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Ferroelectric poly(vinylidene fluoride) (PVDF) nanofilms have been fabricated by the Langmuir–Blodgett technique, possessing mainly a ferroelectric active phase and a controllable film thickness of 2.3 nm per layer. Atomic force microscopy and Fourier transform infrared spectroscopy were utilized to characterize the film properties. Importantly, the PVDF films could act as barrier layers to prepare spin transport devices using Fe3O4 and Co as bottom and top ferromagnetic electrodes, respectively. Spin-dependent electron transport behaviors were systemically studied in these devices by varying the PVDF film thickness from 3 layers (7 nm) to 13 layers (30 nm). With increasing PVDF layer numbers, the magnetoresistance (MR) response decreases likely due to the change in spin transport from tunneling to hopping transport. We further investigated the MR dependence on operation temperatures (150 K, 200 K, 250 K and 300 K). It is noteworthy that the MR effect was observed even at 300 K with an MR ratio exceeding 2.5%, which is achieved for the first time in such organic devices. The device performance could be further improved at lower operation temperatures. The MR ratios, device resistances and electron transport mechanisms in the present devices were also discussed to analyze the spin transport behaviors. The results indicate that the ferroelectric PVDF nanofilms are promising candidates for spin devices operated at room temperature, thereby shedding light on the design of organic ferroelectric spintronics with a higher performance.

Inspired by the marine mussel strategy of adhesion in aqueous environments, catechol-functionalized polysiloxane (CFPS) was synthesized. Facile dip-coating showed good film forming ability on various organic and inorganic substrates with a surface roughness of 4.6 nm (50 μm × 50 μm). Silver nanoparticles (AgNPs) are anchored onto CFPS-modified substrates using a dip coating process. The scanning electron microscopy images revealed that AgNPs were distributed homogeneously on numerous substrates. Moreover, the surface number density and average interspace of the AgNPs were tuned easily by controlling the concentration of AgNP dispersions. A substrate with high-density AgNPs exhibited excellent surface enhanced Raman scattering (SERS) performance with an enhancement factor as high as 7.89 × 107 and an ultra-low detection limitation of 10−10 M, which can be ascribed to the “hotspots” formed between the adjacent AgNPs controlled by CFPS-induced self-assembly. The AgNP structures prepared on different substrates modified using CFPS show a similar high intensity, suggesting a versatile platform of the CFPS film for AgNP assemblies. In addition, AgNPs were anchored to be extremely stable on substrates because of strong hydrogen bonding interactions provided by the high surface-density catechol units of CFPS, which made the substrate a promising SERS sensor for practical applications. In situ SERS detection was also demonstrated on apple peel with no damage to AgNP structures.