Investigating individual point defects, e.g. monovacancies, using TEM-related techniques was believed to be difficult or even not possible because this requires both atomic sensitivity and atomic resolution and the specimens need to be very thin such that one can detect the individual point defects from the image contrast.
Since a monovacancy was first observed by TEM in low-dimensional carbon structures , the studies of point defects in monolayered materials using TEM have been attracting scientists' interest. For instance, the vacancies and topological defects in grapheme, edge structures and point defects in single layer hexagonal boron nitride (h-BN) [2, 7], monovacancies in WS2 nanoribbons  have been successfully identified at atomic level [4–6]. Unfortunately, this type of analyses was only achieved in “natively” grown nanomaterials but no applications have been performed successfully in samples prepared from bulk materials, e.g. by FIB (focused ion beam), mainly because of preparation-induced damages.
The experimental conditions of the microscope are very important for point defect analyses, for instance, a probe current, applied in a JEM-2100F equipped with a delta corrector and cold field emission gun operated at 60 kV, to analyze monovacancy in single-layered h-BN (hexagonal boron-nitride) by STEM-EELS was approximately 40 pA.
In many cases, high energy resolution for EELS technique is needed to detect the point defects, grain boundaries and heterointerfaces in materials.
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