COSY,eine neue Forschungsanlage mit Ultra-Hochvakuum-Technologie

The report shows that the development, construction and later successful operation of UHV facilities in the pressure range of ≤10^?10mbar is not possible without a highly sensitive nondestructive testing technique. The example of the large technical research facility COSY is used to demonstrate that the leakage rates (≤10^?10mbar · I · s^?1) and surface purities required can only be achieved by strict compliance with fundamental UHV production conditions and by the rigorous application of helium leak detection techniques and mass-spectrometric residual gas analysis.     

Innovativer Bayard‐Alpert Sensor mit ausgetrickster Röntgengrenze

Innovative Bayard‐Alpert gauge beats the X‐ray limit In this contribution typical problems that arise when using Bayard‐Alpert (BA) vacuum gauges at UHV and XHV chambers regarding measurement range, accuracy, and reproducibility are discussed. Besides others BA gauges deliver a minor residual current that is inherent to the design of the sensor and that defines the lower measurement limit of the gauge. An investigation of the basic physical processes that contribute to the residual currents in BA gauges yields a novel approach to minimize the residual current in BA gauges directly in the sensor. Experimental results of a new BA gauge with a compensation of the residual current (BARION® XHV) show an extended lower measurement limit by two decades downto XHV and a significantly increased accuracy in the pressure range 10^?9…10^?11 mbar. Due to a respective design, furthermore, an improved reproducibility is ensured.     

Characteristics of a magnetron cold cathode gauge

The discharge characteristics of a cold-cathode gauge of the non-inverted magnetron type were studied in ultra-high vacuum. The experimental magnetron cell of length 56 mm and diameter 32 mm was made of stainless steel. The cathode with a diameter of 6 mm was placed along the anode axis. The diameter of the anode was 25 mm and the length was 50 mm. Discharge current versus voltage and magnetic field was measured in the pressure range between 1×10⁻⁸ and 1×10⁻⁶ mbar. It was found that the current at first slowly increased with increasing voltage, reached a maximum at a certain voltage, and decreased rapidly with further increase of the voltage. The voltage, at which the current reached the maximum, depended on the magnetic field density and slightly on the pressure. A novel type of a cold cathode gauge with a self-adjusting power supply is suggested.     

电离规的新进展

介绍了传统热阴极电离规和冷阴极电离规的发展历程和研究现状、新型场发射阴极(微尖型阴极和碳纳米管阴极)在电离规中的应用、小型化电离规的发展和国内在超高/极高真空电离规研究方面取得的成果和现状。重点回顾了碳纳米管阴极电离规和小型化电离规在近年来取得的重大成就。由于碳纳米管具有长径比大、曲率半径小、机械特性强、导电性好和优异的场发射特性,使得其作为电离规阴极有望解决传统冷阴极电离规在低压下不能放电的困难和传统热阴极电离规的热出气效应,从而为极高真空测量提供一种解决途径。     

Hydrogen pumping at 20 K by molecular sieves 5A

Molecular sieves bonded to the condensing surface of a continuous flow cryopump serve as the adsorbent of a cryosorption pump. A study of cool down and pumpdown characteristics of the pump shows that it can be used to pump hydrogen in a chamber to high vacuum (10^?6 mbar) even from an initial filling pressure in the region of 10 mbar.     

The influence of a hot cathode vacuum gauge on the residual gas composition

The residual atmosphere of an UHV chamber is known to be influenced by the hot cathode gauge (HCG) via processes on the hot cathode and by ionisation. In the presence of such a gauge, some gases are pumped while several residuals are generated, depending on the condition of the chamber's inner surface, gauge parameters and gases that are released spontaneously or introduced on purpose.We analysed the influence of the HCG in three different cases of gas accumulation lasting typically for 1 h: (1) in the leak tight vessel, where the background outgassing from the walls was the only inflow Q_backg=1.6×10⁻⁸ mbar l H₂ s⁻¹, (2) during the constant nitrogen inflow in the vessel and (3) during the constant deuterium inflow. Both inflow values were in the order of 1×10⁻⁶ mbar l s⁻¹. The absolute total pressure in the 13 l system was monitored by a capacitance manometer. After the accumulation, the composition of the accumulated gases was analysed by a quadrupole mass spectrometer (QMS), calibrated with the gases of interest. Regarding the operation of the HCG, an obvious difference is noted both in the pressure rise curves and QMS spectra. The generation of carbon-contained residuals by the HCG was evident, but the most unexpected was its pumping action: nitrogen content decreased from 99% (HCG off) to 62% (HCG on) and deuterium content decreased from 65% (HCG off) to only 2% (HCG on).     

Pressure/current characteristics of a magnetron cold cathode gauge

The gauge characteristics for a magnetron gauge in the pressure range 10⁻⁸-10⁻⁵ mbar with nitrogen as a test gas have been studied. The discharge current versus pressure was measured at different magnetic fields from 0.10 to 0.15 T and anode voltages from 4.0 to 7.0 kV. The results showed that a change of slope appeared at pressures between 5×10⁻⁸ and 5×10⁻⁷ mbar. At higher magnetic fields, a change of slope appeared at lower pressures. The slope of the curve below the inflection was higher than that above the inflection. At the lowest magnetic field (0.10 T), a divergence of the curves was observed at pressures below the inflection. The slope of the curve showed no clear dependence on applied voltage.     

Fabrication of a highly sensitive magnetic sensor using an HTS thick film

A highly sensitive magnetic sensor based on Y₁Ba₂Cu₃O_7−x (YBCO) has been fabricated by the spray technique. The value of resistance R_ms in the transitional region ΔT of the thick film, was highly sensitive to the applied magnetic field B_ex. Here, ΔT is the transitional temperature region between the resistance drop temperature T_c^onset and residual resistance temperature T_c^res. The value of residual resistance R_res for an applied magnetic field of 80×10⁻⁴ T (80 G) exhibited an increase of about 580% over the resistance found in a zero magnetic field, and did not display any evidence of hysteresis. The fabrication and magnetic characteristics are discussed.     

Exciting Dilute Magnetic Semiconductor: Copper-Doped ZnO

The present study is focused on the copper-doped ZnO system. Bulk copper-doped ZnO pellets were synthesized by a solid-state reaction technique and used as target material in pulsed laser deposition. Thin films were grown for different Cu doped pellets on sapphire substrates in vacuum (5×10^?5 mbar). Thin films having (002) plane of ZnO showed different oxidation states of dopants. M–H curves exhibited weak ferromagnetic signal for 1–3 % Cu doping but for 5 % Cu doped thin film sample showed the diamagnetic behavior. For deeper information, thin films were grown for 5 % Cu doped ZnO bulk pellet in different oxygen ambient pressures and analyzed. PL measurement at low temperature showed the emission peak in thin films samples due to acceptor-related transitions. XPS results show that copper exists in Cu²⁺ and Cu⁺¹ valence states in thin films and with increasing O₂ ambient pressure the valence-band maximum in films shifts towards higher binding energy. Furthermore, in lower oxygen ambient pressure (1×10^?2 mbar) thin films showed magnetic behavior but this vanished for the film grown at higher ambient pressures of oxygen (6×10^?2 mbar), which hints towards the decrease in donor defects.     

The design and operation of a new extractor gauge for UHV pressure measurements

The design of a new extractor gauge is described for ultra high vacuum pressure measurements. which employs a separate extractor electrode external to the grid. The advantages to be gained by the use of this system, the importance of providing an adequate ion extraction field and also of preventing the flow of electrons into the collector region, are discussed. A method is described of reducing the effect on the residual current of X-rays reflected onto the collector. This allows a residual current of 10^?14 A, at 1 mA electron current, to be achieved. For a gauge sensitivity of 10 torr^?1 this is equivalent to a residual pressure of 1 × 10^?12 torr. The addition of a modulator has been found to give a high modulation factor of 0.95 which should enable the low pressure limit to be extended to below 10^?14 torr.     

Ultra-high vacuum direct bonding of a p-n junction GaAs wafer using low-energy hydrogen ion beam surface cleaning

Low-energy hydrogen ion bombardment is used to clean GaAs surfaces. The hydrogen ions produce contamination-free surfaces without changes in surface composition (stoichiometry) and surface roughness. The wafers were brought into contact at room temperature after cleaning under ultra-high vacuum (UHV), and bonded over the whole area (2 inches) without application of external mechanical pressure. After bonding, the p-GaAs/n-GaAs wafer pair was annealed at 200 °C for 30 min under UHV conditions (<5×10⁻¹⁰ mbar) to improve the interface bonding strength and to achieve a full-area wafer bonding.Infrared (IR) imaging of the as-bonded wafers directly reveal the real bonding behaviour. High-resolution transmission electron microscopy images reveal that the wafers have been directly bonded without damage of the crystal lattice or intermediate layer and the interface is smooth. Current-voltage characterization shows near-ideal forward characteristics and the recombination in p-n junction space charge region.     

Characterization of CuAlO2 films prepared by dc reactive magnetron sputtering

Thin films of copper aluminum oxide (CuAlO₂) were prepared on glass substrates by dc magnetron sputtering at a substrate temperature of 523 K under various oxygen partial pressures in the range 1 × 10⁻⁴–3 × 10⁻³ mbar. The dependence of cathode potential on the oxygen partial pressure was explained in terms of oxidation of the sputtering target. The influence of oxygen partial pressure on the structural, electrical and optical properties was systematically studied. p-Type CuAlO₂ films with polycrystalline nature, electrical resistivity of 3.1 Ω cm, Hall mobility of 13.1 cm² V⁻¹ s⁻¹ and optical band gap of 3.54 eV were obtained at an oxygen partial pressure of 6 × 10⁻⁴ mbar.     

Mirror boxes and mirror mounts for photophysics beamline

A medium resolution beamline, viz. photophysics beamline is being built at INDUS-I, a 450 Mev synchrotron radiation source (SRS) at the Centre for Advanced Technology (CAT), Indore. To house the pre- and post-focusing toroidal mirrors and permit precision movements for steering the SRS beam up to the sample, two ultra-high vacuum (UHV) compatible mirror boxes and mirrors have been designed, fabricated and tested. Details of the setup, including UHV (P < 10⁻⁹ mbar) testing and performance evaluation of the mirror mounts under UHV conditions, are discussed in this paper.     

Tin Sulfide‐Based Nanohybrid for High‐Performance Anode of Sodium‐Ion Batteries

Nanohybrid anode materials for Na‐ion batteries (NIBs) based on conversion and/or alloying reactions can provide significantly improved energy and power characteristics, while suffering from low Coulombic efficiency and unfavorable voltage properties. An NIB paper‐type nanohybrid anode (PNA) based on tin sulfide nanoparticles and acid‐treated multiwalled carbon nanotubes is reported. In 1 m NaPF₆ dissolved in diethylene glycol dimethyl ether as an electrolyte, the above PNA shows a high reversible capacity of ≈1200 mAh g^?1 and a large voltage plateau corresponding to a capacity of ≈550 mAh g^?1 in the low‐voltage region of ≈0.1 V versus Na⁺/Na, exhibiting high rate capabilities at a current rate of 1 A g^?1 and good cycling performance over 250 cycles. In addition, the PNA exhibits a high first Coulombic efficiency of ≈90%, achieving values above 99% during subsequent cycles. Furthermore, the feasibility of PNA usage is demonstrated by full‐cell tests with a reported cathode, which results in high specific energy and power values of ≈256 Wh kg^?1 and 471 W kg^?1, respectively, with stable cycling.     

Study of microwave components for an electron cyclotron resonance source: Simulations and performance

A high power (2 kW, CW) magnetron-based microwave system operating at 2.45 GHz has been designed, tested, characterized, and used to produce plasma. The system consists of a microwave source, an isolator, a directional coupler, a three-stub tuner, a high voltage break, a microwave vacuum window, and a microwave launcher. These microwave components were simulated using microwave studio software. The low power and full term characterization of the microwave system has been done using vector network analyzer. The system was tested for 2 kW continuous wave of microwave power using glass-water load. The microwave system has been developed to study the microwave interaction with plasma at different operation regimes (Gases: Nitrogen, argon and hydrogen; Gas pressure : 10^?5–10^?3 mbar; Microwave power : 300–1000 W; Magnetic field: 875–1000 G) and to extract the proton beam current with hydrogen produced plasma. A plasma density ～5 × 10¹¹ cm^?3 and average electron temperature of ～13 eV was obtained. This article describes various aspects of the microwave system including design, fabrication, characterization and performance studies of the microwave components.     

An electronic vapour pressure controller

The thermal conductivity of thin gold wire of commercial purity was found to be given by λ = 0.117 T + 7 × 10^?4 T² (WK^?1 cm^?1) between 0.8 and 10 K. The process limiting the conductivity is scattering of electrons by impurities. The moderate deviation of the thermal conductivity from that predicted on the basis of the residual electrical resistivity is probably due to the effect of magnetic impurities on the transport properties.     

Dipolar heat capacity of CMN

The magnetic contribution to the low-temperature specific heat of cerous magnesium nitrate (CMN) was determined by the Casimir-Du Pré ac susceptibility method in the region of 1 K. The value found for the coefficient of the major (T ^?2) term is in good agreement with that determined in this laboratory in magnetic cooling experiments. It is some 10% less than that calculated for the magnetic dipole interaction between the Ce ³⁺ ions.     

Analysis of different vacuum annealing levels for ZnSe thin films as potential buffer layer for solar cells

In order to seek potential buffer layer, the influence of different vacuum annealing levels on physical properties to e-beam evaporated Zinc Selenide (ZnSe) thin films are meticulously investigated herein. The X-ray diffraction patterns of vacuum-annealed ZnSe films confirmed the prominent (111) reflection of the cubic phase where the crystallite size is found maximum (29 nm). The wavy optical transmittance spectra are observed for these ZnSe films, where higher transparency is observed in the visible region. A blue shift in the optical band gap (2.56–2.81 eV) and shrink in refractive index from 2.49 to 2.40 is observed with increasing vacuum levels. The HRTEM images demonstrated (111), (220), and (311) orientations of the lattice planes, and EDS patterns confirmed deposition of ZnSe films. The ohmic nature of the analyzed ZnSe thin films is validated by the I–V characteristics where the resistivity is found in the order of 10² Ω-cm for vacuum-annealed and 10⁴ Ω-cm for the pristine films. The AFM images indicated hill-like structures where the roughness is found to vary with vacuum level. The physical properties of ZnSe films are conspicuously tailored by vacuum annealing levels, and the findings recommend the use of?~?5?×?10^?3 mbar vacuum-annealed ZnSe thin films as potential buffer layer to the solar cells.

     

Field emission from oriented tin oxide rods

Tin oxide (SnO₂) films were grown on silicon substrates by a wet chemical route. It was found from scanning electron microscopy investigations that oriented SnO₂ rods normal to the substrates were obtained. Field emission studies were carried out in diode configuration in an all metal ultra high vacuum chamber at a base pressure ∼ 1.33 × 10^− 8 mbar. The ‘onset’ field required to draw 0.1 μA/cm² current density from the emitter cathode was found to be ∼ 3.4 V/μm for SnO₂ rods. The field emission current and applied field follows the Folwer-Nordheim relationship in low field regime. The observed results indicate that the field emission characteristics of chemically grown SnO₂ structures are comparable to the vapor grown nanostructures.     

Simulations of negative ion extraction from a multi-aperture ion source in the presence of the magnetic filter

The particle-in-cell method based numerical model of negative ion beam extraction from a large volume multi-aperture ion source is briefly described. The model takes into account the influence of the transversal magnetic field and diffusion of electrons across the field. The current-voltage curves for H^- ions and electrons are presented. The results are compared for the three cases: without filter field; with the field but without diffusion; and with the field and electron diffusion. The presence of the magnetic filter field increases H^? yields significantly (by 200%). A random-walk electron diffusion model enables electrons to travel through the magnetic field, which reduces a nonphysical effect of excessive electron aggregation in the filter region. The changes of filter width do not alter H^? current more than 10%.