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23 Apr 2012

Volume 100, Issue 17, Articles (17xxxx)

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Appl. Phys. Lett. 100, 171903 (2012); http://dx.doi.org/10.1063/1.4704193 (3 pages)

Y. Peng and K. Kempa
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Relaxation of a metallic glass to the metastable equilibrium: Evidence for the existence of the Kauzmann pseudocritical temperature

Yu. P. Mitrofanov, V. A. Khonik, A. V. Granato, D. M. Joncich, S. V. Khonik, and A. M. Khoviv

Appl. Phys. Lett. 100, 171901 (2012); http://dx.doi.org/10.1063/1.4705407 (4 pages) | Cited 3 times

Online Publication Date: 23 April 2012

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High-precision isothermal measurements on strongly preannealed metallic glass reveal a decrease of the shear modulus to the metastable equilibrium value both in the glassy state far below the glass transition and in the supercooled liquid state near Tg. The results obtained point out the existence of a low-temperature limit for the supercooled liquid, which is known as the Kauzmann pseudocritical temperature [W. Kauzmann, Chem. Rev. 43, 219 (1948)]. This finding experimentally questions the existence of the “Kauzmann paradox,” which is widely discussed in the literature.
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61.43.Fs Glasses
81.40.Gh Other heat and thermomechanical treatments
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.de Elastic moduli
64.70.P- Glass transitions of specific systems

Identification of polymer stabilized blue-phase liquid crystal display by chromaticity diagram

Yi-Fen Lan, Cheng-Yeh Tsai, Ling-Yung Wang, Po-Jen Ku, Tai-Hsiang Huang, Chu-Yu Liu, and Norio Sugiura

Appl. Phys. Lett. 100, 171902 (2012); http://dx.doi.org/10.1063/1.4705432 (4 pages) | Cited 2 times

Online Publication Date: 23 April 2012

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We reported an identification method of blue phase liquid crystal (BPLC) display status by using Commission International de l’Éclairage (CIE) chromaticity diagram. The BPLC was injected into in-plane-switch (IPS) cell, polymer stabilized (PS) by ultraviolet cured process and analyzed by luminance colorimeter. The results of CIE chromaticity diagram showed a remarkable turning point when polymer stabilized blue phase liquid crystal II (PSBPLC-II) formed in the IPS cell. A mechanism of CIE chromaticity diagram identify PSBPLC display status was proposed, and we believe this finding will be useful to application and production of PSBPLC display.
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42.79.Kr Display devices, liquid-crystal devices
85.60.Pg Display systems
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Controlling light propagation with nanowires

Y. Peng and K. Kempa

Appl. Phys. Lett. 100, 171903 (2012); http://dx.doi.org/10.1063/1.4704193 (3 pages) | Cited 1 time

Online Publication Date: 23 April 2012

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We study the interaction of electromagnetic waves (EM) with metallic nanowire systems for frequencies not far from the surface plasma frequency (polaritonic range). We employ calculation and simulation to show that when excited at one end with axially polarized EM waves, nanowires can function as efficient waveguides of surface plasmon polaritons (SPPs). From the Fabry-Perot resonances of standing SPP waves, we study their dispersion relation and show that for a vanishing SPP wavelength it is identical to that for a planar metallic surface. Nanowire systems can be employed in various nanophotonic applications, and we assess this potential by studying propagation characteristics of these nano-waveguides and their interactions.
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71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)
73.22.Lp Collective excitations
78.68.+m Optical properties of surfaces
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)

Eu luminescence center created by Mg codoping in Eu-doped GaN

Dong-gun Lee, Atsushi Nishikawa, Yoshikazu Terai, and Yasufumi Fujiwara

Appl. Phys. Lett. 100, 171904 (2012); http://dx.doi.org/10.1063/1.4704920 (3 pages) | Cited 4 times

Online Publication Date: 23 April 2012

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We investigated the photoluminescence properties of Eu,Mg-codoped GaN grown by organometallic vapor phase epitaxy. Some emission due to intra-4f shell transition of 5D0-7F2 in Eu3+ ions in a center with Eu and Mg was observed together with typical Eu emission. The peak intensity of the Eu-Mg emission was about five times higher than that of the typical Eu emission. The Eu-Mg emission exhibited a maximum at around 180 K, while the typical Eu emission intensity decreased monotonically with increasing temperature. It was found that only one type of Eu-Mg center contributed to the enhanced intensity up to 180 K.
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78.55.Cr III-V semiconductors
81.05.Ea III-V semiconductors
81.15.Kk Vapor phase epitaxy; growth from vapor phase
61.72.U- Doping and impurity implantation
61.72.uj III-V and II-VI semiconductors
78.66.Fd III-V semiconductors

Dimensional transition and carrier dynamics in CdxZn1−xTe/ZnTe nanostructures on Si substrates

K.-D. Park, S.-Y. Yim, and H. S. Lee

Appl. Phys. Lett. 100, 171905 (2012); http://dx.doi.org/10.1063/1.4705413 (4 pages) | Cited 1 time

Online Publication Date: 24 April 2012

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We investigate the dimensional transition and carrier dynamics in CdxZn1−xTe/ZnTe nanostructures with various Cd mole fractions, grown on Si substrates. Atomic force microscopy images show that the dimensional transition from quantum dots (QDs) to quantum wires occurs with increasing Cd mole fraction. The activation energy of the electrons confined in CdxZn1−xTe QDs with a Cd mole fraction of 0.6 is higher than that of electrons confined in CdxZn1−xTe nanostructures. In addition, the radiative recombination rate shows a linear dependence on the length of the CdxZn1−xTe nanostructures, which is well explained in terms of the “coherence volume” of the bound excitons.
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81.05.Dz II-VI semiconductors
81.07.Ta Quantum dots
81.07.Vb Quantum wires
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
64.70.kg Semiconductors
61.46.-w Structure of nanoscale materials

Strain-induced composition limitation in nitrogen δ-doped (In,Ga)As/GaAs quantum wells

R. Gargallo-Caballero, E. Luna, F. Ishikawa, and A. Trampert

Appl. Phys. Lett. 100, 171906 (2012); http://dx.doi.org/10.1063/1.4705731 (4 pages)

Online Publication Date: 24 April 2012

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The local element distribution across tensile-strained N δ-doped (In,Ga)As/GaAs quantum wells (QWs) is investigated by transmission electron microscopy. The sub-monolayer (ML) insertion results in a several monolayers thick (In,Ga)(As,N) layer with lateral composition fluctuations. We also find an inhomogeneous In incorporation across the QW, with a minimum In content, [In]min, exactly at the position of the N-insertion, where N content is maximum, [N]max. Regardless of the position along the QW, [N]max corresponds to [In]min so that an (In,Ga)(As,N) layer of this composition has a lattice parameter close to aGaAs. The impact of tensile strain on this complex chemical configuration is discussed.
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81.05.Ea III-V semiconductors
81.07.St Quantum wells
68.65.Fg Quantum wells
68.47.Pe Langmuir-Blodgett films on solids; polymers on surfaces; biological molecules on surfaces
61.66.Fn Inorganic compounds

Employing pre-stress to generate finite cloaks for antiplane elastic waves

William J. Parnell, Andrew N. Norris, and Tom Shearer

Appl. Phys. Lett. 100, 171907 (2012); http://dx.doi.org/10.1063/1.4704566 (4 pages) | Cited 1 time

Online Publication Date: 24 April 2012

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It is shown that nonlinear elastic pre-stress of neo-Hookean hyperelastic materials can be used as a mechanism to generate finite cloaks and thus render objects near-invisible to incoming antiplane elastic waves. This approach appears to negate the requirement for special cloaking metamaterials with inhomogeneous and anisotropic material properties in this case. These properties are induced naturally by virtue of the pre-stress. This appears to provide a mechanism for broadband cloaking since dispersive effects due to metamaterial microstructure will not arise.
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62.30.+d Mechanical and elastic waves; vibrations

Correlation between local structure and electrical resistivity in gallium-antimony melts

Tingkun Gu (谷廷坤)

Appl. Phys. Lett. 100, 171908 (2012); http://dx.doi.org/10.1063/1.4706253 (4 pages)

Online Publication Date: 25 April 2012

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First-principles molecular dynamics simulations on the structural and electronic properties of liquid gallium-antimony alloys (GaxSb1−x) were performed. Analysis of the calculated results revealed that changes in the local structure of liquid GaxSb1−x depend on composition. The coordination tendencies of Ga-Ga, Ga-Sb, and Sb-Sb showed different trends as a function of the concentration of Sb, and the electronic structures of liquid GaxSb1−x were consistent with this finding. Further analysis confirmed that there is an explicit correlation between the structural parameters and electrical resistivity of liquid GaxSb1−x.
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71.22.+i Electronic structure of liquid metals and semiconductors and their alloys
72.80.Ph Liquid semiconductors
61.25.-f Studies of specific liquid structures

Enhanced adhesion with pedestal-shaped elastomeric stamps for transfer printing

Seok Kim, Andrew Carlson, Huanyu Cheng, Seungwoo Lee, Jung-Ki Park, Yonggang Huang, and John A. Rogers

Appl. Phys. Lett. 100, 171909 (2012); http://dx.doi.org/10.1063/1.4706257 (4 pages) | Cited 2 times

Online Publication Date: 25 April 2012

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Microscale elastomeric relief structures with “pedestal” shapes provide enhanced operation in stamps designed for deterministic materials assembly via transfer printing. Experimental measurements of adhesion and finite element analysis both show that for certain geometries, exceptionally large enhancements in adhesion strength (over 15×) can be achieved. Transfer printing of microscale platelets of silicon and ultrathin gallium nitride light emitting diodes onto a silicon substrate without adhesive coatings demonstrates some capabilities in assembly that result from this type of stamp, of interest in diverse applications, including those that involve heterogeneous materials integration.
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
81.16.-c Methods of micro- and nanofabrication and processing
85.60.Jb Light-emitting devices
68.35.Np Adhesion

The contribution of quantum confinement to optical anisotropy of a-plane Cd0.06Zn0.94O/ZnO quantum wells

Hiroaki Matsui and Hitoshi Tabata

Appl. Phys. Lett. 100, 171910 (2012); http://dx.doi.org/10.1063/1.4707384 (4 pages) | Cited 1 time

Online Publication Date: 25 April 2012

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We investigated quantum size effects on polarized photoluminescence (PL) from a-plane Cd0.06Zn0.94O/ZnO quantum wells (QWs) with different well widths (LW). The degree of polarized PL at 300 K increased with a narrowing of LW, which obeyed the polarization selection rule based on a Boltzmann-like distribution. Furthermore, the narrowing of LW enhanced the anisotropic lattice distortions in well layers along the growing direction, which resulted in an increase of energy separation between the two topmost valence band levels. The effect of quantum confinement on polarized PL of QWs was accompanied by a change of structural symmetry of the well layers.
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78.67.De Quantum wells
81.07.St Quantum wells
78.55.Et II-VI semiconductors
81.05.Dz II-VI semiconductors
71.20.Nr Semiconductor compounds
73.21.Fg Quantum wells

Photoluminescence induced by twinning interface in CdS nanocrystals

P. Q. Zhao, S. J. Xiong, X. L. Wu, and Paul K. Chu

Appl. Phys. Lett. 100, 171911 (2012); http://dx.doi.org/10.1063/1.4707388 (4 pages) | Cited 1 time

Online Publication Date: 25 April 2012

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The photoluminescence (PL) spectra acquired from CdS nanocrystals encapsulated with oleic acid synthesized by a two-phase approach exhibit two fine features, including a narrow peak arising from near-band edge emission and a broader one composed of two subpeaks at slightly lower energy. Solvent effects suggest that the surface defect states on the nanocrystals are not the origin of this broad PL band. High-resolution transmission electron microscopy examinations and density function theory calculation reveal that the broad low-energy PL band stems from twinning interfaces in the CdS nanocrystals.
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78.55.Et II-VI semiconductors
61.72.Mm Grain and twin boundaries
71.15.Mb Density functional theory, local density approximation, gradient and other corrections

Structure stabilities and transitions in polyhedral metal nanocrystals: An atomic-bond-relaxation approach

Ai Zhang, Ziming Zhu, Yan He, and Gang Ouyang

Appl. Phys. Lett. 100, 171912 (2012); http://dx.doi.org/10.1063/1.4706260 (5 pages) | Cited 2 times

Online Publication Date: 26 April 2012

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We present an atomic-bond-relaxation (ABR) method to illustrate a deeper insight on structure stabilities and transitions of metal nanocrystals with polyhedral structure based on the thermodynamic consideration. It has been found that the end effects in polyhedral nanocrystals induced by the atoms located at edges, side facets, and vertexes play the dominant roles for their structure performances. The theoretical predictions are well consistent with the experimental measurements and simulations, which suggest the ABR model can be an effective method to understand solid-solid phase transition of polyhedral metal nanocrystals.
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61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
64.70.Nd Structural transitions in nanoscale materials
82.60.Qr Thermodynamics of nanoparticles

Large-area nanostructured substrates for surface enhanced Raman spectroscopy

Andriy Shevchenko, Victor Ovchinnikov, and Anna Shevchenko

Appl. Phys. Lett. 100, 171913 (2012); http://dx.doi.org/10.1063/1.4707158 (4 pages) | Cited 1 time

Online Publication Date: 26 April 2012

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We demonstrate substantial enhancement of Raman transitions of organic molecules by nanostructured gold-coated substrates at the excitation wavelength of 785 nm and experimentally study the factors that influence the enhancement. The substrates are fabricated by using a robust and cost-effective nanopatterning technique that allows us to create high-density gold- or silver-coated nanopillars simultaneously on the whole surface of a standard silicon wafer.
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73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
73.22.Lp Collective excitations
78.30.Am Elemental semiconductors and insulators
78.68.+m Optical properties of surfaces
81.16.Rf Micro- and nanoscale pattern formation

Capping effect of GaAsSb and InGaAsSb on the structural and optical properties of type II GaSb/GaAs quantum dots

Jun He, Feng Bao, and Jinping Zhang

Appl. Phys. Lett. 100, 171914 (2012); http://dx.doi.org/10.1063/1.4707385 (4 pages) | Cited 2 times

Online Publication Date: 26 April 2012

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We systematically study the influence of group V intermixing on the structural and optical properties of type II GaSb/GaAs quantum dots (QDs) capped by selected capping layers. Compared to GaSb QDs capped directly by a GaAs layer, we observe a strong enhancement of photoluminescence (PL) intensity and a significant red-shift of the photoluminescence peak energy to 1.35 μm at 300 K by the introduction of a GaAsSb capping layer. In addition, Z-contrast cross sectional transmission electron microscopy shows Sb segregation and group V mixing is greatly suppressed by GaAsSb or InGaAsSb capping layers. The new capping layers offers the possibility of controlling optical properties of type II GaSb/GaAs quantum dots and this opens up new means for achieving high efficient GaSb/GaAs quantum dot solar cell.
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78.67.Hc Quantum dots
81.30.Mh Solid-phase precipitation
78.55.Cr III-V semiconductors
68.65.Hb Quantum dots (patterned in quantum wells)
64.75.Ef Mixing

Shift of Ag diffusion profiles in CdTe by metal/semiconductor interfaces

H. Wolf, J. Kronenberg, F. Wagner, M. Deicher, Th. Wichert, and ISOLDE Collaboration

Appl. Phys. Lett. 100, 171915 (2012); http://dx.doi.org/10.1063/1.4709393 (3 pages)

Online Publication Date: 27 April 2012

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Metal layers deposited on the surface of the semiconductor CdTe effect a shift of the concentration profile of Ag dopants in CdTe by several 100 μm during diffusion anneal at about 550 K. Radio-tracer experiments using 111Ag show that this effect occurs in the case of Al, Ni, Cu, and Au layers. A preliminary explanation relates the effect to an enhancement of the diffusion of Ag atoms in CdTe caused by Cd self-interstitials that are generated at the metal/semiconductor interface.
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66.30.J- Diffusion of impurities
61.72.Cc Kinetics of defect formation and annealing
61.72.jj Interstitials
61.72.uj III-V and II-VI semiconductors

Symmetrically tunable optical properties of InGaN/GaN multiple quantum disks by an external stress

H. Y. Shih, Y. F. Chen, and T. Y. Lin

Appl. Phys. Lett. 100, 171916 (2012); http://dx.doi.org/10.1063/1.4709397 (4 pages)

Online Publication Date: 27 April 2012

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The influence of an external stress on the optical properties of InGaN/GaN multiple quantum disks (MQDs) has been investigated. As a transversal force is applied on the MQDs, both photoluminescence and Raman scattering spectra are altered due to the piezoelectric potential accompanied by the quantum confined Stark effect. Quite interestingly, it is found that the optical spectra possess a sixfold symmetry about the c-axis. This intriguing phenomenon can be attributed to the inherent nature of hexagonal lattice as well as the good flexibility of the composite consisting of polydimethylsiloxane and MQDs. Our results can provide an alternative route to optimize and extend the application of nitride-based devices.
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81.05.Ea III-V semiconductors
78.67.-n Optical properties of low-dimensional, mesoscopic, and nanoscale materials and structures
78.55.Cr III-V semiconductors
78.30.Fs III-V and II-VI semiconductors
78.20.Jq Electro-optical effects

Stress relaxation and critical thickness for misfit dislocation formation in (10math0) and (30math) InGaN/GaN heteroepitaxy

Po Shan Hsu, Matthew T. Hardy, Erin C. Young, Alexey E. Romanov, Steven P. DenBaars, Shuji Nakamura, and James S. Speck

Appl. Phys. Lett. 100, 171917 (2012); http://dx.doi.org/10.1063/1.4707160 (4 pages) | Cited 1 time

Online Publication Date: 27 April 2012

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Cathodoluminescence imaging was used to study the onset of plastic relaxation and critical thickness for misfit dislocation (MD) formation by basal plane (BP) or nonbasal plane (NBP) slip in In0.09Ga0.91N/GaN heterostructures grown on nonpolar (10math0) and semipolar (30math) substrates. Layers grown on both orientations were shown to stress relax initially via generation of NBP MDs as a result of prismatic slip on inclined m-planes. Analysis of the resolved shear stress on the two slip planes (i.e., basal and an inclined m-plane) reveals a crossover at which the resolved shear stress on the m-planes becomes larger than that on the BP.
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61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
78.60.Hk Cathodoluminescence, ionoluminescence
81.05.Ea III-V semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.ag Semiconductors
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