Check out our New Publishers' Select for Free Articles

Applied Surface Science (v.256, #7)

Determination of backbone chain direction of PDA using FFM by Sadaharu Jo; Kentaro Okamoto; Mitsuru Takenaga (pp. 1969-1971).

The effect of backbone chains on friction force was investigated on both Langmuir–Blodgett (LB) films of 10,12-heptacosadiynoic acid and the (010) surfaces of single crystals of 2,4-hexadiene-1,6-diol using friction force microscopy (FFM). It was observed that friction force decreased when the scanning direction was parallel to the [001] direction in both samples. Moreover, friction force decreased when the scanning direction was parallel to the crystallographic [102], [101], [100] and[101¯] directions in only the single crystals. For the LB films, the [001] direction corresponds to the backbone chain direction of 10,12-heptacosadiynoic acid. For the single crystals, both the [001] and [101] directions correspond to the backbone chain direction, and the [102], [100] and[101¯] directions correspond to the low-index crystallographic direction. In both the LB films and single crystals, the friction force was minimized when the directions of scanning and the backbone chain were parallel.

Keywords: Polydiacetylene (PDA); Langmuir–Blodgett (LB) films; Friction force microscope; Backbone chain; Physical vapor growth

Thermal stability of nanocrystalline layers fabricated by surface nanocrystallization by Yong-jin Mai; Xiao-hua Jie; Li-li Liu; Neng Yu; Xiang-xin Zheng (pp. 1972-1975).

A nanocrystalline layer with ultrafine grains (about 30–40nm) on the surface of 7050 aluminum alloy was fabricated by a new technique called High Pressure Shot Peening (HPSP) which is the combination of common Shot Peening equipment with a pressurizing vessel. Relationship between hot flow and temperature was observed by Differential Scanning Calorimetry (DSC) and the activation energy, calculated by Kisssinger equation, of the as-treated sample increased 26.6kJ/mol when it is compared with the as-reserved sample. The Bragg peaks of the as-prepared samples, respectively treated with various annealing treatments were characterized by XRD and the microhardness distribution along the depth from the treated surface were measured at the same time, which indicated that the broadening of Bragg peaks decreased with the increasing of anneal temperature; the grain size, calculated by Scherrer–Wilson equation, increased obviously during 180–220°C, accordingly, the microhardness obviously decreased. According to the results of DSC, XRD and microhardness, it is reasonable to deduce that the temperature range of thermal stability for aluminum alloy nanocrystalline layer is lower than 200°C.

Keywords: Surface nanocrystallization; Thermal stability; Shot peening; Aluminum alloy; Activation energy

Facile synthesis and characterization of glass/cobalt core/shell composite spheres with tunable shell morphologies by Zhen-guo An; Jing-jie Zhang; Shun-long Pan (pp. 1976-1982).

Polyhedral cobalt microcrystals assembled on hollow glass spheres are successfully synthesized by a facile and easy-control hydrothermal reduction process, and thus hierarchical glass/cobalt core/shell composite hollow spheres are fabricated with low-density (0.96gcm⁻³). By properly tuning the process conditions and the component of the reaction solution, a series of composite spheres with gradient in morphologies of the shell layer can be prepared. Based on a series of contrast experiments, the probable formation mechanism of the core/shell hierarchical structures is proposed. The magnetic properties of the products are studied and the results demonstrate that the composite spheres present ferromagnetic properties related to the special shell morphologies. The composite hollow spheres thus obtained may have some promising applications in the fields of low-density magnetic materials, conduction, and catalysis, etc. This work provides an additional strategy to prepared core/shell composite spheres with tailored shell morphology and magnetic properties.

Keywords: Hydrothermal synthesis; Assembly; Cobalt; Core/shell; Magnetic properties

Assessing the equation of state and comparing it with other relationships used for determining the surface tension of solids by Samad Ahadian; Siamak Moradian; Mohammad Amani Tehran (pp. 1983-1991).

Some facts regarding the equation of state (EQS) in calculating the surface tension of solids by means of contact angle measurements were manifested. In the present investigation, it was mathematically proved that the surface tension of a solid as estimated by the EQS is in fact equivalent to the Zisman critical surface tension for that same solid. Additionally, the applicability of the EQS's approach in attaining the surface tension of powdered solids by the aid of the capillary rise procedure is also discussed and its limitations are clarified. Furthermore, a methodology was devised so that the surface tension of solids as determined by the EQS could be compared with those calculated by approaches using components of surface tension. This methodology revealed that the applications of approaches based on the geometric mean (i.e. Owens/Wendt and van Oss et al. relationships) are restricted to achieving only high surface tensions of solids.

Keywords: Solid surface tension; Contact angle measurement; Acid–base interactions; Equation of state; Capillary rise procedure

Fabrication and characterizations of a polymer hybrid OA/MA/St-TiO₂ by Zhongwei Heng; Hongling Chen (pp. 1992-1995).

A nano-hybrid composite of octadecyl acrylate/maleic anhydride/styrene (OA/MA/St) encapsulating nano-TiO₂ with an average particle size of 30–60nm was fabricated based on chemical modification of nanotitania. The polymer hybrid OA/MA/St-TiO₂ and nano-TiO₂ were characterized by infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), static contact angle (CA) as well as transmission electron microscopy (TEM). FT-IR spectra and TGA results suggest that the copolymer OA/MA/St adheres on the surface of nano-TiO₂ through physical adsorption and chemical bonding. The calculated reacted OH surface density is about 0.6OH/nm², and the modification efficiency is approximately 27.28%. In addition, when the molar ratio of OA/MA/St is 7:2:1, the hybrid shows the strongest hydrophobicity, and its static contact angle reaches as high as 146°. TEM image of the hybrid OA/MA/St-TiO₂ reveals that the modified particles have good dispersibility and compatibility with n-hexane.

Keywords: Nano-TiO; ₂; OA/MA/St; Polymer hybrid; Surface modification; Hydrophobic

Effects of gas pressure and plasma power on the growth of carbon nanostructures by Y.X. Liu; J.H. Liu; C.C. Zhu; W.H. Liu (pp. 1996-1999).

Effects of gas pressure and plasma power on the growth of carbon-based nanostructures (CNSs) have been studied in detail. Multi-walled carbon nanotube (MWCNTs) and carbon nanowalls (CNWs) were synthesized on glass substrates via radio frequency plasma-enhanced chemical vapor deposition (RFPECVD) technique. Surface morphologies of the films have been studied by SEM and TEM. When the gas pressure increases from 120 to 300Pa, the deposited carbon material changes from MWCNTs to carbon nanowalls (CNWs). Additionally, the density of carbon nanostructures increases with the gas pressure. The radio frequency (RF) plasma power ranging from 600 to 2400W was applied during the activation and deposition process. The plasma enhances the decomposition of carbon atoms to deposit onto the surfaces of catalyst particles. Whereas an exorbitant RF plasma power can destroy the already deposited carbon nanostructures.

Keywords: Carbon nanotubes; Carbon nanowalls; Plasma power; Gas pressure

Study on the surface performance of carbon fibres irradiated by γ-ray under different irradiation dose by Jun-Qing Li; Yu-Dong Huang; Shao-Yun Fu; Li-Hui Yang; Hai-tao Qu; Guang-shun Wu (pp. 2000-2004).

The technology of high-energy irradiation is widely used in the field of material interface modification because of its high efficiency, energy conservation and environment friendliness. In this paper, γ-ray irradiation graft technology was used in order to enhance the surface performance of the carbon fibre (CF). The surface chemical elements and functional groups of untreated and irradiated CF were observed by photoelectron spectroscopy (XPS). The results show that the value of O/C and the quantity of oxygen functional groups on CF surface were enhanced efficiently after treatment by γ-ray irradiation graft technology. The morphology of CF was characterized by scanning electron microscopy (SEM) and atom forced microscopy (AFM), respectively. The surface roughness of CF was greatly increased compared with the untreated CF. Moreover, the interface performance was clearly improved after irradiation.

Keywords: Surface performance; Carbon fibres; Irradiation; γ-Ray; X-ray photoelectron spectroscopy

The enhanced field-emission properties of screen-printed single-wall carbon-nanotube film by electrostatic field by X.F. Shang; J.J. Zhou; P. Zhao; Z.H. Li; S. Qu; Z.Q. Gu; Y.B. Xu; M. Wang (pp. 2005-2008).

In this work, we improved the field-emission properties of a screen-printed single-wall carbon-nanotube (SWCNT) film by applying a strong electrostatic field during the drying process after the printing. By applying the strong field, more tips of SWCNTs could emerge from the screen-printed film and turn somewhat toward the erecting direction because of the repulsive force among the SWCNTs. The field-emission properties of the film were thus improved obviously. The improved field emitters sample has low electron emission turn-on field ( E_to=1.22V/μm), low electron emission threshold field ( E_th=2.32V/μm) and high brightness with good uniformity and stability. The lowest operating field of the improved sample is below 1.0V/μm and its optimum current density exceeds 3.5mA/cm².

Keywords: Screen-printed method; SWCNTs; Arc-discharge; Field emitters; Electrostatic field

Preparation of thin Si:H films in an inductively coupled plasma reactor and analysis of their surface roughness by Wen-feng Zhao; Jun-fang Chen; Ran Meng; Yang Wang; Hui Wang; Chao-feng Guo; Yong-qi Xue (pp. 2009-2012).

An important concern in the deposition of Si:H films is to obtain smooth surfaces. Herein, we deposit the thin Si:H films using Ar-diluted SiH₄ as feedstock gas in an inductively coupled plasma reactor. And we carry a real-time monitor on the deposition process by using optical emission spectrum technology in the vicinity of substrate and diagnose the Ar plasma radial distribution by Langmuir probe. Surface detecting by AFM and surface profilometry in large scale shows that the thin Si:H films have small surface roughness. Distributions of both the ion density and the electron temperature are homogeneous at h=0.5cm. Based on these experimental results, it can be proposed inductively coupled plasma reactor is fit to deposit the thin film in large scale. Also, Ar can affect the reaction process and improve the thin Si:H films characteristics.

Keywords: ICP reactor; Thin Si:H film; Surface roughness

Photoluminescent behavior of heat-treated porous alumina films formed in malonic acid by I. Vrublevsky; A. Jagminas; S. Hemeltjen; W.A. Goedel (pp. 2013-2017).

In the present work IR spectroscopy, electron probe microanalysis (EPMA) and photoluminescence (PL) spectral measurements were applied to study the effect of treatment temperature ( T) on compositional and luminescent properties of malonic acid alumina films. Our studies have shown that the heat treatment of anodic alumina films at investigated temperatures from 100 up to 700°C changes their photoluminescence spectra considerably. An increase in T results in the PL intensity growth. When reaching its maximum at 600°C the luminescence intensity then decreases drastically with further T growth. The films heat-treated at 500 and 600°C demonstrate asymmetrical PL band with Gaussian peaks at 437 and 502nm. We proved that the malonic acid species incorporated into the alumina bulk during the film formation are responsible for photoluminescence band with its peak at 437nm.

Keywords: Photoluminescence; Anodic alumina; Malonic acid

Effect of frequency on the structure and cell response of Ca- and P-containing MAO films by Yingjun Wang; Lin Wang; Huade Zheng; Chang Du; ChengyunNing; Zhifeng Shi; Caixia Xu (pp. 2018-2024).

The Ca- and P-containing MAO films were prepared on titanium substrate at different frequencies (100–5000Hz) and were characterized by SEM, XRD, XPS and contact angle goniometer. For in vitro test, the rat bone marrow mesenchymal stem cells (rMSCs) were seeded on the films. The fluorescence microscopy and the PicoGreen assay were used to determine the cell initial adhesion and proliferation. It shows that the frequency of the MAO affected the crystallinity, composition, morphology and wetting ability of the oxidation film. At a high frequency, the crystallinity decreased, and the content of Ca and P increased. The structure formed at a high frequency – there were many smaller pores on the wall of the larger ones and many inner pores in the film – could improve the connectivity of the film. The wetting ability of the film was also improved by increasing the frequency. The mechanism of how the frequency of the MAO process could influence the oxidation film was discussed. It could be explained by the theory of electron avalanche and the phenomenon of secondary breakdown. In vitro test showed that the film formed at 5000Hz was more favorable for the initial cell attachment and proliferation.

Keywords: Micro-arc oxidation; Film; Titanium; rMSC; Amorphous calcium phosphate

Effects of annealing time on infrared emissivity of the Pt film grown on Ni alloy by Zhibin Huang; Wancheng Zhou; Xiufeng Tang (pp. 2025-2030).

Platinum films were sputter-deposited on polished nickel alloy substrates. The platinum thin films were applied to serve as low-emissivity layers to reflect thermal radiation. The platinum-coated samples were then heated in the air at 600°C to explore the effects of annealing time on the emissivity of platinum films. The results show that the grain size of the Pt films increased with the increasing annealing time while their dc electrical resistivity decreased. Besides, the IR emissivitiy of the films gradually decreased with the increasing annealing time. Especially, when the annealing time reached 150h, the average IR emissivity at the wavelength of 3–14μm was only about 0.1. Moreover, the chemical analysis indicated that the Pt films on Ni-based alloy exhibit a good resistance against oxidation at 600°C.

Keywords: PACS; 81.05.zx; 61.80.Ba; 68.60.−p; 66.30.NyLow-emissivity layer; Platinum film; Sputter-deposited; Annealing time

Effect of annealing on structural, optical and electrical properties of nanostructured Ge thin films by Abdul Faheem Khan; Mazhar Mehmood; Anwar M. Rana; Taj Muhammad (pp. 2031-2037).

Ge thin films with a thickness of about 110nm have been deposited by electron beam evaporation of 99.999% pure Ge powder and annealed in air at 100–500°C for 2h. Their optical, electrical and structural properties were studied as a function of annealing temperature. The films are amorphous below an annealing temperature of 400°C as confirmed by XRD, FESEM and AFM. The films annealed at 400 and 450°C exhibit X-ray diffraction pattern of Ge with cubic-F structure. The Raman spectrum of the as-deposited film exhibits peak at 298cm⁻¹, which is left-shifted as compared to that for bulk Ge (i.e. 302cm⁻¹), indicating nanostructure and quantum confinement in the as-deposited film. The Raman peak shifts further towards lower wavenumbers with annealing temperature. Optical band gap energy of amorphous Ge films changes from 1.1eV with a substantial increase to ∼1.35eV on crystallization at 400 and 450°C and with an abrupt rise to 4.14eV due to oxidation. The oxidation of Ge has been confirmed by FTIR analysis. The quantum confinement effects cause tailoring of optical band gap energy of Ge thin films making them better absorber of photons for their applications in photo-detectors and solar cells. XRD, FESEM and AFM suggest that the deposited Ge films are composed of nanoparticles in the range of 8–20nm. The initial surface RMS roughness measured with AFM is 9.56nm which rises to 12.25nm with the increase of annealing temperature in the amorphous phase, but reduces to 6.57nm due to orderedness of the atoms at the surface when crystallization takes place. Electrical resistivity measured as a function of annealing temperature is found to reduce from 460 to 240Ω-cm in the amorphous phase but drops suddenly to 250Ω-cm with crystallization at 450°C. The film shows a steep rise in resistivity to about 22.7KΩ-cm at 500°C due to oxidation. RMS roughness and resistivity show almost opposite trends with annealing in the amorphous phase.

Keywords: Nanostructured Ge; Quantum confinement; Raman spectroscopy; Band gap energy; Germanium oxide; Electrical resistivity

Surface structure of Langmuir–Blodgett films of lipophilic guanosine derivatives by Miha Devetak; Stefano Masiero; Silvia Pieraccini; Gian Piero Spada; Martin Čopič; Irena Drevenšek Olenik (pp. 2038-2043).

We studied surface organization of lipophilic guanosine derivatives with one, two and three alkanoyl tails in thin films on water surface and in Langmuir–Blodgett (LB) films transferred onto freshly cleaved mica substrate. The derivative with one alkanoyl group exhibits irreversible pressure–area isotherms and ribbon-like LB film structures. The derivatives with two and three side groups show reversible isotherms with similar critical surface pressures, while their LB film structures are quite different. The derivative with two tails forms films with flat terraces of micrometer size, while the derivative with three tails exhibits irregular thread-shaped assemblies. These observations demonstrate that molecular assembly of LB films of guanosine derivatives can be effectively manipulated by altering the number of attached lipophilic groups.

Keywords: Biosurfaces; Self-assembly; Guanosine; Langmuir–Blodgett films; Atomic force microscopy

Analysis of C₆₀⁺ and Cs⁺ sputtering ions for depth profiling gold/silicon and GaAs multilayer samples by time of flight secondary ion mass spectrometry by Robyn E. Goacher; Joseph A. Gardella Jr. (pp. 2044-2051).

Time of flight secondary ion mass spectrometry (ToF-SIMS) depth profiles of several inorganic layered samples using Cs⁺ and C₆₀⁺ primary sputtering ions of different energies are compared to evaluate sputter yield and depth resolution. A gold/silicon model system is employed to study interfaces between metals and semiconductors, and multilayers of AlGaAs, Al, and InAs in GaAs are analyzed to explore the ability of C₆₀⁺ to analyze semiconductor interfaces in GaAs. Roughness measurements are reported to differentiate between different factors affecting depth resolution. The best depth resolution from all samples analyzed is achieved using 1keV Cs⁺. However, C₆₀⁺ sputtering has advantages for analyzing conductor/insulator interfaces because of its high sputter yield, and for analyzing deeper heterolayers in GaAs due to lower sputter-induced roughness.

Keywords: C; ₆₀; cluster ions; Cs ions; ToF-SIMS; GaAs; Au; Si

Selective etching of InP in NaF solution by Zhankun Weng; Wendan Zhang; Cuiting Wu; Hongxing Cai; Changli Li; Zuobin Wang; Zhengxun Song; Aimin Liu (pp. 2052-2055).

The crossing porous structure of InP has been obtained by electrochemical etching in NaF solutions. The behavior of the periodic oscillation occurs at different potential ranges for the different concentrations of solutions, and it will disappear with the concentration of the solution decreased. The scanning electron microscope (SEM) image shows that the pores have two directions on the surface and are perpendicular to each other. The two directions are assigned to [011] and [01¯1], respectively. The SEM image of the cross-section also shows that the two directions are assigned to [111]B and [11¯1¯]B. Both are due to the selective etching of F⁻ ions. The crossing porous structure of InP is a very promising feature for the three-dimensional structure of III–V compound semiconductors for photonic band gap materials.

Keywords: Porosity; Semiconductors; Electrochemistry etching

Preparation and characterizations of amorphous nanostructured SiC thin films by low energy pulsed laser deposition by H. ElGazzar; E. Abdel-Rahman; H.G. Salem; F. Nassar (pp. 2056-2060).

Amorphous silicon carbide (SiC) thin films were deposited on silicon substrates by pulsed laser ablation at room temperature. Thicknesses and surface morphology of the thin films were characterized using optical profilers, atomic force and field emission scanning electron microscopy. Nanohardnes, modulus and scratch resistance properties were determined using XP nanoindenter. The results show that crack free, smooth and nanostructured thin films can be deposited using low laser energy densities.

Keywords: Pulsed laser deposition; Amorphous SiC thin films; Surface morphology; Nanoindentation

Superhydrophobic poly(vinylidene fluoride) film fabricated by alkali treatment enhancing chemical bath deposition by Zhenrong Zheng; Zhenya Gu; Ruiting Huo; Zhishan Luo (pp. 2061-2065).

Based on the lotus effect principle, the superhydrophobic poly(vinylidene fluoride) (PVDF) film was successfully prepared by the method of alkali treatment enhancing chemical bath deposition. The surface of PVDF film prepared in this work was constructed by many smooth and regular microreliefs. Oxygen-containing functional groups were introduced in PVDF film by treatment with aqueous NaOH solution. The nano-scale peaks on the top of the microreliefs were implemented by the reaction between dimethyldichlorosilane/methyltrichlorosilane solution and the oxygen-containing functional groups of PVDF film. The micro- and nano-scale structures, similar to the lotus leaf, was clearly observed on PVDF film surface by scanning electronic microscopy (SEM) and atomic force microscope (AFM). The water contact angle and sliding angle on the fabricated lotus-leaf-like PVDF film surface were 157° and 1°, respectively, exhibiting superhydrophobic property and self-cleaning property.

Keywords: Polyvinylidene fluoride; Chemical bath deposition; Superhydrophobic; Self-cleaning

Gold nanostructures on chemically reinforced PDMS microwell arrays by Hye Jin Nam; Duk-Young Jung; Yong-Kyun Park; Sungho Park (pp. 2066-2072).

This paper describes a facile strategy for fabricating arrays of two- and three-dimensional gold nanostructures using PDMS-infiltrated polystyrene (PS) colloidal crystals. PDMS molding of colloidal crystal, gold vapor deposition, and subsequent calcination of PS produced gold thin layers over hexagonal PDMS microwell arrays with hemispherical air-voids of approximately 140nm on glass substrates. Vapor deposition of perfluoroalkylsilane thin layers improved the thermal stability of the colloidal template over 100°C, providing a route to preparation of hollow architectures with gold thin layers supported by PDMS nanostructures. Surface modification of the PDMS using poly(allylamine hydrochloride) induced two-dimensional colloidal crystals of PS and PMMA spheres through electrostatic interactions. Particle aggregation of 13nm gold nanoparticles in the PDMS microwells demonstrated a surface plasmon resonance band red-shifted to 810nm, in comparison with that on the flat surface at 720nm.

Keywords: PACS; 68.60.Dv; 81.05.Qk; 81.07.Pr; 81.16.RfOrganic–inorganic hybrid; Thermal stability; Colloidal crystal; Self-assembly; Reinforced polymer; Surface modification

XPS study of PBO fiber surface modified by incorporation of hydroxyl polar groups in main chains by Tao Zhang; Dayong Hu; Junhong Jin; Shenglin Yang; Guang Li; Jianming Jiang (pp. 2073-2075).

Dihydroxy poly(p-phenylene benzobisoxazole) (DHPBO), a modified poly(p-phenylene benzoxazole) (PBO) polymer containing double hydroxyl groups in polymer chains, was synthesized by copolymerization of 4,6-diamino resorcinol dihydrochloride (DAR), purified terephthalic acid (TA) and 2,5-dihydroxyterephthalic acid (DHTA). DHPBO fibers were prepared by dry-jet wet-spinning method. The effects of hydroxyl polar groups on the surface elemental compositions of PBO fiber were investigated by X-ray photoelectron spectroscopy (XPS). The results show that the ratio of oxygen/carbon on the surface of DHPBO fibers is higher than that on the surface of PBO fibers, which indicates the content of polar groups on the surface of DHPBO fiber increase compared with PBO fiber.

Keywords: Poly(p-phenylene benzoxazole) fiber; Surface modification; Hydroxyl groups; XPS analysis

Morphological and optical properties of sol–gel derived 6SrO·6BaO·7Al₂O₃ thin films by P.M. Chavhan; Anubha Sharma; R.K. Sharma; N.K. Kaushik (pp. 2076-2080).

A novel 6SrO·6BaO·7Al₂O₃ (S6B6A7) thin film deposited onto soda lime float glass via sol–gel dip coating technique is reported. The morphological and compositional properties of the S6B6A7 thin films have been investigated using scanning electron microscopy (SEM), atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) revealing that the films were composed of S6B6A7 nanoparticles. The optical properties of the S6B6A7 films are affected by sol concentration, film thickness and annealing temperature as revealed by UV–vis transmittance. The transparency of S6B6A7 films improved on increasing annealing temperature up to 450°C in air. The S6B6A7 films prepared using 2, 5, and 8 (wt.%) sols and annealed at 450°C exhibit an average transmittance of over ∼91% in wide visible range.

Keywords: Barium strontium aluminium oxide; Sol–gel; Thin films; XPS; AFM; Optical properties

Composite SiO₂/TiO₂ and amine polymer/TiO₂ nanoparticles produced using plasma-enhanced chemical vapor deposition by Jeffrey C. Shearer; Mary J. Fisher; D. Hoogeland; Ellen R. Fisher (pp. 2081-2091).

Plasma-enhanced chemical vapor deposition was used to conformally coat commercial TiO₂ nanoparticles to create nanocomposite materials. Hexamethyldisiloxane (HMDSO)/O₂ plasmas were used to deposit SiO₂ or SiO_xC_yH_z films, depending on the oxidant concentration; and hexylamine (HexAm) plasmas were used to deposit amorphous amine-containing polymeric films on the TiO₂ nanoparticles. The composite materials were analyzed using Fourier-transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). These analyses reveal film composition on the nanoparticles was virtually identical to that deposited on flat substrates and that the films deposit a conformal coating on the nanoparticles. The performance of the nanocomposite materials was evaluated using UV–vis spectroscopy to determine the dispersion characteristics of both SiO_x and HexAm coated TiO₂ materials. Notably, the coated materials stay suspended longer in distilled water than the uncoated materials for all deposited films.

Keywords: Plasma deposition; Composite nanomaterials; Titanium dioxide; Surface modification; Nanoparticles

Experimental study of infrared nanosecond laser ablation of silicon: The multi-pulse enhancement effect by Ziyi Fu; Benxin Wu; Yibo Gao; Yun Zhou; Chengjiao Yu (pp. 2092-2096).

Experimental study has been performed on nanosecond (ns) laser ablation of silicon at 1064nm, through which a so-called “multi-pulse enhancement effect” has been revealed, which has been rarely reported in literature. The major features of this effect are: (1) for multi-pulse laser ablation at the same spatial location, the ablation efficiency increases as the pulse number increases and the pulse-to-pulse temporal distance decreases; (2) for multi-pulse ablation performed sequentially at a group of locations, the ablation quality and efficiency starting from the second location can be significantly enhanced if the distance between adjacent locations is sufficiently small. Further study is needed to confirm and understand the underlying physical mechanism for the multi-pulse enhancement effect, which can be utilized to significantly improve the quality and efficiency of laser silicon micromachining using the low-cost and low-energy-consumption infrared ns lasers. This may decrease the cost and energy consumption of many relevant areas, such as the solar cell industry.

Keywords: Keyword; Laser ablation of silicon

Synthesis and characterization of cadmium selenide nanostructures on porous aluminum oxide templates by high frequency alternating current electrolysis by P. Ram Sankar; Pragya Tiwari; Ravi Kumar; Tapas Ganguli; C. Mukherjee; A.K. Srivastava; S.M. Oak; Rajesh K. Pathak (pp. 2097-2103).

We have successfully deposited nanostructured cadmium selenide (CdSe) inside anodic aluminum oxide (AAO) templates from aqueous electrolyte containing cadmium sulfate, selenium oxide and mercuric chloride by using high frequency alternating current (19V_rms, 200Hz). Addition of mercury ions aids in the deposition of CdSe inside anodic oxide pores. Scanning and transmission electron microscopy studies of the deposit etched in phosphoric acid showed the presence of end standing nanostrips. Energy dispersive X-ray analysis of the deposit confirmed the presence of cadmium and selenium in the deposit. X-ray diffraction (XRD) studies of the deposit showed small but broad diffraction peaks consistent with the presence of hexagonal CdSe. Optical studies revealed blue shift in band gap energy due to quantum confinement.

Keywords: PACS; 81.16c; 82.45AaAnodic oxide template; High frequency alternating current; Cadmium selenide; End standing nanostrips; Optical studies; Band gap; Quantum confinement

Comparison of F-12 aramid fiber with domestic armid fiber III on surface feature by Shu-hui Zhang; Guo-qiang He; Guo-zheng Liang; Hong Cui; Wei Zhang; Bin Wang (pp. 2104-2109).

A comparison of F-12 aramid fiber with domestic armid fiber III (DAF III) on surface feature was carried out by scanning electron microscope (SEM), atomic force microscopy (AFM), elements analysis and X-ray Photoelectron Spectroscopy (XPS) analysis. It is found that the two aramid fibers are of “skin-core” structure and fibrillar structure. The microfibrils orient along the fiber axis and rather poorly bond in transverse direction. Many defects exist on the surface of two fibers. Carbon, hydrogen, nitrogen and oxygen are the major elements of two aramid fiber. The element content of the same aramid fiber from surface to interior is different. The surface carbon contents of F-12 aramid fiber and DAF III are increased by 10.75% and 9.95% than those in fiber interior respectively, the surface nitrogen content decreased by 9.72% and 27.02% respectively, and the surface oxygen content increased by 13.99% and 37.95% respectively.

Keywords: Aramid fiber; Surface; XPS

Electrochemical synthesis of Cu/ZnO nanocomposite films and their efficient field emission behaviour by Farid Jamali Sheini; Jai Singh; O.N. Srivasatva; Dilip S. Joag; Mahendra A. More (pp. 2110-2114).

The Cu/ZnO nanocomposite films have been synthesized by cathodic electrodeposition and characterized using X-ray diffractometer (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), photoluminescence (PL) and field emission microscope (FEM). The XRD pattern shows a set of well defined diffraction peaks, which could be indexed to the wurtzite hexagonal phase of ZnO. In addition, characteristic diffraction peaks corresponding to Cu and Zn are also observed. The SEM image shows formation of two-dimensional (2D) hexagonal sheets randomly distributed and aligned almost normal to the substrate. Uniformly distributed small clusters of Cu nanoparticles possessing average diameter of ∼25nm, as revealed from the TEM image, are seen to be present on these 2D ZnO sheets. The selected area electron diffraction (SAED) image confirms the nanocrystalline nature of the Cu particles. From the field emission studies, carried out at the base pressure of ∼1×10⁻⁸mbar, the turn-on field required for an emission current density of 0.1μA/cm² is found to be 1.56V/μm and emission current density of ∼100μA/cm² has been drawn at an applied field of 3.12V/μm. The Cu/ZnO nanocomposite film exhibits good emission current stability at the pre-set value of ∼10μA over a duration of 5h. The simplicity of the synthesis route coupled with the better emission properties propose the electrochemically synthesized Cu/ZnO nanocomposite film emitter as a promising electron source for high current density applications.

Keywords: Cu nanoparticles; ZnO; Electrodeposition; Fowler–Nordheim plot

Control on wetting properties of spin-deposited silica films by surface silylation method by A. Venkateswara Rao; Sanjay S. Latthe; Sunetra L. Dhere; Swapnali S. Pawar; Hiroaki Imai; V. Ganesan; Satish C. Gupta; Pratap B. Wagh (pp. 2115-2121).

Control on the wettability of solid materials by liquid is a classical and key issue in surface engineering. Optically transparent water-repellent silica films have been spin-deposited on glass substrates at room temperature (∼27°C). The wetting behavior of silica films was controlled by surface silylation method using dimethylchlorosilane (DMCS) as a silylating reagent. A coating sol was prepared by keeping the molar ratio of methyltrimethoxysilane (MTMS) precursor, methanol (MeOH) solvent, water (H₂O) constant at 1:8.8:2.64 respectively, with 4M NH₄OH as a catalyst throughout the experiments and the amount of DMCS in hexane was varied from 0 to 12vol.%. It was found that with an increase in vol.% of DMCS, the water contact angle values of the films increased from 78° to 136°. At 12vol.% of DMCS, the film shows static water contact angle as high as 136° and water sliding angle as low as 18°. The hydrophobic silica films retained their water repellency up to a temperature 295°C and above this temperature the films show superhydrophilic behavior. These results are compared with our earlier research work done on silylation of silica surface using hexamethyldisilazane (HMDZ) and trimethylchlorosilane (TMCS). The hydrophobic silica films were characterized by taking into consideration the Fourier transform infrared (FT-IR) spectroscopy, thermo gravimetric-differential thermal (TG-DT) analyses, scanning electron microscopy (SEM), atomic force microscopy (AFM), % of optical transmission, thermal and chemical aging tests, humidity tests, static and dynamic water contact angle measurements.

Keywords: Sol–gel process; Hydrophobic; Wetting; Transparent; Humidity; Coatings

Facile fabrication of a lotus-effect composite coating via wrapping silica with polyurethane by Changhong Su (pp. 2122-2127).

A lotus-effect coating was fabricated by wrapping micro-silica and nano-silica with polyurethane (PU) and subsequent spraying. The coating shows the similar self-cleaning property as lotus leaves: the contact angle is as large as 168° and the sliding angle is as low as 0.5°. Surface morphology of the coating was studied with scanning electron microscopy and atomic force microscopy. The composite coating shows the similar structure as lotus leaves.

Keywords: Lotus-effect; Coating; Contact angle; Sliding angle; Dual-size

Effect of microstructure on the nanomechanical properties of Zn1−_xCd_xSe alloys by Hua-Chiang Wen; Chu-Shou Yang; Wu-Ching Chou (pp. 2128-2131).

We present a study of the nanoindentation behavior of Zn1−_xCd_xSe epilayers grown using molecular beam epitaxy; the surface roughness, microstructure, and crystallinity were analyzed using atomic force microscopy, cross-sectional transmission electron microscopy, and X-ray diffraction; the hardness H and elastic modulus E were studied using nanoindentation techniques. We found that these highly crystalline materials possessed no stacking faults or twins in their microstructures. We observed a very marked increase in the value of H and a significant decrease in the value of E upon increasing the concentration of Cd, presumably because of an increase in the stiffness of the CdSe bond relative to that of the ZnSe bond. We observed a corresponding shrinkage of the contact-induced damage area for those films having a small grain size and a higher value of H. It appears that resistance against contact-induced damage requires a higher Cd concentration.

Keywords: PACS; 61.10.Nz; 62.20.−x; 68.37.−dNanoindentation; ZnCdSe; XTEM; Hardness

Role of Cl⁻ ions in photooxidation of propylene on TiO₂ surface by Jianhui Guo; Liqun Mao; Jiwei Zhang; Caixia Feng (pp. 2132-2137).

The effect of Cl⁻ ions on photooxidation of propylene on TiO₂ semiconductor was investigated. Cl⁻/TiO₂ catalysts were prepared by annealing Degussa P25 TiO₂ in the gas flow of N₂ and Cl₂ under 100–400°C. The photocatalytic oxidation of propylene was carried out in a continuous flow system, with the chromatograph to analyze the products on line. The experimental results showed that the activity of Cl⁻/TiO₂ catalysts increased as heat-treated temperature decreased. The activity of the sample heat-treated at 100°C was about two times higher than that of pure TiO₂. Moreover, as to TiO₂, the main product of the propylene photocatalytic oxidation was CO₂, but with Cl⁻/TiO₂ catalysts, not only CO₂ but also trace CO was determined. The adsorbed species on TiO₂ surface before and after reaction were analyzed by X-ray photoelectron spectroscopy (XPS) and thermogravimetric/differential thermal analyses (TG-DTA) coupled to a mass spectrometer (MS). XPS analysis showed that there was Cl⁻ absorbed on the Cl⁻/TiO₂ surface, and the absorption amount of Cl⁻ decreased after the photooxidation reaction of propylene. TG-DTA-MS analysis confirmed chlorine absorbed on the surface of TiO₂ in the form of Cl⁻ ion. These results illuminated that absorbed Cl⁻ on the surface of TiO₂ formed a weak physical absorption on TiO₂ at low temperature, and subsequently participated in the photooxidation of propylene, finally removed from TiO₂ surface.

Keywords: TiO; ₂; photocatalyst; Propylene; Photooxidation; Absorbed chlorine

Structural and optical properties of ZnO nanorods grown on Mg_xZn1−_xO buffer layers by Liang-Wen Ji; Chih-Ming Lin; Te-Hua Fang; Tung-Te Chu; Huilin Jiang; Wei-Shun Shi; Cheng-Zhi Wu; Tian-Long Chang; Teen-Hang Meen; Jingchang Zhong (pp. 2138-2142).

ZnO nanorod arrays were synthesized by chemical-liquid deposition techniques on Mg_xZn1−_xO ( x=0, 0.07 and 0.15) buffer layers. It is found that varying the Mg concentration could control the diameter, vertical alignment, crystallization, and density of the ZnO nanorods. The X-ray diffraction (XRD), transmission electron microscopy (TEM), and selected area electron diffraction (SAED) data show the ZnO nanorods prefer to grow in the (002) c-axis direction better with a larger Mg concentration. The photoluminescence (PL) spectra of ZnO nanorods exhibit that the ultraviolet (UV) emission becomes stronger and the defect emission becomes weaker by increasing the Mg concentration in Mg_xZn1−_xO buffer layers.

Keywords: PACS; 81.07.−b; 68.65.−k; 78.67.−n; 71.55.Gs; 81.15.LmMg; _x; Zn; 1−; _x; O; Sol–gel; ZnO nanorods; Chemical-liquid deposition; Photoluminescence

Comparison of implantation and diffusion behavior of Ti, Sb and N in ion-implanted single crystal and polycrystalline ZnO: A SIMS study by J. Lee; J. Metson; P.J. Evans; U. Pal; D. Bhattacharyya (pp. 2143-2146).

Implantation and diffusion behavior of Sb, Ti and N in ZnO single crystal and sputter deposited thin films were studied through secondary ion mass spectrometric studies on ion-implanted and thermally annealed samples. Sb was implanted and Ti and N were co-implanted into ZnO single crystals and polycrystalline thin films on Si substrates at room temperature. The implanted samples were then annealed at 800°C. Depth profiles of implant distributions before and after annealing were examined by Secondary Ion Mass Spectrometry (SIMS). As expected, implant range is sensitive to the mass of the dopants; and the dopant distribution is broadened as implanted elements migrate deeper into the film on thermal annealing. While diffusion of N in the ZnO thin film is not significant, Ti tends to diffuse deeper into the sample during annealing. For Ti and N co-implanted single crystal, annealing induced diffusion causes more redistribution of the lighter N than Ti. In general, implanted dopants diffuse more easily in thin films compared to the single crystal due to the presence of grain boundaries in the latter.

Keywords: Ion-implantation; SIMS; Dopant diffusion; ZnO

Functionality of novel black silicon based nanostructured surfaces studied by TOF SIMS by Ivan Talian; Monika Aranyosiova; Andrej Oriňák; Dušan Velič; Daniel Haško; Dušan Kaniansky; Renáta Oriňáková; Jörg Hübner (pp. 2147-2154).

A functionality of the novel black silicon based nanostructured surfaces (BS 2) with different metal surface modifications was tested by time-of-flight secondary ion mass spectrometry (TOF SIMS). Mainly two surface functions were studied: analytical signal enhancement and analyte pre-ionization effect in SIMS due to nanostructure type and the assistance of the noble metal surface coating (Ag or Au) for secondary ion formation. As a testing analyte a Rhodamine 6G was applied. Bi⁺ has been used as SIMS primary ions. It was found out that SIMS signal enhancement of the analyte significantly depends on Ag layer thickness and measured ion mode (negative, positive). The best SIMS signal enhancement was obtained at BS2 surface coated with 400nm of Ag layer. SIMS fragmentation schemes were developed for a model analyte deposited onto a silver and gold surface. Significant differences in pre-ionization effects can play an important role in the SIMS analysis due to identification and spectra interpretation.

Keywords: Nanosurfaces; TOF SIMS; Secondary ion yield enhancement

Organic and inorganic discrimination of ballpoint pen inks by ToF-SIMS and multivariate statistics by John A. Denman; William M. Skinner; K. Paul Kirkbride; Ivan M. Kempson (pp. 2155-2163).

Surface analysis by ToF-SIMS analysis of ballpoint pen ink markings was performed for discrimination. ToF-SIMS provided non-destructive analysis of ink's organic and inorganic components directly off paper with no interference from the paper substrate. Organic and inorganic information were collected simultaneously and processed with PCA, discriminating 41 out of 45 pairs (91%) of pens analysed. Minimal sample preparation and analysis time, the simultaneous acquisition of organics and metals, and ability to analyse trace amounts gives this technique advantages over others currently utilised in the forensic field. Simultaneous acquisition of organics and inorganics has not been presented before for the characterisation of these materials. It was indicated that pens from the same manufacturer, but discrete batches, can be significantly different.

Keywords: Document analysis; Trace analysis; Mass spectrometry; Ink markings; Principal component analysis; Surface analysis

Surface texturing of polytetrafluoroethylene by hot embossing by D. Jucius; A. Guobienė; V. Grigaliūnas (pp. 2164-2169).

In this study, hot embossing by reusable Ni mold with features in the form of rectangular diffraction gratings of 4μm period was successfully employed for surface texturing of polytetrafluoroethylene (PTFE) film above the glass transition temperature of PTFE amorphous phase with the aim to enhance surface hydrophobicity. Imprint pressure was set to 0.5MPa and it was at least tenfold lower than reported by other authors using cold stamping. Embossed gratings were clearly seen on the surface of all imprinted samples even after the annealing at 140°C and aging for 1 month at room temperature. The best results were achieved when imprint temperature was 150°C. Measurements of the water contact angle on imprinted PTFE surfaces have showed that increase of the average contact angle for the current test setup was 8°. Using imprint stamp with the more favorable features may lead to somewhat higher hydrophobicity.

Keywords: Polytetrafluoroethylene; Hot embossing; Hydrophobicity; Contact angle

Understanding the solar photo-catalytic activity of TiO₂–ITO nanocomposite deposited on low cost substrates by H. Chorfi; G. Zayani; M. Saadoun; L. Bousselmi; B. Bessaïs (pp. 2170-2175).

In this work, we report on the photo-catalytic properties of TiO₂–ITO nanocomposite deposited on low cost conventional clay ceramic substrates. The nanocomposite was formed by spraying a solution prepared from the P25 TiO₂ powder (Degussa) mixed with an organometallic paste of a dissolved combination of indium and tin. A TiO₂–ITO powder-like nanocomposite was prepared for X-ray diffraction (XRD) and transmission electron microscopy (TEM) characterization. The mean particle size of the TiO₂–ITO nanocomposite was found to be larger than that of pure TiO₂. The optical features of TiO₂–ITO-based layers (deposited on glass substrates) were investigated using UV–vis spectroscopy. The TiO₂–ITO nanocomposite deposited layers were found to have higher light absorption than the P25 TiO₂ powder. The photo-catalytic properties of the TiO₂–ITO nanocomposite (deposited on low cost clay ceramic substrates) were tested under solar irradiation using a well-known polluting dye. It was shown that the TiO₂–ITO nanocomposite exhibits higher degradation rates towards the pollutant dye than the P25 TiO₂ powder. The optical band gap of the TiO₂–ITO nanocomposite (2.79eV) was found to be lower than that of pure TiO₂ (3.1eV), while ITO (indium tin oxide) has a band gap of about 4.2eV. ITO was found to be entirely transparent to sun light, while it exhibits a slight photo-catalytic activity, signifying the possible existence of an indirect photo-catalysis phenomenon (sensitized semiconductor photocalysis) and potential degradation (oxidation) of the pollutant through electron transfer from the dye to conduction band of the semiconductor. All photo-catalytic activity results were discussed in light of the optical band gap of the various compounds.

Keywords: PACS; 61.10.Nz; 61.43.Gt; 61.46.Df; 68.37.Lp; 78.67.Bf; 81.16.Hc; 82.50.Hp; 92.40.KcTiO; ₂; ITO; Nanocomposite; Solar photo-catalysis; Water treatment

Hydrogen peroxide treatment on Ti–6Al–4V alloy: A promising surface modification technique for orthopaedic application by M. Karthega; N. Rajendran (pp. 2176-2183).

Ti–6Al–4V alloy was treated with various concentrations (5wt.%, 15wt.% and 25wt.%) of hydrogen peroxide (H₂O₂) and then heat treated to produce an anatase titania layer. The surface modified substrates were immersed in simulated body fluid (SBF) solution for the growth of an apatite layer on the surface and the formed apatite layer was characterized using various surface characterization techniques. The results revealed that titania layer with anatase nature was observed for all H₂O₂ treated Ti–6Al–4V alloy, irrespective of the H₂O₂ concentrations. Ti–6Al–4V alloy treated with 15wt.% and 25wt.% of H₂O₂ induced apatite formation, however 5wt.% of H₂O₂ treated Ti–6Al–4V failed to form apatite layer on the surface. The electrochemical behaviour of H₂O₂ treated specimens in SBF solution was studied using potentiodynamic polarization and electrochemical impedance spectroscopy. Ti–6Al–4V alloy treated with 25wt.% of H₂O₂ solution exhibited low current density and high charge transfer resistance values compared to specimens treated with other concentrations of H₂O₂ and untreated Ti–6Al–4V alloy.

Keywords: Surface modification; Ti–6Al–4V alloy; Hydrogen peroxide; Hydroxyapatite; Corrosion

Field emission characteristics of carbon nanotubes post-treated with high-density Ar plasma by Wen-Pin Wang; Hua-Chiang Wen; Sheng-Rui Jian; Huy-Zu Cheng; Jason Shian-Ching Jang; Jenh-Yih Juang; Huang-Chung Cheng; Chang-Pin Chou (pp. 2184-2188).

The field emission characteristics of carbon nanotubes (CNTs) grown by thermal chemical vapor deposition (CVD) and subsequently surface treated by high-density Ar plasma in an inductively coupled plasma reactive ion etching (ICP-RIE) with the various plasma powers were measured. Results indicate that, after treated by Ar plasma with power between 250 and 500W, the emission current density of the CNTs is enhanced by nearly two orders of magnitude (increased from 0.65 to 48mA/cm²) as compared to that of the as-grown ones. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were employed to investigate the structural features relevant to the modified field emission properties of CNTs. The SEM images of CNTs subjected to a 500W Ar plasma treatment exhibit obvious damages to the CNTs. Nevertheless, the turn-on fields decreased from 3.6 to 2.2V/μm, indicating a remarkable field emission enhancement. Our results further suggest that the primary effect of Ar plasma treatment might be to modify the geometrical structures of the local emission region in CNTs. In any case, the Ar plasma treatment appears to be an efficient method to enhance the site density for electron emission and, hence markedly improving the electric characteristics of the CNTs.

Keywords: Multi-walled carbon nanotube; Scanning electron microscopy; Field emission property; Transmission electron microscopy

Influence of radiofrequency power on compositional, structural and optical properties of amorphous silicon carbonitride films by Yinqiao Peng; Jicheng Zhou; Zhichao Zhang; Baoxing Zhao; Xiaochao Tan (pp. 2189-2192).

The silicon carbonitride (SiCN) films were deposited on n-type Si (100) and glass substrates by the radiofrequency (RF) reactive magnetron sputtering of polycrystalline silicon target under mixed reactive gases of acetylene and nitrogen. The films have been characterized by energy dispersive spectrometer (EDS), atomic force microscope (AFM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and ultraviolet–visible spectrophotometer (UVS). The influence of RF power on the compositional, morphological, structural and optical properties of the SiCN films was investigated. The SiCN films deposited at room temperature are amorphous, and the C, Si and O compositions except N in the films are sensitive to the RF power. The surface roughness and optical band gap decrease as the RF power increases. The main bonds in the SiCN films are C–N, N–H_n, C–H_n, C–C, CN, Si–H and Si–C, and the intensities of the CN, Si–H and C–H_n bonds increase with increment of the RF power. The mechanisms of the influence of RF power on the characteristics of the films are discussed in detail.

Keywords: PACS; 71.20.Nr; 73.61.Jc; 78.30.−j; 81.15.CAmorphous SiCN films; Magnetron sputtering; RF power; Composition; Structure; Optical band gap

Characterization of cold-sprayed nanostructured Fe-based alloy by Wen-Ya Li; Chang-Jiu Li (pp. 2193-2198).

The ball-milled Fe–Si alloy was used as feedstock for deposition of nanocrystalline Fe–Si by cold spraying process. The microstructure of the as-sprayed nanostructured Fe–Si was characterized by using optical microscopy, scanning electron microscopy and transmission electron microscopy. The grain sizes of the feedstock and as-sprayed deposit were estimated based on X-ray diffraction analysis. The microhardness and coercivity of the deposited Fe–Si alloy were characterized. The results showed that the as-sprayed deposit presented a dense microstructure. The mean grain size of the as-deposited Fe–Si was several tens nanometers and comparable to that of the corresponding milled feedstock. The temperature of driving gas presented little effect on the microstructure of cold-sprayed nanostructured Fe–Si deposit. The mechanical alloying induced oxygen contents up to 8wt% in the feedstocks and subsequent deposits. The microhardness of the deposit reached about 400Hv. The deposit achieved a high coercivity up to 190kA/m indicating the potential possibility for applications to recording materials.

Keywords: Cold spraying; Mechanical milling; Fe–Si coating; Nanostructure; Coercivity; Microhardness

Substrate effect on electronic sputtering yield in polycrystalline fluoride (LiF, CaF₂ and BaF₂) thin films by Manvendra Kumar; Parasmani Rajput; S.A. Khan; D.K. Avasthi; A.C. Pandey (pp. 2199-2204).

Influence of substrate on electronic sputtering of fluoride (LiF, CaF₂ and BaF₂) thin films, 10 and 100nm thin, under dense electronic excitation of 120MeV Ag²⁵⁺ ions irradiation is investigated. The sputtering yield of the films deposited on insulating (glass) and semiconducting (Si) substrates are determined by elastic recoil detection analysis technique. Results revealed that sputtering yield is higher, up to 7.4×10⁶atoms/ion for LiF film on glass substrate, than that is reported for bulk materials/crystals (∼10⁴atoms/ion), while a lower value of the yield (2.3×10⁶atoms/ion) is observed for film deposited on Si substrate. The increase in the yield for thin films as compared to bulk material is a combined effect of the insulator substrate used for deposition and reduced film dimension. The results are explained in the framework of thermal spike model along with substrate and size effects in thin films. It is also observed that the material with higher band gap showed higher sputtering yield.

Keywords: PACS; 61.80Jh; 68.49.Sf; 72.80.SkSwift heavy ions; Sputtering; Thin films; ERDA; Fluoride

Gold nano-wires and nano-layers at laser-induced nano-ripples on PET by J. Siegel; P. Slepička; J. Heitz; Z. Kolská; P. Sajdl; V. Švorčík (pp. 2205-2209).

Gold nano-layers were deposited onto laser irradiated polyethyleneterephthalate (PET) surfaces. For irradiation, we used the linearly polarized light of a pulsed 248nm KrF and 157nm F₂ laser, respectively. In a certain range of irradiation parameters, the irradiation resulted in the formation of coherent ripples patterns with a lateral periodicity in the order of the wavelength of the laser light and with a corrugation height of several 10nm. The deposited layers were then prepared by sputtering. The layers were analyzed by atomic force microscopy (AFM), focused ion beam (FIB) cuts, scanning electron microscopy (SEM), and angular resolved X-ray induced photoelectron spectroscopy (ARXPS). Gold sputtering on KrF laser irradiated PET led to the formation of separated “nano-wires” at the ridges of the nano-patterns and not to a continuous metal layer, as we obtained in case of gold sputtering onto F₂ irradiated PET. The results of the XPS analysis indicated, that the KrF irradiation caused degradation on the ridge of the ripples, whereas no noticeable degradation occurred for F₂ laser treatment. We attribute the different growth mechanisms of the deposited gold layers mainly to the difference in surface chemical composition of laser irradiated PET with the two different lasers employed.

Keywords: KrF and F; ₂; laser; Polyethyleneterephthalate; Ripples; Au sputtering; Nano-wires; Nano-layers

Comparative study of NH₄OH and HCl etching behaviours on AlGaN surfaces by Rakesh Sohal; Piotr Dudek; Oliver Hilt (pp. 2210-2214).

A controlled AlGaN surface preparation method avails to improve the performance of GaN-based HEMT devices. A comparative investigation of chemical treatments by (1:10) NH₄OH:H₂O and (1:10) HCl:H₂O solutions for AlGaN surface preparation by X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) is reported. The XPS data clearly reveal that the native oxide on AlGaN was composed of Al₂O₃, Ga₂O₃ and NO compounds. These compounds were etched off partially or completely by both the chemical treatments, namely NH₄OH or HCl solutions, independently. The HCl treatment etches out Al₂O₃ completely from native oxide unlike NH₄OH treatment. The HCl treatment results in larger amount of carbon segregation on AlGaN surfaces, however it removes all oxides’ compounds faster than NH₄OH treatment. The AFM results reveal the improvement of surface morphology by both the chemical treatments leading to the surface roughness RMS values of 0.24nm and 0.21nm for NH₄OH and HCl treated AlGaN layers, respectively.

Keywords: HEMT; AlGaN/GaN heterostructure; Wet etching; NH; ₄; OH; HCl; X-ray photoelectron spectroscopy; Atomic force microscopy

Additive-free controllable fabrication of bismuth vanadates and their photocatalytic activity toward dye degradation by Yingna Guo; Xia Yang; Fengyan Ma; Kexin Li; Lei Xu; Xing Yuan; Yihang Guo (pp. 2215-2222).

Bismuth vanadates (BiVO₄) with various crystal structures (tetragonal scheelite, monoclinic scheelite, and tetragonal zircon) and morphologies (sphere-, nanosheet-, dendrite-, and flower-like) were controllably fabricated by using a mild additive-free hydrothermal treatment process under the different preparation conditions. The crystal structures, morphologies, and photophysical properties of the products were well-characterized. Subsequently, their UV- as well as visible-light photocatalytic performance was evaluated via dyes rhodamine B (RB) and methylene blue (MB) degradation. Special attention was paid to evaluate the correlation of the reactivity with crystal structure, morphology, and electronic structure of as-prepared BiVO₄ samples.

Keywords: Bismuth vanadate; Hydrothermal treatment; Visible-light photocatalysis; Dye degradation

Effects of nitrogen doping on the properties of Ge₁₅Sb₈₅ phase-change thin film by Yin Zhang; Jie Feng; Bingchu Cai (pp. 2223-2227).

The effects of nitrogen doping on the chemical bonding state, microstructure, electrical property and thermal stability of Ge₁₅Sb₈₅ film were investigated in detail. The doped N atoms tend to bond with Ge to form Ge₃N₄, as proved by X-ray photoelectron spectroscopy analyses. X-ray diffraction patterns showed that both undoped and N-doped Ge₁₅Sb₈₅ films crystallize into a hexagonal phase very similar to Sb. The thickness reduction upon crystallization for undoped and N-doped Ge₁₅Sb₈₅ films is less than 5%. The crystalline resistivity, crystallization temperature, and thermal stability of amorphous state all increase after nitrogen doping, while the grain size decreases. By adding 7.0at.% N into the Ge₁₅Sb₈₅ film, the crystalline resistivity increases twelve times and the crystallization temperature increases about 50°C. The maximum temperature for 10-year retention of amorphous Ge₁₅Sb₈₅ film is estimated to be 147°C and that of N-doped films is even higher, which will promise better data retention of phase-change random access memory especially in the high-temperature application.

Keywords: Ge; ₁₅; Sb; ₈₅; Nitrogen doping; Chemical bonding state; Crystalline resistivity; Thermal stability; Phase-change random access memory

NaCl islands decorated with 2D or 3D 3,4,9,10-perylene-tetracarboxylic-dianhydride nanostructures by Xiaonan Sun; Fabien Silly (pp. 2228-2231).

The formation of PTCDA (3,4,9,10-perylene-tetracarboxylic-dianhydride) nanostrutures on Au(111)-(22×3) covered with NaCl islands has been studied using scanning tunneling microscopy (STM). Atomically resolved STM images show that NaCl grows as (100)-terminated layers on Au(111)-(22×3). Local atomic hexagonal packing has also been observed in the NaCl(100) layer. At submonolayer NaCl coverage, PTCDA forms two-dimensional islands on the Au(111) surface and nucleate preferentially at the NaCl island step edges. When the Au surface is fully covered with NaCl layers, PTCDA molecules form three-dimensional molecular clusters decorating the step edges of NaCl layers.

Keywords: PACS; 68.37.Ef; 81.16.Rf; 68.55.JkScanning tunneling microscopy; Nanoscale pattern formation; Structure and morphology; Crystalline orientation and texture; Molecular domain

Current transport through InP/InSb heterojunction: Effect of lattice mismatch by Ravikant Sharma; Biplab Paul; P. Banerji (pp. 2232-2235).

Semiconductor heterojunctions of MOCVD grown InP were fabricated on n-InSb to study some features of a current transport in strained heterojunctions. The MOCVD grown undoped InP samples on InP substrates were characterized by XRD and Hall measurements whereas the InP/InSb heterojunction was characterized by XRD, TEM and I– V measurements in the temperature range 160–305K. On increasing the voltage, first the current through the heterojunction is found to increase linearly and then it gets saturate due to surface states saturation. When the misfit dislocation density was increased, overlapping in the depletion regions gave rise to a barrier to the current flow there by saturating the current.

Keywords: MOCVD; Lattice mismatch; Lattice-strain; Dislocation; Current–voltage

Anisotropic defect reduction in non-polar a-plane GaN grown by hydride vapor phase epitaxy on maskless patterned templates by Lubing Zhao; Tongjun Yu; Jiejun Wu; Tao Dai; Zhijian Yang; Guoyi Zhang (pp. 2236-2240).

Several non-polar a-plane GaN films had been grown by hydride vapor phase epitaxy (HVPE) on different designed metal organic chemical deposition (MOCVD) GaN templates, which exhibited various ridge-like sidewall facets surface morphologies. The templates induced a lateral growth at the early stage of the HVPE growth, and resulted in a kind of maskless epitaxy lateral overgrown (ELO) process. It is found that the dislocation reduced differently along [1000] and [11¯00] directions in these HVPE a-plane GaN layers. In [0001] direction, the dislocation reduction resulted from the optimal surface roughness value of the template. In [11¯00] direction, the inclined facet might be a main factor for the dislocation reduction in HVPE-GaN films. The maskless ELO process had a significant influence on decreasing the dislocation density.

Keywords: PACS; 71.55.Eq; 81.15.Kk; 61.72.LkDefects; Morphology; HVPE; GaN

Novel Pd-Cu/bacterial cellulose nanofibers: Preparation and excellent performance in catalytic denitrification by Dongping Sun; Jiazhi Yang; Jun Li; Junwei Yu; Xiaofeng Xu; Xuejie Yang (pp. 2241-2244).

In this work, we describe a novel facile method to prepare long one-dimensional hybrid nanofibers by using hydrated bacterial cellulose nanofibers (BCF) as template. Palladium-copper nanoparticles were prepared in BCF by immersing BCF in a mixture solution of PdCl₂ and CuCl₂ in water and followed reduction of absorbed metallic ion inside of BCF to the metallic Pd-Cu nanoparticles using potassium borohydride. The bare BCF and the composites were characterized by a range of analytical techniques including scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). The results reveal that the Pd-Cu nanoparticles were homogeneously precipitated on the BCF surface. The Pd-Cu/BCF was used as a catalyst for water denitrification, which showed that it has high catalytic activity.

Keywords: Bacterial cellulose; Nanofiber; Pd-Cu catalyst; Nitrate removal

Characterization of Y₂O₃ gate dielectric on n-GaAs substrates by P.S. Das; G.K. Dalapati; D.Z. Chi; A. Biswas; C.K. Maiti (pp. 2245-2251).

Physical and electrical properties of sputtered deposited Y₂O₃ films on NH₄OH treated n-GaAs substrate are investigated. The as-deposited films and interfacial layer formation have been analyzed by using X-ray photoelectron spectroscopy (XPS) and secondary ion mass spectroscopy (SIMS). It is found that directly deposited Y₂O₃ on n-GaAs exhibits excellent electrical properties with low frequency dispersion (<5%), hysteresis voltage (0.24V), and interface trap density (3×10¹²eV⁻¹cm⁻²). The results show that the deposition of Y₂O₃ on n-GaAs can be an effective way to improve the interface quality by the suppression on native oxides formation, especially arsenic oxide which causes Fermi level pinning at high- k/GaAs interface. The Al/Y₂O₃/n-GaAs stack with an equivalent oxide thickness (EOT) of 2.1nm shows a leakage current density of 3.6×10⁻⁶Acm⁻² at a V_FB of 1V. While the low-field leakage current conduction mechanism has been found to be dominated by the Schottky emission, Poole–Frenkel emission takes over at high electric fields. The energy band alignment of Y₂O₃ films on n-GaAs substrate is extracted from detailed XPS measurements. The valence and conduction band offsets at Y₂O₃/n-GaAs interfaces are found to be 2.14 and 2.21eV, respectively.

Keywords: GaAs; Y; ₂; O; ₃; Interface properties; Energy band alignment

Characteristics of electron beam evaporated nanocrystalline SnO₂ thin films annealed in air by Abdul Faheem Khan; Mazhar Mehmood; Muhammad Aslam; Muhammad Ashraf (pp. 2252-2258).

Tin oxide (SnO₂) thin films (about 200nm thick) have been deposited by electron beam evaporation followed by annealing in air at 350–550°C for two hours. Optical, electrical and structural properties were studied as a function of annealing temperature. The as-deposited film is amorphous, while all other annealed films are crystalline (having tetragonal structure). XRD suggest that the films are composed of nanoparticles of 5–10nm. Raman analysis and optical measurements suggest quantum confinement effects that are enhanced with annealing temperature. For instance, Raman peaks of the as-deposited films are blue-shifted as compared to those for bulk SnO₂. Blue shift becomes more pronounced with annealing temperature. Optical band gap energy of amorphous SnO₂ film is 3.61eV, which increases to about 4.22eV after crystallization. Two orders of magnitude decrease in resistivity is observed after annealing at 350–400°C due to structural ordering and crystallization. The resistivity, however, increases slightly with annealing temperature above 400°C, possibly due to improvement in stoichiometry and associated decrease in charge carrier density.

Keywords: Nanocrystalline SnO; ₂; thin films; Quantum confinement; Raman spectroscopy; Band gap energy; FTIR spectroscopy; Electrical resistivity

Effect of Mn doping on the nanostructure and optical properties of ZnO films synthesized by magnetron sputtering by Z.F. Wu; X.M. Wu; L.J. Zhuge; B. Hong; X.M. Yang; T. Yu; J.J. He; Q. Chen (pp. 2259-2262).

We investigated the microstructure and optical properties of Zn1−_xMn_xO films synthesized by the magnetron sputtering technique. Structural analyses suggest that Mn occupied the Zn sites successfully and did not change the wurtzite structure of ZnO. In addition, nanoscale columnar grain arrays were found in the Mn-doped ZnO films. The experimental results indicate that moderate Mn doping could enhance the photoluminescence emission of ZnO. The possible origin of the emissions from our samples was also explored.

Keywords: ZnO; Mn doping; Optical properties; Nanostructure

Influence of substrate hardness transition on built-up of nanostructured WC–12Co by cold spraying by Pei-Hu Gao; Chang-Jiu Li; Guan-Jun Yang; Yi-Gong Li; Cheng-Xin Li (pp. 2263-2268).

The ability of cold spray process to retain the feedstock microstructure into coating makes it possible to deposit nanostructured WC–Co coatings. In the present study, the deposition behavior of nanostructured WC–12Co coating was examined through the surface morphology and cross-sectional structure of the deposited single WC–12Co particle impacting on the substrates with different hardness using a nanostructured WC–12Co powder. Substrates included stainless steel, nickel-based self-fluxing alloy coatings with different hardness. It was observed from the top surface and cross-section of individual WC–12Co particles that the penetration leading to particle deposition depends on substrate hardness. When the substrate surface is covered by WC–12Co particles, the hardness of the newly formed substrate, i.e. the coating, increases greatly. The significant increase of the surface hardness leads to the rebounding off of impacting particles and erosion of the deposited particles, which prohibits effective built-up of coating. However, it was found that with spray jet fixed, a deposit with a thickness up to over 700μm can be built-up. A model involving in substrate hardness transition during deposition is proposed to explain such phenomenon, which can be employed to optimize the conditions to build up a uniform nanostructured WC–12Co coating.

Keywords: Deposition behavior; Nanostructure; WC–12Co; Cold spraying

Shape-controlled synthesis of Cu₂O microcrystals by electrochemical method by Wenyan Zhao; Wuyou Fu; Haibin Yang; Chuanjin Tian; Ruixia Ge; Chunjie Wang; Zhanlian Liu; Yanyan Zhang; Minghui Li; Yixing Li (pp. 2269-2275).

Cuprous oxide (Cu₂O) microcrystals have been successfully synthesized via a facile electrochemical method in alkaline NaCl solution with copper plate and graphite slice as electrodes and Na₂Cr₂O₇ as additive. The as-synthesized products have been systematically studied by X-ray powder diffraction (XRD), field emission scanning electron microscope (FESEM), transmission electron microscope (TEM), selected area electron diffraction (SAED) and ultraviolet–visible spectrum (UV–vis). The results indicate that the pH value, temperature and potential play important roles in the morphology control besides the crystal habits of Cu₂O. The possible mechanism has been explored in the article.

Keywords: Cuprous oxide; Shape-controlled; Icositetrahedron microcrystal; Optical property; Electrochemical growth; Semiconducting materials

UV light induced surface modification of HDPE films with bioactive compounds by Vesna Daniloska; Jadranka Blazevska-Gilev; Vesna Dimova; Radek Fajgar; Radmila Tomovska (pp. 2276-2283).

The development of different techniques for surface modification of polymers becomes popular in a last decade. These techniques preserve useful bulk polymer properties unchanged, while the activation of the polymer surface offers more possibilities for polymer applications.In this work, a new, one-step method for bio-activation of HDPE (high density polyethylene) surface by UV irradiation is presented. HDPE films coupled with selected active compound and a photoinitiator was treated by UV lamp, emitting light at 254nm.For surface functionalization of HDPE films, the following compounds were employed: 2-aminopyridine (AP), N¹-(2-pyridylaminomethyl)-1,2,4-triazole (TA) and benzocaine (BC). The influence of irradiation time on the extent of surface changes was investigated. The modified polymer surfaces were investigated by Fourier transformed infrared (FTIR) and Raman spectroscopy, scanning electron microscopy (SEM) and contact angle measurements, demonstrating successful functionalization of HDPE surface.

Keywords: Surface modification; UV irradiation; High density polyethylene (HDPE); 2-Aminopyridine; Benzocaine; Acetophenone

Synthesis, characterization and electrochemical behavior of polypyrrole/carbon nanotube composites using organometallic-functionalized carbon nanotubes by Hongyu Mi; Xiaogang Zhang; Youlong Xu; Fang Xiao (pp. 2284-2288).

Thorn-like, organometallic-functionalized carbon nanotubes were successfully developed via a novel microwave hydrothermal route. The organometallic complex with methyl orange and iron (III) chloride served as reactive seed template, resulting in the oriented polymerization of pyrrole on the modified carbon nanotubes without the assistance of other oxidants. Morphological and structural characterizations of the carbon nanotube/methyl orange–iron (III) chloride and polypyrrole/carbon nanotube composites were examined using transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), infrared spectroscopy and X-ray diffraction (XRD). The electrochemical property of the polypyrrole/carbon nanotube composite was elucidated by cyclic voltammetry and galvanostatic charge–discharge. A specific capacitance of 304Fg⁻¹ was obtained within the potential range of −0.5–0.5V in 1M KCl solution.

Keywords: Organometallic complex; Carbon nanotube; Polypyrrole; Electrochemical property

Ag–N doped ZnO film and its p–n junction fabricated by ion beam assisted deposition by Zhi Yan; Youpeng Ma; Peiran Deng; Zhishui Yu; Cheng Liu; Zhitang Song (pp. 2289-2292).

Ag–N doped ZnO film was synthesized by ion beam assisted deposition and its electrical properties and annealing property were investigated. The films remained p-type even after annealing at 400°C in air for 10min. While the annealing temperature went up to 500°C, the conduction type of these films shifted from p-type to n-type. The p-type ZnO film revealed low resistivity (0.0016Ωcm), low Hall mobility (0.65cm²V⁻¹s⁻¹) and high carrier concentration (5.8×10²⁰cm⁻³). ZnO p–n homojunction consisting of a p-type layer (Ag–N doped ZnO film) and an n-type layer (In-doped ZnO film) had been fabricated by ion beam assisted deposition. With electrical measurement, its current–voltage curve had a typical rectifying characteristic with current rectification ratio of 25 at bias ±5V and a reverse current of 0.01mA at −5V. The depletion width was estimated 3.8nm by using p–n junction equation.

Keywords: Thin films; Ion beam technology; Semiconductors; Electrical properties

Surface modification of porous poly(tetrafluoraethylene) film by a simple chemical oxidation treatment by Shifang Wang; Juan Li; Jinping Suo; Tianzhi Luo (pp. 2293-2298).

A simple, inexpensive and environmental chemical treatment process, i.e., treating porous poly(tetrafluoroethylene) (PTFE) films by a mixture of potassium permanganate solution and nitric acid, was proposed to improve the hydrophilicity of PTFE. To evaluate the effectiveness of this strong oxidation treatment, contact angle measurement was performed. The effects of treatment time and temperature on the contact angle of PTFE were studied as well. The results showed that the chemical modification decreased contact angle of as-received PTFE film from 133±3° to 30±4° treated at 100°C for 3h, effectively converting the hydrophobic PTFE to a hydrophilic PTFE matrix. The changes in chemical structure, surface compositions and crystal structure of PTFE were examined by attenuated total reflection–Fourier transform infrared spectroscopy (ATR–FTIR), X-ray photoelectron spectroscopy (XPS), environmental scanning electron microscopy (ESEM), X-ray diffraction (XRD), respectively. It was found that the F/C atomic ratio decreased from untreated 1.65–0.10 treated by the mixture at 100°C for 3h. Hydrophilic groups such as carbonyl (CO) and hydroxyl (OH) were introduced on the surface of PTFE after treatment. Furthermore, hydrophilic compounds K_0.27MnO₂·0.54H₂O was absorbed on the surface of porous PTFE film. Both the introduction of hydrophilic groups and absorption of hydrophilic compounds contribute to the significantly decreased contact angle of PTFE.

Keywords: Polytetrafluoraethylene (PTFE); Chemical treatment; Surface modification; Contact angle

A novel method for elimination of the gold-islands formed in the self-assembled monolayers of benzeneselenol on Au(111) surface by Waleed Azzam (pp. 2299-2303).

Molecular ordering of benzeneselenol (BSe) self-assembled monolayers (SAMs) on Au(111) substrates have been investigated by scanning tunnelling microscopy (STM) . After short immersion time (10min), elevated islands with height of 2.4Å were found to cover the entire gold surface. On and among the islands, the STM results exhibited the formation of a highly ordered phase (α-phase) by BSe species. In the present study, a novel method is presented to completely eradicate the elevated gold-islands. The method depends on a repetitive STM scanning over the same part of the SAM at restricted tunnelling conditions. After almost 6h of successive scanning, the surface becomes clean and free of the elevated islands. Moreover, this method was found to induce phase transformation into β-phase. The size of the ordered domains of the β-phase was found to exceed five times that of α-phase. Such a long-range ordering of the β-phase at room temperature has not been previously observed for any system on Au(111). After detailed analyses, the β-phase was found to have a 33.5% of lower packing density than that of α-phase.

Keywords: Self-assembled monolayer; Elevated islands; Scanning tunnelling microscopy and benzeneselenol

Carbon dendrite formation induced by pulsed laser irradiation by Weiwei An; Xiaoli Zhao; Zhiguo Zhang; Runzhou Su (pp. 2304-2307).

Porous carbon dendrite has been prepared by irradiating graphite targets with 532nm, 10ns laser pulses. The prepared samples were characterized by means of scanning electron microscopy, transmission electron microscopy and Raman spectroscopy. The measurement results show that carbon dendrite structures with cluster diameter of 10nm were obtained on the irradiated target surface in an inert gas atmosphere. The evolution of target surface morphology induced by different laser intensities was investigated. The formation mechanism of the dendrite structure has been discussed in detail. The laser intensity plays an important role in the formation of the nanostructures and there exists an optimum intensity to prepare the carbon dendrite.

Keywords: Carbon; Porous dendrite layer; Laser irradiation; Formation mechanism

Sections

Personal tools

Applied Surface Science (v.256, #7)

Sections

Personal tools

Local resources

Applied Surface Science (v.256, #7)