| 1. |
- 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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| 2. |
- 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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| 3. |
- 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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| 4. |
- 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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| 5. |
- 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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| 6. |
- 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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| 7. |
- Valcheva, E, et al.
(författare)
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Interface structure of hydride vapor phase epitaxial GaN grown with high-temperature reactively sputtered AlN buffer
- 2000
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Ingår i: Applied Physics Letters. - 0003-6951 .- 1077-3118. ; 76:14, s. 1860-1862
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Tidskriftsartikel (refereegranskat)abstract
- Thick hydride vapor phase epitaxy GaN layers have been grown on a-plane sapphire using high-temperature ion-assisted reactively sputtered AlN as a buffer layer. Transmission electron microscopy and atomic force microscopy were carried out to study the formation of the two interfaces sapphire/AlN and AlN/GaN, and their influence on the microstructure of both the buffer layer and the main GaN layer. It was demonstrated that the high-temperature reactively sputtered buffer layer provides a good alternative for hydride vapor phase epitaxy growth of GaN layers. In particular, the buffer promotes a specific interface ordering mechanism different from that observed on low-temperature buffers. (C) 2000 American Institute of Physics. [S0003-6951(00)00314-4].
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| 8. |
- Alnis, J, et al.
(författare)
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Sum-frequency generation with a blue diode laser for mercury spectroscopy at 254 nm
- 2000
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 76:10, s. 1234-1236
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Tidskriftsartikel (refereegranskat)abstract
- Blue diode lasers emitting 5 mW continuous-wave power around 400 nm have recently become available. We report on the use of a blue diode laser together with a 30 mW red diode laser for sum-frequency generation around 254 nm. The ultraviolet power is estimated to be 0.9 nW, and 35 GHz mode-hop-free tuning range is achieved. This is enough to perform high-resolution ultraviolet spectroscopy of mercury isotopes. The possibility to use frequency modulation in the ultraviolet is demonstrated; however, at present the ultraviolet power is too low to give advantages over direct absorption monitoring. Mercury detection at atmospheric pressure is also considered which is of great interest for environmental monitoring. (C) 2000 American Institute of Physics. [S0003-6951(00)02810-2].
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| 9. |
- Schneider, Jochen, et al.
(författare)
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Magnetic-field-dependent plasma composition of a pulsed arc in a high-vacuum ambient
- 2000
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Ingår i: Applied Physics Letters. - 0003-6951 .- 1077-3118. ; 76:12, s. 1531-1533
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Tidskriftsartikel (refereegranskat)abstract
- The effect of a magnetic field on the plasma composition of a pulsed Au plasma stream in a high-vacuum ambient is described. The plasma was formed with a pulsed vacuum-arc-plasma source, and the time-resolved plasma composition was measured with time-of-flight charge-to-mass spectrometry. Plasma impurities due to ionization of nonmetallic species (H+, O+, and N+) were found to be below the detection limit in the absence of a magnetic field. However, in the presence of a magnetic field (0.4 T), the contribution of ionized nonmetal species to the plasma composition was up to 0.22 atomic ratio. These results are characteristic of plasma-based techniques where magnetic fields are employed in a high-vacuum ambient. In effect, the impurity incorporation during thin-film growth pertains to the present findings. (C) 2000 American Institute of Physics. [S0003-6951(00)00712-9].
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| 10. |
- Tungasmita, Sukkaneste, et al.
(författare)
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Enhanced quality of epitaxial AlN thin films on 6H-SiC by ultra-high-vacuum ion-assisted reactive dc magnetron sputter deposition
- 2000
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Ingår i: Applied Physics Letters. - 0003-6951 .- 1077-3118. ; 76:2, s. 170-172
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Tidskriftsartikel (refereegranskat)abstract
- Epitaxial AlN thin films have been grown on 6H-SiC substrates by ultra-high-vacuum (UHV) ion-assisted reactive dc magnetron sputtering. The low-energy ion-assisted growth (E-i = 17-27 eV) results in an increasing surface mobility, promoting domain-boundary annihilation and epitaxial growth. Domain widths increased from 42 to 135 nm and strained-layer epitaxy was observed in this energy range. For E-i> 52 eV, an amorphous interfacial layer of AlN was formed on the SiC, which inhibited epitaxial growth. Using UHV condition and very pure nitrogen sputtering gas yielded reduced impurity levels in the films (O: 3.5 x 10(18) cm(-3)). Analysis techniques used in this study are in situ reflection high-energy electron diffraction, secondary-ion-mass spectroscopy, atomic-force microscopy, x-ray diffraction, and cross-section high-resolution electron microscopy. (C) 2000 American Institute of Physics. [S0003-6951(00)01802-7].
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