Effect of surface composition on melting of thin InSb films

We demonstrate the possibility of melting thin (0.1–0.5 μm) InSb films directly in atmosphere under the protective layer of native oxides to obtain high mobility of majority carriers (up to 25 000 cm²/V s). The features of the film synthesis process based on thermal pulsed evaporation of InSb powder in vacuum are studied experimentally. Such a technique makes it possible to provide necessary compositional inhomogeneity of the deposited film for subsequent melting in air.     

Study of dynamics of thin liquid layer breakdown under conditions of spot heating and formation of a droplet cluster

Breakdown dynamics was studied experimentally for the horizontal layers of various liquids (ethanol, water) with the thickness of 300 μm under the conditions of spot heating from the substrate. The main stages of the process of liquid layer breakdown were determined, and time of dry spot formation was measured. Time of dry spot formation for ethanol at the heat flux of 12.6 W/cm² was 7.85 s, and for water at the heat flux of 117 W/cm², it was 0.13 s. It was found that for both working liquids, a residual layer appears in the region of spot heating before liquid layer breakdown. It is shown that together with the thermocapillary effect, evaporation is one of the main factors affecting dynamics of liquid layer breakdown and dry spot formation.     

Degradation of tungsten under the action of a plasma jet

The degradation of the surface and structure of single-crystal tungsten and sintered powder tungsten during the action of a pulsed plasma jet is studied. It is shown that the degradation of a tungsten target during the action of a plasma jet with an energy flux density of 0.25–1 MJ/m² is accompanied by surface evaporation and melting and the fracture of surface layers on scales of 150–250 μm. The results of a numerical simulation of the thermomechanical processes that occur in a tungsten target during the action of a plasma jet are presented. The degradation of tungsten during the action of a plasma jet is shown to proceed almost continuously from the action (evaporation, melting) to the times that are more than three orders of magnitude longer than the action time, which is caused by the thermomechanical processes occurring in the tungsten target. Moreover, the action of thermal stresses leads to structural and morphological changes throughout the sample volume, and these changes are accompanied by recrystallization in adiabatic shear bands.     

Optical properties of a new IR converter for laser beam analysis

This work presents the temporal and spacial resolution of a new infrared (IR) converter based on thermal radiation emission. Using this converter, it is possible to measure the intensity distribution of laser beams with a wavelength between 1 and 20 μm. For this purpose, the laser radiation (for example, 10.6 μm) is converted into a wavelength coverage of 800–1100 nm. In the actual converter thin metal foils provide the basis of this method. The metal foils are heated to a temperature of 600–800 K. The emitted radiation of the foils defers into the near-infrared (NIR) area, thus enabling detection by camera systems based on silicate. Additional heat input of the laser results in a local temperature increase, and then the increase in radiation intensity can be measured. Typical thicknesses of converter metal foils are <5μm. Foil materials with a low thermal conductivity, good absorption of the measured laser beams, and a high melting temperature are particularly suitable. These parameters are well shown by using stainless steels, such as INOX (stainless steel 1.4310 CrNi steel). Using this material, it is possible to gain a maximum spatial resolution of 250 μm and a temporal resolution of 12.5 Hz, by a measurement range from 1 to 100 W/cm². The maximum measured intensity is 125 W/cm².     

Affect of the electrical characteristics depending on the hole and electron injection materials of red organic light-emitting diodes

This study examined the electrical and optical properties of red OLEDs (organic light-emitting diodes) with a four-layer structure, ITO/amorphous fluoropolymer (AF)/N,N′-diphenyl-N,N′-bis(3-methylphenyl)-1,1-biphenyl-4,4′-diamine (TPD)/R-H:R-D/lithium fluoride (LiF)/Al, containing a hole injection material, AF (amorphous fluoropolymer) and an electron injection layer material, LiF. Compared to the basic structure (two-layer structure), the brightness and luminous efficiency of the four-layer structure, ITO/TPD/R-H:R-D/Al, increased approximately 100 times (30,000 lm/m²) and 150 times (51 lm/W), respectively, with an applied voltage. The excellent efficiency of the external proton was also increased 150 times (0.51%). That is, the hole and electron injection layers improved the surface roughness of ITO and Al, and the interfacial physical properties. In addition, these layers allowed the smooth injection of holes and electrons. The luminance, luminous efficiency and external quantum efficiency were attributed to an increase in the recombination rates.     

Influence of a plasma jet on different types of tungsten

The influence of a plasma producing nonstationary thermal loads akin to edge-localized modes in a tokamak on different types of tungsten is investigated. Tungsten is irradiated by a jet of a hydrogen plasma generated in a plasma gun. The plasma density and velocity are on the order of 10²² m^?3 and 100–200 km/s, respectively, and the irradiation time is 10 μs. Two plasma flux densities, 0.70 and 0.25 MJ/m², are used. Structural modifications in irradiated single-crystal and hot-rolled tungsten samples, as well as in V-MP and ITER_D_2EDZJ4 tungsten powders, are examined. It is found that the plasma generates a regular crack network with a period of about 1 mm on the surface of the single-crystal, hot-rolled, and V-MP powder samples, while the surface of the ITER_D_2EDZJ4 powder is more cracking-resistant. The depth of the molten layer equals 1–3 μm, and the extension of intense thermal action is 15–20 μm. The material acquires a distinct regular structure with a typical grain size of less than 1 μm. X-ray diffraction analysis shows that irradiation changes the crystal lattice parameters because of the melting and crystallization of the surface layer. The examination of the V_MP tungsten powder after cyclic irradiation by a plasma with different energy densities shows that high-energy-density irradiation causes the most significant surface damage, whereas low-energy-density irradiation generates defects that are small in size even if the number of cycles is large.     

Temperature dependence of spin pumping in YIG/NiOx/W multilayer

We report the temperature dependence of the spin pumping effect for Y₃Fe₅O₁₂ (YIG, 0.9 μm)/NiO (t_NiO)/W (6 nm) (t_NiO = 0 nm, 1 nm, 2 nm, and 10 nm) heterostructures. All samples exhibit a strong temperature-dependent inverse spin Hall effect (ISHE) signal I_c and sensitivity to the NiO layer thickness. We observe a dramatic decrease of I_c with inserting thin NiO layer between YIG and W layers indicating that the inserting of NiO layer significantly suppresses the spin transport from YIG to W. In contrast to the noticeable enhancement in YIG/NiO (t_NiO ≈ 1-2 nm)/Pt, the suppression of spin transport may be closely related to the specific interface-dependent spin scattering, spin memory loss, and spin conductance at the NiO/W interface. Besides, the I_c of YIG/NiO/W exhibits a maximum near the T_N of the AF NiO layer because the spins are transported dominantly by incoherent thermal magnons.     

Thermal stability and electrical characteristics of NiSi films with electroplated Ni(W) alloy

In this study, an electroplating method to deposited Ni, crystalline NiW(c-NiW), amorphous NiW (a-NiW) films on P-type Si(1 0 0) were used to form Ni-silicide (NiSi) films. After annealed at various temperatures, sheet resistance of Ni/Cu, c-NiW/Cu and a-NiW/Cu was measured to observe the performance of those diffusion barrier layers. With W added in the barrier layer, the barrier performance was improved. The results of XRD and resistance measurement of the stacked Si/Ni(W)/Cu films reveal that Cu atom could diffuse through Ni barrier layer at 450 °C, could diffuse through c-NiW at 550 °C, but could hardly diffuse through a-NiW barrier layer. c-NiW layer has a better barrier performance than Ni layer, meanwhile the resistance is lower than a-NiW layer.     

Experimental investigation of the temperature field in the gas-liquid two-layer system

Results of an experimental investigation of the temperature field across the liquid-gas two-layer system are presented. The liquid layer is locally heated from the bottom substrate, and the intensive liquid evaporation is observed. A technique for measuring the temperature profile across the liquid and gas layers (including their interface) is developed. To do these measurements, the microthermocouple is moved across the layers with the help of precision micropositioner with a step of 1 μm. The temperature jump at the liquid-gas interface is measured, and its value increases with the temperature increase. Detailed information on the temperature field near the interface is obtained by using the precise thermocouple displacement with a small step.     

Oxidation of the (100) surface of a NiFe alloy

The initial stages of oxidation of the (100) surface of a single crystal alloy specimen of approximate atomic composition Ni 59, Fe 41 (at%) have been studied by Auger spectroscopy and electron diffraction techniques. The clean alloy surface shows only a slight iron enrichment over the temperature range of the oxidation studies (373–873 K). Oxidation studies were performed over the O₂ pressure range 5 × 10^?9 to 1 × 10^?6 Torr. Within these experimental conditions the rate of oxygen uptake was found to be linear in pressure and essentially independent of temperature. LEED studies showed that a chemisorbed c(2 × 2) structure preceded the formation of surface oxides. The interaction of oxygen with the surface induced a marked segregation of iron and this was particularly pronounced at elevated temperatures. Chemical shifts were observed in the low energy Ni and Fe Auger spectra during oxidation; these were similar to those previously observed in separate studies of the oxidation of pure Ni and of pure Fe. At the higher temperatures the initial oxide layer grew epitaxially apparently as a (111) cubic oxide on the (100) substrate. The Ni to Fe concentration ratio in oxides several layers thick was found to depend on the temperature of the reaction; at higher temperatures the oxide were more Fe-rich. The Fe to Ni ratio in oxides produced at lower temperatures could be increased by annealing. At large O₂ exposures (about 5000 L) a transition was observed in the structure of the oxide layer.     

Analysis of Thermal Physical Processes and Peculiarities of Modification of a Steel Surface by Pulsed Plasma Flows

The temperature gradient and melting depth of the surface of iron-based alloys under the action of high-temperature pulsed plasma beams have been estimated and compared with the experimental data. It has been shown that the steel surface melts under the action of a pulsed plasma flow at an energy density of 15–20 J/cm²; the heat front propagates to a depth of up to 20 μm, the thickness of the molten layer being less than 10 μm. The characteristic size of the microstructure formed as a result of thermal perturbation is estimated at 17 nm. The formation of new phases with crystallite sizes that vary in the range of 16–270 nm is demonstrated experimentally. It has been shown that the formation of nanosize crystalline structure and modified near-surface region are the main factors responsible for strengthening steels.     

Preparation of thin films of the ternary heavy fermion system CeNi2Ge2

2 Ge₂ layers on W(110). In order to produce well-ordered and atomically clean surfaces of the Ce-based intermetallic system the growth was performed under UHV conditions (p<2×10^-11 mbar). Both the polycrystalline CeNi₂Ge₂ compound and the individual elements Ce, Ni, and Ge were used as evaporants. The characterisation of the layers was made with LEED, SEM, and XPS. We find a significant influence of the substrate temperature and the evaporation power on the growth characteristics. The compound material CeNi₂Ge₂ exhibits complicated behaviour when evaporated. Under carefully selected growth conditions we obtain well-ordered films with a stoichiometry of Ce:Ni:Ge=1:2:2 and a (001) oriented surface of the body-centered tetragonal ThCr₂Si₂-type structure. The k_∥ dispersion and binding energies of the valence bands of these layers were determined with ARUPS. Received: 26 October 1997/Accepted: 27 October 1997     

Tandem organic light-emitting diode with molybdenum tri-oxide thin film interconnector layer

A 10-nm thickness molybdenum tri-oxide (MoO₃) thin film was used as the interconnector layer in tandem organic light-emitting devices (OLEDs). The tandem OLEDs with two identical emissive units consisting of N,N'-bis(naphthalen-1-yl)-N,N'-bis(phenyl)-benzidine (NPB)/tris(8-hydroxyquinoline) aluminum (Alq₃) exhibited current efficiency-current density characteristics superior to the conventional single-unit devices. At 20 mA/cm², the current efficiency of the tandem OLEDs using the interconnector layers of MoO₃ thin film was about 4.0 cd/A, which is about twice of that of the corresponding conventional single-unit device (1.8 cd/A). The tandem OLED showed a higher power efficiency than the conventional single-unit device for luminance over 1200 cd/m². The experimental results demonstrated that a MoO₃ thin film with a proper thickness can be used as an effective interconnector layer in tandem OLEDs. Such an interconnector layer can be easily fabricated by simple thermal evaporation, greatly simplifying the device processing and fabrication processes required by previously reported interconnector layers. A possible explanation was proposed for the carrier generation of the MoO₃ interconnector layer.     

Ion irradiation induced evolution of nanostructure in a graded multi-trilayer system

Nanostructural modifications in a double-graded Pt/Ni/C multi-trilayer, due to irradiation by an energetic ion-beam, have been analyzed using X-ray reflectivity (XRR), X-ray standing wave (XSW) and cross-sectional transmission electron microscopy (X-TEM) techniques. 2 MeV Au²⁺ ions were rastered on Pt/Ni/C multi-trilayer samples producing a uniformly irradiated area at ion-fluences ranging from 1 × 10¹⁴ ions/cm² to 2 × 10¹⁵ ions/cm². Ion irradiation induced modifications of microstructural parameters, e.g., layer thicknesses and electron densities of individual layers and interface roughnesses have been obtained from XRR analysis. Pt- and Ni-fluorescence yield from the as-deposited sample under the XSW condition show the distinct existence of Pt and Ni layers. The almost indistinguishable Pt- and Ni-fluorescence data over the first order Bragg peak from the sample irradiated at the highest ion-fluence, suggest complete mixing of Pt and Ni. Strong mixing between Pt and Ni in the ion irradiated samples is also corroborated by XRR results. X-TEM studies reveal the individual layer structure in the as-deposited sample. This layer structure is lost in the sample irradiated at the highest ion fluence indicating a complete mixing between Pt and Ni layers and nanoscale grain growth of Pt-Ni alloys. Additionally, formation of Pt-Ni alloy nano-clusters in the C-layers is observed. The results are understood in the light of the positive heat of mixing between Pt and C, and Ni and C and the negative heat of mixing between Pt and Ni. The effect of heat of mixing becomes dominant at high fluence irradiation.     

Structural analysis of the fracture surface of a heterogeneous body (quartz sandstone)

The structure of surface layers of quartz sandstone with a thickness of ~1 μm before and after destruction by a compressive stress is studied by methods of infrared, photoluminescent, and Raman spectroscopy. Before destruction, this layer contained quartz grains cemented with montmorrillonite and kaolinite. The grains are covered with a thin water layer and have crystallographic defects: Si–O^–, self-trapped excitons, AlOH and LiOH compounds, [AlO₄]^– centers, etc. The destructed surface contains separate quartz grains with sizes of ~2 μm and a reduced defect concentration. It is assumed that the defects reduce the strength of quartz grains, which are destroyed in the first turn.     

A New Model of Crater Formation by Arc Spots

The forces acting on the cathode arc spot surface and removing the molten layer from the crater bottom are composed mainly of the ion pressure, the neutral gas pressure and the evaporation recoil whilst electrostatic forces diminish the effective pressure that is in the order of some 10⁹ dyn/cm². The motion of the liquid layer caused by these forces is treated with the hydrodynamic equations. A simple solution exists in the special case of constant layer depth, that is achieved a few nanoseconds after spot formation. From this model the layer depths (some 0.1 μm) and the ejection velocities at the crater rims (few 10⁴ cm/s) are calculated. The real spot velocity agrees with the velocity of the melting front below the spot surface, but because of the stochastic character of the spot motion the apparent velocity decreases with growing observation time intervals Δt according to Δt^?1/2.     

Strain relaxation of epitaxial SiGe layer and Ge diffusion during Ni silicidation on cap-Si/SiGe/Si(0 0 1)

Strain relaxation of the epitaxial SiGe layer and Ge diffusion during nickel silicidation by rapid thermal annealing the structure of Ni(≅14 nm)/cap-Si(≅26 nm)/Si_0.83Ge_0.17/Si(0 0 1) at the elevated annealing temperatures, T_A, were investigated by X-ray diffraction analyses of high-resolution ω-2θ scan and reciprocal space mapping. The analyses showed a much larger strain relaxation at a lower T_A and a reduction in Ge content in the SiGe layer of Ni/SiGe/Si(0 0 1) after thermal annealing compared to the case of cap-Si/SiGe/Si(0 0 1). The results indicate that the strain relaxation of the SiGe layers in NiSi/SiGe/Si(0 0 1) is related to the phenomena of NiSi agglomeration and penetration into the SiGe layer during silicidation at elevated anneal temperatures ≥750 °C. At elevated T_A ≥ 750 °C, Ge diffused into the intact cap-Si area during silicidation.     

Reactive resistance welding of Ti6Al4V alloy with the use of Ni(V)/Al multilayers

The freestanding Ni(V)/Al multilayer foil was applied as a filler material in order to join Ti6Al4V alloy with the use of reactive resistance welding (RRW) technique. Present investigations, performed with the use of transmission electron microscopy (TEM) method, allowed to show that an application of high current (I = 400 A for 2 min in vacuum conditions ～10^–1 mbar) transformed the Ni(V)/Al multilayers into fine grain (<300 nm) NiAl phase. It also showed that the RRW process led to the formation of firm connection with nanoporosity limited only to the original contact plane between base material and the foil. Simultaneously, the formation of a narrow strip of crystallites of Ti₃Al intermetallic phase elongated along the joint line (average size of ～200 nm) was observed. The base material was separated from the joint area by a layer of up to ～2 μm thickness of nearly defect free α‐Ti and β‐Ti grains from a heat affected zone (HAZ). The performed experiment proved that Ni(V)/Al multilayer could serve as a filler material for joining of Ti6Al4V alloys even without additional solder layer. (© 2016 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Particular features of the transmission of laser radiation with wavelength 0.438 µm and intensity (3–7)·1014 W/cm2 through an undercritical plasma from polymer aerogels

The velocities of energy transport in an undercritical plasma of polymer aerogel with and without copper nanoparticles were measured. Transmission of the laser light through targets of different thicknesses such as submicron three-dimensional polymer networks with densities below the critical value (0.13–0.52 N _cr) for a wavelength of 0.438 μm and intensity of (3–7)·10¹⁴ W/cm² at a half-height pulse duration of 0.32 ns was studied. The transfer of a heating laser radiation was registered on the rear side of the target. It ranged from a level of ∼0.5% for the thickness of a low-density layer of 400 μm and density of 9 mg/cm³ (mass per unit square of 0.36 mg/cm²) up to 50–60% for a thickness of 100 μm and density of 2.25 mg/cm³ (mass per unit square of 0.02 mg/cm²). The time dependences of the optical emission from the rear side of the targets were measured. They appear to be indicative of the plasma dynamics in two-layer targets (polymer foam on Al foil) and enable the estimation of the absorption depth for the laser light in an undercritical plasma. __________ Translated from Preprint No. 8 of the P. N. Lebedev Physical Institute, Moscow (2007).