SELF-ASSEMBLY AND CHARACTERIZATION OF CANDIDATE MOLECULES FOR MOLECULAR ELECTRONIC AND QUANTUM COMPUTING APPLICATIONS

Open Access
- Author:
- Stapleton, Joshua J
- Graduate Program:
- Chemistry
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- March 01, 2005
- Committee Members:
- David Lawrence Allara, Committee Chair/Co-Chair
Nicholas Winograd, Committee Member
Thomas E Mallouk, Committee Member
Carlo G Pantano, Committee Member - Keywords:
- SAMs
infrared spectroscopy
molecular electronics
XPS - Abstract:
- Chapter 1: An overview of how self-assembly may be utilized in the molecular electronics and quantum computing fields. Chapter 2: SAMs of the nitro-substituted oligo(phenylene-ethynylene) (OPE), 4,4'-(diethynylphenyl)-2'-nitro-1-benzenethiolate, on Au{111} were prepared. Assembly of the nitro-OPE SAM, either via acidic hydrolysis of the thioacetate derivative or from the thiol in neat solvent, produces a well-ordered SAM with a (ã3xã3) superlattice structure and an average molecular tilt of 32-39 degrees from the surface normal. In contrast, when the nitro-OPE SAM is assembled by hydrolysis of the thioacetate derivative under basic conditions, extensive redox reactions arise in which oxidation of the S atoms occurs with accompanying reduction of -NO2 to -NH2, to form mixed composition SAMs. Further, the nitro-OPE SAM, regardless of the preparation method, shows significant chemical instability under storage in air and/or light exposure. Chapter 3: SAMs of the isocyano derivative of 4,4f-di(phenylene-ethynylene)benzene, a member of the gOPEh family of gmolecular wiresh, have been prepared on Au{111} and Pd{111} surfaces. For assembly in oxygen-free environments with freshly deposited metal surfaces, infrared reflection spectroscopy (IRS) indicates the molecules assume a tilted structure with average tilt angles of 18-24 degrees from the surface normal. Both IRS and x-ray photoelectron spectroscopy support a single sigma-type bond of the -NC group to the Au surface and a two-fold type of bonding to the Pd surface. Both SAMs show significant chemical instability with respect to exposure to typical ambient conditions. Chapter 4: We demonstrate that it is possible to mimic the surface chemical properties of standard (~150.0 nm thick) aluminum films using ultrathin Al2O3 films. Formed via the resistive evaporation of ~0.7 nm Al metal and oxidized upon exposure to the laboratory ambient these films form equivalently on SiO2/Si, sapphire, quartz, and fused silica substrates. High quality stearic acid SAMs are formed on all 0.7 nm thick Al films. Chapter 5: The chemical and structural properties of two ƒÖ-nitroxide long-chain alkanoic acids self-assembled onto natively oxidized silver and aluminum surfaces are studied using infrared spectroscopy, single wavelength ellipsometry, contact angles and electron spin resonance.