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23 Sep 2002

Volume 81, Issue 13, pp. 2319-2480

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Study of photocurrent characteristics in PbSrSe thin films for infrared detection

H. F. Yang, W. Z. Shen, and Q. J. Pang

Appl. Phys. Lett. 81, 2394 (2002); http://dx.doi.org/10.1063/1.1509474 (3 pages) | Cited 4 times

Online Publication Date: 16 September 2002

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We have carried out a detailed investigation of photocurrent spectra in Pb1−xSrxSe thin films grown by molecular-beam epitaxy on BaF2 substrates with Sr composition from 0.066 to 0.276 under different temperatures from 77 to 300 K. Strong room temperature infrared detection has been demonstrated with the wavelength from 1.0 to 3.1 μm. By employing a diffusion-recombination model to analyze the temperature- and Sr composition-dependent photocurrent, we find that the photocurrent in the investigated PbSrSe thin films is dominated by bulk excitation, recombination, and transport processes. For the application of infrared detection, the optimal thickness for PbSrSe thin films should be less than 2.5 μm. © 2002 American Institute of Physics.
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07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
85.60.Gz Photodetectors (including infrared and CCD detectors)
72.40.+w Photoconduction and photovoltaic effects
73.50.Pz Photoconduction and photovoltaic effects
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
73.61.Ng Insulators

Hydrogen redistribution induced by negative-bias-temperature stress in metal–oxide–silicon diodes

Ziyuan Liu, Shinji Fujieda, Koichi Terashima, Markus Wilde, and Katsuyuki Fukutani

Appl. Phys. Lett. 81, 2397 (2002); http://dx.doi.org/10.1063/1.1508809 (3 pages) | Cited 4 times

Online Publication Date: 16 September 2002

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Poly-Si/SiO2/Si diodes in which oxides were grown thermally under wet oxidation conditions and subsequently treated by a post-oxidation anneal (POA) have been characterized electrically and chemically before and after applying negative-bias-temperature stress (NBTS). It was confirmed that NBTS produces interface states and that POA suppresses the interface state production. Nuclear reaction analysis indicated that NBTS results in hydrogen redistribution within the oxide layer. POA was shown to partly suppress such hydrogen accumulation. Hydrogen is thus clearly shown to influence the stability against NBTS. © 2002 American Institute of Physics.
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85.30.Kk Junction diodes
85.30.De Semiconductor-device characterization, design, and modeling
73.40.Ty Semiconductor-insulator-semiconductor structures
61.72.S- Impurities in crystals
81.65.Mq Oxidation
81.40.Gh Other heat and thermomechanical treatments
73.20.-r Electron states at surfaces and interfaces
68.35.Ct Interface structure and roughness

Energy level alignment at organic/metal interfaces: Dipole and ionization potential

H. Peisert, M. Knupfer, and J. Fink

Appl. Phys. Lett. 81, 2400 (2002); http://dx.doi.org/10.1063/1.1509472 (3 pages) | Cited 65 times

Online Publication Date: 16 September 2002

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We present a systematic study of the energy level alignment at the interfaces between gold and organic semiconductors. It is shown that there are at least two leading contributions to the potential drop (dipole) across the metal/organic interface: A modification of the metal work function due to the adsorption of the organic molecules and a potential change in the organic semiconductor. © 2002 American Institute of Physics.
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73.20.Hb Impurity and defect levels; energy states of adsorbed species
73.30.+y Surface double layers, Schottky barriers, and work functions

Semimetal–semiconductor transition in Bi1−xSbx alloy nanowires and their thermoelectric properties

Yu-Ming Lin, O. Rabin, S. B. Cronin, Jackie Y. Ying, and M. S. Dresselhaus

Appl. Phys. Lett. 81, 2403 (2002); http://dx.doi.org/10.1063/1.1503873 (3 pages) | Cited 51 times

Online Publication Date: 16 September 2002

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The resistivity of Bi1−xSbx nanowire arrays exhibits complex variations as a function of Sb content x and temperature T due to the unique semimetal-to-semiconductor (SM–SC) transition experienced by the nanowires. Seebeck coefficient measurements show enhanced thermopower due to Sb alloying and the reduction in wire diameter. The theoretical model not only explains these transport measurements, but also suggests a useful technique to experimentally determine (i) whether the wire is semimetallic or semiconducting, (ii) the carrier concentration, and (iii) the conditions for the SM–SC transition. © 2002 American Institute of Physics.
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73.63.Bd Nanocrystalline materials
72.60.+g Mixed conductivity and conductivity transitions
61.46.-w Structure of nanoscale materials
72.15.Jf Thermoelectric and thermomagnetic effects
72.20.Pa Thermoelectric and thermomagnetic effects
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Operation of high-temperature superconductor magnetometer with submicrometer bicrystal junctions

M. I. Faley, U. Poppe, K. Urban, V. Yu. Slobodchikov, Yu. V. Maslennikov, A. Gapelyuk, B. Sawitzki, and A. Schirdewan

Appl. Phys. Lett. 81, 2406 (2002); http://dx.doi.org/10.1063/1.1508419 (3 pages) | Cited 9 times

Online Publication Date: 16 September 2002

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We investigated the noise properties of dc superconducting quantum interference device flip-chip magnetometers with submicrometer-wide bicrystal junctions operating at 77.4 K. The noise of the magnetometers with electronics was about 6 fT/√Hz at frequencies above 100 Hz increasing up to about 20 fT/√Hz at 1 Hz. The operation of the magnetometers was characterized in an electronic axial first order gradiometer system, which was employed for biomagnetic measurements. The system demonstrated a gradient resolution of about 1 fT/cm√Hz at 77.4 K and stable operation in a standard magnetically shielded room under clinical conditions. © 2002 American Institute of Physics.
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85.25.Dq Superconducting quantum interference devices (SQUIDs)
07.55.Ge Magnetometers for magnetic field measurements

Thermal energy barrier distribution measurements in perpendicular media

X. W. Wu, H. Zhou, R. J. M. van de Veerdonk, G. Ju, B. Lu, and D. Weller

Appl. Phys. Lett. 81, 2409 (2002); http://dx.doi.org/10.1063/1.1510177 (3 pages) | Cited 6 times

Online Publication Date: 16 September 2002

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dc demagnetized remanent curves at different applied field time durations have been applied to measure the thermal energy barrier distribution of two sets of perpendicular alloy media. Sharrock’s formula is applied at all levels of percentages of magnetization switching. The measured energy barrier distribution width decreases with increasing intergranular exchange coupling and with reducing intergranular magnetostatic interactions. The results agree well with micromagnetic simulations. © 2002 American Institute of Physics.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Ss Magnetic recording materials
75.30.Et Exchange and superexchange interactions

Minor and major-loop studies of magnetic and reversal properties for synthetic antiferromagnetically coupled media

Z. S. Shan, S. S. Malhotra, D. C. Stafford, G. Bertero, and D. Wachenschwanz

Appl. Phys. Lett. 81, 2412 (2002); http://dx.doi.org/10.1063/1.1509864 (3 pages) | Cited 4 times

Online Publication Date: 16 September 2002

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An approach has been developed to determine the magnetic properties for both the top and bottom layers of synthetic antiferromagnetically coupled (SAF) media by measuring the minor and major loops at different H field sweep rates with an alternating gradient force magnetometer. Using this approach, the effects of the bottom layer thickness on the magnetic and thermally activated properties of both the top and bottom layers were investigated systematically. These results are valuable for optimal design of SAF media. © 2002 American Institute of Physics.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.60.Jk Magnetization reversal mechanisms
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Soft anisotropic high magnetization Cu/FeCo films

H. S. Jung, W. D. Doyle, J. E. Wittig, J. F. Al-Sharab, and J. Bentley

Appl. Phys. Lett. 81, 2415 (2002); http://dx.doi.org/10.1063/1.1510163 (3 pages) | Cited 28 times

Online Publication Date: 16 September 2002

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A remarkable reduction in the coercivity Hc of sputtered Fe65Co35 films from 9.6 to 0.7 kA/m was observed using a Cu underlayer as thin as 2.5 nm. The FeCo without Cu exhibited a wide distribution of anisotropy fields up to >80 kA/m while the FeCo with Cu showed a well-defined in-plane uniaxial anisotropy field of 2.3 kA/m up to FeCo thicknesses of at least 1 μm. The saturation magnetostriction was (4.7±0.4)×10−5, independent of Cu thickness while the in-plane tensile stress gradually decreased from 2 to 0.2 GPa as the Cu thickness increased to 10 nm. The Cu changed the preferred orientation of the FeCo from (100) to (110) but more significantly reduced the average grain size from ∼ 50 to ∼9 nm. This alone is sufficient to explain quantitatively the reduction in Hc using Hoffmann’s ripple theory. © 2002 American Institute of Physics.
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75.70.Ak Magnetic properties of monolayers and thin films
75.50.Vv High coercivity materials
75.50.Bb Fe and its alloys
75.30.Gw Magnetic anisotropy
75.80.+q Magnetomechanical effects, magnetostriction

Room-temperature magnetism in Cr-doped AlN semiconductor films

S. G. Yang, A. B. Pakhomov, S. T. Hung, and C. Y. Wong

Appl. Phys. Lett. 81, 2418 (2002); http://dx.doi.org/10.1063/1.1509475 (3 pages) | Cited 81 times

Online Publication Date: 16 September 2002

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Synthesis and characterization of magnetic semiconductors Al1−xCrxN, in which the atomic fraction of chromium x is up to 0.357, are reported. The films, grown by reactive co-sputtering on silicon, glass, and kapton substrates, have a crystal structure of aluminum nitride. Magnetic and transport properties were studied in the temperature range of 50 to 340 K. The materials are in the dielectric regime and have variable-range-hopping type of conductance. The films are ferromagnetic at temperatures over 340 K. © 2002 American Institute of Physics.
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75.70.Ak Magnetic properties of monolayers and thin films
73.61.Ey III-V semiconductors
75.50.Pp Magnetic semiconductors
81.15.Cd Deposition by sputtering
75.50.Dd Nonmetallic ferromagnetic materials
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
73.50.Dn Low-field transport and mobility; piezoresistance

Formation of Co nanoclusters in epitaxial Ti0.96Co0.04O2 thin films and their ferromagnetism

D. H. Kim, J. S. Yang, K. W. Lee, S. D. Bu, T. W. Noh, S.-J. Oh, Y.-W. Kim, J.-S. Chung, H. Tanaka, H. Y. Lee, and T. Kawai

Appl. Phys. Lett. 81, 2421 (2002); http://dx.doi.org/10.1063/1.1509477 (3 pages) | Cited 113 times

Online Publication Date: 16 September 2002

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Anatase Ti0.96Co0.04O2 films were grown epitaxially on SrTiO3 (001) substrates by using pulsed laser deposition with in-situ reflection high-energy electron diffraction. The oxygen partial pressure, PO2, during the growth was systematically varied. As PO2 decreased, the growth behavior was changed from a two-dimensional layer-by-layer-like growth to a three-dimensional island-like one, which resulted in an increase in the saturation magnetization. These structural and magnetic changes were explained in terms of the formation of cobalt clusters whose existence was proved by transmission-electron-microscope studies. Our work clearly indicates that the cobalt clustering will cause room-temperature ferromagnetism in the Co-doped TiO2 films. © 2002 American Institute of Physics.
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75.50.Tt Fine-particle systems; nanocrystalline materials
75.50.Cc Other ferromagnetic metals and alloys
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.70.Ak Magnetic properties of monolayers and thin films
61.46.-w Structure of nanoscale materials
81.15.Fg Pulsed laser ablation deposition

Critical current density and third-harmonic voltage in superconducting films

Yasunori Mawatari, Hirofumi Yamasaki, and Yoshihiko Nakagawa

Appl. Phys. Lett. 81, 2424 (2002); http://dx.doi.org/10.1063/1.1510159 (3 pages) | Cited 41 times

Online Publication Date: 16 September 2002

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When a sinusoidal drive current I0 cos ωt flows in a small coil close to the surface of a superconducting film, third-harmonic voltage V3 cos(3ωt+θ3) is induced in the coil if the film causes a nonlinear response. We have developed an approximate theoretical method yielding the relationships among I0, V3, and θ3, thus providing the scientific basis for a widely used inductive method for measuring the critical current density Jc in large-area superconducting films. Our results show that V3 is near zero when I0 is smaller than a threshold value Ic0∝Jcd, where d is the film thickness. When I0>Ic0, on the other hand, the third-harmonic voltage is expressed as V3 exp(−iθ3) = ωIc0G(I0/Ic0), where G(x) is a scaling function determined by the configuration of the coil. We demonstrate the scaling law of V3/Ic0 vs I0/Ic0 in a YBa2Cu3O7−δ film. © 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

Magnetocaloric effect in random magnetic anisotropy materials

Xavier Bohigas, Javier Tejada, Francesc Torres, José Ignacio Arnaudas, Enrique Joven, and Agustín del Moral

Appl. Phys. Lett. 81, 2427 (2002); http://dx.doi.org/10.1063/1.1506777 (3 pages) | Cited 10 times

Online Publication Date: 16 September 2002

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In this letter we report the results of entropy variations in random anisotropy magnets composed of TbxY1−xAl2, with x = 0.15, 0.20, 0.25, 0.35, 0.40, and 0.50. We discovered large entropy variation associated with the spin glass to paramagnetic transition. Both temperature transition and entropy changes were studied at different temperatures and with different compositions. Our conclusion is that these materials are suitable candidates for use as magnetic refrigerants in a temperature range below 40 K. © 2002 American Institute of Physics.
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75.50.Lk Spin glasses and other random magnets
75.30.Sg Magnetocaloric effect, magnetic cooling
75.30.Gw Magnetic anisotropy
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.20.En Metals and alloys
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Fe-substituted 0.92Pb(Zn1/3Nb2/3)O3–0.08PbTiO3 single crystals: A “hard” piezocrystal

Shashank Priya, Kenji Uchino, and Dwight Viehland

Appl. Phys. Lett. 81, 2430 (2002); http://dx.doi.org/10.1063/1.1507831 (3 pages) | Cited 24 times

Online Publication Date: 16 September 2002

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The dielectric and electrically induced strain characteristics of Fe-substituted Pb(Zn1/3Nb2/3)O3–PbTiO3 single crystals have been investigated. These investigations have shown that Fe substitution results in: (i) a lowering of the field level required to obtain large strains, (ii) an increased squareness in the ϵ−E response indicative of “hard” piezoelectric properties, and (iii) enhanced linearity in the region where saturation is approached at high field levels. Interestingly, the hard characteristics occur along with an enhanced stability of an intermediate ferroelectric orthorhombic state. © 2002 American Institute of Physics.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.65.Ly Strain-induced piezoelectric fields

Hexagonal polymorph of tantalum–pentoxide with enhanced dielectric constant

M. Hiratani, S. Kimura, T. Hamada, S. Iijima, and N. Nakanishi

Appl. Phys. Lett. 81, 2433 (2002); http://dx.doi.org/10.1063/1.1509861 (3 pages) | Cited 17 times

Online Publication Date: 16 September 2002

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A tantalum–pentoxide dielectric with an enhanced permittivity of over 50 was found to be crystallized in a hexagonal symmetry with a = 0.628 nm and c = 0.389 nm. The incommensurate epitaxy of tantalum pentoxide on hcp-ruthenium metal stabilizes the hexagonal phase with √3-time periodicity in plane, as compared with that of the known hexagonal δ phase. The crystallographic assumption, which is based on one-dimensional Ta–O–Ta chain along the c axis, can explain large polarizability caused by delocalized electrons on the one-dimensional chain. © 2002 American Institute of Physics.
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77.22.Ch Permittivity (dielectric function)
77.55.-g Dielectric thin films
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.

Dielectric loss peak due to platinum electrode porosity in lead zirconate titanate thin-film capacitors

D. J. Jung, M. Dawber, A. Ruediger, J. F. Scott, H. H. Kim, and Kinam Kim

Appl. Phys. Lett. 81, 2436 (2002); http://dx.doi.org/10.1063/1.1509855 (3 pages) | Cited 17 times

Online Publication Date: 16 September 2002

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Impedance spectroscopy measurements were carried out in situ on lead zirconate titanate capacitors 1.2×1.2 μm2 in size on a Samsung 4 Mbit 6 in, wafer. We show here that large dielectric loss appears at low frequencies, which is a constriction effect due to the porosity of the platinum electrode. Porous platinum electrodes facilitate an oxygen electrode reaction. The effect may be removed by annealing the platinum electrode at moderate temperature (300 °C). Such an anneal should thus be considered an essential step in the fabrication of a ferroelectric thin-film capacitor on Pt. © 2002 American Institute of Physics.
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85.50.-n Dielectric, ferroelectric, and piezoelectric devices
84.32.Tt Capacitors
77.22.Gm Dielectric loss and relaxation

Polarized Raman scattering of epitaxial Pb(Zr,Ti)O3 thin films in the tetragonal-phase field

Sun-Hwa Lee, Hyun M. Jang, Hyun H. Sung, and Hyunjung Yi

Appl. Phys. Lett. 81, 2439 (2002); http://dx.doi.org/10.1063/1.1509859 (3 pages) | Cited 12 times

Online Publication Date: 16 September 2002

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In view of the difficulty in preparing single crystals, a c-axis oriented epitaxial lead zirconate titanate (PZT) film was prepared as a model system for the single-crystalline PZT. By employing an extraordinary backscattering configuration in which the relevant phonon wave vector, k, is parallel to the film/substrate interface, we have successfully isolated the E [transverse optical (TO)] symmetry phonons from A1(TO) phonons. Compared with polarized Raman spectra of the c-axis oriented PbTiO3 film, the polarized spectra of the epitaxial PZT film (with Zr/Ti=40/60) exhibited significant asymmetric line broadening with a noticeable downward shift of the mode frequencies. In addition to this, we observed a splitting of the “silent” mode into the B1-symmetry mode and the E(TO) mode using the parallel and cross polarization configurations, respectively. © 2002 American Institute of Physics.
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78.30.Hv Other nonmetallic inorganics
78.66.Nk Insulators
63.20.D- Phonon states and bands, normal modes, and phonon dispersion

Global and secondary ferroelectric minima in ordered Pb(Sc0.25Nb0.25Ti0.5)O3 alloys

A. Al-Barakaty and L. Bellaiche

Appl. Phys. Lett. 81, 2442 (2002); http://dx.doi.org/10.1063/1.1509473 (3 pages) | Cited 4 times

Online Publication Date: 16 September 2002

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A first-principles-derived approach is developed to study properties of two Pb(Sc0.25Nb0.25Ti0.5)O3 alloys that are both atomically ordered along the [001] direction. Unlike the first alloy, the second structure has differently-charged (001) B-planes. Both systems exhibit a global ferroelectric minimum of orthorhombic symmetry and a secondary ferroelectric minimum of tetragonal symmetry. Some electromechanical responses are enhanced in the secondary minimum, especially for the second structure. Mechanisms allowing a switch from the global to the secondary minimum are discussed. © 2002 American Institute of Physics.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.80.Fm Switching phenomena
77.65.-j Piezoelectricity and electromechanical effects
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Control of surface morphology through variation of growth rate in SiGe/Si(100) epitaxial films: Nucleation of “quantum fortresses”

Jennifer L. Gray, Robert Hull, and Jerrold A. Floro

Appl. Phys. Lett. 81, 2445 (2002); http://dx.doi.org/10.1063/1.1509094 (3 pages) | Cited 36 times

Online Publication Date: 16 September 2002

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The surface morphology of Si0.7Ge0.3 films grown at 550 °C by molecular-beam epitaxy is found to be highly controllable through changes in growth rate. A growth rate of 0.9 Å/s results in a surface morphology that begins as shallow pyramidal pits, which then become decorated by ordered quadruplets of islands that surround the edges of the pits. This “quantum fortress” structure represents a symmetry with potential application to quantum cellular automata geometries. A higher growth rate of 3 Å/s produces similar results. However, when the growth rate is reduced to 0.15 Å/s, the surface morphology that develops instead consists of elongated ridges. © 2002 American Institute of Physics.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.-a Thin film structure and morphology
81.05.Hd Other semiconductors
68.35.Dv Composition, segregation; defects and impurities
68.35.B- Structure of clean surfaces (and surface reconstruction)

Optical properties of self-assembled Ge wires grown on Si(113)

M. P. Halsall, H. Omi, and T. Ogino

Appl. Phys. Lett. 81, 2448 (2002); http://dx.doi.org/10.1063/1.1509120 (3 pages) | Cited 12 times

Online Publication Date: 16 September 2002

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We report photoluminescence and Raman scattering measurements of Ge wires formed by self-assembly on Si(113) substrates. The samples were grown at a growth temperature of 500 °C on Si(113) substrates by solid-source molecular-beam epitaxy. Atomic force microscopy results clearly show the formation of coherent wire-shaped islands elongated in the [33-2] direction, some with lengths exceeding 500 nm. Micro-Raman measurements indicate that at this low growth temperature intermixing of the silicon and germanium is restricted with an average Ge fraction exceeding 0.7. Capping of the wires with a 20 nm Si epilayer enables the observation of low-temperature photoluminescence. A series of samples with increasing Ge coverage were studied and the onset of Ge islanding is observed to occur at a coverage of 5 monolayers. Wire formation occurs at coverages of 6 monolayers or greater. The observed emission band from the wires has a line shape quite different from that observed from Ge islands on Si[100], being substantially narrower in energy. A stochastic calculation based on idealized quantum wires is presented which reproduces the observed photoluminescence line shape well. © 2002 American Institute of Physics.
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78.67.Lt Quantum wires
78.30.Am Elemental semiconductors and insulators
78.55.Ap Elemental semiconductors
78.66.Db Elemental semiconductors and insulators

Twinning in TiSi2-island catalyzed Si nanowires grown by gas-source molecular-beam epitaxy

Qiang Tang, Xian Liu, Theodore I. Kamins, Glenn S. Solomon, and James S. Harris

Appl. Phys. Lett. 81, 2451 (2002); http://dx.doi.org/10.1063/1.1509096 (3 pages) | Cited 10 times

Online Publication Date: 16 September 2002

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Using TiSi2 islands as a catalyst, we have grown Si nanowires by gas-source molecular-beam epitaxy using Si2H6 as the gas source. The dominant TiSi2 islands are C49 phase with the orientation: Si[110]//C49-TiSi2[100] and Si(001)//C49-TiSi2(010). Twinning in the grown Si nanowires is observed by reflection high-energy electron diffraction and transmission electron microscopy. The twining also causes kinking, i.e., an abrupt change of growth direction of the Si nanowires. Lattice mismatch stress between the TiSi2 islands and the Si nanowires possibly leads to twinning and kinking of the Si nanowires. © 2002 American Institute of Physics.
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61.46.-w Structure of nanoscale materials
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.07.Bc Nanocrystalline materials
61.72.Mm Grain and twin boundaries
68.55.A- Nucleation and growth

Rapid imaging of nanotubes on insulating substrates

T. Brintlinger, Yung-Fu Chen, T. Dürkop, Enrique Cobas, M. S. Fuhrer, John D. Barry, and John Melngailis

Appl. Phys. Lett. 81, 2454 (2002); http://dx.doi.org/10.1063/1.1509113 (3 pages) | Cited 52 times

Online Publication Date: 16 September 2002

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We demonstrate the use of field-emission scanning electron microscopy for rapid imaging of small-diameter carbon nanotubes on insulating SiO2 substrates. The image contrast stems from local potential differences between the nanotube and substrate and is insensitive to surface roughness and defects. This technique may also be used as a probe of the electrical connectivity of small structures without external leads. © 2002 American Institute of Physics.
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61.46.-w Structure of nanoscale materials
68.37.Vj Field emission and field-ion microscopy
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.37.Ps Atomic force microscopy (AFM)
61.72.-y Defects and impurities in crystals; microstructure

Controlling the size and density of self-assembled PbSe quantum dots by adjusting the substrate temperature and layer thickness

A. Raab and G. Springholz

Appl. Phys. Lett. 81, 2457 (2002); http://dx.doi.org/10.1063/1.1509116 (3 pages) | Cited 10 times

Online Publication Date: 16 September 2002

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The formation of self-assembled PbSe quantum dots by molecular-beam epitaxy of PbSe on PbTe (111) is investigated in dependence of growth temperature and layer thickness. It is shown that in the temperature range of 240 °C to 420 °C, the dot density and dot height vary exponentially with temperature, whereas the wetting layer thickness and the dot shapes remain essentially constant. A different behavior is observed for the dependence on the PbSe thickness, which linearly changes the average dot height but only slightly affects the dot density. Both parameters allow an efficient control of the quantum dot sizes as is essential for device applications. © 2002 American Institute of Physics.
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81.07.Ta Quantum dots
68.65.Hb Quantum dots (patterned in quantum wells)
81.16.Dn Self-assembly
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Experimental evidence of asymmetric carrier transport in InGaAs quantum wells and wires grown on tilted InP substrates

A. F. G. Monte, S. W. da Silva, J. M. R. Cruz, P. C. Morais, and A. S. Chaves

Appl. Phys. Lett. 81, 2460 (2002); http://dx.doi.org/10.1063/1.1507619 (3 pages) | Cited 2 times

Online Publication Date: 16 September 2002

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The influence of the interface morphology upon the electron–hole transport in intrinsic In0.53Ga0.47As/InP quantum structures was investigated by scanning the photoluminescence intensity profile on the sample surface. The results suggest that the carrier diffusion is very sensitive both to the roughness of the interfaces and the presence of finite-width terraces. It was found that the carrier density profile shows asymmetric diffusion normal to the terraces whereas it shows symmetric expansion along the terraces. Simulations of the asymmetry in the carrier density profile using a non-Fickian diffusion equation described by the Lévy statistics show a excellent agreement with the experimental data. © 2002 American Institute of Physics.
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73.63.Hs Quantum wells
73.63.Nm Quantum wires
78.67.De Quantum wells
78.67.Lt Quantum wires
68.65.Fg Quantum wells
68.65.La Quantum wires (patterned in quantum wells)
68.35.Ct Interface structure and roughness
78.55.Cr III-V semiconductors

Ag-induced zero- and one-dimensional nanostructures on vicinal Si(111)

J. Kuntze, A. Mugarza, and J. E. Ortega

Appl. Phys. Lett. 81, 2463 (2002); http://dx.doi.org/10.1063/1.1509857 (3 pages) | Cited 11 times

Online Publication Date: 16 September 2002

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The formation of a Ag-stabilized regular step lattice on vicinal Si(111) miscut towards [11math] is reported. The step bunching characteristic of the clean surface is prevented by single-domain Si(111)-(3×1)-Ag reconstruction. The nanostructured surface is used as a template for growing one-dimensional arrays of 1 nm sized Ag quantum dots with a preferential spacing of 1.5 nm along the rows. © 2002 American Institute of Physics.
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68.65.Hb Quantum dots (patterned in quantum wells)
68.35.B- Structure of clean surfaces (and surface reconstruction)
61.46.-w Structure of nanoscale materials
68.43.-h Chemisorption/physisorption: adsorbates on surfaces

Synthesis of multiwalled carbon nanotubes from carbon black

S. P. Doherty and R. P. H. Chang

Appl. Phys. Lett. 81, 2466 (2002); http://dx.doi.org/10.1063/1.1509470 (3 pages) | Cited 6 times

Online Publication Date: 16 September 2002

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Show Abstract
We describe a method to produce high-crystalline quality multiwalled carbon nanotubes from carbon black. By modifying the arc into a high-temperature oven, carbon black is converted into carbon nanotubes by a solid-state transformation without a catalyst. This process sheds new light onto the growth mechanism of carbon nanotubes and could lead to a scalable method of making multiwall nanotubes. © 2002 American Institute of Physics.
Show PACS
81.07.De Nanotubes
07.20.Hy Furnaces; heaters
64.70.K- Solid-solid transitions
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
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