bluuebunny/crossref_metadata_2025_split huggingface dataset:
Dissociation of H2O molecule adsorbed on Si (001) 2×1 surface: a theoretical study
Authors: Oh Hyun-Chul , Seo Hwa-Il , Kim Yeong-Cheol 
Published: January 2010

AbstractThe adsorption and dissociation behavior of water molecule below and above the critical dissociation temperatures were studied by first principles calculations. We found that water-molecule adsorption (surface coverage, θ=0.25) on the down Si atom of a Si dimer in two dimers surface model was 0.26 eV more favorable than that on the up Si atom. The activation energies of water molecule on the down Si atom for interdimer and intradimer dissociations were 0.17 eV and 0.20 eV, respectively. Due to the lower activation energy, the water molecule splits into H and OH immediately once it adsorbs on down Si atom of the Si (001) surface at room temperature. There were three different adsorption sites among four sites of the two dimers for the second water molecule (θ=0.5): one was preoccupied by OH of the first water molecule; up Si atom of the same-dimer with 76.3 % probability, up Si atom of the adjacent-dimer with 23.6 % probability, and down Si atom of the adjacent-dimer with 0.1 % probability. Thus, ½ monolayer of OH sites on the Si (001) surface are irregularly distributed when water molecules are adsorbed and dissociated at room temperature.
Nonvolatile Charge Storage Characteristics of a MOS Diode with Buried Silicon Nanocrystals and Interfacial Si Nano-pyramids
Authors: Lien Yu-Chung , Pai Yi-Hao , Lin Cheng-Tao , Lin Gong-Ru 
Published: January 2010

AbstractThe memory effect of MOS diodes made on Si substrate with Si nanocrystals (NC-Si) and interfacial Si nano-pyramids deposited by PECVD at different ICP powers is characterized. TEM analysis on the NC-Si reveals that the NC-Si average size are around 3.9±1.1 nm and 4.7±0.7 nmwhen grown at ICP power of 20 W and 30 W, respectively. The interfacial Si nano-pyramids can only be observed by growing at 30 W or larger. The density of NC-Si of 4.4 × 1018 and 5.6 × 1018 cm−3 are relatively in good agreement with the corresponding PL intensities of 45 and 73 count/nm, respectively, for 20 and 30-W grown SiOx samples.. The C–V curves of the NC-Si embedded MOSLEDs show flat-band voltage shift of 0.74 and 18.46 Vfor 20 and 30-W samples, respectively. The C-V hysteresis width also increases by enlarging the range of sweeping voltage. A strong correlation between the size/density of Si nanocrystals and the flatband voltage difference has been concluded. In the case of the C–t measurement, the charging and discharging behaviors were found to depend on charging conditions. Finally, the relationship of the electron/hole charge density with the retention time is analyzed. Our data shows the charge loss rate of 1.3 % for electron is better at 20-Wsample, but the charge loss rate of 0.23 % for hole is better at 30-Wsample with Si NCs embedded in MOSLED after 102 s.
A MHz Modulable Si-based LED Afforded by Engineering Light-emitting Defects in Si
Authors: Tana-ami Norishige , Igarashi Jun , Terada Yosuke , Yasutake Yuhsuke , Fukatsu Susumu 
Published: January 2010

AbstractWe demonstrate a Si-based light-emitting diode (LED) with MHz modulation capability containing a certain class of light-emitting defects in the active region. The emission spectra are characterized by a narrow peak centered at 900 meV (1377 nm), hereafter referred to as E-line, which is attributed to the {311} defects inherent to cubic crystals with the diamond sublattice. The luminescence intensity of the E-line was found to go through a maximum around 20K persisting above 150 K. In spite of the decay lifetimes even longer than 1μs, 31% amplitude modulation was achieved for 1-MHz rectangular pulses at 20 K while near 10-MHz bandwidth was obtained for dynamic operation with modulated pulse widths.
Metal Coated, fs-Laser Fabricated Silicon Spikes as Electron Emitters for Cold Cathode Applications
Authors: Spanakis Emmanuel , Barberoglou Marios , Tzanetakis Panagiotis , Fotakis Costas 
Published: January 2010

AbstractWe have studied the effect of thin metal coatings on the electron emission characteristics of self-assembled silicon microstructures with nearly identical sharp features. We have employed a common template of spikes produced by fs-laser self-driven structuring of Si on which several different metals have been deposited. We find that, in the pristine state and in vacuum conditions achievable in device applications, all metal coatings do not result in marked change of either the minimum electric field necessary for emission or the maximum obtainable current density. In contrast, the durability of the emitters depends strongly on the metal used and is always enhanced with respect to bare Si. Furthermore, no signs of degradation were found within the 3-day time scale of our experiments with gold and chromium. On the contrary, these two metal coatings resulted in emission characteristics improving with time in typical operation conditions.
GaN/ZnO and AlGaN/ZnO Heterostructure LEDs: Growth, Fabrication, Optical and Electrical Characterization
Authors: Benz Julian , Eisermann Sebastian , Klar Peter J. , Meyer Bruno , Detchprohm Theeradetch , Wetzel Christian M. 
Published: January 2010

AbstractThe wide bandgap polar semiconductors GaN and ZnO and their related alloys exhibit fascinating properties in terms of bandgap engineering, carrier confinement, internal polarisation fields, and surface terminations. With a small lattice mismatch of ∼1.8 % between GaN and ZnO and the possibility to grow MgZnO lattice-matched to GaN, the system AlGaN/MgZnO offers the opportunity to design novel optoelectronic devices circumventing the problem of p-type doping of ZnO. In such AlGaN/MgZnO heterostructures with either hetero- or isovalent interfaces, tuning of band offsets is possible in various ways by polarisation fields, surface termination, strain, and composition. These aspects need to be fully understood to be able to make full use of this class of heterostructures. We report on the growth of ZnO films by chemical vapor deposition on p-type GaN and AlGaN grown by metal-organic vapor deposition on sapphire templates and on the fabrication of corresponding light-emitting diode (LED) structures. Electrical and optical properties of the n ZnO/p-GaN and n-ZnO/p-AlGaN LEDs will be compared and the observed differences will be discussed in terms of the band alignment at the heterointerface.
Fabrication, Processing and Characterization of Thin Film ZnO for Integrated Optical Gas Sensors
Authors: Kamińska Eliana , Piotrowska Anna , Pasternak Iwona , Ekielski Marek , Gołaszewska Krystyna , Rzodkiewicz Witold , Wojciechowski Tomasz , Dynowska Elżbieta , Struk Przemysław , Pustelny Tadeusz 
Published: January 2010

AbstractZinc oxide layers deposited on quartz substrates by means of RF reactive magnetron sputtering with subsequent RTP annealing in a nitrogen flow at 400°C and in an oxygen flow at 500°C have been investigated in applications to waveguide structures. The ZnO films reveal a highly c-oriented columnar structure with a surface roughness of 4.3 nm. Annealing causes a significant increase of the lattice constant to the value of 5.210±0.001 Å suggesting the relaxation of the stress in the film. The annealing process causes a significant improvement of propagation properties of the fabricated waveguide structures in comparison to structures using as-deposited ZnO films. The minimal attenuation coefficient of the 630 nm thick films was found to be 2.8 and 3.0 dB/cm for TE0 and TM0 modes respectively.
Electrically Air-stable ZnO Thin Film Produced by Reactive RF Magnetron Sputtering for Thin Film Transistors Applications
Authors: Ngwashi Divine , Cross Richard B. M. , Paul Shashi 
Published: January 2010

AbstractThe influence of native point defects on the electrical and optical stability of zinc oxide (ZnO) layers in air produced by reactive RF magnetron sputtering is investigated. ZnO thin films are strongly affected by oxygen (O2) molecules in ambient atmosphere. For instance, surface defects such as oxygen vacancies act as adsorption sites of O2 molecules, and the chemisorption of O2 molecules depletes the surface electronic states and reduces channel conductivity. Thin films of ZnO produced have electrical resistivities between 8.6 × 103 and 8.3 × 108 Ω-cm, and were found to be electrically-stable in air. TFTs fabricated using these films exhibited effective mobilities of ∼3 cm2V-1s-1 and the threshold voltage shifts by < 5 V under gate bias stress of 1 MV/cm for up to 104 s.
An Inverse electrolysis method to Synthesize Surface Nano-roughened ZnO Contact Electrode
Authors: Liao Yu-Hao , Pai Yi-Hao , Lin Gong-Ru 
Published: January 2010

AbstractThe fabrication of surface nano-roughened zinc oxide (ZnO) is demonstrated by using a zinc/air fuel cell based chemical reactor. The chemical reaction creates the hydroxyl near the Zn and randomizes the pores with accumulated hydroxyls, which causes Zn to be oxidized to form thick and nano-roughened ZnO upon Zn anode or to be transformed into a soluble complex zincate ion in the excess electrolyte. Furthermore, controlling the quantity of (Zn(OH)2) and [Zn(OH)4]2− can significantly decrease the defect-related emission and blue-shift PL spectra to the UV range.
Al2O3 as a Transition Layer for GaN and InGaN Growth on ZnO by MOCVD
Authors: Li Nola , Wang Shen-Jie , Fenwick William E. , Melton Andrew , Huang Chung-Lung , Feng Zhe Chuan , Summers Christopher , Jamil Muhammad , Ferguson Ian 
Published: January 2010

AbstractGaN and InGaN layers were grown on annealed 20 and 50nm Al2O3/ZnO substrates by metalorganic chemical vapor deposition (MOCVD). GaN was only observed by high resolution x-ray diffraction (HRXRD) on 20 nm Al2O3/ZnO substrates. Room temperature photoluminescence (RT-PL) showed the red shift of the GaN near band-edge emission, which might be from oxygen incorporation forming a shallow donor-related level in GaN. HRXRD measurements revealed that (0002) InGaN layers were also successfully grown on 20nm Al2O3/ZnO substrates. In addition, thick InGaN layers (∼200-300nm) were successfully grown on Al2O3/ZnO and bare ZnO substrates. These results are significant as previous studies showed decomposition of the layer at InGaN thicknesses of 100nm or less.
Crystal polarity control of ZnO films and nonlinear optical response
Authors: Park Jin Sub , Yamazaki Yoshiki , Takahshi Yoshihiro , Minegishi Tsutomu , Park Seunghwan , Hong Soonku , Chang Ji-Ho , Fujiwara Takumi , Yao Takafumi 
Published: January 2010

AbstractWe report that the nonlinear optical response of polarity controlled ZnO films grown by selective growth technique of Zn-polar and O-polar ZnO layers on sapphire substrate using Cr-compound buffer layers. ZnO layers grown on CrN/sapphire show Zn polar, while those grown on Cr2O3/sapphire result in O-polar ZnO films. In order to verify the origin of nonlinear optical response of ZnO, the polarity-controlled ZnO thin films grown on different buffer layers were investigated as nonlinear optical materials for second harmonic generation (SHG). The effective nonlinear optical coefficient (deff) of ZnO grown on Cr-compound buffer layers showed a higher value than that of ZnO grown on MgO buffer layers. Finally, by combining suggested in-situ polarity control technique with photolithography technique, we have fabricated 1D and 2D periodically-polarity-inverted (PPI) hetro-structures with periodicity ranging from 60 μm to 2 μm. The lateral polarity inversion is confirmed by piezo response microscopy. Such PPI ZnO heterostructures show the enhancement of SHG intensity comparing with the ZnO films.
Modification of structure and optical property of ZnO nanowires by Ga ion beam
Authors: Cheng Yao , Liang Yao , Lei Ming , Hark Siu Kong , Wang Ning 
Published: January 2010

AbstractBased on the focused ion beam (FIB) technology, we have prepared ZnO nanowires containing periodic nano-sized structures by an ultra thin Ga ion beam. ZnO nanowires can keep a good crystal quality after Ga ion bombardment. The cathodoluminescence (CL) spectroscopy study of the Ga-doped ZnO nanowires at low temperatures shows that the Ga doping effect can largely suppress the green emission that may mainly originate from the defects on the surfaces of ZnO nanowires.
Influence of O2/Ar Ratio on the Properties of Transparent Conductive Titanium-Doped Indium Oxide Films by DC Radio-Frequency Sputtering
Authors: Li Lei , Li Li , Yu Xin , Yu Hai , Chen Chen , Song Zhenyu , Cong Menglong , Wang Yiding 
Published: January 2010

AbstractTitanium doped indium oxide (TIO) thin films were deposited on glass substrate by DC sputtering with different O2/Ar gas ratios at 330 °C. The effects of sputtering on the structural, morphologic, optical and electrical characteristics of TIO thin films were investigated by XRD, Hall measurement and optical transmission spectroscopy. The deposited films exhibited polycrystalline in the preferred (222) orientation, with higher mean grain size and lower resistivity 3.37 ×10-4Ω·cm at O2/Ar ratio of 1/10. The average optical transmittance of the films is over 90%, and the transmittance has no evident change with changing O2/Ar ratio.
ZnO Thin Film Transistors Fabricated by Atomic Layer Deposition Method
Authors: Kawamura Yumi , Hattori Nozomu , Miyatake Naomasa , Murata Kazutoshi , Uraoka Yukiharu 
Published: January 2010

AbstractIn this study, we deposited zinc oxide (ZnO) thin film by atomic layer deposition (ALD) as an active channel layer in thin film transistor (TFT) using two different oxidizers, water (H2O-ALD) and oxygen radical (PA-ALD). The fabricated TFTs were annealed at various temperatures, in an oxygen ambient gas. The electrical properties of TFTs with PA-ALD ZnO film annealed at the temperature up to 400[oC] improved without any degradation of the subthreshold swing or any large shift of the threshold voltage. Through this study, we found that the high performance ZnO TFTs is possibly obtained using PA-ALD at low temperature, and the electrical properties are dependent on the annealing temperature.
Reaction Anisotropy and Size Resolved Oxidation Kinetics of Zinc Nanocrystals
Authors: Ma Xiaofei , Zachariah Michael R. 
Published: January 2010

AbstractIn this work, size-classified substrate-free Zn nanocrystals (NCs) are prepared and investigated for their oxidation kinetics using an in-flight tandem ion-mobility method. The first mobility characterization size selects the NCs, while the second mobility characterization measures changes in mass resulting from a controlled oxidation of the NCs. This method allows for a direct measurement of mass change of individual particles and thus enables us to explore the intrinsic reactivity of NCs while minimizing the sampling error introduced by mass and heat transfer. Two reaction regimes were observed for Zn NC oxidation. A shrinking core model is used to extract the size-dependent oxidation activation energies. We also observed a strong anisotropy effect in the oxidation process as imaged by electron microscopy. An oxidation mechanism is proposed that qualitatively explains the oxidation anisotropy and its relationship to the surface energy of the Zn NCs.
Selective Area Epitaxy of InGaN/GaN Stripes, Hexagonal Rings, and Triangular Rings for Achieving Green Emission
Authors: Feng Wen , Kuryatkov Vladimir , Rosenbladt Dana , Stojanovic Nenad , Pandikunta Mahesh , Nikishin Sergey A , Holtz Mark 
Published: January 2010

AbstractWe report selective area epitaxy of InGaN/GaN micron-scale stripes and rings on patterned (0001) AlN/sapphire. The objective is to elevate indium incorporation for achieving blue and green emission on semi-polar crystal facets. In each case, GaN structures were first produced, and the InGaN quantum wells (QWs) were subsequently grown. The pyramidal InGaN/GaN stripe along the <11-20> direction has uniform CL emission at 500 nm on the smooth {1-101} sidewall and at 550 nm on the narrow ridge. In InGaN/GaN triangular rings, the structures reveal smooth inner and outer sidewall facets falling into a single type of {1-101} planes. All these {1-101} sidewall facets demonstrate similar CL spectra which appear to be the superposition of two peaks at positions 500 nm and 460 nm. Spatially matched striations are observed in the CL intensity images and surface morphologies of the {1-101} sidewall facets. InGaN/GaN hexagonal rings are comprised of {11-22} and {21-33} facets on inner sidewalls, and {1-101} facets on outer sidewalls. Distinct CL spectra with peak wavelengths as long as 500 nm are observed for these diverse sidewall facets of the hexagonal rings.
On the Light Emission in GaN Based Heterostructures at High Injection
Authors: Ni Xianfeng , Li Xing , Liu Huiyong , Izyumskaya Natalia , Avrutin Vitaliy , Özgür Ümit , Morkoç Hadis , Paskova Tanya , Mullholland Greg , Evans Keith R. 
Published: January 2010

AbstractFor light emitting diodes (LEDs) to be used for general lighting, high efficiencies would need to be retained at high injection levels to meet the intensity and efficiency requirements. In this regard, it is imperative to overcome the observed drop in LED efficiency at high injection levels beyond that would be expected from junction temperature. The suggested genesis of efficiency degradation includes electron overflow or spillover, also suggested to be aided by polarization induced electric field, Auger recombination, current crowding, and elevated junction temperature. Setting the junction temperature aside, the degree to which or even whether each of these mechanisms plays a role is still under debate. We have undertaken a series of experiments to isolate, whenever possible, the aforementioned processes in an effort to determine the causes of efficiency loss at high injection levels. By using 1μs pulsed electrical injection with 0.1% duty cycle, we were able to minimize the effect of the junction temperature. By changing the design of the multiple quantum well region as well as by employing or not employing electron blocking layers, we demonstrated the important role that electron overflow plays on efficiency. Furthermore, by also exploring the same on non polar surfaces and observing any lack of dispersion in terms of the effect of the electron blocking layer we can conclude that the polarization induced field does not seem to play a major role. LEDs on non polar surface with no notable efficiency degradation, up to current densities of about 2250 Acm-2 used for measurements, have been obtained which seems to imply that Auger recombination up to these injection levels is not of major importance, at least in the structures investigated. The effect of current crowding on efficiency droop was investigated by comparing semitransparent Ni/Au p-contacts and transparent conducting oxide contacts (Ga-doped ZnO). Because the latter showed notably reduced efficiency degradation at high injection levels, we can conclude that current crowding plays a role as well.
Electronic Properties of III-Nitride Surfaces and Interfaces Studied by Scanning Photoelectron Microscopy and Spectroscopy
Authors: Kuo Cheng-Tai , Lee Hong-Mao , Wu Chung-Lin , Shiu Hung-Wei , Chen Chia-Hao , Gwo Shangjr 
Published: January 2010

AbstractWe report on a method based on cross-sectional scanning photoelectron microscopy and spectroscopy (XSPEM/S) for studying electronic structure of III-nitride surfaces and interfaces on a submicrometer scale. Cross-sectional III-nitride surfaces prepared by in situ cleavage were investigated to eliminate the polarization effects associated with the interface charges/dipoles normal to the cleaved surface. In contrast to the as-grown polar surfaces which show strong surface band bending, the cleaved nonpolar surfaces have been found to be under the flat-band conditions. Therefore, both doping and compositional junctions can be directly visualized at the cleaved nonpolar surfaces. Additionally, we show that the “intrinsic” valence band offsets at the cleaved III-nitride heterojunctions can be unambiguously determined.
Cubic AlGaN/GaN Hetero-Field Effect Transistors with Normally On and Normally Off Operation
Authors: As Donat J. , Tschumak Elena , Niebelschüetz Florentina , Jatal W. , Pezoldt Joerg , Granzner Ralf , Schwierz Frank , Lischka Klaus 
Published: January 2010

AbstractNon-polar cubic AlGaN/GaN HFETs were grown by plasma assisted MBE on 3C-SiC substrates. Both normally-on and normally-off HFETs were fabricated using contact lithography. Our devices have a gate length of 2 μm, a gate width of 25 μm, and source-to-drain spacing of 8 μm. For the source and drain contacts the Al0.36Ga0.64N top layer was removed by reactive ion etching (RIE) with SiCl4 and Ti/Al/Ni/Au ohmic contacts were thermally evaporated. The gate metal was Pd/Ni/Au. At room temperature the DC-characteristics clearly demonstrate enhancement and depletion mode operation with threshold voltages of +0.7 V and −8.0 V, respectively. A transconductance of about 5 mS/mm was measured at a drain source voltage of 10 V for our cubic AlGaN/GaN HFETs, which is comparable to that observed in non-polar a-plane devices. From capacity voltage measurements a 2D carrier concentration of about 7×1012 cm-2 is estimated. The influence of source and drain contact resistance, leakage current through the gate contact and parallel conductivity in the underlaying GaN buffer are discussed.
Direct growth of carbon nanotubes atom by atom during field emission
Authors: Journet Catherine , Marchand Mickaël , Benoit Jean-Michel , Yakobson Boris I. , Purcell Stephen Thomas 
Published: January 2010

AbstractWe have designed a field emission microscope (FEM) coupled to a chemical vapor deposition (CVD) reactor in order to observe directly the growths of individual carbon nanotubes (CNTs) from the nucleation stage. Catalyst metals are first deposited in situ on a sharp metallic tip during direct FEM imaging and formed into nanoparticles by dewetting. CNTs are then grown directly on these nanoparticles by CVD in acetylene or other hydrocarbon gases at appropriate temperatures (600-900°C). The FEM patterns are formed by electrons emitted from individual CNT caps. The videos are analyzed to extract the growth rates and models. In situ field emission I/V measurements are also performed. The most interesting new discovery is that the CNTs often rotate axially during growth, thus strongly supporting a recently proposed model of ‘screw-dislocation-like’ (SDL) mechanism. The event is not rare as four rotating CNT growths versus six non-rotating growths were observed. In one case the CNT rotated quite uniformly ∼180 times during its 11 min growth. This observation should aid researchers to better understand and control the growth of SWNTs.
Post-Synthesis Crystallinity Tailoring of Water-Soluble Polymer Encapsulated CdTe Nanoparticles using Rapid Thermal Annealing
Authors: Rutledge Steven , Farah Abdiaziz A. , Dinglasan Jordan , Anderson Darren , Das Anjan , Goh Jane , Goh Cynthia , Helmy Amr S. 
Published: January 2010

AbstractThe crystallinity of colloidal CdTe nanoparticles has been enhanced post synthesis. This control over the nanoparticles’ properties has been achieved using non-adiabatic thermal processing. The technique preserves the polymer capping and hence introduces no adverse effects on the nanoparticles’ optical properties. The crystallinity is probed primarily through Raman spectroscopy in a hollow core photonic crystal fiber and x-ray diffraction powder studies.
Multiexcitons in a Single Core-Shell Colloidal Quantum dots
Authors: Cheskis Dima , Osovsky Ruth , Kloper Viki , Sashchiuk Aldona , Lifshitz Efrat 
Published: January 2010

AbstractThe micro-photoluminescence (μ-PL) spectra of a single CdTe/CdSe quasi- type II core-shell colloidal quantum dots (CQDs) unambiguously reveal an emission of a biexciton (2X), a triexciton (3X) and a quadraexciton (4X) under continuous-wave excitation. The CQDs were characterized by optical measurements and theoretical consideration of carrier's wavefunctions distribution of a quasi-type II core-shell structure.