bluuebunny/crossref_metadata_2025_split huggingface dataset:
Nanogap Capacitors Used for Impedance Characterization of Living Cells
Authors: Padmaraj Divya , Zagozdzon-Wosik Wanda , Miller John H. , Charlson Joe , Trombetta Len 
Published: April 2011

ABSTRACTNano-gap metal oxide semiconductor (MOS) capacitors were studied to evaluate their limitations in applications of dielectric spectroscopy in living cells. The purpose was to optimize the design of a transducer to avoid interfacial polarization at the electrodes. Silicon IC technology was selected for designing processes in which we could limit electric double layer impedance by precisely controlling dielectric thickness of the capacitors in the range of 17 to 150 nm. The working capacitance was defined by lateral oxide etching of capacitor structures of various configuration to ensure high perimeter to area ratio. Highly doped n+ polysilicon and n+ implanted Si substrate were acting as capacitor's electrodes. Restrictions known from CMOS circuits regarding oxide leakage current, which depends on geometry and increases with the gate area were taken into account. To allow for testing cells (yeasts), which have larger dimensions than nano structures it was necessary to include cell manipulation using dielectrophoresis (DEP). Entrapment of cells at the electrode perimeter preceded electrical measurements. Our focus in analyses was on the frequency dependence of impedance parameters.
Optical Properties of Zn0.46Cd0.54Se/Zn0.24Cd0.25Mg0.51Se Multiple Quantum Wells for Infrared Photodetector Applications
Authors: Zhou Xuecong , Zhang Shengkun , Lu Hong , Shen Aidong , Wang Wubao , Song Chunying , Liu Huichun , Das Bidyut B. , Okoye Nicky , Tamargo Maria C. , Alfano Robert R. 
Published: April 2011

ABSTRACTRecently, lattice-matched Zn0.46Cd0.54Se/ZnCdMgSe multiple-quantum-wells (MQWs) have been recognized as very promising materials to fabricate intersubband (ISB) devices such as quantum cascade lasers and mid-infrared photoconductors. These structures have important applications in biological and chemical detections. The ISB transition covers a wide mid-infrared wavelength range from 1.3 μm to a few tens of μm.In this work, two heavily doped n-Zn0.46Cd0.54Se/Zn0.24Cd0.25Mg0.51Se MQW structures have been grown on InP (001) substrate by molecular beam epitaxy. Temperature dependent steady-state photoluminescence (SSPL), temperature dependent time- resolved photoluminescence (TRPL), and Fourier transform infrared spectroscopy (FTIR) were performed to characterize their interband and ISB properties. These two MQW samples have similar structures except different well widths and different number of periods. The integrated SSPL intensities and the PL decay times of the MQWs were measured as functions of temperature in the range from 77 K to 290 K. The luminescence efficiency of the sample with 28 Å well width is larger than that of the sample with 42 Å well width although both samples exhibit similar temperature dependence of PL intensity. Time-resolved PL measurements show that the PL decay times of both samples decrease with increasing temperature. From 77 K to 290 K, the decay time of the sample with 28 Å well width is in the range of 440 ps ∼ 120 ps and is much longer than that of the sample with 42 Å well width, which is in the range of 65 ps ∼ 25 ps. Strong non-radiative recombinations dominate the luminescence behavior of the wider MQWs. Intersubband absorption spectra of the samples were measured by FTIR and show peak absorption at wavelengths of 3.99 μm and 5.35 μm for the MQWs with well widths of 28 Å and 42 Å, respectively, falling within the 3-5 Åm range, which is of great interest for the infrared photodetector applications.
Searching for Smart Durable Coatings to Promote Bone Marrow Stromal Cell Growth While Preventing Biofilm Formation
Authors: Namavar Fereydoon , Jackson John D. , Sharp J. Graham , Mann Ethan E. , Bayles Kenneth , Cheung Barry Chin Li , Feschuk Connie A , Varma Shailaja , Haider Hani , Garvin Kevin L. 
Published: April 2011

ABSTRACTThere is a great need to develop methods to regulate cellular growth in order to enhance or prevent cell proliferation as needed, to either improve health or prevent disease. In this work we evaluated the adhesion, survival and growth of bone marrow stromal cells on the surface of several new ion beam engineered nano-crystals of ceramic hard coatings such as zirconium, titanium, tantalum and cerium oxides. Cell adhesion and growth on the ceramic coatings were compared to adhesion and growth on a nano-crystalline silver coating which is known to possess antibacterial properties. The initial results of a study to determine the effect of nanocrystalline titanium and silver coating onstaphylococcus aureusbiofilm growth is also discussed.
Drop-by-drop Polymer Deposition by Acoustic Picoliter Droplet Generators for Applications in Semiconductor Industry and Biotechnology
Authors: Lee Grace C. , Cohen Jeremiah R , Demirci Utkan 
Published: April 2011

ABSTRACTPhotoresist droplets are ejected onto a wafer surface by an acoustic two dimensional micromachined ejector array. The spread of single droplets on a silicon wafer surface at varying droplet speeds is studied. Series of photoresist droplets are printed periodically drop-on-demand on a silicon wafer surface and profiles of a single droplet and two droplets overlapping with varying distances of 25 μm and 1 μm on a silicon wafer are demonstrated. Moreover, 3.4 μm thick spinless full coverage of a 4 inch wafer with photoresist is demonstrated which indicates a potential for coating wafers in less than a few seconds.
Al rich AlN/AlGaN Quantum Wells
Authors: Al tahtamouni Talal Mohammed Ahmad , Nepal Neeraj , Lin Jingyu , Jiang Hongxing 
Published: April 2011

ABSTRACTTwo sets of AlN/AlxGa1−xN quantum wells (QW) have been grown by metalorganic chemical vapor deposition (MOCVD). The first set consists of five samples of AlN/AlxGa1−xN QWs with (x ∼ 0.65) with well width, Lw, varying from 1 to 3 nm. The second set consists of four samples of AlN/AlxGa1−xN with (Lw = 1.5 nm) with Al composition, x, varying from 0.70 to 0.85. Low temperature photoluminescence (PL) spectroscopy has been employed to study the Lw dependence of the PL spectral peak position, emission efficiency, and line width. Our results have shown that these AlN/AlGaN QW structures exhibit polarization fields of ∼ 4 MV/cm. Due to effects of quantum confinement and polarization fields, AlN/AlGaN QWs with Lw between 2 and 2.5 nm exhibit the highest quantum efficiency. The dependence of the emission linewidth on Lw yielded a linear relationship. The implications of our results on deep ultraviolet (UV) optoelectronic device applications are also discussed.
Strain-free Low-defect-density Bulk GaN with Nonpolar Orientations
Authors: Paskova Tanya , Paskov Plamen P. , Darakchieva Vanya , Kroeger Roland , Hommel Detlef , Monemar Bo , Lourdudoss Sebastian , Preble Edward , Hanser Andrew , Williams Mark N. , Tutor Michael 
Published: April 2011

ABSTRACTBulk GaN sliced in bars along (11-20) and (1-100) planes from a boule grown in the [0001] direction by HVPE was confirmed as strain free material with a low dislocation density by using several characterization techniques. The high-structural quality of the material allows photoluminescence studies of free excitons, principal donor bound excitons and their two-electron satellites with regard to the optical selection rules. Raman scattering study of the bulk GaN with nonpolar orientations allows a direct access to the active phonon modes and a direct determination of their strain-free positions.
Study of Defects in p-type Layers in III-nitride Laser Diode Structures Grown by Molecular Beam Epitaxy
Authors: Xiu Huixin , Costa Pedro MFJ , Kauer Matthias , Smeeton Tim M , Hooper Stewart E , Heffernan Jonathan , Humphreys Colin J 
Published: April 2011

ABSTRACTThis paper reports on the study of defects in p-type layers in III-nitride laser structures grown by molecular beam epitaxy. Characterization of the heterostructures was carried out using atomic force microscopy and transmission electron microscopy. The results show that a high density of extended defects – possibly inversion domains – exist in the p-type cladding layers of as-grown structures with either AlGaN/GaN superlattices or bulk AlGaN cladding layers. TEM analysis of operated and aged devices does not reveal any significant structural modification of the p-type material which might be the cause of deterioration in the lasing performance or failure.
Ultraviolet light emitting diodes using non-polar A-plane AlGaN multiple quantum wells
Authors: Chandrasekaran Ramya , Bhattacharyya Anirban , France Ryan , Thomidis Christos , Williams Adrian , Moustakas Theodore 
Published: April 2011

ABSTRACTIn this paper, we report the growth and fabrication of non-polar A-plane AlGaN multiple quantum well based ultraviolet light emitting diodes (UV-LEDs). The LEDs were grown on R-plane sapphire substrates using molecular beam epitaxy (MBE). The Current-voltage characteristics of the fabricated devices demonstrated rectifying behavior with a series resistance of 38 ohms. An electro-luminescence emission at 338 nm was obtained.
Low-dislocation-density Nonpolar AlN Grown on 4H-SiC (11-20) Substrates
Authors: Suda Jun , Horita Masahiro , Kimoto Tsunenobu 
Published: April 2011

ABSTRACTGrowth of AlN on 4H-SiC (11-20) substrates by plasma-assisted molecular-beam epitaxy is presented. Very high-quality AlN can be grown under a slightly Al-rich condition. Transmission electron microscopy revealed that the AlN layer has 4H crystalline structure with high-phase purity (stacking-fault density is 5×106cm−1) and the density of threading dislocations is as small as 8×107cm−2.
Optical Transmission Measurements on MOCVD Grown GaMnN Films on Sapphire
Authors: Arkun Fevzi Erdem , El-Masry Nadia A , Muth John , Zhang Xiyao , Mahrouse Amr , Zavada John , Bedair Salah M 
Published: April 2011

ABSTRACTWe demonstrate optical transmission measurements performed on 1.2 μm thick GaMnN films grown by metalorganic chemical vapor deposition on (0001) sapphire substrates. According to the data acquired from these measurements, Mn forms a deep acceptor band at 1.4 eV above the valance band of GaMnN. Full width at half maximum of this absorption band increases from 107 meV to 198meV as the Mn concentration increases from 0.3% to 1.6 %; which indicates that this band becomes wider as the concentration of Mn increases in the lattice. A broad absorption band starting at 1.9eV and extending to the band edge of GaMnN was also determined. This was attributed to the transition from the Mn energy band to the conduction band edge of GaMnN. Absorption at both of these bands scales with the Mn concentration and thickness of the films. The effect of co-doping of GaMnN films with magnesium on the transmission spectra was also investigated. The absorption band initially observed at 1.4 eV was shifted to 1.6 eV as a result of introduction of Magnesium into the lattice of GaMnN. From these results we conclude that Mn is incorporated in the lattice and forms an energy band in the bandgap of GaMnN. The width of this energy band is also a function of the Mn concentration in GaMnN.
Wet Etching of Bulk AlN Crystals
Authors: Zhuang Dejin , Herro Ziad G. , Li Xianglin , Schlesser Raoul , Sitar Zlatko 
Published: April 2011

ABSTRACTAlN bulk crystals of different crystallographic orientations were etched in aqueous KOH solution (general etchant) and molten KOH/NaOH eutectic alloy (defect selective etchant). In the general etchant, the aluminum polar surface (0001) was found to be stable while the nitrogen polar (0001) surface and non-polar m-plane (1010) surfaces showed significant etching. Etch patterns on nitrogen polar surfaces consisted of complete coverage of hexagonal pyramids while the m-plane surfaces were etched in a layer-by-layer mode. TEM studies revealed that the observed etch hillocks on nitrogen polar surfaces were not associated with extended structural defects. When etched in a defect-selective etchant, the aluminum polar surface showed well-defined hexagonal etch pits, with an etch pit density (EPD) of 2×104 cm−2. The nitrogen polar surfaces and m-plane surfaces showed etch features similar to the one obtained during general etching, however, the etch feature density was significantly lower. The etch mechanisms, etch kinetics, as well as the correlation between the observed etch features and structural defects in bulk crystals will be discussed.
Compound-source Molecular Beam Epitaxy of GaN on Si at Low Temperature Using GaN Powder and Ammonia as Sources
Authors: Honda Tohru , Sawada Masaru , Yamamoto Hiromi , Sawadaishi Masashi 
Published: April 2011

ABSTRACTLow-temperature growth of GaN is very attracting for the application to light emitting devices grown on Si substrates because it prevents the melt-back reaction between Ga and Si substrates. The low-temperature growth of GaN by compound-source molecular beam epitaxy (CS-MBE) has been reported. In the previous report, GaN powders were used as a source and no additional nitrogen source was introduced during the growth. At present, its growth mechanism is unclear. In this paper, CS-MBE of GaN layers using GaN and ammonia as sources is discussed. Especially, the reduction of excess Ga in GaN layers by introducing ammonia supply is discussed based on their refraction high-energy electron diffraction (RHEED) patterns and x-ray photoelectron spectroscopy (XPS) spectra.
Investigation of Low Angle Grain Boundaries in Hexagonal Silicon Carbide
Authors: Chen Yi , Chen Hui , Zhang Ning , Dudley Michael , Ma Ronghui 
Published: April 2011

ABSTRACTInteraction between basal plane dislocations and single or well-spaced threading dislocations is discussed based on synchrotron white beam X-ray topographic studies carried out on physical vapor transport grown hexagonal silicon carbide single crystals. The basal plane dislocations are able to cut through single or well-spaced threading edge dislocations even if the formation of kinks/jogs is energetically unfavorable while threading screw dislocations were mostly observed to act as effective pinning points. However, basal plane dislocations can sometimes cut through a threading screw dislocation, forming a superjog and which subsequently migrates on the prismatic plane via a cross-slip process. Threading edge dislocation walls act as obstacles for the glide of basal plane dislocations and the mechanism by which this occurs is discussed. The character of low angle grain boundaries and their dislocation content are discussed.
MBE Growth of Cubic InN
Authors: Schörmann Jörg , As Donat Josef , Lischka Klaus 
Published: April 2011

ABSTRACTCubic InN films were grown on top of a c-GaN buffer layer by rf-plasma assisted MBE at different growth temperatures. X-Ray diffraction investigations show that the c-InN layers consist of a nearly phase-pure zinc blende (cubic) structure with a small fraction of the wurtzite (hexagonal) phase grown on the (111) facets of the cubic layer. The content of hexagonal inclusions is decreasing with decreasing growth temperature. The full-width at half-maximum (FWHM) of c-InN (002) rocking curve is about 50 arcmin. Low temperature photoluminescence measurements reveal a band gap of about 0.61eV for cubic InN.
High Resolution Transmission Electron Microscopy Study of Thermal Oxidation of Single Crystalline Aluminum Nitride
Authors: Chaudhuri Jharna , Lee Rac Gyu , Nyakiti Luke Owuor , Gu Zheng , Edgar James H , Li Peng 
Published: April 2011

ABSTRACTThe impact of process conditions and crystal properties on the structure of thermal oxides formed on AlN were determined by high resolution transmission electron microscopy (HRTEM). Oxidation for 2 hours at both 800 ° and 1000 °C produced mostly amorphous oxide layers whereas oxidation for 4 and 6 hours at 1000 °C produced partly crystalline and epitaxial oxide layers. The crystalline oxide was mostly single phase á-Al2O3 except at the surface where it was a mixture of γ-Al2O3 and á-Al2O3. The amorphous oxide layer first transformed to γ-Al2O3 and then to the stable á-Al2O3 as evidenced by the non-uniform thickness of the oxide and the existence of the γ-Al2O3 at the surface. The AlN crystal contained a high density of defects at the interface at 800 °C but it was nearly defect- and oxygen-free at 1000 °C. This could be due to the rapid diffusion of the nitrogen and aluminum interstitials at high temperatures leading to a point defect equilibrium throughout the nitride. A faceted interface between Al2O3 and AlN could be attributed to non-uniform out diffusion of aluminum.
A Study of Defects and Surface Properties in AlGaN/GaN High Electron Mobility Transistors (HEMTs) Grown by MOCVD on Semi-Insulating SiC Substrates
Authors: Sin Yongkun , Kim Hyun I , Adams Paul , Stupian Gary 
Published: April 2011

ABSTRACTAlGaN/GaN HEMTs (High Electron Mobility Transistors) grown on semi-insulating (SI) SiC substrates are very promising for high power, high speed, and high temperature operation with great potential for both military and commercial applications. These high performance characteristics are possible due to presence of high two-dimensional electron gas (2 DEG) charge sheet density maintaining a high Hall mobility at the AlGaN barrier/GaN buffer hetero-interface. However, reliability of AlGaN HEMTs still remains a major concern because of the large number of defects and traps present both in the bulk as well as at the surface leading to current collapse. We report on the study of defects and surface properties in MOCVD-grown Al0.27Ga0.73N HEMT structures on SI SiC substrates. Our HEMT structures consist of a 25nm thick undoped AlGaN barrier layer and a 3μm thick undoped GaN buffer layer grown on a 100nm thick AlN nucleation layer. Hall measurements showed a charge sheet density of ∼1013/cm2 and a Hall mobility of ∼1500cm2/V·sec. Both cross-sectional and plan view TEMs were employed to study defects in the heterostructures and XPS (X-ray Photoelectron Spectroscopy) and AES (Auger Electron Spectroscopy) employed to study surface properties in both GaN and AlGaN layers. DC characterization results from AlGaN Schottky diodes with Pt/Au Schottky contacts are also reported along with results from AlGaN/GaN HEMT devices.
Piezoelectric Fields in Tilted GaInN Quantum Wells
Authors: Feneberg Martin , Lipski Frank , Sauer Rolf , Thonke Klaus , Wunderer Thomas , Brückner Peter , Scholz Ferdinand 
Published: April 2011

ABSTRACTGaInN/GaN quantum wells (QWs) grown on different crystal facets have been investigated by field-dependent photoluminescence and electroluminescence experiments. Externally applied voltage changes the total field strength and direction of the electric fields inside the quantum wells, consisting of piezoelectric and built-in fields. Electroluminescence with increasing current results in a peak shift due to screening of the field by the injected carriers. By modeling the peak shifts of the photoluminescence (PL) and electroluminescence (EL) signals we found strong piezoelectric fields for a {0001} sample and nearly vanishing fields for a sample grown on the {1-101} plane of GaN.
Optical Properties of Undoped, n-Doped and p-Doped GaN/AlN Superlattices
Authors: Paskov Plamen , Monemar Bo , Kamyiama Satoshi , Amano Hiroshi , Akasaki Isamu 
Published: April 2011

ABSTRACTWe report a photoluminescence study of near-surface GaN/AlN superlattices grown by metalorganic chemical vapor deposition (MOCVD) on a thick GaN layer. Undoped, Si-doped and Mg-doped structures with the well/barrier thickness ratio 3:1 and different periods are investigated. It is found that the energy position, intensity and linewidth of the emission are determined by the interplay of the built-in polarization field, depletion field and screening by the free carriers. In n-type structures an electron accumulation at the bottom interface is evidenced by the observed recombination of the two-electron gas with the photo-excited holes.
Phonon Decay in GaN and AlN and Self-Heating in III-N Devices
Authors: Holtz Mark , Song D. Y. , Nikishin S. A. , Soukhoveev V. , Usikov A. , Dmitriev V. , Mokhov E. , Makarov U. , Helava H. 
Published: April 2011

ABSTRACTWe report studies of the temperature dependence of Raman lines in high quality GaN and AlN. The temperature dependence of the phonon energies and linewidths are used to produce consistent phonon decay properties of zone center optic phonons. In GaN we observe the E22 phonon to decay into three phonons, while the A1(LO) phonon is well described according to the so-called Ridley process – one TO and one LA phonon. For AlN the E22 phonon decays by two phonon emission and the A1(LO) line also exhibits a dependence consistent with the Ridley process. Along with the phonon decay processes, it is important in each case to take into account the contribution of the thermal expansion, including the temperature dependence, to describe observed temperature shifts in the phonon properties.
1.37 - 2.90 Micron Intersubband Transitions in GaN/AlN Superlattices
Authors: DeCuir Eric Anthony , Fred Emil , Manasreh Omar , Xie Jinqiao , Morkoc Hadis , Baumann Esther , Hofstetter Daniel 
Published: April 2011

ABSTRACTIntersubband transitions in the spectral range of 1.37-2.90 °Cm is observed in molecular beam epitaxy grown Si-doped GaN/AlN multiple quantum wells using a Fourier-transform spectroscopy technique. A blue shift in the peak position of the intersubband transition is observed as the well width is decreased. A sample with a well width in the order of 2.4 nm exhibited the presence of three bound states in the GaN well. The bound state energy levels are calculated using a transfer matrix method. An electrochemical capacitance voltage technique is used to obtain the three dimensional carrier concentrations in these samples which further enable the calculation of the Fermi energy level position. Devices fabricated from these GaN/AlN quantum wells are found to operate in the photovoltaic mode.
Evaluation on Crystal and Optical Properties of AlN:Er Prepared by RF magnetron sputtering method
Authors: Uekusa Shin-ichiro , Ohno Takahiko , Arai Tomoyuki , Miura Hiroshi 
Published: April 2011

ABSTRACTThe Er that is rare earth element causes luminescence at 1540 nm, which is a low loss transmission window in silica-based fibers used in optical communications. Moreover, it is known that the temperature quenching of the luminescence of Er becomes smaller with the wide band gap of the host material. We report on the photoluminescence (PL) characteristic and X-ray diffraction (XRD) of AlN:Er thin films which are deposited by RF reactive magnetron co-sputtering method. All the thin films were deposited by RF reactive magnetron co-sputtering method from a 99.999 % Al target and 99.99 % Er chips in a nitrogen gas (99.9998 %) atmosphere. The thin films were achieved with a discharge power of 250 W in a total pressure of 5.0∼10-3 Torr, and the deposition times were one hour. After the deposited, these samples were annealed for 30 minutes in the temperature range from 400 to 900° in a nitrogen gas (99.999 %) atmosphere with an infrared lamp heater. PL spectra of AlN:Er were measured using the 325 nm line of a He-Cd laser at 15 K. Consequently, we observed PL spectra around 1500 nm. The strong luminescence of peak wavelength at 1538 nm is based on the intra-4f emitting centers of Er. We report systematically the experimental results of PL and XRD.