Surface Review and Letters

Electrochemical impedance spectroscopy (EIS) is one of the electrochemical techniques used in materials science. The present measurements are used to evaluate the corrosion resistance of new types of coated steel rebar used in reinforced concrete. In this study, Si-based coating materials are used and evaluated, because adding Si to metals and alloys, including steel, generally increases their corrosion, oxidation, and erosion resistance. The result suggests that electrochemical impedance spectroscopy may be useful for monitoring corrosion activity on coated steel rebars. Based upon impedance changes, it appears that the silicon powder coating bonds well to the steel, and that the coating has a good performance.

Structural and Photoluminescence (PL) studies are carried out for p-type porous silicon materials prepared with different Hydrogen Fluoride (HF) concentration. Surface morphology of porous silicon was analyzed using atomic force microscope (AFM). Fourier Transform Infra Red (FTIR) spectra indicate that surface of porous silicon contain chemical species like SiH_n. PL studies reveal that there is a prominent emission peak around 625 nm. No spectral shift is observed. It is further observed that the emission intensity increases with HF concentration. The PL of the porous silicon layer was found to come from its upper part, which was confirmed by a simulation of the PL spectrum employing an optical model. The refractive indices of the porous silicon layer were also determined through this simulation. The large hydrogen concentration in freshly prepared material has led to the suggestion that a silicon–hydrogen alloy effect is responsible for the luminescence.

Undoped, antimony doped and fluorine doped tin oxide films have been prepared by spray pyrolysis technique. The films were deposited on glass substrates at temperatures ranging between 300°C and 370°C by spraying an alcoholic solution of tin tetra chloride (SnCl₄). Dopants used were antimony tri chloride (SbCl₃) for antimony doped tin oxide (ATO) films, and ammonium fluoride (NH₄F) for fluorine doped tin oxide (FTO) films. Among undoped tin oxide films, the least resistivity was found to be 3.1 × 10^-3 Ω-cm for a molar concentration of 0.75 M. In case of antimony doped films minimum resistivity value was found to be 7.7 × 10^-4 Ω-cm for a film with (Sb/Sn) = 0.065, deposited at 370°C and in case of fluorine doped films it was found to be 1.67 × 10^-3 Ω-cm for a doping percentage of 3 at% of fluorine in 0.1 M solution. The corresponding values of the carrier concentrations were found to be 1.8 × 10²⁰/cm³ and 9.98 × 10²⁰/cm³, respectively. The electrical and optical properties of these films were studied as a function of both doping concentration and substrate temperature. Doping percentage of antimony and fluorine in the spray solution has been optimized for achieving a minimum electrical resistivity. The dependence of electrical properties such as resistivity, carrier concentration and mobility of doped films were analyzed. Influence of antimony dopant on the optical band gap of the films has been reported on the basis of electron conduction mechanism. Air and argon annealing effects on the electrical properties of antimony doped tin oxide films were also studied.

Adsorption and diffusion of a Ba adatom on a reconstructed Si(001) surface were studied using first principles density functional calculation. It was found that the lowest energetic configuration is that the Ba atom resides at the T3' (which is displaced along the direction from the T3 site by ~ 0.26 Å). An anisotropic diffusivity of Ba on the reconstructed surface was found. The preferred direction of diffusion was the trough between Si dimer rows.

The effects of substrate-placing manner, deposition temperature and solution concentration on the preparation of ZnO films by chemical bath deposition were investigated in this work. The structures and the morphologies of as-deposited ZnO films were characterized by X-ray diffraction and scanning electron microscope, respectively. The results show that compared with vertically insertion, floating the substrates on the solutions could greatly improve the c-axis orientation of the films. The growth of ZnO films with orientation would also be favored at lower precursor concentrations and temperatures. When the concentration of Zn(CH₃COO)₂·2H₂O is 0.033 M/L and the deposited temperature is 60°C, ZnO films which are well crystallized and highly c-axis orientated were obtained.

Adsorbed hydrogen layers on the Mo(110) surface have been investigated both experimentally by temperature programmed desorption (TPD) method and theoretically by means of DFT-based optimization of surface structures. We suggest a novel microscopic model of the associative hydrogen desorption, which explains essential features of the process. In this model, the process of hydrogen desorption can be described as association of hydrogen atoms on the surface, but molecular formation is actually accomplished while the molecule moves away from the surface. We also suggest a new algorithm for realistic Monte Carlo simulations of associative desorption, which implements the microscopic description of the association of hydrogen adatoms into a molecule with activation energy, found from the DFT calculations. Good agreement between simulated and experimental TPD spectra gives insight into different behavior of the spectra, obtained for low and high hydrogen coverages on the Mo(110) surface.

The electronic structure of S adsorption on goethite (110) surface has been studied by ASED-MO cluster calculations. For S location, the most exposed surface atoms of goethite surface were selected. The calculations show that the surface offers several places for S adsorption. The most energetically stable system corresponds to S location above H atom.

We studied in detail the configurations that correspond to the higher OP values. For these configurations, the H-S and Fe-S computed distances are 2.1 and 3.7 Å, respectively. The H-S and Fe-S are mainly bonding interaction with OP values of 0.156 and 0.034, respectively. The Fe-S interaction mainly involves Fe 3d_x2-y2 atomic orbitals with lesser participation of Fe 4p_y and Fe 3d_yz atomic orbitals. The O-S interaction shows the same bonding and antibonding contributions giving a small OP value. The O-S interaction involves O 2p orbitals. There is an electron transfer to the Fe atom from the S atom. On the other hand, there is an electron transfer to S atom from the H and O atoms, respectively.

The binding energy of the donor in three different shaped triple graded GaAs-(Ga, Al)As quantum wells which is obtained by changing the depth of the central-well potential (V_o) is calculated by using a variational approach. The results have been obtained in the presence of uniform magnetic and electric fields applied along the growth direction as a function of the impurity position. In addition, we also give the binding energy of the hydrogenic donor impurity for triple square quantum wells having the same physical parameters with triple graded quantum well structures in order to see the effect of different geometric confinements on the donor impurity binding energy.

It is known that the press formability and the elongation of laser textured sheet are improved, and the service life of textured roll is longer than that of the un-textured roll due to hardening of the treated surface. One of the goals to develop high repetitive rate YAG laser-induced discharge texturing (LIDT) is to get deeper hardening zone. By observing and measuring cross-section of LIDT spots in different discharge conditions, it is found that the single-crater, which is formed by the discharge conditions of anode, which is covered by an oil film and with rectangular current waveform, has the most depth of heat affected zone (HAZ) comparing with other crater shapes when discharge energy is the same. The depth of HAZ is mainly depends on pulse duration when the discharge spot is single-crater. The results are analyzed.

A study has been made on TiN coatings deposited on D2 tool steel substrates by using commercially available cathodic arc evaporation, physical vapor deposition technique. The goal of this work is to determine the usefulness of TiN coatings in order to improve the micro-Vickers hardness, coefficient of friction and surface roughness of TiN coating deposited on tool steel, which is vastly use in tool industry for various applications. A pin-on-disc test was carried out to study the coefficient of friction versus sliding distance of TiN coating at various ion etching rates. The tribo-test showed that the minimum value recorded for friction coefficient was 0.386 and 0.472 with standard deviation of 0.056 and 0.036 for the coatings deposited at zero and 16 min ion etching. The differences in friction coefficient and surface roughness was mainly associated with the macrodroplets, which was produced during etching stage. The coating deposited for 16 min metal ion etching showed the maximum hardness, i.e., about five times higher than uncoated one and 1.24 times to the coating deposited at zero ion etching. After friction test, the wear track was observed by using field emission scanning electron microscope. The coating deposited for zero ion etching showed small amounts of macrodroplets as compared to the coating deposited for 16 min ion etching. The elemental composition on the wear scar were investigated by means of energy dispersive X-ray, indicate no further TiN coating on wear track. A considerable improvement in TiN coatings was recorded as a function of various ion etching rates.

This paper dealt with plasma-sprayed hydroxyapatite (HA) coatings on carbon/carbon composites (C/C) and the implantation was carried out in rabbits. Ninety days after the implantation, we found that such materials were favorable for health and no cytotoxic effects were discovered. The histological observation of osteogenic response of HA-coated C/C showed that the osteoplaque had scansorially grown along the surface of the HA coatings and the pure C/C surface had no obvious change. All these results indicate that as a potential bone-repairing material, the surface properties of the C/C has been changed by preparing the HA coatings. Also the new materials may be preferably feasible of clinical application.

In the present work, a combined route involving first doping of iron or neodymium ions via sol–gel method followed by acidification of the metal-doped TiO₂ particles for the improvement of the photocatalytic capability of TiO₂ was reported. The obtained metal-doped/acidified TiO₂ photocatalysts were thoroughly characterized by X-ray diffraction, Fourier transform infrared analysis, and photoluminescence emission spectra. At the same time, their photocatalytic activities were evaluated in simulant photodegradation of methylene blue (MB). The results based on these characterizations showed that not only a rutile layer formed on the surface of original TiO₂ particles after surface cladding, but also the doped Fe or Nd ion had a favorable effect on suppression of the electron–hole recombination in the titania under ultraviolet light irradiation. Furthermore, the photocatalytic activity of the material obtained by Fe doping and acidification was substantially improved in comparison to the untreated TiO₂. However, the sample prepared from Nd-doping and acidification of TiO₂ showed decreased capability relative to the untreated TiO₂ in degradation of MB under similar conditions. Finally, the reason why the photocatalytic activities of the obtained catalysts are sensitive to the metal-doping was discussed in details.

A spectrophotometric study of 1:1 donor–acceptor complex, cobalt (III) acetylacetonate (donor) and iodine (σ-acceptor) has been preformed. The equilibrium constants, (K) and the absorpitivity (ε) for the formation of the iodine complex have been calculated. The predicted structure of the solid triiodide charge-transfer complex reported in this study is further supported by thermal, far and mid infrared spectroscopic measurements. Electron transfer from Co (acac = 2, 4-pentanedionate)₃ to iodine leads to the formation of an organic semiconductor with the formula of . The kinetic parameters (nonisothermal method) for their decomposition have been evaluated by graphical methods using the equations of Freeman–Carroll (FC), Horowitz–Metzger (HM) and Coats–Redfern (CR). The ac conductivity and dielectric properties of have been measured over the frequency 50–10⁶ Hz at temperature 298 K.

Pulsed laser deposition (PLD) is being investigated as an alternative technique to prepare hydroxyapatite coatings. In this research we studied the microstructure and phase composition of the PLD hydroxyapatite films. The surface morphology of the films is composed of droplets for which size ranges from hundreds of nanometers to a few micrometers. The cross-sectional morphology of the films shows that the films adhere to the substrate well and there are no microcracks, pores and other defects between substrate and films. The X-ray diffractometer results show that the deposited films are amorphous and the post heat treatment films consists of crystalline HA and TiO₂.

Conductivity-frequency and capacitance-frequency characteristics of mixed oxides Al–In₂O₃–SnO₂–Al structure are examined to elicit any correlation with the conduction mechanisms most often observed in thin film work. The existence of Schottky barriers is believed to be due to a strong donor band in the insulator established during the vacuum evaporation when a layer of mixed oxides In₂O₃–SnO₂ system is sandwiched between two metal electrodes. Low values of activation energy at low temperatures indicate that the transport of the carriers between localized states is mainly due to electronic hopping over the barrier separating the two nearest neighbor sites. The increase in the formation of ionized donors with increase in temperature during electrical measurements indicates that electronic part of the conductivity is higher than the ionic part. The initial increase in conductivity with increase in Sn content in In₂O₃ lattice is caused by the Sn atom substitution of In atom, giving out one extra electron. The decrease in electrical conductivity above the critical Sn content (10 mol% SnO₂) is caused by the defects formed by Sn atoms, which act as carrier traps rather than electron donors. The increase in electrical conductivity with film thickness is caused by the increase in free carriers density, which is generated by oxygen vacancy acting as two electron donor. The increase in conductivity with substrate and annealing temperatures is due to either the severe deficiency of oxygen, which deteriorates the film properties and reduces the mobility of the carriers or to the diffusion of Sn atoms from interstitial locations into the In cation sites and formation of indium species of lower oxidation state (In²⁺). Calculations of C and σ_ac from tan δ measurements suggest that there is some kind of space-charge polarization in the material, caused by the storage of carriers at the electrodes. Capacitance decreases not only with the rise of frequency but also with the lowering of temperature. At low temperatures the major contribution to capacitance arises from the ionic polarization, however, with the increase of temperature the contribution from orientation polarization would considerably increase. The decrease in capacitance with the increase in frequency may be attributed to interfacial polarization.

Thin nanocrystalline Cu films (< 1 μm) are deposited on a glass substrate using an improved electroless plating technique. The deposition course of the Cu film is illustrated by the variation of surface morphology with different deposition time. The results show that a more uniform and continuous nanocrystalline Cu film with very small nodules can be formed on a glass substrate at the deposition time over 1 min. The roles of SDBS as an additive in the bath are also discussed. According to the relation of the film thickness and the deposition time, it is obvious that the film thickness nearly linearly varies with the deposition time in the present work. An enhanced (111) texture with the diffraction intensity ratio (I₍₁₁₁₎/I₍₂₀₀₎) of about 4.0 and the very fine grain size of 15–28 nm determined by X-ray results has been observed. The variations of the resistivity show that it is strongly affected by the film thickness and grain size.

Nominal compositions of Ni_xTi_1-xFe₂O_5-δ (x = 0, 0.2, 0.4, 0.6, 0.8 and 1) were prepared by a solid state reaction using stoichiometric amounts of Fe₂O₃/TiO₂ system and NiO as a dopant. The effects of small substitution of Ni ions on the electrical and structural properties were studied for the above system. The X-ray diffraction patterns revealed that the ferroelectric phase of iron titanate and the spinel ferrite phase of Ni-ferrite having a single phase at x = 0 and 1, respectively. The substitution of Ni ions increases the average value of lattice constant a_av. Solid–solid interaction took place between the ternary oxides at 1200°C for 4 h yielding a new phase of NiTiO₃. The presence of the three phases was confirmed by X-ray diffraction technique. The resultant compositions have nanocrystallites with average crystalline size "D_av" in the range 100–300 nm. The DC electrical resistivity ρ, Curie temperature T_C and activation energies for electric conduction around T_C region increase as Ni ion substitution increases. The ferrite samples have a semiconductor behavior where electrical resistivity ρ decreases on increasing temperature. The activation energy for electrical conduction was affected by both the ratio "ferroelectric/ferrite" and the position of the Curie temperatures in the compositions depending on the (Ni, Ti) to Fe ratio.

PLT and Doppler broadening S-parameter were used for Al–Mg alloy, namely 5005, 5051, 5052 and 5083. The trapping efficiency was estimated for the pervious alloys as 2.42 × 10⁹, 2.29 × 10⁹, 2.24 × 10⁹ and 2.27 × 10⁹s^-1cm³, respectively and the trapping cross-section was estimated to be as 2.66 × 10^-16, 2.14 × 10^-16, 2.10 × 10^-16 and 3.51 × 10^-16cm², respectively. It is clear that the mean lifetime and S-parameter have the same behavior as a function of deformation degree and saturated at the same value of thickness reduction.

Ni–W/SiC nanocomposite coatings were prepared by electrodeposition in Ni–W plating bath containing SiC nanoparticulates. The effect of incorporation of SiC particulates into the Ni–W matrix on the morphology of the coating surface and corrosion properties was investigated. Scanning electron microscopy (SEM) showed that the SiC nanoparticulates are uniformly distributed in the Ni–W matrix. Corrosion tests were performed in 0.5 M NaCl solution using electrochemical measurements for Ni–W alloy coating and Ni–W/SiC nanocomposite coating. The results showed that the co-deposition of SiC nanoparticulates in the composite coatings increased the corrosion resistance. At last, the anti-corrosion mechanism of the nanocomposite coatings is also discussed.

We have performed Density Functional Theory calculations in the Generalized Gradients Approximation for the (001) surface of the intermetallic compound TiFe. We have focused on the interplay between spin polarization and surface relaxations, and the influence of the chemical species at the surface. We found that the surface shows a magnetic ordering. The magnetic moment at the surface layer depends strongly on the surface termination, being much larger for the case of Fe than Ti termination (3.11 and 0.29 μ_B/atom, respectively). The magnetic moments show an alternating behavior with a slow decaying as we go inside the material. On the other hand, the modification of the atomic positions due to the surface relaxation results in a very small influence on the magnetic moment with respect to the ideal, nonrelaxed configuration.

It is thought that the PEO (plasma electrolysis oxidation) coatings are difficult to be prepared on the cast Al–Si alloys because these alloys contain lots of pure silicon phases. In the present study, oxide coatings with a thickness of about 10 μm were deposited on the substrate of the ZL109 Al–Si alloy by a PEO treatment. XRD showed that the phase composition of the coating was γ-Al₂O₃. SEM showed that the coating surface was porous, and the pore diameter was in the range of 1–5 μm. The cross-section view by EDS indicated that the coating matrix is quite dense, and there are few defects. Phosphorus from the applied electrolyte could be incorporated into the coating during the PEO process. A transitional zone with a thickness of about 3 μm was observed on the interface between the coating and substrate, and a high adhesive strength was expected. The average hardness of the coating was 576 HV_0.025, which was 7.2 times higher than that of the substrate. High alloy element content of the substrate seems to have no remarkable and adverse influence on the structure and composition of the PEO coating.

Laser cladding is one kind of advanced surface modification technology and has the abroad prospect in making the wear-resistant coating on metal substrates. However, the application of laser cladding technology does not achieve the people's expectation in the practical production because of many defects such as cracks, pores and so on. The addiction of rare earth can effectively reduce the number of cracks in the clad coating and enhance the coating wear-resistance. In the paper, the effects of rare earth on metallurgical quality, microstructure, phase structure and wear-resistance are analyzed in turns. The preliminary discussion is also carried out on the effect mechanism of rare earth. At last, the development tendency of rare earth in the laser cladding has been briefly elaborated.

The PVD-TiN film was implanted with titanium ions and the improvement in surface wear resistance was investigated. Ti ion implantation was done using a metal vapor vacuum arc (MEVVA) ion source with an implantation dose of 2 × 10¹⁶ ions/cm² and at an extraction voltage of 48 kV. The wear characteristics of the implanted zone was measured and compared to the performance of the unimplanted zone by a pin-on-disc apparatus and an optical interference microscope. The structure of the implanted zone and unimplanted one was observed by X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). A dynamic TRIM called TRIDYN was used to calculate the concentration depth profile of implanted Ti in TiN to investigate the profile of multi-charge state ions. The results showed that the improved wear resistance of the TiN film was mainly due to the presence of nano-order TiN crystal grains after Ti ion implantation.