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26 Nov 2001

Volume 79, Issue 22, pp. 3561-3731

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Role of annealing conditions and surface treatment on ohmic contacts to p-GaN and p-Al0.1Ga0.9N/GaN superlattices

A. P. Zhang, B. Luo, J. W. Johnson, F. Ren, J. Han, and S. J. Pearton

Appl. Phys. Lett. 79, 3636 (2001); http://dx.doi.org/10.1063/1.1423387 (3 pages) | Cited 18 times

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The effects of the initial Mg reactivation annealing temperature, surface cleaning treatments, and contact annealing conditions on the specific contact resistance of Ni/Au ohmic contacts on p-GaN are reported. The lowest contact resistances were obtained for 900 °C activation annealing and cleaning steps that reduced the native oxide thickness (i.e., KOH rinsing). Removal of this interfacial oxide reduced the barrier for hole transport, providing a contact resistance of 9×10−4 Ω cm2 for Ni/Au metallization annealed at 500 °C. The use of a ten period p-Al0.1Ga0.9N(Mg)/GaN(Mg) superlattice with individual layer thickness 50 Å led to a specific contact resistance of 9×10−5 Ω cm2 under the same conditions. © 2001 American Institute of Physics.
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73.40.Ns Metal-nonmetal contacts
85.40.Ls Metallization, contacts, interconnects; device isolation
81.40.Gh Other heat and thermomechanical treatments
81.40.Rs Electrical and magnetic properties related to treatment conditions
73.63.-b Electronic transport in nanoscale materials and structures
73.40.Cg Contact resistance, contact potential
81.65.Cf Surface cleaning, etching, patterning

Terahertz gain in a SiGe/Si quantum staircase utilizing the heavy-hole inverted effective mass

Richard A. Soref and Gregory Sun

Appl. Phys. Lett. 79, 3639 (2001); http://dx.doi.org/10.1063/1.1421079 (3 pages) | Cited 10 times

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Modeling and design studies show that a strain-balanced Si1−xGex/Si superlattice on Si1−yGey-buffered Si can be engineered to give an inverted effective mass HH2 subband adjacent to HH1, thereby enabling a 77 K edge-emitting electrically pumped p–i–p quantum staircase laser for THz emission at energies below the 37 meV Ge–Ge optical phonon energy. Analysis of hole-phonon scattering, lifetimes, matrix elements, and hole populations indicates that a gain of 450 cm−1 will be feasible at f = 7.3 THz during 1.7 kA/cm2 current injection. © 2001 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation
71.18.+y Fermi surface: calculations and measurements; effective mass, g factor
73.20.At Surface states, band structure, electron density of states
71.38.-k Polarons and electron-phonon interactions

Field-emission characteristics and large current density of heavily Si-doped AlN and AlxGa1−xN (0.38 ⩽ x<1)

Makoto Kasu and Naoki Kobayashi

Appl. Phys. Lett. 79, 3642 (2001); http://dx.doi.org/10.1063/1.1421223 (3 pages) | Cited 16 times

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From a linear relation between the applied bias and the anode–sample distance, the electric field necessary for field emission (FE) can be obtained reproducibly. For heavily Si-doped AlN and AlxGa1−xN (0.38 ⩽ x<1), the band gap (Al-mole fraction, x), Si-dopant density (NSi), and thickness dependences of the field emission are investigated. After optimizing the sample structure, we obtained a FE current density of 0.22 A/cm2 with a 0.3-mm-diameter rod anode from 0.8-μm-thick Si-doped (NSi:1×1021 cm−3) AlN. © 2001 American Institute of Physics.
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79.70.+q Field emission, ionization, evaporation, and desorption
81.05.Ea III-V semiconductors
71.20.Nr Semiconductor compounds
61.72.uj III-V and II-VI semiconductors
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Abnormal temperature dependence of low-field magnetization of FeCr2−xAlxS4

Z. R. Yang, S. Tan, and Y. H. Zhang

Appl. Phys. Lett. 79, 3645 (2001); http://dx.doi.org/10.1063/1.1419031 (3 pages) | Cited 16 times

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In this letter, the abnormal temperature dependence of low-field magnetization of FeCr2−xAlxS4 (0 ⩽ x ⩽ 0.7) is reported. In addition to a large irreversibility between zero-field-cooling (ZFC) and field-cooling (FC) magnetization for all samples, a cusp is also observed in both FC and ZFC curves for x ⩽ 0.2. The cusp and the irreversibility are suppressed under an applied field of 0.5 T. The study of magnetic hysteresis loop reveals that this abnormal low-field magnetic behavior is closely related to coercitivity of the system. Accordingly, the abnormal magnetic behavior is explained qualitatively by taking account of large magnetic anisotropy and domain wall pinning of nonmagnetic ions. © 2001 American Institute of Physics.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Pp Magnetic semiconductors
81.05.Hd Other semiconductors
75.30.Gw Magnetic anisotropy
75.60.Ch Domain walls and domain structure

Shape-dependent magnetization reversal processes and flux-closure configurations of microstructured epitaxial Fe(110) elements

C. König, M. Sperlich, R. Heinesch, R. Calarco, J. O. Hauch, U. Rüdiger, G. Güntherodt, S. Kirsch, B. Özyilmaz, and A. D. Kent

Appl. Phys. Lett. 79, 3648 (2001); http://dx.doi.org/10.1063/1.1418033 (3 pages) | Cited 3 times

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The magnetization reversal processes and magnetic domain states of microstructured epitaxial Fe(110) elements have been investigated by magnetic-force microscopy and longitudinal Kerr hysteresis loop measurements. The characteristic micromagnetic behavior, such as coercive and nucleation fields, can be tailored by taking advantage of the pronounced uniaxial anisotropy and by varying the shape of the elements. The magnetic domain states of rectangular and diamond-shaped elements with lateral dimensions of 1.5 μm×0.5 μm have been investigated after magnetic saturation along the long and short axes of the elements. The observed flux-closure domain states have been compared with micromagnetic simulations. © 2001 American Institute of Physics.
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75.50.Bb Fe and its alloys
75.60.Jk Magnetization reversal mechanisms
75.70.Kw Domain structure (including magnetic bubbles and vortices)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
78.20.Ls Magneto-optical effects
75.30.Gw Magnetic anisotropy

Large magnetoresistance in postannealed Bi thin films

Sunglae Cho, Yunki Kim, A. J. Freeman, G. K. L. Wong, J. B. Ketterson, L. J. Olafsen, I. Vurgaftman, J. R. Meyer, and C. A. Hoffman

Appl. Phys. Lett. 79, 3651 (2001); http://dx.doi.org/10.1063/1.1416157 (3 pages) | Cited 20 times

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We have observed a large increase in the magnetoresistance (MR) of molecular beam epitaxy grown Bi thin films, which were subjected to a postannealing procedure 3 °C below the Bi melting point. We have achieved an increase in the MR by a factor of 2560 at helium temperatures compared with of 343 for an as-grown film. The enhancement of the MR in the annealed films is due to higher electron and hole mobilities (μe ≈ 1×106 cm2/V s at 5 K) relative to those of the as-grown films (μe ≈ 9×104 cm2/V s at 5 K). The enhancement of the mobility in the annealed films is also supported by the observation of Shubnikov–de Haas oscillations. © 2001 American Institute of Physics.
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73.61.At Metal and metallic alloys
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
75.47.De Giant magnetoresistance
61.72.Cc Kinetics of defect formation and annealing
73.50.Dn Low-field transport and mobility; piezoresistance

Spin-dependent transport in the double-perovskite Sr2CrWO6

J. B. Philipp, D. Reisinger, M. Schonecke, A. Marx, A. Erb, L. Alff, R. Gross, and J. Klein

Appl. Phys. Lett. 79, 3654 (2001); http://dx.doi.org/10.1063/1.1421227 (3 pages) | Cited 27 times

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We report on the preparation and characterization of the double-perovskite compound Sr2CrWO6 with a Curie temperature of 390 K. We have fabricated both Sr2CrWO6 bulk sintered polycrystalline bars and high-quality epitaxial thin films on SrTiO3 substrates by pulsed-laser deposition. The samples were characterized by thermogravimetric analysis, x-ray diffraction, electrical transport, and magnetization measurements. Polycrystalline samples containing a large number of grain boundaries show a large low-field magnetoresistance of up to 100% at 5 K. At room temperature, this effect is reduced to a few percent. Our results show that Sr2CrWO6 is an interesting candidate for room-temperature magnetoelectronic materials. © 2001 American Institute of Physics.
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72.20.My Galvanomagnetic and other magnetotransport effects
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
72.25.-b Spin polarized transport
75.50.Dd Nonmetallic ferromagnetic materials
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.40.-s Critical-point effects, specific heats, short-range order
75.70.Ak Magnetic properties of monolayers and thin films
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
68.55.-a Thin film structure and morphology
72.20.Fr Low-field transport and mobility; piezoresistance
73.50.Dn Low-field transport and mobility; piezoresistance
72.80.Sk Insulators

Dependence of electromigration-induced failure lifetimes on NiFe thin-film thickness in giant magnetoresistive spin-valve read heads

Seongtae Bae, Jack H. Judy, I-Fei Tsu, Marshall Davis, and Edward S. Murdock

Appl. Phys. Lett. 79, 3657 (2001); http://dx.doi.org/10.1063/1.1421644 (3 pages) | Cited 6 times

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The physical mechanisms responsible for the dependence of electromigration-induced failure lifetimes on NiFe thin film thickness in giant magnetoresistive spin-valve read heads have been studied to determine the maximum allowable current density. Based on measured median-times-to-failure, a maximum current density of about 1–2×108 A/cm2 was found to be safely used in 3–5 nm thick NiFe films. Grain size analyses using a transmission electron microscopy suggests that the longer lifetimes of thinner films are mainly due to the smaller number of grain boundaries and fewer triple points which result in less atomic flux divergence. © 2001 American Institute of Physics.
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85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.
75.47.De Giant magnetoresistance
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
61.72.Mm Grain and twin boundaries
75.50.Ss Magnetic recording materials
66.30.Qa Electromigration

Why are sputter deposited Nd1+xBa2−xCu3O7−δ thin films flatter than NdBa2Cu3O7−δ films?

S. Bals, G. Van Tendeloo, M. Salluzzo, and I. Maggio-Aprile

Appl. Phys. Lett. 79, 3660 (2001); http://dx.doi.org/10.1063/1.1421622 (3 pages) | Cited 10 times

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High-resolution electron microscopy and scanning tunneling microscopy have been used to compare the microstructure of NdBa2Cu3O7−δ and Nd1+xBa2−xCu3O7−δ thin films. Both films contain comparable amounts of Nd2CuO4 inclusions. Antiphase boundaries are induced by unit cell high steps at the substrate or by a different interface stacking. In Nd1+xBa2−xCu3O7−δ the antiphase boundaries tend to annihilate by the insertion of extra Nd layers. Stacking faults, which can be characterized as local Nd2Ba2Cu4O9 inclusions, also absorb the excess Nd. A correlation is made between the excess Nd and the absence of growth spirals at the surface of the Nd-rich films. © 2001 American Institute of Physics.
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74.78.-w Superconducting films and low-dimensional structures
74.72.-h Cuprate superconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.Nn Stacking faults and other planar or extended defects
61.72.Qq Microscopic defects (voids, inclusions, etc.)
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)

Suppression of interlayer coupling and enhancement of magnetoresistance in spin valves with oxide layer

Kebin Li, Yihong Wu, Jinjun Qiu, Guchang Han, Zaibing Guo, Hong Xie, and Towchong Chong

Appl. Phys. Lett. 79, 3663 (2001); http://dx.doi.org/10.1063/1.1421228 (3 pages) | Cited 25 times

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The interlayer coupling field (Hint) between the free and pinned ferromagnetic (FM) layers in an exchange-biased spin valve deposited by magnetron sputtering is usually dominated by the Néel “orange peel” coupling. The orange peel coupling is suppressed dramatically when an oxide layer (OXL) is inserted into the free/pinned FM layers due to smoother surface roughness at the interface. Hint decreases with increasing oxygen exposure dose of the free/pinned FM layers to pure O2 gas. And it is found that Ruderman–Kittel–Kasuya–Yoshida exchange coupling dominates in OXL spin valves due to smoother surface roughness and enhanced specular electron scattering at the interface between OXL and pinned/free FM layers, which also results in enhancement of magnetoresistance effect. © 2001 American Institute of Physics.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.47.De Giant magnetoresistance
85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.
75.30.Et Exchange and superexchange interactions
75.50.Bb Fe and its alloys
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Dielectric property and conduction mechanism of ultrathin zirconium oxide films

J. P. Chang and Y.-S. Lin

Appl. Phys. Lett. 79, 3666 (2001); http://dx.doi.org/10.1063/1.1418265 (3 pages) | Cited 58 times

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Stoichiometric, uniform, amorphous ZrO2 films with an equivalent oxide thickness of ∼1.5 nm and a dielectric constant of ∼18 were deposited by an atomic layer controlled deposition process on silicon for potential applications in metal–oxide–semiconductor (MOS) devices. The conduction mechanism is identified as Schottky emission at low electric fields and as Poole–Frenkel emission at high electric fields. The MOS devices showed low leakage current, small hysteresis (<50 mV), and low interface state density ( ∼ 2×1011 cm−2 eV−1). Microdiffraction and high-resolution transmission electron microscopy showed a localized monoclinic phase of α-ZrO2 and an amorphous interfacial ZrSixOy layer which has a corresponding dielectric constant of 11. © 2001 American Institute of Physics.
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77.55.-g Dielectric thin films
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
73.61.Ng Insulators
77.22.Ch Permittivity (dielectric function)
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
85.30.Tv Field effect devices
72.20.Fr Low-field transport and mobility; piezoresistance
72.80.Sk Insulators
73.30.+y Surface double layers, Schottky barriers, and work functions
72.20.Ht High-field and nonlinear effects
73.50.Fq High-field and nonlinear effects
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.A- Nucleation and growth

BaPbO3 perovskite electrode for lead zirconate titanate ferroelectric thin films

Yih-Rong Luo and Jenn-Ming Wu

Appl. Phys. Lett. 79, 3669 (2001); http://dx.doi.org/10.1063/1.1421088 (3 pages) | Cited 27 times

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BaPbO3 (BPO) films were prepared by rf-magnetron sputtering at temperatures as low as 350 °C. These films possessed low electrical resistivity of 1.4×10−3 Ω cm, which is appropriate for electrodes. The BPO electrode has an advantage over a Pt electrode in that it lowers the crystallization temperature of Pb(Zr0.53Ti0.47)O3 (PZT) films from 600 to 550 °C. The coercive fields of the PZT films deposited on a BPO/Pt electrode are significantly lower than those deposited on the Pt electrode, but the remanent polarization remained essentially unchanged. The BPO electrode also improved the fatigue resistance and decreased the leakage current of the PZT films deposited. © 2001 American Institute of Physics.
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77.80.-e Ferroelectricity and antiferroelectricity
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.55.-g Dielectric thin films
77.22.Ej Polarization and depolarization
81.15.Cd Deposition by sputtering
68.55.-a Thin film structure and morphology

Ferroelectric SrBi4Ti4O15 thin films with high polarization grown on an IrO2 layer

D. S. Sohn, W. X. Xianyu, W. I. Lee, I. Lee, and I. Chung

Appl. Phys. Lett. 79, 3672 (2001); http://dx.doi.org/10.1063/1.1421078 (3 pages) | Cited 23 times

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Ferroelectric strontium bismuth titanate (SrBi4Ti4O15) thin films with a high remanent polarization were produced by a chemical solution deposition method. Pt and IrO2 layers were used as substrates. It was found that ferroelectric SrBi4Ti4O15 films can be successfully fabricated on IrO2: They demonstrate a saturated hysteresis loop at 5 V with remanent polarization (Pr) of 19 μC/cm2 and coercive field (Ps) of 116 kV/cm. SrBi4Ti4O15 films grown on IrO2 show larger and denser grains and controlled surface morphology. The grains are random oriented, while those of films on Pt are mainly c-axis oriented. It is concluded that the high remanent polarization of the films grown on IrO2 originates from the relatively high concentration of a- and b-axis orientations. © 2001 American Institute of Physics.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.55.-g Dielectric thin films
77.22.Ej Polarization and depolarization
68.55.-a Thin film structure and morphology
77.80.Dj Domain structure; hysteresis
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)

Negligible oxygen liberation during bipolar electric cycling of ferroelectric lead zirconate titanate ceramics

Jürgen Nuffer, Doru C. Lupascu, Jürgen Rödel, and Michael Schroeder

Appl. Phys. Lett. 79, 3675 (2001); http://dx.doi.org/10.1063/1.1421089 (3 pages) | Cited 10 times

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The long-standing question whether or not oxygen gas is liberated from the perovskite lattice during fatigue of ferroelectric lead zirconate titanate ceramics is addressed. During cycling, the surrounding gas atmosphere of the sample was analyzed continuously by a mass spectrometer. It was found that, in contrast to previous statements in the literature, the oxygen detected originates from air dissolved in the surrounding liquid. An upper limit for oxygen liberation from the sample is given. We conclude that all mechanistical approaches for ferroelectric fatigue based on oxygen liberation are in need of revision. © 2001 American Institute of Physics.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.80.-e Ferroelectricity and antiferroelectricity

Direct hysteresis measurements of single nanosized ferroelectric capacitors contacted with an atomic force microscope

S. Tiedke, T. Schmitz, K. Prume, A. Roelofs, T. Schneller, U. Kall, R. Waser, C. S. Ganpule, V. Nagarajan, A. Stanishevsky, and R. Ramesh

Appl. Phys. Lett. 79, 3678 (2001); http://dx.doi.org/10.1063/1.1421638 (3 pages) | Cited 34 times

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Direct hysteresis measurements on single submicron structure sizes were performed on epitaxial ferroelectric Pb(Zr,Ti)O3 thin films grown on SrTiO3 with La0.5Sr0.5CoO3 (LSCO) electrodes. The samples were fabricated by focused-ion-beam milling resulting in pad sizes down to 200 nm×200 nm. The influence of parasitic capacitance of the measurement setup was eliminated by applying an enhanced compensation procedure. No size effects were observed in capacitors milled down to 400 nm×400 nm. Thus, a published increase of Pmax1 for decreasing pad size can be explained by the parasitic influence of the setup. Finally, the inaccuracy of increasing coercive voltage due to the coating of the cantilever of the atomic force microscope is discussed. © 2001 American Institute of Physics.
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84.32.Tt Capacitors
85.50.-n Dielectric, ferroelectric, and piezoelectric devices
77.55.-g Dielectric thin films
77.80.Dj Domain structure; hysteresis
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.22.Ej Polarization and depolarization
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Matrix effects on the structural and optical properties of InAs quantum dots

J. X. Chen, U. Oesterle, A. Fiore, R. P. Stanley, M. Ilegems, and T. Todaro

Appl. Phys. Lett. 79, 3681 (2001); http://dx.doi.org/10.1063/1.1416162 (3 pages) | Cited 25 times

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InAs quantum dots (QDs) have been grown by molecular-beam epitaxy on different InGaAs or GaAs surface layers to investigate the effect of the matrix on the structural and optical properties of the QDs. The density of QDs directly grown on GaAs is 1.1×1010 cm−2, and increases to 2.3×1010 cm−2 for dots grown on a 1 nm InGaAs layer. Single-mirror light-emitting-diode (SMLED) structures with InAs QDs capped by InGaAs and grown on GaAs and InGaAs layers were fabricated to compare the electroluminescence efficiency between the two structures. The maximum external quantum efficiency for QDs on a GaAs structure is 1.1% while that for QDs on InGaAs is 1.3%. The corresponding radiative efficiency could be deduced to be 17.5% for QDs on GaAs and 21.5% for QDs on InGaAs, respectively. © 2001 American Institute of Physics.
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78.67.Hc Quantum dots
68.65.Hb Quantum dots (patterned in quantum wells)
78.60.Fi Electroluminescence
85.60.Jb Light-emitting devices

Neutron scattering study of H2 adsorption in single-walled carbon nanotubes

Y. Ren and D. L. Price

Appl. Phys. Lett. 79, 3684 (2001); http://dx.doi.org/10.1063/1.1421639 (3 pages) | Cited 22 times

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H2 adsorption in single-walled carbon nanotubes (SWCNTs) has been studied with quasielastic and inelastic neutron scattering. At 80 K, under a H2 pressure of 110 atm, H2 molecules gradually condense in the SWCNT sample. After pumping out at 25 K and 20 mTorr, the remaining H2 molecules show a quantum rotational transition at 14.5±0.1 meV, with a peak width that increases linearly with increasing temperature from 4.2 to 35 K. The H2 molecules remain in the sample up to 65 K and then start to desorb with increasing temperature. A broad inelastic scattering spectrum from the adsorbed hydrogen is also observed. The time scale of the dynamics is longer than 15 ps even at 200 K. Our results imply that hydrogen molecules are physisorbed in the interstitial tunnels of the SWCNT bundles. © 2001 American Institute of Physics.
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68.43.Mn Adsorption kinetics
68.43.Vx Thermal desorption
84.60.Ve Energy storage systems, including capacitor banks
62.50.-p High-pressure effects in solids and liquids

Reversible control of silver nanoparticle generation and dissolution in soda-lime silicate glass through x-ray irradiation and heat treatment

Sihai Chen, Tomoko Akai, Kohei Kadono, and Tetsuo Yazawa

Appl. Phys. Lett. 79, 3687 (2001); http://dx.doi.org/10.1063/1.1418257 (3 pages) | Cited 12 times

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Reversible generation and dissolution of 3 nm silver particles in a glass containing only silver ions are repeatedly achieved through a combination of x-ray radiation and heat treatment. X-ray irradiation and 400 °C heat treatment induce a yellow color, whereas heating at 500 °C can change the glass to colorless again. X-ray irradiation produces large amounts of silver atoms and defects, mainly nonbridging oxygen hole centers (NBOs), in glass. Heating at 400 °C accelerates the aggregation of silver atoms into forming silver particles. The NBOs can continuously oxidize the silver atoms of particles into silver ions at higher temperature, leading to dissolution of the silver particles. © 2001 American Institute of Physics.
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61.46.-w Structure of nanoscale materials
81.07.Bc Nanocrystalline materials
81.05.Kf Glasses (including metallic glasses)
61.43.Fs Glasses
64.75.-g Phase equilibria
61.82.Rx Nanocrystalline materials
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
61.80.Cb X-ray effects
81.40.Gh Other heat and thermomechanical treatments
61.72.S- Impurities in crystals

Backscattering in carbon nanotubes: Role of quantum interference effects

Stephan Roche, François Triozon, and Angel Rubio

Appl. Phys. Lett. 79, 3690 (2001); http://dx.doi.org/10.1063/1.1421643 (3 pages) | Cited 5 times

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The backscattering contribution to the conductivity, irrelevant for metallic single-walled carbon nanotubes, is proved to become more significant for doped semiconducting systems, in agreement with experiments. In the case of multiwalled nanotubes, the intershell coupling is further shown to enhance the contribution of backscattering for “metallic” double-walled, whereas it remains insignificant for “metallic/semiconducting” double-walled systems. © 2001 American Institute of Physics.
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73.63.Fg Nanotubes
73.23.-b Electronic transport in mesoscopic systems

Optical characterization of wurtzite gallium nitride nanowires

M. W. Lee, H. Z. Twu, C.-C. Chen, and C.-H. Chen

Appl. Phys. Lett. 79, 3693 (2001); http://dx.doi.org/10.1063/1.1416476 (3 pages) | Cited 23 times

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The optical properties of the gallium nitride (GaN) nanowires are examined by the transmission method in the ultraviolet-visible range (1–5 eV) and by the reflection method in the infrared range (500–4000 cm−1). The absorption edge of the GaN nanowires is blueshifted by 0.2 eV from the bulk edge. The temperature dependence of the energy gap is expressed by, Eg(T) = 3.724−9.97×10−4/(861+T) eV. The plasma frequency and the free-carrier density of the GaN nanowires, deduced from the infrared reflectance minima, are estimated to be ωp = 1100±120 cm−1 and nf = 3.73×1017 cm−3, respectively. Obtaining the free-carrier density from the infrared reflectance spectra is especially useful in research on nanostructured semiconductors. © 2001 American Institute of Physics.
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78.67.Lt Quantum wires
78.40.Fy Semiconductors
78.30.Fs III-V and II-VI semiconductors

Ultrahigh-density nanotransistors by using selectively grown vertical carbon nanotubes

Won Bong Choi, Jae Uk Chu, Kwang Seok Jeong, Eun Ju Bae, Jo-Won Lee, Ju-Jin Kim, and Jeong-O Lee

Appl. Phys. Lett. 79, 3696 (2001); http://dx.doi.org/10.1063/1.1419236 (3 pages) | Cited 44 times

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A type of carbon nanotube transistors, which would be suitable for large-scale integration, has been fabricated from vertically aligned carbon nanotubes. We fabricated highly ordered carbon nanotubes, which are selectively grown on the patterned aluminum oxide nanotemplates. Each device element is formed on a vertical carbon nanotube attached to a bottom (source) and upper (drain) electrodes and a gate electrode, which is electrostatically switchable. The transistors can be integrated in large arrays with the potential for tera-level density (2×1011/cm2). The vertical carbon nanotube transistor shows ON/OFF switching operation at 30 K. © 2001 American Institute of Physics.
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85.35.Kt Nanotube devices
81.07.De Nanotubes
85.30.Tv Field effect devices

Influence of nanoscale geometry on the thermodynamics of electron field emission

T. S. Fisher

Appl. Phys. Lett. 79, 3699 (2001); http://dx.doi.org/10.1063/1.1421418 (3 pages) | Cited 13 times

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The effects of nanoscale emitter size on the energy transport in electron field-emission devices are considered, with emitter radii ranging from 5 nm to infinity. Theoretical results for energy distribution and flux indicate that emitter radii less than 50 nm produce significant filtering in favor of high-energy electrons relative to the planar case. An emitter radius of 5 nm is shown to produce a peak energy flux of 250 W/cm2 away from the emitter at a temperature of 300 K. This high rate of energy transport could prove to be useful in the development of direct refrigeration devices. © 2001 American Institute of Physics.
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79.70.+q Field emission, ionization, evaporation, and desorption
07.20.Mc Cryogenics; refrigerators, low-temperature detectors, and other low-temperature equipment

Preparation and structure analysis of titanium oxide nanotubes

G. H. Du, Q. Chen, R. C. Che, Z. Y. Yuan, and L.-M. Peng

Appl. Phys. Lett. 79, 3702 (2001); http://dx.doi.org/10.1063/1.1423403 (3 pages) | Cited 221 times

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Well crystallized nanoscale tubular materials have been synthesized via the reaction of TiO2 crystals of either anatase or rutile phase and NaOH aqueous solution. The atomic structure of the synthesized tubular material is imaged by high-resolution transmission electron microscopy (HRTEM), and the composition of individual tubular structures is determined using selected area energy dispersive X-ray spectroscopy (EDX). Our results show that the tubular materials are well crystallized tubes with an average diameter of about 9 nm and little dispersion, and are composed of mainly titanium and oxygen. The atomic ratio of O/Ti is found, however, to vary from tube to tube. Detailed electron and x-ray diffraction studies show that the structure of our titanium oxide nanotubes do not agree with those made of TiO2 crystals with either anatase or rutile phase. HRTEM observations revealed that the titanium oxide nanotubes usually have multiple shells, in analogy with multiwalled carbon nanotubes, but the shell spacing is about 0.75 nm which is much larger than that of the carbon nanotube, and the atomic structures of different shells are well correlated. © 2001 American Institute of Physics.
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61.46.-w Structure of nanoscale materials
81.07.De Nanotubes
82.80.Ej X-ray, Mössbauer, and other γ-ray spectroscopic analysis methods

Enhancement of oxidation rate of a-Si nanoparticles during dehydrogenation

D. Das, J. Farjas, P. Roura, G. Viera, and E. Bertran

Appl. Phys. Lett. 79, 3705 (2001); http://dx.doi.org/10.1063/1.1420533 (3 pages) | Cited 10 times

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Oxidation of amorphous silicon (a-Si) nanoparticles grown by plasma-enhanced chemical vapor deposition were investigated. Their hydrogen content has a great influence on the oxidation rate at low temperature. When the mass gain is recorded during a heating ramp in dry air, an oxidation process at low temperature is identified with an onset around 250 °C. This temperature onset is similar to that of hydrogen desorption. It is shown that the oxygen uptake during this process almost equals the number of hydrogen atoms present in the nanoparticles. To explain this correlation, we propose that oxidation at low temperature is triggered by the process of hydrogen desorption. © 2001 American Institute of Physics.
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81.65.Mq Oxidation
68.43.Vx Thermal desorption
61.46.-w Structure of nanoscale materials
61.43.Dq Amorphous semiconductors, metals, and alloys
82.60.Qr Thermodynamics of nanoparticles

Determination of performance on tunnel conduction through molecular wire using a conductive atomic force microscope

Hiroshi Sakaguchi, Atsushi Hirai, Futoshi Iwata, Akira Sasaki, Toshihiko Nagamura, Etsuya Kawata, and Seiichiro Nakabayashi

Appl. Phys. Lett. 79, 3708 (2001); http://dx.doi.org/10.1063/1.1421233 (3 pages) | Cited 25 times

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Performance of nonresonant tunnel conduction through a self-assembled monolayer of conjugated molecules fabricated on gold (111) was determined by virtue of nanometer-scale electrical probe measurement using a conductive atomic force microscope. Electrical measurements with nanometer spatial resolution enabled mapping of tunnel current as well as efficiency of tunnel conduction through molecular wire by analyzing length dependence on current. A series of conjugated molecules with different numbers of oligothiophene rings proved to possess a high tunnel-conduction efficiency. © 2001 American Institute of Physics.
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73.40.Gk Tunneling
68.37.Ps Atomic force microscopy (AFM)
85.65.+h Molecular electronic devices
73.63.-b Electronic transport in nanoscale materials and structures
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