Ion adsorption-enrichment effect and its driving mechanism for nano-dots lithography with SPM probe on water-soluble crystal surfaces

Abstract

HypothesisWater-soluble KDP (KH2PO4) crystals possess excellent optical properties and are employed as frequency converters in clean fusion energy. To improve their performances, there is an immediate necessity to lithograph surface nano-patterns on them. Although the Scanning Probe Microscope (SPM) provides a promising way to achieve this purpose through the water menisci, the driving mechanisms of the lithographic behaviors have not yet been revealed. Simulations and ExperimentsMulti-scale investigations are constructed to explore the underlying driving mechanisms. The SPM probe-induced ion diffusion-transport behaviors are investigated by molecular dynamics. The ion adsorption-enrichment mechanisms are revealed by 18 adsorption models via the ab initio. The SPM probe-induced self-assembly experiments are performed to prove the local heavy concentration. A comprehensive model is developed to describe the lithography mechanisms of the probe-induced self-assembly nano-dots on water-soluble substrates. FindingsIt is interestingly found that the KDP growth units (H2PO4−) exhibit obvious adsorption-enrichment effect at 3.16 Å from the probe surface, causing local heavy concentration. The H2PO4− would spontaneously adsorb onto the probe surface, which is dominated by the Si-O bonding reactions. The nano-dots with the height of 27 ∼ 48 nm and diameter of 2.0 ∼ 2.7 μm are lithographed on the KDP substrate. The proposed model further confirms that the lithography processes are driven by the solution supersaturation, solute diffusion, and surface free energy.