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22 Nov 2004

Volume 85, Issue 21, pp. 4831-5106

Issue Cover Spotlight Figure

Appl. Phys. Lett. 85, 4845 (2004); http://dx.doi.org/10.1063/1.1823019 (3 pages)

Wounjhang Park and Jeong-Bong Lee
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Self-assembled carbon-nanotube-based field-effect transistors

Miron Hazani, Dmitry Shvarts, Dana Peled, Victor Sidorov, and Ron Naaman

Appl. Phys. Lett. 85, 5025 (2004); http://dx.doi.org/10.1063/1.1823017 (3 pages) | Cited 10 times

Online Publication Date: 23 November 2004

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Self-assembled carbon-nanotube-based field-effect transistors (CNTFETs) were produced with high yield using the natural process of DNA hybridization. In principle, the devices made by this method behave like those made using direct metal-carbon nanotube contacts. The inverse subthreshold slope of the CNTFETs depends on the source-drain voltage applied to the device, confirming that the conductance of CNTFETs is determined by the Schottky barriers at the interfaces between the CNTs and the gold electrodes.
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85.30.Tv Field effect devices
85.35.Kt Nanotube devices
73.30.+y Surface double layers, Schottky barriers, and work functions
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
85.65.+h Molecular electronic devices

Magnetic properties of crystalline La0.7Ca0.3MnO3 films including a nanoscale disordered phase

V. G. Prokhorov, V. A. Komashko, V. L. Svetchnikov, Y. P. Lee, Y. H. Hyun, and J. B. Kim

Appl. Phys. Lett. 85, 5028 (2004); http://dx.doi.org/10.1063/1.1825624 (3 pages)

Online Publication Date: 23 November 2004

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The magnetic properties of amorphous, crystalline (with disordered inclusions) and perfectly crystalline La0.7Ca0.3MnO3 thin films have been investigated. It was shown that the amorphous film is a paramagnet with the effective magnetic moment of 4.2 μB∕Mn ion. The crystalline film with nanoscale disordered inclusions demonstrates a superposition of the ferromagnetic (corresponding to the crystalline matrix) and the superparamagnetic (corresponding to the nanocrystalline disordered inclusions) contributions in the magnetization. The completely crystalline film undergoes only a ferromagnetic transition.
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75.50.Kj Amorphous and quasicrystalline magnetic materials
75.50.Dd Nonmetallic ferromagnetic materials
75.20.Ck Nonmetals
75.50.Tt Fine-particle systems; nanocrystalline materials
75.70.Ak Magnetic properties of monolayers and thin films
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Cr Saturation moments and magnetic susceptibilities
61.72.Qq Microscopic defects (voids, inclusions, etc.)

Surface ordering of (In,Ga)As quantum dots controlled by GaAs substrate indexes

Zh. M. Wang, Sh. Seydmohamadi, J. H. Lee, and G. J. Salamo

Appl. Phys. Lett. 85, 5031 (2004); http://dx.doi.org/10.1063/1.1823590 (3 pages) | Cited 24 times

Online Publication Date: 23 November 2004

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Self-organized surface ordering of (In,Ga)As quantum dots in a GaAs matrix was investigated using stacked multiple quantum dot layers prepared by molecular-beam epitaxy. While one-dimensional chain-like ordering is formed on singular and slightly misorientated GaAs(100) surfaces, we report on two-dimensional square-like ordering that appears on GaAs(n11)B, where n is 7, 5, 4, and 3. Using a technique to control surface diffusion, the different ordering patterns are found to result from the competition between anisotropic surface diffusion and anisotropic elastic matrix, a similar mechanism suggested before by Solomon [Appl. Phys. Lett. 84, 2073 (2004)].
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81.05.Ea III-V semiconductors
68.65.Hb Quantum dots (patterned in quantum wells)
68.35.B- Structure of clean surfaces (and surface reconstruction)
81.07.Ta Quantum dots
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.35.Fx Diffusion; interface formation
68.37.Ps Atomic force microscopy (AFM)

Scanning probe energy loss spectroscopy below 50 nm resolution

F. Festy and R. E. Palmer

Appl. Phys. Lett. 85, 5034 (2004); http://dx.doi.org/10.1063/1.1818742 (3 pages) | Cited 9 times

Online Publication Date: 23 November 2004

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We report scanning probe energy loss spectroscopy (SPELS) measurements from a roughened Si(111) surface in ultrahigh vacuum. The experiments, which utilize a scanning tunneling microscope tip in the field emission mode as the electron source, establish that the spatial resolution in SPELS is better than 50 nm. The spectral maps acquired indicate different contrast mechanisms for the inelastically scattered and secondary electrons identified in the energy loss spectrum.
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07.79.Cz Scanning tunneling microscopes
79.20.Uv Electron energy loss spectroscopy
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Vj Field emission and field-ion microscopy

Fabrication of three-dimensional photonic crystal with alignment based on electron beam lithography

G. Subramania and S. Y. Lin

Appl. Phys. Lett. 85, 5037 (2004); http://dx.doi.org/10.1063/1.1825623 (3 pages) | Cited 28 times

Online Publication Date: 23 November 2004

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We demonstrate the fabrication of a three-dimensional woodpile photonic crystal in the near-infrared using a layer-by-layer approach involving electron beam lithography and spin on glass planarization. The alignment accuracy between the first and the fifth layer is within 10% of the lattice spacing as measured from cross section scanning-electron-microscopy images. Optical reflectivity measurements reveal peaks consistent with the photonic gap frequency. The method offers a way of rapid prototyping full three-dimensional photonic band gap devices with considerable flexibility of materials choice. Moreover, lattice structure that can operate at wavelengths into the visible can be fabricated using this approach.
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42.70.Qs Photonic bandgap materials
85.40.Hp Lithography, masks and pattern transfer
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
81.65.-b Surface treatments
78.30.-j Infrared and Raman spectra
78.40.-q Absorption and reflection spectra: visible and ultraviolet

Localized surface plasmon singularities in amplifying media

N. M. Lawandy

Appl. Phys. Lett. 85, 5040 (2004); http://dx.doi.org/10.1063/1.1825058 (3 pages) | Cited 73 times

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The localized surface plasmon resonance of nanostructures is shown to exhibit a singularity when the surrounding medium exhibits amplification with a critical value of gain. This singularity can lead to large enhancements even when the gain is saturated. This composite medium should exhibit strong scattering within the plasmon band leading to low threshold random laser action and light localization effects. This effect could also greatly increase surface enhanced Raman scattering signals for rapid single, molecule detection, identification and sequencing.
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73.22.Lp Collective excitations
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
78.30.-j Infrared and Raman spectra

Charging control of InP∕GaInP quantum dots by heterostructure design

Jonas Persson, Dan Hessman, Mats-Erik Pistol, Werner Seifert, and Lars Samuelson

Appl. Phys. Lett. 85, 5043 (2004); http://dx.doi.org/10.1063/1.1827327 (3 pages)

Online Publication Date: 23 November 2004

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Semiconductor quantum dots are often charged due to accumulation from a doped host material. Using low-temperature photoluminescence, we have studied the charging of single self-assembled InP dots in structures designed to control the electron population in a weakly n-type environment. By using designed heterostructures to position the Fermi level of the structure, not requiring electric fields or currents, we show that the electron accumulation can be reduced from approximately 18 electrons in the dot to approximately 8 electrons. In particular, we show that the single quantum dot luminescence spectrum of the Fermi-level pinned structure perfectly matches the low-energy part of the highly charged reference spectrum, a phenomenon predicted by the model for multiple charging of quantum dots.
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73.21.La Quantum dots
78.67.Hc Quantum dots
78.55.Cr III-V semiconductors
73.63.Kv Quantum dots

Photoexcitation of excitons in self-assembled quantum dots

H. Pettersson, L. Landin, R. Liu, W. Seifert, M.-E. Pistol, and L. Samuelson

Appl. Phys. Lett. 85, 5046 (2004); http://dx.doi.org/10.1063/1.1824174 (3 pages) | Cited 3 times

Online Publication Date: 23 November 2004

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Using an approach of combining Fourier transform infrared spectroscopy with resonant illumination from a secondary external light source, we have measured the photocurrent (PC) for multiple layers of self-assembled InAs dots embedded in a matrix of InP. Without external illumination, we observe photoexcitation of electrons from bound states in the dots to the InP barrier. By additional illumination from the external light source, a strong broadening of the PC signal is observed. We interpret this broadening in terms of photoexcitation of electrons in the presence of additional holes in the dots created by the external light source. We extract the spectral distribution of the photoexcitation process at 6 and 77 K, respectively, and show by comparison with theoretical calculations that it is consistent with an exciton binding energy of 20 meV.
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73.21.La Quantum dots
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
78.67.Hc Quantum dots
78.55.Cr III-V semiconductors
73.50.Pz Photoconduction and photovoltaic effects

Nucleation and growth of deformation twins in nanocrystalline aluminum

Y. T. Zhu, X. Z. Liao, S. G. Srinivasan, Y. H. Zhao, M. I. Baskes, F. Zhou, and E. J. Lavernia

Appl. Phys. Lett. 85, 5049 (2004); http://dx.doi.org/10.1063/1.1823042 (3 pages) | Cited 61 times

Online Publication Date: 23 November 2004

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Deformation twins (DTs) in nanocrystalline (nc) Al were both predicted by atomic simulations, and observed experimentally. However, despite encouraging preliminary results, their formation mechanism remains poorly understood. Here we present an analytical model, based on classical dislocation theory, to explain the nucleation and growth of DTs in nc Al. A 60° dislocation system consisting of a 90° leading partial and a 30° trailing partial is found to most readily nucleate and grow a DT. The model suggests that the stress for twin growth is much smaller than that for its nucleation. It also predicts an optimal grain size for twin nucleation. The model successfully explains DTs observed experimentally in nc Al and is also applicable to other nc metals.
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61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)
62.25.-g Mechanical properties of nanoscale systems
81.40.Lm Deformation, plasticity, and creep
61.72.Mm Grain and twin boundaries
81.07.Bc Nanocrystalline materials
62.20.F- Deformation and plasticity

Fabrication and electrical characteristics of high-performance ZnO nanorod field-effect transistors

Won Il Park, Jin Suk Kim, Gyu-Chul Yi, M. H. Bae, and H.-J. Lee

Appl. Phys. Lett. 85, 5052 (2004); http://dx.doi.org/10.1063/1.1821648 (3 pages) | Cited 141 times

Online Publication Date: 23 November 2004

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We report on fabrication and electrical characteristics of high-mobility field-effect transistors (FETs) using ZnO nanorods. For FET fabrications, single-crystal ZnO nanorods were prepared using catalyst-free metalorganic vapor phase epitaxy. Although typical ZnO nanorod FETs exhibited good electrical characteristics, with a transconductance of ∼140 nS and a mobility of 75 cm2∕V s, the device characteristics were significantly improved by coating a polyimide thin layer on the nanorod surface, exhibiting a large turn-ON/OFF ratio of 104–105, a high transconductance of 1.9 μS, and high electron mobility above 1000 cm2∕V s. The role of the polymer coating in the enhancement of the devices is also discussed.
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85.30.Tv Field effect devices
73.61.Ph Polymers; organic compounds
72.20.Fr Low-field transport and mobility; piezoresistance
73.50.Dn Low-field transport and mobility; piezoresistance
73.63.Bd Nanocrystalline materials
81.65.Rv Passivation

Megasonic-assisted development of nanostructures: Investigations on high aspect ratio nanoholes

David Küpper, Daniel Küpper, Yordan M. Georgiev, Thorsten Wahlbrink, Wolfgang Henschel, Guido Bell, and Heinrich Kurz

Appl. Phys. Lett. 85, 5055 (2004); http://dx.doi.org/10.1063/1.1819986 (3 pages) | Cited 2 times

Online Publication Date: 23 November 2004

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The influence of megasonic agitation on the development of nanostructures with high aspect ratio is investigated thoroughly. The improvements in homogeneity, depth, and quality of nanostructures are related to specific interactions of the sound wave with the resist and developer. Two phases in the development process are operative. The specific role of microstreaming providing physical supply of fresh developer is identified and the reduction of viscosity by megasonic interaction is derived. The advantage of megasonic agitation as a nondestructive development of high aspect ratio nanostructures is demonstrated.
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43.35.Ty Other physical effects of sound
81.16.Nd Micro- and nanolithography
85.40.Hp Lithography, masks and pattern transfer

Enhancement of luminescent properties of ZnS:Mn nanophosphors by controlled ZnO capping

N. Karar, Harish Chander, and S. M. Shivaprasad

Appl. Phys. Lett. 85, 5058 (2004); http://dx.doi.org/10.1063/1.1815059 (3 pages) | Cited 24 times

Online Publication Date: 23 November 2004

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Results of a method is presented for synthesizing ZnS:Mn nanoparticles capped in situ by ZnO. Analysis of Raman spectra and x-ray photoelectron spectra results have reinforced claim of the formation of ZnO capping layer on the surface of ZnS:Mn nanoparticles. Raman spectra results also showed presence of stress at an optimum ZnO capping thickness. In brief, the only variation within samples is in their ZnO capping thickness. Phase formation was analyzed and confirmed from powder x-ray diffraction. ZnS:Mn particle size is about 4 nm. The change in photoluminescent properties with ZnO capping thickness variation is presented. It is shown that the variation in ZnO thickness and the resultant stress leads to an enhanced photoluminescence intensity/efficiency of nano-ZnS:Mn.
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78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.55.Et II-VI semiconductors
78.60.Hk Cathodoluminescence, ionoluminescence
78.30.Fs III-V and II-VI semiconductors
79.60.Bm Clean metal, semiconductor, and insulator surfaces
81.40.Gh Other heat and thermomechanical treatments

Size self-scaling effect in stacked InAs∕InAlAs nanowire multilayers

Z. Z. Sun, S. F. Yoon, J. Wu, and Z. G. Wang

Appl. Phys. Lett. 85, 5061 (2004); http://dx.doi.org/10.1063/1.1818335 (3 pages)

Online Publication Date: 23 November 2004

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Size self-scaling effect in stacked InAs∕In0.52Al0.48As nanowires on InP substrates is revealed, i.e., the base width and height of the InAs nanowires have clear proportional dependence on thickness of the InAlAs spacer layer used in different samples. The photoluminescence wavelength from different samples, which varies between 1.3 and 1.9 μm, is also found closely correlated to the size self-scaling effect. This phenomenon can be well explained in the context of formation mechanism and growth features of the InAs∕InAlAs nanowire arrays. The finding illustrates a degree of freedom to control the structural and optical properties of strained self-organized nanostructures.
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68.65.La Quantum wires (patterned in quantum wells)
68.65.Ac Multilayers
81.05.Ea III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
78.55.Cr III-V semiconductors

Nanoscale polymer recognition by spectral signature in scattering infrared near-field microscopy

T. Taubner, R. Hillenbrand, and F. Keilmann

Appl. Phys. Lett. 85, 5064 (2004); http://dx.doi.org/10.1063/1.1827334 (3 pages) | Cited 54 times

Online Publication Date: 23 November 2004

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We demonstrate—for a typical polymer vibrational infrared line—that scattering-type “apertureless” optical near-field microscopy features a spectral signature that differs characteristically from far-field absorption. Theory predicts a dispersion-like amplitude spectrum (besides an absorption-like, bell-shaped phase spectrum). This signature is experimentally verified for a vibrational resonance of PMMA, by probing with a CO laser tuned from 5.5 to 6 μm. We apply this signature to identify PMMA in the near-field imaging of a nanostructured PMMA/PS polymer blend, at <70 nm resolution. Our results suggest a potentially quantitative chemometry based on near-field infrared vibrational fingerprints with spatial resolution that could reach 10 nm.
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78.66.Qn Polymers; organic compounds
63.50.-x Vibrational states in disordered systems
78.30.Jw Organic compounds, polymers
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters

Biomimetic titanium dioxide film with structural color and extremely stable hydrophilicity

Zhong-Ze Gu, Akira Fujishima, and Osamu Sato

Appl. Phys. Lett. 85, 5067 (2004); http://dx.doi.org/10.1063/1.1825052 (3 pages) | Cited 35 times

Online Publication Date: 23 November 2004

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We biomimeticly fabricated titanium dioxide films with three-dimensionally ordered structure. These films exhibit structural color, photocatalysis, and photoinduced superhydrophilicity. In addition, this biomimetic approach solves the problem of the stability of the superhydrophilicity of titanium dioxide.
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68.55.A- Nucleation and growth
82.50.Hp Processes caused by visible and UV light
61.82.Ms Insulators
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
78.66.Nk Insulators
68.55.-a Thin film structure and morphology
61.72.J- Point defects and defect clusters
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