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Applied Surface Science (v.242, #1-2)
CVD-zirconia on fumed silica and silica gel by M.V. Borysenko; V.M. Gun’ko; A.G. Dyachenko; I.Y. Sulim; R. Leboda; J. Skubiszewska-Zięba; J. Ryczkowski (pp. 1-12).
Two series of CVD-zirconia/silica samples were synthesised on the basis of silica gel Si-60 and fumed silica A-380 as substrates using zirconium tetrachloride chemisorbed then hydrolysed heated. The reaction cycles were repeated up to four times. Structural and adsorption characteristics of zirconia/silicas were investigated using X-ray diffraction (XRD), nitrogen adsorption–desorption, infrared (IR) and ultraviolet/visible (UV–vis) spectroscopies and quantum chemical methods. A tetragonal lattice gives the main contribution to zirconia crystallites. The size of these crystallites depends not only on the number of the reaction cycles ( ir) but also on the type of a silica matrix. The zirconia crystallite size grows on zirconia deposition onto fumed silica with increasing ir, but it is near the same for zirconia/silica gel in consequence of a restricted size of pores of Si-60. The fumed silica substrate inhibits change of phase of zirconia on heating to a greater extent than the silica gel substrate. Motives of several crystalline lattices of zirconia were found after sample calcination at high temperatures. UV–vis and IR spectra of adsorbed probe compounds ((dimethylamino)azobenzene (DMAAB) and pyridine (Py)) suggest that CVD-zirconia/silica surface is characterized by several types of acidic sites.
Keywords: PACS; 61.10.-i; 61.43.Gt; 61.46.+w; 64.70.Kb; 68.35.-p; 68.35.BsCVD-zirconia/silica gel; CVD-zirconia/fumed silica; Structural characteristics; Zirconia crystallite size; Adsorption properties; Infrared spectra; UV–vis spectra; Pyridine adsorption; (Dimethylamino)azobenzene adsorption
Investigation of SnO2 thin film evolution by thermoanalytical and spectroscopic methods by E. Horváth; J. Kristóf; H. Nasser; R.L. Frost; A. De Battisti; Á. Rédey (pp. 13-20).
The thermal evolution process of a SnO2 thin film from SnCl2·2H2O precursor dissolved in ethanol was followed by thermogravimetry combined with mass spectrometry (TG-MS), diffuse reflectance Fourier transform infrared spectroscopy (DRIFT) and infrared emission spectrometry (IRES). The precursor salt solution was deposited on a titanium metal sheet. After evaporation of the solvent, the gel-like film was heated in a thermobalance in an oxidative environment to 600°C. Mass spectrometric ion intensity curves showed the liberation of chlorinated species, alcoholic fragments and CO2 as combustion product and from the decomposition of surface carbonyls, carboxylates and carbonates. The presence of OH, CH and CO bands in the infrared spectra was confirmed and their assignment was made by the deconvolution of the recorded curves as a function of the firing temperature.
Keywords: Tin oxide thin films; Sol–gel process; Thermogravimetry-mass spectrometry (TG-MS); Diffuse reflectance infrared spectroscopy (DRIFT); Infrared emission spectroscopy (IRES)
Ab initio comparative study of montmorillonite structural models by B. Minisini; F. Tsobnang (pp. 21-28).
Montmorillonite is one of the most commonly used 2:1 phyllosilicates. A characteristic feature of the smectites is a high degree of structural disorder leading to a high dispersity of the cation exchange capacity (CEC). The electrostatic interactions due to the CEC are important in a lot of industrial processes. We examine the electrostatic properties of Otay type montmorillonite as a function of the octahedral configuration. We have chosen two models of cis-vacant sites and two models of trans-vacant sites. A plane-wave density functional theory has been used to optimize the atomic positions and perform a Mulliken population analysis. The results of the hydrogen position and the electrostatic charges of the different layers are presented. From these results, the trans-vacant configuration shows a higher hydrophilic character than the cis-vacant configuration.
Keywords: PACS; 91.60; 71.15.M; 71.15.ApMontmorillonite; Density functional theory; Plane-wave; Electrostatic charges
Gallium oxide nanomaterials produced on SiO2 substrates via thermal evaporation by Nam Ho Kim; Hyoun Woo Kim (pp. 29-34).
We have prepared the novel gallium oxide (Ga2O3) nanomaterials on SiO2 substrates by a thermal evaporation of GaN powders. We found that the products consisted of the nanobelts with additional nanostructures formed on the sides of nanobelts. The nanobelts had a single-crystalline monoclinic structure with a width in the range of 100–300nm. We have discussed the possible mechanism leading to the formation of the Ga2O3 nanomaterials. Photoluminescence spectrum under excitation at 325nm showed a blue emission.
Keywords: PACS; 81.07.BcEvaporation; Monoclinic; Gallium oxide; Nanomaterials
Ba and BaO on W and on Sc2O3 coated W by A. Shih; J.E. Yater; C. Hor (pp. 35-54).
Temperature-programmed desorption (TPD) and Auger electron spectroscopy (AES) are used to characterize the surface layers that form under an evaporating flux of a dispenser cathode (which is a Ba and BaO source) on a W substrate and Sc2O3-coated W substrate to simulate the surface layer of a conventional dispenser cathode and scandate cathode, respectively. The surface layers were prepared while the substrate was either at 940°Cb (1272K), a typical operating temperature, or at 1125°Cb (1477K), a typical activation temperature. Our investigation found that a partial layer of BaO formed on W, similar to the surface layer that forms on a dispenser cathode. Heating to the activation temperature causes the BaO to form a stronger bond with W. For the Sc2O3-coated W substrate, heating to the activation temperature is necessary for the inter-diffusion between the Sc2O3 and W to occur. BaO layers form a stronger bond to the inter-diffused layer than to pure W. However, the most important finding is that a stable BaO-containing compound forms and continues to accumulate under the impinging flux on the Sc2O3 and W covered substrate at 940°Cb. Surface emission models describe successfully all other dispenser cathodes, but fail to explain the emission characteristics of scandate cathodes. Raju and Maloney proposed an alternate model, which requires the presence of a thick layer of semi-conducting material. Our finding suggests that it is possible to form a thick layer from simultaneous presence of BaO, Sc2O3 and W. However, further investigation is necessary to determine if the Raju and Maloney type layer is indeed present on top of scandate cathodes.
Keywords: PACS; 82.65My; 79.40+zThermionic emission; Dispenser cathode; Thermal desorption; Scandate cathode; Barium oxide; Scandium oxide
Surface-energy-driven abnormal grain growth in Cu and Ag films by Fei Ma; Jian-Min Zhang; Ke-Wei Xu (pp. 55-61).
A comparative investigation has been made for Cu and Ag films in three states (as-deposited, attaching films after annealing, and free-standing films after annealing) by XRD and TEM. XRD patterns show that, after annealing at 300°C for 2.5h, (111) peak increased obviously in both free-standing Cu and Ag films, on the contrary, (200) and (220) peak increased obviously in attaching films. In addition, a (111)-oriented abnormal large grain was observed in both free-standing Cu and Ag films with TEM, while (100) and (110)-oriented abnormal large grains appeared in attaching Cu films and a (21l)-oriented abnormal grain appeared in attaching Ag films. The experimental results have been explained satisfactorily by the minimizations of surface energy and strain energy.
Keywords: Thin metal films; Preferred orientations; Abnormal grain growth; Surface energy; Strain energy
Effect of O-implantation on the structure and resistance of Ge2Sb2Te5 film by Bo Liu; Zhitang Song; Ting Zhang; Songlin Feng; Bomy Chen (pp. 62-69).
Ge2Sb2Te5 films were deposited by rf magnetron sputtering on Si(100)/SiO2 substrates. In order to increase the Ge2Sb2Te5 sheet resistance, O+ ion was implanted into Ge2Sb2Te5 films. The effect of oxygen implantation on the structure of Ge2Sb2Te5 film was studied in details using XRD, Raman spectra, and XPS methods. It is indicated that the structure of crystalline Ge2Sb2Te5-O annealed at 250°C is identified as a FCC structure even when oxygen implant fluence reaches 1.29 × 1017 ions per cm2 and the lattice parameter increases as oxygen implant fluence increasing. However, phase separation takes place when annealing temperature is 450°C. In the case of the high fluence (higher than 6.44 × 1016 ions per cm2) samples, phase separation no longer takes place and phase transition from FCC to hexagonal structure is suppressed by oxygen implantation. Oxygen implantation has great effect on the resistance-annealing behaviour of Ge2Sb2Te5 film, which may be origin from the structural changes including defect formation, phase separation, suppression of phase transition from FCC to hexagonal structure, and the refinement of grain size, etc. The Rs of Ge2Sb2Te5-O film is higher than that of Ge2Sb2Te5 film when annealing temperature is higher than 340°C, which may be caused by phase separation and current carrier scattering by crystallite boundary.
Keywords: Ge; 2; Sb; 2; Te; 5; Oxygen implantation; Structure; Sheet resistance; Raman spectra
The role of interorbital interference in the formation of STS spectra by Leszek Jurczyszyn; Barbara Stankiewicz (pp. 70-81).
Theoretical study presented in this paper is related to the general problem of the role of interference effects in the tunneling of electrons in STM systems. The specific aim of this work is to clarify the possible influence of the intra-atomic interference connected with the electron tunneling through s andpz orbitals of the tip and the sample on the results of scanning tunneling spectroscopy (STS). This kind of interference can increase or reduce the efficiency of the tunneling through s andpz orbitals of the STM system. It is shown that this factor may significantly influence the current–voltage dependences and modify considerably the STS features connected with s andpz states of the tip and the sample. STS simulations indicate that the shape and origin of important features in the current–voltage dependences and STS spectra may represent the effect of the interorbital interference which cannot be explained by density-of-states distributions of the tip and the sample.
Keywords: PACS; 68.37.Ef; 73.20.; −; r; 73.40.GkScanning tunneling spectroscopy; Tunneling
Quantitative surface analysis of plastic deformation of Pd electrodes in nanoscale by Ali Eftekhari; Mahmood Kazemzad; Mansoor Keyanpour-Rad; Mohammad Ali Bahrevar (pp. 82-87).
Small-angle X-ray scattering (SAXS) was employed as a powerful technique for quantitative surface analysis of Pd electrodes subjected to severe plastic deformation. The experimental data obtained from SAXS measurements were analyzed by means of fractal geometry, as so-called fractal dimensions can be used as a quantitative measure of surface roughness. The influence of the strength of plastic deformation induced to the Pd/H system (due to phase transformation) on the degree of surface roughness was inspected. The powerfulness of this approach is ability for inspecting surface roughness in nanoscale. The surface fractality at nanoscale is significantly different from that at microscale.
Keywords: Nanostructure; Plastic deformation; Pd electrode; SAXS; Fractal; Nanoscale roughness.
Magic behavior and bonding nature in hydrogenated aluminum nitride clusters by Ling Guo; Hai-shun Wu; Zhi-hao Jin (pp. 88-96).
Interaction of hydrogen with aluminum nitride clusters have been investigated using the density functional method of Becke's three-parameter hybrid functional with the nonlocal correlation of Lee, Yang, and Parr. Berny structural optimization and frequency analyses are performed with the basis of 6–311 + G (d). Our results show large binding energies of a single hydrogen atom on small AlN clusters and large highest occupied and lowest unoccupied molecular-orbital gaps for (AlN)H, (AlN)4H, (AlN)6H, (AlN)7H, and (AlN)8H making these species behave like magic clusters. In general the binding energy of H is found to decrease with an increase in the cluster size. Calculations on two hydrogen atoms on AlN clusters show large binding energies for (AlN) nH2 with n = 1, 3, 5, and 7, but significant decrease for (AlN)7H2 as compared to (AlN)7H. The results confirm the magic behavior of (AlN)7H. And the calculations also suggest that hydrogen should be dissociated on (AlN)3, (AlN)5 and (AlN)6.
Keywords: Magic behavior; Bonding nature; Aluminum nitride cluster; Density functional theory
The corrosion performance of polyaniline on nickel plated mild steel by A.T. Özyılmaz; G. Kardaş; M. Erbil; B. Yazıcı (pp. 97-106).
Electrochemical synthesis of polyaniline (PANI) was achieved on Ni plated (1μm) mild steel (MS/Ni) and unplated mild steel (MS). The synthesis was carried out under cyclic voltammetric conditions from 0.1M aniline containing oxalic acid solution. AC impedance spectroscopy (EIS) and anodic polarization curves were used to evaluate the corrosion performance of PANI coated and uncoated electrodes in 3.5% NaCl. It was observed that Ni plating reduced drastically the corrosion rate of mild steel and exhibited an efficient barrier property on MS. However, the porosity of nickel plating increased for longer periods. It was found that polymer film decreased the porosity of Ni coating by catalyzing the passivation of this layer with time and that PANI top coat could provide significant protection efficiency to MS/Ni electrode. While PANI coated mild steel (MS/PANI) showed a protection property against the attack of corrosive products. Its lifetime was limited for extended periods. It was found out that corrosion resistance of Ni plating with PANI top coat (MS/Ni/PANI) was higher for much longer periods with respect to the one observed for mild steel.
Keywords: Nickel plating; Polyaniline; Corrosion; AC Impedance spectroscopy
Auger electron spectroscopy analysis of high metal content micro-structures grown by electron beam induced deposition by F. Cicoira; P. Hoffmann; C.O.A. Olsson; N. Xanthopoulos; H.J. Mathieu; P. Doppelt (pp. 107-113).
An auger electron spectroscopy study was carried out on Rh-containing micro-structures grown by electron beam induced deposition (EBID) of the iso-structural and iso-electronic precursors [RhCl(PF3)2]2 and [RhCl(CO)2]2. A material containing between 55 and 60at.% Rh was obtained from both precursors. The chemical composition of structures grown from the two different precursors indicates a similar decomposition mechanism. Deposits grown from [RhCl(PF3)2]2 showed a chemical composition independent of electron energy and electron dose in the investigated range of conditions.
Keywords: PACS; 82.80. Pv; 81.15.Jj; 81.70.Jb; 85.40.UxChemical vapor deposition; Auger electron spectroscopy; Nanomaterials
Corrosion and inhibition of stainless steel pitting corrosion in alkaline medium and the effect of Cl− and Br− anions by S.A.M. Refaey; F. Taha; A.M. Abd El-Malak (pp. 114-120).
The effect of carbonate anion on the pitting corrosion and inhibition behavior of stainless steel samples (304L SS and 316L SS) has been studied using potentiodynamic and scanning electron microscope (SEM) techniques. The effect of concentration of CO32− ions, pH, potential scanning rate and the composition of stainless steel are discussed. Additions of Cl− and Br− ions into the carbonate solution increase the anodic dissolution of stainless steel and decrease its pitting corrosion resistance. The effect of CO32− anion on the inhibition of chloride and bromide pitting corrosion of the two stainless steel types has been studied also. Pitting corrosion decrease with the increasing of sodium carbonate concentration, i.e. increases the resistance of stainless steels towards the chloride and bromide pitting corrosion. This inhibition effect argued to formation of [Fe,Cr]CO3 film caused by preferential adsorption of the CO32− ion, leading to instantaneous repair of weak sites for pit nucleation.
Keywords: Corrosion; 304L and 316L stainless steels; Sodium carbonate; Chloride and bromide
First-principles study of electronic structure and electron energy-loss-spectroscopy (EELS) of transition-metal aluminates as high- k gate dielectrics by C.B. Samantaray; H. Sim; H. Hwang (pp. 121-128).
We study the electronic structure and electron energy loss function of different transition-metal (Y, Sc, Zr, Hf and Ta) aluminates using density functional theory (DFT) and local density approximation (LDA). The transition metals are substituted favorably at the octahedral Al sites in the α-alumina system. Y and Sc introduced shallow unoccupied d-states near the conduction band edge. Using the calculated orbital resolved partial p-DOS, we have investigated the oxygen K-edge and compared to the experimental results. In addition, the energy-loss-functions were calculated in the low energy-loss region directly reflects the collective electron excitations (plasmons) and single valence electron excitation in to unoccupied states of the conduction band.
Keywords: PACS; 71.15.Mb; 71.15.Hx; 71.20.Be; 85.30.YyAb-initio calculation; Energy-band structures; EELS; Aluminates; High-; k
Magnetic induced vertical crystal growth of perylene cation radicals on ITO glass surface by Ruggero Micheletto; Jun Matsui; Munetaka Oyama; Khalil El-Hami; Kazumi Matsushige; Yoichi Kawakami (pp. 129-133).
Perylene–acetonitrile solution with tetra- n-butyl-ammonium perchlorate (TBAP) is a substance that tends to electro-crystallize and form particular needle-like structures. These perylene materials are studied extensively for their peculiar electrical and optical properties and for the interest in the fundamental phenomena occurring in the electro crystallization process. We introduce here a novel methodology to orient the needle-like crystals by means of electro crystallization in presence of a weak magnetic field. We report details on the technique we used and we present several exceptional SEM pictures of the aggregates growing vertically from the substrate by the effect of the magnetic field. The method introduce a new simple way to control the growth of these intriguing materials and the approach is potentially the basis for the fabrication of new miniaturized devices.
Keywords: PACS; 81.07.−b; 75.10.Dg; 81.10.Aj; 81.10,−hNanoscale structures; Perylene; Crystals; Electrocrystallization; Orientation; Magnetic field; Crystal growth
Magnetotransport properties and the annealing effect of (Ga,Mn)As/Si heterostructures and substrate-free (Ga,Mn)As films by S. Sato; M.A. Osman; Y. Jinbo; N. Uchitomi (pp. 134-139).
We investigated the properties and annealing effects of substrate-free (Ga,Mn)As films prepared by etching Si substrates from (Ga,Mn)As/Si structures, and compared the results with those from (Ga,Mn)As/Si heterostructures. The substrate-free (Ga,Mn)As films with 6% Mn content were annealed at 250°C as a function of time. From Hall-effect measurements, the Curie temperature of substrate-free (Ga,Mn)As films was estimated to be 87K for an as-grown film, enhanced up to 152K after low-temperature annealing for 60min. We found that the (Ga,Mn)As films grown on Si substrates show a relatively high Curie temperature.
Keywords: GaMnAs; Diluted magnetic semiconductor; Low-temperature MBE; GaAs/Si heterostructures
Micro-structural characterization of laser interference irradiated Ni/Al multi-films by C. Daniel; F. Mücklich (pp. 140-146).
Biological solutions to enhance strength and stability often use lateral and hierarchical composite structures from nano- to micro-scale. The effect does not consist of a large chemical variety but it is realized by structural composites (namely phase changes and orientations). A new developed bio-mimetic laser interference structuring technique uses this biological approach to optimize mechanical properties of surfaces and thin films.In past, laser interference irradiated Ni/Al multi-films showed periodical properties in the range of interference period. The hardness and modulus could be varied periodically and the texture and stress situation could be significantly changed.In this work, the micro-structural evolution of irradiated Ni/Al multi-films is analyzed by transmission electron microscopy (TEM) measurements to justify the properties change. The grain size can be obtained to be laterally oscillating between 5 and 10nm and up to 100nm and the layer interface to be semicoherent. Up to a certain depth, intermetallic compounds are found in the layer interface.
Keywords: Thin multi-film; Bio-mimetic laser interference structuring; Structural composite; Transmission electron microscopy
Investigation of 3-mercaptopropyltrimethoxysilane self-assembled monolayers on Au(111) surface by I. Piwoński; J. Grobelny; M. Cichomski; G. Celichowski; J. Rogowski (pp. 147-153).
In this paper, preparation method of two-dimensional (2D) silica-like surface from self-assembled monolayers (SAMs) of 3-mercaptopropyltrimethoxysilane (MPTMS) on Au(111) surface is presented. The surface structure and morphology were characterized by scanning tunneling microscopy (STM) and secondary ion mass spectrometry (SIMS). In a first step, gold surface was imaged in order to find the topography. Then investigations were focused on MPTMS deposited on Au(111). Further steps like hydrolysis and condensation of MPTMS end-groups were performed and monitored by STM and SIMS methods. Hydrolysis and condensation reactions lead to 2D SiO2 network called glass monolayer. It can be also described as 2D sol–gel processes. All procedures were performed in monolayer. When the state of end groups of MPTMS changes, i.e. when methoxy (Si–OCH3) groups undergo hydrolysis to silanols (Si–OH) groups, the surface topography changes. The similar phenomena may be observed when silanols undergo condensation and siloxy (Si–O–Si) bonds are created.
Keywords: STM; ToF-SIMS; SAMs; 3-Mercaptopropyltrimethoxysilane
Structural and energetic heterogeneities and adsorptive properties of synthetic carbon adsorbents by M.M. Seredych; V.M. Gun’ko; A. Gierak (pp. 154-161).
This paper reports results of carbonization of synthetic copolymers 4,4′-diphenyl sulfone dimethacrylate (DPS DM) in the presence of iron salts (Fe(NO3)3 or FeCl3) as catalysts. The synthesized carbon adsorbents have a spherical shape of grains, a high specific surface area and good sorption and mechanical properties. The structural characteristics were studied using the nitrogen, phenol and naphthalene adsorption from gas and liquid phases. The interaction of the organic substances with the synthesized carbons in the aqueous medium depends on the texture of the adsorbents (volume of micro and mesopores, pore size distribution, specific surface area) and the chemical properties (concentrations of functional oxygen-containing groups and mineral admixtures).
Keywords: Synthetic carbon adsorbents; Pore size distribution; Surface heterogeneity; Phenol adsorption; Naphthalene adsorption
Femtosecond versus nanosecond laser machining: comparison of induced stresses and structural changes in silicon wafers by M.S. Amer; M.A. El-Ashry; L.R. Dosser; K.E. Hix; J.F. Maguire; Bryan Irwin (pp. 162-167).
Laser micromachining has proven to be a very successful tool for precision machining and microfabrication with applications in microelectronics, MEMS, medical device, aerospace, biomedical, and defense applications. Femtosecond (FS) laser micromachining is usually thought to be of minimal heat-affected zone (HAZ) local to the micromachined feature. The assumption of reduced HAZ is attributed to the absence of direct coupling of the laser energy into the thermal modes of the material during irradiation. However, a substantial HAZ is thought to exist when machining with lasers having pulse durations in the nanosecond (NS) regime. In this paper, we compare the results of micromachining a single crystal silicon wafer using a 150-femtosecond and a 30-nanosecond lasers.Induced stress and amorphization of the silicon single crystal were monitored using micro-Raman spectroscopy as a function of the fluence and pulse duration of the incident laser. The onset of average induced stress occurs at lower fluence when machining with the femtosecond pulse laser. Induced stresses were found to maximize at fluence of 44Jcm−2 and 8Jcm−2 for nanosecond and femtosecond pulsed lasers, respectively. In both laser pulse regimes, a maximum induced stress is observed at which point the induced stress begins to decrease as the fluence is increased. The maximum induced stress was comparable at 2.0GPa and 1.5GPa for the two lasers. For the nanosecond pulse laser, the induced amorphization reached a plateau of approximately 20% for fluence exceeding 22Jcm−2. For the femtosecond pulse laser, however, induced amorphization was approximately 17% independent of the laser fluence within the experimental range. These two values can be considered nominally the same within experimental error. For femtosecond laser machining, some effect of the laser polarization on the amount of induced stress and amorphization was also observed.
Keywords: PACS; 61.18j Other methods of structural determination; 61.82 fk Radiation effect of semiconductors; 81.65 b Surface treatmentRaman spectroscopy; Laser machining; Micromachining; Silicon amorphization; Induced stress; Femtosecond laser machining
Characterization of copper indium ditelluride/electrolyte interface utilizing electrochemical impedance spectroscopy by Arun Vijayakumar; Tianbao Du; Kalpathy B. Sundaram (pp. 168-176).
Copper indium telluride (CIT) is a promising semiconductor material for use in thin film solar cells, especially photoelectrochemical solar cells (PESC). Impedance measurements were used to evaluate the relative band edge positions of polycrystalline n-CuInTe2 electrodes in various aqueous electrolytes, by measuring the extrapolated flat-band potentials, Vfb. By varying applied dc potential, frequency and pH of the electrolyte, the semiconductor–electrolyte interfaces are studied through capacitance measurements and Mott–Schottky analysis. The flat-band potential and carrier concentrations were determined from the Mott–Schottky plots. It was found that Vfb could be shifted depending on the pH of the electrolyte, while it is independent of the testing frequency. The changes in Vfb with pH could be due to surface states and other modifications through etching and polishing. The surface carrier concentrations were found to increase with pH. The different surface chemistry studied by X-ray photoelectron spectroscopy might account for this change.
Keywords: Copper indium telluride; Semiconductor; Impedance; Flat-band; Surface chemistry
Research progress on laser surface modification of titanium alloys by Y.S. Tian; C.Z. Chen; S.T. Li; Q.H. Huo (pp. 177-184).
Recent developments on laser surface modification of titanium and its alloys are reviewed. Due to the intrinsic properties of high coherence and directionality, laser beam can be focus onto metallic surface to perform a broad range of treatments such as remelting, alloying and cladding, which are used to improve the wear and corrosion resistance of titanium alloys. In addition, the fabrication of bioactive films on the surface of titanium alloys to improve their biocompatibility can be performed by the method of laser ablation deposition. The effect of some laser processing parameters on the resulting surface properties of titanium alloys is discussed. The problems to be solved and the prospects in the field of laser modification of titanium and its alloys are elucidated.
Keywords: Research progress; Laser surface modification; Titanium alloys
Crystallization of amorphous-Si films by flash lamp annealing by B. Pécz; L. Dobos; D. Panknin; W. Skorupa; C. Lioutas; N. Vouroutzis (pp. 185-191).
The crystallization of amorphous silicon films deposited on glass, using the flash lamp annealing process was realized and studied. The duration of the flash is 20ms, about two orders of magnitude shorter than the standard rapid thermal annealing process. The a-Si films deposited on Corning glass were irradiated with different energy densities and crystallized exhibiting grains with a mean size up to 6μm. In order to reduce the strain due to the thermal gradient, the samples were preheated from the backside. The ability of the FLA process to eliminate the ingrain defects in already crystallized poly-Si films at 600°C is also demonstrated.
Keywords: PACS; 61.16.Bg; 61.82.FkSi; Transmission electron microscopy; Crystallization; thin films
Catalytic growth of carbon nanotubes over Ni/Cr hydrotalcite-type anionic clay and their hydrogen storage properties by M.M. Shaijumon; N. Bejoy; S. Ramaprabhu (pp. 192-198).
Carbon nanotubes have been prepared by the catalytic decomposition of acetylene over Ni/Cr hydrotalcite-type anionic clay catalyst. Ni/Cr hydrotalcite-type anionic clay precursors have been prepared by co-precipitation technique. The role of stability of Ni nanoparticles obtained in situ from the decomposition of the catalyst on the growth of MWNTs is discussed. The as-synthesized and purified carbon nanotubes are characterized by thermogravimetry, IR spectroscopy, X-ray diffraction, BET analysis, scanning electron microscopy, transmission electron microscopy and Raman spectroscopy measurements. The hydrogen adsorption capacity of as-synthesized and purified multiwalled carbon nanotubes at 298K has been obtained using a high-pressure hydrogen adsorption set-up and the results are discussed.
Keywords: Catalyst; Nanotube; Ni/Cr hydrotalcite
Self-assembly of lacunary Dawson type polyoxometalates and poly(allylamine hydrochloride) multilayer films: photoluminescent and electrochemical behavior by Min Jiang; Enbo Wang; Xiuli Wang; Aiguo Wu; Zhenhui Kang; Suoyuan Lian; Lin Xu; Zhuang Li (pp. 199-206).
Ultrathin multilayer films containing a lacunary Dawson type polyoxometalate (POM) cluster K17[Ln(P2Mo17O61)2] (LnPMo, Ln = Eu, Tb) and poly(allylamine hydrochloride) have been prepared by electrostatic layer-by-layer self-assembly (ELSA) method. The multilayer films have been characterized by UV–vis absorption spectroscopy, ellipsometry and atomic force microscopy (AFM). The photoluminescent behavior of films at room temperature was investigated to show the Ln3+ characteristic emission pattern. The occurrence of photoluminescent activity confirms the potential applications in creating luminescent materials. Additionally, the electrochemical behavior of multilayer films was studied and the growth of multilayer films can be observed.
Keywords: PACS; 78.55; 82.80.FPolyoxometalates; Multilayers; Photoluminescence; Electrochemistry
Influence of hydrogen and oxygen plasma treatment on field emission characteristics of boron nitride thin films by Weiqing Li; Guangrui Gu; Yingai Li; Zhi He; Lihua Liu; Chunhong Zhao; Yongnian Zhao (pp. 207-211).
Boron nitride (BN) nanometer films are synthesized on Si(100) substrates by RF reactive magnetron sputtering. The surfaces of BN films are treated with hydrogen and oxygen plasma, respectively and studied by Fourier transform infrared (FTIR) spectra, atomic force microscopic (AFM) and field emission characteristics. The results show that the surface negative electron affinity (NEA) of the films is increased, the threshold field reduced and the emission current increased due to hydrogen plasma treatment. The effect of oxygen plasma treatment on field emission characteristics of BN films is obscure. The result shows that only the emission current is slightly decreased due to the surface oxidation of BN films.
Keywords: PACS; 79.70.+q; 81.65.−b; 81.15.CdBN films; Hydrogen and oxygen plasma; Surface treatment; Field emission; Threshold electric fields; Emission current
Zinc oxide nanorod and nanowire for humidity sensor by Yongsheng Zhang; Ke Yu; Desheng Jiang; Ziqiang Zhu; Haoran Geng; Laiqiang Luo (pp. 212-217).
ZnO nanorod and nanowire films were fabricated on the Si substrates with comb type Pt electrodes by the vapor-phase transport method, and their humidity sensitive characteristics have been investigated. These nanomaterial films show high-humidity sensitivity, good long-term stability and fast response time. It was found that the resistance of the films decreases with increasing relative humidity (RH). At room temperature (RT), resistance changes of more than four and two orders of magnitude were observed when ZnO nanowire and nanorod devices were exposed, respectively, to a moisture pulse of 97% relative humidity. It appears that the ZnO nanomaterial films can be used as efficient humidity sensors.
Keywords: PACS; 81.07.Bc; 81.10.Bk; 82.47.RsZinc oxide nanomaterial; Vapor-phase transport; Humidity sensor