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Applied Surface Science (v.254, #2)

The microstructure and specific properties of La/HAP composite powder and its coating by Hui Yang; Lin Zhang; Ke-Wei Xu (pp. 425-430).

La/HAP composite powder, a novel bioactive material, was prepared using co-precipitation method. The La/HAP coating was obtained for the first time through the dip-coating method, starting from the sols of La/HAP and TiO₂ particles. The compositions and coating of as-produced La/HAP composite powder sintered at temperatures from 300 to 750°C were analyzed by means of X-ray diffraction (XRD). The changes of the ion groups in as-prepared La/HAP composite powder were characterized by using Fourier transform infrared (FTIR) spectroscopy. Their surface morphologies were observed by means of scanning electron microscope (SEM). The results show that the La/HAP composite powder has higher thermostability than pure HAP powder and La can refine HAP particle and restrain the decomposition of HAP. Consequently, in coating process the heat-treatment temperature is lower (750°C) using the synthesized La/HAP powder than that using pure HAP (900°C). The La/HAP coating mainly contains HAP, TiP or Ti₃P₅ and TiO₂ phases as well as a little CaTiO₃ crystal, a very ideal composition to enhance bioactivity of biomaterials. These unique properties of the La/HAP composite powder are beneficial to enhance the strength and bioactivity of coating when it is used as a starting material in coating process.

Keywords: Biomaterials; Characterization; Nanomaterials; Phosphates; Rare earth compounds; Calcium compounds

Adsorption structure of germanium on the Ru(0001) surface by Y.H. Lu; Y. Jia; H.J. Zhang; B. Song; H.Y. Li; S.N. Bao; P. He (pp. 431-435).

Coverage-dependent adsorption energy of the Ge/Ru(0001) growth system and the geometrical distortions of the most stable adsorption structure are investigated through first-principles calculations within density functional theory. A local minimum in adsorption energy is found to be at a Ge coverage of 1/7 monolayer with a Ru(0001)-21×21-3Ge symmetry. Based on this stale superstructure, the scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS) images are simulated by means of surface local-density of states (LDOS). The results are consistent well with the STM measurements on the21×21 phase for Ge overlayer on Ru(0001). From this stimulation, the relations between the STM images and the lattice distortion are also clarified.

Keywords: PACS; 71.15.Mb; 68.37.Ef; 68.03.HjGe/Ru growth system; Adsorption structure; Ab initio DFT calculation; Scanning tunneling microscopy

Stress dependence of growth mode change of epitaxial layered cobaltite γ-Na_0.7CoO₂ by J.Y. Son; Han-Bo-Ram Lee; J.H. Cho (pp. 436-440).

We report stress dependence of growth characteristics of epitaxial γ-Na_0.7CoO₂ films on various substrates deposited by pulsed laser deposition method. On the sapphire substrate, the γ-Na_0.7CoO₂ thin film exhibits spiral surface growth with multi-terraces and highly crystallized texture. For the γ-Na_0.7CoO₂ thin film grown on the (111) SrTiO₃ substrate, the nano-islands of ∼30nm diameter on the hexagonal grains are observed. These islands indicate that the growth mode changes from step-flow growth mode to Stranski–Krastanow (SK) growth mode. On the (111) MgO substrate, the large grains formed by excess adatoms covering an aperture between hexagonal grains are observed. These experimental demonstrations and controllability could provide opportunities of strain effects of Na_xCoO₂, physical properties of thin films, and growth dynamics of heterogeneous epitaxial thin films.

Keywords: Thermoelectric material; Growth mode; Epitaxial thin film; Na; _x; CoO2

Cu(II) recognition materials: Fluorophores grafted on mesoporous silica supports by Krzysztof Kledzik; Maja Orłowska; Dorota Patralska; Marcin Gwiazda; Julia Jezierska; Stanisław Pikus; Ryszard Ostaszewski; Andrzej M. Kłonkowski (pp. 441-451).

There were designed and synthesized naphthalene and pyrene derivatives consisting of fluorophore group and of receptor fragment with donor N and O atoms. These fluorosensors were covalently attached by grafting carboxyl group to surfaces of silica xerogel or mesoporous silicas (MCM-41 and MCM-48) functionalized either with 3-aminopropyl or 3-glycidoxypropyl groups. The pyrene derivatives2 and3 covalently grafted on MCM-48 silica functionalized with 3-aminopropyl groups are potential recognition elements of a fluorescence chemical sensor.Fluorescence emission of the prepared recognition materials is quenched specifically owing to photoinduced electron transfer (PET) effect after coordination reactions with Cu(II) ions. Moreover, both the materials exhibit selectivity for Cu(II) ions in aqueous solutions in presence of such metal ions as: alkali, alkaline earth and transition. During UV irradiation the studied recognition elements undergo slowly photochemical degradation.

Keywords: Mesoporous silica; Pyrene derivative; Fluorescence emission; Fluorophore; Recognition element

A novel approach for the preparation of organic-siloxane oligomers and the creation of hydrophobic surface by Baotan Zhang; Bailing Liu; Xiaobo Deng; Shunsheng Cao; Xiaohui Hou; Hualin Chen (pp. 452-458).

In this paper, poly(acrylate- g-siloxane) with novel comb-like structure was designed and prepared so as to create a strongly hydrophobic polymer surface. In order to achieve this goal, a series of organic-siloxane oligomers with different chain lengths and a double bond were firstly synthesized through the catalytic reforming and hydrosilylation reaction. Then, poly(acrylate- g-siloxane) was prepared by the copolymerization of the resulting oligomers with acrylate via emulsion polymerization. The as-synthesized oligomers were characterized by¹H NMR and UV spectrometry, and the morphologies and surface chemical compositions of the dried membrane were investigated by FT-IR, XPS, as well as AFM. XPS analysis result shows that the chemical composition of the membrane's surface was rich in polysiloxane segments, which could be responsible for an increase of surface water repellency (the contact angle could reach 115° at a lower content of polysiloxane). A further investigation suggest that the side chain length of siloxane in the poly(acrylate- g-siloxane) was the dominant factor in influencing the hydrophobicity of the membrane’ surface. When the siloxane chain length reaches to eight, the membrane's surface could exhibit the strongest hydrophobicity.

Keywords: Polysiloxane; Polyacrylate; Oligomers; Emulsion polymerization; Hydrophobic surface

Effects of swift heavy ion irradiation on the electrical characteristics of Au/n-GaAs Schottky diodes by A. Tarun Sharma; Shahnawaz; Sandeep Kumar; Yashpal S. Katharria; Dinakar Kanjilal (pp. 459-463).

Metal-semiconductor diode of Au/n-GaAs is studied under the irradiation of swift heavy ion (SHI) beam (80MeV¹⁶O⁶⁺), using in situ current–voltage characterization technique. The diode parameters like ideality factor, barrier height, and leakage current are observed to vary with irradiation fluence. Significantly, the diode performance improves at a high fluence of 2×10¹³ionscm⁻² with a large decrease of reverse leakage current in comparison to the original as deposited sample. The Schottky barrier height (SBH) also increases with fluence. At a high irradiation fluence of 5×10¹³ionscm⁻² the SBH (0.62±0.01eV) is much larger than that of the as deposited sample (0.55±0.01eV). The diode parameters remain stable over a large range of irradiation up to fluence of 8×10¹³ionscm⁻². A prominent annealing effect of the swift ion beam owing to moderate electronic excitation and high ratio of electronic energy loss to the nuclear loss is found to be responsible for the improvement in diode characteristics.

Keywords: Schottky diodes; in situ; I–V; Barrier height; Reverse leakage current; Energy loss

Topological and chemical investigation on super-hydrophobicity of PTFE surface caused by ion irradiation by Yan Chen; Ziqiang Zhao; Junfeng Dai; Yingmin Liu (pp. 464-467).

Super-hydrophobic PTFE surfaces were obtained by irradiation of 200keV Xe⁺ ion with the fluence of6.2×1013 ions/cm². The contact angle of water on such surface is as large as161±3°. SEM and XPS were used to investigate how the topological and chemical changes affect the wettability of the irradiated surface. Needle like structures at nanometer scale caused by irradiation are considered to be the reason of the super-hydrophobicity. The formation of oxygen containing group and defluorination effect on the treated surface are inferred to have negative contribution to the hydrophobic optimization of PTFE surface.

Keywords: PACS; 61.81.Jh; 68.08.Bc; 61.82.PvSuper-hydrophobic; PTFE; Ion irradiation; XPS; SEM

Fabrication of pulsed-laser deposited V–W–Nd mixed-oxide films by Yusuke Iida; S. Venkatachalam; Yoshikazu Kaneko; Yoshinori Kanno (pp. 468-472).

V–W–Nd mixed-oxide films were prepared by pulse-laser deposition (PLD) technique from the targets sintered at different temperatures. X-ray photoelectron spectroscopy (XPS) data indicate that the films fabricated from the targets sintered at low temperature were composed of various mixed valences. Raman spectroscopy shows that V–W–Nd films were composed of the vanadates as NdVO₄, and the W⁶⁺ doping supplements the formation of vanadate. Atomic force microscopy (AFM) image of the films fabricated from the target sintered at 923K reveals the average particle size is estimated around 86nm. The surface morphology of the films roughness shows a dramatic change at 923–943K.

Keywords: V; ₂; O; ₅; WO; ₃; Nd; ₂; O; ₃; Thin film; Dopant material; Pulsed-laser deposition

Structural study of nanoporous ultra low- k dielectrics using complementary techniques: Ellipsometric porosimetry, X-ray reflectivity and grazing incidence small-angle X-ray scattering by V. Jousseaume; G. Rolland; D. Babonneau; J.-P. Simon (pp. 473-479).

This paper is focused on nanoporous methylsilsesquioxane deposited using a polymer approach and shows the complementarities of three experimental techniques: ellipsometric porosimetry (EP), X-ray reflectivity (XRR), and grazing incidence small-angle X-ray scattering (GISAXS). XRR and EP confirm that the pore volume fraction is larger for smaller dielectric constants. EP and GISAXS find mean pore sizes independent of the porosity, in the range 3–4nm as diameter. GISAXS is the only technique that can estimate the porosity isotropy. Finally, the impact of integration processes such as surface plasma treatment, etching or stripping on the porosity is evaluated: the porosity remains unchanged except in the superficial layer where an increase of the pore size (or of the roughness) is observed.

Keywords: PACS; 61.10.e; 61.18.j; 61.72.Dd; 61.82.Ms; 68.55.aPorous ultra low; k; dielectrics; Materials for microelectronics; Structural determination; GISAXS; XRR; Ellipsometric porosimetry

Characterization of thin Zn–Ni alloy coatings electrodeposited on low carbon steel by A. El Hajjami; M.P. Gigandet; M. De Petris-Wery; J.C. Catonne; J.J. Duprat; L. Thiery; F. Raulin; N. Pommier; B. Starck; P. Remy (pp. 480-489).

The characteristics of initial layer formation in alkaline bath for Zn–Ni (12–15%) alloy electrodeposition on low carbon steel plates are detected in a nanometric thickness range by electron probe microanalysis (EPMA), with both bulk sample and thin film on substrate correction procedure, glow discharge optical emission spectroscopy (GDOES) and gracing incidence X-ray diffraction (GIXRD). The Zn–Ni coatings were elaborated using either intensiostatic or potentiostatic mode. A preferential deposition of Ni, in the initial thin layer, is detected by these analyses; according to EPMA and GDOES measurements, a layer rich in nickel at the interface substrate/deposit is observed (90wt.% Ni) and approved by GIXRD; the thin layer of Ni formed in the first moments of electrolysis greatly inhibits the Zn deposition. The initial layer depends upon the relative ease of hydrogen and metal discharge and on the different substrate surfaces involved. The electrodeposition of zinc–nickel alloys in the first stage is a normal phenomenon of codeposition, whereby nickel – the more noble metal – is deposited preferentially.

Keywords: Zinc–nickel alloy; Nickel layer; Alkaline bath; Normal codeposition

XPS and LEED study of Pd and Au growth on alumina/Cu–Al surface by Slavomír Nemšák; Tomáš Skála; Jiří Libra; Petr Hanyš; Karel Mašek; Michiko Yoshitake; Vladimír Matolín (pp. 490-493).

Metal–insulator–metal system was prepared using the single-crystalline Cu–9at.% Al(111) support. Oxidation of the substrate under well-controlled conditions at elevated temperature leads to the formation of well-ordered aluminium oxide layer. The Pd–Au topmost layer was prepared by a step-by-step deposition of both metals afterwards on the oxide layer at room temperature. Low energy electron diffraction (LEED) measurement did not confirm epitaxial growth of the metal overlayer and gave only a rise of diffuse background after each deposition step. The growth of Pd–Au overlayer exhibited Stranski–Krastanov mode influenced by intermetallic interaction between those metals. No binding energy shifts were visible for the core-level photoelectron peaks of the substrate and the oxide using X-ray photoelectron spectroscopy (XPS). In contrast, the binding energy shifts of Pd 3d and Au 4f photoelectron levels in both directions were observed during all depositions. Bimetallic interactions between the metals as well as size effects are further discussed.

Keywords: XPS; LEED; Palladium; Gold; Alumina; Alloy

Relevant, systematic variation of morphology and magnetism according to annealing in InMnP:Zn by Yoon Shon; S.-W. Lee; C.S. Park; Sejoon Lee; H.C. Jeon; D.Y. Kim; T.W. Kang; Chong S. Yoon; E.K. Kim; Jeoung Ju Lee (pp. 494-498).

InMnP:Zn epilayers doped with Mn (0.290at.%) were annealed at 723–873K for 60s and 473–573K for 30min. Using Auger electron spectroscopy, the changes in concentration profiles of the epilayers correlated to the ferromagnetic origin as a function of the annealing conditions. The epilayers annealed at 723–873K for 60s exhibited InMn₃ persisting up to 583K. For InMnP:Zn epilayers annealed at 523–573K for 30min, the concentration depth profiles remained flat so that the stoichiometry was well maintained without precipitates such as InMn₃ and MnP comparable to the as-grown InP:Zn before doping Mn. These samples showed clear ferromagnetic hysteresis loops. Curie temperature was about 150K. A ferromagnetic hysteresis loop was obtained even at very lower annealing temperature of 473K.

Keywords: MOCVD; MBE; InMnP:Zn epilayer; Morphology; Auger electron spectroscopy; Hysteresis loop

Morphological and chemical study of the initial growth of CdS thin films deposited using an ammonia-free chemical process by D.A. Mazón-Montijo; M. Sotelo-Lerma; M. Quevedo-López; M. El-Bouanani; H.N. Alshareef; F.J. Espinoza-Beltrán; R. Ramírez-Bon (pp. 499-505).

We study the initial growth stages of CdS thin films deposited by an ammonia-free chemical bath deposition process. This ammonia-free process is more environmentally benign because it reduces potential ammonia release to the environment due to its high volatility. Instead of ammonia, sodium citrate was used as the complexing agent. We used atomic force microscopy (AFM), Rutherford backscattering (RBS) and X-ray photoelectron spectroscopy (XPS) to investigate the morphological and chemical modifications at the substrate surface during the first initial stages of the CdS deposition process. Additionally, X-ray diffraction (XRD) and optical transmission spectroscopy measurements were carried out to compliment the study. XPS results show that the first nucleation centers are composed by Cd(OH)₂ which agglomerate in patterns of bands, as demonstrated by AFM results. It is also observed that the conversion to CdS (by anionic exchange) of the first nucleus begins before the substrate surface is completely covered by a homogenous film.

Keywords: Atomic force microscopy; X-ray photoelectron spectroscopy; Cadmium sulfide; Thin film structures; Semi-conducting films

Preparation of activated carbons by microwave heating KOH activation by Yongbin Ji; Tiehu Li; Li Zhu; Xiaoxian Wang; Qilang Lin (pp. 506-512).

Activated carbons with high surface areas were prepared via KOH activation process by microwave (MW) heating. As a comparison, activated carbons were also prepared by conventional heating (EF) method. The influences of KOH/Mesocarbon microbeads (MCMB) weight ratio and activation time on the pore properties of the activated carbons were investigated. For both MW and EF heating methods, the surface area and pore volume increase to a maximum and then decrease with the KOH/MCMB ratio increasing. The effects of activation time on the pore properties depend on the KOH/MCMB ratio. The activated carbons prepared by MW heating have higher surface area and larger pore volume than those by EF heating when KOH/MCMB ratio is the same. The MW heating method shortens the activation time considerably. Activated carbons prepared by MW heating show low content of oxygen containing groups.

Keywords: PACS; 81.05.RmActivated carbon; Microwave (MW); Mesocarbon microbeads (MCMB); KOH; High surface area

Field emission properties of carbon nanotube film using a spray method by Yang Doo Lee; Kyong-Soo Lee; Yun-Hi Lee; Byeong-Kwon Ju (pp. 513-516).

We fabricated carbon nanotube (CNT) emitters by a spray method using a CNT suspension with ethanol. Indium with a low melting pointing metal or indium tin oxide (ITO) was deposited on the glass substrate. The CNTs were sprayed on these layers and thermally annealed. The sprayed CNTs on an ITO were obtained a high emission current density, field enhancement factor, and a uniform emission pattern than the sprayed CNTs on an ITO layer. We found that the sprayed emitters on the indium layer had good field emission characteristics because of the strong adherence between the metal layer and CNTs.

Keywords: PACS; 72.80.Rj; 79.70.+qCarbon nanotubes; Spray; Field emission

Study on impact fusion at particle interfaces and its effect on coating microstructure in cold spraying by Wen-Ya Li; Chao Zhang; Xueping Guo; Chang-Jiu Li; Hanlin Liao; C. Coddet (pp. 517-526).

This paper deals with the impact melting phenomenon at the interfaces between the deposited particles in cold-sprayed coatings and its effect on coating microstructure and particle bonding mechanism. Al-12Si, Al2319, Ti, Ti-6Al-4V, Ni and NiCoCrAlTaY powders were selected as feedstocks, which have various thermal and mechanical properties. The analytical results showed that most of the used materials possibly experienced the local melting at the contact interfaces of particles under certain impact conditions. Low melting point, relatively high gas temperature and chemical reaction with the atmosphere are the main factors contributing to the impact fusion during cold spraying. The results also indicated that the local melting would benefit the formation of a metallurgical bonding between the deposited particles and enhance the coating cohesion.

Keywords: Cold spraying; Particles; Aluminium alloy; Titanium alloy; Nickel alloy; Impact fusion

Ta/Ni/Ta multilayered ohmic contacts on n-type SiC by H. Yang; T.H. Peng; W.J. Wang; D.F. Zhang; X.L. Chen (pp. 527-531).

The interface formation, electrical properties and the surface morphology of multilayered Ta/Ni/Ta/SiC contacts were reported in this study. It was found that the conducting behavior of the contacts so fabricated is much dependent on the metal layer thickness and the subsequent annealing temperature. Auger electron spectroscopy (AES) and X-ray diffraction analyses revealed that Ni₂Si and TaC formed as a result of the annealing. The Ni atoms diffused downward to metal/SiC interface and converted into Ni₂Si layer in adjacent to the SiC substrate. The released carbon atoms reacted with Ta atoms to form TaC layer. Ohmic contacts with specific contact resistivity as low as 3×10⁻⁴Ωcm² have been achieved after thermal annealing. The formation of carbon vacancies at the Ni₂Si/SiC interface, probably created by dissociation of SiC and formation of TaC during thermal annealing, should be responsible for the ohmic formation of the annealed Ta/Ni/Ta contacts. The addition of Ta into the Ni metallization scheme to n-SiC restricted the accumulation of carbon atoms left behind during Ni₂Si formation, improving the electrical and microstructure properties.

Keywords: PACS; 68.55.−a; 73.40.CgSiC; Ohmic contact; Electrical properties; Carbon vacancy

Microstructures and electrical properties of La_0.8Sr_0.2MnO₃ films synthesized by sol–gel method by Xinde Zhu; Shengli Li; Xiaojie Yang; Jie Qiu (pp. 532-537).

La_0.8Sr_0.2MnO₃ (LSMO) thin films were fabricated on alumina substrates by an improved sol–gel dip-coating process. It was found that multiple dip-coating process could not be performed until the pre-firing temperature reached 600°C. Different amounts of LSMO powders were added to precursor solution with an aim to avoid cracks in LSMO thin films during calcining caused by the shrinkage mismatch between the film and the substrate. The structure and surface morphology of the films prepared from precursors with and without LSMO powders were characterized using X-ray diffraction (XRD) and scanning electron microscopy (SEM). It was found that the addition of 56.4wt.% LSMO powders into the sol–gel precursor solution significantly modified the microstructure of films. A single LSMO perovskite phase was obtained on alumina substrate after calcining at 800°C for 4h by the improved sol–gel method. The sheet resistance of the films prepared with different processing parameters was measured by four-point dc method. Results indicated that the sheet resistance of films decreased with increasing the number of coating applications and the amount of LSMO powders.

Keywords: PACS; 81.15; 68.55.JkLa; _0.8; Sr; _0.2; MnO; ₃; Thin film; Sol–gel; Perovskite

Electrodeposition of nanostructured Pt films from lyotropic liquid crystalline phases on α-Al₂O₃ supported dense Pd membranes by Ruijie Guo; Baoquan Zhang; Xiufeng Liu (pp. 538-543).

Using the lyotropic liquid crystalline templating strategy, the nanostructured platinum film was electrochemically deposited on the α-Al₂O₃ supported dense palladium membrane. The XRD and TEM results of the Pt film revealed a hexagonal array of cylindrical pores with a uniform pore diameter of ca. 3.8nm and a pore-to-pore separation of ca. 7.6nm. The structure parameters of the Pt film were almost the same as those of the hexagonal liquid crystalline template. Based on SEM observations, the Pt film was featureless, smooth, and tightly adherent to the dense Pd membrane. The specific surface area of the Pt film, measured by using cyclic voltammetry, was ca. 13.8m²g⁻¹, which was in accord with the theoretical value of 14.5m²g⁻¹ for a perfect hexagonal nanostructure with the same structure parameters. By combining the dense Pd membrane for selective permeation to hydrogen with the Pt film of high specific surface area for catalysis, the as-synthesized two-layer film will be a promising catalytic membrane to intensify hydrogen-related reaction processes.

Keywords: PACS; 82.45.Aa; 81.15.−zNanomaterial; Liquid crystalline template; Thin film

Fabrication and characterization of TS-1 films on α-Al₂O₃ substrates using TiCl₃ as titanium source by Xiaodong Wang; Pingping Zhang; Xiufeng Liu; Baoquan Zhang (pp. 544-547).

The continuous and highly intergrown anatase-free TS-1 film was fabricated with TiCl₃ as the titanium source for the first time. The in situ nucleation and secondary growth method was employed to synthesize the TS-1 film. By means of scanning electron microscopy (SEM) images, X-ray diffraction (XRD) patterns, and FT-IR and UV–vis spectra measurements, the resulting film was observed to be anatase-free, continuous and highly intergrown with the MFI-type structure, and the Ti atoms existed only in tetrahedral coordination.

Keywords: PACS; 68.55.−a; 81.15.Aa; 81.10.−hTiCl; ₃; TS-1 film; Anatase-free

Thickness dependence on thermal stability of sputtered Ag nanolayer on Ti/Si(100) by O. Akhavan; A.Z. Moshfegh (pp. 548-551).

Thermal stability of Ag layer on Ti coated Si substrate for different thicknesses of the Ag layer have been studied. To do this, after sputter-deposition of a 10nm Ti buffer layer on the Si(100) substrate, an Ag layer with different thicknesses (150–5nm) was sputtered on the buffer layer. Post annealing process of the samples was performed in an N₂ ambient at a flow rate of 200ml/min in a temperature range from 500 to 700°C for 30min. The electrical property of the heat-treated multilayer with the different thicknesses of Ag layer was examined by four-point-probe sheet resistance measurement at the room temperature. Phase formation and crystallographic orientation of the silver layers were studied by θ–2 θ X-ray diffraction analysis. The surface topography and morphology of the heat-treated films were determined by atomic force microscopy, and also, scanning electron microscopy. Four-point- probe electrical measurement showed no considerable variation of sheet resistance by reducing the thickness of the annealed Ag films down to 25nm. Surface roughness of the Ag films with (111) preferred crystallographic orientation was much smaller than the film thickness, which is a necessary condition for nanometric contact layers. Therefore, we have shown that the Ag layers with suitable nano-thicknesses sputtered on 10nm Ti buffer layer were thermally stable up to 700°C.

Keywords: PACS; 68.60.Dv; 68.37.Ps; 68.55.JkSilver; Nano-thickness; Ti interlayer; AFM

Influences of oxygen partial pressure on structure and related properties of ZrO₂ thin films prepared by electron beam evaporation deposition by Yanming Shen; Shuying Shao; Hua Yu; Zhengxiu Fan; Hongbo He; Jianda Shao (pp. 552-556).

ZrO₂ thin films were prepared by electron beam evaporation at different oxygen partial pressures. The influences of oxygen partial pressure on structure and related properties of ZrO₂ thin films were studied. Transmittance, thermal absorption, structure and residual stress of ZrO₂ thin films were measured by spectrophotometer, surface thermal lensing technique (STL), X-ray diffraction and optical interferometer, respectively. The results showed that the structure and related properties varied progressively with the increase of oxygen partial pressure. The refractive indices and the packing densities of the thin films decreased when the oxygen partial pressure increased. The tetragonal phase fraction in the thin films decreased gradually as oxygen partial pressure increased. The residual stress of film deposited at base pressure was high compressive stress, the value decreased with the increase of oxygen partial pressure, and the residual stress became tensile with the further increase of oxygen pressure, which was corresponding to the evolution of packing densities and variation of interplanar distances.

Keywords: ZrO; ₂; thin films; Electron beam evaporation; Residual stress; Oxygen partial pressure

Femtosecond laser-induced fragmentation and cluster formation studies of solid phase trinitrotoluene using time-of-flight mass spectrometry by Caroline McEnnis; Yamac Dikmelik; James B. Spicer (pp. 557-562).

We use surface-femtosecond laser mass spectrometry to study the fragments/products formed when trinitrotoluene (TNT) is subjected to femtosecond laser pulse irradiation and to study the conditions under which TNT is removed from a solid surface. In surface-femtosecond laser mass spectrometry a compound is deposited on a solid substrate and is desorbed into vacuum by femtosecond irradiation forming a plume of ionized and neutral species. The positive or negative ions are then accelerated by an electric potential and allowed to drift in the field-free region of a time-of-flight mass spectrometer. The mass-to-charge ratio of each ion is obtained using the value of the accelerating field and the ion flight time. In this paper we report femtosecond laser mass spectra for the positive ions formed by desorbing TNT with 130fs pulses centered at 800nm for fluences ranging from 7 to 1.4×10⁵J/m². The conditions under which TNT removal and ionization occur are also discussed.

Keywords: PACS; 79.20.LA; 82.53.Xa; 82.80.RtFemtosecond laser; Time-of-flight mass spectrometry; Clusters; Explosives; TNT

The effect of surface modification with silane coupling agent on suppressing the photo-catalytic activity of fine TiO₂ particles as inorganic UV filter by Emi Ukaji; Takeshi Furusawa; Masahide Sato; Noboru Suzuki (pp. 563-569).

The effect of surface modification with 3-aminopropyltriethoxysilane (APTES) and n-propyltriethoxysilane (PTES) on photo-catalytic activity and UV-shielding ability of fine TiO₂ particles were investigated. The number of surface groups ( N_R) [nm⁻²] which shows the density of modifier on TiO₂ surface was calculated from the results of elemental analysis and BET measurement. The modified samples of which N_R are different were obtained by changing the concentration of modifier. When the photo-catalytic activity and UV-shielding ability of modified samples were evaluated, it was found that APTES was more effective modifier than PTES to obtained samples with low photo-catalytic activity and high UV-shielding ability. This is probably because the adsorption mechanisms on TiO₂ surface between modifiers were different and N_R is a key factor to control the performances of fine TiO₂ particles. The result of zeta potential showed that surface character of modified samples was varied by changing N_R. It suggested from these results that N_R affected the photo-catalytic activity and UV-shielding ability because N_R changed surface character of modified samples.

Keywords: PACS; 68Titanium dioxide (TiO; ₂; ); Surface modification; Photo-catalytic activity; Silane coupling agents; UV-shielding ability

Preparation and characterization of n-type conductive (Al, Co) co-doped ZnO thin films deposited by sputtering from aerogel nanopowders by L. El Mir; Z. Ben Ayadi; M. Saadoun; K. Djessas; H.J. von Bardeleben; S. Alaya (pp. 570-573).

Highly transparent, n-type conducting ZnO thin films were obtained by low temperature magnetron sputtering of (Co, Al) co-doped ZnO nanocrystalline aerogels. The nanoparticles of ∼30nm size were synthesized by a sol–gel method using supercritical drying in ethyl alcohol. The structural, optical and electrical properties of the films were investigated. The ZnO films were polycrystalline textured, preferentially oriented with the (002) crystallographic direction normal to the film plane. The films show within the visible wavelength region an optical transmittance of more than 90% and a low electrical resistivity of 3.5×10⁻⁴Ωcm at room temperature.

Keywords: Sputtering; Sol–gel method; Zinc oxide; Nanostructures; Transparent conductive oxide (TCO)

High specific surface area TEOS-based aerogels with large pore volume prepared at an ambient pressure by Pradip B. Sarawade; Jong-Kil Kim; Ho-Kun Kim; Hee-Taek Kim (pp. 574-579).

The experimental results on the synthesis of tetraethoxysilane (TEOS)-based silica aerogel with high specific surface area and large pore volume, via ambient pressure drying (APD) route, are reported. The silica aerogels were prepared by the acid–base sol–gel polymerization of TEOS precursor followed by the drying of the alcogels at an ambient pressure. The solvent present in the alcogel (i.e. ethanol) was replaced by a non-polar solvent such as hexane prior to the surface modification step. In order to minimize the drying shrinkage, the surface of the gels was modified using trimethylchlorosilane (TMCS) before the APD. The FTIR spectra of the surface modified aerogels showed Si–CH₃ peaks at 2965 and 850cm⁻¹. The effect of the base catalyst (NH₄OH) addition to the sol, at different time intervals ( T), on the physical and textural properties of the resulting aerogels has been investigated. It has been observed that the surface area and the cumulative pore volume of the aerogels enhanced considerably from 819 to 1108m²g⁻¹ and 2.65 to 4.7cm³g⁻¹, respectively with an increase in the T value from 6 to 48h. Silica aerogels with very low bulk density (0.06gcm⁻³), extremely high specific surface area (1108m²g⁻¹) and large cumulative pore volume (4.7cm³g⁻¹) could be synthesized by drying the alcogels at the ambient pressure. The aerogels were mesoporous solids with the average pore size ranging from 12 to 17nm. The results have been discussed by taking into consideration the hydrolysis and condensation reactions during the sol–gel polymerization of the TEOS precursor.

Keywords: Silica aerogels; Surface modification; Ambient pressure drying; BET surface area; PSD; SEM

The influence of boron concentrations on structural properties in disorder silicon films by R. Saleh; N.H. Nickel (pp. 580-585).

In this work we present a detailed structural of a series of B-doped hydrogenated microcrystalline silicon (μc-Si:H) films deposited by plasma-enhanced chemical vapor deposition (PECVD) and B-doped polycrystalline silicon (poly-Si) films produced by step-by-step laser crystallization process from amorphous silicon. The influence of doping on the structural properties and structural changes during the sequential crystallization processes were monitored by Raman spectroscopy. Unlike μc-Si:H films, that consist of a two-phase mixture of amorphous and ordered Si, partially crystallized sample shows a stratified structure with polycrystalline silicon layer at the top of an amorphous layer. With increasing doping concentration the LO-TO phonon line in poly-Si shift to smaller wave numbers and broadens asymmetrically. The results are discussed in terms of resonant interaction between optical phonons and direct intraband transitions known as a Fano resonance. In μc-Si:H films, on the other hand, the Fano effect is not observed. The increase of doping in μc-Si:H films suppressed the crystalline volume fraction, which leads to an amorphization in the film structure. The structural variation in both μc-Si:H and poly-Si films leads to a change in hydrogen bonding configuration.

Keywords: Doped microcrystalline and polycrystalline silicon; Laser crystallization; Raman spectroscopy; Hydrogen bonding

The effect of cerium and lanthanum surface treatments on early stages of oxidation of A361 aluminium alloy at high temperature by A. Pardo; S. Feliú Jr.; M.C. Merino; R. Arrabal; E. Matykina (pp. 586-595).

X-ray photoelectron spectroscopy analysis has been used to study the surface of A361 aluminium alloy after electrodeposition of cerium and lanthanum compounds followed by oxidation tests in air at 100–500°C for 2h. Cerium and lanthanum oxide deposits are found on the β-AlFeSi second phase particles and to a lesser extent on the eutectic Al–Si areas, while the α-Al phase is covered with a thin aluminium oxide film. This uneven deposition may be related either to a preferential nucleation and growth process on active interfaces or to the differing electrical conductivity of the phases and intermetallic compounds of the alloy. Initial stages of oxidation of A361 alloy disclosed thickening of the aluminium oxide layer and Mg enrichment at the surface, especially above 400°C. Rare earth deposits revealed two different effects: reduced Mg diffusion and enhanced thickening of the aluminium oxide film. A distinctive behaviour of Ce oxide appears at 300–500°C related with Ce(III) to Ce(IV) transition.

Keywords: PACS; 81.65.MqOxides; Rare earth metals; Oxidation; Photoelectron spectroscopy

Characterization of boron carbon nitride film modified by excimer laser annealing by Hidemitsu Aoki; Kazutoshi Ohyama; Hiroshi Sota; Toshiaki Seino; Chiharu Kimura; Takashi Sugino (pp. 596-599).

Boron carbon nitride (BCN) shows promise as a field emitter material because of its mechanical hardness, chemical inertness, and low electron affinity. This study investigated the modification of a BCN film with an amorphous area using KrF excimer laser (wavelength: 248nm, photon energy: 5.0eV) annealing without substrate heating. This achieved significant variation in characteristics, such as an increase in bandgap energy and decrease in electron affinity. Laser annealing reduced electron affinity from 0.7 to 0.3eV. The results indicate that the modification of the BCN film by KrF excimer laser annealing achieves characteristics similar to hexagonal BN (h-BN) film without losing the desirable properties of the BCN film, such as physical stability.

Keywords: Boron carbon nitride; Excimer laser; Anneal; Electron affinity; Field emitter; Low temperature

Raman validity for crystallite size L_a determination on reticulated vitreous carbon with different graphitization index by M.R. Baldan; E.C. Almeida; A.F. Azevedo; E.S. Gonçalves; M.C. Rezende; N.G. Ferreira (pp. 600-603).

The graphitization index provided by X-ray diffraction (XRD) and Raman spectrometry for reticulated vitreous carbon (RVC) substrates, carbonized at different heat treatment temperatures (HTT), is investigated. A systematic study of the dependence between the disorder-induced D and G Raman bands is presented. The crystallite size L_a was obtained for both X-ray diffraction and Raman spectrometry techniques. Particularly, the validity for L_a determination, from Raman spectra, is pointed out comparing the commonly used formula based on peaks amplitude ratio ( I_D/ I_G) and the recent proposed equation that uses the integrated intensities of D and G bands. The results discrepancy is discussed taken into account the strong contribution of the line broadening presented in carbon materials heat treated below 2000°C.

Keywords: Carbon; Raman spectroscopy; X-ray diffraction

Theoretical study of the cracking mechanisms of linear α-olefins catalyzed by zeolites by Yu-Hua Guo; Min Pu; Jing-Yi Wu; Jia-Ying Zhang; Biao-Hua Chen (pp. 604-609).

The cracking reactions of linear C₄–C₁₀ α-olefins over zeolites have been studied by using density functional theory at the B3LYP/6-31G(d,p) level. The obtained results reveal that the β-scission processes of C₄–C₁₀ olefins have the same reaction mechanism. Every pathway only involves a transition state corresponding to the rupture of the C–C bond, while the intrinsic reaction coordinate analysis indicates that the protonated intermediate species is formed during the reaction process. Furthermore, it is found that this intermediate species is not usually highly stable alkoxy group but adsorbed short-lifetime carbocation. This phenomenon can well explain why the carbocations are seldom observed inside the zeolite's cavities. The calculated real activation energy for this pathway is lower than the experimental value for corresponding alkane cracking contrary to the previously reported pathway via an alkoxide intermediate. Therefore, the reaction pathway via a carbocation intermediate species is energetically much more favorable. In addition, the study also shows that the real activation energies of olefin cracking are nearly independent of the olefin chain length, which is in agreement with the existing experimental results of alkane cracking.

Keywords: PACS; 31.15.Ew; 61.46.+w; 68.43.Bc; 82.33.JxOlefin; Cracking; Zeolite; Reaction mechanism; Density functional theory

Effect of temperature on the electron field emission from aligned carbon nanofibers and multiwalled carbon nanotubes by Sk.F. Ahmed; S. Das; M.K. Mitra; K.K. Chattopadhyay (pp. 610-615).

Effect of temperature and aspect ratio on the field emission properties of vertically aligned carbon nanofiber and multiwalled carbon nanotube thin films were studied in detail. Carbon nanofibers and multiwalled carbon nanotube have been synthesized on Si substrates via direct current plasma enhanced chemical vapor deposition technique. Surface morphologies of the films have been studied by a scanning electron microscope, transmission electron microscope and an atomic force microscope. It is found that the threshold field and the emission current density are dependent on the ambient temperature as well as on the aspect ratio of the carbon nanostructure. The threshold field for carbon nanofibers was found to decrease from 5.1 to 2.6V/μm when the temperature was raised from 300 to 650K, whereas for MWCNTs it was found to decrease from 4.0 to 1.4V/μm. This dependence was due to the change in work function of the nanofibers and nanotubes with temperature. The field enhancement factor, current density and the dependence of the effective work function with temperature and with aspect ratio were calculated and we have tried to explain the emission mechanism.

Keywords: PACS; 61.46.Fg; 79.70.+q; 73.30.+yCNF; MWCNT; Field emission; Work function

Aluminum pigment encapsulated by in situ copolymerization of styrene and maleic acid by Hui Liu; Hongqi Ye; Xinde Tang (pp. 616-620).

To improve its anticorrosion property, aluminum pigment was encapsulated by in situ copolymerization of styrene (St) and maleic acid (MA). It was found that the conversion of monomers (C), the percentage of grafting (PG) and the grafting efficiency (GE) could attain 92%, 12%, 25%, respectively, when m(BPO)/ m(St+MA)=10% and m(St+MA)/ m(Al)=10%. The optimum condition for protection factor was studied according to an orthogonal testing. When m(St+MA)/ m(Al) was 20%, the encapsulated aluminum pigment simultaneously showed good anticorrosion property and luster. FTIR, SEM and particle size analysis indicated that aluminum pigment had been successfully encapsulated with styrene–maleic acid copolymer by in situ copolymerization, which remarkably improved its anticorrosion property and the chelate complex formed between SMA and Al(III) was possibly the actual corrosion inhibitor.

Keywords: Aluminum pigment; Encapsulate; In situ copolymerization; Styrene; Maleic acid

Positioning of cationic silver nanoparticle by using AFM lithography and electrostatic interaction by Tetsu Yonezawa; Tetsuya Itoh; Naoto Shirahata; Yoshitake Masuda; Kunihito Koumoto (pp. 621-626).

One-dimensional metal lines of silver nanoparticles with a nano-sized width were generated onto silicon surface by using a nano-level lithography technique, field induced oxidation (FIO) by AFM, on self-assembled monolayer-modified Si wafers. This FIO technique provided SiO₂ lines a width of less than 100nm. Short-time immersion of partially anodized silicon surface which is covered by a cationic silanol surfactant ((CH₃O)₃SiCH₂CH₂CH₂N(CH₃)₃⁺Cl⁻)-monolayer into quaternary ammonium (HSCH₂CH₂N(CH₃)₃⁺Br⁻)-covered silver nanoparticles readily and reproducibly gave nano-metal lines of silver onto silicon wafers. Hydrophilicity of the whole wafer surface was indispensable for homogeneously wetting the anodized SiO₂ area with a nanodimensional width.

Keywords: PACS; 81.16.Dn; 68.37.PsNanoparticle; Silver; Monolayer; AFM

Transformation of a hydrophilic membrane into semi-super-hydrophobic based on self-assembly of stearic acid monolayer over induced nanostructures on the membrane surface by S.S. Madaeni; N. Ghaemi (pp. 627-632).

Both the chemical and structural properties of a surface determine the contact angle. For the formation of super-hydrophobic surfaces, modification of surface chemistry must be always combined with surface roughness enhancement. The used methods to make a super-hydrophobic surface are expensive and need very complicated equipments and cannot be scale up easily. In this study a simple and less expensive method was developed to transform a hydrophilic membrane into a semi-super-hydrophobic. In order to modify the membrane surface geometrically, the required needle-like rugosities were created by boiling the membrane in the water. The chemical modification of the roughened surface was created by the chemical adsorption and controlling the reaction time of stearic acid (STA) on the polymer of the membrane surface. Finally, by controlling the surface roughness, the concentration of the STA solution and duration of reaction time, a semi-super-hydrophobic membrane with the contact angle of 120° was prepared.

Keywords: Semi-super-hydrophobic membrane; Roughness; Atomic force microscopy; Nanostructures; Stearic acid monolayer

Oxide-assisted growth of silicon nanowires by carbothermal evaporation by Sabar D. Hutagalung; Khatijah A. Yaacob; Azma F. Abdul Aziz (pp. 633-637).

Silicon nanowires (SiNWs) have successfully been synthesized by carbothermal evaporation method. By ramping-up the furnace system at 20°Cmin⁻¹ to 1100°C for 6h, the vertically aligned coexist with crooked SiNWs were achieved on the silicon substrate located at 12cm from source material. The processing parameters such as temperature, heating rate, duration, substrate position and location are very important to produce SiNWs. Morphology and chemical composition of deposited products were investigated by field-emission scanning electron microscopy (FESEM) equipped with energy dispersive X-ray analysis (EDX). The existence of small sphere silicon oxide capped nanowires suggested that the formation of SiNWs was governed by oxide-assisted growth (OAG) mechanism.

Keywords: Evaporation and sublimation; Silicon; Carbon; Silicon oxides; Nanostructures

Laser-induced forward transfer technique for maskless patterning of amorphous V₂O₅ thin film by S. Chakraborty; H. Sakata; E. Yokoyama; M. Wakaki; D. Chakravorty (pp. 638-643).

A laser-induced forward transfer technique has been applied for the maskless patterning of amorphous V₂O₅ thin films. A sheet beam of a frequency doubled (SHG) Q-switched Nd:YAG laser was irradiated on a transparent glass substrate (donor), the rear surface of which was pre-coated with a vacuum-deposited V₂O₅ 180nm thick film was either in direct contact with a second glass substrate (receiver) or a 0.14mm air-gap was maintained between the donor film and the receiving substrate. Clear, regular stripe pattern of the laser-induced transferred film was obtained on the receiver. The pattern was characterized using X-ray diffraction (XRD), optical absorption spectroscopy, scanning electron microscopy (SEM), energy dispersive analysis of X-ray (EDAX), atomic force microscopy (AFM), etc.

Keywords: PACS; 81.65.Cf; 42.62.−b; 68.35.−p; 68.37.PsLaser-induced forward transfer; Nd:YAG laser; Maskless patterning; V; ₂; O; ₅; thin film

Metal ion release and surface composition of the Cu–18Ni–20Zn nickel–silver during 30 days immersion in artificial sweat by Ingrid Milošev; Tadeja Kosec (pp. 644-652).

In order to study nickel ion release associated with nickel allergy, Cu–18Ni–20Zn nickel–silver alloy was immersed in artificial sweat and Ringer physiological solution for 30 days. Dissolution of metal ions was measured as a function of time, and the characteristics of the solid surface layer formed after 30 days were studied by SEM/EDS and XPS. The dissolution of nickel prevails over dissolution of copper and zinc. Nickel release in artificial sweat is approximately 10 times higher than in Ringer physiological solution and in both solutions the nickel release exceeds 0.5μgcm⁻² week⁻¹, the threshold above which the allergy is triggered. Evidence of selective nickel dissolution is reported. The composition of the surface layer formed in artificial sweat and in Ringer physiological solution differs in the content of nickel and chlorine. In artificial sweat, the major constituents of the surface layer are dominantly oxides, Cu₂O and ZnO, with traces of chlorine. In Ringer physiological solution, the composition of the surface layer changes to a mixture of oxides, chlorides and/or oxychlorides. Two components peaks were detected in the Cl 2p_3/2 peak; however, it was not possible to distinguish the exact nature of the chloride compound formed. The mechanism of nickel release is discussed as a function of the composition of the solution.

Keywords: Nickel–silver; Artificial sweat; Ringer physiological solution; Nickel release

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Applied Surface Science (v.254, #2)

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Applied Surface Science (v.254, #2)