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  1. Microwave reflection photoconductive decay carrier lifetimes of Ge0.94Sn0.06 materials on oriented GaAs substrates at 300 K.

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    Free, publicly-accessible full text available April 4, 2025
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  5. Germanium alloyed with α-tin (GeSn) transitions to a direct bandgap semiconductor of significance for optoelectronics. It is essential to localize the carriers within the active region for improving the quantum efficiency in a GeSn based laser. In this work, epitaxial GeSn heterostructure material systems were analyzed to determine the band offsets for carrier confinement: (i) a 0.53% compressively strained Ge 0.97 Sn 0.03 /AlAs; (ii) a 0.81% compressively strained Ge 0.94 Sn 0.06 /Ge; and (iii) a lattice matched Ge 0.94 Sn 0.06 /In 0.12 Al 0.88 As. The phonon modes in GeSn alloys were studied using Raman spectroscopy as a function of Sn composition, that showed Sn induced red shifts in wavenumbers of the Ge–Ge longitudinal optical phonon mode peaks. The material parameter b representing strain contribution to Raman shifts of a Ge 0.94 Sn 0.06 alloy was determined as b = 314.81 ± 14 cm −1 . Low temperature photoluminescence measurements were performed at 79 K to determine direct and indirect energy bandgaps of E g,Γ = 0.72 eV and E g,L = 0.66 eV for 0.81% compressively strained Ge 0.94 Sn 0.06 , and E g,Γ = 0.73 eV and E g,L = 0.68 eV for lattice matched Ge 0.94 Sn 0.06 epilayers. Chemical effects of Sn atomic species were analyzed using X-ray photoelectron spectroscopy (XPS), revealing a shift in Ge 3d core level (CL) spectra towards the lower binding energy affecting the bonding environment. Large valence band offset of Δ E V = 0.91 ± 0.1 eV and conduction band offset of Δ E C,Γ–X = 0.64 ± 0.1 eV were determined from the Ge 0.94 Sn 0.06 /In 0.12 Al 0.88 As heterostructure using CL spectra by XPS measurements. The evaluated band offset was found to be of type-I configuration, needed for carrier confinement in a laser. In addition, these band offset values were compared with the first-principles-based calculated Ge/InAlAs band alignment, and it was found to have arsenic up-diffusion limited to 1 monolayer of epitaxial GeSn overlayer, ruling out the possibility of defects induced modification of band alignment. Furthermore, this lattice matched GeSn/InAlAs heterostructure band offset values were significantly higher than GeSn grown on group IV buffer/substrates. Therefore, a lattice matched GeSn/InAlAs material system has large band offsets offering superior carrier confinement to realize a highly efficient GeSn based photonic device. 
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  6. Summary

    Allopolyploidization may initiate rapid evolution due to heritable karyotypic changes. The types and extents of these changes, the underlying causes, and their effects on phenotype remain to be fully understood.

    Here, we designed experimental populations suitable to address these issues using a synthetic allotetraploid wheat.

    We show that extensive variation in both chromosome number (NCV) and structure (SCV) accumulated in a selfed population of a synthetic allotetraploid wheat (genome SbSbDD). The combination of NCVs and SCVs generated massive organismal karyotypic heterogeneity. NCVs and SCVs were intrinsically correlated and highly variable across the seven sets of homoeologous chromosomes. Both NCVs and SCVs stemmed from meiotic pairing irregularity (presumably homoeologous pairing) but were also constrained by homoeologous chromosome compensation. We further show that homoeologous meiotic pairing was positively correlated with sequence synteny at the subtelomeric regions of both chromosome arms, but not with genic nucleotide similarityper se. Both NCVs and SCVs impacted phenotypic traits but only NCVs caused significant reduction in reproductive fitness.

    Our results implicate factors influencing meiotic homoeologous chromosome pairing and reveal the type and extent of karyotypic variation and its immediate phenotypic manifestation in synthetic allotetraploid wheat. This has relevance for our understanding of allopolyploid evolution.

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  7. Perovskite materials passivated by chiral ligands have recently shown unique chiroptical activity with promising optoelectronic applications. However, the ligands have been limited to chiral amines. Here, chiral phosphate molecules have been exploited to synthesize CsPbBr 3 nanoplatelets. The nanoplatelets showed a distinct circular dichroism signal and maintained their chiroptical properties after purification with anti-solvent. 
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