NbN films on vicinal to the X-cut of LiNbO3 surfaces
We report a study of epitaxial superconductive NbN films on vicinal to the X-cut of single crystal LiNbO3 substrates grown using reactive magnetron sputtering of Nb target in Ar -N2 atmosphere. It is found that the NbN films reveal sharp superconductive transition at TC= 15.2 K and anisotropy of critical current. Critical current measured along the Z direction exceeds JC along the Y direction regardless of the orientation of step edges of the vicinal surfaces. The anisotropy effect is attributed to NbN film uniaxial stress due to the lattice mismatch of NbN (0 0 1) layer along the Z direction of LiNbO3.
Stress evolution was studied in up to similar to 3 mu m thick AlN templates, comprising similar to 65 nm thick AlN nucleation layers (NLs) and thick buffer layers (BLs), grown using different growth modes and conditions by plasma-assisted molecular beam epitaxy (PA MBE) on c-Al2O3. Growth of both the NL and BL in a standard PA MBE mode at N-rich conditions (at flux ratio Al/N-2* similar to 0.5) led to instant generation of a relatively high tensile stress (similar to 1.5 GPa) which is maintained throughout the entire growth. On the contrary, NLs, grown using a migration-enhanced epitaxy (MEE), demonstrated a transition from the initial compressive stress to stress-free growth, which is usually observed in the Volmer-Weber films. Further growth of thick AlN BLs on the MEE-NLs at various Al/N-2* ratios revealed a wide variety of stress evolution processes. The BL growth by using metal-modulated epitaxy (MME) at Me-rich conditions with Al/N-2* similar to 1.33 led to a gradual decrease in the initial compressive stress in the 2D AlN layers, whereas standard PA MBE growth of 3D BL at N-rich conditions (Al/N-2* similar to 0.92) exhibited a fast transition from the initial compressive stress to tensile stress. Moreover, we succeeded in achieving the quasi-stress-free growth of a 3.1 mu m thick AlN BL using the MME growth mode at the optimum flux ratio Al/N-2* = 1.05. These results were compared with the results of other authors and explained using a kinetic approach to description of stress evolution during PA MBE of AlN/c-Al2O3 templates, taking into account several simultaneously acting competitive mechanisms of continuous generation of tensile and compressive stresses.
High-throughput laser printing of resonant silicon nanoparticles has emerged as a novel tool for the fabrication
of deeply subwavelength objects with various functionalities. The applications of resonant silicon
nanoparticles crucially depend on their crystalline state. However, the ways to control the crystalline
structure during laser printing remain unstudied. Here we demonstrate, both experimentally and theoretically,
how the crystalline structure of silicon nanoparticles fabricated by a laser printing technique can
be varied from almost amorphous to a polycrystalline state. In particular, we propose a method of crystalline
structure control via changing the distance between the irradiated silicon film and the receiving substrate.
This study allows the most optimal conditions for second harmonic generation to be revealed. We
believe that the proposed method opens the door to fully controllable laser printing of functional nanoparticles
A method for the fabrication of high-Q crystalline whispering gallery mode optical microresonators using diamond turning and further asymptotic abrasive polishing is developed and described. The proposed method allows the fabrication of microresonators with a predefined geometry and a Q-factor higher than 107. A step-by-step fabrication procedure is presented, important parameters ensuring the optimal quality of the surface of the fabricated microresonators are determined, the inspection procedure for the principal parameters is described, and a review of the fabrication of microresonators from different materials is presented.
Mechanical performances of titanium biomedical implants manufactured by superplastic forming are strongly related to the process parameters: the thickness distribution along the formed sheet has a key role in the evaluation of post-forming characteristics of the prosthesis. In this work, a finite element model able to reliably predict the thickness distribution after the superplastic forming operation was developed and validated in a case study. The material model was built for the investigated titanium alloy (Ti6Al4V-ELI) upon results achieved through free inflation tests in different pressure regimes. Thus, a strain and strain rate dependent material behaviour was implemented in the numerical model. It was found that, especially for relatively low strain rates, the strain rate sensitivity index of the investigated titanium alloy significantly decreases during the deformation process. Results on the case study highlighted that the strain rate has a strong influence on the thickness profile, both on its minimum value and on the position in which such a minimum is found.
The ХХV International scientific – technical conference “Foundry 2018” was held of the 18-20 April 2018 at “Rostov” hotel in the city of Pleven, Bulgaria. Its aim is to provide a meeting place for scholars from different countries to present their scientific achievements and to discuss the problems of casting production.
The structural and spectroscopic features of the EuAl3(BO3)4 individual skeletal microcrystals synthesized by a melt solution method have been studied. Their infrared spectra taken from the as-grown microcrystal surfaces mainly contain the lines of the rhombohedral modification of EuAl3(BO3)4 and additional peaks of its monoclinic modification. TEM and X-ray diffraction studies confirm that these additional peaks in the IR spectra belong to the monoclinic C2/c polytype of the EuAl3(BO3)4 compound. We are the first to demonstrate the presence of coherent monoclinic domains in rhombohedral EuAl3(BO3)4 crystals by TEM. Cathodoluminance spectroscopy shows that the microcrystals generate strong emission lines in the range 580–630 nm, and their intensities are strongly influenced by the crystal orientation.
This volume presents new results in the study and optimization of information transmission models in telecommunication networks using different approaches, mainly based on theiries of queueing systems and queueing networks .
The paper provides a number of proposed draft operational guidelines for technology measurement and includes a number of tentative technology definitions to be used for statistical purposes, principles for identification and classification of potentially growing technology areas, suggestions on the survey strategies and indicators. These are the key components of an internationally harmonized framework for collecting and interpreting technology data that would need to be further developed through a broader consultation process. A summary of definitions of technology already available in OECD manuals and the stocktaking results are provided in the Annex section.