Ultra High Vacuum Systems

Several spectroscopic techniques have been used to investigate the presence of contaminants in a commercial purified singlewalled carbon nanotube (SWCNT) bucky paper, to determine their cleaning procedure in ultra-high-vacuum conditions and to study how impurities influence the interaction between SWCNTs and gas phase molecules. Nickel catalyst particles and sodiumcontaining species, likely a residual of the surfactant bath, were fully removed only after prolonged (>2 h) annealing at 1270 ± 30 K. Other impurity elements (S and Si) remain in the material as localised clusters that do not interact with the SWCNTs and do not interfere with their properties.

Remerciements J'aimerais remercier par ces quelques lignes toutes les personnes qui, d'une manière ou d'une autre, ont permis à cette thèse d'avoir lieu, tant d'un point de vue humain que d'un point de vue scientifique. Tout d'abord, je remercie tous les professeurs qui, au cours de mes études, m'ont donné les outils et les connaissances qui m'ont permis d'arriver jusqu'ici. Je pense surtout à Monsieur Bousquet qui m'a communiqué sa passion pour la Physique. MERCI ;o) La thèse est une période exigeante qui nécessite énormément d'investissement personnel dont on n'entrevoit rarement la fin, sauf le jour de la soutenance.. . Je tiens donc à exprimer ma reconnaissance à toutes les personnes bienveillantes qui m'ont aidée, soutenue, conseillée, encouragée et que j'ai eu la chance de rencontrer pendant cette aventure scientifique et humaine. Je tiens donc à remercier chaleureusement : Jean-François Bobo et Christophe Cardinaud d'avoir lu, complété et jugé ce travail, ainsi que Margrit Hanbücken, Bernard Agius et Bernard Mercey d'avoir accepté de faire partie du jury. Bernard Bartenlian de m'avoir proposé ce sujet de thèse qui n'aurait su mieux me convenir, d'avoir relu et corrigé ce manuscrit et de m'avoir défendu à plusieurs occasions. Xavier Le Roux de m'avoir fait partager son expérience, son expertise dans de nombreux domaines (lithographie, gravure, technologie salle blanche.. .) toujours avec sympathie, d'avoir relu et corrigé ce manuscrit et, surtout, de son Amitié.

Molecular machines may resolve three distinct bottlenecks of scientific advancement. Nanofactories (Phoenix, 2003) composed of MM may produce atomically perfect products spending negligible amount of energy (Hess, 2004) thus alleviating the energy crisis. Computers made by MM operating thousands of bits at a time may match biological processors mimicking creativity and intelligence (Hall, 2007), thus far considered as the prerogative of nature. State-of-the-art brain surgeries are not yet fatal-less, MMs guided by a nano-brain may execute perfect bloodless surgery (Freitas, 2005). Even though all three bottlenecks converge to a single necessity of nano-brain, futurists and molecular engineers have remained silent on this issue. Our recent invention of 16 bit parallel processor is a first step in this direction (Bandyopadhyay, 2008). However, the device operates inside ultra-high vacuum chamber. For practical application, one needs to design a 3 D standalone architecture. Here, we identify the minimum nano-brain functions for practical applications and try to increase the size from 2 nm to 20 micro-m.

Several technical modifications related to the fabrication and ultra-high vacuum (UHV) treatments of the scanning tunneling microscope (STM) tips have been implemented to improve a reliability of the tip preparation for high-resolution STM. Widely used electrochemical etching drop-off technique has been further refined to enable a reproducible fabrication of the tips with a radius ⩽3 nm. For tip cleaning by a controllable UHV annealing, simple and flexible setup has been developed. Proper W tip preparation has been demonstrated via an imaging of the TiO2 (1 1 0) surface atomic structure.

Low-power, ultra-high-vacuum compatible, non-contacting position sensors with nanometer resolution and centimeter dynamic range have been developed, built and tested. They have been designed at Virgo as the sensors for low-frequency modal damping of Seismic Attenuation System chains in Gravitational Wave interferometers and sub-micron absolute mirror positioning. One type of these linear variable differential transformers (LVDTs) has been designed to be also insensitive to transversal displacement thus allowing 3D movement of the sensor head while still precisely reading its position along the sensitivity axis. A second LVDT geometry has been designed to measure the displacement of the vertical seismic attenuation filters from their nominal position. Unlike the commercial LVDTs, mostly based on magnetic cores, the LVDTs described here exert no force on the measured structure. r 2002 Elsevier Science B.V. All rights reserved. PACS: 04.80.Nn; 95.30.Sf; 95.55.Ym (H. Tariq). 0168-9002/02/$ -see front matter r 2002 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 8 -9 0 0 2 ( 0 2 ) 0 0 8 0 2 -1

The charge transport through a single ruthenium atom clamped by two terpyridine hinges is investigated, both experimentally and theoretically. The metal-bis(terpyridyl) core is equipped with rigid, conjugated linkers of para-acetyl-mercapto phenylacetylene to establish electrical contact in a two-terminal configuration using Au electrodes. The structure of the [Ru II (L) 2 ](PF 6 ) 2 molecule is determined using single-crystal X-ray crystallography, which yields good agreement with calculations based on density functional theory (DFT). By means of the mechanically controllable break-junction technique, current-voltage (I-V), characteristics of [Ru II (L) 2 ](PF 6 ) 2 are acquired on a single-molecule level under ultra-high vacuum (UHV) conditions at various temperatures. These results are compared to ab initio transport calculations based on DFT. The simulations show that the cardan-joint structural element of the molecule controls the magnitude of the current. Moreover, the fluctuations in the cardan angle leave the positions of steps in the I-V curve largely invariant. As a consequence, the experimental I-V characteristics exhibit lowest-unoccupied-molecular-orbit-based conductance peaks at particular voltages, which are also found to be temperature independent.

The work described in this paper is part of a systematic study of surface cleaning and ohmic contact strategies for GaN. The goal of this investigation was to determine the most effective methods of wet chemical and thermal desorption cleaning for the removal of oxygen (O) and carbon (C) prior to metallization. Hydrochloric (HC1) and hydrofluoric (HF) acid-based cleaning treatments were compared, and thermal desorption as a function of temperature was characterized by sequential heating under ultra high vacuum (UHV) conditions. Auger electron spectroscopy (AES) analysis was used to monitor the presence of surface O and C throughout the study. For the removal of surface oxide, HCl-based solutions were found to be most effective; under as-cleaned, air-exposed conditions, HCI:DI H20 (1:1) solution resulted in the lowest levels of residual O and C. However, HF-based solutions resulted in more effective thermal desorption of C from the surfaces. In contrast to the results typically observed in the thermal desorption cleaning of GaAs, complete removal of oxygen and carbon from airexposed GaN surfaces was not seen using vacuum heating alone, even to temperatures where GaN decomposition occurs (>800-900~

This study measures heat conduction across the annulus of a parabolic trough receiver in the free-molecular, transition, temperature jump, and continuum regimes for argon-hydrogen and xenon-hydrogen mixtures at an absorber temperature of 350°C. Experimental values are predicted successfully by Sherman's interpolation formula and the Direct Simulation Monte Carlo Method. Depending on pressure, heat conduction of hydrogen in the annulus of a receiver can be greater than 500 W/m receiver length and decrease the annual net electricity production of a parabolic trough power plant by more than 50% relative to a plant with evacuated receivers. However, heat conduction can be reduced to 50-100 W/m when hydrogen is mixed with an inert gas such that the molar fraction of the inert gas is 95% or greater. This results in annual net electricity production penalty of 3-7% instead of more than 50%. Assuming 100 Pa of hydrogen in the annulus of a current receiver, the addition of 1900 Pa of xenon or 4900 Pa of argon will effect this reduction while avoiding natural convection in the annulus.

Nanoscience and nanotechnology are tremendously increasing fields of research that aim at producing, characterizing and understanding nanoobjects and assemblies of nanoobjects. Their new physical or chemical properties, which arise from confinement effects, intimately depend on their morphological properties, i.e. their shapes, their sizes and their spatial organization. This calls for dedicated morphological characterization tools, among which is the Grazing Incidence Small Angle X-Ray Scattering (GISAXS). This reciprocal space technique has emerged in the last two decades as a powerful tool that allows investigating in a non-destructive way the morphological properties from one to billions of nanoparticles, either on a surface, or embedded in a matrix, with sizes ranging from 1 nm to several microns. The advantages of the technique are that it is non-destructive; it yields statistical information averaged on a large number of nanoparticles; it allows probing both the surface or deep below it, by changing the incident angle of the X-ray beam; it can be used in very different sample environments, in particular in situ in the course of a given process such as growth, annealing, gas exposure; and it may be given chemical sensitivity by use of anomalous scattering.

In this report we review the fundamentals, applications and future tendencies of dynamic atomic force microscopy (AFM) methods. Our focus is on understanding why the changes observed in the dynamic properties of a vibrating tip that interacts with a surface make possible to obtain molecular resolution images of membrane proteins in aqueous solutions or to resolve atomic-scale surface defects in ultra high vacuum (UHV). Our description of the two major dynamic AFM modes, amplitude modulation atomic force microscopy (AM-AFM) and frequency modulation atomic force microscopy (FM-AFM) emphasises their common points without ignoring the differences in experimental set-ups and operating conditions. Those differences are introduced by the different feedback parameters, oscillation amplitude in AM-AFM and frequency shift and excitation amplitude in FM-AFM, used to track the topography and composition of a surface.

The stability of different vanadium-based catalysts for the selective oxidation of small hydrocarbons under the ultra-high vacuum (UHV) conditions of standard X-ray photoelectron spectroscopy (XPS) was studied by using a multi-purpose surface analysis apparatus which allows time spans of only a few minutes between the sample transfer into vacuum and the first photoelectron spectrum. For vanadium phosphorus oxide catalysts a significant dependence of the average vanadium oxidation state on the time of exposure to the UHV was observed, with a substantial decrease of the V +5 /V +4 ratio within only a few minutes. A much less pronounced reduction was found for alumina-supported VO x catalysts. The observed changes are predominantly due to the vacuum environment with a rather minor (if at all) contribution of the X-ray excitation. #

Thin films of contact metals, specifically Au, Ir, Cr, and Sc, are deposited on exfoliated, bulk MoS 2 using electron beam deposition under two different reactor base pressures to determine the contact metal−MoS 2 interface chemistry and its dependence on the reactor ambient. The high work function metal Au does not react with MoS 2 regardless of reactor ambient. In contrast, interfacial reactions between MoS 2 and another high work function metal, Ir, are observed when it is deposited under both high vacuum (HV, ∼ 1 × 10 −6 mbar) and ultrahigh vacuum (UHV, ∼ 1 × 10 −9 mbar). Interfacial reactions occur between metals with low work functions (Cr, Sc) near the electron affinity of MoS 2 when the contact metal is deposited under UHV conditions. In addition, Sc is rapidly oxidized on the MoS 2 surface, whereas Cr is only partially oxidized when deposited under HV conditions. This indicates that deposition chamber ambient can affect the contact metal chemistry in addition to the chemistry present at the contact metal−MoS 2 interface. These results elucidate the true chemistry of some contact metal−MoS 2 interfaces and its dependence on the deposition ambient, and highlight the need to consider the chemical states present at the interface and their impact on contact resistance with MoS 2 .

We present the fabrication and the superconducting properties of MgB 2 ceramic samples doped with carbon via preceramic polymers: linear and cyclic polysiloxaneg-styrene and linear polysiloxane-g-vinyl-ferrocene. The samples were produced using the spark plasma sintering technique. The use of polysiloxane copolymers was suggested by the appropriate content of carbon, silicon, and oxygen which are necessary to increase the upper critical field and to create pinning centers. The short processing time limits the diffusion length of the chemical elements from the polymer into the superconducting grains. Therefore, in addition to doping with carbon, the rest of the components creates pinning centers along the polymeric chain, able to better pin the flux lines. The copolymerization allowed us to obtain both linear and cyclic copolymers as well as to control the content of chemical elements, including the presence of small amounts of iron oxides. The latter are responsible for the magnetic pinning.

One hydrocarbon-based and two fluorocarbon-based magnetic fluid samples were tested under four different vacuum levels. The weight losses of the samples were measured and the evaporation rates calculated. It was found that under higher vacuum levels (lower pressure levels) the evaporation rate of each sample was significantly higher than under atmospheric conditions, gradually reaching a saturated level while the vacuum level kept increasing. The Langmuir equation is modified to theoretically explain this phenomenon. It was also found that the fluorocarbon-based magnetic fluids are more suitable for ultra-high-vacuum applications. r

We present the fabrication and the superconducting properties of MgB2 ceramic samples doped with carbon via preceramic polymers: linear and cyclic polysiloxane-co-styrene and linear polysiloxane-co-vinyl-ferrocene. The samples were produced using the spark plasma sintering technique. The use of polysiloxane copolymers was suggested by the appropriate content of carbon, silicon, and oxygen which are necessary to increase the upper critical field and to create pinning centers. The short processing time limits the diffusion length of the chemical elements from the polymer into the superconducting grains. Therefore, in addition to doping with carbon, the rest of the components create pinning centers along the polymeric chain, able to better pin the flux lines. The copolymerization allowed us to obtain both linear and cyclic copolymers as well as to control the content of chemical elements, including the presence of small amounts of iron oxides. The latter are responsible for magnetic pinning.

The dissociative chemisorption of N 2 is generally accepted to be the rate-determining step of ammonia synthesis over Ru-based catalysts. The interaction of N 2 with the following three Ru catalysts has been studied: Ru supported on Al 2 O 3 (Ru/Al 2 O 3 ) and on MgO (Ru/MgO), and Ru/MgO promoted with cesium (Cs-Ru/MgO). Temperature-programmed N 2 adsorption and desorption experiments and the isotopic exchange reaction 14 N 14 N + 15 N 15 N 2 14 N 15 N were performed in a microreactor flow system. A microkinetic analysis based on the Langmuir-Hinshelwood Hougen-Watson mechanism has been applied to these kinetic experiments yielding the rate constants of dissociative chemisorption (k ads ) and associative desorption (k des ). The dissociation of N 2 was indeed found to be a slow and activated process. Ru/Al 2 O 3 was found to be rather inactive for N 2 dissociation. Ru/MgO turned out to be a heterogeneous system with respect to the interaction with N 2 due to the presence of promoted active sites which dominate the rate of N 2 dissociation. Promotion by cesium was observed to enhance both k ads and k des significantly and rendered the Ru metal surfaces uniform toward the interaction with N 2 . The initial sticking coefficient and the rate of desorption of N 2 derived from the microkinetic models are in good agreement with results obtained with Ru single crystal surfaces under ultra-high vacuum conditions.

Several nanometer-thick graphene oxide films deposited on silicon nitride-on silicon substrates were exposed to nine different heat treatments (three in Argon, three in Argon and Hydrogen, and three in ultra-high vacuum), and also a film was held at 70°C while being exposed to a vapor from hydrazine monohydrate. The films were characterized with atomic force microscopy to obtain local thickness and variation in thickness over extended regions. X-ray photoelectron spectroscopy was used to measure significant reduction of the oxygen content of the films; heating in ultra-high vacuum was particularly effective.

This paper reviews surface chemistry of carbon monoxide and methanol in ultra high vacuum (UHV) and in the electrochemical environment on clean and Ru modified Pt single crystal surfaces, and on Pt and Pt/Ru nanoparticles. The results show that CO behaves very similarly in UHV and in the electrochemical environment. Cyclic voltammetry (CV), temperature programmed desorption (TPD) and radioactive labeling all show similar behavior in terms of numbers of peaks, peak splitting etc. Both UHV and CV measurements show that there is about a 200-meV change in the potential for CO removal in the presence of ruthenium. Earlier 13 C EC-NMR data indicated a 30% reduction in the E f -LDOS of CO bound to Ru islands deposited on platinum, and 15% of CO bound to Pt sites, and TPD and CV also show that the binding of CO is modified. The present data confirm that Pt atoms away from Ru are only weakly affected, and the overall CO binding energy modification is quite moderate. We conclude that the changes in the CO binding energy only play a small role in enhancing methanol electrooxidation rates. Instead, the main effect of the ruthenium is to activate water to form OH. Quantitative estimates of the reduction in CO desorption barrier indicate that the effect of bifunctional mechanism is about four times larger than that of ligand effect. In contrast to the results for CO, methanol behaves quite differently in UHV and in an electrochemical environment. Pt(111) is unreactive at room temperature in UHV, while Pt(110) is quite reactive. Initially, clean Pt(111) is less reactive than clean Pt(110) even in the electrochemical environment. However, Pt(110) is quickly poisoned in the electrochemical environment, so at steady state, Pt(111) is more reactive than Pt(110). Another issue is that the mechanism of methanol decomposition is quite different in UHV and in the electrochemical environment. There are three pathways in UHV, a simple decomposition via a methoxonium (CH 3 O Ã/ (ad) ) intermediate, an S N 1 pathway via a methoxonium cation ([CH 3 OH 2 ] ' ), and an S N 2 pathway via a methoxonium intermediate. So far, none of these pathways have been observed in an electrochemical environment. Instead, the decomposition goes mainly through a hydroxymethyl (Ã/CH 2 OH (ad) ) intermediate. These results show that there are both similarities and differences in the behavior of simple molecules in UHV and in the electrochemical environment. #

The structures, cohesive energies and HOMO-LUMO gaps of graphene nanoflakes and corresponding polycyclic aromatic hydrocarbons for a large variety of size and topology are investigated at the density functional based tight-binding level. Polyacene-like and honeycomb-like graphene nanoflakes were chosen as the topological limit structures. The influence of unsaturated edge atoms and dangling bonds on the stability is discussed. Our survey shows a linear trend for the cohesive energy as function of N s /N (N − total number of atoms and N s is number of edge atoms). For the HOMO-LUMO gap the trends are more complex and include also the topology of the edges.

Gallium nitride thin films were grown via pulsed laser deposition (PLD) in different atmospheres (N2, NH3 and ultra-high-vacuum) on sapphire. Resistivity, doping and Hall mobility of the films are studied as a function of temperature and growth conditions: we found that the films grown in ammonia have n-type (n≈1016 cm−3) background doping, while growth in N2 (p≈1013 cm−3) and in UHV (p≈1019 cm−3) induces p-type doping. The surface quality of the films is also investigated by atomic force microscopy (AFM) and the values for surface roughness are of the order of tens of nanometers for the films grown in ammonia while films grown in N2 have a roughness of few nanometers.

The formation of the Ti−MoS 2 interface, which is heavily utilized in nanoelectronic device research, is studied by X-ray photoelectron spectroscopy. It is found that, if deposition under high vacuum (∼1 × 10 −6 mbar) as opposed to ultrahigh vacuum (∼1 × 10 −9 mbar) conditions are used, TiO 2 forms at the interface rather than Ti. The high vacuum deposition results in an interface free of any detectable reaction between the semiconductor and the deposited contact. In contrast, when metallic titanium is successfully deposited by carrying out depositions in ultrahigh vacuum, the titanium reacts with MoS 2 forming Ti x S y and metallic Mo at the interface. These results have far reaching implications as many prior studies assuming Ti contacts may have actually used TiO 2 due to the nature of the deposition tools used.

This review assesses the current state of understanding of the calculation of the rate of flow of gases, vapours and liquids confined in channels, in porous media and in permeable materials with an emphasis on the flow of water and its vapour. One motivation is to investigate the relation between the permeation rate of moisture and that of a noncondensable test gas such as helium, another is to assist in unifying theory and experiment across disparate fields. Available theories of single component ideal gas flows in channels of defined geometry (cylindrical, rectangular and elliptical) are described and their predictions compared with measurement over a wide range of conditions defined by the Knudsen number. Theory for two phase flows is assembled in order to understand the behaviour of four standard water leak configurations: vapour, slug, Washburn and liquid flow, distinguished by the number and location of phase boundaries (menisci). Air may or may not be present as a background gas. Slip length is an important parameter that greatly affects leak rates. Measurements of water vapour flows confirm that water vapour shows ideal gas behaviour. Results on carbon nanotubes show that smooth walls may lead to anomalously high slip lengths arising from the properties of 'confined' water. In porous media, behaviour can be matched to the four standard leaks. Traditional membrane permeation models consider that the permeant dissolves, diffuses and evaporates at the outlet side, ideas we align with those from channel flow. Recent results on graphite oxide membranes show examples where helium which does not permeate while at the same time moisture is almost unimpeded, again a result of confined water. We conclude that while there is no a priori relation between a noncondensable gas flow and a moisture flow, measurements using helium will give results within two orders of magnitude of the moisture flow rate, except in the case where there is anomalous slip or confined water, when moisture specific measurements are essential.

This paper is a short review about the principle, mechanisms and applications of epitaxial electrochemical growth of ultrathin metal films on single crystal metal electrode surfaces. Starting from an atomic scale view of electrodeposition the parallel is made with the parent technique molecular beam epitaxy (MBE) in ultra high vacuum (UHV). A first section is devoted to homoepitaxy studies. Subsequent sections deal with selected studies of heteroepitaxy of magnetic materials and electrocatalysts.

Amorphous silicon-nitrogen (a-Sil_xN~:H) alloys with x in the range 0.01-0.57 have been deposited in a dedicated chamber by ultra high vacuum plasma enhanced chemical vapour deposition (PECVD) in sir 4 + NH 3 gas mixtures with different molecule dwell time and by hydrogen diluting the plasma. By optical spectroscopy, Rutherford backscattering spectrometry (RBS), elastic recoil detection analysis (ERDA) and infrared spectroscopy (IR) a complete picture of bonding distribution and structural properties of device-quality a-Sij_ vN~:H films as a function of deposition conditions has been drawn. Annealing experiments under vacuum up to 500°C have shown that in all the compositional range the films are thermally stable up to 400°C, for higher temperature bonded hydrogen effuses from both silicon and nitrogen atoms with behaviours dependent on nitrogen content in the film. © 1997 Elsevier Science S.A.

A summary of the optical coatings for the spectral range from 50 to 200 nm that can be prepared at GOLD is presented. This spectral range, named here far and extreme ultraviolet (FUV/EUV), is characterized by the high absorption of almost all materials and the strong dependence of their optical properties on the deposition parameters and on the exposure of

The presence of water at the surface of sputtered thin films of Ce 0.8 Gd 0.2 O 1.9 , which display elastic anomalies as a function of thermal treatment, and of stoichiometric CeO 2 films, which do not, was monitored using X-ray photoelectron spectroscopy. We find that considerably more water is strongly bound at the surface of the Ce 0.8 Gd 0.2 O 1.9 films than of the CeO 2 films. This supports the theoretical prediction that water binds preferentially at the oxygen vacancy sites. In addition, all films were treated according to the protocol which has been shown to produce inelastic behavior in the doped films: annealed at 500°C, exposed to ambient atmosphere for one month and then heated to 250°C in ultra-high vacuum. Neither the Ce 0.8 Gd 0.2 O 1.9 nor the CeO 2 films show any change in the amount of adsorbed water. We therefore conclude that changes in the amount of surface adsorbed water do not play a role in the elastic anomalies observed as a function of thermal treatment of Ce 0.8 Gd 0.2 O 1.9 films.

A non-contact atomic force microscope (NC-AFM) based on a microfabricated piezoelectric cantilever is presented. A single piezoelectric lead zirconate titanate thin film layer on the cantilever serves as deflection sensing, cantilever oscillation and feedback actuation. Since such an AFM requires neither external oscillator nor external deflection sensor, considerably simple instrumentation becomes possible even for extreme environments such as low temperature or ultra-high vacuum. Also feedback control by the integrated actuator in the cantilever makes faster scanning possible. Images of atomic steps on annealed sapphire (0001) surfaces have been observed in air atmosphere in frequency modulation mode. #

We present two simple cryogenic RF ion trap systems in which cryogenic temperatures and ultra high vacuum pressures can be reached in as little as 12 hours. The ion traps are operated either in a liquid helium bath cryostat or in a low vibration closed cycle cryostat. The fast turn around time and availability of buffer gas cooling made the systems ideal for testing surface-electrode ion traps. The vibration amplitude of the closed cycled cryostat was found to be below 106 nm. We evaluated the systems by loading surface-electrode ion traps with $^{88}$Sr$^+$ ions using laser ablation, which is compatible with the cryogenic environment. Using Doppler cooling we observed small ion crystals in which optically resolved ions have a trapped lifetime over 2500 minutes.

High-resolution electron microscopy has been used to characterize the structure of ultra-thin films of titanium deposited on KBr Ž . substrate by ultra-high vacuum UHV electron-gun evaporation. The size of the grains has an order of magnitude of 10 nm whatever is ² : the substrate temperature. The observations have been carried out along the 1123 zone axis. Some of the grains contain planar defects Ä 4 that were identified as the twin 1011 . The atomic structure of this twin is characterized by a mirror plane similar to that observed in polycrystalline titanium. Additionally, this structure can be modified by a b twinning dislocation. q 1998 Published by Elsevier 2r2 Science S.A.

A Ti:Sapphire (IR 800-nm) femtosecond (fs) pulsed laser was used to ablate a sputtering grade of silicon carbide (SiC) in an ultra-high vacuum chamber. The laser-induced plasma species were then driven and grown to form 3C-SiC films of about 1 mm thick on single crystal silicon wafers at 20 1C (room temperature) and 500 1C. Scanning electron microscopy, atomic force microscopy, X-ray photoelectron microscopy, X-ray diffraction and nanoindentation were used to characterize the structure, composition, thickness and properties of the SiC films. Results of the femtosecond-pulse laser deposited (fs-PLD) films were compared with those obtained by atmospheric pressure chemical vapor deposition (APCVD) and nanosecond-pulse laser (excimer laser at 248-nm) deposition (ns-PLD). The distinctive features of fs-PLD films are their extremely smooth surfaces, stoichiometry, amorphous structure and low defect density compared to APCVD films, along with better film quality and higher growth rates than ns-PLD films. In addition to film growth studies, a SiC microgripper (to grab 20-mm-sized objects) was micromachined by use of the fs-pulsed laser to demonstrate the utility of ultra-short PLD in SiC-device fabrication. r

Abstract
On April 25, 2013 after almost 4 years of development and testing the NEE-01 PEGASUS, the first Ecuadorian satellite took off to orbit on board an LM2D Chinese vector, launching from JiuQuan cosmodrome, it operated correctly until May 23 when a close approach with the SCC 15890 object
probably impaired the attitude control and antennae systems of the satellite. On November 21 of the same
year the NEE-02 KRYSAOR, the second Ecuadorian satellite was launched into orbit by a Russian Dnepr
booster taking off from Yasny cosmodrome; it carried a novel device called PERSEUS which allowed the
Ecuadorian Civilian Space Agency to recover the signal of the NEE-01 PEGASUS via intersatellite
communication.
This is the result of 7 years of indigenous effort on the frame of the Ecuadorian Civilian Space Program,
using only national personnel, devising our own solutions, from the very basics like PCB fabrication and
coating formulation to building entire systems like EPS modules and titanium structures, designing our own
solutions and building them with our own processes, going through the making of our own tools, like the
GOLEM magneto dynamical shaker or the SESCA Space Environment simulation chamber and testing and
developing our ground stations HERMES-1 and HERMES-2. In this paper we will review the results and
the advances made in this path to reach space with our own ingenuity in the effort to share with the
community what we have learned and humbly aspiring to inspire other nations to follow this path of
discovery of their own capabilities, which in time will lead

A scanning tunneling microscope (STM) can provide atomic-resolution images of samples in ultra-high vacuum, moderate vacuum, gases including air at atmospheric pressure, and liquids including oil, water, liquid nitrogen, and even conductive solutions. This review contains images of single-crystal metals, metal films, both elemental and compound semiconductors, superconductors, layered materials, adsorbed atoms, and even DNA. A discussion of results on

Direct simulation Monte Carlo (DSMC) method with simplified Bernoulli-trials (SBT) collision scheme has been used to study the rarefied pressure-driven nitrogen flow through diverging microchannels. The fluid behaviours flowing between two plates with different divergence angles ranging between 0 o to 17 o are described at different pressure ratios (1.5≤Π≤2.5) and Knudsen numbers (0.03≤Kn≤12.7). The primary flow field properties, including pressure, velocity, and temperature, are presented for divergent microchannels and are compared with those of a microchannel with a uniform cross-section. The variations of the flow field properties in divergent microchannels, which are influenced by the area change, the channel pressure ratio and the rarefication are discussed. The results show no flow separation in divergent microchannels for all the range of simulation parameters studied in the present work. It has been found that a divergent channel can carry higher amounts of mass in comparison with an equivalent straight channel geometry. A correlation between the mass flow rate through microchannels, the divergence angle, the pressure ratio, and the Knudsen number has been suggested. The present numerical findings prove the occurrence of Knudsen minimum phenomenon in micro-and Nano-channels with non-uniform cross-sections.

We have studied the desorption mechanism of Ga-and As-oxides on GaAs 100 by subjecting the substrates to two thermal Ž . processes in ultra high vacuum UHV conditions. The first process was an outgassing at 350ЊC, and the second process consisted of an annealing at 530ЊC. The pressure variations in the UHV chambers recorded during both thermal treatments showed a Ž . behavior related to the removal of As-and Ga-oxides from the substrate surface. The thermally treated GaAs 100 substrates Ž . Ž . were analyzed by in situ reflection high-energy electron diffraction RHEED , Auger electron spectroscopy AES , and ex situ Ž . Ž . atomic force microscopy AFM . AFM images clearly showed the presence of surface pits on the GaAs 100 samples exposed to 9 2t he high-temperature oxide desorption process. The pits have a density of the order of 10 rcm , and some are as deep as 120 A. We explain the pits formation mechanism in terms of chemical reactions of the surface oxides with the elements of the substrate. ᮊ

Extremely high financial support has been provided to different scientific institutes due to a world priority to find new kinds of energy sources. This has a clear strategic importance for the energy industry. Hydrogen is the most energetic material known and safe for our environment. However, it creates a lot of problems to achieve safe, effective and reversible storage. Some of the theoretical simulations show that carbon nanotubes (CNTs) and/or CNTs hybrid systems could be quite promising material for hydrogen storage.

The present work focuses on the assessment of two surface treatment procedures employed under ultra high vacuum conditions in order to obtain atomically clean graphene layers without disrupting the morphology and the two dimensional character of the films. Graphene layers grown by chemical vapor deposition on polycrystalline Cu were stepwise annealed up to 750 • C or treated by mild Ar + sputtering. The effectiveness of both methods and the changes that they induce on the surface morphology and electronic structure of the films were systematically studied by X-ray photoelectron spectroscopy, and electron energy loss spectroscopy. Ultraviolet photoelectron spectroscopy was employed for the study of the electronic properties of the as received sample and in combination with the work function measurements, indicated the hybridization of the C-network with Cu d-orbitals. Mild Ar + sputtering sessions were found to disrupt the sp2 network and cause amorphisation of the graphitic carbon. Annealing between 300 • C and 450 • C under ultra high vacuum proved to be an effective and lenient way for achieving an atomically clean graphene surface. At higher temperatures the rigid structure of graphene does not follow the expansion of the copper substrate leading to the graphene/Cu interface breakdown and possibly to further rippling of the graphene layers leaving bare areas of cooper substrate.

ITER is an experimental nuclear reactor, aiming to demonstrate the feasibility of nuclear fusion realization in order to use it as a new source of energy. ITER is a plasma device (tokamak type) which will be equipped with a set of plasma diagnostic tools to satisfy three key requirements: machine protection, plasma control and physics studies by measuring about 100 different parameters. ITER diagnostic equipment is integrated in several ports at upper, equatorial and divertor levels as well internally in many vacuum vessel locations. The Diagnostic Systems will be procured from ITER Members (Japan,

Fracture surfaces of a natural carrollite specimen have been characterised by synchrotron and conventional X-ray photoelectron spectroscopy and near-edge X-ray absorption spectroscopy. For the synchrotron X-ray measurements, the mineral surfaces were prepared under clean ultra high vacuum and were unoxidised. The characterisation was undertaken primarily to establish unequivocally the oxidation state of the Cu in the mineral, but also to obtain information on the electronic environments of the Co and S, and on the surface species. Experimental and simulated Cu L 2,3 -edge absorption spectra confirmed an oxidation state of Cu I , while Co 2p photoelectron and Co L 2,3 absorption spectra were largely consistent with the Co III established previously by nuclear magnetic resonance spectroscopy. S 2p photoelectron spectra provided no evidence for S to be present in the bulk in more than one state, and were consistent with an oxidation state slightly less negative than S -II . Therefore it was concluded that carrollite can be best represented by Cu I Co III 2 (S 4 ) -VII . The Cu I oxidation state is in agreement with that expected for Cu tetrahedrally coordinated by S, but is in disagreement with the Cu II deduced previously from some magnetic, magnetic resonance and Cu L-edge X-ray absorption spectroscopic measurements. A significant concentration of S species with core electron binding energies both lower and higher than the bulk value were formed at fracture surfaces, and these entities were assigned to monomeric and oligomeric surface S species. The density of Cu d states calculated for carrollite differed from that previously reported but was consistent with the observed Cu L 3 X-ray absorption spectrum. The initial oxidation of carrollite in air under ambient conditions was confirmed to be congruent, unlike the incongruent reaction undergone by a number of non-thiospinel sulfide minerals.