Step-height standards based on the rapid formation of monolayer steps on the surface of layered crystals

Highlights: • Easily reproducible step-height standard for SPM calibrations was proposed. • Step-height standard is monolayer steps on the surface of layered single crystal. • Long-term change in surface morphology of Bi₂Se₃ and ZnWO₄ was investigated. • Conducting surface of Bi₂Se₃ crystals appropriate for calibrating STM. • Ability of robust SPM calibrations under ambient conditions were demonstrated. - Abstract: Metrology is essential for nanotechnology, especially for structures and devices with feature sizes going down to nm. Scanning probe microscopes (SPMs) permits measurement of nanometer- and subnanometer-scale objects. Accuracy of size measurements performed using SPMs is largely defined by the accuracy of used calibration measures. In the present publication, we demonstrate that height standards of monolayer step (∼1 and ∼0.6 nm) can be easily prepared by cleaving Bi₂Se₃ and ZnWO₄ layered single crystals. It was shown that the conducting surface of Bi₂Se₃ crystals offers height standard appropriate for calibrating STMs and for testing conductive SPM probes. Our AFM study of the morphology of freshly cleaved (0001) Bi₂Se₃ surfaces proved that such surfaces remained atomically smooth during a period of at least half a year. The (010) surfaces of ZnWO₄ crystals remained atomically smooth during one day, but already two days later an additional nanorelief of amplitude ∼0.3 nm appeared on those surfaces. This relief, however, did not further grow in height, and it did not hamper the calibration. Simplicity and the possibility of rapid fabrication of the step-height standards, as well as their high stability, make these standards available for a great, permanently growing number of users involved in 3D printing activities.