Encoding Active Device Elements at Nanowire Tips

Semiconductor nanowires and other one-dimensional materials are attractive for highly sensitive and spatially confined electrical and optical signal detection in biological and physical systems, although it has been difficult to localize active electronic or optoelectronic device function at one end of such one-dimensional structures. Here we report a new nanowire structure in which the material and dopant are modulated specifically at only one end of nanowires to encode an active two-terminal device element. We present a general bottom-up synthetic scheme for these tip-modulated nanowires and illustrate this with the synthesis of nanoscale p–n junctions. Electron microscopy imaging verifies the designed p-Si nanowire core with SiO₂ insulating inner shell and n-Si outer shell with clean p-Si/n-Si tip junction. Electrical transport measurements with independent contacts to the p-Si core and n-Si shell exhibited a current rectification behavior through the tip and no detectable current through the SiO₂ shell. Electrical measurements also exhibited an n-type response in conductance versus water-gate voltage with pulsed gate experiments yielding a temporal resolution of at least 0.1 ms and ∼90% device sensitivity localized to within 0.5 μm from the nanowire p–n tip. In addition, photocurrent experiments showed an open-circuit voltage of 0.75 V at illumination power of ∼28.1 μW, exhibited linear dependence of photocurrent with respect to incident illumination power with an estimated responsivity up to ∼0.22 A/W, and revealed localized photocurrent generation at the nanowire tip. The tip-modulated concept was further extended to a top-down/bottom-up hybrid approach that enabled large-scale production of vertical tip-modulated nanowires with a final synthetic yield of >75% with >4300 nanowires. Vertical tip-modulated nanowires were fabricated into >50 individually addressable nanowire device arrays showing diode-like current–voltage characteristics. These tip-modulated nanowire devices provide substantial opportunity in areas ranging from biological and chemical sensing to optoelectronic signal and nanoscale photodetection

Electrochemical Deposition of Conformal and Functional Layers on High Aspect Ratio Silicon Micro/Nanowires

Development of new synthetic methods for the modification of nanostructures has accelerated materials design advances to furnish complex architectures. Structures based on one-dimensional (1D) silicon (Si) structures synthesized using top-down and bottom-up methods are especially prominent for diverse applications in chemistry, physics, and medicine. Yet further elaboration of these structures with distinct metal-based and polymeric materials, which could open up new opportunities, has been difficult. We present a general electrochemical method for the deposition of conformal layers of various materials onto high aspect ratio Si micro- and nanowire arrays. The electrochemical deposition of a library of coaxial layers comprising metals, metal oxides, and organic/inorganic semiconductors demonstrate the materials generality of the synthesis technique. Depositions may be performed on wire arrays with varying diameter (70 nm to 4 μm), pitch (5 μ to 15 μ), aspect ratio (4:1 to 75:1), shape (cylindrical, conical, hourglass), resistivity (0.001–0.01 to 1–10 ohm/cm²), and substrate orientation. Anisotropic physical etching of wires with one or more coaxial shells yields 1D structures with exposed tips that can be further site-specifically modified by an electrochemical deposition approach. The electrochemical deposition methodology described herein features a wafer-scale synthesis platform for the preparation of multifunctional nanoscale devices based on a 1D Si substrate

Outside Looking In: Nanotube Transistor Intracellular Sensors

Nanowire-based field-effect transistors, including devices with planar and three-dimensional configurations, are being actively explored as detectors for extra- and intracellular recording due to their small size and high sensitivities. Here we report the synthesis, fabrication, and characterization of a new needle-shaped nanoprobe based on an active silicon nanotube transistor, ANTT, that enables high-resolution intracellular recording. In the ANTT probe, the source/drain contacts to the silicon nanotube are fabricated on one end, passivated from external solution, and then time-dependent changes in potential can be recorded from the opposite nanotube end via the solution filling the tube. Measurements of conductance versus water-gate potential in aqueous solution show that the ANTT probe is selectively gated by potential changes within the nanotube, thus demonstrating the basic operating principle of the ANTT device. Studies interfacing the ANTT probe with spontaneously beating cardiomyocytes yielded stable intracellular action potentials similar to those reported by other electrophysiological techniques. In addition, the straightforward fabrication of ANTT devices was exploited to prepare multiple ANTT structures at the end of single probes, which enabled multiplexed recording of intracellular action potentials from single cells and multiplexed arrays of single ANTT device probes. These studies open up unique opportunities for multisite recordings from individual cells through cellular networks

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Additional file 1: of Light sheet theta microscopy for rapid high-resolution imaging of large biological samples

Figure S1. LSTM microscopy implementation. (a) Image of the physical LSTM setup. (b) 3D model of LSTM and the sample mounting system. The 3D-printed sample chamber is designed to accommodate large biological samples of virtually any dimensions, while still allowing the objectives to be immersed in the immersion oil. Two transparent glass windows, located on the lateral sides, provide visual view of the sample for ease of positioning. An additional window is realized at the bottom part of the chamber to allow the illumination light to pass through. An additional adapter was designed to allow mounting a prism mirror at about approximately 10° from the normal surface to facilitate the optical alignment of the system. (PDF 1623 kb

Additional file 9: of Light sheet theta microscopy for rapid high-resolution imaging of large biological samples

Video 4. High-resolution LSTM imaging of a large tissue of Thy1-eYFP mouse brain. The bounding box is 9.6 mm × 13.5 mm × 5.34 mm. The raw data was down-sampled 4 × 4 fold to make the volume rendering feasible. The high-resolution video is available in the figshare repository at https://doi.org/10.6084/m9.figshare.c.4072160 . (MOV 167936 kb

Additional file 13: of Light sheet theta microscopy for rapid high-resolution imaging of large biological samples

Video 8. Neuronal activity traces of representative neurons. A visualization of the neuronal traces shown in Fig. 7b. The high-resolution video is available in the figshare repository at https://doi.org/10.6084/m9.figshare.c.4072160 . (MOV 11161 kb

Additional file 5: of Light sheet theta microscopy for rapid high-resolution imaging of large biological samples

Video 2. Comparison of image volumes acquired with LSTM in 1-axis scan (1-AS) and 2-axis scan (2-AS) modes. The 3D rendering visualizes the image stacks acquired from the same sample (human brain section stained with DAPI) with LSTM in 1-AS and simultaneous 2-AS modes. The high-resolution video is available in the figshare repository at https://doi.org/10.6084/m9.figshare.c.4072160 . (MOV 104448 kb

Additional file 11: of Light sheet theta microscopy for rapid high-resolution imaging of large biological samples

Video 6. High-resolution LSTM imaging of a large expanded section of Thy1-eYFP mouse brain. A thin (250 μm) coronal section was expanded ~ 4-fold using proExM procedure and imaged using LSTM with 10×/0.6NA detection objective. The resulting dataset (~ 6 TB) consisted of 723,300 full frame images (2048 × 2048). The data was down-sampled 8 × 8 fold to allow high-quality volumetric rendering. The high-resolution video is available in the figshare repository at https://doi.org/10.6084/m9.figshare.c.4072160 . (MOV 439296 kb

Additional file 10: of Light sheet theta microscopy for rapid high-resolution imaging of large biological samples

Video 5. Visualization of an image stack of vasculature-stained rat brain tissue. This video visualizes an image stack acquired from a large rat brain slice (stained for vasculature with tomato lectin) using LSTM in 2-AS mode. The bounding box is 1 mm × 1 mm × 5 mm. The high-resolution video is available in the figshare repository at https://doi.org/10.6084/m9.figshare.c.4072160 . (MOV 143360 kb