Theoretical modeling and surface attachment of molecular quantum-dot cellular automata cells based on the Creutz-Taube ion

The quantum-dot cellular automata (QCA) paradigm describes how information can be transmitted and processed by Coulomb interactions between structures that contain electrical charge. The molecular implementation of QCA (MQCA) investigates the possibilities of extending the QCA idea to the smallest possible size scale, the scale of molecules. Beside extraordinarily densely integrated system, other advantages for molecular implementation include room temperature operation and low power consumption.; In order to know how many cells can work coherently in a MQCA device and how high the temperature it can withstand to, the thermodynamic behavior of MQCA wires and majority gates were modeled using statistical mechanics. Majority gates should give the correct output at temperatures of up to 450K, while wires of hundreds to thousands of QCA cells are predicted to operate coherently at room temperature.; In order to make MQCA devices, QCA cells must be put onto ultraflat surfaces. We developed a cleaning and oxidation procedure which yields a SiO₂ native oxide with root mean square (RMS) roughness less than 0.5 Å. We also investigated the mechanism of octadecyltrichlorosilane (OTS) monolayer and multilayer deposition on SiO₂. By controlling the amount of water in the solution of OTS used to deposit the OTS molecules, either a smooth monolayer or rough multilayer could be obtained selectively.; A well-known mixed-valence compound—the Creutz-Taube ion—was synthesized as a 2-dot MQCA cell. The selective binding of these Creutz-Taube ions on hydrophilic and hydrophobic surfaces was investigated by X-ray photoelectron spectroscopy, ellipsometry and AFM measurements. These molecules only attach to hydrophilic surfaces. Once they are attached, they give an inorganic analog of a self-assembled monolayer in which the molecules adopt a lying-down orientation. Surface reflectance UV and NIR studies suggested that the optical properties of these cells remain unchanged after they are attached to insulating surfaces. With the self-assembly and selective binding properties established, the patterning of 35 nm wide lines of the Creutz-Taube ion through a high resolution PMMA mask was demonstrated.