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Suh, Joonki,Park, Tae-Eon,Lin, Der-Yuh,Fu, Deyi,Park, Joonsuk,Jung, Hee Joon,Chen, Yabin,Ko, Changhyun,Jang, Chaun,Sun, Yinghui,Sinclair, Robert,Chang, Joonyeon,Tongay, Sefaattin,Wu, Junqiao American Chemical Society 2014 NANO LETTERS Vol.14 No.12
<P>Layered transition metal dichalcogenides (TMDs) draw much attention as the key semiconducting material for two-dimensional electrical, optoelectronic, and spintronic devices. For most of these applications, both <I>n</I>- and <I>p</I>-type materials are needed to form junctions and support bipolar carrier conduction. However, typically only one type of doping is stable for a particular TMD. For example, molybdenum disulfide (MoS<SUB>2</SUB>) is natively an <I>n</I>-type presumably due to omnipresent electron-donating sulfur vacancies, and stable/controllable <I>p</I>-type doping has not been achieved. The lack of <I>p</I>-type doping hampers the development of charge-splitting <I>p</I>–<I>n</I> junctions of MoS<SUB>2</SUB>, as well as limits carrier conduction to spin-degenerate conduction bands instead of the more interesting, spin-polarized valence bands. Traditionally, extrinsic <I>p</I>-type doping in TMDs has been approached with surface adsorption or intercalation of electron-accepting molecules. However, practically stable doping requires substitution of host atoms with dopants where the doping is secured by covalent bonding. In this work, we demonstrate stable <I>p</I>-type conduction in MoS<SUB>2</SUB> by substitutional niobium (Nb) doping, leading to a degenerate hole density of ∼3 × 10<SUP>19</SUP> cm<SUP>–3</SUP>. Structural and X-ray techniques reveal that the Nb atoms are indeed substitutionally incorporated into MoS<SUB>2</SUB> by replacing the Mo cations in the host lattice. van der Waals <I>p</I>–<I>n</I> homojunctions based on vertically stacked MoS<SUB>2</SUB> layers are fabricated, which enable gate-tunable current rectification. A wide range of microelectronic, optoelectronic, and spintronic devices can be envisioned from the demonstrated substitutional bipolar doping of MoS<SUB>2</SUB>. From the miscibility of dopants with the host, it is also expected that the synthesis technique demonstrated here can be generally extended to other TMDs for doping against their native unipolar propensity.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/nalefd/2014/nalefd.2014.14.issue-12/nl503251h/production/images/medium/nl-2014-03251h_0005.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nl503251h'>ACS Electronic Supporting Info</A></P>
Nanoscale Friction on Confined Water Layers Intercalated between MoS<sub>2</sub> Flakes and Silica
Lee, Hyunsoo,Jeong, Hochan,Suh, Joonki,Doh, Won Hui,Baik, Jaeyoon,Shin, Hyun-Joon,Ko, Jae-Hyeon,Wu, Junqiao,Kim, Yong-Hyun,Park, Jeong Young American Chemical Society 2019 The Journal of Physical Chemistry Part C Vol. No.
<P>Frictional energy dissipation at the interfaces of two-dimensional (2D) materials through the excitation and transfer processes of kinetic energy into the bulk can be easily influenced by an intercalated water film. An enhancement of friction on water-intercalated graphene has been observed. Is this frictional enhancement by confined water a general phenomenon? We address this issue by investigating the frictional behavior of confined water layers intercalated between single-layer molybdenum disulfide (MoS<SUB>2</SUB>), synthesized using chemical vapor deposition, and a silica substrate. The icelike water was intercalated by exposure to high-humidity air. We found that the intercalated water molecules morphologically deform the 2D MoS<SUB>2</SUB> sheet, forming distinct subdomains after the exposure to high humidity. We found that the adsorption of the icelike water layer between the MoS<SUB>2</SUB> and the silica leads to friction enhancement, compared with a pristine MoS<SUB>2</SUB>/silica sample, which is associated with additional phononic friction energy dissipation at the solid-liquid interface, as indicated by the phonon distribution analysis from the empirical force-field calculations. Moreover, the atomic stick-slip behavior shows that the lattice orientation of the hydrophilic MoS<SUB>2</SUB> affects water molecule diffusion at the interface of the MoS<SUB>2</SUB>/silica substrate. Chemical mapping of the water-intercalated MoS<SUB>2</SUB> on silica using scanning photoelectron microscopy and vacuum annealing processes shows water intercalation without changing the intrinsic composition of the MoS<SUB>2</SUB> on silica.</P> [FIG OMISSION]</BR>
반도체 탄소 중립을 위한 친환경 가스 기반 식각 공정 연구
주정아 ( Jeonga Ju ),박진구 ( Jinkoo Park ),서준기 ( Joonki Suh ),정홍식 ( Hongsik Jeong ) 한국전기전자재료학회 2023 전기전자재료학회논문지 Vol.36 No.2
Currently, semiconductor manufacturing industry heavily relies on a wide range of high global warming potential (GWP) gases, particularly during etching and cleaning processes, and their use and relevant carbon emissions are subject to global rules and regulations for achieving carbon neutrality by 2050. To replace high GWP gases in near future, dry etching using alternative low GWP gases is thus being under intense investigations. In this review, we report a current status and recent progress of the relevant research activities on dry etching processes using a low GWP gas. First, we review the concept of GWP itself and then introduce the difference between high and low GWP gases. Although most of the studies have concentrated on potentially replaceable additive gases such as C<sub>4</sub>F<sub>8</sub>, an ultimate solution with a lower GWP for main etching gases including CF<sub>4</sub> should be developed; therefore, we provide our own perspective in this regard. Finally, we summarize the advanced dry etch process research with low GWP gases and list up several issues to be considered in future research.
장민규(Mingyu Jang),Swati Singh(Swati Singh ),서준기(Joonki Suh) 한국세라믹학회 2023 세라미스트 Vol.26 No.1
Understanding thermal energy transport of crystalline materials, often highly dependent on their crystalline directions, is crucial for energy harvesting and thermal management applications. In this sense, anisotropy in thermal conductivity (κ), which is the unique characteristic of two-dimensional (2D) materials involving graphene and transition metal dichalcogenides (TMDs), has been attracting tremendous attention in terms of fundamental science and application-driven technology aspects. This distinctive heat transport behavior of 2D van der Waals (vdW) materials generally originates from their intrinsic crystal structures and associated lattice vibrations. Here, we thoroughly review and summarize the anisotropic thermal conductivity in 2D vdW crystals in two different categories: 1) in-plane vs. out-of-plane and 2) between two different in-plane directions. In addition, we introduce a range of thermal conductivity measurement techniques that can be employed for 2D vdW materials provided with their working principles, advantages, and limitations. Beyond their intrinsic anisotropic ratio, we conclude with perspectives on the extrinsic modulations of thermal conductivities, thereby maximizing it toward effective thermal management.
Tellurium 기반 휘발성 문턱 스위칭 및 고집적 메모리용 선택소자 응용 연구
김승환,김창환,허남욱,서준기,Seunghwan Kim,Changhwan Kim,Namwook Hur,Joonki Suh 한국전기전자재료학회 2023 전기전자재료학회논문지 Vol.36 No.6
High-density crossbar arrays based on storage class memory (SCM) are ideally suited to handle an exponential increase in data storage and processing as a central hardware unit in the era of AI-based technologies. To achieve this, selector devices are required to be co-integrated with SCM to address the sneak-path current issue that indispensably arises in such crossbar-type architecture. In this perspective, we first summarize the current state of tellurium-based threshold-switching devices and recent advances in the material, processing, and device aspects. We thoroughly review the physicochemical properties of elemental tellurium (Te) and representative binary tellurides, their tailored deposition techniques, and operating mechanisms when implemented in two-terminal threshold switching devices. Lastly, we discuss the promising research direction of Te-based selectors and possible issues that need to be considered in advance.
Wafer-scale synthesis of monolayer two-dimensional porphyrin polymers for hybrid superlattices
Zhong, Yu,Cheng, Baorui,Park, Chibeom,Ray, Ariana,Brown, Sarah,Mujid, Fauzia,Lee, Jae-Ung,Zhou, Hua,Suh, Joonki,Lee, Kan-Heng,Mannix, Andrew J.,Kang, Kibum,Sibener, S. J.,Muller, David A.,Park, Jiwoon American Association for the Advancement of Scienc 2019 Science Vol.366 No.6471
<P><B>Single-layer porphyrin polymerization</B></P><P>Two-dimensional polymers can be made as monolayer sheets through controlled synthesis at an interface. However, it is often difficult to create intact sheets over large areas that can be transferred onto substrates. Zhong <I>et al.</I> polymerized derivatized porphyrin molecules during laminar flow at a sharp pentane-water interface to form sheets that are 5 centimeters in diameter (see the Perspective by MacLean and Rosei). The authors used electron microscopy and spectroscopy to confirm that they had produced intact monolayers. These films were then transferred onto monolayer sheets of molybdenum disulfide to form superlattices for use as capacitors.</P><P><I>Science</I>, this issue p. 1379; see also p. 1308</P><P>The large-scale synthesis of high-quality thin films with extensive tunability derived from molecular building blocks will advance the development of artificial solids with designed functionalities. We report the synthesis of two-dimensional (2D) porphyrin polymer films with wafer-scale homogeneity in the ultimate limit of monolayer thickness by growing films at a sharp pentane/water interface, which allows the fabrication of their hybrid superlattices. Laminar assembly polymerization of porphyrin monomers could form monolayers of metal-organic frameworks with Cu<SUP>2+</SUP> linkers or covalent organic frameworks with terephthalaldehyde linkers. Both the lattice structures and optical properties of these 2D films were directly controlled by the molecular monomers and polymerization chemistries. The 2D polymers were used to fabricate arrays of hybrid superlattices with molybdenum disulfide that could be used in electrical capacitors.</P>