Semiconductor-enhanced Raman scattering: active nanomaterials and applications

Abstract

Surface-enhanced Raman scattering (SERS)-active nanomaterials have extended from noble metals and transition metals to semiconductor materials, since the first discovery of SERS in the mid-1970s. In comparison with metal substrates and transition metals, semiconductor materials have additional optical and electrical properties besides SERS enhancement ability, which enable them to display remarkable charge-transfer enhancement and catalytic ability. Moreover, their superior biocompatibility allows these nanomaterials to have great potential applications in bioscience. Herein we highlight the fast growing research field focusing on SERS-active semiconductor nanomaterials and semiconductor-other material heterostructures developed in our group as well as in other related research studies. The material size, morphology and assembly-dependent SERS enhancement have been discussed in detail. Furthermore, a variety of promising applications of semiconductor-enhanced Raman scattering in photoelectric characterization, redox biochemistry, sensing, and the catalytic degradation of organic pollutants are introduced.

High Electromagnetic Field Enhancement of TiO2 Nanotube Electrodes

“…[10,11] Vibrational spectro-electrochemistry such as confocal Raman spectroscopy is an ideal tool but it necessitates surface enhancement (SE) to gain the required sensitivity for monitoring sub-monolayer coverages of adsorbed molecules. [16][17][18] In nearly all cases,achemical enhancement effect, resulting from formation of chargetransfer complexes between adsorbate and surface,w as identified as the dominant factor for Raman signal amplification. [13][14][15] On TiO 2 ,S Eo fR aman signals has been observed for ar ange of adsorbates,h owever, with typically lower magnitudes than observed on noble metals.…”

“…[12] So far,s trong SE has been established only for noble metals,s uch as Ag,A u, and Cu, due to excitation of surface plasmons upon visible-light illumination. [17,19,20] Recently,w eintroduced nanostructured TiO 2 electrodes as ap latform for surface-enhanced Raman (SER) spectroelectrochemistry. [16][17][18] In nearly all cases,achemical enhancement effect, resulting from formation of chargetransfer complexes between adsorbate and surface,w as identified as the dominant factor for Raman signal amplification.…”

“…Thei ntensity of the SERR spectra of Cyt b 5 on the untreated electrode was found to be at least 2o rders of magnitude lower ( Figure S7, Table 1). [21] Notably,i nvolvement of ac hemical enhancement effect usually attributed to observed SER scattering intensities on TiO 2 [17] can be ruled out here as the relevant heme cofactor does not form ac hemical bond with the TiO 2 surface,a nd, importantly,i st oo far away from the electrode to participate in ad irect CT process.A saconsequence,the signal enhancement should be based purely on an electromagnetic field enhancement effect of the TiO 2 nanostructure itself,which has not been observed at this magnitude before.A lthough several studies report very high EFs for nanostructured TiO 2 systems,inthese examples only directly surface-interacting probes were considered. Theresulting values for EF are listed in Table 1 This value is almost one order of magnitude higher than the previously reported values for Cyt b 5 on randomly nanostructured TiO 2.…”

Effect of TiO2 on Altering Direction of Interfacial Charge Transfer in a TiO2‐Ag‐MPY‐FePc System by SERS

“…It is imperative to develop am ore economical and effective method to investigate CT processes used in ab roader interface system. [21] In general, when only noble metal NPs are used as SERS substrates,t he CT contribution in the system will be covered up by the overwhelming EM enhancement deriving from LSPR of the metal NPs. [17,18] Thei ncreasingly extensive applications of SERS spectroscopy is due to the huge enhancement arising not only from the electromagnetic mechanism (EM), [19] but also from the CT enhancement contribution, associated with interactions between adsorbates and surroundings.…”

“…[20] SERS spectroscopy possesses distinct advantages on studies of interfacial CT processes,s ince CT is one of the main reasons for the tremendous enhancement of SERS signal. [21,23,26,27] Despite plenty of basic researches have been conducted on CT processes by SERS with semiconductors as models,t here are few studies on the interfacial CT in asolar cell-like system. [22] In this case,n oo bvious change from the CT enhancement in the SERS spectrum can be observed even though the structure or the morphology of the metal NPs is changed.…”