Femtosecond Laser Enabled Maskless Nanostructure Fabrications and Applications

Open Access
Author:
Wang, Chao
Graduate Program:
Electrical Engineering
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
January 23, 2015
Committee Members:
  • Shizhuo Yin, Dissertation Advisor
  • James Kenneth Breakall, Committee Member
  • Julio Urbina, Committee Member
  • Julian Decatur Maynard Jr., Committee Member
Keywords:
  • Femtosecond Laser
  • Femtosecond Laser Ablation
  • Nanostructure
  • Sureface Enhanced Raman Spectroscopy
  • Anti-reflection
  • LEDs
Abstract:
Femtosecond laser ablation is quite different when compared to other laser ablation methods due to the ultra-short pulse duration. Two mechanisms, including thermal vaporization and Coulomb explosion, are responsible for femtosecond laser ablation. Nanostructures created by femtosecond laser ablation offer the advantages of having a high efficiency and low cost, which attracted us to investigate the application. The characteristic size of the nanostructures could be varied from several nanometers to several hundred nanometers. Surface enhanced Raman spectroscopy (SERS) was realized on nanostructured copper surface generated by femtosecond laser ablation. An enhancement factor of 863 was achieved, which agreed relatively well with the theoretical analyses found by finite-difference time-domain (FDTD) simulation. In addition, the anti-reflection effect of the nanostructured surface induced by femtosecond laser ablation was studied. The reflectance of the nanostructured silicon surface was reduced to 3% throughout the UV to near IR region (1.1 um) at a large field of view. The ultra-high transmittance of the nanostructured polydimethylsiloxane (PDMS) layer was also measured over the entire range of the visible spectrum and at a large incident angle range of 120 degrees. Finally, a super broadband InGaN/GaN-based light emitting diode (LED) was realized on a nanostructured sapphire substrate. Emission wavelength peaks covering the range between 433 and 519 nm were detected. Furthermore, super broadband emission with a bandwidth of 214 nm was achieved, which basically covered the entire visible spectrum.