Optical properties and applications of surfactant modified deoxyribonucleic acid complex

Abstract

Deoxyribonucleic acid (DNA) was modified with cationic surfactant hexadecyltrimethyl-ammonium chloride (CTMA), and the resultant DNA-CTMA complex was dissolved in an organic solvent. DNA-CTMA thin films, with thicknesses ranging from a few hundred nanometers to a few hundred microns, were obtained by both spin-coating and casting methods. DNA-CTMA channel waveguides were fabricated by two lithographic methods, namely, photolithography assisted reactive ion beam etching (RIE) and direct electron beam lithography (EBL). For the former method, the RIE conditions were optimized using a L16 (45) array based on Taguchi design, and the optimum parameters were obtained using analysis of variables (ANOVA). For the latter method, DNA-CTMA was found to behave as either a positive or a negative resist, depending on the developer. Dose tests were done to determine the optimum exposure and development conditions. EBL approach was also applied to fabricate DNA-CTMA microring resonators with different radii and gap widths. Optical properties of the thin films, channel waveguides and microring resonators were characterized. Refractive index was measured to be ~1.5, whilst material absorption losses were 0.28dB/cm, 0.05dB/cm, 0.43dB/cm and 0.56dB/cm at 0.63µm, 0.85µm, 1.31µm and 1.55µm. Propagation losses of DNA-CTMA channel waveguides were estimated by a cut back method, which were ~0.7dB/cm, ~0.6dB/cm and ~0.5dB/cm at 1.55µm, 1.31µm and 0.63µm. The waveguide surface profiles were examined by an atomic force microscope (AFM) and a scanning electron microscope (SEM), which showed a smooth surface with roughness of ~1nm, and a high anisotropy with undercut ~0.5µm. Transmission spectra of DNA-CTMA microring resonators were captured from an optical spectrum analyzer (OSA). The spectra were theoretically analyzed and compared, from which the major ring parameters like coupling efficiency and round trip loss were extracted. Finally, a temperature sensor was demonstrated based on the microring resonator, with a sensitivity of ~0.1nm/°C. This work explores three dimensional optical waveguides and microring resonators for the first time. The data presented in this thesis demonstrates that DNA-CTMA has characteristics superior to many traditional organic materials, indicating it is a promising material for future optical device applications.

Date of Award	15 Feb 2011
Original language	English
Awarding Institution	City University of Hong Kong
Supervisor	Yue Bun Edwin PUN (Supervisor)