INRIM continuous expansion system as high vacuum primary standard for gas pressure measurements below 9 × 10 Pa

The continuous expansion system can be considered the state of the art for pressure measurement in the ultra high vacuum range. In the last years, at INRIM, a new continuous expansion system was designed, assembled and characterized. The system is the high vacuum primary standard in the pressure range from 1 × 10⁻⁶ Pa to 9 × 10⁻² Pa with relative standard uncertainty ranging from 2.1% at 1 × 10⁻⁶ Pa down to 0.4% at 9 × 10⁻² Pa. The system is based on the passing of a measured gas flow through a fixed and known conductance. The gas flow is generated and measured by a primary gas flowmeter based on the constant-pressure-variable-volume method.In the first part of the paper both a correction for the effect of transitional flow through the orifice and a new analytical evaluation of orifice conductance are presented. In the second part the accuracy of the system and the pressure uncertainty evaluation are described.     

LHC: The world's largest vacuum systems being operated at CERN

With the successful circulation of beams in the Large Hadron Collider (LHC), its vacuum system becomes the world's largest vacuum system under operation. This system is composed of 54 km of ultra high vacuum (UHV) for the two circulating beams and about 50 km of insulation vacuum around the cryogenic magnets and the liquid helium transfer lines (QRL). The LHC complex is completed by 7 km of high vacuum transfer lines for the injection of beams from the SPS and their dumping.Over the 54 km of UHV beam vacuum, 48 km are at cryogenic temperature (1.9 K), the remaining 6 km are at ambient temperature and use extensively non-evaporable getter (NEG) coatings, a technology that was born and industrialised at CERN.The cryogenic insulation vacuum systems, less demanding technically, impress by their size and volume: 50 km and 15,000 m³. Once cooled at 1.9 K, the cryopumping allows pressure in the 10⁻⁴ Pa range to be attained.     

Electronic structure and formation mechanism of complex Ti-Nb oxide

Two-layer thin film specimens of Nb₂O₅ and TiO₂ were deposited on optical-grade quartz and n-type single crystalline silicon substrates with (100) crystallographic orientation by a magnetron deposition source under high vacuum. All samples were subjected to 1-5 h of resistive heating at ultra high vacuum, and in situ X-ray diffraction measurements (XRD) were made in the temperature range of 300-1373 K. Analysis of the XRD data confirmed the growth of TiNbO₄ during cooling of the two-layered specimens which had been previously heated to 1373 K. Optical measurements revealed a band gap value of 3.78 eV for the direct transition and 3.29 eV for the indirect one. The samples had a transmittance of 85% in the visible range. Electrophysical measurements in high vacuum established the electroresistivity vs. temperature dependence in the range of 300-773 K, from 7.3 ? 10^− 1 to 3.9 ? 10^− 2 Ω cm, respectively. X-ray photoelectron spectroscopy measurements were used to examine the chemical shift for Nb 3d, with a value of − 1.1 eV in comparison with Nb⁵⁺ and matched to Nb⁴⁺[1], while the Ti lines correspond to Ti⁴⁺[2].     

Status and performance of MGC-20 cyclotron vacuum system

A variable energy compact cyclotron has been installed at the Nuclear Research Centre NRC, Atomic Energy Authority AEA, Egypt. It is equipped to accelerate protons, deuterons, α-particles and ³He. The vacuum system has to provide high vacuum within the 10⁻⁶ mbar range in order to accelerate particles and to have stable beam. The total vacuum volume includes the acceleration chamber and the ion beam transport line is ≈3 m³. The pump-down time of the system to the steady high vacuum is measured. Results on the performance of the forevacuum and the high-vacuum pumps will be presented. The characteristics of the vacuum system components are evaluated.     

Thick TiN films prepared by vacuum arc deposition and high energetic nitrogen ion beam dynamic mixing implantation

TiN films have many features, such as high wear resistance, high corrosion resistance and good oxidization resistance. With the technology of vacuum arc deposition and high current density nitrogen ion beam dynamic mixing implantation (DMI), the TiN film with a thickness of 33 μm and adhesion 58 N is synthesized on hard alloy and high-speed steel substrates. X-ray diffraction has been used to examine the crystal structure of the films. The results showed that the main phases presented in DMI films are TiN and Ti₂N and that the films revealed random growth. Cross-sectional scanning electron microscopy revealed the dense morphology and the thickness of the films. Micro-hardness tests showed that the average hardness of the films was about 2500 HK. Electrochemical experimental results indicated that DMI-TiN film had excellent corrosion resistance both in 3% NaCl solution and in 0.5 Mol H₂SO₄ solution.     

Optimized annular triode ion pump for experimental areas in the LHC

The large hadron collider will be the world next generation accelerator to be operational in 2007 at CERN. The UHV requirements force the installation of ion pumps in the experimental areas of ATLAS. Due to the unacceptable particle background that standards ion pumps may generate, a reduction in the amount of material constitutive of the pump body is required. Hence, a stainless steel 0.8 mm thick body annular triode ion pump has been designed. A pumping speed of ∼20 l/s at 10⁻⁹ mbar is provided by 15 pumping elements. Finite elements analysis and destructive tests have been performed in its design. Final vacuum tests results are shown.     

Development of integrated ΔE-E silicon detector telescope using silicon planar technology

An integrated ΔE-E silicon detector telescope using silicon planar technology has been developed. The technology developed is based on standard integrated circuit technology and involves double sided wafer processing. The ΔE and E detectors have been realized in a PIN configuration with a common buried N⁺ layer. Detectors with ΔE thicknesses of 10, 15 and 25 μm, and E detector with thickness of 300 μm have been fabricated and tested with alpha particles using ²³⁸Pu-²³⁹Pu dual alpha source. The performance of the detector with ΔE detector of thickness 10 μm and E detector of thickness 300 μm has been studied for identification of charged particles using 12 MeV ⁷Li⁺ ion beam on carbon target. The results of these tests demonstrate that the integrated detector telescope clearly separates the charged particles, such as alpha particles, protons and ⁷Li. Due to good energy resolution of the E detector, discrete alpha groups corresponding to well known states of ¹⁵N populated during the reaction could be clearly identified.     

Tensile behavior of carbon fiber bundles at different strain rates

Quasi-static and high strain rate tensile tests have been performed on T700 carbon fiber bundles and complete stress-strain curves at the strain rate range of 0.001 s^− 1 to 1300 s^− 1 were obtained. Results show that strain rate has negligible effect on both ultimate strength and failure strain, and T700 carbon fiber can be regarded as strain rate insensitive materials. On the basis of the fiber bundles model and the statistic theory of fiber strength, a damage constitutive model based on Weibull distribution function has been developed to describe tensile behavior of T700 fiber bundles. And the method to determine the statistic parameters of fibers by tensile tests of fiber bundles is established, too.     

Instability of threshold voltage under constant bias stress in pentacene thin film transistors employing polyvinylphenol gate dielectric

The instability of threshold voltage and mobility of pentacene thin film transistors using a poly(4-vinylphenol) gate dielectric have been investigated under constant bias stress. The mobility was very stable in vacuum by exhibiting 2% variation after 6 h stress even under the high gate bias stress of V_GS = − 20 V. Meanwhile, we observe a negative shift of threshold voltage under stress in vacuum. This shift is attributed to charges trapped in deep electronic states in pentacene near the gate interface. We propose a model for the negative shift of the threshold voltage and extract the hole concentration, 4.5 × 10¹¹ cm^− 2, needed to avoid the onset of stress effects, resulting in a design rule of the channel width to length ratio larger than 40.     

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.     

Correlations between substrate bias, microstructure and surface morphology of tetrahedral amorphous carbon films

The microstructure and surface morphology of ta-C films deposited on p-type (1 0 0) single crystal silicon with the substrate negative bias varying from 0 to 2000 V by the filtered cathodic vacuum arc technology have been investigated by means of Raman spectroscopy and atomic force microscope. The optimal deposition process of sp³-rich ta-C films can be confirmed in light of the relations between the coupling coefficients or full-width at half-maximum and the substrate negative bias. The surfaces of these films are uniform and smooth and RMS surface roughness is less than 0.4 nm. At the lower energetic grades, the more the content of sp³ is in the film, the smoother the surface of the film is. The dependence of the surface morphology and the impinging energy of the species can be illustrated according to the subimplantation growth mechanism. Nevertheless at the high energetic grade, the impinging ions with appropriate energy sputter and smoothen the surface so that the roughness might be even lower than the one of the films with the richest sp³ component.     

Diffusion of Pb in carbon ion-implanted silicon: Discovery of a new crystalline phase after electron beam annealing

A novel phase has been discovered by dual low-energy ion implantation and high vacuum electron beam annealing. (100) p-type Si was implanted with (a) 20 keV ¹²C⁺ ions to the fluence of 6 × 10¹⁶ cm⁻² and (b) 7 keV Pb⁺ ions to the fluence of 4 × 10¹⁵ cm⁻². The ¹²C ion implantation results in an understoichiometric shallow SiC_x layer that intersects with the surface. The implanted Pb ions decorate a shallow subsurface region. High vacuum electron beam annealing at 1000 °C for 15 s using a temperature gradient of 5 °C s⁻¹ leads to the formation of large SiC nanocrystals on the surface with RBS measurements showing Pb has diffused into the deeper region affected by the ¹²C implantation. In this region, a new crystalline phase has been discovered by XRD measurements.     

Design of the vacuum system for Diamond, the UK third generation light source

The Diamond synchrotron, which is due to come into operation with beam for users in 2007, is being constructed at the Rutherford Appleton Laboratory, Oxford. The design status of the vacuum system of the storage ring as at 31st December 2002 will be reported.Diamond is based on a 24 cell 3 GeV electron storage ring of 561.6 m circumference. As is the case for most such machines, the operational pressure has been specified as 10⁻⁹ mbar to give a beam lifetime >10 h at the design current of 300 mA. The storage ring vacuum system will use conventional technology and most of the vacuum vessels will be constructed of stainless steel. With the exception of the insertion device (ID) vacuum chambers, the ring has not been designed to be baked in situ, but all components will be vacuum baked as sub assemblies before installation. The vacuum system is designed to achieve the required pressure after 100 A h of beam conditioning using the pumping scheme, which will be described.Twenty-one ID straights are available for ID, of which seven will be installed at the start of operations. Three types of vacuum vessel will be used in these straights, a stainless-steel make-up pipe, a NEG coated narrow-gap vacuum chamber for conventional IDs and a wider vacuum chamber to house in vacua IDs. The ID straights have an isolation valve installed at each end, and in situ baking can be used in these restricted locations, for example to activate the NEG coatings.The vacuum system for the beam line front ends has been designed to provide good vacuum isolation between the storage ring and the experimental beam lines, whether or not an interposing window is fitted.Pumping schemes, pressure measurement and calculated pressure profiles will be described.     

Synthesis and nonlinear optical properties of Lead Telluride nanorods

Lead Telluride (PbTe) nanorods have been uniformly grown on silicon substrates, using the thermal evaporation technique under high vacuum conditions. The structural and morphological studies are done using X-ray diffraction and scanning electron microscopy. Optical nonlinearity studies using the open aperture z-scan employing 5 ns and 100 fs laser pulses reveal a three-photon type absorption. For nanosecond excitation the nonlinear absorption coefficients (γ) are in the order of 10⁻²² m³ W⁻² and for femtosecond excitation it is in the order of 10⁻²⁹ m³ W⁻². The role of free carriers and excitons in causing the nonlinearity in both excitation time domains is discussed. Results indicate that PbTe nanorods are good optical limiters with potential device applications.     

Conceptual design of the vacuum system of the Spanish synchrotron light source (ALBA) storage ring

ALBA will be a third generation synchrotron light facility to be built near Barcelona (Spain). The design phase of ALBA is almost completed and the first components are ready to be ordered. Commissioning of the storage ring is foreseen to start at the end of 2008. The circumference of the storage ring of ALBA is 268.8 m and it will be divided into 16 vacuum sections by ultra high vacuum (UHV) gate valves. The vacuum chamber will be made of stainless steel with vertical aperture of 28 mm and 72 mm width. The vacuum chamber will be connected to an antechamber with a slot of 10 mm height. The antechamber will have the crotch absorbers which will absorb the unwanted synchrotron radiation. The pumping will be by sputter ion pumps (SIP), NEG pumps and titanium sublimation pumps (TSP), with an overall pumping speed from SIP of 57,400 l/s. This will maintain an average dynamic pressure of around 1 × 10⁻⁹ mbar to achieve a beam lifetime >15 h at the designed current.     

Synthesis, characterization and optical properties of mono- and bis-chalcone

Mono- and bis-chalcone have been synthesized by the reaction of 3-acetyl-2,5-dimethylthiophene and N, N-di-methylbenzaldehyde/terephthalaldehyde in ethanolic NaOH in microwave oven. The structure of these compounds was established by elemental analysis, IR, ¹H NMR, ¹³ C NMR and GC-MS spectral analysis. Thin films with thickness of 100 nm of mono- and bis-chalcone were evaporated by thermal evaporation onto glass/Si wafer substrates under a vacuum of 10^− 6 Torr. The optical constants (absorption coefficient and optical band gap) of these films have been studied as a function of photon energy in the wavelength region 300-1100 nm. Analysis of the optical absorption data shows that the rule of non-direct transitions predominates. The optical band gaps for mono- and bis-chalcone are found to be 2.31 and 0.99 eV respectively. It has been found that the absorption coefficient changes with increasing photon energy. The peak values of the absorption coefficient are found to be at 370 nm for mono-chalcone and 460 nm for bis-chalcone thin films.     

Residual gas analysis in the TOF vacuum system

The residual gas composition in the time-of-flight (TOF) spectrometer vacuum system has been measured with a quadrupole mass spectrometer. All residual gases except hydrogen and helium are condensed and freezed on the windows of the liquid hydrogen target. As a result it increases the background during the reaction between the cooler synchrotron (COSY) beam and the target. These condensates have to be cleaned from the target windows by fast heating the target cell from 16 K up to room temperature. The partial pressure spectrums of the condensed gases on the liquid hydrogen target are also measured. The residual gas analysis shows that the majority of the condensates on the target windows are nitrogen, oxygen and water vapor. The target area has to be in a high vacuum <1×10⁻⁶ mbar in order to minimize the condensate. The target windows have to be cleaned with the fast heating cycle every 48 h.     

Synthesis of thermally evaporated ZnSe thin film at room temperature

Zinc selenide (ZnSe) thin film on glass substrates were prepared by thermal evaporation under high vacuum using the quasi-closed volume technique at room temperature (300 ± 2 K). The deposited ZnSe properties were assessed via X-ray diffraction, atomic force microscope (AFM), UV-Vis specrophotometry, Raman spectroscopy, photo-luminescence, Fourier transform infrared spectroscopy (FT-IR) and spectroscopic ellipsometry. The X-ray diffraction patterns of the film exhibited reflection corresponding to the cubic (111) phase (2θ = 27.20°). This analysis indicated that the sample is polycrystalline and have cubic (Zinc blende) structure. The crystallites were preferentially oriented with the (111) planes parallel to the substrates. The AFM images showed that the ZnSe films have smooth morphology with roughness 6.74 nm. The transmittance spectrum revealed a high transmission of 89% in the infrared region (≥ 600 nm) and a low transmission of 40% at 450 nm. The maximum transmission of 89.6% was observed at 640 nm. Optical band-gap was calculated from the transmission data of specrophotometry, photo-luminescence and ellipsometry and was 2.76, 2.74 and 2.82 eV respectively. Raman spectroscopic studies revealed two longitudinal optical phonon modes at 252 cm ^-1 and 500 cm ^-1. In photoluminescence study, the luminescence peaks was observed at 452 nm corresponding to band to band emission. FT-IR study illustrated the existence of Zn-Se bonding in ZnSe thin film. The optical constants were calculated using spectroscopic ellipsometry and were determined from the best fit ellipsometric data in the wavelength regime of interest from 370-1000 nm. These results manifested excellent room temperature ZnSe synthesis and characteristics for opto-electronics technologies.     

Degradation in optical reflectance of Al film mirror induced by proton irradiation

Mirror made of Al films can yield high reflectance over a broad wavelength range, and have been widely used in spacecraft optical instruments for high quality optical applications. However, such mirrors might be deteriorated under the irradiation of charged particles in the Earth radiation belt. In order to reveal the deterioration mechanism, the change in optical properties of Al film mirrors induced by proton irradiation with less than 200 keV was studied in a vacuum environment with a heat sink. Experimental results showed that the proton irradiation led to an obvious degradation of spectral reflectance of the Al film mirror within the wavelength range from 250 to 800 nm. The threshold fluence 1 × 10¹⁶ cm⁻² was found, above which the reflectance decreased greatly with increasing proton fluence when the radiation damage primarily occurred in the Al film. According to the experimental results, a formula for the performance evolution of Al film optical mirrors irradiated with protons is proposed.     

Growth and current-voltage characterization of ZnTe/CdTe heterojunctions

ZnTe layers have been grown on a (111) oriented CdTe single crystal substrate by vacuum thermal evaporation technique. The growth temperature was 180 °C at a base pressure of 10^− 4 N/m². The as-grown samples were investigated by X-ray diffraction. The pattern indicated a highly oriented crystallographic growth of ZnTe (111) layer on CdTe (111) substrate. The current-voltage characteristics in both forward and reverse biasing were carried out in the temperature range from 300 down to 200 K. The dark forward current curves were definitely of the diode type in the forward direction. This behavior can be understood as the barrier at the interface limits forward and reverse carrier flow across the junction, where the built-in potential could be developed. Series resistance due to the neutral region was estimated at approximately 320 Ω and the activation energy of the carriers was calculated and found to be 0.11 ± 0.03 eV. The reverse current shows negative resistance behavior at low voltage range.