Investigation on Mass Sensitivity of N-M Type Electrode Quartz Crystal Microbalance

Study of Force-Frequency Characteristics in AT-Cut Strip Quartz Crystal Resonators with Different Rotation Angles

This paper investigated the force-frequency characteristics of AT-cut strip quartz crystal resonator (QCR) employing finite element analysis methods and experiments. We used the finite element analysis software COMSOL Multiphysics to calculate the stress distribution and particle displacement of the QCR. Moreover, we analyzed the impact of these opposing forces on the frequency shift and strains of the QCR. Meanwhile, the resonant frequency shifts, conductance, and quality factor (Q value) of three AT-cut strip QCRs with rotation angles of 30°, 40°, and 50° under different force-applying positions were tested experimentally. The results showed that the frequency shifts of the QCRs were proportional to the magnitude of the force. The highest force sensitivity was QCR with a rotation angle of 30°, followed by 40°, and 50° was the lowest. And the distance of the force-applying position from the X-axis also affected the frequency shift, conductance, and Q value of the QCR. The results of this paper are instructive for understanding the force-frequency characteristics of strip QCRs with different rotation angles.

Impedance Analysis of Chitin Nanofibers Integrated Bulk Acoustic Wave Humidity Sensor with Asymmetric Electrode Configuration

This paper fabricated a high-performance chitin nanofibers (ChNFs)-integrated bulk acoustic wave (BAW) humidity sensor with an asymmetric electrode configuration. The ChNFs were successfully prepared from crab shells and used as moisture-sensitive materials to compare the performance of quartz crystal microbalance (QCM) humidity sensors with symmetric and asymmetric electrode structures. The QCM humidity sensor with a smaller electrode area exhibited high sensitivity of 58.84 Hz/%RH, competitive response/recovery time of 30/3.5 s, and low humidity hysteresis of 2.5% RH. However, it is necessary to choose a suitable electrode diameter to balance the stability and sensitivity because the impedance analysis result showed that the reduction of the electrode diameter leads to a sharp decrease in the Q value (stability). Next, the possible humidity-sensitive mechanism of the ChNFs-integrated asymmetric n-m electrode QCM humidity sensor was discussed in detail. Finally, the reasons for the highest sensitivity of the asymmetric n-m electrode QCM humidity sensors having a smaller electrode diameter were analyzed in detail in terms of both mass sensitivity and fringing field effect. This work not only demonstrates that the chitin nanofiber is an excellent potential material for moisture detection, but also provides a new perspective for designing high-performance QCM humidity sensors.

Measurement of isosteric heat of gas adsorption and Brunauer-Emmett-Teller (BET) surface area using a quartz crystal microbalance

The study of gas adsorption on a solid surface evaluates the affinity between sorbate gas and sorbent substrate and factors that contribute to this. This paper presents a test platform for adsorption experiments of various gases on various solid surfaces. Controlled environmental conditions enable investigations in materials surface science and increase the consistency among adsorption data. The system utilizes a quartz crystal microbalance to perform gravimetric analysis of deposition and adsorption, enabling investigation of the interaction of gaseous molecules with solid surfaces. In this study, a quartz crystal microbalance as gas adsorption detector was integrated with an environmental chamber to create a versatile tool for gas adsorption experiments on thin films. Experimental operation of this apparatus was demonstrated via acquisition of the adsorption isotherms of cyclohexane vapor on a gold surface at 55 and 70 °C. The result indicated International Union of Pure and Applied Chemistry Type II adsorption. Consequentially, application of the Brunauer-Emmett-Teller model to the isotherm data subject to predefined criteria for linear region selection yielded a surface area of the sorbent of 0.53 cm² at 55 °C. From the monolayer region of the isotherms, the isosteric heat of adsorption of the cyclohexane vapor on gold was calculated to be 37 kJ mol^-1.

Analysis of the Effect of Electrode Materials on the Sensitivity of Quartz Crystal Microbalance

This paper investigated the effect of electrode materials on the performance of quartz crystal microbalance (QCM) sensors by means of theoretical calculation, experiment, and finite element analysis methods. First, we calculated the particle displacement amplitude and thus obtained the mass sensitivity function distribution of QCMs with gold, silver and aluminum electrodes, and found that the QCM with the gold electrode has the highest mass sensitivity at the center of the electrode. Then, we tested the humidity-sensing performance of QCMs with gold, silver, and aluminum electrodes using graphene oxide (GO) as the sensitive material, and found that the QCM with the gold electrode has higher humidity sensitivity. Finally, we used the finite element analysis software COMSOL Multiphysics to simulate the specific electrode material parameters that affect the sensitivity of the QCMs. The simulation results show that the density and Young’s modulus of the electrode material parameters mainly affect the sensitivity. The results of this paper are instructive for optimizing QCM sensor performance and improving the capability of QCM quantitative analysis.

Uniformization of Mass Sensitivity Distribution of Silver Electrode QCM

Quartz crystal microbalance (QCM) is a highly sensitive mass sensor and has been widely used in many fields. However, the nonuniform distribution of mass sensitivity will lead to poor reproducibility of QCM, which is not conducive to the application of QCM in some fields. Considering the effect of electrode shape, size, and material on mass sensitivity distribution, we found that for an AT-cut QCM with a fundamental frequency of 10 MHz, when the inner and outer diameters of silver ring electrode and the electrode loading factor are 2 and 5 mm and 0.0033, respectively, an approximately uniform mass sensitivity distribution can be obtained. The plating experiment in which rigid silver films were plated on the surface of electrode verified the uniformity. The uniform mass sensitivity distribution will make the application of QCM more convenient; the reproducibility can also be improved. This design of QCM will enrich QCM products and facilitate the application of QCM in various fields.

Humidity-Sensing Properties of a BiOCl-Coated Quartz Crystal Microbalance

The performance of a bismuth oxychloride (BiOCl)-based quartz crystal microbalance (QCM) humidity sensor was studied using an oscillating circuit method. The BiOCl powder was prepared by a hydrolysis method. Scanning electron microscopy, X-ray diffraction, and Fourier transform infrared spectroscopy were used to characterize the BiOCl sample. Its humidity-sensing property was analyzed by combining it with a QCM at room temperature (25 °C). Experimental results indicated that the BiOCl-based QCM sensor showed good humidity characteristics from 11.3 to 97.3%, such as good logarithmic frequency response to humidity levels (R ² = 0.994), fast response time (5.2 s)/recovery time (4.5 s), good reversibility, stability, repeatability, and low humidity hysteresis. In addition, the response to human nose breaths showed excellent practicability. Finally, the humidity sensing mechanism of the BiOCl-based QCM humidity sensor was discussed in detail. This work demonstrates that BiOCl is a promising candidate material for humidity detection.

Assessing the Mass Sensitivity for Different Electrode Materials Commonly Used in Quartz Crystal Microbalances (QCMs)

Mass sensitivity is vital for quartz crystal microbalance (QCM)-based data analysis. The mass sensitivity distribution of QCMs may differ greatly depending on the shapes, thicknesses, sizes, and materials of the metal electrodes. This is not considered by the Sauerbrey equation, and has a large potential to cause errors in QCM-based data analysis. Many previous works have studied the effects of shape, thickness, and size of metal electrodes on mass sensitivity. However, it is necessary to continue to clarify the relationship between the mass sensitivity and the electrode material of the QCM. In this paper, the results of both theoretical calculation and experimental analysis showed that the mass sensitivity of QCMs with gold electrodes is higher than that of the QCMs with silver electrodes, which in turn indicated that the mass sensitivity of QCMs varies with the electrode material. Meanwhile, the results of this study showed that the mass sensitivity of QCMs with different electrode materials is not proportional to the density of the electrode materials. This result suggests that, in order to obtain more accurate results in the practical applications of QCMs, the influence of electrode material on the mass sensitivity of the QCMs must be considered.