Surface modification of silicon nanowire field-effect devices with Si-C and Si-N bonded monolayers


Masood, Muhammad Nasir (2011) Surface modification of silicon nanowire field-effect devices with Si-C and Si-N bonded monolayers. thesis.

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Abstract:The research work was mainly focused on the surface functionalization of active-gate areas of silicon nanowire field-effect transistor devices (Si-NW FET) using functional Si-Alkyl monolayers and subsequent bioimmobilization for biosensor applications. Efficiency of surface modification was tested and monitored by XPS, SEM, fluorescence spectroscopy and AFM as well as electrical measurements by front and back gating the devices in air and in aqueous solutions. XPS was able to reasonably characterize Si-C and Si-N bonded layers. In contrast to ethylene diamine adsorption on silicon under UHV, our results are unique in the solution phase, showing both amine groups have different chemical environments and one amine group is free or pendant for subsequent bioimmobilization as confirmed by fluorescence and biosensing studies. Selective functionalization of Si-NW FETs after successful modification of surfaces was demonstrated by streptavidin-biotin binding where Streptavidin was conjugated either by gold nanoparticles or Alexa Fluor 488 label to see via SEM or fluorescence spectroscopy, respectively. Effects of monolayers on Si-NW FET electrical characteristics were studied and a mathematical model was proposed giving guidelines for improved sensitivity of Si-NW FET devices after modification via ultra thin layers and put light on the operation regime where maximum sensitivity can be obtained. Use of a reference electrode was shown to be crucial in order to control surface potential in a narrow potential window and to get perceivable results. Effect of doping level and uniformity of the response of the biosensor was taken into consideration and it has been shown that high sensitivity can be obtained in lower doped nanowires with thinner gate-dielectric films and operating the device at smaller possible voltages, however, the sensor response is more uniform at higher doping levels. Biosensing via Si-N bonded monolayers was shown electrically in electrolyte-insulator-semiconductor (EIS) biosensor configuration and showed improved sensitivity of streptavidin-biotin binding event as compared to sensing on oxide surface via APTES based bioimmobilization.
Item Type:Thesis
Electrical Engineering, Mathematics and Computer Science (EEMCS)
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