LETTER pubs.acs.org/NanoLett
Maskless Fabrication of Nanowells Using Chemically Reactive Colloids Neetu Chaturvedi,† Erik Hsiao,† Darrell Velegol,* and Seong H. Kim* Department of Chemical Engineering, Pennsylvania State University, University Park, Pennsylvania 16802, United States
bS Supporting Information ABSTRACT: This letter describes the maskless fabrication of nanowells on a silicon substrate using chemically reactive nanoparticles. The amidine-functionalized polystyrene latex (APSL) colloids are adhered onto a silicon wafer, and hydrolysis of the particles' amidine groups generates the ammonium hydroxide etchant locally. The localized release of reactive species and its fast diffusion into the bulk liquid ensure that the silicon etching takes place only under the APSL colloids. Thus, the basal length of the nanowells is precisely controlled by the diameter of the APSL particles. The shape of the nanowells depends on the structure of the substrate: inverted pyramids on silicon (100) and hexagonal pits on silicon (111). The method described here provides an easy, inexpensive, safe, and high-throughput approach for generating nanowells on silicon surfaces. This maskless and simple nanofabrication method will open doors for new applications with locally generated or locally delivered chemistry from nanoparticles. KEYWORDS: Silicon, maskless nanoetching, locally generated etchant, inverted pyramids, amidine hydrolysis
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and readily available. With these advantages in mind, we sought to answer a few important questions: How does the size of the nanowell change with time? How does the size of the nanowell compare to the size of the particle? What is the mechanism of nanowell formation? The nanowell fabrication process is relatively safe and simple. A layer of APSL particles (Interfacial Dynamics Corporation) is adhered onto a silicon wafer by settling the positively charged particles onto a negatively charged silicon substrate in deionized (DI) water. For smaller APSL particles (
