Conductive Atomic Force Microscopy of Semiconducting Transition Metal Dichalcogenides and Heterostructures

Abstract

Semiconducting transition metal dichalcogenides (TMDs) are promising materials for future electronic and optoelectronic applications. However, their electronic properties are strongly affected by peculiar nanoscale defects/inhomogeneities (point or complex defects, thickness fluctuations, grain boundaries, etc.), which are intrinsic of these materials or introduced during device fabrication processes. This paper reviews recent applications of conductive atomic force microscopy (C-AFM) to the investigation of nanoscale transport properties in TMDs, discussing the implications of the local phenomena in the overall behavior of TMD-based devices. Nanoscale resolution current spectroscopy and mapping by C-AFM provided information on the Schottky barrier uniformity and shed light on the mechanisms responsible for the Fermi level pinning commonly observed at metal/TMD interfaces. Methods for nanoscale tailoring of the Schottky barrier in MoS2 for the realization of ambipolar transistors are also illustrated. Experiments on local conductivity mapping in monolayer MoS2 grown by chemical vapor deposition (CVD) on SiO2 substrates are discussed, providing a direct evidence of the resistance associated to the grain boundaries (GBs) between MoS2 domains. Finally, C-AFM provided an insight into the current transport phenomena in TMD-based heterostructures, including lateral heterojunctions observed within MoxW1–xSe2 alloys, and vertical heterostructures made by van der Waals stacking of different TMDs (e.g., MoS2/WSe2) or by CVD growth of TMDs on bulk semiconductors.

Nano-films of carbo-benzene derivatives: Scanning probe microscopy analysis and prospects of use in organic solar cells

“…Before calibration, HOPG substrate was cleaved by using the adhesive tape technique to achieve an atomically clean surface and, ITO substrate was cleaned sequentially in a soap solution, distilled water, acetone, and isopropanol, in each case for 15 min in an ultrasonic bath and dried in an oven at 80 °C. The work function for PtSi was ∅ = 5 ± 0.13 eV, which agrees with previous reports [37,38]. Once the PtSi tip and KPFM system were calibrated, measurements were consistence on the multiple samples with a standard deviation…”

Multiscale Investigation of the Structural, Electrical and Photoluminescence Properties of MoS2 Obtained by MoO3 Sulfurization

“…Noteworthy, the experimental points in Figure 6a are partially located in the n-type region and partially in the p-type one. Unintentional n-type doping is typically reported for MoS 2 films produced by different synthesis methods (such as mechanical exfoliation or CVD) and it is commonly ascribed to native defects present in the material [57][58][59][60]. Here, the observed p-type doping in some regions of the MoS 2 film produced by sulfurization can be associated with the presence of residual MoO 3 , as deduced by XPS.…”

Direct Atomic Layer Deposition of Ultrathin Aluminum Oxide on Monolayer MoS2 Exfoliated on Gold: The Role of the Substrate

“…Sharp silicon tips with a curvature radius of 5 nm were used for these measurements. Furthermore, the electrical insulating properties of the very thin Al 2 O 3 films deposited on 1L MoS 2 / Au were evaluated by C-AFM analyses [50] using the TUNA module and Pt-coated silicon tips.…”