Thickness Of Few Monolayers Research Articles

Synthesis and electronic structure study on CsPbBr3 nanoplatelets: Thickness manipulation using surface ligands

Cesium Lead Halide based Perovskites have received significant attention due to their potential application in all inorganic solar cells. To date, there is only limited literature on their anisotropic nanostructures. Here, we report synthesis of 2D nanostructures of CsPbBr3 with thickness of few monolayers (MLs). Due to size quantization, the 2D nanostructure showed a blue shifted absorption from bulk absorption. We manipulate acid: amine (capping agents) ratios to achieve a monolayer level thickness control as evidenced by absorption spectroscopy and TEM analysis. The thickness of 1 ML-4 ML could be seamlessly controlled by varying the ratio. The study shows rich solution phase reaction dynamics during growth with size evolution over time. Additionally, we also compute band structure to validate the effect of size quantization on electronic structure for NPLs investigated. This study opens up possibility of synthesis of these nanostructures with good reaction control over growth of NPLs and also sheds light on complex acid base chemistry that exists in reaction.

On the applicability of elastic model to very thin crystalline layers

Elastic model of continuum material is often used to simulate the relaxation of crystalline heterostructures. There are many reports on the successful application of the theory of elasticity to nano-sized crystalline heterostructures, even if the continuum condition for them is hardly fulfilled. On the other hand, progress in epitaxial growth allows for the preparation of stable ultra-thin layers with thickness of few monolayers. For such ultra-thin layers, results provided by continuum model and molecular statics/dynamics calculations become diverging. The key problem seems to be located at the modelling of the interface between layers, which is problematic in the continuum approach. By applying a step-wise substitutive compositional interfacial function, it is possible to obtain good agreement with molecular dynamics calculations, even for a single monolayer heterostructure. We propose another approach that uses composition as an extra parameter during finite element calculations, along with classical nodal displacements. Such an approach creates a chemo-elastic coupling that allows to interpolate the composition much like in the case of atomistic calculations.

3D chrysanthemum-like ReS2 microspheres composed of curly few-layered nanosheets with enhanced electrochemical properties for lithium-ion batteries

As a new member of the transition metal dichalcogenides (TMDs) family, rhenium disulfide (ReS2) is attracting more and more attention because of its many distinctive characteristics, such as extremely weak interlayer coupling and anisotropic electronic, optical, and mechanical properties. The studies on synthesis method and electrochemical properties of ReS2 are still rare. For the first time, three-dimensional (3D) chrysanthemum-like microspheres composed of curly ReS2 nanosheets have been synthesized through a facile hydrothermal method. The high-resolution TEM image indicates that the ReS2 nanosheet is highly crystalline with a thickness of few monolayers. As anode for lithium-ion battery, the as-synthesized 3D chrysanthemum-like ReS2 (C-ReS2) microspheres deliver a large initial discharge capacity of 843.0 mAh g−1 and remain 421.1 mAh g−1 after 30 cycles. These values are much higher than that of commercial ReS2. The significant enhancement in electrochemical performance can be attributed to its porous and chrysanthemum-like microsphere structure constructed by few-layered curly ReS2 nanosheets. This unique architecture can allow for easy electrolyte infiltration, efficient electron transfer, and ionic diffusion. The facile synthesis approach can be extended to synthesize other two-dimensional TMDs semiconductors. The study renders ReS2 a promising future in lithium-ion batteries.