Origin of Image Flickering in Scanning Probe Microscopy on B-Doped Si(111) 7×7 Surfaces

Since the invention of scanning tunneling microscopy (STM) and atomic force microscopy (AFM), the Si(111) 7×7 reconstructed surface has long been regarded as a touchstone for assessing the feasibility and performance of scanning probe microscopes (SPM). Recently, while investigating the role of boron dopants on this complex surface using high-resolution STM and AFM with a CO-functionalized tip, we discovered an image flickering phenomenon, i.e., distinct changes in intensity as the tip approaches the surface.

Our combined experiment–theory analysis shows that boron dopants significantly perturb the local bonding environment beneath selected adatoms, making these surface units structurally bistable and electronically sensitive to the approaching tip. In AFM, the enhanced tip–sample interaction can trigger sudden switching between two metastable surface configurations, resulting in abrupt changes in the measured force and producing the observed flickering. In STM, the doped sites exhibit charge switching that repeatedly causes the dangling-bond state to disappear and regenerate, leading to pronounced fluctuations in tunneling conductance. Our results show that the SPM tip actively couples to and modulates the local structure and charge state of doped Si surfaces, directly contributing to the observed flickering. Considering silicon’s central role in modern semiconductor technology, this work [1] provides a physical foundation for future investigations of doped Si surfaces and tip–sample coupling in SPM.