Stability of boron-doped graphene/copper interface: DFT, XPS and OSEE studies

Two different types of boron-doped graphene/copper interfaces synthesized using two different flow rates of Ar through the bubbler containing the boron source were studied. X-ray photoelectron spectra (XPS) and optically stimulated electron emission (OSEE) measurements have demonstrated that boron-doped graphene coating provides a high corrosion resistivity of Cu-substrate with the light traces of the oxidation of carbon cover. The density functional theory calculations suggest that for the case of substitutional (graphitic) boron-defect only the oxidation near boron impurity is energetically favorable and creation of the vacancies that can induce the oxidation of copper substrate is energetically unfavorable. In the case of non-graphitic boron defects oxidation of the area, a nearby impurity is metastable that not only prevent oxidation but makes boron-doped graphene. Modeling of oxygen reduction reaction demonstrates high catalytic performance of these materials.Comment: 15 pages, 8 figures, to appear in Appl. Surf. Sc

Relativistic spherical plasma waves

Tightly focused laser pulses as they diverge or converge in underdense plasma can generate wake waves, having local structures that are spherical waves. Here we report on theoretical study of relativistic spherical wake waves and their properties, including wave breaking. These waves may be suitable as particle injectors or as flying mirrors that both reflect and focus radiation, enabling unique X-ray sources and nonlinear QED phenomena.Comment: 6 pages; 4 figure

Atomic and electronic structure of a copper/graphene interface as prepared and 1.5 years after

We report the results of X-ray spectroscopy and Raman measurements of as-prepared graphene on a high quality copper surface and the same materials after 1.5 years under different conditions (ambient and low humidity). The obtained results were compared with density functional theory calculations of the formation energies and electronic structures of various structural defects in graphene/Cu interfaces. For evaluation of the stability of the carbon cover, we propose a two-step model. The first step is oxidation of the graphene, and the second is perforation of graphene with the removal of carbon atoms as part of the carbon dioxide molecule. Results of the modeling and experimental measurements provide evidence that graphene grown on high-quality copper substrate becomes robust and stable in time (1.5 years). However, the stability of this interface depends on the quality of the graphene and the number of native defects in the graphene and substrate. The effect of the presence of a metallic substrate with defects on the stability and electronic structure of graphene is also discussed.Comment: 18 pages, 6 figures, accepted to Appl. Surf. Sc

Residual stresses in Ti6Al4V alloy after surface texturing by femtosecond laser pulses

Surface topography and residual stresses in surface layers of α + β titanium alloy Ti6Al4V textured by 1030-nm, 320-fs-laser pulses were studied by scanning electron microscopy and X-ray diffraction analysis. It was found that multipulse laser processing leads to the formation of laser-induced periodic surface structures (LIPSS) on the surface of Ti6Al4V alloy. XRD studies showed that depending on the laser pulse fluence, both tensile and compressive residual stresses are formed in thin near-surface layer

Topological Coherent Modes for Nonlinear Schr\"odinger Equation

Nonlinear Schr\"odinger equation, complemented by a confining potential, possesses a discrete set of stationary solutions. These are called coherent modes, since the nonlinear Schr\"odinger equation describes coherent states. Such modes are also named topological because the solutions corresponding to different spectral levels have principally different spatial dependences. The theory of resonant excitation of these topological coherent modes is presented. The method of multiscale averaging is employed in deriving the evolution equations for resonant guiding centers. A rigorous qualitative analysis for these nonlinear differential equations is given. Temporal behaviour of fractional populations is illustrated by numerical solutions.Comment: 14 pages, Latex, no figure

XPS and DFT study of pulsed Bi-implantation of bulk and thin-films of ZnO - the role of oxygen imperfections

An atomic and electronic structure of the bulk and thin-film morphologies of ZnO were modified using pulsed Bi-ion implantation (1x1017 cm-2 fluence, 70 min exposure under Bi-ion beam, EBi+ = 30 keV, pulsed ion-current density of not more than 0.8 mA/cm2 with a repetition rate of 12.5 Hz). The final samples were qualified by X-ray photoelectron core-level and valence band mapping spectroscopy applying ASTM materials science standard. The spectroscopy data obtained was discussed on the basis of DFT-models for Bi-embedding into ZnO host-matrices. It was established that in the case of direct Bi-impurities insertion into the employed ZnO-host for both studied morphologies neither the only "pure" Bi2O3-like phase nor the only "pure" Bi-metal will be preferable to appear as a secondary phase. An unfavorability of the large cluster agglomeration of Bi-impurities in ZnO-hosts has been shown and an oxygen 2s electronic states pleomorphizm was surely established.Comment: 20 pages, 8 figures, 2 tables, accepted to Appl. Surf. Sc

Formation of the oxide coating on the titanium surface by multipulse femtosecond laser irradiation

The effect of the femtosecond laser irradiation on the formation of oxide layers on the surface of a commercially pure titanium VT1-0 was studied. The methods of X-ray analysis, scanning electron and transmission electron microscopies were used to study the structural and phase state of oxide layers. As a result of the femtosecond laser irradiation, the porous multi-phase nanocrystalline oxide coating with a thickness of 50 µm is formed on the titanium surfac

The formation of oxide layers on a titanium surface by irradiation with femtosecond laser pulses

By subjecting technical grade titanium to irradiation with femtosecond laser pulses with highenergy density, we create a microporous nanocrystalline oxide layer with a thickness of ∼50 μm on its surface. The structure and phase composition of the modified surface layers are studied using X-ray diffraction and high-resolution scanning and transmission electron microscopie