우리 대학원 BK사업단 주관으로 미국 Tech-X Cooperation의 David Smithe와 한양대학교의 Ming-Chieh Lin를 모시고 세미나를 개최합니다.

관심 있는 분들의 많은 참여 부탁드립니다.

* 초청: 이해준 교수님

- 일시: 2019년 5월 3일(금) 오후 2시

- 장소: 제10공학관(특공관) 10311호

- 연사: David Smithe (Tech-X Cooperation, USA)

- 주제: Challenges of cut-cell FDTD-PIC:  metals, dielectrics, and emission

- 강연 내용 요약: Tech-X markets the VSim software which is based on the finite-difference-time-domain (FDTD) particle-in-cell (PIC) algorithm. VSim was one of the early adapters of the “cut-cell” technology, which moves beyond the stair-stepped meshing underlying the finite-difference method, to include cells which are partially filled with metal and dielectric material, at arbitrary angle and intersection with the finite-difference-mesh. We continue to improve on the many cut-cell methodologies in the software, and this talk will cover recent improvements to software, and areas of ongoing-research which may add to the code capabilities in future releases. One recent focus has been on the cut-cell dielectric algorithm, aimed at photonics applications, and devices with curved and complex air/dielectric interfaces. The arbitrary dielectric interface has been one of the most difficult features to model with confidence, as virtually all “dielectric averaging” techniques fail to achieve second-order convergence for some subset of problems. A related problem exists for modeling surface wave phenomenon such as soliton propagation, which depends on precise locality of the dielectric interfaces, and we will illustrate some of the challenges of modeling such in this talk.

- 일시: 2019년 5월 3일(금) 오후 3시30분

- 장소: 제10공학관(특공관) 10311호

- 연사: Ming-Chieh Lin (한양대학교)

- 주제: First principles study on electronic properties of graphene nanostructures for high current density cathode

- 강연 내용 요약: Graphene is a crystalline allotrope of carbon with 2-D properties. Its carbon atoms are densely packed in a nano-scale hexagonal pattern. Graphene has many unusual properties. It is about 200 times stronger than the strongest steel. It can efficiently conduct heat and electricity and is nearly transparent. In this work, we study the electronic properties of graphene using first-principles or ab initio calculations based on density functional theory as implemented in the VASP code in order to explore its applications in field emission devices. The electronic structure and density of states of graphene are calculated. The work function value is a key parameter and highly desirable for successful graphene applications in the field emission research. The change of work function due to the lattice deformation of graphene is investigated using a supercell including a vacuum layer which is thick enough so that the layer interaction is negligible. It is found that the work function is very sensitive to the lattice size. As the lattice site increases, the work function increases proportionally. However, the work function is reduced doubly while the lattice site is reduced. The local work function of graphene has also been determined and this can be used to predict field emission current from Fowler-Nordheim equation more accurately. For realistic applications, this approach has been used to calculate the work function of carbon nanoribbons with different widths and terminating edges with and without passivation. Strain and screening effects on field emission properties of armchair graphene nanoribbon (AGNR)

arrays are found to be interesting. Our findings not only provide an insight into understanding the screening effect on the characteristics of the strained AGNRs but also provide a guideline for their efficient application in field emission devices.