bluuebunny/crossref_metadata_2025_split huggingface dataset:
Magnetic and Transport Properties of Micron Size Magnetic Participate Arrays Fabricated on a 2D Superconducting Nb Films and Sub-Micron Magnetic Wires
Authors: Otani Yoshichika , Fukamichi Kazuaki , Kitakarni Osamu , Shimada Yutaka , Pannetier Bemard , Nozieres Jean-Pierre , Matsuda Tsuyoshi , Tonomura Akira 
Published: April 2011

ABSTRACTMicron size particulate arrays of amorphous R-Co (R = Sm and Gd) alloys with a thickness of 200 nm were fabricated on top of a 20 nm thick Nb film by means of e-beam lithography and sputter deposition. The arrays consist of 2 × 2 μm2 square particles with a spatial periodicity of 4 μm along an edge of the square. Interesting oscillations due to the fluxoid quantization were observed both in the transition lines and the magnetization curves of the underlying Nb film. The superconducting state of the Nb film was found to be modulated by stray fields of the square magnetic particles.Sub-micron size ferromagnetic Fe wires were also prepared in order to investigate the magnetoresistance effect associated with pinning and depinning processes of a magnetic domain wall confined in the wire. Low temperature transport, Lorentz microscopy and electron holography measurements demonstrated a clear change in resistivity associated with the depinning of a pinned single domain wall.
Mocvd of Cu on Teflon-AF and Alumina-Modified Teflon-AF
Authors: Martini D. , Sutcliffe R. , Kelber J. 
Published: April 2011

AbstractXPS studies of Cu(I)hfac(COD)adsorbed on clean and alumina-modified Teflon-AF surfaces show that on the clean polymer surface, Cu(0) formation occurs between 300 K and 600 K in UHV. The corresponding reduction is hindered by the presence of an alumina adlayer. In addition, the Cu Auger kinetic energies indicate the formation of nanoparticles on the alumina surface at both 300 K and 600 K. Annealing from 300 K to 600 K results in a ∼4 eV shift of the Cu(2p) transitions to higher binding energies. These facts indicate that the Cu precursor reacts with the alumina surface and results in limited mobility and hindered Cu(I) to Cu(0) reduction on the modified polymer surface.
Cross-Sectional Tem Sample Preparation of Phase-Change Optical Disk by Ion Milling
Authors: Kouzaki T. , Yoshioka K. , Ohno E. 
Published: April 2011

AbstractIt is very difficult to prepare cross-sectional TEM samples for phase-change optical disks by conventional argon ion milling because of the difference of ion milling rates between multilayers and the polymer substrate. We have been successful in preparing samples of those optical disks by ion milling method with dissolution of the polymer substrate in advance. The cross-sectional structure was observed more clearly in this method rather than in ultramicrotome method.
A Novel Sample Design for Easier X-Tem Specimen Preparation of Surface Coated Hardened High Speed Steel
Authors: Østergaard Klaus F. , Mørch K. A. 
Published: April 2011

AbstractA novel design of test sample for X-TEM specimen preparation is presented. The test sample is particurlarly suited for surface coatings on hardened steel (heat treated materials). The technique for cutting and preparation of a specimen from the test sample is given in some detail and a few hints about ion thinning and X-TEM analysis are included.
Grain Refinement in Undercooled Metals
Authors: Xiao J. Z. , Yang H. , Kui H. W. 
Published: April 2011

ABSTRACTRecently, it was demonstrated that grain refinement in metals can take place through two mechanisms, namely, dynamic nucleation and remelting of initially formed dendrites. In this study, it was found that Ni99.45B0.55 undergoes grain refinement, both by dynamic nucleation or by remelting, depending on the initial bulk undercooling just before crystallization. The nature of the grain refinement process is confirmed by microstructural analysis of the undercooled specimens.
A Possible Mechanism For Atomic Transport in Amorphous Metals
Authors: Van Ee Leon D. , Tthijsse Barend J. , Sietsma Jilt 
Published: April 2011

ABSTRACTThe diffusion process at a temperature just below the glass-transition temperature is studied in a computer model of amorphous Ni81B19. The observed diffusion events cause structural changes that are highly localized and are correlated with low-frequency localized vibrational modes. The excitation of such a mode can result in a “jump”, which is identical to the diffusion event. The jump has a cooperative character involving some tens of atoms and can be of a reversible or of an irreversible nature.
Onion-Like Nanoscale Structures and Fullerene-Type Cages Formed by Electron Irradiation of Turbostratic Bx.C1-x (x<0.2)
Authors: Golberg D. , Bando Y. , Kurashima K. , Sasaki T. 
Published: April 2011

ABSTRACTFlakes of CVD grown BxC1-x, (x<0.2) films were exposed to intense electron irradiation (flux density up to ∼100 A/cm2) in a 300 kV high resolution electron microscope equipped with a field emission gun. The starting flakes revealed a turbostratic BxC1-x structure. The composition of the starting materials and irradiated products was determined by using electron energy loss spectroscopy (EELS). Depending on the electron dose applied, irradiation of the turbostratic material led to formation of soap-bubble-like irregularly-shaped objects (linear dimensions of ∼2–5 nm), onion- and semi-onion-like structures (d∼10nm), nested fullerenes (3–14 shells) and elementary fullerene-type cages (d∼0.7 nm). It is thought that these curled and closed nanostructures arise from a continuous bending of the hexagonal Bx C1-x sheets under electron irradiation. Finally, some possible structural models of BxC1-x fullerenes are considered.
In-Situ TEM Phase Formation in Cold Rolled Aluminum-Nickel Multilayers
Authors: Sieber H. , Perepezko J. H. 
Published: April 2011

ABSTRACTMultilayer samples of Nickel and Aluminum with an overall composition of Al-20Ni were prepared by cold rolling of elemental foils. The sample microstructures and phases were characterized by XRD, SEM and TEM/SAED, and the reactive phase formation was then examined by DSC measurements. XRD, SEM and TEM measurements show that the rolling procedure results in a decrease of the Al and Ni layer thicknesses (down to 100 nm in average) and a decrease of the grain size (down to less than 50 nm). No phase formation is observed during the cold rolling procedure. In isochronal DSC scans of the Al-Ni multilayers, the formation of the Al3Ni phase was found to be a two step reaction process due to 2-dimensional nucleation and lateral growth and a 3-dimensional phase thickening. While XRD measurements showed Al3Ni as the only phase that forms, more detailed TEM investigations of the samples after DSC treatment also showed a small amount of an amorphous Al-Ni phase, formed by a thermally activated solid state amorphization reaction (SSAR). In-situ TEM heating of the amorphous areas under the electron beam in the microscope yielded the crystallization of the amorphous phase to a B2 structure and a growth of the B2 grains up to 100 nm in size.
Multiwafer Movpe of III-Nitride Films for Led and Laser Applications
Authors: Beccard R. , Schoen O. , Schineller B. , Schmitz D. , Heuken M. , Juergensen H. 
Published: April 2011

AbstractProcess for mass production of GaN and its related alloys, InGaN and AlGaN, have been optimized to achieve high device yield and low cost of ownership. Here we present some of the latest results obtained from AIX 2000 HT Planetary Reactor® in a configuration of 7×2” which provides unique uniformity capabilities due to the two fold rotation of the substrates. GaiN single layers with background electron concentrations below 5·1016 cm-3 and intended doping levels up to 1018 cm-3 p-type and 1020 cm-3 n-type with state of the art homogeneities have been achieved. Thickness homogeneities have been shown to be better than 1% standard deviation on full 2” wafers, while composition uniformity of ternary material is determined by room temperature photoluminescence mappings. Low temperature photoluminescence and reflectance spectra of single layer GaN revealed free exciton transitions.
Low Temperature GaN Growth on Nitridated Sapphire Using Remote Plasma Enhanced Ultrahigh Vacuum Chemical Vapor Deposition
Authors: Kim Dong-Jun , Kim Kyoung-Kook , Paek Jong-Sik , Yi Min-Su , Noh Do-Young , Kim Hyo-Gun , Park Seong-Ju 
Published: April 2011

AbstractGaN epitaxial thin films were grown on a nitridated sapphire at low temperature (550°C) using remote plasma enhanced ultrahigh vacuum chemical vapor deposition system and these films were investigated by Rutherford backscattering spectroscopy (RBS), X-ray diffraction(XRD) θ-rocking technique and the Ultraviolet-Visible-Nearinfrared (UV-VIS-NIR) absorption spectrum. The FWHM of the X-ray θ-rocking curve was about 0.4 degree using the (0002) reflection from the GaN layer with 5000Å thickness grown on the nitridated sapphire. An analysis of XRD and the UV-VIS-NIR absorption spectrum showed that the crystalline and optical qualities of GaN are dependent on the nitridation time of the sapphire even at low temperature when a plasma source is used for nitridation. This means that the density of protrusion, which is formed by a relaxation of the elastic energy caused by the lattice difference between the sapphire and AlxO1-xN, with the sapphire nitridation time plays a key role in the crystalline and optical properties of grown GaN films. The RBS channeling data and the FWHM value of the θ-rocking curve for GaNr(0002) also indicated that the truncated hexagonals are tilted towards each other. These results showed that the GaN epitaxial film can be successfully grown on nitridated sapphire by RPE-UHVCVD even at low temperature.
Fine Structure And Magnetooptics Of Excitonic Levels In Wurtzite GaN
Authors: Eckey L. , Hoffmann A. , Thurian P. , Broser I. , Meyer B. K. , Hiramatsu K. 
Published: April 2011

AbstractWe present a comprehensive study of the direct photoluminescence from excitonic states in GaN using polarization-dependent and magnetooptical measurements in fields up to 15 T. We measure and identify fine-structure splittings in the states n=l and n=2 of the A-exciton. The splitting between the energy levels of longitudinal and transverse states in the A-exciton is 0.96 meV. Emission from the spin triplet exciton in the state n=l is observed. We also identify emissions from three sublevels of the state n=2 of the A-exciton. From the analysis of our data we obtain the effective-mass parameters of electrons and holes, g-values and the Rydberg energy of the A-exciton.
Luminescence Properties of Si-Doped GaN and Evidence of Compensating Defects As the Origin of the Yellow Luminescence
Authors: Goepfert I. D. , Schubert E. F. , Redwing J. M. 
Published: April 2011

AbstractWe investigate the optical properties of n-type Gallium Nitride (GaN) with concentrations ranging from 5×1016 to 7×1018 cm−3. The near-band edge ultraviolet (UV) transition increases monotonically with the doping concentration. The photoluminescence linewidth of the near-bandgap optical transition increases from 47 to 78 meV as the doping concentration is increased. The broadening is modeled by taking into account potential fluctuations caused by the random distribution of donor impurities. Excellent agreement is found between experimental and theoretical results. We also investigate the origin of the yellow luminescence in GaN. At low excitation densities the experimental ratio of the UV-to-yellow photoluminescence does not change significantly as the doping concentration is increased by two orders of magnitude. Analysis of the luminescence in terms of a theoretical model indicates that the yellow luminescence is due to compensating impurities or defects.
Deep Trap Characterization In GaN Using Thermal And Optical Admittance Spectroscopy
Authors: Krtschil A. , Witte H. , Lisker M. , Christen J. , Birkle U. , Einfeldt S. , Hommel D. , Topf M. , Meyer B. K. 
Published: April 2011

AbstractDeep defect levels and the optical as well as thermal transitions of carriers from the levels into the corresponding bands were analyzed using Thermal and Optical Admittance Spectroscopy. High resistivity GaN-layers grown by MBE and heterostructures consisting of n-type GaN-layers grown with Low Pressure Chemical Vapor Deposition on 6H-SiC substrates are investigated. In the MBE-grown GaN layers we determine deep electron traps with thermal activation energies of EA=(0.45±0.04)eV and EA=(0.65±0.03)eV. Furthermore, three different kinds of optical transitions were distinguished by Optical Admittance Spectroscopy: near band gap transitions including the transition between the valence band and a shallow donor 50meV below the conduction band, a peak at 2.1eV associated with the yellow photoluminescence band and various deep level-band transitions in the infrared region.The high sensitivity of the TAS to interface defect states was used to investigate GaN/SiC heterostructures. We found an interface defect state at 70 … 90meV. Furthermore, one level was obtained originating from the epitaxial GaN-layer having an activation energy of 63±3meV. A defect distribution was identified in the p-type SiC-substrate with activation energies between 160meV and 180meV.
GaN And Related Materials For High Power Applications
Authors: Shur M. S. 
Published: April 2011

AbstractUnique properties of GaN and related semiconductors make them superior for high-power applications. The maximum density of the two-dimensional electron gas at the GaN/AlGaN heterointerface or in GaN/AlGaN quantum well structures can reach 5×1013 cm−2, which is more than an order of magnitude higher than for traditional GaAs/AlGaAs heterostructures. The mobility-sheet carrier concentration product for these two dimensional systems might also exceed that for GaAs/AIGaAs heterostructures and can be further enhanced by doping the conducting channels and by using “piezoelectric” doping, which takes advantage of high piezoelectric constants of GaN and related materials. We estimate that current densities over 20 A/mm can be reached in GaN-based High Electron Mobility Transistors (HEMTs). These high current values can be combined with very high breakdown voltages in high-power HEMTs. These breakdown voltages are expected to reach several thousand volts. Recent Monte Carlo simulations point to strong ballistic and overshoot effects in GaN and related materials, which should be even more pronounced than in GaAs-based compounds but at much higher electric fields. This should allow us to achieve faster switching, minimizing the power dissipation during switching events. Selfheating, which is unavoidable in power devices, raises operating temperatures of power devices well above the ambient temperature. For GaN-based devices, the use of SiC substrates having high thermal conductivity is essential for ensuring an effective heat dissipation. Such an approach combines the best features of both GaN and SiC technologies; and GaN/SiC-based semiconductors and heterostructures should find numerous applications in power electronics.
Heteroepitaxy And High Density Nucleation Of Diamond On Mirror-Polished Silicon
Authors: Lin Zhangda , Sun Xiaosong , Yu Ge , Lee S. T. 
Published: April 2011

AbstractBy virtue of its excellent electronic properties, diamond may become an important material for high temperature, high speed, high power and high compact electronic devices. However, most of these devices, single crystal or epitaxial films are required. Thus, for obvious reason, large-area heteroepitaxial diamond films are desired. Silicon is the most important material severed as a substrate for diamond heteroepitaxy. However, diamond can hardly be grown on mirror-polished Si, with nucleation density being only about 104 cm−2. Although scratching Si substrate could enhance greatly the nucleation density, it destroyed seriously the periodic structure of the Si surface. Thus diamond film grown on such a substrate will be randomly oriented polycrystallites. In order to overcome this difficulty, several methods have been developed, including (1) bias enhanced nucleation; (2) electron emission enhanced nucleation; (3) nucleation enhanced by slight surface modification; and (4) very low pressure ( 0.1 torr ) nucleation. We will introduce the second, third, and fourth methods, which were developed in our laboratory recently. Special attention will be paid to the relation between heteroepitaxy and high density nucleation. The incubation time for diamond nucleation is a critical parameter for high density nucleation and heteroepitaxy.
High Frequency Capacitance Measurements On Metal-Insulator-Semiconductor Structures In Thermal Non-Equilibrium Condition
Authors: Sadeghi M. , Jauhiainen A. , Liss B. , Sveinbjörnsson E. Ö. , Engström O. 
Published: April 2011

AbstractWe simulate the charge carrier traffic between the energy bands and the interface states in structures like Al/SiO2/6H-SiC, Al/diamond/Si and Al/SIPOS/Si to explain their high frequency capacitance-voltage behavior. The structures have in common that traditional electrical measurement techniques performed at room temperature are strongly influenced by non-equilibrium carrier conditions at the insulator-semiconductor interface. This can result in large errors in the interface data extracted from such studies when thermal equilibrium conditions are assumed. In this work, high frequency capacitance-voltage data are compared to numerical simulations which include such thermal non-equilibrium conditions to enable more accurate estimates of interface state parameters in such structures.
Cl2-Based Dry Etching Of The AIGaInN System In Inductively Coupled Plasmas
Authors: Cho Hyun , Vartuli C. B. , Abernathy C. R. , Donovan S. M. , Pearton S. J. , Shul R. J. , Han J. 
Published: April 2011

AbstractCl2-based Inductively Coupled Plamas with low additional dc self-biases(−100V) produce convenient etch rates(500–1500Å.min−1) for GaN, AIN, InN, InAiN and InGaN. A systematic study of the effects of additive gas(Ar, N2, H2), discharge composition and ICP source power and chuck power on etch rate and surface morphology has been performed. The general trends are to go through a maximum in etch rate with percent C12 in the discharge for all three mixtures, and to have an increase(decrease) in etch rate with source power(pressure). Since the etching is strongly ion-assisted, anisotropic pattern transfer is readily achieved. Maximum etch selectivities of approximately 6 for InN over the other nitrides were obtained.
Design And Fabrication Of Nitride Based High Power Devices
Authors: Bandić Z. Z. , Piquette E.C. , Bridger P.M. , Kuech T.F. , Mcgill T. C. 
Published: April 2011

AbstractWe modeled the breakdown voltage, critical current density and maximum operating frequency of several GaN and GaN/AlN based high power and high temperature electronic devices. Important model parameters which influence device design and performance are minority carrier recombination lifetime and critical field for electric breakdown.GaN Schottky devices have been fabricated in the planar geometry. Current-voltage measurements indicated the importance of the vertical geometry for achieving large breakdown voltages. The minority carrier (hole) recombination lifetimes have been measured by electron beam induced currents (EBIC). The measured hole lifetime of 7 ns and estimate for the critical field indicate the possibility of GaN/AlGaN thyristor switch devices operating at 5KV with current densities approximately equal to 200 A/cm2 and at frequencies above 2MHz.The GaN structural and optical materials quality and processing requirement for etching is discussed.
Room Temperature Growth of Conducting ZnO Films
Authors: Witanachchi S. , Ying Y. , Miyawa A. M. , Mukherjee P. 
Published: April 2011

AbstractSingle and dual-laser ablation techniques have been used to grow conductive ZnO films at room temperature by ablating a Zn metal target in oxygen ambient. The emission spectroscopy of the material plumes shows a significant presence of oxygen ions and Zn ions in the dual-laser ablated plume. Furthermore, dual-laser ablated plumes expanded rapidly in the radial direction resulting in large-area uniform films. The electrical properties of the films deposited on glass substrates depend critically on the ambient oxygen pressure. Conductivities of the order of 103 (ω.cm)-1 have been obtained for films deposited at room temperature by the dual-laser ablation process.
Tailoring the Optical Properties of Si Nanocrystals In SiO2: Materials Issues And Nanocrystal Laser Perspectives
Authors: Brongersma M. L. , MIN K. S. , Boer E. , Tambo T. , Polman A. , Atwater H. A. 
Published: April 2011

AbstractSi nanocrystals (diameter 2 – 5 nm) were formed by 35 keV Si+ implantation at a fluence of 6×1016 Si/cm2 into a 100 nm thick thermally grown SiO2 film on Si (100), followed by thermal annealing at 1100 °C for 10 min. The nanocrystals show a broad photoluminescence spectrum, peaking at 880 nm, attributed to the recombination of quantum confined excitons. Rutherford backscattering spectrometry and transmission electron microscopy show that annealing these samples in flowing O2 at 1000 °C for times up to 30 min. results in oxidation of the Si nanocrystals, first close to the SiO2 film surface and later at greater depths. Upon oxidation for 30 min. the photoluminescence peak wavelength blue-shifts by more than 200 nm. This blueshift is attributed to a quantum size effect in which a reduction of the average nanocrystal size leads to emission at shorter wavelengths. The fabrication of a laser based on SiO2 waveguides doped with Si nanocrystals seems possible, if the nanocrystal size distribution can be narrowed down into the percent range.
Comparative Study of Implanted and Sputtered Systems of Si Nanograins Embedded In SiO2
Authors: Charvet S. , Madelon R. , Rizk R. , Garrido B. , Pó;rez Rodríguez A. , López M. , González Varona O , Morante J. R. 
Published: April 2011

AbstractSi nanograins embedded in silicon oxide matrix have been obtained by thermal annealing at 1100°C during one hour, either after implantation of Si+ into thermal SiO2 layers or after magnetron cosputtering of both Si and SiO2. The spectral distribution of the photoluminescence (PL) in both systems is similar and peaks in the red visible region (1.45–1.60 eV). The results obtained indicate that for high PL efficiency, the films have to be annealed at temperatures high enough to achieve phase separation. This was observed from the gradual shift of the infrared bands of the silica matrix toward those of thermal SiO2, together with the appearance of the crystalline silicon Raman vibrational mode in the spectra. The similar behavior of samples obtained by ion implantation and by sputtering suggests a more complex origin of the PL than quantum confinement.
Time-Resolved Photoluminescence from nm-Sized Silicon Crystallites In SiO2
Authors: Linnros J. , Galeckas A. , Pareaud A. , Lalic N. , Grivickas V. , Hultman L. 
Published: April 2011

AbstractTime resolved photoluminescence (PL) decays have been measured for Si nanocrystals embedded in silicon dioxide. The nanocrystals were formed by Si implantation followed by thermal annealing at 800 – 1200 °C. The observed PL peaked in the wavelength range 640 – 850 nm and the PL decay exhibited a stretched exponential lineshape, characterized by a relatively large time constant. A nonlinear dose dependence of the PL yield and an observed redshifting for increasing doses and/or higher annealing temperatures is discussed in terms of a nucleation and growth mechanism for the nanocrystals. Finally, we argue that Auger recombination is effective at high excitation densities explaining a wavelength dependent saturation of the PL intensity.