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12 Dec 1994

Volume 65, Issue 24, pp. 3039-3153

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Observation of ballistic conductance and Aharonov–Bohm oscillations in Si/SiGe heterostructures

W. X. Gao, K. Ismail, K. Y. Lee, J. O. Chu, and S. Washburn

Appl. Phys. Lett. 65, 3114 (1994); http://dx.doi.org/10.1063/1.112453 (3 pages) | Cited 12 times

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We have fabricated quantum devices from remotely doped Si/SiGe heterostructures. The devices are interferometers (loops) similar in plan to those used in experiments on ballistic GaAs/AlxGa1−xAs devices. The loops are approximately 2r=0.8 μm in diameter with linewidths of w=0.4 μm. We have observed clear Aharonov–Bohm (AB) oscillations that vanish systematically as the carrier temperature increases. Response of up to the second harmonic of the fundamental AB frequency e/h implies a phase coherence length of around Lφ=1.2 μm. In some samples, we see steps in conductance G(Vg) as a function of gate voltage similar to the ballistic mode steps seen in GaAs/AlxGa1−xAs point contacts. © 1994 American Institute of Physics.
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73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)

Real‐time investigations of GaAs surface cleaning with a hydrogen electron cyclotron resonance plasma by optical reflection spectroscopy

L. M. Weegels, T. Saitoh, and H. Kanbe

Appl. Phys. Lett. 65, 3117 (1994); http://dx.doi.org/10.1063/1.112454 (3 pages) | Cited 5 times

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The composition changes during GaAs oxide removal and the subsequent cleaning with a hydrogen electron cyclotron resonance plasma have been investigated with real‐time optical reflection spectroscopy. It is found that the oxide is not completely removed at low temperatures, resulting in a thick damaged surface region. At moderate temperatures (300–500 °C) the plasma exposure is characterized by a two‐step process: a removal of the native oxide in a few seconds followed by a gentle etch of the GaAs. In the latter step the plasma exposure leads to a surface region with little damage to the crystal. © 1994 American Institute of Physics.
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81.65.-b Surface treatments
61.80.Jh Ion radiation effects

Anisotropy of the electron Hall mobility in 4H, 6H, and 15R silicon carbide

M. Schadt, G. Pensl, R. P. Devaty, W. J. Choyke, R. Stein, and D. Stephani

Appl. Phys. Lett. 65, 3120 (1994); http://dx.doi.org/10.1063/1.112455 (3 pages) | Cited 39 times

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Hall effect measurements in a Hall‐bar configuration are performed on nitrogen‐doped n‐type bulk 4H, 6H, and 15R SiC single crystals cut into small parallelepipeds with their longest edges either parallel or perpendicular to the math axis. In the temperature range investigated (40–700 K), an anisotropy of the electron Hall mobility is observed in all three polytypes. While the mobility perpendicular to the math axis—with magnetic field perpendicular or parallel to the math axis—is greater than the mobility parallel to the math axis for 6H and 15R SiC, 4H SiC shows the opposite behavior. © 1994 American Institute of Physics.
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72.20.My Galvanomagnetic and other magnetotransport effects
72.20.Fr Low-field transport and mobility; piezoresistance
72.80.Jc Other crystalline inorganic semiconductors

Electronic microrefrigerator based on a normal‐insulator‐superconductor tunnel junction

M. Nahum, T. M. Eiles, and John M. Martinis

Appl. Phys. Lett. 65, 3123 (1994); http://dx.doi.org/10.1063/1.112456 (3 pages) | Cited 116 times

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We present measurements on a novel electronic microrefrigerator that can cool conduction electrons significantly below the lattice temperature. A normal‐insulator‐superconductor tunnel junction is used to extract electrons from the normal metal electrode whose energy is higher than the Fermi energy. Electrons with an average energy equal to the Fermi energy are returned to the metal by a superconducting contact. Consequently, the high‐energy thermal excitations are removed from the normal metal, thus cooling the electrons. For lattice temperatures higher than 100 mK the data can be explained by a simple theory incorporating the BCS density of states in the superconducting electrode and the coupling between electrons and phonons. At lower temperatures our measurement suggests that the electron energies in the normal electrode depart strongly from an equilibrium distribution. © 1994 American Institute of Physics.
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85.25.Qc Superconducting surface acoustic wave devices and other superconducting devices
74.78.Fk Multilayers, superlattices, heterostructures
74.40.-n Fluctuation phenomena
74.50.+r Tunneling phenomena; Josephson effects

Josephson properties of basal‐plane‐faced tilt boundaries in YBa2Cu3O7−δ thin films

B. H. Moeckly and R. A. Buhrman

Appl. Phys. Lett. 65, 3126 (1994); http://dx.doi.org/10.1063/1.112457 (3 pages) | Cited 16 times

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The Josephson properties of 90° basal‐plane‐faced tilt boundaries formed between c‐axis and a‐axis normal grains in YBa2Cu3O7−δ thin films are reported. These boundaries have a low conductance which results in underdamped junction behavior. The junction capacitance and kinetic inductance both scale directly with junction critical current and conductance. The results emphasize the inhomogeneous and filamentary nature of the superconducting properties of cuprate grain boundaries. © 1994 American Institute of Physics.
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74.50.+r Tunneling phenomena; Josephson effects
74.78.-w Superconducting films and low-dimensional structures
74.81.Bd Granular, melt-textured, amorphous, and composite superconductors

Growth and superconductivity of c‐axis in‐plane aligned YBa2Cu3O7−x films fabricated by the self‐template method

S. Mahajan, J. G. Wen, W. Ito, Y. Yoshida, N. Kubota, C.‐J. Liu, and T. Morishita

Appl. Phys. Lett. 65, 3129 (1994); http://dx.doi.org/10.1063/1.112458 (3 pages) | Cited 11 times

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In‐plane aligned a‐axis oriented and [110] oriented Y1Ba2Cu3O7−x (YBCO) films exhibiting different anisotropic ratio in resistivity were fabricated, respectively, on LaSrGaO4[100] and SrTiO3[110] substrates by the self‐template method. The anisotropic properties of the a‐axis films as studied by resistivity and thermoelectric power measurements are believed to reflect the anisotropy intrinsic to the YBCO system. The measured anisotropic properties of the a‐axis films exhibiting anisotropy ratio ≳8 in resistivity and of the as‐deposited [110] films were found to be related to cracks and the rough surface of these films. Furthermore, high‐resolution microscopy revealed that a‐axis film growth by our self‐template method is dependent on the kinetics of the deposition process. © 1994 American Institute of Physics.
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74.78.-w Superconducting films and low-dimensional structures
81.15.Cd Deposition by sputtering
74.25.F- Transport properties

High quality YBa2Cu3Ox films prepared in air using pulsed laser deposition

H. Jiang, A. J. Drehman, R. J. Andrews, J. A. Horrigan, and C. Vittoria

Appl. Phys. Lett. 65, 3132 (1994); http://dx.doi.org/10.1063/1.113027 (3 pages) | Cited 2 times

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High quality YBa2Cu3Ox superconducting films have been deposited by laser deposition on yttrium stabilized cubic zirconia (YSZ) substrates using a partial pressure of air instead of oxygen. The Tc of these films was over 2° higher than films made in the same deposition system using oxygen. X‐ray diffraction indicated that the films were oriented with the c axis normal to the substrate surface. The critical current densities of the films were on the order of 106 A/cm2 at 77 K and self‐magnetic field, and the room‐temperature resistivities were about 245 μΩ cm. A unique aspect of these films was that the normal state resistivities showed nonlinear behavior with respect to temperatures. No secondary phase was detected by x‐ray diffraction and SQUID magnetometry. © 1994 American Institute of Physics.
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74.78.-w Superconducting films and low-dimensional structures
81.15.Fg Pulsed laser ablation deposition

High magnetic performance in mechanically alloyed Co‐substituted Fe3O4

J. Ding, T. Reynolds, W. F. Miao, P. G. McCormick, and R. Street

Appl. Phys. Lett. 65, 3135 (1994); http://dx.doi.org/10.1063/1.112459 (2 pages) | Cited 23 times

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Nanocrystalline Co0.5Fe2.5O4 has been prepared by mechanical alloying and subsequent vacuum annealing. Significant increase of coercivity was observed after a postannealing at low temperatures in air. Magnetic annealing resulted in anisotropic sample with a coercivity of 2.8 kOe and a remanence of 81% of the saturation magnetization, providing a theoretical maximum energy product of 4 MG Oe. © 1994 American Institute of Physics.
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75.50.Cc Other ferromagnetic metals and alloys
75.50.Vv High coercivity materials
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation
75.60.Nt Magnetic annealing and temperature-hysteresis effects

New high coercivity cobalt alloy thin film medium structure for longitudinal recording

Leo Li Zen Fang and David N. Lambeth

Appl. Phys. Lett. 65, 3137 (1994); http://dx.doi.org/10.1063/1.112460 (3 pages) | Cited 8 times

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A combined underlayer of (110) textured Cr and a hexagonal close‐packed (HCP) Co or CoCrTa intermediate layer yields an improved CoCrPt recording media. The addition of Pt greatly increases the coercivity of the cobalt films but also expands the lattice of Co alloys preventing a good lattice match to the Cr underlayer. However, HCP Co and CoCrTa lattice match reasonably well to Cr. It is shown that an intermediate HCP layer, as thin as 50 Å, provides a HCP template upon which (10.1) CoCrPt texture can develop, resulting in suppressed (00.2) texture. By adjusting the relative layer thicknesses, coercivities between 1700 and 4200 Oe are controllably obtained for an independent variety of Mrt values. © 1994 American Institute of Physics.
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81.15.Cd Deposition by sputtering
75.70.-i Magnetic properties of thin films, surfaces, and interfaces
85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.
81.05.Rm Porous materials; granular materials

Crystallization behavior of sol‐gel derived Pb(Zr,Ti)O3 thin films and the polarization switching effect on film microstructure

Kazushi Amanuma, Takashi Hase, and Yoichi Miyasaka

Appl. Phys. Lett. 65, 3140 (1994); http://dx.doi.org/10.1063/1.112461 (3 pages) | Cited 17 times

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The microstructure of sol‐gel derived Pb(Zr,Ti)O3 thin films was investigated using Auger electron spectroscopy (AES) and transmission electron microscopy (TEM). The AES depth profile revealed that the Ti content decreases and the Zr content increases from the bottom through the thickness as a result of the crystallization into perovskite phase. A cross‐sectional TEM micrograph showed that the PZT grains are columnar and grow epitaxially from the bottom to the surface. It was also shown that the 2.5‐nm‐thick interface layer appeared at the top Au electrode‐PZT interface after 108 polarization switching cycles, while there was no change at the bottom Pt‐PZT interface. © 1994 American Institute of Physics.
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81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
68.55.-a Thin film structure and morphology
77.80.Fm Switching phenomena
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates

Nonresonant detection of electric force gradients by dynamic force microscopy

Hiroshi Yokoyama, Takahito Inoue, and Junji Itoh

Appl. Phys. Lett. 65, 3143 (1994); http://dx.doi.org/10.1063/1.112462 (3 pages) | Cited 32 times

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A mechanoelectric cross‐modulation scheme is proposed to enable direct and nonresonant detection of electric force gradients by dynamic force microscopy. The technique employs an ultrasonic vibration of the sample against a conductive tip, to which an alternating voltage is applied at a frequency near that of mechanical modulation, chosen well above the resonance frequency of the cantilever. The heterodyne mixing between the mechanically and the electrically induced oscillating charge densities on the tip gives rise to low frequency cross‐modulation forces, proportional to the electric force gradients. The nonresonant detection of the first‐ and the second‐order electric force gradients has successfully been performed, resulting in a dramatic enhancement of lateral resolution in surface potential imaging. © 1994 American Institute of Physics.
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68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps Atomic force microscopy (AFM)
68.37.Rt Magnetic force microscopy (MFM)
68.37.Uv Near-field scanning microscopy and spectroscopy
73.30.+y Surface double layers, Schottky barriers, and work functions

Polarization dependence of the temporal response of metal‐semiconductor‐metal photodetectors

J. J. Kuta, H. M. van Driel, D. Landheer, and Y. Feng

Appl. Phys. Lett. 65, 3146 (1994); http://dx.doi.org/10.1063/1.112463 (3 pages) | Cited 4 times

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The effect of grating diffraction on metal‐semiconductor‐metal photodetector temporal response is shown to be significant, and largest for devices with electrode periods less than the optical wavelength. This is related to a polarization dependence of the initial photogenerated carrier densities and distributions. With subpicosecond illumination, the measured difference in peak temporal signal for orthogonal polarizations was up to three times larger than that of the time‐integrated photocurrent, and risetimes differed by as much as 30%. Transmission efficiencies obtained from coupled‐wave analysis of metal grating structures on GaAs show excellent agreement with the time‐integrated photocurrent measurements. © 1994 American Institute of Physics.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
78.47.-p Spectroscopy of solid state dynamics
72.40.+w Photoconduction and photovoltaic effects
FREE

Comment on ‘‘Steric variation of the cerium valence in Ce2Fe14B and related compounds’’ [Appl. Phys. Lett. 63, 3642 (1993)]

J. Chaboy, J. García, and A. Marcelli

Appl. Phys. Lett. 65, 3149 (1994); http://dx.doi.org/10.1063/1.112464 (2 pages) | Cited 4 times

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Abstract Unavailable
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75.30.Mb Valence fluctuation, Kondo lattice, and heavy-fermion phenomena
75.50.Dd Nonmetallic ferromagnetic materials
78.70.Dm X-ray absorption spectra
FREE

Response to ‘‘Comment on ‘Steric variation of the cerium valence in Ce2Fe14B and related compounds’ ’’ [Appl. Phys. Lett. 63, 3642 (1993)]

T. W. Capehart, R. K. Mishra, G. P. Meisner, C. D. Fuerst, and J. F. Herbst

Appl. Phys. Lett. 65, 3151 (1994); http://dx.doi.org/10.1063/1.112465 (2 pages) | Cited 3 times

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Abstract Unavailable
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75.30.Mb Valence fluctuation, Kondo lattice, and heavy-fermion phenomena
75.50.Dd Nonmetallic ferromagnetic materials
78.70.Dm X-ray absorption spectra
FREE

Erratum: ‘‘Hysteresis of trapped charge in AlGaSb barrier as a mechanism for the current bistability in AlGaSb/InAs/AlGaSb double‐barrier structures’’ [Appl. Phys. Lett. 64, 2994 (1994)]

F. A. Buot and A. K. Rajagopal

Appl. Phys. Lett. 65, 3153 (1994); http://dx.doi.org/10.1063/1.113092 (1 page) | Cited 1 time

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73.40.Gk Tunneling
72.20.Ht High-field and nonlinear effects
85.30.De Semiconductor-device characterization, design, and modeling
73.20.Hb Impurity and defect levels; energy states of adsorbed species
99.10.Cd Errata
FREE

Erratum: ‘‘U4+:SrF2 efficient saturable absorber Q switch for the 1.54 μm erbium:glass laser’’ [Appl. Phys. Lett. 64, 948 (1994)]

R. D. Stultz, M. B. Camargo, S. T. Montgomery, M. Birnbaum, and K. Spariosu

Appl. Phys. Lett. 65, 3153 (1994); http://dx.doi.org/10.1063/1.113093 (1 page) | Cited 1 time

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42.55.Rz Doped-insulator lasers and other solid state lasers
42.55.Px Semiconductor lasers; laser diodes
99.10.Cd Errata
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