The ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/adom.202201059.

Nanosheets of silicene, a 2D material made of silicon atoms, have great potential for use in next-generation electronic and optoelectronic devices due to their unique properties. However, issues in the large-scale production of silicene nanosheets and in their degradation still present challenges for these applications. Here, we report a method to obtain large quantities of single to fewlayer thick silicene/silicene oxide ("Si nanosheets") from calcium disilicide (CaSi 2 ). We also show that the silicene nanosheets experience oxidation in air and are highly oxidized after 12 weeks of storage. Density functional theory studies were performed and provide a detailed understanding of this oxidation. Silicene/ silicene oxide nanosheet-based photodetector devices were also fabricated for the first time. They show a broadband response in the visible spectral range with outstanding responsivity (14.3 A/W), detectivity (3 × 10 10 Jones), and external quantum efficiency (44.6%), demonstrating the promising applications of this material for optoelectronic devices.

Metal halide perovskites have emerged as the next generation of light emitting semiconducting materials due to their excellent properties such as tunable bandgaps, high photoluminescence quantum yield, and high color...

contain dendritic structures with a fractal dimension consistent with a diffusionlimited aggregation process. [3,6] Although a variety of degradation prevention techniques have been reported such as encapsulation with hexagonal boron nitride [9] and polymers, [10] use of novel gate dielectrics, [11] and placement in an environment with a desiccant [3] or in a vacuum, [4] such techniques are not applicable for ambientair applications such as gas sensors. To our knowledge, the stability of bilayer (BL) and thicker-layer MoS 2 films in ambient air has not been extensively studied. It is important to understand the stability of such films for developing applications and having a better understanding of ML degradation. In this paper, we report on the structural stability of preheated and as-grown BL and thicker-layer MoS 2 films in ambient air. The films are grown using CVD on SiO 2 substrates and studied using atomic force microscopy (AFM), and Raman and PL spectroscopies.BL and thicker-layer MoS 2 and other TMD films, nanosheets, [12] and nanostructures, [13] although having indirect band gaps, have attracted considerable interest because of their useful properties. For example, BLs and thicker-layers have higher electrical conductivities than MLs due to their higher density of states and more effective screening of impurities in the substrate. [14] In addition, BL device yield is typically higher than ML device yield, due to the greater mechanical strength of BLs. [15,16] BL and thicker-layer TMD films offer layer control of properties such as spin-orbit coupling, [17] interlayer coupling, [18] and band gap. [19] Varying the twist angle between layers in BLs has been reported to result in twist-dependent valley and band alignment, [20] and Moiré pattern excitons. [21] The ambient-air degradation of CVD-grown ML MoS 2 and other ML TMD films was first reported by Gao et al. [3] They observed that ML MoS 2 and WS 2 grown on SiO 2 substrates developed extensive cracking, morphological changes, and quenching of PL after exposure to ambient air at room temperature (RT) for a period of about a year. The degradation was attributed to oxidation along grain boundaries and other defects. It was found that water vapor in the air was necessary for degradation to occur since films did not degrade in a dry box. In addition, Budania et al. [4] reported that mechanically exfoliated thin multilayer MoS 2 flakes on SiO 2 developed speckles in air at a high relative humidity (RH) of 60% over a period of about a year. Kotsakidis et al. [5] reported

The layer edge states or low energy state (LES) in 2D hybrid organic–inorganic perovskites demonstrate a prolonged carrier lifetime for better performance of optoelectronic devices. However, the fundamental understanding of LES in 2D perovskites is still inconclusive. Herein, a photoluminescence (PL) study of LES in 2D Ruddlesden–Popper perovskites is presented with n = 2 and n = 3 from their cleaved cross sections that are more stable than the natural edge. The PL measurements clearly observe reversible, and irreversible surface relaxations (case I and case II) in three laser intensity ranges, further supported by a PL excitation cycle from low to high laser intensity, and vice versa. The PL wavelength of LES is tunable with laser intensity and blueshifts with increasing laser intensity during irreversible surface relaxation process (case I). Fluorescence lifetime imaging (FLIM) shows that the LES has a longer lifetime than the band‐edge emission in the sample without a photodegradation, while the BE lifetime becomes relatively longer in the area with a photodegradation. The presented laser tunable LES and the related irreversible relaxation process provide a new insight that can help improve the photostability in 2D perovskites and understand roles of LESs in optoelectronic device performance.