AsianScientist (Apr. 9, 2018) – A team of researchers in China has grown two-dimensional (2D) quantum well superlattices that are only a few atoms thick. They report their methods and findings in Science Advances.
A superlattice is an artificial crystal structure consisting of two or more materials, which are grown alternately on top of each other in a periodic fashion. Typically, the thickness of each material, or the width of the quantum wells in the stacking direction of the superlattice, is controlled within the range of several nanometers. This causes the quantum confinement effect to become significant within the superlattice, allowing intriguing properties to emerge. However, constructing such 2D superlattices is challenging due to their atomic-scale thickness.
In this study, Professors Wu Zhou and Zhang Yuyang from University of Chinese Academy of Sciences (UCAS) reported that by using the mismatched lateral interface between two semiconducting monolayer materials of different lattice constants, they were able to grow 2D quantum well superlattices just a few atoms thick.
The two semiconducting monolayer materials they used were lateral heterostructures of monolayer tungsten disulfide (WS2) and tungsten diselenide (WSe2), which have about a four percent difference in lattice constants. Using low-voltage aberration-corrected scanning transmission electron microscopy (STEM), the researchers observed a novel quantum well superlattice structure with a uniform width of 1.2 nanometers and periodicity of about 10 nanometers.
The researchers also found that the inherent lattice mismatch between the two materials generates periodic arrays of misfit dislocations. Dislocations, which are considered structural defects, are usually undesired in semiconducting materials. However, in this particular case, their motion drives the growth of the 2D quantum well superlattice.
This misfit-dislocation-driven growth mechanism is expected to be universally applicable to different combinations of 2D materials with lattice mismatch, paving the way for a wide range of 2D quantum well superlattices with interesting electronic and optical properties.
The article can be found at: Wu et al. (2018) Dislocation-driven Growth of Two-dimensional Lateral Quantum-well Superlattices.
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Source: Chinese Academy of Sciences; Photo: Pixabay.
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