  Near total reflection regime has been widely used in X-ray science,
specifically in grazing incidence small angle X-ray scattering and in hard
X-ray photoelectron spectroscopy. In this work, we introduce some practical
aspects of using near total reflection in ambient pressure X-ray photoelectron
spectroscopy and apply this technique to study chemical concentration gradients
in a substrate/photoresist system. Experimental data are accompanied by X-ray
optical and photoemission simulations to quantitatively probe the photoresist
and the interface with the depth accuracy of ~1 nm. Together, our calculations
and experiments confirm that near total reflection X-ray photoelectron
spectroscopy is a suitable method to extract information from buried interfaces
with highest depth-resolution, which can help address open research questions
regarding our understanding of concentration profiles, electrical gradients,
and charge transfer phenomena at such interfaces. The presented methodology is
especially attractive for solid/liquid interface studies, since it provides all
the strengths of a Bragg-reflection standing-wave spectroscopy without the need
of an artificial multilayer mirror serving as a standing wave generator, thus
dramatically simplifying the sample synthesis.
