Fe3O4 on ZnO: A spectroscopic study of film and interface properties

Magnetite (Fe₃O₄) thin films have been grown epitaxially on zinc oxide (ZnO) substrates, using reactive molecular beam epitaxy. The film quality was found to be strongly dependent on the oxygen partial pressure during growth. For a uniform Fe₃O₄ film a certain pressure variation was needed during growth. Structural, electronic, and magnetic properties were analyzed utilizing low energy electron diffraction, Hard X-ray Photoelectron Spectroscopy (HAXPES), Magneto-Optical Kerr Effect (MOKE), and X-ray Magnetic Circular Dichroism (XMCD). Diffraction patterns show clear indication for growth of Fe₃O₄ in the [111] direction on ZnO(0001). Non-destructive depth profiling by HAXPES revealed uniform magnetite thin films. Both, MOKE and XMCD measurements show easy in-plane magnetization. The dichroic spectra clearly support the formation of Fe₃O₄.     

ZnO/Cu/ZnO multilayer films: Structure optimization and investigation on photoelectric properties

A series of ZnO/Cu/ZnO multilayer films has been fabricated from zinc and copper metallic targets by simultaneous RF and DC magnetron sputtering. Numerical simulation of the optical properties of the multilayer films has been carried out in order to guide the experimental work. The influences of the ZnO and Cu layer thicknesses, and of O₂/Ar ratio on the photoelectric and structural properties of the films were investigated. The optical and electrical properties of the multilayers were studied by optical spectrometry and four point probe measurements, respectively. The structural properties were investigated using X-ray diffraction. The performance of the multilayers as transparent conducting coatings was compared using a figure of merit. In experiments, the thickness of the ZnO layers was varied between 4 and 70 nm and those of Cu were between 8 and 37 nm. The O₂/Ar ratios range from 1:5 to 2:1. Low sheet resistance and high transmittance were obtained when the film was prepared using an O₂/Ar ratio of 1:4 and a thickness of ZnO (60 nm)/Cu (15 nm)/ZnO (60 nm).     

Optimization of ZnO:Al/Ag/ZnO:Al structures for ultra-thin high-performance transparent conductive electrodes

Al-doped ZnO (AZO)/Ag/AZO multilayer coatings (50-70 nm thick) were grown at room temperature on glass substrates with different silver layer thickness, from 3 to 19 nm, by using radio frequency magnetron sputtering. Thermal stability of the compositional, optical and electrical properties of the AZO/Ag/AZO structures were investigated up to 400 °C and as a function of Ag film thickness. An AZO film as thin as 20 nm is an excellent barrier to Ag diffusion. The inclusion of 9.5 nm thin silver layer within the transparent conductive oxide (TCO) material leads to a maximum enhancement of the electro-optical characteristics. The excellent measured properties of low resistance, high transmittance in the visible spectral range and thermal stability allow these ultra-thin AZO/Ag/AZO structures to compete with the 1 μm thick TCO layer currently used in thin film solar cells.     

Deposition and characterization of PEDOT/ZnO layers onto PET substrates

ZnO thin films of different thicknesses were deposited by pulsed direct-current magnetron sputtering onto poly(ethylene terephthalate) (PET) substrates and afterwards poly 3, 4-ethylenedioxythiophene:polystyrenesulfonate (PEDOT:PSS) was spin-coated onto the ZnO film. Spectroscopic ellipsometry in the Vis–fUV energy range (1.5–6.5 eV), X-ray diffraction and atomic force microscopy were used to reveal the properties of the deposited films. The size of crystallites increased from 5.1 to 7.4 nm, whereas the crystallinity of the ZnO films has been improved. The influence of different ZnO thickness on the optical properties of the PEDOT:PSS layer was studied as well. As the thickness of ZnO films increased, the surface roughness increased but the energy gap decreased after a critical thickness. Concerning the consequences to the PEDOT:PSS optical properties, no major changes occurred in the transition energies.     

A study of grain-boundary grooving at the platinum/alumina interface

Grain-boundary grooving at the interface between solid platinum and solid alumina has been studied and its relevance to spheroidisation and particle coarsening noted. Analysis of the equilibrium shape of the grooves in conjunction with zero creep studies on platinum shows that the platinum/alumina interfacial energy is 1050 ergs/cm² at 1400° C. The rate of growth of the grooves shows that volume diffusion is the operative mass transport mechanism at all temperatures considered (1240 to 1540° C); however, there are indications that diffusion through the metal is rate-determining at lower temperatures (< 1410° C) while diffusion through the ceramic phase predominates at higher temperatures.     

Atomic structure and electronic properties of the GaN/ZnO (0001) interface

The stability and electronic structure of cation- and anion-compensated interfaces between (0001) lattice-matched slabs of GaN and ZnO have been considered. It was found that, irrespective of interfacial polarity, cation-compensated interfaces are by approximately 20 meV/unit cell more stable than the corresponding anion-compensated interfaces. Valence band offsets of 1.0 and 0.5 eV have been found at the cation- and anion-compensated interfaces, respectively.     

Electrochemical investigation of dopamine at the water/1,2-dichloroethane interface

Dopamine is an important neurotransmitter in mammalian central and peripheral nervous systems and is also a medicament to cure some neuropsychosis. In this work, ion transfer (IT), facilitated ion transfer (FIT) of protonated dopamine, and electron transfer (ET) between dopamine and ferrocene are investigated at the water/1,2-dichloroethane (W/DCE) interface. The IT and FIT reactions of protonated dopamine can be observed simultaneously within the same potential window. The experimental results demonstrate that dibenzo-18-crown-6, dibenzo-24-crown-8, and benzo-15-crown-5 work well with the protonated dopamine. The amperometric detection of dopamine based on either the IT or the FIT of protonated dopamine can get rid of the interference of ascorbic acid, and the lowest concentration that can be determined is approximately 0.05 microM by differential pulse voltammetry. For the ET reaction, its kinetics can be evaluated by scanning electrochemical microscopy, and the results show that the relationship between rate constants and driving force at the unmodified W/DCE interface obeys the Butler-Volmer equation in a rather wide potential region. When the W/DCE interface is modified by egg lecithin, the ET rate constants decrease with increasing concentration of egg lecithin, which indicates that egg lecithin hinders the ET reaction. When the driving force is increased to a certain degree, the linear relationship between ET rate constants and the driving force is distorted. These results will be helpful to understand both the pharmacodynamics and the neural signal transmission mechanism of dopamine at biological membranes and also provide a novel way to detect dopamine.     

Hollow ZnO from assembly of nanoparticles: photocatalytic and antibacterial activity

Hollow shells of ZnO were formed by the assembly of nanoparticles using PEG 400 wherein PEG-400 acted like both a solvent and a structure directing agent. The structure, morphology and optical properties were characterized by using PXRD, SEM, TEM and absorption studies. The hollow shells were found to possess high crystallinity with a surface area of 8 m² g^?1. The assembly was formed by nanoparticles ranging from 50 to 60 nm, whereas the size of the hollow shell ranged from 500 nm to 1 micron. Photocatalytic activity of these nanostructures was studied using Rhodamine B (RhB) and methyl orange (MO). Nearly 99% of the RhB dye was found to be degraded in 60 min while for MO, the degradation was 97% in 50 min. The pseudo-first-order rate constant was calculated as 0.072 min^?1 for the degradation of RhB and 0.075 min^?1 for the degradation of MO. The hollow shells were found to exhibit significant bacterial inhibiting efficacy at a low concentration of the particles. Comparative studies were carried out for photodegradation of Rhodamine B dye and antibacterial activity using spherical particles of ZnO and assembly of particles to form rods of ZnO. The results indicated that these hollow nanostructures could be used as a potential catalyst for the removal of dyes from water and as an antibacterial agent.     

ZnO/TiO2纳米管的制备及光降解性能研究

采用水热法合成TiO2纳米管,在碱性条件下与乙酸锌的无水乙醇溶液反应,得到表面负载ZnO的TiO2复合纳米管(ZnO/TNTs),并研究了复合纳米管在紫外光照射下对罗丹明B的光催化降解性能。通过透射电镜(TEM)、电子衍射能谱(EDS)、X射线衍射(XRD)、比表面积(BET)和紫外-可见光谱(UV-Vis)对所合成的材料进行了表征。结果表明,TiO2纳米管管径约5~10nm,管长约0.1~1μm;经ZnO表面修饰后,纳米管的结构没有发生明显变化,且ZnO粒子呈六方晶系纤锌矿结构均匀分散在纳米管的外表面,粒径约为6nm;光谱分析表明,ZnO/TNTs的吸收光谱有明显红移;且ZnO/TNTs的光催化活性较锐钛矿型TiO2纳米粉末、ZnO纳米粉末和TiO2纳米管有显著提高,且其光催化性能重复性好。     

Analysis of interface states in Au/ZnO/p-InP (MOS) structure

Zinc oxide (ZnO) film was deposited on p-type InP substrate by means of radio frequency magnetron sputtering technique and thus the Au/ZnO/p-InP (MOS) structure was fabricated. The crystal structure and surface morphology of ZnO film deposited on InP were characterized by X-ray diffraction and atomic force microscopy, respectively. The analysis of interface states of the structure is studied using admittance (Y?=?G?+?iωC) measurements at room temperature. It is observed that the capacitance and conductance measurements change with frequency. This change is attributed to the presence of interface states. To determine the interface state density (N_ss), the high-low frequency (C_HF–C_LF) capacitance, Hill–Coleman and conductance methods were used. The N_ss values obtained from these methods are in agreement with each other. Furthermore, the effect of the series resistance (R_s) on admittance measurements was investigated. Thus, the obtained results suggest that the prepared structure can be used in various electronic applications.     

Theoretical investigation of surface acoustic wave in the new, three-layered structure: ZnO/AlN/diamond

The new layered structure, ZnO/AlN/diamond, for surface acoustic wave (SAW) devices is investigated for gigahertz-band applications. This structure combines the advantages of both piezoelectric materials, with a high electromechanical coupling coefficient (K2) of ZnO and high acoustic velocity of AlN. Theoretical results show that Rayleigh mode SAWs with large phase velocities up to 12,200 m/s and large K2 from 1 to 3% were generated with this new structure.     

Role of transport polarization in electrocatalysis:A case study of the Ni-cluster/Graphene interface

As cathodes,iron-series(Fe,Co,Ni)clusters supported by carbon materials exhibit outstanding electrocat-alytic reduction activities in many electrocatalytic appl...     

A microstructural study on the surface and interface of CdTe/CdS solar cells

The surface and interface properties of CdTe/CdS solar cells, including interfacial mixing, surface and interface geometrical morphology, CdTe grain size and preferential crystal orientation of CdTe layers were studied using Auger electron spectroscopy (AES) depth profiling, atomic force microscopy (AFM), Fourier transform infrared (FTIR) spectroscopy, optical reflectance (OR) and X-ray diffraction (XRD) techniques. The correlation between the surface and interface properties and CdTe/CdS solar cell performance was also investigated. AES depth profiling was used to analyse the interdiffusion between the CdTe and CdS layers. Atomic force microscopy (AFM) suggests that the interfacial geometrical morphology has a significant influence on the photovoltaic property of CdTe/CdS solar cells. Rough interfaces tend to increase the photovoltaic conversion efficiency of solar cells because of multiple reflections. X-ray diffraction shows that polycrystalline CdTe/CdS solar cells with higher efficiencies appear to be orientated with more (1 1 1) planes of CdTe parallel to the macrosurface, but CdTe single crystals with differently indexed surface planes show almost the same reflection behaviour. Further theoretical and experimental analyses are therefore needed to clarify this observation. This revised version was published online in July 2006 with corrections to the Cover Date.     

Optimization of ZnO/Ag/ZnO multilayer electrodes obtained by Ion Beam Sputtering for optoelectronic devices

We investigated the electrical and optical properties of ZnO/Ag/ZnO multi-layer electrodes obtained by ion beam sputtering for flexible optoelectronic devices. This multi-layer structure has the advantage of adjusting the layer thickness to favor antireflection and the surface plasmon resonance of the metallic layer. Inserting a thin (Ag) metallic layer between two (ZnO) oxide layers decreases the sheet resistance while widening the optical transmittance window in the visible. We found that the optimal electrode is made up of a 10 nm thin Ag layer between two 35 nm and 20 nm thick ZnO layers, which resulted in a low sheet resistance (R_sq = 6 Ω/square), a high transmittance (T ≥ 80% in the visible) and the highest figure of merit of 1.65 × 10^-2 square/Ω.     

感应耦合辅助磁控溅射氧化锌薄膜在铜铟硒薄膜太阳能电池中的界面

薄膜铜铟硒太阳能电池由于前后电极间欧姆接触导致电流损耗,高阻氧化锌层可以消除因表面空洞或表面损坏造成的前后电极短路,这种作用大小取决于氧化锌薄膜表面形貌和电阻率.本论文研究了用感应耦合等离子辅助磁控溅射氧化锌薄膜在铜铟硒薄膜太阳能电池中的应用,并分析氧化锌薄膜层和铜铟硒层的界面结构特点.实验用氧化锌陶瓷靶在氧气和氩气环境下进行溅射,当溅射气压为4mTorr,射频功率300W,直流偏压30V时,制备的氧化锌具有表面形貌均匀致密,电阻率为7×108Ω·cm、透光率80%以上等特性,与吸收层铜铟硒构成良好的异质结界面.     

Case study: the impact of assembly reorientations on assembly time

Many prior-assembly planners have considered the number of assembly direction reorientations as an assembly sequence evaluation and selection criterion for assembly sequence planning. However, little study has been conducted to evaluate the effectiveness of the selected assembly sequences. This paper studies the impact of assembly direction reorientations on assembly time. Results of the case study show that, for both robot and human operator assembly processes, the number of reorientations in an assembly sequence has a significant impact on assembly time. The results support the study research hypothesis that using an assembly sequence which requires more assembly direction reorientations results in longer assembly time. The study conducted in this paper helps verify and quantify the importance and effectiveness of reducing the number of assembly direction reorientations in assembly sequence planning.     

Rapid thermal annealing of sputter-deposited ZnO/ZnO:N/ZnO multilayered structures

Rapid thermal annealing (RTA) of sputter-deposited ZnO/ZnO:N/ZnO multilayered structures formed by a combination of radio-frequency magnetron sputtering and a microwave plasma source was investigated for the fabrication of highly-crystallized ZnO:N films. The assistance of the microwave plasma source resulted in the enhancement of nitrogen incorporation into the ZnO films and the deterioration of film crystallization. On the other hand, crystallization of the ZnO:N layer was improved by RTA with no significant effusion and diffusion of N atoms using a ZnO/ZnO:N/ZnO multilayered structure. The role of the front and bottom ZnO layers during RTA of ZnO/ZnO:N/ZnO multilayered structures is demonstrated.     

A study on occupational exposure in a PET/CT facility

Staff occupational exposure for (18)F-FDG studies has been assessed. For this purpose, different detectors, all traceable to PTB standards, have been used. Measurements were carried out in different working areas in the facility for different procedures and 400 MBq per patient standard injected activity. A radiological map of the patient lying on the couch was obtained; the largest dose rate result was obtained in contact with the patient's abdomen. The maximum dose to the most exposed staff member for this position is 3.6 mSv y(-1), under some conservative assumptions. A typical value would be 0.9 ± 0.3 mSv y(-1) close to the abdomen, taking into account staff rotations. These results have been obtained from a sample of 50 patients and average values have been statistically tested. Particularly, a negligible probability of reaching 20 mSv in a year (assuming no incidents or contamination) was obtained (P < 0.01). Annual dose received by personnel lies well within the recommended limits (International Commission on Radiological Protection), these measurements help to optimise working procedures in the facility.