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Applied Surface Science (v.252, #2)
Surface and adsorptive properties of carbons prepared from biomass by Abdel-Nasser A. El-Hendawy (pp. 287-295).
A number of activated carbons were prepared from a locally available by-product, corncobs, under currently established activation schemes. Obtained carbons were characterized by N2 adsorption at 77K and the isotherms were analyzed by BET and αs methods. Steam-activation at 900°C produced a microporous carbon having the highest Sα of 788m2g−1, whereas activation with air at 350°C produced a carbon of Sα=321m2/g and possess wider pores. KOH impregnation with char in ratio 1:1 (w/w) and impregnated in the same ratio with the raw material prior to pyrolysis at 700°C for 1h, gave CK700, K700 respectively. An additional sample was obtained by oxidizing part of K700 with conc. HNO3. All three KOH carbons show pore structures much close to char itself which may be due to potassium salt left in pores and is not easily leached with repeated water washings. In addition, KOH is more effective on the precursor itself than on its char of already developed porosity. FT-IR spectra show an increase in oxygen functionalties on the carbon surface as a result of activation process and the bands become stronger in the spectra of the acid-treated sample. The oxidized carbon sample showed relatively higher uptake of Pb2+ and MB and its surface chemistry plays the key role in their adsorption, while sharp decrease was observed in the uptake of phenol and mono-nitrophenols from aqueous solutions. An SEM study showed that air activation produce obvious voids reflecting its erosive effect on the external carbon surface.
Keywords: Activated carbon; Surface treatment; Porosity; Adsorption properties
Low voltage electrodeposition of diamond like carbon (DLC) by K. Sreejith; J. Nuwad; C.G.S. Pillai (pp. 296-302).
Attempt has been made to deposit diamond like carbon (DLC) films from ethanol through electrodeposition at low voltages (80–300V) at 1mm interelectrode separation. The films were characterized by atomic force microscopy (AFM), Scanning electron microscopy (SEM), Raman spectroscopy, Fourier transform infrared (FTIR) spectroscopy and Auger electron Spectroscopy (AES). AFM investigations revealed the grain sizes are of tens of nanometers. The films were found to be continuous, smooth and close packed. Presence of peaks at 2958, 2929 and 2869cm−1 in FTIR spectrum indicates the bonding states to be of predominantly sp3 type (C-H). Raman spectroscopy analysis revealed two broad bands at ∼1350 and ∼1570cm−1. The downshift of the G-band of graphite is indicative of presence of DLC. Analysis of the Raman spectra for the samples revealed an improvement in the film quality with increase in the voltage. Micro Raman investigations indicate the formation of diamond phase at the deposition potential of 80V. The sp2 contents the films calculated from Auger electron spectra were calculated and were found to be 31, 19 and 7.8% for the samples prepared at 80, 150 and 300V, respectively. A tentative mechanism for the formation of DLC has been proposed. These results indicate the possibility of deposition of DLC at low voltage.
Keywords: Diamond like carbon [X]; AFM [B]; Raman spectroscopy [B]; IR spectroscopy [B]; Graphite [D]
Grafting onto poly(ethylene terephthalate) driven by 172nm UV light by Zhengmao Zhu; Michael J. Kelley (pp. 303-310).
The reactivity of the surface of poly(ethylene terephthalate) (PET) film under 172nm UV irradiation (xenon excimer lamp) towards nitrogen-borne 1-octene, n-nonane and heptafluorodecene vapor was investigated. Materials receiving from 0 to 24J/cm2 of UV were examined by X-ray photoelectron spectroscopy (XPS), time of flight secondary ion mass spectroscopy (ToF/SIMS), water and mineral oil contact angle measurement and atomic force microscopy (AFM). A uniform nanoscale layer developed on PET surface attributed to the grafting reaction between photolytically-produced polymer radicals and vapor phase molecules.
Keywords: Photografting; Surface characterization; Excimer lamp; Polymer photochemistry
Electron-assisted chemical etching of oxidized chromium by Y.-M. Sun; S. Wang; J.M. White; A. Stivers; T. Liang (pp. 311-320).
Electron-assisted chemical etching of oxidized chromium, CrO x, has been studied by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and atomic force microscopy (AFM). Two model substrates were used—10nm CrO x deposited on Si(100) that was covered with either native oxide or a 20nm Au/Pd alloy film. Using chlorine and/or oxygen as etching gases, the experiments were conducted in a customized high vacuum system, equipped with a high density electron source and a low pressure reaction cell. On both substrates, electron-assisted chemical etching of CiO x was detected by SEM, EDS and AFM. Making the method questionable for etching applications, there is substantial substrate damage associated with the etching. The SEM images indicate strongly inhomogeneous material removal, apparently initiated and propagated from specific but unidentified sites. In the experiments involving the Au/Pd film, there was phase separation of Au and Pd, and dewetting to form metallic islands. AFM data show that the etched holes were as deep as 200nm, confirming relatively rapid etching of the Si substrate after the top layer of Cr oxide was removed.
Keywords: Scanning electron microscopy; Chromium etching; Electron beam
Low voltage electrodeposition of CN x films and study of the effect of the deposition voltage on bonding configurations by K. Sreejith; J. Nuwad; C.G.S. Pillai (pp. 321-329).
Carbon nitride (CN x) films were deposited from acetonitrile at low voltage (150–450V) through electrodeposition. The films were characterized by atomic force microscopy (AFM), Raman spectroscopy and Fourier transform infrared (FT-IR) spectroscopy. AFM investigations revealed that the grain size was ∼200nm and roughness was ∼10nm. The films were found to be continuous and close packed. IR spectra revealed existence of strong sp3, sp2 type bonding and weak sp type carbon nitrogen bonds and these bonds were found to increase with voltage. The fraction of sp3-bonded species in the sample increased in low voltage range and after reaching maximum at 350V, decreased for higher voltages. However, the concentration of sp2 CN ring structures in the film increased with increasing voltage. Also, the peak width decreased at low voltages reaching a minimum and increased thereafter. It was observed that the voltage dependent increase in the concentration of polymeric type sp2 CN (chain) structures was much more pronounced than that of graphitic type sp2 CN (ring) structures. Raman spectra showed the presence of both the D and G bands. The shift in the G band indicated the presence of nitrogen in the film. The ID/IG ratio was found to increase with the incorporation of nitrogen. Auger electron spectroscopy (AES) showed a clear increase in the nitrogen content with increase in the voltage. The formation of the film could be explained on the basis of dissociation of electrolyte under applied voltage.
Keywords: Carbon nitride; Vibrational properties characterization; Scanning probe techniques
Studies of iron and iron oxide layers by electron spectroscopes by B. Lesiak; A. Jablonski; J. Zemek; P. Jiricek; M. Čerňanský (pp. 330-338).
Thin iron oxide layers prepared “in situ� in the ultra high vacuum on polycrystalline iron substrate were investigated by electron spectroscopy methods—X-ray photoelectron spectroscopy (XPS) and elastic peak electron spectroscopy (EPES), using spectrometer ADES-400. The texture and the average grain size of the iron substrate foil have been examined by glancing angle X-ray diffraction (XRD). Qualitative and quantitative estimation of investigated oxide layers was made using (i) the relative sensitivity factor XPS method, (ii) comparison of binding energy shifts of Fe 2p photoelectron line and (iii) non-linear fitting procedure of Fe 2p photoelectron lines.Both, sputter-clean polycrystalline iron substrate and finally grown Fe2.2O3 layer, were investigated by the EPES method to measure the electron transport parameters used for quantitative electron spectroscopy, such as the electron inelastic mean free path (IMFP) values. The IMFPs were measured in the electron kinetic energy range 200–1000eV with the Cu standard. The surface excitation parameters using Chen and Werner et al. approaches were evaluated and applied for correcting these IMFPs. The discrepancies between the evaluated parameters obtained using the above quantitative and qualitative approaches for characterising the iron oxide layers were discussed.
Keywords: Iron; Iron oxide layers; Fe; 2.2; O; 3; Fe; 2; O; 3; Layer thickness; X-ray photoelectron spectroscopy (XPS); Elastic peak electron spectroscopy (EPES); Cu standard; Inelastic mean free path (IMFP); Surface excitation
1,3-Bis(3-hyroxymethyl-5-methyl-1-pyrazole) propane as corrosion inhibitor for steel in 0.5M H2SO4 solution by A. Ouchrif; M. Zegmout; B. Hammouti; S. El-Kadiri; A. Ramdani (pp. 339-344).
The effect of addition of 1,3-bis(3-hyroxymethyl-5-methyl-1-pyrazole) propane ( M=264g). HMPP on steel corrosion in 0.5M sulphuric acid is studied by weight-loss, electrochemical polarisation and electrochemical impedance spectroscopy (EIS) measurements at various temperatures. The results obtained showed that HMPP acts as a good corrosion inhibitor. The inhibition efficiency increases with the bipyrazole compound to attain 88%. It acts as a mixed-type inhibitor. Trends in the increase of charge-transfer resistance and decrease of capacitance values also show the adsorption of the molecule on the metal surface. The bipyrazole adsorbs on the steel surface according to the Langmuir isotherm adsorption model. Effect of temperature indicates that inhibition efficiency decreases with temperature between 25 and 85°C.
Keywords: Corrosion; Inhibitor; Steel; Bipyrazole; Sulphuric acid
Effect of potassium fluoride in electrolytic solution on the structure and properties of microarc oxidation coatings on magnesium alloy by Jun Liang; Baogang Guo; Jun Tian; Huiwen Liu; Jinfang Zhou; Tao Xu (pp. 345-351).
Oxide coatings were produced on AM60B magnesium alloy substrate making use of microarc oxidation (MAO) technique. The effect of KF addition in the Na2SiO3–KOH electrolytic solution on the microarc oxidation process and the structure, composition, and properties of the oxide coatings was investigated. It was found that the addition of KF into the Na2SiO3–KOH electrolytic solution caused increase in the electrolyte conductivity and decrease in the work voltage and final voltage in the MAO process. Subsequently, the pore diameter and surface roughness of the microarc oxidation coating were decreased by the addition of KF, while the coating compactness was increased. At the same time, the phase compositions of the coatings also varied after the addition of KF in the electrolytic solution, owing to the participation of KF in the reaction and its incorporation into the oxide coating. Moreover, the coating formed in the electrolytic solution with KF had a higher surface hardness and better wear-resistance than that formed in the solution without KF, which was attributed to the changes in the spark discharge characteristics and the compositions and structures of the oxide coatings after the addition of KF.
Keywords: Magnesium alloy; Microarc oxidation; KF; Oxide coating; Tribological properties
Femtosecond pulsed laser ablation of diamond-like carbon films on silicon by Y. Dong; H. Sakata; P. Molian (pp. 352-357).
Femtosecond pulsed laser ablation ( τ=120fs, λ=800nm, repetition rate=1kHz) of thin diamond-like carbon (DLC) films on silicon was conducted in air using a direct focusing technique for estimating ablation threshold and investigating the influence of ablation parameter on the morphological features of ablated regions. The single-pulse ablation threshold estimated by two different methods were ϕth(1)=2.43 and 2.51J/cm2. The morphological changes were evaluated by means of scanning electron microscopy. A comparison with picosecond pulsed laser ablation shows lower threshold and reduced collateral thermal damage.
Keywords: PACS; 81.05.T; 79.20.DDiamond-like carbon; Laser
Analysis of current–voltage characteristics of inhomogeneous Schottky diodes at low temperatures by Subhash Chand; Saroj Bala (pp. 358-363).
Two approaches of Gaussian distribution of barrier heights in inhomogeneous Schottky diodes have been analyzed by comparing the results for consistency between the two. For this the current–voltage characteristics of inhomogeneous Schottky diodes have been generated by using analytically solved thermionic-emission diffusion equation incorporating Gaussian distribution of barrier heights and by direct numerical integration over a barrier height range. The differences in the results obtained in two approaches are discussed and it is shown that the two approaches yield current–voltage characteristics with slightly different features. The discrepancies in the results obtained in two approaches are attributed to the same series resistance assumed for all elementary barriers of the distribution. It is shown that assigning same series resistance to all barrier of the distribution in numerical integration approach causes current saturation at low bias and inhibits intersection of current–voltage curves from being observable which otherwise occurs in the curves obtained using analytical equation. The paper deals with these aspects in details.
Keywords: PACS; 73.30.+y; 73.40.Ns; 73.40.QvSchottky diodes; Gaussian distribution; Numerical simulation; Current–voltage characteristics; Barrier inhomogeneities
Bi induced step-flow growth in the homoepitaxial growth of Au(111) by M. Kamiko; H. Mizuno; H. Chihaya; J.-H. Xu; I. Kojima; R. Yamamoto (pp. 364-371).
Homoepitaxial growth of Au on Bi-covered Au(111) was studied at room temperature using reflection high-energy electron diffraction (RHEED) and Auger electron spectroscopy (AES). From observations of RHEED it is found that the Au(111) (23×1) reconstruction structure changes to a (1×1) by about 0.16–0.5ML deposition of Bi and to a (2√3×2√3) R30° by about 1.0ML deposition of Bi, respectively. The surface morphology evolution by Bi deposition leads to a change of Au homoepitaxial growth behavior from layer-by-layer to step flow. This indicates that the surface diffusion distance of Au atoms on the Bi-precovered (1×1) and (2√3×2√3) R30° surfaces is longer than that on the Au(111) (23×1) clean surfaces. A strong surface segregation of Bi was found at top of surface. It is concluded that Bi atoms acted as an effective surfactant in the Au homoepitaxial growth by promoting Au intralayer mass transport.
Keywords: PACS; 61.14.Hg; 68.55.Ac; 81.15.HiSurface structure; Epitaxy; Metallic films; RHEED; MBE; Gold; Bismuth
Frequency shifts of cantilever in AFM by H.-Y. Xie (pp. 372-378).
The frequency shift and frequency shift image of cantilever in AFM have been studied by numerical integration of the equation of motion of cantilever for silicon tip with rutile TiO2(001) surface in UHV conditions and by the Hamaker summation method for the tip–surface interaction forces. The effects of the excitation frequency at the cantilever base and the equilibrium position of the tip on the frequency shift have been calculated and the results showed the same phenomena as those measured, e.g., the frequency shift increased dramatically or rapidly before the contact point and was then almost level off after the contact point. The effects of scanning speed and the initial closest distance of tip to the contact point have been calculated at different excitation frequencies at the cantilever base and the results showed that proper frequency shift image could be obtained either by noncontact mode at the excitation frequency slightly less than the resonance frequency of free cantilever, or by tapping mode at the excitation frequency a few times smaller than the resonance frequency of free cantilever.
Keywords: PACS; 61.16.Ch; 62.20.−x; 68.45.KgAFM; Frequency shift; Frequency shift image; Noncontact mode; Tapping mode
Temperature dependence of the work function of Bi2Sr2CaCu2O8 single crystal cleaved at low temperature by S. Saito; T. Sutou; Y. Norimitsu; N. Yajima; Y. Uhara; T. Uenosono; T. Soumura; T. Tani (pp. 379-384).
We measured the anomalous change in the work function of Bi2Sr2CaCu2O8 around a critical temperature ( Tc≈85K). The work function becomes a minimum at Tc; the work function decreases in a normal-conductive state and then increases in a superconductive state as the temperature decreases. An increase in the work function for a transition from a normal-conductive state to a superconductive state at 0K is about 9meV. The contribution of the chemical potential and the surface dipole barrier to the work function are discussed.
Keywords: PACS; 73.30.+yWork function; Bi; 2; Sr; 2; CaCu; 2; O; 8; Chemical potential; Surface dipole barrier
Indium tin oxide thin films by bias magnetron rf sputtering for heterojunction solar cells application by Liang Zhao; Zhibin Zhou; Hua Peng; Rongqiang Cui (pp. 385-392).
In this investigation ITO thin films were prepared by bias magnetron rf sputtering technique at substrate temperature of 180°C and low substrate–target distance for future a-Si:H/c-Si heterojunction (HJ) solar cells application. Microstructure, surface morphology, electrical and optical properties of these films were characterized and analyzed. The effects of ion bombardments on growing ITO films are well discussed. XRD analysis revealed a change in preferential orientation of polycrystalline structure from (222) to (400) plane with the increase of negative bias voltage. Textured surface were observed on AFM graphs of samples prepared at high negative bias. Hall measurements showed that the carrier density and Hall mobility of these ITO films are sensitive to the bias voltage applied. We attributed these effects to the sensitivity of energy of Ar+ ions bombarding on growing films to the applied bias voltage in our experiments. At last the figure of merit was calculated to evaluate the quality of ITO thin films, the results of which show that sample prepared at bias voltage of −75V is good to be used in HJ cells application.
Keywords: PACS; 81.15Cd; 73.61−r; 68.55rf sputtering; Indium tin oxide; Negative bias; Ion bombardment; Heterojunction solar cell; Textured surface
A diffusion model for describing the bilayer growth (FeB/Fe2B) during the iron powder-pack boriding by M. Keddam; S.M. Chentouf (pp. 393-399).
In this paper, a diffusion model is proposed for studying the bilayer growth kinetics (FeB/Fe2B) on pure iron substrate during the powder-pack boriding in the temperature range of 1023–1273K.This model based on Fick's laws was solved, under certain assumptions, considering a parabolic growth of iron borides.For this purpose, a computer simulation program was created for predicting the boride layer thickness as a function of process parameters (temperature, time and surface boron content). A fairly good agreement was observed between the simulation calculations and experimental data derived from the literature.
Keywords: Computer simulation; Fe–B phase diagram; Powder-pack boriding; Fick's laws; Growth kinetics
Oxidation protection of copper surfaces using self-assembled monolayers of octadecanethiol by David A. Hutt; Changqing Liu (pp. 400-411).
Self-assembled monolayers (SAMs) of alkanethiols adsorbed onto clean surfaces of face centred cubic (fcc) metals have been studied extensively for their ability to control the chemical functionality of the surface and as a means of preventing the oxidation and corrosion of the substrate metal. However, in many cases it has been found that on reactive substrates such as copper, it is difficult to prepare SAMs without the incorporation of some oxygen into the structure. In this work, self-assembled monolayers of octadecanethiol (ODT) were formed on copper foil substrates using a series of etching treatments to remove the native oxide layer prior to deposition of the ODT coating from a modified solution. X-ray photoelectron spectroscopy was used to analyse the SAMs and showed that monolayers with no detectable oxygen content could be produced. The effect of exposing the samples to air at different temperatures was monitored to examine the rate of the oxidation process, which was found to vary strongly with temperature. Samples stored at room temperature were found to oxidise relatively quickly, while those kept in a refrigerator were slower. Storing samples in a freezer dramatically reduced the oxidation of the copper, such that samples kept for 10 weeks still did not show any clear evidence of oxygen incorporation.
Keywords: Self-assembled monolayers; Alkanethiol; Copper; Temperature; Oxidation; Octadecanethiol
Adsorption of cyclic hydrocarbons on Pt and the interaction of the adsorbed species with hydrogen by Zoltán Hlavathy; Pál Tétényi (pp. 412-419).
The adsorption of six-membered hydrocarbon cycles and cyclopentane and the interaction of hydrogen with the adsorbed layer on polycrystalline Pt-foil have been studied. The work function change (Δ φ) was followed by a Kelvin probe and the C/Pt peak ratio was determined by Auger electron spectroscopy. Combining these two techniques made it possible to distinguish between chemisorption via σ-bonds and π-complex formation. Benzene and toluene adsorbed first as π-complex while cyclohexane showed initially a partial aromatization and a π-complex-like bonding to the surface. Excess hydrocarbon or addition of hydrogen transformed the π-complex into σ-bonded species. Cyclopentane adsorbed via σ-bonds and showed no significant hydrogen effect.
Keywords: PACS; 82.65.−i; 82.65.Y; 82.80.PAromatic rings; π-Complex; Work function change; AES
Single violet luminescence emitted from ZnO films obtained by oxidation of Zn film on quartz glass by X.M. Fan; J.S. Lian; L. Zhao; Y.H. Liu (pp. 420-424).
The photoluminescence (PL) emission properties of ZnO films obtained on quartz glass substrate by the oxidation of Zn films were studied. The strong single violet emission centering about 413–424nm was observed in the room temperature PL spectra of the ZnO films. The intensity of violet emission increased and the peak position shift from 424 to 413nm with increasing oxygen pressures. The violet emission was attributed to the electron transition from the valence band to interstitial zinc (Zni) level under low oxygen pressure conditions (50–500Pa). Under high oxygen pressure conditions (5000–23,000Pa), both interstitial zinc (Zni) and zinc Vacancy (VZn) were thought to be responsible for the violet emission.
Keywords: ZnO; Violet photoluminescence; X-ray diffraction
Transparent carbon nanotube coatings by M. Kaempgen; G.S. Duesberg; S. Roth (pp. 425-429).
Thin networks of carbon nanotubes (CNTs) are sprayed onto glass or plastic substrates in order to obtain conductive transparent coatings. Transparency and conductivity at room temperature of different CNT material are evaluated. CNT coatings maintain their properties under mechanical stress, even after folding the substrate. At a transparency of 90% for visible light we observe a surface resistivity of 1kΩ/sq which is already a promising value for various applications.
Keywords: Carbon nanotubes; Transparent electrodes; ITO
Effects of surface inactivation, high temperature drying and preservative treatment on surface roughness and colour of alder and beech wood by Ismail Aydin; Gursel Colakoglu (pp. 430-440).
Although extensive research has been conducted in wood surface quality analysis, a unified approach to surface quality characterisation does not exist. Measurements of the variation in surface roughness and surface colour are used widely for the evaluation of wood surface quality. Colour is a basic visual feature for wood and wood-based products. Colour measurement is one of the quality control tests that should be carried out because the colour deviations are spotted easily by the consumers. On the other hand, a common problem faced by plywood manufacturers is panel delamination, for which a major cause is poor quality glue-bonds resulting from rough veneer. Rotary cut veneers with dimensions of 500mm×500mm×2mm manufactured from alder ( Alnus glutinosa subsp. barbata) and beech ( Fagus orientalis Lipsky) logs were used as materials in this study. Veneer sheets were oven-dried in a veneer dryer at 110°C (normal drying temperature) and 180°C (high drying temperature) after peeling process. The surfaces of some veneers were then exposed at indoor laboratory conditions to obtain inactive wood surfaces for glue bonds, and some veneers were treated with borax, boric acid and ammonium acetate solutions. After these treatments, surface roughness and colour measurements were made on veneer surfaces. High temperature drying process caused a darkening on the surfaces of alder and beech veneers. Total colour change value (Δ E*) increased linear with increasing exposure time. Among the treatment solutions, ammonium acetate caused the biggest colour change while treatment with borax caused the lowest changes in Δ E* values. Considerable changes in surface roughness after preservative treatment did not occur on veneer surfaces. Generally, no clear changes were obtained or the values mean roughness profile ( Ra) decreased slightly in Ra values after the natural inactivation process.
Keywords: Wood; Surface colour; Surface roughness; Inactivation; High temperature drying
The effects of anodic and cathodic processes on the characteristics of ceramic coatings formed on titanium alloy through the MAO coating technology by Xuetong Sun; Zhaohua Jiang; Zhongping Yao; Xuelin Zhang (pp. 441-447).
This paper reports on the investigation into the effects of the different anodic ja and cathodic jc current densities on the variations of the anodic and cathodic processes and the associated changes in the characteristics of the coatings synthesized on Ti–6Al–4V alloy substrate by microarc oxidation technique. The coated samples were subjected to coating thickness and cross-section fracture observation. Phase and elemental composition at different depth of the coatings were evaluated through X-ray diffraction and energy dispersive spectrum analyses. The experimental results indicate that the increase of ja leads to the increasing slope of anodic voltage U+ versus oxidation time plots, the larger coating thickness and the more coarse surface morphology of MAO coatings; while the aggrandizement of the cathodic process results in the lower growth rate and more uniform structure of coatings. The changes of the elements distribution from the interface towards the coating surface with variation of ja and jc are affected by the Ti anodic dissolution and the electromigration of electriferous particles, such as Al(OH)4−, in electrolytes.
Keywords: Microarc oxidation; Anodic to cathodic current ratio; Electromigration; Titanium alloy
Periodic microstructuring of iron cylinder surface in nitric acid in a magnetic field by S.V. Gorobets; O.Yu. Gorobets; A.N. Brukva (pp. 448-454).
The periodic surface microstructure of an iron cylinder is revealed under its corrosion in a solution of nitric acid in a constant magnetic field. The temporary dependencies of the microstructure parameters have been obtained for the cylinders with different diameters and lengths. The effect of microstructuring is a new example of nonlinear self-organization in a magnetic field. The results of the paper can be used for controlled etching of metallic surfaces with the help of a magnetic field application.
Keywords: PACS; 75.80.+q; 68.08.−p; 81.65.Cf; 68.35.−pPeriodic microstructure; Metal surface; Magnetic field; Nitric acid
SiO2 film electret with high surface potential stability by Ningyi Yuan; Jinhua Li (pp. 455-460).
The plasma surface treatment and ion implantation were utilized to improve the stability of charge storage in the SiO2 film electret. It was found that the SiO2 films treated by argon plasma with the arcing at 700V for 15min, or implanted by 150keV (kilo electron volt) Ar+ with a dose of 2×1011cm−2, after being negatively charged, showed a remnant negative potential as large as 90% of the primary value after being stored in a glass container with desiccant for 10 days. It was also found that after being negatively charged at room temperature and aged at 200–350°C for several times, the SiO2 films implanted by 150keV Ar+ had a relatively high remnant potential and it did not decay significantly even after being heated at the aging temperature of 200–350°C in room atmosphere for 60min.
Keywords: PACS; 61.72; 52.77SiO; 2; film electrets; Plasma treatment; Ion implantation; Repetition charging; Charge storage stability
Domain configuration and dielectric properties of Ba0.6Sr0.4TiO3 thin films by Chunlin Fu; Chuanren Yang; Hongwei Chen; Liye Hu; Linshan Dai (pp. 461-465).
The microstructure and electrical properties of Ba0.6Sr0.4TiO3 thin films have been investigated. Nanometer-sized domains, ranging from 8 to about 30nm, were observed by piezoresponse force microscopy (PFM). The critical size, below which only single domains exist, is found to be about 31nm. The film exhibits ferroelectric behavior characterized by polarization hysteresis loop and capacitance–voltage curve.
Keywords: Barium strontium titanate; Thin film; Domain; Hysteresis loop; Capacitance–voltage
Surface modification of exchange-coupled Co/NiOx magnetic bilayer by bias sputtering by P. Sangpour; O. Akhavan; A.Z. Moshfegh; G.R. Jafari; G. Kavei (pp. 466-473).
We have investigated the effect of bias voltage on sheet resistance, surface roughness and surface coverage of Co/NiOx magnetic bilayer. In addition, interface topography and corrosion resistance of the Ta/Co/Cu/Co/NiOx/Si(1 0 0) system have been studied for Co layers deposited at an optimum bias voltage. Atomic force microscopy (AFM) and four point probe sheet resistance (Rs) measurement have been used to determine surface and electrical properties of the sputtered Co layer at different bias voltages ranging from 0 to−80 V. The Co/NiOx bilayer exhibits a minimum surface roughness and low sheet resistance value with a maximum surface coverage atVb=−60 V resulted in a slight increase of magnetic resistance and its sensitivity for the Co/Cu/Co/NiOx/Si(1 0 0) magnetic multilayers, as compared with the same magnetic multilayers containing unbiased Co layers. The presence of Ta protection layer improves the corrosion resistance of the multilayers by three orders of magnitude in a humid environment.
Keywords: PACS; 81.15.Cd; 68.65.AcSurface modification; Magnetic multilayers; Co/NiO; x; Bias sputtering; AFM
Surface modifications of TiN coating by pulsed TEA CO2 and XeCl lasers by Milan S. Trtica; Victor F. Tarasenko; Biljana M. Gaković; Andrei V. Fedenev; Ljubica T. Petkovska; Bojan B. Radak; Evgeniy I. Lipatov; Mikhail A. Shulepov (pp. 474-482).
Interactions of a transversely excited atmospheric (TEA) CO2 laser and an excimer XeCl laser, pulse durations ∼2μs (initial spike FWHM ∼100ns) and ∼20ns (FWHM), respectively, with polycrystalline titanium nitride (TiN) coating deposited on high quality steel AISI 316, were studied. Titanium nitride was surface modified by the laser beams, with an energy density of 20.0J/cm2 (TEA CO2 laser) and 2.4J/cm2 (XeCl laser), respectively. The energy absorbed from the CO2 laser beam is partially converted to thermal energy, which generates a series of effects such as melting, vaporization of the molten material, shock waves, etc. The energy from the excimer XeCl laser primarily leads to fast and intense target evaporation. The calculated maximum temperatures on the target surface were 3770 and 6300K for the TEA CO2 and XeCl lasers, respectively. It is assumed that the TEA CO2 laser affects the target deeper, for a longer time than the XeCl laser. The effects of the XeCl laser are confined to a localized area, near target surface, within a short time period.Morphological modifications of the titanium nitride surface can be summarized as follows: (i) both lasers produced ablation of the TiN coating in the central zone of the irradiated area and creation of grainy structure with near homogeneous distribution; (ii) a hydrodynamic feature, like resolidified droplets of the material, appeared in the surrounding peripheral zone; (iii) the process of irradiation, in both cases, was accompanied by appearance of plasma in front of the target.Target color modifications upon laser irradiation indicate possible chemical changes, possibly oxidation.
Keywords: Laser surface modification; TiN coating; Grainy microstructure; Pulsed TEA carbon-dioxide laser; Pulsed excimer XeCl laser
Influence of domain boundaries on polarity of GaN grown on sapphire by H. Zhou; F. Phillipp; H. Schröder; J.M. Bell (pp. 483-487).
GaN films were grown on sapphire substrates by laser-induced reactive epitaxy. The domains in the films were determined to be the Ga-polarity by the convergent beam electron diffraction (CBED) technique, while the adjacent matrices had the N-polarity. The domain boundaries were characterized as inversion domain boundaries (IDBs). An atomic structure of the IDB is proposed based on high-resolution transmission electron microscopy (HRTEM) investigations. Control of the polarity of GaN/sapphire films was achieved by suppressing the formation of IDBs with an interlayer of AlGaN and a low-temperature GaN buffer layer.
Keywords: JEL classification; 61.16.Bg; 61.72.Ff; 68.55.−aInversion domain boundary; GaN; Polarity; HRTEM
Application of the chemical vapor-etching in polycrystalline silicon solar cells by M. Ben Rabha; M. Saadoun; M.F. Boujmil; B. Bessaïs; H. Ezzaouia; R. Bennaceur (pp. 488-493).
This paper reports a study of the application of chemical vapor-etching (CVE) for the rear surface and in the emitter of polycrystalline silicon (pc-Si) solar cells. The CVE technique consists of exposing pc-Si wafers to a mixture of HF/HNO3. This technique is used to groove the rear surface of the pc-Si wafers for acid vapors rich in HNO3 (HNO3/HF>1/4), in order to realize rear-buried metallic contacts (RBMC) and the formation of a porous silicon (PS) layer on the frontal surface of the cell for volume ratio of HNO3/HF=1/7. A significant increase of the spectral response in the long wavelength range was observed when a RBMC is formed. This increase was attributed to the reduction of the effective thickness of the base of the cells and grain boundary Al gettering. The achievement of a PS layer on the emitter of the pc-Si cells passivates the surface and reduces the reflectivity. The dark I– V characteristics of pc-Si cells with emitter-based PS show an important reduction of the reverse current together with an improvement of the rectifying behaviour. The I– V characteristic under AM1.5 illumination shows an enhancement of both short circuit current density and fill factor. The internal quantum efficiency is improved, particularly in the short wavelengths region.
Keywords: PACS; 80.05.Rm; 68.37.Hk; 78.30.Hv; 78.40.FyPolycrystalline silicon; Groove; Etching; Porous silicon
Core-shell structure and magnetic properties of magnetite magnetic fluids stabilized with dextran by X.Q. Xu; H. Shen; J.R. Xu; J. Xu; X.J. Li; X.M. Xiong (pp. 494-500).
The adsorption process of different dextran molecules onto the surface of in water dispersed magnetite nanoparticles has been investigated to optimize the preparation of magnetite magnetic fluids (MMFs). An average magnetite core size of 7.1nm was found by X-ray diffraction and that of 8nm was found by transmission electron microscopy for the samples prepared at 90°C. An average hydrodynamic diameter of 25nm was observed by scanning electron microscopy and that of 25–300nm was obtained by photon correlation spectroscopy. The dextran was adsorbed by physical adsorption, a molecular weight of 20kDa gave the best stability of these MMFs. The shell layer of the particles was weakly negatively charged in buffer solutions of pH values between 5.5 and 9.5. The particles seem to be mainly stabilized by sterical repulsion. The maximum available saturation magnetization of the MMFs was 3.5kA/m.
Keywords: PACS; 68.45.D; 75.50.MAdsorption; Dextran; Magnetite; Magnetic nanoparticles