Silicon Nanowire-Based Room-Temperature Multi-environment Ammonia Detection

Abstract

Nanowires represent numerous opportunities for nanoelectronics and sensorics, while metal contact fabrication makes the device development rather challenging. Here, we demonstrate that silicon (Si) nanowires deposited on interdigital metal contacts via simple drop casting exhibit an abrupt increase in conductivity upon exposure to ammonia vapors and aqueous solutions due to adsorption of the analyte species. To reduce the noise of the DC resistance measurements lacking ohmic conductivity, we exploit electronic impedance spectroscopy. The resistive response is found to be dependent on the ammonia content in vapor and liquid matter. The results demonstrate a detection limit of 4 μmol•L −1 (80 ppb), a sensitivity of 0.2% μmol −1 •l (0.01%•ppb −1 ), and applicability for the low-concentration detection of up to 400 μmol•L −1 (8 ppm) ammonia in aqueous solutions both directly and indirectly with a response rate of up to 0.43%•s −1 and a recovery rate of 0.31%•s −1 and show selectivity to oxidizing species. Thus, we demonstrate that the use of semiconductor nanowires in adsorption sensorics does not require the fabrication of ohmic contacts and present a simple fabrication protocol perspective for the development of highly sensitive room-temperature multi-environment sensors.

Si Nanowire-Based Schottky Sensors for Selective Sensing of NH3 and HCl via Impedance Spectroscopy

“…According to the previous results, these contacts provide efficient variation of the sensor electronic parameters upon exposure to the analyte vapors promoting good sensing. 16 Study of the sensors' electrical properties under HCl and NH 3 vapors was carried out with the use of a Z500P impedance meter (Elins, Russia). The impedance spectroscopy was employed at 100 mV bias in the 100 Hz to 500 kHz frequency range, allowing for analysis of various electronic processes that may occur upon the analyte adsorption.…”

“…The low frequency domain follows nearly linear dependence and is considered as the result of the formation of diffusion layers at the nanowire−gold interface. 16 All the obtained EIS spectra were fitted using the equivalent electrical circuit method. The employed circuit (Figure 2c) contains: R Ω �contact resistance corresponding to the resistance of the gold interdigital electrodes, 61 R�resistance related to the Si NWs and Schottky barriers (referred to as the sensor resistance), C�capacitance of the sensor, and CPE� constant phase element associated with the linear low frequency part of the spectra.…”

“…The oxidized surface of a Si NW interacts with OH − ions in the presence of water vapor via surface hydration which increases the concentration of electrons in a NW. 16 In the presence of ammonia, NH 3 0 molecules protonate the surface OH groups with the formation of NH 4+ . As a result, oxygen (O − ) with a valence electron occurs on the NW surface which leads to an additional increase in the number of carriers.…”

“…The sensitivity of the sensor is fourfold lower than the corresponding sensitivity to HCl and found at the level of −0.2% per μmol•L −1 and detection limit of 4 μmol•L −1 (80 ppb) which is in agreement with our previous results. 16 The other sensors exhibit even lower sensitivity at the level of −0.1% per μmol•L −1 . The response is nearly linear throughout the measurement range for HF-treated NWs and saturates at 300 μmol•L −1 for sensor 3 with Ag NPs.…”

“…These nanostructures obtained both by bottom-up 11,12 and top-down methods 13 attract special attention due to the high geometrical aspect ratio 14 providing intense response of their electronic properties to the adsorption of the analyte species. 15,16 Early demonstration of the perspectives for these nanostructures use in sensorics was carried out in pioneering works. 17,18 The main criteria for the sensor's mass production are high sensitivity and selectivity, low cost, and technological feasibility.…”