Nanopatterns of Zinc Phthalocyanines, Gold Nanoparticles, and Porphyrins Prepared Using Particle Lithography: Characterization of Patterning Steps with Scanning Probe Microscopy

Abstract

The growth and self-assembly of molecules on surfaces can be directly visualized at the molecular level using studies which combine nanoscale lithography and high-resolution imaging. Nanopatterning provides a unique and practical approach for direct views of surface changes after the key chemical steps of nanopatterning, providing landmarks and baselines for measuring growth in vertical and lateral dimensions. Controlling the arrangement of materials on surfaces at the nanoscale can be achieved using particle lithography. Arrays of well-defined nanostructures can be prepared with reproducible geometries and arrangement. Results for the preparation of nanopatterns produced with particle lithography are presented using high resolution images acquired with scanning probe microscopy (SPM). Samples were prepared using steps for depositing nanoparticles, porphyrins, and phthalocyanines on patterned surfaces to generate multicomponent nanopatterns. Studies of surface chemistry at the molecular level have practical applications for emerging technologies with photovoltaic and photoelectronic devices. Atomic force microscopy (AFM) was used to characterize samples to gain insight on the changes in surface chemistry after patterning organosilanes, organothiols and nanoparticles. For studies of surface chemistry at the nanoscale, AFM has unique capabilities for molecular visualization and ultrasensitive measurements of surface properties. The history of SPM, instrument set-up, and results for particle lithography with porphyrins, zinc phthalocyanines and gold nanoparticles are described in this dissertation. Protocols for patterning porphyrin nanostructures on Au(111) were developed based on steps with immersion combined with particle lithography. Porphyrins with a central metal ion, 5,10,15,20-tetraphenyl-21H,23H-porphine (TPP) and free-base 5,10,15,20-tetraphenyl-21H,23H-porphine nickel(II) (TPN) were studied. Samples of zinc phthalocyanines were prepared using particle lithography with surfaces that were patterned with organosilanes. The dimensions and spacing can be selectively tuned by using selected sizes of latex ad silica spheres as a surface mask. The metallated phthalocyanines bound selectively to the spatially confined sites of nanopatterns, and did not bind to areas of the organosilane resist. Bare gold nanoparticles and organosilane coated nanoparticles were synthesized for characterizations with AFM. At the nanoscale, variations in the sizes of patterns provide a surface test platform for evaluating size dependent physical properties.