Organometal halide (hybrid) perovskite solar cells have been fabricated following four different deposition procedures and investigated in order to find correlations between the solar cell characteristics/performance and their structure and composition as determined by combining depth-resolved imaging with time-of-flight secondary ion mass spectrometry (ToF-SIMS), X-ray photoelectron spectroscopy (XPS), and analytical scanning transmission electron microscopy (STEM). The interface quality is found to be strongly affected by the perovskite deposition procedure, and in particular from the environment where the conversion of the starting precursors into the final perovskite is performed (air, nitrogen, or vacuum). The conversion efficiency of the precursors into the hybrid perovskite layer is compared between the different solar cells by looking at the ToF-SIMS intensities of the characteristic molecular fragments from the perovskite and the precursor materials. Energy dispersive X-ray spectroscopy in the STEM confirms the macroscopic ToF-SIMS findings and allows elemental mapping with nanometer resolution. Clear evidence for iodine diffusion has been observed and related to the fabrication procedure.

We have used Raman spectroscopy, transmission electron microscopy, x-ray diffraction, and x-ray photoemission spectroscopy to investigate strain relaxation mechanism of Si(0.22)Ge(0.78) heteroepitaxial layer deposited on Si substrates in tensile, neutral, and compressive strain conditions. The three regimes have been obtained by interposing between the SiGe layer and the substrate a fully relaxed Ge layer, a partially relaxed Ge layer, or growing directly the alloy on Si. We found that the deposition of a Ge buffer layer prior to the growth of the SiGe is very promising in view of the realization of thin virtual substrates on silicon to be used for the deposition of strain-controlled high Ge content SiGe alloys. We demonstrate that this is mainly due to the strain relaxation mechanism in the Ge layer occurring via insertion of pure edge 90 degrees misfit dislocations (MDs) and to the confinement of threading arms in to the Ge layer due to a second MD network formed at the SiGe/Ge heterointerface

We report an extensive study of strained Ge/Si0.2Ge0.8 multiquantum wells grown by ultrahigh-vacuum chemical-vapor deposition. The microstructural properties of the samples were characterized by transmission electron microscopy and Raman spectroscopy. Their electronic properties have been investigated by means of infrared absorption measurements. Both interband and intersubband transitions were analyzed. Intersubband absorption energies were found in the 20–50 meV range, depending on the quantum well width. Interband and intersubband transition energies have been successfully described by means of both a k⋅p approach and a tight-binding model. In particular, we found a conduction-band offset between the L edges of 124 meV, well suited for the development of optoelectronic devices operating in the terahertz range. We also found that the energy difference between the Δ2 minima in the barrier and the L minima in the well is only ∼40 meV. This explains the observed ineffectiveness of the transfer doping in the strained heterostructures considered

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The influence of the texture, structure, and chemistry of different carbon supports on the morphological properties, oxygen reduction reaction (ORR) activity, and stability of porous hollow PtNi nanoparticles (NPs) was investigated. The carbon nanomaterials included carbon blacks, carbon nanotubes, graphene nanosheets, and carbon xerogel and featured different specific surface areas, degrees of graphitization, and extent of surface functionalization. The external and inner diameters of the supported porous hollow PtNi/C NPs were found to decrease with an increase in the carbon mesopore surface area. Despite these differences, similar morphological properties and electrocatalytic activities for the ORR were reported. The stability of the synthesized electrocatalysts was assessed by simulating electrochemical potential variations occurring at a proton exchange membrane fuel cell (PEMFC) cathode during startup/shutdown events. Identical location transmission electron microscopy (IL-TEM) and electrochemical methods revealed the occurrence of a carbon-specific degradation mechanism: carbon corrosion into CO2 and particle detachment were noticed on carbon xerogels and graphene nanosheets while, on carbon blacks, surface oxidation prevailed (C → COsurf) and did not result in modified electrical resistance of the catalytic layers, rendering these carbon supports better suited to prepare highly active and stable ORR electrocatalysts.