In order to unleash the potential of the guided growth approach and to explore its principles and generality, it must be extended to new and interesting materials with a wider range of electrical, structural, and optical properties. Zinc selenide (ZnSe) is an important direct bandgap semiconductor with a wide 2.7 eV bandgap and a large 20 meV exciton binding energy. [ 26,27 ] It is interesting from the crystal structure standpoint due to reports of both zinc-blend (ZB) and wurtzite (WZ) NWs, and as an optoelectronic material, since it has a bandgap energy in the VIS range. [ 28,29 ] This chalcogenide holds promise for the fabrication of blue LEDs and lasers, and for diverse applications such as optical switching, photodetection, and second-harmonic generation (SHG) applications. [30][31][32][33] Here we report the guided growth of horizontal and aligned ZnSe NWs with controlled orientations on six different fl at and faceted planes of sapphire (α-Al 2 O 3 ). The concepts and realization of the guide growth are presented in Figure 1 B. Three general growth modes that dictate the reproducible alignment of the NWs were realized: a) epitaxial guided growth along specifi c lattice directions on fl at surfaces, and graphoepitaxial guided growth on nanofaceted surfaces along: b) nanosteps, and c) nanogrooves.The guided ZnSe NWs were fi rst examined with respect to their elemental composition, crystallographic orientation and growth directions. Surprisingly, some new behaviors of guided NWs were found: i) temperature-dependent directional growth of epitaxial NWs was encountered, where some growth directions were observed only at elevated temperatures while others were observed throughout the entire guided growth temperature regime; ii) crystal structure variations were observed where guided NWs on some sapphire planes presented exclusively one crystal phase, either WZ or ZB, while on other planes both ZB and WZ NWs could grow side by side.In order to examine the optoelectronic properties of the ZnSe guided NWs, we exploited the advantages of the guided growth approach and fabricated multiple photodetectors using only parallel fabrication steps. The ZnSe-based photodetectors have the lowest dark currents (below our detection limit 10 −15 A) and the best measured rise and decay times (74 ms and 0.2 s, respectively) for devices that are based on ZnSe 1D nanostructures (see Table S1, Supporting Information, for previous results). [ 31,32,[34][35][36] These results along with the simple and parallel fabrication process and the ability to control the number of NWs in a single device and thus adjust its performance, reveal the advantages of guided ZnSe NWs as building blocks for fast blue and UV-light-sensitive photodetectors.The vapor-liquid-solid (VLS) growth of guided ZnSe NWs was carried out in a two-zone tube furnace system (see the Experimental Section for details). NWs grow horizontally and aligned from the Au catalyst pattern edges or from dispersed nanoparticles. Their typical diameter varied between 10 and Single-cry...
In this study, we demonstrate a versatile approach for the formation of electrochromic nanoscale assemblies on transparent conductive oxides on both rigid and flexible substrates. Our method is based on the application of alternating spin-coated layers of well-defined metal polypyridyl complexes and a palladium(II) salt to form electrochemically addressable films with a high chromophore density. By varying the central metal ion of the polypyridyl complexes (Os, Ru, and Fe) and their ligands and by mixing these complexes, coatings with a wide range of colors can be achieved. These coatings cover a large area of RGB color space. The coloration intensities of these nanoscale films can be tuned by the number of deposition steps. The materials have very attractive ON/OFF ratios, electrochemical stabilities, and coloration efficiencies. Reversible color-to-colorless and color-to-color transitions were demonstrated, and the films were further integrated into sandwich cells.
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.
The interaction between myelinating Schwann cells and the axons they ensheath is mediated by cell adhesion molecules of the
Invadopodia are actin-rich membrane protrusions through which cells adhere to the extracellular matrix and degrade it. In this study, we explored the mechanical interactions of invadopodia in melanoma cells, using a combination of correlative light and electron microscopy. We show here that the core actin bundle of most invadopodia interacts with integrin-containing matrix adhesions at its basal end, extends through a microtubule-rich cytoplasm, and at its apical end, interacts with the nuclear envelope and indents it. Abolishment of invadopodia by microtubules or src inhibitors leads to the disappearance of these nuclear indentations. Based on the indentation profile and the viscoelastic properties of the nucleus, the force applied by invadopodia is estimated to be in the nanoNewton range. We further show that knockdown of the LINC complex components nesprin 2 or SUN1 leads to a substantial increase in the prominence of the adhesion domains at the opposite end of the invadopodia. We discuss this unexpected, long-range mechanical interplay between the apical and basal domains of invadopodia, and its possible involvement in the penetration of invadopodia into the matrix.
A major challenge toward large-scale integration of nanowires is the control over their alignment and position. A possible solution to this challenge is the guided growth process, which enables the synthesis of well-aligned horizontal nanowires that grow according to specific epitaxial or graphoepitaxial relations with the substrate. However, the guided growth of horizontal nanowires was demonstrated for a limited number of materials, most of which exhibit unintentional n-type behavior. Here we demonstrate the vapor–liquid–solid growth of guided horizontal ZnTe nanowires and nanowalls displaying p-type behavior on four different planes of sapphire. The growth directions of the nanowires are determined by epitaxial relations between the nanowires and the substrate or by a graphoepitaxial effect that guides their growth along nanogrooves or nanosteps along the surface. We characterized the crystallographic orientations and elemental composition of the nanowires using transmission electron microscopy and photoluminescence. The optoelectronic and electronic properties of the nanowires were studied by fabricating photodetectors and top-gate thin film transistors. These measurements showed that the guided ZnTe nanowires are p-type semiconductors and are photoconductive in the visible range. The guided growth of horizontal p-type nanowires opens up the possibility of parallel nanowire integration into functional systems with a variety of potential applications not available by other means.
In the RhB Degradation part of the Experimental Section, the concentration of RhB used in the experiments was incorrectly reported. The concentration is hereby corrected to read 10 −5 M. The text should thus read: "The experiments were performed at ambient temperature and pressure using Xe lamp, 175 W (Lambda). The concentration of RhB in all solutions was C 0 = 10 −5 M." The main conclusions are unaffected and the experiments will still work at the lower concentration. The authors apologize for any inconvenience caused.
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