Multifunctional Zn-Doped ITO Sol–Gel Films Deposited on Different Substrates: Application as CO2-Sensing Material

Abstract

Undoped and Zn-doped ITO (ITO:Zn) multifunctional thin films were successfully synthesized using the sol–gel and dipping method on three different types of substrates (glass, SiO2/glass, and Si). The effect of Zn doping on the optoelectronic, microstructural, and gas-sensing properties of the films was investigated using X-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), spectroscopic ellipsometry (SE), Raman spectroscopy, Hall effect measurements (HE), and gas testing. The results showed that the optical constants, the transmission, and the carrier numbers were correlated with the substrate type and with the microstructure and the thickness of the films. The Raman study showed the formation of ITO films and the incorporation of Zn in the doped film (ITO:Zn), which was confirmed by EDX analysis. The potential use of the multifunctional sol–gel ITO and ITO:Zn thin films was proven for TCO applications or gas-sensing experiments toward CO2. The Nyquist plots and equivalent circuit for fitting the experimental data were provided. The best electrical response of the sensor in CO2 atmosphere was found at 150 °C, with activation energy of around 0.31 eV.

Direct Patterned Printing Method of Top-Contact ITO Electrodes for Solution-Processed Metal Oxide Thin-film Transistors

“…39 Thus, we believe that the liquid contact in the printing process mitigates the effects of the long alkyl chains and creates a good interface regardless of the existing long alkyl chains. Besides, according to the previous research relationship to the Zn-doped ITO by solution processing, 40,41 the electrical parameters, such as carrier concentration and conductivity, can be enhanced by Zn doping due to lowered film porosity. We consider this doping effect is also able to obtain good electrical characteristics.…”

Structural, Optical, and Sensing Properties of Nb-Doped ITO Thin Films Deposited by the Sol–Gel Method

“…Different substrates (Si, SiO 2 /glass, and glass) were coated by five successive layers using the ITO/Nb sol–gel solution. To highlight the influence of the dopant on the ITO film structure, previously reported data [ 30 ] on the undoped ITO thin films are presented in Figure 1 . The diffraction lines, corresponding to crystal planes (2 2 2), (4 0 0), (4 4 0), and (6 2 2), were observed for both ITO/Nb and ITO thin films.…”

“…The morphology of the layer-by-layer deposited ITO film is strongly affected by the crystal growth process, because the final size of the ITO crystallites is bigger than the initial thickness of each deposited layer (about 5 nm). If we compare these results with the case of Zn-doped ITO films [ 30 ], it can be observed that the crystallization process and the total film thickness are influenced by the dopant nature [ 30 ].…”

“…In terms of the gas sensing properties, these materials based on doped or undoped ITO thin films have been proven to detect formaldehyde [ 27 ], CO 2 [ 28 , 29 , 30 ], CO [ 31 , 32 , 33 ], NO 2 [ 34 , 35 ], chlorine [ 35 ], benzene [ 36 ], toluene [ 37 ], and ammonia gases [ 38 , 39 , 40 ]. Additionally, ITO thin films can sense ethanol [ 41 , 42 ] and water vapors [ 43 ].…”

“…Over time, researchers have studied metal-oxides based systems, such as SnO 2 , In 2 O 3 , ZnO [ 8 , 54 ], and indium-tin oxide (ITO) [ 55 , 56 ], with the aim to develop CO sensors. According to scientific reports, the properties of ITO thin films can be tailored by doping with various metals: Ag [ 57 ], Ga [ 58 ], Cr [ 59 ], Zn [ 30 , 60 ], Ti [ 61 ], Nb [ 62 ], and so on. In contrast with metal-doped ITO films, there are few reports concerning Nb-doped ITO thin films [ 51 , 62 , 63 , 64 ].…”