Indigenous development of ultra high vacuum (UHV) magnetron sputtering system for the preparation of Permalloy magnetic thin films

We have designed and developed an indigenous ultra high vacuum (UHV) sputtering system which can deposit magnetic thin films with high purity and good uniformity. The equipment consists of state-of the-art technologies and sophistication. With this system it is possible to deposit coatings of various materials on a sample size of 3”3” 3”. The Ni81Fe19 ferromagnetic thin films, with Tantalum (Ta) as a buffer and cap layers have been deposited on silicon substrates using this ultra high vacuum (UHV) sputtering system. The magneto transport measurement study indicated a significant variation in the AMR values of the films for varying thicknesses of tantalum and NiFe layers

Investigation of interface properties of sputter deposited TiN/CrN superlattices by low-angle X-ray reflectivity

Approximately 1.8 m thick nanolayered multilayer coatings of TiN/CrN (also known as superlattices) were deposited on silicon (100) substrates at different modulation wavelengths (4.6–12.8 nm), substrate temperatures (50-400 °C) and substrate bias voltages (-50 to -200 V) using a reactive direct current magnetron sputtering system. X-ray reflectivity (XRR) technique was employed to determine various properties of the multilayers such as interface roughness, surface roughness, electron density, critical angle and individual layer thicknesses. The modulation wavelengths of the TiN/CrN superlattice coatings were calculated using modified Bragg’s law. Furthermore, the experimental X-ray reflectivity patterns were simulated using theoretically generated patterns and a good fit was obtained for a three layer model, i.e., (1) top surface roughness layer, (2) TiN/CrN multilayer coating (approximately 1.8 m) and (3) Ti interlayer (~ 0.5 m) at the film-substrate interface. For the superlattice coatings prepared at a modulation wavelength of 9.7 nm, a substrate bias of -200 V and a substrate temperature of 400 C the XRR patterns showed Bragg reflections up to 5th order, indicating well-defined periodicity of the constituent layers and relatively sharp interfaces. The simulation showed that the superlattice coatings prepared under the above conditions exhibited low surface and interface roughnesses. We also present the effect of substrate temperature and substrate bias, which are critical parameters for controlling the superlattice properties, onto the various interface properties of TiN/CrN superlattices

Studies on hot-filament chemical vapor deposition grown graphene sheets

Graphene was grown on high purity Cu foils using hot-filament chemical vapor deposition method. The foils were kept directly below the tungsten filament and the whole assembly was kept inside a vacuum chamber. CH4 and H2 were used as precursor gases and were allowed to shower on a hot filament, which was kept at a predetermined temperature. The optimization of the process parameters such as gas flow rates, temperature, durations, etc. was done to grow single layer and multilayer graphene. The graphene was characterized using optical microscopy, field emission scanning electron microscopy and micro-Raman spectroscopy techniques. The graphene layers grown at different methane flow rates are shown in Figure 1. By varying the methane flow rates, graphene domains of different sizes and shapes were achieved and are clearly evident from Figures 1a-c. The curved white lines (Figure 1a) present in the FESEM micrographs correspond to Cu terraces. The graphene grown on Cu foils was successfully transferred to SiO2 substrate and the micrograph of which is shown in Figure 1d. The presence of D, G and G’ bands in the Raman spectrum confirmed the growth of graphene in the Cu foil (Figure 2)

Structural and optical properties of graphene oxide prepared by modified hummers' method

Graphene oxide was synthesized from graphite flakes using modified Hummers' method. The interlayer spacings of graphite, graphite oxide and graphene oxide were measured using X-ray diffraction technique. The C/O atomic ratios of graphite oxide and graphene oxide were calculated from XPS measurements. The transformation of graphite to graphite oxide and finally to graphene oxide was clearly observed from the micro-Raman spectroscopy data and was confirmed from the FESEM micrographs. UV-VIS-NIR spectrophotometer was used to study the absorbance of graphene oxide and reduced graphene oxide samples. Finally, the chemically reduced graphene oxide was heat-treated in air to obtain chemically modified graphene

Development of pinned electrode for magnetic tunnel junction with perpendicular magnetic anisotropy

The magnetic electrodes with perpendicular magnetic anisotropy (PMA) have gained a great deal of attention in magnetic information storage technology. The use of perpendicular magnetic tunnel junctions (p-MTJs) enhances the storage density due to the reduction in area required for a unit bit. Among two electrodes in a MTJ structure (ferromagnetic/insulator/ferromagnetic), one electrode should be fixed or pinned to a specific direction of magnetization in order to have a unidirectional magnetic anisotropy with higher exchange field. This can be achieved by a phenomenon of exchange bias observed between the ferromagnetic (FM) and the anti-ferromagnetic (AFM) materials as a shift in a hysteresis loop when they are deposited in a presence of an external applied field

Enhanced defect emission in Co doped ZnO nanorods synthesized by electrochemical route

We present the effects of Co doping on the morphology, structural and optical properties of ZnO nanocoatings in detail. Highly oriented wurtzite ZnO nanorods were fabricated by electrodeposition method using Zn(NO3)2 as the electrolyte. Again, the Co doped (0.03 mM CoSO4) ZnO nanocoatings were synthesized on ITO coated glass substrates. The surface morphology and the structural properties of the coatings were studied using field emission scanning electron microscopy (FESEM) and X-ray diffraction (XRD), respectively. The FESEM data (Fig. 1) showed the top view of oriented hexagonal ZnO nanorods. The XRD pattern showed a shift in (002) diffraction peak of ZnO towards higher 2Ѳ values by the substitution of dopant, which indicates that the Zn2+ site is successfully replaced by the dopant Co2+. Moreover, the photoluminescence spectroscopy (PL, 325 nm excitation) was used to study the UV emission and the defect emission of the doped and undoped ZnO nanostructures. The PL data (Fig. 2) revealed a blue shift in the UV emission for the doped sample which signifies that for ZnO coating prepared with 0.03 mM CoSO4, the energy gap increased from 378 nm (3.27 eV) to 375 nm (3.30 eV). Also, the intensity of deep level emission (~ 600 nm) increased for the doped one as compared to the pure ZnO coating. Our results demonstrate that Co doping may be responsible for the blue shift in band gap of ZnO nanocrystals. The oxygen defects or Zn interstitials may be responsible for the broadening of the PL peak at 600 nm

An experimental investigation on the machining characteristics of Nimonic 75 using uncoated and TiAlN coated tungsten carbide micro-end mills

We report the machining characteristics and machinability of a nickel based superalloy in this study. A micro-milling operation is loaded on Nimonic 75 using uncoated and TiAlN coated tungsten carbide micro-end mills. A full factorial design of experiments was devised to optimize the machining conditions to reduce the flank wear on the tool surface. The optimized machining conditions for uncoated micro-tools were found to be a cutting speed (vc) of 13 m/min and a feed rate (fz) of 6 mm/min. Following this, the tools were coated with TiAlN using a semi-industrial four-cathode reactive pulsed direct current unbalanced magnetron sputtering system. Further experiments were then performed using these optimized machining conditions using both uncoated and TiAlN coated micro-tools in order to ascertain the tool wear and surface integrity. The change in geometry of the machined slot was estimated based on the variation in tool radius of the micro-end mill with progression of the operation. A direct comparison was made between the results observed using both uncoated and TiAlN coated tungsten carbide to illustrate the effect of the nanocomposite TiAlN coating. It was seen that TiAlN coated micro-tools exhibited a superior performance as compared to the uncoated ones with respect to tool life and micro-burr formation

Nanocolumnar Crystalline Vanadium Oxide-Molybdenum Oxide Antireflective Smart Thin Films with Superior Nanomechanical Properties

Vanadium oxide-molybdenum oxide (VO-MO) thin (21-475 nm) films were grown on quartz and silicon substrates by pulsed RF magnetron sputtering technique by altering the RF power from 100 to 600 W. Crystalline VO-MO thin films showed the mixed phases of vanadium oxides e.g., V2O5, V2O3 and VO2 along with MoO3. Reversible or smart transition was found to occur just above the room temperature i.e., at similar to 45-50 degrees C. The VO-MO films deposited on quartz showed a gradual decrease in transmittance with increase in film thickness. But, the VO-MO films on silicon exhibited reflectance that was significantly lower than that of the substrate. Further, the effect of low temperature (i.e., 100 degrees C) vacuum (10(-5) mbar) annealing on optical properties e.g., solar absorptance, transmittance and reflectance as well as the optical constants e.g., optical band gap, refractive index and extinction coefficient were studied. Sheet resistance, oxidation state and nanomechanical properties e.g., nanohardness and elastic modulus of the VO-MO thin films were also investigated in as-deposited condition as well as after the vacuum annealing treatment. Finally, the combination of the nanoindentation technique and the finite element modeling (FEM) was employed to investigate yield stress and von Mises stress distribution of the VO-MO thin films

Nanoindentation and atomic force microscopy measurements on reactively sputtered TiN coatings

Titanium nitride (TiN) coatings were deposited by d.c. reactive magnetron sputtering process. The films were deposited on silicon (111) substrates at various process conditions, e.g. substrate bias voltage (VB) and nitrogen partial pressure. Mechanical properties of the coatings were investigated by a nanoindentation technique. Force vs displacement curves generated during loading and unloading of a Berkovich diamond indenter were used to determine the hardness (H) and Youngx2019;s modulus (Y) of the films. Detailed investigations on the role of substrate bias and nitrogen partial pressure on the mechanical properties of the coatings are presented in this paper. Considerable improvement in the hardness was observed when negative bias voltage was increased from 100x2013;250 V. Films deposited at VB = 250 V exhibited hardness as high as 3300 kg/mm2.13; This increase in hardness has been attributed to ion bombardment during the deposition. The ion bombardment13; considerably affects the microstructure of the coatings. Atomic force microscopy (AFM) of the coatings revealed fine-grained morphology for the films prepared at higher substrate bias voltage. The hardness of the coatings was found to increase with a decrease in nitrogen partial pressure

A Raman-scattering study on the interface structure of nanolayered TiAlN/TiN and TiN/NbN multilayer thin films grown by reactive dc magnetron sputtering

Nanolayered multilayer coatings of TiAlN/TiN and TiN/NbN were deposited on Si (100) substrates at various modulation wavelengths (i.e., bilayer thickness,A) using a reactive dc magnetron sputtering system. These coatings were characterized using micro-Raman spectroscopy to study the effect of interfaces on the optical-phonon modes. For TiAlN/TiN multilayers, the optical-phonon band shifts to higher frequencies with a decrease in the modulation wavelength. Furthermore, the optical-phonon band shifts to higher frequencies with an increase in the substrate13; temperature for TiAlN/TiN multilayers deposited at A=80 xC5;. No such shift was observed for single-layer TiN and TiN/NbN multilayer coatings. This observed shift has been attributed to interdiffusion between the layers during deposition, which is more for TiAlN/TiN multilayers as13; compared to TiN/NbN multilayers. The x-ray-diffraction data showed well-defined satellite reflections for TiN/NbN multilayers at low modulation wavelengths and very weak satellite reflections for TiAlN/TiN multilayers, indicating that interfaces were very broad for TiAlN/TiN13; multilayers. The nanoindentation data showed no significant improvement in the hardness of13; TiAlN/TiN multilayers as compared to the rule-of-mixture value, whereas TiN/NbN multilayers showed an improvement in the hardness, which was two times the rule-of-mixture value. The low hardness of TiAlN/TiN multilayers has been attributed to interfacial diffusion. xA9; 2005 American13; Institute of Physics. (DOI: 10.1063/1.1946193