Tim P Levine
email: tim.levine@ucl.ac.uk

Franck Perez
email: franck.perez@curie.fr

Yasunori Saheki
email: yasunori.saheki@ntu.edu.sg

Julia Von Blume
email: julia.vonblume@yale.edu

Meeting Report from the 2019 "Organelle Zone" Symposium in Osaka, Japan

On May 29 at the

yeast: tricalbins Tcb1-3). E-Syts are PI(4,5)P 2 -dependent and Ca 2+ -regulated ER-PM tethers. E-Syts transport glycerolipids via the SMP domain, an evolutionarily conserved lipid-harbouring module present in various membrane contact sites. They are important for PM lipidome, not for steady state phospholipid levels, but for rapid adaptation to signalling, where recycling of diacylglycerol following phospholipase C activation requires E-Syts, as can be seen in cells lacking E-Syts. In unpublished studies, his lab is working on the three human GramD1a-c proteins in the LAM/LTC family, which have been shown in multiple systems to contribute to sterol transport from the PM to the ER. He showed that the GRAM domain, a pleckstrin homology-like domain, is a coincidence detector for cholesterol and phosphatidylserine, binding the PM because it is enriched for both ligands. The lipid transfer domain catalyses inter-membrane transfer of cholesterol. In gene-edited human cells lacking GramD1 proteins, PM cholesterol homeostasis is impaired. An acutely regulatable system which the lab has created shows that cholesterol is extracted from the PM within minutes of the recruitment of GramD1 proteins to ER-PM contacts.

Tim Levine (University College London, UK) talked about expanding the known range of intracellular communication by identification of more "two phenylalanine in an acidic tract" (FFAT) motifs, which target proteins on other organelles to VAP on the cytoplasmic face of the ER. He described how the originally tight definition of the motif by their discovery in oxysterol binding protein (OSBP) and other lipid transfer proteins had been widened too far as to be impossible to detect by a simple linear description. He then introduced his unpublished bioinformatics study that aimed to identify all FFAT motifs present in yeast. Using a position weighted matrix, he predicted that approximately 1% of all proteins possess FFAT or FFAT-like motifs. Among these were some that implicate the existence of zones of intracellular communication previously either unknown (ER-eisosome) or largely overlooked (ER-nucleolus).

The second session addressed how the biosynthetic organelles have separate zones for distinct functions ("Response Zones"). Kazutoshi Mori (Kyoto University, Japan) spoke about multiple organelle zones present in the ER, which his group identified using superresolution microscopy, namely the folding zone, the sensing zone for the unfolded protein response (UPR), and ER-associated degradation (ERAD) zone.

Next, Julia von Blume (Yale University, USA) described her work on cargo sorting in the trans Golgi network (TGN). Proteins destined for secretion such as Lysozyme-C (LyzC) and Cartilage Oligomeric Protein (COMP) depend on the TGN-localized membrane-anchored Ca 2+ ATPase SPCA1, and the calcium binding protein Cab45 to exit the TGN. She showed how Ca 2+ induces Cab45 to cluster into oligomers, both in vitro and in vivo, where Cab45 and client were shown to bud together in vesicles that then reach the PM. The identification of TGN-derived sphingomyelin-rich vesicles uncovered an exciting link between synthesis of sphingolipids and Cab45-dependent sorting. Purification and proteomics analysis of these vesicles identified Cab45 as one of the most abundant native cargoes of this pathway. Using the RUSH technique (see below), she showed that the lipid sphingomyelin is required in the TGN to allow cargo to reach the plasma membrane, but not for other destinations, such as the lysosome. She then linked the lipid requirement to previous findings, by showing that SPCA1 accumulates in detergent-resistant membranes, that the enzyme both requires sphingomyelin for in vitro reconstitution, and that it can be cross-linked with a derivatized sphingosine. Using an in vivo sensor of Ca 2+ levels in the TGN, she confirmed the link with calcium levels by showing that the enzyme SMS1, which makes SM in the TGN, is required for normal levels of Ca 2+ .

Taroh Kinoshita (Osaka University, Japan) discussed his lab's work on regulation of a specific step in synthesis of glycosylphosphatidylinositol (GPI) anchors at two stages in the secretory pathway. Early on, GPI is affected by components of the ERAD pathway. A genome-wide CRISPR screen identified B3GALT4, known before only for its role as GM1 synthase, as the Golgi-localized enzyme that modifies GPI anchors by adding a terminal galactose to its sugar side-chain. In addition there were unexpected hits among ERAD components. The link to ERAD was exemplified by showing that this pathway prevents massive build-up of free GPI anchors (the glycolipid with no attached protein) when the transamidase enzyme that links the GPI to proteins is missing. Thus, ERAD is part of the cell's response that inhibits the GPI pathway when its capacity is excess to requirement. Later in the secretory pathway, GPI synthesis is tightly linked to production of lactosylceramide in the Golgi. This glycosphingolipid, which itself is produced by addition of a terminal galactose, is a critical cofactor for B3GALT4's terminal modification of GPI, as it interacts with both enzyme and substrate to permit glycosylation.

The final session was on technical aspects of imaging and focussed on organelle zones that operate in protein transport ("Sorting Zones"). Akihiro Nakano (RIKEN, Japan) talked about his lab's work on techniques to visualize such zones. He has developed and improved 4D super-resolution confocal live imaging microscopy (SCLIM) systems to study the secretory pathway in action. The first iteration, SCLIM1, has at its core a spinning disk microscope and highly sensitive camera for ultrafast single molecule detection. SCLIM1 microscopy of budding yeast showed that early in secretion the cis-Golgi cisternal elements capture COPII vesicles not floating free, but likely by directly handover from ER. The cis-Golgi approaches ER exit sites in an oscillatory manner, remaining nearby for a few seconds. The lab's initial work in yeast has now been generalised to plant and animal cells. The second microscopy set-up, SCLIM2, has vastly improved sensitivity, speed and resolution, able to detect and track every cisterna and even individual clathrin coated vesicles in real time. This system allowed to show that Golgi cisternae are highly dynamic at the 50 millisecond time-scale. He visualized cisternal dynamics in the Golgi ribbon of an animal cell, transient tubular connections between cisternae, and cargo moving through the ribbon by applying the RUSH technique (see next talk). This leads to the proposal that the cisternal maturation model does not explain all aspects of intra-Golgi traffic.

The final speaker was Franck Perez (Institut Curie, France), who started by presenting his RUSH technique. An expressed protein is retained in one organelle, typically the ER by binding a second expressed protein. The interaction is broken by adding biotin, and synchronous wave of forward movement can reveal new details of secretory pathways. Within the Golgi, different secretory cargos show distinct behaviour in terms of both speed of transit and sub-Golgi location. After leaving the Golgi, preferential sites of exocytosis can be found. These sites were more accurately defined either by patterning cells in a crossbow shape, or by capturing exocytosed GFP-tagged cargo with an antibody coated onto the slide pre-plating. Both tools suggest adhesion sites as hot-spots, and these results were confirmed using TIRF microscopy. Using these assays, he started to study some of the mechanisms responsible for such a restricted exocytosis. For example, he showed that the Rab6dependent machinery is involved, together with a subset of microtubules. Even further along the secretory pathway, he has studied the cell-to-cell repulsion system based on ephrin signalling. He found that cells transport the GPI-anchored Ephrin A1 to actin-rich filipodial extensions where it is endocytosed by EphR expressing cells. The receiving cell eats part of its neighbour in trans -hence the process is called "transendocytosis" (also known as trogocytosis). The EphR-EphrinA1 complex remains in a modified endosome for many hours, signalling continually. Thus, the repelled cell takes away with it a part of the cell that repelled it, presumably as a molecular memory of the contact.

All eight talks use the study of single proteins to throw fresh light on how whole organelles have sub-organelle specializations in the way they communicate, respond and sort. By addressing the complexity of membrane cell biology at this level, the Organelle Zones group are making progress toward a more complete multi-dimensional understanding of how cells achieve the myriad tasks required for life.

Contact (Thousand Oaks). Author manuscript; available in PMC 2019 October 04.

Funding

The authors would like to thank Ministry of Education, Culture, Sports, Science and Technology of Japan (MEXT) for their support of the Organelle Zones Project as a whole, hence this symposium (Grant-in-Aid for Scientific Research on Innovative Areas: 17H06413). TPL was supported by the BBSRC (BB/P003818/1). YS was supported by an Academic Research Fund Tier 2 from the Singapore Ministry of Education (MOE2017-T2-2-001), a Grantin-Aid for Young Scientists (A) from the Japan Society for the Promotion of Science (17H05065), a Nanyang Assistant Professorship (NAP), and a Lee Kong Chian School of Medicine startup grant (LKCMedicine-SUG). JvB was supported by Plus 3 Perspective Program (Boehringer Ingelheim Foundation) and a project grant (BL 1186/4-1) from the Deutsche Forschungsgemeinschaft (DFG). FP was supported by the Institut Curie, the Centre National pour la Recherche Scientifique (CNRS) and by grants from the Agence Nationale de la Recherche (ANR-17-CE15-0025-02; ANR-17-CE13-0021-02; ANR-17-CE13-0015-02) and the Institut National du Cancer (INCa 2018-1-PL BIO-04ICR-1).


Madeline Chapelet

Chrystel Dezayes
email: c.dezayes@brgm.fr

Thomas Dewez

Characterization of fracture network based on photogrammetry

Keywords: Fractures, photogrammetry, geothermal energy, Valence Basin of France

Nowadays, deep geothermal exploitation projects in France are mostly localized in deep fractured geological contexts as rift basins. This study contributes to a project aimed at developing a theoretical model of geothermal reservoirs in fault zone in rift areas (grabens) such as the South-East Basin of France. The knowledge of the fracture network and the structural characterization of the potential geothermal reservoirs is essential to the development of a thermo-hydro-mechanical model.

The orientation and spatial organization of the fracture networks in the targeted sedimentary formations have been studied from virtual outcrop models acquired using photogrammetry.

The results have shown that most fractures observed on the outcrop level are oriented in accordance with the 1:50 000 map faults orientation, i.e. NW-SE to NNW-SSE. These local faults are related to the geodynamics events that occurred during the Valence Basin tectonic evolution such as those developed during the Tethysian rifting. The fractures frequency increases with closeness to these main faults. In the first 5 meters from the fault, the fractures are grouped together as a corridor, with a mean spacing S of 25 cm. After that, fractures are regularly located but more spaced (S > 50 cm) over several tens meters on both sides of the fault.

All these information can therefore be used as input parameters to the thermo-hydro-mechanical modelling of the geothermal reservoir in order to characterize fluid circulations, heat transfer and to predict the mechanical behavior during the exploitation.

The work conducted in this study also revealed the usefulness and relevance of the use of photogrammetry in analyzing fracture networks at the outcrop level. The virtual outcrop models delivered reliable and complementary measurements to those carried out directly on the field.

INTRODUCTION

In France, deep geothermal projects and exploration works are mainly located in basins linked to the West European rift system. One of the rift basins targeted by industrial projects to exploit deep fractured reservoirs is the Valence Basin located in the South-East Basin of France. Within the framework of optimizing the exploitation of deep geothermal energy, we want to refine the implementation of drilling programs by reducing the geological uncertainties. For that, a project is set up with the aims at developing a theoretical model of geothermal reservoirs in fault zone in rift areas. An important feature of developing a thermo-hydro-mechanical model of the reservoir is to understand the fluid circulation by studying the fracture network and its geometry. The better the characterization is, the better the fluid flow modelling expects the fluid pathway and therefore the geological risk is reduced.

Our study have a purpose to make a contribution towards achieving better knowledge about geometry of the fracture network in the reservoir rocks localized in the Valence Basin. The study area lies to the west of the basin, on the eastern border of the Massif Central where Triassic sandstones crops out, which constitutes analogs to the targeted formations. On several accessible quarries, we characterized the fracture network geometry. For that, we use of a ground-based photogrammetric method which consists in taking convergent pictures to cover the walls of the quarries from different locations to compute a 3D virtual geological outcrop based on 3D point cloud. We performed structural data measurements on these virtual outcrop models in order to determine the main fracture sets and their spatial organization. This work contributes to the main project in providing additional information regarding the potential geothermal reservoirs but it also allows us to evaluate the photogrammetric method relevance for purposes of fracture network characterization at the outcrop scale.

GEOLOGICAL CONTEXT

Geological history of the Valence Basin of France

The Valence Graben is a part of the South-East Basin of France belonging to West European Rifting event [START_REF] Ziegler | European Cenozoic Rift System[END_REF] (Figure 1A). Sediment thickness can reach 6000 m in the center of the Valence Basin [START_REF] Lienhardt | Synthèse Géologique Du Bassin de Valence (26)[END_REF][START_REF] Deville | Tectonic Styles, Reevaluation of Plays in Southeastern France[END_REF], which is mostly filled by Mesozoic and Tertiary sediments (Figure 1B).

During the Hercynian orogeny, the N-S compression resulted in the formation of NE-SW trending sinistral strike-slip faults (Cevennes, Nîmes and Durance Faults) and ENE-WSW to E-W thrust faults [START_REF] Arthaud | Les Decrochements Tardi-Hercyniens Du Sud-Ouest de l'europe[END_REF] (Figure 1A).

A long period of extensional regimes followed, beginning during the Triassic period: the Tethysian rifting. This E-W extension [START_REF] Bergerat | Le Couloir Rhodanien Au Paléogène; Analyse de La Fracturation et Interprétation Cinématique Régionale[END_REF]Martin, 1993) created N30°E andN160°E normal faults (Blès et al., 1989;[START_REF] Martin | Palaeo-Stresses Inferred from Macro-and Microfractures in the Balazuc-1 Borehole (GPF Programme). Contribution to the Tectonic Evolution of the Cevennes Border of the SE Basin of France[END_REF]. While the Tethys Ocean is forming, the first sediments are deposited in a small neoformed basin. The thermal subsidence replaces the tectonic subsidence at the end of the Jurassic [START_REF] Lemoine | Etapes et Modalités de La Subsidence d'une Paléo-Marge Passive: Les Alpes Occidentales Au Mésozoïque[END_REF]. In the lower Cretaceous, the extensive phase ends and the basin borders undergoes strong erosion (2000 to 2500m thick) [START_REF] Bonijoly | The Ardeche Palaeomargin of the South-East Basin of France : Mesozoic Evolution of a Part of the Tethyan Continental Margin (Geologie Profonde de La France Programme)[END_REF]. The subduction of the Tethys Ocean leads to the Pyrenean collision in the Eocene [START_REF] Choukroune | Bay of Biscay and Pyrenees[END_REF], which created NNE-SSW sinistral strike-slip faults and NW-SE dextral strike-slip faults [START_REF] Bergerat | Le Couloir Rhodanien Au Paléogène; Analyse de La Fracturation et Interprétation Cinématique Régionale[END_REF].

The main phase of the Valence Basin opening occurred during the West European Rifting event in Oligocene. This E-W extensive phase fractured all of Western Europe [START_REF] Ziegler | European Cenozoic Rift System[END_REF] and reactivated N-S to NNE-SSW trending tectonic structures. After this large period of sedimentation, the Valence Basin underwent a tectonic inversion during the Alpine compression, which reactivate the normal faults of the Tethysian rifting with reverse movement [START_REF] Roure | Geometry and Kinematics of Extensional Structures in the Alpine Foreland Basin of Southeastern France[END_REF][START_REF] Roure | Multiphase Extensional Structures, Fault Reactivation, and Petroleum Plays in the Alpine Foreland Basin of Southeastern France[END_REF]) (Figure 1B).

Target of the geothermal projects and their analogs

Following the extensive phases of Jurassic and Oligocene periods, the continental crust in the Valence Basin area has thinned to reach a thickness of 22km [START_REF] Sapin | Results of Explosion Seismology in the Southern Rhône Valley[END_REF][START_REF] Guieu | Conséquence Possible de l'extension Crustale Pré-Oligocène En Provence Méridionale : La Mise En Place Gravitaire Des Chevauchements[END_REF]. The rise up of the Moho led to an increase in the geothermal gradient to the crust scale with 4 to 4.5 °C/100m, highlighted by the work carried out by [START_REF] Garibaldi | Bassin Du Sud-Est de La France et Relations Entre Anomalies Thermiques[END_REF]. Indeed, this work shows positive thermal anomalies along the major faults and particularly at the southwestern edge of the Valence Basin with temperatures ranging from 170 to 195°C at 5000m deep [START_REF] Garibaldi | Bassin Du Sud-Est de La France et Relations Entre Anomalies Thermiques[END_REF] (Figure 2). The sedimentary layers targeted by the deep geothermal exploitation project in the Valence Graben as potential reservoirs are the Triassic sandstones. Those sediments are located at a depth of about 4000m in the center of the graben but there are some Triassic outcrops at its western border (Figure 1A). In order to characterize the fracture network of these sandstone formations, two analog sites were chosen on the eastern border of the Massif Central for structural study: the Moulin des Vignes quarry and the Lyas quarry (Figure 3).

METHODOLOGY

To characterize the fracture network of the Triassic sandstone formations, we have carried out structural analysis on the two analog sites (Moulin des Vignes and Lyas quarries) by using two different methods: the classic one called the scanline method and an innovative one using a ground-based photogrammetric method.

Collection of structural measurements using the scanline method

Structural data has been collected on our analog sites by the use of the scanline method. The principle of this method is to measure and characterize every fractures spotted along a predefined line on the ground [START_REF] Priest | Discontinuity Analysis for Rock Engineering[END_REF]. Every structure is characterized by its orientation (dip and dip direction), position, movement, filling and other useful observations. This method helps to ensure the objectivity in the measurement and the description of structural elements on the ground [START_REF] Bonnet | Scaling of Fracture Systems in Geological Media[END_REF].

Implementation of a ground-based photogrammetric method

Acquisition on the ground

The ground-based photogrammetric method aims at identify the three-dimensional form of an object, like shape, dimension and position, in order to produce a virtual 3D model from photographs recording different viewpoints of this object. This method was performed within the quarries in order to produce a virtual outcrop model that most closely reflects reality.

Before conducting a photographic campaign, the targeted rock wall was prepared by the installing equipment useful for its scaling and positioning. For that, two rows of photogrammetric targets are installed to define horizontality in three dimensions (Figure 4A-B). The distance between of the second row to the rock wall should always be between 20 and 100% of the width of the outcrop. Rods are also placed along the rock wall to ensure a consistent scale. Lastly, three tripods are positioned in order to obtain three different viewpoint of the whole device (Figure 4B). This redundancy is necessary for the subsequent calculations of the targets positions by triangulation. For that, the targets-tripods and tripod-tripod distances are measured using a Leica Disto laser distance meter. The targets coordinates are calculated by triangulation and are used for the georeferencing of the virtual outcrop model. Subsequently, the photo acquisition is performed using the "one panorama each step" method proposed by [START_REF] Wenzel | Image Acquisition and Model Selection for Multi-View Stereo[END_REF]. 'One panorama each step" is a capturing approach which ensure complete coverage and sufficiently redundant observations for a very precise and reliable reconstruction of the outcrop. The principle of their approach is to acquire a panorama of the whole desired object at different viewpoints (camera stations). Camera stations used are determined according to the distance between them (the step size B) and their distance to the object (Z) [START_REF] Wenzel | Image Acquisition and Model Selection for Multi-View Stereo[END_REF]. These parameters can be determined as:

𝐵 = 1 3 𝐻 (1)
where B, H are step size and height of the outcrop, respectively.

𝑍 = √3𝑓𝐵 𝜎 𝑧 𝑝 (2)
where Z is the distance station-object, f the focal length of the camera, B the step size, σz the precision object space, and p the pixel pitch (width).

At each station, a panorama is acquired using multiple images that are slightly overlapped.

Construction of the virtual outcrop model

3D digital outcrop models were built via Agisoft Metashape Professional (1.5.2) software, using images captured on the ground. Before aligning the selected images, the blurred ones have been removed. For that, the software uses an algorithm based on the principle of Structure-from-Motion (SfM) method which consists in finding the correspondences between the 2D images in order to produce a sparse 3D point cloud of the rock wall [START_REF] Snavely | Skeletal Graphs for Efficient Structure from Motion[END_REF]. Following this, the dense point cloud is calculated according to the selected "quality" (Figure 5). The virtual outcrop model obtained is then positioned and dimensioned using the targets coordinates.

Structural analysis

Digital structural measurements

Fracture orientation measurements were performed on 3D virtual outcrop model, using the CloudCompare software (2.11 alpha) and its Compass plugin [START_REF] Thiele | Rapid, Semi-Automatic Fracture and Contact Mapping for Point Clouds[END_REF] which is a structural geology toolbox for the analysis of virtual outcrop models. Two main tools are available for orientation measurements:

-Plane tool: measures the orientations of fully exposed planar structures selected by hand. For that, a plane is fitting to all points sitting in the selected area and the orientation is estimate by the dip and dip direction of the plane.

-Trace tool: digitizes and measures traces and contacts produced by the intersection of the fracture plan with the rocky surface. For that, a least-cost path algorithm is used to follow the intersection trace and the digitize it to calculate its best fit plane. The orientation is given by the dip and dip direction of the calculated plane.

Spatial distribution

The geometric parameters of the fracture network on which we focused are the fracture orientation and the spatial distribution of fractures. The latter entails determining the inter-fractures spacing along the studied profile, using a computer program, which calculate the inter-fractures spacing of a family of orientation selected.

The results are presented graphically, using stick plots and cumulative frequency diagrams. In order to analyze the spacing distribution along a profile, we determine the coefficient of variation CV which a dimensionless measure of the spacing variation [START_REF] Gillespie | Measurement and Characterisation of Spatial Distributions of Fractures[END_REF][START_REF] Gillespie | Scaling Relationships of Joint and Vein Arrays from The Burren , Co . Clare , Ireland[END_REF]) that provides an indication of the distribution of the fractures. The value of the CV is given by:

𝐶 𝑉 = 𝜎 𝑆 𝑆 (3)
where CV , σS , S are coefficient of variation, standard deviation of the spacing between fractures, mean spacing, respectively.

For example, CV < 1 indicates regularly spaced fractures whereas CV > 1 is a characteristic of fractures that are more irregularly spaced [START_REF] Sanderson | Line Sampling of Fracture Swarms and Corridors[END_REF] and a profile that often displays a clustering of the fractures [START_REF] Gillespie | Measurement and Characterisation of Spatial Distributions of Fractures[END_REF].

RESULTS

Moulin des Vignes quarry

Terrestrial photogrammetric survey was conducted along a 27 m long profile oriented N30°E, by capturing 106 images of the rock wall. A total of 26 million points make up the dense point cloud on which we performed a digital scanline. 56 fracture measurements were performed on the virtual outcrop model. The global orientation of the fractures measured shows a main set oriented N140°E-N150°E (Figure 6A).

This fracture set was also analyzed in terms of spatial distribution. The average spacing is 0.532 m. Stick plot diagram allows initial visual examination of the fracture distribution on the line and the fractures seem to be regularly spaced in this case (Figure 6B). Furthermore, the cumulative frequency plot shows only minor fluctuations from the uniform distribution (Figure 6C). The CV for the spacing is 0.82, which is < 1. These features all indicate that the fractures are regularly spaced over 37 m with a spacing S > 0.50 m at a distance of ≥ 30 m distance from the fault. By comparing the fracture orientation obtained from the scanline method (Figure 7A) and the ones obtained by the photogrammetric method (Figure 7B), we notice that there is a clear similarity. Indeed, the main fracture set is characterize by the same global direction: NW-SE.

Lyas quarry

The first profile oriented N075°E is 20 m long and starts in a crushed zone to the west. The photogrammetric campaign captured 90 images of the outcrop and a dense point cloud of 7.7 million points was built. Out of a total of 38 fracture orientations measures along this profile, we can distinguished a main fracture set oriented N170°E-N20°E (Figure 8A). The fractures positions of this fracture set along the line are represented in figure 8B on which we can observe high heterogeneity of the distribution of fractures with higher frequency at the beginning of the profile (Figure 8B). The cumulative frequency plot shows a significant irregular distribution (Figure 8C). Moreover, the CV for the spacing is 1.33, greater than 1, indicating heterogeneity or clustering of the fractures. Indeed, we can observe a fracture corridor in the first 5 m of the line with an average spacing of 0.252 m. The 15 m that follows consists in fractures more spaced by a mean spacing S = 1.193 m. As profile n°1, the second profile is oriented N75°E and 20 m long. This line is the continuity of the first one. Scanline method has been applied here, for which 31 measurements were collected. A main fracture set is observed and it is globally oriented N170°E (Figure 8A).

A photogrammetric campaign was conducted on the third profile, which is split in two 15 m long sections: one oriented N120°E and another one oriented N150°E. A dense point cloud of 5.5 million points was built from 50 images captured on the field. The digital scanline performed on the virtual outcrop model enable the collection of 34 measurements. Two fracture sets can be distinguished: the main one oriented N150°E-N160°E and a minor one oriented N80°E-N90°E (Figure 8A).

These last two profiles could not be analyzed in terms of spatial distribution of fractures due to a lack of data that would lead to a statistical bias.

Note that the orientation of the fractures rotates slightly from N-S -N10°E to the west to N160°E-N170°E to the east.

DISCUSSION

Fault interpretation

Regarding the western zone of the Lyas quarry, the field observations show a crushed corridor located west of the first profile. Furthermore, the structural data shows an increasing in fracture frequency with closeness to this zone. These features suggest us that a fault is running through this area. We propose to define the orientation of this fault according to the main fracture orientation found around this corridor, i.e. oriented N-S to N10°E (Figure 9).

Fracture orientation

The main fracture set highlighted in the Moulin des Vignes quarry that is oriented N140°E-N150°E coincide with the direction of the large cartographic structure oriented N140°E, bordering the north-eastern part of the quarry (Figure 6A). That strongly suggests that the fractures observed at the outcrop scale are linked to regional-scale structures. This global direction NW-SE can be associated with the N160°E normal faults created during the Tethysian rifting (Blès et al., 1989;[START_REF] Martin | Palaeo-Stresses Inferred from Macro-and Microfractures in the Balazuc-1 Borehole (GPF Programme). Contribution to the Tectonic Evolution of the Cevennes Border of the SE Basin of France[END_REF], which are probably reactivated during the partial basin inversion [START_REF] Roure | Geometry and Kinematics of Extensional Structures in the Alpine Foreland Basin of Southeastern France[END_REF][START_REF] Roure | Multiphase Extensional Structures, Fault Reactivation, and Petroleum Plays in the Alpine Foreland Basin of Southeastern France[END_REF].

Regarding the results achieved in the Lyas quarry, the fracture orientations observed at the outcrop scale on the first profile are associated with the N-S to N10°E fault as noted above (Figure 9). In the eastern part of the quarry, the fractures are mostly oriented N160°E-N170°E, which correspond to the direction of the major fault oriented N160°E, located at the west side of the Lyas quarry (Figure 8A). The formation of this NNW-SSE fault is also probably due to the synsedimentary deformations during the Tethysian rifting event. The orientation of the minor fracture set observed on the third profile does not appear on the others owing to the observation bias caused by the direction of the first two profiles. The fractures of this N80°E-N90°E set, can be interpreted to Riedel shears associated with the N70°E cartographic fault located in the south of the quarry (Figure 8A). According to the Riedel shear model proposed by [START_REF] Cloos | Experimenten Zur Inneren Tektonik, Centralblatt Fur Mineralogie and Paleontologie[END_REF] and [START_REF] Riedel | Zur Mechanik Geologischer Brucherscheinungen[END_REF], the 'R-shears' are always present in a Riedel shear system: they are synthetic shears oriented ~ +15° (i.e. 15° clockwise) from the trace of right-handed strike-slip shear zones (Barlett, 1981;[START_REF] Davis | Conjugate Riedel Deformation Band Shear Zones[END_REF]. This means that the N70°E cartographic structure moved in a dextral displacement. However, this fracture set is composed of a very few measurements. Our understandings from this data should therefore be interpreted with caution.

The outcome of these results is that the main fracture sets observed at the outcrop scale are linked to the orientation of the regionalscale structures present in the area. In the case of the Triassic sandstone formations on the western border of the Valence Basin, fractures are mostly oriented NW-SE to NNW-SSE according to the main faults orientation (Figure 10).

Spatial distribution of fractures

Concerning the spatial arrangement of the fractures, the results obtained on the first profile of the Lyas quarry shows that the fractures frequency is increasing with closeness to the fault. Indeed, we can consider that there is a fracture corridor at the edge of the major faults, which measures approximately 5 meters wide. Within this corridor, the mean spacing between the fractures is around 25 cm (Figure 10).

The regularity observed in the spatial organization of fractures in the Moulin des Vignes quarry, suggests that the distribution of the NNW-SSE fractures is homogeneous across several tens of meters near the major faults, after the corridor previously mentioned (Figure 10). In this regularly fractured zone, the mean spacing is > 50 cm.

Relevance of the photogrammetric method

This study allowed us to compare results from the field measurements (scanline method) and the digital measurements using photogrammetric method. As shown in the case of the Moulin des Vignes quarry, the results are similar with both methods (Figure 7A-B), which demonstrate the efficiency of the photogrammetric method in reconstructing an outcrop and in finding the observations found on the field.

However, digital measurements are sometimes improperly selected and miscalculated because of the observation bias and the misinterpretation of the structures. For example, it is difficult to distinguish the tectonic fractures and the decompression fractures only based on the digital model. Furthermore, the fractures only observed by their "trace" on the rock surface are an additional difficulty for the digital measurement.

Within the framework of a structural study, the main asset of the photogrammetric method is to ensure access to all parts of the targeted outcrop as long as it is covered by the photographic acquisition (like in high places). Another advantage of this method is the possibility to have an unlimited access to the virtual outcrop model in time.

CONCLUSION

This work reveals that the orientation of the outcrop scale fractures studied on the western edge of the Valence Basin are linked to the regional-scale structures indicated on the geological map at 1:50.000 scale. These major faults are related to the geodynamic events that occurred in the basin, such as the E-W extension of the Tethysian rifting. Thus, the main orientation pointed out in the fracture network of the Triassic sandstones is NW-SE to NNW-SSE.

Within these sandstones, we can describe the spatial distribution of the fractures bordering the major faults in two distinct parts:

-A corridor about 5 meters wide to the foot of the fault, with a mean spacing S = 25 cm. -A homogeneous zone present on several tens of meters after the corridor area, with a mean spacing S > 50 cm.

The geometric information of the fracture network determined in this study will be used as input parameters for hydro-thermalmechanical modelling of the geothermal reservoir. These models will allow the prediction of the fluid circulation and the heat transfer within the fractured reservoir.

The terrestrial photogrammetric method appears to be an efficient and relevant tool for the fracture measurements by the production of a virtual outcrop model. Therefore, it is an appropriate method for a structural study at the outcrop scale. Note that this digital tool is only a complementary method to the field observations.

Figure 1 :

 1 Figure 1: A. Location and simplified geological map of the South-East Basin of France (Garibaldi et al., 2010). The red line indicates the location of the cross-section of the Figure 1B. The black square indicates the location of our study sites (Triassic outcrops). B. Simplified cross-section through the Valence Basin (Deville et al., 1994).

Figure 2 :

 2 Figure 2: Thermal map of the South-East Basin of France, at 5000m depth (Garibaldi, 2010).

Figure 3 :

 3 Figure 3: Simplified geological map of the western border of the Valence Basin (black square on the Figure1A). Study sites are localized. A: Moulin des Vignes quarry. B: Lyas quarry. The Triassic formations quarried in Lyas and Moulin des Vignes are composed of medium grained arkosic sandstones deposited during middle and upper Triassic periods, respectively. Those quarries are bordered by major local faults that are indicated on the geological map of Privas at 1:50.000 scale (Ledru et al., 2014): -Moulin des Vignes quarry: faults oriented N40°E and N140°E -Lyas quarry: faults oriented N70°E and N160°E

Figure 4 :

 4 Figure 4: A. Image showing the equipment used at the Lyas quarry for the terrestrial photogrammetry campaign. B. Schematic plan of the equipment positioning (example of the Lyas quarry). Red crosses indicates the position of the photogrammetric targets. Black triangles indicates the position of the tripods.

Figure 5 :

 5 Figure 5: Virtual outcrop model of the targeted rock wall at the Lyas quarry, produced under Agisoft Metashape Professional software. The white zones corresponds to area with not enough images to reconstruct the model. The rods are 5 m long.

Figure 6 :

 6 Figure 6: A. Location of the studied profile within the Moulin des Vignes quarry and direction of the fractures measured. Rose diagram of strike direction with 10° classes. Red lines represents the major faults that are indicated on the geological map of Privas at 1:50.000 scale (Ledru et al., 2014). B. Spatial distribution of fractures on the line represented as stick plots. B. Cumulative plot of % frequency against % distance for the Moulin des Vignes profile. Blue circles show cumulative % frequency and diagonal line represents a uniform distribution.

Figure 7 :

 7 Figure 7: Results of the fracture planes measurements at the Moulin des Vignes quarry A. Stereogram showing the poles of fracture planes measured on the field by the scanline method. B. Stereogram showing the poles of fracture planes measured on the virtual outcrop model produced from the photogrammetric method.

Figure 8 :

 8 Figure 8: A. Location of the studied profile within the Lyas quarry and direction of the fractures measured. Rose diagram of strike direction with 10° classes. Green and red lines represents the major faults that are indicated on the geological map of Privas at 1:50.000 scale (Ledru et al., 2014). B. Spatial distribution of fractures on the line is represented as stick plots. B. Cumulative plot of % frequency against % distance for the Lyas profile. Blue circles show cumulative % frequency and diagonal line represents a uniform distribution.

Figure 9 :

 9 Figure 9: Location and orientation of the fault (blue line) determined from the field observations and the geometric features of the fracture network analyzed in the area. The colors of the different orientations in rose diagrams illustrates the corresponding fault.

Figure 10 :

 10 Figure 10: 3D block diagram summarizing the geometric parameters of the fracture network determined in the Triassic sandstones of the Valence Basin resulting from the photogrammetric survey.


Keywords:

Tribological properties of amorphous carbon films obtained by electrodeposition from DMF using 2HEAL protic ionic liquid as dopant Tiago Falcade a, ⁎, Viviane Turq b , Jean-Pierre Bonino b , Celia de Fraga Malfatti b a Federal University of Rio Grande do Sul, Brazil b Université Toulouse III -Paul Sabatier, France a b s t r a c t a r t i c l e i n f o Amorphous carbon films are widely used for improving the surface mechanical properties of metallic materials, substantially increasing the wear resistance [START_REF] Jiang | Some special tribological features of DLC coatings deposited on soft substrates[END_REF][START_REF] Mohan | Corrosion behavior of titanium alloy Beta-21S coated with diamond like carbon in Hank's solution[END_REF]. Traditionally this type of film is obtained by vapor phase methods, which, in spite of being in a high technical and scientific development level have been associated with a number of limitations, in particular with regards to the implementation cost and large film production. In this context, electrodeposition shows itself as an alternative to traditional methods: it has low cost and limits the use of complex techniques, which generally require high temperatures and vacuum and cannot be applied for coating on substrate with complex shapes and large dimensions. It is true that the electrodeposition of carbon films also has experimental limitations, such as the limited deposition rate and, therefore, the aim of this work is to investigate the influence of the ionic liquid 2 HydroxyEthylAmine Lactate (2HEAL) in obtaining amorphous carbon films. An improvement in deposition rate by increasing electrolyte conductivity with the addition of ionic liquid is expected. This work is meant to investigate the changes occurring in the films with the addition of ionic liquid, especially from the standpoint of surface mechanical properties such as tribological behavior and interfa cial properties. The results show that the addition of the ionic liquid led to change in the structure of the film, resulting in an improvement in the mechanical properties, as observed by reduced friction coefficient. An in crease of abraded area of counterface and an increase of elastic work also indicates that behavior. Novelty statement: The aim of this study was to obtain carbon films by electrodeposition using 2 HydroxyEthylAmine Lactate doped N,N DiMethylFormamide as electrolyte, in order to increase deposition rate. It will be the first report about the use of ionic liquids as dopants in the electrodeposition of carbon films. In addition, mechanical properties of the obtained films were evaluated and their relationship with the amounts of dopant was explored.

Introduction

Carbon films present excellent tribological properties and they can be used as coatings of metallic materials in various applications, espe cially in order to increase wear resistance [1 5]. For this purpose, carbon coatings show up as an interesting alternative coating of titanium alloys for biomedical [6 9] and aerospace applications [START_REF] Fanning | Properties of TIMETAL 555 (Ti-5Al-5Mo-5V-3Cr-0.6Fe)[END_REF][START_REF] Arrazola | Machinability of titanium alloys (Ti6Al4V and Ti555.3)[END_REF]. Traditionally this type of coating is obtained by physical or chemical vapor deposition [12 15]. However, these techniques are expensive and require complex experimental apparatus. In this way, to obtain carbon films directly on the surface of titanium alloys, in an efficiently and economically viable manner becomes a challenge.

In this context, the electrodeposition shows enormous potential, especially for not requiring vacuum systems and high temperature [START_REF] Namba | Attempt to grow diamond phase carbon films from an organic solution[END_REF][START_REF] Zhu | Aroused problems in the deposition of diamond-like carbon films by using the liquid phase electrodeposition technique[END_REF]. In addition, this technique allows coating components of complex geometry and it has several operating parameters that allow controlling the properties of the films. Typically, the electrodeposition of carbon films uses organic solvents as electrolyte, and N,N DiMethylFormamide (DMF) and ACetoNitrile (ACN) are among the most widely explored in the literature [START_REF] Zhu | Aroused problems in the deposition of diamond-like carbon films by using the liquid phase electrodeposition technique[END_REF][START_REF] Cai | Evaluation of diamond-like carbon films deposited on conductive glass from organic liquids using pulsed current[END_REF]. However, the deposition with these solvents leads to experimental limitations, in particular with respect to deposition time and to voltage required for polarization, acti vation and reaction of organic molecules [START_REF] Zhu | Aroused problems in the deposition of diamond-like carbon films by using the liquid phase electrodeposition technique[END_REF].

Some work has been reported on the use of dopants in deposition solutions, in order to increase the conductivity of the electrolyte. These dopants are mostly aqueous solutions containing possibly some kind of salt [START_REF] Pang | Characterization of diamond-like carbon films by SEM, XRD and Raman spectroscopy[END_REF][START_REF] Li | Synthesis and tribological properties of diamondlike carbon films by electrochemical anode deposition[END_REF]. The problem of this dopant type is inevitable occurrence of parallel reactions during the deposition and the compati bility with the original organic solution.

Aiming to improve the characteristics of the electrolyte leading to an increase in the deposition rate of the films, this research proposes the use of ionic liquids as dopants, operating as supporting electrolyte and consequently increasing the conductivity of the deposition solution [START_REF] Fuller | The room temperature ionic liquid 1-ethyl-3-methylimidazolium tetrafluoroborate: electrochemical couples and physical properties[END_REF][START_REF] Santos | Synthesis and physico-chemical properties of two protic ionic liquids based on stearate anion[END_REF], favoring polarization of organic molecules. After the deposition, the different films obtained were compared regarding their morpholog ical, structural, tribological and mechanical properties, checking the ef fect of doping on their characteristics.

Materials and methods

The substrate used in this work was a titanium alloy, Ti6Al4V disks that were mechanical polished using #600 #4000 SiC sandpaper and subsequently polished with 1 μm size diamond paste. The samples were cleaned with distilled water and ethanol.

Electrodeposition technique was used for the deposition of carbon films. The cell was a traditional two electrodes: a working and a counter electrode. The working electrode was the substrate sample itself, in a Teflon holder, with a constant exposed area of 0.31 cm 2 , and the counter electrode was a graphite plate, 10 mm distant from the working elec trode. Temperature was kept constant at 20 °C using a thermostatic bath. For the deposition, an electric voltage of 1200 V was applied be tween the electrodes using a high voltage source, many authors report ed this magnitude of voltage in order to obtain carbon films with amorphous characteristics [18,23 25]. In all systems, the deposition time was 24 h.

One of the most important parameters in the electrodeposition pro cess is the electrolyte composition. In this work N N; DiMethylFormamide (DMF) (FMaia 99%) was tested as electrolytes, as well as mixtures of DMF and 2 HydroxyEthylAmine Lactate (2HEAL), used as dopant, in order to increase the electrolyte conductivity, it is common to use ionic liquids as support electrolyte in electrodeposition process [ 26 29]. Normally, aprotic ionic liquids are used in this way, however this kind of ionic liquid have high cost and low stability, for this reason in this work a protic ionic liquid is used. The main difference of protic ionic liquids compared to the traditional aprotic is the presence of at least a proton, which is/are able to promote extensive hydrogen bonding [START_REF] Kennedy | Large aggregated ions found in some protic ionic liquids[END_REF]. In addition this family of ionic liquids are interesting alter native due their low cost and simple synthesis rout [START_REF] Mattedi | High pressure CO2 solubility in N-methyl-2-hydroxyethylammonium protic ionic liquids[END_REF]. Three concen trations of this ionic liquid in the electrolyte were tested: 0.03 vol% (DMF30LI), 0.05 vol% (DMF50LI) and 0.1 vol% (DMF100LI).

Morphology of the samples before and after the deposition of the films was observed by atomic force microscopy (Shimadzu contact mode, size 2 μm × 2 μm), scanning electron microscopy (Jeol, 6060, 20 kV, Secondary Electron and Backscattered Electron Imaging mode) and optical microscopy (Keyence 3D optical microscope). The local roughness was measured using the profiles of AFM. Raman spectrosco py (Renishaw; laser 514 nm, 5 accumulations, exposure time 20 s 120 s) was used in order to analyze the type and amount of carbon bonds in the structure of the film, this procedure allows evaluating the type of amorphous carbon film obtained. The reference used for peak position was based on the studies of Beeman et al. [START_REF] Beeman | Modeling studies of amorphous carbon[END_REF], Dillon et al. [START_REF] Dillon | Use of Raman scattering to investigate disorder and crystallite formation in as-deposited and annealed carbon films[END_REF] and Ferrari and Robertson [START_REF] Ferrari | Interpretation of Raman spectra of disordered and amorphous carbon[END_REF].

Adhesion of the films was investigated by Scratch tests, with a Nano Scratch Tester (CSM Instruments) with spherical diamond indenter (di ameter of 5 μm) applying a progressive loading from 3 to 500 mN. The facies and the optical critical loads of tracks were analyzed by optical microscopy, and the elastic recovery of the groove was evaluated by measuring the penetration depth during the scratch test and after the test. The mechanical properties (Young's modulus, surface hardness) were evaluated using nanoindentation test (UltraNanoIndenter, CSM Instruments) with a normal force of 10 mN, with a modified Berkovich indenter. The Oliver & Pharr analysis method [START_REF] Oliver | An improved technique for determining hardness and elastic modulus using load and displacement sensing indentation experiments[END_REF] was used for calculation.

Friction tests were performed on a linear ball on plate tribometer (CSM Instruments). To evaluate the tribological behavior of the films, sliding was conducted with a reciprocal linear motion of an alumina ball (diameter of 6 mm). Constant normal force of 1 N, corresponding to an average Hertzian pressure of 400 MPa; sliding speed of 0.63 cm/ s and track length of 2 mm were used. The dimensions and facies of the tracks were evaluated by optical and electronic microscopy.

Results and discussion

The analysis of the substrate indicates that the mechanically polished surface is characterized by a uniform texturing which could favor the deposition, providing well distributed sites to anchor the film, as shown in the AFM image (Fig. 1). The substrate presents very low local roughness as showed in Fig. 4. However, after deposition there was a clear change in the appearance of the surface: globular for mations of the film onto the substrate lead to an increase in surface roughness (Fig. 3a). This fact is associated with a phenomenon of pref erential polarization, wherein the material is favorably deposited on the substrate inhomogeneities or defects, such as peaks or valleys on the surface. As observed by Zhang [START_REF] Zhang | Synthesis and tribological behaviors of diamondlike carbon films by electrodeposition from solution of acetonitrile and water[END_REF] and Gupta [START_REF] Gupta | Synthesis of DLC films by electrodeposition technique using formic acid as electrolyte[END_REF][START_REF] Gupta | Field emission characteristics of diamond-like carbon films synthesized by electrodeposition technique[END_REF], after the nu cleation phase, the carbon nuclei come into a growth phase, and began to thicken the film. As the deposition rate is low, the carbon globules formed were coarse. The insertion of protic ionic liquid in DMF increases the conduc tivity of the solution as can be seen in Fig. 2, thereby increasing the electrodeposition current density and consequently increasing the deposition rate (Table 1). AFM images of the films obtained from so lutions containing 0.03 vol%, 0.05 vol% and 0.10 vol% of ionic liquid Figs. 3b; c; andd, respectively show a globular structure with ag glomerates constituting the film. The same mechanism of nucleation and growth in thickness was observed. However, since the deposi tion rate is higher for systems with dopant, a larger quantity of nuclei was formed, followed by growth in thickness. This effect, locally ob served by AFM, showed a structure with finer agglomerates with in creasing amounts of dopant, leading to increased local roughness (Fig. 4), as observed by Zhang [START_REF] Zhang | Synthesis and tribological behaviors of diamondlike carbon films by electrodeposition from solution of acetonitrile and water[END_REF].

In addition, the presence of dopant caused a progressive increase in the thickness of the films measured from cross sections by scanning electron microscopy, as can be seen in Table 1. This increase is related to the higher conductivity of the electrolyte and the consequent in crease in current deposition, leading to a higher deposition rate. In fact, the films obtained without the dopant showed a deposition rate of 190 nm/h while the addition of 0.1 vol% of 2HEAL led to an increase to rates around 750 nm/h. Regardless of presence or absence of ionic liquid in the deposition solution the films have typical characteristics of amorphous carbon films, as can be observed in the Raman spectra (Fig. 5). These spectra show the presence of G band associated with the presence of sp 2 type hybridizations and D band associated with the disorder of sp 2 bonds, this disorder may be associated with the presence of carbon atoms bonds with sp 3 type hybridizations.

The positions of D and G and the I D /I G ratio can be correlated with the percentage of four fold coordinate bonds, characterizing the sp 3 type hybridizations [START_REF] Beeman | Modeling studies of amorphous carbon[END_REF] and the number and/or size of graphite crystallites [START_REF] Dillon | Use of Raman scattering to investigate disorder and crystallite formation in as-deposited and annealed carbon films[END_REF]. The I D /I G intensity ratio was calculated and the values were around 0.73 for DMF and between 0.67 and 0.72 for the systems that uses ionic liquids as dopants in the deposition solution. The crystallite size could be calculated through the linear model proposed by Dillon et al. [START_REF] Dillon | Use of Raman scattering to investigate disorder and crystallite formation in as-deposited and annealed carbon films[END_REF], leading to typical crystallite size of 25 nm. These values are consistent with those proposed in the literature, both for films obtained by electro deposition, as those obtained by vapor phase techniques. As reported by Dines [START_REF] Dines | Raman spectra of hard carbon films and hard carbon films containing secondary elements[END_REF], a C carbon films obtained by PVD can present I D /I G ranging between 0.82 and 1.62. Carbon films obtained by electrodeposition using organic liquid and organic liquids in aqueous solutions showed I D /I G between 0.4 and 1.4 [38,40 42].

The analysis of D and G bands enables interpreting the influence of the ionic liquid in amount of sp 3 hybridizations and graphite crys tallites [START_REF] Ferrari | Interpretation of Raman spectra of disordered and amorphous carbon[END_REF][START_REF] Robertson | Diamond-like amorphous carbon[END_REF]. All the films presented a graphitic character with presence of graphitic clusters. Fig. 5 and Table 2 show the depen dence of ionic liquids content in the position and intensity of D and G bands. The position of D band shifted slightly down with in creased amount of dopant, while the I D /I G ratio shifted slightly upwards, which could indicate a greater amount of sp 3 hybridiza tions and a reduction in number and/or size of graphite crystallites when the amount of ionic liquid increases. However, the most no ticeable effect is the downward displacement of the G band with the amount of dopant, possibly indicating a reduction in the amount of sp 2 hybridizations.

Changes in the structure of the carbon films influenced their physi cochemical characteristics and therefore their properties. From the viewpoint of surface mechanics, scratch tests showed that the films ob tained from DMF showed no delamination of the coating, only lateral material displacement was observed, with lateral pile up formation, which indicates good adhesion between the film and the substrate, as can be seen in the images of scratch tracks in Fig. 6 but plastic character. Plastic deformation indeed occurs at the beginning of the test, indicating that the minimum load is sufficient to permanently deform the films. The addition of ionic liquid to deposition solution did not affect signifi cantly the interfacial properties of carbon films, in the same way as for systems without dopant are observed scratch tracks with plastic defor mation since the beginning of load application, but induce a shift in the critical load value for lateral pile up formation Lateral pile up formation begins for slightly higher loads for the systems with addition of ionic liquids (Table 3). In the case of pure DMF, the critical load to lateral displacement was 11 mN and after addition of dopant, critical loads ranged from 35 mN to 40 mN. There appears to be no significant influence of the amount of ionic liquid to the critical load of material displacement because even low dopant concentrations have increased their value, and the addi tion of a greater amount does only result in a slight increase in re sistance to displacement. This increased resistance to lateral pile up plastic formation can be related to the increase of the elastic nature of the films obtained with the addition of dopant, as evi denced by an increase in elastic work ratio during scratch test shown in Table 3.

Nanoindentation tests performed on the top surface of the studied films result in dispersed values of surface hardness. Probably this is re lated to the lack of surface homogeneity of the films in relation to the low load applied during the tests. Nevertheless, the substrate presents hardness reliable with titanium alloys, around 4400 MPa [START_REF] Boyer | American Society for Metals, Materials Properties Handbook: Titanium Alloys[END_REF][START_REF]Properties and Selection: Nonferrous Alloys and Special-Purpose Materials[END_REF]. Among the films all had the same hardness range of between 3000 MPa and 3500 MPa (Fig. 7). These values are relatively smaller than those traditionally found by carbon films with high amount of sp 3 hybridizations, between 10 GPa and 30 GPa [43, 46 49], however, were consistent with those observed by Thejaswini et al. in the case of sp 2 rich films [START_REF] Thejaswini | Deposition and Characterization of Diamond-Like Carbon Films by Microwave Resonator Microplasma at One Atmosphere[END_REF].

Young modulus of uncoated substrate (125 GPa) and films obtained with and without addition of ionic liquid are shown in Fig. 7. Substrate presents values befitting to the literature [START_REF] Boyer | American Society for Metals, Materials Properties Handbook: Titanium Alloys[END_REF][START_REF]Properties and Selection: Nonferrous Alloys and Special-Purpose Materials[END_REF][START_REF]ASM Handbook Committee, Properties and Selection-Irons and Pure Metals[END_REF]. In the case of car bon films, a reduction in elastic modulus with increasing the amount of ionic liquid was observed; this is in good agreement with the increase of the elastic nature of the films as evidenced by scratch tests (Fig. 7). Chung et al. [START_REF] Chung | Biaxial elastic modulus of very thin diamond-like carbon (DLC) films[END_REF] studied the deposition of amorphous carbon films onto Si by Plasma Assisted CVD (PACVD) and proposed a direct relation ship between the reduction of elastic modulus to the shift in G band to lower wavelengths, the same behavior was observed with the addition of ionic liquid. Furthermore Jardret et al. have shown that the propor tion of plastic deformation during scratch test increases with the E/H ratio [START_REF] Jardret | Understanding and quantification of elastic and plastic deformation during a scratch test[END_REF]. This could explain the increase of the elastic deformation ratio with the dopant addition.

Observing comparatively the coefficient of friction (COF) curves for all systems studied (Fig. 8) is quite clear the influence of the type of elec trolyte in the mechanical characteristics of the surface of the coated systems.

The coefficient of friction of the uncoated substrate showed an initial period in which polished substrate sliding against the alumina ball, followed by a period where COF oscillates around a mean value. This is due to the presence of a large number of particles (third body) arising from the worn substrate in the contact with the counterface [START_REF] Bhushan | Principles and Applications of Tribology[END_REF]. When these particles were removed from the interface during the test, there was a reduction in the coefficient of friction which in creased again when new particles are formed and injected into the contact interface.

For the friction tests on the sample coated with a film obtained from DMF, the initial profile present very low COF values, between 0.2 and 0.3; this value were in agreement with typical carbon films for similar sliding conditions [START_REF] Abdollah | Deformation-wear transition map of DLC coating under cyclic impact loading[END_REF][START_REF] Li | Synthesis and tribological properties of diamondlike carbon films by electrochemical anode deposition[END_REF][START_REF] Yang | Friction reduction mechanisms in boundary lubricated W-doped DLC coatings[END_REF] and remains in this range until three me ters slip. Thereafter, the film began to delaminate and consequently the COF began to increase and goes to values around 0.7, these values coincide with those of the uncoated substrate.

Films obtained from DMF with addition of ionic liquid exhibited low coefficient of friction in relation to sliding distances tested. The system that used 0.03 vol% dopant showed a progressive increase in the coeffi cient of friction did not exceed 0.5. Even though slightly above typical COF of amorphous carbon films, it was still relatively lower than the un coated substrate. For the films with higher ionic liquid concentration, in the case of adding 0.05 vol% or 0.10 vol% the coefficient of friction was lower than 0.25 throughout the sliding distance tested. This behavior is associated to the structure of the film, with increased amount of sp 3 hybridization giving better surface properties while the presence of cer tain amount of hybridization sp 2 imparts a self lubricating nature to the films.

The friction coefficient observed for the films obtained from DMF with addition of ionic liquid, remained low in long term tests, without showing catastrophic wear of the film even after significant worn dis tances (Fig. 9).

The analysis of uncoated substrate wear tracks showed typical scratch marks of abrasive wear both on the track (Fig. 10a) and on the counterface side (Fig. 10b). Material transferred to the counterface sur face (Fig. 10b), typical of adhesive wear, was also observed. Considering these two phenomena the wear mechanism of the substrate was a mix ture of abrasive and adhesive wear, as expected for wear of metallic ma terials [START_REF] Stachowiak | Engineering Tribology[END_REF].

The appearance of the wear tracks and the alumina counterface for the coated system indicated the same mechanism observed for uncoat ed substrate, scratch marks of abrasive wear can be viewed in SEM image (Fig. 11b). However, there was a reduced wear evidenced by the large reduction in track width (Fig. 11a) and the abraded area in the alu mina ball Fig. 11c). There appears to be less amount of material trans ferred to the counterface, as shown in Fig. 11c. The addition of ionic liquid to the electrolyte resulted to a change in the wear mechanism: without scratch marks of abrasive wear (Fig. 12a, c ande), both in the film and in the counterface. While the analysis of the counterface (Fig. 12b,d andf) shows adhered material, indicating adhesive wear mechanism, with presence of debris shifted to the ex tremities of the abraded area. This change of wear mechanism may be associated with more elastic character of these coatings as shown by the interfacial behavior analysis (Table 3).

Comparative analysis of wear tracks and counterfaces (Fig. 13) showed that, regardless the presence and amount of ionic liquid, there was no significant change in the width of the wear tracks. On the other hand, an increase in the abraded area of the sphere was observed with addition of small amounts of dopant, and an even greater increased with the addition of larger amounts of dopant. This phenomena is in good agreement with the increase of the contact area due to the reduc tion of Young modulus predicted by the Hertz contact model. The ex pected contact diameters for the test configurations are between 0.63 μm and 0.65 μm, in concordance with de values reached for the track width of the coated systems.

This increase of abraded area could be related with the amount of sp 2 hybridizations in the film, the displacement of G band to lower wavelengths evoked the reduction of amount and size of graphite clusters in the film, this reduction limited the lubricating character istics, increasing counterface wear. Fig. 14 shows that additions of small amounts of dopant led a significant influence in graphite clus ters, which means there was an important increase in counterface wear.

Conclusions

The films obtained had typical characteristics of amorphous carbon structure, formed by sp 3 and sp 2 bonds and presence of graphite clus ters. Ionic liquid influenced the structure of the film, probably increasing the amount of sp 3 bonds and reducing the amount sp 2 hybridizations, even if a more detailed and in depth Raman analysis, beyond the scope of this paper, would be necessary to better understand the coating structure. This amorphous carbon nature gave the film interesting prop erties with regard to wear resistance, reducing the COF for much lower (0.25) than the uncoated substrate values (0.7). An optimum combina tion between the amount of sp 2 and sp 3 hybridization was observed for the films obtained from DMF with 0.05% of 2HEAL, resulting the lowest COF value, which was accompanied by intermediate wear against the face of alumina.

It was observed good adhesion between the film and the substrate, which showed only lateral pile up pad formation without delamination, regardless the presence or absence of dopant in the deposition solution. The ionic liquid addition led to an increased resistance to lateral pile up pad formation, which was observed to four times higher loads for sys tems containing dopant. Furthermore, addition of dopant modified elastoplastic character of the films, being observed an increase in the percentage of elastic work with the amount of ionic liquid, this influ enced the wear mechanism, reducing the abrasive nature and leading to a more adhesive nature for the wear, possibly allowing easier tribofilm formation. No clear evidence of hardness evolution could be shown but there was a tendency of reduction of Young modulus with increasing amount of dopant, in good agreement with the increase of the elastic recovery obtained by scratch tests.

Fig. 1 .

 1 Fig. 1. AFM image of the polished substrate before deposition.

Fig. 2 .

 2 Fig. 2. Conductivity of the tested electrolytes.

Fig. 3 .

 3 Fig. 3. AFM image of the film surface obtained from: (a) DMF; (b) DMF30LI; (c) DMF50LI; (d) DMF100LI.

Fig. 4 . 5 .

 45 Fig. 4. Average local roughness of the studied systems obtained by AFM measurements. Fig. 5. Raman spectra of the films obtained from different electrolytes.

Fig. 6 .

 6 Fig. 6. Scratch tracks of the films obtained from: (a) DMF; (b) DMF30LI; (c) DMF50LI; (d) DMF100LI.

Fig. 8 .

 8 Fig. 8. Influence of the dopant in the Coefficient Of Friction (COF) for the film compared to the uncoated substrate.

Fig. 9 .

 9 Fig. 9. Long duration friction test for DMF50LI system.

Fig. 7 .

 7 Fig. 7. Influence of the dopant in the hardness and the Young modulus of the film compared to the uncoated substrate.

Fig. 10 .

 10 Fig. 10. Appearance of uncoated substrate wear: (a) track; (b) counterface.

Fig. 11 .Fig. 12 . 13 .

 111213 Fig. 11. Appearance of film obtained from DMF wear: (a) optical image of track; (b) SEM image of track; (c) counterface.

Table 1

 1 Layer thickness of the films obtained from organic liquids with and without dopant.

System

Layer thickness (μm) DMF 4.5 ± 0.2 DMF30LI 8.1 ± 0.4 DMF50LI 12.9 ± 1.8 DMF100LI

18.1 ± 0.5

Table 2

 2 Positions of the D and G bands and intensity I D /I G ratio for the films.

	System	D center (cm 1 )	G center (cm 1 )	I D /I G
	DMF	1341 ± 0.58	1591 ± 0.6	0.73 ± 0.006
	DMF30LI	1341 ± 0.60	1585 ± 2.5	0.67 ± 0.010
	DMF50LI	1340 ± 1.53	1586 ± 0.6	0.69 ± 0.015
	DMF100LI	1336 ± 1.15	1579 ± 1.5	0.72 ± 0.021

Table 3

 3 Interfacial properties of the films obtained from different solutions.

	System	W elast /W total	Critical load to lateral pile-up formation [mN]
	DMF	68%	11
	DMF30LI	76%	35
	DMF50LI	77%	35
	DMF100LI	83%

Acknowledgements

The authors would like to thank the Brazilian and French scientific funding agencies: CAPES, CNPq and CNRS for financial and scientific support this research.