Electronic mechanism of ion expulsion under UV nanosecond laser excitation of silicon: Experiment and modeling

We present experimental and modeling studies of UV nanosecond pulsed laser desorption and ablation of (111) bulk silicon. The results involve a new approach to the analysis of plume formation dynamics under high-energy photon irradiation of the semiconductor surface. Non-thermal, photo-induced desorption has been observed at low laser fluence, well below the melting threshold. Under ablation conditions, the non-thermal ions have also a high concentration. The origin of these ions is discussed on the basis of electronic excitation of Si surface states associated with the Coulomb explosion mechanism. We present a model describing dynamics of silicon target excitation, heating and harge-carrier transport

A Surface Enhanced Raman Spectroscopy study of aminothiophenol and aminothiophenol-C60 self-assembled monolayers: evolution of Raman modes with experimental parameters

International audienceP-aminothiophenol (PATP) is a well known molecule for the preparation of self-assembled monolayers on gold via its thiol functional group. After adsorption, it has been demonstrated that this molecule is anchored to gold through its thiol group, and standing nearly upright at the surface with the amino functional group on top. This molecule has been extensively studied by Surface Enhanced Raman Spectroscopy but its exact SERS spectrum remains unclear. Here we demonstrate that it can be strongly affected by at least two experimental parameters: laser power and layer density. Those features are discussed in terms of a dimerization of the PATP molecules. The free amino group affords the adsorption of other molecules, like C60. In this case, a complex multilayer system is formed and the question of its precise characterisation remains a key point. In this article, we demonstrate that surface enhanced Raman spectroscopy combined with X-Ray photoelectron spectroscopy can bring very important information about the organisation of such a self-assembled multilayer on gold. In our study, the strong evolution of Raman modes after C60 adsorption suggests a change in the organisation of aminothiophenol molecules during C60 adsorption. These changes, also observed when the aminothiophenol layer is annealed in toluene, do not prevent the adsorption of C60 molecules

Interaction des photons UV avec le silicium massif et nanocristallin

In FrenchInternational audienceThe studies of interaction of the UV photons with bulk and nanocristalline silicon by time-of-flight (TOF) mass-spectrometry allowed to reveal two populations of Si ion monomers. The first rapid population ejected even at low laser fluences is attributed to Colombian repulsion between the surface charges which are induced by emission of the photoelectrons. When the laser fluence increases, the second slow ion population appears. This population originates from the thermal processes in the irradiated material. The original result of this work is the observation of the non-thermal ion population which represents a considerable part of the laser-induced plume.L'étude de l'interaction entre photons UV et le silicium massif et nanocristallin par spectrométrie de masse à temps de vol permet de distinguer deux populations de monomères ioniques Si+. Une population rapide est éjectée dès les faibles fluences laser, dont l'origine est attribuée aux répulsions Coulombiennes entre les charges de surface créées par l'émission de photo-électrons. Alors que la fluence d'irradiation est augmentée, une population plus lente apparaît issue de phénomènes thermiques initiés dans le matériau irradié. La mise en évidence d'une population ionique non thermique qui constitue une part importante des ions présents dans la plume laser est un résultat original de cette étude

Growth and organization of (3-Trimethoxysilylpropyl) diethylenetriamine within reactive amino-terminated self-assembled monolayer on silica

Alkane chains are the most commonly used molecules for monolayer fabrication. Long chains are used for their strong van der Waals interactions inducing good layer organization. Amine function-terminated alkyl chains are of great interest and are widely used for further surface functionalization. Since it is mandatory that such layers be organized to provide amine moieties at the surface, the present study deals with exploring amine-terminated SAM formation as an alternative to the usual aminopropylalkylsilane SAM. Additionally, using a long NH2terminated alkyl chain allows the formation of hydrogen bonding thanks to the two NH moieties born along the chain. Furthermore, such hydrogen bonding makes possible to shorten the molecule length while preserving a well-organized monolayer. For this purpose we performed a complete study of the grafting of (3-Trimethoxysilylpropyl) diethylenetriamine (DETAS) on native silicon oxide using various solvents, relative humidity and temperature values. Grafting kinetics was monitored by ellipsometry and goniometry, and SAM structure and organization using AFM and ATR-FTIR spectroscopy. Hydrogen bonding was evidenced within the SAM growth process and in the final complete SAM. We believe such study enables a better control of good quality DETAS SAM in order to improve their efficiency in further surface functionalization applications

Grafting a homogeneous transition metal catalyst onto a silicon AFM probe: a promising strategy for chemically constructive nanolithography

International audienceWe report a novel approach to chemically selective lithography using an atomic force microscope (AFM) probe with immobilized homogeneous catalyst, potentially giving access to diverse nanoscale transformations of the surface-bound functional groups. This new concept was proven for the local epoxidation of an alkene-terminated self-assembled monolayer on silicon using H2O2 as an oxidant and a catalytic silicon AFM tip charged with manganese complexes with 1,3,7-triazacyclononane type ligands

Influence of Molecular Organization on the Electrical Characteristics of {\pi}-conjugated Self-assembled Monolayers

Two new thiol compounds with {\sigma}-{\pi}-{\sigma} structure were synthesized and self-assembled on gold substrates. The morphology and the structural characterization of SAMs assessed by infrared spectroscopy, contact angle, XPS, electrochemistry and scanning tunneling microscopy (STM) show the formation of monolayers. SAMs with a terthiophene (3TSH) core as conjugated system are much better organized compared to those with a naphthalene carbodiimide (NaphSH) core as demonstrated by the cyclic voltammetry and STM studies. The surface concentration of 3TSH and NaphSH is respectively three and six times lower than ordered SAMs of pure alkyl chains. A large number of I/V characteristics have been studied either by STS measurements on gold substrates or by C-AFM on gold nanodots. Transition Voltage Spectroscopy (TVS) was used to clearly identify the transport in these partially organized monolayers. The chemical nature of the conjugated system, donor for 3TSH and acceptor for NaphSH, involves an opposite rectification associated to the asymmetrical coupling of the molecular orbitals and the electrodes. The conductance histograms show that the 3TSH junctions are less dispersed than those of NaphSH junctions. This is explained by a better control of the molecular organization in the molecular junctions.Comment: Full paper with supporting informatio

A História da Alimentação: balizas historiográficas

Os M. pretenderam traçar um quadro da História da Alimentação, não como um novo ramo epistemológico da disciplina, mas como um campo em desenvolvimento de práticas e atividades especializadas, incluindo pesquisa, formação, publicações, associações, encontros acadêmicos, etc. Um breve relato das condições em que tal campo se assentou faz-se preceder de um panorama dos estudos de alimentação e temas correia tos, em geral, segundo cinco abardagens Ia biológica, a econômica, a social, a cultural e a filosófica!, assim como da identificação das contribuições mais relevantes da Antropologia, Arqueologia, Sociologia e Geografia. A fim de comentar a multiforme e volumosa bibliografia histórica, foi ela organizada segundo critérios morfológicos. A seguir, alguns tópicos importantes mereceram tratamento à parte: a fome, o alimento e o domínio religioso, as descobertas européias e a difusão mundial de alimentos, gosto e gastronomia. O artigo se encerra com um rápido balanço crítico da historiografia brasileira sobre o tema

Auto-assemblage de macrocycles conjugués sur surfaces d'or et d'oxyde de silicium

Ce travail de thèse a été consacré à l étude du greffage et de l arrangement de macrocycles conjugués tels que : les protoporphyrines (FePP, ZnPP) et une phtalocyanine de zinc octacarboxylée (ZnPc(COOH)8) sur deux types de surfaces : or et oxyde de silicium. Les couches ont été obtenues par adsorption spontanée des molécules en solution sur le substrat, puis caractérisées par ellipsométrie, mesure d angle de contact, spectroscopie UV-Visible, ATR-IRTF, SERS et par microscopie champ proche AFM, STM. Dans une première partie, les macrocycles ont été déposés directement sur le substrat d or. Les couches obtenues sont formées de molécules agglomérées. Il a été montré que la taille de ces agglomérats était directement liée aux conditions de solvatation des molécules lors du dépôt. D autre part, nous avons observé un arrangement différent entre les macrocycles au sein de ces agglomérats suivant la nature de l ion métallique. Dans une seconde partie, les dépôts ont été réalisés par voie chimique à partir d une surface pré-fonctionnalisée par des groupements amines. Nous avons observé que les macrocycles s adsorbent sur la surface par interactions électrostatiques issues de la formation d un carboxylate d ammonium. Dans le cas des protoporphyrines, on note un dépôt inhomogène contrairement à la phtalocyanine de zinc octacarboxylée qui présente une organisation compacte et ordonnée favorisée par l existence d interactions hydrogènes entre les groupements carboxyliques placés sur l ensemble de la périphérie du cycle. Par ailleurs, l utilisation d un catalyseur (CDI) a permis la formation d une liaison covalente de type amide entre les molécules et la surface, observée par IRTF. La caractérisation de ces couches a montré que les macrocycles de zinc se déposaient relativement perpendiculaires à la surface alors que la protoporphyrine de fer s oriente d avantage à plat sur la surface du fait d interaction entre l atome de fer et les groupements amines. Cette dernière méthode de greffage réalisée à la fois sur or et oxyde de silicium s est révélée être peu dépendante de la nature du substrat et peut donc être facilement transposable à d autres types de surface.AIX-MARSEILLE3-BU Sc.St Jérô (130552102) / SudocSudocFranceF

Nano-agrégats de silicium et de germanium préparés par ablation laser (Elaboration et propriétés électroniques)

AIX-MARSEILLE2-BU Sci.Luminy (130552106) / SudocSudocFranceF