Contributed Talk  - Thursday, 16 September I 10:10 AM (CEST)

Tomas Daugalas: "Force-current spectroscopy for graphene-based van der Waals structures"

Tomas Daugalas, Algimantas Lukša, Virginijus Bukauskas, Arūnas Šetkus
Department of Physical Technologies, Center for Physical Sciences and Technology (FTMC), Lithuania

During the last decade, there were a lot of attempts to scale down electronic devices, in order to significantly improve the characteristic such as power consumption, speed, better integration at reduced cost of the device. This scaling down leads to the use of the nanoscale materials, such as graphene, TMD’s, which, in combination with metal contacts, are used as functional devices for detection of pressure, humidity [1], gases [2] and other physical and chemical parameters. Due to their low dimensions, it is often hard to investigate the nanoscaled devices using traditional methods, and consequently, it is a high challenge to intentionally produce the devices with required parameters, adapted for a specific application.

Therefore, in this work we present force-current spectroscopy method, which was used to investigate a model structure that included the monolayer graphene and the Au contacts. The model was arranged as a vertical van der Waals structure. The experiments were performed under ambient conditions. It followed from our experiments, that an external mechanical force applied to the system at the same time as an external voltage resulted in the electric current, that was a specific characteristic of the system state, and was a function of the applied tip force (Fig 1). The current extremes were detected for the specific magnitudes of the applied force. Compared to the model systems without graphene, the current peaks were quite different from the typical signals, detected for the current saturation in the reference metallic systems and the calibration samples (Platinum Grating).

Since the mechanical force applied to the sample can be associated with the distances, at which the van der Waals structures appear to be at the stable state, the electrical structure of the system was also modeled in the terms of the distance dependent interaction between the layers of the system. Accepting the applied external bias, the changes in the system were explained by the variations in the energy states, that depend on the overlapping of the electronic states in the system layers. Furthermore, by applying the mechanical force and external bias, we can detect how system changes at the nanoscale distances. These changes were explicitly demonstrated by the experimental force-distance curves, which were acceptable to describe quantitatively the adhesion, attraction, dissipation forces and others (Fig. 1).

[1] H. Lang, Y. Peng, X. Cao, K. Zou, Atomic-Scale Friction Characteristics of Graphene under Conductive AFM with Applied Voltages, ACS Appl. Mater. Interfaces, 2020 12 (22), 25503-25511.
[2] Q. Li, et al., Gas adsorption characteristics of graphene/metal structures, Applied Surface Science 514 (2020), 145823.