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7 Dec 1998

Volume 73, Issue 23, pp. 3321-3467

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Dependence of the silicon nanowire diameter on ambient pressure

H. Z. Zhang, D. P. Yu, Y. Ding, Z. G. Bai, Q. L. Hang, and S. Q. Feng

Appl. Phys. Lett. 73, 3396 (1998); http://dx.doi.org/10.1063/1.122778 (3 pages) | Cited 39 times

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Our present work provides a method to control the diameters of the silicon nanowires. As a dominant experimental parameter, the ambient pressure was controlled between 150 and 600 Torr. It is found that the average size of the silicon nanowires increases with increasing ambient pressure. The mean diameter of the silicon nanowires in our study is proportional to the 0.4 power of ambient pressure. Catalytic nanoparticles and the periodic instability of the nanowires suggest a vapor-liquid-solid growth mechanism. For the growth of nanowires, an explanation of the relationship between the mean diameter of the silicon nanowires and the ambient pressure has been proposed. © 1998 American Institute of Physics.
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81.07.-b Nanoscale materials and structures: fabrication and characterization
61.46.-w Structure of nanoscale materials
64.70.F- Liquid-vapor transitions
64.70.D- Solid-liquid transitions

Spectroscopic characterization of the evolution of self-assembled CdSe quantum dots

J. C. Kim, H. Rho, L. M. Smith, Howard E. Jackson, S. Lee, M. Dobrowolska, J. L. Merz, and J. K. Furdyna

Appl. Phys. Lett. 73, 3399 (1998); http://dx.doi.org/10.1063/1.122779 (3 pages) | Cited 22 times

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We have investigated the evolution of molecular beam epitaxy (MBE)-grown, CdSe self-assembled quantum dots on ZnSe surfaces using microphotoluminescence techniques. Bare CdSe dots at room temperature undergo Ostwald ripening over a time scale measured in days. At the elevated temperatures maintained for MBE growth and dot formation, ripening is expected to progress much faster. Capping the dots with a thin ZnSe layer “freezes” the ripening, allowing one to sample different stages of the dot evolution and subsequent characterization. We have grown eleven samples, each with a different time interval, or growth interruption, between dot formation and capping; the growth interruption times ranging from 0 to 300 s, during which the samples were kept at 300 °C. Using microphotoluminescence spectroscopy, we have resolved the sharp emission peaks due to individual dots in each sample and, by analyzing the ensemble characteristics, have identified a new regime in the evolution of CdSe dots. © 1998 American Institute of Physics.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
81.05.Dz II-VI semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
78.55.Et II-VI semiconductors
78.66.Hf II-VI semiconductors

Ohmic contacts formed by electrodeposition and physical vapor deposition on p-GaN

J. M. DeLucca, H. S. Venugopalan, S. E. Mohney, and R. F. Karlicek

Appl. Phys. Lett. 73, 3402 (1998); http://dx.doi.org/10.1063/1.122756 (3 pages) | Cited 9 times

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Electrodeposited Pt and sputtered Ni/Pt contacts to p-GaN (p = 4.6×1017 cm−3) are reported and compared to sputtered Ni, Pt, and Ni/Au contacts and electron beam and thermally evaporated Ni contacts. Sequential rapid thermal annealing was employed with samples receiving an initial five minute heat treatment of 400 °C followed by 1 min anneals at 500, 600, and 700 °C, all under flowing N2. Plots of current versus voltage for all contacts showed nonlinearity through the origin as deposited and for all annealing conditions. Extracted values of specific contact resistance are thus determined using the measured resistance for a given value of applied current. The lowest contact resistivity was reproducibly provided by the electrodeposited Pt contacts. After a 1 min anneal at 600 °C, a contact resistivity of 1.50×10−2 Ω cm 2 was obtained using the circular transmission line method at a measurement current of 10 mA. Sputtered Ni/Pt contacts provided a contact resistivity of 1.81×10−2 Ω cm2 at 10 mA after a 1 min anneal at 600 °C, while all other metallizations yielded contact resistivities from 3–4×10−2 Ω cm 2. Possible reasons for the lower contact resistivity of the electrodeposited contacts are discussed. © 1998 American Institute of Physics.
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73.40.Ns Metal-nonmetal contacts
81.15.Pq Electrodeposition, electroplating
81.15.Cd Deposition by sputtering
81.05.Bx Metals, semimetals, and alloys
61.72.Cc Kinetics of defect formation and annealing
73.40.Cg Contact resistance, contact potential

Improved optical response of superlattice graded InAlAs/InGaAs p-i-n photodetectors

C. Lenox, H. Nie, G. Kinsey, P. Yuan, A. L. Holmes, B. G. Streetman, and J. C. Campbell

Appl. Phys. Lett. 73, 3405 (1998); http://dx.doi.org/10.1063/1.122757 (3 pages) | Cited 3 times

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A number of important optoelectronic device utilize the InAlGaAs/InP material system. The reduction of carrier trapping at the In0.53Ga0.47As/In0.52Al0.48As heterointerface is advantageous towards improving both the quantum efficiency and frequency response of devices utilizing InGaAs active regions. Direct current and transient optical response characteristics were measured for p-i-n double-heterojunction photodiodes utilizing either abrupt or superlattice (SL) graded heterointerfaces. SL graded devices showed improved collection efficiency at electric fields <3 kV/cm and faster temporal response at electric field <70 kV/cm as compared to identical devices having abrupt interfaces. © 1998 American Institute of Physics.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
85.60.Dw Photodiodes; phototransistors; photoresistors
73.61.Ey III-V semiconductors
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors

Improved carrier collection in intermixed InGaAs/GaAs quantum wells

L. V. Dao, M. B. Johnston, M. Gal, L. Fu, H. H. Tan, and C. Jagadish

Appl. Phys. Lett. 73, 3408 (1998); http://dx.doi.org/10.1063/1.122780 (3 pages) | Cited 16 times

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We have used photoluminescence up conversion to study the carrier capture times into intermixed InGaAs/GaAs quantum wells. We have found that the capture into the intermixed wells is markedly faster than capture into the reference (unintermixed) quantum wells. The reasons for the significant reduction in the capture time is related to the shape of the intermixed quantum well. Such a reduction in the capture time is beneficial both in terms of the quantum efficiency and the frequency response of intermixed optoelectronic devices. © 1998 American Institute of Physics.
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73.61.Ey III-V semiconductors
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
66.30.Ny Chemical interdiffusion; diffusion barriers
68.35.Fx Diffusion; interface formation
78.47.-p Spectroscopy of solid state dynamics

Highly packed InGaAs quantum dots on GaAs(311)B

Kouichi Akahane, Takahiro Kawamura, Kenji Okino, Hiromichi Koyama, Shen Lan, Yoshitaka Okada, Mitsuo Kawabe, and Masahiro Tosa

Appl. Phys. Lett. 73, 3411 (1998); http://dx.doi.org/10.1063/1.122781 (3 pages) | Cited 31 times

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We have fabricated highly packed and ordered In0.4Ga0.6As quantum dots (QDs) array on GaAs(311)B substrate without coalescence of QDs. Reflection high-energy electron diffraction and Auger spectra suggest the inhomogeneous distribution of In and Ga in QD. In concentration near the surface of QD is larger than that of the inside, and the inhomogeneous distribution of In and Ga in QDs prevents QDs from merging. © 1998 American Institute of Physics.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
81.05.Ea III-V semiconductors
79.20.Fv Electron impact: Auger emission

Investigation of broadband p-type quantum-well infrared photodetectors

J. Chu, Sheng S. Li, and A. Singh

Appl. Phys. Lett. 73, 3414 (1998); http://dx.doi.org/10.1063/1.122782 (3 pages) | Cited 2 times

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Typical quantum-well infrared photodetectors (QWIPs) exhibit rather narrow spectral bandwidths of 1–2 μm. For certain applications, such as spectroscopy, sensing of a broad range of infrared photons is necessary. In this letter, we report on the design of two p-type broadband (BB) QWIPs for detection in the 7–14 μm long-wavelength infrared band. Two different QWIP structures were designed: QWIP-A with three wells of different InxGa1−xAs(x = 0.2,0.25,0.3) compositions and QWIP-B with three wells of In0.25Ga0.75As of different thicknesses (4.5, 5.5, and 6.2 nm) and an undoped GaAs barrier (40 nm thick) to form a unit cell, which are then repeated 20 times to create the BB-QWIPs. The spectral response for QWIP-A covers the wavelengths from the 7 to 11 μm range, while QWIP-B has a broader spectral response bandwidth from 7 to 14 μm. A maximum responsivity of 25 mA/W was obtained for QWIP-B at Vb = 1.1 V, λp = 10.2 μm, and T = 40 K with a spectral bandwidth of Δλ/λ = 63%, a cut-on wavelength at 6.2 μm, and a cut-off wavelength around 14 μm. © 1998 American Institute of Physics.
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07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
85.60.Gz Photodetectors (including infrared and CCD detectors)
78.66.Fd III-V semiconductors
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

Direct detection and imaging of low-energy electrons with delta-doped charge-coupled devices

Shouleh Nikzad, Qiuming Yu, Aimée L. Smith, Todd J. Jones, T. A. Tombrello, and S. Tom Elliott

Appl. Phys. Lett. 73, 3417 (1998); http://dx.doi.org/10.1063/1.122783 (3 pages) | Cited 10 times

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We report the use of delta-doped charge-coupled devices (CCDs) for direct detection of electrons in the 50–1500 eV energy range. We show that modification of the CCD back surface by molecular beam epitaxy can greatly improve sensitivity to low-energy electrons by introducing an atomically abrupt dopant profile to eliminate the dead layer. Using delta-doped CCDs, we have extended the energy threshold for detection of electrons by over an order of magnitude. We have also measured high gain in response to low-energy electrons using delta-doped CCDs. The effect of multiple electron hole pair production on the observed signals is discussed. Electrons have been directly imaged with a delta-doped CCD in the 250–750 eV range. © 1998 American Institute of Physics.
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29.40.Wk Solid-state detectors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Observation of wire width fluctuations in the optical spectra of GaAs–AlGaAs V-groove quantum wires

W. R. Tribe, M. J. Steer, A. N. Forshaw, K. L. Schumacher, D. J. Mowbray, D. M. Whittaker, M. S. Skolnick, J. S. Roberts, and G. Hill

Appl. Phys. Lett. 73, 3420 (1998); http://dx.doi.org/10.1063/1.122784 (3 pages) | Cited 10 times

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Optical spectroscopy of a single GaAs–AlGaAs V-groove quantum wire is reported. Photoluminescence spectra are recorded over a five order-of-magnitude variation of incident laser power. With decreasing laser power, a continuous transition is observed from multiple wire subband occupancy to single subband occupancy through to the observation of the recombination of excitons localized by discrete potential fluctuations. The effect of single monolayer wire thickness fluctuations on the subband transitions is calculated using a finite difference technique which includes the Luttinger Hamiltonian description of the valence band states. These calculations indicate that the main contribution to the exciton localization potential is probably monolayer fluctuations of the wire thickness. © 1998 American Institute of Physics.
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78.66.Fd III-V semiconductors
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
78.55.Cr III-V semiconductors
71.35.Cc Intrinsic properties of excitons; optical absorption spectra

Current-induced persistent capacitance in Au/n-In0.08Ga0.92As0.51P0.49 Schottky contacts

Ho Ki Kwon, Y. Kim, and H. Lim

Appl. Phys. Lett. 73, 3423 (1998); http://dx.doi.org/10.1063/1.122785 (3 pages)

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The zero-bias capacitance of a Schottky diode formed on a nominally undoped In0.08Ga0.92As0.51P0.49 is found to be persistently increased after a high current injection at low temperatures. The increment of capacitance grows as the amplitude or duration of the current pulse is increased. When a high current is injected at low temperatures before the deep level transient spectroscopy measurements, the concentration of the so-called ET1 defects is decreased. It is discussed that all these results are related to the hole injection from the Schottky contact and the charge-state controlled stability of the ET1 defects. © 1998 American Institute of Physics.
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73.30.+y Surface double layers, Schottky barriers, and work functions
73.40.Ns Metal-nonmetal contacts
73.20.Hb Impurity and defect levels; energy states of adsorbed species
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
71.55.Eq III-V semiconductors

Piezoelectric effects on the optical properties of GaN/AlxGa1−xN multiple quantum wells

H. S. Kim, J. Y. Lin, H. X. Jiang, W. W. Chow, A. Botchkarev, and H. Morkoç

Appl. Phys. Lett. 73, 3426 (1998); http://dx.doi.org/10.1063/1.122786 (3 pages) | Cited 66 times

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Piezoelectric effects on the optical properties of GaN/AlGaN multiple quantum wells (MQWs) have been investigated by picosecond time-resolved photoluminescence (PL) measurements. For MQWs with well thicknesses 30 and 40 Å, the excitonic transition peak positions at 10 K in continuous wave (cw) spectra are redshifted with respect to the GaN epilayer by 13 and 45 meV, respectively. The time-resolved PL spectra of the 30 and 40 Å well MQWs reveal that the excitonic transition is in fact blueshifted at early delay times due to quantum confinement of carriers. The spectral peak position shifts toward lower energies as the delay time increases and becomes redshifted at longer delay times. We have demonstrated that the results described above are due to the presence of the piezoelectric field in the GaN wells of GaN/AlGaN MQWs subject to elastic strain together with screening of the photoexcited carriers. By comparing experimental and calculation results, we conclude that the piezoelectric field strength in GaN/Al0.15Ga0.85N MQWs has a lower limit value of about 560 kV/cm. The electron and hole wave function distributions have also been obtained. The implication of our findings on the practical applications of GaN based optoelectronic devices is also discussed. © 1998 American Institute of Physics.
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78.66.Fd III-V semiconductors
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
78.47.-p Spectroscopy of solid state dynamics
77.65.-j Piezoelectricity and electromechanical effects
73.61.Ey III-V semiconductors
78.55.Cr III-V semiconductors
71.35.Cc Intrinsic properties of excitons; optical absorption spectra

Charge-ring model for the charge-induced confinement enhancement in stacked quantum-dot transistors

A. M. Rudin, L. J. Guo, L. I. Glazman, and S. Y. Chou

Appl. Phys. Lett. 73, 3429 (1998); http://dx.doi.org/10.1063/1.122787 (3 pages) | Cited 6 times

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A model is proposed to explain the charge-induced confinement enhancement observed in a stacked quantum-dot transistor that has a floating dot on top of a channel quantum dot. The model assumes that the charge on the floating dot distributes on its rim, forming a ring and creating a confinement potential that squeezes the electrons in the channel dot toward its center. The charge on the floating dot can be calculated from the device geometry and from the measured threshold voltage difference before and after the charging. Given the charge on the floating dot, the spatial confinement and the energy level spacing increase induced by the charging can be obtained. The calculation based on the model agrees with the observed increase of the energy level spacing.© 1998 American Institute of Physics.
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85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
85.30.Tv Field effect devices
85.35.Gv Single electron devices
85.30.De Semiconductor-device characterization, design, and modeling
73.61.Cw Elemental semiconductors

Photoconductivity mechanism of quantum well infrared photodetectors under localized photoexcitation

M. Ershov

Appl. Phys. Lett. 73, 3432 (1998); http://dx.doi.org/10.1063/1.122788 (3 pages) | Cited 4 times

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The physics of photoconductivity of quantum well infrared photodetectors (QWIPs) under nonuniform illumination across QWIP structure (in the direction normal to QWs plane) is studied theoretically with the use of numerical simulation. Local responsivity is a strong function of a coordinate across QWIP; it decreases from emitter to collector, having a constant value in the bulk of QWIP. The mechanism of photoconductivity under localized photoexcitation is related to the formation of the dipole layer (DL), with positive charge located in the photoexcited QW, and negative charge located in a few next QWs towards collector. As a result, electric field outside the DL is increased to cause photocurrent. Parameters of the DL and local responsivity for QWIPs with multiple QWs is calculated using an analytical model. © 1998 American Institute of Physics.
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85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
73.50.Pz Photoconduction and photovoltaic effects
85.60.Gz Photodetectors (including infrared and CCD detectors)
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems

Free-carrier generation in amorphous semiconductors by intense subgap excitation

Keiji Tanaka

Appl. Phys. Lett. 73, 3435 (1998); http://dx.doi.org/10.1063/1.122789 (3 pages) | Cited 5 times

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Photoconduction spectra in three amorphous semiconductors have been measured as a function of light intensity. In As2S3, shrinkage of photoconductive response peak from 2.7 to 2.0 eV occurs with an increase in the light intensity from 10−3 to 108 W/cm2. In a-Si:H, intense illumination just enhances photocurrents, and intermediate features appear in As2Se3. The anomalous red shift of the photoconduction spectrum discovered in As2S3 can be accounted for as arising from a wide valence-band tail and slow hole transport. © 1998 American Institute of Physics.
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72.40.+w Photoconduction and photovoltaic effects
72.80.Ng Disordered solids
72.80.Cw Elemental semiconductors

Correlation between the surface defect distribution and minority carrier transport properties in GaN

P. M. Bridger, Z. Z. Bandić, E. C. Piquette, and T. C. McGill

Appl. Phys. Lett. 73, 3438 (1998); http://dx.doi.org/10.1063/1.122790 (3 pages) | Cited 15 times

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We have studied linear dislocations and surface defects in p- and n-type metalorganic chemical vapor deposition, hydride vapor phase epitaxy, and molecular beam epitaxy grown GaN films on sapphire with atomic force microscopy. The surface pits due to threading dislocations were found not to be distributed randomly but on the boundaries of growth columns. The dislocations are thought to be electrically active since the average distance between them (average column size) is comparable to minority carrier diffusion lengths as measured by electron beam induced current experiments on Schottky diodes fabricated with the same material. Diffusion lengths found for holes and electrons are on the order of Lp = 0.28 μm and Le = 0.16 μm which corresponded to the sizes of regions free from surface dislocations in both cases and can be described by a simple model of recombination on grain boundaries. © 1998 American Institute of Physics.
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72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
68.35.B- Structure of clean surfaces (and surface reconstruction)
73.61.Ey III-V semiconductors
72.80.Ey III-V and II-VI semiconductors
61.72.Lk Linear defects: dislocations, disclinations
73.25.+i Surface conductivity and carrier phenomena

Examination of deuterium transport through device structures

P. J. Chen and R. M. Wallace

Appl. Phys. Lett. 73, 3441 (1998); http://dx.doi.org/10.1063/1.122791 (3 pages) | Cited 18 times

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We use secondary ion mass spectrometry to characterize the hydrogen/deuterium distribution and concentration on 0.18 μm “metal” oxide silicon test structures subjected to deuterium anneals. We examine the temperature dependence and the influence of doping on the transport of deuterium to the gate oxide interfaces resulting in interface passivation. We find that undoped polycrystalline silicon appears to be an efficient barrier for deuterium transport at typical postmetallization sintering temperatures. © 1998 American Institute of Physics.
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68.35.Fx Diffusion; interface formation
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
81.65.Rv Passivation

Mechanism of generation of f–f radiation in semiconductor heterostructures

G. G. Zegrya and V. F. Masterov

Appl. Phys. Lett. 73, 3444 (1998); http://dx.doi.org/10.1063/1.122758 (3 pages) | Cited 5 times

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A mechanism is proposed by which inverse distribution of Er3+ f electrons can be created in semiconductors with quantum wells. It is shown that, if the electrons are localized in quantum wells, the Coulomb excitation of Er3+ f electrons by electrons of the semiconductor has resonant nature. The resonant Coulomb excitation of f electrons I15/2→I11/2 produces electron population inversion for the I13/2 level. A possibility is demonstrated of developing a laser with wavelength λ=1.54 μm based on I13/2→I15/2 transitions.© 1998 American Institute of Physics.
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78.45.+h Stimulated emission
78.66.-w Optical properties of specific thin films
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
42.55.Px Semiconductor lasers; laser diodes
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Spatially resolved microwave field distribution in YBaCuO disk resonators visualized by laser scanning

T. Kaiser, M. A. Hein, G. Müller, and M. Perpeet

Appl. Phys. Lett. 73, 3447 (1998); http://dx.doi.org/10.1063/1.122792 (3 pages) | Cited 12 times

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The applicability of superconducting films in high-performance microwave devices suffers from inhomogeneous growth and local defects. Therefore we have installed a laser scanning system to visualize with spatial resolution the distribution of the microwave fields in 2-in.-diam YBaCuO disk resonators. The TM310 mode was imaged at a loaded quality factor of 8.3×104 via changes of the resonant frequency at 2.21 GHz and 40 K. The field distribution agreed with a magnetic-wall model, indicating at the contour of the disk fringe fields, but without strong edge enhancement. The data also indicated an inhomogeneous effective microwave penetration depth. The spatial resolution is presently limited to about 2 mm by heat diffusion. © 1998 American Institute of Physics.
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74.72.-h Cuprate superconductors
74.78.-w Superconducting films and low-dimensional structures
74.25.Ha Magnetic properties including vortex structures and related phenomena
85.25.Hv Superconducting logic elements and memory devices; microelectronic circuits
84.40.-x Radiowave and microwave (including millimeter wave) technology

Dependence on the microwave field of the surface resistance for YBa2Cu3O7−δ films fabricated on copper substrates

Jian-Fei Liu, Kiyomitsu Asano, Eizi Ezura, Shigemi Inagaki, Shigeru Isagawa, Hiroshi Nakanishi, Masao Fukutomi, Kazunori Komori, and Masakazu Saito

Appl. Phys. Lett. 73, 3450 (1998); http://dx.doi.org/10.1063/1.122793 (3 pages) | Cited 2 times

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The microwave field dependence of the surface resistance for YBa2Cu3O7−δ films was studied at field levels up to 400 A/m. The c-axis normal YBa2Cu3O7−δ films were deposited onto copper disks 36 mm in diameter by a laser ablation method. The surface resistance increased linearly below 50 K as the microwave magnetic field increased, which is explained better by the critical-state model than by the coupled-grain model. The critical current density decreased almost linearly with increasing temperature from 2.8×105 A/cm2 at 20 K to 4×104 A/cm2 at 77 K. © 1998 American Institute of Physics.
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74.72.-h Cuprate superconductors
74.78.-w Superconducting films and low-dimensional structures
74.25.Sv Critical currents
81.15.Fg Pulsed laser ablation deposition
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CoPt/Ag nanocomposites for high density recording media

S. Stavroyiannis, I. Panagiotopoulos, D. Niarchos, J. A. Christodoulides, Y. Zhang, and G. C. Hadjipanayis

Appl. Phys. Lett. 73, 3453 (1998); http://dx.doi.org/10.1063/1.122794 (3 pages) | Cited 65 times

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Nanocomposite CoPt/Ag films have been successfully fabricated and their microstructural and magnetic properties have been investigated for potential applications in magnetic recording media. This was done by first making sputtered CoPt/Ag multilayers with the face-centered cubic (fcc) structure which is magnetically soft and then annealing the multilayers to transform the fcc phase to the highly anisotropic face-centered tetragonal phase (fct) which is magnetically hard. The final nanocomposite structure consists of CoPt nanoparticles with the hard fct phase embedded in a fcc Ag matrix. Large values of coercivity in the range of 1–17 kOe were achieved with grain sizes in the range of 7–100 nm, respectively. © 1998 American Institute of Physics.
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75.50.Kj Amorphous and quasicrystalline magnetic materials
81.07.-b Nanoscale materials and structures: fabrication and characterization
75.50.Ss Magnetic recording materials
75.50.Cc Other ferromagnetic metals and alloys
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
85.70.Li Other magnetic recording and storage devices (including tapes, disks, and drums)
75.50.Vv High coercivity materials
61.46.-w Structure of nanoscale materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.60.Nt Magnetic annealing and temperature-hysteresis effects
81.40.Rs Electrical and magnetic properties related to treatment conditions

Magnetic homogeneity of colossal-magnetoresistance thin films determined by alternating current magnetic susceptibility

F. M. Araujo-Moreira, M. Rajeswari, A. Goyal, K. Ghosh, V. Smolyaninova, T. Venkatesan, C. J. Lobb, and R. L. Greene

Appl. Phys. Lett. 73, 3456 (1998); http://dx.doi.org/10.1063/1.122795 (3 pages) | Cited 13 times

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We report measurements of the alternating current (ac) magnetic susceptibility, χac = χ′+iχ″, performed on colossal-magnetoresistance (CMR) materials. We have studied thin film samples of La0.67Ca0.33MnO3 and Nd0.7Sr0.3MnO3. For homogeneous samples, the temperature of the peak observed in χ″(T) is in agreement with the temperature of peak resistivity (TP) obtained from transport measurements. This agreement is not found for inhomogeneous samples, where χ″(T) shows multiple peaks. The analysis of χ″(T) enables one to determine the quality of the CMR materials. The results obtained in thin films of La0.67Ca0.33MnO3 and Nd0.7Sr0.3MnO3, are consistent with those obtained from an homogeneous single crystal of La0.80Sr0.20MnO3. We show that the contactless ac magnetic susceptibility technique is a quick method to reveal inhomogeneities which are not directly evident in direct current transport measurements. © 1998 American Institute of Physics.
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75.47.De Giant magnetoresistance
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
75.50.Dd Nonmetallic ferromagnetic materials

Spin-dependent band structure, Fermi surface, and carrier lifetime of permalloy

D. Y. Petrovykh, K. N. Altmann, H. Höchst, M. Laubscher, S. Maat, G. J. Mankey, and F. J. Himpsel

Appl. Phys. Lett. 73, 3459 (1998); http://dx.doi.org/10.1063/1.122796 (3 pages) | Cited 41 times

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Angle-resolved photoemission is used to determine the energy bands of permalloy (Ni0.8Fe0.2) and compare them to Ni, Co, and Cu. The energy and momentum resolution (≈0.01 eV and ≈0.01 Å−1) is high enough to resolve the magnetically split bands at the Fermi level that are responsible for spin-dependent conductivity and tunneling. For the Σ1 band we find the magnetic exchange splittings δEex = 0.27 eV (0.23 eV for Ni), δkex = 0.16±0.02 Å−1 (0.12±0.01 Å−1 for Ni), the Fermi velocity vF↑ = (0.22±0.02)106 m/s (0.28×106 m/s for Ni, 0.33×106 m/s for fcc Co), and the widths δk↑ ⩽ 0.11 Å−1 and δk↓ = 0.24 Å−1. Compared to Ni, permalloy features a 27% larger magnetic splitting of the Fermi surface and an extremely short mean free path of 4–8 Å for minority spins. © 1998 American Institute of Physics.
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71.18.+y Fermi surface: calculations and measurements; effective mass, g factor
71.20.Be Transition metals and alloys
71.70.Gm Exchange interactions
75.30.Et Exchange and superexchange interactions
75.50.Bb Fe and its alloys
79.60.Bm Clean metal, semiconductor, and insulator surfaces
75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)
75.70.Ak Magnetic properties of monolayers and thin films
73.61.At Metal and metallic alloys

Giant magnetoresistance near the magnetostructural transition in Gd5(Si1.8Ge2.2)

L. Morellon, J. Stankiewicz, B. García-Landa, P. A. Algarabel, and M. R. Ibarra

Appl. Phys. Lett. 73, 3462 (1998); http://dx.doi.org/10.1063/1.122797 (3 pages) | Cited 100 times

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Zero-field electrical resistivity over the temperature range of 4–300 K and magnetoresistance in magnetic fields of up to 12 T have been measured in Gd5(Si1.8Ge2.2). This system undergoes a first-order magnetostructural transition at TC ≅ 240 K, from a high-temperature paramagnetic to a low-temperature ferromagnetic phase, accompanied by a large drop in the resistivity. The application of an external magnetic field above TC can induce this transition, and a giant negative magnetoresistance effect (Δρ/ρ ≅ −20%) is observed associated with this first-order field-induced transition. © 1998 American Institute of Physics.
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75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
72.15.Gd Galvanomagnetic and other magnetotransport effects
64.70.K- Solid-solid transitions
75.50.Cc Other ferromagnetic metals and alloys
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Single-walled carbon nanotube probes for high-resolution nanostructure imaging

Stanislaus S. Wong, Adam T. Woolley, Teri Wang Odom, Jin-Lin Huang, Philip Kim, Dimitri V. Vezenov, and Charles M. Lieber

Appl. Phys. Lett. 73, 3465 (1998); http://dx.doi.org/10.1063/1.122798 (3 pages) | Cited 67 times

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Single-walled carbon nanotube (SWNT) tips have been used to image nanostructures with high resolution. Studies of gold nanocrystal standards showed that SWNT tips provide a significant improvement in lateral resolution with respect to multi-walled nanotube tips and microfabricated Si tips. The nanotube tips were also used to resolve substructure within SWNTs deposited on surfaces. These results suggest that observed 1.5 nm high structures can correspond to several SWNTs aligned in parallel. In addition, SWNT tips exhibited superior resolution compared to conventional tips when imaging biological nanostructures, such as double-stranded DNA. The potential and future challenges of SWNT tips are discussed. © 1998 American Institute of Physics.
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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
61.46.-w Structure of nanoscale materials
87.64.Dz Scanning tunneling and atomic force microscopy
87.80.-y Biophysical techniques (research methods)
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