bluuebunny/crossref_metadata_2025 huggingface dataset:
Elemental Analysis of Human Cremains Using ICP‐OES to Classify Legitimate and Contaminated Cremains*
Authors: Brooks Timothy R. , Bodkin Tom E. , Potts Gretchen E. , Smullen Stephanie A.
Published: August 2006

ABSTRACT: The Tri‐State Crematory Incident in Nobel, GA (February 2001) revealed limitations in traditional human cremated remains (cremains) analytical methodology. The goal of this study was to develop a method for effectively classifying questionable sets of cremains as legitimate or contaminated. Eighty‐eight samples of known human cremains, concrete, mixtures of the two, and questionable sets of cremains were acid digested and analyzed for 21 elements by Inductively Coupled Plasma‐Optical Emission Spectroscopy (ICP‐OES). Variable cluster and principle component analyses identified the seven elements (Sb, B, Li, Mn, Sr, Tl, and V) used to develop discriminant functions to classify questionable sets into two groups: cremains and concrete. The discriminant analysis shows that at the 0.90 probability level, mixtures of 50% or less human content were classified as concrete. Mixtures with 90% human content classified as cremains. Sixty percent and 75% human content mixtures remained in the questionable classification, but as the concentration of human increased in the mixture, the probability of assignment to the known cremains group increased. Most of the questionable human samples classified as cremains. This is a pilot study and cannot yet satisfy Daubert standards for courtroom admissibility, but it indicates that it is possible to determine the legitimacy of cremains using elemental analysis by ICP‐OES coupled with multivariate statistical analysis.
Herpes simplex and Epstein‐Barr virus lymphadenitis in a patient with chronic lymphocytic leukemia treated with fludarabine
Authors: Mercadal Santiago , Martinez Antonio , Nomdedeu Benet , Rozman María , Gaya Anna , Salamero Olga , Campo Elías
Published: August 2006

Abstract:  Multiple herpes virus co‐infection is a very rare complication in patients with chronic lymphocytic leukemia (CLL). We describe a patient with a CLL who developed an herpes virus lymphadenitis. Inmunohistochemical study was positive for HSV‐1, HSV‐2, and Epstein‐Barr Virus (EBV). The coinfection of EBV with a profile of expresion of viral latent genes type III, is usually seen in inmunodepressed patients. To the best of our knowledge, this is the first reported case of a multiple human herpes virus infection mimicking Richter syndrome.
Bone mass index analysis in elderly people before and after change prosthesis
Authors: Gomes Vanessa Neves , Frigerio Maria Luiza Moreira Arantes , Fidelix Marcia
Published: August 2006

Objectives:  To evaluate the bone mass index (BMI) of senescent patients before and after prosthetic rehabilitation by complete dentures and evaluating any correlations between prosthetic rehabilitation and changes in BMI.

Subjects:  Thirty‐two edentulous elder patients who were in need of new complete dentures.

Setting:  Dental clinic of the Prosthodontics Department (Dental Branch) of the University of São Paulo, Brazil.

Materials and methods:  The study was performed in three different phases: the first one took place before any procedures relating to the new complete dentures had started and consisted of clinical records and a prosthetic anamnesis. The second and third phases took place after the prosthetic rehabilitation was completed, normally after 3 and 5–6 months respectively. The data collected in the different phases were analysed by using bioestat 3.0; the level of significance was p < 0.05, in a bilateral proof.

Results:  The non‐parametric statistical analysis of BMI did not show any significant differences when compared with the three phases analysed during the study.

Conclusion:  There was no evidence that accurate prosthetic rehabilitation could influence BMI.
First‐time dental care and the most recent dental treatment in relation to utilisation of dental services among dentate elderly patients in Lithuania
Authors: Vyšniauskaité Sonata , Vehkalahti Miira M.
Published: August 2006

Objectives:  To describe the initial dental treatments of Lithuanian dentate elderly patients and the content of the most recent treatment in relation to their dentist‐visiting behaviour.

Materials and methods:  A cross‐sectional questionnaire study was carried out at two public dental offices in Kédainiai, Lithuania, among dentate patients aged 60+ years. A self‐administered questionnaire covered first‐time dental care, the most recent dental treatment, check‐up behaviour, interval since the most recent dental visit, and number of teeth. Age, gender and education served as background information. Statistical evaluation was by chi‐squared test, anova and logistic regression for odds ratio (OR).

Results:  In all, 174 dentate elderly responded, mean age being 69.2 (SD = 6.6) years. The mean age at the first visit was 16.3 years [95% confidence interval (CI) 14.9–17.6]. Regular dental check‐ups were reported by 30%, and 36% had visited a dentist within the past 12 months. As to the content of the most recent treatment, 78% of the elderly reported filling therapy, 50% endodontics, 48% tooth extraction, 21% radiography, 10% cleaning or scaling and 6% polishing of fillings. Those going for check‐ups were more likely to report diagnostic (OR 1.9; 95% CI 1.1–2.8; p = 0.01) and preventive (OR 4.8; 95% CI 2.5–9.0; p = 0.002) treatment when analysed by a logistic regression model, controlling for age, gender, education and number of teeth.

Conclusions:  Check‐up‐orientated utilisation of dental services should be encouraged among the Lithuanian elderly. Dentists and health officials should place greater emphasis on prevention.
Dietary Beta‐Glucans and Nucleotides Enhance Resistance of Red‐Tail Black Shark (Epalzeorhynchos bicolor, fam. Cyprinidae) to Streptococcus iniae Infection
Authors: Russo Riccardo , Yanong Roy P. E. , Mitchell Hugh
Published: August 2006

Two experiments were conducted to examine the effect of commercially available beta‐glucan (Macrogard) and nucleotide (Aquagen) on the resistance to Streptococcus iniae infections in vaccinated or nonvaccinated juvenile red‐tail black sharks (Epalzeorhynchos bicolor, RTB) (1.4 ± 0.4 g weight total (WT), 5.6 ± 0.5 cm total length (TL)). The immunostimulants were added to a control diet formulated without any yeast source following the recommended doses of 1 g/kg feed for the beta‐glucan and 2 g/kg feed for the nucleotide. Beginning 4 d after introduction into tanks, fish were fed the experimental diets for 24 d, at 3% body weight per day, divided into two feedings. At the end of this period, fish were challenged by an intracoelomic injection of S. iniae. In the first experiment, both vaccinated and nonvaccinated fish were fed one of the two immunostimulants. In the second experiment, only vaccinated fish were fed the immunostimulants. Fish were vaccinated a week after being introduced into the system and challenged by intracoelomic injection with 1.5 × 105 S. iniae colony‐forming units /fish after three additional weeks; mortality was recorded for 2 wk after the bacterial challenge. In the first experiment, the mortality of both vaccinated and nonvaccinated fish fed beta‐glucan (23 ± 7% and 82 ± 1%, respectively) or nucleotide (28 ± 6% and 86 ± 5%, respectively) was significantly lower than the mortality of the control groups (35 ± 4% and 93 ± 5%, respectively), but there was no significant difference in mortality between fish fed beta‐glucan or nucleotide. In the second experiment, the mortality of vaccinated fish fed beta‐glucan (25 ± 7%) or nucleotide (43 ± 9%) was significantly lower than that of vaccinated fish fed the control diet (69 ± 7%). In both experiments, there was no significant difference in growth rate among fish fed immunostimulants or the control diet. The results of this investigation demonstrated the efficacy of beta‐glucans and nucleotides in increasing resistance to S. iniae in RTB sharks.
Neurodegeneration with Features of NIFID and ALS—Extended Clinical and Neuropathological Spectrum
Authors: Roeber Sigrun , Bäzner Hansjoerg , Hennerici Michael , Porstmann Romy , Kretzschmar Hans A.
Published: August 2006

Heterogeneous clinical and neuropathological features have been observed in the recently described neuronal intermediate filament inclusion disease (NIFID). The immunohistological findings common to all cases are α‐internexin and neurofilament‐positive neuronal cytoplasmic inclusions, which have not been found in comparable density in other neurodegenerative disorders. Notwithstanding these common features, the cases reported so far have shown differences concerning age at onset, constellation and dominance of symptoms as well as type and distribution of additional neuropathological findings. Here we present the first NIFID case that exhibits severe involvement of lower motor neurons. Also, this patient may have had a clinical onset of disease in early childhood, as she was diagnosed as having dysarthria, which could not be attributed to any other cause at the age of 3 years. This case is a further contribution to the spectrum of this novel neurodegenerative disease.
Change of Constitutive Relations due to Interaction Between Strain-Gradient Effect and Material Gradation
Authors: Chan Youn-Sha , Paulino Glaucio H. , Fannjiang Albert C.
Published: August 2006

For classical elasticity, the constitutive equations (Hooke’s law) have the same functional form for both homogeneous and nonhomogeneous materials. However, for strain-gradient elasticity, such is not the case. This paper shows that for strain-gradient elasticity with volumetric and surface energy (Casal’s continuum), extra terms appear in the constitutive equations which are associated with the interaction between the material gradation and the nonlocal effect of strain gradient. The corresponding governing partial differential equations are derived and their solutions are discussed.
Vector J-Integral Analysis of Crack Interaction With Pre-existing Singularities
Authors: Ma Lifeng , Lu Tian Jian , Korsunsky Alexander M.
Published: August 2006

In this paper, the mechanics of a semi-infinite crack interacting with near crack-tip singularities (e.g., dislocations) in two-dimensional solids is investigated using the concept of potential energy release rate. The spontaneous relationship between the crack potential energy release rate and the well-known vector conservative integral Ji(i=1,2) is derived. It is demonstrated that J1 and J2 integrals are equally important in solving crack problems. This allows a more rational criterion to be proposed, based on the criterion of maximum energy release rate, to assess the so-called shielding/amplification effect on the crack tip due to the presence of the singularities. It is shown that the new criterion can not only assess the shielding/amplification effect under pure mode I or mode II remote loading, but also efficiently assess crack-singularity interaction under mixed mode remote loading. Simultaneously, it is found by re-examining the Ji integrals that there exists a simple but universal relation among the three values of the vector Ji integral corresponding separately to the contributions induced from the semi-infinite crack tip, the singularity, and the remote loading. Next, a multi-singularity-crack interaction model is addressed, and the closed-form solution is obtained. Finally, as an example, the problem of a single dislocation interacting with a main crack is solved to demonstrate the validity of the proposed model and the new criterion.
A Theory of Fracture Based Upon an Extension of Continuum Mechanics to the Nanoscale
Authors: Oh Eun-Suok , Walton Jay R. , Slattery John C.
Published: August 2006

A theory of fracture is presented that is based upon an extension of continuum mechanics to the nanoscale through the incorporation of long-range intermolecular forces which correct bulk material descriptions near interfaces. The surface energy on crack surfaces, which is given in terms of the long-range intermolecular forces, plays an important role in an expression for the stress distribution near the crack tip. It is observed through numerical simulation that the incorporation of these long-range intermolecular forces removes the square-root stress singularity predicted by classical linear elastic fracture mechanics.
Mechanical Characterization of Released Thin Films by Contact Loading
Authors: Zhang Rongjing , Shilo Doron , Ravichandran Guruswami , Bhattacharya Kaushik
Published: August 2006

The design of reliable micro electro-mechanical systems (MEMS) requires understanding of material properties of devices, especially for free-standing thin structures such as membranes, bridges, and cantilevers. The desired characterization system for obtaining mechanical properties of active materials often requires load control. However, there is no such device among the currently available tools for mechanical characterization of thin films. In this paper, a new technique, which is load-controlled and especially suitable for testing highly fragile free-standing structures, is presented. The instrument developed for this purpose has the capability of measuring both the static and dynamic mechanical response and can be used for electro∕magneto∕thermo mechanical characterization of actuators or active materials. The capabilities of the technique are demonstrated by studying the behavior of 75nm thick amorphous silicon nitride (Si3N4) membranes. Loading up to very large deflections shows excellent repeatability and complete elastic behavior without significant cracking or mechanical damage. These results indicate the stability of the developed instrument and its ability to avoid local or temporal stress concentration during the entire experimental process. Finite element simulations are used to extract the material properties such as Young’s modulus and residual stress of the membranes. These values for Si3N4 are in close agreement with values obtained using a different technique, as well as those found in the literature. Potential applications of this technique in studying functional thin film materials, such as shape memory alloys, are also discussed.
A Hybrid Numerical-Analytical Method for Modeling the Viscoelastic Properties of Polymer Nanocomposites
Authors: Liu Hua , Brinson L. Catherine
Published: August 2006

In this paper, we present a novel hybrid numerical-analytical modeling method that is capable of predicting viscoelastic behavior of multiphase polymer nanocomposites, in which the nanoscopic fillers can assume complex configurations. By combining the finite element technique and a micromechanical approach (particularly, the Mori-Tanaka method) with local phase properties, this method operates at low computational cost and effectively accounts for the influence of the interphase as well as in situ nanoparticle morphology. A few examples using this approach to model the viscoelastic response of nanotube and nanoplatelet polymer nanocomposite are presented. This method can also be adapted for modeling other behaviors of polymer nanocomposites, including thermal and electrical properties. It is potentially useful in the prediction of behaviors of other types of nanocomposites, such as metal and ceramic matrix nanocomposites.
Solid Oxide Fuel Cell System and the Economical Feasibility
Authors: Fontell Erkko , Phan Tho , Kivisaari Timo , Keränen Kimmo
Published: August 2006

In the paper, a solid oxide fuel cell (SOFC) system is briefly described and its economical feasibility in three different applications is analyzed. In the feasibility analysis, the SOFC system is part of commercial applications where energy is used for power and heat generation. In the economical analysis, the three applications have different load profiles which are studied separately at different geographical locations with associated local energy market conditions. The price for natural gas and electricity varies by location, leading to a different feasibility condition for stationary fuel cell application as well as for other distributed generation equipment. In the study, the spark spread of natural gas and electricity is used as a base variable for the analysis. The feasibility is analyzed in the case of an electricity-only application as well as with two combined heat and power applications, where an economical value is assigned to the produced and consumed heat. The impact on economical competitiveness of possible incentives for the generated fuel cell power is estimated. A sensitivity analysis with different fuel cell-units’ electrical efficiency, maintenance cost, and payback period is presented. Finally, the maximum allowed investment cost levels for the SOFC system at different locations and market conditions is presented.
Flow Control and Unsteady-State Analysis on Thermal Performance of Solar Air Collectors
Authors: Ito Sadasuke , Kashima Minoru , Miura Naokatsu
Published: August 2006

Promotion of the use of renewable energy, such as solar heat, for space heating and drying crops and wood is desired to prevent global warming. High-temperature collection of heat by air collectors producing as much as 50°C in winter for space heating and about 80°C in summer for exchanging heat to circulating water for hot water supply would be appropriate applications. In this study, first, a flow control system for constant outlet temperature was installed in a hot air supply system to examine the feasibility of the control system. After experiments, it was found that the control system could function satisfactory. Second, an unsteady-state analysis was made to predict the thermal performance of a flat-plate collector under a given condition of variable flow rate. The analytical model became simple by the assumptions that the heat capacity of the air in the collector and heat conduction in the flow direction through the air and the materials of the collector could be neglected. The maximum differences in outlet temperature and collector efficiency for constant flow rate between the analysis and the experiment were 1.8°C and 6% of the collector efficiency, respectively, except in the beginning of experiments. The biggest difference in the collector efficiency was 30% at 3:00 P.M., which occurred at the end of one of the experiments. The analytical results generally agreed well with the experimental results even when the flow rate and solar radiation changed greatly as time went on. Transient effects are important to predict outlet temperature for variable solar radiation intensity, wind speed, and flow rate.
Bayesian and Sensitivity Analysis Approaches to Modeling the Direct Solar Irradiance
Authors: Lauret Philippe , David Mathieu , Fock Eric , Bastide Alain , Riviere Carine
Published: August 2006

In this paper, emphasis is put on the design of a neural network (NN) to model the direct solar irradiance. Since, unfortunately, a neural network is not a statistician-in-a-box, building a NN for a particular problem is a nontrivial task. As a consequence, we argue that in order to properly model the direct solar irradiance, a systematic methodology must be employed. For this purpose, we propose a two-step approach to building the NN model. The first step deals with a probabilistic interpretation of the NN learning by using Bayesian techniques. The Bayesian approach to modeling offers significant advantages over the classical NN learning process. Among others, one can cite (i) automatic complexity control of the NN using all the available data and (ii) selection of the most important input variables. The second step consists of using a new sensitivity analysis-based pruning method in order to infer the optimal NN structure. We show that the combination of the two approaches makes the practical implementation of the Bayesian techniques more reliable.
Flow Through a Solar Chimney Power Plant Collector-to-Chimney Transition Section
Authors: Kirstein Carl F. , von Backström Theodor W.
Published: August 2006

A solar chimney power plant consists of a large greenhouse-type collector surrounding a tall chimney. The air, heated within the collector, passes through an inlet guide vane (IGV)cascade and then through a transition section to a turbine that powers a generator. The transition section contains the turbine inlet guide vanes that support the whole chimney and guides the flow entering the turbine. The primary objective of the study was to determine the loss coefficient and mean exit swirl angle of the flow passing through the collector-to-chimney transition section of a full-scale solar chimney power plant as dependent on IGV stagger angle and collector roof height. Very good agreement was found between experimental values measured in a scaled model and commercial CFD code predictions of flow angles, velocity components, and internal and wall static pressures. The agreement between measured and predicted total pressure loss coefficient was reasonable when considering how small it is. The CFD code served to extend the predictions to a proposed full-scale geometry. Semi-empirical equations were developed to predict the loss coefficient and turbine mean inlet flow angles of solar chimney power plants as dependent on collector deck height and inlet guide vane setting angle. The two empirical equations may be useful in solar chimney plant optimization studies.
The Thermodynamic Performance Analysis of an Irreversible Space Solar Dynamic Power Brayton System and its Parametric Optimum Design
Authors: Zhang Y. , Chen J.
Published: August 2006

A solar dynamic (SD) power system composed of a concentrating solar collector and an irreversible Brayton cycle system is set up, where the heat losses of the collector are dominated by the radiation, the heat transfer between the collector and the Brayton cycle system obeys Newton’s law, and the heat transfer between the Brayton cycle system and the ambient obeys the radiant heat transfer law. The cycle model is used to investigate synthetically the influence of the radiant heat losses of the collector, the finite-rate heat transfer, and the irreversible adiabatic processes in the Brayton cycle system on the performance of a space SD power Brayton system. The overall efficiency of the system and the other performance parameters are optimized. The optimal values of the important parameters and their corresponding upper or lower bounds are determined. Finally, the optimal performance of an endoreversible SD power Carnot system is simply derived.
Generation of a Radiation Absorbing Medium for a Solar Receiver by Elutriation of Fine Particles From a Spouted Bed
Authors: Klein Hanna H. , Rubin Rachamim , Karni Jacob
Published: August 2006

In high-temperature solar-thermal systems the conversion of solar to thermal energy requires a radiation absorbing surface to transfer the radiative solar energy to the working fluid. The present study focuses on the generation of a moving radiation absorber using particles suspended in the working fluid. Three methods of particle entrainment in a gas were investigated. Elutriating fine particles from a spouted bed was found to be the preferred method. The diameter range of the entrained carbon black particles was 0.030-25μm, with 99.7% of the particles having an equivalent diameter less than 1μm, and 48% of the projected surface area was due to agglomerated particles with average equivalent diameter >5μm. The moving radiation absorber was tested in a solar receiver using nitrogen as a working fluid. The inner wall temperatures in the receiver cavity were below the gas exit temperature, which shows that the bulk heat transfer from the incoming solar radiation to the gas takes place via the moving radiation absorbing particles.
Solar Production of Hydrogen Using “Self-Assembled” Polyoxometalate Photocatalysts
Authors: Muradov N. , T-Raissi A.
Published: August 2006

The near-term and cost-effective production of solar hydrogen from inexpensive and readily available hydrogen containing compounds (HCCs) can boost the prospects of future hydrogen economy. In this paper, we assess the prospects of the solar-assisted conversion of HCCs into hydrogen using polyoxometalate (POM) based photocatalysts, such as isopolytungstates (IPT) and silicotungstic acid (STA). Upon exposure to solar photons, IPT aqueous solutions containing various HCCs (e.g., alcohols, alkanes, organic acids, sugars, etc.) produce hydrogen gas and corresponding oxygenated compounds. The presence of small amounts of colloidal platinum increases the rate of hydrogen evolution by one order of magnitude. A solar photocatalytic flat-bed reactor, approximately 1.2m×1.2m in size, was fabricated and tested for the production of hydrogen from water-alcohol solutions containing IPT and STA and small amounts of colloidal Pt. The solar photoreactor tests demonstrated steady-state production of hydrogen gas for several days. IPT immobilized on granules of anion exchange resins with quaternary ammonium active groups show good photocatalytic activity for hydrogen production from water-alcohol solutions exposed to near-UV or solar radiation.
Reliability Analysis of the Tube Hydroforming Process Based on Forming Limit Diagram
Authors: Li Bing , Metzger Don R. , Nye Tim J.
Published: August 2006

Tube hydroforming is an attractive manufacturing process in the automotive industry because it has several advantages over alternative methods. In order to determine the reliability of the process, a new method to assess the probability of failure is proposed in this paper. The method is based on the reliability theory and the forming limit diagram, which has been extensively used in metal forming as the criteria of formability. From the forming limit band in the forming limit diagram, the reliability of the forming process can be evaluated. A tube hydroforming process of free bulging is then introduced as an example to illustrate the approach. The results show this technique to be an innovative approach to avoid failure during tube hydroforming.
Heat Transfer Simulation in the Mold With Generalized Curvilinear Formulation
Authors: Monteiro Eliseu L. M. , Rouboa Abel I. , Monteiro António A. C.
Published: August 2006

The production of a part by foundry techniques is influenced by its complex geometry configuration, which affects the solidification conditions and subsequent cooling. For example certain pipes, some vessels and most valves are produced by casting. To model the solidification of the complex shapes such as valves is difficult if Cartesian coordinates are used. Even simpler parts like pipes may become difficult to model because they usually are not orthogonally ruled shapes. The main objective of this paper is to describe the development of a finite volume method intended to simulate the heat transfer phenomena during the phase change process. Because of the mold design complexity, the finite volume is described using the generalized curvilinear formulation.
Why Do Shallow Caps Deflect More Than Deep Ones?
Authors: Ostraich B. , Kochavi E. , Nizri E. , Cohen I.
Published: August 2006

The deflection of a clamped thin shell spherical cap is evaluated by the finite element method. Elastic material properties are assumed. The ratio of the center height to the base radius of the cap is used to distinguish shallow from deep caps. Comparing the deflection of clamped shallow caps to deep ones resulted in a very interesting behavior which may contradict the intuition of some engineers. For example, the deflection of a shallow clamped cap is considerably larger than that of a sphere or hemisphere with the same radius of curvature. The causes for this behavior are discussed. Results are presented for a wide range of geometries, pressures, and material properties for design purposes.
Performance improvement of flash memories with HfOxNy∕SiO2 stack tunnel dielectrics
Authors: Lai Hsiang-Yueh , Chang-Liao Kuei-Shu , Wang Tien-Ko , Wang Ping-Kun , Cheng Chin-Lung
Published: August 2006

The operating characteristics of flash memory devices with tunnel dielectrics comprising a hafnium oxynitride (HfOxNy) layer or a hafnium oxynitride/silicon dioxide (HfOxNy∕SiO2) stack, annealed at various temperatures, were studied. The present work indicates that flash memory devices with a HfOxNy∕SiO2 stack tunnel dielectric have a higher program/erase speed and better reliability than those with a single HfOxNy layer. The stack tunnel dielectric composed of a thick HfOxNy layer and a thin SiO2 layer exhibits an even better performance in the flash memory operation. In addition, devices with HfOxNy∕SiO2 stack tunnel dielectrics annealed at 850°C show the best performance in terms of the program/erase speed, charge retention, and read disturbance.
Smoothing of polycrystalline copper with rough surface by oblique argon-ion irradiation
Authors: Hino T. , Nakai T. , Nishikawa M. , Hirohata Y. , Yamauchi Y.
Published: August 2006

Mechanically polished polycrystalline copper was obliquely irradiated by an argon-ion beam with an ion energy of 1keV. The incident angle and fluence of the argon ion were changed to obtain the dependences of incident angle and ion fluence on the surface flatness. After argon-ion irradiation, the surface flatness was examined using atomic force microscopy. Before the irradiation, the sample had a rough surface consisting of groove structures with an average width of 400nm and an average elevation of 37nm. The percentage of the surface area with a height more than 50nm was 13%. The incident angle was changed from 0° (perpendicular injection) to 70° for the fluence of 1×1018Ar∕cm2. The fluence was changed in the range of 1×1017–1×1018Ar∕cm2 for the incident angle of 70°. A smooth surface was obtained when the incident angle was largest, 70°, and the fluence was greater than 5×1017Ar∕cm2. The percentage of the surface area with an elevation more than 50nm was reduced to 2%, and the number of grooves per unit area was reduced to about half. The reduction of the elevation is mainly due to the selective sputtering for protruding parts, and the reduction of the groove number is mainly due to the redepositing of sputtered particles. The present results show that the oblique ion irradiation is useful for reducing both the elevation and the number of grooves of uneven surfaces.
Modeling and characterization of direct-tunneling current in dual-layer ultrathin-gate dielectric films
Authors: Wong Hei , Iwai Hiroshi
Published: August 2006

This work presents a comprehensive investigation on the modeling and characterization of the direct-tunneling (DT) current in ultrathin-gate dielectric film based on the classical model equation. Merit of replacement, which takes both the capacitance gain and the DT current suppression into consideration, was introduced to have a better comparison of different gate dielectric materials. A simple approach for modeling the dual-layer dielectric film is also developed. The tunneling characteristics of a dual-layer stack are modeled with an effective barrier and an effective thickness. The simple approach is particularly useful for device designs and process evaluation.
Improved Au Schottky contacts on GaAs using cryogenic metal deposition
Authors: Wang Hung-Ta , Jang S. , Anderson T. , Chen J. J. , Kang B. S. , Ren F. , Herrero A. , Gerger A. M. , Gila B. P. , Pearton S. J. , Shen H. , LaRoche Jeffrey R. , Smith Kurt V.
Published: August 2006

The use of low temperatures (∼77K) during Au Schottky contact deposition onto n-GaAs produces an increase in barrier height from 0.73eV for room temperature diodes to 0.82eV. There is no evidence of drift in the forward current in either type of diode and the low temperature deposited samples show smoother Au layers and more abrupt Au∕GaAs interfaces as determined by x-ray reflectivity measurements. Both types of diodes show surface and bulk contributions to the reverse bias current. The diodes with Au deposited at cryogenic temperature did show higher ideality factors, which may result from contaminants gettered to the cold GaAs surface.
Type-II InAs∕GaSb superlattices grown on GaSb (311)B by molecular beam epitaxy for long-wavelength infrared applications
Authors: Shao H. , Li W. , Torfi A. , Moscicka D. , Wang W. I.
Published: August 2006

Type-II InAs∕GaSb superlattices have been grown by solid-source molecular beam epitaxy on GaSb (311)B substrates. The performances of these superlattices are compared with the same structure on GaSb (100). The x-ray diffraction measurements show that InAs∕GaSb superlattices on (311)B and (100) GaSb both exhibit excellent material qualities with the full width at half maximum of the zeroth-order peak within 25arcsec. In comparison with the superlattice photodiodes on GaSb (100) substrate, the 80K dark current density at 0.2V reversed bias of the (311)B photodiodes is reduced by more than one order of magnitude. The 80K zero bias resistance (R0A) of the (311)B photodiodes is enhanced by a factor of 2.9. The 50% cutoff wavelength is extended to 10.7μm when using GaSb (311)B substrate, as compared to 10.2μm for the photodiodes on GaSb (100) substrate. The 9μm zero bias detectivity of 4.4×1010cmHz1∕2∕W is achieved at 80K for unpassivated photodiodes on GaSb (311)B, twice as high as their (100) counterparts. Data reported here demonstrate the potential of fabricating InAs∕GaSb superlattice photodiodes on GaSb (311)B substrates with improved performance.
Absorbance measurement of polymers at extreme ultraviolet wavelength: Correlation between experimental and theoretical calculations
Authors: Kwark Young-Je , Bravo-Vasquez J. Pablo , Chandhok Manish , Cao Heidi , Deng Hai , Gullikson Eric , Ober Christopher K.
Published: August 2006

Performance requirements for extreme UV (EUV) resists will require the development of polymer platforms. A challenge in designing photoresists for EUV wavelengths is the selection of molecular structures that have minimal absorbance. For example, elements that are commonly used in photoresists at other wavelengths, such as oxygen and fluorine, are highly absorbing at ∼13nm making them problematic for EUV applications. In order to provide a tool for EUV resist design, this article presents a study of the absorbance of common photoresist structures and compares it to theoretical estimates of resist absorbance based on composition and density. On this basis, several potential structures suitable for EUV resists are assessed.
Effect of reverse flow by differential pressure on the protection of critical surfaces against particle contamination
Authors: Kim Jung Hyeun , Fissan Heinz , Asbach Christof , Yook Se-Jin , Wang Jing , Pui David Y. H.
Published: August 2006

Mask protection from particulate contaminants is one of the most serious concerns for the success of deploying extreme ultraviolet lithography (EUVL) technology for future semiconductor manufacturing. Standard pellicles are not applicable for an EUVL mask surface because of the high absorption of the EUV beam by any material. Therefore, methods such as thermophoresis and electrophoresis are desirable for protection, instead of using organic membrane pellicles. A reverse flow concept by introducing differential pressure between different operating zones (mask zone with higher pressure and optics zone with lower pressure) is introduced for protection of critical surfaces against particulate contamination. In this study, we show systematic investigations of the differential pressure effect on the protection of critical surfaces using 125nm polystyrene latex spheres at a chamber pressure of 50mTorr, whereas the critical surface zone pressure was varied up to 550mTorr. We found that a higher particle speed needs a higher differential pressure between the mask zone and the optics zone to protect the mask from incoming particles. The higher differential pressure and higher relative flow velocity for the reverse flow provide more drag force for particles to stop before reaching the critical surface. The particles having an injection speed of up to 180m∕s could be completely repelled using the differential pressure approach, but the deposition of particles with a speed of 270m∕s is hardly prevented by this reverse flow concept. Different gases showed different amounts of protection efficiency due to the change of gas properties such as density and molecular weight. Argon showed better protection efficiency against particle contamination than air. By drag force comparison, argon has about 18% higher drag force than air. The experimental results showed that argon reduced the particle deposition between 6% and 50%, depending on the particle injection speed and the differential pressures.
Structure of sputtered nanocomposite CrCx∕a-C:H thin films
Authors: Gassner G. , Patscheider J. , Mayrhofer P. H. , Hegedus E. , Tóth L. , Kovacs I. , Pécz B. , Srot V. , Scheu Ch. , Mitterer C.
Published: August 2006

This work presents the structural evolution of nanocomposite CrCx∕a-C:H coatings prepared by unbalanced magnetron sputtering of a metallic Cr target in Ar+CH4 glow discharges using low negative dc bias voltages. Raman spectroscopy and x-ray photoelectron spectroscopy were used to characterize the phase composition and the chemical bonding in the films deposited at different experimental conditions. The results were correlated to the chemical composition obtained by elastic recoil detection analysis. The coating microstructure was investigated on selected samples by high-resolution transmission electron microscopy combined with electron energy-loss spectroscopy analysis. The nanocomposite coatings can be divided into hard CrCx dominated films, when prepared at low CH4 partial pressure to total pressure (pt) ratios (pCH4∕pt<0.4), and into low-friction a-C:H dominated films, when prepared at pCH4∕pt>0.4. The structure of the low-friction a-C:H dominated coatings consists of 2–10nm sized fcc CrC crystallites embedded in a Cr containing a-C:H matrix.
Local photocurrent mapping as a probe of contact effects and charge carrier transport in semiconductor nanowire devices
Authors: Gu Y. , Romankiewicz J. P. , David J. K. , Lensch J. L. , Lauhon L. J. , Kwak E.-S. , Odom T. W.
Published: August 2006

Three types of two-terminal CdS nanowire devices with distinct current versus voltage characteristics were fabricated by forming Schottky and/or Ohmic contacts in a controlled manner. Argon ion bombardment of CdS nanowires increased the carrier concentration allowing the formation of Ohmic Ti–CdS contacts. Scanning photocurrent microscopy (SPCM) was used to explore the influence of the contacts on the spatially resolved photoresponse in two-terminal devices and to analyze charge carrier transport processes. Modeling of the spatial profiles of the local photocurrent images enabled the quantitative extraction of electron and hole mobility-lifetime products in Ohmic devices and the hole mobility-lifetime product in Schottky devices. Analysis of the evolution of SPCM images with bias suggests that the electric field is localized to the optical generation region in the Ohmic devices and localized beneath the contacts in the Schottky devices.
Nature of high-temperature superconductivity
Authors: Dow John D. , Harshman Dale R.
Published: August 2006

Evidence is presented that the superconducting hole condensate generally does not reside in the cuprate planes of high-temperature superconductors, but in the SrO layers, in the BaO layers, or in the regions of interstitial oxygen. Evidence that electrons, not holes, transfer to the cuprate planes of HgBa2Can−1CunO2+n+δ as a function of pressure, number n of layers, and increasing Tc is presented; holes transfer to the BaO layers. The hole transfer in YBa2Cu3O7 is also to the BaO layers. PrBa2Cu3O7 superconducts (as predicted) when it is free of pair-breaking PrBa defects in its BaO layers. The chosen locus of the superconductivity is consistent with the observation of magnetism in both the CuO layers and the cuprate planes of YBa2Cu3O7. Four materials were successfully predicted to superconduct by assuming that the cuprate planes are normal. There are no n-type high-temperature superconductors; Nd2−zCezCuO4 is p type and doped with interstitial oxygen. When Y+3 is replaced by Am+4, Pb2Sr2YCu3O8 becomes n type and stops superconducting. Holes remain near interstitial oxygen in Tl2Ba2Can−1CunO2n+4+δ. Gd2−zCezCuO4, unlike Nd2−zCezCuO4, does not superconduct because Gd has L=0 and J≠0 and breaks Cooper pairs associated with its interstitial oxygen, but Gd2−zCezSr2Cu2NbO10 does superconduct (in its SrO layers). YBa2Cu3O7 exhibits bulk nodeless (s-wave) superconductivity. We argue that the superconductivity of YBa2Cu3O7 is representative of high-Tc superconductors. The pairing mechanism is electronic (not phononic) and associated with holes on certain oxygen ions (or sulfur ions, in the case of some organic superconductors). We explore a Bardeen-Cooper-Schrieffer-type formalism applied to cuprates, ruthenates, and other compounds.
Growth temperature dependent evolution of the interface structure in Co2FeSi∕GaAs(001) hybrid structures
Authors: Hashimoto M. , Herfort J. , Trampert A. , Schönherr H.-P. , Ploog K. H.
Published: August 2006

The growth temperature dependence of the interface perfection of full Heusler alloy Co2FeSi∕GaAs(001) hybrid structures have been examined using transmission electron microscopy (TEM) and high-resolution x-ray diffraction (HRXRD). The film grown at 100°C shows an atomically abrupt interface without interfacial reaction. In the high-resolution transmission electron microscope (HRTEM) image from the 200°C film, however, a 1–2 ML (monolayer) interlayer having a contrast different from both Co2FeSi and GaAs was observed at the interface, indicating that interfacial reaction starts at this growth temperature. The layer grown at 350°C shows a further reacted interface in the HRTEM image, i.e., undulations and large steps at the interface. The interface perfection strongly correlates with the in-plane uniaxial magnetic anisotropy (UMA) as the UMA constant rapidly decreases above 200°C in accordance with the progress of the interfacial reaction.
Stress evolution during ripening of self-assembled InAs∕GaAs quantum dots
Authors: Schaadt D. M. , Hu D. Z. , Ploog K. H.
Published: August 2006

We have investigated the annealing behavior of InAs quantum dots (QDs) grown on GaAs(001) substrates by molecular beam epitaxy. An in situ cantilever beam setup was employed to record the stress evolution during deposition and subsequent annealing at the growth temperature. Ex situ atomic force microscopy (AFM) was used to characterize the morphological evolution of the QDs. During growth of InAs QDs, a stress of 4.05±0.5GPa develops in the wetting layer. Beyond a critical thickness of 1.5–1.6 monolayer, the strain is relieved by the QD formation. During subsequent annealing the build-up stress relaxes. For annealing at temperatures around 440 and 470°C, QDs undergo standard ripening. Models based on different mechanisms for Ostwald ripening, namely, kinetic and diffusion limited, are developed and fitted to the stress relaxation curves. Although the relaxation curve for annealing at 440°C can be fitted reasonably well with all models, the model describing ripening limited by diffusion along dot boundaries yields a slightly better fit. On the other hand, at 455 and 470°C, the relaxation curve can be fitted very well only with the model in which ripening is controlled by attachment/detachment of atoms on the dot surface. For samples grown and annealed at 500°C, the stress accumulated during QD formation relaxes below the value which was built up by wetting-layer growth. AFM images taken at different annealing stages reveal that the QDs ripen first and then dissolve after 7.5–10min annealing. These observations are explained by a combination of In desorption and interdiffusion between Ga and In.
Epitaxial Bi∕GaAs diodes via electrodeposition
Authors: Bao Zhi Liang , Kavanagh Karen L.
Published: August 2006

Epitaxial Bi∕GaAs diodes have been formed by electrodeposition from bismuth nitrate and ammonium sulfate ((NH4)2SO4) aqueous solutions. Bi grows (0001) oriented on both GaAs (111)B and (001) substrates while it tilts 16° to a (011̱8) surface orientation for (011) GaAs. The metal orients in all cases with its {112̱0} planes parallel the GaAs {110} planes. Diodes prepared on (001), (111)B, and (011) wafers have current-voltage barrier heights ΦBIV that vary from 0.74, to 0.76, to 0.83eV (n=1.01–1.11), respectively. These barrier heights straggle values from earlier reports for polycrystalline Bi deposited by ultrahigh vacuum techniques or electrodeposition. Barrier heights measured from high frequency, capacitance-voltage characteristics are higher than the ΦBIV results, 0.06–1.5eV, as a function of the GaAs orientation, increasing in value in order of (011), (001), to (111)B. This is explained by a combination of image force lowering and field emission corrections, and interface state/dipoles that are likely dependent on the GaAs orientation and on the degree of (0001) Bi alignment. These results are supported by cross-sectional transmission electron microscopy investigations indicating abrupt Bi∕GaAs interfaces without evidence of a significant interfacial oxide or reacted layer.
Three-dimensional nanochannels formed by fast etching of polymer
Authors: Peng C. , Pang S. W.
Published: August 2006

Nanochannels are widely used in biomedical applications such as DNA analysis and biomolecule detection. We report a study using sacrificial polymer and oxide to form three-dimensional (3D) nanochannels. Polymer nanostructures were patterned on Si substrates using optical lithography or nanoimprint lithography, followed by oxide deposition to form the sealed channels. A high-speed dry etching technique for removing the sacrificial polymer was developed using an O2 plasma at high power, high pressure, and elevated temperature. This dry etching technique provides a fast lateral etch rate of 3.91μm∕min for the polymer inside nanochannels, which is an order of magnitude higher than conventional reactive ion etching. High selectivity of 1200 was obtained between the lateral etch rate of polymer inside the nanochannels and the vertical etch rate of oxide. Etch rate dependence on pressure, temperature, and channel width were studied. It was found that the etch rate increases with pressure and temperature. To form multiple levels of nanochannels, the oxide covering the channels was planarized by a photoresist coating and etch-back process. After oxide planarization, the channel formation process is repeated and multiple levels of nanochannels can be stacked to build 3D nanostructures. A two-level channel structure was demonstrated. Interconnect openings between channels of adjacent levels were also demonstrated. With such technique, complex 3D system can be fabricated. Since oxide is transparent to visible light and the channels have hydrophilic surfaces, therefore such a 3D nanofluidic system is suitable for various biomedical studies.