bluuebunny/crossref_metadata_2025_split huggingface dataset:
Low-Temperature Hetero-Epitaxial Growth of Ge on Si by High Density Plasma Chemical Vapor Deposition
Authors: Carroll Malcolm , Sheng Josephine , Verley Jason C. 
Published: April 2011

ABSTRACTDemand for integration of optoelectronic functionality (e.g., optical interconnects) with silicon complementary metal oxide semiconductor (CMOS) technology has for many years motivated the investigation of low temperature (∼ 450°C) germanium deposition processes that may be integrated in to the back-end CMOS process flow. A common challenge to improving the germanium quality is the thermal budget of the in-situ bake, which is used to reduce defect forming oxygen and carbon surface residues. Typical cleaning temperatures to remove significant concentrations of oxygen and carbon have been reported to be approximately 750°C for thermal hydrogen bakes in standard chemical vapor deposition chambers. Germanium device performance using lower peak in-situ cleans (i.e., ∼450°C) has been hampered by additional crystal defectivity, although epitaxy is possible with out complete removal of oxygen and carbon at lower temperatures.Plasma enhanced chemical vapor deposition (PECVD) is used to reduce the processing temperature. Hydrogen plasma assisted in-situ surface preparation of epitaxy has been shown to reduce both carbon and oxygen concentrations and enable epitaxial growth at temperatures as low as ∼150°C. The hydrogen is believed to help produce volatile Si-O and H2O species in the removal of oxygen, although typically this is not reported to occur rapidly enough to completely clear the surface of all oxygen until ∼550°C. In this paper, we describe the use of an in-situ argon/germane high density plasma to help initiate germanium epitaxy on silicon using a peak temperature of approximately 460°C. Germanium is believed to readily break Si-O bonds to form more volatile Ge-O, therefore, argon/germane plasmas offer the potential to reduce the necessary in-situ clean temperature while obtaining similar results as hydrogen in-situ cleans. To the authors knowledge this report is also the first demonstration of germanium epitaxy on silicon using this commercially available high density plasma chamber configuration instead of, for example, remote or electron cyclotron resonance configurations.
The Medium-Depending Fluorescence of Quadrupolar Donor-Acceptor-Donor Substituted Distyrylbenzenes with High Two-Photon Absorption Cross-Sections
Authors: Detert Heiner , Schmitt Volker , Glang Stefan 
Published: April 2011

ABSTRACT1,4-Distyrylbenzenes with terminal dialkylamino groups and a central 2,5-disubstitution with electron-accepting groups were prepared via twofold Horner-olefination. These chromophores with a quadrupolar donor-acceptor-donor substitution and C2-symmetry absorb in the violet to green region of the visible spectrum exhibit large two-photon-absorption cross-sections when irrdiated in the NIR. Whereas a variation of the solvent polarity only slightly alters the absorption spectra, the fluorescence appears to be highly responsive. Besides a positive solvatochromism, the emission is very sensitive towards protonation. Quenching or appearance of new emitting species depends on the substitution pattern and is controlled by the concentration of the acid.
Bi-stable State for WORM Application Based on Carbazole-containing Polymer
Authors: Teo Eric Yeow Howee , Ling Qidan , Song Yan , Tan Yoke Ping , Wang Wen , Kang En-Tang , Chan Daniel Siu Hung , Zhu Chunxiang 
Published: April 2011

ABSTRACTRecently, several studies have been done by various groups to understand the memory effects behind organic materials, which include understanding in terms of conformation changes, conjugation modification and oxidation-reduction process. In this paper, a WORM (write-once read-many times) memory device using a new polymer material 2-(9H-carbazol-9-yl)ethyl methacrylate (PCz) containing carbazole donor group has been demonstrated. The device uses a MIM (metal-insulator-metal) structure with ITO coated glass as bottom electrode, the synthesized polymer material PCz as the active layer and Al as the top electrode. The toluene solution of PCz was spin-coated on the ITO, followed by solvent removal in a vacuum chamber. Finally, Al was thermally evaporated through shadow mask onto the PCz film.The memory effect of PCz was observed in the I-V characteristic of the MIM structure. The as-fabricated device is found to be in its OFF state, and can be programmed to ON state which is not reversible. The WORM device exhibits a high ON/OFF current ratio of up to 106, and shows a good retention time for both the ON and OFF states which can be sustained within a 24 h timeframe, and extrapolated to sustain for another 10 years. The effect of continuous read pulse on the ON and OFF states was evaluated and no resistance degradation is observed for read cycles up to 107 times. By comparing the electrical characteristics of PCz and PVK as well as their optimized geometry simulation corresponding to their minimized energy states, the memory effect or bi-stable states of PCz can be attributed to the long linker between the carbazole groups and backbone present in PCz which play a part in the conduction mechanism.
Ab inito Calculation of Electron Transport Through Single Molecules by the RTM/NEGF Method
Authors: Hirose Kenji , Kobayashi Nobuhiko 
Published: April 2011

ABSTRACTUsing the recursion-transfer-matrix (RTM) method, which is a powerful method to obtain accurate scattering waves, combined with non-equilibrium Green's function (NEGF) method, we study the transport properties through single molecules sandwiched between electrodes with finite bias voltages. Especially, we investigate the effects of atomic-scale contacts on the I-V characteristics. We find strong nonlinear behaviors appear in the I-V characteristics when the atomic-scale contact at one electrode is not formed well.
Single Crystal InSb Nanowires: Synthesis, Characterization, Properties and Applications
Authors: Ye Qi Laura , Yamada Toshishige , Liu Hongbing , Scheffler Raymond , Mingo Natalio , Leverenz Ryan 
Published: April 2011

ABSTRACTWe report the first large-scale synthesis of single crystal InSb nanowires using vapor-liquid-solid (VLS) transport process. Narrow growth window for achieving single crystal InSb nanowires has been discovered. Our batch produced InSb nanowires are 50-180 nm in diameter and 10-30 μ in length. Materials composition analysis by Energy-Dispersive X-ray Spectroscopy (EDAX) reveals that the as-grown InSb nanowires are pure single crystals of InSb. Structural analysis by High Resolution Transmission Electron Microscopy (HRTEM) and Selected Area Electron Diffraction (SAED) reveals that InSb nanowires have body-centered-cubic (BCC) crystal structure with cubic unit cell length of 10.15 Å. The nanowire growth direction is found to be [001], 45 degrees toward the most dense lattice planes in BCC structure.
Growth of GeO2 Nanowires by Thermal Annealing
Authors: Wu Chun-I , Hogan T. P. 
Published: April 2011

ABSTRACTGermanium dioxide nanowires have gained considerable interest lately [1, 2], in part this is due to the bandgap of 2.44 eV, and high index of refraction, n = 1.63 [3]. In this paper we report a simple fabrication technique for making large quantities of GeO2 wires with diameters ranging from 40 nm to >500 nm on different substrates. The nanowires show strong preferential growth at gold catalyst locations on the silicon substrate. The nanowires were grown on silicon, tungsten, quartz, and nickel substrates at locations where a ∼10 nm film of Au was deposited. Growth and diameter of the wires are strongly dependent on the background gas (room air) and the length of time exposed to air at the growth temperature. Presented here are the growth conditions, and images of the resulting wires fabricated. The products are characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM) as well as X-Ray diffraction (XRD). The observations show the products are crystalline GeO2 nanowires.
Large Nonlinear Kerr Angle in non-Centrosymmetric Fe/AlGaAs (001) Heterostructure
Authors: Zhao Haibin , Talbayev Diyar , Luepke Gunter , Hanbicki Aubrey , Li Connie , Jonker Berend 
Published: April 2011

AbstractA large nonlinear magneto-optical effect is observed in a non-centrosymmetric Fe/AlGaAs (001) heterostructure. This effect is a direct consequence of interference between second-harmonic optical waves of magnetic and crystallographic origin, generated at ferromagnetic Fe interface and bulk AlGaAs, respectively. The longitudinal nonlinear Kerr rotation is measured to be 1.6° along the [1-10] hard axis, about two orders of magnitude stronger than the linear equivalent. The rotational second-harmonic signal shows large magnetic contrast along all the in-plane directions, demonstrating a high sensitivity to the magnetization of an anisotropic interface in the longitudinal geometry.
Onset of Exchange Anisotropy in Epitaxial fct-Cobalt(001)/fct-Manganese(001) Bilayers
Authors: Kohlhepp Jürgen T. , Wieldraaijer Harm , de Jonge Wim J. M. 
Published: April 2011

ABSTRACTManganese (Mn) grows in a meta-stable expanded (c/a > 1) face-centered-tetragonal (fct) phase on thin fct-Co(001) template films. For small Mn thicknesses a close to a layer-by-layer growth is observed. Antiferromagnetism (AFM) of fct-Mn is evidenced by the observation of shifted magnetization loops antiparallel to the cooling field direction (negative bias) and enhanced coercive fields for Co/Mn bilayers. At low temperatures magnetic Co/Mn interface exchange interactions are detected for nominal Mn thicknesses as low as 1.3 monolayer (ML), indicating the onset of AFM in 2 ML thick Mn islands. However, between 2 ML and 5 ML Mn a positive bias of the magnetization loops is observed in a certain temperature range below the blocking temperature (TB) of the films. This peculiar behavior is explained by the dependence of TB on both the local Mn ML thickness and the Mn island size, leading to a unidirectional coercivity enhancement in a temperature range where both blocked and unblocked regions are coexisting in the Mn layers.
Magnetic Rare Earth (Gd) Implanted Tetrahedral Amorphous Carbon (ta-C)
Authors: Zeng Li , Helgren Erik , Zutz Hayo , Ronning Carsten , Hellman Frances 
Published: April 2011

ABSTRACTTetrahedrally bonded amorphous carbon (ta-C) thin films were prepared by mass selected ion beam deposition (MSIBD) using 100 eV carbon ions at room temperature. Gadolinium, a magnetic rare earth element, was implanted as a dopant into ta-C with two different fluences. The doping level of the ta-C:Gdx layers was in maximum 4 or 7 at.%, respectively. The Gd is believed to be electrically activated in as-implanted films, although contributions from the sp2 sites cannot be ruled out. A transition temperature (T') was found, below which there is a large negative magnetoresistance (MR) with a strong temperature dependence. Thermal annealing greatly increases the sample conductivity due to the increase of sp2 sites. However, the MR persists at least up to an annealing temperature of 500°C. Magnetically, the Gd dopants behave like non-interacting local moments. Similarities and differences in physical properties between the ta-C:Gdx films and other Gd doped amorphous semiconductors are compared.
A Novel Simple Route to Synthesize Aqueous Niobium and Tantalum Precursors for Ferroelectric and Photocatalytic Applications
Authors: Li Ai-Dong , Cheng Jin-Bo , Tang Rong-Lu , Shao Qi-Yue , Tang Yue-feng , Wu Di , Ming Nai-Ben 
Published: April 2011

ABSTRACTA simple novel route to synthesize aqueous tantalum and niobium precursors has been developed using cheap and stable Nb2O5 or Ta2O5 as starting source, based on basic flux technique. Various analytical techniques have been employed to characterize the purity, and thermal decomposition features of the precursors. Using home-made Ta and Nb precursors, several photocatalysts and ferroelectric powders such as LiNbO3, LiTaO3, Sr0.75Ba0.25Nb2O6, and SrBi2Ta2O9 have been prepared at lower processing temperature by a polymerizable complex route successfully.
Wet-Chemical Synthesis of ZnTe Quantum Dots
Authors: Zhang Jun , Sun Zhaoyong , Fang Jiye 
Published: April 2011

ABSTRACTZnTe quantum dots (QDs) have been very attractive because of their potential applications in optoelectronic devices operating in the blue-green region of the spectrum. This paper describes a convenient one-step synthesis of high-quality ZnTe QDs in high-temperature organic solution with high yield. Anhydrous zinc chloride was dissolved in phenyl ether under argon protection and oleic amine was used as coordinating agent. Complex solution of metal tellurium in trioctylphosphine (TOP) was injected into the hot reaction mixture as a source of tellurium. The reaction was complete in several minutes and the resulting QDs were isolated by centrifugation and re-dispersed in hexane. The produced spherical ZnTe QDs are monodispersed and their sizes could be controlled simply by varying the growth temperature. The morphology and phase structure were investigated using TEM and XRD. Photoluminescence (PL) spectra were also studied and quantum size effects were observed as well.
AFM Studies on the Morphological Evolution of Chemically Deposited In2S3 Thin Films as a Function of Deposition Time
Authors: Sotelo-Lerma Merida , Castelo-Gonzalez Omar Armando , Ramirez-Bon Rafael , Espinoza-Beltran Francisco Javier 
Published: April 2011

ABSTRACTIndium sulphide (In2S3) is a very promising semiconductor material for window layers in solar cell devices. It is currently being investigated for high efficiency solar cell based on Cu(In,Ga)Se2-In2S3 heterostructures. The chemical bath deposition (CBD) technique is one of the most convenient methods to obtain In2S3 films because of its simplicity, low cost and some other advantages. Amorphous and polycrystalline In2S3 films on glass substrates have been obtained by the CBD technique. Like in many others CBD processes, the deposition mechanism and kinetic growth of In2S3 films on glass substrates is not very well understood [1-6]. In this work we have chemically deposited In2S3 films for different times from 6 up to 39 hours, in order to study by atomic force microscopy (AFM) the formation of the films on glass substrates. The AFM measurements were performed in a liquid medium in which the cantilever tip and the sample are completely immersed in the liquid. A specially designed AFM cell is composed of a tip attached to a circular transparent window, the liquid level is between the upper and lower surface of the window, and a circular meniscus is established around the window, preventing the tip could be affected or destroyed by the surface tension of the liquid. By using this liquid AFM technique, we can at real-time observe the thin film forming process, and thereby clearly reveal the growing mechanism. It is an ideal and more practical tool for in situ investigation of samples which are normally found in liquid environments.
Non-Contact Metrology for Electrical Characterization of Photo-Voltaic Materials
Authors: Current Michael Ira , Faifer Vladimir , Wong Tim , Walecki Wojtek , Nguyen Tan 
Published: April 2011

ABSTRACTA non-contact metrology for electrical characterization of p-n junctions has been developed for use on photo-voltaic materials. By analysis of junction photo-voltage (JPV) measurements at multiple light beam modulation frequencies and multiple light penetration depths, a comprehensive electrical analysis of photo-voltaic materials is provided for junction sheet resistance, leakage current, capacitance and bulk carrier diffusion length. The JPV analysis can be made with screen and native oxides on the surface, so no pre-measurement chemical etching is required. Since the probe does not contact the p-n junction surface, measurements can be made in a continuous fashion with the junction moving under the probe, providing a method for efficient high-resolution mapping of local electrical properties. The non-contact probing also allows for non-damaging measurements in both “hard” (Si) and “soft” (organic) photo-voltaic materials. Examples of p-n junction properties in polished, crystalline-Si and cast poly-Si will be discussed.
Development of YBCO film approached by TFA-MOD method using the Y2Ba1Cu1Ox and Ba3Cu5O8 powders
Authors: Lim Jun Hyung , Jang Seok Hern , Yoon Kyung Min , Joo Jinho , Jung Seung-Boo , Nah Wansoo 
Published: April 2011

ABSTRACTThe YBCO films were fabricated by TFA-MOD method in route of ¡°211 process¡± and evaluated the phase formation, texture evolution, and critical properties as a function of the humidity firing process. In the fabrication process, Y2Ba1Cu1Ox and Ba3Cu5O8 powders, instead of Y-, Ba- and Cu-based acetates, were used as precursors. In order to evaluate the effect of humidity during the firing process, the films calcined at 430¡É were fired at 775¡É in dry Ar(0%), 4.2%, 8.0%, 12.1%, and 20.0% humidified Ar gas mixed with 1000 ppm oxygen.We observed that the amount of BaF2 phase was effectively reduced and that a sharp and strong biaxial texture formed under a humidified atmosphere, leading to increased critical properties. The film became denser and the degree of texture and phase purity varied as the humidity increased. For the film fired in 0% humidity, the measured value of Tc(onset) was found to be 82.5 K, but the Tc(zero) could not be measured. When the humidity was increased to 4.2%, the corresponding Tc(onset) and Tc(zero) were increased to 91.5 K and 88.6 K, respectively. For the films in the humidity range of 12.1-20.0%, the critical current was found to be 30 A/cm-width (the corresponding critical current density is 1.54 MA/cm2).
New Macroporous Crosslinked Polymer Gels Prepared via Living Radical Polymerization
Authors: Kanamori Kazuyoshi , Nakanishi Kazuki , Hanada Teiichi 
Published: April 2011

ABSTRACTMacroporous crosslinked polymer gels have been prepared via TEMPO-mediated living radical polymerization of divinylbenzene (DVB) in a solvent with a counter polymer. Incorporating a counter polymer, poly(dimethylsiloxane) (PDMS), induced macroscopic spinodal-type phase separation during the course of polymerization of DVB while suppressing the segregation of DVB-derived particles from the solution by living polymerization. Well-defined macroporous morphologies comprising continuous DVB-derived skeletons have thus obtained. Macropore volume and diameter were independently controlled by altering the concentrations of PDMS and the solvent. Since the present polymer gels are prepared using only the multifunctional “crosslinker”, mechanical durability against bending and compression was found to be as high as inorganic ceramics with similar morphologies and porosities.
Polymer Adsorption onto Selective Mixed Brushes
Authors: Chervanyov Alexander , Heinrich Gert 
Published: April 2011

ABSTRACTWe theoretically studied the reversible adsorption of polymers onto selective mixed brushes. Mixed brushes are recently developed self-adoptive materials that reversibly change their morphology in response to altering external stimuli. The above changes in the morphology result in the reversible formation of different patterns on the outer surface of the brush. It is shown that thus achieved patterning of the adsorbing surface of the mixed brush can dramatically enhance the adsorption of polymers onto this brush, as compared to the adsorption onto the homogeneous brush surface. By making use of the developed self-consistent field theory we calculate the surface excesses of homo- and co-polymers adsorbed on the binary mixed brush for the two different morphologies (`ripple' and random). The interplay between the depletion effect caused by the loss of the polymer entropy in the interior of the brush and binding interactions is shown to lead to a rich adsorption-desorption behavior. The surface excess of the adsorbed polymers is calculated as a function of the relation between the radius of gyration of the adsorbed polymers and characteristic size of the surface pattern. Shorter (relative to the size of the pattern) polymers are shown to better adsorb onto the regular patterned brush surface, as compared to the random brush surface.
A Simple Method to Grow Polymer Nanofibers from Superglue
Authors: Mankidy Pratik , Rajagopalan Ramakrishnan , Pantano Carlo , Foley Henry 
Published: April 2011

ABSTRACTA novel template-less method for polymerization of ethyl 2-cyanoacrylate to form an intrinsically nanofibrous polymer is investigated. Effect of the anionic initiator used for polymerization is examined to explain the mechanism of formation of nanofibers or film of polymer. A suitable classification of the initiators is established based on the Hard Soft Acid Base principle to explain the mechanism. Infrared analysis, SEM and Gel permeation chromatography is utilized for characterization of the different polymer samples.
Polyethylene Oxide Nanofibers as Ultraviolet Sensors
Authors: Khan Saima Naz , Rack Jeffrey J. , Rachford Aaron R. , Kordesch Martin E. 
Published: April 2011

ABSTRACTUsing the electrospinning technique, we have prepared [Ru (pic) 2 (dmso) 2] doped-polyethylene oxide nanofibers for ultraviolet sensing. The diameter of the as-prepared fibers is in the range of 1μm-100nm. These fibers change color from pale yellow to orange when exposed to ultraviolet light (wavelength∼350nm) and return to their original color after approximately 2-3 days. The intensity of the color increases with an increased time of exposure to UV. The color changing behavior in the nanofibrous mat is almost the same as that in cast films prepared from the same solutions. The scanning electron microscope (SEM) studies of the fibers show that the morphology of the fibers remains unchanged after exposure to UV.
Formation of Palladium Structures Combining Electrospinning and dc Sputtering
Authors: Otaño Wilfredo , Otero Ariel O. , Otaño José M. , Otaño Carlo S. , Santiago Jorge J. , Pantojas Víctor M. 
Published: April 2011

ABSTRACTElectrospinning and dc sputtering techniques were combined for the formation of a variety of nano-to-microscale structures of palladium metal. Polyethylene fibers created by electrospinning were used as templates for the dc sputtering of palladium on top of them. Heating the fibers to 320 °C in air eliminated the central polymer core (fugitive phase) resulting in the formation of open and closed core fibers, depending on the amount of Pd previously deposited. The formation of the structures is best explained as a consequence of sputtering being a line-of-sigh technique. Palladium is preferentially sputtered on top of the fiber part facing the target, resulting in a non-uniform deposition. Furthermore, it is proposed that the deposition of palladium on top of the fibers results in the nucleation of palladium crystals growing outward of the surface and producing interesting nanoscale features observed resembling thorns and scales.