1,721,124 research outputs found
Silicene on Other Two-dimensional Materials: Formation of Heterostructure
Full text linkSilicene is one of the most interesting two-dimensional materials, because of not only the extraordinary properties similar to graphene, but also easy compatibility with existing silicon-based devices. However, non-existing graphitic-like structure on silicon and unstable free-standing silicene structure leads to difficulty in commercialization of this material. Therefore, substrates are essential for silicene, which affects various properties of silicene and supporting unstable structure. For maintaining outstanding properties of silicene, van der Waals bonding between silicene and substrate is essential because strong interaction, such as silicene with metal, breaks the band structure of silicene. Therefore, we review the stability of silicene on other two-dimensional materials for van der Waals bonding. In addition, the properties of silicene are reviewed for silicene-based heterostructure.clos
Observation of spin-polarized Anderson state around charge neutral point in graphene with Fe-clusters
No full text© 2020, The Author(s).The pristine graphene described with massless Dirac fermion could bear topological insulator state and ferromagnetism via the band structure engineering with various adatoms and proximity effects from heterostructures. In particular, topological Anderson insulator state was theoretically predicted in tight-binding honeycomb lattice with Anderson disorder term. Here, we introduced physi-absorbed Fe-clusters/adatoms on graphene to impose exchange interaction and random lattice disorder, and we observed Anderson insulator state accompanying with Kondo effect and field-induced conducting state upon applying the magnetic field at around a charge neutral point. Furthermore, the emergence of the double peak of resistivity at ν = 0 state indicates spin-splitted edge state with high effective exchange field (>70 T). These phenomena suggest the appearance of topological Anderson insulator state triggered by the induced exchange field and disorde
Atomic Arrangements of Graphene-like ZnO
Full text linkZnO, which can exist in various dimensions such as bulk, thin films, nanorods, and quantum dots, has interesting physical properties depending on its dimensional structures. When a typical bulk wurtzite ZnO structure is thinned to an atomic level, it is converted into a hexagonal ZnO layer such as layered graphene. In this study, we report the atomic arrangement and structural merging behavior of graphene-like ZnO nanosheets transferred onto a monolayer graphene using aberration-corrected TEM. In the region to which an electron beam is continuously irradiated, it is confirmed that there is a directional tendency, which is that small-patched ZnO flakes are not only merging but also forming atomic migration of Zn and O atoms. This study suggests atomic alignments and rearrangements of the graphene-like ZnO, which are not considered in the wurtzite ZnO structure. In addition, this study also presents a new perspective on the atomic behavior when a bulk crystal structure, which is not an original layered structure, is converted into an atomic-thick layered two-dimensional structure
In-situ formation of co particles encapsulated by graphene layers
No full textThe process of encapsulating cobalt nanoparticles using a graphene layer is mainly direct pyrolysis. The encapsulation structure of hybrids prepared in this way improves the catalyst stability, which greatly reduces the leaching of non-metals and prevents metal nanoparticles from growing beyond a certain size. In this study, cobalt particles surrounded by graphene layers were formed by increasing the temperature in a transmission electron microscope, and they were analyzed using scanning transmission electron microscopy (STEM). Synthesized cobalt hydroxide nanosheets were used to obtain cobalt particles using an in-situ heating holder inside a TEM column. The cobalt nanoparticles are surrounded by layers of graphene, and the number of layers increases as the temperature increases. The interlayer spacing of the graphene layers was also investigated using atomic imaging. The success achieved in the encapsulation of metallic nanoparticles in graphene layers paves the way for the design of highly active and reusable heterogeneous catalysts for more challenging molecules
Elucidation of Novel Potassium-Mediated Oxidation and Etching of Two-Dimensional Transition Metal Dichalcogenides
No full text© 2021 American Chemical Society.Preparation of edge-rich two-dimensional (2D) transition metal dichalocogenides (TMDs) has been actively investigated with the aim to improve their electrical and catalytic properties. Here, we elucidate the role of potassium ions in oxidation of TMDs and suggest a consequent novel anisotropic etching mechanism driven by self-running oxide droplets. We discover that potassium-mediated oxidation of MoS2 leads to the formation of K-intercalated hexagonal-phase molybdenum oxides (h-KxMoO3), whereas orthorhombic-phase oxides are formed in the absence of potassium ions. Metastable h-KxMoO3 appears to have decomposed into oxide droplets at higher temperature. Self-running of the oxide droplets leads to layer-by-layer anisotropic etching of MoS2 along the armchair direction. The motion of the droplets appears to be triggered by the surface energy instability between the oxide droplets and the underlying MoS2 layer. This study opens new possibilities to design and manufacture novel edge-rich 2D TMDs that do not follow the equilibrium Wulff shape by modulating their oxidation with the assistance of alkali metals and also offers fundamental insights into the interactions between nanodroplets and 2D materials toward edge engineering.11Nsciescopu
Observation of the Initial Stage of 3C-SiC Heteroepitaxial Growth on the Si Nanomembrane
No full textOne considerable concern in 3C-SiC growth is the different lattice constant between the 3C-SiC and Si substrate, which causes defects and strain at the interface. Although the heteroepitaxial growth has been achieved, there have been no experimental studies on the initial process of 3C-SiC growth. In this research, we directly observe heteroepitaxial growth of 3C-SiC on the (001) Si nanomembrane (Si NM) step by step. We used in situ heating transmission electron microscopy (TEM) to study the initial growth process of 3C-SiC growth at the nanoscale in a highvacuum environment. We demonstrate the growth of 3C-SiC at the preferential (110) direction without defects. The heteroepitaxial grown 3C-SiC without defects is attributed to the bowing effect at the nanoscale to compensate for the lattice misfit. Based on these results, we proposed a new method to heteroepitaxially grow on the Si NM through in situ heating TEM study
Novel high-k gate dielectric properties of ultrathin hydrocarbon films for next-generation metal-insulator-semiconductor devices
No full text© 2019 Elsevier LtdNew high-k gate dielectrics are highly necessary in facilitating the continuous down-scaling of metal–oxide–semiconductor devices to the sub-10 nm range. This study presents ultrathin organic hydrocarbon (HC) films as a novel high-k gate insulator for metal–insulator–semiconductor (MIS) devices. During inductively-coupled plasma chemical vapor deposition with CH4 and H2 gases, the growth temperature greatly affects the structure of the carbon layers and consequently their dielectric characteristics. Specifically, sp2-rich dielectric HC layers are formed below 600 °C, whereas highly-ordered sp2-hybridized graphene is formed at 950 °C. The k value of the resulting HC films increases up to a maximum value of 90 at 350 °C. Moreover, the MIS devices exhibit excellent gate-insulating properties, including almost no hysteresis in the capacitance–voltage curve, low leakage current, and high dielectric strength, which surpass those of existing high-k gate oxides. These results reveal that the organic HC films are a promising next-generation high-k gate dielectric material for sub-10 nm node Si and organic semiconductor technologies11Nsciescopu
OH molecule-involved formation of point defects in monolayer graphene
No full textPoint defects in freestanding graphene monolayers such as monovacancies (MVs) and divacancies have been investigated at atomic scale with aberration-corrected transmission electron microscopy and theoretical calculations. In general, these defects can be formed simply by the absence of individual carbon atoms and carbon bond reconstructions in the graphene lattice under electron and ion irradiation. However, in this study, we found that oxygen and hydrogen atoms can be involved in the formation of these point defects caused by the simultaneous detachment of oxygen-carbon atoms. Here we report the effect of the oxygen and hydrogen atoms on the graphene surface forming the point defects under electron beam irradiation, and their role of stabilizing other MVs when composed of 13-5 ring pairs. In addition, theoretical analysis using density functional theory calculations demonstrates that the participating atoms can form the point defects in the intermediate states and stabilize 13-5 ring pairs under electron beam irradiation
Thermally driven phase transition of cobalt hydroxide sheets via cobalt oxides to cobalt nanoparticles
No full textTransition metal oxides, which include many stoichiometric variations, are formed into various crystal structures by the atomic arrangement of cations and anions according to stoichiometric composition and are used for a wide range of applications based on this. Among them, cobalt oxide, which has wide crystal structures depending on the lattice points of the anion and the valence of the Co cation, from its hydroxide formula, is attracting a lot of attention due to its interesting catalytic properties due to its crystal structure. In this study, using the synthesized Co(OH)(2) nanosheets, the real-time behavior of the phase transition that occurs when continuous heat is applied to the sample has been systematically analyzed using an aberration-corrected scanning transmission electron microscope. The layered Co(OH)(2) phase passes through hexagonal CoO and cubic CoO phases to finally become Co nanoparticles, but when the temperature is dropped in the hexagonal phase, spinel Co3O4 is formed. These results suggest that various phases included in transition metal oxides can be selectively implemented according to temperature range control
The Origin of Improved Electrical Double-Layer Capacitance by Inclusion of Topological Defects and Dopants in Graphene for Supercapacitors
No full textLow-energy density has long been the major limitation to the application of supercapacitors. Introducing topological defects and dopants in carbon-based electrodes in a supercapacitor improves the performance by maximizing the gravimetric capacitance per mass of the electrode. However, the main mechanisms governing this capacitance improvement are still unclear. We fabricated planar electrodes from CVD-derived single-layer graphene with deliberately introduced topological defects and nitrogen dopants in controlled concentrations and of known configurations, to estimate the influence of these defects on the electrical double-layer (EDL) capacitance. Our experimental study and theoretical calculations show that the increase in EDL capacitance due to either the topological defects or the nitrogen dopants has the same origin, yet these two factors improve the EDL capacitance in different ways. Our work provides a better understanding of the correlation between the atomic-scale structure and the EDL capacitance and presents a new strategy for the development of experimental and theoretical models for understanding the EDL capacitance of carbon electrodes. © 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinhei123231sciescopu
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