Since 2009: Research scientist (CNRS) at Center for Interdisciplinary Nanoscience of Marseille, France 2004-2009: Research scientist (CNRS) at Lavoisier Institute of the University of Versailles, France 2003-2004: Assistant Professor at Ecole Nationale Superieure de Chimie de Paris, France 2002-2003: Post-doc at University of Provence, Marseille, France 2000-2002: PhD Thesis at Friedrich-Alexander-University-Erlangen-Nurnberg, Germany 1998-2000: PhD Thesis at Swiss Federal Institute of Technology Lausanne (EPFL), Switzerland
Abstract: Depending on the applied electrochemical parameters, various oxide films can be grown onto InP in aqueous media. In this work, two oxide layers have been grown in borate buffer solution at pH = 9 by applying a low (0.2 mA cm(-2)) or a high (30 mA cm(-2)) current density, but a similar coulometric charge. Capacitance-voltage measurements performed before and after the anodic processes have been made to investigate the electrical properties of new interfaces, while X-ray photoelectron spectroscopy (XPS) analysis and atomic force microscopy (AFM) observations were used to access to the chemical and topographic aspects of the two oxidized surfaces. It is demonstrated that AFM observations coupled with electrochemical and XPS measurements is a good probe for the study of thin oxide on InP. A correlation between the anodization parameters and the resulting electrical and morphological aspects of the anodic layers is clearly evidenced.
Abstract: In this paper we-report the pore formation onto n-InP (100) in acidic liquid ammonia at 223 K, by applying a constant current density of 2 mA.cm(-2). The evolution of the electrode potential and the pore morpholoty has been investigated in this uncommon non-aqueous medium. This solvent provides true water free and oxygen free consitions. Specific and reproducible electrochemical behaviour have been obtained. An original evolution of the porous structure has been observed by scanning electron microscopy. Tortuous current line oriented pores are formed. Pores are organized in hemispherical depressions and a multilayered structure is also evidenced. A three distinguished steps evolution has been established. In the first step, an insoluble passive layer is formed on surface, followed by the nucleation of the porous layer. The second phase corresponds to the formation of the, first porous layer; while the third stage corresponds to the periodic lift-off of the porous layer constituting thus a multilayered structure. (c) 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Abstract: In this paper, we report on the anodic behavior of n-InP (100) in acidic liquid ammonia at 223 K. Electrochemical, morphological and optical characterizations have been performed on InP after galvanostatic polarizations in different ranges. Prior to any dissolution processes, the formation of a stable anodic passivating thin film with a chemical composition close to "HN=P-NH2" (phosphinimidic amide) is observed. Depending on the current, two different phenomena occur: at low current density a thick amorphous film is formed, while tortuous current line oriented pores are grown when a high current is applied. For high coulometric charges, this last porous film can exhibit a multilayered structure. A decrease of the photoluminescence intensity without any peak shifts is observed whatever the applied current. This has been ascribed to the absorbent property of the layers.
Abstract: In this paper, we report selective electrochemical gold deposition onto p-type Si (1 0 0) into nanoscratches produced through a thin oxide layer using an atomic force microscope. A detailed description of the substrate engraving process is presented. The influence of the main scratching parameters such as the normal applied force, the number of scans and the scanning velocity are investigated as well as the mechanical properties of the substrate. Gold deposition is carried out in a KAu(CN)(2) + KCN solution by applying cathodic voltages for various durations. The gold deposition process is investigated by cyclic voltammetry. Reactivity enhancement at the scratched locations was studied by comparing the electrochemical behaviour of intact and engraved surfaces using a micro-electrochemical setup. Selective electrochemical gold deposition is achieved: metallic patterns with a sub-500 nm lateral resolution are obtained demonstrating, therefore, the bearing potential of this patterning technique.
Abstract: In this paper, a review on electrochemical porous etching of semiconductors is proposed. After a brief history, chemical and electrochemical etching of semiconductors are considered and the pore formation models are discussed. The influences of the key parameters on porous etching are illustrated by listing the numerous pore morphologies reported in the literature. A short inventory of typical applications in various fields is given in the conclusion.
Abstract: This work gives a short overview of recent electrochemical techniques that are employed to grow tin nanowires. After a brief description about patterning and templating methods, a novel protocol based on the formation of tin nanowires which are electrochemically grown on titania nanotube guide layers will be presented.
Abstract: For the first time, pore formation on n-InP(100) has been carried out by galvanostatic treatments in acidic liquid ammonia at 223 K. Voltage oscillations correlated to a specific current line oriented pore morphology have been evidenced by scanning electron microscopy. Whatever the anodic charge, a constant pore depth was formed (2-3 mu m). Porous layers have been characterized by ex situ photoluminescence measurements that have revealed a dead layer behavior. This work demonstrates the crucial role of interfacial phenomena illustrated by the use of this uncommon nonaqueous electrolyte. (c) 2007 The Electrochemical Society.
Abstract: In this paper we report on galvanostatic pore formation on both n-InP and n-GaAs in acidic liquid ammonia (223 K). Quantitative analyses by atomic absorption have revealed two different dissolution mechanisms (involving 6 or 8 holes) without secondary reaction. Electrochemical behaviours have also shown diverse evolutions. Potential oscillations were observed onto InP while a constant voltage is measured for GaAs. Distinguished pore morphologies observed by scanning electron microscopy have confirmed the different porosification processes. (c) 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Abstract: Porous structures have been anodically grown onto n-InP (100) in HCl. Surface chemistry and pore morphology have been respectively studied by X-ray photoelectron spectroscopy and scanning electron microscopy but in situ electrochemical investigations have been emphasized. Capacitance and photocurrent experiments have been performed while the porous etching occurred. No modifications of the electronic structure (flat band potential remains constant) are observed during the pore formation. However, for high dissolution charges, the photocurrent spectra are sharpened because the porous films behave like electrically "dead layers". (c) 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Abstract: The present work deals with semiconductor nano-patterning technique based on scratching an insulating layer using the tip of either a micro-indenter or an atomic force microscope. The insulating or masking layer can be a thin oxide film (10 nut thick) grown on a p-Si (100) or self-assembled organic monolayer covalently bound to a n-Si (111) surface. Electrochemical techniques are used for Cu deposition in the openings made by scratching through the masking layers. Engraving properties at both micro- and nanoscale are investigated. It is shown that under optimized deposition parameters selective and well-defined metallic structures onto Si surfaces can be produced with a lateral resolution in the several 100 nm range. (c) 2005 Elsevier B.V. All rights reserved.
Abstract: We demonstrate selective electrodeposition of Pd into atomic force microscopy (AFM) nanoscratches produced in thermal oxide covered p-type Si(100) without creating substantial damage in the silicon substrate. A 10 nm thick thermal SiO2 film was scratched about 5-7 nm deep with a diamond tip of an AFM. Then, etching in HF was used to remove uniformly 4-5 nm SiO2, thus to expose the Si within the nanoscratches while still maintaining an oxide layer on the rest of the surface. Pd was selectively electrodeposited into these scratches. The underlying silicon exhibits no significant damage induced by scratching. (C) 2004 The Electrochemical Society.
Abstract: The present work investigates the fabrication of Au nanostructures using the masking effect of carbon patterns deposited by the electron-beam (E-beam) of a scanning electron microscope for electrochemical reactions. E-beam induced deposition is based on the decomposition of residual hydrocarbon species (molecules from the pump oil) to create a solid deposit at the point of impact of the E-beam. Subsequently, such E-beam deposited matter is used to completely block the electrochemical deposition of Au in the nanometer scale. In this work, several factors affecting the resolution of the process are studied. Electrochemical conditions as well as control of the E-beam C-deposit are investigated to optimize the lateral resolution of the process. Especially, it is demonstrated that the beam energy used for depositing the C-mask plays a crucial role in fabricating Au nanostructures in the sub-50 nm range. (C) 2004 The Electrochemical Society.
Abstract: Anodic oxide films were galvanostatically grown on n-InSb(1 0 0) surfaces at various pH in sodium hydroxide (0.1 M NaOH, pH = 13), borate buffer (0.075 M Na2B4O7 + 0.3 M H3BO3, pH = 8.4) and phosphate buffer (0.3 M NH4H2PO4, pH = 4.4). Thickness, composition and morphology of the oxide films were determined by various surface analytical techniques such as Auger electron spectroscopy, X-ray photoelectron spectroscopy, scanning and transmission electron microscopy and atomic force microscopy. The oxides comprise mainly In2O3 and Sb2O3 and the oxide thickness increases with pH. Electrical properties of oxides indicate that the films may be useful as insulators in some device applications. (C) 2004 Elsevier Ltd. All rights reserved.
Abstract: Gel polymer electrolyte (GPE) membranes based on two polymers, the polyethylene oxide (PEO) and a copolymer of polyvinylidene fluoride-hexafluoropropylene (PVdF-HFP), and a plasticizer, the dibutylphthalate (DBP), were elaborated in two ways. First, the polymers and the plasticizer were mixed together to obtain a single membrane. Second, a bilayer separator membrane was made by adjunction, through lamination, of a DBP plasticized PVdF-HFP film and a homemade DBP-PEO thin film. The physicochemical properties of the gels were analyzed. AC impedance spectroscopy was carried out on symmetric Li/GPE/Li cells using either the single layer or bilayer membrane as a function of aging (isothermal at 20 and 70degreesC), temperature (-40 to 70degreesC), and finally, galvanostatic cell polarization. Both GPE membranes exhibit high ionic conductivities, but the most spectacular result was the measured decrease in the interface resistance, indicative of a deep modification of the interface Li/GPE when the cells were polarized. Aside from having a good interface with the Li metal electrode, such membranes were also shown to form good interfaces with the cathode because assembled Li/GPE/Li4Ti5O12 flat cells were able to sustain, at room temperature, more than 80% of their initial capacity for more than 300 cycles. (C) 2004 The Electrochemical Society.
Abstract: The present work describes direct porous silicon patterning based on electron-beam induced carbon deposition used as a mask against pore formation on Si. Under ideal conditions the C-deposits act as a negative resist to suppress completely and selectively the formation of light emitting porous Si at treated locations. Carbon patterns were written at different electron doses on p-type Si(100) surfaces. Subsequently by contamination writing in a scanning electron microscope the silicon surface was porosified by galvanostatic experiments in a 20% HF solution. The carbon masks as well as the etched surface were characterized by scanning electron microscopy and Raman spectroscopy. The selectivity of the technique depends on several factors such as the electron dose during masking and the electrochemical parameters. Under conditions typical for porous silicon formation, already a relatively low electron dose is sufficient to achieve the desired mask effect to produce patterned porous silicon structures. (C) 2002 Elsevier Science B.V. All rights reserved.
Abstract: The present work deals with anodization processes of n-type InSb(100). Preferential etching of InSb can be electrochemically initiated in HCl, HBr and HF solutions. Except for etch features also the formation of porous layers can be observed. The resulting features were characterized by SEM and AES measurements. Due to the narrow bandgap of the material the results of the anodization process are neither sensitive to illumination of the n-type material nor to the doping level. The morphology of the attack depends strongly on the electrochemical conditions and the type of halogen acid present in the electrolyte. In HCl and HBr a black porous layer can be formed that is likely to consist to a certain extent of an antimony-oxo-chloride or antimony-oxo-bromide. In HF, however, polarization under a wide range of electrochemical conditions leads to a uniform etching of the InSb surface.
Abstract: The present work investigates the selective electrochemical deposition of palladium nano-structures into scratches produced through thin oxide layers covering p-Si (1 0 0) surfaces. Using an atomic force microscope equipped with a single-crystalline diamond tip scratches in the 100 nm range were produced through a 10 nm thick dry oxide layer. Pd deposition was carried out in PdCl2 (0.01 g l(-1)) + HCl (0.1 M) by cathodic potential steps. Investigation of the palladium nucleation and growth processes onto silicon surfaces is presented. Under optimized Conditions sub-100 mm palladium structures call be obtained with a very high selectivity. (C) 2003 Elsevier Ltd. All rights reserved.
Abstract: The present work investigates the masking effect of carbon contamination patterns deposited by the electron-beam (E-beam) of a scanning electron microscope (SEM) for metal electrodeposition reactions. Carbon contamination lines were written at different electron doses on n-type Si(100) surfaces. Subsequently Au was electrochemically deposited from a 1 M KCN + 0.01M KAu(CN)(2) solution on the E-beam treated surface sites. The carbon masks as well as the Au deposits were characterized by SEM, atomic force microscopy, and scanning Auger electron spectroscopy. We demonstrate that carbon deposits in the order of 1 nm thickness can be sufficient to achieve a negative resist effect, i.e., can block the electrodeposition of Au completely selectively. The lateral resolution of the process is in the sub-100 nm range. The nucleation and growth of Au deposits and their morphology as well as the selectivity and resolution of the process depend on several factors such as the electron dose during masking, and the applied potential and polarization time during Au deposition. The process opens new perspectives for selective electrodeposition, i.e., for high definition patterning of surfaces with a wide range of materials. (C) 2001 The Electrochemical Society.
Abstract: Carbon patterns were deposited on Si(100) by electron beam-induced contamination decomposition. The feasibility of using such patterns as a mask for a subsequent electrochemical deposition of Au is studied. We demonstrate that under optimized electrochemical conditions electrodeposition of Au can be blocked selectively by single line carbon deposits in the order of only 1 nm thickness. The lateral resolution of this negative patterning process is in the sub 100 nm range. The principle opens perspectives for high definition patterning of semiconductor surfaces by selective electrodeposition. (C) 2001 American Institute of Physics.
Abstract: The present work investigates the use of carbon masks, deposited on n-type Si(100) surfaces in a scanning electron microscope (SEM), for electrochemical nanopatterning. Carbon contamination lines were written at different electron doses on the n-type Si(100) surfaces and characterized by AFM. Subsequently, deposition of US was carried out by electrodeposition of Cd from a 1 mM CdF2 + 0.05 M NaF solution followed by a chemical treatment in 1 M Na2S. US deposits were prepared under various electrochemical conditions and were characterized by SEM, scanning Auger electron spectroscopy and optical techniques including fluorescence and photoluminescence measurements. It is demonstrated that under optimized electrochemical conditions carbon deposits of less than 1 nm thickness and in a width of 100 nm range can act as a negative resist, i.e. can block the deposition of US completely and selectively and thus can be used for nanopatterning. (C) 2001 Elsevier Science Ltd. All rights reserved.
Abstract: In this. study, we investigate the possibilities of selectively electrodepositing Cu on surface defects created in p-type and n-type Si(100) by scratching the surface with the tip of an atomic force microscope (AFM). Nanosized grooves were produced on Si surfaces with a diamond-coated AIM tip at heavy forces. Cu was electrodeposited on these grooved surfaces from a 0.01 M CuSO4 + 0.05 M H2SO4 electrolyte under various conditions. The results clearly show that defects created on H-terminated p-type Si(100) lead to an enhanced reactivity, i.e., preferential Cu deposition at such defects is possible. However, a much higher degree of selectivity of the deposition is obtained if AFM-induced grooves are produced on surfaces that carry a native oxide layer. The masking effect of this insulator film is demonstrated by selective Cu electrodeposition into scratches on oxide-covered p- and n-type silicon. After an optimization of electrochemical parameters, we achieved the deposition of uniform and well-defined nanostructures. The process presented here opens new perspectives for selective electrodeposition and direct patterning of Si surfaces. (C) 2001 The Electrochemical Society.
Abstract: We demonstrate selective electrodeposition of Cu into nanoscratches produced in native oxide covered p-type and n-type Si(100). Nanosize. grooves were produced with a diamond-coated atomic force microscope tip at heavy forces. Onto these grooved surfaces, Cu was electrodeposited from a 0.01 M CuSO4+0.05 M H2SO4 electrolyte under various conditions. The results clearly show that these scratches represent activated sites for metal electrodeposition-the surrounding intact oxide layer acts as a highly efficient mask. After optimization of electrochemical parameters, we were able to achieve the deposition of uniform and well-defined structures with a lateral resolution in the 100 mn range. In general, the process opens alternate perspectives for selective electrodeposition and direct patterning of Si surfaces. (C) 2001 American Institute of Physics.
Abstract: The present work deals with localized dissolution processes of n-type InP(100). pore growth call be electrochemically initiated on the n-type material in the dark in HCl HBr and HF solutions and leads after extended polarization to the formation of a porous InP structure. The porous structures were characterized by SEM, AES, and PL measurements. The pore morphology depends strongly on the electrochemical conditions and the type of halogen acid present in the electrolyte. AES depth profiles show that the composition of the porous layer is strongly affected by the electrolyte. For all electrolytes depletion of In was observed; this effect is the strongest for HBr and the weakest for IIE Uptake of electrolyte anions is the highest for HBr and lowest for HE From scratch experiments it is clt al that the pole initiation process is strongly influenced by surface defects. The morphology of the dissolution process also strongly depends on illumination as assessed by an experiment using a laser beam for a local surface illumination. At high illumination intensity, electropolishing instead of port: formation takes place. The finest pore structure was obtained in the dark. Structures for mcd in HF show visible photoluminescence in the yellow to red range of the spectrum, whereas fur HCl and HBr treated samples no significant visible PL was obtained.
Abstract: The present work investigates the behavior of InSb (100) in 0. 1 M KOH with and without addition of halogen ion species in the electrolyte. In the absence of halogen-ion species, a compact oxide layer can be formed. The thickness, composition and morphology of the oxide layers were examined as a function of the applied potential. The results indicate that the anodic oxidation of InSb essentially shows a valve metal-like behavior. Up to several tens of volts, a thick oxide layer can be grown that is of a high quality. In the presence of halogen ions, breakdown of the oxide film occurs at very low applied voltages leading to localized corrosion of the InSb. The effect of different anions F-, Cl-, Br- and their concentration were studied. The results show a behavior that is very similar to pitting corrosion of metals.
Abstract: AFM-scratching was performed through thin oxide layer which was either a native oxide layer, (1.5-2 nm thick) or a thermal oxide layer (10 nm thick). Due to their insulating properties, the SiO2 films act as masks for the metal electrochemical deposition. In the scratched openings copper deposition can take place selectively and thus nano-scale metal lines could be successfully plated onto the p-type silicon substrates. Using particularly, if sufficiently thick thermal oxide has advantages over the native oxide, it allows a H-termination of the Si within the grooves (HF treatment) without eliminating the oxide layer on the rest of the surface.
Abstract: The present study follows up on previous work that has demonstrated that electron-beam (E-beam) induced carbon deposition can be used as a negative resist for electrodeposition of metals on semiconductor surfaces. The E-beam activates the reaction of the residual hydrocarbon molecules issued from the pump oil in scanning electron microscope (SEM) chamber to form a deposit with mechanical and electrical properties close to diamond (i.e: the deposits are electrically insulating). Carbon deposits in the order of 1 nm thickness are sufficient to block an electrodeposition reaction of materials completely selectively and thus can be used for high definition patterning of semiconductor surfaces in the 1-100 nm range. In the present work we demonstrate how to use C-masks for porous silicon patterning, Le: to use contamination writing in a SEM to suppress selectively the pore formation process at treated locations.
Abstract: Nowadays most of the fabrication processses used in semiconductor industry are based on photolithographic techniques. Although the high level of performance, these methods exhibit two main drawbacks: the resolution limit and the numerous steps. Therefore a great deal of interest has recently appeared for âdirectâ structuring techniques, i.e., processes excluding the use of asensible resist layer in order to improve the resolution limits and supress steps in the fabrication process. The present work investigates therefore a new âdirectâ patterning method based on selective metal electrochemical deposition onto silicon surfaces induced by nanometer scaled scratches created using an atomic force microscope (AFM) equipped with hard tips such as diamond coated silicon tip and single-crystalline diamond tip. The first step of this process consists of creating the nano-scratches using an AFM in order to initiate the metal deposition. The influence of the scratching parameters on the groove morphology is firstly investigated. As expected when the normal applied force and the number of cycles (n) are increased the grooves sizes increases and the linear evolution of the scratch dimensions with n indicates that the material removal follows a layer by layer mechanism. No effect of the scanning velocity on the groove topography is detected. The thickness of the oxide layer present on the surface (native or thermal oxide) has a non negligible influence on the groove morphology. A better wear resistance is observed for the single-crystalline diamond tips than for the diamondcoated tips. Therefore nanometer scaled grooves with a controlled and reproducible geometry are obtained with the bulk diamond probes. The second step is the selective metal electrochemical deposition onto Si surfaces. The Cu and Pd depositions onto p-Si were studied. It appeared that nucleation and growth occur according to the Volmer â Weber mechanism. These investigations led therefore to an optimization of the plating conditions. Electrochemical analysis such as micro-electrochemistry and capacitance measurements were performed onto H-terminated Si surfaces in order to prove the reactivity enhancement at the scratched locations. Micro-capillary experiments were carried out to probe the electrochemical behavior of the scratched surfaces without any contribution from the native defects of the p-Si (100) wafers. The results clearly demonstrate that a higher cathodic current density is always observed for the scratched surfaces indicating therefore an activating effect of the grooves. The determination of the surface states density by capacitance measurements has also pointed out that the surface states density is higher in the case of scratched surface. After demonstration of the total selectivity of the process for Cu deposition onto AFM scratched Si surfaces covered by the native oxide layer, an optimization of the process consisted of scratching the surface through thin thermal oxide films also used as mask for electrodeposition. Three different metals were thus selectively deposited (Cu, Pd and Au) on both p- and n-type silicon. After optimization of the electrochemical parameters sub-100 nm metallic structures were achieved and the selectivity of the process was confirmed by chemical analysis performed by Auger electron spectroscopy.
