이차원 자성체를 활용한 스핀트로닉스

최준우 한국자기학회 2024 韓國磁氣學會誌 Vol.34 No.3

최근 자기적 성질을 가진 반데르발스 이차원물질들이 발견되면서, 이차원 자성체에서 나타나는 저차원 자성에 대한 연구가 활발히 진행되고 있다. 나아가, 이차원 자성체를 활용한 스핀트로닉스 소자도 많이 구현되었다. 저차원 자성 연구와 스핀소자 개발을 위해 기존에 많이 활용된 자성 초박막에 비해, 이차원 자성체들은 몇 가지 고유한 특성과 장점이 있다. 이차원 자성체와 다양한 성질의 이차원물질 간 이종접합구조나 비틀림 격자구조 제작을 통해 여러 자기적 특성들을 변조시키는 계면 공정이 가능하다. 뿐만 아니라, 층간 약한 상호작용으로 인해 기존 자성박막과는 상이한 스핀 수송 현상이 나타날 것을 기대할 수 있다. 본 해설논문에서는 이차원 자성체를 활용한 스핀트로닉스(스핀밸브, 자기터널접합, 전압제어 스핀 소자, 스핀필터 소자, 스핀-궤도 토크 소자 등)의 최근 대표적 연구 결과들에 대해 소개하고자 한다. The recent discovery of van der Waals two-dimensional magnetic materials has stimulated research on emergent low dimensional magnetic phenomena in these materials. Furthermore, many spintronic devices utilizing two-dimensional magnetic materials have been realized. Two-dimensional magnets offer several unique characteristics and advantages compared to ultra-thin magnetic films, which has been the material-of-choice for spintronic applications. Heterostructures and twisted lattices between two-dimensional magnets and various families of two-dimensional materials, with clean and well-defined interfaces, can be fabricated, which enable interfacial engineering of many magnetic properties. In addition, the weak layer-to-layer coupling suggest that spin transport properties of the layered materials might be distinct from conventional magnetic thin films. In this review article, we highlight selected research results in two-dimensional-magnet-based spintronics, focusing on spin valves, magnetic tunnel junctions, spin filter devices, and spin-orbit torque devices.

Three-Dimensional Atomistic Tomography of W-Based Alloyed Two-Dimensional Transition Metal Dichalcogenides

Seo, Juyeon,Hwang, Kyo-Jin,Baik, Sung-Il,Lee, Suryeon,Cho, Byungjin,Jo, Euihyun,Choi, Minseok,Hahm, Myung Gwan,Kim, Yoon-Jun American Chemical Society 2018 ACS APPLIED MATERIALS & INTERFACES Vol.10 No.36

<P>Increased interest in two-dimensional (2D) materials and heterostructures for use as components of electrical devices has led to the use of an atomically mixed phase between semiconducting and metallic transition metal dichalcogenides that exhibited enhanced interfacial characteristics. To understand the lattice structure and properties of 2D materials on the atomic scale, diverse characterization methods such as Raman spectroscopy, high-resolution transmission electron microscopy (HR-TEM), and X-ray photoemission spectroscopy (XPS) have been applied. However, determination of the exact chemical distribution, which is a critical factor for the interfacial layer, was hindered by limitations of these typical methods. In this work, atom-probe tomography (APT) was introduced for the first time to analyze the three-dimensional atomic distribution and composition variation of the atomic-scale multilayered alloy structure W<I><SUB>x</SUB></I>Nb<SUB>(1-<I>x</I>)</SUB>Se<SUB>2</SUB>. Composition profiles and theoretical calculations for each atom demonstrated the reaction kinetics and stoichiometric inhomogeneity of the W<I><SUB>x</SUB></I>Nb<SUB>(1-<I>x</I>)</SUB>Se<SUB>2</SUB> layer. The role of the intermediate layer was investigated by fabrication of a WSe<SUB>2</SUB>-based field-effect transistor. Introduction of W<I><SUB>x</SUB></I>Nb<SUB>(1-<I>x</I>)</SUB>Se<SUB>2</SUB> between metallic NbSe<SUB>2</SUB> and semiconducting WSe<SUB>2</SUB> layers resulted in improved charge transport with lowering of the contact barrier.</P> [FIG OMISSION]</BR>

van der Waals Layered Materials: Opportunities and Challenges

Duong, Dinh Loc,Yun, Seok Joon,Lee, Young Hee American Chemical Society 2017 ACS NANO Vol.11 No.12

<P>Since graphene became available by a scotch tape technique, a vast class of two-dimensional (2D) van der Waals (vdW) layered materials has been researched intensively. What is more intriguing is that the well-known physics and chemistry of three-dimensional (3D) bulk materials are often irrelevant, revealing exotic phenomena in 2D vdW materials. By further constructing heterostructures of these materials in the planar and vertical directions, which can be easily achieved <I>via</I> simple exfoliation techniques, numerous quantum mechanical devices have been demonstrated for fundamental research and technological applications. It is, therefore, necessary to review the special features in 2D vdW materials and to discuss the remaining issues and challenges. Here, we review the vdW materials library, technology relevance, and specialties of vdW materials covering the vdW interaction, strong Coulomb interaction, layer dependence, dielectric screening engineering, work function modulation, phase engineering, heterostructures, stability, growth issues, and the remaining challenges.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/ancac3/2017/ancac3.2017.11.issue-12/acsnano.7b07436/production/images/medium/nn-2017-074362_0021.gif'></P>

Synthesis of a Carbonaceous Two-Dimensional Material

Kim, Taewoo,Lee, Junho,Lee, Geonhui,Lee, Jaewoo,Song, Hyelynn,Jho, Jae Young,Lee, Hong H.,Kim, Yong Hyup American Chemical Society 2019 ACS APPLIED MATERIALS & INTERFACES Vol.11 No.24

<P>Despite tremendous accomplishments achieved in 2D materials, little progress has been made in carbonaceous 2D materials beyond graphene and graphene oxide. Here, we report a 2D material of carbonaceous nanoplates (CANP). The bottom-up synthesis of CANP is green, separation-free, and massive. The nanoplates are 2 to 3 monolayers thick with an average interlayer spacing of 0.57 nm. The synthesis involves viscosity-aided two-dimensional growth of fragmented glucose derivatives and leads to the complete conversion of glucose to the 2D nanoplates. Application tests demonstrate the usefulness of the affordable 2D material.</P> [FIG OMISSION]</BR>

Measuring the optical permittivity of two-dimensional materials without <i>a priori</i> knowledge of electronic transitions

Jung, Gwang-Hun,Yoo, SeokJae,Park, Q-Han De Gruyter 2019 Nanophotonics Vol.8 No.2

<P><B>Abstract</B></P><P>We propose a deterministic method to measure the optical permittivity of two-dimensional (2D) materials without<I>a priori</I>knowledge of the electronic transitions over the spectral window of interest. Using the thin-film approximation, we show that the ratio of reflection coefficients for s and p polarization can give a unique solution to the permittivity of 2D materials within the measured spectral window. The uniqueness and completeness of our permittivity measurement method do not require<I>a priori</I>knowledge of the electronic transitions of a given material. We experimentally demonstrate that the permittivity of monolayers of MoS<SUB>2</SUB>, WS<SUB>2</SUB>, and WSe<SUB>2</SUB>in the visible frequency range can be accurately obtained by our method. We believe that our method can provide fast and reliable measurement of the optical permittivity of newly discovered 2D materials.</P>

Hole Defects on Two-Dimensional Materials Formed by Electron Beam Irradiation: Toward Nanopore Devices

Park, Hyo Ju,Ryu, Gyeong Hee,Lee, Zonghoon Korean Society of Microscopy 2015 Applied microscopy Vol.20 No.1

Two-dimensional (2D) materials containing hole defects are a promising substitute for conventional nanopore membranes like silicon nitride. Hole defects on 2D materials, as atomically thin nanopores, have been used in nanopore devices, such as DNA sensor, gas sensor and purifier at lab-scale. For practical applications of 2D materials to nanopore devices, researches on characteristics of hole defects on graphene, hexagonal boron nitride and molybdenum disulfide have been conducted precisely using transmission electron microscope. Here, we summarized formation, features, structural preference and stability of hole defects on 2D materials with atomic-resolution transmission electron microscope images and theoretical calculations, emphasizing the future challenges in controlling the edge structures and stabilization of hole defects. Exploring the properties at the local structure of hole defects through in situ experiments is also the important issue for the fabrication of realistic 2D nanopore devices.

Recent advanced in energy harvesting and storage applications with two-dimensional layered materials

Han, Sang A,Sohn, Ahrum,Kim, Sang-Woo Elsevier 2017 Flatchem Vol.6 No.-

<P><B>Abstract</B></P> <P>Because of the depletion of existing fossil fuels and environmental pollution issues, securing sustainable green energy is globally becoming an important issue. To solve this problem, various complementary measures, such as solar cells, fuel cells and thermal power generation are being studied. Also, everything becomes user-centered, society is increasingly dependent on larger amount of data. In order to analyze such large amount of data and provide customized services to users, a small, semi-permanent power source that is continuously driven is required. Because current technologies have limitations on life-time, size, and mechanical properties, it is very important to develop next-generation ultra-compact, light-weight energy generating devices. Two-dimensional (2D) layered materials, such as graphene, hexagonal boron nitride, and transition metal dichalcogenides have shown potential as peculiar energy materials due to their unique properties. In this paper, we will give an overall review about recent progress in energy applications of 2D-based layered structure materials. First, a brief introduction of synthesis method and characterization of 2D layered materials are presented. Then, the energy application of 2D layered structure materials will be discussed in the field of batteries, solar cells, hydrogen storage, supercapacitors, and nanogenerators.</P> <P><B>Highlights</B></P> <P> <UL> <LI> We discuss the recent advances that have made in both the energy harvesting and the storage field, including batteries, solar cells, hydrogen production and storage, supercapacitors, and nanogenerators using the two-dimensional (2D) layered materials. </LI> <LI> We give an overall review about recent progress in energy applications of 2D-based layered structure materials. </LI> <LI> A brief introduction of synthesis method and characterization of 2D layered materials are presented. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>Two-dimensional layered materials provide new challenges and opportunities for researchers in various energy fields such as batteries, solar cell, supercapacitor, hydrogen storage, and nanogenerators.</P> <P>[DISPLAY OMISSION]</P>

Novel electrodes and gate dielectrics for field-effecttransistors based on two-dimensional materials

송인택 대한화학회 2023 Bulletin of the Korean Chemical Society Vol.44 No.6

Two-dimensional (2D) materials are atomically thin materials that show quan-tum confinement effect. They have been studied as promising materials forfield-effect transistors (FETs). The fabrication of an FET mainly concerns how todeposit metal electrodes and dielectrics onto the 2D material channel. Andconventional fabrication processes are not optimized for novel applications of2D FETs. This review aims to introduce recent studies regarding novel elec-trodes and dielectrics for 2D FETs. The devices made by these approachesshow comparable performance to conventional FETs. And they feature newapplications and easy fabrication. This review covers the topics in two sections:evaporation-free electrodes and nonoxide dielectrics. The former covers elec-trodes prepared without direct deposition of metals using evaporators or sput-ters. The latter encompasses alternatives to oxide dielectrics. These topicswould be beneficial to realize the intrinsic properties of 2D materials and toassist fundamental research with prototyping FETs on a tabletop.

Effects of two-dimensional materials on human mesenchymal stem cell behaviors

Suhito, Intan Rosalina,Han, Yoojoong,Kim, Da-Seul,Son, Hyungbin,Kim, Tae-Hyung Academic Press 2017 Biochemical and biophysical research communication Vol. No.

<P><B>Abstract</B></P> <P>Graphene, a typical two-dimensional (2D) material, is known to affect a variety of stem cell behaviors including adhesion, spreading, growth, and differentiation. Here, we report for the first time the effects of four different emerging 2D materials on human adipose-derived mesenchymal stem cells (hADMSCs). Graphene oxide (GO), molybdenum sulfide (MoS<SUB>2</SUB>), tungsten sulfide (WS<SUB>2</SUB>), and boron nitride (BN) were selected as model two-dimensional materials and were coated on cell-culture substrates by a drop-casting method. Acute toxicity was not observed with any of the four different 2D materials at a low concentration range (<5 μg/ml). Interestingly, the 2D material-modified substrates exhibited a higher cell adhesion, spreading, and proliferation when compared with a non-treated (NT) substrate. Remarkably, in the case of differentiation, the MoS<SUB>2</SUB>-, WS<SUB>2</SUB>-, and BN-modified substrates exhibited a better performance in terms of guiding the adipogenesis of hADMSCs when compared with both NT and GO-modified substrates, based on the mRNA expression level (qPCR) and amount of lipid droplets (ORO staining). In contrast, the osteogenesis was found to be most efficiently induced by the GO-coated substrate (50 μg/mL) among all 2D-material coated substrates. In summary, 2D materials could act as favorable sources for controlling the stem cell growth and differentiation, which might be highly advantageous in both biomedical research and therapy.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The toxicity of four different two-dimensional materials on hADMSCs was studied. </LI> <LI> All four different 2D materials enhanced the cell adhesion, spreading and proliferation. </LI> <LI> WS<SUB>2</SUB>-, MoS<SUB>2</SUB>-, and BN-coated substrates enhanced the adipogenesis of hADMSCs. </LI> <LI> GO showed the best performance for guiding the osteogenesis of hADMSCs. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Two-dimensional material-based bionano platforms to control mesenchymal stem cell differentiation

Ee-Seul Kang,Da-Seul Kim,Intan Rosalina Suhito,Wanhee Lee,Inbeom Song,Tae-HyungKim 한국생체재료학회 2018 생체재료학회지 Vol.22 No.2

Background: In the past decade, stem cells, with their ability to differentiate into various types of cells, have been proven to be resourceful in regenerative medicine and tissue engineering. Despite the ability to repair damaged parts of organs and tissues, the use of stem cells still entails several limitations, such as low differentiation efficiency and difficulties in guiding differentiation. To address these limitations, nanotechnology approaches have been recently implemented in stem cell research. It has been discovered that stem cells, in combination with carbon-based functional materials, show enhanced regenerative performances in varying biophysical conditions. In particular, several studies have reported solutions to the conventional quandaries in biomedical engineering, using synergetic effects of nanohybrid materials, as well as further development of technologies to recover from diverse health conditions such as bone fracture and strokes. Main text: In this review, we discuss several prior studies regarding the application of various nanomaterials in controlling the behavior of stem cells. We focus on the potential of different types of nanomaterials, such as two-dimensional materials, gold nanoparticles, and three-dimensional nanohybrid composites, to control the differentiation of human mesenchymal stem cells (hMSCs). These materials have been found to affect stem cell functions via the adsorption of growth/differentiation factors on the surfaces of nanomaterials and the activation of signaling pathways that are mostly related to cell adhesion and differentiation (e.g., FAK, Smad, Erk, and Wnt). Conclusion: Controlling stem cell differentiation using biophysical factors, especially the use of nanohybrid materials to functionalize underlying substrates wherein the cells attach and grow, is a promising strategy to achieve cells of interest in a highly efficient manner. We hope that this review will facilitate the use of other types of newly discovered and/or synthesized nanomaterials (e.g., metal transition dichalcogenides, non-toxic quantum dots, and metal oxide frameworks) for stem cell-based regenerative therapies.