SCANNING PROBE MICROSCOPY MEASUREMENTS ON 2D MATERIALS AND IRIDATES

In the past two decades, there has been a quest to understand and utilize novel materials such as iridates and two-dimensional (2D) materials. These classes of materials show a lot of interesting properties both in theoretical predictions as well as experimental results. Physical properties of some of these materials have been investigated using scanning probe measurements, along with other techniques. One-dimensional (1D) catalytic etching was investigated in few-layer hexagonal boron nitride (hBN) films. Etching of hBN was shown to share several similarities with that of graphitic films. As in graphitic films, etch tracks in hBN commenced at film edges and occurred predominantly along certain crystal directions of its lattice, though it was shown that the tracks were generally narrower than those of few-layer graphene under similar processing conditions. This ability for thin hBN films to be etched completely through allowed for a crystalline substrate to guide the etching process, which was demonstrated with the successful etch track formation of few-layer hBN on single-crystalline sapphire substrates as well as graphene on sapphire. The heterostructure of graphene on hBN with different thicknesses has been studied by an atomic force microscope (AFM) using electrostatic force microscopy (EFM) technique resulting in the measurement of the electronic surface potential. The sizes of the gold nanoparticles grown on the surface of the graphene/hBN heterostructure were studied as well. Also, we have studied the high-quality single crystal Na2IrO3, which is a 5d transition metal oxide with a scanning tunneling microscope (STM). Na2IrO3 has a layered structure with a honeycomb lattice. The insulating gap is measured to be about 400 meV according to the dI / dV curve, which is consistent with other measurements. We will show topographic images and discuss the evolution of the density of states and the behavior of the gap from room temperature down to 100 K