Papers by Keyword: Thin Layers

Abstract: In order to selectively analyze active thin layers close to surface in power devices structures, Raman scattering is necessary with UV excitation. However, the Raman spectra of GaN are usually affected by the direct bandgap photoluminescence of the material, which interferes with the Raman measurements and decreases the quality and resolution of the Raman spectra. In this work, we demonstrate experimentally that nanostructured aluminum films deposed on GaN epitaxial layers decrease the influence of the photoluminescence on the resonant Raman spectra and increase its overall spatial resolution under UV illumination.

Abstract: We have proposed and investigated a new technique for growing thin uniform layers onto a large semiconductor substrates. The method uses the system of hexagonally arranged round local sources filled with liquid growth substance. The growth substance evaporates on very close substrate, which is removed from the discrete source by about 1 mm. In these conditions vapor pressure of the residual gases is reduced by two orders of magnitude. It is found that to obtain uniform thickness layers by the proposed technique it is strongly necessary that the distance between the discrete source and the substrate will be greater than the critical thickness lcr. It is shown that this parameters lcr increases with the increasing of radius of local sources and the distance between the local sources. For example, to achieve uniformity of better than 97% the critical thickness must be equal to lcr = 1.2 mm for a hexagonal arranged system of round local sources with the radius of r = 0.75 mm and the distance between the sources of h = 0.5 mm.

Abstract: In this paper were analyzed Tungsten electrode depositions using electro-spark deposition method, on stainless steel, used for hydraulic turbine vanes and blades of mixing blades for chemical industry, in order to achieve an improved wear resistance. This deposition method was chosen due to its relatively low cost, easy to achieve, and leads to obtaining thin layers with good adherence to the substrate, and with different thicknesses, depending on the number of deposited layers. The chosen electrode is an alpha character element and generates an increase of the mechanical properties at low and high temperatures for austenitic stainless steels. Tungsten does not modify the corrosion resistance for the stainless steels. The samples were analyzed on scanning electrons microscope (SEM) and also the chemical analysis (EDX) for distinguish the layer-support structure and the elements repartition on the surface and in line.

Abstract: It is known that during the cutting process the tool wears out. This is due to the high temperatures, the relative velocities and shocks between the contact surfaces of the tool-part and the mechanical and thermal stresses which appear on the active surfaces of the tool. The result is loss of cutting and reduced processing quality. This involves taking measures to increase the values of the cutting tools and/or the durability of their cutting inserts. Tool durability can be increased by various coating methods by the depositing in a vacuum of some different materials which achieve the necessary effect. These methods are being researched globally. So far there are several methods of applying these layers. They are classified as: vacuum thermal evaporation, pulverization, ion plating and chemical vapor depositing. In order to increase the durability of the cutting tools, and to increase the wear resistance of the metal carbide insert, the authors propose in this paper the depositing of a titanium thin layer on these cutting inserts by the ionic plating method. This method has produced increased durability of the coated cutting insert and increased resistance to wear, higher than in the uncoated case. The values slightly vary depending on the complexity of the cutting insert profile and the dimensions of the work pieces dimensions being processed.

Abstract: Properties of metallic materials can be improved with special materials depositions. Materials deposited on base materials are qualitatively better than the base materials, with a better hydroabrasive wear and corrosion resistance, also with a chemical attack or mechanical stress improved resistance.The thin layer deposition represents depositions (coatings) with hardening, lubricating, or decorative function, having a thickness of less than 10 micrometers.Such special materials are used in cutting-edge technology, such as nuclear turbines and turbine airplanes, space crafts or submarines, which must withstand high temperature, erosion and different chemical attacks.Along with traditional technologies for obtaining coatings, we assist in the development, improvement and expansion of deposition modern techniques, which ensures high purity and adhesion through a wide variety of processes. These thin layer coated materials should not be very expensive from the economic point of view. That is why, scientists are looking to find out the easiest deposition methods and also with great technical efficiency.In this paper we presented several methods of thin film deposition. We also highlighted some of the advantages and disadvantages of some deposition methods.

Abstract: Superstructure transformation processes in intermetallics have beenstudied at the atomistic scale using Monte Carlo algorithms within two dis-tinct models: two-body interactions Ising-like system and Analytic Bond-Order Potentials. The transformation from “in-plane” to “off-plane” L10 vari-ant in [001]-oriented FePt nano-layers was observed and analysed by analyt-ical calculations providing clear explanation of the origin of the process, aswell as by “rigid-lattice” and “off-lattice” Monte Carlo simulations showingthe kinetics of the superstructure transformation.

Abstract: Along with technologies development rise demands on the technical level of new machinery and equipment and also the reliability and efficiency of tools used in the production processes. One of the options for increasing tool life and wear resistance is the use of tools surface treatment technology called as CVD (chemical vapor deposition) and PVD (Physical Vapor Deposition) process. Chemical vapor deposition is a widely used materials-processing. CVD is an atomistic surface modification process, where a thin solid coating is deposited on an underlying heated substrate via a chemical reaction from the vapor or gas phase, PVD process is atomistic deposition process in which material is vaporized from a solid or liquid source in the form of atoms or molecules, transported in the form of a vapor through a vacuum or low pressure gaseous (or plasma) environment to the substrate where it condenses. The paper introduces the possibilities of application of these processes for cold forming tools used at operating conditions of Železiarne Podbrezová, a.s. Tools (formers and straightening rolls) are evaluated in terms of CVD and PVD coating thickness, microstructure and microhardness of tool material and coating.

Abstract: Multilayered electronic components, typically of heterogeneous materials, delaminate under thermal and mechanical loading. A phenomenological model focused on modeling the shape of such interface cracks close to corners in layered interconnect structures for calculating the critical stress for steady-state propagation has been developed. The crack propagation is investigated by estimating the fracture mechanics parameters that include the strain energy release rate, crack front profiles and the three-dimensional mode-mixity along the crack front. The developed numerical approach for the calculation of fracture mechanical properties has been validated with three-dimensional models for varying crack front shapes. A custom quantitative approach was formulated based on the finite element method with iterative adjustment of the crack front to estimate the critical delamination stress as a function of the fracture criterion and corner angles.

Abstract: Corner cracks under steady-state delamination were investigated. The fracture mechanics parameters that include the strain energy release rate and the three-dimensional mode-mixity along the interface crack front are estimated. A numerical approach was then applied for coupling the far field solutions based on the Finite Element Method to the near field (crack tip) solutions based on the J-integral methodology. A quantitative approach was formulated based on the finite element method with iterative adjustment of the crack front nodal coordinates to estimate the critical delamination stresses as a function of the fracture criterion and corner angles.

Abstract: The determination of the characteristics and properties of thin films deposited on substrates is necessary in any device application in various fields. Adequate mechanical properties are highly required for the majority of surface waves and semiconductor devices. In this context, modelling the ultrasonic-material interaction, we present results of simulation curves of acoustic signatures for multiple thin film/substrate combinations. The results obtained on several structures (Al, SiO2, ZnO, Cu, AlN, SiC and Cr)/(Al2O3, Si, Cu or Quartz) showed a velocity dispersion of the Rayleigh wave as a function of layer thickness. The development of a theoretical calculation model based on the acoustic behaviour of these structures has enabled us to quantify the dispersive evolution (positive and negative) density. Thus, we have established a universal relationship describing the density-thickness variation. In addition, networks of dispersion curves, representing the evolution of elasticity modulus (Young and shear), were determined. These charts can be used to extract the influence of thickness of layers on the variation of elastic constants