X-Ray Photoelectron Spectroscopy of Nanostructures

Nanoarchitectures represent a promising future for nanotechnology. Therefore, many scientists recently devoted their efforts to the synthesis, characterization and properties of nanosized ionic and molecular systems. XPS is a surface technique suitable to probe thicknesses of the same order of the photoelectron inelastic mean free path, (a few tens of Å). This technique allows to immediately obtaining qualitative and quantitative analyses as well as oxidation states. Moreover, analysis of particular spectral features as shake-up phenomena, Auger parameters, presence of screened and unscreened states, etc. can be used for more elegant studies. If, in addition, the XPS instrument allows a high stability, precise and reproducible adjustment of the emission angle of the sample stage, one can afford reliable angle resolved measurements (AR-XPS) that are important to obtain film thickness and surface coverage for flat samples. For these reasons, XPS revealed to be a unique technique for an in-depth chemical and structural characterization of nanostructures. Recently some new synchrotron based XPS applications on non-destructive depth profiling of nano-scaled surface layers have been published. The technique delivers data comparable to AR-XPS and self-assembled molecular nanoarchitectures have been studied. Additionally, variable excitation energy XPS (ERXPS), available at synchrotrons, offers a relatively new and increasingly powerful alternative to obtaining depth information from nanoparticles, powders and other real surfaces that are not ideally smooth. ERXPS offers, therefore, an attractive potential for the analysis of the outmost surface layer of real materials. Often, mono and multi-layer materials are fabricated on atomically flat and chemically well-defined silicon surfaces, in the perspective of fabrication of electronic devices that can be easily integrated within electronic circuits. Besides to silicon, also high quality quartz surfaces revealed to be excellent substrates for optical applications. In this general filed some recent important applications of XPS in the study of self-assembled material are presented.