Minbaek Lee

Flexible Nanocomposite Generator Made of BaTiO 3 Nanoparticles and Graphitic Carbons

Outdoor renewable energy sources such as solar energy (15 000 μ W/cm 3 ), [ 3 , 4 ] wind energy (380 μ W/cm 3 ), [ 5 ] and wave energy (1 000 W/cm of wave crest length) [ 6 , 7 ] can provide largescale needs of power. However, for driving small electronics in indoor or concealed environments [ 3 , 8 ] (such as in tunnels, clothes, and artifi cial skin) and implantable biomedical devices, innovative approaches have to be developed. One way of energy harvesting without such restraints is to utilize piezoelectric materials that can convert vibrational and mechanical energy sources from human activities such as pressure, bending, and stretching motions into electrical energy. [ 9–11 ]

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.

Lead-free NaNbO3 nanowires for a high output piezoelectric nanogenerator.

Perovskite ferroelectric nanowires have rarely been used for the conversion of tiny mechanical vibrations into electricity, in spite of their large piezoelectricity. Here we present a lead-free NaNbO(3) nanowire-based piezoelectric device as a high output and cost-effective flexible nanogenerator. The device consists of a NaNbO(3) nanowire-poly(dimethylsiloxane) (PDMS) polymer composite and Au/Cr-coated polymer films. High-quality NaNbO(3) nanowires can be grown by hydrothermal method at low temperature and can be poled by an electric field at room temperature. The NaNbO(3) nanowire-PDMS polymer composite device shows an output voltage of 3.2 V and output current of 72 nA (current density of 16 nA/cm(2)) under a compressive strain of 0.23%. These results imply that NaNbO(3) nanowires should be quite useful for large-scale lead-free piezoelectric nanogenerator applications.

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 ]

Fabric‐Based Integrated Energy Devices for Wearable Activity Monitors

A wearable fabric-based integrated power-supply system that generates energy triboelectrically using human activity and stores the generated energy in an integrated supercapacitor is developed. This system can be utilized as either a self-powered activity monitor or as a power supply for external wearable sensors. These demonstrations give new insights for the research of wearable electronics.

Self-powered environmental sensor system driven by nanogenerators

We demonstrate a fully stand-alone, self-powered environmental sensor driven by nanogenerators with harvesting vibration energy. Such a system is made of a ZnO nanowire-based nanogenerator, a rectification circuit, a capacitor for charge storage, a signal transmission LED light and a carbon nanotube-based Hg2+ ion sensor. The circuit lights up the LED indicator when it detects mercury ions in water solution. It is the first demonstration of a nanomaterial-based, self-powered sensor system for detecting a toxic pollutant.

Large-Scale Assembly of Silicon Nanowire Network-Based Devices Using Conventional Microfabrication Facilities

We present a method for assembling silicon nanowires (Si-NWs) in virtually general shape patterns using only conventional microfabrication facilities. In this method, silicon nanowires were functionalized with amine groups and dispersed in deionized water. The functionalized Si-NWs exhibited positive surface charges in the suspensions, and they were selectively adsorbed and aligned onto negatively charged surface regions on solid substrates. As a proof of concepts, we demonstrated transistors based on individual Si-NWs and long networks of Si-NWs.

Stretchable Carbon Nanotube Charge-Trap Floating-Gate Memory and Logic Devices for Wearable Electronics

Electronics for wearable applications require soft, flexible, and stretchable materials and designs to overcome the mechanical mismatch between the human body and devices. A key requirement for such wearable electronics is reliable operation with high performance and robustness during various deformations induced by motions. Here, we present materials and device design strategies for the core elements of wearable electronics, such as transistors, charge-trap floating-gate memory units, and various logic gates, with stretchable form factors. The use of semiconducting carbon nanotube networks designed for integration with charge traps and ultrathin dielectric layers meets the performance requirements as well as reliability, proven by detailed material and electrical characterizations using statistics. Serpentine interconnections and neutral mechanical plane layouts further enhance the deformability required for skin-based systems. Repetitive stretching tests and studies in mechanics corroborate the validity of the current approaches.

Fibronectin–Carbon-Nanotube Hybrid Nanostructures for Controlled Cell Growth

Recently, carbon nanotube (CNT)-based devices have been extensively utilized for various cellular applications, including neural-signal amplifi cation, [ 1 , 2 ] cancer therapeutics, [ 3 ] and tissue engineering. [ 4 ] For those applications, it is often crucial to control the location and direction of cell growth on CNTs while mimicking an in-vivo-like cellular environment to retain in-vivo-like cellular activity. Several research groups have reported that bulk CNT substrates can support cell adhesion, growth, and differentiation. [ 5–8 ] CNT patterns were also reported to induce the selective growth of neurons and human mesenchymal stem cells (hMSCs). [ 9 , 10 ] However, the effects of CNTs on cells are still controversial and the underlying mechanism for selective cell adhesion and growth is still obscure. In this Communication, we report a study of the role of extracellular matrix (ECM) proteins, such as fi bronectin (FN), in CNT–cell interactions and propose FN–CNT hybrid nanostructures as an effi cient means for cell-growth control. In this work, we fi rst investigated the adhesion properties and conformational change of FNs on the CNTs via immunofl uorescence and force-spectroscopy study. FNs exhibited a strong affi nity to CNTs and maintained a high binding capability to biomolecules even after being adsorbed onto the CNTs. Moreover, the results of our force-spectroscopy-based protein-unfolding experiment confi rm that FNs maintained their native structures on the CNTs. FN–CNT hybrid nanostructures had a stronger affi nity to cells than conventional surfaces, such as FN-coated glass. Importantly, cells formed focal adhesion and grew selectively on the FN–CNT hybrid nanostructures, indicating that the selective growth of cells on

Biosensor system-on-a-chip including CMOS-based signal processing circuits and 64 carbon nanotube-based sensors for the detection of a neurotransmitter

We developed a carbon nanotube (CNT)-based biosensor system-on-a-chip (SoC) for the detection of a neurotransmitter. Here, 64 CNT-based sensors were integrated with silicon-based signal processing circuits in a single chip, which was made possible by combining several technological breakthroughs such as efficient signal processing, uniform CNT networks, and biocompatible functionalization of CNT-based sensors. The chip was utilized to detect glutamate, a neurotransmitter, where ammonia, a byproduct of the enzymatic reaction of glutamate and glutamate oxidase on CNT-based sensors, modulated the conductance signals to the CNT-based sensors. This is a major technological advancement in the integration of CNT-based sensors with microelectronics, and this chip can be readily integrated with larger scale lab-on-a-chip (LoC) systems for various applications such as LoC systems for neural networks.