Molecular beam epitaxy Research Papers (original) (raw)
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Recent papers in Molecular beam epitaxy
The melting behavior of restrained isotactic polypropylene fibers is examined quantitatively in terms of the influence the anisotropic structural state of the polymer has on the observed properties. Two endotherm peaks are observed to... more
The melting behavior of restrained isotactic polypropylene fibers is examined quantitatively in terms of the influence the anisotropic structural state of the polymer has on the observed properties. Two endotherm peaks are observed to occur in some of the samples. The formation and location of the multiple peaks are determined by the orientation of the noncrystalline chains, and is independent of the fabrication path used to achieve that orientation. Above a certain minimum orientation of the noncrystalline chains, multiple endotherm peak formation occurs. The high-temperature endotherm (T2M) extrapolates to an ultimate melting point for fully oriented noncrystalline chains of 220°C, while the lower-temperature endotherm (T1M) extrapolates to an ultimate melting point of 185°C. Noncrystalline chain orientation influences the endotherm temperature through its changing configurational entropy. It is shown quantitatively that the noncrystalline polymer must be considered as plastically deformed, since rubber elasticity theory is not followed as predicted. The melting behavior of isothermally crystallized samples are also reported to further elucidate the nature of the observed endotherms.
A set of heavily doped Al0.48In0.52As samples grown by molecular beam epitaxy on InP (Fe) substrates was investigated using the photoreflectance (PR) technique. The spectra at 300 K are characterized by a transition in the vicinity of the... more
A set of heavily doped Al0.48In0.52As samples grown by molecular beam epitaxy on InP (Fe) substrates was investigated using the photoreflectance (PR) technique. The spectra at 300 K are characterized by a transition in the vicinity of the InP energy gap, followed by strongly damped Franz-Keldysh oscillations (FKOs) which do not appear when the spectra are obtained at 77 K. The builtin electric field estimated from FKOs shows a small doping dependence but is substantially affected by the inclusion of a thin layer of AlxGayIn1-x-yAs (x≡0.22) at the interface between InP (Fe) and AlInAs:Si. In order to explain these results, a model based on the discontinuity of the energy bands in the InP/AlInAs and InP/AlGaInAs/AlInAs systems and also on the matching of the Fermi levels between the different materials is suggested.
We report the demonstration of a N-polar InGaN based green light emitting diode (LED) grown by N2 plasma-assisted molecular beam epitaxy (PAMBE). High quality multiple quantum well LEDs with In0.29Ga0.71N quantum wells were grown at a... more
We report the demonstration of a N-polar InGaN based green light emitting diode (LED) grown by N2 plasma-assisted molecular beam epitaxy (PAMBE). High quality multiple quantum well LEDs with In0.29Ga0.71N quantum wells were grown at a temperature of 600 °C by applying a new growth model. LED structures exhibited green emission, and electroluminescence measurements on the test structure showed peak emission wavelengths varying from 564.5 to 540 nm. The full width at half-maximum reduced from 74 to 63 nm as the drive current was increased to 180 A/cm2. This work is the first demonstration of an N-polar LED with emission in the green wavelength range.
In our research group, we develop novel dots-in-a-well (DWELL) photodetectors that are a hybrid of the quantum dot infrared photodetector (QDIP). The DWELL detector consists of an active region composed of InAs quantum dots embedded in... more
In our research group, we develop novel dots-in-a-well (DWELL) photodetectors that are a hybrid of the quantum dot infrared photodetector (QDIP). The DWELL detector consists of an active region composed of InAs quantum dots embedded in InGaAs quantum wells. By adjusting the InGaAs well thickness, our structure allows for the manipulation of the operating wavelength and the nature of the
Two aluminum metal matrix composites (MMC) reinforced with 13 vol.% of SiC or B4C particles were made by stir casting followed by hot extrusion. Effects of sliding velocity on the wear, friction and tribochemistry of the worn surfaces of... more
Two aluminum metal matrix composites (MMC) reinforced with 13 vol.% of SiC or B4C particles were made by stir casting followed by hot extrusion. Effects of sliding velocity on the wear, friction and tribochemistry of the worn surfaces of both composites sliding against a commercial phenolic brake pad have been investigated under dry condition. The wear tests were carried out using a pin-on-disc type apparatus at two linear sliding speeds: 1.62 and 4.17 m s-1 under a constant contact pressure of 0.75 MPa for a sliding distance of 5832 m. The coefficient of friction was recorded and wear rate of the MMC pins calculated from mass loss measurement. Scanning electron microscope (SEM) equipped with energy dispersive X-ray spectroscopy (EDX) was used to investigated the worn surface. It is observed that higher sliding velocity leads to lower wear rate and lower friction coefficient for both MMCs. Formation of a compact transfer layer has been identified in the matrix region of the worn surface of the MMCs. The transfer layer mostly consists of constituents of the phenolic pad material which acted as counterbody. The amount of the constituents of the counterbody in the transfer layer is seen to increase as sliding velocity increases. It is suggested that the transfer layer on MMC acts as a protective cover and helps reduce both wear rate and friction coefficient.
- by A. Jasik and +1
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- Materials Engineering, Arsenic, Solid State Laser, Molecular beam epitaxy
AlxGayIn1−x−yAs/InP strained-layer multiple-quantum-well lasers emitting at 1.3 µm have been grown by solid source molecular beam epitaxy, and the performance characteristics have been studied. The lasers contain 4, 5, or 6 compressively... more
AlxGayIn1−x−yAs/InP strained-layer multiple-quantum-well lasers emitting at 1.3 µm have been grown by solid source molecular beam epitaxy, and the performance characteristics have been studied. The lasers contain 4, 5, or 6 compressively strained quantum wells in the active region. They exhibit low transparency current densities, high gain coefficients, and high characteristic temperatures compared to conventional GaInAsP/InP quantum well lasers. The results show that desired lasing features can be achieved with relatively simple layer structures if the doping profiles and waveguide structures are properly designed and the material is grown to high structural perfection.
This thesis reports on electron transport and the magnetization dynamics of crystalline multilayers grown on Fe-whiskers(001) and clean GaAs(001) wafers by means of molecular beam epitaxy (MBE). The high quality magnetic multilayers with... more
This thesis reports on electron transport and the magnetization dynamics of crystalline multilayers grown on Fe-whiskers(001) and clean GaAs(001) wafers by means of molecular beam epitaxy (MBE). The high quality magnetic multilayers with well defined interfaces are required to allow one to compare quantitatively the experimental results with the theoretical predictions. The electrical properties of crystalline Fe/MgO/Fe-whisker structures were characterized by in-situ scanning tunneling spectroscopy. Far mast of the scanned area, the tunneling I-V characteristics have revealed a tunneling barrier of 3.6 V which corresponds to the perfect MgO layer. At negative bias voltages, the localized spikes in the tunneling current have been observed indicating ballistic transport in crystalline tunnel junctions. Kerr microscopy has shown, that the magnetization of Fe-whisker and Fe film are coupled via stray field of the Fe-whisker domain wall. Atom force microscope (AFM) operating in an exter...