ultra high vacuum

Top PDF ultra high vacuum:

Production of ultra-high-vacuum chambers with integrated getter thin-film coatings by electroforming

Production of ultra-high-vacuum chambers with integrated getter thin-film coatings by electroforming

Keywords: Vacuum, getter, electroforming, pump Titanium Zirconium Vanadium (TiZrV) thin film coatings are used in particle accelerators and synchrotron light sources to maintain ultra-high vacuum conditions. They are deposited on the internal walls of the vacuum chambers, transforming them from a gas source into a chemical pump. The trend in electron accelerators design consists in approaching the poles of the steering magnets close to the electron beam. This implies reducing the bore hosting the vacuum chamber and using very small diameter vacuum pipes. The application of physical vapor deposition (PVD) in such small diameter chambers becomes then very difficult. The aim of this project is to develop a novel procedure of coating/assembly, using a sacricial aluminium mandrel as substrate of the thin film together with the creation of a surrounding copper chamber by electroforming. The first part of the study deals with the production and characterization of the electroformed chambers. The mechanical robustness of the assembly is checked, and the film characterization is performed by secondary electron microscopy (SEM), X-ray diffraction analysis (XRD), X-ray Fluorescence Spectroscopy (XRF) and X-Ray Photoelectron Spectroscopy (XPS). Moreover, the pumping performance is measured and compared with reference values of coatings produced by the standard PVD technique. The second part of the study evaluates the impurities included during the different steps of the process: PVD coating, electroforming and chemical etching of the mandrel. Thermal desorption spectroscopy and XPS depth profiling allow to quantify the impurities in the electroformed copper and the TiZrV thin film. Furthermore, the presence of hydrogen trapped in the electroformed copper is studied for different copper sulphate baths. One of them, without additives, require the use of pulse currents. The electrochemical behaviour of the bath allows the selection of different pulse parameters, derived from typical situations on the transient curves. Finally, the development of real-scale prototypes was achieved with the creation of a 4 mm diameter, 2 meters TiZrV coated vacuum chamber, which is unrivalled up to date.
En savoir plus

161 En savoir plus

Resistive Non-Volatile Memories Characteri-zation by Conductive Atomic Force Micros-copy (C-AFM) in Ultra-High Vacuum Environment

Resistive Non-Volatile Memories Characteri-zation by Conductive Atomic Force Micros-copy (C-AFM) in Ultra-High Vacuum Environment

Resistive non-volatile memories characterization by conductive atomic force microscopy (C-AFM) in ultra-high vacuum environment The ongoing research in the field of non-volatile memories aims to overcome the limitation of flash memories in terms of scalability. Several emerging memory technologies especially OxRAMs and PCRAMs are being explored as potential suc- cessors due to many advantages like good scalability, long data retention time, fast read & write speed and low power consumption. In MIM structures for OxRAM, forming and disruption of the nanometer sized conductive filament is commonly accepted as the physical phenomenon for the switching, but still a debate is going on to understand the nature and characteristics of the conductive filament. Hence, in this thesis work we studied mechanisms related to the conductive filament based resistive switching at nanoscale. To do the electrical characterization, a new tech- nique using conductive atomic force microscopy (C-AFM) in ultra-high vacuum is proposed. It is found that in the case of HfO2 based OxRAM, the filament is formed by Ti diffusion from the bottom electrode through the oxide layer. Also, phase tran- sition in phase change materials for PCRAM is investigated for GST-225 and Ge rich GST. It was found that the phase transition from amorphous to crystalline is possible at nanoscale. Finally, the threshold for GST-225 is observed at values nearer to those observed on devices than former observations with standard C-AFM.
En savoir plus

195 En savoir plus

Cu-TBPP and PTCDA molecules on insulating surfaces studied by ultra-high-vacuum non-contact AFM

Cu-TBPP and PTCDA molecules on insulating surfaces studied by ultra-high-vacuum non-contact AFM

The majority of such studies have been performed using metallic substrates, the high electric conductivity of which could prevent their use for transistor-like devices. In order to separate the functional electronic systems from the substrate, molecules with spacer legs have been designed [1] and adsorption on thin insulating spacer films has been explored [4]. As more complex systems of structured molecular monolayers and metallic wiring on insulating

7 En savoir plus

Ultra-high-rate pseudocapacitive energy storage in two-dimensional transition metal carbides

Ultra-high-rate pseudocapacitive energy storage in two-dimensional transition metal carbides

Preparation of Ti 3 C 2 T x hydrogels. Ti3C2T x hydrogel films were prepared by vacuum filtration of a delaminated Ti3C2T x colloidal solution. It should be noted that the vacuum was disconnected immediately once there was no free Ti3C2T x colloidal solution on the filtrate. Afterwards, the obtained hydrogel film was immersed in acetone and carefully peeled off from the filter membrane. After immersing in the electrolyte for 72 h, the hydrogel film was then used for electrochemical characterizations directly. Resulting electrode density values fall in the range from 2.8 to 4.3 g cm − 3 . Thinner electrodes (1 to 15 µm thick) possessed the highest density of ∼ 4 g cm − 3 , while thicker ones ( ∼ 40 µm) showed the lowest density of ∼ 2.8 g cm − 3 . This can be explained by better alignment of MXene flakes in thinner electrodes.
En savoir plus

13 En savoir plus

Cytosolic delivery of siRNA by ultra-high affinity dsRNA binding proteins

Cytosolic delivery of siRNA by ultra-high affinity dsRNA binding proteins

Our experimental findings were unexpected, as high affin- ity in the intracellular space has generally been deemed un- desirable for delivery systems relying on non-covalent pack- aging of siRNA, in some cases motivating the development of vehicles that decrease affinity in response to environmen- tal cues within the cell ( 36 ). In the cytoplasm, inefficient dis- sociation of the siRNA complex can prevent the release of free siRNA for loading onto RISC. In the endosome, in- efficient dissociation may hinder the endosomal escape of siRNA ( 37 ). Although the exact mechanisms underlying en- dosomal escape are not clearly understood for most delivery systems, it is also conceivable that the endosome-disrupting component itself requires liberation, necessitating the deliv- ery particle to dissociate globally. Consequently, with deliv- ery systems that are packaged into a single entity in partic- ular, siRNA–carrier binding strength may be coupled with
En savoir plus

14 En savoir plus

Diffuse Ultra-High Energy Neutrino Fluxes and Physics Beyond the Standard Model

Diffuse Ultra-High Energy Neutrino Fluxes and Physics Beyond the Standard Model

Abstract We study spectral distortions of diffuse ultra-high energy (UHE) neutrino flavour fluxes resulting due to physics beyond the Standard Model (SM). Even large spectral differences between flavours at the source are massaged into a common shape at earth by SM oscillations, thus, any significant observed spectral differences are an indicator of new physics present in the oscillation probability during propagation. Lorentz symmetry violation (LV) and Neutrino decay are examples, and result in significant distortion of the fluxes and of the well-known bounds on them, which may allow UHE detectors to probe LV parameters, lifetimes and the mass hierarchy over a broad range.
En savoir plus

7 En savoir plus

Mechanical and durabiliry properties of environmentally friendly Ultra-High-Performance Concrete (UHPC)

Mechanical and durabiliry properties of environmentally friendly Ultra-High-Performance Concrete (UHPC)

depth, after an exposure of 1 year. Indeed, the decrease of porosity, when BFS is added, is balanced by the decrease of pH, which promotes CO 2 diffusion. Résumé Le présent article traite des performances mécaniques et de durabilité d'un Béton Ultra- Haute Performance (BUHP) plus durable, avec des teneurs en laitier élevées. Trois taux de substitution du ciment par des laitiers des hauts fourneaux (LHF) sont explorés (30%, 50% et 80%). Les résultats montrent qu'une teneur de 30% de laitier améliore légèrement la résistance à la compression, alors qu’avec 50% et 80% de LHF, la résistance à la compression chute significativement. A 3 jours, lorsque la teneur en LHF augmente, la porosité du béton augmente. A 90 jours, la réaction des LHF induit une diminution de la porosité capillaire et le réseau poreux devient plus fin. Ainsi, la perméabilité au gaz et la diffusion des ions chlore diminuent significativement. Les résultats montrent aussi que tous les bétons testés ont une profondeur de carbonatation similaire, après une année d’exposition au CO 2 . En effet, la
En savoir plus

9 En savoir plus

Ultra-high repetition rate InAs/InP quantum dot mode-locked lasers

Ultra-high repetition rate InAs/InP quantum dot mode-locked lasers

chemical beam epitaxy (CBE) on exactly (100) oriented n-type InP substrates. The undoped active region of the QD sample consisted of five stacked layers of InAs QDs with In 0.816 Ga 0.184 As 0.392 P 0.608 (1.15Q) barriers. The QDs were tuned to operate in the C- or L-band using a QD double cap growth procedure and a GaP sublayer [16,17] . In the double cap process the dots are partially capped with a thin layer of barrier material, followed by a 30 s growth interruption and then complete capping. The thickness of the partial cap controls the height of the dots, and hence their emission wavelength. It also helps to narrow the height distribution of the dots, and therefore narrow the 3-dB gain spectrum. Growing the dots on a thin GaP layer allows a high dot density to be obtained and improved layer uniformity when stacking multiple layers of dots, providing maximum gain. This active layer was embedded in a 355 nm thick 1.15Q waveguiding core, providing both carrier and optical confinement. An average dot density of approximately 3.5 × 10 10 cm − 2 per layer was obtained. The
En savoir plus

6 En savoir plus

Simplified flexural design approach of ultra high performance concrete bridge girders

Simplified flexural design approach of ultra high performance concrete bridge girders

Lounis, Z., and Mirza, M.S. 1997. High strength concrete in spliced prestressed concrete bridge girders, PCI/FHWA Int. Symp. on High Performance Concrete, New Orleans, LA, PCI, , 39-59. Resplendino, J., Bouteille, S., Delauzun, O., Maleco, E., Dumont, C., Cantrelle, P., Chanliaud, G., Clergue, C., Lingard, Y., Capra, A., Linger, J., Martin, L., Guilloud, M. 2006. Construction of an overpass on the A51 Motorway, made of a prestressed box beam built with UHPFRC, in the French technologie of concrete, AFGC, The second fib congress, Naples.
En savoir plus

11 En savoir plus

Acquiring High to Ultra-High Resolution Geological Records of Past Climate Change by Scientific Drilling

Acquiring High to Ultra-High Resolution Geological Records of Past Climate Change by Scientific Drilling

4.) The Bipolar Seesaw, North-South Gradients, and Interhemispheric Linkages. Records from the last glacial indicate that the abrupt warmings and coolings recorded in Greenland ice appear to be out of phase with their counterpart temperature excursions in the high-latitude Southern Hemisphere, an observation consistent with changes in the Atlantic’s meridional overturning circulation and its effects on ocean heat transport (EPICA Community Members, 2006). We know little about whether this “bipolar seesaw” is operative at other times in the past and of how changing temperature gradients affect such climatic variables as the distri- bution of tropical precipitation and ITCZ position. Transects of drill sites on land and in the ocean spanning the high to low latitudes in both hemispheres are the only way to examine how gradients and interhemi- spheric linkages have varied through time.
En savoir plus

12 En savoir plus

Exploratory Visualization of Astronomical Data on Ultra-high-resolution Wall Displays

Exploratory Visualization of Astronomical Data on Ultra-high-resolution Wall Displays

Ultra-walls have properties that make them well-suited to the visualization of very large datasets. They can represent the data with a high level of detail while at the same time retaining context: users can transition from an overview of the data to a detailed view simply by physically moving 4 in front of the display. Wall displays also offer good support for collaborative work, enabling multiple users to simultaneously visualize and interact with the displayed data. 5 – 7 In this paper, we introduce FITS-OW, an application that enables astronomers to visualize and interact with very large FITS images and collections thereof. They can pan and zoom in images that are several hundred thousand pixels in both width and height, overlay the results of data analyses, fetch and display additional images of a specific object or region in the sky, showing observations in different ranges of the electromagnetic spectrum or made at different times. Additionally, FITS-OW lets astronomers query databases such as SIMBAD 8 servers, and visualize the results of such queries in-place, right next to the
En savoir plus

16 En savoir plus

Ultra-high-rate pseudocapacitive energy storage in two-dimensional transition metal carbides

Ultra-high-rate pseudocapacitive energy storage in two-dimensional transition metal carbides

Processing control for hydrogel films. The thicknesses and mass loadings of the hydrogel films were controlled by starting with different volumes of Ti 3 C 2 T x colloidal solutions during vacuum filtration. However, as mentioned above, the water from the Ti 3 C 2 T x colloidal solutions was not completely removed following drying. Therefore, the mass loadings and thicknesses of the hydrogel films were only precisely measured after the electrochemical tests. Specifically, the tested films were washed with deionized water and ethanol to remove the electrolyte, and then dried in a vacuum oven for more than 24 h. Lastly, the mass and thicknesses of the dried films were measured with a microbalance and SEM, respectively.
En savoir plus

14 En savoir plus

Rapid synthesis of ultra-long silver nanowires for high performance transparent electrodes

Rapid synthesis of ultra-long silver nanowires for high performance transparent electrodes

There is an increasing demand for optoelectronic devices such as displays, solar cells, transparent heaters, sensors, light- emitting diodes (LEDs), paper-like displays and e-skins. 1,2 In order to produce such components, the development of trans- parent and mechanically exible electrodes remains a task of major importance. 3 Most of the transparent electrodes reported to date rely on the use of metal oxide semiconductor layers, 4 indium tin oxide (ITO) being the most common. However, the scarcity and brittleness of the latter has prompted the search for indium-free and exible transparent electrodes. 5 Silver nano- wire (AgNW) networks constitute one of the most promising alternatives, particularly for exible applications. 6 They combine high electrical conductance with excellent optical transparency, and show minimal conductance decrease with bending. 7,8 Furthermore, low temperature processing methods exist that enable conductance and transparency values on plastics that approach those on glass. 9 It is known from the literature that networks made from longer AgNWs achieve the highly desirable goal of being more conductive at a given transparency. 10 This is because, for a given areal coverage, longer NWs overlap more than shorter NWs, decreasing the extent of NW dead ends not connected into the network. 11
En savoir plus

6 En savoir plus

Laser-Ultrasonic Monitoring of Metallurgical Transformations in Advanced Ultra-High Strength Steels

Laser-Ultrasonic Monitoring of Metallurgical Transformations in Advanced Ultra-High Strength Steels

Grain size determination is a classical application of ultrasound to microstructure characterization. The mechanism of acoustic wave scattering by grains is well-known and models for attenuation in a wide frequency range are available. Laser-ultrasonics can monitor austenite grain size evolution at high temperatures in-situ and in real time both in laboratory [5,6] and in production lines [4]. Austenite grain size can determine to a significant extent the mechanical properties of steels, but measuring the grain size of the prior austenitic phase at room temperature by conventional metallographic methods can be very challenging. Often the microstructures are more complex than a log-normal size distribution of single phase, equiaxed grains, and neither the definition of grain size nor its relationship to the model grain size parameter is straightforward. Even in this case the ultrasonic evaluation can be very useful, giving a quantitative measurement of how coarse (or fine) the microstructure is.
En savoir plus

7 En savoir plus

Nano-shaped hot-wire for ultra-high resolution anemometry in cryogenic helium

Nano-shaped hot-wire for ultra-high resolution anemometry in cryogenic helium

FIG. 3. Schematic of the three main etching shapes that were realized. Between the 3 shapes: (i) saw cut, (ii) directional erosion, and (iii) hole drilling, (iii) gave the best results. contacts between the wire and the prongs and that would lead to additional and undesired hot spots. The wire surface is thus first cleaned with an Ar plasma. A thick layer (in general 1 μm) of alu- minum or gold is then deposited by evaporation under secondary vacuum. During this operation, the central region of the wire is pro- tected against metal deposition by a 1 mm wide mechanical mask so that the sensitive part of the wire is not short-circuited by the metal.
En savoir plus

9 En savoir plus

Automated Segmentation of Hippocampal Subfields From Ultra-High Resolution In Vivo MRI

Automated Segmentation of Hippocampal Subfields From Ultra-High Resolution In Vivo MRI

EXPERIMENTS We performed experiments on ultra-high resolution MRI data collected as part of an ongoing imaging study assessing the effects of normal aging and AD on brain structure. Using a prototype custom-built 32-channel head coil with a 3.0T Siemens Trio MRI system (Wiggins et al., 2006), we acquired images via an optimized high-resolution MPRAGE sequence that enables 380 µm in-plane resolution (TR/TI/TE = 2530/1100/5.39 ms, FOV = 448, FA = 7°, 208 slices acquired coronally, thickness = 0.8 mm, acquisition time = 7.34 min). To increase the signal-to-noise ratio, five acquisitions were collected and motion-corrected to obtain a single resampled (to 380 µm isotropic) high contrast volume that covers the entire medial temporal lobe.
En savoir plus

16 En savoir plus

Design and manufacture of an ultra-high field ex vivo coil assembly

Design and manufacture of an ultra-high field ex vivo coil assembly

where the pressure differential required to produce a given flow is linearly related to the length of the pipe (or tube in this case). This was not a huge factor for less v[r]

89 En savoir plus

Design of Nano-Composites for Ultra-High Strengths and Radiation Damage Tolerance

Design of Nano-Composites for Ultra-High Strengths and Radiation Damage Tolerance

A summary of experiments performed in our team to document bubble nucleation in Cu-Nb multilayers is presented in table 1. Ion implantation results in a non-uniform concentration profile of the implanted species with a maximum in concentration occurring at a depth that depends on the implantation energy. Note that implanted helium doses of 6 x 10 16 /cm 2 at 33 keV and 1 x 10 17 /cm 2 at 150 keV produce equivalent maximum helium concentrations, but at different depths of 120 nm and 450 nm respectively. For these room temperature implantations, the doses we used resulted in two different maximum helium concentrations: (i) 5 at.% in Cu and 7 at.% in Nb, and (ii) 13 at.% in Cu and 21 at.% in Nb. At the 5-7% maximum He concentration, no bubbles were detected in through-focus transmission electron microscopy (TEM) images in the 2.5 nm Cu-Nb multilayers. Also, high-resolution TEM imaging revealed no amorphization or gross changes in interface structure indicating lack of any significant ion-beam mixing between Cu and Nb. However, monolithic films and 100 nm multilayers exhibited 1-2 nm size bubbles. At higher doses (> 13 at.% helium in Cu), bubbles are observed at all layer thicknesses. At the very smallest layer thickness (< 5 nm), helium bubbles were found to decorate the interfaces. In all cases of bubbles nucleated at room temperature, the bubble size was on the order of 1-2 nm.
En savoir plus

9 En savoir plus

Effect of turbulence on the wavefront of an ultra high intensity laser beam

Effect of turbulence on the wavefront of an ultra high intensity laser beam

1 INTRODUCTION There is nowadays in Europe a strong interest in the field of high power lasers. Several multi- petawatt lasers are currently in operation, among which the three ELI projects in eastern Europe [1] and Apollon in France [2]. When designing the solid-state amplifier of a high power laser, thermal management is a critical element to attain a high repetition rate [3]. The solid-state laser amplifier DiPOLE100 (105 J per pulse) demonstrated stable operation at a repetition rate of 10 Hz using cryogenically cooled multi-slab amplifiers [4]. Cooling the amplifying material at cryogenic tem- peratures, i.e. below 150 K, presents advantages both from the thermal and the optical point of view, as reviewed by Brown et al. [5]. Compared to room temperature, the thermal conductivity of amplifying materials is higher at low temperature. A more homogeneous temperature is therefore expected in the amplifying material, reducing the thermo-mechanical stresses and the geometric deformations. The optical performances are also enhanced, especially for ytterbium-doped crys- tals: from quasi-three level laser materials at 300 K they become four level materials at 77 K, thus increasing the overall laser efficiency [6].
En savoir plus

50 En savoir plus

AlGaN/GaN High Electron Mobility Transistors with Ultra -Wide Bandgap AlN buffer

AlGaN/GaN High Electron Mobility Transistors with Ultra -Wide Bandgap AlN buffer

AlGaN/GaN High Electron Mobility Transistors with Ultra -Wide Bandgap AlN buffer I. Abid 1* , R. Kabouche 1 , M. Zegaoui 1 , C. Bougerol 2 , R.Comyn 3 , Y. Cordier 3 , F. Medjdoub 1* 1 CNRS-IEMN, UMR8520, Av. Poincaré, 59650 Villeneuve d'Ascq, France 2

4 En savoir plus

Show all 6717 documents...