bluuebunny/crossref_metadata_2025 huggingface dataset:
Fe-modified TiO2 nanocatalyst under blue-light irradiation
Authors: Wei Y. L. , Chen K. W. , Wang H. P.
Published: May 2009

Ultraviolet (UV) and visible light active photocatalysts, 13–20 nm in size, were prepared by doping iron into anatase TiO2 (Fe/Ti at. ratio: 0.11% and 0.49%). Greater Fe dosage led to stronger light absorbance in both UV and visible regions, and also to generally better photocatalytic activity. Fe2+ and Fe3+ coexisted in 0.11% Fe–TiO2, while only Fe3+ existed in 0.49% Fe–TiO2. A dramatic change in the molecular environment of Fe was observed after the doping process; from cubic (Fe3O4) and trigonal (Fe2O3) structures into tetragonal TiO2. Different Fe speciation in catalysts led to different kinetics for methylene blue photocatalytic degradation.
Development of a system for laser-assisted molding of micro- and nanostructures
Authors: Michaeli Walter , Klaiber Fritz
Published: May 2009

Biotechnology, information, and medical industries have high growth potential. A key technology for those industries is the replication of micro- and nanostructures. Precise micro-and nanostructured parts with functional surfaces can be produced economically by injection molding. The whole process chain (thermal mold condition, molding, demolding, measurement, and analysis) must be analyzed carefully to ensure the highest accuracy and reliability. To enable the precise production of such structures, a new technique for variothermal injection molding was developed at the IKV. An innovative laser heating unit was developed, designed, and built. In experiments the laser unit was analyzed and implemented into an injection mold to heat the cavity surface efficiently. Using this technique selective parts of the cavity could be heated with high temperature gradients of up to 300°C∕s. Preliminary measurements were done to correlate the laser power and the temperature change on the mold surface. A pyrometer and a laser control unit were implemented and realize a precise temperature profile on the mold surface and avoid a temperature overshoot.
Ion sensitivity of the flowerlike ZnO nanorods synthesized by the hydrothermal process
Authors: Chiang Jung-Lung , Hsu Jung-Fu , Lee Shih-Fong , Lee Li-Ying , Liu Han-Ying
Published: May 2009

Flowerlike ZnO nanorods were synthesized by the hydrothermal process. A simple two-step process was developed for growing ZnO nanorods on the silicon substrates at about 85°C. The concentration of zinc acetate dehydrate pretreatment is 0.01M. The x-ray diffractometer pattern of ZnO nanorods at 2θ=31.77°, 34.42°, and 36.25° indicates three reflection peaks of hexagonal wurtzite structure, (100), (002), and (101), respectively. It has been shown that the ZnO nanorods are of single hexagonal phase of wurtzite structure. The scanning electron microscopy image revealed that the average diameter of ZnO nanorods was about 360nm. In addition, the ZnO nanorods/Si structure was utilized as a pH sensor head and connected with the metal-oxide-semiconductor field-effect transistor when the extended-gate field-effect transistor was finished. Afterward, the semiconductor parameter analysis instrument (Keithley 4200) was used to measure the current-voltage characteristic curves in the different pH buffer solutions. The experimental result found that the pH sensing response is obtained and the output voltage shifted right with increasing pH values.
Design and calibration method for microvision three-dimensional laser scanner
Authors: Sun Changku , Liu Bin , Wang Peng
Published: May 2009

A microvision three-dimensional (3D) laser scanner with micron accuracy and the calibration method are presented in this article. The system is designed to measure and reconstruct the 3D shape of miniature objects. A new two-step calibration method is proposed to reduce measurement errors and improve the measurement precision. Repeated measurements show that the repeatability is better than ±1μm. Moreover, the system has been successfully applied to extracting the height of solder pastes, which is beneficial in surface mount technology quality control.
Microelectromechanical systems motion measurement and modal analysis based on Doppler interferometry
Authors: Zhang G. X. , Zhong Y. , Hong X. , Leng C. L.
Published: May 2009

Microelectromechanical systems (MEMSs) have been growing rapidly over recent years. However, measurement of their motions is a difficult problem. A laser Doppler interferometric system for measuring the instantaneous velocity and displacement of the periodic and nonperiodical in-plane and out-of-plane motions of the vibrating combs simultaneously has been developed. The working principle and optical diagram of the system are explained. The instantaneous velocity and displacement of vibrating combs are acquired by demodulating the frequency modulated Doppler signal by using a phase-locked loop. The developed laser Doppler interferometer provides a powerful means in studying the performance of the MEMS devices, particularly in studying their vibration modals. Modal analyses of the vibrating combs are carried out theoretically and experimentally. Due to the nonrigid structure of the MEMS resonator besides the basic modal there are also high order modals in the MEMS vibration. The basic modal is the desired in-plane lateral vibration. The second order vibration is a torsion vibration about the axis perpendicular to the fingers of the movable combs. Both third and fourth order vibrations are lateral bending of the supporting beams. The measured experimental data are presented. The accuracy of the developed interferometer has been checked by an acceleration calibrator.
Light-scattering study of the morphology, structure, and mechanical properties of high impact polystyrene alloys with poly(cis-butadiene) rubber
Authors: Ma Gui-Qiu , Yuan Xu-Bo , Han Yun-Ping , Cui Li-Li , Sheng Jing
Published: May 2009

The interface layer thickness between two phases, i.e., the compatible domain between interfaces, is calculated in the high impact polystyrene (HIPS)alloys with poly(cis-butadiene) rubber (PcBR) by the intensity of small angle x-ray scattering. The phase structure and morphology of the HIPS alloys with PcBR are studied by scanning electron microscope images. The size of the phase structure is calculated by graph processing and its variation is discussed. The structure parameters of the small angle light scattering are analyzed. The authors found that the mechanical properties of the modulus and yield stress have a linear correlation with the composition and structure parameters of the alloys when PcBR is a dispersed phase.
Dopant activation in homoepitaxial MgZnO:P thin films
Authors: Brandt Matthias , von Wenckstern Holger , Meinecke Christoph , Butz Tilman , Hochmuth Holger , Lorenz Michael , Grundmann Marius
Published: May 2009

Homoepitaxial MgxZn1−xO:P thin films with variable magnesium content (x<0.05) have been grown by pulsed-laser deposition. The film compositions have been determined by proton induced x-ray analysis. The phosphorous and magnesium content of the films decreases with increasing oxygen partial pressure during growth. High-resolution x-ray diffraction shows a pseudomorphic growth of the thin films with a nominal MgO content of 2 wt %. Hall-effect measurements show electron mobilities of the as-grown films as high as 820 cm2/V s at 55 K, which compares to the value observed for ZnO:P homoepitaxial thin films. Upon annealing, the free carrier concentration was reduced by several orders of magnitude, depending on the oxygen partial pressure used during growth of the MgZnO:P films, while it remained nearly unchanged in ZnO:P samples. The role of the MgO concentration in the films in acceptor defect formation is discussed.
Stable p-type ZnO:P nanowire/n-type ZnO:Ga film junctions, reproducibly grown by two-step pulsed laser deposition
Authors: Lorenz Michael , Cao Bingqiang , Zimmermann Gregor , Biehne Gisela , Czekalla Christian , Frenzel Heiko , Brandt Matthias , von Wenckstern Holger , Grundmann Marius
Published: May 2009

ZnO p-n junctions were grown by two-step pulsed laser deposition (PLD) on a-plane sapphire substrates using a Ga-doped ZnO thin film as n-type conducting material. On top of these n-type films, phosphorous-doped ZnO (ZnO:P) nanowires were prepared by high-pressure PLD. Rectifying I-V curves with threshold voltage of about 3.2 V and a forward/reverse current ratio of 100 at ±3.5 V were measured reproducibly on these junctions. There are three independent indications for reproducible and about 1 year stable p-type conductivity of the ZnO:P wires: (1) Low-temperature cathodoluminescence of single ZnO:P nanowires exhibits phosphorus acceptor-related peaks: (A0,X), (e,A0), and donor-acceptor pair [B. Q. Cao et al., Nanotechnology 18, 455707 (2007)], (2) bottom-gate field effect transistors using undoped (n-type) ZnO and ZnO:P wires showed opposite transfer characteristics [B. Q. Cao et al., Phys. Status Solidi (RRL) 2, 37 (2008)], and (3) the rectifying I-V characteristics of the ZnO:P nanowire/ZnO:Ga-film junctions as shown here.
Ferroelectric thin film field-effect transistors based on ZnO/BaTiO3 heterostructures
Authors: Brandt Matthias , Frenzel Heiko , Hochmuth Holger , Lorenz Michael , Grundmann Marius , Schubert Jürgen
Published: May 2009

The authors have grown epitaxial ZnO/BaTiO3 (BTO) heterostructures by pulsed laser deposition on lattice matched Nb-doped SrTiO3 substrates. Epitaxial growth of the BTO layers has been confirmed by x-ray diffraction. The electrical properties of ZnO/BTO heterostructures have been investigated by current-voltage and capacitance-voltage measurements, showing that the BTO layers are highly insulating (leakage current density jl<10−9 A/cm2 at 5 V). The structures were processed into field-effect transistors, and their output and transfer properties have been determined. A large memory effect of the source-drain current on the previously applied “programm” gate voltage (−7 or +20 V) has been observed. It is reproducible in repeated switching cycles, showing the suitability of the structure as a nonvolatile memory device.
Effects of nanolubricant on performance of hydrocarbon refrigerant system
Authors: Jwo Ching-Song , Jeng Lung-Yue , Teng Tun-Ping , Chang Ho
Published: May 2009

This work discusses the replacement of the R-134a refrigerant and polyester lubricant with a hydrocarbon refrigerant and mineral lubricant. The mineral lubricant included added Al2O3 nanoparticles (0.05, 0.1, and 0.2wt% ) to improve the lubrication and heat-transfer performance. Experimental results indicated that the 60% R-134a and 0.1wt% Al2O3 nanoparticles were optimal. Under these conditions, the power consumption was reduced by about 2.4%, and the coefficient of performance was increased by 4.4%. These results show that replacing R-134a refrigerant with hydrocarbon refrigerant and adding Al2O3 nanoparticles to the lubricant effectively reduced power consumption.
In-implanted ZnO: Controlled degenerate surface layer
Authors: Look D. C. , Farlow G. C. , Yaqoob F. , Vanamurthy L. H. , Huang M.
Published: May 2009

In was implanted into bulk ZnO creating a square profile with a thickness of about 100nm and an In concentration of about 1×1020cm−3. The layer was analyzed with Rutherford backscattering, temperature-dependent Hall effect, and low-temperature photoluminescence measurements. The implantation created a nearly degenerate carrier concentration n of about 2×1019cm−3, but with a very low mobility μ, increasing from about 0.06cm2∕Vs at 20K to about 2cm2∕Vs at 300K. However, after annealing at 600°C for 30min, n increased to about 5×1019cm−3, independent of temperature, and μ increased to about 38cm2∕Vs, almost independent of temperature. Also, before the anneal, no excitons bound to neutral In donors, called I9 in literature, were observed in the photoluminescence spectrum; however, after the anneal, the I9 line at 3.3568eV was by far the dominant feature. Analysis of the Hall-effect data with a parametrized, two-layer model showed that the conduction before the anneal was mainly due to very high concentrations of native donors and acceptors, produced by the implantation, whereas the conduction after the anneal was due to In ions that were nearly 100% activated. These results show that strongly degenerate conductive layers with designed profiles can be created in ZnO with implantation and relatively low-temperature anneals.
Bond lengths, phase stability, and band gaps in MgxZn1−xO alloys
Authors: Boonchun Adisak , Lambrecht Walter R. L.
Published: May 2009

The main question studied in this article is how the preference of MgO for six- or fivefold bonding in rocksalt or h-MgO structures, respectively, affects the local bond lengths near Mg atoms in wurtzite structured MgxZn1−xO alloys. A first-principles study of MgxZn1−xO alloys has been carried out in the range 0<x<0.5 to determine the local wurtzite parameter u, axial bond lengths, and the band gaps. Disorder in the alloys is simulated using the special quasirandom structure approach. The authors found that axial Mg–O bond lengths are longer than the axial Zn–O bond lengths for all possible concentrations, but the u values are still far away from the h-MgO value of 0.5. The band gap is found to increase linearly with Mg content. They found no signs of transformation to the lower energy h-MgO structure until x is about 50%.
Micro-ink-jetting of silver nanoparticles on low temperature cofired ceramic substrates for drop-on-demand metallization
Authors: Liang Y. N. , Shan Xuechuan , Gian P. W. , Lok B. K. , Lu C. W.
Published: May 2009

The authors demonstrated the feasibility of patterning conductive inks on sintered low temperature cofired ceramic (LTCC) substrates using ink-jetting technology. The objective of this study is to realize drop-on-demand metallization on plain or structured ceramic substrates. The sintered LTCC substrates can be viewed as a porous ceramic medium with rough surface finishes, and its porosity is one of the major impediments for achieving high pattern quality via ink-jetting in terms of pattern uniformity and resolution. To improve the uniformity and minimize the dimension of ink-jetted patterns, the authors proposed and demonstrated three technical solutions, i.e., ink-jetting on patterned ceramic substrates, heating substrates during ink-jetting, and coating substrates with a dielectric layer. Improvement in resolution and uniformity of ink-jetting was achieved using the proposed approaches.
Integrated microactuation scanning probe microscopy system
Authors: Chen Xing , Lee Dong-Weon
Published: May 2009

This article reports on a highly integrated system that combines a scanning probe cantilever with an X-Y-Z scanner through monolithic microfabrication without any manual assembly or alignment for scanning probe microscopy. This compact system included an integrated scanning probe cantilever with a sharp tip and an electrostatic comb-drive microstage with a novel structure that enables both a large in-plane displacement and out-of-plane actuation even for tilt motion. Additionally, interdigitated comb-drive capacitors allow for sensitive self-sensing on both the translational position and vertical height without any external detectors or special extra integrated sensors. The cantilever, with a sharp tip fabricated by new hybrid wet and dry etching, was developed for the scanning probe system. The authors successfully demonstrated the miniaturized scanning probe microscopy system to show how microelectromechanical system techniques have an influence on the conventional bulk system and macroscopic instruments.
Metal contacts on bulk ZnO crystal treated with remote oxygen plasma
Authors: Fang Z.-Q. , Claflin B. , Look D. C. , Dong Y.-F. , Brillson L.
Published: May 2009

To study the quality of thin metal/ZnO Schottky contacts (SCs), temperature-dependent current-voltage (I-V), capacitance-voltage, deep level transient spectroscopy, and photoluminescence measurements were performed using bulk, vapor-phase ZnO, treated by remote oxygen plasma (ROP). Au∕ZnO and Pd∕ZnO contacts on both O and Zn faces are compared as a function of the ROP processing sequence and duration. We find that (i) as the duration of ROP treatment increases from 2to4h, Au∕ZnO contacts on the Zn face, deposited before ROP treatment, become rectifying, while those on the O face remain Ohmic; (ii) with long-term ROP treatments prior to metallization, both Au∕ZnO and Pd∕ZnO show high-quality SCs; however, their I-V characteristics can be significantly degraded by electric field and high temperatures; (iii) ROP treatment can cause more H removal on the Zn face than on the O face, resulting in a decrease in the near-surface carrier concentration for the Zn face only; (iv) in addition to the dominant bulk-trap E3, surface traps, E6/E7 and E8, and Es, can be observed in Au∕ZnO and Pd∕ZnO SCs, respectively, on the Zn face, with shorter ROP treatment; and (v) with long-term ROP treatment, E3 (or L2) significantly increases and shifts in Au∕ZnO SCs on the Zn face.
New approach of dispersing silver nanopowder in water using ultrasonic atomizer 1.63MHz
Authors: Nguyen Manh Toan , Tsung Tsing Tshih , Chang Ho
Published: May 2009

In this research, the combination of resonance and vibration of ultrasound created by ultrasonic atomizer 1.63MHz was employed to disperse silver nanopowder (4–40nm in diameter) in water without any additional chemical phases, which has been considered very difficult. To evidence the dispersive function of a proposed technique, it was compared to other two well-known conventional mechanical ultrasonic dispersing techniques, viz., ultrasonic cavitation (at 20kHz) and sonication bath (at 19kHz). Dynamic light scattering and transmission electron microscope were utilized to analyze the distribution behavior of silver nanoparticles in colloids after being dispersed. The comparison indicated that the proposed technique dispersed silver nanopowder in water much more homogeneously than the other two conventional techniques, with the average size of dispersed particles of a round 202nm. In particular, small silver nanoparticles in the size of around 7nm were almost dispersed separately one by one, a report that has not been reached by conventional ultrasonic cavitation dispersing technique or sonication dispersing technique either. Moreover the colloid dispersed by the proposed technique was stable with its zeta potential factor of approximately 30mV at pH=7.5.
Ultraviolet photodetector fabricated from atomic-layer-deposited ZnO films
Authors: Shan C. X. , Zhang J. Y. , Yao B. , Shen D. Z. , Fan X. W. , Choy K. L.
Published: May 2009

Zinc oxide (ZnO) films have been prepared on glass substrate in layer-by-layer mode using an atomic-layer deposition (ALD) technique, and a metal-semiconductor-metal structured photodetector has been fabricated on the ZnO films employing interdigital Au as metal contacts. The photodetector shows a cutoff wavelength at around 390nm and has an obvious responsivity in the whole UVA spectral range. Because the response of the ZnO photodetector covers the whole UV solar irradiation that can reach the earth, the photodetector promises to be useful in monitoring UV solar irradiation to protect people from harm caused by the solar irradiation. Furthermore, the capability of preparing large-area uniform ZnO films of ALD makes it favorable for possible mass production of this kind of photodetector.
Optical and electrical properties of amorphous InGaZnO
Authors: Yamaguchi Norihiko , Taniguchi Satoshi , Miyajima Takao , Ikeda Masao
Published: May 2009

The authors observed the photoluminescence (PL) spectra of amorphous InGaZnO (a-IGZO) for the first time. At liquid nitrogen temperature, even weak near-band-edge emission was clearly observed at a wavelength of ∼400 nm (3.1 eV) accompanied by a much stronger broad deep emission peaking at around 700 nm (1.77 eV) for 1-μm-thick samples deposited by sputtering on sapphire substrates at room temperature. The PL intensity of each emission strongly depends on the electron concentration of a-IGZO ranging from 1016 to 1018 cm−3. As the carrier concentration increased, the PL intensity of the broad deep emission decreased. The near-band-edge emission energy of 3.0 eV (413 nm) was in good agreement with the estimated absorption energy of 3.03–3.08 eV (403–409 nm) at 77 K. The depth profile of the carrier concentration of the a-IGZO layer was estimated using step-etching Hall measurements and was found to be uniform. The width of the depletion layer was determined by the film-thickness dependence of the sheet carrier concentration. If the substrate-side depletion layer is negligible, they estimated the upper limit of Vbi as ∼1.9 eV (653 nm), in the middle of the bandgap, when assuming an 11.5 value for permittivity.
Optical characterization of zinc oxide microlasers and microwire core-shell heterostructures
Authors: Czekalla Christian , Sturm Chris , Schmidt-Grund Rüdiger , Cao Bingqiang , Pérez Jesús Zúñiga , Lorenz Michael , Grundmann Marius
Published: May 2009

Zinc oxide microwire lasers show whispering gallery mode lasing, exhibiting high Q-factors. The energetic positions of the lasing modes agree with those calculated from a simple plane wave model. The characteristic temperature of the microlasers was determined from temperature dependent measurements. Additionally, the authors demonstrate the successful growth of MgZnO/ZnO core-shell heterostructures by pulsed laser deposition.
Analysis on vibration rejection ratio of scanning probe microscope
Authors: Chen Jinping , Guo Tong , Hu Xiaodong , Hu Xiaotang
Published: May 2009

In order to investigate the influence of external vibration on the tip-sample interaction in scanning probe microscope, a concept, vibration rejection ratio (VRR), was proposed by Thompson et al. In the present article, a concise theoretical background was introduced, a vibration stimulating and measuring system for SPM was built up, and an experimental research of the influence on SPM VRR was carried out with different SPM probes, samples, tip preloads, and open/close loops of tip-sample interaction. Based on the experiments, it was proved that SPM VRR had correlations with the spring constant, the air damping constant, the effective mass of the cantilever, the contact spring constant, the contact damping constant between tip and sample, etc. Being different from the traditional theoretical analysis, other than the resonant frequency, a “leading coefficient” was proposed to describe the VRR. A conclusion was drawn after an experimental analysis that SPM’s vibration rejecting ability can be improved by longer cantilever probe, softer sample surface, greater tip preload, and close-loop control for tip-sample interaction. More attention should be paid to a proper combination of the above parameters.
Multi-WO3 nanowire based gas detector
Authors: Kang Sungmu , Battogtokh Jugdersuren , McKeown David A. , Buechele Andrew C. , Pegg Ian L. , Philip John
Published: May 2009

The authors have grown high quality WO3 nanowires and fabricated devices with single and multiple nanowires. Devices with single WO3 nanowire exhibit n-type semiconducting behavior and the conductivity increases with hydrogen annealing. The authors also demonstrate significant gas sensitivity of multi-WO3 nanowire devices at room temperature. The sensitivity measurements are carried out in a field-effect transistor geometry with many nanowires connected in between the source and drain electrodes. The sensitivity can be tuned with gate voltages, which will be useful for several applications where controlled gas adsorption is required.
Fabrication and characterization of novel hybrid green light emitting diodes based on substituting n-type ZnO for n-type GaN in an inverted p-n junction
Authors: Bayram C. , Razeghi M. , Rogers D. J. , Teherani F. Hosseini
Published: May 2009

Details of the fabrication and characterization of hybrid green light emitting diodes, composed of n-ZnO/(InGaN/GaN) multi-quantum-wells/p-GaN on AlN/sapphire, are reported. Scanning electron microscope, atomic force microscopy, high resolution x-ray diffraction, and photoluminescence were used to study the hybrid device. The effects of solvents, annealing, and etching on n-ZnO are discussed. Successful hybridization of ZnO and (In)GaN into a green light emitting diode was realized.
Low-cost x-ray mask based on micropattern sputtered lead film for x-ray lithography
Authors: Mongpraneet S. , Wisitsora-at A. , Phatthanakun R. , Chomnawang N. , Tuantranont A.
Published: May 2009

In this work, a low-cost x-ray micromask is developed by sputtering a lead (Pb) film on a Mylar sheet substrate through microshadow masks and the x-ray mask is experimented for patterning an SU-8 negative photoresist on a stainless steel substrate. In addition, the required Pb layer thickness as a function of SU-8 photoresist thickness is studied and compared to that of conventional gold x-ray mask. The Pb layer and SU-8 photoresist thicknesses are varied from 8 to 19 μm and from 150 to 350 μm, respectively. Sputtering is selected for Pb thick film deposition due to its high sputtering yield. The Pb mask is used for x-ray lithography of SU-8 photoresist with 125 μm wide microchannel patterns, designing for microfluidic chip fabrication. The x-ray source for x-ray lithography is produced by synchrotron radiation at Siam Photon Laboratory, Thailand. For 180 μm thick SU-8 photoresist, Pb film thickness of around 8 μm is required to block x ray at a dose of 4200 mJ/cm3. This is less than twice the thickness required for a gold absorbing layer, which is about 5 μm. A similar relationship is seen for different SU-8 photoresist thicknesses. In addition, a steep sidewall angle of ∼89.5° for SU-8 microchannel pattern is obtained. The results demonstrate that the Pb based x-ray mask offers high lithographic quality at a very low cost. Therefore, it is highly promising for commercial applications.
Stochastic approach to modeling photoresist development
Authors: Mack Chris
Published: May 2009

In this paper a continuous approximation to the critical ionization (CI) model has been derived and shown to match the CI model extremely closely. Further, both of these models were shown to match the widely used Mack model of dissolution over the lithographically significant ranges of development rates. The variance of the dissolution rate is shown to arise from the variation in the development path required to bypass randomly insoluble polymer molecules rather than just the variance in the polymer solubility itself. Percolation theory, where the percolation probability is equal to the probability that a polymer molecule will become soluble, has the potential for providing the theoretical framework required to determine this variance in dissolution path.
Unexpected Coulomb binding between Ca and H+ in ZnO
Authors: Li Xian-Bin , Limpijumnong Sukit , Tian Wei Quan , Zhang S. B.
Published: May 2009

First-principles calculations show unexpectedly large binding (0.7 eV) between positive H+ at oxygen antibonding site (ABO) and Ca, which replaces isovalent Zn in ZnO. It is explained by a large spatial undulation of the host charge and the change in the charge due to Ca replacement of the Zn. Our findings are consistent with a number of infrared measurements.
Polarity-related asymetry at ZnO surfaces and metal interfaces
Authors: Dong Yufeng , Fang Z.-Q. , Look D. C. , Doutt D. R. , Hetzer M. J. , Brillson L. J.
Published: May 2009

Clean ZnO (0001) Zn- and (0001¯) O-polar surfaces and metal interfaces have been systematically studied by depth-resolved cathodoluminescence spectroscopy, photoluminescence, current-voltage and capacitance-voltage measurements, and deep level transient spectroscopy. Zn-face shows higher near band edge emission and lower near surface defect emission. Even with remote plasma decreases of the 2.5eV near surface defect emission, (0001)-Zn face emission quality still exceeds that of (0001¯)-O face. The two polar surfaces and corresponding metal interfaces also present very different luminescence evolution under low-energy electron beam irradiation. Ultrahigh vacuum-deposited Au and Pd diodes on as-received and O2∕He plasma-cleaned surfaces display not only a significant metal sensitivity but also a strong polarity dependence that correlates with defect emissions, traps, and interface chemistry. Pd diode is always more leaky than Au diode due to the diffusion of H, while Zn-face is better to form Schottky barrier for Au compared with O-face. A comprehensive model accounts for the metal-and polarity-dependent transport properties.
Growth and structural properties of ZnO films on (10−10) m-plane sapphire substrates by plasma-assisted molecular beam epitaxy
Authors: Kim Jung-Hyun , Han Seok Kyu , Hong Sun Ig , Hong Soon-Ku , Lee Jae Wook , Lee Jeong Yong , Song Jung-Hoon , Park Jin Sub , Yao Takafumi
Published: May 2009

Growth and structural properties of ZnO films on (10−10) m-plane sapphire substrates by plasma-assisted molecular beam epitaxy were studied. The ZnO films were grown at a wide range of growth temperature of 100–800°C. From the x-ray diffraction θ-2θ measurements, overwhelming ZnO (10−10) reflection was confirmed in addition to the very weak (0002) and (10−13) reflections. The sample grown at 500°C showed the highest purity with the very weak (10−13) and the negligible (0002) reflections. The full widths at half maximum (FWHMs) for the (10−10) x-ray rocking curves (XRCs) with ϕ=0° is much higher than those for with ϕ=90°, which indicates that the films have an anisotropic structural property. The FWHMs for the off-axis (10−11) XRCs were larger than by about 0.1° than those for the (10−10) XRCs with ϕ=90°. Two distinct features of the striated surface morphology with the grains along the ZnO ⟨0001⟩ direction and the inhomogeneity with the appearance of islands on the surface were observed. Detailed investigation on the microstructure by transmission electron microscopy revealed that ZnO (10−13) inclusion was present above the ZnO∕Al2O3 interface not at the interface. The ZnO (10−13) inclusion did reach to the top surface, which is believed to the cause for the extra spots in the reflection high energy electron diffraction patterns and the inhomogeneous islands in the atomic force microscope images.
Field-emission properties of multiwalled carbon nanotubes in gas
Authors: Zou Q. , Wang M. Z.
Published: May 2009

Ar gas effects on the field-emission (FE) properties of multiwalled carbon nanotubes (CNTs) were investigated. The FE measurement was carried out in vacuum and in Ar gas using a scanning-electron microscope (SEM) chamber with a removable gas cell fitted in the SEM chamber. The gap between electrodes was set by observing a SEM image. The electrodes were characterized in situ before and after FE measurements by SEM observation. The FE properties of CNTs in Ar gas at 80kPa and lower pressures were the same as those in vacuum before and after the measurements in gas. At pressures more than 80kPa, the FE threshold voltages in Ar gas were higher than those in vacuum and increased with increasing Ar gas pressure. However, the FE properties in vacuum after the measurement in gas were the same as before. When the FE threshold voltages became higher than the voltage for gas breakdown, a gas discharge was ignited before the FE appearance. After the gas discharge, the carbon nanotube cathode was damaged.
Fabrication and characterization of the substrate-free InGaN-based resonant-cavity light-emitting diodes for plastic optical fiber communications
Authors: Tsai Chia-Lung , Lin Jia-Qing , Huang Ju-Ping
Published: May 2009

In this article, the authors report on the realization of substrate-free InGaN-based thin-film resonant-cavity light-emitting diodes (TF-RCLEDs). Experimentally, the sapphire substrate was stripped by using the laser lift-off technique. The λ∕4-thick Ta2O5∕SiO2 distributed Bragg reflector and the metallic Ag film with mirror reflectivities of 68% and 97% were, respectively, coated onto the top and bottom of the substrate-free LEDs to form a Fabry–Pérot cavity. The performances of LEDs are characterized by light output power, external quantum efficiency, emission spectrum, angular-resolved intensity distribution, and dynamic response. As a result, the fabricated TF-RCLEDs exhibit a low operating voltage of 3.34V at 20mA, a maximum light output power of 6.3mW at 140mA, and an external quantum efficiency of 5.5% at 4mA. In addition, the TF-RCLEDs show temperature insensitivity as compared to the normal LEDs directly grown on the sapphire substrates. Furthermore, the 50% viewing angle of TF-RCLED is smaller than that of normal LED, i.e., 146° versus 168° at 60mA. Finally, the eye pattern of the TF-RCLEDs is improved compared to that of the normal LEDs as operated at the data transmission rate of 100Mbit∕s. These results exhibit that the InGaN-based TF-RCLEDs are excellent candidates for the use in short-distance plastic optical fiber communications.
Research on the influence of membrane on the performance of vibration sensor
Authors: Li Rui , Xiao Wen , Yi Xiaosu , Xu Bingshi , Chang Junlei
Published: May 2009

Intensity modulated fiber optic sensor is one of the fastest growing and most widely used fiber optic sensors. A double optical-fiber vibration sensing system with a new kind of membrane is introduced in this article. The system is based on optical intensity modulation and is characterized by the membrane that is used to sense vibration. The mechanism of film sensing is described and the model showing the relationship between film parameters (reflection coefficient and radius of curvature) and the sensor performance is established. With the simulated responses, a membrane structure with high sensitivity is developed. The experimental setup used to test the performance of the sensor is presented. The sensor can detect the minimum vibration amplitude of 0.02μm. The frequency response is from 300Hzto1.8kHz.
Protein patterning by thermal nanoimprint lithography and NH3-plasma functionalization of polystyrene
Authors: Trabadelo V. , Retolaza A. , Merino S. , Cruz A. , Heredia P. , Foelske A. , Schift H. , Padeste C.
Published: May 2009

New approach to create a pattern of specific protein binding sites via nanoimprint lithography is presented. NH3-plasma functionalized, patterned polystyrene covalently binds a biotin linker to which streptavidin is bound. The streptavidin is used as a versatile anchor for biotinylated functional proteins by means of a sandwich-type quantitative fluorescence immunoassay. Rabbit IgG is the analyte used as a “proof of concept” for the designed system, yielding a detection limit of approximately 50 ng/ml.
Carbon nanotube array vias for interconnect applications
Authors: Ting Jyh-Hua , Chiu Ching-Chieh , Huang Fuang-Yuan
Published: May 2009

The purpose of this study is to investigate the effect of carbon nanotube (CNT) growth parameters on CNT via resistance and examine the transverse motion of electrons in the CNT bundle vias. Single vias of 3.85×3.85 and 2.45×2.45μm2 correspond to 0.35×0.35μm2 6×6 and 4×4 array vias, respectively. With nickel catalyst, CNTs were grown by microwave plasma-enhanced chemical vapor deposition method. Two-terminal CNT via chains of single via and array vias were fabricated on the tantalum metal electrodes. The increase in pretreatment power or substrate temperature resulted in the decrease in CNT diameters and thus the increase in CNT packing density due to the etching effect of exciting hydrogen. This led to the decrease in CNT via resistance owing to more conducting channels. The increase in growth power or substrate temperature enhanced the CNT graphitization and hence yielded the decrease in CNT resistances as well as CNT via resistances. In the same via area, the CNT via resistance of array vias is lower than that of a single via. This could be ascribed to less tube-tube junctions and thus lower electrical resistance in the array vias. Accordingly, the transverse motion of electrons in the CNT bundle vias was demonstrated. Therefore, the integration of CNT array vias with CNT bundles is proposed for optimizing the conductivity of CNT vias in the global interconnects where the via dimensions are more alleviated.
Inductively coupled plasma etching in fabrication of 2D InP-based photonic crystals
Authors: Wang Hailing , Xing Mingxin , Ren Gang , Zheng Wanhua
Published: May 2009

The authors developed an inductively coupled plasma etching process for the fabrication of hole-type photonic crystals in InP. The etching was performed at 70°C using BCl3∕Cl2 chemistries. A high etch rate of 1.4μm∕min was obtained for 200nm diameter holes. The process also yields nearly cylindrical hole shape with a 10.8 aspect ratio and more than 85° straightness of the smooth sidewall. Surface-emitting photonic crystal laser and edge emitting one were demonstrated in the experiments.
Electronic coupling in MgxZn1−xO/ZnO double quantum wells
Authors: Zippel Jan , Lenzner J. , Benndorf G. , Lange M. , Hochmuth H. , Lorenz M. , Grundmann M.
Published: May 2009

The electronic coupling in ZnO/MgZnO double-quantum-well (DQW) structures grown with pulsed-laser deposition is investigated. The two ZnO quantum wells, separated by a thin MgxZn1−xO barrier (x≈0.14–0.16), have either an equal (SDQW) or a different thickness (ADQW). The authors report here a detailed investigation by spatially and spectrally resolved cathodoluminescence (CL). For the SDQW structures, the shift of the transition energy of the free exciton at room temperature to lower energies due to electron coupling, with decreasing barrier width, is in good agreement with effective mass theory. For a barrier thickness LB≤5 nm, the ADQWs show an additional recombination peak located spectrally between the luminescence maxima of the corresponding single quantum wells. It is tentatively attributed to a spatially indirect excitonic transition involving the electron subband of the narrow well and the heavy hole subband of the wide well. An extension of the barrier thickness to 300 nm allows an estimation of the exciton diffusion length via lateral CL scans. In the case here the diffusion length in the MgZnO barrier is about 135 nm at 10 K and below 75 nm at room temperature.
Micromachining of aluminum pipes using magnetic abrasive finishing
Authors: Vahdati Mehrdad , Vahdati Nader
Published: May 2009

The demand for highly finished surfaces has increased dramatically in recent years. There are obstacles toward fulfilling the requirements for creating such finished parts. Disability of traditional surface finishing methods, which is due to particular shape and geometry of work pieces, and tool inaccessibility to every feature of work pieces are samples of such obstacles. This has lead to innovating new finishing processes. One of these methods, which uses moving abrasive particles in magnetic field, is called magnetic abrasive finishing of machined surface roughness, an approach to optimize the principles of this process. In this research, some effective parameters on surface roughness such as magnetic flow density, process time, amount of magnetic abrasive powder, and rotational speed of work piece have been tested and roughness sensation against these parameters has been studied. According to the results, using permanent magnets of 1T, the amount of 8g of ilmenite powder of mesh 150, rotating speed of 750rpm, and 30–40min of process time, will result into a surface roughness of 0.45μm Ra from the original value of 2μm Ra under other conditions kept on their best values.
Carrier backscattering characteristics of nanoscale strained complementary metal-oxide-semiconductor devices featuring the optimal stress engineering
Authors: Chang Shu-Tong , Liao Ming-Han , Lee Chang-Chun , Huang Jacky , Wang Wei-Ching , Hsieh Bing-Fong
Published: May 2009

The authors present stress distribution simulation characterization of the three-dimensional boundary effects and show how these effects can impact the achievable transistor performance gain. The high-performance complementary metal-oxide-semiconductor (CMOS) device has been achieved by stressors such as contact etch stop layer (CESL) and SiGe S/D and optimal geometric structure design. The biaxial-like stress distribution resulting from symmetry structure and uniaxial-like stress distribution resulting from asymmetry structure seems to be promising when considering drive current enhancement, the ballistic efficiency, and carrier injection velocity for CMOS devices. The comprehensive study helps the future nanoscale CMOS device design and demonstrates that the stress enhancement factors remain valid for future technology.
Novel tapered macrogate structure for carbon nanotube based field emission display
Authors: Jeong Jin-Woo , Kim Dae-Jun , Cho Kyung-Ik , Song Yoon-Ho
Published: May 2009

The tapered macrogate (TMG) structure is proposed to overcome the difficulties in carbon nanotube (CNT) based field emission display (FED) with high-voltage phosphors used in cathode ray tube screens. In order to achieve an ideal triode operation for field emission devices, the TMG was designed to have a very thick gate insulator with the inclined gate holes compared with the CNT emitters. The inclined gate holes with a narrower outlet than the bottom of the hole were shown to protect the CNT emitters from the anode field perfectly, enabling the authors to apply a high anode voltage over 10 kV needed for high-voltage FED. Also, the TMG structure had additional useful functions such as an electron-beam self-focusing and high durability against electrical damage. The authors successfully fabricated and demonstrated a 5 in. active-matrix CNT-FED panel with the TMG, showing color moving images with a low addressing voltage of about 15 V using amorphous silicon thin-film transistor as a switching device.
Formulation and characterization of doxorubicin nanovesicles
Authors: Honary S. , Ebrahimi P. , Tabbakhian M. , Zahir F.
Published: May 2009

Ascorbyl palmitate formed vesicles in combination with cholesterol and a negatively charged lipid (dicetyl phosphate). Niosomes were prepared by the film hydration method, followed by sonication, in which aqueous doxorubicin solution (in phosphate buffer saline pH=7.4) was encapsulated in aqueous regions of lipid layers. Vesicle’s formation was confirmed by either scanning electron microscopy images or observation of unsonicated vesicles by light microscope. The percent efficiencies of doxorubicin encapsulation of the different formulations were determined by fluorescence spectrophotometry. Cholestrol content in niosomes did not exhibit any relation to vesicle size, zeta potential, percent entrapment, or release rate. Differential scanning calorimetric data of pure lipids, vesicle dispersion, and mixture of lipids confirmed the formation of niosomes.
Effects of two-step growth by employing Zn-rich and O-rich growth conditions on properties of (112¯) ZnO films grown by plasma-assisted molecular beam epitaxy on sapphire
Authors: Han Seok Kyu , Kim Jae Goo , Kim Jung-Hyun , Hong Soon-Ku , Lee Jae Wook , Lee Jeong Yong , Song Jung-Hoon , Nam Yoon Sung , Chang Soo-Kyung , Yao Takafumi
Published: May 2009

The authors report properties of a-plane ZnO films on r-plane sapphire substrates by plasma-assisted molecular beam epitaxy in which two-step growth is employed. They show that the two-step growth is effective in improving structural and optical properties of a-plane ZnO films. Here, the two-step growth is preceded by growing the first layer under Zn-rich (O-rich) conditions and growing the second layer under O-rich (Zn-rich) conditions. All the grown samples show striated anisotropic morphology. The samples with the first, thin, O-rich layer plus the second, thick, Zn-rich layer show smaller root-mean-square (rms) roughness than those with the first, thin, Zn-rich layer plus the second, thick, O-rich layer. The sample with the 20-nm-thick first layer grown under O-rich condition shows the smallest rms roughness of 1.06nm, which is a smaller rms value than that of the sample grown under the single-step, stoichiometric condition. This sample shows the highest intensity of DX0 emission at 3.392eV and small full width at half maxima of (112¯0) and (101¯1) x-ray rocking curves, which indicate the good crystal quality.
Growth of ZnO films on R-plane sapphire substrates by atmospheric-pressure chemical vapor deposition using Zn powder and H2O as source materials
Authors: Terasako Tomoaki , Shigematsu Yosuke , Hiji Masanori , Yamaguchi Tomoya , Shirakata Sho
Published: May 2009

Films of ZnO have been grown on R-plane sapphire substrates by atmospheric-pressure chemical vapor deposition (AP-CVD) using Zn powder and H2O as source materials. Variation in growth rate as a function of substrate temperature can be divided into three regions: re-evaporation region, mass transport controlled region, and surface controlled region. Scanning electron microscope observations revealed that the surface morphology of the film is dependent not only on substrate temperature but also on Zn source and H2O source temperatures. X-ray diffraction patterns of most of the films showed a dominant (110) peak, indicating highly A-axis oriented growth. A single crystalline A-plane ZnO film without mixed domain was successfully grown by optimizing the growth condition. Visible region photoluminescence changed from orange-red emission to blue-green emission systematically by adjusting Zn source and H2O source temperatures. This result suggests the possibility of defect control in our AP-CVD system. For the films grown at TS=700°C in the mass transport controlled region, resistivity decreased from 0.45to0.007Ωcm as TH2O rised from 54to75°C.
Structural anisotropy in a-MgxZn1−xO (≤x≤0.33) films on r-sapphire
Authors: Saraf Gaurav , Siegrist Theo , Lu Yicheng
Published: May 2009

The a-plane MgxZn1−xO (0≤x≤0.25) films were grown on r-plane (011¯2) sapphire substrates using metal-organic chemical vapor deposition. Growth was done at temperatures from 520 °C, with a typical growth rate of ∼500 nm/h. Film thickness was varied by changes in deposition time, while Mg/Zn metal-organic flow was varied for changes in Mg composition. The a-plane films are dense and uniform. Strain anisotropy in the films was characterized by synchrotron x-ray diffraction. In-plane strain anisotropy increases with an increase in ZnO film thickness and reduces with an increase in Mg composition of MgxZn1−xO. The surface of the films characterized by atomic force microscopy showed rippled morphology with needles running along the surface. The morphology anisotropy in the films increases with an increase in ZnO film thickness and reduces with Mg composition of MgxZn1−xO films. The morphology anisotropy with ZnO film thickness and Mg composition of MgxZn1−xO is correlated with respective strain anisotropy variation.
Structural, electrical, and piezoelectric properties of ZnO films on SiC-6H substrates
Authors: Chen Ying , Saraf Gaurav , Reyes Pavel Ivanoff , Duan Ziqing , Zhong Jian , Lu Yicheng
Published: May 2009

Epitaxial ZnO films were grown on c-plane SiC-6H substrates using metal-organic chemical vapor deposition. X-ray diffraction coupled θ-2θ and ϕ-scans show that the n-type ZnO films have c-axis orientation and in-plane registry with the n-type 6H-SiC substrates. This isotype ZnO∕SiC heterojunction shows rectifying characteristics. Electrical measurements exhibit that the reverse current is in the picoampere (10−12–10−10A) range under the reverse bias of less than 5V, the on-off current ratio is ∼107, and the ideality factor is ∼1.23. The surface acoustic wave characteristics in the structure consisting of a piezoelectric ZnO and a semi-insulating SiC-6H substrate were also studied. The structure shows promise for high frequency and low loss rf applications.