光電所所訊

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第十二屆有庠科技講座

光電科技

孫啟光教授

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第六屆有庠科技發明獎

混合型異質接面薄膜太陽能電池結構及其製作方法
Mixed-typed heterojunction thin-film solar cell structure and method for fabrication the same

林清富教授

Graphene to substrate energy transfer through out-of-plane longitudinal acoustic phonons

Professor Chi-Kuang Sun

Graduate Institute of Photonics and Optoelectronics, National Taiwan University

臺灣大學光電所孫啟光教授

Graphene is often deposited on substrates for practical purposes. The graphene-substrate interactions have been the focus of many discussions because they induce property modifications and result in considerable energy transfer at the interface. However, the proposed mechanisms were restricted to the 2D plane and interface, while the energy conduction in the third dimension is hardly considered. Herein, we applied nano-ultrasonic spectroscopy with a piezoelectric nano-layer embedded in the substrate to study the energy transfer perpendicular to the interface of the combined system of the 2D graphene and the 3D base. The result revealed energy dissipation of optically excited graphene via emitting out-of-plane longitudinal acoustic phonon into the substrate. We found that, under photo-excitation by a femtosecond laser pulse, graphene can emit longitudinal coherent acoustic phonons (CAPs) with frequency bandwidth over 1 THz into the substrate. In addition, the waveform of the CAP pulse infers that the photo-carriers and sudden lattice heating in graphene caused modification of graphene-substrate bond and consequently generated longitudinal acoustic phonons in the substrate. The direct observation of this unexplored graphene to substrate vertical energy transfer channel brings new insights into the understanding of the energy dissipation and limited transport properties of supported graphene.

Fig. (Left)The schematic of applying femtosecond laser pulses to study energy transfer at the interface of graphene and substrate. (Right) The experimental data of differential transient transmission (T/T) that reveals the generation of out-of-plane longitudinal acoustic phonon in the substrate by the exclusively photo-excited graphene.

Reference: I-Ju Chen, Pierre-Adrien Mante, Cheng-Kai Chang, Szu-Chi Yang, Hui-Yuan Chen, Yu-Ru Huang, Li-Chyong Chen, Kuei-Hsien Chen, Vitalyi Gusev, and Chi-Kuang Sun, “Graphene-to-substrate energy transfer through out-of-plane longitudinal acoustic phonons,” Nano Letters, 1317−1323, 14, 2014

Investigation of designated eye position and viewing zone for a two-view autostereoscopic display

Professor Hoang-Yan Lin

Graduate Institute of Photonics and Optoelectronics, National Taiwan University

臺灣大學光電所林晃巖教授

Designated eye position (DEP) and viewing zone (VZ) are important optical parameters for designing a two-view autostereoscopic display (Figs. 1 and 2). Although much research has been done to date, little empirical evidence has been found to establish a direct relationship between design and measurement. More rigorous studies and verifications to investigate DEP and to ascertain the VZ criterion will be valuable. We propose evaluation metrics based on equivalent luminance (EL) and binocular luminance (BL) to figure out DEP and VZ for a two-view autostereoscopic display. Simulation and experimental results (Fig. 3) prove that our proposed evaluation metrics can be used to find the DEP and VZ accurately. (Optics Express, Vol. 22, Issue 4, pp.4751-4767, 2014.)

Fig. 1. Schematic diagram for a two-view autostereoscopic display design. The figure is for illustration and not to the scale. In practice, Z>>f and P_E >>P_D.

Fig. 2. The VZ defined by geometric line plot from side sub-pixels. The figure is for illustration and not to the scale. In practice, Z is much greater than f and P_Eis much greater than P_D.

Fig. 3. Experiment for verifying the reconstruction map based on equivalent luminance. Calcuated peak L_Req at the first lobe (+1) is at (x, y, z)= (17.5~17.75, 0, 103~104.5). The observed pictures for (a) a B/W pattern and (b) natural picture are shown at the observation point (17.5, 0, 103) marked at (c). Those for (d) a B/W pattern and (e) natural picture are shown at the observation point (15.5, 0, 103) marked at (f).