Thermal and mechanical properties of the near-surface layers of comet 67P/Churyumov-Gerasimenko

Thermal and mechanical material properties determine comet evolution and even solar system formation because comets are considered remnant volatile-rich planetesimals. Using data from the Multipurpose Sensors for Surface and Sub-Surface Science (MUPUS) instrument package gathered at the Philae landing site Abydos on comet 67P/Churyumov-Gerasimenko, we found the diurnal temperature to vary between 90 and 130 K. The surface emissivity was 0.97, and the local thermal inertia was 85 +/- 35 J m(-2) K(-1)s(-1/2). The MUPUS thermal probe did not fully penetrate the near-surface layers, suggesting a local resistance of the ground to penetration of >4 megapascals, equivalent to >2 megapascal uniaxial compressive strength. A sintered near-surface microporous dust-ice layer with a porosity of 30 to 65% is consistent with the data.

Analysis of the surface state of epi-ready Ge wafers

The surface state of Ge epi-ready wafers (such as those used on III-V multijunction solar cells) supplied by two different vendors has been studied using X-ray photoemission spectroscopy. Our experimental results show that the oxide layer on the wafer surface is formed by GeO and GeO2. This oxide layer thickness differs among wafers coming from different suppliers. Besides, several contaminants appear on the wafer surfaces, carbon and probably chlorine being common to every wafer, irrespective of its origin. Wafers from one of the vendors show the presence of carbonates at their surfaces. On such wafers, traces of potassium seem to be present too.

In situ control of the GE(100)surface domain structure for III-V multijunction solar cells

Vicinal Ge(100) is the common substrate for state of the art multi-junction solar cells grown by metal-organic vapor phase epitaxy (MOVPE). While triple junction solar cells based on Ge(100) present efficiencies mayor que 40%, little is known about the microscopic III-V/Ge(100) nucleation and its interface formation. A suitable Ge(100) surface preparation prior to heteroepitaxy is crucial to achieve low defect densities in the III-V epilayers. Formation of single domain surfaces with double layer steps is required to avoid anti-phase domains in the III-V films. The step formation processes in MOVPE environment strongly depends on the major process parameters such as substrate temperature, H2 partial pressure, group V precursors [1], and reactor conditions. Detailed investigation of these processes on the Ge(100) surface by ultrahigh vacuum (UHV) based standard surface science tools are complicated due to the presence of H2 process gas. However, in situ surface characterization by reflection anisotropy spectroscopy (RAS) allowed us to study the MOVPE preparation of Ge(100) surfaces directly in dependence on the relevant process parameters [2, 3, 4]. A contamination free MOVPE to UHV transfer system [5] enabled correlation of the RA spectra to results from UHV-based surface science tools. In this paper, we established the characteristic RA spectra of vicinal Ge(100) surfaces terminated with monohydrides, arsenic and phosphorous. RAS enabled in situ control of oxide removal, H2 interaction and domain formation during MOVPE preparation.

A Fast XPS study of the surface chemistry of ethanol over Pt{1 1 1}

The adsorption and reaction of ethanol over Pt{1 1 1} has been investigated by Fast XPS and TPD. Ethanol adsorbs molecularly at 100 K, with a saturation coverage of 0.44 ML giving rise to C 1s components with binding energies of 283.7 eV (CH3–) and 284.8 eV (–H2COH). Ethanol multilayers desorb above 150 K, while ∼60% of the monolayer desorbs intact above 200 K in competition with decomposition pathways. Reaction initially proceeds via progressive dehydrogenation to form a metastable acetyl intermediate with components at 283.5 eV (CH3–) and 285.2 eV (-C=O), which in turn undergoes decarbonylation above 250 K to chemisorbed CO and methyl groups. A significant fraction of the latter are hydrogenated above 270 K, desorbing as CH4, with the remainder further decomposing to liberate H2 and surface CHx moeities.

The surface chemistry of nanocrystalline MgO catalysts for FAME production:an in situ XPS study of H2O, CH3OH and CH3OAc adsorption

An in situ XPS study of water, methanol and methyl acetate adsorption over as-synthesised and calcined MgO nanocatalysts is reported with a view to gaining insight into the surface adsorption of key components relevant to fatty acid methyl esters (biodiesel) production during the transesterification of triglycerides with methanol. High temperature calcined NanoMgO-700 adsorbed all three species more readily than the parent material due to the higher density of electron-rich (111) and (110) facets exposed over the larger crystallites. Water and methanol chemisorb over the NanoMgO-700 through the conversion of surface O2 − sites to OH− and coincident creation of Mg-OH or Mg-OCH3 moieties respectively. A model is proposed in which the dissociative chemisorption of methanol occurs preferentially over defect and edge sites of NanoMgO-700, with higher methanol coverages resulting in physisorption over weakly basic (100) facets. Methyl acetate undergoes more complex surface chemistry over NanoMgO-700, with C–H dissociation and ester cleavage forming surface hydroxyl and acetate species even at extremely low coverages, indicative of preferential adsorption at defects. Comparison of C 1s spectra with spent catalysts from tributyrin transesterification suggest that ester hydrolysis plays a key factor in the deactivation of MgO catalysts for biodiesel production.

Mécanisme de salissage et de nettoyage en surface de matériaux polymères

Résumé: Le développement de l’industrie des polymères fourni de plus en plus de choix pour la formulation de matériaux pour les couvre-planchers. Les caoutchoucs, le PVC et le linoleum sont les polymères habituellement utilisés dans l’industrie des couvre-planchers. Ce projet répond à un problème de facilité de nettoyage des couvre-planchers de caoutchouc qui sont reconnus pour être mous, collants et ayant une surface rugueuse. L’INTRODUCTION couvrira l’état actuel de la recherche sur les couvre-planchers, surtout en regard au problème de la «nettoyabilité». La théorie pertinente et les informations générales sur les polymères, les composites polymériques et la science des surfaces seront introduites au CHAPITRE 1. Ensuite, le CHAPITRE 2 couvrira la méthode utilisée pour déterminer la nettoyabilité, l’évaluation des résultats ainsi que l’équipement utilise. Le CHAPITRE 3, discutera des premières expériences sur l’effet de la mouillabilité, la rugosité et la dureté sur la facilité de nettoyage des polymères purs. Plusieurs polymères ayant des surfaces plus ou moins hydrophobes seront investigués afin d’observer leur effet sur la nettoyabilité. L’effet de la rugosité sur la nettoyabilité sera investigué en imprimant une rugosité définie lors du moulage des échantillons; l’influence de la dureté sera également étudiée. Ensuite, un modèle de salissage/nettoyage sera établi à partir de nos résultats et observations afin de rationaliser les facteurs, ou « règles », qui détrminent la facilité de nettoyage des surfaces. Finalement, la réticulation au peroxyde sera étudiée comme une méthode de modification des polymères dans le but d’améliorer leur nettoyabilité; un mécanisme découlant des résultats de ces études sera présenté. Le CHAPITRE 4 étendra cette recherche aux mélanges de polymères; ces derniers servent habituellement à optimiser la performance des polymères purs. Dans ce chapitre, les mêmes tests discutés dans le CHAPITRE 3 seront utilisés pour vérifier le modèle de nettoyabilité établi ci-haut. De plus, l’influence de la non-miscibilité des mélanges de polymères sera discutée du point de vue de la thermodynamique (DSC) et de la morphologie (MEB). L’utilisation de la réticulation par peroxyde sera étudié dans les mélanges EPDM/ (E-ran-MAA(Zn)-ran-BuMA) afin d’améliorer la compatibilité de ces polymères. Les effets du dosage en agent de réticulation et du temps de cuisson seront également examinés. Finalement, un compatibilisant pré-réticulé a été développé pour les mélanges ternaires EPDM/ (E-ran-MAA(Zn)-ran-BuMA)/ HSR; son effet sur la nettoyabilité et sur la morphologie du mélange sera exposé.

Modifying the band gap and optical properties of Germanium nanowires by surface termination

Semiconductor nanowires, based on silicon (Si) or germanium (Ge) are leading candidates for many ICT applications, including next generation transistors, optoelectronics, gas and biosensing and photovoltaics. Key to these applications is the possibility to tune the band gap by changing the diameter of the nanowire. Ge nanowires of different diameter have been studied with H termination, but, using ideas from chemistry, changing the surface terminating group can be used to modulate the band gap. In this paper we apply the generalised gradient approximation of density functional theory (GGA-DFT) and hybrid DFT to study the effect of diameter and surface termination using –H, –NH2 and –OH groups on the band gap of (001), (110) and (111) oriented germanium nanowires. We show that the surface terminating group allows both the magnitude and the nature of the band gap to be changed. We further show that the absorption edge shifts to longer wavelength with the –NH2 and –OH terminations compared to the –H termination and we trace the origin of this effect to valence band modifications upon modifying the nanowire with –NH2 or –OH. These results show that it is possible to tune the band gap of small diameter Ge nanowires over a range of ca. 1.1 eV by simple surface chemistry.

Hall Effect and transient surface photovoltage (SPV) study of Cu3BiS3 thin films

Se presentan las propiedades eléctricas del compuesto Cu3BiS3 depositado por co-evaporación. Este es un nuevo compuesto que puede tener propiedades adecuadas para ser utilizado como capa absorbente en celdas solares. Las muestras fueron caracterizadas a través de medidas de efecto Hall y fotovoltaje superficial transiente (SPV). A través de medidas de efecto Hall se encontró que la concentración de portadores de carga n es del orden de 1016 cm-3 independiente de la relación de masas de Cu/Bi. También se encontró que la movilidad de este compuesto (μ del orden de 4 cm2V -1s-1) varía de acuerdo con los mecanismos de transporte que la gobiernan en dependencia con la temperatura. A partir de las medidas de SPV se encontró alta densidad de defectos superficiales, defectos que son pasivados al superponer una capa buffer sobre el compuesto Cu3BiS3.

TiAlN coatings deposited by triode magnetron sputtering varying the bias voltage

TiAlN films were deposited on AISI O1 tool steel using a triode magnetron sputtering system. The bias voltage effect on the composition, thickness, crystallography, microstructure, hardness and adhesion strength was investigated. The coatings thickness and elemental composition analyses were carried out using scanning electron microscopy (SEM) together with energy dispersive X-ray (EDS). The re-sputtering effect due to the high-energy ions bombardment on the film surface influenced the coatings thickness. The films crystallography was investigated using X-ray diffraction characterization. The X-ray diffraction (XRD) data show that TiAlN coatings were crystallized in the cubic NaCl B1 structure, with orientations in the {111}, {200} {220} and {311} crystallographic planes. The surface morphology (roughness and grain size) of TiAlN coatings was investigated by atomic force microscopy (AFM). By increasing the substrate bias voltage from -40 to -150 V, hardness decreased from 32 GPa to 19 GPa. Scratch tester was used for measuring the critical loads and for measuring the adhesion. (C) 2011 Elsevier B. V. All rights reserved.

Improved moisture and hydrocarbons barrier of epoxy resin-based coating

To improve the surface characteristics of epoxy resin coatings, a treatment by fluorine-containing plasma was used to develop a coating with low surface free energy and improved chemical resistance. Through the coating analysis it was possible to verify information about the CF(n) bond formation and the fluorination depth. The best plasma process parameters presented the best fluorination depth, 90 nm, and fluorine concentration was nearly 30%. The improvement in contact angle of water was 50% and of raw petroleum was 130%. Salt spray test proves that the coating fluorination decreases the chance of substrate corrosion.

KDP/PEDOT: PSS mixture as a new alternative in the fabrication of pressure sensing devices

In this work we studied the mixture of poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS), a commercial polymer, with monobasic potassium phosphate (KDP), a piezoelectric salt, as a possible novel material in the fabrication of a low cost, easy-to-make,flexible pressure sensing device. The mixture between KDP and PEDOT: PSS was painted in a flexible polyester substrate and dried. Afterwards, I x V curves were carried out. The samples containing KDP presented higher values of current in smaller voltages than the PEDOT: PSS without KDP. This can mean a change in the chain arrays. Other results showed that the material responds to directly applied pressure to the sample that can be useful to sensors fabrication. (c) 2008 Elsevier B.V. All rights reserved.

Predicting the mechanical behavior of amorphous polymeric materials under strain through multi-scale simulation

Polymeric materials have become the reference material for high reliability and performance applications. However, their performance in service conditions is difficult to predict, due in large part to their inherent complex morphology, which leads to non-linear and anisotropic behavior, highly dependent on the thermomechanical environment under which it is processed. In this work, a multiscale approach is proposed to investigate the mechanical properties of polymeric-based material under strain. To achieve a better understanding of phenomena occurring at the smaller scales, the coupling of a finite element method (FEM) and molecular dynamics (MD) modeling, in an iterative procedure, was employed, enabling the prediction of the macroscopic constitutive response. As the mechanical response can be related to the local microstructure, which in turn depends on the nano-scale structure, this multiscale approach computes the stress-strain relationship at every analysis point of the macro-structure by detailed modeling of the underlying micro- and meso-scale deformation phenomena. The proposed multiscale approach can enable prediction of properties at the macroscale while taking into consideration phenomena that occur at the mesoscale, thus offering an increased potential accuracy compared to traditional methods.

Morphological and structural characterization of CrO2/Cr2O3 films grown by laser-CVD

This work reports on the synthesis of chromium (III, IV) oxides films by KrF laser-assisted CVD. Films were deposited onto sapphire substrates at room temperature by the photodissociation of Cr(CO)(6) in dynamic atmospheres containing oxygen and argon. A study of the processing parameters has shown that partial pressure ratio Of O-2 to Cr(CO)(6) and laser fluence are the prominent parameters that have to be accurately controlled in order to co-deposit both the crystalline oxide phases. Films consistent with such a two-phase system were synthesised for a laser fluence of 75 mJ cm(-2) and a partial pressure ratio of about 1. (c) 2005 Elsevier B.V. All rights reserved.

Ageing effects on the wettability behavior of laser textured silicon

In the present work we investigate the ageing of acid cleaned femtosecond laser textured < 100 > silicon surfaces. Changes in the surface structure and chemistry were analysed by Rutherford backscattering spectrometry (RBS) and X-ray photoelectron spectroscopy (XPS), in order to explain the variation with time of the water contact angles of the laser textured surfaces. It is shown that highly hydrophobic silicon surfaces are obtained immediately after laser texturing and cleaning with acid solutions (water contact angle >120 degrees). However these surfaces are not stable and ageing leads to a decrease of the water contact angle which reaches a value of 80 degrees. XPS analysis of the surfaces shows that the growth of the native oxide layer is most probably responsible for this behavior. (C) 2010 Elsevier B.V. All rights reserved.