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Title Page

Abstract

Contents

Ⅰ. Introduction 11

Ⅱ. Theoretical background 18

2.1. Faraday effect 18

2.2. Faraday rotation in ferromagnet 20

2.3. Surface plasmon 22

Ⅲ. Sample fabrications 25

3.1. Photolithography 25

3.2. Electron beam lithography 27

3.3. Design of micro slot antenna array 30

3.4. Fabrication of slot antenna array 32

Ⅳ. Experimental measurements 33

4.1. Terahertz time-domain spectroscopy 33

4.2. Measurement method of Faraday effect 35

Ⅴ. Results and discussion 37

5.1. Terahertz transmission of slot antenna measurement 37

5.2. Faraday rotation angle measurement 40

Ⅵ. Conclusion 42

References 43

List of Figures

Figure 1.1. The nanohole array sample schematic and the cross-polarized transmission spectra were measured in the magneto-plasmonic crystal with nanohole array sample under varying incident light... 12

Figure 1.2. The Faraday rotation [dashed line] and optical transmittance spectra [solid line] were measured for the bilayer system consisting of an Au film (68 nm thick) that is perforated and a uniform... 12

Figure 1.3. The Kerr polarization rotation angle was measured using magneto-plasmonic rulers, where the electric and magnetic fields were set at 45° (p-45), aligned with the tangential ruler axis (p-short),... 13

Figure 1.4. The dielectric metasurface's schematic unit cell is illustrated, along with the magnetic hysteresis loops of [Pt/Co]N, where N＝1, 2, and 3. For N＝2, toxide＝100 nm (pink) and 30 nm... 14

Figure 1.5. The structure of the chiral metasurface and a visual representation demonstrating its manipulation of circularly polarized waves. Copyright 2021, Nanoscale Adv. 15

Figure 1.6. Diagram depicting the magnetization process of the ferromagnetic nanofluid influenced by the biased magnetic field. Refractive index alterations, Faraday rotation angle variations, and... 15

Figure 1.7. Diagram representing a chiral metasurface magnetizing a 100 μm thick layer of ferromagnetic nanofluid. It illustrates the Faraday rotation angle and transmission spectra. Reproduced... 16

Figure 2.3.1. Schematic of the SPPs at the interface when the incident wave is TM mode. 22

Figure 3.1.1. Schematic diagram of the photolithography process: exposure, development, iron deposition, and lift-off. 25

Figure 3.2.1. Schematic diagram of the electron-beam lithography process: electron-beam exposure, development, iron deposition, and lift-off. 27

Figure 3.2.2. (a) Schematic of the automated stage. (b) FE-SEM image and movement path of the pattern created by the automated stage. 28

Figure 3.2.3. The FE-SEM images of nanohole arrays at different magnifications. (a) 100x, (b) 450x, (c) 2.00k x, (d) 10.0k x, (e) 90.0k x magnification. 29

Figure 3.3.1. Schematic of the slot antenna array in a iron thin film onto a Si substrate. 30

Figure 3.4.1. (a) The FE-SEM image of a 20 μm slot antenna array with 50 μm length. (b-e) The FE-SEM image of a 2 μm, 400 nm, 300 nm, and 200 nm slot antenna. 32

Figure 4.1.1. Experimental set-up for terahertz time-domain spectroscopy. 33

Figure 4.2.1. The image depicts Faraday rotation caused by TM-polarized incident light in a magneto-optic material, where θ represents the Faraday rotation angle. 35

Figure 4.2.2. Schematic of calculating the Faraday rotation angle θFR by comparing before and after applying a magnetic field.[이미지참조] 36

Figure 5.1.1. (a) Transmission spectrum of terahertz slot antennas. (b) Transmission error at resonance peak position. 38

Figure 5.1.2. Results of transmission that given an external magnetic field at (a) 20 μm, (b) 2 μm, (c) Fe film. 39

Figure 5.2.1. (a) Measured Faraday rotation angle of the transmitted THz wave. (b) Maximum polarization rotation angle in each sample. 40

초록보기

 The magneto-optic effects are enhanced in structures with periodicity and ferromagnetic materials. The magneto-optic effect refers to changes in the optical characteristics of a substance when influenced by an external magnetic field. The Faraday effect, one of the magneto-optical effects, refers to the shift in the polarization axis of linear polarization wave due to an external magnetic field applied to a material. Based on these attempts, this thesis explores the terahertz transmission characteristics and magneto-optical effects by varying the gap size of slot antennas. Slot antennas, rectangular structures with a gap width on a metallic film, are known to show strong resonance at certain frequency and sensitivity to the dielectric environment in transmission properties. Slot antennas were fabricated using photolithography and electron beam lithography. The slot antennas exhibited decreased transmission when exposed to a magnetic field and observed maximum Faraday rotation near the resonance frequency were noted. The tendency of this phenomenon becomes larger with smaller antenna's gap. With well-controlled quality of the ferromagnetic material and antenna structure, this scheme is expected to demonstrate substantial Faraday rotation within a specific frequency range.

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