Formation of silicon nanocrystals in Si—SiO<Subscript>2</Subscript>—<Emphasis Type="Italic">α</Emphasis>-Si—SiO<Subscript>2</Subscript> heterostructures during high-temperature annealing: Experiment and simulation

Experiments and simulations are performed to study the formation of silicon nanocrystals (Si-NCs) in multilayer structures with alternating ultrathin layers of SiO₂ and amorphous hydrogenized silicon (α-Si:H) during high-temperature annealing. The effect of annealing on the transformation of the structure of the α-Si:H layers is studied by methods of high-resolution transmission electron microscopy, Raman spectroscopy, and photoluminescence spectroscopy. The conditions and kinetics of Si-NC formation are analyzed by the Monte Carlo technique. The type of the resultant crystalline silicon clusters is found to depend on the thickness and porosity of the original amorphous silicon layer located between SiO₂ layers. It is shown that an increase in the thickness of the α-Si layer in the case of low porosity leads to the formation of a percolation silicon cluster instead of individual Si nanocrystals.     

Voltage-current characteristics of diodes on MBE-grown Hg<Subscript>0.78</Subscript>Cd<Subscript>0.22</Subscript>Te layers

Results of measuring the voltage-current characteristics (VCCs) of diodes for IR detectors with the cutoff wavelength λ _c = 11μm are presented. The diodes are based on variband Hg_0.78Cd_0.22Te layers grown by molecular beam epitaxy on semi-insulating GaAs substrates. It is found that diffusion current and generation current in the depletion layer of the p-n junction are the main mechanisms of carrier generation at the reverse bias voltage V ₁ < −0.2 V. It is shown that good agreement between calculated and experimental VCCs is achieved if the decrease of the effective depth of recombination levels in the depletion layer as a result of the Poole — Frenkel effect is taken into account, as well as the longitudinal charge spreading in the reverse current diffusion component.     

Transmission electron microscopy characterization of the erbium silicide formation process using a Pt/Er stack on a silicon-on-insulator substrate

Very thin erbium silicide layers have been used as source and drain contacts to n‐type Si in low Schottky barrier MOSFETs on silicon‐on‐insulator substrates. Erbium silicide is formed by a solid‐state reaction between the metal and silicon during annealing. The influence of annealing temperature (450 °C, 525 °C and 600 °C) on the formation of an erbium silicide layer in the Pt/Er/Si/SiO₂/Si structure was analysed by means of cross‐sectional transmission electron microscopy. The Si grains/interlayer formed at the interface and the presence of Si grains within the Er‐related layer constitute proof that Si reacts with Er in the presence of a Pt top layer in the temperature range 450–600 °C. The process of silicide formation in the Pt/Er/Si structure differs from that in the Er/Si structure. At 600 °C, the Pt top layer vanishes and a (Pt–Er)Si_x system is formed.     

Tribological properties of anatase TiO<Subscript>2</Subscript> sol–gel films controlled by mutually soluble dopants

Tribological properties of TiO2 sol–gel thin films with mutually soluble dopants were studied on a glass substrate. The results showed that the formation of mutually soluble solid solution played a very important role in the growth of titania grains. The fine-grained TiO₂ films controlled by SiO₂ dopant were superior to pure TiO₂ film in wear resistance and endurance life, although both films greatly improve the surface characteristics of glass substrate, enhancing its tribological characteristics. High resistance to microfracture because of the very small grain size as well as a good adhesion of the film to the substrate is believed to be the determining factors influencing the tribological properties of SiO₂ doped TiO₂ films. However, excessive SiO₂ seriously deteriorates wear resistance of film due to phase separation. The wear mechanisms were also discussed based on the observation of the surface morphologies by scanning electron microscope (SEM).     

Dry-sliding Tribological Properties of Nano-Eutectic Fe<Subscript>83</Subscript>B<Subscript>17</Subscript> Alloy

This paper reports the tribological performance of the nano-eutectic Fe₈₃B₁₇ alloy under dry sliding against Si₃N₄ ceramic ball in ambient environment with varying applied loads and sliding speeds. Worn surfaces of the nano-eutectic Fe₈₃B₁₇ alloy were examined with a scanning electron microscope (SEM) and an X-ray energy dispersive spectroscope (EDS). The wear debris of the samples were also analyzed by X-ray diffractometer (XRD). The wear rate of the nano-eutectic Fe₈₃B₁₇ alloy was of the magnitude of 10⁻⁴ mm³/m, which was lower than that of the coarse grained Fe₈₃B₁₇ alloy. The friction coefficient of the nano-eutectic Fe₈₃B₁₇ alloy was almost the same as that of the coarse grained Fe₈₃B₁₇ alloy. The Fe₂SiO₄ oxide layer was formed on the worn surface of the nano-eutectic Fe₈₃B₁₇ alloy. However, on the worn surface of the coarse grained Fe₈₃B₁₇ alloy was found only a little Fe₂SiO₄. These results demonstrated that the nanostructure improved the wear resistance of the Fe₈₃B₁₇ alloy, but did not significantly affect the friction coefficient. The wear mechanism of the nano-eutectic Fe₈₃B₁₇ alloy was delamination abrasion mainly.     

Growing HgTe/Cd<Subscript>0.735</Subscript>Hg<Subscript>0.265</Subscript>Te quantum wells by molecular beam epitaxy

HgTe/Cd_0.735Hg_0.265Te nanostructures with HgTe quantum wells 16.2 and 21.0 nm thick are grown without additional doping on (013)CdTe/ZnTe/GaAs substrates by the method of molecular beam epitaxy. The compositions and thicknesses of the wide-gap layer and quantum well in the course of growth are performed by means of ellipsometry. The accuracy is Δx ? ±0.002 mole fractions of cadmium telluride in determining the composition and Δd ? 0.5 nm in determining the thickness of the wide-gap layer and quantum well. The central fragments of the wide-gap layers ≈ 10 nm thick are additionally doped by indium for a ～ 10¹⁵ cm^?3 volume concentration of charge carriers to be reached. Galvanomagnetic research in a wide range of magnetic field intensities at liquid helium temperatures reveals dimensional quantization levels and the presence of a two-dimensional electron gas in grown nanostructures. High mobility of the two-dimensional electron gas μ _e is obtained: 2 · 10⁵ and 5 · 10⁵ cm²/V · s for electron densities N _s equal to 1.5 · 10¹¹ and 3.5 · 10¹¹ cm^?2, respectively.     

Synergistic Effect of Nano-MoS<Subscript>2</Subscript> and Anatase Nano-TiO<Subscript>2</Subscript> on the Lubrication Properties of MoS<Subscript>2</Subscript>/TiO<Subscript>2</Subscript> Nano-Clusters

A MoS₃ precursor deposited on anatase nano-TiO₂ is heated at 450 °C in an H₂ atmosphere to synthesize MoS₂/TiO₂ nano-clusters. The nano-clusters are then characterized, and their tribological properties are evaluated. MoS₂ is found to be composed of layered structures with 1–10 nm thicknesses, 10–30 nm lengths, and 0.63–0.66 nm layer distances. The MoS₂ sizes in the MoS₂/TiO₂ nano-clusters are smaller and their layer distances are larger than those of pure nano-MoS₂. The MoS₂/TiO₂ nano-clusters also present a lower average friction coefficient than pure nano-MoS₂, but the anti-wear properties of both the nano-clusters and pure nano-MoS₂ are similar. X-ray photoelectron spectroscopy indicates that nano-TiO₂ and the element Mo are transferred to the friction surface from the MoS₂/TiO₂ nano-clusters through a tribochemical reaction. This produces a lubrication film containing TiO₂, MoO₃, and other chemicals. The nano-MoS₂ changes in size and layer distance when combined with nano-TiO₂, producing a synergistic effect. This may further be explained using a micro-cooperation model between MoS₂ nano-platelets and TiO₂ solid nanoparticles.     

Energy dependence of the relative light output of YAlO<Subscript>3</Subscript>:Ce,Y<Subscript>2</Subscript>SiO<Subscript>5</Subscript>:Ce,and YPO<Subscript>4</Subscript>:Ce scintillators

The nonlinear dependence of the relative light output on the energy deposited in single-crystal scintillation materials YAlO₃:Ce (YAP:Ce), Y₂SiO₅:Ce (YSO:Ce), and YPO₄:Ce (YPO:Ce) has been studied. The investigations have been conducted under quasi-monochromatic X-ray excitation in the energy range of 9.5–100 keV. In addition to the standard technique for measuring the nonproportional scintillator response based on the dependence of the full-energy peak position on the energy of incident radiation, a method is proposed for measuring the light output by X-ray fluorescence peaks. Using this method for YAP:Ce, it is possible to investigate the nonlinear dependence of the light output on the photon energy in the energy range of 2–40 keV. Along with this method, the K-dip spectroscopy method has been proposed and tested by measuring the dependence of the relative light output on the electron energy in the range of 0.1–80.0 keV. The processes resulting in the loss of the scintillation material efficiency at a high ionization density are considered.     

Wear Resistance of the La<Subscript>62</Subscript>Cu<Subscript>12</Subscript>Ni<Subscript>12</Subscript>Al<Subscript>14</Subscript> Bulk Metallic Glass Under Dry Friction Conditions

The wear properties of a La₆₂Cu₁₂Ni₁₂Al₁₄ bulk metallic glass (BMG) using sliding wear system under the various normal loads and the annealing conditions have been investigated. Although the La₆₂Cu₁₂Ni₁₂Al₁₄ BMG is brittle during the tensile testing, it exhibits ductile behaviors during the sliding wear process. The SEM and the EDS analyses of the wear tracks and the debris after the sliding wear processes indicate that the wear mechanism is a combination of abrasion, adhesion, and oxidation. It is found that the wear resistance is significantly affected by the normal loads. With the increases in the wear load, the wear loss and the friction coefficient decrease. In addition, it is found that the wear properties are significantly affected by the annealing conditions. Compared with the annealed BMG alloys, the as-cast BMG alloy with a low hardness exhibits good wear resistance, which is attributed to the better ductility during the wear testing.     

Tribological Performance of Fe<Subscript>67</Subscript>B<Subscript>33</Subscript> Alloy Prepared by a Self-Propagating High-Temperature Synthesis Technique

A bulk Fe₆₇B₃₃ alloy was prepared by a self-propagating high-temperature synthesis technique that is convenient, low in cost, and capable of being scaled up for tailoring the bulk materials. The Fe₆₇B₃₃ alloy is composed of dendrites with the t-Fe₂B phase and eutectic matrix with the α-Fe and t-Fe₂B phases. The content of the dendrite t-Fe₂B is above 80 vol.%. The compressive fractured strength and Vickers microhardness are 3400 MPa and 12.4 GPa, respectively. The tribological performance of the Fe₆₇B₃₃ alloy is investigated under dry sliding and water lubricant against Si₃N₄ ceramic ball. The wear rates of the Fe₆₇B₃₃ alloy are of the magnitude of 10⁻⁵ to 10⁻⁴ mm³/m under water lubricant. It is lower than that of the Fe₆₇B₃₃ alloy under dry sliding (10⁻⁴ mm³/m). But both the friction coefficients are almost identical. Oxide layers form in both environments via different tribochemical mechanisms, which led to significant differences in wear behavior.     

Surface nanostructuring of steel 35 by electrospark machining with electrodes based on tungsten carbide and added Al<Subscript>2</Subscript>O<Subscript>3</Subscript> nanopowder

The formation of an alloyed layer on steel 35 by VK8 hard alloy with added Al₂O₃ increases its wear resistance. Effective conditions for this process are determined. The formation of regular tungsten-carbide nanostructure is observed.     

Molecular beam epitaxy of BaF<Subscript>2</Subscript>/CaF<Subscript>2</Subscript> buffer layers on the Si(100) substrate for monolithic photoreceivers

This paper describes the study of the surface morphology of BaF2 epitaxial films grown by means of molecular beam epitaxy in various growth regimes on a CaF₂/Si(100) surface, which is performed by means of atomic force microscopy. The CaF₂ layers were obtained on a Si(100) substrate in a low-temperature growth regime (T _s = 500 °C). The technological regimes of growth of BaF₂ continuous films with a smooth surface on CaF₂/Si(100), suitable as buffer layers for the subsequent growth of PbSnTe layers or other semiconductors, such as A₄B₆, and solid solutions based on them.     

Tribological behavior of intermetallic Fe<Subscript>3</Subscript>Al alloy treated by intensive beams of nitrogen ions

The structure, phase composition, and tribological behavior of intermetallic Fe₃Al alloy subjected to ion-beam nitriding at 670–870 have been studied. The ion-beam treatment of the alloy proved to result in nitrogen-modified layers of up to 15–18 nm thick and microhardness up to 13200 MPa. The formation of nitride AlN phases with cubic and hexagonal lattices was registered in the nitrided layers. The formation of aluminum nitrides with the cubic lattice of NaCl structural type is shown to increase the wear resistance of Fe₃Al alloy 25–28 times, and with the hexagonal one it increases 5–8 times.     

Effect of deposition pressure on microstructure and tribological behavior of MoS<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>/MoS<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>-Mo nanoscale multi-layer films

MoS _x /MoS _x -Mo multi-layer films consisted of several bilayers and a surface layer on steel substrate were deposited by d.c. magnetron sputtering at different deposition pressures. Each bilayer contained a MoS _x layer with 80 nm in thickness and a MoS _x -Mo composite layer with 20 nm in thickness. With the increase of deposition pressure, the perpendicular orientation of the basal plane prevailed while the parallel orientation decreased. The tribological properties of the multi-layer films were investigated by using a ball-on-disk tribometer both in vacuum and in humid air. The multi-layer film deposited at 0.24 Pa had a compact, consistent layered structure with high intensity of (002) plane and low S content compared to the others deposited at 0.32 and 0.40 Pa, and showed the lowest friction coefficient and wear rate in humid air.     

Comparison of the efficiency of modification of SHMPE by nanofibers (C,Al<Subscript>2</Subscript>O<Subscript>3</Subscript>) and nanoparticles (Cu,SiO<Subscript>2</Subscript>) when obtaining antifriction composites

The effect of various nanofillers (nanofibers of Al₂O₃ and carbon, nanopowders of copper and SiO₂) on the physico-mechanical and tribotechnical properties of superhigh-molecular polyethylene is investigated. It is determined that the modification of superhigh-molecular polyethylene by nanofibers and nanoparticles within the limits of 0.1–05 wt % results in a substantial rise in its deformation-strength characteristics and a multifold increase in its tribotechnical characteristics. By the methods of X-ray structure analysis, infrared spectroscopy, and electron microscopy, it is shown that modification of the polymer by the mentioned nanofillers results in the formation of an ordered (lamellar) permolecular structure. It is revealed that nanofibers form a stable film of friction transfer more quickly in comparison with nanoparticles. The optimum compositions of nanofillers, which determine the high wear resistance and the low constant of friction for polymer, are determined. The mechanical activation of the binder and filler powders provides a uniform distribution of the nanopowder within the binder and additionally enhances the physico-mechanical and tribotechnical properties of the composite.     

Friction and wear properties of CN<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>/SiC in water lubrication

Amorphous carbon nitride coatings (a-CN_x) were deposited on SiC disk by ion beam assisted deposition (IBAD). The tribological behavior of a-CN_x coating sliding against SiC ball in water was investigated and compared with that of SiC/SiC system at room temperature. The influences of testing conditions on friction coefficient and specific wear rate of both kinds of tribopairs were studied. The worn surfaces on disks were observed by scanning electron microscope (SEM). The results indicate that the running-in period of a-CN_x/SiC was shorter than that of SiC/SiC system in water. At a sliding velocity of 120 mm/s, the mean steady-state friction coefficients of SiC/SiC (0.096) was higher than that of a-CN_x/SiC (0.05), while at 160 mm/s, lower friction coefficient (0.01) was obtained for SiC/SiC in water. With an increment of normal load, the mean steady-state friction coefficients after running-in first decreased, reaching a minimum value, and then increased. For self-mated SiC, the specific wear rate of SiC ball was a little higher than that of SiC disk, while for a-CN_x/SiC, the specific wear rate of SiC ball were 10 times smaller than that of a-CN_x coating. Furthermore, the specific wear rate of SiC ball sliding against a-CN_x coating was reduced by a factor up to 100~1000 in comparison to that against SiC in water. The wear mechanism of SiC/SiC system in water is related to micro-fracture of ceramic and instability of tribochemical reaction layer. Conversely, wear mechanism for a-CN_x/SiC is related to formation and transfer of easy-shear friction layer.     

Microstructure,chemical composition,wear, and corrosion resistance of FeB–Fe<Subscript>2</Subscript>B–Fe<Subscript>3</Subscript>B surface layers produced on Vanadis-6 steel using CO<Subscript>2</Subscript> laser

The paper presents the study results of laser modification of FeB–Fe₂B surface layers produced on Vanadis-6 steel using pack cementation method. Microstructure, x-ray phase analysis, chemical composition study using wave dispersive spectrometry method, microhardness, corrosion resistance as well as surface condition, roughness, and wear resistance were investigated. The diffusion boronizing processes were performed at 900 °C for 5 h in the EKabor® powder mixture. The boronized layers had a dual-phase microstructure composed of two types of iron borides, FeB and Fe₂B, and their microhardness ranged from 1800 to 1400 HV. The laser surface modification was carried out on specimens after diffusion boronizing process using CO₂ laser with a nominal power of 2600 W. Laser beam power used in this experiment was equal to 1040 W and was constant. While the three values of scanning speed were used: 19, 48, and 75 mm/s. During laser modification, the multiple tracks were made where distance between of axis tracks was equal to 0.5 mm. As a result of this process, microstructure consisted of remelted zone, heat-affected zone, and substrate was obtained. In remelted zone, the boron-martensite eutectic was observed. Boronized layers after laser modification were characterized by the mild gradient of microhardness from surface to the substrate and their value was dependent on the scanning speed used and was between 1700 and 1100 HV. Corrosion resistance tests revealed reducing the current of corrosion in case of laser modification process. Wear resistance of laser modified specimens was improved in comparison to diffusion boronized layers.     

Wear Behavior of Composites Based on ZA-27 Alloy Reinforced by Al<Subscript>2</Subscript>O<Subscript>3</Subscript> Particles Under Dry Sliding Condition

In present study, the effect of Al₂O₃ particle reinforcement on the sliding behavior of ZA-27 alloy composites was investigated. The composites with 3, 5, and 10 wt% of Al₂O₃ particles were produced by the compocasting procedure. Tribological properties of unreinforced alloy and composite were studied, using block-on-disk tribometer under unlubricated sliding conditions at different specific loads and sliding speeds. The worn surfaces of samples were examined by the scanning electron microscopy (SEM). The test results revealed that those composite specimens exhibited significantly lower wear rate than the ZA-27 matrix alloy specimens in all combinations of applied loads and sliding speeds. The difference in the wear resistance of composite with respect to the matrix alloy, increased with the increase of the applied load/sliding speed and Al₂O₃ particle content. The highest degree of improvement of the ZA-27 alloy tribological behavior corresponded with change of the Al₂O₃ particles content from 3 to 5 wt%. At low sliding speed, moderate lower wear rate of the composites over that of the matrix alloy was noticed. This has been attributed to micro cracking tendency of the composites. Significantly reduced wear rate, experienced by the composite over that of the matrix alloy at the higher sliding speeds and loads, could be explained due to enhanced compatibility of matrix alloy with dispersoid phase and greater thermal stability of the composite in view of the presence of the dispersoid. Level of wear rate of tested ZA-27/Al₂O₃ samples pointed to the process of mild wear, which was primarily controlled by the formation and destruction of mechanical mixed layers (MMLs).     

An experimental study on laminar CH<Subscript>4</Subscript>/O<Subscript>2</Subscript>/N<Subscript>2</Subscript> premixed flames under an electric field

This work investigates the electric field effect on gas temperature, radiative heat flux and flame speed of premixed CH₄/O₂/N₂ flames in order to gain a better insight into the mechanism of controlling the combustion process by electrophysical means. Experiments were performed on laminar Bunsen flames (Re<2200) of lean to rich mixture composition (φ =0.8–1.2) with slight oxygen enrichment (Ω=0.21-0.30). The Schlieren flame angle technique was used to determine the flame speed, and thermocouple measurements at the post flame gas were conducted. The radiative heat flux was measured by using a heat flux meter. At high field strengths, coincident with the appearance and enhancement of flame surface curvatures, an apparent change in flame speed and gas temperature was observed. However, the application of an electric field had no significant effect on flame speed and temperature when the flame geometry was unaltered. This was supported by radiative heat flux showing negligible electric field effects. The modification in flame temperature and flame speed under electric field was attributed to the field-induced flame stretch due to the body forces produced by the ionic winds. This additional flame stretch, coupled with the influence of non-unity Lewis number, accounts for such changes. This reinforces the idea that the action of an electric field on flames with a geometry that remains practically undeformed produces very minimal effect on flame speed, temperature and radiative heat flux. A possible mechanism of combustion control by the application of flame stretch using electric field was introduced.     

Phase separation as a basis for the formation of light-emitting silicon nanoclusters in SiO x films irradiated with swift heavy ions

This paper presents a study of the effect of swift heavy Xe ions of energy 130–167 MeV at doses of 10¹²–10¹⁴ cm^?2 and Bi ions of 700 MeV at doses of 3·10¹²–3·10¹³ cm^?2 on films of stoichiometric thermal silicon dioxide, silicon dioxide films with ion-implanted excess silicon, and SiO _x films with the stoichiometric parameter x varying from 0 to 2. According to electron microscopy and Raman spectroscopy data, irradiation with the swift heavy ions resulted in the formation of silicon nanoclusters. The luminescence spectra depended on the size, number, and structure of the Si nanoclusters formed. Their size can be controlled by varying both the effect parameters (primarily, the ion energy loss per unit length of the track) and the stoichiometric composition of the films.