Doping studies of Ga0.5In0.5P organometallic vapor-phase epitaxy

Journal ArticlePresents doping studies of gallium[sub0.5] indium[sub0.5] phosphorus organometallic vapor-phase epitaxy. Distribution coefficient of indium; Description of growth conditions; Case of poor growth morphology for gallium[sub0.5] indium[sub0.5] phosphorus

Characterization of unicompositional GaInP2 ordering heterostructures grown by variation of V/III ratio

Journal ArticlePhotoluminescence (PL) and photoluminescence excitation (PLE) spectroscopies are employed to investigate single heterostructures based on two GaInP2 layers that have the same composition but different degrees of order on the cation sublattice. Four sample configurations are studied: two complementary single heterostructures, a more ordered layer grown on a less ordered layer and vice versa, and two single layers nominally equivalent to the constituent layers of the heterostructures. The degree of order of the two layers was controlled via the V/III ratio used during organometallic vapor phase epitaxial growth. From our measurements, the difference between the band gaps of the two layers is 20-30 meV. The PLE spectra show clearly that the emission comes from both layers of the heterostructures and that the PL is excited by direct absorption of the exciting light into each layer as well as the injection of carriers from the less ordered (higher band gap) layer into the more ordered (lower band gap) layer. The data clearly show that the heterostructures contain two layers, each very similar to the corresponding single layer sample

Low pressure pyrolysis of alternate phosphorus precursors for chemical beam epitaxial growth of InP and related compounds

Journal ArticleThe most widely used phosphorous source in chemical beam epitaxy (CBE) is phosphine (PH3). However, because it is highly toxic, alternatives to phosphine have been sought for the growth of phosphorous-containing compounds. We have investigated the pyrolysis rates and reaction products, in low pressure conditions, of three alternative phosphorous precursors: tertiarybutylphosphine (TBP), bisphosphinoethane (BPE) and trisdimethylaminophosphorous (TDMAP)

Control of ordering in Ga0.5In0.5P using growth temperature

Journal ArticleThe kinetic processes leading to ordering in Gas,, In o.4P8 have been studied by observing the effects of substrate misorientation (O-9), growth rate (0.1-0.5), and substrate temperature (570- 670 "C) during growth. The ordered structure and degree of ordering are determined using transmission electron microscopy and photoluminescence (PL) spectroscopy. Low growth rates were used for samples with misorientations of O"-9" toward the [110] lattice direction to elucidate the ordering mechanism; however, due to the long times required to grow layers thick enough for PL characterization (-1 pm), at a temperature of 670 "C the samples became less ordered with increasing misorientation angle, This was attributed to a disordering annealing process occurring during growth which leads to disorder. In order to reduce the rate of this annealing process, the growth temperature was reduced from 670 to 570 "C. At this temperature, a growth rate of 0.5 pm/h produces material with an increasing degree of order as the angle of substrate misorientation is increased from 0" to 9". This shows that the kinetics of the ordering process are assisted by an increasing density of [110] steps on the surface

V1647 Ori (IRAS 05436-0007) in Outburst: the First Three Months

We report on photometric (BVRIJHK) and low dispersion spectroscopic observations of V1647 Ori, the star that drives McNeil's Nebula, between 10 February and 7 May 2004. The star is photometrically variable atop a general decline in brightness of about 0.3-0.4 magnitudes during these 87 days. The spectra are featureless, aside from H-alpha and the Ca II infrared triplet in emission, and a Na I D absorption feature. The Ca II triplet line ratios are typical of young stellar objects. The H-alpha equivalent width may be modulated on a period of about 60 days. The post-outburst extinction appears to be less than 7 mag. The data are suggestive of an FU Orionis-like event, but further monitoring will be needed to definitively characterize the outburst.Comment: Accepted for publication in the Astronomical Journa

Evaluating Soybean Meal Quality Using Near-Infrared Reflectance Spectroscopy

The objective of this study was to establish a range of soybean meal quality to evaluate the correlations between official analytical methods and near-infrared reflectance spectroscopy (NIRS). Crushed soybean white flakes (Mark Hershey Farms, Lebanon, PA) exposed to mechanical oil extraction, but not heat processing, were used in this experiment. Ground samples (500 g) were put into cotton bags and autoclaved at 262°F for 0, 5, 10, 15, 30, 45, and 60 min at 29 PSI. This was done to simulate varying degrees of heat processing. A total of 2 samples per treatment were autoclaved in 3 separate blocks. The duplicate samples were divided and analyzed using NIRS and official analytical analysis (wet chemistry). Crude protein (CP), total lysine (Lys), Lys:CP, available Lys, available Lys:total Lys, protein solubility in potassium hydroxide (KOH), trypsin inhibitor activity (TIA), urease activity index (UAI), individual amino acids (AA), and total AA were analyzed to determine the degree of processing using official analytical methods. The correlation coefficient (R) and coefficient determination (r2) between NIRS and official analytical methods were established for CP, total Lys, available/reactive Lys, Lys:CP and available/reactive Lys:total Lys. Data were analyzed using the SAS (v. 9.4, SAS Institute Inc., Cary, NC) GLIMMIX procedure and the CORR procedure to determine the degree of association of NIRS and official analytical analysis. When measured using official analytical methods, CP, total AA, Ala, Asp, Glu, Gly, Iso, Leu, and Val decreased (linear, P \u3c 0.05), whereas available/reactive Lys:total Lys, Lys:CP, available Lys, KOH, trypsin inhibitor, urease, Lys, and Cys decreased (quadratic, P \u3c 0.05) with increasing exposure time to the autoclave. There was a positive correlation between official analytical and NIRS results for CP, Lys:CP, available Lys:total Lys, total AA, Ala, Cys, Lys, and a negative correlation for Thr. A linear model was best fit (P = 0.011, r2 = 0.489) to predict CP using NIRS. A quadratic model was best fit to use NIRS total Lys (P = 0.011, r2 = 0.969), reactive Lys (P = 0.001, r2 = 0.988), and their ratio (P = 0.001, r2 = 0.981) to predict official analytical results. In conclusion, increasing soybean autoclave exposure time decreased soybean meal quality as measured by crude protein, total Lys, Lys:CP, available Lys, available Lys:total Lys, KOH solubility total AA, and additional AA. In addition, regression models were successful at using NIRS for Lys, reactive Lys, Lys:CP, and reactive Lys:total Lys to predict official analytical results

Effects of anharmonic strain on phase stability of epitaxial films and superlattices: applications to noble metals

Epitaxial strain energies of epitaxial films and bulk superlattices are studied via first-principles total energy calculations using the local-density approximation. Anharmonic effects due to large lattice mismatch, beyond the reach of the harmonic elasticity theory, are found to be very important in Cu/Au (lattice mismatch 12%), Cu/Ag (12%) and Ni/Au (15%). We find that is the elastically soft direction for biaxial expansion of Cu and Ni, but it is for large biaxial compression of Cu, Ag, and Au. The stability of superlattices is discussed in terms of the coherency strain and interfacial energies. We find that in phase-separating systems such as Cu-Ag the superlattice formation energies decrease with superlattice period, and the interfacial energy is positive. Superlattices are formed easiest on (001) and hardest on (111) substrates. For ordering systems, such as Cu-Au and Ag-Au, the formation energy of superlattices increases with period, and interfacial energies are negative. These superlattices are formed easiest on (001) or (110) and hardest on (111) substrates. For Ni-Au we find a hybrid behavior: superlattices along and like in phase-separating systems, while for they behave like in ordering systems. Finally, recent experimental results on epitaxial stabilization of disordered Ni-Au and Cu-Ag alloys, immiscible in the bulk form, are explained in terms of destabilization of the phase separated state due to lattice mismatch between the substrate and constituents.Comment: RevTeX galley format, 16 pages, includes 9 EPS figures, to appear in Physical Review

A comprehensive comparison between APOGEE and LAMOST: Radial Velocities and Atmospheric Stellar Parameters

We undertake a critical and comprehensive comparison of the radial velocities and the main stellar atmospheric parameters for stars in common between the latest data releases from the APOGEE and the LAMOST surveys. There is a total of 42,420 dwarfs/giants stars in common between the APOGEE DR14 - LAMOST DR3 stellar catalogs. A comparison between the RVs shows an offset of 4.54 $\pm$ 0.03 km/s, with a dispersion of 5.8 km/s, in the sense that APOGEE RVs are larger. We observe a small offset in the Teff of about 13 K, with a scatter of 155 K. Small offset in [Fe/H] of about 0.06 dex together with a scatter of 0.13 dex is also observed. We notice that the largest offset between the surveys occurs in the surface gravities. Using only surface gravities in calibrated red giants from APOGEE DR14, where there are 24,074 stars in common, a deviation of 0.14 dex is found with substantial scatter. There are 17,482 red giant stars in common between APOGEE DR14 and those in LAMOST tied to APOGEE DR12 via the Cannon. There is generally good agreement between the two data-sets. However, we find dependencies of the differences of the stellar parameters on effective temperature. For metal-rich stars, a different trend for the [Fe/H] discrepancies is found. Surprisingly, we see no correlation between the internal APOGEE DR14 - DR12 differences in Teff and those in DR14 - LAMOST tied to DR12, where a correlation should be expected since LAMOST has been calibrated to APOGEE DR12. We also find no correlation between the [Fe/H] discrepancies, suggesting that LAMOST/Cannon is not well coupled to the APOGEE DR12 stellar parameters scale. A [Fe/H] dependence between the stellar parameters in APOGEE DR12 and those in DR14 is reported. We find a weak correlation in the differences between APOGEE DR14 - DR12 and LAMOST on DR12 surface gravity for stars hotter than 4800 K and in the log g range between 2.0 and 2.8.Comment: 14 pages, 20 figures. Accepted for publication in Astronomy & Astrophysics (A&A