Optimum beam transfer in the environmental scanning electron microscope

The gas density of argon along the axis of a pressure-limiting aperture in an environmental scanning electron microscope is found by the direct simulation Monte Carlo method. The aperture is made on a thin material plate, producing the sharpest possible transition region between the specimen chamber and the differentially pumped region downstream of the gas flow. The entire regime from free molecule to continuum flow has been studied, which covers any size of aperture diameter and any pressure from vacuum to one atmosphere. The amount of electron beam transmitted without scattering at any point along the aperture axis is found in the range of accelerating voltage between 1 and 30 kV for argon. The electron beam transmission is further computed for helium, neon, hydrogen, oxygen, nitrogen and water vapour. This study constitutes the basis for the design and construction of an environmental scanning electron microscope having an optimum electron beam transfer, which is the primary requirement for an optimum performance instrument.     

X-ray microanalysis of wet biological specimens in the environmental scanning electron microscope. 1. Reduction of specimen distance under different atmospheric conditions

X-ray microanalysis of non-biological and biological specimens was carried out in the environmental scanning electron microscope (ESEM) under different conditions of specimen distance (the distance travelled by the electron probe within the specimen chamber) and chamber atmosphere. Using both water vapour and argon atmospheres, it was shown that reduction in specimen distance had no effect on atmospheric gas X-ray signal in either case. Unlike water vapour, increased levels of argon (up to 10 torr) caused a marked depression of specimen P/B ratios, with a decrease in both characteristic and background (continuum) counts. These effects in argon were not altered by reduction in specimen distance. Specimen distance was important in relation to beam skirting and elemental analysis. With an extended assembly (short specimen distance), beam skirting in a water-vapour atmosphere was much reduced – leading to enhanced element detectability in a discrete biological specimen (Anabaena cyclindrica).     

Improvement of four anode rods ion source

In this work, an improved form of a saddle field ion source has been designed and constructed. It consists of four anode rods made from copper and two copper cathode discs. The two cathode discs are placed symmetrically on both sides of the four anode rods. The electrical discharge and output ion beam characteristics were measured at different pressures using argon gas. The optimum distance between each two anode rods was determined. Also the optimum distance between the four anode rods and any cathode disc was obtained. It was found that the optimum distance between each two anode rods equal to 6 mm, while the optimum distance between the four anode rods and any cathode disc equal to 16 mm, where a stable discharge current and maximum output ion beam current can be obtained. The effect of negative extraction voltage applied to both the extractor electrode and Faraday cup on the output ion beam current was studied. The sputter yield of copper and aluminum targets using argon ions of different energies was determined.     

Hollow target magnetron-sputter-type solid material ion source

A thin-walled aluminum (Al) hollow electrode has been inserted into an ion source to serve as an electrode for a radio frequency magnetron discharge. The produced plasma stabilized by argon (Ar) gas sputters the Al electrode to form a beam of Al(+) and Ar(+) ions. The total beam current extracted through a 3 mm diameter extraction hole has been 50 μA, with the Al(+) ion beam occupying 30% of the total beam current.     

Characteristics of low-energy ion beams extracted from a wire electrode geometry

Beams of argon ions with energies less than 50 eV were extracted from an ion source through a wire electrode extractor geometry. A retarding potential energy analyzer (RPEA) was constructed in order to characterize the extracted ion beams. The single aperture RPEA was used to determine the ion energy distribution function, the mean ion energy and the ion beam energy spread. The multi-cusp hot cathode ion source was capable of producing a low electron temperature gas discharge to form quiescent plasmas from which ion beam energy as low as 5 eV was realized. At 50 V extraction potential and 0.1 A discharge current, the ion beam current density was around 0.37 mA/cm(2) with an energy spread of 3.6 V or 6.5% of the mean ion energy. The maximum ion beam current density extracted from the source was 0.57 mA/cm(2) for a 50 eV ion beam and 1.78 mA/cm(2) for a 100 eV ion beam.     

高强铝合金厚板窄间隙激光焊接新工艺

针对铝合金厚板激光焊接存在的问题,提出采用窄间隙激光焊接的工艺技术路线,在分析了这种工艺方法的难点后,采用3.5 kW高光束质量扩散冷却slab CO2激光器,通过工艺方案的优化,首次成功实现了20 mm厚铝合金的窄间隙激光焊接.     

Comparison of ion beam sputtered chromium and iridium films for electron microscopy applications

The structure and composition of thin, conductive metallic films of chromium and iridium that are typical of the coatings used for electron microscopy is described. The purpose of this study was to determine the grain size and composition of the films deposited, with thicknesses of 1 nm, 2.5 nm, and 5 nm, onto amorphous carbon films using ion beam sputtering with argon as the sputtering gas. A comparison between chromium films deposited under conditions of liquid nitrogen (LN) trapping or of no trapping revealed slight differences in their microstructure. As expected, the grain size of the films increased with the thickness, and the average grain sizes varied between 10 and 25 nm. Grain size was also found to depend on the source of ion beam energy; the correlation between grain size and beam energy was more pronounced in the iridium films than in the chromium films. This effect was greater when the deposition chamber was not LN trapped. As the ion beam energy increased from 18 W to 24 W, there was a corresponding increase in grain size in some of the films. Although transmission electron diffraction analysis indicated the presence of about 5% chromium oxide in the chromium films, no oxide was detected in the iridium films.     

Measuring the local density of light gases by characteristic X-rays

Until recently, the measurement of the local gas and plasma density through the intensity of the characteristic radiation induced by an electron beam was being carried out for argon only. The difficulty in applying this method to light gases, e.g., N₂ and O₂, resides in the necessity of resolving the low-energy (0.4–0.6 keV) spectral lines against the background of high-energy (15–50-keV) bremsstrahlung. X-ray and magnetic filters helped measure light-gas spectra under the given conditions. Deceased.     

天然气中Ar同位素对比测定及数据分析

近年实验室研制了高精度、超高真空的净化系统与VG5400质谱计在线连接,实现了天然气中He、Ar同位素的在线测量。在测量过程中为杜绝进样过程的氩同位素质量分馏效应,本次工作采用了“分段静态平衡移样”法,提高了天然气中氩同位素测量的精度。应国家重大基础研究“973”天然气项目的要求和安排,对过去测量过氩同位素的一批钢瓶样(51个)进行了对比测量分析。研究结果表明,过去测量过程中存在空气本底的污染和同位素分馏效应,但两次测量结果有73%的数据在估算源岩年代公式的数据误差范围之内,本实验室认为原测量数据能够满足源岩地质年代段的粗略估算要求。另外,对比研究结果还表明,过去认为同一样品40Ar/36Ar测量结果较高值是正确的这一说法是不全面的。     

Methods for detecting events in double-phase argon chambers

Multichannel wire gas electron multipliers in combination with pin anodes are proposed for detection of events in the gas phase of a double-phase argon chamber. Hydrogen with a concentration of 10 vol % is added to argon to eliminate feedbacks by photons emitted by excited argon molecules in avalanche development processes while detecting events in the argon gas. A maximum electron multiplication coefficient of ～300 has been obtained for the multichannel wire gas electron multipliers with a 1-mm gap used to detect α particles in the Ar + 10% H₂ mixture at a pressure of 1 atm (abs.). When a pin anode is used, the maximum electron multiplication factor is ～2.5 × 10⁵ for α particles and 3 × 10⁶ for β particles (⁶³Ni). It has been experimentally shown that adding H₂ with a concentration of 100 ppm to liquid argon has no effect on the singlet component of the scintillation signal in the liquid argon and reduces the emission efficiency relative to the pure argon gas phase only slightly (by 20%).     

Ion energy distribution functions of low energy beams formed by wire extraction electrodes

The two-electrode extractor system made of 0.1 mm diameter tungsten wires separated by 0.7 mm has formed an argon ion beam with 50 V extraction potential. Energy spreads of the extracted beams were typically less than 2 eV when the beam current density was low. The beam intensity rapidly decreased as the distance between the extractor and the beam detector increased, indicating space charge limited transport of the beam. Problems associated with the emittance measurements are also discussed.     

A new satellite-borne neutral wind instrument for thermospheric diagnostics

The bulk motion of the neutral gas at altitudes between about 200 and 600 km is an important factor in predicting the onset of plasma instabilities that are known to distort and/or disrupt high frequency radio communications. These neutral winds have historically been quite difficult to measure, especially from a moving spacecraft. A new space science instrument called the ram wind sensor has been developed to measure the component of the neutral gas velocity that lies along the orbit track of a satellite in low Earth orbit. Laboratory tests of an engineering model of the instrument have been carried out using a supersonic neutral argon beam, in order to validate the measurement concept. The results show that the technique is viable for measurements of neutral flow velocities in future satellite missions.     

A gas-ion source with a grid-stabilized plasma cathode

A two-stage source of a broad beam of gas ions is described. The source contains a grid-stabilized plasma cathode and an anode stage with a multicusp magnetic field. The emission current of the plasma cathode (which is based on a glow discharge with a hollow cathode) is controlled between 0.1 and 1 A. The voltage that is applied to a bipolar diode between its cathode grid and anode plasma and determines the energy of fast electrons ranges from 50 to 200 V. The operating pressure of the argon in the anode stage is 4 × 10^–3–1 × 10^–1 Pa. A beam of argon ions having an energy of up to 5 keV and a current of >100 mA is formed by a two-electrode ion-optical system with a working area of 50 cm².__________Translated from Pribory i Tekhnika Eksperimenta, No. 2, 2005, pp. 107–111.Original Russian Text Copyright © 2005 by Gavrilov, Kamenetskikh.     

Cryogenic gas loading in a Mao-Bell-type diamond anvil cell for high pressure-high temperature investigations

A simple system for loading argon fluid at cryogenic temperatures in a Mao-Bell-type diamond anvil cell (DAC) has been developed. It is done in a two step process in which the piston-cylinder assembly alone is submerged in the cryogenic chamber for trapping the liquefied inert gas. Liquid nitrogen is used for condensing the argon gas. This system is now being efficiently used for loading liquid argon in the DAC for high pressure-high temperature experiments. The success rate of trapping liquefied argon in the sample chamber is about 75%. The performance of the gas loading system is successfully tested by carrying out direct conversion of pyrolitic graphite to diamond under high pressure-high temperature using laser heated DAC facility.     

Cold plasma brush generated at atmospheric pressure

A cold plasma brush is generated at atmospheric pressure with low power consumption in the level of several watts (as low as 4 W) up to tens of watts (up to 45 W). The plasma can be ignited and sustained in both continuous and pulsed modes with different plasma gases such as argon or helium, but argon was selected as a primary gas for use in this work. The brush-shaped plasma is formed and extended outside of the discharge chamber with typical dimension of 10-15 mm in width and less than 1.0 mm in thickness, which are adjustable by changing the discharge chamber design and operating conditions. The brush-shaped plasma provides some unique features and distinct nonequilibrium plasma characteristics. Temperature measurements using a thermocouple thermometer showed that the gas phase temperatures of the plasma brush are close to room temperature (as low as 42 degrees C) when running with a relatively high gas flow rate of about 3500 ml/min. For an argon plasma brush, the operating voltage from less than 500 V to about 2500 V was tested, with an argon gas flow rate varied from less than 1000 to 3500 ml/min. The cold plasma brush can most efficiently use the discharge power as well as the plasma gas for material and surface treatment. The very low power consumption of such an atmospheric argon plasma brush provides many unique advantages in practical applications including battery-powered operation and use in large-scale applications. Several polymer film samples were tested for surface treatment with the newly developed device, and successful changes of the wettability property from hydrophobic to hydrophilic were achieved within a few seconds.     

A source of broad homogeneous beams of low-energy (∼0.5 keV) gas ions

A source of gas ions (argon, oxygen, nitrogen, etc.), the operating principle of which is based on the use of a glow discharge in an electrode system of a wide-aperture hollow cathode and anode in a magnetic field, is described. The exit aperture diameter of the hollow cathode, increased up to a size close to the ion beam diameter (10 cm), ensures the uniform ion emission of the plasma generated in the discharge region near the anode. A decreased angular divergence or increased ultimate ion-beam current density is achieved by a change in the potential drop in the space charge sheath between the plasma and the ion optics. The source generates broad (50 cm²) slightly diverging (ω/2∼3°–5°) ion beams with energies of 300–1000 eV at a beam current density of ∼0.5 mA/cm².     

The impact of plasma-wall interaction on the gas mixing efficiency in electron cyclotron resonance ion source

It is generally accepted that different effects are necessary to explain the gas mixing method of increasing the output of highly charged ions from an ECRIS. The two most important effects are the mass effect and the dilution effect. Their relative weights have not been determined experimentally yet, but it is generally assumed that the mass effect is dominant in standard ECRIS installations with stainless steel plasma chambers. In order to gain more insight into the physics of the gas mixing effect and in particular on the relevance of the dilution process, we have carried out a study where we have investigated the role of the plasma-wall interaction on the gas mixing effect. In this contribution, we shall discuss Charge state distributions spectra, measured at the Frankfurt ECRIS using different working gases, pure argon, a mixture of argon and oxygen, and argon mixed with neon.     

气压对大尺寸Gasarite铜孔隙率的影响

在氢气和氩气混合气氛下,采用金属-气体共晶定向凝固法制备了具有长圆柱状孔隙结构大尺寸(圆柱直径大于140 mm)的多孔铜,在不同气压下得到了具有不同孔隙率的Gasarite铜,研究了气压对其孔隙率的影响.结果表明:当氩气分压一定且较小时,孔隙率随氢气分压的增大而减小;当氩气分压一定且较大时,孔隙率随氢气分压的增大而增大...     

气相色谱-质谱法测定高压汞灯真空度

高压汞灯石英管内惰性气体的填充是保证灯性能的关键因素。本研究采用气相色谱-质谱法测定高压汞灯真空度，测得氩气的相对质量校正因子和氩气/氮气的峰面积比(A_Ar/A_N2)，然后根据气体状态方程，计算出灯内氩气压力，并比较5种不同性能的高压汞灯灯管中氩气填充量的差异。结果表明，不同类型的高压汞灯其氩气压力明显不同，而同一类型的高压汞灯内氩气压力值国产的比国外的高，并从惰性气体（氩气）填充量的角度表征了高压汞灯的性能。     

Ni80Cr20合金薄膜制备影响因素的试验研究

利用直流磁控溅射的方法制备Ni80Cr20合金薄膜,以氩气流量、氩气工作压强、溅射功率作为三因素进行正交试验,在溅射时间相同的条件下分别测试了薄膜厚度、表面粗糙度、电阻率并进行了极差分析。分析结果表明:在一定范围内,氩气工作压强与溅射功率对薄膜厚度的影响较大;在氩气工作压强为3.0Pa时,薄膜厚度与溅射功率近似成正比关系;随着氩气流量的增大,Ni80Cr20薄膜厚度呈现先增大后减小的趋势;在氩气流量为50cm~3/min时,薄膜厚度达到最大值;各因素对薄膜表面粗糙度及电阻率影响不明显。