Applied Surface Science (v.255, #12)

Effects of cap layer on ohmic Ti/Al contacts to Si+ implanted GaN by Marcel Placidi; A. Pérez-Tomás; A. Constant; G. Rius; N. Mestres; J. Millán; P. Godignon (6057-6060).
A low resistivity ohmic contact to Si-implanted GaN was achieved using a metal combination of Ti/Al. The effect of a protection cap during post-implantation annealing is investigated, and how it affects the specific contact resistivity (ρ c). Relevant differences between the protected (PR) sample with SiO2 and unprotected (UP) sample during the post-implantation annealing were observed after metal alloying at 700 °C. The lower values of ρ c have been obtained for UP sample, but with very low reproducibility. In contrast, SiO2 cap layer has demonstrated its relevance in yielding a much more uniformity of a relatively low ρ c around 10−5  Ω cm2. Related mechanism for the uniformity in ρ c was discussed based on the results obtained from electrical measurements, XRD (X-ray diffraction) analysis, AFM (atomic force microscopy) and SEM (scanning electron microscopy) observations.
Keywords: Ti/Al contacts; Implantation to GaN; Cap layer;

In this paper, a surface molecular imprinting technique was reported for preparing core–shell microbeads of protein imprinting, and bovine hemoglobin or bovine serum albumin were used as model proteins for studying the imprinted core–shell microbeads. 3-Aminophenylboronic acid (APBA) was polymerized onto the surface of polystyrene microbead in the presence of the protein templates to create protein-imprinted core–shell microbeads. The various samples were characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and Brunauer–Emmett–Teller (BET) methods. The effect of pH on rebinding of the template hemoglobin, the specific binding and selective recognition were studied for the imprinted microbeads. The results show that the bovine hemoglobin-imprinted core–shell microbeads were successfully created. The shell was a sort of imprinted thin films with porous structure and larger surface areas. The imprinted microbeads have good selectivity for templates and high stability. Due to the recognition sites locating at or closing to the surface, these imprinted microbeads have good property of mass-transport. Unfortunately, the imprint technology was not successfully applied to imprinting bovine serum albumin (BSA).
Keywords: Coating; Proteins; Molecular imprinting; Surface adsorption; XPS;

Titanium dioxide (TiO2) films were fabricated on fluorine doped tin oxide (FTO) coated glass substrate using successive ionic layer adsorption and reaction (SILAR) method. The X-ray diffraction, scanning electron microscopy, transmission electron microscopy, optical absorption and contact angle measurement were applied to study the structural, surface morphological, optical and surface wettability properties of the as-deposited and annealed TiO2 films. The X-ray diffraction studies revealed both as-deposited and annealed TiO2 films are amorphous. Irregular shaped spherical grains of random size and well covered to the fluorine doped tin oxide coated glass substrates were observed from SEM studies with some cracks after annealing. The optical band gap values of virgin TiO2, annealed, methyl violet and rose bengal sensitized TiO2 were found to be 3.6, 3.5, 2.87 and 2.95 eV, respectively. Surface wettability studied in contact with liquid interface, showed hydrophobic nature as water contact angles were greater than 90°. The adsorption of dyes, as confirmed by the photographs, is one of the prime requirements for dye sensitized solar cells (DSSC).
Keywords: TiO2; SILAR; XRD; SEM; TEM; Optical; Contact angle;

Two kinds of novel phenyl-functionalized mesoporous silica materials have fabricated for the first time by an instant-direct-templating method using poly(ethylene glycol)-block–poly(propylene glycol)-block–poly(ethylene glycol) and tetraethyl orthosilicate as surfactant template and precursor, respectively. Samples were characterized by Fourier transform infrared spectroscopy, small-angle X-ray diffraction, thermogravimetric analysis, N2 adsorption–desorption, scanning electron micrography and transmission electron micrography. The results show that phenyl groups are attached covalently to the pore wall of mesoporous materials after modification. The functionalized materials still preserve a desirable ordered hexagonal P6mm and cubic Ia3d mesophase structure, respectively, have high specific surface area, large pore volume and narrow pore size distribution.
Keywords: Mesoporous materials; Sol–gel chemistry; X-ray diffraction; Surface properties;

Low infrared emissivity of polyurethane/Cu composite coatings by Huijuan Yu; Guoyue Xu; Xingmei Shen; Xiaoxing Yan; Chuangwei Cheng (6077-6081).
Polyurethane/Cu composite coatings with low infrared emissivity near to 0.10 at the wavelength of 8–14 μm were prepared by a simple and convenient process. The influences of the content of Cu powder, surface roughness, coating thickness and temperature on infrared emissivity of the coatings were systematically investigated. The results indicated that the emissivity decreases significantly with increasing content of Cu powder and coating thickness. The coatings with smooth surface exhibit lower emissivity values than those with rough coatings. Moreover, we found the relationship between the emissivity of coatings and temperature presents a “U” type, and the emissivity reaches to the minimum at about 380 K. The mechanisms of low emissivity were proposed by optical theories, which are found to be in a good agreement with the experimental results.
Keywords: Infrared emissivity; Polyurethane; Cu; Coatings;

Fabrication and characterization of a Cu seed layer on a 60-nm trench-patterned SiO2 substrate by a self-assembled-monolayer (SAM) process by Won-Kyu Han; Gil-Ho Hwang; Seok-Jun Hong; Chong-Seung Yoon; Joon-Shik Park; Jin-Ki Cho; Sung-Goon Kang (6082-6086).
Continuous electroless deposition of a 10-nm thick layer of Cu was successfully performed on a SiO2/Si substrate coated with a 3-nm Au catalytic layer. The Au catalytic layer was formed by a self-assembled monolayer (SAM) process terminated with NH2 headgroups, upon which negatively charged Au particles were deposited via electrostatic interaction with the positively charged NH2-SAM. The Au and NH2-SAM layers were analyzed by X-ray photoelectron spectroscopy (XPS) and contact angle analysis. Atomic force microscopy, field emission scanning electron microscopy, and XPS revealed that the Cu layer formed by this electroless processes had good step-coverage, small grain size, and excellent adhesion to the substrate. The proposed process is a very promising method for fabrication of a conductive Cu seed layer in a 60-nm trench-pattern.
Keywords: Electroplating; Self-assembled monolayer; Copper seed layer; 60-nm trench pattern;

Porous scaffold containing 30 wt% nano-hydroxyapatite (n-HA) and 70 wt% polyurethane (PU) from castor oil was prepared by a foaming method and investigated by X-ray diffraction (XRD), Fourier transform infrared absorption (FTIR), scanning electron microscopy (SEM) techniques. The results show that n-HA particles disperse homogeneously in the PU matrix. The porous scaffold has not only macropores of 100–800 μm in size but also a lot of micropores on the walls of macropores. The porosity and compressive strength of scaffold are 80% and 271 kPa, respectively. After soaking in simulated body fluid (SBF), hydrolysis and deposition partly occur on the scaffold. The biological evaluation in vitro and in vivo shows that the n-HA/PU scaffold is non-cytotoxic and degradable. The porous structure provides a good microenvironment for cell adherence, growth and proliferation. The n-HA/PU composite scaffold can be satisfied with the basic requirement for tissue engineering, and has the potential to be applied in repair and substitute of human menisci of the knee-joint and articular cartilage.
Keywords: Nano-hydroxyapatite; Polyurethane; Scaffold; Degradation; Cytocompatibility;

Effect of surface property of polyimide substrate on the formation of pentacene thin-film by Chung-Jong Yu; Youngill Choi; Seungmoon Pyo; Mihye Yi; Jong Soo Kim; Kilwon Cho; Dong Ryeol Lee (6092-6096).
We investigated the effect of surface property of polyimide substrate on the formation of pentacene thin-film by using atomic force microscopy (AFM) and X-ray reflectivity (XRR) and diffuse scattering (XDS). Two types of polymer films were prepared: (1) polyimide (PAA-PI) from poly(amic acid) (PAA) (2) polyimide hybrid (PAA-PI-H) prepared by hybridizing the PAA and soluble polyimide (PI) with a octadecyl side chain. The hybridization ratio of PI to PAA was 2/98 in wt%. The water contact angle for PAA-PI-H and PAA-PI were around 80° and 64°, respectively. Morphology of pentacene with a ropelike structure and (1 1 0) peak around 1.4 Å in q z was found when it was deposited on PAA-PI thin-film. Different pentacene morphology was observed when it was deposited on PAA-PI-H thin-film. The different morphology might be due to a 5–6 nm thick additional layer (∼0.95 ρ film) at the interface between pentacene and PAA-PI-H thin-film caused by a long alkyl side chain introduced to the polymer main chain.
Keywords: Surface property; Thin-film; Polyimide; Pentacene;

Dislocation evolution in titanium during surface severe plastic deformation by Ming Wen; Gang Liu; Jian-feng Gu; Wei-ming Guan; Jian Lu (6097-6102).
Surface mechanical attrition treatment (SMAT) is an innovative technique which can produce nanocrystalline (nc) layers of several tens of micrometers thickness on surfaces of metallic materials. In this work, the grade structures of commercially pure titanium (CP Ti) processed by SMAT was studied intensively, and the microstructure observations indicated that the dislocation evolution could be separated into three steps: (1) formation of dislocation tangles; (2) formation of dislocation bands; and (3) dynamic recrystallization of dislocation bands until the formation of nc Ti.
Keywords: SMAT; Titanium; Dislocation; Dynamic recrystallization;

Surface modification of the polyethyleneimine layer on silicone oxide film via UV radiation by Hyobong Hong; Soohyung Lee; Taewan Kim; Myungae Chung; Cheljong Choi (6103-6106).
We herein report a novel method of employing 254 nm of UV radiation (UV) for the modification of a polyethyleneimine (PEI) layer on silicone oxide film. In this study, a PEI layer composed of a 50 mM sodium carbonate solution (pH 8.2) was formed on the surface of a silicone oxide film with spontaneous adsorption. Then, thin film of PEI was patterned by UV radiation. To determine the effect of the UV radiation, fluorescence microscopy, X-ray electron spectroscopy (XPS), and Fourier Transform Infrared spectroscopy (FT-IR) analyses were performed. These results indicated that UV radiation could cause changes in the surface characteristics of the PEI layer. Subsequently, FT-IR analysis showed changes in the chemical composition of the PEI exposed to UV radiation, such as the disappearance of the amine. Based on these results, we can conclude that UV radiation could be used to eliminate the amine group selectively and that this technique could be applied to create a pattern on the surface of a PEI layer.
Keywords: Surface; Treatment; PEI; UV; Patterning;

Removal of organic contaminants from aqueous solution by cattle manure compost (CMC) derived activated carbons by Qingrong Qian; Qinghua Chen; Motoi Machida; Hideki Tatsumoto; Kazuhiro Mochidzuki; Akiyoshi Sakoda (6107-6114).
The activated carbons (ACs) prepared from cattle manure compost (CMC) with various pore structure and surface chemistry were used to remove phenol and methylene blue (MB) from aqueous solutions. The adsorption equilibrium and kinetics of two organic contaminants onto the ACs were investigated and the schematic models for the adsorptive processes were proposed. The result shows that the removal of functional groups from ACs surface leads to decreasing both rate constants for phenol and MB adsorption. It also causes the decrement of MB adsorption capacity. However, the decrease of surface functional groups was found to result in the increase of phenol adsorption capacity. In our schematic model for adsorptive processes, the presence of acidic functional groups on the surface of carbon is assumed to act as channels for diffusion of adsorbate molecules onto small pores, therefore, promotes the adsorption rate of both phenol and MB. In phenol solution, water molecules firstly adsorb on surface oxygen groups by H-bonding and subsequently form water clusters, which cause partial blockage of the micropores, deduce electrons from the π-electron system of the carbon basal planes, hence, impede or prevent phenol adsorption. On the contrary, in MB solution, the oxygen groups prefer to combine with MB+ cations than water molecules, which lead to the increase of MB adsorption capacity.
Keywords: Activated carbon; Phenol; Methylene blue; Adsorption; Schematic model;

Nanocrystalline thin films of CdS have been grown onto flexible plastic and titanium substrates by a simple and environmentally benign chemical bath deposition (CBD) method at room temperature. The films consist of clusters of CdS nanoparticles. The clusters of CdS nanoparticles in the films were successfully converted into nanowire (NW) networks using chemical etching process. The possible mechanism of the etching phenomenon is discussed. These films were examined for their structural, surface morphological and optical properties by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM) and UV–vis spectrophotometry techniques, respectively. Photoelectrochemical (PEC) investigations were carried out using cell configuration as n-CdS/(1 M NaOH + 1 M Na2S + 1 M S)/C. The film of nanowires was found to be hexagonal in structure with the preferential orientation along the (0 0 2) plane. The nanowires have widths in the range of 50–150 nm and have lengths of the order of a few micrometers. Optical studies reveal that the CdS nanowires have value of band gap 2.48 eV, whereas it is 2.58 eV for nanoparticles of CdS. Finally, we report on the ideality of junction improvement of PEC cells when CdS nanoparticles photoelectrode converted into nanowires photoelectrode.
Keywords: Chemical bath deposited CdS; Nanoparticles and nanowires; XRD; Surface morphology; Optical property; Photoelectrochemical cells;

Investigation of GaN layer grown on different low misoriented sapphire by MOCVD by Yanhui Xing; Jun Han; Jun Deng; Jianjun Li; Chen Xu; Guangdi Shen (6121-6124).
GaN layer on c-plane misoriented sapphire, grown by metal organic chemical vapor deposition, has been studied. It was observed that the random and non-uniform distribution of the step was caused by the step reconstruction for GaN grown on 0° sapphire by atomic force microscopy. The image quality parameter analysis of electron back-scatter diffraction indicated that the strains were reduced for GaN grown on 0.2° and 0.3° sapphire, and optical and electrical properties were improved. The electroluminescence intensity of LED grown on 0.2° and 0.3° sapphire was 2 times as that of 0° sapphire.
Keywords: Nitrides; Atom force microscopy; Metal organic chemical vapor deposition; Electron back-scatter diffraction; Photoluminescence;

The composites of Co–B coatings on hollow microspheres (Co–B/HMSs) have been successfully synthesized through electroless plating in this paper. The time-dependent microstructure evolution and magnetic properties of the composites were carefully investigated by scanning electron microscope (SEM), energy dispersive X-ray (EDX), and X-ray photoelectron spectroscopy (XPS) and vibrating sample magnetometer (VSM). It was found that small Co–B clusters appeared on the surface of hollow microspheres at catalytic nuclei during the initial stage. Further growth, they converged to form continuous coatings, which were actually stacking of Co–B nuclei. Interestingly, there was an increment of B content in the coating as time wore on, this phenomenon could be interpreted by electrochemical mechanism. Besides, the composites showed magnetic properties, which might be potentially important for the novel materials as magnetic carriers.
Keywords: Hollow microspheres; Co–B; Microstructure evolution; Electroless plating; Magnetic properties;

Synthesis of nano-crystalline zirconium aluminium oxynitride (ZrAlON) composite films by dense plasma Focus device by I.A. Khan; M. Hassan; T. Hussain; R. Ahmad; M. Zakaullah; R.S. Rawat (6132-6140).
Zirconium aluminium oxynitride multiphase composite film is deposited on zirconium substrate using energetic nitrogen ions delivered from dense plasma Focus device. X-ray diffractometer (XRD) results show that five Focus shots are sufficient to initiate the nucleation of ZrN and Al2O3 whereas 10 Focus shots are sufficient to initiate the nucleation of AlN. XRD results reveal that crystal growth of nitrides/oxides increases by increasing Focus shots (up to 30 Focus shots) and resputtering of the previously deposited film is taken place by further increase in Focus shots (40 Focus shots). Scanning electron microscopic (SEM) results indicate the uniform distribution of spherical grains (∼35 nm). A smoother surface is observed for 20 Focus shots at 0° angular position. SEM results also show a net-type microstructure (thread like features) of the sample treated for 30 Focus shots whereas rough surface morphology is observed for 40 Focus shots. Energy dispersive spectroscopic profiles show the distribution of different elements present in the deposited composite films. A typical microhardness value of the deposited composite films is 5255 ± 10 MPa for 10 grams imposed load which is 3.3 times than the microhardness values of unexposed sample. The microhardness values of the exposed samples increases with increasing Focus shots (up to 30 Focus shots) and decreases for 40 Focus shots treatment due to resputtering of the previously deposited composite film. The microhardness values of the composite films decreases by increasing the sample's angular position.
Keywords: Plasma Focus; Composite film; Nucleation; Grains; Nano-wires; Microhardness;

Electrical characterization of p-ZnO/p-Si heterojunction by S. Majumdar; S. Chattopadhyay; P. Banerji (6141-6144).
Nitrogen doped p-ZnO film, with urea as nitrogen source, is fabricated by pulsed laser deposition on well-cleaned p-type (1 0 0) Si substrates. The structural and electrical properties of the p–p heterojunction are investigated by current–voltage (IV) and capacitance–voltage (CV) measurements. It shows a diode-like behavior with turn-on voltage of 0.5 V. The ideality factor η determined by applying positive potential in p-ZnO and negative potential along p-Si is found to be 6. Such a high value of η is attributed to lattice mismatch between ZnO and Si. and other factors responsible are thermoionic emission, minority carrier injection and recombination. CV results indicate an abrupt interface and a band bending of 0.9 V in the silicon. Heterojunction band diagram for p-ZnO/p-Si is proposed.
Keywords: ZnO; p-Type conduction; Heterojunction; Pulsed laser deposition;

Preparation and infrared emissivity of ZnO: Al (AZO) thin films by Dongmei Zhu; Kun Li; Fa Luo; Wancheng Zhou (6145-6148).
ZnO:Al(AZO) thin films with different Al-doped concentration were developed under different temperature. The effects of the temperature and Al-doped concentration on the infrared emissivity were investigated. Results show that the crystalline phase of the AZO films is hexagonal wurtzite which is the same as that of the un-doped ZnO film. The crystalline size become larger and the particle shapes become more regular with the increase of temperature, which lead to the increase of resistivity and the decreases of the infrared emissivity.
Keywords: Thin film; Crystallization; Infrared emissivity;

This article describes the systemic investigation of the interface chemical and electronic properties of ultrathin Fe/Al multilayer structure (MLS) as a function of annealing temperature. For this purpose electron beam evaporated [Fe/Al]×15 ML samples have been prepared under ultrahigh vacuum conditions. The chemical and electronic information of the interfaces at different depth has been obtained from XPS technique.The core level study show a gradual change in the nature of the electronic bonding at the interface as a result of annealing. In particular, the MLS annealed at 200 °C and 400 °C clearly show shifts in the binding energy position of Fe-2p3/2 core line towards higher energy and Al-2p3/2 core line towards lower energy side as compared to as-deposited sample, suggesting the formation of FeAl alloy phase at the interface. Another important finding with annealing is that the intensity of peak corresponding to pure Al-2p increases and that of Fe-2p decreases as compared to as-deposited case. The increase in intensity of Al-2p core line suggests the migration of Al atoms towards the surface owing to annealing induced inter-diffusion. The corresponding valence band spectra show appreciable changes in the Fe-3d as well as Al-3s density of states due to strong hybridization of sp–d states at the Fermi level as a result of charge transfer and also provide strong evidence for FeAl alloy formation.
Keywords: Fe/Al; Soft magnetic multilayers; Phase evolution; XPS;

The fabrication of high reflective Ni/Ag/(Ti, Mo)/Au Ohmic contacts for flip-chip light-emitting diode (FCLED) are proposed and considered, Ni/Ag/Au Ohmic contacts are also fabricated to compare their resulting reflectivities. From secondary ion mass spectrometry (SIMS) depth profiles, it indicates that the Au in-diffusion occurs in Ni/Ag/Au contacts after annealing. It is considered that Au in-diffusion, which is intermixed with Ag, Ni and GaN in Ni/Ag/Au contacts after annealing, is responsible for the resulting low reflectance (63% at the wavelength of 465 nm). To avoid Au in-diffusion and enhance the reflectivity, a diffusion barrier metal (Ti or Mo) between Ni/Ag and Au is fabricated and examined. It is demonstrated and found that an insertion of diffusion barrier metal of Ti enables to block Au diffusion effectively and also improve the reflectivity significantly, up to 93%.
Keywords: GaN; FCLED; Diffusion barrier; Ohmic contact; Reflectance;

Thin films deposited on the phosphonate 3-aminopropyltriethoxysilane (APTES) self-assembled monolayer (SAM) were prepared on the hydroxylated silicon substrate by self-assembling process from specially formulated solution. Chemical compositions of the films were detected by X-ray photoelectron spectrometry (XPS). The thickness of the films was determined with an ellipsometer, and the morphologies and nanotribological properties of the samples were analyzed by means of atomic force microscopy (AFM). As a result, the target film was obtained and the thin films were deposited on the silicon substrate. It was also found that the thin films showed the lowest friction and adhesion followed by APTES–SAM and phosphorylated APTES–SAM, while silicon substrate showed high friction and adhesion. Microscale scratch/wear studies clearly showed that thin films were much more scratch/wear resistant than the other samples. The superior friction reduction and scratch/wear resistance of thin films were attributed to low work of adhesion of non-polar terminal groups and the strong bonding strength between the films and the substrate.
Keywords: Thin films; Friction; Adhesion; Scratch/wear;

The study of hexanethiol-passivated gold nanoparticles is reported. Depending on the age of the solution two kind of structures are obtained, “foam-like” in fresh solution and “cluster-like” few weeks after the solution preparation. Both kind of structures have been studied regarding to their structural and electrical properties. The cluster-like structures have shown lower electrical resistivity compared to foam-like ones. Some other factors like sonication, have shown to have no effect on the formation of one or another kind of structure.
Keywords: Nanomaterials; Nanofoams; Gold nanoparticles;

The effect of periodic variation of external pressure on the catalytic oxidation of CO is simulated for a modified Ziff–Gulari–Barshad (ZGB) model including the Eley–Rideal (ER) step. The external CO partial pressure is periodically varied between its values in reactive and CO poisoned states. The results show different amplitudes of such perturbation significantly influence the CO2 production rate. Latter also changes with the period of such oscillations, especially for perturbations with larger amplitudes. However, for a given period there is a critical value of the amplitude above which, the catalyst surface becomes irreversibly poisoned.
Keywords: Catalytic surface reactions; ZGB model; Eley–Rideal mechanism; Phase transitions; Monte Carlo simulation;

Series of Co x Cr1−x thin films have been evaporated under vacuum onto Si(1 0 0) and glass substrates. Thickness ranges from 17 to 220 nm, and x from 0.80 to 0.88. Alternating gradient field magnetometer (AGFM) measurements provided saturation magnetization values ranging from 220 to 1200 emu/cm3. Values of squareness exceeding 0.8 have been measured. Coercive field may reach values up to 700 Oe, depending on the percentage of chromium, as well as the substrate nature and the direction of the applied magnetic field. The saturation magnetization value decreases as the Cr content increases. In order to study their dynamical magnetic properties, Brillouin Light Scattering (BLS) measurements have been performed on these samples. Stiffness constant value and anisotropy magnetic field were adjusted to fit the experimental BLS spectra. These results are analyzed and correlated.
Keywords: CoCr system; Thin films; Hysteresis; Magnetic anisotropy; Brillouin Light Scattering (BLS);

Investigation of oxidation resistance of Ni–Ti film used as oxygen diffusion barrier layer by B.T. Liu; X.B. Yan; X. Zhang; Y. Zhou; Y.N. Guo; F. Bian; X.Y. Zhang (6179-6182).
Ni–Ti films prepared at 10 W and 70 W by rf magnetron sputtering are investigated as the oxygen diffusion barrier layer, it is found that crystallinity of Ni–Ti film does not greatly depend on the deposition power. X-ray photoelectron spectroscopy indicates that Ni is still in the form of metallic state from the binding energies of both Ni 2p3/2 and Ni 2p1/2 spectra for the sample with 10 W prepared Ni–Ti, however, Ni is oxidized for 70 W prepared Ni–Ti film. Moreover, the (La0.5Sr0.5)CoO3/Pb(Zr0.40Ti0.60)O3/(La0.5Sr0.5)CoO3 capacitor grown on high power prepared Ni–Ti film is leaky, however, the capacitor on low power prepared Ni–Ti film possesses very promising physical properties (i.e. remnant polarization of ∼27 μC/cm2 at 5 V and maximum dielectric constant of 940). Leakage current density of the capacitor grown on low power prepared Ni–Ti film is further investigated, it meets ohmic behavior (<1.0 V) and agrees well with the space-charge-limited current theory (>1.0 V).
Keywords: Ni–Ti film; Barrier layer; PZT capacitor;

A note on TiN/Si (1 0 0) contacts by Joshua Pelleg; Roy Goldman (6183-6189).
The contact properties of TiN on p- and n-type Si (1 0 0) obtained by magnetron reactive sputtering were investigated. Schottky diode characteristics were observed on p-type Si (1 0 0) as determined by forward current–voltage (IV) measurements, but on n-type Si (1 0 0) the reverse IV relation has shown a nonsymmetrical character. The zero-bias barrier heights evaluated by IV on both type diodes were in the range of ∼0.60–0.64 V within the range of a few mVs, not more than ∼±(10–30) mV from each other. Incorporation of the effect of the series resistance in the IV analysis resulted in a significant reduction in the magnitude of the ideality factor of the TiN/p-type specimen. Almost no change has occurred in the barrier height values. The contradictory reports on the TiN/n-type Si (1 0 0) diode characteristics in earlier works have been explained in terms of surface passivation of Si by the HF cleaning solution. It was stated in these reports that following annealing at 673 K the diodes have shown rectifying behavior. It has been speculated, that the nonsymmetrical nature of the TiN/n-Si (1 0 0) showing an intermediate behavior between Ohmic and rectifying behavior is a result of the specimen being exposed to a temperature lower than 673 K during sputtering where no complete depassivation took place. In order to obtain a rectifying behavior of TiN on both n-type and p-type Si surface passivation has to be eliminated.
Keywords: TiN/Si diodes; Current–voltage; Series resistance; Si surface passivation;

Ellipsometric study of a-Be3N2 thin films prepared by radio frequency magnetron sputtering by J.M. Khoshman; W.D. Jennings; M.E. Kordesch (6190-6194).
The ellipsometric characterizations of amorphous beryllium nitride (a-Be3N2) thin films deposited on Si (1 0 0) and quartz at temperature <50 °C using reactive RF sputtering deposition were examined in the wavelength range 280–1600 nm. X-ray diffraction of the films showed no structure, suggesting the Be3N2 films grown on the substrates are amorphous. The composition and chemical structures of the amorphous thin films were determined by using electron spectroscopy for chemical analysis. The surface morphology of a-Be3N2 was characterized by atomic force microscopy. The thicknesses and optical constants of the films were derived from spectroscopic ellipsometry measurements. The variation of the optical constants with thickness of the deposited films has been investigated. From the angle dependence of the polarized reflectivity we deduced a Brewster angle of 64°. At any angle of incidence, the a-Be3N2 shown high transmissivity (80–99%) and low reflectivity (<18%) in the visible and near infrared regions. Hence, the a-Be3N2 could be a good candidate for antireflection optical coatings under conditions of optimized the type of polarization and the angle of incidence.
Keywords: Ellipsometry; Optical constants; Amorphous; Transmissivity; Sputtering;

Dependence of film thickness on the structural and optical properties of ZnO thin films by Ebru Şenadım Tüzemen; Sıtkı Eker; Hamide Kavak; Ramazan Esen (6195-6200).
ZnO thin films are prepared on glass substrates by pulsed filtered cathodic vacuum arc deposition (PFCVAD) at room temperature. Optical parameters such as optical transmittance, reflectance, band tail, dielectric coefficient, refractive index, energy band gap have been studied, discussed and correlated to the changes with film thickness. Kramers–Kronig and dispersion relations were employed to determine the complex refractive index and dielectric constants using reflection data in the ultraviolet–visible–near infrared regions. Films with optical transmittance above 90% in the visible range were prepared at pressure of 6.5 × 10−4  Torr. XRD analysis revealed that all films had a strong ZnO (0 0 2) peak, indicating c-axis orientation. The crystal grain size increased from 14.97 nm to 22.53 nm as the film thickness increased from 139 nm to 427 nm, however no significant change was observed in interplanar distance and crystal lattice constant. Optical energy gap decreased from 3.21 eV to 3.19 eV with increasing the thickness. The transmission in UV region decreased with the increase of film thickness. The refractive index, Urbach tail and real part of complex dielectric constant decreased as the film thickness increased. Oscillator energy of as-deposited films increased from 3.49 eV to 4.78 eV as the thickness increased.
Keywords: X-ray diffraction; Optical microscopy; Semiconducting II–VI materials; Kramers–Kronig and dispersion relations;

Temperature effect on the electrical, structural and optical properties of N-doped ZnO films by plasma-free metal organic chemical vapor deposition by Ying Zhu; Shisheng Lin; Yinzhu Zhang; Zhizhen Ye; Yangfan Lu; Jianguo Lu; Binghui Zhao (6201-6204).
N-doped p-type ZnO films were grown by plasma-free metal-organic chemical vapor deposition (MOCVD). The effect of substrate temperature on the electrical, optical, and structural properties of the N-doped ZnO films was investigated by Hall-effect, photoluminescence, X-ray diffraction measurements. The electrical properties of the films were extremely sensitive to the substrate temperature and the conduction type could be reversed in a narrow range from 380 °C to 420 °C. Based on X-ray photoelectron spectroscopy, a high compensation effect in the N-doped ZnO films grown by plasma-free MOCVD was suggested to explain the temperature-dependent phenomenon.
Keywords: ZnO; Thin films; p-type; N-doped;

Assessment of surface acidity in mesoporous materials containing aluminum and titanium by Rinaldo S. Araújo; Débora A.S. Maia; Diana C.S. Azevedo; Célio L. Cavalcante; E. Rodríguez-Castellón; A. Jimenez-Lopez (6205-6209).
The surface acidity of mesoporous molecular sieves of aluminum and titanium was evaluated using four different techniques: n-butylamine volumetry, cyclohexylamine thermodesorption, temperature-programmed desorption of ammonia and adsorption of pyridine. The nature, strength and concentration of the acid sites were determined and correlated to the results of a probe reaction of anthracene oxidation to 9,10-anthraquinone (in liquid phase). In general, the surface acidity was highly influenced by the nature, location and coordination of the metal species (Al and Ti) in the mesoporous samples. Moderate to strong Brönsted acid sites were identified for the Al-MCM-41 sample in a large temperature range. For mesoporous materials containing Ti, the acidity was represented by a combination of weak to moderate Brönsted and Lewis acid sites. The Ti-HMS sample exhibits a higher acidity of moderate strength together with a well-balanced concentration of Brönsted and Lewis acid sites, which enhanced both conversion and selectivity in the oxidation reaction of anthracene.
Keywords: MCM; HMS; Titanium; Brönsted; Lewis; Redox activity;

Au-assisted electroless etching of silicon in aqueous HF/H2O2 solution by Nacéra Megouda; Toufik Hadjersi; Gaëlle Piret; Rabah Boukherroub; Omar Elkechai (6210-6216).
The Au-assisted electroless etching of p-type silicon substrate in HF/H2O2 solution at 50 °C was investigated. The dependence of the crystallographic orientation, the concentration of etching solution and the silicon resistivity on morphology of etched layer was studied. The layers formed on silicon were investigated by scanning electron microscopy (SEM). It was demonstrated that although the deposited Au on silicon is a continuous film, it can produce a layer of silicon nanowires or macropores depending on the used solution concentration.
Keywords: Silicon nanostructures; Silicon nanowires; Electroless etching;

Study on electron scattering in solid targets using accurate transport cross-sections by Z. Rouabah; N. Bouarissa; C. Champion; N. Bouaouadja (6217-6220).
The Vicanek and Urbassek theory [M. Vicanek, H.M. Urbassek, Phys. Rev. B 44 (1991) 7234] combined with a Monte Carlo simulation are used to investigate the transport of 0.5–4 keV electrons in solid targets. The cross-sections used to describe the electron transport have been calculated via a new improved version of the approximate analytical expression given by Jablonski [A. Jablonski, Phys. Rev. B 58 (1998) 16470]. Some applications are presented here for the calculation of electron backscattering coefficient in semi-infinite Al and Cu targets. The obtained results accord with success with the experiment and clearly represent an improvement with respect to previous theoretical calculations.
Keywords: Electron scattering; Transport cross-sections;

TiO2-based superhydrophobic–superhydrophilic patterns: Fabrication via an ink-jet technique and application in offset printing by Shunsuke Nishimoto; Atsushi Kubo; Kenji Nohara; Xintong Zhang; Noriaki Taneichi; Toshiki Okui; Zhaoyue Liu; Kazuya Nakata; Hideki Sakai; Taketoshi Murakami; Masahiko Abe; Takashi Komine; Akira Fujishima (6221-6225).
A superhydrophobic–superhydrophilic pattern was prepared on an anodized Al plate by a new fabrication process. The process consists of five key steps: (1) TiO2 coating of the plate, (2) surface modification with self-assembled monolayers (SAMs), (3) formation of aqueous UV light-resistant ink patterns by an ink-jet technique, (4) photocatalytic decomposition of SAMs and surface conversion to the superhydrophilic state and (5) removal of the aqueous ink patterns by water washing. It is particularly noteworthy that the wettability pattern can be quickly formed on the plate, without the use of a photomask. The fabricated superhydrophobic–superhydrophilic pattern is shown to be applicable to offset printing.
Keywords: TiO2 photocatalyst; Superhydrophobic–superhydrophilic; Self-assembled monolayers; Ink-jet technique; Offset printing;

280 nm-thick Ni films were deposited on SiO2/Si(1 0 0) and MgO(0 0 1) substrates at 300 K, 513 K and 663 K by a direct current magnetron sputtering system with the oblique target. The films deposited at 300 K mainly have a [1 1 0] crystalline orientation in the film growth direction. The [1 1 0]-orientation weakens and the [1 1 1]- and [1 0 0]-orientations enhance with increasing deposition temperature. The lattice constant of the Ni films is smaller than that of the Ni bulk, except for the film grown on MgO(0 0 1) at 663 K. Furthermore, as the deposition temperature increases, the lattice constant of the films grown on the SiO2/Si(1 0 0) decreases whereas that of the films grown on the MgO(0 0 1) increases. The films deposited at 300 K and 513 K grow with columnar grains perpendicular to the substrate. For the films deposited at 663 K, however, the columnar grain structure is destroyed, i.e., an about 50 nm-thick layer consisting of granular grains is formed at the interface between the film and the substrate and then large grains grow on the layer. The Ni films deposited at 300 K consist of thin columnar grains and have many voids at the grain boundaries. The grains become thick and the voids decrease with increasing deposition temperature. The resistivity of the film decreases and the saturation magnetization increases with increasing deposition temperature.
Keywords: Ni film; Oblique target sputtering; Structure; Resistivity; Magnetization;

TiO2-based coating containing amorphous calcium phosphate (CaP) was prepared on titanium alloy by microarc oxidation (MAO). The increase in the EDTA–2Na concentration was unfavorable for the crystallization of TiO2. After heat treatment, the amorphous CaP was crystallized. The thickness of the MAO coatings did not change when heat-treated at 400, 600 and 700 °C; while it increased slightly after heat treatment at 800 °C due to the crystallization of amorphous CaP and growth of TiO2. No apparent discontinuity between the coatings and substrates was observed at various heat-treatment temperatures, indicating the MAO coatings with good interfacial bonding to the substrate. The heat treatment did not alter the chemical composition of the MAO coating and the chemical states of Ti, Ca and P elements. However, it increased the roughness (Ra) of the MAO coating and improved the wetting ability of the MAO coating. In this work, preliminary investigation of the MG63 cell proliferation on the surface of the MAO and heat-treated MAO coatings was conducted. The MAO coating surface with about Ra = 220 nm may be suitable for the MG63 cell adhesion and proliferation. The increased roughness of the heat-treated MAO coatings may result in a decrease in the ability for cell adhesion and proliferation.
Keywords: Coating; Titanium alloy; Amorphous calcium phosphate; Microarc oxidation; Heat treatment; MG63 cell proliferation; EDTA–2Na;

In situ formation of ceramic coatings on Q235 carbon steel was achieved by plasma electrolytic oxidation (PEO) in carbonate electrolyte and silicate electrolyte, respectively. The surface and cross-section morphology, phase and elemental composition of PEO coatings were examined by means of scanning electron microscopy (SEM), X-ray diffraction (XRD) and energy-dispersive X-ray spectroscopy (EDS). The bond strength of the coating was determined using a direct pull-off test. The hardness as well as tribological properties of the ceramic coating was primarily studied. The results indicated that the coating obtained in carbonate electrolyte was Fe3O4, while the coating achieved from silicate electrolyte was proved to be amorphous. Both kinds of coatings showed coarse and porous surface. The Fe3O4 coatings obtained in carbonate electrolyte showed a high bonding strength to the substrate up to 20 ± 2 MPa and the value was 15 ± 2 MPa for the amorphous coatings obtained in carbonate electrolyte. The micro hardness of the amorphous coating and the Fe3O4 coating was 1001 Hv and 1413 Hv, respectively, which was more than two and three times as that of the Q235 alloy substrate (415 Hv). The friction coefficient exhibited by amorphous coating and Fe3O4 coating was 0.13 and 0.11, respectively, both lower than the uncoated Q235 substrate which ranged from 0.17 to 0.35.
Keywords: Ceramic coating; Plasma electrolytic oxidation; Carbon steel; Friction coefficient;

Examination of the oxidation resistance of high-alloyed tool steels at elevated temperatures by D. Chaliampalias; G. Vourlias; E. Pavlidou; G. Stergioudis; K. Chrissafis (6244-6251).
In the present work the structure of two different tool steels is examined before and after oxidation up to 1000 °C in air. The materials under examination have different chromium contents. Also, the first contains vanadium (S1 tool steel) and the second tungsten (S2 tool steel) as alloying element, while the rest are common. The examination took place by thermogravimetric analysis, scanning electron microscopy, transmission electron microscopy and X-ray diffraction. From this study it is deduced that the structure of the two steels, before oxidation, has several distinguishing differences mostly in the chromium distribution in the iron matrix. The oxidation tests revealed that S2 oxidizes at higher temperatures than S1, but finally, at 1000 °C, S2 tool steel has greater mass gain, because it oxidizes at a higher rate.
Keywords: Metals and alloys; Microstructure; Oxidation; Scanning electron microscopy; Transmission electron microscopy;

Highly conducting and transparent Ti-doped CdO films by pulsed laser deposition by R.K. Gupta; K. Ghosh; R. Patel; P.K. Kahol (6252-6255).
Titanium-doped cadmium oxide thin films were deposited on quartz substrate by pulsed laser deposition technique. The effect of substrate temperature on structural, optical and electrical properties was studied. The films grown at high temperature show (2 0 0) preferred orientation, while films grown at low temperature have both (1 1 1) and (2 0 0) orientation. These films are highly transparent (63–79%) in visible region, and transmittance of the films depends on growth temperature. The band gap of the films varies from 2.70 eV to 2.84 eV for various temperatures. It is observed that resistivity increases with growth temperature after attaining minimum at 150 °C, while carrier concentration continuously decreases with temperature. The low resistivity, high transmittance and wide band gap titanium-doped CdO films could be an excellent candidate for future optoelectronic and photovoltaic applications.
Keywords: Semiconductors; Vacuum deposition; Electrical properties; Optical properties; Cadmium oxide;

Tuning of surface properties of thin polymer films by electron beam treatment by Sina Burkert; Marco Kuntzsch; Cornelia Bellmann; Petra Uhlmann; Manfred Stamm (6256-6261).
Keywords: Polymer brushes; Polystyrene; Poly-2-vinylpyridine; Electron irradiation; Surface modification; Gradient;

A numerical study is presented on the transport processes in the manganite–titanate Schottky junction by using the Poisson equation, the drift-diffusion formulas, the direct and thermally assisted tunneling model. Comparing with the experimental data, it is found that the non-monotonically temperature-dependent IV curves under reverse bias is caused by the competition between the direct and thermally assisted tunneling processes. In addition, it is also found that the electric field dependence of the permittivity in Nb-doped SrTiO3 plays an important role on the transport properties of the manganite–titanate Schottky junctions based on our calculation.
Keywords: Perovskite oxide; Schottky junction; Transport;

Effect of medium on friction and wear properties of compacted graphite cast iron processed by biomimetic coupling laser remelting process by Qing-chun Guo; Hong Zhou; Cheng-tao Wang; Wei Zhang; Peng-yu Lin; Na Sun; Luquan Ren (6266-6273).
Stimulated by the cuticles of soil animals, an attempt to improve the wear resistance of compact graphite cast iron (CGI) with biomimetic units on the surface was made by using a biomimetic coupled laser remelting process in air and various thicknesses water film, respectively. The microstructures of biomimetic units were examined by scanning electron microscope and X-ray diffraction was used to describe the microstructure and identify the phases in the melted zone. Microhardness was measured and the wear behaviors of biomimetic specimens as functions of different mediums as well as various water film thicknesses were investigated under dry sliding condition, respectively. The results indicated that the microstructure zones in the biomimetic specimens processed with water film are refined compared with that processed in air and had better wear resistance increased by 60%, the microhardness of biomimetic units has been improved significantly. The application of water film provided finer microstructures and much more regular grain shape in biomimetic units, which played a key role in improving the friction properties and wear resistance of CGI.
Keywords: Cast iron; Biomimetic; Laser remelting; Water film; Microstructure; Microhardness; Wear properties;

Photocatalytic activity enhancement of TiO2 films by micro and nano-structured surface modification by M. Bizarro; M.A. Tapia-Rodríguez; M.L. Ojeda; J.C. Alonso; A. Ortiz (6274-6278).
Titanium oxide thin films were deposited by spin coating using a precursor solution of titanium oxide (IV) acetylacetonate. To increase the contact surface area of the films, TiO2 microspheres were added to the surface of the films. These spheres were 2 μm in diameter and formed agglomerates on the surface. They did not spread uniformly across the substrate, creating different roughnesses and morphologies along the surface of films. Photocatalytic properties of the samples were tested by the degradation of a methyl orange solution. The degradation performance was compared between plain films, films with microspheres and films covered with commercial TiO2 P25 powder. The results indicate that the samples that were surface modified with TiO2 microspheres present a photodegradation reaction rate 62 times higher than that obtained for plain TiO2 films. The rate of reaction of the samples covered with P25 was 2 times greater than that obtained for the samples with microspheres, but the adhesion to the film was better in the case of microspheres. Moreover, samples with microspheres could be reused several times maintaining the same structural and photocatalytic properties.
Keywords: Photocatalysis; Thin films; Titanium oxide; Water treatment;

This paper describes a simple and versatile method for growing highly anisotropic rectangular shaped nanobat-like CuO nanostructures by simple, low temperature and cost effective hydrothermal method. Field emission scanning electron microscopy illustrated that these CuO nanostructures have diameter of ∼70 nm, thickness of ∼8 nm and length of ∼174 nm. Structural analysis reveals that the CuO nanostructures have a high crystal quality with monoclinic crystal structure. X-ray photoelectron spectroscopy studies demonstrate that the sample is composed of CuO. The Raman study also indicates the single phase property and high crystallinity of as-grown CuO nanostructures. The plausible growth mechanism for the formation of nanobat-like CuO structure is proposed.
Keywords: Copper oxide; Rectangular shaped nanobat-like CuO; Hydrothermal method; Transmission electron microscopy;

Synthesis and optical properties of CuS nanoplate-based architectures by a solvothermal method by Fei Li; Tao Kong; Wentuan Bi; Dachang Li; Zhen Li; Xintang Huang (6285-6289).
The controlled synthesis of copper sulfide (CuS) nanoplate-based architectures in different solvents has been realized at low cost by simply reaction of Cu(NO3)2·3H2O and S under solvothermal conditions without the use of any template. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV–vis spectrometer and fluorescence measurement were used to characterize the products. The products were all in hexagonal phase with high crystallinity and the morphology was significantly influenced by the solvents. The CuS products synthesized in dimethylformamide (DMF) were nanoplates and the samples prepared in ethanol were flower-like morphology composed of large numbers of nanoplates, but those synthesized in ethylene glycol (EG) were CuS architectures with high symmetry made up of several nanoplates arranged in a certain mode. The optical properties were investigated and the growth mechanisms of these CuS crystals were also proposed.
Keywords: Copper sulfide; Nanoplate; Solvothermal; Optical properties;

Porous surface-fluorinated TiO2 (F-TiO2) films were prepared through PEG modified sol–gel method and surface fluorination. The as-prepared films were characterized with XRD, FTIR, AFM, XPS and UV–vis DRS. The effects of surface fluorination on the photocatalytic activity and hydrophilicity of porous TiO2 film were studied by photocatalytic degradation of rhodamine B (RhB) as well as water contact angle (CA) on porous TiO2 film. The results showed that the surface fluorination increased the adsorption of RhB on the porous TiO2 film and enhanced the photocatalytic degradation of RhB. The concentration and pH of NaF solutions affected much the photocatalytic activity of porous TiO2 film. Porous F-TiO2 film prepared in 40 mM NaF solution at pH 4.0 showed the highest photocatalytic activity. Because of its porous structure, the porous F-TiO2 film had original water CA of 22.7°, which is much smaller than that of normal F-TiO2 film. Under UV light irradiation, the water CA of porous F-TiO2 film decreased to 5.1° in 90 min.
Keywords: Surface fluorination; Porous TiO2 film; Photocatalytic activity; Hydrophilicity; Rhodamine B;

Particles generated by 2.94 μm pulsed IR laser ablation of liquid 3-nitrobenzyl alcohol were irradiated with a 351 nm UV laser 3.5 mm above and parallel to the sample target. The size and concentration of the ablated particles were measured with a light scattering particle sizer. The application of the UV laser resulted in a reduction in the average particle size by one-half and an increase in the total particle concentration by a factor of nine. The optimum delay between the IR and UV lasers was between 16 and 26 μs and was dependent on the fluence of the IR laser: higher fluence led to a more rapid appearance of particulate. The ejection velocity of the particle plume, as determined by the delay time corresponding to the maximum two-laser particle concentration signal, was 130 m/s at 1600 J/m2 IR laser fluence and increased to 220 m/s at 2700 J/m2. The emission of particles extended for several ms. The observations are consistent with a rapid phase change and emission of particulate, followed by an extended emission of particles ablated from the target surface.
Keywords: Laser; Desorption; Infrared; Ablation; Aerosol; Particle;

Kinetic electron emission due to perpendicular impact of carbon ions on tungsten surfaces by Jan Lorincik; Zdenek Sroubek; Michael Brunmayr; Gregor Kowarik; Friedrich Aumayr (6303-6307).
Total electron yields for perpendicular impact of C+ ions on W have been measured for projectile energies from 0.2 keV to 7 keV. The data are compared with the data of C+ bombardment of gold and graphite in order to demonstrate general trends in kinetic electron yields at low projectile velocities. The total electron yields in the studied combinations of projectiles and substrates show a similar exponential dependence Γ  ∝ (v/A) exp(−A/v), where A is a constant and v is the projectile velocity.
Keywords: Kinetic electron emission; Tungsten; Carbon;

ZnO and indium-doped ZnO (I x ZO) thin films were prepared on silica–glass substrates by the sol–gel method. The thin films were crystallized at 600 °C and 700 °C for 1 h in 6.9 × 10−1  Torr under pure O2 atmosphere. The analyzed results were compared to investigate the structural characteristics and optical properties. The surface morphology of the I x ZO films was different from that of the ZnO films, and showed a thin overlay structure. In addition, the crystallization of I x ZO film was depleted at higher crystallized temperatures. From XRD analysis, the ZnO and I x ZO thin films possessed hexagonal structures. Notably, micro-In2O3 phases were observed in the I x ZO thin films using EDS. Both of In2O3 phases and the crystallization mechanism not only improved the peeling of structure, but also improved the electrical conductivity of I x ZO thin films. For the PL spectrum, the optical property of the I x ZO film was raised at a higher crystallization temperature. Although the In2O3 phases reduced the structural defects of I x ZO thin film, the optical effect of the residual In3+ was not enhanced completely at higher crystallized temperatures.
Keywords: Sol–gel; ZnO; Crystallization; Indium;

The structure and optical characters of the ZnO film grown on GaAs/Al2O3 substrate by Xiaochuan Xia; Wang Zhao; Yuantao Jian; Xiangping Li; Xin Dong; Yongguo Cui; Yuantao Zhang; Xiujun Fang; Guoxing Li; Huichao Zhu; Yan Ma; Baolin Zhang; Guotong Du (6313-6317).
In this paper ZnO films are grown on GaAs/Al2O3 substrates at different temperature by metal-organic chemical vapor deposition (MOCVD). The GaAs/Al2O3 substrates are formed by depositing GaAs layer (∼35 nm) on the Al2O3 substrate. The results of X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) demonstrate that most of the Ga and As atoms form Ga–As bond and the GaAs layer does not present any orientation. The characters of the ZnO films grown on GaAs/Al2O3 substrates are investigated by XRD, photoluminescence (PL), atomic force microscopy (AFM) and Raman scattering. Compared with ZnO film grown on Al2O3 substrate, ZnO film prepared by our fabrication scheme has good crystal and optical quality. Meanwhile its grain size becomes bigger according to the AFM image. Raman analysis indicates that the intrinsic defects and the in-plane tensile stress are obviously reduced in ZnO/GaAs/Al2O3 samples.
Keywords: Metal-organic chemical vapor deposition; Oxides; Semiconducting II–VI materials;

The distribution of different free chemical functional groups on wood and pulp fibres has been determined by means of atomic force microscopy (AFM) with chemically modified tips. Because these functional groups show a higher affinity to similar groups on the substrate surface during scanning, AFM images determined with an additional digital pulsed-force mode (DPFM) controller allow the distribution of the chemical components to be imaged and to a degree also to be quantified. The investigated tip coatings showed a different sensitivity towards the major chemical components present in wood fibres, determined on spin-coated films and on wood fibres. A clear distinction between cellulose and lignin was possible in both cases. This technique could therefore be used to differentiate between cellulose and lignin present on pulp fibre surfaces and confirm the successful removal of lignin by pulping.
Keywords: Pulp fibres; Functional groups; Chemical force microscopy; Adhesive force;

Growth of multiwalled carbon nanotube arrays by chemical vapour deposition over iron catalyst and the effect of growth parameters by J.K. Radhakrishnan; P.S. Pandian; V.C. Padaki; H. Bhusan; K.U.B. Rao; J. Xie; J.K. Abraham; V.K. Varadan (6325-6334).
Multiwalled carbon nanotube (CNT) arrays were grown by catalytic thermal decomposition of acetylene, over Fe-catalyst deposited on Si-wafer in the temperature range 700–750 °C. The growth parameters were optimized to obtain dense arrays of multiwalled CNTs of uniform diameter. The vertical cross-section of the grown nanotube arrays reveals a quasi-vertical alignment of the nanotubes. The effect of varying the thickness of the catalyst layer and the effect of increasing the growth duration on the morphology and distribution of the grown nanotubes were studied. A scotch-tape test to check the strength of adhesion of the grown CNTs to the Si-substrate surface reveals a strong adhesion between the grown nanotubes and the substrate surface. Transmission electron microscopy analysis of the grown CNTs shows that the grown CNTs are multiwalled nanotubes with a bamboo structure, and follow the base-growth mechanism.
Keywords: Multiwalled carbon nanotube; Chemical vapour deposition; Fe-catalyst; Thermal annealing; Bamboo structure;

Nitrogen plasma cleaning of Ge(1 0 0) surfaces by Katsuhiro Kutsuki; Gaku Okamoto; Takuji Hosoi; Takayoshi Shimura; Heiji Watanabe (6335-6337).
We propose a dry method of cleaning Ge(1 0 0) surfaces based on nitrogen plasma treatment. Our in situ Auger electron spectroscopy (AES) and low-energy electron diffraction (LEED) analyses demonstrate that surface contamination remaining after wet treatment was effectively removed by nitrogen radical irradiation at low substrate temperatures. The nitrogen plasma cleaned Ge(1 0 0) surface shows a well-ordered 2 × 1 reconstruction, which indicates the formation of a contamination-free Ge(1 0 0) surface with good crystallinity. We discuss the possible reaction mechanism considering how chemisorbed carbon impurities are removed by selective C–N bond formation and subsequent thermal desorption. These findings imply the advantage of plasma nitridation of Ge surfaces for fabricating nitride gate dielectrics, in which we can expect surface pre-cleaning at the initial stage of the plasma treatment.
Keywords: Ge MIS; Surface treatment; Nitrogen plasma;

Density functional theory study of hydrogenation mechanism in Fe-doped Mg(0 0 0 1) surface by Guangxin Wu; Jieyu Zhang; Yongquan Wu; Qian Li; Kuochih Chou; Xinhua Bao (6338-6344).
Using density functional theory (DFT) in combination with nudged elastic band (NEB) method, the dissociative chemisorptions and diffusion processes of hydrogen on both pure and Fe-doped Mg(0 0 0 1) surfaces are studied. Firstly, the dissociation pathway of H2 and the relative barrier were investigated. The calculated dissociation barrier (1.08 eV) of hydrogen molecule on a pure Mg(0 0 0 1) surface is in good agreement with comparable experimental and theoretical studies. For the Fe-doped Mg(0 0 0 1) surface, the activated barrier decreases to 0.101 eV due to the strong interaction between the s orbital of H and the d orbital of Fe. Then, the diffusion processes of atomic hydrogen on pure and Fe-doped Mg(0 0 0 1) are presented. The obtained diffusion barrier to the first subsurface is 0.45 eV and 0.98 eV, respectively. Finally, Chou method was used to investigate the hydrogen sorption kinetic mechanism of pure MgH2 and Mg mixed with 5 at.% Fe atoms composites. The obtained activation energies are 0.87 ± 0.02 and 0.31 ± 0.01 eV for H2 dissociation on the pure surface and H atom diffusion in Fe-doped Mg surfaces, respectively. It suggests that the rate-controlling step is dissociation of H2 on the pure Mg surface while it is diffusion of H atom in the Fe-doped Mg surface. And both of fitting data are matching well with our calculation results.
Keywords: Density functional theory; Adsorption energy; Dissociation; Diffusion;

Growth of hydrogel nano- and microlayers covalently bounded onto PE surface by Rafael Silva; Edvani C. Muniz; Adley F. Rubira (6345-6354).
Surface modifying strategies were developed to immobilize PAA cross-linked layers (hydrogel layers) with different thicknesses by chemical binding to the surface of polyethylene (PE). Polyethylene films were functionalized by two methods, chromic acid oxidation and maleic anhydride grafting. The reaction of the functional groups placed onto the film surface with ethylenediamine promoted the formation of an amine-functionalized surface. The thickness of the hydrogel layer was correlated with the presence and the release of impregnated ethylenediamine during the immobilization of the PAA chains by thermal esterification. Ethylenediamine acts as a cross-linking agent between different PAA chains. Attenuated total reflectance (ATR) FTIR spectroscopy and scanning electron microscopy (SEM) were used to characterize the chemical composition and the morphologies of the modified film surface.
Keywords: Polyethylene (PE); Surface; Nanolayers; Microlayers; Hydrogels;

A N-rich Zr–N film with Th3P4 structure (denoted as c-Zr3N4) was grown on Si and glass substrate by radio frequency (rf) magnetron sputtering technique with high pure Zr as target and high pure N2 as sputtering gas. The crystal structure and composition of the c-Zr3N4 was characterized by X-ray diffractometry, transmission electron microscopy and X-ray photoelectron spectroscopy. The lattice constant of the c-Zr3N4 was measured to be about 0.674 nm. Hall measurement indicates that the c-Zr3N4 compound is a p-type semiconductor with resistivity of 2.121 × 104  Ω cm, carrier concentration of 9 × 1014  cm−3 and Hall mobility of 0.34 cm2/(V s). Its bandgap was evaluated by absorption spectroscopy to be about 2.8 eV. A mechanism of formation of the c-Zr3N4 compound was suggested in the present work.
Keywords: rf magnetron sputtering; c-Zr3N4 film; Crystal structure; Characterization and properties;

Comparative study on modification of single wall carbon nanotubes by sodium dodecylbenzene sulfonate and melamine sulfonate superplasticiser by Z. Marković; S. Jovanović; D. Kleut; N. Romčević; V. Jokanović; V. Trajković; B. Todorović-Marković (6359-6366).
In this work, the results of synthesis and characterization of single wall carbon nanotubes (SWCNTs) functionalized by two surfactants (sodium dodecylbenzene sulfonate and melamine sulfonate superplasticiser) have been presented. The properties of pristine and modified SWCNTs have been compared by different techniques: Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR) and atomic force microscopy (AFM). Raman analysis reveals the changes in vibrational spectra of SWCNTs after modification by different surfactant molecules. FTIR analysis has shown the presence of sulfonate group which is strong evidence for nanotube modification. AFM analysis has shown separation of big single wall carbon nanotube bundles into thin bundles of them.
Keywords: Single wall carbon nanotubes; Atomic force microscopy; Raman spectroscopy; Fourier transform infrared spectroscopy;

X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) studies have been used to analyze the surface of diffusion layer (PTFE/C) and catalyst layer (Pt/C/PTFE) of electrode. Detail analysis of carbon C1s peak showed that the carbon was of the form of C, C–O, C=O, CF, CF2 and CF3 with CF2 is more dominated on the surface compared to CF and CF3. The oxygen O1s photoelectron peak showed that the oxygen was of the form of C=O and C–O. The platinum was of the form of Pt0 with some Pt oxidized to PtO. The scanning electron microscopy was used to observe the dispersion of Teflon in the diffusion layer, the distribution of platinum in the catalyst layer loaded with 0.38 mg Pt/cm2 and also the cross section of the membrane electrode assembly. The prepared electrode delivers a superior performance compared with the commercial electrode (E-TEK). The difference in performance between the two electrodes is due to the good localization of the platinum particles.
Keywords: Fuel cell; Diffusion layer; Catalyst layer; XPS; SEM;

The Zn–Al layered double hydroxides (LDH) with Zn/Al molar ratio of 2 were prepared by coprecipitation, followed by hydrothermal treatment at various hydrothermal conditions. The phase transformation was observed, accompanied by drastical morphological changes. As the results indicated, in aqueous system the decomposition product was phase segregated into wurtzite ZnO and spinel ZnAl2O4 by dissolution of the precursor hydroxide followed by recoprecipitation of the oxide phases. As a single-source precursor, LDH facilitated the formation of ZnAl2O4 crystallites and their coating on ZnO nanowires via the inherent linkage through interactions of coordination as well as hydrogen bonding via medium of surface –OH on particles. The addition of ethanol with high vapor tension and low polarity was against the adsorptive attachment of ZnAl2O4 on ZnO but in favor of the crystallization and size decrease of the resulting oxides. Improved crystallization in LDH precursors was beneficial to intensify the interactions to overcome the breaking effect of ethanol, achieving better coating of ZnAl2O4 on ZnO. With the silane grafting of KH570, hydrothermal treatment promoted the formation of four phases by partial decomposition of layered structure of ZnAl–CO3 and new emergence of smectite-like materials with basal spacing of 12.35 Å. As the aging time for LDH precursors gradually elongated, the whole products finally transformed to ultrafine nanorods with mean size of 50 nm in length which were segregated without any type of attachment.
Keywords: Layered double hydroxides; Solution decomposition; KH570; Hydrothermal treatment;

To prevent the natural processes of decay and to develop and improve the treatments of conservation and restoration of artistic bronzes meaning statues and sculptures, it is important understanding the patination processes and the knowledge of artificially corroded surfaces. Chemical and physical characterization of artificial patinas obtained on artistic bronzes and coppers by using the 19th century Western traditional patination techniques and recipes by means of SEM–EDS, light microscopy and ATR/FT-IR has been done in previous studies [I.Z. Balta, L. Robbiola, Characterization of artificial black patinas on artistic cast bronze and pure copper by using SEM–EDS and light microscopy, in: Proceedings of the 13th European Microscopy Congress, 22–27 August 2004, Antwerp, Belgium, EMC 2004 CD-Rom Conference Preprints; I.Z. Balta, L. Robbiola, Traditional artificial artistic bronze and copper patinas—an investigation by SEM–EDS and ATR/FT-IR, in: Proceedings of the 8th International Conference on Non Destructive Investigations and Microanalysis for the Diagnostics and Conservation of the Cultural and Environmental Heritage, 15–19 May 2005, Lecce, Italy, ART’05 CD-Rom Conference Preprints]. Differences in morphology (structure, thickness, porosity, adherence, compactity, uniformity, homogeneity) and also in composition, on both artistic cast bronze and pure copper patinas, were clearly evidenced. Further in-depth investigation is required to be carried out in order to better understand the patinas mechanisms of formation and the layers kinetics of growth. The elemental and chemical analysis, either on a surface monolayer or in a depth profile, by using the Secondary Ion Mass Spectrometry (SIMS) and X-ray Photoelectron Spectroscopy (XPS) techniques, can provide this kind of information, unique at trace-level sensitivity. SIMS has proved to be a suitable analytical technique for analyzing small amounts of material with high atomic sensitivity (ppm or even ppb) and high depth/lateral resolution in the micron and sub-micron range [R.G. Wilson, F.A. Stevie, C.W. Magee, Secondary Ion Mass Spectrometry: A Practical Handbook for Depth Profiling and Bulk Impurity Analysis, Wiley & Sons, New York, 1989; M. Dowsett, A. Adriaens, The role of SIMS in cultural heritage studies, Nucl. Instr. Meth. Phys. Res. B 226 (2004) 38–52]. XPS has the ability to provide detailed chemical information on virtually each kind of solid sample, and elemental identification is therefore possible due to the core level photoemission. The most important advantage is the high surface sensitivity of the chemical information (a few monolayers) [E. Ciliberto, G. Spoto, Modern Analytical Methods in Art and Archaeology, John Wiley & Sons, Inc., New York, 2000]. In addition elements’ relative abundance can be made semi-quantitative or quantitative and information on chemical bonds can be derived.The aim of the present work is to highlight the advantages and the limits of XPS and Dynamic SIMS surface analytical techniques for the characterization of artistic bronze and copper artificial patinas. The results obtained on the analyzed samples allowed the distribution of the main elements in the corrosion patinas layers and the contribution of each elements present in bronze matrix to the color of the resulting patinas to be precisely revealed. This information could be used for comparative studies between artificial and natural patinas, and also for provenience and authentication studies for artistic and archaeological bronzes.
Keywords: D-SIMS; XPS; Artificial patinas; Artistic bronze; Copper;

In this paper the hydrolysis process of γ-methacryloxypropyltrimethoxysilane (MPS) at 1% in an aqueous solution by means of Fourier transform infrared (FTIR) spectroscopy was studied. The aim of this work is to determine the hydrolysis time for which a greater number of Si–OH groups has been obtained. Different hydrolysis times at pH 4 were studied to establish the most optimal application conditions for bonding to the substrate. It was possible to observe how the bands corresponding to the Si–O–C groups present in the pure silane spectrum continued to appear after short periods of hydrolysis. However these bands practically disappeared upon increasing of this hydrolysis time, with other new ones appearing corresponding to the Si–OH vibration. The silanization of 6063 aluminum alloy samples was also carried out. Analysis of the silane layers by means of FTIR indicated that the immersion time may be important according to the hydrolysis conditions, and it also allowed optimizing the drying time.
Keywords: γ-Methacryloxypropyltrimethoxysilane (MPS); Hydrolysis; FTIR; Aluminum;

Electron beam initiated grafting of methacryloxypropyl-trimethoxysilane to fused silica glass by A.Yu. Shmykov; S.V. Mjakin; I.V. Vasiljeva; V.N. Filippov; M.E. Vylegzhanina; T.E. Sukhanova; V.E. Kurochkin (6391-6396).
The effect of electron beam pretreatment of fused silica glass upon its surface functional composition and possibility for subsequent immobilization of methacryloxypropyl-trimethoxysilane (MOPTMS) layer is studied using FTIR spectroscopy and adsorption of acid–base indicators. The content of Brensted acidic centers (silanol groups) on the irradiated fused silica surface is found to follow an “oscillatory” trend as function of the absorbed dose below 100 kGy at electron beam processing due to the alternating reactions of hydroxylation (probably as a result of Si–O–Si bond disruption and interaction with radiolyzed physically adsorbed water) and thermal dehydration/dehydroxylation at radiation heating. The best conditions for MOPTMS layer formation are based on the increased acidity of both silica surface (formation of acidic hydroxyls) and the reaction medium (MOPTMS deposition from acetic acid solution). The optimal value of absorbed dose at electron beam processing providing the highest efficiency of MOPTMS grafting is 50 kGy at accelerated electron energy 700 keV. Electron beam pretreatment of fused silica surface is shown to provide more efficient MOPTMS immobilization in comparison with conventional chemical and thermal grafting procedures. The obtained results are promising for the enhancement of the processes for the production of fused silica glass capillaries for electrochromatography and electrophoresis at the stage of an intermediate bifunctional layer formation required for the subsequent deposition of specific polymer coatings.
Keywords: Quartz; Fused silica; Glass; Electron beam; Surface functionalization; Polymer coatings; Capillary electrochromatography; Capillary electrophoresis;

Effect of the thermal and hydrothermal treatment on textural properties of Zr-MCM-41 mesoporous molecular sieve by Qian Zhao; Xuping Zhou; Yanhui Li; Mei Li; Tingshun Jiang; Hengbo Yin; Changsheng Li (6397-6403).
Zr-containing mesoporous molecular sieves were synthesized by hydrothermal method using cetyltrimethyl ammonium bromide as a template and sodium silicate and zirconium sulfate as raw materials. The structure and morphology of the synthesized samples were characterized via various physicochemical methods, including X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared (FT-IR) spectroscopy, solid state nuclear magnetic resonance (29Si MAS-NMR) techniques, thermal gravimetric–differential scanning calorimeter (TG–DSC) and N2 physical adsorption, respectively. The effect of the different initial ZrO2:SiO2 molar ratio, the different thermal treatment temperature and the different hydrothermal treatment time on textural property was investigated. The experimental results reveal that the as synthesized samples possess a typical mesoporous structure of MCM-41. On the other hand, the specific surface area and pore volume of the synthesized Zr-MCM-41 mesoporous molecular sieve decrease with the increase of the amount of zirconium incorporated in the starting material, the rise of thermal treatment temperature and the prolonging of hydrothermal treatment time, the mesoporous ordering becomes poor. Also, when the molar ratio of ZrO2:SiO2 in the starting material is 0.1, the mesoporous structure of the Zr-MCM-41 mesoporous molecular sieve still retains after calcination at 750 °C for 3 h or hydrothermal treatment at 100 °C for 6 d, and have specific surface areas of 423.9 and 563.9 m2/g, respectively.
Keywords: Zr-MCM-41 mesoporous molecular sieve; Synthesis; Characterization; Textural property; Thermal treatment; Hydrothermal treatment;

Fabrication of aligned carbon nanotubes on Cu catalyst by dc plasma-enhanced catalytic decomposition by Zhejuan Zhang; Maziar Shakerzadeh; BengKang Tay; Xiaocheng Li; Chongwei Tan; LiFeng Lin; Pingsheng Guo; Tao Feng; Zhuo Sun (6404-6407).
Aligned multi-walled carbon nanotubes (ACNTs) are deposited using copper (Cu) catalyst on Chromium (Cr)-coated substrate by plasma-enhanced chemical vapor deposition at temperature of 700 °C. Acetylene gas has been used as the carbon source while ammonia is used for diluting and etching. The thicknesses of Cu films on Cr-coated Si (100) substrates are controlled by deposition time of magnetron sputtering. The growth behaviors and quality of ACNTs are investigated by scanning electron microscopy (SEM) and transmission electron microscopy. The different performance of ACNTs on various Cu films is explained by referring to the graphitic order as detected by Raman spectroscopy. The results indicate that the ACNTs are formed in tip-growth model where Cu is used as a novel catalyst, and the thickness of Cu films is responsible to the diameter and quality of synthesized CNTs.
Keywords: Cooper catalyst; Aligned CNTs; DC–PECVD;

The tribological properties of three different films commonly used in microelectromechanical systems (MEMS) under the lubrication of ionic liquid (IL)/water mixtures with various concentrations in the running-in process have been investigated. Results show that coefficients of friction (COFs) and wear rates for low temperature silicon oxide (LTO)/Si3N4 vary in a similar way to the ones for poly-Si/Si3N4 under the lubrications of different IL/water mixtures. In contrast, the differences in COFs and wear rates are more significant in that the COFs and wear rates increase dramatically with the decrease in IL/water concentration in the case of self-mated Si3N4, while the differences in COFs and wear rates for the two other tribopairs are relatively small when the concentration is changed. The period of the running-in process reduces with the increase in IL/water concentration for all the tribopairs. Effective hydrodynamic lubrication can be found in the case of Si3N4/Si3N4 tribopair at higher IL/water concentrations without an evident running-in process, however, such a phenomenon cannot be observed for the other two tribopairs. Different wear mechanisms will also be analyzed in this paper.
Keywords: Ionic liquid/water; Water-based lubrication; Running-in process; Thin films;

ZnO nanorod arrays on ZnO-coated seed layers were fabricated by aqueous solution method using zinc nitrate and hexamethylenetetramine at low temperature. The seed layers were coated on ITO substrates by electrochemical deposition technique, and their textures were dominated by controlling the deposition parameters, such as deposition potential and electrolyte concentration. The effects of the electrodeposited seed layers and the growing parameters on the structures and properties of ZnO nanorod arrays were primarily discussed. The orientation and morphology of both the seed layer and successive nanorods were analyzed by using X-ray diffraction (XRD), SEM and TEM. The results show that the seed layer deposited at −700 mV has evenly distributed crystallites and (0 0 2) preferred orientation; the density of resultant nanorods is high and ZnO nanorods stand completely perpendicular onto substrates. Meanwhile, the size of nanorods quite also depends on the growth solution, and the higher concentration of growth solution primary leads to a large diameter of the ZnO nanorods.
Keywords: ZnO; Nanorod; Electrodeposition; Aqueous solution method; Seed layer;

On the short-range order of the SiO x (0 ≤  x  ≤ 2) surface by O. Bondarchuk; S. Goysa; I. Koval; P. Melnik; M. Nakhodkin (6421-6425).
Fine (oscillating) structure (FS) in the elastically scattered electron spectra (ESES) [O. Bondarchuk, S. Goysa, I. Koval, P. Melnik, M. Nakhodkin, Surf. Sci. 258 (1991) 239; O. Bondarchuk, S. Goysa, I. Koval, P. Melnik, M. Nakhodkin, Surf. Rev. Lett. 4 (1997) 965] was used to investigate surface structure of the SiO x (0 ≤  x  ≤ 2). SiO x surface with different stoichiometry was prepared by implantation of 500 eV oxygen ions into a silicon wafer. Fourier transformation of the FS ESES contains one peak at 2.32 Å for Si, two peaks at 1.62 Å and 2.65 Å for a-SiO2 and three peaks centered at 1.6–1.7 Å, 2.1–2.2 Å and 2.65–3.04 Å for SiO x . Peaks at 1.62 Å and 2.65 Å are assigned to Si–O and O–O nearest distances correspondently. Ratio of the area under the peak at 2.65 Å to the area under the peak at 1.62 Å turned out to be not constant but grows linearly with the composition parameter x. The latter is considered to prove validity of the Random Bond Model to describe short-range order on the surface of non-stoichiometric silicon oxide.
Keywords: Silicon oxide; Short-range order; Fine structure; Elastic electron scattering;

Enhancing accuracy to Stoney equation by J.M. Pureza; M.M. Lacerda; A.L. De Oliveira; J.F. Fragalli; R.A.S. Zanon (6426-6428).
This paper proposes a three-dimensional system for modelling stress in thin films deposited on plane substrates much thicker than the film itself. The approach is the minimization of the deformation energy of the sample (substrate + film), considering the deformed substrate as a small spherical surface with large curvature radius. Results of the model show the validity limits of the well-established Stoney equation that satisfy the upper theoretical limit of Poisson ratio (ν) for isotropic materials. Our main result is that the stress values obtained in general literature using Stoney equation are underestimated when considering a typical Poisson ratio for substrates in the range of 0.25 ≤  ν s  ≤ 0.4.
Keywords: Stress; Strain; Stoney equation; Deformation energy;

Revealing of water surface pollution with liquid marbles by Edward Bormashenko; Albina Musin (6429-6431).
Floating of “liquid marbles” on the surface of water contaminated with organic compounds was studied. Marbles were obtained with spreading of hydrophobic polyvinylidene fluoride particles on the surface of water droplets. Marbles floated stably on the water surface, whereas they were destroyed on the water surfaces contaminated with silicon oil and kerosene. Limiting conditions of floating were studied experimentally with the water/alcohol mixtures.
Keywords: Liquid marbles; Non-stick surfaces; Surface tension; Liquid surface; Water pollution; Hydrophobic particles;