In this work, we experimentally synthesized the Fe<sub>3</sub>O<sub>4</sub>@Au nanocomposites and used them as surface-enhanced Raman scattering (SERS) substrates. The Fe<sub>3</sub>O<sub>4</sub>@Au nanocomposites retained the metallic plasmon resonant effect and possessed the magnetic field controllable characteristics. The Raman spectra of Rhodamine B (RhB) probe molecules were studied under different external magnetic field. The magnitude of external magnetic field varied from 0 Gs to 700 Gs (1 Gs = 10<sup>−4</sup> T) with intervals of 100 Gs. When the magnetic field magnitude increased, the Raman intensity of RhB probe molecules at 1356 cm<sup>-1</sup> increased linearly. The slope of the linear fitting curves for the Raman intensity and area were 0.118/Gs and 3.700/Gs. The Raman enhancement could raise up to 7 times for RhB probe molecules when the magnetic field magnitude increased to 700 Gs. After removing the external magnetic field, the Raman peaks returned to its original intensity in several minutes. Under the external magnetic field, the Fe<sub>3</sub>O<sub>4</sub>@Au nanocomposites were concentrated, leading to the increase number of SERS “hot spots” and the surface Au density. The results show that the magnetic field controlled Fe<sub>3</sub>O<sub>4</sub>@Au nanocomposites can realize the enhanced and controllable SERS effect, which can be used in the reversible optical sensing and bio-medical applications.
Optics is one of the most important courses for students whose majors are optics-related. In this article, we would like to share our teaching experiences of introducing the newest holographic display technologies which are understandable for undergraduate students. According to the feedbacks from the students, it can stimulate the students' interest in the course by introducing the up-to-date research achievements. And the students can understand the basic concepts and principles quite well while we link them with the scientific frontier. We think it is important for the course instructors to keep in steps with the discipline frontier, thus we can introduce the newest contents to the students. The teaching mode is more flexible, the teaching process will be more attractive.
It is interesting to investigate the nature of interactions between metal nanoparticles and graphene oxide (GO), which is the fundamental of the potential applications of the GO. Resonant Raman technique provides a useful way to explore the influence of metal nanoparticles on the electronic structure of GO. For this purpose, GO has been decorated by nanoparticles of metals such as silver (Ag), gold (Au) and palladium (Pd), and then measured using micro Raman spectroscopy. Several different laser lines are used in the experiment. There is a red shift in the D-band as well as the G-band in addition to the changes in the Raman bandwidth. Comparing the changes in the Raman spectra of the GO caused by the different metal nanoparticles, we find that the effect of Ag on GO is large. On the other hand, Au nanoparticles cause small changes. Such difference is related to the intrinsic properties of the metal nanoparticles which have different ionization energies. When the laser wavelength increases, the ratio between the intensities of the D-band and G-band (I<sub>D</sub>/I<sub>G</sub>) increases. And the Raman enhancement effects of Pd, Ag, and Au nanoparticles are different since they have different surface plasmon resonance frequencies.