Effect of slip boundary condition on the design of nanoparticle focusing lenses

The importance of nanoparticles as a building block for novel application has been emphasized in various fields. Especially, nanoparticle beam has been widely used to measure particle size distribution, synthesize materials, and generate micro-patterns, as it can enhance the measurement resolution and transport efficiency. The aerodynamic lens system has been developed to focus particles in a certain size range. The manufacturing of nanoparticles in gas phase is typically performed at the low pressure conditions and the design and simulation of lens at low pressure have been steadily reported. The computational fluid dynamics (CFD) has been utilized to analyze the flow field and obtain particle trajectories. However, previous work has used no-slip boundary condition at low pressure. This paper describes the lens design and simulation with slip boundary condition at low pressure (approximately 1 Torr). The design of lens is discussed on the basis of the Wang et al.'s guidelines and the commercial code FLUENT is used for simulation. The results of this study show that the difference of particle beam radius between no-slip and slip boundary conditions is 0.03 approximately 0.9 mm for particle size ranging from 3 to 200 nm with Brownian diffusion and that the transport efficiency is slightly higher with slip boundary condition.