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Opinion polarisation in social media has recently become a significant issue. The existing literature mainly attributes polarisation to online friends' informational social influence, that is, users are more likely to interact with others with similar opinions, which leads to the echo chamber effect. However, the impact of social interaction on individual polarisation may also result from normative social influence, which varies with social settings on the platform. In this paper, we leverage a quasi‐experiment to investigate the normative social influence of online friends on focal users' review polarity. We use fixed effects and difference‐in‐differences approaches, along with propensity score matching, to address the potential endogeneity in users' friend function adoption decisions. Our results indicate that adopting the friend function leads users to post less extreme ratings. We further separate the reviews into positive and negative, finding that the reduction in the review polarity for positive reviews is more prominent than for negative ones. Regarding user heterogeneity, our causal forest analysis uncovers that users with a higher engagement level on the platform are less affected by adopting the friend function than those with less engagement. Our study has clear implications for managers and platform designers, highlighting the importance of social function design in reducing social media induced polarisation. [ABSTRACT FROM AUTHOR]

Monocrystalline silicon is etched by alkaline solution to prepare an ordered pyramid structure. A certain thickness of gold film is plated on the surface of the silicon-based pyramid by magnetron sputtering as a surface-enhanced Raman scattering active substrate. The surface morphology and optical properties of the samples were characterized by SEM and UV-Vis spectrophotometer. With methylene blue as the probe molecule, more Raman characteristic peaks were detected. Raman spectra of melamine and pesticide diphenoquinone were detected by improving silicon fund nanosubstrate. The experimental results show that the prepared silicon fund nanosubstrate has potential application prospects in food safety and pesticide detection. [ABSTRACT FROM AUTHOR]