The 274th MANA & the 117th ICYS Joint Seminar
Dr. Hiroyuki Takeda, Dr. Xianlong Wei, Prof. Joost VandeVondele
| Date | July 6, Friday |
| Time | 15:00-16:45 |
| Place | Seminar room #811, 8F, Central Bldg., SENGEN Site, NIMS |
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15:00-15:30
All-optical modulation and amplification in a photonic-crystal cavity with two-level systems
I theoretically demonstrate the all-optical modulation and amplification in a one-dimensional photonic-crystal (PC) cavity with a large number of two-level quantum dots (QD’s). Populations at the ground and excited states of two-level QD’s with large transition dipole moments greatly change by an external laser, and this affects the electric susceptibility of QD’s. In other words, all-optical modulation, in which light (the signal light) is modulated by light (the external laser), becomes possible. Moreover, a large contrast of electromagnetic local densities of states in the PC cavity enables steady-state population inversion in two-level systems which is generally considered impossible. Then, output signal powers exceed twice as large as input ones at certain frequencies.
Speaker
Dr. Hiroyuki Takeda, ICYS-Sengen Researcher, NIMS
Chair
Dr. Kazuaki Sakoda, Unit Director, Photonic Materials Unit, NIMS
15:30-16:00
Electron emission from one-atom-thick surfaces of carbon nanotubes and graphene nanoribbons driven by internal electric field
Electron emission from the surface of a one-atom-thick crystal is expected to be quite different from that from a three-dimensional (3D) bulk one because of the following two features associated with monoatomic thickness: (i) electrons are confined in a quantum well along emission direction; (ii) all electrons in a one-atom-thick crystal always keep staying at the emission boundary with vacuum. Herein, a study of electron emission from the one-atom-thick surfaces of individual carbon nanotubes (CNTs) and graphene nanoribbons (GNRs) driven by internal electric field will be presented. You will see what happens to electron emission as a result of monatomic thickness. Some new experimental phenomena peculiar to electron emission from a one-atom-thick crystal, as well as a new mechanism for electron emission, will be introduced.
Speaker
Dr. Xianlong Wei, ICYS-MANA Researcher, MANA, NIMS
Chair
Dr. Dmitri Golberg, MANA Principal Investigator, MANA, NIMS
16:00-16:45
Towards an atomistic picture of the active interface in dye sensitized solar cells
In order to optimize the performance of dye sensitized solar cells (DSSC), detailed insight in the atomistic processes at the sensitized solid/liquid interface is very valuable. We will present results of computer simulations based on atomistic models and density functional theory. The aim of these simulations is to provide an atomistic model of the interface, which takes all important components (oxide, dye, electrolyte), explicitly into account.
In particular, we have computed various binding modes of the N3 dye on anatase (101), and have compared computed with experimental IR spectra. These results allow for predicting the most stable surface conformation, and clarify the various carboxylate-Ti interactions. Extensive classical simulations of the TiO2-acetonitrile interface provide an explanation for the good performance of the acetonitrile/I3-/I- electrolyte. Finally, we have studied the interaction of the redox mediator with the N3 dye in solution, suggesting an efficient pathway for dye regeneration and an alternative mechanism for the formation of I3-.
Speaker
Prof. Joost VandeVondele, Nanoscale Simulations, Department of Materials, Swiss Federal Institute of Technology (ETH) Zurich, Switzerland
Chair
Dr. Yoshitaka Tateyama, Group Leader, Nano-System Computational Science Group, MANA, NIMS