Raman spectroscopy is a very sensitive tool for probing semiconductor nanocrystals. The underlying mechanism behind the size-dependent Raman shifts is still quite controversial. Here we offer a new theoretical method for the quantum confinement effects on the Raman spectra of semiconductor nanocrystals. We propose that the shift of Raman spectra in nanocrystals can result from two overlapping effects: the quantum effect shift and surface effect shift. The quantum effect shift is extracted from an extended Kubo formula, the surface effect shift is determined via the first principles calculations. Fairly good prediction of Raman shifts can be obtained without the use of any adjustable parameter. Closer analysis shows that the size-dependent Raman shifts in Si nanocrystals mainly result from the quantum effect shifts. For nanodiamond, the proportion of surface effect shift in Raman shift is up to about 40%. Such model can also provide a good baseline for using Raman spectroscopy as a tool to measure size.

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The asymmetric peak broadening towards the low-frequency side of the Raman-active mode of Si nanocrystals with the decreasing size has been extensively reported in the literatures. In this study, an atomic coordination model is developed to study the origin of the ubiquitous asymmetric peak on the optical phonon fundamental in the Raman spectra of Si nanocrystals. Our calculation results accurately replicate the line shape of the experimentally measured optical Raman curves. More importantly, it is revealed that the observed asymmetric broadening is mainly caused by the surface bond contraction and the quantum confinement.

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The interface closely related to carrier transport plays a vital role in high-performance perovskite solar cells (PSCs). In this work, an ionic liquid (IL) 1-butyl-3-methylimidazole hexafluorophosphate (BMIMPF 6 ) has been introduced to simultaneously modify the TiO 2 and perovskite films, which improves the energy level matching and contact of the TiO 2 / CsPbI 2 Br interface as well as provides perovskite films with larger grain size, leading to more faster charge transfer and lower energy loss. Furthermore, the BMIMPF 6 modifier passivates the perovskite film defects and reduces defect-induced charge trapping and recombination in CsPbI 2 Br PSCs. Under dual-interface modification, the open-circuit voltage of the modified device increased to 1.22 V, and the power conversion efficiency (PCE) increased from 10.65 to 13.19%. Moreover, the unencapsulated modified devices exhibit an enhanced stability and maintain 91% of their initial PCE after 60 days of storage. This work has provided a strategy for efficient and stable PSCs by exploiting an IL to optimize the dual-interface at the same time.

Surface enhanced Raman scattering (SERS) has been widely used in detection of food safety due to the nondestructive examination property. Here, we reported a flexible SERS film based on a polymer-immobilized gold nanorod polymer metafilm. Polystyrene-polyisoprene-polystyrene (SIS), a transparent and flexible, along with having excellent elasticity, polymer, was chosen as the main support of gold nanorods. A simple phase transfer progress was adopted to mix the gold nanorods with the polymer, which can further be used in most water-insoluble polymers. The SERS film performed satisfactorily while being tested in a series of standard Raman probes, like crystal violet (CV) and malachite green (MG). Moreover, the excellent reproducibility and elastic properties make the film a promising substrate in practical detection. Hence, the MG detection on the fish surface and trace thiram detection on orange pericarp were inspected with detection results of 1 × 10 and 1 × 10 M, which were below the demand of the National standard of China, exactly matching the realistic application requirements.

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