bluuebunny/crossref_metadata_2025 huggingface dataset:
Visible cathodoluminescence from nanocrystalline GaSb obtained by mechanical milling
Authors: Borini S. , Méndez B. , Piqueras J.
Published: December 2003

The luminescence of mechanically milled GaSb has been investigated by means of cathodoluminescence (CL) in the scanning electron microscope. Transmission electron microscopy reveals that the GaSb powders obtained after the milling process contain nanocrystals with sizes of few nanometers. CL spectra of the GaSb powders show a bright blue-green luminescence visible to the naked eye, even at room temperature. Furthermore, a shift from blue to green has been observed depending on the milling time. In order to clarify the origin of this visible luminescence, we have performed a CL study on gallium oxide (Ga2O3) and antimony oxide (Sb2O3) powders, which exhibit several emission bands in the visible range. Comparison of these results with CL spectra from GaSb powders shows that oxidation during the milling process of GaSb plays an important role in the luminescence features observed.
Defect assessment of Mg-doped GaN by beam injection techniques
Authors: Dı́az-Guerra C. , Piqueras J. , Castaldini A. , Cavallini A. , Polenta L.
Published: December 2003

The electronic recombination properties of Mg-doped GaN have been investigated by steady state and time-resolved cathodoluminescence (TRCL) in the scanning electron microscope, photocurrent (PC) spectroscopy, and optical beam induced current (OBIC). CL and OBIC maps reveal an inhomogeneous recombination activity in the investigated material. Deep levels giving rise to level-to-band transitions were detected by PC spectroscopy. A large PC quenching observed upon illumination with light of (2.65–2.85) eV is tentatively attributed to metastable traps within the band gap. CL spectra reveal the existence of emission bands centered at 85 K at 3.29, 3.20, 3.15, and 3.01 eV, respectively. Both time-resolved and steady-state CL measurements carried out under different excitation conditions indicate that the 3.15 and 3.01 eV emissions are likely related to donor-acceptor pair transitions. TRCL measurements also reveal different recombination kinetics for these bands and suggest that deep donors are involved in the mechanism responsible for the 3.01 eV emission.
Electron field emission properties of carbon nanotubes during thermal heating and laser irradiation
Authors: Chen Yi-Chun , Cheng Hsiu-Fung , Hsieh Yun-Shuo , Tsau You-Ming
Published: December 2003

Multiwall carbon nanotubes, CNTs, were grown by microwave heated chemical vapor deposition. In order to investigate the thermal effect on electron field emission properties of the CNTs, the emission currents were measured for different substrate temperatures. Moreover, the pulsed laser-heating effect was also studied. The field emission properties of the CNTs were enhanced by increasing the substrate temperature as well as by irradiating pulsed laser. However, the emission–current behaviors are quite different. After the substrate was heated from 25 °C to 700 °C, the maximum field emission current density of CNTs increased from 29 μA/cm2 to 1500 μA/cm2, and unstable fluctuation of emission current was observed at temperature higher than 500 °C. On the contrary, when laser pulses were applied, the maximum current density increased to 700 μA/cm2, and the measured current is reversible before and after the laser irradiation.
Magnetotransport study of temperature dependent magnetic anisotropy in a (Ga,Mn)As epilayer
Authors: Hamaya K. , Taniyama T. , Kitamoto Y. , Moriya R. , Munekata H.
Published: December 2003

The anisotropic magnetotransport properties of a (Ga,Mn)As epilayer and the magnetization switching are studied as a function of temperature. The magnetization switching field shows asymmetry for crystallographically equivalent [110] and [1̄10] directions at 4 K, and the asymmetry is more significant at 40 K. The magnetization switching features clearly show that cubic magnetocrystalline anisotropy along 〈100〉, which is biased by a small uniaxial anisotropy along the [110] easy axis, is dominant at 4 K. On the other hand, the [110] uniaxial anisotropy competes with the cubic anisotropy and dominates the magnetization switching at 40 K. Accordingly, the magnetization reversal in the (Ga,Mn)As epilayer occurs via 90° and 180° domain-wall displacement at 4 and 40 K, respectively. A mechanism of the change in the magnetic anisotropy is discussed within a theoretical description of the hole band structure.
Effect of dislocations on local transconductance in AlGaN/GaN heterostructures as imaged by scanning gate microscopy
Authors: Hsu J. W. P. , Weimann N. G. , Manfra M. J. , West K. W. , Lang D. V. , Schrey F. F. , Mitrofanov O. , Molnar R. J.
Published: November 2003

The spatial variations of transconductance in AlGaN/GaN heterostructures were mapped using a conducting tip atomic force microscope. The conducting tip locally modulates the two-dimensional electron gas (2DEG) while the change in the drain current was monitored as a function of tip position. A spatial resolution of 250 nm was obtained. This technique enables us to investigate the role of defects in transistor performance. In particular, when biased near the depletion of the 2DEG, the transconductance map displays a cell structure, with low signal regions correlating with the positions of negatively charged threading dislocations.
Temperature-dependent spectral generalized magneto-optical ellipsometry
Authors: Neuber G. , Rauer R. , Kunze J. , Korn T. , Pels C. , Meier G. , Merkt U. , Bäckström J. , Rübhausen M.
Published: November 2003

We present a setup for temperature-dependent spectral generalized magneto-optical ellipsometry (SGME). This technique gives access to the electronic as well as the magnetic properties of ferromagnetic materials within one single magneto-optical measurement. It also allows the determination of the orientation of the magnetization. We show spectra of the real and the imaginary part of the refractive index N as well as the magneto-optical coupling parameter Q of permalloy and iron films for in-plane magnetization. Our findings demonstrate the relevance of SGME for the understanding of the interplay between electronic and magnetic properties of ferromagnetics.
Structural, magnetic, and spectroscopic magneto-optical properties aspects of Pt–Co multilayers with intentionally alloyed layers
Authors: Poulopoulos P. , Angelakeris M. , Papaioannou E. Th. , Flevaris N. K. , Niarchos D. , Nyvlt M. , Prosser V. , Visnovsky S. , Mueller Ch. , Fumagalli P. , Wilhelm F. , Rogalev A.
Published: December 2003

Polycrystalline Pt–Co multilayers with intentionally alloyed layers were grown by e-beam evaporation on polyimide, Si, and glass substrates. X-ray diffraction spectra show that the multilayered structure of the samples degrades as compared to conventional Pt–Co multilayers. This degradation depends on the compositional variation of the intentionally alloyed layers. Magnetometry measurements reveal enhanced magnetization values for all samples, exceeding even by 90% the one of bulk Co, at a temperature of 10 K. This is attributed to both Pt-induced and enhanced Co magnetic moments, according to x-ray magnetic circular dichroism experiments. Spectroscopic magneto-optic measurements reveal large negative polar Kerr rotation maxima at photon energies between 4 and 4.4 eV due to the intense magneto-optic response of spin-polarized Pt.
Capping-induced suppression of annealing effects on Ga1−xMnxAs epilayers
Authors: Stone M. B. , Ku K. C. , Potashnik S. J. , Sheu B. L. , Samarth N. , Schiffer P.
Published: November 2003

We have studied the effects of capping ferromagnetic Ga1−xMnxAs epilayers with a thin layer of undoped GaAs, and we find that even a few monolayers of GaAs have a significant effect on the ferromagnetic properties. In particular, the presence of a capping layer only 10 monolayers thick completely suppresses the enhancement of the ferromagnetism associated with low temperature annealing. This result, which demonstrates that the surface of a Ga1−xMnxAs epilayer strongly affects the defect structure, has important implications for the incorporation of Ga1−xMnxAs into device heterostructures.
Waveguide tapers and waveguide bends in AlGaAs-based two-dimensional photonic crystals
Authors: Dinu M. , Willett R. L. , Baldwin K. , Pfeiffer L. N. , West K. W.
Published: November 2003

In transmission studies of two-dimensional AlGaAs-based photonic crystal waveguide structures, we demonstrate high coupling efficiencies from ridge waveguides to photonic crystal waveguides using photonic crystal waveguide tapers. Enhanced bending efficiencies and bend bandwidths are achieved by use of modified waveguide bends.
Heteroepitaxy of GaN on Si(111) realized with a coincident-interface AlN/β-Si3N4(0001) double-buffer structure
Authors: Wu Chung-Lin , Wang Jhih-Chun , Chan Meng-Hsuan , Chen Tom T. , Gwo Shangjr
Published: November 2003

We present a stacked buffer mechanism for heteroepitaxial growth with large lattice mismatch. The stacked buffer consists of constituent layers, which can form coincident lattices at layer/layer and layer/substrate interfaces. For the case of GaN-on-Si(111) heteroepitaxy, we utilize the 1:2 and 5:2 coincident lattices formed at the β-Si3N4(0001)/Si(111) and AlN(0001)/β-Si3N4(0001) interfaces, respectively, to facilitate the double-buffer layer for GaN-on-Si heteroepitaxial growth. By using this buffer technique, we resolve the issue of autodoping resulting from Si outdiffusion when grown with a single AlN(0001) buffer. As a result, the epitaxial quality of GaN film is also significantly improved.
Transverse susceptibility of hard-disk media by dc methods
Authors: Papusoi C. , Suzuki T.
Published: December 2003

A torque method for measuring the transverse susceptibility of magnetic recording media is discussed. With respect to the previous methods involving an ac probe field HP, the present method introduces a concept of measurement involving a dc HP. The high precision of the proposed method makes it suitable for modern hard-disk media, unlike the previously reported methods. The measurement of the transverse susceptibility is performed in two different experimental conditions, denoted by zero-field blocked and field blocked, allowing a straightforward interpretation of the thermal relaxation effects on the transverse susceptibility. A theoretical interpretation of the experimental results is also proposed, that is based on the Stoner–Wohlfarth and two-level models. The proposed theory could be used for extracting the anisotropy field distribution from the experimental dc transverse susceptibility.
Intersublevel photoresponse of (In,Ga)As/GaAs quantum-dot photodetectors: Polarization and temperature dependence
Authors: Pal D. , Chen L. , Towe E.
Published: November 2003

We report on the polarization dependence of intraband photoresponse of (In,Ga)As/GaAs quantum-dot device structures for light polarized parallel and perpendicular to the layers. Strong photoresponse due to intersublevel transitions induced by both s- and p-polarized infrared light was observed. Within the plane of the layers, it is found that the photoresponse for s-polarized light aligned along the [110] crystallographic direction is virtually identical to that in the [1̄10] direction, suggesting that, at least in the x-y plane, the dots are symmetric. The devices studied were found to operate up to a temperature of around 100–105 K.
Strong influence of Ga/N flux ratio on Mn incorporation into Ga1−xMnxN epilayers grown by plasma-assisted molecular beam epitaxy
Authors: Kuroda S. , Bellet-Amalric E. , Giraud R. , Marcet S. , Cibert J. , Mariette H.
Published: November 2003

We report the growth of Mn-doped wurtzite GaN epilayers by nitrogen plasma-assisted molecular beam epitaxy, with a systematic attention to the dependence on the growth conditions. The addition of Mn modifies the growth diagram related to the Ga/N flux ratio. In particular, the stable Ga-bilayer coverage on the growth surface for the Ga-rich condition is destabilized in the presence of Mn. Mn incorporation in the epilayers is found to strongly depend on the Ga/N flux ratio: it varies by two orders of magnitude between the Ga-rich and the N-rich growth conditions. X-ray diffraction measurements on epilayers grown in the stoichiometric condition reveal a clear contrast between the precipitation of perovskite GaMn3N clusters at Mn compositions higher than 1.7%, and the single phase of wurtzite Ga1−xMnxN at lower Mn compositions.
Room temperature vibrational photoluminescence and field emission of nanoscaled tris-(8-hydroxyquinoline) aluminum crystalline film
Authors: Chiu Jiann-Jong , Wang Way-Seen , Kei Chi-Chung , Cho Chun-Pey , Perng Tsong P. , Wei Pei-Kuen , Chiu Sheng-Yu
Published: November 2003

The nanoscaled tris-(8-hydroxyquinoline) aluminum (AlQ3) crystalline film was synthesized by vapor condensation. It was stacked with nanometer-sized rods, approximately 100 nm wide and 1 μm long, and had a surface roughness of about 100 nm. The vibronic progression with several separated peaks was observed in the photoluminescence spectrum at room temperature. It is attributed to the crystallinity of AlQ3 and the coupling of vibrations of the individual ligands to the fluorescence transition. The emission current was also observed with a turn-on field of 12.0 V/μm, and a current density of about 0.8 mA/cm2 at 22 V/μm. Therefore, the AlQ3 crystalline film provides a choice for field emission.
Improvement of InAs quantum-dot optical properties by strain compensation with GaNAs capping layers
Authors: Zhang X. Q. , Ganapathy S. , Suemune I. , Kumano H. , Uesugi K. , Nabetani Yoichi , Matsumoto Takashi
Published: November 2003

Two kinds of self-assembled InAs quantum dots (QDs) grown on GaAs (001) substrates were studied. One is capped with GaAs layers and the other with GaNAs strain-compensating layers. Photoluminescence (PL) measurements on the two kinds of InAs QDs showed distinct dependence on the selection of the capping layers. The homogeneity and luminescence efficiency of the InAs QDs were much improved when the net strain was reduced with GaNAs layers. These results demonstrate the importance of net strain compensation for the improved optical quality of InAs QDs.
Probing subtle fluorescence dynamics in cellular proteins by streak camera based fluorescence lifetime imaging microscopy
Authors: Krishnan R. V. , Biener Eva , Zhang Jian-Hua , Heckel Robert , Herman Brian
Published: November 2003

We report the cell biological applications of a recently developed multiphoton fluorescence lifetime imaging microscopy system using a streak camera (StreakFLIM). The system was calibrated with standard fluorophore specimens and was shown to have high accuracy and reproducibility. We demonstrate the applicability of this instrument in living cells for measuring the effects of protein targeting and point mutations in the protein sequence, which are not obtainable by conventional intensity-based fluorescence microscopy methods. We discuss the relevance of such time-resolved information in quantitative energy transfer microscopy and in measurement of the parameters that characterize the intracellular physiology.
Negative charge injection to a positively charged SiO2 hole exposed to plasma etching in a pulsed two-frequency capacitively coupled plasma in CF4/Ar
Authors: Ohmori T. , Goto T. K. , Kitajima T. , Makabe T.
Published: November 2003

As microchips become smaller, the threat of damage to the device elements of Si semiconductors by charging during plasma etching will become significant. It will be of first importance to establish a plasma-etching technique that does not involve charging, i.e., “charging-free plasma processing.” Here, we utilize the effect of negative charge acceleration under a double layer in order to neutralize the charge inside a microstructure exposed to plasma etching. We have constructed a dual measurement system consisting of an emission in an interface and a contact hole charging on a SiO2 wafer during etching in two-frequency capacitively coupled plasma (2f-CCP) in CF4/Ar and pure Ar. A reduction in charging voltage is measured in the pulsed operation both of the plasma power source and of the wafer bias in the 2f-CCP in electronegative gases, CF4/Ar.
Room-temperature electroluminescence properties of Er,O-codoped GaAs injection-type light-emitting diodes grown by organometallic vapor phase epitaxy
Authors: Koizumi A. , Fujiwara Y. , Urakami A. , Inoue K. , Yoshikane T. , Takeda Y.
Published: November 2003

Room-temperature Er-related electroluminescence (EL) properties have been investigated in Er,O-codoped GaAs (GaAs:Er,O) light-emitting diodes grown by organometallic vapor phase epitaxy. Under forward bias, characteristic emission due to a luminescence center consisting of Er coordinated by O and As was clearly observed at room temperature. The injection current density dependence of the EL intensity and its dynamics revealed extremely large excitation cross section of 1–2×10−15 cm2. The excitation cross section for current injection (σc) is by five orders of magnitude larger than that for optical excitation (σo) in Er-doped fiber amplifiers (10−21–10−20 cm2).
Direct growth of aligned carbon nanotube field emitter arrays onto plastic substrates
Authors: Hofmann S. , Ducati C. , Kleinsorge B. , Robertson J.
Published: November 2003

The direct growth of vertically aligned carbon nanotubes onto flexible plastic substrates using plasma-enhanced chemical vapor deposition is reported. We show that individual lines and dots of free-standing 20–50 nm diameter nanotubes can be grown onto chromium covered commercially available polyimide foil. The scalable deposition method allows large area coverage without degrading or bending the sensitive substrate material. Field emission measurements show a low turn-on field (3.2 V/μm) and a low threshold field (4.2 V/μm). The result establishes a method of flexible field emitter fabrication, which is well suited for display production and integration of nanotubes into plastic electronics.
Resonant light scattering from metal nanoparticles: Practical analysis beyond Rayleigh approximation
Authors: Kuwata Hitoshi , Tamaru Hiroharu , Esumi Kunio , Miyano Kenjiro
Published: November 2003

We propose a simple analytical formula that can quantitatively predict resonant light scattering from metal nanoparticles of arbitrary shape, whose sizes are too large for Rayleigh approximation to be applicable. The formula has been derived as an empirical extension of Mie’s rigorous calculation for light scattering from spheres. It can very well reproduce the experimental characteristics of light scattering from Au nanorods.
High extraction efficiency InGaN micro-ring light-emitting diodes
Authors: Choi H. W. , Dawson M. D. , Edwards P. R. , Martin R. W.
Published: November 2003

Light-emitting diodes (LEDs) based on an interconnected array of GaN/InGaN micro-ring elements have been demonstrated. The devices have electrical characteristics similar to those of conventional broad-area devices. However, due to the large surface areas provided by the sidewalls, the extraction efficiency is greatly enhanced. Intense light emission at the periphery of the micro-rings is observed upon excitation by an electron beam, suggesting scattering of the photons which are extracted through the sidewalls. The devices provide a doubling in total light output compared to a broad-area reference LED of equal light-generation area.
Interface stability and solid-state amorphization in an immiscible Cu–Ta system
Authors: Gong H. R. , Liu B. X.
Published: November 2003

Assisted by ab initio calculation, a realistic Cu–Ta potential is derived and applied to determine the energies of Cu/Ta interfaces with various orientations by molecular dynamics simulations. It turns out that the (111) Cu/(100) Ta and (111) Cu/(110) Ta interfaces are thermally stable at a temperature of 873 K and that for the other Cu/Ta interfaces, the interface energies are sufficiently high to drive interfacial reaction and solid-state amorphization, which features an asymmetric behavior, i.e., the amorphous interlayer grows faster toward Cu than that toward Ta.
Radiation-induced acceptor deactivation in bipolar devices: Effects of electric field
Authors: Rashkeev S. N. , Fleetwood D. M. , Schrimpf R. D. , Pantelides S. T.
Published: November 2003

We show that radiation-induced boron acceptor deactivation in silicon bipolar transistors is due primarily to direct neutralization by protons. The strong dependence of the deactivation process on electric field is due mainly to the transport of H+ in the depletion region. The observed dependence of the neutralized-acceptor concentration on the irradiation bias is explained by analytical modeling and Monte Carlo simulations. Neutralization of protons in the Si is not necessary to describe the observed dopant deactivation.
Nonparabolicity of the conduction band of wurtzite GaN
Authors: Syed S. , Heroux J. B. , Wang Y. J. , Manfra M. J. , Molnar R. J. , Stormer H. L.
Published: November 2003

Using cyclotron resonance, we measure the effective mass, m*, of electrons in AlGaN/GaN heterostructures with densities, n2D∼1 to 6×1012 cm−2. From our extensive data, we extrapolate a band edge mass of (0.208±0.002)me. By comparing our m* data with the results of a multiband k⋅p calculation, we infer that the effect of remote bands is essential in explaining the observed conduction-band nonparabolicity (NP). Our calculation of polaron mass corrections—including finite width and two-dimensional (2D) screening—suggests those to be negligible. It implies that the behavior of m*(n2D) can be understood solely in terms of NP. Finally, using our NP and polaron corrections, we are able to reduce the large scatter in the published band edge mass values.
Electrically tunable ring resonators incorporating nematic liquid crystals as cladding layers
Authors: Maune Brett , Lawson Rhys , Gunn Cary , Scherer Axel , Dalton Larry
Published: December 2003

We have demonstrated electrical tuning in ring resonators fabricated from silicon-on-insulator wafers by incorporating nematic liquid crystals (NLCs) as the waveguide top and side cladding material. Photolithographically defined electrodes aligned around the ring resonator were used to control the orientation of the NLCs to modulate the cladding refractive index and, hence, the resonant wavelengths of the ring resonator.
Enhancement of Mn luminescence in ZnS:Mn multi-quantum-well structures
Authors: Taghavinia N. , Makino H. , Yao T.
Published: November 2003

Multi-quantum-well structures of ZnS:Mn-SiO2 were prepared by sequential rf sputtering. The thickness of ZnS:Mn layers differed from 2 to 10 nm, while that of SiO2 layers was 40 nm. It was shown that the efficiency of Mn luminescence is considerably larger in samples with ZnS:Mn thickness of 2 nm compared to samples with thicker layers. A possible mechanism to explain this effect is the formation of quantum-dot-like features in the low thickness layers, resulting in regions with higher local Mn concentration, hence higher luminescence efficiency.
Experimental test of scaling of mixing by chaotic advection in droplets moving through microfluidic channels
Authors: Song Helen , Bringer Michelle R. , Tice Joshua D. , Gerdts Cory J. , Ismagilov Rustem F.
Published: November 2003

This letter describes an experimental test of a simple argument that predicts the scaling of chaotic mixing in a droplet moving through a winding microfluidic channel. Previously, scaling arguments for chaotic mixing have been described for a flow that reduces striation length by stretching, folding, and reorienting the fluid in a manner similar to that of the baker’s transformation. The experimentally observed flow patterns within droplets (or plugs) resembled the baker’s transformation. Therefore, the ideas described in the literature could be applied to mixing in droplets to obtain the scaling argument for the dependence of the mixing time, t∼(aw/U)log(Pe), where w [m] is the cross-sectional dimension of the microchannel, a is the dimensionless length of the plug measured relative to w, U [m s−1] is the flow velocity, Pe is the Péclet number (Pe=wU/D), and D [m2 s−1] is the diffusion coefficient of the reagent being mixed. Experiments were performed to confirm the scaling argument by varying the parameters w, U, and D. Under favorable conditions, submillisecond mixing has been demonstrated in this system.
Spin polarization of self-assembled CdSe quantum dots in ZnMnSe
Authors: Oh Eunsoon , Yee K. J. , Soh S. M. , Lee J. U. , Woo J. C. , Jeon H. S. , Kim D. S. , Lee S. , Furdyna J. K. , Ri H. C. , Chany H. S. , Park S. H.
Published: November 2003

Nearly complete spin polarization (SP) of carriers was observed in photoluminescence (PL) experiments on CdSe self-assembled quantum dots (QDs) embedded in ZnMnSe at 5 K in magnetic fields above 1 T. The redshift of the PL from CdSe QDs in the presence of the magnetic field was less than that of ZnMnSe, but still sufficiently large to account for the high SP. At low fields, however, the SP of carriers in CdSe QDs is observed to be smaller than in the surrounding ZnMnSe. This, along with time-resolved PL data, suggests that the SP in CdSe QDs is mainly due, not to the injection of SP carriers from ZnMnSe, but rather due to the Zeeman splitting of internal QD states.
Current suppression in a double-island single-electron transistor for detection of degenerate charge configurations of a floating double-dot
Authors: Brenner R. , Greentree Andrew D. , Hamilton A. R.
Published: November 2003

We have investigated a double-island single-electron transistor (DISET) coupled to a floating metal double-dot (DD). Low-temperature transport measurements were used to map out the charge configurations of both the DISET and the DD. A suppression of the current through the DISET was observed whenever the charge configurations of the DISET and the DD were energetically codegenerate. This effect was used to distinguish between degenerate and nondegenerate charge configurations of the DD. We also show that this detection scheme reduces the susceptibility of the DISET to interference from random charge noise.
Self-organized, one-dimensional Pt nanowires on Ge(001)
Authors: Gurlu Oguzhan , Adam Omer A. O. , Zandvliet Harold J. W. , Poelsema Bene
Published: November 2003

Pt atoms adsorbed onto Ge(001) surface form extremely well-ordered nanowire arrays by self-organization after high-temperature annealing. Using scanning tunneling spectroscopy/microscopy, it is shown that they are metallic and defect free. They are only 0.4 nm thick with a spacing of 1.6 nm in between, and have aspect ratios up to 1000. Their formation can be discussed in terms of a relativistic property possessed by heaviest 5d elements, and the pathway to their formation can be explained by dimer breakup on Ge(001) surface at elevated temperatures followed by a surface polymerization reaction.
Luminescent spin-valve transistor
Authors: Appelbaum Ian , Russell K. J. , Monsma D. J. , Narayanamurti V. , Marcus C. M. , Hanson M. P. , Gossard A. C.
Published: November 2003

A magneto-optical sensor, the luminescent spin-valve transistor, is demonstrated, showing direct control of a light source using a magnetic field. By manipulating the relative magnetizations of thin-film ferromagnets in the transistor’s base, the luminescence intensity is modulated by approximately 200%.
A magnetic-field-effect transistor and spin transport
Authors: Gurzhi R. N. , Kalinenko A. N. , Kopeliovich A. I. , Yanovsky A. V. , Bogachek E. N. , Landman Uzi
Published: November 2003

A magnetic-field-effect transistor is proposed that generates a spin-polarized current and exhibits a giant negative magnetoresistance. The device consists of a nonmagnetic conducting channel (wire or strip) wrapped, or sandwiched, by a grounded magnetic shell. The process underlying the operation of the device is the withdrawal of one of the spin components from the channel, and its dissipation through the grounded boundaries of the magnetic shell, resulting in a spin-polarized current in the nonmagnetic channel. The device may generate an almost fully spin-polarized current, and a giant negative magnetoresistance effect is predicted.
Magneto-optical properties of nickel nanowire arrays
Authors: Melle Sonia , Menéndez José Luis , Armelles Gaspar , Navas David , Vázquez Manuel , Nielsch Kornelius , Wehrspohn Ralf B. , Gösele Ulrich
Published: November 2003

We report on the magneto-optical properties of hexagonally arranged Ni nanowires embedded in anodic alumina templates. Due to the nanowire geometry, these samples show different response depending on the polarization orientation of the incident light, which leads to a high anisotropy of both their optical and magneto-optical properties. A strong increase of the magneto-optical activity is clearly observed with respect to the Ni bulk material. We associate this behavior to plasmon resonance of the Ni nanowires.
Superparamagnetism in Co-ion-implanted anatase TiO2 thin films and effects of postannealing
Authors: Kim D. H. , Yang J. S. , Kim Y. S. , Kim D.-W. , Noh T. W. , Bu S. D. , Kim Y.-W. , Park Y. D. , Pearton S. J. , Jo Y. , Park J.-G.
Published: November 2003

We observed superparamagnetism in Co-ion-implanted anatase TiO2 thin films on SrTiO3 (001) substrates. After postannealing under oxygen pressure of 1.0×10−6 Torr, the blocking temperature increased with increasing annealing temperature. Eventually, the 600 °C-annealed sample became ferromagnetic at room temperature. These phenomena can be explained by the formation of Co (or ferromagnetic Co compound) particles and their growth during postannealing, as directly observed with transmission electron microscopy. High oxygen pressure during annealing reduced the size of the clusters and saturation magnetization moment, which indicates that cobalt clustering should be the main cause of the room-temperature ferromagnetism in the Co-ion-implanted films.
Tuning the microcavity resonant wavelength in a two-dimensional photonic crystal by modifying the cavity geometry
Authors: Subramania G. , Lin S. Y. , Wendt J. R. , Rivera J. M.
Published: November 2003

High-quality-factor microcavities in two-dimensional photonic crystals at optical frequencies have a number of technological applications, such as cavity quantum electrodynamics, optical switching, filtering, and wavelength multiplexing. For such applications, it is useful to have a simple approach to tune the microcavity resonant wavelength. In this letter, we propose a microcavity design by which we can tune the resonant wavelength by changing the cavity geometry while still obtaining a high quality factor.
Magnetic nanofibers of nickel ferrite prepared by electrospinning
Authors: Li Dan , Herricks Thurston , Xia Younan
Published: November 2003

This letter describes a simple procedure for fabricating randomly and uniaxially aligned nanofibers of nickel ferrite by electrospinning. Polycrystalline nanofibers of NiFe2O4 with an average diameter of 46 nm have been prepared by electrospinning a solution that contained poly(vinyl pyrrolidone) and alkoxide precursors to nickel and iron oxides, followed by hydrolysis and calcination at 550 °C in air. Magnetic hysteresis scans were performed on these nanofibers, in comparison with a powder sample prepared using the conventional sol–gel process. Significant differences in magnetic properties were noted between these two samples, and these differences seemed to be associated with the size and morphological differences between the nanofibers and the powders.
Optical properties of gallium oxide films deposited by electron-beam evaporation
Authors: Al-Kuhaili M. F. , Durrani S. M. A. , Khawaja E. E.
Published: November 2003

Thin films of gallium oxide were deposited by electron-beam evaporation on unheated substrates. Samples were deposited either without oxygen, or under an oxygen partial pressure of 5×10−4 mbar. The films were amorphous. Films deposited with oxygen were stoichiometric, whereas those deposited without oxygen were substoichiometric. The optical properties of the films were derived from measurements, at normal incidence, of transmittance and reflectance. Films deposited without oxygen had higher values of the refractive index and extinction coefficient. The energy gaps were 5.04 and 4.84 eV for films deposited with and without oxygen, respectively.
Ultrahigh efficiency green polymer light-emitting diodes by nanoscale interface modification
Authors: Xu Qianfei , Ouyang Jianyong , Yang Yang , Ito Takayuki , Kido Junji
Published: December 2003

We report highly efficient green polymer light-emitting diodes (PLEDs) achieved by introducing a nanoscale interfacial layer, made of calcium (2) acetylacetonate [Ca(acac)2], between the aluminum cathode and the green polyfluorene polymer. Ca(acac)2 is solution processible, therefore it is ideal for the fabrication of PLEDs. It is believed that the Ca(acac)2 layer plays multiple roles in enhancing the device performance. Firstly, it enhances the injection of electrons, which are the minority carriers in our green polyfluorene PLEDs. Secondly, it provides a buffer layer, preventing the quenching of luminescence from the aluminum electrode. Thirdly, it behaves as a hole-blocking layer, and subsequently enhances exciton formation. Based on Ca(acac)2/aluminum cathode, we obtained device efficiency as high as 28 cd/A at 2650 cd/m2 brightness, which is an improvement by a more than a factor of 3 over devices using calcium/aluminum as the cathode.
Low-temperature growth and Raman scattering study of vertically aligned ZnO nanowires on Si substrate
Authors: Zhang Ye , Jia Hongbo , Wang Rongming , Chen Chinping , Luo Xuhui , Yu Dapeng , Lee Cheoljin
Published: November 2003

High-density ZnO nanowires (ZnONWs) were aligned onto Au-catalyzed Si substrate through a simple low-temperature physical vapor deposition method. Scanning electron microscope (SEM) observations, x-ray diffraction (XRD) analysis, and photoluminescence spectra showed that the ZnONWs were single-crystalline, with a hexagonal wurzite structure. All of the results inferred from the SEM observations, the XRD rocking curves, and the Raman spectra for the investigated samples confirm that the ZnONWs are well aligned and c-axis oriented. The Raman spectra also indicated that the ZnONWs on Si substrates are under the biaxial compressive stress. Since it takes the advantage of low-cost, easily controlled deposition spot (due to the selective deposition trait of the Au layer), potential for scale-up production, and ability to integrate with Si substrate, this technique has a potential in future for fabricating the ZnONW array-based optoelectronic devices.
Formation of pure polarization gratings in 4-methoxyazobenzene containing polymer films using off-resonant laser light
Authors: Kawatsuki Nobuhiro , Uchida Emi , Ono Hiroshi
Published: November 2003

Polarization holographic recordings in polymer liquid-crystal films with azobenzene side groups were investigated using two orthogonal linearly polarized 633 nm He-Ne laser beams and subsequent annealing. Although the electric transitions of the polymer material were almost off-resonant, stable pure polarization gratings were created with a first-order diffraction efficiency greater than 30%.
Spectral engineering with defect multiple-quantum-well structures
Authors: Deych L. I. , Erementchouk M. V. , Lisyansky A. A.
Published: November 2003

It is shown that it is possible to significantly modify optical spectra of Bragg multiple-quantum-well structures by introducing wells with different exciton energies. The reflection spectrum of the resulting structures is characterized by high contrast and tuning possibilities.
Integrated nanoscale silicon sensors using top-down fabrication
Authors: Elibol O. H. , Morisette D. , Akin D. , Denton J. P. , Bashir R.
Published: November 2003

Semiconductor device-based sensing of chemical and biological entities has been demonstrated through the use of micro- and nanoscale field-effect devices and close variants. Although carbon nanotubes and silicon nanowires have been demonstrated as single molecule biosensors, the fabrication methods that have been used for creating these devices are typically not compatible with modern semiconductor manufacturing techniques and their large scale integration is problematic. These shortcomings are addressed by recent advancements in microelectronic fabrication techniques which resulted in the realization of nanowire-like structures. Here we report a method to fabricate silicon nanowires at precise locations using such techniques. Our method allows for the realization of truly integrated sensors capable of production of dense arrays. Sensitivity of these devices to changes in the ambient gas composition is also shown.
Fast characterization of magnetic impurities in single-walled carbon nanotubes
Authors: Chen Feng , Xue Yuyi , Hadjiev Viktor G. , Chu C. W. , Nikolaev Pasha , Arepalli Sivaram
Published: November 2003

We have demonstrated that the magnetic susceptibility measurement is a nondestructive, fast, and accurate method to determine the residual metal catalysts in a few microgram single-walled carbon nanotube (SWCNT) sample. We have studied magnetic impurities in raw and purified SWCNTs by magnetic susceptibility measurements, transmission electron microscopy, and thermogravimetry. The data suggest that the saturation magnetic moment and the effective field, which are caused by the interparticle interactions, decrease and increase, respectively, with the decrease of the particle size. Methods are suggested to overcome the uncertainty associated.
Pareto-optimal alloys
Authors: Bligaard Thomas , Jóhannesson Gisli H. , Ruban Andrei V. , Skriver Hans L. , Jacobsen Karsten W. , Nørskov Jens K.
Published: November 2003

Large databases that can be used in the search for new materials with specific properties remain an elusive goal in materials science. The problem is complicated by the fact that the optimal material for a given application is usually a compromise between a number of materials properties and the cost. In this letter we present a database consisting of the lattice parameters, bulk moduli, and heats of formation for over 64 000 ordered metallic alloys, which has been established by direct first-principles density-functional-theory calculations. Furthermore, we use a concept from economic theory, the Pareto-optimal set, to determine optimal alloy solutions for the compromise between low compressibility, high stability, and cost.
Photocurrent mechanism in a hybrid system of 1-thioglycerol-capped HgTe nanoparticles
Authors: Kim Hyunsuk , Cho Kyoungah , Song Hyunwoo , Min Byungdon , Lee Jong-Soo , Kim Gyu-Tae , Kim Sangsig , Kim Sung Hyun , Noh Taeyong
Published: November 2003

Photoluminescence, absorption, and photocurrent measurements were made for a hybrid system of 1-thioglycerol-capped HgTe nanoparticles synthesized by colloidal method to investigate the photocurrent mechanism in this hybrid system. Absorption and photoluminescence spectra taken for the capped HgTe nanoparticles reveal strong exciton peaks in the near-infrared wavelength range. The wavelength dependence of the photocurrent for these capped nanoparticles is very close to that of the absorption spectrum. For the photocurrent mechanism of the hybrid system, on the basis of our experimental results and energy diagram for the 1-thioglycerol-capped HgTe nanoparticles, it is suggested in this letter that holes among electron-hole pairs created by incident photons in the HgTe nanoparticles are transferred to capping 1-thioglycerol while electrons are strongly confined in these nanoparticles and that the holes contribute to the photocurrent flowing in the medium of 1-thioglycerol.
Step instability and island formation during annealing of pseudomorphic InGaAs/GaAs layers
Authors: Riposan A. , Martin G. K. M. , Millunchick J. Mirecki
Published: November 2003

The morphological stability of compressively strained In0.27Ga0.73As/GaAs pseudomorphic layers has been investigated during annealing. Large three-dimensional islands form at the beginning of annealing on initially flat surfaces, likely to relieve strain energy. The islands disappear with increasing annealing, being reabsorbed into the terraces. At the same time, the step line destabilizes forming cusps that inject two-dimensional vacancy islands into the terrace. At high temperatures, this process leads to a severe deterioration of the morphology that is not due to decomposition. The island dissolution and the development of the step instability are likely alternative paths towards the reduction of surface energy.
Strain relaxation during in situ growth of SrTiO3 thin films
Authors: Peng Luke S.-J. , Xi X. X. , Moeckly Brian H. , Alpay S. P.
Published: November 2003

We report a real-time observation of strain relaxation during in situ growth of SrTiO3 thin films by measuring the in-plane lattice constant at the film surface using reflection high-energy electron diffraction. The initial misfit strain in the SrTiO3 film is tensile on MgO and compressive on LaAlO3 as expected from the lattice mismatches between the film and the substrates. Strain relaxation begins immediately after the deposition starts, but is not complete until the film thickness reaches 500–2500 Å depending on the substrate and the deposition temperature. The strain relaxation at the growth temperature influences the film strain at room temperature, which is compressive for both substrates for thin SrTiO3 films.
Correlation between the volume change during crystallization and the thermal stability of supercooled liquids
Authors: Shen T. D. , Harms U. , Schwarz R. B.
Published: November 2003

We have measured the density of Pd40Ni40−xCuxP20 (x=0–40) alloys in the amorphous and crystalline states. For x>30, the alloys are denser in the amorphous than in the crystalline states, which is contrary to the behavior of all known metallic glasses. For Pd40Ni40−xCuxP20 and all other bulk metallic glasses where density data are available in both the amorphous and crystalline states, we find a correlation between the stability of the supercooled liquids and the difference between the molar volumes of the glassy and crystalline phases. The supercooled liquid region is largest for those alloys that show no change in molar volume upon crystallization.
Ridge waveguide as a near-field optical source
Authors: Itagi A. V. , Stancil D. D. , Bain J. A. , Schlesinger T. E.
Published: November 2003

We investigate the feasibility of using a ridge waveguide at optical frequencies as a near-field optical transducer, using the finite difference time domain method. The complete electromagnetic field picture of the ridge waveguide, in the absence and presence of the irradiated medium, is presented. A power efficiency of 7% and an optical spot with full width half maximum of 50 nm×80 nm is obtained in the medium. We show that impedance considerations play a major role in the transducer-medium optical coupling.
Effect of electron irradiation on the electrical properties of fibers of aligned single-walled carbon nanotubes
Authors: Mikó Cs. , Milas M. , Seo J. W. , Couteau E. , Barišić N. , Gaál R. , Forró L.
Published: November 2003

We carried out in situ resistivity measurements on macroscopic oriented ropes of single wall carbon nanotubes in a transmission electron microscope. We have found a minimum in the resistivity as a function of irradiation dose. This minimum is interpreted as a result of a twofold effect of the irradiation: the domination of covalent bond formation between tubes in a bundle due to broken bonds in the tube walls and the amorphization of the sample at high dose. Despite this improvement, the temperature dependence of the resistivity remains hopping-like.
Surface acoustic waves on a sphere with divergent, focusing, and collimating beam shapes excited by an interdigital transducer
Authors: Ishikawa Satoru , Nakaso Noritaka , Takeda Nobuo , Mihara Tsuyoshi , Tsukahara Yusuke , Yamanaka Kazushi
Published: November 2003

The surface acoustic wave (SAW) device on a ball is expected to provide high-performance sensors. Since we must deal with three-dimensional wave fields for precise design of ball SAW devices, numerical methods, such as the finite element method, will require too many elements. Therefore, we applied an analytical solution to a practical calculation of the full-field acoustic waves. For an IDT aperture of 6° and 80° with a wave number parameter of 45, the SAW has a divergent beam and a focusing beam, respectively. For an intermediate aperture of 30°, the SAW forms a collimating beam. This calculation confirmed the possibility of an extremely sensitive sensor with diffraction-free SAWs without disturbance by spurious bulk waves.
Sonoplasma generated by a combination of ultrasonic waves and microwave irradiation
Authors: Nomura Shinfuku , Toyota Hiromichi
Published: November 2003

Plasma chemical vapor deposition (plasma CVD) is a generic term for methods in which a precursor containing a material to be deposited is dissociated in a plasma where it is subject to chemical reactions, and is then deposited as a film on the surface of a heated substrate. A drawback of plasma CVD is that this process cannot be used to synthesize large amounts of adsorbate, or to deposit onto substrates that are vulnerable to high temperatures. As liquids are much denser than gases, synthesis rates are thought to be much higher in the former. The authors have observed the ignition and maintenance of a stable plasma in a liquid hydrocarbon exposed to a combination of ultrasonic waves and microwave radiation. Microwave energy is effectively injected into the interior of acoustic cavitation bubbles, which act as nuclei for the ignition and maintenance of the plasma. Because the plasma is formed in a liquid environment, it is possible to obtain much higher film deposition rates at much lower plasma temperatures than ever before. In addition, this process can be carried out at normal temperatures and pressures.
Optical waveguide focusing system with short free-working distance
Authors: Wang Haifeng , Groen F. H. , Pereira S. F. , Braat J. J. M.
Published: November 2003

In photonics, light usually diffracts in all directions when it emerges from a planar optical waveguide. Besides this fact, in this letter we show that a waveguide with a rectangular cross section can be turned to a focusing system by using three-dimensional self-imaging technique. We obtained a configuration where the focus of the field lies outside the waveguide, in air, with a spot size of approximately the resolution limit of half a wavelength. This type of waveguide could be used as a coupling element in integrated optics or in high numerical aperture optical systems.
Room temperature terahertz phase shifter based on magnetically controlled birefringence in liquid crystals
Authors: Chen Chao-Yuan , Tsai Tsong-Ru , Pan Ci-Ling , Pan Ru-Pin
Published: November 2003

We present the use of magnetically controlled birefringence in a nematic liquid crystal cell for phase shifting of electromagnetic waves in the range of terahertz frequencies. This device can be operated at room temperature. A maximum phase shift of 141° has been demonstrated at 1.025 THz and the results are in good agreement with theoretical predictions.
Ultrabroadband transmission measurements on waveguides of silicon-rich silicon dioxide
Authors: Neal R. T. , Charlton M. D. C. , Parker G. J. , Finlayson C. E. , Netti M. C. , Baumberg J. J.
Published: November 2003

We report ultrabroadband measurements on waveguides of photoluminescent silicon-rich silicon dioxide produced by plasma enhanced chemical vapor deposition. Material absorption below 700 nm and waveguide loss above 1300 nm leave a broad spectral region of good transmission properties, which overlaps with the photoluminescence spectrum of the core material. Proposed mechanisms for the material absorption and photoluminescence are discussed based on our findings.