Topography and KPFM of CVD grown molybdenum disulfide monolayers measured by AFM

In this application note, monolayer MoS2 grown by chemical vapor deposition (CVD) was imaged with Kelvin probe force microscopy (KPFM) using a Flex-Axiom to study the contact potential difference variation on a single crystal.

Molybdenum disulfide (MoS2) is one of the most commonly studied graphene-like 2D materials.[1]  Atomically thin MoS2 is a semiconductor with unique electrical[2], optical[3], and mechanical[4] properties, which make it a useful material for piezoelectric[5], photovoltaic[6,7], and other optoelectronic applications[8].

In this application note, monolayer MoS2 grown by chemical vapor deposition (CVD) was imaged with Kelvin probe force microscopy (KPFM) using a Flex-Axiom to study the contact potential difference variation on a single crystal.

Optical micrograph of MoS2 monolayers on SiO2 substrate. (inset) Single MoS2 monolayer.

Monolayers of MoS2 were grown on a silicon substrate by chemical vapor deposition.

Sample courtesy: University of Illinois – Urbana-Champlain

a) AFM topography image of single MoS2 monolayer. Location where profile is taken indicted by red line. b) Height (top) and KPFM voltage (bottom) profile across monolayer

Measurements using the Flex-Axiom show a step height of 0.6 nm for the MoS2 monolayer. Concurrent KPFM measurements show a 650 mV contact potential difference between the monolayer and the SiO2 substrate.

Non-uniformity of the contact potential signal across the monolayer can inform about doping profiles and other surface defects.

Overlay of contact potential on 3D topography of a MoS2 monolayer.

All measurements were performed using a Flex-Axiom system equipped with a ANSCM-PA cantilever from AppNano. Images were processed using MountainsMap SPM.

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[1] Subbaiah, Y.P.V., et al., Advanced Functional Materials 26 (2016) 2046
[2] Mak, K.F., et al., Physical Review Letters 105 (2010) 136805
[3] Splendiani, A., et al., Nano Letters 10 (2010) 1271
[4] Akinwande, D., Nature Communications 5 (2014) 56787
[5] Wu, W., et al., Nature 514 (2014) 470
[6] Tsai, M.-L., et al., ACSNano 8 (2014) 8317
[7] Wi, S., et al., ACS Nano 8 (2014) 5270
[8] Sanne, A., et al., Nano Letters 15 (2015) 5039

Nanosurf application note AN01154

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