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8 Jan 2001

Volume 78, Issue 2, pp. 139-257

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Studies on the fabrication and properties of luminescent silicon films on foreign substrates

G. Di Francia, V. La Ferrara, L. Lancellotti, and P. Morvillo

Appl. Phys. Lett. 78, 213 (2001); http://dx.doi.org/10.1063/1.1330228 (3 pages) | Cited 3 times

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Thin luminescent silicon layers are fabricated and placed on various substrates using a purely wet-chemical process at room temperature. To this aim, silicon powder with an average grain size of about 0.1 μm is etched in a HF:HNO3 solution. During the reaction, a coalescence phenomenon is observed resulting in the formation of the photoluminescent film (PLF). This film has been picked up and placed on silicon, gallium arsenide, and glass substrates, respectively. Physical properties of PLF depend on the etching time. Under our processing conditions the film with a thickness between 20 and 14 μm has a porosity ranging between 40% and 50%, respectively, and has very high electrical resistance. © 2001 American Institute of Physics.
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78.55.Ap Elemental semiconductors
78.66.Db Elemental semiconductors and insulators
78.55.Mb Porous materials
81.05.Cy Elemental semiconductors
73.61.Cw Elemental semiconductors
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
81.05.Rm Porous materials; granular materials
81.65.Cf Surface cleaning, etching, patterning
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Electronic structure of cubic silicon–carbide doped by 3d magnetic ions

V. A. Gubanov, C. Boekema, and C. Y. Fong

Appl. Phys. Lett. 78, 216 (2001); http://dx.doi.org/10.1063/1.1336813 (3 pages) | Cited 23 times

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We have studied the electronic properties of cubic silicon–carbide (3C-SiC) doped with Cr, Mn, Fe, and Co magnetic atoms using the tight-binding linear combination of muffin-tin orbitals with atomic sphere approximation method. By directly comparing the difference of the total energy between a vacancy and a dopant filling the vacant site, we found that the Mn doped at C site gains the least energy as compared to the other cases. Heavier Fe and Co atoms appear to be nonmagnetic. For lighter Cr and Mn atoms at the Si site, the dopings result in 1.6 μB (Bohr magneton) for Cr and 0.7 μB for Mn, respectively. The magnetic moment for Cr atom substituting a C atom is 0.907 μB. 3d down spin hole states exist, but the mobility associated with these states is not expected to be large. Photoluminescence measurements are suggested to probe the narrow 3d structures in the gap. © 2001 American Institute of Physics.
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71.55.Ht Other nonmetals
71.15.Ap Basis sets (LCAO, plane-wave, APW, etc.) and related methodology (scattering methods, ASA, linearized methods, etc.)
75.30.Cr Saturation moments and magnetic susceptibilities
78.55.Hx Other solid inorganic materials

X-ray analysis of spontaneous lateral modulation in (InAs)n/(AlAs)m short-period superlattices

J. H. Li, V. Holý, Z. Zhong, J. Kulik, S. C. Moss, A. G. Norman, A. Mascarenhas, J. L. Reno, and D. M. Follstaedt

Appl. Phys. Lett. 78, 219 (2001); http://dx.doi.org/10.1063/1.1338499 (3 pages) | Cited 5 times

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The lateral composition modulation in (InAs)n/(AlAs)m short-period superlattices was studied by means of synchrotron x-ray diffraction. By choosing specific diffraction vectors having a large component closely parallel to the modulation direction, we are able to observe a number of lateral satellite peaks around the zero-order short-period superlattice peak. A model, incorporating both composition and strain, is used to simulate the intensities of these satellites. Our results provide a quantitative fit and permit the evaluation of the composition amplitude. © 2001 American Institute of Physics.
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68.65.Cd Superlattices
61.05.cp X-ray diffraction
68.60.Bs Mechanical and acoustical properties

Electrical properties of p-type GaN:Mg codoped with oxygen

R. Y. Korotkov, J. M. Gregie, and B. W. Wessels

Appl. Phys. Lett. 78, 222 (2001); http://dx.doi.org/10.1063/1.1335542 (3 pages) | Cited 33 times

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Codoping of p-type GaN with Mg and oxygen was investigated. By codoping with oxygen the hole concentrations increased to 2×1018 cm−3 at 295 K, an order of magnitude greater than in Mg-doped epilayers. The resistivity of codoped layers decreased from 8 to 0.2 Ω cm upon oxygen codoping. Variable temperature Hall effect measurements indicated that the acceptor activation energy decreases from 170±5 meV in Mg-doped films to 135±5 meV upon oxygen doping. The higher hole concentration results in part from a decrease in the ionization energy of the acceptor. © 2001 American Institute of Physics.
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72.80.Ey III-V and II-VI semiconductors
72.20.My Galvanomagnetic and other magnetotransport effects
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
71.55.Eq III-V semiconductors

Mesoscopic approach to the soft breakdown failure mode in ultrathin SiO2 films

Enrique Miranda and Jordi Suñé

Appl. Phys. Lett. 78, 225 (2001); http://dx.doi.org/10.1063/1.1339259 (3 pages) | Cited 5 times

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We present an analytic model for the soft breakdown failure mode in ultrathin SiO2 films based on the conduction theory through quantum point contacts. The breakdown path across the oxide is represented by a three-dimensional constriction in which, due to the lateral confinement of the electron wave functions, discrete transverse energy levels arise. In the longitudinal direction, such levels are viewed by the incoming electrons as effective potential barriers, which can be treated using the one-dimensional tunneling formalism. In addition, it is shown that our mesoscopic approach is also consistent with the hard breakdown conduction mode. © 2001 American Institute of Physics.
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73.61.Ng Insulators
73.23.-b Electronic transport in mesoscopic systems

Ion-modulated ambipolar electrical conduction in thin-film transistors based on amorphous conjugated polymers

X. Linda Chen, Zhenan Bao, J. Hendrik Schön, Andrew J. Lovinger, Yen-Yi Lin, Brian Crone, Ananth Dodabalapur, and Bertram Batlogg

Appl. Phys. Lett. 78, 228 (2001); http://dx.doi.org/10.1063/1.1339849 (3 pages) | Cited 20 times

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Through gate-modulated electrochemical doping, ambipolar operation in thin-film transistors (TFTs) can be realized in air with solution processable conjugated polymers. Unlike other typical organic TFTs, which rely on high crystallinity for better charge transport, these electrochemically-doped transistors operate under a different mechanism and show very high current output even with completely amorphous polymers. © 2001 American Institute of Physics.
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85.30.Tv Field effect devices
73.61.Ph Polymers; organic compounds

Diffusion of implanted beryllium in silicon carbide studied by secondary ion mass spectrometry

T. Henkel, Y. Tanaka, N. Kobayashi, H. Tanoue, and S. Hishita

Appl. Phys. Lett. 78, 231 (2001); http://dx.doi.org/10.1063/1.1335850 (3 pages) | Cited 5 times

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The diffusion behavior of beryllium implanted in silicon carbide has been investigated by secondary ion mass spectrometry. The shape of the as implanted profile changed considerably after annealing at temperatures above 1300 °C due to redistribution processes. In addition, strong out diffusion into the annealing ambient and in diffusion into the bulk material was observed. Moreover, beryllium diffuses faster in epitaxial layers than in bulk crystals grown by sublimation. Effective diffusion coefficients with an activation energy of 3.1 eV were determined in bulk crystals in the temperature range 1500–1700 °C. Beryllium is suggested to diffuse via interstitial sites. © 2001 American Institute of Physics.
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66.30.J- Diffusion of impurities
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.S- Impurities in crystals
61.72.up Other materials
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
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Thermal stability of magnetic tunnel junctions studied by x-ray photoelectron spectroscopy

David J. Keavney, Sungkyun Park, Charles M. Falco, and J. M. Slaughter

Appl. Phys. Lett. 78, 234 (2001); http://dx.doi.org/10.1063/1.1338957 (3 pages) | Cited 17 times

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We have studied the evolution of chemical state of the metallic layers in NiFe/Al oxide/NiFe tunnel junction structures in as-deposited films and after postdeposition annealing. Both top and bottom NiFe layers in as-deposited films show significant Fe oxidation, but no Ni oxidation. This Fe is reduced in annealed samples, implying that oxygen migrates from the FeNi layers, possibly into the Al oxide layer. We also find that both top and bottom electrodes are significantly oxidized even in optimally annealed films. © 2001 American Institute of Physics.
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75.75.-c Magnetic properties of nanostructures
68.60.Dv Thermal stability; thermal effects
79.60.Jv Interfaces; heterostructures; nanostructures
72.25.Mk Spin transport through interfaces
75.45.+j Macroscopic quantum phenomena in magnetic systems
85.75.Mm Spin polarized resonant tunnel junctions
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
81.65.Mq Oxidation

Dispersion of the pinning field direction of a ferromagnet/antiferromagnet coupled system

Chunhong Hou, Jian Chen, Mark T. Kief, Zheng Gao, Sining Mao, and Taras Pokhil

Appl. Phys. Lett. 78, 237 (2001); http://dx.doi.org/10.1063/1.1335842 (3 pages) | Cited 10 times

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The exchange bias field of a ferromagnet/antiferromagnet bilayer is usually measured by the unidirectional shift of the hysteresis loop of the ferromagnetic layer. The exchange bias field results from interfacial exchange coupling between the spins in the ferromagnetic and antiferromagnetic layers. In general, the spins of the antiferromagnetic layer can vary locally in their anisotropy directions resulting in a distribution in local pinning directions. This letter reports a quantitative study on this distribution or dispersion using the anisotropic magnetoresistive (AMR) effect in a small rotating magnetic field. The AMR data as a function of the rotating angle of the field measured at a low field reveal the dispersion inside the ferromagnetic layer and at the interface of a ferromagnet/antiferromagnet system. The interaction between the domains within the ferromagnetic layer also plays a significant role in the dispersion inside the ferromagnetic layer. © 2001 American Institute of Physics.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.30.Gw Magnetic anisotropy
75.70.Kw Domain structure (including magnetic bubbles and vortices)
75.30.Et Exchange and superexchange interactions

Epitaxial-strain-induced insulator-superconductor transition in undoped and lightly doped La2CuO4

Weidong Si and X. X. Xi

Appl. Phys. Lett. 78, 240 (2001); http://dx.doi.org/10.1063/1.1338966 (3 pages) | Cited 14 times

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We have studied the epitaxial-strain effects on transport properties of pulsed-laser-deposited undoped and lightly doped La2CuO4 thin films. The epitaxial strain is controlled by using SrLaAlO4 buffer layers of different thicknesses on SrTiO3 substrates. The La2CuO4 films are insulating under tensile epitaxial strain, but when the strain is sufficiently compressive they become superconducting. Since the undoped and lightly doped La2CuO4 are known to be superconducting when interstitial oxygen is inserted, the epitaxial-strain-induced insulator–superconductor transition suggests a significant interplay between strain and oxygenation in the films. © 2001 American Institute of Physics.
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74.72.-h Cuprate superconductors
74.62.Bf Effects of material synthesis, crystal structure, and chemical composition

Magnetotransport and magnetic properties of La0.7MnO3−δ and Pr0.65Ba0.05Ca0.3MnO3−δ superlattices

Srinivas V. Pietambaram, D. Kumar, Rajiv K. Singh, and Clinton B. Lee

Appl. Phys. Lett. 78, 243 (2001); http://dx.doi.org/10.1063/1.1338498 (3 pages) | Cited 4 times

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Superlattice structures consisting of La0.7MnO3−δ (LMO) and Pr0.65Ba0.05Ca0.3MnO3−δ (PBCMO) systems, in which the thickness of La0.7MnO3−δ is fixed and that of Pr0.65Ba0.05Ca0.3MnO3−δ varied from 1 to 8 unit cells, have been grown in situ on (100) LaAlO3 substrates using a pulsed-laser deposition technique. Microstructural characterization carried out on these films shows the presence of characteristic intense satellite peaks, indicating the chemical modulation of the superlattice structure. The insulator-to-metal transition and the magnetoresistance (MR) ratio are found to vary with the number of unit cells. The samples with 1, 2, 5, and 8 unit cells of Pr0.65Ba0.05Ca0.3MnO3−δ show transition temperatures of 240, 230, 150, and 160 K and MR ratios of 540%, 592%, 3150%, and 2875%, respectively. We have observed an enhancement of magnetoresistance ratios in the case of superlattices with a thickness of PBCMO greater than 5 unit cells, which may be attributed to a ferromagnetic biasing provided by the LMO layers acting as a ferromagnetic film below its transition temperature. © 2001 American Institute of Physics.
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75.47.De Giant magnetoresistance
75.75.-c Magnetic properties of nanostructures
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
68.65.Cd Superlattices
75.50.Dd Nonmetallic ferromagnetic materials
72.60.+g Mixed conductivity and conductivity transitions
81.15.Fg Pulsed laser ablation deposition

Rotational giant magnetoimpedance in soft magnetic wires: Modelization through Fourier harmonic contribution

C. Gómez-Polo, M. Vázquez, and M. Knobel

Appl. Phys. Lett. 78, 246 (2001); http://dx.doi.org/10.1063/1.1336814 (3 pages) | Cited 21 times

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A method to investigate the giant magnetoimpedance effect based on Fourier analysis is introduced. The study is carried out on a FeCoSiB amorphous wire with vanishing magnetostriction subjected to joule heating (current annealing) treatment that induces an enhancement of circumferential magnetic anisotropy and modifies the magnetoimpedance response of the samples. Experimental results are interpreted within the framework of the classical electrodynamical model, where the circumferential permeability plays the dominant role in the field dependence of the complex impedance of the sample. A rotational magnetization model is employed to determine the circular magnetization process, and a mean value of the circumferential permeability is obtained through the harmonic components obtained through Fourier analysis of the time derivative of the circular magnetization. This simple model is able to reproduce the observed experimental behavior, i.e., evolution of the field dependence of the complex impedance with annealing and the asymmetrical field dependence under a dc biased electrical current. © 2001 American Institute of Physics.
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75.47.De Giant magnetoresistance
75.30.Gw Magnetic anisotropy
72.15.Gd Galvanomagnetic and other magnetotransport effects
75.50.Kj Amorphous and quasicrystalline magnetic materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
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Complex micromachines produced and driven by light

Péter Galajda and Pál Ormos

Appl. Phys. Lett. 78, 249 (2001); http://dx.doi.org/10.1063/1.1339258 (3 pages) | Cited 199 times

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A method is introduced to build microscopic light driven rotors that are created and manipulated in laser tweezers. Laser light-induced two-photon polymerization of light curing resins is applied to generate effective rotating particles several microns in size. The dynamics of rotation are evaluated. Mechanical devices consisting of multiple moving parts driven by these rotors are produced. It is shown that the combination of the techniques of microfabrication by two-photon polymerization by light and the light-induced trapping and rotation offers a powerful tool with which to build complex mechanical machines of micrometer size. © 2001 American Institute of Physics.
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07.10.Cm Micromechanical devices and systems
37.10.Vz Mechanical effects of light on atoms, molecules, and ions
82.35.Ej Nonlinear optics with polymers

Study of single-cycle pulse propagation inside a terahertz near-field probe

O. Mitrofanov, R. Harel, M. Lee, L. N. Pfeiffer, K. West, J. D. Wynn, and J. Federici

Appl. Phys. Lett. 78, 252 (2001); http://dx.doi.org/10.1063/1.1338962 (3 pages) | Cited 9 times

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Propagation of 0.5 THz single cycle pulses inside an aperture-type near-field probe is studied. The E-field amplitude attenuation is experimentally measured at various distances from the aperture. Numerical simulations based on a two-dimensional model illustrate the pulse waveform transformation and the spectral blueshift, which is experimentally observed. The study shows that the sensitivity of such a near-field probe can be improved by more than a factor of 10 by decreasing the aperture-to-detector separation without reduction of the spatial resolution. © 2001 American Institute of Physics.
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07.79.Fc Near-field scanning optical microscopes
02.60.-x Numerical approximation and analysis
42.25.Bs Wave propagation, transmission and absorption
42.65.Re Ultrafast processes; optical pulse generation and pulse compression

Digital thin-film color optical memory

C. J. Chi and A. J. Steckl

Appl. Phys. Lett. 78, 255 (2001); http://dx.doi.org/10.1063/1.1339250 (3 pages)

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A promising optical memory device called digital thin-film (DTF) color optical memory is presented. The DTF optical memory utilizes localized regions of varying thickness to adjust the spectral characteristic of reflected light from a broad band source. The DTF structure has been fabricated by Ga+ focused ion beam milling on thermally grown silicon dioxide on Si to prove the concept. A charge-coupled device array is used as the optical detector for the readout of the stored data. The reflected light image of the DTF memory reveals easily discriminated color levels and proves the suitability of using optical means to extract the stored data. DTF optical memory structures with 16 physical levels or 4 bits/pixel have been fabricated providing an equivalent storage density in excess of 5 Gb/in.2 © 2001 American Institute of Physics.
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42.79.Vb Optical storage systems, optical disks
78.66.-w Optical properties of specific thin films
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