bluuebunny/crossref_metadata_2025 huggingface dataset:
Electrical and Microstructural Changes of β-PVDF under Different Processing Conditions by Scanning Force Microscopy
Authors: Nunes J. Serrado , Sencadas V. , Wu A. , Kholkin A. L. , Vilarinho P. M. , Lanceros-Méndez S.
Published: April 2011

Poly vinylidene fluoride (PVDF) has been widely investigated due to its important pyro- and piezoelectric properties. These properties have found various applications, especially as sensor and actuators. The existence and optimization of these properties is intimately related with the fraction of the polymer in the crystalline phase, its structure, microstructure and orientation. All of these in turn heavily depend on the processing conditions. PVDF is a semi-crystalline polymer which shows polymorphism and is commonly crystallized in non-polar crystalline α-phase. The piezo- and pyroelectric properties mainly depend on the β-phase, so that increasing β-phase content has always been of great concern in this field.

β-phase can be obtained by mechanical stretching of α-phase films at a given temperature or directly from solution. Conversion of α into β-phase takes place at stretching temperatures below 100 °C, at a stretch ratio of about 3–5. Nevertheless the achieved amount of β-phase in the crystalline fraction of the material is never 100%. In the films obtained from solution, 100% beta phase films can be achieved in either a porous or non-porous form. The degree of crystallinity is also larger for the samples obtained from solution.

This work is mainly devoted to the study of the variations in the topological morphology and piezoelectric domain response of PVDF prepared by the aforementioned methods by scanning force microscopy in a piezo-response mode.
Melt Crystallization of Nanocomposites of Poly(Vinylidene Fluoride) with OMS
Authors: Ince-Gunduz Bedriye Seyhan , Amare Debeshu , Alpern Robert , Cebe Peggy , Crawford Jennifer , Dolan Breanna , Jones Stacey , Kobylarz Ryan , Reveley Matthew
Published: April 2011

In our previous work [1] we investigated the impact of cold-crystallization on the structure of nanocomposites of PVDF with Lucentite STN™ OMS and observed the crossover composition in which the crystallographic beta phase dominated over alpha phase. Here, melt crystallization of PVDF/OMS nanocomposites was studied in the range of 0 to 1.0 wt% of OMS. In crystallization from melt, a decrease in crystallinity index occurs as a result of an increase in OMS. While beta phase fraction increased with an increase of OMS content in the range of interest, the amount of alpha crystals was found to be dominant even at high OMS compositions. At 1.0 wt% of OMS, beta crystals had reached at most 30% of the total crystallinity. Polarizing optical microscopy (POM) studies showed smaller, less birefringent spherulites with higher melting temperature compared to alpha spherulites appeared with OMS addition. Growth rate of these weakly birefringent spherulites is smaller than that of the strongly birefringent alpha spherulites. The increase in size and amount of the weakly birefringent spherulites with an increase of OMS and their higher melting point suggests these spherulites may be in the beta crystallographic phase.
Dynamic Behavior Investigation of the Piezoelectric PVDF for Flexible Fingerprint
Authors: Chang Wen-Yang , Cheng Ying-Hui , Liu Shu-Yuan , Hu Ying-Chiang , Lin Yu-Cheng
Published: April 2011

The paper reported a novel flexible concept for acquiring the fingerprint that based on the piezoelectric PVDF (polyvinylidene fluoride) was integrated into the flexible polyimide substrate to form the fingerprint. In this study, it focused on the array PVDF fabrication and dynamic control circuit to read pressure signal for fingerprint identification. The fabrication of PVDF powder was melt at 180°C, pressed under 2 tons and subsequently quenched at 10°C/min to form the PVDF films. Next the PVDF films were put into the oven at different temperatures for 40 minutes to stretch 4 times from its original length. As for the dynamic control, the sensing circuit was presented two parts, one is charge amplifier and the other is capacitance detect by using frequency oscillator. We demonstrated that the dynamic pressure measurement of PVDF could achieve fingerprint acquisition. Experimental results showed the response speed of sensing is as fast as 5 ms. Therefore, the aim of this study is to speed up the technology for promoting the flexible fingerprint.
Ionic Polymer Conductor Nano-Composites as Distributed Nanosensors, Nanoactuators and Artificial Muscles - A Review
Authors: Shahinpoor Mohsen
Published: April 2011

Basic recent results, properties and characteristics of ionic polymer conductor nano-composites (IPCNC) as biomimetic distributed nanosensors, nanoactuators and artificial muscles are briefly discussed in this paper. Some fundamental considerations on biomimetic distributed nanosensing and nanoactuation are first presented and then expanded to cover some recent advances in manufacturing techniques, force optimization, 3-D fabrication of IPMC's, recent modeling and simulations, sensing and transduction and product development. This paper also covers some recent industrial and medical applications including a multi-fingered grippers (macro, micro, nano), biomimetic robotic fish and caudal fin actuators, diaphragm micropump, multi-string musical instruments, linear actuators made with IPMNC's, IPMNC-based data glove and attire, IPMNC-based heart compression/assist devices and systems, wing flapping flying system made with IPMNC's and a host of others.
PLD Growth of CNTs using a Nanostuctured Ni Buffer Layer: Dependence of H2 partial Pressure
Authors: Chandran Maneesh , Kant K. Mohan , Rama N. , Rao M.S. Ramachandra
Published: April 2011

The effect of hydrogen partial pressure on the growth of CNT thin films using on-axis PLD has been studied. Using nickel as buffer layer, carbon nanotubes can be produced with good yield in Hydrogen atmosphere. We have found strong visible-near infrared (NIR) photoluminescence (PL) from carbon nanotube thin films synthesized under various hydrogen partial pressures. The present result shows that bright, narrow PL from CNTs can be obtained without any post growth processing.
Use of High Surface Area TiO2 Nanosheet in Dye-sensitized Solar Cell
Authors: Pavasupree Sorapong , Ngamsinlapasathian Supachai , Suzuki Yoshikazu , Yoshikawa Susumu
Published: April 2011

High surface area nanosheet TiO2 with mesoporous structure were synthesized by hydrothermal method at 130 °C for 12 h. The samples characterized by XRD, SEM, TEM, SAED, and BET surface area. The nanosheet structure was slightly curved and approximately 50-100 nm in width and several nanometers in thickness. The as-synthesized nanosheet TiO2 had average pore diameter about 3-4 nm. The BET surface area and pore volume of the sample were about 642 m2/g and 0.774 cm3/g, respectively. The solar energy conversion efficiency (η) of the cell using nanorods/nanoparticles TiO2 (from the nanosheet calcined at 450 °C for 2 h) with mesoporous structure was about 7.08 % with Jsc of 16.35 mA/cm2, Voc of 0.703 V and ff of 0.627; while η of the cell using P-25 reached 5.82 % with Jsc of 12.74 mA/cm2, Voc of 0.704V and ff of 0.649.
Design, Fabrication and Testing of a Novel Gas Sensor utilizing Vertically Aligned Zinc Oxide Nanowire Arrays
Authors: Parthangal Prahalad , Cavicchi Richard , Zachariah Michael
Published: April 2011

We report on a novel, non-destructive, in-situ approach toward connecting and electrically contacting vertically aligned zinc oxide nanowire arrays using conductive gold nanoparticles. A chemical gas-sensing device was constructed and tested using this nano-architecture. Well-aligned, single-crystalline zinc oxide nanowires were grown through a direct thermal evaporation process at 550 °C on gold catalyst layers. Electrical contact to the top of the NW array was established by creating a contiguous nanoparticle film through electrostatic attachment of conductive gold nanoparticles exclusively onto the tips of nanowires. The gas-sensing device fabricated through this approach was found to be sensitive to both reducing (methanol) and oxidizing (nitrous oxides) gases. This assembly approach is amenable to any array of one-dimensional nanostructures for which a top contact electrode is needed.
Mechanoluminescence Studies upon Single Nanoparticles by AFM-photomeasurement System
Authors: Terasaki Nao , Sakai Kazufumi , Koga Toshiaki , Li Chengzhou , Imai Yusuke , Yamada Hiroshi , Adachi Yoshio , Nishikubo Keiko , Xu Chao-Nan
Published: April 2011

We successfully measured the mechanoluminesence (ML) from a single ML nanoparticle at the first time. In order to measure the weak light emission from a single nanoparticle induced by applying a micro force, we developed an AFM-based new apparatus with a photomultiplier. Interestingly, the emission (ML) intensity from a nanoparticle was approximately proportional to the load, the phenomena is similar to the macroscopic ML emission properties.
Endothelial Cell Adhesion on Highly Controllable Compared to Random Nanostructured Titanium Surface Features
Authors: Lu Jing , Webster Thomas J.
Published: April 2011

The application of vascular stents using conventional metals is limited because the implantation process will cause significant injury to the vascular wall and endothelium, resulting in neointima hyperplasia and then the development of long-term restenosis. The objective of this in vitro study was to investigate endothelial cell function (especially their adhesion behavior) on highly controllable nanostructured surface features. Considering the importance of the endothelium and its properties, highly controllable nanostructured surface features of titanium (a popular vascular stent metal) were created using E-beam evaporation to promote endothelialization and to control the direction of endothelial cells on vascular stents. Endothelial cells are aligned with blood flow naturally in the body. In this manner, the present in vitro study provides much promise for the use of nanotechnology for improving metals for vascular stent applications.
Importance of Nanosensors: Feynman's Vision and the Birth of Nanotechnology
Authors: Devreese Jozef T.
Published: April 2011

In his visionary 1959 lecture at Caltech, Feynman envisaged the potential of the ability to manipulate matter at the atomic scale. I discuss implementations of Feynman's vision in the field of nanosensors and perspectives of its further development and applications.
Stimuli-Responsive Hydrogels Based on the Genetically Engineered Proteins: Actuation, Drug Delivery and Mechanical Characterization
Authors: Moschou Elizabeth A. , Chopra Nitin , Khatwani Santoshkumar L. , Ehrick Jason D. , Deo Sapna K. , Bachas Leonidas G. , Daunert Sylvia
Published: April 2011

Herein, we describe a biomimetic approach aimed at the development of synthetic biohybrid materials inspired by nature's sensing and actuating mechanism of action. The biomaterials are based on the incorporation of the hinge-motion binding protein calmodulin (CaM) and its low affinity ligand phenothiazine (TAPP) within the bulk of an acrylamide hydrogel network, which is accomplished through covalent binding. At the initial state and in the presence of Ca2+ ions, CaM interacts with TAPP creating chemical (non-covalent) cross-links within the bulk of the hydrogel, forcing the material to assume a constrictive configuration. Upon the removal of Ca2+, CaM releases TAPP, breaking the non-covalent cross-links within the bulk of the hydrogel and letting the material relax into a swollen state. The same type of effect is observed when a higher affinity ligand for CaM, like chlorpromazine (CPZ), is employed. In the presence of CPZ, the protein releases TAPP and binds CPZ, allowing the biomaterial to swell into a relaxed state. This swelling response of the biomaterial is reversible, and is directly related to the levels of CPZ used. The sensing and subsequent actuating mechanism of the CaM-based stimuli-sensitive hydrogels makes them suitable for a variety of applications, including sensing, mechanical actuation, high-throughput screening, and drug delivery. Additionally, it is shown that the CaM-based stimuli-sensitive hydrogels developed present unique mechanical properties, suitable for integration within microfluidics and MEMS structures. It is envisioned that these biomaterials will find a number of applications in a variety of fields, including drug delivery.
A Semiconductor-based Field-effect Platform for (Bio-)Chemical and Physical sensors: From Capacitive EIS Sensors and LAPS over ISFETs to Nano-scale Devices
Authors: Schöning Michael J. , Abouzar Maryam H. , Wagner Torsten , Näther Niko , Rolka David , Yoshinobu Tatsuo , Kloock Joachim P. , Turek Monika , Ingebrandt Sven , Poghossian Arshak
Published: April 2011

The coupling of semiconductor field-effect devices (FED) together with chemical and biological recognition elements, like functional intelligent materials, biomolecules and living cells, represents an attractive platform for the creation of different (bio-)chemical sensors, multi-parameter analysis systems and bio-chips. This paper summarises recent developments and current research activities in the field of (bio-)chemically modified FEDs, scaling down from capacitive EIS (electrolyte-insulator-semiconductor) sensors and LAPS (light-addressable potentiometric sensor) to ISFETs (ion-sensitive field-effect transistor) that have been realised in our laboratory. Selected examples of application of ISFETs for the detection of physical parameters in liquids are presented, too. With the aim of future development of nano-devices for the detection of single biomolecules, the possibility of a simple preparation of different self-aligned nano-structures by using conventional photolithography and pattern-size reduction technique has been experimentally demonstrated.
Ferroelectric PTCR Films for Photonic Crystal Gas Sensor
Authors: RaviPrakash J. , Trolier-McKinstry Susan , Cheng Jing-Gong , McNeal Mark , Greenwald Anton , Puscasu Irina , Johnson Edward , Pralle Martin , Shah Ashak
Published: April 2011

We examined lanthanum doped lead barium titanate films for temperature measurements of photonic crystal - MEMS devices. Films were deposited by sol-gel techniques and crystallized in air above 650°C. X-ray diffraction spectra consistent with the perovskite structure were detected. The room temperature dielectric constant was ∼570 at 10 kHz of La-doped (0.3 mol%) Pb0.3Ba0.7TiO3 films. These films had a remanent polarization of ∼20μC/cm2 and a coercive field of 145 kV/cm. The leakage current density was ∼ 2×10−7 amps/cm2 at 100 kV/cm field. The resistivity of the films extracted from the linear region of the I-V data (electric fields in excess of 100 kV/cm) measured as a function of temperature shows an increase in resistivity at temperatures above Tc (120°C for BaTiO3 and 240°C for Pb0.3Ba0.7TiO3) of the film consistent with positive coefficient of resistance (PTCR) effect. However, the change in resistance was small when compared to bulk samples of similar compositions.
Thermo-Reversible Protein Fibrillar Hydrogels
Authors: Miller Aline , Saiani Alberto , Yan Hui
Published: April 2011

Hen egg white lysozyme (HEWL) was exposed to various physical and chemical denaturing environments to encourage protein denaturation and consequent gelation. Its phase behavior was examined as a function of pH, temperature and also in the presence of the reductant dithiothreitol (DTT). Transparent viscoelastic gels form at low pH values while opaque gels form under alkaline conditions. No increase in viscosity was observed for systems in pure water unless 20 mM of DTT was added, which is known to break the disulfide bridges present in HEWL. The microstructure of the gel was studied using transmission electron microscopy (TEM) and environmental scanning electron microscopy (ESEM). Gels formed at low pH contain fibrils ∼10 nm in diameter with various lengths while at high pH the gels are dominated by particulate aggregates. Thinner fibrils that are 4-6 nm in diameter are observed in the gels formed in the presence of DTT. In this case the distinct feature of the gels is they are thermoreversible and can be melted and reformed easily by varying the temperature.
Spin-Orbit Coupling and Zero-Field Electron Spin Splitting in AlGaN/AlN/GaN Heterostructures with a Polarization Induced Two-Dimensional Electron Gas
Authors: Kurdak Ç. , Biyikli N. , Cheng H. , Ozgur U. , Morkoç H. , Litvinov V. I.
Published: April 2011

We studied spin-orbit coupling in wurtzite AlxGa1−xN/AlN/GaN heterostructures with different Al concentrations using weak antilocalization measurements at 1.6 K. Using the persistent photoconductivity effect we change the carrier density in controllable manner. We find that the electron spin splitting energies does not scale linearly with the Fermi wavevector at high carrier densities. From this deviation, for the first time, we are able to extract the cubic spin-orbit parameter for this material system.
Epitaxial Growth of ZrO2 on GaN by MOMBE for High Dielectric Material Applications
Authors: Gu Xing , Xie Jinqiao , Chevtchenko Serguei , Izyumskaya Natalia , Avrutin Vataliy , Morkoç Hadis
Published: April 2011

Epitaxial growth of ZrO2 has been achieved on MOCVD grown GaN template by oxides MBE using a reactive H2O2 oxygen source. Using the low temperature buffer followed by high temperature in-situ annealing and high-temperature growth, monoclinic, (100)-oriented ZrO2 thin film with decent structural quality and smooth surface morphology was achieved. The full width at half maximum of ZrO2 (100) rocking curve is 0.4 arc degree and the rms roughness for a 5μm by 5 μm AFM scan is 4.1Å. The use of epitaxially grown ZrO2 in the AlGaN/GaN HFET structure as a gate dielectric layer have resulted in the increase of the saturation-current density and pinch-off voltage as well as showed near symmetrical gate-drain I-V behavior.
Defects in Electron and Neutron Irradiated n-GaN: Disordered Regions Versus Point Defects
Authors: Polyakov Alexander Y , Smirnov Nikolai B , Govorkov Anatoliy V , Markov Alexander V , Lee Cheul-Ro , Lee In-Hwan , Kolin Nikolai G , Merkurisov Denis I , Boiko Vladimir M , Wright James S , Pearton Stephen J
Published: April 2011

Effects of 10 MeV electron and fast reactor neutron irradiations on carrier removal rate and deep traps spectra were compared for undoped n-GaN samples. It is shown that for electron irradiation the carrier removal rate is well accounted for by the difference in introduction rates of nitrogen-vacancy-related donors with activation energy 0.2 eV and of nitrogen-interstitial-related acceptors at Ec-1.2 eV. In the case of neutron irradiation the introduction rate of all deep traps was much lower than the carrier removal rate indicating that the main contribution to electron removal was due to disordered regions. These regions give rise to a marked persistent photocapacitance signal and a hole-trap-like feature in deep traps spectra. The Fermi level position in the core of disordered regions is located near Ec-(0.85-1) eV.
Defect reduction in (11-20) a-plane GaN by two-step epitaxial lateral overgrowth
Authors: Ni X. , Özgür Ü. , Fu Y. , Biyikli N. , Morkoç H. , Liliental-Weber Z.
Published: April 2011

We report a two-step growth method to obtain uniformly coalesced epitaxial lateral overgrown a-plane GaN by metalorganic chemical vapor deposition (MOCVD). By obtaining a large wing height to width aspect ratio in the first step followed by enhanced lateral growth in the second step via controlling the growth temperature, we reduced the tilt angle between the advancing Ga-polar and N-polar wings for improved properties. Transmission electron microscopy (TEM) showed that the threading dislocation density in the wing area was 1.0×108cm−2, more than two orders of magnitude lower than that in the window area (4.2×1010cm−2). However, a high density of basal stacking faults, 1.2×104cm−1, was still observed in the wing area. Near field scanning optical microscopy (NSOM) at room temperature revealed that the luminescence was mainly from the wing regions with very little contribution from the windows and meeting fronts. These observations suggest that due to significant reduction of threading dislocations radiative recombination is enhanced in the wings.
Localisation of Excitation in InGaN Epilayers and Quantum wells
Authors: O'Donnell Kevin Peter
Published: April 2011

Using a synchrotron radiation source, extended X-Ray Absorption Fine Structure (EXAFS) measurements were performed at the gallium and indium K-edges of a range of (In,Ga)N samples, grown either by MBE or MOCVD. The resulting determinations of local alloy structure, complemented in selected cases by asymmetric x-ray diffraction reciprocal space mapping (XRD-RSM), show an inequality in the “mixed cation” separations, Ga-In and In-Ga, for samples with InN content less than about 50%. This asymmetry, whichincreaseswith decreasing InN content of the layers, is related to the high luminescence efficiency of the materials through a combination of percolation and localisation of excitation on the GaN and InN sub-lattices, respectively.
Estimation of Junction Temperature in Operating Light Emitting Diodes
Authors: Sakhawat Md. Shahrukh , Guha Arindra N , Akpa Okechukwu , Hagler Ping Z , Wang Dake , Park Minseo , Das Kalyankumar
Published: April 2011

Light emitting diodes (LEDs) are normally operated at high current levels resulting in substantial junction heating. However, the junction temperature cannot be measured directly. In the study reported here, it was attempted to estimate junction temperature in LEDs with peak emission 400 nm. Temperature was estimated from current-voltage (I-V) measurements as a function temperature and peak-shift of optical emission spectra with increasing temperature. For a diode operated at a current-level of 100 mA, a temperature of 100 °C was estimate from current voltage measurement and 160 °C from the peak-shift in the optical emission spectra. The difference in temperature estimated using the two different technique is not understood at this point.
Traps in Si-doped AlxGa1-xN Grown by Molecular Beam Epitaxy on Sapphire Characterized by Deep Level Transient Spectroscopy
Authors: Ahoujja Mo , Elhamri S , Hogsed M , Yeo Y. K. , Hengehold R. L.
Published: April 2011

Deep levels in Si doped AlxGa1−xN samples, with Al mole fraction in the range of x = 0 to 0.30, grown by radio-frequency plasma activated molecular beam epitaxy on sapphire substrates were characterized by deep level transient spectroscopy (DLTS). DLTS measurements show two significant electron traps, P1 and P2, in AlGaN at all aluminum mole fractions. The electron trap, P2, appears to be a superposition of traps A and B , both of which are observed in GaN grown by various growth techniques and are thought to be related to VGa-shallow donor complexes. Trap P1 is related to line defects and N-related point defects. Both of these traps are distributed throughout the bulk of the epitaxial layer. An additional trap P0 which was observed in Al0.20Ga0.80N and Al0.30Ga0.70N is of unknown origin, but like P1 and P2, it exhibits dislocation-related capture kinetics. The activation energy measured from the conduction band of the defects is found to increase with Al mole content, a behavior consistent with other III-V semiconductors.
Characterization of GaN/Si Using Capacitance Spectroscopies
Authors: Smith Steven R. , Roberts John C. , Rajagopal P. , Cook J. W. , Piner E. L. , Linthicum K. J. , Elhamri Said
Published: April 2011

Layers of GaN deposited on Si substrates have been studied using Thermal Admittance Spectroscopy (TAS) and Optical Admittance Spectroscopy (OAS). Transparent front-side contacts were used to facilitate the optical measurements. Six specimens were cut from the same location in two different wafers, and three samples were randomly chosen from other growths. A shallow level at EC − 0.051 eV was found in all the specimens using TAS. In some specimens this peak was asymmetric, indicating more than one level near this energy. Deeper levels were also seen in the high-temperature portion of the spectra, but were poorly resolved in most specimens. Illuminating the specimen with UV light at 25 K resulted in the thermal position of the peak shifting to a lower temperature, and hence, the calculated energy, of the peak shifting lower. The amplitude of the peak also decreased. Transient OAS measurements revealed the interesting phenomenon of negative persistent photo conductance at room temperature in some of the specimens when the illumination photon energy was less than the bandgap. The negative response time was very short. At lower temperatures, below 100 K, the negative response diminished, but the response time was still short. At wavelengths above the bandgap energy, normal transient response was seen, with a longer time constant.
GaAsN Thin Film Growth by Chemical Beam Epitaxy with Source Gas Flow Rate Modulation
Authors: Ohshita Yoshio , Saito Kenji , Nishimura Kenichi , Suzuki Toshihide , Yamaguchi Masafumi
Published: April 2011

The amount of residual carbon in the GaAsN film deposited by chemical beam epitaxy (CBE) is decreased by the flow rate modulation growth method (FM-CBE). The number of carbon atoms remained in the grown film increases as the growth temperature decreases. At low temperatures below 440°C, the carbon atoms are mainly originated from the nitrogen source gas mono-methylhydrazine. However, increasing the substrate temperature during the growth causes the deterioration of film qualities and the high growth temperature is not the solution for reducing the impurities. On the other hand, by intermitting the supply of gallium source triethylgallium while the arsenic and nitrogen sources are continuously supplied, the carbon concentration drastically decreases as compared with that grown by the conventional CBE growth. The results of temperature programmed desorption and ab initio calculations suggest that the desorption of adsorbates that contain C atom, such as, NHCH3, is enhanced by the FM-CBE growth, resulting in the decrease of the residual C concentration.
Thinking about Diamond
Authors: Stoneham A. Marshall
Published: April 2011

Diamond is valued mainly as a symbol of power and value (the girl's best friend) and as a solution to many materials processing problems (the engineer's best friend). The 1950s saw both striking developments in diamond synthesis and the beginnings of the rise of silicon as the semiconductor of choice. Since then, silicon has transformed the world. Diamond has reinforced its known roles, and found niches that exploit its special qualities. It is also one of the carbon materials that, in combination, have a variety of superb properties. Could there be bigger opportunities for diamond, more than mere niches, arising from the major social needs: the life sciences, the information technologies, energy, and perhaps others. I attempt to identify areas that might develop formidably.
Device Simulation and Design Optimization for Diamond Based Insulated-gate Bipolar Transistors
Authors: Ye Haitao , Tumilty Niall , Garner David , Jackman Richard B.
Published: April 2011

A diamond based insulated gate bipolar transistor is incorporated into a two-dimensional device simulator (MEDICI) to examine the current gain (β) and potential distribution across the device. Initially, work has focused on an important component of IGBT structure, the PNP bipolar transistor, which has been simulated and is reported upon in this paper. Empirical parameters for emitter and collector regions were used. Various carrier concentrations for base region were used to optimize the simulation. It was found that decreasing the thickness of base region leads to an increase in current gain. A buffer layer is needed to prevent the punch-through at low carrier concentration in the base region. Various approaches of increasing the current gain are also discussed in this paper.
Electrical Transport and Defect Spectroscopy of Free Standing Single Crystal CVD Diamond Prepared from Methane Rich Mixtures
Authors: Bogdan Andrey , Bogdan Ganna , De Ceuninck Ward , Haenen Ken , Nesladek Milos
Published: April 2011

Transient photocurrent measurements in the Time-of-Flight (TOF) configuration were used to study the electrical transport in single crystalline diamond layers using a Nd:YAG - pumped OPO (2.7 nsec) laser pulse excitation source working at a wavelength of ∼ 218 nm. The amount of collected charge was measured and the hole and electron drift mobilities were determined at room temperature for natural IIa diamond and intrinsic single crystalline CVD diamond samples. A variation of the laser intensity over several orders of magnitude enabled switching between the so called “small signal TOF” and “space charge limited current” (SCLC) modes. Experiments were done using electrical fields in the range of 0.05-1.2 V/μm.
Diamond-like Carbon Film Deposition on an Artificial Heart Blood Pump Using a Flexible Type Electrode with r.f. Plasma CVD Processing
Authors: Kanasugi Kazuya , Ohgoe Yasuharu , Tsuchimoto Katsuya , Sato Keisuke , Hirakuri Kenji K. , Miyashita Osamu , Funakubo Akio , Fukui Yasuhiro
Published: April 2011

Diamond-like carbon (DLC) film was deposited uniformly on an irregular structure such as a polyurethane artificial heart blood pump using a special 3-dimensional type electrode. Process of applying the DLC film coating is accomplished by inserting a large number of small metallic balls (φ0.8 mm chromium balls). It is then possible to adjust the shape of the electrode in such a way that the DLC film coating can be applied to the irregular surface of the artificial heart. In investigating the availability of the electrode, under helium (He) plasma, the plasma states were measured using double probe analysis. Lateral profiles of the electron temperature were higher in the centre and decreased towards the edges of the electrode. On the other hand, the plasma density profiles were lower in the centre part than at the edges. The electrode kept ion sheath on the artificial heart blood pump's surface at self-bias voltage uniformly. The results were that the DLC film was deposited completely on the artificial heart blood pump at the film thickness of approximately 350 - 380 nm. Additionally the film structure was uniform.
Electrochemical Charge Transfer to Diamond
Authors: Chakrapani Vidhya , Angus John C. , Anderson Alfred B. , Sumanasekera Gamini U.
Published: April 2011

Electrochemically mediated charge transfer has been primarily studied by its effect on the surface conductivity of diamond. In this paper we show that the effect is not restricted to diamond, but may occur in other material systems as well, for example, semiconducting single-walled carbon nanotubes and gallium nitride.
DNA-ISFETs from Single Crystalline Diamond
Authors: Nebel Christoph E. , Shin Dongchan , Yamamoto Tomoko , Nakamura Takako
Published: April 2011

DNA sensitive field-effect transistors (DNA-FET) have been realized using single crystalline diamond grown by plasma-enhanced chemical vapor deposition (CVD). To bond DNA to diamond, amine linker-molecules are covalently attached by photochemical means to H-terminated diamond surfaces. Using hetero-bifunctional cross-linker and thiol-modified single-strand (ss) marker DNA, the gate of diamond FETs is modified to sense hybridization of DNA, forming double-strand (ds) DNA molecules on the gate. The density of DNA bonded to diamond is varied between 1012 and 1013 cm−2 to explore sensitivity enhancements by reduction of the DNA molecule density. DNA-FET characterization in 1M NaCl buffer solution (pH 7.2) reveal gate-potential threshold shifts by hybridization in the range 30 mV to 100 mV with decreasing DNA density. The variation is discussed based on the transfer doping model which predicts with decreasing pH increasing hole-densities in the surface conductive layer of diamond.
Temperature Dependent Hall Measurements on PLD Thin Films
Authors: von Wenckstern Holger , Brandt Matthias , Zimmermann Gregor , Lenzner Jörg , Hochmuth Holger , Lorenz Michael , Grundmann Marius
Published: April 2011

The electrical properties of epitaxial ZnO thin films grown on sapphire substrates by pulsed laser deposition were investigated by temperature dependent Hall measurents. The thin films investigated were grown at different oxygen partial pressures ranging from 10-2 mbar to 1 mbar. The formation of a degenerate layer, determining the low temperature Hall data, depends on the oxygen partial pressure applied during growth. Further, the formation of such a layer can be correlated to the grain size of the samples. The thermal activation energy of dominant donors decreases in tendency with increasing oxygen partial pressure p(O2); it is about 100 meV for p(O2) ≤ 3 × 10-2 mbar and about 30 meV for p(O2) ≥ 0.1 mar. The concentration of donors and compensating acceptors increases with increasing p(O2).
Vertically Aligned Single Crystalline ZnO Nanorods Grown by Hydrothermal Synthesis and the Theoretical Model for Predicting the Rod Density
Authors: Chua Soo Jin , LE Hong Quang , TAY Chuan Beng , LOH Kian Ping , Fitzgerald Eugene
Published: April 2011

ZnO nanorods are grown by hydrothermal synthesis on a GaN substrate. The nanorods are charcterised by X-ray diffraction, photoluminescence and electron diffraction. A phenomenological model is proposed to predict the areal density and rod length.
ZnO-Sn Bilayer Ultraviolet (UV) Photon Detector with Improved Responsitivity
Authors: Yadav Harish Kumar , Sreenivas K. , Gupta Vinay
Published: April 2011

The influence of the integration of ultra-thin layer of different metals (Al, Cu, Sn, Te, Pb and Au) with the c-axis oriented ZnO thin film on the ultraviolet (UV) photoresponse is investigated. The transfer of electrons from the metal layer to the semiconductor at the interface compensate the surface states which otherwise takes electrons from the interior of ZnO layer and thereby increases the conductivity under UV illumination. The Sn/ZnO sample exhibits a responsivity of the order of 8.5 KV/W at a low UV intensity of 140 μW/cm2 (⎻ = 365 nm) with a fast rise and fall time of 105 and 400 ms respectively.
Two-Dimensional Organization of Single Crystal ZnO Nanopillars
Authors: Cui Jingbiao , Gibson Ursula J
Published: April 2011

Periodically ordered ZnO nanopillar arrays were fabricated by a combination of soft templates created by e-beam lithography and an electrochemical process. Growth at 90 °C in an aqueous solution ensured compatibility with the polymethyl methacrylate used as a template material. We demonstrate that individual ZnO nanopillars with diameters around 100 nm can be precisely placed in desired locations to form two-dimensional periodic structures. This approach provides a new method for design and fabrication of ZnO photonic materials. The process is compatible with standard microfabrication techniques and may have potential applications in the manufacture of photonic and optoelectronic devices.
Donors and Acceptors in Bulk ZnO Grown by the Hydrothermal, Vapor-phase, and Melt Processes
Authors: Look David
Published: April 2011

The optical and electrical properties of commercially available bulk ZnO samples grown by the hydrothermal, vapor-phase, and melt methods are compared. Low-temperature photoluminescence (PL) is used to identify the presence of common impurities, such as H, Al, Ga, and In, and temperature-dependent Hall-effect (T-Hall) measurements are used to obtain donor energies and to quantify donor and acceptor concentrations. All three types of material produce sharp donor-bound-exciton (D0X) PL lines, I4, I6, I8, and I9, generally associated with H, Al, Ga, and In, respectively. However, the I4 and I9 lines are weak in hydrothermal ZnO, and the I4 line is also weak in melt material. Another D0X line I5, possibly associated with donors near the surface, appears in some hydrothermal samples. Electrically, hydrothermal ZnO has a much lower bulk conductivity than vapor-phase or melt ZnO, partly because the donor concentration is lower, but also because the acceptor concentration is higher. A consequence of the low bulk conductance is that surface conductance becomes much more important and must be included in the Hall-effect modeling. An interesting result of this study is a close correlation between the PL-derived Al (I6) donor energy of 51 meV, and the T-Hall-derived energy of 52 meV.
Ferromagnetic Ordering at Room Temperature in ZnO:Co Nanoparticles
Authors: Chaudhary Sujeet , Bhatti Kanwal Preet , Kundu Shankhmala , Kashyap Subhash C. , Pandya Dinesh K.
Published: April 2011

Intrinsic room temperature ferromagnetism is reported in sequentially sintered (in air ambient) nanocrystalline ZnO:Co (1 to 10 at% Co) samples prepared by chemical route. The Curie temperature of the ZnO:Co ferromagnetic samples is determined to be ∼495°C. The saturation magnetization of the ferromagnetic phase is found to first increase with Co concentration (up to 5%) and then decrease. It is also found to decrease with increase in sintering temperature up to 800°C; there after it remains unaffected till 1000°C. The d-d band transitions in the optical spectrum confirm that Co2+ substitutes Zn2+ in the ZnO lattice. A plausible explanation of the observed ferromagnetic ordering is presented in terms of Bound Magnetic Polarons model.
Magnetic Properties of ZnO:Ni Aerogel Nanopowders: Effect of Thermal Treatments
Authors: El Mir Lassaad , von Bardeleben H.Jurgen , Saadoun M , Ben Mahmoud Aroussi , Cantin Jean-Louis
Published: April 2011

We report the elaboration of Ni doped ZnO nanoparticles prepared by a sol-gel processing technique. In our approach the water for hydrolyse was slowly released by esterification of the metal acetate with methanol followed by a supercritical drying in ethyl alcohol. Doping concentrations between 5 and 25 at% have been investigated. In the as-prepared state the powders with an average particle size of 30nm present ferromagnetic properties; thermal annealing in the 500°C to 700°C temperature range in air or oxygen modifies the magnetic properties. We ascribe the observed ferromagnetism to the presence and transformation of Ni based secondary phases.
Transport Properties and Conduction Band Offset of n-ZnO/n-6H-SiC Heterostructures
Authors: Alivov Yahya , Bo Xiao , Qian Fan , Johnstone Daniel , Litton Cole , Morkoç Hadis
Published: April 2011

The conduction band offset of n-ZnO/n-6H-SiC heterostructures fabricated by rf-sputtered ZnO on commercial n-type 6H-SiC substrates has been measured. Temperature dependent current-voltage characteristics, photocapacitance, and deep level transient spectroscopy measurements showed the conduction band offsets to be 1.25 eV, 1.1 eV, and 1.22 eV, respectively.
Influence of Annealing Temperature on ZnO Thin Films Prepared by Single and Multi-step Sol-gel Processes
Authors: Kelly Koh Lee Huat , O'Brien Shane , Lovera Pierre , Redmond Gareth , Crean Gabriel M
Published: April 2011

ZnO thin films were prepared on borosilicate glass from both single- and multi- step coating deposition of a sol-gel prepared with anhydrous zinc acetate [Zn(C2H3O2)2], monoethanolamine [H2NC2H4OH ] and isopropanol. ZnO films prepared over a range of zinc acetate concentrations, for a fixed annealing temperature, showed that sol-gels prepared with a 0.3M zinc acetate concentration resulted in the formation of films with the greatest degree of c-axis orientation. In this study, a detailed investigation of the influence of process annealing temperature over the range 450 – 550°C on the microstructural, physical, electronic and optical properties of these single and multi-step ZnO thin films around this 0.3M zinc concentration set point is presented. X-ray analysis showed that all single-step deposition thin films were preferentially orientated along the [002] c-axis direction of the crystal. In contrast, only the multi-layer film annealed at 550°C showed similar preferential orientation. All single step deposited films showed a similar average optical transmittance above 87%, independent of annealing temperature. The transmittance of the multi-step films was shown to be strongly correlated to the degree of c-axis orientation. The optical band-gap energy was evaluated to be 3.298 – 3.316 eV for all samples. The photoluminescence spectra of the single layer ZnO films showed a strong emission centred at ca. 405 nm, which blue shifted with increasing annealing temperature. The multi-layer ZnO samples emitted throughout the UV and the visible range, with the samples prepared at 500 and 550°C showing the expected ZnO emission peak at 380 nm. Despite being thicker, the emission from the multi- layer samples was less than measured for the single layer samples. The effect of sol-gel annealing temperature and deposition process on film microstructure, morphology, electrical resistivity and optical transparency is detailed.
The Impact of Hydrogen Plasma Treatments at Moderate Temperatures on Sintered Zinc Oxide Samples - Evidence for Hydrogen Induced Nano-Void Formation
Authors: Job Reinhart
Published: April 2011

Using μ-Raman spectroscopy (μRS) analyses, the impact of hydrogen plasma treatments on sintered zinc oxide (ZnO) samples was investigated. H-plasma exposures (150 W, 13.56 MHz) were carried out for 1 hour at substrate temperatures between 250 °C and 500 °C. μRS reveals that plasma hydrogenated ZnO samples are more defective than non-treated ones. On one hand non-specified defect species are created with a maximal density upon plasma hydrogenation at 350 °C, on the other hand the formation of oxygen vacancies (VO) can be traced. The density of VO defects, appearing upon H-plasma exposure, is not significantly correlated to the applied substrate temperatures. μRS also reveals vibration modes of H2 molecules trapped in nano-voids. The μRS results indicate that those nano-voids are created by the coalescence of VO defects.
Investigation of Nitrogen Induced closely coupled Sb based Quantum Dots for Infrared Sensors Application
Authors: Kim Seongsin M , Hatami Fariba , Yuen Homan B , Harris James S
Published: April 2011

We report the growth and structural properties of InSb and InSb:N quantum dots on InAs and GaAs substrates. Strain induced, self-assembled quantum dots are grown using solid-source molecular beam epitaxy. For improved growth control, we developed a growth technique similar to atomic layer epitaxial methods. InSb and InSb:N multiple quantum dots formed on both InAs and GaAs. We explain the formation of multiple quantum dots by the anisotropic distribution of strain energy within the quantum dot, the long adatom lifetime during atomic layer epitaxy, and the low bond energy of InSb. Nitrogen incorporation during formation of quantum dots changes surface energy barrier and causes anisotropic distribution of strain energy, results in formation of closely coupled multiple quantum dots in <110> orientation. We obtained mid infrared luminescence around 3.6 μm from InNSb QDs grown on InAs substrate, where it exhibits relatively low efficiencies of nitrogen incorporation compared to the quantum well structure.
A Voltage-Tunable Two-Color InGaAs/AlGaAs Quantum well Infrared Photodetector
Authors: Passmore Brandon , Liang Jie , Zhuang Da , Manasreh Omar , Kunets Vasyl , Salamo Greg
Published: April 2011

A voltage-tunable two-color multiple quantum well infrared photodetector was fabricated with two bands at 6.0 and 10.3 ìm. The molecular beam epitaxy grown structure consists of two stacks of n-type InGaAs wells and GaAs/AlGaAs superlattice barriers. The 6.0 ìm band was found to be dominant at low bias voltages while the 10.3 ìm band is dominant at high bias voltages. The optical absorption measurements confirm the presence of both bands. Furthermore, the transfer matrix method is used to estimate the peak position energies of the intersubband transitions in the two stacks.
Synthesis and Electronic Application of Germanium Nanocrystals in Silicon Oxide Matrix
Authors: Choi Wee Kiong , Chim Wai Kin , Chew Han Guan
Published: April 2011

The size of germanium (Ge) nanocrystals in a trilayer memory device structure was controlled by varying the thickness of the middle co-sputtered Ge plus silicon oxide layer. Such confinement of nanocrystals was not effective in a trilayer structure with a pure Ge middle layer. Significant diffusion of Ge atoms through the tunnel oxide or rapid thermal oxide (RTO) layer and into the silicon substrate was observed when the RTO layer thickness of the trilayer structure was reduced. This resulted in no (or very few) nanocrystals formed in the system. A higher charge storage capability was obtained from devices with a thinner RTO layer.
Temperature Dependence of Optical Transitions of One Dimensional InGaAs/GaAs Quantum Structures
Authors: Ma Zhixun , Holden Todd , Wang Zhiming , Mao Samuel S. , Salomo Gregory J.
Published: April 2011

We have studied the temperature dependence of CER spectra of layered InGaAs QWRs and QDCs and found strain-induced splitting of lh and hh states occur in both InGsAs and GaAs layers. By fitting experimental data using Varshni law and Bose-Einstein type relation, various parameters are obtained, which are similar to those of bulk GaAs. We pointed out that a caution must be excised when extracting the electron-phonon interaction parameters by subtracting the thermal dilation part from the experimental data of the embedded semiconductor microstructures because in these structures the temperature-induced lattice-dilation may produce additional strain besides the lattice mismatch.
Vertically self-organized gold nanoparticles in amorphous alumina matrices
Authors: Jin Chunming , Zhou Honghui , Wei Wei , Narayan Roger J.
Published: April 2011

In this study, self-organized growth of gold nanoparticles dispersed in amorphous alumina matrices was investigated. Au/Al2O3 multilayered structures were grown on silicon (001) substrates using pulsed laser deposition. Vertical ordering of particles was examined with cross-sectional transmission electron microscopy and image Fourier transformation. Self-organization of gold nanoparticles along the vertical direction was observed in the samples grown at room temperature and 320 °C. This process occurred through two-different growth modes, known as top-on-top growth and top-on-middle growth. The driving force for the vertical ordering was attributed to long-range elastic interactions among nanoparticles during the film deposition process.
Defects Study in Gold Surfaces produced by Ion Bombardment
Authors: Carrasco Esther , de la Fuente O. Rodríguez , Rojo J.M. , García M.A. , de Julián C.
Published: April 2011

We present new experimental results regarding the surface defect structure of ion bombarded gold surfaces. We report annealing mechanisms of surface defects on reconstructed Au(001) after medium fluence ion bombardment. We show how (001) and (111) gold surfaces can be nanostructured with a certain degree of lateral order by means of high fluence and high flux ion irradiation. We prove that ion irradiation nanostructuring strongly changes optical (plasmonic) properties of gold polycrystalline thin films.
Effects of P Content on Morphology of Nanocrystals Induced by FIB Irradiation in Ni-P Amorphous Alloy
Authors: Sato Koji , Ishiyama Chiemi , Sone Masato , Higo Yakichi
Published: April 2011

We studied the effects of phosphorus (P) on Ni nanocrystalline morphology formed by focused ion beam (FIB) irradiation for Ni-P amorphous alloy thin films. The P content in the amorphous alloy was varied from 8 to 12 wt.%. The nanocrystals induced by the FIB irradiation for Ni-11.8, 8.9, 7.9 wt.% amorphous alloy had an f.c.c. structure and showed unique crystallographic orientation relationships to the geometry of the focused ion beam, that is, {111}f.c.c. parallel to the irradiated plane and <110>f.c.c. parallel to the projected ion beam direction, respectively. The Ni nanocrystals precipitated like aggregates with decreasing of the P content. These results represent that the P content does not affect crystallographic orientation relationships, while influences the precipitation distribution of Ni nanocrystals generated by the FIB irradiation.