Engineering Heteromaterials to Control Lithium Ion Transport Pathways.

Safe and efficient operation of lithium ion batteries requires precisely directed flow of lithium ions and electrons to control the first directional volume changes in anode and cathode materials. Understanding and controlling the lithium ion transport in battery electrodes becomes crucial to the design of high performance and durable batteries. Recent work revealed that the chemical potential barriers encountered at the surfaces of heteromaterials play an important role in directing lithium ion transport at nanoscale. Here, we utilize in situ transmission electron microscopy to demonstrate that we can switch lithiation pathways from radial to axial to grain-by-grain lithiation through the systematic creation of heteromaterial combinations in the Si-Ge nanowire system. Our systematic studies show that engineered materials at nanoscale can overcome the intrinsic orientation-dependent lithiation, and open new pathways to aid in the development of compact, safe, and efficient batteries

Orientation-dependent x-ray absorption fine structure of ZnO nanorods

The local structure of two samples of vertically well-aligned ZnO nanorods with average diameters of 13 and 37 nm were studied using orientation-dependent x-ray absorption fine structure (XAFS) at the Zn K edge. The aligned ZnO nanorod samples were fabricated on sapphire (0001) substrates with a catalyst-free metalorganic vapor-phase epitaxy method. The XAFS measurements showed that both nanorod samples have a well-ordered wurtzite structure and that no vacancy was observed at either site of zinc or oxygen atoms. However, we found that in both samples the lattice constants of a and b were shrunken by similar to0.04 Angstrom while c was elongated by similar to0.1 Angstrom, compared with those of their bulk counterparts. Furthermore, there was a substantial amount of disorder in the bond length of the only Zn-O pairs located near the ab plane. This may suggest that the terminating atoms at the boundaries of the nanorods are oxygen atoms. (C) 2005 American Institute of Physics

Enhanced field emission properties from well-aligned zinc oxide nanoneedles grown on the Au/Ti/n-Si substrate

The authors investigated the field emission from vertically well-aligned zinc oxide (ZnO) nanoneedles grown on the Au/Ti/n-Si (100) substrate using metal organic chemical vapor deposition. The turn-on field of ZnO nanoneedles was about 0.85 V/mu m at the current density of 0.1 mu A/cm(2), and the emission current density of 1 mA/cm(2) was achieved at the applied electric field of 5.0 V/mu m. The low turn-on field of the ZnO nanoneedles was attributed to very sharp tip morphology, and the high emission current density was mainly caused by the formation of the stable Ohmic contact between the ZnO nanoneedles and Au film.This work was supported by the SRC program of Center for Nanotubes and Nanosructured Composites of MOST/KOSEF, by the National R&D Project for Nano Science and Technology, and by the Ministry of Commerce, Industry, and Energy of Korea through a Components and Materials Technology Development project (No.0401-DD2-0162)

Nanophotonic switch using ZnO nanorod double-quantum-well structures

The authors report on time-resolved near-field spectroscopy of ZnO/ZnMgO nanorod double-quantum-well structures (DQWs) for a nanometer-scale photonic device. They observed nutation of the population between the resonantly coupled exciton states of DQWs. Furthermore, they demonstrated switching dynamics by controlling the exciton excitation in the dipole-inactive state via an optical near field. The results of time-resolved near-field spectroscopy of isolated DQWs described here are a promising step toward designing a nanometer-scale photonic switch and related devices.The work at POSTECH was supported by the National Creative Research Initiative Project, Korea and AOARD 04-49 (Quotation No. FA5209-040T0254)

Spatially resolved X-ray excited optical luminescence

Spatially resolved luminescence distributions in semiconductor heterostructures were investigated by core level excitation using hard X-ray (sub-) microbeams. Compact and mobile XEOL instruments have been developed and well adapted on the hard X-ray beamline ID22 of the European Synchrotron Radiation Facility for different wavelength collection ranges: UV-VIS and NIR. Linked by multimode optical fibers, their special designs provide precise scanning microscopy and allow easy access for multiple detection modes. Based on the hard X-ray microprobe station of ID22, details of the equipments, spectral data and representative examples are briefly described. Data collections from InAs and InGaN quantum heterostructures support the excellent performance of the optical devices. © 2011 Elsevier B.V. All rights reserved.This work was partially supported by the NANOWIRING Marie Curie ITN (EU project No. PITN-GA-2010-265073).Peer Reviewe

Ultra-Sharp Nanowire Arrays Natively Permeate, Record, and Stimulate Intracellular Activity in Neuronal and Cardiac Networks

Intracellular access with high spatiotemporal resolution can enhance our understanding of how neurons or cardiomyocytes regulate and orchestrate network activity, and how this activity can be affected with pharmacology or other interventional modalities. Nanoscale devices often employ electroporation to transiently permeate the cell membrane and record intracellular potentials, which tend to decrease rapidly to extracellular potential amplitudes with time. Here, we report innovative scalable, vertical, ultra-sharp nanowire arrays that are individually addressable to enable long-term, native recordings of intracellular potentials. We report large action potential amplitudes that are indicative of intracellular access from 3D tissue-like networks of neurons and cardiomyocytes across recording days and that do not decrease to extracellular amplitudes for the duration of the recording of several minutes. Our findings are validated with cross-sectional microscopy, pharmacology, and electrical interventions. Our experiments and simulations demonstrate that individual electrical addressability of nanowires is necessary for high-fidelity intracellular electrophysiological recordings. This study advances our understanding of and control over high-quality multi-channel intracellular recordings, and paves the way toward predictive, high-throughput, and low-cost electrophysiological drug screening platforms.Comment: Main manuscript: 33 pages, 4 figures, Supporting information: 43 pages, 27 figures, Submitted to Advanced Material

Probing quantum confinement within single core-multishell nanowires

Theoretically core-multishell nanowires under a cross-section of hexagonal geometry should exhibit peculiar confinement effects. Using a hard X-ray nanobeam, here we show experimental evidence for carrier localization phenomena at the hexagon corners by combining synchrotron excited optical luminescence with simultaneous X-ray fluorescence spectroscopy. Applied to single coaxial n-GaN/InGaN multiquantum-well/p-GaN nanowires, our experiment narrows the gap between optical microscopy and high-resolution X-ray imaging and calls for further studies on the underlying mechanisms of optoelectronic nanodevices. © 2012 American Chemical Society.The authors thank Irina Snigireva and Armando Vicente Sole for their assistance with the SEM measurements and data processing using PyMca, respectively. We thank Remi Tocoulou and Peter Cloetens for their help and the ESRF for the beam time allocated. We also thank Andrei Rogalev for the valuable discussions and Gary Admans for the critical reading of the manuscript. This work has been partially supported by the NANOWIRING Marie Curie ITN (EU project no. PITN-GA-2010-265073), as well as by the EPIC-NANOTICS (TEC2011-29120-C05-04) and Q&C-LIGHT (S2009ESP-1503) from Spanish MEC and CAM, respectively.Martínez Criado, G.; Homs Puron, AA.; Alen, B.; Sans Tresserras, JÁ.; Segura Ruiz, J.; Molina Sánchez, A.; Susini, J.... (2012). Probing quantum confinement within single core-multishell nanowires. Nano Letters. 12(11):5829-5834. https://doi.org/10.1021/nl303178uS58295834121