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16 Nov 1998

Volume 73, Issue 20, pp. 2857-3009

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Role of buffer surface morphology and alloying effects on the properties of InAs nanostructures grown on InP(001)

J. Brault, M. Gendry, G. Grenet, G. Hollinger, Y. Desières, and T. Benyattou

Appl. Phys. Lett. 73, 2932 (1998); http://dx.doi.org/10.1063/1.122634 (3 pages) | Cited 68 times

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We show the role played by the buffer surface morphology and by alloying effects on the size, shape and lateral distribution of InAs nanostructures grown on InP(001) substrates by molecular beam epitaxy. Three buffers, viz., In0.53Ga0.47As, In0.52Al0.48As, and InP lattice matched on InP have been studied. Differences in nanostructure morphology and in carrier confinement have been evaluated by atomic force microscopy and by low-temperature photoluminescence measurements, respectively. Alongside the classical relaxation mode through two-dimensional/three-dimensional surface morphology change, a chemical relaxation mode has to be introduced as a competitive mode of relaxation of strained layers. This chemical relaxation mode, due to alloying between the InAs deposit and the buffer, is thought to be responsible for most of the observed differences in the InAs nanostructure properties. © 1998 American Institute of Physics.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
68.35.B- Structure of clean surfaces (and surface reconstruction)
73.61.Ey III-V semiconductors
68.35.Fx Diffusion; interface formation
78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors

Argon ion damage in self-assembled quantum dots structures

W. V. Schoenfeld, C.-H. Chen, P. M. Petroff, and E. L. Hu

Appl. Phys. Lett. 73, 2935 (1998); http://dx.doi.org/10.1063/1.122635 (3 pages) | Cited 20 times

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The effects of radiation damage exposure on InGaAs quantum wells and InAs quantum dots are compared using luminescence spectroscopy techniques. A large increase in the radiation resistance of the InAs quantum dots is observed and attributed to exciton localization in the quantum dots and a point defect strain gettering effect. © 1998 American Institute of Physics.
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61.82.Fk Semiconductors
61.80.Jh Ion radiation effects
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
78.66.Fd III-V semiconductors
71.35.Cc Intrinsic properties of excitons; optical absorption spectra
78.55.Cr III-V semiconductors
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems

Mapping the influence of stress on the surface elasticity with an atomic force microscope

Eric Finot, Eric Lesniewska, Jean-Pierre Goudonnet, and Jean-Claude Mutin

Appl. Phys. Lett. 73, 2938 (1998); http://dx.doi.org/10.1063/1.122636 (3 pages) | Cited 1 time

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This letter reports an original experimental observation of the lateral stress effects on pure surface. The surface elasticity has been separated from topographical informations at the microscopic and atomic levels. The stress applied to the sample leads to modify the stiffness of the surface and affect the force modulation images. Measurements also revealed that the spring constant and the quality factor of cantilevers play an important role in the contrast mechanism of the elasticity images. © 1998 American Institute of Physics.
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68.35.Gy Mechanical properties; surface strains
62.20.D- Elasticity
07.79.Lh Atomic force microscopes
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

Charge stability of pulsed-laser deposited polytetrafluoroethylene film electrets

Reinhard Schwödiauer, Simona Bauer-Gogonea, Siegfried Bauer, Johannes Heitz, Enno Arenholz, and Dieter Bäuerle

Appl. Phys. Lett. 73, 2941 (1998); http://dx.doi.org/10.1063/1.122637 (3 pages) | Cited 20 times

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Pulsed-laser deposited (PLD) polytetrafluoroethylene (Teflon-PTFE) films from press-sintered powder targets are found to be highly crystalline, with spherulite sizes adjustable over more than one order of magnitude by suitable thermal annealing. Films with large spherulites show an excellent charge stability, comparable and even superior to commercially available Teflon-PTFE foils. PLD-PTFE enlarges the family of Teflon materials and may thus become interesting for potential miniaturized electret devices. © 1998 American Institute of Physics.
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81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
81.15.Fg Pulsed laser ablation deposition
73.61.Ph Polymers; organic compounds
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Cracking behavior of xerogel silica films on silicon substrates

L. A. Chow, Y. H. Xu, B. Dunn, K. N. Tu, and C. Chiang

Appl. Phys. Lett. 73, 2944 (1998); http://dx.doi.org/10.1063/1.122638 (3 pages) | Cited 10 times

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An analysis of the cracking behavior of sol–gel derived silica, “xerogel,” films on silicon substrates is presented. At the onset of film cracking, xerogel films on 〈100〉 Si substrates show a crosshatched crack pattern, while such films on 〈111〉 Si substrates show a random pattern. This is explained by the fact that for an isotropic film the critical film thickness for cracking decreases for increasing substrate compliance. For a 〈100〉 Si wafer, the directions of highest compliance in the plane of the wafer are in the 〈100〉 directions, which lead to cracks in the film parallel to them. A 〈111〉 Si substrate is isotropic in the plane of the wafer and, hence, there is no preferred direction for film cracking. A random pattern is the result. © 1998 American Institute of Physics.
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68.60.Bs Mechanical and acoustical properties
62.20.M- Structural failure of materials
81.05.Rm Porous materials; granular materials
81.10.Dn Growth from solutions
81.10.Fq Growth from melts; zone melting and refining
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
77.55.-g Dielectric thin films
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.

Lateral etching and filling of high aspect ratio nanometer-size cavities for silicon device structures

C. A. King, Y. O. Kim, and K. K. Ng

Appl. Phys. Lett. 73, 2947 (1998); http://dx.doi.org/10.1063/1.122639 (3 pages) | Cited 2 times

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We study a process technique involving SiO2 lateral etching coupled with amorphous Si (α-Si) refilling as a possible alternative to improve performance and lower costs for bipolar complementary metal–oxide semiconductor technologies. We investigated the lateral etching of oxide layers with thicknesses between 50 and 2.5 nm confined between a Si substrate and a multilayer stack composed of polycrystalline Si, WSix, and Si3N4. We found that the lateral etching of SiO2 proceeds even with the smallest thickness (2.5 nm) to create extremely small cavities. The etch extent (fixed time) dependence with SiO2 thickness suggests that capillary action may be an important mechanism. Using standard amorphous Si deposition techniques, we refilled all the small cavities without void formation as witnessed from transmission electron micrographs.
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
81.65.Cf Surface cleaning, etching, patterning
85.40.Hp Lithography, masks and pattern transfer

Carrier pocket engineering to design superior thermoelectric materials using GaAs/AlAs superlattices

T. Koga, X. Sun, S. B. Cronin, and M. S. Dresselhaus

Appl. Phys. Lett. 73, 2950 (1998); http://dx.doi.org/10.1063/1.122640 (3 pages) | Cited 39 times

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A large enhancement in the thermoelectric figure of merit for the whole superlattice, Z3DT, is predicted for short-period GaAs/AlAs superlattices relative to bulk GaAs. Various superlattice parameters (superlattice growth direction, superlattice period, and layer thicknesses) are explored to optimize Z3DT, including quantum well states formed from carrier pockets at various high symmetry points in the Brillouin zone. The highest room-temperature Z3DT obtained in the present calculation is 0.41 at the optimum carrier concentration for either (001)- or (111)-oriented GaAs (20 Å)/AlAs (20 Å) superlattices, which is about 50 times greater than the corresponding ZT for bulk GaAs. © 1998 American Institute of Physics.
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73.50.Lw Thermoelectric effects
73.61.Ey III-V semiconductors
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems

Low resistance Pd/Au ohmic contacts to p-type GaN using surface treatment

Jong Kyu Kim, Jong-Lam Lee, Jae Won Lee, Hyun Eoi Shin, Yong Jo Park, and Taeil Kim

Appl. Phys. Lett. 73, 2953 (1998); http://dx.doi.org/10.1063/1.122641 (3 pages) | Cited 111 times

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Ohmic contact to p-type GaN with the lowest contact resistivity was developed by the surface treatment prior to Pd/Au metal deposition. The contact resistivity drastically decreased from 2.9×10−2 to 4.3×10−4 Ω cm2 by the surface treatment using aqua regia. The surface treatment plays a role in removing the surface oxide formed on p-type GaN during epitaxial growth, and subsequently in reducing the barrier height for holes at the interface of Pd/p-type GaN, resulting in the good ohmic contacts to p-type GaN. © 1998 American Institute of Physics.
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73.40.Ns Metal-nonmetal contacts
73.40.Cg Contact resistance, contact potential
81.05.Ea III-V semiconductors
81.65.Cf Surface cleaning, etching, patterning
73.61.Ey III-V semiconductors

Nonconservative Ostwald ripening of dislocation loops in silicon

Y. L. Huang, M. Seibt, and B. Plikat

Appl. Phys. Lett. 73, 2956 (1998); http://dx.doi.org/10.1063/1.122642 (3 pages) | Cited 3 times

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We have investigated the effects of the proximity of the surface on the ripening behavior of dislocation loops in preamorphized silicon. Starting from well-defined initial conditions, we have varied the location depth of the loops by successive chemical removal of surface layers and measured changes of the size–distribution function during subsequent annealing by means of transmission electron microscopy. Our results show that the amount of Si atoms bound in the loops is not conserved during annealing and that the loop location depth has a prominent effect on the ripening kinetics. Both these observations prove the nonconservative nature of Ostwald ripening of dislocation loops near wafer surfaces. In addition, we observed different ripening kinetics for annealing in vacuum and in Ar which show that different boundary conditions at the surface are established during annealing in these two ambients. © 1998 American Institute of Physics.
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61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
61.72.Cc Kinetics of defect formation and annealing
61.72.uf Ge and Si
61.82.Fk Semiconductors
61.80.Jh Ion radiation effects

Selective carrier injection into V-groove quantum wires

H. Weman, E. Martinet, A. Rudra, and E. Kapon

Appl. Phys. Lett. 73, 2959 (1998); http://dx.doi.org/10.1063/1.122643 (3 pages) | Cited 14 times

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We have observed selective carrier injection into GaAs/AlGaAs V-groove quantum wires (QWRs) via self-ordered vertical quantum wells (VQWs). Room-temperature I–V characteristics of QWR diodes show a turn-on voltage lower by 0.2 V as compared with planar QW diodes, consistent with the band-gap reduction of 0.2 eV at the vertical QW. This selective injection results in narrow linewidth electroluminescence (∼5 nm at 300 K) emanating exclusively from the QWR from 10 K up to 300 K. © 1998 American Institute of Physics.
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85.60.Jb Light-emitting devices
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
73.61.Ey III-V semiconductors
78.66.Fd III-V semiconductors
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
78.60.Fi Electroluminescence
78.55.Cr III-V semiconductors

Mechanism of photoluminescence of Si nanocrystals fabricated in a SiO2 matrix

K. S. Zhuravlev, A. M. Gilinsky, and A. Yu. Kobitsky

Appl. Phys. Lett. 73, 2962 (1998); http://dx.doi.org/10.1063/1.122644 (3 pages) | Cited 23 times

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The luminescence properties of silicon nanocrystals fabricated by Si ion implantation into a SiO2 matrix and subsequent thermal annealing have been studied. To identify the mechanism of photoluminescence of Si nanocrystals, the dependencies of the steady-state photoluminescence on temperature and excitation power density, and the time-resolved photoluminescence have been investigated. The experimental results point to the mechanism of recombination via the levels of centers which are presumably localized at the silicon nanocrystal–silicon dioxide boundary. © 1998 American Institute of Physics.  
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78.55.Ap Elemental semiconductors
78.47.-p Spectroscopy of solid state dynamics
73.20.At Surface states, band structure, electron density of states
81.07.-b Nanoscale materials and structures: fabrication and characterization

Solid-immersion photoluminescence microscopy of carrier diffusion and drift in facet-growth GaAs quantum wells

Masahiro Yoshita, Motoyoshi Baba, Shyun Koshiba, Hiroyuki Sakaki, and Hidefumi Akiyama

Appl. Phys. Lett. 73, 2965 (1998); http://dx.doi.org/10.1063/1.122645 (3 pages) | Cited 15 times

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Carrier diffusion and drift in facet-growth quantum wells (QWs) on mesa-patterned substrates by molecular beam epitaxy was studied by high-resolution microscopic photoluminescence spectroscopy and imaging using a solid immersion lens at low temperatures. Under point excitation, excitation-position-dependent anisotropic carrier migration was observed, which was explained by carrier diffusion and drift due to spatial change in the quantization energy in QWs. © 1998 American Institute of Physics.
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78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
73.61.Ey III-V semiconductors
81.05.Ea III-V semiconductors
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
07.60.Pb Conventional optical microscopes

Photoluminescence of GaN: Effect of electron irradiation

I. A. Buyanova, Mt. Wagner, W. M. Chen, B. Monemar, J. L. Lindström, H. Amano, and I. Akasaki

Appl. Phys. Lett. 73, 2968 (1998); http://dx.doi.org/10.1063/1.122646 (3 pages) | Cited 27 times

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The effect of electron irradiation on the optical properties of GaN material with various electrical conductivity (i.e., n type, compensated, and p type) is studied in detail by photoluminescence (PL) spectroscopy. Electron irradiation with a dose <1017 cm−2 is found to have a minor effect on photoluminescence, indicating a high radiation resistance of GaN. For higher doses, two major effects of electron irradiation on PL properties can be distinguished, i.e., radiation-induced quenching of the PL, likely caused by a radiation-induced formation of competing recombination channels, and radiation-induced formation/activation of new optically active centers. © 1998 American Institute of Physics.
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78.55.Cr III-V semiconductors
61.82.Fk Semiconductors
61.80.Fe Electron and positron radiation effects
78.66.Fd III-V semiconductors

An equation for thermionic currents in vacuum energy conversion diodes

Albert C. Marshall

Appl. Phys. Lett. 73, 2971 (1998); http://dx.doi.org/10.1063/1.122647 (3 pages) | Cited 2 times

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Apparent thermionic emission constants A∗ are commonly reported with values deviating from the theoretical value of 120 A/cm2 K2. For thermionic energy conversion diodes, using A∗ in the conventional equation for predicting net currents is found to violate basic physics laws and may result in poor predictive accuracy. A general equation for vacuum energy conversion diodes is proposed to prevent misuse of A∗. © 1998 American Institute of Physics.
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84.60.Ny Thermionic conversion
84.47.+w Vacuum tubes

Nanoscale surface clustering on CdTe epilayers

L. Marsal, H. Mariette, Y. Samson, J. L. Rouvière, and E. Picard

Appl. Phys. Lett. 73, 2974 (1998); http://dx.doi.org/10.1063/1.122648 (3 pages) | Cited 14 times

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We have studied the surface morphology of two dimensional CdTe films grown by atomic layer epitaxy on CdZnTe buffers. Atomic force microscopy observations in air show a strong evolution of the surface after the growth by forming clusters of around 20 nm in diameter and 3 nm in height. The size increase of these clusters as time proceeds is directly related to the formation of tellurium and cadmium oxides on the surface as revealed by x-ray photoelectron spectroscopy data. This nanoscale clustering then occurs ex situ, due to exposure to atmosphere which induces an oxidation of the CdTe epilayers. © 1998 American Institute of Physics.
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68.55.-a Thin film structure and morphology
68.35.B- Structure of clean surfaces (and surface reconstruction)
81.05.Dz II-VI semiconductors
81.65.Mq Oxidation
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
79.60.Bm Clean metal, semiconductor, and insulator surfaces
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy

Neutralized (NH4)2S solution passivation of III–V phosphide surfaces

Z. L. Yuan, X. M. Ding, B. Lai, X. Y. Hou, E. D. Lu, P. S. Xu, and X. Y. Zhang

Appl. Phys. Lett. 73, 2977 (1998); http://dx.doi.org/10.1063/1.122649 (3 pages) | Cited 12 times

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Synchrotron radiation photoelectron spectroscopy has been used to investigate III–V phosphide GaP and InP (100) surfaces treated with a neutralized (NH4)2S solution. Compared to the conventional basic (NH4)2S solution treatment, a thick sulfide layer with P–S bond and strong Ga–S (In–S) bond of high thermal stability is formed on the neutralized (NH4)2S-treated GaP (InP) (100) surfaces. The possible passivation mechanisms of the two (NH4)2S solutions to III–V phosphide surfaces are also discussed. © 1998 American Institute of Physics.
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81.65.Rv Passivation
81.05.Ea III-V semiconductors
79.60.Bm Clean metal, semiconductor, and insulator surfaces
73.20.-r Electron states at surfaces and interfaces

Depth profiling of vacancy clusters in MeV-implanted Si using Au labeling

V. C. Venezia, D. J. Eaglesham, T. E. Haynes, Aditya Agarwal, D. C. Jacobson, H.-J. Gossmann, and F. H. Baumann

Appl. Phys. Lett. 73, 2980 (1998); http://dx.doi.org/10.1063/1.122650 (3 pages) | Cited 51 times

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A technique for profiling the clustered-vacancy region produced by high-energy ion implantation into silicon is described and tested. This technique takes advantage of the fact that metal impurities, such as Au, are trapped in the region of excess vacancies produced by MeV Si implants into silicon. In this work, the clustered-vacancy regions produced by 1-, 2-, and 8-MeV Si implants into silicon have been labeled with Au diffused in from the front surface at 750 °C. The trapped Au was profiled with Rutherford backscattering spectrometry. The dynamics of the clustered-vacancy region were monitored for isochronal annealing at 750–1000 °C, and for isothermal annealing at 950 °C, for 10–600 s. Cross-sectional transmission electron microscopy analysis revealed that after the drive-in anneal, the Au in the region of vacancy clusters is in the form of precipitates. The results demonstrate that the Au-labeling technique offers a convenient and potentially quantitative tool for depth profiling vacancies in clusters. © 1998 American Institute of Physics.
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61.72.Yx Interaction between different crystal defects; gettering effect
61.72.uf Ge and Si
61.72.J- Point defects and defect clusters
61.82.Fk Semiconductors
61.80.Jh Ion radiation effects
61.72.Cc Kinetics of defect formation and annealing
64.75.-g Phase equilibria
82.80.Yc Rutherford backscattering (RBS), and other methods of chemical analysis

Ultrafast detection and autocorrelation of picosecond THz radiation pulses with a GaAs/AlAs superlattice

S. Winnerl, W. Seiwerth, E. Schomburg, J. Grenzer, K. F. Renk, C. J. G. M. Langerak, A. F. G. van der Meer, D. G. Pavel’ev, Yu. Koschurinov, A. A. Ignatov, B. Melzer, V. Ustinov, S. Ivanov, and P. S. Kop’ev

Appl. Phys. Lett. 73, 2983 (1998); http://dx.doi.org/10.1063/1.122651 (3 pages) | Cited 14 times

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We used a wide miniband GaAs/AlAs superlattice (at room temperature) for detection and autocorrelation of picosecond THz radiation pulses (frequency 4.3 THz) from a free-electron laser. The detection was based on a THz-field induced change in conductivity of the superlattice, and the correlation on the nonlinearity of the conductivity change at strong THz-pulse-power. The nonlinear conductivity change was due to two effects, which we attribute to dynamical localization of miniband electrons and to ionization of deep impurity centers. © 1998 American Institute of Physics.
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73.50.Fq High-field and nonlinear effects
73.61.Ey III-V semiconductors
71.55.Eq III-V semiconductors
85.60.Gz Photodetectors (including infrared and CCD detectors)

Indium transient enhanced diffusion

P. B. Griffin, M. Cao, P. Vande Voorde, Y.-L. Chang, and W. M. Greene

Appl. Phys. Lett. 73, 2986 (1998); http://dx.doi.org/10.1063/1.122652 (3 pages) | Cited 22 times

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Indium, an acceptor dopant in silicon, is a large atom with a low diffusion coefficient potentially suitable for doping the channel of transistors. Systematic experiments are described which measure the susceptibility of indium to transient enhanced diffusion caused by ion implant damage introduced during the transistor fabrication process. We find that indium diffusion is dramatically enhanced by a source of interstitials and that the amount of enhancement is comparable to that seen for boron. Indium is preferable as a channel dopant not because of its diffusion behavior, but rather because a narrow ion implanted distribution can be obtained using the heavy indium ion, giving a more steeply retrograde profile than can be achieved by boron doping. These results help clarify the physics of indium and boron doping in small devices. © 1998 American Institute of Physics.
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66.30.J- Diffusion of impurities
61.72.uf Ge and Si
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
85.40.Ry Impurity doping, diffusion and ion implantation technology
72.80.Cw Elemental semiconductors
81.05.Cy Elemental semiconductors
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High critical current density in epitaxial HgBa2CaCu2OX thin films

S. L. Yan, Y. Y. Xie, J. Z. Wu, T. Aytug, A. A. Gapud, B. W. Kang, L. Fang, M. He, S. C. Tidrow, K. W. Kirchner, J. R. Liu, and W. K. Chu

Appl. Phys. Lett. 73, 2989 (1998); http://dx.doi.org/10.1063/1.122653 (3 pages) | Cited 32 times

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High quality superconducting HgBa2CaCu2Ox (Hg-1212) thin films have been reproducibly fabricated using cation-exchange method. The thin films have pure Hg-1212 phase and have smooth surface morphology. The superconducting transition temperatures of these films are in the range of 120–124 K. The critical current density Jc is up to 3.2×106 A/cm2 at 77 K and drops only by a factor of 2 at 100 K and self field. At 110 K, a Jc of 7.8×105 A/cm2 has been obtained. X-ray diffraction pole figures show that these films are epitaxially grown on LaAlO3(001) substrates, which is consistent with a χmin of 19% obtained using Rutherford backscattering/channeling analysis. © 1998 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
74.62.Bf Effects of material synthesis, crystal structure, and chemical composition
68.55.-a Thin film structure and morphology
74.10.+v Occurrence, potential candidates

Vacuum tunneling of superconducting quasiparticles from atomically sharp scanning tunneling microscope tips

S. H. Pan, E. W. Hudson, and J. C. Davis

Appl. Phys. Lett. 73, 2992 (1998); http://dx.doi.org/10.1063/1.122654 (3 pages) | Cited 51 times

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We report on the study of atomically sharp superconducting tips for scanning tunneling microscopy and spectroscopy. The results clearly show vacuum tunneling of superconducting quasiparticles from atomically sharp tips. Observed deviations of the energy gap of the superconducting tip from its bulk value are attributed to the proximity effect. We show that a combination of a superconducting tip and an atomic resolution scanning tunneling microscope provides a means of achieving very high resolution local spectroscopy. We also discuss how this combination paves the way for a number of important applications. © 1998 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
74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)
74.50.+r Tunneling phenomena; Josephson effects

Observation of ultrahigh-quality crystalline YBa2Cu3Ox in submicron thick films

Wen-Jih Lin, Peter D. Hatton, F. Baudenbacher, and J. Santiso

Appl. Phys. Lett. 73, 2995 (1998); http://dx.doi.org/10.1063/1.122655 (3 pages) | Cited 2 times

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By examining low-angle Bragg reflections of submicron thick YBa2Cu3O7 grown on SrTiO3 substrates with synchrotron radiation, we have found evidence that some high-Tc oxide thin films are composed of extremely high-quality single-crystal material. Our results evidence material ordered over a distance ten times that previously measured, displaying a micron-sized lateral correlation length and completely correlated vertically. The partially correlated roughness of the lattice planes causes the intensity of the Bragg reflections from this ultrahigh-quality crystal to quickly diminish, such that conventional high-angle x-ray measurements cannot observe it. These observations may thus account for the enhanced transport properties of thin films compared to their bulk counterparts. © 1998 American Institute of Physics.
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74.78.-w Superconducting films and low-dimensional structures
74.72.-h Cuprate superconductors
68.55.-a Thin film structure and morphology
61.05.cm X-ray reflectometry (surfaces, interfaces, films)
81.15.Fg Pulsed laser ablation deposition
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Doping effects arising from Fe and Ge for Mn in La0.7Ca0.3MnO3

J. R. Sun, G. H. Rao, B. G. Shen, and H. K. Wong

Appl. Phys. Lett. 73, 2998 (1998); http://dx.doi.org/10.1063/1.122656 (3 pages) | Cited 47 times

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Structural, magnetic, and transport properties of polycrystalline La0.7Ca0.3Mn1−xFexO3 and La0.7Ca0.3Mn1−xGexO3 are experimentally studied. Single-phase samples are obtained in the range x = 0–0.12 for Fe, and x = 0–0.06 for Ge. There are no appreciable structure changes due to the introduction of Fe and Ge. The Mn-site doping favors a reduced magnetic/resistive transition, at rates of ∼22 K for 1% Fe and ∼28 K for 1% Ge, and an elevated resistivity. No metal–insulator transition occurs when the content of Fe exceeds ∼0.1. The enhanced doping effects in La0.7Ca0.3Mn1−xGexO3 can be ascribed to the reduced hole concentration noting that the presence of Fe and Ge influence the contents of mobile eg electrons and holes in the compounds, respectively. Equivalence of the effects from Fe and Ge doping, respectively, to those due to eg electron and hole trapping and the relation between Mn- and O-site doping are discussed. © 1998 American Institute of Physics.
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72.60.+g Mixed conductivity and conductivity transitions
61.72.up Other materials
75.50.Dd Nonmetallic ferromagnetic materials
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
72.20.Fr Low-field transport and mobility; piezoresistance
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
72.80.Sk Insulators
61.66.Fn Inorganic compounds

Hydrogenation disproportionation desorption recombination in Sm–Co alloys by means of reactive milling

O. Gutfleisch, M. Kubis, A. Handstein, K.-H. Müller, and L. Schultz

Appl. Phys. Lett. 73, 3001 (1998); http://dx.doi.org/10.1063/1.122657 (3 pages) | Cited 18 times

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Sm–Co-type alloys were disproportionated by milling in hydrogen at enhanced temperatures. X-ray diffraction confirmed the disproportionation of the SmCo5 and Sm2Co17 phases into Sm hydride and α-Co. This “reactive milling” procedure facilitates the disproportionation of these alloys which are characterized by a very high thermodynamic stability, and therefore are not available for a standard hydrogenation disproportionation desorption recombination treatment. Recombination of the reactively milled powders leads to the formation of the original phases, now with dramatically refined grain sizes of around 25 nm and significant coercivities such as μ0JHC = 3.7 T in the case of the SmCo5 alloy. Exchange coupling between the nanoscaled grains resulted in magnetically single phase behavior despite a multiphase microstructure. In particular, for the Sm2Co17 alloy, a remanence enhancement was observed for recombination temperatures ⩽ 700 °C. © 1998 American Institute of Physics.
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75.50.Ww Permanent magnets
81.05.Bx Metals, semimetals, and alloys
81.20.Wk Machining, milling
75.50.Kj Amorphous and quasicrystalline magnetic materials
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation
75.50.Cc Other ferromagnetic metals and alloys
75.50.Tt Fine-particle systems; nanocrystalline materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
81.07.-b Nanoscale materials and structures: fabrication and characterization

Fabrication and physical properties of c-axis oriented thin films of layered perovskite La2−2xSr1+2xMn2O7

Y. Konishi, T. Kimura, M. Izumi, M. Kawasaki, and Y. Tokura

Appl. Phys. Lett. 73, 3004 (1998); http://dx.doi.org/10.1063/1.122658 (3 pages) | Cited 24 times

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We have grown c-axis oriented films of a layered perovskite La2−2xSr1+2xMn2O7 (x = 0.4) by pulsed laser deposition under the limited growth condition; above 900 °C and below 100 mTorr for substrate temperature and oxygen pressure (PO2), respectively. Otherwise, epitaxial but composition-unidentified films were deposited. The films show a resistive transition around 100 K in coincidence with the magnetic transition. The value of resistivity at low temperature is larger than that of a single crystal by about two orders of magnitude, perhaps due to the canted spin ordering. The films show gigantic magnetoresistance accompanied with hysteresis. © 1998 American Institute of Physics.
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75.70.Ak Magnetic properties of monolayers and thin films
75.47.De Giant magnetoresistance
81.15.Fg Pulsed laser ablation deposition
81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
72.60.+g Mixed conductivity and conductivity transitions
81.15.Kk Vapor phase epitaxy; growth from vapor phase
75.50.Cc Other ferromagnetic metals and alloys
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
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