Use of Scanning Probe Microscopy in Dip Pen Nanolithography

One of the innovative applications of scanning probe microscopy for nanolithography is dip pen nanolithography (DPN). In this special technique the water meniscus formed between the tip and the substrate acts as a medium for molecular transport. The technique depends on the key phenomenon that the molecule to be deposited on the substrate (which is referred as the ink ) can be transported in a controlled way from the tip (which is initially coated with the ink) to the substrate. The molecule (the ink) to be deposited on the substrate should interact with the substrate to form a chemical bond, leading to a stable structure [82]. 

The core concept that the water meniscus at the tip-substrate contact can indeed be controlled and can be used as the molecular transport medium came from basic investigations of water meniscus on lateral force microscopy (LFM) [83]. It was 

The observation that the relative humidity, the hydrophobic or hydrophilic nature of the substrate and the scan speed can be used to control the amount of water being transported from the tip to the substrate led to the technique of DPN. Currently the technique can achieve feature sizes down to 10-15 nm with the capability of using multiple ink [84] as well as both serial and parallel writing capability [85]. 

Depositing ink on the nk being transferred tip from ink-pot . from tip to substrate 

The condition of deposition depends on the molecules to be deposited and their capability to form a self-assembled monolayer (SAM). The two widely used molecules are 16-mercaptohexadeconic acid (MHA) and 1-octadecane thiol (ODT) and the most used substrate is Au (111) film. 

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