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.

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

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>

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.

Sound Velocity and Van Der Waal's Force in Liquids

Jhon, Mu Shik The Korean Society of Oceanography 1969 韓國海洋學會誌 Vol.4 No.2

Tehoretical calculations of the sound velocity and Van der Waal's force in liquids according to significant structure theory are carried out. The excellent agreements between theory and experiment provide another piece of evidence for its general paalicability of the model. The technique to evaluate those properties may be useful to understand the some properties and structures of sea water.

A Calculation for the Viscosity of Fluids by Using Van Der Waals Equation of State

Jhon, Mu Shik,Chair, Tong Seek,Pak, Hyung Suk,Kim, Won Soo 한국화학공학회 1989 NICE Vol.7 No.3

A new equation for the viscosity of fluid is presented by considering that the viscosity is equal to the product of the shear pressure and the shear relaxation time. The shear pressure and the shear relaxation time are calculated thermodynamically by applying the van der Waals model for fluids. The calculated viscosities for various simple substances are in good agreements with those of the observed values through liquid-critical point-gas region.

Subacute Thyroiditis After Receiving the mRNA COVID-19 Vaccine (Moderna): The First Case Report and Literature Review in Korea

Jhon Min,Lee Sun-Ho,Oh Tae-Hoon,Kang Ho-Cheol 대한의학회 2022 Journal of Korean medical science Vol.37 No.6

Subacute thyroiditis (SAT) is a painful thyroiditis that often requires steroid therapy. Here, we report the first case of severe SAT in a patient who received the first dose of mRNA coronavirus disease 2019 (COVID-19) vaccination. A 34-year-old man without a viral prodrome felt a lump when swallowing 5 days after his first dose of mRNA-1273 (Moderna) vaccination. Ten days after vaccination, the patient visited the hospital and was advised to rest and take nonsteroidal anti-inflammatory drugs. He revisited the hospital 10 days later as symptoms aggravated with anterior neck pain, headache, fatigue, muscle weakness, and weight loss. Thyroid hormone levels and inflammatory markers were consistent with thyrotoxicosis. A thyroid ultrasound scan revealed typical SAT findings. His symptoms rapidly improved after receiving prednisone. A week later, the patient successfully completed his second dose of the vaccine. The thyroid function test results were nearly normal 1 month after the completion of the vaccination. We report this case to raise awareness of the occurrence of SAT after COVID-19 vaccination. As the risk of COVID-19 outweighs the minor risks of the vaccine, managing the side effects of the first vaccine dose is crucial to complete COVID-19 vaccination.

A sub-0.5 V operating RF low noise amplifier using tunneling-FET

Jhon, Hee-Sauk,Jeon, Jongwook,Kang, Myunggon,Choi, Woo Young Institute of Pure and Applied Physics 2017 Japanese Journal of Applied Physics Vol. No.

<P>60 nm tunneling FET (TFET) based low noise amplifier (LNA) with a sub-0.5 V supply voltage for 2.4GHz WSN application has been evaluated systematically from device level up to circuit level design. With the help of TFET's unique property of high subthreshold swing, it shows that substantial increase of gain performance was confirmed compared to that of conventional LNA using 60nm bulk MOSFET at ultra-low voltage (ULV) condition. From the simulation study, TFET LNA at 0.4 V operating voltage has the gain of 15.1 dB and noise figure 50 of 3.5 dB while dissipating DC power consumption of 0.41 mW. (C) 2017 The Japan Society of Applied Physics</P>