Effects of deposition temperature on the surface roughness and the nonlinear optical susceptibility of sprayed deposited ZnO:Zr thin films

Zirconium doped zinc oxide thin films were deposited by reactive chemical pulverization spray pyrolysis technique on heated glass substrates at 400 °C, 450 °C and 500 °C using zinc and zirconium chlorides as precursors. The effect of zirconium dopant and surface roughness on the nonlinear optical properties was investigated using atomic force microscopy (AFM) and third harmonic generation (THG). The best value of susceptibility χ⁽³⁾ was obtained from the doped films with less roughness. A strong third order nonlinear optical susceptibility χ⁽³⁾ = 20.49 × 10⁻¹² (esu) of the studied films was found for the 5% doped sample at 450 °C.     

Mechanical and electrical characteristics of silver stabilizer layer prepared by using nano silver paste for coated conductor

Mechanical and electrical properties of silver stabilizer layer of coated conductor, which was prepared using nano silver paste as starting materials, have been investigated. Nano silver paste was coated on YBCO (Y₁Ba₂Cu₃O_7−δ) film by a dip coating method with a speed of 25 mm/min. Coated film was dried in air and heat treated at 400–700 °C in a flowing oxygen atmosphere. Adhesion strength between YBCO and silver layer was measured by Tape test (ASTM D 3359). The hardness and electrical conductivity of the sample were measured by pencil hardness test (ASTM D 3363). Surface and volume resistance were measured by using LORESTA-GP (MITSUBISHI). The sample heat treated at 500 °C showed poor adhesiveness of 1B but it is clearly enhanced to 5B when samples were heat treated at higher than 600 °C. The silver layer heat treated at 700 °C showed a high hardness value of higher than 9H and a volume resistance of 1.417 × 10⁻⁷ Ω mm at room temperature. SEM observations showed that a dense silver layer was formed with a thickness of about 2 μm. Dip coated silver layer prepared by using nano silver paste showed superior electrical and mechanical characteristics which is comparable to those that sputter deposited Ag layer.     

EVA-enhanced embedding medium for histological analysis of 3D porous scaffold material

When sectioning a 3D porous scaffold made of a soft elastomeric material embedded in paraffin medium, it is not easy to obtain a section because of the different mechanical properties of the paraffin and tissue/scaffold. We describe a new embedding material for histological analysis of various biomaterials that is composed of paraffin and ethylene vinyl acetate (EVA) resin (0, 3, 7, and 13 wt.%). 3D porous poly(l-lactide--caprolactone) (PLCL) and chitosan scaffolds were fabricated to test the sectioning efficiency of the paraffin/EVA embedding material. The new embedding material was characterized by rheological analysis and solvent solubility testing in xylene and n-hexane. The hydrophilicity of the new material was assessed by contact angle measurement and its surface roughness was measured using AFM analysis. The staining efficiency of sections embedded in a paraffin/EVA mixture was determined by eosin staining of the chitosan scaffold and chitosan/collagen hybrid scaffold using a fluorescently labeled collagen. Section roughness decreased with increasing EVA content. The softening temperature of the paraffin/EVA mixture was similar to that of paraffin (50–60 °C by rheometer). The paraffin/EVA mixture dissolved completely in xylene after 30 min at 50 °C, and after 30 min in n-hexane at 60 °C. Therefore, the new embedding medium can be used for histological analysis of various biomaterials and natural tissues.     

Effects of rapid thermal annealing on the energy levels of InAs/InP self-assembled quantum dots

We have studied the effects of thermal annealing on the electrical properties of InAs/InP self-assembled quantum dots (QDs) using deep level transient spectroscopy (DLTS). It was found from the DLTS measurements that the activation energy of the QD signal varied from 0.47 to 0.60 eV and the emission cross section changed from 1.01×10⁻¹⁵ to 9.63×10⁻¹⁴ cm² when the annealing temperature increased up to 700 °C. As a result of the thermal annealing process at the temperature ranging from 500 to 600 °C, the higher activation energy and the larger emission cross section of the QD related signal were observed for the annealed samples compared to those for the as-grown sample. On the basis of the capture barrier height for the QDs structure being lowered from 0.24 to 0.06 eV at the annealing temperature of 700 °C, thermal damage was considered as the reason. The appropriate annealing process can provide a clue for the engineering of the energy levels in the self-assembled QD structures.     

Surface structures of in (√3 × √3 )R30° and (5√3 × 2) phases studied by surface extended X-ray absorption fine structure spectroscopy

The local surface structures of in the ( √3 × √3) R30° and (5√3 × 2) phases have been investigated by means of polarization-dependent sulfur K-edge surface EXAFS. In the (√3 × √3 ) R30° phase, sulfur adatoms are found to occupy threefold hollow sites with a S---Ni distance of 2.13 Å and an inclination angle ω of the Sz.sbnd;Ni bonds at 44° from the surface plane. In contrast, in the (5√3 × 2) phase, it is determined that the Sz.sbnd;Ni bond is longer, 2.18 Å, more inclined, ω = 31°, and that the coordination number is not 3 but 4. These results strongly support a picture involving reconstruction of the top nickel layer to form a rectangular structure. Consideration of several models proposed for the (5√3 × 2) phase leads to one which is compatible with both the present results and results recently reported using STM.     

Noninvasive monitoring of brain temperature during mild hypothermia

The main purpose of this study was to verify the feasibility of brain temperature mapping with high-spatial- and reduced-spectral-resolution magnetic resonance spectroscopic imaging (MRSI). A secondary goal was to determine the temperature coefficient of water chemical shift in the brain with and without internal spectral reference. The accuracy of the proposed MRSI method was verified using a water and vegetable oil phantom. Selective decrease of the brain temperature of pigs was induced by intranasal cooling. Temperature reductions between 2°C and 4°C were achieved within 20 min. The relative changes in temperature during the cooling process were monitored using MRSI. The reference temperature was measured with MR-compatible fiber-optic probes. Single-voxel ¹H MRS was used for measurement of absolute brain temperature at baseline and at the end of cooling. The temperature coefficient of the water chemical shift of brain tissue measured by MRSI without internal reference was −0.0192±0.0019 ppm/°C. The temperature coefficients of the water chemical shift relative to N-acetylaspartate, choline-containing compounds and creatine were −0.0096±0.0009, −0.0083±0.0007 and −0.0091±0.0011 ppm/°C, respectively. The results of this study indicate that MRSI with high spatial and reduced spectral resolutions is a reliable tool for monitoring long-term temperature changes in the brain.     

Status of the INR experiment on 2β decay of Cd

Measurements of ¹¹⁶Cd double beta decay with help of enriched¹¹⁶CdWO₄ crystal scintillator are in progress in the Solotvina Underground Laboratory. The last part of the exposition with the background rate less than 0.6 counts/y·kg·keV (in the region of interest 2.7–2.9 MeV) is about 19000 hours. The half-life limit T1/2(0ν)≥3.2·10²² y (90% C.L.) is obtained for neutrinoless 2β decay of ¹¹⁶Cd. It corresponds to restrictions on the values of the neutrino mass m_ν≤3.9 eV, right-handed admixtures in weak interaction η≤5.7·10⁻⁸, λ5.0·10⁻⁶ and R-parity violating parameter of minimal supersymmetric standard model ≤1.1·10⁻³. For neutrinoless modes with emission of one and two Majorons, the limits T1/2(0νM1)≥1.2·10²¹ y and T1/2(0νM2)≥2.4·10²⁰ y (90% C.L.) are determined. To advance these results to a level of the limit m_ν≤1–2 eV, the improved set-up with four enriched ¹¹⁶CdWO₄ crystals is in mounting low.     

Electrical conductivity of Ag/Na ion-exchanged titanosilicate glasses

The Ag₂O–TiO₂–SiO₂ glasses were prepared by Ag⁺/Na⁺ ion-exchange method from Na₂O–TiO₂–SiO₂ glasses at 380–450 °C below their glass transition temperatures (T_g), and their electrical conductivities were investigated as functions of TiO₂ content and the ion-exchange ratio (Ag/(Ag+Na)). In a series of glasses 20R₂O·xTiO₂·(80−x)SiO₂ with x=10, 20, 30 and 40 in mol%, the electrical conductivities at 200 °C of the fully ion-exchanged glasses of R=Ag were in the order of 10⁻⁵ or 10⁻⁴ S cm⁻¹ and were 1 or 2 orders of magnitude higher than those of the initial glasses of R=Na. The glass of x=30 exhibited the highest increase of conductivity from 3.8×10⁻⁷ to 1.3×10⁻⁴ S cm⁻¹ at 200 °C by Ag⁺/Na⁺ ion exchange among them. When the ion-exchange ratio was changed in 20R₂O·30TiO₂·50SiO₂ system, the electrical conductivity at 200 °C exhibited a minimum value of 7.6×10⁻⁸ S cm⁻¹ around Ag/(Ag+Na)=0.3 and increased steeply in the region of Ag/(Ag+Na)=0.5–1.0. When the ion-exchange temperature was changed from 450 to 400 °C, the conductivity of the ion-exchanged glass of x=30 decreased. The infrared spectroscopy measurement revealed that the ion-exchange temperature of 450 °C induced a structural change in the glass of x=30. The T_g of the fully ion-exchanged glass of x=30 was 498 °C. It was suggested that the incorporated silver ions changed the average coordination number of titanium ions to form higher ion-conducting pathway and resulted in high conductivity in the titanosilicate glasses.     

Effect of surface roughness of TiO2 films on short-circuit current density of photoelectrochemical cell of ITO/TiO2/PVC-LiClO4/graphite

This paper reports the effect of surface topography of titanium dioxide films on short-circuit current density of photoelectrochemical solar cell of ITO/TiO₂/PVC-LiCLO₄/graphite. The films were deposited onto ITO-covered glass substrate by screen-printing technique. The films were tempered at 300 °C, 350 °C, 400 °C, 450 °C and 500 °C for 30 min to burn out the organic parts and to achieve the films with porous structure. The surface roughness of the films were studied using scanning electron microscope (SEM). Current–voltage relationship of the devices were characterized in dark at room temperature and under illumination of 100 mW cm⁻² light from tungsten halogen lamp at 50 °C. The device utilising the TiO₂ film annealed at 400 °C produces the highest short-circuit current density and open-circuit voltage as it posses the smoothest surface topography with the electrolyte. The short-circuit current density and open-circuit voltage of the devices increase with the decreasing grain size of the TiO₂ films. The short-circuit current density and open-circuit voltage are 0.6 μA/cm² and 109 mV respectively.     

Epitaxial growth of highly transparent and conducting Sc-doped ZnO films on c-plane sapphire by sol–gel process without buffer

Highly transparent and conductive scandium doped zinc oxide (ZnO:Sc) films were deposited on c-plane sapphire substrates by sol–gel technique using zinc acetate dihydrate [Zn(CH₃COO)₂·2H₂O] as precursor, 2-methoxyethanol as solvent and monoethanolamine as a stabilizer. The doping with scandium is achieved by adding 0.5 wt% of scandium nitrate hexahydrate [(ScNO₃·6H₂O)] in the solution. The influence of annealing temperature (300–550 °C) on the structural, optical and electrical properties was investigated. X-ray Diffraction study revealed that highly c-axis oriented films with full-width half maximum of 0.16° are obtained at an annealing temperature of 400 °C. The surface morphology of the films was judged by SEM and AFM images which indicated formation of grains. The average transmittance was found to be above 92% in the visible region. ZnO:Sc film, annealed at 400 °C exhibited minimum resistivity of 1.91 × 10⁻⁴ Ω cm. Room-temperature photoluminescence measurements of the ZnO:Sc films annealed at 400 °C showed ultraviolet peak at 3.31eV with a FWHM of 11.2 meV, which are comparable to those found in high-quality ZnO films. Reflection high-energy electron diffraction pattern confirmed the epitaxial nature of the films even without introducing any buffer layer.     

Surface-roughness wakefield measurements at brookhaven accelerator test facility

An experiment has been carried out at the Brookhaven Accelerator Test Facility to investigate the effect of a surface-roughness wakefield in narrow beam tubes with artificially created bumps. The measurements show that the synchronous modes decay significantly due to the randomization of the roughness pattern. It is pointed out that this decay mechanism has not been investigated in the previous experiment at DESY and the investigators' conclusion does not apply for surface-roughness wakefields in real surfaces.     

A simple optical method for the measurement of glass wool fiber diameter

An optical method for measuring glass wool fiber diameter has been proposed and discussed from the viewpoint of practical use. The method is based on both light scattering and light reflection on the glass wool. The method can measure the mean fiber diameter, d, in the area illuminated by laser light in realtime. The accuracy of the method, i.e., the dimensional resolution, was found to be about 0·7 μm within the diameter range of d7·0 μm.     

Characterization of InN epilayers grown on Si(1 1 1) substrates at various temperatures by MBE

InN films have been grown by plasma-assisted molecular beam epitaxy (PAMBE) and characterized by various technologies. It was found that the structural, optical and electrical properties can be drastically improved by raising growth temperature from 440 to 525 °C. Grainy morphology was found in the grain size was found in atomic force microscope images. The large grain size was about 360 nm for a film grown at 525 °C. These films exhibited Wurtzite structure with a c/a ratio ranging from 1.59 to 1.609. The dislocation densities estimated by X-ray diffraction techniques closely agreed with those analyzed by plan-view transmission electron microscopy. Photoluminescence (PL) studies confirmed near band-to-band transitions and the narrowest low-temperature PL peak width was found to be 24 meV at 0.666 eV. Carrier concentrations decreased from 1.44×10¹⁹ to 1.66×10¹⁸ cm⁻³ and Hall mobility increased from 226 to 946 cm² V⁻¹ s⁻¹ as the growth temperature is progressively increased from 440 to 525 °C. Raman spectra also indicated improved crystal quality as the growth temperature was raised.     

A fibre-optic thermometric sensor based on the thermo-optic effect of titanium dioxide coatings

An experimental determination of the thermo-optic effect of titanium dioxide is described in which the test element is a thin film deposited onto the end face of an optical fibre. The film acts as an etalon. The reflectivity of titanium dioxide films was measured as a function of temperature experimentally over the range 20 °C to 500 °C, and modelled theoretically to yield a value of the thermo-optic coefficient of − 1.49 × 10⁻⁴ K⁻¹. The use of the data in the design of a thin-film optical fibre temperature sensor is described.     

Effect of annealing upon the structure and adhesion properties of sputtered bio-glass/titanium coatings

Bio-glass films were deposited by radio-frequency magnetron sputtering technique onto medical grade Ti6Al7Nb alloy substrates from prepared silica based bio-glass target. A low deposition temperature was used (150 °C) and three different working pressures, followed by annealing in air at 550 and 750 °C. A quasi-stoichiometric target to substrate atomic transfer was found for Si, Ca and P, along with strong enrichment in Na and depletion in K and Mg, as evidenced by the energy dispersive microanalysis. The best results, taking into account stoichiometry and surface roughness, were obtained for the BG layers deposited at 0.3 Pa argon working pressure. The infrared spectroscopy of the as-sputtered and of the annealed films evidenced the characteristic molecular vibrations of silicate, phosphate and carbonate functional groups. The as-deposited films are amorphous and became partly crystalline after annealing at 750 °C, as evidenced by X-ray diffraction. The pull-out measurements, performed with a certified pull-test machine, gave very strong film–substrate adhesion strength values. For the non-crystalline layers, the pull-out strength is higher than 85 MPa, and decreases after annealing at 750 °C to 72.9 ± 7.1 MPa. The main objective of this work was to establish the influence of the working pressure upon the composition and morphology of the as-deposited films, and of the annealing temperature upon structure and film–substrate adhesion.     

Internal rotation in acetaldehyde

The microwave spectrum of acetaldehyde has been investigated in the frequency range from 7 to 40 GHz. A rather complete assignment of rotational transitions in the ground and torsionally excited states has been found with the help of microwave-microwave double resonance techniques. The spectral data have been analyzed using three different models for the overall and internal rotation problem including a nonrigid model. The threefold component of the internal rotation barrier was determined to be V₃ = 400 ± 2 cm⁻¹. The sixfold contribution V₆ = −10.9 ± 0.3 cm⁻¹ could only be adjusted reliably from data for both ground and torsionally excited states using the nonrigid model. The methods of barrier determinations have been critically reviewed. In an appendix, the Hamiltonian for a nonrigid model is derived based on structure relaxation of the methyl top during internal rotation.     

Design of an optical fiber sensor for linear thermal expansion measurement

Design and operation of an optical fiber device for temperature sensing and thermal expansion measurement are reported. The modulated intensity has been measured by using a pair of 450 μm core fiber, one acting as the source and the other one as receiving fiber. In this design, the light intensity modulation is based on the relative motion of the optical fibers and a reflective coated lens. By using displacement calibration data for this sensor, the linear thermal expansion of the aluminum rod is determined. This sensor shows an average sensitivity of about 11.3 mV/°C for temperature detection and 7 μm/°C for thermal expansion detection. Device resolution for a linear expansion measurement is about 3 μm for a dynamic range of 600 μm corresponding to a temperature change of 100°C. The measured linear expansion results are checked against the expected theoretical ones and an agreement within ±2 μm is noticed. The operation of this sensor was also compared with other types and some advantages are observed, which verify the capability of this design for such precise measurements.     

Design of a hybrid diffractive/refractive achromatized telecentric f·θ lens

The design of a hybrid diffractive/refractive achromatized telecentric f·θ lens with a field of view (FOV) 50° and an effective focal length of 750 mm is presented. The optical stop is placed at the front focal plane so that it is a telecentric system. The design is based on a traditional refractive counterpart, and the designed system consists of a hybrid diffractive/refractive lens and four refractive lenses. The designed f·θ lens shows a considerable reduction in weight with a simplified structure, and exhibits superior performance compared to the refractive system. It is emphasized that the designed f·θ lens can be applied to modern color scanning systems that operate in the visible wavelength range with high performance. It can also be applied to high-energy scanning systems. When applying the designed hybrid diffractive/refractive f·θ lens to the high-energy scanning system, a big laser operating in one longitudinal mode can be replaced by a small multi-mode laser, and the scanning system can be simplified greatly with the accuracy improved.     

Microscopic modeling of intersubband resonances in InAs/AlSb quantum wells

Linear absorption spectra from intersubband resonance in InAs/AlSb quantum wells are analyzed theoretically using the intersubband semiconductor Bloch equation approach. Our model goes beyond the Hartree–Fock approximation and treats particle–particle correlations under the second Born approximation. Electron–electron and longitudinal optical phonon scatterings from such a treatment describe intrinsic line broadening to the intersubband resonance. Electron subbands are determined self-consistently with a spurious-state-free 8-band k·p Hamiltonian under the envelope function approximation. To compare with experimental measurements, we also included line broadening due to electron-interface roughness scattering. Excellent agreement was achieved for temperature-dependent absorption spectra in the mid-infrared frequency range, after taking into careful account the interplay of material parameters, nonparabolicity in bandstructure, and many-body effects.     

Temperature measurements using fiber optic polarization interferometer

A novel measurement method of temperature based on the phenomena that the phase difference between principle polarization states in the optical retarder is function of temperature is described. The polarization state of optical beam is changed as it passes through the optical retarder, which depends on the temperature. The temperature of optical retarder is determined by comparison of the power difference between principal polarization states. We demonstrate successfully the temperature measurement by using a polarization maintaining fiber as the optical retarder. With a 100 mm length of the fiber optic retarder, the change rate of phase difference on temperature was 0.236 rad/°C and the measurement error was ±0.038°C over the temperature range of −2.6 – +3.4°C. With a 11.5 mm length of the fiber optic retarder, the change rate of phase difference on temperature was 0.021 rad/°C and the measurement error was ±0.79°C over the temperature range of −8.5 – +86.5°C.