In Situ Reproducible Sharp Tips for Atomic Force Microscopy

Abstract

Atomically sharp tips are a requirement for scanning-probe microscopy, such as scanning tunneling microscopy (STM) and atomic force microscopy (AFM). Compared with STM, AFM imaging is more sensitive to the sharpness of tip apices because long-range forces act as a background signal on the high-resolution AFM images originating from short-range forces. Here we report the investigation of in situ reproducible sharp tips for AFM. We make an ${\mathrm{Ag}}_{2}\mathrm{S}$ crystal, a mixed ionic and electronic conductor, on a conventional $\mathrm{Si}$ cantilever, and controllably grow and shrink the $\mathrm{Ag}$ nanoprotrusion by changing the polarity of the bias voltage between the tip and the sample. We are able to reduce the contribution of long-range forces by growing a $\mathrm{Ag}$ nanoprotrusion on the ${\mathrm{Ag}}_{2}\mathrm{S}$ tip, and obtain atomic-resolution AFM images. We also confirm that the ${\mathrm{Ag}}_{2}\mathrm{S}$ tip with a $\mathrm{Ag}$ nanoprotrusion, the end of which presumably terminates in $\mathrm{Si}$ atoms, is capable of simultaneous AFM and STM measurements.