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6 Jun 2011

Volume 98, Issue 23, Articles (23xxxx)

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Appl. Phys. Lett. 98, 233101 (2011); http://dx.doi.org/10.1063/1.3597211 (3 pages)

Yu-Jung Lu (呂宥蓉), Hon-Way Lin (林弘偉), Hung-Ying Chen (陳虹穎), Yu-Chen Yang (楊右丞), and Shangjr Gwo (果尚志)
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Single InGaN nanodisk light emitting diodes as full-color subwavelength light sources

Yu-Jung Lu (呂宥蓉), Hon-Way Lin (林弘偉), Hung-Ying Chen (陳虹穎), Yu-Chen Yang (楊右丞), and Shangjr Gwo (果尚志)

Appl. Phys. Lett. 98, 233101 (2011); http://dx.doi.org/10.1063/1.3597211 (3 pages) | Cited 6 times

Online Publication Date: 6 June 2011

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Subwavelength electroluminescent sources with spatial, spectral, and polarization controlling capabilities are critical elements for optical imaging and lithography beyond the diffraction limit. Here, we show that the electroluminescence from single, strain-free InGaN nanodisks embedded in self-assembled GaN p-n nanorods can span the entire visible spectrum with a large linear polarization ratio ( ∼ 0.85). Furthermore, this unique nanodisk-in-nanorod geometry enables the realization of the ultrasmall footprint light-emitting diodes (LEDs) to be used as subwavelength light sources. Using these nano-LEDs, we are able to demonstrate near-field, subwavelength photolithography by controlling the exposure time and light intensity from single InGaN nanodisks at chosen wavelengths.
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85.60.Jb Light-emitting devices
42.72.-g Optical sources and standards

Dispersion of electron g-factor with optical transition energy in (In,Ga)As/GaAs self-assembled quantum dots

A. Schwan, B.-M. Meiners, A. B. Henriques, A. D. B. Maia, A. A. Quivy, S. Spatzek, S. Varwig, D. R. Yakovlev, and M. Bayer

Appl. Phys. Lett. 98, 233102 (2011); http://dx.doi.org/10.1063/1.3588413 (3 pages) | Cited 2 times

Online Publication Date: 6 June 2011

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The electron spin precession about an external magnetic field was studied by Faraday rotation on an inhomogeneous ensemble of singly charged, self-assembled (In,Ga)As/GaAs quantum dots. From the data the dependence of electron g-factor on optical transition energy was derived. A comparison with literature reports shows that the electron g-factors are quite similar for quantum dots with very different geometrical parameters, and their change with transition energy is almost identical.
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71.18.+y Fermi surface: calculations and measurements; effective mass, g factor
81.07.Ta Quantum dots
78.67.Hc Quantum dots
78.20.Ls Magneto-optical effects
78.55.Cr III-V semiconductors
81.05.Ea III-V semiconductors

Ultrafast spectroscopy with a scanning tunneling microscope

Ian Moult, Marie Herve, and Yan Pennec

Appl. Phys. Lett. 98, 233103 (2011); http://dx.doi.org/10.1063/1.3597351 (3 pages) | Cited 1 time

Online Publication Date: 7 June 2011

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We present a method combining a scanning tunneling microscope and a pulse generator to achieve unprecedented spatiotemporal resolution for spectroscopy at surfaces. Using the so-called pulsed scanning tunneling spectroscopy (P-STS) we identify the stacking schemes at the surface of graphite with a probe time down to 300 ps while conserving atomic resolution. The technique is simple to implement and requires only increasing the signal bandwidth on the bias side of the tunneling junction. We foresee the P-STS as a highly versatile dynamical probe which could be applied to track in time the variation in the sample local density of states induced by any possible excitation.
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07.79.Cz Scanning tunneling microscopes
06.60.Jn High-speed techniques (microsecond to femtosecond)

In situ compression study of taper-free metallic glass nanopillars

O. V. Kuzmin, Y. T. Pei, and J. T. M. De Hosson

Appl. Phys. Lett. 98, 233104 (2011); http://dx.doi.org/10.1063/1.3598400 (3 pages) | Cited 4 times

Online Publication Date: 7 June 2011

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Because tapering leads to inevitable artifacts in the analyses of compression experiments on micrometer sized pillars, in this study taper-free nanosized pillars of Zr-based metallic glass of Zr61.8Cu18Ni10.2Al10 composition with diameter ranging from 600 to 90 nm were fabricated. These pillars were compressed in situ in a transmission electron microscope as a function of pillar diameter. Under compression each pillar of large diameter exhibits predominant inhomogeneous and intermittent plastic flow characterized by shear banding (SB) events. However, pillars around 150 nm in diameter and below show homogeneous deformation during compression without SB.
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81.07.Bc Nanocrystalline materials
62.20.fq Plasticity and superplasticity
81.40.Lm Deformation, plasticity, and creep
61.43.Fs Glasses
61.46.-w Structure of nanoscale materials

Force mode dip-pen nanolithography on soft polydimethylsiloxane surface

Haijun Yang, Guangxia Shen, and Shouwu Guo

Appl. Phys. Lett. 98, 233105 (2011); http://dx.doi.org/10.1063/1.3597158 (3 pages) | Cited 1 time

Online Publication Date: 8 June 2011

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Control on the loading force supplied on atomic force microscopy tip and the tip dwell time on substrate are important for dip-pen nanolithography (DPN), especially operating on soft substrate. A force mode DPN (FMDPN) method has been developed in this letter. Using FMDPN, the loading force can be properly tuned by presetting a “trigger threshold” parameter, and the dwell time can be adjusted by changing the “surface delay” data. Thus, the DPN can be conducted more controllably, and the nanopatterns could be prepared on soft substrate easily.
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81.16.Nd Micro- and nanolithography
81.16.Ta Atom manipulation

Three-dimensional nanojunction device models for photovoltaics

Artit Wangperawong and Stacey F. Bent

Appl. Phys. Lett. 98, 233106 (2011); http://dx.doi.org/10.1063/1.3595411 (3 pages) | Cited 4 times

Online Publication Date: 8 June 2011

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A model is developed to describe the behavior of three-dimensionally nanostructured photovoltaic devices, distinguishing between isolated radial pn junctions and interdigitated pn junctions. We examine two specific interdigitated architectures, the point-contact nanojunction and the extended nanojunction, which are most relevant to experimental devices reported to date but have yet to be distinguished in the field. The model is also applied to polycrystalline CdTe devices with inverted grain boundaries. We demonstrate that for CdTe/CdS solar cells using low-quality materials, the efficiency of the extended nanojunction geometry is superior to other designs considered.
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88.40.J- Types of solar cells
88.40.hj Efficiency and performance of solar cells
85.30.De Semiconductor-device characterization, design, and modeling
85.30.Hi Surface barrier, boundary, and point contact devices

Single-wire photodetectors based on InGaN/GaN radial quantum wells in GaN wires grown by catalyst-free metal-organic vapor phase epitaxy

A. De Luna Bugallo, L. Rigutti, G. Jacopin, F. H. Julien, C. Durand, X. J. Chen, D. Salomon, J. Eymery, and M. Tchernycheva

Appl. Phys. Lett. 98, 233107 (2011); http://dx.doi.org/10.1063/1.3596446 (3 pages) | Cited 6 times

Online Publication Date: 8 June 2011

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We present a letter on single-wire photodetectors based on radial n-i-n multiquantum well (QW) junctions. The devices are realized from GaN wires grown by catalyst-free metalorganic vapor phase epitaxy coated at their top by five nonpolar In0.16Ga0.84N/GaN undoped radial QWs, and are sensitive to light with energy E>2.6 eV. Their photoconductive gain is as high as 2×103. The scanning photocurrent microscopy maps evidence that the detector response is localized at the extremity containing the QWs for both below (at λ = 488 nm) and above GaN band gap (at λ = 244 nm) excitation. This confirms that the device operates as a radial n-i-n junction.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

Tunable metal–insulator transitions in bilayer graphene by thermal annealing

Gopinadhan Kalon, Young Jun Shin, and Hyunsoo Yang

Appl. Phys. Lett. 98, 233108 (2011); http://dx.doi.org/10.1063/1.3598403 (3 pages) | Cited 3 times

Online Publication Date: 9 June 2011

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Tunable and highly reproducible metal–insulator transitions have been observed in bilayer graphene upon thermal annealing at 400 K under high vacuum conditions. Before annealing, the sample is metallic in the whole temperature regime of study. Upon annealing, the conductivity changes from metallic to that of an insulator and the transition temperature is a function of annealing time. The pristine metallic state can be reinstated by exposing to air thereby inducing changes in the electronic properties by adsorbing water vapor, which makes graphene a technologically promising material for sensor applications.
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71.30.+h Metal-insulator transitions and other electronic transitions
81.40.Gh Other heat and thermomechanical treatments
81.05.ue Graphene
72.80.Vp Electronic transport in graphene
68.43.Mn Adsorption kinetics

{111} local configurations: The main source of silicon defects during solid phase epitaxial regrowth modeled by lattice kinetic Monte Carlo

Ignacio Martin-Bragado

Appl. Phys. Lett. 98, 233109 (2011); http://dx.doi.org/10.1063/1.3596466 (3 pages) | Cited 6 times

Online Publication Date: 9 June 2011

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A lattice kinetic Monte Carlo model for defect generation during solid phase epitaxial regrowth (SPER) is presented. It assumes two simple causes for defective Si formation: amorphous atoms in local {111} configurations having a probability to become defective and random nucleation and growth creating alternative crystalline seeds. Simulations are compared with experimental results for (001) and (011) Si substrates with different topologies and aligned to 〈100〉 and 〈110〉 crystalline axes, showing the model accuracy and validating its assumptions. {111} local recrystallization is the main cause for defective Si generation during SPER, by providing the seeds for defects propagated by SPER.
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81.10.Jt Growth from solid phases (including multiphase diffusion and recrystallization)
64.60.Q- Nucleation
61.72.Mm Grain and twin boundaries

Nanopatterning on rough surfaces using optically trapped microspheres

Y.-C. Tsai, R. Fardel, and C. B. Arnold

Appl. Phys. Lett. 98, 233110 (2011); http://dx.doi.org/10.1063/1.3598427 (3 pages) | Cited 2 times

Online Publication Date: 9 June 2011

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While nanofabricated structures find an increasingly large number of applications, few techniques are able to pattern rough or uneven surfaces, or surfaces with pre-existing structure. In this letter we show that optical trap assisted nanopatterning (OTAN), a near-field laser based technique, is able to produce nanoscale features on surfaces with large roughness but without the need for focus adjustment. Patterning on model surfaces of polyimide with vertical steps greater than 0.5 μm shows a high degree of uniformity, demonstrating that OTAN is a suitable technique to pattern nontraditional surfaces for emerging technologies.
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81.16.Rf Micro- and nanoscale pattern formation
68.35.B- Structure of clean surfaces (and surface reconstruction)

On the thermal conductivity of particulate nanocomposites

J. Ordonez-Miranda, Ronggui Yang, and J. J. Alvarado-Gil

Appl. Phys. Lett. 98, 233111 (2011); http://dx.doi.org/10.1063/1.3593387 (3 pages) | Cited 10 times

Online Publication Date: 10 June 2011

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The modified effective medium approximation model proposed by Minnich and Chen [Appl. Phys. Lett. 91, 073105 (2007)] for the thermal conductivity of nanocomposites is extended for spheroidal inclusions. It is shown that the dependence of the thermal conductivity of nanocomposites on the shape and size of particle inclusions can be described by: (1) the collision cross-section per unit volume of the particles and (2) the mean distance that the energy carriers (electrons or phonons) can travel inside the particles. The predictions of this analytical approach are in good agreement with available data obtained through numerical calculations of the Boltzmann equation.
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66.70.Lm Other systems such as ionic crystals, molecular crystals, nanotubes, etc.
61.46.-w Structure of nanoscale materials
61.72.Qq Microscopic defects (voids, inclusions, etc.)
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