Here, we design and engineer an axially asymmetric GaAs/AlGaAs/GaAs (G/A/G) nanowire (NW) photodetector that operates efficiently at room temperature. Based on the I-type band structure, the device can realize a two-dimensional electron–hole tube (2DEHT) structure for the substantial performance enhancement. The 2DEHT is observed to form at the interface on both sides of GaAs/AlGaAs barriers, which constructs effective pathways for both electron and hole transport in reducing the photocarrier recombination and enhancing the device photocurrent. In particular, the G/A/G NW photodetector exhibits a responsivity of 0.57 A/W and a detectivity of 1.83 × 1010 Jones, which are about 7 times higher than those of the pure GaAs NW device. The recombination probability has also been significantly suppressed from 81.8% to 13.2% with the utilization of the 2DEHT structure. All of these can evidently demonstrate the importance of the appropriate band structure design to promote photocarrier generation, separation, and collection for high-performance optoelectronic devices.

Cone snails, which are predatory marine gastropods, produce a cocktail of venoms used for predation, defense and competition. The major venom component, conotoxin, has received significant attention because it is useful in neuroscience research, drug development and molecular diversity studies. In this study, we report the genomic characterization of nine conotoxin gene superfamilies from 18 Conus species and investigate the relationships among conotoxin gene structure, molecular evolution and diversity. The I1, I2, M, O2, O3, P, S, and T superfamily precursors all contain three exons and two introns, while A superfamily members contain two exons and one intron. The introns are conserved within a certain gene superfamily, and also conserved across different Conus species, but divergent among different superfamilies. The intronic sequences contain many simple repeat sequences and regulatory elements that may influence conotoxin gene expression. Furthermore, due to the unique gene structure of conotoxins, the base substitution rates and the number of positively selected sites vary greatly among exons. Many more point mutations and trinucleotide indels were observed in the mature peptide exon than in the other exons. In addition, the first example of alternative splicing in conotoxin genes was found. These results suggest that the diversity of conotoxin genes has been shaped by point mutations and indels, as well as rare gene recombination or alternative splicing events, and that the unique gene structures could have made a contribution to the evolution of conotoxin genes.

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Size-dependent optical properties of germanium (Ge) nanocrystals (NCs) make them a desirable material for optoelectronic applications. So far, the synthesis of ligand-free and tunable-size Ge NCs by inert gas condensation has been scarcely reported. In this work, we introduce a gas-phase approach to synthesize quantum-confined Ge NCs by inert gas condensation, where the size of the Ge NCs can be readily tuned by controlling the thickness of a Cu plate supporting the Ge target. As explained by simulations using the finite element method, the magnetic field configuration above the target can be manipulated by varying the thickness of the Cu backing plate. In-depth analysis based on transmission electron microscopy (TEM) results reveals the morphology and crystalline structure of Ge NCs. X-ray photoelectron spectroscopy has proven the formation of a substoichiometric Ge oxide shell for the as-deposited Ge NCs. In addition, Raman spectroscopy indicated peak shifts according to the phonon confinement model that yielded nanoparticle sizes in a good agreement with the TEM results. Furthermore, the quantum confinement effect for Ge NCs was demonstrated by analysis of the absorption (UV−vis−NIR) spectrum, which indicated that the band gap of the Ge NCs was increased from ∼0.8 to 1.1 eV with decreasing size of Ge NCs. Comparison with theory shows that the quantum confinement effect on the band gap energy for different-sized Ge NCs follows the tight-binding model rather well.

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