| 1. |
- Jayakumar, O. D., et al.
(författare)
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Structural and magnetic properties of (In1-xFex)(2)O-3 (0.0 <= x <= 0.25) system : Prepared by gel combustion method
- 2007
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 91:5
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Tidskriftsartikel (refereegranskat)abstract
- (In1-xFex)(2)O-3 polycrystalline samples with x=(0.0,0.05,0.10,0.15,0.20, and 0.25) have been synthesized by a gel combustion method. Reitveld refinement analysis of x-ray diffraction data indicated the formation of single phase cubic bixbyite structure without any parasitic phases. This observation is further confirmed by high resolution transmission electron microscopy imaging, indexing of the selected-area electron diffraction patterns, x-ray absorption spectroscopy, and Raman Spectroscopy. dc magnetization studies as a function of temperature and field indicate that they are ferromagnetic with Curie temperature (T-C) well above room temperature.
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| 2. |
- Adamovic, Dragan, et al.
(författare)
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Low-energy ion irradiation during film growth: Kinetic pathways leading to enhanced adatom migration rates
- 2005
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 86, s. 211915-
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Tidskriftsartikel (refereegranskat)abstract
- Embedded-atom molecular dynamics simulations are used to investigate the effects of low-energy self-ion irradiation of Pt adatoms on Pt(111). Here, we concentrate on self-bombardment dynamics, i.e., isolating and monitoring the atomic processes, induced by normally incident Pt atoms with energies E ranging from 5 to 50 eV, that can affect intra- and interlayer mass transport.. We find that adatom scattering, surface channeling, and dimer formation occur at all energies. Atomic intermixing events involving incident and terrace atoms are observed at energies 15 eV, while the collateral formation of residual surface vacancies is observed only with E>40 eV. The overall effect of low-energy self-ion irradiation is to enhance lateral adatom and terrace atom migration. ©2005 American Institute of Physics
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| 3. |
- Adell, M., et al.
(författare)
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Photoemission study of the valence band offset between low temperature GaAs and (GaMn)As
- 2006
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 89:17
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Tidskriftsartikel (refereegranskat)abstract
- Using synchrotron based photoelectron spectroscopy (GaMn) AsGaAs interfaces prepared in situ by low temperature molecular beam epitaxy have been studied. No band offset between the two systems is observed. The continuous transition is explained as an effect of dilution of the (GaMn)As by GaAs adlayers.
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| 4. |
- Adell, Martin, et al.
(författare)
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Postgrowth annealing of (Ga,Mn) As under As capping: An alternative way to increase T-C
- 2005
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 86, s. 112501-
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Tidskriftsartikel (refereegranskat)abstract
- In situ postgrowth annealing of (Ga,Mn)As layers under As capping is adequate for achieving high Curie temperatures (T-C) in a similar way as ex situ annealing in air or in N-2 atmosphere practiced earlier. Thus, the first efforts give an increase of T-C from 68 to 145 K after 2 h annealing at 180 degrees C. These data, in combination with lattice parameter determinations and photoemission results, show that the As capping acts as an efficient sink for diffusing Mn interstitials.
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| 5. |
- Ahmed, S., et al.
(författare)
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Annealing characteristics of electrically isolated InGaAsP devices
- 2007
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 91:6, s. 062112-
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Tidskriftsartikel (refereegranskat)abstract
- The authors report on the effects of fluorine implants on the sheet resistivity of n-type InGaAsP layers grown lattice matched to InP by metal organic molecular beam epitaxy. Projected range matched fluorine ions are implanted at multiple energies and single MeV energy at room temperature (RT) and 77 K in both cases. Hall and resistivity measurements are carried out for the van der Pauw samples and the evolution of sheet resistivity (R-s) as a function of annealing temperature was studied in both cases. Fluorine multienergy implantation at 77 K produces higher as-implanted resistivity layers of similar to 10(7) Omega/square compared to RT implants. It is further observed that RT and 77 K implants recover to their preimplanted sheet resistivity values as soon as they are annealed at temperatures higher than 500 degrees C. Substrate temperature and collision cascade density due to multiple energy implants are found to play an important role to optimize the isolation process.
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| 6. |
- Al-Hilli, Safaa, 1965, et al.
(författare)
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Zinc oxide nanorod for intracellular pH sensing
- 2006
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 89:17, s. 073119-1-073119-3
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Tidskriftsartikel (refereegranskat)abstract
- pH determination is a prerequisite for many biochemical and biological processes. The authors have used two methods, namely, the electrochemical potential method and the site binding method to study the sensitivity of zinc oxide (ZnO) nanorods for the use as intracellular pH sensing device. The dimensions of these nanorods were varied with radii between 50–300 nm and lengths between 2 and 10 μm. The ZnO nanorods showed a high sensitivity ≈ 59 mV per decade at room temperature for a pH range (1–14), assuming that the solution is water. This is expected due to the polar and nonpolar surfaces of the ZnO nanorods.
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| 7. |
- Alami, J., et al.
(författare)
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On the deposition rate in a high power pulsed magnetron sputtering discharge
- 2006
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Ingår i: Applied Physics Letters. - : American Institute of Physics (AIP). - 0003-6951 .- 1077-3118. ; 89:15, s. 154104-
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Tidskriftsartikel (refereegranskat)abstract
- The effect of the high pulse current and the duty cycle on the deposition rate in high power pulsed magnetron sputtering (HPPMS) is investigated. Using a Cr target and the same average target current, deposition rates are compared to dc magnetron sputtering (dcMS) rates. It is found that for a peak target current density I-Tpd of up to 570 mA cm(-2), HPPMS and dcMS deposition rates are equal. For I-Tpd greater than 570 mA cm(-2), optical emission spectroscopy shows a pronounced increase of the Cr+/Cr-0 signal ratio. In addition, a loss of deposition rate, which is attributed to self-sputtering, is observed.
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| 8. |
- Alling, Björn, 1980-, et al.
(författare)
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First-principles study of the effect of nitrogen vacancies on the decomposition pattern in cubic Ti1-xAlxN1-y
- 2008
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 92, s. 071903-1-071903-3
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Tidskriftsartikel (refereegranskat)abstract
- The effect of nitrogen substoichiometry on the isostructural phase stabilities of the cubic Ti1−xAlxN1−y system has been investigated using first-principles calculations. The preferred isostructural decomposition pattern in these metastable solid solutions was predicted from the total energy calculations on a dense concentration grid. Close to the stoichiometric Ti1−xAlxN1 limit, N vacancies increase the tendency for phase separation as N sticks to Al while the vacancies prefers Ti neighbors. For nitrogen depleated conditions, N sticks to Ti forming TiN (0<<1) while Al tends to form nitrogen-free fcc-Al or Al–Ti alloys.
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| 9. |
- Alling, Björn, et al.
(författare)
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Pressure enhancement of the isostructural cubic decomposition in Ti1−xAlxN
- 2009
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 95:181906
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Tidskriftsartikel (refereegranskat)abstract
- The influence of pressure on the phase stabilities of Ti1−xAlxN solid solutions has been studied using first principles calculations. We find that the application of hydrostatic pressure enhances the tendency for isostructural decomposition, including spinodal decomposition. The effect originates in the gradual pressure stabilization of cubic AlN with respect to the wurtzite structure and an increased isostructural cubic mixing enthalpy with increased pressure. The influence is sufficiently strong in the composition-temperature interval corresponding to a shoulder of the spinodal line that it could impact the stability of the material at pressures achievable in the tool-work piece contact during cutting operations
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| 10. |
- Andersson, David A., et al.
(författare)
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Redox properties of CeO2-MO2 MO2 (M=Ti, Zr, Hf or Th) solid solutions from first principles calculations
- 2007
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 90:3, s. 031909-
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Tidskriftsartikel (refereegranskat)abstract
- The authors have used density functional theory calculations to investigate how the redox thermodynamics and kinetics of CeO2 are influenced by forming solid solutions with TiO2, ZrO2, HfO2, and ThO2. Reduction is facilitated by dissolving TiO2 (largest improvement), HfO2, or ZrO2 (least improvement), while ThO2 makes reduction slightly more difficult. The migration barrier is much lower in the neighborhood of a Ti (largest decrease), Hf, or Zr (least decrease), while the binding energy of solute ions and vacancies increases in the same sequence. They rationalize the properties of ceria solid solutions in terms of defect cluster relaxations.
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| 11. |
- Andersson, Jon M., et al.
(författare)
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Molecular content of the deposition flux during reactive Ar/O2 magnetron sputtering of Al
- 2006
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Ingår i: Applied Physics Letters. - : Institutionen för fysik, kemi och biologi. - 0003-6951 .- 1077-3118. ; 88:05, s. Art. No. 054101 JAN 30 2006-
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Tidskriftsartikel (refereegranskat)abstract
- The deposition flux obtained during reactive radio frequency magnetron sputtering of an Al target in Ar/O2 gas mixtures was studied by mass spectrometry. The results show significant amounts of molecular AlO+ (up to 10% of the Al+ flux) in the ionic flux incident onto the substrate. In the presence of ~10–4 Pa H2O additional OH+ and AlOH+ were detected, amounting to up to about 100% and 30% of the Al+ flux, respectively. Since the ions represent a small fraction of the total deposition flux, an estimation of the neutral content was also made. These calculations show that, due to the higher ionization probability of Al, the amount of neutral AlO in the deposition flux is of the order of, or even higher than, the amount of Al. These findings might be of great aid when explaining the alumina thin film growth process.
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| 12. |
- Andersson, Lars Mattias, et al.
(författare)
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Acceptor influence on hole mobility in fullerene blends with alternating copolymers of fluorene
- 2006
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 88, s. 082103-
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Tidskriftsartikel (refereegranskat)abstract
- Hole mobility in polyfluorene/fullerene blends has been studied with field effect transistors. Two different C60 derivatives and one C70 derivative have been investigated together with two different polyfluorenes. Mobility is presented as a function of acceptor loading at ratios suitable for photovoltaics and varies between 10–3 and 10–5 cm2 V–1 s–1 depending on the polymer/acceptor combination. The hole mobility is increased in blends with the commonly used acceptor [6-6]-phenyl-C61-butyric acid methylester (PCBM). With related C60 and C70 derivatives the hole mobility is decreased under the same circumstances.
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| 13. |
- Andersson, Lars Mattias, et al.
(författare)
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Bipolar transport observed through extraction currents on organic photovoltaic blend materials
- 2006
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 89, s. 142111-
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Tidskriftsartikel (refereegranskat)abstract
- Both electron and hole mobilities have been simultaneously measured through charge extraction by linearly increasing voltage on polymer heterojunction solar cells with varying stoichiometry of polymer and acceptor. The polymer is a low band gap copolymer of fluorene, thiophene, and electron accepting groups named APFO-Green 5, and the acceptor is [6,6]-phenyl-C61-butyric acid methylester. Results are correlated to field effect transistor measurements on the same material system. A monotonous increase in mobility for both carrier types is observed with increased acceptor loading.
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| 14. |
- Andersson, Lars Mattias, et al.
(författare)
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Stoichiometry, mobility, and performance in bulk heterojunction solar cells
- 2007
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 91:7, s. 071108-
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Tidskriftsartikel (refereegranskat)abstract
- Bipolar transport in blends of a copolymer of fluorene, thiophene and electron accepting groups, and the substituted fullerene [6,6]-phenyl-C61-butyric acid methylester have been studied through charge extraction by linearly increasing voltage on solar cells and with field effect transistors. Between 10% and 90% polymer has been used and the results show a clear correlation to solar cell performance. Optimal solar cells comprise 20% polymer and have a power conversion efficiency of 3.5%. The electron mobility is increasing strongly with fullerene content, but is always lower than the hole mobility, thus explaining the low amount of polymer in optimized devices.
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| 15. |
- Andersson, Viktor, et al.
(författare)
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An optical spacer is no panacea for light collection in organic solar cells
- 2009
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 94:4, s. 043302-
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Tidskriftsartikel (refereegranskat)abstract
- The role of an optical spacer layer has been examined by optical simulations of organic solar cells with various bandgaps. The simulations have been performed with the transfer matrix method and the finite element method. The results show that no beneficial effect can be expected by adding an optical spacer to a solar cell with an already optimized active layer thickness.
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| 16. |
- Andreasson, Björn Pererik, 1979-, et al.
(författare)
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Spatial distribution of oxygen vacancies in Cr-doped SrTiO3 during an electric-field-driven insulator-to-metal transition
- 2009
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Ingår i: Applied Physics Letters. - College Park, MD : American Institute of Physics (AIP). - 0003-6951 .- 1077-3118. ; 94:1, s. Article number: 013513-
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Tidskriftsartikel (refereegranskat)abstract
- Spatially resolved x-ray fluorescence maps are presented that show the introduction and the evolution of oxygen vacancies in chromium-doped strontium titanate during an electric-field-driven insulator-to-metal transition. The vacancies are introduced at the anode and diffuse through the crystal toward the cathode. The spatial distribution of vacancies is explained by a model describing the electrical breakdown as a percolation process. Strong differences in the vacancy distribution were found when the transition took place in air and in a hydrogen-enriched atmosphere. In air, the vacancies disappeared from the surface, whereas in the reducing hydrogen atmosphere, they remained at the surface. © 2009 American Institute of Physics.
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| 17. |
- Ao, Xianyu, et al.
(författare)
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Polarization beam splitter based on a two-dimensional photonic crystal of pillar type
- 2006
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 89:17, s. 171115-
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Tidskriftsartikel (refereegranskat)abstract
- Negatively and positively refractive behaviors are achieved in a two-dimensional photonic crystal of pillar type for TE and TM polarizations, respectively, at the same frequency. The photonic crystal is formed by a triangular lattice of silicon pillars of finite height on a silicon substrate. A polarization beam splitter based on such a photonic-crystal slab is demonstrated. Measurements at near infrared wavelengths indicate that two beams of different polarizations can be split with an extinction ratio of over 10 dB in a wide wavelength range.
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| 18. |
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| 19. |
- Araújo, C. Moysés, et al.
(författare)
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On the structural and energetic properties of the hydrogen absorber Li2Mg(NH)2
- 2007
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 91:9, s. 091924-
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Tidskriftsartikel (refereegranskat)abstract
- The authors have performed density functional theory based calculations of several possible conformations for the crystal structure of Li2Mg(NH)2 and they confirm the α phase, resolved from both x-ray and neutron diffraction data, as the ground-state configuration. It is also found that although the N-H bond is stronger in Li2Mg(NH)2 than in Li2NH, hydrogen release from Li2Mg(NH)2/LiH mixture displays more favorable thermodynamics than that from the Li2NH/LiH mixture. The insights gained from this seemingly counterintuitive result should prove helpful in the search for promising hydrogen storage materials.
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| 20. |
- Araujo, Carlos Moyses, et al.
(författare)
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Role of titanium in hydrogen desorption in crystalline sodium alanate
- 2005
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 86:25
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Tidskriftsartikel (refereegranskat)abstract
- The role of Ti in improving the thermodynamics of hydrogen desorption in crystalline sodium alanate (NaAlH4) has been investigated by using the density functional theory. The total energy calculations reveal that Ti prefers to occupy the Na site over that of the Al site when the atomic energies are used as the reference. However, the use of the cohesive energies of Al, Na, and Ti leads to the Al site being the least unfavourable site. Irrespective of whether Ti occupies the Na or the Al site, the energy necessary to remove a hydrogen atom from Ti substituted sodium alanate is significantly lowered from that of the pure alanate. The understanding gained here may help in designing hydrogen storage materials suitable for industrial applications.
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| 21. |
- Araujo, C. M., et al.
(författare)
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Thermodynamic analysis of hydrogen sorption reactions in Li-Mg-N-H systems
- 2008
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 92:2
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Tidskriftsartikel (refereegranskat)abstract
- We report a comprehensive first-principles study of the thermodynamics of the hydrogen release reaction from xLiH-yMg(NH2)(2) mixtures involving the composition ratios (x=2, y=1), (x=8, y=3), and (x=12, y=3), with special emphasis on the effect of the different intermediate steps. For all three mixing ratios of LiH/Mg(NH2)(2) we find that the hydrogen release is initiated by the same reaction with an enthalpy of 46.1 kJ/mol of H-2 in excellent agreement with recent experimental results. Additionally, we also investigated the substitution of LiH by MgH2 as reaction partner of Mg(NH2)(2) in the fully hydrogenated state.
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| 22. |
- Arulkumaran, S., et al.
(författare)
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Enhancement of both direct-current and microwave characteristics of AlGaN/GaN high-electron-mobility transistors by furnace annealing
- 2006
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 88:2
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Tidskriftsartikel (refereegranskat)abstract
- The enhancement of both direct-current (dc) and microwave characteristics of AlGaN/GaN high-electron-mobility transistors (HEMTs) were demonstrated by conventional furnace annealing at 400 degrees C for 5 min. Due to the improvement in Ni/Au Schottky contact properties by furnace annealing, about 17%, 34%, 23%, and 25% of enhancements in maximum drain current density, maximum extrinsic transconductance (g(m max)), cutoff frequency and maximum oscillation frequency were observed, respectively. A positive threshold voltage shift and the increase in g(m max) can also be correlated to the improved Schottky parameters such as ideality factor and barrier height. The annealed devices exhibited low reverse gate-leakage-current by more than three orders of magnitude and low drain-leakage-current by two orders of magnitude. Correspondingly, the devices exhibited 55% of higher breakdown voltage after annealing. The furnace annealing is an effective and viable means to enhance both dc and microwave characteristics of AlGaN/GaN HEMTs.
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| 23. |
- Asif, Muhammad H, 1978-, et al.
(författare)
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Functionalized zinc oxide nanorod with ionophore-membrane coatingas an intracellular Ca2+ selective sensor
- 2009
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Ingår i: Applied Physics Letters. - : EBSCO/American Institute of Physics. - 0003-6951 .- 1077-3118. ; 95:2, s. 23703-
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Tidskriftsartikel (refereegranskat)abstract
- The tip of a borosilicate glass capillary with functionalized hexagonal ZnO nanorods was used to make a sensitive electrochemical intracellular Ca2+ sensor. To adjust the sensor for Ca2+ measurements with sufficient selectivity and stability, polyvinyl chloride (PVC) membrane containing Ca2+ ionophores were coated on the surface. The membrane covered ZnO nanorods exhibited a Ca2+-dependent electrochemical potential difference versus an Ag/AgCl reference electrode. The potential difference was linear over a large concentration range (100 nM to 10 mM). The measurements of Ca2+ concentrations using our ZnO nanorods sensor in human fat cells or in frog egg cells were consistent with values of Ca2+ concentrations reported in the literature. This nanoelectrode device paves the way to measurements of intracellular biochemical species in specific locations within single living cells.
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| 24. |
- Astrath, N. G. C., et al.
(författare)
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Band gap energy determination by photoacoustic spectroscopy under continuous light excitation
- 2006
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 89:23
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Tidskriftsartikel (refereegranskat)abstract
- In this work the authors used the photoacoustic spectroscopy under continuous light excitation to determine the optical band gap of semiconductors. The experiments were performed in lead iodide PbI2 and hexagonal silicon carbide 4H-SiC samples. The nonradiative relaxation processes are discussed in terms of the generated signal. A mechanism to describe the signal increase/decrease under the continuous excitation is presented. The results showed that the method was useful to locate the band gap directly from the optical absorption spectra.
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| 25. |
- Atlasov, K.A., et al.
(författare)
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Site-controlled single quantum wire integrated into a photonic-crystal membrane microcavity
- 2007
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 90, s. 153107-
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Tidskriftsartikel (refereegranskat)abstract
- Integration of a site-controlled semiconductor V-groove quantum wire (QWR) into a photonic-crystal (PhC) membrane microcavity is reported. Reproducible coupling of the QWR emission to a mode of the PhC cavity is evidenced by the narrower linewidth, higher intensity, and variation with temperature and PhC parameters of the QWR line. Finite difference time domain simulations of the cavity are employed for identifying the observed mode. The presented PhC-QWR coupled structures are promising for achieving very low-threshold lasers and for studies of one-dimensional photon-exciton coupled systems
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