Subsurface imaging of two-dimensional materials on the nanoscale

Year: 2017

Authors: Dinelli F., Pingue P., Kay N.D., Kolosov O.V.

Autors Affiliation: CNR, INO, Via Moruzzi 1, I-56124 Pisa, Italy; Scuola Normale Super Pisa, Lab NEST, Piazza San Silvestro 12, I-56127 Pisa, Italy; CNR, Ist Nanosci, Piazza San Silvestro 12, I-56127 Pisa, Italy; Univ Lancaster, Phys Dept, Lancaster LA1 4YB, England.

Abstract: Scanning probe Microscopy (SPM) represents a powerful tool that, in the past thirty years, has allowed one to investigate material surfaces in unprecedented ways at the nanoscale level. However, SPM has shown very little power of depth penetration, whereas several nanotechnology applications would require it. Subsurface imaging has been achieved only in a few cases, when subsurface features influence the physical properties of the surface, such as the electronic states or the heat transfer. Ultrasonic Force Microscopy (UFM), an adaption of the contact mode Atomic Force Microscopy (AFM), can dynamically measure the stiffness of the elastic contact between the probing tip and the sample surface. In particular, UFM has proven highly sensitive to the near surface elastic field in non-homogeneous samples.
In this paper, we present an investigation of two-dimensional (2D) materials, namely flakes of graphite and molybdenum disulphide placed on structured polymeric substrates. We show that UFM can non-destructively distinguish suspended and supported areas and localize defects, such as buckling or delamination of adjacent monolayers, generated by residual stress. Specifically, UFM can probe small variations in the local indentation induced by the mechanical interaction between the tip and the sample. Therefore, any change in the elastic modulus within the volume perturbed by the applied load or the flexural bending of the suspended areas can be detected and imaged. These capabilities of investigation are very promising in order to study the buried interfaces of nanostructured 2D materials such as in graphene-based devices.

Journal/Review: NANOTECHNOLOGY

Volume: 28 (8)      Pages from: 085706-1  to: 085706-8

More Information: FD acknowledges funding from the ´Short Term Mobility´ programme by the CNR and Paolo Baschieri for helping in the construction of the UFM setup. PP acknowledges Sandro Meucci for COC sample preparation and Vittorio Pellegrini and the ´Graphene Flagship´ initiative for supporting his stay at Lancaster University. OVK acknowledges support of the EC grant ´QUANTIHEAT´ (grant agreement no 604668), EPSRC funding to ´Graphene NowNANO´, and Lancaster University support. All authors are grateful to Ben Robinson for the experimental support and Volodya Falko for stimulating discussions.
KeyWords: SPM; UFM; 2D Materials; Subsurface; Elastic properties
DOI: 10.1088/1361-6528/aa55e2

Citations: 23
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