Shrinking of Solid-state Nanopores by Direct Thermal Heating

Waseem Asghar,Joseph Anthony Billo,Samir Muzaffar Iqbal,Azhar Ilyas

doi:10.1186/1556-276x-6-372

Abstract

Solid-state nanopores have emerged as useful single-molecule sensors for DNA and proteins. A novel and simple technique for solid-state nanopore fabrication is reported here. The process involves direct thermal heating of 100 to 300 nm nanopores, made by focused ion beam (FIB) milling in free-standing membranes. Direct heating results in shrinking of the silicon dioxide nanopores. The free-standing silicon dioxide membrane is softened and adatoms diffuse to a lower surface free energy. The model predicts the dynamics of the shrinking process as validated by experiments. The method described herein, can process many samples at one time. The inbuilt stress in the oxide film is also reduced due to annealing. The surface composition of the pore walls remains the same during the shrinking process. The linear shrinkage rate gives a reproducible way to control the diameter of a pore with nanometer precision.

Highlights

The use of a-hemolysin protein nanopores inspired the fabrication of solid-state nanopores
A boron-doped double-side-polished Si (100) wafer was thermally oxidized to a thickness of 400 nm
Free-standing SiO2 membranes (30 × 30 μm2) were achieved using wet tetramethylammonium hydroxide (TMAH) anisotropic etching through the whole wafer thickness

Summary

Introduction

The use of a-hemolysin protein nanopores inspired the fabrication of solid-state nanopores. Solid-state nanopores have emerged as novel biosensors for single molecule analysis of DNA, proteins, etc. The diameter of the nanopore should be almost at the same scale as the size of the translocating species. The pores fabricated with conventional processes result into initial diameters larger than the size of species of interest [12,13,14,15,16]. The nanopore diameter is reduced using transmission electron microscope (TEM) or field emission scanning electron microscope (FESEM) to induce the shrinking [15,17] and FIB for the sculpting processes [18]. During the TEM shrinking process, the viscous flow of SiO2 membrane is induced by an electron beam of optimal intensity. The nanopore, fulfilling the condition r < t/2, would shrink under the electron beam at optimal conditions

Methods

Results

Conclusion