Orientation dependence of the fracture behavior of graphene

Jhon, Y.I.,Jhon, Y.M.,Yeom, G.Y.,Jhon, M.S. Pergamon Press ; Elsevier Science Ltd 2014 Carbon Vol.66 No.-

Graphene has unique mechanical properties in that it is simultaneously very strong and stretchy, which severely hampers the prediction of its orientation-dependent fracture behavior based on conventional theories used for common brittle or ductile materials. For the first time, by exploring the entire range of available tensile orientations, this study reveals the unique anisotropic fracture response of graphene using molecular dynamics simulations. We found that, as the uniaxial tensile direction rotates from armchair (0<SUP>o</SUP>) to zigzag orientation (30<SUP>o</SUP>), both the tensile strength and strain remain almost constant up to an orientation angle of ~12<SUP>o</SUP>, then they rapidly increase (exponential growth), resulting in a remarkable degradation of the tensile strength compared to brittle fracture counterpart (inverse-sinusoidal growth). This typical fracture pattern holds for 100-700K. We propose a model that can explain its physical origin in good agreement with the simulation results. We also found that the elastic behavior of graphene is quasi-isotropic for all tensile orientations, in contrast to its anisotropic fracture behavior. Using indentation simulations of graphene, we showed that the anisotropic/isotropic features of fracture/elasticity are also well-preserved in the two-dimensional tensile systems but its fracture anisotropicity is greatly attenuated due to the inherent sixfold symmetry of graphene.

Topological Insulators for Mode-Locking of 2-μm Fiber Lasers

Jhon, Young In,Lee, Jinho,Jhon, Young Min,Lee, Ju Han IEEE 2018 IEEE journal of selected topics in quantum electro Vol.24 No.5

<P>We performed density functional theory calculations for the topological insulators (TIs) of Bi<SUB>2</SUB>Se<SUB>3 </SUB> and CoSb<SUB>3</SUB> (skutterudite) in a comparison with Bi<SUB>2</SUB>Te<SUB>3</SUB> and In<SUB>2</SUB>Co<SUB>4 </SUB>Sb<SUB>12</SUB> (filled skutterudite) to explore whether the former TIs can serve as saturable-absorption materials for laser mode-locking at the wavelengths of 2 μm and beyond. The calculated electronic-band structures and optical-absorption spectra indicate the potential of these TIs in terms of midinfrared saturable-absorption applications. Especially, in consideration of the film and bulk forms of Bi<SUB>2</SUB>Se<SUB>3 </SUB> and Bi<SUB>2</SUB>Te<SUB>3</SUB>, we investigated the electronic and/or optical properties of the metallic surface states and the semiconducting interior states, respectively. They exhibited an excellent broadband operability regardless of the state, and particularly, we noted a linearly dispersive relation around the Fermi levels of all of the electrons of the Bi<SUB>2</SUB>Se<SUB>3</SUB> surface in both the conduction and valence bands, whereas this is not evident for Bi<SUB>2</SUB>Te<SUB>3</SUB>. Assuming the importance of linear dispersion for a fast electronic relaxation, and considering the decent oxidation resistance of the Bi<SUB>2</SUB>Se<SUB>3</SUB> surface, we suggest that Bi<SUB>2</SUB>Se<SUB>3</SUB> is superior to Bi<SUB>2</SUB>Te<SUB>3</SUB> for midinfrared mode-locking. A review of the experimental studies regarding TI-based 2-μm saturable absorbers that have been performed so far is presented, and the discussion and rationalization of the possible universality of TIs regarding mid- to far-infrared passive mode lockers results in the suggestion of a new CoSb<SUB>3</SUB>-TI-based saturable absorber.</P>

The mechanical responses of tilted and non-tilted grain boundaries in graphene

Jhon, Y.I.,Zhu, S.E.,Ahn, J.H.,Jhon, M.S. Pergamon Press ; Elsevier Science Ltd 2012 Carbon Vol.50 No.10

Various mechanical characteristics of tilted and non-tilted grain boundaries in graphene were investigated under tension and compression in directions perpendicular and parallel to the grain boundaries using molecular dynamics simulation. In contrast to the non-tilted grain boundary and the pristine graphene, the mechanical response of tilted grain boundary was observed to be quite unique under perpendicular tension, exhibiting distinct crack propagation prior to tensile failure and the subsequent pattern of incomplete fracture. These features are manifested as a remarkable decrease in the slope and a rugged pattern in the stress-strain curves. The characteristic of incomplete fracture was striking especially for large misorientation angles with formation of long monoatomic carbon chains, suggesting a methodology for feasible production of the monoatomic carbon chains that have been difficult to synthesize and extract. Under perpendicular compression, the folding of the sheet occurred consistently along grain boundaries during the entire process, indicating a tunable folding, while the folding line wandered extensively for pristine graphene. Under parallel compression, we found that folding along grain boundaries disturbed the bending of the graphene substantially for intrinsic reinforcement.

Understanding time-resolved processes in atomic-layer etching of ultra-thin Al₂O₃ film using BCl₃ and Ar neutral beam

Jhon, Young I.,Min, Kyung S.,Yeom, G. Y.,Jhon, Young Min American Institute of Physics 2014 APPLIED PHYSICS LETTERS Vol.105 No.9

Thermodynamic Properties of Aliphatic and Aromatic Hydrocarbons in Liquid Water

성용길,김은식,전무식,Sung Yong Kiel,Kim Un Shik,Jhon Mu Shik Korean Chemical Society 1972 대한화학회지 Vol.16 No.5

지방족 및 방향족 탄화수소의 수용액을 Jhon 등이 제창한 liquid water의 significant structure theory 를 이용하여 연구하였으며 Helmholtz free energy, internal energy, entropy, heat capacity 등의 열역학적 성질을 계산하였다. 계산결과는 문헌에 발표된 실험치와 잘 일치됨을 볼 수 있다 The aqueous solutions of aliphatic and aromatic hydrocarbons have been studied on the basis of the significant structure theory of liquid water proposed by Jhon, et al. The thermodynamic properties such as Helmholtz free energy, internal energy entropy, and heat capacity have been calculated. The results show good agreements with the experiments in the literature.

Theoretical Calculation of Hydration Number and Activity Coefficients of Salts in Concentrated Electrolyte Solutions

성용길,전무식,Yong Kil Sung,Mu Shik Jhon Korean Chemical Society 1970 대한화학회지 Vol.14 No.2

The extension of the theory of the electrolyte solution to the calculation of the hydration number and the mean activity coefficient of some 1:1 electrolytes in the concentrated solutions has been made. In this derivation, the hydration number has been calculated from the equation of the dielectric constant proposed by Hobbs, Jhon, and Eyring, and the mean activity coefficient from the theoretical formula developed by Jhon and Eyring. The agreement between theory and experiment over a.wide concentration range is quite satisfactory.

저 가격 0.18-㎛ 혼성신호 CMOS공정에 기반한 WSN용 2.4-GHz 밴드 VCO설계

Jhon, Heesauk,An, Chang-Ho,Jung, Youngho 한국정보통신학회 2020 한국정보통신학회논문지 Vol.24 No.2

This paper demonstrated a voltage-controlled oscillator (VCO) using cost-effective (1-poly 6-metal) mixed signal standard CMOS process. To have the high-quality factor inductor in LC resonator with thin metal thickness, patterned-ground shields (PGS) was adopted under the spiral to effectively reduce the ac current of low resistive Si substrate. And, because of thin top-metal compared with that of RF option (2 ㎛), we make electrically connect between the top metal (M6) and the next metal (M5) by great number of via array along the metal traces. The circuit operated from 2.48 GHz to 2.62 GHz tuned by accumulation-mode varactor device. And the measured phase noise of LC VCO has -123.7 dBc/Hz at 1MHz offset at 2.62 GHz and the dc-power consumption shows 2.07 mW with 1.8V supply voltage, respectively.

The Increase of Activity of Erythrocyte Glucose Transporter by Carboxyl Methylation

Jhon, Gil-Ja,Hah, Jong-Sik 이화여자대학교 생명과학연구소 1991 생명과학연구논문집 Vol.2 No.-

Protein carboxyl methyltransferase(EC 2.1.1.77)에 의한 메칠화반응의 생리적 기능을 알아보기 위해 사람 적혈구에서 포도당 이동체를 분리하여 메칠화시켰다. 메칠화 됨으로써 이동체의 포도당 이동능력이 메칠화 되지 않은 것에 비해 34% 증가하였다. 당뇨병 쥐의 적혈구에서 포도당 이동체가 정상 쥐의 것에 비해 54% 밖에 존재하지 않으나 메칠화가 많이 되었다. 이러한 결과로 당뇨병 쥐의 포도당 이동체가 메칠화 됨으로써 포도당의 이동능력이 증가되었다고 설명할 수 있다. 따라서 포도당 이동체의 메칠화는 비정상 아미노산에 작용하여 이동체의 포도당 운반능력을 증가시킨 것으로 추정할 수 있다. For the purpose of showing the physiological role of methyl esterification by protein carboxyl methyltransferase as a post-translational modification, the glucose transporter of human erythrocyte membrane was partially purified using octyl glucoside. The activity of human transporter was increased by 34% as a result of the methylation of transporter. The increase of methylatability and decrease(47%)of the amount of glucose transporter in erythrocyte of diabetic rats could be explained from the above result. It was also found that a small amount of glucose transporter (about 1/20 of human erythrocytes) was existed in rat erythrocytes. The physiological significance of this methylation is not clear, but our results support that protein carboxyl methyltransferase functions in increasing the activity of damaged erythrocyte glucose transporter.

0.7 V supply highly linear subthreshold low-noise amplifier design for 2.4 GHz wireless sensor network applications

Jhon, Hee-Sauk,Jung, Hakchul,Koo, Minsuk,Song, Ickhyun,Shin, Hyungcheol Wiley Subscription Services, Inc., A Wiley Company 2009 MICROWAVE AND OPTICAL TECHNOLOGY LETTERS - Vol.51 No.5

<P>A low supply voltage and highly linear subthreshold CMOS low noise amplifier (LNA) for 2.4 GHz wireless sensor network applications is presented in this letter. We applied multiple gated transistor (MGTR) technique in subthreshold region to compensate the linearity degradation of low supply cascode topology. Moreover, the feedback capacitor, C<SUB>f</SUB> is used to enhance the power gain of amplifier without additional dc-power dissipation. The proposed LNA has gain of 13.1 dB, noise figure (NF) of 3.8 dB, and −2.5 dBm IIP3 while dissipating only 0.49 mW from 0.7 V supply. The LNA has been designed using a 0.13 μm 1P8M standard CMOS process with top metal thickness of 3.3 μm. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 1316–1320, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24333</P>

Gas Chromatography-Based Assay for the Quantification of Protein Carboxyl Methyltransferase at the Picomole Level

Jhon, Gil-Ja,Lee, Sun-Wha 梨花女子大學校 韓國生活科學硏究院 1988 韓國生活科學硏究院 論叢 Vol.42 No.-

방사성 동위원소를 사용하지 않고 Protein Carboxyl Methyltransferase를 분석하는 방법을 연구하였다. 이 효소에 의해 생성되는 Protein Methylester를 알칼리 용액에서 가수분해 시켜, 나오는 Methanol을 Gas Chromatography(HP-20M Column)로 pmol 단위 가지 정량이 가능하였다. 그러나 방사성 동위원소를 사용한 분석법 보다는 감도가 떨어졌다. A new GC-based assay for the indirect determination of the extent of protein carboxyl methyltransferase without radioisotope is described. The rationale is founded on the GC detection of methanol that results from cleavage of protein methylester at the high pH treatment. Protein carboxyl methyltransferase (S-adenosylmethionine:protein carboxyl methyltransferase, EC 2.1.1.77) methyl esterifies free carboxyl groups of proteins with S-adenosyl-L-methionine(SAM) as the methyl donor. The function of this enzyme is not clear but it has been suggested that PCM plays a surveillant role in the cell to identify abnormal proteins and may participate in their degradation or rejuvenation. (Johnson et al., 1987; McFadden and Clarke, 1982; Murray and Clarke, 1986). The enzyme is widely distributed in mammalian organs with higher activities in testis, brain, pituitary gland, and blood (Paik and Kim, 1971; Diliberto, Jr. and Axelrod, 1974; Kim, 1974). A striking feature of the reaction is the formation of an unstable protein methylester that yields methanol nonenzymatically in weak aqueous alkaline solution. Owing to this methanol formation from the immediate enzymatic product, the enzyme has also been referred to as "methanol-forming enzyme" (Kim, 1973; Diliberto, Jr. and Axlrod, 1974). Various techniques have been attempted to quantify protein carboxyl methyltransferase. By far the most accurate and certain technique is by use of stable isotope. Two techniques have been used to quantify the amounts of protein carboxyl methyltransferase by use of radioisotope, ^14C-SAM: (ⅰ) a direct quantification of the incorporated (^14C) methyl groups into TCA-precipitable protein(Kim and Paik, 1970; Kim et al., 1975) and (ⅱ) indirectly by extracting the alkaline-hydrolyzed methanol form protein methyl ester by isoamyl alcohol (Jamaluddin et al., 1976; Kim and Paik, 1978). We attempt the quantification of protein carboxyl methyltransferase with radio-isotopes. In this report we describe a new assay method for use cold SAM. The method is based on the GC detection of methanol that results from the cleavage of unstable methylester at the alkaline solution.