bluuebunny/crossref_metadata_2025_split huggingface dataset:
Scanning Tunneling Microscopy and Spectroscopy of Short Multiwall Carbon Nanotubes
Authors: Hassanien A. , Mrzel A. , Tokumoto M. , Zhao X. , Ando Y. , Tománek D. 
Published: April 2011

AbstractWe report on the structural analysis of multiwall carbon nanotubes (MWNTs), produced by DC arc discharge in hydrogen gas, using a scanning tunneling microscope operated at ambient conditions. On a microscopic scale the images show tubes condensed in ropes as well as individual tubes which are separated from each other. Individual nanotubes exhibit various diameters (2.5-6 nm) and chiralities (0-30Å). For MWNTs rope, the outer portion is composed of highly oriented nanotubes with nearly uniform diameter (4-5 nm) and chirality. Strong correlation is found between the structural parameters and the electronic properties in which the MWNTs span the metallic-semiconductor regime. True atomic-resolution topographic STM images of the outer shell show hexagonal arrangements of carbon atoms that are unequally visible by STM tip. This suggests that the stacking nature of MWNTs, may effect the electronic band structure of the tube shells. Unlike other MWNTs produced by arc discharge in helium gas, the length of the tubes are rather short (80-500 nm), which make it feasible to use them as a components for molecular electronic devices.
Application of Carbon Nanotubes and Fullerenes for Thermal Management in Ceramics
Authors: Yowell Leonard L. , Mayeaux Brian M. , Wang Hsin , Barrera Enrique V. 
Published: April 2011

AbstractNew techniques for thermal management in ceramics at the nanoscale level have been investigated using low percentages of carbon nanotubes to reduce thermal conductivity of bulk ceramics. Samples of yttria-stabilized zirconia containing purified single-walled carbon nanotubes (SWNT) or vapor grown carbon fibers (VGCF) have been prepared by tape casting and analyzed using the laser flash method to evaluate reductions in thermal conductivity at high temperatures. New features in the samples due to the presence of carbon nanotubes have been characterized using Raman, SEM, TEM and, in the case of VGCFs, are related to significant reductions in thermal conductivity (>25%). The inclusion of a low percentage of nanoscale carbon fibers, the intimate relationship between the fibers and ceramic particles, and the indication that the fibers possess a crystalline overcoating, all contribute to the lowering of the thermal conductivity.
Rapid, Room Temperature, High-Density Hydrogen Adsorption on Single-Walled Carbon Nanotubes at Atmospheric Pressure Assisted by a Metal Alloy
Authors: Heben M.J. , Dillon A.C. , Gennett T. , Alleman J.L. , Parilla P.A. , Jones K.M. , Hornyak G.L. 
Published: April 2011

AbstractLaser-generated, carbon single-walled nanotubes (SWNTs) adsorb hydrogen in a matter of minutes at room temperature and atmospheric pressure in the presence of a Ti-6Al-4V metal alloy. The unusual hydrogen adsorption properties are activated when the SWNTs are sonicated in nitric acid with a Ti-6Al-4V probe. The process cuts the SWNTs and introduces ∼15-40 wt% metal alloy into the previously pure single-walled nanotube material. Subsequent hydrogen adsorption occurs in two separate sites with a maximum adsorption capacity of ∼7 wt% on a total sample weight basis. Approximately 2.5 wt% hydrogen is evolved at 300 K while the remainder desorbs between 475-850 K. The pure metal alloy adsorbs ∼ 2.5 wt% H2, and evolvesydrogen with increasing temperature in a manner similar to the alloy-doped SWNTs. However, it is clear from studies presented here that the SWNT fraction is quite active in H2 uptake, adsorbing as much as 7 % on a SWNT weight basis.
Electrical Rectification by a Monolayer of Hexadecylquinolinium Tricyanoquinodimethanide Sandwiched between Gold Electrodes
Authors: Metzger Robert M. 
Published: April 2011

AbstractUnimolecular rectification, previously reported between oxide-bearing electrodes, was detected between oxide-free Au electrodes for a Langmuir-Blodgett monolayer of the zwitterionic D+-π-A− molecule hexadecylquinolinium tricyanoquinodimethanide, C16H33Q-3CNQ. The top gold electrode was deposited from a Au vapor pre-cooled by multiple collisions with Ar atoms. The maximum rectification ratio is 27.5 at 2.2 Volts (the average rectification ratio is 7.55). The currents are as large as 9.04 × 104 electrons molecule−1 s−1. The result reinforces previous work with oxide-bearing Al electrodes, but the currents with Au electrodes are larger by three to five orders of magnitude.
A New Assembling Method for Nano-sized Particles Using an Electrified Pattern Drawn by a Focused Ion Beam
Authors: Fudouzi Hiroshi , Kobayashi Mikihiko , Shinya Norio 
Published: April 2011

AbstractThis paper describes a new technique to fabricate two-dimensional microstructures assembled with nano-sized particles. The nano-sized particles attract a lot of attention because of their unique properties compared to bulk materials. Micro- and nano- structures assembled with nano-sized particles have potential applications in electronic, optical and biochemical fields. The Self-Assembled Monolayer (SAM) film patterning is one of the methods to assemble the nano-sized particles. We have proposed a new method to assemble nano-sized particles on a substrate using an electric field generated by an electrified pattern. In this study, following our methods titanium oxide (TiO2, diam.=21nm) particles were patterned on an n-type (100) silicon substrate having an oxidized layer. The particle deposition on the substrates was carried out using a colloidal suspension process and an aerosol process.
Laser Ablation Fabricated Nano-Composite of Metal Silicide Crystallines in Silicon Wire
Authors: Qi Jifa , Masumoto Yasuaki 
Published: April 2011

AbstractSilicon nanowires containing a high density of copper atoms were prepared by laser ablation of Si/metal mixture targets at 1200 °C in argon gas flow. Copper atoms can gather in Si nanowires and precipitate into copper silicide nanocrystals distributed alone the wire axis. The diameters of the copper silicide nanocrystals increase with that of the host nanowire. The possible growth process of the composite nanowires was proposed.
Full Color Luminescence from Amorphous Silicon Quantum Dots Embedded in Silion Nitride
Authors: Park Nae-Man , Kim Tae-Soo , Choi Chel-Jong , Seong Tae-Yeon , Park Seong-Ju 
Published: April 2011

AbstractAmorphous silicon quantum dots (a-Si QDs), which show a quantum confinement effect, were grown in a silion nitride film by plasma enhanced chemical vapor deposition. Red, green, blue, and white photolumiscence were observed from the a-Si QD strictures by controlling the fot size. An organe light-emitting device (LED) was fabricated using a-Si QDs with a mean size of 2.0 nm. The turn-on vottage was less than 5 V. An external quantum effiency of 2×10−3 % was also demonstrated. These results show that an LED using a-Si QDs embedded in the silicon nitride film is superior in terms of electrical and optical properties to other Si-based LEDs.
Low Temperature growth of poly-crystalline film of Silicon-rich Silicon-Germanium by Reactive Thermal Chemical Vapor Deposition
Authors: Shimizu Kousaku , Zhang Jianjun , Lee Jeong-Woo , Hanna Jun-Ichi 
Published: April 2011

AbstractLow temperature growth of poly-SiGe has been investigated by reactive thermal chemical vapor deposition method, which is a newly developed technique for preparing poly-SiGe by using redox reactions in a set of source materials, i.e., Si2H6 and GeF4. In order to prepare silicon-rich poly-SiGe of high mobility, a series of experiment on total pressure, gas flow rates of the source materials and dilution gas of He, and residence time at 450°C has been investigated.At 0.45 Torr, high crystallinity films with high silicon content were prepared, however, homogeneity of film thickness and reproducibility of the film growth was quite low for device application. For overcoming this problem, the growth condition has been studied especially in higher-pressure range of 5-15 Torr. Appropriate choice of the residence time and the gas flow ratios lead to significant improvement in the Si content in the films. Finally, more than 95% of silicon-rich poly-SiGe films, which is p-type, has 7.5 cm2/Vs of Hall mobility and (220) orientation, have been prepared at 10 Torr and 450°C within ±2% fluctuation of reproducibility which is enough to fabricate devices.
Nanocrystalline Silicon by Microwave CVD for Thin Film Transistors and Solar Cells
Authors: Song Young J. , Lee Hak-Gyu , Teng Lihong , Anderson Wayne A. 
Published: April 2011

AbstractMicrowave chemical vapor deposition (MCVD) is utilized to deposit nanocrystalline silicon (nc-si) thin films onto a variety of substrates for application to thin film transistors (TFT's) and solar cells. It is especially important to gain reproducible control of the processing. Thus, an in-situ mass spectrometer (MS) records the plasma conditions with variation of process conditions such as gas selection, pressures, partial pressures, and substrate temperature. These data are correlated with electrical and optical properties of the films. Raman spectra show a FWHM of 11/cm with position at 522/cm as desired for crystalline Si. Typical film thickness is 100nm with grain size of 20-30 nm, using standard deposition, and 50-80 nm when the substrate is intensely optically illuminated during deposition, called photon assist (PA). Hydrogen dilution serves to increase the crystallinity of the films. The ratio of photo-to dark conductivity exceeds 10+5 with dark conductivity as low as 1.5 × 10-10 S/cm. Thin film transistors have been fabricated with Ion/Ioff of 10+7. Hetrojunction solar cells were fabricated using amorphous Si/ nc-Si/ crystlline Si giving a conversion efficiency of above 10.5%, without an antireflection coating. The use of MS in device design will be emphasized.
Fluctuation Microscopy Studies of Medium-range Order Structures in Amorphous Tetrahedral Semiconductors
Authors: Chen Xidong , Gibson J. Murray , Sullivan John , Friedmann Tom , Voyles Paul 
Published: April 2011

AbstractWe applied fluctuation microscopy technique to study medium-range order in tetrahedral semiconductor materials, such as amorphous silicon, amorphous diamond-like carbon films. It is shown that this technique is very sensitive to local structure changes in the medium range order and promises solutions to open questions that cannot be answered by current techniques. For asdeposited amorphous germanium and silicon, we previously identified a fine-grain para-crystallite structure [1, 2], which will be relaxed into a lower-energy continuous random network structure after thermal annealing. With the same fluctuation microscopy technique, we however found that thermal annealing introduces medium-range order in amorphous diamond-like carbon films. Future studies will be focused on modeling and systematic exploration of annealing effects.
CMOS compatible Si/SiO2 multilayers for Light Emitting Diodes
Authors: Gaburro Z. , Pavesi L. , Pucker G. , Bellutti P. 
Published: April 2011

AbstractWe report photoluminescence and electroluminescence at room temperature in diodes based on Si/SiO2 multilayers. The multilayers are fabricated by alternating Si and SiO2 layers, whose thickness is, respectively, 2 and 5 nanometers. In photoluminescence, a single band is observed, centered at 800 nm, which is due to electron-hole pair recombination under quantum confinement. On the other hand, in electroluminescence, two bands are reported. The first band is in the infrared spectrum, and is blackbody radiation. The second band is visible, and is originated by relaxation of a single type of electrical carrier (electrons), as suggested by a fast decay time (less than 0.1 µs). Possible mechanisms can be hot-electron relaxation or coupling with surface plasmon-polaritons.
Strong Enhancement of Porous Silicon Photoluminescence by Dry Photo-Chemical Surface Treatment
Authors: Stolyarova S. , El-Bahar A. , Nemirovsky Y. 
Published: April 2011

AbstractPorous silicon has been subjected to NF3/UV photochemical surface treatment in the range of 300-4000C. This treatment is found to enhance strongly the photoluminescence of porous silicon by couple orders of magnitude. The effect of photoluminescence enhancement has been observed only when the NF3 treated porous silicon was exposed to air environment. The photoluminescence intensity continued to grow with the aging time in air, even at the room temperature. Using atomic force microscope, scanning electron microscope and Auger measurements, it is found that the photoluminescence enhancement correlated with the formation of crystalline oxide layer at the porous silicon surface. This oxide layer SiOx (x≅2) is much more stoichiometric as compared to the native oxide SiOx (x≅1) covering the reference porous silicon surface (not treated by NF3). The rapid growth of the SiO2 layer is supposed to be due to the NF3/UV photo-thermal etching of the as-formed native oxide as well as to the cleaning and passivation of the porous silicon surface with fluorine.
Transport of carriers in thin Metal/PS/c-Si device Structures based on Porous Silicon
Authors: Balagurov Leonid A. , Bayliss Sue C. , Petrova Elena A. , Unal Bayram , Yarkin Dmitrii G. 
Published: April 2011

AbstractThin porous silicon (PS) based metal/PS/p-c-Si structures were prepared on moderate-and high- resistivity substrates. Measurements of current-voltage (I-V) dependencies and impedance at various temperatures were used for the investigation of carrier transport in these structures. The exponential forward bias I-Vdependencies for both types of structures spread over several orders of magnitude with a low value of quality factor (close to 2) and have activation temperature dependencies with an activation energy equal to half the c-Si band gap. The reverse current has a square root dependence on the reverse bias voltage and the activation energy is equal to half the c-Si band gap. Therefore, it was concluded that the reverse and forward currents in thin PS-based device structures were determined by the generation and recombination of carriers in the depletion region of the c-Si substrate. It was shown that a large area spreading current exists in structures made on highly resistive substrates, which appears to be due to a highly conductive inverse (n-type) layer formed in the c-Si substrate at the PS/c-Si heterojunction.
Testing of porous silicon membranes as a novel humidity sensor
Authors: Quercia L. , Noce M. Della , Ferrara V. La , Francia G. Di 
Published: April 2011

AbstractA new gas sensor device based on a porous silicon membrane has been fabricated. The sensible membrane has been bonded to a 1 cm2 Al2O3 substrate [1], where electrical contacts have been previously deposited by vacuum evaporation. In this work we present the results of DC measurements showing a good response of this device to humidity gradients. In this frame, the most striking properties of our device are its selectivity and a fast and full recovery after exposure to humidity levels up to 90%. Moreover, the new fabrication process used to realize the sensor merges the advantages typical of porous silicon with thin film ones, by means of a simple process.
The Chemistry of GaN Growth
Authors: Kuech T.F. , Gu Shulin , Wate Ramchandra , Zhang Ling , Sun Jingxi , Dumesic J.A. , Redwing J.M. 
Published: April 2011

ABSTRACTThe development of new chemically based growth techniques has opened the range of possible GaN applications. This paper reviews some of the challenges in the chemically based growth of GaN and related materials. Ammonothermal-based growth, hydride vapor phase epitaxy and metal organic vapor phase epitaxy (MOVPE) are chemically complex systems wherein the underlying mechanisms of growth are not well understood at present. All these systems require substantial experimental and theoretical efforts to determine the nature and kinetics of GaN growth. In the case of metal organic vapor phase epitaxy, the application of computational techniques based on density functional theory have augmented the more conventional experimental approaches to determining the growth chemistry. These chemical reaction schemes, when combined with computational thermal-fluid models of the reactor environment, provide the opportunity to predict growth rates, uniformity and eve ntually materials properties.
Performance characteristics of cw InGaN multiple-quantum-well laser diodes
Authors: Kneissl Michael , Wong William S. , Walle Chris. G. Van de , Northrup John E. , Treat David W. , Teepe Mark , Miyashita Naoko , Kiesel Peter , Johnson Noble M. 
Published: April 2011

ABSTRACTThe performance characteristics are reported for continuous-wave (cw) InGaN multiple-quantum-well laser diodes grown on epitaxially laterally overgrown GaN on sapphire substrates by metalorganic chemical vapor deposition. Room-temperature cw threshold currents as low as 41mA with operating voltages of 6.0V were obtained. The emission wavelength was near 400 nm with output powers greater than 20 mW per facet. Under cw conditions laser oscillation was observed up to 90°C. A significant reduction in thermal resistance was observed for laser diodes transferred from sapphire onto Cu substrates by excimer laser lift-off, resulting in increased cw output power of more than 100mW.
Non-Stationary Photoconductivity of GaN Nanocomposites In Artificial Opal Matrix
Authors: Niehus M. , Koynov S. , Schwarz R. , Feoktistov N.A. , Golubev V.G. , Kurdyukov D.A. , Pevtsov A.B. 
Published: April 2011

ABSTRACTIt was recently proposed to use synthetic opals as a host matrix for obtaining 3D arrays of electronic nanodevices [1]. In the present work the opal matrices were infiltrated with GaN. We study electronic properties of opal-GaN, by means of transient photoconductivity (TPC) measurements using 5 ns laser pulses at wavelengths above (266 nm) and below (532 nm) the GaN bandgap (3.4 eV). A broad plateau is observed in the photocurrent decay covering several orders of magnitude. We compare the results with measurements in conventional GaN.
Plasma-Induced Effects on The Thermal Conductivity of Hydride Vapor Phase Epitaxy Grownn-GaN/Sapphire (0001)
Authors: Florescu D.I. , Pollak Fred H. , Lanfor William B. , Khan Farid , Adesida I. , Molnar R.J. 
Published: April 2011

ABSTRACTWe have measured high spatial/depth resolution (2-3 [.proportional]m) thermal conductivity (κk) at 300K before and after plasma-induced effects on a series ofn-GaN/sapphire (0001) samples fabricated by hydride vapor phase epitaxy (HVPE) using a ThermoMicroscope'as scanning thermal microscope (SThM). The sample thicknesses were 50 ± 5 [.proportional]m and the carrier concentrations ~ 8 × 1016cm-3, as determined by Hall effect measurements. The thermal conductivity before treatment was found to be in the 1.70 – 1.75 W/cm-K range, similar to that previously reported for HVPE material with this carrier concentration and thickness [D. I. Florescuet al., J. Appl. Phys. 88, 3295 (2000)]. The samples were processed under constant Ar gas flow and pressure fora fixed period of time (5 min). The only variable processing parameter was the DC bias voltage (125 – 500 V). After the initial 125 V procedure κ exhibited a decrease linear in the DC voltage in the investigated range. At 125 V the thermal conductivity was only slightly less (κ ~ 1.65 W/cm-K) than the untreated case. κ had dropped to ~ 0.3 W/cm-K for the 500 V situation. The implications of these results for device applications in the area of high power opto-electronics and high power electronics will be discussed.
Effect of Externally-Imposed Radial Strain on the Piezoelectric Response of MOCVD-Grown Gallium Nitride
Authors: Himes Jennifer A. , Willis James R. , Gulino Daniel A. 
Published: April 2011

ABSTRACTThe large piezoelectric constants of GaN suggest possible application of GaN-based materials in piezoelectric sensors, among other areas. GaN's wide band gap implies that these sensors will fare well over a broad temperature range and/or in a harsh environment.In this work, films of gallium nitride approximately 0.75 micron thick and grown by MOCVD were subject to an externally-imposed radial stress condition. Deposition was performed in a commercial MOCVD reactor (CVD, Inc.) at 1323K using trimethylgallium and ammonia as the chemical precursors. The substrate was one-inch diameter silicon (111). After deposition, titanium dots were deposited in various locations, including the wafer center, by evaporation. Stress was applied to the film/substrate system using a modified micrometer head (Mitutoyo) mounted to an Ionic Systems Basic Stressgauge (model 30285). Stress levels were calculated based on the magnitude of the imposed deflection as read from the micrometer head display, and the piezoelectric response at any particular dot with respect to the center dot was measured by measuring the voltage difference using a digital multimeter (Keithley 175). The micrometer head impinged on the center dot and served as one electrical contact point.Effective piezoelectric coefficients were measured as a function of imposed radial stress. Applied stresses in the range of 1 to 5 GPa resulted in effective piezoelectric coefficients ranging from –0.6 to –2.0 × 10-5 C/m2
A new mechanism in the growth process of GaN by HVPE
Authors: Trassoudaine A. , Aujol E. , Cadoret R. , Paskova T. , Monemar B. 
Published: April 2011

ABSTRACTExperimental results obtained in two different HVPE reactors are analyzed and compared to the theoretical curves, taking into account the surface kinetics, the mass transfer, and parasitic deposition on the glass walls before the substrate. Unexpected high growth rate values, up to 50νm/h, were measured in conditions of expected substrate etching by HCl. A systematic experimental study of this new phenomenon is presented together with a theoretical analysis. This analysis suggests a new mixed general mechanism of growth.
Vapor Phase Synthesis and Characterization of Gallium Nitride Powders
Authors: Hara Kazuhiko , Matsuo Yoshinori , Matsuno Yuuki 
Published: April 2011

ABSTRACTGaN crystalline powders have been synthesized by the reaction of a Ga vapor with an ammonia gas at the reaction temperature Tr = 900 - 1100°C in an atmospheric-pressure open-tube reactor. The size of GaN particles ranges from 0.2 to 2νm. It was found that the structural and luminescent properties depend strongly on Tr. The mean size of the GaN particles increased as Tr is raised. The GaN powders exhibited photoluminescence (PL) dominated by the band edge emissions. Thermal quenching is relatively significant for the powders synthesized at lower Tr. This is presumably due to enhanced non-radiative recombination at the surface because of their smaller particle size.
Interaction Between Basal Stacking Faults and Prismatic Inversion Domain Boundaries in GaN
Authors: Komninou Philomela , Kioseoglou Joseph , Sarigiannidou Eirini , Dimitrakopulos George P. , Kehagias Thomas , Georgakilas Alexandros , Nouet Gerard , Ruterana Pierre 
Published: April 2011

ABSTRACTThe interaction of growth intrinsic stacking faults with inversion domain boundaries in GaN epitaxial layers is studied by high resolution electron microscopy. It is observed that stacking faults may mediate a structural transformation of inversion domain boundaries, from the low energy types, known as IDB boundaries, to the high energy ones, known as Holt-type boundaries. Such interactions may be attributed to the different growth rates of adjacent domains of inverse polarity.