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15 Nov 2004

Volume 85, Issue 20, pp. 4561-4807

Issue Cover Spotlight Figure

Appl. Phys. Lett. 85, 4768 (2004); http://dx.doi.org/10.1063/1.1818331 (3 pages)

G. Walter, N. Holonyak, M. Feng, and R. Chan
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Field-controlled suppression of phonon-induced transitions in coupled quantum dots

Andrea Bertoni, Massimo Rontani, Guido Goldoni, Filippo Troiani, and Elisa Molinari

Appl. Phys. Lett. 85, 4729 (2004); http://dx.doi.org/10.1063/1.1818345 (3 pages) | Cited 16 times

Online Publication Date: 16 November 2004

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We suggest that order-of-magnitude reduction of the longitudinal-acoustic phonon scattering rate, the dominant decoherence mechanism in quantum dots, can be achieved in coupled structures by the application of an external electric or magnetic field. Modulation of the scattering rate is traced to the relation between the wavelength of the emitted phonon and the length scale of delocalized electron wave functions. Explicit calculations for realistic devices, performed with a Fermi golden rule approach and a fully three-dimensional description of the electronic quantum states, show that the lifetime of specific states can achieve tens of microseconds. Our findings extend the feasibility basis of many proposals for quantum gates based on coupled quantum dots.
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63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials
73.21.La Quantum dots
63.20.K- Phonon interactions

Structural transformation and field emission enhancement of carbon nanofibers by energetic argon plasma post-treatment

C. H. Weng, K. C. Leou, H. W. Wei, Z. Y. Juang, M. T. Wei, C. H. Tung, and C. H. Tsai

Appl. Phys. Lett. 85, 4732 (2004); http://dx.doi.org/10.1063/1.1815062 (3 pages) | Cited 30 times

Online Publication Date: 16 November 2004

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Vertically aligned carbon nanofibers (CNFs) grown by plasma enhanced chemical vapor deposition (PECVD) were transformed into cone-shaped nanostructures after treatment by argon (Ar) plasma. Significant enhancement of field emission characteristics of the post-treated CNFs has been achieved. Analysis by electron microscopy and energy dispersive spectroscopy (EDS) suggests that the structural transformation is a result of a cosputtering∕deposition process by energetic plasma ions. The enhancements can be attributed to the combining effects of an additional Si∕C layer coverage, catalytic nanoparticles removal and the sharpening of CNFs tips. The argon plasma post-treatment processes developed here can be easily extended to in situ PECVD processes for fabricating CNFs based emitters.
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81.07.Bc Nanocrystalline materials
81.05.U- Carbon/carbon-based materials
64.70.Nd Structural transitions in nanoscale materials
79.70.+q Field emission, ionization, evaporation, and desorption
61.46.-w Structure of nanoscale materials
64.70.K- Solid-solid transitions
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
78.30.Na Fullerenes and related materials
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
52.77.-j Plasma applications

Reflection property of nano-acoustic wave at the air∕GaN interface

Chia-Lung Hsieh, Kung-Hsuan Lin, Shr-Bin Wu, Chang-Chi Pan, Jen-Inn Chyi, and Chi-Kuang Sun

Appl. Phys. Lett. 85, 4735 (2004); http://dx.doi.org/10.1063/1.1819989 (3 pages) | Cited 9 times

Online Publication Date: 16 November 2004

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We present a study on the total internal reflection of nano-acoustic waves (NAWs) at the air∕GaN interface. The coherent NAW was generated and detected by piezoelectric InGaN∕GaN multiple quantum wells using a femtosecond transient transmission technique. With suitably designed sample structures, the fact that strain of the NAW experiences a sign change after total internal reflection at the air∕solid interface is examined directly. The surface roughness of the sample was found to distort the wave front of the NAW and to diminish the measured amplitude of the reflected NAW.
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62.65.+k Acoustical properties of solids
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.35.Iv Acoustical properties
77.65.Dq Acoustoelectric effects and surface acoustic waves (SAW) in piezoelectrics

Phase imaging and the lever-sample tilt angle in dynamic atomic force microscopy

Matthew J. D’Amato, Matthew S. Marcus, Mark A. Eriksson, and Robert W. Carpick

Appl. Phys. Lett. 85, 4738 (2004); http://dx.doi.org/10.1063/1.1812839 (3 pages) | Cited 12 times

Online Publication Date: 16 November 2004

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The phase shift in amplitude-controlled dynamic atomic force microscopy (AFM) is shown to depend on the cantilever-sample tilt angle. For a silicon sample and tip the phase shift changes by nearly 15° for a change in tilt angle of 15°. This contribution to the phase results from the oscillating tip’s motion parallel to the surface, which contributes to the overall energy dissipation. It occurs even when the measurements are carried out in the attractive regime. An off-axis dynamic AFM model incorporating van der Waals attraction and a thin viscous damping layer near the surface successfully describes the observed phase shifts. This effect must be considered to interpret phase images quantitatively.
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07.79.Lh Atomic force microscopes
46.40.Ff Resonance, damping, and dynamic stability

Periodicity and alignment of large-scale carbon nanotubes arrays

Y. Wang, J. Rybczynski, D. Z. Wang, K. Kempa, Z. F. Ren, W. Z. Li, and B. Kimball

Appl. Phys. Lett. 85, 4741 (2004); http://dx.doi.org/10.1063/1.1819992 (3 pages) | Cited 17 times

Online Publication Date: 16 November 2004

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Intensive studies have been carried out on controlling the periodicity and alignment of large-scale periodic arrays of carbon nanotubes (CNTs) using plasma-enhanced chemical vapor deposition. Catalytic dots are first prepared by self-assembly of polystyrene spheres on chromium-coated silicon substrates. Preparation parameters for CNTs growth including temperature, thickness of catalytic dots, plasma current intensity, and pregrowth plasma etching time are fine tuned and analyzed to achieve optimal combinations. High-quality aligned CNTs arrays with long-range periodicity and controlled diameters have been achieved. The good periodicity and alignment are critical for their applications such as photonic crystals, negative index of refraction, etc.
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81.07.De Nanotubes
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.65.Cf Surface cleaning, etching, patterning
61.46.-w Structure of nanoscale materials

Environment effects on the Raman spectra of individual single-wall carbon nanotubes: Suspended and grown on polycrystalline silicon

Hyungbin Son, Yuki Hori, S. G. Chou, D. Nezich, Ge. G. Samsonidze, G. Dresselhaus, M. S. Dresselhaus, and Eduardo B. Barros

Appl. Phys. Lett. 85, 4744 (2004); http://dx.doi.org/10.1063/1.1818739 (3 pages) | Cited 25 times

Online Publication Date: 16 November 2004

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An enhanced Raman signal is observed from individual suspended single-wall carbon nanotubes (SWNTs) and from isolated SWNTs grown on an n-doped polycrystalline silicon film used in standard silicon processing. The radial breathing modes of the Raman spectra taken from suspended SWNTs exhibit narrow linewidths, which indicate a relatively unperturbed environment for suspended SWNTs. Clear Raman signals from intermediate frequency modes in the frequency range from 520 to 1200 cm−1 are presented, which might allow a detailed study of the phonon band structure of individual SWNTs.
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78.67.Ch Nanotubes
78.30.Na Fullerenes and related materials
82.70.Kj Emulsions and suspensions

Overgrowing single crystalline ZnB2O4 on multiwall carbon nanotubes: Straightening the curly tubes

P. X. Yan, J. Z. Liu, J. Wang, and Z. G. Wu

Appl. Phys. Lett. 85, 4747 (2004); http://dx.doi.org/10.1063/1.1821652 (3 pages) | Cited 3 times

Online Publication Date: 16 November 2004

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Single crystals of ZnB2O4 have been grown from a supercooled molten ZnO-B2O3 system on multiwall carbon nanotubes. Transmission electron microscopy investigations indicated that the originally curly carbon nanotubes were well straightened after the single-crystal coating. The coating and straightening mechanism are discussed.
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81.10.Fq Growth from melts; zone melting and refining
61.46.-w Structure of nanoscale materials
68.37.Lp Transmission electron microscopy (TEM)

Long-range ordered self-assembled InAs quantum dots epitaxially grown on (110) GaAs

J. Bauer, D. Schuh, E. Uccelli, R. Schulz, A. Kress, F. Hofbauer, J. J. Finley, and G. Abstreiter

Appl. Phys. Lett. 85, 4750 (2004); http://dx.doi.org/10.1063/1.1819987 (3 pages) | Cited 21 times

Online Publication Date: 16 November 2004

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We report on a promising approach for positioning of self-assembled InAs quantum dots on (110) GaAs with nanometer precision. By combining self-assembly of quantum dots with molecular beam epitaxy on previously grown and in situ cleaved substrates (cleaved-edge overgrowth), arrays of long-range ordered InAs quantum dots have been fabricated. Both atomic force microscopy and micro-photoluminescence measurements demonstrate the ability to control size, position, and ordering of the quantum dots. Furthermore, single dot photoluminescence investigations confirm the high optical quality of the quantum dots fabricated.
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81.07.Ta Quantum dots
81.05.Ea III-V semiconductors
68.65.Hb Quantum dots (patterned in quantum wells)
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
78.67.Hc Quantum dots
78.55.Cr III-V semiconductors
68.37.Ps Atomic force microscopy (AFM)

Electron side-emission from corrugated CNx nanotubes

R. C. Che, L.-M. Peng, and M. S. Wang

Appl. Phys. Lett. 85, 4753 (2004); http://dx.doi.org/10.1063/1.1824177 (3 pages) | Cited 19 times

Online Publication Date: 16 November 2004

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Horizontally grown and vertically aligned carbon nitrogen (CNx) nanotubes encapsulated with Fe2O3 particles were synthesized on silicon substrates. Electron field-emission measurements were carried out on these CNx nanotubes using both the top-emission and side-emission geometries, and compared with that of the usual carbon nanotubes (CNTs). It was found that the turn-on field of the CNx nanotubes is at least ∼2 V∕μm less and the field conversion factor under low bias voltage is about four times more than that of the CNTs. For the two types of CNx films, the field emission property of the horizontally grown honeycombed film is clearly better than that of the vertically aligned film, indicating that for the corrugated nanotubes the “side-emission” geometry is superior to the more widely used “top-emission” geometry. Electrostatic potential distributions were calculated for some simplified models of the nanotubes, these calculations suggest that the enhanced field-emission of the “side-emission” geometry could be attributed to the increased corrugation and lowered potential barrier along the side of the corrugated nanotube compared with that along the top of the usual carbon nanotube.
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79.70.+q Field emission, ionization, evaporation, and desorption
61.46.-w Structure of nanoscale materials

Temperature-dependent molecular conduction measured by the electrochemical deposition of a platinum electrode in a lateral configuration

B. Kim, S. J. Ahn, J. G. Park, S. H. Lee, Y. W. Park, and E. E. B. Campbell

Appl. Phys. Lett. 85, 4756 (2004); http://dx.doi.org/10.1063/1.1821657 (3 pages) | Cited 4 times

Online Publication Date: 16 November 2004

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Temperature-dependent current–voltage (I–V) characteristics of a molecule, 1,4-benzenedimethanethiol, was measured for 30 K<T<300 K by a method of contact made by the electrochemical deposition of a platinum electrode in a lateral configuration. The I–V characteristics are nonlinear and asymmetric in the entire temperature range and the current decreases with decreasing temperature down to 40 K. Below 40 K, the I–V characteristics become temperature independent. The asymmetric I–V characteristics can be understood as arising from a better contact on one side (made by the self-assembled monolayer) than on the other side (made by the electrochemically deposited Pt electrode). The activation energy of thermally activated conduction for T>100 K is typically 0.11 eV. For T<40 K, the observed temperature independent I–V characteristics are fitted to the Fowler–Nordheim tunneling expression with barrier height of 1–2 eV depending on the contact strength of samples.
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73.40.Gk Tunneling
82.45.Fk Electrodes
73.61.Ph Polymers; organic compounds

Single-crystalline tin-doped indium oxide whiskers: Synthesis and characterization

Q. Wan, Z. T. Song, S. L. Feng, and T. H. Wang

Appl. Phys. Lett. 85, 4759 (2004); http://dx.doi.org/10.1063/1.1808877 (3 pages) | Cited 33 times

Online Publication Date: 16 November 2004

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An in situ doping approach was adopted to synthesize single-crystalline Sn-doped In2O3 [indium tin oxide (ITO)] nanowhiskers. Similar synthesis strategy could be used in the production of various doped metal oxide nanowhiskers. The growth mode of ITO nanowhiskers was discussed based on a self-catalytic vapor–liquid–solid growth mechanism. At room temperature, a photoluminescence peak at 510 nm was observed, which was likely related to the surface defects of ITO nanowhiskers. In air ambient, the resistivity of individual ITO whisker was measured to be 0.40 Ω cm, which was much higher than that of ITO films. A possible explanation for the high resistivity was proposed based on the influence of surface oxygen absorption.
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81.07.Bc Nanocrystalline materials
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
61.72.up Other materials
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
73.63.Bd Nanocrystalline materials
78.55.Hx Other solid inorganic materials
61.46.-w Structure of nanoscale materials
68.70.+w Whiskers and dendrites (growth, structure, and nonelectronic properties)
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