Humidity Sensing Properties of CdS Nanoparticles Synthesized by Chemical Bath Deposition Method

Abstract

Thin films of CdS nanoparticles were synthesized by the chemical bath deposition (CBD) technique to investigate humidity response characteristics. The morphology and the crystal structure of CdS thin films were investigated by scanning electron microscopy (SEM) and X-ray diffraction (XRD), respectively. The quartz crystal microbalance (QCM) technique was used to measure the water vapor adsorption and desorption rates of CdS thin films. The dynamic Langmuir model was used to analyze the kinetics of the moisture adsorption and desorption process under relative humidity (RH) between 17 and 85% RH. Our results indicate that CdS thin films have a great affinity to humidity at room temperature.

Electrical Characterization of CdS Nanoparticles for Humidity Sensing Applications

“…They found that the QCM resonance frequency changes linearly with varying relative humidity between 10 and 90%, which is directly related to mass uptake (the mass change (Δm) on the surface of the quartz crystal can be calculated using the Sauerbrey linear frequency change relationship 39 ). CdS nanoparticles studied here show similar behavior: the change in the frequency during the QCM measurements in our previous work 12 showed a linear relationship to relative humidity for RH values between 17 and 80%. However, it shows larger slope due to the condensation of water molecules at RH values above 80%.…”

“…At low RH values, the large surface area of the first layer of the CdS nanoparticles with active OH groups will be filled with water molecules, which can be explained using the Langmuir model. 12 However, the resistance change shows a nonlinear (decreasing exponential) behavior as a function of increasing RH as a result of the possible condensation at higher relative humidity levels above 60%. On the other hand, the adsorption of water vapor on the CdS nanostructured surface is governed by a multilayer adsorption process, such that at higher RH values the decreasing rate in the resistance of the CdS nanoparticle sensing element can be explained by considering the increase in the ionic conduction mechanism of hydroxyl groups due to the decomposition of adsorbed water molecules under the influence of a relatively high electric field (close to 1 kV/cm) under various relative humidity conditions between 17 and 85% RH.…”

“…Our recent quartz microbalance study indicated that CdS nanoparticles synthesized by the chemical bath deposition method have a great affinity to humidity at room temperature. 12 We suggest that the presence of moisture is an important parameter for degradation of device parameters, e.g., conversion efficiency and lifetime of CdS solar cells. 34,35 In this work, CdS nanoparticles were fabricated using the CBD method and their electrical response to relative humidity changes between 17 and 85% relative humidity (RH) was measured to show the effect of moisture on a resistive type sensor.…”

“…CdS nanoparticles were synthesized by the CBD technique as given in our previous work. 12 CdS nanoparticles were dispersed in ethanol solvent, and then 5 μL of CdS−ethanol solutions was drop-cast between the gold electrodes as shown in Figure 1. Gold electrodes (120 nm thick, placed 17 μm apart, and with each electrode having a width of 1400 μm) were thermally evaporated on the glass substrates using a shadow mask as shown in Figure 1.…”

VOC sensors based on a metal oxide nanofibrous membrane/QCM system prepared by electrospinning

“…The Langmuir adsorption isotherm model has been frequently used 23,[34][35][36][37] for various gases such as humidity on organic or inorganic films to describe adsorption kinetics. According to this model, the rate of surface reaction to form a monolayer on the surface is given using the following equations:…”