Hoyoung Suh

Programmable synthesis of shape-, structure-, and composition-modulated one-dimensional heterostructures by galvanic displacement reaction

One-dimensional heterostructures consisting of periodically modulated bismuth telluride tube/wire were synthesized by galvanic displacement reaction of Co/Ni multi-segmented sacrificial nanowires. Utilizing the difference in redox potential and corrosion behavior of Co and Ni, segments, dimension, composition, and structure of the individual segments were also precisely engineered. The programmable ability to synthesize heterostructures with simultaneously modulation of various dimensions in ambient conditions may lead to an effective route to synthesize high performance nanodevices including nanoelectronics, optoelectronics, sensors, and thermoelectrics.

Titanium oxynitride microspheres with the rock-salt structure for use as visible-light photocatalysts

Novel photocatalysts (TiO2@TiO1−xNx) with the core–shell geometry were synthesized by controlled nitridation of TiO2 microspheres using ammonia gas. The oxynitride phases (TiO1−xNx) with a cubic rock-salt structure are exclusively formed on the surface of the TiO2 microspheres while the cores of the microspheres retain the TiO2 phase without nitrogen doping. Various spectroscopic data confirm the formation of the core–shell structure, denoted as TiO2@TiO1−xNx. The TiO2@TiO1−xNx materials showed superior photocatalytic activities for the decomposition of methylene blue as well as the generation of photocurrent under visible-light. It is evident that the TiO1−xNx phase is the key element to induce the photocatalytic activity. Specifically, the partial doping of nitrogen into the TiO matrix is crucial for visible-light absorption.

Advanced method for the accurate measurement of tilt angle in a transmission electron microscopy goniometer

BackgroundIn order to improve the reliability of the electron tomography (ET) technique, which reveals three-dimensional information of nanostructured materials from a series of tilted two-dimensional images, it is essential that the mechanical tilt angle be accurately measured by the transmission electron microscopy (TEM) goniometer.FindingsIn this study, a calibration specimen was fabricated by nanohole patterning using a focused ion beam in order to determine mechanical tilt angles. The TEM goniometer tilt-angle accuracies were directly confirmed by measuring the changing areas of the projected nanosized hole. New calibration equations were developed and applied for the accurate determination of tilt angle.ConclusionWe expect that the calibration specimen will effectively determine and correct the mechanical tilt angles in TEM goniometers leading to improvements in the ET technique.