Piezoelectric Quartz Tuning Forks Research Articles

Miniaturized and highly-sensitive fiber-optic photoacoustic gas sensor based on an integrated tuning fork by mechanical processing with dual-prong differential measurement

A proof-of-concept gas sensor based on a miniaturized and integrated fiber-optic photoacoustic detection module was introduced and demonstrated for the purpose of developing a custom tuning-fork (TF)-enhanced photoacoustic gas sensor. Instead of piezoelectric quartz tuning fork (QTF) in conventional quartz-enhanced photoacoustic spectroscopy (QEPAS), a low-cost custom aluminum alloy TF fabricated by mechanical processing was employed as a photoacoustic transducer and the vibration of TF was measured by fiber-optic Fabry-Pérot (FP) interferometer (FPI). The mechanical processing-based TF design scheme greatly increases the flexibility of the TF design with respect to the complex and expensive manufacture process of custom QTFs, and thus it can be better exploited to detect gases with slow vibrational-translational (V-T) relaxation rates and combine with light sources with poor beam quality. The resonance frequency and the quality factor of the designed custom TF at atmospheric pressure were experimentally determined to be 7.3 kHz and 4733, respectively. Dual-prong differential measurement method was proposed to double the photoacoustic signal and suppress the external same-direction noise. After detailed optimizing and investigating for the operating parameters by measuring H2O, the feasibility of the developed sensor for gas detection was demonstrated with a H2O minimum detection limit (MDL) of 1.2 ppm, corresponding to a normalized noise equivalent absorption (NNEA) coefficient of 3.8 × 10−8 cm−1 W/Hz1/2, which are better than the QTF-based photoacoustic sensors. The proposed gas sensing approach combined the advantages of QEPAS and fiber-optic sensing, which can greatly expand the application domains of PAS-based gas sensors.

Passive Electrical Damping of a Quartz Tuning Fork as a Path to Fast Resonance Tracking in QEPAS.

In Quartz-Enhanced PhotoAcoustic Spectroscopy (QEPAS) gas sensors, the acoustic wave is detected by the piezoelectric Quartz Tuning Fork (QTF). Due to its high-quality factor, the QTF can detect very low-pressure variations, but its resonance can also be affected by the environmental variations (temperature, humidity, …), which causes an unwanted signal drift. Recently, we presented the RT-QEPAS technique that consistently corrects the signal drift by continuously measuring the QTF resonance. In this article, we present an improvement of RT-QEPAS to fasten the QTF characterization time by adding a passive electronic circuit, which causes the damping of the QTF resonance. The damping circuit is optimized analytically and through SPICE simulation. The results are supported by experimental observations, showing a 70 times improvement of the relaxation times compared to the lone QTF, which opens the way to a fast and drift-free QEPAS sensor.

Long-distance in-situ methane detection using near-infrared light-induced thermo-elastic spectroscopy

A wavelength-locked light-induced thermo-elastic spectroscopy (WL-LITES) gas sensor system was proposed for long-distance in-situ methane (CH4) detection using a fiber-coupled sensing probe. The wavelength-locked scheme was used to speed the sensor response without scanning the laser wavelength across the CH4 absorption line. A small-size piezoelectric quartz tuning fork (QTF) with a wide spectral response range was adopted to enhance the photo-thermal signal. The optical excitation parameters of the QTF were optimized based on experiment and simulation for improving the signal-to-noise ratio of the LITES technique. An Allan deviation analysis was employed to evaluate the limit of detection of the proposed sensor system. With a 0.3 s lock-in integration time and a ∼ 100 m optical fiber, the WL-LITES gas sensor system demonstrates a minimum detection limit (MDL) of ∼ 11 ppm in volume (ppmv) for CH4 detection, and the MDL can be further reduced to ∼ 1 ppmv with an averaging time of ∼ 35 s. A real-time in-situ monitoring of CH4 leakage reveals that the proposed sensor system can realize a fast response (< 12 s) for field application.

Damping Mechanisms of Piezoelectric Quartz Tuning Forks Employed in Photoacoustic Spectroscopy for Trace Gas Sensing

A study of the dependence of main loss mechanisms on the geometry of piezoelectric quartz tuning forks (QTFs) is reported. The influence of these loss mechanisms on the quality factor Q occurring while the QTF vibrates at the in‐plane flexural fundamental and first overtone resonance modes is investigated. From this study, two QTFs efficiently operating both at the fundamental and first overtone mode are designed and realized. Data analysis demonstrates that air viscous damping is the dominant energy dissipation mechanism for both flexural modes. However, at the first overtone mode the air damping is reduced and higher quality factors can be obtained when operating at the first overtone mode with respect to the fundamental one.

Review of Recent Advances in QEPAS-Based Trace Gas Sensing

Quartz-enhanced photoacoustic spectroscopy (QEPAS) is an improvement of the conventional microphone-based photoacoustic spectroscopy. In the QEPAS technique, a commercially available millimeter-sized piezoelectric element quartz tuning fork (QTF) is used as an acoustic wave transducer. With the merits of high sensitivity and selectivity, low cost, compactness, and a large dynamic range, QEPAS sensors have been applied widely in gas detection. In this review, recent developments in state-of-the-art QEPAS-based trace gas sensing technique over the past five years are summarized and discussed. The prospect of QEPAS-based gas sensing is also presented.

A novel photoacoustic spectroscopy gas sensor using a low cost polyvinylidene fluoride film

A proof-of-concept gas sensor based on innovative photoacoustic spectrophone was introduced for purpose of developing a low cost and simple configuration photoacoustic spectroscopy gas sensor and demonstrated, in which the photoacoustic signal was detected with a low cost polyvinylidene fluoride (PVDF) film being used as transducer, instead of using conventional microphone or quartz tuning fork. In such a PVDF-based photoacoustic spectroscopy (PVDF-PAS) approach, the PVDF film plays a role both as a cantilever used in cantilever-enhanced photoacoustic spectroscopy and as a piezoelectric quartz tuning fork used in quartz-enhanced photo-acoustic spectroscopy. Feasibility of the introduced PVDF-PAS for trace gas sensing was demonstrated by measuring H2O vapor with a minimum detection limit of 40 ppmv using a lock-in time constant of 30 ms, this corresponding to a normalized noise equivalent absorption coefficient (NNEA) of 2.4 × 10−7 cm-1W/Hz1/2. The use of polyvinylidene fluoride film as transducer for photoacoustic signal sensing offers good flexibility, water resistance, chemical stability and low cost for applications under harsh or/and specific environmental conditions.

Autonomous system for in Situ Assay of Antibiotic Activity on Bacterial Biofilms Using Viscosity and Density Sensing Quartz Tuning Forks

Piezoelectric quartz tuning forks (QTF) were used for viscosity and density measurements. Compact autonomous system, based on the modulated excitation signal technique, providing the QTF excitation, measurement of the ring-down oscillations and signal processing was built and calibrated. It was used for in situ determination of the antibiotic activity od ciprofloxacin on the biofilm formation in real time. The effect of the antibiotic concentration and the time at which it was introduced to the culture were shown.

Piezoelectric tuning fork biosensors for the quantitative measurement of biomolecular interactions

The quantitative measurement of biomolecular interactions is of great interest in molecular biology. Atomic force microscopy (AFM) has proved its capacity to act as a biosensor and determine the affinity between biomolecules of interest. Nevertheless, the detection scheme presents certain limitations when it comes to developing a compact biosensor. Recently, piezoelectric quartz tuning forks (QTFs) have been used as laser-free detection sensors for AFM. However, only a few studies along these lines have considered soft biological samples, and even fewer constitute quantified molecular recognition experiments. Here, we demonstrate the capacity of QTF probes to perform specific interaction measurements between biotin–streptavidin complexes in buffer solution. We propose in this paper a variant of dynamic force spectroscopy based on representing adhesion energies E (aJ) against pulling rates v (nm s–1). Our results are compared with conventional AFM measurements and show the great potential of these sensors in molecular interaction studies.

An all-electrical torque differential magnetometer operating under ambient conditions

An all-electrical torque differential magnetometry (also known as cantilever magnetometry) setup employing piezoelectric quartz tuning forks is demonstrated. The magnetometer can be operated under ambient conditions as well as low temperatures and pressures. It extends the allowed specimen mass range up to several 10 $\mu$g without any significant reduction in the sensitivity. Operation under ambient conditions and a simple all-electrical design of the magnetometer should allow for an easy integration with other experimental setups. The uniaxial magnetic anisotropy of a 25 $\mu$m diameter iron wire, measured under ambient conditions with a high signal to noise ratio, was found to be in good agreement with its literature value. Further applications of the technique are discussed.

Quartz tuning fork as in situ sensor of bacterial biofilm

Piezoelectric quartz tuning forks (QTFs) were used as in situ sensors of biofilm formation. Modulated excitation technique allowed to measure the current generated by the QTF during the ring-down of the oscillations at conductive environments such as a liquid culture growth medium. New algorithm of the digital analysis of the ring-down signal was elaborated and used to determine the decay time constant of the vibrations and the damped vibration frequency. The dependence of these parameters on the time for QTF placed in liquid growth medium contained four strains of Pseudomonas aeruginosa was measured. It allowed to detect the biofilm formation at the QTF after few hours of incubation for all used strains at 106cfu/ml initial concentration (2h for PA01 strain) or 10h for ATCC 27853 strain at 10cfu/ml initial concentration.

Quartz Tuning Fork as in-situ Sensor of Bacterial Biofilm

Piezoelectric Quartz Tuning Forks (QTFs) were used as a biofilm formation sensors. Modulated excitation technique allowed to measure the current generated by the QTF during the ringdown of the oscillations at conductive environments such as a liquid culture growth medium. New algorithm of the digital analysis of the ring-down signal was elaborated and used to determine the decay time constant of the vibrations and the damped vibration frequency. The dependence of these parameters on the time for QTF placed in liquid growth medium contained four strains of Pseudomonas aeruginosa was measured. It allowed to detect the biofilm formation at the QTF after few hours of incubation for all used strains (2hours for PA01 strain).

Piezoelectric tuning fork probe for atomic force microscopy imaging and specific recognition force spectroscopy of an enzyme and its ligand

Piezoelectric quartz tuning fork has drawn the attention of many researchers for the development of new atomic force microscopy (AFM) self-sensing probes. However, only few works have been done for soft biological materials imaging in air or aqueous conditions. The aim of this work was to demonstrate the efficiency of the AFM tuning fork probe to perform high-resolution imaging of proteins and to study the specific interaction between a ligand and its receptor in aqueous media. Thus, a new kind of self-sensing AFM sensor was introduced to realize imaging and biochemical specific recognition spectroscopy of glucose oxidase enzyme using a new chemical functionalization procedure of the metallic tips based on the electrochemical reduction of diazonium salt. This scanning probe as well as the functionalization strategy proved to be efficient respectively for the topography and force spectroscopy of soft biological materials in buffer conditions.

Evaporation of a sessile liquid droplet from the shear or flexural surfaces of a quartz tuning fork

A piezoelectric quartz tuning fork (QTF) has been used to investigate the evaporation of a sessile water droplet with nanogram sensitivity. A water droplet is placed on one facet of a QTF tine and the changes in the resonance frequency and dissipation factor, which are related to the changes in mass and viscous damping, respectively, are measured in situ during the evaporation. Depending on the facet of the QTF tine on which the water droplet is placed, the changes in the frequency and dissipation factor arise in different vibration modes: the flexural or shear modes. The shear mode measurement is affected by the penetration depth, so changes in the frequency and dissipation factor are observed only when the water droplet is sufficiently thin, whereas the changes in the flexural mode measurements are observed during the entire evaporation process. When a droplet of polystyrene nanoparticle suspension is evaporated from the flexural surface, the concentration of the nanoparticle suspension can be determined from the difference in mass between the initial droplet and the dry nanoparticles. In contrast, changes in the physical properties of the suspension are obtained in situ from the evaporation from the shear surface. These results demonstrate that QTFs are useful tools for the investigation of the evaporation of suspensions from solid surfaces.

Carbon-fiber tips for scanning probe microscopes and molecular electronics experiments

We fabricate and characterize carbon-fiber tips for their use in combined scanning tunneling and force microscopy based on piezoelectric quartz tuning fork force sensors. An electrochemical fabrication procedure to etch the tips is used to yield reproducible sub-100-nm apex. We also study electron transport through single-molecule junctions formed by a single octanethiol molecule bonded by the thiol anchoring group to a gold electrode and linked to a carbon tip by the methyl group. We observe the presence of conductance plateaus during the stretching of the molecular bridge, which is the signature of the formation of a molecular junction.

Calibration of Piezoelectric Positioning Actuators Using a Reference Voltage-to-Displacement Transducer Based on Quartz Tuning Forks

We use a piezoelectric quartz tuning fork to calibrate the displacement of ceramic piezoelectric scanners that are widely employed in scanning probe microscopy. We measure the static piezoelectric response of a quartz tuning fork and find it to be highly linear, nonhysteretic and with negligible creep. These performance characteristics, close to those of an ideal transducer, make quartz transducers superior to ceramic piezoelectric actuators. Furthermore, quartz actuators in the form of a tuning fork have the advantage of yielding static displacements comparable to those of local probe microscope scanners. We use the static displacement of a quartz tuning fork as a reference to calibrate the three axis displacement of a ceramic piezoelectric scanner. Although this calibration technique is a nontraceable method, it can be more versatile than using calibration grids because it enables characterization of the linear and nonlinear response of a piezoelectric scanner in a broad range of displacements, spanning from a fraction of a nanometer to hundreds of nanometers. In addition, the creep and the speed dependent piezoelectric response of ceramic scanners can be studied in detail.

A low temperature scanning probe microscope using a quartz tuning fork

A frequency modulation-atomic force microscope (FM-AFM) designed to measure atomic scale topography at low temperatures is developed. Piezoelectric quartz tuning forks are employed as a force sensor for low temperatures use. In order to perform high-resolution measurements, detection of attractive forces between a tip and a sample is important. Measurements of attractive van der Waals forces on a SrTiO3 substrate is successfully performed down to 4.2 K by minimizing an amplitude of the tuning fork. Topographic imaging of atomic steps of the SrTiO3 substrate is also achieved at room temperatures in vacuum (10-3 Pa).

Cryogenic AFM-STM for mesoscopic physics

Electronic spectroscopy based on electron tunneling gives access to the electronic Density of States (DoS) in conductive materials, and thus provides detailed information about their electronic properties. During this thesis work, we have developed a microscope in order to perform spatially resolved (10 nm) tunneling spectroscopy, with an unprecedented energy resolution (10 µeV), on individual nanocircuits. This machine combines an Atomic Force Microscope (AFM mode) together with a Scanning Tunneling Spectroscope (STS mode), and functions at very low temperatures (30mK). In the AFM mode, the sample topography is recorded using a piezoelectric quartz tuning fork, which allows locating and imaging nanocircuits. Tunneling can then be performed on conductive areas of the circuit. With this microscope, we have measured the local DoS in a hybrid Superconductor-Normal metal-Superconductor (S-N-S) structure. In such circuit, the electronic properties of N and S are modified by the superconducting proximity effect. In particular, for short N wires, we have observed a minigap in the DoS of the N wire, independent of position. Moreover, when varying the superconducting phase difference between the S electrodes, we have measured the modification of the minigap, and its disappearance when the phase difference equals p. Our experimental results for the DoS, and its dependences (with phase, position, N length) are quantitatively accounted for by the quasiclassical theory of superconductivity. Some predictions of this theory are observed for the first time.

Variable temperature magnetic force microscopy with piezoelectric quartz tuning forks as probes optimized using Q-control

We have performed magnetic force microscopy at various temperatures utilizing piezoelectric quartz tuning forks as probes. Due to their large force constants (∼104N∕m), quartz tuning forks are intrinsically less sensitive to force gradients than conventional cantilevers. However, we demonstrate that the technique of Q-control can be used to increase their sensitivity, making their use as probes for variable temperature magnetic force microscopy a viable option.

Scanning μ-superconduction quantum interference device force microscope

A scanning probe technique is presented: Scanning μ-superconducting quantum interference device (SQUID) force microscopy (SSFM). The instrument features independent topographic and magnetic imaging. The force microscope uses a piezoelectric quartz tuning fork as the detector and magnetic imaging is obtained by scanning μ-SQUID microscopy. The μ-SQUID is placed at the edge of a silicon chip attached to the tuning fork. A topographic vertical resolution of 0.02 μm is demonstrated and magnetic flux as weak as 10−3 Φ0 is resolved with a 1 μm diameter μ-SQUID loop. The SSFM operates in a dilution refrigerator in a cryogenic vacuum. Sample and probe can be cooled to 0.45 K.

Dynamic force microscopy in superfluid helium

Piezoelectric quartz tuning forks have been used for topographic dynamic force imaging in superfluid helium and in high magnetic fields. This has been achieved by immobilizing one tine of the tuning fork to stabilize its behavior in superfluid. Images acquired at room temperature and at 50 K are also presented. Frequency–distance curves are shown to be markedly different in superfluid than in air due to a long-range fork–sample interaction in liquid. Evidence is presented that this is due to a change in the hydrodynamic effective mass of the fork as the gap between the fork and sample is reduced. In addition, Q-control has been implemented and used to both increase and decrease the quality factors of tuning forks in both vacuum and superfluid helium.