bluuebunny/crossref_metadata_2025 huggingface dataset:
Growth stresses and cracking in GaN films on (111) Si grown by metal-organic chemical-vapor deposition. I. AlN buffer layers
Authors: Raghavan Srinivasan , Redwing Joan M.
Published: July 2005

Intrinsic stress evolution during the growth of GaN by metal-organic chemical-vapor deposition on (111) Si, using an AlN buffer layer, was monitored in situ with a multiple-beam optical stress sensor. Data show that stress evolution takes place in two stages: an initial compressive regime up to about 100nm in thickness followed by a transition to a constant tensile stress, ∼0.3GPa, in films up to 1μm thick. Correlation of the stress evolution with surface morphological evolution by sequential atomic force microscopy images clearly shows that the incremental stress remains compressive in spite of grain coalescence, which is generally considered to be the dominant source of tensile stress in GaN films on sapphire. Rather, the most dominant feature accompanying the transition in stress from compressive to tensile, which takes place after grain coalescence, is an increase in the lateral size of individual islands. It is shown that this incremental tensile stress accompanied by an increase in lateral grain size can be accounted for by the annihilation of free volume associated with the grain boundaries. On samples cooled to room temperature, surface cracks mainly on the (1010) planes are observed to have channeled in films thicker than 250nm. Analysis of cracking using the theory of brittle fracture, using the measured growth stress profile and value for the critical thickness, yields a thermal-expansion mismatch stress off 1.1GPa for GaN films deposited at 1100°C and cooled to room temperature.
Protocol for measuring permeability and form coefficient of porous media
Authors: Lage José L. , Krueger Paul S. , Narasimhan Arunn
Published: July 2005

The experimental determination of permeability K and form coefficient C, two hydraulic properties necessary to characterize a porous medium, is beset with undesired secondary effects, which augment the uncertainties in their determination. This study sets forth a new measuring protocol, with derived model equations, to guide the design of experiments for accurate determination of K and C, using Darcy’s law of flow through a porous medium and Newton’s law of flow around a bluff body as constitutive equations defining K and C, respectively. The analysis shows that the model equation for measuring C requires the separation between the viscous-drag effect imposed by the porous medium and the viscous effect of the boundary walls on the measured pressure drop when defining K. Furthermore, the model equations suggest large aspect ratio channels and laminar flow with maximum Re as the best choice for measuring K and C (contrary to prevailing belief). The protocol is applicable to either individual or concurrent determination of K and C.
Laser-cantilever anemometer: A new high-resolution sensor for air and liquid flows
Authors: Barth Stephan , Koch Holger , Kittel Achim , Peinke Joachim , Burgold Jörg , Wurmus Helmut
Published: July 2005

In this article, we present a technical description of a new type of anemometer for gas and especially liquid flows with high temporal and spatial resolution. The principle of the measurement is based on the atomic force microscope technique where microstructured cantilevers are used to detect extreme small forces. We demonstrate the working principle and the design of the sensor, as well as calibration measurements and initial measurements of turbulent flows, which were performed in air and water flows.
Estimation of wafer warpage profile during thermal processing in microlithography
Authors: Tay Arthur , Ho Weng Khuen , Hu Ni , Chen Xiaoqi
Published: July 2005

Wafer warpage is common in microelectronics processing. Warped wafers can affect device performance, reliability, and linewidth control in various processing steps. Early detection will minimize cost and processing time. We propose in this article an in situ approach for estimating wafer warpage profile during the thermal processing steps in the microlithography process. The average air gap between wafer and bake-plate at multiple locations of a multizone bake-plate can be estimated and a profile can be obtained by joining these points. Experimental results demonstrate the feasibility and repeatability of the approach. This is a major improvement over our previously developed approach, in which only the average warpage could be obtained. The proposed approach requires no extra processing steps and time, as compared to conventional off-line methods.
Sample handler for x-ray tomographic microscopy and image-guided failure assessment
Authors: Wyss Peter , Thurner Philipp , Brönnimann Rolf , Sennhauser Urs , Stampanoni Marco , Abela Rafael , Müller Ralph
Published: July 2005

X-ray tomographic microscopy (XTM) yields a three-dimensional data model of an investigated specimen. XTM providing micrometer resolution requires synchrotron light, high resolution area detectors, and a precise sample handler. The sample handler has a height of 270 mm only, is usable for 1μm resolution, and is able to carry loading machines with a weight of up to 20 kg. This allows exposing samples to load between scans for image-guided failure assessment. This system has been used in the XTM end station of the materials science beamline of the Swiss Light Source at the Paul Scherrer Institut.
High-pressure x-ray tomography microscope: Synchrotron computed microtomography at high pressure and temperature
Authors: Wang Yanbin , Uchida Takeyuki , Westferro Frank , Rivers Mark L. , Nishiyama Norimasa , Gebhardt Jeff , Lesher Charles E. , Sutton Steve R.
Published: July 2005

A new apparatus has been developed for microtomography studies under high pressure. The pressure generation mechanism is based on the concept of the widely used Drickamer anvil apparatus, with two opposed anvils compressed inside a containment ring. Modifications are made with thin aluminum alloy containment rings to allow transmission of x rays. Pressures up to 8GPa have been generated with a hydraulic load of 25T. The modified Drickamer cell is supported by thrust bearings so that the entire pressure cell can be rotated under load. Spatial resolution of the high pressure tomography apparatus has been evaluated using a sample containing vitreous carbon spheres embedded in FeS matrix, with diameters ranging from 0.01to0.2mm. Spheres with diameters as small as 0.02mm were well resolved, with measured surface-to-volume ratios approaching theoretical values. The sample was then subject to a large shear strain field by twisting the top and bottom Drickamer anvils. Imaging analysis showed that detailed microstructure evolution information can be obtained at various steps of the shear deformation, allowing strain partition determination between the matrix and the inclusions. A sample containing a vitreous Mg2SiO4 sphere in FeS matrix was compressed to 5GPa, in order to evaluate the feasibility of volume measurement by microtomography. The results demonstrated that quantitative inclusion volume information can be obtained, permitting in situ determination of P-V-T equation of state for noncrystalline materials.
Effects of crystallite size distribution on the Raman-scattering profiles of silicon nanostructures
Authors: Islam Md. Nazrul , Pradhan Asima , Kumar Satyendra
Published: July 2005

Raman scattering (RS) from semiconductor nanostructures provide excellent information on the size of the crystallites. Processing history of most nanocrystalline semiconductors suggests natural incorporation of a distribution of crystallite sizes. In this paper, we report on the influence of crystallite size distribution on the shifts in RS frequencies and line shapes. A phenomenological model is developed to obtain an analytical expression for the Raman spectral profile from semiconductor nanostructures having a Gaussian distribution in the crystallite sizes. Computer simulations of RS profiles on nanocrystalline silicon (nc-Si) demonstrate the effects of a size distribution on the Raman shifts. In particular, the effects on the asymmetry in Raman line shapes are emphasized. The model is applied to the published Raman data on nc-Si samples where size distributions are known from the direct measurements. The size distribution obtained from Raman analysis is in good agreement with that reported by direct measurement techniques. Further, Raman as well as photoluminescence measurements were made on the same spots on our stress-free porous silicon samples using a Raman microprobe. The present model leads to crystallite size distributions self-consistent with the photoluminescence data.
Dielectric properties of Pb0.5Ca0.5TiO3 thin films
Authors: Mendiola J. , Jiménez R. , Ramos P. , Alemany C. , Bretos I. , Calzada M. L.
Published: July 2005

A dielectric study is carried out on chemical solution-deposited calcium lead titanate (Pb,Ca)TiO3 thin films, with calcium contents of 50 at. %, by measuring capacitance versus voltage as a function of temperature. A moderate ferroelectric activity is observed that remains in a broad temperature range, and that depends on the applied voltage and thickness of the films. This behavior is associated with the built-in fields generated as result of the space charge inside the films. From the diffusivity of dielectric constant versus temperature (K′−T) curves, the relaxorlike nature of the films is also demonstrated. The feasibility of these films for fabrication of voltage tuneable capacitors and charge store devices (dynamic random access memories) is confirmed.
In-plane anisotropy in the microwave dielectric properties of SrTiO3 films
Authors: Chang Wontae , Kirchoefer Steven W. , Bellotti Jeffrey A. , Qadri Syed B. , Pond Jeffrey M. , Haeni Jeffrey H. , Schlom Darrell G.
Published: July 2005

Microwave tunable dielectric properties of strained (001) SrTiO3 thin films epitaxially deposited on (110) DyScO3 substrates were studied for in-plane film orientations ([100], [010], [110], and [−110]). A significant in-plane anisotropy in dielectric constant and tuning was observed in these SrTiO3 films. The highest dielectric constant and tuning at room temperature are observed along the [010] direction of the SrTiO3 film (1000 Å thick) (3500 and 70% at 1V∕μm, respectively), the lowest ones are observed along the [100] direction (i.e., 2000 and 50% at 1V∕μm, respectively). The dielectric constant and tuning along [−110] and [110] are about 2500 and 30% at 1V∕μm, respectively, which are intermediary to those along the [010] and [100] directions. The dielectric Q(=1∕tanδ) does not show any large difference for the four directions (i.e., Q∼10−20). Also, the phase-transition peak for the [−110] and [110] directions of the SrTiO3 film (300 Å thick) is observed at 275 K, which is lower than that for the [010] and [100] directions. The observed in-plane anisotropic dielectric properties have been interpreted based on the phenomenological thermodynamics of film strain.
Plasma jet emission in fast-pulsed capillary discharges
Authors: Caballero L. S. , Chuaqui H. , Favre M. , Mitchell I. , Wyndham E.
Published: July 2005

The properties of a plasma jet generated in low-pressure pulsed capillary discharge have been measured. The discharge operates in a 5 cm long and 1.6-mm-inner diameter alumina capillary, with argon in a pressure range between 20 and 100 Torr, at 11-kV applied voltage. The temporal and spatial evolutions of the plasma density in the plasma jets are measured close to the capillary end with a Michelson interferometry based on a 10-ns-pulse Nd:yttrium aluminum garnet laser. The maximum on-axis plasma density is of the order of 1017cm−3 at the capillary output, with an ∼6-ns rise time to reach a significative electron density. At lower pressure the plasma density is seen to decay in a time scale of 50 ns and over an axial distance of the order of 0.5 mm, whereas at the higher pressure, 100 Torr, it remains more or less stationary for up to ∼300ns. The discharge is characterized by a high efficiency in energy coupling, as the local-stored energy is much less than 1 J per pulse.
Performance of single-crystal Pb(Mg1∕3Nb2∕3)-32%PbTiO3 stacked actuators with application to adaptive structures
Authors: Woody Shane C. , Smith Stuart T. , Jiang Xiaoning , Rehrig Paul W.
Published: July 2005

This article presents the performance of ultra-high-strain single-crystal piezoelectric stacked actuators using the composition Pb(Mg1∕3Nb2∕3)-32%PbTiO3 (PMN-32%PT)for adaptive structures (in particular for space-based applications). Generally, dimensionally adaptive or smart structures often utilize piezoelectric actuators [in particular lead zirconate titanate (PZT) elements] to provide high-frequency response motion. However, most commercial stacks are limited in range (often <0.1% strain) and the motion is further reduced at low or cryogenic temperatures for satellite-based and many other applications. Comparatively, single-crystal actuators such as the ultra-high-strain PMN-32%PT provide greater than a factor of 4 displacement, factor of 2 strain energy density, and cryogenic displacements are comparable to room-temperature conditions for PZT actuators. Nonetheless, there are some technological and fundamental limitations, such as plate thickness, which is generally greater than 0.5mm, low elastic modulus, and low strain at each end of the stacks. Three stack configurations with 3, 5, and 40 active layers are tested and discussed. This report discusses each configuration type as a function of lost motion, obtainable strain rates, preload designs, applied stiffness, stress gradients, electric fields, and bandwidth performances. The results obtained in this study aim to show performance and discuss the relative merits and limitations of using this actuator material for adaptive structures. A case study is presented for a high bandwidth steering mirror using ultra-high-strain single crystals. Closed loop control results from the platform’s response are briefly discussed.
Photoluminescence of highly porous nanostructured Si-based thin films deposited by pulsed laser ablation
Authors: Yang D.-Q. , Ethier V. , Sacher E. , Meunier M.
Published: July 2005

Nanostructured, Si-based cottonlike, highly porous thin films of Si, SiNx, and SiOx were deposited by the excimer laser ablation of Si targets in He, He∕N2, and He∕O2 ambients, respectively. Photoluminescence (PL), x-ray photoelectron spectroscopy, and photoacoustic Fourier transform IR have been used to characterize these deposits. After exposure to air, broad PL bands appear at 1.7eV (Si), 2.0eV (SiNx), and 2.3eV (SiOx); air oxidation causes the separation of the PL spectra into two identical component peaks, at 1.5 and 2.3eV, whose relative ratios differ with film composition. The present results indicate that the red PL peak at 1.5eV is due to the localized states at the oxidized surfaces of these materials, while the green PL peak at 2.3eV is due to oxygen-related defects in their local disordered nanostructures.
Calibration of second-order correlation functions for nonstationary sources with a multistart, multistop time-to-digital converter
Authors: Choi Wonshik , Lee Moonjoo , Lee Ye-Ryoung , Park Changsoon , Lee Jai-Hyung , An Kyungwon , Fang-Yen C. , Dasari R. R. , Feld M. S.
Published: July 2005

A novel high-throughput second-order correlation measurement system is developed that records and makes use of all the arrival times of photons detected at both start and stop detectors. This system is suitable, particularly for a light source having a high photon flux and a long coherence time, since it is more efficient than conventional methods by an amount equal to the product of the count rate and the correlation time of the light source. We have used this system in carefully investigating the dead time effects of detectors and photon counters on the second-order correlation function in the two-detector configuration. For a nonstationary light source, a distortion of the original signal was observed at high photon flux. A systematic way of calibrating the second-order correlation function has been devised by introducing the concept of an effective dead time of the entire measurement system.
Effects of postgrowth rapid thermal annealing on InAlAs∕InGaAs metamorphic high-electron-mobility transistor grown on a compositionally graded InAlAs∕InGaAlAs buffer
Authors: Ihn Soo-Ghang , Jo Seong-June , Song Jong-In
Published: July 2005

Effects of postgrowth rapid thermal annealing (RTA) on structural and electrical properties of an In0.52Al0.48As∕In0.52Ga0.48As metamorphic high-electron-mobility transistor (MHEMT) structure grown on a GaAs substrate utilizing a compositionally graded InAlAs∕InGaAlAs buffer layer were investigated. High-resolution triple-axis x-ray diffraction, photoluminescence, and van der Pauw–Hall measurements were used for the investigation. While the RTA improved the structural property of the MHEMT, it degraded the channel mobility of the MHEMT due to defect-assisted impurity redistribution.
Microstructure and magnetoresistance of sputtered bismuth thin films upon annealing
Authors: Chang Joonyeon , Kim Hijung , Han Junhyun , Jeon M. H. , Lee W. Y.
Published: July 2005

We investigated the microstructure and magnetotransport properties of sputtered Bi upon annealing. The grain size and the orientation of polycrystalline Bi thin films can be manipulated through a proper annealing treatment. Weak-oriented fine grains, of which size is about 0.1μm, were found in as-sputtered Bi films. Careful annealing at 270°C results not only in a grain growth of up to 1.1μm but also in a [001]-preferred orientation structure. The grain size increases exponentially with annealing time in the temperature range of 266–270°C. The grain-growth exponent (n) and the activation energy (Q) were evaluated to be 0.32±0.05 and 70.7kJ∕mol, respectively. The magnetoresistance (MR) of Bi films is strongly dependent on the microstructure and thickness of the film, and on the measured temperature. A very high MR of 30,000% can be observed in the annealed 7-μm-thick Bi films when measured at low temperature (4K). The drastic increase in MR after annealing is largely attributed to the trigonal-axis-oriented texture diminishing anisotropy scattering as well as to the significant grain-growth decreasing grain-boundary scattering of carriers. The measured temperature and film thickness on which the phonon scattering relies are also important factors in determining the magnetoresistance of sputtered Bi films.
Phase-only modulation using a normal-mode liquid-crystal gel
Authors: Ren Hongwen , Wu Janet R. , Wu Shin-Tson
Published: July 2005

A normal-mode liquid-crystal (LC) gel for phase-only modulation is demonstrated. In the absence of an electric field, the gel has negligible light scattering. Upon application of an electric field, the gel becomes highly transparent and exhibits phase modulation capability. For a 20-μm transmissive E48 LC gel, the phase shift reaches 0.55π at λ=633nm and the response time is ∼2ms. Although the phase change is not very large, it is sufficient for making adaptive microphotonic devices. Such a normal-mode LC gel-based phase modulator is free from scattering and hysteresis and has a fast response time and good long-term operation stability.
Comparative study on emission characteristics of extreme ultraviolet radiation from CO2 and Nd:YAG laser-produced tin plasmas
Authors: Tanaka Hiroki , Matsumoto Atsushi , Akinaga Kouzi , Takahashi Akihiko , Okada Tatsuo
Published: July 2005

The direct comparison of the emission characteristics of an extreme ultraviolet (EUV) light between the CO2 and the Nd:YAG laser-produced plasmas (LPP) with a solid tin target is reported. In the case of the Nd:YAG LPP, the conversion efficiency (C.E.) peaked at a laser intensity of about 5×1010W∕cm2 and decreased at higher laser intensity. In the case of the CO2 LPP, the C.E. monotonically increased up to 2×1010W∕cm2, where the C.E. is comparable to the maximum C.E. of the Nd:YAG LPP. The spectral efficiency of the Nd:YAG LPP within the 2% bandwidth around 13.5 nm decreased with laser intensity. The corresponding spectral efficiency of the CO2 LPP was almost constant. This observation indicates the potential of the CO2 laser-produced LPP as the EUV light source for the EUV lithographic systems.
Re-entrant spin glass behavior in Mn-rich YMnO3
Authors: Chen W. R. , Zhang F. C. , Miao J. , Xu B. , Dong X. L. , Cao L. X. , Qiu X. G. , Zhao B. R. , Dai Pengcheng
Published: July 2005

We use magnetism and specific heat measurements to investigate the hexagonal Mn-rich YMnO3. It is found that upon cooling from a high temperature, the compound first orders antiferromagnetically at TN∼72K and then undergoes a re-entrant spin glass (RSG) transition at TSG∼42K. This RSG behavior results from the competition between the ferromagnetic interaction and the antiferromagnetic interaction, which is related to the intrinsic geometric magnetic frustration in this system.
White organic light-emitting devices with a solution-processed and molecular host-employed emission layer
Authors: Jou Jwo-Huei , Sun Ming-Chen , Chou Hung-Hsing , Li Chien-Hung
Published: July 2005

The brightness, efficiency, chromaticity, and processibility of white organic light-emitting devices have been markedly improved by forming therein via spin-coating a single white emission layer, in which the red, green, and blue dyes of iridium-based complexes were previously solution-mixed into the host matrix composed of small molecules instead of polymers. Among the hosts studied, the 4,4′-bis(carbazol-9-yl)-biphenyl-based devices performed best in terms of luminance and efficiency for having the lowest-energy barrier for electrons to inject from the hole-blocking layer to the host layer. The device having a pure white emission of (0.34, 0.35) had a maximum power efficiency of 2.9lm∕W at an applicable luminance of 1680cd∕m2, while 5.6lm∕W at 550cd∕m2 for that of (0.34, 0.39).
Highly sensitive ultrafast all-optical light modulation by complex refractive-index changes in guided mode geometry composed of a photoresponsive polymer and a low-refractive-index polymer
Authors: Nagamura Toshihiko , Matsumoto Ryuji , Naito Atsushi , Nagai Yasuyuki
Published: July 2005

Highly sensitive ultrafast all-optical light modulation is proposed on the basis of photoinduced complex refractive-index changes in composite guided wave mode (GWM) geometry composed of a low-refractive-index polymer and a photoresponsive polymer. Both calculated and observed results indicated that reflectance, which was unity at an extinction coefficient k=0, decreased rapidly with increasing k until a certain value (kc), and increased again after that. The kc-value and the GWM dip width decreased with increasing the thickness of both polymer layers. The real-part changes shifted the GWM dip very sensitively. The low-refractive polymer contributed great improvements, such as high sensitivity and durability against a repeated femtosecond laser. The present device can give highly enhanced changes of probe light as compared with simple transmission-type devices or the GWM geometry on a metal thin film. A photoelectrochromic polymer was employed in this geometry to demonstrate ultrafast reflectance control upon femtosecond laser excitation.
Self-forming diffusion barrier layer in Cu–Mn alloy metallization
Authors: Koike J. , Wada M.
Published: July 2005

Advancement of semiconductor devices requires the realization of an ultrathin diffusion barrier layer between Cu interconnect and insulating layers. The present work investigated the possibility of the self-forming barrier layer in Cu–Mn alloy thin films deposited directly on SiO2. After annealing at 450 °C for 30 min, a Mn containing amorphous oxide layer of 3–4 nm in thickness was formed uniformly at the interface. Residual Mn atoms were removed to form a surface oxide layer, leading to a drastic resistivity decrease of the film. No interdiffusion was detected between Cu and SiO2 within the detection limit of x-ray energy dispersive spectroscopy.
Low-voltage ZnO thin-film transistors with high-KBi1.5Zn1.0Nb1.5O7 gate insulator for transparent and flexible electronics
Authors: Kim Il-Doo , Choi YongWoo , Tuller Harry L.
Published: July 2005

We report on the fabrication of field-effect transistors with transparent oxide semiconductor ZnO serving as the electron channel and high-KBi1.5Zn1.0Nb1.5O7 (BZN) as the gate insulator. The devices exhibited very low operation voltages (<4V) due to high capacitance of the BZN dielectric. The field effect mobility and the current on/off ratio were 0.024cm2∕Vs and 2×104, respectively, at an operating voltage of 4 V. The threshold voltage and subthreshold swing were 2 V and 0.25V∕dec, respectively. The high optical transparency (>80% for wavelength >400nm), low-temperature processing, and low operation voltage of ZnO-based thin-film transistors with integrated BZN dielectric offer a promising route for the development of transparent and flexible electronics.
Controlling field-emission patterns of isolated single-walled carbon nanotube rope
Authors: Tong Yu , Lim Seong Chu , Park Kyung Ah , Jeong Hee Jin , Jeong Seung Yoi , Lee Young Hee , Liu Chang , Cheng Hui-Ming , Choi Yoon
Published: July 2005

We report a method of controlling field-emission patterns from an isolated single-walled carbon nanotube (SWCNT) rope. By positioning two soda-lime glass flakes on both sides of a SWCNT rope, we found an anomalous current jump, enlarging the field emission current above the threshold bias voltage. The electron trajectories were systematically controlled with different configurations of glass flakes. This was explained by the induced charges on the surface of the dielectric that modified the electric field distribution near the cathode and anode, and hence, the electron trajectories and the field emission patterns as well. This opens a possibility of tuning electron beam trajectories in field emission that can be applied to various electron sources such as field emission displays and cold cathode lamps.
Overlay metrological system for overlaid linear gratings by an interferoscatterometer
Authors: Shyu Deh-Ming , Lu Mao-Hong
Published: July 2005

Interferoscatterometry is an optical measurement technology based on the analysis of light scattered and interfered from a periodic structure. In this work, first we build up a model for this system by the rigorous coupled wave analysis. With the model we calculate the diffractive efficiency of overlaid linear gratings with a mirror located in the incident region. Then, from the analyses of the overlaid linear gratings we obtain the best structure which has the highest sensitivity in the interferoscatterometry. Finally, we measure a sample and get experimental signatures. In order to get the overlay between the upper and lower grating, we compare the experimental signatures with theoretical signatures which are built in a library. The application of the interference technique on the scatterometry shows a higher sensitivity and a longer measurement range.
Synchronization of femtosecond laser and electron pulses with subpicosecond precision
Authors: Park H. , Hao Z. , Wang X. , Nie S. , Clinite R. , Cao J.
Published: July 2005

The temporal evolution of electron shadow images, formed by the projection of primary femtosecond electron pulses (probe) over a metal target and perturbed by the transient space-charge field near the target surface induced by the excitation of femtosecond optical pulses (pump), is recorded in real time. By quantitatively analyzing the evolution of these shadow images as a function of pump-probe delay times, we are able to synchronize the femtosecond laser and electron pulses with sub-ps precision. This approach is independent of the structural dynamics under investigation and can be applied to a variety of diffraction setups and target materials using laser pulses of different wavelengths.
Microdevice assembling by adhesive type probe in humid environment
Authors: Wu Jianhua , Lu Jian , Chu Jiaru , Guo Rui , Xiao Shizhou , Huang Wenhao
Published: July 2005

A one-finger adhesive type probe was constructed to assemble objects tens to hundreds of microns in size by utilizing adhesion forces in a humid environment. The interactive forces and the influencing factors during the assembly operation were analyzed with a theoretical contact model. Micro-objects with different surface conditions and materials were tested. Experimental results achieved in a humid environment (relative humidity=60%) of lifting polymer spheres are presented here. The success rate of picking up polymer spheres with sizes from 90 to 190μm from a gold coated substrate was about 0.7. Using this method, microgears with a size of 54μm and their shafts fabricated by two-photon stereo lithography technology were assembled successfully. Our experimental results demonstrate that an adhesive type probe is competent for small batch microdevice assembly tasks in humid environments.
Development of a short pulsed corona discharge ionization source for ion mobility spectrometry
Authors: An Yuan , Aliaga-Rossel R. , Choi Peter , Gilles Jean-Paul
Published: July 2005

The development of a pulsed corona discharge ionization source and its use in ion mobility spectrometry (IMS) is presented. In a point-plane electrode geometry, an electrical pulse up to 12 kV, 150 ns rise time and 500 ns pulse width was used to generate a corona discharge in air. A single positive high voltage pulse was able to generate about 1.6×1010 ions at energy consumption of 22μJ. Since the temporal distribution of ions is in a pulsed form, the possibility of removal the ion gate has been investigated. By purposely arranging the interface between discharge field and drift field, nearly 107 positive ions were drawn into the drift region with absence of the ion gate after every single discharge. The positive spectrum of acetone dimer (working at room temperature) was obtained with a resolving power of 20 by using this configuration. The advantages of this new scheme are the low power consumption compared with the dc method as well as the simplicity of the IMS cell structure.
Mobility evaluation in transistors with charge-trapping gate dielectrics
Authors: Bersuker G. , Zeitzoff P. , Sim J. H. , Lee B. H. , Choi R. , Brown G. , Young C. D.
Published: July 2005

Fast electron trapping in high-k gate dielectrics is shown to effectively increase the magnitude of the threshold voltage during the dc measurements of the drain current, which leads to underestimation of the intrinsic channel carrier mobility. An approach based on the pulse Id-Vg technique is proposed to estimate a correction factor to the dc mobility.
Highly transparent and low resistance gallium-doped indium oxide contact to p-type GaN
Authors: Lim Jae-Hong , Yang Eun-Jung , Hwang Dae-Kue , Yang Jin-Ho , Oh Jin-Yong , Park Seong-Ju
Published: July 2005

We report on a transparent gallium-doped indium oxide (GIO) ohmic contact to the p-GaN. The GIO contact film yielded a low specific contact resistance of 8.1×10−5Ωcm2 on p-GaN when annealed at 600 °C under a nitrogen ambient. The low specific contact resistance can be attributed to the formation of acceptorlike Ga vacancies and an InN or InxGa1−xN phase at the interface between the GIO and p-GaN films. The forward voltage of a light-emitting diode (LED) with a GIO ohmic layer was slightly increased by 0.2 V compared to that of a LED with a standard Ni∕Au contact. However, a light transmittance of 85.7%, which was higher than that of indium tin oxide, was observed in the GIO film at a wavelength of 470 nm after thermal annealing at 600 °C. These results suggest that the GIO contact scheme is suitable for use as a highly transparent and low specific contact resistance contact layer for p-GaN.
Zone-axis diffraction study of pressure-induced inhomogeneity in single-crystal Fe1−xO
Authors: Ding Yang , Liu Haozhe , Xu Jian , Prewitt Charles T. , Hemley Russell J. , Mao Ho-kwang
Published: July 2005

A zone-axis synchrotron diffraction study of complex and inhomogeneous Fe1−xO thin single crystal under pressure is presented in this letter. Using this method, four phases are observed to coexist in a single crystal of Fe1−xO at 35 GPa in diamond-anvil cells. One phase has cubic symmetry, whereas the other three phases have not been reported previously and can be interpreted as either orthorhombic or monoclinic. The discovery of multiple phases existing in Fe1−xO indicates that structural inhomogeneity of the sample can be induced under high pressure, a result that has important implications for the high P-T behavior of this complex material. Such information is not available using conventional diffraction techniques.
Photonic crystals for biochemical sensing in the terahertz region
Authors: Kurt Hamza , Citrin D. S.
Published: July 2005

The propagation of terahertz waves in two-dimensional photonic-crystal waveguides was studied computationally to investigate the effects of introducing small quantities of molecules, such as deoxyribonucleic acid, into selected air holes for sensor applications. Comparison with bulk systems shows that photonic-crystal waveguides are promising for biochemical sensing.
Fully-screened polarization-induced electric fields in blue∕violet InGaN∕GaN light-emitting devices grown on bulk GaN
Authors: Franssen G. , Suski T. , Perlin P. , Bohdan R. , Bercha A. , Trzeciakowski W. , Makarowa I. , Prystawko P. , Leszczyński M. , Grzegory I. , Porowski S. , Kokenyesi S.
Published: July 2005

Photocurrent spectroscopy and hydrostatic-pressure-dependent electroluminescence are used to show that heavy 1×1019cm−3 Si doping of quantum barriers is sufficient to achieve full screening of polarization-induced electric fields (PIEFs) in nitride light emitting diodes (LEDs) and laser diodes (LDs) with InGaN quantum wells. Furthermore, it is shown that at currents close to lasing threshold in nitride LDs injected charge alone is sufficient to achieve full screening of PIEFs. In contrast, full screening at low currents can only be accomplished via Si doping of quantum barriers.
Optical enhancement of diode laser-photoacoustic trace gas detection by means of external Fabry-Perot cavity
Authors: Rossi Alessandro , Buffa Roberto , Scotoni Mario , Bassi Davide , Iannotta Salvatore , Boschetti Andrea
Published: July 2005

An optical enhancement method applied to a diode laser photoacoustic trace gas detector is presented. In order to improve the detection sensitivity, the light intensity inside the acoustic resonator is amplified using a Fabry-Perot cavity. A feedback signal stabilizes the laser frequency to the optical cavity length, in order to maintain the light amplification constant during the probe frequency scan. The usefulness of the optical amplifier is demonstrated by showing two ethylene spectra obtained at 1.624μm with and without the optical enhancement. Tens to hundreds ppb (part per billion) sensibility for molecules absorbing in the region between 1.5–1.7μm can be obtained.
Timing the origin and expansion of the Mexican tropical dry forest
Authors: Becerra Judith X.
Published: July 2005

Macroevolution examines the temporal patterns of biological diversity in deep time. When combined with biogeography, it can provide unique information about the historical changes in the distribution of communities and biomes. Here I document temporal and spatial changes of diversity in the genus
Bursera
and relate them to the origin and expansion of the tropical dry forests of Mexico.
Bursera
is very old, highly adapted to warm dry conditions, and a dominant member of the Mexican tropical dry forest. These characteristics make it a useful indicator of the history of this vegetation. I used a time-calibrated phylogeny to estimate
Bursera
's diversification rate at different times over the last 60 million years. I also reconstructed the geographic center and time of origin of all species and nodes from information on current distributions. Results show that between 30 and 20 million years ago,
Bursera
began a relatively rapid diversification. This suggests that conditions were favorable for its radiation and thus, very probably for the establishment of the dry forest as well. The oldest lineages diverged mostly in Western Mexico, whereas the more recent lineages diverged in the south-central part of the country. This suggests that the tropical dry forest probably first established in the west and then expanded south and east. The timing of the radiations in these areas corresponds to that suggested for formations of the mountainous systems in Western and Central Mexico, which have been previously recognized as critical for the persistence of the Mexican dry forest.
Human vision fails to distinguish widespread sexual dichromatism among sexually “monochromatic” birds
Authors: Eaton Muir D.
Published: July 2005

Historical scenarios of evolution of avian plumage coloration have been called into question with the discoveries that most birds can see UV light (which normal humans cannot), and that UV-reflecting plumages are widespread in birds. Several examples of sexual dichromatism not detectable with human visual capabilities suggest that our categorizations of plumages as sexually mono- or dichromatic might often be incorrect. Nonetheless, given the limited taxonomic scope of those examples, the vast majority of sexually monochromatic birds are still treated as such without question in avian research. Herein, I show that >90% of 139 species, in a broad sampling of presumed sexually monochromatic passerine birds, were actually sexually dichromatic from an avian visual perspective, based on comparisons of plumage reflectance data using a visual model of color discrimination thresholds. The taxonomic ubiquity of this result suggests that many existing interpretations of evolutionary patterns of sexual dichromatism in birds are erroneous. The visual model used herein provides a method for quantifying sexual dichromatism, revealing that most (58.7%) feather patches sampled lie along a continuum of dichromatism between avian and human discriminatory abilities and could represent unrecognized sexually selected signals. Sexual dichromatism in this study rarely resulted from intersexual differences in UV coloration
alone
, emphasizing the need for analysis of bird coloration in relation to the full extent of avian visual discriminatory abilities, including, but not limited to, UV-visual capabilities.
Evolution of heterochromatic genes of
Drosophila
Authors: Yasuhara Jiro C. , DeCrease Christine H. , Wakimoto Barbara T.
Published: July 2005

Heterochromatin is generally associated with gene silencing, yet in
Drosophila melanogaster
, heterochromatin harbors hundreds of functional protein-encoding genes, some of which depend on heterochromatin for expression. Here we document a recent evolutionary transition of a gene cluster from euchromatin to heterochromatin, which occurred <20 million years ago in the drosophilid lineage. This finding reveals evolutionary fluidity between these two genomic compartments and provides a powerful approach to identifying differences between euchromatic and heterochromatic genes. Promoter mapping of orthologous gene pairs led to the discovery of the “slippery promoter,” characterized by multiple transcriptional start sites predominately at adenines, as a common promoter type found in both heterochromatic and euchromatic genes of
Drosophila
. Promoter type is diverse within the gene cluster but largely conserved between heterochromatic and euchromatic genes, eliminating the hypothesis that adaptation to heterochromatin required major alterations in promoter structure. Transition to heterochromatin is consistently associated with gene expansion due to the accumulation of transposable elements and increased A-T content. We conclude that heterochromatin-dependent regulation requires specialized enhancers or higher-order interactions and propose a facilitating role for transposable elements.
Ganglioside GD3 promotes cell growth and invasion through p130Cas and paxillin in malignant melanoma cells
Authors: Hamamura Kazunori , Furukawa Keiko , Hayashi Takanori , Hattori Takeshi , Nakano Junji , Nakashima Hideyuki , Okuda Tetsuya , Mizutani Hideki , Hattori Hisashi , Ueda Minoru , Urano Takeshi , Lloyd Kenneth O. , Furukawa Koichi
Published: July 2005

Although ganglioside GD3 levels are highly elevated in malignant melanomas, the role of GD3 in melanomas' malignant properties has not been clearly shown. To investigate this problem, we genetically generated GD3-positive (GD3+) transfectant cells from a GD3-negative (GD3-) mutant line SK-MEL-28-N1 and analyzed the phenotypic changes in the transfected cells. GD3+cells showed markedly increased cell growth and invasive characteristics. Two bands that underwent stronger tyrosine phosphorylation in GD3+cell lines than in controls after treatment with FCS were found with molecular masses of 130 and 68 kDa. They were identified as p130Cas and paxillin by sequential immunoprecipitation. Their roles in cell growth and invasion were analyzed with a small interfering RNA (siRNA) approach. Cell growth, as analyzed by BrdUrd uptake, was strongly suppressed in GD3+cells to near the levels of GD3-cells when treated with siRNA for p130Cas but not when treated with siRNA for paxillin. However, treatment with siRNAs of either p130Cas or paxillin resulted in the marked suppression of the invasive activity of GD3+cells almost to the levels of control cells. These results suggested that these two molecules function as effectors of GD3-mediated signaling, leading to such malignant properties as rapid cell growth and invasion.
Chromatin immunoprecipitation cloning reveals rapid evolutionary patterns of centromeric DNA in Oryza species
Authors: Lee Hye-Ran , Zhang Wenli , Langdon Tim , Jin Weiwei , Yan Huihuang , Cheng Zhukuan , Jiang Jiming
Published: July 2005

The functional centromeres of rice (
Oryza sativa
, AA genome) chromosomes contain two key DNA components: the CRR centromeric retrotransposons and a 155-bp satellite repeat, CentO. However, several wild
Oryza
species lack the CentO repeat. We developed a chromatin immunoprecipitation-based technique to clone DNA fragments derived from chromatin containing the centromeric histone H3 variant CenH3. Chromatin immunoprecipitation cloning was carried out in the CentO-less species
Oryza rhizomatis
(CC genome) and
Oryza brachyantha
(FF genome). Three previously uncharacterized genome-specific satellite repeats, CentO-C1, CentO-C2, and CentO-F, were discovered in the centromeres of these two species. An 80-bp DNA region was found to be conserved in CentO-C1, CentO, and centromeric satellite repeats from maize and pearl millet, species which diverged from rice many millions of years ago. In contrast, the CentO-F repeat shows no sequence similarity to other centromeric repeats but has almost completely replaced other centromeric sequences in
O. brachyantha
, including the CRR-related sequences that normally constitute a significant fraction of the centromeric DNA in grass species.
A free boundary problem for a singular system of differential equations: An application to a model of tumor growth
Authors: Cui Shangbin , Friedman Avner
Published: July 2005

In this paper we consider a free boundary problem for a nonlinear system of two ordinary differential equations, one of which is singular at some points, including the initial point

r
=
0

r=0

. Because of the singularity at

r
=
0

r=0

, the initial value problem has a one-parameter family of solutions. We prove that there exists a unique solution to the free boundary problem. The proof of existence employs two “shooting” parameters. Analysis of the profiles of solutions of the initial value problem and tools such as comparison theorems and weak limits of solutions play an important role in the proof. The system considered here is motivated by a model in tumor growth, but the methods developed should be applicable to more general systems.
Sharp Fourier type and cotype with respect to compact semisimple Lie groups
Authors: García-Cuerva José , Marco José , Parcet Javier
Published: July 2005

Sharp Fourier type and cotype of Lebesgue spaces and Schatten classes with respect to an arbitrary compact semisimple Lie group are investigated. In the process, a local variant of the Hausdorff-Young inequality on such groups is given.
A path-transformation for random walks and the Robinson-Schensted correspondence
Authors: O’Connell Neil
Published: July 2005

The author and Marc Yor recently introduced a path-transformationG(k)G^{(k)}with the property that, forXXbelonging to a certain class of random walks onZ+k\mathbb {Z}_+^k, the transformed walkG(k)(X)G^{(k)}(X)has the same law as the original walk conditioned never to exit the Weyl chamber{x: x1≤⋯≤xk}\{x:\ x_1\le \cdots \le x_k\}. In this paper, we show thatG(k)G^{(k)}is closely related to the Robinson-Schensted algorithm, and use this connection to give a new proof of the above representation theorem. The new proof is valid for a larger class of random walks and yields additional information about the joint law ofXXandG(k)(X)G^{(k)}(X). The corresponding results for the Brownian model are recovered by Donsker’s theorem. These are connected with Hermitian Brownian motion and the Gaussian Unitary Ensemble of random matrix theory. The connection we make between the path-transformationG(k)G^{(k)}and the Robinson-Schensted algorithm also provides a new formula and interpretation for the latter. This can be used to study properties of the Robinson-Schensted algorithm and, moreover, extends easily to a continuous setting.
Planar convex bodies, Fourier transform, lattice points, and irregularities of distribution
Authors: Brandolini L. , Iosevich A. , Travaglini G.
Published: July 2005

Let

B
B

be a convex body in the plane. The purpose of this paper is a systematic study of the geometric properties of the boundary of

B
B

, and the consequences of these properties for the distribution of lattice points in rotated and translated copies of

ρ
B

\rho B

(

ρ
\rho

being a large positive number), irregularities of distribution, and the spherical average decay of the Fourier transform of the characteristic function of

B
B

. The analysis makes use of two notions of “dimension” of a convex set. The first notion is defined in terms of the number of sides required to approximate a convex set by a polygon up to a certain degree of accuracy. The second is the fractal dimension of the image of the Gauss map of

B
B

. The results stated in terms of these quantities are essentially sharp and lead to a nearly complete description of the problems in question.
Complete homogeneous varieties: Structure and classification
Authors: Sancho de Salas Carlos
Published: July 2005

Homogeneous varieties are those whose group of automorphisms acts transitively on them. In this paper we prove that any complete homogeneous variety splits in a unique way as a product of an abelian variety and a parabolic variety. This is obtained by proving a rigidity theorem for the parabolic subgroups of a linear group. Finally, using the results of Wenzel on the classification of parabolic subgroups of a linear group and the results of Demazure on the automorphisms of a flag variety, we obtain the classification of the parabolic varieties (in characteristic different from

2
,
3

2,3

). This, together with the moduli of abelian varieties, concludes the classification of the complete homogeneous varieties.
Anderson’s double complex and gamma monomials for rational function fields
Authors: Bae Sunghan , Gekeler Ernst-Ulrich , Kang Pyung-Lyun , Yin Linsheng
Published: July 2005

We investigate algebraic

Γ
\Gamma

-monomials of Thakur’s positive characteristic

Γ
\Gamma

-function, by using Anderson and Das’ double complex method of computing the sign cohomology of the universal ordinary distribution. We prove that the

Γ
\Gamma

-monomial associated to an element of the second sign cohomology of the universal ordinary distribution of

F

q

(
T
)

\mathbb {F}_{q}(T)

generates a Kummer extension of some Carlitz cyclotomic function field, which is also a Galois extension of the base field

F

q

(
T
)

\mathbb {F}_{q}(T)

. These results are characteristic-

p
p

analogues of those of Deligne on classical

Γ
\Gamma

-monomials, proofs of which were given by Das using the double complex method. In this paper, we also obtain some results on

e
e

-monomials of Carlitz’s exponential function.