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Applied Surface Science (v.253, #8)

Inorganic UV absorbers for the photostabilisation of wood-clearcoating systems: Comparison with organic UV absorbers by F. Aloui; A. Ahajji; Y. Irmouli; B. George; B. Charrier; A. Merlin (pp. 3737-3745).

Inorganic UV absorbers which are widely used today were originally designed neither as a UV blocker in coatings applications, nor for wood protection. In recent years however, there has been extensive interest in these compounds, especially with regard to their properties as a UV blocker in coating applications.In this work, we carried out a comparative study to look into some inorganic and organic UV absorbers used in wood coating applications. The aim of this study is to determine the photostabilisation performances of each type of UV absorbers, to seek possible synergies and the influences of different wood species. We have also searched to find eventual correlation between these performances and the influence of UV absorbers on the film properties. Our study has compared the performances of the following UV absorbers: hombitec RM 300, hombitec RM 400 from the Sachtleben Company; transparent yellow and red iron oxides from Sayerlack as inorganic UV absorbers; organic UV absorbers Tinuvin 1130 and Tinuvin 5151 from Ciba Company.The study was carried out on three wood species: Abies grandis, tauari and European oak.The environmental constraints (in particular the limitation of the emission of volatile organic compounds VOCs) directed our choice towards aqueous formulations marketed by the Sayerlack Arch Coatings Company.The results obtained after 800h of dry ageing showed that the Tinuvins and the hombitecs present better wood photostabilisations.On the other hand in wet ageing, with the hombitec, there are appearances of some cracks and an increase in the roughness of the surface. This phenomenon is absent when the Tinuvins are used. With regard to these results, the thermomechanical analyses relating to the follow-up of the change of the glass transition temperature ( T_g) of the various coating systems, show a different behaviour between the two types of absorbers. However, contrary to organic UV absorbers, inorganic ones tend to increase T_g during ageing, and, consequently decrease the flexibility of films. These phenomena can lead to the appearance of cracks found in the case of the wet weathering.

Keywords: Wood surface; Aging; UV absorbers; Transparent coating

Minimizing silicone transfer during micro-contact printing by Penny S. Hale; Peter Kappen; Walaiporn Prissanaroon; Narelle Brack; Paul J. Pigram; John Liesegang (pp. 3746-3750).

Methods to minimize the transfer of silicone from PDMS stamps during micro-contact printing have been investigated. This study focused on amino-silanes stamped onto PTFE substrates. Analysis of the stamped surfaces was through surface sensitive techniques such as XPS and time-of-flight secondary ion mass spectroscopy (TOF-SIMS). It was found that curing the PDMS at elevated temperatures minimized the amount of silicone transferred. The amount of silicone transferred also depended on the pretreatment of the stamp and the type of ink used.

Keywords: PACS; Codes: 79.60; 07.75; 81.65CMicro-contact printing; PDMS; Micropatterning; XPS; TOF-SIMS

Successive preparation of decorated zinc oxide organic sol by pulsed laser ablation and their luminescence characteristics by Chen Qian-Huo; Zhang Wen-Gong (pp. 3751-3756).

Nano-ZnO organic sols which were modified in situ were successively produced through focused pulsed laser ablation of ZnO target in interface of solid and flowing liquid which contained modification agents or polymer. It is found that the ZnO ethanol sol decorated by Q (8-hydroxylquinoline) radiates intense green light under ultraviolet radiation and has a broad emission band centered at 555nm in the emission fluorescence spectrum. The influence of factors including different modification agents and their added methods, laser fluence, aging time after preparation, compositions of flowing liquid and their velocity on luminescence characteristics of nano-ZnO organic sol was characterized by TEM, UV–vis and fluorescence spectrum.

Keywords: PACS; 42.15.EqNano-ZnO organic sol; Decoration; Pulsed laser ablation; Fluorescence; Flowing liquid; Modification agent

A SiC whisker-toughened SiC–CrSi₂ oxidation protective coating for carbon/carbon composites by Fu Qian-Gang; Li He-Jun; Shi Xiao-Hong; Li Ke-Zhi; Zhang Wei; Huang Min (pp. 3757-3760).

A SiC whisker-toughened SiC–CrSi₂ oxidation protective coating was prepared on the surface of C/C composites by a two-step technique of slurry and pack cementation. The oxidation protective ability and thermal stress resistance of the coating exhibit the trend of increase first and decrease afterwards as the SiCw content increases from 0 to 20wt.%. The compound effect of SiCw and CrSi₂ on the oxidation protective ability of SiC coating is better than their individual ones.

Keywords: Carbon/carbon composites; Coating; Oxidation

Photoemission studies of initial oxidation for ultra-thin zinc film on 6H-SiC(0001) surface with synchrotron radiation by C.W. Zou; Y.Y. Wu; B. Sun; P.S. Xu; H.B. Pan; F.Q. Xu (pp. 3761-3765).

The thermal oxidation process of metallic zinc on 6H-SiC(0001) surface has been investigated by using atomic force microscopy (AFM), synchrotron radiation photoelectron spectroscopy (SRPES) and XPS methods. The AFM images characterize the surface morphology of ZnO film formed during the thermal oxidation and SRPES record the valence band, Si 2p and Zn 3d spectra at different stages. The O 1s peak is recorded by XPS because of the energy limit of the synchrotron radiation. Our results reveal that the silicon oxides layer of SiC substrate can be reduce by hot metallic zinc atom deposition. The oxygen atoms in the silicon oxides are captured by the zinc atoms to form ZnO_x at the initial stage and as a result, the oxidized SiC surface are deoxidized. After the zinc deposition with the final thickness of 2.5nm, the sample is exposed in oxygen atmosphere and annealed at different temperatures. According to the evolution of peaks integrated intensities, it is considered that the Zn/SiC system will lose zinc atoms during the annealing in oxygen flux at high temperature due to the low evaporation temperature of pure zinc. After further annealing in oxygen flux at higher temperature, the substrate is also oxidized and finally the interface becomes a stable SiC–SiO_x–ZnO sandwich structure.

Keywords: PACS; 78.70.En; 79.60.Jv; 73.21.Cd; 73.61.AtThermal oxidation; Zinc oxide (ZnO); 6H-SiC; Photoemission; Synchrotron radiation

Effect of cryogenic temperature deposition on Au contacts to bulk, single-crystal n-type ZnO by J.S. Wright; Rohit Khanna; L.F. Voss; L. Stafford; B.P. Gila; D.P. Norton; S.J. Pearton; Hung-Ta Wang; S. Jang; T. Anderson; J.J. Chen; B.S. Kang; F. Ren; H. Shen; Jeffrey R. LaRoche; Kelly Ip (pp. 3766-3772).

Au contacts were deposited on bulk, n-type single-crystal ZnO at either 77K or 300K.The room temperature deposition produced contacts with ohmic characteristics. By sharp contrast, the cryogenic deposition produced rectifying characteristics with barrier heights around 0.4eV. The differences in contact behavior were stable to anneal temperatures of ∼300°C. There were no differences in near-surface stoichiometry for the different deposition temperatures, while the low temperature contacts showed a more uniform appearance. With further optimization of the pre-deposition cleaning process, this may be a useful method for engineering barrier heights on ZnO.

Keywords: ZnO; Schottky contacts

Dry etching of zinc-oxide and indium-zinc-oxide in IBr and BI₃ plasma chemistries by W.T. Lim; L. Stafford; Ju-Il Song; Jae-Soung Park; Y.W. Heo; Joon-Hyung Lee; Jeong-Joo Kim; S.J. Pearton (pp. 3773-3778).

The dry etching characteristics of bulk single-crystal zinc-oxide (ZnO) and RF-sputtered indium-zinc-oxide (IZO) films have been investigated using an inductively coupled high-density plasma in Ar/IBr and Ar/BI₃. In both plasma chemistries, the etch rate of ZnO is very similar to that of IZO, which indicates that zinc and indium atoms are driven by a similar plasma etching dynamics. IBr and BI₃-based plasmas show no enhancement of the etch rate over pure physical sputtering under the same experimental conditions. The etched surface morphologies are smooth, independent of the discharge chemistry. From Auger electron spectroscopy, it is found that the near-surface stoichiometry is unchanged within experimental error, indicating a low degree of plasma-induced damage.

Keywords: ZnO; Indium-zinc-oxide; Dry etching

Calculation of the formation energies of isolated vacancy and adatom–vacancy pair at low-index surfaces of fcc metals with MAEAM by Jian-Min Zhang; Yan-Ni Wen; Ke-Wei Xu (pp. 3779-3784).

The formation energies of isolated vacancy and adatom–vacancy pair (where the two are separated by a large distance) at low-index surfaces of fcc metals calculated by using the modifies analytical embedded atom method (MAEAM). The results predict the prevailing formation of vacancies on the surfaces (111), (100) (but Pd), Cu and Ni on the (110) surfaces at low temperature, and the defect formation energies consistently create in the sequence (110)→(100)→(111). With good accuracy, the calculated energy values coincide with those obtained by the embedded atom methods (EAM) and from experiments. The correctness of the method by which calculated the formation energies of point defects on the surface was proved.

Keywords: Vacancy; Adatom–vacancy pair; Formation energy; Fcc metals; Metal surfaces; MAEAM

Atomistic simulation of the vacancy in Ni (110) surface by Jian-Min Zhang; Xiang-Lei Song; Ke-Wei Xu (pp. 3785-3788).

Both the formation energies and the intra- and inter-layer diffuse activation energies of a vacancy in the first six atomic planes of Ni (110) surface have been investigated by means of molecular dynamics (MD) in conjunction with the semi-experiential many-body potential of the modified analytical embedded-atom method (MAEAM). The results show that the effect of the surface is only down to the fifth-layer. It is easer for a vacancy in the first or second layer to form and to migrate in intra-layer. For the inter-layer migration, a vacancy in the second or third layer is favorable to migrate to the upper layer, this is not the case for a vacancy in the fourth or fifth layer.

Keywords: Vacancy; Energy; MAEAM; MD

Electron stimulated desorption of H₃O⁺ from 316L stainless steel by C.R. Cole; R.A. Outlaw; R.L. Champion; B.C. Holloway; M.A. Kelly (pp. 3789-3798).

Surface ions generated by electron stimulated desorption from mass spectrometer ion source grids are frequently observed, but often misidentified. For example, in the case of mass 19, the source is often assumed to be surface fluorine, but since the metal oxide on grid surfaces has been shown to form water and hydroxides, a more compelling case can be made for the formation of hydronium. Further, fluorine is strongly electronegative, so it is rarely generated as a positive ion. A commonly used metal for ion source grids is 316L stainless steel. Thermal vacuum processing by bakeout or radiation heating from the filament typically alters the surface composition to predominantly Cr₂O₃. X-ray photoelectron spectral shoulders on the O 1s and Cr 2p_3/2 peaks can be attributed to adsorbed water and hydroxides, the intensity of which can be substantially increased by hydrogen dosing. On the other hand, the sub-peak intensities are substantially reduced by heating and/or by electron bombardment. Electron bombardment diode measurements show an initial work function increase corresponding to predominant hydrogen desorption (H₂) and a subsequent work function decrease corresponding to predominant oxygen desorption (CO). The fraction of hydroxide concentration on the surface was determined from X-ray photoelectron spectroscopy and from the deconvolution of temperature desorption spectra. Electron stimulated desorption yields from the surface show unambiguous H₃O⁺ peaks that can be significantly increased by hydrogen dosing. Time of flight secondary ion mass spectrometry sputter yields show small signals of H₃O⁺, as well as its constituents (H⁺, O⁺ and OH⁺) and a small amount of fluorine as F⁻, but no F⁺ or F⁺ complexes (HF⁺, etc.). An electron stimulated desorption cross-section of σ⁺∼1.4×10⁻²⁰cm² was determined for H₃O⁺ from 316L stainless steel for hydrogen residing in surface chromium hydroxide.

Keywords: PACS; 68.43.Rs; 79.20.LaElectron stimulated desorption (ESD); Stainless steel; Hydronium; Chromium

Silicidation in Ni/Si thin film system investigated by X-ray diffraction and Auger electron spectroscopy by S. Abhaya; G. Amarendra; S. Kalavathi; Padma Gopalan; M. Kamruddin; A.K. Tyagi; V.S. Sastry; C.S. Sundar (pp. 3799-3802).

Silicide formation induced by thermal annealing in Ni/Si thin film system has been investigated using glancing incidence X-ray diffraction (GIXRD) and Auger electron spectroscopy (AES). Silicide formation takes place at 870 K with Ni₂Si, NiSi and NiSi₂ phases co-existing with Ni. Complete conversion of intermediate silicide phases to the final NiSi₂ phase takes place at 1170 K. Atomic force microscopy measurements have revealed the coalescence of pillar-like structures to ridge-like structures upon silicidation. A comparison of the experimental results in terms of the evolution of various silicide phases is presented.

Keywords: Nickel silicides; X-ray diffraction; Auger electron spectroscopy

Atomic structure and electronic properties of Ta(1 1 2) and W(1 1 2) surfaces by Leszek Jurczyszyn; Piotr Ha¸dzel; Tadeusz Radoń (pp. 3803-3813).

We present results of theoretical and experimental studies of the structural and electronic properties of Ta(1 1 2) and W(1 1 2) surfaces. Atomic geometries of these surfaces and their electronic structures have been obtained from the first-principles pseudo-potential calculations based on the density functional theory and the use of the plane wave basis set. In the experimental part of our studies we have performed measurements of the photofield emission spectroscopy. The calculated density-of-states distributions are compared and discussed with energy distributions of electrons extracted from photofield emission characteristics. The photofield emission spectra measured for the surface regions of considered systems present very dense structures of features, while the corresponding dependences obtained for the bulk have much more smooth shape. Experimental results correspond very well with calculated density-of-states distributions.

Keywords: Tantalum; Tungsten; Density functional calculations; Surface relaxation and reconstruction; Field emission; Photoexcitation

Electrochemical deposition and tribological behaviour of Ni and Ni–Co metal matrix composites with SiC nano-particles by Meenu Srivastava; V.K. William Grips; K.S. Rajam (pp. 3814-3824).

Metal matrix composites reinforced with nano-sized particles have attracted scientific and technological interest due to the enhanced properties exhibited by these coatings. Ni–SiC composites have gained widespread application for the protection of friction parts in the automobile industry. The influence of variables like SiC content, current density and stirring speed on microhardness of nano-composite coatings has been studied. The improved microhardness was associated with the reduction in crystallite size determined by X-ray diffraction studies. The influence of incorporation of nano-SiC in hardened Ni–Co alloy matrix was also studied. It was observed that for 28wt.% Co content in the matrix the microhardness was higher compared to 70wt.% for a given nano-SiC content. This was associated to the crystal phase of Ni–28Co–SiC being fcc compared to hcp phase exhibited by Ni–70Co–SiC. The wear resistance of pure Ni, Co and nano-composite coatings was studied using pin-on-disc wear tester under dry sliding condition. The volumetric wear loss indicated that, the wear resistance of Ni–SiC nano-composite is better than that of pure nickel deposit. The wear resistance of Ni–Co composites was observed to be superior to Ni composite. The wear behaviour of Ni and Ni–28Co composite was in accordance with the Archard's law. However, the superior wear characteristic exhibited by Ni–70Co–SiC composite followed the reverse Archard's behaviour.

Keywords: Nano-composite; Nano-SiC; Ni–SiC; Ni–Co–SiC; Microhardness; Wear

Fabrication of high hole-carrier density p-type ZnO thin films by N–Al co-doping by Zhang Xiaodan; Fan Hongbing; Zhao Ying; Sun Jian; Wei Changchun; Zhang Cunshan (pp. 3825-3827).

In order to obtain p-type ZnO thin films, effect of atomic ratio of Zn:N:Al on the electronic and structural characteristic of ZnO thin films was investigated. Hall measurement indicated that with the increase of Al doping, conductive type of as-grown ZnO thin films changed from n-type to p-type and then to n-type again, reasons are discussed in details. Results of X-ray diffraction revealed that co-doped ZnO thin films have similar crystallization characteristic (002 preferential orientation) like that of un-doping. However, SEM measurement indicated that co-doped ZnO thin films have different surface morphology compared with un-doped ZnO thin films. p-type ZnO thin films with high hole concentration were obtained on glass (4.6×10¹⁸cm⁻³) and n-type silicon (7.51×10¹⁹cm⁻³), respectively.

Keywords: PACS; 68.55.−a; 73.61.Ga; 78.55.EtZnO; p-Type conduction; Ultrasonic spray pyrolysis; N–Al co-doping

Improved performance of organic light-emitting devices with plasma treated ITO surface and plasma polymerized methyl methacrylate buffer layer by Jae-Sung Lim; Paik-Kyun Shin (pp. 3828-3833).

Transparent indium-tin-oxide (ITO) anode surface was modified using O₃ plasma and organic ultra-thin buffer layers were deposited on the ITO surface using 13.56MHz rf plasma polymerization technique. A plasma polymerized methyl methacrylate (ppMMA) ultra-thin buffer layer was deposited between the ITO anode and hole transporting layer (HTL). The plasma polymerization of the buffer layer was carried out at a homemade capacitively coupled plasma (CCP) equipment. N, N′-Diphenyl- N, N′-bis(3-methylphenyl)-1,1′-diphenyl-4,4′-diamine (TPD) as HTL, Tris(8-hydroxy-quinolinato)aluminum (Alq₃) as both emitting layer (EML)/electron transporting layer (ETL), and aluminum layer as cathode were deposited using thermal evaporation technique. Electroluminescence (EL) efficiency, operating voltage and stability of the organic light-emitting devices (OLEDs) were investigated in order to study the effect of the plasma surface treatment of the ITO anode and role of plasma polymerized methyl methacrylate as an organic ultra-thin buffer layer.

Keywords: OLED; Efficiency; Stability; O; ₃; plasma; Plasma polymerization; ppMMA

The use of zinc and iron emission lines in the depth profile analysis of zinc-coated steel by K. Novotný; T. Vaculovič; M. Galiová; V. Otruba; V. Kanický; J. Kaiser; M. Liška; O. Samek; R. Malina; K. Páleníková (pp. 3834-3842).

In this study we report on the results of experiments devoted to the depth profile analysis of zinc-coated steel samples using the laser-induced breakdown spectroscopy (LIBS) technique. The dependence of zinc and iron emissions in three ablation atmospheres (air, argon, helium) was measured using the fundamental wavelength (1064nm) of the Nd:YAG laser. The highest possible depth resolution was achieved by optimizing the experimental parameters, such as the delay time (which affects the tailing of the zinc emission signal), focusing conditions, energy delivered to the sample, and choice of buffer gases. Current research indicates that there is a constant need to optimize these parameters so that reliable depth-profiling analysis can be performed.

Keywords: PACS; 42.62.Fi; 42.62.CfLaser-induced breakdown spectrometry (LIBS); Laser ablation; Coating; Depth profiling; Depth resolution

Effect of nickel on the initial growth behavior of electroless Ni–Co–P alloy on silicon substrate by W.L. Liu; W.J. Chen; T.K. Tsai; S.H. Hsieh; S.Y. Chang (pp. 3843-3848).

In this work the small amounts of NiSO₄ was added to a basic electroless plating bath of CoSO₄ with Na₂H₂PO₂ as reducing agent for the deposition of Co–Ni–P film on a silicon substrate. The initial growth behavior, containing plating rate, chemical composition, crystal structure, surface morphology and micro-structure, of the electroless plating film was characterized by scanning electron microscope (SEM) and transmission electron microscope (TEM). The results showed that the growth morphology variation of the Co–Ni–P films deposited in the basic CoSO₄+small amounts of NiSO₄ bath is the same as that of Co–P film deposited in the basic CoSO₄ bath, the plating rate of the Co–Ni–P film is much more rapid than that of the Co–P film, the Ni/Co wt.% in the Co–Ni–P film is greatly larger than that in the plating bath, and the structure of as-deposited film is crystalline at first stage and later stage.

Keywords: Electroless deposition; Co–Ni–P alloy; Electron microscopy; Growth behavior

Control of Ti³⁺surface defect on TiO₂ nanocrystal using various calcination atmospheres as the first step for surface defect creation and its application in photocatalysis by Kongkiat Suriye; Piyasan Praserthdam; Bunjerd Jongsomjit (pp. 3849-3855).

A new development to create the surface defect (Ti³⁺) on TiO₂ was reported in this paper and compared to the common methods which must prepare the crystalline TiO₂ in the first step prior, and then create the surface defect in the second step. In this work, the surface defect creation was performed in the first step coinciding with the crystalline TiO₂ preparation using the sol–gel method. The creation was performed by varying the amounts of oxygen fed during calcination. Based on the CO₂-temperature programmed desorption (CO₂-TPD) and electron spin resonance (ESR) results, the surface defect (Ti³⁺) substantially increased with the amount of oxygen fed. Moreover, the samples resulting from calcination were used as photocatalysts for ethylene decomposition. The reactivity of those samples was also discussed.

Keywords: TiO; ₂; Surface defect controlling; First step creation; Calcination atmosphere; Ti; ³⁺; Photocatalyst

Chemical analysis of semiconducting and metallic SmS thin films by X-ray photoelectron spectroscopy by Yukimasa Mori; Sakae Tanemura (pp. 3856-3859).

We studied the chemical state of semiconducting and metallic SmS thin films by X-ray photoelectron spectroscopy (XPS), which were fabricated using dual-target magnetron sputtering by controlling the power applied to both metal and chalcogenide targets. On the basis of the valence band spectra obtained, it was suggested that semiconducting SmS has the final state corresponding to the Sm²⁺(4f⁶) configuration below the Fermi level, and metallic SmS has mainly the Sm³⁺(4f⁵) final state and a virtual band state in the Sm 5d band, contributing to the delocalization of 4f electrons and the emergence of metallic conductivity (4f⁶d⁰–4f⁵d¹). Thus, the spectra of our fabricated SmS thin films correspond to the band structure obtained from the dielectric property. This is the first work performed on the intrinsically prepared metallic SmS while the former works done for the sample transformed from semiconductor to metal phase by hard polishing.

Keywords: PACS; 82.80.Pv; 79.60.D; 68.35.Rh; 31.15.RSmS thin film; Semiconducting SmS; Metallic SmS; Sm valence states; X-ray photoelectron spectroscopy

Preparation of the subnanometer thick epitaxial Al₂O₃(0001) layers on Fe(110) for magnetic tunnel junctions by Yu.S. Dedkov; M. Fonin (pp. 3860-3864).

Growth as well as crystallographic and electronic properties of thin AlO_x layers on Fe(110) were studied by means of low-energy electron diffraction and Auger-electron spectroscopy. Al layers of different thickness were deposited on Fe(110) and successfully oxidized to AlO_x. The step-by-step oxidation of thin Al layers at room temperature leads to the formation of amorphous AlO_x on top of the Fe(110) surface. A subsequent annealing at 250°C of the oxidized 7-Å thick Al layer results in the formation of a well-ordered Al₂O₃(0001) layer on the Fe(110) surface.

Keywords: Auger spectroscopy; LEED; Surface oxide

Surface oxidation of a Melinex 800 PET polymer material modified by an atmospheric dielectric barrier discharge studied using X-ray photoelectron spectroscopy and contact angle measurement by Nai-Yi Cui; Deepesh J. Upadhyay; Colin A. Anderson; Brian J. Meenan; Norman M.D. Brown (pp. 3865-3871).

Surface properties of a Melinex 800 PET polymer material modified by an atmospheric-pressure air dielectric barrier discharge (DBD) have been studied using X-ray photoelectron microscopy (XPS) and contact angle measurement. The results show that the material surface treated by the DBD was modified significantly in chemical composition, with the highly oxidised carbon species increasing as the surface processing proceeds. The surface hydrophilicity was dramatically improved after the treatment, with the surface contact angle reduced from 81.8° for the as-supplied sample to lower than 50° after treatment. Post-treatment recovery effect is found after the treated samples were stored in air for a long period of time, with the ultimate contact angles, as measured, being stabilised in the range 58–69° after the storage, varying with the DBD-treatment power density. A great amount of the C–O type bonding formed during the DBD treatment was found to be converted into the CO type during post-treatment storage. A possible mechanism for this bond conversion has been suggested.

Keywords: PET; X-ray photoelectron spectroscopy; Dielectric barrier discharge; Surface modification

Effect of annealing temperature on luminescence of Eu³⁺ ions doped nanocrystal zirconia by Liu Huangqing; Wang Lingling; Chen Shuguang; Zou Bingsuo; Peng Zhiwei (pp. 3872-3876).

Effect of annealing temperature on luminescence of Eu³⁺ ions was studied in nanocrystal zirconia prepared by co-precipitation. The XRDs reveal with annealing temperature increasing the tetragonal crystal phase of the samples is stable. The emission spectra show the strong emission at 595 and 604nm at 394nm excitation. Under continuous UV (394nm) irradiation the 604nm emission intensity changes of the samples show as a function of irradiation time. In addition, the charge-transfer states of the samples are affected by the annealing temperature. These are associated with the defects at/in the surface of the nanocrystalline ZrO₂ with Eu³⁺ ions.

Keywords: PACS; 73.61 Tm; 74.25GzEffect; Annealing temperature; Luminescence; Eu; ³⁺; ions; Nanocrystal zirconia

The surface modified composite layer formation with boron carbide particles on magnesium alloy surfaces through pulse gas tungsten arc treatment by W.B. Ding; H.Y. Jiang; X.Q. Zeng; D.H. Li; S.S. Yao (pp. 3877-3883).

A novel fabrication process of surface modified composite layer by pulse current gas tungsten arc (GTA) surface modification process was used to deposit B₄C particles on the surface of magnesium alloy AZ31. This method is an effective technique in producing a high performance surface modified composite layer. During the pulse current GTA surface modification process, considerable convection can exist in the molten pool due to various driving forces and the pulse current could cause violent stirring in the molten pool, and the large temperature gradient across the boundary between the GTA modified surface and matrix metal resulted in rapid resolidification with high cooling rates in the molten pool, so that the process result notable grain refinement in the GTA surface modified composite layer. The hardness and wear resistance of the GTA surface modified composite layer are superior to that of as-received magnesium alloy AZ31. The hardness values and wear resistance of GTA surface modified composite layer depend on the GTA process parameters and the B₄C particles powder concentration and distribution. The optimum processing parameters for the formation of a homogeneous crack/defect-free and grain refinement microstructure were established.

Keywords: Magnesium alloy; Gas tungsten arc; Surface modified composite layer; Boron carbide particles

Synthesis and surface characteristics of CeTbO3+_δ induced by femtosecond laser irradiation by W.W. An; J.P. Miao; Z.G. Zhang; Z. Lü; W.H. Su; A.A. Sjögren; C.-G. Wahlström; S. Svanberg (pp. 3884-3887).

This work describes the use of focused, high-intensity light from a Ti:sapphire laser that generates femtosecond pulses to irradiate mixture of CeO₂ and Tb₄O₇ under ambient conditions. The prepared samples were investigated by means of X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and scanning electron microscope (SEM). XRD and XPS measurement results demonstrated that solid solution CeTbO3+_δ with cubic fluorite structure has been synthesized on the irradiated target surface. SEM micrographs showed that the ultra-short laser irradiation resulted in the formation of foamy structure and spherical particles with size varying from about 30 to 200nm. The formation mechanism has been discussed in detail.

Keywords: Rare earth oxide; Laser irradiation; Synthesis; Nanostructure

Effects of annealing temperature and method on structural and optical properties of TiO₂ films prepared by RF magnetron sputtering at room temperature by Dongsun Yoo; Ilgon Kim; Sangsoo Kim; Chang Hie Hahn; Changyu Lee; Seongjin Cho (pp. 3888-3892).

TiO₂ thin film was deposited on non-heated Si(100) substrate by RF magnetron sputtering. The as-deposited films were annealed by a conventional thermal annealing (CTA) and rapid thermal annealing (RTA) at 700 and 800°C, and the effects of annealing temperature and method on optical properties of studied films were investigated by measuring the optical band gaps and FT-IR spectra. And we also compared the XRD patterns of the studied samples. The as-deposited film showed a mixed structure of anatase and brookite. Only rutile structures were found in samples annealed above 800°C by CTA, while there are no special peaks except the weak brookite B(232) peak for the sample annealed at (or above) 800°C by RTA. FT-IR spectra show the broad peaks due to Ti–O vibration mode in the range of 590–620cm⁻¹ for the as-deposited film as well as samples annealed by both annealing methods at 700°C. The studied samples all had the peaks from Si–O vibration mode, which seemed to be due to the reaction between TiO₂ and Si substrate, and the intensities of these peaks increased with increasing of annealing temperature. The optical band gap of the as-deposited film was 3.29eV but it varied from 3.39 to 3.43eV as the annealing temperature increased from 700 to 800°C in the samples annealed by CTA. However, it varied from 3.38 to 3.32eV as the annealing temperature increased from 700 to 800°C by RTA.

Keywords: RF magnetron sputtering; Titanium oxide; Thermal annealing; RTA

Study on the anodizing of AZ31 magnesium alloys in alkaline borate solutions by C.S. Wu; Z. Zhang; F.H. Cao; L.J. Zhang; J.Q. Zhang; C.N. Cao (pp. 3893-3898).

A kind of environmentally friendly anodizing route for magnesium alloys, based on a new kind of organic additive (AA) contained traditional alkaline borate solution and 50Hz civil ac current, has been studied. It is found that the formation of the anodic films is always coupled with the additive depended sparking and oxygen evolution, and the optimized ivory-white smooth anodic film possesses high corrosion resistance and excellent binding strength to AZ31 substrate. Meanwhile, The results also show that the structure, the corrosion resistance and the morphology of the anodic films are mainly dependent on the anodizing voltage, time and additives.

Keywords: Magnesium alloy; Anodization; Additive; Potentiodynamic polarization; Electrochemical impedance spectroscopy

Temperature-dependent optical absorption measurements and Schottky contact behavior in layered semiconductor n-type InSe(:Sn) by S. Duman; B. Gurbulak; A. Turut (pp. 3899-3905).

The layered n-InSe(:Sn) single crystal samples have been cleaved from a large crystal ingot grown from non-stoichiometric melt by the Bridgman–Stockbarger method. It has been made the absorption measurements of these samples without Schottky contact under electric fields of 0.0 and 6000Vcm⁻¹. The band gap energy value of the InSe:Sn has been calculated as 1.36±0.01eV (at 10K) and 1.28±0.01eV (at 300K) under zero electrical field, and 1.31±0.01eV (at 10K) and 1.26±0.01eV (at 300K) under 6000Vcm⁻¹. The current–voltage ( I– V) characteristics of Au–Ge/InSe(:Sn)/In Schottky diodes have been measured in the temperature range 80–320K with a temperature step of 20K. An experimental barrier height (BH) Φ_ap value of about 0.70±0.01eV was obtained for the Au–Ge/InSe(:Sn)/In Schottky diode at the room temperature (300K). An abnormal decrease in the experimental BH Φ_b and an increase in the ideality factor n with a decrease in temperature have been explained by the barrier inhomogeneities at the metal–semiconductor interface. From the temperature-dependent I– V characteristics of the Au–Ge/InSe(:Sn)/In contact, that is,Φ¯bo and A^* as 0.94±0.02 and 0.58±0.02eV, and 27±2 and 21±1(A/cm²K²), respectively, have been calculated from a modifiedln(I0/T2)−q2σs2/2k2T2 versus 1/ T plot for the two temperature regions. The Richardson constant values are about two times larger than the known value of 14.4(A/cm²K²) known for n-type InSe. Moreover, in the temperature range 80–320K, we have also discussed whether or not the current through the junction has been connected with TFE.

Keywords: PACS; 73.30.+y; 73.40.Ei; 73.40.Ns; 73.40.SxInSe; Layered semiconductors; The absorption measurements; Schottky barrier height; Metal–semiconductor–metal contacts; Barrier inhomogeneity

Vertical phase separation in spin-coated films of a low bandgap polyfluorene/PCBM blend—Effects of specific substrate interaction by Cecilia M. Björström; Svante Nilsson; Andrzej Bernasik; Andrzej Budkowski; Mats Andersson; Kjell O. Magnusson; Ellen Moons (pp. 3906-3912).

We report on the effect of the substrate on the vertical phase separation in spin-coated thin films of poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-5,5-4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole] (APFO-3) blended with [6,6]-phenyl-C₆₁-butyric acid methyl ester (PCBM). Compositional depth profiles of the films are measured by dynamic secondary ion mass spectrometry (SIMS). We found that changing the substrate from silicon to gold affects the composition profile near the substrate interface. This is caused by a specific interaction between the polymer (APFO-3) and the gold surface, as confirmed by X-ray photoelectron spectroscopy (XPS). The composition profile in the area away from the substrate interface, as well as the enrichment of the free surface with APFO-3, remain however unaffected by the choice of substrate. The vertical composition was also analysed for APFO-3:PCBM films spin-coated on indium tin oxide (ITO) coated with a thin layer of (3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS).

Keywords: Conjugated polymer; X-ray photoelectron spectroscopy (XPS); Secondary ion mass spectrometry (SIMS); Spinodal decomposition; Adsorption; Thiophene

Electrochemical and quantum chemical studies of some Schiff bases on the corrosion of steel in H₂SO₄ solution by Rovshan Hasanov; Murat Sadıkoğlu; Semra Bilgiç (pp. 3913-3921).

The efficiency, as steel-corrosion inhibitors in 0.1M and 1M H₂SO₄, of two Schiff bases, 2-{[(4-methoxyphenyl)imino]methyl}phenol and 1-{[(4-methoxyphenyl)imino]methyl}-2-naphthol, (abbreviated SB-1 and SB-2, respectively) was investigated by Tafel extrapolation and linear polarization methods. Corrosion parameters and adsorption isotherms were determined from current–potential curves. It was found that the percent inhibition efficiencies ( η%) and surface coverage ( θ) increase with an increases in the concentrations of inhibitors. The results showed that these compounds act as good corrosion inhibitors especially at high concentrations. The adsorption of used compounds on the steel surface obeys Langmuir's isotherm. Obvious correlation was found between corrosion inhibition efficiency and quantum chemical parameters obtained by B3LYP/6-31g(d) method. The obtained theoretical results have been compared with the experimental findings.

Keywords: PACS; 81.65. KnSteel; Corrosion; Inhibitor; Schiff bases; Quantum chemical calculations

Photosensitization of nanocrystalline TiO₂ film electrode with cadmium sulphoselenide by R.S. Mane; C.D. Lokhande; V.V. Todkar; Hoeil Chung; Moon-Young Yoon; Sung-Hwan Han (pp. 3922-3926).

Nanocrystalline titanium dioxide (TiO₂) thin films composed of densely packed nanometer-sized grains have been successfully deposited onto an indium-doped-tin oxide (ITO) substrate. Then cadmium sulphoselenide (CdSSe) thin film was deposited onto pre-deposited TiO₂ to form a TiO₂/CdSSe film, at low temperature using a simple and inexpensive chemical method. The X-ray diffraction, selected area electron diffraction, scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX) and water contact angle techniques were used for film characterization. Purely rutile phase of TiO₂ with super-hydrophilic and densely packed nanometer-sized spherical grains of approximate diameter 30–40 (±2)nm was observed. The increase in optical absorption was observed after CdSSe film deposition. Nest like surface morphology of CdSSe on TiO₂ surface results in air trapping in the crevices which prevents water from adhering to the film with increase in water contact angle. Photosensitization of TiO₂ with CdSSe was confirmed with light illumination intensity of 80mW/cm².

Keywords: TiO; ₂; -CdSSe; Surface morphology; Optical absorption; I; –; V; Photoelectrochemical cells

Field-effect transistor based on a combination of nanometer film and undoped semiconductor by Qi Yang; Dejie Li; Baolun Yao (pp. 3927-3929).

The metal oxide nanometer film semiconductor field-effect transistor (MONSFET) is reported. In this device, a combination of undoped semiconductor and nanometer film serves as the active layer. When a negative gate-source voltage is applied, electrons from the nanometer film enter into the semiconductor layer to form the conducting channel, and the drain current increases without saturation. This structure makes more materials available for the active layer, and thus suggests a new route to enrich the applications as well as to enhance the performances.

Keywords: PACS; 85.30.De; 85.30.TvField-effect transistor; Nanometer film; Discontinuous film; Undoped semiconductor

Blocking of interfacial diffusion at Ag/Alq₃ by LiF by X.Z. Wang; Z.T. Xie; X.J. Wang; Y.C. Zhou; W.H. Zhang; X.M. Ding; X.Y. Hou (pp. 3930-3932).

X-ray photoelectron spectroscopy has been applied to interface studies of Ag/tris-(8-hydroxyquinoline) aluminum (Alq₃) and Ag/LiF/Alq₃. For Ag/Alq₃, diffusion of Ag atoms into the Alq₃ layer occurs immediately after the adhesion of the metal onto the organic layer and the process lasts several hours. Insertion of a monolayer-thick LiF buffer at the interface can effectively block the diffusion process. This is quite different from what is observed from Al/LiF/Alq₃, where Al penetrates into the LiF layer as deep as several nanometers. It is thus concluded that the LiF buffer may play different roles in Ag/LiF/Alq₃ and Al/LiF/Alq₃ and hence different mechanisms may dominate in the two cases for the enhanced carrier injection observed.

Keywords: Interfacial diffusion; X-ray photoelectron spectroscopy; Metal/organic interface; Organic light-emitting device; Alq; ₃

Fabrication and annealing analysis of three-dimensional photonic crystals by Xiying Ma; Baojun Li; Bharat S. Chaudhari (pp. 3933-3936).

Three-dimensional face-centered-cubic (fcc) photonic crystals (PhCs) are fabricated on quartz substrate using vertical deposition technique, and followed by annealing in a temperature range of 200–700°C. The monodispersed SiO₂ microspheres with a diameter of 220nm in colloidal solution are synthesized using tetraethylorthosilicate as a precursor material. The as grown opal structure exhibits a strong photonic band gap (PBG) around 450nm in the transmission spectrum. We find that the position of PBG peak in the spectrum is relevant to incident angle of light. Moreover, it is very sensitive to annealing temperature. It quickly shifts to short wavelength direction with annealing temperature increasing. The effect results from the decrease in refraction index due to the moisture evaporation in silica microspheres.

Keywords: PACS; 8270D; 6146w; 61.82.Rx; 68.37.HkPhotonic crystal; Three-dimensional; Colloidal photonic band gap

Compositional contrast in Al_xGa1−_xN/GaN heterostructures using scanning spreading resistance microscopy by I.S. Fraser; R.A. Oliver; J. Sumner; C. McAleese; M.J. Kappers; C.J. Humphreys (pp. 3937-3944).

Scanning spreading resistance microscopy has found extensive use as a dopant-profiling technique for silicon-based devices, and to a lesser extent for some III–V materials. Here we demonstrate its efficacy for wide bandgap nitrides and, in particular, show that it may be used to differentiate between layers of different Al-content in an Al_xGa1−_xN/GaN heterostructure. A monotonic increase in resistance signal with increasing Al-content is demonstrated, under optimal imaging conditions. The variation in measured resistance with applied bias is shown to be dependent on the aluminium content, and this is discussed, along with other issues, in the context of potential quantification of unknown samples. The procedure for forming an optimal image is different from that for silicon, in terms of contact forces and applied biases.

Keywords: PACS; 68.37.Ps; 81.05.Ea; 74.78.FkScanning spreading resistance microscopy; Gallium nitride

A calibrated atomic force microscope using an orthogonal scanner and a calibrated laser interferometer by Dong-Yeon Lee; Dong-Min Kim; Dae-Gab Gweon; Jinwon Park (pp. 3945-3951).

A compact and two-dimensional atomic force microscope (AFM) using an orthogonal sample scanner, a calibrated homodyne laser interferometer and a commercial AFM head was developed for use in the nano-metrology field. The x and y position of the sample with respect to the tip are acquired by using the laser interferometer in the open-loop state, when each z data point of the AFM head is taken. The sample scanner, which has a motion amplifying mechanism was designed to move a sample up to 100μm×100μm in orthogonal way, which means less crosstalk between axes. Moreover, the rotational errors between axes are measured to ensure the accuracy of the calibrated AFM within the full scanning range. The conventional homodyne laser interferometer was used to measure the x and y displacements of the sample and compensated via an X-ray interferometer to reduce the nonlinearity of the optical interferometer. The repeatability of the calibrated AFM was measured to sub-nanometers within a few hundred nanometers scanning range.

Keywords: PACS; 81.70.Fy; 83.85.EiCalibrated atomic force microscope; Laser interferometer; Orthogonal scanner; Flexure-guide

A non-thermal chemical synthesis of hydrophilic and amorphous cobalt oxide films for supercapacitor application by Sunil G. Kandalkar; C.D. Lokhande; R.S. Mane; Sung-Hwan Han (pp. 3952-3956).

Present work explored a room temperature, simple and low cost chemical route for the preparation of hydrophilic cobalt oxide films from alkaline cobalt chloride (CoCl₂:6H₂O) and double distilled water precursor solutions. As-deposited cobalt oxide films showed amorphous nature, which is one of the prime requirements for supercapacitor, as confirmed from X-ray diffraction studies. Changes in direct band gap energy and electrical resistivity of as-deposited cobalt oxide films were confirmed after annealing. Spherical grains of about 40–50nm diameters were uniformly distributed over the substrate surface. Surface wettability studied in contact with liquid interface, showed hydrophilic nature as water contact angle was <90°. Finally, presence of cobalt–oxygen covalent bond was observed from Raman shift experiment.

Keywords: Cobalt oxide; Non-thermal process; Raman shift; Electrical resistivity

Effects of (NH₄)₂S_x treatment on surface work function and roughness of indium–tin-oxide by Yow-Jon Lin; Chang-Feng You; Chia-Lung Tsai (pp. 3957-3961).

In this study, the effects of an (NH₄)₂S_x treatment on the surface work function (SWF) and roughness of indium–tin-oxide (ITO) have been investigated. From the observed X-ray photoelectron spectroscopy results, optical transmittance measurements, atomic force microscopy measurements and four-point probe measurements, it is suggested that the surface chemical changes and an increase in the sheet resistance had strong effects on the SWF of ITO. We find that the S occupation of oxygen vacancies near the ITO surface after (NH₄)₂S_x treatment may result in a marked increase in the SWF and a slight increase in the surface roughness.

Keywords: PACS; 81.65.−b; 81.70.Jb; 73.30.+y; 82.80.Ej; 87.64.Gb; 78.40.FySurface treatment; ITO; Work function; XPS

Electrical properties of thin yttria-stabilized zirconia overlayers produced by atomic layer deposition for solid oxide fuel cell applications by C. Brahim; A. Ringuedé; M. Cassir; M. Putkonen; L. Niinistö (pp. 3962-3968).

Thin films of yttria-stabilized zirconia (YSZ) electrolyte were prepared by atomic layer deposition at 300°C for solid oxide fuel cell (SOFC) applications. YSZ samples of 300–1000nm thickness were deposited onto La_0.8Sr_0.2MnO₃ (LSM) cathodes. A microstructural study was performed on these samples and their electrical properties were characterised between 100 and 390°C by impedance spectroscopy. A remarkable feature is that the as-deposited layers were already crystalline without any annealing treatment. Their resistance decreased when reducing the layer thickness; nevertheless, their conductivity and activation energy were significantly lower than those reported in the literature for bulk YSZ.

Keywords: ALD; Yttria-stabilized zirconia; SOFC; Electrical properties

GeSbTe deposition for the PRAM application by Junghyun Lee; Sangjoon Choi; Changsoo Lee; Yoonho Kang; Daeil Kim (pp. 3969-3976).

GeSbTe (GST) chalcogenide thin films for the phase-change random access memory (PRAM) were deposited by an atomic layer deposition (ALD) process. New precursors for GST thin films made with an ALD process were synthesized. Among the synthesized precursors, Ge(N(CH₃)₂)₄, Sb(N(CH₃)₂)₄, and Te( i-Pr)₂ ( i-Pr= iso-propyl) were selected. Using the above precursors, GST thin films were deposited using an H₂ plasma-assisted ALD process. Film resistivity abruptly changed after an N₂ annealing process above a temperature of 350°C. Cross-sectional scanning electron microscope (SEM) photographs of the GST films on the patterned substrate with aspect ratio of 7 shows that the step coverage is about 90%.

Keywords: PACS; 81.05Gc; 81.15.Gh; 61.10.NzGeSbTe chalcogenide; ALD; TEM; AFM; XRD

Characterization of iron oxide layers using Auger electron spectroscopy by Milan Bizjak; Anton Zalar; Peter Panjan; Benjamin Zorko; Borut Praček (pp. 3977-3981).

Metals can form several kinds of oxides. Iron forms wustite (FeO), magnetite (FeO+Fe₂O₃ or Fe₃O₄) and haematite (Fe₂O₃). Iron oxides, especially magnetite, are used for insulation between the lamellas of an electromotor made of electromagnetic sheet. In this work, iron oxide layers were characterized on industrial samples of electromagnetic sheet by AES depth profile analysis, and iron oxides with known chemical composition were used as reference samples, i.e. a magnetite mineral and a standard haematite reference sample. The magnetite mineral was chosen because it can be found in nature in a very pure form. The selection of reference samples was also verified on samples with an oxide layer of known composition, which were prepared by sputter deposition. The composition of the sputtered oxide layers was analysed by the weight-gain method and Rutherford backscattering without the use of standard reference materials (SRM), and the results were then compared with those obtained by AES depth profile analysis.

Keywords: PACS; 81.65; 8170.JbOxidation; Iron oxides; Auger electron spectroscopy; Rutherford backscattering spectrometry; Weight-gain technique

Multiple nano-TiO₂ layers to prevent dye/nano-TiO₂ from photodegradation under a UV-exposure environment by Leo Chau-Kuang Liau; Po-I Chiang (pp. 3982-3986).

A device of multiple nano-TiO₂ layers was proposed and fabricated to prevent a dye/nano-TiO₂ region from serious photo-degradation. In this device, the top of the dye/TiO₂ region was designed to be coated using sol–gel nano-TiO₂ thin films to shield UV irradiation from the photo-degradation effect. The sol–gel TiO₂ was prepared in a low temperature (75°C) and verified as nano-sized particles and an anatase crystalline structure. Different devices of the multi-layer samples fabricated using different compositions of nano-TiO₂ were produced and exposed for UV irradiation tests. Results show that the presence of the sol–gel TiO₂ films coated on top of the dye/TiO₂ region can significantly alleviate the dye photo-degradation under UV irradiation. This multi-layer device can effectively improve the photo-stability of the dye/TiO₂ region in a UV-exposure environment.

Keywords: Multiple nano-TiO; ₂; layers; Sol–gel processing; Photo-degradation; UV irradiation

Self-assembled growth of MgO nanosheet arrays via a micro-arc oxidation technique by T. Qiu; X.L. Wu; F.Y. Jin; A.P. Huang; Paul K. Chu (pp. 3987-3990).

Unique magnesia (MgO) nanosheet arrays were fabricated via a promising micro-arc oxidation (MAO) technique on the surface of magnesium alloy. The non-uniform patterning of oxygen evolution on the sample surface and trapping of gas bubbles in the growing film are associated with the formations of the sheet and flower-like structures. These MgO structures may be useful in reinforcing composite materials or in further modifying other nanostructures.

Keywords: PACS; 81.07.−b; 81.20.−n; 81.65.MqMgO nanosheet; Micro-arc oxidation technique; Fabrication

Atomic structure of CaF₂/MnF₂–Si(1 1 1) superlattices from X-ray diffraction by Simon G. Alcock; C.L. Nicklin; P.B. Howes; C.A. Norris; R.N. Kyutt; N.S. Sokolov; N.L. Yakovlev (pp. 3991-3999).

X-ray reflectivity and non-specular crystal truncation rod scans have been used to determine the three-dimensional atomic structure of the buried CaF₂–Si(1 1 1) interface and ultrathin films of MnF₂ and CaF₂ within a superlattice. We show that ultrathin films of MnF₂, below a critical thickness of approximately four monolayers, are crystalline, pseudomorphic, and adopt the fluorite structure of CaF₂. High temperature deposition of the CaF₂ buffer layer produces a fully reacted, CaF₂–Si(1 1 1) type-B interface. The mature, “long” interface is shown to consist of a partially occupied layer of CaF bonded to the Si substrate, followed by a distorted CaF layer. Our atomistic, semi-kinematical scattering method extends the slab reflectivity method by providing in-plane structural information.

Keywords: PACS; 61.10.; −; i; 68.65.CdSuperlattice; MnF; ₂; CaF; ₂; Crystal truncation rods

Research on the properties of ZnO thin films deposited by using filtered cathodic arc plasma technique on glass substrate under different flow rate of O₂ by C. Li; X.C. Li; P.X. Yan; E.M. Chong; Y. Liu; G.H. Yue; X.Y. Fan (pp. 4000-4005).

ZnO thin film has been deposited on the glass substrate at a temperature of 200°C using the filtered cathodic arc plasma (FCAP) technique with the oxygen flow rate of 1.0, 3.0, 5.0, 7.0, 9.0 and 10.0sccm. The deposition processes are only held in pure oxygen atmosphere. The as-grown films exhibit a polycrystalline hexagonal wurtzite structure. With the oxygen flow rate increase, the crystallinity of the samples first increases and then decreases as measured by X-ray diffractometry (XRD). And the tensile stress exists in all the as-grown thin films. The small grain with a mean diameter of 13nm is observed by the field emission scanning electron microscopy (FESEM). The electrical resistivity values of the thin films are very low ranging from 5.42×10⁻³Ωcm to 4.0×10⁻²Ωcm. According to the result from room temperature photoluminescence spectra measurement, the luminescent bands also depend on the oxygen supply.

Keywords: ZnO thin films; Filtered cathodic arc plasma; Tensile stress; Electrical resistivity; Photoluminescence

Impact of the interaction with the positive charge in adsorption of benzene and other organic compounds from aqueous solutions on carbons by Artur P. Terzyk; Magdalena S. Ćwiertnia; Marek Wiśniewski; Piotr A. Gauden; Gerhard Rychlicki; Grzegorz S. Szymański (pp. 4006-4009).

We present the results of benzene adsorption at the acidic pH level determined on the series of chemically modified activated carbons and at three temperatures. The influence of carbon surface chemical composition on benzene adsorption is discussed. It is shown that the decrease in the pH level from 7 up to 1.5 increases benzene adsorption and the only exception is carbon modified with gaseous ammonia. Basing on the results of current work and those published previously (for phenol, paracetamol, acetanilide and aniline) and using the results of quantum chemistry calculations (DFT, Gaussian 98) we show, that the value of the energy of interaction with unit positive charge is crucial during the analysis of the influence of pH level on adsorption. Obtained results allow to predict the changes in adsorption of aromatics on carbons with the decrease in the pH level.

Keywords: Adsorption from solution; Activated carbon; Gaussian 98; Benzene; Phenol; Paracetamol; Acetanilide; Aniline; DFT

A computational study on nanocrystalline SnO₂: Adsorption of CO and O₂ onto defective nanograins by A.M. Mazzone; V. Morandi (pp. 4010-4015).

This work presents a study of the adsorption properties of defective nanostructures. The calculations have quantum mechanical detail and are based on a semi-empirical Hamiltonian, which is applied to the evaluation of both the electronic structure and of the conductance. The material considered in this study, i.e. SnO₂, has a widespread use as gas sensor and oxygen vacancies are known to act as active catalytic sites for the adsorption of small molecules. In the following calculations crystalline SnO₂ nanograins, with a size and shape comparable with the experimental ones, have been considered. The grains lattice, which has the rutile structure of the bulk material, includes oxygen vacancies and the adsorbed system is generated by depositing a gaseous molecule, either CO or O₂, above an atom on the grain surface. The calculations show that the presence of the defects enhances the grain cohesion and favors adsorption. The conductance has a functional relationship with the structure and the defective state of the nanograins and its dependence on these quantities parallels the one of the binding energy.

Keywords: SnO; ₂; nanograins; Defects; CO adsorption; Ab initio; calculations

Microstructure of yttric calcium phosphate bioceramic coatings synthesized by laser cladding by Diangang Wang; Chuanzhong Chen; Jie Ma; Tingquan Lei (pp. 4016-4020).

The yttric calcium phosphate (CaP) coatings were in situ prepared on pure titanium substrate by laser cladding. The morphologies and phases constitution of CaP coatings were studied by electron probe microanalysis, X-ray diffraction and so on. The bonding state between the coating and the substrate is fine metallurgical combination, and the addition of yttria can fine the structure and increase the tensile strength of the coatings. The X-ray result shows that the coating is composed of the phases of HA, α-Ca₂P₂O₇, β-Ca₂P₂O₇ and CaTiO₃.

Keywords: Biomaterial; Yttria; Microstructure; Laser cladding

Preparation and field emission properties of carbon nanotubes cold cathode using melting Ag nano-particles as binder by Yuxiang Qin; Ming Hu; Haiyan Li; Zhisheng Zhang; Qiang Zou (pp. 4021-4024).

A new preparation process for carbon nanotubes (CNTs) cold cathode was studied through the replacement of traditional organic or inorganic binder with Ag nano-particles. This method has the advantages of low preparation temperature and fine electrical contact between CNTs paste and substrate. A mixture paste of CNTs, Ag nano-particles and other organic solvents was spreaded on Si substrate. By melting and connecting of Ag nano-particles after sintered 30min at 250°C, a flat CNTs films with good field emission properties was obtained. The measurements reveal that the turn on electric field and the threshold electric field of as-prepared CNTs cathode are 2.1 and 3.9V/μm respectively and the field emission current density is up to 41mA/cm² at an applied electric field of 4.7V/μm.

Keywords: PACS; 79.70.+q; 81.20.EvCarbon nanotubes; Field emission; Ag nano-particles; Binder

The effect of electric field strength on electroplex emission at the interface of NPB/PBD organic light-emitting diodes by De-Wei Zhao; Zheng Xu; Fu-Jun Zhang; Shu-Fang Song; Su-Ling Zhao; Yong Wang; Guang-Cai Yuan; Yan-Fei Zhang; Hong-Hua Xu (pp. 4025-4028).

Organic light-emitting diode (OLED) based on two kinds of blue emission materials N, N′-bis(1-naphthyl)- N, N′-diphenyl-l,l′-diphenyl-4,4′-diamine (NPB) and 2-(4-biphenylyl)-5(4- tert-butyl-phenyl)-1,3,4-oxadiazole (PBD) was fabricated. There is only one emission peak in photoluminescence (PL) spectrum which originates from NPB exciton emission. And the electroluminescence (EL) emission peaks have an apparent red-shift with the increase of driving voltage. The red-shift emission from exciplex emission could be ruled out. Thus, by the method of Gaussian fitting it should be ascribed to the overlap of exciton emission and electroplex emission which occurs at the interface between NPB and PBD. The formation of the electroplex emission under high electric field is analyzed.

Keywords: Electroplex emission; Exciton emission; Red-shift

Synthesis of amorphous boron carbide by single and multiple charged boron ions bombardment of fullerene thin films by B. Todorović-Marković; I. Draganić; D. Vasiljević-Radović; N. Romčević; M. Romčević; M. Dramićanin; Z. Marković (pp. 4029-4035).

In this paper, results of structural modification of fullerene thin films by single and multiple charged boron ions (B⁺, B³⁺) are presented. The applied ion energies were in the range of 15–45keV. The characterization of as-deposited and irradiated specimens has been performed by atomic force microscopy, Raman and Fourier transform infrared spectroscopy and UV/vis spectrophotometry. The results of Raman analysis have shown the formation of amorphous layer after irradiation of fullerene thin films. Fourier transform infrared spectroscopy has confirmed the formation of new B–C bonds in irradiated films at higher fluences (2×10¹⁶cm⁻²). The morphology of bombarded films has been changed significantly. The optical band gap was found to be reduced from 1.7 to 1.06eV for irradiated films by B³⁺ ions and 0.7eV for irradiated films by B⁺ ions.

Keywords: Atomic force microscopy; Raman scattering spectroscopy; Fourier transform infrared spectroscopy; Ion bombardment; Boron carbides

High temperature STM/STS investigations of resonant image states on Au(111) by P. Kowalczyk (pp. 4036-4040).

Scanning tunneling microscopy (STM) and spectroscopy (STS) were used to study the electronic structure of Au(111) surface in the range of 2–5.5eV above the Fermi level. In this paper, we concentrate firstly on the position of the upper band gap edge (BE) existing in [111] direction in Au(111) and secondly on the position of the resonant image potential surface state (RIS) located in the bulk states approximately 1.1eV above BE. The experiment was carried out in UHV at two temperatures 294K and 580K. Our high temperature STS (HT-STS) results clearly show the presence of RIS and BE local maxima at both temperatures. What is more, a slight shift towards the Fermi level of BE and RIS was observed. Those shifts were the consequence of the change of [111] band gap and lowering gold work function due to the thermal extension of interatomic distances. Finally, estimation of the work function was given at 294K and 580K.

Keywords: PACS; 65.40.−b; 68.37.−d; 68.37.Ef; 73.20.−r; 73.20.FzHigh temperature STM; STS; Gold; Resonant image states

Effect of thermal annealing on microstructural properties of Ti/Ge₂Sb₂Te₅/Ti thin films deposited on SiO₂/Si substrates by a sputtering method by S.Y. Kim; H.S. Lee; I.S. Chung; Y.J. Park; J.Y. Lee; T.W. Kim (pp. 4041-4044).

Ti/Ge₂Sb₂Te₅/Ti thin films deposited by a sputtering method on SiO₂/Si substrates were annealed at 400°C in N₂ atmosphere and characterized by using transmission electron microscopy (TEM) and Auger electron spectroscopy (AES) in order to investigate the inter-diffusion of the Ti/Ge₂Sb₂Te₅/Ti system due to annealing. The TEM and AES results showed that the interface between the Ti and the Ge₂Sb₂Te₅ layers was unstable and Ti atoms were incorporated into the Ge₂Sb₂Te₅ thin film upon annealing. The Te and Sb atoms of the Ge₂Sb₂Te₅ layer diffused into the Ti layer. The intermixing layers between the Ge₂Sb₂Te₅ layer and two Ti layers were formed. These results indicate that the microstructural properties of the Ti/Ge₂Sb₂Te₅/Ti systems can be degraded by the postgrowth thermal annealing.

Keywords: PACS; 68.37.Lp; 68.55.Jk; 61.50.KsGe; ₂; Sb; ₂; Te; ₅; Diffusion; Transmission electron microscopy

Growth of high-density Ru- and RuO₂-composite nanodots on atomic-layer-deposited Al₂O₃ film by Wei Chen; Min Zhang; D.W. Zhang; Shi-Jin Ding; J.-J. Tan; Min Xu; Xin-Ping Qu; L.-K. Wang (pp. 4045-4050).

Growth of Ru- and RuO₂-composite (ROC) nanodots on atomic-layer-deposited Al₂O₃ film has been studied for the first time using ion-beam sputtering followed by post-deposition annealing (PDA). X-ray photoelectron spectroscopy analyses reveal that RuO₂ and Ru co-exist before annealing, and around 10% RuO₂ is reduced to metallic Ru after PDA at 900°C for 15s. Scanning electron microscopy measurements show that well-defined spherical ROC nanodots are not formed till the PDA temperature is raised to 900°C. The mean diameter of the nanodots enlarges with increasing PDA temperature whereas the nanodot density decreases, which is attributed to coalescence process between adjacent nanodots. It is further illustrated that the resulting nanodot size and density are weakly dependent on the annealing time, but are markedly influenced by the decomposition of RuO₂. In this article, the ROC nanodots with a high density of 1.6×10¹¹cm⁻², a mean diameter of 20nm with a standard deviation of 3.0nm have been achieved for the PDA at 900°C for 15s, which is promising for flash memory application.

Keywords: PACS; 81.07.−b; 81.07.TaRuthenium; Ruthenium oxide; Nanodot; Flash memory

An optical emission spectroscopy study of the plasma generated in the DC HF CVD nucleation of diamond by M.M. Larijani; F. Le Normand; O. Crégut (pp. 4051-4059).

Optical emission spectroscopy (OES) was used to study the plasma generated by the activation of the gas phase CH₄+H₂ both by hot filaments and by a plasma discharge (DC HF CVD) during the nucleation of CVD diamond. The effects of nucleation parameters, such as methane concentration and extraction potential, on the plasma chemistry near the surface were investigated. The density of the diamond nucleation and the quality of the diamond films were studied by scanning electron microscopy (SEM) and Raman scattering, respectively. The OES results showed that the methane concentration influenced strongly the intensity ratio of H_β–H_α implying an increase of electron mean energy, as well as CH, CH⁺, C₂. A correlation between the relative increase of CH⁺ and the diamond nucleation density was found, conversely the increase of C₂ contributed to the introduction of defects in the diamond nuclei.

Keywords: Diamond; HFCVD; Nucleation; Optical emission spectroscopy

Seed layer-free synthesis and characterization of vertically grown ZnO nanorod array via the stepwise solution route by Xiang-Dong Gao; Xiao-Min Li; Wei-Dong Yu; Lei Li; Ji-Jun Qiu (pp. 4060-4065).

A novel stepwise method was developed for the deposition of ZnO nanorod array (NRA) from the simple inorganic aqueous solution. Different from the traditional one-pot synthesis route, merely a thin liquid precursor layer adsorbed on the substrate instead of the bulk solution underwent the reaction at elevated temperature in a typical deposition cycle. Sparse and vertically grown wurtzite ZnO NRA was deposited on seed layer-free glass substrate after 20 cycles (in typically 20min). Each individual ZnO rod possessed the well-defined hexagonal facet, the side length of about 150nm, the aspect ratio of 2:3, and the small size dispersity. Also the overall ZnO NRA exhibited high ultraviolet photoluminescence and weak blue emission, indicating its good optical properties. Mechanism analysis indicated that, the decrease of the supersaturation degree in solution after the climax in the reaction period of each deposition cycle is the root cause of the sparse nucleation and the vertical growth of ZnO nanorods. The work has opened up a novel stepwise approach toward high quality ZnO NRA, being valuable for extending the synthetic methods of semiconductor nanostructures in mild solutions.

Keywords: ZnO; Nanorod array; Stepwise; Photoluminescence

Negative differential resistance of TEMPO molecules on Si(111) by Ann-Sofie Hallbäck; Bene Poelsema; Harold J.W. Zandvliet (pp. 4066-4071).

Negative differential resistance (NDR) has been observed for individual 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) molecules on Si(111) in ultra high vacuum (UHV) scanning tunneling microscopy (STM) and spectroscopy (STS) measurements at room temperature. NDR effects were observed exclusively at negative bias voltage using an n-type Si(111) sample. At 77K no NDR effects were observed, but the I( V) curves were similar in shape to those recorded on bare Si(111) sites. TEMPO was observed to adsorb preferentially at corner adatom sites of the Si(111)-7×7 structure. Although the Si(111)-7×7 reconstruction was conserved, local defects were frequently observed in the vicinity of the TEMPO adsorbates.

Keywords: PACS; 85.65.+h; 73.63.−bSemiconductors; Adsorption; Charge transport; STM; Molecular electronics

Shape alterations of ZnO nanocrystal arrays fabricated from NH₃·H₂O solutions by Ke Yu; Zhengguo Jin; Xiaoxin Liu; Juan Zhao; Junyi Feng (pp. 4072-4078).

Well-aligned crystalline ZnO nanorod arrays were synthesized via an aqueous solution route with ammonia and zinc nitrate as inorganic precursors. ZnO crystalline seed films were firstly coated on ITO substrates for epitaxial growth of rods through sol–gel processing and heat treatment. SEM, TEM, SAED and XRD were utilized to characterize morphologies and structures of ZnO crystals. Heterogeneous nucleation is crucial for rod growth. A broad scope of pH favorable for heterogeneous nucleation was disclosed at zinc concentration from 0.04 to 0.1M in the inorganic system due to the complex reaction of ammonia with Zn²⁺. Elevation of initial zinc concentration or pH promoted growth rate of rods and enlarged rod size. ZnO nanorods were transformed to nanotubes, nanosheets and rods with blanket-like shaped surface mainly by secondary pH adjustment. All ZnO nanocrystals are wurtzite structure preferentially oriented in c-axis direction.

Keywords: ZnO; Nanocrystal arrays; Aqueous solution; Ammonia

A simple model for high fluence ultra-short pulsed laser metal ablation by Benxin Wu; Yung C. Shin (pp. 4079-4084).

The ultra-short laser metal ablation is a very complex process, the complete simulation of which requires applications of complicated hydrodynamics or molecular dynamics models, which, however, are often time-consuming and difficult to apply. For many practical applications, where the laser ablation depth is the main concern, a simplified model that is easy to apply but at the same time can also provide reasonably accurate predictions of ablation depth is very desirable. Such a model has been developed and presented in this paper, which has been found to be applicable for laser pulse duration up to 10ps based on comparisons of model predictions with experimental measurements.

Keywords: Ultra-short pulsed laser; Laser ablation; Modeling of laser ablation

The oxidation of calcium implanted titanium in water: A depth profiling study by D.A. Armitage; R. Mihoc; T.J. Tate; D.S. McPhail; R. Chater; J.A. Hobkirk; L. Shinawi; F.H. Jones (pp. 4085-4093).

Ion implantation of calcium has been proposed previously as a route to bioactive titanium surfaces and has been shown to stimulate promising cell and tissue responses. While the precise reasons for this behaviour remain poorly understood, it is clear that the nature of the Ca implanted surface changes rapidly on exposure to body fluids. In order to understand the processes taking place more clearly, the current work examined the simple interaction of Ca implanted Ti with water. The surface chemistry and compositional changes within the sub-surface region of the modified Ti were examined. On immersion in water, the concentration of implanted Ca ions was found to decrease both at the surface and throughout the implanted region. At the same time, the sub-surface oxygen concentration was found to increase dramatically. Although Ca implantation into Ti results in a thicker oxide layer at the surface, it appears that this layer no longer affords the underlying Ti the same protection from further oxidation provided by the native oxide. By examining samples implanted with O, Ti or Ar it was possible to conclude that this was specific to Ca implantation and not a result of the ion implantation process itself.

Keywords: Ion implantation; Titanium; Calcium; Biomaterials; X-ray photoelectron spectroscopy; Secondary ion mass spectrometry

Surface free energy of non-stick coatings deposited using closed field unbalanced magnetron sputter ion plating by Chen-Cheng Sun; Shih-Chin Lee; Shyue-Bin Dai; Shein-Long Tien; Chung-Chih Chang; Yaw-Shyan Fu (pp. 4094-4098).

Semiconductor IC packaging molding dies require wear resistance, corrosion resistance and non-sticking (with a low surface free energy). The molding releasing capability and performance are directly associated with the surface free energy between the coating and product material. The serious sticking problem reduces productivity and reliability. Depositing TiN, TiMoS, ZrN, CrC, CrN, NiCr, NiCrN, CrTiAlN and CrNiTiAlN coatings using closed field unbalanced magnetron sputter ion plating, and characterizing their surface free energy are the main object in developing a non-stick coating system for semiconductor IC molding tools. The contact angle of water, diiodomethane and ethylene glycol on the coated surfaces were measured at temperature in 20°C using a Dataphysics OCA-20 contact angle analyzer. The surface free energy of the coatings and their components (dispersion and polar) were calculated using the Owens–Wendt geometric mean approach. The surface roughness was investigated by atomic force microscopy (AFM). The adhesion force of these coatings was measured using direct tensile pull-off test apparatus. The experimental results showed that NiCrN, CrN and NiCrTiAlN coatings outperformed TiN, ZrN, NiCr, CiTiAlN, CrC and TiMoS coatings in terms of non-sticking, and thus have the potential as working layers for injection molding industrial equipment, especially in semiconductor IC packaging molding applications.

Keywords: Contact angle; Surface free energy; Closed field unbalanced magnetron sputter ion plating

Ripple surface generated on hydrogenated amorphous carbon nitride films by Chengbing Wang; Shengrong Yang; Junyan Zhang (pp. 4099-4102).

It is reported for the first time that the periodical ripple surface feature at micrometer-scale was observed on hydrogenated amorphous carbon nitride films deposited by pulse plasma chemical vapor deposition (CVD) technique. Nitrogen incorporation to hydrogenated amorphous carbon films and the different growing environments of pulse dc plasma discharge perhaps played crucial role in the surface morphology transformation of hydrogenated amorphous carbon nitride films.

Keywords: Carbon nitride films; Ripple morphology

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Applied Surface Science (v.253, #8)

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Applied Surface Science (v.253, #8)