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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 ...

Nanostructured silicon was formed by means of the ionized N2 gas reaction on SiO2/Si, and the electronic structure, surface morphology, and optical properties were investigated. The physicochemically modified thin layers were resolved to SiNy and SiOxNy through the observation of Si 2p, O 1s, and N 1s core-level spectra in x-ray photoelectron spectroscopy. The formations of SiOxNy and SiO2 nanostructures (3–4 nm in size), performed by the etching process followed by adsorption of ionized nitrogen, were confirmed by atomic force microscopy. The nanocrystalline Si (6 nm in size) distributed within the modified layer (approximately 10 nm thick) was observed after the in situ rapid thermal annealing processes, using high-resolution transmission electron microscopy. Photoluminescence with a wavelength peaking at around 400 nm was emitted from the nanocrystalline Si formed from the SiOxNy/SiO2/Si structures. This work suggests that the nanocrystalline-Si formation and the nanostructured surface modification met...

To find the cause of N2 → N + N dissociation in Ge(001) at low temperature, the N2+ ion implantation process was carried out on a Ge(001) substrate, followed by rapid thermal annealing (RTA). After N2+ ion implantation, the presence of N2 molecules and the chemical states of GeNx were determined using near-edge x-ray absorption of fine structure (NEXAFS) and high-resolution x-ray photoelectron spectroscopy with synchrotron radiation, respectively. Rapid thermal annealing was performed at 600 °C, after which a change in chemical state from the chemically meta-stable state of GeNx to the stable state of Ge3N4 was observed. In addition, the intensity of the N2 vibration mode peak in NEXAFS was decreased, although it did not completely disappear. To explain the N2 →N + N dissociation at the low temperature, a first-principle calculation for N2 bonding length was performed in both vacuum and Ge(001) states. We confirmed that implantation resulted in the trapping of N2 molecules in Ge(001), and their bonding le...

We introduce single-phase In–Ge–Sb–Te (IGST) quaternary thin film (fcc structure when crystallized) deposited by cosputtering from Ge2Sb2Te5(GST) and In3Sb1Te2 targets. This film, compared with the GST ternary system, provides a significant increase of amorphous-to-crystalline transformation temperature. High-resolution x-ray photoelectron spectroscopy (HRXPS) revealed that, with increasing In amounts, the Sb 4d and Ge 3d core peaks shift toward lower binding energies (BEs), with negligible changes in spectral linewidths, whereas the In 4d and Te 4d core peaks show insignificant changes in BEs. HRXPS interpretation suggests that the Na site in IGST can be occupied by Te, Sb, In, and vacancy, whereas in GST it is occupied only by Te.

We present chemical state information on contamination-free Ge2Sb2Te5 thin film using high-resolution x-ray photoelectron spectroscopy (HRXPS) and the corresponding theoretical understanding of the chemical states, on both amorphous and metastable phases, illuminating the phase-change mechanism of the system. HRXPS data revealed that the Sb 4d shallow core level was split into two components having different binding energies and that the spin-orbit splitting feature of the Ge 3d level was enhanced as the system became metastable. Negligible change was observed in the Te 4d shallow core level, and in contrary to the previous report’s prediction less change in valance band spectra was observed. The results imply that Sb movement is also involved in the phase-change mechanism and that acquisition of shallow core-level spectra can be a useful measure for understanding phase-change mechanism. Hydrogenated SbTe6 octahedral-like cluster model was introduced to schematically interpret the generation of the two co...

An ultrathin Si oxide film grown on a 6H-SiC(0001) wafer was irradiated with 1MeV electron beam to examine its effect on the chemical species of a Si oxide/SiC wafer, where the Si oxide film was composed of SiO2, Si suboxides (Si3+, Si2+, and Si1+), and Si oxycarbides (Si–C–O). Scanning photoelectron microscopy and Si 2p core-level spectroscopy show that e-beam irradiation induces chemical phase transitions from the Si suboxides and Si oxycarbides to SiO2. This suggests that e-beam irradiation is an efficient and simple method of producing a chemically uniform SiO2 film on SiC without thermal and chemical treatments.

The chemical state of N in N-doped amorphous Ge2Sb2Te5 (a-GST) samples with 0–14.3Nat.% 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 (GeNx) peak developed at the binding energy of 30.2eV and increased in intensity as the N-doping concentration increased. Generation of GeNx was confirmed by the Ge K-edge absorption spectra. These results indicate that the N atoms bonded with the Ge atoms to form GeNx, 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.

The electronic structures of SrMn1−xFexO3 (0⩽x⩽1) have been investigated by using photoemission spectroscopy (PES) and soft x-ray absorption spectroscopy (XAS). Mn ions in SrMnO3 are found to be in the nearly tetravalent (Mn4+) states, but with a small mixture of the Mn2+ configuration. With increasing x in SrMn1−xFexO3, Mn ions remain in the 4+ states. Fe ions in SrMn1−xFexO3 are also in the nearly tetravalent (Fe4+) states for the whole range of x. Valence-band PES reveals that the occupied Mn t2g3 states are located about 2.5eV below EF, while the occupied Fe t2g3eg1 states are broader than the Mn 3d occupied states, and are located between 3 and 6eV below EF. The large overlap between Fe 3d and the O 2p states is found in SrFeO3, reflecting the strong hybridization between the Fe 3d states and the O 2p states, in agreement with the metallic nature of SrFeO3.

When an organic layer on a conducting substrate is exposed to intense x rays, such as in scanning photoelectron microscopy (SPEM), the photoelectron spectrum for the exposed area shows a kinetic energy shift towards higher binding energy due to the accumulation of local charges. We present experimental evidence that in the thin organic layer of approximately 100nm thickness in organic light-emitting devices, there exists an unshifted spectral component besides the local-charging-shifted spectral component. This finding enabled us to reliably investigate the chemical structures of organic layers using SPEM, which was shown to be advantageous in obtaining the space-resolved chemical structural information of a specimen.

The authors present space-resolved spectroscopic data on organic layers of a degraded organic light-emitting device. The data were obtained using a scanning photoelectron microscope (SPEM) coupled with peel-off technique to directly probe the uncontaminated organic layers, which were covered with cathode layer. The SPEM images of the degraded device show different and small size distributions of tris-8-hydroxy quinoline aluminum (Alq3) and hole-transport layers compared to that of as-prepared device. The analysis indicates that bonding strength between Alq3 and cathode layers and between the Alq3 and hole transport layers becomes weak as the device degrades, presumably due to structural deformation of the organic layers.

Amorphous Ge2Sb2Te5 (a-GST) film, 100nm thick, was grown by cosputtering from GeTe and Sb2Te3 targets on a silicon wafer at room temperature. The native oxidized layer, which was formed in air and about 20nm thick measured by secondary ion mass spectroscopy, was removed by Ne+ ion sputtering for 1h with 0.6kV beam energy. Core-level spectra of the Te 3d and 4d, Sb 3d and 4d, and Ge 3d of the oxygen-free a-GST were obtained by high-resolution x-ray photoelectron spectroscopy with synchrotron radiation and compared with those from Ge and GeTe. The analysis implies that the a-GST is composed on the base of chemical states of GeTe.