Magnetic noise from ultrathin abrasively deposited materials on diamond

Sensing techniques based on the negatively charged nitrogen-vacancy (NV) center in diamond have emerged as promising candidates to characterize ultrathin and 2D materials. An outstanding challenge to this goal is isolating the contribution of 2D materials from undesired contributions arising from surface contamination and changes to the diamond surface induced by the sample or transfer process. Here we report on such a scenario, in which the abrasive deposition of trace amounts of materials onto a diamond gives rise to a previously unreported source of magnetic noise. By deliberately scratching the diamond surface with macroscopic blocks of various metals (Fe, Cu, Cr, Au), we are able to form ultrathin structures (i.e., with thicknesses down to