Silicon-Gold-Silica Lamellar Structures for Sample Substrates That Provide an Internal Standard for Raman Microspectroscopy

Crystalline silicon, widely used in the electronic industry, is also a very popular material for calibrating Raman spectrometry instruments. Silicon chips cut or cleaved from commercially available silicon wafers are low-cost monolithic monocrystalline materials that give a strong Raman line at 521 cm(-1) with almost no background. Such chips have at least one optically flat surface and can be used in place of glass microscope slides as sample substrates that provide an internal calibration standard during Raman measurements. The Raman signal intensity from the silicon can be selectively attenuated by depositing a gold layer on top of the silicon surface with variable thickness such that the far-field silicon Raman signal is comparable with the Raman signal of an investigated material adjacent to this structure. This gold layer provides the additional advantage of increased sensitivity of the spectral signal from the sample due to the reflectivity of the gold surface, which allows forward and backscattered analyte Raman excitation and signal collection. An additional thin encapsulating overlayer of SiO2 provides a protective and biocompatible surface to facilitate Raman microspectroscopic investigation of live cells.