Spectroscopy of carbon: from diamond to nitride films

Abstract

Every surface scientist knows about the importance of carbon spectroscopy: the signals of C 1 s and C KLL usually are indicating the surface cleanness, whereas C 1 s peak is often used as a reference for the calibration of energy scale. Carbon spectroscopy becomes even more important in the case of the studies dedicated to new carbon-based materials, such as nanotubes, graphene, diamond-like carbon (DLC), carbon nitride, carbides, etc. It is well-known that the carbon atoms can be arranged in a great variety of crystalline and disordered structures, because their electrons can hybridize in sp 3 , sp 2 and even in linear sp configurations. Namely, the hybridization of carbon electrons defines the mechanical, electrical and optical properties of these materials. Indeed, between the pure diamond (sp 3 ) and graphite (sp 2 ), there are many phases of amorphous material characterized by different sp 2 /sp 3 ratios and generally named DLC. Electron spectroscopies (X-ray photoelectron spectroscopy, Auger electron spectroscopy and electron energy loss spectroscopy) are widely recognized as analytical techniques, able to identify the bonds of diamond, graphite and amorphous phases of carbon. The binding energy of C 1 s spectrum together with its plasmon losses, the shape of Auger peak and valence band spectra can be used to characterize the structure of carbon-based materials. In this study, an overview is reported on carbon spectroscopy, comparing different experimental methods. Their application for the characterization of DLC and carbon nitride films, including the determination of carbon's sp 2 /sp 3 ratio is discussed and illustrated by experimental results obtained for a series of thin films of these materials.

Solid state magnetic resonance investigation of the thermally-induced structural evolution of silicon oxide-doped hydrogenated amorphous carbon

“…Among the three methods, the echo provides the most accurate estimation of the sp 2 and sp 3 resonance intensities. However, it is noted that significant paramagnetic density is encountered for this sample (~10 20 e/g, where e is the number of unpaired electron magnetic moments) and undoubtedly some of the 13 C NMR signal is rendered unobservable due to extremely short transverse magnetic relaxation, regardless of DP, CP or echo. This issue will be revisited below in light of the experimental results.…”

“…This lack of knowledge inhibits developing a fundamental understanding of the mechanisms by which the excellent thermal stability and tribological performance of a-C:H:Si:O are achieved. To gain insights into the structure and composition of DLCs, some of the most powerful tools in the material characterization arsenal have been used, including Raman spectroscopy [9,[16][17][18][19], X-ray photoelectron spectroscopy (XPS) [13,20,21], near edge X-ray absorption fine structure (NEXAFS) spectroscopy [22][23][24], electron energy loss spectroscopy (EELS) [25], Fourier-transform infrared spectroscopy (FT-IR) [26], X-ray reflectivity (XRR) [25], forward recoil elastic scattering (FRES) [27], nuclear magnetic resonance (NMR) spectroscopy [27][28][29][30][31][32][33][34][35][36][37][38][39][40][41], and electron paramagnetic resonance (EPR) spectroscopy [42][43][44][45][46].…”

Graphene quantum dots: structural integrity and oxygen functional groups for high sulfur/sulfide utilization in lithium sulfur batteries

“…The C 1 s spectra of the as-prepared electrodes (Figure 4a) show peaks at 283.8 eV and 284.5 eV attributed to sp 2 and sp 3 hybridized carbons, respectively, whereas the peak at 285.3 eV corresponds to C-S bonding. 34,35 The peak at 286.2 eV is assigned to C-OH bonding, which is more intense in GQDs-S/CB than in S/CB because the GQDs have a high density of -OH surface functional groups. The two peaks that correspond to carbonyl and carboxyl groups are located at 287.0 and 289.0 eV, respectively.…”

Quantitative Evaluation of the Carbon Hybridization State by Near Edge X-ray Absorption Fine Structure Spectroscopy

“…The characterization of the bonding configuration of carbon is usually carried out by XPS through the acquisition and fitting of the C1s spectrum [16][17][18][19][20][26][27][28] . However, the validity of the methodology for the quantitative evaluation of the hybridization state of carbon on the basis of the C1s signal, which relies on fitting it with two distinct features for sp 2 -and sp 3 -bonded carbon 16,26,27 , has been refuted 17,18 , since the binding energy values of the C1s transition for graphite (100% sp 2 -bonded carbon), diamond (100% sp 3 -bonded carbon), and ultrananocrystalline diamond (94±1% sp 3 -bonded carbon 21 ) are not significantly different 17,18 . Instead, insights into the carbon hybridization state in the near-surface region of a-C materials can be gained by XPS through the analysis of the plasmon band near the C1s signal 18,24 , the π-π* shake-up satellites 42,43 , or the X-ray induced C KVV Auger spectrum 17,18,22,23,25,28 .…”