We study the mechanisms of CH₃NH₃PbI₃ degradation and its transformation to PbI₂ by means of X-ray diffraction and the density functional theory. The experimental analysis shows that the material can degrade in both air and vacuum conditions, with humidity and temperature-annealing strongly accelerating such process. Based on ab initio calculations, we argue that even in the absence of humidity, a decomposition of the perovskite structure can take place through the statistical formation of molecular defects with a non-ionic character, whose volatility at surfaces should break the thermodynamic defect equilibria. We finally discuss the strategies that can limit such phenomenon and subsequently prolong the lifetime of the material.

The temperature dependence of the electrical properties of $\mathrm{Pt}∕\mathrm{Ga}\mathrm{N}$ Schottky barrier was studied. In particular, a Schottky barrier height of $0.96\mathrm{eV}$ and an ideality factor of 1.16 were found after a postdeposition annealing at $400°\mathrm{C}$ . Nanoscale electrical characterization was carried out by the conductive biased tip of an atomic force microscope both on the bare GaN surface and on the $\mathrm{Pt}∕\mathrm{Ga}\mathrm{N}$ contacts. The presence of a lateral inhomogeneity of the Schottky barrier, with a Gaussian distribution of the barrier height values, was demonstrated. Moreover, GaN surface defects were demonstrated to act as local preferential paths for the current conduction. The temperature dependent electrical characteristics of the diodes were discussed in terms of the existing models on inhomogeneous barriers and correlated to the nanoscale electrical characterization of the barrier. In this way, the anomalous electrical behavior of the ideality factor and of the Schottky barrier and the low experimental value of the Richardson’s constant were explained.

Gold-assisted mechanical exfoliation currently represents a promising method to separate ultralarge (centimeter scale) transition metal dichalcogenide (TMD) monolayers (1L) with excellent electronic and optical properties from the parent van der Waals (vdW) crystals. The strong interaction between Au and chalcogen atoms is key to achieving this nearly perfect 1L exfoliation yield. On the other hand, it may significantly affect the doping and strain of 1L TMDs in contact with Au. In this paper, we systematically investigated the morphology, strain, doping, and electrical properties of large area 1L MoS₂ exfoliated on ultraflat Au films (0.16–0.21 nm roughness) and finally transferred to an insulating Al₂O₃ substrate. Raman mapping and correlative analysis of the E′ and A₁′ peak positions revealed a moderate tensile strain (ε ≈ 0.2%) and p-type doping (n ≈ −0.25 × 10¹³ cm^–2) of 1L MoS₂ in contact with Au. Nanoscale resolution current mapping and current–voltage (I–V) measurements by conductive atomic force microscopy (C-AFM) showed direct tunneling across the 1L MoS₂ on Au, with a broad distribution of tunneling barrier values (Φ_B from 0.7 to 1.7 eV) consistent with p-type doping of MoS₂. After the final transfer of 1L MoS₂ on Al₂O₃/Si, the strain was converted to compressive strain (ε ≈ −0.25%). Furthermore, an n-type doping (n ≈ 0.5 × 10¹³ cm^–2) was deduced by Raman mapping and confirmed by electrical measurements of an Al₂O₃/Si back-gated 1L MoS₂ transistor. These results provide a deeper understanding of the Au-assisted exfoliation mechanism and can contribute to its widespread application for the realization of novel devices and artificial vdW heterostructures.