Stimulated Raman scattering in x-, y-, and z-cut lithium formate monohydrate (LiHCOO H20) crystals was studied in a resonator configuration with use of a g-switched ruby laser. The temperature dependence of the stimulated Raman threshold intensity was measured from 2 to 300 K for different polarizations of the laser light. Stimulated Raman scattering from the 79-cm ' yy A, (z) mode, the 104or 1372-cm ' zz A&(z) modes, the 76-cm ' A2 mode, or the 82-, 113-, or 163-cm B,(x) modes was observed, depending on the propagation direction in the crystal, the polarization of the laser light, and the temperature. The results of stimulated Raman scattering are discussed using the measured temperature-dependent spontaneous Raman data from the same lattice modes.Steady-state and transient theories of stimulated Raman scattering for a broadband pump laser (ruby-laser linewidth 0.7 cm ) are applied to explain the experimental results.

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Surface‐enhanced Raman scattering (SERS) technology is a cutting‐edge analytical tool for molecule detection. Attractive SERS performance has been achieved on noble metal nanostructures; however these substrates usually suffer from difficulties of direct adjusting of the physical structures to achieve tunable SERS performance. Studies on semiconductor oxides have revealed that attractive SERS performance can be obtained on them, but strategies of engineering material properties for SERS performance improvement still pose a challenge. Here, an electrically programmable SERS substrate is prepared by depositing hydrothermally synthesized MoOx/Ag hybrids within electrodes as the SERS active region. In the experiment, an electrical field is applied on the electrodes to regulate Ag+ ion migration and redeposition in the MoOx solid electrolyte. Through adjusting the leakage current level, the size of the Ag nanoparticles in the MoOx/Ag hybrids is electrically controlled. The SERS performance of the substrate is evaluated using rhodamine 6G as the Raman reporter. The results evidence that Raman enhancement factors of 1.13 × 105, 4.75 × 105, and 1.04 × 106 can be obtained by programming the leakage current level to 10−7, 10−5, and 10−3 A, respectively. A maximum detection limit of 10−8 m is achieved on the 10−3 A substrate.

Surface-enhanced Raman scattering (SERS) is a non-destructive spectra analysis technique. It has the virtues of high detectivity and sensitivity, and has been extensively studied for low-trace molecule detection. Presently, a non-noble-metal-based SERS substrate with excellent enhancement capabilities and environmental stability is available for performing advanced biomolecule detection. Herein, a type of molybdenum carbide/molybdenum oxide (Mo2C@MoOx) heterostructure is constructed, and attractive SERS performance is achieved through the promotion of the charge transfer. Experimentally, Mo2C was first prepared by calcinating the ammonium molybdate tetrahydrate and gelatin mixture in an argon atmosphere. Then, the obtained Mo2C was further annealed in the air to obtain the Mo2C@MoOx heterostructure. The SERS performance was evaluated by using a 532 nm laser as an excitation source and a rhodamine 6G (R6G) molecule as the Raman reporter. This process demonstrates that attractive SERS performance with a Raman enhancement factor (EF) of 1.445 × 108 (R6G@10−8 M) and a limit of detection of 10−8 M can be achieved. Furthermore, the mechanism of SERS performance improvement with the Mo2C@MoOx is also investigated. HRTEM detection and XPS spectra reveal that part of the Mo2C is oxidized into MoOx during the air-annealing process, and generates metal–semiconductor mixing energy bands in the heterojunction. Under the Raman laser irradiation, considerable hole–electron pairs are generated in the heterojunction, and then the hot electrons move towards MoOx and subsequently transfer to the molecules, which ultimately boosts the Raman signal intensity.

Surface enhanced Raman scattering (SERS) is a highly sensitive spectral analysis technique for ultra‐low trace molecule detection. Conventionally, noble metals like silver (Ag) and gold (Au) are used to prepare the SERS substrates; however, it usually requires careful experiment design and accurate process control, which defers their wide applications in practice. In this paper, a one‐step and low‐cost approach to prepare silver decorated porous carbon (Ag NPs/PCN) films for SERS application is reported. Experimentally, gelatin‐silver nitrate mixed solution was first spin‐coated on the Si substrates to form the thin films, and then, the substrates were carbonized at the different temperatures to obtain the Ag NPs/PCN films. The SERS performance of the Ag NPs/PCN films was evaluated by using the R6G as Raman reporter. Results reveal that the SERS activity is closely related to the spin‐coating rate and carbonization temperature. And detection limit of 10−8 M with the Raman enhancement factor of 1.64 × 106 (10−4‐M R6G) can be obtained on the most optimal substrate. Moreover, large‐scale mapping measurement further evidences that excellent Raman signal uniformity with the RSD of 6.93% also can be achieved.