Cho, Kyeongjae
Permanent URI for this collectionhttps://hdl.handle.net/10735.1/3651
Kyeongjae Cho is a Professor of Materials Science. His research interests include:
- Computational modeling study of nanomaterials with applications to nanoelectronic devices
- Renewable energy technology
ORCID page
Browse
Browsing Cho, Kyeongjae by Author "0000-0003-4771-3633 (Nie, Y)"
Now showing 1 - 3 of 3
- Results Per Page
- Sort Options
Item A Kinetic Monte Carlo Simulation Method of Van Der Waals Epitaxy for Atomistic Nucleation-Growth Processes of Transition Metal Dichalcogenides(Nature Publishing Group, 2018-08-31) Nie, Yifan; Liang, Chaoping; Cha, Pil-Ryung; Colombo, Luigi; Wallace, Robert M.; Cho, Kyeongjae; 0000-0003-4771-3633 (Nie, Y); Nie, Yifan; Liang, Chaoping; Cha, Pil-Ryung; Wallace, Robert M.; Cho, KyeongjaeControlled growth of crystalline solids is critical for device applications, and atomistic modeling methods have been developed for bulk crystalline solids. Kinetic Monte Carlo (KMC) simulation method provides detailed atomic scale processes during a solid growth over realistic time scales, but its application to the growth modeling of van der Waals (vdW) heterostructures has not yet been developed. Specifically, the growth of single-layered transition metal dichalcogenides (TMDs) is currently facing tremendous challenges, and a detailed understanding based on KMC simulations would provide critical guidance to enable controlled growth of vdW heterostructures. In this work, a KMC simulation method is developed for the growth modeling on the vdW epitaxy of TMDs. The KMC method has introduced full material parameters for TMDs in bottom-up synthesis: metal and chalcogen adsorption/desorption/diffusion on substrate and grown TMD surface, TMD stacking sequence, chalcogen/metal ratio, flake edge diffusion and vacancy diffusion. The KMC processes result in multiple kinetic behaviors associated with various growth behaviors observed in experiments. Different phenomena observed during vdW epitaxy process are analysed in terms of complex competitions among multiple kinetic processes. The KMC method is used in the investigation and prediction of growth mechanisms, which provide qualitative suggestions to guide experimental study.Item Quantum Transport and Band Structure Evolution under High Magnetic Field in Few-Layer Tellurene(American Chemical Society) Qiu, G.; Wang, Y.; Nie, Yifan; Zheng, Yongping; Cho, Kyeongjae; Wu, W.; Ye, P. D.; 0000-0003-4771-3633 (Nie, Y); 0000-0003-2698-7774 (Cho, K); 369148996084659752200 (Cho, K); Nie, Yifan; Zheng, Yongping; Cho, KyeongjaeQuantum Hall effect (QHE) is a macroscopic manifestation of quantized states that only occurs in confined two-dimensional electron gas (2DEG) systems. Experimentally, QHE is hosted in high-mobility 2DEG with large external magnetic field at low temperature. Two-dimensional van der Waals materials, such as graphene and black phosphorus, are considered interesting material systems to study quantum transport because they could unveil unique host material properties due to the easy accessibility of monolayer or few-layer thin films at the 2D quantum limit. For the first time, we report direct observation of QHE in a novel low-dimensional material system, tellurene. High-quality 2D tellurene thin films were acquired from recently reported hydrothermal method with high hole mobility of nearly 3000 cm2/(V s) at low temperatures, which allows the observation of well-developed Shubnikov-de Haas (SdH) oscillations and QHE. A four-fold degeneracy of Landau levels in SdH oscillations and QHE was revealed. Quantum oscillations were investigated under different gate biases, tilted magnetic fields, and various temperatures, and the results manifest the inherent information on the electronic structure of Te. Anomalies in both temperature-dependent oscillation amplitudes and transport characteristics were observed that are ascribed to the interplay between the Zeeman effect and spin-orbit coupling, as depicted by the density functional theory calculations. ©2018 American Chemical Society.Item WSe₂ Homojunctions and Quantum Dots Created by Patterned Hydrogenation of Epitaxial Graphene Substrates(IOP Publishing Ltd, 2019-01-17) Pan, Y.; Fölsch, S.; Lin, Y. -C; Jariwala, B.; Robinson, J. A.; Nie, Yifan; Cho, Kyeongjiae; Feenstra, R. M.; 0000-0003-2698-7774 (Cho, K); 0000-0003-4771-3633 (Nie, Y); Nie, Yifan; Cho, KyeongjiaeScanning tunneling microscopy (STM) at 5 K is used to study WSe₂ layers grown on epitaxial graphene which is formed on Si-terminated SiC(0 0 0 1). Specifically, a partial hydrogenation process is applied to intercalate hydrogen at the SiC-graphene interface, yielding areas of quasi-free-standing bilayer graphene coexisting with bare monolayer graphene. We find that an abrupt and structurally perfect homojunction (band-edge offset ∼0.25 eV) is formed when WSe₂ overgrows a lateral junction between adjacent monolayer and quasi-free-standing bilayer areas in the graphene. The band structure modulation in the WSe₂ overlayer arises from the varying work function (electrostatic potential) of the graphene beneath. Scanning tunneling spectroscopy measurements reveal that this effect can be also utilized to create WSe₂ quantum dots that confine either valence or conduction band states, in agreement with first-principles band structure calculations. ©2019 IOP Publishing Ltd.