Surface properties of Hafnium diboride(0 0 0 1) as determined by X-ray photoelectron spectroscopy and scanning tunneling microscopy C.L. Perkins a,1 , R. Singh a , M. Trenary a, * , T. Tanaka b , Yu. Paderno c a Department of Chemistry M/C 111, Room 4500, University of Illinois at Chicago, 845 W. Taylor Street, Chicago, IL 60607 7061, USA b National Institute for Research in Inorganic Materials, 1-1 Namiki, Tsukuba, Ibaraki 305 0044, Japan c Institute for Problems in Materials Science, Academy of Sciences of Ukraine, 3 Kryzanovsky Str., Kiev 252680, Ukraine Received 16 June 2000; accepted for publication 18 September 2000 Abstract The surface structure and properties of the HfB 2 (0 0 0 1) (Hafnium diboride, HfB 2 ) surface have been investigated with X-ray photoelectron spectroscopy, low energy electron diraction (LEED), and scanning tunneling microscopy (STM). Annealing temperatures above 1900°C produce a sharp (1  1) LEED pattern, which corresponds to STM images showing ¯at (0 0 0 1) terraces with a very low contamination level separated by steps 3.4  A in height, corre- sponding to the separation of adjacent Hf planes in the HfB 2 bulk structure. For lower annealing temperatures, extra p(2  2) spots were observed with LEED, which correspond to intermediate terraces of a p(2  1) missing row structure as observed with STM. Ó 2001 Elsevier Science B.V. All rights reserved. Keywords: Hafnium; Surface structure, morphology, roughness, and topography; Scanning tunneling microscopy; Low index crystal surfaces; X-ray photoelectron spectroscopy 1. Introduction Transition metal diborides are of interest for fundamental reasons as well as for practical ap- plications. The diborides are members of a broad class of materials known as the boron-rich solids [1], which consist of extended networks of cova- lently bonded B atoms stabilized through donation of electrons from the metal atoms. Most of the metal diborides have the AlB 2 structure in which layers of close-packed metal atoms alternate with planes of B atoms with a graphite-like geometric structure. The B sheets in the diborides of the AlB 2 structure would be isoelectronic with graphite [2] if the bonding involved a full transfer of two elec- trons to give M 2 B 2 2 . However, the fact that the B±B bond length in the diborides ranges from 1.7 to 1.8  A, values typical of B±B single bonds, immediately suggests that there is an insigni®cant degree of p bonding between the B atoms. This conclusion is supported by recent electronic structure calculations and other data indicating Surface Science 470 (2001) 215±225 www.elsevier.nl/locate/susc * Corresponding author. Tel.: +312-996-0777; fax: +312-966- 0431. E-mail address: mtrenary@uic.edu (M. Trenary). 1 Present address: National Renewable Energy Laboratory, 1617 Cole Boulevard, Golden, Co, USA. 0039-6028/01/$ - see front matter Ó 2001 Elsevier Science B.V. All rights reserved. PII:S0039-6028(00)00862-1