Branched High Aspect Ratio Nanostructures Fabricated by Focused Helium Ion Beam Induced Deposition of an Insulator.

Frances I Allen

doi:10.3390/mi12030232

Abstract

Helium ion beam induced deposition using the gaseous precursor pentamethylcyclopentasiloxane is employed to fabricate high aspect ratio insulator nanostructures (nanopillars and nanocylinders) that exhibit charge induced branching. The branched nanostructures are analyzed by transmission electron microscopy. It is found that the side branches form above a certain threshold height and that by increasing the flow rate of the precursor, the vertical growth rate and branching phenomenon can be significantly enhanced, with fractalesque branching patterns observed. The direct-write ion beam nanofabrication technique described herein offers a fast single-step method for the growth of high aspect ratio branched nanostructures with site-selective placement on the nanometer scale.

Highlights

Fabricated by Focused Helium IonFocused ion beams (FIB) are widely used for additive and subtractive nanofabrication, either via direct-write exposure, or using resist-based methods
A gaseous precursor is injected into the microscope chamber and its molecules become dissociated upon interaction with the primary ions, scattered ions, and with the ion-induced secondary electrons [2]
In the dark-field scanning TEM (STEM) image of Figure 2a, these branched structures are clearly evident for the fourth nanopillar from the left onwards

Summary

Introduction

Fabricated by Focused Helium IonFocused ion beams (FIB) are widely used for additive and subtractive nanofabrication, either via direct-write exposure, or using resist-based methods. In the direct-write approaches, the ion beam locally removes material by sputtering, or adds material by FIB-induced deposition (FIBID) [1]. In the latter, a gaseous precursor is injected into the microscope chamber and its molecules become dissociated upon interaction with the primary ions, scattered ions, and with the ion-induced secondary electrons [2]. New FIB sources include the plasma source (principally xenon ions) [3], liquid-metal alloy sources (gold, bismuth, silicon ions, etc.) [4], cold-atom-based sources (principally lithium and cesium ions) [5], and the gas field-ionization source (GFIS) (helium and neon ions) [6]. With the wide choice of ion species available, along with a wide choice of other beam parameters such as beam energy and current, nanofabrication tasks can be optimized and new ones enabled by choosing the appropriate FIB

Methods

Results

Conclusion