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5 Feb 2007

Volume 90, Issue 6, Articles (06xxxx)

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Appl. Phys. Lett. 90, 063114 (2007); http://dx.doi.org/10.1063/1.2457525 (3 pages)

Thomas J. Mullen, Charan Srinivasan, J. Nathan Hohman, Susan D. Gillmor, Mitchell J. Shuster, Mark W. Horn, Anne M. Andrews, and Paul S. Weiss
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Nanometer scale x-ray absorption spectroscopy and chemical states mapping of ultra thin oxides on silicon using electrostatic force microscopy

M. Ishii, B. Hamilton, N. R. J. Poolton, N. Rigopoulos, S. De Gendt, and K. Sakurai

Appl. Phys. Lett. 90, 063101 (2007); http://dx.doi.org/10.1063/1.2437073 (3 pages) | Cited 8 times

Online Publication Date: 5 February 2007

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Electrostatic force microscopy (EFM) was used to obtain highly spatially resolved spectroscopic and image information of semiconductor surface region. EFM with x-ray source (X-EFM) can probe x-ray induced photoionization of near surface electron trapping. The X-EFM signal dependent on x-ray photon energy results in nanometer scale x-ray absorption spectra. Furthermore, probing tip scanning at fixed x-ray photon energy provides chemical states imaging of the trapping. The authors demonstrate characterization of substoichiometric chemical oxidation of a Si surface with less than 1 nm spatial resolution.
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68.37.Ps Atomic force microscopy (AFM)
68.37.Yz X-ray microscopy
78.70.Dm X-ray absorption spectra
82.40.Np Temporal and spatial patterns in surface reactions

Comparative study of InAs quantum dots with different InGaAs capping methods

C. H. Lin, Woei Wu Pai, F. Y. Chang, and H. H. Lin

Appl. Phys. Lett. 90, 063102 (2007); http://dx.doi.org/10.1063/1.2454425 (3 pages) | Cited 9 times

Online Publication Date: 6 February 2007

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The authors have used cross-sectional scanning tunneling microscopy to examine strain relaxation profiles of InAs quantum dots with In0.33Ga0.67As layers overgrown by three distinct capping methods. A statistical analysis of strain relaxation profile allowed them to infer that the long wavelength emission (>1.3 μm) of InAs quantum dots capped with sequential GaAs/InAs binary growth is mainly due to a weaker quantum confinement effect. This particular capping method is better than the traditional molecular beam epitaxy with simultaneous In/Ga/As deposition, and much better than a capping method with separated Ga deposition followed by As and InAs growth.
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68.65.Hb Quantum dots (patterned in quantum wells)
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
73.21.La Quantum dots

Origin of the red luminescence band in photoluminescence spectra of ZnSe nanowires

U. Philipose, S. Yang, T. Xu, and Harry E. Ruda

Appl. Phys. Lett. 90, 063103 (2007); http://dx.doi.org/10.1063/1.2457190 (3 pages) | Cited 16 times

Online Publication Date: 6 February 2007

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In this work, the origin of the deep level, defect related photoluminescence emission band in ZnSe is investigated. Using the dependence of the peak energy on excitation intensity, it was shown to originate from donor-acceptor pair recombination. The binding energy of the donor-acceptor pair was estimated to be 18±0.5 meV and the shallow impurity Bohr radius was estimated to be 9.1±0.2 nm. Using a postgrowth annealing treatment in a Zn atmosphere, the two species involved in the donor-acceptor pair recombination process were attributed to Zn vacancies and Zn interstitials.
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78.67.Lt Quantum wires
78.55.Et II-VI semiconductors
71.55.Gs II-VI semiconductors
61.72.Cc Kinetics of defect formation and annealing

Effect of surface energy on the yield strength of nanoporous materials

W. X. Zhang and T. J. Wang

Appl. Phys. Lett. 90, 063104 (2007); http://dx.doi.org/10.1063/1.2459115 (3 pages) | Cited 15 times

Online Publication Date: 6 February 2007

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The effect of surface energy on the yield strength of nanoporous materials is investigated in this letter. The conventional micromechanics method is extended to consider the surface effect and an analytical expression of the yield surface of nanoporous materials in a complex stress state is derived. It is seen that surface energy has obvious effect on the overall yield strength of nanoporous materials, and the smaller the nanosized void, the more significant the effect of surface energy. The yield strength of nanoporous materials is size dependent.
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81.05.Rm Porous materials; granular materials
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
68.35.Md Surface thermodynamics, surface energies
61.72.Qq Microscopic defects (voids, inclusions, etc.)

Plasma etch method for extreme ultraviolet lithography photomask

Banqiu Wu and Ajay Kumar

Appl. Phys. Lett. 90, 063105 (2007); http://dx.doi.org/10.1063/1.2470470 (3 pages) | Cited 3 times

Online Publication Date: 6 February 2007

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Studies on extreme ultraviolet mask etch were carried out by using the Gibbs energy minimization method to select plasma etch chemistries and to determine product volatility when etching absorber material to ensure a clean process and chamber operation. A self-mask method and corresponding etch conditions were proposed and experimentally examined using the antireflective portion of an absorber layer as a hard mask for the bulk absorber layer beneath. This approach overcame the intrinsic soft mask disadvantage of large etch critical dimension (CD) bias and low pattern transfer fidelity, producing significantly reduced etch CD bias (2 nm) and high pattern transfer fidelity.
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52.77.Bn Etching and cleaning
81.65.Cf Surface cleaning, etching, patterning
85.40.Hp Lithography, masks and pattern transfer

High-frequency electrical properties of individual and bundled carbon nanotubes

J. J. Plombon, Kevin P. O’Brien, Florian Gstrein, Valery M. Dubin, and Yang Jiao

Appl. Phys. Lett. 90, 063106 (2007); http://dx.doi.org/10.1063/1.2437724 (3 pages) | Cited 53 times

Online Publication Date: 6 February 2007

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Bundles of single wall carbon nanotubes have been proposed as an interconnect that could potentially replace copper in state-of-the-art ultralarge-scale-integrated circuits if theoretically predicted inductance, resistance, and capacitance scale with the number of carbon nanotubes within the bundle. The authors report direct measurement of the kinetic inductance of individual single wall carbon nanotubes and measurement of the high-frequency impedance of bundles showing that the bundle inductance scales with the number of individual carbon nanotubes.
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73.63.Fg Nanotubes
72.30.+q High-frequency effects; plasma effects
85.40.Ls Metallization, contacts, interconnects; device isolation

Midinfrared metamaterials fabricated by nanoimprint lithography

Wei Wu, Zhaoning Yu, Shih-Yuan Wang, R. Stanley Williams, Yongmin Liu, Cheng Sun, Xiang Zhang, Evgenia Kim, Y. Ron Shen, and Nicholas X. Fang

Appl. Phys. Lett. 90, 063107 (2007); http://dx.doi.org/10.1063/1.2450651 (3 pages) | Cited 16 times

Online Publication Date: 6 February 2007

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A metamaterial comprising an ordered array of four metallic L-shaped components designed to operate in the mid-IR frequency regime has been fabricated and characterized. The fourfold rotational symmetry of the unit cell should suppress the undesirable bianisotropy observed for split-ring resonators. Nanoimprint lithography was used to demonstrate scalability for mass production. A dipole plasmon resonance with a negative permittivity and a magnetic resonance with a negative permeability were observed at wavelengths of 3.7 and 5.25 μm, respectively, in agreement with theoretical predictions.
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42.70.-a Optical materials
81.16.Nd Micro- and nanolithography

Raman scattering studies of cobalt nanoclusters formed during high energy implantation of cobalt ions in a silica matrix

P. Gangopadhyay, T. R. Ravindran, K. G. M. Nair, S. Kalavathi, B. Sundaravel, and B. K. Panigrahi

Appl. Phys. Lett. 90, 063108 (2007); http://dx.doi.org/10.1063/1.2434158 (3 pages) | Cited 6 times

Online Publication Date: 7 February 2007

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Nanoscale cobalt clusters are synthesized in a silica glass matrix through implantation of high energy cobalt ions. Surface acoustic symmetrical vibrational modes of cobalt nanoclusters are detected using Raman spectroscopy. Mode intensity is found to depend strongly on excitation wavelengths. X-ray diffraction studies reveal face-centered-cubic phase of cobalt nanoclusters in postannealed samples. Postannealing in vacuum has led to significant growth of the cobalt nanoclusters in the matrix.
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78.30.Er Solid metals and alloys
81.40.Gh Other heat and thermomechanical treatments
61.46.Bc Structure of clusters (e.g., metcars; not fragments of crystals; free or loosely aggregated or loosely attached to a substrate)

Enhanced visible-light absorption from PdO nanoparticles in nitrogen-doped titanium oxide thin films

Qi Li, Wei Liang, and Jian Ku Shang

Appl. Phys. Lett. 90, 063109 (2007); http://dx.doi.org/10.1063/1.2454344 (3 pages) | Cited 13 times

Online Publication Date: 8 February 2007

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Composite films were made by embedding nanoparticles of p-type PdO semiconductor in a n-type titanium oxide matrix. With the assistance of nitrogen ion beam, these PdO nanoparticles were confined to less than a couple of nanometers. The resulting nanocomposite films demonstrated an unusual “redshift” in the optical absorption spectrum, contrary to the well-known quantum size effect from semiconductor nanoparticles. The absorption in the visible-light range is shown to result from absorption by metallic-like nanoparticles as palladium changed its valence state from Pd2+ to Pd in nitrogen-doped titanium oxide matrix under visible-light illumination.
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78.66.-w Optical properties of specific thin films
78.40.-q Absorption and reflection spectra: visible and ultraviolet
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
77.55.-g Dielectric thin films

Generation of electricity in GaN nanorods induced by piezoelectric effect

W. S. Su, Y. F. Chen, C. L. Hsiao, and L. W. Tu

Appl. Phys. Lett. 90, 063110 (2007); http://dx.doi.org/10.1063/1.2472539 (3 pages) | Cited 24 times

Online Publication Date: 8 February 2007

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Conversion of mechanical energy into electric energy has been demonstrated in GaN nanorods. The measurement was achieved by deflecting GaN nanorods with a conductive atomic force microscope PtIr tip in contact. The mechanism relies on the coupling between piezoelectric and semiconducting properties in GaN nanorod, which creates a strain field and drives the charge flow across the nanorod. The result shown here opens up an opportunity for harvesting electricity from wasted mechanical energies in the ambient environment, which may lead to the realization of self-powered nanodevices.
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77.65.Ly Strain-induced piezoelectric fields
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
68.37.Ps Atomic force microscopy (AFM)
73.30.+y Surface double layers, Schottky barriers, and work functions
73.40.Ns Metal-nonmetal contacts

Large flexible nanowire grid visible polarizer made by nanoimprint lithography

Lei Chen, Jian Jim Wang, Frank Walters, Xuegong Deng, Mike Buonanno, Stephen Tai, and Xiaoming Liu

Appl. Phys. Lett. 90, 063111 (2007); http://dx.doi.org/10.1063/1.2472532 (3 pages) | Cited 17 times

Online Publication Date: 8 February 2007

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117 and 150 nm pitch polymer gratings were successfully fabricated on plastic substrate over large area by nanoimprint lithography. Nanowire-grid polarizers were made by depositing Al on the sidewalls of the gratings at oblique angles. The effects of grating period, grating linewidth, Al depth, and thickness were studied in detail. Excellent contrast ( ∼ 1000:1) and high transmittance (80%–90%) (without antireflection coating) at the wavelength of 500 nm and above were demonstrated.
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42.79.Ci Filters, zone plates, and polarizers
42.79.Dj Gratings
81.16.Nd Micro- and nanolithography
42.70.Jk Polymers and organics

Tenfold catalytic activity enhancement of Pt/C by doping with single walled carbon nanotube for methanol oxidation

Jayasri Narayanamoorthy, Sumitha Durairaj, Youngsik Song, Yuan Xu, and Jaewu Choi

Appl. Phys. Lett. 90, 063112 (2007); http://dx.doi.org/10.1063/1.2472720 (3 pages) | Cited 7 times

Online Publication Date: 9 February 2007

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Tenfold enhancement in catalytic activity of platinum supported by carbon black for methanol oxidation was achieved by doping with single walled carbon nanotubes less than 2 wt % of catalyst composite. The catalytic activity enhancement is attributed to the increase of catalyst utilization by improving interconnectivity among carbon blacks. This complies with the morphology, conductivity, and durability enhancement of the catalyst composites. Enhancement of the catalytic activity by doping a small fraction of carbon nanotubes into the catalyst composite is very promising as a highly efficient and cost-effective catalyst.
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82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
61.72.up Other materials
81.65.Mq Oxidation
72.80.Tm Composite materials
81.40.-z Treatment of materials and its effects on microstructure, nanostructure, and properties

Master-equation approach to understanding multistate phase-change memories and processors

C. David Wright, Konstantin Blyuss, and Peter Ashwin

Appl. Phys. Lett. 90, 063113 (2007); http://dx.doi.org/10.1063/1.2475606 (3 pages) | Cited 10 times

Online Publication Date: 9 February 2007

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A master-equation approach is used to perform dynamic modeling of phase-transformation processes that define the operating regimes and performance attributes of electronic (and optical) processors and multistate memory devices based on phase-change materials. The predictions of the so-called energy accumulation and direct-overwrite regimes, prerequisites for processing and memory functions, respectively, emerge in detail from the model, providing a theoretical framework for future device design and evaluation.
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85.30.De Semiconductor-device characterization, design, and modeling
84.30.Sk Pulse and digital circuits

Microcontact insertion printing

Thomas J. Mullen, Charan Srinivasan, J. Nathan Hohman, Susan D. Gillmor, Mitchell J. Shuster, Mark W. Horn, Anne M. Andrews, and Paul S. Weiss

Appl. Phys. Lett. 90, 063114 (2007); http://dx.doi.org/10.1063/1.2457525 (3 pages) | Cited 18 times

Online Publication Date: 9 February 2007

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The authors describe a chemical patterning technique, “microcontact insertion printing,” that utilizes conventional microcontact printing to pattern isolated molecules diluted within a preexisting self-assembled monolayer. By modifying the preexisting monolayer quality, the stamping duration, and/or the concentration of the patterned molecule, they can influence the extent of molecular exchange and precisely control the molecular composition of patterned self-assembled monolayers. This simple methodology can be used to fabricate complex patterns via multiple stamping steps and has applications ranging from bioselective surfaces to molecular-scale electronic components.
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81.16.Nd Micro- and nanolithography
81.16.Dn Self-assembly
81.16.Rf Micro- and nanoscale pattern formation
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