bluuebunny/crossref_metadata_2025 huggingface dataset:
Extension of Coulomb blockade region by quantum confinement in the ultrasmall silicon dot in a single-hole transistor at room temperature
Authors: Saitoh Masumi , Hiramoto Toshiro
Published: April 2004

First room-temperature (RT) observation of extended Coulomb blockade (CB) region due to quantum confinement in the ultrasmall silicon dot in a single-hole transistor (SHT) is described. We fabricate single-dot SHTs in the form of metal-oxide-semiconductor field-effect transistors with an extremely constricted channel. Both large CB oscillation with the peak-to-valley current ratio (PVCR) of 40.4 and clear negative differential conductance (NDC) with the PVCR of 11.8 (highest ever reported) are observed at RT in the fabricated device. The observed NDC is attributable to the resonant tunneling due to the large quantum level spacing in the ultrasmall dot whose size is estimated to be about 2 nm.
High-efficiency chemical oxygen–iodine laser using a streamwise vortex generator
Authors: Endo Masamori , Osaka Tatsuo , Takeda Shuzaburo
Published: April 2004

A supersonic expansion nozzle has allowed us to achieve highly efficient operation of the supersonic mixing chemical oxygen–iodine laser (COIL). The nozzle’s shape produced a rapid mixing of the primary and secondary flows. Made up of a series of thin alternating wedges placed adjacent to each other, the nozzle looks like the letter X when it is viewed from the side. Iodine is injected at the exit plane of the nozzle and is strongly entrained by the streamwise vortices generated by the nozzle. 599 W of output power with a chemical efficiency of 32.9% is obtained, values higher by a factor of 1.4 than those of the conventional COIL.
Enhanced efficiency of plastic photovoltaic devices by blending with ionic solid electrolytes
Authors: Chen Fang-Chung , Xu Qianfei , Yang Yang
Published: April 2004

One of the major technology bottlenecks of polymer photovoltaic cells is the low photoinduced current, due to the low carrier mobility and short exciton migration distance. In this letter we demonstrated that the electric current for polymer PV cells can be significantly enhanced by adding a small amount of ionic solid electrolyte. Heterojunction polymer photovoltaic devices, consisting of poly[2-methoxy-5-(2′-ethyl-hexyoxy)-1,4-phenylene vinylene] (MEH-PPV) C60 and/or methanofullerene([6,6]-phenyl C61-butyric acid methyl ester) (PCBM) as the active materials, were fabricated. It has been found that the power efficiency of the organic was enhanced by blending ionic solid electrolyte, such as polyethylene oxide into the active layer. It is believed that the optimized polymer morphology, the improved electrical conductivity, and the in situ photodoping of MEH-PPV contribute to this enhancement of photovoltaic efficiency.
Visible light emission from polymer-based field-effect transistors
Authors: Sakanoue Tomo , Fujiwara Eiichi , Yamada Ryo , Tada Hirokazu
Published: April 2004

Field-effect transistors (FETs) based on poly [2-methoxy, 5-(2′-ethyl-hexoxy)-1, 4-phenylenevinylene] (MEH-PPV) were prepared with bottom-contact type interdigital electrodes of Cr/Au and Al/Au on the SiO2/Si substrates. MEH-PPV exhibited a p-type semiconducting behavior and orange light emission was observed when the devices were operated in vacuum. It was found that the luminescence efficiency of the FETs with Al/Au electrodes was higher than that of Cr/Au electrodes. The simultaneous injection of holes and electrons into MEH-PPV occurred efficiently with the application of Al/Au heteroelectrodes.
Antiphase-type planar defects in Pb(Mg1/3Nb2/3−δ)O3/SrTiO3 thin films
Authors: Seo S. H. , Kang H. C. , Noh D. Y. , Yamada Y. , Wasa K.
Published: April 2004

We fabricated epitaxial Pb(Mg1/3Nb2/3−δ)O3 (PMN) relaxor ferroelectric thin films using radio-frequency magnetron sputtering. The structure of the PMN(001) thin films evolves from tetragonal to pseudocubic as the strain is relieved with increasing the film thickness. In films of intermediate thickness, antiphase type planar defects across which atoms are displaced by 1/2[±1 ±1 0] are identified by synchrotron x-ray scattering. The planar defects appear during the course of the strain relaxation.
Polarization retention in Pb(Zr0.4Ti0.6)O3 capacitors with IrO2 top electrodes
Authors: Kang B. S. , Kim D. J. , Jo J. Y. , Noh T. W. , Yoon Jong-Gul , Song T. K. , Lee Y. K. , Lee J. K. , Shin S. , Park Y. S.
Published: April 2004

The retention characteristics of Ir/IrO2/Pb(Zr0.4Ti0.6)O3(PZT)/Pt/IrO2 capacitors were investigated by measuring the switching and nonswitching polarizations, the switching current profiles, and the P–V hysteresis loops. The retention losses of Ir/IrO2/PZT/Pt/IrO2 capacitors were compared with those of the Pt/PZT/Pt capacitors, and a significant improvement of an opposite-state retention was observed. It was found that the growth and the relaxation behaviors of the internal field are quite similar for both capacitors, but that the polarization backswitching becomes significantly smaller for the PZT capacitors with the IrO2 top electrodes. The difference in polarization backswitching might originate from the nature of the ferroelectric/electrode interfaces, possibly suppressing the nucleation of opposite domains at the interfaces.
Possibility of a metallic field-effect transistor
Authors: Rotkin Slava V. , Hess Karl
Published: April 2004

We develop theoretical arguments that demonstrate the possibility of metallic field-effect transistors in one-dimensional systems and particularly in armchair carbon nanotubes. A very inhomogeneous electric field, such as the field of a tunneling tip, can penetrate the relatively weakly screened nanotubes and open an energy gap. As a consequence, an energy barrier forms that impedes electron flow and thus permits transistor action. This type of metallic field effect is advantageous because of the high conductance of the metallic tubes in the ON state.
Temperature gradient in Hall thrusters
Authors: Staack D. , Raitses Y. , Fisch N. J.
Published: April 2004

Plasma potentials and electron temperatures were deduced from emissive and cold floating probe measurements in a 2 kW Hall thruster, operated in the discharge voltage range of 200–400 V. An almost linear dependence of the electron temperature on the plasma potential was observed in the acceleration region of the thruster both inside and outside the thruster. This result calls into question whether secondary electron emission from the ceramic channel walls plays a significant role in electron energy balance. The proportionality factor between the axial electron temperature gradient and the electric field is also significantly smaller than might be expected by fluid models.
Determination of the ionization energy of nitrogen acceptors in zinc oxide using photoluminescence spectroscopy
Authors: Wang Lijun , Giles N. C.
Published: April 2004

Photoluminescence spectroscopy of nitrogen-related emissions in ZnO is used to establish the ionization energy of the substitutional nitrogen acceptor. The temperature dependence of the nitrogen-related electron-acceptor (e,A0) emission band has been monitored in as-grown single crystals of ZnO. Line shape analysis of this band is used to determine the acceptor ionization energy. The temperature dependence of the band gap for ZnO was included in our analysis and the low-temperature acceptor ionization energy for substitutional nitrogen at an oxygen site in ZnO was found to be EA=209±3 meV. Our line shape analysis indicates a small temperature-dependent decrease in EA for T>5 K.
Fracture toughness from submicron derived indentation cracks
Authors: Scholz T. , Schneider G. A. , Muñoz-Saldaña J. , Swain M. V.
Published: April 2004

Indentation tests with loads between 0.5 and 10 mN were performed on fused quartz, (0001) oriented sapphire and (001) oriented barium titanate. The resulting submicron cracks were used to determine the fracture toughness KIC of the tested samples. The indentation crack length method was applicable, but a c/a dependency of the constant of proportionality was found. In addition, a very effective and simple approach—using the extra penetration of the indenter, due to the formation of cracks, so called pop-in—was used to determine KIC.
Middle-infrared transmission enhancement through periodically perforated metal films
Authors: Ye Y.-H. , Zhang Jia-Yu
Published: April 2004

Experimental results of extraordinary optical transmission through periodically perforated metal films in the middle-infrared region are reported. The position of the transmission pass bands depends slightly on the aperture size but mainly on the periodicity. The transmission enhancement, due to the involvement of surface plasmon polaritons, can be improved by forming a symmetrical structure.
Room-temperature optically pumped laser emission from a-plane GaN with high optical gain characteristics
Authors: Kuokstis E. , Chen C. Q. , Yang J. W. , Shatalov M. , Gaevski M. E. , Adivarahan V. , Khan M. Asif
Published: April 2004

Photoluminescence (PL) and optical gain (OG) spectra of a-plane GaN layers have been analyzed over a wide range of excitation intensities. The samples were fully coalesced layers grown by metalorganic chemical vapor deposition over r-plane sapphire substrates using epitaxial layer overgrowth (ELOG) and selective area lateral epitaxy (SALE) procedures. ELOG and SALE a-plane samples showed a strong stimulated emission line in backscattering-geometry PL spectra along with extremely high OG coefficient values (in SALE samples more than 2000 cm−1). Structures prepared with natural cleaved facet cavities based on these films were used to demonstrate optically pumped room-temperature lasing.
Anomalous threshold voltage change by 2 MeV electron irradiation at 100 °C in deep submicron metal-oxide-semiconductor field-effect transistors
Authors: Hayama K. , Ohyama H. , Simoen E. , Rafı́ J. M. , Mercha A. , Claeys C.
Published: April 2004

The degradation of the electrical properties of deep submicron metal-oxide-semiconductor field-effect transistors (MOSFETs) by 2 MeV electron irradiation at high temperatures was studied. The irradiation temperatures were 30, 100, 150 and 200 °C, and the fluence was fixed at 1015 e/cm2. For most experimental conditions, the threshold voltage (VT) is observed to reduce in absolute value both for n- and p-MOSFETs. This reduction is most pronounced at 100 °C, as at this irradiation temperature, the radiation-induced density of interface traps is highest. It is proposed that hydrogen neutralization of the dopants in the substrate plays a key role, whereby the hydrogen is released from the gate by the 2 MeV electrons.
1.24 μ
m
InGaAs/GaAs quantum dot laser grown by metalorganic chemical vapor deposition using tertiarybutylarsine
Authors: Kaiander I. N. , Sellin R. L. , Kettler T. , Ledentsov N. N. , Bimberg D. , Zakharov N. D. , Werner P.
Published: April 2004

Metalorganic chemical vapor deposition of GaAs-based laser diodes, using self-organized InGaAs quantum dots (QDs), emitting at >1.24 μm is demonstrated. The environment-friendly alternative precursor tertiarybutylarsine is used as a substitute for arsenic hydride. The active region contains ten closely stacked InGaAs QD layers embedded in a GaAs matrix. Lasing emission at such long wavelengths was achieved by overgrowing the In0.65Ga0.35As QDs with a thin In0.2Ga0.8As film. The application of an in situ annealing step leading to the evaporation of plastically relaxed defect clusters is shown to be decisive for the laser performance. A transparency current density of 7.2 A/cm2 per QD layer and an internal quantum efficiency of 75% were achieved at room temperature.
Remote collection and measurement of photogenerated carriers swept by surface acoustic waves in GaN
Authors: Palacios T. , Calle F. , Grajal J.
Published: April 2004

The interaction of surface acoustic waves and photogenerated carriers in GaN has been used for the fabrication of a remote ultraviolet detector where the carrier collector electrode is far away from the illuminated region. In this device, the recombination of the photogenerated carriers at the region where they are created is prevented by the potential fields associated with the acoustic wave, and the carriers are swept by the acoustic wave to the collector electrode. This effect is strongly dependent on the frequency and power of the acoustic waves and therefore of the input radio frequency signal. New optoelectronic devices based on the combination of the acoustic and electronic properties of the semiconductors can be envisaged.
Microscopic quantum theory of spatially resolved photoluminescence in semiconductor quantum structures
Authors: Pistone G. , Savasta S. , Di Stefano O. , Girlanda R.
Published: April 2004

We present a microscopic analysis of spatially resolved photoluminescence and photoluminescence excitation spectroscopy in semiconductor quantum structures. Such theoretical and numerical framework provides a general basis for the description of spectroscopic imaging in which the excitation and detection energies and spatial positions can all independently be scanned. The numerical results clarify the impact of the near-field optical setup on the obtained images and resolutions.
Phosphorescence of aluminum tris(quinoline-8-olate)
Authors: Cölle M. , Gärditz C.
Published: April 2004

Phosphorescence from an aluminum tris(quinoline-8-olate) (Alq3)-based organic light-emitting diode was observed by measuring the delayed electroluminescence at low temperatures. The spectra as well as the transient intensities were investigated. Vibronic progressions of the phosphorescence (T1→S0 transition) were resolved and the triplet energy of Alq3 was measured to be 2.05±0.1 eV. The lifetimes of the triplet state were determined from the delayed fluorescence as well as from the phosphorescence decay to be 8.1±0.5, 7.0±0.5, and 5.6±0.5 ms at 30, 50, and 80 K, respectively.
Body-centered-cubic phase hydrogen storage alloy with improved capacity and fast activation
Authors: Yu Xuebin , Wu Zhu , Li Feng , Xia Baojia , Xu Naixin
Published: April 2004

The hydrogen storage performance of body-centered cubic (bcc) phase Ti–20Cr–12Mn–24V–5Fe alloy is reported. It was found that the alloy has better activation property, flatter hydrogen absorption–desorption pressure plateau, lower cost, and larger hydrogen storage capacity. Compared to as-cast sample, the pressure plateau characteristics of melt-quenching alloy are improved significantly. This could be attributed to the formation of single bcc phase, which results in the increase of the effective hydrogen capacity. A maximum capacity of 3.3 wt % and an effective capacity of 2.2 wt % were obtained for the quenched alloy with a quenching rate of 20 m s−1 under moderate pressure and temperature, which is of great importance to the practicality of bcc phase alloy for hydrogen storage systems.
Giant magnetoresistance in PtMn alloys
Authors: Carey M. J. , Banful A. B. , Folks L. , Gurney B. A. , Farrow R. F. C. , Kellock A. J.
Published: April 2004

The onset of chemical and magnetic order in PtMn is accompanied by a large increase in the resistivity, ρ, contrary to that observed in nonmagnetic or ferromagnetic disorder–order transitions. We attribute this to a giant magnetoresistance like magnetic scattering off the antiferromagnetically aligned spins within the PtMn. The characteristics of the resistance change with anneal time in two regimes, with only the second regime involving a disorder/order transition. We have used the change of ρ with time to calculate the activation energy for the L10 transformation in PtMn and found it to be about 1.5 eV for thick films. The activation energy increases significantly for thinner films.
Transition of magnetic state from A-type antiferromagnetic to ferromagnetic in electron-doped Nd1−xCexMnO3
Authors: Zhang Shixiong , Luan Lan , Tan Shun , Zhang Yuheng
Published: April 2004

The transition of the magnetic state with x increasing in electron-doped manganite Nd1−xCexMnO3 is investigated through the measurements of magnetism, including the M–T and hysteresis curves. For x=0.04, with temperature increasing, M under zero-field cooling indicates that the magnetic structure changes from ferromagnetic (FM) to antiferromagnetic then to FM again and finally turns to paramagnetic (PM). However, the field-cooling M–T curve shows a negative M at 5 K then increases rapidly to a positive maximum and finally turns to PM. The experiment results are well fitted with Weiss’s molecular field theory and Néel’s ferrimagnetic model. With the enhancement of Ce content (x=0.08 and 0.10), this system gradually exhibits simple transition from FM to PM.
Photoinduced partial charge transfer between conjugated polymer and fullerene in solutions
Authors: Lin Hongzhen , Weng Yufeng , Huang Hongmin , He Qingguo , Zheng Min , Bai Fenglian
Published: April 2004

Photoinduced charge transfer between a conjugated polymer and C60 and the related processes were investigated in dilute solutions. The substantial fluorescence quenching is correlated with the efficient exciton diffusion within the polymer chains, according to which a sphere-of-action mechanism is proposed. An emissive exciplex was found formed between the conjugated polymer and fullerene in a nonpolar solvent, indicating the occurrence of a photoinduced partial charge transfer process. The low-energy sites in the polymer are believed to play a crucial role in the partial charge transfer. The asymmetry of the exciplex provides a method for evaluating the tendency of photoinduced charge separation between the donor and the acceptor. This method allows screening candidates for photovoltaic applications.
Crystal structure and magnetic properties of SmCo5.85Si0.90 compound
Authors: Luo J. , Liang J. K. , Guo Y. Q. , Liu Q. L. , Yang L. T. , Liu F. S. , Rao G. H.
Published: April 2004

The crystal structure and magnetic properties of SmCo7−xSix (x=0.1–0.9) compounds were studied by means of x-ray powder diffraction and magnetic measurements. Rietveld refinement of x-ray powder diffraction pattern shows that the as-cast compound SmCo7−xSix with x=0.9 crystallizes in the TbCu7-type structure with the space group P6/mmm, and the doping element Si has a distinct preference to occupy the 3g site. According to the refinement result, the composition of the compound is derived as SmCo5.85Si0.90. The compound SmCo5.85Si0.90 exhibits ferromagnetic order with the Curie temperature of about 717 K and a saturation moment of about 6.58±0.05 μB/f.u. The SmCo5.85Si0.90 compound shows a strong uniaxial magnetocrystalline anisotropy, and an anomalous increase of magnetization at low temperature is observed in an external field applied perpendicular to the easy direction of magnetization.
Optical and magneto-optical studies of two-dimensional metallodielectric photonic crystals on cobalt films
Authors: Diwekar M. , Kamaev V. , Shi J. , Vardeny Z. V.
Published: April 2004

We studied the optical transmission and magneto-optical effect through a subwavelength hole array fabricated on a ferromagnetic cobalt (Co) thin film in comparison to a control unperforated Co film having the same thickness. We found that the perforated film sustains extraordinary transmission bands through the hole array, which can be well explained as due to light coupling to surface plasmons on the two film interfaces. We also found that due to resonant coupling to the surface plasmons, the magneto-optical Kerr effect in the spectral range of the anomalous transmission bands of the perforated Co film is much smaller than that in the control Co film.
Effect of mass and stress on resonant frequency shift of functionalized Pb(Zr0.52Ti0.48)O3 thin film microcantilever for the detection of C-reactive protein
Authors: Lee Jeong Hoon , Kim Tae Song , Yoon Ki Hyun
Published: April 2004

A micromachined PZT (52/48) thin film cantilever composed of SiO2/Ta/Pt/PZT/Pt/SiO2 on a SiNx supporting layer for simultaneous self-exciting and sensing was fabricated. We present the resonant frequency change of piezoelectric microcantilevers due to a combination of mass loading and spring constant variation arisen from antigen-antibody interaction of C-reactive protein (CRP). Experimentally measured resonant frequency shift is larger than that of theoretically calculated resonant frequency by two orders of magnitude due to a compressive stress arising from CRP antigen-antibody interaction. The changes in normalized resonant frequency shift δf expt/f1 expt were found to increase as the value of 40.5, 74.7, and 185×10−4 as the CRP antibody site ratio, increased 10%, 50%, and 100%, respectively.
Electrical isolation, thermal stability and rf loss in a multilayer GaAs planar doped barrier diode structure bombarded by H+ and Fe+ ions
Authors: Vo V. T. , Koon K. L. , Hu Z. R. , Dharmasiri C. N. , Subramaniam S. C. , Rezazadeh A. A.
Published: April 2004

Electrical isolation in multilayer GaAs planar doped barrier (PDB) diode structures produced by H+ and Fe+ ion implantation were investigated. For an H+ bombardment with a dose of 1×1015 cm−2, a sheet resistivity as high as 3×108 Ω/sq and thermal stability up to 400 °C has been achieved. For samples bombarded by Fe+ ions, a similar high sheet resistivity has also been achieved although a longer annealing time (15 min) and a higher annealing temperature (550 °C) were needed. The rf dissipation losses of coplanar waveguide (CPW) “thru” lines fabricated on bombarded multilayer PDBD structure samples were also examined. The measured rf losses were 1.65 dB/cm at 10 GHz and 3 dB/cm at 40 GHz, similar to the values that a CPW line exhibits on a semi-isolating GaAs substrate.
Faraday rotation in Co0.85Zn0.15Fe2O4 spinel ferrite nanoparticulate films under low applied fields
Authors: Anderson Richard M. , Vestal Christy R. , Samia Anna C. S. , Zhang Z. John
Published: April 2004

Films of Co0.85Zn0.15Fe2O4 nanoparticles were prepared on silanized glass substrates using aminobenzoic acid/imidazole-modified magnetic nanoparticles. Dispersive Faraday rotations in the nanoparticulate films were observed as 1.0°–3.0° under relatively low applied magnetic field strengths of less than 500 Oe. The magnitude of the Faraday rotation increases with increasing thickness of the prepared films. No differences in the Faraday rotation were observed for Co0.85Zn0.15Fe2O4 nanoparticles as the particle size varied from 12 to 18 nm.
Optical vibration detection with a photoconductance monitoring array
Authors: Heinz P. , Garmire E.
Published: April 2004

An approach for the detection of intensity variations at frequencies in the megahertz range is proposed. An array of semi-insulating GaAs photoconductance sensors is used to detect the intensity variations that result from lateral motion of a speckle or interference pattern. The outputs of the individual array elements are summed to obtain a large signal. A prominent application that may benefit from this approach is the detection of speckle motion induced by ultrasonic surface displacements of optically rough surfaces in nondestructive testing.
Nanoscale electrical characterization of trap-assisted quasibreakdown fluctuations in SiO2
Authors: Pakes C. I. , Ramelow S. , Prawer S. , Jamieson D. N.
Published: April 2004

Conductive atomic force microscopy has been used to electrically image quasibreakdown sites in thin, native SiO2 films. Local current–voltage spectroscopy reveals, at individual sites, fluctuations in the breakdown current between well-defined conductivity states. Theoretical modeling has been performed to show that conduction through the film is governed by local trap-assisted tunneling, with typically one or two charge traps contributing to conduction through a quasibreakdown site. Our study provides a semiquantitative analysis to characterize the effective trap states that give rise to local random telegraph signals in the oxide film.
Photoemission study and band alignment of the CuInSe2(001)/CdS heterojunction
Authors: Schulmeyer T. , Hunger R. , Klein A. , Jaegermann W. , Niki S.
Published: April 2004

The contact formation of thin-film epitaxial CuInSe2(001) with a physical-vapor-deposited CdS layer is presented in this work. Synchrotron-excited photoelectron spectroscopy was used for this investigation. The epitaxial CuInSe2 films contain a surface layer of reduced Cu stoichiometry similar to the ordered defect compound CuIn3Se5. A valence band offset of 0.79±0.15 eV has been determined for this heterojunction. The comparison to literature data indicates that neither surface orientation nor surface copper content have a major impact on the valence band offset of CuIn3Se5, respectively, CuInSe2 with CdS.
Spin-dependent single-electron-tunneling effects in epitaxial Fe nanoparticles
Authors: Ernult F. , Yamane K. , Mitani S. , Yakushiji K. , Takanashi K. , Takahashi Y. K. , Hono K.
Published: April 2004

Fe/MgO/Fe nanoparticles/MgO/Co double tunnel junctions were prepared by molecular beam epitaxy for current-perpendicular-to-plane transport measurements on submicrometer-sized pillars. Microstructural observations indicate that the samples exhibit a fully epitaxial layered structure with sharp and flat interfaces including well-defined separated Fe nanoparticles between the barriers. The introduction of asymmetric MgO tunnel barriers, i.e., with different thicknesses, in the double junction leads to a clear observation of Coulomb staircase and associated tunnel magnetoresistance oscillations. An estimation of the capacitance of the system indicates that these transport phenomena are due to charging effects of the magnetic particles.
Light outcoupling efficiency of top-emitting organic light-emitting diodes
Authors: Smith L. H. , Wasey J. A. E. , Barnes W. L.
Published: April 2004

We report results obtained from modeling the light outcoupling efficiency of top–emitting organic light-emitting diode (OLED) structures and compare them with results from conventional substrate-emitting structures. We investigate two types of emissive material, small molecule and conjugated polymers, and study three different cathode materials; aluminum, silver, and calcium. We show that top-emitting OLEDs may have outcoupling efficiencies comparable to their substrate-emitting counterparts, and that the choice of cathode material is critical to the optical performance of the device.
Nanothermodynamic analysis of the low-threshold-pressure-synthesized cubic boron nitride in supercritical-fluid systems
Authors: Wang Cheng-Xin , Yang Yu-Hua , Yang Guo-Wei
Published: April 2004

A thermodynamic model in nanoscale was developed to elucidate the nucleation of the cubic boron nitrides (c-BN) synthesized in the high-pressure and high-temperature (HPHT) supercritical-fluid systems under the conditions of the low-threshold-pressure (from 2.0±0.1 to 3.0 GPa) and low-temperature (1300–1500 K). Notably, taking the nanosize-induced interior pressure into account, the nucleation of c-BN could be driven to the new stable region from the metastable region in the general accepted equilibrium phase (P,T) diagram of BN proposed by Corrigan and Bundy, upon HPHT supercritical-fluid systems. The threshold pressure of the formation of c-BN was calculated based on our model, and these results are in excellent agreement with the experiment.
Analytic modeling for the limit of mask mean-to-target from the photolithographic standpoint
Authors: Lee Sung-Woo , Lee Doo-Youl , Cho Han-Ku , Han Woo-Sung
Published: April 2004

The critical dimension (CD) deviation from a nominal CD induced by the mask mean-to-target (MTT) is normally compensated by adjusting the exposure dose. However, the compensation is not accomplished to both cell and peripheral patterns which have different pitch sizes. In general, the exposure dose is adjusted to obtain the nominal CD of the cell pattern which has smaller pitch size than the peripheral pattern. The final CD of the cell pattern recovers its nominal CD by changing the exposure dose while that of the peripheral pattern does not but the final CD of the peripheral pattern should be located within a given tolerance range. Based on this idea, an analytic model for the limits of the mask MTT is proposed in this letter. Mask error enhancement factors and exposure latitudes for an island and two types of line and space patterns are obtained experimentally. Then, arguments adopted to derive the analytic expression for the MTT are assessed by comparing measured peripheral CDs with calculated ones for three types of patterns. Results are shown to match within 2% of nominal CDs under the different mask MTTs of 13.1, 19.7, and 26.2 nm at the mask scale (4×). The mask MTT specifications for three types of patterns are calculated at the CD tolerances of ±4 nm. The calculated limit of the mask MTT is ±4.3 nm for the island pattern. ±9.8 nm and ±9.3 nm of mask MTT limits are obtained for two types of line and space patterns.
Effect of sample size on magnetic Jc for MgB2 superconductor
Authors: Horvat J. , Soltanian S. , Wang X. L. , Dou S. X.
Published: April 2004

A strong effect of sample size on magnetic Jc(H) was observed for bulk MgB2 when Jc is obtained directly from the critical state model. Thus obtained zero-field Jc (Jc0) decreases strongly with the sample size, attaining a constant value for the samples larger than a few millimeters. On the other hand, the irreversibility field (Hirr) defined at Jc=100 A/cm2 increases with the sample size. The decrease of Jc0 is described in terms of voids in the bulk MgB2 samples and superconducting screening around the cells of superconducting material between these voids (35 μm), because of concentration of the current in the narrow bridges connecting the cells. For samples larger than a few millimeters, the value of magnetic Jc is in agreement with the transport Jc and it is restricted by the voids. The critical state model is not suitable for obtaining Jc for small bulk MgB2. The increase of Hirr with the sample size is an artifact of defining Hirr by the value of Jc at which an additional superconducting screening on 1 μm scale dominates Δm.
Thermal and electrical characterization of Cu/CoFe superlattices
Authors: Yang Y. , Liu W. , Asheghi M.
Published: April 2004

The present work is directed at thermal and electrical characterization of the Cu/CoFe multilayer, which is made of extremely thin periodic layers, using steady-state Joule heating and thermometry in suspended bridges in the temperature range of 50–300 K. The total thickness of the layer is ds=144 nm, while the thickness of individual repeats are 12 and 21 Å for CoFe and Cu layers, respectively. The experimental data for thermal conductivity of a 144-nm-thick single Cu layer is also presented for comparison. The experimental data indicates that the spin-dependent electron scattering at the Cu/CoFe interface contributes to a strong reduction in thermal conductivity of these layers compared to the bulk values. The calculated Lorenz numbers (from the thermal and electrical conductivity data) varies by nearly a factor 2 from 4×10−8 W Ω K−2 at 50 K to 1.8×10−8 W Ω K−2 at 300 K and is different from the free electron value of L0=2.45×10−8 W Ω K−2. This implies that the Wiedemann-Franz law does not hold for Cu/CoFe thin films.
Bias-induced threshold voltages shifts in thin-film organic transistors
Authors: Gomes H. L. , Stallinga P. , Dinelli F. , Murgia M. , Biscarini F. , de Leeuw D. M. , Muck T. , Geurts J. , Molenkamp L. W. , Wagner V.
Published: April 2004

An investigation into the stability of metal-insulator-semiconductor (MIS) transistors based on α-sexithiophene is reported. In particular, the kinetics of the threshold voltage shift upon application of a gate bias has been determined. The kinetics follow stretched-hyperbola-type behavior, in agreement with the formalism developed to explain metastability in amorphous-silicon thin-film transistors. Using this model, quantification of device stability is possible. Temperature-dependent measurements show that there are two processes involved in the threshold voltage shift, one occurring at T≈220 K and the other at T≈300 K. The latter process is found to be sample dependent. This suggests a relation between device stability and processing parameters.
4.2% efficient organic photovoltaic cells with low series resistances
Authors: Xue Jiangeng , Uchida Soichi , Rand Barry P. , Forrest Stephen R.
Published: April 2004

We demonstrate double-heterostructure copper phthalocyanine/C60 organic photovoltaic cells with series resistances as low as 0.1 Ω cm2. A high fill factor of ∼0.6 is achieved, which is only slightly reduced at very intense illumination. As a result, the power conversion efficiency increases with the incident optical power density, reaching a maximum of (4.2±0.2)% under 4–12 suns simulated AM1.5G illumination. The cell performance is accurately described employing an analysis based on conventional semiconductor p–n junction diodes. The dependence of the series resistance on the device area suggests the dominance of the bulk resistance of the indium-tin-oxide anode as a limiting factor in practical cell efficiencies.
A unidirectional photonic crystal dispersion-based emitter
Authors: Chen Caihua , Jin Ge , Shi Shouyuan , Sharkawy Ahmed , Prather Dennis W.
Published: April 2004

In this letter, we present a unidirectional photonic crystal (PhC) dispersion-based emitter. This device combines a PhC microcavity with a dispersion-based region that is used to produce a unidirectional emission. The three-dimensional finite-difference time-domain method is used to evaluate the performance of the device. The simulation shows a unidirectional emission beam with a small aperture. The principle of this device can be applied in the design of light-emitting diodes or lasers with a unidirection and a small beam aperture in integrated optical circuits.
Noncollinear type-II second-harmonic generation in a Al(0.3)Ga(0.7)As/Al2O3 one-dimensional photonic crystal
Authors: Bosco A. , Centini M. , Sciscione L. , Sibilia C. , Fazio E. , Bertolotti M. , Fiore A. , Convertino A. , Cerri L. , Scalora M.
Published: April 2004

We demonstrate noncollinear type-II second-harmonic generation in one-dimensional photonic crystals. A 15-period Al(0.3)Ga(0.7)As/Al2O3 structure, 3.5 μm long, was designed, fabricated, and experimentally characterized. We measured an effective nonlinearity of (52±12) pm/V in perfect phase-matching conditions.
Direct and highly sensitive measurement of defect-related absorption in amorphous silicon thin films by cavity ringdown spectroscopy
Authors: Aarts I. M. P. , Hoex B. , Smets A. H. M. , Engeln R. , Kessels W. M. M. , van de Sanden M. C. M.
Published: April 2004

Cavity ringdown spectroscopy has been applied to hydrogenated amorphous silicon (a-Si:H) showing that this fully optical method is suited for the detection of defect-related absorption in thin films with a minimal detectable absorption of 1×10−6 per laser pulse and without the need for a calibration procedure. Absolute absorption coefficient spectra for photon energies between 0.7 and 1.7 eV have been obtained for thin a-Si:H films (4–98 nm) revealing a different spectral dependence for defects located in the bulk and in the surface/interface region of a-Si:H.
Laser frequency stabilizations using electromagnetically induced transparency
Authors: Moon Han Seb , Lee Lim , Kim Kyoungdae , Kim Jung Bog
Published: April 2004

We present two techniques to lock a laser frequency on an atomic transition line by using an electromagnetically induced transparency (EIT) signals, which give optical and electric feedback. We employed these methods to the D2 line of Rb87 atoms. Spectral characteristics of subnatural linewidth EIT allow us to improve frequency stability. By optical feedback of EIT signals, we were able to obtain locking bandwidths of 12 MHz, while frequency stability was 5×10−13 at best after 100 s of integration using a frequency modulation technique.
Time-resolved photoluminescence of InAs quantum dots in a GaAs quantum well
Authors: Pulizzi F. , Kent A. J. , Patanè A. , Eaves L. , Henini M.
Published: April 2004

We study the time-resolved photoluminescence emission of InAs self-assembled quantum dots (QDs) incorporated in a GaAs/(AlGa)As quantum well. We show that the quantum well confinement affects the decay time of the dot photoluminescence. In addition, we use the strong dependence of the decay time on excitation energy and temperature to shed light on carrier relaxation mechanisms in QDs.
Slab-edge modes in two-dimensional photonic crystals
Authors: Yang Jin-Kyu , Kim Se-Heon , Kim Guk-Hyun , Park Hong-Gyu , Lee Yong-Hee , Kim Sung-Bock
Published: April 2004

We demonstrate the existence of surface waves in two-dimensional photonic crystal slab edges. In finite-sized air-terminated photonic crystal boundaries, the slab-edge mode turns into a lasing mode under pulsed optical pumping conditions. Analyses of the modal behaviors of the slab-edge modes by means of calculations based on the plane wave expansion method and the finite-difference time-domain method show that resonant frequencies and quality factors are strongly dependent on the termination parameter and the shape of the slab corner.
Dielectric nonlinear characteristics of Ba(Zr0.35Ti0.65)O3 thin films grown by a sol-gel process
Authors: Zhai Jiwei , Yao Xi , Zhang Liangying , Shen Bo
Published: April 2004

Ba(Zr 0.35 Ti 0.65 ) O 3 (BZT) thin films were deposited via a sol-gel process on Pt-coated silicon substrates. The BZT films were in the perovskite phase and had polycrystalline structure. Temperature-dependent dielectric measurements revealed that the thin films have relaxor behavior and diffuse phase transition characteristics. The tunability K of the dielectric constant (at 600 kV/cm) is about 40% in the temperature range of 179–293 K. The improved temperature stability from this BZT thin film is beneficial to applications requiring a wide range of operating temperatures, thereby eliminating the need for environmental controls. Although the K value is not extraordinarily large compared to (Ba,Sr)TiO3, the low dielectric constant of BZT is attractive for microwave frequency applications. This provides an additional possibility in balancing K and dielectric constant through materials engineering for optimum device performance.
Heteroepitaxial growth of (111) 3C–SiC on well-lattice-matched (110) Si substrates by chemical vapor deposition
Authors: Nishiguchi Taro , Nakamura Mitsuhiro , Nishio Koji , Isshiki Toshiyuki , Nishino Shigehiro
Published: April 2004

Heteroepitaxial growth of 3C–SiC on (110) Si substrates by chemical vapor deposition was carried out, and the grown epitaxial layers were investigated by high resolution transmission electron microscopic (HRTEM) analysis. The interface structure between 3C–SiC and Si substrates depended on the flow rate of C3H8 during the carbonization process. In the case of the growth under C3H8=0.4 sccm, the interface was flat and 3C–SiC layer was grown epitaxially on (110) Si substrate in a well-lattice-matched relationship of (110) Si//(111) 3C–SiC and [1̄10] Si//[1̄10] 3C–SiC. In contrast, the interface was rough under C3H8=1.2 sccm and polycrystalline 3C–SiC grew without epitaxial relationship to the substrate. HRTEM observations revealed that an atomically flat (110) Si substrate surface is significant in order to grow high quality 3C–SiC with suppressing the generation of stacking faults.
Amorphization of silicon by femtosecond laser pulses
Authors: Jia Jimmy , Li Ming , Thompson Carl V.
Published: April 2004

We have used femtosecond laser pulses to drill submicron holes in single crystal silicon films in silicon-on-insulator structures. Cross-sectional transmission electron microscopy and energy dispersive x-ray analysis of material adjacent to the ablated holes indicates the formation of a layer of amorphous Si. This demonstrates that even when material is ablated using femtosecond pulses near the single pulse ablation threshold, sufficient heating of the surrounding material occurs to create a molten zone which solidifies so rapidly that crystallization is bypassed.
Three-dimensional microfabrication in bulk silicon using high-energy protons
Authors: Teo E. J. , Breese M. B. H. , Tavernier E. P. , Bettiol A. A. , Watt F. , Liu M. H. , Blackwood D. J.
Published: April 2004

We report an alternative technique which utilizes fast-proton irradiation prior to electrochemical etching for three-dimensional microfabrication in bulk p-type silicon. The proton-induced damage increases the resistivity of the irradiated regions and acts as an etch stop for porous silicon formation. A raised structure of the scanned area is left behind after removal of the unirradiated regions with potassium hydroxide. By exposing the silicon to different proton energies, the implanted depth and hence structure height can be precisely varied. We demonstrate the versatility of this three-dimensional patterning process to create multilevel free-standing bridges in bulk silicon, as well as submicron pillars and high aspect-ratio nanotips.
Polymer gratings with low surface relief based on photopolymerization-induced internal diffusion
Authors: Zhou Jinbo , Sun Changzheng , Xiong Bing , Wang Jian , Luo Yi
Published: April 2004

A photopolymer formulation sensitive to 325 nm ultraviolet light is proposed for the fabrication of polymer gratings based on photopolymerization-induced internal diffusion process. A very low surface relief depth ranging from 12.4 to about 1.0 nm has been demonstrated with a refractive index modulation Δn of about 0.010. Such polymer gratings show promising potentials for the fabrication of low-order distributed feedback polymer lasers.
Ectopic expression of a Eucalyptus grandis SVP orthologue alters the flowering time of Arabidopsis thaliana
Authors: Brill Elizabeth M. , Watson John M.
Published: April 2004

A new MADS-box gene, EgrSVP was isolated from vegetative tips of Eucalyptus grandis Hill ex Maiden saplings. This gene was expressed in vegetative tissues such as shoots, leaves and roots, as well as in unopened floral buds. DNA sequence alignments indicate that EgrSVP shares the highest level of sequence identity with PkMADS1, JOINTLESS, IbMADS3 and SVP. Phylogenetically, it is grouped in the JOINTLESS clade, the members of which share similar expression patterns. Transgenic Arabidopsis thaliana (L.) Heynh. plants overexpressing EgrSVP, exhibited a variety of altered phenotypes, including homeotic floral organ transformation, indeterminate floral development, multiple inflorescences and coflorescences, and some degree of late flowering.The nucleotide sequence data reported will appear in the GenBank Nucleotide Database under the accession number AY263809.
The Tic40 translocon components exhibit preferential interactions with different forms of the Oee1 plastid protein precursor
Authors: Ko Kenton , Banerjee Susitna , Innes Jennette , Taylor Darcie , Ko Zdenka
Published: April 2004

The transport of proteins across the plastid envelope involves a host of proteinaceous components that attend to varying structural needs of the process. This study focuses on interactions between two select forms (designated Tic40 and Toc36) of the Tic40-related components and different structural versions of the Oee1 precursor to dissect the components' mode of operation. Interaction profiling revealed several features pertaining to how Tic40-related components might work during the transport process. The main operational features revealed are: (1) Tic40 interacts preferentially with Oee1 precursors containing only the plastid-targeting domain, (2) Toc36 interacts preferentially with Oee1 precursors containing both plastid- and thylakoid lumen-targeting domains, (3)�carboxyl truncations to either the entire Oee1 precursor or Toc36 affect interactions negatively, and (4) the general reduction of Tic40-related protein levels in transgenic plants appears to exert a greater negative impact on endogenous Oee1 levels than the other proteins assessed, a trend that corroborates the findings of the protein interaction experiments.
Die and let live: leaf senescence contributes to plant survival under drought stress
Authors: Munné-Bosch Sergi , Alegre Leonor
Published: April 2004

Leaf senescence is a highly regulated physiological process that leads to leaf death and is, as such, the last developmental stage of the leaf. Plant aging and environmental stresses may induce the process of senescence. Here we will focus on the role of leaf senescence in field-grown plants as a response to adverse climatic conditions and, more specifically, on how it contributes to plant survival under drought stress. Drought induces several responses in plants including leaf senescence, which plays a major role in the survival of several species. Drought-induced leaf senescence contributes to nutrient remobilisation during stress, thus allowing the rest of the plant (i.e. the youngest leaves, fruits or flowers) to benefit from the nutrients accumulated during the life span of the leaf. In addition, drought-induced leaf senescence, especially when accompanied by leaf abscission, avoids large losses through transpiration, thus contributing to the maintenance of a favourable water balance of the whole plant. Drought-induced leaf senescence occurs gradually and is characterised by specific macroscopic, cellular, biochemical and molecular changes. Leaf yellowing (i.e. chlorophyll degradation) and specific changes in cell ultrastructure (e.g. chromatin condensation, thylakoid swelling, plastoglobuli accumulation), metabolism (e.g.�protein degradation, lipid peroxidation) and gene expression occur during leaf senescence in drought-stressed plants. Cytokinins and ABA have been shown to be involved in the regulation of drought-induced leaf senescence, although the possible role of other plant hormones should not be excluded. Reactive oxygen species, whose concentrations increase during drought-induced leaf senescence, are also known to be regulators of this process. The complex mechanisms of regulation of leaf senescence in drought-stressed plants are discussed, and attention is drawn to those aspects that still require investigation.