1. |
- Jayakumar, O. D., et al.
(author)
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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
-
In: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 91:5
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Journal article (peer-reviewed)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.
(author)
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Time-gated x-ray tomography
- 1998
-
In: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 73:20, s. 2899-2901
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Journal article (peer-reviewed)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.
(author)
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Template-synthesized BN : C nanoboxes
- 2000
-
In: Applied Physics Letters. - 0003-6951 .- 1077-3118. ; 76:7, s. 825-827
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Journal article (peer-reviewed)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.
(author)
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Generating positrons with femtosecond-laser pulses
- 2000
-
In: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 77:17, s. 2662-2664
-
Journal article (peer-reviewed)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.
(author)
-
Si/SiGe electron resonant tunneling diodes
- 2000
-
In: Applied Physics Letters. - 0003-6951 .- 1077-3118. ; 77:11, s. 1653-1655
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Journal article (peer-reviewed)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.
(author)
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Influence of epitaxial growth and substrate-induced defects on the breakdown of 4H-SiC Schottky diodes
- 2000
-
In: Applied Physics Letters. - 0003-6951 .- 1077-3118. ; 76:19, s. 2725-2727
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Journal article (peer-reviewed)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.
(author)
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Design of composite InAsP/InGaAs quantum wells for a 1.55 mu m polarization independent semiconductor optical amplifier
- 1999
-
In: Applied Physics Letters. - : American Institute of Physics (AIP). - 0003-6951 .- 1077-3118. ; 75:18, s. 2782-2784
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Journal article (peer-reviewed)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.
(author)
-
Bound exciton dynamics in GaN grown by hydride vapor-phase epitaxy
- 1999
-
In: Applied Physics Letters. - 0003-6951 .- 1077-3118. ; 75:26, s. 4124-4126
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Journal article (peer-reviewed)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
(author)
-
Reactivity of curved and planar carbon-nitride structures
- 2000
-
In: Applied Physics Letters. - 0003-6951 .- 1077-3118. ; 77:24, s. 3941-3943
-
Journal article (peer-reviewed)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.
(author)
-
Optical spectroscopy of GaN grown by metalorganic vapor phase epitaxy using indium surfactant
- 2000
-
In: Applied Physics Letters. - 0003-6951 .- 1077-3118. ; 76:23, s. 3388-3390
-
Journal article (peer-reviewed)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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11. |
- Valcheva, E, et al.
(author)
-
Interface structure of hydride vapor phase epitaxial GaN grown with high-temperature reactively sputtered AlN buffer
- 2000
-
In: Applied Physics Letters. - 0003-6951 .- 1077-3118. ; 76:14, s. 1860-1862
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Journal article (peer-reviewed)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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12. |
- Alnis, J, et al.
(author)
-
Sum-frequency generation with a blue diode laser for mercury spectroscopy at 254 nm
- 2000
-
In: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 76:10, s. 1234-1236
-
Journal article (peer-reviewed)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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13. |
- Morvan, E, et al.
(author)
-
Channeling implantations of Al+ into 6H silicon carbide
- 1999
-
In: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 74, s. 3990-3992
-
Journal article (peer-reviewed)abstract
- A strong channeling effect of Al+ ions implanted into crystalline SiC has been observed by Monte Carlo simulations and experiments especially designed to demonstrate this phenomenon have been performed. Depth distributions of implanted Al were measured for on- and controlled off-axis Al implantations using secondary ion mass spectrometry (SIMS). Much deeper and wider profiles are obtained for the on-axis implantations as compared to off-axis implants. For higher doses, the experiment also reveals the growth of an intermediate peak slightly deeper than the random peak. The origin of the intermediate peak can be understood by combining SIMS results with Monte Carlo simulations, which motivates the development of advanced simulation tools for the ion implantation process in SiC. (C) 1999 American Institute of Physics. [S0003-6951(99)01426-6].
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14. |
- Schneider, Jochen, et al.
(author)
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Magnetic-field-dependent plasma composition of a pulsed arc in a high-vacuum ambient
- 2000
-
In: Applied Physics Letters. - 0003-6951 .- 1077-3118. ; 76:12, s. 1531-1533
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Journal article (peer-reviewed)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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15. |
- Kemerink, Martijn, et al.
(author)
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Spectrally resolved luminescence from an InGaAs quantum well induced by an ambient scanning tunneling microscope
- 1999
-
In: Applied Physics Letters. - : American Institute of Physics (AIP). - 0003-6951 .- 1077-3118. ; 75:23, s. 3656-3658
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Journal article (peer-reviewed)abstract
- Spectrally resolved scanning tunneling microscope-induced luminescence has been obtained under ambient conditions, i.e., at room temperature, in air, by passivating the sample surface with sulfur. This passivation turned out to be essential to suppress the local anodic oxidation induced by the tunneling current. From the dependence of the luminescence signal on tunneling current and voltage, we find that the passivation solution and post-passivation annealing temperature strongly modify the surface density of states (SDOS). More specifically, we found evidence that, after annealing at 400 degrees C, no SDOS is left above the bottom of the conduction band. For annealing at 200 degrees C, the SDOS is found to be extended up to 1.0 +/- 0.2 eV above the bottom of the conduction band. In all cases, the passivated (001) surface appears to be completely pinned. (C) 1999 American Institute of Physics. [S0003-6951(99)01949-X].
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16. |
- Tungasmita, Sukkaneste, et al.
(author)
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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
-
In: Applied Physics Letters. - 0003-6951 .- 1077-3118. ; 76:2, s. 170-172
-
Journal article (peer-reviewed)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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17. |
- Pozina, Galia, et al.
(author)
-
InGaN/GaN multiple quantum wells grown by metalorganic vapor phase epitaxy with mass transport
- 2000
-
In: Applied Physics Letters. - 0003-6951 .- 1077-3118. ; 77:11, s. 1638-1640
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Journal article (peer-reviewed)abstract
- We report on studies of In0.12Ga0.88N/GaN heterostructures with three 35-Angstrom-thick quantum wells (QWs) grown on sapphire substrates by metalorganic vapor phase epitaxy with employment of mass transport. The structure is demonstrated to show good structural and optical properties. The threading dislocation density is less than 10(7) cm(-2) for the mass-transport regions. The photoluminescence (PL) spectrum is dominated by the rather narrow near-band gap emission at 2.97 eV with a linewidth of 40 meV. This emission has a typical PL decay time about 5 ns at 2 K within the PL contour. With increasing excitation intensity, an additional transition with longer decay time (about 200 ns) is enhanced at energy about 2.85 eV. The position of this line depends strongly on the excitation power. We explain the data in terms of a model, where the PL is a result of contribution from at least two nonequivalent QWs, which could be realized due to a potential gradient across the layers. (C) 2000 American Institute of Physics. [S0003- 6951(00)04337-0].
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18. |
- Chang, KC, et al.
(author)
-
High-carbon concentrations at the silicon dioxide-silicon carbide interface identified by electron energy loss spectroscopy
- 2000
-
In: Applied Physics Letters. - 0003-6951 .- 1077-3118. ; 77:14, s. 2186-2188
-
Journal article (peer-reviewed)abstract
- High carbon concentrations at distinct regions at thermally-grown SiO2/6H-SiC(0001) interfaces have been detected by electron energy loss spectroscopy (EELS). The thickness of these C-rich regions is estimated to be 10-15 Angstrom. The oxides were grown on n-type 6H-SiC at 1100 degrees C in a wet O-2 ambient for 4 h immediately after cleaning the substrates with the complete RCA process. In contrast, C-rich regions were not detected from EELS analyses of thermally grown SiO2/Si interfaces nor of chemical vapor deposition deposited SiO2/SiC interfaces. Silicon-rich layers within the SiC substrate adjacent to the thermally grown SiO2/SiC interface were also evident. The interface state density D-it in metal-oxide-SiC diodes (with thermally grown SiO2) was approximately 9x10(11) cm(-2) eV(-1) at E- E-v=2.0 eV, which compares well with reported values for SiC metal-oxide-semiconductor (MOS) diodes that have not received a postoxidation anneal. The C-rich regions and the change in SiC stoichiometry may be associated with the higher than desirable D-it's and the low channel mobilities in SiC-based MOS field effect transistors. (C) 2000 American Institute of Physics. [S0003-6951(00)01940-9].
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19. |
- Mamor, M, et al.
(author)
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High-energy He-ion irradiation-induced defects and their influence on the noise behavior of Pd/n-Si1-xGex Schottky junctions
- 2000
-
In: Applied Physics Letters. - 0003-6951 .- 1077-3118. ; 76:25, s. 3750-3752
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Journal article (peer-reviewed)abstract
- We report on the electrical properties of defects introduced by high-energy 5.4 MeV He ions in n-type strained n-SiGe and the impact of this irradiation on the noise properties of Pd/n-Si1-xGex Schottky barrier diodes (SBDs). From the deep level transient spectroscopy measurements, the main defects EA1 and EA2 are observed in both Si and Si0.96Ge0.04 and have energy levels at 0.24 and 0.44 eV, respectively, below the conduction band. EA1 and EA2 have been correlated with the V-V and the P-V pairs, respectively. For both defects EA1 and EA2, the energy level position is found to be the same for x = 0 and 0.04, indicating that such levels are pinned to the conduction band. Furthermore, the impact of the high-energy He-ion irradiation on the electrical noise properties of Pd/n-Si1-xGex SBDs is also studied. From the noise experimental data, the main noise source observed in these irradiated diodes was attributed to the generation-recombination noise inducing an abnormal peak in their noise spectra at around f(1) = 180 Hz. This peak is found to be independent of Ge concentration. (C) 2000 American Institute of Physics. [S0003-6951(00)02125-2].
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20. |
- Abadei, S., et al.
(author)
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DC field dependent properties of Na0.5 K0.5 NbO3/SiO2/Si structures at millimeter-wave frequencies
- 2001
-
In: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 78:13, s. 1900-1902
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Journal article (peer-reviewed)abstract
- Dielectric properties of laser-ablated 0.5-μm-thick c-axis epitaxial Na0.5K0.5NbO3 films on high-resistivity (7.7 Ω cm) silicon SiO2/Si substrate are studied experimentally at frequencies up to 40 GHz. For measurements, planar 0.5-μm-thick gold electrodes (interdigital and straight slot) are photolithography defined on the top surface of Na0.5K0.5NbO3 films. The slot width between the electrodes is 2 or 4 μm. 13% capacitance change at 40 V dc bias and Q factor more than 15 are observed at 40 GHz, which makes the structure useful for applications in electrically tunable millimeter-wave devices
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21. |
- Abadei, S., et al.
(author)
-
DC field dependent properties of Na0.5K0.5NbO3/SiO2/Si structures at millimeter-wave frequencies
- 2001
-
In: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 78:13, s. 1900-1902
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Journal article (peer-reviewed)abstract
- Dielectric properties of laser-ablated 0.5-mum-thick c-axis epitaxial Na0.5K0.5NbO3 films on high-resistivity (7.7 Omega cm) silicon SiO2/Si substrate are studied experimentally at frequencies up to 40 GHz. For measurements, planar 0.5-mum-thick gold electrodes (interdigital and straight slot) are photolithography defined on the top surface of Na0.5K0.5NbO3 films. The slot width between the electrodes is 2 or 4 mum. 13% capacitance change at 40 V dc bias and Q factor more than 15 are observed at 40 GHz, which makes the structure useful for applications in electrically tunable millimeter-wave devices.
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22. |
- Abbondanza, Giuseppe, et al.
(author)
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Anisotropic strain variations during the confined growth of Au nanowires
- 2023
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In: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 122:12
-
Journal article (peer-reviewed)abstract
- The electrochemical growth of Au nanowires in a template of nanoporous anodic aluminum oxide was investigated in situ by means of grazing-incidence transmission small- and wide-angle x-ray scattering (GTSAXS and GTWAXS), x-ray fluorescence (XRF), and two-dimensional surface optical reflectance. The XRF and the overall intensity of the GTWAXS patterns as a function of time were used to monitor the progress of the electrodeposition. Furthermore, we extracted powder diffraction patterns in the direction of growth and in the direction of confinement to follow the evolution of the direction-dependent strain. Quite rapidly after the beginning of the electrodeposition, the strain became tensile in the vertical direction and compressive in the horizontal direction, which showed that the lattice deformation of the nanostructures can be artificially varied by an appropriate choice of the deposition time. By alternating sequences of electrodeposition with sequences of rest, we observed fluctuations of the lattice parameter in the direction of growth, attributed to stress caused by electromigration. Furthermore, the porous domain size calculated from the GTSAXS patterns was used to monitor how homogeneously the pores were filled.
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23. |
- Aberg, D., et al.
(author)
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Nitrogen deactivation by implantation-induced defects in 4H-SiC epitaxial layers
- 2001
-
In: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 78:19, s. 2908-2910
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Journal article (peer-reviewed)abstract
- Ion implantation causes free charge carrier reduction due to damage in the crystalline structure. Here, nitrogen-doped 4H silicon carbide (n type) epitaxial layers have been investigated using low ion doses in order to resolve the initial stage of the charge carrier reduction. It was found that the reduction of free carriers per ion-induced vacancy increases with increasing nitrogen content. Nitrogen is suggested to be deactivated through reaction with migrating point defects, and silicon vacancies or alternatively interstitials are proposed as the most likely candidates.
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24. |
- Aberg, I, et al.
(author)
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Nanoscale tungsten aerosol particles embedded in GaAs
- 2002
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In: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 80:16, s. 2976-2978
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Journal article (peer-reviewed)abstract
- GaAs containing buried nanoscale tungsten particles has been characterized electrically. The particles were produced using a special aerosol process and were embedded in GaAs by epitaxial overgrowth. Two different particle sizes were investigated separately. When the particle concentration was increased, a conductance drop of about 500 times was observed. A simulation model, based on a random distribution of the particles, was developed and used to support our findings. The major advantage of our method is the simplicity and low processing cost.
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25. |
- Abergel, David
(author)
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Excitonic condensation in spatially separated one-dimensional systems
- 2015
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In: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 106:21
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Journal article (peer-reviewed)abstract
- We show theoretically that excitons can form from spatially separated one-dimensional ground state populations of electrons and holes, and that the resulting excitons can form a quasicondensate. We describe a mean-field Bardeen-Cooper-Schrieffer theory in the low carrier density regime and then focus on the core-shell nanowire giving estimates of the size of the excitonic gap for InAs/GaSb wires and as a function of all the experimentally relevant parameters. We find that optimal conditions for pairing include small overlap of the electron and hole bands, large effective mass of the carriers, and low dielectric constant of the surrounding media. Therefore, one-dimensional systems provide an attractive platform for the experimental detection of excitonic quasicondensation in zero magnetic field.
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