2.10 Xps of carbon nanomaterials  (Page 4/5)

The survey XP spectrum of the sodium salt shows a Na1s peak ( [link] ) and the high resolution scans of Na1s and S2p show that the relative atomic percentages of Na1s and S2p are nearly equal ( [link] ), which supports the formation of the sodium salt.

Further characterization

High resolution scans of each of the element peaks of interest can be obtained to give more information about the material. This is a way to determine with high accuracy the presence of elements as well as relative ratios of elements present in the sample. This can be used to distinguish species of the same element in different chemical states and environments, such as through bonding and hybridization, present in the material. The distinct peaks may have binding energies that differ slightly from that of the convoluted elemental peak. Assignment of peaks can be done using XPS databases, such as that produced by NIST . The ratios of the intensities of these peaks can be used to determine the percentage of atoms in a particular state. Discrimination between and identity of elements in different states and environments is a strength of XPS that is of particular interest for carbon nanomaterials.

Hybridization

The hybridization of carbons influences the properties of a carbon nanomaterial and has implications in its structure. XPS can be used to determine the hybridization of carbons on the surface of a material, such as graphite and nanodiamond. Graphite is a carbon material consisting of sp ² carbons. Thus, theoretically the XPS of pure graphite would show a single C1s peak, with a binding energy characteristic of sp ² carbon (around 284.2 eV). On the other hand, nanodiamond consists of sp ³ bonded carbons. The XPS of nanodiamond should show a single C1s peak, with a binding energy characteristic of sp ³ carbon (around 286 eV). The ratio of the sp ² and sp ³ peaks in the C1s spectrum gives the ratio of sp ² and sp ³ carbons in the nanomaterial. This ratio can be altered and compared by collecting the C1s spectra. For example, laser treatment of graphite creates diamond-like material, with more sp ³ character when a higher laser power is used. This can be observed in [link] , in which the C1s peak is broadened and shifted to higher binding energies as increased laser power is applied.