signal centered at 161.8, 162.9 and 163.9 eV, the spin orbit splitting being the same
as for bulk CdS. Similarly, the S 2s spectrum can also be fitted with three Gaussian
functions (not shown here) with their energy separations and intensity ratios the
same as for the S 2p fitting, establishing the validity of the fitting procedure. The
dotted lines in Figure 11.15 are the three fitted Gaussian curves. The individual
components centered at 161.8, 162.9 and 163.9 eV were interpreted to arise from
three different sulfur species, namely the core (labelled 1), surface (labelled 2) and
thiol (labelled 3) sulfur, respectively, based on the binding energies of these species. Using these experimental intensities and with the assumption that the nanocrystals are spherical, it is possible to model the nanocrystal as a layered particle
with core, surface and capping layers as shown in Figure 11.16. Analyzing the relative intensities this way, Nanda et al. [99] calculated the thickness of the various
shells of the nanocrystals tabulated in Table 11.2 compared with the diameter of
the particles determined from X-ray diffraction experiments.
Winkler et al. [101] performed similar studies on CdS nanocrystals of 70, 40 and
27 A ˚ diameter, capped with mercaptopropanoic acid, using a synchrotron source.
R 2
R 0
R 1
Core
Surface
Capping
Fig. 11.16. Schematic model of a CdS nanocrystallites based
on the photoemission core-level analysis. R 0 is the radius of
the core, R 1 is the radius of the surface layer, and R 2 is the
radius of the capping layer. Adapted from [99].
Tab. 11.2. Sizes of the various regions in the nanocrystals, CdS-4.5 and CdS-2.2 obtained from
an analysis of the photoelectron intensities. The symbols R 0 , R 1 and R 2 are the radii of the core,
core þ surface shell, and core þ surface shell þ capping layer.
Sample
Core Diam.
2R 0 (nm)
Surface Layer
Diam. 2R 1 (nm)
Capping Layer
Diam. 2R 2 (nm)
Diam. from
Expt. 2R * (nm)
CdS-4.5
4.1
4.4
4.9
4.4
CdS-2.2
2.0
2.3
2.7
2.2
11.6 Photoemission Studies 397
as for bulk CdS. Similarly, the S 2s spectrum can also be fitted with three Gaussian
functions (not shown here) with their energy separations and intensity ratios the
same as for the S 2p fitting, establishing the validity of the fitting procedure. The
dotted lines in Figure 11.15 are the three fitted Gaussian curves. The individual
components centered at 161.8, 162.9 and 163.9 eV were interpreted to arise from
three different sulfur species, namely the core (labelled 1), surface (labelled 2) and
thiol (labelled 3) sulfur, respectively, based on the binding energies of these species. Using these experimental intensities and with the assumption that the nanocrystals are spherical, it is possible to model the nanocrystal as a layered particle
with core, surface and capping layers as shown in Figure 11.16. Analyzing the relative intensities this way, Nanda et al. [99] calculated the thickness of the various
shells of the nanocrystals tabulated in Table 11.2 compared with the diameter of
the particles determined from X-ray diffraction experiments.
Winkler et al. [101] performed similar studies on CdS nanocrystals of 70, 40 and
27 A ˚ diameter, capped with mercaptopropanoic acid, using a synchrotron source.
R 2
R 0
R 1
Core
Surface
Capping
Fig. 11.16. Schematic model of a CdS nanocrystallites based
on the photoemission core-level analysis. R 0 is the radius of
the core, R 1 is the radius of the surface layer, and R 2 is the
radius of the capping layer. Adapted from [99].
Tab. 11.2. Sizes of the various regions in the nanocrystals, CdS-4.5 and CdS-2.2 obtained from
an analysis of the photoelectron intensities. The symbols R 0 , R 1 and R 2 are the radii of the core,
core þ surface shell, and core þ surface shell þ capping layer.
Sample
Core Diam.
2R 0 (nm)
Surface Layer
Diam. 2R 1 (nm)
Capping Layer
Diam. 2R 2 (nm)
Diam. from
Expt. 2R * (nm)
CdS-4.5
4.1
4.4
4.9
4.4
CdS-2.2
2.0
2.3
2.7
2.2
11.6 Photoemission Studies 397