Thermal expansion of nanostructured PbS films and anharmonicity of atomic vibrations

The dependences of the coherent scattering region size and thermal expansion coefficient α of a PbS nanofilm on the annealing temperature in the range of 293–473 K and on the duration of annealing at a constant temperature of 423 K have been measured. It has been found that the thermal expansion coefficient α of the PbS nanofilm is almost twice as much as the coefficient α of coarse-grained lead sulfide. It has been shown that the large difference in the coefficients α is associated with the small size of particles in the film, which leads to an increase in the anharmonicity of atomic vibrations. The contribution from the small size of particles to the thermal expansion coefficient of the PbS nanofilm has been evaluated theoretically.     

Spectrum of vibrational frequencies of crystalline tungsten at temperatures of 293 and 2400 K

The slow neutron inelastic scattering spectra for a refractory (T _melt = 3680 K) Group VI transition metal of the Periodic Table, namely, tungsten, were measured for the first time in the range from room temperature to 2400 K. Measurements of the neutron scattering spectra of tungsten were performed on a DIN-2PI time-of-flight spectrometer installed at the IBR-2 reactor (Dubna, Russia). The sample was heated in a TS3000 K high-temperature thermostat. The spectrum of vibrational frequencies of the crystal lattice of tungsten at temperatures of 293 and 2400 K was determined from the measured neutron scattering spectra by the iterative method. A softening of the frequency spectrum of tungsten was observed with increasing temperature. This was explained by the increasing role of vibrational anharmonicity effects at high temperatures. The experimental results were compared with model calculations of the frequency spectrum of tungsten.     

Deformation of doped NaCl crystals during uniaxial compression at temperatures of 4.2–293 K

The impurity weakening of crystalline NaCl:Mg and NaCl:Mn associated with purification of the matrix in a melt is demonstrated. This effect is manifested in a consistent change in the yield strength and mobility of dislocations. Its unusual temperature dependence is determined: in a number of cases weakening becomes greater as the temperature is lowered within the interval 293–4.2 K. A deviation in the elastic region of the stress-strain curves is observed to increase as the temperature is lowered. Plasticizing of crystalline NaCl is established: when the deformation temperature is lowered from 293 to 77 and 4.2 K the rate of rise in the yield strength of Cd²⁺ and Sr²⁺ doped samples is lower than that of undoped samples. An explanation for this fact is proposed. Fiz. Tverd. Tela (St. Petersburg) 39, 313–317 (February 1997) Deceased.     

非晶硅薄膜的低温快速晶化及其结构分析

在镀铝的廉价玻璃衬底上高速沉积的非晶硅薄膜在不同的温度下退火10min.退火温度为500℃时,薄膜表面形成了硅铝的混合相,非晶硅薄膜开始呈现了晶化现象 退火温度为550℃时,大部分(约80%)的非晶硅晶化为多晶硅,平均晶粒尺寸为500nm 退火温度为600℃时,几乎所有的非晶硅都转化为多晶硅,其平均晶粒尺寸约为15μm.     

Study of nanoconductive and magnetic properties of nanostructured iron films prepared by sputtering at very low temperatures

A combined study of the surface nanostructure and electrical characteristics of iron thin films prepared on naturally passivated silicon wafers is presented. By means of conductive-scanning force microscopy, the influence of the substrate temperature during film preparation on both surface morphology and conductivity response is investigated. In addition, magnetic properties of these films are reported and correlated with the nanostructural properties. Films prepared at 200 K show granular core–shell magnetic behaviour exhibiting exchange bias. Both conductive and magnetic data indicate that samples prepared at low temperature behave as a percolated network of nanometric metallic iron clusters (with typical sizes of 20 nm) interconnected by oxidized chains (of 10 nm in diameter), showing an excellent system for nanotechnological exchange bias applications.     

Microstructure and crystal structure of nanocrystalline powders and films of PbS

The microstructure and crystal structure of nanocrystalline powders and nanostructured films of lead sulfide PbS have been investigated using X-ray diffraction and electron microscopy. It has been found that, in the synthesized nanopowders, the average size of PbS nanoparticles ranges from 20 to 8 nm, whereas the average size of PbS nanoparticles in nanofilms varies from 80 to 40 nm. It has been shown that the nanocrystalline PbS powders have a cubic (space group $Fm\bar 3m$ ) structure of the B1 type. The nanostructured PbS films prepared by chemical precipitation on a glass substrate have a cubic (space group $Fm\bar 3m$ ) structure of the D0₃ type with the S atoms located in positions of two types: 4(b) and 8(c).     

非晶硅薄膜的低温快速晶化及其结构分析

在镀铝的廉价玻璃衬底上高速沉积的非晶硅薄膜在不同的温度下退火10min.退火温度为500℃时,薄膜表面形成了硅铝的混合相, 非晶硅薄膜开始呈现了晶化现象;退火温度为550℃时,大部分(约80%)的非晶硅晶化为多晶硅,平均晶粒尺寸为500nm;退火温度为600℃时,几乎所有的非晶硅都转化为多晶硅,其平均晶粒尺寸约为1.5μm.     

Iron arachidate Langmuir-Blodgett films: magnetic behavior studied at temperatures down to 4.2 K

Langmuir-Blodgett (LB) multilayers of ferric arachidate on silicon wafers have been investigated by means of conversion electron Mössbauer spectroscopy (CEMS) and absorption Mössbauer spectroscopy (AMS) at different temperatures between 4.2 K and room temperature. At low temperatures we observe antiferromagnetic ordering in the two-dimensional model substance and determined the magnitude and the orientation of the internal magnetic field. We studied the phase transition and found with increasing temperature a slow decrease of the ordered phase, which has completely vanished at 130 K. In the present state it cannot be decided if we just observe superparamagnetic relaxation or if we observe additional effects arising from the low dimensionality of the system. Comparable measurements on small iron arachidate LB-particles have been performed but no significant difference between the films and the small particles can be observed. This has been expected because the two-dimensional structure is mainly preserved in the LB-particles.     

Structure and optical properties of nanostructured zinc oxide films with different growth temperatures

ZnO films were prepared by pulsed laser deposition (PLD) on glass substrate with temperature ranging from room temperature (RT) to 500 °C. All the films formed the hexagonal wurtzite structure and showed the c-axis (0 0 2) preferred orientation. The films deposited at 200 °C showed the narrowest full width at half maximum of both X-ray diffraction (XRD) and rocking curve, largest height grain size, smallest macrostress and least point defects. Meanwhile, it was found that the films deposited at 350 °C displayed the most intense diffraction peak in XRD and a strong UV emission while it showed the most intense defect-related green emission, fastest growth rate and larger macrostress. In addition, the cross section images showed all films grew with a columnar form along (0 0 2) orientation.     

Photoluminescence studies on nanostructured cadmium sulfide thin films prepared by chemical bath deposition method and annealed at different temperatures

Nanostructured cadmium sulfide (CdS) thin films have been prepared by chemical bath deposition (CBD) method and after post deposition annealing of the thin films at different temperatures, photoluminescence (PL) property has been studied. The effects of various photoexcitation wavelengths on the PL behaviour of different annealed films of CdS were studied by recording the PL spectra. The intensity of PL, the profile of the PL spectra and the effects of photoexcitation wavelength depend drastically on the temperature of the post deposition annealing of the thin films. The XRD patterns of the films show the presence of both the hexagonal and cubic phases (mixed phases). The emission peak arises from the surface defects of the CdS nanocrystalline thin films. Significant modification in the surface morphology of the CdS films upon annealing has been observed from the FESEM images. The morphology of the thin films is expected to influence the PL behaviour of the CdS thin films. The quantum size effect and size dependant PL have been observed.     

The magnetic domain structure of gadolinium between 230 and 293 K

The magnetic domain structure of gadolinium has been studied over the temperature range 230 K to 293 K. This temperature range includes the two magnetic phase transitions that exist in gadolinium, that at the Curie temperature, 291 K, and the change in the easy direction of magnetization at 240 K. A clear uniaxial type domain structure was observed to form as the temperature was lowered through the Curie temperature. This structure was found to disappear as the temperature approached 230 K and no further structure was observed at temperatures below 230 K. Calculations of wall parameters using a numerical integration technique indicate that a stable domain structure should be present and the reasons for the non-appearance of a low temperature domain structure in the present work are not clear.     

The delay time of gravitational wave – gamma-ray burst associations

The first gravitational wave (GW) – gamma-ray burst (GRB) association, GW170817/GRB 170817A, had an offset in time, with the GRB trigger time delayed by ~1.7 s with respect to the merger time of the GW signal. We generally discuss the astrophysical origin of the delay time, Δt, of GW-GRB associations within the context of compact binary coalescence (CBC) – short GRB (sGRB) associations and GW burst – long GRB (lGRB) associations. In general, the delay time should include three terms, the time to launch a clean (relativistic) jet, Δt_jet; the time for the jet to break out from the surrounding medium, Δt_bo; and the time for the jet to reach the energy dissipation and GRB emission site, Δt_GRB. For CBC-sGRB associations, Δtjet and Δt_bo are correlated, and the final delay can be from 10 ms to a few seconds. For GWB-lGRB associations, Δt_jet and Δt_bo are independent. The latter is at least ~10 s, so that Δt of these associations is at least this long. For certain jet launching mechanisms of lGRBs, Δt can be minutes or even hours long due to the extended engine waiting time to launch a jet. We discuss the cases of GW170817/GRB 170817A and GW150914/GW150914-GBM within this theoretical framework and suggest that the delay times of future GW/GRB associations will shed light into the jet launching mechanisms of GRBs.     

Composition, structure, and properties of tantalum boride nanostructured films

The structure, as well as the phase and elemental compositions, of tantalum diboride-based nanostructured films deposited by rf magnetron sputtering under various conditions are studied by X-ray diffraction, electron microscopy, and secondary ion mass spectrometry. The physicomechanical properties of the films (hardness, as well as elastic and plastic properties) are determined. The maximum hardness and elastic modulus of the synthesized films are 42 are 240 GPa, respectively. The grain size is found to influence the physicomechanical and electrical properties of the films.     

Luminescent properties of ytterbium-erbium nanostructured lead fluoride silicate glass-ceramics at low temperatures

We have studied the luminescent properties of lead fluoride silicate nanostructured glass-ceramics doped with ytterbium and erbium ions. We have measured luminescence spectra of glass-ceramics in the visible and near-IR ranges at temperatures of 300 and 77 K and under their pumping at a wavelength of 975 nm. We have examined changes in the luminescence spectra of glass-ceramics depending on the time of their secondary thermal treatment, concentration of dopant ions, specimen temperature, and power of excitation radiation.     

Morphology and electronic structure of nanostructured carbon films embedding transition metal nanoparticles

Inclusions of metals in the growth process of carbon cluster assembled materials (ns-C) induce modifications in the structural and electronic properties of the material. A novel pulsed microplasma cluster source (PMCS) is able to deliver highly intense, collimated and stable beams suitable for producing bulk quantities of cluster-assembled nanocomposite films. Loading of metal nanoparticles into carbon cluster based films is obtained either by mixing a gas phase metallorganic compound with the carrier gas (He) before entering into the source (for example molybdenum (V) isopropoxide), or by using a double component sputtering target (metal (Ti, Ni)/graphite). The study of film morphology on nanometer scale, carried out by transmission electron microscopy (TEM), reveals the dispersion in a ns-C matrix of metallic particles and, in the case of molybdenum containing films, also of carbide particles. Spatially resolved ultraviolet photoemission spectroscopy confirms the segregation of metal particles and exhibits evident anisotropy in the Mo:ns-C films, mainly ascribable to the formation of carbide nanoparticles.     

Substrate-dependent structure, microstructure, composition and properties of nanostructured TiN films

Titanium nitride films of a thickness of ∼1.5 μm were deposited on amorphous and crystalline substrates by DC reactive magnetron sputtering at ambient temperature with 100% nitrogen in the sputter gas. The growth of nanostructured, i.e. crystalline nano-grain sized, films at ambient temperature is demonstrated. The microstructure of the films grown on crystalline substrates reveals a larger grain size/crystallite size than that of the films deposited on amorphous substrates. Specular reflectance measurements on films deposited on different substrates indicate that the position of the Ti-N 2s band at 2.33 eV is substrate-dependent, indicating substrate-mediated stoichiometry. This clearly demonstrates that not only structure and microstructure, but also chemical composition of the films is substrate-influenced. The films deposited on amorphous substrates display lower hardness and modulus values than the films deposited on crystalline substrates, with the highest value of hardness being 19 GPa on a lanthanum aluminate substrate.     

Electrical conductivity of InAs films prepared at different temperatures

Conclusion The structure and electrical conductivity of thin InAs films, prepared by flash evaporation, are seen to be dependent on the substrate temperature, post-deposition heat treatment and thickness. The structure was found to improve from amorphous polycrystalline preferred orientation as the substrate temperature was increased. The corresponding micrographs showed increasingly bigger grain sizes. The post-deposition heat treatment was successfully employed to improve the structure from amorphous crystalline, which was reflected in the increased electrical conductivity. An interesting observation was that the room temperature electrical conductivities after heat treatment were the same for all films irrespective of the temperature at which they were prepared. The activation energies increased with increasing temperature but decreased with increasing substrate temperature and increasing thickness. These values throw important light on the conduction mechanism operative in the film in various temperature ranges.One of the authors (AKS) wishes to acknowledge the financial assistance provided by the CSIR, New Delhi, India.     

Formation of two-component two-phase metal films at elevated temperatures

This paper is devoted to the study of two-component thin films deposited at elevated temperatures. The dependence of plasma-assisted film deposition from a flow of sputtered Cu and Fe atoms on the substrate temperature and type, concentration of sputtered components in the flow, and film thickness is investigated.