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10 Nov 2008

Volume 93, Issue 19, Articles (19xxxx)

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Appl. Phys. Lett. 93, 192501 (2008); http://dx.doi.org/10.1063/1.3013857 (3 pages)

O. Hellwig, A. Moser, E. Dobisz, Z. Z. Bandic, H. Yang, D. S. Kercher, J. D. Risner-Jamtgaard, D. Yaney, and E. E. Fullerton
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Simulation of a plasmonic tip-terminated scanning nanowire waveguide for molecular imaging

Nathan P. Malcolm, Alex J. Heltzel, Konstantin V. Sokolov, Li Shi, and John R. Howell

Appl. Phys. Lett. 93, 193101 (2008); http://dx.doi.org/10.1063/1.3013816 (3 pages) | Cited 2 times

Online Publication Date: 10 November 2008

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Finite difference time domain simulation reveals plasmon coupling and local field enhancement at the gap between the gold nanoparticle (NP) tip of a ZnO nanowire (NW) waveguide and a gold-coated substrate or a gold NP probe. The region of field enhancement is about three times smaller than the 100 nm diameter of the gold NP tip, making the NW waveguide grown on a transparent microcantilever well-suited for near field imaging of single molecules immobilized on a gold substrate or gold NP-labeled cell membranes with superior spatial resolution and signal to noise ratio.
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68.65.La Quantum wires (patterned in quantum wells)
61.46.Km Structure of nanowires and nanorods (long, free or loosely attached, quantum wires and quantum rods, but not gate-isolated embedded quantum wires)

GaN-nanowire/amorphous-Si core-shell heterojunction diodes

Abhishek Motayed and Albert V. Davydov

Appl. Phys. Lett. 93, 193102 (2008); http://dx.doi.org/10.1063/1.3021390 (3 pages) | Cited 6 times

Online Publication Date: 10 November 2008

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We report the electrical characterization of gallium-nitride/amorphous-silicon (n-type nanowire/p-type shell) diodes fabricated by postgrowth silicon shell formation technique. The n-type (unintentionally doped) gallium-nitride (GaN) nanowires were aligned on prepatterned sapphire substrates using dielectrophoresis. The amorphous silicon (a-Si) shell was deposited using plasma enhanced chemical vapor deposition technique and doped using spin-on boron dopant. Using photolithography, plasma etching, and metal deposition, complete p-n (p-type a-Si shell on n-type GaN nanowire) heterojunction diodes were developed. These diodes had reliable electrical characteristics with 1 V forward turn-on voltage. These nanowire core-shell heterojunction diodes exhibited negative differential resistance, which can be explained by phonon-assisted interband tunneling mechanism.
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85.30.Kk Junction diodes

Enhanced absorption by nanostructured silicon

S. Bandiera, D. Jacob, T. Muller, F. Marquier, M. Laroche, and J.-J. Greffet

Appl. Phys. Lett. 93, 193103 (2008); http://dx.doi.org/10.1063/1.3021480 (3 pages) | Cited 6 times

Online Publication Date: 10 November 2008

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Some applications such as ultrafast detectors or high efficiency photovoltaics require absorption by thin films. However, close to the bandgap, silicon absorbs very poorly. In this letter, we show that the absorption of a 100 nm slab can be as high as 50% in the range of wavelengths 700–830 nm when using a periodic structure properly designed.
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78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
68.55.-a Thin film structure and morphology
61.46.Hk Nanocrystals
73.22.-f Electronic structure of nanoscale materials and related systems
78.30.Am Elemental semiconductors and insulators

Fountain-pen controlled dielectrophoresis for carbon nanotube-integration in device assembly

Timo Schwamb, Niklas C. Schirmer, Brian R. Burg, and Dimos Poulikakos

Appl. Phys. Lett. 93, 193104 (2008); http://dx.doi.org/10.1063/1.3026531 (3 pages) | Cited 2 times

Online Publication Date: 10 November 2008

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A method to integrate functional nanoparticles, exemplified by carbon nanotubes (CNTs), in devices is presented. This method combines the dielectrophoretic deposition of nanoparticles with microscale liquid handling by the fountain-pen principle. This combination allows an automatable, precise, and point-wise deposition of nanoparticles. Furthermore, a method-intrinsic separation mechanism was observed, based on which, the unwanted deposition of spaghettilike CNT bundles could be controlled. The feasibility of the method was proven numerically and experimentally.
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85.35.Kt Nanotube devices
85.40.Sz Deposition technology

Effects of p-doping on the thermal sensitivity of individual Si nanowires

A. Brioude, D. Cornu, P. Miele, C. Mouchet, J.-P Simonato, and E. Rouvière

Appl. Phys. Lett. 93, 193105 (2008); http://dx.doi.org/10.1063/1.2968134 (3 pages) | Cited 1 time

Online Publication Date: 11 November 2008

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A gradual downshift and broadening of the Si optical phonon peak was observed by Raman scattering measurements on individual undoped and p-doped silicon nanowire (SiNW) when heated by a laser beam. This dual effect can be interpreted by an induced compressive stress resulting from structural defects. The p-doped SiNW was shown to be the most sensitive to heating and its structure was clearly modified with a large diffusion of gold atoms forming numerous gold nanoparticles.
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78.67.Lt Quantum wires
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
63.22.Gh Nanotubes and nanowires
61.46.Km Structure of nanowires and nanorods (long, free or loosely attached, quantum wires and quantum rods, but not gate-isolated embedded quantum wires)
61.72.uf Ge and Si
78.30.Am Elemental semiconductors and insulators

A metal-wire/quantum-dot composite metamaterial with negative ε and compensated optical loss

Alexander Bratkovsky, Ekaterina Ponizovskaya, Shih-Yuan Wang, Petter Holmström, Lars Thylén, Ying Fu, and Hans Ågren

Appl. Phys. Lett. 93, 193106 (2008); http://dx.doi.org/10.1063/1.3013331 (3 pages) | Cited 19 times

Online Publication Date: 12 November 2008

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Numerical simulations of a binary mixture of quantum dots exhibiting gain with silver nanorods are performed, showing the feasibility of lossless negative ε operation for realistic material structures and parameters.
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77.22.Ch Permittivity (dielectric function)
77.22.Gm Dielectric loss and relaxation
72.80.Tm Composite materials
71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Graphene: A perfect nanoballoon

O. Leenaerts, B. Partoens, and F. M. Peeters

Appl. Phys. Lett. 93, 193107 (2008); http://dx.doi.org/10.1063/1.3021413 (3 pages) | Cited 32 times

Online Publication Date: 12 November 2008

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We have performed a first-principles density functional theory investigation of the penetration of helium atoms through a graphene monolayer with defects. The relaxation of the graphene layer caused by the incoming helium atoms does not have a strong influence on the height of the energy barriers for penetration. For defective graphene layers, the penetration barriers decrease exponentially with the size of the defects but they are still sufficiently high that very large defects are needed to make the graphene sheet permeable for small atoms and molecules. This makes graphene a very promising material for the construction of nanocages and nanomembranes.
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61.46.Hk Nanocrystals
61.72.jd Vacancies

Magneto-optical and magnetotransport properties of amorphous ferromagnetic semiconductor Ge1−xMnx thin films

Shinsuke Yada, Satoshi Sugahara, and Masaaki Tanaka

Appl. Phys. Lett. 93, 193108 (2008); http://dx.doi.org/10.1063/1.3023070 (3 pages) | Cited 8 times

Online Publication Date: 12 November 2008

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The authors investigate the magnetooptical and magnetotransport properties of Mn-doped amorphous Ge (a-Ge1−xMnx) thin films deposited on thermally oxidized Si substrates. Magnetic circular dichroism measurements reveal that their ferromagnetic ordering appears for x>0.02 and the films show magnetically homogeneous behavior. The resistivity of the films decreases with increasing x, and the temperature dependence of the resistivity shows semiconductor-like behavior. The anomalous Hall effect of the a-Ge1−xMnx films also exhibits ferromagnetic behavior. The temperature dependence of magnetization is consistent with that of the magnetooptical and magnetotransport results. These results indicate that the a-Ge1−xMnx films behave as a ferromagnetic semiconductor.
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78.20.Ls Magneto-optical effects
75.70.Ak Magnetic properties of monolayers and thin films
73.61.Jc Amorphous semiconductors; glasses
75.50.Pp Magnetic semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)

Near-field thermal imaging of nanostructured surfaces

A. Kittel, U. F. Wischnath, J. Welker, O. Huth, F. Rüting, and S.-A. Biehs

Appl. Phys. Lett. 93, 193109 (2008); http://dx.doi.org/10.1063/1.3025140 (3 pages) | Cited 17 times

Online Publication Date: 12 November 2008

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We show that a near-field scanning thermal microscope, which essentially detects the local density of states of the thermally excited electromagnetic modes at nanometer distances from some material, can be employed for nanoscale imaging of structures on that material’s surface. This finding is explained theoretically by an approach which treats the surface structure perturbatively.
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78.67.-n Optical properties of low-dimensional, mesoscopic, and nanoscale materials and structures
73.22.-f Electronic structure of nanoscale materials and related systems
61.46.-w Structure of nanoscale materials

Displacement detection of silicon nanowires by polarization-enhanced fiber-optic interferometry

John M. Nichol, Eric R. Hemesath, Lincoln J. Lauhon, and Raffi Budakian

Appl. Phys. Lett. 93, 193110 (2008); http://dx.doi.org/10.1063/1.3025305 (3 pages) | Cited 13 times

Online Publication Date: 12 November 2008

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We describe the displacement detection of freestanding silicon [111] nanowires by fiber-optic interferometry. We observe approximately a 50-fold enhancement in the scattered intensity for nanowires 40–60 nm in diameter for incident light polarized parallel to the nanowire axis, as compared to perpendicular polarization. This enhancement enables us to achieve a displacement sensitivity of 0.5 pm/math for 15 μW of light incident on the nanowire. The nanowires exhibit ultralow mechanical dissipation in the range of (2×10−15)–(2×10−14) kg/s and could be used as mechanical sensors for ultrasensitive scanning probe force measurements.
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06.30.Bp Spatial dimensions (e.g., position, lengths, volume, angles, and displacements)
42.81.Pa Sensors, gyros
42.81.Gs Birefringence, polarization
07.60.Ly Interferometers

Room temperature ferromagnetism at self-assembled monolayer modified Ag nanocluster–ZnO nanowire interface

S. Deng, K. P. Loh, J. B. Yi, J. Ding, H. R. Tan, M. Lin, Y. L. Foo, M. Zheng, and C. H. Sow

Appl. Phys. Lett. 93, 193111 (2008); http://dx.doi.org/10.1063/1.3025853 (3 pages) | Cited 3 times

Online Publication Date: 12 November 2008

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Magnetic characterization of ZnO nanowires (NW) decorated with thiol-capped Ag nanoclusters (NCs) reveals spontaneous field-dependent magnetization and hysteresis at room temperature. The saturation magnetization is temperature independent for the 13 nm thiol-capped Ag NCs but unexpectedly increases with temperature for the 4 nm thiol-capped Ag NCs. The high magnetic moment results from the efficient dispersal of Ag NCs on the ZnO NW scaffold and charge transfer interaction between Ag and ZnO. The anomalous magnetic behavior in 4 nm NCs may be due to the spin reorientation of Ag–S dipoles mediated by Zn–S dipoles.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.75.-c Magnetic properties of nanostructures
81.16.Dn Self-assembly
75.70.Ak Magnetic properties of monolayers and thin films
75.30.Cr Saturation moments and magnetic susceptibilities

High capacitance carbon-based xerogel film produced without critical drying

Yousheng Tao, Morinobu Endo, Risa Ohsawa, Hirofumi Kanoh, and Katsumi Kaneko

Appl. Phys. Lett. 93, 193112 (2008); http://dx.doi.org/10.1063/1.2976684 (3 pages) | Cited 2 times

Online Publication Date: 13 November 2008

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We report the production of carbon-based xerogel film without the need for supercritical drying. Xerogel samples were characterized with field emission scanning electron microscopy, nitrogen adsorption/desorption at 77 K, Raman spectroscopy, thermogravimetric analysis, and electrical conductivity and cyclic voltammetry measurements. Experimental results reveal that the film is largely crack free and homogeneous in thickness, and, importantly, has high surface area, large nanopore volume, and an excellent performance for electrical charge storage—both per unit mass and unit volume. These results indicate that the film has potential applications for electrical energy storage devices.
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81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
73.61.Ng Insulators
84.32.Tt Capacitors
78.30.-j Infrared and Raman spectra
68.43.Mn Adsorption kinetics
82.70.Gg Gels and sols

Vertical integration on plastic substrates using transfer printing

A. J. Tunnell, V. W. Ballarotto, D. R. Hines, and E. D. Williams

Appl. Phys. Lett. 93, 193113 (2008); http://dx.doi.org/10.1063/1.3026744 (3 pages) | Cited 4 times

Online Publication Date: 13 November 2008

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A process for preparing vertical interconnects for flexible electronics using transfer printing is reported. The interconnects are initially prepared on a sacrificial transfer substrate in a four step process that yields a subassembly of upper electrode, interconnect, and dielectric. This subassembly is printed as a unit onto the lower electrodes. The average contact resistance is less than 1 Ω/25 μm2 interconnect cross section. The quality of the resulting conductive paths is established by fabricating and characterizing (to 5 GHz) the inductances and quality factors of a series of square planar spiral inductors.
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85.40.Ls Metallization, contacts, interconnects; device isolation
84.32.Hh Inductors and coils; wiring
82.35.Gh Polymers on surfaces; adhesion
81.65.Cf Surface cleaning, etching, patterning

Structure map for embedded binary alloy nanocrystals

C. W. Yuan, S. J. Shin, C. Y. Liao, J. Guzman, P. R. Stone, M. Watanabe, J. W. Ager, III, E. E. Haller, and D. C. Chrzan

Appl. Phys. Lett. 93, 193114 (2008); http://dx.doi.org/10.1063/1.3027066 (3 pages) | Cited 4 times

Online Publication Date: 13 November 2008

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The equilibrium structure of embedded nanocrystals formed from strongly segregating binary alloys is considered within a simple thermodynamic model. The model identifies two dimensionless interface energies that dictate the structure and allows prediction of the stable structure for any choice of these parameters. The resulting structure map includes three distinct nanocrystal morphologies: core/shell, lobe/lobe, and completely separated spheres.
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61.46.Hk Nanocrystals
65.40.gp Surface energy

Evidence of Cd1−xMnxS nanocrystal growth in a glass matrix by the fusion method

N. O. Dantas, E. S. F. Neto, R. S. Silva, D. R. Jesus, and F. Pelegrini

Appl. Phys. Lett. 93, 193115 (2008); http://dx.doi.org/10.1063/1.3027471 (3 pages) | Cited 16 times

Online Publication Date: 13 November 2008

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In this work, CdS nanocrystals (NCs) doped with Mn were synthesized in a glass matrix by fusion. The as-grown Cd1−xMnxS NCs were investigated by optical absorption, atomic force microscopy, and electron paramagnetic resonance (EPR). The incorporation of Mn2+ ions in CdS NCs was confirmed by an absorption transition blueshift with increasing Mn concentration x. EPR spectra demonstrated the existence of two distinct Mn2+ ion locations: one incorporated in the core and the other near the surface of the Cd1−xMnxS NCs. The hyperfine interaction constants used to simulate the EPR spectra were A = 7.6 and 8.2 mT, respectively. The synthesis of high quality Cd1−xMnxS NCs may allow the control of optical and magnetic properties.
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81.16.-c Methods of micro- and nanofabrication and processing
61.46.Hk Nanocrystals
68.35.bg Semiconductors
71.70.Jp Nuclear states and interactions
76.30.-v Electron paramagnetic resonance and relaxation

Comparison of nanoscale measurements of strain and stress using electron back scattered diffraction and confocal Raman microscopy

Mark D. Vaudin, Yvonne B. Gerbig, Stephan J. Stranick, and Robert F. Cook

Appl. Phys. Lett. 93, 193116 (2008); http://dx.doi.org/10.1063/1.3026542 (3 pages) | Cited 26 times

Online Publication Date: 13 November 2008

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Stresses in Si as small as 10 MPa have been measured using electron backscattered diffraction (EBSD) and confocal Raman microscopy (CRM) with spatial resolutions of 10 nm and 100 nm, respectively. In both techniques, data were collected across wedge indentations in (001) Si. EBSD measured the stress and strain tensors and CRM measured the uniaxial stress. The results agreed very well except close to the indentation, where the surface-sensitive EBSD results indicated larger stresses. Results converged when the CRM laser excitation wavelength was reduced, probing smaller depths. The stress profiles are consistent with the inverse-square power law predicted by Eshelby analysis.
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81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.Qp Friction, tribology, and hardness
78.30.Am Elemental semiconductors and insulators
79.20.Kz Other electron-impact emission phenomena

Nanometer-scale sharpness in corner-overgrown heterostructures

L. Steinke, P. Cantwell, D. Zakharov, E. Stach, N. J. Zaluzec, A. Fontcuberta i Morral, M. Bichler, G. Abstreiter, and M. Grayson

Appl. Phys. Lett. 93, 193117 (2008); http://dx.doi.org/10.1063/1.2988526 (3 pages) | Cited 1 time

Online Publication Date: 14 November 2008

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A corner-overgrown GaAs/AlGaAs heterostructure is investigated with transmission and scanning transmission electron microscopy, demonstrating self-limiting growth of an extremely sharp corner profile 3.5 nm wide. In the AlGaAs layers, we observe self-ordered diagonal stripes, precipitating exactly at the corner, which show increased Al content measured with x-ray spectroscopy. A quantitative model for self-limited growth is adapted to the present case of faceted molecular beam epitaxial growth, and the corner sharpness is discussed in relation to quantum confined structures. We note that corner overgrowth maintains nanometer sharpness after microns of growth, allowing corner-shaped nanostructures.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.16.-c Methods of micro- and nanofabrication and processing
78.70.-g Interactions of particles and radiation with matter
61.46.-w Structure of nanoscale materials
68.55.ag Semiconductors

Free flight of an oscillated string pendulum as a tool for the mechanical characterization of an individual polymer nanofiber

Michael Burman, Arkadii Arinstein, and Eyal Zussman

Appl. Phys. Lett. 93, 193118 (2008); http://dx.doi.org/10.1063/1.3000016 (3 pages) | Cited 8 times

Online Publication Date: 14 November 2008

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The physical principles of a method for the mechanical testing of individual nanofibers are presented. A fiber with an attached mass undergoing a test is considered as a string pendulum. In addition to regular oscillations under the elastic force, the suspended bob performs free flight only under gravity which can be easily tracked. Based on a model developed to analyze the resonant frequency dependence of these flights, the Young’s modulus of the nanofiber was determined. The proposed method was verified with testing of individual nanofibers of nylon-66, which demonstrated the increase in the Young’s modulus for fiber diameters below 500 nm.
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62.25.-g Mechanical properties of nanoscale systems
61.41.+e Polymers, elastomers, and plastics
62.20.de Elastic moduli

Temperature dependent Raman spectroscopy of chemically derived graphene

Matthew J. Allen, Jesse D. Fowler, Vincent C. Tung, Yang Yang, Bruce H. Weiller, and Richard B. Kaner

Appl. Phys. Lett. 93, 193119 (2008); http://dx.doi.org/10.1063/1.3011030 (3 pages) | Cited 13 times

Online Publication Date: 14 November 2008

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Reduced graphite oxide (GO) has shown promise as a scalable alternative to mechanically exfoliated specimens. Although many measurements show that reduced GO has properties approaching those of pristine graphene, it has been difficult to quantify the extent to which the graphitic network is restored upon reduction. Raman spectroscopy is widely used for the characterization of mechanically exfoliated graphene, but has not been fully explored for reduced GO. In this work, hydrazine suspensions of reduced GO are deposited on micro-hot-plates and examined over a range of temperatures by Raman spectroscopy. The work highlights the benefits of solution processing.
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78.67.-n Optical properties of low-dimensional, mesoscopic, and nanoscale materials and structures
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
82.70.Kj Emulsions and suspensions
78.30.Na Fullerenes and related materials

Defect annihilation and morphological improvement of hydrothermally grown ZnO nanorods by Ga doping

A. Escobedo-Morales and U. Pal

Appl. Phys. Lett. 93, 193120 (2008); http://dx.doi.org/10.1063/1.3026746 (3 pages) | Cited 7 times

Online Publication Date: 14 November 2008

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One dimensional zinc oxide nanostructures were grown by a low temperature hydrothermal process. Effects of Ga doping on the growth, crystallization, and defect distribution in them were studied by x-ray diffraction, scanning electron microscopy, photoluminescence, and Fourier-transform infrared spectroscopy techniques. It has been shown that Ga doping improves the morphological homogeneity and optical properties of ZnO nanostructures. Improved morphology of the doped nanostructures have been associated with the catalytic effect of Ga. Effects of Ga doping on the quenching of defect emission and improvement of excitonic emission in ZnO nanostructures are discussed.
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81.16.-c Methods of micro- and nanofabrication and processing
81.10.Dn Growth from solutions
78.55.Et II-VI semiconductors
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
61.72.uj III-V and II-VI semiconductors
78.30.Fs III-V and II-VI semiconductors

Enhanced thermoelectric figure of merit in nanostructured n-type silicon germanium bulk alloy

X. W. Wang, H. Lee, Y. C. Lan, G. H. Zhu, G. Joshi, D. Z. Wang, J. Yang, A. J. Muto, M. Y. Tang, J. Klatsky, S. Song, M. S. Dresselhaus, G. Chen, and Z. F. Ren

Appl. Phys. Lett. 93, 193121 (2008); http://dx.doi.org/10.1063/1.3027060 (3 pages) | Cited 78 times

Online Publication Date: 14 November 2008

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The dimensionless thermoelectric figure of merit (ZT) of the n-type silicon germanium (SiGe) bulk alloy at high temperature has remained at about one for a few decades. Here we report that by using a nanostructure approach, a peak ZT of about 1.3 at 900 °C in an n-type nanostructured SiGe bulk alloy has been achieved. The enhancement of ZT comes mainly from a significant reduction in the thermal conductivity caused by the enhanced phonon scattering off the increased density of nanograin boundaries. The enhanced ZT will make such materials attractive in many applications such as solar, thermal, and waste heat conversion into electricity.
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72.20.Pa Thermoelectric and thermomagnetic effects
73.63.-b Electronic transport in nanoscale materials and structures
81.07.Wx Nanopowders
81.16.-c Methods of micro- and nanofabrication and processing
66.70.Df Metals, alloys, and semiconductors
63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials
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