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

Abstract

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 R ⃗ 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/cm 2 , 100 nm), (0.05 mM, −0.5 μC/cm 2 , 100 nm), (0.5 mM, −1.5 μC/cm 2 , 150 nm), and (0.05 mM, −0.8 μC/cm 2 , 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.