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Applied Surface Science (v.253, #24)

Effect of temperature on pulsed laser deposition of HgCdTe films by M. Liu; B.Y. Man; X.C. Lin; X.Y. Li; C.S. Chen (pp. 9291-9294).

HgCdTe thin films have been deposited on Si(111) substrates at different substrate temperatures by pulsed laser deposition (PLD). An Nd:YAG pulsed laser with a wavelength of 1064nm was used as laser source. The influences of the substrate temperature on the crystalline quality, surface morphology and composition of HgCdTe thin films were characterized by X-ray diffraction (XRD), selected area electron diffraction (SAED), atomic force microscopy (AFM) and energy dispersive X-ray spectroscopy (EDS). The results show that in our experimental conditions, the HgCdTe thin films deposited at 200°C have the best quality. When the substrate temperature is over 250°C, the HgCdTe film becomes thermodynamically unstable and the quality of the film is degraded.

Keywords: PACS; 68.55.−a; 73.40.SxPLD; HgCdTe thin films; Temperature effects

The effects of xenon ion irradiation on the photoluminesce behavior of poly( p-cresolformaldeyde)/diazonaphtoquinone thin films by Irene T.S. Garcia; F.C. Zawislak; Naira Balzaretti; D. Samios; U. Sias (pp. 9295-9300).

In the present paper, we investigate the origin of photoluminescence (PL) and the changes in the optical properties: refractive index and absorption coefficient, in poly( p-cresolformaldeyde) and diazonaphtoquinone thin films irradiated with Xe ions. Films 400nm thick have been irradiated with 800keV Xe²⁺ ions in a fluence range from 10¹³ to 6×10¹⁵Xecm⁻². The structural modifications were followed by the techniques of nuclear reaction analysis, elastic recoil detection analysis, Rutherford backscattering, Fourier transform infrared and Raman spectroscopies. The PL behavior was characterised with 488nm excitation wavelength. The pristine films show emission with maxima of the main bands located at 635, 720 and 830nm. For fluences up to 10¹⁴Xecm⁻², the photoluminescence intensity increases with the irradiation fluence. The chain mobility lowering, characterized by the crosslinked structure, explains this behavior in organic systems. Other possible contribution for increasing of PL intensity, at these fluences, is the presence of oxygen trapped in the polymer chains by the dangling bonds. At intermediate and higher fluences, the photoluminescence starts to decrease. At fluences higher than 10¹⁴Xecm⁻², irreversible changes of the organic structure occur and they are characterized by large losses of oxygen and hydrogen, transforming the material into amorphous carbon films. The loss of photoluminescent behavior is associated with the light absorption characteristics of the amorphous carbon structure. This conclusion is supported by the observed increase of the refractive indexes and absorption coefficients, obtained in the infrared region, as well as by the Raman results. Also, the effect of irradiation modifying the refractive index in the infrared region suggests the application of these films as waveguide in this region of wavelength.

Keywords: Photoluminescence; Ion irradiation; Organic thin films

Phase composition and tribological properties of Ti–Al coatings produced on pure Ti by laser cladding by Baogang Guo; Jiansong Zhou; Shitang Zhang; Huidi Zhou; Yuping Pu; Jianmin Chen (pp. 9301-9310).

Ti–Al coatings with ∼14.7, 18.1, 25.2 and 29.7at.% Al contents were fabricated on pure Ti substrate by laser cladding. The laser cladding Ti–Al coatings were analyzed with X-ray diffraction (XRD), scanning electron microscope (SEM) and X-ray energy dispersive spectroscopy (EDS). It was found that with the increase of Al content, the diffraction peaks shifted gradually to higher 2 θ values. The laser cladding Ti–Al coatings with 14.7 and 18.1at.% Al were composed of α-Ti and α₂-Ti₃Al phases, while those with 25.2 and 29.7at.% Al were composed of α₂-Ti₃Al phase. With the increase of Al content, the cross-sectional hardness increased, while the fracture toughness decreased. For the laser cladding Ti–Al coatings, when the Al content was ≤18.1at.%, the wear mechanism was adhesive wear and abrasive wear; while when the Al content ≥25.2at.%, the wear mechanism was adhesive wear, abrasive wear and microfracture. With the increase of Al content, the wear rate of laser cladding Ti–Al coatings decreased under 1N normal load, while the wear rate firstly decreased and then increased under a normal load of 3N. Due to its optimized combination of high hardness and high fracture toughness, the laser cladding Ti–Al coating with 18.1at.% Al showed the best anti-wear properties at higher normal load.

Keywords: Laser cladding; Ti–Al coating; Phase composition; Tribological properties

Characterization of optical waveguide in Nd: GdVO₄ by triple-energy oxygen ion implantation by Chuan-Lei Jia; Xue-Lin Wang; Ke-Ming Wang; Hong-Ji Ma; Rui Nie (pp. 9311-9314).

We report on the optical planar waveguide formation and modal characterization in Nd: GdVO₄ crystals by triple oxygen ion implantation at energies of (2.4, 3.0, and 3.6MeV) and fluences of (1.4, 1.4, and 3.1)×10¹⁴ions/cm². The prism-coupling method is used to investigate the dark-mode property at wavelength of 632.8nm. The refractive index profiles of the waveguide are reconstructed by an effective refractive index, n_eff method. The modal analysis shows that the fields of TE modes are well restricted in the guiding region, which means the formation of nonleaky waveguide in the crystal.

Keywords: PACS; 42.79.Gn; 78.20.Ci; 61.80.JhWaveguide; Ion implantation; Nd:GdVO; ₄; crystal

Surface modifications of crystalline silicon created by high intensity 1064nm picosecond Nd:YAG laser pulses by M.S. Trtica; B.M. Gakovic; D. Maravic; D. Batani; T. Desai; R. Redaelli (pp. 9315-9318).

A study of silicon modification induced by a high intensity picosecond Nd:YAG laser, emitting at 1064nm, is presented. It is shown that laser intensities in the range of 5×10¹⁰–0.7×10¹²Wcm⁻² drastically modified the silicon surface. The main modifications and effects can be considered as the appearance of a crater, hydrodynamic/deposition features, plasma, etc. The highest intensity of ∼0.7×10¹²Wcm⁻² leads to the burning through a 500μm thick sample. At these intensities, the surface morphology exhibits the transpiring of the explosive boiling/phase explosion (EB) in the interaction area. The picosecond Nd:YAG laser-silicon interaction was typically accompanied by massive ejection of target material in the surrounding environment. The threshold for the explosive boiling/phase explosion (TEB) was estimated to be in the interval 1.0×10¹⁰Wcm⁻²10Wcm⁻².

Keywords: Silicon; Laser-matter interaction; Picosecond Nd:YAG laser

Growth of cubic Mg_xZn1−_xO alloy films by electron beam evaporation by Y.M. Zhao; J.Y. Zhang; K.W. Liu; D.Y. Jiang; C.X. Shan; Y.M. Lu; B. Yao; D.X. Zhao; B.H. Li; Z.Z. Zhang; D.Z. Shen (pp. 9319-9322).

We report the growth of cubic Mg_xZn1−_xO alloy thin films on quartz by electron beam evaporation. It can be found that all the samples have sharp absorption edges by the absorption measurements. X-ray diffraction measurements indicate the Mg_xZn1−_xO films are cubic phase with preferred orientation along the (111) direction. Energy dispersive spectrometry (EDS) demonstrates that the Mg concentration in Mg_xZn1−_xO films is much higher than the ceramic target used, and the composition can be tuned in a small scope by varying the substrate temperature and the beam electric current. The reasons of this phenomenon are also discussed.

Keywords: Electron beam evaporation; Mg; _x; Zn; 1−; _x; O thin film; Beam electric current

Description of a hybrid PECVD-PVD process: Application to Zn–Si–O and Ti–Si–O composites thin films by A. Daniel; T. Duguet; T. Belmonte (pp. 9323-9329).

A radio frequency hybrid process where sputtering and plasma enhanced chemical vapour deposition (PECVD) occur simultaneously is studied to describe the specificity it gains when the two techniques are merged. A model is developed to describe how the deposition rate evolves when the flow rate of the PECVD precursor increases. First, it is shown that it is constant below a critical value of the precursor flow rate because of the wind effect due to sputtering that strongly limits the transport of the precursor. Then it increases almost linearly with the precursor flow rate when PECVD and sputtering simultaneously occur. Finally, above a certain threshold in the precursor flow rate, the surface of the target is poisoned by the precursor and composite thin films can no longer grow. The previous model is deduced from results obtained in deposition of Zn–Si–O and Ti–Si–O thin films. These composites are synthesised respectively by sputtering of zinc and titanium targets in a vapour of oxygen and hexamethyldisiloxane (HMDSO–Si₂C₆H₁₈O). Limitations of the model used are also discussed.

Keywords: PACS; 81.15.-z Methods of deposition of films and coatings; Film growth and epitaxyHybrid process; Sputtering; PECVD; Zinc oxide; Titanium oxide; HMDSO

Luminescence enhancement of Mn doped ZnS nanocrystals passivated with zinc hydroxide by Daixun Jiang; Lixin Cao; Ge Su; Hua Qu; Dake Sun (pp. 9330-9335).

Mn-doped ZnS nanocrystals prepared by solvothermal method have been successfully coated with different thicknesses of Zn(OH)₂ shells through precipitation reaction. The impact of Zn(OH)₂ shells on luminescent properties of the ZnS:Mn nanocrystals was investigated. X-ray diffraction (XRD) measurements showed that the ZnS:Mn nanocrystals have cubic zinc blende structure. The morphology of nanocrystals is spherical shape measured by transmission electron microscopy (TEM). ZnS:Mn/Zn(OH)₂ core/shell nanocrystals exhibited much improved luminescent properties than those of unpassivated ZnS:Mn nanocrystals. The luminescence enhancement was observed with the Zn(OH)₂ shell thickening by photoluminescence (PL) spectra at room temperature and the luminescence lifetime of transition from⁴T₁ to⁶A₁ of Mn²⁺ ions was also prolonged. This result was led by the effective, robust passivation of ZnS surface states by the Zn(OH)₂ shells, which consequently suppressed nonradiative recombination transitions.

Keywords: ZnS:Mn/Zn(OH); ₂; Passivation; Luminescence enhancement; Nanocrystals

An infrared study of the surface chemistry of lithium titanate spinel (Li₄Ti₅O₁₂) by Mark Q. Snyder; William J. DeSisto; Carl P. Tripp (pp. 9336-9341).

While there are numerous studies examining the performance of lithium titanate spinel (LTS) as a lithium-ion battery, little is known about the surface chemistry of this material. In this paper, diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy spectroscopy was used to study the type of surface groups present on LTS as a function of temperature. The surface was found to contain isolated and hydrogen-bonded TiOH groups and the dehydroxylation behavior with thermal treatment was similar to that of TiO₂. In addition, hexamethyldisilazane (HMDZ) and pyridine were used to probe the reactivity of surface hydroxyl groups and the presence of Lewis acid sites, respectively. The reaction of HMDZ occurred with both LiOH and TiOH groups to form Li–O–Si and Ti–O–Si. In addition, the reaction of gaseous CO₂ with the Li⁺ ions resulted in the formation of surface carbonate ions. The carbonate ions are removed by heating at 400°C in air.

Keywords: Electrode; Diffuse reflectance infrared Fourier transform spectroscopy; Pyridine; Hexamethyldisilazane; Metal oxide powder; Surface chemistry

Influence of water cavitation peening with aeration on fatigue behaviour of SAE1045 steel by B. Han; D.Y. Ju; W.P. Jia (pp. 9342-9346).

Water cavitation peening (WCP) with aeration is a recent potential method in the surface enhancement techniques. In this method, a ventilation nozzle is adopted to improve the process capability of WCP by increasing the impact pressure, which is induced by the bubble collapse on the surface of components in the similar way as conventional shot peening. In this paper, fatigue tests were conducted on the both-edge-notched flat tensile specimens to assess the influences of WCP on fatigue behaviour of SAE1045 steel. The notched specimens were treated by WCP, and the compressive residual stress distributions in the superficial layer were measured by X-ray diffraction method. The tension–tension ( R= S_min/ S_max=0.1, f=10Hz) fatigue tests and the fracture surfaces observation by scan electron microscopy (SEM) were conducted. The experimental results show that WCP can improve the fatigue life by inducing the residual compressive stress in the superficial layer of mechanical components.

Keywords: PACS; 61.10.Nz; 62.20.Mk; 68.37.Hk; 68.47.DeWater cavitation peening; X-ray diffraction; Residual stress; Fatigue life

Investigations of the inhibition of copper corrosion in nitric acid solutions by ketene dithioacetal derivatives by A. Fiala; A. Chibani; A. Darchen; A. Boulkamh; K. Djebbar (pp. 9347-9356).

Ketene dithioacetal derivatives, namely 3-[bis(methylthio)methylene] pentane-2,4-dione (1), 3-(1,3-dithian-2-ylidene) pentane-2,4-dione (2) and 3-(1,3-dithiolan-2-ylidene) pentane-2,4-dione (3) were synthesized and their respective capacity to inhibit copper corrosion in 3M HNO₃ was investigated by means of weight loss, potentiodynamic polarization, scanning electron microscopy (SEM) and energy dispersive X-ray fluorescence (XRF). The obtained results indicate that the addition of these compounds significantly decreases the corrosion rate. Potentiodynamic polarization studies clearly showed that the inhibition efficiency increases with increasing concentration of the investigated compounds at a fixed temperature, but decreases with increasing temperature. These results on the whole showed that the studied substances are good cathodic inhibitors for copper corrosion in nitric acid medium. SEM and energy dispersive X-ray (EDAX) examination of the copper surface revealed that these compounds prevented copper from corrosion by adsorption on its surface to form a protective film, which acts as a barrier to aggressive agents. The presence of these organic compounds adsorbed on the electrode surface was confirmed by XRF investigations.

Keywords: PACS; 81. 65. K; _nCopper; Corrosion inhibition; Ketene dithioacetal

Effects of roughness on interfacial performances of silica glass and non-polar polyarylacetylene resin composites by Z.X. Jiang; Y.D. Huang; L. Liu; J. Long (pp. 9357-9364).

The influence of roughness on interfacial performances of silica glass/polyarylacetylene resin composites was investigated. In order to obtain different roughness, silica glass surface was abraded by different grits of abrasives and its topography was observed by scanning electron microscopy and atomic force microscopy. At the same time, the failure mechanisms of composites were analyzed by fracture morphologies and the interfacial adhesion was evaluated by shear strength test. The results indicated that shear strength of silica glass/polyarylacetylene resin composites firstly increased and then decreased with the surface roughness of silica glass increased. The best surface roughness range of silica glass was 40–60nm. The main mechanism for the improvement of the interfacial adhesion was physical interlocking at the interface.

Keywords: PACS; 68.35.NpPolyarylacetylene resin; Interlocking; Scanning electron microscopy

Structural, optical and electrochromic properties of nickel oxide thin films grown from electrodeposited nickel sulphide by M.M. Uplane; S.H. Mujawar; A.I. Inamdar; P.S. Shinde; A.C. Sonavane; P.S. Patil (pp. 9365-9371).

Nickel oxide thin films were grown onto FTO-coated glass substrates by a two-step process: electrodeposition of nickel sulphide and their thermal oxidation at 425, 475 and 525°C. The influence of thermal oxidation temperature on structural, optical, morphological and electrochromic properties was studied. The structural properties undoubtedly revealed NiO formation. The electrochromic properties were studied by means of cyclic voltammetry. The films exhibited anodic electrochromism, changing from a transparent state to a coloured state at +0.75V versus SCE, i.e. by simultaneous ion and electron ejection. The transmittance in the coloured and bleached states was recorded to access electrochromic quality of the films. Colouration efficiency and electrochromic reversibility were found to be maximum (21mC/cm² and 89%, respectively) for the films oxidized at 425°C. The optical band gap energy of nickel oxide slightly varies with increase in annealing temperature.

Keywords: Nickel oxide thin films; Electrochemical properties (CV, CC); Scanning electron microscopy; XRD; Optical properties

Material and device properties of ZnO-based film bulk acoustic resonator for mass sensing applications by Zhi Yan; Zhitang Song; Weili Liu; Hongxuan Ren; Ning Gu; Xiaoyuan Zhou; Li Zhang; Yu Wang; Songlin Feng; Lihui Lai; Jianzhao Chen (pp. 9372-9380).

Zinc oxide based film bulk acoustic resonator as mass sensor was fabricated by multi-target magnetron sputtering under optimized deposition condition. Each layer of the device was well crystallized and highly textural observed by transmission electron microscopy and X-ray diffraction measurement. Through piezoelectric test, the device vibrated with significant distance. The influence of top electrode on resonant frequency and the bio-specimen of mass loading effect were investigated. Data show that the device has qualified properties as mass biosensor, with a resonant frequency of 3–4GHz and a high sensitivity of 8–10kHzcm²/ng.

Keywords: PACS; 73.61Ga; 77.65Dq; 81.15−zZnO film; Sputtering; Resonator; Mass sensor

Topographic control on silicone surface using chemical oxidization method by Teng-Kai Shih; Jeng-Rong Ho; Chia-Fu Chen; Wha-Tzong Whang; Chien-Chung Chen (pp. 9381-9386).

The paper describes a wet process for modifying the surface of polydimethylsiloxane (PDMS) using H₂SO₄/HNO₃ solutions. The oxidation on the surface of PDMS was confirmed by the examinations of Fourier transform infrared spectrometry (FTIR), contact angle of water drop and X-ray photoelectron spectroscopy (XPS). The hydrophobic surface of pristine PDMS was not only changed to hydrophilic, but also formed wrinkles on it after chemical modification. Bilayer systems, stiff oxidized PDMS layers were capped on soft PDMS foundations, would generate easily compressive stresses due to the large difference in volumetric contraction rates and led to form wrinkles on the surface. Experimental results demonstrated the periodicity of wrinkles was controllable by controlling the duration of oxidation. Therefore, wrinkles could be arranged orderly by the guidance of external forces before oxidization. The potential technology for generating and ordering wrinkles on the PDMS surface is valuable in the applications of pressure sensors, biology, micro-optics and nano-/micro-fabrication in the future.

Keywords: Wrinkles; PDMS; Chemical modification

The anodization of ZK60 magnesium alloy in alkaline solution containing silicate and the corrosion properties of the anodized films by Wu Hai-lan; Cheng Ying-liang; Li Ling-ling; Chen Zhen-hua; Wang Hui-min; Zhang Zhao (pp. 9387-9394).

The anodization of ZK60 magnesium alloy in an alkaline electrolyte of 100g/l NaOH+20g/l Na₂B₄O₇·10H₂O+50g/l C₆H₅Na₃O₇·2H₂O+60g/l Na₂SiO₃·9H₂O was studied in this paper. The corrosion resistance of the anodic films was studied by electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization techniques and the microstructure and composition of films were examined by SEM and XRD. The influence of anodizing time was studied and the results show that the anodizing time of 60min is suitable for acquiring films with good corrosion resistance. The influence of current density on the corrosion resistance of anodizing films was also studied and the results show that the film anodized at 20mA/cm² has the optimum corrosion resistance. The film formed by anodizing in the alkaline solution with optimized parameters show superior corrosion resistance than that formed by the traditional HAE process. The XRD pattern shows that the components of the anodized film consist of MgO and Mg₂SiO₄.

Keywords: ZK60; Anodized film; Corrosion; Alkaline solution; EIS

Improved surface morphology of flow-modulated MOVPE grown AIN on sapphire using thin medium-temperature AIN buffer layer by Da-Bing Li; Masakazu Aoki; Hideto Miyake; Kazumasa Hiramatsu (pp. 9395-9399).

High-temperature (HT) AIN films were grown on (0001) sapphire by low-pressure flow-modulated (FM) metal organic vapor phase epitaxy (MOVPE) with and without inserting a thin medium-temperature (MT) AIN layer. To suppress parasitic reactions between the sources of trimethylaluminum (TMA) and ammonia (NH₃), TMA and NH₃ was introduced to the reactor of MOVPE by alternating supply way. Surface morphology and crystalline quality were characterized by a scanning electronic microscopy (SEM), atomic force microscopy (AFM) and X-ray rocking curve (XRC) measurements of (0002) and (10–12) diffractions. The AFM and SEM measurements indicated that the thin MT-AIN layer had a strong influence on the surface morphology of the HT-AIN films. The surface morphology became quite smooth by inserting the thin MT-AIN layer and surface RMS roughness values were 0.84nm and 13.4nm for the HT-AIN films with and without inserting the thin MT-AIN buffer layer, respectively. By etching the samples in aqueous KOH solution, it was found that the polarity of AIN films was different, the HT-AIN film with the thin MT-AIN layer could not be etched, indicating that the film had an Al-polar surface; however, the film without the MT-AIN layer was etched, which was explained that that film had a N- or mixed-polar surface. The mechanism for the origin of the different polarity of HT-AIN with and without the thin MT-AIN layer was proposed and discussed in detail.

Keywords: Metalorganic vapor phase epitaxy; AIN; Polarity; AFM; SEM; Flow-modulated method

Structure and acid–base properties of surface-modified mesoporous silica by Ying Chen; Jinyu Han; Haitao Zhang (pp. 9400-9406).

A series of surface-modified mesoporous silica endowing with acid–base properties have been successfully synthesized in one pot by in situ introduction of zirconium and magnesium salts into the initial mixture of synthesizing mesoporous silica (SBA-15) and this method combines into a single step to form a novel material with a periodically ordered mesoporous backbone and specific chemical reactivity of the acid-basic sites. X-ray diffraction, high-resolution transmission electron microscopes (HRTEM), N₂ adsorption, FT-IR transmission spectra,²⁹Si MAS NMR spectra, NH₃- and CO₂-temperature programmed desorption (TPD) are employed to characterize the titled mesoporous materials. The results indicate that the product possesses excellent acid-basic properties with well mesoporous structure, which make it promising for their application in heterogeneous catalysis and adsorption–separation processes.

Keywords: Mesoporous materials; Acid–base properties; MgO–ZrO; ₂; –SBA-15; Surface modification

Effect of Li₂O and CoO-doping of CuO/Fe₂O₃ system on its surface and catalytic properties by H.G. El-Shobaky; M.M. Mokhtar (pp. 9407-9413).

Physicochemical, surface and catalytic properties of pure and doped CuO/Fe₂O₃ system were investigated using X-ray diffraction (XRD), energy dispersive X-ray analysis (EDX), nitrogen adsorption at −196°C and CO-oxidation by O₂ at 80–220°C using a static method. The dopants were Li₂O (2.5mol%) and CoO (2.5 and 5mol%). The results revealed that the increase in precalcination temperature from 400 to 600°C and Li₂O-doping of CuO/Fe₂O₃ system enhanced CuFe₂O₄ formation. However, heating both pure and doped solids at 600°C did not lead to complete conversion of reacting oxides into CuFe₂O₄. The promotion effect of Li₂O dopant was attributed to dissolution of some of dopant ions in the lattices of CuO and Fe₂O₃ with subsequent increase in the mobility of reacting cations. CoO-doping led also to the formation of mixed ferrite Co_xCu1−_xFe₂O₄. The doping process of the system investigated decreased to a large extent the crystallite size of unreacted portion of Fe₂O₃ in mixed solids calcined at 600°C. This process led to a significant increase in the S_BET of the treated solids. Doping CuO/Fe₂O₃ system with either Li₂O or CoO, followed by calcination at 400 and 600°C decreased its catalytic activity in CO-oxidation by O₂. However, the activation energy of the catalyzed reaction was not much affected by doping.

Keywords: CuFe; ₂; O; ₄; Li; ₂; O-doping; Copercipitation; CO oxidation; EDX; XRD

Effect of oxygen partial pressure on the structural and optical properties of ZnO film deposited by reactive sputtering by J.P. Zhang; G. He; L.Q. Zhu; M. Liu; S.S. Pan; L.D. Zhang (pp. 9414-9421).

Effects of variation of the oxygen partial pressure on the structural and optical properties of zinc oxide (ZnO) thin films prepared by reactive radio-frequency sputtering were investigated. Measurements by X-ray diffraction (XRD) and atomic force microscopy (AFM) indicated that the crystallinity and the surface morphology were sensitive to the oxygen partial pressure. The interfacial and optical properties of the targeted films were investigated by spectroscopic ellipsometry (SE) characterization. Based on Tauc-Lorentz (TL) model, the optical constants of ZnO films were tentatively extracted in the photon energy ranging from 1.5 to 6.0eV. Analyses by XRD and SE revealed that the oxygen partial pressure had effect on the orientation of the ZnO films, the surface morphology, the packing density, and the interfacial layers. And the relationship between crystallinity and interfacial layer, as well as the relationship between surface roughness and packing density was discussed. All these had a significant impact on the optical properties illustrated by SE analysis.

Keywords: Zinc oxide thin film; Partial pressure; Tauc-Lorentz; Spectroscopic ellipsometry

Opto-electrical properties of Ti-doped In₂O₃ thin films grown by pulsed laser deposition by R.K. Gupta; K. Ghosh; S.R. Mishra; P.K. Kahol (pp. 9422-9425).

By ablating titanium containing In₂O₃ target with a KrF excimer laser, highly conducting and transparent films on quartz were obtained to investigate the effects of growth temperature and oxygen pressure on the structural, optical and electrical properties of these films. We find that the transparency of the films depends more on the growth temperature and less on the oxygen pressure. Electrical properties, however, are found to be sensitive to both the growth temperature and oxygen pressure. We report in this paper that a growth temperature of 500°C and an oxygen pressure of 7.5×10⁻⁷bar lead to titanium-doped indium oxide films which have high mobility (up to 199cm²V⁻¹s⁻¹), low resistivity (9.8×10⁻⁵Ωcm), and relatively high transmittance (∼88%).

Keywords: PACS; 72.20; 78.66; 73.50J; 61.16CSemiconductor; Electrical properties; Thin films; Indium oxide; Titanium; Optical materials and properties

Modification of medical metals by ion implantation of copper by Y.Z. Wan; G.Y. Xiong; H. Liang; S. Raman; F. He; Y. Huang (pp. 9426-9429).

The effect of copper ion implantation on the antibacterial activity, wear performance and corrosion resistance of medical metals including 317L of stainless steels, pure titanium, and Ti–Al–Nb alloy was studied in this work. The specimens were implanted with copper ions using a MEVVA source ion implanter with ion doses ranging from 0.5×10¹⁷ to 4×10¹⁷ions/cm² at an energy of 80keV. The antibacterial effect, wear rate, and inflexion potential were measured as a function of ion dose. The results obtained indicate that copper ion implantation improves the antibacterial effect and wear behaviour for all the three medical materials studied. However, corrosion resistance decreases after ion implantation of copper. Experimental results indicate that the antibacterial property and corrosion resistance should be balanced for medical titanium materials. The marked deteriorated corrosion resistance of 317L suggests that copper implantation may not be an effective method of improving its antibacterial activity.

Keywords: PACS; 87.68.+z; 68.55.LnIon implantation; Copper; Antibacterial activity; Corrosion resistance; Medical metals; Wear

Preparation of hybrid film with superhydrophobic surfaces based on irregularly structure by emulsion polymerization by Ailan Qu; Xiufang Wen; Pihui Pi; Jiang Cheng; Zhuoru Yang (pp. 9430-9434).

A superhydrophobic surface originated from quincunx-shape composite particles was obtained by utilizing the encapsulation and graft of silica particles to control the surface chemistry and morphology of the hybrid film. The composite particles make the surface of film form a composite interface with irregular binary structure to trap air between the substrate surface and the liquid droplets which plays an essential role in obtaining high water contact angle and low water contact angle hysteresis. The water contact angle on the hybrid film is determined to be 154±2° and the contact angle hysteresis is less than 5°. This is expected to be a simple and practical method for preparing self-cleaning hydrophobic surfaces on large area.

Keywords: Hybrid fluoropolymer; Superhydrophobic surface; Hierarchical irregularly structure; Silica particles

UV-laser-assisted liquid phase fluorination of PMMA by C. Wochnowski; M. Di Ferdinando; C. Giolli; F. Vollertsen; U. Bardi (pp. 9435-9442).

Polymethylmethacrylate (PMMA) substrate was covered with liquid 1,2,3,5-tetrafluorobenzene by spin coating. Then the sample was irradiated by a KrF-excimer laser ( λ=248nm). Thus, fluorine is released from the fluorine-containing precursor diffusing into the polymeric substrate material where it is expected to substitute the hydrogen atoms of the polymeric molecule and form a water-repellent (hydrophobic) fluorinated polymer. After drying out the polymeric substrate, the sample surface was investigated by SEM, EDX, XPS and contact angle measurement method in order to determine the fluorine content and the wettability of the treated polymeric surface as well as the substitution sites inside the polymeric molecule. The measurements indicate some chemically bonded fluorine at the top of the sample layer. A UV-photochemical fluorination mechanism is proposed based on the XPS spectra evaluation.

Keywords: PMMA; Excimer laser; UV-photochemistry; Fluorination; Wettability

Investigation of zinc powder modified by ultrasonic impregnation of rare earth lanthanum by Liqun Zhu; Hui Zhang; Weiping Li; Huicong Liu (pp. 9443-9449).

Different lanthanum conversion films coated directly on zinc particles are prepared by ultrasonic impregnation with the variable concentration of lanthanum nitrate solution and the adjusted ultrasonic time to modify zinc powder, and the characterization as well as electrochemical behavior of zinc are analyzed using scanning electron microscopy, energy dispersion spectrometry, potentiodynamic polarization, cyclic voltammetry. The lanthanum conversion films are found to enhance the property of corrosion resistance, suppress the dendritic growth and reduce the capacity loss for zinc electrode made of such modified zinc powder. Furthermore, the particle size of zinc powder immersed in lanthanum nitrate solution becomes thin and slim under the effect of ultrasound, which is beneficial to improve the electrochemical reaction activity of zinc powder at the assurance of high corrosion resistance for zinc electrode.

Keywords: Modified zinc powder; Ultrasonic impregnation; Rare earth lanthanum; Conversion film; Electrochemical performance

Influence of surface structure of SiC nano-sized powder analyzed by X-ray photoelectron spectroscopy on basic powder characteristics by Kazuya Shimoda; Joon-Soo Park; Tatsuya Hinoki; Akira Kohyama (pp. 9450-9456).

SiC nano-sized powder with high specific surface area is potentially of considerable interest to form fully dense SiC ceramics at lower sintering conditions (temperature/pressure). Surface structure of six kinds of commercially available SiC nano-sized powders produced by three different venders was analyzed in detail by X-ray photoelectron spectroscopy (XPS). The overall XPS spectra of all nano-sized powders detected O-based bond (O1s peak), C-based bond (C1s peak) and Si-based bond (Si2s and Si2p peak). Surface structure of nano-sized powders included one of three impurity phases: (1) free carbon, (2) silica and (3) silicon oxycarbide. Furthermore, the influences of surface structure by XPS were systematically investigated on basic powder characteristics, such as chemical composition, morphology, particle density and primary particle size. It was revealed that the basic powder characteristics had a close relationship to the surface structure of nano-sized powder each impurity.

Keywords: Silicon carbide; Nano-sized powder; XPS; Surface

Sapphire (0001) surface modifications induced by long-pulse 1054nm laser irradiation by Sheng-Nian Luo; Pedro D. Peralta; Chi Ma; Dennis L. Paisley; Scott R. Greenfield; Eric N. Loomis (pp. 9457-9466).

We have investigated modifications of sapphire (0001) surface with and without coating, induced by a single laser pulse with a 1054nm wavelength, 2.2μs duration, 7.75mm spot and energy of 20–110J. A holographic optical element was used for smoothing the drive beam spatially, but it induced small hotspots which initiated damage on the uncoated and coated surfaces. The individual damage effects of hotspots became less pronounced at high fluences. Due to high temperature and elevated non-hydrostatic stresses upon laser irradiation, damage occurred as fracture, spallation, basal and rhombohedral twinning, melting, vitrification, the formation of nanocrystalline phases, and solid–solid phase transition. The extent of damage increased with laser fluences. The formation of regular linear patterns with three-fold symmetry (〈112¯0〉 directions) upon fracture was due to rhombohedral twinning. Nanocrystallineα-Al₂O₃ formed possibly from vapor deposition on the coated surface and manifested linear, triangular and spiral growth patterns. Glass and minor amounts ofγ-Al₂O₃ also formed from rapid quenching of the melt on this side. Theα- toγ-Al₂O₃ transition was observed on the uncoated surface in some partially spalled alumina, presumably caused by shearing. The nominal threshold for laser-induced damage is about 47Jcm⁻² for these laser pulses, and it is about 94Jcm⁻² at the hotspots.

Keywords: Sapphire; Laser irradiation; Spall; Fracture; Twinning; Nanocrystals

Sticking coefficient of nitrogen on solid N₂ at low temperatures by S.H.M. Deng; D.B. Cassidy; R.G. Greaves; A.P. Mills Jr. (pp. 9467-9469).

The sticking coefficient of nitrogen gas on a thick solid nitrogen film on a copper cold finger was studied at low temperature. For surface temperatures of about 12K the sticking coefficient is measured to be 99.0±0.6%. Our result implies that it will be possible to make a intense and high brightness slow positron source starting from a small diameter deposit of the gaseous positron emitter¹³N₂ produced in the reaction¹²C(d,n)¹³N.

Keywords: PACS; 67.70.+n; 68.43.−hSticking coefficient; Nitrogen

The influence of cobalt on the corrosion resistance and electromagnetic shielding of electroless Ni–Co–P deposits on Al substrate by Y. Gao; L. Huang; Z.J. Zheng; H. Li; M. Zhu (pp. 9470-9475).

Electroless Ni–P and Ni–Co–P deposits were obtained on Al substrate. Their surface morphology, microstructure and composition were analyzed using SEM and XRD. Their corrosion resistance was characterized by anodic polarization curves. Based on the measurement of the thickness, electrical conductivity and magnetic conductivity of the deposits, their electromagnetic shielding effect values were calculated and the influence of cobalt on the corrosion and electromagnetic shielding properties of Ni–Co–P deposits was revealed. The results showed that cobalt improved the corrosion resistance and greatly enhanced the electromagnetic shielding property of Ni–Co–P deposits. Electroless Ni–Co–P deposits on Al substrate would impart the product with high corrosion resistance, good electromagnetic shielding effect and light weight.

Keywords: Al substrate; Electroless Ni–Co–P deposit; Corrosion resistance; Electromagnetic shielding

XPS study on the correlation between chemical state and oxygen-sensing properties of an iron oxide thin film by M. Aronniemi; J. Sainio; J. Lahtinen (pp. 9476-9482).

We have studied the correlation between the chemical state and the oxygen-sensing properties of an iron oxide thin film using a setup that allows simultaneous sensor resistance measurements and X-ray photoelectron spectroscopy (XPS) data acquisition. The gas exposures were performed at the highest operating pressure of the XPS spectrometer at a controlled sample temperature which allows direct comparison between the sensor response and the chemical state of the surface. The iron oxide film was modified by a sequence of argon ion sputtering steps and the induced changes in the chemical state, resistance, and sensitivity to oxygen were investigated. The sputtering was found to reduce the iron from the Fe³⁺ to the Fe²⁺ state and to decrease the sensor resistance. The measured sensitivity to oxygen first increased by a factor of two but then collapsed to its original level. The mechanism for oxygen sensing was found to be filling of the oxygen vacancies in the lattice. The effect of the sputtering on the resistance and sensitivity could be explained first with an increase in the density of oxygen vacancies and then, as the iron became more reduced, with an increase in the p-type conductivity.

Keywords: XPS; Iron oxide; Thin film; Gas sensor; Oxygen; Factor analysis; Chemical state

Optical and mechanical properties of alumina films fabricated on Kapton polymer by plasma immersion ion implantation and deposition using different biases by Yongxian Huang; Xiubo Tian; Shiqin Yang; Ricky K.Y. Fu; Paul K. Chu (pp. 9483-9488).

Alumina films are fabricated on Kapton polymer by aluminum plasma immersion ion implantation and deposition in an oxidizing ambient and the effects of the bias voltage on the film properties are investigated. Rutherford backscattering spectrometry (RBS) reveals successful deposition of alumina films on the polymer surface and that the O to Al ratio is higher than that of stoichiometric Al₂O₃. The thickness of the modified layers decreases from 200 to 120nm when the bias voltage is increased from 5 to 20kV. Our results indicate that higher bombardment energy may lead to higher crack resistance and better film adhesion. However, a higher sample bias degrades the optical properties of the films as indicated by the higher absorbance and lower energy band gap. Therefore, the processing voltage must be optimized to yield a protective layer with the appropriate thickness, superior optical properties, as well as high crack resistance.

Keywords: PACS; 52.77.Dq; 61.82.PvPlasma immersion ion implantation and deposition; Alumina films; Rutherford backscattering spectrometry; Optical properties; Crack resistance

Flame treatment of low-density polyethylene: Surface chemistry across the length scales by Jing Song; Ullrich Gunst; Heinrich F. Arlinghaus; G. Julius Vancso (pp. 9489-9499).

The relationship between surface chemistry and morphology of flame treated low-density polyethylene (LDPE) was studied by various characterization techniques across different length scales. The chemical composition of the surface was determined on the micrometer scale by X-ray photoelectron spectroscopy (XPS) as well as with time of flight secondary ion mass spectrometry (ToF-SIMS), while surface wettability was obtained through contact angle (CA) measurements on the millimeter scale. The surface concentration of hydroxyl, carbonyl and carboxyl groups, as a function of the “number” of the flame treatment passes (which is proportional to the treatment time) was obtained. Moreover, a correlation was found with chemical composition and polarity, emphasizing the role of oxygen-containing functional groups introduced during the treatment. Carboxyl functional groups were specifically identified by fluorescent labeling and the results were compared with the ToF-SIMS data. In addition, atomic force microscopy (AFM) was used to evaluate changes in surface topography and roughness on the nanometer to micrometer length scales. After flame treatment, water-soluble low molecular weight oxidized materials (LMWOM), which were generated as products of oxidation and chain scission of the LDPE surface, agglomerated into small topographical mounds that were visible in the AFM micrographs. After rinsing the flame treated samples with water and ethanol, bead-like nodular surface structures were observed. The ionization state of flame treated LDPE surfaces was monitored by chemical force microscopy (CFM). The effective surface p K_a values of carboxylic acid (–COOH) obtained by AFM were revealed by chemical force titration curves and the effective surface p K_a values were found to be around 6.

Keywords: Flame treatment; Low-density polyethylene; ToF-SIMS; XPS; AFM; Fluorescence microscopy

Structural characterization and optical properties of ZnSe thin films by G.I. Rusu; M. Diciu; C. Pîrghie; E.M. Popa (pp. 9500-9505).

Zinc selenide (ZnSe) thin films ( d=0.11–0.93μm) were deposited onto glass substrates by the quasi-closed volume technique under vacuum. Their structural characteristics were studied by X-ray diffraction (XRD) and atomic force microscopy (AFM). The experiments showed that the films are polycrystalline and have a zinc blende (cubic) structure. The film crystallites are preferentially oriented with the (111) planes parallel to the substrate surface. AFM images showed that the films have a grain like surface morphology. The average roughness, R_a=3.3–6.4nm, and the root mean square roughness, R_rms=5.4–11.9nm, were calculated and found to depend on the film thickness and post-deposition heat treatment.The spectral dependence of the absorption coefficient was determined from transmission spectra, in the range 300–1400nm.The values of optical bandgap were calculated from the absorption spectra, E_g=2.6–2.7 eV.The effect of the deposition conditions and post-deposition heat treatment on the structural and optical characteristics was investigated.

Keywords: PACS; 68.55. Jk; 72.80.Ey; 73.61.Ga; 78.40.Fy; 78.66.HfZinc selenide; Thin films; XRD; AFM; Transmission spectra; Absorption spectra

Effect of incorporating nonlanthanoidal indium on optical properties of ferroelectric Bi₄Ti₃O₁₂ thin films by Caihong Jia; Yonghai Chen; Linghong Ding; Weifeng Zhang (pp. 9506-9512).

Bi₄Ti₃O₁₂ (BTO) and Bi_3.25In_0.75Ti₃O₁₂ (BTO:In) thin films were prepared on fused quartz and LaNiO₃/Si (LNO) substrates by chemical solution deposition (CSD). Their microstructures, ferroelectric and optical properties were investigated by X-ray diffraction, scanning electron microscope, ferroelectric tester and UV–visible–NIR spectrophotometer, respectively. The optical band-gaps of the films were found to be 3.64 and 3.45eV for the BTO and BTO:In films, respectively. Optical constants (refractive indexes and extinction coefficients) were determined from the optical transmittance spectra using the envelope method. Following the single electronic oscillator model, the single oscillator energy E₀, the dispersion energy E_d, the average interband oscillator wavelength λ₀, the average oscillator strength S₀, the refractive index dispersion parameter ( E₀/ S₀), the chemical bonding quantity β, and the long wavelength refractive index n_∞ were obtained and analyzed. Both the refractive index and extinction coefficient of the BTO:In films are smaller than those of the BTO films. Furthermore, the refractive index dispersion parameter ( E₀/ S₀) increases and the chemical bonding quantity β decreases in the BTO and BTO:In films compared with those of bulk.

Keywords: PACS; 77.84.Dy; 81.15.Fg; 78.55.Hx; 78.66.LiFerroelectric thin film; Optical transmittance; Bi; ₄; Ti; ₃; O; ₁₂; Bi; _3.25; In; _0.75; Ti; ₃; O; ₁₂; Chemical solution deposition

Bio-inspired wearable characteristic surface: Wear behavior of cast iron with biomimetic units processed by laser by Hong Zhou; Na Sun; Hongyu Shan; Dianyi Ma; Xin Tong; Luquan Ren (pp. 9513-9520).

Stimulated by the cuticles of soil animals, an attempt to improve the wear resistance of compact graphite cast iron (CGI) with biomimetic units on the surface was made by using a biomimetic coupled laser remelting (BCLR) process. The microstructure and microhardness of biomimetic units were examined. The wear behaviors of biomimetic specimens as functions of laser input energy and biomimetic unit shape were investigated under dry sliding condition, respectively. The results indicated that the biomimetic specimens had better wear resistance than the untreated specimens. The wear resistance of the biomimetic specimens increases with the increase of laser input energy due to the increase of the depth and the width of biomimetic units as well as the increase of the microhardness. The specimen with grid biomimetic units had the best resistance, the stria took the second place and the convex showed the worst. The application of laser remelting provided desirable microstructural changes in biomimetic units, which generated the intensified particles effect for improving the wear resistance. The adhesive wear was the dominative wear mechanism for the biomimetic specimens.

Keywords: Biomimetic; Cast iron; Microstructure; Wear behavior; Laser

Target-plane deposition of diamond-like carbon in pulsed laser ablation of graphite by S.S. Yap; T.Y. Tou (pp. 9521-9524).

In pulsed Nd:YAG laser ablation of highly oriented pyrolytic graphite (HOPG) at 10⁻⁶Torr, diamond-like carbon (DLC) are deposited at laser wavelengths of 1064, 532, and 355nm on substrates placed in the target-plane. These target-plane samples are found to contain varying sp³ content and composed of nanostructures of 40–200nm in size depending on the laser wavelength and laser fluence. The material and origin of sp³ in the target-plane samples is closely correlated to that in the laser-modified HOPG surface layer, and hardly from the backward deposition of ablated carbon plume. The surface morphology of the target-plane samples shows the columnar growth and with a tendency for agglomeration between nanograins, in particular for long laser wavelength at 1064nm. It is also proposed that DLC formation mechanism at the laser-ablated HOPG is possibly via the laser-induced subsurface melting and resolidification.

Keywords: Nanostructure; Laser ablation; Diamond-like carbon; Raman spectra

Schottky diode based on porous GaN for hydrogen gas sensing application by F.K. Yam; Z. Hassan (pp. 9525-9528).

This article reports the study of Pd Schottky contact on porous n-GaN for hydrogen gas sensing. Upon exposure to 2% H₂ in N₂, porous GaN sensor exhibited significant change of current. Morphological studies revealed that Pd contact deposited on porous GaN has ridge-trench-like morphology, a dense porous network was found in between the ridges. The dramatic change of current was attributed to the unique microstructure at Pd/porous GaN interface, which allowed higher accumulation of hydrogen; this resulted in a stronger effect of H-induced dipole layer and led to a significant change in the electrical characteristics of the porous sensor.

Keywords: PACS; 73.40.Ei; 73.61.Ey; 81.05.Rm; 85.30.HiPorous GaN; Hydrogen sensing; Schottky barrier height

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Applied Surface Science (v.253, #24)