Atomically flat ultra-clean Cr(0 0 1) surfaces produced by cleavage of a single crystal: scanning tunneling microscopy and spectroscopy study

Abstract

Using fracture of Cr single crystals at liquid helium temperature, we were able to obtain atomically clean and flat Cr(0 0 1) surfaces. The cleaved surfaces have been characterized by means of low-temperature scanning tunneling microscopy and spectroscopy techniques. Atomically resolved images taken at different locations on the cleaved surfaces show clearly the atomically resolved Cr(0 0 1) lattice with fourfold symmetry. The impurity concentrations did not exceed the bulk concentration, e.g., the brittle fracture process does not appear to cause segregation of impurities to the surface. Larger scans revealed that the cleaved surface consists of clean terraces separated by monoatomic steps with widths from a few to several hundred nanometers belonging to the (0 0 1) cleavage plane. We also found that the Cr(0 0 1) cleavage plane yields [1 0 0] and [1 1 0] steps. High-resolution spectroscopic investigations showed that the surface electronic structure has a very narrow and strong peak located at 26 meV above the Fermi level and allowed us to resolve its intrinsic width and shape. We also found that the peak is strongly reduced above the terrace edges.