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25 Jul 2011

Volume 99, Issue 4, Articles (04xxxx)

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Appl. Phys. Lett. 99, 041102 (2011); http://dx.doi.org/10.1063/1.3615051 (3 pages)

M. Davanço, M. T. Rakher, D. Schuh, A. Badolato, and K. Srinivasan
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Mechanical and thermal transport properties of graphene with defects

Feng Hao, Daining Fang, and Zhiping Xu

Appl. Phys. Lett. 99, 041901 (2011); http://dx.doi.org/10.1063/1.3615290 (3 pages) | Cited 26 times

Online Publication Date: 25 July 2011

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The roles of defects including monatomic vacancies and Stone-Wales dislocations in the mechanical and thermal properties of graphene are investigated here through molecular dynamics (MD) simulations. The results show that Young’s modulus of a defected graphene sheet has a gentle dependence with the concentration of defects, while the thermal conductivity is much more sensitive. Analysis based on the effective medium theory (EMT) indicates that this sensitivity originates from the scattering of phonons by defects and delocalized interaction between them, which leads to a transition from propagating to diffusive mode as the concentration increases.
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66.70.Lm Other systems such as ionic crystals, molecular crystals, nanotubes, etc.
61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)
66.30.Lw Diffusion of other defects
81.40.Jj Elasticity and anelasticity, stress-strain relations
61.72.jd Vacancies
62.20.de Elastic moduli

Phonon mode and phase transition behaviors of (1-x)PbSc1/2Ta1/2O3-xPbHfO3 relaxor ferroelectric ceramics determined by temperature-dependent Raman spectra

W. J. Zhang (张文娟), W. W. Li (李文武), X. G. Chen (陈贤贵), Z. G. Hu (胡志高), W. Liu (刘伟), G. S. Wang (王根水), X. L. Dong (董显林), and J. H. Chu (褚君浩)

Appl. Phys. Lett. 99, 041902 (2011); http://dx.doi.org/10.1063/1.3614431 (3 pages) | Cited 4 times

Online Publication Date: 27 July 2011

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The composition dependence of phase transition temperature in (1-x)PbSc1/2Ta1/2O3-xPbHfO3 (PSTH) ceramics (0 ≤ x ≤ 0.2) has been investigated by Raman spectra. From the typical phonon mode variations, the PSTH ceramics unambiguously undergoes three structural transformations with increasing the temperature from 82 to 673 K. It was found that the F2g phonon mode disappears above the Curie temperature. Moreover, the PSTH ceramics exhibited the paraelectric to ferroelectric phase transitions at 287, 293, 313, 320, and 330 K with the composition. The phenomena can be ascribed to the enhanced length of Pb-O-Ta bonds induced by the incorporation of Hf4+ ions.
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77.80.B- Phase transitions and Curie point
77.80.Jk Relaxor ferroelectrics
77.84.Ek Niobates and tantalates
78.30.Hv Other nonmetallic inorganics
81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
63.20.D- Phonon states and bands, normal modes, and phonon dispersion

Cross-plane thermal conductivity of a PbSnSe/PbSe superlattice material

James D. Jeffers, Khosrow Namjou, Zhihua Cai, Patrick J. McCann, and Leonard Olona

Appl. Phys. Lett. 99, 041903 (2011); http://dx.doi.org/10.1063/1.3615797 (3 pages) | Cited 2 times

Online Publication Date: 27 July 2011

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The cross-plane thermal conductivity of a PbSnSe/PbSe multi-period superlattice (SL) grown by molecular beam epitaxy is obtained from continuous wave photoluminescence (PL) measurements and finite element analysis (FEA). PL measurement and FEA for a structure consisting of a multiple quantum well light emitting layer on top of a PbSnSe/PbSe SL with three different periodicities of 2.4, 3.6, and 4.8 nm revealed a cross-plane lattice thermal conductivity of 0.8 W/mK. The 58% reduction relative to the 1.9 W/mK value for bulk PbSe is attributed to enhanced scattering and/or reflection of acoustic phonons within the short-period SL material.
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66.70.Df Metals, alloys, and semiconductors
78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
63.22.Np Layered systems
78.55.Hx Other solid inorganic materials
78.67.De Quantum wells
81.07.St Quantum wells

Folding and stacking defects of graphene flakes probed by electron nanobeam

L. Persichetti, F. Tombolini, S. Casciardi, M. Diociaiuti, M. Fanfoni, G. Palleschi, A. Sgarlata, F. Valentini, and A. Balzarotti

Appl. Phys. Lett. 99, 041904 (2011); http://dx.doi.org/10.1063/1.3615802 (3 pages)

Online Publication Date: 27 July 2011

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Combining nanoscale imaging with local electron spectroscopy and diffraction has provided direct information on folding and stacking defects of graphene flakes produced by unrolled multi-walled carbon nanotubes. Structural data obtained by nanoarea electron diffraction complemented with systematic electron energy loss spectroscopy measurements of the surface plasmon losses of single flakes show the presence of flat bilayer regions coexisting with folded areas where the topology of buckled graphene resembles that of warped carbon nanostructures.
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81.05.ue Graphene
61.72.Nn Stacking faults and other planar or extended defects
79.20.Uv Electron energy loss spectroscopy
61.48.Gh Structure of graphene
61.80.Fe Electron and positron radiation effects

Temperature-dependent photoluminescence from chemically and thermally reduced graphene oxide

Tran Viet Cuong, Viet Hung Pham, Eun Woo Shin, Jin Suk Chung, Seung Hyun Hur, Eui Jung Kim, Quang Trung Tran, Hoang Hung Nguyen, and Paul A. Kohl

Appl. Phys. Lett. 99, 041905 (2011); http://dx.doi.org/10.1063/1.3616142 (3 pages) | Cited 7 times

Online Publication Date: 27 July 2011

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Temperature-dependent photoluminescence (PL) of graphene oxide (GO) reduced with hydrazine and heat has been measured to investigate the effect of reduction type on the bandgap of the reduced GO. Nitrogen functionalities formed in the hydrazine-treated GO were responsible for a strong localization of carriers that caused in a fluctuation in PL peak position with temperature. The intensity of C-OH peak was relatively low in the heat-treated GO, indicating that raising temperature facilitated the removal of hydroxyl groups, resulting in larger sp2 domain size and smaller bandgap energy.
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81.05.ue Graphene
81.40.Gh Other heat and thermomechanical treatments
81.40.Tv Optical and dielectric properties related to treatment conditions
78.67.Wj Optical properties of graphene
78.55.Hx Other solid inorganic materials
71.20.Tx Fullerenes and related materials; intercalation compounds

Photoluminescence enhancement in CdS nanoparticles by surface-plasmon resonance

Dae-Ryong Jung, Jongmin Kim, Seunghoon Nam, Changwoo Nahm, Hongsik Choi, Jae Ik Kim, Junhee Lee, Chohui Kim, and Byungwoo Park

Appl. Phys. Lett. 99, 041906 (2011); http://dx.doi.org/10.1063/1.3615782 (3 pages) | Cited 12 times

Online Publication Date: 29 July 2011

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To examine the influence of metal nanoparticles on the photoluminescence of semiconductors, colloidal mixtures of CdS and Au nanoparticles were prepared with different CdS/Au fractions. Compared to the cadmium-sulfide nanocrystals (quantum efficiency ≅ 7%), the CdS/Au mixtures showed enhanced luminescence properties (quantum efficiency ≅ 14%). The existence of an optimum ratio of metal to semiconductor nanoparticles for the photoluminescence intensity indicates that interactions between the metal and semiconductor nanoparticles induced by surface-plasmon resonance occur constructively at appropriate distances.
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81.07.Bc Nanocrystalline materials
81.16.-c Methods of micro- and nanofabrication and processing
73.22.Lp Collective excitations
78.55.-m Photoluminescence, properties and materials

Generic relation between the electron work function and Young's modulus of metals

Guomin Hua and Dongyang Li

Appl. Phys. Lett. 99, 041907 (2011); http://dx.doi.org/10.1063/1.3614475 (3 pages) | Cited 4 times

Online Publication Date: 29 July 2011

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In this study, efforts were made to establish a generic relation between the Young’s modulus and the electron work function of polycrystalline metals, in which Young’s Modulus was defined as the second order derivative of interaction potential with respect to the equilibrium distance. The obtained Young’s modulus shows a sextic relation with the work function. Data of Young’s modulus and work function of polycrystalline metals, including Alkali earth metals, transition metals, and rare earth metals, can be fitted reasonably well by this derived generic relationship.
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81.05.Bx Metals, semimetals, and alloys
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.de Elastic moduli
65.40.gh Work functions
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