ti content of around 30 at.%, the εr is equal to 7 for MO and to 29.5 for NC. This implies that the introduction of TiO2 NPs in SiO2 matrix is a more efficient process to increase εr.

10 Fig. 3 .

 103 Fig. 3. (a-c) Surface topography and (d-f) εr map probed by EFM. (a, d) SiO2, (b,e) TixSi1-xO2 with x=33% and (c,f) TiO2 in SiO2 NC with 28.9% of Ti.

Fig. 4 .Fig. 5 .

 45 Fig.4. Evolution of the relative dielectric permittivity as function of Ti contents.2 nm

Fig. 5 .

 5 Fig. 5.a and 5.b compare the surface topography and the current map for -30 V applied on MO films with x = 0.33. The current is homogeneously distributed over the whole scanning area and a mean value of -80 pA was recorded. A homogeneous current map, with different mean value is observed for TixSi1-xO2 with x ≥ 0.33. Fig. 5.c and 5.d compare the surface topography and current map for -18 V applied on TiO2 in SiO2 NC with N = 30. Similarly, to the εr map (Fig. 3.f), the current flowing through the NC films is not homogeneously distributed over the surface and 3 different areas are identified. (i) A low current area (white in Fig. 5.d), represents around 25% of the surface and exhibits a current ranging from -5 pA and -25 pA. This area corresponds to SiO2-rich zone identified on εr map (Fig 3.f). (ii) A medium current area (light brown on Fig. 5.d), represents around 60% of the surface and exhibits a current ranging from -25 pA and -200 pA. (iii) A high current area (dark brown on Fig. 5.d)represents 15% of the surface and exhibits a current ranging from -100 pA to -600 pA. This area could be related to the presence of several TiO2 NPs (i.e. high εr area on Fig.4.f), as TiO2 conductivity for electrons is important[START_REF] Mitronika | TiO2 -SiO2 nanocomposite thin films deposited by direct liquid injection of colloidal solution in an O2 /HMDSO low-pressure plasma[END_REF]. For NC with N = 20, only 10% of the surface is conductive (current around -20 pA for -28 V) and these areas should correspond to TiO2rich ones. For NC with N ≤ 20 no current was probed whatever the applied voltage value. Fig.6compares the evolution of the C-AFM mean current over 1 µm x 1 µm surface as a function of the bias for MO and NC films. For a Ti amount of 30 at.%, the NC film (N = 30) presents a mean current two order of magnitude higher than MO. Thus, for a same amount of Ti, NC films present higher εr but equally higher current than MO.

Fig. 6 .

 6 Fig.6. Evolution of the mean value of the current probed by over the probed area (1 µm x 1 µm) as function of the applied bias.

TABLE I .

 I Evolution of Ti content (at.% relatively to silicon) from XPS analyses and of TiO2 volume fraction from SE as function of number of pulses N for TiO2 in SiO2 NC.

	N	Ti content	TiO2 volume fraction (%)
	1	0.13	3.1
	10	2.8	13.3
	15	6.2	36.8
	20	9.16	51
	30	29.8	57

TABLE II

 II

					.
	Comparison of εr, EOT (films thickness of 50nm) and leakage current density
	J at 25V (Sc = 2 10 -3 µm²). High-k materials with similar εr [13].
		Ti (%)	εr	EOT (nm)	J (A/cm -2 )	High-k material
	NC	6.2	11	17.7	0	Al2O3, HfSiO4
		9.16	17	11.5	8	Y2O3
		29.8	30	6.5	2 10 2	a-LaAlO3
	MO 54	18	12	45 10 2	Y2O3

ACKNOWLEDGMENT

This work was financially supported by the French GDR SEEDS.


Syalie Liu

Sacha Altay

Hugo Mercier

Being green or being nice? People are more likely to share nicer but potentially less impactful green messages

Keywords: Climate change, Reputation, Expressive behavior, Two-step process

Citizens can play an important role in disseminating scientific information about climate change, if motivated to do so. However, expressing green positions has the potential to negatively affect people's reputation, by making them look judgmental for instance. In three experiments among US and UK participants (N = 1197) we investigate the reputational costs of sharing statements about climate change that vary in accuracy and in potential impact. In Experiment 1, we show that participants judge more negatively someone sharing a bleak (but arguably more accurate) statement about climate change (e.g., calling it "climate breakdown"), compared to a control statement. Experiment 2 replicates this finding with control statements (e.g. "The richest 1% in the world is responsible for most of the greenhouse gas emissions") compared to accusatorial statements (adding "because most citizens in countries like the United States consume too much energy"). Experiment 3 shows that participants are less willing to share more accusatorial statements-even though they are thought to exert a greater effect on their audience. Our results further show that the fear of appearing judgmental and unfriendly might make people less likely to share bleaker or more accusatorial-even if more accurate or potentially effective-statements about climate change.

Citizens play a crucial role in relaying messages from the media, politicians, or scientists to other citizens. This two-step flow process has been well studied in the context of political information [START_REF] Katz | Personal influence: The part played by people in the flow of mass communications[END_REF], and it has been suggested that the same process could fuel the diffusion of climate change-related opinions [START_REF] Nisbet | A two-step flow of influence? Opinion-leader campaigns on climate change[END_REF]; see also: [START_REF] Anderson | Effects of social media use on climate change opinion, knowledge, and behavior[END_REF][START_REF] Geiger | Creating a climate for change: Interventions, efficacy and public discussion about climate change[END_REF][START_REF] Swim | Social construction of scientifically grounded climate change discussions[END_REF]. Similarly, word-of-mouth has been shown to be an important driver in the diffusion of technological innovations [START_REF] Czepiel | Word-of-mouth processes in the diffusion of a major technological innovation[END_REF][START_REF] Mazzarol | The role of word of mouth in the diffusion of innovation[END_REF][START_REF] Parry | The effect of personal and virtual wordof-mouth on technology acceptance[END_REF]. Recent studies have demonstrated the importance of interpersonal discussions in the domain of environment-related technology-for example, people talking to each other is a crucial vector in the adoption of solar panels [START_REF] Baranzini | What drives social contagion in the adoption of solar photovoltaic technology[END_REF][START_REF] Baranzini | Social contagion in the adoption of renewables (SCAR)[END_REF]-and of opinions-discussions with friends and family allows people to learn about the scientific consensus on global warming, which leads to increased acceptance of that consensus view [START_REF] Geiger | Spread the green word: A social community perspective into environmentally sustainable behavior[END_REF][START_REF] Goldberg | Discussing global warming leads to greater acceptance of climate science[END_REF].

In this article, we investigate one factor that might slow the spread of accurate beliefs about climate change in the population: sharing some of these beliefs might make the sender appear less friendly. Consider the statement "The richest 1% in the world is responsible for most of the greenhouse gas emissions," variants of which became widely shared in 2020, following an Oxfam report (Oxfam, 2020). In wealthy countries, many people who hear that statement might not realize that they are likely part of the richest 1%, considered across the world. Instead, they might blame the superrich from their own country, and not see why they would need to change their own behavior. People exposed to this statement might also find the source agreeable, as they point out morally reprehensible behavior by others. By contrast, consider "The richest 1% in the world is responsible for most of the greenhouse gas emissions, because most citizens in countries like the United States consume too much energy." This statement is, arguably, more accurate, since it makes people in wealthy countries realize they are likely part of the problemwhich might lead them to change their behavior. However, such a statement is more directly accusatorial, and might make those who hear it dislike its source. This is an example of the tradeoffs between accuracy of the statement and likeableness of the source that we explore in this article. Note that although we focus here on members of the public (given our participants pool), similar effects might be observed in the media (see, e.g., [START_REF] Feldman | Upping the ante? The effects of "emergency" and "crisis" framing in climate change news[END_REF], 2018;[START_REF] O'neill | Fear won't do it" promoting positive engagement with climate change through visual and iconic representations[END_REF]. After briefly reviewing the literature on the perception of people who are environmentally conscious, we introduce our hypotheses and the three experiments that test them.

Much research has been dedicated to the impact of green behavior (including expressive behavior) on reputation, and "social status is emerging as an important variable in studies of [these behaviors]" [START_REF] Brooks | The influence of contextual cues on the perceived status of consumption-reducing behavior[END_REF][START_REF] De Nardo | Social signals and sustainability: Ambiguity about motivations can affect status perceptions of efficiency and curtailment behaviors[END_REF][START_REF] Sturman | Status striving and hypercompetitiveness as they relate to overconsumption and climate change[END_REF][START_REF] Uren | High-status proenvironmental behaviors: Costly, effortful, and visible[END_REF]. On the one hand, many studies have established that engaging in some green behaviors-such as buying green products-can make people appear more altruistic, warm, cooperative, and even better romantic prospects [START_REF] Aagerup | Green consumer behavior: Being good or seeming good[END_REF][START_REF] Barclay | Greener than thou: People who protect the environment are more cooperative, compete to be environmental, and benefit from reputation[END_REF][START_REF] Griskevicius | Going green to be seen: Status, reputation, and conspicuous conservation[END_REF][START_REF] Johnson | From Gucci to green bags: Conspicuous consumption as a signal for pro-social behavior[END_REF][START_REF] Palomo-Vélez | Is green the new sexy? Romantic of conspicuous conservation[END_REF]. On the other hand, people who engage in expressive green behaviors-activists, people who go to protestsare often perceived negatively [START_REF] Bashir | The ironic impact of activists: Negative stereotypes reduce social change influence[END_REF][START_REF] Geiger | Climate of silence: Pluralistic ignorance as a barrier to climate change discussion[END_REF][START_REF] Klas | Not All Environmentalists Are Like That…": Unpacking the Negative and Positive Beliefs and Perceptions of Environmentalists[END_REF]. In particular, people who are thought to be alarmists about climate change are perceived as ""whiny", "nagging", and "complainers"" [START_REF] Geiger | Climate of silence: Pluralistic ignorance as a barrier to climate change discussion[END_REF], cited in: Geiger & Swim, 2016, p.81) (at least in some US universities in the early 2010s).

Why would people who try to alert others of environmental issues be perceived negatively?

They might be perceived as 'cheap talkers,' people who only talk about the issue, without engaging in personally costly actions to address it. A recent review noted that proenvironmental behavior is more likely to be perceived positively when it is "costly, effortful, and visible" [START_REF] Uren | High-status proenvironmental behaviors: Costly, effortful, and visible[END_REF]: expressive behavior might be visible, but many might not see it as costly or effortful. Moreover, expressive behavior can be more directly accusatorial than other types of behavior, as it allows people to explicitly point out moral failures in others.

Whatever the causes of these negative perceptions, they might hamper the spread of accurate information about climate change, since such information would often be perceived as alarmist, or accusatorial. Ironically, a recent study even suggests that using arguably more accurate language (i.e. "climate emergency" instead of "climate change") led to decreased credibility [START_REF] Feldman | Upping the ante? The effects of "emergency" and "crisis" framing in climate change news[END_REF].

Here, we study how sources are perceived as a function of the type of climate change-related statements they make. Some statements are, arguably, more accurate, but also bleaker, or pointing more explicitly at the role played by the audience. We expect that these statements would lead their source to being evaluated more negatively-as less friendly and more judgmental. We focus on perceptions of warmth because it tends to prime over perceptions of competence, as people appear to be, as a rule, more worried about appearing unlikeable than incompetent [START_REF] Abele | Communal and agentic content in social cognition: A dual perspective model[END_REF][START_REF] Leary | Self-Presentation: Impression Management and Interpersonal Behavior[END_REF][START_REF] Sedikides | Pancultural self-enhancement[END_REF]. Finally, we also test whether such statements (in particular statements that point fingers at the audience) are less likely to be shared, plausibly because they would lead to negative perceptions of those who share them.

In Experiment 1, we compare how the source of a bleak and of a control climate change statement is perceived. One statement describes climate change and its effects in a very neutral manner (inspired by descriptions found on media such as the BBC), while the other presents a much bleaker view (for instance by talking about 'climate breakdown' instead of 'climate change'). We hypothesize that sources who share the bleaker statement will be perceived as more committed to pro-environmental causes, but also as being more judgmental and less friendly.

In Experiment 2, we compare how the source of an accusatory and of a control climate change statement is perceived. We make the same predictions as in Experiment 1, but regarding statements such as that provided above, about "The richest 1% in the world is responsible for most of the greenhouse gas emissions," with, or without specifying that this is "because most citizens in countries like the United States consume too much energy." These stimuli were chosen such that the full statements (with the latter clause added) are perceived as having more effect on their audience (by making the audience think the statement applies to them, making them feel guilty, and prompting them to change their behavior). Finally, in Experiment 3, we test whether people are less likely to share the more accusatorial statement.

General Methods

We pre-registered the experiments' sample size, exclusion criteria, hypotheses, research questions, and statistical analyses. In all but the first experiment, we use linear mixed effect models with participants as random effect to account for the non-independence of the observations. We refer to 'statistically significant' as the p-value being lower than an alpha of 0.05. All the betas reported in this article have been standardized. The Confidence Intervals (CI) reported are 95%. All statistical analyses were conducted in R (v.4.0.3), using R Studio In Experiment 1, participants (from the UK, then replicated in the US) were presented with one of two statements describing climate change, either a control statement, or a bleaker (but also, arguably, more accurate) statement, and they were asked to evaluate the source of the statement.

Based on the literature reviewed above, we formulated two hypotheses:

H1: Participants perceive people sharing the bleak statement about climate change more negatively than people sharing the control statement.

Since the bleaker statement was based on vocabulary used by institutions more explicitly committed to pro-environmental causes, we formulated a second hypothesis:

H2: Participants perceive people sharing the bleak statement about climate change as more committed to pro-environmental causes than people sharing the control statement.

Participants

Based on a pre-registered power analysis, we recruited 200 UK participants on Prolific Academic, paid £0.38. We removed one participant who failed the attention check, leaving 199 participants (144 women, MAge = 38.94, SD = 12.29). We recruited 200 US participants on Prolific Academic, paid £0.38. We removed one participant who failed the attention check, leaving 199 participants (86 women, MAge = 34.71, SD = 12.65).

Materials, Design, and Procedure

We wrote two statements on climate change. One stressed the dangers of climate change and its human causes (bleak statement), the other was more descriptive, used more neutral words, and did not attribute climate change exclusively to humans (control statements). The control statement was inspired by definitions of climate change from mainstream media such as BBC News1 or Nature 2 , while the bleak statement was inspired by sources more explicitly committed to fighting climate change.

Results

UK sample

In support of H1, participants perceived someone sharing the bleak statement more negatively (M = 3.44, SD = .99) than someone sharing the control statement (M = 2.83, SD = .70) (ß = -

.68 [-.94, -.84], t(197) = -5.08, p < .001) (see Figure 1).

In support of H2, participants deemed someone sharing the bleak statement as more committed to pro-environmental causes (M = 4.73, SD = 1.10) than someone sharing the control statement (M = 4.12, SD = 1.09) (ß = -.54 [-.81, -.27], t(197) = -3.91, p < .001).

US sample

In support of H1, participants perceived someone sharing the bleak statement more negatively (M = 3.35, SD = 0.91) than someone sharing the control statement (M = 2.90, SD = .62) (ß = -

.55 [-.82, -.28], t(197) = -4.05, p < .001) (see Figure 1).

Discussion

Experiment 1 showed that an individual sharing a statement about climate change stressing its dangers and its human causes (bleak statement), compared to an individual who shared a more neutral statement, was perceived as more committed to pro-environmental causes, but also more negatively on the whole (a combination of more judgmental, less likeable, and less friendly).

The risk of being perceived negatively might help explain why people-including those committed to pro-environmental causes-might refrain from sharing particularly bleak to be more committed to pro-environmental causes, but also judged more negatively.

Experiment 2

Experiment 2 is a conceptual replication of Experiment 1, with different types of statements.

Instead of a neutral and a bleak description of climate change, we compared control and accusatorial statements. In each pair, one statement did not explicitly point to the audience's responsibility (control), while the other did (accusatorial, see materials below). We pre-tested the statements in a pilot study reported in Electronic Supplementary Material (ESM). In the pilot study, participants judged the accusatorial statements to be higher on a composite measure of (i) being likely to apply to the audience, (ii) making their audience feel guilty, and (iii) being likely to induce behavior change in the audience.

We hypothesized that participants would judge the sources of the accusatorial messages more

Participants

Based on a pre-registered power analysis, we recruited 200 UK participants on Prolific Academic, paid £0.38. We removed one participant who failed the attention check, leaving 199 participants (105 women, MAge = 32.18, SD = 12.10). We also recruited 200 US participants on Prolific Academic, paid £0.38. No US participants failed the attention check (140 women, MAge = 36.72, SD = 12.33).

Materials, Design and Procedure

Procedure was identical to Experiment 1, except that we added the following question: "Would you think that this individual is critical of you?" (6-point scale, from 1[Not at all] to 6[Extremely critical of you]). Our composite measure 'Negativity' was defined as the mean of the 'Judgmental', 'Likeable' (reverse coded), 'Friendly' (reverse coded), and 'Critical of you' ratings. Participants were only exposed to one condition (between-participants design) and presented with the three statements of this condition, described as coming from the same source.

The three pairs of statements read:

Results

UK sample

In support of H1, participants perceived someone sharing accusatorial statements more negatively (M = 3.74, SD = .87) than someone sharing control statements (M = 3.19, SD = .85) (ß = -.61 [-.82, -.39], t(198) = -5.57, p < .001) (see Figure 2).

In opposition to H2, participants did not deem someone sharing control statements as significantly less committed to pro-environmental causes (M = 4.23, SD = 1.24) than someone sharing accusatorial statements (M = 4.13, SD = 1.20) (ß = .08 [-.15, .32], t(198) = .69, p = .49).

US sample

In No US participants failed the attention check (102 women, MAge = 32.26, SD = 11.52).

Materials, Design and Procedure

We used the same pairs of statements related to climate change as in Experiment 2. After having completed a consent form, each participant was randomly presented with either three accusatorial statements or three control statements about climate change. For each statement, two questions were presented: "How likely would you be to share this statement in a discussion?" (6-point scale, from 1[Very unlikely] to 6[Very likely]), and "How likely would you be to share this statement on social media like Facebook or Twitter?" (6-point scale, from 1[Very unlikely] to 6[Very likely]). We created a composite measure 'Sharing' defined as the mean of these two questions. Before finishing the experiment, participants' environmental attitudes were assessed with five questions from the questionnaire of the European Value Survey (see ESM). Finally, participants completed an attention check (see ESM) and provided demographics information.

Results

UK sample

In support of H3, participants were more likely to share control statements (M = 3.11, SD = 1.34) than accusatorial statements (M = 2.69, SD = 1.35) (ß = .31 [.08, .55], t(198) = 2.61, p = .009) (see Figure 3).

US sample

In support of H3, participants were more likely to share control statements (M = 3.51, SD = 1.45) than accusatorial statements (M = 3.06, SD = 1.62) (ß = 0.29 [.05, .53], t(198) = 2.36, p = .019) (see Figure 3).

Discussion of Experiments 2 and 3

A pilot study conducted prior to Experiment 2 (distinct from Experiment 1) showed that accusatorial statements were deemed to have more effect on their audience (e.g. making them feel more guilty) than control statements. However, Experiment 2 revealed that people who share accusatorial statements, compared with control statements, are judged more negatively, and Experiment 3 that participants were less likely to share accusatorial statements. Contrary to our predictions, people who shared accusatorial statements were not perceived as more committed to pro-environmental causes, thereby negating a potential benefit of sharing such statements.

In Experiment 3, participants were less willing to share accusatorial compared to control statements about climate change. This finding may appear to contradict previous results in the literature about the advantage that moral and negative content enjoys compared to more neutral content [START_REF] Brady | Estimating the effect size of moral contagion in online networks: A pre-registered replication and meta-analysis[END_REF][START_REF] Robertson | Negativity drives online news consumption[END_REF][START_REF] Schöne | Negativity spreads more than positivity on Twitter after both positive and negative political situations[END_REF]. However, it is important to note that our control statements are not exactly neutral, being negative and somewhat moralistic (e.g. "The US federal government doesn't do enough to reduce emissions ). The difference between the accusatorial and control statement is whether ordinary citizens are also being blamed or not, but in both cases powerful institutions such as the government are being blamed. Thus, our findings do not contradict the existing literature.

Conclusion

Citizens can be crucial relays for official sources of information: when they are motivated to discuss issues with their friends, families, or colleagues, citizens can effectively convey information about politics, new technologies, and, in the case at hand, the environment. For citizens to play this role, however, they must be motivated to share information. Past research suggests that expressive green behavior-taking green positions, going to green protests-can negatively affect people's reputation, making them appear for instance more judgmental. This reputational risk could reduce their motivation to take green positions, and to share even relevant and accurate information about the environment [START_REF] Bashir | The ironic impact of activists: Negative stereotypes reduce social change influence[END_REF][START_REF] Geiger | Climate of silence: Pluralistic ignorance as a barrier to climate change discussion[END_REF][START_REF] Klas | Not All Environmentalists Are Like That…": Unpacking the Negative and Positive Beliefs and Perceptions of Environmentalists[END_REF].

Here, we tested whether sources who shared bleak, or accusatorial statements about the environment, compared to control statements, would be perceived more negatively (less friendly, more judgmental). Experiments 1 (bleak vs. control) and 2 (accusatorial vs. control)

showed that this was indeed the case for participants in the UK and US. Experiment 3 further showed that participants declared being less willing to share the accusatorial, compared to control, statements-even though a pilot study had shown that the accusatorial statements were perceived by participants as having more effect on their audience.

Past studies had suggested that, in some cases, people 'self-silence' because of an undue fear to be judged negatively if they discuss climate change [START_REF] Geiger | Climate of silence: Pluralistic ignorance as a barrier to climate change discussion[END_REF]. Our results

suggest that, unless one uses very neutral language, avoiding bleak or accusatorial statements, these fears might be justified. However, there might be ways to attenuate these negative perceptions, in particular if the individual uttering the accusatorial statements 'walks the walk' by having low carbon footprint (see, [START_REF] Attari | Climate change communicators' carbon footprints affect their audience's policy support[END_REF]. Conversely, if they only 'talk the talk'

and have a high carbon footprint, these negative perceptions will likely be enhanced because hypocrites are judged very negatively [START_REF] Jordan | Why do we hate hypocrites? Evidence for a theory of false signaling[END_REF].

A limitation of our study is that it focuses entirely on the 'warmth' (or communion, see [START_REF] Fiske | Universal dimensions of social cognition: Warmth and competence[END_REF] dimension of person evaluation. People are also evaluated on the 'competence' (or agency) dimension. It is therefore possible that people who share bleaker or more accusatorial statements are deemed more competent, if these statements are thought to be more accurate for instance. Even if that were the case, since the warmth dimension tends to take priority in reputation management [START_REF] Abele | Communal and agentic content in social cognition: A dual perspective model[END_REF][START_REF] Leary | Self-Presentation: Impression Management and Interpersonal Behavior[END_REF][START_REF] Sedikides | Pancultural self-enhancement[END_REF], a chance of being perceived as more competent should typically not compensate for the risk of being perceived as much less warm (on the importance of the motivation to appear warm for sharing information, see Altay & Mercier, 2020). [START_REF] Geiger | Climate of silence: Pluralistic ignorance as a barrier to climate change discussion[END_REF] found that people refrained from discussing climate change because they were worried of appearing less competent (due to an underestimation of the share of people who are concerned about climate change). In our studies, however, both control and accusatorial statements suggest that the sender is worried about climate change; what differs is whether ordinary people are blamed or not. This dimension in particular, blaming ordinary people in addition to more systemic factors (e.g. how the economy is regulated), is likely what is driving these negative warmth perceptions.

Another limitation is that we do not directly demonstrate that people share the accusatorial statements less than the control statements because the accusatorial statements lead to being perceived as less friendly, etc. Other features of the accusatorial statements could explain this effect. For instance, if the accusatorial statements were deemed less accurate, people might refrain to share them for fear of appearing incompetent (see, Altay et al., 2020). However, given that the importance of warmth in reputation management is well established, it seems very plausible that the fear of being perceived as less warm explains at least some of the unwillingness to share accusatorial statements.

Another potential brake to sharing information about climate change is that people (wrongly) perceive discussions on that topic to be futile (see, [START_REF] Geiger | Creating a climate for change: Interventions, efficacy and public discussion about climate change[END_REF]. A knowledge-based intervention aimed at changing this perception proved effective, generating more engagement in climate change related discussion in participants [START_REF] Geiger | Creating a climate for change: Interventions, efficacy and public discussion about climate change[END_REF]. In the case at hand, the-well-founded-fear of appearing less warm by sharing bleaker or more accusatorial statements might also be attenuated. Future studies could test whether it is possible to convey the same bleak or accusatorial meaning in a way that doesn't have the same reputational fallout, and whether showing one's warmth in other ways dampens the negative effects of sharing such statements.

In conclusion, we found that people refrain from sharing accusatorial statements about climate change, likely because they fear appearing judgmental and unfriendly. These fears appear to be justified and are not compensated by appearing more committed to pro-environmental causes.

  (v.1.3.1093). Preregistrations, data, materials, ESM, and the scripts used to analyze the data /osf.io/stbeq/?view_only=07251875767d4ce1811dbe77c87a01fb Experiment 1

  In support of H2, participants deemed someone sharing the bleak statement as more committed to pro-environmental causes (M = 4.76, SD = 1.11) than someone sharing the control statement (M = 4.32, SD = 1.32) (ß = -.35 [-.63, -.08], t(197) = -2.54, p = .012).

Figure 1 .

 1 Figure 1. Negativity ratings of the bleak and the control statements in Experiment 1. Density plots representing the distribution of participants' answers according to the type of statement (Bleak or Control). The negativity ratings are the average of three questions about how judgmental, likeable (reverse coded), and friendly (reverse coded) the individual sharing the statements is.

  change and its causes. Experiment 2 aims at replicating the effect observed in Experiment 1 with novel materials, testing whether people who share proenvironmental statements that are more accusatorial (compared to less accusatorial) are deemed

  negatively, as measured by our composite measure of being judgmental, dislikeable, not friendly, and critical of you (on negative reactions to guilt-inducing messages, see, e.g.[START_REF] Moser | Toward the social tipping point: Creating a climate for change[END_REF]: H1: Participants perceive people sharing accusatorial statements about climate change more negatively than people sharing control statements about climate change.On the other hand, the more accusatorial statements might be more likely to be effective (on the power of guilt to motivate activism for instance, seeFerguson & Branscome, 2010; Mallett, Melchiori & Strickroth, 2013). As a result, we also hypothesized, as in Experiment 1, that the accusatorial statements would lead their sources to be perceived as being more committed to pro-environmental causes: H2: Participants perceive people sharing accusatorial statements about climate change as more committed to pro-environmental causes than people sharing control statements about climate change.

  support of H1, participants perceived someone sharing accusatorial statements about climate change more negatively (M = 3.74, SD = .98) than someone sharing control statements (M = 3.14, SD = .89) (ß = -.61 [-.83, -.39], t(197) = -5.41, p < .001) (see Figure 2.)In opposition to H2, participants did not deem someone sharing accusatorial statement as significantly more committed to pro-environmental causes (M = 4.34, SD = 1.29) than someone sharing control statements (M = 4.27, SD = 1.28) (ß = -.06 [-.29, .17], t(197) = -0.51, p = 0.61).

Figure 2 . 3

 23 Figure 2. Ratings of accusatorial statements and control statements in Experiment 2. Density plots represent the distribution of participants' answers according to the type of statement (Accusatorial or Control) for negativity. The negativity ratings are the average of four questions about how judgmental, likeable (reverse coded), friendly (reverse coded), and critical of you the individual sharing the statements is.

Figure 3 .

 3 Figure 3. Willingness to share accusatorial statements and control statements in Experiment 3. Density plots represent the distribution of participants' answers according to the type of statement (Accusatorial or Control) for likelihood on sharing the statements. Sharing was the mean of two questions, one related to sharing in a discussion, and one to sharing on social media.

  and to tackle climate change."

  The US federal government doesn't do enough to reduce emissions of greenhouse gases and to tackle climate change, but this is largely because most citizens do not mobilize enough for this cause." (Accusatorial version).

	Pair 1
	"The richest 1% in the world is responsible for most of the greenhouse gas emissions."
	(Control version)
	"The richest 1% in the world is responsible for most of the greenhouse gas emissions,
	because most citizens in countries like the United States consume too much energy."
	(Accusatorial version)
	Pair 2
	"Agriculture, forestry and other land use are accountable for 24% of the world's
	greenhouse gas emissions." (Control version)
	"Agriculture, forestry and other land use are accountable for 24% of the world's
	greenhouse gas emissions, in large part because of those who eat meat." (Accusatorial
	version)
	Pair 3

"The US federal government doesn't do enough to reduce emissions of greenhouse gases and to tackle climate change." (Control version) "

"Climate Change: What Do All the Terms Mean?". BBC News. (1 May

2019)