bluuebunny/crossref_metadata_2025 huggingface dataset:
Computer Aided Loaded Tooth Contact Analysis in Cylindrical Worm Gears
Authors: Simon Vilmos
Published: August 2005

A method for computer aided loaded tooth contact analysis in different types of cylindrical worm gears is proposed. The method covers both cases—that of the theoretical line and point contact. The geometry and kinematics of a worm gear pair based on the generation of worm gear teeth by a hob is presented. The full loaded tooth contact analysis of such a gear pair is performed. A computer program based on the theoretical background presented has been developed. By using this program the path of contact, the potential contact lines, the separations of mating surfaces along these contact lines, the load distribution and transmission errors for different types of modified and nonmodified worm gear pairs are calculated and graphically presented. The influence of gear tooth modifications on tooth contact is investigated and discussed.
Geometric Modeling and Meshing Characteristics of the Toroidal Drive
Authors: Yao Ligang , Dai Jian S. , Wei Guowu , Li Huamin
Published: August 2005

This paper investigates the geometric properties of the toroidal drive, reveals the meshing characteristics, and develops analytical models of both axial section and normal section of the toroidal tooth profile. Based on coordinate transformation, the meshing function is obtained and leads to the necessary condition of existence of the enveloping surface. The helix and helix lead angle are then proposed for meshing between the sun-worm and planet worm-gears and both undercutting curve and meshing limit curve are introduced. This further leads to the induced normal curvature for evaluating gearing properties and the selection of the best suitable meshing parameters. The geometric analysis and analytical modeling present a tool for design, leading to three tables of numerical results and design parameters. This is then demonstrated in a three-dimensional modeling of both helical sun-worm and stationary internal gear of the toroidal drive.
Metal etching with organic based plasmas. II. CO∕NH3 plasmas
Authors: Orland A. S. , Blumenthal R.
Published: August 2005

The chemical processes that underlie metal etching in high-density CO∕NH3 plasmas have been investigated using supersonic pulse, plasma sampling mass spectrometry. The chemical processes have been found to be consistent with Fischer–Tropsch chemistry resulting in the generation of formamide in the plasma environment. Formamide, closely related to acetic acid in both chemical structure and ligand binding capabilities, is suggested as being responsible for the two and one-half-fold increase in etch rate previously observed [K.B. Jung, J. Hong, H. Cho, S. Onishi, D. Johnson, Y.D. Park, J.R. Childress, and S.J. Pearton, J. Vac. Sci. Technol. A 17(2), 535 (1999)] when small amounts of CO are added to NH3 plasmas.
Fabrication and characterization of a planarized vertical-cavity surface-emitting laser by using the silicon oxide
Authors: Tsai Chia-Lung , Lee Feng-Ming , Hu Chih-Wei , Wu Meng-Chyi , Ko Sun-Chien , Wang Hai-Lin , Ho Wen-Jeng
Published: August 2005

In this article, an alternative method is presented to fabricate a planar-type oxide-confined 850-nm vertical-cavity surface-emitting laser (VCSEL). The threshold voltage, threshold current, light output power, external differential quantum efficiency, emission spectrum, and dynamic response of VCSELs planarized with a silicon oxide (SiOx) have been evaluated. These devices exhibit excellent static characteristics, including a threshold voltage (Vth) of 2.05V corresponding to a threshold current of 0.88mA, a minimum threshold current of 0.7mA near 60°C, a maximum output power of 4.28mW at 11mA, a maximum external differential quantum efficiency (ηex) of 43% just above threshold, and an operation temperature beyond 130°C. In addition, the transverse modes of the device initially are low-order, while high-order modes appear at elevated current levels. The fundamental transverse mode at the longest wavelength increases with injected current with a redshift of 0.49nm∕mA due to the Joule effect. Since the thermal resistance of the VCSEL with a SiOx buried layer is less than that of device without it, the VCSEL with the buried layer displays less redshift and better performance. Finally, the VCSEL with a SiOx buried layer shows a clear eye-opening feature as operating at 2.488Gbit∕s with a bias current of 2mA. Further increasing the current level, the device can work at the maximum bit rate of 8Gbit∕s and a bias current of 3.7mA.
Growth of InAsSb-channel high electron mobility transistor structures
Authors: Tinkham B. P. , Bennett B. R. , Magno R. , Shanabrook B. V. , Boos J. B.
Published: August 2005

We discuss the molecular beam epitaxial growth of the random alloy InAsSb for use as the channel in high electron mobility transistors (HEMTs). Room-temperature mobilities of 22000cm2∕Vs have been achieved at a sheet carrier density of 1.4×1012∕cm2. This is a marked improvement over the mobility of 13000cm2∕Vs at the same carrier density obtained in previous attempts to grow the InAsSb channel using a digital alloy procedure [J. B. Boos, M. J. Yang, B. R. Bennett, D. Park, W. Kruppa, R. Bass, Electron. Lett. 35, 847 (1999)]. We have also implemented different barriers and buffer layers to enhance the transport properties and overall performance of the HEMT structure.
Combined molecular beam epitaxy low temperature scanning tunneling microscopy system: Enabling atomic scale characterization of semiconductor surfaces and interfaces
Authors: Krause M. , Stollenwerk A. , Awo-Affouda C. , Maclean B. , LaBella V. P.
Published: August 2005

A molecular beam epitaxy and low temperature scanning tunneling microscopy chamber have been integrated to characterize both compound and elemental semiconductor surfaces and interfaces. The integration of these two commercially available systems has been achieved using a custom designed sample transfer mechanism. The MBE growth chamber is equipped with electron diffraction and provides substrate temperature measurements and control by means of band-edge thermometry accurate to within ±0.5°C. In addition, the microscope can operate at temperatures as low as 4K and perform ballistic electron emission microscopy measurements. The chamber that houses the microscope includes a preparation chamber with an evaporation source for metals. The entire STM chamber also rests on an active vibration isolation table, while still maintaining an all ultrahigh vacuum connection to the MBE system.
Compatibility of high pressure cleaning mixtures with a porous low dielectric constant film: A positronium annihilation lifetime spectroscopic study
Authors: Myneni Satyanarayana , Peng Hua-Gen , Gidley David W. , Hess Dennis W.
Published: August 2005

High pressure CO2 based cleaning mixtures have recently been proposed as an environmentally benign approach for postplasma etch residue removal. These mixtures must remove etch residues without damaging the low-k dielectric film that will be used to isolate interconnect structures in future generation devices. In this work, the compatibility of a CO2-based mixture with a porous low-k film is evaluated. Positronium annihilation lifetime spectroscopy (PALS) is used to monitor the change in pore size and film chemistry in a porous methyl silsesquioxane film after treatments under several different elevated pressure conditions. Spectroscopic ellipsometry and infrared spectroscopy are used to complement the PALS technique in order to better understand cleaning mixture effects on the dielectric film. CO2–TMAHCO3–methanol mixtures cause negligible changes in pore dimensions and bulk composition of the film. The high pressure treatments cause a small decrease in positronium formation which may be attributed to contamination in the high pressure system.
Synthesis of metallic nanocrystals with size and depth control: A case study
Authors: Jacobsohn L. G. , Zhang X. , Misra A. , Nastasi M.
Published: August 2005

The goal of this work is to investigate the use of thermal annealing of thin metallic layers buried in a capping ceramic material to obtain controlled synthesis of metallic nanocrystals, i.e., to achieve nanocrystal formation with size control and narrow size distribution. SiO2∕Pt∕SiO2 films were deposited by electron beam evaporation with different Pt layer thickness, 5, 10, and 25 Å. After deposition, films were annealed in vacuum at 500, 700 and 900 °C for times from 10 to 180 min. High-resolution transmission electron microscopy revealed the presence of Pt nanocrystals, their average size, and size distribution. By tuning the Pt layer thickness and the annealing conditions, it was possible to control the final nanocrystal size with narrow size distribution typically of ±1nm.
MOS-diode characteristics of ultrathin Al2O3 gate dielectrics after exposure to an electron-cyclotron-resonance plasma stream
Authors: Jin Yoshito , Saito Kunio , Shimada Masaru , Ono Toshiro
Published: August 2005

We demonstrate that exposure to a plasma stream produced by electron-cyclotron resonance (ECR) of a gas mixture of Ar and O2 improves the metal-oxide-semiconductor (MOS) diode characteristics of ultrathin films of Al2O3. Al2O3 films were formed by ECR sputtering deposition under “metal-mode” conditions. The films were then left as is or exposed to the above plasma stream or an Ar plasma stream in order to test the relative improvements in their electrical properties. The MOS-diode characteristics of films after plasma exposure and annealing in a high vacuum (around 10−4Pa) were studied in detail. While exposure to the Ar–O2 plasma stream for 10–120s had little effect on the flatband voltage shift, a very small width of capacitance-voltage hysteresis (+3mV), a small equivalent-oxide thickness (1.0nm), and a low value for leakage current (1.5×10−4A∕cm2) were obtained for films after 20–30s of exposure. Exposure to the Ar plasma stream, however, did not improve the MOS-diode characteristics of the films. Through x-ray photoelectron spectroscopy analysis, we found energy shifts indicating that exposure to the Ar–O2 plasma stream oxidized the metal bonds in the metal-mode-deposited Al2O3 films.
Electronic and magnetotransport properties of ferromagnetic p-(In,Mn)As∕n-InAs heterojunctions
Authors: May S. J. , Wessels B. W.
Published: August 2005

The electronic and magnetotransport properties of epitaxial p-(In,Mn)As∕n-InAs heterojunctions have been studied. The junctions were formed by depositing ferromagnetic (In,Mn)As films on InAs (100) substrates using metal-organic vapor phase epitaxy. The current-voltage characteristics of the junctions have been measured from 78 to 295 K. At temperatures below 150 K, ohmic current dominate transport at low bias, followed by defect-assisted tunneling current with increasing bias. At high forward bias, junction transport is dominated by diffusion current. The magnetoresistance of the junctions was measured as a function of forward bias and applied magnetic field. The magnitude and field dependence of the longitudinal magnetoresistance depend directly on the junction transport mechanism. Under high bias, a magnetoresistance of 15.7% at 78 K and 8% at 295 K in a 4400 Oe field was measured in an In0.96Mn0.04As∕InAs junction. At 78 K, the high bias magnetoresistance increases linearly with magnetic field from 1000 to 4600 Oe.
Anisotropic strain fields in granular GaAs:MnAs epitaxial layers: Towards self-assembly of magnetic nanoparticles embedded in GaAs
Authors: Moreno M. , Jenichen B. , Däweritz L. , Ploog K. H.
Published: August 2005

Granular GaAs:MnAs, consisting of MnAs nanoclusters embedded in a GaAs matrix, is a hybrid ferromagnet-semiconductor material with potential applications in information storage, magneto-optical, and spin electronics devices. It can be obtained, through phase separation, by high-temperature annealing of diluted (Ga,Mn)As films grown by molecular-beam epitaxy. The granular material thus obtained exhibits room-temperature ferromagnetism and excellent crystal quality, but the magnetic anisotropy is weak and control of the ordering of the clusters in lateral directions of the film has not been achieved yet. We have investigated the strain state of granular GaAs:MnAs films on GaAs(001) substrates at room temperature by x-ray diffraction. Two-dimensional reciprocal-space maps are presented, including x-ray reflections from the GaAs matrix and from the nanosized MnAs crystallites. Based on the x-ray diffraction results, we propose strategies to guide the assembly of the MnAs precipitates within the GaAs matrix, such that (i) lateral order within the film and (ii) single crystallographic orientation of the precipitates relative to the matrix can be achieved. The approach is based on the use of anisotropies and inhomogeneities in the elastic interaction of the crystallites with the matrix to control the precipitation process.
Imaging of thickness and compositional fluctuations in InGaN∕GaN quantum wells by scanning capacitance microscopy
Authors: Zhou X. , Yu E. T. , Florescu D. I. , Ramer J. C. , Lee D. S. , Ting S. M. , Armour E. A.
Published: August 2005

We have used scanning capacitance microscopy (SCM) and atomic force microscopy (AFM) to characterize structural and electronic properties of InxGa1−xN∕GaN quantum-well structures at the nanoscale. Macroscopic capacitance-voltage measurements combined with numerical simulations indicate that either electron or hole accumulation in the quantum-well layer can be induced by application of forward or reverse bias, respectively. Under reverse bias conditions (hole accumulation), features corresponding to monolayer fluctuations in InxGa1−xN quantum-well thickness are clearly evident. Under forward bias conditions (electron accumulation), samples exhibiting high luminescence efficiencies are found to contain regions of increased carrier accumulation within the quantum well, which on the basis of spatially resolved spectroscopy, bias-dependent imaging, and numerical simulations are attributed to nanoscale In-rich clusters in the quantum well. No such features are observed in samples exhibiting lower luminescence efficiencies. Together, these studies demonstrate the ability to image, and distinguish, nanoscale variations in subsurface electronic properties arising from either monolayer thickness fluctuations or compositional inhomogeneities in InxGa1−xN∕GaN quantum-well structures.
Fabrication of nanometer-sized ferromagnetic probe
Authors: Tsai J. T. H. , Wu C. H.
Published: August 2005

A sharp needlelike metal probe can be used in a scanning tunneling microscopy (STM) for surface analysis. The probe requires a small-apex tip to maintain a tunneling current from the sample surface. These conditions give STM an atomic resolution. Such a sharp probe also can be applied in the scanning-electron microscope (SEM) for the electron-beam source from electric-field-induced tunneling-electrons. This field-induced current comprises a high brightness and coherent e-beam which gives the SEM a better resolution. Regardless of the different applications, the sharpness of the metal tip dominates the performance of these applications. Tungsten is a common material that can be etched electrochemically to an ultrasharp needlelike probe for these applications. Soft magnetic materials such as iron and nickel also can be fabricated into a similar shape but it is difficult to generate an ultrasharp probe from a simple electrochemical-etch process due to less anisotropic etching. We report a method to fabricate iron and nickel probes within 40nm of the tip’s radius. The iron and nickel wires were first electrochemically etched at the interface of an air bubble in the electrolyte. Because very high surface tension of the micron sized bubble gives a higher anisotropic etching to the wire which in results in the wire etched into needle like sharp probe. By additional sharpen process, the small air bubble acts as a sharpener, the tip was then “sharpened” into nanometer size by periodic stripping the apex of the tip surface.
Molecule-solid interfaces studied with infrared ellipsometry: Ultrathin nitrobenzene films
Authors: Gensch M. , Roodenko K. , Hinrichs K. , Hunger R. , Güell A. G. , Merson A. , Schade U. , Shapira Y. , Dittrich Th. , Rappich J. , Esser N.
Published: August 2005

This paper aims to demonstrate the high capability of infrared spectroscopic ellipsometry (IRSE) for the characterization of very thin organic films and the organic to inorganic interfaces. It is shown that the detection limit of IRSE facilitates the investigation of ultrathin nitrobenzene (NB) films with monolayer sensitivity. This accounts for substrates from semiconductors to metals. The process of reoxidation of a NB terminated silicon (001) surface is also reflected in the infrared ellipsometric parameters and evidently proceeds despite the organic layer. As a complementary method, x-ray photoelectron spectroscopy (XPS) measurements were performed.
Optimization of the active region of InGaN∕GaN 405 nm light emitting diodes using statistical design of experiments for determination of interaction effects
Authors: Grandusky J. R. , Jamil M. , Shahedipour-Sandvik F. , DeLuca J. A. , LeBoeuf S. F. , Cao X. A. , Arthur S. D.
Published: August 2005

Output performance of InGaN based violet light emitting diode structures emitting at 405 nm was optimized using the statistical design of experiments (DOE) approach. Two separate DOEs were utilized to optimize the active region. The variables studied included the gallium flow rate, indium flow rate, temperature, well and barrier growth times, NH3 flow rate, and the silicon doping of the barrier while holding all other parameters and layers constant. Photoluminescence (PL) measurements were analyzed for wavelength, intensity, and full width at half maximum (FWHM) for each sample in both DOEs while electroluminescence measurements were completed for the samples from the second DOE and analyzed based on optical output power. Statistically valid transfer functions were obtained for each response based on the variables investigated. An overall improvement of 7% in the intensity with a reduction of 20% in the FWHM of the 405 nm PL band was obtained based on the starting point of the first DOE, while an improvement of 80% in intensity of PL with a 64% improvement in optical output power was obtained in the second DOE. Results show several interactions between various variables and indicate the complexity of GaN based growth kinetics. The significant effects are explained based on simulation of the structures.
Scanning tunneling microscopy study of single molecule motion on the Si(100)-2×1 surface
Authors: Basu R. , Tovar J. D. , Hersam M. C.
Published: August 2005

Room temperature ultrahigh vacuum (UHV) scanning tunneling microscopy (STM) is used to characterize the motion of individual organic molecules on the Si(100)-2×1 surface. In particular, 4-methoxystyrene molecules are observed to translate laterally on the surface during UHV STM imaging. Switching between the two most favored conformations occurs on the time scale of 0.1–1 s. On the other hand, styrene molecules imaged under identical conditions are not observed to undergo lateral translations, thus suggesting that the rotational freedom of the methoxy group is enabling the apparent motion of 4-methoxystyrene. To test this hypothesis, the rotational freedom of the methoxy group was eliminated by synthesizing an analog molecule (5-vinyl-2,3-dihydrobenzofuran) where the methoxy group was covalently linked back to the aromatic ring. UHV STM studies of 5-vinyl-2,3-dihydrobenzofuran confirm the expected suppression of molecular motion. Overall, this study suggests that the motion of surface-mounted adsorbates can be controlled by engineering intramolecular rotational degrees of freedom.
Effects of doping profile and post-growth annealing on spin injection from Fe into (Al,Ga)As heterostructures
Authors: Adelmann C. , Xie J. Q. , Palmstrøm C. J. , Strand J. , Lou X. , Wang J. , Crowell P. A.
Published: August 2005

The influence of the Fe∕Ga0.9Al0.1As interface on spin injection into a spin light-emitting diode is studied. Spin injection is found to depend strongly on the interfacial doping profile demonstrating the importance of band bending in the semiconductor near the interface. The effect of post-growth annealing on spin injection from Fe contacts into GaAs-based spin light-emitting diodes is also examined. Post-growth annealing up to 250 °C is found to increase the spin injection efficiency. It is demonstrated that the annealing modifies electronic properties of the Fe∕Ga0.9Al0.1As interface, as evidenced by an increase of the Schottky barrier height.
GaN films deposited at low temperature on (111)Si by compound-source molecular beam epitaxy technique
Authors: Honda T. , Aoki Y. , Akiyama M. , Obinata N. , Egawa S. , Kawanishi H.
Published: August 2005

GaN films were deposited at the low temperature by compound-source molecular beam epitaxy technique. Structural ordering of the GaN films was investigated using x-ray photoelectron spectroscopy (XPS) and refractive high-energy electron diffraction (RHEED) techniques. XPS spectra show that excess Ga in the films was oxidized. The binding energy of Ga–N bonds in the deposited GaN film is almost equal to that in GaN crystals. On the other hand, the RHEED patterns of the films deposited on SiO2∕(111) indicate that the long-range tetrahedral ordering in deposited GaN is disappeared although those on (111) Si were streaky.
Phase behavior of thin film Mn∕GaAs interfacial reactions
Authors: Hilton J. L. , Schultz B. D. , McKernan S. , Spanton S. M. , Evans M. M. R. , Palmstrøm C. J.
Published: August 2005

Rutherford backscattered spectrometry, x-ray diffraction, and cross-sectional transmission electron microscopy were used to examine Mn∕GaAs interfacial reactions. Mn films deposited in situ on molecular beam epitaxy (MBE)-grown GaAs(001) epilayers resulted in significant interfacial reactions following post-growth anneals above 200 °C. These reactions initially resulted in the formation of a two-phase region of tetragonal Mn2As and tetragonal δ-MnGa, with an average composition of Mn0.6Ga0.2As0.2, and were found to be limited by the rate of Mn diffusion through the reacted region. The two phases formed an epitaxial lamellar layer on the GaAs substrate with Mn2As(001)⟨100⟩ and δ-MnGa(001)⟨100⟩∕∕GaAs(001)⟨110⟩. Higher temperature anneals resulted in the dissociation of the Mn0.6Ga0.2As0.2 region into a δ-MnGa layer near the sample surface and a Mn2As layer near the GaAs substrate. Results of these reaction studies have been used to make predictions of the Mn–Ga–As ternary phase diagram for temperatures up to 400 °C, which indicates that both Mn2As and δ-MnGa are thermodynamically stable in contact with GaAs.
Effect of interface roughness on silicon-on-insulator–metal-semiconductor field-effect transistor mobility and the device low-power high-frequency operation
Authors: Khan T. , Vasileska D. , Thornton T. J.
Published: August 2005

We have developed a simulation model based on the solution of the Boltzmann transport equation (BTE) for modeling n-channel silicon-on-insulator (SOI) metal-semiconductor field-effect transistor (MESFETs) using the ensemble Monte Carlo device simulation technique. All relevant scattering mechanisms for the silicon material system have been included in the model. In addition to phonon scattering, to properly describe the operation of the SOI MESFET devices, in our theoretical model we have also included surface or interface-roughness scattering. Following Fischetti and Laux[J. Appl. Phys. 89, 1205 (2001)] we first model interface roughness as a real space scattering event, separated into specular and diffusive (isotropic) type of reflection from an ideal atomically flat interface. This model gives rise to low-field silicon electron mobility values in agreement with available experimental data. To further verify our mobility results, we also treat interface roughness as a boundary condition based on the Boltzmann-Fuch method. To examine the performance improvement of this device structure, in contrast to some previous studies, here we have simulated analogous SOI MESFET and SOI MOSFET devices. The results of these investigations suggest that the mobility of the SOI MOSFET device follows the experimental values and the mobility of the SOI MESFET is three to five times higher than that of the SOI MOSFET in the subthreshold and the on-state regime. These high mobility values suggest that this device structure is a promising candidate for low-power high-frequency applications.
Nanometer metal line fabrication using a ZEP520∕50K PMMA bilayer resist by e-beam lithography
Authors: An Lihua , Zheng Yuankai , Li Kebin , Luo Ping , Wu Yihong
Published: August 2005

In this work, we propose a bilayer resist system with 50K poly methylmethacrylate as the bottom layer and ZEP520 as the top layer for lift-off process. By making use of the different dissolution rates in the rinser for the top and bottom layers, it is possible to create an overhang resist pattern suitable for lift-off. In this specific study, a set of process parameters have been optimized to fabricate Cr metal lines with a width of about 70nm. The process has been used to fabricate nanometer scale magnetic sensors for data storage applications.
Surface etching of YBCO films by xenon difluoride
Authors: Crossley Benjamin L. , Drehman Alvin J. , Reid James R. , Derov John S. , Corrales Alfredo A. , Crisman Everett E.
Published: August 2005

We have demonstrated that xenon difluoride (XeF2) etches thin films of YBa2Cu3O7−x, the superconducting form of yttrium–barium–copper–oxide (YBCO), during dry etch processing. Both c-axis and mixed a∕c-axis YBCO films show evidence of such etching with a axis being more reactive. Profiles of YBCO films examined by ESCA show that the surfaces of both etched and unetched films are barium rich at the expense of yttrium. After XeF2 etching, fluorine was found to be present to a depth of at least 40nm. Despite the etching and the presence of fluorine in the YBCO films, the superconducting transition temperature, Tc, was unaffected by the XeF2 treatment.
Solvent vapor annealed block copolymer films on organosilane self-assembled monolayers
Authors: Harant Adam W. , Bowman Christopher N.
Published: August 2005

Solvent vapor annealing is shown to be a useful technique for controlling the formation of poly(isoprene-b-styrene) (PI-b-PS) block copolymer thin film nanostructures. Annealing in methyl ethyl ketone (MEK) solvent vapor yields a hexagonal-type structure (78nm repeat distance), while toluene yields a fingerprint texture. Solvent choice for spin coating dramatically changes the initial order in these films: MEK provides a useful hexagonal structure without annealing, while toluene yields a disordered nanostructure. N-octadecyltriethoxysilane is used to form a low surface energy self-assembled monolayer which effectively reduces pinning of the copolymer to the substrate, allowing the development of regions (∼1μm in diameter) with a high degree of hexagonal order. However, after several hours of annealing in MEK vapor, the copolymer ultimately dewets from the surface. Contact mode scanning probe microscopy has proven itself to be a very useful tool for imaging the nanostructures, without damaging the films. Friction mode provides high contrast images of PI-b-PS nanostructures, suggesting the lack of a wetting layer in the solvent vapor annealed films.
Growth of high quality Ge∕Si1−xGex on nano-scale patterned Si structures
Authors: Vanamu G. , Datye A. K. , Zaidi Saleem H.
Published: August 2005

Heteroepitaxial growth of thick (∼6μm) Ge∕3μm SixGe1−x layers on nano-scale patterned Si substrates has been investigated. These nm scale structures are fabricated using interferometric lithography with reactive ion and wet-chemical etching techniques. The quality of the growth on the nanopatterned substrates was compared to growth on planar substrates. The quality of the epitaxial layers was characterized using scanning electron microscopy, transmission electron microscopy, high-resolution x-ray diffraction and etch pit density measurements. We demonstrated the nanopatterned structures produce significantly superior quality heteroepitaxial epilayers in comparison with unpatterned Si surfaces. The dislocation density of Ge epilayers on the nanopatterned Si was ∼ three orders magnitude lower than on planar Si. Growth on nanopatterned surfaces also reduced surface roughness and eliminated crosshatch patterns characterstic of planar surfaces.
Effect of growth conditions, surface orientation, and alloy composition on Cl incorporation and activation in ZnSe and Zn1−xMgxSe grown by molecular beam epitaxy
Authors: VanMil B. L. , Tompkins R. P. , Feng Ke , Swartz C. H. , Giles N. C. , Myers T. H.
Published: August 2005

While chlorine can be incorporated in ZnSe at levels up to about 2×1020cm−3, it is only electrically active at levels up to 1×1019cm−3 with almost complete compensation occurring beyond this point. The doping level at which this compensation occurs coincides with a dramatic decrease in growth rate when using ZnCl2 as the chlorine source during growth by molecular beam epitaxy. The decrease in growth rate is likely due to competition for Zn atoms between growth and the chlorine. Compensation and degradation of photoluminescence edge emission intensity appear to be directly correlated to the reduced growth rate. Surface chemistry effects on point defect formation and surface reaction kinetics are investigated through comparison of growth and Cl doping of ZnSe on (100) and (211)B oriented substrates, and by dramatically modifying Zn-to-Se ratios during growth. It is shown that growth conditions can be modified to overcome Cl-related growth rate reduction, recovering to some extent the optical and electrical properties. ZnMgSe alloys have a higher Cl solubility than ZnSe, increasing the rate of Cl incorporation by an order of magnitude for the same ZnCl2 flux. The growth rate for ZnMgSe was not observed to decrease under high Cl flux. The ZnMgSe alloys were electrically active for roughly an order of magnitude larger Cl concentration than ZnSe. However the increase in band gap with Mg results in a lower net activation of carriers than for equivalently doped ZnSe.
Growth optimization of GaAsSb lattice matched to InP by gas-source molecular-beam epitaxy
Authors: Wu Bing-Ruey , Xu Chaofeng , Chang Kuo-Lih , Hsieh Kuang-Chien , Cheng K. Y.
Published: August 2005

Bulk GaAsSb samples were grown lattice matched to InP substrates at different temperatures using gas-source molecular-beam epitaxy in order to optimize the crystal quality. Growth temperatures from 15 °C above the InP surface oxide desorption temperature to 145 °C below it have been investigated. Undesirable properties such as Sb composition variation and natural composition superlattices in the growth direction have occurred at high growth temperature possibly due to phase separation. High quality, single phase GaAsSb lattice matched to InP has been grown at 135 °C below the desorption temperature as evidenced by narrow linewidths and clear Pendellösung fringes displayed in high-resolution x-ray diffraction spectra.
Emission limited electrostatic atomization and the fine structure constant
Authors: Kelly A. J.
Published: August 2005

Quadrupole mass spectrometer measurements of charged Octoil sprays reveal that operation in what is interpreted to be the emission limited regime is accurately represented by Z=exp(ε0∕ε−rs∕f), where: Z is the fraction of the emission limited charge level, rs the coupling parameter, and f the inverse fine structure constant (137.04). The coupling parameter, defined as 1∕(a0√πn), where a0 is the first Bohr radius, and n the surface charge density (m−2), is a nondimensional measure of intercharge spacing, and a fundamental descriptor of two-dimensional (2D) electron structures. The appearance of the coupling parameter, and the fine structure constant as empirical correlating constants for the data implies that the surface 2D electrons are in a gaseous or liquid state. This is consistent with the view that the emission limit—Rayleigh limit transition reflects a phase change of the 2D surface electron cloud from a gas∕liquid to a crystalline state. For Octoil, the data indicate that this transition occurs when spray droplet radii are about 0.9μm. This corresponds to emission field strength of 0.13GV∕m. Bimodal droplet size distributions characterized by approximately fixed energy levels of one and two Rydbergs [1 Rydberg (Ry)=13.6eV], and noncontinuous charging behavior is observed. In all instances studied, surface charge energy levels are high, and are conveniently ordered in terms of the Rydberg.
Importance of evaporation in the design of materials for step and flash imprint lithography
Authors: Kim Eui Kyoon , Ekerdt John G. , Willson C. Grant
Published: August 2005

Step and flash imprint lithography is a low cost process capable of generating sub-50nm patterns. Although the printing resolution is better than optical lithography, the throughput at the available production tools is lower, in part, due to the time required to fill the imprint template features. The throughput can be improved by lowering the viscosity of the imprint material and reducing the drop size. Decreasing viscosity generally increases the volatility of a material and decreasing drop size increases the area available for evaporation. This study compares measured and predicted rates for volatilization of acrylate and vinyl ether monomers. The predicted rates are based on the methods of Lee-Kesler and Joback-Reid that employ group contributions. The predictions were used to explore the effect of drop size (200nl,1nl,80pl) on evaporation rate at 20°C for t-butyl acrylate, hexyl acrylate, ethylene glycol diacrylate, lauryl acrylate, t-pentyl vinyl ether, ethylene glycol vinyl ether, 1,4-butanediol divinyl ether, and triethylene glycol divinyl ether. The predicted rates correlate well with experiment.
Monolithic organic-oxide microcavities fabricated by low-temperature electron-beam evaporation
Authors: Persano Luana , Cingolani Roberto , Pisignano Dario
Published: August 2005

We report on monolithic symmetric vertical microcavities formed by depositing dielectric-distributed Bragg reflectors (DBRs) by reactive electron-beam evaporation at low temperature (T). The DBRs consist of alternating TiOx and SiOx layers with a refractive index contrast of about 0.55 in the visible range. The DBRs, consisting of a very few index-contrast pairs, exhibit high peak reflectivity (93%) around 590nm with a full width at half maximum of about 160nm. The excellent compatibility of thin low-T reactive electron-beam evaporated films with a thicker cavity medium comprised of molecular organic compound, and prepared either in a single growth-run, or ex situ, opens the way for novel symmetric vertical-emitting resonators and monolithic photo- and electroluminescent microcavities.
Twol-amalgamated priority queues
Authors: Goh Rick Siow Mong , Thng Ian Li-Jin
Published: August 2005

Priority queues are essential function blocks in numerous applications such as discrete event simulations. This paper describes and exemplifies the ease of obtaining high performance priority queues using a two-tier list-based structure. This new implementation, called the
Twol
structure, is amalgamated with three priority queues, namely, the Henriksen's queue, splay tree and skew heap, to enhance the efficiency of these
basal
priority queue structures. Using a model that combines traditional average case and amortized complexity analysis, Twol-amalgamated priority queues that maintain
N
active events are theoretically proven to offer O(1)
expected amortized complexity
under reasonable assumptions. They are also demonstrated empirically to offer stable near O(1) performance for widely varying priority increment distributions and for queue sizes ranging from 10 to 10 million. Extensive empirical results show that the Twol-amalgamated priority queues consistently outperform those basal structures (i.e., without the Twol structure) with an average speedup of about three to five times on widely different hardware architectures. These results provide testimony that the Twol-amalgamated priority queues are suitable for implementation in sizeable application scenarios such as, but not limited to, large-scale discrete event simulation.
Acknowledgements
Authors: Lee Newton
Published: August 2005

Flash homepage design volunteers
—Alex Lieu, Johnny Rodriguez, Michael Borys

3-Pin Media
Flash animation volunteers
— Jay Popeski, Jeffrey Blyseth

Axis Graphics
HTML design volunteer
— Joe Raymond

Video and sound editing volunteer
— Eric Huff

Producer and editor-in-chief
— Newton Lee

Also thanks to all authors, interviewees, reviewers, editorial board advisors, and the entire ACM staff including Mark Mandelbaum, John White, Roma Simon, Irma Strolia, Carol Wierzbicki, Edwin Rodriguez, and Jono Hardjowirogo for their support.
The content digital divide
Authors: Josephson Joel H.
Published: August 2005

Dear Editor-in-Chief,

I would like to describe briefly how the non-profit kindersite project is utilizing digital media content in an innovative way to address social problems. Firstly to answer who we are; the two founders are Ziv Avidor, a technology specialist and consultant to government and corporations and Joel Josephson, an Internet strategist and high tech consultant.

Our concept is to use content on a wide-scale over the Internet or within control groups to understand what constitutes effective and engaging digital content. This will be achieved through quantitative and qualitative research of users usage of the content. Our belief is that a bottom-up investigation will achieve focused and constructive results that will help raise the effectiveness and outcomes of content usage within the social causes targeted.

Initially the team have implemented their ideas in two social projects involving education and the digital divide.

The education project is targeted at gaining answers to the many and critical questions that surround the introduction of technology to early learners (ages 2 to 8) plus answering similar questions regarding the introduction of digital content for the teaching of English as a second language. This, more advanced project, is based around an Internet site http://www.kindersite.org that offers educators and parents of small children a free resource of 1,000s of links to content in the form of games, songs and stories. The content is being graded according to educational and appropriateness parameters.

This project is currently being used globally with 152 officially participating schools in 27 countries plus registrations from about 80 countries.

The second project utilizes an adaptation of the existing technology and focuses on the Content Digital Divide. This project will study how the effectiveness of introducing technology (computers and the Internet) to digitally divided communities can be improved. The project looks at the introduction to technology from a content perspective and will attempt to ensure that the recipients of the new technology are made fully aware from the first exposure, of the personal and community benefits of technology.

The commissioning of content or adaptation will be completed on a local level with the additional purpose of stimulating growth in locally-based content providers.

This proposal has gained the support of potential implementing partners in a number of developing countries including, Sierra Leone, Uganda, Nigeria, Cameroon, Kazakhstan, India etc.

We are now looking to gain corporate and governmental support to help implement these projects on the scale we envisage and be very interested in the comments, sponsorship or practical help of your readership.

Joel H. Josephson, Founder and Executive Director

Kindersite Project

http://www.kindersite.org

Email : joel_josephson@kindersite.org
Automating Lighting Design for Interactive Entertainment
Authors: El-Nasr Magy Seif , Horswill Ian
Published: August 2005

Recent advances in computer graphics, particularly in real-time rendering, have resulted in major improvements in 3D graphics and rendering techniques in interactive entertainment. In this article we focus on the scene-lighting process, which we define as configuring the number of lights in a scene, their properties (e.g., range and attenuation), positions, angles, and colors. Lighting design is well known among designers, directors, and visual artists for its vital role in influencing viewers' perception by evoking moods, directing their gaze to important areas (i.e., providing visual focus), and conveying visual tension. It is, however, difficult to set positions, angles, or colors for lights within interactive scenes to accommodate these goals because an interactive scene's spatial and dramatic configuration, including mood, dramatic intensity, and the relative importance of different characters, change unpredictably in real-time. There are several techniques developed by the game industry that establish spectacular real-time lighting effects within 3D interactive environments. These techniques are often time- and labor-intensive. In addition, they are not easily used to dynamically mold the visual design to convey communicative, dramatic, and aesthetic functions as addressed in creative disciplines such as art, film, and theatre. In this article we present a new real-time lighting design model based on cinematic and theatric lighting design theory. The proposed model is designed to automatically, and in real-time, adjust lighting in an interactive scene to accommodate the dramatic, aesthetic, and communicative functions described by traditional lighting design theories, while taking artistic constraints on style, visual continuity, and aesthetic function into account.
Security in embedded systems
Authors: Ravi Srivaths , Raghunathan Anand , Kocher Paul , Hattangady Sunil
Published: August 2005

Many modern electronic systems---including personal computers, PDAs, cell phones, network routers, smart cards, and networked sensors to name a few---need to access, store, manipulate, or communicate sensitive information, making security a serious concern in their design. Embedded systems, which account for a wide range of products from the electronics, semiconductor, telecommunications, and networking industries, face some of the most demanding security concerns---on the one hand, they are often highly resource constrained, while on the other hand, they frequently need to operate in physically insecure environments.Security has been the subject of intensive research in the context of general-purpose computing and communications systems. However, security is often misconstrued by embedded system designers as the addition of features, such as specific cryptographic algorithms and security protocols, to the system. In reality, it is
a new dimension
that designers should consider throughout the design process, along with other metrics such as cost, performance, and power.The challenges unique to embedded systems require new approaches to security covering all aspects of embedded system design from architecture to implementation. Security processing, which refers to the computations that must be performed in a system for the purpose of security, can easily overwhelm the computational capabilities of processors in both low- and high-end embedded systems. This challenge, which we refer to as the "security processing gap," is compounded by increases in the amounts of data manipulated and the data rates that need to be achieved. Equally daunting is the "battery gap" in battery-powered embedded systems, which is caused by the disparity between rapidly increasing energy requirements for secure operation and slow improvements in battery technology. The final challenge is the "assurance gap," which relates to the gap between functional security measures (e.g., security services, protocols, and their constituent cryptographic algorithms) and actual secure implementations. This paper provides an introduction to the challenges involved in secure embedded system design, discusses recent advances in addressing them, and identifies opportunities for future research.
Efficient digit-serial normal basis multipliers over binary extension fields
Authors: Reyhani-Masoleh Arash , Hasan M. Anwar
Published: August 2005

In this article, two digit-serial architectures for normal basis multipliers over (
GF
(2
m
)) are presented. These two structures have the same gate count and gate delay. We also consider two special cases of optimal normal bases for the two digit-serial architectures. A straightforward implementation leaves gate redundancy in both of them. An algorithm that can considerably reduce the redundancy is also developed. The proposed architectures are compared with the existing ones in terms of gate and time complexities.
A fast string-matching algorithm for network processor-based intrusion detection system
Authors: Liu Rong-Tai , Huang Nen-Fu , Chen Chih-Hao , Kao Chia-Nan
Published: August 2005

Network intrusion detection systems (NIDSs) are one of the latest developments in security. The matching of packet strings against collected signatures dominates signature-based NIDS performance. Network processors are also one of the fastest growing segments of the semiconductor market, because they are designed to provide scalable and flexible solutions that can accommodate change quickly and economically. This work presents a fast string-matching algorithm (called FNP) over the network processor platform that conducts matching sets of patterns in parallel. This design also supports numerous practical features such as case-sensitive string matching, signature prioritization, and multiple-content signatures. This efficient multiple-pattern matching algorithm utilizes the hardware facilities provided by typical network processors instead of employing the external lookup co-processors. To verify the efficiency and practicability of the proposed algorithm, it was implemented on the Vitesse IQ2000 network processor platform. The searching patterns used in the present experiments are derived from the well-known Snort ruleset cited by most open-source and commercial NIDSs. This work shows that combining our string-matching methodology, hashing engine supported by most network processors, and characteristics of current Snort signatures frequently improves performance and reduces number of memory accesses compared to conventional string-matching algorithms. Another contribution of this work is to highlight that, besides total number of searching patterns, shortest pattern length is also a major influence on NIDS multipattern matching algorithm performance.
Call for papers
Authors: Lee Newton
Published: August 2005

The ACM Computers in Entertainment online magazine (http://www.acmcie.org) covers a wide range of theoretical and practical computer applications in the field of entertainment. It features video interviews of leading professionals. It publishes high-quality papers on the latest development in software, hardware, and business policies that improve existing mainstream entertainment and that create new genres of entertainment. Topics of interest include but are not limited to: animation, animatronics, digital asset management, digital cinema, digital rights management, games, interactive television, Internet, movies, music, performing arts, robotics, toys, and virtual reality. The magazine welcomes submissions of articles from scholars and professionals involved in all aspects of entertainment technology.
Acknowledgements
Authors: Lee Newton
Published: August 2005

Flash homepage design volunteers
—Alex Lieu, Johnny Rodriguez, Michael Borys

3-Pin Media

Flash animation volunteers
—Jay Popeski, Jeffrey Blyseth

Axis Graphics

HTML design volunteer
—Joe Raymond

Video and sound editing volunteer
—Eric Huff

Producer and editor-in-chief
—Newton Lee

Also thanks to all authors, interviewees, reviewers, editorial board advisors, and the entire ACM staff including Mark Mandelbaum, John White, Roma Simon, Irma Strolia, Carol Wierzbicki, Edwin Rodriguez, Jono Hardjowirogo, and Virginia Gold for their support.