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Applied Surface Science (v.250, #1-4)
Nanocrystals formation and fractal microstructural assessment in Au/Ge bilayer films upon annealing by Z.W. Chen; J.K.L. Lai; C.H. Shek; H.D. Chen (pp. 3-8).
Nanocrystals formation and fractal microstructural assessment in Au/Ge bilayer films upon annealing have been investigated by transmission electron microscopy and high-resolution transmission electron microscopy observations. Experimental results indicated that the microstructure of the metal Au film plays an important role in metal-induced crystallization for Au/Ge bilayer films upon annealing. Synchronously, the crystallization processes of amorphous Ge accompanied by the formation of Ge fractal clusters, which were composed of Ge nanocrystals. We found that the grain boundaries of polycrystalline Au film were the initial nucleation sites of Ge nanocrystals. High-resolution transmission electron microscopy observations showed successive nucleation of amorphous Ge at Au grain boundaries near fractal tips. The crystallization process was suggested to be diffusion controlled and a random successive nucleation and growth mechanism.
Keywords: PACS; 61.43.Hv; 68.55.−a; 81.05.GcNanocrystal; Fractal; Au/Ge bilayer films; HRTEM
Field emission from self-assembly structure of carbon-nanotube films by L.M. Sheng; M. Liu; P. Liu; Y. Wei; L. Liu; S.S. Fan (pp. 9-13).
Chemical vapor deposited (CVD) carbon nanotube (CNT) arrays were immersed in ethanol to make shrunk structures with separate nanotube “walls� for better field emission properties, such structures decreased the screening effects and reduced the turn-on electric field at 10μA/cm2 from 1.68 to 1.23V/μm. The field enhancement factor was calculated to increase by 23% according to Fowler–Nordheim (F–N) equation. The number of emission sites also increased and their distribution was more uniform.
Keywords: PACS; 79.70.+q; 85.45.Db; 81.65.−bField emission; Carbon nanotube; Ethanol treatment
Growth behavior of high k LaAlO3 films on Si by metalorganic chemical vapor deposition for alternative gate dielectric application by Qi-Yue Shao; Ai-Dong Li; Jin-Bo Cheng; Hui-Qin Ling; Di Wu; Zhi-Guo Liu; Yong-Jun Bao; Mu Wang; Nai-Ben Ming; Cathy Wang; Hong-Wei Zhou; Bich-Yen Nguyen (pp. 14-20).
LaAlO3 (LAO) is explored in this work to replace SiO2 as the gate dielectric material in metal–oxide–semiconductor field effect transistor. Amorphous LAO gate dielectric films were deposited on Si (001) substrates by low pressure metalorganic chemical vapor deposition using La(dpm)3 and Al(acac)3 sources. The effect of processing parameters such as deposition temperature and precursor vapor flux on growth, structure, morphology, and composition of LAO films has been investigated by various analytical methods deeply. The film growth mechanism on Si is reaction limiting instead of mass transport control. The reaction is thermally activated with activation energy of ∼37kJ/mol. In the initial growth stage, Al element is deficient due to higher nucleation barrier on Si. The LAO films show a smooth surface and good thermal stability and remain amorphous up to a high temperature of 850°C. The electrical properties of amorphous LAO ultrathin films on Si have also been evaluated, indicating LAO is suitable for high k gate dielectric applications.
Keywords: PACS; 82.33.Ya; 68.55.−a; 77.55.+f; 81.40.−zLaAlO; 3; film; MOCVD; Gate dielectric; Growth mechanism
Characterization of WO3:Ag films: ToF-SIMS studies of ammonia adsorption by C. Bittencourt; M.P. Felicissimo; A. Felten; L.A.O. Nunes; P. Ivanov; E. Llobet; J.-J. Pireaux; L. Houssiau (pp. 21-28).
In this work, the composition and morphology of WO3 films loaded with different levels of Ag, prepared by screen-printing onto Si substrates and annealed in air were investigated. The TEM micrography showed that the films are grain-like; the grain size increases with the increase of the Ag loading level. The Raman spectroscopy showed the formation of a AgWO3 bronze structure. XPS and ToF-SIMS results showed that while undergoing annealing, the Ag atoms migrate to the surface forming clusters. The molecular images obtained by ToF-SIMS showed that the NH3 binds preferentially at the surface of the Ag clusters. No preferential binding site was found for hydrocarbon contamination.
Keywords: ToF-SIMS; Transition metal oxides; Semiconductor
Study of strong interaction between Pt and TiO2 under oxidizing atmosphere by Min Zhang; Zhensheng Jin; Zhijun Zhang; Hongxin Dang (pp. 29-34).
The strong interaction between Pt and TiO2 under oxidizing atmosphere was studied by means of X-ray photoelectron spectroscopy (XPS) and Ar+ sputtering test. The results obtained show that under oxidizing atmosphere Pt0 atoms can thermally diffuse into TiO2 lattice and be oxidized to Pt2+ to substitute for Ti4+ or form the interstitial ions at 673K.
Keywords: Pt–TiO; 2; strong interaction; Ar ion sputtering; XPS
Surface roughness and color characteristics of wood treated with preservatives after accelerated weathering test by Ali Temiz; Umit C. Yildiz; Ismail Aydin; Morten Eikenes; Gry Alfredsen; Gürsel Çolakoglu (pp. 35-42).
Wood samples treated with ammonium copper quat (ACQ 1900 and ACQ 2200), chromated copper arsenate (CCA), Tanalith E 3491 and Wolmanit CX-8 have been studied in accelerated weathering experiments. The weathering experiment was performed by cycles of 2h UV-light irradiation followed by water spray for 18min. The changes on the surface of the weathered samples were characterized by roughness and color measurements on the samples with 0, 200, 400 and 600h of total weathering.The objective of this study was to investigate the changes created by weathering on impregnated wood with several different wood preservatives. This study was performed on the accelerated weathering test cycle, using UV irradiation and water spray in order to simulate natural weathering.Surface roughness and color measurement was used to investigate the changes after several intervals (0–200–400–600h) in artificial weathering of treated and untreated wood.
Keywords: Photodegradation; Surface roughness; Color changes; Pine; Alder; Copper-containing wood preservatives
On the barrier inhomogeneities of polyaniline/p-Si/Al structure at low temperature by Ş. Aydoğan; M. Sağlam; A. Türüt (pp. 43-49).
The current–voltage ( I– V) characteristics of Au/polyaniline(PANI)/p-Si/Al structures were determined at various temperatures in the range of 90–300K. The evaluation of the experimental I– V data reveals a decrease of the zero-bias barrier height (BH) and an increase of the ideality factor ( n) with decreasing temperature. It was shown that the occurrence of a Gaussian distribution of then BHs is responsible for the decrease of the apparent BH, increase of the ideality factor n due to barrier height imhomogeneities that prevail at the interface. A Φb0 versus 1/ T plot has been drawn for evidence of the Gaussian distribution of the barrier height, andΦ¯b0=0.878eV and σ0=0.0943V for the mean barrier height and zero-bias standard deviation, respectively, have been obtained from this plot. Thus, a modifiedln(I0/T2)−q2σ02/2k2T2 versus 1/ T plot givesΦ¯b0 and A* as 0.885eV and A*=55.80A/K2cm2, respectively. Hence, it can be concluded that Au/PANI/p-Si/Al structure has a good rectifying contact and the temperature dependence of I– V characteristics of the rectifying contact on p-Si successfully have been explained on the basis of TE mechanism with Gaussian distribution of the barrier heights.
Keywords: I; –; V; characteristics; Gaussian distribution; p-Si/Al structures
Corrosion inhibition of steel in 0.5M H2SO4 by [(2-pyridin-4-ylethyl)thio]acetic acid by M. Bouklah; A. Ouassini; B. Hammouti; A. El Idrissi (pp. 50-56).
The influence of [(2-pyridin-4-ylethyl)thio]acetic acid (P1) and pyridine (P2) on the corrosion inhibition of steel in sulphuric acid solution is studied using weight loss, potentiodynamic polarisation and linear polarisation resistance ( Rp) and electrochemical impedance spectroscopy (EIS) measurements. Results obtained show that P1 is the best inhibitor and its inhibition efficiency ( E%) increases with the increase of concentration. The highest E% of 82% is observed at 5×10−3M. Potentiodynamic polarisation studies clearly reveal that P1 acts as a mixed inhibitor. The inhibitor studied reduces the corrosion rates. E% values obtained from various methods used are in good agreement. Adsorption of P1 on steel surface obeys to Langmuir adsorption isotherm. Effect of temperature indicates that E% decreases with temperature between 298 and 353K.
Keywords: Steel; Pyridine; Inhibition; Corrosion; Acid; Langmuir
Photoelectron spectroscopic study of Li oxides on Li over-deposited V2O5 thin film surfaces by Qi-Hui Wu; A. Thissen; W. Jaegermann (pp. 57-62).
The Li oxides species formed on Li over-deposited V2O5 thin film surfaces have been studied by using X-ray and UV induced photoelectron spectroscopy (XPS and UPS). The photoelectron spectroscopic data show that the Li over-deposited V2O5 system itself is not stable. Further chemical decomposition reactions are taken place even under UHV conditions and lead to form Li2O and Li2O2 compounds on the surface. The formation of Li2O2 causes to arise an emission line at about 11.3eV in the valence band spectra.
Keywords: XPS; UPS; Li deposition; V; 2; O; 5
On the role of the interface charge in non-ideal metal–semiconductor contacts by Dean Korošak; Bruno Cvikl (pp. 63-69).
The bias dependent interface charge is considered as the origin of the observed non-ideality in current–voltage and capacitance–voltage characteristics. Using the simplified model for the interface electronic structure based on defects interacting with the continuum of interface states, the microscopic origin of empirical parameters describing the bias dependent interface charge function is investigated. The results show that in non-ideal metal–semiconductor contacts the interface charge function depends on the interface disorder parameter, density of defects, barrier pinning parameter and the effective gap center. The theoretical predictions are tested against several sets of published experimental data on bias dependent ideality factor and excess capacitance in various metal–semicoductor systems.
Keywords: Admittance; Schottky barrier; Metal–semiconductor interface; Disorder; Interface charge; Ideality factor
Structural and optical properties of thermally evaporated Bi2Te3 films by H.E.A. El-Sayed (pp. 70-78).
Bi2Te3 films were prepared by thermal evaporation technique. X-ray diffraction analysis for as-deposited and annealed films in vacuum at 150°C were polycrystalline with rhombohedral structure. The crystallite size is found to increase as the film thickness increases and has values in the range 67–162nm. The optical constants (the refractive index, n, and absorption index, k) were determined using transmittance and reflectance data in the spectral range 2.5–10μm for Bi2Te3 films with different thicknesses (25–99.5nm). Both n and k are independent on the film thickness in the investigated range. It was also found that Bi2Te3 is a high refractive index material ( n has values of 4.7–8.8 in the wavelength range 2.5–10μm). The allowed optical transitions were found to be direct optical transitions with energy gapEgd=0.21eV. The optical conductivities σ1=ƒ( hν) and σ2= f( hν) show distinct peaks at about 0.13 and 0.3eV, respectively. These two peaks can be attributed to optical interband transitions.
Keywords: PACS; 01.10.Nz; 78.20.CiOptical constants; Bi; 2; Te; 3; film
Adsorption and diffusion of cyclopentane in silicalite-1: a thermodynamic and kinetic study by Linhai Duan; Xiaotong Zhang; Ke Tang; Lijuan Song; Zhaolin Sun (pp. 79-87).
The adsorption isotherm, differential thermal gravimetry (DTG), thermal gravimetry (TG), diffusion and thermodynamic parameters of cyclopentane at various adsorption coverages have been investigated using microgravimetric technique over a range of temperature. The differences in equilibrium adsorption capacity and in diffusion coefficient at different temperature are discussed in terms of the characteristics of silicalite-1 and the features of cyclopentane molecule. The heat of sorption Qst varies significantly with sorption coverage indicating that the adsorption and diffusion mechanism is complex. The dependences of thermodynamic properties like free energy change (Δ G) and entropy change (Δ S) on sorption coverage show a sharp decrease and increase suggesting that the adsorption sites of the silicalite-1 are not energetically uniform to cyclopentane. Two desorption peaks in the DTG and TG curves suggest that two heterogenous binding sites surely exist in silicalite-1 to cyclopentane.
Keywords: PACS; 66.30H; 68.35F; 81.05R; 82.60SCyclopentane; Silicalite-1; Adsorption; Diffusion; Thermodynamic
Morphological study of ternary Ni–Cu–P alloys by atomic force microscopy by J.N. Balaraju; C. Anandan; K.S. Rajam (pp. 88-97).
Ternary electroless Ni–Cu–P alloy films were deposited by using nickel sulphate (B1)- and nickel chloride (B2)-based alkaline baths. Alloy films were characterized for their structure, morphology, chemical composition and microhardness. A single broad peak was obtained in XRD for both B1 and B2 films and the calculated grain sizes are 1.6 and 1.9nm, respectively. Optical microscopic examination of the deposited coatings revealed a less nodular structure for B2-based coatings. SEM micrographs showed that films were smooth and nodular. Compositional analysis made on these deposits using EDX and the chemical state identification by XPS showed that the coatings are almost identical. AFM studies showed that the deposits from B2 bath are comparatively smoother with less nodular structure. Microhardness measurements and potentiodynamic polarization studies in 3.5% NaCl solution showed that both deposits have similar properties.
Keywords: Ni–Cu–P; Electroless deposition; XPS; AFM; Corrosion
Influence of laser remelting on the microstructure and phases constitution of plasma sprayed hydroxyapatite coatings by Chuanzhong Chen; Diangang Wang; Quanhe Bao; Liang Zhang; Tingquan Lei (pp. 98-103).
In this paper, the plasma sprayed coatings were treated by laser remelting. The morphologies, elements analysis and phases of both sprayed and remelted coatings were studied by means of electron probe microanalysis (EPMA), X-ray diffraction (XRD) and so on. The results show that the structure of the sprayed coatings is coarse, the amorphization of HA is tremendous, and the bonding state between the coating and the substrate is mechanical combination. After the sprayed coatings were treated by laser remelting in a proper conditions, the properties of the coatings are improved greatly. The microstructure of remelted coatings is columnar and cellular dendritic crystal which is homogeneous and compact, and the coating consists of HA, α-TCP and CaO phases, the Ca/P ratio of transition layer is close to 1.67, but the Ca/P ratio of surface layer is higher than that of HA because of the loss of P.
Keywords: Hydroxyapatie; Microstructure; Phases constitution; Plasma spraying; Laser remelting
Promotion of partial oxidation of methanol over thin Pt and Pd film catalysts by resonance oscillation of acoustic waves by Y. Yukawa; N. Saito; H. Nishiyama; Y. Inoue (pp. 104-108).
The thickness extension mode resonance oscillation (TERO) of bulk acoustic waves generated on z-cut LiNbO3 by rf electric power was employed to the catalytic oxidation of methanol over thin Pt and Pd film catalysts deposited. Both the catalysts produced formaldehyde, methyl formate, and carbon dioxide as carbon-containing products in the gas phase. The TERO considerably increased the selectivity for formaldehyde production on Pt at a moderate rf power, indicating the ability of promoting the partial oxidation of methanol, whereas a small and monotonous decrease in the selectivity of the reaction on Pd occurred with power. The different TERO effects on the selectivity are discussed.
Keywords: Resonance oscillation; Acoustic wave; Partial oxidation of methanol; Thin Pd film catalysts; Thin Pt film catalysts; Selectivity of partial oxidation
A simple method for selective immobilization of silver nanoparticles by Zhi Li; Yi Li; Xue-Feng Qian; Jie Yin; Zi-Kang Zhu (pp. 109-116).
Size-adjustable silver nanoparticles were selectively in situ produced and immobilized on glass surface by simply UV exposing poly(vinylpyrrolidone) (PVP) film containing silver nitrate and 4,4′-diazostilbene-2,2′-disulfonic acid disodium salt (DAS) with the presence of a photomask, during which the crosslink between PVP and DAS completed and the silver nitrate was reduced to silver nanoparticles under the assistance of UV. Because the reduction speed of silver nitrate is much slower than the crosslink reaction of PVP, and a mount of unreduced silver nitrate still existed in the formed PVP micro-scale patterns after removing unexposed PVP by water, we can easily adjust the size of silver nanoparticles through further controlling the reduction of unreduced silver nitrate in the formed PVP micro-scale patterns. Optical microscope, UV–vis-spectroscopy, AFM and SEM-EDX were used to characterize the morphology and distribution of those silver nanoparticles immobilized on glass surface. The results indicate that it is an effective way to immobilize silver nanoparticles with high selectivity.
Keywords: Silver; Nanoparticles; PVP; Selective immobilization; Size tunable
Electrochromic properties of spray deposited TiO2-doped WO3 thin films by P.S. Patil; S.H. Mujawar; A.I. Inamdar; S.B. Sadale (pp. 117-123).
TiO2-doped WO3 thin films were deposited onto fluorine-doped tin oxide coated conducting glass substrates using spray pyrolysis technique at 525°C. The volume percentage of TiO2 dopant was varied from 13% to 38%. The thin film samples were transparent, uniform and strongly adherent to the substrates. Electrochromical properties of TiO2-doped WO3 thin films were studied with the help of cyclic voltammetry (CV), chronoamperometry (CA) and chronocoulometry (CC) techniques. It has been found that TiO2 doping in WO3 enhances its electrochromic performance. Colouration efficiency becomes almost double and samples exhibit increasingly high reversibility with TiO2 doping concentrations, in the studied range.
Keywords: Thin films; Electrochromism; WO; 3; TiO; 2; Spray pyrolysis
Corrosion resistance study of Fe–Mn–Al–C alloys using immersion and potentiostatic tests by Vanessa F.C. Lins; Marta Afonso Freitas; Evando M. Paula e Silva (pp. 124-134).
The interaction of the Fe–32.7Mn–6.59Al–1.26Si–0.25C (wt.%) and Fe–32.3Mn–8.54Al–1.31Si–0.54C (wt.%) alloys with the environment was evaluated. Potentiostatic and total immersion tests, planned and analyzed by the statistic model of fixed effects were used for the evaluation of corrosion in gasoline, alcohol fuel, lactic acid solution (40wt.%), sodium chloride solution (3wt.%), and boiler water. Potentiostatic tests in 1N H2SO4 medium presented that the alloys showed a tendency towards passivation. The role that aluminum and silicon play in alloy corrosion mechanism was discussed.
Keywords: Alloy; Potentiostatic; Acid corrosion; Passivity
Moisture barrier of Al xO y coating on poly(ethylene terephthalate), poly(ethylene naphthalate) and poly(carbonate) substrates by HongYee Low; Yongan Xu (pp. 135-145).
The moisture barrier property of Al xO y coated poly(ethylene terephthalate) (PET), poly(ethylene naphthalate) (PEN) and poly(carbonate) (PC), have been investigated. The differences in the morphology of the Al xO y sputtered grown on these substrate were investigated using atomic force microscopy (AFM). The initial growth of the Al xO y followed closely the topology of the substrate and an amplified roughness was observed. In the fully grown Al xO y, the comparative roughness followed that of the substrates. It has been found that a single layer Al xO y improved the moisture barrier of PET by an order of magnitude, PC by two orders of magnitude while no improvement was observed for PEN. UV-ozone treatment on PC further improved the moisture barrier, while no improvement was observed for PET and PEN. The comparative effects of the substrate surface roughness and surface energy on the moisture barrier are discussed.
Keywords: PACS; 73.50; 73.61; 81.15.EMoisture barrier; PET; PEN; PC; UV-ozone; Surface roughnees; Surface energy
First-principles study of electronic structure and optical properties of barium strontium titanates (Ba xSr1− xTiO3) by C.B. Samantaray; H. Sim; H. Hwang (pp. 146-151).
Using first-principles calculations based on density-functional theory in its local-density approximation, we investigate the energy band structures and total density of states (TDOS) of barium strontium titanates (BSTs). Direct band gaps of 1.89 and 1.87eV at the Γ point in the Brillouin zone are calculated for Ba xSr1− xTiO3 ( x=2/3 and 1/3), respectively. The optical properties of the above perovskites in the core-level spectra are investigated by the first-principles under scissor approximation. The real and imaginary parts of the complex dielectric function and derive optical constants, viz., the refractive index, extinction coefficient, reflectivity, and the electron energy-loss spectrum are calculated.
Keywords: PACS; 71.15.Hx; 71.15.Mb; 71.20.Ps; 77.84.Dy; 78.20.CiFerroelectrics; Band structure; Optical properties; BST
Pore size control of Pitch-based activated carbon fibers by pyrolytic deposition of propylene by Jinchuan Xie; Xuhui Wang; Jiyong Deng; Lixing Zhang (pp. 152-160).
In this paper, we attempted to narrow the pore size of Pitch-based activated carbon fiber (Pitch-ACF) by chemical vapor deposition (CVD) of propylene at 700°C. The BET equation was used to estimate the specific surface areas. The micropore volumes were determined using DR equation, t-plot and αs-plot, and mesopore surface areas were determined by t-plot and αs-plot. The pore size distribution (PSD) of micropores and mesopore was investigated by micropore analysis method (MP method) and MK method, respectively. The relation between the graphite-like crystal interlayer distance and pore size was analyzed by X-ray diffraction (XRD). The results showed that the pore size of Pitch-ACF was gradually narrowed with increasing deposition time. The catalytic activation of Ni was attempted when Pitch-ACF was modified simultaneously by pyrolysis of propylene. The results obtained from the analysis of PSD of micropores, mesopores and macropores in Ni–P-ACF by density function theory (DFT) showed that the pore structure and surface chemistry were greatly changed due to introducing nickel catalyst.
Keywords: PACS; 81.05.Z; 61.43.G; 81.05.R; 68.10.J; 52.75.R; 81.15.G; 82.30.LActivated carbon fiber; Propylene; Chemical vapor deposition; Physical adsorption; Porosity
Bismuth oxide thin films prepared by chemical bath deposition (CBD) method: annealing effect by T.P. Gujar; V.R. Shinde; C.D. Lokhande; R.S. Mane; Sung-Hwan Han (pp. 161-167).
Bismuth oxide thin films have been deposited by room temperature chemical bath deposition (CBD) method and annealed at 623K in air. They were characterized for structural, surface morphological, optical and electrical properties. From the X-ray diffraction patterns, it was found that after annealing a non-stoichiometric phase, Bi2O2.33, was removed and phase pure monoclinic Bi2O3 was obtained. Surface morphology of Bi2O3 film at lower magnification SEM showed rod-like structure, however, higher magnification showed a rectangular slice-like structure perpendicular to substrate, giving rise to microrods on the surface. The optical studies showed the decrease in band gap by 0.3eV after annealing. The electrical resistivity variation showed semiconductor behavior and from thermoemf measurements, the electrical conductivity was found to be of n-type.
Keywords: Bi; 2; O; 3; Chemical bath deposition; Optical; Electrical resistivity; SEM
Si–SiO2 interface formation in low-dose low-energy separation by implanted oxygen materials by Tula Jutarosaga; Srinivas Manne; Supapan Seraphin (pp. 168-181).
The evolution of the Si–SiO2 interface morphology of low-dose low-energy separation by implanted oxygen materials was investigated by transmission electron microscopy and atomic force microscopy. The Si–SiO2 interface morphology and the RMS roughness are strongly affected by the implantation conditions and the annealing process. Three main types of the domains including round, square, and pyramid shapes with the step-terrace structure were observed on the buried SiO2 surface. Round domains are observed in the early stage of the annealing process, while the square and pyramid domains are observed after the high temperature annealing. The mean RMS roughness decreases with increasing time and annealing temperature, while in the 1350°C 4-h annealed samples, the mean RMS roughness decreases with either increasing the implantation dose or decreasing implantation energy. The scaling analysis shows that the Si–SiO2 interfaces were found to be self-affine on the short length scales with a roughness exponent above 0.50. Qualitative mechanisms of Si–SiO2 surface flattening are presented in terms of the variations of morphological features with the processing conditions.
Keywords: PACS; 68.35.Bs; 68.35.Ct; 68.35.FxSeparation by implanted oxygen materials; Si–SiO; 2; interfaces; Scaling analysis; Atomic force microscopy; Self-affine scaling
The solubility of phosphorus in GaN by X.S. Wu; Z.Y. Zhai; Y.H. Fan; D.J. Chen; B. Shen; R. Zhang; Y.D. Zheng; S.S. Jiang (pp. 182-187).
IIIV xN1− x ternary alloys are promising materials for their applications in light-emitting devices in the range of wavelength from ultra violet to the infrared ray due to the large bowing of band gap energy. In this paper, molecular dynamical method was used to calculate the solubility of phosphorus in GaN by using the Gibbs free energy and the dielectric theory. The calculation results show that the content of P in GaN varies with the growth temperature, which may be larger than 25% in the N-rich GaP xN1− x or less than 90% in the P-rich GaP xN1− x, at the growth temperature of about 1500K. We compared our theoretical results with those reported in references. By using light-radiation heating together with low-pressure metal-organic chemical vapor deposition, and ion implantation techniques, we have successfully synthesized N-rich ( x<0.17) and P-rich GaP xN1− x ( x>0.90) compounds.
Keywords: GaN; 1−; x; P; x; ternary alloys; Solubility of P; MOCVD; Ion implantation
Effects of poly(ethylene glycol) on electrical conductivity of poly(3,4-ethylenedioxythiophene)–poly(styrenesulfonic acid) film by Tiejun Wang; Yingqun Qi; Jingkun Xu; Xiujie Hu; Ping Chen (pp. 188-194).
A series of poly(3,4-ethylenedioxythiophene)–poly(styrenesulfonic acid) composite thin films with prescribed concentrations of poly(ethylene glycol) were prepared. The PEDOT–PSS pristine film and PEDOT–PSS/PEG films were studied using four-probe method, photoelectron spectroscopy and atomic force microscopy. The electrical conductivity of PEDOT–PSS/PEG hybrid films was found to be enhanced compared to the PEDOT–PSS pristine film, depending on the PEG concentration and molecular weight. XPS analysis and AFM results showed that PEG induces the phase separation between the PEDOT–PSS conducting particles and the excessive PSSNa shell. Simultaneously PEG may form hydrogen bond with sulfonic groups of PSSH, and hence weaken the electrostatic interactions between PEDOT cationic chains and PSS anionic chains. These resulted in the creation of a better conduction pathway among PEDOT–PSS particles, attributed to the improvement of conductivity.
Keywords: PACS; 68.35.-p; 78.30.Jw; 72.80.LePEDOT–PSS; Electrical conductivity; X-ray photoelectron spectroscopy; Atomic force microscopy
Laser-induced damage of Ta2O5/SiO2 narrow-band interference filters under different 1064nm Nd:YAG laser modes by Weidong Gao; Meiqiong Zhan; Shuhai Fan; Janda Shao; Zheng-Xiu Fan (pp. 195-202).
The laser-induced damage (LID) behavior of narrow-band interference filters was investigated with a Nd:YAG laser at 1064nm under single-pulse mode and free-running mode. The absorption measurement of such coatings was performed with surface thermal lensing (STL) technique. The damage morphologies under the two different laser modes were also studied in detail. It was found that all the filters exhibited a pass-band-center-dependent absorption and laser-induced damage threshold (LIDT) behavior, but the damage morphologies were diverse. The explanation was given with the analysis of the electric field distribution and the operational behavior of the irradiation laser.
Keywords: Laser-induced damage; Narrow-band interference filter; Single-pulse laser; Free-running laser
The dependence of I– V and C– V characteristics on temperature in the H-terminated Pb/p-Si(100) Schottky barrier diodes by Ç. Nuhoğlu; E. Özerden; A. Türüt (pp. 203-208).
The current–voltage ( I– V) and capacitance–voltage ( C– V) characteristics of H-terminated Pb/p-Si/Al contacts fabricated by us have been measured in the temperature range of 77–300K. The experimental values of the barrier height (BH) Φbo and the ideality factor n for the device range from 0.674 and 1.072eV (at 300K) to 0.352 and 2.452eV (at 77K), respectively. The ideality factors become larger with lowering temperature while the barrier height decreases. The Φbo( n) plot shows a linear dependence in the temperature range of 77–300K that can be explained by the barrier inhomogeneity at the metal/semiconductor interface. The extrapolation of the linear Φbo( n) plot to n=1 has given a homogeneous barrier height of approximately 0.713eV for the Pb/p-Si(100) contact. A Φbo versus 1/ T plot was drawn to obtain evidence of a Gaussian distribution of the BHs, and values ofΦ¯bo=0.819eV and σs=80.5mV for the mean BH and zero-bias standard deviation have been obtained from this plot, respectively. Then, a modifiedln(I0/T2)−q2σs2/2k2T2 versus 1/ T plot givesΦ¯bo and A* as 0.828eV and 54.89A/cm2K2, respectively. Furthermore, an average value of −0.687meV/K for the temperature coefficient has been obtained, the value of −0.687meV/K for hydrogen terminated p-type Si differs from those given for p-type Si without hydrogen termination in the literature.
Keywords: PACS; 73.30.+y; 73.40.Ei; 73.40.Ns; 73.40.SxSchottky diodes; Metal–semiconductor–metal contacts; Barrier inhomogeneity
Application of a self-sensing conductive probe for Si device imaging by Yuichi Naitou; Norio Ookubo (pp. 209-215).
For the evaluation of two-dimensional carrier profiles in semiconductor devices, we have developed a novel form of probe–sensor combined unit that uses an etched tungsten wire as a conductive probe, and commercially available quartz tuning fork as the force sensor. This unit has a self-sensing capability due to the piezoelectric effect of quartz tuning fork, thus obviating optical setup, and its conductivity is higher and more stable than that of conventional metal-coated Si cantilever. In addition, this probe–sensor combined unit is inexpensive and easy to use, when compared to the well-known optical methods of Si-based cantilever vibration detection system. Our scanning probe microscope using this probe–sensor combined unit is able to mapping the capacitive gradient signal (d C/d Z image) and internal damping of quartz tuning fork oscillation (dissipation image) while scanning the sample surface. In this letter, we show the results of visualization of the p–n junction locus of a Si metal–oxide–semiconductor field effect transistor in both d C/d Z and dissipation images.
Keywords: PACS; 07.79.LhScanning probe microscope; Tuning fork; Self-sensing probe; Dissipation
Photoconductivity in the ordered vacancy compound CuIn5Se8 by Rachel Reena Philip; B. Pradeep; T. Shripathi (pp. 216-222).
Thin films of the ordered vacancy compound CuIn5Se8 are deposited on glass substrates by multisource co-evaporation method and photoconductivity measurements are done on the films at various temperatures from 10 up to 300K. The two photoactive bands that are identified in the spectral response spectra of CuIn5Se8 thin films at all measured temperatures are attributed to photoactive transitions between acceptor VCu to donor InCu and valence band to conduction band transitions respectively. From the spectra, a shift in band-to-band gap from 1.36 to 1.3eV is observed with a temperature variation from 10 to 300K. The non-exponential long-term decay observed in the transient photoconductivity spectra suggests a deep level trap-emptying process to be associated with the decay process and the decay constants are calculated by the differential life-time concept. From the steady state photocurrent analysis, a reduction in intergrain potential barrier on illumination has been noted as one reason for increase in conductivity on illumination. X-ray photoelectron spectroscopy analysis has been done to determine the binding energies of Cu, In and Se in the compound.
Keywords: PACS; 73.50.Pz; 73.50.GrTransient photoconductivity; Spectral photoconductivity; X-ray photoelectron spectroscopy
Laser surface alloying of pure titanium with TiN–B–Si–Ni mixed powders by Y.S. Tian; C.Z. Chen; D.Y. Wang; Q.H. Huo; T.Q. Lei (pp. 223-227).
Laser alloying was carried out on the surface of pure titanium substrate with TiN–B–Si–Ni mixed powders. The result of X-ray diffraction (XRD) analysis shows that the alloyed layer consists of many kinds of intermetallic compounds. The test results show that the alloyed layers have high microhardness (1500–1600HV0.1), low friction coefficient (about 0.4), and are more resistant to oxidation than untreated substrate.
Keywords: Laser alloying; Friction coefficient; Oxidation resistance; Titanium
Exact solution of the frequency shift in dynamic force microscopy by Shueei-Muh Lin (pp. 228-237).
The exact frequency shift of an AFM non-uniform probe with an elastically restrained root, subjected to van der Waals force, is derived. The original distributed system is considered and then its exact fundamental solutions and the general frequency equation are derived. Results are compared with those by the force gradient method and the perturbation method. The effects of several parameters on the sensitivity of measurement are investigated. Results show that the interpretation of frequency shift by using the force gradient method is unsatisfactory. The smaller the amplitude of oscillation and the tip–surface distance are, the larger the frequency shift. The design of a taper beam is recommended for increasing the sensitivity of measurement.
Keywords: AFM; Frequency shift; Non-contact mode
Microstructure and oxidation of hot-dip aluminized titanium at high temperature by Wang Deqing; Shi Ziyuan; Teng Yingli (pp. 238-246).
High-temperature diffusion of a hot-dip aluminized titanium is conducted to study microstructure changes and oxidation behavior of the aluminized titanium. After aluminizing, the titanium substrate is covered by a black layer in which tiny block-shaped TiAl3 particles are scattered in aluminum matrix. Based on the diffusion experiment results, the thickness of the aluminum diffusion layer at 800°C increases with diffusion time. However, the aluminum diffusion layer at 900°C grows and reaches its maximum thickness in 6h, and then the thickness of the aluminum diffusion layer is reduced with prolonged diffusion time. An inversion of the diffusion layer thickness versus time appears for the aluminized titanium treated at 1000°C, and the thickness of the diffusion layer keeps declining with diffusion time. The phases present in the outer and middle sublayers are titanium-rich TiAl3 and equilibrium TiAl3, respectively. However, the phase in inner sublayer changes from titanium-rich TiAl3 to TiAl2 and TiAl as diffusion temperature and time increase. Through energy-dispersive X-ray and X-ray diffraction analysis, the oxides formed in the oxidation process are Al2O3 and Al2TiO5. Although the oxide scale formed on the surface of the aluminized titanium has an insufficient stability and integrity, the thermal oxidation resistance of the aluminized titanium is still improved by over 5 times compared with that of the pure titanium.
Keywords: PACS; 81.65; 81.65.M; 64.70.KAluminizing; Titanium aluminide; Diffusion; Oxidation
Ti/Al p-GaN Schottky barrier height determined by C– V measurements by Jae Wook Kim; Jhang Woo Lee (pp. 247-251).
Data are presented on the rigorous method of capacitance–voltage ( C– V) measurements to the barrier height of Ti/Al p-GaN Schottky junction. For a sample with Hall concentration of 5.5×1016/cm3 the upper limit of the modulation frequency leading the full response of the activated carriers is defined as 1.5kHz from the capacitance versus modulation frequency ( C– f) plot. The activation energy of the Mg acceptors determined from the temperature-dependent C– f plot is 0.12eV. The barrier height estimated with this activation energy and the intercept voltage of the 1/ C2– V plot drawn with the 1.5kHz C– V data is 1.43eV at 300K and 1.41eV at 500K. This is the most reliable barrier height ever reported. A reliable room temperature C– V doping profile is demonstrated using the 1.5KHz modulation, which is sensitive enough to resolve the presence of a ∼15nm thin highly doped (8×1018/cm3) layer formed near the surface.
Keywords: PACS; 71.55.−i; 71.55.Eq; 72.20.Jv; 73.40.Ns; 73.61.−r; 73.61.EyGaN; Barrier height; C; –; V; characteristics
Surface structure and composition of flat titanium thin films as a function of film thickness and evaporation rate by Kaiyong Cai; Michael Müller; Jörg Bossert; Annett Rechtenbach; Klaus D. Jandt (pp. 252-267).
To correlate flat titanium film surface properties with deposition parameters, titanium flat thin films were systematically deposited on glass substrates with various thicknesses and evaporation rates by electron-beam evaporation. The chemical compositions, crystal structure, surface topographies as well as wettability were investigated by using X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), atomic force microscopy (AFM) and water contact angle measurement, respectively. The films consisted mainly of TiO2. Small percentages of Ti2O3 and metallic Ti were also found at the film surface using high-resolution XPS analysis. Quantitative XPS showed little differences regarding elemental compositions among different groups of films. The films were obtained by varying the deposition rate and the film thickness, respectively. XRD data showed consistent reflection patterns of the different titanium samples deposited using different film thicknesses. Without exception measurements of all samples exhibited contact angles of 80°±5°. Quantitative AFM characterization demonstrated good correlation tendency between surface roughness and film thickness or evaporation rate, respectively. It is important to notice that titanium films with different sizes of grains on their surfaces but having the same chemistry and film bulk structure can be obtained in a controllable way. By increasing the film thickness and evaporation rate, the surface roughness increased. The surface morphology and grain size growth displayed a corresponding trend. Therefore, the control of these parameters allows us to prepare titanium films with desired surface properties in a controllable and reproducible way for further biological investigations of these materials.
Keywords: PACS; 81.15; 68.35.B; 61.16.C; 79.60Titanium thin film; Surface characterization; XPS; AFM; XRD; Contact angle; Nanostructure
Picosecond nonlinear optical response of Ba0.5Sr0.5TiO3 thin films fabricated by pulsed laser deposition by Weitian Wang; Zhenhong Dai; Yuming Sun; Yuanping Sun; Dongyi Guan (pp. 268-272).
Well-crystallized Ba0.5Sr0.5TiO3 thin films with good surface morphology were prepared on MgO(100) substrates by pulsed laser deposition technique at a deposition temperature of 800°C under the oxygen pressure of 2×10−3Pa. X-ray diffraction and atomic force microscopy were used to characterize the films. The full width at half maximum of the (002) Ba0.5Sr0.5TiO3 rocking curve and the root-mean-square surface roughness within the 5μm×5μm area were 0.542° and 0.555nm, respectively. The nonlinear optical properties of the films were determined by a single beam Z-scan method at a wavelength of 532nm with laser duration of 55 ps. The results show that Ba0.5Sr0.5TiO3 thin films exhibit a fast third-order nonlinear optical response with the nonlinear refractive index and nonlinear absorption coefficient being n2=5.04×10−6cm2/kW and β=3.59×10−6(m/W), respectively.
Keywords: PACS; 42.70.-a; 68.55.-a; 81.15.Fg; 78.66.-wBa; 0.5; Sr; 0.5; TiO; 3; films; Optical nonlinearity; Pulsed laser deposition; Z; -scan
Studies on the surface modification of diatomite with polyethyleneimine and trapping effect of the modified diatomite for phenol by Baojiao Gao; Pengfei Jiang; Fuqiang An; Shuying Zhao; Zhen Ge (pp. 273-279).
The adsorption isotherm of polyethyleneimine (PEI) on diatomite was studied using UV spectrophotometry, the surface of diatomite was modified with polyethyleneimine by using impregnation method, and the trapping behavior of the modified diatomite for phenol was investigated by using 4-aminoantipyrine (4-AAP) spectrophotometric method. The experiment results show that negatively charged diatomite particles have very strong absorption effect for cationic macromolecule PEI, the adsorption isotherm fits in Freundlich equation. The character that there is a maximum value after intitial sharp increase of adsorption capacity on the adsorption curve indicates that there is strong affinity between diatomite particles and polyethyleneimine macromolecules, and it attributes to the strong electrostatic interaction. After modification with PEI, the electric property of diatomite particle surface changes essentially, and the isoelectric point of diatomite particles moves from pH 2.0 to 10.5. In acidic solution, phenol exists as molecular state, and the modified diatomite particles adsorb phenol through hydrogen bond interaction. However, the hydrogen bond interaction between nitrogen atoms on PEI chains and phenol is weaker because of high degree of protonation of polyethyleneimine macromolecules, so the adsorption quantity is lower. In basic solution, phenol exists as negative benzene–oxygen ion, and the modified diatomite particles adsorb phenol through electrostatic interaction. However, the electrostatic interaction between PEI and negative benzene–oxygen ion is very weak because of low degree of protonation of polyethyleneimine macromolecules, so the adsorption quantity is much lower. The modified diatomite particles produce very strong trapping effect for phenol in neutral aqueous solution via the cooperating of strong electrostatic interaction and hydrogen bond interaction, and the saturated adsorption capacity can attain to 92mgg−1.
Keywords: Polyethyleneimine; Diatomite; Phenol; Surface modification; Adsorption; Electrostatic interaction; Hydrogen bond interaction
Well-aligned ZnO nanowires grown on Si substrate via metal–organic chemical vapor deposition by Yu-Jia Zeng; Zhi-Zhen Ye; Wei-Zhong Xu; Li-Ping Zhu; Bing-Hui Zhao (pp. 280-283).
ZnO nanowires were grown on silicon substrate by metal–organic chemical vapor deposition (MOCVD) without catalysts. The scanning electron microscopy (SEM) observations along with X-ray diffraction (XRD) results suggest that the ZnO nanowires are single crystals vertically well-aligned to silicon substrate. Room-temperature photoluminescence (PL) measurement reveals strong UV emission and weak green emission, which demonstrates that the nanowires are of good optical properties. The mechanism of the catalyst-free growth of ZnO nanowires on silicon substrate is proposed.
Keywords: PACS; 78.66.J; 61.46; 81.05.Dz; 81.15.KkNanowires; Metal–organic chemical vapor deposition; Zinc compounds; Scanning electron microscopy