Diamond and Related Materials 13 (2004) 445–450 0925-9635/04/$ - see front matter  2003 Elsevier B.V. All rights reserved. doi:10.1016/j.diamond.2003.11.077 Measurement of the relative abundance of sp and sp hybridised atoms 2 3 in carbon based materials by XPS: a critical approach. Part I G. Speranza*, N. Laidani ITC-irst, Sommarive str. 18, I-38050, Povo, Trento, Italy Received 1 August 2003; received in revised form 5 November 2003; accepted 21 November 2003 Abstract A few of the approaches put forward to measure the fraction of sp and sp hybridised carbons in carbon systems via photon 2 3 excited electron spectroscopies are compared. To test the various methods, synthesised (part I of the work) and real non- synthesised spectra, (part II) were used. The first were generated as linear combinations of the spectra of polycrystalline diamond and graphite. Reasonable results are found, at least within the assumptions at the basis of the present work. Methods based on spectral fitting are generally superior to others provided the relevant spectral region is carefully chosen and the fitting procedure is well specified.  2003 Elsevier B.V. All rights reserved. Keywords: Carbon films; Sputtered HOPG; s–p hybridisation; Electron spectroscopy 1. Introduction Low temperature, low pressure C deposition has long been investigated as a promising method to obtain films that mimic the properties of diamond. This occurs if the bonding configuration is unlike that of graphite. It is well known that crystalline graphite is organized in a trigonal structure where all the atoms are in an sp 2 hybridised electronic configuration. Presence of graphit- ic-like clusters in the film’s bulk, which corresponds to a high percentage of sp hybrids, is described to worsen 2 the film’s quality. On the contrary, the presence of a possibly high percentage sp hybridized C atoms 3 involved in tetrahedral bonds organized in a completely disordered matrix, leads to carbon films able to imitate the characteristics of diamond. For this reason they are called diamond-like carbon (DLC) films. Measuring the relative abundance of the two hybri- disationforms,isthereforeofgreatimportancetopredict the macroscopic properties of the films and this justifies the continuous efforts to find reliable methods in this respect. *Corresponding author. Tel.: q39-0461-314487; fax: q39-0461- 810851. E-mail address: speranza@itc.it (G. Speranza). Several analytical techniques and various approaches have been proposed and used; so far though, to the best of our knowledge, they were never validated by system- atic studies. The aim of the present paper is to perform such an investigation for a subset of methods, namely those based on the analysis of the occupied electron states obtained via electron spectroscopies. It follows that high-energy loss (or core-edge) electron spectra, beingprobesoftheunoccupiedstates,arenotconsidered in the present paper, though it is worth remembering that using the near-edge structure at the carbon K absorption edge is one of the most popular approaches to assess the relative amount of sp and sp hybridised 2 3 carbon atoms in carbon systems w1,2x. We will further confine ourselves to photon excited electron spectra, whicharecausinglessdamagetothenearsurfaceregion as compared to, for example, electron excited spectra. Differences in the proposed approaches are due to different investigated spectral regions (which include the C KVV Auger spectrum, the C1s core line together with the associated electron energy loss spectrum (EELS) and the valence band spectrum (VB)) or to the type of measurement suggested on the chosen spectral region. However, common to each method is the assumption that the electronic structure of an amorphous C film is