Enhanced growth of low-resistivity titanium silicides on epitaxial Si0.7Ge0.3 on (001)Si with a sacrificial amorphous Si interlayer

Enhanced growth of low-resistivity self-aligned titanium silicides on epitaxial Si_0.7Ge_0.3 with a sacrificial amorphous Si (a-Si) interlayer has been achieved. The a-Si layer with appropriate thickness was found to prevent Ge segregation, decrease the growth temperature, as well as maintain the interface flatness and morphological stability in forming low-resistivity C54-TiSi₂ on Si_0.7Ge_0.3 grown by molecular beam epitaxy. The process promises to be applicable to the fabrication of high-speed Si-Ge devices.     

Photocapacitance study of deep levels in thin CdTe PV devices

Steady state photocapacitance (PHCAP) was used to survey the deep levels in the energy range 0.73 eV to 1.38 eV with respect to the valence band in CdS/CdTe PV devices. The effect of the cadmium chloride treatment process on deep level densities is shown qualitatively. Estimates of the optical transition thresholds E_p^o for three deep minority type levels E1, E2, and E3 are given and a discussion of possible assignment to specific defects is presented. Preliminary results using deep level optical spectroscopy (DLOS) to measure the optical cross sections for holes σ_p^o of the E2 and E3 levels are given. The thermal emission rates e_n^t for electrons at 79 K are estimated for the E2 and E3 levels.     

Effect of micro-characterization on thrombus formation ability of TiO2 film

The thrombus formation ability of a biomedical microcoil for hemangioma treatment is one of the basic requirements in clinical intervention application. Surface modification of a biomedical microcoil can improve its thrombus formation ability. In this work, TiO₂ films were deposited using the unbalanced magnetron sputtering method. The structures, components and micro-morphologies of the films were investigated by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), atomic force microscope (AFM), and scanning electron microscope (SEM). The thrombus formation ability of the films was studied by in vitro platelet adhesion test. The results indicated that a certain characteristic TiO₂ film has the ability to increase thrombus formation. Furthermore, the biological behavior of cultured human umbilical vein endothelial cells (HUVECs) onto different films was investigated by an in vitro HUVECs cultured experiment. The results showed that endothelial cells on certain TiO₂ film surfaces have good adherence, growth and proliferation. Additionally, the relationship between the micro-characterization and biological properties of TiO₂ films is discussed.     

Preparation and second harmonic generation of Ba2TiSi2O8 films

The synthesis and characterization of the Ba₂TiSi₂O₈ films are described. The Ba₂TiSi₂O₈ crystal was obtained after heat treatment at above 630 °C of a sol-gel derived glassy material which has a chemical composition (mole ratio) 2BaO, TiO₂, 2SiO₂, and then the Ba₂TiSi₂O₈ films were formed from the hydration of CaO-P₂O₅ glass powders. Heat treatment conditions and crystallization of the synthesized materials were studied by DSC-TG, XRD, and FT-IR. Second order nonlinear optical property has been verified by second harmonic generation test at 1064 nm. These results showed that the hydration process has a potential in rendering shape-comfortable optical materials.     

Optical properties of transparent Dy doped Ba2TiSi2O8 glass ceramic

The Ba₂TiSi₂O₈ is a well known piezoelectric, ferroelectric and non-linear crystal. Nanocrystals of Ba₂TiSi₂O₈ doped with 1.5 Dy³⁺ have been obtained by thermal treatment of a precursor glass and their optical properties have been studied. X-ray diffraction patterns and optical measurements have been carried out on the precursor glass and glass ceramic samples. The emission spectra corresponding to the Dy³⁺: ⁴F_9/2 → ⁶H_13/2 (575 nm), ⁴F_9/2 → ⁶H_11/2 (670 nm) and ⁴F_9/2 → ⁶H_9/2 (757 nm) transitions have been obtained under laser excitation at 473 nm. These measurements confirm the incorporation of the Dy³⁺ ions into the Ba₂TiSi₂O₈ nanocrystals which produces an enhancement of luminescence at 575 nm. At this wavelength has been demonstrated a maximum optical amplification around 1.9 cm⁻¹ (∼8.2 dB/cm).     

Novel properties of AZO film sputtered in Ar+H2 ambient at high temperature

AZO (ZnO:Al) transparent conductive thin film was prepared by RF magnetron sputtering with a AZO (98 wt% ZnO 2 wt% Al₂O₃) ceramic target in the same Ar+H₂ ambient at different substrate temperatures ranging from 100 to 300 °C. The minimum resistivity of AZO films was 7.9×10⁻⁴ Ω cm at the substrate temperature of 200 °C. The average transmission in the visible rang was more than 90%. Scanning electron microscopy and XRD analyses showed that the surface morphology of the AZO samples altered with the increasing of the substrate temperature. AZO film prepared at 200 °C in the pure Ar ambient was also made as comparison about the resistivity, carrier concentration and the average crystallite size. The resistivity became about 3 times higher. The carrier concentration became lower and the average crystallite size was smaller.     

Atomic layer deposited TiO2 for implantable brain-chip interfacing devices

In this paper we investigated atomic layer deposition (ALD) TiO₂ thin films deposited on implantable neuro-chips based on electrolyte-oxide-semiconductor (EOS) junctions, implementing both efficient capacitive neuron-silicon coupling and biocompatibility for long-term implantable functionality.The ALD process was performed at 295 °C using titanium tetraisopropoxide and ozone as precursors on needle-shaped silicon substrates. Engineering of the capacitance of the EOS junctions introducing a thin Al₂O₃ buffer layer between TiO₂ and silicon resulted in a further increase of the specific capacitance. Biocompatibility for long-term implantable neuroprosthetic systems was checked upon in-vitro treatment.     

CO2 capture at high temperature using calcium-based sorbents

Calcium-based sorbents synthesized from CaO, CaCO₃, and Ca(OH)₂ precursors were demonstrated as high-temperature CO₂ capture materials. The effect on CO₂ capture capability of calcium-based sorbents receiving different activations was also investigated. After proper activation, the best carbon capturing material is CaO that captured 75% of available CO₂ in nine cyclic tests and captured 61% even after 40 cyclic experiments. The correlation of the structural difference in the three activated sorbents and CO₂ conversion has been discussed. The sintering effect is presumably a major cause for activity decline of calcium-based sorbents… after cyclic carbonation/decarbonation runs.     

Preparation of TiSi nanowires by APCVD used for improving dielectric properties of PST thin film

Nanoelectrode of conductive TiSi nanowires with Ti₅Si₃ conductive bottom layer underneath is prepared on glass substrate by atmosphere pressure chemical vapor deposition (APCVD) method. Pb_0.4Sr_0.6 (Ti_0.97 Mg_0.03) O_2.97 (PST) thin film is deposited on the nanoelectrode by rf-sputtering method. The morphology and phase structure of the nanoelectrode are measured by FE-SEM and XRD, respectively. The dielectric property of a PST thin film deposited on the nanoelectrode substrate is obtained by Agilent 4294A Impedance Analyzer. The results show that the conductive Ti₅Si₃ crystalline phase bottom layer is formed at deposition temperature above 710 °C, and the conductive TiSi single crystal nanowires are formed on the bottom layer perfectly in this case. By using the substrate on which the TiSi nanowire planted Ti₅Si₃ electrode is prepared, the PST thin film is deposited and it exhibits the high tunability of approximately 61% which is much higher than that deposited on the Ti₅Si₃ coated glass substrates without TiSi nanowires.     

水热合成的MoS2/石墨烯/N-TiO2复合材料的可见光催化性能

以氧化石墨烯(GO)、钼酸、硫脲和TiN为原料,成功制备了MoS_2/石墨烯/N-TiO_2(MGNT)复合材料。利用X射线衍射仪(XRD)、扫描电子显微镜(SEM)、高分辨透射电子显微镜(HR-TEM)、X射线光电子能谱(XPS)及紫外-可见漫反射光谱(UV-Vis DRS)等手段测试分析了样品的物相组成、形貌、成分和光吸收性能。紫外-可见漫反射测试结果表明,MoS_2、石墨烯共同修饰及氮掺杂使得TiO_2的吸收带边发生红移,且其可见光吸收性能明显提高。可见光照射下降解亚甲基蓝溶液的实验结果表明,MoS_2/石墨烯共同修饰的氮掺杂TiO_2的光催化降解性能分别是氮掺杂TiO_2(NT)和石墨烯修饰氮掺杂TiO_2(GNT)的1.82倍和1.59倍,其吸附性分别为氮掺杂TiO_2、石墨烯修饰氮掺杂TiO_2的11.14倍和4.77倍。     

Influence of annealing on humidity response of RF sputtered nanocrystalline MgFe2O4 thin films

Humidity response of Radio Frequency sputtered MgFe₂O₄ thin films onto alumina substrate, annealed at 400 °C, 600 °C and 800 °C has been investigated. Crystalline phase formation of thin films annealed at different temperature was analyzed by X-ray Diffraction. A particle/grain like microstructure in the grown thin films was observed by Scanning Electron Microscope and Atomic Force Microscope images. Film thickness for different samples was measured in the range 820-830 nm by stylus profiler. Log R (Ω) response measurement was taken for all thin films for 10-90% relative humidity (% RH) change at 25 °C. Resistance of the film increased from 5.9 × 10¹⁰ to 3 × 10¹² at 10% RH with increase in annealing temperature from 400 °C to 800 °C. A three-order magnitude, 10¹² Ω to 10⁹ Ω drop in resistance was observed for the change of 10 to 90% RH for 800 °C annealed thin film. A good linear humidity response, negligible humidity hysteresis and minimum response/recovery time of 4 s/6 s have been measured for 800 °C annealed thin film.     

Inelastic neutron scattering from Tl2CaBa2Cu2O8

Coherent inelastic neutron scattering measurements have been carried out on the high temperature superconductors Tl₂CaBa₂Cu₂O₈ (Tl-2122,T _c =107 K) and YBa₂Cu₃O₇ (Y-123,T _c =92 K), at the Dhruva reactor at Trombay. The density of phonon states in Tl-2122 is enhanced at 6–17 meV and reduced at 40–70meV compared to that in Y-123.     

ZrO2 as a high-K dielectric for strained SiGe MOS devices

The potential of ZrO₂ thin film as a high-K gate dielectric for scaled MOSFET devices has been studied. ZrO₂ has been deposited directly on a Si_0.8Ge_0.2 substrate by reactive RF magnetron sputtering. An equivalent oxide thickness of < 20 Å with a leakage current of the order of 10^-4 A/cm² at 1 V has been obtained. Well-behaved capacitance-voltage characteristics with an interface state density of 2 × 10¹¹ cm^-2eV^-1 have been achieved. The deposited dielectric exhibits low charge trapping under constant current stressing.     

The effects of O2/Ar ratio on the structure and properties of hafnium dioxide (HfO2) films

HfO₂ films at various O₂/Ar flow ratios were prepared by reactive dc magnetron sputtering. The effects of O₂/Ar ratio on the structure and properties of HfO₂ films were studied using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM) and UV-Visible spectroscopy. The results showed that the HfO₂ films were amorphous at different O₂/Ar ratios, and the atomic ratio of O/Hf in the HfO₂ films at high O₂/Ar ratio was nearly to 2:1. The peaks of Hf4f and O1s shifted to higher binding energy with increasing the oxygen flow proportion. The HfO₂ films at high O₂/Ar ratio had high transmissivity at the range of 400-1100 nm.     

Effect of assist ion beam voltage on intrinsic stress and optical properties of Ta2O5 thin films deposited by dual ion beam sputtering

The optical properties and intrinsic stress of Ta₂O₅ thin films deposited by dual ion beam sputtering (DIBS) were studied as a function of the assist ion beam voltage (250-650 V). When the assist ion beam voltage was in the range of 350-450 V, the transmittance at the quarter-wave point reached its highest value (lowest absorption). The refractive index increased to 2.185 as the assist ion beam voltage increased from 250 to 350 V, but decreased as the assist ion beam voltage was further increased from 350 to 650 V.     

Synthesis of homogeneous PVP-capped SnS2 submicron particles via microwave irradiation

Homogeneous PVP-capped tin disulfide (SnS₂) submicron particles with narrow size distribution of ca. 300–500 nm have been successfully synthesized via microwave irradiation for 10 min for the first time. The samples were characterized using X-ray diffraction (XRD) and transmission electron microscope (TEM). In contrast, SnS₂ particles without PVP obtained under the same condition have irregular morphology. The experimental result indicated that PVP played an important role in controlling the shape and size distribution of particles, and in reducing the agglomeration degree of SnS₂ particles. The mechanism of PVPs improving the well dispersion of SnS₂ particles was discussed. The influence of solvent on the crystallinity of the as-prepared particles under microwave irradiation was primarily investigated.     

Enhanced performance in organic light-emitting diodes by sputtering TiO2 ultra-thin film as the hole buffer layer

Organic light-emitting diodes were prepared using titanium oxide (TiO₂) ultra-thin film by RF magnetron sputtering as the hole buffer layer. The device configuration is ITO/TiO₂/N-N′-diphenyl-N-N′-bis(1-naphthyl)-1,1′-biphenyl-4,4′-diamine/tris(8-quinolinolato)-aluminum/LiF/Al. The maximum luminous efficiency for the 1.2 nm TiO₂ device is increased by approximately 46% (6.0 cd/A), in comparison with that of the control device (4.1 cd/A). The atomic force microscopy shows that with the insertion of TiO₂ buffer layer, the roughness of ITO surface decreases, which is favorable to improve the device luminance and increase the device lifetime. The mechanism behind the enhanced performance is that the TiO₂ layer enhances most of the holes injected from the anode and improves the balance of the hole and electron injections.     

YBa2Cu3O7 superconductor as a mild,deep oxidation catalyst

Several Y-Ba-Cu-O compositions including the superconducting YBa₂Cu₃O₇ are scanned for their oxygen uptake using low temperature oxygen chemisorption (LTOC) technique as the principal probe at 195 K. BET surface area and pore size distribution were also determined. The results indicate their potential for use as mild, deep oxidation catalysts even under ambient and sub-ambient conditions.     

Evidence for supercooling across a vortex-matter phase transition: studies on CeRU2 and Bi2Sr2CaCu2O8

We present DC magnetization data indicating a first-order phase transition in the vortex state of CeRu₂, with the higher entropy phase exhibiting enhanced pinning. Minor hysteresis loops show evidence of supercooling of the higher entropy phase as the phase boundary is crossed both isothermally as well as at constant field. These features are shown to be absent across the Bragg-glass to vortex-glass transition in Bi₂Sr₂CaCu₂O₈. The supercooling is more persistent in the constant field case.     

In situ fabrication of Bi2S3 nanocrystal film for photovoltaic devices

A facile wet-chemical method to prepare Bi₂S₃ thin films with flake nanostructures directly on ITO glass substrate is presented in this paper for the first time. The product was characterized by X-ray powder diffractometer (XRD), Raman spectrometer, scanning electron microscope (SEM), and atomic force microscope (AFM). The one-step solvothermal elements treatment on the ITO substrate spare time to form film by spin-coating process and the film could be tightly attached to the ITO electrode. A conjugated polymer, poly 3-hexylthiophene (P3HT), was then spin-coated on the as-prepared Bi₂S₃ film to form an inorganic-organic hybrid thin film. The photovoltaic performance of the resulting solar cell device was also investigated.