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28 Jan 2002

Volume 80, Issue 4, pp. 535-701

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Amorphous silicon thin-film transistors and arrays fabricated by jet printing

W. S. Wong, S. Ready, R. Matusiak, S. D. White, J.-P. Lu, J. Ho, and R. A. Street

Appl. Phys. Lett. 80, 610 (2002); http://dx.doi.org/10.1063/1.1436273 (3 pages) | Cited 25 times

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Phase-change wax-based printed masks, in place of conventional photolithography, were used to fabricate hydrogenated amorphous silicon thin-film transistors (TFTs). Wax-mask features with a minimum feature size of ∼20 μm were achieved using an acoustic-ink-printing process. Both discrete and matrix addressing structured bottom-gate TFTs with source–drain contacts overlapping the channel were created using a four-mask process. The TFTs had current–voltage characteristics comparable to photolithographically patterned devices, with mobility of 0.6–0.9 cm2/V s, threshold voltage of 2–3 V, and on/off ratios exceeding 107 for devices with channel lengths below 50 μm. © 2002 American Institute of Physics.
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85.30.Tv Field effect devices
85.40.Hp Lithography, masks and pattern transfer
73.61.Jc Amorphous semiconductors; glasses

Accurate impact ionization model which accounts for hot and cold carrier populations

T. Grasser, H. Kosina, C. Heitzinger, and S. Selberherr

Appl. Phys. Lett. 80, 613 (2002); http://dx.doi.org/10.1063/1.1445273 (3 pages) | Cited 3 times

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Conventional macroscopic impact ionization models which use the average carrier energy as a main parameter can not accurately describe the phenomenon in modern miniaturized devices. Here, we present a model which is based on an analytic expression for the distribution function. In particular, the distribution function model accounts explicitly for a hot and a cold carrier population in the drain region of metal–oxide–semiconductor transistors. The parameters are determined by three-even moments obtained from a solution of a six-moments transport model. Together with a nonparabolic description of the density of states, accurate closed form macroscopic impact ionization models can be derived based on familiar microscopic descriptions. © 2002 American Institute of Physics.
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72.20.Ht High-field and nonlinear effects
73.50.Fq High-field and nonlinear effects
72.30.+q High-frequency effects; plasma effects
73.50.Mx High-frequency effects; plasma effects
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Advanced laminated antiferromagnetically coupled recording media with high thermal stability

S. I. Pang, S. N. Piramanayagam, and J. P. Wang

Appl. Phys. Lett. 80, 616 (2002); http://dx.doi.org/10.1063/1.1436281 (3 pages) | Cited 10 times

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A layered structure to improve the antiferromagnetic exchange coupling constant (J) in laminated antiferromagnetically coupled (LAC) media is proposed. This structure has a much larger thermal stability in comparison to simple LAC structures. It also improves the coercivity and decreases the remnant moment-thickness product to achieve a high resolution and a low pulse width. The recording measurements indicate that this structure has a slightly larger noise than the simple LAC structures. However, its overall signal-to-noise ratio (SNR) is comparable to that of the simple LAC structures. High SNR and much higher thermal stability make this structure suitable for ultrahigh areal densities. © 2002 American Institute of Physics.
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75.50.Ss Magnetic recording materials
85.70.Li Other magnetic recording and storage devices (including tapes, disks, and drums)
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
68.60.Dv Thermal stability; thermal effects
75.30.Et Exchange and superexchange interactions
75.50.Gg Ferrimagnetics
75.50.Vv High coercivity materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Irreversibility field and superconducting screening currents in EuBa2Cu3O7 films

K. Senapati, Leena K. Sahoo, N. K. Pandey, and R. C. Budhani

Appl. Phys. Lett. 80, 619 (2002); http://dx.doi.org/10.1063/1.1436525 (3 pages) | Cited 7 times

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Measurements of the critical current density (Jc) and irreversibility field [Birr(T)] of epitaxial, c-axis-oriented EuBa2Cu3O7 (Eu-123) films are reported. The transition temperature (Tc), Jc, and Birr(T) of these pulsed-laser-deposited films depend critically on the growth temperature (TD), growth rate (Gr), and the oxygen partial pressure (pO2) during growth. As compared to YBa2Cu3O7, Eu-based films require lower Gr, higher pO2, and higher TD. These differences are attributed to the lower adatom mobility of Eu and its propensity for a 2+ oxidation state. The lattice mismatch between (100) LaAlO3 and the ab-plane of Eu-123 leads to an elongated c axis and some randomly oriented islands whose growth is truncated by epitaxial lateral overgrowth as the film thickness increases. © 2002 American Institute of Physics.
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74.78.-w Superconducting films and low-dimensional structures
74.72.-h Cuprate superconductors
74.25.Sv Critical currents
74.10.+v Occurrence, potential candidates

Epitaxial growth and valence control of strained perovskite SrFeO3 films

Hiroyuki Yamada, M. Kawasaki, and Y. Tokura

Appl. Phys. Lett. 80, 622 (2002); http://dx.doi.org/10.1063/1.1445805 (3 pages) | Cited 14 times

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We have fabricated single-crystalline thin films of perovskite-type iron oxide SrFeO3 which include high valent iron (Fe4+). The fabrication is accomplished on the lattice-mismatched substrates of SrTiO3 [(STO), 1.4% tensile strain] and (LaAlO3)0.3(SrAl0.5Ta0.5O3)0.7 [(LSAT), 0.5% tensile strain] by pulsed-laser deposition of SrFeO2.5 with Fe3+ state and subsequent annealing in ozone. The SrFeO2.5 films are grown in a layer-by-layer mode, exhibiting atomically smooth surfaces. The ozone annealed films on LSAT show metallic conductivity as observed in bulk SrFeO3, whereas those on STO remain semiconducting due to large tensile strain. A pseudomorphically strained epitaxial structure can be maintained by the proper choice of substrates and growth conditions through the huge volume change accompanied by the valence change from Fe3+ to Fe4+. © 2002 American Institute of Physics.
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81.15.Fg Pulsed laser ablation deposition
81.15.Kk Vapor phase epitaxy; growth from vapor phase
68.55.A- Nucleation and growth
61.72.Cc Kinetics of defect formation and annealing

Large magnetoresistance using hybrid spin filter devices

P. LeClair, J. K. Ha, H. J. M. Swagten, J. T. Kohlhepp, C. H. van de Vin, and W. J. M. de Jonge

Appl. Phys. Lett. 80, 625 (2002); http://dx.doi.org/10.1063/1.1436284 (3 pages) | Cited 88 times

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A magnetic “spin filter” tunnel barrier, sandwiched between a nonmagnetic metal and a magnetic metal, is used to create a magnetoresistive tunnel device, somewhat analogous to an optical polarizer-analyzer configuration. The resistance of these trilayer structures depends on the relative magnetization orientation of the spin filter and the ferromagnetic electrode. The spin filtering in this configuration yields a previously unobserved magnetoresistance effect, exceeding 100%. © 2002 American Institute of Physics.
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85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.
75.47.De Giant magnetoresistance
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Enhanced low-field magnetoresistance in La2/3Ca1/3MnO3/Pr2/3Ca1/3MnO3 superlattices

H. Li, J. R. Sun, and H. K. Wong

Appl. Phys. Lett. 80, 628 (2002); http://dx.doi.org/10.1063/1.1445802 (3 pages) | Cited 22 times

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We report on the observation of enhanced low-field magnetoresistance in La2/3Ca1/3MnO3/Pr2/3Ca1/3MnO3 (LCMO/PCMO) superlattices with ultrathin PCMO layers. In particular, [LCMO(100 Å)/PCMO(10 Å)]17 superlattice exhibits magnetoresistance MR = Δρ/ρ0 = −55% in a magnetic field of 500 Oe and at temperature 219 K. The enhancement is associated with the ultrasharp metal–insulator transition. © 2002 American Institute of Physics.
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75.47.De Giant magnetoresistance
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
72.15.Gd Galvanomagnetic and other magnetotransport effects
75.50.Dd Nonmetallic ferromagnetic materials
72.60.+g Mixed conductivity and conductivity transitions

Magnetic coupling and magnetoresistance in Fe/Si1−xAgx multilayers

Hai Wang, Yunjun Tang, Xiang Li, Xi Chen, Yinjun Wang, Tao Zhu, Hongwu Zhao, and Wenshan Zhan

Appl. Phys. Lett. 80, 631 (2002); http://dx.doi.org/10.1063/1.1445466 (3 pages)

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In this letter, we present a study on the magnetic coupling and magnetoresistance (MR) properties in Fe/Si1−xAgx multilayers (MLs) with a granular Si1−xAgx spacer layer. We found that with increasing silver content (x) in a silicon matrix, the magnetic state of MLs varies from a nonmagnetic-coupling state to a weak-antiferromagnetic state around the percolation point of the ∼24-Å-thick granular spacer Si1−xAgx. The MR measurements also reveal an abrupt increase of MR near the same percolation point. These variations are ascribed to the formation of the percolation path in the granular spacer. © 2002 American Institute of Physics.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.47.De Giant magnetoresistance

Magnetic properties and shape memory of Fe-doped Ni52Mn24Ga24 single crystals

G. H. Wu, W. H. Wang, J. L. Chen, L. Ao, Z. H. Liu, W. S. Zhan, T. Liang, and H. B. Xu

Appl. Phys. Lett. 80, 634 (2002); http://dx.doi.org/10.1063/1.1447003 (3 pages) | Cited 30 times

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Single crystals of a pseudoquaternary Heusler alloy, Ni52Mn16Fe8Ga24, have now been synthesized. The substitution of Fe for Mn strengthens the magnetic exchange interactions, increasing the Curie temperature to 381 K. The Fe also increases the Ni magnetic moment to 0.41 μB relative to that in the stoichiometric Heusler composition. The strain accompanying the martensitic transformation is 2.4% in zero field and can be enhanced to 4.2% by a field of 1.2 T. A field-induced strain of 1.15% has been induced along [001] in unstressed crystals with magnetic fields of 1.2 T applied at 291 K. © 2002 American Institute of Physics.
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75.30.Cr Saturation moments and magnetic susceptibilities
62.20.F- Deformation and plasticity
75.40.-s Critical-point effects, specific heats, short-range order
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.30.Et Exchange and superexchange interactions
81.40.Lm Deformation, plasticity, and creep
81.30.Kf Martensitic transformations
64.70.K- Solid-solid transitions
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Ferroelectric properties of laser-ablated Sr1−xAxBi2Ta2O9 thin films (where A = Ba, Ca)

Rasmi R. Das, P. Bhattacharya, W. Pérez, Ram S. Katiyar, and Seshu B. Desu

Appl. Phys. Lett. 80, 637 (2002); http://dx.doi.org/10.1063/1.1436528 (3 pages) | Cited 19 times

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Bismuth-layered ferroelectric thin films of Sr1−xAxBi2Ta2O9, with composition x = 0 and 0.2, were fabricated by using the pulsed-laser deposition technique. Structural characterization of the films by x-ray diffraction and atomic force microscopy, revealed that the films are polycrystalline in nature with average grain size of 180 nm. The films displayed spherical grains with a surface roughness of 12 nm. The ferroelectric measurements of Sr0.8Ba0.2Bi2Ta2O9, SrBi2Ta2O9, and Sr0.8Ca0.2Bi2Ta2O9 showed saturated hysteretic behavior with remanent polarization (2Pr) of 23.5, 17.9, 14 μC/cm2 and coercive field (Ec) of 31.06, 74.2, 86.3 kV/cm for a maximum applied electric field of 360 kV/cm. Films exhibited minimal ( ⩽ 17%) degradation of polarization for up to 1010 switching cycles. It was observed that the coercive field decreased with increase in the ionic size of partially substituted cations. The leakage current density of films were found to be of the order of ∼ 10−8 A/cm2 for up to a breakdown field of about 75 kV/cm. © 2002 American Institute of Physics.
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77.55.-g Dielectric thin films
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
81.15.Fg Pulsed laser ablation deposition
77.80.Fm Switching phenomena
77.22.Ej Polarization and depolarization
77.22.Jp Dielectric breakdown and space-charge effects
77.80.Dj Domain structure; hysteresis

Dielectric properties of 1 MeV electron-irradiated polyimide

P. S. Alegaonkar, V. N. Bhoraskar, P. Balaya, and P. S. Goyal

Appl. Phys. Lett. 80, 640 (2002); http://dx.doi.org/10.1063/1.1435408 (3 pages) | Cited 5 times

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The dielectric parameters of 50-μm-thick polyimide samples irradiated in air with 1 MeV electrons and in BF3 solution with Co-60 gamma rays were studied. The dielectric constant of polyimide was found to decrease with increasing electron fluence and dose of gamma rays. At an electron fluence of ∼ 1015 e/cm2, the dielectric constant decreased from its virgin value of 3.15 to 2.4, measured at a frequency of ∼ 7 MHz. Furthermore, by irradiating polyimide samples in BF3 solution with gamma rays, boron and fluorine diffused into each polyimide sample from both sides. In these polyimide samples, the dielectric constant decreased further to ∼ 2.1 (7 MHz). In a plot of dielectric loss, ϵ″, vs log (f ), two peaks were observed over a frequency range 100 Hz–7 MHz, in virgin as well as in the electron- and gamma-ray-irradiated polyimide samples. The dielectric loss increased with increasing electron fluence or dose of gamma rays. The refractive index (632.8 nm) of polyimide decreased from the virgin value of 1.74 to 1.69, at an electron fluence of ∼ 1015 e/cm2. The observed decrease in the dielectric constant and the refractive index can be attributed to the induced changes in the polarization and density of the irradiated polyimide samples. © 2002 American Institute of Physics.
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77.84.Jd Polymers; organic compounds
77.22.Ch Permittivity (dielectric function)
77.22.Gm Dielectric loss and relaxation
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
61.80.Fe Electron and positron radiation effects
61.82.Pv Polymers, organic compounds

Dielectric and conduction behavior of La-doped SrTiO3 with suppressed quantum-paraelectric background

Zhi Yu and Chen Ang

Appl. Phys. Lett. 80, 643 (2002); http://dx.doi.org/10.1063/1.1435409 (3 pages) | Cited 8 times

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The dielectric and conduction behavior of La-doped SrTiO3 annealed in different atmospheres was studied. The results showed that the quantum-paraelectric behavior was purely suppressed by La doping. A variable-range-hopping conduction was observed for the samples annealed in a strongly reducing atmosphere, and subsequently an insulator-metal transition occurred. The possible correlation of the singular dielectric behavior and the electrical conduction behavior is pointed out. The validity of the Barrett relation derived from the mean-field theory for quantum paraelectrics is discussed. © 2002 American Institute of Physics.
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72.60.+g Mixed conductivity and conductivity transitions
71.30.+h Metal-insulator transitions and other electronic transitions
72.20.Fr Low-field transport and mobility; piezoresistance
72.80.Ga Transition-metal compounds
61.72.Cc Kinetics of defect formation and annealing
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates

Correlation radius of polarization fluctuations in the disordered ferroelectrics

M. D. Glinchuk, E. A. Eliseev, V. A. Stephanovich, E. V. Kirichenko, and L. Jastrabik

Appl. Phys. Lett. 80, 646 (2002); http://dx.doi.org/10.1063/1.1430266 (3 pages) | Cited 6 times

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We calculate correlation radius of polarization fluctuations in the disordered ferroelectrics. The consideration is performed in the model suitable for relaxor ferroelectrics. We consider reference Burns phase in a mean field approximation subjected to random electric field E. The “entire relaxor” is then obtained by averaging of characteristics of the reference phase with distribution function of the random field. For correlation radius (Rc) calculation we take into account the damping of the reference phase soft mode and its dependence on E and perform the averaging over the random field distribution. The obtained temperature dependence of Rc is shown to be strongly dependent on the decay parameter. It appears to be completely different for the disordered system either in the dipole-glass state or in mixed ferroglass phase. The fitting of calculated and measured Rc(T) in PbMg1/3Nb2/3O3 is performed. © 2002 American Institute of Physics.
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77.22.Ej Polarization and depolarization
77.80.-e Ferroelectricity and antiferroelectricity

Dielectric constant of boron carbon nitride films synthesized by plasma-assisted chemical-vapor deposition

Takashi Sugino, Yoshihiro Etou, Tomoyoshi Tai, and Hirotaro Mori

Appl. Phys. Lett. 80, 649 (2002); http://dx.doi.org/10.1063/1.1436522 (3 pages) | Cited 9 times

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Polycrystalline boron carbon nitride (BCN) films are synthesized at various temperatures by plasma-assisted chemical-vapor deposition. BCN films are characterized by x-ray photoelectron spectroscopy, transmission electron microscopy, and transmission electron diffraction. The dielectric constant is estimated from the accumulation region of capacitance–voltage (C–V) characteristics of Au/BCN/p-Si samples. Reduction in the crystal grain size and increase of the amorphous region of the BCN film are observed with decreasing growth temperature. The dielectric constant is found to decrease with decreasing growth temperature. A dielectric constant as low as 2.4 is achieved for the BCN film. © 2002 American Institute of Physics.
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77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
77.55.-g Dielectric thin films
77.22.Ch Permittivity (dielectric function)
79.60.Dp Adsorbed layers and thin films
68.55.-a Thin film structure and morphology

Crystal orientation dependence of the piezoelectric d33 coefficient in tetragonal BaTiO3 as a function of temperature

Dragan Damjanovic, Franziska Brem, and Nava Setter

Appl. Phys. Lett. 80, 652 (2002); http://dx.doi.org/10.1063/1.1445481 (3 pages) | Cited 28 times

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Using the Landau–Ginzburg–Devonshire approach, the longitudinal piezoelectric coefficient in an arbitrary direction, d33∗(θ), was calculated as a function of temperature in tetragonal BaTiO3 crystals. The direction along which d33∗(θ) is maximum is a function of piezoelectric dij coefficients referred to the crystallographic coordinate system. Below a critical ratio of the shear and longitudinal coefficients, d15/d33, the maximum d33∗(θ) lies along the [001] axis. As the low-temperature orthorhombic phase is approached on cooling, the d15 increases, reflecting softening of the lattice along the axis of the incipient orthorhombic distortion, and the direction of maximum d33∗(θ) deviates significantly from the [001] axis. Our results suggest that the enhanced d33∗(θ) coefficient along a direction other than the polar axis recently reported in some ferroelectrics is at least in part controlled by these intrinsic lattice effects. © 2002 American Institute of Physics.
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77.65.Bn Piezoelectric and electrostrictive constants
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
64.70.K- Solid-solid transitions

Electrical conduction mechanism in high-dielectric-constant (Ba0.5,Sr0.5)TiO3 thin films

Shao-Te Chang and Joseph Ya-min Lee

Appl. Phys. Lett. 80, 655 (2002); http://dx.doi.org/10.1063/1.1436527 (3 pages) | Cited 42 times

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The electrical conduction mechanism of (Ba0.5,Sr0.5)TiO3 (BST) as a function of the temperature was studied. Au/BST/Pt metal–insulator–metal capacitors were fabricated. The temperature range was from 300 to 423 K. The conduction current depended on the voltage polarity. At high electrical field (>800 kV/cm) and with the Pt electrode biased negatively, the Pt/BST interface forms a Schottky barrier with a barrier height of 0.58 eV from 300 to 373 K. The Au/BST interface forms an ohmic contact. The conduction current when the Au electrode is biased negatively shows space-charge-limited-current behavior. An energy band diagram is proposed to explain the experimental results. © 2002 American Institute of Physics.
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77.55.-g Dielectric thin films
77.22.Ch Permittivity (dielectric function)
77.22.Jp Dielectric breakdown and space-charge effects
84.32.Tt Capacitors
73.40.Rw Metal-insulator-metal structures
77.80.-e Ferroelectricity and antiferroelectricity
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
85.50.-n Dielectric, ferroelectric, and piezoelectric devices
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Surface-emitting spin-polarized In0.4Ga0.6As/GaAs quantum-dot light-emitting diode

S. Ghosh and P. Bhattacharya

Appl. Phys. Lett. 80, 658 (2002); http://dx.doi.org/10.1063/1.1436526 (3 pages) | Cited 13 times

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We report the properties of a spin-polarized In0.4Ga0.6As/GaAs quantum-dot surface-light-emitting diode with a Ga0.974Mn0.026As spin injector layer. Spin-polarized holes from this ferromagnetic layer recombine with electrons in the quantum dots to produce circularly polarized light output. The peak optical polarization efficiency at 5.1 K is 18% and the spin injection efficiency is estimated to be ∼36%. The temperature dependence of spin injection is almost identical to the temperature dependence of magnetization in the (Ga, Mn)As layer. © 2002 American Institute of Physics.
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85.60.Jb Light-emitting devices
78.67.Hc Quantum dots
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

Size-controlled highly luminescent silicon nanocrystals: A SiO/SiO2 superlattice approach

M. Zacharias, J. Heitmann, R. Scholz, U. Kahler, M. Schmidt, and J. Bläsing

Appl. Phys. Lett. 80, 661 (2002); http://dx.doi.org/10.1063/1.1433906 (3 pages) | Cited 287 times

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Phase separation and thermal crystallization of SiO/SiO2 superlattices results in ordered arranged silicon nanocrystals. The preparation method which is fully compatible with Si technologies enables independent control of particle size as well as of particle density and spatial position by using a constant stoichiometry of the layers. Transmission electron microscopy investigations confirm the size control in samples with an upper limit of the nanocrystal sizes of 3.8, 2.5, and 2.0 nm without decreasing the silicon nanocrystal density for smaller sizes. The nanocrystals show a strong luminescence intensity in the visible and near-infrared region. A size-dependent blueshift of the luminescence and a luminescence intensity comparable to porous Si are observed. Nearly size independent luminescence intensity without bleaching effects gives an indirect proof of the accomplishment of the independent control of crystal size and number. © 2002 American Institute of Physics.
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78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.55.Ap Elemental semiconductors
78.66.Db Elemental semiconductors and insulators
81.07.Bc Nanocrystalline materials
61.46.-w Structure of nanoscale materials
64.75.-g Phase equilibria
68.37.Lp Transmission electron microscopy (TEM)
68.65.Cd Superlattices

Characterization of a two-dimensional cantilever array with through-wafer electrical interconnects

Eugene M. Chow, Goksen G. Yaralioglu, Calvin F. Quate, and Thomas W. Kenny

Appl. Phys. Lett. 80, 664 (2002); http://dx.doi.org/10.1063/1.1435804 (3 pages) | Cited 11 times

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The characterization of two-dimensional micromachined silicon cantilever arrays with integrated through-wafer electrical interconnects is presented. The approach addresses alignment and density issues associated with operating two-dimensional scanning probe arrays. The tungsten based interconnect (30 μm diameter, 1 Ω resistance) is shown not to degrade the sensitivity of the piezoresistive deflection sensor embedded on each cantilever. Operation of the array (up to 2×7) as a microscope for imaging large areas (3.8×0.45 mm2) and with vertical row stitching is demonstrated with images of samples orders of magnitude larger than images possible with standard atomic force microscope techniques. © 2002 American Institute of Physics.
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85.40.Ls Metallization, contacts, interconnects; device isolation
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices

Single-electron tunneling effects in a metallic double dot device

T. Junno, S. -B. Carlsson, H. Q. Xu, L. Samuelson, A. O. Orlov, and G. L. Snider

Appl. Phys. Lett. 80, 667 (2002); http://dx.doi.org/10.1063/1.1436532 (3 pages) | Cited 6 times

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We report on differential conductance measurements on a gold double-dot structure at 4.2 K. The two dots were connected in series by tunnel junctions formed by atomic force microscopy manipulation of nanodisks. The tunnel junctions were made strongly asymmetric. The characteristic honeycomb-shaped charging diagram separating different Coulomb blockade regions of well-defined occupancy of electrons was observed and the cells in the charging diagram were found to be skewed by the asymmetry of the tunnel junctions. In addition, a double-dot Coulomb staircase structure, with steps of varying width, was observed and was studied for varying gate voltage. The occupancy of electrons on the two dots was determined as a function of both drain source and gate voltages. © 2002 American Institute of Physics.
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85.35.Gv Single electron devices
85.35.Ds Quantum interference devices
73.63.Kv Quantum dots
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
73.21.La Quantum dots
73.23.Hk Coulomb blockade; single-electron tunneling
81.07.Ta Quantum dots
81.16.Ta Atom manipulation

Irradiation-induced formation of nanoparticles in cadmium niobate pyrochlore

W. Jiang, W. J. Weber, J. S. Young, and L. A. Boatner

Appl. Phys. Lett. 80, 670 (2002); http://dx.doi.org/10.1063/1.1445808 (3 pages) | Cited 5 times

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Sequential irradiation with 3 MeV He+ and 10 MeV C3+ ions performed at T = 150 K produces two separate amorphous buried layers in cadmium niobate pyrochlore single crystals. Further irradiation at room temperature results in the formation of nanometer-scale particles in the amorphized regions. An ion-cleaving technique was used to facilitate the observation of these nanoparticles by using scanning electron microscopy. Complete granulation with particle sizes ranging from 30 to 150 nm was observed. X-ray energy-dispersive spectrometry analysis indicates that the numerically large population of smaller particles ( ∼ 50 nm) contains a high Cd content ( ∼ 70%) and the numerically smaller population of larger particles (>100 nm) contains negligible Nb with a Cd-to-O ratio of about 1:0.54.© 2002 American Institute of Physics.
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61.46.-w Structure of nanoscale materials
61.80.Jh Ion radiation effects
61.82.Ms Insulators
64.70.Nd Structural transitions in nanoscale materials

Production of nanostructures of silicon on silicon by atomic self-organization observed by scanning tunneling microscopy

D. Jones and V. Palermo

Appl. Phys. Lett. 80, 673 (2002); http://dx.doi.org/10.1063/1.1445813 (3 pages) | Cited 10 times

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The possibility of exploiting the self-organization of mobile silicon atoms on silicon surfaces during ultrahigh vacuum thermal annealing for the construction of silicon-on-silicon structures is demonstrated. Rearrangement of the surface during thermal decomposition of an oxide layer can be controlled allowing the growth of primary structures surrounded by voids which can then be seeded by adsorbed gas molecules for the subsequent growth of secondary structures around the primary one. The controlled growth of these structures could find possible applications in Si-based microelectronic devices. © 2002 American Institute of Physics.
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81.07.Bc Nanocrystalline materials
81.05.Cy Elemental semiconductors
61.46.-w Structure of nanoscale materials
61.72.Cc Kinetics of defect formation and annealing
61.72.Qq Microscopic defects (voids, inclusions, etc.)
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)

Bandstructure modulation for carbon nanotubes in a uniform electric field

James O’Keeffe, Chengyu Wei, and Kyeongjae Cho

Appl. Phys. Lett. 80, 676 (2002); http://dx.doi.org/10.1063/1.1432441 (3 pages) | Cited 51 times

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A method to electronically modulate the energy gap and bandstructure of semiconducting carbon nanotubes is proposed. We investigate this bandstructure modulation mechanism using tight-binding and density functional theory (DFT). Results show that the energy gap of a semiconducting nanotube can be narrowed, when the tube is placed in an electric field perpendicular to the tube axis. In contrast, Metallic tubes were found to exhibit a screening behavior, whereby free charge redistributes about the tube circumference as a result of the external field. In this case, the bandstructure shows little perturbation in response to an applied electric field. © 2002 American Institute of Physics.
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73.22.Dj Single particle states
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
71.15.Ap Basis sets (LCAO, plane-wave, APW, etc.) and related methodology (scattering methods, ASA, linearized methods, etc.)
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Light-emitting electrochemical cells using a molten delocalized salt

S. Panozzo, M. Armand, and O. Stéphan

Appl. Phys. Lett. 80, 679 (2002); http://dx.doi.org/10.1063/1.1436534 (3 pages) | Cited 26 times

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The device performances of light-emitting electrochemical cells are improved by adding a room-temperature molten salt (tetrahexylammonium-bis-trifluoro-methyl-sulfonyl imide) directly into the light-emitting layer. For poly(9,9-dihexyl-fluorene-2,7-diyl) with an indium-tin-oxide anode and an aluminum cathode, the power efficiency can be increased by more than one order of magnitude. An even more pronounced effect is observed for poly [2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylenevinylene]. Equally important for both luminescent polymers, the operating voltage is drastically reduced. © 2002 American Institute of Physics.
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82.47.-a Applied electrochemistry
85.60.Jb Light-emitting devices
82.45.Fk Electrodes
78.60.Fi Electroluminescence
42.70.Jk Polymers and organics

Shot noise in low-resistance magnetic tunnel junctions

Peter K. George, Y. Wu, R. M. White, Ed Murdock, and Mark Tondra

Appl. Phys. Lett. 80, 682 (2002); http://dx.doi.org/10.1063/1.1446210 (3 pages)

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Shot noise measurements made on low-resistance magnetic tunnel junctions show results inconsistent with the resistance of the samples examined. The results yield lower than expected shot noise which is consistent with parallel path conduction (pinholes). A simple electrical model shows this should be true for noise measurements as well as for the tunneling magnetoresistance (TMR) as the resistance-area product (R×A) is reduced. The model suggests that a correlation between TMR and shot noise should exist assuming the presence of pinholes and that shot noise offers a useful experimental monitoring technique. The difficulties of making these measurements related to high frequency 1/f noise are discussed. Noise results are presented for high R×A and low R×A low-resistance samples which, in this particular case, both show the influence of pinhole shunting. © 2002 American Institute of Physics.
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72.70.+m Noise processes and phenomena
73.40.Gk Tunneling
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
73.43.Qt Magnetoresistance
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