The chemical state of N in N-doped amorphous ${\mathrm{Ge}}_2{\mathrm{Sb}}_2{\mathrm{Te}}_5$ $\left(a\text{-}\mathrm{GST}\right)$ samples with $0–14.3\mathrm{N}\mathrm{at.}\%$ doping concentrations was investigated by high-resolution x-ray photoelectron spectroscopy (HRXPS) and Ge $K$ -edge x-ray absorption spectroscopy (XAS). HRXPS showed negligible change in the Te $4d$ and Sb $4d$ core-level spectra. In the Ge $3d$ core-level spectra, a Ge nitride $\left(\mathrm{Ge}{\mathrm{N}}_x\right)$ peak developed at the binding energy of $30.2\mathrm{eV}$ and increased in intensity as the N-doping concentration increased. Generation of $\mathrm{Ge}{\mathrm{N}}_x$ was confirmed by the Ge $K$ -edge absorption spectra. These results indicate that the N atoms bonded with the Ge atoms to form $\mathrm{Ge}{\mathrm{N}}_x$ , rather than bonding with the Te or Sb atoms. It has been suggested that the formation of Ge nitride results in increased resistance and phase-change temperature.

${\mathrm{Ge}}_2{\mathrm{Sb}}_2{\mathrm{Te}}_5$ (GST) film in the crystalline state was nitrogen doped using the reactive sputtering method in order to increase sheet resistance. High-resolution x-ray absorption spectroscopy revealed that molecular nitrogen $\left({\mathrm{N}}_2\right)$ existed in the N-doped GST film. This finding implies that both molecular nitrogen and atomic-state nitrogen should be taken into account in understanding the structures of N-doped GST film. The molecular nitrogen is believed to exist at interstitial and vacancy sites, and more likely at grain boundaries.

We report the presence of CH₃NH₂ neutral species not only on the surface but also at grain boundaries in the interior of thin polycrystalline films of methylammonium lead iodide perovskite CH₃NH₃PbI₃ (thickness ∼ 50 nm) that were prepared using a standard solution method. Different chemical states for C K-edge were observed at the surfaces and in the interiors of perovskite films. Salient features of σ*(CH₃-NH₃⁺: methylammonium cation) and σ*(CH₃-NH₂: methylamine neutral species) were observed at 290.3 and 292.8 eV in both partial (surface-sensitive) and total (bulk) electron yield modes by near-edge x-ray absorption fine structure measurements. Consistently, two chemical states originated from CH₃NH₃⁺ and CH₃NH₂ in C 1s and N 1s core-level spectra were observed using high-resolution x-ray photoelectron spectroscopy. Using density functional theory calculations, we show that CH₃NH₂ cannot reside stably in the MAPbI₃ perovskite crystal structure. Therefore, we propose that these CH₃NH₂ neutral species are mainly located on the surface or at grain boundaries in the interior of CH₃NH₃PbI₃ films.

We report on the fabrication of efficient inverted organic light-emitting diodes (IOLEDs) using pentacene films as an electron injection/transport layer between Al and ${\text{Alq}}_3$ layers. These IOLED devices turn on at 4.7 V and exhibit a luminous efficiency of 9.5 cd/A without any dopants or reactive metals. Analysis using space-charge-limited characteristics of electron-only devices and ultraviolet photoelectron spectroscopy measurement of metal/organic interfaces indicates that the efficient IOLED characteristics can be attributed partly to the electron mobility of pentacene that is ${10}^2–{10}^4$ times larger than that of ${\text{Alq}}_3$ and to the effective reduction in injection barrier at contacts.