Surface Review and Letters

Nitrogenated diamond-like carbon films have been deposited on glass and p-type Si (100) substrates by radio frequency (r.f.) plasma-enhanced chemical vapor deposition (PECVD) with a frequency of 13.56 MHz at room temperature using CH₄ as precursor of carbon source and H₂ as a carrier gas. The deposition was performed at a different flow rate of nitrogen from 0 to 12 sccm under a constant r.f. power. The effect of nitrogen incorporation on the bonding states and growth kinetics of the deposited films have been investigated by Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, X-ray photoelectron spectroscopy and optical properties by UV spectroscopy measurement. Our experimental results show that the incorporation of nitrogen has a considerable effect on the properties of the deposited films. FTIR spectra show that the nitrogen is bonded to carbon and hydrogen as C=N, C≡N, N–H and C–H bonding configurations in the as-deposited film. The incorporation of nitrogen is found to shift the Raman G peak toward the higher wave number and to increase the Raman I_D/I_G ratio demonstrating the graphitic character of the hydrogenated amorphous carbon–nitrogen films. Band gap is found to reduce with the increase in nitrogen concentration.

Boron-doped hydrogenated amorphous carbon (a-C:B:H) thin films have been deposited by radio frequency plasma-enhanced chemical vapor deposition (r.f. PECVD) with a frequency of 13.56 MHz at room temperature using pure methane as a precursor of carbon source mixed with hydrogen (H₂) as a carrier gas. The films were prepared by varying the r.f. power, different gas flow rates of CH₄, and partial pressure of mixed gas (CH₄/H₂) using boron as a solid target. The thickness, structural bonding, and optical properties of the as-deposited films were studied by Alpha-step surface profiler, Raman spectroscopy (Raman), Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and UV–visible spectroscopy. It was found that changing the deposition pressure in addition of using solid boron target in the r.f. PECVD process has a profound effect on the properties of the deposited films as evidenced from their Raman scattering and optical results. The grown a-C:B:H films were found to be smooth and their thicknesses were in the range of 200 to 400 nm for 1 h of deposition time. Films deposited at lower pressure appear brownish in color, whereas those deposited at higher pressure appear pale yellowish. The as-deposited film was found to be dominated by trigonal (sp²) rather than tetrahedral (sp³), which might be due to the formation of small crystallites. The optical band gap is found to be reduced from 2.60 to 1.62 eV as the partial pressure of CH₄/H₂ gas is reduced.

ZnO thin films were prepared on silica glass substrates by a sol–gel spin coating technique. The thickness of the films was about 200 nm. At 370 nm in the ultraviolet region, there is a sharp absorption edge that corresponds to the ZnO intrinsic band gap of 3.30 eV. The structural properties of the films were examined by X-ray diffraction, which demonstrates that the ZnO films were c-axis oriented. From the infrared spectrum, we conclude that ZnO was deposited on silica glass substrates through a high temperature process at 700°C.

The interaction energies between two similar plane double layers for CaCl₂-type asymmetric electrolytes at positive surface potential are expanded in the power series at lower potential and smaller absolute value of integral constant as well as higher potential and larger absolute value of integral constant, respectively. When dimensionless surface potential y₀ ≤ 20, the number of the series terms required to obtain the interaction energies with six significant digits are not more than eight if higher potential expressions are combined with lower potential expressions. The accurate numerical results are given and they can be used to check up the validity of approximate expressions that will be obtained. The present results are also fit for Na₂SO₄-type asymmetric electrolytes at negative surface potential.

The adsorption and the growth of ZnO on α-Al₂O₃(0001) surface at various temperatures are theoretically calculated by using a plane wave pseudopotentials (USP) method based on density functional theory. The average adsorption energy of ZnO at 400, 600, and 800°C is 4.16±0.08, 4.25±0.11, and 4.05±0.23 eV, respectively. Temperature has a remarkable effect on the structure of the surface and the interface of ZnO/α-Al₂O₃(0001). It is found that the Zn-hexagonal symmetry deflexion does not appear during the adsorption growth of ZnO at 400°C, and that the is parallel with the of the α-Al₂O₃(0001), which is favorable for forming the ZnO film with the Zn-terminated surface. It can be observed from our simulation that there are two surface structures in the adsorption of ZnO at 600°C: one is the ZnO surface that has the Zn-terminated structure, and whose parallels with the substrate surface , and the other is the ZnO// sapphire with the O-terminated surface. The energy barrier of the phase transition between the two different surface structures is about 1.6 eV, and the latter is more stable. Therefore, the ideal temperature for the thin film growth of ZnO on sapphire is about 600°C, and it facilitates the formation of wurtzite structure containing Zn-O–Zn-O–Zn-O double layers as a growth unit cell. At 600°C, the average bond length of ZnO is 0.190±0.01 nm, and the electron localization function value indicates that the bond of (substrate) –O–Zn–O has a distinct covalent character, whereas the (Zn)O–Al (substrate) shows a clear character of ionic bond. However, at the temperature of 800°C, the dissociation of Al and O atoms on the surface of the α-Al₂O₃(0001) leads to a disordered surface and interface structure. Thus, the Zn-hexagonal symmetry structure of the ZnO film is not observed under the condition.

Ti and its alloys are considered to be very promising in biological material field. But their biological activity and corrosion resistance in body fluid still need to be improved. As a novel technique for surface treatment, Micro-arc oxidation (MAO) is attracting interest from those who want to improve their implant properties through surface modification. This paper reviewed the application of MAO on biomedical Ti-alloys. The structure characteristic such as surface and cross-section micrographs, phase components, and element distribution were analyzed. The mechanical and biological properties of MAO films were further discussed on this basis. The effects of current density, voltage, and electrolyte on the structure and properties of the films were summarized.

The initial oxidation process of a clean diamond (100) surface was studied by first-principles calculations. The O-bridge with C–O–C bond chemisorption, O-on-dimer chemisorption with epoxy structure, and O-on-top chemisorption with C=O bond structure are found to be stable on the diamond (100) surfaces. The epoxy structure is more stable than the O-bridge structure. The calculation also shows that the oxygen atom can be replaced by hydrogen in the oxidized diamond (100) surface.

In this paper, Au-loaded TiO₂(Au/TiO₂) photocatalysts were prepared by photochemical deposition method and characterized by transmission electron microscopy, diffuse reflectance spectroscopy and X-ray photoelectron spectroscopy. The results indicated the metallic Au nanoparticles were deposited on the surface of TiO₂ after the high-pressure mercury irradiation and regarded as an electronegative center. The photocatalytic decomposition of gaseous ozone was investigated on TiO₂ and Au-loaded TiO₂ at room temperature. Results indicated that the photocatalytic conversion of ozone can be improved by Au/TiO₂ and photocatalytic activity increased with the increase of the photodeposition time. The photocatalytic removal rate of ozone remained above 96% on the surface of 1% Au/TiO₂ with photodeposition for 120 min under black lamp irradiation for 20 h. Au cluster deposited on the surface of TiO₂ functioned not only as the electron trap center but also as the adsorption site of O₃ in photocatalytic reaction.

The adsorption behavior of dodecylamine and its effect on the wettability and corrosion of carbon steel in hydrochloric acid solution were studied. Polarization data suggest that inhibition of carbon steel corrosion is due to geometric blocking effect of adsorbed dodecylamine molecules on the metal surface, which leads to the formation of a monolayer on the metal. Phase images measured by tapping-mode atomic force microscopy (AFM) reveal different properties of the surface with and without various concentrations of dodecylamine. AFM force–distance curves indicate that sample surface exhibits adhesion characteristic after the adsorption of dodecylamine. Contact angle measurements show that dodecylamine reduces surface wettability obviously.

Ceramic-like coatings were deposited on the substrate of the AZ91 alloy by micro-arc oxidation (MAO). Many methods like X-ray diffraction (XRD), scanning electron microscopy (SEM), and electron diffraction spectroscopy (EDS) were used to analyze the structure and composition of the coating. XRD showed that the MAO coating was mainly composed of MgO. The results of SEM showed that the coating surface possessed a porous microstructure and the pore size was in the range of 1–3 μm. EDS indicated that the coating matrix was relatively dense and had a homogeneous thickness. The element silicon from the applied electrolyte could be absorbed into the coating in the MAO process. The hardness of the MgO coatings could reach 513 HV_0.025 that was about four times higher than that of the substrate. It is expected that the coatings have a great potential in the surface protection of magnesium alloys.

Al_1-xMg_x with different concentrations of Mg was produced by spectroscopically technique from melting the ingredient in graphite crucibles sealed under vacuum in quartz ampoules. The samples have been characterized by X-ray studies and electrical measurements. A cubic phase of polycrystalline aluminum has been observed. There is no new phases appearing with different concentrations of Mg contents and quenching temperatures. The results show that the crystallinity (intensity of (200) plane) increases with both Mg concentration (<4.44 wt%) and quenching temperature (<898 K). The grain size of the obtained phase decreased with increasing the Mg contents. The resistivity is calculated for different concentrations of Mg at room temperature and found increasing with Mg contents. The grain size is found to be a parameter affecting the resistivity than the preferred orientation.

Under the dielectric continuum model and Loudon's uniaxial crystal model, the interface optical (IO) phonon modes in a quasi-one-dimensional (Q1D) wurtzite rectangular quantum wire are deduced and analyzed. Numerical calculation on a wurtzite GaN/AlN rectangular wurtzite quantum wire was performed. Results reveal that the dispersion frequencies of IO modes sensitively depend on the geometric structures of the Q1D wurtzite rectangular quantum wires. The degenerating behavior of the IO phonon modes in the Q1D wurtzite rectangular quantum wire has been clearly observed for small free wave number k_z in z-direction. The limited frequency behaviors of IO modes have been analyzed deeply, and detailed comparisons with those in wurtzite planar quantum wells and cylindrical quantum wires are also done. Moreover, once the anisotropy of the wurtzite material has been ignored, the present theories can be naturally reduced to the situation of Q1D cubic rectangular quantum wire systems.

It is argued that in the long wavelength limit of electromagnetic, far infrared, field optical response of an ultrafine metal particle threaded by uniform magnetic field can be properly modeled by equations of semiclassical electron theory in terms of the surface inertial-wave-like oscillations of free electrons driven by Lorentz restoring force. The detailed calculation of the frequency of size-independent gyromagnetic plasmon resonances computed as a function of multipole degree of electron cyclotron oscillations is presented. This spectrum is derived in juxtaposition with the canonical Mie's spectral formula for the surface plasmon resonances caused by the Coulomb-force-driven plasma oscillations of conduction electrons.

Titanium oxide thin films were prepared by sputtering technique onto glass substrates at room temperature (RT). The structure of the films was confirmed using X-ray diffraction (XRD) and revealed the stoichiometry with an O and Ti ratio of 2. The deposited films at RT were found to be amorphous and the films annealed at 300 and 400°C for 2 h were crystalline with orthorhombic structure. The lattice constants and grain size of the film are calculated. The electrical resistivity was found to depend on the film thickness and decreased with increasing the film thicknesses. The optical constants of the films such as the refractive index, extinction coefficient, and absorption coefficient were also determined using the optical transmittance measurements, and the results were discussed. The optical band gap varies from 3.2 to 3.5 eV as a function of oxygen/argon ratios.

Since the discovery of Bioglass^® by Hench, bioactive glasses have been used in many medical applications, such as drug delivery systems, nonload-bearing implants, and bone cements because of their excellent bioactivity and biocompatibility. However, due to their poor mechanical properties, these glasses cannot be used in load-bearing applications, where the metallic alloys are still main materials. One useful approach to solving the mechanical limitations of bioactive glasses is to apply the glasses as the coating on mechanically tough substrates; it was also recognized early that bioactive glasses could be used as coatings for prosthetic metallic implants. In this paper, the mechanism, characterization, and current status of some methods of preparation for bioactive glass coating on implants are introduced. In the end, to get the homogeneous and compact coating with perfect bonding strength, some ideas of improving the performance of coatings are also presented.

Electrophoretic deposition (EPD) is a good method in the fabrication of the coating materials. Its processing parameters are easy to be operate. It is a nonbeeline process and can be used in the deposition on complex shape and porous surface. It has been widely used in many ways. This paper reviews the principles and fabrication steps of EPD and points out the influencing factors. The developments of EPD in the fabrication of materials, such as solid surface coatings, porous structure materials and gradient materials, are introduced in detail. The future of the application of EPD is also discussed.

Morphology of the {100} cleavage faces of L-arginine phosphate monohydrate single crystal before and after its growth at 40°C at a supersaturation of 0.031 has been studied. Monolayer and multilayer steps are found on the original cleaved surfaces. The regrowth morphology varies in nature with different growth time. With the increase of the growth time more growth layers and two-dimensional nucleus come into being, and they become more stable.

Lotus-leaf-like amorphous carbon (a-C) films were fabricated on glass and Si substrates by a magnetron sputtering system and fluorinated in carbon tetrafluoride plasma. The fluorinated films (a-C:F) had a maximum contact angle (CA) of about 162°, which is much larger than that of the nonfluorinated films (105°). Furthermore, the geometric microstructure and chemical composition of the a-C:F films were investigated by scanning electron microscopy and Fourier transform infrared spectrometry, respectively. The characterization results indicated that the CA on the surfaces of the a-C:F films can be improved remarkably by the plasma-fluorinated process. Such a-C:F films that combine superhydrophobicity with other properties may have many potential applications.

Polycrystalline silicon carbide (P-SiC) films containing SiC nanoparticles and Er were prepared by r.f. reactive magnetron co-sputtering technique with SiC and Er targets on low-temperature silicon (111) and silicon dioxide substrates with the mixed gas of pure argon, methane, and hydrogen. Surface morphology and photoluminescence (PL) properties of them were measured by field-emission scanning electron microscope and Raman spectroscopy. The peak position, intensity, and the full width at half maximum (FWHM) of PL spectra were relevant with Er doping levels and deposition conditions.

A novel, simple, and efficient method to calculate the interaction energies of double layers, λ parameter method, is presented by introducing a parameter λ in the elliptical integral. The interaction energies between two similar plane parallel double layers are expanded in the power series with such a method. The series converge very fast. When the dimensionless surface potential of double layers is less than or equal to 30, the number of the series terms required does not exceed 3 to obtain the interaction energies with six significant digits.