Fabrication of sub-10 nm solid-state nanopores by electrical breakdown

Abstract: Nanopore sensing is a versatile technique that employs very small openings, known as nanopores, to study biomolecules. The use of nanopores on solid-state membranes has gained attention due to its potential for low-cost and high-throughput sensing of single molecules in liquids. Controlled dielectric breakdown (CBD) is a method for fabricating nanopores in a suspended membrane using computer control, and can be performed in liquid, making it a more practical alternative to traditional techniques that require specialized equipment and high vacuum. Multilevel Pulse-Voltage Injection (MPVI) is a variant of CBD that allows for better control over the size and shape of the nanopore being fabricated. The main focus of this research is to develop electrical techniques for fabricating sub-10 nm solid-state nanopores in silicon nitride and graphene membranes, and to study the characteristics of the resulting nanopores. Two different MPVI schemes were implemented for fabricating nanopores in silicon nitride. The MPVI technique for Scheme 1 sets two thresholds to check if a pore is formed or not. Scheme 2 was developed by adding a threshold in order to avoid extra pore enlargement. For nanopores on a silicon nitride membrane with a 23 nm deep hole, the ratio of sub-20 nm pores improved from 20 % (Scheme 1) to around 90 % (Scheme 2). Additionally, the ratio of sub-10 nm nanopores via Scheme 2 was around 70 %. For nanopores on a silicon nitride membrane damaged by a single femtosecond laser pulse, 50 % of the fabricated nanopores via Scheme 2 were sub-10 nm. For bi-layer graphene membranes, the electrochemical reaction (ECR) technique was used to fabricate nanopores, resulting in three nanopores with diameters of 6.4, 5.9, and 1.2 nm. The nanopores on all types of membranes were enlarged using MPVI of Scheme 1, resulting in a successful increase in pore size by 0.1 to 1 nm. Finally, DNA translocation experiments were conducted to verify the suitability of the fabricated nanopores. DNA translocation events were observed using fabricated nanopores on two types of silicon nitride membranes. They are not observed for the graphene nanopore.