Vapor-Phase Nanopatterning of Aminosilanes with Electron Beam Lithography: Understanding and Minimizing Background Functionalization

Effect of Ionic Strength, Nanoparticle Surface Charge Density, and Template Diameter on Self-Limiting Single-Particle Placement: A Numerical Study

For the bottom-up approach where functional materials are constructed out of nanoscale building blocks (e.g., nanoparticles), it is essential to have methods that are capable of placing the individual nanoscale building blocks onto exact substrate positions on a large scale and on a large area. One of the promising placement methods is the self-limiting single-particle placement (SPP), in which a single nanoparticle in a colloidal solution is electrostatically guided by electrostatic templates and exactly one single nanoparticle is placed on each target position in a self-limiting way. This paper presents a numerical study on SPP, where the effects of three key parameters, (1) ionic strength (IS), (2) nanoparticle surface charge density (σ_NP), and (3) circular template diameter (d), on SPP are investigated. For 40 different parameter sets of (IS, σ_NP, d), a 30 nm nanoparticle positioned at R⃗ above the substrate was modeled in two configurations (i) without and (ii) with the presence of a 30 nm nanoparticle at the center of a circular template. For each parameter set and each configuration, the electrostatic potentials were calculated by numerically solving the Poisson-Boltzmann equation, from which interaction forces and interaction free energies were subsequently calculated. These have identified realms of parameter sets that enable a successful SPP. A few exemplary parameter sets include (IS, σ_NP, d) = (0.5 mM, -1.5 μC/cm², 100 nm), (0.05 mM, -0.5 μC/cm², 100 nm), (0.5 mM, -1.5 μC/cm², 150 nm), and (0.05 mM, -0.8 μC/cm², 150 nm). This study provides clear guidance toward experimental realizations of large-scale and large-area SPPs, which could lead to bottom-up fabrications of novel electronic, photonic, plasmonic, and spintronic devices and sensors.

Nanofabrication Techniques: Challenges and Future Prospects

Nanofabrication of functional micro/nano-features is becoming increasingly relevant in various electronic, photonic, energy, and biological devices globally. The development of these devices with special characteristics originates from the integration of low-cost and high-quality micro/nano-features into 3D-designs. Great progress has been achieved in recent years for the fabrication of micro/nanostructured based devices by using different imprinting techniques. The key problems are designing techniques/approaches with adequate resolution and consistency with specific materials. By considering optical device fabrication on the large-scale as a context, we discussed the considerations involved in product fabrication processes compatibility, the feature's functionality, and capability of bottom-up and top-down processes. This review summarizes the recent developments in these areas with an emphasis on established techniques for the micro/nano-fabrication of 3-dimensional structured devices on large-scale. Moreover, numerous potential applications and innovative products based on the large-scale are also demonstrated. Finally, prospects, challenges, and future directions for device fabrication are addressed precisely.

High-Resolution Nanopatterning of Free-Standing, Self-Supported Helical Polypeptide Rod Brushes via Electron Beam Lithography

In this study of nanopatterned helical poly(benzyl-l-glutamate) (PBLG) brushes, rod-type brush arrays were fabricated via an integrated process of high-resolution lithography and surface-initiated vapor deposition polymerization (SI-VDP). "Nanospikes" of polymer brushes with spacings of less than 100 nm were produced. The topology and areal behavior of the resulting patterned rod-like brushes were analyzed and compared with patterned coil-type brushes. A geometric study of these self-assembled "nanospikes" was carried out, and their cross sections were investigated via focused ion beam (FIB) and scanning electron microscopy (SEM). Furthermore, the presence of poly(N-isopropylacrylamide) (PNIPAM) brushes in unpatterned regions was shown to inhibit undesired "inter-spike" bridging of the PBLG brushes, resulting in more well-defined nanostructures. It was shown that rod-like polypeptide brushes are capable of self-segregation and become arranged vertically without any external support from their surroundings, to form a rod bundle end-point functional topography that could provide possible pathways for studies of model biological surfaces, directed assembly of nanoparticles, or binary mixed brush surfaces with dual properties.

Heterogeneous assembly of water from the vapor phase-Physical experiments and simulations with binding trifunctional organosilanes at the vapor/solid interface

A trace amount of interfacial water is required to initiate hydrosilation reactions of trifunctional organosilanes to form surface assemblies. In recent studies, we have learned that water also has a critical role in directing molecular placement on surfaces because water can react with silicon to provide oxygenated sites for surface binding. Consequently, the wettability nature of substrates influences the placement and density of organosilane films formed by vapor-phase reactions. Nanopatterning protocols were designed using vapor-phase organosilanes and colloidal lithography to compare the wettability differences of hydrophilic mica(0001) compared to relatively hydrophobic Si(100) as a strategy for tracking the location of water on surfaces. The competition between hydrophobic and hydrophilic domains for the adsorption and coalescence of water condensed from vapor can be mapped indirectly by mapping the organosilanes, which bind to water at the solid interface, using atomic force microscopy. Trifunctional octadecyltrichlorosilane (OTS) was used as a marker molecule to map out the areas of the surface where water was deposited. The effect of systematic changes in film thickness and surface coverage of OTS was evaluated at the vapor/solid interface by adding an incremental amount of water to sealed reaction vessels to wet the surface and assessing the outcome after reaction with vapor-phase trichlorosilane. Reactive molecular dynamics simulations of the silicon-water vapor interface combined with electronic structure calculations of oxygenated silicon clusters with methyltrichlorosilane provided insight of the mechanism for surface binding, toward understanding the nature of the interface and wettability factors, which influence the association and placement of silane molecules on surfaces.