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22 Oct 2001

Volume 79, Issue 17, pp. 2681-2850

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Intersubband absorption dynamics in coupled quantum wells

T. Müller, R. Bratschitsch, G. Strasser, and K. Unterrainer

Appl. Phys. Lett. 79, 2755 (2001); http://dx.doi.org/10.1063/1.1413728 (3 pages) | Cited 16 times

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We apply an interband pump/intersubband probe technique to monitor the temporal evolution of the electron population in the first and second subband of an undoped GaAs/AlGaAs asymmetric double quantum well after interband optical excitation. The spacing between the two subbands is smaller than the longitudinal optical phonon energy. The time dependence of the intersubband absorption can be explained by a simple rate equation model. We extract an intersubband lifetime of T21 = 100 ps and a recombination time of τ = 410 ps at an excitation density of nS = 2×1011 cm−2. © 2001 American Institute of Physics.
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73.21.Fg Quantum wells
78.67.De Quantum wells
78.66.Fd III-V semiconductors
73.25.+i Surface conductivity and carrier phenomena
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths

Influence of tensile and compressive strain on the band gap energy of ordered InGaP

J. Novák, S. Hasenöhrl, M. I. Alonso, and M. Garriga

Appl. Phys. Lett. 79, 2758 (2001); http://dx.doi.org/10.1063/1.1413725 (3 pages) | Cited 3 times

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The band gap energy of ordered and strained InxGa1−xP as a function of ternary composition was studied. Epitaxial growth using a metalorganic vapor phase epitaxy technique at a reactor pressure of 20 mbar and Tg = 580 °C allowed us to prepare a set of samples with nearly constant ordering parameter η. Optical measurements were performed at room temperature using a rotating polarizer ellipsometer with a spectral energy range 1.4–5.1 eV. Comparing the experimental data with the theory, we have shown that the band gap energy Eg dependence on composition closely follows the prediction of Wei and Zunger [S. Wei and A. Zunger, Phys. Rev. B 49, 14337 (1994)]. This prediction is more valid as the commonly used parabolic interpolation of Eg between InP and GaP values. © 2001 American Institute of Physics.
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71.20.Nr Semiconductor compounds
68.60.Bs Mechanical and acoustical properties
78.66.Fd III-V semiconductors
78.40.Fy Semiconductors
68.55.-a Thin film structure and morphology
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.05.Ea III-V semiconductors

Reduction of doping and trap concentrations in 4H–SiC epitaxial layers grown by chemical vapor deposition

Tsunenobu Kimoto, Satoshi Nakazawa, Koichi Hashimoto, and Hiroyuki Matsunami

Appl. Phys. Lett. 79, 2761 (2001); http://dx.doi.org/10.1063/1.1413724 (3 pages) | Cited 42 times

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High-purity and thick 4H–SiC(0001) epilayers have been grown by a horizontal hot-wall chemical vapor deposition (CVD) system, which was designed and built at the authors’ group. The background donor concentration has decreased by reducing pressure during CVD, and a low donor concentration of 1–3×1013 cm−3 was achieved by CVD growth at 80 Torr. The free exciton peaks dominated in low- and room-temperature photoluminescence spectra without titanium or point-defect related peaks. The electron mobility reaches 981 cm2/V s at room temperature and 46 200 cm2/V s at 42 K. The total trap concentration could be reduced to 4.7×1011 cm−3 by increasing the input C/Si ratio. © 2001 American Institute of Physics.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.05.Hd Other semiconductors
71.55.Ht Other nonmetals
73.61.Le Other inorganic semiconductors
78.66.Li Other semiconductors
78.55.Hx Other solid inorganic materials
73.50.Dn Low-field transport and mobility; piezoresistance
71.35.Cc Intrinsic properties of excitons; optical absorption spectra

Selective growth of GaN on a SiC substrate patterned with an AlN seed layer by ammonia molecular-beam epitaxy

H. Tang, J. A. Bardwell, J. B. Webb, S. Moisa, J. Fraser, and S. Rolfe

Appl. Phys. Lett. 79, 2764 (2001); http://dx.doi.org/10.1063/1.1413956 (3 pages) | Cited 5 times

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Highly selective growth of GaN on 4H–SiC using the SiC substrate as a pseudomask has been demonstrated using the ammonia molecular-beam-epitaxy technique. A total lack of nucleation on the bare SiC surface was observed under typical GaN growth conditions. The nucleation of the GaN layer occurred preferentially from a patterned thin (300 Å) AlN seed layer, which had been predeposited on the SiC surface using the magnetron-sputter-epitaxy technique and patterned into parallel stripes by photolithography and chemically assisted ion-beam etching. Evidence of lateral overgrowth was observed by scanning electron microscopy and x-ray diffraction studies. The GaN stripes grown show extremely smooth side facets due to the lateral growth. © 2001 American Institute of Physics.
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81.05.Ea III-V semiconductors
68.55.A- Nucleation and growth
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.65.Cf Surface cleaning, etching, patterning
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Single-crystalline superconducting thin films of electron-doped infinite-layer compounds grown by molecular-beam epitaxy

Shin-ichi Karimoto, Kenji Ueda, Michio Naito, and Tadayuki Imai

Appl. Phys. Lett. 79, 2767 (2001); http://dx.doi.org/10.1063/1.1410872 (3 pages) | Cited 18 times

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Single-crystalline Sr1−xLaxCuO2 thin films of electron-doped infinite-layer compounds were grown by molecular-beam epitaxy. Crucial to our success was the use of KTaO3 substrates. The best film showed Tconset = 41.5 K and Tczero = 39.0 K, which is close to the highest Tconset of 43 K for the bulk value. The resistivity of the optimum-doped film exhibited metallic temperature dependence with a low resistivity of 320 μΩ cm at room temperature and 120 μΩ cm just above Tc. © 2001 American Institute of Physics.
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74.72.-h Cuprate superconductors
74.78.-w Superconducting films and low-dimensional structures
74.25.F- Transport properties
74.62.Bf Effects of material synthesis, crystal structure, and chemical composition
68.55.-a Thin film structure and morphology
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy

Pulse-induced switches in a Josephson tunnel stacked device

G. P. Pepe, G. Peluso, M. Valentino, A. Barone, L. Parlato, E. Esposito, C. Granata, M. Russo, C. De Leo, and G. Rotoli

Appl. Phys. Lett. 79, 2770 (2001); http://dx.doi.org/10.1063/1.1402652 (3 pages) | Cited 3 times

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Pulse-activated transitions from the metastable to the running state and vice versa have been observed in a stacked double tunnel Nb-based Josephson system. Experimental results are compared with numerical simulations based on the Sine–Gordon model of the stacked junctions by injecting pulses with variable amplitude in one of the junctions of the stack, and observing the voltage response of the other junction. Both experimental and numerical results show the possibility to induce both direct and back-switching transitions from the metastable to the running state simply by changing the amplitude of the electronic pulses injected across the stack device. © 2001 American Institute of Physics.
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85.25.Cp Josephson devices
74.50.+r Tunneling phenomena; Josephson effects
74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)
74.45.+c Proximity effects; Andreev reflection; SN and SNS junctions
74.40.-n Fluctuation phenomena

Micromagnetic structure images taken using platinum coated tips

O. Teschke

Appl. Phys. Lett. 79, 2773 (2001); http://dx.doi.org/10.1063/1.1413730 (3 pages) | Cited 2 times

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We report on magnetic force microscopy images of data tracks written in recording media taken using Pt-coated tips. The force acting on the tip when immersed in the magnetic field of the substrate was modeled assuming diamagnetic and paramagnetic interactions. The sample scanning using Pt-coated tips shows an improvement in the image delineation of the magnetic field distribution compared to the images taken using Co-coated hard magnetic tips and the display of at least a twice higher data track density. © 2001 American Institute of Physics.
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75.50.Ss Magnetic recording materials
68.37.Rt Magnetic force microscopy (MFM)
07.05.Pj Image processing
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.70.Ak Magnetic properties of monolayers and thin films

Room-temperature ferromagnetism in zincblende CrSb grown by molecular-beam epitaxy

J. H. Zhao, F. Matsukura, K. Takamura, E. Abe, D. Chiba, and H. Ohno

Appl. Phys. Lett. 79, 2776 (2001); http://dx.doi.org/10.1063/1.1413732 (3 pages) | Cited 113 times

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Thin films of CrSb grown by solid-source molecular-beam epitaxy on GaAs, (Al, Ga)Sb, and GaSb are found to exhibit ferromagnetism. Reflection high-energy electron diffraction and high-resolution cross sectional transmission electron microscopy both indicate that the structure is zincblende. Temperature dependence of remanent magnetization shows that the ferromagnetic transition temperature is beyond 400 K. © 2001 American Institute of Physics.
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75.50.Pp Magnetic semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
75.70.Ak Magnetic properties of monolayers and thin films
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Anisotropy of superconductivity from MgB2 single crystals

M. Xu, H. Kitazawa, Y. Takano, J. Ye, K. Nishida, H. Abe, A. Matsushita, N. Tsujii, and G. Kido

Appl. Phys. Lett. 79, 2779 (2001); http://dx.doi.org/10.1063/1.1413729 (3 pages) | Cited 106 times

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Magnesium diboride (MgB2) single crystals, with a maximum size of 0.5×0.5×0.02 mm3, were grown by the vapor transport method in a sealed molybdenum crucible. A superconducting transition with the onset temperature of 38.6 K was confirmed by both transport and magnetization measurements. The upper critical field anisotropy ratio, Hc2∥ab(0)/Hc2∥c(0), was estimated to be 2.6 from the magnetic field-temperature phase diagram for MgB2 single crystals. © 2001 American Institute of Physics.
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74.72.-h Cuprate superconductors
74.62.Bf Effects of material synthesis, crystal structure, and chemical composition
74.25.Op Mixed states, critical fields, and surface sheaths
74.25.Ha Magnetic properties including vortex structures and related phenomena
81.10.Fq Growth from melts; zone melting and refining
74.25.Dw Superconductivity phase diagrams
74.25.F- Transport properties

Ion-beam-assisted growth of CoPt3 films

D. Vasumathi, B. B. Maranville, and F. Hellman

Appl. Phys. Lett. 79, 2782 (2001); http://dx.doi.org/10.1063/1.1412430 (3 pages) | Cited 1 time

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CoPt3 films are known to exhibit room-temperature perpendicular magnetic anisotropy when grown between 200 °C–400 °C. We have used Ar ion-beam-assisted growth of CoPt3 films in an effort to enhance the anisotropy and also lower the temperature range where it occurs. We present a systematic study of the dependence of magnetic properties of the films on substrate temperature during growth, ion beam energy, and ion to atom arrival ratio, R, at the substrate. We find a significant increase of the anisotropy in films grown at 100 °C compared to the R = 0 value resulting in perpendicular anisotropy at moderate growth temperatures. At 250 °C and 400 °C, however, there is a monotonic decrease in anisotropy with R for all energies. © 2001 American Institute of Physics.
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81.15.Jj Ion and electron beam-assisted deposition; ion plating
75.70.Ak Magnetic properties of monolayers and thin films
68.55.A- Nucleation and growth
81.05.Bx Metals, semimetals, and alloys
75.30.Gw Magnetic anisotropy
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Defect-modified exchange bias

Joo-Von Kim and R. L. Stamps

Appl. Phys. Lett. 79, 2785 (2001); http://dx.doi.org/10.1063/1.1413731 (3 pages) | Cited 17 times

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The influence of local defects in exchange biased ferromagnetic/antiferromagnetic bilayers is studied using numerical simulations. The location of defects relative to the interface is found to be the main factor determining the magnitude of coercive and bias field modifications. One consequence is that some types of defects control stability of partial wall structures. This may explain coercivity enhancement as arising from irreversible pinning of partial domain walls in the antiferromagnet. © 2001 American Institute of Physics.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.30.Et Exchange and superexchange interactions
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
73.20.Hb Impurity and defect levels; energy states of adsorbed species
75.40.Mg Numerical simulation studies
75.60.Ch Domain walls and domain structure
75.70.Kw Domain structure (including magnetic bubbles and vortices)

Switch-free read operation design and measurement of magnetic tunnel junction magnetic random access memory arrays

Yuankai Zheng, Xiaoyan Wang, Dan You, and Yihong Wu

Appl. Phys. Lett. 79, 2788 (2001); http://dx.doi.org/10.1063/1.1410875 (3 pages) | Cited 1 time

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A switch-free read operation design and cell measurement method for magnetic tunnel junction magnetic random access memory arrays with a peripheral circuitry is presented. The design effectively reduces the shunting effect and maintains the signal at the original level even for the cases when the lead resistance cannot be neglected. It also allowed us to measure the magnetoresistance curve of each cell independently without the need of a transistor or a diode. Both simulation and experiments showed that this method is useful in the readout operation of the tunnel junction magnetic random access memory as well as in the characterization of its individual cells. © 2001 American Institute of Physics.
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85.75.Dd Magnetic memory using magnetic tunnel junctions
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Crystal and electronic structures of Bi4−xLaxTi3O12 ferroelectric materials

Y. Shimakawa, Y. Kubo, Y. Tauchi, H. Asano, T. Kamiyama, F. Izumi, and Z. Hiroi

Appl. Phys. Lett. 79, 2791 (2001); http://dx.doi.org/10.1063/1.1410877 (3 pages) | Cited 149 times

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The crystal structures of Bi4Ti3O12 and Bi3.25La0.75Ti3O12 were refined by neutron powder diffraction. Large structural distortions were revealed, and ferroelectric polarizations along the a and c axes were calculated from the displacements of the constituent ions. In Bi3.25La0.75Ti3O12, La atoms substitute for Bi atoms in a perovskite-type unit only, and the substitution causes less distortion of the structure, resulting in smaller spontaneous polarization and lower ferroelectric Curie temperature. Electronic-structure calculations revealed that covalent interaction, which originates from the strong hybridization between Ti 3d and O 2p orbitals, plays an important role in the structural distortion and ferroelectricity of the materials. Changes in ceramic-sample density with sintering temperature give information concerning device fabrication temperature; that is, substituting La for Bi atoms appears to “increase” the synthesis temperature of the Bi4Ti3O12 and Bi3.25La0.75Ti3O12 systems. © 2001 American Institute of Physics.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
61.66.Fn Inorganic compounds
77.80.B- Phase transitions and Curie point
71.20.Ps Other inorganic compounds
81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation
77.22.Ej Polarization and depolarization

Ultrasonic characterization of poling in lead zirconate titanate ceramics

James Friend, Eric Jamieson, Marvin Pennell, and Wayne Huebner

Appl. Phys. Lett. 79, 2794 (2001); http://dx.doi.org/10.1063/1.1412595 (3 pages) | Cited 3 times

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A method for measuring the spatial variation of the macroscopic poling state of a piezoelectric material using an ultrasonic transducer is described. The relatively simple method clearly indicates the distribution of poling within the material, demonstrated by the testing of a collection of partially poled lead zirconate titanate samples. © 2001 American Institute of Physics.
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77.65.-j Piezoelectricity and electromechanical effects
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.22.Ej Polarization and depolarization
62.65.+k Acoustical properties of solids

Photovoltaic response and dielectric properties of epitaxial anatase-TiO2 films grown on conductive La0.5Sr0.5CoO3 electrodes

B. H. Park, L. S. Li, B. J. Gibbons, J. Y. Huang, and Q. X. Jia

Appl. Phys. Lett. 79, 2797 (2001); http://dx.doi.org/10.1063/1.1412822 (3 pages) | Cited 13 times

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We have grown epitaxial anatase-TiO2 (001) films on La0.5Sr0.5CoO3 (001) bottom electrodes using pulsed-laser deposition. The small lattice mismatch (0.5%) between the anatase-TiO2 and the La0.5Sr0.5CoO3 makes it possible to grow anatase-TiO2 films with excellent crystallinity on conductive metal oxides. The photovoltaic properties of the epitaxial anatase-TiO2 on the La0.5Sr0.5CoO3 were characterized using a Kelvin probe. The optical band-gap energy was found to be 3.05 eV. The dielectric properties of the epitaxial anatase-TiO2 films were characterized using a capacitor structure of Au/anatase-TiO2/La0.5Sr0.5CoO3 on a LaAlO3 substrate. The dielectric dispersion exhibited a power-law dependence, and the dielectric constant measured at room temperature and 1 MHz was 38. © 2001 American Institute of Physics.
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73.61.Le Other inorganic semiconductors
81.15.Fg Pulsed laser ablation deposition
77.22.Ch Permittivity (dielectric function)
73.50.Pz Photoconduction and photovoltaic effects
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.66.Li Other semiconductors

Field-induced sharp ferroelectric phase transition in Sr0.66Ba0.34Nb2O6 relaxor ferroelectric

I. A. Santos, D. Garcia, J. A. Eiras, E. R. Manoel, and A. C. Hernandes

Appl. Phys. Lett. 79, 2800 (2001); http://dx.doi.org/10.1063/1.1413727 (3 pages) | Cited 8 times

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Field-induced sharp ferroelectric phase transition was observed in Sr0.66Ba0.34Nb2O6 single crystals. The peaks of the real and imaginary parts of dielectric permittivity arise upon cooling under weak dc bias electric fields and subsequently heating under zero fields or upon cooling under zero fields and subsequently heating under weak electric fields. The applied electric field cancels the random fields that destroy the phase transition and give rise to low temperature domain state if E = 0. These results strongly suggest that the SBN system belongs to the random field Ising universality class, a rare case among structural phase transitions. © 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.B- Phase transitions and Curie point
77.22.Ch Permittivity (dielectric function)
77.22.Gm Dielectric loss and relaxation

Temperature dependence of gate currents in thin Ta2O5 and TiO2 films

Z. J. Luo, Xin Guo, T. P. Ma, and T. Tamagawa

Appl. Phys. Lett. 79, 2803 (2001); http://dx.doi.org/10.1063/1.1412823 (2 pages) | Cited 17 times

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This letter reports our study of the temperature dependence of gate currents in thin Ta2O5 and TiO2 films. The study was conducted (1) to study the conduction mechanisms and band alignments, and (2) to determine whether the gate leakage current is tolerable at high temperatures for either of these high-dielectric-constant (high-k) oxides. The I–V characteristics of these oxides were measured and analyzed over a wide temperature range from 25 to 400 °C. Currents in Ta2O5 samples exhibited stronger temperature dependence than those in TiO2 samples, especially at high fields, mainly due to a much smaller electron barrier height of Ta2O5 over Si (0.28 eV) than that of TiO2 over Si (0.9 eV). © 2001 American Institute of Physics.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
73.61.Ng Insulators
84.32.Tt Capacitors

Control of domain structure of epitaxial PbZr0.2Ti0.8O3 thin films grown on vicinal (001) SrTiO3 substrates

V. Nagarajan, C. S. Ganpule, H. Li, L. Salamanca-Riba, A. L. Roytburd, E. D. Williams, and R. Ramesh

Appl. Phys. Lett. 79, 2805 (2001); http://dx.doi.org/10.1063/1.1402645 (3 pages) | Cited 10 times

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We have investigated the polydomain formation in 100–200-nm-thick PbZr0.2Ti0.8O3 epitaxial thin films on vicinally cut (100) oriented SrTiO3 substrates. Our results show that there is a preferential location of the nucleation of the a domains along the step edges of the underlying substrate. By piezo-response microscopy, we show that all a domains have their polarization aligned along the same direction. This result is in contrast to flat substrates where fourfold symmetry of a domains is observed. We observe that the critical thickness for a domain formation is much lower than that for PbZr0.2Ti0.8O3 films grown on flat substrates. We have developed a model based on minimization of elastic energy to describe the effect of localized stresses at step edges on the formation of a domains in the ferroelectric layer. © 2001 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
81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
77.80.Dj Domain structure; hysteresis
68.55.-a Thin film structure and morphology
68.60.Bs Mechanical and acoustical properties
77.22.Ej Polarization and depolarization
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Nonlinear ground-state absorption observed in a single quantum dot

Evelin Beham, Artur Zrenner, Frank Findeis, Max Bichler, and Gerhard Abstreiter

Appl. Phys. Lett. 79, 2808 (2001); http://dx.doi.org/10.1063/1.1411987 (3 pages) | Cited 23 times

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We report level bleaching in the ground state of a single In0.5Ga0.5As quantum dot. This behavior arises from the nonlinear absorption of a single quantum state. The level bleaching is observed in terms of a saturation of the photocurrent with increasing excitation power under the condition of resonant excitation in the quantum dot ground state. Furthermore, the photocurrent saturation is put down to a fundamental rate equation model. The steady-state solutions are in good agreement with the experimentally observed power dependence of the photocurrent. © 2001 American Institute of Physics.
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73.21.La Quantum dots
78.67.Hc Quantum dots
73.50.Pz Photoconduction and photovoltaic effects
42.50.Md Optical transient phenomena: quantum beats, photon echo, free-induction decay, dephasings and revivals, optical nutation, and self-induced transparency

High-current field emission from a vertically aligned carbon nanotube field emitter array

J. T. L. Thong, C. H. Oon, W. K. Eng, W. D. Zhang, and L. M. Gan

Appl. Phys. Lett. 79, 2811 (2001); http://dx.doi.org/10.1063/1.1412590 (3 pages) | Cited 37 times

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Arrays of vertically aligned carbon nanotubes (CNTs) were grown on a patterned sputtered cobalt film by chemical vapor deposition from ethylenediamine at 900 °C. Each square array comprises a moderate density of nanotubes with an average height of 90 μm covering a total area of 3.6×10−3 cm2. Field emission measurements were carried out on individual arrays at pressures below 10−8 mbar. The spacing between the anode and the top of the CNT array is 935 μm and a total current of 2 mA could be obtained at 2.5 kV. A Fowler–Nordheim plot of the I–V data shows an unusually high field enhancement factor at lower fields. At an average field strength of 1.925 V/μm, the corresponding emission current density is 130 mA/cm2. This emission current was found to be very stable, with short-term fluctuations (5 Hz measurement bandwidth) of no more than ±1.5%, while the current drifted less than 1.5% over a test period of 20 h. © 2001 American Institute of Physics.
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85.45.Db Field emitters and arrays, cold electron emitters
81.07.De Nanotubes
85.35.Kt Nanotube devices
79.70.+q Field emission, ionization, evaporation, and desorption
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Growth and magneto-optical properties of sub 10 nm (Cd, Mn)Se quantum dots

P. R. Kratzert, J. Puls, M. Rabe, and F. Henneberger

Appl. Phys. Lett. 79, 2814 (2001); http://dx.doi.org/10.1063/1.1413735 (3 pages) | Cited 25 times

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We report on the formation of self-assembled semimagnetic (Cd, Mn)Se quantum dots via thermally activated reorganization of an initially two-dimensional film. Incorporation of Mn causes a marked decrease of the dot density, while the size is only slightly affected. Magneto-optical data are consistent with a homogeneous distribution of the magnetic ions. We observe g factors as large as 200, enabling control of individual carrier spins on a sub 10 nm length scale. © 2001 American Institute of Physics.
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75.50.Pp Magnetic semiconductors
68.65.Hb Quantum dots (patterned in quantum wells)
78.67.Hc Quantum dots
81.07.Ta Quantum dots
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
78.20.Ls Magneto-optical effects

Self-assembled epitaxial and polycrystalline magnetic nickel nanocrystallites

D. Kumar, H. Zhou, T. K. Nath, Alex V. Kvit, and J. Narayan

Appl. Phys. Lett. 79, 2817 (2001); http://dx.doi.org/10.1063/1.1412428 (3 pages) | Cited 17 times

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Nanocrystalline nickel particles were embedded in amorphous alumina and crystalline TiN matrices using a pulsed-laser deposition process to investigate the effect of texturing on magnetic properties of nickel nanocrystallites. The crystalline quality of both the matrix and magnetic particles were investigated by cross-sectional high-resolution transmission electron microscopy. The embedded Ni nanocrystals were found to be epitaxial in case of TiN matrix and polycrystalline in Al2O3 amorphous matrix. The Ni nanocrystals on TiN/Si grow epitaxially because the TiN acting as a template grows epitaxially on Si substrate via domain epitaxy. On the other hand, Ni nanocrystals in Al2O3 matrix are polycrystalline because of the amorphous nature of the alumina matrix. Magnetization versus temperature measurements have shown that the blocking temperature, above which the samples lose magnetization-field (M–H) hysteretic behavior, of Ni–TiN sample (∼190 K) is significantly higher than that of Ni–Al2O3 sample (∼30 K) with a similar size distribution of embedded magnetic particles. A comparison of the values of coercivity (Hc) of the two samples, measured from M–H data, indicates that epitaxial Ni nanocrystals also exhibit significantly higher coercivity than polycrystalline Ni particles. The high values of TB and Hc of Ni–TiN samples with respect to TB of Ni–Al2O3 samples are believed to be associated with preferred alignment of nanocrystallites. © 2001 American Institute of Physics.
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61.46.-w Structure of nanoscale materials
75.50.Tt Fine-particle systems; nanocrystalline materials
81.07.Bc Nanocrystalline materials
81.16.Dn Self-assembly
68.37.Lp Transmission electron microscopy (TEM)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.70.Ak Magnetic properties of monolayers and thin films

Nanolithography of silicon: An approach for investigating tip-surface interactions during writing

R. D. Ramsier, R. M. Ralich, and S. F. Lyuksyutov

Appl. Phys. Lett. 79, 2820 (2001); http://dx.doi.org/10.1063/1.1413736 (3 pages) | Cited 4 times

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We report an approach for monitoring tip-surface interactions. The approach is based on power spectrum analysis of atomic force microscope (AFM) tip oscillations during scanning probe nanolithography on Si surfaces. A single mode harmonic oscillator model allows us to determine the main characteristics of the AFM tip-surface interaction: the amplitude of oscillation, the resonant frequency, and the damping factor, during the writing process. We measure these quantities in scanning probe anodization versus the bias voltage. By fixing the length of lithographically patterned lines, and the energy deposited into each line, we search for trends which may reveal the major factors controlling the quality of AFM-written nanostructures. Our data are consistent with the concepts that a water meniscus and electrostatic tip-surface interactions dominate contact AFM lithography. © 2001 American Institute of Physics.
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81.05.Cy Elemental semiconductors
81.16.Nd Micro- and nanolithography
07.79.Lh Atomic force microscopes
81.16.Ta Atom manipulation

Quantum waveguide array generator for performing Fourier transforms: Alternate route to quantum computing

R. Akis and D. K. Ferry

Appl. Phys. Lett. 79, 2823 (2001); http://dx.doi.org/10.1063/1.1413500 (3 pages) | Cited 4 times

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Recently, quantum computing has gained attention as a possible means of greatly increasing the speed of certain calculations when compared with traditional, binary computing. A key part of many quantum computing algorithms is the performance of a Fourier transform. In this letter, we propose a quantum waveguide array device that can perform such operations quickly with a parallel approach that uses the analog properties of waves and rather than the qubit concept. © 2001 American Institute of Physics.
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03.67.Lx Quantum computation architectures and implementations
02.30.Nw Fourier analysis
02.30.Uu Integral transforms

Spontaneous formation of ordered indium nanowire array on Si(001)

Jian-Long Li, Xue-Jin Liang, Jin-Feng Jia, Xi Liu, Jun-Zhong Wang, En-Ge Wang, and Qi-Kun Xue

Appl. Phys. Lett. 79, 2826 (2001); http://dx.doi.org/10.1063/1.1413722 (3 pages) | Cited 24 times

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Growth of In on the Si(001)-2×n nanostructured surface is investigated by an in situ scanning tunneling microscope (STM). The deposited In atoms predominantly occupy the normal 2×1 dimer-row structure, and develop into a uniform array of In nanowires at a coverage of ∼0.2 ML. High-resolution STM images show that the In atoms form a stable local 2×2 reconstruction that removes surface Si dangling bonds states and saturates all In valency. Since the dimensions of the Si(001)-2×n vacancy line structure depend on impurity concentrations, this study demonstrates that the 2×n surface can be used for spontaneous fabrication of various metal nanowire arrays. © 2001 American Institute of Physics.
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81.07.Bc Nanocrystalline materials
68.43.Hn Structure of assemblies of adsorbates (two- and three-dimensional clustering)
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
73.20.Hb Impurity and defect levels; energy states of adsorbed species
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.35.Rh Phase transitions and critical phenomena
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