QCA Cells Research Articles

Characterization of Molecular QCA Cells by Q-Controlled Enhanced Amplitude Modulation Atomic Force Microscopy

Extended abstract of a paper presented at Microscopy and Microanalysis 2004 in Savannah, Georgia, USA, August 1–5, 2004.

Molecular QCA cells. 2. Characterization of an unsymmetrical dinuclear mixed-valence complex bound to a Au surface by an organic linker.

Utilization of binary information encoded in the charge configuration of quantum-dot cells (the quantum-dot cellular automata, QCA, paradigm) requires surface-bound molecule-sized dots for room temperature operation. Molecular QCA cells are mixed-valence complexes, and the evaluation of a surface-bound unsymmetrical, heterobinuclear, two-dot, Fe-Ru molecular QCA cell is described. The tailed complex, trans-[Ru(dppm)(2)(C[triple bond]CFc)(N[triple bond]CCH(2)CH(2)-NH(2))][PF(6)] (dppm = methylbis(diphenylphosphane), Fc = (eta(5)-C(5)H(5))Fe(eta(5)-C(5)H(4))), is covalently modified with the molecular adapter, HS(CH(2))(10)COOH, for binding to a Au surface. Preparation and characterization of the films by AFM, XPS, and electrochemical techniques are reported. Cyclic voltammetric techniques are used to assess film growth, coverage and uniformity, effects of thiol diluents on areal densities of the complex, and stabilities of the accessible redox states. Amperometric techniques are used to investigate the efficiency of both chemical and electrochemical oxidation in producing the mixed-valence dication on the surface.

Molecular QCA cells. 1. Structure and functionalization of an unsymmetrical dinuclear mixed-valence complex for surface binding.

Utilization of binary information encoded in the charge configuration of quantum-dot cells (the quantum-dot cellular automata, QCA, paradigm) requires molecule-sized dots for room temperature operation. Molecular QCA cells are mixed-valence complexes, and the evaluation and functionalization of an unsymmetrical heterobinuclear, two-dot, Fe-Ru molecular QCA cell is described. The solid state structures of trans-RuCl(dppm)(2)(C[triple bond]CFc) (1) (dppm = methylbis(diphenylphosphane), Fc = (eta(5)-C(5)H(5))Fe(eta(5)-C(5)H(4))) and mixed-valence [trans-RuCl(dppm)(2)(C[triple bond]CFc)][BF(4)] (1a) as well as XPS and spectroscopic data suggest class II behavior suitable for the intended application. Utilization of the trans-Cl position of 1 permits functionalization for surface binding. Two "tailed" complexes of 1, trans-Ru(dppm)(2)(C[triple bond]CFc)(C[triple bond]CPhOCH(3)) (2) and trans-[Ru(dppm)(2)(C[triple bond]CFc)(N[triple bond]CCH(2)CH(2)NH(2))][PF(6)] (3), have been prepared and characterized. The solid state structure of 3 and multinuclear NMR experiments define the structures. In addition, the spectroscopic properties of all complexes and their mixed-valence species are used to define the effect of the substituent "tail" on mixed-valence properties. Further, the electrochemistry of these compounds permits assessment of the extent of perturbation of the substituents on the comproportionation constants and overall electrochemical stability. The complexes possess properties necessary for candidate QCA molecules.