Atomically flat ultra-clean Cr(001) surfaces produced by cleavage of a single crystal: scanning tunneling microscopy and spectroscopy study

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 su rfaces have been characterized by means of low-temperature scanning tunneli ng 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 concentrat ions did not exceed the bulk concentration, e.g., the brittle fracture proc ess does not appear to cause segregation of impurities to the surface. Larg er scans revealed that the cleaved surface consists of clean terraces separ ated by monoatomic steps with widths from a few to several hundred nanomete rs 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 spectros copic investigations showed that the surface electronic structure has a ver y narrow and strong peak located at 26 mev above the Fermi level and allowe d us to resolve its intrinsic width and shape. We also found that the peak is strongly reduced above the terrace edges. (C) 2001 Elsevier Science B.V. All rights reserved.