Heterostuctures of 4-(chloromethyl)phenyltrichlorosilane and 5,10,15,20-tetra(4-pyridyl)-21H,23H-porphine prepared on Si(111) using particle lithography: Nanoscale characterization of the main steps of nanopatterning

Nanostructures of 4-(chloromethyl)phenyltrichlorosilane (CMPS) were used as a foundation to attach and grow heterostructures of porphyrins and organosilanes. A protocol was developed with particle lithography using steps of immersion in organosilane solutions to selectively passivate the surface of Si(111) with octadecyltrichlorosilane (OTS). A methyl-terminated matrix was chosen to direct the growth of CMPS nanostructures to fill the uncovered sites of Si(111) to enable spatial confinement of the surface reaction. Silica spheres with a diameter of 500 nm were used as a surface mask to prepare nanoscopic holes within the OTS matrix film. Next, the samples were immersed in solutions of CMPS dissolved in toluene or bicyclohexane. Nanostructures of CMPS formed within the nanoholes, to furnish spatially selective sites for binding porphyrins. The samples were then characterized with AFM to evaluate the height and morphology of the CMPS nanostructures that had formed within the nanoholes of OTS. The samples were then refluxed in a porphyrin solution for selective binding to produce heterostructures. The attachment of porphyrins was evidenced by increases in the height and width of the CMPS nanopatterns. The measurements of size indicate that multiple layers of porphyrins were added. Through each step of the surface reaction the surrounding matrix of OTS showed minimal areas of nonspecific adsorption. The AFM studies provide insight into the mechanism of the self-polymerization of CMPS as a platform for constructing porphyrin heterostructures.

Chemical approaches for nanoscale patterning based on particle lithography with proteins and organic thin films

Nanopatterning methods based on particle lithography offer generic capabilities for high-throughput fabrication with thin film materials, such as organothiol and organosilane self-assembled monolayers (SAMs), polymer films, biological samples, and nanoparticles. Combining scanning probe microscopy with sample preparation based on approaches with particle lithography produces robust test platforms for ultrasensitive surface measurements. For example, nanopatterns of octadecyltrichlorosilane (OTS) can be prepared on surfaces of Si(111) using designed protocols of particle lithography combined with steps of either vapor deposition, immersion, or contact printing. Changing the physical approaches for applying molecules to masked surfaces produces nanostructures with designed shapes and thickness. Billions of nanostructures can be prepared using strategies for particle lithography, requiring only basic steps of mixing, heating, centrifuging, and drying. Arrays of exquisitely small and regular nanopatterns can be prepared with few defects and high reproducibility. For nanopatterns prepared with SAMs, the endgroups can be designed to spatially define the interfacial selectivity for adsorption of proteins, nanoparticles, or electrolessly deposited metals. Particle lithography has become a mature technique, with broad applicability for thin film materials. Images and measurements acquired with scanning probe microscopy will be described for samples prepared using particle lithography-based approaches.