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Physical Study by Surface Characterizations of Sarin Sensor on the Basis of Chemically Functionalized Silicon Nanoribbon Field Effect Transistor

Surface characterizations of an organophosphorus (OP) gas detector based on chemically functionalized silicon nanoribbon field-effect transistor (SiNR-FET) were performed by Kelvin Probe Force Microscopy (KPFM) and ToF-SIMS, and correlated with changes in the current-voltage characteristics of the devices. KPFM measurements on FETs allow (i) to investigate the contact potential difference (CPD) distribution of the polarized device as function of the gate voltage and the exposure to OP traces and, (ii) to analyze the CPD hysteresis associated to the presence of mobile ions on the surface. The CPD measured by KPFM on the silicon nanoribbon was corrected due to side capacitance effects in order to determine the real quantitative surface potential. Comparison with macroscopic Kelvin probe (KP) experiments on larger surfaces was carried out. These two approaches were quantitatively consistent. An important increase of the CPD values (between + 399 mV and + 302 mV) was observed after the OP sensor grafting, corresponding to a decrease of the work function, and a weaker variation after exposure to OP (between - 14 mV and - 61 mV) was measured. Molecular imaging by ToF-SIMS revealed OP presence after SiNR-FET exposure. The OP molecules were essentially localized on the Si-NR confirming effectiveness and selectivity of the OP sensor. A prototype was exposed to Sarin vapors and succeeded in the detection of low vapor concentrations (40 ppm).