Applied Surface Science (v.210, #3-4)
Editorial Board (ii).
Subject Index (III-IX).
Author index (I-II).
Formation of high quality gallium nitride thin films on Ga-diffused Si(1 1 1) substrate by Chengshan Xue; Li Yang; Cuimei Wang; Huizhao Zhuang; Qinqin Wei (153-157).
High quality gallium nitride thin films have been successfully grown on the Ga-diffused Si(1 1 1) substrates through ammoniating Ga2O3 thin films deposited by r.f. magnetron sputtering. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), atomic force microscope (AFM) and photoluminescence (PL) were used to characterize the synthesized samples. The analyses reveal that the formed films are high quality polycrystalline hexagonal gallium nitride. The as-formed GaN films show a flat surface topography with RMS roughness varied from 29 to 48 Å. The strong near-band-edge-emission peak around 368 nm was observed at room temperature. This is a novel method to fabricate GaN thin films based on the direct reaction between Ga2O3 and NH3 on the Ga-diffused Si(1 1 1) substrates.
Keywords: Ga2O3; GaN; r.f. Magnetron sputtering; Ammoniating;
Local surface cleaning and cluster assembly using contact mode atomic force microscopy by D.-Q Yang; E Sacher (158-164).
Conventional contact mode atomic force microscopy (AFM) has been used for local surface cleaning and cluster alignment. By using the AFM tip to sweep and push in contact mode, we have demonstrated that Cu clusters, prepared by vacuum evaporation onto Dow Cyclotene 3022 polymer and subsequent exposure to atmosphere, can easily be moved by the AFM tip, and assembled at the outer edge of the scanned region to form a line of clusters. We have found that the force applied by the tip plays an important role in the ease of cluster motion. Cyclotene surface treatment that enhances cluster adhesion hinders this ability, and may be used as a method of nanofabrication.
Keywords: Copper nanoclusters; AFM; Cluster manipulation; Dow Cyclotene polymer; Local surface cleaning;
Temperature effect on the Cu2O oxide morphology created by oxidation of Cu(0 0 1) as investigated by in situ UHV TEM by Guangwen Zhou; Judith C Yang (165-170).
The temperature effect on the Cu2O oxide morphology was investigated by oxidizing Cu(1 0 0) thin films at the temperature ranging from 150 to 1000 °C and constant oxygen partial pressure of 5×10−4 Torr. The evolution of the oxide island size and shape was followed inside an in situ ultrahigh vacuum transmission electron microscope (UHV TEM). Of particular interest, we find that the oxide morphology can be triangular, hut, rod or pyramid shaped depending only on the oxidation temperature.
Keywords: Oxidation; Copper thin film; Cu2O; Morphology; In situ ultrahigh vacuum transmission electron microscope (UHV TEM);
Enhancement of organic nanoparticle preparation by laser ablation in aqueous solution using surfactants by Bo Li; Tomonori Kawakami; Mitsuo Hiramatsu (171-176).
Nanoparticle and metal phthalocyanine (MPc) transparent colloidal aqueous solutions were directly obtained by 355 nm YAG laser ablation. We found that too long an irradiation time does not contribute to producing nanoparticles and their generation efficiency increases with a low solution temperature. We believe this due to nanoparticle reassociation which is caused by hydrophobicity. To prevent generated nanoparticles from reassociating we performed experiments adding two kinds of ionic and nonionic surfactants into solution. We found five characteristics of nanoparticle generation from adding surfactants to a solution regardless of the type of surfactant used. These characteristics are that: (1) production efficiency increases; (2) stability is better after irradiation; (3) irradiation intensity needed to induce nanoparticle generation becomes lower; (4) mean size of the generated nanoparticles becomes smaller; and (5) crystalline structures of oxo(phthalocyaninato) vanadium (IV) (VOPc) are controllable by changing the surfactant concentration.
Keywords: Laser ablation; Nanoparticles; Phase change; Surfactants; Phthalocyanine;
Formation of p-type ZnO film on InP substrate by phosphor doping by Kyu-Hyun Bang; Deuk-Kyu Hwang; Min-Chul Park; Young-Don Ko; Ilgu Yun; Jae-Min Myoung (177-182).
ZnO thin film was initially deposited on InP substrate by radio frequency (rf) magnetron sputtering and the diffusion process was performed using the closed ampoule technique where Zn3P2 was used as the dopant source. To verify the junction formation of ZnO thin films, the electrical properties were measured, and the effects of Zn3P2 diffusion on ZnO thin films were investigated. It is observed that the electrical property of the film is changed from n-type to p-type by dopant diffusion effect. Based on the results, it is confirmed that ZnO thin films can be a potential candidate for ultraviolet (UV) optical devices.
Keywords: ZnO; rf magnetron sputtering; Diffusion; Homojunction;
Comparison of the electroluminescence and its related properties of two cyclopentadiene derivatives by Xi-Cun Gao; Hong Cao; Ling Huang; Yan-Yi Huang; Bao-Wen Zhang; Chun-Hui Huang (183-189).
In order to fully understand the dependence of device electroluminescence (EL) on the chemical structure of two light-emitting materials: 1,2,3,4-tetraphenyl-1,3-cyclopentadiene (TPCP) and 1,2,3,4,5-pentaphenyl-1,3-cyclopentadiene (PPCP), their properties in solution and as evaporated thin films of UV-Vis absorption, geometric structures, photoluminescence (PL), electrochemistry, glass transition temperature and EL were compared. Compared with that of TPCP, the first absorption band of PPCP shifts to the shorter wavelength region both in solution and thin film state; the photoluminescence in solution exhibits lower quantum efficiency but in thin film state has a higher intensity; the electrochemical oxidation happens at a higher potential; the solid powder exhibits higher glass transition temperature; and the electroluminescent device shows higher luminescence and efficiency. Reasons responsible for the differences were analyzed.
Keywords: Electroluminescence; 1,2,3,4-Tetraphenyl-1,3-cyclopentadiene; 1,2,3,4,5-Pentaphenyl-1,3-cyclopentadiene;
Localized corrosion effects and modifications of acidic and alkaline slurries on copper chemical mechanical polishing by Tzu-Hsuan Tsai; Shi-Chern Yen (190-205).
This study demonstrates the CMP performance can be enhanced by modifying the corrosion effects of acidic and alkaline slurries on copper. A corrosion test-cell with a polishing platform is connected with the potentiostat to investigate the corrosion behaviors of copper CMP in various alumina slurries. Experiments show that the slurry needs to be maintained in acidic pH<4.56 or alkaline pH>9.05 surroundings and thus better dispersion of alumina particles and less residual contaminant on copper surface can be obtained. The surface defects after copper CMP using acidic and alkaline slurries are described by pitting corrosion mechanisms, and these mechanisms can be regarded as a basis to modify their corrosion effects. Experimental results indicate that it is necessary to modify the dissolution of HNO3 and oxidization of NH4OH for copper CMP slurries. Consequently, the slurries of 5 wt.% HNO3 by adding 0.1 wt.% BTA or 5 wt.% KNO3 by adding 1 wt.% NH4OH achieve good CMP performance for copper with higher CMP efficiency factor (CMPEF), 1460 and 486, and lower surface roughness (R q), 4.019 and 3.971 nm, respectively. It is found that AFM micrographs can support the effectiveness of corrosion modifications for copper CMP in various slurry chemistries.
Keywords: Chemical mechanical polishing; Copper; Pitting corrosion; Alumina slurry; Potentiodynamic curve; Surface roughness;
Surface chemistry and microstructural analysis of Ce x Zr1−x O2−y model catalyst surfaces by Alan E. Nelson; Kirk H. Schulz (206-221).
Cerium-zirconium mixed metal oxides are widely used as promoters in automotive emissions control catalyst systems (three-way catalysts). The addition of zirconium in the cubic lattice of ceria improves the redox properties and the thermal stability, thereby increasing the catalyst efficiency and longevity. The surface composition and availability of surface oxygen of model ceria-zirconia catalyst promoters was considered to develop a reference for future catalytic reactivity studies. The microstructure was characterized with X-ray diffraction (XRD) to determine the effect of zirconium substitution on crystalline structure and grain size. Additionally, the Ce/Zr surface atomic ratio and existence of Ce3+ defect sites were examined with X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) for samples with different zirconium concentrations. The surface composition of the model systems with respect to cerium and zirconium concentration is representative of the bulk, indicating no appreciable surface species segregation during model catalyst preparation or exposure to ultrahigh vacuum conditions and analysis techniques. Additionally, the concentration of Ce3+ defect sites was constant and independent of composition. The quantity of surface oxygen was unaffected by electron bombardment or prolonged exposure to ultrahigh vacuum conditions. Additionally, XRD analysis did not indicate the presence of additional crystalline phases beyond the cubic structure for compositions from 100 to 25 at.% cerium, although additional phases may be present in undetectable quantities. This analysis is an important initial step for determining surface reactions and pathways for the development of efficient and sulfur-tolerant automotive emissions control catalysts.
Keywords: Cerium; Zirconium; Oxide; Model; Catalyst; Emissions; Automotive;
XPS, FTIR and TPR characterization of Ru/Al2O3 catalysts by V. Mazzieri; F. Coloma-Pascual; A. Arcoya; P.C. L’Argentière; N.S. Fı́goli (222-230).
The properties of Ru/Al2O3 catalysts prepared using RuCl3 as precursor and subjected to different treatments after impregnation, were studied using different techniques: XPS, FTIR, hydrogen chemisorption and thermal programmed reduction. Differences in the Ru species (Ru0, ruthenium oxides and ruthenium oxychloride), metal dispersion and chlorine content in the catalysts as well as in their catalytic activity and selectivity during benzene selective hydrogenation to cyclohexene, were found according to the preparation procedure used.
Keywords: Ru/Al2O3; XPS; FTIR; Benzene hydrogenation;
Properties including step coverage of TiN thin films prepared by atomic layer deposition by J Kim; H Hong; K Oh; C Lee (231-239).
The physical properties including the step coverage of the TiN films deposited by atomic layer deposition (ALD) technique, using TiCl4 and NH3 as the precursors have been investigated. The deposition rate of the TiN film is constant and moderately high (∼0.6 Å per cycle) under an optimum deposition condition. The film resistivity is appreciably low (∼200 μΩ cm). The XRD analysis results indicate polycrystalline nature of the TiN films with a (1 1 1) preferred orientation. The XPS and AES analysis results establish that the Cl impurity concentration in the TiN films is lower than 1 at.% and the ratio of Ti and N by atomic concentration in the TiN films is nearly equal to 1:1 AFM analysis reveals that the RMS surface roughness is low. Also it is found by SEM observation that the step coverage of the TiN films with trenches (the aspect ratio being 10:1) is excellent. One hundred percent conformality is observed for both the side/bottom and the side/top sections.
Keywords: TiN; ALD; Resistivity; AES; Aspect ratio; Step coverage;
Formation of luminescent (NH4)2SiF6 phase from vapour etching-based porous silicon by M. Saadoun; B. Bessaı̈s; N. Mliki; M. Ferid; H. Ezzaouia; R. Bennaceur (240-248).
In this paper we describe the formation of a luminescent (NH4)2SiF6 via porous silicon (PS) obtained from HNO3/HF vapour etching (VE) silicon (Si) substrates. It was found that at specific conditions, PS transforms in a luminescent thick white powder (WP) layer. Scanning electron microscopy (SEM) revealed that the WP has a coral-like structure. It was also found that PS persists as an intermediate layer between the Si substrate and the WP, and seems to be the seed that transforms into the WP. SEM microanalysis show that the WP is essentially composed of silicon (Si), nitrogen (N) and fluorine (F). Fourier transform infrared (FTIR) spectroscopy investigations show that this WP contains SiF6 2− and NH4 + ions and NH chemical bonds. X-ray diffraction (XRD) patterns of the WP confirm that a (NH4)2SiF6 cubic phase is concerned. SEM microanalyses show an excess of Si in the WP matrix. FTIR spectroscopy and XRD analysis reveal the presence of crystalline Si particles and SiO x , both originating from the excess of Si. The (NH4)2SiF6 WP phase emits an intense photoluminescence (PL) band, shifted towards higher energies as compared to the starting PS layer. The possible origin and mechanism of the luminescence emission was discussed taking into account the ability of small SiO x -surrounded Si particles to emit PL at rather high energy. The wide range variation of the thickness of the (NH4)2SiF6 WP may be easily used for the grooving of Si wafers.
Keywords: Silicon; Etching; Porous silicon; Ammonium silico-fluoride; Luminescence;
Electrical characterization of low temperature deposited TiO2 films on strained-SiGe layers by G.K. Dalapati; S. Chatterjee; S.K. Samanta; C.K. Maiti (249-254).
Thin films of titanium dioxide have been deposited on strained Si0.82Ge0.18 epitaxial layers using titanium tetrakis-isopropoxide [TTIP, Ti(O-i-C3H7)4] and oxygen by microwave plasma enhanced chemical vapor deposition (PECVD). The films have been characterized by X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). Dielectric constant, equivalent oxide thickness (EOT), interface state density (D it), fixed oxide charge density (Q f /q) and flat-band voltage (V FB) of as-deposited films were found to be 13.2, 40.6 Å, 6×1011 eV−1 cm−2, 3.1×1011 cm−2 and −1.4 V, respectively. The capacitance–voltage (C–V), current–voltage (I–V) characteristics and charge trapping behavior of the films under constant current stressing exhibit an excellent interface quality and high dielectric reliability making the films suitable for microelectronic applications.
Keywords: Electrical characterization; Low temperature deposition; TiO2 films; High-K;
Increased surface roughness by oxygen plasma treatment of graphite/polymer composite by U. Cvelbar; S. Pejovnik; M. Mozetiè; A. Zalar (255-261).
The technology of selective plasma etching was applied to increase the surface roughness of graphite/polymer composite. Etching was performed with a low pressure weakly ionised oxygen plasma created with a RF generator of the output power of 200 W and frequency of 27.12 MHz. The density of charged particles, density of neutral oxygen atoms and the electron temperature was about 1×1016 m−3, 4×1021 m−3, and 5 eV, respectively. The effects of plasma treatment were observed by scanning electron microscope (SEM), electron microprobe (EMPA) and Talysurf. It was found that the surface roughness was increased by approximately 15 times, from a virgin sample at the roughness of R a =0.27 μm to a very rough surface with R a =4 μm. The roughness increased with increasing plasma exposure time. The EMPA results showed that the amount of sulphur in the surface layer decreased with increasing etching time indicating that PPS polymer was the material etched preferentially.
Keywords: Plasma etching; Oxygen; Graphite; Polymer; Composite;
Comparison of nanosecond laser ablation at 1064 and 308 nm wavelength by L Torrisi; S Gammino; L Andò; V Nassisi; D Doria; A Pedone (262-273).
To study the solid Cu ablation in vacuum, two different laser sources operating at 1064 and 308 nm wavelength are employed at similar values of laser fluences. The infrared laser is a Q-switched Nd:Yag having 9 ns pulse width (INFN-LNS, Catania), while the ultraviolet one is a XeCl excimer having 20 ns pulse width (INFN-LEA, Lecce). Both experiments produced a narrow angular distribution of the ejected material along the normal to the target surface. The ablation showed a threshold laser power density, of about 7 and 3 J/cm2 at 1064 and 308 nm, respectively, below which the ablation effect was negligible. The laser interaction produces a plasma at the target surface, which expands very fast in the vacuum chamber. Time-of-flight (TOF) measurements of the ion emission indicated an average ion velocity of the order of 4.7×104 and 2.3×104 m/s for the infrared and ultraviolet radiation, respectively. We also estimated approximately the corresponding temperature of the plasma from which ions originated, i.e. about 106 and 105 K for IR and UV wavelength, respectively. A discussion of the analysis of the ablation mechanism is presented. At the used laser power densities the produced Cu ions showed ionisation states between 1+ and 5+ in both cases.
Keywords: Pulsed laser irradiation; Laser plasma; Time of flight; Ion beam;
Surface modification and oxidation kinetics of hot-pressed AlN–SiC–MoSi2 electroconductive ceramic composite by Kristoffer Krnel; Diletta Sciti; Elena Landi; Alida Bellosi (274-285).
The effects of oxidation on the microstructural modification and on the electrical resistivity and mechanical strength of a hot-pressed AlN–SiC–MoSi2 electroconductive ceramic composite were studied. The kinetic of the oxidation was also evaluated. After the oxidation at temperatures below 1000 °C samples do not gain weight, due to simultaneous formation of SiO2 and evaporation of MoO3 formed by the oxidation of MoSi2. However, the AlN/SiC matrix disables the “pesting” phenomena and strength degradation, despite the fact that at these temperatures MoSi2 oxidizes rapidly. At temperatures above 1000 °C, the composite gains weight due to protective mullite layer formation on the surface, that provides a good oxidation resistance for use at higher temperatures. The kinetics of the oxidation follows the parabolic law. The possible rate-controlling mechanism is the diffusion of oxygen through the mullite-rich surface oxide scale.
Keywords: AlN–SiC–MoSi2 composite; Oxidation; Kinetics; Microstructure;
Study of adsorption of oxygen on β-Al2O3 + Au and β-Al2O3 + Pt by N Guillet; A Rives; R Lalauze; C Pijolat (286-292).
To improve the understanding of the electrochemical effects observed on an original potentiometric gas sensor, interactions of oxygen with the device were investigated. This gas sensor is made of a solid electrolyte (treated Na-β-alumina) associated with two metallic electrodes (gold and platinum) located in the same gas mixture. Adsorption of charged oxygen species, considered responsible for the electrical response developed by the sensor, was investigated by work function measurements. Results showed that charged oxygen species only form on partially gold or platinum covered solid electrolyte. Comparison of these results with those obtained in a previous calorimetric study of interactions between oxygen and the same materials suggests the existence of at least two different oxygen species adsorbed on the surface of the sensitive element. The first one, located on the solid electrolyte surface, is neutral and characterized by an endothermal reaction of formation. The second one is charged and probably produced at the gas/solid electrolyte/metallic electrode interface. A mechanism based on the concept of “three phase boundary” and similar to the “reverse spillover” phenomenon is proposed to account for the adsorption of these oxygen species.
Keywords: Oxygen adsorption; β-Alumina; Gold; Platinum; Work function; Kelvin probe;
The investigation of carbon nitride films annealed at different temperatures by Zhimin Zhou; Lifang Xia; Mingren Sun (293-300).
The effects of thermal annealing on the component and microstructure of carbon nitride films deposited by vacuum cathodic arc method are reported. The bonding structure of the films is investigated by Raman spectroscopy, FTIR, XPS and valence band XPS. Upon annealing, the N content of the film drops gradually from original 31.0 to 17.0 at.% at 600 °C. The results of Raman spectroscopy, FTIR and valence XPS demonstrate that the films below 500 °C mainly consist of aromatic cluster component and polymeric component, which is rather stable upon the increasing of anealing temperatures. With the further increasing of the annealing temperatures from 400 to 600 °C, the fraction of polymeric component decreases and the aromatic component develops greatly. Meanwhile the films tend to transform towards the fullerene-like microstructure, which can be seen from the large separation of the N 1s peaks (>2.0 eV). As a result the N sp3 C bonds increase due to the rising of cross-linking between the graphite plane.
Keywords: Carbon nitride; Vaccum cathodic arc; Thermal annealing;
Crystalline silicon films sputtered on molybdenum by P Reinig; F Fenske; W Fuhs; A Schöpke; B Selle (301-306).
Polycrystalline silicon films were grown on molybdenum (Mo)-coated substrates at high deposition rate using the pulsed magnetron sputtering technique. Our study investigates the silicon–molybdenum interface of these films to elucidate stimulating mechanisms for an ordered crystalline silicon thin film growth. Both Auger electron spectroscopy and Rutherford backscattering reveal that at a substrate temperature as low as T S=450 °C during the deposition process intermixing of Si and Mo at the Si–Mo interface takes place leading to a compositional ratio Mo:Si of about 1:2. By Raman spectroscopy hexagonal β-MoSi2 could be identified as the dominant phase in this intermixed region. The dependence of the resulting thickness of the reacted interface layer on the deposition conditions is not fully understood yet.
Keywords: Silicide; Polycrystalline silicon; Rutherford backscattering spectroscopy; Raman spectroscopy; Pulsed sputtering; Thin films;
Picosecond and femtosecond pulsed laser ablation and deposition of quasicrystals by R Teghil; L D’Alessio; A Santagata; M Zaccagnino; D Ferro; D.J Sordelet (307-317).
A Nd:glass laser with pulse duration of 250 fs and 1.3 ps has been used to evaporate a Al65Cu23Fe12 quasicrystalline target. The gaseous phase obtained from the ablation process has been characterised by several techniques such as emission spectroscopy, quadrupole mass spectrometry and ICCD imaging, used to study the plume composition, energy and morphology. The results show that the ablation processes in the short-pulse regimes are very different to the nanosecond one. In particular the plume angular distribution shows a characteristic high cosine exponent and the composition is completely stoichiometric and independent from the laser fluence. Furthermore the mass spectra indicate the presence of clusters, both neutral and ionised and the emission from the target suggest a rapid thermalisation leading to the melting of the surface. To clarify the ablation process some films have been deposited, on oriented silicon, at different experimental conditions and analysed by scanning electron microscopy, atomic force microscopy, energy dispersive X-ray analysis and X-ray diffraction. The analyses show the presence of nanostructured films retaining the target stoichiometry but consisting of different crystalline and non crystalline phases. In particular the nanostructure supports the hypothesis of the melting of the target during the ablation and a mechanism of material ejection is proposed for both picosecond and femtosecond regimes.
Keywords: Laser ablation; Quasicrystals; Ultrashort laser pulses;
Comparative study of morphology and surface composition of Al–Cr–Fe alloy powders produced by water and gas atomisation technologies by A.V Krajnikov; V.V Likutin; G.E Thompson (318-328).
The morphology and surface composition of Al–Cr–Fe alloy powders of 0–63 and 63–100 μm size fractions, produced by gas and water atomisation, have been studied by scanning electron microscopy and Auger electron spectroscopy. While gas atomised particles are of spherical shape, water atomised powders are usually irregular in shape with a complex branched relief. The morphology and composition of surface oxides have been estimated. The surface oxide film is composed of aluminium oxides/hydroxides and contains no Fe and Cr atoms. Two to five water molecules are associated with one Al2O3 molecule on the surface of powders. The surface oxide film has a non-uniform thickness, with thick oxide islands separated by thinner oxide film. The parameters of the surface film morphology, such as the island coverage, the oxygen content and the thin film thickness, depend on the atomisation technology used and powder size fraction. Heavily and weakly oxidised powder groups present in all powder fractions are distinguished by Auger spectra analysis. Relationships between heavily and weakly oxidised powder groups are discussed as a function of atomisation technology and size fraction.
Keywords: Aluminium powder; Water atomisation; Surface segregation; Oxide film; AES;
Formation of tubular silicon carbide from a carbon–silica material by using a reactive replica technique: infra-red characterisation by C Vix-Guterl; I Alix; P Gibot; P Ehrburger (329-337).
Thermal treatment of carbon fibres covered with silica prepared by a sol–gel technique leads to the formation of a tubular silicon carbide material keeping the morphology of the carbon source. The conversion of silica into silicon carbide, its kinetics and the structure of the final material were mainly determined by infra-red (IR) spectroscopy. The analytical results were crossed examined with those obtained by gravimetric and microscopic methods. In particular, it is shown, here, that IR-spectroscopy is a suitable technique to quantitatively determine the amount of SiC formed during the heat treatment of a C/SiO2 material.
Keywords: SiC tube; IR-spectroscopy; Carbothermal reaction; Carbon fibres; Silica; Sol–gel process;
The effect of the proton on electropolymerization of the thiophene by Muzaffer Can; Fatma Sevin; Attila Yildiz (338-345).
Electropolymerization of thiophene was investigated in neutral and acidic medium from the standpoint of film formation and conductivity. Results obtained from voltammetric investigations have shown that proton affects both the electropolymerization of thiophene and its conductivity. This effect was explained by theoretical calculations using molecular mechanic (MM+, MM2) and semi-empirical (AM1) methods. From these calculations, it is seen that proton is significantly important in the stabilization and growth of the polymer. Proton is added to the sulfur atom in the polymer, which has a basic character because of its lone-pair electrons. With the addition of proton, the effect of the lone-pair electrons to the delocalization existing in the ring and the contribution to the conductivity of polythiophene is removed. Thus, the conjugation in the ring is reduced to the π-system in carbon skeleton and the structure of the protonated polythiophene resembles to that of polyacetylene.
Keywords: Electropolymerization; Thiophene; Polythiophene; Proton effect; Theoretical calculation;
The thermal spreading of antimony oxides onto Fe2O3 by Yan. Huang; Guojia Wang; Rita X. Valenzuela; Vicente Cortés Corberán (346-352).
The uniform antimony-rich surface layer on Fe2O3 was carried out via thermal spreading of Sb2O3 and Sb2O4. TG–DTA results indicate that the oxidation temperature of Sb2O3 was decreased ca. 100 K due to thermal spreading effect. Although Sb2O4 is almost catalytically inert for oxidation of isobutane and Fe2O3 is a typical non-selective catalyst for this reaction, the formation of antimony-rich layer suppresses the combustion reactions and favors the partial oxidation reactions. When Sb2O4 instead of Sb2O3 was used as antimony resource, the enrichment of antimony on Fe2O3 surface was much lower. However, the reaction atmosphere of isobutane oxidation enhances antimony spreading over Fe2O3 surface. According to Mars–Van Krevelen mechanism, some Sb2O4 in catalysts could be intermediately reduced into Sb2O3 during reaction of isobutene oxidation, which thermal spreading is much easier. As shown by Raman results, the Sb2O4 that has been spread on Fe2O3 surface is probably amorphous.
Keywords: Thermal spreading; Antimony oxide; Iron oxide; Surface enrichment; Isobutane oxidation;
Annealing effects on structure and laser-induced damage threshold of Ta2O5/SiO2 dielectric mirrors by Yuanan Zhao; Yingjian Wang; Hui Gong; Jianda Shao; Zhengxiu Fan (353-358).
The effects of annealing on structure and laser-induced damage threshold (LIDT) of Ta2O5/SiO2 dielectric mirrors were investigated. Ta2O5/SiO2 multilayer was prepared by ion beam sputtering (IBS), then annealed in air under the temperature from 100 to 400 °C. Microstructure of the samples was characterized by X-ray diffraction (XRD). Absorption of the multilayer was measured by surface thermal lensing (STL) technique. The laser-induced damage threshold was assessed using 1064 nm free pulsed laser at a pulse length of 220 μs.It was found that the center wavelength shifted to long wavelength gradually as the annealing temperature increased, and kept its non-crystalline structure even after annealing. The absorbance of the reflectors decreased after annealing. A remarkable increase of the laser-induced damage threshold was found when the annealing temperature was above 250 °C.
Keywords: Annealing; Ta2O5/SiO2 dielectric mirrors; Structure; Laser-induced damage threshold;
Cuprite, paramelaconite and tenorite films deposited by reactive magnetron sputtering by J.F. Pierson; A. Thobor-Keck; A. Billard (359-367).
Copper oxides films (Cu2O, Cu4O3 and CuO) have been deposited by magnetron sputtering of a copper target in various Ar–O2 reactive mixtures. The films are characterized by X-ray diffraction, scanning electron microscopy, four-point probe method and UV-Vis spectrometry. The three defined compounds in the CuO binary system can be deposited by varying the oxygen flow rate introduced into the reactor. All the films are crystallized with a mean crystal size ranging from 10 to about 35 nm. They are highly resistive and present a direct optical band gap higher than 2 eV. The application of a bias voltage during the deposition phase modifies the texture of the Cu2O films and also induces a preferential resputtering of oxygen from the Cu4O3 ones. This resputtering phenomenon leads firstly to the occurrence of the cuprite phase mixed with the paramelaconite one and secondly to the amorphisation of the films. Finally, the thermal stability in air of cuprite, paramelaconite and tenorite films has been investigated. The results show that the stability of Cu2O and Cu4O3 films in air is influenced by the thickness and/or the texture of the films. Tenorite films with a low optical band gap (1.71 eV) can be formed after air annealing at 350 °C of an unbiased cuprite film.
Keywords: Reactive sputtering; Copper oxides; Structure; Electrical resistivity; Optical band gap; Oxidation;