bluuebunny/crossref_metadata_2025 huggingface dataset:
Simulation and Design of Amorphous Silicon Thin-Film Transistors for Driving Color Detectors
Authors: Caputo D. , Colalongo L. , Irrera F. , Lemmi F. , Palma F.
Published: April 2011

Practical use of amorphous silicon stacked-junction color detectors in large-area arrays requires periodic readout of the photo-charge stored in the capacitance of the device by a transient technique of sensing. In any stacked-junction devices, color information is obtained by the “self-biasing” process: during an integration time, the three junctions independently lose charge; during the readout pulse, the capacitances of the three junctions in electrical series are re-charged. Equilibrium is reached after a few cycles, when the charge integrated in a cycle by each junction is the same, and equals the readout charge. The amount of charge is determined by the reverse biased junction and accounts for the light intensity.

Dimensioning the amorphous silicon Thin Film Transistor (TFT) used as a pixel switch for the detector is a critical part of the project of a color imager. The actual design determines the self-bias process duration and the readout accuracy. The typical large thickness difference between the detector junctions makes the constraints for the switching process extremely demanding: since a greater capacitance is expected in the thinner top junction detecting blue radiation, the on-resistance must be reduced. Since the front junction does not ensure full rejection of green and red light, a calculation must be performed to extract the information on blue radiation. This requires further precision in the readout process.

In this work we present a simulation study of the self-biasing process. Both a-Si:H TFT and the a-Si:H p-i-n-i-p two-color detectors are simulated by a finite-elements two-dimensional simulator ensuring a correct modeling of both the devices. Simulations allow to study in detail the timing and the accuracy of the self-biasing process. Including electrostatic capacitance and trapped charge, a set of design rules for the TFT is achieved in terms of on-state design. Similar considerations can be extended to the case of ATCD three-color detectors.
Fast growth of amorphous silicon layers by amplitude modulation PECVD
Authors: Biebericher A. C. W. , Bezemer J. , Weg W. F. van der , Goedheer W. J.
Published: April 2011

Hydrogenated amorphous silicon has been deposited by Plasma Enhanced Chemical Vapor Deposition (PECVD) with a square wave amplitude modulated rf signal of 50 MHz. We studied the dependence of the deposition rate on the modulation frequency, using optical emission spectroscopy and plasma modeling. We observed an enhancement in deposition rate by modulating the plasma. This behavior is explained by the characteristics of the electronenergy distribution during the periodical onset of the plasma. According to a one-dimensional fluid model, high-energy electrons cause a large production of radicals at the onset. The heating occurs over the whole plasma volume, leading to an increase of the homogeneity of the layers. The discharge structure is changed completely. A comparison is made between results obtained at 13.56 MHz and at 50 MHz deposition voltages.
Wide Bandgap ≥1.8eV Amorphous Silicon for Solar Multijunction Cell and Image Sensor Applications
Authors: Kolodziej Andrzej , Krewniak Pawel , Tadeusiewicz Ryszard
Published: April 2011

This paper discusses the use of wide bandgap a-Si:H prepared by reactive magnetron sputtering (RMS) in low temperature and hydrogen control process deposition for multijunction cell applications. Primarily technological experiments are presented. The studies were carried out on a-Si:H films and TCO / n+ a-Si:H / i a-Si:H / Nickel Schottky barrier structures with i layer thicknesses ranging between 0.1 and 0.5 μm, using AFM, X-ray small angle and Raman spectroscopy, and optical transmission and reflection measurements after a degraded steady state. The properties exhibited by the films obtained in various ways are compared. In particular, fill factor dependence on light, field, and thickness is presented for RMS films.
Solar-Cell Suitable μc-Si Films Grown by ECR-CVD
Authors: Birkholz M. , Conrad E. , Lips K. , Selle B. , Sieber I. , Christiansen S. , Fuhs W.
Published: April 2011

The preparation of μc-Si films from SiH4-H2 mixtures by electron-cyclotron resonance (ECR) CVD at deposition temperatures ≤ 400°C on foreign substrates is reported. Deposition conditions were identified for which Si films with a high degree of crystallinity were grown as was confirmed by Raman spectroscopy. A factorial analysis was carried out, for which the influence of deposition temperature, microwave power, hydrogen dilution and total pressure on film growth were investigated. Samples of optimized crystallinity were prepared in a lowpressure and high-hydrogen dilution regime. In-plane grain sizes were measured by TEM and found to be on the order of 10 - 12 nm. Next to the optimization of crystallinity several sources of impurity contamination during film deposition were identified and eliminated. Intrinsic μc-Si layers could be prepared under these conditions that exhibited a dark conductivity σd of 2 × 10-7 S/cm and photosensitivity σph/σd of 150. It is concluded that ECR CVD is capable of producing intrinsic layers with electronic properties as necessary for use in state-of-the-art n-i-p μc-Si solar cells.
Si + SiH4 Reactions and Implications for Hot-Wire CVD of a-Si:H: Computational Studies
Authors: Muller Richard P. , Holt Jason K. , Goodwin David G. , Goddard William A.
Published: April 2011

Gas phase chemistry is believed to play an important role in hot-wire CVD of amorphous silicon, serving to convert the highly-reactive atomic Si produced at the wire into a less-reactive species by reaction with ambient SiH4. In this paper, we use quantum chemistry computations (B3LYP/cc-pvTZ) to examine the energetics and rates of possible gas-phase reactions between Si and SiH4. The results indicate that formation of disilyne (Si2H2) is energetically favorable. Unlike other products of this reaction, Si2H2 does not require collisional stabilization, and thus this species is the most likely candidate for a benevolent precursor that participates in the growth of high-quality Si films.
Effect of Ramp Annealing to Ni Induced Lateral Crystallization of Amorphous Silicon
Authors: Shivani S. , Poon M.C. , Chan M. , Ko P.K.
Published: April 2011

Nickel Metal-Induced-Lateral-Crystallization (MILC) has been used to enlarge the grain size and improve the quality of (poly-Si) Thin-Film-Transistors (TFTs). However, the MILC temperature is still low and the grain size is still small. The feasibility of forming very large grains (single crystal like) from amorphous silicon (a-Si) by combining MILC with ramp annealing has been studied. It has been found that the grain size after ramp annealing is remarkably enhanced and can reach of the order of several ten's of microns. The velocity of MILC with ramp annealing is faster than that of MILC with isothermal annealing. The grain size becomes maximal at around 625°C/2hrs, and saturates at higher temperatures of 625- 1000°C. The effect of temperature, time and other parameters has also been studied in order to maximize the grain size and quality. MILC with ramp annealing at 625°C can greatly lower the process time and reduce the need of subsequent annealing to enhance the grain size. The new technology can have numerous novel applications such as providing a low cost alternative to form silicon-on-insulator (SOI) substrates and a breakthrough for high performance TFTs and novel multi-layers SOI like devices and circuits.
Concentration and Stress Evolution During Electromigration in Passivated Al(0.25 at. % Cu) Conductor Lines
Authors: Kao H.-K. , Cargill G. S. , Hu C.-K.
Published: April 2011

We have used x-ray microbeam fluorescence and diffraction for in-situ measurements of electromigration-induced Cu diffusion and stress evolution in passivated, polycrystalline 10[.proportional]m-wide, 200[.proportional]m-long Al(0.25 at.% Cu) conductor lines. Cu migration is in the direction of the electron flow and is determined by the direction and magnitude of the current and by the temperature during electromigration. The effective charge and diffusivity of Cu in Al(Cu) have been obtained from analysis of the Cu concentration profiles. The evolution of electromigration-induced strains normal to the sample surface has been monitored by x-ray microbeam diffraction. A linear strain profile developed after about 9 hrs of electromigration with 1.5[.dotmath]105 A/cm2 at 300°C, corresponding to 3MPa/[.proportional]m equi-biaxial stress. From the Cu profile measured at the same time, the critical Cu concentration for significantly slowing down Al grain boundary diffusion is estimated to be ∼0.15 at. %. These data also confirm that downstream Cu transport is accompanied by a counter flow of Al in the upstream direction.
Curing Study of Hydrogen Silsesquioxane Under H2/N2 Ambient
Authors: Liou Huey-Chiang , Dehate Evan , Duel Jerry , Dall Fred
Published: April 2011

Thin film properties of hydrogen silsesquioxane (HSQ) cured at different temperature under N2 and H2/N2 ambients have been studied. In this study, it was found that compared to an N2 ambient, film curing in an H2/N2 ambient will impact HSQ properties when the temperature is 400°C – 500°C. H2/N2 ambient can be used to minimize the dielectric constant while increasing modulus of the films. The data indicates that H2 can minimize the oxidation of the HSQ films and maintain the dielectric properties.
Properties of Tin Thin Films Deposited by Alcvd as Barrier for Cu Metallization
Authors: Satta Alessandra , Beyer Gerald , Maex Karen , Elers Kai , Haukka Suvi , Vantomme A.
Published: April 2011

In advanced multi-level metallization schemes, the application of copper as interconnect metal requires the prevention of Cu diffusion into the active area and into interlevel dielectrics by total encapsulation of Cu with barrier films. Critical requirements for diffusion barriers are very small thicknesses, low resistivity, low deposition temperature and conformality on high aspect ratio trenches and vias. For this application, we have studied TiN films deposited by atomic layer chemical vapour deposition (ALCVD) at 400°C and 350°C. This paper discusses the ALCVD TiN films properties and compares them to the properties of TiN deposited by ionized physical vapour deposition (I-PVD).

The ALCVD TiN deposited at 400°C exhibits a resistivity comparable to I-PVD TiN resistivity. However, the ALCVD films deposited at 350°C show higher resistivity. The Cl residue in ALCVD films is 1.5% at 400°C and 3% at 350°C. The microstructure is fine-grained. A very high level of conformality on trenches characterizes the ALCVD TiN films. We believe this property gives a clear advantage over the sputtered I-PVD TiN since its coverage in high aspect ratio trenches and vias is expected to be limited for the future devices interconnection scheme.
Optimal Design of Reactors for Metalorganic Vapor Phase Epitaxy of Group III Nitrides
Authors: Pawlowski R. P. , Theodoropoulos C. , Mountziaris T.J. , Moffat H.K. , Han J. , Thrush E. J.
Published: April 2011

Metalorganic Vapor Phase Epitaxy (MOVPE) has emerged as the technique of choice for growing thin films and structures of group III-nitrides. The objective of this work is to address the optimal design of vertical rotating disk and stagnation flow MOVPE reactors in order to achieve film thickness uniformity over large area substrates. Gas inlets that preserve the axial symmetry and enable alternating feeding of the precursors through coaxial rings were studied. The growth of GaN films from trimethyl-gallium and ammonia was used as a typical example. A fundamental reaction-transport model of the MOVPE process including gas-phase reactions and gas-surface interactions has been developed. The model was validated through comparison with growth rate data obtained from both research-scale and industrial-scale reactors. Performance diagrams for industrial-scale stagnation flow and rotating disk reactors were developed by varying the reactor geometry and operating conditions to identify regions of uniform film growth.
Composition and Structure of Sputter Deposited Erbium Hydride thin Films
Authors: Adams D.P. , Romero J.A. , Rodriguez M.A. , Floro J.A. , Banks J.C.
Published: April 2011

Erbium hydride thin films are grown onto polished, a-axis α Al2O3 (sapphire) substrates by reactive ion beam sputtering and analyzed to determine composition, phase and microstructure. Erbium is sputtered while maintaining a H2 partial pressure of 1.4 ×10−4 Torr. Growth is conducted at several substrate temperatures between 30 and 500°C. Rutherford backscattering spectrometry (RBS) and elastic recoil detection analyses after deposition show that the H/Er areal density ratio is approximately 3:1 for growth temperatures of 30, 150 and 275°C, while for growth above ∼430 °C, the ratio of hydrogen to metal is closer to 2:1. However, x-ray diffraction shows that all films have a cubic metal sublattice structure corresponding to that of ErH2. RBS and Auger electron spectroscopy confirm that sputtered erbium hydride thin films are relatively free of impurities.
Room Temperature Growth of Indium Tin Oxide Films By Ultraviolet-Assisted Pulsed Laser Deposition
Authors: Craciun V. , Craciun D. , Chen Z. , Hwang J. , Singh R.K.
Published: April 2011

The characteristics of indium tin oxide (ITO) films grown at room temperature on (100) Si and Coming glass substrates by an in situ ultraviolet-assisted pulsed laser deposition (UVPLD) technique have been investigated. The most important parameter, which influenced the optical and electrical properties of the grown films, was the oxygen pressure. For oxygen pressure below 1 mtorr, films were metallic, with very low optical transmittance and rather high resistivity values. The resistivity value decreased when using higher oxygen pressures while the optical transmittance increased. The optimum oxygen pressure was found to be around 10 mtorr. For higher oxygen pressures, the optical transmittance was better but a rapid degradation of the electrical conductivity was noticed. X-ray photoelectron spectroscopy investigations showed that ITO films grown at 10 mtorr oxygen are fully oxidized. All of the grown films were amorphous regardless of the oxygen pressure used.
Improvement Of Cavitation Erosion Resistance and Corrosion Resistance Of Brass by Laser Surface Modification
Authors: Tam K. F. , Cheng F. T. , Man H. C.
Published: April 2011

Laser surface modification of brass (Cu-38Zn-1.5Pb) using AISiFe and NiCrSiB alloy was achieved by using a 2kW continuous wave Nd-YAG laser with the aim of improving the cavitation erosion resistance and corrosion resistance. The alloying powder was preplaced on the brass substrate by thermal spraying to a thickness of 350µm, followed by laser beam scanning to effect melting, mixing and alloying. A modified surface was achieved by overlapping of adjacent tracks. The cavitation erosion resistance and the anodic polarization characteristics of the laser surface modified specimens in 3.5% NaCI solution at 23°C were studied by means of a 20kHz ultrasonic vibrator at a peak to peak amplitude of 60µm and a potentiostat respectively. The cavitation erosion resistance of the specimens modified with AlSiFe and NiCrSiB was improved by a factor of 3 and 7 respectively, compared with that of the brass substrate. Potentiodynamic test, however, indicated that the corrosion resistance of specimens modified with AlSiFe deteriorated, as reflected by a shift of the polarization curve towards higher current densities. On the other hand, the corrosion resistance of specimens modified with NiCrSiB was significantly improved, as evidenced by the presence of a passive region (from −175 mV to −112 mV) and a reduction in the anodic current density by at least an order of magnitude compared with the substrate at the same anodic potential. The hardness profile and the compositional profile were measured using a Vickers hardness tester and EDX respectively. The microstructure and the surface morphology of the specimens were investigated with the aid of SEM and optical microscopy.
Laser Induced Fluorescence Measurement Of Plasma Plume During Pulsed Laser Deposition Of Diamond-Like Carbon
Authors: Yamagata Yukihiko , Kozai Yuji , Mitsugi Fumiaki , Ikegami Tomoaki , Ebihara Kenji , Sharma Ajay , Mayo Robert M. , Narayan Jagdish
Published: April 2011

Dynamics of carbon ablation plasma plume during the preparation of diamond-like carbon films by KrF excimer pulsed laser deposition was investigated using laser induced fluorescence (LIF) and optical emission spectroscopy. LIF signal from C2molecule (Swan band, d 3Φg – a3Φu) was detected using a photomultiplier tube and an intensified CCD camera. Temporal evolution and spatial distribution of C2 molecules in the ablated plume were measured as a function of laser energy density and ablation area. LIF intensity is found to be weaker in the central part of the plume than that at the periphery at incident energy greater than 6 J/cm2. It is conjectured that some of C2molecules are dissociated by collision with energetic species in central part of the ablation plume. Dynamics of ablation plasma plume is strongly dependent on the size of ablated area.
Surface morphology studies of phthalocyanine thin films: mechanism of the α → β1 phase transition
Authors: Heutz Sandrine , Bayliss Sallie M. , Rumbles Garry , Jones Tim S.
Published: April 2011

Free base phthalocyanine films have been grown on glass substrates by organic molecular beam deposition. In situ post-growth annealing of the samples leads to the α → β1 transformation. Different transition states have been identified and their morphological properties studied by atomic force and optical microscopy. The transition occurs via a discrete number of nucleations and is preceded by an elongation of the α crystallites. The β1 crystallites grow but are confined to domains of similar orientation. Increased thickness produces larger domains and better orientation, while only partial transformation occurs below 94 nm.
Angular Fourier Mapping; Highlighting lattice structures without destroying original data
Authors: Kindt Johannes H. , Thompson James B. , Paloczi George T. , Michenfelder Martina , Smith Bettye L. , Stucky Galen , Morse Daniel E. , Hansma Paul K.
Published: April 2011

A two-dimensional Fourier transformation, FT, is used to isolate two different lattice structures within one scanning probe microscope, SPM, image. The isolated structures are then used to create a two-color map that encodes the presence of these structures within the image. The color map is normalized in brightness and then used to color-code the original black and white SPM data. The distribution of different structures becomes obvious, while all original brightness information is preserved in this combined image.
Electroluminescent Devices with Nanostructured ZnS:Mn Emission Layer Operated at 20 V0-p
Authors: Toyama Toshihiko , Adachi Daisuke , Okamoto Hiroaki
Published: April 2011

We have developed a new type of a thin-film electroluminescence (TFEL) device with nano- structured (NS)-ZnS:Mn utilizing its enhanced luminescent efficiency due to the quantum confinement (QC) effects. As NS-ZnS:Mn, ZnS:Mn/Si3N4 multilayers with thicknesses of 1.9–3.5 nm for ZnS were prepared by a rf-magnetron sputtering method. From the results of grazing incidence X-ray reflectometry and X-ray diffractmetry, formation of ZnS:Mn nanocrystals in the ZnS layers are confirmed. With a decrease in the ZnS:Mn layer thickness, the photoluminescence (PL) efficiency associated with the Mn2+ transitions is increased, and the PL excitation spectrum is shifted toward higher energies, indicating appearance of the QC effects. As the results of the application of NS-ZnS:Mn to the emission layer of the TFEL device, we have successfully observed reddish-orange emission above the threshold voltage of 12 V0-p, and the maximum luminance is 3.0 cd/m2 operated with the 1-kHz sinusoidal voltage of 20 V0-p.
Photo and Cathodoluminescence in Cerium-Activated Yttrium-Aluminium Borates
Authors: Mordkovich V. Z.
Published: April 2011

Ce3+ luminescence in Ce-activated yttrium aluminium borates was studied. Photoluminescnece was excited by continuous-wave UV or by pulse laser irradiation. Cathodoluminescence was excited at the acceleration voltage in the range 5 to 600 V. These phosphors show under continuous wave UV excitation three emission peaks: in near UV, deep blue and light blue ranges. The light blue peak at around 490 nm which may be connected to forbidden 2D3/2 → 2F7/2 transition appears in continuous wave-excited photoluminescence only and does not appear in cathodoluminescence nor under pulse excitation. The blue-emitting Ce- activated yttrium aluminium borates exhibit unusually strong activator ion-host lattice interaction. As a result a substantial red shift in the emission is induced by Ce concentration increase and complicated concentration dependence of the emission intensity is observed.
Green Emission from Er-Doped AlN Thin Films Prepared by RF Magnetron Sputtering
Authors: Dimitrova V. I. , Perjeru F. , Chen Hong , Kordesch M. E.
Published: April 2011

Thin films of Er doped AlN, ∼ 200 nm thick, were grown on indium tin oxide/aluminum titanium oxide/glass substrates using RF magnetron sputtering in a pure nitrogen atmosphere. To optically activate Er all films were subject to post-deposition annealing in flowing nitrogen atmosphere at atmospheric pressure at temperatures between 1023-1223 K for 10-60 minutes. The visible cathodoluminescence (CL) in the green was detected at both 11 K and 300K. The strongest CL peaks were observed at 558 nm and 537 nm (11 K), which correspond to the transitions from 4S3/2 and 2H11/2 to the 4I15/2 ground level. Electroluminescence (EL) studies of AlN:Er alternating-current thin-film electroluminescent (ACTFEL) devices were performed at 300 K. The turn-on voltage was found to be around 80-100 V for our ACTFEL devices. The intensity of the EL emission rapidly increases with the voltage increasing in the investigated range of 110-130 V.
Effect of TiO2 Addition on the Secondary Electron Emission and Discharge Properties of MgO Protective Layer
Authors: Kim Younghyun , Kim Rakhwan , Kim Hee Jae , Jeon Hyeongtag , Park Jong-Wan
Published: April 2011

Secondary electron emission from a cathode material in AC PDP (Plasma Display Panel) is dominated by potential emission mechanism, which is sensitive to band structure of a protective layer. Therefore, the secondary electron emission property can be modified by a change in the energy band structure of the protective layer. Mg2-2xTixO2 films were prepared by e-beam evaporation method to be used as possible substitutes for the conventional MgO protective layer. The oxygen content in the films and in turn, the ratio of metal to oxygen gradually increased with the increasing TiO2 content in the starting materials. The pure MgO films exhibited the crystallinity with strong (111) orientation. The Mg2-2xTixO2 films, however, had the crystallinity with (311) preferred orientation. The stress relaxation, when the [TiO2/(MgO+TiO2)] ratio in the evaporation starting materials was 0.15, seems to be related to inhomogeneous film surface due to an excessive addition of TiO2 to MgO. When the [TiO2/(MgO+TiO2)] ratios of 0.1 and 0.15 were used, the deposited films exhibited the secondary electron emission yields improved by 50% compared to that of the conventional MgO protective layer, which resulted in reduction in discharge voltage by 12%.
Low Temperature Laser-Doping Process Using PSG and BSG Films for Poly-Si TFTs
Authors: Kim Cheon-Hong , Jung Sang-Hoon , Jeon Jae-Hong , Han Min-Koo
Published: April 2011

A simple low-temperature excimer-laser doping process employing phosphosilicate glass (PSG) and borosilicate glass (BSG) films as dopant sources is proposed in order to form source and drain regions for polycrystalline silicon thin film transistors (poly-Si TFTs). We have successfully controlled sheet resistance and dopant depth profile of doped poly-Si films by varying PH3/SiH4 flow ratio, laser energy density and the number of laser pulses. The penetration depth and the surface concentration of dopants were increased with increasing laser energy density and the number of laser pulses. The minimum sheet resistance of 450ω/ for phosphorus (P) doping and 1100ω/ for boron (B) doping were successfully obtained. Our experimental results show that the proposed laser-doping process is suitable for source/drain formation of poly-Si TFTs.
Crystallization of Amorphous Si Thin Films Using a Viscous Ni Solution
Authors: Ahn Jin Hyung , Kim Sung Chul , Ahn Byung Tae
Published: April 2011

We prepared a viscous Ni solution by dissolving NiCl2 in 1N HCl and mixing it with propylene glycol to control the amount of Ni on Si surface. A uniform film was formed after spin coating and oven dry. The a-Si films deposited by LPCVD with Si2H6 gas were crystallized more uniformly and more reproducibly. And the crystallization was enhanced from 600°C, 30h to 500°C, 10h. The surface roughness of poly-Si film crystallized with the viscous solution was much smaller than that of poly-Si film crystallized from Ni/Si direct contact. The TFT mobility was improved even though the crystallization temperature was much lower.
Crystal Growth of Laser Annealed Polycrystalline Silicon as a Function of Hydrogen Content of Precursors
Authors: Tamura Takuo , Ogata Kiyoshi , Takahashi Michiko , Suzuki Kenkichi , Yamaguchi Hironaru , Todoroki Satoru
Published: April 2011

The influence of hydrogen in a precursor on excimer laser crystallization behavior was investigated. The crystal orientation and lattice constant of polycrystalline silicon films were analyzed by X-ray diffraction measurement. An intensity ratio of 111 to 220 was used as an index of the (111) preferred orientation. A randomly oriented film with an index of 2 at lower energy density changed to the highly (111) oriented phase with an index of more than 15 at higher energy density. It was observed in the PE-CVD films that increasing the hydrogen in the precursor films decreased the orientation index. The lattice constant of the laser-annealed PE-CVD silicon was found to be larger than that of the PVD silicon and to decrease with an increase in laser energy density. The network structure of as-deposited PVD film with less hydrogen content was denser than that of as-deposited PE-CVD. The network structure of the precursor strongly affected the crystal growth, and the structure of the ELC poly-Si was still affected by the precursors, even though the hydrogen content decreased after laser annealing.
Sequential Lateral Solidification of PECVD and Sputter Deposited a-Si Films
Authors: Crowder M. A. , Sposili Robert S. , Limanov A. B. , Im James S.
Published: April 2011

We have investigated sequential lateral solidification (SLS) of amorphous Si films that have been prepared via PECVD and sputter deposition methods. The focus of the work was on identifying and analyzing the energy density and per-pulse translation distance parameter space that permits SLS of these films. Experimental details include the use of a two-axisprojection irradiation system to image a straight-slit beamlet pattern onto the sample, and analyzing the resulting microstructures by SEM and optical microscopy of Secco-etched samples. High-temperature-deposited LPCVD films were also examined to enable further comparative analysis. We conclude from these results that there are no major differences in both the SLS process characteristics and the resulting microstructure among the investigated films (provided that the films are dehydrogenated in the case of PECVD a-Si). Based on the controlled super-lateral growth (C-SLG) model of the SLS process, we attribute these findings to the fact that the SLS method involves—as one of its essential features—complete melting of the Si film at fluences that are sufficient to thoroughly melt crystalline Si films, during which all pre-irradiation phase and microstructural details are erased.
Chemical effects observed in the SERS spectra of single wall nanotubes
Authors: Baibarac Michaela , Baltog Ioan , Lefrant Serge , Chauvet Olivier , Mévellec Jean-Yves , Vaccarini Laetitia , Bernier Patrick
Published: April 2011

In this paper, we present results obtained by Surface Enhanced Raman Scattering (SERS) on SWNTs films with different thicknesses. We show that the “D” band associated to disorder in graphitic compounds can also be due to intrinsic defects in SWNTs. In addition, we put in evidence strong interfacial reactions at the SWNTs/metallic support interface when NMP is used as solvent to disperse the tubes. Our observations suggest that these reactions can induce a breaking of the SWNTs. Presumably a reconstruction of compounds close to C60 molecules can occur.
Time and Space Evolution of Emitting Carbon Nanoparticles – Correlation with the Formation of Fullerenes and Carbon Nanotubes –
Authors: Suzuki Shinzo , Sen Rahul , Yamaguchi Hirofumi , Ishigaki Toshinobu , Ohtsuka Yohsuke , Achiba Yohji , Kataura Hiromichi
Published: April 2011

The temporal and spatial evolution of emitting carbon nanoparticles were investigated using a laser furnace apparatus combined with a high-speed video camera. An apparent increase in the blackbody emission intensity at Δt > 400 [.proportional]sec after laser vaporization of a graphite rod was clearly recognized. Also, it was found that this increasing tendency corresponds well to that of the fullerene yield, where fullerene species was obtained as sublimed carbon material using in situ sublimation method. These findings suggest that a certain exothermic process related to the formation of C60, other higher fullerenes, and carbon nanotubes should occur at Δt > 400 νsec inside the furnace.
Gas Molecules Adsorption on Carbon Nanotubes
Authors: Zhao Jijun , Buldum Alper , Han Jie , Lu Jian Ping
Published: April 2011

We study electronic properties of single-walled carbon nanotubes (SWNTs) upon gas molecules adsorption with first principles methods. The adsorption energy, charge transfer, and electronic structures are studied for various gas molecules (NO2, O2, NH3, N2, CO2, CO, H2O, H2, He). Most molecules adsorb weakly on SWNTs and can be either charge donor or accepter to the nanotubes. The electronic properties of nanotubes are sensitive to the adsorption of certain molecules such as NO2 and O2. Charge transfer and gas-induced charge fluctuations are found to significantly affect the transport properties of SWNTs. Our results are consistent with recent experiments.
Catalyst-Free Synthesis of Single-Wall Boron Nitride Nanotubes via Laser Ablation
Authors: Lee Roland S. , Gavillet Julie , Chapelle Marc Lamy de la , Cochon Jean-Lou , Pigache Daniel , Thibault Jany , Willaime François , Loiseau Annick
Published: April 2011

Boron nitride nanotubes (BN-NTs) were synthesized in “mass” quantities (∼0.6 g/h) using a continuous CO2 laser ablation reactor described in the literature [1]. High-resolution electron microscopy (HRTEM) analyses have shown the nanotubes to be organized in “ropes” comprising ∼10 tubes. Analysis of HRTEM images indicate that the majority of the tubes are zig-zag. The chemical composition of the tubes was confirmed using electron energy loss spectroscopy (EELS) analysis, which also determined that nanoparticles terminating tube ends were composed of pure boron covered by BN fullerene-like “cages”. The growth mechanism of the nanotubes seems to be “root-based” with tubes growing from boron nanoparticles dispersed throughout the samples; the non-particle-terminated ends of the tubes exhibit flat “caps” characteristic of BN-NTs [2].
Magnetic Properties of 100 NM-Period Nickel Nanowire Arrays Obtained from Ordered Porous-Alumina Templates
Authors: Nielsch K. , Wehrspohn R.B. , Fischer S.F. , Kronmüller H. , Barthel J. , Kirschner J. , Gösele U.
Published: April 2011

Ni nanowires were grown in highly-ordered anodic alumina templates using pulsed electrodeposition. This technique yields completely metal-filled alumina membranes. The magnetic behavior of 100 nm period arrays of Ni nanowires with a length of 1 μ and different diameters has been characterized using SQUID magnetometry and magnetic force microscopy. Reducing the diameter from initially 50 to 25 nm while keeping the interwire distance constant leads to increasing coercive fields from 600 Oe to 1200 Oe and to increasing remanence from 30% to 100% of the hysteresis. The deposition of Ni65Fe35 gave a further improvement of the coercive fields up to 1350 Oe.
Fabricating Two-Dimensional Metal Nanocrystal Arrays Using Pulsed-Laser Deposition and Focused Ion-Beam Technologies
Authors: Haglund Richard F. , Weller Robert A. , Heiner Cynthia E. , McMahon Matthew D. , Magruder Robert H. , Newton Allen T. , Shen Liyong , Feldman Leonard C.
Published: April 2011

We describe recent experiments in which we attempted the initial steps for fabricating twodimensional arrays of metal nanocrystals. We use a commercial pulsed-laser deposition system in concert with a focused ion beam to attempt control over both lateral and vertical dimensions at the nanometer length scale. In our experiments, regular arrays of holes typically 80 nm in diameter were drilled in Si substrates using the focused ion beam. Silver atoms were then deposited onto these substrates by pulsed laser evaporation from a metallic target in high vacuum. Under certain conditions of substrate temperature, laser pulse repetition rate, and fluence, small silver nanoclusters form preferentially around the structures previously etched in the silicon surfaces by the focused ion beam.
Nanofabrication of Planar High Temperature Superconducting Josephson Junctions Using Focused Ion Beam Technology
Authors: Zhai Hong-Ying , Chen Quark Y. , Liu Jiarui , Chu Wei-Kan
Published: April 2011

Superconductor-normal metal-superconductor (SNS) high-Tc Josephson junctions have been fabricated on c-oriented YBa2Cu3O7-δ (YBCO) films. Focused ion beam (FIB) nano-structure modification (cutting of the film and local deposition of a metal) was used to form the junction with tungsten barrier. The junctions exhibit resistively shunted junction (RSJ) -like I-V characteristics.
A New Simple Method for Fabrication of Fine Metal Patterns
Authors: Hotta Yasuyuki , Asakawa Koji , Matake Shigeru , Hiraoka Toshiro
Published: April 2011

We developed a new method for easy fabrication of micrometer-scale fine metal patterns on substrates. The patterns can be fabricated at low cost, at low processing temperature, and on uneven substrates as well as on plane surfaces. The method involves, first, forming hydrophilic and hydrophobic patterns on the substrates, and, second, depositing metal by electroless plating on the hydrophilic area. Hydrophilic and hydrophobic patterns were formed on a sensitizer containing naphthoquinonediazide (NQD) units coated on the substrates by the exposure. In the exposed areas, metal particles that are catalysts for electroless copper plating were adsorbed in the ion-exchange reaction and then the reduction treatment was performed. Copper was selectively deposited by the self-catalyst mechanism, according to the exposed patterns. All experimental processes can be carried out at room temperature. Using this new method, copper line patterns of 25 μm and copper dot patterns of 15 μm diameter were fabricated on the substrate.
Low Pressure Band Tuning in Wurtzite CdSe Quantum Dots
Authors: Meulenberg R.W. , Offen H.W. , Strouse G.F.
Published: April 2011

Several studies to date have probed structural phase transitions in quantum dots (QDs) at high pressure. At low pressure (< 1 GPa), the optical properties of solvated nanomaterials are modulated by pressure induced electronic level tuning, particularly for surface and trap states. In fact, low pressure studies on solvated CdSe QDs may provide insight into the participation of surface hole traps and electron traps on the excited state optical properties in these materials. We report findings of QD size dependent pressure coefficients and postulate that trap state tuning, surface reconstruction events, and electron-hole exchange interactions may play a role in the low-pressure regime.
Self-Assembled Monolayers as High-Resolution Etch Masks and Templates for Organic Molecular Assembly
Authors: Harnett C. K. , Lopez A. G. , Satyalakshmi K. M. , Chen Y.-F. , Craighead H. G.
Published: April 2011

We have used a variety of self-assembled monolayers as resists for low energy electron beam patterning. These compounds can be used as high-resolution patternable linker molecules for selected area binding of proteins and other organic compounds, as well as nanoparticles with organic chemical coatings. Because these systems can be aligned in registry to existing patterns, the organic systems may be positioned with the accuracy of electron-beam lithography. We have also explored the use of self-assembled monolayers for the creation of sub-wavelength artificial dielectric systems. The ultra-thin patterned monolayer is combined with a contrast-enhancing etch process to create high aspect ratio structures. This technique can be used to fabricate diffractive optical devices in a single-step process.
Photoluminescence and ESR study of Si1−xGex alloy nanocrystals
Authors: Toshikiyo K. , Tokunaga M. , Takeoka S. , Fujii M. , Hayashi S.
Published: April 2011

Dangling bond defects in Si1−xGex alloy nanocrystals (nc-Si1−xGex) as small as 4 nm in diameter embedded in SiO2 thin films were studied by electron spin resonance (ESR), and the effects of the defects on photoluminescence (PL) properties were discussed. It was found that the ESR spectrum is a superposition of signals from Si and Ge dangling bonds at the interfaces between nc-Si1−xGex and SiO2 matrices (Si and Ge Pb centers). As Ge concentration increased, the intensity of the signal from the Ge Pb centers increased, while that from the Si Pb centers was almost independent of Ge concentration. The increase in the number of Ge Pb centers was accompanied by strong quenching of the PL. The observed correlation between the two measurements suggests that Ge Pb centers act as efficient non-radiative recombination centers for photogenerated carriers, resulting in the quenching of the PL.
Formation of Ge Nanocrystals Passivated with Si by Gas Evaporation of Si and Ge
Authors: Si Junjie , Ono H. , Uchida K. , Nozaki S. , Morisaki H.
Published: April 2011

Two methods are employed in the gas evaporation technique to form Ge nanocrystals with the Si-passivated surface. One uses one boat with a SiGe alloy as a source, and the other uses two boats each with Si and Ge. As a result of characterization by the x-ray diffraction (XRD) measurement, Raman scattering and x-ray photoelectron spectroscopy (XPS), it is found that Ge nanocrystals with the Si-passivated surface were formed by coevaporation of Si and Ge from two boats, while SiGe alloy nanocrystals were formed by evaporation of the Si-Ge alloy source from one boat.
Low-Field Electron Emission Properties from Intrinsic and S-Incorporated Nanocrystalline Carbon Thin Films Grown by Hot- Filament CVD
Authors: Gupta S. , Weiner B. R. , Weiss B. L. , Morell G. , Johnson Kenyetta , Oritz Oscar O.
Published: April 2011

Results are reported on the electron field emission properties of intrinsic and S- incorporated nanocrystalline carbon (n-C:S) thin films grown on molybdenum substrates by hotfilament CVD technique from methane-hydrogen (CH4/H2) and hydrogen sulphide-hydrogen (H2S/H2) gas pre mixtures respectively. The field emission properties for the S-incorporated films were investigated as a function of substrate temperature (TS). Lowest turn-on field was observed at 4.5 V/μm for one of the sample, which was grown at 900 °C, demonstrating the effect of sulfur addition. The S-incorporation also causes microstructural and structural changes, as characterized with ex situ techniques such as SEM, AFM and Raman spectroscopy (RS). Sassisted films show smoother surfaces and finer-grained than those grown without it. The electron field emission properties of S-assisted films is also compared to the film grown without it (intrinsic) at a particular deposition temperature and the turn-on field was found to be almost half for the S-assisted film than for the non S-assisted film. The influence of growth temperature was also conducted and an inverse correlation was found with the turn-on field (Ec). These studies were performed in order attempt to “tailor-the-material” as a viable cold cathode material by introducing the defecTS and altering the electronic structure.
A Memory Device Utilizing Resonant Tunneling in Nanocrystalline Silicon Superlattices
Authors: Montès Laurent , Grom Galina F. , Krishnan Rishi , Fauchet Philippe M. , Tsybeskov Leonid , White Bruce E.
Published: April 2011

A quantum structure based on Si/SiO2 and fabricated using standard Si technology has strong potential for applications in non-volatile and scaled dynamic memories. Among standard requirements, such as long retention time and endurance, a structure utilizing resonant tunneling offers lower bias operation and faster write/read cycle. In addition, degradation effects associated with Fowlher-Nordheim (FN) hot electron tunneling can be avoided. Superlattices of nanometer size layers of silicon and silicon dioxide were obtained by sputtering. The size of the silicon nanocrystallites (nc-Si) is fixed by the thickness of the silicon layer which limits the size dispersion. A detailed analysis of the storage of charges in the dots, as a function of the nanocrystals size, is investigated using capacitance methods. Constant voltage and constant capacitance techniques are used to monitor the discharge of the structure. Room temperature non-volatile memory with retention times as long as months is evidenced.
Optical and Structural Characterization of Nanocrystalline Silicon Superlattices: Toward Nanoscale Silicon Metrology
Authors: Zollner Stefan , Konkar Atul , Liu Ran , Yapa Himansu , Dryer Patricia F. , Neeley Victoria A. , Xie Qianghua , Grom Galina F. , Zhu Qingyuan , Krishnan Rishikesh , Fauchet Philippe M. , Tsybeskov Leonid V.
Published: April 2011

Short-period superlattices consisting of nanocrystalline Si wells and amorphous SiO2 barriers were analyzed using various structural (transmission electron microscopy, atomic force microscopy, and x-ray diffraction) and optical (Raman scattering and spectroscopic ellipsometry) characterization techniques. We observe parallel layers containing polycrystalline Si wells, primarily with <111> orientation, and an interesting surface morphology due to sputtering damage. Raman spectra show a redshift and broadening due to finite-size effects. The ellipsometry data can be described using the effective medium approximation (since the superlattice period is much shorter than the wavelength of the optical excitation) or a superlattice approach based on the Fresnel equations with a polycrystalline Si dielectric function.
AlGaN p-i-n Photodiode Arrays for Solar-Blind Applications
Authors: Lamarre P. , Hairston A. , Tobin S. , Wong K. K. , Taylor M. F. , Sood A. K. , Reine M. B. , Schurman M. J. , Ferguson I. T. , Singh R. , Eddy C. R.
Published: April 2011

This paper presents UV imaging results for a 256×256 AlGaN Focal Plane Array that uses a back-illuminated AlGaN heterostructure p-i-n photodiode array, with 30×30 μm2 unit cells, operating at zero bias voltage, with a narrow-band UV response between 310 and 325 nm. The 256×256 array was fabricated from a multilayer AlGaN film grown by MOCVD on a sapphire substrate. The UV response operability (>0.4×average) was 94.8%, and the UV response uniformity (σ/μ) was 16.8%. Data are also presented for back-illuminated AlGaN p-i-n photodiodes from other films with cutoff wavelengths ranging between 301 and 364 nm. Data for variable-area diagnostic arrays of p-i-n AlGaN photodiodes with a GaN absorber (cutoff=364 nm) show: (1) high external quantum efficiency (50% at V=0 and 62% at V=-9 V); (2) the dark current is proportional to junction area, not perimeter; (3) the forward and reverse currents are uniform (σ/μ=50% for forty 30×30 μm2 diodes at V=−40 V); (4) the reverse-bias dark current data versus temperature and bias voltage can be fit very well by a hopping conduction model; and (5) capacitance versus voltage data are consistent with nearly full depletion of the unintentionally-doped 0.4 μm thick GaN absorber layer and imply a donor concentration of 3-4×1016 cm−3.
AlGaN/InGaN Heterostructure Field Effect Transistors Grown on Sapphire by Metal-Organic Chemical Vapor Deposition
Authors: Chuo Chang-Cheng , Kan Chia-Min , Chyi Jen-Inn , Nee Tzer-En , Lee Chia-Ming , Peng Chin-Kun
Published: April 2011

AlGaN/InGaN heterostructure field effect transistors were grown on sapphire by metalorganic chemical vapor deposition. Transmission electron microscopy shows that there are no additional dislocations induced by inserting the InGaN channel while a variation of strain field across the channel is observed. The transistors exhibit good pinch-off characteristics with a threshold voltage of about −2.9 V and a saturation current density of 0.55 A/mm. At room temperature, a peak transconductance of 132 (mS/mm) was obtained for a 1.0 μm-device. Current gain cutoff frequency fT of 9.4 GHz and maximum oscillation frequency fmax of 28.2 GHz were measured for the 1.0 μm-device. As the temperature is increased to 300 °C, the transconductance decreases to 50 mS/mm accompanied by a reduction of saturation current density of 0.24 A/mm due to the enhanced carrier scattering, gate leakage, and drain-source resistance.
High-Temperature Electron Transport Properties in AlGaN/GaN Heterostructure Field Effect Transistors
Authors: Maeda Narihiko , Saitoh Tadashi , Tsubaki Kotaro , Nishida Toshio , Kobayashi Naoki
Published: April 2011

Electron transport properties in the Al0.15Ga0.85N/GaN heterostructure field effect transistors (HFETs) have been examined from room temperature up to 400°C. The temperature dependencies of the two-dimensional electron gas (2DEG) mobility have been systematically measured for the samples with different 2DEG densities. The 2DEG mobility has decreased with increasing the temperature, however, its decrease ratio has been no longer large above 300°C. Moreover, the 2DEG mobility has found to be less dependent on the 2DEG density at higher temperatures. These observed features indicate that the 2DEG mobility above room temperature is limited by longitudinal optical (LO) phonon scattering, as is expected by theoretical prediction. The observed 2DEG mobilities at 400°C were as high as from 100 to 120 cm2/Vs, directly providing the evidence for suitability of the HFET of this material system for high-temperature applications. The temperature dependence of the transconductance (gm) of a HFET device has also been examined up to 400°C. It has been revealed that the temperature dependence of gm has basically the same features as those of the 2DEG mobility in the corresponding temperature region.
High-Frequency Capacitance-Voltage Characteristics of Pecvd-Grown SiO2 Mis Structure on GaN and GaN/AL0.4Ga0.6N/GaN Heterostructure
Authors: Chen P. , Zhou Y.G. , Bu H.M. , Li W.P. , Chen Z.Z. , Shen B. , Zhang R. , Zheng Y.D.
Published: April 2011

Metal-insulator-semiconductor structures are fabricated by depositing SiO2 films on an MOCVD-grown n-type GaN epitaxial layer and a GaN/Al0.4Ga0.6N/GaN double heterojunction. The SiO2 films are grown by plasma-enhanced chemical vapor deposition. High-frequency C-V characteristics show the agreement of the measured C-V curve of SiO2/n-GaN with an ideal curve in deep depletion and the very small hysteresis, which indicates that the interface traps concentration in the sample is low. However, for SiO2/GaN/Al0.4Ga0.6N/GaN, the measured C-V curves show a notable flat-band shift of about 9.2 V and a typical polarization hysteresis window. These show the influence of the polarization charges in this structure. The capacitance on SiO2/GaN/Al0.4Ga0.6N/GaN reaches a minimum value under around –5V bias. The saturation at a minimum value of the C-V curve indicates the presence of holes accumulation in the MIS structure. These results imply that the piezoelectric effect in GaN/Al0.4Ga0.6N/GaN play an important role for the formation of the p-channel.