Vacuum performance of a carbon fibre cryosorber for the LHC LSS beam screen

A new carbon fibre material was developed at the Institute of Solid State Chemistry and Mechanochemistry at the Siberian Branch of the Russian Academy of Science (SB RAS) to meet the requirements of a cryosorber for the large hadron collider (LHC) vacuum chamber. The material must have a large sorbing capacity, a certain pumping speed, a working temperature range between 5 and 20 K, a low activation temperature (below room temperature), a certain size in order to fit into the limited space available and it should be easy to mount. The vacuum parameters of the LHC vacuum chamber prototype with a carbon fibre cryosorber mounted onto the beam screen were studied in the beam screen temperature range from 14 to 25 K at the Budker Institute of Nuclear Physics SB RAS. This carbon fibre material has shown sufficient sorption capacity for hydrogen at operational temperatures of the beam screen in the LHC long straight sections. It is also very important that this material does not crumble and makes a convenient fixation onto the beam screen in comparison to the widely used granulated charcoal. The problem of fluff and ways of reducing the quantity of fluff in the beam channel were studied. The results of these studies show that the carbon fibre material is a possible cryosorber-candidate for use in the LHC and other long vacuum system at cryogenic temperatures. The experimental set-up and results of measurements of the H₂ cryosorption capacity of this carbon fibre material are presented in this paper.     

Development of an ultra-high vacuum system for space application

The aim of this paper is to present the development of a very specific ultra-high vacuum system for the space application PHARAO. In order to reach the specified pressure (2.6×10⁻⁸ Pa) during 3 years in a self-contained system, specific solutions have been developed. A calculation of partial pressures of different chemical species (typically hydrogen, rare gases and cesium) in the different areas of the vacuum tube has been computed. Experiments have been also performed in order to verify the possibility of using different kind of materials (outgassing rates of bulk and porous titanium, silicon carbide reinforced aluminum, graphite, etc.) and pumping systems such as getters and a specially developed ion pump.     

Application of diamond-like Carbon (DLC) coatings for gravitational wave detectors

A laser interferometer gravitational wave detector requires an ultra high vacuum in the tubes in which the laser beams pass. To avoid noise due to scattered light from the surface of tubes, the surface should be treated with “black” coating without increasing the outgassing rate. We found that diamond-like Carbon (DLC) coatings are suitable for this aim. An outgassing rate of at was achieved for DLC coatings on SUS304 without baking. This rate was better than the surface of SUS316 with baking. The reflectivity of the DLC surface was 5% at minimum for a laser beam of Nd:YAG () which is used as a light source for the gravitational wave detector.     

玻璃衬底上钯多晶膜的制备

在乙二醇和乙酰丙酮混合溶剂中将钯多晶膜沉积在玻璃片上.钯膜表面平整,由球形钯晶小颗粒密堆积而成,颗粒均匀,形状规则,直径约为130nm.对混合溶液进行了研究,给出了制备均匀的钯膜的最佳反应条件.颗粒大小和膜层厚度可以通过改变反应条件加以控制.探讨了溶剂所起的作用,提出了混合溶剂中钯膜沉积的可能机理.     

Mechanical properties of polymer thin film measured by the bulge test

The bulge test was used to measure the mechanical properties of polymer thin films with thickness in the range of 77 nm to 352 nm. The mechanical properties of polymeric thin films were extracted by comparing differences between curves of load vs. bulge height obtained from composite film configurations with and without the polymer layer. Both square and long rectangular windows were used to obtain the Poisson ratio and Young's Modulus. Composite film with 230 nm silicon nitride layer and 30 nm Al layer has a composite Poisson ratio of 0.29 and a Young's Modulus of 234 ± 0.8 GPa. The Poisson ratio extracted for a 352 nm Poly(methyl methacrylate)-based thermoplastic polymeric thin film was 0.39. The Young's Modulus extracted for the 77 nm thick polymeric film is 4.9 ± 0.8 GPa and for the 352 nm thick film is 5.8 ± 0.2 GPa. In the thickness range investigated, no clear thickness dependence of the Young's modulus was observed using the Bulge test.     

Tantalum-based thin film coatings for wear resistant arthroprostheses

Cobalt-chromium-molybdenum alloys with high carbon content (HC-CoCrMo) are widely used as materials for arthroprosthesis, in particular in metal-on-metal (MoM) hip joints. In spite of their good wear and corrosion resistance, production of metallic wear particles and metal ion release will occur on a large time-scale. An enhancement of the metal ion level in the patient's blood and urine is often reported in clinical data. Hypersensitivity, inflammatory response and cell necrosis can occur as consequence. So implants on young patients and women on childbearing age are not so widespread. The aim of this research is the realization of a thin film coating in order to improve the biocompatibility of Co-based alloys and to reduce debris production, ion release and citotoxicity. The innovative process consists of a thermal treatment in molten salts, in order to obtain a tantalum enriched thin film coating. Tantalum is chosen because it is considered a biocompatible metal with high corrosion resistance and low ion release. Three HC-CoCrMo alloys, produced by different manufacturing processes, are tested as substrates. The coating is a thin film of TaC or it can be composed by a multilayer of two tantalum carbides and metallic tantalum, depending on the temperature of the treatment and on the carbon content of the substrate. The thin films as well the substrates are characterized from the structural, chemical and morphological point of view. Moreover mechanical behaviour of treated and untreated materials is analyzed by means of nanohardness, scratch and ball-on-disc wear tests. The coating increases the mechanical and tribological properties of HC-CoCrMo.     

XPS study of palladium sensitized nano porous silicon thin film

Nano porous silicon (PS) was formed on p-type monocrystalline silicon of 2–5 Ω cm resistivity and (100) orientation by electrochemical anodization method using HF and ethanol as the electrolytes. High density of surface states, arising due to its nano structure, is responsible for the uncontrolled oxidation in air and for the deterioration of the PS surface with time. To stabilize the material PS surface was modified by a simple and low cost chemical method using PdCl₂ solution at room temperature. X-ray photoelectron spectroscopy (XPS) was performed to reveal the chemical composition and the relative concentration of palladium on the nanoporous silicon thin films. An increase of SiO₂ formation was observed after PdCl₂ treatment and presence of palladium was also detected on the modified surface. I–V characteristics of Al/PS junction were studied using two lateral Al contacts and a linear relationship was obtained for Pd modified PS surface. Stability of the contact was studied for a time period of around 30 days and no significant ageing effect could be observed.     

Si3N4薄膜的表面微观特性

利用偏心静电单探针诊断了反应室内的等离子体密度的空间分布;在不同的工艺条件下制备了Si3N4薄膜,由STM和Telystep-Hobbso轮廓仪研究了ECR－PECVD制备的Si3N4薄膜的表面微观特性,分析了沉积温度对ECR－PECVD制备的Si3N4薄膜表面平整度特性影响的物理机理;结果表明ECR－PECVD制备的薄膜是一种表面均匀致密的纳米Si3N4薄膜。     

Comparisons to establish a force-balanced piston gauge and a spinning rotor gauge as the new measurement standards of MIKES

Centre for Metrology and Accreditation (MIKES) has worked towards expanding its calibration capabilities in the absolute pressure range downwards from 0.2 Pa and lowering measurement uncertainties in the range <10 kPa using a force-balanced piston gauge (FPG) and a spinning rotor gauge (SRG).MIKES was the first national pressure laboratory to purchase a novel type of piston manometer, FPG, developed by DH Instruments Inc., USA. The effective area of the FPG was at first determined at MIKES by a comparison with a conventional pressure balance. The result was confirmed in comparisons in the same pressure range with two other laboratories, Swedish National Testing and Research Institute (SP), Sweden and Institute for Metrology and Technology—Van Swinden Laboratorium (NMi-VSL), Netherlands. Next a direct comparison with the mercury column manometer of Physikalisch-Technische Bundesanstalt (PTB), Germany in the absolute pressure range from 1 to 15 kPa was carried out. Use of the FPG for calibration of capacitance diaphragm gauges (CDGs) is also presented.MIKES now uses two SRGs as reference standards, manufactured by MKS Instruments, Inc., USA. A comparison of SRGs in the range from 0.1 to 5 Pa between MIKES, SP and Vaisala Oyj accredited laboratory was performed in 2001-2002.     

Optical and electrical properties of hydrided palladium thin films studied by an inversion approach from transmittance measurements

Palladium (Pd) thin films have been deposited by electron beam evaporation, and exposed to increasing hydrogen pressures. Transmittance spectra in the range of visible light have been measured to obtain from them, by means of a spectral projected gradient method, the wavelength dependence of the dielectric function. The decreasing metallic character of Pd with hydrogen absorption is displayed. This effect is more pronounced when Pd is deposited on metallic substrates, and there is a correlation with an increase in the effective polarization of the core electrons determining the optical dielectric constant value. Another optimization approach is devised to separate the contribution of the free carriers and of the interband transitions to the optical conductivity and to the dielectric function. Very good agreement is found between the optimized parameters characterizing the free carrier contribution and the corresponding values reported in the literature and obtained by independent experimental methods.     

沉积硬质涂层技术的新发展

本文介绍了新型硬质涂层和硬质涂层沉积技术中电弧离子镀和磁控溅射镀技术的新进展。     

Metal properties and thin film oxidation

The dependence of thin film oxidation rates on the metal properties is discussed in terms of a surface state charge at the metal-oxide interface and a space charge layer in the growing oxide. The properties considered are the magnetic change at the Curie temperature, allotropic transformation and crystal orientation of the metal substrate. Experimental data on the direct logarithmic oxidation of iron, nickel, cobalt and copper forming p-type semiconducting oxides are analysed.     

Inkjet-printed InGaZnO thin film transistor

We report inkjet-printed InGaZnO (IGZO) thin film transistors (TFTs). IGZO ink was prepared by dissolving indium nitrate hydrate, gallium nitrate hydrate and zinc acetate dihydrate into 2-methoxyethanol with additional stabilizers. The resulting films were inkjet-printed with a resolution of 300 dots per inch using droplets with a diameter of 40 µm, and a volume of 35 pl. The films exhibited high optical transparency in the visible range and had a polycrystalline phase of InGaO₃(ZnO)₂ after thermal annealing treatment. The chemical composition of this IGZO sample was also determined, and shown to have high stoichiometric characteristics of low oxygen deficiency. The TFTs with a conventional inverted staggered structure using inkjet-printed IGZO as an active channel layer had a field-effect mobility of ~ 0.03 cm²/Vs in saturation region and an on-to-off current ratio greater than ~ 10⁴.     

Industrialisation of the insulation vacuum barrier for the large hadron collider (LHC) magnet cryostats

The insulation vacuum (<10⁻⁴ Pa) of the large hadron collider magnet cryostats, thermally protecting the superconducting magnets which operate at 1.9 K in superfluid helium, is divided in to 214 m long segments separated by means of insulation vacuum barriers.The insulation vacuum barrier is a leak-tight stainless steel welded structure, composed of two concentric corrugated cylinders and one internal bellows linked together by a 6 mm thick central plate. As the vacuum barrier mechanically links the cryostat vacuum vessel operating at ambient temperature and the 1.9 K superconducting magnets, it is designed to have minimum heat conductivity. Conduction heat in-leak is intercepted at 65 K by a high-purity copper ring brazed onto the stainless steel central plate and thermally linked to a cryogenic line by a copper-aluminium soldering. The thermal performance has been experimentally validated by cryogenic testing.This paper presents the results obtained after industrialisation, manufacture and testing of prototypes and series units. Qualification of leak-tight welds in thin-sheet stainless steel (thickness 0.15-1.3 mm) has been carried out. Ultrasonic testing is performed on all brazing and soldering. Helium leak testing is performed, using dedicated tooling, to ensure a leak-tightness to a rate better than 10⁻⁹ Pa m³ s⁻¹.     

Three dimensional imaging of deformation modes in TiN-based thin film coatings

A TiN thin film coating, approximately 4 μm in thickness, deposited on a ductile steel substrate, was subject to surface deformation via nanoindentation using a spherical indenter, 5 μm in radius, with loads up to 500 mN. Pop-ins were observed during loading, which are characteristic of the onset of cracking and the formation of shear steps at the coating-substrate interface. Focused ion beam microscopy was used to prepare cross-sections through the indentation that revealed the presence of both intercolumnar and inclined cracks. Three-dimensional reconstructions of the deformation zone beneath the indentation were performed using a dual-beam focus ion beam instrument. These constructions provided more detailed images of the morphology of cracks, which were observed to be consistent with theoretical models of plastic deformation of such brittle coatings.     

Influence of DC magnetron sputtering parameters on the properties of amorphous indium zinc oxide thin film

Amorphous or crystalline indium zinc oxide (IZO) thin films, which are highly transparent and conducting, were deposited by DC magnetron sputtering. X-Ray diffraction technique was used for analyzing microstructures of the films, and also differential thermal analysis was performed for observing their crystallization behavior. The IZO thin films prepared were crystallized at much higher temperature than ITO films were. The crystallized samples showed (222) preferred orientations. By varying process parameters, the optimum conditions for the highest electrical conductivity and optical transmittance, and the lowest surface roughness were found. The resistivity of IZO films decreased as the deposition temperature increased until 250 °C, but sharp rise occurred at or above 300 °C. The extinction coefficients diminished in the films prepared with the conditions of higher deposition temperature, sputtering gas of light mass, and heat treatment. However, excessive amount of oxygen flow during deposition brought about the increase of the extinction coefficients. The variations of extinction coefficients mainly influenced the transmittance of the samples. On the basis of X-ray photoelectron spectroscopy analysis, atomic force microscopy measurement, spectroscopic ellipsometry and spectrophotometer measurement, several characteristics of IZO thin films were discussed comparing with those of ITO thin films. Very low surface roughness of IZO thin films could satisfy the requirement for organic light-emitting diode.     

Dielectric reference coatings for the evaluation of thin film characterization techniques

Thin film technology has an increasing demand for industrial reliable characterization techniques. A precise absolute determination of layer thickness, interface width and the quantification of depth profiles in dependence on resolution limits of the measurement are required. Certified reference materials, certified reference coatings (CRCs) and non-destructive evaluation techniques can meet these requirements. Dielectric reference coatings (SiO₂, Si₃N₄) were used for metallographic preparation (e.g. bevelled cross-sections), optical characterization techniques (e.g. spectroscopic ellipsometry (SE)), and films of SiO₂, Si₃N₄ and Al₂O₃ were applied to reference measurements in depth profiling of layer stacks (e.g. radio frequency glow discharge optical emission spectroscopy). Thickness and refractive index of these dielectric single-and multilayer coatings on different substrate materials are accurately determined in advance by means of SE. These values are subsequently used for precise angle determination of bevelled cross-sections, for reference and re-calibration purposes in thin film characterization (system reproducibility) and in surface analysis (determination of sputter and erosion rates, depth profiles). Examples are discussed for different applications and the calculated data are compared with experimental results. It is shown that reproducible commercial coatings are also of importance for use as CRCs.     

Molecular pumping properties of the LHC arc beam pipe and effective secondary electron emission from Cu surface with artificial roughness

A simplified 2D method of angular coefficients is applied to calculations of the molecular pumping properties of complex vacuum systems. An optimization of geometry for the cold LHC beam vacuum chamber with electron shields is performed.An additional interesting application of the angular coefficients method is the estimation of the effective secondary electron emission from surface with artificial roughness. This method allows to take into account re-reflection of electrons using experimental data of the secondary electron energy distributions and surface reflectivity. The suppression efficiency of the secondary electron emission from Cu as a function of roughness parameter is presented. This result is a good input for designing future accelerators and storage rings with potential electron-cloud problems.