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3 Nov 1997

Volume 71, Issue 18, pp. 2557-2712

Page 2 of 3 Pages Previous Page Next Page | Jump to Page

Mapping of electrical double-layer force between tip and sample surfaces in water with pulsed-force-mode atomic force microscopy

Tatsuya Miyatani, Miki Horii, Armin Rosa, Masamichi Fujihira, and Othmar Marti

Appl. Phys. Lett. 71, 2632 (1997); http://dx.doi.org/10.1063/1.120162 (3 pages) | Cited 36 times

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Pulsed-force-mode atomic force microscopy (PFM-AFM) using a cantilever with a Si3N4 tip was applied to map charge distribution on a sample surface in water. In order to confirm the applicability of the present PFM, we prepared a patterned sample by vapor deposition of Al on a quartz plate covered with silica beads, followed by oxidation of Al with O2 and removal of the beads with ultrasonication. The two different areas of Al2O3 and SiO2 had different isoelectric points and bore positive and negative charge, respectively, at pH 8.6. The lateral resolution of the present method was found to be ca. 30 nm. © 1997 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
73.25.+i Surface conductivity and carrier phenomena
07.79.Lh Atomic force microscopes

Polarity of (00.1) GaN epilayers grown on a (00.1) sapphire

M. Seelmann-Eggebert, J. L. Weyher, H. Obloh, H. Zimmermann, A. Rar, and S. Porowski

Appl. Phys. Lett. 71, 2635 (1997); http://dx.doi.org/10.1063/1.120163 (3 pages) | Cited 101 times

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The polarity is found to be a key parameter for the growth of high quality epitaxial GaN films on sapphire (00.1) substrates. A model is suggested which may consistently explain the observed influence of the process parameters on the polar orientation of the epitaxial film. A simple etching technique is proposed for quick distinction of the film polarity. The assignment of the etching behavior to the proper crystal structure is achieved by an analysis of the respective two-dimensional photoelectron diffraction patterns. © 1997 American Institute of Physics.  
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81.05.Ea III-V semiconductors
68.55.-a Thin film structure and morphology
81.15.Kk Vapor phase epitaxy; growth from vapor phase
81.65.Cf Surface cleaning, etching, patterning
61.66.Fn Inorganic compounds

Lateral epitaxy of low defect density GaN layers via organometallic vapor phase epitaxy

Ok-Hyun Nam, Michael D. Bremser, Tsvetanka S. Zheleva, and Robert F. Davis

Appl. Phys. Lett. 71, 2638 (1997); http://dx.doi.org/10.1063/1.120164 (3 pages) | Cited 123 times

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Organometallic vapor phase lateral epitaxy and coalescence of GaN layers originating from GaN stripes deposited within 3-μm-wide windows spaced 3 μm apart and contained in SiO2 masks on GaN/AlN/6H–SiC(0001) substrates are reported. The extent and microstructural characteristics of the lateral overgrowth were a strong function of stripe orientation. A high density of threading dislocations, originating from the interface of the underlying GaN with the AlN buffer layer, were contained in the GaN grown in the window regions. The overgrowth regions, by contrast, contained a very low density of dislocations. The coalesced layers had a rms surface roughness of 0.25 nm. © 1997 American Institute of Physics.
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81.05.Ea III-V semiconductors
81.15.Kk Vapor phase epitaxy; growth from vapor phase
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
68.35.B- Structure of clean surfaces (and surface reconstruction)

Photoluminescence spectroscopy of erbium implanted gallium nitride

Myo Thaik, U. Hömmerich, R. N. Schwartz, R. G. Wilson, and J. M. Zavada

Appl. Phys. Lett. 71, 2641 (1997); http://dx.doi.org/10.1063/1.120165 (3 pages) | Cited 53 times

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Results of a photoluminescence (PL) and photoluminescence excitation (PLE) study of Er implanted GaN are presented. Upon optical excitation at 325 and 488 nm, we observed strong 1.54 μm Er3+ PL which remained temperature stable from 15 to 550 K. At 550 K, the integrated PL intensity decreased by ∼ 10% for above gap excitation (λex=325 nm) and ∼ 50% for below gap excitation (λex=488 nm) relative to its value at 15 K. The excellent temperature stability makes GaN:Er very attractive for high temperature optoelectronic device applications. PLE measurements were conducted to gain insight into the Er3+ excitation mechanisms in the GaN host. The PLE results show that Er3+ can be excited continuously over a broad wavelength region spanning from 425 to 680 nm. In addition, sharp PLE features were observed at approximately 495, 525, 553, 651, and 980 nm. The PLE spectrum suggests that optically active Er3+ ions can be excited either through carrier-mediated processes involving defects in the host or through resonant pumping into Er3+ 4f energy levels. With respect to these two excitation schemes, distinct Er3+ PL properties were observed for resonant and off-resonant Er3+ excitation indicating the presence of different subsets of Er3+ ions in GaN. © 1997 American Institute of Physics.
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78.55.Cr III-V semiconductors
71.55.Eq III-V semiconductors

Semiconductor based light emitters powered by tritium

Harry E. Ruda, Lech Z. Jedral, and L. Mannik

Appl. Phys. Lett. 71, 2644 (1997); http://dx.doi.org/10.1063/1.120166 (3 pages) | Cited 1 time

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We report on radioluminescence (RL) studies of the wide band gap semiconductors GaP and GaInAsP exposed to tritium gas. All samples were prepared by liquid phase epitaxy. RL tests were performed as a function of tritium pressure, sample temperature, and time, enabling the limiting factors for developing high efficiency visible RL sources to be identified. The studies were complemented by photoluminescence (PL) and cathodoluminescence (CL) measurements. Reduction of surface recombination velocity was shown to be essential for obtaining low threshold CL response and improved PL efficiency. This factor resulted in tritium-activated RL visible to the naked eye. With appropriate materials optimization, these structures should be suitable for developing high efficiency RL devices. © 1997 American Institute of Physics.
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78.66.Fd III-V semiconductors
78.60.Hk Cathodoluminescence, ionoluminescence
78.55.Cr III-V semiconductors
72.80.Ey III-V and II-VI semiconductors
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Coherent control of cyclotron emission from a semiconductor using sub-picosecond electric field transients

P. G. Huggard, J. A. Cluff, C. J. Shaw, S. R. Andrews, E. H. Linfield, and D. A. Ritchie

Appl. Phys. Lett. 71, 2647 (1997); http://dx.doi.org/10.1063/1.120167 (3 pages) | Cited 5 times

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We have demonstrated the excitation and control of coherent cyclotron emission from a semiconductor using a THz beam containing pairs of sub-picosecond electric field pulses closely spaced in time. The source of THz radiation in these experiments is a biased coplanar stripline fabricated on semi-insulating GaAs and edge illuminated with pairs of temporally and spatially separated 70 fs pulses of near infrared light. A GaAs/AlGaAs two-dimensional electron gas was used in the experiments because of its long intraband phase relaxation time. Changes in the amplitude and phase of the cyclotron emission are observed when varying the interpulse delay and are well described within the theoretical framework of a two level system. © 1997 American Institute of Physics.
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73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
84.40.Az Waveguides, transmission lines, striplines
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
85.30.-z Semiconductor devices

Nondegenerate four-wave mixing in a semiconductor microcavity

M. Tsuchiya, J. Shah, T. C. Damen, and J. E. Cunningham

Appl. Phys. Lett. 71, 2650 (1997); http://dx.doi.org/10.1063/1.120168 (3 pages) | Cited 4 times

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We report the observation of highly nondegenerate four-wave mixing from a semiconductor microcavity. The phase mismatch originating from the unique relationship between a beam incidence angle and its cavity resonance frequency was minimized by using a new method where both of pump and probe beams are obliquely incident. External efficiency of 1.6% was measured at 10 K for 1.5 THz frequency conversion of probe pulses by using 1 ps pump pulses of 55 pJ incident pulse energy. © 1997 American Institute of Physics.
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42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation

In situ real-time analysis of alloy film composition and segregation dynamics with parallel detection reflection electron energy loss spectroscopy

C. C. Ahn, H. Yoshino, T. Tambo, S. S. Wong, G. He, M. E. Taylor, and H. A. Atwater

Appl. Phys. Lett. 71, 2653 (1997); http://dx.doi.org/10.1063/1.120136 (3 pages)

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Real-time measurements of GexSi1−x/Si(001) composition and segregation dynamics in Sn/Si(001) in molecular beam epitaxy are demonstrated using parallel detection reflection electron energy loss spectroscopy. Parallel detection enables quantitative acquisition of low-loss spectra in a time of <500 μs and surface composition determination in GexSi1−x/Si(001) via Ge L2,3 core loss analysis to a precision of approximately 2% in time of order 1 s. Segregation and trapping kinetics of monolayer thickness Sn films during Si epitaxy on Sn-covered Si(100) has also been studied using the Sn M4,5 core loss. © 1997 American Institute of Physics.  
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79.20.Kz Other electron-impact emission phenomena
64.75.-g Phase equilibria
61.85.+p Channeling phenomena (blocking, energy loss, etc.)
68.55.-a Thin film structure and morphology
68.35.Ct Interface structure and roughness

Pd/Ge/Ti/Au ohmic contact to AlGaAs/InGaAs pseudomorphic high electron mobility transistor with an undoped cap layer

Yi-Tae Kim, Jong-Lam Lee, Jae Kyoung Mun, and Haecheon Kim

Appl. Phys. Lett. 71, 2656 (1997); http://dx.doi.org/10.1063/1.120169 (3 pages) | Cited 6 times

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The Pd/Ge/Ti/Au ohmic contact to AlGaAs/InGaAs pseudomorphic high electron mobility transistor was investigated with the etch depth of an undoped GaAs/AlGaAs cap layer. The contact resistivity decreases from 9.5×10−5 to 2.3×10−6 Ω cm2 when the contacts were formed on a n-Al0.23Ga0.77As layer by removing the undoped cap layer. X-ray diffraction results show that the good ohmic contact is due to the formation of Au2Al as well as β-AuGa. Both compounds play a role to create group-III vacancies, followed by the incorporation of Ge into group-III vacancies, namely, creation of free electron below the contact. This results in the considerable elimination of contact resistivity by lowering the effective tunneling barrier. © 1997 American Institute of Physics.
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85.30.Tv Field effect devices
73.40.Cg Contact resistance, contact potential
73.40.Gk Tunneling

Surface reaction of trisdimethylaminoarsenic on GaAs(001)-c(4×4) and (4×6)

Jie Cui, Masashi Ozeki, and Masafumi Ohashi

Appl. Phys. Lett. 71, 2659 (1997); http://dx.doi.org/10.1063/1.120170 (3 pages) | Cited 7 times

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The surface decomposition of trisdimethylaminoarsenic (TDMAAs) on GaAs (001) has been studied employing supersonic molecular beam scattering. It was found that TDMAAs molecules adsorbed dissociatively on GaAs (001) surfaces at room temperature through a Langmuir adsorption mechanism. The initial Ga-rich (4×6) surface changed into an As-rich c(4×4) surface after the injection of TDMAAs. The species such as dimethylamine and methylmethyleneimine desorbed at the surface temperatures of 150 and 230 °C, respectively, as measured by temperature-programmed desorption (TPD) spectra. The polar-angle dependence of desorption showed that the desorption of species has two maximal intensities, at the directions along surface normal and 60°, respectively. © 1997 American Institute of Physics.
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73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
68.03.Fg Evaporation and condensation of liquids
68.43.Mn Adsorption kinetics
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
68.43.-h Chemisorption/physisorption: adsorbates on surfaces

Trap-mediated excitation of Er3+ photoluminescence in Er-implanted GaN

S. Kim, S. J. Rhee, D. A. Turnbull, X. Li, J. J. Coleman, S. G. Bishop, and P. B. Klein

Appl. Phys. Lett. 71, 2662 (1997); http://dx.doi.org/10.1063/1.120171 (3 pages) | Cited 48 times

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Site-selective photoluminescence (PL) spectra obtained at 6 K from the 1540 nm 4I13/2→4I15/2 emissions characteristic of four distinct Er3+ centers in Er-implanted films of GaN are compared with the Er3+ PL excited by 325 nm above-gap pump light. Two of the site-selective 1540 nm Er3+ PL spectra pumped by below-gap, trap-mediated excitation bands dominate the Er3+ PL spectrum excited by above-gap light. A third broad band-excited spectrum and a fourth spectrum pumped by direct Er3+ 4f-band absorption are apparently not strongly excited by above-gap light. These results indicate that trap-mediated excitation dominates above-gap pumping of Er3+ emission in GaN:Er, and suggest an explanation for the reduced thermal quenching of Er3+ emission in GaN. © 1997 American Institute of Physics.
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78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
71.55.Eq III-V semiconductors

Thermal limitation of self-pulsation in 650 nm AlGaInP laser diodes with an epitaxially integrated absorber

H. D. Summers and P. Rees

Appl. Phys. Lett. 71, 2665 (1997); http://dx.doi.org/10.1063/1.120172 (3 pages) | Cited 8 times

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Self-pulsation within 650 nm, AlGaInP laser diodes can be achieved via the use of a saturable absorbing, epitaxial layer within the structure. A rate equation model of this type of device is presented, which includes the process of thermally activated charge transfer from the quantum well and gain region to the absorbing layer. The results indicate that this thermal leakage mechanism saturates the absorber and hence destroys the self-pulsation at high temperatures. Comparison of the model with recently published experimental data shows good agreement and provides a consistent explanation for the loss of pulsation at temperatures in excess of 60 °C. © 1997 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
42.50.Md Optical transient phenomena: quantum beats, photon echo, free-induction decay, dephasings and revivals, optical nutation, and self-induced transparency

Observation of boron bound excitons in boron-implanted and annealed natural IIa diamonds

H. Sternschulte, S. Wahl, K. Thonke, R. Sauer, M. Dalmer, C. Ronning, and H. Hofsäss

Appl. Phys. Lett. 71, 2668 (1997); http://dx.doi.org/10.1063/1.120173 (3 pages) | Cited 4 times

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Cathodoluminescence at 77 K was used to study the optical properties of ion-implanted and annealed natural type IIa diamonds. The substrates were implanted at room temperature with 12C+, 11B+, 31P+, and 75As+ -ions with energies of up to 350 keV and doses of up to 3×1013 cm−2. After annealing at 1200 °C, the cathodoluminescence spectra show a number of transitions which are induced by the radiation damage independent of the implanted ion species. Only in the B+implanted samples are there two transitions related to the implanted ion species: the 4.5 eV band and the boron bound exciton. The appearance of the bound exciton spectrum demonstrates the presence of isolated boron on substitutional lattice sites implying electrical acceptor activity. Our annealing studies indicate a minimum annealing temperature of 1000 °C for the activation of the implanted boron atoms onto the acceptor states. © 1997 American Institute of Physics.
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71.35.Cc Intrinsic properties of excitons; optical absorption spectra
78.60.Hk Cathodoluminescence, ionoluminescence
61.72.up Other materials
85.40.Ry Impurity doping, diffusion and ion implantation technology
61.72.Cc Kinetics of defect formation and annealing
71.55.Cn Elemental semiconductors

Infrared photothermal radiometric deep-level transient spectroscopy of shallow B+ dopant states in p-Si

A. Salnick, A. Mandelis, and C. Jean

Appl. Phys. Lett. 71, 2671 (1997); http://dx.doi.org/10.1063/1.120174 (3 pages)

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Infrared photothermal radiometric deep-level transient spectroscopy (PTR-DLTS) has been applied to noncontact diagnostics of a p-Si wafer. Both negative and positive peaks in the PTR-DLTS signal temperature scans have been detected. A behavior consistent with photoinjected carrier lifetime enhancement due to the thermal filling of B+ dopant levels in the band gap has been observed. The activation energies of 43 meV (negative peaks) and 60 meV (positive peaks) have been extracted from the corresponding Arrhenius plots. © 1997 American Institute of Physics.  
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71.55.Cn Elemental semiconductors
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
78.20.N- Thermo-optic effects
78.20.nb Photothermal effects
78.30.Am Elemental semiconductors and insulators
72.80.Cw Elemental semiconductors

Polarization-independent large field-induced refractive index change in a strained five-step GaAs–InAlGaAs asymmetric coupled quantum well

H. Feng, K. Tada, and Y. Nakano

Appl. Phys. Lett. 71, 2674 (1997); http://dx.doi.org/10.1063/1.120175 (3 pages) | Cited 3 times

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A tensile-strained five-step asymmetric coupled quantum well (FACQW) structure is proposed for large field-induced refractive index change without polarization dependence and redshift of the absorption edge. A strong exciton absorption peak is caused by electron-hole transitions between symmetric wave functions and antisymmetric wave functions with a small applied electric field. The field-induced refractive index change of strained the FACQW is larger by one order of magnitude compared to that of a rectangular quantum well and the difference in the refractive index change of TE and TM modes is under 2% when the operation wavelength is not at the absorption edge. © 1997 American Institute of Physics.
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78.66.Fd III-V semiconductors
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
71.35.Cc Intrinsic properties of excitons; optical absorption spectra
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
78.20.Jq Electro-optical effects

Bias effects in high performance GaAs homojunction far-infrared detectors

W. Z. Shen, A. G. U. Perera, H. C. Liu, M. Buchanan, and W. J. Schaff

Appl. Phys. Lett. 71, 2677 (1997); http://dx.doi.org/10.1063/1.120176 (3 pages) | Cited 29 times

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A high performance, bias tunable, p-GaAs homojunction interfacial workfunction internal photoemission far-infrared detector is demonstrated. A responsivity of 3.10±0.05 A/W, a quantum efficiency of 12.5%, and a detectivity D∗ of 5.9×1010 cmmath/W were obtained at 4.2 K for cutoff wavelengths from 80 to 100 μm. The bias dependences of the quantum efficiency, detectivity, and cutoff wavelength were measured and are well explained by the theoretical model. The effect of the layer number on detector performance and the uniformity of the detectors are discussed. A comparison with Ge:Ga photoconductive detectors suggests that similar or even better performance may be obtainable with a far-infrared detector. © 1997 American Institute of Physics.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors

Wavelength shifting in GaAs quantum well lasers by proton irradiation

H. H. Tan and C. Jagadish

Appl. Phys. Lett. 71, 2680 (1997); http://dx.doi.org/10.1063/1.120177 (3 pages) | Cited 26 times

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Proton irradiation followed by rapid thermal annealing was used to selectively induce layer intermixing and thus shift the emission wavelengths of GaAs–AlGaAs graded-index separate-confinement-heterostructure quantum well lasers. Up to 40 nm shifts were observed in 4 μm ridge waveguide devices irradiated to a dose of 1.5×1016 cm−2. Although the wavelength shifts were accompanied by some degradation in the lasing threshold current and differential quantum efficiency, they were still quite acceptable at moderate wavelength shifts. This technique provides a simple and promising postgrowth process of integrating lasers of different wavelengths for wavelength-division-multiplexing applications. © 1997 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
81.05.Ea III-V semiconductors
61.72.Cc Kinetics of defect formation and annealing
66.30.Ny Chemical interdiffusion; diffusion barriers
68.35.Fx Diffusion; interface formation
61.80.Jh Ion radiation effects
42.79.Ry Gradient-index (GRIN) devices
42.82.-m Integrated optics

Critical temperature of 1.3 μm InP-based strained-layer multiple-quantum-well lasers

Shunji Seki and Kiyoyuki Yokoyama

Appl. Phys. Lett. 71, 2683 (1997); http://dx.doi.org/10.1063/1.120178 (3 pages) | Cited 1 time

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We study the critical behavior of 1.3 μm InP-based strained-layer (SL) multiple-quantum-well (MQW) lasers at elevated temperatures. We show that, under the critical injection condition where the carrier density in the quantum wells reaches the maximum possible without causing any extra pile-up of carriers in the separate heterostructure confinement regions, an InP-based SL-MQW system exhibits an absorption-to-gain phase transition at some critical temperature (Tc). The characteristic feature of this phase transition shows excellent agreement with Landau theory of second-order phase transitions. It is demonstrated that Tc is a significant and meaningful quantity not only for laser design but also for characterizing the nature of an InP-based SL-MQW system in terms of condensed matter physics. © 1997 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

Charge carrier mobility in poly(p-phenylenevinylene) studied by the time-of-flight technique

E. Lebedev, Th. Dittrich, V. Petrova-Koch, S. Karg, and W. Brütting

Appl. Phys. Lett. 71, 2686 (1997); http://dx.doi.org/10.1063/1.120179 (3 pages) | Cited 82 times

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The charge carrier transport in poly(p-phenylenevinylene) (PPV) is investigated by the time-of-flight technique. Mobilities of positive carriers in PPV are determined and the dispersive character of transport is established. The dispersion parameters are analyzed in the frame of a multiple trapping model. The drift mobility of the positive carriers is in the range of 10−5 cm2/V s at room temperature for an electric field of 105 V/cm and increases with increasing field and temperature. The mobility shows thermally activated behavior with an activation energy of about 0.75 eV at zero field. It is shown that the experimental results can be interpreted by polaron transport. © 1997 American Institute of Physics.
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72.15.Nj Collective modes (e.g., in one-dimensional conductors)
71.38.-k Polarons and electron-phonon interactions

Semiconductor quantum point contact fabricated by lithography with an atomic force microscope

R. Held, T. Heinzel, P. Studerus, K. Ensslin, and M. Holland

Appl. Phys. Lett. 71, 2689 (1997); http://dx.doi.org/10.1063/1.120137 (3 pages) | Cited 44 times

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We report on the experimental realization of a quantum point contact in a semiconductor heterostructure by lithography with an atomic force microscope (AFM). A thin, homogeneous titanium film on top of the chip surface was patterned by local anodic oxidation, induced by a current applied to an n-doped AFM tip. We demonstrate that self-aligned gate structures in the sub-micron regime can be fabricated with this technique. © 1997 American Institute of Physics.
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85.40.Hp Lithography, masks and pattern transfer
73.23.-b Electronic transport in mesoscopic systems
42.82.Cr Fabrication techniques; lithography, pattern transfer
81.65.Mq Oxidation

Infrared absorption in amorphous silicon from ab initio molecular dynamics

Alberto Debernardi, Marco Bernasconi, Manuel Cardona, and Michele Parrinello

Appl. Phys. Lett. 71, 2692 (1997); http://dx.doi.org/10.1063/1.120188 (3 pages) | Cited 20 times

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We present an ab initio calculation of the infrared vibrational spectrum of amorphous silicon. The electron polarization, which is the main ingredient to obtain the infrared spectra, is evaluated using the recent formulation in terms of Berry’s phase, while the time evolution of the system is studied using Car–Parrinello molecular dynamics. Our results are in quantitative agreement with experimental data and also with the results of empirical calculations based on a bond-dipole model. © 1997 American Institute of Physics.
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78.30.Am Elemental semiconductors and insulators
78.35.+c Brillouin and Rayleigh scattering; other light scattering
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
63.50.-x Vibrational states in disordered systems

Self-field ac losses in biaxially aligned Y–Ba–Cu–O tape conductors

Y. Iijima, M. Hosaka, N. Sadakata, T. Saitoh, O. Kohno, and K. Takeda

Appl. Phys. Lett. 71, 2695 (1997); http://dx.doi.org/10.1063/1.120180 (3 pages) | Cited 16 times

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Self-field ac losses were measured by the conventional ac four-probe method in biaxially aligned Y–Ba–Cu–O tapes using polycrystalline Hastelloy tapes with textured yttria-stabilized-zirconia buffer layers. The ac losses increased in proportion to the fourth power of transport current in the high Jc sample, and agreed well with Norris’ equation for thin strip conductors. However, the low Jc sample had rather higher losses than Norris’ prediction, suggesting excessive magnetic flux penetration caused by percolated current paths. The results confirmed Norris’ prediction of the low ac losses for thin strip conductors, and indicated the importance of removing percolated structures of current paths to avoid higher ac losses than the theoretical predictions based on uniform conductors. © 1997 American Institute of Physics.
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74.72.-h Cuprate superconductors
84.71.Mn Superconducting wires, fibers, and tapes
74.25.Sv Critical currents
74.25.Ha Magnetic properties including vortex structures and related phenomena

Faraday rotation in magnetic γ-Fe2O3/SiO2 nanocomposites

H. Guerrero, G. Rosa, M. P. Morales, F. del Monte, E. M. Moreno, D. Levy, R. Pérez del Real, T. Belenguer, and C. J. Serna

Appl. Phys. Lett. 71, 2698 (1997); http://dx.doi.org/10.1063/1.120181 (3 pages) | Cited 21 times

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Faraday rotation spectrum has been measured at room temperature in a magnetic nanocomposite of γ-Fe2O3/SiO2. The material consists of isolated γ-Fe2O3 nanoparticles dispersed in a silica matrix, and it was prepared through a sol-gel method. The composite contains 18% of γ-Fe2O3 in weight with an average particle size of 20 nm. It has a coercitivity of 30 Oe and an MS of 6 emu/g. The specific Faraday rotation spectrum exhibits a narrow peak centered around 765 nm, reaching a value of 110°/cm and an absorption coefficient of 64 cm−1. Faraday rotation versus applied field has also been measured, and a cycle similar to the one described by the magnetization has been found. © 1997 American Institute of Physics.
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78.20.Ls Magneto-optical effects
75.50.Tt Fine-particle systems; nanocrystalline materials
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Transport properties and colossal magnetoresistance in epitaxial La0.67Cd0.33MnO3 thin film

M. Sahana, M. S. Hegde, N. Y. Vasanthacharya, V. Prasad, and S. V. Subramanyam

Appl. Phys. Lett. 71, 2701 (1997); http://dx.doi.org/10.1063/1.120182 (3 pages) | Cited 10 times

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An optimal composition of La0.67Cd0.33MnO3 was synthesized by ceramic route. The compound crystallized in a rhombohedral structure with lattice parameters a = 5.473(4) Å and α = 60°37′. Resistivity measurement showed an insulator-to-metal transition coupled with a ferromagnetic transition of around 255 K. Epitaxial thin films were fabricated on the LaAlO3 (100) substrate by a pulsed laser deposition technique. The psuedocubic lattice parameter a of the film is 3.873(4) Å. The insulator-to-metal transition of the film was observed at 250 K which is comparable with the bulk value. The film was ferromagnetic below this temperature. Magnetoresistance defined as ΔR/R0 = (RH−R0)/R0 was over −86% near the insulator-to-metal transition temperature of 240 K at 6 T magnetic field and over-30% at relatively low fields of 1 T. No magnetoresistance was observed at low temperatures in the film unlike in the polycrystalline sample, where about a 40% decrease in resistance was observed on applying 6 T magnetic field due to the spin dependent scattering at the grain boundaries. © 1997 American Institute of Physics.
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75.47.De Giant magnetoresistance
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
73.61.Ng Insulators
71.30.+h Metal-insulator transitions and other electronic transitions
72.60.+g Mixed conductivity and conductivity transitions
75.50.Dd Nonmetallic ferromagnetic materials
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
61.72.Mm Grain and twin boundaries

Electron emission from boron nitride coated Si field emitters

Takashi Sugino, Seiji Kawasaki, Kazuhiko Tanioka, and Junji Shirafuji

Appl. Phys. Lett. 71, 2704 (1997); http://dx.doi.org/10.1063/1.120183 (3 pages) | Cited 59 times

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Electron emission characteristics of sulfur (S)-doped boron nitride (BN) films synthesized by plasma-assisted chemical vapor deposition (PACVD) are investigated. The BN film consists of hexagonal grains of 3 nm in size. The energy gap is estimated to be as wide as 6.0 eV from ultraviolet-visible optical transmission measurement. The electrical resistivity is reduced to 4.9×102 Ω cm. Si tip field emitters coated with the BN film are fabricated. The electron emission occurs at an electric field as low as 6 V/μm, while a high electric field of 20 V/μm is needed to emit electrons from the Si tip array without BN coating. It is deduced that the tunneling barrier height of 0.1 eV exists at the surface of the BN film. © 1997 American Institute of Physics.
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79.70.+q Field emission, ionization, evaporation, and desorption
78.66.Fd III-V semiconductors
78.40.Fy Semiconductors
73.61.Ey III-V semiconductors
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