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23 Sep 2002

Volume 81, Issue 13, pp. 2319-2480

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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 13 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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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.
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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

Photoluminescence study of carrier transfer among vertically aligned double-stacked InAs/GaAs quantum dot layers

Yu. I. Mazur, X. Wang, Z. M. Wang, G. J. Salamo, M. Xiao, and H. Kissel

Appl. Phys. Lett. 81, 2469 (2002); http://dx.doi.org/10.1063/1.1510157 (3 pages) | Cited 30 times

Online Publication Date: 16 September 2002

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Photoluminescence (PL) properties of self-organized quantum dots (QDs) in a vertically aligned double-layer InAs/GaAs QD structure are studied as a function of temperature from 10 to 290 K. The QDs in a sample with a 1.8 ML InAs seed layer and a second 2.4 ML InAs layer are found to self-organize in pairs of unequal sized QDs with clearly discernible ground-states transition energy. The unusual temperature behavior of the PL for such asymmetrical QD pairs provides clear evidence for carrier transfer from smaller to larger QDs by means of a nonresonant multiphonon-assisted tunneling process in the case of interlayer transfer and through carrier thermal emission and recapture within one layer. © 2002 American Institute of Physics.
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78.55.Cr III-V semiconductors
78.67.Hc Quantum dots
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