bluuebunny/crossref_metadata_2025 huggingface dataset:
Revisiting the Role of the Mother Centriole in Centriole Biogenesis
Authors: Rodrigues-Martins A. , Riparbelli M. , Callaini G. , Glover D. M. , Bettencourt-Dias M.
Published: April 2007

Centrioles duplicate once in each cell division cycle through so-called templated or canonical duplication. SAK, also called PLK4 (SAK/PLK4), a kinase implicated in tumor development, is an upstream regulator of canonical biogenesis necessary for centriole formation. We found that overexpression of SAK/PLK4 could induce amplification of centrioles in
Drosophila
embryos and their de novo formation in unfertilized eggs. Both processes required the activity of DSAS-6 and DSAS-4, two molecules required for canonical duplication. Thus, centriole biogenesis is a template-free self-assembly process triggered and regulated by molecules that ordinarily associate with the existing centriole. The mother centriole is not a bona fide template but a platform for a set of regulatory molecules that catalyzes and regulates daughter centriole assembly.
Influence of Annealing Treatments on the Morphology and Electrical Properties of GeOI Substrates Obtained by Ge Condensation
Authors: Damlencourt Jean-Francois , Campidelli Yves , Nguyen Tuan , Vincent Benjamin , Le Royer Cyrille , Morand Yves , Cristoloveanu S. , Clavelier Laurent
Published: April 2007

We have investigated the influence of subsequent annealing treatments in terms of gas ambient and duration on thickened GeOI substrates morphology and resistivity. A H2 bake seems to be more efficient than a N2 one to decrease the layer roughness and to increase the in-situ resistivity. The condensed GeOI (ρ GeOI) and the epi Ge layer (ρGe) resistivities have been extracted by considering the system as 2 parallel sheet resistances. After annealing treatment, ρGeOI is increased by a factor of 8 while the ρGe is increased by a factor of 2. The electrically active defects, acting like a p-type doping and created during both the Ge enrichment and the epitaxial thickening are cured by the annealing treatment. Thanks to this anneal, the blocking capability (i.e. full depletion) of pseudo MOSFET structures is strongly improved. The annealing parameters have a limited impact on the extracted values of the hole mobility.
Nanoscaled Silicon Based Heterostructures Formed by Interface Mediated Endotaxy
Authors: Popov Vladimir P. , Tyschenko Ida , Cherkov Elexander , Pokhil G P. , Fridman V M. , Voelskow M
Published: April 2007

New types of substrates are needed for further scaling in CMOS microelectronics. We speculate that this new type of materials can be semiconductor heterostructure on insulator (HOI) compatible with current silicon planar CMOS technology. In this work an effect of interface mediated endotaxial (IME) growth of thin InSb film at Si/SiO2 bonded interface was experimentally observed and investigated for the first time. Joint semiconductor material stack obtained by hydrogen transfer of one layer material (silicon) and endotaxially grown second one (indium antimonide) placed initially into amorphous silicon dioxide film is presented. Thermodynamic, kinetic and lattice mismatch parameter influences on IME process are considered.
Influence of Ru Dopant on the Dielectric Properties of Zr-doped HfO2 High-k Thin Film
Authors: Lin Chen-Han , Kuo Yue , Lu Jiang
Published: April 2007

The ruthenium (Ru) modified Zr-doped HfOx high-k thin films were prepared and studied. Electrical properties of the ZrHfOx film were greatly influenced by doping with Ru or embedding RuOx in the structure, e.g., (1) lowering equivalent oxide thickness (EOT) from 1.79nm (ZrHfOx film) to 1.19nm and 1.21nm, respectively, and (2) decreasing oxide trapped charge and fixed charge density. The high-k/Si interface composition was changed by the added Ru. The RuOx-embedded film has a much smaller leakage current density than that of the thermally grown SiO2 with the same EOT and better interface quality than the Ru- doped film.
Theoretical Studies on Metal/High-k Gate Stacks
Authors: Shiraishi Kenji , Akasaka Yasushi , Nakamura Genji , Nakayama Takashi , Miyazaki Seiichi , Watanabe Heiji , Ohta Akio , Ohmori Kenji , Chikyow Toyohiro , Nara Yasuo , Yamabe Kikuo , Yamada Keisaku
Published: April 2007

We consider the cause of different behavior of effective work function of gate metals after high and low temperature treatments. After high temperature treatment, reaction between Hf-based high-k dielectrics and a Si substrate generates oxygen vacancies (Vo) in high-k dielectrics, which leads to the subsequent electron transfer from Vo to gate metals. As a result, effective work function of gate metals becomes small and Fermi level pinning of gate metals occurs. Thus, Fermi level pinning is unavoidable phenomena for gate-first- processes. On the other hand, intrinsic hybridization between metal and high-k wave function at the interface is crucial factor to determine effective work function of gate metals after low temperature treatment. Accordingly, interface structures and band structures of metals govern the intrinsic effective work functions of metals.
On the Depth Profiling of the Traps in MOSFET's with High-k Gate Dielectrics
Authors: Bauza Daniel , Ghobar Oussama , Guillaumot Bernard
Published: April 2007

A general and reliable model for charge pumping (CP) proposed recently has been extended to trap depth distributions towards oxides depth. The fundamental features concerning the energy and depth region probed at the Si-SiO2 interface and in the direction of oxides depth are presented in the case of the different basic CP curves. The effect of the electric field is accounted for and its impact on the results is discussed. Then, MOSFET's with HfO2 gate dielectric are studied. Trap depth concentration profiles recorded from devices after different technological processes are presented and discussed.
Structural and Electrical Properties of High Pressure Hydrogen Post-Annealed Pt-Er Alloy Metal Gate on HfO2 Film
Authors: Choi Chel-Jong , Jang Moon-Gyu , Kim Yark-Yeon , Jeon Myung-Sim , Lee Seong-Jae , Yang Hyun-Doek , Jung Ran-Ju , Chang Man , Hwang Hyunsang
Published: April 2007

We have investigated electrical and structural properties of high-pressure hydrogen postannealed (HPHA) Pt-Er alloy metal gate on HfO2 film. It is shown that the HPHA process causes the removal of micro-voids formed near interface between Pt-Er alloy and HfO2 films, resulting in the increase of gate electrode contact areas. It is further shown that the HPHA process plays a role in the reduction of PtOx and the interface trap density, leading to the negative shift of flat- band voltage and the improvement of the HfO2 interface quality, respectively. By considering the presence of an interfacial layer (IL) between the HfO2 film and a Si substrate and a negative charge at the HfO2/IL interface, the effective metal work function values of the Pt-Er alloy metal gate before and after HPHA are calculated to be ~ 4.6 and ~ 4.8 eV, respectively.
Diffraction Originated Local Heating of Nanometer Scale Device Patterns in Lamp-Based Rapid Thermal Annealing
Authors: Yoo Woo Sik , Kang Kitaek
Published: April 2007

The process results on blanket Si and patterned Si wafers are often very different. Process variations in conventional lamp- based rapid thermal processing (RTP) systems due to pattern size, density and structure dependence under nearly identical process conditions are well known as the pattern effect , but without identifying the root cause. As device dimensions shrink, pattern-induced variability of process results increases which significantly affects the process window, device yield and manufacturability. Understanding the underlying physical causes of the pattern effect is very important to systematically improve device performance, yields and manufacturability. In this paper, the impact of device pattern size and density on process variations in RTP steps was analyzed. According to the analysis, diffraction of light from the periodicity of the nanometer scale device features can result in significant local heating near the critical depths for junctions and contacts.
MOSCAP's and MOSFET's on III-V Channel Materials with Si, Ge and SiGe Interface Passivation Layer
Authors: Lee Jack , Ok Injo , Kim Hyoung-Sub , Zhu Feng , Zhang Manhong , Park Sung Il , Yum Jung Hwan , Zhao Han
Published: April 2007

The electrical characteristics of TaN/HfO2/GaAs MOS capacitors with various interface passivation layers (Si, Ge and SiGe IPLs) under various PDA (post-deposition anneal), PMA (post-metal anneals) and process conditions are presented. High-k GaAs MOSFETs with reasonable electrical characteristics (i.e. thin EOT (< 2nm), low frequency dispersion (<5%) and peak mobility (1218 cm2/V-s) have been obtained.
Interface Engineering by PVD-Based In-Situ Fabrication Method for Advanced Metal/High-k Gate Stacks
Authors: Watanabe Heiji , Horie Shinya , Arimura Hiroaki , Kitano Naomu , Minami Takashi , Kosuda Motomu , Shimura Takayoshi , Yasutake Kiyoshi
Published: April 2007

We fabricated high-quality silicate gate dielectrics by utilizing a solid phase interface reaction (SPIR) between ultrathin metal layers and SiO2 underlayers. Metal diffusion to the SiO2 underlayer forms a high-quality silicate interlayer, and preserving the initial SiO2/Si bottom interface ensures good electrical properties. The Hf silicate dielectrics were fabricated by the SPIR method using Hf layers less than 0.5-nm-thick that were fully consumed by interface reactions, resulting in Hf silicate layers that remained amorphous after activation annealing. The superior electrical properties of the poly-Si/HfSixOy/SiO2/Si MOSFETs were demonstrated through low leakage current and high electron mobility. We also recently proposed a novel in-situ fabrication method that continuously fabricates high-k dielectrics using SPIR and metal electrodes with a low-damage sputtering system. We investigated structural and electrical properties of metal/high-k gate stacks and demonstrated the effectiveness of the in-situ method in improving electrical properties.
Polysilicon Interface Engineering for Improved PIP Capacitors
Authors: Towner Janet M. , Naughton John , Prasad Jagdish
Published: April 2007

The capacitor module has been a challenge for both extrinsic and intrinsic oxide quality for polysilicon/insulator/polysilicon capacitors integrated into ASIC mixed-signal devices. A change in the process sequence where the bottom polysilicon surface is protected from subsequent processing has been found to greatly improve oxide integrity. However this approach is cost prohibitive for an existing product line, as there are many mission critical, high reliability customers who require extended qualification. Nonetheless, these same customers are driving toward zero defectivity for their existing products. A plasma-based interclean etch inserted between the two wet cleans prior to capacitor oxide deposition was found to substantially improve oxide integrity. The increase in the capacitor linearity as a result of the etch was minimal and was attributed to the removal of a portion of the phosphorus-rich material at the polysilicon surface.
New Characterization Methodology of Borderless Silicon Nitride Charge Kinetic using C(V) Hysteresis Loops
Authors: Beylier Gaelle , Sylvie Bruyere , Pascal Mora , Gerard Ghibaudo
Published: April 2007

In this paper a new characterization methodology of borderless silicon nitride is presented. This material, deposited by Plasma Enhanced Chemical Vapor Deposition process, contains a large charge quantity attributed to K centres. Actually, a steady state has been searched, while taking into account charge considerations, electrical field and time influence during C(V) hysteresis. It is achieved by a capacitance versus time at constant voltage experiment, after a complete C(V) hysteresis used to set up an initial state of charge. The charge evolution occurring during stress time is related to the charge transformation kinetics. An empirical kinetic model has been extracted from these results, with time constant dependent on field and temperature. A faster positive to negative charge transformation has been shown, attributed to an easier holes trapping. Finally, this new characterization method demonstrates that data retention charge loss is correlated to trapping kinetics in borderless silicon nitride.
Accurate TDDB Lifetime Prediction of High-k Stacked Gate Dielectrics
 with Regarding High Density Initial Traps
Authors: Okada Kenji , Ota Hiroyuki , Nabatame Toshihide , Toriumi Akira
Published: April 2007

Essentials required for the accurate TDDB lifetime (TBD) prediction of high-k stacked gate dielectrics are discussed. For this purpose, thorough understanding of the time dependent dielectric breakdown (TDDB) mechanism is indispensable, along with clarifying its stress gate voltage (VG) dependence. As for the TDDB mechanism, we propose the Generated Subordinate Carrier Injection (GSCI) model, which presumes that the degradation is dominated by the injected subordinate carriers (IDC). Because of the coexistence of the current component which does not contribute to the breakdown such as the trap-assisted current, the decomposition of the subordinate carrier current to each component is needed. On the other hand, to obtain the stress VGdependence of TBD, we point out the universal relationship between the voltage acceleration factor of TBD and the stress VG. It is demonstrated that the accurate lifetime prediction can be realized on the basis of the GSCI model combined with this universality.
Curing Dielectric Layers for Microelectronics with Microwaves: Chemistry, Mechanisms, and Applications
Authors: Hubbard Robert L.
Published: April 2007

Recent work in curing new polyimide (PI) and polybenzoxazole (PBO) films on silicon device wafers with Variable Frequency Microwaves (VFM) rapidly (total cycle times less than 15 minutes) and also below 200ºC has produced equal or better film properties than conventional curing at 350ºC and in a fraction of the standard cycle time. The nature of the microwave heating mechanism will be discussed as well as the results of experiments that enable the custom synthesis of polymers and additives that take advantage of this unique heating process. Emphasis will be placed on the changes in chemical polymerization that appear to occur under microwave energies and the resultant network structures and mechanical property predictions for the films. Parallels to the curing of polymer adhesives at lower temperatures will also be examined with respect to the effects of unique network formation and cross-linking recently discovered with the use of VFM.
Morphology and Composition of Praseodymium Based High-k Materials and Their Relevance to Dielectric Properties of Thin-Films
Authors: Lippert Gunther , Dabrowski Jarek , Costina Ioan , Lupina Grzegorz , Ratzke Markus , Zaumseil Peter , Muessig Hans-Joachim
Published: April 2007

We discuss some of the issues associated with the relation between the leakage current and the dielectric constant on the one hand, and the crystallographic structure and the chemical composition of the film on the other. We compare the technology requirements for various appli-cations, the open questions, and the known answers and physical mechanisms. We focus mostly on dielectrics containing Pr oxides. Starting with the binary Pr2O3, we investigate electronic properties and formation energies of point defects as revealed by ab initio calculations and we attempt to associate this data with the experimental information on the influence of processing on the dielectric quality of the film. We then consider Pr silicates on Si for MOSFETs and PrxAl2-xO3 on TiN for MIM front-end applications. In the latter case, annealing above about 800{degree sign}C needed to noticeably increase the effective dielectric con-stant causes an increased leakage. In this context, we discuss the diffu- sion mechanism for Ti and the influence of Ti on the leakage current.
Physics and Integration of Fully-Depleted Silicon-On-Insulator Devices
Authors: Vandooren Anne
Published: April 2007

This paper gives an overview of the device physics and the process integration challenges of fully-depleted (FD) silicon-on-insulator (SOI) devices for advanced technology nodes. In the first part of the presentation, the physics related to the operation of ultra-thin film devices is described as well as how device scaling is impacted by the device parameters. Next, major fabrication challenges faced by fully-depleted SOI devices are reviewed along with their most recent progress. The technology modules reviewed include isolation, substrate engineering (limits of ultra-thin layers, strained layers, buried insulator materials,...), gate stack (high k and gate workfunction engineering techniques), methods for reducing SD parasitic resistance, such as elevated source/drain, as well as stress techniques.
Integration of SOI-Based 2D- and Si-Based 3D Photonic Crystals
Authors: Kocher Gudrun , Khunsin Worawut , Romero Vivas Javier , Vynck Kevin , Arpiainen Sanna , Romanov Sergei , Langer Birger , Mulot Mikael , Jonsson Frederik , Charvolin Thomas , Hajdi Emmanuel , Cassagne David , Zentel Rudolf , Ahopelto Jouni , Sotomayor Torres Clivia M.
Published: April 2007

We present progress towards a generic approach to integrate 2D photonic components embedded in 3D PhCs and couple them to single-mode ridge waveguides. 3D photonic crystals are fabricated by spatially selective self-assembly of silica and PMMA beads into an fcc lattice on a SOI patterned substrate. 2D defect layers are fabricated on 3D PMMA opals by controlled removal of specific beads through electron beam lithography. Simulations of mode matching and coupling efficiencies are presented, which provide guidelines for the fabrication of experimental structures on inverted silicon opals.
Implant Metrology for Bonded SOI Wafers using a Surface Photo-Voltage Technique
Authors: Bertuch Adam F. , Smith Wesley , Steeples Kenneth , Standley Robert , Stefanescu Anca , Johnson Ron
Published: April 2007

Small signal Surface Photo-voltage (SPV) measurement techniques have been applied to monitor ion implants typical of those used for layer-transfer SOI processes. This SPV wafer mapping technique was investigated for sensitivity to dose, implant uniformity, and repeatability for hydrogen and helium implants into (100) silicon wafers through a 1450Aå surface oxide. A normalized sensitivity of approximately 1.2 for the investigated cases was observed. A demonstrated repeatability of less than 0.5% 1-sigma standard deviation was measured for a multi-day period on hydrogen implanted wafers. The small signal SPV metrology technique presented allows in-line SPC control of the critical ion implant step within the SOI wafer manufacturing process.
Effective Control of Strain in SOI by SiN Deposition
Authors: Kosemura Daisuke , Ogura Atsushi , Yamasaki Kosuke , Kakemura Yasuto , Yoshida Tetsuya
Published: April 2007

Strain introduction in SOI substrates by SiN capping film was evaluated by UV-Raman spectroscopy. Induced strain became larger with increasing SiN film thickness. SOI substrates originally had tensile strain and the SiN cap shifted the strain toward the compressive direction. The induced strain was larger in the thinner SOI substrates with the same thickness of the SiN capping film. We also evaluated a substrate after SiN patterning with a high spatial resolution of 200-nm, and found strain enhancement at the pattern edge.
Structural Properties of Tensile-Strained Si Layers Grown on Si1-xGex Virtual Substrates (x = 0.2, 0.3, 0.4 and 0.5)
Authors: Hartmann Jean-Michel , Rouchon Denis , Barnes Jean-Paul , Mermoux Michel , Billon Thierry
Published: April 2007

We have studied the structural properties of tensile-strained Si (sSi) layers grown on polished Si0.8Ge0.2 and Si0.7Ge0.3 virtual substrates as a function of their thickness. The surface morphology, the tensile-strain, the linear density of defects and the threading dislocation density have been quantified for different sSi layer thickness. Results are compared to those previously obtained on sSi layers grown on top of polished Si0.6Ge0.4 and Si0.5Ge0.5 virtual substrates (ECS Trans. 3, No. 7, 319 (2006)).
A Chromium-free Defect Etching Solution for Application on SOI
Authors: Maehliss Jochen , Abbadie Alexandra , Kolbesen Bernd O.
Published: April 2007

A new defect etching solution is presented especially developed for application on silicon-on-insulator (SOI) substrates. This FS Cr-free SOI etching solution is free of toxic hexavalent chromium. Very efficient in revealing crystalline defects, it provides a low etch rate, which makes it a promising candidate for Secco replacement on SOI films. Excellent correlation of etch pit densities with Secco solution has been obtained. The mechanism and characteristics of this solution will also be discussed.
Epitaxial Regrowth of Ge on SGOI and GeOI Substrates Obtained by Ge Condensation
Authors: Damlencourt Jean-Francois , Campidelli Yves , Roure Marie-Christine , Vincent Benjamin , Martinez Eugenie , Fillot Frederic , Arrazat Brice , Nguyen Tuan , Cristoloveanu S. , Clavelier Laurent , Morand Yves
Published: April 2007

In this paper, we have investigated the influence of process parameters (bake temperature, bake duration and growth temperature) on the morphology of GeOI substrate thickened by Ge epitaxial regrowth. We have seen that the optimum bake temperature in terms of layer roughness and interfacial contamination is 600{degree sign}C. For higher bake temperatures, the layer morphology is 3D due to a layer dewetting. The efficiency of the surface preparation prior to the epitaxial regrowth has been assessed by Angle resolved X-Ray Photoelectrons Spectroscopy. No residual oxygen contamination has been detected. Furthermore, we have investigated the influence of the growth temperature on the layer morphology and resistivity. For temperatures higher than 450{degree sign}C, some thermal grooving assisted by the crystal defects (cross hatch) occurred and 3D Ge layers were obtained. Finally, GeOI substrates thickened with the best growth condition were evaluated by Pseudo MOSFET technique. An exceptional high hole mobility, beyond 400 cm2/V.s was observed.
Ordered Lattices of Quantum Dots on Ultrathin SOI Nanomembranes
Authors: Ritz Clark , Flack Frank , Savage Donald , Detert Douglas , Evans Paul , Lagally Max , Cai Zhonghou
Published: April 2007

Undercut or fully released silicon template layers of ultrathin silicon-on-insulator are structurally compliant and allow long- range mechanical interactions that are impossible on supported SOI, thick SOI, or on bulk surfaces. SiGe quantum dots create and respond to strain in these freestanding Si substrates. We show that elastic effects lead to long-range order in the positions of quantum dots grown on both sides of a free- standing thin SOI substrate. A statistical analysis of the distribution of quantum dots shows that the ordered lattice of dots is coherent over distances of at least several hundred of nanometers. X-ray microdiffraction probes the structure of the SOI and finds that curvature in the Si lattice is consistent with the proposed deformation of the substrate by quantum dots.
Improved Model to Determine the Generation Lifetime in Short Channel SOI nMOSFETs
Authors: Galeti Milene , Martino Joao Antonio A. , Simoen Eddy , Claeys Cor
Published: April 2007

An improvement of the one-dimensional analytical model for the extraction of the generation lifetime in partially depleted SOI nMOSFETs is proposed. This refined technique, based on the drain current switch-off transient, considers the influence of the halo implanted region and the channel length reduction. The results obtained are compared with measurements and two- dimensional numerical simulations, showing a good agreement. The improved model can be applied as a simple tool for the electrical characterization of short channel devices.
High Performance W-Band Wafer-Scale Assembly for III-V Semiconductor MMICs
Authors: Zeng Xiang , Chang-Chien Patty , Tsai Roger
Published: April 2007

Two high performance Wafer-Scale Assembled W-Band passive 3-D architectures are presented. The first is constructed of two GaAs wafers that are bonded together to form an 8um high intra- wafer cavity. The second is composed of four GaAs wafers of various thicknesses which are stacked and bonded to form a range of intra-wafer cavity heights. The robustness of both architectures are examined with DC test structures. Advanced 3- D passive RF elements with low insertion loss, high return loss, and excellent isolation are successfully integrated into these WSAs.
High Quality InAs Quantum Dots with an In(Ga,Al)AsSb Strain-Reducing Layer for Long Wavelength Photonic Devices
Authors: Chyi Jen-Inn , Liu Wei-Sheng , Chiu Pei-Chin , Shiau Meng-Jie , Kuo David M. , Chen Wen-Yen , Chang Hsing-Szu , Hsu Tzu-Min
Published: April 2007

The effects of InGaAsSb and InAlAsSb strain-reducing layers on the optical properties of InAs/GaAs QDs are investigated. With these Sb-containing overgrown layers, InAs QDs exhibit much enhanced photoluminescence efficiency and thermal stability in the wavelength of 1.3 um and above, which is essential for long wavelength photonic devices.
Heteroepitaxy of One Dimensional (1-D) Ga2O3-GaN Core-Shell Nanorods
Authors: Hsieh Chin-Hua , Chou L.-J.
Published: April 2007

1-D Ga2O3-GaN core-shell nanorods were successfully fabricated by two-step synthesis processes. The Ga2O3 nanorods were synthesized by the reaction of Ga with SiO2 at 600{degree sign}C. Subsequently, one dimensional Ga2O3-GaN core-shell nanorods were successfully achieved by nitrifying the as-synthesized Ga2O3 nanorods under ammonia ambient at 700{degree sign}C for 6 hours. The field-emission scanning electron microscope (FESEM, JSM- 6500F), X-ray spectrometer (SHINMADZU), and the field-emission transmission electron microscope (FETEM, JEM-3000F) were utilized to investigate the morphologies, crystal structures, and compositions of nanorods in detail, respectively. Furthermore, optical investigation of Ga2O3-GaN coaxial nanorods heterostructures was carried out by photoluminescence (PL) measurements in present study.
High Performance GaN-based Hydrogen Sensors
Authors: Hsu Wei C. , Huang Jun-Rui , Lin Kun-Wei , Chen Huey-Ing , Liu Wen-Chau
Published: April 2007

The hydrogen sensing characteristics of the catalytic Pd/GaN and Pd/InGaP MS diodes are systematically studied and compared over wide hydrogen concentration and temperature regimes. Experimentally, upon exposing to hydrogen-containing gases, both forward- and reverse-biased currents of both studied devices are substantially increased with increasing the hydrogen concentration. In other words, both studied devices can be operated under applied bipolarly voltages. Furthermore, particularly under very wide hydrogen concentration regimes, the studied Pd/GaN MS diode can withstand higher temperature operation with remarkable forward and reverse sensitivities of hydrogen detection. In addition, due to larger Schottky barrier height lowering effect, the hydrogen adsorption performance for the Pd/GaN MS diode manifests the superior sensitivity of Schottky barrier variation, especially at higher temperature operation. In contrast, the studied Pd/InGaP MS diode offers remarkable shorter response time of hydrogen adsorption process than the Pd/GaN one particularly at lower temperature operation and is suitable for the lower hydrogen concentration detection.
Improved Luminance Intensity of InGaN-GaN Light-Emitting Diode by Roughening both p-GaN and Undoped-GaN Surfaces and Applying a Mirror to the Sapphire Substrate Surface
Authors: Wu Yewchung S. , Liao Cheng
Published: April 2007

InGaN-GaN light emitting diodes (LEDs) with double roughened surfaces and silver mirror was fabricated by surface- roughening, wafer-bonding and laser lift-off technologies. It was found the light intensity of DRM-LED (with mirror between undoped-GaN/sapphire interface) was 3.05 times higher than that of the PR-LED (with only roughened p-GaN surface), and 1.45 times higher than that of the DRSM-LED (with mirror on the backside of sapphire substrate).
Influence of Sinking-Gate on Al0.24Ga0.76As/In0.22Ga0.78As Double Heterojunction High Electron Mobility Transistors
Authors: Hsu Meng-Kai , Chen Hong-Rung , Chen Wei-Tien , Chiu Shao-Yen , Lour Wen S.
Published: April 2007

The influence of gate metal with thermal annealed process adopt to control the distance between gate and channel on pseudomorphic Al0.24Ga0.76As/ In0.22Ga0.78As double heterojunction high electron mobility transistors (DH-HEMTs) were studied. Compared to device with gate-recess process, the distance of gate-to-channel could be controlled through the thermal annealed process and therefore exhibit a lower series resistance. Measured transconductance of 150 mS/mm and an open- drain voltage gain of 136 for the DH-HEMT with an as deposited gate are enhanced to 175 mS/mm and 160 for the DH-HEMT with a 330-{degree sign}C annealed gate. Good device linearity is also obtained with a low second-harmonic to fundamental ratio of 3.55 %. In addition, good microwave performances such as unit-current gain- and maximum power gain- frequency were also obtained from devices with gate-annealed process.
Electronic Properties of Organic-inorganic Hybrid Systems
Authors: Li Yang , Sun Ke , Yang Jianyong , Dutta Mitra , Stroscio Michael A.
Published: April 2007

Organic-inorganic hybrid structures enable integration of useful organic and inorganic characteristics within a single molecular scale. In addition to exhibiting useful properties, the hybrid materials can be fabricated into optoelectronic devices using simple and inexpensive fabrication techniques. Among the phenomena of importance in these systems are the mechanisms by which carrier transport occurs in such organic- inorganic hybrid structures. We have made hybrid nanostructures based on poly[2-methoxy-5-ethylhexyloxy-1,4-phenylenevinylene] (MEH-PPV) and several various nanocrystalline quantum dots. Employing both optical and electronic techniques, we examine the charge transfer in different materials and study current through the structures. A minibands model is used to study the transmission of current.
Electrochemical and Photo-Electrochemical Properties of Porous n-InP Layers
Authors: Santinacci Lionel , Goncalves Anne-Marie , Etcheberry A.
Published: April 2007

In this paper, we investigate the properties of porous structures anodically grown onto n-InP (100) in 1 M HCl. The relation between growth parameters and the pore morphology is firstly reported. In situ electrochemical characterizations show that the pore formation strongly influences the physical properties of n InP surfaces. Capacitance measurements reveal a modification of the electronic distribution but no variation of the flat band potential. Photocurrent spectra performed during the pore growth are strongly modified: uniform increase of the photocurrent followed by a decrease with narrowing of the spectrum is observed, red shift. Finally ex situ photoluminescence experiments carried out onto porous films show both a quantum size effect and a dead layer behavior.
Controlling Macropores Etching in n-Si by Means of in-situ FFT Voltage- and Photoimpedance Spectroscopy
Authors: Foca Eugen , Carstensen Juergen , Popkirov Georgi , Foell Helmut
Published: April 2007

In this work we use FFT-impedance spectroscopy for in-situ characterization of the macropores growth process in n-Si. The impedance is done in the applied voltage. Additionally a new type of photoimpedance is proposed that is calculated from the response of the etching current to the modulation of the backside illumination intensity. Both types of impedance offer a huge amount of data that can be used to interpret the state of the macropores at any instance in time. We consider that this information can be used, in a later stage, for in-situ control the pores growth process hence conceiving an automated etching system.
Etching of Germanium in Hydrogenperoxide Solutions
Authors: Huygens Inge M. , Gomes W.P. , Strubbe K.
Published: April 2007

In this paper, the etching behaviour of germanium in hydrogen peroxide solutions is described. Electrochemical experiments showed that the etching process is most probably purely chemical. The etch rate was found to depend upon the H2O2 concentration, the pH value, the amount of KCl in the solution and , in some cases, upon the rotation rate. Based on all of these findings, possible etching mechanisms for Ge in H2O2 are discussed on a molecular level.
Micro Patterning of Silicon by Chemical Etching Using Patterned Noble Metals as Catalyst
Authors: Asoh Hidetaka , Arai Fusao , Ono Sachiko
Published: April 2007

Si convex arrays and Si hole arrays with ordered periodicities were fabricated by the site-selective chemical etching of a Si substrate using patterned noble metals such as Ag, Pt/Pd, and Au as a catalyst. Metal particles were deposited selectively on the Si substrate by a combination of colloidal crystal templating and subsequent electroless plating or ion sputtering. The obtained metal patterns were of two different types: networklike honeycomb and isolated-island microarrays. On the basis of this process, the dimensions of the resultant pattern could be adjusted easily by changing the diameter of the polystyrene spheres used as a mask.
Growth and Formation of Thin Anodic Films on InP
Authors: Simon Nathalie , Etcheberry A.
Published: April 2007

Growth, formation and stability of anodic oxides obtained on n- InP were investigated by coupling electrochemical methods and XPS analyses. Using transient photocurrent and Mott-Schottky behavior, as in situ probes, we have pointed out several steps for InP oxidation process, related to a gradual oxide coverage evidenced by XPS characterizations. The current density chosen to perform the oxidation governs the resulting chemical composition, the texture and the electrical properties of the oxide. Low applied current densities lead to the formation of thin (around few nanometers) and homogeneous films, while high current densities induce thicker and less homogeneous oxides. The resulting electrical properties also strongly depend on the anodization mode. The thinner homogeneous layers, grown with low current densities, exhibit the best passivating features.
Chemistry of delta-SnS: New Tin Monosulfide Polymorph Thin Films from Galvanostatic Electrodeposition
Authors: Brownson Jeffrey R. , Georges Cécile , Larramona Gerardo , Levy-Clement Claude
Published: April 2007

Galvanostatic deposition of tin monosulfide thin films (d-SnS phase) on transparent conductive glass was studied. Uniform films were deposited in aqueous baths with tartaric acid. Cyclic voltammetry suggested tin-tartrate complexes were crucial to film electrodeposition, suppressing tin metal reduction in favor of sulfur species reduction. X-ray diffraction showed primitive orthorhombic symmetry for d-SnS (a = 11.380 Aå, b= 4.029 Aå, c = 4.837 Aå). d-SnS was converted to a-SnS (a = 11.172 Aå, b = 3.994 Aå c = 4.311 Aå) following annealing at ~ 270 {degree sign}C in Ar(g). Characterization of the as-deposited films confirmed 1:1 Sn/S. The d-SnS structure was consistent over a range of deposition temperatures (50, 70, and 90 {degree sign}C). UV/Vis spectrometry confirmed increased disorder in films deposited at 50 {degree sign}C. A direct allowed optical band gap transition of lower energy for the d-SnS phase (1.05 eV) was obtained compared to that for a-SnS (direct, 1.2 eV).
Helicobacterand gastrin stimulate Reg1 expression in gastric epithelial cells through distinct promoter elements
Authors: Steele Islay A. , Dimaline Rod , Pritchard D. Mark , Peek Richard M. , Wang Timothy C. , Dockray Graham J. , Varro Andrea
Published: April 2007

The gastric pathogen Helicobacter pylori accelerates the progression to gastric cancer but the precise mechanisms that mediate carcinogenesis remain unidentified. We now describe how Helicobacter and gastrin stimulate the expression of a putative growth factor, Reg1, in primary gastric epithelial cells. RT-PCR and Western immunoblotting of human gastric corpus and antrum showed significantly increased Reg1α in H. pylori-infected patients. Similarly, Reg1 was increased in the stomachs of H. felis-infected INS-GAS mice. To study transcriptional regulation of the Reg1 gene, we transfected primary mouse gastric glands with −2111 bp and −104 bp Reg1 promoter-luciferase reporter constructs. Expression of both constructs was detected in pepsinogen- and VMAT-2-expressing cells, which corresponds to the normal pattern of expression of human and mouse endogenous Reg1. The expression of both constructs was increased in response to gastrin and H. pylori, and there were potentiating interactions between them; in contrast, only the −2111 bp construct responded to H. felis. Mutation of a C-rich putative regulatory element within the −104 bp sequence abolished the response to gastrin but not to H. pylori whereas mutation of the proximal −98 to −93 region of the promoter reduced the response to H. pylori but not to gastrin. Stimulation of Reg1 by H. pylori required the virulence factor CagA. These data indicate that expression of the putative growth factor Reg1 is controlled through separate promoter elements by gastrin and Helicobacter.
Leptin regulates gallbladder genes related to absorption and secretion
Authors: Swartz-Basile Deborah A. , Lu Debao , Basile David P. , Graewin Shannon J. , Al-Azzawi Hayder , Kiely James M. , Mathur Abhishek , Yancey Kyle , Pitt Henry A.
Published: April 2007

Dysregulation of gallbladder ion and water absorption and/or secretion has been linked to cholesterol crystal and gallstone formation. We have recently demonstrated that obese, leptin-deficient (Lep ob) mice have enlarged gallbladder volumes and decreased gallbladder contractility and that leptin administration to these mice normalizes gallbladder function. However, the effect of leptin on gallbladder absorption/secretion is not known. Therefore, we sought to determine whether leptin would alter the expression of genes involved in water and ion transport across the gallbladder epithelium. Affymetrix oligonucleotide microarrays representing 39,000 transcripts were used to compare gallbladder gene-expression profiles from 12-wk-old control saline-treated Lep ob and from leptin-treated Lep ob female mice. Leptin administration to Lep ob mice decreased gallbladder volume, bile sodium concentration, and pH. Leptin repletion upregulated the expression of aquaporin 1 water channel by 1.3-fold and downregulated aquaporin 4 by 2.3-fold. A number of genes involved in sodium transport were also influenced by leptin replacement. Epithelial sodium channel-α and sodium hydrogen exchangers 1 and 3 were moderately downregulated by 2.0-, 1.6-, and 1.3-fold, respectively. Carbonic anhydrase-IV, which plays a role in the acidification of bile, was upregulated 3.7-fold. In addition, a number of inflammatory cytokines that are known to influence gallbladder epithelial cell absorption and secretion were upregulated. Thus leptin, an adipocyte-derived cytokine involved with satiety and energy balance, influences gallbladder bile volume, sodium, and pH as well as multiple inflammatory cytokine genes and genes related to water, sodium, chloride, and bicarbonate transport.
Forearm blood flow responses to fatiguing isometric contractions in women and men
Authors: Thompson Benjamin C. , Fadia Tanvi , Pincivero Danny M. , Scheuermann Barry W.
Published: April 2007

Previous studies suggest that women experience less vascular occlusion than men when generating the same relative contractile force. This study examined forearm blood flow (FBF) in women and men during isometric handgrip exercise requiring the same relative force. Thirty-eight subjects [20 women and 18 men, 22.8 ± 0.6 yrs old (means ± SE)] performed low- and moderate-force handgrip exercise on two occasions. Subjects performed five maximum voluntary contractions (MVC) before exercise to determine 20% and 50% MVC target forces. Time to task failure (TTF) was determined when the subject could not maintain force within 5% of the target force. Mean blood velocity was measured in the brachial artery with the use of Doppler ultrasonography. Arterial diameter was measured at rest and used to calculate absolute FBF (FBFa; ml/min) and relative FBF (FBFr; ml·min−1·100 ml−1). Women generated less ( P < 0.05) absolute maximal force (208 ± 10 N) than men (357 ± 17 N). The TTF was longer ( P < 0.05) at 20% MVC for women (349 ± 32 s) than for men (230 ± 23 s), but no difference between the sexes was observed at 50% MVC (women: 69 ± 5 s; men: 71 ± 8 s). FBFa and FBFr increased ( P < 0.05) from rest to TTF in both women and men during 20% and 50% MVC trials. FBFr was greater in women than in men at ≥30% TTF during 50% MVC. At exercise durations ≥60% of TTF, FBFa was lower ( P < 0.05) in women than in men during handgrip at 20% MVC. Despite the longer exercise duration for women at the lower contraction intensity, FBFr was similar between the sexes, suggesting that muscle perfusion is matched to the exercising muscle mass independent of sex.
Vascular aging in the longest-living rodent, the naked mole rat
Authors: Csiszar Anna , Labinskyy Nazar , Orosz Zsuzsanna , Xiangmin Zhao , Buffenstein Rochelle , Ungvari Zoltan
Published: April 2007

The naked mole rat (NMR; Heterocephalus glaber) is the longest-living rodent known [maximum lifespan potential (MLSP): >28 yr] and is a unique model of successful aging showing attenuated declines in most physiological function. This study addresses age-related changes in endothelial function and production of reactive oxygen species in NMR arteries and vessels of shorter-living Fischer 344 rats (MLSP: ∼3 yr). Rats exhibit a significant age-dependent decline in acetylcholine-induced responses in carotid arteries over a 2-yr age range. In contrast, over a 10-yr age range nitric oxide (NO)-mediated relaxation responses to acetylcholine and to the NO donor S-nitrosopencillamine (SNAP) were unaltered in NMRs. Cellular superoxide anion (O2•−) and H2O2 production significantly increased with age in rat arteries, whereas they did not change substantially with age in NMR vessels. Indicators of apoptotic cell death (DNA fragmentation rate, caspase 3/7 activity) were significantly enhanced (∼250–300%) in arteries of 2-yr-old rats. In contrast, vessels from 12-yr-old NMRs exhibited only a ∼50% increase in apoptotic cell death. In the hearts of NMRs (2 to 26 yr old), expression of endothelial NO synthase, antioxidant enzymes (Cu,Zn-SOD, Mn-SOD, catalase, and glutathione peroxidase), the NAD(P)H oxidase subunit gp91 phox, and mitochondrial proteins (COX-IV, ATP synthase, and porin, an indicator of mitochondrial mass) did not change significantly with age. Thus long-living NMRs can maintain a youthful vascular function and cellular oxidant-antioxidant phenotype relatively longer and are better protected against aging-induced oxidative stress than shorter-living rats.
Turning on the central contribution to contractions evoked by neuromuscular electrical stimulation
Authors: Dean J. C. , Yates L. M. , Collins D. F.
Published: April 2007

Neuromuscular electrical stimulation can generate contractions through peripheral and central mechanisms. Direct activation of motor axons (peripheral mechanism) recruits motor units in an unnatural order, with fatigable muscle fibers often activated early in contractions. The activation of sensory axons can produce contractions through a central mechanism, providing excitatory synaptic input to spinal neurons that recruit motor units in the natural order. Presently, we quantified the effect of stimulation frequency (10–100 Hz), duration (0.25–2 s of high-frequency bursts, or 20 s of constant-frequency stimulation), and intensity [1–5% maximal voluntary contraction (MVC) torque generated by a brief 100-Hz train] on the torque generated centrally. Electrical stimulation (1-ms pulses) was delivered over the triceps surae in eight subjects, and plantar flexion torque was recorded. Stimulation frequency, duration, and intensity all influenced the magnitude of the central contribution to torque. Central torque did not develop at frequencies ≤20 Hz, and it was maximal at frequencies ≥80 Hz. Increasing the duration of high-frequency stimulation increased the central contribution to torque, as central torque developed over 11 s. Central torque was greatest at a relatively low contraction intensity. The largest amount of central torque was produced by a 20-s, 100-Hz train (10.7 ± 5.5 %MVC) and by repeated 2-s bursts of 80- or 100-Hz stimulation (9.2 ± 4.8 and 10.2 ± 8.1% MVC, respectively). Therefore, central torque was maximized by applying high-frequency, long-duration stimulation while avoiding antidromic block by stimulating at a relatively low intensity. If, as hypothesized, the central mechanism primarily activates fatigue-resistant muscle fibers, generating muscle contractions through this pathway may improve rehabilitation applications.
Basic Mechanisms of the Aging Gastrointestinal Tract
Authors: Salles N.
Published: April 2007

The goal of this short review is to summarize recent data on gastrointestinal changes with aging, focusing on gastrointestinal motility disorders, and mucosal variations. First of all, this review focused on gastrointestinal motility disorders with aging, even though an increased prevalence of several gastrointestinal motor disorders (i.e., dysphagia, dyspepsia, anorexia, and constipation) occurs in older people, aging per se appears to have a minor direct effect on most gastrointestinal functions. Secondly, this review focused on histological changes with aging, i.e., regulation of gastrointestinal mucosal growth, gastrointestinal carcinogenesis, and gastric mucosal changes, especially changes in gastric acid secretion, bacterial overgrowth and its consequences on elderly patients.
Mechanisms of Aging and Liver Functions
Authors: Gagliano Nicoletta , Grizzi Fabio , Annoni Giorgio
Published: April 2007

Background/Aims: Morphofunctional studies suggest that the liver, compared with other organs, ages fairly well. Its success is ascribable to its lasting ability to regenerate, even if the potential of the cells to replicate progressively declines with age. The aim of this study was to analyze some aspects of the early phases of liver regeneration, its capacity to mount a stress response, and the inflammatory response in the early stage of an acute injury. Methods: Rats aged 2, 6, 12 and 19 months received a single intraperitoneal injection of CCl4, and morphological, biochemical and molecular evaluations were done 2 and 24 h later. Results: AST and ALT, starting at age 12 months, were significantly higher than in the younger rats after CCl4. Histological modifications were already detectable after 2 h in rats aged 12 and 19 months, thereafter becoming more diffuse and marked, whereas they become evident only 24 h after the intoxication in rats aged 2 and 6 months. Albumin, c-fos, c-myc, hepatocyte growth factor, transforming growth factor-α and HSP70 mRNA levels decreased 24 h after CCl4 starting at age 12 months. Mast cell density was higher in the young rats than the old ones. Conclusion: Our results point to: (a) a basically preserved regenerative response of the aged liver, although somehow weaker and slower, with reduced ability to counteract agents inducing cell necrosis; (b) a decrease in the HSP70 response suggesting a reduction in homeostatic capacity, and (c) a lower inflammatory response during aging.