Amplitude Dependence of Resonance Frequency and its Consequences for Scanning Probe Microscopy

Enhancement of the CO2 Sensing/Capture through High Cationic Charge in M-ZrO2 (Li+, Mg2+, or Co3+): Experimental and Theoretical Studies

The capture and storage of CO₂ are of growing interest in atmospheric science since greenhouse gas emission has to be reduced considerably in the near future. The present paper deals with the doping of cations on ZrO₂, i.e., M-ZrO₂ (M = Li⁺, Mg²⁺, or Co³⁺), defecting the crystalline planes for the adsorption of carbon dioxide. The samples were prepared by the sol-gel method and characterized completely by different analytical methods. The deposition of metal ions on ZrO₂ (whose crystalline phases: monoclinic and tetragonal are transformed into a single-phase such as tetragonal for LiZrO₂ and cubic for MgZrO₂ or CoZrO₂) shows a complete disappearance of the XRD monoclinic signal, and it is consistent with HRTEM lattice fringes: 2.957 nm for ZrO₂ (101, tetragonal/monoclinic), 3.018 nm for tetragonal LiZrO₂, 2.940 nm for cubic MgZrO₂, and 1.526 nm for cubic CoZrO₂. The samples are thermally stable, resulting an average size of ∼5.0-15 nm. The surface of LiZrO₂ creates the oxygen deficiency, while for Mg²⁺ (0.089 nm), since the size of the atom is relatively greater than that of Zr⁴⁺ (0.084 nm), the replacement of Zr⁴⁺ by Mg²⁺ in sublattice is difficult; thus, a decrease of the lattice constant was noticed. Since the high band gap energy (ΔE > 5.0 eV) is suitable for CO₂ adsorption, the samples were employed for the selective detection/capture of CO₂ by using electrochemical impedance spectroscopy (EIS) and direct current resistance (DCR), showing that CoZrO₂ is capable of CO₂ capture about 75%. If M⁺ ions are deposited within the ZrO₂ matrix, then the charge imbalance allows CO₂ to interact with the oxygen species to form CO₃^2- which produces a high resistance (21.04 × 10⁶ (Ω, Ohm)). The adsorption of CO₂ with the samples was also theoretically studied showing that the interaction of CO₂ with MgZrO₂ and CoZrO₂ is more feasible than with LiZrO₂, subscribing to the experimental data. The temperature effect (273 to 573 K) for the interaction of CO₂ with CoZrO₂ was also studied by the docking method and observed the cubic structure is more stable at high temperatures as compared to the monoclinic geometry. Thus, CO₂ would preferably interact with ZrO₂^c (E_RS = -19.29 kJ/mol) than for ZrO₂^m (22.4 J/mmol (ZrO₂^c = cubic; ZrO₂^m = monoclinic).

Equivalent Electromechanical Model for Quartz Tuning Fork Used in Atomic Force Microscopy

Quartz tuning forks (QTFs) are self-sensing and possess a high quality factor, allowing them to be used as probes for atomic force microscopes (AFMs) for which they offer nano-scale resolution of sample images. Since recent work has revealed that utilizing higher-order modes of QTFs can offer better resolution of AFM images and more information on samples, it is necessary to understand the relationship between the vibration characteristics of the first two symmetric eigenmodes of quartz-based probes. In this paper, a model that combines the mechanical and electrical characteristics of the first two symmetric eigenmodes of a QTF is presented. Firstly, the relationships between the resonant frequency, amplitude, and quality factor between the first two symmetric eigenmodes are theoretically derived. Then, a finite element analysis is conducted to estimate the dynamic behaviors of the analyzed QTF. Finally, experimental tests are executed to verify the validity of the proposed model. The results indicate that the proposed model can accurately describe the dynamic properties of a QTF in the first two symmetric eigenmodes either under electrical or mechanical excitation, which will provide a reference for the description of the relationship between the electrical and mechanical responses of the QTF probe in the first two symmetric eigenmodes as well as the optimization of higher modal responses of the QTF sensor.

Planform Geometry and Excitation Effects of PVDF-Based Vibration Energy Harvesters

In the present paper, we report a systematic investigation of planform geometry and excitation level effects on the dynamics and power generation characteristics of polyvinylidene difluoride (PVDF)-based cantilevered vibration energy harvesters. Piezoelectric vibration energy harvesters provide a promising energy harvesting solution for widespread use of wireless sensors in remote locations. Highly flexible PVDF polymers offer resonant frequencies at suitable range for harvesting mechanical energy within low-frequency applications, though information on the efficient sizing of these devices is currently limited. We test the response of a set of eight harvesters to typical vibration sources excitation levels in the range 0.2–0.6 g. This set comprises four widths and two lengths, incrementing each time by a factor of two. The selected range of dimensions is sufficient to identify optimal power output versus width for both lengths tested. This optimal width value depends on excitation amplitude in such a way that narrower harvesters are more suited for small excitations, whereas wider harvesters perform better upon experiencing large excitations. Non-linear effects present in longer harvesters are demonstrated to significantly reduce performance, which motivates the selection of planform dimensions inside the linear range. Finally, we explore the correlation of performance with various geometric quantities in order to inform future design studies and highlight the value of using the second moment of planform area to measure harvester efficiency in terms of power density. This points towards the use of harvesters with non-rectangular planform area for optimal performance.