bluuebunny/crossref_metadata_2025 huggingface dataset:
Study of a single dangling bond at the SiO2/Si interface in deep submicron metal–oxide–semiconductor transistors
Authors: Militaru L. , Souifi A.
Published: September 2003

Two-level charge pumping (CP) measurements have been used for the study of a single trap situated at the SiO2/Si interface of sub-100 nm metal–oxide–semiconductor transistors (50 nm length). At room temperature, we have measured the emission time constant (τ) of the single trap and verified that the generation-recombination process was consistent with the Shockley–Read–Hall theory. Temperature-dependent CP measurements have been used to determine the thermal variation of the emission time constant. We show that an Arrhenius plot of the emission time constant versus the temperature (τxT2 vs 1/T) allows the determination of the capture cross section and energy position of the trap within the silicon band gap. The single trap, which has been characterized here, is shown to be the well-known donor Pb0 center (dangling bond) at the SiO2/Si (100) interface.
Studying the local chemical environment of sulfur atoms at buried interfaces in CdS/ZnSe superlattices
Authors: Heske C. , Groh U. , Fuchs O. , Weinhardt L. , Umbach E. , Grün M. , Petillon S. , Dinger A. , Klingshirn C. , Szuszkiewicz W. , Fleszar A.
Published: September 2003

Soft x-ray emission spectroscopy has been employed to study the local chemical environment of sulfur atoms in sulfide II–VI semiconductors (ZnS, CdS, HgS) and CdS/ZnSe superlattices. By using fluorescence transitions involving metal d-state-derived valence bands and S 2p core holes, a distinction between S–Zn and S–Cd bonds in the superlattices can be made. We find that, in addition to the expected S–Cd bonds, interfacial S–Zn bonds are present in superlattices grown at 170 °C, and that the amount of S–Zn bonds significantly increases for growth at 300 °C due to interface intermixing.
Effects of Rayleigh scattering in transient nonlinear optical measurements
Authors: Shou Qian , Zhang Hai-Chao , Deng Li , Liu Ye-Xin , Lai Tian-Shu , Lin Wei-Zhu
Published: September 2003

An interference phenomenon in femtosecond four-wave mixing and pump-probe experiments on AlGaAs/GaAs multiple-quantum-well films is observed, which is interpreted as the interference of Rayleigh scattering field and the third-order polarization of the sample. Based on the Rayleigh scattering mode, a population relaxation time of 150 fs and a dephasing time of 44 fs of the sample are deduced.
Suppression of native oxide growth in sputtered TaN films and its application to Cu electroless plating
Authors: Wang Zenglin , Yaegashi Osamu , Sakaue Hiroyuki , Takahagi Takayuki , Shingubara Shoso
Published: September 2003

Electroless plated copper can be deposited on a TaN surface initiated by displacement plating when the surface oxide layer is removed by wet chemical etching. For application to ultra-large-scale integrated (ULSI) interconnection technology in which very thin TaN barrier films are used, it is essential to form a stable TaN film with minimal native oxide thickness. In this study, TaN films with various N/Ta atomic ratios were fabricated by reactive sputtering and native oxide growth on the surface was investigated by x-ray photoelectron spectroscopy, high resolution Rutherford backscattering spectrometry, and x-ray diffraction (XRD). It was found that when the N/Ta atomic ratio in the film was lower than 1.2, surface oxidation of the TaN film advanced with time. When the ratio was higher than 1.2, oxidation of the TaN film stopped at 1 ML. The XRD spectra indicated that when the N/Ta atomic ratio was between 0.82 and 1.25, face-centered-cubic TaN films were formed and the resistivity increased with an increase in the N/Ta ratio. Thus, a TaN film with a N/Ta ratio of 1.25 ratifies the minimal surface oxide thickness as well as low-resistivity requirements, and is appropriate for ULSI Cu interconnections using electroless Cu deposition.
Shock wave coupling between terahertz transmission lines on GaAs
Authors: Desplanque L. , Peytavit E. , Lampin J.-F. , Lippens D. , Mollot F.
Published: September 2003

We experimentally study the behavior of an electromagnetic shock wave radiated by a picosecond electrical pulse propagating on a coplanar stripline at the interface between air and a GaAs substrate. The shock wave is directly measured by time-resolved electroabsorption sampling. We show that after a few millimeters of propagation this shock wave is in fact constituted by substrate modes causing large leakage resonances in the spectrum of the propagating pulse. At last, we show that the presence of adjacent transmission lines on the substrate has an influence on these leakage resonances.
Temperature-dependent adsorption of Hg on CdTe(211)B studied by spectroscopic ellipsometry
Authors: Badano G. , Chang Y. , Garland J. W. , Sivananthan S.
Published: September 2003

The adsorption of Hg on CdTe(211)B is studied by reflective high-energy electron diffraction and by spectroscopic ellipsometry in the range of 1.8–4.1 eV. We use a Hg molecular beam to create a high equilibrium coverage of Hg on CdTe. We find that at least two types of Hg are present at the surface: A physisorbed form, which displays a Drude-type dielectric function, and a chemisorbed form, which gives rise to a dielectric function similar to that of bulk Hg1−xCdxTe, but with sharper structure characteristic of lower dimensionalities. The dependence of the relative amounts of these two forms of Hg on the temperature and the impinging flux is obtained from the data analysis.
Liner materials for direct electrodeposition of Cu
Authors: Lane M. W. , Murray C. E. , McFeely F. R. , Vereecken P. M. , Rosenberg R.
Published: September 2003

We identified a family of materials which can be directly electroplated with Cu in acidic plating baths commonly found in the microelectronics industry. Details are presented illustrating a number of important properties of the electroplated Cu/linear material system. These include the adhesion of the plated film to liner material, the recrystallization behavior of the plated film, the texture of the plated film, and the resistivity of the plated film after high-temperature anneals. Finally, an example is presented illustrating the direct plating of Cu across an 8 in. wafer without the use of a Cu seed layer.
Drain voltage scaling in carbon nanotube transistors
Authors: Radosavljević M. , Heinze S. , Tersoff J. , Avouris Ph.
Published: September 2003

Decreasing the oxide thickness in carbon nanotube field-effect transistors (CNFETs) improves the turn-on behavior. However, we demonstrate that this also requires scaling the range of the drain voltage. This scaling is needed to avoid an exponential increase in off-current with drain voltage, due to modulation of the Schottky barriers at both the source and drain contact. We illustrate this with results for bottom-gated ambipolar CNFETs with oxides of 2 and 5 nm, and give an explicit scaling rule for the drain voltage. Above the drain voltage limit, the off-current becomes large and has equal electron and hole contributions. This allows the recently reported light emission from appropriately biased CNFETs.
Magnetic photonic band-gap material at microwave frequencies based on ferromagnetic nanowires
Authors: Saib A. , Vanhoenacker-Janvier D. , Huynen I. , Encinas A. , Piraux L. , Ferain E. , Legras R.
Published: September 2003

We present an experimental investigation of a class of microwave photonic band-gap (PBG) materials, in which the magnetic permeability μ varies periodically within the material. This material is fabricated using a periodic arrangement of arrays of magnetic nanowires. As for dielectric or metallic PBG, the band-gap behavior varies with the geometrical parameters fixing the spatial periodicity of the magnetic structure. The magnetic photonic band gap is induced by the presence of a ferromagnetic resonance effect in the vicinity of the band gap.
Terahertz imaging using an interferometric array
Authors: Federici John F. , Gary Dale , Schulkin Brian , Huang Feng , Altan Hakan , Barat Robert , Zimdars David
Published: September 2003

Most methods of imaging in the terahertz (THz) spectral region utilize either pulsed-laser sources or require the THz generation and detection sources to be phase coherent. The application of interferometric imaging to the THz range is described. Interferometric imaging offers considerable advantages in this regard due to its ability to image with only a handful of detector elements, image many sources of THz radiation at once, image incoherent as well as coherent sources, and provide spectral information as well as spatial imaging information. The THz interferometric imaging method is potentially useful for remote detection of explosives.
Self-assembled Co nanorods in diamond-like carbon thin films synthesized by plasma-assisted magnetron sputtering
Authors: Wang F. L. , Jiang J. C. , Meletis E. I.
Published: September 2003

We report on self-assembled, high-aspect-ratio nanostructures of Co rods in diamond-like carbon (DLC) thin films synthesized by plasma-assisted magnetron sputtering. Cross-sectional and plan-view transmission electron microscopy investigations show that the nanorods continuously grow vertically to the substrate and have a relatively narrow distributed lateral size. The nanorods in the as-deposited thin films are found to have an ε-Co structure with a high density of defects and are encapsulated by 1–2 nm of an amorphous DLC matrix.
Large piezoelectric response in (111)-oriented epitaxial Pb(Zr,Ti)O3 films consisting of mixed phases with rhombohedral and tetragonal symmetry
Authors: Yokoyama Shintaro , Honda Yoshihisa , Morioka Hitoshi , Oikawa Takahiro , Funakubo Hiroshi , Iijima Takashi , Matsuda Hirofumi , Saito Keisuke
Published: September 2003

Pb ( Zr,Ti ) O 3 films with a Zr/(Zr+Ti) ratio of 0.48 having 1.5 μm in thickness were grown on (100)c-, (110)c-, and (111)c-oriented SrRuO3//SrTiO3 substrates by metalorganic chemical vapor deposition. It was ascertained by θ–2θ scans of x-ray diffraction that (001)T-/(100)T-/(100)R-, {110}-, and {111}-oriented films were epitaxially grown on (100)c-, (110)c-, and (111)c-oriented substrates. Polarization and field-induced strain in these films were simultaneously observed through a scanning probe microscope that was attached to a ferroelectric test system. About three times larger field-induced strain than that on other substrates was observed together with the largest spontaneous polarization for a film grown on a (111)cSrRuO3//(111)SrTiO3 substrate. High-resolution x-ray diffraction analysis suggested that the film grown on the (111)cSrRuO3//(111)SrTiO3 substrate consisted of rhombohedral and tetragonal mixture phases. Its crystal structure possibly contributed to the large piezoelectric response.
Domain structure of epitaxial Bi4Ti3O12 thin films grown on (001) SrTiO3 substrates
Authors: Pan X. Q. , Jiang J. C. , Theis C. D. , Schlom D. G.
Published: September 2003

The domain structure of epitaxial (001) Bi4Ti3O12 thin films grown on (001) SrTiO3 substrates by reactive molecular beam epitaxy was studied using transmission electron microscopy. It was found that the Bi4Ti3O12 thin films contain randomly distributed rotation domains of two different types, which are related by a 90° rotation around the c axis of Bi4Ti3O12. These domains result from the difference in crystallographic symmetry between the Bi4Ti3O12 (001) plane and the SrTiO3 (001) surface. Moreover, out-of-phase boundaries were frequently observed in the epitaxial Bi4Ti3O12 films. Detailed quantitative high-resolution transmission electron microscopy studies showed that the growth of epitaxial Bi4Ti3O12 film on the SrTiO3 (001) surface begins with the energetically favorable central TiO2 layer in the middle of the triple perovskite block within Bi4Ti3O12. As a result, a number of out-of-phase domain boundaries are formed at the atomic steps on the substrate surface. These studies suggest that Bi4Ti3O12 films grow on (001) SrTiO3 substrates through two-dimensional island growth mechanism, where individual domains nucleate with random orientations of their polar a axis along either [110] or [11̄0] direction of SrTiO3.
Potential imaging of pentacene organic thin-film transistors
Authors: Nichols J. A. , Gundlach D. J. , Jackson T. N.
Published: September 2003

Scanning Kelvin probe microscopy (SKPM) has been used to simultaneously obtain high-resolution topographical and potential images of pentacene organic thin-film transistors (OTFTs) during device operation. SKPM images of OTFTs show large potential drops at the source with the magnitude dependent on contact metallurgy and relatively small potential drops at grain boundaries in polycrystalline pentacene films.
High-efficiency white phosphorescent organic light-emitting devices with greenish-blue and red-emitting layers
Authors: Tokito Shizuo , Iijima Toshiki , Tsuzuki Toshimitsu , Sato Fumio
Published: September 2003

We demonstrate high-efficiency white light emission from a phosphorescent organic light-emitting device with greenish-blue and red emissive layers. Bis{2-[3,5-bis(trifluoromethyl)phenyl]-pyridinato-N,C2′}iridium(III)picolinate [(CF3ppy)2Ir(pic)] and bis{2-[2′-benzo(4,5-a)thienyl]pyridinato-N,C3′}iridium(III)acetylacetonate were employed for the greenish-blue and red phosphorescent materials for the emissive layers. To enhance the emission efficiency of (CF3ppy)2Ir(pic), 4,4′-bis(9-carbazolyl)-2,2′-dimethyl-biphenyl was used as the charge-transporting host. White light emission was obtained by controlling the layer thickness and the concentration of each phosphorescent material in the emissive layers. A maximum external quantum efficiency of 12%, a luminance efficiency of 18 cd/A, and a maximum power efficiency of 10 lm/W were achieved at a current density of 0.01 mA/cm2. This high efficiency is primarily attributed to the improvement of greenish-blue emission efficiency due to the strong confinement of triplet excitons on the (CF3ppy)2Ir(pic) molecules.
Fluorination of carbon nanotubes in CF4 plasma
Authors: Plank N. O. V. , Jiang Liudi , Cheung R.
Published: September 2003

The effect of CF4 gaseous plasma exposure to single-wall carbon nanotubes (CNTs) has been studied. Raman spectroscopy results show that CNTs have gained more disordered sp3 bonds associated with functionalization, as both the flow rates of gas in the plasma and exposure time in the plasma are increased. Scanning electron microscopy images indicate the CNTs have been preserved after CF4 plasma exposure. X-ray photoelectron spectroscopy provides evidence of carbon to fluorine bonds (C–F) on the CNTs samples after CF4 plasma exposure. Semi-ionic and covalent C–F bonds are prevalent on the CNTs after CF4 exposure with the intensity ratio of the semi-ionic to covalent C–F bond decreasing as the flow rate of CF4 and exposure time in the CF4 plasma is increased.
Plasticity in Ni59Zr20Ti16Si2Sn3 metallic glass matrix composites containing brass fibers synthesized by warm extrusion of powders
Authors: Bae D. H. , Lee M. H. , Kim D. H. , Sordelet D. J.
Published: September 2003

Deformation behavior of centimeter-scale Ni-based metallic glass matrix composites reinforced by brass fibers, synthesized by warm extrusion of gas atomized powders, has been investigated under the uniaxial compression condition at room temperature. Throughout the extrusion process, all blended spherical powders are elongated along the extrusion direction. The brass fibers are well distributed in the metallic glass matrix for the metallic glass matrix composites containing the brass up to 0.4 in volume fraction and no pores are visible. With increasing the brass content, elastic modulus and strength decrease due to the softness of the brass, but enhanced macroscopic plasticity is observed due to the formation of multiple shear bands, initiated from the interface between brass fiber and metallic glass matrix, as well as their confinement between the brass fibers. These behaviors are not observed in the sample synthesized by warm extrusion of only metallic glass powders.
Control of microelectromechanical systems membrane curvature by silicon ion implantation
Authors: Jin S. , Mavoori H. , Kim J. , Aksyuk V. A.
Published: September 2003

Thin silicon membranes in microelectromechanical systems (MEMS) optical devices such as beam-steering, movable mirrors may exhibit undesirable curvature when their surface is metallized with light-reflecting metals to enhance optical performance. We have applied Si+ ion implantations at dose levels of 0.4–5×1016/cm2 into the gold metallization layer to successfully reduce the mirror curvature as well as the degree of its temperature-dependent changes. The curvature change as well as the temperature dependence is found to be dependent on the implantation dose. The mechanism of the observed curvature flattening effect is attributed mostly to the induced compressive stress in gold metallization caused by the insertion of foreign implanted atoms of silicon. Such a Si implantation approach can be useful as a means for post-fabrication correction of unwanted curvature in MEMS membranes, as well as a technique to intentionally introduce a desired degree of curvature if needed. A convenient blanket implantation process can be utilized with minimal contamination problems as Si is a common element already present in the MEMS.
Germanium nanowire field-effect transistors with SiO2 and high-κ HfO2 gate dielectrics
Authors: Wang Dunwei , Wang Qian , Javey Ali , Tu Ryan , Dai Hongjie , Kim Hyoungsub , McIntyre Paul C. , Krishnamohan Tejas , Saraswat Krishna C.
Published: September 2003

Single-crystal Ge nanowires are synthesized by a low-temperature (275 °C) chemical vapor deposition (CVD) method. Boron doped p-type GeNW field-effect transistors (FETs) with back-gates and thin SiO2 (10 nm) gate insulators are constructed. Hole mobility higher than 600 cm2/V s is observed in these devices, suggesting high quality and excellent electrical properties of as-grown Ge wires. In addition, integration of high-κ HfO2 (12 nm) gate dielectric into nanowire FETs with top-gates is accomplished with promising device characteristics obtained. The nanowire synthesis and device fabrication steps are all performed below 400 °C, opening a possibility of building three-dimensional electronics with CVD-derived Ge nanowires.
On the origin of shot noise in CdTe detectors
Authors: Ferrari G. , Sampietro M. , Bertuccio G. , Gomila G. , Reggiani L.
Published: September 2003

Semi-insulating CdTe-based detectors exhibit shot noise at normal operating applied voltage, in spite of their linear symmetric current–voltage characteristic. In the present letter, we provide theoretical and experimental evidence that the origin of shot noise in these detectors under dark conditions can be explained in terms of a diffusion model. The physical reason for this behavior is that the dielectric relaxation time can become longer than the dynamic transit time depending on the applied bias, thus allowing carriers to cross the sample in an independent way. The predictions of the model are confirmed by detailed current noise measurements performed at different temperatures.
Solvation in molecular ionic liquids
Authors: Shim Y. , Duan Jinsong , Choi M. Y. , Kim Hyung J.
Published: September 2003

Solvation in 1-ethyl-3-methylimidazolium chloride and 1-ethyl-3-methylimidazolium hexafluorophosphate is studied via molecular dynamics simulations by employing a diatomic solute as a probe. It is found that solvent fluctuations are chacterized by at least two distinct dynamics occurring on vastly different time scales—rapid subpicosecond dynamics arising mainly from anion translations and slow relaxation ascribed to anion and cation diffusions. Fast subpicosecond dynamics are responsible for more than 50% of the entire relaxation of solvent fluctuations in the temperature range 350 K⩽T⩽500 K. It is also found that solvent spectral shifts and reorganization free energies in these liquids are comparable to those in ambient water.
60 ns time scale short pulse interlayer tunneling spectroscopy for Bi2Sr2CaCu2O8+δ
Authors: Anagawa Kenkichi , Yamada Yoshiharu , Shibauchi Takasada , Suzuki Minoru , Watanabe Takao
Published: September 2003

We utilize the short pulse interlayer tunneling spectroscopy on a 60 ns time scale for the Bi2Sr2CaCu2O8+δ system. The results indicate that the influence of self-heating is negligible up to an injection current density of ∼60 kA/cm2 and an injection power areal density of ∼90 kW/cm2. By means of this technique, we are able to observe the superconducting gap, the pseudogap, and the dip-and-hump structure precisely with little influence from the self-heating.
Molecular-beam-epitaxy growth of ferromagnetic Ni2MnGe on GaAs(001)
Authors: Lu J. , Dong J. W. , Xie J. Q. , McKernan S. , Palmstrøm C. J. , Xin Y.
Published: September 2003

Single-crystal Heusler alloy Ni2MnGe thin films have been grown on GaAs(001) by molecular-beam epitaxy. X-ray diffraction and transmission electron microscopy were used for postgrowth structural characterization. The Ni2MnGe grew in a tetragonally distorted L21-like structure (a=5.65 Å, c=5.96 Å) with the c axis perpendicular to the film surface. An in-plane ordering with 2× periodicity and an out-of-plane ordering with 3× periodicity was observed for the as-grown films. Magnetometry measurements performed at 50 K indicate that the films are ferromagnetic and have a weak in-plane anisotropy with a coercivity ∼5.5 Oe and saturation magnetization of ∼450 emu/cm3. The Curie temperature was measured to be ∼320 K.
Design of realistic switches for coupling superconducting solid-state qubits
Authors: Storcz Markus J. , Wilhelm Frank K.
Published: September 2003

Superconducting flux qubits are a promising candidate for solid-state quantum computation. One of the reasons is that implementing a controlled coupling between the qubits appears to be relatively easy, if one uses tunable Josephson junctions. We evaluate possible coupling strengths and show how much extra decoherence is induced by the subgap conductance of a tunable junction. In light of these results, we evaluate several options of using intrinsically shunted junctions and show that based on available technology, Josephson field effect transistors and high-Tc junctions used as π shifters would be a good option, whereas the use of magnetic junctions as π shifters severely limits quantum coherence.
Low-temperature atomic-layer-deposition lift-off method for microelectronic and nanoelectronic applications
Authors: Biercuk M. J. , Monsma D. J. , Marcus C. M. , Becker J. S. , Gordon R. G.
Published: September 2003

We report a method for depositing patterned dielectric layers with submicron features using atomic layer deposition. The patterned films are superior to sputtered or evaporated films in continuity, smoothness, conformality, and minimum feature size. Films were deposited at 100–150 °C using several different precursors and patterned using either electron-beam or photoresist. The low deposition temperature permits uniform film growth without significant outgassing or hardbaking of resist layers. A lift-off technique presented here gives sharp step edges with edge roughness as low as ∼10 nm. We also measure dielectric constants (κ) and breakdown fields for the high-κ materials aluminum oxide (κ∼8–9), hafnium oxide (κ∼16–19), and zirconium oxide (κ∼20–29), grown under similar low temperature conditions.
Nonlinear-optical probing of nanosecond ferroelectric switching
Authors: Mishina E. D. , Sherstyuk N. E. , Stadnichuk V. I. , Sigov A. S. , Mukhorotov V. M. , Golovko Yu. I. , van Etteger A. , Rasing Th.
Published: September 2003

It is demonstrated that the switching dynamics of the ferroelectric polarization in thin Ba(SrTi)O3 (BST) films can be followed by optical second harmonic generation with a time resolution that is only limited by the gating electronics. It is shown that the characteristic time of electric-field induced polarization switching in 70 nm BST films is less than τ=5 ns.
Optical properties of organic dyes in nanoporous zeolite crystals
Authors: Li Irene L. , Tang Z. K. , Xiao X. D. , Yang C. L. , Ge W. K.
Published: September 2003

Organic dye molecules of styryl 7 were introduced into the channels of AlPO4-5 single crystals. Polarized absorption and photoluminescence spectra of the dye molecules were investigated. The polarization angle dependence of the absorption and photoluminescence intensity indicates that the dye molecules are highly oriented in the channels. The hexagonal-shaped AlPO4-5 single crystal serves as a natural microcavity for lasing action of the dye molecules. The microcavity modes of the lasing action were also demonstrated.
An electrostatic barrier to trap filling in CuIn1−xGaxSe2
Authors: Young David L. , Crandall Richard S.
Published: September 2003

Voltage pulses of variable length were applied to CuIn1−xGaxSe2/CdS (0<x<1) junction solar cells. The resulting nonexponential transient capacitance emission signal was recorded for several minutes. The amplitude of the capacitance emission signal increased linearly with the log of pulse time. These data do not follow the standard model for trap capture and emission of carriers. Instead, they follow a simple model based on electrostatic charging of localized regions of traps. The potential barrier height to trap filling was found to be ∼0.3 eV for all-alloy compositions. Hole capture cross-section data for a single defect are obtained.
Low-loss, tunable bismuth zinc niobate films deposited by rf magnetron sputtering
Authors: Lu Jiwei , Stemmer Susanne
Published: September 2003

Near-stoichiometric Bi1.5Zn1.0Nb1.5O7 (BZN) films were deposited by rf magnetron sputtering. The relative permittivity and dielectric loss of BZN films were measured with frequencies up to 100 MHz using planar Al2O3/Pt/BZN/Pt and Si/SiO2/Pt/BZN/Pt capacitor structures. BZN films with thicknesses in the range of 160 to 170 nm exhibited electric field tunable permittivities up to 220, and dielectric loss tangents less than 0.0005. A maximum applied bias field of 2.4 MV/cm resulted in a ∼55% tunability of the dielectric constant. The permittivity was independent of the measurement frequency over a wide frequency range (10 kHz–100 MHz). Above 1 MHz, losses were increasingly dominated by conductor losses of the Pt bottom electrode. Their excellent dielectric properties make BZN films attractive candidates for low-loss, medium-permittivity integrated device applications.
High-Tc interferometers using all YBa2Cu3O7−δ trilayer junctions
Authors: Sato H. , Fujimoto E. , Yamada T. , Akoh H. , Nakajima T. , Hohkawa K. , Nakagawa H. , Aoyagi M.
Published: September 2003

We have demonstrated high-Tc interferometers using YBaCuO trilayer junctions, which are two-junction-type interferometers with a direct current injection. In order to realize a small loop inductance value without a ground plane, the interferometers were designed to have loop inductance with a vertical stacked structure by overlapping junction bridges on base electrodes. The interferometers showed clear threshold characteristics in the control current dependence of the gate current at temperatures below 70 K. The temperature dependence of the loop inductance showed good agreement with a calculation result based on a strip-line model. The sheet inductance was estimated to be 0.85 pH/□ at 4.2 K from the threshold characteristics of the interferometers by changing the bridge length between the two junctions, which was in good agreement with the design value.
Long-range transport of magnetic microbeads using simple planar coils placed in a uniform magnetostatic field
Authors: Rida A. , Fernandez V. , Gijs M. A. M.
Published: September 2003

We propose an approach for magnetic microbead transport in microfluidic channels over long-range distances using an array of simple planar coils. The latter are placed in a uniform static magnetic field, the role of which is to impose a permanent magnetic moment to the microbeads. The very small magnetic field gradient of a simple planar coil is then sufficient to displace the microbeads. The long-range displacement is assured by arranging adjacent coils in the array with spatial overlap in a three-phase actuation scheme.
Self-switching of branched multiterminal junctions: a ballistic half-adder
Authors: Worschech L. , Reitzenstein S. , Hartmann P. , Kaiser S. , Kamp M. , Forchel A.
Published: September 2003

We demonstrate a self-switching effect of narrow current channels, which allows the control of multiterminal junctions without using external gates. The self-switching leads to negative differential resistance and is interpreted in terms of a bias voltage controlled gating of the junction and the injection of electrons from different terminals. The self-switched multiterminal junction realized in a single conducting plane is exploited as a nanoelectronic half-adder. Our results demonstrate that self-switching effects may be used to increase the functionality of a given number of nanoelectronic devices.
Orientation dependence of ferroelectric properties of pulsed-laser-ablated Bi4−xNdxTi3O12 films
Authors: Garg A. , Barber Z. H. , Dawber M. , Scott J. F. , Snedden A. , Lightfoot P.
Published: September 2003

Epitaxial (001)-, (118)-, and (104)-oriented Nd-doped Bi4Ti3O12 films have been grown by pulsed-laser deposition from a Bi4−xNdxTi3O12 (x=0.85) target on SrRuO3 coated single-crystal (100)-, (110)-, and (111)-oriented SrTiO3 substrates, respectively. X-ray diffraction illustrated a unique epitaxial relationship between film and substrate for all orientations. We observed a strong dependence of ferroelectric properties on the film orientation, with no ferroelectric activity in an (001)-oriented film; a remanent polarization 2Pr of 12 μC/cm2 and coercive field Ec of 120 kV/cm in a (118)-oriented film; and 2Pr=40 μC/cm2, Ec=50 kV/cm in a (104)-oriented film. The lack of ferroelectric activity along the c-axis is consistent with the orthorhombic nature of the crystal structure of the bulk material, as determined by powder neutron diffraction.
Optically driven transport into a living cell
Authors: Kubo Koji , Ichikawa Masatoshi , Yoshikawa Kenich , Koyama Yoshiyuki , Niidome Takuro , Yamaoka Tetsuji , Nomura Shin-Ichirou M.
Published: September 2003

We report a method for transporting foreign substances into a desired living cell through the use of laser trapping. A single giant DNA molecule can be delivered into a cytoplasmic space if the DNA is folded into a compact state. We also find that microparticles of zeolite are very effective as a vehicle for transferring foreign compounds into a living cell by optical manipulation.
Enhanced intergrain magnetoresistance in bulk Sr2FeMoO6 through controlled processing
Authors: Sharma A. , Berenov A. , Rager J. , Branford W. , Bugoslavsky Y. , Cohen L. F. , MacManus-Driscoll J. L.
Published: September 2003

Enhanced low field magnetoresistance (LFMR) values have been obtained in bulk Sr2FeMoO6 through controlled processing. MR values, R(H)/R(0) of ∼60% [(R(H)−R(H=0)/R(H=0)=40%] were achieved at 50 K, in 1 T, and R(H)/R(0)∼8% [(R(H)−R(H=0)/R(H=0)=92%] at 290 K, in 1 T. For a ∼1 μm starting particle size, the optimum sintering temperature was 1300 °C, 100 °C higher than normally used. The optimum sintering time in Ar/H2 was only 5 h, much shorter than normally used. The magnitude of the LFMR appears to depend strongly on grain boundary oxygen content, controlled through optimization of sintering temperature and time.
Site-selective silicon adatom desorption using femtosecond laser pulse pairs and scanning tunneling microscopy
Authors: Futaba D. N. , Morita R. , Yamashita M. , Tomiyama S. , Shigekawa H.
Published: September 2003

We performed an experimental study of silicon adatom desorption from the Si(111)-7×7 surface using femtosecond laser pulse pair excitation with 80 fs pulse duration, 800 nm center wavelength, 300 mW average power, and a 100 MHz repetition rate. Using scanning tunneling microscopy, we directly recorded the desorption characteristics at each delay setting for each of the four adatom binding sites. The study revealed a preferential dependence between the delay time and the adatom sites within a 66.6–1000 fs delay range.
Pattern uniformity control in room-temperature imprint lithography
Authors: Hong Pil S. , Lee Hong H.
Published: September 2003

Nonuniformity in patterning that can arise in room-temperature imprint lithography is analyzed and a condition is presented under which the uniformity is assured. The condition is developed in such a way that the elastic recovery of stain-hardened polymer after the mold is removed does not cause the nonuniformity. Experimental testing of the condition reveals that it is a reliable criterion for uniform patterning.
Optical properties of InAlAs/GaAsSb heterostructures grown by metalorganic vapor phase epitaxy
Authors: Chamberlin D. R. , Yi S. S. , Isaacson D. , Girolami G. , Moll N.
Published: September 2003

The optical properties of GaAsSb/InAlAs heterostructures grown on InP have been measured with cathodoluminescence, photoluminescence, and Fourier-transform infrared spectroscopy (FTIR) at <10 K. A heterostructure with heavily carbon-doped GaAsSb shows little shift of emission wavelength with incident intensity. A heterostructure with undoped GaAsSb has emission that is redshifted with respect to the doped structure and has a blueshift of 6 meV per decade of increasing beam intensity. Low-temperature FTIR shows that the lower energy level transition is redshifted in the undoped sample relative to the doped sample. These observations are consistent with the presence of donor-acceptor (D–A) pair recombination in the undoped structures, which is overwhelmed by free electron-bound acceptor recombination in the doped structure. We conjecture that the anomalously large difference between emission and absorption and blueshift in D–A transition observed result from spontaneous ordering in the GaAsSb.
Growth and characterization of Sin28/Sin30 isotope superlattices
Authors: Kojima T. , Nebashi R. , Itoh K. M. , Shiraki Y.
Published: September 2003

We present silicon isotope superlattices: Si structures in which alternating layers are predominantly composed of the stable isotopes Si28 and Si30. Using solid-source molecular beam epitaxy, the thickness of each isotope layer has been precisely controlled to produce isotope superlattices denoted Sin28/Sin30, where n is the number of atomic monolayers, each one 0.136 nm thick. We have produced and studied Si828/Si830, Si1228/Si1230, and Si2428/Si2430, whose structures have been confirmed by secondary ion mass spectrometry. Further confirmation was provided by Raman spectroscopy, which showed the confinement of phonons within specific isotope layers (Si28 or Si30 layers) due to the mass periodicity created by isotope layering.
Nanoscroll formation from strained layer heterostructures
Authors: Grundmann Marius
Published: September 2003

Nanoscrolls develop when thin, strained semiconductor multilayers are peeled off from their substrate. We model the strain relaxation using continuum strain theory and predict that the scroll diameter depends on the winding direction if the cubic symmetry of zinc blende semiconductors is taken into account, 〈100〉 being the preferred winding direction. The effects of nonlinear strain and third order elastic coefficients are considered, the latter leading to smaller scroll diameter.
Temperature effect on ultrathin SiO2 time-dependent-dielectric-breakdown
Authors: Cheung Kin P.
Published: September 2003

The unusually high temperature acceleration in ultrathin oxide time-dependentdielectric-breakdown and the non-Arrhenius behavior are one of the current outstanding puzzles in oxide reliability research. In this letter, both phenomena are explained using the recently developed kinetic model. It is found that in thick oxide the degradation kinetic is controlled by hole trapping while in thin oxide it is controlled by the consumption of trapped holes. The consumption of trapped holes is further found to be a competition between hole detrapping and electron capturing, leading to the observed non-Arrhenius behavior.
First compounds with argon–carbon and argon–silicon chemical bonds
Authors: Cohen Arik , Lundell Jan , Gerber R. Benny
Published: September 2003

Argon is an extremely chemically inert element. HArF is presently the only experimentally known neutral molecule containing a chemically bound argon atom. Ab initio calculations at the MP2 and CCSD(T) levels presented here suggest, however, the existence of whole families of additional molecules. Explicitly predicted are FArCCH, with an argon–carbon bond, and FArSiF3, with an argon–silicon bond. These metastable compounds are found to be protected from decomposition by relatively high energy barriers. Other organo–argon and organo-silicon molecules derived from the above should be equally stable. The results may open the way to a substantial field of “argon chemistry.”
Sampling the complex energy landscape of a simple β-hairpin
Authors: Wei Guanghong , Derreumaux Philippe , Mousseau Normand
Published: September 2003

The folding trajectories of a 16-residue β-hairpin are studied using the activation–relaxation technique with a generic energy model. From more than 70 trajectories, three folding pathways emerge. All involve a simultaneous optimization of the complete hydrophobic and hydrogen bonding interactions. The first two follow closely those observed by previous theoretical studies, while the third can be described as a reptation move of one strand of the β-sheet with respect to the other. This reptation move indicates that non-native interactions can play a dominant role in the folding of secondary structures.
Holographic volume gratings in bulk perylene-orange-doped hybrid inorganic-organic materials by the coherent field of a femtosecond laser
Authors: Qian Guodong , Guo Jiayu , Wang Minquan , Si Jinhai , Qiu Jianrong , Hirao Kazuyuki
Published: September 2003

Holographic volume gratings with high first-order Bragg diffraction efficiency (greater than 35%) were fabricated in bulk laser-dye-doped hybrid inorganic-organic materials by the coherent fields of a femtosecond laser. Observations of optical microscopy show that refractive-index-modulated volume gratings were realized inside the sample through multiphoton absorption process. The isomerization and alignment of the laser dye molecules are responsible for the grating formation. We suggest that the materials codoped with laser dye and azodye and with photoinduced gratings inside are promising materials for making the distributed feedback tunable lasers.
Surface photovoltage spectroscopy of epitaxial structures for high electron mobility transistors
Authors: Solodky S. , Khramtsov A. , Baksht T. , Leibovitch M. , Hava S. , Shapira Yoram
Published: September 2003

AlGaN/GaN high electron mobility transistor, AlGaAs/InGAs/GaAs pseudomorphic HEMT, and InAlAs/InGaAs metamorphic HEMT (MHEMT) epitaxial structures have been characterized using surface photovoltage spectroscopy. The effects of the transistor top and bottom delta-doping levels δtop, δbot, and surface charge Qsur on the spectrum features have been studied using numerical simulations. Based on the latter, an empirical model has been developed, which allows extraction and comparison of δtop, δbot, and Qsur and is applicable for both double-sided and single-sided delta-doped structures. Prediction of the final device performance by the model is shown for two MHEMT structures. Devices produced on these structures show maximum drain currents, which correlate well with δtop values calculated using the model.
Observation of self-organized filaments in a dielectric barrier discharge of Ar gas
Authors: Shirafuji Tatsuru , Kitagawa Takayuki , Wakai Tatsuro , Tachibana Kunihide
Published: September 2003

Symmetric self-organized discharge filaments have been observed in the rf (500 kHz) dielectric barrier discharge of Ar gas between two parallel quartz plates with a MgO film. The arrangement of the filaments is confined around the center on the quartz plate plane. With increasing voltage, the number of filaments increases, and the area of filament arrangement also increases. The arrangement of the filaments does not move if the quartz plate with a MgO film is employed, while the whole arrangement rotates without a MgO film. According to the results of current–voltage measurements, Lorentz attractive force is much smaller than Coulomb repulsive force. This suggests that a confinement potential exists as in the case of two-dimensional Coulomb systems in a parabolic potential. However, some of the filament arrangements do not match to those for charged particles in the Coulomb systems, which suggests that the confinement potential does not have pure parabolic profile.
Remarkable thermal stability of BF3-doped polyaniline
Authors: Chaudhuri Debangshu , Menezes Prashanth W. , Sarma D. D.
Published: September 2003

We show that the recently synthesized BF3-doped polyaniline (PANI) exhibits remarkable stability against thermal aging. Unlike the protonated PANI, which shows rapid degradation of the conductivity on heating in air, BF3-doped PANI shows more than an order of magnitude improvement in conductivity. We employ x-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and x-ray diffraction to understand this unexpected phenomenon.
Giant growth rate in nano-oxidation of p-silicon surfaces by using ethyl alcohol liquid bridges
Authors: Tello Marta , Garcı́a Ricardo
Published: September 2003

We demonstrate that local oxidation nanolithography can be performed in liquid environments different from aqueous solutions with a significant improvement in the aspect ratio of the fabricated motives. Here, we perform a comparative study of noncontact atomic force microscopy oxidation experiments in water and ethyl alcohol. The growth rate of local oxides can be increased by almost an order of magnitude by using oxyanions from ethyl alcohol molecules. We propose that the enhanced growth rate is a consequence of the reduction of the trapped charges within the growing oxide. The present results open the possibility of using local oxidation nanolithography to directly fabricate vertical oxide structures while keeping lateral sizes in the nanometer range.
Atomic force microscope laser illumination effects on a sample and its application for transient spectroscopy
Authors: Buh G. H. , Kopanski J. J.
Published: September 2003

The effect of illumination from the laser of an optical-beam-deflection atomic force microscope (AFM) on a semiconductor sample is monitored with a (connected in parallel) scanning capacitance microscope (SCM). The photoexcitation of carriers in a silicon sample is quantified using the SCM measured capacitance–voltage curves. A significant difference is seen between SCM capacitance–voltage characteristics measured under true-dark and normal (illuminated) conditions, and is attributed to light spillage over the edges of the AFM cantilever and light transmission through the cantilever. We developed a light-induced transient spectroscopy through simple modification of a commercial SCM and demonstrate it as a tool for the measurement of carrier lifetime with microscopic scale.
Contribution of interface capacitance to the electric-field breakdown in thin-film Al–AlOx–Al capacitors
Authors: Singh-Bhalla Guneeta , Du Xu , Hebard Arthur F.
Published: September 2003

We present a systematic study of the dependence of breakdown voltages on oxide thickness d in Al–AlOx–Al thin-film capacitor structures. For sufficiently thin dielectrics, we find that a significant portion of the measured breakdown potential Vb occurs across the electrode interfaces, thereby leading to an overestimate (Vb/d) of the true breakdown electric field Eb across the dielectric. By modeling this interface contribution as an “interface” capacitance in series with the geometric “bulk” capacitance, we find for high-quality rf magnetron-sputtered AlOx dielectrics that Eb is independent of d over the range 30–300 Å.
Stabilization of porous silicon electroluminescence by surface passivation with controlled covalent bonds
Authors: Gelloz B. , Sano H. , Boukherroub R. , Wayner D. D. M. , Lockwood D. J. , Koshida N.
Published: September 2003

Stabilization of electroluminescence (EL) from nanocrystalline porous silicon (PS) diodes has been achieved by replacing silicon–hydrogen bonds terminating the surface of nanocrystalline silicon with more stable silicon–carbon (Si–C) and silicon–oxygen (Si–O–C) bonds without significant effects on the electrical properties. The surface modification is performed by a thermal treatment of partially and anodically oxidized PS sample at about 90 °C with organic molecules: 1-decene, ethyl undecylenate, or n-caprinaldehyde. The porous silicon device whose surface has been modified with stable covalent bonds shows no degradation in the EL efficiency and EL output intensity under dc operation for several hours. The improved stability can be attributed to the high chemical resistance of Si–C and Si–O–C bonds against current-induced surface oxidation associated with the generation of nonradiative defects.
Bulk glassy Cu-based alloys with a large supercooled liquid region of 110 K
Authors: Inoue Akihisa , Zhang Wei
Published: September 2003

The replacement of Cu by 5%Ag for Cu50Hf45Al5 glassy alloy was found to increase significantly the stability of supercooled liquid against crystallization. The supercooled liquid region reached as large as 110 K for Cu45Hf45Al5Ag5. The extension of the supercooled liquid region is due to an increase in the crystallization temperature, accompanying the change in the primary crystalline phases. The effectiveness of Ag addition was interpreted to result from the retardation of long-range atomic rearrangements for the progress of crystallization reaction. The selection of the quaternary composition enabled us to form bulk glassy alloys with diameters up to 3 mm. The Young’s modulus and compressive fracture strength of the 5%Ag-containing alloy are 119 GPa and 2220 MPa, respectively.
Formation of quasicrystals by partial devitrification of ball-milled amorphous Zr57Ti8Nb2.5Cu13.9Ni11.1Al7.5
Authors: Scudino S. , Eckert J. , Kühn U. , Schultz L.
Published: September 2003

Amorphous Zr57Ti8Nb2.5Cu13.9Ni11.1Al7.5 powder with low oxygen contamination was prepared by ball milling of crystalline intermetallic compounds. The comparison with the corresponding alloy produced by melt spinning shows that the first crystallization phase does not depend on the way of preparation. In fact, devitrification of both powder and ribbon is characterized by the formation of a metastable nanoscale quasicrystalline phase during the first stage of the crystallization process. This suggests that both the amorphous ball-milled powder and the melt-spun ribbon have the same short-range order and that if this short-range order is icosahedral, it can be achieved also by solid-state processing.
Synthesis and spectroscopic investigation of ruby microstructures
Authors: Ribeiro C. T. M. , Zanatta A. R.
Published: September 2003

Light-emitting structures with microscopic dimensions have been produced after thermal annealing Cr-doped amorphous (a-)AlN films in an atmosphere of dry oxygen. The annealing treatments were performed at 1050 °C and induced the formation of structures that emit red light at room temperature. Depending on the time taken during thermal anneal, there appears regions which emit light either at approximately 683 or 693 nm, as indicated by photoluminescence (PL) measurements. Their presence is attributed to different local environments to the Cr3+ ions: oxygen-rich regions (rendering PL at ∼693 nm) and nitrogen-rich regions (with narrow PL lines at ∼683 nm and a broad contribution at higher wavelengths). In view of their spatial dimensions, and distinctive PL characteristics, the features emitting at approximately 693 nm were designated by ruby microstructures (RbMSs). Both PL imaging and atomic force microscopy indicate that isolated RbMSs are almost circular having their origin from defects on the surface of the substrate or in the film itself.