Guided CdSe Nanowires Parallelly Integrated into Fast Visible-Range Photodetectors

One-dimensional semiconductor nanostructures, such as nanowires (NWs), have attracted tremendous attention due to their unique properties and potential applications in nanoelectronics, nano-optoelectronics, and sensors. One of the challenges toward their integration into practical devices is their large-scale controlled assembly. Here, we report the guided growth of horizontal CdSe nanowires on five different planes of sapphire. The growth direction and crystallographic orientation are controlled by the epitaxial relationship with the substrate as well as by a graphoepitaxial effect of surface nanosteps and grooves. CdSe is a promising direct-bandgap II–VI semiconductor active in the visible range, with potential applications in optoelectronics. The guided CdSe nanowires were found to have a wurtzite single-crystal structure. Field-effect transistors and photodetectors were fabricated to examine the nanowire electronic and optoelectronic properties, respectively. The latter exhibited the fastest rise and fall times ever reported for CdSe nanostructures as well as a relatively high gain, both features being essential for optoelectronic applications

Bottom-Up Tri-gate Transistors and Submicrosecond Photodetectors from Guided CdS Nanowalls

Tri-gate transistors offer better performance than planar transistors by exerting additional gate control over a channel from two lateral sides of semiconductor nanowalls (or “fins”). Here we report the bottom-up assembly of aligned CdS nanowalls by a simultaneous combination of horizontal catalytic vapor–liquid–solid growth and vertical facet-selective noncatalytic vapor–solid growth and their parallel integration into tri-gate transistors and photodetectors at wafer scale (cm²) without postgrowth transfer or alignment steps. These tri-gate transistors act as enhancement-mode transistors with an on/off current ratio on the order of 10⁸, 4 orders of magnitude higher than the best results ever reported for planar enhancement-mode CdS transistors. The response time of the photodetector is reduced to the submicrosecond level, 1 order of magnitude shorter than the best results ever reported for photodetectors made of bottom-up semiconductor nanostructures. Guided semiconductor nanowalls open new opportunities for high-performance 3D nanodevices assembled from the bottom up

Plate-like Guanine Biocrystals Form via Templated Nucleation of Crystal Leaflets on Preassembled Scaffolds

Controlling the morphology of crystalline materials is challenging, as crystals have a strong tendency toward thermodynamically stable structures. Yet, organisms form crystals with distinct morphologies, such as the plate-like guanine crystals produced by many terrestrial and aquatic species for light manipulation. Regulation of crystal morphogenesis was hypothesized to entail physical growth restriction by the surrounding membrane, combined with fine-tuned interactions between organic molecules and the growing crystal. Using cryo-electron tomography of developing zebrafish larvae, we found that guanine crystals form via templated nucleation of thin leaflets on preassembled scaffolds made of 20-nm-thick amyloid fibers. These leaflets then merge and coalesce into a single plate-like crystal. Our findings shed light on the biological regulation of crystal morphogenesis, which determines their optical properties

Plate-like Guanine Biocrystals Form via Templated Nucleation of Crystal Leaflets on Preassembled Scaffolds

Controlling the morphology of crystalline materials is challenging, as crystals have a strong tendency toward thermodynamically stable structures. Yet, organisms form crystals with distinct morphologies, such as the plate-like guanine crystals produced by many terrestrial and aquatic species for light manipulation. Regulation of crystal morphogenesis was hypothesized to entail physical growth restriction by the surrounding membrane, combined with fine-tuned interactions between organic molecules and the growing crystal. Using cryo-electron tomography of developing zebrafish larvae, we found that guanine crystals form via templated nucleation of thin leaflets on preassembled scaffolds made of 20-nm-thick amyloid fibers. These leaflets then merge and coalesce into a single plate-like crystal. Our findings shed light on the biological regulation of crystal morphogenesis, which determines their optical properties

Plate-like Guanine Biocrystals Form via Templated Nucleation of Crystal Leaflets on Preassembled Scaffolds

Controlling the morphology of crystalline materials is challenging, as crystals have a strong tendency toward thermodynamically stable structures. Yet, organisms form crystals with distinct morphologies, such as the plate-like guanine crystals produced by many terrestrial and aquatic species for light manipulation. Regulation of crystal morphogenesis was hypothesized to entail physical growth restriction by the surrounding membrane, combined with fine-tuned interactions between organic molecules and the growing crystal. Using cryo-electron tomography of developing zebrafish larvae, we found that guanine crystals form via templated nucleation of thin leaflets on preassembled scaffolds made of 20-nm-thick amyloid fibers. These leaflets then merge and coalesce into a single plate-like crystal. Our findings shed light on the biological regulation of crystal morphogenesis, which determines their optical properties

Crystallographic Mapping of Guided Nanowires by Second Harmonic Generation Polarimetry

The growth of horizontal nanowires (NWs) guided by epitaxial and graphoepitaxial relations with the substrate is becoming increasingly attractive owing to the possibility of controlling their position, direction, and crystallographic orientation. In guided NWs, as opposed to the extensively characterized vertically grown NWs, there is an increasing need for understanding the relation between structure and properties, specifically the role of the epitaxial relation with the substrate. Furthermore, the uniformity of crystallographic orientation along guided NWs and over the substrate has yet to be checked. Here we perform highly sensitive second harmonic generation (SHG) polarimetry of polar and nonpolar guided ZnO NWs grown on <i>R</i>-plane and <i>M</i>-plane sapphire. We optically map large areas on the substrate in a nondestructive way and find that the crystallographic orientations of the guided NWs are highly selective and specific for each growth direction with respect to the substrate lattice. In addition, we perform SHG polarimetry along individual NWs and find that the crystallographic orientation is preserved along the NW in both polar and nonpolar NWs. While polar NWs show highly uniform SHG along their axis, nonpolar NWs show a significant change in the local nonlinear susceptibility along a few micrometers, reflected in a reduction of 40% in the ratio of the SHG along different crystal axes. We suggest that these differences may be related to strain accumulation along the nonpolar wires. We find SHG polarimetry to be a powerful tool to study both selectivity and uniformity of crystallographic orientations of guided NWs with different epitaxial relations

Plate-like Guanine Biocrystals Form via Templated Nucleation of Crystal Leaflets on Preassembled Scaffolds

Controlling the morphology of crystalline materials is challenging, as crystals have a strong tendency toward thermodynamically stable structures. Yet, organisms form crystals with distinct morphologies, such as the plate-like guanine crystals produced by many terrestrial and aquatic species for light manipulation. Regulation of crystal morphogenesis was hypothesized to entail physical growth restriction by the surrounding membrane, combined with fine-tuned interactions between organic molecules and the growing crystal. Using cryo-electron tomography of developing zebrafish larvae, we found that guanine crystals form via templated nucleation of thin leaflets on preassembled scaffolds made of 20-nm-thick amyloid fibers. These leaflets then merge and coalesce into a single plate-like crystal. Our findings shed light on the biological regulation of crystal morphogenesis, which determines their optical properties

Host and viral membrane fusion generates a tunnel though which viral DNA is ejected.

<p>A-G. PBCV-1-infected chlorella cells at 1.5–2 min PI were immobilized with HPF-FS and thick sections were analyzed by STEM tomography. A. A 5.2 nm tomographic slice from a 220 nm-thick STEM tomogram showing the close proximity between the viral and host internal membranes resulting from their convergence at the infection site. B. A 7.8 nm tomographic slice of a high magnification of the inset in panel A. C. A 5.2 nm tomographic slice from a different 220 nm STEM tomogram. D. High magnification of the inset of panel C. The generation of a continuous tunnel is evident. E, F. Two different 5.2 nm STEM tomography slices from the same tomogram showing the same PBCV-1-infected cells with almost completely empty capsids in which the membrane tunnel is still detected. G. A 5.2 nm tomographic slice from a 216 nm-thick STEM tomogram exhibiting an empty capsid attached near thylakoid membrane stacks (red arrowheads). In all panels the membrane tunnel and the protrusion of the host membrane are marked with blue and white arrowheads, respectively. Asterisk: viral DNA. H, I. Volume rendering representation of the STEM tomogram shown in panel A. The 3D surface representation highlights the barriers that viral DNA has to overcome to reach the host nucleus (including cell wall, plasma membrane, cytoplasmic vesicles, Golgi, and photosynthetic membranes that were not captured in this tomogram). A PBCV-1 virion is attached to the cell wall (brown). The host membranes as well as cytoplasmic vesicles are marked in blue. The capsid is depicted in yellow, the internal viral membrane and the membrane tunnel (arrowheads) are shown in blue. Viral DNA is shown in green. Scale bars: A, C, G: 100 nm; B, D, E, F: 50 nm.</p

Representative projections of the entire volume of PBCV-1 infected cells.

<p>A, B. Views of the entire volume of de-convoluted fluorescence images showing 3h PI PBCV-1 infected cells stained for DNA (Sytox; green) capsids (anti-capsid antibody, magenta) and chloroplast auto-florescence (red). Arrows point to the possible infecting viruses near the chloroplasts. New viral progeny packed with DNA are represented by green dots in the cytoplasm of the cells, indicating successful infection. Scale bars: 2 μm.</p

A model depicting early stages of PBCV-1 infection and highlighting the similarity between PBCV-1 infection and that of bacteriophages.

<p>A. The main components involved in PBCV-1 infection, including the PBCV-1 icosahedral capsid (yellow), internal membrane (dark blue), genome (gray) and spike (magenta) on the left side of the panel, as well as the cell wall (brown), cellular membrane (dark blue), thylakoid stacks (green), nuclear membrane (light blue) and nucleus (gray) of the host on the right side. B-D. Spike-mediated perforation of the host cell wall, protrusions of the viral and cellular internal membranes and their subsequent fusion into a membrane tunnel. D, E. Internalization of PBCV-1 genome into the host cytoplasm through a membrane tunnel, accompanied by the perforation of the photosynthetic thylakoid stacks and apparently promoted by viral DNA condensation. Significantly, perforation of the host cell wall, generation of a membrane portal and genome condensation represent crucial infection stages of bacteriophages (see text for details).</p