Recrystallization of silicon-on-sapphire structures at various amorphization-ion-beam energies

Silicon films on sapphire substrates are grown via recrystallization from the silicon-sapphire interface. An amorphous layer is formed using ion implantation with silicon ion energies of 90–150 keV. An X-ray rocking curve is used to estimate the crystalline perfection of the silicon films. After recrystallization, the silicon layer consists of two parts with different crystalline quality. The recrystallized silicon-on-sapphire structures have a highly perfect upper layer (for fabricating microelectronic devices) and a lower layer adjacent to the sapphire substrate containing a large number of defects.     

Theory of High Temperature Superconductivity Beyond BCS with Realistic Coulomb and Fröhlich Interactions

Along with some other researches we have realised that the true origin of high-temperature superconductivity is found in the strong Coulomb repulsion combined with a significant electron–phonon interaction. Both interactions are strong (on the order of 1 eV) compared with the low Fermi energy of doped carriers which makes the conventional BCS-Eliashberg theory inapplicable in cuprates and related doped insulators. Based on our recent analytical and numerical results we argue that high-temperature superconductivity from repulsion alone is impossible for any strength of the Coulomb interaction. Major steps of the alternative polaron theory are outlined starting from the generic Hamiltonian including the unscreened (bare) Coulomb and electron–phonon interactions. The theory accounts for high superconducting critical temperatures, unconventional isotope effects and reconciles tunnelling, photoemission and quantum oscillation data.     

Solidification dynamics under random external-temperature fluctuations

The nonlinear dynamic mechanisms of solid-phase formation with a phase transition region are studied under periodic and random fluctuations of the cooling-boundary temperature. It is theoretically shown that a mushy zone can form even at close liquid and cooling-boundary temperatures due to random temperature field fluctuations. The growth of a solid phase with the mushy zone is investigated as a function of the autocovariance characteristics of random noises.     

Microstructure Evolution in a Cu-0.5Cr-0.2Zr Alloy Subjected to Equal Channel Angular Pressing,Rolling or Aging

Journal of Materials Engineering and Performance - The evolution of microstructure in the Cu-0.5%Cr-0.2%Zr alloy subjected to thermomechanical treatment has been studied by means of the x-ray...     

A synchronized X-pinch driver

The efficiency of the X-ray point-projection radiography technique has been demonstrated on a terawatt pulse power generator using a detached compact current generator driving an X-pinch load. This technique has been approved in an experiment on the multiwire-array implosion performed at the Angara-5-1 generator with a peak power as high as 6 TW. The advantage of this experiment over earlier experiments on terawatt generators is in the use of a separate X-pinch driver, which makes it possible to arbitrarily vary the sample probing time. The X-pinch driver is connected to the load unit by means of a flexible low-inductance transmission line. The flexibility of the transmission line is an additional advantage of this technique, since it allows the accuracy of the X-ray radiography system adjustment to be improved and the X-pinch to be located near the plasma load. When compared to the laser method for producing a probe radiation source, the proposed technique features a smaller size, a lower cost of the facility, the absence of high-price optical elements, and a higher efficiency of X-ray generation. Owing to the small size of the synchronized X-pinch driver, it can be transported for use in experiments performed at other research organizations.     

A study of pyrolysis of polymethylsiloxanes by Fourier transform infrared

This paper is dedicated to a comparative study of pyrolysis of decamethylcyclopentasiloxane and hexamethyldisiloxane, widely used as precursors for CVD of silicon dioxide films. The pyrolysis process was carried out in a hot-wall horizontal tube reactor made from quartz within the temperature range 25-1000 degrees C. FTIR spectroscopy has been used for the analysis of gaseous reaction products in the exhaust line of the reactor. It has been found that transformation of DMPSO was initiated by the open ring in the precursor molecules with its further transformation to linear biradicals followed by the chain's growth due to radical reactions. HMDSO transformation is connected with separation of silanon, silyl and methyl radicals with following multi-type interactions of siloxane radicals and formation of non-rigorously organized three-dimensional molecules.     

Formation of fractal structures from silicon dioxide nanoparticles synthesized by RF atmospheric pressure plasma enhanced chemical vapor deposition

Fractal structures were formed on silicon substrates from SiO2 nanoparticles homogeneously synthesized in low temperature atmospheric pressure plasma from tetraethoxysilane (TEOS). RF discharge (power absorbed was about 10 W) sustained between two parallel mesh electrodes was used to generate plasma. The average size of nanoparticles was in the range of 8-20 nm and was determined by process parameters. The obtained products were analyzed by SEM (scanning electron microscopy) and XPS (X-ray photoelectron spectroscopy). Values of fractal dimension parameter of bidimensionals agglomerates formed on the substrate surface from nanoparticles were calculated with the use of Gwyddion and others. It was found that values of this parameter of the deposited structures varied in the range of 1.48-2 and were determined by combination of the process parameters. An empirical model explaining mechanism of the fractal structures formation and variation of the fractal dimension parameter with the process parameters was proposed.     

Bose–Einstein Condensation in the Pseudogap Phase of Cuprate Superconductors

We have identified the unscreened Fröhlich electron–phonon interaction (EPI) as the most essential for pairing in cuprate superconductors as now confirmed by isotope substitution, recent angle-resolved photoemission (ARPES), and some other experiments. Low-energy physics is that of mobile lattice polarons and bipolarons in the strong EPI regime. Many experimental observations have been predicted or explained in the framework of our “Coulomb–Fröhlich” model, which fully takes into account the long-range Coulomb repulsion and the Fröhlich EPI. They include pseudo-gaps, unusual isotope effects and upper critical fields, the normal state Nernst effect, diamagnetism, the Hall–Lorenz numbers, and a giant proximity effect (GPE). These experiments along with the parameter-free estimates of the Fermi energy and the critical temperature support a genuine Bose–Einstein condensation of real-space lattice bipolarons in the pseudogap phase of cuprates. On the contrary, the phase fluctuation (or vortex) scenario is incompatible with the insulating-like in-plane resistivity and the magnetic-field dependence of orbital magnetization in the resistive state of underdoped cuprates.     

Editorial—Multidisciplinary Design Optimization

Optimization and Engineering -