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25 Oct 2004

Volume 85, Issue 17, pp. 3657-3939

Issue Cover Spotlight Figure

Appl. Phys. Lett. 85, 3851 (2004); http://dx.doi.org/10.1063/1.1808886 (3 pages)

P. Guha, S. Kar, and S. Chaudhuri
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Quantum confinement in ZnO nanorods

Y. Gu, Igor L. Kuskovsky, M. Yin, S. O’Brien, and G. F. Neumark

Appl. Phys. Lett. 85, 3833 (2004); http://dx.doi.org/10.1063/1.1811797 (3 pages) | Cited 90 times

Online Publication Date: 29 October 2004

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The colloidal-synthesized ZnO nanorods with radius of 1.1±0.1 nm (less than the bulk exciton Bohr radius, aB∼2.34 nm) have been studied by optical methods combined with simple model calculations. The quantum confinement has been observed in these nanorods. The exciton binding energy is shown to be significantly enhanced due to one-dimensional confinement. Additionally, it is suggested that the green luminescence in ZnO involves free holes.
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81.07.Bc Nanocrystalline materials
81.05.Dz II-VI semiconductors
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.55.Et II-VI semiconductors
73.22.Lp Collective excitations

Precise formation of nanoscopic dots on polystyrene film using z-lift electrostatic lithography

Shane Juhl, David Phillips, Richard A. Vaia, Sergei F. Lyuksyutov, and Pavel B. Paramonov

Appl. Phys. Lett. 85, 3836 (2004); http://dx.doi.org/10.1063/1.1807012 (3 pages) | Cited 17 times

Online Publication Date: 29 October 2004

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Z-lift electrostatic lithography on thin (10–50 nm) polystyrene (PS) films is discussed. The height of nanostructures can be controlled via mechanically drawing or depressing the cantilever height (z-lift) during the application of a voltage. Since polymer is not removed or crosslinked during structure formation, the features are erasable. Various aspects such as voltage doses, film thickness, z-lift height, and rate are explored. Structure height formation relies mainly on, and is proportional, to the z-lift magnitude; however, only a narrow range of voltages yields structures for any given film thickness. Structures ranging from 0–10 nm are produced on a 40 nm thick PS film using −36 V by varying the z-lift on a 0.1–0.9 N∕m cantilever from −20 nm to +400 nm.
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68.55.-a Thin film structure and morphology
81.16.Nd Micro- and nanolithography
61.46.-w Structure of nanoscale materials
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity

Anisotropic photoconductivity of InGaAs quantum dot chains measured by terahertz pulse spectroscopy

D. G. Cooke, F. A. Hegmann, Yu. I. Mazur, W. Q. Ma, X. Wang, Z. M. Wang, G. J. Salamo, M. Xiao, T. D. Mishima, and M. B. Johnson

Appl. Phys. Lett. 85, 3839 (2004); http://dx.doi.org/10.1063/1.1807959 (3 pages) | Cited 20 times

Online Publication Date: 29 October 2004

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We report results of time-resolved terahertz (THz) pulse spectroscopy experiments on laterally ordered chains of self-assembled InGaAs quantum dots photoexcited with 400 nm, 100 fs laser pulses. A large anisotropy in the transient photoconductive response is observed depending on the polarization of the THz probe pulse with respect to the orientation of the dot chains. Fast (3.5–5 ps) and efficient carrier capture into the dots and one-dimensional wetting layers underneath the dot chains is observed below 90 K. At higher temperatures, thermionic emission into the two-dimensional wetting layers and barriers becomes significant and the anisotropy in the photoconductive signal is reduced.
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73.63.Kv Quantum dots
72.40.+w Photoconduction and photovoltaic effects
79.40.+z Thermionic emission
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
78.67.Hc Quantum dots
78.47.-p Spectroscopy of solid state dynamics
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)

Laser manipulation of iron for nanofabrication

G. Myszkiewicz, J. Hohlfeld, A. J. Toonen, A. F. Van Etteger, O. I. Shklyarevskii, W. L. Meerts, Th. Rasing, and E. Jurdik

Appl. Phys. Lett. 85, 3842 (2004); http://dx.doi.org/10.1063/1.1811804 (3 pages) | Cited 23 times

Online Publication Date: 29 October 2004

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We fabricate iron nanolines by depositing an atomic beam of iron through a far-off resonant laser standing wave (SW) onto a glass-ceramic substrate. The laser SW is tuned 200 MHz above the 5D4→5F5o 56Fe transition at a vacuum wavelength of 372.099 nm. The resulting nanolines exhibit a period of 186 nm, a height above the background of 8 nm and a full width at half maximum of 95 nm. These nanostructures cover a surface area of ≃1.6×0.4 mm2, corresponding to ≃8600 iron lines with a length of ≃400 μm.
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81.07.Bc Nanocrystalline materials
81.16.Ta Atom manipulation
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
61.82.Rx Nanocrystalline materials
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
61.46.-w Structure of nanoscale materials
61.82.Bg Metals and alloys
42.62.-b Laser applications
75.50.Tt Fine-particle systems; nanocrystalline materials
75.50.Bb Fe and its alloys

Surface structures of cerium oxide nanocrystalline particles from the size dependence of the lattice parameters

S. Tsunekawa, S. Ito, and Y. Kawazoe

Appl. Phys. Lett. 85, 3845 (2004); http://dx.doi.org/10.1063/1.1811771 (3 pages) | Cited 20 times

Online Publication Date: 29 October 2004

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Cerium oxide nanocrystalline particles are synthesized and monodispersed in the size range from 2 to 8 nm in diameter. The dependence of the lattice parameters on particle size is obtained by x-ray and electron diffraction analyses. The size dependence well coincides with the estimation based on the assumption that the surface is composed of one layer of Ce2O3 and the inside consists of CeO2. The effect of particle size on lattice parameters is discussed from the differences in the fabrication method and the surface structure.
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61.46.-w Structure of nanoscale materials
68.35.B- Structure of clean surfaces (and surface reconstruction)
61.66.Fn Inorganic compounds

Nanovoids in InGaAs∕GaAs quantum dots observed by cross-sectional scanning tunneling microscopy

A. Lenz, H. Eisele, R. Timm, S. K. Becker, R. L. Sellin, U. W. Pohl, D. Bimberg, and M. Dähne

Appl. Phys. Lett. 85, 3848 (2004); http://dx.doi.org/10.1063/1.1808884 (3 pages) | Cited 22 times

Online Publication Date: 29 October 2004

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We present cross-sectional scanning tunneling microscopy data of a type of InGaAs∕GaAs quantum-dot structure characterized by a hollow center. This void structure develops during a long growth interruption applied after deposition of a quantum dot layer and a thin cap layer, resulting in an eruption of indium-rich material. Subsequent fast overgrowth does not fill the void completely. This growth behavior demonstrates limitations of current strategies to grow large quantum dots.
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81.05.Ea III-V semiconductors
81.07.Ta Quantum dots
68.65.Hb Quantum dots (patterned in quantum wells)
61.72.Qq Microscopic defects (voids, inclusions, etc.)
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
81.15.Kk Vapor phase epitaxy; growth from vapor phase
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Direct synthesis of single crystalline In2O3 nanopyramids and nanocolumns and their photoluminescence properties

P. Guha, S. Kar, and S. Chaudhuri

Appl. Phys. Lett. 85, 3851 (2004); http://dx.doi.org/10.1063/1.1808886 (3 pages) | Cited 50 times

Online Publication Date: 29 October 2004

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Single crystalline indium oxide pyramid and column structures were synthesized by a simple physical evaporation technique. The pyramid structure was obtained without any catalytic action while the column structure was produced using gold as the catalyst. The nanostructures were characterized by x-ray diffraction, scanning electron microscopy and transmission electron microscopy. A blue-green photoluminescence band in the visible region was observed in the In2O3 structures which could be ascribed to the existence of a large amount of singly ionized oxygen vacancies, confirmed by electron paramagnetic resonance.
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81.07.Bc Nanocrystalline materials
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.55.Hx Other solid inorganic materials
81.20.-n Methods of materials synthesis and materials processing
61.46.-w Structure of nanoscale materials
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
61.72.J- Point defects and defect clusters
76.30.Mi Color centers and other defects
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
68.37.Lp Transmission electron microscopy (TEM)

Near-field optical beam-induced currents in CdTe∕CdS solar cells: Direct measurement of enhanced photoresponse at grain boundaries

S. Smith, P. Zhang, T. Gessert, and A. Mascarenhas

Appl. Phys. Lett. 85, 3854 (2004); http://dx.doi.org/10.1063/1.1809271 (3 pages) | Cited 11 times

Online Publication Date: 29 October 2004

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Using near-field optical beam induced current, we spatially resolve the photocurrent in polycrystalline CdTe∕CdS solar cells, and observe increased photocurrent collection at grain boundaries (relative to the intragrain volume). This observation supports previously reported hypotheses that grain boundaries present a hole-barrier, thereby assisting in charge separation at the grain boundaries in these devices. The results offer compelling evidence, in an actual working-device structure, of the role of grain boundaries in explaining the surprisingly high performance of these highly defected devices.
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84.60.Jt Photoelectric conversion
72.40.+w Photoconduction and photovoltaic effects
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
61.72.Mm Grain and twin boundaries

Effect of coiling on the electronic properties along single-wall carbon nanotubes

P. Castrucci, M. Scarselli, M. De Crescenzi, M. A. El Khakani, F. Rosei, N. Braidy, and J.-H. Yi

Appl. Phys. Lett. 85, 3857 (2004); http://dx.doi.org/10.1063/1.1809277 (3 pages) | Cited 20 times

Online Publication Date: 29 October 2004

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Straight and coiled single-wall carbon nanotubes (SWCNTs) synthesized by laser vaporization were dispersed on highly oriented pyrolitic graphite. Their morphology and electrical properties were investigated by scanning tunneling microscopy (STM). STM images revealed that the SWCNTs (either straight or coiled) often self-organize into bundles of two or more tubes and are rarely found alone. The conductance measured along a periodically coiled CNT was found to increase at locations where the CNT is squeezed, while it decreases significantly in unsqueezed regions characterized by an unperturbed hexagonal network. This provides experimental evidence of significant conductance modulation along a one-dimensional system on the nanometer scale.
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81.07.De Nanotubes
73.63.Fg Nanotubes
61.46.-w Structure of nanoscale materials
81.15.Fg Pulsed laser ablation deposition
81.16.Mk Laser-assisted deposition
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.35.B- Structure of clean surfaces (and surface reconstruction)

Preparation of ruthenium dioxide nanorods and their field emission characteristics

Chih-Sung Hsieh, Dah-Shyang Tsai, Reui-San Chen, and Ying-Sheng Huang

Appl. Phys. Lett. 85, 3860 (2004); http://dx.doi.org/10.1063/1.1812373 (3 pages) | Cited 19 times

Online Publication Date: 29 October 2004

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RuO2 nanometer-sized rods with pyramidal tips have been grown on Cu-coated Si(100) substrates using metalorganic chemical vapor deposition. The geometry of these nanorods resembles an obelisk with an off-center tip. The aspect ratios of nanorod tips are between 0.55 and 0.73. The field emission properties of the RuO2 nanorods are studied and the stability of its emission current is assessed. The field emission results demonstrate that RuO2 nanorods material is an emitter of potential.
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81.07.Bc Nanocrystalline materials
68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
79.70.+q Field emission, ionization, evaporation, and desorption
61.46.-w Structure of nanoscale materials
73.61.Ng Insulators
73.63.Bd Nanocrystalline materials

Single-molecule spontaneous emission close to absorbing nanostructures

M. Thomas, J.-J. Greffet, R. Carminati, and J. R. Arias-Gonzalez

Appl. Phys. Lett. 85, 3863 (2004); http://dx.doi.org/10.1063/1.1812592 (3 pages) | Cited 78 times

Online Publication Date: 29 October 2004

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The spontaneous emission of a single molecule is substantially modified close to a metallic nanostructure. We study the spectral behavior of the radiative and nonradiative decay rates and of the local-field factor in the vicinity of a plasmon resonance. We show that the highest fluorescence enhancement is obtained for an emission wavelength redshifted from the plasmon resonance, and that quenching always dominates at plasmon resonance. These results may have experimental implications in spectroscopy and monitoring of elementary light sources.
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78.66.Bz Metals and metallic alloys
78.55.Hx Other solid inorganic materials
73.22.Lp Collective excitations
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)

Wetting-layer transformation for Pb nanocrystals grown on Si(111)

R. Feng, E. H. Conrad, M. C. Tringides, C. Kim, and P. F. Miceli

Appl. Phys. Lett. 85, 3866 (2004); http://dx.doi.org/10.1063/1.1812593 (3 pages) | Cited 8 times

Online Publication Date: 29 October 2004

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We present the results of in situ x-ray scattering experiments that investigate the growth of Pb nanocrystalline islands on Si(111). It is conclusively shown that the Pb nanocrystals do not reside on top of a Pb wetting layer. The nucleating Pb nanocrystals transform the highly disordered Pb wetting layer beneath the islands into well-ordered fcc Pb. The surface then consists of fcc Pb islands directly on top of the Si surface with the disordered wetting layer occupying the region between the islands. As the Pb nanocrystals coalesce at higher coverage we observe increasing disorder that is consistent with misfit strain relaxation. These results have important implications for predicting stable Pb island heights.
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61.46.-w Structure of nanoscale materials
78.70.Ck X-ray scattering
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
68.35.B- Structure of clean surfaces (and surface reconstruction)

Template-free synthesis on single-crystalline InP nanotubes

L. W. Yin, Y. Bando, D. Golberg, and M. S. Li

Appl. Phys. Lett. 85, 3869 (2004); http://dx.doi.org/10.1063/1.1812596 (3 pages) | Cited 9 times

Online Publication Date: 29 October 2004

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A simple template-free thermal chemical route has been developed to prepare InP nanotubes with zinc blende structure by controlling the reaction temperature and flowing gas. The synthesized InP nanotubes are single-crystalline, free from defects and dislocations, and partially filled with In. The presence of metallic indium at tips of and within the synthesized InP nanotubes indicated a vapor–liquid–solid mechanism for the formation of InP nanotubes. The synthesized InP single-crystalline nanotubes grew along [math10] direction. The synthesized InP nanotubes have a uniform outer diameter of 50–60 nm and a wall thickness of 7–10 nm. The photoluminescence spectrum at room temperature exhibits a great shift from the bulk band gap of 1.35 eV to high energy of 1.49 eV.
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81.07.De Nanotubes
81.05.Ea III-V semiconductors
81.16.Be Chemical synthesis methods
81.10.-h Methods of crystal growth; physics and chemistry of crystal growth, crystal morphology, and orientation
78.67.Ch Nanotubes
61.46.-w Structure of nanoscale materials
78.55.Cr III-V semiconductors

Mn12-acetate film pattern generated by photolithography methods

K. Kim, D. M. Seo, J. Means, V. Meenakshi, W. Teizer, H. Zhao, and K. R. Dunbar

Appl. Phys. Lett. 85, 3872 (2004); http://dx.doi.org/10.1063/1.1808492 (3 pages) | Cited 12 times

Online Publication Date: 29 October 2004

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We demonstrate a straightforward way to lithographically fabricate Mn12-acetate thin film patterns on Si∕SiO2 surfaces, a significant step in light of the chemical volatility of this organic complex. Atomic force micrographs show low surface roughness. X-ray photoelectron spectroscopy data and magnetic measurements of the Mn12-acetate film indicate properties reminiscent of crystalline Mn12-acetate, suggesting that this approach can be used to fabricate lithographically patterned devices of Mn12-acetate.
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75.50.Xx Molecular magnets
68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
85.40.Hp Lithography, masks and pattern transfer
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
75.70.Ak Magnetic properties of monolayers and thin films
68.37.Ps Atomic force microscopy (AFM)
79.60.Dp Adsorbed layers and thin films
79.60.Fr Polymers; organic compounds
68.35.B- Structure of clean surfaces (and surface reconstruction)
75.30.Cr Saturation moments and magnetic susceptibilities

Immobilization of molecular tubes on self-assembled monolayers of β-cyclodextrin and dodecanethiol inclusion complexes

Sadaki Samitsu, Takeshi Shimomura, Kohzo Ito, and Masahiko Hara

Appl. Phys. Lett. 85, 3875 (2004); http://dx.doi.org/10.1063/1.1804256 (3 pages) | Cited 4 times

Online Publication Date: 29 October 2004

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A molecular tube (MT) is a tubular macromolecule formed by the one-dimensional linkage of α-cyclodextrins and exhibits molecular recognition for selecting the diameter of a polymer chain. In this letter, we immobilized MTs on a self-assembled monolayers (SAM) of inclusion complexes (DDT-CD) between dodecanethiol (DDT) and β-cyclodextrin (β-CD). The DDT-CD inclusion complexes formed uniform self-assembled monolayers on gold. We confirmed that the MTs were immobilized on the DDT-CD SAM using dynamic contact angle measurements, surface-plasmon resonance (SPR), and scanning probe microscopy (SPM).
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68.43.Mn Adsorption kinetics
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps Atomic force microscopy (AFM)
81.16.Dn Self-assembly

Zinc oxide nanodisk

C. X. Xu, X. W. Sun, Z. L. Dong, and M. B. Yu

Appl. Phys. Lett. 85, 3878 (2004); http://dx.doi.org/10.1063/1.1811380 (3 pages) | Cited 91 times

Online Publication Date: 29 October 2004

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Using the mixture of zinc oxide and graphite powders as source materials, zinc oxide nanodisks with bulk quantity were fabricated by vapor-phase transport method. The nanodisks have perfect hexagonal shape with about 3 μm in diagonal and 300 nm in thickness. The growth is favored along six symmetric directions of ±[10math0], ±[1math00], and ±[01math0] with the typical growth along [0001] direction suppressed, which directly leads to the formation of zinc oxide nanodisk. The microstructure and growth mechanism are discussed.
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81.07.Bc Nanocrystalline materials
81.05.Dz II-VI semiconductors
61.46.-w Structure of nanoscale materials
78.66.Hf II-VI semiconductors
78.30.Fs III-V and II-VI semiconductors
68.35.B- Structure of clean surfaces (and surface reconstruction)

Nanoscale velocity–drag force relationship in thin liquid layers measured by atomic force microscopy

Ádám Mechler, Brian Piorek, Ratnesh Lal, and Sanjoy Banerjee

Appl. Phys. Lett. 85, 3881 (2004); http://dx.doi.org/10.1063/1.1808504 (3 pages) | Cited 8 times

Online Publication Date: 29 October 2004

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The relationship between velocity and drag force acting on a nanoprobe has been measured with an atomic force microscope (AFM). A special nanoprobe “whisker” was partially submerged in thin layers of glycerol–water mixtures and moved by using the AFM in scanning mode. The viscous drag force-caused torsion of the cantilever probe was recorded as a function of scanning speed and submersion depth. A linear drag force–velocity function was determined for cylindrical bodies with diameters of the order of 50 nm. The experimental results were supported by calculations for the torsional force exerted on an AFM probe dragged through a viscous medium. The viscosity was calculated for each experiment assuming no slip conditions and was in agreement with the macroscopically determined values. With some refinements, this offers a possible means of determining viscosity in thin liquid layers.
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68.15.+e Liquid thin films
66.20.-d Viscosity of liquids; diffusive momentum transport
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