More NW PapersEE C235 / NSE C203Discussion #9Apr 9, 2007Chang-Hasnain Group, UC Berkeley 2Proprietary Information; do not distribute.Paper #1Chang-Hasnain Group, UC Berkeley 3Proprietary Information; do not distribute.Evolution of NW Structural ComplexityChang-Hasnain Group, UC Berkeley 4Proprietary Information; do not distribute.Paper #2Chang-Hasnain Group, UC Berkeley 5Proprietary Information; do not distribute.Nanotree Production Process(a) Au particles are deposition(b) Group III and V precursor materials (arrows) introduction(c) III–V nanowire trunk growth.(d) Second set of Au particles deposition onto trunks.(e) Nanowire branches grown by the same procedure as illustrated in (c).Chang-Hasnain Group, UC Berkeley 6Proprietary Information; do not distribute.GaP Nanotrees(a) Single nanotree viewed at 45° from the surface normal.(b) Overview of “nanoforest” viewed at 30° from the surface normal.(c) Nano-forest viewed from above. The six branch directions observed indicate the presence of stacking faults perpendicular to the trunk growth.Chang-Hasnain Group, UC Berkeley 7Proprietary Information; do not distribute.TEM Analysis of InAs Nanotree Stacking faults can be seen.(a) Interface between branch (red arrow) and trunk (blue arrow). Note that branch growth is perpendicular to trunk growth, and there is a large triangular overgrowth region at the interface.(b) View of same branch illustrating that stacking faults (dark lines perpendicular to the trunk) continue out into the branch.(c) High-resolution image of the end of the branch showing that stacking faults continueall the way out to the particle, parallel to the branch.Chang-Hasnain Group, UC Berkeley 8Proprietary Information; do not distribute.Paper #3Chang-Hasnain Group, UC Berkeley 9Proprietary Information; do not distribute.III-V NWs on Group IV Sub. - Orientations(a) SEM image (top view) of InP wires grown by MOVPE on a Si(111) substrate. Inset shows the mechanism to relieve compressive strain in the nanowire base by a change into another <111> growth directionwithout a rotational twin dislocation.(b) Expected wire orientations on a (111) - oriented silicon or germanium substrate.One way to relieve strain –changing growth direction.Chang-Hasnain Group, UC Berkeley 10Proprietary Information; do not distribute.Proof of Epitaxial Growth(a) Cross-sectional TEM of GaP wire on Si(111).The red vertical line signifies the position of the EDX line scan.(b) High resolution image of the GaP/Si interface.The white dotted line indicates the position of the heterointerface and a twin boundary.(c) EDX line scan across the GaP/Si junction.The blueshaded area indicates the position of the heterointerface.Chang-Hasnain Group, UC Berkeley 11Proprietary Information; do not distribute.III-V NW Transistor on Si(a) Schematic illustration of a vertical NW transistor. The active channel is a III-V NW epitaxially connected to the silicon substrate, and the gate is wrapped around the channel.(b) SEM (side view, 30°) of a nearly finished vertical device consisting of a p-type InP wire covered with gate oxide and gate metal.Chang-Hasnain Group, UC Berkeley 12Proprietary Information; do not distribute.Paper #4Chang-Hasnain Group, UC Berkeley 13Proprietary Information; do not distribute.Concept of NW Thin-Film Transistors(a) In polycrystalline silicon TFTs, electrical carriers have to travel across multiple grain boundaries, resulting in low carrier mobility.(b) NW-TFTs have conducting channels consisting of multiple single-crystal nanowires in parallel and thus charges travel from source to drain within single crystals, ensuring high carrier mobility.Chang-Hasnain Group, UC Berkeley 14Proprietary Information; do not distribute.NW Thin-Film-Transistor Fabrications(a) SEM of Si NWs (scale bar, 5 µm). Inset: TEM (scale bar, 5 nm).(b) NW solution obtained by dispersing NWs into a proper solvent such as ethanol.(c) Optical micrograph of a NW thin film assembled from solution using fluidic-flow directed assembly approach (scale bar, 100 µm).(d) Optical micrograph of an NW-TFT with the source (S) to the drain (D) electrodes bridged by parallel arrays of NWs (scale bar, 5 µm).Chang-Hasnain Group, UC Berkeley 15Proprietary Information; do not distribute.NW-TFT Characteristics(e) IDS-VDSat increasing gate voltages ( VGS) in steps of 1 V, starting from top curve at VGS-10 V.(f) -IDSversus VGSat VDS-1 V. The inset shows -IDSversus VGSat VDS-1 V in the exponential scale, highlighting on - off ratio of nearly 108.(g) Histogram of threshold voltage ( Vth) distribution from 20 NW-TFT devices, showing high device-to-device reproducibility and a tight distribution. Gaussian fitting shows a standard deviation of only 0.22 V.Chang-Hasnain Group, UC Berkeley 16Proprietary Information; do not distribute.NW-TFTs on Plastic(a), The devices (substrate, ~1 in.2) show high mechanical flexibility.(b), –IDSversus VGSrelation at VDS–1 V. The black (red) curves show the transfer characteristics of the same devicebefore (after) flexing and releasing the plastic substrate, demonstrating the mechanical flexibility of NW-TFTs on plastic. Radius of curvature, 55 mm.Chang-Hasnain Group, UC Berkeley 17Proprietary Information; do not distribute.NW TFT Inverter – on a Glass Substrate(a) Circuit diagram and schematics of NW-TFT inverters.(b) Output waveform (green) of an inverter fabricated on glass driven by a 1 MHz sine wave (red) with Vsupply=15 V.Chang-Hasnain Group, UC Berkeley 18Proprietary Information; do not distribute.NW TFT Oscillator – on a Glass Substrate(c) Optical images and circuit diagram of an NW-TFT ring oscillator (scale bar, 100 µm).(d) Oscillation of 11.7 MHz in a ring oscillator structure with Vsupply=43 VChang-Hasnain Group, UC Berkeley 19Proprietary Information; do not distribute.Paper #5Chang-Hasnain Group, UC Berkeley 20Proprietary Information; do not distribute.Polar Surfaces of ZnO NWs– Allows the Formation of Nanobelts(a) Wurtzite structure model of ZnO.(b) Structure model of ZnO projected along [2-1-10], displaying the±(0001), ±(01-11), and ±(0-111) polar surfaces.(c) Model showing the formation of a nanospring by spiral coiling of a polar-surface-dominated nanobelt.Chang-Hasnain Group, UC Berkeley 21Proprietary Information; do not distribute.ZnO Nanostructures resulting from polar-surface-induced growth phenomena.Chang-Hasnain Group, UC Berkeley 22Proprietary Information; do not distribute.Formation of Nanohelices
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