In-Mook Choi

Bio: In-Mook Choi is an academic researcher from Korea Research Institute of Standards and Science. The author has contributed to research in topics: Pressure measurement & Pressure sensor. The author has an hindex of 12, co-authored 46 publications receiving 401 citations. Previous affiliations of In-Mook Choi include Korea University of Science and Technology & KAIST.

CCM.G-K2 key comparison

Abstract: In November 2013 an International Key Comparison, CCM.G-K2, was organized in the Underground Laboratory for Geodynamics in Walferdange. The comparison has assembled 25 participants coming from 19 countries and four different continents. The comparison was divided into two parts: the key comparison that included 10 NMIs or DIs, and the pilot study including all participants. The global result given by the pilot study confirms that all instruments are absolutely coherent to each other. The results obtained for the key comparison confirm a good agreement between the NMI instruments.

Flexible force or pressure sensor array using semiconductor strain gauge, fabrication method thereof and measurement method thereof

Abstract: The force or pressure sensor array of the present invention effectively has both flexibility and elasticity. Since the substrate itself is a kind of a polymer material, the substrate can be bent or expanded. Although silicon, which is a material of the semiconductor strain gauge, is easily broken and solid, mechanical flexibility can be secured if it is fabricated extremely thin. To this end, particularly, disclosed is a flexible force or pressure sensor array using semiconductor strain gauges 110 , the sensor array comprising: a substrate 10 including: the semiconductor strain gauges 110 in which a plurality of elements formed in a certain array pattern is deformed by force or pressure, a pair of polymer film layers 120 and 130 having film surfaces contacted facing each other and containing the semiconductor strain gauge 110 between the film surfaces contacted with each other, and a pair of signal line layers formed on top and bottom surfaces of an insulating layer using either of the pair of polymer film layers 120 and 130 as the insulating layer and connected to the elements 111 of the array pattern to form electrodes, for fetching deformation signals outputted due to deformation of the elements 111 to outside; and a pair of elastomer layers 20 and 30 formed on both sides of the substrate 10 to contain the substrate 10 inside.

Application of carbon nanotube field emission effect to an ionization gauge

Abstract: Using the field emission effect of a carbon nanotube (CNT), we characterized a new type of technology for detecting low pressure. The fabricated low pressure sensor is of a triode type, consisting of a cathode (carbon nanotubes field emitter arrays), a grid, and a collector. The gauge described here has a triode configuration similar to that of a conventional hot cathode ionization gauge but also has a cold emission source. Due to the excellent field emission characteristics of CNT, it is possible to make a cost effective cold cathode type ionization gauge. For an effective CNT cathode, we used the screen-printing method and also, we controlled the collector and the grid potentials in order to obtain a high ionization current. We found that the ratio of the ionization current to the CNT cathode current changes according to the pressure in the chamber. In short, we elaborate the various metrological characteristics of a home-made pressure sensor that uses CNTs.

Improved metrological characteristics of a carbon-nanotube-based ionization gauge

Abstract: A low-pressure detection technology utilizing the field emission of carbon nanotubes (CNTs) is introduced and its performance is characterized. To overcome the limitations of conventional ionization gauges, the CNTs had been proposed as an electron source. However, the simple triode structure of previous CNT pressure sensor not only has suffered from a limited measurement range but is also subject to a serious CNT array degradation problem. In this letter, the authors report the characterization results of an improved CNT-based pressure gauge, which is implemented by a screen-printing method, a modified mesh structure, and a pulse width modulation signal.

Single-shot nanometer-scale holographic imaging with laser-driven x-ray laser

Abstract: Single-shot nanometer-scale imaging techniques have become important because of their potential application in observing the structural dynamics of nanomaterials. We report here the image reconstruction results obtained using single-shot Fourier transform x-ray holography with an x-ray laser driven by a table top laser system. A minimum resolution of 87 nm was obtained from the reconstructed image. We could also discriminate the aggregates of carbon nanotubes, which shows the feasibility of single-exposure nanoimaging for real specimens using a laser-driven x-ray laser.

Search for New Physics with Atoms and Molecules

Abstract: Advances in atomic physics, such as cooling and trapping of atoms and molecules and developments in frequency metrology, have added orders of magnitude to the precision of atom-based clocks and sensors. Applications extend beyond atomic physics and this article reviews using these new techniques to address important challenges in physics and to look for variations in the fundamental constants, search for interactions beyond the standard model of particle physics, and test the principles of general relativity.

Enhancement of electron energy to the multi-GeV regime by a dual-stage laser-wakefield accelerator pumped by petawatt laser pulses.

Abstract: Laser-wakefield acceleration offers the promise of a compact electron accelerator for generating a multi-GeV electron beam using the huge field gradient induced by an intense laser pulse, compared to conventional rf accelerators. However, the energy and quality of the electron beam from the laser-wakefield accelerator have been limited by the power of the driving laser pulses and interaction properties in the target medium. Recent progress in laser technology has resulted in the realization of a petawatt (PW) femtosecond laser, which offers new capabilities for research on laser-wakefield acceleration. Here, we present a significant increase in laser-driven electron energy to the multi-GeV level by utilizing a 30-fs, 1-PW laser system. In particular, a dual-stage laser-wakefield acceleration scheme (injector and accelerator scheme) was applied to boost electron energies to over 3 GeV with a single PW laser pulse. Three-dimensional particle-in-cell simulations corroborate the multi-GeV electron generation from the dual-stage laser-wakefield accelerator driven by PW laser pulses.

Double-walled carbon nanotube solar cells

Abstract: We directly configured double-walled carbon nanotubes as energy conversion materials to fabricate thin-film solar cells, with nanotubes serving as both photogeneration sites and a charge carriers collecting/transport layer. The solar cells consist of a semitransparent thin film of nanotubes conformally coated on a n-type crystalline silicon substrate to create high-density p-n heterojunctions between nanotubes and n-Si to favor charge separation and extract electrons (through n-Si) and holes (through nanotubes). Initial tests have shown a power conversion efficiency of >1%, proving that DWNTs-on-Si is a potentially suitable configuration for making solar cells. Our devices are distinct from previously reported organic solar cells based on blends of polymers and nanomaterials, where conjugate polymers generate excitons and nanotubes only serve as a transport path.

Mobile quantum gravity sensor with unprecedented stability

Abstract: Changes of surface gravity on Earth are of great interest in geodesy, earth sciences and natural resource exploration. They are indicative of Earth system's mass redistributions and vertical surface motion, and are usually measured with falling corner-cube- and superconducting gravimeters (FCCG and SCG). Here we report on absolute gravity measurements with a mobile quantum gravimeter based on atom interferometry. The measurements were conducted in Germany and Sweden over periods of several days with simultaneous SCG and FCCG comparisons. They show the best-reported performance of mobile atomic gravimeters to date with an accuracy of 39 nm/s^2, long-term stability of 0,5 nm/s^2 and short-term noise of 96 nm/s^2/(Hz)^1/2. These measurements highlight the unique properties of atomic sensors. The achieved level of performance in a transportable instrument enables new applications in geodesy and related Fields, such as continuous absolute gravity monitoring with a single instrument under rough environmental conditions.

Display panel and display device

Abstract: A display panel and a display device are provided. The display panel comprises a central region and peripheral regions. The peripheral regions are provided at two opposite ends of the display panel and have a first curvature; the central region is provided between the two opposite ends of the display panel and has a second curvature; and the second curvature of the central region is smaller than the first curvature of the peripheral regions.