bluuebunny/crossref_metadata_2025_split huggingface dataset:
Microstructure and Electrical Characteristics of Plasma Sprayed Thick Film Mn-Co-Ni Oxide Thermistor
Authors: Liang Shanshan , Ravi Bhuvaragasamy , Sampath Sanjay , Gambino Richard J. 
Published: April 2011

ABSTRACTMn-Co-Ni-O spinel, owing to its large temperature dependant resistivity, is an attractive ternary system for negative temperature coefficient (NTC) thermistor applications, particularly in oxygen rich environments. This research explores the potential of plasma spray as a method for the fabrication of thick film Mn-Co-Ni-O thermistors. Nanostructured Mn-Co-Ni-O spinel powders were synthesized by gel combustion method and were air-plasma-sprayed on to alumina substrates. The as-sprayed deposit formed a rocksalt structure rather than a cubic spinel structure. Annealing in air at 600°C for 3 hours resulted in transformation to the spinel structure while higher temperature annealing resulted in phase separation of rocksalt phase at 1250°C and recombination into spinel monophase at 1350°C. Temperature dependent measurement of resistivity showed -4 to -1% temperature coefficient of resistivity (TCR) from room temperature to 250oC with high reproducibility, making the low temperature annealed coating suitable in thermistor applications.
A Kinetic Study of Mediator-Template Assembly of Gold Nanoparticles
Authors: Zhong I-IM Stephanie , Ip Wui , Pak Alice , Luo Jin , Zhong Chuan-Jian 
Published: April 2011

ABSTRACTThis paper describes a kinetic study of the mediator-template assembly of gold nanoparticles in solutions based on the spectrophotometric measurement of the surface plasmon resonance optical property. Gold nanoparticles of ∼5 nm diameter encapsulated with tetraoctylammonium bromide shells were studied as a model system. The core-shell nanoparticles were assembled into 3D spherical assemblies via a mediator-template assembly route in which a thioether-based multidentate ligand functions as a mediator and the tetraoctylammonium shell molecules function as a templating agent. In this report, the results were compared with those obtained for the assembly of gold nanoparticles in several different systems with features similar to the mediator-template assembly. The findings further provided further insights into understanding the kinetic factors governing the assembly of nanoparticles, and have important implications to the design and control of the nanostructures for sensory and catalytic applications.
Selective Detection of Cholesterol Using Carbon Nanotube Based Biochip
Authors: Roy Somenath , Vedala Harindra , Choi Won Bong 
Published: April 2011

ABSTRACTA novel type of working electrode based on MWCNT is fabricated on silicon substrate for detection of total cholesterol. Multiwall carbon nanotubes (MWNT), which are vertically grown on a silicon platform, promote heterogeneous electron transfer between the enzyme and the working electrode. Immobilization of cholesterol oxidase (Pseudomonas fluorescens.) on the electrode is done by entrapment of the enzyme in a bio-friendly, water soluble polymer, polyvinyl alcohol (PVA), which also increases the hydrophilicity of the carbon nanotube (CNT) surface (with experimental evidence) and thereby facilitating the intimate attachment of the protein molecules. Cyclic voltammograms exhibit efficient detection of cholesterol in the range of 100-300 mg/dl, which covers the entire range of possible cholesterol concentration in human blood. The influence of interferents, like glucose, ascorbic acid and uric acid, present in the physiological fluids, is also examined. Owing to its compatibility with standard silicon microfabrication technology, the signal processing circuitry can also be integrated onto the same silicon substrate yielding a compact miniaturized biochip.
Properties of gas sensor using CNTs thin film prepared by PLD/CVD method
Authors: Ueda Tsuyoshi , Norimatsu Hideyuki , Bhuiyan M.M.H. , Ikegami Tomoaki , Ebihara Kenji 
Published: April 2011

ABSTRACTCarbon nanotube (CNT) is a promising material which has potential for applications to various nanotechnology devices owing to its unique features like high electrical conductivity, mechanical strength and large specific surface area. Recently, gas sensors using CNTs or carbon nano-fiber, which have extremely high sensitivity at a room temperature with fast response, have been reported. Being exposed to oxidizing gas like NO, NO2 or O3, the conductance of the single-walled carbon nanotubes (SWNTs) changes due to charge transfer between the SWNT surface and gas molecules adsorbed. Therefore CNTs will be applicable to O2 and O3 gas sensors in various fields.CNTs thin film sensor was prepared and its performance was investigated. CNTs thin film was prepared on a SiN substrate using PLD/CVD method. To prepare a sensor device an Al2O3 substrate with Pt interdigital electrodes (sensor substrate) was used. In this method, Fe catalytic thin film was deposited by pulsed laser deposition (PLD) method using KrF excimer laser of wavelength 248 nm, repetition rate 10 Hz, energy fluence 3 J/cm2. During PLD process the substrate temperature and the ambient gas pressure were kept at room temperature of 25 °C and 3.5×10−5 Torr, respectively. The thickness and roughness of the films were modified by changing a number of ablation laser pulses from 300 to 3,000. A small number of laser pulses deposited Fe nano-particles of less than 10 nm in diameter on the substrate. We used 1000 pulses for a catalytic Fe film preparation as small-sized catalyst is necessary to grow SWNTs. CNTs were grown from Fe thin film on Si or sensor substrates by thermal CVD method. Ethylene gas was used as carbon source. The substrate was set in the quartz reaction tube heated to 1000 °C in an electric furnace. CNTs were grown for 20 ∼ 40 minutes. In our previous studies, it was found that SWNTs can grow under this process. The prepared CNTs were characterized using SEM, TEM and Raman spectroscopy. From SEM observation, randomly oriented CNTs were found on both the Si substrate and the sensor substrate. A diameter of CNTs was found 20 ∼ 50 nm which tended to be proportional to the size of catalyst particle.The Sensitivity of CNT gas sensor was evaluated by measuring the electrical characteristic of the sensor. The sensor was exposed to NO gas of different concentration in a chamber. Resistance of the sensor was measured by two-terminal method, while the sensor was heated from room temperature to a high temperature on a block heater. The Sensitivity of CNT gas sensors, response time and reproducibility was measured. Initial resistance of the film was about 450 and it decreases with temperature increase. This shows that a prepared CNTs sensor film has semiconductor characteristics. Measured maximum sensitivity of CNTs gas sensor was 6.9 % at sensor temperature 290 deg. Detail studies and the latest data will be presented at the symposium.
Preparation of Titanium Oxide and Metal Titanates as Powders, Thin Films, and Microspheres by Novel Inorganic Sol-Gel Process
Authors: Deptuła A. , Goretta Kenneth C , Olczak Tadeusz , Lada Wieslawa , Chmielewski Andrzej G. , Jakubaszek U. , Sartowska Bozena , Alvani Carlo , Casadio Sergio , Contini Vittoria 
Published: April 2011

ABSTRACTTitanium oxide and titanates based on Ba, Sr and Ca were prepared from commercial solutions of TiCl4 and HNO3. The main preparation steps for the sols consisted of elimination of chloride anions by distillation with nitric acid and addition of metal hydroxides for the titanates. Resulting sols were gelled and used to (1) prepare irregularly shaped powders by evaporation; (2) produce by a dipping technique thin films on glass, Ag, or Ti substrates; and (3) produce spherical powders (diameters <100 μm) by solvent extraction. Results of thermal and X-ray-diffraction analyses indicated that the temperatures required to form the various compounds were lower than those necessary to form the compounds by conventional solid-state reactions and comparable to those required with use of organometallic based sol-gel methods. Temperatures of formation could be further reduced by addition of ascorbic acid to the sols.
Ultrafast Pd/AAO Nanowell Hydrogen Sensor
Authors: Lu Jianjiang , Yu Shufang , Wang H.Hau 
Published: April 2011

ABSTRACTAnodized aluminum oxide (AAO) membranes consist of highly uniform and aligned nanopores with pore diameters ranging between 10 and 200 nm. Based on these nanoporous materials, we developed a new AAO nanowell structure that was synthesized through short-term anodization of aluminum foil. The nanowell structure was made of shallow wells that were oriented in a hexagonally closed packed configuration with well diameter around 50 nm and depth less than 100 nm. The chemical composition was amorphous alumina on aluminum substrate. Thin palladium film was then fabricated on the surface of the as-synthesized AAO nanowell to prepare a Pd/AAO nanowell structure. These devices demonstrated unexpectedly high hydrogen sensitivity. The response time ranged from a few hundred milliseconds to a few seconds with hydrogen concentration between 1 and 0.05%. They also showed modest responses at hydrogen concentration as low as 5 ppm.
Characterization of Lead Zirconate Titanate Powders Prepared by a Hydrothermal Method
Authors: Che Lingjuan , Ding Yongping , Cheng Jinrong , Chen Chao , Meng Zhongyan 
Published: April 2011

AbstractLead Zirconate Titanate (PZT) powders have been synthesized by a hydrothermal method at the processing temperatures of 120-220 °C for 1.5-50 hours, based on the reaction of Pb(CH3COOH)2·3H2O, ZrOCl2·8H2O, Ti(C4H9O)4 and KOH. Hydrothermally treated PZT powders were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), and Fourier transformation infrared (FTIR) techniques respectively. The influences of hydrothermal synthesize conditions on the crystalline structure and the morphology of PZT particles were investigated. Crystallized PZT powders could be synthesized at the KOH concentration of >2.5 mol/l.
High Carrier Lifetime Bulk-Grown 4H-SiC Substrates for Power Applications
Authors: Malta David , Jenny J.R. , Tsvetkov V.F. , Das M. , Müller St. G. , Hobgood H. McD. , Carter C.H. , Kumar R.J. , Borrego J.M. , Gutmann R.J. 
Published: April 2011

AbstractA thermal anneal process has been developed that significantly enhances minority carrier lifetime (MCL) in bulk-grown substrates. Microwave photoconductivity decay (MPCD) measurements on bulk grown substrates subjected to this process have exhibited decay times in excess of 35 μs. Electron Beam Induced Current (EBIC) measurements indicated a minority carrier diffusion length (MCDL) of 65 μm resulting in a calculated MCL of 15 μs, well within the range of that measured by MPCD. Deep level transient spectroscopic (DLTS) analysis of samples subjected to this anneal process indicated that a significant reduction of deep level defects, particularly Z1/2, may account for the significantly enhanced lifetimes. The enhanced lifetime is coincident with a transformation of the original as-grown crystal into a strained or disordered lattice configuration as a result of the high temperature anneal process. PiN diodes were fabricated employing 350 μm thick bulk-grown substrates as the intrinsic drift region and thin p- and n-type epitaxial layers on either face of the substrate to act as the anode and cathode, respectively. Conductivity modulation was achieved in these diodes with a 10x effective carrier concentration increase over the background doping as extracted from the differential on-resistance. Significant stacking fault generation observed during forward operation served as additional evidence of conductivity modulation and underscores the importance of reducing dislocation densities in substrates in order to produce a viable bulk-grown drift layer.
Investigation of Dislocation Behavior during Bulk Crystal Growth of SiC
Authors: Ohtani Noboru , Katsuno Masakazu , Nakabayashi Masashi , Tsuge Hiroshi , Fujimoto Tatsuo , Yashiro Hirokatsu , Sawamura Mitsuru , Aigo Takashi , Hoshino Taizo 
Published: April 2011

AbstractIt is well-known that SiC crystal deficiencies are delaying the realization of outstandingly superior SiC power electronics. Efforts to date have centered on eradicating micropipes, and 4H-SiC substrates with extremely low micropipe densities have been achieved. Nevertheless, SiC substrates and epilayers still contain several types of dislocations in densities on the order of thousands per square centimetres, which are nearly 100-fold micropipe densities. While not nearly as detrimental to SiC device performance as micropipes, it has recently been demonstrated that dislocations existing in SiC crystals degrade several characteristics of SiC devices, e.g., the forward bias characteristics of SiC pin diodes and the gate oxide reliability of SiC MOSFETs.This paper reports several dislocation processes occurring during the growth of hexagonal SiC bulk crystals. Particularly, we focus on the dislocation formation and propagation processes in SiC crystals. We have investigated dislocation processes in 4H-SiC bulk crystals grown by the physical vapor transport (PVT) growth method, using defect selective etching and transmission electron microscopy (TEM).It was found that foreign polytype inclusions introduced a high density of dislocations at the polytype boundary. In the polytype-transformed areas of the crystal, very few medium size hexagonal etch pits due to threading screw dislocations were observed, indicating that the polytype transformation ceased the propagation of threading screw dislocations. The oval-shaped etch pit arrays observed on the etched vicinal (0001)Si surface, indicative of the dislocation multiplication in the basal plane, showed characteristic distribution around micropipes and low angle grain boundaries. Based on the results, we will argue the dislocation behavior in PVT grown SiC crystals, suggesting that dislocation interaction and conversion are relevant processes to understanding the behavior.
Do You Really Expect To Grow Epilayers On That? A Rationale For Growing Epilayers On Roughened Surfaces
Authors: Sumakeris Joseph John , Hull Brett A. , O'Loughlin Michael J. , Ha S. , Skowronski Marek , Palmour John W. , Carter Calvin H. 
Published: April 2011

AbstractWe describe surface preparation and epilayer growth techniques that readily reduce the density of Vf drift inducing basal plane dislocations in epilayers to less than 10 cm-2 and permit the fabrication of bipolar SiC devices with very good Vf stability. The optimal process route requires etching the substrate surface prior to epilayer growth to enhance the natural conversion of basal plane dislocations into threading edge dislocations during epilayer growth. The surface of this relatively rough “conversion” epilayer is subsequently repolished prior to growing the device structure. We provide details on processing parameters and potential problems as well as describe devices produced using this low basal plane dislocation growth processes.
SIMS Analysis of Nitrogen in Silicon Carbide Using Raster Change Technique
Authors: Wang Larry , Park Byoung-Suk 
Published: April 2011

AbstractToday's state of the art silicon carbide (SiC) growth can produce semi-insulating crystals with a background doping around 5×1015 atoms/cm3 or lower. It is essential to have an accurate measurement technique with low enough detection limit to measure low level nitrogen concentration. Current SIMS detection limit of low E15 atoms/cm3 will provide accurate determination for nitrogen doping level of 5E16 at/cm3 or higher. In order to determine the lower nitrogen concentration, it is necessary to provide a better detection limit and to separate the contribution of background nitrogen properly. The “raster changing” method provides an accurate way to determine and remove contribution of background nitrogen to the signal, because secondary ion intensities and matrix ion intensities can be analyzed at the same location of the sample by changing the primary beam raster size during a profile. In this study we have succeeded in applying the raster changing method to (a) N in the SiC substrate located under an SiC epi layer, and (b) the detection of N as low as 3E14/ cm3 a bulk-doped SiC substrate.
Growth Mechanism and Dislocation Characterization of Silicon Carbide Epitaxial Films
Authors: Dhanaraj Govindhan , Chen Yi , Chen Hui , Vetter William M , Zhang Hui , Dudley Michael 
Published: April 2011

AbstractSiC homo-epitaxial layers were grown in a chemical vapor deposition process using silicon tetrachloride and propane precursors with hydrogen as a carrier gas. Growth rates were found to increase as temperatures increased at high carrier gas flow rate, while at lower carrier gas flow rate growth rates were observed to decrease as temperature increased. Based on the equilibrium model, “thermodynamically controlled growth” accounts for the growth rate reduction. The grown epitaxial layers were characterized using various techniques. Reduction in the threading screw dislocation (SD) density in the epilayers was observed. Suitable models were developed for explaining the reduction in the screw dislocation density as well as the conversion of basal plane dislocations (BPD) into threading edge dislocations (TED).
Atomic Structure of Non-Basal-Plane SiC Surfaces: Hydrogen Etching and Surface Phase Transformations
Authors: Soubatch Serguei , Lee Wai Y. , Hetzel Martin , Virojanadara Chariya , Coletti Camilla , Saddow Stephen E. , Starke Ulrich 
Published: April 2011

AbstractA-plane (11-20) and diagonal cut (1-102) and (-110-2) surfaces of 4H-SiC have been investigated using atomic force microscopy (AFM), low-energy electron diffraction (LEED), Auger electron spectroscopy (AES), X-ray photoemission spectroscopy (XPS) and scanning tunneling microscopy (STM). After hydrogen etching the surfaces show large, flat terraces. On SiC(11-20) steps down to single atomic heights are observed. On the diagonal cut surfaces steps run parallel and perpendicular to the [-1101] direction, yet drastically different morphologies for the two isomorphic orientations are found. All surfaces immediately display a sharp LEED pattern. For SiC(1-102) and SiC(-110-2) the additional significant presence of oxygen in the AES spectra indicates the development of an ordered oxide. All three surfaces show an oxygen free, well ordered surface after Si deposition and annealing. A transformation between different surface phases is observed upon annealing.
Thermal Interactions of Ni on Stepped 6H-SiC Surfaces: Implications for Thin Film Microstructure
Authors: Woodworth Andrew , Raghavan Srikanth , Stinespring Charter D 
Published: April 2011

AbstractNi films are important as both Schottky junctions and Ohmic contacts for high temperature SiC devices. Ni/SiC Schottky junctions are observed to become Ohmic upon annealing. This transition has been attributed to changes in film microstructure. The experiments reported here compare the thermal behavior of Ni films deposited on standard 6H-SiC (0001) surfaces with films deposited on periodically stepped surfaces. The former were prepared by wet chemical etching and are typical of those used in device fabrication. The latter were prepared by high temperature hydrogen etching. Ni films ranging from monolayer to nominal device thickness (~50 nm) were annealed on both surfaces. Analysis of these surfaces by in-situ Auger electron spectroscopy (AES) and ex-situ atomic force microscopy (AFM) provided elemental, chemical and morphological information. The results show that the morphology and microstructure of annealed films are dependent on initial film thickness and substrate surface conditions.
Fabrication and Characterization of 5 kV IGBTs on 4H-SiC
Authors: Jonas Charlotte Elizabeth , Zhang Qingchun , Ryu Sei-Hyung , Agarwal Anant , Palmour John 
Published: April 2011

AbstractP-channel planar IGBT devices were made on 4H-SiC. Punch-through buffer and drift layers were designed to block 5 kV were grown on 4H-SiC n-type substrate. Ion implantion was used for all selective doping such as n-well, p+, n+, JFET region and terminations. Gate oxidation was thermally grown and annealed. Blocking voltage of 5.7 kV was demonstrated. IGBTs exhibit VTH of -12 V, VT = -3.1 V, Rdiff,on = 400 mΩcm2 at Vg = -34 V at room temperature. Ron decreased to 108 mΩcm2 at Vg = -30 V at 300°C.
Template Routes to Non-Oxide Ceramic Nano- and Micro-Structures
Authors: Kusari Upal , Bao Zhihao , Ye Cai , Ahmad Gul , Sandhage Kenneth H , Sneddon Larry G 
Published: April 2011

AbstractNon-oxide ceramic materials like boron carbide and silicon carbide are technologically relevant as advanced high temperature materials, while boron nitride is a thermally robust low-k insulating material with electronic applications. Efficient routes to boron carbide, boron nitride, and silicon carbide ceramic nanostructures have been developed which employ molecular and polymeric precursors, including the boron carbide precursor 6, 6'-bis(decaboranyl)hexane, the boron nitride precursor polyborazylene, and a commercially available silicon carbide precursor allylhydridopolycarbosilane(AHPCS), in conjunction with colloidal silica and biological silica “diatom” templates. Layered submicron-sized ordered void structures with three-dimensional periodicity and tunable length scales were fabricated by the melt infiltration of the precursors into ordered colloidal silica bead templates. Pyrolytic ceramic conversion followed by dissolution of the silica beads by chemical treatment with aqueous HF or NaOH generated highly uniform ceramic structures with thicknesses up to 50μm and ordered voids ranging in diameter from 50-150 nm. Following on earlier work by Sandhage who generated polymer and oxide ceramic structures, vacuum filtration of the ceramic precursor solutions through bioclastic silica diatom frustule templates generated polymer coated replicas of their 3-D micro- and nanostructures. Subsequent pyrolysis and dissolution of the frustules in 48% HF yielded free-standing ceramic structures with fine features on length scales of 60-200 nm. This technique therefore provides a large scale route to nano- and micro structured non-oxide ceramic materials. Structural control of the end products was achieved by changing the concentration of the precursor solution, pore size and/or the frustule template. Characterization by XRD, DRIFT, SEM, TEM and possible uses of these uniform nano- and micro-structured ceramics will be discussed.
Pattern Evolution of Self-Assembled Quantum Dots Under Biaxial Stresses
Authors: Pang Yaoyu , Huang Rui 
Published: April 2011

AbstractA stressed epitaxial film can undergo surface instability. The stress field and the interface interaction have profound effects on the dynamics of surface evolution that leads to self-assembled quantum dots. In this paper, by using a nonlinear evolution equation, we investigate pattern evolution of self-assembled quantum dots under general biaxial stresses. It is found that the shape of quantum dots and their spatial ordering are strongly influenced by the relative magnitudes of the biaxial stresses. Linear perturbation analysis and nonlinear numerical simulations are conducted to elucidate the effect of stress anisotropy on the process of self-assembly that selects different patterns.
Use of sub-10 nm Diameter Upconversion Nanophosphors as Bio-labels
Authors: Lim Shuang Fang , Riehn Robert , Tung Chih-Kuan , Tank David , Ryu William S. , Yao Nan , Austin Robert H. 
Published: April 2011

ABSTRACTWe have synthesized rare-earth doped sub-10 nm diameter upconverting yttrium oxide based nanophosphors by flame spray pyrolysis. We have investigated the emitted visible fluorescence of the sub-10nm nanophosphors under both infrared excitation and electron excitation, and observed comparable narrow band emission spectra. The viability of the nanoparticles for biological imaging was confirmed by imaging the digestive system of the nematode worm C. elegans in the upconversion mode. We have surface functionalized the nanophosphors making them suitable for bio labeling.