Evaluation of the discrete thickness of exfoliated artificially synthesized mica nanosheets on silicon substrates: Toward characterization of the tunneling current through the nanosheets

Insulating two-dimensional (2D) materials, as well as conductive materials, should be further exploited for fabrication of nanomaterial devices and extension of their functions. Structural and elemental analyses of 2D materials are fundamental for nanoscale electronic devices. Here, as a 2D insulator, nanosheets of single-crystal layered artificially synthesized pure phlogopite (KMg3AlSi3O10F2) were prepared by mechanical exfoliation from its bulk crystal and then affixed to Si substrates using a polyurethane hand roller. Phlogopite is a member of the cleavable mica family with a band gap energy of similar to 7 eV. The nanosheets were extended to a few tens of micrometer widths on the substrates. Their discrete thicknesses were determined from several layers to a single layer (1 nm) by atomic force microscopy (AFM), and their chemical components were analyzed by scanning Auger electron spectroscopy/microscopy (SAM). Because the elemental peak intensities from Auger electron spectroscopy of the nanosheets changed with increasing number of layers up to five layers, conventional methods based on SAM are proposed to evaluate their thickness. The current-voltage characteristics of metal-nanosheet-metal contacts with different nanosheet thicknesses were investigated by conductive AFM, and they exhibited strong thickness dependence because of electron tunneling through the nanosheets.