bluuebunny/crossref_metadata_2025 huggingface dataset:
MODELS OF STOCK MARKET PREDICTABILITY
Authors: Malkiel Burton G.
Published: October 2004

I briefly review the success of past studies purporting to explain equity valuations and predict future equity returns. The Campbell‐Shiller mean reversion models are contrasted with an expanded version of the so‐called Federal Reserve model. At least from 1970 to 2003, Federal Reserve–type models did somewhat better at predicting long‐horizon returns than did a mean reversion model based on dividend yields and price‐earnings multiples. However, timing investment strategies based on any of these prediction models do no better than a buy‐and‐hold strategy. Although some predictability of returns exists, there is no evidence of any systematic inefficiency that would enable investors to earn excess returns.
CAN INEFFICIENT TRADERS CREATE VALUE?
Authors: Krishnan C. N. V.
Published: October 2004

I examine the aggregate expected profit generated by informed traders of diverse ability in a competitive market. I assume that efficient traders get perfect information on asset values whereas inefficient traders get noisy information. In the presence of order size restrictions, I show that the aggregate expected profit generated by efficient and inefficient traders together can be higher than that generated by efficient traders alone. Thus, inefficient traders can create value in a constrained trading environment.
ANALYZING STOCK MARKET VOLATILITY USING EXTREME‐DAY MEASURES
Authors: Jones Charles P. , Walker Mark D. , Wilson Jack W.
Published: October 2004

We develop a simple measure of volatility based on extreme‐day returns and apply it to market returns from 1885 to 2002. Because returns are not normally distributed, the extreme‐day measure, which is distribution free, might provide a better measure of stock market risk than the traditional standard deviation. The extreme‐day measure more accurately explains investor behavior relative to standard deviation as shown by equity fund flows, and we find evidence that large negative changes appear to influence investor behavior more than large positive changes.
Riparian Restoration in the Western United States: Overview and Perspective
Authors: Goodwin Craig N. , Hawkins Charles P. , Kershner Jeffrey L.
Published: October 2004

This historical and conceptual overview of riparian ecosystem restoration discusses how riparian ecosystems have been defined, describes the hydrologic, geomorphic, and biotic processes that create and maintain riparian ecosystems of the western USA, identifies the main types of anthropogenic disturbances occurring in these ecosystems, and provides an overview of restoration methods for each disturbance type. We suggest that riparian ecosystems consist of two zones: Zone I occupies the active floodplain and is frequently inundated and Zone I1 extends from the active floodplain to the valley wall. Successful restoration depends on understanding the physical and biological processes that influence natural riparian ecosystems and the types of disturbance that have degraded riparian areas. Thus we recommend adopting a process‐based approach for riparian restoration. Disturbances to riparian ecosystems in the western USA result from streamflow modifications by dams, reservoirs, and diversions; stream channelization; direct modification of the riparian ecosystem; and watershed disturbances. Four topics should be addressed to advance the state of science for restoration of riparian ecosystems: (1) interdisciplinary approaches, (2) a unified framework, (3) a better understanding of fundamental riparian ecosystem processes, and (4) restoration potential more closely related to disturbance type. Three issues should be considered regarding the cause of the degraded environment: (1) the location of the causative disturbance with respect to the degraded riparian area, (2) whether the disturbance is ongoing or can be eliminated, and (3) whether or not recovery will occur naturally if the disturbance is removed.
Prioritizing Watersheds in Oregon for Salmon Restoration
Authors: Nehlsen Willa
Published: October 2004

This paper describes an ecosystem approach (the Bradbury framework) to prioritizing watersheds for watershed restoration and salmon recovery, and gives an example of its application. The framework was applied at three spatial scales (in descending order) to prioritize (1) river basins within the north coast geographic area of Oregon (USA), (2) watersheds within the Tillamook Bay basin, and (3) restoration activities at the watershed level. Implementing the framework identified the Nehalem and Tillamook Bay basins as high priority for the north coast of Oregon. Within the Tillamook Bay basin, the Wilson, Kilchis, and Trask river watersheds emerged as high priority. Preliminary analysis indicated that controlling sediment sources by addressing upland road conditions and allowing floodplain and riparian ecosystems to recover are highest priority protection and restoration activities within the Tillamook Bay basin. The sample application demonstrates that an ecosystem approach (the Bradbury framework) is particularly advantageous where data are limited, although previous identification of relatively intact areas is required. Implementing the framework is intended to lead to restoration of native species, but it may not provide immediate assistance for some species or populations of concern.
Two‐Stage System for Prioritizing Riparian Restoration at the Stream Reach and Community Scales
Authors: Harris Richard , Olson Craig
Published: October 2004

This paper describes a two‐stage system for prioritizing stream reaches and riparian communities along a given river for protection or restoration. The system uses associations between geomorphology and riparian vegetation at stream reach and community scales as a basis for defining reference conditions. First‐stage reach classification involves collecting and analyzing data from topographic maps and aerial photographs. These data, along with judgment‐based criteria for ranking reaches relative to reference conditions, are used to classify stream reaches as suitable for protection, recommended for mitigation or restoration within existing site‐specific regulatory procedures, or requiring further analysis to evaluate community‐scale restoration needs. Second‐stage field sampling is conducted on the reaches needing further analysis to determine the riparian communities present, the associations between communities and floodplain landforms, and reference community conditions. This stage requires collection of field data on geomorphic conditions, plant species composition, and plant community structure. Cluster analysis or a comparable technique is used to classify plant communities associated with floodplain landforms and identify reference conditions for each landform. Community structure and species composition are compared to reference conditions to define restoration possibilities at the community scale. The combined results from stream reach and community‐scale analysis provide a strategy for protecting and restoring riparian resources for a whole river. Implementation requires further site‐specific information on hydrology, geomorphology, and other factors.
Vulnerability of Riparian Vegetation to Catastrophic Flooding: Implications for Riparian Restoration
Authors: Hawkins Charles P. , Bartz Kate L. , Neale Christopher M. U.
Published: October 2004

In this study, we examined the site‐specific effects of a large episodic flood on the riparian vegetation within the floodplain of the San Luis Rey River in southern California. Using multispectral airborne videography, we quantified percent cover of riparian vegetation, cultivated agricultural land, urban surfaces, upland vegetation, bare soil, and water within 22 sections of floodplain, both before and after a large flood (January 13, 1993). We also quantified the amount of these cover types within bands of the watershed 1 km wide × 5 km long directly upstream of each floodplain site. The amount of riparian vegetation destroyed by the flood within each section varied from nearly zero to almost 40% of pre‐flood coverage. The magnitude of loss in riparian vegetation was most strongly related to the amount of riparian vegetation initially present in the floodplain and the amount of urban surfaces in the nearby watershed. These results suggest that riparian vegetation within the San Luis Rey River floodplain is generally at high risk of destruction from large floods, and that this risk is exaggerated in areas with high urban development. We infer from these results that sites near existing large areas of intact riparian vegetation and away from urban development will have the highest potential for successful long‐term restoration.
Abnormal craniofacial development and expression patterns of extracellular matrix components in transgenic Del1 mice harboring a deletion mutation in the type II collagen gene
Authors: Savontaus M , Rintala‐Jämsä M , Morko J , Rönning O , Metsäranta M , Vuorio E
Published: October 2004

Structured Abstract

Authors – Savontaus M, Rintala‐Jämsä M, Morka J, Rönning O, Metsäranta M, Vuorio E

Objective – To analyze the effect of a type II collagen mutation on craniofacial development in transgenic Del1 mice.

Design – Samples from homozygous (+/+) and heterozygous (+/−) transgenic Del1 mice harboring mutations in the type II collagen gene as well as non‐transgenic (−/−) littermates were collected at days 12.5, 14.5, 16.5 and 18.5 of gestation. The cartilaginous and bony elements of the craniofacial skeleton were analyzed after staining with alcian blue, alizarin red S and von Kossa. The expression patterns of type II, IX and X collagens and aggrecan were analyzed by immunohistochemistry and in situ hybridization.

Results – Several abnormalities were observed in the craniofacial skeleton of transgenic Del1 mice. These include an overall retardation of chondrogenesis and osteogenesis in Del1 +/+ mice, and to a lesser extent also in Del1+/− mice. Characteristic findings in Del1 +/+ mice included a reduced anterioposterior length, a smaller size of the mandible, a palatal cleft and a downward bending snout. We also detected retarded ossification of calvarial bones in Del1 +/+ and +/− mice when compared with Del1 −/− mice. A surprising finding was the presence of both type II and X collagens and their mRNAs in the periosteum of the cranial base.

Conclusion – The present study confirms the important role of type II collagen mutation in craniofacial development and growth. In addition to affecting endochondral ossification, the type II collagen mutation also disturbs intramembranous ossification in the developing craniofacial skeleton.
The efficacy of a fluoride varnish in reducing enamel demineralization adjacent to orthodontic brackets: an in vitro study
Authors: Demito CF , Vivaldi‐Rodrigues G , Ramos AL , Bowman SJ
Published: October 2004

Structured Abstract

Authors – Demito CF, Vivaldi‐Rodrigues G, Ramos AL, Bowman SJ

Objectives – To test the hypothesis that fluoride varnish is effective in reducing demineralization (white spot) lesions adjacent to bonded orthodontic brackets.

Design – Two similar samples of extracted bovine incisors, with bonded orthodontic brackets, were separated into an experimental group (fluoride varnish was applied) and control group (no fluoride varnish) to examine the preventive effects of fluoride varnish.

Setting and Sample Population – The dental clinic of the State University of Maringá– UEM (Maringá, Paraná, Brazil). Thirty‐eight extracted bovine incisors with bonded orthodontic brackets.

Experimental Variable – Fluoride varnish was applied topically to half of the sample of extracted bovine teeth. No varnish was applied to the other half.

Outcome Measure – The depths of enamel demineralization (white spot) lesions were measured from polarized light microscopy images using image analysis software.

Results – The teeth in both the experimental and control groups had been exposed to a cariogenic environment twice a day for 35 days. Those teeth that had been treated with two applications of fluoride varnish (one at the outset and another 15 days later) demonstrated about 38% less mean lesion depth than teeth where no varnish had been applied.

Conclusion – Orthodontists may wish to consider the application of fluoride varnish during fixed orthodontic therapy to help reduce the development of enamel white spot lesions.
The Use of Aniline Blue for the Determination of Dead Phytoplankton, Zooplankton and Meroplankton in LC50 Testings After 96 Hours… A Re-Evaluation of the US Environmental Protection Agency Methodology
Authors: Seepersad Balram , Ramnath Kelvin , Dyal Shyam , Mohammed Reeza
Published: October 2004

There is a need for a reliable staining technique to distinguish between live and dead organisms following LC50 tests. This is especially so in cases where organisms can be stressed or even become unconscious and appear dead to the aided or naked eyes. Visual observations under such conditions can result in an LC50 value shifting to the lower concentration thereby imposing stiffer guidelines for compliance. Aniline blue can only stain individuals which are physiologically dead imposing an accurate live-dead evaluation and producing a true LC50 value. Guidelines imposed using such data will facilitate compliance and provide an accurate value for an LC50.
Configuring Marine Riser Tapered Stress Joints Used in Top-Supported Applications
Authors: Gordon Cormack C. , Dareing Don W.
Published: October 2004

The objective of this paper is to present a direct and useful method for establishing the configuration of tapered stress joints for marine risers so that stress levels are fairly balanced over the length of the stress joint and within acceptable stress levels. The method of solution approximates straight tapered stress joints with one, whose cross sectional moment of inertia varies parabolically along the stress joint. This approximation leads to the classic Euler type differential equation, which can be solved directly giving a closed form solution. The formulation of deflection and stresses should be of use to designers of marine tubulars. Even though the focus of the study is on a static analysis of top located stress joints, the method of solution can be adapted to mudline attachment locations as well as dynamic analyses.
Flow Patterns in Heavy Crude Oil-Water Flow
Authors: Bannwart Antonio C. , Rodriguez Oscar M. H. , de Carvalho Carlos H. M. , Wang Isabela S. , Vara Rosa M. O.
Published: October 2004

This paper is aimed to an experimental study on the flow patterns formed by heavy crude oil (initial viscosity and density 488 mPa s, 925.5kg/m3 at 20°C) and water inside vertical and horizontal 2.84-cm-i.d. pipes. The oil-water interfacial tension was 29 dyn/cm. Effort is concentrated into flow pattern characterization, which was visually defined. The similarities with gas-liquid flow patterns are explored and the results are expressed in flow maps. In contrast with other studies, the annular flow pattern (“core annular flow”) was observed in both horizontal and vertical test sections. These flow pattern tends to occur in heavy oil-water flows at low water input fractions. Because of the practical importance of core flow in providing an effective means for heavy oil production and transportation, this paper discusses criteria that favor its occurrence in pipes.
A Numerical Model Coupling Reservoir and Horizontal Well Flow Dynamics—Applications in Well Completions, and Production Logging
Authors: Vicente Ronaldo , Sarica Cem , Ertekin Turgay
Published: October 2004

A fully implicit, three-dimensional simulator with local grid refinement around the wellbore is developed to solve reservoir and horizontal well flow equations simultaneously, for single-phase liquid and gas cases. The model consists of conservation of mass and Darcy’s law in the reservoir, and mass and momentum conservation in the wellbore for isothermal conditions. Establishing the continuity of pressure and preserving mass balance at the sandface satisfy the coupling requirements. The proposed simulator is tested against and verified with the results obtained from a commercial code ECLIPSE-100™, and available public domain simulators and semi-analytical models. The proposed model can be used for multiple purposes such as well productivity prediction, transient analyses, well length optimization, completion design and optimization, and production logging interpretation. Different completion scenarios and reservoir anisotropy are simulated and their effects on the productivity of the horizontal wells are discussed. Completion cases include open-hole and partial completions. During the production logging of a horizontal well, the coil tubing reduces the wellbore cross sectional area and may cause substantial changes in the wellbore flow behavior. Depending on the well and coil tubing diameters, a significant difference between the actual production rates and the rates obtained from a production log can be observed.
Controllable fabrication of fiber nano-tips by dynamic chemical etching based on siphon principle
Authors: Gu Ning , Li Chang-an , Sun Long , Liu Zhan-hui , Sun Yong-kang , Xu Li-na
Published: October 2004

A dynamic chemical etching method based on siphon principle has been developed for controllable fabrication of fiber nano-tips, which could be used in near-field optical microscope and optical nanosensors. Compared with traditional static chemical etching, this method has advantages such as reproducibility, controllability, convenience, less cost, and making tip surface smooth. The overall shape and the tape angle of the tip can be effectively controlled through the speed and direction of water flux. Tips with taper angles from 20° to 55°, and tips with double tapers have been achieved by this method.
Changes in electrical and optical properties of p-AlGaN due to proton implantation
Authors: Polyakov A. Y. , Smirnov N. B. , Govorkov A. V. , Baik K. H. , Pearton S. J. , Zavada J. M.
Published: October 2004

The effects of proton implantation with energy of 100keV on the electrical, optical and luminescent properties of p-AlGaN films are reported. The proton implantation leads to a decrease in the concentration of uncompensated shallow acceptors and, after high implantation doses, to formation of highly resistive compensated material. The dominant deep traps observed in implanted p-AlGaN films are hole traps with activation energy of 0.26, 0.4, and 0.9eV. Proton implantation is also shown to lead to a decrease in the intensity of near-band-edge microcathodoluminescence and, after high implantation doses, to the emergence of a yellow luminescence band.
Interface-blocking mechanism for reduction of threading dislocations in SiGe and Ge epitaxial layers on Si(100) substrates
Authors: Yang T. H. , Luo G. L. , Chang E. Y. , Hsieh Y. C. , Chang C. Y.
Published: October 2004

A mechanism of interface blocking was proposed to reduce the threading dislocations in the SiGe and Ge layers on Si(100) substrates. In this work, epitaxial Si1−xGex∕Si1−(x−y)Gex−y and Ge∕SiyGe1−y layers were grown by UHV/CVD. It was surprisingly found that if the variation of the Ge composition, y, across the interface of Si1−xGex∕Si1−(x−y)Gex−y or Ge∕SiyGe1−y is higher than a certain value, most of the threading dislocations appear to be blocked and confined in the underlying Si1−(x−y)Gex−y or SiyGe1−y layer by the interface. It implies that this finding can provide a simple way to grow high-quality relaxed SiGe and Ge layers on the Si substrates.
Equivalent oxide thickness reduction of interpoly dielectric using ALD-Al2O3 for flash device application
Authors: Lee Tai-Peng , Jang Chuck , Haselden Barbara , Dong Mark , Park Seung , Bartholomew Lawrence , Chatham Hood , Senzaki Yoshihide
Published: October 2004

An interpoly dielectric stack consisting of silicon dioxide, aluminum oxide, and silicon dioxide (OAO stack) has been proposed to replace the oxide-nitride-oxide (ONO) stack in flash memory. Atomic layer deposition and annealing conditions of Al2O3 films were studied to achieve low equivalent oxide thickness (EOT) and leakage current. Aluminum oxide films were deposited from alternating pulses of trimethylaluminum and ozone. The within-wafer nonuniformity and wafer-to-wafer thickness repeatability were both typically below 1.0% (1σ). The OAO interpoly dielectric exhibited leakage current density below 0.1μA∕cm2 at an electric field of 5MV∕cm while an 11% reduction in EOT to 12.5nm was achieved as compared with an ONO stack. The OAO stack has higher breakdown field and greater charge to breakdown than the ONO stack.
Direct CoSi2 thin-film formation with homogeneous nanograin-size distribution by oxide-mediated silicidation
Authors: Chang Juin-Jie , Liu Chuan-Pu , Chen Shih-Wei , Chang Chih-Chia , Hsieh Tsung-Eong , Wang Ying-Lang
Published: October 2004

By annealing at 460°C for 120s followed by 600°C120s, nanocrystalline CoSi2 thin film with an average grain size of 5nm can be directly formed from a Co∕SiOx∕Si multilayer with the SiOx as a mediated layer. It is found that annealing at 460°C for enough time is crucial for generating enough diffusion channels within the SiOx layer. After these channels are created, subsequent annealing at 600°C keeps these channels open and is responsible for rapid grain growth. In other words, by using two-step annealing, nucleation and growth processes can be effectively controlled and, hence, the resulting microstructure. The homogeneous nanograin-size distribution is important for ultralarge-scale integration technology below 90nm to prevent resistance degradation induced by CoSi2 agglomeration.
Strain relaxation and surface roughness of InxAl1−xAs graded buffer layers grown on InP for 6.05Å applications
Authors: Noori A. M. , Sandhu R. S. , Hayashi S. L. , Meserole E. D. , Hardev V. , Cavus A. , Lange M. , Monier C. , Hsing R. , Sawdai D. , Wojtowicz M. , Block T. R. , Gutierrez-Aitken A. , Goorsky M. S.
Published: October 2004

In this study, metamorphic compositionally graded InxAl1−xAs layers grown on InP by molecular beam epitaxy with a final indium mole fraction of x=1.0(6.05Å) are investigated. To examine the effects of relative growth temperature on strain relaxation and surface morphology at different stages of the buffer layer growth, a series of samples was produced with the indium mole fraction graded from x=0.52tox=0.64, 0.79, and 1.0 with a constant grading rate. The high misfit dislocation velocity in this system allows the grading to be accomplished with a thin layer (∼1μm), complete strain relaxation and low threading dislocation densities. The evolution of the strain relaxation, threading dislocation density, and surface morphology were evaluated by triple axis x-ray diffraction, transmission electron microscopy (TEM), etch pit density (EPD), and atomic force microscopy. Higher growth temperature led to threading densities as low as 106cm−2, as measured by plan-view TEM and EPD. The final surface roughness was controlled by the growth temperature of a constant composition cap layer.
System optimization of membrane mask distortion correction based on Fourier analysis
Authors: Murooka Ken-ichi , Lim Michael H. , Smith Henry I.
Published: October 2004

We have studied the distortion correction scheme of a membrane mask in the spatial frequency domain by using Fourier analysis. The relationship between stress and distortion tells us that distortion is inversely proportional to spatial frequency, which means the high spatial frequency component of the stress has little effect on the distortion. Also, the Fourier analysis of the thermal diffusion compensation tells us that the heat input is required to be large as the spatial frequency becomes large, i.e., the upper limit of the heat input power gives the upper limit of the correctable spatial frequency in the distortion correction. Assuming that the total heat input power is 100 W, and the membrane is 1 μm thick SiNx in air, it turned out that the acceptable stress in low spatial frequency region is about 200 MPa, and the distortion correction system is required to have only the spatial frequency corresponding to the wavelength of 0.26 mm or more, which can be easily implemented with a commercially available 640×480 Video Graphics Array resolution system.
High performances of InGaP∕InGaAs∕GaAs pseudomorphic modulation-doped field effect transistors using camel-gate structure
Authors: Tsai Jung-Hui , Zhu King-Poul , Chiu Shao-Yen , Chu Ying-Cheng
Published: October 2004

In this article, high-performance InGaP∕InGaAs∕GaAs δ-doped pseudomorphic modulation-doped field effect transistors (pMODFETs) employing n+-GaAs∕p+-InGaP∕n-InGaP camel-gate structure are characterized. Because of the depleted p-n junction in the gate region and the presence of the large conduction-band discontinuity of the InGaP∕InGaAs heterostructure, a large gate turn-on voltage is obtained. The dc and microwave characteristics of single- and double-δ-doped pMODFETs are demonstrated. The double-δ-doped pMODFET exhibits a higher drain saturation current, a larger transconductance, a broader gate voltage swing, and better high-frequency responses than the single-δ-doped device. The excellent performance of the studied devices is promising for linear and large signal amplifiers and high-frequency circuit applications.
Thermally grown ruthenium oxide thin films
Authors: Jelenkovic Emil V. , Tong K. Y.
Published: October 2004

Thin ruthenium films were sputtered on oxidized silicon wafers and subsequently thermally oxidized in oxygen∕nitrogen or oxygen ambient in the temperature range from 400 to 700 °C. The morphological and structural properties of grown ruthenium oxide films were analyzed by atomic force microscopy, Raman spectroscopy, and x-ray diffraction, with electrical properties analyzed by van der Pauw technique and metal–oxide semiconductor (MOS) structures. Significant roughening of RuO2 was observed for prolonged oxidation in oxygen∕nitrogen atmosphere, or for short times in pure oxygen atmosphere. Raman spectroscopy revealed superior structural properties of thermally grown RuO2, in comparison to sputtered or metalorganic chemical vapor deposition RuO2 films. Thermally grown RuO2 is shown to have a work function of 5.1 eV, making it a suitable choice of metals, together with Ru (4.6 eV work function) for electrodes in complementary MOS n-channel and p-channel transistors.
Formation of p+ shallow junctions using SiGe barriers
Authors: Thompson Phillip E. , Crosby Robert , Bennett Joe , Felch Susan
Published: October 2004

Ultrashallow p+ junctions are required for next generation electronics. We present a technique for the formation of ultrashallow p+ junctions that increases the thermal stability of the junctions formed by either epitaxy or ion implantation. By using a 10nm Si1−xGex barrier layer, the diffusion of B is inhibited during high temperature processes. Alloys having a composition from x=0–0.4 were investigated and it is shown that the most effective barrier had the maximum Ge fraction. The junction depth decreased to 36.7nm for a 5×1015∕cm2 1kV BF3 plasma implant spike annealed at 1050°C, compared to a junction depth of 48nm for a Si control sample having the identical implant and anneal. It is hypothesized that the inhibition of B diffusion in the alloy layer is caused by a reduction of the Si self-interstitials in the alloy.
Surface photovoltage spectroscopy of metamorphic high electron mobility transistor structures
Authors: Solodky S. , Baksht T. , Khramtsov A. , Leibovitch M. , Hava S. , Shapira Yoram
Published: October 2004

In Al As ∕ In Ga As metamorphic high electron mobility transistor (MHEMT) epitaxial structures have been characterized using surface photovoltage spectroscopy (SPS). The measurements have been extended to pseudomorphic high electron mobility transistor (PHEMT) epitaxial structures and to complete devices. The direct current characteristics of the latter were also measured. An empirical model, which correlates the top and bottom delta-doping concentrations (δtop and δbot) and the surface charge density Qsur with spectral features, has been applied to the MHEMT and PHEMT structures before and after processing. The results show correlations between extracted Qsur and the measured threshold voltage and drain saturation current of the devices. The analysis shows general correlations between epistructure parameters and final device performance and indicates the universality of the model for the different HEMT structures. Thus, SPS is sensitive not only to epitaxial structure parameters but to final device performance and may be used for technology evaluation from the wafer incoming inspection stage to the final device.
Linear alignment of SiC dots on silicon substrates
Authors: Cimalla V. , Schmidt A. A. , Stauden Th. , Zekentes K. , Ambacher O. , Pezoldt J.
Published: October 2004

A linear alignment of self-assembled, cubic SiC dots grown by molecular beam epitaxy on Si substrates is demonstrated. The formation of well-ordered biatomic steps on (111) Si was used to control the nucleation sites. The resulting terraces promote an alignment along their step edges. SiC on Si represents self-organization in a system with chemical interactions. The resulting instability of the Si surface during the nucleation requires a precise control of the process conditions. By atomic force microscopy we demonstrate the achieved linear chains of SiC dots.
Effectiveness of reactive sputter-deposited Ta–N films as diffusion barriers for Ag metallization
Authors: Adams Daniel , Malgas Gerald F. , Theodore N. David , Gregory Rich , Kim H. C. , Misra E. , Alford T. L. , Mayer J. W.
Published: October 2004

Tantalum nitride films on silicon were prepared by reactive sputtering of Ta under nitrogen partial flow rates varying from 15% to 40% N2. Rutherford backscattering spectroscopy (RBS) and x-ray diffraction (XRD) analysis revealed that the composition and phases of the Ta–N films were influenced by the N2 flow rate. Increasing the nitrogen partial flow rate from 25% to 40% N2, results in the films changing from metal-rich to stoichiometric Ta–nitride. High N2 flow rates (30%–40% N2) resulted in a disordered tantalum–nitride. The tantalum nitride films were evaluated as potential diffusion barriers for Ag metallization. Sheet resistance measurements, XRD and RBS analysis confirmed that Ta–N films, used as diffusion barriers in the Ag∕Ta–N∕Si system, were thermally stable up to 650°C when annealed for 30min in vacuum. The thermal stability was independent of N2 flow rate within this temperature range. However, at 700°C, the barrier failed as a result of Ta–silicide formation by reaction with the underlying Si substrate, and dewetting of Ag on Ta–N occurred.
Studies of the driving force for room-temperature microstructure evolution in electroplated copper films
Authors: Lee Haebum , Nix William D. , Wong S. Simon
Published: October 2004

The fundamental mechanism of room-temperature grain growth during self-annealing in electroplated Cu films has been an issue of great interest. We have investigated the microstructure evolutions in a variety of electroplated Cu films prepared with different plating rates and their correlation with the crystalline defects in the as-deposited films. The recrystallization process in all Cu films is greatly accelerated as the plating current density is increased, while the grains are initially small and about the same in sizes (∼0.1μm) in as-deposited films regardless of the plating current density. Using plan-view transmission electron microscopy imaging, the existence of a high density of dislocation loops is demonstrated successfully in the pre-recrystallization grains of as-deposited Cu films. The density of the dislocation loops is higher for the film deposited at higher plating current density (higher plating rate). These observations lead us to propose that the change of self-annealing rate with the plating rate is related to the dislocation loop density in the film before the self-annealing starts. Plating with high deposition rate produces a large amount of intrinsic stress induced by the formation of dislocation loops and increases the total energy stored in the Cu film, which will act as the major driving force for self-annealing process. Kinetic calculations including this effect in the driving force for the self-annealing process give a good correspondence to the experimental observations.
Influence of radio frequency plasma cell conditions on the incorporation of nitrogen into GaAsN and GaInAsN
Authors: Carrère H. , Arnoult A. , Bedel-Pereira E. , Ricard A.
Published: October 2004

We have studied the influence of rf plasma cell operating conditions on the plasma assisted molecular beam epitaxy growth of bulk GaAsN and GaInAsN quantum wells. A plasma physics approach together with optical spectroscopy of the plasma emission lines and bands have been performed in order to understand the mechanisms of nitrogen incorporation and material deterioration. Both atoms and molecules do participate in the incorporation of N into the growing material. For high N2 flow rates, the species that mostly incorporate are vibrationaly excited molecules of the N2(X,v) ground state. The characteristic vibrational temperature of the N2(X,v) ground state has been found to be higher than 104K. For low N2 flow rates, the species that mostly incorporate are atoms and the dissociation fraction of N2 for the lowest flow rate and the highest rf power has been found to be up to 0.7. Finally, the ion damage has been decreased by increasing the N2 pressure, which induces a decrease of the electron temperature and consequently a decrease of the plasma ionization.
Diffusion barrier properties of metalorganic chemical vapor deposition -WNx compared with other barrier materials
Authors: Lee Brad H. , Yong Kijung
Published: October 2004

Tungsten nitride (WNx) is a potentially strong candidate for Cu diffusion barrier. The WNx films were deposited by chemical vapor deposition (CVD) using W(CO)6 and NH3 sources at 430°C. The diffusion barrier properties of WNx were investigated by comparison with other materials. In order to study the barrier properties, Cu/barrier/substrate structures were fabricated. A 120-nm-thick Cu film was deposited by evaporation onto various barrier materials including CVD-WNx, CVD-W, and sputter-deposited Ti,Ta, and TaN. After annealing for 1h in argon, variations in the film sheet resistances and the x-ray diffraction patterns were examined. Both results showed that a 15-nm-thick W2N film prevented Cu diffusion up to 600°C, and started to fail at 620°C, while no barrier and the CVD-W barrier samples failed at 100–150°C and 525–550°C, respectively. Also, 20nm sputtered Ti,Ta, and TaN films failed at 400–450°C, 550–575°C, and 650–700°C, respectively, in our annealing conditions. From these results, our WNx, deposited by CVD using the simple, nonfluorine precursor, W(CO)6, can be evaluated as a competent diffusion barrier candidate.
B diffusion in Si with pre-amorphization of different species
Authors: Li Hong-Jyh , Zeitzoff Peter , Larson Larry , Banerjee Sanjay
Published: October 2004

Boron diffusion in Si in shallow pre-amorphization implants (SPAI) of different species, including F, Ge, GeF2, BF2, and their combination was studied. Results show that different species have different impact on B diffusion. In addition to the chemical effect, the interaction of SPAI species with B, leading to immobile B clustering, is another important cause for B diffusion reduction. Fluorine is more effective than Ge in the B diffusion reduction. Adding more F in the amorphous region results in more B diffusion reduction. Aside from the effect on the B diffusion, fluorine itself manifests a large amount of out-diffusion for the shallow F implant case and as F is implanted deeper, a bell-shaped F profile exists around the end-of-range damage. The out-diffusion of F is further enhanced by the implanted damage.
Structural and chemical characterization of functional SiOxCy:H coatings for polymeric lenses
Authors: Fernández-Hidalgo P. , Martín-Palma R. J. , Conde A. , Gago R. , Simancas J. , García-Diego I. , Egio A. , Martínez-Duart J. M.
Published: October 2004

The deposition of suitable hard protective coatings onto organic substrates for ophthalmic applications faces several challenges, such as proper surface preparation to ensure the adhesion to the rigid substrate and a delicate balance between hardness and flexibility. In this work it is shown that SiOxCy:H-based protective coatings grown by plasma enhanced chemical vapor deposition (PECVD) from mixtures of hexamethyldisiloxane and oxygen, can be used as protective buffer coatings between the soft and easily scratchable substrate and the antireflection stack that might be applied on top of it. These coatings must show absence of optical absorption and require index matching with the substrate. To meet these conditions, a three-phase multifunctional coating PECVD deposition method has been developed, in which a progressive decrease towards the surface in the carbon content of the SiOxCy:H hard coat has been implemented. Fourier transform infrared spectroscopy, x-ray photoelectron spectroscopy and Rutherford backscattering spectroscopy characterization of the individual layers that compose the multilayer functional structure has been performed. The comparison of the results obtained from each spectroscopy shows the complementarity of these techniques and allows optimizing the protective coating performance from the optical and mechanical points of view.
Comparative study of Ti∕Al∕Mo∕Au, Mo∕Al∕Mo∕Au, and V∕Al∕Mo∕Au ohmic contacts to AlGaN∕GaN heterostructures
Authors: Selvanathan Deepak , Mohammed Fitih M. , Tesfayesus Asrat , Adesida Ilesanmi
Published: October 2004

Ohmic contact formation by Ti∕Al∕Mo∕Au, Mo∕Al∕Mo∕Au, and V∕Al∕Mo∕Au on AlGaN∕GaN heterostructure field effect transistor layers have been studied and compared. Mo∕Al∕Mo∕Au ohmic contacts exhibited the lowest contact resistance of 0.22±0.02Ωmm over a range of anneal temperatures from 650to800°C. The minimum contact resistances of Ti∕Al∕Mo∕Au and V∕Al∕Mo∕Au ohmic contacts were measured to be 0.38±0.04Ωmm at an anneal temperature of 800°C and 0.35±0.07Ωmm at an anneal temperature of 700°C, respectively. Long-term thermal stability measurements were performed at 500, 600, and 700°C. Of the three metallization schemes, Ti∕Al∕Mo∕Au exhibited the best thermal stability (up to 8.5h at 700°C). Intermetallic reactions were investigated using Auger electron spectroscopy and x-ray diffraction measurements.
Surface segregation of photoresist copolymers containing polyhedral oligomeric silsesquioxanes studied by x-ray photoelectron spectroscopy
Authors: Eon D. , Cartry G. , Fernandez V. , Cardinaud C. , Tegou E. , Bellas V. , Argitis P. , Gogolides E.
Published: October 2004

Copolymers containing polyhedral oligomeric silsesquioxane (POSS) pendant groups and various acrylate type monomers are studied by x-ray photoelectron spectroscopy. These copolymers have potential application as bilayer resist material for next generation lithography. Two methods are used in order to characterize resist surfaces, angular resolved XPS and inelastic background signal quantification (Tougaard method). The existence of a surface layer rich in POSS is proven. About 1.5nm thick, this layer stands above a material with uniform POSS concentration. Evaluation of POSS concentration depth profiles shows that surface segregation depends on the polymer comonomers and on the silicon content.
Effects of Cu at the device junction on the properties of CdTe∕CdS photovoltaic cells
Authors: Berniard T. J. , Albin D. S. , To B. , Pankow J. W. , Young M. , Asher S. E.
Published: October 2004

Fabrication techniques used in processing cadmium telluride (CdTe) solar cell devices have been shown to introduce copper (Cu) into the cell structure. In fact, an accumulation of Cu in the cadmium sulfide (CdS) region has been seen, especially after back-contact processing. However, exactly how the presence of Cu near the device junction affects performance has yet to be determined. This study explores how CdS films are affected by Cu diffusion from a metallic layer and how these Cu-diffused layers (CdS:Cu) change the properties of thin-film CdS∕CdTe devices. Spectrophotometric analysis shows the optical bandgap of CdS films was 2.31eV following thermal diffusion of a 50Å Cu layer, compared to 2.43eV for CdS films that did not contain Cu. Characterization of the CdS:Cu films using grazing incidence x-ray diffraction (GIXRD) also produced noticeable shifts in the CdS peaks, likely due to Cu incorporation in the films. GIXRD, supported by Auger electron spectroscopy data, indicate that a Cu gradient is present in the CdS films as a result of the Cu treatments. Devices were completed using the CdS:Cu films, and the resulting performance was compared with standard CdS∕CdTe devices (i.e., no Cu evaporated at the interface). Standard devices had an open-circuit voltage (Voc) of 825mV, short-circuit current (Jsc) of 21mA∕cm2, fill factor (FF) of 64.2%, and efficiency (%η) of 11.1%. A similar device stressed for 900h had a Voc of 726mV, Jsc of 21mA∕cm2, FF of 29.2%, and efficiency of 6.9%. The device with a 10Å Cu layer diffused into the CdS (unstressed) had a Voc of 651mV, Jsc of 20.2mA∕cm2, FF of 44.2%, and efficiency of 5.8%. Similar trends in the performance parameters are seen between the stressed cell and the cell containing CdS:Cu. Modeled quantum efficiency (QE) curves for CdTe devices showed a reduction and shifting of the QE response near 500nm as the bandgap of the CdS is shifted to lower energy. This is consistent with trends in the QE curves, as a standard CdS∕CdTe device goes from an unstressed to a stressed state. The presence of Cu at the interface, perhaps incorporated in the CdS layer, may help explain the degradation seen in standard CdTe devices.
Study of the evolution of nanoscale roughness from the line edge of exposed resist to the sidewall of deep-etched InP∕InGaAsP heterostructures
Authors: Jang J. H. , Zhao W. , Bae J. W. , Adesida I. , Lepore A. , Kwakernaak M. , Abeles J. H.
Published: October 2004

The evolution of line edge roughness and sidewall roughness was monitored during the fabrication of deep-etched optical waveguides in InP∕InGaAsP heterostructures. Scanning electron microscopy was used to extract line edge profiles of the electron beam exposed resist and the lifted-off NiCr metal mask. Atomic force microscopy with an ultrasharp tip was utilized to extract the sidewall profiles of InP∕InGaAsP mesa waveguides that were etched using inductively coupled plasma reactive ion etching. The processing step that critically influences the roughness of the etched waveguides was determined by studying the evolution of the roughness.
Imprinting of polymer at low temperature and pressure
Authors: Tan L. , Kong Y. P. , Pang S. W. , Yee A. F.
Published: October 2004

We have developed a method to pattern polymeric materials, including nonthermoplastic polymers and biomaterials, at low temperature and low pressure. In this method, plasticizers are added to increase the chain mobility of the polymers, resulting in lower imprinting temperature and/or pressure. Three established imprinting and transfer techniques were chosen to demonstrate this method: conventional nanoimprint lithography (NIL), microcontact printing (μCP), and soft ink-pad (SIP). These three techniques were used to pattern poly(3,4-ethylenedioxythiophene) (PEDOT) and chitosan. PEDOT and chitosan were chosen because both of them are nonthermoplastic polymer and therefore cannot be easily patterned using conventional NIL. Imprinting of PEDOT and chitosan films from the poly(dimethylsiloxane) mold was achieved at a low pressure of 10kPa and 25°C by controlled addition of glycerol as a plasticizer using conventional NIL; well-defined arrays of 2μm wide, 185nm high PEDOT dots have also been demonstrated by μCP; and residual-layer-free recessed PEDOT circles 2μm in diameter were formed by SIP. In contrast, patterning of PEDOT film without plasticizer requires higher temperature (80°C) and pressure (10MPa), which could cause severe deformation of the transferred patterns. This method of plasticizer-assisted imprint lithography broadens the applicability of NIL to a wide range of polymeric materials.
Inverted sidewall spacer and inner offset oxide process for excellent 2-bit silicon-oxide-nitride-oxide-silicon memory under 100nm gate length
Authors: Lee Yong Kyu , Lee Jong Duk , Park Byung-Gook , Kang Sung Taeg , Chung Chilhee , Park Donggun
Published: October 2004

By forming physically separated 30nm twin ONOs with an inverted sidewall spacer patterning method under a single gate based on damascene gate process, problems of the charge distribution and diffusion during and after the channel hot electron injection program in the 2-bit operation of the localized trap memory were cleared out. The two charge storage nodes of nitride with length of 30nm under the 100nm channel length can be created by adopting inverted amorphous polysilicon spacer and inner offset oxide process made in the groove. This inverted amorphous silicon spacer process does not suffer from unit-cell size increase, photoresolution limit, nor photo misalign between gate and oxide-nitrogen-oxide structures. In addition, the inner offset oxide protects the ultrathin amorphous Si spacer from the loss due to the subsequent etch process and plays an important role of minimizing the overlap between gate and source/drain. In this structure, the spatial distribution can be controlled and lateral charge diffusion is blocked, so that stable 2-bit operation with high erase speed and reliabilities such as endurance and retention can be achieved, compared with the conventional single silicon-oxide-nitride-oxide-silicon structure under 100 nm regimes.
Periodic structure formation by focused electron-beam-induced deposition
Authors: Bret T. , Utke I. , Gaillard C. , Hoffmann P.
Published: October 2004

Focused electron-beam-induced deposition from a copper precursor is shown to allow self-formation of periodic features when the beam is scanned at lateral speeds of the order of the vertical deposition rate. The period of the structures can be tuned by the scan speed. Simultaneous monitoring of the electron-beam-induced sample current and secondary electron signal shows in situ evidence of the phenomenon. The spatial distribution of scattered electrons and the influence of the structure geometry on the deposition yield are discussed. The growth rate decreases with increasing distance from the substrate. This is a growth reduction counterpart to the constant electron flow and induces the periodicity. A semi-empirical model is proposed. The study widens the understanding of the mechanism of focused electron-beam-induced deposition. This understanding will help with the future design of complex three-dimensional nanoarchitectures.
Investigation into the effects of aluminum cathode modification and ion-beam-induced damage in organic light-emitting devices
Authors: Jeong Soon Moon , Koo Won Hoe , Choi Sang Hun , Jo Sung Jin , Baik Hong Koo , Lee Se-Jong , Song Kie Moon
Published: October 2004

We report a fabrication of organic light-emitting diodes (OLEDs) based on soluble phenyl-substituted poly-p-phenylene-vinylene (Ph-PPVs) thin films with aluminum cathode prepared by ion-beam-assisted deposition (IBAD). The electrical properties of the aluminum cathode, prepared by IBAD, on Ph-PPV have been investigated and compared to those by thermal evaporation. Energetic particles of Al assisted by an Ar+ ion may damage the organic material generating undesirable leakage current even though a thin Al buffer layer is applied to avoid Ar+-ion-induced damages. Substantial improvements of passivation characteristics were observed in IBAD device because the dense Al cathode inhibits the permeation of H2O and O2 into Ph-PPV film through pinhole defects, and thus retards dark spot growth. These results may be deduced from the highly packed structure that has small contact resistance between Al and Ph-PPV in ion-beam-assisted aluminum devices.