Laser-induced photofragment emission spectrum of vapor phase triethylgallium using 193 nm excitation
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Triethylgallium
Epitaxial layers of nominally undoped GaAs have been grown by metalorganic chemical vapor deposition using liquid tertiarybutylarsine and triethylgallium. n-type layers were obtained having total residual shallow acceptor concentrations of ∼1013 cm−3 and Hall mobilities comparable to those obtained with arsine and triethylgallium in the same reactor. Liquid-nitrogen Hall mobilities up to 116 000 cm2 /V s were observed.
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The GALAH survey: characterization of emission-line stars with spectral modelling using autoencoders
We present a neural network autoencoder structure that is able to extract essential latent spectral features from observed spectra and then reconstruct a spectrum from those features. Because of the training with a set of unpeculiar spectra, the network is able to reproduce a spectrum of high signal-to-noise ratio that does not show any spectral peculiarities even if they are present in an observed spectrum. Spectra generated in this manner were used to identify various emission features among spectra acquired by multiple surveys using the HERMES spectrograph at the Anglo-Australian telescope. Emission features were identified by a direct comparison of the observed and generated spectra. Using the described comparison procedure, we discovered 10,364 candidate spectra with a varying degree of H$\alpha$/H$\beta$ emission component produced by different physical mechanisms. A fraction of those spectra belongs to the repeated observation that shows temporal variability in their emission profile. Among emission spectra, we find objects that feature contributions of a nearby rarefied gas (identified through the emission of [NII] and [SII] lines) that was identified in 4004 spectra, which were not all identified as having H$\alpha$ emission. Positions of identified emission-line objects coincide with multiple known regions that harbour young stars. Similarly, detected nebular emission spectra coincide with visually-prominent nebular clouds observable in the red all-sky photographic composites.
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A reaction model for the epitaxial growth of GaAs by chemical beam epitaxy using triethylgallium and tris(dimethylamino) arsine is presented. The model is developed by properly combining surface decomposition mechanisms of the two metalorganic species. Computer simulations based on the model are carried out to make comparison with the experimental observations for this growth system. The model is shown to provide very good agreement with the growth kinetics observed.
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Chemical beam epitaxy
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Mass spectrometry was applied to study the thermal decomposition of triethylgallium (TEG) on a GaAs (111)B surface. Gallium-containing species desorbed or reflected from three kinds of differently reconstructed surfaces were measured at 420 °C. The signal intensities of the Ga containing species changed largely with the surface reconstruction in the following order: 2×2 As stabilized ≳√19 ×√19 Ga stabilized ≳1×1 Ga saturated. This result indicates that larger As coverage suppresses the thermal decomposition of TEG on a GaAs (111)B surface.
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Triethylgallium
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In the late stages of type I supernovae evolution (t greater than 50 days) the spectrum is without doubt an emission line spectrum, but in the early stages it is difficult to tell if an emission line spectrum is observed, or a continuum spectrum modified by the overlaying absorption formed in the outer layers. The mechanism of formation of the observed spectra, the physical conditions in the shell, different possible sources of heating of the shell, identification of the lines, and theoretical computations of the line intensities are discussed. An attempt is made to interpret the set of spectra assuming that a spectrum of widely broadened emission lines truncated by an overlaying absorption is seen. The absorption spectrum is first studied. An identification for the emission lines is proposed, and their intensity on the observed spectra is tentatively estimated. These identifications have to be justified by the theoretical computations of a model of the shell.
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We present the first medium-resolution (R ∼ 600) mid-infrared (8–13.3 μm) spectra of 11 Be stars. A large number of lines are observed and identified in these spectra, including, as an example, 39 hydrogen recombination lines in the spectrum of γ Cas. In the majority of our spectra, all of the observed lines are attributable to hydrogen recombination. Two of the sources, β Lyr and MWC 349, also show emission from other species. Both of these objects show evidence of [Ne II] emission, and β Lyr also shows evidence of He I emission. We tabulate the effective line strength and line widths for the observed lines and briefly discuss the physical implications of the observed line series. We also use a simple model of free-free emission to characterize the disks around these sources.
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The growth of high-purity GaAs by chemical beam epitaxy using triethylgallium and arsine is reported. Purity of the epilayer is affected by the cracking efficiency of arsine, V/III ratio, and the substrate temperature. Samples generally show p-type conductivity with carbon as the residual impurity. The growth conditions to achieve net carrier concentration below 1014 cm−3 are identified. The low-temperature photoluminescence spectrum shows well-resolved excitonic structures, an indication of excellent optical quality.
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Chemical beam epitaxy
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The Mα and Mβ emission spectra and the MIV and MV absorption spectra have been studied for the rare earth elements. It is conclusively shown that the complicated multiplet structure observed in the emission spectra is not real emission structure but is, instead, produced by sample self-absorption. This is demonstrated by observing the emission spectra over wide variations in take-off angle and bombarding-electron energies and finally by comparing the detailed structure of both the emission and absorption spectra. The MIV and MV absorption structure completely overlaps the Mα and Mβ emission lines which are each found to have but one intensity maximum when obtained under conditions of minimum self-absorption. Some of these spectra have never been shown previously, while others have been studied in detail by several investigators. Points of agreement and disagreement with previous work are mentioned and the wavelengths of the emission lines and absorption edges are listed for all of the lanthanides. It is concluded that 4f→3d electron transitions are reversible in these elements.
Multiplet
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Abstract We present medium-resolution (R ~ 600) mid-infrared (8-13.3 μ m) spectra of γ Cas and a coadded spectrum of nine Be stars. A large number of lines have been observed and identified in these spectra, including 39 hydrogen recombination lines in the spectrum of γ Cas. In the majority of our spectra, all of the observed lines are attributable to hydrogen recombination. Two additional sources, β Lyr and MWC 349, show [Ne II] emission and β Lyr also displays [He I] emission. We tabulate the effective line strength and line widths for the observed lines, and briefly discuss the physical implications of the observed line series. We also use a simple model of free-free emission to characterize the disks around these sources.
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