First-principles computational design of unknown flat arsenene epitaxially grown on copper substrate

Kang, Joonhee,Noh, Seung Hyo,Han, Byungchan Elsevier 2019 APPLIED SURFACE SCIENCE - Vol.467 No.-

<P><B>Abstract</B></P> <P>Two-dimensional materials play essential roles in utilizing surface reactions, such as catalysts, adsorption and separation of chemicals. Especially, group-V mono-elemental materials are highlighted for transistors, optoelectronic devices, and mechanical sensors. Here, we identify unknown honeycomb-type arsenene epitaxially grown on copper substrate using first-principles density functional theory calculations. Key materials properties of lattice mismatch, thermodynamic stability, and surface transport properties are evaluated to verify the feasibility of the structural formation. Furthermore, <I>ab-initio</I> molecular dynamic simulations and scanning tunneling microscopy simulations clearly describe the mechanism of the initial nucleation and growth process. Electronic structure-level calculations characterize a strong covalency between each As atom pair. Our approach combining electronic structure calculations and thermodynamic/kinetic property predictions can be useful for quick screening and plausible design of new low-dimensional materials, which can efficiently functionalize emerging surface systems.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Graphene-like arsenene on Cu substrate was designed based on the DFT calculations. </LI> <LI> Thermodynamic and kinetic properties of flat honeycomb arsenene were investigated. </LI> <LI> AIMD and STM simulations were used to guide the experimental MBE process. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

First-Principles Study on the Thermal Stability of LiNiO₂ Materials Coated by Amorphous Al₂O₃ with Atomic Layer Thickness

Kang, Joonhee,Han, Byungchan American Chemical Society 2015 ACS APPLIED MATERIALS & INTERFACES Vol.7 No.21

<P>Using first-principles calculations, we study how to enhance thermal stability of high Ni compositional cathodes in Li-ion battery application. Using the archetype material LiNiO<SUB>2</SUB> (LNO), we identify that ultrathin coating of Al<SUB>2</SUB>O<SUB>3</SUB> (0001) on LNO(012) surface, which is the Li de-/intercalation channel, substantially improves the instability problem. Density functional theory calculations indicate that the Al<SUB>2</SUB>O<SUB>3</SUB> deposits show phase transition from the corundum-type crystalline (c-Al<SUB>2</SUB>O<SUB>3</SUB>) to amorphous (a-Al<SUB>2</SUB>O<SUB>3</SUB>) structures as the number of coating layers reaches three. Ab initio molecular dynamic simulations on the LNO(012) surface coated by a-Al<SUB>2</SUB>O<SUB>3</SUB> (about 0.88 nm) with three atomic layers oxygen gas evolution is strongly suppressed at <I>T</I> = 400 K. We find that the underlying mechanism is the strong contacting force at the interface between LNO(012) and Al<SUB>2</SUB>O<SUB>3</SUB> deposits, which, in turn, originated from highly ionic chemical bonding of Al and O at the interface. Furthermore, we identify that thermodynamic stability of the a-Al<SUB>2</SUB>O<SUB>3</SUB> is even more enhanced with Li in the layer, implying that the protection for the LNO(012) surface by the coating layer is meaningful over the charging process. Our approach contributes to the design of innovative cathode materials with not only high-energy capacity but also long-term thermal and electrochemical stability applicable for a variety of electrochemical energy devices including Li-ion batteries.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/aamick/2015/aamick.2015.7.issue-21/acsami.5b02572/production/images/medium/am-2015-025723_0001.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/am5b02572'>ACS Electronic Supporting Info</A></P>

First-Principles Computational Screening of Highly Active Pyrites Catalysts for Hydrogen Evolution Reaction through a Universal Relation with a Thermodynamic Variable

Kang, Joonhee,Hwang, Jeemin,Han, Byungchan American Chemical Society 2018 The Journal of Physical Chemistry Part C Vol.122 No.4

<P>Hydrogen gas has been regarded as a promising fuel for securing energy and environmental sustainability of our society. Accordingly, efficient and large scale production of hydrogen is central issue due to high activation barrier unless costly transition metal catalysts are used. Here, we screen optimum catalysts toward hydrogen evolution among cheap pyrites using first-principles density functional theory calculations and rigorous thermodynamic approach. A key thermodynamic state variable accurately describes the catalytic activity, of which the mechanism is unveiled by a universal linear correlation between kinetic exchange current density in hydrogen evolution reaction and thermodynamic adsorption energy of hydrogen atom over various pyrites. On the basis of the results, we propose a design principle for substantial tuning the catalytic performance.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jpccck/2018/jpccck.2018.122.issue-4/acs.jpcc.7b09294/production/images/medium/jp-2017-09294x_0006.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/jp7b09294'>ACS Electronic Supporting Info</A></P>

First-principles database driven computational neural network approach to the discovery of active ternary nanocatalysts for oxygen reduction reaction

Kang, Joonhee,Noh, Seung Hyo,Hwang, Jeemin,Chun, Hoje,Kim, Hansung,Han, Byungchan The Royal Society of Chemistry 2018 Physical chemistry chemical physics Vol.20 No.38

<P>An elegant machine-learning-based algorithm was applied to study the thermo-electrochemical properties of ternary nanocatalysts for oxygen reduction reaction (ORR). High-dimensional neural network potentials (NNPs) for the interactions among the components were parameterized from big dataset established by first-principles density functional theory calculations. The NNPs were then incorporated with Monte Carlo (MC) and molecular dynamics (MD) simulations to identify not only active, but also electrochemically stable nanocatalysts for ORR in acidic solution. The effects of surface strain caused by selective segregation of certain components on the catalytic performance were accurately characterized. The computationally efficient and precise approach proposes a promising ORR candidate: 2.6 nm icosahedron comprising 60% of Pt and 40% Ni/Cu. Our methodology can be applied for high-throughput screening and designing of key functional nanomaterials to drastically enhance the performance of various electrochemical systems.</P>

멀티스케일 계산을 위한 제일원리 전산 데이터 기반 머신 러닝 포텐셜 개발

강준희 ( Joonhee Kang ),한병찬 ( Byungchan Han ) 한국공업화학회 2019 공업화학전망 Vol.22 No.4

최근 가공할만한 성능의 슈퍼컴퓨터에 머신 러닝 기법을 연동한 인공 지능형 소재 정보학이 과학 기술 및 산업계에 새로운 연구개발 패러다임으로 급속히 확산되고 있다. 본 기고문에서는 이 기법의 성공에 핵심적 요소인 정확한 데이터베이스 구축을 위해 제일원리 전산을 적용하는 것과 이를 기반으로 소재를 구성하는 원소 간 인공 신경망 포텐셜을 만드는 방법을 소개하고자 한다. 이 연구 방법론은 나노 스케일 신소재 개발에 적용할 경우, 양자역학 수준의 정밀도로 순수 제일원리 전산 대비 100배 이상의 빠른 결과를 도출할 가능성이 있음을 예시한다. 이는 향후 다양한 산업계에 막대한 파급효과를 가져올 것으로 예상된다.

시각장애인을 위한 RFID 의약품 음성안내 단말기 개발

강준희(Joonhee Kang),안성수(Sung Soo Ahn),김진영(Jin Young Kim) 大韓電子工學會 2010 電子工學會論文誌 IE (Industry electronics) Vol.47 No.3

의약품 정보에 대한 접근이 쉽지 않은 시각장애인을 위해 의약품 정보 안내 단말기를 개발하였다. 본 연구에서는 시각장애인에게 의약품 관련 정보를 전달하기 위하여 RFID 기술을 사용하였다. 안내단말기로 의약품에 부착된 RFID 태그를 인식하면 태그의 고유 ID에 따라 단말기를 통해 음성으로 의약품 정보를 안내하도록 하였다. 의약품 정보는 식품의약품안전청에서 운영하는 이지드럭 사이트를 통해 의약품 정보를 취득하도록 하였다. 정보 안내 단말기는 휴대가 간편하도록 목걸이 형태로 제작 하였으며, 평상시에도 유용하게 사용할 수 있도록 mp3 재생기능을 탑재하였다. 본 연구에서는 단말기의 코어칩으로 ARM 계열의 Cortex M3 칩을 사용하였고, RFID 회로를 구현하기 위하여 저전력의 NXP의 MFRC523 칩셋을 사용하였다. MFRC523 칩은 모바일에 적용되는 저전력 기능이 탑재되어 있다. 음성회로를 구현하기 위해서는 VS1003B MP3 Decoder IC를 사용하였고 의약품 정보서버와의 무선 통신을 위해는 CC2500 칩셋을 사용하였다. RFID 프로토콜은 ISO 14443A 타입과 B타입을 모두 지원하도록 개발하여 다양한 프로토콜로 확장이 가능하도록 개발하였다. 본 시스템을 사용하면 시각장애인에게 의약품 정보를 편리하게 전달할 수 있어 시각장애인의 의약품 오남용을 줄일 수 있다. We developed a RFID terminal to voice guide the blind who have difficulties in reaching out to the pharmaceutical information. In this work, we used RFID technology to instruct the pharmaceutical information to the blind. The voice guidance reader was made to read the RFID tag attached to the drugs and announced the pharmaceutical information matching to the tag specific ID. We had the reader to obtain the pharmaceutical information from the ezDrug site operated by Korea Food & Drug Association. The voice guidance reader was fabricated as necklace type for the easy carry, and we added mp3 player as dual uses. ARM series Cortex M3 chip was used for the reader's core chip and low power MFRC523 chipset of NXP was used to construct RFID circuit. MFRC523 chip uses low power to meet the mobile application. We used VS1003B MP3 Decoder IC to make the voice generation circuit and CC2500 chipset for the wireless communication to the pharmaceutical information server. We also developed the system that can support ISO 14443A type and ISO 14443B type so that the system can be used to extend to various RFID protocols. Utilization of this system can conveniently convey the pharmaceutical information to the blind and reduce the drug abuse.

Strain Relaxation of Graphene Layers by Cu Surface Roughening

Kang, Jin Hyoun,Moon, Joonhee,Kim, Dong Jin,Kim, Yooseok,Jo, Insu,Jeon, Cheolho,Lee, Jouhahn,Hong, Byung Hee American Chemical Society 2016 NANO LETTERS Vol.16 No.10

<P>The surface morphology of copper (Cu) often changes after the synthesis of graphene by chemical vapor deposition (CVD) on a Cu foil, which affects the electrical properties of graphene, as the Cu step bunches induce the periodic ripples on graphene that significantly disturb electrical conduction. However, the origin of the Cu surface reconstruction has not been completely understood yet. Here, we show that the compressive strain on graphene induced by the mismatch of thermal expansion coefficient with Cu surface can be released by forming periodic Cu step bunching that depends on graphene layers. Atomic force microscopy (AFM) images and the Raman analysis show the noticeably longer and higher step bunching of Cu surface under multilayer graphene and the weaker biaxial compressive strain on multilayer graphene compared to monolayer. We found that the surface areas of Cu step bunches under multilayer and monolayer graphene are increased by similar to 1.41% and similar to 0.77% compared to a flat surface, respectively, indicating that the compressive strain on multilayer graphene can be more effectively released by forming the Cu step bunching with larger area and longer periodicity. We believe that our finding on the strain relaxation of graphene layers by Cu step bunching formation would provide a crucial idea to enhance the electrical performance of graphene electrodes by controlling the ripple density of graphene.</P>

Graphene layer-dependent copper step bunching

Joonhee MOON,Jin Hyoun KANG,Insu JO,Dong Jin KIM,Yooseok KIM,Cheollho JEON,Byung Hee HONG,Jouhahn LEE 한국진공학회 2016 한국진공학회 학술발표회초록집 Vol.2016 No.8

Development of an infant formula certified reference material for the analysis of organic nutrients

Lee, Joonhee,Kim, Byungjoo,Lee, Sun Young,Choi, Jongoh,Kang, Dukjin,Lee, Hwasim,Choi, KiHwan,Lee, Hyeyoung,Sim, Hee-Jung,Baek, Song-Yee,Lee, Honghee,Hyung, Seok-Won,Ahn, Seonghee,Seo, Dongwon,Hwang, J Applied Science Publishers 2019 Food chemistry Vol.298 No.-

<P><B>Abstract</B></P> <P>Infant formula certified reference material (CRM, KRISS CRM 108-02-003) were developed for the analysis of organic nutrients. The CRM is a milk-based infant formula powder, packaged at 14 g per unit. Ten thousand units were prepared and stored at −70 °C. For the certification of each nutrient, ten units were analyzed for simultaneous value-assignment and homogeneity test. Analytical methods used were isotope dilution mass spectrometry (IDMS) based on liquid chromatography mass spectrometer (LC/MS) or gas chromatography mass spectrometer (GC/MS) as higher-order reference methods.13 vitamins, 3 fatty acids, and total cholesterol were certified. The between-unit relative standard deviation of measurement results for each nutrient ranged 0.2% to 2.5%, showing very good homogeneity. The expanded relative uncertainties of the certified values ranged from 1% to 8%, indicating that they have higher-order metrological quality. The values of proximates (proteins, lipids, carbohydrates, water, and ash) were assigned through inter-laboratory comparisons.</P> <P><B>Highlights</B></P> <P> <UL> <LI> An infant formula CRMs for the analysis of organic nutrients was developed. </LI> <LI> Organic nutrients were certified by IDMS approaches as higher-order reference methods. </LI> <LI> Homogeneities and stability of the CRM were evaluated by IDMS approaches. </LI> <LI> Metrological qualities of the certified values were proved by their small uncertainties. </LI> <LI> Five proximates were value-assigned by interlaboratory comparison. </LI> </UL> </P>

One-Step Synthesis of N-doped Graphene Quantum Sheets from Monolayer Graphene by Nitrogen Plasma

Moon, Joonhee,An, Junghyun,Sim, Uk,Cho, Sung-Pyo,Kang, Jin Hyoun,Chung, Chul,Seo, Jung-Hye,Lee, Jouhahn,Nam, Ki Tae,Hong, Byung Hee Blackwell Publishing Ltd 2014 Advanced Materials Vol.26 No.21