Papers by Keyword: Multilayers

Abstract: Multilayer antireflection coatings have been modeled in visible and infrared regions (1-5 μm) bands to increase the transmittance of glass and silicon substrates. The transmittance was studied using different semiconductor materials with different thickness ( single, double and three) layers to determine the best design that depends on the manufacture of antireflection coatings at low costs and few layers of coatings to reduce the stress generated by the increased number of layers. MgF₂ and TiO₂ materials are used in the visible region (300-1000 nm) at the central wavelength (500 nm). The transmittance of MgF₂ single–layer with a quarter waves optical thickness is reached (98.61%) and the transmittance value is (98.74%) for arrangement (. The transmittance of the infrared spectrum for antireflection coating materials depends on the thickness and temperature of these materials because of scattering and absorption in such materials. LaF₃, ZrO₂, ZnSe, and CdTe materials are used in the infrared region at a design wavelength (3000 nm). The maximum value of transmittance is around (99.99%) for the best design that consisting of three layers with quarter wavelength thickness. Keywords: Antireflection Coatings, Multilayers, Semiconductor, Transmittance

Abstract: Multilayers zinc oxide thin films were synthesized by the sol–gel spin coating process to fabricate sensing membranes in an electrolyte-insulator-semiconductor (EIS) sensor for pH detection. The effect of various layers (single, three and five layers) on the crystallinity, morphological and optical properties of ZnO films were investigated by XRD, FE-SEM, and Photoluminescence respectively. The ZnO thin films grown were polycrystalline with hexagonal wurtzite structure. The films were not smooth, with grains and porosity in between them, and become denser as film thickness increased. The PL spectra exhibit two main emission peaks at near band edge 360-380 nm region (strong and sharp UV radiation) and 450–600 nm region (broad blue, green, and yellow radiation). Sensitivity, linearity was measured to determine the sensing and reliability performance of fabricated devices. The result confirmed that, the sensitivity for the three samples increased with increased layer from 48.3 mV/pH to 82.58 mV/pH. Compared to single and three layers of the ZnO electrolyte-insulator-semiconductor (EIS), ZnO grown with five layers exhibits a higher sensitivity of 82.58 mV/pH in solutions from pH 2–12 and linearity of 99.015 %. This is due to the increased of ZnO thickness, which produces dense surface and a well-crystallized grain structure.

Abstract: We report for the first time the successful heteroepitaxial growth of Si(100) oriented layer on top of a 3C-SiC(001) seed. By using a post-growth modification of the 3C-SiC surface (pulse insertion of precursors during cooling), it led to a change in Si nucleation, favoring squared (100) islands instead of elongated (110) ones. Without this surface modification step, the Si layers grown on 3C-SiC were always polycrystalline with a mixture of (110) and (100) orientations. Using such Si(100) layer grown on top of 3C-SiC(100), a (100) oriented 3C-SiC single crystalline layer was successfully grown on top, fabricating thus for the first time a fully (100) oriented multilayer heterostructure made of Si_(substrate)/SiC/Si/SiC.

Abstract: Cr/CrN multilayers with a bilayer period λ = 62 ÷ 1000nm, were investigated. They were deposited by PLD technique on austenitic and ferritic stainless steel substrates. Coating hardness and adhesion to substrates were measured by nanoindentation and scratch testing. Multilayer properties were compared with single Cr and CrN coatings. The 2xCr/CrN and 4xCr/CrN multilayers exhibited hardness slightly lower than the hardness of a single CrN coating, while the critical load of the 4xCr/CrN multilayer, measured in the scratch test, was two times higher than for CrN. Furthermore, the character of coating failure also indicates the higher fracture toughness of multilayers than ceramic ones. The highest scratch resistance of the hardest multilayer with a bilayer period λ = 250nm is extremely interesting. The measured values of the critical loads L_C1 and L_C2 of all coatings were higher for harder ferritic than austenitic substrates. However, analysis of scratch track geometry indicated that coating failure occurred under the same deformation of the coating-substrate system, while the higher values of critical load for coatings on ferrite derived from the higher hardness of the substrate.

Abstract: Thin Co films were fabricated by DC magnetron sputtering. The effect of argon pressure on the microstructure, surface morphology and magnetic properties of the samples was systematically studied. It was found that with the increase of argon pressure, the sharpness of the crystalline texture of the samples declines, the roughness of film surfaces and the coercivity of the films increase. Based on these results, a Co/Cu/Co pseudo spin-valve system was designed and the corresponding structures were fabricated. The difference in coercivity of magnetic layers was obtained by deposition of the Co layers at different Ar pressures. Change of the resistance of this trilayer is induced at a moderate field by the spin rotation in the soft layer with lower coercivity.