In this paper we report about the characterization of chemoresistive devices based on pure-zinc oxide (ZnO) and doped-ZnO nanostructures with tin as dopant. The nanostructured materials, prepared by a simple and fast microwave irradiation method, have been widely characterized by X-Ray Diffraction (XRD), Fourier Transform Infrared spectroscopy (FT-IR), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), Energy Dispersive Spectroscopy (EDS). The electrical and gas sensing properties of pure and Sn-doped ZnO nanoparticles were investigated for the monitoring of reducing (CO) and oxidizing (NO2) gases which are dangerous air pollutants. Sensors were made by screen-printing films (1-10 µm thick) of the nano-powders dispersed in water on alumina substrates (6 mm x 3 mm) provided with Pt interdigitated electrodes and a Pt heater located on the backside. The electrical characterization of the sensing films was performed both in DC and in AC by measuring the resistance value and the electrical impedance respectively. Impedance data can be employed in the circuit model of the tested devices, in order to better understand the role of the sensing film properties on the sensor response [1]. Electrical measurements were carried out in the temperature range from RT to 400 °C, under a synthetic dry air total stream of 100 sccm. Gases coming from certified bottles can be further diluted in air at a given concentration by mass flow controllers. A multimeter data acquisition unit Agilent 34970A was used for this purpose, while a dual-channel power supplier instrument Agilent E3632A was employed to bias the built-in heater of the sensor to perform measurements at super-ambient temperatures. The gas response for CO is defined as SCO = R0/R where R0 the baseline resistance in dry synthetic air (20% O2 in nitrogen) and R is the electrical resistance of the sensor at different CO concentrations in dry synthetic air. Whereas for NO2 SNO2 = R/R0, where R is the electrical resistance of the sensor at different NO2 concentrations in dry synthetic air and R0 the baseline resistance in dry synthetic air. The Impedance values were recorded by means of Stanford SR830 Lock-In Amplifier and an Agilent U1700 LCR Meter both interfaced with a personal computer through a home-made GUI interface made with Matlab environment. Experiments have shown that pure ZnO sample is very sensitive to low concentration of CO, in the range between 5 and 80 ppm. Fig. 1(a) shows that the maximum response was found at 400 °C. Results obtained in the monitoring of CO with the Sn-doped ZnO sensor are reported in Fig. 1(b). It can be noted that Sn doping allows to increase the sensitivity to CO compared to ZnO and contemporary to decrease the operating temperature. Fig. 2 and Fig.3 show preliminary frequency characterization results of the Sn-doped ZnO towards NO2 in the concentration range between 1 and 4 ppm. It can be observed that the range of Zr parameter in the Nyquist plot vs. NO2 concentration increased as the NO2 concentration was increased. The acquisition of further data is planned in order to construct an equivalent electrical circuit that, allowing the determination of individual contributions to resistance, namely: grain bulk, grain boundaries, etc., help to models the electrical response of these sensor devices.
ELECTRICAL CHARACTERIZATION OF NANOSTRUCTURED Sn-DOPED ZnO GAS SENSORS
S Trocino;
2014
Abstract
In this paper we report about the characterization of chemoresistive devices based on pure-zinc oxide (ZnO) and doped-ZnO nanostructures with tin as dopant. The nanostructured materials, prepared by a simple and fast microwave irradiation method, have been widely characterized by X-Ray Diffraction (XRD), Fourier Transform Infrared spectroscopy (FT-IR), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), Energy Dispersive Spectroscopy (EDS). The electrical and gas sensing properties of pure and Sn-doped ZnO nanoparticles were investigated for the monitoring of reducing (CO) and oxidizing (NO2) gases which are dangerous air pollutants. Sensors were made by screen-printing films (1-10 µm thick) of the nano-powders dispersed in water on alumina substrates (6 mm x 3 mm) provided with Pt interdigitated electrodes and a Pt heater located on the backside. The electrical characterization of the sensing films was performed both in DC and in AC by measuring the resistance value and the electrical impedance respectively. Impedance data can be employed in the circuit model of the tested devices, in order to better understand the role of the sensing film properties on the sensor response [1]. Electrical measurements were carried out in the temperature range from RT to 400 °C, under a synthetic dry air total stream of 100 sccm. Gases coming from certified bottles can be further diluted in air at a given concentration by mass flow controllers. A multimeter data acquisition unit Agilent 34970A was used for this purpose, while a dual-channel power supplier instrument Agilent E3632A was employed to bias the built-in heater of the sensor to perform measurements at super-ambient temperatures. The gas response for CO is defined as SCO = R0/R where R0 the baseline resistance in dry synthetic air (20% O2 in nitrogen) and R is the electrical resistance of the sensor at different CO concentrations in dry synthetic air. Whereas for NO2 SNO2 = R/R0, where R is the electrical resistance of the sensor at different NO2 concentrations in dry synthetic air and R0 the baseline resistance in dry synthetic air. The Impedance values were recorded by means of Stanford SR830 Lock-In Amplifier and an Agilent U1700 LCR Meter both interfaced with a personal computer through a home-made GUI interface made with Matlab environment. Experiments have shown that pure ZnO sample is very sensitive to low concentration of CO, in the range between 5 and 80 ppm. Fig. 1(a) shows that the maximum response was found at 400 °C. Results obtained in the monitoring of CO with the Sn-doped ZnO sensor are reported in Fig. 1(b). It can be noted that Sn doping allows to increase the sensitivity to CO compared to ZnO and contemporary to decrease the operating temperature. Fig. 2 and Fig.3 show preliminary frequency characterization results of the Sn-doped ZnO towards NO2 in the concentration range between 1 and 4 ppm. It can be observed that the range of Zr parameter in the Nyquist plot vs. NO2 concentration increased as the NO2 concentration was increased. The acquisition of further data is planned in order to construct an equivalent electrical circuit that, allowing the determination of individual contributions to resistance, namely: grain bulk, grain boundaries, etc., help to models the electrical response of these sensor devices.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
