In a previous article, we studied the influence of spectral noise on a new method for three-dimensional X-ray photoelectron spectroscopy (3D XPS) imaging, which is based on analysis of the XPS peak shape [Hajati, S., Tougaard, S., Walton, J. & Fairley, N. (2008). Surf Sci602, 3064–3070]. Here, we study in more detail the influence of noise reduction by principal component analysis (PCA) on 3D XPS images of carbon contamination of a patterned oxidized silicon sample and on 3D XPS images of Ag covered by a nanoscale patterned octadiene layer. PCA is very efficient for noise reduction, and using only the three most significant PCA factors to reconstruct the spectra restores essentially all physical information in both the intensity and shape of the XPS spectra. The corresponding signal-to-noise improvement was estimated to be equivalent to a reduction by a factor of 200 in the required data acquisition time. A small additional amount of information is obtained by using up to five PCA factors, but due to the increased noise level, this information can only be extracted if the intensity of the start and end points for each spectrum are obtained as averages over several energy points.

The painting materials and drawing techniques of a pair of two-panel folding screens entitled Red and White Plum Blossoms by Ogata Korin, a national treasure in Japan, were investigated directly and nondestructively by XRF, X-ray radiography, and high resolution digital imaging. Several assumptions were made about the materials used in the red and white plum trees drawn on the right and left screens, respectively, and the river drawn at the center. By the present investigation, the materials used for the paintings were revealed, and some of them contradicted what have been previously believed.