Gas discharge source of metal vapor and fast gas atoms

A source of metal atom flow coinciding in time and space with a flow of fast gas atoms has been studied and the study results are presented. The fast particles are produced due to charge exchange collisions of ions accelerated by potential difference between a plasma emitter inside the source and secondary plasma inside a process vacuum chamber. The emitter is the glow discharge plasma, whose electrons are confined in an electrostatic trap formed by a cold hollow cathode and an emissive grid the latter being negative both to the cathode and the chamber. The metal atoms are produced due to sputtering a target placed at the hollow cathode bottom by ions from the plasma emitter with energy up to 3 keV. Sputtered atoms cross the emitter, together with accelerated ions enter the chamber through the emissive grid and deposit on pieces placed therein. When a mixture of argon and nitrogen is used, the metal nitride coatings are being synthesized and interruptedly bombarded during the synthesis by atoms and molecules with energy variable from ～10 to ～300 eV.     

Broad beam source of fast atoms produced as a result of charge exchange collisions of ions accelerated between two plasmas

Experimental study of a fast argon atom beam source is carried out and the study results are presented. The source comprises a 90-mm deep and 210-mm in diameter hollow cathode as well as a flat emission grid, both electrodes made of titanium. The study revealed main factors, which influence the zone diameter of homogeneous substrate etching by a broad beam of fast argon atoms, produced as a result of charge exchange collisions of ions, accelerated between a plasma emitter inside the hollow cathode and a secondary plasma in the working vacuum chamber, the plasmas being separated from each other with the grid. It is shown that at a distance from the grid, exceeding the resonant charge exchange length up to 4 times, elastic collisions have no appreciable impact on the spatial distribution of the etching rate in the vacuum chamber. The homogeneous etching zone diameter is mainly influenced by angular characteristics of accelerated particles in the grid plane. At a constant beam power up to 3–5 kW the diameter is rising with a decrease of their energy and with a corresponding increase of the beam current. Original Russian Text ? S.N. Grigoriev, Yu.A. Melnik, A.S. Metel, V.V. Panin, 2009, published in Pribory i Tekhnika Eksperimenta, 2009, No. 4, pp. 166–172.     

Broad beam sources of fast molecules with segmented cold cathodes and emissive grids

Experimental study of fast neutral atom and molecule beam sources with rectangular and circular cross-section of the beam up to 0.8 m² is carried out and the study results are presented. The fast particles are produced as a result of charge exchange collisions between gas molecules and ions accelerated by potential drop between the plasma emitter of the beam source and the secondary plasma inside the processing vacuum chamber. As the emitter is used a glow discharge plasma, whose electrons are confined in an electrostatic trap formed by a cold hollow cathode and an emissive grid, which is negative both to the cathode and to the chamber. In order to prevent from breakdowns between the emitter and the cathode at a current in the cathode circuit up to 10 A as well as between the emitter and the grid at a voltage between them up to 10 kV the cathode and the grid are composed of isolated from each other segments, which are connected to power supplies through resistors. When resistance of the resistorR > U/I ₀, where U is the power supply voltage and I ₀ is the minimal current of stable vacuum arc for a given segment material, then transition from the glow discharge to the steady-state vacuum arc is totally excluded in spite of numerous breakdowns of microsecond duration due to contamination of the source electrodes during its operation with dielectric films and other stimulants of the arc.     

A compact vapor source of conductive target material sputtered by 3-keV ions at 0.05-Pa pressure

A vapor source is developed its 80-mm-diameter and 15-mm-thick flat target being positioned on the bottom of a 120-mm-diameter and 70-mm-deep hollow cathode, isolated from the cathode and sputtered by 1–4-keV argon ions. A permanent magnet induces an axially symmetric heterogeneous magnetic field, the field induction on the target surface reaching 20 mT and the field lines of force being diverging from the target surface and crossing the cathode surface. The cathode bombardment by 1–3-keV secondary electrons emitted by the target results in an increase of the electron emission current in the cathode circuit and enables to reduce the argon pressure down to 0.05 Pa. It allows a collisionless transport of the sputtered metal atoms to a substrate thus keeping their initial energy amounting to tens of electronvolts. A higher energy of deposited atoms improves quality of coatings, for instance of Ti₃SiB₂ films, their deposition rate on a substrate distanced at 0.1–0.2 m from the target amounting to 10–20 μm/h at 1-A current in the target circuit and 3-keV energy of sputtering ions. This value is one order of magnitude higher in comparison with the target sputtering in a planar magnetron discharge by 300–500-eV argon ions at the same 1-A current in the target circuit.     

Shear-Induced Surface-to-Bulk Transport at Room Temperature in a Sliding Metal–Metal Interface

Predictions from molecular dynamics (MD) simulations, that sliding at a metal–metal interface causes vortices in the near-surface region that transport atoms from the surface into the subsurface region, is tested experimentally. This is accomplished by rubbing a methyl thiolate overlayer grown on a clean copper foil by exposure to dimethyl disulfide at room temperature. Repeatedly rubbing a 1.27 × 10⁻² m diameter pin over a thiolate-covered copper surface at an applied load of 0.44 N and sliding speed of 4 × 10⁻³ m/s in an ultrahigh vacuum tribometer, results in the removal of sulfur from the wear track as measured using spatially resolved Auger spectroscopy. Any remaining surface species, in particular, outside the wear track, are removed by argon ion bombardment. Since sulfur is more thermodynamically stable at the surface, heating the sample causes the sulfur to resegregate to the surface only inside the wear track, thereby directly confirming the predictions from MD simulations.     

Generation of an ion beam in a glow-discharge source

A mechanism of ion extraction from a glow-discharge ion source based on a hollow cathode and used for elemental analysis of solids, is considered Experiments have shown that two oppositely directed ion flows are formed from ions produced in the region of negative glow-discharge fluorescence. One flow has an ion energy ≥ 100 eV, is directed to the cathode, and bombards and sputters the analyzed sample. The sputtered atoms diffuse into the negative-glow region and are ionized. The second flow (low-energy ions) is extracted from the same negative-glow region and transported from the cathode to the surface of the anode chamber owing to an ambipolar diffusion. These ions are extracted from a hole in the anode chamber of a standard ion source by an electric field and are used for mass-spectrum analysis. The energy-distribution width for these ions is ∼5 eV. The intensity of the ion beam extracted from the anode hole is an order of magnitude higher than the intensity of the ion beam extracted from the cathode region. Original Russian Text ? G.G. Sikharulidze, 2009, published in Pribory i Tekhnika Eksperimenta, 2009, No. 2, pp. 105–109.     

Interpretation of unexpected rocking curve asymmetry in LACBED patterns of semiconductors

Transmission electron microscopy rocking curves diffracted from inclined planes in argon ion-thinned Si and III-V semiconductors display a significant asymmetry around the Bragg condition. Kinematical and dynamical calculations of the rocking curves show that such an asymmetry can be attributed to the dilation of coherent crystalline surface layers implanted with argon atoms. The surface layers are characterized with two parameters, their width h and the strain component epsilon (z) normal to the thin foil plane. The dark-field rocking curve asymmetry is shown, for sufficiently high values of h (> approximately 2 nm), to strongly depend on epsilon (z) which is directly related to the density of implanted argon atoms in the surface layers. Calculations also show that a significant rocking curve asymmetry is only observed for intermediate values of epsilon (z) of about a few percentage points.     

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。     

Temperature-dependent contact phenomena of PVD- and CVD-deposited DLC films sliding on the thin aluminium foil

This paper reports on tribological properties of magnetron-sputtered WC–C and chemical vapour-deposited diamond-like carbon films coated onto hard-metal surfaces when sliding on aluminium foil (0.2 mm nominal thickness) at different temperatures. The study addresses the evolution of the coefficient of friction at the interfaces of the coated hard metal and the aluminium foil under dry-lubrication conditions, in a ball-on-disc configuration. The wear mechanisms of the aluminium foil and the damage produced on the coated surfaces due to the sticking of aluminium were evaluated as a function of the deposited coating and the temperature at their interfaces. Aluminium-transfer to WC–C coated hard-metal surfaces during the sliding operation seemed to be a non-continuous process, which appeared after a certain number of sliding cycles. Temperatures above 70°C accelerated the transfer of aluminium to the WC–C tool surfaces. Chemical vapour-deposited diamond-like carbon films hindered the transfer of aluminium to the hard metal even at temperatures of around 125°C. At greater temperatures, an aluminium–aluminium tribosurface is formed at the interface, which increases the wear rate of the foils and rapidly degrades the quality of coatings of the hard-metal surfaces.     

A pulse-type evaporator for ultrafast deposition of thin films in ultrahigh vacuum

The design of a simple pulse-type evaporator ensuring a high rate (up to ～10⁴ nm/s) of deposition of thin films (0.01–100 nm thick) onto a solid surface in ultrahigh vacuum is described. The evaporation pulse is created by discharge of a capacitor bank via a fast-response evaporator produced from a tungsten foil. Results illustrating the efficiency of this device are presented.     

Tribological Properties of 1-Alkenes on Copper Foils: Effect of Low-Coordination Surface Sites

It has been suggested from molecular dynamics simulations that low-coordination-number sites are produced at a sliding metal–metal interface, but, because of their instability, they may rapidly relax to increase their coordination number. The possible presence of such low-coordination sites on the surface is tested by exploiting the observation that the desorption temperatures of 1-alkenes on copper increase with both the number of carbons atoms in the 1-alkenes and the surface roughness. Thus, 1-alkenes desorb from a Cu(111) single crystal, with relatively few low-coordination sites, at temperatures between 60 and 100 K lower than from a polycrystalline copper foil. The decrease in friction after impinging a flux of various 1-alkenes on a copper foil, while rubbing in an ultrahigh vacuum tribometer, correlates very well with the corresponding 1-alkene coverages on a copper foil, estimated using the desorption kinetics. This suggests either that rubbing does not result in the formation of lower-coordination sites or that they relax sufficiently rapidly that they do not influence the surface chemistry of 1-alkenes. Surface analyses indicate that shear at the interface causes carbon to diffuse into the subsurface region to form a tribofilm.     

Characteristics of a fast neutral atom source with electrons injected into the source through its emissive grid from the vacuum chamber

In order to increase the equivalent current of a fast neutral atom beam the cold hollow cathode of the beam source is bombarded with electrons extracted from the plasma produced in the vacuum chamber and accelerated in the sheath between the plasma emitter of the source and its emissive grid. The cold cathode bombardment by accelerated electrons raises its electron emission current by an order of magnitude and as a result voltage U _c between the anode and the cathode of the source diminishes more than two times. This allows of increasing several times the beam equivalent current or decreasing the working gas pressure. A slight decrease in the U _c with increasing the accelerating voltage U at an overall cutoff of the electrons from the chamber reveals the influence of secondary electrons emitted by the grid. Measurement of the beam current is discussed.     

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.     

Thermal Management Techniques for Oil-Free Turbomachinery Systems

Tests were performed to evaluate three different methods of utilizing air to provide thermal management control for compliant journal foil air bearings. The effectiveness of the methods was based on bearing bulk temperature and axial thermal gradient reductions during air delivery. The first method utilized direct impingement of air on the inner surface of a hollow test journal during operation. The second, less indirect method achieved heat removal by blowing air inside the test journal parallel to the shaft axis to simulate air flowing axially through a hollow shaft. The third method emulated the most common approach to removing heat by forcing air axially through the bearing's support structure. Internal bearing temperatures were measured with three type K thermocouples embedded in the bearing that measured general internal temperatures and axial thermal gradients. Testing was performed in a 1 atm, 260°C ambient environment with the bearing operating at 60 krpm, and supporting a load of 222 N. Air volumetric flows of 0.06, 0.11, and 0.17 m³/min at approximately 150 to 200°C were used.

The tests indicate that all three methods provide thermal management but at different levels of effectiveness. Axial cooling of the bearing support structure had a greater effect on the bulk temperature for each air flow and demonstrated that the thermal gradients could be influenced by the directionality of the air flow. Direct air impingement on the journal's inside surface provided uniform reductions in both bulk temperature and thermal gradients. Similar to the direct method, indirect journal cooling had a uniform cooling effect on both bulk temperatures and thermal gradients but was the least effective of the three methods.     

A DOE nano-tribological study of thin amorphous carbon-based films

A design of experiment (DOE) matrix of 150 nm non-hydrogenated amorphous C and Cr doped amorphous C films was produced to investigate the effect of four key coating process parameters (use of an adhesion layer, Cr magnetron current, cathodic substrate bias voltage and Ar flow to the chamber) using a new rapid method of nano-scale wear test under conditions relevant to MEMS and similar devices. The condition of nano-wear was produced by controlled oscillation of the sample mounting within a nanoindentation system under ultra-low normal load. Specific wear rates were low, typically in the range 6-24×10⁻¹⁷ m³ N⁻¹ m⁻¹. The results were processed using an analysis of variance (ANOVA) procedure which showed that: hardness was reduced in the Cr containing films whilst specific wear rate and data scatter increased, increasing the cathodic substrate bias voltage reduced the specific wear rate due to increased coating hardness, the use of a Cr adhesion layer reduced the specific wear rate and scatter of results with Cr doped films but had no effect on pure a-C films, and Ar flow rate had no significant effect on specific wear rate but strongly interacted with the effect of the cathodic bias voltage.     

A Plasma Stopper in a Hollow Cathode

A cap with a hole was mounted on the top of a cylindrical hollow cathode. The hole diameter ranged from 10 to 90% of the inner diameter of the hollow cathode. As a result, a plasma stopper was formed in the cathode cavity near the hole. The stopper hindered the plasma-forming gas flow from the cathode cavity into the vacuum chamber. This caused a pressure difference between the cathode cavity and the vacuum chamber. It was found that the pressure difference depended on the diameter of the hole in the cap. A cap with a hole of 4 mm in diameter mounted on the top of a hollow cathode with an inner diameter of 20 mm allowed a pressure difference of three orders of magnitude to be attained.     

Micro channel forming with ultra thin metallic foil by cold isostatic pressing

The objective of this study is to establish the limit of the metal forming process in terms of size and accuracy. In the present investigation, micro channel forming with ultra thin metallic foil by the sheet metal forming process was studied. In order to examine the fabrication limit of the process, both the channel size needed to be as small as possible and the sheet thickness to be as thin as possible. Copper foil 1.0 μm thick was made into 5.6 μm wide and 3.2 μm deep channels. The shapes of the channels were straight line, concentric circle, cross, and other curved shapes. Forming was done by cold isostatic pressing. Single crystal silicon wafer was used as the die material, and die grooves were made by micro machining techniques. The die, metallic foil, and plasticine as the pressure-transmitting medium were vacuum packed in a bag made of multilayered film. The forming was conducted with a cold hydrostatic press where the forming pressure was 240 MPa. The formed channels were examined in terms of their dimensions and surface qualities. Based on the examinations, channel formability was also discussed.     

Effect of fast positive ions incident on caesiated plasma grid of negative ion source

This paper describes the effect on negative ion formation on a caesiated surface of the backscattering of positive ions approaching it with energy of a few tens of eV. For a positive ion energy of 45 eV, the surface produced negative ion current density due to these fast positive ions is 12 times larger than that due to thermal atoms, thus dominating the negative ion surface production instead of the thermal atoms, as considered until now.     

润滑用齿轮泵内部流场的动态模拟

齿轮泵是液压传动及润滑系统中的常用部件,为了准确地捕捉泵内流场的变化,采用动网格技术对柴油机的润滑齿轮泵进行动态数值模拟,分析齿轮泵在齿轮旋转情况下的内部流场的变化.结果表明:1)泵内的压力不同瞬时有所变化,但都保持进油腔压力低,排油腔压力高;2)进/排油腔内高/低速区在不同的瞬时位于不同齿轮侧,对齿轮产生冲击.     

A Test Bench for the Shock Loading by an Electrical Explosion of Foils

Pulsed mechanical loads on objects are produced upon an electrical explosion of metal foils with an area of <400 cm². A bank of 48 ИК 100-0.4 УХЛ4 capacitors is mounted in four metallic tanks with oil insulation and stores an energy of up to 96 kJ. Each two capacitors are switched by a thyratron and transfer a current along a cable line to a common electrical explosion unit. Twenty-four spark gaps operate with a time spread of ±3 ns relative to the trigger pulse and have an electric strength margin of ∼80%. The total inductance of the circuit is ∼70 nH. The discharge current amplitude reaches 1.68 MA, and its oscillation quarter-period lasts ∼1.8 µs. Various designs for the electrical explosion unit, based on an aluminum foil 7 µm thick, and methods for measuring the mechanical impulse values are described. The distribution of impulse over the foil area is controlled by the number of exploded foil layers. All of the test bench units can be transported and promptly put into operation at a new site.__________Translated from Pribory i Tekhnika Eksperimenta, No. 4, 2005, pp. 101–106.Original Russian Text Copyright © 2005 by Gerasimov, Zolotov, Kul’gavchuk.