bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effect of Temperature Gradient near the Target and Gas Flow Rate on the Diameter Distribution of Single-Walled Carbon Nanotubes Grown by the Laser Ablation Technique
Authors: Sen Rahul , Kataura Hiromichi , Ohtsuka Yohsuke , Ishigaki Toshinobu , Suzuki Shinzo , Achiba Yohji 
Published: April 2011

AbstractGas dynamic and time resolved imaging studies have been performed on the growth of single-walled carbon nanotubes (SWNTs) in the laser ablation process. SWNTs were synthesized by laser ablation of Ni-Co catalyzed graphite targets at 1200°C under argon flow. The effects of the temperature gradient near the target and the gas flow rate were studied in order to understand the effect of gas dynamics over the diameter distribution of SWNTs. The gas flow rate affects the diameter distribution of SWNTs especially when the growth species flow through a large temperature gradient. Scattering images from the growth species at different flow rates was recorded by high-speed video imaging. The results indicate that the velocities of these species are dependent on the gas flow rate but this dependence is evident 30 ms after the laser ablation. These findings are used to estimate the time period for the nucleation and the growth of SWNTs.
Multiwall Carbon Nanotubes by Hydrothermal Treatment
Authors: Calderon-Moreno Jose M. , Yoshimura Masahiro 
Published: April 2011

AbstractMultiwall carbon nanotubes have been obtained from carbon soot after hydrothermal treatment at 800°C and 100 MPa. High-resolution electron microscopy (HRTEM) study reveals multiwall carbon nanotubes and carbon nanoparticles made of a hollow core enclosed in well-ordered concentric graphitic layers after hydrothermal treatment. Condensed solid products are free of the amorphous phase. Micro-Raman spectroscopy reveals that the hydrothermal multiwall nanotubes have a characteristic perfectly closed graphitic lattice in the basal plane, without edges or plane terminations.
Carbon Nanotube/Polyelectrolyte Composites as Novel Actuator Materials
Authors: Chattopadhyay Debjit , Galeska Izabela , Baughman Ray , Zakhidov Anwar , Papadimitrakopoulos Fotios 
Published: April 2011

AbstractMechanical actuators that simultaneously provide high power densities and large force generation capacities are of great scientific and technological interest. Recently single wall carbon nanotube (SWNT) papers (“bucky” papers) were shown to possess significant promise as electrochemical actuators. Embedding polyelectrolytes, like Nafion™, within the nanotube matrix has the potential to address the limitations of SWNT bundling and tube slippage thus increasing force generation. In this paper two types of Nafion/SWNT composite actuators have been investigated depending on the method of fabrication. In the first case, infiltration of Nafion within SWNT paper matrix was followed by annealing at 150°C to invert Nafion's micellar structure and render it insoluble. This has resulted in a substantially exfoliated layer morphology that causes a reduction in both conductivity and actuation strain (c.a. 0.03%). In the second case, slow casting of a methanolic suspension of Nafion and SWNT soot, followed by annealing at 150°C, resulted in a more homogeneous structure. This composite, upon electrochemical cycling between -1 and +1 V in aqueous electrolytes, exhibited actuation strains (as high as 0.43%). However, these higher strains are accompanied by an order of magnitude reduction in modulus largely due to Nafion swelling.
NMR chemical shift of single-wall carbon nanotubes
Authors: Latil Sylvain , Goze Christopher , Bac Goze , Bernier Patrick , Henrard Luc , Rubio Angel 
Published: April 2011

AbstractWe report calculation of the NMR chemical shift anisotropy (CSA) tensor →μ of single-wall carbon nanotubes, within the London approximation (ring currents contribution). Our results indicate that the isotropic line as measured by high resoultion experiments is splited about 11ppm between metallic and semiconductor nanotubes. We carefully check that this result remains vaild and observable when the bundle packing is taken into account. The resulting broadening is aroune 20ppm, but reduces onto a sharp lorentzian (<1ppm) when averaging by high resoultion NMR measurements.
Adsorption of Hydrogen on Carbon Single-Walled Nanotubes as Measured by the Volumetric Technique
Authors: Parilla Philip A. , Dillon Anne C. , Gennett Thomas , Alleman Jeff L. , Jones Kim M. , Heben Michael J. 
Published: April 2011

AbstractWe report on hydrogen adsorption onto carbon single-walled nanotube (SWNT) material as measured by the volumetric technique. This method determines the amount adsorbed by monitoring the pressure in a known volume at a known temperature with a given number of moles of hydrogen introduced. The raw material for the samples is produced by pulsed laser vaporization of a graphite target containing Ni (0.6 at%) and Co (0.6 at%) dopants. This is followed with a purification procedure and then by a cutting procedure. Finally, the sample is degassed before the hydrogen adsorption is measured. The cutting procedure introduces a titanium alloy which participates in the overall hydrogen adsorption of the SWNT material. Importantly though, the amount of hydrogen adsorbed in the SWNT material cannot be explained by absorption from the alloy alone. A description of the apparatus that has allowed us to measure these samples is given and we discuss crucial experimental procedures needed to activate the SWNT samples for hydrogen adsorption.
Defect energetics, thermal stability and localized electronic states in carbon nanotubes
Authors: Conversano Roberto , Cleri Fabrizio , D'Agostino Gregorio , Rosato Vittorio , Volpe Manuela 
Published: April 2011

AbstractTight Binding molecular dynamics simulations have been performed on single wall carbon nanotubes, in order to evaluate thermal stability and the effect of the most relevant defects (the single vacancy and a Stone-Wales -SW- defect). The nanotubes are stable up to the graphite instability temperature. Both the considered defects have a large formation energy (EF(vac)=6.10 eV, EF(SW)= 5.55 eV).
A Soft Lithographic Approach to the Fabrication of Single Crystalline Silicon Nanostructures with Well-Defined Dimensions and Shapes
Authors: Yin Yadong , Gates Byron , Xia Younan 
Published: April 2011

AbstractA procedure was developed for large-scale fabrication of nanometer-sized structures of single crystalline silicon with well-defined dimensions and shapes. Near-field optical lithography was used to define the nanostructures in a thin film of positive-tone photoresist with an elastomeric phase mask. The nanostructures were then transferred into the underlying silicon-on-insulator (SOI) substrate through a reactive ion etching (RIE) process. With this method, we can routinely generate silicon nanostructures ∼130 nm in lateral dimension. They can be supported on the surface of a solid substrate as a patterned array, or released into a freestanding form. The lateral dimension of these silicon structures could be further reduced to as small as ∼40 nm using stress-limited oxidation at elevated temperatures. The flexibility of this approach was demonstrated by fabricating nanoscale wires, rods, rings, and interconnected triangles of silicon. Using a two-step exposure method, the silicon nanowires can be precisely “cut” into silicon nanorods with specific lengths.
Electrochemical Synthesis of Multi-Material Nanowires as Building Blocks for Functional Nanostructures
Authors: Pena David J. , Razavi Baharak , Smith Peter A. , Mbindyo Jeremiah K. , Natan Michael J. , Mayer Theresa S. , Mallouk Thomas E. , Keating Christine D. 
Published: April 2011

AbstractNanostructures are electrochemically deposited into alumina or polycarbonate templates resulting in monodisperse, anisotropic particles with a range of tunable sizes. These particles have been synthesized with diameters of 20–250 nm and with lengths of 1–10 μm. Currently, structures have been made with stripes of Au, Ag, CdSe, Co, Cu, Ni, Pd, and Pt. These materials offer a variety of different properties. In particular, many of the metals in this group are excellent conductors, meaning these particles can actually be used as nanowires. Co and Ni are ferromagnetic and may be used for separation or assembly. CdSe is a semiconductor, possibly allowing for the synthesis of electronic devices such as transistors. Furthermore, many of these materials have different surface chemistries, making the orthogonal functionalization and assembly of these nanowires more accessible. This research focuses on increasing the number of materials available, especially semiconductors, incorporating these potentially useful materials into multilayered nanowires and evaluating their electrical properties, either individually or in small bundles. In addition, the surface chemistry of the various materials in the nanowires is being compared to aid in orthogonal self-assembly of functional nanostructures such as memory devices. The work presented will demonstrate the effects of rod composition on electrical properties. In particular, the effects of changing the work function of the materials on either side of a semiconductor to form Schottky junctions or ohmic contacts will be shown.
Surface Potentials of Conjugated Molecules on Metal Surfaces: Measurements Using Electrostatic Force Microscopy and Calculations using a Preliminary Physically-Based Model.
Authors: Howell S. , Kuila D. , Ghosh A. W. , Rakshit T. , McNally H. , Janes D. , Datta S. , Kashibhatla B. , Kubiak C. , Reifenberger R. 
Published: April 2011

AbstractThe electrostatic surface potential of self-assembled monolayers (SAMs) of aliphatic and aromatic thiols has been measured using electrostatic force microscopy. The variation of the surface potential of chemisorbed alkanethiols, with respect to bare Au(111), is observed to increase with increasing chain length. The trend is similar to that observed in the literature. A preliminary theoretical model, based on treating the monolayer as a sheet of dipoles, has been used to calculate the surface potential of alkanethiols. Similar measurements on several aromatic thiols, with a symmetric and non-symmetric molecular structure, reveal that non-symmetric systems have significantly higher potential (≥ 170mV) than the symmetric molecules.
A Potential Interconnection Method in Molecular Electronics
Authors: Tao Meng 
Published: April 2011

AbstractA method to electrically connect molecular devices is proposed, which has the potential to develop into an interconnection technology for 3-dimensional molecular electronic circuits. The method is based on electric-bias-induced polarization and electric-pulse-induced chemical reactions. Two molecules to be connected are oppositely biased to induce opposite charges in them. The opposite charges will create electrostatic attraction that pulls together or aligns the two molecules. An electric pulse is then applied across the two molecules to trigger a chemical linking reaction between them. The electric pulse overcomes the activation energy for such a reaction. Chemical linking reactions to produce conjugated molecular chains are proposed for several conjugated molecules, such as phenylene, ethylene, and acetylene based molecules, with different end groups, such as phenyl and acetyl groups. Applications of this method in assembling 3-terminal molecular devices and 3-dimesional molecular electronic circuits are speculated. Major challenges in realizing this interconnection method are also outlined.
Properties of Silicon Nanoparticles Produced by Picosecond Pulsed Laser Ablation
Authors: Wu M. H. , Mu R. , Ueda A. , Henderson D. O. 
Published: April 2011

AbstractSilicon nanocrystals have been fabricated by picosecond pulsed laser ablation. Size control over the nanocrystals can be achieved by careful selection of experimental geometry, laser fluence, laser wavelength, backing gas pressure and distance from plume center. Measurements of optical absorption and photoluminescence confirm that particle size variation does significantly affect bandgap and emission efficiency. Differences between results published previously for nanosecond pulsed laser ablation will also be discussed.
Resonant excitation of Er3+ by the energy transfer from Si nanocrystals
Authors: Watanabe Kei , Fujii Minoru , Hayashi Shinji 
Published: April 2011

AbstractPhotoluminescence (PL) of SiO2 films co-doped with Si nanocrystals (nc-Si) and Er was studied. The average size of nc-Si was changed in a wide range in order to tune the exciton energy of nc-Si to the energy separations between the discrete electronic states of Er3+. PL from exciton recombination in nc-Si and the intra-4f shell transition of Er3+ were observed simultaneously. At low temperatures, periodic features were observed in the PL spectrum of nc-Si. The period agreed well with the optical phonon energy of Si. The appearance of the phonon structures implies that nc-Si which satisfy the energy conservation rule during the energy transfer process can resonantly excite Er3+. The effects of the quantum confinement of excitons in nc-Si on the energy transfer process are discussed.
Silicon Nanocrystallite Light Emitting Devices Fabricated by Full Pulsed-Laser-Ablation Process
Authors: Yamada Yuka , Makino Toshiharu , Suzuki Nobuyasu , Yoshida Takehito 
Published: April 2011

AbstractWe have developed silicon (Si) nanocrystallite light-emitting devices synthesized by a novel integrated process in which a size-controlling unit of differential mobility analyzer (DMA) is combined to a nanocrystallite formation unit of pulsed laser ablation (PLA). The size-controlled Si nanocrystallites as active layers have been deposited on Si substrates, and have been covered with stoichiometric indium oxide (In2O3) thin films synthesized also by the PLA process. The electroluminescence (EL) spectra had a narrow bandwidth of 0.15 eV peaked at slightly higher energy region (1.17 eV) than the bulk Si energy gap (1.10 eV), at room temperature.
Stabilization of Porous Silicon Electroluminescence by Surface Capping With Silicon Dioxide Films
Authors: Koshida N. , Kadokura J. , Takahashi M. , Imai K. 
Published: April 2011

AbstractTo prolong the operation life of electroluminescence (EL) from porous silicon (PS) diodes without affect on the efficiency, the surface passivation technique is applied to the active PS layer. By combining a postanodization electrochemical oxidation (ECO) technique for the PS layer with a surface capping by SiO2 films sputtered using electron cyclotron resonance (ECR) method, the degradation of the EL efficiency is effectively suppressed for a long time over several hours under a cw operation. It is shown that from thermal desorption spectra analyses, the capability of capped films as a barrier against penetration of water molecules is a key factor for stabilizing the EL operation due to preventing luminescent PS layers from current-induced oxidation.
Charging Effect in Amorphous Silicon Quantum Dots Embedded in Silicon Nitride
Authors: Park Nae-Man , Jeon Sang-Hun , Hwang Hyunsang , Choi Suk-Ho , Park Seong-Ju 
Published: April 2011

AbstractCapacitance-voltage was investigated for amorphous silicon quantum dots (a-Si QDs) embedded in a silicon nitride as a function of dot size and nitride thickness. a-Sci QDs were grown by plasma enhanced chemical vapor deposition. The electron charging was decreased as the dot size was decreased. These results showed that the conduction band shift is larger than the valence band shift as the dot size decreased and, as a result, electrons are easily discharged in a-Si QDs due to the lower barrier height. For high dot-density-sample, the capacitance-voltage curves were also shifted toward the negative voltage direction when a higher forward bias was applied at forward condition due to the transfer of electrons trapped in the a-Sci QDs from the a-Sci QDs near Si substrate to those near the top metal.
Photoluminescence from nano porous silicon prepared by photoelectrochemical etching of n-type single crystalline silicon
Authors: Lee Chi-Woo , Kim Buem-Suck , Kim Dong-Il , Min Nam-Ki , Hong Suk-In 
Published: April 2011

AbstractThe influence of operating parameters in producing light-emitting porous silicon materials was investigated in ethanolic solutions of hydrofluoric acid. Photoluminescence spectra depended on applied potential, the intensity and wavelength of illumination, and electrolyte concentration. When the applied potential and the illumination wavelength increased, the photoluminescence shifted to longer wavelength. Change in HF concentration resulted in different intensity in photoluminescence.
Growth and Investigation of GaN/AlN Quantum Dots
Authors: Morkoç Hadis , Reshchikov Michael A. , Jones Keith M. , Yun Feng , Visconti Paolo , Nathan Marshall I. , Molnar Richard J. 
Published: April 2011

ABSTRACTWe have fabricated GaN quantum dots (QDs) in AlN confined layer structures by molecular beam epitaxy. The size distribution and density of the QDs have been estimated from an atomic force microscopy study. Very high quantum efficiency of photoluminescence (PL) has been obtained in some samples with QDs. Compared to the GaN bulk samples, it increased by orders of magnitude. In some samples the quantum size effect dominated, resulting in the blue-shift of the QD related PL peak, whereas in the samples with larger dots a red-shift up to 0.8 eV has been observed, which is related to strong polarization effects. We have observed a blue-shift of the PL peak with excitation intensity in the samples with large dots due to screening effect. The temperature-induced quenching of PL occurs at higher temperatures compared to bulk GaN due to the confinement of nonequilibrium carriers in the QDs. An excited state has been observed in some samples.
Investigation of Sidewall Recombination in GaN Using a Quantum Well Probe
Authors: Haberer E. D. , Woods M. , Stonas A. , Chen C-H. , Keller S. , Hansen M. , Mishra U. , Denbaars S. , Bowers J. , Hu E. L. 
Published: April 2011

ABSTRACTIn this study, we use a quantum well (QW) probe structure to explore the size dependent effects of sidewall recombination in GaN. Mesas 0.8-7 μm in width with pitches of 4 μm, 8 μm, and 12 μm were etched into the QW probe structure, exposing the QW at the sidewalls. Several etch conditions were investigated. Room temperature photoluminescence (PL) measurements, using a He-Cd laser as an excitation source and laser spot size of approximately 230 μm, were taken before and after the mesas were etched. The effects of sidewall formation were quantified by comparing the maximum PL intensity of the QW before and after etch. Higher remaining PL intensity was observed for etch conditions which used both Ar ions and Cl2 gas instead of only Ar ions. The fraction of remaining PL decreased with decreasing mesa width, however the remaining PL intensity was relatively large even for small features. The preliminary data suggested that GaN is relatively insensitive to sidewall damage.
Self-Aligned Process For Emitter- And Base- Regrowth GaN HBTs And BJTs
Authors: Lee K. P. , Zhang A. P. , Dang G. , Ren F. , Han J. , Chu S.N.G. , Hobson W. S. , Lopata J. , Abernathy C. R. , Pearton S. J. , Lee J. W. 
Published: April 2011

ABSTRACTThe development of a self-aligned fabrication process for small emitter contact area (2×4 um2) GaN/AlGaN heterojunction bipolar transistors and GaN bipolar junction transistors is described. The process features dielectric-spacer sidewalls, low damage dry etching and selected-area regrowth of p-GaAs(C) on the base contact or n-GaN/AlGaN on the emitter contact. Series resistance effects are still found to influence the device performance.
High Efficiency Uv Emitter Using High Quality GaN/AlxGa1−xN Multi-Quantum Well Active Layer
Authors: Iwaya M. , Terao S. , Ukai T. , Nakamura R. , Kamiyama S. , Amano H. , Akasaki I. 
Published: April 2011

ABSTRACTWe investigated temperature dependence of the photoluminescence (PL) efficiency of GaN/Al0.08Ga0.92N multi-quantum wells (MQWs) with variations of Si-doping condition and threading dislocation density. Si-doping in the GaN/Al0.08Ga0.92N MQWs, especially in the barrier layer improves the PL efficiency. In addition, reduction of threading dislocation density also improves the PL intensity. The PL intensity of the GaN/Al0.08Ga0.92N MQW is drastically increased at least by a factor of 40, by a combination of the Si-doping and reduction of threading dislocation density. We fabricated a light emitting diode (LED) emitting at 357 nm using such a GaN/Al0.08Ga0.92N MQWs. Electro-luminescence intensity from the region with threading dislocation density of less than 108 cm−2 was much larger than that from the region with threading dislocation density of 6×109 cm−2.
Optical Study of GaN Doped with Mn Grown by Metal Organic Vapor Phase Epitaxy
Authors: Korotkov R. Y. , Gregie J. M. , Wessels B. W. 
Published: April 2011

ABSTRACTThe optical properties of Mn-doped GaN were investigated. The films were grown by metalorganic vapor phase epitaxy using tricarbonyl (methylcyclopentadienyl) manganese as the dopant source. Two characteristic bands were observed in the absorption spectra of Mn-doped epilayers. The low energy band had a threshold at 1.4 ± 0.05 eV with a maximum at 1.5 ± 0.02 eV, with a full width half maximum of 245 ± 10 meV at 296 K. A second higher energy band was observed as a shoulder to the band edge absorption with a threshold energy of 2.06 eV at room temperature. Using photoluminescence spectroscopy, a new broad band was observed in the infrared spectra of GaN:Mn at 1.27 ± 0.02 eV with a full width half maximum of 0.26 ± 0.01 eV at 20K. From analysis of optical absorption and emission spectra Mn forms a deep acceptor level with optical transitions at 1.4 and 2.06 eV. The deep level nature of Mn indicates that it is a potential dopant for semi-insulating GaN.
Cross-sectional Cathodoluminescence Study in Ga-polar and N-polar GaN Epilayers
Authors: Du X. L. , Lim D. H. , Xu K. , Liu B. L. , Jia A. W. , Takahashi K. , Yoshikawa A. 
Published: April 2011

ABSTRACTHighly spatial resolved cross-sectional cathodoluminescence (CL) has been used to study the difference in the defect-formation and growth-mechanism between Ga-polar and N-polar GaN epitaxial layers. These epilayers were grown on sapphire substrates by low pressure MOCVD. Their polarities were controlled by the sapphire nitridation and the trimethylaluminum (TMAl) pre-flow just before the conventional two-step growth, and were confirmed with the coaxial impact collision ion scattering spectroscopy (CAICISS). For the Ga-polar GaN epilayers, cross-sectional CL images show distinct two layers, the upper layer with dark lines along c-direction and the layer close to the film-substrate interface with pyramidal dark regions. These two layers correspond to quasi 2D and 3D growth mode respectively. Whereas, the crosssectional CL image taken on the N-polar epilayers is predominated with small dark spots which were randomly distributed throughout the whole GaN epilayer, illustrating the predominant island growth mode in N-polar films.
Comparison of Er3+ Photoluminescence and Photoluminescence Excitation Spectroscopy in In-situ-doped GaN:Er and Er-implanted GaN
Authors: Mitofsky Andrea M. , Papen George C. , Bishop Stephen G. , Lee Dong-Seon , Steckl Andrew J. 
Published: April 2011

ABSTRACTSite-selective photolumiescence (PL) and photoluminescence excitation (PLE) spectroscopies have been carried out at 6 K on the ∼1540nm 41/32 → 4I1/52 Er3+ transition in in-situ-doped GaN:Er which have detected nine differenct Er3+ sites and associated PL spectra. Three distinct Er3+ sites are identified in the in-situ-doped samples. For the in-situ-doped samples, the concentration of the various Er+3 sites are comparable while for the ion-implanted sample, the concertration of one Er3+ site was higher than the concentration of the other sites. In-situ-doped samples grown with different Ex-cell temperatures were considered, and the width of the PLE spectrum appears to be a function of the Er-cell temperature.