Spectroscopic and Electronic Characterization of Microfabricated Solid State Molecular Electronic Junctions

• Author / Creator

  Mahmoud Mohamed, Amr Mohamed

• The objective of the research described in this thesis is structural characterization of molecular electronic devices and investigation of their compatibility with widely use conventional microelectronics. Back-side spectroscopy was performed to probe organic molecular later integrity at buried interfaces, during and after fabrication. Modifications of optically transparent substrates with organic molecules were achieved using ultrathin Ti as a primer, which then spontaneously reduced aromatic diazonium ions in solution to form free radicals. The free radicals then bond covalently to the substrate. Then, a second conducting contact was deposited by direct physical vapor deposition onto the molecular layer. The molecular layer integrity was probed by “back-side” Raman and infrared spectroscopy. The results demonstrated that metal deposition had minimal influence on molecular layer structure.
  The compatibility of carbon based molecular junctions with various microfabrication processes such as elevated temperatures, photolithographic processing and metal deposition was investigated. Flat carbon surfaces were modified electrochemically by reduction of aromatic diazonium ions. The aromatic molecules bond covalently to the electrode though strong C-C bonds. Then the top metal contact was deposited to form a complete junction. Molecular layer integrity after deposition of various metals was inspected by “back-side” spectroscopy. Both Ti and Pt metals caused significant damage to the molecular layer, while Au and Cu had no observable effect on the molecular layer. The modified samples were thermally stable up to 400 oC and the complete junctions were stable up to 250 oC under vacuum. Carbon based molecular junctions were compatible with a photolithographic process and different solvents used during the process.
  The charge transport mechanism through silicon based molecular junctions was investigated by replacing carbon of previous investigations by a Si electrode. Heavily doped n- and p-Si (111) substrates were modified electrochemically with aromatic molecular layers and Cu contact was deposited, resulting in reproducible junctions with high yield. The junctions were characterized spectroscopically and electrically. Junctions made with n-Si exhibited significantly higher conductivity than those made with either p-Si or carbon substrates. This difference in conductivity was attributed to difference in the barrier height for tunneling as estimated from ultraviolet photoemission spectroscopy measurements.

• Subjects / Keywords

  • Surface characterization
  • Microfabrication
  • Raman Spectroscopy
  • Molecular Electronic Junctions

• Graduation date

  Fall 2012

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R3XD0R81J

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.