Papers by Keyword: Bilayer

Abstract: Bilayer graphene has been widely studied in recent years due to its intriguing physical properties and potential engineering applications. Here, we report on the stability measurements of isotope-labeled bilayer graphene with different stacking sequences. The results showed evidence of different defect intensity after the Ar plasma treatment. We found that the AB stacked bilayer graphene shows better stability when compared to twisted bilayer and monolayer graphene. However, for the protection of the under layer graphene, the twisted bilayer graphene showed better results. Our work demonstrates that the stability of bilayer graphene strongly depends on the layer stacking sequence.

Abstract: Thin film is a thin material that is resulting from the condensation of species through the deposition of atoms on the substrate. Thin films are usually used in the production of electronic devices, optical coatings, solar cells, and for decorative items. The bilayer of TiO₂/ZnO and ZnO TiO₂ thin films have some advantages such as can enhance the surface state and surface atomic mobility, which are useful for improving the photocatalytic activity. The motivation to a used double layer of ZnO and TiO₂ is to enhance the properties and photocatalytic activity using the different deposition temperature between the layers. The structural of ZnO/TiO₂ thin films were studied using X-Ray diffraction (XRD). Field Emission Scanning Electron Microscope (FESEM) was used to determine the surface morphology of ZnO/TiO₂ thin films. The photocatalytic activity of ZnO/TiO₂ thin films was analysed using the photodegradation of methylene blue (MB) solution. The XRD analysis revealed that highest anatase crystalline phase for TiO₂ growth with orientation (1 0 1), while the ZnO crystal phase, zincite occurred at the highest intensity with (1 0 1) orientation.. The bilayer TiO₂/ZnO thin film had the highest reaction rate, K, which is 0.0972 h-1 for photocatalytic activity. The characteristics of bilayer TiO₂/ZnO and ZnO/TiO₂ thin-film is strongly influenced by the calcination temperature and the presence and combination between the two types of materials.

Abstract: This study presents an investigation on copper oxide (CuO) composited with polyethylene glycol (PEG) thin film. The main objective for this compositing thin film is to explore and determine the characteristic of the thin film when the value of PEG is varied. In this study, PEG plays a role as phase change material (PCM), where this type of material has the capability to absorb and release heat based on its surrounding condition. Due to this characteristic, the amount of PEG is vary from 0.5, 1.0, 1.5 and 2.0 ml to confirm its influence towards CuO thin film. As for comparison, CuO thin film without PEG is also fabricated. Both of the materials used were prepared using sol-gel route and deposited onto indium tin oxide (ITO) substrate using spin coating method. The influences of the PEG values on CuO thin film were investigated using field emission scanning electron microscope (FESEM), x-ray diffraction (XRD), ultra-violet visible microscope (UV-Vis), and current-voltage (IV) measurement. Based on the investigation conducted, the characteristics of CuO thin film produced in this study are affected with the different value of PEG.

Abstract: Nanoscratching and nanoindentation simulations are performed to study the processability of Cu/Ni bilayers with interfaces using molecular dynamics (MD) method. Single crystals Cu and Ni are served as comparisons. In the nanoscratching processes, the interfaces of Cu/Ni bilayers appear as a barrier of dislocations gliding, and lead to larger friction forces and normal forces. For single crystals and bilayers, both their friction forces and normal forces increase with the increasement of scratch velocity at 100-300 m/s. Friction coefficients under scratching processes are calculated, and they are smaller than macrosacle scratching process because of coating effects of nano-chips on the tool. The effects are analyzed by conducting both molecular dynamics simulations in nanoscale and finite element simulations (FES) in macroscale. In the indentation process, the processing properties of Cu-Ni and Ni-Cu bilayers are different from each other, and their indentation forces are both larger than their single crystals. Recovery deformation takes place during the relaxation stage. When the tool is unloading, some workpiece atoms adhere to the tool. The simulation results of the two nanoscale machining processes reveal the strengthening mechanism of interface, and show comprehensive processability of metal bilayers.

Abstract: Lightweight design for vehicle industry is not anymore an optional condition but a mandatory need to reduce the fuel consumption and adhere to environmental regulations. To achieve this goal many single parts have been removed and complex design have been implied. This includes implementation of tailored-welded blanks and multi-layer materials. Due to the increase use of dissimilar materials in a component it is also called as hybrid components. It was observed that due to use of hybrid component the part weight decrease and thus increase fuel efficiency. To continue this aspect, in this bilayer tube flaring is investigated. The metal tubular material from inside and polymer from outside is considered for flaring. The flaring behavior of the tube is analyzed and compared with the single metal layer. The strength difference and effect of that on the formability is discussed and resulted. It was observed that due to contact of lower strength material from outside the formability of the metal tube increased and failure is delayed.

Abstract: The target of processing bimaterial components by cost effective powder metallurgy is to combine unique properties from different parts of the component. Differential shrinkage rate and more often, radial mismatch which is more consistent in bilayer owing to sintering conditions (time, rate, temperature etc.) is known to compromise the interfacial bond strength and integrity of these components. Therefore, the aim of this study is to analyze the sintering compatibility and evaluate the mismatch strain in cemented tungsten carbide (WC-Fe-C) and steel (Fe-W-C) bilayer processed through powder metallurgy (PM) to combine the hardness and toughness properties applicable in machining industries for drilling tools. Through geometrical measurement, mismatch strain rate between layers at different sintering temperatures was calculated and a value as low as 13.7% was observed at the interfacial zone of MC–0.2 specimen sintered at 1280°C indicating a stronger bond between layers compared to those sintered at 1290°C and 1295°C where a huge mismatch was found increasing the tendency for delamination.

Abstract: Charge ordering of nonstoichiometric LuFe₂O_4+δ is discussed. Properties of triangular bilayer are investigated via mean field theory with Coulomb interaction between sites. It is shown that low temperature state of bilayer has dipole moment essentially under any doping parameter. Correlation between sites in neighbor layers is estimated and dimer partially disordered antiferroelectric phase is extended for the case of nonstoichiometric samples. Competition of correlation effect with bilayer interaction and external electric field is discussed. Phase diagrams for doped specimen are presented. The results of investigation are used to clarify a significant surface impact.

Abstract: The structures and magnetic properties of monolayer and bilayer of transitional metallo-porphine (MP) species (M = Mn, Fe, Co, Ni, Cu) on the Ag (111) substrate are investigated by DFT based first-principle method. The MP monolayer has a distortion about 10° towards the substrate due to strong interaction between adsorbed molecule and substrate. The molecule-substrate interaction could quench the magnetic moment of the adsorbed molecule. For MP bilayer adsorption on the Ag (111), the top layer remains its planar structure and magnetic moment due to the screening of substrate effects by bottom layer, meanwhile the bottom layer has strong structural distortions and obvious variations of magnetic moment.

Abstract: Related with the detection of weak magnetic fields, the anisotropic magnetoresistive (AMR) effect is widely utilized in sensor applications. Exchange coupling between an antiferromagnet (AF) and the ferromagnet (FM) has been known as a significant parameter in the field sensitivity of magnetoresistance because of pinning effects on magnetic domain in FM layer by the bias field in AF. In this work we have studied the thermal evolution of the magnetization reversal processes in nanocrystalline exchange biased Ni₈₀Fe₂₀/Ni-O bilayers with large training effects and we report the anisotropic magnetoresistance ratio arising from field orientation in the bilayer.

Abstract: Diamond-like carbon (DLC) bilayer films with Cu interlayer were prepared on silicon substrate by direct-current and pulsed cathode arc plasma technique, and annealed at various temperatures in vacuum. Structure, morphology and mechanical properties of the bilayer films were investigated by Raman spectroscopy, Auger electron spectroscopy, scanning electron microscopy and atomic force microscopy, surface profilometer and Vickers sclerometer. The results show that Cu interlayer changes the bilayer microstructure, including the thickness and element distribution of diffusion layer, the relative fraction of sp³/sp² bonding and growth model of bilayer. A simple three-layer model was used to describe the interdiffusion between Cu and C layer. Cu interlayer could be more effective against graphitization upon annealing. Morphological characteristics of the films were studied by analyzing the surface features of substrate. Cu/DLC bilayer exhibits highly dispersed nano-agglomerates with smaller size on the surface due to low surface energy of Cu interlayer. The stress and hardness of the films were affected accordingly. Cu/DLC bilayer shows a relatively high hardness at low annealing temperature but the stress almost no change. By changing Cu interlayer and annealing temperature, excellent DLC films could be designed for the protective, hard, lubricating and wear resistant coatings on mechanical, electronic and optical applications.