Scalable Patterning of Encapsulated Black Phosphorus.

Nick Clark,Yang Cao,Edward A Lewis,Lan Nguyen,Matthew J Hamer,Eric Prestat,Reza Kashtiban,Jeremy Sloan,Alistair Garner,Sarah J Haigh,Demie Kepaptsoglou,Fredrik Schedin,Mengjian Zhu,Roman V Gorbachev

doi:10.1021/acs.nanolett.8b00946

Nick Clark, Yang Cao + Show 12 more

Open Access

https://doi.org/10.1021/acs.nanolett.8b00946

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Abstract

Atomically thin black phosphorus (BP) has attracted considerable interest due to its unique properties, such as an infrared band gap that depends on the number of layers and excellent electronic transport characteristics. This material is known to be sensitive to light and oxygen and degrades in air unless protected with an encapsulation barrier, limiting its exploitation in electrical devices. We present a new scalable technique for nanopatterning few layered BP by direct electron beam exposure of encapsulated crystals, achieving a spatial resolution down to 6 nm. By encapsulating the BP with single layer graphene or hexagonal boron nitride (hBN), we show that a focused electron probe can be used to produce controllable local oxidation of BP through nanometre size defects created in the encapsulation layer by the electron impact. We have tested the approach in the scanning transmission electron microscope (STEM) and using industry standard electron beam lithography (EBL). Etched regions of the BP are stabilized by a thin passivation layer and demonstrate typical insulating behavior as measured at 300 and 4.3 K. This new scalable approach to nanopatterning of thin air sensitive crystals has the potential to facilitate their wider use for a variety of sensing and electronics applications.

Highlights

The successful isolation of few-layer black phosphorus (BP) has generated remarkable excitement in a very short time.[1−3] Such isolation is possible due to its highly anisotropic crystal structure where corrugated layers of phosphorus atoms are bonded by weak van-der-Waals interactions and can be separated
We demonstrate that introducing atomic scale defects in the encapsulation layer with a focused electron beam allows air species to come into contact with selected areas of the embedded BP crystal and generate a few-nanometer oxide region around the perforation point
For scanning transmission electron microscope (STEM) experiments, monolayer graphene or hexagonal boron nitride (hBN) sheets were used to encapsulate thin (2−5 layer) BP flakes, which were transferred to a TEM support film

Summary

Introduction

The successful isolation of few-layer black phosphorus (BP) has generated remarkable excitement in a very short time.[1−3] Such isolation is possible due to its highly anisotropic crystal structure where corrugated layers of phosphorus atoms are bonded by weak van-der-Waals interactions and can be separated. We demonstrate that introducing atomic scale defects in the encapsulation layer with a focused electron beam allows air species to come into contact with selected areas of the embedded BP crystal and generate a few-nanometer oxide region around the perforation point. We induce such local oxidation controllably within both STEM and EBL instruments and use electron diffraction, energy dispersive X-ray spectroscopy (EDXS), and electron energy loss spectroscopy (EELS) to study the atomic and chemical structure of the etched locations. We further show that oxidized lines as narrow as 10 nm demonstrate clear insulating behavior with a breakdown voltage well above that of vacuum even at room temperature

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