X-ray Photoelectron Spectroscopy and Diffuse Reflectance Infrared Fourier Transform Spectroscopy Insight into the Pathways of Manganese Oxalate Thermal Decomposition to MnO and MnCO3.

X-ray photoelectron spectroscopy (XPS) and in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) were employed to study the isothermal decomposition of MnC2O4 under ultrahigh vacuum and N2 environmental conditions, respectively. High-resolution core-level XP spectra, X-ray-induced Auger spectra, and infrared spectra were obtained as a function of annealing time. In XPS studies, the time-dependent thermal decomposition characteristics were elucidated by analyzing surface composition, chemical shifts, satellites in the Mn 2p3/2 and Mn LMV bands, and Auger parameters for Mn and O. Functional groups developing during the ongoing reaction were identified by DRIFTS from characteristic vibrations. For the first time, the isothermal decomposition of manganese oxalate was shown to proceed via two pathways involving nucleation and accumulation of MnO and MnCO3. The kinetics of the decomposition in vacuum could be described by the Prout-Tompkins or/and by the Avrami-Erofeev models. The results obtained by XPS, DRIFTS, and ex situ XRD allowed concluding that the final product of oxalate decomposition was composed of MnO and MnCO3 or/and unidentate/polydentate carbonate structures populating the surface of the sample. A substantial formation of graphitic carbon was also observed and associated with interface chemical reactivities between the MnO particles and the supporting gold foil.

Au 4f spin-orbit coupling effects in supported gold nanoparticles.

Using X-ray photoelectron spectroscopy we examine the Au 4f spin-orbit components in Au 4f spectra of nanosized Au particles on a TiO2 support. In general, the peak ratios of the Au 4f7/2 and 4f5/2 excitations are found to deviate from the statistical ratio of 4 : 3 and their linewidths (FWHM) are not equal. We reveal that both the FWHM and the Au 4f7/2-to-4f5/2 peak ratios increase appreciably as the Au atomic concentration on the surface of the TiO2 support and the size of Au nanoparticles decrease. On the contrary, the Au 4f spin-orbit splitting remains essentially unchanged. Our findings are discussed in terms of alterations in the electronic band structure.