Electrical properties of chemical vapor deposited hBN : study by scanning probe microscopy

The hBN thin film has been the subject of great interest since the emergence of research on 2D heterostructures. Thanks to its outstanding physical, chemical and thermal properties, as well as its smooth surface and low density of dangling bonds, hBN is a prime choice as a substrate for heterostructures. Adding its graphene-like structure with only 1.8% lattice mismatch, hBN is considered to be the best choice for the graphene substrate. Numerous studies have investigated the fabrication of hBN in thin films in order to be able to manufacture it in monolayers with the best possible quality. One of the most promising manufacturing techniques to achieve this goal is chemical vapour deposition (CVD). With the development of scanning probe microscopy, especially in electrical modes such as CS-AFM and KPFM, the characterisation of the surface at the nanometer scale has been made possible. Through the characterisation of thin insulating films developed on metal substrates using electrical modes of scanning probe microscopy, a metal-insulator-metal (MIM) system is established. In this system a tunnel current can exist if the insulation is sufficiently thin. Thanks to the numerous studies carried out on the characterisation of these MIMs, the behaviour of the switching resistance in thin films has been highlighted and a theory has been developed to try to understand its mechanism. Within the framework of this master, research with scanning probe microscopy in electric mode such as CS-AFM and KPFM has been carried out on thin films of hBN manufactured by CVD on a copper film substrate. Experiments with CS-AFM scanning over the sample area were carried out in order to demonstrate whether scanning probe microscopy modes are relevant for the quality characterisation of such films. CS-AFM ramps were also investigated to study the tunnel current in the MIM formed by thin layers of hBN analysed by a conductive AFM tip on a copper substrate. By applying CS-AFM ramps with variable applied voltage and contact force, the resistive switching behaviour in the hBN thin film was studied. With the use of the resiscope module of the agile 5500 picoplus, the KPFM and CS-AFM modes were combined to investigate the switching resistance phenomenon. The study succeeded in identifying the behaviour of tunnel current and switching resistance behaviour with CS-AFM and showed interesting results with the combined KPFM and CS-AFM modes. However, the appearance of the switching resistance behaviour during characterisation with a voltage applied to the sample makes the latter difficult to interpret, and the theory of electrochemical metallization which try to understand the behaviour of the switching resistance present in insulating thin films in the MIM system is still uncertain.