NV microscopy of thermally controlled stresses caused by Cr$_2$O$_3$ thin films

Abstract

Many modern applications, including quantum computing and quantum sensing, use substratefilm interfaces. Particularly, thin films of chromium or titanium and their oxides are commonly used to bind various structures, such as resonators, masks, or microwave antennas, to a diamond surface. Due to different thermal expansions of involved materials, such films and structures could produce significant stresses, which need to be measured or predicted. In this paper, we demonstrate imaging of stresses in the top layer of diamond with deposited structures of Cr2O3 at temperatures 19 • C and 37 • C by using stress-sensitive optically detected magnetic resonances (ODMR) in NV centers. We also calculated stresses in the diamond-film interface by using finite-element analysis and correlated them to measured ODMR frequency shifts. As predicted by the simulation, the measured high-contrast frequency-shift patterns are only due to thermal stresses, whose spin-stress coupling constant along the NV axis is 21±1 MHz/GPa that is in agreement with constants previously obtained from single NV centers in diamond cantilever. Our widefield imaging demonstrates the NV microscopy as a convenient platform that could optically detect and quantify spatial distributions of stresses in diamond-based photonic devices with a micrometer precision. Our results also show that thin film structures produce significant stresses in them, that should be accounted for in NV-based applications.