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15 Apr 2002

Volume 80, Issue 15, pp. 2625-2806

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Passivation of defects at the SrTiO3/Si interface with H and H2

R. J. Browne, E. A. Ogryzlo, K. Eisenbeiser, Z. Yu, R. Droopad, and C. Overgaard

Appl. Phys. Lett. 80, 2699 (2002); http://dx.doi.org/10.1063/1.1472475 (2 pages) | Cited 2 times

Online Publication Date: 10 April 2002

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A silicon surface covered with ∼150 Å of strontium titanium oxide was exposed to both atomic and molecular hydrogen at temperatures between 20 and 300 °C. A rf probe was used to continuously monitor changes in charge-carrier recombination centers at the SrTiO3/Si interface by following the steady-state photogenerated carrier concentration in the silicon. Independent passivation of interfacial defects was observed by both atomic and molecular hydrogen. © 2002 American Institute of Physics.
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81.65.Rv Passivation
81.05.Cy Elemental semiconductors
73.20.Hb Impurity and defect levels; energy states of adsorbed species
71.55.Cn Elemental semiconductors
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
72.40.+w Photoconduction and photovoltaic effects
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Hysteresis curves and self-field alternating-current losses in superconducting tapes with transport current: Edge barrier effect

I. L. Maksimov and A. A. Elistratov

Appl. Phys. Lett. 80, 2701 (2002); http://dx.doi.org/10.1063/1.1458691 (3 pages) | Cited 3 times

Online Publication Date: 10 April 2002

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The combined influence of both bulk pinning and edge barrier on zero-field transport properties and alternating-current (ac) losses in superconducting tapes and films is considered. The equilibrium distributions of the magnetic flux density n(y) and of the sheet current density i(y) are found analytically for the tapes with an oscillating transport current. The critical current is calculated taking into account both bulk and edge pinning of the magnetic flux, and the dependence of the dissipation loss power upon the ac amplitude I0 is found. The crossover from barrier- to pinning-controlled ac losses is predicted with the increase of current oscillation amplitude I0. © 2002 American Institute of Physics.
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74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)
84.71.Mn Superconducting wires, fibers, and tapes
74.78.-w Superconducting films and low-dimensional structures
74.25.Sv Critical currents
74.25.F- Transport properties
74.25.Ha Magnetic properties including vortex structures and related phenomena

Thermodynamic calculations of the effect of B and Ta on magnetically induced phase separation in Co–Cr–Pt alloys

K. Oikawa, G. W. Qin, S. Okamoto, O. Kitakami, Y. Shimada, K. Fukamichi, and K. Ishida

Appl. Phys. Lett. 80, 2704 (2002); http://dx.doi.org/10.1063/1.1469684 (3 pages) | Cited 6 times

Online Publication Date: 10 April 2002

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In order to clarify the relation between the magnetically induced phase separation and the recording media characteristics, the thermodynamic calculations of Co–Cr–Pt–B and Co–Cr–Pt–Ta systems have been carried out by using the available binary assessment data and Miedema’s semiempirical values. B is segregated to the boundary in a similar manner as Cr, which makes the boundary region paramagnetic. This result is consistent with available data that B weakens the intergranular magnetic coupling and increases the magnetic anisotropy in Co–Cr–Pt recording media. By adding Ta, the Cr content in the paramagnetic phase is also increased, reducing the intergranular magnetic coupling. However, the Ta content in the ferromagnetic phase is higher than in the paramagnetic phase, decreasing the magnetic anisotropy. Accordingly, the thermodynamic calculations successfully explain experimental magnetic data for Co–Cr–Pt–B and Co–Cr–Pt–Ta recording media. © 2002 American Institute of Physics.
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75.50.Ss Magnetic recording materials
75.50.Cc Other ferromagnetic metals and alloys
75.70.Ak Magnetic properties of monolayers and thin films
64.75.-g Phase equilibria
65.40.G- Other thermodynamical quantities
75.30.Gw Magnetic anisotropy
75.20.Ck Nonmetals

Oxygen-deficiency-activated phase transition in a long-aged La0.8Ca0.2MnO3 film

V. G. Prokhorov, G. G. Kaminsky, V. A. Komashko, Y. P. Lee, J. S. Park, and H. C. Ri

Appl. Phys. Lett. 80, 2707 (2002); http://dx.doi.org/10.1063/1.1470244 (3 pages) | Cited 10 times

Online Publication Date: 10 April 2002

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The magnetic and transport properties of as-deposited and long-aged La0.8Ca0.2MnO3−δ films have been investigated in a wide temperature range. The x-ray diffraction data have shown separation of the film into two crystalline phases of the cubic and rhombohedral symmetry with different oxygen contents of δ ≃ 0.08 and 0.16, respectively, after a half-year aging at room temperature in air. Both phases testify two different electronic (metal–insulator) and magnetic transitions with similar maximum values of magnetoresistance. The possible mechanism for such a type of structural transition in the aged manganite thin films is discussed. © 2002 American Institute of Physics.
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68.55.Nq Composition and phase identification
75.47.De Giant magnetoresistance
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
71.30.+h Metal-insulator transitions and other electronic transitions
64.70.K- Solid-solid transitions

All solution-chemistry approach for YBa2Cu3O7−δ-coated conductors

M. P. Siegal, P. G. Clem, J. T. Dawley, R. J. Ong, M. A. Rodriguez, and D. L. Overmyer

Appl. Phys. Lett. 80, 2710 (2002); http://dx.doi.org/10.1063/1.1470225 (3 pages) | Cited 46 times

Online Publication Date: 10 April 2002

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A need exists for low-cost coated-conductor fabrication methods for applications in magnet and electric-power technologies. We demonstrate high-critical current density (Jc) YBa2Cu3O7−δ (YBCO) films grown on Nb-doped SrTiO3 (Nb:STO) buffered Ni(100) tapes. All buffer and superconductor layers are deposited using solution chemistry. A 50 nm thick Nb:STO seed layer on Ni(100) acts as a template for the growth of subsequent thicker layers of Nb:STO. Nb doping improves the electrical conductivity and oxygen diffusion barrier properties of STO. YBCO grows heteroepitaxially directly on this buffer layer, resulting in a transport Jc(77 K) = 1.3 MA/cm2. © 2002 American Institute of Physics.
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74.78.-w Superconducting films and low-dimensional structures
74.25.Sv Critical currents
74.72.-h Cuprate superconductors
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)

Scanning magnetoresistance microscopy with a magnetoresistive sensor cantilever

Motonori Nakamura, Michiya Kimura, Kazuhisa Sueoka, and Koichi Mukasa

Appl. Phys. Lett. 80, 2713 (2002); http://dx.doi.org/10.1063/1.1469681 (3 pages) | Cited 10 times

Online Publication Date: 10 April 2002

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In this work, a cantilever with a magnetoresistive (MR) sensor is fabricated for scanning magnetoresistance microscope, in order to realize the simultaneous imaging of surface topography and stray magnetic field distribution. A constant current flowing through a meander-patterned metal wire produces a defined magnetic field, and the wire is used as a sample to demonstrate the simultaneous imaging and to reveal the field sensitivity of the cantilever. A MR image has been successfully obtained with lateral spatial resolution of a few μm and a field sensitivity (Hmin ≈ 1.7 Oe) at room temperature. © 2002 American Institute of Physics.
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07.79.Lh Atomic force microscopes
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
07.55.Ge Magnetometers for magnetic field measurements
06.30.Bp Spatial dimensions (e.g., position, lengths, volume, angles, and displacements)

Low-temperature growth of NiMnSb thin films by pulsed-laser deposition

J. Giapintzakis, C. Grigorescu, A. Klini, A. Manousaki, V. Zorba, J. Androulakis, Z. Viskadourakis, and C. Fotakis

Appl. Phys. Lett. 80, 2716 (2002); http://dx.doi.org/10.1063/1.1469211 (3 pages) | Cited 17 times

Online Publication Date: 10 April 2002

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We report the growth of thin films of the ferromagnetic half-Heusler alloy NiMnSb by pulsed-laser deposition on Si (111) and polycrystalline InAs substrates. Highly crystalline films are grown using low substrate temperatures (190–210 °C), without any postdeposition annealing. The structural, magnetic, and transport properties of the films are relatively consistent with those of the bulk NiMnSb used as target, which suggests that thin layers of this material grown by laser ablation could be used in multilayer structures as effective spin-polarized conducting layers. © 2002 American Institute of Physics.
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81.15.Fg Pulsed laser ablation deposition
75.50.Cc Other ferromagnetic metals and alloys
75.70.Ak Magnetic properties of monolayers and thin films
68.55.-a Thin film structure and morphology

Improved thermal stability of synthetic ferrimagnetic media with enhanced exchange coupling strength

A. Inomata, E. N. Abarra, B. R. Acharya, A. Ajan, and I. Okamoto

Appl. Phys. Lett. 80, 2719 (2002); http://dx.doi.org/10.1063/1.1467696 (3 pages) | Cited 8 times

Online Publication Date: 10 April 2002

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The effect of the antiferromagnetic interlayer exchange coupling strength J between the initial or stabilization magnetic layer L1 and the top magnetic layer L2 on the thermal stability of synthetic ferrimagnetic media (SFM) is investigated. Enhanced J is achieved by the insertion of a thin Co-rich hexagonal close-packed layer between the Ru layer and L1, and such a structure did not change the read/write properties significantly. The contribution of the anisotropy energy of L1 to the thermal stability of SFM is improved by increasing J. However, a significant increase in the contribution of L1 to the thermal stability is achieved at relatively low J values (0.14 erg/cm2) which translate into only a 3–4% increase in the switching field H0. © 2002 American Institute of Physics.
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75.50.Ss Magnetic recording materials
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
68.65.Ac Multilayers
75.50.Gg Ferrimagnetics
68.60.Dv Thermal stability; thermal effects
75.30.Et Exchange and superexchange interactions
75.30.Gw Magnetic anisotropy
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Magnetization reversal probed by spin-polarized tunneling

Moon-Ho Jo, N. D. Mathur, and M. G. Blamire

Appl. Phys. Lett. 80, 2722 (2002); http://dx.doi.org/10.1063/1.1469678 (3 pages) | Cited 10 times

Online Publication Date: 10 April 2002

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We report magnetic reversal processes in the magnetic tunnel junction (MTJ) based on a half metallic manganite, La0.7Ca0.3MnO3 by comprehensive spin-polarized tunneling (SPT) measurements. The large tunnel magnetoresistance up to 77% of (Rap−Rp)/Rap in the present MTJ is highly sensitive to the local magnetization fluctuation in the ferromagnetic electrodes and thus enables us to establish an instantaneous one-to-one correlation between the magnetization reversal and the SPT with the two-dimensional SPT measurements. We have found the systematic angular variations of the SPT features in the resistance-field curves, and based on the observed angular dependences, we propose a crucial role of the edge-domain pinning and the resultant multi-domain breakup for the magnetization reversal. © 2002 American Institute of Physics.
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85.75.Mm Spin polarized resonant tunnel junctions
75.50.Dd Nonmetallic ferromagnetic materials
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.60.Jk Magnetization reversal mechanisms
75.47.De Giant magnetoresistance
75.70.Kw Domain structure (including magnetic bubbles and vortices)

Improved superconducting properties in nanocrystalline bulk MgB2

A. Gümbel, J. Eckert, G. Fuchs, K. Nenkov, K.-H. Müller, and L. Schultz

Appl. Phys. Lett. 80, 2725 (2002); http://dx.doi.org/10.1063/1.1469654 (3 pages) | Cited 98 times

Online Publication Date: 10 April 2002

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High density nanocrystalline MgB2 bulk superconductors with distinctly improved pinning were prepared by mechanical alloying of Mg and B powders at ambient temperatures followed by hot pressing. The nanocrystalline samples reveal high jc = 105 A/cm2 at 20 K and 1 T together with an irreversibility line strongly shifted towards higher fields resulting in Hirr(T) ∼ 0.8 Hc2(T), whereas typically Hirr(T) ∼ 0.5 Hc2(T) is observed for untextured bulk samples. These values exceed those of all other reported bulk samples and are in the range of values for thin films. The improved pinning of this material, which mainly consists of spherical grains about 40–100 nm in size, is attributed to the large number of grain boundaries in the nanocrystalline state. © 2002 American Institute of Physics.
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74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)
61.46.-w Structure of nanoscale materials
81.07.Bc Nanocrystalline materials
74.25.Sv Critical currents
74.72.-h Cuprate superconductors
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation
81.07.Wx Nanopowders
61.72.Mm Grain and twin boundaries
74.25.Ha Magnetic properties including vortex structures and related phenomena
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Structural and morphologic evolution of Pt/Ba0.7Sr0.3TiO3/Pt capacitors with annealing processes

Y. L. Qin, C. L. Jia, K. Urban, R. Liedtke, and R. Waser

Appl. Phys. Lett. 80, 2728 (2002); http://dx.doi.org/10.1063/1.1469683 (3 pages) | Cited 10 times

Online Publication Date: 10 April 2002

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The microstructure and chemistry of the as-grown, the postannealed and the forming-gas-atmosphere-treated Pt/Ba0.7Sr0.3TiO3/Pt capacitors are studied by means of high-resolution transmission electron microscopy and energy-disperse x-ray spectroscopy. It is found that the annealed Ba0.7Sr0.3TiO3 films have larger grain size and more smooth top film-electrode interfaces. High-resolution images reveal the presence of disordered or amorphous regions at the interfaces in the Ba0.7Sr0.3TiO3 film heated in the forming-gas atmosphere. These regions show a higher Ti/(Ba+Sr) ratio than the grain matrix. The effects of these amorphous regions on the electrical properties of Ba0.7Sr0.3TiO3 films are discussed. © 2002 American Institute of Physics.
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85.50.-n Dielectric, ferroelectric, and piezoelectric devices
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
84.32.Tt Capacitors
68.55.-a Thin film structure and morphology
68.35.Ct Interface structure and roughness
77.55.-g Dielectric thin films
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
68.37.Lp Transmission electron microscopy (TEM)

Phase transition at low temperature in NaNbO3 ceramic

S. Lanfredi, M. H. Lente, and J. A. Eiras

Appl. Phys. Lett. 80, 2731 (2002); http://dx.doi.org/10.1063/1.1470260 (3 pages) | Cited 27 times

Online Publication Date: 10 April 2002

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The electric permittivity of the sodium niobate ceramic was investigated in the temperature range from 15 up to 900 K, at frequencies from 100 Hz to 1 MHz. Three anomalies were found in the permittivity curve. A phase transition for NaNbO3 was assigned to anomaly at around 280 K, while other two ones have previously been reported. In addition, the dielectric permittivity dependence with the temperature and frequency, at temperatures lower than 400 K, showed two regions with typical characteristics of a relaxor ferroelectric materials. © 2002 American Institute of Physics.
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77.80.B- Phase transitions and Curie point
77.22.Ch Permittivity (dielectric function)
77.22.Gm Dielectric loss and relaxation

Improvement in electrical insulating properties of 10-nm-thick Al2O3 film grown on Al/TiN/Si substrate by remote plasma annealing at low temperatures

Jihoon Kim, Jaewon Song, Ohsung Kwon, Sungkeun Kim, Cheol Seong Hwang, Sang-Hee’Ko Park, Sun Jin Yun, Jaehack Jeong, and Kwang Soo Hyun

Appl. Phys. Lett. 80, 2734 (2002); http://dx.doi.org/10.1063/1.1468916 (3 pages) | Cited 10 times

Online Publication Date: 10 April 2002

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The electrical conduction properties of 10-nm-thick atomic-layer deposited Al2O3 thin films with Al bottom and Pt top electrodes were characterized for use in field emission display. The as-deposited films, grown at 300 °C, exhibited such a high electrical leakage that their electrical properties could not be measured. However, post-treatment at 300 °C under a remote O2 or H2O plasma for 30 min improved the insulating properties of the Al2O3 films. However, the electrical conduction mechanism, particularly in the high field (>4 MV/cm) was not Fowler–Nordheim (F–N) tunneling but was influenced by space charge limited conduction implying that there were many traps inside the dielectric film or the electrode interfaces. Postannealing of the top electrode at 300 °C in an oxygen atmosphere resulted in a F–N conduction mechanism by removing the interfacial traps. The calculated barrier height at the Al/Al2O3 interface from the F–N fitting of the current density versus voltage curves using the electron effective mass (m∗) of 0.5 m0 was approximately 2.0 eV. © 2002 American Institute of Physics.
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73.61.Ng Insulators
77.22.Jp Dielectric breakdown and space-charge effects
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
73.40.Ns Metal-nonmetal contacts
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
85.45.Fd Field emission displays (FEDs)
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
61.72.Cc Kinetics of defect formation and annealing
73.50.Fq High-field and nonlinear effects
73.20.Hb Impurity and defect levels; energy states of adsorbed species
77.55.-g Dielectric thin films

Effect of annealing on the dielectric parameters of ferroelectric TSiKN65

Devanand Shenoy, Antonio Lavarello, Jawad Naciri, and Ranganathan Shashidhar

Appl. Phys. Lett. 80, 2737 (2002); http://dx.doi.org/10.1063/1.1470245 (3 pages) | Cited 2 times

Online Publication Date: 10 April 2002

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The ionic conductivity of ferroelectric liquid crystals used for pyroelectric detection is a measure of the noise contribution to the output of the device. This is obtained from a measurement of the dielectric loss of the liquid crystal material. An annealing procedure has been developed that reduces the ionic conductivity and hence the dielectric loss significantly. The procedure consists of subjecting the ferroelectric liquid crystal sample to an electric field in the isotropic phase and cooling it into the smectic phase at a certain rate. After measurement of the dielectric parameters, the sample is reheated into the isotropic phase and then cooled again at a slower rate into the smectic phase. The dielectric measurements are repeated again. The entire process is repeated for successively slower cooling rates. We present the results of the effect of this annealing treatment on the dielectric parameters and explain the origin of this phenomenon.
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61.30.Gd Orientational order of liquid crystals; electric and magnetic field effects on order
77.80.-e Ferroelectricity and antiferroelectricity
77.84.Nh Liquids, emulsions, and suspensions; liquid crystals
66.10.Ed Ionic conduction
77.22.Gm Dielectric loss and relaxation

Coercive fields in ferroelectrics: A case study in lithium niobate and lithium tantalate

Sungwon Kim, Venkatraman Gopalan, and Alexei Gruverman

Appl. Phys. Lett. 80, 2740 (2002); http://dx.doi.org/10.1063/1.1470247 (3 pages) | Cited 39 times

Online Publication Date: 10 April 2002

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The experimentally measured coercive electric fields for domain reversal in ferroelectrics are typically many orders of magnitude lower than the estimates from phenomenological free-energy theory. This letter specifically investigates the influence of polarization gradients at pre-existing 180° domain walls in ferroelectrics on coercive fields for domain wall motion. It is shown that the ratio of theoretical coercive field without and with a preexisting domain wall is directly proportional to the ratio xo/a, where a is the lattice parameter and 2xo is the polarization wall width. This factor is 7.5–45 for a 20–120 nm wall width, the latter width determined here as the experimental upper limit for polarization wall width in lithium tantalate. © 2002 American Institute of Physics.
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77.80.Dj Domain structure; hysteresis
77.22.Ej Polarization and depolarization
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates

Exoelectron emission spectroscopy of silicon nitride thin films

G. Rosenman, M. Naich, M. Molotskii, Yu. Dechtiar, and V. Noskov

Appl. Phys. Lett. 80, 2743 (2002); http://dx.doi.org/10.1063/1.1469656 (3 pages) | Cited 7 times

Online Publication Date: 10 April 2002

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Thermally stimulated exoelectron emission method is applied to amorphous silicon nitride (α-Si3N4) thin insulating films in the temperature region (300–550) K for energy spectroscopy of electronic states. The measured spectrum of electron (hole) traps is in good agreement with the known data obtained by other methods. The experimental data are interpreted on the basis of the model of electron-hole recombination in the two-center Auger process. © 2002 American Institute of Physics.
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79.75.+g Exoelectron emission
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
73.20.At Surface states, band structure, electron density of states
79.20.Fv Electron impact: Auger emission

Large remanent polarization of (Bi,Nd)4Ti3O12 epitaxial thin films grown by metalorganic chemical vapor deposition

Takashi Kojima, Tomohiro Sakai, Takayuki Watanabe, Hiroshi Funakubo, Keisuke Saito, and Minoru Osada

Appl. Phys. Lett. 80, 2746 (2002); http://dx.doi.org/10.1063/1.1468914 (3 pages) | Cited 156 times

Online Publication Date: 10 April 2002

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(104)-oriented Bi4Ti3O12, La-substituted Bi4Ti3O12[(Bi3.44La0.56)Ti3O12] and Nd-substituted Bi4Ti3O12[(Bi3.54Nd0.46)Ti3O12] films were epitaxially grown on (111)SrRuO3//(111)SrTiO3 substrates at 700 °C by metalorganic chemical vapor deposition. All deposited films showed strong (104) orientations. The values of the remanent polarization (Pr) and coercive field (Ec) of the (104)-oriented epitaxial (Bi3.54Nd0.46)Ti3O12 thin film were 25 μC/cm2 and 135 kV/cm, respectively. This Pr value was larger than that of the (104)-oriented (Bi3.44La0.56)Ti3O12 film: Pr and Ec values of the (Bi3.44La0.56)Ti3O12 were 17 μC/cm2 and 145 kV/cm, respectively. These good ferroelectric properties of (Bi3.54Nd0.46)Ti3O12 films can be explained by a large tilting of TiO6 octahedra induced by the substitution of Nd3+, the ionic radius of which is smaller than that of La3+. Moreover, this Pr value is almost equal to that of commercially used lead zirconate titanate (PZT) films for nonvolatile ferroelectric random access memory (FeRAM) applications. These (104)-oriented epitaxial (Bi3.54Nd0.46)Ti3O12 thin films also showed a fatigue-free character. As a result, lead-free Nd-substituted Bi4Ti3O12 films with good ferroelectric properties comparable with those of PZT films are useful candidates for FeRAM applications. © 2002 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
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
77.22.Ej Polarization and depolarization
68.55.-a Thin film structure and morphology
77.80.Dj Domain structure; hysteresis

Measurement of barrier heights in high permittivity gate dielectric films

S. Zafar, E. Cartier, and E. P. Gusev

Appl. Phys. Lett. 80, 2749 (2002); http://dx.doi.org/10.1063/1.1468915 (3 pages) | Cited 16 times

Online Publication Date: 10 April 2002

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Based on theoretical studies of tunneling current phenomenon, a method for measuring barrier heights in metal–oxide–semiconductor structures is illustrated. Using this method, barrier heights associated with the Al2O3 gate dielectric films are investigated. Also, the main conduction mechanism in Al2O3 gate dielectric films is identified to be tunneling. © 2002 American Institute of Physics.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
73.40.Gk Tunneling
73.30.+y Surface double layers, Schottky barriers, and work functions
73.61.Ng Insulators
77.22.Ch Permittivity (dielectric function)
77.55.-g Dielectric thin films
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
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Growth mechanism of carbon nanotube forests by chemical vapor deposition

Oleg A. Louchev, Yoichiro Sato, and Hisao Kanda

Appl. Phys. Lett. 80, 2752 (2002); http://dx.doi.org/10.1063/1.1468266 (3 pages) | Cited 40 times

Online Publication Date: 10 April 2002

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Analysis of kinetics processes involved in carbon nanotube (NT) forest growth during chemical vapor deposition suggests that: (i) carbon species are unable to penetrate to the forest bottom whenever the mean free path in gas is much larger than the typical distance between NTs; instead they collide with NT surfaces, chemisorbing within the top few microns, diffuse along the surface, and feed the growth at nanotube tips, (ii) wherever a catalyst nanoparticle is present, at the substrate or on the nanotube tip, in the postnucleation stage its role in feeding NT growth by C dissolution and bulk diffusion is negligibly small in comparison with the surface diffusion of C species adsorbing on the lateral surface of nanotubes, and (iii) bulk diffusion of C through the catalyst nanoparticle, defining the characteristic times of C penetration to nanoparticle base and surface saturation with C, is shown to play a major role in selection of the initial mode of nanotube nucleation and growth. © 2002 American Institute of Physics.
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81.07.De Nanotubes
82.33.Ya Chemistry of MOCVD and other vapor deposition methods
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.16.Hc Catalytic methods
66.30.Pa Diffusion in nanoscale solids
68.43.Jk Diffusion of adsorbates, kinetics of coarsening and aggregation
68.43.Mn Adsorption kinetics

Interband transition distributions in the optical spectra of InAs/GaAs self-assembled quantum dots

Weidong Sheng and Jean-Pierre Leburton

Appl. Phys. Lett. 80, 2755 (2002); http://dx.doi.org/10.1063/1.1469214 (3 pages) | Cited 24 times

Online Publication Date: 10 April 2002

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The interband optical spectra of InAs/GaAs self-assembled quantum dots (SAD) are investigated with a three-dimensional eight-band k⋅p technique involving strain and piezoelectric effect. We show that the separation between hole states contributes to a significant fraction of the interband transition energy, thereby invalidating the two-dimensional harmonic oscillator model for the electronic structures of SADs. Moreover, aside from the threshold low energy peak which results from the strong ground state electron–hole transition, the major photoluminescence peaks observed experimentally are made of a significant number of equal-strength optical transitions. © 2002 American Institute of Physics.
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78.67.Hc Quantum dots
73.21.La Quantum dots
78.55.Cr III-V semiconductors
71.15.-m Methods of electronic structure calculations
77.65.-j Piezoelectricity and electromechanical effects

The role of p-type doping and the density of states on the modulation response of quantum dot lasers

O. B. Shchekin and D. G. Deppe

Appl. Phys. Lett. 80, 2758 (2002); http://dx.doi.org/10.1063/1.1469212 (3 pages) | Cited 56 times

Online Publication Date: 10 April 2002

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The modulation response of quantum dot (QD) lasers is analyzed using a quasi-equilibrium approach. The model suggests that present QD lasers are limited due to hole levels that are closely spaced in energy, as well as inhomogeneous broadening. Significant improvements are predicted through p-type modulation doping. The results are consistent with present QD lasers being limited in their modulation response by their differential gain as opposed to carrier capture. © 2002 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
42.60.By Design of specific laser systems
42.55.Ah General laser theory
68.65.Hb Quantum dots (patterned in quantum wells)
73.21.La Quantum dots
78.67.Hc Quantum dots
61.72.up Other materials
85.30.De Semiconductor-device characterization, design, and modeling

An approach to transport measurements of electronic molecules

Islamshah Amlani, Adam M. Rawlett, Larry A. Nagahara, and Raymond K. Tsui

Appl. Phys. Lett. 80, 2761 (2002); http://dx.doi.org/10.1063/1.1469655 (3 pages) | Cited 62 times

Online Publication Date: 10 April 2002

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We present a hybrid assembly technique to facilitate the transport measurements of electronic molecules. The technique consists of forming a self-assembled monolayer of the investigated molecule on prepatterned electrodes and then bridging the electrodes with nanoparticles using an alternating electric field. This technique can potentially provide a quick and simple way to screen a large number of electronic molecules. As an example, we report preliminary transport measurements of 1-nitro-2,5-di(phenylethynyl-4*-thioacetyl)benzene as a test molecule. The data show qualitative agreement with previously published results for a similar molecule. © 2002 American Institute of Physics.
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73.61.Ph Polymers; organic compounds
85.65.+h Molecular electronic devices
81.16.Dn Self-assembly

Nanoelectronic devices with reactively fabricated semiconductor

Jooho Kim, Hiro Akinaga, Nobufumi Atoda, and Junji Tominaga

Appl. Phys. Lett. 80, 2764 (2002); http://dx.doi.org/10.1063/1.1470711 (3 pages) | Cited 3 times

Online Publication Date: 10 April 2002

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The economic fabrication of complete circuits at the nanometer level remains challenging because of the difficulty of connecting nanodevices to one another. Here, we report the electronic nanodevices fabrication method based on the Hall effect including the connection through a thermally activated reaction. By combining incident current and external perpendicular magnetic field in the reactively fabricated memory cell, electronic signal is put in storage. It is suggested that 2.5×109–2.5×1011 (2.5 G–250 G) bits/in.2 capacity flash memory or dynamic random access memory can be fabricated by means of the nanosecond pulse laser or electron-beam-induced reaction. © 2002 American Institute of Physics.
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85.35.-p Nanoelectronic devices
81.16.-c Methods of micro- and nanofabrication and processing
81.07.Nb Molecular nanostructures
85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology
81.05.Dz II-VI semiconductors
66.30.Ny Chemical interdiffusion; diffusion barriers
85.65.+h Molecular electronic devices
85.30.-z Semiconductor devices

Carbon nanotube composites for thermal management

M. J. Biercuk, M. C. Llaguno, M. Radosavljevic, J. K. Hyun, A. T. Johnson, and J. E. Fischer

Appl. Phys. Lett. 80, 2767 (2002); http://dx.doi.org/10.1063/1.1469696 (3 pages) | Cited 469 times

Online Publication Date: 10 April 2002

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Single-wall carbon nanotubes (SWNTs) were used to augment the thermal transport properties of industrial epoxy. Samples loaded with 1 wt % unpurified SWNT material showed a 70% increase in thermal conductivity at 40 K, rising to 125% at room temperature; the enhancement due to 1 wt % loading of vapor grown carbon fibers was three times smaller. Electrical conductivity data showed a percolation threshold between 0.1 and 0.2 wt % SWNT loading. The Vickers hardness rose monotonically with SWNT loading up to a factor of 3.5 at 2 wt %. These results suggest that the thermal and mechanical properties of SWNT-epoxy composites are improved, without the need to chemically functionalize the nanotubes. © 2002 American Institute of Physics.
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65.80.-g Thermal properties of small particles, nanocrystals, nanotubes, and other related systems
62.25.-g Mechanical properties of nanoscale systems
81.05.Qk Reinforced polymers and polymer-based composites
72.80.Tm Composite materials
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.Qp Friction, tribology, and hardness

Intraband-transition-induced dipoles in self-assembled InAs/GaAs(001) quantum dots

Zhonghui Chen, Eui-Tae Kim, and Anupam Madhukar

Appl. Phys. Lett. 80, 2770 (2002); http://dx.doi.org/10.1063/1.1468896 (3 pages) | Cited 8 times

Online Publication Date: 10 April 2002

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We present experimental evidence for the existence and directionality of dipoles induced by intraband transitions from the electron ground states to high, bound excited states in self-assembled InAs/GaAs quantum dots (QDs). Moreover, the orientation of the interband transition induced dipoles is also determined for the same QDs. The findings indicate the potential use of intraband dipoles in asymmetric QDs in proposed quantum gates. © 2002 American Institute of Physics.
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73.21.La Quantum dots
78.67.Hc Quantum dots
71.35.-y Excitons and related phenomena
78.30.Fs III-V and II-VI semiconductors
73.63.Kv Quantum dots
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