**2. Experimental**

Key properties of a sample are often exposed in their responses to a core-level excitation. The specific responses have been discovered using the tunable synchrotron irradiation and became the basis of advanced techniques [3]. The X-ray absorption fine structure (XAFS) appears near the edge of photoionization threshold (XANES) and reveals the vacant state structure, while the XAFS beyond the absorption edge (EXAFS) exhibits the local geometry [4]. The resonant inelastic X-ray scattering (RIXS) is enabled by the energy and momentum transferred by a photon near the absorption edge and exhibits the intrinsic excitations [5]. Resonant photoemission (RPES) and Auger electron spectroscopy (RAES) disclose the local electronic structure and correlations in a system, respectively [6]. The use of the electron impact instead of the X-ray, as a source of the core-level excitation, has discovered the similar effects of the conjugate electron excitation (CEE) [7–11]. The CEE shows itself as a set of satellites in disappearance potential spectra (DAPS), which answers to valence band (VB) structures of near-surface atoms, including the adsorbed species, and plasmon excitations. Experimental evidence for the CEE phenomenon is based on DAPS spectra, obtained from various adsorbed layers and on its mechanism represented by the combination of ordinary electron transitions. For example, plasmon oscillations are often observed by means of X-ray photoelectron (XPS) and Auger electron spectroscopies (AES) [12, 13]. Ionization of the VB, of the substrate and adsorbed species, is a basis of ultraviolet photoelectron spectroscopy (UPS) [14]. Similar satellite structures, above different thresholds, in DAPS spectra confirm that the core electrons are identical with regard to CEE transitions [7, 8]. CEE phenomena represent, in whole, the multichannel route for energy dissipation within the DAPS probing depth of 2–3 monolayer (ML), which does not

Novel as well as advanced technologies strongly require the next generation materials in the fields of tribology [15–17], hardness [18, 19], corrosion and wear performance of the material [20], and many others [21–23]. The progress of material science in these fields is resulted, in large measure, from the fundamental studies by means of modern techniques, including the XPS as well [16, 17, 21–23]. The X-ray photoelectron spectroscopy is a powerful analytical tool; however, this method is limited by the content and charge state of the atoms, while it cannot disclose the chemical behavior and structural features of the atoms in a sample, which are urgently needed in case of the multicomponent substrate. These properties and many others are direct products of the DFT. In turn, the DFT runs give greatly different results depending on starting conditions and the operational parameters, which have to be found indirectly. A reliable intersection between the XPS and DFT outputs would help to employ the hidden

The CEE phenomenon is a true multi-channel route of energy dissipation through the VB. The identity of electronic nature of the surface and bulk atoms allows one to suggest the similarity of inelastic electron scattering mechanisms on the surface and in the bulk of a solid. Then, the CEE should also occur, under the X-ray core-level excitation, and manifest itself in the XPS spectra as energy losses. The plasmons in AES and XPS spectra correspond indeed to the collective CEE phenomena. Highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) transitions, which are often used for assignment the XPS, RPES and XANES spectra [24, 25], are also clear CEE manifestations. The electron energy dissipation, accompanying the core-level excitation, is the general trend of any electronic configuration.

undermine the general concepts in the field of electron scattering.

resources of both techniques.

148 Advanced Surface Engineering Research

Inelastic electron scattering has been monitored by the elastic scattering, using the DAPS. Disappearance potential spectroscopy is based on the threshold core-level excitation by an electron beam of the time-based energy *E*p [32]. Whenever the incident potential exceeds the corelevel energy, a part of electrons disappears from the elastic current *I* and provides a dip in the dependence of *dI(E*p*)/dE*p on *E*p. The event occurs if *E*p is equal to difference between the core and vacant state energy. The spectrum shape is determined by the self-convolution of vacant density of states (DOS), as the destination of interacting electrons. The adsorption of test gases over the Auger-clean Pt(100)-(1 × 1) single crystal was performed at 300 K [33]; exposures are given in Langmuir (1 L = 10−6 Torr s). The Fermi level (*E*<sup>F</sup> ) in DAPS spectra corresponds to *E*<sup>p</sup> = 314.8 eV, which is close to the reference Pt4d5/2 core-level energy [34]. Other experimental details and the spectrum processing can be found elsewhere [7–11].

The XPS studies were performed on a Phoibos 150 SPECS spectrometer (Germany) using monochromatized Al Kα radiation (1486.7 eV). The backgrounds of external and surface energy losses in XPS spectra have been subtracted [35]. Other experimental details, the lowtemperature synthesis technique, and characterization of HOPG, pristine and fluorinated C<sup>2</sup> F can be found elsewhere [36, 37]. The Br<sup>2</sup> embedding into C<sup>2</sup> F was performed as in Ref. [38] and resulted in the ~C<sup>2</sup> FBr0.15 stoichiometry.
