Morphological, Structural, and Chemical Effects in Response of Novel Carbide Derived Carbon Sensor to NH3, N2O, and Air

The response of two carbide derived carbons (CDCs) films to NH3, N2O, and room air is investigated by four probe resistance at room temperature and pressures up to 760 Torr. The two CDC films were synthesized at 600 (CDC-600) and 1000 degrees C (CDC-1000) to vary the carbon morphology from completely amorphous to more ordered, and determine the role of structure, surface area, and porosity on sensor response. Sensor response time followed kinetic diameter and indicated a more ordered carbon structure slowed response due to increased tortuosity caused by the formation of graphitic layers at the particle fringe. Steady state sensor response was greater for the less-ordered material, despite its decreased surface area, decreased micropore volume, and less favorable surface chemistry, suggesting carbon structure is a stronger predictor of sensor response than surface chemistry. The lack of correlation between adsorption of the probe gases and sensor response suggests chemical interaction (charge transfer) drive sensor response within the material; N2O response, in particular, did not follow simple adsorption behavior. Based on Raman and FTIR characterization, carbon morphology (disorder) appeared to be the determining factor in overall sensor response, likely due to increased charge transfer between gases and carbon defects of amorphous or disordered regions. The response of the amorphous CDC-600 film to NH3 was 45% without prior oxidation, showing amorphous CDCs have promise as chemical sensors without additional pretreatment common to other carbon sensors.