Surface Review and Letters

H13 steel samples were implanted with tungsten using a metal vapor vacuum arc (MEVVA) ion source, with an implantation dose of 1×10¹⁷cm^-2, an extraction acceleration of 30 kV and pulsed ion beam fluxes of between 0.3 mA·cm^-2 and 6 mA·cm^-2. The surface mechanical properties and microstructure for the W-implanted samples was characterized by the Rutherford backscattering spectroscope (RBS) and a high voltage electron microscope (HVEM). Experimental results of wear and hardness indicated that the hardness and wear of H13 steel increased when the voids were produced by tungsten ion implantation with a high pulsed current density. Forming causes for voids and their influence on the tungsten concentration depth profile in the implanted H13 steel and the surface mechanical properties were discussed in terms of spike theory.

Ceramic coatings were fabricated on Ti6Al4V alloy surface by microarc oxidation (MAO) in Na₂SiO₃–(NaPO₃)₆–NaAlO₂ solution using an AC power supply. Microstructure and phase composition of coating were characterized by SEM and XRD, respectively. The antifriction property of the coating with and without solid lubricant sliding against SAE 52100 steel ball was investigated on a pin-on-disk friction and wear tester. The results show that the microarc oxidation coating is relatively dense and uniform, mainly composed of rutile and anatase. The coating sliding against the steel has friction coefficient as low as 0.2–0.3 at an applied load of 0.5 N and sliding cycle below 2500, which is much smaller than that of uncoated Ti6Al4V against the same counterpart. The transferring of materials from the softer steel ball onto the coating surface is the main wear event, while the microarc oxidation coating is characterized by slight abrasive wear and adhesive wear. Introducing solid graphite lubricant into the porous surface of microarc oxidation coating significantly improves the long-term antifriction property (registering friction efficient of 0.15 in the long-term sliding) under a similar sliding condition. This improvement is attributed to the reduction of materials that are transferred from the softer steel ball onto the coating surface.

A simple, direct synthesis method was used to grow the core-shell SiC-SiOx nanowires by heating the NiO catalyzed silicon substrate. The carbothermal reduction of WO₃ by C provided a reductive environment to synthesize the crystalline SiC nanowires covered with the SiO_x sheath in the growth temperature of 1000–1100°C. After hydrofluoric acid (HF) etching, the cubic β-SiC nanowires were extracted from the core-shell nanowires in large quantities. A solid-liquid-solid (SLS) mechanism was proposed for the growth of the core-shell SiC-SiO_x nanowires.

Growth steps and 2D nuclei of the {100} faces of the deuterated L-arginine phosphate (DLAP) crystals have been studied using ex-situ atomic force microscopy (AFM). Straight steps along the b direction as well as meandered steps are detected. The bunched steps have wider terraces than the elementary ones, which are supposed to result from the slower growth rate of the former than the latter. Many 2D nuclei exist on the step terraces and edges acting as the growth sources. Occasionally, 2D islands generated by 2D nuclei could also be observed. In conclusion, the crystal grows by layer growth mechanism.

The adsorption of N₂O on Ir(110) was investigated with high-resolution resonant photoemission at 135 K. The results obtained show evidence of molecular adsorption of N₂O, along with some dissociation. It is found that the nitrogen photoemission spectra measured at the terminal and central nitrogen energy positions of the N₂O/Ir(110) system are equivalent to those of N₂O in the gas phase. In contrast, the oxygen spectrum shows little resemblance to the gas phase oxygen spectrum of N₂O. In the nitrogen resonant photoemission spectra one can only discover resonant behavior with constant binding energy peaks. In contrast, the oxygen resonant photoemission spectra shows dominantly Auger behavior with peaks at constant kinetic energies. Both observations reveal that the oxygen is bonded to the Ir surface. A systematic study as a function of coverage and temperature and a comparison with other surfaces differing in structure and composition is needed to understand the variations in the adsorption behavior of N₂O on metal surfaces.

This paper reports the characterization of the velocity (energy) dependencies of the Al⁺ secondary ion emission produced by 0.5 keV and 5 keV Ne⁺ and Ar⁺ bombardment of polycrystalline pure aluminium. The distributions of secondary Al⁺ ions over their kinetic energy were measured for emission energies of 1–1000 eV without applying electric fields to force the ions into the mass–energy analyzer. To extract the ionization probability, the measured energy distributions of emitted ions were normalized with respect to reference energy distributions of neutral atoms. The reference distributions were obtained by original numerical simulations, as well as analytically, through a sophisticated normalization of the Thompson distribution. It was shown that for both extraction methods, the logarithmic plots of the normalized secondary ion fraction versus the normal component of the reciprocal ion velocity (the reciprocal or inverse velocity plots) are nonmonotonic, with two peaks and two linear portions situated at a low emission energy (E_k=5–25 eV) and at a high emission energy (E_k=80–280 eV). The linear portions were fit by exponential dependency P⁺∝exp(-v₀/v_n) with two different values of the characteristic velocity v₀. For the low emission energy, the value v₀₁~(3.3±0.2)×10⁶cm/s was independent of the mass and energy of the projectiles. However, for the high emission energy, the characteristic velocity depended on the projectile's mass, M, namely v₀₂~(5.3±0.3)×10⁶cm/s for Ne⁺ and v₀₂~(8.1±0.3)×10⁶cm/s for Ar⁺; the ratio v₀₂(Ne⁺)/v₀₂(Ar⁺) is close to the value . This indicates that ballistic mechanisms might contribute to affect the high-energy part of the reciprocal velocity plots along with nonballistic ionization processes, which are generally believed to be the only significant factor for the plots.

Magnetic field and intense laser radiation effects on the exciton binding energy and interband optical transitions in quantum well wires is calculated using a variational method and in the effective mass approximation. The results obtained show that the exciton binding energies and op interband absorption depend on the sizes of the quantum well wire, intense laser field and magnetic field. The additional confinement of the particles in the quantum well wire offers greater variety of the intense laser field and magnetic field dependence in comparison to three- and two-dimensional materials.

Using a variational approach, we have calculated the impurity position dependence of the photoionizaton cross-section and the binding energy for a hydrogenic donor impurity in a quantum well wire in the presence of the electric and magnetic field as a function of the photon energy. Our calculations have revealed the dependence of the photoionizaton cross-section and the impurity binding on the applied electric and magnetic field, and the impurity position.

The electronic properties of very thin Ni films on the SrTiO₃(100)-Fe doped surfaces and their interaction with oxygen have been studied by soft X-rays photoelectron spectroscopy measurements. Nickel starts to become metallic on the surface in the very early adsorption stages. Oxygen adsorption on the nickel covered SrTiO₃(100) surface leads gradually to an almost complete oxidation of the nickel overlayer. The oxidation seems to take place through two different oxidation states, which according to the literature are due to the Ni²⁺ and Ni³⁺ species. The heating of the O/Ni/SrTiO₃ system at 850 K, causes a partial reduction of the nickel overlayer.

The measurements of Positron Annihilation Lifetime Technique (PALT) have been performed on AlSi_11.35Mg_0.23 Alloys. It has been shown that positrons can become trapped at imperfect locations in solids and their mean lifetime can be influenced by changes in the concentration of such defects. No change has been observed in the mean lifetime values at the saturation of defect concentration. The trapping rates of positrons can be determined for thickness reduction up to 11% for dislocation. The concentration of defect (ρ') range varies from 8.65×10¹⁵ to 2.35×10¹⁸cm^-3 up to the maximum value of strain (ε) 0.23.

The nanocrystalline nickel coating was synthesized by pulse-jet electrodeposition from modified Watts bath. Pulse and jet plating was employed to increase the deposition current density, decrease diffusion layer, increase the nucleation rate and in this case the prepared method would result in fine-grained deposits. Transmission and scanning electron microscopy and X-ray diffraction (XRD) were used to study the microstructure, the surface morphology, the crystal preferred orientation and the variety of the lattice parameter respectively. The influence of pulse parameters, namely peak current density, the duty cycle and pulse frequency on the grain size, surface morphology, crystal orientation and microstructure was studied. The results showed that with increasing peak current density, the deposit grain size was found to decrease markedly in other parameters at constant. However, in our experiment it was found that the grain size increased slightly with increasing pulse frequency. For higher peak current density, the surface morphology was smoother. The crystal orientation progressively changed from an almost random distribution to a strong (111) texture. This means that the peak current density was the dominated parameter to effect the microstructure of electrodeposited nanocrystalline nickel coating. In addition, the lattice parameter for the deposited nickel is calculated from XRD and it is found that the calculated value is less than the lattice parameter for the perfect nickel single crystal. This phenomenon is explained by the crystal lattice mismatch.

Temperature dependence of the Vickers microhardness of Sn_0.2Bi_1.8Te₃ single crystals has been studied. Loading time dependence of microhardness at different temperatures has been used for creep study in the temperature range 303 K–373 K. The activation energy for indentation creep of the crystals has been evaluated.

The important role of surface resonances in determining the intensities of electron beams diffracted from the Cu(111) surface is shown and interpreted in model calculations with a step-barrier of variable thickness in front of the crystal surface. The importance of using a finely tuned surface barrier potential in VLEED intensity calculations is stressed.

Al has unique intrinsic characteristics, which are of interest to scientists as well as engineers. Al and its alloys are slightly paramagnetic materials. Al has very low cross section for thermal neutrons of 0.23 barn, hence Al can be used in nuclear fields as a structural material which is virtually transparent to neutrons. We report VRT as a new technique to study material problems. We also discuss, the results of sound velocity and internal friction, and resonance frequency as a function of temperature range for a pure aluminum sample under investigation. By using VRT, we found that the annealing temperature (450°C) is sufficient to remove the type of defects introduced in the materials under study. The activation energy to remove point defect for Al samples was calculated and found to be about 0.0624 eV. Also, we could easily observe that Q^-1 is a function of annealing time. From these measurements of sound velocity and internal friction we can conclude that VRT is a powerful tool for detecting and probing the physical properties of the material under study. Internal friction is a microscopic property for the indication of the purity of the sample. Sound velocity depends on the state of the materials (which depends on the process of treatment).

Translational energy (E_T) dependence of oxygen (O₂) adsorption on clean and modified Cu{100} has been studied by molecular beam surface scattering (MBSS) experiments. The role of surface defects on the adsorption dynamics has been investigated by blocking the defects with Ag and oxygen atoms, and by increasing the defect density with Ar⁺-ion bombardment. At low E_T the adsorption of O₂ is shown to be indirect and facilitated either by a dynamical steering mechanism or a precursor state. At high E_T the defects have only marginal effect on the adsorption. Additionally, the modification of the surface electronic structure by preadsorbed oxygen is shown to have a pronounced effect on the adsorption dynamics, whereas the electronic structure modification by preadsorbed Ag is shown to be relatively inefficient in changing the reactivity of Cu{100} towards O₂ adsorption.

We have measured the morphological grain sizes of nanostructured platinum and gold thin films. In previous works their electrical resistivities have been measured and a theoretical approach was proposed to explain the resistivity experimental data. It will be shown that within the framework of our theoretical approach, the morphological grain sizes play an essential role in the electrical resistivity of these metallic thin films.