bluuebunny/crossref_metadata_2025_split huggingface dataset:
Characterization of nanographite and carbon nanotubes by polarization dependent optical spectroscopy
Authors: Grüneis Alexander , Saito Riichiro , Samsonidze Georgii G. , Pimenta Marcos A. , Jorio Ado , Souza Filho Antonio G. , Dresselhaus Gene , Dresselhaus Mildred S. 
Published: April 2011

ABSTRACTThe optical absorption for ? electrons as a function of the electron wavevector k is investigated by first order perturbation theory in graphite and single wall carbon nanotubes (SWNTs). The matrix element connecting two states in the valence and conduction bands is found to be significantly anisotropic in k-space and polarization dependent. In the case of graphite, the absorption shows a node around the equi-energy contour, and in the case of SWNTs we obtain selection rules that allow only transitions between certain pairs of subbands. The strength of the optical absorption is not only diameter dependent but also chirality dependent. The implications of the optical absorption matrix element on the resonant conditions are discussed.
Quantitative V-L-S Growth Model and Experiments of Fe Catalyzed Si Nanowire Formation
Authors: Zhou Guangwen , Yang Judith C. , Xu Fengting , Barnard John A. , Zhang Z. 
Published: April 2011

ABSTRACTWe report the formation of Si nanowires (SiNWs) by vapor-liquid-solid (V-L-S) mechanism where Si atoms are pumped from Si wafer. This happens when a material has the large difference of activity in its pure (Si) and alloy state (Si-Fe). We developed a kinetic model to quantitatively describe the growth of the nanowires. The model predicts that the length of the nanowires increases linearly with the growth time.
Field Emission Properties of BN/C and BN@C Hybrid Nanotubes
Authors: Meunier Vincent , Buongiorno Nardelli Marco , Shelton William , Roland Christopher , Bernholc Jerry , Zacharia Thomas 
Published: April 2011

ABSTRACTOur simulations predict that boron-nitride (BN) doping in carbon nanotubes can greatly improve the field emission properties of these systems. The intrinsic electric field associated with the polarity of the B-N bond enhances the emitted current density through a reduction of the work function at the tip. Using a combination of real-space and plane-wave ab initio methods, we show that this effect is present in both coaxial (BN@C) and linear (BN/C) nanotubular assemblies. While in the coaxial geometry the improvement amounts to a factor of five, the current density is predicted to increase by up to two orders of magnitude in BN/C superlattices.
Synthesis, Self-assembly and Magnetic Properties of FePtCu Nanoparticle Arrays
Authors: Sun Xiangcheng , Kang S. S. , Harrell J. W. , Nikles David E. , Dai Z. R. , Li J. , Wang Z. L. 
Published: April 2011

ABSTRACTFePtCu nanoparticles with varying composition were synthesized by chemical solution-phase reduction of platinum and copper reagents and thermal decomposition of iron pentacarbonyl in the presence of oleic acid and oleyl amine stabilizers. As prepared the particles had fcc structure with an average diameter of 3.5 nm and were superparamagnetic. The particles were well dispersed in hydrocarbon solvents and could be self-assembled into two or three dimensions particles arrays with a variety of close-packing arrangements. Heat-treatment of the self-assembled films at temperatures above 550°C transformed the particles from the fcc to the L10 phase, giving in-plane coercivities as high as 9000 Oe. X-ray diffraction revealed that the Cu remained in the annealed FePtCu films and the presence of an extra peak, indicated a second phase was present. Consistent with one or more phases, the magnetic hysteresis curves could be decomposed into a hard component (Hc > 5,000 Oe) and a soft component (Hc < 2,000 Oe). Unlike our earlier results for Ag in FePt, adding Cu to FePt did not lower the temperature required for phase transformation from the fcc to the fct L10 phase.
Molecular-Dynamics Study of the Mechanical Properties of Metallic Nanowires
Authors: Nakajima T. , Shintani K. 
Published: April 2011

ABSTRACTThe method of molecular-dynamics is employed to simulate and investigate the deformation of metallic nanowires under tensile strain. The interactions between metallic atoms are calculated by using the embedded-atom method potential. A model nanowire is preliminarily equilibrated at a specified temperature. Then, the uniform uniaxial extension of the nanowire is performed. The thinning process of a metallic nanowire is observed in the sequential snapshots of its morphological change.
3-D Nanoengineering of Metal Oxides and Oxyhydroxides by Aqueous Chemical Growth
Authors: Vayssieres Lionel , Manthiram Arumugam 
Published: April 2011

ABSTRACTAdvanced nanoparticulate thin films of transition metal oxides consisting of nanorods with different orientations onto various substrates have been successfully grown by aqueous chemical growth without template, surfactant, or applied electric/magnetic field. The synthesis involves the aqueous condensation of metal ions from solutions of metal salts or metal complexes. Such low-cost fabrication of nanoengineered 3-D arrays consisting of 1-D nanorods of iron oxide (hematite), zinc oxide (zincite), and manganese oxyhydroxide (manganite) with parallel and perpendicular orientations onto various substrates are presented.
Luminescence and EPR Study of Lithium-Diffused ZnO Crystals
Authors: Garces N. Y. , Wang Lijun , Chirila M. M. , Halliburton L. E. , Giles N. C. 
Published: April 2011

ABSTRACTZinc oxide (ZnO) crystals grown by the seeded chemical vapor transport method have been studied using photoluminescence (PL), thermoluminescence (TL), and electron paramagnetic resonance (EPR) techniques. Lithium acceptors were diffused into the crystals during anneals in LiF powder at temperatures in the 750 to 850°C range. After a lithium diffusion, EPR was used to monitor neutral lithium acceptors and neutral shallow donors, as well as Ni3+, Fe3+, and Cu2+ impurities unintentionally present. Excitonic and deep-level PL emissions were also monitored before and after these diffusions. Two broad overlapping TL emission bands were observed at 117 and 145 K when a Li-diffused crystal was illuminated at 77 K with 325-nm light and then rapidly warmed to room temperature. The two TL bands have the same spectral dependence (the peak in wavelength is 540 nm when the intensity of the light reaches a maximum). These “glow” peaks occur when electrons are thermally released from Ni2+ and Fe2+ ions and recombine with holes at neutral lithium acceptors.
Pulsed Laser Deposition of Stable Cubic ZnO/MgO Multilayers
Authors: Bhattacharya P. , Das Rasmi R. , Katiyar Ram S. 
Published: April 2011

ABSTRACTWide bandgap (∼6 eV) ZnO/MgO multilayer thin films have been fabricated using pulsed laser deposition technique from their respective targets on c-plane Al2O3 substrates. The thickness of single ZnO sublayer thickness was varied in the range of 0.75–2.5 nm with a fixed MgO sublayer thickness of 1 nm in order to achieve a total film thickness of ∼300 nm. The structural transition from hexagonal to cubic phase was observed with the decrease in the thickness of single ZnO layer from 2.5 to 0.75 nm that resulted in the increase in bandgap from 3.5 to 6.2 eV. Mg contents of the films were increased from 40 % to 60 % for hexagonal and cubic phases, respectively. The surface roughness and grain structure were not influenced much with the increase of Mg concentration. Resistivity of the films was increased six orders of magnitude with the increase in Mg incorporation. The post annealing at 750° C did not show any significant change in the crystal structure and the optical properties.
Optical Absorption of Large Band-Gap SbxBi1-xI3 Alloys
Authors: Persson C. , Ahuja R. , Souza de Almeida J. , Johansson B. , An C. Y. , Ferreira F.A. , Souza Dantas N. , Pepe I. , Ferreira da Silva A. 
Published: April 2011

ABSTRACTThe optical properties of SbBiI3 alloys have been investigated experimentally by absorption measurements and theoretically by a full-potential augmented plane wave (FPLAPW) method within the generalized gradient approximation. The fundamental band-gap energy of these alloys changes from BiI3- to SbI3-like with increasing percentage of Sb content. The calculated band-gap energies as well as the optical absorption were found to be in a very good qualitatively agreement with the experimental results. We present calculated density-of-states as well as the dielectric functions for evaluation of future experiments.
Carrier recombination in InAs/GaAs Quantum Dot and GaInNAs/GaAs Quantum Well LEDs emitting near 1300 nm.
Authors: Bennett A J , Lofgren L , Stavrinou P N , Roberts C , Murray R , Parry G , Roberts J S 
Published: April 2011

ABSTRACTWe have studied the emission from LEDs based on GaInNAs Quantum Wells (QWs) and InAs Quantum Dots (QDs) as a function of temperature and current. It is found that the carrier loss in GaInNAs QWs is dominated by non-radiative monomolecular and Auger processes resulting in an external quantum efficiency of only 0.08 % at 10 °C and 1000 A cm-2. In contrast, the InAs QDs have a higher external quantum efficiency, peaking at 0.8 % at 10 °C and 5 A cm-2, but this value rapidly decreases as the excited states of the QDs are filled and Auger-like processes become dominant. These results highlight the issues that must be addressed if these materials are to find commercial application: namely, the areal density of QDs must be increased and the material quality of the GaInNAs QWs must be improved.
Changes in Structural and Optical Properties of CdS Thin Films During the Process of Chemical Bath Deposition
Authors: Wei Li , Liang-huan Feng , Ya-ping Cai , Jing-quan Zhang , Jia-gui Zheng , Wei Cai , Li-li Wu , Bing Li , Ye Shao , Dao-lin Cai , Wen-jian Len 
Published: April 2011

ABSTRACTChemical bath deposition (CBD) techniques for the growth of CdS polycrystalline thin films are now well developed. However, there usually appear different structures, grain sizes and energy gaps in CdS polycrystalline films by CBD, which implies that the influence of growth process on the structures and properties of CBD CdS thin films must be considered. In this paper, the optical, compositional and structural properties of CBD CdS thin films in the reaction process have been studied by XRD, AFM, XPS and optical transmission spectra measurements. The results can be explained using atomic mechanism and lattice transition in the CdS thin films.
Development of An On-Chip Semiconducting Readout For Subsurface Optical Data
Authors: Loghry William K. , Ianno N. J. , Dillon R. O. 
Published: April 2011

ABSTRACTA preliminary device was investigated as a first step in making an on-chip electrical readout based on the semiconductor CdS for a novel 3-D optical data storage method. The optical data is stored in glass as subsurface nanometer size defects called voxels. These voxels display secondary harmonic generation (SHG) to 800 nm input light. The device begins with an indium tin oxide film on a glass substrate coated with a film of Al2O3. In this preliminary device the Al2O3 was patterned via optical lithography with a periodic array of 10 micron holes that were filled with electrodeposited CdS. X-ray diffraction, and energy dispersive X-ray analysis were used to characterize the CdS. The device operation depends on the ability of the CdS with a bandgap of 2.4 eV to detect the 3.1 eV SHG light from the voxels while remaining unresponsive to 1.6 eV input light. The electrodeposited CdS was found to absorb 400 nm light at least a factor of 10 times greater than 800 nm light. Light to dark photocurrent ratios of 15 to 63 were observed from the CdS pillars using a 150 W xenon broadband light source. A light to dark ratio of about one was found when a long pass optical filter allowed only wavelengths above 750 nm. Thus the 10 micron CdS pillars have detected 400 nm light while rejecting the 800 nm input light.
Comparison of the Strain and Stress in Bonded and Epitaxial Gallium Arsenide on Silicon by Photoreflectance Spectroscopy Measurements
Authors: Gallis Spyros , Deligeorgis George , Georgakilas Alexandros , Alexe Marin 
Published: April 2011

ABSTRACTThe presence of an internal strain arising from the GaAs/spin-on-glass (SOG)/Si bonding procedure was investigated. In addition, the magnitude of any residual stress at room temperature and the mechanisms that may impose a stress, leading to elastic or plastic deformation of the bonded GaAs films, were identified.A comparative study of biaxial strain and stress, as a function of temperature in the range of 80- 300 K, in a bonded 2 μm-thick GaAs/SOG/Si sample and in an epitaxial 2 μm-thick GaAs/Si sample, grown by molecular beam epitaxy (MBE), will be presented. The type and magnitude of strain were determined by photoreflectance spectroscopy. In the case of GaAs/SOG/Si, the strain in the GaAs layer was found to be negligible, with compressive character, at room temperature and tensile in all other measured temperatures, whereas for the epitaxial GaAs/Si, the strain was taking significant tensile values in all temperatures. Furthermore, the strain for both samples was increasing with temperature reduction, as it is expected for a thermal strain induced by the different thermal expansion coefficients of GaAs and Si.The comparative study indicated clearly that the bonded GaAs/SOG/Si films are essentially strain-free at room temperature. This is a very important result for the good reliability of laser diodes that can be processed from such bonded GaAs material, which also has a crystal quality similar to that of the available GaAs substrates.
Interdiffusion, Crystallinity and Exchange Bias in MnxPt1-x/Co Bilayers
Authors: Morales Erie H. , Wang Yikuan , Lederman D. 
Published: April 2011

AbstractThe structure of the antiferromagnet (AF) in the Ta/ MnxPt1-x/Co /Ta system must have the face-centered tetragonal CuAu structure in order to obtain a measurable exchange bias (HE). The formation of this structure has an onset temperature of approximately 240 °C. Increasing the annealing temperature increases the amount of CuAu ordering, which increases HE, and also increases the MnPt/Co interdiffusion, which decreases HE. These two competing processes result in an optimum annealing temperature that maximizes HE.
Crystal-field Effect on Magnetic Moment and Exchange-Coupling for Fe/W(100) and Fe/W(110)
Authors: Qian X. , Hübner W. 
Published: April 2011

AbstractThe Full-potential Linearized Augmented Plane-wave (FP-LAPW) method was employed to investigate the magnetic properties of 1 monolayer (ML) Fe on W(100) and W(110) substrates. Magnetic moments of the Fe overlayer are found to be very different with ∼2.0 μB for Fe on W(100) and ∼2.56 μB for Fe on W(110). The exchange coupling between Fe film and W substrate are also found to be orientation-dependent. The electronic coupling in Fe/W(100) thin film is found to be more long-range, compared to the one in Fe/W(110). These differences could be explained by the differences of local atomic bonding and crystal-field splitting in these two orientations.
Correlation between Magnetic Property and Cation Distribution in Z-type Hexagonal Barium-Ferrite (Ba3Co2-xFe24+xO41) by Neutron Diffraction
Authors: Takada Yukio , Tachibana Takeshi , Nakagawa Takashi , Yamamoto Takao A. , Shimada Takeshi , Kawano Shinji 
Published: April 2011

ABSTRACTZ-type hexagonal ferrite samples in which cobalt is partially substituted with iron, Ba3Co2-xFe24+xO41(x= 0, 0.2, 0.4, 0.6), were prepared by the ceramic process under a sintering oxygen partial pressure,PO2= 21.3 or 101.3 kPa, at 1573 K. The influence of the substitution ratio and oxygen partial pressure on the complex permeability was investigated by examining the cobalt distribution over various cation sites in the Z-type structure with the neutron powder diffraction analysis performed at 294 K (neutron wave length was 1.006Å). The neutron diffraction pattern was studied with the Rietveld method. A significant difference in the preferential occupation of cobalt on various kind of cation sites was observed between the samples obtained underPO2= 21.3 and 101.3 kPa. Almost all cobalt atoms are on the 12koctahedral site at the boundary between S- and R-blocks in the sample ofx= 0,PO2= 21.3 kPa. On the other hand, in the sample ofx= 0,PO2= 101.3 kPa, cobalt atoms are as well on other sites, the 12koctahedral site at the boundary between S- and T-blocks, the 4etetrahedral site in S-block, the 2aoctahedral site in T-block and the 2dfive fold (trigonal bypiramid) site in T-block.
Magnetoresistance and Hall Effect Characterisation on Magnetic Thin Films Multilayers
Authors: Neamtu Jenica , Volmer Marius 
Published: April 2011

ABSTRACTWe have performed both Hall effect, and magnetoresistance measurements on thin films of Permalloy (Py 10 nm) and Py(tPy)/Cu(tCu)/Py(tPy) multilayers deposited on thermally oxidized Si substrates, where tPy=4 and 10 nm and tCu=4 and 8 nm. The measurements were made at room temperature in a setup that allows us to perform both Hall effect and magnetoresi stance measurements. The Hall effect measurements were performed varying the angle, Δθ, between the magnetic field direction and the normal to the film plane from 0 to 90 degrees. The measured voltages present hysteresis loops at low magnetic field even for Δθ=0°. From these measurements we can obtain some information regarding the magnetic properties of our samples.
Progress in Epitaxial Oxides on Semiconductors
Authors: Yu Z. , Liang Y. , Li H. , Curless J. , Overgaard C. , Droopad R. , Wei Y. , Hu X. , Craigo B. , Finder J. , Eisenbeiser K. , Talin A. , Smith S. , Voight S. , Wang J. , Marshall D. , Jordan D. , Edwards J. , Moore K. 
Published: April 2011

ABSTRACTIn this paper, we review the recent progress in the area of epitaxial oxides on semiconductors at Motorola Labs. Critical issues such as surface preparation, initial nucleation and growth behaviors of SrTiO3 (STO) thin film epitaxy on Si(001) are addressed. Using a systematic approach, high-quality epitaxial STO films are successfully grown on semiconductor substrates such as Si, silicon-on-insulator (SOI) and Ge. Amorphous interfacial layer between the epitaxial STO and the semiconductor can be eliminated or tailored by controlling oxide growth process and parameters. STO-based metal-oxide-semiconductor (MOS) capacitors and transistors are fabricated and tested, in order to explore the potential of STO as high-k gate dielectrics for future generation CMOS transistor technology. In addition, high-quality STO epitaxial films are utilized as thin buffer layers for fabricating integrated oxide heterostructures on semiconductors. Various perovskite oxide films such as SrZrO3, LaAlO3 and Pb(Zr,Ti)O3 are deposited epitaxially on STO-buffered Si(001) for potential high-k gate dielectrics and surface-acoustic-wave (SAW) device applications.
The Influence of Defects on Compatibility and Yield of the HfO2-PolySilicon Gate Stack for CMOS Integration
Authors: Kaushik V. S. , DeGendt S. , Carter R. , Claes M. , Rohr E. , Pantisano L. , Kluth J. , Kerber A. , Cosnier V. , Cartier E. , Tsai W. , Young E. , Green M. , Chen J. , Jang S-A. , Lin S. , Delabie A. , Elshocht S. V. , Manabe Y. , Richard O. , Zhao C. , Bender H. , Caymax M. , Heyns M. 
Published: April 2011

ABSTRACTHafnium-based dielectrics are under wide consideration for high-K gate dielectric applications. Since the gate electrode typically used in CMOS integration consists of polysilicon with n- or p-type dopants, compatibility of the HfO2layer with the polySi deposition and dopant activation steps is critical. Capacitors were fabricated with HfO2films deposited by ALD and MOCVD, and using polysilicon gate electrodes deposited by CVD processes. These devices showed leakage failures with yields that were observed to depend on the area, dielectric thickness and annealing conditions during the process. Investigation of the root cause of these leakage failures suggested that the leakage failures may be caused by a defect-related mechanism. The implication of this is that the leakage occurs at localized ‘defect’ sites rather than broadly through the HfO2layer. Emission microscopy analysis and physical characterization of the HfO2film were used to corroborate the proposed model. Defect density was observed to be strongly dependent on the processing of the dielectric film. In order to make Hf-based dielectric stacks compatible with polysilicon for conventional CMOS transistor integration with acceptable yield, further postdeposition treatment may be necessary to eliminate or cure the defects.
Recent Development of Al2O3-based Gas-sensing Materials
Authors: Yu P. , Xiao D. Q. , Pan Y. , Li P. , Yang Z. H. , Zhu J. G. 
Published: April 2011

ABSTRACTγ-Al2O3-based gas sensing materials were invented, and three kinds of gas sensors, i.e. hydrogen, methane, and alcohol gas sensors, made from these materials were fabricated in our group years ago. Recently, the ether, ethane and gasoline gas sensors have also been made respectively from the nano-powders of γ-Al2O3-based gas sensing materials with different additives. In this paper the sensitivities and selectivites of the three new kinds of the gas sensors are reported, and the effect of the particle size of the nano-powder of the material on the performance of the methane sensors is also studied.
Intermediate Annealing Behavior And Grain Growth Of Al-Cu-Fe Quasicrystalline Coatings
Authors: Daniels M. J. , King D. , Zabinski J. S. , Bilello J. C. 
Published: April 2011

ABSTRACTA powder composite AlCuFe target was used to produce 10 micron films of a quasicrystalline precursor phase by RF sputtering onto polycrystalline alumina substrates. X-ray studies have determined this precursor to be a nano-quasicrystalline phase, despite previous reports of an amorphous structure. Anneals for various times at temperatures between 450°C and 550°C showed the evolution and grain growth of the quasicrystalline approximant structure as a function of both variables. Synchrotron diffraction studies showed a bimodal grain size distribution of the quasicrystalline approximant structure for anneals at 450 °C for 1 hour, below a previously reported transition temperature of 475 °C. Composition analysis of annealed films by XPS depth profiling showed the surface composition to be nearly stoichiometric Al2O3 and extensive oxygen penetration to 160 nm. X-ray diffraction studies have been correlated with cross section microscopy to characterize the development of quasicrystalline films from their precursors. Anneals for longer times and at higher temperatures showed no evidence of a bimodal distribution or remaining nanoquasicrystalline phases.
A Simple Model for the Formation of Step-Free Surfaces
Authors: Chang Kee-Chul , Blakely Jack M. 
Published: April 2011

ABSTRACTArrays of step-free regions on the surface of silicon have been created either by evaporating atoms from craters[1] or by depositing atoms on mesas[2]. In most cases the maximum extent of the step-free regions is limited by the occurrence of circular pits or islands in the crater or mesa structures. We model the process of step clearing and nucleation of these pits and islands by approximating the initial surface by an array of circular steps whose movement is mediated by adatoms. BCF (Burton-Cabrera-Frank) theory[3] is used to incorporate the effects of surface diffusion, evaporation and the deposition of atoms on the surface. We include the effects of step curvature and step interactions. If the step spacing is large enough, we find that the innermost step moves outwards to create a step-free region; otherwise it moves inward and leads to large scale smoothening of the surface. Pit or island nucleation in the center of the craters or mesas is also included in the model by using classical nucleation theory. We investigate the effect of deposition flux and temperature on the formation of step-free surfaces and compare the results to reported experiments on silicon and to some of our recent work on sapphire.