bluuebunny/crossref_metadata_2025_split huggingface dataset:
Optical properties of self-assembled InAs quantum dots grown on InAlAs/InP(001)
Authors: Salem B. , Benyattou T. , Guillot G. , Bremond G. , Brault J. , Gendry M. 
Published: April 2011

ABSTRACTSelf-organized InAs quantum islands (QIs) were grown in the Stranski-Krastanov regime, by solid source molecular beam epitaxy (SSMBE), on In0.52Al0.48As layer lattice matched to InP(001) substrate. The growth parameters are chosen to produce dot shaped InAs islands as indicated by the photoluminescence (PL) linear polarization which is about 9%. The PL spectrum reveals several resolvable components. PL versus power excitation and photoluminescence excitation (PLE) measurements show clearly that this multi-component spectrum is related to emission from transitions associated to fundamental and related excited states of quantum dots (QDs) having monolayer-height fluctuations. The integrated PL intensities have been measured as a function of temperature in the 8–300 K range. The PL intensity measured at 300K is only 8 times lower than at 8 K, indicating good carrier confinement in these InAs/InAlAs QDs. An enhancement of the PL intensity in the 8–90 K temperature range has been tentatively attributed to the exciton dissociation from the InAlAs barriers which then recombine radiatively in the InAs QDs.
Patterned Structures of Silicon Nanocrystals Prepared by Pulsed Laser Interference Crystallization of Ultra-Thin A-Si:H Single-Layer
Authors: Wang Xiaowei , Qiao Feng , Zhu Leyi , Li Wei , Li Jian , Huang Xinfan , Chen Kunji 
Published: April 2011

ABSTRACTWe employ the method of phase-modulated KrF excimer pulsed laser interference crystallization to fabricate nanometer-sized crystalline silicon (nc-Si) with the two-dimensional (2D) patterned distribution within the ultra-thin a-Si:H single-layer. The local crystallization occurs after interference laser irradiation under proper energy density. The results of atomic force microscopy, Raman scattering spectroscopy, cross-section transmission electron microscopy and scanning electron microscopy demonstrate that Si nano-crystallites are formed within the initial a-Si:H single-layer, selectively located in the discal regions with the diameter of 350 nm and patterned with the same 2D periodicity of 2.0 μm as the phase-shifting grating. The results show that the present method can be used to fabricate patterned nc-Si films for device applications.
Si Nanoparticle Synthesis and Self – Organization
Authors: Fowlkes J. D. , Pedraza A. J. 
Published: April 2011

ABSTRACTSi nanoparticle linear arrays have been produced by pulsed KrF laser irradiation in inert atmospheres. The Si nanoparticles have a Gaussian size distribution with a mean diameter of 2.9 nm and a FWHM of 2 nm. The self – organized lines are spaced at a distance approximately equal to the laser beam wavelength, λ. The evolution of this self – organization process and that of laser – induced periodic surface structures (LIPSS) are closely related. The nanoparticles scatter light that interferes with the incident light. Similar to LIPSS, the inhomogeneous deposition of laser light due to this interference pattern created at the surface drives the particle formation and clustering. A detailed study of the clustering formation as a function of the laser pulses is presented.
Characterization of Co-catalyzed Multiwalled Carbon Nanotubes by High-Resolution Transmission Electron Microscopy
Authors: Wang Chih-Chin , Liu Chuan-Pu , Liu Ruo-Mei , Liao Kuen-Hou 
Published: April 2011

ABSTRACTThe dependence of characteristics of multiwalled carbon nanotubes (MWCNT) on the microstructure of cobalt catalysts are intensively investigated by high-resolution transmission electron microscopy (HREM). The cobalt catalysts are prepared by either molecule beam epitaxy (MBE) or by DC magnetron sputtering, followed by MWCNT growth by microwave plasma CVD. The MBE-grown Co thin films consist of large epitaxial grains, whereas the Co nanoparticles of FCC or HCP crystal structures can be directly grown on Si(001) substrates by sputtering. Various HREM technologies are applied to completely characterize the microstructures of those Co catalysts and MWCNT. The results reveal that the morphology and microstructures of MWCNT are greatly controlled by the characteristics of Co catalysts. Better quality of carbon nanotube can be grown by FCC cobalt rather than HCP cobalt. The different effects of cobalt catalysts on MWCNT are discussed in this paper.
Si Nanocrystals by Metal Induced Growth using Different Catalyzing Metals
Authors: Ji Chunhai , Anderson Wayne A. 
Published: April 2011

ABSTRACTA comparative study of nanocrystalline silicon thin films grown on 25 nm thick catalyzing metals by dc magnetron sputtering from a highly doped Si target has been performed. In our previous study, the growth of Si was catalyzed by the silicide reactant from sputtered Si and Ni. These new experiments compared the effect of two types of catalyzing metals, Ni and Co. The structural and electrical characteristics of nano-Si were examined by scanning electron microscopy (SEM), cross-section SEM (XSEM), transmission electron microscopy (TEM), four-point-probe measurement and Schottky contact I-V measurement. The SEM and XSEM revealed that, for both catalyzing metals, the nano-Si thin films have columnar nano-grains with length of 500 nm in the vertical direction. However, the diameter of grains strongly depends on the catalyzing metals. For Co, the nano-Si grains had a typical diameter of 30 nm, while for Ni, the grains were much larger. TEM analysis showed that this difference in grain size begins at the initial growth stage. In the later-on growth, the Si grains mainly grow in a vertical direction instead of a lateral direction. This implies that the dimensions of Si nanostructures are strongly determined by the initially formed metal silicide nanoparticles. The current-voltage curve of a fabricated Al Schottky diode on P-type Co catalyzed nano-Si exhibited good rectifying characteristics. The dopant has been naturally synthesized in the Si nanocrystals during the growth of nano-Si by using a doped sputtering target. The above measured electrical properties show that metal induced grown nanocrystalline Si is applicable to various electronic and photonic devices.
The Effects of Crystallinity and Catalyst Dynamics on Boron Carbide Nanospring Formation
Authors: McIlroy D. N. , Zhang D. , Kranov Y. , Han H. , Alkhateeb A. , Grant Norton M. 
Published: April 2011

ABSTRACTThe formation of helical nanowires—nanosprings—of boron carbide have been observed and a growth mechanism, based on the work of adhesion of the metal catalyst and the tip of the nanowire, developed. The model demonstrates that the asymmetry necessary for helical growth is introduced when the following conditions are met:(1) The radius of the droplet is larger than the radius of the nanowire, and(2) The center of mass of the metal droplet is displaced laterally from the central axis of the nanowire.Furthermore, this model indicates that only amorphous nanowires will exhibit this unique form of growth and that in monocrystalline nanowires it is the crystal structure that inhibits helical growth. High-resolution transmission electron microscopy and electron diffraction has been used to compare the structure of both amorphous and crystalline nanowires.
Synthesis of SiO2 Nanowires and CdS/SiO2 Composite Nanowires and Investigation of Their Electron Field Emission Properties
Authors: Jiao Jun , Dong Lifeng , Tuggle David W. , Petty Jeremy , Love Logan , Coulter Michael 
Published: April 2011

ABSTRACTA thermal evaporation method was used to obtain SiO2 and CdS/SiO2 nanowires by heating Si substrates coated with a gold thin film in a quartz tube furnace. During growth, pure CdS powder was placed at the heating zone in the furnace, serving as the CdS source for the CdS/SiO2 composite nanowires. It was found that both non-porous and porous Si substrates served as the Si source for the growth of SiO2 nanowires and the CdS/SiO2 composite nanowires. It was also found that the effect of the temperature gradient in the reaction chamber plays an important role in the density distribution of different nanowires (SiO2 or CdS/SiO2 nanowires). The electron field emission properties of these nanowires were investigated using an electron field emission microscope equipped with a Faraday cup.
Simple Use of SiO2 Film Thickness for the Control of Carbon Nano-Tube Diameter During Ferrocene Catalyzed CVD Growth
Authors: Chopra N. , Kichambare P.D. , Andrews R. , Hinds B. J. 
Published: April 2011

ABSTRACTSelective growth of carbon nano-tubes (CNT) on micron scale patterned substrates has been accomplished by taking advantage of the non-reactivity of ferrocene catalyst on H-terminated Si surfaces in a CVD process. Demonstrated here is that this phenomenon can be used to control the diameter of CNTs when sufficiently narrow lines of SiO2 surrounded by H-terminated Si are used. Narrow lines of SiO2 (12–60nm) are formed at the etched face of a Si/SiO2/Si multilayer structure. This allows the precisely controllable thickness of an SiO2 film to determine an exposed SiO2 line width. There is no need for e-beam lithography since film thickness determines nm-scale line dimensions. CNTs are then formed by CVD with a ferrocene/H2/Ar mixture at 700°C. CNTs are observed to grow only on the exposed SiO2 surface at the edge of the ‘mesa’ structure. CNT diameters of 13.2, 20.5, 34.2, 64.3nm are observed for SiO2 film thickness of 12, 19, 35, and 65 nm. The larger distribution of CNT diameter with increased line width is consistent with wider SiO2 linewidths not being able to affect smaller nucleation centers. These results are consistent with the use of self-assembly chemistry of iron catalyst onto nano-particles of catalyst support.
Fabrication of Perforated Film Nanostructures
Authors: Elias A. L. , Harris K. D. , Brett M. J. 
Published: April 2011

ABSTRACTWe have demonstrated the fabrication of perforated thin films (PTFs), comprised of thin coatings perforated with unusual pore shapes such as helices or chevrons. PTFs are fabricated using a template of nanohelices or nanochevrons produced using the Glancing Angle Deposition (GLAD) technique. PTFs can be produced by filling GLAD films with a variety of substances, etching back the coating to reveal the tips of the helices or chevrons, and etching out the template film. A process for fabricating nickel PTFs has been developed, and a nickel PTF of helical pores with nominal diameters of 100nm has been produced.
Metal-Induced Low-Temperature Crystallization of Amorphous SiGe on Insulating Films
Authors: Miyao M. , Kanno H. , Tsunoda I. , Sadoh T. , Kenjo A. 
Published: April 2011

ABSTRACTMetal-induced low temperature (≤ 550 °C) crystallization of a-Si1-xGex (0 ≤ × ≤ 1 ) layers on SiO2 films has been investigated. For low Ge fractions below 20 %, Ge-doping enhanced plane growth was observed. This realized strain-free poly-Si0.8Ge0.2 films with large grains (18 μm). On the other hand, dendrite growth was dominant for intermediate Ge fractions with 40–60 %. Directions and widths of dendrites became straight and narrow with decreasing annealing temperature. As a result, very sharp needlelike crystals (width: 0.05 μm, length: 10 μm) were obtained at the optimized growth conditions (x: 0.4, annealing: 450 °C, 20 h). These new polycrystalline SiGe films on insulators should be used for the advanced system-in-displays and novel one-dimensional wires.
Implant isolation of ZnO epitaxial layers
Authors: Kucheyev S. O. , Jagadish C. , Williams J. S. , Deenapanray P. N. K. , Yano Mitsuaki , Koike Kazuto , Sasa Shigehiko , Inoue Masataka , Ogata Ken-ichi 
Published: April 2011

ABSTRACTThe formation of highly resistive films of single-crystal ZnO as a result of irradiation with MeV Li, O, and Si ions is demonstrated. Results show that the ion doses necessary for electrical isolation close-to-inversely depend on the number of ion-beam-generated atomic displacements. Results show that an increase in the dose of 2 MeV O ions (up to ∼ 2 orders of magnitude above the threshold isolation dose) and irradiation temperature (up to 350 °C) has a relatively minor effect on the thermal stability of electrical isolation, which is limited to temperatures of ∼ 300 — 400 °C. For the case of multiple-energy implantation with keV Cr, Fe, or Ni ions, the evolution of sheet resistance with annealing temperature is consistent with defect-induced isolation, with a relatively minor effect of Cr, Fe, or Ni impurities on the thermal stability of isolation. Based on these results, the mechanism for electrical isolation in ZnO by ion bombardment is discussed.
Ultraviolet Emitting SrS:Te Thin Films
Authors: Fitz-Gerald J.M. , Hoekstra J. , Fowlkes J.D. , Rack P.D. 
Published: April 2011

ABSTRACTIn the bulk SrS has an indirect bandgap of ∼ 4.32 eV. When SrS is doped with tellurium, ultraviolet emission occurs at 360 nm (for singlet) and 400nm (for Te-Te dimers) due to recombination from bound exciton states. In this paper we discuss the ultraviolet emission of pulsed laser deposited thin films of SrS:Te grown at room temperature on Si. Deposited film thickness ranged from 0.1 – 1.5 mm, with optimized films grown at ∼0.5 mm to avoid peeling and cracking. Te doping was incorporated by both ion implantation and conventional diffusion of deposited Te capping films. The characteristics of the ultraviolet emission will be discussed along with results from microstructural, chemical and optical characterization techniques.
Intersubband Transitions in Proton Irradiated InGaAs/InAlAs Multiple Quantum Wells Grown on Lattice Matched InP Substrate
Authors: Zhou Qiaoying , Manasreh M. O. , Weaver B. D. , Missous M. 
Published: April 2011

ABSTRACTRadiation hardness on intersubband transition in proton-irradiated InGaAs/InAlAs multiple quantum wells is investigated using Fourier transform infrared absorption (FTIR) technique and compared to the results observed for the GaAs/AlGaAs multiple quantum wells. It is observed that the intersubband transition remains almost unchanged in samples irradiated with 1 MeV protons and with doses as high as 1×1014 cm-2. This dose on the other hand, was found to completely deplete the intersubband transition in GaAs/AlGaAs multiple quantum wells samples. The intersubband transition in InGaAs/InAlAs multiple quantum wells was almost washed out in samples irradiated with doses as high as 3×1015 cm-2. The partial thermal annealing recovery of the depleted intersubband transition in the proton irradiated InGaAs/InAlAs multiple quantum wells will be reported.
1.5 μm Range Self-Organized In0.65Ga0.35As/In0.52Al0.48As Quantum Wire Structures Grown on (775)B-Oriented InP Substrates by Molecular Beam Epitaxy
Authors: Hyodo K. , Ohno Y. , Kanamori H. , Kitada T. , Shimomura S. , Hiyamizu S. 
Published: April 2011

ABSTRACTHigh quality quantum wire (QWR) structures with an emitting wavelength in the 1.5-μm range were self-organized in an In0.65Ga0.35As/In0.52Al0.48As quantum well layer grown on a (775)B-oriented InP substrate by molecular beam epitaxy. Photoluminescence (PL) from the (775)B In0.65Ga0.35As/In0.52Al0.48As QWRs with a nominal well width of 4.8 nm was observed at 1.43 μm at 12 K, which corresponds to a PL wavelength of about 1.5 μm at room temperature. The PL peak was considerably polarized along the wire direction with a polarization degree of P [= (I∥ - I⊥) / (I∥ + I] ⊥)] = 0.14, indicating its good one-dimensionality. The FWHM of the PL peak was as small as 17 meV, which is the best value for InGaAs QWRs on InP substrates.
Noise Sources in Polycrystalline Silicon Thin-Film Transistors
Authors: Han Il Ki , Park Young Ju , Cho Woon Jo , Choi Won Jun , Lee Jungil , Chovet Alain , Brini Jean 
Published: April 2011

ABSTRACTSources for low frequency noise in polycrystalline silicon thin-film transistors are analytically investigated. The grain boundary is modeled as symmetric Schottky barrier and a new device equation for current conduction in thin-film transistors is presented. At lower currents where barrier height is large enough to provide necessary distribution of time constants for 1/f noise, the number fluctuation via barrier height modulation at the grain boundary is found to be the main noise generation mechanism. At higher currents, mobility and diffusivity fluctuation are found to be dominant
Photoreflectance study of hydrogenated (InGa)(AsN)/GaAs heterostructures
Authors: Geddo M. , Guizzetti G. , Pezzuto R. , Polimeni A. , Capizzi M. , Bissiri M. , Baldassarri Höger von Högersthal G. , Gollub D. , Forchel A. 
Published: April 2011

ABSTRACTWe report on photoreflectance measurements performed in the 0.8–1.6 eV photon energy range in as grown and hydrogenated InxGa1-xAs1-yNy/GaAs single quantum wells grown on GaAs substrates by molecular beam epitaxy. In the hydrogenated samples, a blue-shift of all the QW spectral features and a surprising change with temperature in the nature of the lowest energy transition are found. These features are related to the interaction of H with N atoms. An increase in the binding energy of the heavy-hole exciton upon N introduction into the InxGa1-xAs lattice has been measured also and explained in terms of an increase in the electron effective mass.
Improved Device Performance of In0.5Ga0.5P/In0.22Ga0.78As/GaAs MOS p-HEMT using a Selective Liquid Phase Oxidation
Authors: Kang I-H , Lee J-W , Kang S-J , Jo S-J , In S-K , Song H-J , Kim J-H , Song J-I 
Published: April 2011

ABSTRACTThe DC and RF characteristics of In0.5Ga0.5P/In0.22Ga0.78As/GaAs MOS p-HEMTs with different gate oxide thickness were investigated and compared with those of Schottky-gate p-HEMT without the gate oxide layer. The oxide layer was implemented by using a liquid phase oxidation technique. It was found that transconductance (gm), threshold voltage and breakdown voltage characteristics of MOS p-HEMTs depended strongly on the gate oxide thickness. The MOS p-HEMTs showed superior DC and RF performances compared with those of GaAs-based MOSFET having oxide/n-GaAs or oxide/InGaAs interface.
Oxygen incorporation into MBE-grown AlGaAs layers
Authors: Naritsuka S. , Kobayashi O. , Mitsuda K. , Maruyama T. , Nishinaga T. 
Published: April 2011

ABSTRACTThe incorporation mechanism of oxygen into MBE-grown AlGaAs layers was systematically studied by changing the growth temperature and AlAs mole fraction. It was found that segregation of oxygen atoms strongly influences oxygen incorporation. By taking into account the surface segregation of oxygen, all of the particular characteristics observed in the oxygen incorporation into MBE-grown AlGaAs layers can be explained including a peak and a dip formation in the profile. Oxygen atoms accumulate on the surface of the substrate due to surface segregation and the number multiplied by the coefficient of surface segregation determines the oxygen incorporation.
Thermal Stability in HgCdTe IR Photodiodes
Authors: Dell J. M. , Nguyen T. , Musca C. A. , Antoszewski J. , Faraone L. , Pal R. 
Published: April 2011

ABSTRACTPackaging of HgCdTe photodiode detector arrays in a dewar involves degassing at elevated temperatures for several days so as to achieve vacuum integrity. This sustained exposure to relatively high temperatures can influence the HgCdTe bulk material properties, p-n junction integrity, and the passivant-HgCdTe interface. This work investigates the effects of bake-out treatment on the performance of HgCdTe based photodiodes formed using a new plasma induced type conversion process. Experimental results of a series of experiments in both long-wavelength infrared (LWIR) and mid-wavelength infrared (MWIR) devices are presented.Bulk lifetime was used as an indicator of the change in the bulk material resulting from baking in vacuum and was measured by photoconductive decay. These measurements did not show any appreciable changes as a result of baking. Modification of the doping profile in the n-p junction may also result from high temperature baking. Doping profiles of the photodiodes were studied by measuring the junction capacitance-voltage relation before and after baking. The results of these tests after baking showed no changes to C-V measurements from those before bake.The effect of baking on the passivant/HgCdTe interface was also examined by carrying out surface recombination velocity measurements by photoconductive decay on samples with different passivation layers.Variable area HgCdTe photodiodes have also been fabricated and studied to understand the effect of the surface condition of the performance of the devices. Initial bake tests on LWIR devices show that the technology is stable when employing a double layer passivation technique. Bake tests on the more advanced MWIR technology indicates that the plasma induced type conversion process produces stable photodiodes with state of the art performance.
Ferromagnetic Single-Electron Transistor with RC Gate
Authors: Shirakashi Jun-ichi , Takemura Yasushi 
Published: April 2011

ABSTRACTFerromagnetic single-electron transistors coupled to the controlling gate potential by the gate resistance and gate capacitance in series are studied quantitatively. In this type of the device, several metastable charge states are possible within the Coulomb blockade range. The enhancement and hysteresis of tunnel magnetoresistance on drain and gate voltages are predicted. Inelastic macroscopic quantum tunneling of charge and existence of several charge states play an important role for the unique behavior of the tunnel magnetoresistance. This implies that RC-coupled ferromagnetic single-electron transistors have a new functionality as novel magnetoresistive nanostructure devices.
Annealing of CoxCu1-x / Cu Multilayers
Authors: Ebert Jörg , Ghafari Mohammad , Stahl Branko , Hahn Horst 
Published: April 2011

ABSTRACTIn the multilayer system cobalt / copper at the second antiferromagnetic coupling maximum (2. AFM) with a copper thickness of dCu = 2,2 nm it is possible to reduce magnetoresistive hysteresis by the use of either very thin Co-layers or by alloyed magnetic layers Co1-xCux. It was possible to achieve values for the giant magnetoresistance effect of GMR ≈ 20 % for as prepared samples. A heat treatment was applied to study the degeneration of the system. For annealing at moderate temperatures (Tanneal ≤ 250°C) an increase up to GMR ≈ 25 % was observed. Annealing at slightly higher temperatures lead to an rapid decrease in the GMR effect. To study the structural changes the method of x-ray reflectivity was utilized showing changes in interface roughness as well as in bilayer thickness.
Observation of the Verwey Transition in Fe3O4 Nanocrystals
Authors: Markovich Gil , Fried Tcipi , Poddar Pankaj , Sharoni Amos , Katz David , Wizansky Tommer , Millo Oded 
Published: April 2011

ABSTRACTThe electronic properties of arrays and isolated magnetite nanocrystals were studied using tunneling spectroscopy. Macroscopic tunnel junctions were used to study stacked arrays of the nanocrystals. The temperature dependent resistance measurements showed an abrupt increase of the resistance around 100 K, attributed to the Verwey metal-insulator transition, while the current-voltage characteristics exhibit a sharp transition from an insulator gap to a peak in the density of states near the Fermi energy. This conductance peak was sensitive to in-plane magnetic field showing large magnetoresistance. The tunneling spectra obtained on isolated particles using a Scanning Tunneling Microscope exhibit a gap-like structure below the transition temperature that gradually disappeared with increasing temperature, ending with a small peak structure around zero bias.