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24 May 2004

Volume 84, Issue 21, pp. 4141-4340

Issue Cover Spotlight Figure

Appl. Phys. Lett. 84, 4316 (2004); http://dx.doi.org/10.1063/1.1756684 (3 pages)

Seok Pil Jang and Stephen U. S. Choi
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Visible quantum cutting through downconversion in Eu3+-doped KGd3F10 and KGd2F7 crystals

Nobuhiro Kodama and Yamato Watanabe

Appl. Phys. Lett. 84, 4141 (2004); http://dx.doi.org/10.1063/1.1713038 (3 pages) | Cited 39 times

Online Publication Date: 6 May 2004

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Visible quantum cutting (visible two-photon luminescence) through downconversion is observed for the Gd3+–Eu3+ couple in Eu3+-doped KGd3F10 (KG3F) and KGd2F7 (KG2F). The dependence of the efficiency of cross-relaxation required for visible quantum cutting on the Eu3+-doping concentration and crystal structure is discussed in terms of the probability of energy transfer as a function of the rare-earth interatomic distance. Eu3+-doped KG3F exhibits a higher efficiency in the cross-relaxation step than Eu3+-doped KG2F. The highest efficiency of the cross-relaxation step, 0.65, is obtained for the KG3F crystal doped with 2 at. % Eu3+. It is also suggested from dependence of the lifetime of 5D0 emission of Eu3+ in KG3F on Eu3+ concentration that interactions between rare-earth ions are strong at greater than 2 at. % Eu3+. © 2004 American Institute of Physics.
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78.40.Ha Other nonmetallic inorganics
61.72.S- Impurities in crystals
61.66.Fn Inorganic compounds
78.55.Hx Other solid inorganic materials
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
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Vacuum response and gas leak detection in piezoelectrically driven sound-resonance cavity

Shuxiang Dong, Feiming Bai, Li Yan, Hu Cao, Jie-Fang Li, and D. Viehland

Appl. Phys. Lett. 84, 4144 (2004); http://dx.doi.org/10.1063/1.1751217 (3 pages) | Cited 1 time

Online Publication Date: 6 May 2004

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It has been found that a piezoelectrically driven sound-resonance cavity (PSRC) is quite sensitive to low-pressure changes: a change from ambient to vacuum (67 Pa) conditions results in a 89° phase shift and a −81% voltage decrease. Under vacuum conditions, the PSRC is highly sensitive (∼7 ppm) to leakage of H2 gas. © 2004 American Institute of Physics.
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07.30.Hd Vacuum testing methods; leak detectors
43.58.-e Acoustical measurements and instrumentation
77.65.Dq Acoustoelectric effects and surface acoustic waves (SAW) in piezoelectrics
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Nonlinear microwave properties of ferroelectric thin films

R. Ott, P. Lahl, and R. Wördenweber

Appl. Phys. Lett. 84, 4147 (2004); http://dx.doi.org/10.1063/1.1751223 (3 pages) | Cited 12 times

Online Publication Date: 6 May 2004

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The nonlinear microwave properties of ferroelectric SrTiO3 thin films are characterized via complex analysis of the intermodulation distortion (IMD) signals up to high microwave power. The measurements reveal an unusual dependence of the IMD signals on the input power, which indicates the presence of two different nonlinear properties being responsible for the generation of IMD, i.e., the nonlinear permittivity and conductivity at low and high rf power levels, respectively. The IMD signal strength cannot be explained in terms of the classical description based on a Taylor expansion of the nonlinear parameter. In contrast, simulations of the frequency spectra using more appropriate descriptions of two nonlinear parameters yield an excellent agreement between theory and experiment, and, thus, demonstrate that the IMD experiments together with the simulation might provide further insight into the mechanism of nonlinear behavior of these materials. © 2004 American Institute of Physics.
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77.55.-g Dielectric thin films
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.22.Ch Permittivity (dielectric function)
73.61.Ng Insulators
78.70.Gq Microwave and radio-frequency interactions
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Investigation of forward and reverse current conduction in GaN films by conductive atomic force microscopy

J. Spradlin, S. Dogan, J. Xie, R. Molnar, A. A. Baski, and H. Morkoç

Appl. Phys. Lett. 84, 4150 (2004); http://dx.doi.org/10.1063/1.1751609 (3 pages) | Cited 16 times

Online Publication Date: 6 May 2004

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We have used conductive atomic force microscopy (C–AFM) to investigate the forward and reverse bias current conduction of homo- and heteroepitaxial GaN-based films grown by molecular beam epitaxy. In the case of homoepitaxy, C–AFM shows enhanced current conduction at the centers of ∼30% of spiral hillocks, which are associated with screw dislocations. Local current–voltage spectra taken by C–AFM on and off such hillocks indicate Frenkel–Poole and field emission mechanisms, respectively, for low current levels in forward conduction. In the case of heteroepitaxial GaN films grown on sapphire, the correlation between conduction pathways and topography is more complex. We do observe, however, that films with more rectifying nominal Schottky behavior (less reverse leakage current) produce forward and reverse bias C–AFM images with strong asymmetry. © 2004 American Institute of Physics.
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73.61.Ey III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
68.37.Ps Atomic force microscopy (AFM)
79.70.+q Field emission, ionization, evaporation, and desorption
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Conformal sensor skin approach to the safety-monitoring of H2 fuel tanks

Shuxiang Dong, Hu Cao, Feiming Bai, Li Yan, J. F. Li, D. Viehland, and Yongkang Gao

Appl. Phys. Lett. 84, 4153 (2004); http://dx.doi.org/10.1063/1.1753651 (2 pages) | Cited 2 times

Online Publication Date: 6 May 2004

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A conformal sensor skin approach has been developed for safety monitoring of H2 fuel tanks. Small piezoelectrically driven sound resonance cavities were embedded in a porous polymer. When placed on a structural composite plate, it was found feasible to detect the leakage of small concentrations of H2 in real time. © 2004 American Institute of Physics.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
43.38.Fx Piezoelectric and ferroelectric transducers
85.50.-n Dielectric, ferroelectric, and piezoelectric devices
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Electrically injected InGaAs/GaAs quantum-dot microcavity light-emitting diode operating at 1.3 μm and grown by metalorganic chemical vapor deposition

V. Tasco, M. T. Todaro, M. De Vittorio, M. De Giorgi, R. Cingolani, A. Passaseo, J. Ratajczak, and J. W. Katcki

Appl. Phys. Lett. 84, 4155 (2004); http://dx.doi.org/10.1063/1.1755411 (3 pages) | Cited 7 times

Online Publication Date: 6 May 2004

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We present a quantum-dot microcavity light-emitting diode emitting at 1.3 μm at room temperature. The long wavelength emission is achieved by using InGaAs quantum dots directly grown on GaAs, by metalorganic chemical vapor deposition. The device exhibits electroluminescence bright emission, peaked at 1298 nm and with a full width at half maximum of 6.5 meV. © 2004 American Institute of Physics.
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81.05.Ea III-V semiconductors
85.60.Jb Light-emitting devices
81.07.Ta Quantum dots
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
78.67.Hc Quantum dots
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
78.60.Fi Electroluminescence
78.66.Fd III-V semiconductors
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Unpinning of Fermi level in nanocrystalline semiconductors

Cesare Malagù, Vincenzo Guidi, Maria Cristina Carotta, and Giuliano Martinelli

Appl. Phys. Lett. 84, 4158 (2004); http://dx.doi.org/10.1063/1.1755419 (3 pages) | Cited 14 times

Online Publication Date: 6 May 2004

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A theoretical model has been developed to interpret the size dependent behavior of nanostructured metal-oxide semiconductors. It is based on the determination of the surface-state density, which pins the Fermi level of the semiconductor, thus removing the linear relationship between the work function and the Schottky barrier. To provide the model with numerical input, measurements of the Schottky barrier height were performed at different temperatures on nanocrystalline SnO2 and TiO2 films. The obtained solution predicts the unpinning of the Fermi level when the material can be considered as nanostructured, and the evidence confirms it. © 2004 American Institute of Physics.
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71.20.Nr Semiconductor compounds
73.20.At Surface states, band structure, electron density of states
73.30.+y Surface double layers, Schottky barriers, and work functions
73.22.Dj Single particle states
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Reduced dielectric dispersion in ferroelectric (Pb,La)TiO3/(Pb,Ca)TiO3 thin-film multilayer heterostructures due to a mechanical stress relaxation mechanism

Rosalía Poyato, M. Lourdes Calzada, and Lorena Pardo

Appl. Phys. Lett. 84, 4161 (2004); http://dx.doi.org/10.1063/1.1755422 (3 pages) | Cited 7 times

Online Publication Date: 6 May 2004

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The dielectric dispersion of (Pb,Ca)TiO3/(Pb,La)TiO3/(Pb,Ca)TiO3 and (Pb,La)TiO3/(Pb,Ca)TiO3/(Pb,La)TiO3 ferroelectric thin-film multilayer heterostructures onto Si-based substrates has been studied and compared with that of identically prepared (Pb,La)TiO3 and (Pb,Ca)TiO3 films. Grazing incidence x-ray diffraction analysis reveals that the tetragonal distortion of the heterostructures is higher than the ones for the single-component films, which evidences a mechanical stress relaxation mechanism in the heterostructures. A lower dielectric dispersion has been obtained in the heterostructures with respect to the single-component films. This is also a consequence of the stress relaxation by plastic deformation through vacancy diffusion present in the former. Vacancy diffusion decreases the number of VPb–VO defect-dipoles, which could contribute to the dielectric permittivity at low frequencies in the heterostructures. © 2004 American Institute of Physics.
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77.22.Ch Permittivity (dielectric function)
77.55.-g Dielectric thin films
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
62.20.F- Deformation and plasticity
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Lasing mode pattern of a quantum cascade photonic crystal surface-emitting microcavity laser

Kartik Srinivasan, Oskar Painter, Raffaele Colombelli, Claire Gmachl, Donald M. Tennant, A. Michael Sergent, Deborah L. Sivco, Alfred Y. Cho, Mariano Troccoli, and Federico Capasso

Appl. Phys. Lett. 84, 4164 (2004); http://dx.doi.org/10.1063/1.1755423 (3 pages) | Cited 8 times

Online Publication Date: 6 May 2004

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The identification of the lasing mode within a quantum cascade photonic crystal microcavity laser emitting at λ∼8 μm is presented. The symmetry of the lasing mode is determined by the position of nodal lines within micro-bolometer camera measurements of its polarized spatial distribution. Full three-dimensional finite-difference time-domain simulations are also performed, and the resulting vertically emitted radiation field pattern is seen to follow the experimental results closely. © 2004 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.55.Tv Photonic crystal lasers and coherent effects
42.55.Sa Microcavity and microdisk lasers
85.30.De Semiconductor-device characterization, design, and modeling
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Control of surface roughness in amorphous thin-film growth

F. Elsholz, E. Schöll, and A. Rosenfeld

Appl. Phys. Lett. 84, 4167 (2004); http://dx.doi.org/10.1063/1.1755425 (3 pages) | Cited 21 times

Online Publication Date: 6 May 2004

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The growth of optical layers of SiO2 and Nb2O5 on amorphous substrates is investigated. We develop a kinetic Monte Carlo model which mimics the amorphous structure by randomly fluctuating binding energies. The resulting surface profiles are characterized by their root-mean-square roughness, height–height correlation functions, and growth exponents. For strong random fluctuations, the growth exponents exceed the value of 0.5, in good agreement with experiment. © 2004 American Institute of Physics.
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81.16.-c Methods of micro- and nanofabrication and processing
81.15.Cd Deposition by sputtering
68.37.Ps Atomic force microscopy (AFM)
68.35.Ct Interface structure and roughness
85.40.Sz Deposition technology
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First-principles study of magnetism in (11math0) Zn1−xMnxO thin film

Q. Wang and P. Jena

Appl. Phys. Lett. 84, 4170 (2004); http://dx.doi.org/10.1063/1.1755834 (3 pages) | Cited 24 times

Online Publication Date: 6 May 2004

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First-principles calculations of total energies and magnetism of Zn1−xMnxO thin film are performed by simulating it with a slab consisting of seven layers along (11math0). It is shown that a single Mn atom shows very little preference for the site it occupies. This is consistent with the experimental finding that Mn atoms are homogeneously distributed in ZnO films. As the concentration of Mn atoms increases, antiferromagnetic coupling between Mn atoms becomes more favorable, and there is a tendency for Mn atoms to form clusters around oxygen, in agreement with recent experiments. © 2004 American Institute of Physics.
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75.70.Ak Magnetic properties of monolayers and thin films
75.50.Pp Magnetic semiconductors
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Role of intericosahedral chains on the hardness of sputtered boron carbide films

L. G. Jacobsohn, R. D. Averitt, C. J. Wetteland, R. K. Schulze, M. Nastasi, L. L. Daemen, Z. Jenei, and P. Asoka-Kumar

Appl. Phys. Lett. 84, 4173 (2004); http://dx.doi.org/10.1063/1.1755841 (3 pages) | Cited 8 times

Online Publication Date: 6 May 2004

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The relationship between the structure and mechanical properties of sputter-deposited boron carbide films was investigated. Changes in the structure induced by annealing were characterized in terms of chemical composition, chemical bonding, and concentrations of defects and trapped impurities. The creation of intericosahedral chains for higher annealing temperatures was revealed by infrared and Raman measurements, and the intensity of the infrared band at 1500 cm−1 was found to be related to the hardness. The presence of residual trapped Ar atoms and of open-volume defects is insensitive to relatively high annealing temperatures and does not influence the recovery of the hardness. Our results suggest postdeposition annealing as a pathway to enhance the mechanical properties of boron carbide films. © 2004 American Institute of Physics.
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68.55.-a Thin film structure and morphology
68.60.Bs Mechanical and acoustical properties
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.15.Cd Deposition by sputtering
78.30.Jw Organic compounds, polymers
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Growth and transport properties of complementary germanium nanowire field-effect transistors

Andrew B. Greytak, Lincoln J. Lauhon, Mark S. Gudiksen, and Charles M. Lieber

Appl. Phys. Lett. 84, 4176 (2004); http://dx.doi.org/10.1063/1.1755846 (3 pages) | Cited 141 times

Online Publication Date: 6 May 2004

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n- and p-type Ge nanowires were synthesized by a multistep process in which axial elongation, via vapor–liquid–solid (VLS) growth, and doping were accomplished in separate chemical vapor deposition steps. Intrinsic, single-crystal, Ge nanowires prepared by Au nanocluster-mediated VLS growth were surface-doped in situ using diborane or phosphine, and then radial growth of an epitaxial Ge shell was used to cap the dopant layer. Field-effect transistors prepared from these Ge nanowires exhibited on currents and transconductances up to 850 μA/μm and 4.9 μA/V, respectively, with device yields of >85%. © 2004 American Institute of Physics.
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85.30.Tv Field effect devices
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
73.63.Nm Quantum wires
61.46.-w Structure of nanoscale materials
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Cold electron Josephson transistor

A. M. Savin, J. P. Pekola, J. T. Flyktman, A. Anthore, and F. Giazotto

Appl. Phys. Lett. 84, 4179 (2004); http://dx.doi.org/10.1063/1.1756192 (3 pages) | Cited 13 times

Online Publication Date: 6 May 2004

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A superconductor-normal metal-superconductor mesoscopic Josephson junction has been realized in which the critical current is tuned through normal current injection using a symmetric electron cooler directly connected to the weak link. Both enhancement of the critical current by more than a factor of two, and supercurrent suppression have been achieved by varying the cooler bias. Furthermore, this transistor-like device demonstrates large current gain (∼20) and low power dissipation. © 2004 American Institute of Physics.
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85.25.Cp Josephson devices
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Brillouin observation of bulk and confined acoustic waves in silica microspheres

H. S. Lim, M. H. Kuok, S. C. Ng, and Z. K. Wang

Appl. Phys. Lett. 84, 4182 (2004); http://dx.doi.org/10.1063/1.1756206 (3 pages) | Cited 18 times

Online Publication Date: 6 May 2004

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Brillouin scattering from loose silica microspheres has been investigated as a function of their diameter (140 nm to 4 μm). The measured linear dependence of the confined acoustic mode frequencies on the inverse sphere diameters accords well with Lamb’s theory. Bulk acoustic modes are also observed in the larger microspheres, suggesting that the limiting size of a particle for these modes to be observable is about three times their wavelength. Internal consistency in the analyses of the bulk and confined mode data shows the validity of this Brillouin technique in the evaluation of the elastic properties of microspheres. Additionally it also affords a means of sizing the diameters of microspheres. © 2004 American Institute of Physics.
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78.35.+c Brillouin and Rayleigh scattering; other light scattering
78.66.Vs Fine-particle systems
62.30.+d Mechanical and elastic waves; vibrations
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High-speed 1.55 μm operation of low-temperature-grown GaAs-based resonant-cavity-enhanced p–i–n photodiodes

B. Butun, N. Biyikli, I. Kimukin, O. Aytur, E. Ozbay, P. A. Postigo, J. P. Silveira, and A. R. Alija

Appl. Phys. Lett. 84, 4185 (2004); http://dx.doi.org/10.1063/1.1756208 (3 pages) | Cited 3 times

Online Publication Date: 6 May 2004

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We report the design, growth, fabrication, and characterization of GaAs-based high-speed p–i–n photodiodes operating at 1.55 μm. A low-temperature-grown GaAs (LT-GaAs) layer was used as the absorption layer and the photoresponse was selectively enhanced at 1.55 μm using a resonant-cavity-detector structure. The bottom mirror of the resonant cavity was formed by a highly reflecting 15-pair GaAs/AlAs Bragg mirror. Molecular-beam epitaxy was used for wafer growth, where the active LT-GaAs layer was grown at a substrate temperature of 200 °C. The fabricated devices exhibited a resonance around 1548 nm. When compared to the efficiency of a conventional single-pass detector, an enhancement factor of 7.5 was achieved. Temporal pulse-response measurements were carried out at 1.55 μm. Fast pulse responses with 30 ps pulse-width and a corresponding 3 dB bandwidth of 11.2 GHz was measured. © 2004 American Institute of Physics.
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85.60.Dw Photodiodes; phototransistors; photoresistors
85.30.De Semiconductor-device characterization, design, and modeling
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Voltage gain effect in a ring-type magnetoelectric laminate

Shuxiang Dong, J. F. Li, and D. Viehland

Appl. Phys. Lett. 84, 4188 (2004); http://dx.doi.org/10.1063/1.1756676 (3 pages) | Cited 38 times

Online Publication Date: 6 May 2004

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It has been observed that a ring-type magnetoelectric laminate composite of circumferentially magnetized magnetostrictive Tb1−xDyxFe2 and circumferentially polarized piezoelectric Pb(Zr,Ti)O3 layers has a large magnetoelectric voltage gain effect, offering potential in high-power miniature transformer applications. © 2004 American Institute of Physics.
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75.80.+q Magnetomechanical effects, magnetostriction
75.50.Bb Fe and its alloys
77.84.Lf Composite materials
85.75.-d Magnetoelectronics; spintronics: devices exploiting spin polarized transport or integrated magnetic fields
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Observation of photoluminescence emission in ferromagnetic semiconductor GaCrN

M. Hashimoto, H. Tanaka, R. Asano, S. Hasegawa, and H. Asahi

Appl. Phys. Lett. 84, 4191 (2004); http://dx.doi.org/10.1063/1.1756678 (3 pages) | Cited 11 times

Online Publication Date: 6 May 2004

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Optical properties of GaN-based diluted magnetic semiconductor GaCrN were studied. The GaCrN layers were grown by electron-cyclotron-resonance plasma-assisted molecular-beam epitaxy. They exhibited ferromagnetic behavior at room temperature and strong photoluminescence (PL) emission at 3.29 eV (10 K). The PL emission peak energy of the GaCrN decreases with increasing temperature in accordance with the Varshini formula similar to the GaN excitonic transition peak. The 3.29 eV PL emission was assigned to be a band-to-band transition in GaCrN from the temperature- and the excitation-power-density dependences of the PL. © 2004 American Institute of Physics.
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75.50.Pp Magnetic semiconductors
78.55.Cr III-V semiconductors
75.50.Cc Other ferromagnetic metals and alloys
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Fluidic adaptive lens of transformable lens type

De-Ying Zhang, Nicole Justis, and Yu-Hwa Lo

Appl. Phys. Lett. 84, 4194 (2004); http://dx.doi.org/10.1063/1.1756679 (3 pages) | Cited 25 times

Online Publication Date: 6 May 2004

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Fluidic adaptive lenses with a transformable lens type were demonstrated. By adjusting the fluidic pressure, not only can the lens properties, such as the focal distance and numerical aperture, be tuned dynamically but also different lens types, such as planoconvex, planoconcave, biconvex, biconcave, positive meniscus, and negative meniscus lenses, can be formed. The shortest focal length for a 20 mm aperture adaptive lens is 14.3 mm when the device is transformed into a positive lens, and −6.3 mm when transformed into a negative lens. The maximum resolution of the fluidic lens is better than 40 line pairs/mm. © 2004 American Institute of Physics.
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42.79.Bh Lenses, prisms and mirrors
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Magneto-optical Kerr effect in Fe21Ni79 films on Si(100): Quantum behavior for film thicknesses below ∼6 nm

J. M. Talmadge, J. Gao, M. P. Riley, R. J. Roth, S.-O. Kim, J. G. Eden, F. A. Pudonin, and I. V. Mel’nikov

Appl. Phys. Lett. 84, 4197 (2004); http://dx.doi.org/10.1063/1.1737465 (3 pages) | Cited 2 times

Online Publication Date: 7 May 2004

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The magneto-optical Kerr effect (MOKE) has been observed and characterized in 1–80 nm thick Fe21Ni79 films deposited onto Si(100), for an external magnetic field (variable in strength up to 400 G) oriented parallel or orthogonal to the magnetization axis of the film. A measurable response is observed for film thicknesses (d) as small as 2 nm and, if the external magnetic field lies in the plane of the film, two-dimensional quantum behavior is evident for d≲6 nm. A precipitous decline in the magnitude of the MOKE response is accompanied by an increase in the coercivity and, when the external field is perpendicular to the film magnetization axis, a rapid rise in the saturation field. Experiments also confirm the existence of a component of the film magnetization oriented out of the plane of the film, a result consistent with the prediction of computational studies [T. Trunk et al., J. Appl. Phys. 89, 7606 (2001)] that the transition between Bloch and Néel wall domain structure occurs in FeNi films for film thicknesses of ≈30 nm. © 2004 American Institute of Physics.
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78.20.Ls Magneto-optical effects
75.70.Ak Magnetic properties of monolayers and thin films
75.70.Kw Domain structure (including magnetic bubbles and vortices)
75.50.Bb Fe and its alloys
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Dip-pen nanopatterning of photosensitive conducting polymer using a monomer ink

Ming Su, Mohammed Aslam, Lei Fu, Nianqiang Wu, and Vinayak P. Dravid

Appl. Phys. Lett. 84, 4200 (2004); http://dx.doi.org/10.1063/1.1737469 (3 pages) | Cited 29 times

Online Publication Date: 7 May 2004

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Controlled patterning of conducting polymers at a micro- or nanoscale is the first step towards the fabrication of miniaturized functional devices. Here, we introduce an approach for the nanopatterning of conducting polymers using an improved monomer “ink” in dip-pen nanolithography (DPN). The nominal monomer “ink” is converted, in situ, to its conducting solid-state polymeric form after patterned. Proof-of-concept experiments have been performed with acid-promoted polymerization of pyrrole in a less reactive environment (tetrahydrofuran). The ratios of reactants are optimized to give an appropriate rate to match the operation of DPN. A similar synthesis process for the same polymer in its bulk form shows a high conductance and crystalline structure. The miniaturized conducting polymer sensors with light detection ability are fabricated by DPN using the improved ink formula, and exhibit excellent response, recovery, and sensitivity parameters. © 2004 American Institute of Physics.
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82.35.Cd Conducting polymers
85.40.Hp Lithography, masks and pattern transfer
81.16.Nd Micro- and nanolithography
82.50.-m Photochemistry
78.40.Me Organic compounds and polymers
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
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Effects of finite deformed length in carbon nanotubes

Jun-Qiang Lu, Jian Wu, Wenhui Duan, and Bing-Lin Gu

Appl. Phys. Lett. 84, 4203 (2004); http://dx.doi.org/10.1063/1.1751608 (3 pages) | Cited 13 times

Online Publication Date: 7 May 2004

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The effect of finite deformed length is demonstrated by squashing an armchair (10,10) single-walled carbon nanotube with two finite tips. Only when the deformed length is long enough, an effectual metal–semiconductor–metal heterojunction can be formed in the metallic tube. The effect of finite deformed length is explained by the quantum tunneling effect. Furthermore, some conceptual designs of nanoscale devices are proposed from the metal–semiconductor–metal heterojunction. © 2004 American Institute of Physics.
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73.20.At Surface states, band structure, electron density of states
73.22.-f Electronic structure of nanoscale materials and related systems
61.46.-w Structure of nanoscale materials
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Characterization and reduction of unexplained noise in superconducting transition-edge sensors

J. N. Ullom, W. B. Doriese, G. C. Hilton, J. A. Beall, S. Deiker, W. D. Duncan, L. Ferreira, K. D. Irwin, C. D. Reintsema, and L. R. Vale

Appl. Phys. Lett. 84, 4206 (2004); http://dx.doi.org/10.1063/1.1753058 (3 pages) | Cited 40 times

Online Publication Date: 7 May 2004

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The noise in superconducting transition-edge sensors (TESs) commonly exceeds simple theoretical predictions. The reason for this discrepancy is presently unexplained. We have measured the amplitude and frequency dependence of the noise in TES sensors with eight different geometries. In addition, we have measured the dependence of the noise on operating resistance, perpendicular magnetic field, and bath temperature. We find that the unexplained noise contribution is inversely correlated with the temperature width of the superconducting-to-normal transition and is reduced by a perpendicular field and in certain geometries. These results suggest paths to improved sensor performance. © 2004 American Institute of Physics.
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85.25.Oj Superconducting optical, X-ray, and γ-ray detectors (SIS, NIS, transition edge)
85.25.Pb Superconducting infrared, submillimeter and millimeter wave detectors
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Doping effects on the valence band of Tl2Mn2O7 pyrochlores: Relation to magnetoresistance

J. Sánchez-Benítez, A. de Andrés, C. Prieto, J. Ávila, L. Martín-Carrón, J. L. Martínez, J. A. Alonso, M. J. Martínez-Lope, and M. T. Casais

Appl. Phys. Lett. 84, 4209 (2004); http://dx.doi.org/10.1063/1.1755413 (3 pages) | Cited 2 times

Online Publication Date: 7 May 2004

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Photoemission and x-ray absorption near edge spectroscopy measurements have been performed in Tl2Mn2O7 oxides doped with 10% different ions, Bi, Cd, or Sb, which produce colossal changes in the magnetoresistance values. The contributions to the valence band related to Mn, O, and the doping ions have been obtained. We found that the paramagnetic phase of doped Tl pyrochlores is charge-transfer insulator type with oxygen character of the upper edge of the valence band. Bi 6s and Cd 4d orbitals lie also at the upper edge of the valence band. Mn valence is identical for all samples while oxygen content varies to compensate for the charge introduced by doping. The density of carriers, which is correlated to the magnetoresistance values, is determined by the density of states near the Fermi level provided by Tl and O content. © 2004 American Institute of Physics.
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75.47.Gk Colossal magnetoresistance
75.47.Lx Magnetic oxides
71.20.Ps Other inorganic compounds
61.72.up Other materials
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Temperature stability of the refractive index and the direct bandedge in TlInGaAs quaternary alloys

A. Imada, H.-J. Lee, A. Fujiwara, T. Mukai, S. Hasegawa, and H. Asahi

Appl. Phys. Lett. 84, 4212 (2004); http://dx.doi.org/10.1063/1.1755415 (3 pages) | Cited 3 times

Online Publication Date: 7 May 2004

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TlInGaAs quaternary alloy layers were grown on InP substrates by gas-source molecular-beam epitaxy. Refractive index dispersions were determined at the temperature range of 300–340 K in the photon-energy region below and a little above the direct bandedge E0 by the optical reflectance measurements. The temperature dependence of the refractive index was analyzed with the first-order Sellmeier equation. The temperature dependence of the E0 edge was also determined by the absorption measurements. It was found that the temperature coefficients of both refractive index and E0 edge of TlInGaAs are much smaller than those for InGaAs. These results facilitate the fabrication of the temperature-stable-wavelength optoelectronic devices using this alloy system. © 2004 American Institute of Physics.
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78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.66.Fd III-V semiconductors
85.60.-q Optoelectronic devices
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
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