The effect of the periodic boundary conditions of a ZnO-coated nanospring on its surface redox-induced electrical response

Abstract

A redox chemical sensor (chemiresistor) was constructed with a single ZnO coated silica nanospring. The chemiresistor response to toluene vapor as a function of the sensor temperature (T(NS)) and vapor temperature (T(V)) was measured and analyzed. The maximum sensitivity of the single ZnO coated nanospring device occurred at the sensor temperature (T(NS)) of 310 °C and at the vapor temperature (T(V)) of 250 °C. The characteristics of the electrical response of a single ZnO coated nanospring device were compared to those of a ZnO thin film. The single ZnO nanospring sensor was less responsive to small changes in toluene concentration relative to the ZnO thin film, but has a lower ultimate detection level. A computational model to simulate an electrical response of the single nanospring sensor and the thin film indicated that the differences between their response characteristics is due to the geometry of the nanospring and corresponding periodic boundary conditions imposed by the nanospring geometry, which is absent in a thin film.

Signal-to-Noise Enhancement of a Nanospring Redox-Based Sensor by Lock-in Amplification

“…The contribution of the glass substrate to the total electrical conductivity of the device was examined by comparing the I-V characteristics of the Ti–Au terminals with and without the presence of a ZnO coated nanospring [ 5 ]. In the absence of a nanospring, at a temperature of 300 °C, an open circuit with a nominal current (orders of magnitude less than with a nanospring present) was observed, where the nominal current is attributed to residual carbon on the glass surface.…”

“…With that said, shot noise and flicker (1/ f ) noise can become dominant sources of noise at low temperatures with diminished thermal noise [ 5 ]. Shot noise is a white noise source associated with the discreteness of the electric charge with a power density spectrum, S Shot , given by, where e is the electron charge and I is the average current in the device.…”

“…In addition, they can be used for environmental monitoring [ 1 , 2 ] and to detect hazardous materials, such as explosives vapors [ 3 , 4 , 5 , 6 , 7 , 8 , 9 ]. Redox-based sensors, or artificial noses, convert chemical information specific to the analyte into analytical electrical signals [ 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 ]. Hence, they are also excellent scientific tools to analyze molecular interactions at surfaces, be it physisorption or chemisorption.…”

“…Hence, they are also excellent scientific tools to analyze molecular interactions at surfaces, be it physisorption or chemisorption. The use of metal oxide nanocrystalline thin films, as well as other more complex nano-morphologies, in the capacity of gas sensitive layers in chemiresistors is well documented [ 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 ]. For metal oxides, the sensing mechanism of the sensors (chemiresistors) is attributed to the depletion, or repletion, of the oxygen at a metal oxide semiconductor (MOS) surface.…”

“…Consequently, this impacts the depth of the surface depletion layer, thereby producing significant swings in the electrical resistance of a chemiresistor. These studies have demonstrated that a sensor is more responsive to small changes in surface stoichiometry (oxidation state of the metal) if the thickness of the thin film, or the size of the nanostructures, of the MOS layer are comparable to the width of the intrinsic surface depletion layer [ 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 ].…”