Preparation of Octadecyltrichlorosilane Nanopatterns Using Particle Lithography: An Atomic Force Microscopy Laboratory

Abstract

Experiments are described that involve undergraduates learning concepts of nanoscience and chemistry. Students prepare nanopatterns of organosilane films using protocols of particle lithography. A few basic techniques are needed to prepare samples, such as centrifuging, mixing, heating, and drying. Students obtain hands-on skills with nanoscale imaging using an atomic force microscope (AFM) when they learn to characterize samples. Designed surfaces are made using a surface mask of latex or silica spheres to generate nanopatterns of organosilanes. An organic thin film is applied to the substrate using steps of either heated vapor deposition or immersion in solution. The steps for preparing samples are not complicated; however, the nanostructures that are produced by particle lithography are exquisitely regular in geometry and surface arrangement. At the molecular level, two types of sample morphology can be made depending on the step for depositing organosilanes. Ring-shaped nanostructures are produced with heated vapor deposition through a particle mask, and nanoholes are produced within a matrix film using immersion of masked substrates. Experience with advanced AFM instrumentation is obtained for data acquisition, digital image processing, and analysis. Skills with chemical analysis are gained with bench methods of sample preparation. Concepts such as the organization of molecules on surfaces and molecular self-assembly are demonstrated with the visualization of nanopatterns prepared by students. Experiments with particle lithography can be used as a laboratory module or for undergraduate research projects, and are suitable for students with a multidisciplinary science background.

Periodic Silver and Gold Nanodot Array Fabrication on Nanosphere Lithography-Based Patterns Using Electroless Deposition

“…A solution of nanospheres was prepared by diluting the stock nanosphere solution 1:1 with water to generate a monolayer of nanospheres on the Si substrate. Surfactant from the nanosphere solution was washed off by vortexing and centrifugation to promote intersphere interactions as previously reported. , The spheres pack well on the surface in a repeating hexagonal arrangement, as shown in Figure b and d, due to intersphere interactions and capillary forces. During formation of the OTS SAM (Figure c and d), the contact of the spheres with the substrate effectively mask self-assembly of OTS on those areas, creating nanopores (Figure e and f) at the sphere contact locations with diameters determined by the contact area and spacing determined by the nanosphere diameter.…”

“…Silane-based monolayer formation is a well-studied process that involves the hydrolysis and subsequent condensation with surface hydroxyl groups to form a uniform, monolayer thick coating on the silicon surface with OTS molecules utilizing their longer alkyl chains to produce particularly well-packed SAMs films. , The residual water on the native oxide of silicon plays a critical role in the monolayer formation process as it is required for the hydrolysis reactions . Therefore, the effect of relative humidity on the fabrication process was investigated to optimize the monolayer formation conditions. , Garno et al previously demonstrated that the relative humidity at which the samples are dried prior to monolayer formation effects the quality, packing, and thickness of the monolayer formed on the SiO 2 surface . Our results, shown in Figure S1, demonstrate the importance of the relative humidity.…”

“…In this approach, monodispersed nanospheres in water are drop cast on a glass/silica substrate, allowing the surface tension of water to produce a uniformly packed hexagonal array of spheres covering the substrate. Using a glass or Si substrate, organosilanes can be self-assembled from solution , or evaporated in the vapor phase , onto the sphere-coated substrate to modify the surface chemistry and leave the contact areas between the spheres and the substrate unmodified. Upon removal of the spheres, arrays of periodic holes in the monolayer resist, commensurate with the hexagonal sphere packing, are revealed.…”

Three-Dimensional Printing of a Model Atomic Force Microscope to Measure Force–Distance Profiles

“…Atomic force microscopy has been a useful tool in chemistry and materials science due to its exquisitely high spatial resolution that has been used to visualize materials, molecules, and atoms. , However, using an atomic force microscope (AFM) in the laboratory curriculum is typically restricted to upper-division undergraduate or higher-level courses. − At the lower-division undergraduate level, AFM use is uncommon and generally restricted to laboratories with fewer than 10 students − or to use of the AFM as a demonstration during class . To understand and take full advantage of its technical capabilities, an understanding of an AFM’s operating principles is necessary, and in our view, should start at the first-year undergraduate level.…”