bluuebunny/crossref_metadata_2025 huggingface dataset:
A Review of Desiccant Cooling Systems
Authors: Waugaman D. G. , Kini A. , Kettleborough C. F.
Published: April 2008

This paper describes recent published design advances that have been made in desiccant cooling systems. In desiccant cooling cycles, the desiccant reduces the humidity of the air by removing moisture from the air. Then the temperature is reduced by other components such as heat exchangers, evaporative coolers, or conventional cooling coils. The main advantage that desiccant cooling systems offer is the capability of using low-grade thermal energy. Desiccant cooling systems for residential and commercial applications are now being used to reduce energy-operating costs. However, the initial costs are comparatively high. The focus of research for the past decade has been to develop desiccant systems with a high coefficient of performance. Recent studies have emphasized computer modeling and hybrid systems that combine desiccant dehumidifiers with conventional systems.
Three-Dimensional Analysis of Extrusion Process Utilizing the Physical Modeling Technique
Authors: Sofuog˜lu H. , Rasty J.
Published: April 2008

The purpose of this study was to simulate the metal extrusion processes via three-dimensional physical modeling technique. Plasticine was utilized as the modeling material, while plexiglass was incorporated in the design and fabrication of a labscale extrusion apparatus. The extrusion setup was designed to accommodate dies of different semi-cone angle while also making it possible to change the extrusion ratio R = A0/Af. Cylindrical billets were prepared utilizing alternating layers of two colors of plasticine. Extrusion of cylindrical billets was conducted at three different reduction ratios and three different die angles for each reduction ratio. Dissection of the extruded billets along a centroidal plane revealed the internal deformation patterns which were subsequently utilized for determining the effect of the die angle and extrusion ratio on the state of strain in the final product as well as the required extrusion loads.
The Effects of Heat Transfer on Gas Spring Performance
Authors: Kornhauser A. A. , Smith J. L.
Published: April 2008

Experiments were performed on a piston-cylinder gas spring. Speed, cyclic mean pressure, gas, bore/stroke ratio, volume ratio, and internal extended surface geometry were varied. Hysteresis loss, pressure wave magnitude, and pressure-volume phase shift were measured. Nondimensional variables were found to correlate results, and a theoretical model was found to predict results well, over most of the operating range.
Engineering Functional Analysis—Part I
Authors: von Spakovsky M. R. , Evans R. B.
Published: April 2008

In this paper, the essential building blocks of a new formalism called Engineering Functional Analysis (EFA) are presented. This formalism results in higher degrees of decentralization for engineering system optimization than is otherwise possible. By decentralization, it is meant that the improvement or optimization of individual components by themselves (i.e., components which are isolated economically from the rest of the overall system), serves to improve or optimize the system as a whole (within some degree of error, which defines the degree of decentralization). Higher degrees of decentralization are important in that they provide a more stable economic environment for individual components, thus permitting more rapid synthesis and greater system improvement than could otherwise be obtained.
A Liquid-Pool Simulation of Droplet Combustion in a Swirl
Flow
Authors: Hou S.-S. , Lin T.-H.
Published: April 2008

The influence of flow rotation on droplet combustion and evaporation are experimentally studied by using a burning liquid-pool system, and numerically investigated by considering a nonreactive, rotating, stagnation-point flow, respectively. The experiment involves measurements of flame temperature, flame position and evaporation rate of the liquid pool, observations of the recirculation zone and the soot layer, and identification of flame extinction. A finite-volume method is employed to numerically solve the corresponding transport equations. Calculated results show that in the vicinity of the liquid surface, both convection and diffusion transports are weakened by the flow rotation, resulting in the suppression of the evaporation strength of liquid; the recirculation zone can be identified and compared with experimental observation. For the steady burning of an ethanol pool in a swirling air jet, it is found that as the angular velocity increases, the diffusion flame shifts closer to the upper burner, has a larger flame thickness, experiences a smaller flame stretch, but suffers from the reduction of mass diffusion of ethanol vapor to the flame. However, the evaporation rate of ethanol is usually decreased with increasing angular velocity. In the flame extinction experiment, the critical volumetric oxygen concentration at extinction first decreases to a minimum value and then increases with angular velocity. It is generally concluded that flow rotation reduces the rates of both droplet combustion and evaporation.
Helical Buckling of Pipes in Extended Reach and Horizontal Wells—Part
1: Preventing Helical Buckling
Authors: Wu J. , Juvkam-Wold H. C. , Lu R.
Published: April 2008

This paper studies the helical buckling of pipes (drillstring and tubing) in extended reach and horizontal wells, theoretically and experimentally, resulting in new equations to correctly predict and effectively prevent the helical buckling of pipes in such wells. The theoretical study shows that the so-called helical buckling load that appears in the current literature is only the average axial load in the helical buckling development process. The laboratory experiments confirm the theoretical analysis. The new helical buckling load equations are formulated by combining the theoretical analysis and the experimental results, thereby resolving the existing assumption-and result inconsistency in the current literature. The new equation predicts the true helical buckling load to be about 1.3 times the so-called helical buckling load in the current literature, and about 1.8 times the critical buckling load that predicts the onset of sinusoidal buckling. Consequently, larger bit weights or packer setting loads can be applied to increase the drilling rate or to ensure a proper seal, before the helical buckling of the pipes can occur.
Helical Buckling of Pipes in Extended Reach and Horizontal Wells—Part
2: Frictional Drag Analysis
Authors: Wu J. , Juvkam-Wold H. C.
Published: April 2008

This paper studies the frictional drag of helically buckled pipes (drillstring and tubing) in extended reach and horizontal wells to correctly predict the actual bit weight or packer load, in cases where helical buckling of pipes may have occurred. Helical buckling of pipes in such wells may occur, since large axial loads are often required. The differential equation of axial force balance with consideration of the axial friction for helically buckled pipes is resolved, and the solution shows that when the pipes are helically buckled, the frictional drag will become very large. The actual bit weight for drilling or packer load for well completion may therefore become much smaller than estimated under the unbuckled pipe conditions. The analytical solution is also shown to agree with the results from laboratory experiments, which simulate the real wellbore-pipe conditions. An example is provided to show the calculation procedure and the importance of the results.
Macroscopic Analysis of Axisymmetric Functionally Gradient Materials Under Thermal Loading
Authors: Kwon P. , Dharan C. K. H. , Ferrari M.
Published: April 2008

The axisymmetric functionally gradient materials (FGMs) subject to nonuniform temperature variations were studied with the combined use of homogenization and inhomogeneous eigenstrained media analysis. The material properties and the temperature variations were assumed to depend on the radial coordinate only. The inhomogeneous material properties of the FGM cylinder can be obtained by modulating the concentration level of spherical alumina particles in an aluminum matrix. The resulting stresses due to the temperature variation are presented for numerous distribution functions of alumina particles. It is shown that the particle distribution extensively influences the intensity and profile of the thermal stresses.
Effect of Process Damping on Longitudinal Vibrations in Drillstrings
Authors: Elsayed M. A. , Wells R. L. , Dareing D. W. , Nagirimadugu K.
Published: April 2008

This paper shows the effect of process damping—caused by the interference between the cutter and the previously cut surface—on the stability of drillstrings. The method of including process damping in the calculation of the stability diagram is outlined. Previously published stability diagrams of drillstrings equipped with drag bits showed decreased stability at low cutting speeds, and that the addition of a shock absorber decreased the size of stability pockets. In this paper, we show that the introduction of process damping confirms field observations of increased stability at low speeds. We also show that a properly designed shock absorber produces large stability pockets where drilling is most effective.
Performance Evaluation of Two Azeotropic Refrigerant Mixtures of HFC-134a With R-290 (Propane) and R-600a (Isobutane)
Authors: Kim M. S. , Mulroy W. J. , Didion D. A.
Published: April 2008

The reduction in chlorofluorocarbon (CFC) and hydrochlorofluorocarbon (HCFC) production and the scheduled phase-out of these ozone-depleting refrigerants require the development and determination of environmentally safe refrigerants for use in heat pumps, water chillers, air conditioners, and refrigerators. This paper presents a performance evaluation of a generic heat pump with two azeotropic refrigerant mixtures of HFC-134a (1,1,1,2-tetrafluoroethane) with R-290 (propane) and R-600a (isobutane); R-290/134a (45/55 by mass percentage) and R-134a/600a (80/20 by mass percentage). The performance characteristics of the azeotropes were compared with pure CFC-12, HFC-134a, HCFC-22, and R-290 at the high temperature cooling and heating conditions including those using liquid-line/suction-line heat exchange. The coefficient of performance of R-290/134a is lower than that of HCFC-22 and R-290, and R-134a/600a shows higher coefficient of performance than CFC-12 and HFC-134a. The capacity for R-290/134a is higher than that for HCFC-22 and R-290, and R-134a/600a exhibits higher system capacity than CFC-12 and HFC-134a. Experimental results show that the discharge temperatures of the studied azeotropic mixtures are lower than those of the pure refrigerants, CFC-12 and HCFC-22.
Submerged Electric Arc Decomposition of Methanol for Cold-Starting Methanol-Fueled Engines
Authors: Sethuraman R. , Parker H. W. , Maxwell T. T. , Jones J. C.
Published: April 2008

Methanol is an attractive alternative fuel based on its engine performance and emission characteristics. Methanol can be synthesized from biomass or urban waste, and as a result, it does not contribute to the net addition of carbon dioxide to the atmosphere. Cold-starting of methanol-fueled engines is difficult at temperatures below 10°C, and at sub-zero temperatures, starting may be impractical without significant engine modifications. In this research, an attempt has been made to study and prevent the cold-starting problem by using hydrogen and carbon monoxide gas mixture produced by decomposing liquid methanol using a submerged electric arc device. The electric arc has the advantage of instantaneous gas production and the experimental data relating to the performance of the device and its design are reported. The device is capable of producing up to 0.01 cu m (10 L) per min of a gas which is primarily carbon monoxide and hydrogen with a thermal efficiency of 18 percent relative to the theoretical energy requirements for methanol decomposition. The feasibility of using this arc device is analyzed based on the simulated cold-starting data collected for a single-cylinder Kawasaki engine at −20°C.
Role of Porosity in Estimates of Composite Elastic Constants
Authors: Berryman J. G.
Published: April 2008

The presence of small amounts of residual void space (on the order of one percent by volume) is sufficient to make estimates of composite elastic constants (obtained while ignoring this porosity) violate the Hashin-Shtrikman bounds in many cases. Experimental values falling below the incorrectly estimated lower bound is the normal direction of violation, but erroneous neglect of porosity in “pure” samples can also lead to experimental values rising above the incorrectly computed upper bound. Examples are presented to illustrate the nature of the error and methods of correcting it for data on composite ceramics. The result is improved agreement between the Hashin-Shtrikman bounds, effective medium theory estimates, and experimental data.
Pore Collapse in Weakly Cemented and Porous Rocks
Authors: Zaman M. , Roegiers J.-C. , Abdulraheem A. , Azeemuddin M.
Published: April 2008

Withdrawal of fluids from hydrocarbon reservoirs results in a decrease in pore pressure which in turn leads to an increase in effective stress on rock matrix. Such a situation may lead to the occurrence of pore collapse in reservoirs having weakly cemented, porous rocks. It is considered to be a potential problem in several producing reservoirs. Numerical simulation of a compacting reservoir due to pore collapse requires an appropriate constitutive model. Consequently, a constitutive model based on the concept of elasto-plasticity using isotropic hardening is developed to predict pre and post-pore collapse behavior of reservoir rocks. An experimental study is carried out on a high-porosity rock susceptible to pore collapse for different stress paths. The developed constitutive model is tested with respect to two different materials exhibiting such behavior. Parameters for the model are evaluated based on the experimental results, highlighting the procedure involved. Further, the data is used to demonstrate the strengths and the weaknesses of the constitutive model. Experimental data for the second material is obtained from literature. Satisfactory agreement is achieved between experimental data and model predictions.
An Analytical Examination of Various Criteria for Defining Autoignition Within Heated Methane-Air Homogeneous Mixtures
Authors: Zhou G. , Karim G. A.
Published: April 2008

Different criteria for establishing ignition within reactive methane-air mixtures are discussed. It is shown that for relatively low initial mixture temperature using the different ignition criteria tends to produce very small relative differences in the values of the ignition delay. These differences can become very significant at relatively high initial mixture temperatures. Criteria for ignition based on sudden changes in pressure and temperature are recommended for reliably establishing the onset of autoignition, both in modeling and experimental studies.
A Numerical Study of the Unsteady Effects of Droplet Evaporation and Ignition in Homogeneous Environments of Fuel and Air
Authors: Samuel P. , Karim G. A.
Published: April 2008

The transient processes of droplet heating, vaporization and ignition in a quiescent heated environment of a homogeneous mixture of air and fuel that is potentially combustible are analyzed. A system of partial differential equations that governs this hybrid diffusional-premixed processes is presented. The equations were solved numerically for an n-heptane droplet vaporizing in a homogeneous environment of methane and air. The effective reaction rate of the oxidation processes was assumed throughout to equal the sum of the reaction rates due to droplet and auxiliary fuels. The gross reaction rates used in the model for the droplet and auxiliary fuels were obtained from curve fitting of reaction rates results obtained from detailed chemical kinetics for the two fuels system. It is to be shown, for example, that the presence of an auxiliary fuel with the air in the surrounding environment of the droplet enhances the rates of the ignition/combustion processes of the droplet.
Low Invasion Corehead Reduces Mud Invasion While Improving Performances
Authors: Clydesdale G. M. , Leseultre A. , Lamine E.
Published: April 2008

A corehead was designed, manufactured and tested to reduce fluid invasion of the core. This is obtained by minimizing the exposure time of the core to the drilling fluid in increasing the rate of penetration (ROP). The design incorporates a medium heavyset polycrystalline diamond compact (PDC) cutting structure developed in accordance with cutting models and balancing methods used for drill bits. The highest ROP is achieved by a particular hydraulic design: flow ports shape and positioning to clean the cutting structure enhance the drilled cuttings removal while preventing drilling fluid in the throat of the corehead. Moreover, an internal lip works with a special inner barrel shoe to effectively seal off mud flow from the throat. All the design features have been subjected to laboratory tests, including measurement of pressure drop across the corehead and flow visualization studies. Flow visualization tests include high-speed filming of the flow and paint tracing to indicate the special flow pattern. In conjunction with lab tests, a numerical simulation was performed using fluid dynamics software to optimize hydraulic parameters. The low invasion core bit has been used in numerous applications. The performance achieved was significantly better than the average achieved over a period of years using various PDC coreheads. The rate of penetration was increased by a factor of 4.8 and bit life by 2.3 (often with reusable condition).
The Wear of Thermally Stable Diamond During Rock Cutting
Authors: Cooper G. , Liu Z. , Yang M.
Published: April 2008

Single-cutter experiments have been performed to investigate the cutting and wear of thermally stable diamond (SYNDAX3) during rock cutting. Cutting forces increase linearly with depth of cut, but are unaffected by cutting speed. The wear of the cutter per mass of rock removed is found to decrease with increasing depth of cut. Excessive cutting speed is harmful to the cutter since both the cutter temperature and the change in cutter temperature per power input increase with cutting speed. In the cutting experiments, evidence of delayed fracturing is observed. For essentially constant cutting conditions, fractures develop in the cutter only after a significant amount of cutting is done. Damage of this type is very harmful to the cutter as cutter temperature rises and efficiency drops with increasing wear.
Scanning atom probe study of graphite nanofibers
Authors: Nishikawa O. , Taniguchi M. , Ushirozawa M.
Published: April 2008

Field emission characteristics of graphite nanofibers (GNFs) are studied by operating a scanning atom probe as a field emission microscope. The Fowler-Nordheim plot indicates that the work function of GNF is larger than that of carbon nanotubes and is comparable to tungsten. Field emission patterns indicate that electrons are emitted from the edges of graphene sheets in the direction perpendicular to the GNF axis. The ratio of the field emission voltage and that of the field evaporation voltage implies that the binding between the graphene sheets is weak. The field evaporated cluster ions of carbon and hydrogen indicate that hydrogen is not distributed randomly but is forming the characteristic carbon-hydrogen cluster, C23H2. The proposed structure of the cluster is the triangularly arranged six hexagonal cells with hydrogen terminated two carbon atoms and an extra carbon atom.
Improving the electron emission properties of ion-beam-synthesized Ag–SiO2 nanocomposites by pulsed laser annealing
Authors: Tsang W. M. , Adikaari A. A. D. T. , Stolojan V. , Silva S. R. P.
Published: April 2008

The effects of pulsed laser annealing on the structural and electron field emission (FE) properties of Ag–SiO2 nanocomposites are reported. The nanocomposites were synthesized by Ag+ implantation into thermally oxidized Si substrates with a dose of 7×1016Ag+∕cm2. The annealing was performed using a 248nm KrF excimer laser. Multiple pulses, with duration of 25ns, at an energy density of 250mJ∕cm2 were accumulated onto the same area of the sample. Surface protrusion structures of the as-implanted samples, causing geometrical field enhancement, are eliminated after laser annealing, and a reduction in concentration and coalescence of the Ag nanoclusters is observed from atomic force microscopy and transmission electron microscopy measurements. The threshold field for emission for the as-implanted sample is altered from 28 to 104, 16, and 35V∕μm after annealing with 5, 10, and 20 laser pulses, respectively. The FE properties of laser annealed samples are discussed in terms of two distinct field enhancement effects using their structural properties.
Field electron emission from free-standing flexible PDMS-supported carbon-nanotube-array films
Authors: Hong Nguyen Tuan , Yim Jong Hyuk , Koh Ken Ha , Lee Soonil , Minh Phan Ngoc , Khoi Phan Hong
Published: April 2008

Fabrication of free-standing carbon-nanotube- (CNT) array films supported by PDMS (poly-dimethylsiloxane) matrix, which opens up the possibility to transform deliberate CNT-array architecture into flexible electronic and photonic components, is reported. Low viscosity and good wetting characteristics of uncured PDMS prepolymer solution are important for thorough infiltration, and robustness and elasticity of cured PDMS are important for realization of deformable free-standing films detachable from substrates. Field-emission characterization of a series of CNT column arrays in diode configuration shows that fabrication of a flexible electron emitter is feasible, but the excellent emission characteristics of as-grown CNT column arrays is compromised after PDMS infiltration. In particular, emission current level and stability of a free-standing PDMS-supported CNT array is inferior to those of as-grown or PDMS-infiltrated CNT arrays on silicon substrates.
Physics of generalized Fowler-Nordheim-type equations
Authors: Forbes Richard G.
Published: April 2008

Cold field electron emission (CFE) from metals is described by a large family of approximate equations called Fowler-Nordheim-type (FN-type) equations. This article discusses FN-type equations that give emission current density in terms of local work function and barrier field. Starting from the widely used standard FN-type equation [E. L. Murphy and R. H. Good, Phys. Rev. 102, 1464 (1956)], which is a hybrid physical/mathematical equation applicable to CFE from flat free-electron-metal surfaces at 0K, this article builds up a generalized “physical FN-type equation” in which physical correction factors are used to represent effects not included in standard CFE theory. The derivation starts by separating mathematical and physical aspects of standard theory, making use of a new independent physical variable (the scaled barrier field) and a physical “barrier-shape correction factor” that applies to any well-behaved barrier. Correction of long-standing error in applying Jeffries-Wentzel-Kramers-Brillouin-type approximations to CFE theory introduces a tunneling prefactor and a related small correction factor associated with integration over occupied electron states. Further correction factors represent effects due to non-free-electron band structures and emitter temperature. The outcome is an equation that provides a physical framework for FN-type equations that apply to CFE from a single metal-like conduction band. This equation is conceptually more complete than the equations normally used. Estimates are presented for the sizes of correction factors.
Application of a general electron emission equation to surface nonuniformity and current density variation
Authors: Jensen Kevin L. , Petillo John J. , Montgomery Eric J. , Pan Zhigang , Feldman Donald W. , O’Shea Patrick G. , Moody Nathan A. , Cahay M. , Yater Joan E. , Shaw Jonathan L.
Published: April 2008

Electron emission nonuniformity is a cause of intrinsic emittance from the electron source, and is a consequence of work function variation due to crystal faces and coatings such as cesium, field enhancement effects due to surface structure, and temperature. Its investigation using particle-in-cell (PIC) codes such as MICHELLE is hampered due to the lack of an emission model that can treat thermal, field, and photoemission effects particularly in crossover regions where the canonical equations, e.g., the Fowler-Nordheim, Richardson-Laue-Dushman, and Fowler-Dubridge equations are compromised. A recently developed thermal-photo-field emission equation is used here to simulate the consequences of nonuniformity due to work function variation induced by coating variation. The analysis is performed both theoretically using simple models as well as using particle-in-cell codes (MICHELLE) to assess changes in current density and emittance. PIC simulations considering an idealized model of geometric effects and crystal face variation indicate that a flat, grainy surface causes the emittance to increase by a factor of 5 while the addition of hemispherical bumps causes the emittance to increase by an additional factor of 6 even though the current is but 10% larger.
Work functions of cathode surfaces with adsorbed atoms based on ab initio calculations
Authors: Lin Ming-Chieh , Jao Ruei-Fu , Lin Wei-Chih
Published: April 2008

Ab initio calculations are used to study the reduction of the work functions of tungsten (W) surfaces with 1 ML of adsorbed barium (Ba) and lithium atoms. The authors carefully and systematically tested the convergence of density-functional-theory (DFT) calculations in the local-density approximation or generalized-gradient approximation with a plane-wave basis set and ultrasoft pseudopotentials or the projector-augmented wave method as implemented in the Vienna ab-initio simulation package. The DFT calculation shows that the work function of the Ba adsorbed onto a p(2×2) W(001) substrate is dramatically lowered by about 2.2eV, provided that the fourfold hollow sites are occupied. With this approach, one can investigate more complex adsorbates onto the cathode surface of different materials.
Electroluminescence of silicon nanoclusters excited by tunneling carrier injection
Authors: Filip Valeriu , Wong Hei , Wong C. K. , Nicolaescu Dan
Published: April 2008

A simple model for the electroluminescence of a network of silicon nanoclusters (Si-NCs) embedded in a wide band gap material is presented. The model assumed that electrons and holes travel across the network through tunneling mechanisms and confine in excitonic states. Recombination of electron-hole pairs gives rise to the light emission. It shows that differences between the tunneling rates into neighboring Si-NCs of electrons and holes make the recombination events more frequent in a region close to the positive electrode of the device. Results further demonstrated that both total recombination rate and dissipated power increase with the spatial density of the nanoclusters in the matrix, but that a technological optimum range of density exists.
Modeling of linear carbon nanotube nanotriodes with improved field uniformity
Authors: Nicolaescu D. , Filip V. , Gotoh Y. , Ishikawa J.
Published: April 2008

A linear array of gated carbon nanotubes (CNTs) is proposed for improving the array electron emission properties by controlling the electric field conversion factor and its uniformity. The CNT emission current has been computed according to a previously developed model that takes into account the low dimensionality of the CNT electronic system. The CNT field conversion factor (for single CNT and linear array gated CNTs) has been numerically derived using the OPERA3D/TOSCA software and then expressed analytically. For better performance, controlling the parallelism of the CNTs in the array is not a strong requirement, but controlling their height is. The position of the CNT array emission current optimum depends on the value of parameters chosen, but generally it is obtained for array packing density ratio a∕hn (array pitch/CNT height) taking value in the range of 0.5–1.
Thermal-field treatment for creating single-crystal tungsten tips with ultimate sharpness
Authors: Fujita Shin , Shimoyama Hiroshi
Published: April 2008

Thermal-field (TF) treatment conditions for ⟨111⟩ oriented single-crystal tungsten tips have been systematically studied using the remolding process, which employs a reversely polarized field in the treatment, in order to establish a treatment sequence for producing the nanotip that ends with a very sharp ⟨111⟩ apex at the end. As the remolding voltage is increased at a specific temperature, initially hemispherical tungsten tip evolves in shape due to the growth of low index facets such as (110), (211), and (110) crystal-planes. The tip finally takes a polyhedral shape. The treatment temperature has a significant effect in the shape evolution course. When the temperature is high enough, the (211) planes shrink as the treatment field is increased. Three (110) planes make the ⟨111⟩ apex in this case. At lower temperatures, the ⟨111⟩ apex remains formed by the (211) planes until the remolding voltage is increased to an extreme, which results in a number of microprotrusions on the tip surface. A scheme has been proposed for the creation of the nanotip with ultimate sharpness. Here, the TF treatment is first conducted at a relatively high temperature until the (211) plane collapse takes place. Then, the temperature is reduced and the increase of the remolding voltage resumed. It is possible, by periodically observing field-emission patterns, to terminate the TF treatment at the right stage where the ⟨111⟩ apex achieves the sharpest configuration. The field emission from the nanotip can provide electron beam with much better angular intensity and confinement than conventional field emitters.
Fabrication process for cantilevers with integrated tunnel junctions
Authors: Tanner S. M. , Rogers C. T.
Published: April 2008

The authors have developed a process for making submicron cantilevers, clamped beams, and more complicated electromechanical structures that carry integrated electrical leads. Such objects are useful as test structures for measuring the electrical properties of molecular sized objects, as high frequency electromechanical components for radio frequency and microwave applications, and as sensor components for studying fluctuations in small systems. Their process uses two realigned electron beam lithography steps, a thin-film angled deposition system, and differential removal of sacrificial aluminum layers to produce freely suspended submicron electromechanical components. The authors have produced cantilevers and beams on a variety of substrates (silica, silicon, and polyimide) and have produced insulating, conductive, and multilayer electromechanical structures. The process allows the use of essentially any material that can be deposited from a thermal or electron-beam deposition source. The authors have integrated mechanically adjustable gold-vacuum-gold contacts onto the cantilevers and have demonstrated vacuum tunneling. The behavior of these contacts indicates an exponential dependence on tunneling gap. The authors have demonstrated electrostatic control over the tunnel gap spacing as well.
Characteristics of nanosilicon ballistic cold cathode in aqueous solutions as an active electrode
Authors: Ohta Toshiyuki , Gelloz Bernard , Koshida Nobuyoshi
Published: April 2008

The effect of ballistic electron injection into aqueous solutions has been studied by nanocrystalline silicon (nc-Si) planar cold cathode. The present article shows that the nc-Si ballistic emitter operates in both pure water and a dilute H2SO4 solution, and that hydrogen gas is generated with no by-product like oxygen. The hydrogen evolution rate in H2SO4 solution was higher than that in water as expected. In water, the pH value shows a significant increase toward the alkaline side during the device operation without using any counterelectrode. These results support the model that energetic electrons emitted from the device into solutions directly reduce H+ ions at the interface. The ballistic emitter is useful in solutions not only for hydrogen generation but also for control of pH level and related electrochemical properties.
Evidence of electronic cooling from resonance states of nanocrystalline graphite field emitters
Authors: Busta Heinz , Tao Kevin , Feinerman Alan
Published: April 2008

We have measured the temperature of a nanocrystalline graphite/carbon nanotube field emitter film as a function of emission current in the range from 1to200μA. Theoretical considerations predict that cooling takes place from these emitters if the electron emission is governed by resonant tunneling. Resonant tunneling manifests itself by a saturation behavior in the I-V curve. Maximum cooling should take place near the saturation region. A thermally insulating test system was configured capable of measuring temperature changes in the millikelvin range. For the test sample, at an emission current of about 10μA, which is the current where saturation is observed, a reduction in the temperature of about 0.01°C is obtained. The reduction in temperature is attributed to cooling.
Field emission characteristics of a lanthanum monosulfide cold cathode array fabricated using microelectromechanical systems technology
Authors: Samiee M. , Garre K. , Cahay M. , Kosel P. B. , Fairchild S. , Fraser J. W. , Lockwood D. J.
Published: April 2008

Using microelectromechanical systems technology, an array of cold cathodes was fabricated by pulsed laser deposition of chemically and thermally stable lanthanum monosulfide (LaS) thin film anode and cathode contacts. The latter were defined via etching and processing of two different pieces of (100) Si wafers separated via a highly resistive sputter deposited aluminum nitride (AlN) layer, whose thickness was used to control the anode to cathode spacing. The top and bottom Si wafers were aligned and glued together using high temperature, vacuum compatible epoxy. Field emission characteristics were recorded in a vacuum chamber with a base pressure less than 10−7Torr. An average electric field threshold for Fowler-Nordheim field emission in the range of 100V∕μm was measured. The largest emission current measured was about 5×10−7A, above which thermal runaway occurred, leading to a failure of the cathode. The failure mechanism is analyzed in terms of a patchwork field emission model from the LaS thin film reported recently. Suggestions for improvements in the cathode design are discussed.
Possibility of generating terahertz radiation by photomixing with clusters of carbon nanotubes
Authors: Hagmann Mark J.
Published: April 2008

A focused laser diode (20mW, 658nm) causes an increase of 5% in the dc field emission current from a single-walled or multiwalled metallic carbon nanotube (MCNT), and the author’s hypothesis that this effect is due to optical rectification is confirmed by analysis. Measurements with the MCNT at audio frequencies, and with microwave prototypes, as well as analyses, suggest that photomixing (optical heterodyning) with two such lasers would cause a terahertz mixer current with a peak value equal to 10% of the dc field emission current. Single-walled MCNT (SWMCNT) act as terahertz transmission lines with a characteristic impedance of 40kΩ. Consider a cluster of 800 SWMCNT having a common junction at a 50Ω load, with two lasers causing photomixing at the free end of each SWMCNT. The mixer current would cause a surface wave to propagate on each SWMCNT with a broadband impedance match to the load (50Ω=40kΩ∕800), so the mixer currents would add coherently at the load. Thus, a dc field emission current of 50μA causing a peak mixer current of 5μA at each of the 800 SWMCNT would provide a wideband-tunable terahertz output at a power of 400μW.
Multilayer soft mold for UV imprinting the 50nm pitch dot array
Authors: Lee Duhyun , Cho E. H. , Kim H. S. , Lee B. K. , Lee M. B , Sohn J. S. , Lee C. H. , Suh S. J.
Published: April 2008

A novel concept of multilayer soft mold for ultraviolet nanoimprint lithography was introduced. It is composed of (tridecafluoro-1,1,2,2-tetrahydro-octyl)-trichlorosilane (FOTS)∕SiO2/pattern polymer (perfluorinated acrylate mixture)/glass, where the FOTS is for releasing and SiO2 is for surface hardening and adhesion between the FOTS and pattern polymer. By using the multilayer soft mold, a dot array as small as 50nm pitch was replicated from the Si master and imprinted on a Ru∕Ta∕Si substrate successfully. The x-ray photoelectron spectroscopy, contact angle measurement, and nanoindentation test revealed that the multilayer soft mold has good adhesion between layers, lower surface energy, and stiffer surface than the soft mold of pattern polymer/glass, respectively.
Improvement of emission efficiency of nanocrystalline silicon planar cathodes
Authors: Shimawaki Hidetaka , Neo Yochiro , Mimura Hidenori , Murakami Katsuhisa , Wakaya Fujio , Takai Mikio
Published: April 2008

A planar cathode based on nanocrystalline Si covered with a thin oxide film was fabricated and the emission characteristics were examined. The electron emission occurred at the gate voltage higher than the work function of the Au gate, and the emission efficiency was improved up to 4% by reducing the thickness of the Au electrode. A lot of nanoholes in the thin Au film were observed, suggesting emission included electrons directly emitted from nanocrystalline aligned under nanoholes. The energy distribution of the emitted electron and the emission angle of the cathode are also discussed.
Density control of carbon nanofibers on titanium buffer layer using electroplated Ni catalyst
Authors: Yoo Hyeong-Suk , Lee Sang-Joo , Joo Seung-Ki , Sung Woo-Yong
Published: April 2008

With a view to controlling the density of carbon nanofibers (CNFs), the density of Ni catalysts was varied using direct current (dc) electroplating technique coupled with titanium (Ti) buffer layer which is deposited between catalytic layer and substrate. The dc electroplating technique is used for the deposition and formation of islands of Ni catalysts simultaneously, without any additional process. The islands of Ni catalysts were formed on the substrate with Ti buffer layer, while the smooth and continuous film of Ni catalyst was formed on the substrate without the Ti buffer layer, using the same electroplating process. The site density of Ni catalysts was controlled via the dc electroplating technique coupled with the deposition of Ti buffer layer successfully. Then, CNFs were synthesized using a direct current plasma enhanced chemical vapor deposition (dc-PECVD) system at a temperature of 480°C. The morphologies of the electroplated Ni catalysts and CNFs were compared at different electroplating conditions. The CNFs grown from density-controlled Ni catalysts were found to have the turn-on fields of 2.5 and 5.0V∕μm for current densities of 1μA∕cm2 and 1.4mA∕cm2, respectively.
Optimization of resolution-enhancement technology and dual-layer bottom-antireflective coatings in hypernumerical aperture lithography
Authors: Li Yanqiu , Zhou Yuan
Published: April 2008

Resolution-enhancement technique (RET) and dual-layer bottom-antireflective coatings (DL-BARC) must be adopted in hypernumerical aperture (NA>1) lithography for a 45nm half-pitch device. However, interactions of RET, polarization effect, and the resist process significantly impact on lithography performance. An in-house program and PROLITH 9.0 were employed to perform comprehensive optimization of RET and DL-BARC structures in order to improve pattern fidelity with a reasonable process window (PW). High-fidelity resist patterns are obtained when we employed optimum DL-BARC structures in conjunction with optimum RET. An alternating phase-shift mask and a conventional illumination is one kind of optimum combination of RET. An attenuated phase-shift mask and a cross-dipole illumination is the other one. Line-width changes are controlled within 4nm. Sidewall angles are greater than 88°.
Silicon laterally resonant microcantilevers for absolute pressure measurement with integrated actuation and readout
Authors: Cocuzza M. , Ferrante I. , Ricci A. , Giuri E. , Scaltrito L. , Bich D. , Merialdo A. , Schina P. , Correale R.
Published: April 2008

This work is focused on the design, fabrication, and characterization of silicon laterally resonant microcantilevers for measuring absolute pressure. The authors have demonstrated the integration of resonance electrostatic actuation and capacitive readout with a microstructure based on a couple of electrodes and an external amplifier. The microcantilevers have been fabricated with a standard silicon on insulator micromachining process. The characterization method is based on measuring the current at the third harmonic of the excitation frequency flowing through the time-varying cantilever-based capacitor. The variation in resonance response of microcantilevers has been investigated as a function of pressure (10−2−105 Pa), both in terms of resonance frequency and quality factor. Theoretical models and experimental data show very good agreement. The microstructure behavior demonstrates the feasibility of an absolute pressure sensor working over a six-decade range with integrated electrical actuation and readout.
One-dimensional combined field and thermionic emission model and comparison with experimental results
Authors: He Xin , Scharer John , Booske John , Sengele Sean
Published: April 2008

An integrated theoretical model has been developed to predict the entire range of emission from thermionic to field emission, including the mixed emission regime. The model assumes a Sommerfeld free electron model supply function, for which the Fermi-Dirac distribution applies with a nonzero temperature. The electron transmission coefficient is calculated in one dimension using a transfer matrix method (TMM) to solve the steady-state Schrödinger equation. Emission current densities have been measured for a periodic copper knife-edge cathode to compare with the TMM model result. It is shown that the computational result utilizing this model provides good agreement with the experimental data. Unambiguous and reliable estimates of the effective field enhancement factor βeff (βeff=Es∕Eg, where Es is the cathode surface electric field and Eg is the gap electric field between the cathode and anode) and the effective work function ϕeff are obtained from experimental measurements using this model by simultaneously fitting thermionic and field emission data for the cathode. Comparing the experimental and theoretical results reveals that finite temperature thermal contributions to the current emission can be significant in the operation of many field emission cathodes.
Comparison of deep silicon etching using SF6/C4F8 and SF6/C4F6 plasmas in the Bosch process
Authors: Rhee Hyongmoo , Kwon Hyeokkyu , Kim Chang-Koo , Kim HyunJung , Yoo Jaisuk , Kim Yil Wook
Published: April 2008

Silicon was etched with the Bosch process using C4F8 and C4F6 plasmas in the deposition step to show a feasibility of the use of UFC plasmas in the Bosch process. The use of C4F8 and C4F6 plasmas resulted in different characteristics of fluorocarbon films and radicals, affecting the etch profiles. It was shown that the use of a C4F6 plasma in the deposition step of the Bosch process produced thicker and more strongly bonded fluorocarbon films, compared to a C4F8 plasma. It was because more CF2 radicals and lower F/C ratio fluorocarbon films were generated in C4F6 plasmas than those in C4F8 plasmas, confirmed by OES and XPS measurements. By changing only the duration of the deposition step under the same process conditions, highly anisotropic deep etching of silicon was successfully achieved using both SF6/C4F8 and SF6/C4F6 plasmas in the etching and/deposition steps of the Bosch process.
High-aspect-ratio nanopillar structures fabricated by nanoimprinting with elongation phenomenon
Authors: Kuwabara Kosuke , Miyauchi Akihiro
Published: April 2008

The authors found that fine pillar structures (nanopillars) with a high aspect ratio were formed by nanoimprinting with elongation phenomenon. Polymer nanopillars with higher aspect ratios than that of corresponding holes on the mold were obtained without any etching processes after nanoimprinting. The finest nanopillars were 95 nm in diameter and 4.1 μm high made of polystyrene. Elongated nanopillars of poly(methylmethacrylate) and polystyrene were confirmed. Elongation of nanopillars depended on process conditions such as the diameter of holes on the mold, the unmolding temperature, and the molecular weight of the polymer resin.
Route to production of suspended perforated membranes
Authors: Burckel D. B. , Brueck S. R. J.
Published: April 2008

The authors report a flexible approach to fabrication of suspended perforated membranes. Interferometric lithography is used to pattern photoresist to create an etch mask on a silicon substrate. Reactive ion etching results in the formation of a matrix of silicon pillars. The interstices of the pillar matrix are then filled with the membrane material. Subsequent removal of the silicon matrix and underlying substrate yields a suspended membrane with perforations where the pillar matrix protruded prior to removal. The method combines interferometric lithography and conventional lithography to provide both periodic and nonperiodic patterns in a seamless process flow. The use of a matrix of sacrificial pillars enables the formation of higher aspect ratio holes than standard liftoff or etched film approaches. Perforated membranes of a siloxane based silica, photocurable polymer, and evaporated Cr are presented, demonstrating the wide process latitude of this approach. Such suspended membranes have application in photonic, metamaterials, DNA translocation, and biological and chemical sensors.
Novel method for measuring nanofriction by atomic force microscope
Authors: Salvadori M. C. , Lisboa F. S. , Fernandes F. M. , Brown I. G.
Published: April 2008

The authors describe a novel approach to the measurement of nanofriction, and demonstrate the application of the method by measurement of the coefficient of friction for diamondlike carbon (DLC) on DLC, Si on DLC, and Si on Si surfaces. The technique employs an atomic force microscope in a mode in which the tip moves only in the z (vertical) direction and the sample surface is sloped. As the tip moves vertically on the sloped surface, lateral tip slipping occurs, allowing the cantilever vertical deflection and the frictional (lateral) force to be monitored as a function of tip vertical deflection. The advantage of the approach is that cantilever calibration to obtain its spring constants is not necessary. Using this method, the authors have measured friction coefficients, for load range 0<L<6μN, of 0.047±0.002 for Si on Si, 0.0173±0.0009 for Si on DLC, and 0.0080±0.0005 for DLC on DLC. For load range 9<L<13μN, the DLC on DLC coefficient of friction increased to 0.051±0.003.
Patterning chalcogenide glass by direct resist-free thermal nanoimprint
Authors: Solmaz M. , Park H. , Madsen C. K. , Cheng X.
Published: April 2008

In this article, patterning As2S3 chalcogenide glass is investigated from a nanoimprint perspective. Thermal nanoimprint was used to successfully pattern As2S3 microstructures. Due to the high melt viscosity of As2S3, patterns of a few microns and submicrons can be well formed, while larger patterns cannot be faithfully replicated due to limited melt flow when a thin initial film is used. Accelerated crystallite formation after nanoimprint was observed and a method to suppress crystallites was explored. In patterned As2S3 microstructures, optical birefringence was observed near the pattern edges, which potentially has a significant impact on the optical properties of patterned microstructures. It was also observed that significant surfactant wear occurs after just a few nanoimprints. A new surfactant with better temperature stability was proposed and its durability was compared to commonly used nanoimprint surfactant such as heptadecafluoro-1,1,2,2-tetrahydrodecyl trichlorosilane.