Lih-Juann Chen

Plasmonic Nanolaser Using Epitaxially Grown Silver Film

Going Green with Nanophotonics Plasmons are optically induced collective electronic excitations tightly confined to the surface of a metal, with silver being the metal of choice. The subwavelength confinement offers the opportunity to shrink optoelectronic circuits to the nanometer scale. However, scattering processes within the metal lead to losses. Lu et al. (p. 450) developed a process to produce atomically smooth layers of silver, epitaxially grown on silicon substrates. A cavity in the silver layer is capped with a SiO insulating layer and an AlGaN nanorod was used to produce a low-threshold emission at green wavelengths. An atomically smooth layer of silver enhances the performance of nanophotonic devices. A nanolaser is a key component for on-chip optical communications and computing systems. Here, we report on the low-threshold, continuous-wave operation of a subdiffraction nanolaser based on surface plasmon amplification by stimulated emission of radiation. The plasmonic nanocavity is formed between an atomically smooth epitaxial silver film and a single optically pumped nanorod consisting of an epitaxial gallium nitride shell and an indium gallium nitride core acting as gain medium. The atomic smoothness of the metallic film is crucial for reducing the modal volume and plasmonic losses. Bimodal lasing with similar pumping thresholds was experimentally observed, and polarization properties of the two modes were used to unambiguously identify them with theoretically predicted modes. The all-epitaxial approach opens a scalable platform for low-loss, active nanoplasmonics.

Metal sulfide nanostructures : synthesis, properties and applications in energy conversion and storage

Metal sulfide nanomaterials have attracted great attention because of their excellent properties and promising applications in electronic, optical and optoelectronic devices. Well-aligned nanostructure arrays on substrates are highly attractive for their enhanced properties and novel applications. The general solution route and thermal evaporation under controlled conditions have been utilized for oriented growth of various metal sulfide nanostructure arrays and demonstrated their applications in energy conversion and storage. The article provides an overview of recent research and significant advances reported in the literature, covering from synthesis to properties and to applications especially in energy conversion and storage, such as lithium-ion batteries, solar cells, fuel cells and piezoelectric nanogenerators.

Piezoelectric Nanogenerator Using p-Type ZnO Nanowire Arrays

Using phosphorus-doped ZnO nanowire (NW) arrays grown on silicon substrate, energy conversion using the p-type ZnO NWs has been demonstrated for the first time. The p-type ZnO NWs produce positive output voltage pulses when scanned by a conductive atomic force microscope (AFM) in contact mode. The output voltage pulse is generated when the tip contacts the stretched side (positive piezoelectric potential side) of the NW. In contrast, the n-type ZnO NW produces negative output voltage when scanned by the AFM tip, and the output voltage pulse is generated when the tip contacts the compressed side (negative potential side) of the NW. In reference to theoretical simulation, these experimentally observed phenomena have been systematically explained based on the mechanism proposed for a nanogenerator.

Direct growth of aligned zinc oxide nanorods on paper substrates for low-cost flexible electronics.

www.MaterialsViews.com C O M M U Direct Growth of Aligned Zinc Oxide Nanorods on Paper Substrates for Low-Cost Flexible Electronics N IC A By Afsal Manekkathodi , Ming-Yen Lu , Chun Wen Wang , and Lih-Juann Chen * IO N Contemporary science and technology are hoping to revolutionize modern society with soft portable electronic devices, such as rollup displays, wearable devices, electronic paper, chip smart cards, and basic components in various devices. Research is actively focused on using paper or paper-like substrates for basic electronics components, which make excellent alternative substrates with exceptional technological attributes and commercial perspectives for the many substrates available. [ 1–10 ] The innovative techniques and strategies that are required for these fl exible paper-like platforms are just beginning to emerge from research laboratories in the form of realistic prototypes and have yet to be commercialized. Various electronic devices have already been realized, such as electronic paper displays (EPDs), [ 2 ] printed circuit boards, [ 3 ] thin fi lm transistors (TFTs), [ 4 – 6 ] active-matrix organic light-emitting diodes (AMOLEDs), [ 7 ] paper batteries, [ 8 ]

Observation of atomic diffusion at twin-modified grain boundaries in copper.

Grain boundaries affect the migration of atoms and electrons in polycrystalline solids, thus influencing many of the mechanical and electrical properties. By introducing nanometer-scale twin defects into copper grains, we show that we can change the grain-boundary structure and atomic-diffusion behavior along the boundary. Using in situ ultrahigh-vacuum and high-resolution transmission electron microscopy, we observed electromigration-induced atomic diffusion in the twin-modified grain boundaries. The triple point where a twin boundary meets a grain boundary was found to slow down grain-boundary and surface electromigration by one order of magnitude. We propose that this occurs because of the incubation time of nucleation of a new step at the triple points. The long incubation time slows down the overall rate of atomic transport.

GaN Nanowire Arrays for High-Output Nanogenerators

Three-fold symmetrically distributed GaN nanowire (NW) arrays have been epitaxially grown on GaN/sapphire substrates. The GaN NW possesses a triangular cross section enclosed by (0001), (2112), and (2112) planes, and the angle between the GaN NW and the substrate surface is approximately 62 degrees . The GaN NW arrays produce negative output voltage pulses when scanned by a conductive atomic force microscope in contact mode. The average of piezoelectric output voltage was about -20 mV, while 5-10% of the NWs had piezoelectric output voltages exceeding -(0.15-0.35) V. The GaN NW arrays are highly stable and highly tolerate to moisture in the atmosphere. The GaN NW arrays demonstrate an outstanding potential to be utilized for piezoelectric energy generation with a performance probably better than that of ZnO NWs.

ZnO−ZnS Heterojunction and ZnS Nanowire Arrays for Electricity Generation

Vertically aligned ZnO-ZnS heterojunction nanowire (NW) arrays were synthesized by thermal evaporation in a tube furnace under controlled conditions. Both ZnO and ZnS are of wurtzite structure, and the axial heterojunctions are formed by epitaxial growth of ZnO on ZnS with an orientation relationship of [0001](ZnO)//[0001](ZnS). Vertical ZnS NW arrays have been obtained by selectively etching ZnO-ZnS NW arrays. Cathodoluminescence measurements of ZnO-ZnS NW arrays and ZnS NW arrays show emissions at 509 and 547 nm, respectively. Both types of aligned NW arrays have been applied to convert mechanical energy into electricity when they are deflected by a conductive AFM tip in contact mode. The received results are explained by the mechanism proposed for nanogenerator.

Near UV LEDs made with in situ doped p-n homojunction ZnO nanowire arrays.

Catalyst-free p-n homojunction ZnO nanowire (NW) arrays in which the phosphorus (P) and zinc (Zn) served as p- and n-type dopants, respectively, have been synthesized for the first time by a controlled in situ doping process for fabricating efficient ultraviolet light-emitting devices. The doping transition region defined as the width for P atoms gradually occupying Zn sites along the growth direction can be narrowed down to sub-50 nm. The cathodoluminescence emission peak at 340 nm emitted from n-type ZnO:Zn NW arrays is likely due to the Burstein-Moss effect in the high electron carrier concentration regime. Further, the electroluminescence spectra from the p-n ZnO NW arrays distinctively exhibit the short-wavelength emission at 342 nm and the blue shift from 342 to 325 nm is observed as the operating voltage further increasing. The ZnO NW p-n homojunctions comprising p-type segment with high electron concentration are promising building blocks for short-wavelength lighting device and photoelectronics.

Dynamic evolution of conducting nanofilament in resistive switching memories.

Resistive random access memory (ReRAM) has been considered the most promising next-generation nonvolatile memory. In recent years, the switching behavior has been widely reported, and understanding the switching mechanism can improve the stability and scalability of devices. We designed an innovative sample structure for in situ transmission electron microscopy (TEM) to observe the formation of conductive filaments in the Pt/ZnO/Pt structure in real time. The corresponding current-voltage measurements help us to understand the switching mechanism of ZnO film. In addition, high-resolution transmission electron microscopy (HRTEM) and electron energy loss spectroscopy (EELS) have been used to identify the atomic structure and components of the filament/disrupted region, determining that the conducting paths are caused by the conglomeration of zinc atoms. The behavior of resistive switching is due to the migration of oxygen ions, leading to transformation between Zn-dominated ZnO(1-x) and ZnO.

Direct growth of high-rate capability and high capacity copper sulfide nanowire array cathodes for lithium-ion batteries

A general solution method for the growth of highly ordered large-scale Cu2S nanowire arrays onto the copper metal current collector substrates has been developed. The electrochemical behaviors of Cu2S nanowire array cathodes for lithium-ion battery applications reveal that they exhibit stable lithium-ion insertion/extraction reversibility, high reversible lithium storage capacity, long cycle life and outstanding rate capability. The superb electrochemical performance can be attributed to the nanowire arrays having increased reaction sites, improved cycle life in the face of mechanical strain and efficient charge transport. With the simplicity of fabrication and good electrochemical properties, the Cu2S nanowire arrays are promising cathode materials for the practical use in the next generation lithium-ion batteries.