Nanostructured porous silicon by laser assisted electrochemical etching

Nanostructured porous silicon (pSi) was fabricated by combining electrochemical etching with 355 nm laser processing. pSi prepared in this way proves to be an excellent substrate for desorption/ionization on silicon (DIOS) mass spectrometry (MS). Surfaces prepared by electrochemical etching and laser irradiation exhibit strong quantum confinement as evidenced by the observation of a red shift in the Si Raman band at ∼520–500 cm−1. The height of the nanostructured columns produced by electrochemical etching and laser processing is on the order of microns compared with tens of nanometers obtained without laser irradiation. The threshold for laser desorption and ionization of 12 mJ/cm2 using the pSi substrates prepared in this work is lower than that obtained for conventional matrix assisted laser desorption ionization (MALDI)-MS using a standard matrix compound such as α-cyano-4-hydroxycinnamic acid (CHCA; 30 mJ/cm2). Furthermore, the substrates prepared by etching and laser irradiation appear to resist laser damage better than those prepared by etching alone. These results enhance the capability of pSi for the detection of small molecular weight analytes by DIOS-MS.

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