Jackie Vigneron

Modification of TiO2 by Bimetallic Au-Cu Nanoparticles for Wastewater Treatment

Au, Cu and bimetallic Au-Cu nanoparticles were synthesized on the surface of commercial TiO2 compounds (P25) by reduction of the metal precursors with tetrakis (hydroxymethyl) phosphonium chloride (THPC) (0.5 % in weight). The alloyed structure of Au-Cu NPs was confirmed by HAADF-STEM, EDS, HRTEM and XPS techniques. The photocatalytic properties of the modified TiO2 have been studied for phenol photodegradation in aqueous suspensions under UV-visible irradiation. The modification by the metal nanoparticles induces an increase in the photocatalytic activity. The highest photocatalytic activity is obtained with Au-Cu/TiO2 (Au/Cu 1:3). Their electronic properties have been studied by time resolved microwave conductivity (TRMC) to follow the charge-carrier dynamics. TRMC measurements show that the TiO2 modification with Au, Cu and Au-Cu nanoparticles plays a role in charge-carrier separations increasing the activity under UV-light. Indeed, the metal nanoparticles act as a sink for electron, decreasing the charge carrier recombination. The TRMC measurements show also that the bimetallic Au-Cu nanoparticles are more efficient in electron scavenging than the monometallic Au and Cu ones.

Electrocrystallization Mechanism of Cu–In–Se Compounds for Solar Cell Applications

Chalcogenide semiconductors, such as CuInSe 2 , are promising materials for optoelectronic applications such as solar cells. Conversion efficiencies up to 14% based on Cu-In-Se layers electrodeposited have been achieved. However, the electrocrystallization of this multinary system, whose components exhibit different electrochemical and chemical properties, is a complex process. In the present work, the electrocrystallization mechanism of CuInSe 2 is investigated in dilute acidic solutions by in situ electrochemical investigation (polarization, electrochemical quartz crystal microbalance, and impedance spectroscopy) and ex situ chemical and structural analyses. A detailed X-ray photoelectron spectroscopy analysis is carried out to determine the surface composition and the chemical environment of the elements. Marked differences between surface and bulk concentrations are evidenced. At low polarizations, binary Cu-Se phases are obtained, which facilitate the reduction of Se(IV) species into elemental selenium. An intermediate CuSe 2 phase is formed which, in turn, enables the incorporation of indium beyond a potential threshold close to -0.6 V/mercurous sulfate electrode. In this potential zone, major transitions are observed in composition, morphology, structure, and electrochemical behavior. A reaction path is proposed, which accounts for the main experimental observations. It emphasizes the role of surface reactions, occurring via passivating and nucleation sites, in the incorporation of indium.

Studies of buried interfaces Cu(In,Ga)Se2/CdS XPS and electrical investigations

The formation of interface Cu(In,Ga)Se2/CdS in solar cells is not yet well understood but seems to be the key to further improvements of their performance. This interface depends on many parameters such as the initial chemical state of the CIGS surface or the chemical bath deposition conditions used to grow the CdS layer. In this paper, we focus our attention on the CIGS/CdS hetero-interface at different stages of its formation using mainly XPS studies of buried interfaces which were studied after gradual sputtering. We have investigated interfaces on CIGS submitted to various surface treatments, analogue to those involved in fabrication steps (NH3 dipping…). Kelvin probe and admittance spectroscopy measurements have been also performed on several interfaces prepared in the same conditions to correlate the chemical composition with the electrical response of the buried interfaces.

XPS and electrical studies of buried interfaces in Cu(In,Ga)Se2 solar cells

The active interface of Cu(In,Ga)Se2 solar cells is the key to further improvements of their performance. The formation of this interface is not yet well understood. It depends on the initial state of the CIGS layer, then on the evolution of the interfacial chemistry during the CdS deposition. We present a contribution to its understanding using XPS studies at different steps of the interface formation. Attention has been brought to the surface preparation and to the buried interface CIGS/CdS. Buried interfaces were studied after gradual sputtering. Well-resolved spectra have been obtained. We aimed at a clarification of the role of the various segregated/intermixed phases at the interface. To achieve this, admittance spectroscopy and Kelvin probe measurements have been performed on the same devices to correlate the chemical composition to the electrical responses associated with the buried interface.

Laboratory analogues simulating Titan's atmospheric aerosols: Compared chemical compositions of grains and thin films

Two sorts of solid organic samples can be produced in laboratory experiments simulating Titans atmospheric reactivity: grains in the volume and thin films on the reactor walls. We expect that grains are more representative of Titans atmospheric aerosols, but films are used to provide optical indices for radiative models of Titans atmosphere. The aim of the present study is to address if these two sorts of analogues are chemically equivalent or not, when produced in the same N2-CH4 plasma discharge. The chemical compositions of both these materials are measured by using elemental analysis, XPS analysis and Secondary Ion Mass Spectrometry. The main parameter probed is the CH4/N2 ratio to explore various possible chemical regimes. We find that films are homogeneous but significantly less rich in nitrogen and hydrogen than grains produced in the same experimental conditions. This surprising difference in their chemical compositions could be explained by the efficient etching occurring on the films, which stay in the discharge during the whole plasma duration, whereas the grains are ejected after a few minutes. The higher nitrogen content in the grains possibly involves a higher optical absorption than the one measured on the films, with a possible impact on Titans radiative models.

Modification of a cyclo-olefin surface by radio-sterilization: Is there any effect on the interaction with drug solutions?

A cyclo-olefin copolymer was subjected to an e-beam ionizing treatment. Two doses were studied: one corresponding to the recommended dose for the sterilization of pharmaceutical packaging (25 kGy), and a greater one to enhance the modifications caused by the treatment (150 kGy). The surface modifications were studied by X-ray photoelectron spectroscopy (XPS), contact angle measurements and atomic force microscopy (AFM). The roughness and the wettability of the surface were enhanced by the treatment. The consequences of the surface modifications on the drug interaction with the polymer were studied.

Towards a better understanding of the use of additives in Zn(S,O,OH) deposition bath for high efficiency Cu(In,Ga)Se2-based solar cells

CBD-Zn(S,O,OH) remains one the most studied and promising Cd-free buffer layer for Cu(In,Ga)Se2-based solar cells, and has already demonstrated its potential to lead to high-efficiency solar cells. However Zn(S,O,OH) deposition time and metastable behavior of the final devices remain critical to outperform CdS-based devices. The aim of this work is to study and understand the influence of additives such as H2O2 on the deposition bath and on the surface of the absorber. These results will be related with final performances of the devices. A new promising additive, persulfate S2O82-, will be presented and could be the key to go beyond CdS-based solar cell records.

Chemical engineering of self-assembled Alzheimer's peptide on a silanized silicon surface.

The aim of this work is to develop a sensitive and specific immune-sensing platform dedicated to the detection of potential biomarkers of Alzheimers disease (AD) in biological fluids. Accordingly, a controlled and adaptive surface functionalization of a silicon wafer with 7-octenyltrichlorosilane has been performed. The surface has extensively been characterized by atomic force microscopy (AFM; morphology) and X-ray photoelectron spectroscopy (XPS; chemical composition) and contact angle measurements. The wettability of the grafted chemical groups demonstrated the gradual trend from hydrophilic to hydrophobic surface during functionalization. XPS evidenced the presence of silanes on the surface after silanization, and even carboxylic groups as products from the oxidation step of the functionalization process. The characterization results permitted us to define an optimal protocol to reach a high-quality grafting yield. The issue of the quality of controlled chemical preparation on bioreceiving surfaces was also investigated by the recognition of one AD biomarker, the amyloid peptide Aβ 1-42. We have therefore evaluated the biological activity of the grafted anti Aβ antibodies onto this silanized surface by fluorescent microscopy. In conclusion, we have shown, both qualitatively and quantitatively, the uniformity of the optimized functionalization on slightly oxidized silicon surfaces, providing a reliable and chemically stable procedure to determine specific biomarkers of Alzheimer disease. This work opens the route to the integration of controlled immune-sensing applications on lab-on-chip systems.

Cross strategy of surface and volume characterizations of chalcogenides thin films: Practical case of CIGS absorbers

Photovoltaic cells based on chalcogenides CIGS (Cu(In, Ga)Se2) thin films are a very promising technology. To improve cells performances, a fine optimization of the CIGS absorber properties is needed. Hence, we developed a cross strategy method combining the surface, volume and specific interfaces of the final device characterizations. These features deal with a large panel of physico-chemical techniques for the chemical composition (XPS, EDS, ICP-OES, GD-OES, AES), the morphology (SEM, AFM) and the optical parameters (spectroscopic ellipsometry) determination. This article demonstrates the crucial interest of this cross strategy on CIGS absorbers and focus on the accuracy and complementarities of each technique.

Interface Defects in CIGS-Based Solar Cells From Coupled Electrical and Chemical Points of View

Chemistry of co-evaporated CIGS surfaces submitted to chemical treatments relevant to fabrication steps were investigated by XPS and admittance spectroscopy. A Se XPS signal specific of the CIGS surfaces was identified. Surface states seen by Admittance and surface chemistry are seen to change significantly during the elaboration steps. Consequences for device elaboration are briefly discussed.