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26 Nov 1990

Volume 57, Issue 22, pp. 2285-2377

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Efficient InGaAsP/InP multiple quantum well waveguide optical phase modulator

H. K. Tsang, J. B. D. Soole, H. P. LeBlanc, R. Bhat, M. A. Koza, and I. H. White

Appl. Phys. Lett. 57, 2285 (1990); http://dx.doi.org/10.1063/1.103910 (3 pages) | Cited 11 times

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We report an InGaAsP/InP multiple quantum well optical phase modulator which has a high phase modulation efficiency and low loss modulation over the entire 1.5–1.56 μm fiber band. For a 4‐mm‐long device, π phase modulation requires a modulation voltage of only 0.6 V at 1.49 μm and 1.1 V at 1.55 μm wavelength. The absorption modulation for a 0–5 V bias change is negligible at 1.55 μm, rising to 0.7 cm−1 at 1.49 μm. The spectral dependence of the electrorefraction from the quantum‐confined Stark effect has also been measured for the first time over a wide continuous wavelength range. Far from the absorption edge the electrorefraction decreases approximately as the square of the energy detuning.
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42.79.Hp Optical processors, correlators, and modulators
78.20.Jq Electro-optical effects
78.66.Fd III-V semiconductors
78.66.Hf II-VI semiconductors

Use of black diamond‐like carbon films as a contrast enhancement layer for liquid‐crystal displays

B. Singh, S. McClelland, F. Tams, B. Halon, O. Mesker, and D. Furst

Appl. Phys. Lett. 57, 2288 (1990); http://dx.doi.org/10.1063/1.103890 (3 pages) | Cited 6 times

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We report development of single‐layer, highly durable, pinhole‐free, abrasion‐resistant, chemically inert ‘‘black coating’’ suitable for use as a contrast enhancement layer for liquid‐ crystal display devices. The single layer is a diamond‐like carbon coating that has a high extinction coefficient and appears black due to optical absorption. The optical transmittance is less than 2% over the visible spectrum, and the reflectance is about 20%. Furthermore, this coating is easy to deposit onto large‐area substrates at high deposition rates. The coating is sufficiently durable, electrically insulating, and chemically compatible with liquid‐crystal display materials. Its hardness exceeds that of SiC (9+ on Mohs scale), and it is resistant to abrasion and most common solvents and acids. It exhibits good adhesion to glass, silicon, metal, and oxide substrates. Films of this material have been used to provide an increased contrast enhancement ratio in liquid‐crystal displays. Details on the synthesis of these films are presented. Also, data on the optical and mechanical properties of these films as well as their use as contrast enhancement layers for liquid‐crystal displays are presented.
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85.60.Pg Display systems
07.07.Hj Display and recording equipment, oscilloscopes, TV cameras, etc.
73.61.Ng Insulators

Investigation of the temperature dependence of the threshold current density of GaInP/AlGaInP double‐heterostructure lasers

S. H. Hagen, A. Valster, M. J. B. Boermans, and J. van der Heyden

Appl. Phys. Lett. 57, 2291 (1990); http://dx.doi.org/10.1063/1.103891 (3 pages) | Cited 7 times

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The temperature dependence of the threshold current density of GaInP/AlGaInP double‐heterostructure lasers is investigated over a wide temperature range. Using a theoretical calculation of the temperature dependence of the recombination rate in the active layer, the experimentally obtained threshold current density is separated into a component due to recombination in the active layer and an additional component responsible for an increased temperature dependence at higher temperature. For the additional component, a thermal activation energy of 0.27 eV is found. It is argued that this value is too low for a simple explanation based on carrier leakage.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

Noncritical phase matching for guided‐wave frequency conversion

E. J. Lim, S. Matsumoto, and M. M. Fejer

Appl. Phys. Lett. 57, 2294 (1990); http://dx.doi.org/10.1063/1.104166 (3 pages) | Cited 10 times

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Inhomogeneities in waveguide dimensions are a serious problem for guided‐wave frequency conversion devices. We discuss waveguide designs that make the phase matching ‘‘noncritical’’ with respect to small changes in dimensions. Application of noncritical phase matching results in larger fabrication tolerances, facilitating the practical realization of nonlinear devices with long interaction lengths. We experimentally demonstrate the existence of a noncritical thickness in a lithium niobate waveguide, and analyze the dimensional tolerances for second‐harmonic generation in a polymer waveguide.
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42.79.Gn Optical waveguides and couplers
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.82.-m Integrated optics
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Behavior of charged particles in an electron cyclotron resonance plasma chemical vapor deposition reactor

Yoshikazu Nakayama, Mitsuru Kondoh, Kohji Hitsuishi, Mei Zhang, and Takao Kawamura

Appl. Phys. Lett. 57, 2297 (1990); http://dx.doi.org/10.1063/1.103892 (3 pages) | Cited 2 times

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This letter presents the behavior of electrons and ions in an electron cyclotron resonance (ECR) plasma chemical vapor deposition (CVD) reactor. The reactor consists of an ECR chamber with a hydrogen plasma and a CVD chamber into which a source gas of SiH4is fed. It is found that electrons and ions of H+ extracted from the ECR chamber by a divergent magnetic field move along the magnetolines of force and play respective roles in the production of the film precursor from SiH4 and in the relaxation of the silicon network. The precursor for films on the substrate perpendicular to the magnetic flux is mainly produced on the growing surface.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
52.80.Sm Magnetoactive discharges (e.g., Penning discharges)
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
41.60.-m Radiation by moving charges

Preparation and structure of amorphous semiconductor hydrogenated tin

M. Vergnat, G. Marchal, and Ph. Mangin

Appl. Phys. Lett. 57, 2300 (1990); http://dx.doi.org/10.1063/1.103893 (2 pages)

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Evaporation on substrates maintained at 77 K under an atomic hydrogen flow allows us to prepare amorphous semiconductor tin. The resistivity is very high, 3×103 Ω cm and the diffraction pattern is typical of the random continuous networks of amorphous germanium and silicon. This structure is stable up to 180 K.
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81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
68.55.-a Thin film structure and morphology
68.55.Nq Composition and phase identification
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties

Photostimulated evaporation of SiO2 films by synchrotron radiation

H. Akazawa, Y. Utsumi, J. Takahashi, and T. Urisu

Appl. Phys. Lett. 57, 2302 (1990); http://dx.doi.org/10.1063/1.104167 (3 pages) | Cited 29 times

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Irradiation by synchrotron radiation on SiO2 films induces continuous removal of this material at elevated temperatures. The photostimulated evaporation rate for a thermally grown SiO2 film increases steeply with temperature giving an activation energy of 0.7 eV. The experimental results indicate that photon‐induced bond breaking assists decomposition and thermal desorption of the film. Applications to microfabrication of a line‐and‐space pattern and low‐temperature cleaning of Si(100) surface are demonstrated.
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61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
82.50.Bc Processes caused by infrared radiation
82.50.Hp Processes caused by visible and UV light

Strain modification in coherent Ge and SixGe1−x epitaxial films by ion‐assisted molecular beam epitaxy

C. J. Tsai, H. A. Atwater, and T. Vreeland

Appl. Phys. Lett. 57, 2305 (1990); http://dx.doi.org/10.1063/1.103877 (3 pages) | Cited 24 times

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We have observed large changes in Ge and SixGe1−x layer strain during concurrent molecular beam epitaxial growth and low‐energy bombardment. Layers are uniformly strained, coherent with the substrate, and contain no dislocations, suggesting that misfit strain is accommodated by free volume changes associated with injection of ion bombardment induced point defects. The dependence of layer strain on ion energy, ion‐atom flux ratio, and temperature is consistent with the presence of a uniform dispersion of point defects at high concentration. Implications for distinguishing ion‐surface interactions from ion‐bulk interactions are discussed.
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68.35.Gy Mechanical properties; surface strains
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
61.80.Jh Ion radiation effects
68.60.Bs Mechanical and acoustical properties

Molecular view of the interfacial adhesion in aluminum‐silicon carbide metal‐matrix composites

B. K. Rao and P. Jena

Appl. Phys. Lett. 57, 2308 (1990); http://dx.doi.org/10.1063/1.103878 (3 pages) | Cited 10 times

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The binding energies, electron charge transfer, bond lengths, and core level shifts of Al‐Al, Al‐Si, Al‐C, and Si‐C dimers have been calculated self‐consistently using the linear combination of atomic orbitals‐molecular orbital theory. The exchange interactions are treated using the unrestricted Hartree–Fock theory and correlation corrections are included through the Möller–Plesset perturbation scheme up to fourth order. The results are used to understand the nature and strength of bonding at the interface of Al and SiC crystals. The strong bonding of Al‐C dimers compared to Al‐Al and Al‐Si is shown to be responsible for the aluminum carbide formation at the interface. The charge transfer between the constituent atoms in the dimer and the accompanying core level shifts are also shown to be characteristic of what has been observed at the Al/SiC interface.
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68.35.B- Structure of clean surfaces (and surface reconstruction)
68.35.Fx Diffusion; interface formation
31.15.-p Calculations and mathematical techniques in atomic and molecular physics

Resonant tunneling of electrons from quantized levels in the accumulation layer of double‐barrier heterostructures

J. S. Wu, C. Y. Chang, C. P. Lee, K. H. Chang, D. G. Liu, and D. C. Liou

Appl. Phys. Lett. 57, 2311 (1990); http://dx.doi.org/10.1063/1.103879 (2 pages) | Cited 13 times

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We report the first observation of the resonant tunneling features associated with the quantized levels in the accumulation layer of the double‐barrier resonant tunneling structure (DBRTS) with undoped electrodes. This quantum effect causes additional kinks in the current‐voltage (I‐V) characteristic and an increasingly enhanced oscillation behavior in the differential conductance‐voltage (G‐V) curve. Three discrete quantum levels have been observed based on the room‐temperature G‐V curve. Our measurements are made without the presence of magnetic field and thus the experimental results are totally different from the magneto‐oscillation.
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73.40.Gk Tunneling
73.40.Kp III-V 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
73.61.Ey III-V semiconductors

Comparative study of the substrate‐film interfaces of GaAs grown by two molecular beam epitaxial methods

K. Tappura, A. Salokatve, K. Rakennus, H. Asonen, and M. Pessa

Appl. Phys. Lett. 57, 2313 (1990); http://dx.doi.org/10.1063/1.103880 (2 pages) | Cited 1 time

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Carrier concentration profiles in the region of a substrate‐film homojunction for n‐ and p‐type GaAs were studied using a capacitance‐voltage carrier profiling technique. The GaAs films were grown on GaAs substrates by molecular beam epitaxy (MBE) and by gas‐source molecular beam epitaxy (GSMBE). The GaAs homojunctions grown by MBE exhibited a much larger reduction in carrier concentration than those prepared by GSMBE. The highest quality interface, without an observable depletion region, was obtained when an additional hydrogen plasma was used during heat treatment prior to GSMBE growth.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
68.35.Dv Composition, segregation; defects and impurities

Exciton saturation in electrically biased quantum wells

A. M. Fox, D. A. B. Miller, G. Livescu, J. E. Cunningham, J. E. Henry, and W. Y. Jan

Appl. Phys. Lett. 57, 2315 (1990); http://dx.doi.org/10.1063/1.104113 (3 pages) | Cited 30 times

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We have measured the heavy hole excitation saturation intensity in GaAs/AlGaAs quantum wells as a function of applied electric field and AlGaAs barrier design. We find that the saturation intensity increased with increasing applied field, and decreasing barrier thickness or height, because of increased carrier sweep‐out rates. Time‐resolved sweep‐out time and temperature‐dependent saturation intensity measurement point out the roles of both thermionic emission and tunneling in the field and barrier‐dependent carrier escape time. By reducing the barrier Al composition from 30 to 20%, we achieved an increase in the saturation intensity by a factor of ∼6.
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78.66.Fd III-V semiconductors
78.66.Hf II-VI semiconductors
71.35.-y Excitons and related phenomena
73.40.Gk Tunneling
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems

Microscopic model for hot‐electron trapping and detrapping in silicon dioxide

W. Porod and R. L. Kamocsai

Appl. Phys. Lett. 57, 2318 (1990); http://dx.doi.org/10.1063/1.104168 (3 pages) | Cited 3 times

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We present a microscopic theory for high‐field stressing and oxide degradation in SiO2. Hot electrons lead to a charge buildup in the oxide according to a dynamical trapping and detrapping model, where detrapping events are modeled as trap‐to‐band impact ionization processes. Electronic distributions obtained from Monte Carlo high‐field transport simulations are used to determine ensemble averaged detrapping cross sections and experimentally observed flat‐band voltage shifts. In comparing our microscopic theory to previously employed empirical rate equation models, we find significant differences in the predicted spatial distribution of oxide charge.
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72.10.Bg General formulation of transport theory
72.20.Ht High-field and nonlinear effects
77.22.Jp Dielectric breakdown and space-charge effects
73.50.Fq High-field and nonlinear effects

Unintentional indium incorporation in GaAs grown by molecular beam epitaxy

D. R. Myers, L. R. Dawson, J. F. Klem, T. M. Brennan, B. E. Hammons, D. S. Simons, J. Comas, and J. Pellegrino

Appl. Phys. Lett. 57, 2321 (1990); http://dx.doi.org/10.1063/1.103881 (3 pages) | Cited 2 times

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We have quantified unintentional indium incorporation in GaAs grown by molecular beam epitaxy in a variety of commercial systems. We find that the unintentional indium density in the epitaxial GaAs is more a function of mounting technique and prior machine history than of the manufacturer’s design. The indium densities detected in the epitaxial GaAs for substrates that only partially obscure an indium‐bearing mount are equal to levels reported to result in minimum defect densities and narrowest photoluminescence linewidths in In‐doped GaAs.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.sd Impurity concentration
61.72.sh Impurity distribution
61.72.sm Impurity gradients
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces

Independently contacted two‐dimensional electron systems in double quantum wells

J. P. Eisenstein, L. N. Pfeiffer, and K. W. West

Appl. Phys. Lett. 57, 2324 (1990); http://dx.doi.org/10.1063/1.103882 (3 pages) | Cited 103 times

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A new technique for creating independent ohmic contacts to closely spaced two‐dimensional electron systems in double quantum well (DQW) structures is described. Without use of shallow diffusion or precisely controlled etching methods, the present technique results in low‐resistance contacts which can be electrostatically switched between the two‐conducting layers. The method is demonstrated with a DQW consisting of two 200 Å GaAs quantum wells separated by a 175 Å AlGaAs barrier. A wide variety of experiments on Coulomb and tunnel‐coupled 2D electron systems is now accessible.
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73.40.Cg Contact resistance, contact potential
73.50.Dn Low-field transport and mobility; piezoresistance
73.61.Ey III-V semiconductors

Strongly directional emission from AlGaAs/GaAs light‐emitting diodes

A. Köck, E. Gornik, M. Hauser, and W. Beinstingl

Appl. Phys. Lett. 57, 2327 (1990); http://dx.doi.org/10.1063/1.103883 (3 pages) | Cited 28 times

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We show for the first time that strongly directional emission of defined polarization can be achieved from conventional AlGaAs/GaAs double‐heterostructure surface‐emitting light‐emitting diodes (LEDs) via coupling to surface plasmons. By microstructuring the surface, we have fabricated LEDs with a beam divergence of less than 4° and an increased quantum efficiency. It is demonstrated that the surface plasmon excitation and emission mechanism have the potential to improve the performance of LEDs.
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85.60.Jb Light-emitting devices
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

Observation of power gain in an inductive energy pulsed power system with an optically controlled semiconductor opening switch

C. C. Kung, E. A. Chauchard, Chi H. Lee, M. J. Rhee, and L. Yan

Appl. Phys. Lett. 57, 2330 (1990); http://dx.doi.org/10.1063/1.103884 (3 pages) | Cited 2 times

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Power gain has been observed, for the first time, in an inductive energy storage pulsed power system with an optically controlled semiconductor opening switch. A specially tailored 1.054 μm pulse from a Nd:glass laser was utilized to activate a GaAs switch of the p‐i‐n diode configuration, producing an output pulse with a power gain of more than 10.
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84.30.Sk Pulse and digital circuits
84.70.+p High-current and high-voltage technology: power systems; power transmission lines and cables
85.60.Dw Photodiodes; phototransistors; photoresistors
84.60.Ve Energy storage systems, including capacitor banks

Photoluminescence and reflection high‐energy electron diffraction study of GaAs/AlxGa1−xAs(100) single quantum wells grown via molecular beam epitaxy employing two forms (As2 and As4) of arsenic

J. Y. Kim, D. Bassi, J. Ellis, and L. Jostad

Appl. Phys. Lett. 57, 2333 (1990); http://dx.doi.org/10.1063/1.103885 (3 pages) | Cited 2 times

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Photoluminescence (PL) and intensity behavior of a reflected high‐energy electron diffraction (RHEED) beam are examined for GaAs/AlxGa1−xAs (x=0.5 and 0.7) single quantum wells grown via molecular beam epitaxy under dimeric (As2) and tetrameric (As4) arsenic pressures. The growth conditions for AlxGa1−xAs and GaAs layers in a single quantum well are determined via RHEED. Results show that PL linewidth and intensity are correlated with RHEED intensity and that the dual arsenic source scheme produces superior quality GaAs/AlxGa1−xAs heterostructures.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
78.66.Fd III-V semiconductors
78.66.Hf II-VI semiconductors
78.55.Cr III-V semiconductors

Reactive partially ionized beam deposition of BaTiO3 thin films

P. Li and T.‐M. Lu

Appl. Phys. Lett. 57, 2336 (1990); http://dx.doi.org/10.1063/1.104169 (3 pages) | Cited 23 times

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A dual‐source reactive partially ionized beam deposition has been employed to deposit thin BaTiO3 films on the Si(100) substrate at room temperature. It is shown that with a small amount (3%) of Ti and oxygen ions in the beam one can dramatically control the electrical properties of the films. From the capacitance versus voltage (C‐V) characteristics, the flatband voltage and the total interface charge density were measured to be 0.3 V and 1×1011/cm2, respectively. These ferroelectric compound oxide thin films with high‐dielectric constant are potentially useful in high density memory applications.
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73.61.Ng Insulators
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
81.15.Jj Ion and electron beam-assisted deposition; ion plating

Conduction‐band minima of InP: Ordering and absolute energies

Stefan Zollner, Uwe Schmid, Niels E. Christensen, and Manuel Cardona

Appl. Phys. Lett. 57, 2339 (1990); http://dx.doi.org/10.1063/1.103886 (3 pages) | Cited 9 times

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Since the conduction‐band structure of InP is still controversial, we perform an ab initio linear muffin tin orbital (LMTO) band structure calculation to obtain the valence bands with high accuracy. The LMTO is based on the local density approximation (LDA) which suffers from the well known ‘‘band‐gap problem.’’ We therefore combine our calculated valence‐band energies with carefully evaluated optical data from the literature and confirm the interconduction‐band separation energies ΔEΓL=0.86±0.02 eV and ΔEΓX=0.96±0.02 eV. We also give new empirical local pseudopotential form factors adjusted to reproduce these experimental values.
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71.20.Nr Semiconductor compounds
71.20.Ps Other inorganic compounds

Structure, chemistry, and band bending at Se‐passivated GaAs(001) surfaces

S. A. Chambers and V. S. Sundaram

Appl. Phys. Lett. 57, 2342 (1990); http://dx.doi.org/10.1063/1.103887 (3 pages) | Cited 24 times

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Se‐passivated n‐GaAs(001) surfaces prepared in a metalorganic chemical vapor desposition reactor have been investigated by means of x‐ray photoelectron spectroscopy, low‐energy electron diffraction, and x‐ray photoelectron diffraction. The band bending of these free surfaces was as low as ∼0.1 eV, indicating excellent passivation. It was found that Se undergoes an anion exchange reaction with As to depths of at least five atomic layers. This result suggests that the reduction of surface states is brought about by the formation of a GaAsxSe1−x/GaAs heterojunction interface of very high structural quality.
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73.61.Ey III-V semiconductors
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
61.05.cf X-ray scattering (including small-angle scattering)
61.05.cj X-ray absorption spectroscopy: EXAFS, NEXAFS, XANES, etc.
61.05.jh Low-energy electron diffraction (LEED) and reflection high-energy electron diffraction (RHEED)

Characterization of SiGe/Si heterostructures formed by Ge+ and C+ implantation

Akira Fukami, Ken‐ichi Shoji, Takahiro Nagano, and Cary Y. Yang

Appl. Phys. Lett. 57, 2345 (1990); http://dx.doi.org/10.1063/1.103888 (3 pages) | Cited 35 times

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Formation of SiGe/Si heterostructures by germanium ion implantation was investigated. A germanium‐implanted layer was grown epitaxially in the solid phase by thermal annealing. Two kinds of crystalline defects were observed. One is a misfit dislocation, and the other is a residual dislocation caused by ion bombardment. The p‐n junction formed in the SiGe layer has a leakage current three orders of magnitude larger than that of a pure Si p‐n junction fabricated with an identical process except for the Ge+ implantation. Carbon doping in the SiGe layer improves its crystalline quality and the junction characteristics.
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68.35.Fx Diffusion; interface formation
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
68.55.-a Thin film structure and morphology
73.61.Cw Elemental semiconductors
73.61.Jc Amorphous semiconductors; glasses
73.61.Le Other inorganic semiconductors

p‐type doping limit of carbon in organometallic vapor phase epitaxial growth of GaAs using carbon tetrachloride

P. M. Enquist

Appl. Phys. Lett. 57, 2348 (1990); http://dx.doi.org/10.1063/1.103889 (3 pages) | Cited 40 times

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The doping limit of carbon in GaAs grown by organometallic vapor phase epitaxy (OMVPE) using carbon tetrachloride (CCl4) as a p‐type dopant source has been investigated by variation of the V/III ratio, growth temperature, and CCl4 flow rate. Lower V/III ratios, lower growth temperatures, and higher CCl4 flow rates generally yielded higher hole concentrations. Hole concentrations as high as 1020 cm−3 were achieved. Attempts to achieve higher hole concentrations via higher CCl4 flow rates were limited by inhibition of growth and morphology degradation. Majority‐carrier hole mobilities of carbon‐doped GaAs were more than 50% greater than that of zinc‐doped GaAs for comparable hole concentrations obtained in previous work. Nonalloyed contacts to this material resulted in contact resistivities of 4×10−7 Ω cm2.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.Kk Vapor phase epitaxy; growth from vapor phase
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.

Scanning tunneling microscopy of the Abrikosov flux lattice with ferromagnetic probes

R. Berthe, U. Hartmann, and C. Heiden

Appl. Phys. Lett. 57, 2351 (1990); http://dx.doi.org/10.1063/1.104170 (3 pages) | Cited 18 times

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Using a low‐temperature scanning tunneling microscope spatial variations of the current‐voltage characteristics have been investigated on NbSe2 single crystals employing PtIr and ferromagnetic Ni tips. At 4.2 K a clear superconducting energy gap is visible even when tunneling through the Ni tip. After field‐induced transfer of the sample into the superconducting mixed state a complete Abrikosov flux lattice is imaged for both types of probes by recording the tunneling current at a fixed voltage within the superconducting gap. Comparison of the images obtained by the two probe materials clearly shows that no distortion of the flux lattice is produced by magnetostatic interactions between the ferromagnetic tip and the individual vortices. This provides the basis for future investigations of flux distributions in superconductors by magnetic force microscopy.
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07.79.Cz Scanning tunneling microscopes
61.05.-a Techniques for structure determination
74.50.+r Tunneling phenomena; Josephson effects
74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)
74.25.Ha Magnetic properties including vortex structures and related phenomena
74.70.Dd Ternary, quaternary, and multinary compounds (including Chevrel phases, borocarbides, etc.)

Accelerated formation of the three Cu‐O layered Tl‐(Pb,Bi)‐Sr‐Ca‐Cu‐O compound

Y. T. Huang, S. F. Wu, C. K. Chiang, and W. H. Lee

Appl. Phys. Lett. 57, 2354 (1990); http://dx.doi.org/10.1063/1.104171 (2 pages) | Cited 6 times

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Bulk samples containing nearly single phase of the three Cu‐O layered compound in the Tl‐Pb(Bi)‐Sr‐Ca‐Cu‐O system have been readily synthesized. By partially substituting Ca for Sr, an accelerated formation of the desired three Cu‐O layered phase was observed when the Ca/Sr ratio reached up to 2.4/1.6. The phase purity was clearly evidenced by x‐ray diffraction and magnetization measurement. The synthesis is valuable for further application interests.
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74.78.Fk Multilayers, superlattices, heterostructures
74.70.-b Superconducting materials other than cuprates
74.78.-w Superconducting films and low-dimensional structures
68.55.Nq Composition and phase identification
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