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Applied Surface Science (v.240, #1-4)

Author Index (pp. i-iv).

Subject Index (pp. v-xvii).

Nanosized titania encapsulated silica particles using an aqueous TiCl₄ solution by Han-Ho Choi; Joodong Park; R.K. Singh (pp. 7-12).

In this study, sub-micron sized silica particles were encapsulated with nanosized titania particles using an aqueous TiCl₄ solution. The particle size distribution of the synthesized titania particles in the coating layer was estimated to be 10nm from X-ray powder diffraction and transmission electron microscopy. The thickness of the coating layer ranged from a few nm to about 30nm from transmission electron microscopy analysis. Zeta potential analysis demonstrated the presence of a titania particle coating layer and the extent of its coverage on the surface of silica particles. X-ray photoelectron spectroscopy analysis also demonstrated that titania particles were successfully deposited on the surface of core silica particles from the chemical shift of binding energies of O 1s, Ti 2p and Si 2p.

Keywords: PACS; 61.46Nanoencapsulation; Titania coated silica particles

Self-organization of surfactant molecules on solid surface: an STM study of sodium alkyl sulfonates by Xiu-Li Yin; Li-Jun Wan; Zheng-Yu Yang; Jia-Yong Yu (pp. 13-18).

Adsorption and self-organization of sodium alkyl sulfonates (STS and SHS) on HOPG have been studied by using in situ scanning tunneling microscopy (STM). Both SHS and STS molecules adsorb on HOPG surface and form long-range well-ordered monolayers. The molecular rows and the axes of alkyl chain of the molecules cross each other at angles of 60° and 90° in the STS and SHS layers, respectively. Molecular details such as sulfonate functional group (head) and alkyl chain are clearly imaged. The neighboring molecules in different rows form a “head to head�? configuration. Structural models for the molecular arrangement of the two adlayers are proposed.

Keywords: Scanning tunneling microscopy; Self-organization; Sodium; n; -tetradecyl sulfonate; Sodium; n; -hexadecyl sulfonate; HOPG

Microstructure evolution of electroless Ni-B film during its depositing process by Qun-li Rao; Gang Bi; Qing-hua Lu; Hao-wei Wang; Xiao-lan Fan (pp. 28-33).

An electroless Ni-B film was deposited in natural state of the plating bath. The structure and composition distribution in depth of the film were explored by X-ray diffraction (XRD) and Auger electron spectroscopy (AES) after the deposition. It was found that the film experienced morphologic transformations during the deposition. The morphology of the film varied in-step with its structure and was presumably relevant with the changes of depositing rate. The mechanism that leads to the morphologic transformations has been discussed.

Keywords: Electroless; Ni-B film; Deposit structure

Influence of different deposition potentials on morphology and structure of CdSe films by C.M. Shen; X.G. Zhang; H.L. Li (pp. 34-41).

Cadmium selenide (CdSe) thin films have been electrodeposited on the titanium or ITO substrate in an electrolyte containing CdSO₄ and H₂SeO₃ at pH = 2.50 and temperature 298K. Influence of different deposition potentials on the surface morphology and crystal structure of CdSe films has been discussed. Compared with other deposition potentials (−0.65, −0.71 and −0.72V versus SCE), the nearly stoichiometric CdSe nanocrystalline films with smaller grain sizes of 80nm were obtained from 0.25M CdSO₄ + 0.25mM H₂SeO₃ + 0.25M Na₂SO₄ solution at deposition potential of −0.70V versus SCE. X-ray diffraction, atomic force microscope and scanning electron microscope were used to measure structure and morphology of CdSe films. The results indicated that the electrodeposited films were the smooth, compact and uniform at deposition potentials of −0.70V versus SCE.

Keywords: PACS; 81.15.P; 73.61.J; 71.20.M; NCadmium selenide; Electrodeposition; Thin films; Semiconductors

Interface behavior study of WC92–Co8 coating produced by electrospark deposition by Wang Ruijun; Qian Yiyu; Liu Jun (pp. 42-47).

WC92–Co8 coating produced by electrospark deposition effectively improves the surface performance of the substrate. The behavior of the interface between the WC92–Co8 coating and the substrate is studied in this paper. The high-melting-point WC92–Co8 was deposited onto the surface of Ti alloy, and the coating was usually more than 50μm thick. The surface of the coating is mainly composed of TiC and W₂C besides a small amount of W, and its micro hardness reaches HV1129. The coating dramatically improves the performance of the substrate.

Keywords: Electrospark deposition; Interface behavior; WC92–Co8

Pillar effects in MoS₂ catalysts supported on Al and Zr pillared clays in a hydrotreatment reaction by J.A. Col�n L.; J.A. de los Reyes; A. V�zquez; A. Montoya (pp. 48-62).

Molybdenum (Mo) supported on aluminum-pillared clay (Al-PILC) and zirconium-pillared clay (Zr-PILC) with contents of 0.6, 1.4 and 2.8 atoms of Mo/nm² were prepared and tested in the hydrogenation (HYD) of naphthalene (NP). It was found that the molybdenum sulfide (MoS₂) catalysts supported on Zr- pillared clays were more active than the samples supported on Al-pillared clays and catalysts supported on alumina. The catalysts were characterized by X-ray diffraction (XRD), thermogravimetric analysis, nitrogen adsorption and transmission electron microscopy (TEM). Characterization analysis clearly pointed out to a close interaction of MoS₂ with ZrO₂ in the pillared clays. Therefore, the highest hydrogenation activities can be related to the presence of an interaction of MoS₂ with ZrO₂, probably with a different electronic interaction between the active phase and the support, than that reported for the MoS₂/Al₂O₃ system.

Keywords: Clay; Zirconium-pillared clay; Aluminum-pillared clay; Hydrogenation; Naphthalene; Sulfur molybdenum

Effect of carbon content on the microstructure and the cracking susceptibility of Fe-based laser-clad layer by Sheng Li; Qian-Wu Hu; Xiao-Yan Zeng; Sheng-Qin Ji (pp. 63-70).

The laser cladding of Fe-based alloys on a medium carbon steel substrate was performed using a CO₂ laser and Ar shielding gas that was blown into a molten pool. The microstructure and cracking susceptibility of the laser-clad layers were studied in terms of carbon additions. Results show that the small change of the carbon content in the alloy powders can obviously change the microstructure and properties of the layers. When the carbon content is in the range of 0.3–0.4wt.%, the decrease of the carbon content in alloy powders will increase the hardness and toughness of the layers simultaneously under the same process parameters. As a result, crack-free coatings with high hardness can be obtained. As the carbon content increases from 0.2wt.% to 0.4wt.%, the segregation ratio of chromium increases, while the segregation ratios of nickel, manganese, and silicon first decrease and then increase. At the same time, a new designing principle concerning the composition and microstructure has been put forward, and the principal mechanisms of strengthening and toughening of the layers are fine-grain strengthening and low carbon martensitic phase transformation strengthening.

Keywords: PACS; 42.62.−b; 61.82.BgLaser cladding; Fe-based alloy; Carbon content; Cracking susceptibility; Peritectic

Structural characteristics of 2024 aluminum alloy plasma-based ion implanted with nitrogen then titanium by J.X. Liao; L.F. Xia; M.R. Sun; W.M. Liu; T. Xu; C.R. Yang; H.W. Chen; C.L. Fu; W.J. Leng (pp. 71-76).

As an interlayer in the gradient layers such as AlN/Ti/TiN/DLC prepared by plasma-based ion implantation (PBII) on 2024 aluminum alloy, titanium layer plays an important role in enhancing adhesion, reducing thermal stress, limiting the crack propagation, etc. A series of dual-layers prepared by PBII with nitrogen then titanium at various sputtering currents of titanium target on 2024 aluminum alloy have been reported in this paper. The composition distributions and the chemical states are analyzed using X-ray photoelectron spectroscopy (XPS). The structures are studied with grazing X-ray diffraction (GXRD). The results show that PBII with titanium strongly depends on the sputtering current. It is found that there exists a critical sputtering current corresponding only to a titanium-implanted layer containing TiAl₃. When the sputtering current exceeds the critical value, a titanium-deposited layer rich in α-Ti is formed on a titanium-implanted layer. By controlling the sputtering current an appropriate titanium interlayer can be prepared to meet the requirement of forming a proper gradient layer.

Keywords: Plasma-based ion implantation; Sputtering current; Interlayer

Characterization and performances of an Algerian diatomite-based gas chromatography support by O. Hadjadj-Aoul; R. Belabbes; M. Belkadi; M.H. Guermouche (pp. 131-139).

A sample of an Algerian diatomite is characterized and treated in order to use it as gas chromatographic solid column support. This sample has been characterized by various analytical methods such as X-ray diffraction, scanning electron microscopy (SEM), atomic absorption and emission spectrometries and mercury porosimetry.Tests of separation of various hydrocarbon and alcohol mixtures have been performed. Results show that the prepared supports have similar performances than those of commercial products. On the other hand, enrichment process does not show any significant increase in the support quality.

Keywords: Gas chromatography; Diatomite; Solid support; Characterization

Crystallographically-dependent ripple formation on Sn surface irradiated with focused ion beam by H.X. Qian; W. Zhou; Y.Q. Fu; B.K.A. Ngoi; G.C. Lim (pp. 140-145).

The metallographically polished polycrystalline Sn surface was sputtered by 30kV focused Ga⁺ ions at room temperature. The experiment was carried out using various FIB incidence angles (0°, 15°, 30°, and 45°) over a wide range of doses (10¹⁶–10¹⁸ions/cm²). The surface morphology was carefully characterized under the optical microscope, scanning electron microscope (SEM) and atomic force microscope (AFM). Ripples were observed on the irradiated areas even at the normal FIB incidence angle, which is not consistent with the Bradley–Harper (BH) rippling model. The orientation of ripples relies on crystallographic orientation rather than projected ion beam direction as predicted by BH model. The ripple wavelength is independent of ion dose, while ripple amplitude increases with ion dose. It is found that the ripples are formed by self-organization due to anisotropic surface diffusion in the low melting point metal.

Keywords: PACS; 79.20.Rf; 68.35.Fx; 81.65.CfSn; Focused ion beam; Ripple; Crystallographic orientation; AFM; Surface diffusion

The study of the influence of uniaxial stress on impurity complexes in silicon by G. Tessema; R. Vianden (pp. 146-154).

The influence of external uniaxial stress on the different indium-donor complexes in silicon has been studied using the perturbedγ –γ angular correlation (PAC) method. Such effect of an applied stress is detected by means of the probe atoms situated at different complexes in the sample. The current results showed that the responses of the probes in an extrinsic silicon samples are found to be dissimilar for the same value of stress. Such change in the local environments of the probe atoms could be associated with the various strain field created by the implantations of varied size of impurities. The phosphorous implantation in silicon has even lead to the complete absence of observable effect of the applied stress suggesting significant lose of the elasticity of the sample.

Keywords: PACS; 61.72.Cc; 61.72.Ji; 61.72.TtHyperfine interaction; Impurity defects; Silicon; Uniaxial stress

Nickel induced lateral crystallization behavior of amorphous silicon films by J.F. Li; X.W. Sun; M.B. Yu; G.J. Qi; X.T. Zeng (pp. 155-160).

Nickel induced lateral crystallization of amorphous silicon with and without electric field has been studied. Dendritic silicon growth behavior is observed, with crystallites of a few hundred nanometers in width and up to a few microns in length. The behavior can be understood from the preferential epitaxial growth of silicon from the (111) facets of the NiSi₂ precipitate, which forms during the early stage of the annealing process. The dendritic growth fronts are different with and without electric field in the nickel induced lateral crystallization process. Electric field is found to be beneficial in increasing the lateral crystallization rate and improving the film crystallinity. Joule heating plays an important role as well to enhance the lateral crystallization.

Keywords: PACS; 81.10.Jt; 94.20.Ss; 73.61.Cw.Crystallization; Polycrystalline silicon; Amorphous silicon; Nickel

Determination of growth modes via spectroscopy: new simple analytical models by Qiang Fu; Thomas Wagner (pp. 189-196).

Analytical models for the determination of thin film growth modes were developed on the basis of the simultaneous multilayer (SM) growth model. The models take into account up-step and down-step diffusion, enabling quick identification of the growth modes from experimentally obtained spectroscopic data. We tested the models by applying them to growth data from the literature that had been recorded via Auger electron spectroscopy (AES), X-ray photoelectron spectroscopy (XPS), and low-energy ion scattering (LEIS). We discuss the applicability of the new analytical models in comparison with the diffusion-corrected simultaneous multilayer (DCSM) model.

Keywords: PACS; 68.55.Ac; 68.47.Jn; 81.15.Aa; 68.35.FxFilm growth; Growth model; Auger electron spectroscopy (AES); X-ray photoelectron spectroscopy (XPS); Low energy ion scattering (LEIS); Surface diffusion

Detergency of stainless steel surface soiled with human brain homogenate: an XPS study by M. Richard; Th. Le Mogne; A. Perret-Liaudet; G. Rauwel; J. Criquelion; M.I. De Barros; J.C. C�tre; J.M. Martin (pp. 204-213).

In the detergency field of re-usable medical devices, a special attention is focused on the non conventional transmissible agent called prions which is a proteinaceous infectious agent. Few cleaning procedures are effective against prions and few techniques are available to study cleaning effectiveness with respect to proteins in general. In our study, X-ray photoelectron spectroscopy (XPS) has been used to evaluate the effectiveness of detergent formulations to remove proteins from stainless steel surface soiled with a brain homogenate (BH) from human origin. Our results showed that XPS is a reliable surface analysis technique to study chemical species remaining on surface and substrate properties after cleaning procedures. A semi-quantitative evaluation of the detergency effectiveness could also be performed.

Keywords: Detergency; Proteins; XPS; Stainless steel; Medical device; Human brain homogenate

Study of the multilayer metallic films topography modified by laser interference irradiation by A. Lasagni; F. M�cklich (pp. 214-221).

The thin bimetallic film systems Fe–Al, Fe–Ni, Ti–Al, and Ti–Ni were irradiated using a laser interference pattern with laser fluence values from 50 to 250mJ/cm². The thermal simulation was carried out to analyze the topographical effects. It was found that according to the laser fluence value, three different types of topographies can be obtained. For lower laser fluence values, the molten material in the lower layer induces deformation over the upper one obtaining a periodic pattern with a structure depth in the order of the layer thickness. If the laser fluence is high enough so that the upper layer reaches the melting point, this last is broken obtaining a high structured pattern consisting on a large depression and next two consecutive peaks. This threshold value can be estimated using the thermal simulation calculating the laser fluence at which the upper layer starts to melt. For higher laser fluence values, this pattern transforms into a periodical peak–valley structure with high structure depth. In both last two cases, the material at the interference peaks is removed. A model is suggested for explaining this behavior.

Keywords: PACS; 61.80.B; 07.05.T; 73.30; 68.35.B; 64.70.D; 42.25.HThermal simulation; Topography; Laser interference; Fe–Al; Fe–Ni; Ti–Al; Ti–Ni

Structural and energetic heterogeneities of pyrocarbon/silica gel systems and their adsorption properties by O. Seledets; V.M. Gun’ko; J. Skubiszewska-Zięba; R. Leboda; M. Musiatowicz; P. Podkościelny; A. Dąbrowski (pp. 222-235).

Two series of pyrocarbon/silica gel (CS) samples were prepared using pyrolysis of different amounts of glucose adsorbed onto silica gel under dynamic conditions in a rotary reactor and a high-pressure autoclave. The structural characteristics and the morphology of the CS samples studied by means of the AFM, TG, nitrogen and p-nitrophenol (PNP) adsorption and quantum chemical methods depend not only on the amounts of pyrocarbon deposits but also on the synthesis methods, since the autoclave process gives a stronger effect of the pore wall hydrolysis by water formed on the carbonization of glucose. A displacement of the main peak of the pore size distribution of CS samples depends on pyrocarbon content. CS samples prepared in the autoclave possess larger microporosity and adsorb greater amounts of PNP in comparison with the samples synthesized in the rotary reactor.

Keywords: Abbreviations; AFM; atom force microscopy; B3LYP; electron-exchange correlation functional; CONTIN; program for solution of integral equation with regularization; CS; pyrocarbon/silica gel; carbosil; CS-A; samples prepared in the autoclave; CS-R; samples prepared in the reactor; DFT; density functional theory; DTA; differential thermal analysis; INTEG; program for solution of integral equation with regularization; IPSD; _V; incremental PSD with respect to the pore volume; IPSD; _S; incremental PSD with respect to the specific surface area; LJ; Lennard–Jones potential; ND; Nguyen and Do method; PCM; solvation model; PNP; p; -; nitrophenol; PSD; pore size distribution; SPE; solid-phase extraction; Si-100; silica gel; Si-60; silica gel; Si-40; silica gel; TEM; transmission electron microscopy; TG; thermal gravimetryPACS; 61.43.Gt Powders, porous materials; 68.35.Bs Surface structure and topography; 68.35.Ct Interface structure and roughness; 68.35.Md Surface energy; thermodynamic propertiesSilica gel; Pyrocarbon/silica; Pore size distribution; Surface heterogeneity; p; -Nitrophenol adsorption; Pyrocarbon deposit structure

Passivation of TiO₂ by ultra-thin Al-oxide by Th. Dittrich; H.-J. Muffler; M. Vogel; T. Guminskaya; A. Ogacho; A. Belaidi; E. Strub; W. Bohne; J. R�hrich; O. Hilt; M.Ch. Lux-Steiner (pp. 236-243).

The passivation of sol–gel TiO₂ by ultra-thin layers of Al-oxide has been investigated using transient and spectral photovoltage (PV) techniques. The ultra-thin layers of Al-oxide were prepared by the ion-layer gas reaction (ILGAR) technique and modified by thermal treatments in air, vacuum or Ar/H₂S atmosphere. The samples where characterized by elastic recoil detection analysis (ERDA), X-ray photoelectron spectroscopy (XPS), and contact potential difference (CPD) technique. Without an Al-oxide surface layer, electronic states in the forbidden gap of TiO₂ are formed during thermal treatments in vacuum and Ar/H₂S. The trap density is strongly reduced at the TiO₂/Al-oxide interface. The formation of electronic defects is prevented by a closed ultra-thin layer of Al-oxide.

Keywords: PACS; 81.65.Rv; 73.50.Pz; 81.05.JePassivation; Photovoltage; Titania; Al-oxide

Variation in surface fractal of graphite due to the adsorption of polyoxyethylene sorbitan monooleate by Hou Qing-Feng; Lu Xian-Cai; Liu Xian-Dong; Hu Bai-Xing; Lu Zhi-Jun; Shen Jian (pp. 244-250).

The fractal analysis is carried out to study the influence of adsorption of polyoxyethylene sorbitan monooleate (Tween 80) on the surface properties of graphite. The surface fractal dimension (dSF), BET surface area (SBET) and pore size distribution (PSD) are calculated from low temperature nitrogen adsorption isotherms. The decline in thedSF of graphite surface is found as the adsorption amount of Tween 80 increases, which suggests that the adsorbed Tween 80 smoothes the graphite surface. Additionally, the observation of atomic force microscopy (AFM) proves that the original slit pores in pure graphite are blocked up and the step defect sites are screened by Tween 80, which may result in the reduction of graphite roughness. The PSD pattern of graphite changes after the adsorption due to the pore blocking effect.SBET of the graphite decreases as the adsorption amount of Tween 80 increases, which is attributed to both pore blocking effect and surface screening effect.

Keywords: Fractal dimension of surface; Graphite; Tween 80; Adsorption

Ultrathin multilayer of Fe and Ge: structure and magnetic properties by Surendra Singh; Saibal Basu; M. Vedpathak; R.H. Kodama; R. Chitra; Y. Goud (pp. 251-259).

Metal-semiconductor multilayers are interesting, artificial structures as prospective candidates for spin injection devices. A Fe–Ge multilayer sample with very thin individual layers (few crystallographic planes) has been deposited by sputtering on Si[100] substrate. We have characterized the structure of this multilayer sample using X-ray diffraction, X-ray reflectometry and neutron reflectometry. The magnetic moment density in the ferromagnetic Fe layer has been obtained by polarized neutron reflectometry and the bulk magnetic behavior of the thin film by SQUID magnetometer measurements. We found that the film is a soft ferromagnet at room temperature with a substantially reduced magnetic moment of the Fe atoms.

Keywords: PACS; 61.10.Kw; 61.12.Ha; 68.35.Et; 68.65.Ac; 75.70.CnNeutron reflectometry; X-ray reflectometry; Interface; Multilayer; structure; Magnetic moment

A simple method for the preparation of ultrahigh sensitivity surface enhanced Raman scattering (SERS) active substrate by Gang Wei; Hualan Zhou; Zhiguo Liu; Zhuang Li (pp. 260-267).

By immersing mica modified with cetyltrimethylammonium bromide (CTAB) into the silver colloid, a high efficient surface enhanced Raman scattering (SERS) active substrate was formed within 2h at room temperature. The limit of detection of the substrate for Rhodamine 6G is up to 1×10⁻¹⁴M. Changing the concentration of silver colloid and the treating time, various silver aggregates such as nanocrystals, clusters and films were found, and the SERS spectra of these aggregates were also obtained. The results of SERS revealed that CTAB could accelerate aggregation of the silver colloid and cause great Raman enhancement. Bilayer of CTAB is very important for aggregation of silver colloid and the aggregation extent is the main factor for the enormous enhancement on this substrate.

Keywords: PACS; 82.65.P; 61.43.H; 61.16.C; 82.70.DSurface enhanced Raman scattering; Aggregation; Atomic force microscopy; Colloid

Adhesion strength study between plasma treated polyester fibres and a rubber matrix by H. Krump; M. Šimor; I. Hudec; M. Jaššo; A.S. Luyt (pp. 268-274).

In this work, the adhesion strength between poly(ethylene terephthalate) (PET) fibres and styrene-butadiene rubber (SBR) was studied. The effects of atmospheric plasma treatment, used to increase adhesion strength between PET fibres and the rubber matrix, were investigated and compared. It was confirmed that lubricants on the fibres caused a decrease in adhesion strength between the plasma treated reinforcing PET fibres and the SBR rubber matrix. These lubricants can be removed by acetone. When washed and treated in plasma, a substantial improvement in adhesion strength was observed. No ageing in air before combination with the rubber matrix was observed. This confirmed that the plasma streamers caused the creation of a new, relatively stable chemical species on the polymer surface. It suggests that the surface modification of PET fibres by plasma treatment at atmospheric gas pressure is a suitable and technologically applicable method for the improvement of adhesion strength of polyester reinforcing materials to rubber.

Keywords: Adhesion strength; Atmospheric plasma treatment; Poly(ethylene terephthalate); Styrene-butadiene rubber (SBR); Lubricants; Ageing; GC–MS

Effect of excess Pb on crystallinity and ferroelectric properties of PZT(40/60) films on LaNiO₃ coated Si substrates by MOD technique by J.H. Ma; X.J. Meng; J.L. Sun; T. Lin; F.W. Shi; G.S. Wang; J.H. Chu (pp. 275-279).

Pb(Zr_0.4Ti_0.6)O₃ [PZT(40/60)] films were deposited onto LaNiO₃ (LNO) coated Si substrates by metal-organic decomposition (MOD) technique. Excess Pb was incorporated in the film by using excess Pb (2%–15%) in the solution. The crystallinity and ferroelectric properties of PZT films were investigated by using X-ray diffraction (XRD), RT66A test system and HP4194 impedance analyzer, respectively. Rayleigh law was employed to analyze the defect concentration in the films. The results show that all the PZT films show the (100) preferential orientation with complete perovskite structure except for the 2% film displaying some pyrochlore phase. The (100) preferential orientation is mainly attributed to LNO bottom electrode, which has the highly (100) preferential orientation. The 10% film shows the best polarization and dielectric properties. The remnant polarization and coercive field are about 10.1μC/cm² and 73kV/cm under an electric field around 330kV/cm, respectively. And the dielectric constant and dissipation factor are about 656 and 0.022 at a frequency of 1kHz, respectively. The good ferroelectric properties of the 10% film are mainly attributed to the low defect concentration in the film.

Keywords: PACS; 77.84.Dy; 68.55.JK; 77.80.-ePZT thin films; Excess Pb; Crystallinity; Ferroelectric properties

The fabrication and characterization of ZnO UV detector by Tae-Hyoung Moon; Min-Chang Jeong; Woong Lee; Jae-Min Myoung (pp. 280-285).

ZnO films were deposited on GaAs substrates by radio frequency (rf) magnetron sputtering followed by an ambient-controlled heat treatment process for arsenic doping. In Hall measurements, the As-doped ZnO films showed the characteristics of p-type semiconductor. The ZnO thin film p–n homojuctions were then fabricated to investigate the electrical properties of the films. The p–n homojunctions exhibited the distinct rectifying current–voltage ( I– V) characteristics. The turn-on voltage was measured to be ~3.0V under the forward bias. When ultraviolet (UV) light (λ = 325nm) was irradiated on the p–n homojunction, photocurrent of ~2mA was detected. Based on these results, it is proposed that the p–n homojunction herein is a potential candidate for UV photodetector and optical devices.

Keywords: PACS; 68.55.−a; 73.90.+f; 78.66.HfZnO homojunction; UV detector; rf Magnetron sputtering; Photocurrent

Fine grain growth of nickel electrodeposit: effect of applied magnetic field during deposition by V. Ganesh; D. Vijayaraghavan; V. Lakshminarayanan (pp. 286-295).

The electrodeposition of nickel from a nickel sulphamate bath in the presence of a magnetic field applied at an angle of 45° to the cathode surface produces a nickel deposit with a fine grain structure. The sizes of grains vary from ∼17 to 25nm. We have used scanning electron microscopy (SEM), scanning tunneling microscopy (STM) and X-ray diffraction (XRD) to characterize the surface morphology of the deposit. The SEM pictures show the formation of domain growth of nickel in which the nickel nanoparticles are mostly concentrated at domain boundaries while STM and XRD analysis show the existence of individual nanoparticles. From the chronopotentiometry studies during magnetoelectrolysis of nickel, we find a significant lowering of overpotential with time and large negative shift in electrode potential in the presence of a magnetic field. We believe from these results that magnetic field induced convection increases the mass transfer rate, reduces the concentration polarisation and leads to the growth of fine grain deposit. The large shift in electrode potential on the application of magnetic field is attributed to the field-induced shift in chemical potential of the ferromagnetic nickel electrode. We have used cyclic voltammetry (CV) to determine the roughness factor and steady state current-potential plots to study the hydrogen evolution reaction on the nickel-electrodeposited surface.

Keywords: PACS; 81.15.P; 61.46; 75.50.KConvective flow; Magnetoelectrolysis; Magnetohydrodynamic effect; Nanoparticles; Overpotenial; Roughness factor

Sub-micron scale patterning using femtosecond laser and self-assembled monolayers interaction by Wonseok Chang; Moojin Choi; Jaegu Kim; Sunghak Cho; Kyunghyun Whang (pp. 296-304).

Standard positive photoresist techniques were adapted to generate sub-micron scale patterns of gold substrate using self-assembled monolayers (SAMs) and femtosecond laser. Self-assembled monolayers formed by the adsorption of alkanethiols onto gold substrate are employed as very thin photoresists. The process underlying photopatterning of SAMs on gold is well-known at the phenomenological level. Alkanethiolates formed by the adsorption of alkanethiols are oxidized on exposure to UV light in the presence of air to alkylsulfonates. Specifically, it is known that deep UV light of wavelength less than 200nm is necessary for oxidation to occur. In this study, solid state femtosecond laser of wavelength 800nm is applied for photolithography. The results show that ultrafast laser of near infrared (NIR) range wavelength can replace deep UV laser source for photopatterning using thin organic films. The essential basis of our approach is the photochemical excitation of specific reactions in a particular functional group (in this case a thiolate sulfur atom) distributed with monolayer coverage on a solid surface. Femtosecond laser photolithography could be applied to fabricate the patterning of surface chemical structure and the creation of three-dimensional nanostructures by combination with suitable etching methods.

Keywords: PACS; 81.16.Rf; 81.16.Dn; 07.79.FcFemtosecond laser patterning; Self-assembled monolayer; Photodecomposition; Photooxidation

Surface structure of low-coveraged Cs on Si(0 0 1)-(2�1) system by J.Y. Park; J.H. Seo; J.Y. Kim; C.N. Whang; S.S. Kim; D.S. Choi; K.H. Chae (pp. 305-311).

Alkali metals (AM) on semiconductors have been investigated as a simple model system for the metal-semiconductor interfaces due to their simple electronic structures. Especially, cesium (Cs) on Si(0 0 1) surface has been studied with various experimental techniques. In this study, we investigated the atomic structure of initial Cs adsorption on Si(0 0 1)-(2�1) surface using coaxial impact collision ion scattering spectroscopy. When Cs atoms are adsorbed on Si(0 0 1)-(2�1) up to 0.2 ML at room temperature, the initial adsorption site is on-top T3 site with poor periodicity and the length of Si dimer is reserved as in the clean Si(0 0 1) surface. It is also found that Cs atoms adsorbed on Si(0 0 1) surface with a height of2.83�0.05 � from the second layer of Si(0 0 1) surface.

Keywords: PACS; 61.18.Bn; 68.35.Bs; 68.55.JkSurface structure; Morphology, Roughness and topography; Silicon; Cesium; Alkali metals; Low energy ion scattering (LEIS)

Microthermal machining using scanning thermal microscopy by Te-Hua Fang; Win-Jin Chang (pp. 312-317).

Microthermal machining using scanning thermal microscopy (SThM) has been performed on polymethylmethacrylate (PMMA) materials, which are a soft polymer and suitable for microthermal machining. The probe of the SThM is heated and used as a machining tool on the PMMA material. Adjustment of the resistance can control the probe’s temperature. To obtain good machining quality, the probe temperature must be continuously controlled. The temperature of the machined area of the sample’s surface must be higher than the melting point of the PMMA material. However, a lower machined quality occurs when the probe temperature is too high. Furthermore, the adhesive phenomenon is very apparent when the contact mode is used in SThM machining. The microthermal machining of PMMA materials using SThM in semi-contact mode at a probe temperature of 400°C has the best results. The technique can be used to process a complicated pattern and applied for use of high-density data storage.

Keywords: SThM; Microthermal machining; High-density data storage; Polymer

Influence of surface roughness on water- and oil-repellent surfaces coated with nanoparticles by Chien-Te Hsieh; Jin-Ming Chen; Rong-Rong Kuo; Ta-Sen Lin; Chu-Fu Wu (pp. 318-326).

Various rough surfaces coated with titanium oxide nanoparticles and perfluoroalkyl methacrylic copolymer were conducted to explore the influence of surface roughness on the performance of water- and oil-repellence. Surface characteristics determined from nitrogen physisorption at −196°C showed that the surface area and pore volume increased significantly with the extent of nanoparticle ratio, indicating an increase of surface roughness. Due to the surface nano-coating, the maximum contact angles of water and ethylene glycol (EG) droplets increased up to 56 and 48%, respectively, e.g. from 105° to 164° for water droplets and from 96° to 144° for EG droplets. The excellent water- and oil-repellence of the prepared surfaces was ascribed to this increase of surface roughness and fluorinated-contained surface. Compared with Wenzel model, the Cassie model yielded a fairly good fit to the simulation of contact angle with surface roughness. However, a derivation of 3°–10° at higher roughness still existed. This phenomenon was very likely due to the surface heterogeneity with different pore size distributions of the fractal surfaces. In this case, it was unfavorable for super repellency from rough surface with larger mesopore fraction because of its capillary condensation, reflecting that micropore provided more air resistance against wettability.

Keywords: Water-repellency; Oil-repellency; Surface roughness; Nanostructures

Investigation of the inhibiting action of O-, S- and N-dithiocarbamato(1,4,8,11-tetraazacyclotetradecane)cobalt(III) complexes on the corrosion of iron in HClO₄ acid by K. Babić-Samardžija; K.F. Khaled; N. Hackerman (pp. 327-340).

The inhibiting properties of four macrocyclic cobalt(III) complexes of the general formula [Co^III(Rdtc)cyclam](ClO₄)₂, where cyclam and Rdtc⁻ refer to 1,4,8,11-tetraazacyclotetradecane and morpholine-, thiomorpholine-, piperazine-, N-methylpiperazine-dithiocarbamates, respectively, has been studied on the corrosion of iron in aerated 0.1M HClO₄ solutions by potentiodynamic polarization (dc) technique and electrochemical impedance spectroscopy (ac). Inhibitor efficiency for the corrosion of iron is found to be better for cobalt complexes then for related amino-ligands. The impedance increases with inhibitor concentration. Polarization curves indicate that the inhibitors are predominantly mixed-type. Better protection by the complex inhibitors was obtained with longer immersion time. The best fit for inhibitors adsorption is obtained using the Langmuir isotherm model. Molecular modeling calculations were used to correlate structural properties of the complex species and their inhibition efficiency.

Keywords: Corrosion inhibition; Iron; Perchloric acid; Cobalt complexes

Pyridine–pyrazole compound as inhibitor for steel in 1M HCl by M. Bouklah; A. Attayibat; B. Hammouti; A. Ramdani; S. Radi; M. Benkaddour (pp. 341-348).

The influence of 3,5-dimethyl-1 H-pyrazole (P1), pyridine (P2) and 2-(3-methyl-1 H-pyrazol-5-yl) pyridine (P3) on the corrosion inhibition of steel in molar hydrochloric acid solution is studied using weight-loss, potentiodynamic and EIS measurements. Results obtained shows that P3 is the best inhibitor and its inhibition efficiency increases with the increase of concentration to attain 89% since 10⁻³M. Potentiodynamic polarisation studies clearly reveal that it acts essentially as a cathodic inhibitor. The inhibitor studied reduces the corrosion rates. E (%) values obtained from various methods used are in good agreement. Adsorption of P3 on steel surface has an S-shaped adsorption isotherm.

Keywords: Steel; Pyridine–pyrazole; Inhibition; Corrosion; Hydrochloric acid

The stability of SiC coating and SiO₂/SiC multilayer on the surface of graphite for HTGRs at normal service condition by Fu Zhiqiang; Liang Tongxiang; Robin Jean-Charles; Tang Chunhe (pp. 349-354).

The stability of SiC coating in helium with a low concentration of O₂, CO₂, and H₂O is a key factor for their application in improvement of oxidation resistance of graphite for high temperature gas-cooled reactors (HTGRs). Through thermodynamic analysis, it is found that the influence factor controlling the critical temperature of passive oxidation for SiC is partial pressure of active gas in helium; the critical temperature of passive oxidation for SiC increases with the partial pressure of O₂, CO₂, and H₂O, SiC is prone to undergo active oxidation in He–CO₂ and He–H₂O system. SiO₂/SiC multilayer coating can improve the oxidation resistance of graphite at higher temperature than SiC coating does under normal operation condition for HTGRs.

Keywords: HTGRs; SiC; SiO; ₂; /SiC multiplayer; Thermodynamics

Evolution of morphologic properties on the preparation of Ir/Al₂O₃ catalysts with high metallic contents by T.G. Soares Neto; A.J.G. Cobo; G.M. Cruz (pp. 355-365).

Ir/Al₂O₃ catalysts with high metallic contents are applied on satellite thruster to decompose hydrazine. The present work has as principal aim the study of the morphologic evolution of Ir/Al₂O₃ catalysts with metallic contents from 12 to 30wt.%. The catalysts were prepared through consecutive impregnations from the H₂IrCl₆ precursor, using three different types of aluminas. The specific surface area, volume and distribution of pore size, specific metallic area and metallic particles average diameter, as well as the mechanical resistance were determined. Results show that the Ir addition leads to a decrease of the specific surface area and the pores volumes, while increases the mechanical resistance. Values for average diameter of metallic particles are comprised between 1.4 and 2.4nm when the metallic content increases from 12 to 30wt.%. Catalysts containing 30wt.% of Ir presents specific metallic areas around 30m²/g, although pores volumes and distributions of pore size were considerably different for the three supports. Their metallic particles dispersion and size values are very close to those of a commercial catalyst Shell 405, even though the preparation methods were different. These results show that there is a strong interaction between the alumina and the iridium precursor.

Keywords: PACS; 61.46.+wAlumina; Catalysts characterization; Catalysts preparation; Hydrazine decomposition; Iridium catalysts; Spacecraft propulsion

Characteristic responses of a semiconductor gas sensor depending on the frequency of a periodic temperature change by Satoshi Nakata; Hirokazu Okunishi (pp. 366-374).

A novel gas-sensing system based on a dynamic nonlinear response is reported to enhance the selectivity toward sample gases using a single detector. A periodic temperature change was applied to a semiconductor gas sensor and the resulting conductance of the sensor was evaluated by fast Fourier transformation (FFT). The dynamic nonlinear response to the sample gases was further characterized depending on the frequency of the temperature change. The characteristic sensor response under the application of a temperature change was theoretically simulated by considering the kinetics of gas molecules on the semiconductor surface.

Keywords: Semiconductor; Gas sensor; Nonlinear; Tin dioxide; Temperature change

Dependence of the electronic parameters on the In _yGa₁₋ _yAs quantum well width in modulation-doped Al _xGa₁₋ _xAs/In _yGa₁₋ _yAs/GaAs strained single quantum wells by D.U. Lee; T.W. Kim; K.H. Yoo (pp. 375-380).

The variation of the electronic parameters in the subband as a function of the In _yGa₁₋ _yAs quantum well width in modulation-doped strained Al _xGa₁₋ _xAs/In _yGa₁₋ _yAs/GaAs single quantum wells were investigated by means of Shubnikov-de Haas (S-dH) and Van der Pauw Hall-effect measurements. The fast Fourier transform (FFT) of the S-dH oscillations and the Hall-effect data showed that the carrier density and the mobility of the two-dimensional electron gas (2DEG) occupied in the subband increased as the quantum well width increased. The increase in the 2DEG density with increasing the In _yGa₁₋ _yAs well width originated from an increase in the energy difference between the energy level of the electronic subband and Fermi energy, and the increase in the 2DEG mobility is attributed to a decrease of the scattering source. The electronic subband energies, the corresponding wavefunctions, and the Fermi energies in the Al _xGa₁₋ _xAs/In _yGa₁₋ _yAs/GaAs single quantum wells were calculated by a self-consistent method taking into account the exchange-correlation effect together with the strain and nonparabolicity effects. These results indicate that the electronic parameters in Al _xGa₁₋ _xAs/In _yGa₁₋ _yAs/GaAs strained single quantum wells are significantly dependent on the quantum well width.

Keywords: PACS; 68.55; Bd.73.20.Dx; 73.25.+iQuantum structures; Two-dimensional electron gas; Electronic structure

A study on the reaction between chlorine trifluoride gas and glass-like carbon by Yoji Saito; Takashi Nishizawa; Maki Hamaguchi (pp. 381-387).

The reaction between glass-like carbon (GC) and chlorine trifluoride (ClF₃) gas was investigated with weight measurements, surface analysis, and gas desorption measurements, where the ClF₃ gas is used for the in situ cleaning of tubes in silicon-related fabrication equipment. From Auger electron spectroscopy and X-ray photoelectron spectroscopy measurements, a carbon mono-fluoride, –(CF) _n–, film near the surface of GC is considered to be grown onto the GC surface above 400°C by the chemical reaction with ClF₃, and this thickness of the fluoride film depends on the temperature. The grown fluoride film desorbs by annealing in a vacuum up to 600°C. Although GC is apparently etched by ClF₃ over 600°C, the etch rate of GC is much lower than that of SiC and quartz.

Keywords: PACS; 81.65.Cf; 81.65.Kn; 82.80.PvGlass-like carbon; Chlorine trifluoride; Photoelectron spectroscopy; Temperature-programmed desorption

Variations of work function and corrosion behaviors of deformed copper surfaces by W. Li; D.Y. Li (pp. 388-395).

Surface work function (WF) and the corrosion behavior of copper under influence of plastic strain were investigated using experimental and computational approaches. It was observed that both the corrosion potential (Ecorr) and the WF decreased while the corrosion rate increased with an increase in plastic strain, indicating that the strained surface layer became more electrochemically active. Ecorr and WF eventually became stable when the plastic strain reached a certain level. However, the corrosion rate continuously increased. It was demonstrated that this continuous increase in corrosion rate could be dominated by the dislocation density rather than the corrosion potential. The study has shown that the WF is closely related to the corrosion potential and could thus be a sensitive parameter for investigating mechanisms responsible for corrosive wear. The investigation of the effects of plastic deformation on the corrosion behavior would help to fundamentally understand the synergism of wear and corrosion.

Keywords: PACS; 68.35.Ct; 71.15.Dx; 73.30.+yWork function; Corrosion potential; Dislocation density

Inhibition of steel pitting corrosion in HCl by some inorganic anions by S.A.M. Refaey (pp. 396-404).

The effect of Mn and V content on corrosion behavior of mild steel in different concentration of HCl was investigated. The increase of Mn and V content in the steel sample leads to increasing corrosion resistance. The effect of phosphate, molybedate and chromate anions on the corrosion of steel in HCl solution has been studied using weight loss, potentiodynamic and scanning electron microscope (SEM) techniques. The addition of increasing concentrations of phosphate, molybedate and chromate anions causes a shift of the pitting potential ( E_pit) in the positive direction, indicating the inhibitive effect of the added anions on the pitting attack. The phosphate anion has a stronger inhibitive effect of the pitting corrosion. The inhibition efficiency (IE) of different inhibitors increases with the increasing of phosphate concentration and decreases with the increasing the concentration of molybedate and chromate anions. The presence of these anions inhibits the pitting corrosion of steel samples in the order phosphate > molybedate > chromate. The effect of different inorganic anions on the corrosion behavior of two different composition steel samples was also studied in HCl solution.

Keywords: Steel; Corrosion; HCl; Inhibition

Kinetic interface roughening and magneto resistance of sputter-deposited Fe/Ni₇₅B₂₅ multilayers by R. Mustafa �ks�zoglu; Gerhard Miehe; Hartmut Fuess (pp. 405-413).

The roughening of interfaces as a function of layer thickness and magneto transport properties have been investigated on sputter-deposited Fe/Ni₇₅B₂₅ multilayer films. X-ray reflectivity data were recorded for Ni₇₅B₂₅(72nm) film and for [Fe(2nm)/Ni₇₅B₂₅(2nm)]₁₆ and [Fe(4nm)/Ni₇₅B₂₅(4nm)]₈ multilayer films. A power law dependence of the interfacial width of growing Fe/Ni₇₅B₂₅ interfaces was observed. The resulting growth exponents β were found to be in the range of 0.55–0.58 in the initial growth stage of the multilayer with lower Fe/Ni₇₅B₂₅ repetition thickness and at approximately 0.34 for multilayer with higher repetition thickness. The growth exponents were compared with theoretical calculations. High resolution electron microscopy revealed the columnar growth of the Fe/Ni₇₅B₂₅ multilayer. Additionally, an increase of magnetoresistance was observed by the multilayering of Ni₇₅B₂₅ films with Fe interlayers.

Keywords: PACS; 68.35.Ct; 61.10.Kw; 68.65.Ac; 75.47.DeKinetic interface roughening; Fe/Ni; ₇₅; B; ₂₅; interfaces; Magneto transport properties; X-ray reflectivity; DC-magnetron-sputtering

Eutectic alloy microstructure: atomic force microscopy analysis by C.A.R. Costa; W.W. Batista; C.T. Rios; S. Milenkovic; M.C. Gon�alves; R. Caram (pp. 414-423).

The exciting microstructures found in several eutectic alloys are a result of a cooperative growth, which is connected to the atomic transfer in the melt ahead the solid/liquid interface. In a eutectic system, the growth of solid phases depends on the simultaneous rejection of constituents to the liquid phase, which causes adjustments of the melt composition and hence, mass transport by diffusion normal to the growth direction. Generally, eutectic microstructures are examined by using optical (OM) and scanning electron microscopy (SEM). While OM may not provide the necessary resolution, the eutectic microstructure may present three-dimensional features, as a result of etching, which is not always possible to be observed by SEM. As an alternative, this paper describes the use of atomic force microscopy (AFM) in understanding micro-scale feature of a eutectic microstructure. For such a purpose, directionally solidified samples of a Ni–Al–V lamellar eutectic, a Ni–Al–Mo fibrous eutectic and a Ni–Al–Nb three-phase eutectic were examined. The results obtained provided a new picture of multi-phase microstructures and allows one to understand their new characteristics.

Keywords: Composites; Intermetallic compounds; Microstructure; Atomic force microscopy; Solidification

Microstructured silicon surfaces for field emission devices by G. Sotgiu; L. Schirone (pp. 424-431).

Enhanced field emission of electrons from silicon surfaces was obtained by surface microstructuring, by means of electrochemical oxidation in organic solutions containing HF. Morphological characterisations showed the formation of cylindrical rods, randomly distributed with relative spacing of a few microns. They are originated at the top of silicon pyramids and have typical diameter in the 100nm range. Variable length in the 1–50μm range was obtained, by adjusting the process parameters. Electron field emission properties were characterised for several samples, prepared in different conditions: the emission threshold was found to be strongly correlated with the overall charge exchanged during electrochemical oxidation. In the most favourable conditions, the threshold field for the emission of an electron current I_th = 10⁻¹⁰A was 11.1V/μm.

Keywords: PACS; 68.55−a; 79.70.+q; 81.20.Zx; 85.45.−wElectron field emission; Microstructured silicon; Si tip array

Reciprocating sliding wear behavior of laser-clad small amplitude Mo₂Ni₃Si/NiSi metal silicide composite coatings by X.D. Lu; H.M. Wang; Z.R. Zhou (pp. 432-440).

Mo₂Ni₃Si/NiSi metal silicide composite coatings with a fine microstructure consisting of Mo₂Ni₃Si primary dendrites and the interdendritic Mo₂Ni₃Si/NiSi eutectics were fabricated on austenitic stainless steel AISI 321 by laser cladding process. Small amplitude reciprocating sliding wear resistance of the coatings is evaluated as functions of normal load and slip amplitude and the wear mechanisms were discussed based on worn surface morphology observations. Results showed that the Mo₂Ni₃Si/NiSi coatings have excellent small amplitude reciprocating sliding wear resistance.

Keywords: Metal silicide; Reciprocating sliding wear; Coatings; Laser cladding

Surface free energies of electroless Ni–P based composite coatings by Q. Zhao; Y. Liu; E.W. Abel (pp. 441-451).

Surface free energy of a solid surface gives a direct measure of intermolecular interactions at interfaces and has a strong influence on adsorption and adhesion behaviour. However few data are available for the surface free energies of electroless Ni–P based composition coatings. In this paper, the electroless Ni–P, Ni–P-surfactant, Ni–Cu–P, Ni–P–PTFE and Ni–Cu–P–PTFE composite coatings were prepared under various coating conditions. The chemical compositions, surface morphology and thickness of the coatings were measured using an energy dispersive X-ray microanalysis (EDX), a scanning electron microscope (SEM) and a digital micrometer respectively. The contact angles of water, diiodomethane and ethylene glycol on the coatings were measured automatically using dataphysics OCA-20 contact angle analyser. The surface free energy of the coatings and their components (e.g. dispersion, polar or acid/base portions) were calculated using various methods. The experimental results showed that the incorporation of surfactant or PTFE particles into Ni–P matrixes has a significant influence on the surface free energy of the coatings, while the incorporation of copper into Ni–P matrixes has no significant influence on the surface free energy of the coatings.

Keywords: Surface free energy; Electroless; Ni–P; Ni–Cu–P; Ni–P–PTFE; Ni–Cu–P–PTFE

Interband Stark effects in In _xGa₁₋ _xAs/In _yAl₁₋ _yAs coupled step quantum wells by J.H. Kim; T.W. Kim; K.H. Yoo (pp. 452-455).

The effects of an electric field on the interband transitions in In _xGa₁₋ _xAs/In _yAl₁₋ _yAs coupled step quantum wells have been investigated both experimentally and theoretically. A In _xGa₁₋ _xAs/In _yAl₁₋ _yAs coupled step quantum well sample consisted of the two sets of a 50Å In_0.53Ga_0.47As shallow quantum well and a 50Å In_0.65Ga_0.35As deep step quantum well bounded by two thick In_0.52Al_0.48As barriers separated by a 30Å In_0.52Al_0.48As embedded potential barrier. The Stark shift of the interband transition energy in the In _xGa₁₋ _xAs/In _yAl₁₋ _yAs coupled step quantum well is larger than that of the single quantum well, and the oscillator strength in the In _xGa₁₋ _xAs/In _yAl₁₋ _yAs coupled step quantum well is larger than that in a coupled rectangular quantum well. These results indicate that In _xGa₁₋ _xAs/In _yAl₁₋ _yAs coupled step quantum wells hold promise for potential applications in optoelectron devices, such as tunable lasers.

Keywords: PACS; 73.21.Fg; 78.55.Cr.Nanostructures; Optical properties; Electronic states

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Applied Surface Science (v.240, #1-4)