Figure 1b and c show the TEM grid before and after treatment with methylbenzene respectively. The methylbenzene dissolved the organic polymer film and destroyed the skeleton structure of the TEM grid. The holes damaged by the organic solvent are circled with red dotted lines in Fig. 1c. Uneven and impaired grid will result in a difficult sample searching and sample drift, which will negatively affect the acquisition of high-quality TEM images (Stinson-Bagby et al. 2018; Nair et al. 2010; Duchamp et al. 2014). Therefore, it is necessary to develop a method that can obtain high-quality TEM sample of oil-soluble nanomaterials and avoid damaging the organic polymer layer in TEM grid.
Here, a new method for nanomaterial sample preparation was designed by introduce sublimable naphthalene as the transition layer. First, naphthalene was deposited on the substrate and nanomaterials were sprayed onto naphthalene layer. Next, the side of the naphthalene layer with the nanomaterial was transferred to covered on the TEM grid, and then place the sample in a vacuum to sublimate naphthalene. The process is shown in Fig. 2.
Based on this method, we obtained a continuous large-scale highly-dispersed oil-soluble PbS nanocrystal sample and captured high-quality TEM (Fig. 3a), High-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) (Fig. 3b) and HRTEM (Fig. 3c) images. It proves that images with low background contrast, accurate material morphology, and clear lattice fringes can be obtained via this new sample preparation method.