Study of Si/SiO2 hybrid antireflective coatings on SLD prepared by DSEBET - art. no. 69842P

We introduce a double source electron beam evaporation (DSEBET) technique in this paper. The refractive index coatings were fabricated on K9 glass substrate by adjusting the evaporation rates of two independent sources. The coatings, which were described by atomic force microscopy (AFM), show good compactness and homogeneity. The antireflective (AR) coatings were fabricated on Superluminescent Diodes (SLD) by DSEBET. The hybrid AR coatings on the facets of SLD were prepared in evaporation rates of 0.22nm/s and 0.75nm/s for silicon and silicon dioxide, respectively. The results of AFM and spectral performance of coated SLD show that DSEBET has a promising future in preparing the coatings on optoelectronic devices.

EFFECT OF A SI LAYER ON THE SUPERCONDUCTIVE PROPERTIES OF A BIPBSRCACUO THIN-FILM

The Pb-doped BiSrCaCuO superconducting films were grown by the single source mixed evaporation technique. The microbridges of dimensions 50 mum x 40 mum were fabricated by standard photolithography technologies. Si films with a thickness of 2500 angstrom were deposited on the microbridge area surfaces of BiPbSrCaCuO superconducting films by rf-magnetron sputtering. A greatly lowered zero resistance temperature of the microbridge area of the BiPbSrCaCuO film after Si sputtering was found. A non-linear effect of the current-voltage (I-V) characteristics at 78 K was shown. The high-frequency capacitance-voltage (C-V) curve of this structure at 78 K was symmetrical with the maximum capacitance at V = 0, and the capacitance decreased with increasing applied bias voltage. Afl experimental results are discussed.

INVESTIGATION OF GAAS/SI MATERIAL BY X-RAY DOUBLE-CRYSTAL DIFFRACTION

GaAs epilayer films on Si substrates grown by molecular-beam epitaxy were investigated by the x-ray double-crystal diffraction method. The rocking curves were recorded for different diffraction vectors of samples. The results show that the unit-cell volumes of GaAs epilayers are smaller than that of the GaAs bulk material. The strained-layer superlattice buffer layer can improve the quality of the film, especially in the surface lamella. The parameter W' = W(expt)/(square-root \gamma-h\/gamma-0/sin 2-theta-B) is introduced to describe the quality of different depths of epilayers. As the x-ray incident angle is increased, W' also increases, that is, the quality of the film deteriorates with increasing penetration distance of the x-ray beam. Therefore, W' can be considered as a parameter that describes the degree of perfection of the epilayer along the depth below the surface. The cross-section transmission electron microscopy observations agree with the results of x-ray double-crystal diffraction.

Dependence of wet etch rate on deposition, annealing conditions and etchants for PECVD silicon nitride film

The influence of deposition, annealing conditions, and etchants on the wet etch rate of plasma enhanced chemical vapor deposition (PECVD) silicon nitride thin film is studied. The deposition source gas flow rate and annealing temperature were varied to decrease the etch rate of SiN_x:H by HF solution. A low etch rate was achieved by increasing the SiH_4 gas flow rate or annealing temperature, or decreasing the NH_3 and N_2 gas flow rate. Concen-trated, buffered, and dilute hydrofluoric acid were utilized as etchants for SiO_2 and SiN_x:H. A high etching selectivity of SiO_2 over SiN_x:H was obtained using highly concentrated buffered HF.

Low-Temperature Growth of ZnO Films on GaAs by Metal Organic Chemical Vapor Deposition

ZnO thin films were grown on GaAs （001） substrates by metal-organic chemical vapor deposition （MOCVD） at low temperatures ranging from 100 to 400℃. DEZn and 1-12 O were used as the zinc precursor and oxygen precursor, respectively. The effects of the growth temperatures on the growth characteristics and optical properties of ZnO films were investigated. The X-ray diffraction measurement （XRD） results indicated that all the thin films were grown with highly c- axis orientation. The surface morphologies and crystal properties of the films were critically dependent on the growth temperatures. Although there was no evidence of epitaxial growth, the scanning electron microscopy （SEM） image of ZnO film grown at 400℃ revealed the presence of ZnO microcrystallines with closed packed hexagon structure. The photoluminescence spectrum at room temperature showed only bright band-edge （3. 33eV） emissions with little or no deep-level e- mission related to defects.

Fluorescence Hydrogen Peroxide Probe Based on a Microstructured Polymer Optical Fiber Modified with a Titanium Dioxide Film

A highly sensitive microstructured polymer optical fiber (MPOF) probe for hydrogen peroxide was made by forming a rhodamine 6G-doped titanium dioxide film on the side walls of array holes in an MPOF. It was found that hydrogen peroxide only has a response to the MPOF probe in a certain concentration of potassium iodide in sulfuric acid solution. The calibration graph of fluorescence intensity versus hydrogen peroxide concentration is linear in the range of 1.6 x 10(-7) mol/L to 9.6 x 10(-5) mol/L. The method, with high sensitivity and a wide linear range, has been applied to the determination of trace amounts of hydrogen peroxide in a few real samples, such as rain water and contact lens disinfectant, with satisfactory results.

Preparation of palladium membrane over porous stainless steel tube modified with zirconium oxide

A palladium membrane has been prepared by electroless plating on the surface of a porous stainless steel tube. Since the large surface pores of the tube are obstacle for preparation of a defect-free palladium film on the surface, zirconium oxide particles were deposited inside the pores. The mean thickness of the resulting Pd membrane on the modified tube was ca. 10 mum. It is suggested that the permeability of hydrogen is partly governed by gas diffusion in the pores. (C) 2004 Elsevier B.V. All rights reserved.

Effect of interfacial roughness on dewetting behavior of polystyrene/poly(methyl methacrylate) bilayer film

The dewetting behavior of polystyrene (PS) film on poly(methyl methacrylate) (PMMA) sublayer was investigated by changing the short-range roughness of the PMMA sublayer systemically. When the bilayer film was heated to the temperature above both Tgs, the protuberances formed in both layers to reduce the system energy. By tracing the dewetting process of the PS up-layer, the dewetting velocity was found to increase with the roughness of the sublayer.

Fabrication of an integrated pixel with an organic light-emitting diode driven by copper phthalocyanine organic thin film transistors

An organic integrated pixel with organic light-emitting diodes (OLEDs) driven by organic thin film transistors (OTFTs) is fabricated by a greatly simplified processing. The OTFTs are based on copper phthalocyanine as the active medium and fabricated on indium-tin-oxide (ITO) glass with top-gate structure, thus an organic integrated pixel is easily made by integrating OLED with OTFT. The OTFTs show field-effect mobility of 0.4 cm(2) /Vs and on/off ratio of 10(3) order. The OLED is driven well and emits the brightness as large as 2100cd/m(2) at a current density of 14.6 mu A/cm(2) at -19.7 V gate voltage. This simple device structure is promising in the future large-area flexible OLED displays.

Dewetting of polymethyl methacrylate on the patterned elastomer substrate by solvent vapor treatment

The dewetting evolution process of polymethyl methacrylate (PMMA) film on the flat and prepatterned polydimethylsiloxane (PDMS) substrates (with square microwells) by the saturated solvent of methyl ethyl ketone (MEK) treatment has been investigated at room temperature by the optical microscope (OM) and atomic force microscope (AFM). The final dewetting on the flat PDMS substrate led to polygonal liquid droplets, similar to that by temperature annealing. However, on the patterned PDMS substrate, depending on the microwells' structure of PDMS substrate and defect positions that initiated the rupture and dewetting of PMMA, two different kinds of dewetting phenomena, one initiated around the edge of the microwells and another initiated outside the microwells, were observed. The forming mechanism of these two different dewetting phenomena has been discussed. The microwells were filled with liquid droplets of PMMA after dewetting due to the formation of fingers caused by the pinning of the three-phase-line at the edge of the microwells and their rupture.

Studies on microstructure bilayer film of ultrasonic dipped cadmium sulfide and d.c. sputtered indium tin oxide

A bilayer CdS/ITO film was obtained. The dipped CdS was grown by an ultrasonic colloid deposition (USCD) method. Microstructure of the CdS film made by USCD has a wider transmission range and a higher transmittance. Amorphous indium-tin-oxide (ITO) thin film was deposited using d.c. magnetron-sputtering at room temperature. The ITO films exhibited good conductivity and maximum transmittance of 94%. The CdS/ITO bilayer was investigated by means of GIXD (grazing incidence X-ray diffraction) at different incidence angles (alpha = 0.20-5.00degrees) and XRD. We discuss a model for the thin bilayer film. SEM and AFM show that homogeneous CdS films with a bar-shaped ultrafine particles and ITO film with nanometer structure. The mechanism of the bilayer CdS/ITO film is discussed.

Modification of electrode surface through electrospinning followed by self-assembly multilayer film of polyoxometalate and its photochromic

Electrospun poly (vinyl alcohol) (PVA) nanofibers mat was collected on indium tin oxide (ITO) substrate. Heat crosslinked nanofibers mat became water-insoluble and firmly fixed on ITO substrate even in water. Oppositely charged poly (allylamine hydrochloride) (PAH) and Dawson-type polyoxometalate (POM), Na6P2Mo18O62 (P2Mo18), were alternately assembled on PVA nanofibers-coated ITO substrate to construct multilayer film through an electrostatic layer-by-layer (LBL) technique. The scanning electron microscope (SEM) images showed that P2Mo18 multilayer film was selectively deposited on PVA nanofibers while the unoccupied space by nanofibers on bare ITO was acted as substrate at the same time because the electrospun nanofibers have larger surface area and surface energy than the flat substrate. The cyclic voltammograms current responses of the P2Mo18 multilayer film on PVA/ITO electrode showed three well-defined redox couples of P2Mo18, but very small because P2Mo18 multilayer film was selectively deposited on PVA nanofibers with poor conductivity. In addition, the photochromic behavior of P2Mo18 multilayer film on PVA/ITO was investigated through UV-vis spectra and electron spin resonance (ESR). Fourier-transform infrared (FT-IR) spectroscopy and X-ray photoelectron spectroscopy (XPS) proved that the charge-transfer complex was formed between PAH and P2Mo18 after UV irradiation.

Unidirectional current flow of reversible redox couples on a MoO3 film-modified microelectrode

In this paper, we have investigated the reactivity of the molybdenum oxide film toward some standard redox systems (e.g., ferrocene (Fc) and its derivatives) and observed a few interesting phenomena. The results demonstrate that the electrochemical behaviour of Fc and its derivatives at the oxide-modified carbon fiber (CF) microelectrode differs from that at a bare CF microelectrode, The conductivity of the molybdenum oxide film is seriously affected by the range and the direction of the potential scan, which influences the electrochemical behaviour of these redox systems at the film electrode. If the cycling potential is more positive than the reduction potential of the molybdenum oxide film, the reduction and oxidation peak currents of Fc and its derivatives could not be observed. The result indicates that the molybdenum oxide film on a microelectrode surface cannot transfer electrons between the surface of the electrode and Fc or its derivatives due to the existence of a high resistance between the interface in these potential ranges. On the other hand, if the lower limit of the scan potential was extended to a potential more negative than the reduction peak potential of the film, the oxidation peak of Fc or its derivatives appeared at about the potential relative to E-0 of Fc or its derivatives on the bare electrode, and the peak current is proportional to the concentration of these couples in the electrolyte. To our surprise, the peak height on the modified electrode is much larger than that on the bare CF microelectrode under the same conditions in the range of low concentration of these couples, and the oxidation peak potential of these couples is more negative than that on the bare CF microelectrode. On the basis of the experimental observation, we propose that these redox couples may undergo an interaction with the reduction state of the molybdenum oxide film. The new phenomena that we observed have been explained by using this interaction. (C) 1997 Elsevier Science S.A.

STUDY ON ELECTRODE PROCESS OF MYOGLOBIN AT A POLYMERIZED AZURE A FILM ELECTRODE

The electrochemically polymerized azure A film electrode was firstly reported in this paper. A quasi-reversible electrode processes of myoglobin with the formal heterogeneous electron transfer rate constant (k(sh)) of 1.73 x 10(-4) cm.s-1 at the polymerized azure A modified electrode have been achieved using in-situ UV-visible spectroelectrochemistry. The adsorption of myoglobin on the polymerized azure A film electrode surface was confirmed by XPS. With simultaneously studying of cyclic voltammetry and in-situ cyclic voltabsorptometry, the attribution of the voltammetry responses of myoglobin at the film electrode has been studied. The mechanism for the heterogeneous electron transfer of myoglobin at the polymerized azure A film modified electrode has been proposed as well.

WATER-SOLUBLE AND AMPHIPHILIC POLYMERS .6. A STUDY ON THE SURFACE-COMPOSITION OF CAST FILMS OF PST/PMAA AND PEO-PST-PEO BLOCK POLYMERS BY XPS

Thin films of PSt/PMAA and PEO-PSt-PEO block polymers were deposited on a polystyrene substrate by solution adsorption (with or without solvent treatment), and the film surfaces were characterized by means of XPS. Direct solvent - casting of PEO-PSt-PEO from benzene solutions resulted in PSt-rich surfaces, whereas PMAA richer surfaces were obtained for PSt/PMAA films cast from DMF solutions. Moreover, solvent treatment after casting had profound effect on the film surface composition. Treatment with water markedly increased the surface concentration of polar PEO segments. In the case of PSt-PMAA block polymers, the PSt content on the surface increased in the order of water < ethanol < cyclohexane < petroleum ether, the last-named giving films with almost pure PSt surface. It is well worth noticing that the bulk composition had little to do with the surface composition for both PSt/PMAA and PEO-PSt-PEO block polymers within the composition range investigated when subsequent solvent treatment was applied.