| 1. |
- Jayakumar, O. D., et al.
(författare)
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Structural and magnetic properties of (In1-xFex)(2)O-3 (0.0 <= x <= 0.25) system : Prepared by gel combustion method
- 2007
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 91:5
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Tidskriftsartikel (refereegranskat)abstract
- (In1-xFex)(2)O-3 polycrystalline samples with x=(0.0,0.05,0.10,0.15,0.20, and 0.25) have been synthesized by a gel combustion method. Reitveld refinement analysis of x-ray diffraction data indicated the formation of single phase cubic bixbyite structure without any parasitic phases. This observation is further confirmed by high resolution transmission electron microscopy imaging, indexing of the selected-area electron diffraction patterns, x-ray absorption spectroscopy, and Raman Spectroscopy. dc magnetization studies as a function of temperature and field indicate that they are ferromagnetic with Curie temperature (T-C) well above room temperature.
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| 2. |
- Gratz, M, et al.
(författare)
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Time-gated x-ray tomography
- 1998
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 73:20, s. 2899-2901
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Tidskriftsartikel (refereegranskat)abstract
- Time-gated x-ray tomography with scatter reduction is demonstrated using a laser-produced plasma as an ultrashort-pulse x-ray source in combination with a time-resolving streak-camera detector. Backprojections of a phantom imbedded in 9 cm of water show an effective 50% increase in contrast when scattered x-ray quanta (being delayed in time) are suppressed by gating on the prompt, nonscattered photons. Implications for future volumetric tomography, in particular concerning possible dose reductions, are discussed. (C) 1998 American Institute of Physics. [S0003-6951(98)02846-0].
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| 3. |
- Johansson, MP, et al.
(författare)
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Template-synthesized BN : C nanoboxes
- 2000
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Ingår i: Applied Physics Letters. - 0003-6951 .- 1077-3118. ; 76:7, s. 825-827
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Tidskriftsartikel (refereegranskat)abstract
- Box-shaped nanostructures of B-C-N compounds were synthesized by reactive sputtering of boron carbide in mixed argon and nitrogen discharges. Transmission electron microscopy showed that these nanoboxes were grown on self-patterned NaCl substrate with projected areas ranging from similar to 1x10(2) to similar to 5x10(4) nm(2), sizes 50-100 nm, and number density similar to 100 mu m(-2). Electron energy loss spectroscopy revealed a phase separation of BN and C:N layers. (C) 2000 American Institute of Physics. [S0003-6951(00)00507-6].
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| 4. |
- Gahn, C, et al.
(författare)
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Generating positrons with femtosecond-laser pulses
- 2000
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 77:17, s. 2662-2664
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Tidskriftsartikel (refereegranskat)abstract
- Utilizing a femtosecond table-top laser system, we have succeeded in converting via electron acceleration in a plasma channel, low-energy photons into antiparticles, namely positrons. The average intensity of this source of positrons is estimated to be equivalent to 2x10(8) Bq and it exhibits a very favorable scaling for higher laser intensities. The advent of positron production utilizing femtosecond laser pulses may be the forerunner to a table-top positron source appropriate for applications in material science, and fundamental physics research like positronium spectroscopy. (C) 2000 American Institute of Physics. [S0003-6951(00)00143-1].
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| 5. |
- Paul, DJ, et al.
(författare)
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Si/SiGe electron resonant tunneling diodes
- 2000
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Ingår i: Applied Physics Letters. - 0003-6951 .- 1077-3118. ; 77:11, s. 1653-1655
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Tidskriftsartikel (refereegranskat)abstract
- Resonant tunneling diodes have been fabricated using strained-Si wells and strained Si0.4Ge0.6 barriers on a relaxed Si0.8Ge0.2 n-type substrate, which demonstrate negative differential resistance at 298 K. Peak current densities of 5 kA/cm(2) with peak-to-valley current ratios of 1.1 have been achieved. Theoretical modeling of the structure demonstrates that the major current peak results from the tunneling of light-mass electrons from the relaxed substrate and not from the heavy-mass electrons in the emitter accumulation layer. (C) 2000 American Institute of Physics. [S0003- 6951(00)02337-8].
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| 6. |
- Wahab, Qamar Ul, et al.
(författare)
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Influence of epitaxial growth and substrate-induced defects on the breakdown of 4H-SiC Schottky diodes
- 2000
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Ingår i: Applied Physics Letters. - 0003-6951 .- 1077-3118. ; 76:19, s. 2725-2727
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Tidskriftsartikel (refereegranskat)abstract
- Morphological defects and elementary screw dislocations in 4H-SiC were studied by high voltage Ni Schottky diodes. Micropipes were found to severely limit the performance of 4H-SiC power devices, whereas carrot-like defects did not influence the value of breakdown voltage. The screw dislocation density as determined by x-ray topography analysis under the active area of the diode was also found to directly affect the breakdown voltage. Only diodes with low density of screw dislocations and free from micropipes could block 2 kV or higher. (C) 2000 American Institute of Physics. [S0003-6951(00)01119-0].
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| 7. |
- Haverkort, JEM, et al.
(författare)
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Design of composite InAsP/InGaAs quantum wells for a 1.55 mu m polarization independent semiconductor optical amplifier
- 1999
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Ingår i: Applied Physics Letters. - : American Institute of Physics (AIP). - 0003-6951 .- 1077-3118. ; 75:18, s. 2782-2784
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Tidskriftsartikel (refereegranskat)abstract
- We investigate a composite InAsP/InGaAs quantum well in which an 8 nm tensile strained InGaAs well is surrounded by two compressively strained InAsP layers which feature a 70:30 conduction band offset ratio. The composite quantum well is found to provide a high TM differential gain. The InAsP layers provide strain compensation while simultaneously shifting the band gap to the relevant 1.55 mu m wavelength region and increasing the electron confinement. Composite InAsP/InGaAs quantum wells are a promising candidate for realizing a polarization independent semiconductor optical amplifier at 1.55 mu m. (C) 1999 American Institute of Physics. [S0003-6951(99)01944-0].
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| 8. |
- Pozina, Galia, et al.
(författare)
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Bound exciton dynamics in GaN grown by hydride vapor-phase epitaxy
- 1999
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Ingår i: Applied Physics Letters. - 0003-6951 .- 1077-3118. ; 75:26, s. 4124-4126
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Tidskriftsartikel (refereegranskat)abstract
- Temperature-dependent time-resolved photoluminescence measurements were performed on thick GaN layers grown by hydride vapor-phase epitaxy on Al2O3 substrates. Radiative lifetimes were determined for the neutral-donor-bound exciton with position at 3.478 eV and for two neutral-acceptor-bound excitons at 3.473 and 3.461 eV. We report a value of 3600 ps for the radiative lifetime of the acceptor-bound exciton transition at 3.461 eV. The dominant mechanism responsible for the nonradiative recombination of the bound excitons is shown to be connected with dissociation of the bound excitons into free excitons. (C) 1999 American Institute of Physics. [S0003-6951(99)00752-4].
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| 9. |
- Stafström, Sven
(författare)
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Reactivity of curved and planar carbon-nitride structures
- 2000
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Ingår i: Applied Physics Letters. - 0003-6951 .- 1077-3118. ; 77:24, s. 3941-3943
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Tidskriftsartikel (refereegranskat)abstract
- The reactivity of different carbon-nitride structures has been studied using density functional theory calculations. The studies involve C59N and clusters of curved and planar CNx structures. Nitrogen is shown to lower the energy of pentagon defects in the graphite like structures, whereas heptagons are unlikely to be present. From this observation, it follows that nitrogen stimulates growth of fullerene like structures in CNx. The presence of nitrogen also increases the reactivity of the carbon atoms around the nitrogen. This leads to cross linking between basal planes which can explain the hardness and elasticity of CNx films. (C) 2000 American Institute of Physics. [S0003-6951(00)03751-7].
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| 10. |
- Pozina, Galia, et al.
(författare)
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Optical spectroscopy of GaN grown by metalorganic vapor phase epitaxy using indium surfactant
- 2000
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Ingår i: Applied Physics Letters. - 0003-6951 .- 1077-3118. ; 76:23, s. 3388-3390
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Tidskriftsartikel (refereegranskat)abstract
- The effect of In surfactant during metalorganic vapor phase epitaxial growth on sapphire substructure on the properties of GaN layers is studied using time-resolved photoluminescence. cathodoluminescence. and scanning electron microscopy. The samples are divided into two groups. where hydrogen and nitrogen, respectively, have been used as a carrier gas during growth. It is shown that In-doped samples have a lower dislocation density, a narrower photoluminescence linewidth, and a longer foe exciton lifetime. The influence of indium is stronger for GaN layers grown in nitrogen-rich conditions. The improvements of structural and optical properties are attributed to the effect of In on dislocations. (C) 2000 American Institute of Physics. [S0003-6951(00)02723-6].
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