ST-cut Quartz Research Articles

Colloidal quantum dot-based surface acoustic wave sensors for NO2-sensing behavior

Surface acoustic wave (SAW) sensors have great advantages in real-time and in-situ gas detection due to their wireless and passive characteristics. Using nanostructured sensing materials to enhance the SAW sensor’s responses has become a research focus in recent years. In this paper, solution-processed PbS colloidal quantum dots (CQDs) were integrated into quartz SAW devices for enhancing the performance of NO2 detection operated at room temperature. The PbS CQDs were directly spin-coated onto ST-cut quartz SAW delay lines, followed by a ligand exchange treatment using Pb(NO3)2. Upon exposure to 10 ppm of NO2 gas, the sensor coated with untreated PbS CQDs showed response and recovery times of 487 s and 302 s, and a negative frequency shift of −2.2 kHz, mainly due to the mass loading effect caused by the absorption of NO2 gas on the surface of the dense CQD film. Whereas the Pb(NO3)2-treated sensor showed fast response and recovery times of 45 s and 58 s, and a large positive frequency shift of 9.8 kHz, which might be attributed to the trapping of NO2 molecules in the porous structure and thus making the film stiffer. Moreover, the Pb(NO3)2-treated sensor showed good stability and selectivity at room temperature.

Interaction of Love waves with coupled cavity modes in a 2D holey phononic crystal

The interaction of Love waves with square array of pillars deposited on a cavity defined in a 2D holey phononic crystal is numerically investigated using Finite Element Method. First, the existence of SH surface modes is demonstrated separately for phononic crystals that consist of square arrayed holes, or rectangular arrayed Ni pillars, respectively in, or on, a SiO2 film deposited on a ST-cut quartz substrate. The coupling between SH modes and torsional mode in pillars induces a transmission dip that occurs at a frequency located in the range of the band-gap of the holey phononic crystal. Second, a cavity is constructed by removing lines of holes in the holey phononic crystal and results in a transmission peak that matches the dip. The optimal geometrical parameters enable us to create a coupling of the cavity mode and the localized pillar mode by introducing lines of pillars into the cavity, which significantly improved the efficiency of the cavity without increasing the crystal size. The obtained results will pave the way to implement advanced designs of high-performance electroacoustic sensors based on coupling modes in phononic crystals.

Surface acoustic wave NO2 sensors utilizing colloidal SnS quantum dot thin films

Colloidal quantum dots (CQDs) have shown their advantages in gas-sensing applications due to their extremely small particle size and facile solution based processes. In this study, a high sensitivity of surface acoustic wave (SAW) NO2 sensor was demonstrated using SnS CQDs as the sensing layer. The delay line based SAW device with a resonant frequency of 200 MHz were fabricated on ST-cut quartz substrate. The SnS CQDs with average sizes of 5.0 nm were synthesized and deposited onto SAW sensors using a spin-coating method. The fabricated SAW sensor was capable of detecting a low concentration of NO2 gas at room temperature with a good efficiency and selectivity e.g., with a 1.8 kHz decrease of center frequency of the SAW delay line when exposed to 10 ppm NO2 at room temperature.

Highly confined Love waves modes by defect states in a holey SiO2/quartz phononic crystal

Highly confined Love modes are demonstrated in a phononic crystal based on a square array of etched holes in SiO2 deposited on the ST-cut quartz. An optimal choice of the geometrical parameters contributes to a wide stop-band for shear waves’ modes. The introduction of a defect by removing lines of holes leads to the nearly flat modes within the bandgap and, consequently, paves the way to implement advanced designs of electroacoustic filters and high-performance cavity resonators. The calculations are based on the finite element method in considering the elastic and piezoelectric properties of the materials. Interdigital transducers are employed to measure the transmission spectra. The geometrical parameters enabling the appearance of confined cavity modes within the bandgap and the efficiency of the electric excitation were investigated.

Epitaxial growth of horizontally aligned single-crystal arrays of perovskite

Well-aligned single-crystal nanowire arrays of CH3NH3PbI3 have shown potentials in laser sources and photovoltaic applications. Here we developed a solution based epitaxial method to grow CH3NH3PbI3 nanowire arrays. By confining the precursor solution between a silicon wafer and ST-cut quartz, the evaporation rate of the solvent was slowed down which brings a more stable and controllable solution environment. Relying on the lattice match between CH3NH3PbI3 and ST-cut quartz, arrays of single-crystal nanowires of CH3NH3PbI3 have been grown epitaxially. The densities and lengths of CH3NH3PbI3 nanowires can be tuned. The lengths of the resultant crystals range from several microns to over one millimeter. Such CH3NH3PbI3 arrays with good alignment and crystallinity were then applied to fabricate photovoltaic devices with good performances.

Fabrication of surface acoustic wave based wireless NO2 gas sensor

Surface acoustic wave (SAW) devices provide a convenient platform for the realization of sensors in the present decade. 99.4MHz SAW resonator has been fabricated over the ST cut quartz. Subsequently PZT thin film has been deposited by pulsed laser deposition technique as a sensing layer over the fabricated SAW resonator. Shift in resonance frequency was measured precisely for varying concentration of NO2 gas. The calibration curve was found to be linear having a sensitivity of 9.6Hz/ppm. The fabricated sensor is advantageous for its room temperature, handheld and wireless sensing.

A surface acoustic wave ICP sensor with good temperature stability.

Intracranial pressure (ICP) monitoring is very important for assessing and monitoring hydrocephalus, head trauma and hypertension patients, which could lead to elevated ICP or even devastating neurological damage. The mortality rate due to these diseases could be reduced through ICP monitoring, because precautions can be taken against the brain damage. This paper presents a surface acoustic wave (SAW) pressure sensor to realize ICP monitoring, which is capable of wireless and passive transmission with antenna attached. In order to improve the temperature stability of the sensor, two methods were adopted. First, the ST cut quartz was chosen as the sensor substrate due to its good temperature stability. Then, a differential temperature compensation method was proposed to reduce the effects of temperature. Two resonators were designed based on coupling of mode (COM) theory and the prototype was fabricated and verified using a system established for testing pressure and temperature. The experiment result shows that the sensor has a linearity of 2.63% and hysteresis of 1.77%. The temperature stability of the sensor has been greatly improved by using the differential compensation method, which validates the effectiveness of the proposed method.

ZnO/ST-Quartz SAW resonator: An efficient NO2 gas sensor

A Surface Acoustic Wave (SAW) resonator operating at a frequency of 99.50MHz using piezoelectric ST-cut quartz has been fabricated. The resonator device has been successfully integrated with ZnO sensing layer for detection of NO2 gas. The fabricated sensor device is found to be detecting trace level concentration of NO2 gas (400ppb to 16ppm) efficiently and selectively. The ZnO/Quartz SAW sensor is useful for wireless detection of NO2 gas.

Room-Temperature Ammonia Sensor Based on ZnO Nanorods Deposited on ST-Cut Quartz Surface Acoustic Wave Devices.

Using a seed layer-free hydrothermal method, ZnO nanorods (NRs) were deposited on ST-cut quartz surface acoustic wave (SAW) devices for ammonia sensing at room temperature. For a comparison, a ZnO film layer with a thickness of 30 nm was also coated onto an ST-cut quartz SAW device using a sol-gel and spin-coating technique. The ammonia sensing results showed that the sensitivity, repeatability and stability of the ZnO NR-coated SAW device were superior to those of the ZnO film-coated SAW device due to the large surface-to-volume ratio of the ZnO NRs.

Diameter-specific growth of single-walled carbon nanotubes using tungsten supported nickel catalysts

We developed a W/WOx-supported Ni catalyst for the diameter-controlled growth of single-walled carbon nanotubes (SWNTs) by chemical vapor deposition (CVD) valid for different substrates and broad growth conditions. The Ni nanoparticles anchored on W/WOx are well dispersed and show superior stability to high temperature. Under broad CVD windows of temperature and carbon feedstock supply conditions, SWNTs with narrow diameter distribution of ∼1.3 ± 0.1 nm can be steadily synthesized. This strategy also works well in the growth of surface lattice oriented SWNT arrays. The aligned SWNTs grown on ST-cut quartz show similar diameters to those obtained on silicon wafers.

A Low-cost Biomarker-based SAW-Biosensor Design for Early Detection of Prostate Cancer

Early detection of prostate cancer is crucial for the treatment. Currently rectal examination, ultrasound and ELISA test for blood-PSA biomarker level are used for diagnosis. However these methods require professional assistance that makes point-of care (POC) testing impossible. A POC, low-cost, high-precision biosensor can increase the early-detection and survival rates. Recently, we have proposed a low-cost and an easy-to-use surface acoustic wave biosensor that enables the quantification of PSA level. In this study, we focused to the electronic circuitry and signal processing algorithms for accurate protein level assessment using cost efficient and low-profile hardware. Simplifying the hardware will potentially lead to the development of single chip monolithic integrated biosensor.The MEMS based biosensor designed in our studies utilizes shear-horizontal (SH) SAWs on ST-cut Quartz substrate to sense the mass loading change by protein adhesion. The driver circuitry employs signal-processing algorithms to detect the phase change, which quantifies the protein level in the sample dropped on the surface.The signal applied to the sensor input is a 16.9 MHz square wave generated by using a simple counter circuit. The output is under-sampled at an extremely low rate (100 KHz), then, the phase information is extracted using the under-sampled signal. A low-profile microcontroller (μC) is used to determine the phase shift. The simulated and experimental results are demonstrated, and they agreed well with each other. The results show that, the phase error level is 1% and minimum delay measured is 0.3 ns. Increasing number of samples used for calculation enhances the detection performance. Our studies also showed that using excessive number of samples enables the accurate phase calculation even if a simple 1-bit ADC is employed.

Gene Regulation As A Function of Epigenetic Marks (H3K4ME3, H3K27AC) And Cell Types (Neuronal And Non Neuronal Cells) In Human Brain

We developed a W/WOx-supported Ni catalyst for the diameter-controlled growth of single-walled carbon nanotubes (SWNTs) by chemical vapor deposition (CVD) valid for different substrates and broad growth conditions. The Ni nanoparticles anchored on W/WOx are well dispersed and show superior stability to high temperature. Under broad CVD windows of temperature and carbon feedstock supply conditions, SWNTs with narrow diameter distribution of ∼1.3 ± 0.1 nm can be steadily synthesized. This strategy also works well in the growth of surface lattice oriented SWNT arrays. The aligned SWNTs grown on ST-cut quartz show similar diameters to those obtained on silicon wafers.

Investigating the cross-interference effects of alumina refinery process gas species on a SAW based mercury vapor sensor

In this study, the effect of some common alumina refinery process gas species on the response of a surface acoustic wave (SAW) based elemental mercury (Hg0) vapor microsensor was investigated. The developed sensor was based on a SAW delay line, fabricated on a ST-cut quartz substrate with nickel (Ni) interdigitated transducer (IDT) electrodes and gold (Au) film sensitive layer. Ni was chosen as IDT material due to its immiscibility in mercury and thus allowing the sensor to operate for a longer time, as required by the industries. The sensor was exposed to mercury vapor concentrations between 24 and 365ppbv without/with the presence of ammonia, acetaldehyde, ethyl mercaptan, dimethyl disulphide, methyl ethyl ketone and humidity. The detection limit of the sensor toward Hg0 vapor was calculated to be 1.4ppbv and 4.0ppbv at operating temperatures of 35 and 75°C, respectively. The coefficient of variance of the sensor response magnitude was found to be within ±1.86 and ±5.73% at 75°C when exposed to repeated pulses of 365ppbv of Hg0 vapor without and with the presence of interfering gas species, respectively. This indicates high precision of sensor while measuring low concentrations of Hg0 vapor. Results showed that when any one of the interfering gas species was exposed along with Hg0 vapor, the response magnitude of the sensor deviated up- to 7% (93% selectivity) at an operating temperature of 75°C. Furthermore, the sensor showed a selectivity of 87% when Hg0 vapor was tested along with a mixture of all interfering gases. There was insignificant cross-sensitivity effect when the humidity content was increased within the range of 15,300 to 30,600ppmv (equivalent to 50 to 100% relative humidity at room temperature). The overall results indicate that the developed sensor is able to detect Hg0 vapor selectively even in simulated industrial conditions and can be a potentially cheaper and more reliable alternative to the current Hg0 monitoring methods used in alumina refineries.

High frequency surface acoustic wave resonator-based sensor for particulate matter detection

This paper describes the characterization of high frequency Surface Acoustic Wave Resonator based (SAWR) sensors, for the detection of micron and sub-micron sized particles. The sensor comprises two 262MHz ST-cut quartz based Rayleigh wave SAWRs where one is used for particle detection and the other as reference. Electro-acoustic detection of different sized particles shows a strong relationship between mass sensitivity (Δf/Δm) and particle diameter (Dp). This enables frequency-dependent SAWR sensitivity to be tailored to the size of particles, thus making these types of sensors good candidates for PM10, PM2.5 and ultrafine particle (UFP) sensing. Our initial characterisation demonstrated a typical SAWR frequency shift of 60Hz in response to a deposition of ca. 0.21ng of 0.75μm-sized gold particles (∼50 particles) on the sensor surface. Sensor responses to different sized particles, such as ∼30μm diameter silicon, gold (diameters of ∼0.75μm and ∼20μm), ∼8μm fine sugar, PTFE (∼1μm and ∼15μm), ∼4μm talcum powder, and ∼2μm molybdenum powder were evaluated, and an average mass sensitivity of 275Hz/ng was obtained. Based on the results obtained in this study we believe that acoustic wave technology has great potential for application in airborne particle detection. Moreover, acoustic resonator devices can be integrated with CMOS interface circuitry to obtain sensitive, robust, low-power and low-cost particle detectors for a variety of applications including outdoor environmental monitoring.

Re-growth of single-walled carbon nanotube by hot-wall and cold-wall chemical vapor deposition

Single-walled carbon nanotube (SWCNT) was synthesized from short nanotubes using chemical vapor deposition (CVD) and the associated factors affecting the re-growth of the SWCNT were both investigated and optimized. Long, dense nanotubes were prepared from a mixture of acetylene and ethanol on air-annealed ST-cut quartz substrates by hot-wall CVD. Raman and photoluminescence analyses of the resulting material demonstrated that SWCNT was generated from the initial seeds since the chiralities of the seeds were maintained in the re-grown SWCNT. The re-growth of SWCNT was also achieved by cold-wall CVD. In both CVD systems, the efficiency of SWCNT re-growth was largely determined by the pretreatment conditions and growth parameters. By varying these factors, the growth of SWCNT from seeds was controlled. The re-growth mechanism is discussed based on experimental observations.

A novel sensitive cell-based Love Wave biosensor for marine toxin detection

A novel HepG2 cell-based biosensor using Love Wave sensor was developed to implement the real-time and sensitive detection of a diarrheic shellfish poisoning (DSP) toxin, Okadaic acid (OA). Detachable Love Wave sensor unit and miniaturized 8-channel recording instrument were designed for the convenient experimental preparation and sensor response signal measurement. The Love Wave sensor, whose synchronous frequency is around 160 MHz, was fabricated with ST-cut quartz substrate. To establish a cell-based biosensor, HepG2 cells as sensing elements were cultured onto the Love Wave sensor surface, and the cell attachment process was recorded by this biosensor. Results showed this sensor could monitor the cell attachment process in real time and response signals were related to the initial cell seeding densities. Furthermore, cell-based Love Wave sensor was treated with OA toxin. This biosensor presented a good performance to various OA concentrations, with a wide linear detection range (10-100 μg/L). Based on the ultrasensitive acoustic wave platform, this cell-based biosensor will be a promising tool for real-time and convenient OA screening.

Room temperature fabrication of ZnO/ST-cut quartz SAW UV photodetector with small temperature coefficient.

Room-temperature fabricated ZnO/ST-cut quartz is adopted for SAW ultraviolet (UV) photodetector. The ST-cut quartz substrate and ZnO layer are used for SAW excitation and photodetection, respectively. High resolution x-ray diffraction (XRD) and photoluminescence (PL) measurement indicate that high quality ZnO films can be deposited on ST-cut quartz using radio frequency (RF) sputtering. As the SAW devices under UV illumination (6 mW/cm(2)), a downshift in frequency of about 35 KHz can be observed. The observed small temperature coefficient of frequency (TCF) indicates that SAW devices exhibit good temperature stability. The results present feasibility of using ZnO/ST-cut quartz SAW photodetectors in ultraviolet region.

Selective scission of C-O and C-C bonds in ethanol using bimetal catalysts for the preferential growth of semiconducting SWNT arrays.

For the application of single-walled carbon nanotubes (SWNTs) to electronic and optoelectronic devices, techniques to obtain semiconducting SWNT (s-SWNT) arrays are still in their infancy. We have developed herein a rational approach for the preferential growth of horizontally aligned s-SWNT arrays on a ST-cut quartz surface through the selective scission of C-O and C-C bonds of ethanol using bimetal catalysts, such as Cu/Ru, Cu/Pd, and Au/Pd. For a common carbon source, ethanol, a reforming reaction occurs on Cu or Au upon C-C bond breakage and produces C(ads) and CO, while a deoxygenating reaction occurs on Ru or Pd through C-O bond breaking resulting in the production of O(ads) and C2H4. The produced C2H4 by Ru or Pd can weaken the oxidative environment through decomposition and the neutralization of O(ads). When the bimetal catalysts with an appropriate ratio were used, the produced C(ads) and C2H4 can be used as carbon source for SWNT growth, and O(ads) promotes a suitable and durable oxidative environment to inhibit the formation of metallic SWNTs (m-SWNTs). Finally, we successfully obtained horizontally aligned SWNTs on a ST-cut quartz surface with a density of 4-8 tubes/μm and an s-SWNT ratio of about 93% using an Au/Pd (1:1) catalyst. The synergistic effects in bimetallic catalysts provide a new mechanism to control the growth of s-SWNTs.

Large-scale aligned crystalline CH3NH3PbI3 perovskite array films

Owing to the lattice match, large-scale aligned crystalline CH3NH3PbI3 perovskite array films were fabricated on ST cut quartz.

Performance Prediction and Sensitivity Analysis of SAW Gas Sensors

An improved adaptive neuro-fuzzy inference system (IANFIS) is proposed to build a model to predict the resonant frequency shift performance of surface acoustic wave (SAW) gas sensors. In the proposed IANFIS, by directly minimizing the root-mean-squared-error performance criterion, the Taguchi-genetic learning algorithm is used in the ANFIS to find both the optimal premise and consequent parameters and to simultaneously determine the most suitable membership functions. The five design parameters of SAW gas sensors are considered to be the input variables of the IANFIS model. The input variables include the number of electrode finger pairs, the electrode overlap, the separation distance of two interdigital transducers on the substrate, the dimensions of the stable temperature-cut (ST-cut) quartz substrate, and the electrode thickness. The output variable of the IANFIS model is composed of the resonant frequency shift performance. The results predicted by the proposed IANFIS are compared with those obtained by the back-propagation neural network. The comparison has shown that the performance prediction of resonant frequency shift using the proposed IANFIS is effective. In addition, the sensitivity analyses of the five design parameters have also shown that both the electrode overlap and the dimensions of the ST-cut quartz substrate have the most influence on the resonant frequency shift performance.