Matthieu Petit

Abstract: The Curie temperature of Mn5 Ge3 has been successfully enhanced by carbon doping. In this context the diffu- sion of a carbon thin film in Mn5 Ge3 has been studied at room temperature. A value of the diffusivity of about D = 2.4x10-23 ± 0.5x10-23 m2 s-1 is reported. This value is in the typical range of interstitial diffusion coefficients. Moreover Auger Ge and Mn peaks shifts and Ge3d core level have been investigated to get some details on the reactivity of carbon atoms in Mn5 Ge3 . Mn Auger transitions display a shift of 4 eV whereas Ge transitions do not. Similarly Ge3d core level does not contain C related contribution but presents a Mn one. These observations confirmed the fact that carbon atoms are not inert species for Mn. It suggests that a ternary Ge- Mn-C alloy could occur and should be taken into account when doping the Mn5 Ge3 with carbon.

Abstract: We have combined structural and magnetic characterisations to investigate the effect of carbon incorporation in epitaxial Mn5Ge3Cx films grown on Ge(111) by Molecular Beam Epitaxy (MBE). It is shown that up to a carbon content of saturation of ~0.6, most of carbon can be incorporated into the interstitial sites of the Mn5Ge3 lattice. Such a process results in a linear increase in the Curie temperature (TC) of the alloy, which can reach a value as high as ~430 K. Above this carbon content, TC is found to decrease. Structural characterisations reveal that Mn5Ge3Cx films are in perfect epitaxy when x ≤0.6 whereas cluster formation in the grown layers is detected above that threshold. The clusters can be attributed to manganese carbide (MnC) compounds, which are formed when the carbon content exceeds the saturation value of 0.6 by consuming previously deposited carbon. In addition, we also show that after post-thermal annealing, the carbon-doped Mn5Ge3Cx alloys remain magnetically and structurally stable up to a temperature as high as 1123 K. The obtained results are very promising for integrating Mn5Ge3Cx into ferromagnetic/semiconductor heterostructures, the ultimate goal being the realisation of spintronics devices.

Abstract: The benefits of using a low power glow discharge nitrogen plasma source to create high quality GaN layers on GaAs (001) surface are first highlighted. This uncommon type of plasma source has the particularity of working at a low power (3–10 W) and a low pressure (10- 1 Pa) which induce creation of small quantity of active nitrogen species. We put in evidence that this distinctiveness allows the growth of a stoichiometric and As-free GaN ultra-thin film on a GaAs (001) substrate by the mean of the inter-diffusion of As and N atoms. XPS, EELS, AFM are used to monitor surface composition and structure changes and to estimate the GaN thickness. A near saturation of the nitride layer thickness versus plasma exposure time is found. Furthermore, the possibility to crystallize the amorphous GaN layer by an annealing at 620 °C in a cubic structure with a lattice parameter close to that of c-GaN is put in evidence by the mean of TEM and LEED measurements. These measurements also show the homogeneity of the GaN thickness. In addition, the passivating effect of the GaN ultra-thin film to protect the GaAs surface is proved with the monitoring by XPS of the surface oxidation during several days of air exposure.

Abstract: The interface states in Au/Mn5Ge3/Ge Schottky barrier diodes prepared for spintronic applications are investigated using dc I-V-T as well as ac admittance measurements. The latter were performed under forward and reverse biases over a wide range of frequencies (1 kHz–3 MHz) while varying the temperature from 50 to 300 K. Variations of the ideality factor with temperature are related to the density of interface states, the presence of which is also evidenced as an excess capacitance in the capacitance—frequency characteristics as well as a peak in the conductance versus frequency. The temperature dependence of these interface state densities, determined to be of the range 1013–1014 eV−1 cm−2, and their energy distribution with respect to the bottom of the conduction band are examined.

Abstract: Structural and magnetic characterizations have been combined to investigate the growth kinetics of Ge1−xMnx diluted magnetic semiconductors (DMSs) on Ge(001) substrates by means of molecular beam epitaxy (MBE). We have identified the growth process window allowing stabilization of a high Curie temperature (TC) nanocolumn phase and provide evidence that the growth of semiconducting Ge1−xMnx nanocolumns and metallic Mn5Ge3 clusters is a competing process. Due to a continuous increase of the Mn concentration inside nanocolumns, induced by Mn segregation along the growth direction from the interface toward the film surface, nanocolumns become unstable when the Mn concentration reaches a value of ~40 at.% then transform into Mn5Ge3 clusters. We propose a real-time approach to realize stacked layers consisting of nanocolumns separated by a Ge barrier layer, allowing exploitation of the effect of giant magneto-resistance in multilayer structures

Abstract: High crystalline quality Mn5Ge3 films with thicknesses ranging 4–200 nm have been grown on Ge(111) substrates by solid phase epitaxy. The basal hexagonal plane of Mn5Ge3 is in epitaxy with the Ge(111) plane. Magnetic properties of the films have been investigated as a function of the film thickness and the magnetization curves have been analyzed using a theory that includes a description of magnetic domains in uniaxial thin films. The results clearly indicate the existence of a critical thickness below which the magnetic stripe phase disappears. We have determined the value of this thickness to lie between 10 and 25 nm from the analysis of experimental magnetization curves and the theoretical fit of the in-plane remanent magnetization. Although analogies can be drawn between the behavior observed in our system and that of hcp Co, we have shown that the critical thickness is considerably smaller in Mn5Ge3; this has the potential to open new fields of applications for Mn5Ge3 thin films in magnetic recording and spintronics.

Abstract: The Mn5Ge3 compound, thanks to its room-temperature ferromagnetism, metallic character and ability to epitaxially grow on germanium, acts as a potential candidate for spin injection into group-IV semiconductors. Understanding and controlling Ge overgrowth behaviour on Mn5Ge3/Ge heterostructures represents a crucial step to realize Ge/Mn5Ge3/Ge multilayers for numerous spintronic applications. Here, we have combined structural and morphological characterizations with magnetic analyses to study the mechanisms of Ge overgrowth on epitaxial Mn5Ge3 layers in the temperature range of 450–550 °C. It is found that deposited Ge instantly reacts with Mn to form a Mn5Ge3 surface layer, which, acting as a surfactant, continuously floats upwards from the growing surface to a distance larger than 70 nm. New Ge layers are successively formed underneath, allowing such a floating Mn5Ge3 surface layer to be stabilized by epitaxy. These observations can be considered as a typical example in which the stabilization of metastable thin films by epitaxy can overcome thermodynamic equilibrium. We have also investigated the effect of carbon adsorption on the top of the Mn5Ge3 layer prior to Ge deposition to control the Mn:Ge reaction. It is shown that adsorbed carbon effectively reduces the out-diffusion of Mn from Mn5Ge3, allowing Ge layers to stack up on top of Mn5Ge3. However, at temperatures of 450–550 °C, carbon may react with Mn to form manganese carbides and the resulting Ge overlayers are found to change their orientation from the (111) plane to the (001) plane, which has a higher surface energy. Finally, a strategy to realize Ge/Mn5Ge3/Ge multilayers will be addressed.

Abstract: We investigate the chemical and morphological structure of the Au nanodots on Ge(111), which serve as catalysts for the formation of epitaxial Ge nanowires. We show that dewetting of an Au film on Ge(111) gives rise to a thin Au-Ge wetting layer and Au-Ge dots. These dots are crystallized but not with a single crystallographic orientation. Thanks to the spatially resolved x-ray and transmission electron microscopy measurements, a chemical characterization of both binary Au-Ge catalysts and wetting layer is obtained at the nanoscale. We show that Ge vertical growth is achieved even without an external Ge supply.

Abstract: Heteroepitaxial growth of Ge nanowires was carried out on Si(111) substrates by MBE. Au seeds were used as precursor for the VLS growth of the nanowires. Even if the Au droplets do not act as catalyst for the dissociation of gas, they are local preferential areas where the energetic barrier of Ge nucleation is lowered compare to the remaining non activated surface. Two sets of Au seeds were used as precursors for the VLS process. The first set have an average diameter of 125 nm and the second of 25 nm. In-situ RHEED monitoring showed a Au wetting layer between these seeds before the nanowires growth as well as at the end of the Ge nanowires growth. It means that the wetting layer acted as a surfactant from the Si(111) surface to the Ge grown layer between the nanowires. Analysis of SEM images brought the fact that the diffusion of gold from the droplets on the surface and the sidewalls of the nanowires via the Ostwald ripening is a key parameter of the growth of the nanowires.

Abstract: Mn5Ge3 compound, with its room-temperature ferromagnetism and possibility to epitaxially grow on Ge, acts as a potential spin injector into group-IV semiconductors. It is shown that the realization of Ge/Mn5Ge3 heterostructures is highly hampered by Mn segregation toward the Ge growing surface. The Mn segregation length can be estimated in-situ and in real time by means of reflection high-energy electron diffraction. We present here an approach allowing to greatly reduce or even to prevent the Mn segregation, whose principle is based on filling the Mn5Ge3 lattice with interstitial carbon atoms. In addition, we show that interstitial carbon in Mn5Ge3 allows to enhance not only the Curie temperature of Mn5Ge3Cx layers but also in the whole Ge/Mn5Ge3/Ge heterostructures.

Abstract: Mn5Ge3 compound, with its room-temperature ferromagnetism and possibility to epitaxially grow on Ge, acts as a potential spin injector into group-IV semiconductors. However, the realization of Ge/Mn5Ge3 multilayers is highly hampered by Mn segregation toward the Ge growing surface. Here, we show that adsorption of some monolayers of carbon on top of the Mn5Ge3 surface prior to Ge deposition allows to greatly reduce Mn segregation. In addition, a fraction of deposited carbon can diffuse down to the underneath Mn5Ge3 layers, resulting in an enhancement of the Curie temperature up to $360 K. The obtained results will be discussed in terms of the formation of a C diffusion barrier by filling interstitial sites of Mn5Ge3 by carbon.

Abstract: We report on the Mn segregation and diffusion during the epitaxial overgrowth of Ge on Mn5Ge3/Ge(111) heterostructures. It is shown that the underneath Mn5Ge3 layers remain stabilized at the interface with the substrate while a small amount of Mn can leave the layers and floats at the Ge growth front. Mn can then act as a surfactant during Ge growth along the (111) orientation. The Mn segregation length and also the state of Mn atoms incorporated in the Ge layers are found to depend on the growth temperature. At a growth temperature of 250 °C, a segregation length of ~ 10 nm is observed and Mn atoms incorporated in the Ge layers are uniformly distributed. At 450 °C, segregated Mn atoms can react with Ge to form Mn5Ge3 clusters inside the Ge overgrown layer. Such Mn5Ge3 clusters display random orientations and induce modification of the magnetic anisotropy of the whole film.

Abstract: We examined the film morphologies and transistor properties of hetero-molecular bilayer consisting of N, N’-dioctyl-3, 4, 9, 10- perylenedicarboximide (PTCDI-C8) and quaterrylene. First, the structure and carrier conduction of PTCDI-C8 films were studied, followed by an analysis of the carrier accumulation process in a PTCDI-C8/quaterrylene hetero-bilayer transistor. Based on the displacement current measurement (DCM), we stress the potential of the hetero-bilayer for tuning carrier accumulation like carrier doping techniques in field-effect transistors.

Abstract: A molecular superlattice consisting of alternate layers of N,N′-dioctyl-3,4,9,10-perylenedicarboximide (PTCDI-C8) and quaterrylene was prepared by using an ultra-slow deposition technique. Film growth under equilibrium conditions with precise optimization of the substrate temperature enabled the layer-by-layer stacking of hetero-molecules at a single-layer level. The morphology of the films and the orientation of the molecules in each layer were analyzed by atomic force microscopy (AFM) and an X-ray reflection (XRR) technique.

Abstract: Organic thin film transistors (OTFT) based on N,N′-Bis(n-pentyl)terrylene-3,4:11,12-tetracarboxylic diimide (TTCDI-5C) with Al or Au top-contact electrodes were deposited on SiO2 (200 nm)/p-Si (0 0 1) substrates. Carrier mobility was examined as a function of temperature in the range from 50 to 310 K. Two distinct carrier transfer behaviours were observed: temperature independent behaviour below 150 K and thermally activated behaviour above 150 K. Activation energies presented values of 85–130 meV depending on the metal electrodes (Au, Al), which can be attributed to the carrier traps at the interface and the energy-level offset between the lowest unoccupied molecular orbital (LUMO) and the work functions of the respective metals.

Abstract: A n-type semiconductor molecule N,N’-Bis(n-pentyl)terrylene-3,4:11,12-tetracarboximide (TTCDI-5C) was synthesized. Theoretical calculations predict several advantages in electrical properties, including large adiabatic electron affinity and small reorganization energy. The molecule was deposited on SiO2 surfaces and the structure of the resultant thin film was studied. Grain size and thin film cristallinity improve as the temperature increases. Top-contact organic thin film transistors (OFETs) using TTCDI-5C as the semiconductor layer were fabricated using SiO2 as the gate dielectric. Values of charge carrier mobility up to 7.24x10–2 cm2V–1s–1 and current on/off ratios higher than 104 were obtained, demonstrating the potential of TTCD-5C for use in OFETs.

Abstract: Quaterrylene field-effect transistors FETs with top-contact Au electrodes were formed on a SiO2 200 nm / p-Si 001 substrate by an ultraslow vacuum deposition technique, and their carrier transport was investigated. The quaterrylene FETs showed typical p-channel transistor behavior. The dependence of carrier mobility on grain size, film thickness, and temperature was examined to gain insight into the transport mechanism. Carrier mobility increased with grain size, showing that carrier transport was limited by grain boundaries. Temperature dependence in the range from 300 to 60 K was divided into two distinct behaviors. Above 210 K, carrier mobility showed thermally activated behavior, with energies of 100–150 meV required to overcome the potential barriers at grain boundaries. In contrast, the conduction mechanism became tunnel-transfer-like below 210 K. In the low temperature range, tunnel transfer through potential barriers at grain boundaries predominated over the thermally activated type. The change in carrier mobility was correlated with film thickness. Carrier mobility rose sharply with increasing thickness in the two-dimensional 2D growth region, followed by saturation at 3 or 4 ML, where the growth process changed from 2D to three-dimensional mode. This result reveals that the first few layers of 2D growth work as an effective transistor channel. Enhancement in 2D growth in the vertical direction is crucial to improving carrier transport.

Abstract: We investigated the impact of interface modification by an octadecyltrichlorosilane self-assembled monolayer (OTS-SAM) on growth mode and transistor performance of quaterrylene thin films. Interface modification by OTS-SAM contributed effectively to stress-free film growth and highly molecular ordering, particularly in the initial layers, dramatically improving transistor performance. We found that the structural features in a few layers were key factors for determining the overall thin film growth mode and ameliorating carrier transport in organic field-effect transistors (OFETs). These results clearly demonstrated the effectiveness of interface engineering in the OFETs

Abstract: In this study, InP(1 0 0) surfaces were bombarded by argon ions in ultra high vacuum. Indium metallic droplets were created in well controlled quantities and played the role of precursors for the nitridation process. A glow discharge cell was used to produce a continuous plasma with a majority of N atomic species. X-ray photoelectron spectroscopy (XPS) studies indicated that the nitrogen combined with indium surface atoms to create InN thin films (two monolayers) on an In rich-InP(1 0 0) surface. This process occurred at low temperature: 250 C. Synchrotron radiation photoemission (SR-XPS) studies of the valence band spectra, LEED and EELS measurements show an evolution of surface species and the effect of a 450 C annealing of the InN/InP structures. The results reveal that annealing allows the crystallization of the thin InN layers, while the LEED pattern shows a (4 1) reconstruction. As a consequence, InN related structures in EELS and valence bands spectra are different before and after the annealing. According to SR-XPS measurements, the Fermi level is found to be pinned at 1.6 eV above the valence band maximum (VBM).

Abstract: This study deals with the growth mode of N,N '-dipenthyl-3,4,9,10-perylenetetracarboxylic diimide (PTCDI-5C) thin films from less than 1 monolayer to 23 monolayers thick. The effects of growth temperature and the thickness and nature of the substrates-SiO2 on Si(001) or octadecyltrichlorosilane (OTS) self-assembled monolayer terminated Si(001) surfaces-are discussed. Thin films were deposited from a homemade Knudsen cell by using a hot-wall deposition technique. Films were analyzed by atomic force microscopy, X-ray diffraction, and X-ray reflectivity. Films exhibited a (001) orientation with a 1.63 nm d spacing, and a metastable thin film phase was observed without any distinction of the nature of the substrate. However, differences were noticed in the early stages of growth: PTCDI-5C/SiO2 first monolayers presented a Stransky-Krastanov growth mode, whereas PTCDI-5C/OTS first monolayers showed a more complex mode with incomplete wetting of the substrate surface. Differences between the two morphologies softened as the film thickness increased.

Abstract: Quaterrylene molecules, which have a planar and highly π-conjugated chemical structure, were deposited on a SiO2 surface, and their thin film structures, including surface morphology and molecular orientation, were examined by atomic force microscopy (AFM) and X-ray diffractometry (XRD). AFM observations revealed the grain size and surface roughness to be closely dependent on the substrate temperature in the range from 27 °C to 200 °C. Particularly at a substrate temperature of 140 °C, grain sizes of up to 6 μm and low surface roughness of 1.67 nm were successfully obtained in the 8 ML-thick film. XRD measurements of the quaterrylene thin film revealed (0 0 l) Bragg reflections, corresponding to a spacing of 1.89 nm. This value coincides with the average height of the terraces of the stepped structure observed in the AFM images. These results clearly demonstrate the quaterrylene molecules to have an upright orientation and that thin films grow as layered structures on the surface. From the full width of half maximum (FWHM) of the XRD rocking curve, the degree of alignment of the molecular planes (mosaicity) was estimated to be 0.09°, which shows that the film has a highly ordered structure.

Abstract: Quaterrylene thin films were grown on a SiO2 surface at an ultralow flux rate using a vacuum deposition technique with a hot wall cell, and their detailed growth process was investigated. We discuss the influence of growth parameters such as substrate temperature, flux rate of molecules, and film thickness. Atomic force microscopy (AFM) observations revealed the presence of two different phases: one with a layered structure and the other with a fibrous structure. X-ray diffractometry (XRD) clarified the orientation of the molecules in each phase, which were lying down in the fibrous structure and standing up in the layered one. The fibrous structure appeared on the surface of the underlying layered structure at low substrate temperature and high flux rate, showing that the phase was formed under nonequilibrium conditions. On the other hand, the layered structure with an upright orientation grew consistently under equilibrium conditions of high substrate temperature and low flux rate. Next, the initial growth process was evaluated under optimized conditions. The films were found to evolve following a Stranski-Krastanov (S-K) mode. First, the films were grown two-dimensionally with a standing-up orientation up to 4 monolayers (ML) followed by three-dimensional (3D) island growth. This result showed 2D growth to be enhanced by ultraslow deposition. XRD measurement demonstrated that the c-lattice constant expanded in the 2D growth region but relaxed as film thickness increased up to 4 ML, eventually coinciding with that of the bulk crystal in the 3D growth region. These results indicate that molecules are subjected to compressive stress in the lateral direction in the 2D growth region, whereas the crystal lattice relaxes as the growth mode changes from the 2D growth to the 3D growth. We concluded that relaxation of the crystal lattice was the origin of the transformation of growth mode from 2D growth to 3D growth.

Abstract: The evolution of thin InN overlayer grown on InP (100) rich In substrate was investigated at room temperature by photoluminescence method versus the duration of nitridation process. The main important parameters were the duration of the process, and the angle of the reactive nitrogen flow. The nitridation was performed by a glow discharge source (GDS). The correlations between the electronic properties, gathered from photoluminescence (PL) measurements, and the chemical composition of InN–InP interfaces, derived from Auger electron spectroscopy (AES) were found. AES revealed that the nitridation process proceeds quickly in time showing self-limiting behavior. It is more effective for grazing nitrogen flux. The interface state density distributions, NSS(E), were determined via advanced computer-aided analysis of dependencies of band edge PL efficiency, YPL, versus excitation light intensity, Φ. The analysis showed that the substrates were well passivated with NSS(E) minima on the order of 5·1011 cm− 2 eV− 1. The nitrogen flux angle during the nitridation was found to have an influence on YPL(Φ) spectra. In all analyzed cases the grazing nitrogen flux generated the interface with slightly improved NSS(E) distribution. Finally, the behavior of YPL versus Φ and NSS(E) was precisely examined.

Abstract: This article investigates the nitridation effect of InP(100) semiconductor surfaces performed using a glow discharge cell. Auger electron spectroscopy and XPS were used to understand the different steps of this process. An important point is the initial quantity of metallic indium on the InP(100) surfaces. Indeed the indium droplets, created in well-known quantity, play the role of precursor. At a relatively low temperature of 523 K the system undergoes surface restructuring, which includes removal of the In droplets and the formation of two InN monolayers. Phosphorus-nitrogen bonds have been detected by the analysis of P LMM Auger peaks, and InN bonds by analysis of the In 4d XPS peak. However, the presence or not of metallic indium inside this InN overlayer is crucial for passivation of the substrate. Ex situ photoluminescence measurements correlated to the electron spectroscopies results have shown the good passivation effect of the InP(100) surfaces by InN overlayers for 40 min of nitridation.

Abstract: The nitridation of InP(1 0 0) surfaces has been studied using synchrotron radiation photoemission. The samples were chemically cleaned and then ion bombarded, which cleaned the surface and also induced the formation of metallic indium droplets. The nitridation with a Glow Discharge Cell (GDS) produced indium nitride by reaction with these indium clusters. We used the In 4d and P 2p core levels to monitor the chemical state of the surface and the coverage of the species present. We observed the creation of In–N and P–N bonds while the In–In metallic bonds decrease which confirm the reaction between indium clusters and nitrogen species. A theoretical model based on stacked layers allows us to assert that almost two monolayers of indium nitride are produced. The effect of annealing on the nitridated layers at 450 °C has also been analysed. It appears that this system is stable up to this temperature, well above the congruent evaporation temperature (370 °C) of clean InP(1 0 0): no increase of metallic indium bonds due to decomposition of the substrate is detected as shown in previous works [L. Bideux, Y. Ould-Metidji, B. Gruzza, V. Matolin, Surf. Interface Anal. 34 (2002) 712] studying the InP(1 0 0) surfaces.

Abstract: Auger electron spectroscopy (AES) was used to investigate the processes taking place during the initial stages of InP(100) surfaces nitridation. This AES study combined with electrical measurements (intensity–voltage) shows that the processes greatly differ depending on the nitridation angles. Results show that with grazing angle for nitrogen flow, the nitridation process is more efficient. Results obtained with AES spectra are coherent with electrical measurements: Hg/InN/InP(100) Schottky diodes present different electrical characteristics for the grazing and normal flow. The passivation effect of the nitride layers depends on the incident nitrogen angle flow.

Abstract: Electron inelastic mean free paths (IMFPs) in AuxNi1−x alloy samples (x=1, 2 and 5 at.%) were determined experimentally by elastic peak electron spectroscopy. In addition, we also explored the effect of the Au surface segregation in the determination of the IMFP. The measurements were performed with respect to a Ni standard (relative measurements) and without a standard material (absolute measurements). Two Monte Carlo (MC) algorithms were used to calculate the IMFPs. The energy dependence of the IMFP for alloy surfaces with both a nominal composition and enriched in Au up to not, vert, similar25 at.% was obtained in the electron energy range 200–2000 eV. The measured IMFPs were compared with IMFPs calculated from the TPP-2M predictive formula. It was found that the IMFPs for the studied alloys determined from absolute measurements were considerably lower than the calculated IMFP values and IMFPs determined from relative measurements as well. This deviation can be explained by the surface composition change since the experimental IMFPs depend considerably on the Au surface concentration in the low energy electron range 200–1000 eV.

Abstract: The nitrides of group III metals: AlN, GaN and InN are very important materials due to their applications for short wavelength opto-electronics (light-emitting diodes and laser diodes). It is essential for the realization of such novel devices to grow highquality nitride single crystals. In this paper, we report the first stages of the InP(1 0 0) surfaces nitridation in order to grow highquality nitride films. Indeed, the nitridation process is an important step in the growth of nitrides [J. Vac. Sci. Technol. A 17 (1999) 2194; Phys. Status Solidi A 176 (1999) 595]. Previous works [Synth. Met. 90 (1997) 2233; Appl. Phys. Lett. 63 (1993) 1957] have shown that in situ Arþ ions bombardment is useful on the one hand to clean the surface, and on the other hand to create droplets of metallic indium in well-controlled quantity. Then the indium metallic enrichment of the surface, monitoring by elastic peak electron spectroscopy (EPES) and Auger electron spectroscopy (AES) allows to prepare the III–V semiconductors surfaces to the nitridation step. The nitridated process has been performed with a high voltage plasma discharge cell and has been studied using quantitative Auger electron spectroscopy, elastic peak electron spectroscopy and electron energy loss spectroscopy (EELS), in order to optimize the conditions of InN layers formation.

Abstract: The present work tackles with the coupling of model neuron networks with functionalized silicon surfaces and the integration of nano field effect transistors to stimulate and record their activity (neuroFETs project).

Abstract: This work deals with the nitridation of the indium phosphide. Indium phosphide is a III-V semiconductor with some great potential applications in micro- and opto-electronic devices. The nitridation is a surface treatment used in crystal growth of heterosctucture such as InN/InP. A good knowledge of the surface state of InP(100) substrates is required for the study of nitridation process of InP(100). Electron spectroscopies like Auger electrons spectroscopy, X-ray electrons spectroscopy, electrons energy loss spectroscopy and elastic peak electron spectroscopy were used for this study. The effects of ionic argon bombardment –a key step before nitridation- and heating of the substrate up to a temperature of 250°C used for nitridation were investigated. Ionic bombardment entails the creation of metallic indium droplets which are 3D-2D transformed under the temperature. The nitridation is operated in an ultravacuum chamber. The InP sample is exposed to the nitrogen flow created by a glow discharge cell. Nitrogen species used the indium metallic droplets to formed InN. The effects of nitridation time and incident angle of nitrogen exposure were monitored. The nitride layers were found to be thicker for 40 minutes of nitridation with an grazing incident angle for impinging nitrogen. Actually annealing at 450°C of these InP(100) substrates covered by InN atomic monolayers was studied. The substrate did not present any significant damaging while the congruent evaporation temperature of InP is 370°C. Thus it showed that nitride film has a passivating effect.