bluuebunny/crossref_metadata_2025 huggingface dataset:
Clinical Science: Peripheral and Central Trigeminal Targets for Acute Migraine Therapy: Early Clinical Trial Results
Authors: Ramadan Nabih M. , Buchanan Thomas M. , Pearlman Starr H.
Published: July 2004

In the decade since the introduction of sumatriptan on the market, second‐ and third‐generation triptans have been advanced with the goal of reducing side effects while maintaining or improving efficacy. While these efforts have yielded relatively minor changes to the sumatriptan molecule, the new triptans enhance the ability of clinicians to individualize therapy. More recent strategies focus on novel neuronal targets for acute migraine treatments without the liability of adverse cardiovascular effects. Current research is focusing on calcitonin gene‐related peptide antagonists, glutamate modulators, selective serotonin 1F or 1D agonists, and adenosine type 1 agonists. Clinical data on these approaches are emerging and seem encouraging. However, these potential therapies are in an early stage of development, and to date, none has reached phase III clinical research.
Vibratory Stress Relief in Manufacturing the Rails of a Maglev System
Authors: Rao, Delin , Ge, and Jingguo , Chen Ligong
Published: July 2004

To reduce the welding induced residual stress in the rails of a magnetic levitation (maglev) transport system, the procedure of vibratory stress relief (VSR) is applied and discussed in this paper. Suitable welding sequence for the rails is introduced to keep the residual stress low. Qualitative analysis with scanning curve shows that the peak of acceleration becomes higher after the procedure of VSR and the resonant frequency becomes lower. It means that the procedure of VSR is effective according to the JB/T5926-91 standard. The residual stress in the rail was measured before VSR and after VSR, using hole-drilling method, and the result shows that the average principal stresses was reduced by about 30% after VSR.
A New Tool Wear Examination Model by Least Square Method for Shearing Process of Thin Metal Sheet
Authors: Lin Zone-Ching , Chang Dar-Yuan
Published: July 2004

A new method that accounts for material loss in the normal direction has been developed. Most research applied wear length and wear area to present the status of the tool. Nevertheless, these methods cannot detect the wear in the normal direction of the contact surface between tool and material, and cannot make accurate judgments in precision machining process. In the proposed model, both of the least square lines of the inspected positions and the least square planes of the examined flanks calculating by the wear depth of measuring points are used to infer the relative wear indices, such as flank wear angle, wear depth of punch top face, straightness error, area loss, and volume loss of punch flanks. By using these indices more objective estimations can be acquired than that of wear length and wear area. A series of shearing experiments of thin phosphor bronze sheet are executed to explore the effects of shearing parameters on punch flank wear, and several regressive equations are derived to express the relationships between the wear indices and number of shearing strokes.
Compliant Assembly Variation Analysis Using Component Geometric Covariance
Authors: Camelio Jaime A. , Hu S. Jack , Marin Samuel P.
Published: July 2004

Dimensional variation is one of the most critical issues in the design of assembled products. This is especially true for the assembly of compliant parts since clamping and joining during assembly may introduce additional variation due to part deformation and springback. This paper discusses the effect of geometric covariance in the calculation of assembly variation of compliant parts. A new method is proposed for predicting compliant assembly variation using the component geometric covariance. It combines the use of principal component analysis (PCA) and finite element analysis in estimating the effect of part/component variation on assembly variation. PCA is used to extract deformation patterns from production data, decomposing the component covariance into the individual contributions of these deformation patterns. Finite element analysis is used to determine the effect of each deformation pattern over the assembly variation. The proposed methodology can significantly reduce the computational effort required in variation analysis of compliant assemblies. A case study is presented to illustrate the methodology.
Determination of a Major Design Parameter for Forward Extrusion of Spur Gears
Authors: Song Jong-Ho , Im Yong-Taek
Published: July 2004

In this study, a major design parameter was identified for cold forward extrusion of solid or hollow spur gears by investigating the effect of gear geometries and forming variables on formation of gear teeth by finite element simulations. A limiting extrusion ratio was determined for reducing the likeliness of underfilling in the die cavity. An equivalent radius of the cross-sectional geometry of a gear was also determined to predict the forming load requirement from an axi-symmetric approximation. Based on this approximation, a modified empirical equation was determined for simple determination of forming loads required.
The Analysis and Control of Micro-Hardness Distribution During Wire Drawing
Authors: Gifford Robert B. , Bandar Alexander R. , Coulter John P. , Misiolek Wojciech Z.
Published: July 2004

During wire drawing processes a critical parameter is the micro-hardness distribution imposed. The present numerical and experimental investigation focused on the effects of and interdependence between processing parameters such as die angle, bearing length, lubrication, and draw speed during wire drawing. The micro-hardness distribution imparted by the drawing process was selected as the focal product quality attribute. The goal of the study was to evaluate the ability to create desired hardness levels in a drawn wire product. The numerical component of the study was performed using DEFORM-2D™, a commercially available metal forming software package based on the finite element method. In addition, experimental verifications of the software predictions were completed wherever possible. Full factorial designs of the processing parameters were studied, and it was found that the final hardness distribution was primarily affected by the die angle. Interactions between the four processing parameters were negligible. Based upon this finding, it was concluded that strength and hardness variations inherent to stock wire could be detected and minimized during wire drawing through the appropriate science-based selection of die angle. This could dramatically enhance the consistency of the wide range of common metal products that are manufactured from wire stock.
Control-Oriented Modeling of Thermal Deformation of Machine Tools Based on Inverse Solution of Time-Variant Thermal Loads with Delayed Response
Authors: Fraser S. , Attia M. H. , Osman M. O. M.
Published: July 2004

With the new emerging technologies of high performance machining and the increasing demand for improved machining accuracy in recent years, the problem of thermal deformation of machine tool structures is becoming more critical than ever. The major problem in implementing real-time control systems is the difficulty of measuring the relative thermal displacement between the tool and the workpiece during machining. Therefore, the design of a generic multi-axis control system requires the development of control-based models to estimate the transient thermal load and the thermal deformation of the structure in real-time. To satisfy the stringent accuracy and stability requirements of the control system, a new inverse heat conduction problem IHCP solver is developed. This solution is capable of including the inertia effect and the delay in the thermal response, in order to accommodate situations where the measured points cannot be located near the heat source, which may be buried into the structure. Experimental validation of these models showed their inherent stability even when the temperature measurements are contaminated with random errors. The excellent computational efficiency of the integrated system, which is well suited for real-time control applications involving multi-dimensional structures, was achieved by incorporating an inverse numerical Laplace transformation procedure. The results also showed that the thermal deformation transfer function behaves as low-pass filters, and as such it attenuates the high frequency noise associated with temperature measurement error.
Spatially Resolved Characterization of Residual Stress Induced by Micro Scale Laser Shock Peening
Authors: Chen Hongqiang , Yao Y. Lawrence , Kysar Jeffrey W.
Published: July 2004

Single crystal aluminum and copper of (001) and (110) orientation were shock peened using laser beam of 12 micron diameter and observed with X-ray micro-diffraction techniques based on a synchrotron light source. The X-ray micro-diffraction affords micron level resolution as compared with conventional X-ray diffraction which has only mm level resolution. The asymmetric and broadened diffraction profiles registered at each location were analyzed by sub-profiling and explained in terms of the heterogeneous dislocation cell structure. For the first time, the spatial distribution of residual stress induced in micro-scale laser shock peening was experimentally quantified and compared with the simulation result obtained from FEM analysis. Difference in material response and microstructure evolution under shock peening were explained in terms of material property difference in stack fault energy and its relationship with cross slip under plastic deformation. Difference in response caused by different orientations (110 and 001) and active slip systems was also investigated.
Modeling of Advanced Melting Zone for Manufacturing of Optical Fibers
Authors: Wei Zhiyong , Lee Kok-Meng , Zhou Zhi , Hong Siu-Ping
Published: July 2004

Optical fibers are drawn from preforms (fused silica glass rods) typically made up of two concentric cylinders (the core rod and the clad tube), which are usually joined in a separate fusion process. The setup time and hence manufacturing cost can be significantly reduced if the two cylinders can be joined in the same furnace in which the fiber is drawn. A good understanding of the transient temperature distribution is needed for controlling the feed rate to avoid thermally induced cracks. Since direct measurement of the temperature fields is often impossible, the geometrical design of the preform and the control of the feed rate have largely been accomplished by trials-and-errors. The ability to predict the transient temperature distribution and the thermally induced stresses will provide a rational basis to design optimization and feed rate control of the process. In this paper, we present an analytical model to predict the transient conductive-radiative transfer as two partially joined, concentric glass cylinders with specular surfaces are fed into the furnace. Finite volume method (FVM) is used to solve the radiative transfer equation (RTE). The specular surface reflectivity is obtained by the Fresnel’s law and the Snell’s law. The boundary intensities are obtained through the coupling of the interior glass radiative transfer and the exterior furnace enclosure analysis. The model has been used to numerically study the transient conductive-radiative transfer in the advanced melting zone (AMZ) of an optic fiber drawing process. This problem is of both theoretical and practical interest in the manufacture of optical fibers. The computational method for the radiation transfer developed in this paper can also be applied to the simulation of the fiber drawing process and other glass-related manufacturing processes.
Transport Phenomena in Two-Phase Micro-Channel Heat Sinks
Authors: Qu Weilin , Mudawar Issam
Published: July 2004

The design and reliable operation of a two-phase micro-channel heat sink require a fundamental understanding of the complex transport phenomena associated with convective boiling in small, parallel coolant passages. This understanding is the primary goal of this paper. This goal is realized by exploring the following aspects of boiling in micro-channels: hydrodynamic instability, two-phase flow patterns, pressure drop, and convective boiling heat transfer. High-speed photographic methods were used to determine dominant flow patterns and explore as well as characterize hydrodynamic instabilities. Two types of dynamic instability were identified, a severe pressure drop oscillation and a mild parallel channel instability, and a simple method is recommended to completely suppress the former. Predictions of three popular two-phase pressure drop models and correlations were compared to micro-channel water data, and only a separated flow (Lockhart-Martinelli) correlation based on the assumption of laminar flow in both phases gave acceptable predictions. Several popular heat transfer correlations were also examined and deemed unsuitable for micro-channel heat sinks because all these correlations are based on turbulent flow assumptions, and do not capture the unique features of micro-channel flow such as abrupt transition to slug flow, hydrodynamic instability, and high droplet entrainment in the annular regime. These findings point to the need for further study of boiling behavior and new predictive tools specifically tailored to micro-channel heat sinks.
Low-temperature Si growth on Si (001): Impurity incorporation and limiting thickness for epitaxy
Authors: Baribeau J.-M. , Wu X. , Lockwood D. J. , Tay L. , Sproule G. I.
Published: July 2004

We present a structural and chemical analysis of high-vacuum deposited Si films grown on clean or oxidized Si (001) wafers by low-temperature molecular-beam epitaxy. For growth on clean Si, we observed a limiting thickness for epitaxy that decreases with decreasing temperature with an activation energy of 0.47 eV. The onset of defect formation is correlated to a peak in the H impurity concentration. The transition to an amorphous phase is, however, observed beyond the depth where impurities are first observed pointing to surface disorder/roughening as a source of epitaxy breakdown. The O and C content in these films remains low until the film crystallinity has strongly deteriorated and reaches a saturation concentration of 2–4 at. % in the fully amorphous regions. The impurity profiles in amorphous-Si films grown on oxidized Si are similar to those obtained on clean Si when grown at the same temperature and indicate that the impurity uptake depends primarily on residual gas and surface condition. Raman scattering results show the structural changes and evolution of the Si bond configuration.
Electron emission from carbon black-based field emitters including diesel engine exhaust
Authors: Busta H. , Boldridge D. , Myers R. , Snider G. , Korotkov A. , Edwards E. , Feinerman A.
Published: July 2004

Field emission properties of carbon black, carbon black and silica, and diesel engine exhaust were investigated and compared to multiwall carbon nanotubes prepared in a similar manner. Sample preparation consisted of pressing the nanopowders into pellet form, dispersing them in isopropanol, or dispersing them in Shipley S1818 photoresist to achieve better adhesion to the substrates. Turn-on fields, at room temperature, ranged from 3–6 V/μm for the pressed and isopropanol prepared samples and shifted to 10–18 V/μm for the photoresist dispersed samples. At 120 °C, the turn-on fields for the photoresist dispersed samples shifted to lower values. This very strong temperature dependence is explained by a resonant Fowler–Nordheim tunneling model. It assumes that a thin barrier layer forms at the elevated temperatures due to outgassing/sublimation events. The macroscopic current densities reached for these samples are about 1–2 mA/cm2.
Improvement in electron emission from carbon nanotube cathodes after Ar plasma treatment
Authors: Kanazawa Yasunori , Oyama Takeshi , Murakami Katsuhisa , Takai Mikio
Published: July 2004

Carbon nanotube (CNT) cathode surfaces have been exposed to Ar plasma and the emission characteristics were measured. When a CNT cathode was exposed to Ar plasma for 3 min, the emission characteristics were improved. The emission current increased after an Ar plasma treatment for 3 min by three orders of magnitude from 9.0×10−5 to 3.3×10−1 mA/cm2 at 4.0 V/μm with a decrease in turn-on voltage from 3.3 to 1.7 V/μm. According to scanning electron microscopy images, entangled CNT bundles were raveled out by Ar plasma treatment.
Material properties and performance of metamorphic optoelectronic integrated circuits grown by molecular beam epitaxy on GaAs substrates
Authors: Hoke W. E. , Leoni R. E. , Whelan C. S. , Kennedy T. D. , Torabi A. , Marsh P. F. , Zhang Y. , Xu C. , Hsieh K. C.
Published: July 2004

Solid source molecular beam epitaxy was used to deposit in a continuous process an integrated metamorphic high electron mobility transistor (HEMT) and PIN photodiode structure. A metamorphic buffer layer was first grown on a GaAs substrate to expand the lattice constant to that of In0.53Ga0.47As used in the device layers. The HEMT layers were subsequently grown followed by the PIN diode structure. Cross-sectional and plan-view transmission electron micrographs showed planar layer interfaces and a dislocation density in the device layers of 1×106 cm−2. The device characteristics of the HEMT transistors were not adversely affected by growth of the PIN structure on top. Also the bandwidth and responsivity of the metamorphic PIN photodiode were comparable to an InP PIN photodiode with similar dark currents. The integrated HEMT/PIN diode circuit had a 3 dB bandwidth 20% greater than a hybrid combination of devices due to a decrease in parasitic losses from device interconnects. The frequency performances of circuits fabricated from the same wafer exhibited a high degree of uniformity.
CdSe quantum dots grown on ZnSe and Zn0.97Be0.03Se by molecular-beam epitaxy: Optical studies
Authors: Zhou Xuecong , Muñoz Martin , Guo Shiping , Tamargo Maria C. , Gu Yi , Kuskovsky Igor L. , Neumark Gertrude F.
Published: July 2004

We report detailed studies of the photoluminescence (PL) properties of CdSe quantum dots (QDs) grown on ZnSe and Zn0.97Be0.03Se by molecular-beam epitaxy. We performed steady-state and time-resolved PL measurements and observed that nonradiative processes dominate at room temperature (RT) in the CdSe/Zn0.97Be0.03Se QD structures while these nonradiative processes do not dominate in the CdSe/ZnSe QD structures up to RT. We developed a method to estimate the capped CdSe/Zn0.97Be0.03Se QD size and composition, based on PL and photoluminescence excitation as well as Raman scattering spectroscopy measurements. Assuming spherical QDs, we estimate the QD radii to be in the range of 2.5 nm to 4.0 nm with the Cd concentration in the range of 47%–54%. This size is smaller than the exciton Bohr radius, suggesting a nearly zero-dimensional character. We also performed contactless electroreflectance measurements on the CdSe/ZnSe QDs, and observed the transitions due to the QDs and the wetting layer. In this case, assuming lens-shaped QDs, we extracted the QD radius to be around 9.52 nm, the height about 3.24 nm. This size is larger than the exciton Bohr radius, indicating a quasi-two-dimensional character. Studies based on Raman scattering spectroscopy suggest that the Cd concentration is about 44% for this structure. The temperature dependences of the PL lifetimes are consistent with the results of the QD size and Cd concentration estimated by these two methods.
Influence of preamorphization and recrystallization on indium doping profiles in silicon
Authors: Duffy R. , Venezia V. C. , Heringa A. , Pawlak B. J. , Hopstaken M. J. P. , Tamminga Y. , Dao T. , Roozeboom F. , Wang C. C. , Diaz C. H. , Griffin P. B.
Published: July 2004

The effect of preamorphization and solid-phase epitaxial regrowth on indium doping profiles in silicon has been investigated. It is shown that preamorphized silicon significantly reduces channeling during indium ion implantation, producing a much more abrupt doping profile. During recrystallization by thermal annealing, indium segregates in front of the moving amorphous/crystalline interface, creating a clearly visible peak in the doping profile. We establish that the physical mechanism for this phenomenon in the 1018–1019 cm−3 concentration range is segregation determined, as there is no significant concentration dependence for those doses studied in this work. We also demonstrate that this phenomenon is enhanced at lower temperatures.
Batch fabrication and characterization of ultrasensitive cantilevers with submicron magnetic tips
Authors: Jenkins Neil E. , DeFlores Lauren P. , Allen Jack , Ng Tse Nga , Garner Sean R. , Kuehn Seppe , Dawlaty Jahan M. , Marohn John A.
Published: July 2004

We have batch fabricated ultrasensitive silicon cantilevers with integrated submicron magnetic tips and have characterized both their mechanical and magnetic properties. Cantilevers with spring constants as small as 10−5 N/m were fabricated, with quality factors in the range of 2.5–3.5×104 and a force sensitivity as good as 64×10−18 N Hz−1/2 at room temperature in vacuum. Cantilever spring constants were measured by observing thermomechanical position fluctuations with a fiber optic interferometer, while resonance frequencies and quality factors were inferred from cantilever ring down transients. Polycrystalline nickel tips as small as 1.2 μm×0.4 μm×0.2 μm were fabricated on the cantilevers by electron beam lithography, thermal evaporation, and lift-off. Tip magnetic moments were inferred from the shift of the cantilever frequency versus magnetic field and show a 0.60±0.12 T saturation magnetization, indicating that less than 28 nm of oxide forms on the tips during processing. Force sensitivity was demonstrated by using the cantilevers to detect electron spin resonance at 115 K in the sample-on-cantilever configuration.
Synthesis and field-emission testing of carbon nanoflake edge emitters
Authors: Wang Jianjun , Zhu Mingyao , Zhao Xin , Outlaw Ron A. , Manos Dennis M. , Holloway Brian C. , Park Chinho , Anderson Tim , Mammana Victor P.
Published: July 2004

A nanometer-edged carbon structure [carbon nanoflake (CNF)] has been synthesized on 50–150-nm-diameter nickel arrays. The Ni dot arrays are patterned using a polystyrene nanosphere lithography technique capable of creating arrays of regularly spaced nanometer-diameter structures of Ni. The flake-like morphology was formed by an inductively coupled rf plasma-enhanced chemical vapor deposition system, with H2 as the carrier gas and CH4 as the carbon source. Typical deposition conditions are: substrate temperature of 680 °C, chamber pressure of 70–90 mTorr, overall gas flow rate of 10 sccm, and CH4 concentration in the range of 10%–40%. Scanning electron microscopy (SEM) shows CNF preferentially growing on the Ni dots, with the irregular carbon flakes standing vertically on the substrate. The flake edge widths are ∼10 nm and the interflake spacing on a given Ni dot is on the order of 15–100 nm. Experiments show that the density, height, and interspacing of the flakes are controllable by varying patterning and deposition parameters. The structures show no degradation or vibration under small-spot SEM imaging, indicating good thermal stability. Raman spectra show a typical carbon feature with D and G peaks at 1350 and 1580 cm−1, respectively. Intensity ratio of these two peaks, I(D)/I(G), increases with CH4 concentration. The work function of this structure determined by Kelvin probe measurement is about 4.3 eV, which is near that of graphitic carbon. Preliminary results of I–V curve testing indicate that this structure could act as a conductive, robust, edge emitter.
Temperature dependence of optical properties of Ga0.3In0.7NxAs1−x quantum dots grown on GaAs (001)
Authors: Nishikawa A. , Hong Y. G. , Tu C. W.
Published: July 2004

The temperature dependence of optical properties of Ga0.3In0.7NxAs1−x quantum dots (QDs) grown by gas-source molecular beam epitaxy has been investigated using photoluminescence (PL) spectroscopy in the temperature range from 10 to 300 K. Unlike Ga0.7In0.3NxAs1−x quantum wells, these Ga0.3In0.7NxAs1−x QDs exhibit no S-shaped temperature dependence of the PL peak due to localized states, indicating that emission comes from the ground state, not from defect-related localized states. Thermal quenching of the integrated PL intensity is observed at temperatures over 50 K. The activation energy of Ga0.3In0.7NxAs1−x QDs decreases with an increase in nitrogen composition, contrary to the expectation that it would increase due to lowering of the GaInNAs conduction band. Moreover, the activation energy is much smaller than the difference in energy between the ground state and the wetting-layer state, indicating that the activation energy of Ga0.3In0.7NxAs1−x QDs corresponds to nonradiative recombination processes due to nitrogen incorporation. These defect-related states can be reduced by rapid thermal annealing.
Sb-mediated growth of n- and p-type AlGaAs by molecular beam epitaxy
Authors: Johnson S. R. , Sadofyev Yu. G. , Ding D. , Cao Y. , Chaparro S. A. , Franzreb K. , Zhang Y.-H.
Published: July 2004

The Sb-mediated growth of Al0.65Ga0.35As is studied for Sb/III flux ratios from 0% to 2% and growth temperatures from 580 to 720 °C. The surface morphology and electrical properties are found to strongly depend on both the growth temperature and Sb flux. As an isoelectronic dopant, Sb improves the conductivity of n-Al0.65Ga0.35As and reduces the conductivity of p-Al0.65Ga0.35As. As a surfactant, Sb improves the surface morphology of Al0.65Ga0.35As at all growth temperatures with the most dramatic improvement occurring at 670 °C. The smoothest surface (0.2 nm root-mean-square roughness height) was obtained at 700 °C using a Sb/III flux ratio of 0.02. This work demonstrates that Sb-mediated molecular beam epitaxy growth of n-AlGaAs effectively eliminates the “forbidden temperature gap” for device quality n-AlGaAs.
Room-temperature nanoimprinting on metallo-organic complexes
Authors: Mele Elisa , Pisignano Dario , Mazzeo Marco , Persano Luana , Gigli Giuseppe , Cingolani Roberto
Published: July 2004

We apply room-temperature nanoimprint lithography to rare-earth metallo-organic complexes, for patterning 600 nm period gratings onto europium-based 612 nm light-emitting compounds. After patterning, an increase of up to 6.2 times of the integrated photoluminescence emitted around Θ=35° was observed, resulting from the combination of the effective Bragg scattering induced by the printed grating, with the very narrow-linewidth emission of the metallo-organic complexes. These results are quite promising for the realization of nanoimprinted rare-earth-based optoelectronic devices, such as light-emitting diodes and displays, and distributed feedback elements.
Hydrophobic/hydrophilic surface modification within buried air channels
Authors: Salas-Vernis Jose Luis , Jayachandran Joseph Paul , Park Seongho , Kelleher Hollie A. , Bidstrup Allen Sue Ann , Kohl Paul A.
Published: July 2004

Recently, a method for fabricating air channels using a photodefinable sacrificial material (Unity 2203P) with acid-catalyzed degradation at low temperature was reported [J. P. Jayachandran et al. J Microelectromech. Syst. 12, 147 (2003)]. The acid is created via a ‘photoacid’ generator (PAG) either photolytically (when exposed to UV irradiation) or thermolytically (when heated to the decomposition temperature of the PAG). This approach to the fabrication of micro air-channel structures using low-temperature decomposable sacrificial materials has applications to air-gap formation for electrical/optical interconnects, microelectromechanical systems, microfluidics, and microreactors. In this study, the surface characteristics of the silica surface after the decomposition of Unity 2203P was explored. It was found that the surface inside the air-channel after low-temperature Unity 2203P decomposition was hydrophilic and was then converted to hydrophobic after higher-temperature treatment. The modification of the silicon surface using silane-based chemistries and a method for creating alternating hydrophobic/hydrophilic textures within a buried air channel has been demonstrated. Trifluoropropyl dimethylchlorosilane was the most effective surface treatment for creating hydrophobic channels. The hydrophobic/hydrophilic nature of the silicon surfaces is shown by the contact angle measurements and x-ray photoelectron spectroscopy analyses.
Environment influence on Ti diffusion and layer degradation of a SiC/Ni2Si/TiW/Au contact structure
Authors: Baeri A. , Raineri V. , La Via F. , Puglisi V. , Condorelli G. G.
Published: July 2004

X-ray diffraction, x-ray photoelectron spectroscopy, and “in situ” sheet resistance measurements were used to study the thermal stability of TiW films as diffusion barriers between a gold overlay and the Ni2Si/SiC ohmic contact. The degradation phenomenon is totally different in the O2 environment as compared to the vacuum ambient. The sheet resistance shows an anomalous behavior with thermal annealing in vacuum from 300 to 580 °C, which is correlated to the Ti diffusion through the Au layer. In particular, Ti diffuses through Au grain boundaries at 315 °C forming TiOx on the sample surface, while at 400 °C, Ti bulk diffusion occurs. The activation energy for titanium diffusion in gold layers is 1.9±0.2 eV, a typical value for the volume diffusion in a metal layer. Thermal annealing performed in an oxygen environment prevented the Ti grain boundary diffusion at low temperature (until 450 °C) while at higher temperatures (higher than 500  °C) a complete degradation of the diffusion barrier occurs.
Tungsten pedestal structure for nanotriode devices
Authors: Blackburn A. M. , Hasko D. G. , Ahmed H. , Williams D. A.
Published: July 2004

The nanotriode is a vacuum nanoelectronic device with a turn-on voltage for a field emission of ∼8 V, in which electrons are emitted from a metal nanotip with a radius ∼1 nm in an integrated vacuum chamber, over a distance of ∼100 nm. However, surface breakdown of the gate-cathode dielectric within the device chamber occurs ∼2 V outside of its operating range, limiting the reliable range of field-emission observation. To increase this surface breakdown voltage, while maintaining the operating voltage range, a pedestal structure has been developed that can be incorporated into the nanotriode. This structure has a thicker dielectric layer, while maintaining a gate-cathode separation similar to that used previously. Measurements on vacuum-encapsulated two-terminal devices show field emission in the same voltage range and with similar characteristics to those previously observed; in consequence of the pedestal, higher surface breakdown voltages are achieved and the significance of the leakage current is reduced.
Modeling of emitted current distribution and electron trajectories in the thin-film field-emission triode
Authors: Garner D. M.
Published: July 2004

Conformal mapping was used to find a closed-form solution to Laplace’s equation in the thin-film cathode field-emission triode, a structure commonly used in field-emission display applications. The equation was used to find the electric field on the surface of the cathode and this, together with the Fowler–Nordheim equation and published data on a carbon nanotube film, was used to find the emitted current density across the surface of the cathode. The equation of motion of the electron was integrated using a Runge–Kutta algorithm to find the electron trajectories. A range of anode voltages was investigated, and it was found that the beam divergence that occurred at low anode voltages could be turned into beam convergence by an increase in the anode voltage sufficient such that the vertical field in the device due to the anode was greater than that due to the gate. Furthermore, the modeling showed that when the anode voltage was this high, emission occurred preferentially from the center of the cathode, rather than from the edges, which occurred at lower anode voltages. This modeling provides a method of controlling beam divergence in field-emission-display pixels, without having to resort to additional focusing electrodes, hence, reducing fabrication complexity and system cost.
Optimization of silicon field-emission arrays fabrication for space applications
Authors: Wang Ling , Stevens Robert , Huq Ejaz , Loader Ian , Kent Barry , Aplin Karen , She Juncong
Published: July 2004

Optimization of fabrication of silicon field-emission arrays has been carried out on 4 in. silicon wafers for field-emission electric propulsion neutralizer application. A mixture of SF6, O2, and Ar for silicon tip etches has been optimized to improve the uniformity and process repeatability. A thin aluminum nitride (AlN) film has been coated on gated emitter arrays to enhance the field at the tip and to protect tips from ion bombardment. A statistical analysis of emission characteristic shows a narrow distribution of the turn-on voltage from array to array, which makes it possible to achieve a few milliamperes current emission by connecting several arrays in parallel. Lifetime tests over 1000 h have been carried out on single arrays, producing in excess of 10 μA of emission current under continuous mode of operation.
Effects of O2 and He on the properties of the trimethyl silane based low-k films
Authors: Widodo J. , Goh L. N. , Lu W. , Mhaisalkar S. G. , Ong S. , Sudijono J. L. , Hsia L. C. , Tan P. Y. , Zeng K. Y.
Published: July 2004

In this work, chemical vapor deposited carbon doped oxide films using trimethyl silane precursors with dielectric constant in the range of 2.75 to 3.62 were studied. Process parameters studied included low frequency RF (LFRF) and high frequency RF (HFRF) power, pressure, and helium flow rates as the oxidation influencing agents. Reliability and thermal stability of the films were studied and the dielectric constant (k), breakdown voltage, and leakage current were measured at 1 MHz. Numerous film properties (film stresses, hardness, modulus, refractive indices, and chemical bonding) were characterized. Results indicate that reduction of LFRF or HFRF power and the increase in pressure reduces the dielectric constant. Helium gases dissociate the Si–CH3 and C–H bond in the structure causing the dielectric constant to increase linearly as the helium flow rate increased while keeping the oxygen flow rate constant (O2+He process). It was observed that the O2 process window lowers the k value range and imparts slightly higher hardness and modulus compared with a O2+He process. In both processes, it was found that the dielectric constant was inversely proportional to the Si–CH3/Si–O ratio. Furthermore, the dielectric constant was found to have a linear relationship with hardness and modulus. It is believed that introduction of a methyl group in the film has reduced the covalency of the Si–O bond thus reducing its dielectric constant in comparison with silica. In terms of films electrical properties and stability, all films show Ebd and Jleak values comparable to silica, stress value ranged −10–70 MPa, and good thermal stability.
Microelectron field emitter array with focus lenses for multielectron beam lithography based on silicon on insulator wafer
Authors: Ngoc Minh Phan , Ono Takahito , Sato Nobuyuki , Mimura Hidenori , Esashi Masayoshi
Published: July 2004

We report on a device concept, results of fabrication, and characterization of a monolithic electron field emitter array with focus lenses for multielectron beam lithography and high-density nano data storage. An array of individually addressable emitters of various materials was patterned on oxidized etch pits of a silicon on insulator (SOI) wafer. Si active layer of the SOI with gate hole array that self-aligned with the emitters was used as a common gate electrode. An array of cylindrical holes formed at the Si base of the SOI was used as a common lens electrode. For a single Pt emitter with gate hole of 2 μm diameter, the emission current started at a gate voltage Vgate=90 V and reached to 1.2 μA current and 0.84 mW beam power at Vgate=300 V and anode voltage Vanod=0.7 kV. The emission current was found to be stable with a fluctuation smaller than 10%/h. The emitter-gate and emitter-lens leak currents were found to be less then 1% compared with the emission current. The focusing characteristic of the device was experimentally confirmed by observing emission patterns on a phosphor anode screen. A simulation work using a finite-element method has shown that the emitted electron beam with emission cone angle within 15° can be focused at a spot of 40 nm diameter and 200 μm focal length at a lens voltage Vlens=−6 V.
Influence of the preferred orientation and thickness of zirconium nitride films on the diffusion property in copper
Authors: Chen Cheng-Shi , Liu Chuan-Pu , Yang Heng-Ghieh , Tsao Chi Y. A.
Published: July 2004

Zirconium nitride (ZrN) films of different preferred orientations are grown on Si (100) substrates at various substrate temperatures during deposition in a dc magnetron sputtering system. The thermal stability of the as-deposited ZrN films are shown to be stable with Si up to 900 °C annealing for 30 min. The structural characterization of the thin films is carried out by x-ray diffraction and the electrical resistivity is measured by four-point probe. The decrease of the resistivity in the as-deposited films upon annealing is ascribed to the release of the lattice strain. Subsequently, copper is deposited on top of the ZrN films and the interdiffusion of each species upon annealing is studied by Auger electron spectroscopy as a function of ZrN preferred orientation and thickness. The diffusion coefficient and activation energy of Cu in the ZrN barrier are derived. The results indicate that the thicker (111) oriented crystalline ZrN films with larger grain sizes provide a higher activation energy against Cu diffusion and can act as an excellent diffusion barrier for Cu up to 800 °C. The detailed mechanisms accounted for the better performance are discussed in terms of a proposed grain boundary model.
Evolution of tungsten-oxide whiskers synthesized by a rapid thermal-annealing treatment
Authors: Cho M.-H. , Park S. A. , Yang K.-D. , Lyo I. W. , Jeong K. , Kang S. K. , Ko D.-H. , Kwon K. W. , Ku J. H. , Choi S. Y. , Shin H. J.
Published: July 2004

Tungsten oxide whiskers were prepared on a tungsten thin film by oxidation with H2O and a subsequent annealing treatment at a temperature of over 900 °C in a vacuum. The tungsten oxide formed by oxidation was transformed into smooth, straight whiskers with a monoclinic-crystalline structure after the vacuum annealing treatment. The whiskers showed an oxygen-deficient stoichiometry and a crystalline structure consistent with W18O49, which was dependent on the annealing temperature and vacuum used. The competition between the whisker growth and the dissociation of W oxide has a significant effect on the crystal shape, as well as the size of the whiskers. A change in the binding state during whisker formation indicates that some of the dissociated W oxide contributes to whisker formation and that crystalline whiskers are grown at nucleation sites through this process.
Adsorption of alkanethiol molecules onto carbon nanotube surface
Authors: Roh Seungkwang , Oh Jihoon , Choi Youngwook , Sohn Daewon , Kim Wonsuk , Cho Cheongyu , Yi Whikun , Yoo Jibeom , Lee Changsoo , Kim Jongmin
Published: July 2004

Adsorption behaviors of alkanethiol molecules are investigated on the surface of single-walled carbon nanotubes with vibrational spectrophotometer. Butanethiol (C4H9SH), hexanethiol (C6H13SH), nonanethiol (C9H20SH), and dodecanethiol (C12H25SH) molecules are adsorbed on the nanotube surface, and infrared spectra are measured as a function of concentration of the adsorbed molecules and molecular chain length. Alkanethiol molecules are thought to be strongly adsorbed on the SWNT surface. The active adsorption sites in the nanotube surface are thought to be Stone–Wales defects (5–7 ring defects).
Formation of graphite nanocones using metal nanoparticles as plasma etching masks
Authors: Park Hyoungjoon , Choi Seungho , Lee Soonil , Koh Ken Ha
Published: July 2004

Arrays of graphite nanocones were fabricated by oxygen-plasma etching of highly oriented pyrolytic graphite (HOPG). As it turned out gold nanoparticles, which were deposited by immersing HOPG samples pretreated with 3-(2-aminoethylamino) propyltrimethoxysilane into colloidal gold solutions, were very efficient for the self-aligned formation of graphite nanocones; the density of nanocones were found comparable with that of gold nanoparticles deposited on HOPG surfaces. We were able to control the shapes and sizes of nanocones by manipulating the plasma-etching parameters such as plasma power and etching time. In particular, nanopillars were formed using high plasma-etching power together with relatively short etching time. Graphite nanocones showed a potential to be good electron-emitters. The emission from the graphite nanocone arrays was turned on at 2.3 V/μm, and the emission current from the area of 6 mm diameter reached the level of 100 μA.
Sub-100 nm organic light-emitting diodes patterned with room temperature imprint lithography
Authors: Suh Dongchul , Lee Hong H.
Published: July 2004

We demonstrate fabrication of structurally regular, nanoscale organic light-emitting diodes (OLEDs) using room temperature imprint lithography (RTIL). An insulating polymer layer spin-coated onto indium-tin oxide (ITO) glass is patterned by RTIL, followed by etching with an oxygen plasma to define the light-emitting area for the fabrication of OLEDs with 80 nm linewidth. The process of etching by oxygen plasma leads to an oxygen treatment of the exposed ITO surface and brings about the beneficial effects of the treatment. A regular periodic structure of the polymer that results from the patterning scatters the emitted light, resulting in a small shift in the electroluminescence spectrum and anisotropic far-field radiation intensity. The nanoscale patterning is found not to affect the luminance.
Synthesis of very dense carbon nanotube bundles using silica supported metal catalyst
Authors: Yim Jong Hyuk , Choi Seungho , Lee Soonil , Koh Ken Ha
Published: July 2004

We prepared iron-impregnated silica films, which turned out to be very efficient catalysts for carbon nanotube synthesis, by a sol-gel process starting from the mixture of tetraethyl orthosilicate (TEOS), aqueous solution of iron nitrate (Fe(NO3)3⋅9H2O), and ethanol. The Fe/silicate-composite catalyst films consisted of nanoparticles, the composition and diameter of which depended on the iron-nitrate molarity in aqueous solution. Within the range of 0.5–1.5 M, the nanocomposite particles maintained good catalytic capacity, and very long and dense bundles of multiwall carbon nanotubes were synthesized regardless of the iron-nitrate molarity. The carbon nanotube density was so high that the nanotube bundles appeared made of aligned nanotubes in spite of the curliness of the individual nanotubes. However, carbon nanotubes were scarcely synthesized below 0.4 M of iron-nitrate molarity, which we attributed to the unfavorable composition and distribution of Fe-species in nanocomposite particles.
Growth of aligned Cu2S nanowire arrays with AAO template and their field-emission properties
Authors: Wu Q. B. , Ren S. , Deng S. Z. , Chen J. , Xu N. S.
Published: July 2004

The details are given of an experimental study of the growth process of aligned Cu2S nanowire arrays by a gas–solid reaction and by using an anodic-aluminum-oxide (AAO) template. It was found that the template played an important role in controlling growth with good alignment. X-ray diffraction and scanning-electron microscopy (SEM) were employed to characterize the nanowire arrays. The nanowire arrays had similar diameters (about 100 nm) and heights (about 1 μm). Their electron-field-emission characteristics were also measured. A turn-on field of 2.2 V/μm (for an emission-current density of 10 μA/cm2) and a threshold field of 8 V/μm (for an emission-current density of 10 mA/cm2) were observed, respectively.
Studies of oxide desorption from GaAs substrates via Ga2O3 to Ga2O conversion by exposure to Ga flux
Authors: Wasilewski Z. R. , Baribeau J.-M. , Beaulieu M. , Wu X. , Sproule G. I.
Published: July 2004

Removal of the native oxide from GaAs wafers in the process of thermal desorption in the presence of As flux causes very significant surface degradation. We examine the merits of an alternative oxide desorption method that consists in a standard thermal oxide removal procedure preceded by a partial oxide removal at lower temperatures via conversion of the stable Ga2O3 surface oxide into a volatile Ga2O oxide by a pulsed supply of Ga in the absence of As flux. We find that a reduction of the substrate roughness by more than one order of magnitude is obtained on most epi-ready GaAs substrates regardless of their age, even if only 70% of the original gallium oxide is removed with Ga pulses, and that nearly atomically smooth surfaces are obtained with 90% oxide removal. In addition, we demonstrate that the Ga-induced oxide removal process is laterally inhomogeneous, making this method vulnerable to the accumulation of Ga droplets on the GaAs surface when more than about 90% of the surface oxide is removed. The Ga2O desorption pattern monitored with quadrupole mass spectrometry indicates that other nonvolatile species initially present on the top of the gallium oxide are also converted to a volatile species by Ga exposure before large areas of Ga2O3 become exposed. We examine the residual surface contamination left at the substrate–epilayer interface and find no significant influence of the age of the substrate, or the oxide removal method, on the measured levels of silicon, oxygen, and carbon.
Metamorphic 6.00 Å heterojunction bipolar transistors on InP by molecular-beam epitaxy
Authors: Lange M. D. , Cavus A. , Monier C. , Sandhu R. S. , Block T. R. , Gambin V. F. , Sawdai D. J. , Gutierrez-Aitken A. L.
Published: July 2004

In this article we present results from heterojunction bipolar transistor (HBT) devices that were designed for low power consumption by taking advantage of the small bandgap of high-indium composition In0.86Ga0.14As in the base layer. These were grown by solid-source molecular-beam epitaxy. Both single- and double-HBT devices were grown and fabricated. The 6.00 Å lattice parameter of these device structures was accommodated by first growing metamorphic, relaxed, linearly graded InxAl1−xAs buffers on semi-insulating InP substrates, grading from In0.52Al0.48As lattice-matched with InP at 5.87 Å to In0.86Al0.14As at 6.00 Å. The total thickness of each buffer was 1.2 μm or greater. These graded buffer layers developed the crosshatched morphology that is associated with the strain-relaxation process. The density of threading dislocations reaching the buffer surface was measured by EPD to be as low as 2×106 cm−2. Although this density is still more than an order of magnitude greater than that measured for lattice-matched material on InP, these 6.00 Å HBT devices exhibited good electrical characteristics. For these electrical tests, both large (70×70 μm2) and small (1.5×10 or 2×10 μm2) devices were fabricated. All devices exhibited significantly lower turn-on and knee voltages compared to the GaAs and lattice-matched In0.52Ga0.48As-on-InP HBT technologies. The 6.00 Å single HBT demonstrated a VBE∼0.4 V for operation at 1 mA compared to 0.7 V for lattice-matched In0.52Ga0.48As on InP and 1.3 V for GaAs. The 6.00 Å HBT approach additionally benefits from a favorable valence band alignment between the p-type In0.86Ga0.14As base and the n-type In0.86Al0.14As emitter, which reduces hole injection into the emitter and increases device current gain. The rf measurements of this structure exhibited a transistor cut-off frequency fT exceeding 100 GHz. Small double-HBT devices presented a breakdown voltage BVCEO>2 V, which was twice that of small single-HBT devices. This enables further vertical scaling of the device to reduce the collector transit time.