bluuebunny/crossref_metadata_2025 huggingface dataset:
Calculated characteristics of radio-frequency plasma display panel cells including the influence of xenon metastables
Authors: Pitchford L. C. , Kang J. , Punset C. , Boeuf J. P.
Published: December 2002

Although alternating-current plasma display panels (ac PDPs) are now produced by several companies, improvements are still necessary. In particular, the overall efficiency of the discharge in the standard configuration is low, on the order of 1 lm/W i.e., about 0.5% of the power dissipated in the discharge is transformed into useful visible photons. One way to substantially improve the efficiency of PDPs is to use radio-frequency (rf) excitation because, when compared to ac PDPs, less of the electrical energy input is dissipated by ions in the sheath and relatively more power is deposited in excitation of the xenon, which produces the ultraviolet photons used to excite the phosphors. In this article, we show calculated discharge characteristics for typical rf PDP conditions and pay particular attention to the role of the xenon metastable atoms in the ionization balance. Our discussion is limited to the sustaining regime, the “on-state,” of a PDP cell.
Border collision bifurcations at the change of state-space dimension
Authors: Parui Sukanya , Banerjee Soumitro
Published: December 2002

We present the theory of border collision bifurcation for the special case where the state space is piecewise smooth, but two-dimensional in one side of the borderline, and one dimensional in the other side. This situation occurs in a class of switching circuits widely used in power electronic industry. We analyze this particular class of bifurcations in terms of the normal form, where the determinant of the Jacobian matrix at one side of the borderline is greater than unity in magnitude, and in the other side it is zero.
Generation of large-amplitude solitons in the extended Korteweg–de Vries equation
Authors: Grimshaw Roger , Pelinovsky Dmitry , Pelinovsky Efim , Slunyaev Alexey
Published: December 2002

We study the extended Korteweg–de Vries equation, that is, the usual Korteweg–de Vries equation but with the inclusion of an extra cubic nonlinear term, for the case when the coefficient of the cubic nonlinear term has an opposite polarity to that of the coefficient of the linear dispersive term. As this equation is integrable, the number and type of solitons formed can be determined from an appropriate spectral problem. For initial disturbances of small amplitude, the number and type of solitons generated is similar to the well-known situation for the Korteweg–de Vries equation. However, our interest here is in initial disturbances of larger amplitude, for which there is the possibility of the generation of large-amplitude “table-top” solitons as well as small-amplitude solitons similar to the solitons of the Korteweg–de Vries equation. For this case, and in contrast to some earlier results which assumed that an initial disturbance in the shape of a rectangular box would be typical, we show that the number and type of solitons formed depend crucially on the disturbance shape, and change drastically when the initial disturbance is changed from a rectangular box to a “sech”-profile.
A novel perturbation-based complete active space–self-consistent-field algorithm: Application to the direct calculation of localized orbitals
Authors: Angeli Celestino , Evangelisti Stefano , Cimiraglia Renzo , Maynau Daniel
Published: December 2002

A complete active space–self-consistent-field (CAS–SCF) algorithm based on molecular orbitals that conserve their physical nature during the iterative process is proposed. The algorithm consists of an iterative procedure based on the imposition of the generalized Brillouin theorem to a complete active space-configuration interaction wave function. At convergence, the wave function is identical to the corresponding one obtained using canonical CAS–SCF orbitals, provided the nature of the active space is the same. If localized guess orbitals are used, the locality property is conserved by the final orbitals. Test calculations illustrate the interest of the proposed approach, that permits to control the nature of the active space.
Metal-dielectric band alignment and its implications for metal gate complementary metal-oxide-semiconductor technology
Authors: Yeo Yee-Chia , King Tsu-Jae , Hu Chenming
Published: December 2002

The dependence of the metal gate work function on the underlying gate dielectric in advanced metal-oxide-semiconductor (MOS) gate stacks was explored. Metal work functions on high-κ dielectrics are observed to differ appreciably from their values on SiO2 or in vacuum. We applied the interface dipole theory to the interface between the gate and the gate dielectric of a MOS transistor and obtained excellent agreement with experimental data. Important parameters such as the slope parameters for gate dielectrics like SiO2, Al2O3, Si3N4, ZrO2, and HfO2 were extracted. In addition, we also explain the weaker dependence of n+ and p+ polysilicon gate work functions on the gate dielectric material. Challenges for gate work function engineering are highlighted. This work provides additional guidelines on the choice of gate materials for future MOS technology incorporating high-κ gate dielectrics.
Mechanism of C2 hydrocarbon formation from methane in a pulsed microwave plasma
Authors: Heintze M. , Magureanu M. , Kettlitz M.
Published: December 2002

Methane dissociation, followed by the formation of C2 hydrocarbons, in a pulsed microwave discharge in methane was investigated by mass spectrometry and optical emission spectroscopy (OES). Long microwave pulses (>200 μs) are characterized by a pronounced dehydrogenation, but have a disadvantage in the saturation of the methane conversion at relatively low values, due to methane depletion toward the end of the pulse. For shorter pulses, the conversion degree increases approximately linearly as a function of energy input, and a maximum conversion of 90% with 80% selectivity toward acetylene was obtained for 60 μs pulses at 1 kHz repetition frequency. A further decrease of the pulse duration (20 μs) at higher frequency, in order to ensure a similar energy input, resulted in a decrease in conversion and dehydrogenation. The explanation of the effect of the pulse duration is based on information provided by optical emission spectroscopy of active species generated in the discharge. Atomic hydrogen, formed by methane dissociation, was found to play an essential role in methane plasma chemistry. A qualitative estimation of the variation of H atom concentration with operating conditions was done by actinometry, since time-resolved OES provides evidence that atomic hydrogen is mainly formed in the ground state and dissociative excitation can be neglected. In addition to the concentration of atomic hydrogen, the second key parameter is the gas temperature. It was determined from the relative intensity distribution in the rotational structure of the (0,0) C2 Swan band and of the (2,2) H2 Fulcher-α band. Gas temperatures between 1500 and 2500 K were determined for the present discharge conditions. The hydrogen abstraction by hydrogen atoms, favored at high temperature, is responsible for the high methane conversion and low energy requirement achieved (9–10 eV/molecule) and for the distribution of the reaction products.
Evolution of anisotropic microstructure and residual stress in sputtered Cr films
Authors: Zhao Z. B. , Yalisove S. M. , Rek Z. U. , Bilello J. C.
Published: December 2002

A series of Cr films with varying thicknesses have been prepared using a multiple moving substrate deposition geometry. These films have been investigated with several experimental techniques, including synchrotron x-ray scattering, pole figures, electron microscope, and double crystal diffraction topography. It was found that the in-plane stresses are highly anisotropic in these Cr films. The anisotropic stresses, characterized by two principal stresses in two characteristic directions defined by the deposition geometry, are quantified based on a methodology given in the Appendix. The plan view transmission electron microscopy observations reveal that the Cr films develop well-organized microstructures. The grains, which are elongated along the radial direction, are crystallographically aligned as well. The development of crystallographic texture in the Cr films, further revealed by pole figures and azimuthal (φ) x-ray scans, depends on both the deposition geometry and the film thickness. The preferential orientation of film growth is [110] for thinner films (<1.6 μm), and then becomes [111] for thicker films. Correspondingly, the in-plane texture varies in a conformal manner. In the former case, [100] and [110] directions of grains preferentially align along the radial direction and the direction of platen rotation, respectively. In the latter case, the preferential orientation of grains in the radial direction becomes [112], while that in the direction of rotation remains to be [110]. The occurrence of the anisotropic stresses and their dependence on film thickness is related to the evolution of the anisotropic structure and in-plane texture. The correlation is discussed in terms of the modulus effect associated with in-plane texture, the stress relief at intercolumnar voids, and the texture transition.
Modeling of direct wafer bonding: Effect of wafer bow and etch patterns
Authors: Turner K. T. , Spearing S. M.
Published: December 2002

Direct wafer bonding is an important technology for the manufacture of silicon-on-insulator substrates and microelectromechanical systems. As devices become more complex and require the bonding of multiple patterned wafers, there is a need to understand the mechanics of the bonding process. A general bonding criterion based on the competition between the strain energy accumulated in the wafers and the surface energy that is dissipated as the bond front advances is developed. The bonding criterion is used to examine the case of bonding bowed wafers. An analytical expression for the strain energy accumulation rate, which is the quantity that controls bonding, and the final curvature of a bonded stack is developed. It is demonstrated that the thickness of the wafers plays a large role and bonding success is independent of wafer diameter. The analytical results are verified through a finite element model and a general method for implementing the bonding criterion numerically is presented. The bonding criterion developed permits the effect of etched features to be assessed. Shallow etched patterns are shown to make bonding more difficult, while it is demonstrated that deep etched features can facilitate bonding. Model results and their process design implications are discussed in detail.
Close packed transitions in slit-shaped pores: Density functional theory study of methane adsorption capacity in carbon
Authors: Nguyen T. X. , Bhatia S. K. , Nicholson D.
Published: December 2002

An important feature of improving lattice gas models and classical isotherms is the incorporation of a pore size dependent capacity, which has hitherto been overlooked. In this paper, we develop a model for predicting the temperature dependent variation in capacity with pore size. The model is based on the analysis of a lattice gas model using a density functional theory approach at the close packed limit. Fluid–fluid and solid–fluid interactions are modeled by the Lennard-Jones 12–6 potential and Steele’s 10–4–3, potential respectively. The capacity of methane in a slit-shaped carbon pore is calculated from the characteristic parameters of the unit cell, which are extracted by minimizing the grand potential of the unit cell. The capacities predicted by the proposed model are in good agreement with those obtained from grand canonical Monte Carlo simulation, for pores that can accommodate up to three adsorbed layers. Single particle and pair distributions exhibit characteristic features that correspond to the sequence of buckling and rhombic transitions that occur as the slit pore width is increased. The model provides a useful tool to model continuous variation in the microstructure of an adsorbed phase, namely buckling and rhombic transitions, with increasing pore width.
Charge-dipole energy in imperfect molecular crystals: Application to carbazole in anthracene
Authors: Tsiaousis D. , Munn R. W.
Published: December 2002

The charge–dipole energy in a perfect crystal of polar molecules is shown to be zero in the absence of bulk polarization. Rigorous algebraic expressions are derived for the change in charge–dipole energy in an imperfect crystal, taking into account the effective dipole moments induced in the crystal, including the change in polarizability caused by the defect. The results consist of two terms, one from the permanent dipole change at the defect, and the other from the induced dipole change, which arises from the polarizability change at the defect responding to the permanent dipole field in the crystal. Numerical calculations for the charge–dipole energy change and the polarization energy change at molecules near a substitutional carbazole impurity in an otherwise perfect anthracene crystal show that the charge–dipole energy dominates, producing trapping and scattering regions in a distorted dipolar arrangement. The calculated trap depths reach 60 meV, but for electrons are compatible with the published interpretation of mobilities in carbazole-doped anthracene in terms of a trap of depth 34 meV but an apparent concentration 15 times the carbazole concentration, consistent with X trapping at anthracene. Traps as deep as 0.25 eV could be produced by more highly polar substituent molecules.
Characterization of GaAs-based n-n and p-n interface junctions prepared by direct wafer bonding
Authors: Shi Frank , Chang Kuo-Lih , Epple John , Xu Chao-Feng , Cheng K. Y. , Hsieh K. C.
Published: December 2002

In this study, the electrical characteristics and interface microstructures of GaAs-based n-n and p-n interface junctions prepared from direct wafer bonding have been systematically investigated through current-voltage measurements and transmission electron microscopy. It is found that a nearly continuous amorphous interface layer exists in all samples bonded at 400 °C. A drastic change in interface morphology caused by atomic rearrangement during high-temperature annealing at 600 °C leads to the formation of a locally perfect junction interface combined with an array of nanoscale, bubblelike amorphous regions. Each of them plays a different role in affecting carrier transports. The regions with local crystalline perfection can result in a considerable reduction of interface resistance for the majority carrier transport. However, the non-negligible interface resistance suggests that at interface boundary, there still exits a large number of interface states resulting from atomic imperfections, such as point defects and dangling bonds. On the other hand, the array of nanoscale, bubblelike regions is believed to provide a significant leakage path for minority carriers in p-n junctions. The p-n junction bonded at 400 °C exhibits an ideality factor of about 1.9 compared to 1.1 from an epitaxially grown p-n junction. After annealing at 600 °C, the increased leakage current along the bubblelike amorphous regions results in a deteriorating ideality factor from 1.9 to 2.5.
Morphological and phase stability of nickel–germanosilicide on Si1−xGex under thermal stress
Authors: Jarmar T. , Seger J. , Ericson F. , Mangelinck D. , Smith U. , Zhang S.-L.
Published: December 2002

Continuous and uniform Ni(Si,Ge) layers are formed on polycrystalline Si and Si0.42Ge0.58 substrate films at 500 °C by rapid thermal processing. The germanosilicide is identified as NiSi0.42Ge0.58, i.e., with the same Si-to-Ge ratio as in the substrate. The NiSi0.42Ge0.58 layer has agglomerated at 600 °C. This is accompanied by a diffusion of Ge out from the germanosilicide grains and the growth of a Ge-rich SiGe region in their close vicinity. These changes cause a slight variation in the atomic composition of Ni(Si,Ge) detectable for individual grains by means of energy dispersive spectroscopy. Above 600 °C, substantial outdiffusion of Ge from the Ni(Si,Ge) grains occurs concurrently with the migration of the grains into the substrate film away from the surface area leaving a Ge-rich SiGe region behind. These observations can be understood with reference to calculated Ni–Si–Ge ternary phase diagrams with and without the inclusion of NiSi2. When Ge is present, the Ni-based self-aligned silicide process presents a robust technique with respect to device applications.
Intersubband absorption at λ∼1.3 μm in optimized GaN/AlGaN Bragg-confined structures
Authors: Radovanović J. , Milanović V. , Indjin D. , Ikonić Z.
Published: December 2002

A method is developed for the analysis and extracting the optimal structural parameters of GaN/AlGaN Bragg-confined structures, in order to maximize the intersubband absorption on bound–above-the-barrier transitions at wavelengths in the near infrared spectral range. The “built-in” electrostatic field originating from piezoelectric and spontaneous polarization, and band nonparabolicity are taken into account. The optimal GaN/Al0.65Ga0.35N Bragg-confined structure designed for maximal absorption at λ=1.3 μm (950 meV) provides a fractional absorption of 1.5%, at 2×1012 cm−2 doping per active well.
Ultrasonic manipulation of locomotive microorganisms and evaluation of their activity
Authors: Saito Mitsunori , Kitamura Norio , Terauchi Masaki
Published: December 2002

Acoustic manipulation of locomotive microorganisms, i.e., euglena and paramecia, was conducted by using ultrasonic standing waves of ∼3 MHz. Microorganisms were trapped at the intersections of the nodes in the two orthogonal standing waves and were transferred horizontally and vertically by the suitable ultrasonic frequency change. Aggregation of microorganisms was also observed in the process of the cyclic frequency change. The trapping efficiency depended on both ultrasonic power density and the activity of microorganisms. The effects of water temperature and illumination on their activity were evaluated by measuring the ultrasonic trapping efficiency.
Structures and magnetic properties of Nd1−xCaxFeO3 nanoparticles
Authors: Li Jiangong , Kou Xinli , Qin Yong , He Haiying
Published: December 2002

Using a sol-gel method, Nd1−xCaxFeO3 nanoparticles with nearly the same average particle size and different Ca contents (x=0.1–0.5) and Nd0.9 Ca0.1 FeO3 nanoparticles with different particle sizes were prepared. Crystal structure and magnetic properties for the Nd1−xCaxFeO3 (x=0.1–0.5) nanoparticles have been investigated by x-ray diffraction and magnetic measurements. Both series samples have orthorhombic perovskite structure and the space group Pbnm. The Nd(Ca) ions and O ions are displaced from the ideal cubic positions. The oxygen octahedra around the Fe ions are distorted. Both the increasing Ca content and the increasing particle size lead to a decrease in Fe–O bond length and an increase in Fe–O–Fe bond angle. Magnetic measurements show the existence of a weak ferromagnetism and the mainly antiferromagnetic ordering of the spins in the Nd1−xCaxFeO3 nanoparticles. The spontaneous magnetization of the weak ferromagnetism decreases with increasing Ca content or increasing particle size. The influence of structure on magnetic properties is discussed.
Approach to saturation in nanomagnetic systems
Authors: Iglesias R. , Rubio H.
Published: December 2002

The approach to the saturation process of the magnetization as a function of the applied field angle is studied in three-dimensional nanomagnetic materials. The dependence of the magnetization on the applied field has been examined, giving the usual coefficients at high and intermediate field ranges and finding a crossover between them, which is appropriately justified. Based on these results, we propose two methods, one exact (numerical) and the other approximate (more useful in experiment), which allow for the determination of the anisotropy easy axis distribution and the interaction strength.
Optical detection of electroacoustic signals in electrolytes in the low frequency range
Authors: Tankovsky N. , Nikolov I. , Buchvarov I. , Baerner K.
Published: December 2002

An improved electroacoustic cell construction and an optical detection technique, based on time-varying, pressure-induced deformations of a small liquid droplet, serving as a microlens for a probing laser beam, have been developed. This technique has been applied to measure electroacoustic signals within different electrolyte solutions in the low frequency range 0 to 1 kHz, where the obtained electroacoustic spectra contain more information about the structure of the solution and the ion migration, as compared to previous sound excitation measurements in the high kilohertz range.
Multidirectional rubbed liquid-crystal cells
Authors: Huang Chi-Yen , Lin Chi-Huang , Wang Jyun-Ruei , Huang Chun-Wei , Tsai Ming-Shann , Ying-Guey Fuh Andy
Published: December 2002

The alignment characteristics of the homogeneous liquid-crystal (LC) cell rubbed multidirectionally were examined. LC molecules align along an axis between two different rubbing directions. The rubbing strength, cell thickness, and ambient temperature markedly influence the final orientation of the LC molecules. The orientation of the LC molecules and the transmission of a multidirectionally rubbed cell can be controlled according to the ambient temperature. A model that assumes substrate with various groove densities along various rubbing directions is presented. The elastic constant and the viscosity of the LC molecules are found to be the key factors that influence the orientation of the LC molecules.
Transport properties of annealed CdSe colloidal nanocrystal solids
Authors: Drndić M. , Jarosz M. V. , Morgan N. Y. , Kastner M. A. , Bawendi M. G.
Published: December 2002

Transport properties of artificial solids composed of colloidal CdSe nanocrystals (NCs) are studied from 6 to 250 K, before and after annealing. After the solids are annealed, three changes are observed. First, transmission electron micrographs show that the separation between NCs decreases with annealing. Second, the optical absorption spectrum changes: the excitonic peaks of the NC solids shift to lower energies and broaden with annealing. These redshifts can result from the change of the dielectric environment around the NCs. Last, annealing results in greatly enhanced dark current and photocurrent. This increased current can be attributed to the enhancement of interdot tunneling caused by the decreased separation between NCs and by chemical changes in their organic cap. In addition, the dark current is an exponential function of the applied electric field and it is only weakly temperature dependent. Our measurements also suggest that Coulomb interactions between charges on neighboring NCs play an important role in the tunneling current.
Fabrication of electro-optic devices using liquid crystals with a single glass substrate
Authors: Kim Il , Kim Jae-Hoon , Kang Daeseung , Agra-Kooijman Dena M. , Kumar Satyendra
Published: December 2002

A recently developed phase separated composite film method has been employed to fabricate a liquid crystal (LC) based electro-optical device using a single glass substrate. The resultant device is made of adjacent parallel layers of LC and polymer created by phase separation. The LC layer is confined between a film of solidified polymer layer on one side and the glass substrate on the other. Electro-optical properties of these devices demonstrate their technological potential in light weight and hand-held electronic products.
Dephasing in modulation-doped quantum structures probed by THz time-domain spectroscopy
Authors: Ascazubi R. , Akin O. C. , Zaman T. , Kersting R. , Strasser G.
Published: December 2002

The dephasing of intersubband transitions in semiconductor heterostructures was investigated by time-resolved THz spectroscopy. Single quantum structures show dephasing rates, which are nearly identical to scattering rates obtained by conventional Hall measurements and allow insight into the dephasing dynamics. In multiple quantum wells, inhomogeneous broadening of the density of states is the main dephasing mechanism.
Microwave loss-factor of BaxSr1−xTiO3 as a function of temperature, biasing field, barium concentration, and frequency
Authors: Vendik O. G. , Zubko S. P. , Nikol’ski M. A.
Published: December 2002

A correct and verifiable model of the dielectric loss factor of BaxSr1−xTiO3 as a function of temperature, biasing field, barium concentration, and frequency has been developed in frequency range 0.1–100 GHz. Contributions to the loss factor of fundamental, quasi-Debye, acoustic, and low frequency relaxation mechanisms have been modeled. The specified frequency dependence of the loss factor has been taken into account. The fitting parameters of the model provide a good agreement between experimental and simulated data.
Iron nanoparticles in amorphous BaTiO3 thin films with large third-order optical nonlinearity
Authors: Wang Weitian , Yang Guang , Chen Zhenghao , Zhou Yueliang , Lu Huibin , Yang Guozhen
Published: December 2002

Composite thin films comprising nanometer-size iron particles embedded in an amorphous BaTiO3 matrix (Fe/BTO) were fabricated by alternate pulsed-laser deposition from pure metallic Fe and ceramic BaTiO3 targets. The distribution of Fe nanoparticles in BTO matrix was observed using high-resolution transmission electron microscope. X-ray photoelectron spectroscopy was used to check the Fe chemical bond state for the deposited films. Optical absorption spectra showed no significant surface plasma resonance peak in the wavelength range of 330–800 nm. The nonlinear optical properties of the Fe/BTO films were determined using the Z-scan method at the wavelength of 532 nm with laser duration of 10 ns. The real and imaginary parts of the third-order nonlinear susceptibility χ(3) were determined to be 7.18×10−7 esu and −8.60×10−8 esu, respectively. The results show that Fe/BTO composite thin films have great potential in designing nonlinear optical devices.
Morphological and optical properties of Si nanostructures imbedded in SiO2 and Si3N4 films grown by single source chemical vapor deposition
Authors: Torrison L. , Tolle J. , Smith David J. , Poweleit C. , Menendez J. , Mitan M. M. , Alford T. L. , Kouvetakis J.
Published: December 2002

Luminescent Si nanocrystals imbedded in amorphous SiO2 and Si3N4 networks have been prepared using an approach based on deposition of Si-rich Si–O and Si–N films by ultrahigh vacuum-chemical vapor deposition reactions of the single-source precursors O(SiH3)2 and N(SiH3)3 respectively. The film growth is conducted on Si (100) at temperatures of 750–850 °C and at extremely high rates of 20–30 nm per min with complete hydrogen elimination. Rapid thermal annealing of the as-deposited films at 1100–1200 °C for 30–60 s generates Si nanocrystals with tunable sizes, discrete shapes, and uniform distributions. The phase, composition, and microstructure of the films are characterized by a variety of analytical techniques including high-resolution electron microscopy. The room temperature photoluminescence (PL) is blueshifted substantially with respect to pure Si and appears to be independent of the Si3N4 and SiO2 dielectric medium. The PL energy increases with decreasing crystal size in accordance with quantum confinement concepts. The key aspects of this approach include the use of completely inorganic (C–H free) and volatile siloxanes and silyl amines with built-in Si–N and Si–O atomic arrangements that allow stoichiometric control at the atomic level leading to formation of highly homogeneous crystallite profiles with adjustable densities and sizes throughout the amorphous matrix.
Supercritical carbon dioxide extraction to produce low-k plasma enhanced chemical vapor deposited dielectric films
Authors: Lubguban J. A. , Sun J. , Rajagopalan T. , Lahlouh B. , Simon S. L. , Gangopadhyay S.
Published: December 2002

A treatment to reduce the dielectric constant of plasma enhanced chemical vapor deposition (PECVD) films is presented. The method involved extracting low molecular weight or CO2 soluble species in the films by post deposition supercritical CO2 pressurization (SCCO2). We observed a decrease in k value of about 10%–14% in a composite film of organosilicate and a-C:F after SCCO2 treatment at 200 °C for 8 h. The composite films were deposited by PECVD using C4F8 and tetravinyltetramethylcyclotetrasiloxane (TVTMCTS) liquid source and H2 carrier gas at room temperature. As-deposited films were also annealed at 200 °C for 8 h in N2 atmosphere to compare the effect of thermal annealing without SCCO2 treatment. The result shows that there is no change in the k of the films after annealing. Thus, SCCO2 extraction is a good method for reducing the dielectric constant of these PECVD composite films. Supercritical CO2 pressurization of the film deposited using TVTMCTS and H2 only without the addition of C4F8 has no effect on the dielectric properties of the film while SCCO2 treatment of a-C:F samples deposited using C4F8 only dissolved the film. Therefore, in the composite film, we expect that CFx species dissolve during SCCO2 treatment while the organosilicate structure is preserved. Analysis of the Fourier-transform infrared spectra of the samples supports this hypothesis based on the decrease in the C–F absorption intensity after SCCO2 treatment.
Extremely small diffusion constant of Cs in multiwalled carbon nanotubes
Authors: Suzuki S. , Watanabe Y. , Ogino T. , Heun S. , Gregoratti L. , Barinov A. , Kaulich B. , Kiskinova M. , Zhu W. , Bower C. , Zhou O.
Published: December 2002

The Cs intercalation process in multiwalled carbon nanotubes (MWNTs) was studied by cross-sectional scanning photoemission microscopy. Cs atoms initially deposited on the tips of aligned nanotubes diffused toward their roots. The Cs diffusion constant for the MWNTs at room temperature was evaluated from the Cs distribution measured along the axes of the tubes. The value of 2×10−12 cm2/s obtained is seven orders of magnitude smaller than that in graphite, although the local atomic structure of an intercalated MWNT is very similar to that of intercalated graphite.
Energy-filtered imaging in a field-emission scanning electron microscope for dopant mapping in semiconductors
Authors: Schönjahn C. , Humphreys C. J. , Glick M.
Published: December 2002

Two-dimensional dopant mapping using secondary electrons in a scanning electron microscope (SEM) is a useful and rapid technique for studying dopant distributions with high spatial resolution in semiconductor materials and devices. However, the technique has a major drawback: although p–n junctions and differently doped p-type regions can be imaged, the contrast from differently doped n-type regions is extremely low, hence, such regions cannot normally be detected. We demonstrate that energy filtering of the secondary electrons substantially enhances the contrast of differently doped n-type regions, so that they are easily differentiated and mapped. This is because the contrast is based on the shift of energy spectra from n and p regions rather than secondary electron yield differences that lead to the conventional dopant contrast. We have used a standard commercially available Schottky field emission gun SEM for our work. Energy-filtered secondary electron imaging in a SEM therefore provides a rapid technique for the imaging and mapping of both p-type and n-type dopants. Our initial results indicate that a spatial resolution of <6 nm can be expected for favorable specimens.
Emission through one of two metal electrodes of an organic light-emitting diode via surface-plasmon cross coupling
Authors: Gifford Dawn K. , Hall Dennis G.
Published: December 2002

We report strong surface emission from an organic light-emitting diode in which the luminescent material resides between two nearly opaque metal electrodes. Experimental and theoretical analyses indicate that cross coupling between surface plasmons on opposite sides of the metal cathode layer enables the transmission of electroluminescence through the practically opaque metal. The application of this physical process has the potential to expand the range of device structures possible for organic light-emitting diodes and other electroluminescent devices.
Effects of hole depth on enhanced light transmission through subwavelength hole arrays
Authors: Degiron A. , Lezec H. J. , Barnes W. L. , Ebbesen T. W.
Published: December 2002

We studied the role of the aperture depth on the enhanced transmission of light through subwavelength holes in free-standing Ag films by measuring the transmission properties of square arrays of cylindrical holes. Two regimes are found which give insight into the transmission mechanism and will be of importance for device applications.
Optical characteristics of SiO2 photonic band-gap crystal with ferroelectric perovskite oxide
Authors: Kim Bog G. , Parikh Kunjal S. , Ussery Geoffrey , Zakhidov Anvar , Baughman Ray H. , Yablonobitch Eli , Dunn Bruce S.
Published: December 2002

We have made SiO2 photonic band-gap crystal infiltrated with ferroelectric perovskite oxide (BaTiO3, PbTiO3, SrTiO3) by using self-assembly and sol-gel methods. Microscopic optical reflectivity has been measured to characterize pseudogap properties of small single crystallites with different orientations. We have found significant redshift of pseudogap in opal infiltrated with BaTiO3 or PbTiO3, whereas negligible shift in opal with SrTiO3 infiltration.
Ultrafast ac Stark effect switching of the active photonic band gap from Bragg-periodic semiconductor quantum wells
Authors: Prineas J. P. , Zhou J. Y. , Kuhl J. , Gibbs H. M. , Khitrova G. , Koch S. W. , Knorr A.
Published: December 2002

The ultrafast suppression and recovery of an active photonic band-gap structure constructed from the periodic complex susceptibility of quantum well excitons is demonstrated. For resonant pumping, the corresponding superradiant mode is slaved by the external field, and the structure forms a mirror that can be switched on and off at a bandwidth limited only by the width of the pump-pulse and the photonic band gap. Absorption and creation of free carriers is suppressed by the accelerated decay of the superradiant mode of the light-coupled quantum wells.
“Gentle lithography” with benzene on Si(100)
Authors: Kruse Peter , Wolkow Robert A.
Published: December 2002

A scanning tunneling microscopy (STM) based nanolithographic method has been demonstrated. The previously reported tip-induced desorption of benzene from Si(100) was utilized to pattern the surface with close to atomic precision. This kind of lithography can take place under very mild conditions. Writing occurs with a STM tip bias of 2.8 V. No heating, etching, or exposure to photons is required. The method is best suited for small to medium sized molecules and can be said to be reliable for resolutions of 2 nm and above. In this letter, we have demonstrated patterning areas of the surface with ethylene and vinyl ferrocene.
High-average-power, high-duty-cycle (λ∼6 μm) quantum cascade lasers
Authors: Slivken S. , Evans A. , David J. , Razeghi M.
Published: December 2002

High-power quantum cascade lasers emitting at λ=6.1 μm are demonstrated. Accurate control of growth parameters and strain balancing results in a near-perfect lattice match, which leads to excellent material quality. Excellent peak power for uncoated lasers, up to 1.5 W per facet for a 21 μm emitter width, is obtained at 300 K for 30 period structures. The threshold current density at 300 K is only 2.4 kA/cm2. From 300 to 425 K, the laser exhibits a characteristic temperature T0 of 167 K. Next, Y2O3/Ti/Au mirror coatings were deposited on 1.5 mm cavities and mounted epilayer down. These lasers show an average output power of up to 225 mW at 17% duty cycle, and still show 8 mW average power at 45% duty cycle.
Effects of nitridation of silicon and repeated spike heating on the electrical properties of SrTiO3 gate dielectrics
Authors: Liu Chih-Yi , Lue Hang-Ting , Tseng Tseung-Yuen
Published: December 2002

Electrical properties of SrTiO3 (STO) gate dielectrics on Si substrates grown by rf-magnetron sputtering were studied. We employed the surface nitridation and repeated spike heating to improve the interfacial properties of STO/Si. The nitrogen was moderately incorporated at the interface by first growing a thin SiON layer and then removing this sacrificial layer before growing STO gate dielectric. The experimental results indicate that this nitridation treatment may retard the formation of thin interfacial layer during the high-temperature growth of STO gate dielectric and consequently decrease the equivalent oxide thickness (EOT) by about 10% toward 24% at various deposition pressures. The STO gate dielectric with this nitridation treatment exhibited slightly lower leakage current at an accumulation region and nearly 2 orders of magnitude lower leakage current at an inversion region. The repeated spike heating technique was also employed to deposit a STO gate dielectric at repeated oscillating temperatures. The results show that this thermal treatment reduced the interfacial trap states and the leakage current was also reduced by about 1 order of magnitude at the same EOT.
Fabrication of nanoporous gold nanowires
Authors: Ji Chunxin , Searson Peter C.
Published: December 2002

We report a method for the fabrication of nanoporous nanowires with high surface area and well-defined pore morphology. The nanoporous nanowires are formed in a two-step process involving electrochemical deposition of a single-phase, two-component AxB1−x alloy into a nanoporous template, and subsequent chemical etching of one component from the alloy after removal from the template. Here, we demonstrate the fabrication of nanoporous gold nanowires and also show that nonporous segments can be incorporated into multisegment nanowires.
Effect of particle size on magnetic properties of zinc chromite synthesized by sol–gel method
Authors: Chen X. H. , Zhang H. T. , Wang C. H. , Luo X. G. , Li P. H.
Published: December 2002

Spinel zinc chromite nanocrystals with various grain sizes ranging from 6.8 to 32 nm have been synthesized using a formalin sol–gel method. Samples were characterized by x-ray diffraction, transmission electron micrograph, and superconducting quantum interference device magnetometer. An effect of particle size on magnetic properties is observed. The decrease in particle size leads to a large enhancement of magnetization. Antiferromagnetic transition disappears when the particles reach a critical size, which can be explained by the deviation from the normal spinel structure in the cation distribution induced by particle size.
Pressure effect on crystallization kinetics in Zr46.8Ti8.2Cu7.5Ni10Be27.5 bulk glass
Authors: Jiang J. Z. , Gerward L. , Xu Y. S.
Published: December 2002

Crystallization kinetics of a Zr46.8Ti8.2Cu7.5Ni10Be27.5 bulk glass in the supercooled liquid region have been investigated by performing in situ high-temperature and high-pressure x-ray diffraction measurements using synchrotron radiation. A pressure–time–temperature–transformation diagram, describing the onset of crystallization as a function of time during isothermal annealing under pressure, is presented. Different pressure dependences of crystallization kinetics in the temperature range for the glass have been observed and further be explained by a model of competing processes of the thermodynamic potential barrier of nucleation and the diffusion activation energy under pressure.
Size effect on intragranular elastic constants in thin tungsten films
Authors: Villain P. , Goudeau Ph. , Renault P.-O. , Badawi K. F.
Published: December 2002

The size effect on the elastic constants of nanocrystalline tungsten has been investigated in the case of W/Cu multilayers with two modulation wavelengths (3.1 and 24.0 nm). Tungsten Young’s modulus and Poisson’s ratio have been measured thanks to a technique coupling x-ray diffraction with in situ tensile testing. It is demonstrated that the in-grain thin film elastic constants are highly microstructure—sensitive: in the “3.1 nm” multilayer, tungsten Poisson’s ratio is larger than the bulk one while it is smaller in the “24.0 nm” multilayer; a softening of tungsten Young’s modulus is evidenced in the case of the specimen with the smallest period.
Photon mapping of quantum dots using a scanning tunneling microscope
Authors: Håkanson U. , Johansson M. K.-J. , Holm M. , Pryor C. , Samuelson L. , Seifert W. , Pistol M.-E.
Published: December 2002

Scanning tunneling microscopy (STM) and scanning tunneling luminescence (STL) have been used to investigate the geometric and optical properties of individual self-assembled InP quantum dots overgrown with a thin layer of GaInP. STL spectra and monochromatic photon maps were used to correlate the surface topography with the optical properties of single quantum dots. We find a spatial resolution of about 10 nm in the photon maps. Theoretical emission spectra were calculated by six-band k⋅p theory using a realistic shape of the dot as well as of the cap layer. The calculated emission spectrum of a single dot is in good agreement with the experimental findings.
Polymer thin-film transistors with chemically modified dielectric interfaces
Authors: Salleo A. , Chabinyc M. L. , Yang M. S. , Street R. A.
Published: December 2002

The characteristics of polymeric thin-film transistors can be controlled by chemically modifying the surface of the gate dielectric prior to the deposition of the organic semiconductor. The chemical treatment consists of derivatizing the silicon oxide surface with organic trichlorosilanes to form self-assembled monolayers (SAMs). The deposition of an octadecyltrichlorosilane SAM leads to a mobility of 0.01–0.02 cm2/V s in a polyfluorene copolymer, a 20-fold improvement over the mobility on bare silicon oxide. The mobility enhancement mechanism is likely to involve molecular interactions between the polymer and the SAM.
Low-pressure, high-current hollow cathode with a ferroelectric plasma source
Authors: Krokhmal A. , Gleizer J. Z. , Krasik Ya. E. , Felsteiner J.
Published: December 2002

We report the parameters of a hollow cathode with a ferroelectric plasma source incorporated in it. It was found that this source allows the ignition and sustaining of a high-current discharge (⩽1.4 kA, ⩽2×10−5 s) at N2 gas pressure of (3–5)×10−4 Torr. It was shown that ∼85% of the discharge current is emitted by the ferroelectric sample. The plasma in the cathode acquires a positive potential (⩽50 eV) with respect to the anode and the plasma density and temperature are ⩽8×1012 cm−3 and ⩽18 eV, respectively. Generation of an electron beam (0.3–1.6 kA, 300 ns) was demonstrated under an accelerating pulse ⩽300 kV.
Nanowire resonant tunneling diodes
Authors: Björk M. T. , Ohlsson B. J. , Thelander C. , Persson A. I. , Deppert K. , Wallenberg L. R. , Samuelson L.
Published: December 2002

Semiconductor heterostructures and their implementation into electronic and photonic devices have had tremendous impact on science and technology. In the development of quantum nanoelectronics, one-dimensional (1D) heterostructure devices are receiving a lot of interest. We report here functional 1D resonant tunneling diodes obtained via bottom-up assembly of designed segments of different semiconductor materials in III/V nanowires. The emitter, collector, and the central quantum dot are made from InAs and the barrier material from InP. Ideal resonant tunneling behavior, with peak-to-valley ratios of up to 50:1 and current densities of 1 nA/μm2 was observed at low temperatures.
GRP94 (gp96) and GRP94 N-Terminal Geldanamycin Binding Domain Elicit Tissue Nonrestricted Tumor Suppression
Authors: Baker-LePain Julie C. , Sarzotti Marcella , Fields Timothy A. , Li Chuan-Yuan , Nicchitta Christopher V.
Published: December 2002

In chemical carcinogenesis models, GRP94 (gp96) elicits tumor-specific protective immunity. The tumor specificity of this response is thought to reflect immune responses to GRP94-bound peptide antigens, the cohort of which uniquely identifies the GRP94 tissue of origin. In this study, we examined the apparent tissue restriction of GRP94-elicited protective immunity in a 4T1 mammary carcinoma model. We report that the vaccination of BALB/c mice with irradiated fibroblasts expressing a secretory form of GRP94 markedly suppressed 4T1 tumor growth and metastasis. In addition, vaccination with irradiated cells secreting the GRP94 NH2-terminal geldanamycin-binding domain (NTD), a region lacking canonical peptide-binding motifs, yielded a similar suppression of tumor growth and metastatic progression. Conditioned media from cultures of GRP94 or GRP94 NTD-secreting fibroblasts elicited the up-regulation of major histocompatibility complex class II and CD86 in dendritic cell cultures, consistent with a natural adjuvant function for GRP94 and the GRP94 NTD. Based on these findings, we propose that GRP94-elicited tumor suppression can occur independent of the GRP94 tissue of origin and suggest a primary role for GRP4 natural adjuvant function in antitumor immune responses.
Correction of the Iron Overload Defect in β-2-Microglobulin Knockout Mice by Lactoferrin Abolishes Their Increased Susceptibility to Tuberculosis
Authors: Schaible Ulrich E. , Collins Helen L. , Priem Friedrich , Kaufmann Stefan H.E.
Published: December 2002

As a resident of early endosomal phagosomes, Mycobacterium tuberculosis is connected to the iron uptake system of the host macrophage. β-2-microglobulin (β2m) knockout (KO) mice are more susceptible to tuberculosis than wild-type mice, which is generally taken as a proof for the role of major histocompatibility complex class I (MHC-I)–restricted CD8 T cells in protection against M. tuberculosis. However, β2m associates with a number of MHC-I–like proteins, including HFE. This protein regulates transferrin receptor mediated iron uptake and mutations in its gene cause hereditary iron overload (hemochromatosis). Accordingly, β2m-deficient mice suffer from tissue iron overload. Here, we show that modulating the extracellular iron pool in β2m–KO mice by lactoferrin treatment significantly reduces the burden of M. tuberculosis to numbers comparable to those observed in MHC class I–KO mice. In parallel, the generation of nitric oxide impaired in β2m–KO mice was rescued. Conversely, iron overload in the immunocompetent host exacerbated disease. Consistent with this, iron deprivation in infected resting macrophages was detrimental for intracellular mycobacteria. Our data establish: (a) defective iron metabolism explains the increased susceptibility of β2m-KO mice over MHC-I–KO mice, and (b) iron overload represents an exacerbating cofactor for tuberculosis.
Computer Aided Design of Elliptical Gears
Authors: Bair Biing-Wen
Published: December 2002

An elliptical gear drive, whose rotation axis coincides with its geometric center, is simulated using generation with a rack cutter. The mathematical model of an elliptical gear based on the theory of gearing and gear generation mechanism is also developed. Owing to its complex geometry, the profile of elliptical gears may exhibit tooth undercutting, and pointed teeth. In addition, tooth undercutting of an elliptical gear based on the developed mathematical model of the elliptical gear and the theory of gearing is also investigated. Pointed teeth usually appear on the major axis of the gear elliptical pitch curve. Moreover, a geometric relation is developed and applied to prevent the pointed teeth appearing on elliptical gears. Furthermore, a computer simulation program is developed to generate the tooth profile of elliptical gears without tooth undercutting and pointed teeth. Various numerical examples illustrate the effectiveness of the computerized design process.