Revealing Interaction of Organic Adsorbates with Semiconductor Surfaces Using Chemically Enhanced Raman

Abstract

Surface enhanced Raman spectroscopy (SERS) is frequently associated with "chemical enhancement" (CE), which is an effect of the chemical coupling between reporting molecules and surfaces. While SERS technique is mainly attributed to the studies of metallic surfaces, chemical coupling must be present on semiconductor surfaces as well. Here, we examine binding of trans-1,2-two(4-pyridyl) ethylene (BPE) to various crystallographic facets of PbSe semiconductor. The calculated off-resonant Raman spectra vary significantly on different crystallographic facets of PbSe, correlating with the electronic structure of each type of semiconductor surface. We distinguish situations when the charge transfer is present and when it is not, which raises the question about what exactly should be called the "chemical enhancement". We attempt to clarify this situation by introducing the concept of the "charge-transfer" and "charge-transfer-less" chemical enhancement. We also demonstrate a transition between these two regimes, which exhibits a nonlinear behavior of the vibrational coupling and a significantly stronger contribution to the Raman intensity.

Remarkable SERS Activity Observed from Amorphous ZnO Nanocages

“…[9] This enhanced vibrational coupling significantly increased the ICTP and thus magnified the Raman signals.Based on the above findings,we believe optimization of the morphology geometry and promotion of the ICTP between the semiconductor and molecules are two effective approaches for EF enhancement in semiconductor SERS.S pecially,t he ICTP depends on the distribution of electron cloud density on the surface of semiconductor substrates. [15,16] Generally,t he highly ordered periodic lattices of crystalline semiconductor materials would enhance the constraint to the electrons. [17] In contrast, the long-range disordered structure of amorphous materials can cause dangling bonds and band tails,w hich could lead the energy of the system to am etastable state [17][18][19] and thus facilitate the surface electron escape and transfer.Motivated by these exciting findings,w ed eveloped an ovel semiconductor nanomaterial for competitive SERS technology,that is,amorphous ZnO nanocages (a-ZnO NCs).…”

Direct Experimental Observation of Facet‐Dependent SERS of Cu2O Polyhedra

“…Several theoretical models have been developed to study SERS activity of semiconductor nanostructures . For example, it has been reported that the optical resonance of surface complex can greatly increase the Raman cross section .…”

“…Also, the photoinduced charge transfer process in semiconductor‐molecule system can effectively lead to larger molecular polarization tensor . Furthermore, the facet‐dependent SERS has been predicted by density functional theory calculations, where facets have significant impact on the interfacial charge transfer process between molecules and semiconductor substrates . However, the convincing experimental evidences for facet‐dependent SERS are still missing due to the complexity of physical and chemical properties of semiconductor surfaces.…”

“…Several theoretical models have been developed to study SERS activity of semiconductor nanostructures. [5,6,[11][12][13] For example, it has been reported that the optical resonance of surface complex can greatly increase the Raman cross section. [11] Also, the photoinduced charge transfer process in semiconductor-molecule system can effectively lead to larger molecular polarization tensor.…”

“…[6,8] Density functional theory calculations have predicted that the chemical enhancement mechanism of semiconductor-based SERS might be attributed to the interfacial charge transfer process between the facet of semiconductors and the adsorbed target molecules. [12,13] To clearly understand the facet-dependent SERS effect, the facet electronic work function was firstly investigated by KPFM, which is a powerful technology in detecting the surface potential of nanostructures. Schematic illustration of surface potential measurement was shown in stronger SERS, which can be attributed to more efficient interfacial charge transfer process.…”