High-performance, large-area flexible SERS substrates prepared by reactive ion etching for molecular detection

In the realm of molecular detection, the surface-enhanced Raman scattering (SERS) technique has garnered increasing attention due to its rapid detection, high sensitivity, and non-destructive characteristics. However, conventional rigid SERS substrates are either costly to fabricate and challenging to prepare over a large area, or they exhibit poor uniformity and repeatability, making them unsuitable for inspecting curved object surfaces. In this work, we present a flexible SERS substrate with high sensitivity as well as good uniformity and repeatability. First, the flexible polydimethylsiloxane (PDMS) substrate is manually formulated and cured. SiO2/Ag layer on the substrate can be obtained in a single process by using ion beam sputtering. Then, reactive ion etching is used to etch the upper SiO2layer of the film, which directly leads to the desired densely packed nanostructure. Finally, a layer of precious metal is deposited on the densely packed nanostructure by thermal evaporation. In our proposed system, the densely packed nanostructure obtained by etching the SiO2layer directly determines the SERS ability of the substrate. The bottom layer of silver mirror can reflect the penetrative incident light, the spacer layer of SiO2and the top layer of silver thin film can further localize the light in the system, which can realize the excellent absorption of Raman laser light, thus enhancing SERS ability. In the tests, the prepared substrates show excellent SERS performance in detecting crystalline violet with a detection limit of 10-11M. The development of this SERS substrate is anticipated to offer a highly effective and convenient method for molecular substance detection.

Dual-Layered Interfacial Evolution of Lithium Metal Anode: SEI Analysis via TOF-SIMS Technology

Lithium metal battery has been considered as one of the most promising candidates for the next generation of energy storage systems due to its high energy density. However, the lithium metal may react with the electrolyte, resulting in the instability of the solid/liquid interface. The solid electrolyte interface (SEI) layer was found to affect the interface stability of the lithium metal anode; the real structure of SEI couldn't be accurately analyzed so far. Time-of-flight secondary ion mass spectrometry (TOF-SIMS) has been thought as a powerful tool to carry out three-dimensional (3D) characterization and structural reconstruction at a high-resolution nanoscale, as well as detect ionized elements and molecule fragments at the ppb level due to its excellent sensitivity. Herein, we employed TOF-SIMS to investigate the chemical composition of SEI at the surface of the lithium metal anode after electrochemical cycles. We find that SEI is not a completely dense interface layer. The organic phase of SEI can accommodate part of the electrolyte, enhancing the lithium-ion conductivity. Meanwhile, SEI is an interface layer that changes with the state of the electrolyte, and this process of change is expressed by conventional characterization methods. However, the distribution of lithium salt can be analyzed by TOF-SIMS to judge the change degree of SEI. Our work provides significant guidance for accurately characterizing the SEI layer, as well as constructing a more realistic interface layer model.