Thirdly,SERS enhancement mechanism in association with oxygen extraction/incorporation.Now, the SERS enhancement of semiconductors benefiting from either oxygen extraction or incorporation has already been unified, which is further supported by the results of theoretical calculations. Based on the chemical mechanism (CM) of semiconductor-molecule system, both adding and extracting of oxygen into/from the semiconductor lattice are all proved to be effective means in its band-structure modification. Deep levels in the bandgap introduced by “oxygen extraction” acts as an springboard for electron transfer, while the increased density of state near Fermi level after “oxygen incorporation” narrows the bandgap, both of which will facilitate the charge carrier generation in a laser-stimulated semiconductor, further contribute to the charge-transfer between substrate and analyte through vibronic coupling, then increase the polarization tension of adsorbed molecule, and finally give the increased Raman signals.
The systematic work reveals that under a suitable modulation of the lattice oxygen density in semiconductor oxides, the SERS activity of which can be dramatically promoted. These findings break through the limitation of noble metal substrates in common SERS applications, and provide important clues in the future design strategy for highly-efficient semiconducting SERS substrates.
This work was supported by the National Natural Science Foundation of China (51372266, 51572286, 21503266, 51772319 and 51772320), the Outstanding Youth Fund of Jiangsu Province (BK20160011), and the Youth Innovation Promotion Association, CAS. Relative results have been successively published in Nature Communications (on July 17, 2015 and December 8, 2017), with the title of “Noble metal-comparable SERS enhancement from semiconducting metal oxides by making oxygen vacancies”and“Semiconductor SERS enhancement enabled by oxygen incorporation”, respectively. (DOI: 10.1038/ncomms8800 & DOI: 10.1038/s41467-017-02166-z)
Prof. ZHAO Zhigang, Suzhou Institute of Nano-Tech and Nano-Bionics, Chinese Academy of Sciences