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30 Apr 2012

Volume 100, Issue 18, Articles (18xxxx)

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Appl. Phys. Lett. 100, 181901 (2012); http://dx.doi.org/10.1063/1.4705414 (4 pages)

Etienne Brasselet, Arnaud Royon, and Lionel Canioni
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Dense arrays of microscopic optical vortex generators from femtosecond direct laser writing of radial birefringence in glass

Etienne Brasselet, Arnaud Royon, and Lionel Canioni

Appl. Phys. Lett. 100, 181901 (2012); http://dx.doi.org/10.1063/1.4705414 (4 pages) | Cited 1 time

Online Publication Date: 30 April 2012

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We report on the generation of permanent singular light mode converters at the microscale using femtosecond direct laser writing in photo-thermo-refractive glass. It relies on the irreversible light-induced radial birefringence in the bulk of the material. The ability of such birefringence pattern to convert the spin angular momentum of light into orbital optical angular momentum is exploited to demonstrate the production of large arrays of optical vortex generators with surface densities up to 104cm-2.
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42.62.-b Laser applications
42.70.Ce Glasses, quartz
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
78.20.Fm Birefringence
78.20.nb Photothermal effects

Electron transport in suspended semiconductor structures with two-dimensional electron gas

A. G. Pogosov, M. V. Budantsev, E. Yu. Zhdanov, D. A. Pokhabov, A. K. Bakarov, and A. I. Toropov

Appl. Phys. Lett. 100, 181902 (2012); http://dx.doi.org/10.1063/1.4709485 (3 pages) | Cited 1 time

Online Publication Date: 30 April 2012

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We study electron transport in suspended semiconductor microstructures fabricated from AlAs/GaAs membranes containing a high mobility two-dimensional electron gas. In quantizing magnetic fields, a reflection of edge current channels from the border of suspended area is observed resulting in the absence of vanishing magnetoresistance in the quantum Hall effect (QHE) regime. Relocation of this border out of the Hall bar revives the QHE. We have also found that the critical current of the breakdown of QHE in suspended samples is three times lower than in non-suspended samples due to the peculiarity of heat transport in the membranes.
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73.63.-b Electronic transport in nanoscale materials and structures
75.47.-m Magnetotransport phenomena; materials for magnetotransport
72.20.My Galvanomagnetic and other magnetotransport effects
73.43.Qt Magnetoresistance

Screened hybrid density functional study on Sr2Nb2O7 for visible light photocatalysis

J. Nisar, B. Pathak, and R. Ahuja

Appl. Phys. Lett. 100, 181903 (2012); http://dx.doi.org/10.1063/1.4709486 (5 pages) | Cited 1 time

Online Publication Date: 30 April 2012

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The electronic structure of pure Sr2Nb2O7 and its electronic band position are being aligned with respect to the water oxidation/reduction potential level using hybrid functional (HSE06) theory. The experimental band gap (3.90 eV) of pure Sr2Nb2O7 can be reproduced (3.92 eV) using this level of theory. The cationic-anionic co-doping (Mo-N) in layered perovskite Sr2Nb2O7 structure reduces the band gap significantly, and its electronic band position is excellent for the visible-light photocatalysis. The respective cationic and anionic mono-doped systems create an occupied or unoccupied impurity states in the band gap, which can reduce the efficiency of the photocatalysis.
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71.20.Ps Other inorganic compounds
61.72.up Other materials
71.15.Mb Density functional theory, local density approximation, gradient and other corrections

Stress-relaxed growth of n-GaN epilayers

J. H. Ryu, Y. S. Katharria, H. Y. Kim, H. K. Kim, K. B. Ko, N. Han, J. H. Kang, Y. J. Park, E.-K. Suh, and C.-H. Hong

Appl. Phys. Lett. 100, 181904 (2012); http://dx.doi.org/10.1063/1.4710561 (4 pages) | Cited 1 time

Online Publication Date: 2 May 2012

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A significant stress-relaxation was observed in GaN epilayers by integrating a heavily Si-doped GaN (n+-GaN) sacrificial layer in the undoped GaN templates grown on sapphire substrates by metal-organic chemical vapor deposition. Selective GaN growth and electrochemical etching were exploited to achieve embedded air-gaps. Stress-relaxation and its local variations were probed by Raman mapping of high-frequency transverse-optical E2 (high) phonon mode of GaN. Enhanced In incorporation and improved light emission were observed in InGaN/GaN multi-quantum well visible light emitting diode structures fabricated on stress-relaxed GaN-epilayers with embedded air-gaps. Relevant sources for stress reduction and improved optical emission have been discussed.
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81.05.Ea III-V semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.ag Semiconductors
78.55.Cr III-V semiconductors
78.60.Fi Electroluminescence
78.66.Fd III-V semiconductors

The influence of silicon nanoclusters on the optical properties of a-SiNx samples: A theoretical study

Roberto Guerra, Mariella Ippolito, Simone Meloni, and Stefano Ossicini

Appl. Phys. Lett. 100, 181905 (2012); http://dx.doi.org/10.1063/1.4711017 (4 pages) | Cited 3 times

Online Publication Date: 2 May 2012

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By means of ab-initio calculations, we investigate the optical properties of pure a-SiNx samples, with x∈[0.4,1.8], and samples embedding silicon nanoclusters (NCs) of diameter 0.5 ≤ d ≤ 1.0 nm. In the pure samples, the optical absorption gap and the radiative recombination rate vary according to the concentration of Si-N bonds. In the presence of NCs, the radiative rate of the samples is barely affected, indicating that the intense photoluminescence of experimental samples is mostly due to the matrix itself rather than to the NCs. Besides, we evidence an important role of Si-N-Si bonds at the NC/matrix interface in the observed photoluminescence trend.
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78.55.Hx Other solid inorganic materials
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Dynamic observations of dislocation behavior in SrTiO3 by in situ nanoindentation in a transmission electron microscope

Shun Kondo, Naoya Shibata, Tasuku Mitsuma, Eita Tochigi, and Yuichi Ikuhara

Appl. Phys. Lett. 100, 181906 (2012); http://dx.doi.org/10.1063/1.4710558 (4 pages) | Cited 1 time

Online Publication Date: 3 May 2012

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The plastic deformation process of a SrTiO3 single crystal has been dynamically and microscopically observed by in situ nanoindentation in a transmission electron microscope. The plastic deformation of SrTiO3 was found to proceed by dislocation slips even at room temperatures under the present experimental condition, and the dynamic behavior of dislocations such as nucleation, propagation, and annihilation have been clearly captured. The detailed dislocation analyses revealed that the activated slip system is 〈110〉{1math0} type, which is consistent with the results of macroscopic deformation experiments reported so far. The mechanisms of dislocation behavior are discussed based on the experimentally obtained results.
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81.40.Lm Deformation, plasticity, and creep
62.20.fq Plasticity and superplasticity
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)

Light-induced off-diagonal thermoelectric effect via indirect optical heating of incline-oriented CaxCoO2 thin film

Kouhei Takahashi, Tsutomu Kanno, Akihiro Sakai, Hideaki Adachi, and Yuka Yamada

Appl. Phys. Lett. 100, 181907 (2012); http://dx.doi.org/10.1063/1.4711020 (4 pages)

Online Publication Date: 3 May 2012

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Light-induced off-diagonal thermoelectric (ODTE) effect has been investigated in CaxCoO2 thin film coupled with a gold black light absorption layer. Increased light absorption at the gold black layer resulted in considerable enhancement of the steady-state thermoelectric voltage from the CaxCoO2 film upon continuous light heating. However, we found that the indirect optical heating process highly deteriorates the input thermal energy pulse in time-domain, and leads to significant reduction in the transient voltage generated upon pulsed light heating. The result manifests the importance of adequate thermal design of absorption layers for fabrication of light detection devices based on the ODTE effect.
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73.50.Lw Thermoelectric effects
78.66.Nk Insulators
78.20.nd Thermophotonic effects
68.60.Dv Thermal stability; thermal effects
72.20.Pa Thermoelectric and thermomagnetic effects

A liftoff process of GaN layers and devices through nanoporous transformation

Yu Zhang, Benjamin Leung, and Jung Han

Appl. Phys. Lett. 100, 181908 (2012); http://dx.doi.org/10.1063/1.4711218 (4 pages) | Cited 1 time

Online Publication Date: 4 May 2012

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A process to slice and separate GaN device layers for vertical light emitting diodes (LEDs) is presented through a developed electrochemical anodization process to create nanoporous (NP) GaN of designed porosity profiles. The NP GaN serves dual purposes of supporting subsequent overgrowth of LED structures while undergoing, during growth, shape transformation into a largely voided morphology. It is shown that this voided region decreases the lateral fracture resistance and enables large-area separation of the LED structures after appropriate wafer bonding. The separated LED layers are shown to have comparable material quality before and after the liftoff process. Blue emitting GaN LEDs are transferred to silicon substrates with vertical configuration by this unique process.
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81.65.-b Surface treatments
81.05.Ea III-V semiconductors
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
85.60.Jb Light-emitting devices
61.43.Gt Powders, porous materials
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