| 1. |
- Doyle, J P, et al.
(författare)
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Observation of near-surface electrically active defects in n-type 6H-SiC
- 1998
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 83, s. 3649-3651
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Tidskriftsartikel (refereegranskat)abstract
- In n-type 6H-SiC epitaxial layers grown by vapor phase epitaxy, we find that in contrast to the majority of the epitaxial layer, where electrically active defects are observed with a concentration less than 1 X 10(-13) cm(-3), a region near the front surface contains defects with concentrations approaching 10(14) cm(-3). A relationship between the near-surface defects and metallic impurities is suggested by a Ti concentration of 1 X 10(16) cm(-3) in this region. The high concentration of near surface defects is found to significantly reduce the carrier lifetime. (C) 1998 American Institute of Physics. [S0021-8979(98)03007-2].
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| 2. |
- Greczynski, G, et al.
(författare)
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Energy level alignment in organic-based three-layer structures studied by photoelectron spectroscopy
- 2000
-
Ingår i: Journal of Applied Physics. - 0021-8979 .- 1089-7550. ; 88:12, s. 7187-7191
-
Tidskriftsartikel (refereegranskat)abstract
- The alignment of energy band edges at interfaces in three-layer structures, important in polymer-based electroluminescent devices, have been studied using photoelectron spectroscopy. Careful choice of the materials allows investigation of the role of the substrate work function. These results are in agreement with the energy level diagram commonly assumed for the metal/polymer/metal structure, with the potential drop over the polymer layer being equal to the difference between the work functions of the metal contacts. Direct indication of the alignment of the electrochemical potential across the three-layer structure has been observed by photoelectron spectroscopy. (C) 2000 American Institute of Physics. [S0021-8979(00)06801-3].
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| 3. |
- Granlund, T, et al.
(författare)
-
Luminescence probing of crystallization in a polymer film
- 2000
-
Ingår i: Journal of Applied Physics. - 0021-8979 .- 1089-7550. ; 87:12, s. 8549-8556
-
Tidskriftsartikel (refereegranskat)abstract
- We report studies of a thin film multilayer stack including a highly emissive substituted polythiophene, poly[3-(2,5-dioctylphenyl)thiophene]. Analysis of the photoluminescence spectra revealed an inhomogeneous polymer film. X-ray diffraction studies attribute the existence of an inhomogeneous film as originating from crystallization of the polymer. We used the interference effect of light to detect the region of crystallization in the film. Photoluminescence and absorption were redshifted upon crystallization and displayed an enhanced vibronic structure. Comparison between calculated and measured photoluminescence shows that the crystallization starts from the top of the film and not from the supporting substrate. (C) 2000 American Institute of Physics. [S0021- 8979(00)08112-3].
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| 4. |
- Ratnikov, V, et al.
(författare)
-
Bragg and Laue x-ray diffraction study of dislocations in thick hydride vapor phase epitaxy GaN films
- 2000
-
Ingår i: Journal of Applied Physics. - 0021-8979 .- 1089-7550. ; 88:11, s. 6252-6259
-
Tidskriftsartikel (refereegranskat)abstract
- The dislocation structure of hydride vapor phase epitaxial thick GaN layers grown on sapphire is studied by analysis of the microdistortion tensor components. Symmetrical reflections (including reflections from planes forming a large angle with the basal plane) with two modes of scanning (theta and theta -2 theta) in two geometries (Bragg and Laue) are used to obtain the tensor components. The instant connections between the tensor components and major dislocation types are specified. Different types of dislocation distributions have been identified in the thick GaN films grown on sapphire with and without undoped and Si-doped metalorganic chemical vapor deposited templates. Transmission electron microscopy was used to confirm the x-ray results by direct visualization of defect rearrangements. (C) 2000 American Institute of Physics. [S0021-8979(00)06023-0].
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| 5. |
- McCaffrey, JP, et al.
(författare)
-
Determination of the size, shape, and composition of indium-flushed self-assembled quantum dots by transmission electron microscopy
- 2000
-
Ingår i: Journal of Applied Physics. - 0021-8979 .- 1089-7550. ; 88:5, s. 2272-2277
-
Tidskriftsartikel (refereegranskat)abstract
- Single and multiple layers of self-assembled InAs quantum dots (QDs) produced by the indium-flush technique have been studied by transmission electron microscopy (TEM) in an effort to develop techniques to reproducibly grow QDs of uniform size and shape. To monitor the changes in QD dimensions, plan-view samples of capped single layers were studied as well as cross-sectional samples of QDs in multiple layers and stacks. The changes in the observed round- and square-shaped QD images under various plan-view TEM imaging conditions, as well as the contrast reversal in the center of QD images viewed in cross-section are modeled using the many-beam Bloch-wave approach, including strain. The sizes and shapes of the QDs are determined through the interpretation of the observed (primarily strain) contrast in plan-view and the observed (primarily atomic number) contrast in cross-sectional TEM. (C) 2000 American Institute of Physics. [S0021-8979(00)03217-5].
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| 6. |
- Zangooie, S, et al.
(författare)
-
Microstructural and infrared optical properties of electrochemically etched highly doped 4H-SiC
- 2000
-
Ingår i: Journal of Applied Physics. - 0021-8979 .- 1089-7550. ; 87:12, s. 8497-8503
-
Tidskriftsartikel (refereegranskat)abstract
- Pores in porous 4H-SiC are found to propagate first nearly parallel with the basal plane and then gradually change plane of propagation towards the direction of the c axis. A similar anisotropy in pore propagation is found in porous 6H-SiC. A disordered phase is encountered at the interface between crystalline SiC and the pores. Formation of this phase was attributed to the etching conditions. Characterization of the material with nondestructive infrared spectroscopic ellipsometry in the photon energy range 0.062-0.62 eV provides average thickness and porosity in good agreement with electron microscopy observations. Anodization of SiC introduces remarkable changes to the reststrahlen band. A shallow minimum at 0.113 eV is attributed to the Berreman effect. In addition, a sharp peak at 0.126 eV is discussed to be related to the in-depth inhomogeneity and particle shape effects in the material. (C) 2000 American Institute of Physics. [S0021-8979(00)07312-6].
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| 7. |
- Ouacha, H, et al.
(författare)
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Impact of plasma etching on the noise performance of Ti/p-Si and Ti/p-Si1-xGex Schottky contacts
- 2000
-
Ingår i: Journal of Applied Physics. - 0021-8979 .- 1089-7550. ; 87:8, s. 3858-3863
-
Tidskriftsartikel (refereegranskat)abstract
- The effect of plasma etching on the noise properties of Ti/p-Si and Ti/p-Si1-xGex (with x=0.05) Schottky junctions has been investigated. The noise measurements were performed over a temperature range of 77-300 K at frequencies of 10-100 kHz. The main noise source observed in these diodes during argon plasma sputter etching was attributed to the generation-recombination noise. From the analysis of the noise data, we have determined the interface state density and evaluated the introduced damage. The results indicate two optimum operating temperatures where low-noise level can be achieved. Furthermore, the activation energies of trap levels have been extracted by using noise spectroscopy (NS) and compared with those measured by deep-level transient spectroscopy (DLTS). We found two additional trap states using NS not detected by DLTS measurements. Finally, a noise comparison between Ti/p-Si and Ir/p-Si fabricated on an unetched substrate has been made. (C) 2000 American Institute of Physics. [S0021-8979(00)00608-3].
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| 8. |
- Paskova, Tanja, et al.
(författare)
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Effect of Si doping of metalorganic chemical vapor deposition-GaN templates on the defect arrangement in hydride vapor phase epitaxy-GaN overgrown layers
- 2000
-
Ingår i: Journal of Applied Physics. - 0021-8979 .- 1089-7550. ; 88:10, s. 5729-5732
-
Tidskriftsartikel (refereegranskat)abstract
- Two different types of dislocation arrangements have been observed in hydride vapor-phase epitaxial GaN films grown on sapphire substrates using both undoped and Si-doped GaN templates grown by metalorganic chemical vapor deposition: (i) predominantly straight threading dislocations parallel to the [0001] direction in the layer grown on an undoped template, and (ii) a network of interacting dislocations of edge, screw, and mixed character in the layer grown on a Si-doped template. The two types of defect distribution result in essentially different surface morphologies, respectively: (i) low-angle grain boundaries formed by pure edge dislocations around spiral grown hillocks, and (ii) smooth surface intersected by randomly distributed dislocations. The Si doping of the GaN templates was found to enhance defect interaction in the templates and to enable a reduction of the dislocation density in the overgrown thick GaN films, although it does not lead to an improvement of the overall structural properties of the material. (C) 2000 American Institute of Physics. [S0021-8979(00)08422-X].
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| 9. |
- Pozina, Galia, et al.
(författare)
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Origin of multiple peak photoluminescence in InGaN/GaN multiple quantum wells
- 2000
-
Ingår i: Journal of Applied Physics. - 0021-8979 .- 1089-7550. ; 88:5, s. 2677-2681
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Tidskriftsartikel (refereegranskat)abstract
- Optical spectroscopy has been performed for a set of In0.12Ga0.88N/GaN multiple quantum wells (MQW) grown by metalorganic vapor phase epitaxy at 820 degrees C. Time-resolved, temperature- and power-dependent photoluminescence as well as spatially-resolved cathodoluminescence measurements have been applied to elucidate the nature of the recombination mechanisms responsible for the radiative transitions in the samples. The photoluminescence spectra in this set of samples are dominated by strong multiple peak emissions associating with both confined levels of the MQW system (the higher energy band) and with strongly localized states of energies much lower than the QW band gap. We suggest that the photoluminescence originate from (i) the MQW exciton recombination, (ii) excitons localized in the quasidot regions with indium concentrations higher than in the alloy due to segregation processes, and (iii) from localized states in zero-dimensional quantum islands created by surface defects such as pits and V defects. Buried side-wall quantum wells caused by V defects might also influence the photoluminescence spectra. (C) 2000 American Institute of Physics. [S0021-8979(00)00117-1].
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| 10. |
- Syväjärvi, Mikael, et al.
(författare)
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Structural improvement in sublimation epitaxy of 4H-SiC
- 2000
-
Ingår i: Journal of Applied Physics. - 0021-8979 .- 1089-7550. ; 88:3, s. 1407-1411
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Tidskriftsartikel (refereegranskat)abstract
- The sublimation epitaxy growth process has been studied. The structural quality of the grown layers improves compared with the substrate mainly due to a diminished domain structure misorientation. Optical microscopy shows that the as-grown surfaces are free of typical defects appearing in silicon carbice (SiC) epitaxy, whereas atomic force microcopy measurements show macrosteps. As a possible technique to produce high-quality 4H-SiC, sublimation epitaxy was performed on substrates containing a layer grown by liquid phase epitaxy which is a growth process for closing micropipes in the initial substrate. In spite of the initial surface roughness of the liquid phase epitaxy layer, the surface morphology of the sublimation grown epilayers remained smooth and the structural quality improvement was maintained. This does not occur if the initial surfaces are too rough. A suggestion for roughness reduction is presented. The growth conditions (growth rate ramp up, growth temperature, temperature gradient, source to substrate distance, and substrate surface orientation) leading to the results are presented. A model for the mechanism for structural improvement is outlined and supporting experimental observations are given. (C) 2000 American Institute of Physics. [S0021-8979(00)07915-9].
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| 11. |
- Aberg, D, et al.
(författare)
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Ultrashallow thermal donor formation in silicon by annealing in ambient oxygen
- 1999
-
Ingår i: Journal of Applied Physics. - 0021-8979 .- 1089-7550. ; 85, s. 8054-8059
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Tidskriftsartikel (refereegranskat)abstract
- Czochralski-grown silicon wafers doped with phosphorus (similar to 10(14) cm(-3)) have been annealed in nitrogen, wet nitrogen, oxygen, argon, and vacuum ambients at 470 degrees C for times up to 500 h. Sample characterization was made using predominantly electrical techniques such as admittance spectroscopy and thermally stimulated capacitance measurements but also secondary ion mass spectrometry (SIMS) and Fourier transform infrared spectroscopy were employed. In all samples, an increasing concentration of free carrier electrons is observed with increasing annealing time, reaching a maximum of similar to 10(16) cm(-3) at 100 h. For durations in excess of 100 h gradual decrease of the free electron concentration takes place except for the samples treated in wet nitrogen and oxygen atmospheres, which display donors stable even after 200 h. These stable centers are found to have shallower donor level positions in the energy band gap (similar to 25 meV below the conduction band edge E-c) than those of the centers formed in vacuum, argon, and nitrogen atmospheres (similar to 35 meV below E-c). The latter centers are associated with the well-established shallow thermal donors (STDs) while the origin of the former ones, which are labeled ultrashallow thermal donors (USTDs) is less known. However, on the basis of a wealth of experimental results we show that the USTDs are most likely perturbated STDs modified through interaction with fast-in diffusing oxygen species, possibly oxygen dimers. Further, comparison between the electrical data and the SIMS measurements reveals unambiguously that neither the STD nor the USTD centers involve nitrogen, in contrast to recent suggestions in the literature. (C) 1999 American Institute of Physics. [S0021-8979(99)06512-3].
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| 12. |
- Hellgren, N, et al.
(författare)
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Influence of plasma parameters on the growth and properties of magnetron sputtered CNx thin films
- 2000
-
Ingår i: Journal of Applied Physics. - 0021-8979 .- 1089-7550. ; 88:1, s. 524-532
-
Tidskriftsartikel (refereegranskat)abstract
- Carbon nitride CNx thin films were grown by unbalanced dc magnetron sputtering from a graphite target in a pure N-2 discharge, and with the substrate temperature T-s kept between 100 and 550 degrees C. A solenoid coil positioned in the vicinity of the substrate was used to support the magnetic field of the magnetron, so that the plasma could be increased near the substrate. By varying the coil current and gas pressure, the energy distribution and fluxes of N-2(+) ions and C neutrals could be varied independently of each other over a wide range. An array of Langmuir probes in the substrate position was used to monitor the radial ion flux distribution over the 75-mm-diam substrate, while the flux and energy distribution of neutrals was estimated through Monte Carlo simulations. The structure, surface roughness, and mechanical response of the films are found to be strongly dependent on the substrate temperature, and the fluxes and energies of the deposited particles. By controlling the process parameters, the film structure can thus be selected to be amorphous, graphite-like or fullerene-like. When depositing at 3 mTorr N-2 pressure, with T-s> 200 degrees C, a transition from a disordered graphite-like to a hard and elastic fullerene-like structure occurred when the ion flux was increased above similar to 0.5-1.0 mA/cm(2). The nitrogen-to-carbon concentration ratio in the films ranged from similar to 0.1 to 0.65, depending on substrate temperature and gas pressure. The nitrogen film concentration did, however, not change when varying the nitrogen ion-to-carbon atom flux ratios from similar to 1 to 20. (C) 2000 American Institute of Physics. [S0021-8979(00)00413-8].
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| 13. |
- Abadei, S., et al.
(författare)
-
Low-frequency and microwave performances of laser-ablated epitaxial Na0.5K0.5NbO3 films on high-resistivity SiO2/Si substrates
- 2002
-
Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 91:4, s. 2267-2276
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Tidskriftsartikel (refereegranskat)abstract
- The dielectric properties of laser-ablated 0.5-mum-thick c-axis epitaxial Na0.5K0.5NbO3 (NKN) films on high-resistivity (>7.7 kOmega cm) silicon SiO2/Si substrates are studied experimentally in the temperature interval of 30-320 K and at frequencies of 1.0 MHz-40 GHz. The films are grown by laser ablation from a stoichiometric target. For the measurements, planar 0.5-mum-thick gold electrodes (interdigital and straight slot) are photolithography defined on the top surface of NKN films. The slot width between the electrodes is 2.0 or 4.0 mum. At low frequencies (f<1.0 GHz), the structure performance is that of a typical metal-dielectric-semiconductor type, where two of this type of capacitor are connected back to back. At these frequencies, the large change in the capacitance (more than 10 times at 1.0 MHz), due to the applied dc field, is mainly due to the changes in depletion layer thickness at the surface of silicon. The associated losses are also large, tan delta>1. At microwave frequencies (f>10 GHz), the voltage dependence of the capacitance is given by the NKN film. More than a 13% capacitance change at 40 V dc bias and a Q factor of more than 15 are observed at 40 GHz, which make the structure useful for applications in electrically tunable millimeter-wave devices.
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| 14. |
- Abadei, Saeed, 1961, et al.
(författare)
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Low-frequency and microwave performances of laser-ablated epitaxialNa 0.5 K 0.5 NbO 3 films on high-resistivitySiO 2 /Si substrates
- 2002
-
Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 91, s. 2267-
-
Tidskriftsartikel (refereegranskat)abstract
- The dielectric properties of laser-ablated 0.5-μm-thick c-axis epitaxialNa 0.5 K 0.5 NbO 3 (NKN) films on high-resistivity (>7.7 kΩ cm) siliconSiO 2 /Si substrates are studied experimentally in the temperature interval of 30–320 K and at frequencies of 1.0 MHz–40 GHz. The films are grown by laser ablation from a stoichiometric target. For the measurements, planar 0.5-μm-thick gold electrodes (interdigital and straight slot) are photolithography defined on the top surface of NKN films. The slot width between the electrodes is 2.0 or 4.0 μm. At low frequencies(f 1. At microwave frequencies(f>10 GHz), the voltage dependence of the capacitance is given by the NKN film. More than a 13% capacitance change at 40 V dc bias and a Q factor of more than 15 are observed at 40 GHz, which make the structure useful for applications in electrically tunable millimeter-wave devices
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| 15. |
- Aberg, J, et al.
(författare)
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Electrical properties of the TiSi2-Si transition region in contacts : The influence of an interposed layer of Nb
- 2001
-
Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 90:5, s. 2380-2388
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Tidskriftsartikel (refereegranskat)abstract
- The influence of an interposed ultrathin Nb layer between Ti and Si on the silicide formation and the electrical contact between the silicide formed and the Si substrate is investigated. The presence of the Nb interlayer results in the formation of ternary alloy (Nb,Ti)Si-2 in the C40 crystallographic structure adjacent to the Si substrate. Depending on the nature of the Si substrates and/or the amount of the initial Nb, the interfacial C40 (Nb,Ti)Si-2 leads, in turn, to either epitaxial growth of a highly faulted metastable C40 TiSi2 or formation of the desired C54 TiSi2 at a lower temperature than needed for it to form in reference samples with Ti deposited directly on Si. On p-type substrates doped to various concentrations, the Nb also leads to a considerably lower specific contact resistivity than that obtained in the reference samples: a twofold to fourfold reduction in the contact resistivity is found using cross-bridge Kelvin structures in combination with two-dimensional numerical simulation. As C40 (Nb,Ti)Si-2 forms at the interface when an interfacial Nb is present, the interface characterized is likely to represent the one between (Nb,Ti)Si-2 and Si. For the reference samples, the interface studied is between TiSi2 and Si.
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| 16. |
- Abom, A.E., et al.
(författare)
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Characterization of the metal-insulator interface of field-effect chemical sensors
- 2003
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 93:12, s. 9760-9768
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Tidskriftsartikel (refereegranskat)abstract
- The metal-insulator interface of hydrogen-sensitive metal-insulator-semiconductor capacitors, with SiO2 as the insulator and Pt as the metal contact, was discussed. It was found that the difference in hydrogen response between differently prepared devices was explained by a difference in concentration of available adsorption sites. The analysis showed that the concentration of Pt atoms in contact with the oxide affected both the hydrogen response and the metal-oxide adhesion.
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| 17. |
- Abrasonis, Gintautas, et al.
(författare)
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Nanoscale precipitation patterns in carbon-nickel nanocomposite thin films: Period and tilt control via ion energy and deposition angle
- 2010
-
Ingår i: JOURNAL OF APPLIED PHYSICS. - : American Institute of Physics. - 0021-8979 .- 1089-7550. ; 108:4, s. 043503-
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Tidskriftsartikel (refereegranskat)abstract
- Periodic precipitation patterns in C:Ni nanocomposites grown by energetic ion codeposition are investigated. Films were grown at room temperature by ionized physical vapor deposition using a pulsed filtered cathodic vacuum arc. We reveal the role of the film composition, ion energy and incidence angle on the film morphology using transmission electron microscopy and grazing incidence small angle x-ray scattering. Under these growth conditions, phase separation occurs in a thin surface layer which has a high atomic mobility due to energetic ion impacts. This layer is an advancing reaction front, which switches to an oscillatory mode, producing periodic precipitation patterns. Our results show that the ion induced atomic mobility is not random, as it would be in the case of thermal diffusion but conserves to a large extent the initial direction of the incoming ions. This results in a tilted pattern under oblique ion incidence. A dependence of the nanopattern periodicity and tilt on the growth parameters is established and pattern morphology control via ion velocity is demonstrated.
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| 18. |
- Adachi, N., et al.
(författare)
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Epitaxial Bi3Fe5O12(001) films grown by pulsed laser deposition and reactive ion beam sputtering techniques
- 2000
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 88:5, s. 2734-2739
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Tidskriftsartikel (refereegranskat)abstract
- We report on processing and comparative characterization of epitaxial Bi3Fe5O12 (BIG) films grown onto Gd-3(ScGa)(5)O-12[GSGG,(001)] single crystal using pulsed laser deposition (PLD) and reactive ion beam sputtering (RIBS) techniques. A very high deposition rate of about 0.8 mu m/h has been achieved in the PLD process. Comprehensive x-ray diffraction analyses reveal epitaxial quality both of the films: they are single phase, exclusively (001) oriented, the full width at half maximum of the rocking curve of (004) Bragg reflection is 0.06 deg for PLD and 0.05 deg for RIBS film, strongly in-plane textured with cube-on-cube film-to-substrate epitaxial relationship. Saturation magnetization 4 pi M-s and Faraday rotation at 635 nm were found to be 1400 Gs and -7.8 deg/mu m in PLD-BIG, and 1200 Gs and -6.9 deg/mu m in RIBS-BIG. Ferromagnetic resonance (FMR) measurements performed at 9.25 GHz yielded the gyromagnetic ratio gamma=1.797x10(7) l/s Oe, 1.826x10(7) l/s Oe; the constants of uniaxial magnetic anisotropy were K-u(*)=-8.66x10(4) erg/cm(3), -8.60x10(4) erg/cm(3); the cubic magnetic anisotropy K-1=-2.7x10(3) erg/cm(3),-3.8x10(3) erg/cm(3); and the FMR linewidth Delta H=25 and 34 Oe for PLD and RIBS films correspondingly. High Faraday rotation, low microwave loss, and low coercive field less than or equal to 40 Oe of BIG/GSGG(001) films promise their use in integrated magneto-optic applications.
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| 19. |
- Adamczyk, Krzysztof, et al.
(författare)
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Recombination activity of grain boundaries in high-performance multicrystalline Si during solar cell processing
- 2018
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Ingår i: Journal of Applied Physics. - : American Institute of Physics (AIP). - 0021-8979 .- 1089-7550. ; 123:5, s. 1-6
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Tidskriftsartikel (refereegranskat)abstract
- In this work, we applied internal quantum efficiency mapping to study the recombination activity of grain boundaries in High Performance Multicrystalline Silicon under different processing conditions. Wafers were divided into groups and underwent different thermal processing, consisting of phosphorus diffusion gettering and surface passivation with hydrogen rich layers. After these thermal treatments, wafers were processed into heterojunction with intrinsic thin layer solar cells. Light Beam Induced Current and Electron Backscatter Diffraction were applied to analyse the influence of thermal treatment during standard solar cell processing on different types of grain boundaries. The results show that after cell processing, most random-angle grain boundaries in the material are well passivated, but small-angle grain boundaries are not well passivated. Special cases of coincidence site lattice grain boundaries with high recombination activity are also found. Based on micro-X-ray fluorescence measurements, a change in the contamination level is suggested as the reason behind their increased activity.
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| 20. |
- Adamyan, Astghik, 1984, et al.
(författare)
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Superconducting microwave parametric amplifier based on a quasi-fractal slow propagation line
- 2016
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 119:8
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Tidskriftsartikel (refereegranskat)abstract
- Quantum limited amplifiers are sought after for a wide range of applications within quantum technologies and sensing. One promising candidate is the travelling wave parametric amplifier which exploits the non-linear kinetic inductance of a superconducting transmission line. This type of microwave amplifier promises to deliver a high gain, a quantum limited noise performance over several GHz bandwidth, and a high dynamic range. However, practical realizations of this type of device have so far been limited by fabrication defects, since the length of the superconducting transmission line required for achieving substantial parametric gain is on the order of similar to 1m. Here, we report on a design for a microwave traveling wave amplifier based on a slow propagation line comprising a central strip with high kinetic inductance and quasi-fractal line-to-ground capacitors. Due to an enhanced per unit length inductance (73 nH cm(-1)) and capacitance (15 pF cm(-1)), the line has a microwave propagation velocity as low as 9.8 x 10(8) cm s(-1). This translates into parametric gain up to 0.5 dB cm(-1) and a total gain of 6 dB for just a similar to 10 cm long transmission line. Moreover, the flexibility of the presented design allows balancing the line inductance and capacitance in order to keep the characteristic impedance close to 50 Omega and to suppress standing waves, both factors being essential in order to implement a practical parametric amplifier in the microwave domain.
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| 21. |
- Adolfsson, Göran, 1981, et al.
(författare)
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Realization of spectrally engineered semiconductor Fabry-Perot lasers with narrow geometrical tolerances
- 2011
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 109:9, s. 093112-
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Tidskriftsartikel (refereegranskat)abstract
- Spectrally engineered semiconductor Fabry-Perot laser resonators are designed to enhance the optical feedback for selected longitudinal modes, which thereby require less gain for lasing. This is achieved by introducing refractive index perturbations along the length of the resonator. However,the physical realization of these resonators is a challenge because of very narrow tolerances; in particular the need for precise positioning of the end facets of the resonator in relation to the perturbations, and the excess propagation loss associated with the perturbations, has been a majorconcern. We report on a method to achieve high-quality end facet mirrors enabling precise positioning relative to the perturbations, the latter which are realized as lateral corrugations of the waveguide. Measurements show that the mirror quality is comparable to that of cleaved mirrorsand that the additional loss introduced by the perturbations adds
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| 22. |
- Afanas´ev, V.P., et al.
(författare)
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Study of A1/Nb interface by spectroscopy of reflected electrons
- 2007
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 101:064912, s. 1-6
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Tidskriftsartikel (refereegranskat)abstract
- We have studied Al/Nb interface with help of spectroscopy of reflected electrons. Ion sputtering combined with monitoring of Auger peaks has been used to approach the interface. The developed method of quantitative interpretation of spectra allowed us to characterize the distribution of Al and Nb in the interface region with a nanometer depth resolution. The Al/Nb interface was found to have an intermediate layer of about 10 nm thickness, which is more likely due to the interface roughness, rather than diffusion smearing. We discuss the possibility to distinguish by means of spectroscopy of reflected electrons either material under analysis is a single phase or a mixture of two phases.
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| 23. |
- Agnarsson, Björn, et al.
(författare)
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Influence of initial surface reconstruction on nitridation of Al2O3 (0001) using low pressure ammonia
- 2007
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 101:1, s. 013519-
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Tidskriftsartikel (refereegranskat)abstract
- The purpose of this study is to investigate the effect of initial surface reconstruction on the nitridation process of Al2O3 (0001). This was done by exposing differently reconstructed sapphire substrates at different temperatures to low pressure ammonia (NH3). Structural and chemical analysis were carried out using low-electron energy diffraction and x-ray photoelectron spectroscopy. The experiments revealed that using low pressure ammonia (P-NH3 < 1 X 10(-5) Torr), no nitridation takes place on (1x1) unreconstructed surfaces. However, when the unreconstructed surface starts to change to a (root 31 x root 31) R +/- 9 degrees reconstructed surface, with increasing substrate temperature, the nitridation becomes successful. When using the initially reconstructed surface, the nitridation is successful even from the lowest temperature used. These results suggest that the initial surface reconstruction has a major effect on the nitridation process. This kinetic behavior has not been reported before, with most nitridation studies mainly focusing on the effect of surface temperature on the resulting surface morphology, rather than the actual kinetics of the process itself.
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| 24. |
- Ahadi, Zohreh, et al.
(författare)
-
Stability and thermal behavior of molybdenum disulfide nanotubes: Nonequilibrium molecular dynamics simulation using REBO potential
- 2017
-
Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 122:22
-
Tidskriftsartikel (refereegranskat)abstract
- This study is an attempt to perform equilibrium molecular dynamics and non-equilibrium molecular dynamics (NEMD) to evaluate the stability and thermal behavior of molybdenum disulfide nanotubes (MoS2NTs) by reactive empirical bond order potential. The stability of nanotubes, cohesive energy, isobaric heat capacity, and enthalpies of fusion in armchair and zigzag structures with different radii were calculated. The observed results illustrate that SWMoS2NTs, which have larger diameters, are more stable with more negative energy than the smaller ones. Moreover, it was found that the melting point is increased with an increase in the nanotube's radius. During the melting process, the structural transformation of nanotubes was investigated using a mean-square displacement and radial distribution function diagrams. Afterwards, using a NEMD simulation, the thermal conductivity of nanotubes with various diameters was calculated at a constant nanotube length. The obtained results show that the thermal conductivity coefficient increases with increasing nanotube diameters when the nanotube length is constant.
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| 25. |
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| 26. |
- Ahuja, Rajeev, et al.
(författare)
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Electronic and optical properties of lead iodide
- 2002
-
Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 92:12, s. 7219-7224
-
Tidskriftsartikel (refereegranskat)abstract
- The electronic properties and the optical absorption of lead iodide (PbI2) have been investigated experimentally by means of optical absorption and spectroscopic ellipsometry, and theoretically by a full-potential linear muffin-tin-orbital method. PbI2 has been recognized as a very promising detector material with a large technological applicability. Its band-gap energy as a function of temperature has also been measured by optical absorption. The temperature dependence has been fitted by two different relations, and a discussion of these fittings is given.
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| 27. |
- Ahuja, Rajeev, et al.
(författare)
-
Optical properties of 4H-SiC
- 2002
-
Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 91:4, s. 2099-2103
-
Tidskriftsartikel (refereegranskat)abstract
- The optical band gap energy and the dielectric functions of n-type 4H-SiC have been investigated experimentally by transmission spectroscopy and spectroscopic ellipsometry and theoretically by an ab initio full-potential linear muffin-tin-orbital method. We present the real and imaginary parts of the dielectric functions, resolved into the transverse and longitudinal photon moment a, and we show that the anisotropy is small in 4H-SiC. The measurements and the calculations fall closely together in a wide range of energies.
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| 28. |
- Ahuja, Rajeev, et al.
(författare)
-
Optical properties of SiGe alloys
- 2003
-
Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 93:7, s. 3832-3836
-
Tidskriftsartikel (refereegranskat)abstract
- The optical properties of Si1-xGex have been investigated theoretically using a full-potential linear muffin-tin-orbital method. We present the density-of-states as well as the real and imaginary parts of the dielectric function. The calculated dielectric function was found to be in good agreement with the spectroscopic ellipsometry measurements by J. Bahng , J. Phys.: Condens. Matter 13, 777 (2001), and we obtained a static dielectric constant of epsilon(0)=12.19+2.45x in the Si rich regime (xless than or equal to0.5).
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| 29. |
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| 30. |
- Aiempanakit, Montri, 1977-, et al.
(författare)
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Understanding the discharge current behavior in reactive high power impulse magnetron sputtering of oxides
- 2013
-
Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 113:13, s. 133302-
-
Tidskriftsartikel (refereegranskat)abstract
- The discharge current behavior in reactive high power impulse magnetron sputtering (HiPIMS) of Ti-O and Al-O is investigated. It is found that for both metals, the discharge peak current significantly increases in the oxide mode in contrast to the behavior in reactive direct current magnetron sputtering where the discharge current increases for Al but decreases for Ti when oxygen is introduced. In order to investigate the increase in the discharge current in HiPIMS-mode, the ionic contribution of the discharge in the oxide and metal mode is measured using time-resolved mass spectrometry. The energy distributions and time evolution are investigated during the pulse-on time as well as in the post-discharge. In the oxide mode, the discharge is dominated by ionized oxygen, which has been preferentially sputtered from the target surface. The ionized oxygen determines the discharge behavior in reactive HiPIMS.
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| 31. |
- Aïssa, B., et al.
(författare)
-
Influence of single-walled carbon nanotubes induced exciton dissociation improvement on hybrid organic photovoltaic devices
- 2019
-
Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 126:11
-
Tidskriftsartikel (refereegranskat)abstract
- Torch-plasma-grown single-walled carbon nanotubes (SWCNTs) are integrated with regioregular poly(3-hexylthiophene) (P3HT) and a fullerene derivative 1-(3-methoxycarbonyl) propyl-1-phenyl[6,6]C61 (PCBM) as a hybrid photoactive layer for bulk heterojunction solar cell devices. We demonstrate that molecular information could be accurately obtained by time-of-flight secondary ion mass spectrometry throughout the hybrid organic photoactive solar cell layers when sputtering is performed using a Cs+ 2000 eV ion source. Furthermore, the photovoltaic (PV) performance of the fabricated devices show an increase in the short-circuit current density (Jsc) and the fill factor (FF) as compared to the pristine devices fabricated without SWCNTs. The best results are obtained with 0.5 wt. % SWCNT loads, where an open-circuit voltage (VOC) of 660 mV is achieved, with a Jsc of 9.95 mA cm-2 and a FF of 54%, leading to a power conversion efficiency of 3.54% (measured at standard test conditions, AM1.5 g). At this optimum SWCNT concentration of 0.5 wt. %, and to further understand the charge-transfer mechanisms taking place at the interfaces of P3HT:PCBM:SWCNT, Jsc is measured with respect to the light intensity and shows a linear dependency (in the double logarithmic scale), which implies that losses in the charge carrier are rather governed by monomolecular recombination. Finally, our results show that our hybrid devices benefit from the fullerene electron accepting nature and from the SWCNT fast electron transportation feature that improve substantially the exciton dissociation efficiency. The influence of the SWCNTs on the Fermi level and the work function of the photoactive composite and its impact on the PV performance is also investigated.
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| 32. |
- Akabori, M., et al.
(författare)
-
Realization of In0.75Ga0.25As two-dimensional electron gas bilayer system for spintronics devices based on Rashba spin-orbit interaction
- 2012
-
Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 112:11, s. 113711-
-
Tidskriftsartikel (refereegranskat)abstract
- Narrow gap InGaAs two-dimensional electron gas (2DEG) bilayer samples are fabricated and confirmed to have good electronic qualities as well as strong Rashba-type spin-orbit interactions (SOIs). The 2DEG systems are realized by molecular beam epitaxy in the form of wide quantum wells (QWs) with thicknesses tQW∼40-120nm modulation doped in both the upper and lower InAlAs barriers. From the Hall measurements, the overall mobility values of μe ∼15 m2/V s are found for the total sheet electron density of ns ∼8 × 1011/cm2, although the ns is distributed asymmetrically as about 1:3 in the upper and lower 2DEGs, respectively. Careful low temperature magneto-resistance analysis gives large SO coupling constants of α ∼20 × 10 -12eV m as well as expected electron effective masses of m*/m0 ∼0.033-0.042 for each bilayer 2DEG spin sub-band. Moreover, the enhancement of α with decrease of tQW is found. The corresponding self-consistent calculation, which suggests the interaction between the bilayer 2DEGs, is carried out and the origin of α enhancement is discussed.
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| 33. |
- Al-Hamadandy, Raied, et al.
(författare)
-
Oxygen vacancy migration in compressively strained SrTiO3
- 2013
-
Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 113:2
-
Tidskriftsartikel (refereegranskat)abstract
- The intrinsic properties of strontium titanate render it promising in applications such as gate dielectrics and capacitors. However, there is growing evidence that oxygen vacancies significantly impact upon its use, with the diffusion and deep donor level of the oxygen vacancy leading to electrical leakage. Where grown epitaxially on a lattice mismatched substrate, SrTiO 3 undergoes bi-axial strain, altering its crystal structure and electronic properties. In this paper, we present the results of first-principles simulations to evaluate the impact of strain in a (001) plane upon the migration of oxygen vacancies. We show that in the range of strains consistent with common substrate materials, diffusion energies in different directions are significantly affected, and for high values of strain may be altered by as much as a factor of two. The resulting diffusion anisotropy is expected to impact upon the rate at which oxygen vacancies are injected into the films under bias, a critical factor in the leakage and resistive switching seen in this material
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| 34. |
- Al-Hamadany, R., et al.
(författare)
-
Impact of tensile strain on the oxygen vacancy migration in SrTiO3 : Density functional theory calculations
- 2013
-
Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 113:22
-
Tidskriftsartikel (refereegranskat)abstract
- Strontium titanate is a promising dielectric material for device applications including capacitors and gate dielectrics. However, oxygen vacancies, which are inevitable donor defects mobile under bias at room temperature, lead to undesirable leakage current in SrTiO3 thin films. Epitaxially grown SrTiO3 on lattice mismatched substrates leads to strained SrTiO3, inducing structural phase transitions from a cubosymmetric non-ferroelectric geometry to tetragonal and orthorhombic structures, depending upon the sign of the strain. In this study, density functional calculations have been performed to determine the impact of isotropic biaxial tensile strain in a (001) plane upon the phase of SrTiO3 and the activation energy for the migration of oxygen vacancies in such strained SrTiO3. The phase transition of the host material yields anisotropy in oxygen vacancy diffusion for diffusion within and between planes parallel to the strain. We found a general reduction in the barrier for diffusion within and normal to the plane of tensile strain. The inter-plane diffusion barrier reduces up to 25% at high values of strain. The variation in the barrier corresponding to in-plane diffusion is smaller in comparison to inter-plane diffusion. Finally, we reflect upon how the interplay between lattice strain with native defects plays a crucial role in the conduction mechanism of thin film, strained SrTiO3
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| 35. |
- Al-Hilli, Safaa, 1965, et al.
(författare)
-
Zinc oxide nanorods grown on two-dimensional macroporous periodic structures and plane Si as a pH sensor
- 2008
-
Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 103:1, s. 014302-014309
-
Tidskriftsartikel (refereegranskat)abstract
- pH determination is a strong prerequisite for many biochemical and biological processes. We used two methods, namely, the electrochemical potential method (experimental) and site binding method (theoretical), to study the sensitivity of zinc oxide (ZnO) nanorods grown on two-dimensional macroporous periodic structures (2DMPPS) (p-and n-type) and plane n-type Si substrates for use as an intracellular pH sensing device. The dimension of these nanorods varied in radius between 50 and 300 nm and lengths of 1–10 μm. We found that the sensitivity of ZnO nanorods increases with reductions in size, from 35 mV/pH for D = 300 nm and L = 10 μm, to 58 mV/pH for D = 50 nm and L = 1 μm, using the site binding model. The experimental electrochemical potential difference for the ZnO nanorods working electrode versus Ag/AgCl reference electrode showed a high sensitivity range for ZnO nanorods grown on 2DMPPS n-Si substrate as compared to plane n-Si at room temperature for pH ranging from 4 to 12 in buffer and NaCl solutions
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| 36. |
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| 37. |
- Al-Zoubi, Noura, et al.
(författare)
-
The bain path of paramagnetic Fe-Cr based alloys
- 2011
-
Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 110:1, s. 013708-
-
Tidskriftsartikel (refereegranskat)abstract
- Employing the first-principles exact muffin-tin orbital method in combination with the coherent potential approximation, we calculated the total energy and local magnetic moments of paramagnetic Fe-Cr-M (M = Cr, Mn, Fe, Co, Ni) alloys along the tetragonal distortion (Bain) path connecting the body centered cubic (bcc) and the face centered cubic (fcc) structures. The paramagnetic phase is modeled by the disordered local magnetic moment scheme. For all alloys, the local magnetic moments on Fe atoms decrease from the maximum value corresponding to the bcc phase toward the minimum value realized for the fcc phase. Cobalt atoms have non-vanishing local magnetic moments only for tetragonal lattices with c/a < 1.30, whereas the local magnetic moments of Mn show weak crystal structure dependence. We find that Cr stabilizes the bcc lattice and increases the energy barrier as going from the bcc toward the fcc phase. Both Co and Ni favor the fcc lattice and decrease the energy barrier relative to the bcc phase. On the other hand, the tetragonal distortion around the fcc phase is facilitated by Cr and to a somewhat lesser extent also by Ni, but strongly impeded by Co. Manganese has negligible effect on the structural energy difference as well as on the energy barrier along the Bain path. Our findings on the alloying induced softening or hardening of Fe-Cr based alloys against tetragonal distortions are important for understanding the interstitial driven martensitic transformations in alloy steels.
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| 38. |
- Alarco, J A, et al.
(författare)
-
Early stages of growth of YBa2Cu3O7− high Tc superconducting films on (001) Y-ZrO2 substrates
- 1994
-
Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 75, s. 3202-3204
-
Tidskriftsartikel (refereegranskat)abstract
- Theearly stages of growth of high quality YBa2Cu3O7− (YBCO) filmsgrown on (001) Y-ZrO2 (YSZ) substrates by pulsed laser depositionhave been studied using a combination of atomic force microscopyand transmission electron microscopy. A one unit cell thick YBCOlayer and relatively large CuO particles formed in the initialstages. Additional YBCO grew on top of the first layerin the form of one or a few unit cellhigh c-axis oriented islands about 30 nm in diameter. Therounded islands subsequently coalesced into faceted domains. Elongated Y2BaCuO5 particlesnucleated after the first layer of YBCO. A highly texturedBaZrO3 layer formed between the YSZ and the YBCO witha cube-on-cube dominant orientation relationship with respect to the YBCOfilm. Journal of Applied Physics is copyrighted by The American Institute of Physics.
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| 39. |
- Alavian Ghavanini, Farzan, 1978, et al.
(författare)
-
Direct measurement of bending stiffness and estimation of Young's modulus of vertically aligned carbon nanofibers
- 2013
-
Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 113:19
-
Tidskriftsartikel (refereegranskat)abstract
- The bending stiffness of individual, as-grown, vertically aligned carbon nanofibers was measured using a custom-built atomic force microscope placed inside a scanning electron microscope. The internal structure of the nanofiber was best modeled as dual-phase, composed of an inner graphitic core covered with a tapered amorphous carbon shell. It was found that the fibers have a relatively low bending stiffness, with Young's modulus values of about 10 GPa for the inner core and 65 GPa for the outer shell. The low Young's modulus of the inner core is attributed to a non-zero angle between the graphitic sheets and the nanofiber axis. The weak shear modulus between graphitic sheets thereby dominates the mechanical behaviour of the fibers.
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| 40. |
- Alavian Ghavanini, Farzan, 1978, et al.
(författare)
-
Vertically aligned carbon based varactors
- 2011
-
Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 110:2
-
Tidskriftsartikel (refereegranskat)abstract
- This paper gives an assessment of vertically aligned carbon based varactors and validates their potential for future applications. The varactors discussed here are nanoelectromechanical devices which are based on either vertically aligned carbon nanofibers or vertically aligned carbon nanotube arrays. A generic analytical model for parallel plate nanoelectromechanical varactors based on previous works is developed and is used to formulate a universal expression for their voltage-capacitance relation. Specific expressions for the nanofiber based and the nanotube based varactors are then derived separately from the generic model. This paper also provides a detailed review on the fabrication of carbon based varactors and pays special attention to the challenges in realizing such devices. Finally, the performance of the carbon based varactor is assessed in accordance with four criteria: the static capacitance, the tuning ratio, the quality factor, and the operating voltage. Although the reported performance is still far inferior to other varactor technologies, our prognosis which stems from the analytical model shows a promise of a high quality factor as well as a potential for high power handling for carbon based varactors.
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| 41. |
- Alfieri, G., et al.
(författare)
-
Annealing behavior between room temperature and 2000 degrees C of deep level defects in electron-irradiated n-type 4H silicon carbide
- 2005
-
Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 98:4
-
Tidskriftsartikel (refereegranskat)abstract
- The annealing behavior of irradiation-induced defects in 4H-SiC epitaxial layers grown by chemical-vapor deposition has been systematically studied by means of deep level transient spectroscopy (DLTS). The nitrogen-doped epitaxial layers have been irradiated with 15-MeV electrons at room temperature and an isochronal annealing series from 100 to 2000 degrees C has been performed. The DLTS measurements, which have been carried out in the temperature range from 120 to 630 K after each annealing step, revealed the presence of six electron traps located in the energy range of 0.45-1.6 eV below the conduction-band edge (E-c). The most prominent and stable ones occur at E-c-0.70 eV (labeled Z(1/2)) and E-c-1.60 eV(EH6/7). After exhibiting a multistage annealing process over a wide temperature range, presumably caused by reactions with migrating defects, a significant fraction of both Z(1/2) and EH6/7 (25%) still persists at 2000 degrees C and activation energies for dissociation in excess of 8 and similar to 7.5 eV are estimated for Z(1/2) and EH6/7, respectively. On the basis of these results, the identity of Z(1/2) and EH6/7 is discussed and related to previous assignments in the literature.
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| 42. |
- Alfieri, G., et al.
(författare)
-
Defect energy levels in hydrogen-implanted and electron-irradiated n-type 4H silicon carbide
- 2005
-
Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 98:11
-
Tidskriftsartikel (refereegranskat)abstract
- Using deep level transient spectroscopy (DLTS), we have studied the energy position and thermal stability of deep levels in nitrogen doped 4H-SiC epitaxial layers after 1.2 MeV proton implantation and 15 MeV electron irradiation. Isochronal annealing was performed at temperatures from 100 to 1200 degrees C in steps of 50 degrees C. The DLTS measurements, which were carried out in the temperature range from 120 to 630 K after each annealing step, reveal the presence of ten electron traps located in the energy range of 0.45-1.6 eV below the conduction band edge (E-c). Of these ten levels, three traps at 0.69, 0.73, and 1.03 eV below E-c, respectively, are observed only after proton implantation. Dose dependence and depth profiling studies of these levels have been performed. Comparing the experimental data with computer simulations of the implantation and defects profiles, it is suggested that these three new levels, not previously reported in the literature, are hydrogen related. In particular, the E-c-0.73 eV level displays a very narrow depth distribution, confined within the implantation profile, and it originates most likely from a defect involving only one H atom.
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| 43. |
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| 44. |
- Alijan Farzad Lahiji, Faezeh, et al.
(författare)
-
Unusual tilted growth and epitaxial relationship of NaCl B1-structured NiO and CrN on r-plane Al2O3
- 2024
-
Ingår i: Journal of Applied Physics. - : American Institute of Physics Inc.. - 0021-8979 .- 1089-7550. ; 135:6
-
Tidskriftsartikel (refereegranskat)abstract
- Epitaxial NiO and CrN thin films were deposited on a single-crystal Al2O3(11¯02) (r-plane sapphire) using magnetron sputtering. The two materials were intentionally deposited into two different deposition chamber designs and under different conditions (temperature, pressure, gases, and energy of sputtered particles). Despite the differences in the deposition condition and material system, both materials had the same feature with uncommon tilted epitaxial growth. Through an in-depth x-ray diffraction analysis of the NaCl (B1)-structured materials on r-plane sapphire, the full twin domain epitaxial relations were determined and can be described as (110)NaCl(B1)∥(44¯03)Al2O3 and [11¯2]NaCl(B1)∥[1¯1¯20]Al2O3. This relationship differs from the previously observed orientation of (100)NaCl(B1)∥(11¯02)Al2O3 and [100]NaCl(B1)∥[101¯0]Al2O3. These results are of general relevance for the growth of the extended NaCl (B1)-structured cubic material family onto a r-plane sapphire substrate where similar epitaxial growth can be expected.
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| 45. |
- Alkhadi, H.S., et al.
(författare)
-
The influence of capping layers on pore formation in Ge during ion implantation
- 2016
-
Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 120:21
-
Tidskriftsartikel (refereegranskat)abstract
- Ion induced porosity in Ge has been investigated with and without a cap layer for two ion species, Ge and Sn, with respect to ion fluence and temperature. Results without a cap are consistent with a previous work in terms of an observed ion fluence and temperature dependence of porosity, but with a clear ion species effect where heavier Sn ions induce porosity at lower temperature (and fluence) than Ge. The effect of a cap layer is to suppress porosity for both Sn and Ge at lower temperatures but in different temperatures and fluence regimes. At room temperature, a cap does not suppress porosity and results in a more organised pore structure under conditions where sputtering of the underlying Ge does not occur. Finally, we observed an interesting effect in which a barrier layer of a-Ge that is denuded of pores formed directly below the cap layer. The thickness of this layer (∼ 8 nm) is largely independent of ion species, fluence, temperature, and cap material, and we suggest that this is due to viscous flow of a-Ge under ion irradiation and wetting of the cap layer to minimize the interfacial free energy.
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| 46. |
- Allaf Navirian, Hengameh, et al.
(författare)
-
Repetitive ultrafast melting of InSb as an x-ray timing diagnostic
- 2008
-
Ingår i: Applied Physics Reviews. - : AIP Publishing. - 1931-9401. ; 103:10, s. 6-103510
-
Tidskriftsartikel (refereegranskat)abstract
- We have demonstrated the possibility of using repetitive ultrafast melting of InSb as a timing diagnostic in connection with visible-light pump/x-ray probe measurements at high-repetition-rate x-ray facilities. Although the sample was molten and regrown approximately 1x10(6) times, a distinct reduction in time-resolved x-ray reflectivity could be observed using a streak camera with a time resolution of 2.5 ps. The time-resolved x-ray reflectivity displayed this distinct decrease despite the fact that the average reflectivity of the sample had fallen to approximately 50% of its original value due to accumulated damage from the prolonged laser exposure. The topography of the laser-exposed sample was mapped using an optical microscope, a stylus profilometer, photoelectron microscopy, and a scanning tunneling microscope. Although the surface of the sample is not flat following prolonged exposure at laser fluences above 15 mJ/cm(2), the atomic scale structure regrows, and thus, regenerates the sample on a nanosecond timescale. In the fluence range between 15 and 25 mJ/cm(2), the laser power is sufficient to melt the sample, while regrowth occurs with a sufficiently good structure to allow the extraction of timing information via ultrafast time-resolved x-ray measurements. This can be applied for timing purposes at synchrotron radiation and x-ray free-electron laser facilities. It is also noteworthy that we were able to reproduce the fluence dependencies of melting depth and disordering time previously obtained in single-shot, nonthermal melting experiments with higher temporal resolution.
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| 47. |
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| 48. |
- Alling, Björn, 1980-, et al.
(författare)
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Comparison of thermodynamic properties of cubic Cr 1-x Al x N and Ti 1-x Al x N from first-principles calculations
- 2007
-
Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 102:044314
-
Tidskriftsartikel (refereegranskat)abstract
- In order to investigate the stability of the cubic phase of Cr1−xAlxN at high AlN content, first principles calculations of magnetic properties, lattice parameters, electronic structure, and mixing enthalpies of the system were performed. The mixing enthalpy was calculated on a fine concentration mesh to make possible the accurate determination of its second concentration derivative. The results are compared to calculations performed for the related compound Ti1−xAlxN and with experiments. The mixing enthalpy is discussed in the context of isostructural spinodal decomposition. It is shown that the magnetism is the key to understand the difference between the Cr- and Ti-containing systems. Cr1−xAlxN turns out to be more stable against spinodal decomposition than Ti1−xAlxN, especially for AlN-rich samples which are of interest in cutting tools applications.
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| 49. |
- Almer, J., et al.
(författare)
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Strain and texture analysis of coatings using high-energy x-rays
- 2003
-
Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 94:1, s. 697-702
-
Tidskriftsartikel (refereegranskat)abstract
- We investigate the internal strain and crystallographic orientation (texture) in physical-vapor deposited metal nitride coatings of TiN and CrN. A high-energy diffraction technique is presented that uses synchrotron x rays and an area detector, and which allows the strain and intensity distributions of multiple crystallographic planes to be measured by a single x-ray exposure. Unique texture states and nonlinear sin2 strain distributions are observed for all coatings investigated. Quantitative analysis indicates that existing micromechanical models can reasonably predict strain and corresponding stress for mixed-hkl reflections but are inadequate for fully describing measured data. Alternative mechanisms involving deposition-induced defects are proposed
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| 50. |
- Alnoor, Hatim, et al.
(författare)
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An effective low-temperature solution synthesis of Co-doped [0001]-oriented ZnO nanorods
- 2017
-
Ingår i: Journal of Applied Physics. - : AMER INST PHYSICS. - 0021-8979 .- 1089-7550. ; 121:21
-
Tidskriftsartikel (refereegranskat)abstract
- We demonstrate an efficient possibility to synthesize vertically aligned pure zinc oxide (ZnO) and Co-doped ZnO nanorods (NRs) using the low-temperature aqueous chemical synthesis (90 degrees C). Two different mixing methods of the synthesis solutions were investigated for the Co-doped samples. The synthesized samples were compared to pure ZnO NRs regarding the Co incorporation and crystal quality. Electron paramagnetic resonance (EPR) measurements confirmed the substitution of Co2+ inside the ZnO NRs, giving a highly anisotropic magnetic Co2+ signal. The substitution of Zn2+ by Co2+ was observed to be combined with a drastic reduction in the core-defect (CD) signal (g similar to 1.956) which is seen in pure ZnO NRs. As revealed by the cathodoluminescence (CL), the incorporation of Co causes a slight red-shift of the UV peak position combined with an enhancement in the intensity of the defect-related yellow-orange emission compared to pure ZnO NRs. Furthermore, the EPR and the CL measurements allow a possible model of the defect configuration in the samples. It is proposed that the as-synthesized pure ZnO NRs likely contain Zn interstitial (Zn-i(+)) as CDs and oxygen vacancy (V-O) or oxygen interstitial (O-i) as surface defects. As a result, Co was found to likely occupy the Zn-i(+), leading to the observed CDs reduction and hence enhancing the crystal quality. These results open the possibility of synthesis of highly crystalline quality ZnO NRs-based diluted magnetic semiconductors using the low-temperature aqueous chemical method. Published by AIP Publishing.
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