A Detailed examination of layer-dependent photoemission spectra and surface potential of CrCl3

The modifications in the electronic properties induced by the thickness and size of an individual flake of transition metal halides on different substrates (Si oxide or In-doped tin oxide) are of particular interest in the case of the well-known ambient-resistant chromium trihalide, a serious candidate to play a role in the implementations of 2D magnetism in devices. By employing synchrotron-based Scanning Photoelectron Microscopy (SPEM) with 0.1 microns resolution and Kelvin Probe Force Microscopy (KPFM), we established the correlations between chemical and structural modifications locally, composition versus thickness and/or surface oxidation during the preparation and measurements. By comparing the SPEM maps from the different regions, we clearly single out how the thinner flakes are more immune from the modifications observed in thicker flakes, which resembled what occurs in bulk cleaved samples. In addition, the KPFM provides maps of the surface potential of CrCl${\$}$_3${\$}$ flakes of different thicknesses that can be put in relation with the above effect. Here, we investigated the surface evolution on exfoliated thin layers (1 - 10 ML) of CrCl3 by using the Scanning Photoelectron Microscopy (SPEM) at Cr and Cl core levels by collecting the chemical maps and spectra at room temperature (RT) as well as at 300 degree Celsius temperature. By tracking the Cr, Cl and valence band spectra using different spatial resolutions of 130 nm, 2 and 70 microns, we could determine quantitative maps of the chemical composition to put in relation with thickness, including the effect of the substrate through weak van der Waals adhesion between CrCl3 flakes and substrate. As a complementary technique the correlation between the microscopy and the surface potential of the flakes have been investigated by the Kelvin probe at the nanometer scale. Kelvin probe force microscopy (KPFM) was developed as a tool for measuring the local contact potential difference between conducting AFM tips and samples, thereby mapping the work function and surface potentials of the samples with high spatial resolution is particularly convenient to correlate the photoemission information to the morphological ones.