The Electronic Properties of Silicon Nanowires during Their Dissolution under Simulated Physiological Conditions

Silicon nanowires are considered promising future biomedical sensors. However, their limited stability under physiological conditions poses a challenge in sensor development and necessitates a significantly improved knowledge of underlying effects as well as new solutions to enhance silicon nanowire durability. In the present study, we deduced the dissolution rates of silicon nanowires under simulated physiological conditions from atomic force microscopy measurements. We correlated the relevant change in nanowire diameter to changes in the electronic properties by examining the I-V characteristics of kinked silicon nanowire p-n junctions. Contact potential difference measurements and ambient pressure photoemission spectroscopy additionally gave insights into the electronic surface band structure. During the first week of immersion, the Fermi level of n-type silicon nanowires shifted considerably to higher energies, partly even above the conduction band edge, which manifested in an increased conductivity. After about a week, the Fermi level stabilized and the conductivity decreased consistently with the decreasing diameter caused by continuous nanowire dissolution. Our results show that a physiological environment can substantially affect the surface band structure of silicon nanowire devices, and with it, their electronic properties. Therefore, it is necessary to study these effects and find strategies to gain reliable biomedical sensors.