Optimum film thickness of thin metallic coatings on silicon substrates for low load sliding applications

The frictional behaviour of thin metallic films on silicon substrates sliding against 52100 steel balls is presented. The motivation of this work is to identify an optimum film thickness that will result in low friction under relatively low loads for various metallic films. Dry sliding friction experiments on silicon substrates with soft metallic coatings (silver, copper, tin and zinc) of various thickness (1–2000 nm) were conducted using a reciprocating pin-on-flat type apparatus under a controlled environment. A thermal vapour deposition technique was used to produce pure and smooth coatings. The morphology of the films was examined using an atomic force microscope, a non-contact optical profilometer and a scanning electron microscope. Following the sliding tests, the sliding tracks were examined by various surface characterization techniques and tools. The results indicate that the frictional characteristics of silicon are improved by coating the surface with a thin metallic film, and furthermore, an optimum film thickness can be identified for silver, copper and zinc coatings. In most cases ploughing marks could be found on the film which suggests that plastic deformation of the film is the dominant mode by which frictional energy dissipation occurred. Based on this observation, the frictional behaviour of thin metallic coatings under low loads is discussed and friction coefficients are correlated with an energy based friction model.     

An experimental setup for exciting semiconductors and dielectrics with picosecond electron-beam and electric-field pulses

An experimental facility for forming high-voltage pulses with amplitudes of 30–250 kV and durations of 100–500 ps and electron beams with a current density of up to 1000 A/cm² is described. The facility was built using the principle of energy compression of a pulse from a nanosecond high-voltage generator accompanied by the subsequent pulse sharpening and cutting. The setup is equipped with two test coaxial chambers for exciting radiation in semiconductor crystals by an electron beam or an electric field in air at atmospheric pressure and T = 300 K. Generation of laser radiation in the visible range under field and electron pumping was attained in ZnSSe, ZnSe, ZnCdS, and CdS (462, 480, 515, and 525 nm, respectively). Under the exposure to an electric field (up to 10⁶ V cm^?1), the lasing region was as large as 300–500μm. The radiation divergence was within 5°. The maximum integral radiation power (6 kW at λ = 480 nm) was obtained under field pumping of a zinc selenide sample with a single dielectric mirror.     

A technique and setup for obtaining the differential conductance of resonant-tunneling structures

A technique for obtaining the differential conductance within the negative differential resistance region for resonant-tunneling and tunneling heterostructures is developed. An experimental setup for this technique is created and tested with a resonant tunneling diode device.     

An experimental setup for simulation of two-phase hydrocarbon mixture flow in porous stratums

A procedure for simulating the two-phase flow of three-component hydrocarbon gas mixtures (for example, of the methane-propane-butane mixture gas condensate) in a porous stratum with the use of strain-gauge pressure sensors is proposed. Results are presented of experimental studies of two-phase hydrocarbon methane-propane-butane mixture filtration through a porous medium on the PLAST setup of the Joint Institute for High Temperatures under conditions close to reality. It is shown that the coordinate of the gas condensate plug formation region in the experimental section of a pipe can be determined with an accuracy up to 10% of its length.     

STRELA experimental setup for studying charge-exchange processes

The STRELA experimental setup designed for studying charge-exchange processes in deuteron-proton collisions at energies above 1 GeV is described. The setup is a one-arm magnetic spectrometer the main elements of which are drift chambers. The setup has been tested by irradiation in a deuteron beam with a momentum of 3.5 GeV/c at the Nuclotron accelerator complex (Laboratory of High Energy Physics, Joint Institute for Nuclear Research (JINR)). Algorithms for track searching and reconstruction in drift chambers have been developed and tested using real events. The attained spatial resolution of the chambers is in the range of 90–120 μm, which is sufficient for studying the process we are interested in.     

An investigation into the effect of film thickness on nanowear with amorphous carbon-based coatings

A sample oscillation module linked to a nanoindentation unit was used to perform nano-scale wear testing on a series of sputtered Cr doped amorphous C films deposited over a range of thicknesses (10, 20, 50, 150, and 2000 nm) under conditions relevant to MEMS and micro-scale engineering devices. A ruby sphere was used as the counter-body. Specific wear rates (defined as volume of worn material per unit applied load per unit of slid distance) were quantified and the effect of film thickness, applied load and test duration was investigated. Specific wear rate reduced exponentially with decreasing film thickness over the range of 10–2000 nm. The lowest wear rates were in the range of 0.1–6.1 × 10^?17 m³ N^?1 m^?1. Specific wear rate reduced with increased applied load over the range of 0.1–10 mN. The data scatter of replicated testing reduced along with the reduction of wear rate. A rapid reduction of specific wear rate was observed during the first 3000 oscillation cycles. This was analogous to the ‘running in’ process observed with macroscopic tribology systems.     

An experimental setup for investigation of arc and erosion processes in high-voltage high-current breakers

An experimental test setup for investigating arc and erosion processes in gas-filled high-voltage high-current switches is described and some results that were obtained on it are presented. The setup includes a discharge chamber that allows simulation of the process of disconnecting the ring and pin contacts, a capacitive energy storage with a capacitance of 0.11 F and a charging voltage of up to 10 kV, and a remotely controlled gas-supply system. The diagnostic complex includes systems for measuring the discharge current, the voltage across the arc, and the pulse pressure in the chamber, as well as high-speed filming and optical spectroscopy. Experiments with a current amplitude of 30–300 kA can be performed on the test bench. During the first current half-period of 1.0–3.0 ms, the contacts move apart to a distance of 3–4 cm. The arc is cooled via transverse gas blowing at a pressure in the chamber of 0.5–1.5 MPa. A movable contact is displaced due to the pressure of the gas that is pumped into the chamber.     

An experimental setup for investigating prebreakdown phenomena on a vacuum surface of a ceramic insulator

A setup for investigating prebreakdown phenomena on the surfaces of cathode insulators in vacuum is described. The setup reproduces the conditions under which an insulator is during operation of an actual vacuum device. The results from studying the effect of charged-particle fluxes and X-ray or optical radiations in a vacuum chamber under a stepped increase in the applied voltage to 150 kV are presented. In order to predict the development of a high-voltage breakdown, the following parameters are simultaneously recorded during measurements: the pressure in the vacuum chamber, the gas composition, and the leakage currents over the insulator surface and through the vacuum gap. The data are recorded automatically, and the collected information is stored on the hard disk of a computer.     

Effect of the number of layers in Zr-Y-O/Si-Al-N multilayer coatings on their mechanical properties and wear resistance

The peculiarities of the wear of multilayer coatings comprised of crystalline Zr-Y-O and amorphous Si-Al-N layers during tribological tests under conditions of dry friction are investigated. It is shown that the simultaneous development of the abrasive and adhesive wear mechanisms gives rise to the extreme dependence of the wear resistance of specified coatings on the number of layers. The major factors that allow one to enhance the mechanical properties and wear resistance of the investigated coatings are discussed.     

A laboratory setup for obtaining silicon carbide films by the direct ion deposition method

A laboratory setup for direct ion deposition intended for obtaining silicon carbide films under the conditions of the condensation of carbon and silicon ions with energies of ≥100 eV is described. The setup contains an original vacuum-arc source of carbon-silicon plasma with an extended cathode and an inhomogeneous magnetic field. The design features of the plasma source, the main technological characteristics of the setup, and the regimes of deposition of nanocrystalline silicon carbide films are presented.     

Advances and problems with TEM characterization of Cr/CrN multilayer coatings

Multilayer Cr/CrN/Cr/Cr(N,C) and Cr/CrN with 8 and 32 layer coatings were deposited on austenite substrates using pulsed laser deposition (PLD) technique. The microstructure observations were performed using Philips CM20?, TECNAI G² F20 – TWIN? and JEOL EX4000? transmission microscopes. The performed experiments indicated that lowering the argon flow from 60 to 30 cm³/s during chromium ablation changes buffer layers microstructure from nearly amorphous to nano‐crystalline. The nitride or carbo‐nitride layers turned out to be less sensitive to changes in nitrogen flow during deposition. The columnar microstructure of Cr layers is coarser than those in CrN ones under the same deposition condition. This observation proved also that relying on PLD technique as thin as 30 nm layers might be formed within multilayer Cr/CrN coatings.     

Corrosion-wear behaviour of PVD Cr/CrN multilayer coatings for gear applications

At present, one of the most important problems in automobile engines and transmission components is due to tribological processes (friction and wear) that in many cases come accompanied by corrosion processes due to the environmental conditions to which these materials are exposed during their lifetime. Both mechanisms can be minimized by means of the development and the application of adequate coatings that combine low friction with a high corrosion and wear resistance.The new tendencies in industrial PVD coatings to improve their properties are focused in the development of new multilayer and nanostructured coatings. These structures allow in a relatively simple way enhancing their tribological properties and the corrosion resistance that can not be reached by means of the traditional monolayer coatings. The background of this type of coatings consists of the stacking up of several layers with good individual tribological and mechanical properties, but every individual layer has a thickness that can be from hundreds of nanometres down to only 5-10 nm. The properties of these nanostructured coatings depend strongly on the thickness modulation of every individual layer.Concerning PVD coatings, the chrome nitride coatings have demonstrated to possess excellent wear resistance properties. In this work, multilayer Cr/CrN coatings with different individual layer thickness have been deposited on substrates of steel F1272 and silicon. The deposition has been carried out by means of the cathodic arc method alternating an atmosphere of pure Ar with a reactive mixture of N₂/Ar. The multilayers obtained have been analyzed by means of Glow Discharge Optical Emission Spectroscopy (GD-OES) and in some cases by means of FE-SEM obtaining bilayer (Cr/CrN) periods of the order of 220 and 45 nm. The coating characterization has been complemented with hardness and composition measurements as well as by the performance of several wear and corrosion-wear tests.     

An efficient setup for femtosecond stimulated Raman spectroscopy

We present an efficient and robust setup for femtosecond stimulated Raman (FSR) spectroscopy with 60 fs and 10 cm(-1) resolution. Raman pulses of 0.5-5 ps are tunable between 450-750 nm with energies 1-10 μJ. Experimental features of the setup, signal processing, and data treatment are discussed in detail to be readily reproduced in other labs. The setup is tested by measuring FSR spectra of stilbene in solution.     

An experimental setup for high resolution 10.5 eV laser-based angle-resolved photoelectron spectroscopy using a time-of-flight electron analyzer

We present an experimental setup for laser-based angle-resolved time-of-flight photoemission. Using a picosecond pulsed laser, photons of energy 10.5 eV are generated through higher harmonic generation in xenon. The high repetition rate of the light source, variable between 0.2 and 8 MHz, enables high photoelectron count rates and short acquisition times. By using a time-of-flight analyzer with angle-resolving capabilities, electrons emitted from the sample within a circular cone of up to ±15° can be collected. Hence, simultaneous acquisition of photoemission data for a complete area of the Brillouin zone is possible. The current photon energy enables bulk sensitive measurements, high angular resolution, and the resulting covered momentum space is large enough to enclose the entire Brillouin zone in cuprate high-T(c) superconductors. Fermi edge measurements on polycrystalline Au shows an energy resolution better than 5 meV. Data from a test measurement of the Au(111) surface state are presented along with measurements of the Fermi surface of the high-T(c) superconductor Bi(2)Sr(2)CaCu(2)O(8 + δ) (Bi2212).     

An experimental setup for studying neutron-neutron final state interaction on the neutron channel of the Moscow Meson Factory

A setup for measuring the singlet nn-scattering length in the n + d → p + n + n reaction is described. It is composed of a neutron hodoscope with an angular aperture of 12° and a scintillation detector for protons escaping at an angle of 90° with the beam direction. The exit angles and the energies of a proton and both neutrons are measured. The neutron energies are measured using the time-of-flight method. At a time resolution of ∼0.6 ns and a flight base of ∼5.5 m, the accuracy in measuring the neutron energy is ∼1% at an energy of ∼15 MeV. The dependence of the reaction yield on the relative energy of two neutrons is investigated. The neutron-neutron final-state interaction manifests itself as a peak in this distribution.     

An experimental analysis of process parameters to manufacture metallic micro-channels by micro-milling

Miniaturisation of products is a current megatrend, and it presents a wider range of opportunities to expand manufacturing markets. Micro-device design and manufacturing is a growing area of scientific interest for large number of industrial fields. This paper reports the characterisation of micro-milling process to manufacture micro-channels in order to understand the behaviour of process parameters when a standard milling machine is used. This study is based on micro-channel manufacturing through a set of experiments varying parameters such as spindle speed (N), depth of cut per pass (a _p), depth (d), feed per tooth (fz) and coolant application. Materials used were aluminium and copper with a hardness of 21 HRB and 72 HRB copper, respectively. Results are obtained by evaluating dimensions, shape and surface finish of the micro-channel. The use of coolant in micro-milling is found to be a relevant factor to improve micro-channel-achieved dimensions and surface finish. In general, micro-channels in aluminium were found to achieve better quality than those in copper.     

A multilayer approach for enhancing the erosive wear resistance of CVD diamond coatings

The erosive wear behavior of mono-, bi- and multilayered diamond composite coatings grown by hot filament chemical vapor deposition (HFCVD) is investigated. The effect of the surface pre-treatment on the silicon nitride substrates was firstly evaluated revealing that flat lapping mechanical treatment combined with chemical CF₄ plasma etching is the best surface preparation to achieve high adhesion levels. Multilayers were designed to combine the excellent adhesion of microcrystalline diamond (MCD) with a top nanocrystalline diamond (NCD) layer of reduced surface roughness. Indeed, the multilayered diamond coatings revealed the best erosive resistance, whose damage occurred by gradual loosening of material from the outer layer after longer testing time. The absence of areas with film spallation or substrate exposure is given by the action of the MCD/NCD interfaces in deflecting cracks, thus acting as “energy sinks” to further propagation. An analytical model of the stress field distribution within the coatings based on the von Mises criterion was developed to elucidate the erosive mechanical behavior of the different diamond composites.