A c c e p t e d M a n u s c r i p t Highlights (for review) -The dynamics of UV-induced oxygen vacancy is studied from the change of surface resistance.-The formation of 2DEG at the insulating surface of SrTiO 3 is confirmed by ARPES.-The UV-induced change in resistance responds differently to oxygen/gas exposure.-The behavior of resistance recovery suggests an alternative method of low-pressure sensing.Page 2 of 5 A c c e p t e d M a n u s c r i p t The effect of ultra-violet (UV) irradiation on the electronic structure and the surface resistance of an insulating SrTiO3(001) crystal is studied in this work. Upon UV irradiation, we shows that the two-dimensional electron gas (2DEG) emerges at the insulating SrTiO3 surface and there is a pronounced change in the surface resistance. By combining the observations of the change in valance band and the resistance change under different environments of gas pressure and gas species, we find that UV-induced oxygen vacancies at the surface plays a major role in the resistance change. The dynamic of the resistance change at different oxygen pressures also suggests an alternative method of low-pressure sensing.

X-ray photoelectron spectroscopy (XPS) and KLL Auger spectra of aqueous KCl solution were measured for the K + and Cledges. While the XPS spectra of potassium and chloride have similar structures, both exhibiting only weak satellite structures near the main line, the Auger spectra of these isoelectronic ions differ dramatically. A very strong satellite peak was found in the K + KLL Auger spectrum at the low kinetic energy side of the 1 D state. Using equivalent core models and ab initio calculations this spectral structure was assigned to electron transfer processes from solvent water molecules to the solvated K + cation. Contrary to the potassium case, no extra peak was found in the KLL Auger spectrum of solvated Cl -indicating on a strong dependence of the underlying processes on ionic charge. The observed charge transfer processes are suggested to play an important role in charge redistribution following single and multiple core-hole creation in atomic and molecular systems placed into an environment.Charge transfer (CT) processes and related phenomena are topics of wide relevance in chemistry, physics and biology. They are responsible for numerous important transformations in living organisms and are involved in fundamental steps describing, e.g., the photosynthesis [1] and respiration [2] mechanisms. The creation of a charge (or hole) in a DNA chain, by oxidation or photoionization processes, is quickly followed by its migration along portions of the molecular backbone leading to possible bonds breaking and irreversible damages [3]. Naturally, the use of such very fast elemental processes for technological purposes has attracted an extraordinary large amount of scientists whose research programs -both theoretical and experimental -focus on energy conversion based for instance on photovoltaic or optoelectronic devices [see e.g. ref. [4]].CT may accompany core-hole creation in atoms and molecules which have neighbors, and the corresponding spectral signatures are manifested in XPS spectra as lowenergy CT satellites. Particularly strong CT screening satellites were found in XPS spectra of weak chemisorption systems [5,6], in crystals [7,8], in weakly bound atomic [9] and microsolvated [10][11][12] clusters. As shown in the latter studies, the energy positions and intensities of CT satellites are sensitive to cluster geometries. Furthermore, the type and number of neighbors have strong effects on CT states [13]. CT processes from core-excited metal ions to solvent molecules may quench radiative relaxation processes as observed in fluorescence-yield spectra [14].For elements from the first rows of the periodic table, electronic Auger decay is the main relaxation channel of core-hole states. Core-hole lifetime ranging usually in the femtosecond and sub-femtosecond timescales may serve as an internal reference clock. Using this reference and the relative intensities of spectral peaks, the core-hole clock method allows one to determine timescales of various processes competing to Auger decay, in particular ...

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X-ray absorption and Auger electron spectroscopies are demonstrated to be powerful tools to unravel the electronic structure of solvated ions. In this work for the first time, we use a combination of these methods in the tender X-ray regime. This allowed us to address electronic transitions from deep core levels, to probe environmental effects, specifically in the bulk of the solution since the created energetic Auger electrons possess large mean free paths, and moreover, to obtain dynamical information about the ultrafast delocalization of the core-excited electron. In the considered exemplary aqueous KCl solution, the solvated isoelectronic K and Cl ions exhibit notably different Auger electron spectra as a function of the photon energy. Differences appear due to dipole-forbidden transitions in aqueous K whose occurrence, according to the performed ab initio calculations, becomes possible only in the presence of solvent water molecules.

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