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Applied Surface Science (v.253, #21)

Fabrication and optical properties of 3D composite photonic crystals of core–shell structures by Yanping Liu; Zhijun Yan; Wei Lan; Chunming Huang; Yinyue Wang (pp. 8571-8574).

Three-dimensional (3D) composite colloidal photonic crystals with SiO₂ core and ZnO shell were fabricated on borosilicate glass (BSG) substrate by a two-stage deposition method. Scanning electron microscopy (SEM) measurements show that both the pre-deposited SiO₂ and SiO₂/ZnO core–shell structures are oriented with their (111) axes parallel to the substrates. Optical measurement reveals that the periodic arrays exhibit a photonic band gap in the (111) direction. The optical properties of SiO₂/ZnO core–shell structures strongly depend on the size dispersions of colloidal spheres and the intrinsic defects in the sample.

Keywords: Two-stage deposition; Core–shell structures; Photonic band gap

Induced assembly and photoluminescence of lanthanum (Tb, Eu, Dy) complexes/ZnO/polyethylene glycol hybrid phosphors by Bing Yan; Xi Chen; Jianhua Wu (pp. 8575-8580).

Some novel kinds of hybrid phosphors were assembled with lanthanum (Tb, Eu, Dy) complexes (with four kinds of terbium complexes is 2,4-dihydroxybenzonic acid (DHBA), 1,10-phenanthroline (phen), acetylacetone (AA) and nicotinic acid (Nic), respectively) doped ZnO/PEG particles by co-precipitation approach derived from Zn(CH₃COO)₂ (Zn(AC)₂), NaOH, PEG as precursors at room temperature. The characteristic luminescence spectra for f–f transitions of Tb³⁺, Eu³⁺, Dy³⁺ were observed. It is worthy to point out that ZnO is the excellent host for lanthanum ions by the assembly of PEG matrices.

Keywords: Optical properties; Luminescence; Phosphors; Organic–inorganic hybrids

Modulation grating achieved by two interfered femtosecond laser pulses on the surface of the silica glass by Zhongyi Guo; Shiliang Qu; Lingling Ran; Shutian Liu (pp. 8581-8583).

Modulation grating has been achieved by two interfered femtosecond laser pulses on the surface of the silica glass. The modulation grating formed at the middle of each bulge of the common grating and was attributed to the higher-order modulation arising from second-harmonic generation (SHG) of the femtosecond laser pulse incident to the surface of silica glass. The periods and depths of the fundamental grating and the modulation grating have been observed by using an atomic force microscopy (AFM). Experimental results show that the average depth of the modulation grating is nearly a half of the depth of the fundamental grating.

Keywords: PACS; 42.79.Dj; 52.38.Mf; 82.50.Pt; 42.65.KyFemtosecond laser pulse; Common grating; Modulation grating; SHG

Temperature dependent energy-dispersive X-ray diffraction and magnetic study of Fe/Al interface by R. Brajpuriya; S. Tripathi; A. Sharma; S.M. Chaudhari; D.M. Phase; Ajay Gupta; T. Shripathi; W. Leitenberger; U. Pietsch; N. Laxmi (pp. 8584-8587).

In situ temperature dependent energy-dispersive structural and magnetic study of electron beam evaporated Fe/Al multilayer sample (MLS) has been investigated. The structural studies show the formation of an intermixed FeAl transition layer of a few nanometers thick at the interface during deposition, which on annealing at 300°C transforms to B2FeAl intermetallic phase. Magnetization decreases with increase in temperature and drops to minimum above 300°C due to increase in anti-ferromagnetic interlayer coupling and formation of nonmagnetic FeAl phase at the interface. The Curie temperature ( T_c) is found to be 288°C and is much less than that of bulk bcc Fe.

Keywords: Fe/Al; Soft magnetic multilayers; Phase evolution; GIXRD

Electrochemically deposited photoactive CdIn₂Se₄ thin films: Structural and optical studies by Ju-Hyun Ahn; Gangri Cai; Rajaram S. Mane; V.V. Todkar; Arif V. Shaikh; Hoeil Chung; Moon-Young Yoon; Sung-Hwan Han (pp. 8588-8591).

Electrochemical synthesis of photoactive cadmium–indium–selenide (CdIn₂Se₄) thin films at ambient temperature was reported. The nanocrystalline nature and 1:2:4 elemental chemical stoichiometric ratio for Cd, In and Se were obtained from the X-ray diffraction and energy dispersive X-ray analysis, respectively. Irregular shaped islands of about 400–500nm in sizes composed of large number of small (∼30–40nm) spherical grains were confirmed from the atomic force microscopy and the scanning electron microscopy images. The photoelectrochemical measurement of CdIn₂Se₄ film electrode in presence of 1M polysulphide electrolyte revealed 0.42% photoelectrochemical device conversion efficiency, under the light illumination intensity of 80mW/cm².

Keywords: Electrochemical synthesis; CdIn; ₂; Se; ₄; thin films; XRD; SEM; AFM; Photoelectrochemical cell

Spinel LiMn₂O₄ active material with high capacity retention by Xifei Li; Youlong Xu (pp. 8592-8596).

Heating the mixture of LiMn₂O₄ and NiO at 650°C was employed to enhance the cyclability of spinel LiMn₂O₄. The results of scanning electron microscopy (SEM), X-ray diffraction (XRD) and Fourier transform infrared (FT-IR) spectroscopy analyses implied that a LiNi_xMn2−_xO₄ solid solution was formed on the surface of LiMn₂O₄ particles. And charge–discharge tests showed that the enhancement of the capacity retention of modified LiMn₂O₄ is significant, maintained 97.2% of the maximum capacity after 100 cycles at charge and discharge rate of C/2, while the pure one only 75.2%. The modified LiMn₂O₄ also results in a distinct improvement in rate capability, even at the rate of 12 C. The improvement of electrochemical cycling stability is greatly attributed to the suppression of Jahn–Teller distortion at the surface of spinel LiMn₂O₄ particles.

Keywords: PACS; 71.20.Be (transition metals and alloys)Solid solution; Modified LiMn; ₂; O; ₄; Capacity retention; Rate capability

Investigation of electrical properties of organic 4-tricyanovinyl- N, N-diethylaniline thin film by M.M. El-Nahass; H.M. Zeyada; K.F. Abd-El-Rahman; A.A.A. Darwish (pp. 8597-8601).

Thin films of 4-tricyanovinyl- N, N-diethylaniline (TCVA) with different thickness were prepared using thermal evaporation technique. A relative permittivity, ɛ_r, of 3.04 was estimated from the dependence of capacitance on film thickness. The current density–voltage ( J– V) characteristics of TCVA thin films have been investigated at different temperatures. At low-voltage region, the current conduction in the Au/TCVA/Au sandwich structures obeys Ohm's law. At the higher-voltage regions, the charge transport phenomenon appears to be space-charge-limited current (SCLC) dominated by an exponential distribution of traps with total trap concentration of 1.21×10²²m⁻³. In addition, various electrical parameters were determined.

Keywords: PACS; 73.40.Sx; 73.61.Ph; 81.15.Ef; 85.30.FgOrganic thin films; Electrical properties; SCLC

Scaling of submonolayer island growth with reversible adatom exchange in surfactant-mediated epitaxy by Daimu Wang; Zhuping Wang; Hui Zhu (pp. 8602-8606).

Surfactant-mediated epitaxial growth is studied with a realistic model, which includes three main kinetic processes: diffusion of adatoms on the surfactant terrace, exchange of adatoms with their underneath surfactant atoms, and reexchange in which an exchanged adatom resurfaces to the top of the surfactant layer. The scaling behavior of nucleus density and island size distributions in the initial stage of growth is investigated by using kinetic Monte Carlo simulations. The results show that the temperature dependence of nucleus density and island size distributions governed by the reexchanging-controlled nucleation at high temperatures exhibits similar scaling behavior to that obtained by the standard diffusion-mediated nucleation at low temperatures. However, at intermediate temperatures, the exchanging-controlled nucleation leads to an increase of nucleus density with temperature, while the island size distribution scales to a monotonically decreasing function, showing nonstandard scaling behavior.

Keywords: Monte Carlo simulation; Epitaxy; Growth; Surface diffusion; Nucleation

Anatase TiO₂ films based CO gas sensor: Film thickness, substrate and temperature effects by Ibrahim A. Al-Homoudi; J.S. Thakur; R. Naik; G.W. Auner; G. Newaz (pp. 8607-8614).

Electrical response of anatase TiO₂ films is discussed for different concentrations of CO gas (20–100ppm) in a nitrogen gas ambient. We investigated temperature (100–300°C) and film thickness (100–1000nm) effects for films deposited on glass, sapphire (0001) and, Si(100) substrates. In general, there is a drop in resistance of the device when exposed to CO gas. Films deposited on sapphire showed a larger decrease in the resistance at 300°C compared to those deposited on glass and silicon substrates. However, films grown on glass and silicon substrates showed a larger decrease in the resistance values for temperature around 200°C when CO (ppm) values are greater than 40. The change in resistance of the films varies as square root of the CO gas concentration at 200°C for films deposited on all the three substrates. In general, the decrease in resistance for thicker films is large compared to thinner ones, indicating participation of the bulk in the detection of CO gas. In the presence of O₂, film loses its sensitivity to CO gas when the concentration level of O₂ approaches 1800ppm.

Keywords: Anatase; Titanium oxide; Thin film; Carbon monoxide; Sputtering

Effect of the Pd–Au thin film thickness uniformity on the performance of an optical fiber hydrogen sensor by Donato Luna-Moreno; David Monzón-Hernández (pp. 8615-8619).

Thin alloy film of Pd and Au, formed by simultaneous electron-beam and thermal evaporation techniques, respectively, is used in the design of an optical fiber hydrogen sensor. The sensor consists of a multimode fiber (MMF) in which a short section of single mode fiber (SMF), coated with the Pd–Au thin film, is inserted. Due to core diameter mismatch, the SMF cladding guides light, allowing the interaction between the sensing layer and the guided light. When the sensor is exposed to hydrogen, the Pd–Au layer refractive index diminishes and causes attenuation changes on the transmitted light. Several samples with different layer thickness uniformity were fabricated and tested in a very simple experimental set-up. We have observed that the sensor signal change is dependant on layer thickness uniformity, since the effective interaction length between the evanescent field and the sensing layer is increased. By contrast, such uniformity practically has no influence on the time response of the sensor. The resulting Pd–Au film can detect 4% hydrogen with a response time of 15s.

Keywords: PACS; 42.81.Pa; 82.45.MpOptical fiber sensors; Hydrogen sensors; Evanescent wave absorption; Core diameter mismatch; Thin film coating

Atomistic simulation of the self-diffusion in Fe (111) surface by Yan-Ni Wen; Jian-Min Zhang; Ke-Wei Xu (pp. 8620-8625).

The formation energies, the intra- and inter-layer self-diffusion activation energies of a single vacancy in Fe (111) surface have been investigated with the modified analytical embedded-atom method (MAEAM). The results show that the effect of the surface is down to the sixth layer for the formation and intra-layer migration of the vacancy. It is easier for a vacancy to form and to migrate in intra-layer in the first (especially), the second and the third layer. For inter-layer migration, a single vacancy in each of the first six layers is favorable to migrate to the upper layers. On the contrary, a single vacancy in the seventh, the eighth and the ninth layers is favorable to migrate to the lower layers.

Keywords: Fe; Vacancy; Self-diffusion; MAEAM

Corrosion behavior of X-70 pipe steel in near-neutral pH solution by L. Niu; Y.F. Cheng (pp. 8626-8631).

The mechanism of near-neutral pH stress corrosion cracking (SCC) of natural gas pipelines has not been well-established since the first accident was found in the 1980s. In particular, the role of hydrogen in near-neutral pH SCC has remained unknown. In this work, cyclic voltammetry was used to comprehensively investigate the fundamentals of the electrochemical corrosion reactions occurring at the steel/solution interface in diluted, 5% CO₂/N₂-purged, near-neutral pH bicarbonate solutions. It is shown that there is no stable oxide film formed on the steel surface in near-neutral pH solution. The dissolution-based cracking mechanism does not apply for near-neutral pH SCC of pipelines. The formation of a metastable Fe(OH)₂ deposit layer shows a catalytic activity on hydrogen evolution reaction, indicating that a significant amount of hydrogen could be generated under near-neutral pH condition. The presence of corrosive anions in the soil electrolyte enhances both the anodic polarization of the steel and the cathodic hydrogen evolution reaction, resulting in an increased hydrogen evolution rate. The introduction of oxygen could form a stable oxide film on the surface of steel, resulting in the loss of the surface catalytic effect on hydrogen evolution reaction. Thus, a hydrogen-based mechanism does not apply for SCC in the presence of oxygen.

Keywords: Corrosion; Hydrogen evolution; X-70 pipeline steel; Near-neutral pH stress corrosion cracking; Cyclic voltammetry

Influence of experimental parameters on physical properties of porous silicon and oxidized porous silicon layers by J. Charrier; V. Alaiwan; P. Pirasteh; A. Najar; M. Gadonna (pp. 8632-8636).

This paper reports physical properties of porous silicon and oxidized porous silicon, manufactured by anodisation from heavily p-type doped silicon wafers as a function of experimental parameters. The growth rate and refractive index of the layers were studied at different applied current densities and glycerol concentrations in electrolyte. When the current density varied from 5 to 100mA/cm², the refractive index was between 1.2 and 2.4 which corresponded to a porosity range from 42 to 85%. After oxidation, the porosity decreased and was between 2 and 45% for a refractive index range from 1.22 to 1.46. The thermal processing also induced an increase in thickness which was dependent on the initial porosity. This increase in thickness was more important for the lowest porosities. Lastly, the roughness of the porous layer/silicon substrate interface was studied at different applied current densities and glycerol concentrations in solution. Roughness decreased when the current density or glycerol concentration increased. Moreover, roughness was also reduced by thermal oxidation.

Keywords: Porous silicon; Thermal oxidation; Composition of electrolyte; Growth rate; Porosity; Refractive index; Roughness

Study of surface treatment processes for improvement in the wettability of silicon-based materials used in high aspect ratio through-via copper electroplating by Pradeep Dixit; Xiaofeng Chen; Jianmin Miao; Sheeja Divakaran; Robert Preisser (pp. 8637-8646).

We report the improvements in wetting characteristics of silicon-based materials with copper electrolyte by various surface treatments to achieve uniform and void free copper deposition in high aspect ratio through-via electroplating. The contact angles of samples such as native silicon, thermally oxidized silicon, silicon nitride, deep reactive ion etched silicon etc, with copper electrolyte, were measured before and after the surface treatments. The wetting of copper electrolyte with silicon nitride coated silicon samples was found to be more than that with thermally oxidized samples. Due to its better wettability, silicon nitride was later used as an insulating layer instead of commonly used silicon oxide in the electroplating experiments. After the SC1 wet surface treatment, the contact angles of all the samples were found to be significantly lower, thus making the surface more suitable for electroplating applications. X-ray photoelectron spectroscopy results verified the presence of polar functional groups on the samples surface, which has helped to improve wetting with copper electrolyte. The conclusions drawn by the experimental results were employed in the high aspect ratio through-via copper electroplating; and void free copper interconnects, having aspect ratio as high as 20, were fabricated.

Keywords: PACS; 81.15.Pq; 81.65.-b; 68.08.BcThrough-wafer electroplating; Contact angle; Surface treatment; Deep reactive ion etching; Wettability

Effects of hydrogen plasma annealing on the luminescence from a-Si:H/SiO₂ and nc-Si/SiO₂ multilayers by Yunjun Rui; Deyuan Chen; Jun Xu; Wei Li; Zhanhong Cen; Xinfan Huang; Kunji Chen (pp. 8647-8651).

Effects of post-hydrogen plasma annealing (HPA) on a-Si:H/SiO₂ and nc-Si/SiO₂ multilayers have been investigated and compared. It is found that photoluminescence (PL) from hydrogen-passivated samples was improved due to the reduction of non-radiative recombination defects. Some interesting difference is that during HPA, atomic hydrogen can directly passivate defects of a-Si:H/SiO₂, which results in the reappearance of luminescence band at 760nm, while for nc-Si/SiO₂, hydrogen passivation requires additional thermal annealing after nc-Si/SiO₂ multilayer was treated by HPA. It is indicated that higher atomic mobility is needed to passivate defects at nc-Si/SiO₂ interface compared with a-Si:H/SiO₂ interface.

Keywords: PACS; 81.65.Rv; 81.15.Gh; 78.67.PtNanostructures; Optical properties; Plasma annealing

Study of the effects of an adatom Sn on the Cu surface electromigration using a first principles method by Chun Yu; Junyan Liu; Hao Lu; Junmei Chen (pp. 8652-8656).

It is well known that the doped Sn can effectively suppress the electromigration of Cu thin-film interconnects in integrated circuits. In this paper, the first-principles method was introduced to investigate the suppression mechanism. All the calculations were performed on Sn or Cu adatom/Cu (001), (110) and (111) surface systems within local density approximation. As a Sn adatom was attached to the Cu surface, stable CuSn bonds were formed. The energy calculations show that the Sn/Cu system was more stable than Cu/Cu system with the same structure. Analysis of density of states shows that the nearest neighbor Cu atoms were stabilized by CuSn bond relative to the Cu atoms which are far away from the adatom. The diffusion barrier energies were calculated and found to be consistent with the experimental results. Also, bond population analysis shows that stronger covalent bonds were formed between Sn and Cu relative to that between Cu and Cu. All the results indicate that the CuSn bond plays an important role in the suppression of Cu electromigration.

Keywords: Cu interconnect; Sn; Surface electromigration; First principles; Bond Population

Formation of silicon nanodots from dysprosium-doped amorphous SiC_xO_y films grown by hot-filament assisted chemical vapor deposition of CH₃SiH₃ and Dy(DPM)₃ gas jets by Yoshifumi Ikoma; Takayoshi Masaki; Shinji Kawai; Teruaki Motooka (pp. 8657-8660).

We report on Si nanodot formation by chemical vapor deposition (CVD) of ultrathin films and following oxidation. The film growth was carried out by hot-filament assisted CVD of CH₃SiH₃ and Dy(DPM)₃ gas jets at the substrate temperature of 600°C. The transmission electron microscopy observation and X-ray photoelectron spectroscopy analysis indicated that ∼35nm Dy-doped amorphous silicon oxycarbide (SiC_xO_y) films were grown on Si(100). The Dy concentration was 10–20% throughout the film. By further oxidation at 860°C, the smooth amorphous film was changed to a rough structure composed of crystalline Si nanodots surrounded by heavily Dy-doped SiO₂.

Keywords: PACS; 68.55.−a; 68.55.Jk; 81.07.−b; 81.15.Gh; 81.65.Mq; 85.40.RyChemical vapor deposition; Oxidation; Nanodots; Cross-sectional transmission electron microscopy; X-ray photoelectron spectroscopy

Mg²⁺ substitutions in ZnO–Al₂O₃ thin films and its effect on the optical absorption spectra of the nanocomposite by Soumen Das; Subhadra Chaudhuri (pp. 8661-8668).

ZnO–Al₂O₃ nanocomposite thin films were prepared by sol–gel technique. The room temperature synthesis was mainly based on the successful peptization of boehmite (AlO(OH)) and Al(OH)₃ compounds, so as to use it as matrix to confine ZnO nanoparticles. The relative molar concentrations of xZnO to (1− x) Al₂O₃ were varied as x=0.1, 0.2 and 0.5. The optical absorption spectra of the thin films showed intense UV absorption peaks with long tails of variable absorption in the visible region of the spectra. The ZnO–Al₂O₃ nanocomposites thin films were doped with MgO by varying its molar concentrations as y=0.05, 0.75, 0.1, 0.125, 0.15 and 0.2 with respect to the ZnO present in the composite. The MgO doped thin films showed suppression of the intense absorption peaks that was previously attained for undoped samples. The disappearance of the absorption peaks was analyzed in terms of the crystalline features and lattice defects in the nanocomposite system. The bulk absorption edge, which is reportedly found at 3.37eV, was shifted to 5.44eV (for y=0.05), 5.63eV (for y=0.075) and maximum to 5.77eV (for y=0.1). In contrast, beyond the concentration, y=0.1 the absorption edges were moved to 5.67eV (for y=0.125), 5.61eV (for y=0.15) and to 5.49eV (for y=0.2). This trend was explained in terms of the Burstein–Moss shift of the absorption edges.

Keywords: PACS; 81.20.Fw; 78.66.Hf; 61.72.Vv; 78.66.−wSol–gel; Nanocomposite; Thin films; Optical absorption

Oxygen plasma functionalization of poly( p-phenilene sulphide) by Uroš Cvelbar; Miran Mozetič; Ita Junkar; Alenka Vesel; Janez Kovač; Aleksander Drenik; Tjaša Vrlinič; Nina Hauptman; Marta Klanjšek-Gunde; Boštjan Markoli; Nikša Krstulović; Slobodan Milošević; Freddy Gaboriau; Thierry Belmonte (pp. 8669-8673).

Surface effects during plasma activation of poly( p-phenilene sulphide)—PPS have been studied. Samples that were exposed to weakly ionized highly dissociated oxygen plasma created an inductively coupled radiofrequency discharge with the power of 100W. The electron density and temperature were measured with a double Langmuir probe and were 4×10¹⁵m⁻³ and 3eV, respectively, while the neutral atom density was measured with a fiber optics catalytic probe and was 4×10²¹m⁻³. The surface tension was determined by measuring the contact angle of deionized water, while the appearance of surface functional groups was detected by XPS. The surface tension of untreated PPS was 7×10⁻³N/m or/and increased to 7×10⁻²N/m in few seconds of plasma treatment. It remained fairly constant for longer plasma treatments. The XPS survey spectrum showed little oxygen on untreated samples, but its concentration increased to about 20at.% in few seconds. Detailed high resolution XPS C 1s peak showed that the carbon was left fairly stable during plasma treatment. The main functional groups formed were rather sulphate in sulphite groups, as determined from high resolution S 2p peak. Namely, a strong transition from sulphide to sulphate state of sulfur was observed. The spontaneous deactivation of the polymer surface was measured as well. The deactivation was fairly logarithmic with the characteristic decay time of several hours.

Keywords: PACS; 81.65.−b; 81.65.CfOxygen plasma; Polymer; Functionalization; PPS

Bacterial adhesion on ion-implanted stainless steel surfaces by Q. Zhao; Y. Liu; C. Wang; S. Wang; N. Peng; C. Jeynes (pp. 8674-8681).

Stainless steel disks were implanted with N⁺, O⁺ and SiF₃⁺, respectively at the Surrey Ion Beam Centre. The surface properties of the implanted surfaces were analyzed, including surface chemical composition, surface topography, surface roughness and surface free energy. Bacterial adhesion of Pseudomonas aeruginosa, Staphylococcus epidermidis and Staphylococcus aureus, which frequently cause medical device-associated infections was evaluated under static condition and laminar flow condition. The effect of contact time, growth media and surface properties of the ion-implanted steels on bacterial adhesion was investigated. The experimental results showed that SiF₃⁺-implanted stainless steel performed much better than N⁺-implanted steel, O⁺-implanted steel and untreated stainless steel control on reducing bacterial attachment under identical experimental conditions.

Keywords: Ion implantation; Surface properties; Bacterial adhesion

Oxidation temperature dependent optical properties of bismuth oxide thin films: Effect of vapour chopping and air exposure by R.B. Patil; R.K. Puri; Vijaya Puri (pp. 8682-8688).

The optical properties of vapour chopped and nonchopped bismuth oxide thin films of two thicknesses 1500Å and 2000Å have been studied. The films were prepared by thermal oxidation in air; of vacuum evaporated vapour chopped and nonchopped bismuth thin films. As revealed by XRD studies, multiphase and polycrystalline bismuth oxide thin films were obtained. The refractive index was found to increase with the thickness and exposure to air for 40 days. The vapour chopped films showed higher refractive index, band gap and lower grain size than those of nonchopped films. The films showed high transmittance in the visible spectrum. The ageing effect on the vapour chopped films was found low.

Keywords: PACS; 78.20.CiAir ageing; Vapour chopping; Optical properties; Thermal oxidation; Thin films

Effect of swift (∼100MeV) heavy ion irradiation on surface morphology and electronic transport in Fe film on Si substrate by J.K. Tripathi; P.C. Srivastava (pp. 8689-8694).

Fe film (∼50nm) have been deposited on pSi substrate by electron beam evaporation technique. The bilayers have been irradiated by 100MeV Fe⁷⁺ ions having fluences of 1×10¹³, 1×10¹⁴ and 5×10¹⁴ionscm⁻². SEM study of the unirradiated devices show surface modifications having a annular structures. From XRD study of the bilayer, it is observed that grain size has reduced from 70 to 25nm after the irradiation for a fluence of 1×10¹⁴ionscm⁻². Moreover electronic transport data of the bilayer show practically no effect on the current flow for a fluence of 1×10¹³ionscm⁻² irradiation whereas for 1×10¹⁴ionscm⁻² fluence, there is very significant change in current flow (by two orders in magnitude) across the bilayer. However, for a higher fluence of irradiation 5×10¹⁴ionscm⁻², the bilayer becomes highly resistive. It has been found from the above observations that the fluence of 1×10¹⁴ionscm⁻² of swift heavy ion irradiation is a optimum fluence.

Keywords: Swift heavy ion irradiation effect; Granular structure; Surface morphology

The analysis of structural and electronic environments of silicon network in HWCVD deposited a-SiC:H films by Bibhu P. Swain (pp. 8695-8698).

Hydrogenated amorphous silicon carbon alloys (a-SiC:H) films were deposited by hot wire chemical vapour deposition (HWCVD) using SiH₄ and C₂H₂ as precursor gases. a-SiC:H films were characterized by Fourier Transform Infrared (FTIR) spectroscopy, Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). Solid-state plasmon of Si network shifts from 19.2 to 20.5eV by varying C₂H₂ flow rate from 2 to 10sccm. Incorporation of carbon content changes the valence band structure and s orbital is more dominant than sp and p orbital with carbon incorporation.

Keywords: HWCVD; Plasmon energy; Valence band; Raman and XPS

Oxidation and reduction of thin Ru films by gas plasma by Y. Iwasaki; A. Izumi; H. Tsurumaki; A. Namiki; H. Oizumi; I. Nishiyama (pp. 8699-8704).

The oxidation and reduction of Ru thin films grown on a Si(1 0 0) surface were studied by X-ray photoemission spectroscopy (XPS). Ru thin films were oxidized with O₂ plasma generated by an rf discharge, and their XPS spectra were measured. The spectra were decomposed into several components for Ru suboxides attributable to different stages of oxidation. After sufficient exposure to oxygen, a stoichiometric rutile RuO₂ layer was found to have formed near the surface. Thermal annealing at 500 K resulted in a thicker RuO₂ layer. Experiments demonstrated that the Ru oxide layer can be removed by H(D) atoms via the desorption of water molecules.

Keywords: Ru; Oxidation; Reduction; Surface reaction; Plasma treatment

Preparation and performance of polysulfone-sulfonated poly(ether ether ketone) blend ultrafiltration membranes. Part I by G. Arthanareeswaran; D. Mohan; M. Raajenthiren (pp. 8705-8712).

Ultrafiltration membranes were prepared from blends with polysulfone (PSf) and sulfonated poly(ether ether ketone) (SPEEK) by phase inversion technique. The blend membranes were prepared with polymer composition from 0 to15wt%. Sulfonated poly(ether ether ketone) was used to improve the performance and permeability of blended membranes. The effects of polymer composition on compaction, pure water flux, water content, and membrane hydraulic resistance were studied. The membranes were also subjected to the determination of pore statistics and molecular weight cut-off (MWCO) determination studies by using different molecular weight of proteins. The porosity, pore size of the membranes increased with increasing concentrations of SPEEK in the casting solution. Similarly, the MWCOs of the blend membranes ranged from 20 to 45kDa, depending on the various polymer blend compositions. The pure water flux of the PSf/SPEEK blend membranes increases from 16.7 to 61.5lm⁻²h, when the concentration of SPEEK increased from 0 to 15wt%. Scanning electron microscope (SEM) results qualitative evidence for the trends observed for the pore statistics and MWCO studies.

Keywords: Polysulfone; Phase inversion; Ultrafiltration; Sulfonated poly(ether ether ketone); Pore statistics

X-ray photoelectron spectroscopic studies on phase identification and quantification of nickel aluminides by Naofumi Ohtsu; Masaoki Oku; Toetsu Shishido; Kazuaki Wagatsuma (pp. 8713-8717).

Core-level XPS spectra for clean surfaces of Ni₃Al, NiAl, and NiAl₃ alloys were studied. The clean surfaces were obtained by fracturing in the ultra-high vacuum chamber. The positive chemical shifts of Ni 2p_3/2 peak for NiAl and NiAl₃ from Ni metal were 0.2 and 1.0eV, respectively. The negative shift for Al 2p peak and the positive shift for Ni 3p peaks increased with the decreasing concentration of the corresponding elements. The peak position of the bulk plasmon loss peak for Al 2s peak shifted toward higher energy side, and further, the intensity ratio decreased with the decrease in aluminum concentration. Both the peak intensity ratios of Al 2p to Ni 3p determined by factor analysis and convenient separation are proportional to the atomic ratio of aluminum to nickel. The results indicate that the intensity ratio of Al 2p to Ni 3p determined by these two methods can be applied to the quantification for the surface of the nickel–aluminum alloys.

Keywords: Nickel aluminides; Core-level XPS spectra; Fracturing; Chemical shift; Quantification

Effect of O₂ gas partial pressure on structures and dielectric characteristics of rf sputtered ZrO₂ thin films by C.Y. Ma; F. Lapostolle; P. Briois; Q.Y. Zhang (pp. 8718-8724).

Amorphous and polycrystalline zirconium oxide thin films have been deposited by reactive rf magnetron sputtering in a mixed argon/oxygen or pure oxygen atmosphere with no intentional heating of the substrate. The films were characterized by high-resolution transmission electron microscopy (HR-TEM), atomic force microscopy (AFM), spectroscopic ellipsometry (SE), and capacitance versus voltage ( C– V) measurements to investigate the variation of structure, surface morphology, thickness of SiO₂-like interfacial layer as well as dielectric characteristics with different oxygen partial pressures. The films deposited at low oxygen partial pressures (less than 15%) are amorphous and dense with a smooth surface. In contrast, the films prepared at an oxygen partial pressure higher than 73% are crystallized with the microstructure changing from the mixture of monoclinic and tetragonal phases to a single monoclinic structure. The film structural transition is believed to be consequences of decrease in the oxygen vacancy concentration in the film and of increase of the energetically neutral particles in the plasma due to an increased oxygen partial pressure. SE measurements showed that significant interfacial SiO₂ growth has taken place above approximately 51%. The best C– V results in terms of relative dielectric constant values are obtained for thin films prepared at an oxygen partial pressure of 15%.

Keywords: Rf magnetron sputtering; ZrO; ₂; films; Structure; Interfacial layer; Dielectric constant

Dependence of electron and positron backscattering coefficients on Al film thickness by A. Bentabet; N. Bouarissa (pp. 8725-8728).

The backscattering coefficient of 1–4keV electron and positron beams normally incident impinging on Al thin film targets is stochastically modeled within a Monte Carlo frame work. The aim of the present paper is to study the behavior of the backscattering coefficient as a function of the Al film thickness. To the authors’ knowledge, no theoretical or experimental work on the dependence of the positron backscattering coefficient on film thickness targets has been reported so far. It is found that the backscattering coefficient for both electron and positron beams presents different behaviors when the Al film thickness belongs to the nano-scale. Beyond this scale, the behavior becomes qualitatively similar.

Keywords: PACS; 02.70.Uu; 68.37.−d; 68.37.NqElectron scattering; Positron scattering; Thin films; Monte Carlo simulation

Spatial dependence of the local field enhancement in dielectric shell coated silver nanospheres by Jian Zhu (pp. 8729-8733).

The dependence of the local field factor around dielectric shell coated silver nanospheres was investigated by theoretical calculation as a function of the spatial distance. The local field factors in the dielectric shell are sensitive to the distance from particle center and shell thickness. When the shell dielectric constant is greater than that of surrounding medium, the maximum of local field factor at inner surface of the shell red shift and increases nonlinearly with increasing the shell thickness. On the contrary, when shell dielectric constant is less than that of surrounding medium, increasing the shell thickness leads the maximum of local field factor at inner surface blue shifts and decreases nonlinearly. However, with increasing the shell thickness, the maximum of local field factor at exterior surface of the shell always decrease nonlinearly. Furthermore, with increasing shell thickness, all these variations get gentle approach to a constant value when the shell thickness is two times of the core radius. When the core and shell diameter have fixed values, the local field factors in dielectric shell decrease with increasing the distance from particle center, but the peak position is not sensitive to the distance.

Keywords: PACS; 78.67.Bf; 73.20.Mf; 36.40.Gk; 78.66.Bz; 73.20.MfSilver nanosphere; Local field enhancement; Dielectric shell; Quasi-static theory

Electrochemical and molecular simulation studies on the corrosion inhibition of 5,10,15,20-tetraphenylporphyrin adlayers on iron surface by Yuanyuan Feng; Shenhao Chen; Wenjuan Guo; Guangzeng Liu; Hongfang Ma; Ling Wu (pp. 8734-8742).

5,10,15,20-Tetraphenylporphyrin (TPP) was synthesized and self-assembled on iron surface to form adlayers. Some surface analysis techniques such as XPS, FT-IR and SEM were performed to characterize the adlayers. The corrosion inhibition ability was investigated by using the technique of electrochemical impedance spectroscopy (EIS) and polarization curves in 0.5M H₂SO₄. Results showed that the presence of the porphyrin adlayers was able to protect iron from corrosion effectively and longer immersion time would lead to better inhibition performance. In addition, molecular simulation studies were applied to optimize the adsorption structures of TPP molecules on iron surface. Calculated results indicated that the middle macrocycle of the TPP molecules assumed a nearly flat orientation with respect to the iron surface and the four centrosymmetric benzene rings were tilted by 44.8° and 58.8° because of the steric hindrance effect.

Keywords: Adlayers; Tetraphenylporphyrin; XPS; FT-IR; EIS; Molecular simulation

Etching of SiC by energetic F₂: Molecular dynamics simulation by F. Gou; M.C. Liang; Z. Chen; Qiu Qian (pp. 8743-8748).

Molecular dynamics (MD) simulations were performed to investigate F₂ continuously bombarding silicon carbide (SiC) surfaces with energies in the range of 50–200eV at normal incidence and room temperature. The Tersoff–Brenner form potential was used. The simulation results show that the uptake of F atoms, the etch yields of C and Si from the initial substrate, and the surface structure profile are sensitive to the incident energy. Like occurrence in Si etching, steady-state etching is observed and an F-containing reaction layer is formed through which Si and C atoms are removed. A carbon-rich surface layer after bombarding by F₂ is observed which is in good agreement with experiments. In the reaction layer, SiF in SiF₂ species are dominant; with increasing incident energy, the total fraction of SiF and SiF₂ increases, while the amount of SiF₃ and SiF₄ decreases. Finally, etching mechanisms are discussed.

Keywords: PACS; 52.65.Yy; 81.65.Cf; 52.77.DqMolecular dynamics methods; Surface; Silicon carbide; Plasma etching

Effects of gas composition on the growth of multi-walled carbon nanotube by Te-Hua Fang; Win-Jin Chang; Deng-Maw Lu; Wen-Chieh Lien (pp. 8749-8753).

This paper studies the effects of different gas compositions on the growth of multi-walled carbon nanotube (MWCNT) films by using an electron cyclotron resonance chemical vapor deposition (ECR-CVD) method. The Raman spectrum was employed to explore the composition of the MWCNT films grown under different mixtures of C₃H₈ and H₂. The results showed that the optimum relative intensity ratio of the D band to G band (i.e., I_D/ I_G) is 2 for the cases considered in this study. In addition, the morphology and microstructure of the MWCNTs were examined by field emission scanning electron microscopy (FE-SEM) and field emission gun transmission electron microscopy (FEG-TEM). Furthermore, atomic force microscopy (AFM) and scanning thermal microscopy (SThM) were used to study the surface topography and thermal properties of the MWCNTs.

Keywords: Carbon nanotubes; Gas composition; Material properties; ECR-CVD

Preparation of alumina/silica core-shell abrasives and their CMP behavior by Hong Lei; Pengzhen Zhang (pp. 8754-8761).

Abrasive is one of key influencing factors on the surface quality during the chemical mechanic polishing (CMP). α-Alumina particles, as a kind of widely used abrasive in CMP slurries, often cause to surface defects because of its high hardness. In the present paper, a series of novel alumina/silica core-shell abrasives in slurries were described. The CMP performances of the alumina/silica core-shell abrasives on hard disk substrate were investigated by using a SPEEDFAM-16B-4M CMP equipment. Experimental results indicate that the CMP performances are strong dependent on the coated SiO₂ content of the alumina/silica composite abrasives. Slurries containing the alumina/silica composite abrasives exhibited lower surface roughness and waviness as well as lower topographical variations and less scratch than that containing pure alumina abrasive under the same testing conditions.

Keywords: CMP; Hard disk substrate; Alumina/silica core-shell abrasives; Planarization

Heterogeneity of activated carbons in adsorption of aniline from aqueous solutions by P. Podkościelny; K. László (pp. 8762-8771).

The heterogeneity of activated carbons (ACs) prepared from different precursors is investigated on the basis of adsorption isotherms of aniline from dilute aqueous solutions at various pH values. The APET carbon prepared from polyethyleneterephthalate (PET), as well as, commercial ACP carbon prepared from peat were used. Besides, to investigate the influence of carbon surface chemistry, the adsorption was studied on modified carbons based on ACP carbon. Its various oxygen surface groups were changed by both nitric acid and thermal treatments. The Dubinin–Astakhov (DA) equation and Langmuir–Freundlich (LF) one have been used to model the phenomenon of aniline adsorption from aqueous solutions on heterogeneous carbon surfaces. Adsorption-energy distribution (AED) functions have been calculated by using an algorithm based on a regularization method. Analysis of these functions for activated carbons studied provides important comparative information about their surface heterogeneity.

Keywords: PACS; 68.43.-hHeterogeneity; Porosity; Surface chemistry characterization; Adsorption from liquid phase; Aniline; Activated carbon

Characterization of Ti6Al4V implant surface treated by Nd:YAG laser and emery paper for orthopaedic applications by M.E. Khosroshahi; M. Mahmoodi; J. Tavakoli (pp. 8772-8781).

A more noble and biocompatible Ti alloy was achieved at fluence of 140Jcm⁻² where the implant indicated a higher degree of hardness (825HV), higher corrosion resistance (−0.21V) and highest hydrophilicity (i.e. θ_c=37°) compared with 70° of the control sample. These values corresponded to 58 and 39mNm⁻¹ of surface tension respectively. The laser treated samples at 140Jcm⁻² showed higher wettability characteristics than mechanically roughened surface. Cell growth and their spreading condition in a specific area were analyzed by SEM and Image J Program software. Clearly, more cells were attached (1.2×10⁵) to and spread (488μm²) over the surface at 140Jcm⁻² than in any other condition. Pathologically, the treated samples indicated no sign of infection.

Keywords: Cell adhesion; Titanium alloy; Nd:YAG laser; Wettability; Corrosion; Surface microhardness

Influence of deposition conditions on the microstructure of oxides thin films by Guanglei Tian; Shigang Wu; Kangying Shu; Laishun Qin; Jianda Shao (pp. 8782-8787).

Thin films of ZrO₂, HfO₂ and TiO₂ were deposited on kinds of substrates by electron beam evaporation (EB), ion assisted deposition (IAD) and dual ion beam sputtering (DIBS). Then some of them were annealed at different temperatures. X-ray diffraction (XRD) was applied to determine the crystalline phase and the grain size of these films, and the results revealed that their microstructures strongly depended on the deposition conditions such as substrate, deposition temperature, deposition method and annealing temperature. Theory of crystal growth and migratory diffusion were applied to explain the difference of crystalline structures between these thin films deposited and treated under various conditions.

Keywords: X-ray diffraction; Crystal structure; Nucleation; Oxides films

Influence of thermal treatment of low dielectric constant SiOC(H) films using MTES/O₂ deposited by PECVD by R. Navamathavan; Seung Hyun Kim; Yong Jun Jang; An Soo Jung; Chi Kyu Choi (pp. 8788-8793).

Low dielectric constant SiOC(H) films are deposited on p-type Si(100) substrates by plasma enhanced chemical vapor deposition (PECVD) using methyltriethoxysilane (MTES, C₇H₁₈O₃Si) and oxygen gas as precursors. The SiOC(H) films are deposited at room temperature, 100, 200, 300 and 400°C and then annealed at 100, 200, 300 and 400°C temperatures for 30min in vacuum. The influence of deposition temperature and annealing on SiOC(H) films are investigated. Film thickness and refractive index are measured by field emission scanning electron microscopy and ellipsometry, respectively. Chemical bonding characteristics of as-deposited and annealed films are investigated by Fourier transform infrared (FTIR) spectroscopy in the absorbance mode. As more carbon atoms are incorporated into the SiOC(H) films, both film density and refractive index are decreased due to nano pore structure of the film. In the SiOC(H) film, CH₃ group as an end group is introduced intoOSiO network, thereby reducing the density to decrease the dielectric constant thereof. The dielectric constant of SiOC(H) film is evaluated by C– V measurements using metal–insulator–semiconductor (MIS), Al/SiOC(H)/ p-Si structure and it is found to be as low as 2.2 for annealed samples deposited at 400°C.

Keywords: PACS; 77.55.+f; 77.22.-d; 81.15.Gh; 78.55.MbSiOC(; H) films; PECVD; Low-; k; dielectrics; MTES; FTIR

A spectroscopic study of uranium(VI) interaction with magnetite by S. El Aamrani; J. Giménez; M. Rovira; F. Seco; M. Grivé; J. Bruno; L. Duro; J. de Pablo (pp. 8794-8797).

The uranium sorbed onto commercial magnetite has been characterized by using two different spectroscopic techniques such as X-ray photoelectron spectroscopy (XPS), and extended X-ray absorption fine structure (EXAFS). Magnetite samples have been put in contact with uranium(VI) solutions in conditions in which a high uranium uptake is expected. After several days, the magnetite surface has been analysed by XPS and EXAFS. The XPS results obtained are not conclusive regarding the uranium oxidation state in the magnetite surface. On the other hand, the results obtained with the EXAFS technique show that the uranium–magnetite sample spectrum has characteristics from both the UO₂ and schoepite spectra, e.g. a relatively high coordination number of equatorial oxygens and two axial oxygens, respectively. These results would indicate that the uranium sorbed onto magnetite would be a mixture of uranium(IV) and uranium(VI).

Keywords: PACS; 82.65.+rUranium; Magnetite; Spent nuclear fuel; EXAFS; XPS

Fabrication and characterization of Fe³⁺-doped titania semiconductor electrodes with p–n homojunction devices by Leo Chau-Kuang Liau; Chu-Che Lin (pp. 8798-8801).

The nano-TiO₂ electrode with a p–n homojunction device was designed and fabricated by coating of the Fe³⁺-doped TiO₂ (p-type) film on top of the nano-TiO₂ (n-type) film. These films were prepared from synthesized sol–gel TiO₂ samples which were verified as anatase with nano-size particles. The semiconductor characteristics of the p-type and n-type films were demonstrated by current–voltage ( I– V) measurements. Results show that the rectifying curves of undoped TiO₂ and Fe³⁺-doped TiO₂ sample films were observed from the I– V data illustration for both the n-type and p-type films. In addition, the shapes of the rectifying curves were influenced by the fabrication conditions of the sample films, such as the doping concentration of the metal ions, and thermal treatments. Moreover, the p–n homojunction films heating at different temperatures were produced and analyzed by the I– V measurements. From the I– V data analysis, the rectifying current of this p–n junction diode has a 10mA order higher than the current of the n-type film. The p–n homojunction TiO₂ electrode demonstrated greater performance of electronic properties than the n-type TiO₂ electrode.

Keywords: TiO; ₂; electrode; p–n homojunction; I; –; V; measurement; Fe; ³⁺; -doped TiO; ₂

A frequency response study of thiophene adsorption in zeolite catalysts by Feifei Li; Lijuan Song; Linhai Duan; Xiuqi Li; Zhaolin Sun (pp. 8802-8809).

The frequency response (FR) technique has been applied to study adsorption processes of thiophene (TP) on NaY zeolite and CeY zeolite. The FR spectra of TP on NaY and CeY were recorded at temperatures between 335 and 473K and in the pressure range of 0.1–4.0Torr. On NaY and CeY, adsorption of thiophene (TP) in the supercage is found to be the rate-controlling step and diffusion of benzene in the supercage is the rate-controlling step, respectively. On NaY, the adsorption process by π-electronic interaction of TP and adsorption via pore-filling mechanism were caught. Adsorption by π-electronic interaction is not the main sorption process but its effect is significant. While on Ce³⁺Y, the adsorption processes relating to the π-complexation and the direct forming of SM bond were observed, the adsorption by forming π-complexation is the main process. The relaxation time of the strong sorption interaction coming from the FR spectrum is two orders magnitude shorter than that of the weak adsorption process and the number of sites available for adsorption of TP in each process is calculated. The value of relaxation time reflects the ability of different processes and concentration of adsorption site. Combining the FR spectra and other methods such as isotherms and Langmuir model, thoroughly understanding of the thiophene adsorption process in zeolites can be got.

Keywords: Frequency response; Thiophene; Benzene; Relaxation time; Adsorption process

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Applied Surface Science (v.253, #21)