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Full-Text Articles in Physics
Determining Magnetic Nanoparticle Size Distributions From Thermomagnetic Measurements., R. S. Dipietro, H. G. Johnson, S. P. Bennett, T. J. Nummy, L. H. Lewis, D. Heiman
Determining Magnetic Nanoparticle Size Distributions From Thermomagnetic Measurements., R. S. Dipietro, H. G. Johnson, S. P. Bennett, T. J. Nummy, L. H. Lewis, D. Heiman
Laura H. Lewis
Thermomagnetic measurements are used to obtain the size distribution and anisotropy of magnetic nanoparticles. An analytical transformation method is described which utilizes temperature-dependent zero-field cooling magnetization data to provide a quantitative measurement of the average diameter and relative abundance of superparamagnetic nanoparticles. Applying this method to self-assembled MnAs nanoparticles in MnAs–GaAs composite films reveals a log-normal size distribution and reduced anisotropy for nanoparticles compared to bulk materials. This analytical technique holds promise for rapid assessment of the size distribution of an ensemble of superparamagnetic nanoparticles.
Determining Magnetic Nanoparticle Size Distributions From Thermomagnetic Measurements., R. S. Dipietro, H. G. Johnson, S. P. Bennett, T. J. Nummy, L. H. Lewis, D. Heiman
Determining Magnetic Nanoparticle Size Distributions From Thermomagnetic Measurements., R. S. Dipietro, H. G. Johnson, S. P. Bennett, T. J. Nummy, L. H. Lewis, D. Heiman
Donald Heiman
Thermomagnetic measurements are used to obtain the size distribution and anisotropy of magnetic nanoparticles. An analytical transformation method is described which utilizes temperature-dependent zero-field cooling magnetization data to provide a quantitative measurement of the average diameter and relative abundance of superparamagnetic nanoparticles. Applying this method to self-assembled MnAs nanoparticles in MnAs–GaAs composite films reveals a log-normal size distribution and reduced anisotropy for nanoparticles compared to bulk materials. This analytical technique holds promise for rapid assessment of the size distribution of an ensemble of superparamagnetic nanoparticles.
Self-Assembly On (111)-Oriented Iii-V Surfaces, Paul J. Simmonds, Minjoo Larry Lee
Self-Assembly On (111)-Oriented Iii-V Surfaces, Paul J. Simmonds, Minjoo Larry Lee
Paul J. Simmonds
We demonstrate the self-assembly of tensile strained GaP into three-dimensional dots on GaAs(111)A. Size and areal density of the dislocation-free GaPdots are readily tunable with both substrate temperature and deposition thickness. GaP dot growth obeys island scaling theory, allowing us to predict dot size distributions a priori.
Molecular Beam Epitaxy Approach To The Graphitization Of Gaas(100) Surfaces, Paul J. Simmonds, John Simon, Jerry M. Woodall, Minjoo Larry Lee
Molecular Beam Epitaxy Approach To The Graphitization Of Gaas(100) Surfaces, Paul J. Simmonds, John Simon, Jerry M. Woodall, Minjoo Larry Lee
Paul J. Simmonds
The authors present a method for obtaining graphitized carbon on GaAs(100) surfaces. Carbon-doped GaAs is grown by molecular beam epitaxy before controlled thermal etching within the growth chamber. An AlAs layer beneath the carbon-doped GaAs acts as a thermal etch stop. As the GaAs is etched away, the carbondopant atoms remain on the surface due to their low vapor pressure. The total number of carbon atoms available is precisely controllable by the doping density and thickness of the carbon-doped GaAs layer. Characteristic phonon modes in Raman spectra from the thermally etchedsurfaces show that the residual surfacecarbon atoms form sp2 …
Molecular Beam Epitaxy Of Metamorphic InYGa1−YP Solar Cells On Mixed Anion GaasXP1−X/Gaas Graded Buffers, Stephanie Tomasulo, John Simon, Paul J. Simmonds, Jonathan Biagiotti, Minjoo L. Lee
Molecular Beam Epitaxy Of Metamorphic InYGa1−YP Solar Cells On Mixed Anion GaasXP1−X/Gaas Graded Buffers, Stephanie Tomasulo, John Simon, Paul J. Simmonds, Jonathan Biagiotti, Minjoo L. Lee
Paul J. Simmonds
The authors have grown metamorphic InyGa1−yP on optimized GaAsxP1−x/GaAs graded buffers via solid source molecular beam epitaxy(MBE) for multijunction solar cell applications. In this work, the authors show that a previously developed kinetic growth model can be used to predict the composition of mixed anion GaAsxP1−x alloys on GaAs as a function of substrate temperature and group-V flux. The advantages of using a high growth temperature of 700 °C are then described, including the minimized dependence of composition on small temperature variations, a linear dependence of film composition on …
Graphitized Carbon On Gaas(100) Substrates, J. Simon, P. J. Simmonds, J. M. Woodall, M. L. Lee
Graphitized Carbon On Gaas(100) Substrates, J. Simon, P. J. Simmonds, J. M. Woodall, M. L. Lee
Paul J. Simmonds
We report on the formation of graphitized carbon on GaAs(100) surfaces by molecular beam epitaxy. We grew highly carbon-doped GaAs on AlAs, which was then thermally etched in situ leaving behind carbon atoms on the surface. After thermal etching, Raman spectra revealed characteristic phonon modes for sp2-bonded carbon, consistent with the formation of graphitic crystallites. We estimate that the graphitic crystallites are 1.5–3 nm in size and demonstrate that crystallite domain size can be increased through the use of higher etch temperatures.
Metamorphic Gaasp Buffers For Growth Of Wide-Bandgap Ingap Solar Cells, J. Simon, S. Tomasulo, P. J. Simmonds, M. Romero, M. L. Lee
Metamorphic Gaasp Buffers For Growth Of Wide-Bandgap Ingap Solar Cells, J. Simon, S. Tomasulo, P. J. Simmonds, M. Romero, M. L. Lee
Paul J. Simmonds
GaAsxP1−x graded buffers were grown via solid source molecular beam epitaxy(MBE) to enable the fabrication of wide-bandgap InyGa1−yP solar cells. Tensile-strained GaAsxP1−x buffers grown on GaAs using unoptimized conditions exhibited asymmetric strain relaxation along with formation of faceted trenches, 100–300 nm deep, running parallel to the [011] direction. We engineered a 6 μm thick grading structure to minimize the faceted trench density and achieve symmetric strain relaxation while maintaining a threading dislocation density of ≤106 cm−2. In comparison, compressively-strained graded GaAsxP1−x buffers on …