Surface Review and Letters

The present study aims at enhancing the wear resistance of Ti–6Al–4V by laser surface nitriding. Laser surface treatment has been carried out by melting of the sand blasted Ti–6Al–4V substrate using a high power continuous wave Diode laser with nitrogen as shrouding environment (at a gas flow rate of 51/min). Laser surface nitriding led to formation of dendrites of titanium nitrides. The microhardness is improved to a maximum of 900–950 VHN (Vickers hardness number) in laser surface nitriding as compared to 260 VHN of the as-received substrate. Surface nitriding increased primary potential for pit formation (E_pp1) as compared to Ti–6Al–4V. Biocompatibility behavior showed a better cell viability due to surface nitriding as compared to the as-received Ti–6Al–4V.

Influence of lithium doping on the crystallization, the surface morphology, the chemical states and the luminescent properties of Y₂O₃:Eu³⁺ phosphors was investigated. The structural, surface morphology characteristics and chemical states of the phosphors were analyzed by using X-ray diffraction (XRD), scanning electron microscope (SEM), and X-ray photoelectron spectroscopy (XPS), respectively. The crystallinity, the surface morphology, and the cathodoluminescence (CL) of phosphors highly depended on the Li doping. The relationship between the crystalline and morphological structures and the luminescent properties was studied, and Li⁺ doping affected not only the crystallinity but also the luminescent brightness of Y₂O₃:Eu³⁺ phosphors. In particular, the incorporation of the Li⁺ ion into the Y₂O₃ lattice could induce remarkable increase in the CL intensity. The enhanced photoluminescence brightness with Li doping may result both from the improved crystallinity leading to higher oscillating strengths for the optical transitions, and the increased surface area due to the larger particle sizes. The strongest emission intensity was observed with Li doped Y₂O₃:Eu³⁺ ceramics whose brightness was increased by a factor of 1.8 in comparison with that of Y₂O₃:Eu³⁺ ceramics.

The long-term operation tests of two types of solid-state organic photovoltaic (OPV) cells, p–n heterojunction type cells and p–i–n junction type cells, were performed. In both cells, a drastic decrease in photocurrent within 1 h was observed in air. This rapid decrease was revealed to be caused by oxygen molecules which act as a electron trap in the electron transporting organic layer. Initial decrease of photocurrent was effectively suppressed under high vacuum (10^-7 Torr). In the case of a p–n type cell, the decrease in short-circuit photocurrent was only 15% even under prolonged light irradiation of 260 h.

Highly ordered crystalline and amorphous Si nanoarrays have been formed by using self-assembled monolayer of polystyrene nanospheres as a template followed by dry ion etching treatments. The template was removed by annealing at 8°C and pattern transfer process was revealed by atomic force microscopy. It was shown that the ordered Si nanotips with a height about 70–80 nm and an average lateral size around 150 nm can be obtained. Field emission with low threshold electric field (<10 V/μm) was demonstrated for both samples which can be attributed to the enhancement of local field due to the existence of surface nanostructures. Our results provide a simple and cheap way to make Si field emitters.

Superhydrophobic materials have been extensively studied because of their wonderful array of properties and applications. In this study, normal and superhydrophobic surface of silk fabric have been prepared via deposition of different shapes of PTFE nanostructure using magnetron sputter coating. The effects of PTFE sputter coating on surface morphology and surface chemical properties were characterized using atomic force microscopy (AFM) and ATR-FTIR (attenuated total reflection-Fourier transform infrared spectroscopy). The wettability of the fabric was characterized through measuring the surface contact angle by drop shape analysis apparatus and dynamic contact angle by Wilhelmy technique. As evaluated by water contact angle measurements, all the treatments resulted in a significant enhancement in the hydrophobicity of silk fabric, while larger sputtering pressures brought bigger PTFE nanoparticles, which led to higher contact angles. The results have also revealed that alternant working pressures, could bring gradient nanostructures which generated both high contact angle and less contact angle hysteresis.

Nanostructured silver films were deposited on polypropylene (PP) nonwovens by RF magnetron sputter coating to obtain the antibacterial properties. Shake flask test was used to evaluate the antibacterial properties of the materials. Atomic force microscope (AFM) was utilized to observe the surface morphology. Energy-dispersive X-ray (EDX) was also employed to analyze the surface elemental compositions. The antibacterial results indicated that the prolonged deposition time led to a significant improvement in antibacterial effect, and sputtering power and argon pressure did not show obvious effect on antibacterial performance. It is believed that the total amount of silver ions released from the silver coating was increased as the deposition time increased. AFM images and quantitative analysis of EDX, respectively revealed that increase in deposition time led to the increased coverage of silver film and the increased silver weight percentage per unit surface, which provided evidences for the increased release rate of silver ions from the coating. Moreover, it was found that the optimum silver coating thickness was about 3 nm, taking antibacterial effect and cost of production into account.

Wool fiber is commonly used in textile industry, however, it has some technical problems which affect the quality and performance of the finished products such as felting shrinkage, handle, lustre, pilling, and dyeability. These problems may be attributed mainly in the presence of wool scales on the fiber surface. Recently, chemical treatments such as oxidation and reduction are the commonly used descaling methods in the industry. However, as a result of the pollution caused by various chemical treatments, physical treatment such as low temperature plasma (LTP) treatment has been introduced recently because it is similarly capable of achieving a comparable descaling effect. Most of the discussions on the applications of LTP treatment on wool fiber were focused on applying this technique for improving the surface wettability and shrink resistance. Meanwhile, little discussion has been made on the mechanical properties, thermal properties, and the air permeability. In this paper, wool fabric was treated with LTP treatment with the use of a non-polymerizing gas, namely oxygen. After the LTP treatment, the fabrics low-stress mechanical properties, air permeability, and thermal properties were evaluated and discussed.

Fiber modifications by environmentally friendly processing are essential in order to simplify the preparation and finishing processes, in addition to minimizing the chemical waste and associated disposal problem. In this regard, enzymes have been used extensively because it can remove the small fiber ends from yarn surface to create a smooth fabric surface appearance and introduce a degree of softness without using traditional chemical treatment. However, a significant strength reduction and slow reaction rate of the enzymatic reaction limit its industrial application. In this paper, the potential of using low-temperature plasma (LTP) as a surface pre-treatment prior to enzyme treatment on flax fiber has been studied. By means of the LTP pre-treatment, the effectiveness of enzyme treatment can be enhanced.

In order to prevent cotton wrinkling, hydroxyl groups in the cellulose chain of cotton are partially crosslinked to keep the chain fixed relative to each other with dimethylol dihydroxy ethylene urea (DMDHEU). However, DMDHEU suffers disadvantages of reduced fabric strength and releasing of free formaldehyde. Recently, 1,2,3,4-butane tetracarboxylic acid (BTCA) has been explored as a new wrinkle-resistant agent providing similar performance to that of DMDHEU. In BTCA finishing, catalyst of inorganic phosphorus-containing acids was used but such phosphorus compounds have an adverse impact on the environment. In this paper, nano-TiO₂ was used as a co-catalyst with sodium hypophophite in the treatment of cotton with BTCA, and the final properties were assessed.

A phosphate protective film was prepared on carbon steel. The structure of the film was analyzed with X-ray photoelectron spectra (XPS) and atomic is force microscope (AFM). AFM observed the full process of film formation clearly. XPS with rotation etch displayed multilayer structure of nanometer phosphate film. During film formation, small insoluble particles (ZnCa₂(PO₄)₂) deposit on the carbon steel surface and grew up gradually, until cover the surface entirely.

By a wet chemical method we have prepared nano-LiNbO₃ with different crystallite sizes. Their ⁷Li NMR spectra each show, on top of a broad band accompanied by two satellites, a sharp central peak whose strength decreases with growing grain size. On the other hand, for a given sample and as temperature rises, the separation between the two satellites gets wider, but the sharp peak gets narrower. From the satellite splitting we may estimate the molar ratio [Li]/[Nb] inside the nanocrystals, and this ratio is seen to be nearer to unity in a sample of smaller grain size. The sharp peak, indiscernible in bulk (mono- or microcrystalline) LiNbO₃, is attributed to Li ions in the disproportionally large surface regions of our samples. The narrowness of its linewidth arises from the fast diffusion of these ions caused by high oxygen deficiency on the surface.

The oxygen reduction on solid oxide fuel cell cathode electrode, Sm_0.5Sr_0.5CoO₃, was studied by using emission Fourier transform infrared spectroscopy (FTIR). Superoxide species was detected with appearance of an IR peak at wavenumber about 1124 cm^-1. Moreover, we interpreted for the first time that there would be a close relationship between the baseline shift of IR spectra and the oxygen vacancy concentration (OVC) of the samples. The downward baseline shift of IR spectra is due to the decrease of OVC in the bulk, while, the increase of the OVC in the bulk would cause the upward baseline shift.

This work describes electroless deposition of copper layers onto a polyimide (PI) film. The film was modified by etching with 1.0 M KOH solution treatment, and an activated Ag thin film was developed on this surface using 0.1 M AgNO₃. The Cu layers were coated on the activated surface of polyimide films by electroless plating method. The thickness and surface morphology of Cu layers on the PI films were characterized with atomic force microscopy. The surface properties of PI film were identified with contact angle measurements.

The present study aims at enhancing the wear resistance and biocompatibility of Ti-6Al-4V by forming a thin layer of oxide. Surface oxidation has been carried out by controlled heating of the surface of Ti-6Al-4V substrate in air at the temperature ranging from 400–600°C and time from 25–60 h. The phase formed under thermal oxidation was predominantly the rutile and anatase phase. The thickness of the oxide layer varied from 1.5–7.0 μm. The microhardness on the surface was significantly improved as compared to the as-received substrate. Both the corrosion resistance property and biocompatibility were improved.

C₆₀ films were fabricated by vacuum sublimation and studied with dielectric spectroscopy regarding glass transition. With annealing, the dielectric loss peaks decreased in height, and the apparent activation energy deduced from their frequency dependence dropped in magnitude. The peaks, broad and asymmetrical, were fitted with Ngai's correlated-states model. The calculated value of the correlation constant β increased after annealing, which may be explained by the reduction in extrinsic dipole density. Some annealed films were further charged with Ar under high pressure, and found to have suppressed transition temperature and activation energy, attributable to the negative pressure effect of intercalation. Freshly charged films exhibited a feature near 137 K in their impedance spectra, probably due to domains of exceptionally high Ar concentration.

Arrays of tungsten oxide nanorods, approximately 500 nm in diameter and 10 μm in length, have been grown in a catalyst-free reaction by heating tungsten wires at 900°C in a humid argon flow. They were systematically characterized using different surface analysis techniques. The chemical composition was determined to be stable stoichiometric binary oxide monoclinic tungsten trioxide. Water vapor was found to be crucial for the formation of these WO₃ nanorods. The vapor–solid (VS) process was introduced to discuss the growth mechanism.

Nanosized Ti–Ni–O catalysts prepared by a modified sol–gel method had been investigated in the oxidative dehydrogenation of ethane and propane to the corresponding alkene. The best yield is obtained over the 9.1 wt% Ti–Ni–O catalyst. The results of catalyst characterization indicated that there is strong interaction between TiO₂ and NiO. It is observed that a decline in temperature for low-temperature oxygen desorption and an augmentation in reduction difficulty of the catalysts would result in poor activity and enhanced alkene selectivity, respectively, over the Ti–Ni–O catalysts in the oxidative dehydrogenation reactions.

A detailed quantitative investigation of the current–voltage (I–V) relationship under the low and the high electric field in the La_0.8Ca_0.2MnO₃/PbZr_0.2Ti_0.8O₃/Si heterostructure over a wide range of temperature was performed. The effective mobility and carrier concentration were then calculated through the electric field effect theory. The differential mobility can be modulated and enhanced significantly by the gate voltage in the vicinity of the metal–insulator-transition temperature. The carrier concentration is proportional to the applied gate voltage. At the room temperature the carrier concentration is found to be 2.5 × 10^-9 under 10 V bias and remains almost unchanged at different temperatures.

The dynamics of surface atoms and simple molecules is closely related to the growth of surface nanostructures. The questions we ask are how atoms diffuse and interact on the surface and what kind of surface nanostructures are formed from such interactions. We also study how the physical property of surface nanostructures is related to their size and thickness. In the last few years we found that metallic nanostructures grown on the Si(111) surface exhibit strong quantum confinement and finite size effects. These effects in turn affect their growth. Some of these studies are (1) how the quantum properties of nanoislands can serve as a template for their own growth, (2) a finite size effect in a structure phase transition of nanoislands of Pb, and (3) growth of metallic nanometer size 2D magic clusters due to both electronic shell structure and atomic bond and geometrical shell structure effects. These studies demonstrate clearly that surface dynamics, electronic and atomic bond effects as well as statistical finite size effect become more and more important as the size of surface islands and clusters reduces to the nanometer range.

The circular dichroism of photoelectron forward focusing peak rotation around the incident-light axis reflects the orbital angular momentum of the excited core level and is inversely proportional to the distance between the emitter and scatterer atoms. This is the basis for the stereo photograph of the atomic arrangements. These rotations are also found in the case of the valence band excitation. The rotation for the 2p_xy band of graphite was about twice those from 2s and 2p_z bands, corresponding to the difference in the orbital angular momentum quantum number of each band. Simultaneously, photoelectron intensity from the bottom of the 2s band was observed at the Γ point of every other Brillouin zone reflecting the photoelectron structure factor that corresponds to the interference of photoelectron waves from 2s atomic orbitals within a unit cell. The origin of the dual behavior that appeared in the observation of a local angular momentum from a delocalized valence band is discussed.

Selective oxidation of light alkanes remains to be a great challenge for the wider use of alkanes as feedstocks. To achieve high activity and at the same time high selectivity, some key issues have to be addressed: (1) the stability of the desired products with respect to the reactants; (2) the roles of the active components in the catalysts, the structure and the functionality of the active centers; (3) the reducibility of the metal cations, the Lewis acid sites and their synergic effects with the basic sites of the lattice oxygen anions; (4) spatial isolation of the active centers; and (5) the mechanisms for the formation and transformation of the intermediates and their kinetic controls. In this contribution, we took selective oxidation of propane to acrolein as our target reaction, and reviewed mainly our own work, trying to provide some thinking and answers to these five questions.

The initial stage of Au adsorption on the Si(111)-7 × 7 surface has been investigated by the first-principles calculations. Different configurations have been considered and the high coordination sites were determined as the most possible places for the Au adsorption. The diffusion barriers for Au atoms on the Si surface have also been evaluated. The results indicated that the Au atoms could diffuse from the top of the Si rest atoms to the high coordination sites only by overcoming a small barrier of 0.11 eV.

Size-dependent elastic properties of Ni nanofilms are investigated by molecular dynamics (MD) simulations with embedded atom method (EAM). The surface effects are considered by calculating the surface relaxation, surface energy, and surface stress. The Young's modulus and yield stress are obtained as functions of thickness and crystallographic orientation. It is shown that the surface relaxation has important effects on the the elastic properties at nanoscale. When the surface relaxation is outward, the Young's modulus decreases with the film thickness decreasing, and vice versa. The results also show that the yield stresses of the films increase with the films becoming thinner. With the thickness of the nanofilms decreasing, the surface effects on the elastic properties become dominant.

A theoretical model is presented to investigate the size-dependent elastic moduli of nanostructures with the effects of the surface relaxation surface energy taken into consideration. At nanoscale, due to the large ratios of the surface-to-volume, the surface effects, which include surface relaxation surface energy, etc., can play important roles. Thus, the elastic moduli of nanostructures become surface- and size-dependent. In the research, the three-dimensional continuum model of the nanofilm with the surface effects is investigated. The analytical expressions of five nonzero elastic moduli of the nanofilm are derived, and then the dependence of the elastic moduli is discussed on the surface effects and the characteristic dimensions of nanofilms.

Adhesion forces of Dipalmitoylphosphatidylcholine (DPPC) membrane in the gel phase are investigated by molecular dynamics (MD) simulation. In the simulations, individual DPPC molecules are pulled out of DPPC membranes with different rates and we get the maximum adhesion forces of DPPC membrane. We find that the maximum adhesion forces increase with pull rate, from about 400 to 700 pN when pull rates are from 0.001 to 0.03 nm/ps. We analyze the relationship between pull rate and adhesion forces of different origins using Brownian dynamics and notice that viscosity of solvent plays an important role in adhesion forces. Then we simulate the motion of a single DPPC molecule in solvent and it elucidates that the maximum drag force is almost linear with respect to the pull rate. We use Stokes' relation to describe the motion of a single DPPC molecule and deduce the effective length of a DPPC molecule. Conformational analyses indicate that the free energy variation of a DPPC molecule inside and outside of the DPPC membrane is an essential part of adhesion energy.

The segregation energy of diluted species in a matrix can be calculated by first principles. These calculations are generally very computational demanding. The existing empirical models which use the difference in surface tensions to predict the segregation energy are limited, because they do not take the surface orientation of the matrix into account. In this investigation a model was developed which can estimate the segregation energies of segregating species in a binary system. The model makes use of the sublimation energies and takes the orientation of the surface into account. The model shows that the driving force for segregation is not the difference in surface tensions (between the surface tension of the pure element and the surface tension of the element in the alloy) but the difference in surface energies. The results of the calculations were used to simulate the Ag and Sb segregation to the (111) surface of copper.

Profiles of surface concentrations as a function of temperature, where the temperature is increased at a constant rate, contain the necessary information to extract segregation parameters. A model using rate equations can be used to simulate these profiles. Even on a high-speed computer, solving these equations can take hours. For ternary and higher component alloys the fit parameters are at least nine and finding the best fit manually can extend the search to days. Theoretical segregation and diffusion models show two temperature regions of interest. In the low-temperature region, representing the kinetics of segregation, the diffusion coefficients of the species dominate the flux of atoms to the surface, and in the high-temperature region the surface concentrations are independent of the diffusion coefficients. In the high-temperature equilibrium region the surface concentrations are determined only by the segregation energies and interaction coefficients. A procedure is presented that can find a good set of segregation parameters within seconds. The sensitivity of selecting the kinetics, as well as the equilibrium temperature regions will be demonstrated. The procedure is used to extract the segregation parameters for a Cu(111) 0.13 at% Sn 0.18 at% Sb system.

The discovery of the single-walled carbon nanotubes (SWCNTs) with a diameter of 0.4 nm has attracted extensive attentions. In this paper we report our attempt with two methods to directly observe these SWCNTs by AFM. The first one is to deposit the SWCNTs extracted from the zeolite matrix to a flat surface for AFM observation. While one-dimensional features have been observed, the SWCNT was suspected not to adhere well to the substrate. To overcome the difficulties of weak adhesion, we attempt to expose only part of the SWCNT from the zeolite channel by cutting the zeolite crystal at an angle. This alternative method, in which the SWCNT contained zeolite crystal is polished and etched by HCl, however, did not result in a smooth enough surface and thus no one-dimensional features can be observed. The difficulties in sample preparation and possible improvements are discussed.

Ag nanoparticles were synthesized by using thermal decomposition of Ag⁺–oleate complex. The mean size of Ag nanoparticle was confirmed as 10 nm with transmission electron microscopy (TEM). The crystal structure and optical property of Ag nanoparticles were studied with X-ray powder diffraction (XRD) and UV–vis spectroscopy, respectively. The Ag nanoparticles were used as seeds for Ag(core)/SiO₂(shell) nanocomposite particles. TEM images of Ag(core)/SiO₂(shell) nanocomposite particles showed that silver core was coated with 15 nm thickness of SiO₂ shell. The thickness of SiO₂ shells could be conveniently controlled by changing the concentration of sol–gel precursor or reaction time. The composition of Ag(core)/SiO₂(shell) nanocomposite particle was investigated with energy-dispersive X-ray (EDX) spectrometer.

PbS nanoparticle phosphors embedded in SiO₂ were synthesized at room temperature by the sol–gel method. The as-prepared SiO₂:0.134 mol% PbS nanoparticles were ground and annealed in atmosphere. Changes in the cathodoluminescence (CL) brightness and the surface chemical composition of the SiO₂:0.134 mol% PbS nanoparticle powders were investigated using a Fiber Optics PC2000 spectrometer for CL and Auger Electron Spectroscopy (AES) and X-ray Photoelectron Spectroscopy (XPS) for the surface chemical analysis. The chemical composition of the powders was analyzed by an energy-dispersive spectrometer (EDS). The CL intensity decreased when the powders were irradiated with a beam of electrons at 2 keV energy and a beam current density of 54 mA/cm² in an ultra-high vacuum chamber at oxygen (O₂) pressures ranging between 5 × 10^-8 and 2 × 10^-7 Torr for several hours. The O₂ Auger peak-to-peak height (APPH) decreased as the CL intensity decreased. XPS analysis on the degraded spot showed the development of characteristic SiO, SiO_x, and elemental Si peaks on the low-energy side of the SiO₂ peak. The desorption of O₂ from the surface, which resulted in a decrease in the CL intensity is attributed to the dissociation of SiO₂ into elemental Si and O₂ by the electron bombardment. The degradation was less severe at higher oxygen pressures. PbSO₄ was also formed on the surface during the electron beam degradation process.

Interdiffusion parameters are often extracted from depth profiles of the interface of annealed thin films by measuring the annealing time of the sample as well as the distance over which interdiffusion took place. The annealing time is usually taken as the time from the moment the sample enters the oven to the exact moment the sample is removed from the oven. However, diffusion does not start and stop at these points, as the temperature of the sample does not change instantaneously. Any calculation performed with the instantaneous and therefore erroneous time will result in incorrect diffusion parameters extracted from the depth profiles. The influence of the extended heating period is studied by solving Fick's second law numerically and employing three distinct heating profiles in the calculations, namely instantaneous, actual, and linear. The results indicate a clear difference between the first two calculated depth profiles. Using these calculations and some experimental results, a method that employs linear heating and cooling of a sample is proposed for studying the interdiffusion of fast diffusing elements (with low activation energies).

We present the fabrication of large-scale two-dimensional periodic silicon nanoarrays using nanosphere lithography. The techniques start from a monolayer of self-assembled polystyrene (PS) spheres of 220 nm in diameter on water surface, which works as a mask to fabricate large-scale periodic silicon nanoarrays by direct plasmatherm reactive ion (RIE) etching. AFM images of the nanoarrays show that the patterns of PS templates are well transferred to the Si surface. The tips stand 50–80 nm high and the lateral size is around 150 nm. The optimum fabrication conditions can be chosen via the analysis of the experimental data.

The single hydroxyl-terminated urethane acrylate oligomers were synthesized from 2-mercaptoethanol (2-MEOH), alkyl (methyl, butyl, and 2-ethylhexyl) acrylate, and 2,2-azobisisobutyronitrile (AIBN, initiator), with dibutyltin dilaurate (DBTDL) as a catalyst. 2-MEOH was used as a functional chain transfer agent. Poly(alkyl urethane) acrylate oligomers were obtained by the reaction of single hydroxyl-terminated polyalkyl acrylates and 2-isocyanatoethyl acrylate. They were characterized by NMR, FT-IR spectroscopy, rheometer, and DSC. Because poly(alkyl urethane) acrylate oligomers have lower T_g and viscosity than hydroxyl-terminated polyalkyl acrylate oligomers (HTPAO) non-containing urethane groups, they can be used for ultraviolet (UV) curable coatings, inks, and adhesives.

Raman spectroscopy, which is a non-destructive technique, has been used to investigate the effect of sample temperature on indentation-induced crystallographic phase transitions in crystalline silicon and amorphous silicon films deposited on a sapphire crystal. It has been shown that in both types of sample, whereas 300 K Vickers diamond indentations lead to the transformation to the Si-II phase during indenter loading on the crystalline and amorphous samples, there is no such transformation in either sample when it is cooled down to 77 K. An explanation of the experimental results has been provided using the pressure–temperature phase diagram of silicon.

Lead tungstate (PbWO₄) (PWO) crystals doped with high concentration trivalent rare earth ions have demonstrated to be a promising Cherenkov radiator material and also a potential material for optoelectronic application. In this paper, the doping mechanisms of the trivalent ions (La₃₊, Nd³⁺, and Gd³⁺) in the PWO host were studied using X-ray photoelectron spectroscopy (XPS), and the results were consistent with those of computer simulation. It was found that when heavily doped, La³⁺ may substitute for the W sites as well as the Pb sites for self-compensation by forming La dimers or small aggregates. However, the doping mechanism of heavily doped PWO:Nd³⁺ and PWO:Gd³⁺ might be different from that of heavily doped PWO:La³⁺ crystals.

The powerful RHEED technique has been demonstrated for the structural determination of the nano-crystals grown on metal and oxide substrate surfaces. Pt was electrochemically deposited onto a electrode, while Pb and cobalt were vapor deposited onto Ag(111) and oxide film/NiAl(100), respectively under UHV conditions. At any Pt coverage, 3D-clusters develop for which the Pt clusters grow in (311) orientation on the substrate surface, where the atomic rows of the (311) facet are parallel to the atomic rows of the surface. Due to the strong bonding at Pb/Ag(111) interface, the Pb deposit grows in 2D-islands with a phase (Θ < 1 ML). On the other hand, the β-crystallites of ≈ 1 nm in diameter with inclusion of smaller-sized particles (D < 1 nm) are observed on Θ-Al₂O₃ after Co deposition at room temperature. Annealing at 900 K Co clusters (≈ 3 nm) grow larger at expense of small particles on thin oxide film on NiAl(100) and become better ordered, where the [110] axis of the Co(001) facet is parallel to the [100] direction of the (001)-oxide surface. The in-plane lattice constant of Co clusters is ca. 4 larger than that of bulk Co, yielding less strain at the (001)-oxide surface. These results demonstrate that both orientation and phase of metal nano-clusters are governed by surface structure of the substrate.

An alternative approach to a sputtering process was examined where a single incident beam of Xe ions was used to simultaneously sputter a carbon target and bombard a growing film. The hypothesis that by positioning a substrate at grazing angles to the central axis of the ion beam, the additional energy provided will be beneficial to the formation of sp³ bonding. Amorphous carbon (a-C) and diamond-like carbon (DLC) films were synthesized by sputtering a graphite target from a Kaufmann-type ion source. Experimental results revealed that when a substrate was placed at grazing angles due to a secondary resputtering process, it was not possible to fabricate DLCs but only sp²-rich polymeric a-C. For DLC synthesis the optimal angles of the target and the substrate to the ion flux were found to be 30° and 0°, respectively, and the ion energies of 0.8–1 keV.

We report a scanning tunneling microscopy (STM) study of potassium (K)-doped C₆₀ (K_xC₆₀) on Cu(111) and Ag(111), with focus on the observation of novel K-induced superstructures. On Cu(111), K-intercalation leads to various superstructures, i.e., p(3 × 3), p(2 × 2), and a disordered "maze-like" structure. Concomitant removal of C₆₀-induced substrate reconstruction was also observed. On Ag(111), K-doping induces C₆₀ reorientation and results in a p(2 × 2) superstructure. All observed superstructures suggest intrinsic inhomogeneity of K-doping in fullerene materials, which must be further understood.

The inverted-gate colossal magnetoresistance-field-effect-transistors (CMR-FETs) were designed and successfully fabricated on the Si substrate by using semiconductor techniques. The studies on the capacitance properties were carried out under different temperatures, different frequencies, and different gate biases. The results indicate that La_0.8Ca_0.2MnO₃ is the typical p-type semiconductor. It was shown that the capacitance increases with the increasing of the temperature under certain gate bias. The sudden increase of the capacitance at 160 K was observed and needeed to be studied further. Meanwhile the capacitance decreased as the frequency increased with first order exponential decay fitting.

The microstructures in the YBa₂Cu₃O_y films grown on Eu₂CuO₄/Y-ZrO₂(YSZ) buffered silicon were studied by means of transmission electron microscopy. Our effort was emphasized on the influence of the interfacial microstructures on the formation and epitaxy of the grown layer. It was found that a native Si-oxide layer ~ 5 nm was formed at the boundary between YSZ and silicon. Such an intermediate layer should be formed after the initial formation of the grown YSZ layer as the epitaxy of YSZ still remain. The epitaxy can be kept through all layers without the formation of big grain boundaries. No amorphous layers and secondary phases were observed at the interfaces of YSZ/ECO and YBCO/ECO. The results demonstrate that the crystallinity and the epitaxy of YBCO have been greatly improved by the bi-layer buffer.

CdTe thin films were grown on GaAs(100) substrates by using molecular beam epitaxy at various temperatures. The results of the X-ray diffraction (XRD) patterns showed that the orientation of the grown CdTe thin films was the (100) orientation. XRD patterns, atomic force microscopy images, high-resolution transmission electron microscopy (HRTEM) images, and photoluminescence spectra showed that the crystallinity of CdTe(100) epilayers grown on GaAs(100) substrates was improved by increasing the substrate temperature. HRTEM images showed that misfit dislocations existed at the CdTe/GaAs heterointerface. These results can help improve understanding of the substrate temperature effect on the structural and the optical properties of CdTe(100)/GaAs(100) heterostructures.

An undoped p-type nanocrystalline diamond (NCD) film was grown by an electron assisted hot filament chemical vapor deposition (EA-HFCVD) technology on an n-type single-crystalline Si substrate to fabricate p-NCD/n-Si heterojunction. The structure and morphology of the NCD film, which was analyzed by Raman spectroscopy, X-ray diffraction (XRD), and scanning electron microscopy (SEM), showed that the film consisted of 40–60 nm polycrystalline nano-grains. The results showed that with EA-HFCVD method, not only an undoped NCD film with high conductivity but also a p–n heterojunction diode between the NCD film and n-Si substrate was fabricated successfully. The p-NCD/n-Si heterostructure was also used for ultraviolet (UV) photodetector application. Operating at a bias voltage of 10 V, this photodetector showed a significant discrimination between UV and visible light, and the UV/visible-blind ratio was about three orders of magnitude.

Pd/Si_0.9Ge_0.1/Si Schottky barrier diodes subjected to irradiation are characterized using capacitance and conductance measurements performed under forward and reverse bias while varying the temperature and frequency. The C–V technique has been used in particular to determine the carriers profile as well as the interface state density and its energy distribution.

The surface of La_1/3Ca_2/3MnO₃ (LCMO) films with thickness, t, ranging from 4 to 150 nm has been studied. Highly ordered palpus-like crystals induced by strain are observed in the films grown on the substrate of SrTiO₃ (with thickness t ranging from 20 to 50 nm) and on sapphire (with thickness t ranging from 30 to 50 nm). The strain is identified to result from thermal expansion mismatch between the substrate and the film, and thermal expansion anomaly may exist at a high temperature induced by possible phase transition in LCMO with t = 30 nm. Such a phenomenon may arrest the film growth and the understanding of colossal magnetoresistance materials as well as provide a new way to make ordered structures for applications.

Highly epitaxial thin films of YBa₂Cu₃O_y (YBCO) have been successfully grown on Si using a double buffer of Eu₂CuO₄ (ECO)/(yttrium-stabilized zirconia) YSZ. The severe reaction between Si and YBCO is blocked by YSZ, and the crystallinity and superconductivity of the grown YBCO due to the lattice mismatch between YBCO and YSZ are improved by the ECO layer. The grown films were characterized by high-resolution X-ray diffraction, grazing incidence X-ray reflection, scanning electron microscopy (SEM), and Doppler broadened annihilation radiation spectroscopy, respectively. Very clear interfaces were found at YBCO/ECO/YSZ boundaries without any intermediate layer. The YBCO film surface was more smooth and stable. The results obtained indicate that highly epitaxial YBCO thin films can be successfully grown on Si wafers, demonstrating advantages of such a double buffer structure.

SrTiO₃ films are fabricated on DyScO₃ substrates by pulse laser deposition. In situ X-ray diffraction (XRD) is used to characterize the thermal expansion coefficient at low temperature. The abnormal behavior in lattice parameter at 80 K may be the hint of a phase transition. High resolution XRD is performed to detect the two kinds of dislocations, i.e. screw and edge. Results show that the density of edge dislocation is a little larger than that of the screw one. The total dislocation density has the order of about 10⁸ cm^-2. Edge dislocation density decreases with the increase of the film thickness. We argue that the ratio between these two dislocation densities results in the growth mode of the film.

High quality homo-epitaxial ZnO films were grown on Zn-terminated surfaces of ZnO (0001) single-crystal substrates with high-temperature annealing and Ar⁺ ion etching. These films were prepared by low-pressure MO-CVD using zinc acetylacetonate (C₅H₇O₂)₂ and oxygen as source materials. High quality ZnO (0001) substrate was synthesized by the hydrothermal technique. The atomically flat surface without scratches was obtained by high temperature annealing at 800°C–1300°C in oxygen atmosphere. Ar⁺ ion etching for the surface of ZnO substrates was critically important to the growth of ZnO films with good crystallinity. The epitaxial film and the ZnO substrate were characterized using reflection high-energy electron diffraction, atomic force microscope, and X-ray photoelectron spectroscopy.

An adherent nano-superhard titanium nitride (TiN) film on the substrate of Cr₁₂Mo₄V high speed steel was prefabricated in a vacuum cathode multi-arc ion-plating system. Microhardness, film-to-substrate adhesion, and microstructure of the film were investigated typically using Vickers hardometer, scratch tester, and X-ray diffractometer. Results show that: (i) the achievable film microhardness is in the range of 35–45 GPa; (ii) the critical load (Lc) of the superhard TiN film is approximately 64 N; (iii) the nm scale mean main grain sizes of the film are approximately of 12.7 nm for TiN₁₁₁, 19.7 nm for TiN₂₀₀, and 9.6 nm for TiN₂₂₀; and (iv) compared with the standard TiN film with the hardness of 22 GPa, the accomplishment of the nano-superhard TiN film may be due to (a) the ion bombardment induced residual stress within the film, and (b) the combined effect of the decrease of crystalline size and preferred orientation in the plane (111).

To improve the oxidation protective ability of SiC coating for carbon/carbon (C/C) composites, MoSi₂ was introduced in the SiC coating by infiltration technique. XRD and SEM analysis show that the SiC coating obtained by pack cementation is a porous structure with a thickness of about 60–100 μm. After infiltration treatment, MoSi₂ was filled in the holes of the porous SiC-coating, and the as-received coating becomes dense without through-thickness crack. Oxidation test shows that, the weight loss of the SiC-coated C/C is up to 9.23% after 53 h oxidation in air at 1773 K, while the weight loss of the MoSi₂-improved SiC-coated C/C composites is only 0.73% after oxidation for 265 h. The oxidation of C/C composites is primarily due to the formation of the penetration cracks and the holes on the glass layer.

Nominally undoped ZnO thin films were grown on polyimide (PI) substrates at various temperatures by using radio-frequency magnetron sputtering. Atomic force microscopy images showed that the root mean squares of the average surface roughnesses for the ZnO thin films grown on the PI substrates at 27°C, 100°C, 200°C, and 300°C were 4.08, 4.50, 4.18, and 3.89 nm, respectively. X-ray diffraction patterns showed that the crystallinity of the ZnO films had a preferential (0001) direction and that the full width at half-maxima for the (0002) ZnO diffraction peak for the ZnO thin films grown on the PI substrates at 27°C, 100°C, 200°C, and 300°C were 0.22, 0.22, 0.22, and 0.23, respectively. The average optical transmittances in the visible ranges between 550 and 750 nm for the ZnO/PI heterostructures grown at 27°C, 100°C, 200°C, and 300°C were 87%, 83%, 87%, and 78%, respectively.

Carrier density of a two-dimensional electron gas (2DEG) in Al_0.3Ga_0.7N/GaN and Al_0.3Ga_0.7N/AlN/GaN heterostructures was investigated by performing Shubnikov-de Haas (SdH) measurements. The angular-dependent SdH measurements and the fast Fourier transformation results for the SdH data indicated 2DEG occupation of one subband in the triangular potential wells. The carrier densities of the 2DEGs in the Al_0.3Ga_0.7N/AlN/GaN and the Al_0.3Ga_0.7N/GaN heterostructures at 1.5 K, determined from the SdH data, were 1.28 × 10¹³ and 1.12 × 10¹³ cm^-2, respectively. The electron carrier density of the 2DEG in the Al_0.3Ga_0.7N/GaN heterostructure with an AlN embedded potential barrier layer was larger than that in the Al_0.3Ga_0.7N/GaN heterostructure. The electronic subband energies, the wave functions, and the Fermi energies in the Al_0.3Ga_0.7N/AlN/GaN and Al_0.3Ga_0.7N/GaN heterostructures were calculated by using a self-consistent method taking into account spontaneous and piezoelectric polarizations.

Thin films of La_0.9Sr_0.1MnO₃ (LSMO) were grown on SrTiO₃ substrate by pulsed laser deposition technique at different temperatures and with various oxygen partial pressures. X-ray diffraction spectra confirmed that the grown films are of single phase. The influence of oxygen deficiency on the structure of these grown films has been studied. X-ray diffraction data suggested that higher oxygen content generally results in smaller out-of- plane lattice parameters and annealing in oxygen may further decrease the lattice parameters. The 2-θ value increases with oxygen pressure. Typically, the oxygen-deficient films behave like semiconductors. For films grown at the same temperature, the conductivity is enhanced if the oxygen content is increased. Those films grown in 1 mbar oxygen partial pressure show an upturn at low temperature. Resistivity is dominated by the hopping of adiabatic small polarons at high temperature.

SiC coating for carbon/carbon composites was prepared by pack cementation method. The effects of coating process on the microstructure and the mechanical properties of C/C composites were analyzed by SEM and three-point bending test, respectively. As the infiltrated Si improved the interfaces bonding during the coating process, the flexural strength and flexural modulus of SiC-coated carbon/carbon composites were both increased by about 10% than the naked C/C composites. In addition, the mechanism of the change of failure mode of SiC coated C/C composites and naked C/C composites was addressed.

Polytetrafluoroethylene (PTFE) has been increasingly used in many industries due to its low frictional coefficient and excellent chemical inertness. The surface properties of PTFE are of importance in various applications. The surface properties of PTFE can be modified by different techniques. In this study, PTFE film was treated in oxygen plasma for improving surface wettability. The effects of plasma treatment on dynamic wetting behavior were characterized using Scanning Probe Microscopy (SPM), Fourier transform infrared spectroscopy (FTIR), and dynamic contact angle (DCA) measurements. SPM observations revealed the etching effect of the plasma treatment on the film. The introduction of hydrophilic groups by plasma treatment was detected by FTIR. The roughened and functionalized surface resulted in the change in both advancing and receding contact angles. Advancing and receding contact angles were significantly reduced, but the contact angle hysteresis was obviously increased after plasma treatment.

We studied the growth kinetics and characteristics of electroless nickel–phosphorus (EN–P) deposition layer on Cu substrate in an acid plating bath with sodium hypophosphite as the reducing agent. The individual nodules of the EN–P layer increased in size but decreased in number with increasing plating time and pH, i.e. the root-mean-square (RMS) roughness of the EN deposit decreased. In addition, the plating rate of the EN layer increased with increasing plating bath pH. X-ray diffraction (XRD) analyses revealed that the as-plated deposit was in an amorphous phase, while the heat-treated layer was composed of crystallized Ni and Ni₃P compound. The solderability of the EN layer increased with decreasing P content. In addition, the wetting force increased with increasing surface roughness. The present study clearly showed that the solderability behavior of the EN layer is affected by both surface composition (P content) and morphology.

The frequency tuning can be achieved by integrating SrTiO₃ (STO) thin films into high-temperature superconducting YBa₂Cu₃O_y (YBCO) devices and tuning the dielectric constant of the STO films by an electrical bias. We have fabricated epitaxial STO thin films on superconducting YBCO. By the combination of various surface characterizations such as scanning probe microscope, structural and dielectric measurements, we attempted to understand the fundamental mechanisms of dielectric properties in STO thin films. Substrate surface and structural properties of the heterostructure were studied. We have measured the temperature dependence of dielectric constant and loss tangent of STO thin films. The system exhibits 41% dielectric constant tuning over a bias of 4 V at low temperature.

Effects of Si₃N₄ passivation layer on the lattice strain of Al_0.22Ga_0.78N layer with the thickness of 100 nm has been studied by in situ X-ray diffraction by the temperature range of 25°C–550°C. Results show that the temperature dependence of the strain relaxations can be separated into three linear regions. After passivation, an additional in-plane tensile strain is observed. The residual tensile strain increases with increasing temperature at low temperature, while at higher temperature the residual tensile strain decreases slightly. There is clear influence when a passive layer is deposited on the surface of the heterostructures. The linear regions in the temperature dependence of strain vary after the passive layer deposited on the heterostructure. These results indicate that the variation of the lattice strain relates to the difference in thermal stability between the epitaxy layer and the substrate.

The structure and transport properties for La_2/3Ca_1/3MnO₃ (LCMO)/YBa_1.8Eu_0.2Cu₃O₇ (YBECO) multilayers are studied. The lattice constants for each sub-layer decrease with decreasing the temperature. The morphology of the films depends on the thickness of each sub-layer. Grains growing on the surface of each sample are believed to release the lattice strain. We believe that the lattice strain may affect the transport properties of LCMO and YBECO in the periodic films. The grains appearing on the surface of the film may enlarge the width of the superconducting transition of YBECO, and the metal-to-insulator transition of LCMO.

(La_2/3-xY_x) (Ca_1/3-ySr_y) MnO₃ (LYCSMO) thin films with x = 0.08 and y = 0.0868 deposited on SrTiO₃ (STO), Yttrium-stabilized ZrO₂ (YSZ), LaAlO₃ (LAO), and MgO substrates are fabricated. Atomic force microscopy measurements reveal that the morphology is quite different for all films. A two-dimensional growth mode is suitable for LYCSMO film on STO, while on LAO, YSZ, and MgO, an island growth mode may be a good description for the growth of LYCSMO films. X-ray diffraction studies show that the films epitaxially grow along c axis on STO, LAO, and MgO substrates, while grows along a axis on YSZ substrate. The in-plane and out-of-plane lattice parameters are also obtained for films grown on all substrates.

The plasma treatment on SiO₂ substrate surfaces increased the oxygen-containing functional groups or the polar component of the surface free energy and, the wetting characteristics of the underfills/SiO₂. The plasma treatment condition which gave the smallest contact angle between the underfills and SiO₂ was an operating time of 60 sec under O₂ gas atmosphere and a power of 200 W.