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Kim, Donghwi,Kim, Sungjune,Son, Seungwoo,Jung, Maeng-Joon,Kim, Sunghwan American Chemical Society 2019 ANALYTICAL CHEMISTRY - Vol.91 No.12
<P>In this study, Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS), combined with quadrupolar detection (QPD), was applied for online liquid chromatography (LC) MS analysis of natural organic matter (NOM). Although FT-ICR MS has emerged as an important analytical technique to study NOM, there are few previous reports on online LC FT-ICR MS analysis of NOM due to the long acquisition time (2-8 s) required to obtain high-resolution mass spectra. The QPD technique provides a critical advantage over the conventional dipolar detection (DPD) technique for LC-MS analysis because a spectrum with the same resolving power can be obtained in approximately half the acquisition time. QPD FT-ICR MS provides resolving powers ([FORMULA OMISSION]) of ∼300000 and 170000 at <I>m</I>/<I>z</I> 400 with acquisition times per scan of 1.2 and 0.8 s, respectively. The reduced acquisition time per scan allows increased number of acquisitions in a given LC analysis time, resulting in improved signal to noise (<I>S</I>/<I>N</I>) ratio and dynamic range in comparison to conventional methods. For example, 40% and 100% increases in the number of detected peaks were obtained with LC QPD FT-ICR MS, in comparison to conventional LC DPD FT-ICR MS and direct-injection FT-ICR MS. It is also possible to perform more quantitative comparison and molecular level investigation of NOMs with 2 μg of a NOM sample. The data presented herein demonstrate a proof of principle that QPD combined with LC FT-ICR MS is a sensitive analytical technique that can provide comprehensive information about NOM.</P> [FIG OMISSION]</BR>
Kim, Donghwi,Yim, Un Hyuk,Kim, Byungjoo,Cha, Sangwon,Kim, Sunghwan American Chemical Society 2017 ANALYTICAL CHEMISTRY - Vol.89 No.17
<P>Sensitivity is an important factor determining successful mass spectrometry (MS) analysis of metabolome, protein, drugs, and environmental samples. Currently, nano-electrospray ionization (ESI) is widely used as a sensitive ionization method. However, application of nano-ESI is limited to polar molecules and there is no atmospheric pressure ionization technique developed that can be used for MS analysis of low- and nonpolar compounds with sensitivity that can match with nano-ESI. Herein, we propose paper spray chemical ionization (PSCI) as an ionization technique that can be used to analyze low- and nonpolar aromatic compounds with high sensitivity. PSCI is based on paper spray ionization utilizing corona discharge phenomenon. PSCI can sensitively and quantitatively detect down to picogram (or femtomole) levels of low and nonpolar aromatic compounds.</P>
Kim, Donghwi,Lee, Joonhee,Kim, Byungjoo,Kim, Sunghwan American Chemical Society 2018 ANALYTICAL CHEMISTRY - Vol.90 No.20
<P>In this study, paper-based ionization techniques-paper spray ionization (PSI) and paper spray chemical ionization (PSCI)-were evaluated and applied for high-resolution mass spectrometry (MS)-based analysis of natural organic matter (NOM). Methanol:isopropyl alcohol (50:50, v/v) and ethanol emerged as good spray solvents for PSI, and hexane:dichloromethane (50:50, v/v) was a good spray solvent for PSCI. PSI-MS spectra could be obtained with NOM samples on the microgram scale, which is a critical advantage over conventional electrospray ionization (ESI)-MS when the amount of available sample is limited. In addition, PSI is more tolerant to salt contamination than ESI for NOM analysis. PSCI preferentially ionized less polar compounds, which may not be ionized well using ESI. Therefore, PSCI can be used as a complementary method to ESI or PSI. Comparison of the numbers of peaks obtained with ESI-, PSI-, and PSCI-MS showed that employing PSI and PSCI can increase the number of compounds that can be detected by high-resolution MS. In conclusion, the data presented in this study showed that PSI and PSCI are suitable ionization techniques for NOM analysis. To the best of our knowledge, this is the first study evaluating and applying PSI and PSCI for NOM analysis.</P> [FIG OMISSION]</BR>
Epitaxial van der Waals Contacts between Transition-Metal Dichalcogenide Monolayer Polymorphs
Lee, Chang-Soo,Oh, Seung Jae,Heo, Hoseok,Seo, Seung-Young,Kim, Juho,Kim, Yong Hyeon,Kim, Donghwi,Ngome Okello, Odongo Francis,Shin, Hocheol,Sung, Ji Ho,Choi, Si-Young,Kim, Jun Sung,Kim, Jong Kyu,Jo, M American Chemical Society 2019 Nano letters Vol.19 No.3
<P>We have achieved heteroepitaxial stacking of a van der Waals (<I>vdW</I>) monolayer metal, 1T’-WTe<SUB>2</SUB>, and a semiconductor, 2H-WSe<SUB>2</SUB>, in which a distinctively low contact barrier was established across a clean epitaxial <I>vdW</I> gap. Our epitaxial 1T’-WTe<SUB>2</SUB> films were identified as a semimetal by low temperature transport and showed the robust breakdown current density of 5.0 × 10<SUP>7</SUP> A/cm<SUP>2</SUP>. In comparison with a series of planar metal contacts, our epitaxial <I>vdW</I> contact was identified to possess intrinsic Schottky barrier heights below 100 meV for both electron and hole injections, contributing to superior ambipolar field-effect transistor (FET) characteristics, i.e., higher FET mobilities and higher on-off current ratios at smaller threshold gate voltages. We discuss our observations around the critical roles of the epitaxial <I>vdW</I> heterointerfaces, such as incommensurate stacking sequences and absence of extrinsic interfacial defects that are inaccessible by other contact methods.</P> [FIG OMISSION]</BR>
Kim, Dongwook,Quagliato, Luca,Park, Donghwi,Kim, Naksoo Elsevier 2019 Wear: An international journal on the science and Vol.420 No.-
<P><B>Abstract</B></P> <P>The research presented in this paper deals with the development of an integrated numerical model for the estimation of the incremental surface wear and damage accumulation in linear slide rails. The target is the estimation of the progressive increment of the end-point deflection of the last member of the slide rail during the operational lifetime. The surface abrasion is accounted for by utilizing a modified Archard equation with the aim of estimating the amount of wear along the vertical direction of the slide rails members. In addition to that, the Lemaitre damage model is utilized for the estimation rolling contact fatigue (pitting), considering the total strain and not only the plastic strain. Experiments have been carried out on a small-scale slide rail testing machine in order to define the wear increment on the slide rail inner groove for increasing number of cycles and, accordingly, estimate the modified Archard model constants. In addition to that, the wear parameters for the Lemaitre damage model have been inversely calibrated from the results of tensile tests. A numerical model has been implemented in ABAQUS/Explicit and an external geometry-update subroutine has been employed to update the geometry of the slide rail groove for increasing number of cycles as a consequence of wear and roll contact fatigue. The comparison between numerical and experimental results on real rails have shown a maximum deviation equal to 12.9%, supporting the reliability of the proposed approach.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Modified Archard wear model to estimate the vertical wear. </LI> <LI> Modified Lemeitre damage model to include the elastic strain contribution. </LI> <LI> Numerical model to estimate the rail members deflection due to wear and RCF. </LI> <LI> Reduction of the computational time due to external program. </LI> <LI> Reliable experimental-numerical approach for the slide rail lifetime prediction. </LI> </UL> </P>