Papers by Keyword: Surface Effects

Abstract: Selective Laser Melting is an additive manufacturing practice that permits the production of metal alloy-based parts. While facilitating the design of complex geometry, SLM leads to the fabrication of a unique material structure that showcases distinct behavioural characteristics relative to their traditional methods of material manufacture. Defects that are innate to SLM inspire the presence of a compositional outlook that is inhomogeneous in nature and only serves to hinder part efficiency. Thus, the Theory of Critical Distances offers a refreshed proposal to evaluating notched Ti-6Al-4V material produced by additive manufacturing processes. Key principles of the theory’s working mechanisms are outlined. Subsequently, symmetrical notches of contrasting size are assessed. Findings reveal that the Theory of Critical Distances is adequately compatible with accurate fatigue prediction of SLM Ti-6Al-4V in its as-built state. Additionally, fracture surface analysis reveals that crack initiation is predominantly a surface-based phenomenon. Hereby, increased focus must be given to the quality of processed material that is located at the externalities of additively manufactured components, in order to enhance their service life capabilities. This will induce an increasingly uniform material structure that will allow for more predictable behavioural characteristics.

Abstract: By using first-principle density-functional theory (DFT) calculations supplemented with symmetry analysis, we investigated the effect of thin-film thickness on the electronic properties of non-polar ( ZnO-wz and GaN-wz. We find that the electronic band structures of thin-film non-polar ( surface with layer variations from two until ten bilayers show the Rashba spin splitting. Importantly, we revealed that this splitting is found to be strongly anisotropic observed in the valence band maximum (VBM) around the Γ point. We clarified the origin of the anisotropic spin splitting in the electronic band structures by considering the point-group symmetry (PGS) of the present system. We found that the changes of the PGS from C_6v (for polar [0001] direction) to C_s (for non-polar ( direction) are responsible for inducing the anisotropic of the spin splitting. To further confirm the anisotropic splitting, we calculated the Rashba spin splitting parameters for different directions of the k-path. We found that these parameters are different in magnitude for a different direction of the k-path indicating the anisotropic spin splitting quantitatively, which is consistent well with symmetry analysis. Finally, we conclude that the observed Rashba spin splitting in the wurtzite surface structure is promising for spintronics applications.

Abstract: Nanotubes, fabricated by mechanical bending of thin films, have been widely used in numerous fields. For a bilayer nanofilm, it could bend itself driven by effects of adsorption and ambient temperature. Therefore, in this work, we simulate the phenomenon of bilayer AuSi nanofilm bending into nanotube with the effects of surface stress induced by vdW interaction between adsorbed O or Hg atoms and atoms on Au surface and ambient temperature change by finite element emulation. The curves of nanotube calculated by finite element software accord with theoretical prediction results very well, that demonstrate our theoretical prediction formula has a great feasibility and efficiency in practical application.

Abstract: New techniques that can control Casimir forces in nanosacle structures may soon ensure the physical realization of switchable Casimir-force devices. In order to provide useful insights into the behaviour of this class of switches, the idea of Casimir-force actuation window has been proposed here to assist in the design of such switches. The influence of surface effects including residual surface stress and surface elasticity on the pull-in parameters of Casimir actuated switches has been demonstrated. These effects, together with other currently known difficulties due to uncertainties such as surface roughness and trapped electric charge may hinder the realization of this class of devices. An Euler-Bernoulli beam model has been employed to demonstrate surface effects in a nanocantilever switch, and numerical solutions employing a finite difference approach have been obtained for the static bending of this switch. The results demonstrate that surface effects play a significant role in the selection of basic design parameters of Casimir actuated switches, such as static deflection and detachment length. Threshold value of residual surface stress is also studied for these switches. The predictions reveal that exclusion of surface effects in Casimir-force actuation window may result in non-functional switch designs.

Abstract: The method of SQUID-based relaxometric diagnostics has been applied to the ensembles of non-interacting near-spherical Fe3O4 and Co nanoparticles in order to reveal the behavior of the anisotropy constant upon varying the molecular surrounding of nanoparticles by using different polymer matrices. The transmission electron microscopy (TEM) and X-ray diffraction techniques have been employed to obtain the structural information about objects of study. The relaxation curves measured with the SQUID-relaxometer in the time range from about 50 s to several tens of seconds after application of a pulse of low dc magnetizing field have been approximated by theoretical dependences calculated within the framework of activation Néel–Arrhenius law with account for the size distribution functions retrieved from TEM data. From results of approximations, the values of anisotropy constant have been determined.

Abstract: The forward current was investigated in 4H-SiC p+n structures grown by sublimation epitaxy. The doping level, Nd-Na, of the n-layer was about (3-4)x1016 cm-3 and the diode area was in the range from 1x10-5 to 2x10-4 cm2. The observed current can be considered as current due to bulk recombination in the space charge region of the pn junction via deep level center or due to surface recombination. The criterion which was performed in this study to differentiate such currents was the investigation of recombination current versus perimeter/area ratio dependence. It was found that no pronounced difference in the recombination current parameters for diodes with different perimeter/area ratio was observed, i.e. current due to surface recombination was not observed for the 4H-SiC pn structures investigated.