Kwanyong Seo

We demonstrate that vertical silicon nanowires take on a surprising variety of colors covering the entire visible spectrum, in marked contrast to the gray color of bulk silicon. This effect is readily observable by bright-field microscopy, or even to the naked eye. The reflection spectra of the nanowires each show a dip whose position depends on the nanowire radii. We compare the experimental data to the results of finite difference time domain simulations to elucidate the physical mechanisms be

A monolithically integrated, single-unit PV–LIB device shows exceptional electrochemical performance that lies far beyond those achievable by conventional PVs or LIBs alone.

We have observed unusual ferromagnetic properties in single-crystalline CoSi nanowire ensemble, in marked contrast to the diamagnetic CoSi in bulk. High-density freestanding CoSi nanowires with B20 crystal structure are synthesized by a vapor-transport-based method. The reaction of cobalt chloride precursor with a Si substrate produces high-aspect-ratio CoSi nanowires. The high-resolution transmission electron microscopy and electron diffraction studies reveal superlattice structure in CoSi nano

Transparent photovoltaics (TPVs), which combine visible transparency and solar energy conversion, are being developed for applications in which conventional opaque solar cells are unlikely to be feasible, such as windows of buildings or vehicles. In this paper, we review recent progress in TPVs along with strategies that enable the transparency of conventional photovoltaics, including thin-film technology, selective light-transmission technology, and luminescent solar concentrator technology. Fr

Abstract Stretchable electronics are considered as next‐generation devices; however, to realize stretchable electronics, it is first necessary to develop a deformable energy device. Of the various components in energy devices, the fabrication of stretchable current collectors is crucial because they must be mechanically robust and have high electrical conductivity under deformation. In this study, the authors present a conductive polymer composite composed of Jabuticaba‐like hybrid carbon filler

We report the density-functional calculations of NO2 adsorption on single-walled carbon nanotube walls. A single molecular adsorption was endothermic with an activation barrier, but a collective adsorption with several molecules became exothermic without an activation barrier. We find that NO2 adsorption is strongly electronic structure- and strain-dependent. The NO2 adsorption on metallic nanotubes was energetically more favorable than that on semiconducting nanotubes and furthermore the adsorp

Flexible crystalline silicon radial junction photovoltaics with tapered microwires are presented, which simultaneously show high flexibility and efficiency.

Free-standing CrSi2 nanowires are synthesized by a vapor transport based method for the first time. High-quality CrSi2 nanowires with a hexagonal cross section are produced by the reaction of a CrCl2 precursor and a Si substrate without using any metal catalyst. We have studied the crystal structure and electrical transport properties of CrSi2 nanowires. Transmission electron microscopy and X-ray diffraction studies confirm the single-crystalline nature of the CrSi2 nanowires of a C40 type struc

We report the simultaneous and selective synthesis of single-crystalline Co(n)Si NWs (n = 1-3) and their corresponding crystal structures--simple cubic (CoSi), orthorhombic (Co(2)Si), and face-centered cubic (Co(3)Si)--following a composition change. Co(n)Si NWs were synthesized by placing the sapphire substrates along a temperature gradient. The synthetic process is a successful demonstration of tuning the chemical composition in Co(n)Si NWs. The synthesis and detailed crystal structure of sing

We developed a unique nano- and microwire hybrid structure by selectively modifying only the tops of microwires using metal-assisted chemical etching. The proposed nano/micro hybrid structure not only minimizes surface recombination but also absorbs 97% of incident light under AM 1.5G illumination, demonstrating outstanding light absorption compared to that of planar (59%) and microwire arrays (85%). The proposed hybrid solar cells with an area of 1 cm(2) exhibit power conversion efficiencies (E

We report fabrication of Heusler alloy Fe(3)Si nanowires by a diffusion-driven crystal structure transformation method from paramagnetic FeSi nanowires. Magnetic measurements of the Fe(3)Si nanowire ensemble show high-temperature ferromagnetic properties with T(c) >> 370 K. This methodology is also successfully applied to Co(2)Si nanowires in order to obtain metal-rich nanowires (Co) as another evidence of the structural transformation process. Our newly developed nanowire crystal transformation

Silicon microwire arrays have attracted considerable attention recently due to the opportunity they present as highly efficient and cost-effective solar cells. In this study, we report on efficient Si microwire array solar cells with areas of 1 cm(2) and Air Mass 1.5 Global conversion efficiencies of up to 10.6%. These solar cells show an open-circuit voltage of 0.56 V, a short-circuit current density of 25.2 mA/cm(2), and a fill factor of 75.2%, with a silicon absorption region that is only 25

We report the synthesis of free-standing MnSi nanowires via a vapor transport method with no catalyst and measurements of their electrical and magnetic properties for the first time. The single-crystalline MnSi nanowire ensemble with a simple cubic (B20) crystal structure shows itinerant helimagnetic properties with a T(c) of about 30 K. A single MnSi nanowire device was fabricated by a new method using photolithography and a nanomanipulator that produces good ohmic contacts. The single-nanowire