Surface Review and Letters

We present an experimental technique to determine the thickness of hydration layers on solid surfaces in aqueous solutions by using an atomic force microscope (AFM). This technique is based on the phenomenon where a small line bending in the AFM force–distance plot of hydrated solid surface in aqueous solutions, may be due to the existence of hydration layers on the tip and the solid surface. The thickness of hydration layers on mica plate immersed in water and NaCl solutions were determined with this technique.

Growth mechanisms of the {110} planes of the manganese mercury thiocyanate, MnHg(SCN)₄ (MMTC), crystals have been investigated by using atomic force microscopy (AFM). The results show that spiral dislocation controlled mechanism and two-dimensional (2D) nucleation mechanism operate simultaneously during growth. 2D nuclei are found to cover up the outcrop of dislocation hillocks. Pairs of circular 2D nuclei appear on the wider steps terraces and the slope of 2D nucleation islands. Hillocks introduced by both simple spiral dislocation sources and 2D nucleation are elliptical in shape. It is determined the long sides orientate along the c-direction or the direction about 45° to the c-axis. Anisotropic growth hillocks and isotropic 2D nuclei coexist on the surface, which may be due to unequal supersaturations in the mother solution during the evaporation process.

The microscopic morphology and microstructure of Ti-N and Ti-Ni phase between the dilution zone and the clad zone in laser remelting NiCrBSi/TiN layer on a Ti-6Al-4V alloy were characterized using TEM and SEM. The experimental results showed that during laser irradiation heating, TiN particles were partially dissolved into the melted Ni-base alloy, and the dissolved Ti and N atoms were precipitated in the form of TiN, TiN_0.3. Ti exhibits height activity, it combines with Ni forming Ti₂Ni, TiNi matrix intermetallic during laser remelting, faults exist in the Ti₂Ni and TiNi phase, and crystal lattice of TiNi phase is superlattice. Lastly, the cause of the formation of the Ti-N and Ti-Ni phase is discussed.

Neodymium-doped Bi₄Ti₃O₁₂ (Bi_3.15Nd_0.85Ti₃O₁₂) thin films have been synthesized by metalorganic solution decomposition and deposited on SiO₂/p-Si(111) substrate by spin coating. The structural characteristic and crystallization of the films were examined by X-ray diffraction and atomic force microscope. The insulating property, dielectric constant and dissipation loss were found to be dependent on the annealing temperature. Nonhysteretic C–V curves at various frequencies were also collected. The films in the ON and OFF states were relatively stable.

α-Al₂O₃(0001), surface and ZnO/α-Al₂O₃(0001) interface are theoretically studied by using a plane wave ultrasoft pseudo-potential method based on the density functional theory. The larger relaxing occurs at the top Al-O layer on α-Al₂O₃(0001) surface. We have found that greater amounts of charge transfer occur on the [0001] Zn surface than in the case of the surface, and that the O-terminated surface of ZnO is more stable. We have also demonstrated that ZnO thin films growth on α-Al₂O₃(0001) has the orientation of with the interface structure of the (substrate)-Al-Zn-O-Zn-O atomic layer, and also the O-terminated surface.

Low-temperature growth of SiCN nanoparticle films on an AlN buffer layer on Si(100) by consecutive RF magnetron sputtering is reported. The visible photoluminescence (PL) is observed between 620 and 670 nm using a single photo excitation at 514.5 nm. The growth of film at room temperature is found to yield the strongest PL intensity, whereas the film grown at 200°C corresponds to the lowest PL intensity. A similar variation of SiC diffraction intensity is also observed in XRD spectra. The photoluminescence of the SiCN film is discussed on the base of the morphological, structural and elemental analyse.

Presented are initial, S₀, and coverage, Θ, dependent, S(Θ), adsorption probability measurements, respectively, of CO₂ adsorption on a hydrogen precovered, polar, Zn-terminated surface of ZnO, parametric in the impact energy, E_i, and atomic hydrogen precoverage, Θ_H. Furthermore, CO₂ Thermal Desorption Spectroscopy has been used to estimate Θ_H as well as the binding energy of CO₂ on H/Zn-ZnO. The S(Θ) curves are below E_i=0.56 eV, consistent with precursor-mediated adsorption (S~const), and above that impact energy with adsorbate-assisted adsorption (S increases with Θ). Although a decrease in the CO₂ binding energy from 32.5 to 28.8 kJ/mol with Θ_H is present, S(Θ, Θ_H) curves are consistent with a physical site blocking, as demonstrated by Monte Carlo Simulations.

Generally in both elemental and compound rare earth systems, the 4f levels are treated as core states with little interaction with the 5d hybrid conduction and valence band states. In the present study, the band dispersions of the rare-earth pnictide erbium arsenide (ErAs) are observed to be perturbed from this expectation. Both photoemission symmetry selection rules and ab initio calculations provide evidences of the 4f-5d hybridization. This finding is also supported by the f–f resonant transition excitation energy shifts in characteristic electron-energy-loss spectroscopy (EELS).

The aim of this work is to present an up-to-date study of acoustic phonon excitations that can propagate in multilayered structure with constituents arranged in quasiperiodic fashion. In this paper, the dispersion relation of acoustic phonons for the quasiperiodic superlattice using different semiconducting materials, with the help of transfer matrix method, is derived at normal angle of incidence. Calculation is presented for (a) Ge/Si and (b) Nb/Cu semiconductor superlattices from 5th to 9th generations and dispersion diagrams are plotted using the famous Kronning–Penny model obtained from the transfer matrix of the structure. The concept of allowed and forbidden bands with the help of these dispersion curves in various generations of Fibonacci superlattices and the relation between imaginary value of propagation vector and the existence of forbidden bands is demonstrated.

The influence of methane gas (CH₄) pressure on the optical, electrical and structural properties of the nitrogenated amorphous carbon nitride (a-C:N) films grown by microwave surface wave plasma chemical vapor deposition (SWP-CVD) on quartz and silicon (100) substrates have been studied. The a-C:N films are deposited with varying CH₄ gas ranging from 5 to 20 ml/min. To incorporate nitrogen in the film, we have introduced nitrogen gas (N) at 5 ml/min in the chamber. The effects of CH₄ gas pressure on the surface morphology, composition, structure, and electrical properties of the N-incorporated camphoric carbon thin films have been investigated using scanning electron microscopy (SEM), atomic force microscopy (AFM), Auger electron spectroscopy (AES), UV-visible spectroscopy and four-probe resistance measurement. We have succeed in growing a-C:N thin films using SWP-CVD at room temperature and found that the amorphous structure of a-C films can be changed and is strongly dependent on the CH₄ gas source.

This paper reports the band gap shifting due to nitrogen (N₂) doping, microwave power and composition gas pressure of nitrogenated amorphous carbon (a-C:N) thin films deposited by newly-developed surface wave microwave plasma chemical vapor deposition (SWMP-CVD). Results show that the optical band gap decreased from 4.1 eV to 2.4 eV corresponding to the increase of N₂ doping from 0 to 5% in the gas ratio. However, further increase of N₂ doping beyond 5% did not decrease the band gap. It was found that composition gas pressure and launched MW power during film deposition also largely control the optical band gap. Investigation of annealing effects on optical band gap and film thickness of the N₂ doped films revealed that both band gap and film thickness decrease significantly with increase of annealing temperature. The optical band gap decreased from 2.4 eV to 1.1 eV, while film thickness decreases from 320 nm to 50 nm corresponding to 200 to 400°C annealing temperature. The results revealed that the properties of a-C:N can be tuned by changing the annealing temperature, composition gas pressure and microwave power of the SWMP-CVD system.

Ag thin films deposited on Ru (0001) surface by molecular beam epitaxy, at temperatures of 20°C and 450°C, have been investigated using reflection high-energy electron diffraction (RHEED), atomic force microscopy (AFM) and X-ray diffraction (XRD) techniques. For both growth temperatures, the in situ RHEED patterns of the Ag films exhibited an in-plane six-fold symmetry, indicating that the Ag deposit is in epitaxy with the Ru buffer surface. At RT, the RHEED technique indicated a three-dimensional growth (3D), while a layer-by-layer growth (2D) takes place at HT. The AFM images showed a granular structure of the surface of the deposited Ag layers with a large variation of the roughness with the growth temperature. XRD analysis gave indication of a strongly textured thin film along the growth direction. The lattice mismatch between the Ag and Ru is at the origin of a stress at the interface and defects structure in the film.

The phosphorus doped n-type (n-C:P) carbon films and fabrication of n-C:P/p-Si heterojunction solid-state solar cells by pulsed laser deposition (PLD) technique at room temperature using graphite target have been studied. The P atoms incorporated in the films were determined by X-ray photoelectron spectroscopy (XPS) to be in the range of 0.22–1.77 atomic percentages. The cells performances have been given in the dark I–V rectifying curve and I–V working curve under illumination when exposed to AM 1.5 illumination condition (100 mW/cm², 25°C). The open circuit voltage (V_oc) and short circuit current density (J_sc) for the cells are observed to vary from 215 to 265 mV and from 7.5 to 10.5 mA/cm², respectively. The cell fabricated using the target with the amount of P by 7 weight percentages (Pwt%) shows the highest energy conversion efficiency, η=1.14% and fill factor, FF=41%. In this paper, the dependence of P content on the electrical and optical properties of the deposited n-C:P films and the photovoltaic characteristic of the n-C:P/p-Si cells are reported.

The transparent semiconducting copper iodide (CuI) films were deposited by pulsed laser deposition (PLD) and their structural and optoelectrical properties in the power output of TiO₂|Dye|CuI cells are reported. These CuI films exhibited optical transmittance of over 80% in the wavelength range from 400 to 900 nm and a minimum resistivity of about 2 KΩ-cm. An efficient charge generation is observed through the illumination of the TiO₂ layer of the fabricated p-CuI|Dye|n-TiO₂ cells. The cells performances have been given in the current–voltage (I–V) working curve under illumination when exposed to AM 1.5 illumination condition (100 mW/cm², 25°C). The maximum short circuit photo current density (J_sc) of about 12.2 mA/cm² and open circuit photo voltage (V_oc) of about 480 mV were obtained for the TiO₂|Dye|CuI cells with good reproducibility. The fill factor (FF) and power conversion efficiency (η) were about 47.8% and 2.8%, respectively.

Nitrogen-doped amorphous carbon (a-C:N) thin-films have been deposited on novel heat tolerant flexible plastic substrates by a newly developed microwave surface wave plasma chemical vapor deposition (MWSWP-CVD) method. Methane gas and also camphor dissolved with ethyl alcohol gas composition have been used as plasma source. Nitrogen gas has been used as a dopant material for a-C:N films. In this paper, the optical characteristics of absorption coefficients and band gaps for a-C:N are discussed. The optical band gap of a-C:N films was found to be approximately 1.7 eV, which is close to the suitable band gap for solar cell. The optical band gap of a-C:N was found to be dependent on the composition gas source pressures.

The BFS method for alloys is applied to the study of Co growth on Cu(111). Atomistic simulations are performed to investigate the behavior of Co on Cu(111) as a function of temperature. Atom-by-atom analysis of the energy contributions of each atom in the island explain the observed features.

The regeneration mechanism of ion-exchange resins in the electrodeionization process has been studied with theoretical and experimental investigation. Theoretically, contact forms of resins and membranes can be divided into 4 types, and the possible places of water-splitting are located at the contact faces of different types resins and membranes, for example, cation ion-exchange resins contact with anion ion-exchange resins or membranes, anion ion-exchange resins contact with cation ion-exchange resins and membranes, according to the theoretical calculation. And the exhausted ion-exchange resins can be regenerated by the electrodeionization process with the regeneration efficiency at 70–80% in this work.

In this paper, the design of a long and short wavelength cutoff filter using three-component periodic structure is presented. It is predicted that the manipulation of layers to obtain maximum transmission in three-component periodic structures are more suitable than two-component periodic structures. It is demonstrated that periods up to 22 bring maximum transmission with less oscillation within the high transmission band. Calculation for bandwidth is presented using the transfer matrix approach. It is suggested that for making the ideal filter, the optimization of layers with the three-component base system should be the best option for obtaining a desired transmission.