Seung-nam Cha

A Hybrid Piezoelectric Structure for Wearable Nanogenerators

A hybrid-fiber nanogenerator comprising a ZnO nanowire array, PVDF polymer and two electrodes is presented. Depending on the bending or spreading action of the human arm, at an angle of ∼90°, the hybrid fiber reaches electrical outputs of ∼0.1 V and ∼10 nA cm(-2) . The unique structure of the hybrid fiber may inspire future research in wearable energy-harvesting technology.

Sound‐Driven Piezoelectric Nanowire‐Based Nanogenerators

Thus, sound power can be used for various novel applications including mobile phones that can be charged during conversations and sound-insulating walls near highways that generate electricity from the sound of passing vehicles. The latter development would have the additional benefi t of reducing noise levels near highways by absorbing the sound energy of vehicles. Here, we report the fi rst power-generating performance of sound-driven nanogenerators based on piezoelectric ZnO nanowires. Figure 1a and b show a schematic diagram of an integrated nanogenerator with piezoelectric ZnO nanowires and a crosssectional fi eld-emission scanning electron microscopy (FE-SEM) image of vertically well-aligned ZnO nanowire arrays (acting as a piezoelectric active layer), respectively. The nanowires were grown using a thermal chemical vapor deposition (CVD) system via a vapor-liquid-solid mechanism on an n-type GaN thin fi lm (acting as a bottom electrode)-deposited sapphire substrate. [ 14 ] It was found that there are no additional peaks other than (0002) and (0004) peaks of ZnO in X-ray diffraction measurements (not shown), indicating good alignment of the ZnO nanowires along the c -axis direction on GaN. A palladium gold (PdAu)coated polyethersulfone (PES) substrate were used as both a top electrode and a vibration plate and placed above the ZnO nanowire arrays. The integrated device was then sealed at the edges to prevent physical and chemical damage. The average length and diameter of the ZnO nanowires were ∼ 10 µ m and ∼ 150 nm, respectively. The integrated nanogenerator was then connected to a measurement system.

Single‐Fiber‐Based Hybridization of Energy Converters and Storage Units Using Graphene as Electrodes

Recently, there has been great interest in wearable and stretchable energy generation and storage devices utilizing nanotechnology for applications such as self-powering nanosystem that harvests its operating energy from the environment. [ 1 ] Solar, mechanical and thermal energy can be scavenged from the environment using devices that were fabricated using fl exible or stretchable substrates. For example, textile-fi bre-based nanogenerators have been demonstrated utilizing ZnO nanowires (NWs) grown on Kevlar fi bres to scavenge low-frequency mechanical energy. [ 2 ] Twisted fi bre-like electrodes have been used for harvesting solar energy using the dye-sensitized solar cells (DSSCs) approach. [ 3 ] Once the energy is harvested from the environment, an energy storage device is required in order to maintain the operation of the system, but it is usually a separated unit from the energy converters. Flexible batteries. [ 4 ]

Carbon nanotube electron emitters with a gated structure using backside exposure processes

We have fabricated fully vacuum-sealed 5 in. diagonal carbon nanotube field-emission displays of a gated structure with reliable electron emission characteristics. Single-walled carbon nanotube tips were implemented into the gate structure using self-aligned backside exposure of photosensitive carbon nanotube paste. An onset gate electrode voltage for emission was about 60 V and the luminance as high as 510 cd/m2 was exhibited under an application of 100 V and 1.5 kV to gate electrode and anode, respectively.

Design and evaluation of novel Zn doped mesoporous TiO2 based anode material for advanced lithium ion batteries

We report Zn doped mesoporous TiO2 microspheres synthesized via a combined sol–gel and solvothermal method exhibiting excellent Li-ion insertion–extraction properties. The specific capacity of Zn doped mesoporous TiO2 microspheres was significantly higher than that of TiO2 nanopowder at high charge–discharge rates. The superior rate performance offered by Zn doped mesoporous TiO2 microspheres may be attributed to enhanced electronic and ionic conductivity, which was achieved by improving the donor density via Zn doping and by providing a well interconnected mesoporous network of nanoparticles for the effective diffusion of Li ions. Zn doped mesoporous TiO2 microspheres showed more than an 87% capacity retention after 100 cycles at a charge–discharge rate of 1 C, demonstrating it to be a promising approach for the development of high-performance Li ion batteries.

p‐Type Conduction Characteristics of Lithium‐Doped ZnO Nanowires

Nanostructured electronic devices are expected to facilitate the continuing miniaturization of electronic devices and enable ultralow power device operation. In particular, 1D nanostructures such as nanowires (NW) and nanotubes have attracted great interest over the past decade because of their specifi c physical properties and their potential as building blocks for next-generation nanoelectronic devices. [ 1 , 2 ] Among various 1D materials, zinc oxide (ZnO), which has a direct and wide bandgap, is a promising candidate for light-emitting diodes, UV and gas sensors, transistor channels, and other devices that can utilize the unique vertical alignment characteristics and highly ordered single crystalline properties of NW structures. [ 3–6 ] However, because undoped ZnO NWs are intrinsically n-type, their use in practical devices has been hindered and much effort has been dedicated toward the development of p-type ZnO NWs. In particular, control and manipulation of the doping process is increasingly becoming a key approach for the realization of p-type ZnO NWs. To realize p-type ZnO NWs, the initial dopant candidates tested included group V elements to substitute for O and group III elements to substitute for Zn, despite the large size mismatches in both cases. Recently, group I species such as Li and Na have been used to synthesize p-type ZnO NWs based on the expectation that these elements would function as shallow acceptors in ZnO host materials. [ 7–9 ] Li has the smallest ionic radius (0.76 Å) of group I species, which is very close to that of Zn (0.74 Å). Furthermore, several reports of excited centers observed using electron paramagnetic resonance spectroscopy have indicated that Li atoms can act as shallow acceptors in substantial forms of Zn sites (Li Zn ). [ 10 , 11 ] In addition, it is well-known that Li has specifi c advantages over other dopant

Low temperature growth of multi-wall carbon nanotubes assisted by mesh potential using a modified plasma enhanced chemical vapor deposition system

Abstract Well-aligned carbon nanotubes have been synthesized on Corning and silicon substrates at extremely low temperatures of 450 °C using a slightly modified conventional plasma enhanced chemical vapor deposition (PECVD). The deposition system was intentionally designed to impose mesh potential on the substrates through an external electrode that was a critical parameter for low temperature growth. Mixture gases of C2H2 and NH3 with the imposed mesh potential of about 50 V effectively aligned multi-wall carbon nanotubes at 450 °C on Ni-coated substrates.

Radio-frequency transmission characteristics of a multi-walled carbon nanotube

Carbon nanotubes (CNTs) are considered as promising candidates for transmission lines as well as microcircuit interconnects in future nanoscale electronic systems. Owing to the growing interest in the use of microwave signals, understanding the transmission properties at high frequencies is essential to assess the applicability of multi-walled carbon nanotubes (MWNTs). In this work, we measured two-port properties of individual MWNTs using a network analyser from a frequency of 0.5 to 50 GHz. The radio-frequency transmission parameters were obtained from the measured S-parameter data. Our results show the frequency dependence of the equivalent resistance of MWNTs, which decreases with increasing frequency. This confirms that metallic CNTs will be useful for transmitting GHz signals in nanoelectric devices.

Enhancement of piezoelectricity via electrostatic effects on a textile platform

We have shown the enhanced piezoelectricity by electrostatic effects on a textile based platform. The electrostatic and piezoelectric effects were hybridized by integrating piezoelectric ZnO nanowires and a charged dielectric film on a wearable textile substrate. The hybrid textile nanogenerator produced an output voltage of 8 V and an output current of 2.5 μA. Using a simple AC–DC converter circuit, we operated the green organic light-emitting diode and a liquid crystal display panel using a 100 dB sonic wave.

Controlled growth of vertically aligned ZnO nanowires with different crystal orientation of the ZnO seed layer

A novel synthesis and growth method achieving vertically aligned zinc oxide (ZnO) nanowires on a silicon dioxide (SiO(2)) coated silicon (Si) substrate is demonstrated. The growth direction of the ZnO nanowires is determined by the crystal structure of the ZnO seed layer, which is formed by the oxidation of a DC-sputtered Zn film. The [002] crystal direction of the seed layer is dominant under optimized thickness of the Zn film and thermal treatment. Vertically aligned ZnO nanowires on SiO(2) coated Si substrate are realized from the appropriately thick oxidized Zn seed layer by a vapor-solid growth mechanism by catalyst-free thermal chemical vapor deposition (CVD). These experimental results raise the possibility of using the nanowires as functional blocks for high-density integration systems and/or photonic applications.