Characterization of Carbon Nanostructures by Photoelectron Spectroscopies

Abstract

Recently, the scientific community experienced two revolutionary events. The first was the synthesis of single-layer graphene, which boosted research in many different areas. The second was the advent of quantum technologies with the promise to become pervasive in several aspects of everyday life. In this respect, diamonds and nanodiamonds are among the most promising materials to develop quantum devices. Graphene and nanodiamonds can be coupled with other carbon nanostructures to enhance specific properties or be properly functionalized to tune their quantum response. This contribution briefly explores photoelectron spectroscopies and, in particular, X-ray photoelectron spectroscopy (XPS) and then turns to the present applications of this technique for characterizing carbon nanomaterials. XPS is a qualitative and quantitative chemical analysis technique. It is surface-sensitive due to its limited sampling depth, which confines the analysis only to the outer few top-layers of the material surface. This enables researchers to understand the surface composition of the sample and how the chemistry influences its interaction with the environment. Although the chemical analysis remains the main information provided by XPS, modern instruments couple this information with spatial resolution and mapping or with the possibility to analyze the material in operando conditions at nearly atmospheric pressures. Examples of the application of photoelectron spectroscopies to the characterization of carbon nanostructures will be reviewed to present the potentialities of these techniques.

Transforming Nature’s Bath Sponge into Stacking Faults-Enhanced Ag Nanorings-Decorated Catalyst for Hydrogen Evolution Reaction

“…The deconvoluted high-resolution XPS spectrum of C 1s in Figure b shows clear signs of C–C (284.6 eV) corresponding to the sp3 hybridization of amorphous carbon, CC (284.3 eV) brought in by partial graphitization, C–O/C–N (285.8 eV) which is due to the effect of surface oxygen and N-doping of the carbon structure, CO (288.75 eV) due to surface oxidation, and finally π–π* (291.1 eV) shakeup satellite peaks arising from π–π* type transitions . These transitions involve the promotion of electrons from the highest occupied molecular orbital to the lowest unoccupied molecular orbital in the graphitic islands of the C matrix . The N 1s spectra in Figure c can be further deconvoluted into three peaks at 398.6, 400.7, and 401.6 eV, corresponding to the pyridinic-N, pyrrolic-N, and graphitic-N, respectively, further confirming the successful doping of N into the carbon matrix.…”

Energy level measurement for organic semiconductors

“…The UPS full spectrum records these emitted electron energies, which allows for mapping out the valence electronic states of the organic semiconductor. 53 As shown in Fig. 3, 16.57 eV is defined as the secondary-electron cutoff ( E cutoff ), which illustrates the minimum energy necessary to remove an electron from organic semiconductors.…”

“…Thus, the measured HOMO is the polarized HOMO and the value is eventually overestimated. 53 Secondly, UPS is a surface-sensitive technique. Therefore, the measurement is extremely sensitive to surface environments, which leads to a wide range of HOMOs, owing to the variations in handling or fabrication history.…”

The formation of active phases in Pt-containing catalysts for bicyclohexyl dehydrogenation in hydrogen storage

“…5) are identical for all investigated samples and are observed as a narrow asymmetric line with a maximum at 284.4 eV, which is typical for sp 2 -carbon. [52][53][54]…”