The dielectric and optical properties of thin films at gigahertz and terahertz frequencies

다국어 초록 (Multilingual Abstract)

Thin films have attracted the attention of physicists because the dimensionally constraint system of the thin films can create an intermediate system between macroscopic systems and molecular systems. This system might show anomalies in the optical, electrical, mechanical, or magnetic properties, compared to the properties of bulk materials. The most conspicuous phenomena associated with the thin films are the anomalies of dielectric and optical properties. This thesis will investigate the anomalous phenomena of thin films by the study of the dielectric and optical properties of a variety of thin films at GHz and THz frequencies (in the millimeter and sub-millimeter wave regime).
A coherent THz wave source and electro-optic detection method are used for the experiment. For a coherent THz frequency source, a THz emitter was used, which was driven by a 100 femto-second pulse from a Ti:sapphire laser to produce the coherent THz wave radiation while the electro-optic detector was gated by the laser pulse split from the laser for the coherent THz wave detection.
The dielectric and optical properties of a variety of thin film materials are discussed and analyzed in detail. The microscopic structural contribution to the dielectric and optical properties of thin films are especially emphasized in this thesis.
Because the currently available methods for the characterization of thin films at the THz frequency have difficulties when the films are in the range of nanometer to micron in thickness, a new method, THz differential time-domain spectroscopy, is developed. The theory of the THz differential time-domain spectroscopy is also developed to obtain information on the real and imaginary parts of dielectric properties and the optical properties. The dual phase lock-in detection was performed to measure the very small differential THz signal with a high dynamic range up to 105. This THz differential time-domain spectroscopy is able to characterize the properties of nanometerscaled thin films.
A variety of materials have been experimentally investigated, including a 930㎚ silicon dioxide film, a 1.8 ㎛ parylene-n polymer free standing film, a 1.8㎛ parylene-n polymer film on silicon substrate, a 300㎚ parylene-n polymer film, a 100㎚ tantalum oxide high dielectric film, protein monolayers, water molecule layer on the surface of ice crystal, and a carbon nanotube film.
We found that there are anomalies in the dielectric and optical properties of several thin films. These anomalous behaviors are believed to be caused by fine grain formation, mechanical stresses, formation of interfacial layers, or rough interfaces during thin film deposition processes.

목차 (Table of Contents)

• LIST OF TABLES = v
• LIST OF FIGURES = vi
• PUBLICATIONS = x
• ACKNOWLEGEMENT = xii
• ABSTRACT = xiii
• 1. Introduction = 1
• 2. Principles of coherent THz processes = 8
• 2. 1 Coherent wave THz generation = 8
• 2. 1. 1 THz wave generation via optical rectification = 12
• 2. 1. 2 THz wave generation via current transport = 14
• 2. 1. 3 THz wave generation in semiconductor structures = 15
• 2. 2 Coherent THz wave detection = 17
• 2. 2. 1 Electro-optic detection = 17
• 2. 2. 2 Photoconductive antenna = 22
• 3. Generation and detection of the THz wave by LT-GaAs PC anfienna = 24
• 4. The dielectric properties of solids = 34
• 4. 1 Microscopic structural contribution to the dielectric property = 39
• 5. Experimental setup = 40
• 6. THz time-domain spectroscopy = 46
• 6. 1 Background = 46
• 6. 2 Optical constants of hexagonal ice crystal (Ih) at THz frequency = 47
• 6. 3 The dielectric and optical properties of a carbon nanotubes = 54
• 6. 4 The measurement of water monolayer on ice surface = 59
• 7. THz differential time-domain spectroscopy = 61
• 7. 1 Background = 61
• 7. 2 Mathematical aspect = 62
• 7. 3 Experiment = 64
• 7. 3. 1 Double phase lock-in detection = 65
• 7. 4 Results = 67
• 7. 4. 1 Silicon dioxide = 70
• 7. 4. 2 Parylene = 75
• 7. 4. 3 Tantalum oxide = 81
• 7. 4. 4 Protein monolayers = 85
• 7. 5 Noise analysis = 89
• 7. 6 Summary = 91
• 8. Discussion and conclusion = 93
• LITERATURE CITED = 97