Sensitive Thin Film Research Articles

The Effect of Loading W&V:TiO2 Nanoparticles with Noble Metals for CH4 Detection

TiO2 nanoparticles (NPs) doped with W (W:TiO2), double-doped with W and V (W&V:TiO2), and loaded with noble metals (W:TiO2 @Pt/Pd/Ag and W&V:TiO2@Pt/Pd/Ag) were synthesized by laser pyrolysis followed by chemical impregnation and reduction. Due to its exceptional properties, TiO2 is considered a key material being used in a wide range of applications. To improve its detection activity, the increase in the specific surface of the material, and the presence of defects in its structure play a decisive role. Doped and double-doped TiO2 nanoparticles with dimensions in the range of 25–30 nm presented a mixture of phases corresponding to titania, with the anatase phase accounting for the majority (95%). By loading these nanoparticles with small particles of noble metals, a significant increase in the specific surface area by three or even five times the original values was achieved. Sensitive thin films for surface acoustic wave (SAW) sensors were made with the NPs, embedded in polyethyleneimine (PEI) polymer and deposited by spin-coating. Each sensor was tested at CH4 concentrations between 0.4 and 2%, at room temperature, and the best results were obtained by the sensor with NPs doped with V and decorated with Pd, with a limit of detection (LOD) of 17 ppm, due to the strong catalytic effect of Pd.

Highly sensitive surface acoustic wave magnetic field sensor based on the loss mechanism

Currently, the surface acoustic wave (SAW) magnetic field sensing technique utilises the SAW velocity/frequency mechanism of magnetoacoustic interaction as an indicator of the magnetic sensitivity mechanism. However, this method has low sensitivity and poor stability. To address this problem, a dynamic magnetoelastic coupling theoretical model is constructed to theoretically simulate the influence of the ΔE effect of magnetically sensitive thin films on SAW propagation attenuation. This study describes a high-sensitivity SAW magnetic field sensing mechanism based on magnetoacoustic attenuation. The simulation results show a clear relationship between the acoustic propagation loss and external magnetic field, indicating a structure-property relationship. An amorphous soft magnetic material (Fe90Co10)78Si12B10 was used as a magnetically sensitive thin film due to its high permeability, low coercivity (Hc), low hysteresis, ease of magnetisation and demagnetisation. SAW magnetosensitive device operating on a frequency of 200 MHz has been experimentally developed using a standard semiconductor photolithography process. A SiO2 layer was deposited on a 36° YX-LiTaO3 substrate as a waveguide, and a (Fe90Co10)78Si12B10 layer was on the top of the propagation area as a magnetosensitive film. The experimental results showed that the acoustic loss change due to the magnetic field variation was 4.63 dB within a magnetic field range of 0 Oe to ±10 Oe, which agreed with the theoretical results. The sensor had a sensitivity of 0.7546 dB Oe−1 within the range of 0–4 Oe and the lower detection limit of magnetic fields was 0.272 Oe, low hysteresis error of 0.54%, multiple repeatability error of 0.13%, excellent repeatability and stability were achieved in the experiments from the developed sensing device.

Gallium oxide cantilevered thin film-based solar-blind photodetector and its arc detection applications

The performance of gallium oxide (Ga<sub>2</sub>O<sub>3</sub>) thin film detector based on metal-semiconductor-metal (MSM) is highly dependent on the uniformity of the Ga<sub>2</sub>O<sub>3</sub> thin film, and the manufacturing process is quite sophisticated, which poses a challenge for the scale-up and mass production of thin film photodetectors. In this work, an MSM Ga<sub>2</sub>O<sub>3</sub> thin film solar-blind photodetector with five-finger interdigital electrodes is fabricated by physically depositing Ga<sub>2</sub>O<sub>3</sub> thin film on the surface of a mass-produced cantilevered thin film chip. Through the microelectromechanical system (MEMS) process, the cantilever electrode structure is prepared, which protects the internal circuit and the integrity of the thin film. The Ga<sub>2</sub>O<sub>3</sub> thin film treated by argon plasma at a low temperature is amorphous, but the photodetector still possesses considerable ultraviolet detection performance. At a bias voltage of 18 V, it approaches the detection performance of crystalline Ga<sub>2</sub>O<sub>3</sub> thin film, with a detectivity of 7.9×10<sup>10</sup> Jones, an external quantum efficiency of 1779%, rise time and decay time of 1.22 s and 0.24 s, respectively. Moreover, a system of arc detection is built in outdoor environments. Without any optical focusing system, this photodetector achieves sensitive detection of pulsed arc in an outdoor sunlight environments. For pulsed arcs with an output voltage of 100 kV, the photodetector is capable of sensitive detection at a distance of 25 cm. Besides, the maximum detection distance of 155 cm indicates that the photodetector will have a favorable potential application value in the field of solar-blind detection. This work develops a sensitive functional thin film deposition technology based on the cantilever electrode structure fabricated by the MEMS process, which avoids the influence of the large-area uniformity of the functional thin film on the etching circuit. It provides a new technical approach and process route for preparing MSM photodetectors.

Design and fabrication of a new sol-gel based sensor for the visual detection of oxalate and investigation of the effect of boiling on the oxalate content of some foods

Sol–gel chemistry is a unique method for constructing high-performance flexible sensors. Sol-gel silica matrices doped with a controlled amount of sensing agent (dopant) lead to the fabrication of suitable sensors. According to this knowledge, we decided to describe the development and performance characteristics of the sol-gel glasses with a nanoporous structure as the novel naked eye sensor for fast detection of oxalate based on the incorporation of indole inside pores of the silica matrix obtained by sol–gel technology. Several sols were made with different water: alkoxide ratios and pHs to design a highly sensitive and selective thin film without dopant leaching. The Field emission scanning electron microscopy (FE-SEM) technique was employed to evaluate the surface morphology and porosity growth. Also, the sol–gel films were characterized by Fourier-transform infrared (FTIR) spectroscopy. The optimum performance in terms of sensitivity, leaching, and response time was achieved using water: alkoxide ratio of 4:1, water acidity (HCl concentration) of 0.01 M, and ethanolic solution of Indole 0.01 mol L-1. The calibration plot was obtained within 0.01–6.00 μg mL−1 of oxalate with a detection limit value of 0.005 μg mL−1. Meanwhile, the prepared sensor exhibited excellent and acceptable RSDs for both inter-day and intra-day precision. The present sensor was used to measure oxalate in various samples and investigate the effects of the celeryʼs cooking time and the brewing duration of tea on oxalate content.

Reusability, Long‐Life Storage and Highly Sensitive Zirconium Nitride (ZrN) Surface‐Enhanced Raman Spectroscopy (SERS) Substrate Fabricated by Reactive Gas‐Timing Rf Magnetron Sputtering

AbstractTransition metal nitrides (TMN) are promising material alternative to replace noble metals in the field of plasmonic applications, especially surface‐enhanced Raman spectroscopy (SERS). Here we demonstrate a practical surface enhanced Raman spectroscopy (SERS) substrate using zirconium nitride (ZrN) thin films grown by reactive gas‐timing (RGT) rf magnetron sputtering. The tailored properties of ZrN thin film exploited for SERS activity could be achieved to obtain a highly sensitive ZrN thin film SERS substrate with the enhancement factor (EF) of 1.24 × 106 and 4.8 %RSD at 1626 cm‐1 toward methylene blue (MB) analyte which are comparable to the optimized Au sputtered thin films (EF=1.18 × 106 and with 5.1%RSD). We find that the spatial plasmonic hotspots on the surface of ZrN SERS substrate controlled by the turn‐on timing of Ar:N2 sputtered gas sequence, leading to the discrete conductive surface profile, strongly relates to non‐stoichiometric composition and the degree of (200)‐oriented texture at the surface of ZrN thin film. Furthermore, ZrN thin film SERS substrates exhibit an excellent recyclability more than 30 cycles with simple cleaning process and a storage time longer than 6 months. The detection and reusability of ZrN SERS substrate on the low concentration of trinitrotoluene (TNT) for homeland security are also performed.

Highly Sensitive Wireless NO2 Gas Sensing System

There is a need for reliable and accurate air quality monitoring systems in order to secure human health from the air pollutants such as nitrogen dioxide (NO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ). The development of low-cost and modern technology-compatible sensing systems is essential. In this work, a highly sensitive and selective Indium Gallium Zinc oxide (IGZO) thin film transistor has been used to design an efficient and wireless NO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> sensing system. The sensing system uses the IGZO TFT as a current source for the current-starved ring oscillator where exposed NO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> concentration determines the oscillation frequency. The presented NO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> gas sensing system exhibited excellent sensitivity of 5.39 MHz/ppm with the lowest detection limit (LOD) of 50 ppb at room temperature. To the best of the authors’ knowledge, the achieved sensitivity is the best-reported performance for frequency-based NO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> sensors. The sinusoidal output of the sensor obviates the need for costly peripheral signal conditioning circuits and allows direct integration with wireless systems. The 13.56 MHz RFID antenna connected to the output of the sensor is used to show wireless sensing compatibility and highlights the excellent candidacy of the proposed work for the growing Internet of Things (IoT) and untethered sensor applications.

Highly Sensitive Broadband Bolometric Photodetectors based on 2D PdSe2 Thin Film

AbstractPdSe2, a semiconductor with a narrow band gap, shows tremendous promise for high‐performance broadband photodetectors. In this study, highly sensitive, broadband, and flexible PdSe2 thin film photodetectors on polyimide (PI) substrates that can detect light from the UV (365 nm) to infrared (2200 nm) regions are reported. The devices with thick (21 nm) PdSe2 films show decent performance with a decent responsivity of 37.6 mA W−1 at 1550 nm and a fast response time. For the thick PdSe2 film, the bolometric effect dominates the positive photoresponse across all wavelength regions, whereas for the thin PdSe2 film (4.5–13 nm), which shows both positive and negative photoresponses, it dominates in the infrared region. The negative photoresponse of thin PdSe2 in the UV to the VIS region is attributed to the charge transfer‐related adsorption‐desorption of gas molecules. Detailed investigations revealed that the temperature coefficient of resistance (TCR) value is closely correlated to film thickness, with the thinnest film exhibiting the highest absolute TCR value of up to 4.3% °C−1. The value is much larger than that of metals, most 2D materials, amorphous Si, and even commercial VOx. These findings suggest that PdSe2 films have a promising future in broadband photodetectors.

PH sensitive thin films of iron phthalocyanines as electrocatalysts for the detection of neurotransmitters

pH sensitive thin films of iron phthalocyanines as electrocatalysts for the detection of neurotransmitters

An efficient way of harvesting mechanoluminescent light: Flexible pressure sensor application

Mechanoluminescent (ML) materials are used for fabricating sensors and other devices such as artificial skin, colorful displays, and energy harvesting devices. However, a key challenge in developing ML-based sensors is the ability to effectively capture and efficiently transmit ML light from the sensing location. Here we report a flexible and sensitive thin film pressure sensor, created using a novel combination of ML material and perovskite. In this work, we adopted a simple lateral type design of a thin pressure sensor primarily consisting of (i) a sensing layer of copper-doped zinc sulfide (ZnS:Cu)/polydimethylsiloxane (PDMS) composite and (ii) a light absorbing layer of perovskite. The mixed halide perovskite, a light absorbing material, fully absorbs the green light emitted from ZnS:Cu. The sensor demonstrated consistent signal output under the mechanical bending test. A thin encapsulation layer of PMMA on the perovskite layer prevents moisture inclusion. This innovative technique of utilizing integrated thin perovskite to efficiently harvest ML light has the potential to open up new avenues for advanced research in ML-perovskite-based sensor systems.

Highly sensitive pure molybdenum trioxide thin films at a higher annealing temperature for liquefied petroleum gas and humidity sensing at room temperature

Highly sensitive pure molybdenum trioxide thin films at a higher annealing temperature for liquefied petroleum gas and humidity sensing at room temperature

High Sensitive and Selective Cu-doped ZnO Thin film for No2 Sensing with Chemical Root Method

Copper Doped Zinc Oxide-Thin films are prepared by the Sol-Gel method and annealing at 400°C, For sol preparation, we prepare 2- different types of solution, one is zinc nitrate hexahydrate and the second is copper nitrate, that are deeply discussed in this paper. The thin size was varied by XRD, the detected (h k l) peaks are confirmed with 2θ values and the morphology was also studied by field emission scanning electron microscopy (FESEM), the Nano-bubbles and nano-balls was observed. Electrical properties and VI- Characteristics were also done, and getting highly sensitive Performing results, finally, the gas sensing characteristic was taken by chemiresistive process. And the Gas Sensing performance was done with closed chamber methods and the High sensitive and selective performance result have been shown. The sensing parameters such as electrical properties, and VI- characteristics, for gases, are also observed we shown the response time and recovery time, The S=Rg/Ra formula is used for calculate the response of the films. The best of lower gas detection limits, towards NO2 gas, and also finalize the selectivity and sensitivity performance of the thin film. The final result shown that ZnO thinfilm can act as NO2 sensor and breath analyzer, for diabetes.

Transparent, photosensitive and highly efficient pseudocapacitive binder-free Mo-modified NiO thin film electrode for bifunctional optoelectronic and energy storage applications

We report a novel highly sensitive and pseudocapacitive transparent nickel oxide (NiO) thin film based electrode material fabricated on a conductive glass substrate using a facile binderless electrodeposition process. Effect of the incorporation of Mo-dopant ion on some surface structural and electrochemical properties of the electrode was examined for high performance optoelectronic and charge storage potentials. The material showed some uniqueness in some microstructural features and enhanced degree of crystallinity, suitable for charge extraction and transport with Mo doping. The deposited NiO film demonstrated red shift in band structure by exhibiting optical band gap narrowing from 3.88 to 3.61 eV with increasing Mo content. The degree of disorder as revealed from Urbach response of NiO film was found varying with Mo-content. The material also exhibited enhanced Ni2+ electronic transition states with increasing Mo content which quenched at a critical dopant concentration of 2.4 %. The fabricated NiO thin film electrode showed increased supercapacitive specific capacitance and areal capacity up to a peak value of 1412 Fg−1 and 101 mAh m−2 for 3 % Mo dopant content at 5 mVs−1 scan rate and 0.5 mA cm−2, respectively, but returned diminished at higher dopant content. Excellent cycling stability at ∼ 85 % after 5000 cycles, was also exhibited. Impedance spectroscopic features of Mo-doped NiO electrode indicated fast electrolytic ion transfer response with high rate charge storage capability. The study presents successful fabrication of Mo-modified NiO nanostructured electrode film and demonstrated the influence of Mo impurity on tailoring the properties of NiO host film as suitable electrode in high performance photocatalytic and supercapacitor devices.

High porosity silica aerogel thin film to monitoring vanadium: Synthesis, characterization and implementation

Sol–gel chemistry is a very unique method for constructing high-performance flexible sensors. Sol-gel silica matrices doped with a controlled amount of sensing agent (dopant) lead to the fabrication of suitable sensors. According to this knowledge, we decided to describe the development and performance characteristics of the sol-gel glasses with a nanoporous structure as novel naked eye sensor for fast detection of vanadium (V) based on physical entrapment of 4-(2-pyridylazo) resorcinol inside pores of the silica matrix obtained by sol–gel technology. To design a highly sensitive and selective thin film without dopant leaching, several sols were made with different water: alkoxide ratios and pHs. In summary, this study revealed that the characteristics of porous matrix as well as its average pore size could play significant roles in almost all critical parameters affecting the sensor performance, including sensitivity, selectivity, and response time. The FE-SEM technique equipped with EDAX was also employed to evaluate the surface morphology, porosity growth, and elemental identification of the thin films. The calibration plot was obtained within 0.004–3.000 μg mL−1 of vanadium (V) with a detection limit value of 0.0014 μg mL−1.

Optimization of gold germanium (Au0.17Ge0.83) thin films for high sensitivity resistance thermometry

Gold–germanium (AuxGe1−x) solid solutions have been demonstrated as highly sensitive thin film thermometers for cryogenic applications. However, little is known regarding the performance of the films for thicknesses less than 100 nm. In response, we report on the resistivity and temperature coefficient of resistance (TCR) for sputtered films with thicknesses ranging from 10 to 100 nm and annealed at temperatures from 22 to 200 °C. The analysis is focused upon composition x=0.17, which demonstrates a strong temperature sensitivity over a broad range. The thinnest films are found to provide an enhancement in TCR, which approaches 20% K−1 at 10 K. Furthermore, reduced anneal temperatures are required to crystallize the Ge matrix and achieve a maximum TCR for films of reduced thickness. These features favor the application of ultra-thin films as high-sensitivity, on-device thermometers in micro- and nanolectromechanical systems.

Enhancing Transition Dipole Moments of Heterocyclic Semiconductors via Rational Nitrogen-Substitution for Sensitive Near Infrared Detection.

Designing ultrastrong near-infrared (NIR) absorbing organic semiconductors is a critical prerequisite for sensitive NIR thin film organic photodetectors (OPDs), especially in the region of beyond 900nm, where the absorption coefficient of commercial single crystalline silicon (c-Si) is below 103 cm-1 . Herein, a pyrrolo[3,2-b]thieno[2,3-d]pyrrole heterocyclic core (named as BPPT) with strong electron-donating property and stretched geometry is developed. Relative to their analogue Y6, BPPT-contained molecules, BPPT-4F and BPPT-4Cl, show substantially upshifted and more delocalized highest occupied molecular orbitals, and larger transition dipole moments, leading to bathochromic and hyperchromic absorption spectra extending beyond 1000nm with very large absorption coefficients (up to 3.7-4.3 × 105 cm-1 ) as thin films. These values are much higher than those (104 to 1 × 105 cm-1 ) of typical organic semiconductors, and 1-2 orders higher than those of commercial inorganic materials, such as c-Si, Ge, and InGaAs. The OPDs based on BPPT-4F or BPPT-4Cl blending polymer PBDB-T show high detectivity of above 1012 Jones in a wide wavelength range of 310-1010nm with excellent peak values of 1.3-2.2 × 1013 Jones, respectively, which are comparable with and even better than those commercial inorganic photodetectors.

Sensitive optical thin film sensor based on incorporation of 2-(2′-hydroxynaphthylazo)-benzothiazole in a sol–gel matrix for detection of manganese(II) in environmental samples

A novel selective and precise optical thin film sensor reliant on the incorporation of synthesized 2-(2′-hydroxynaphthylazo)-benzothiazole (HNABT) as a selective ionophore into the nonporous of a clear glass like material via the sol–gel process is examined for its ability to assess Mn(II) ions in aqueous solutions. The sensor was constructed by spin-coating prepared sol onto a glass plate and the influence of sonication time on immobilization of HNABT into silica matrix was demonstrated through calculation of leaching percentage. The results designated that a sonication time of 25 min is the optimum to accomplish more stable thin films without fluctuation in sensitivity and response time of the introduced sensor for a wide period. The offered sensor can be employed to evaluate Mn(II) ions within the range of 6.0 × 10−8 – 1.5 × 10−5 M with detection and quantification limits of 1.7 × 10−8 and 5.5 × 10−8 M, respectively. The relative standard deviation of 2.1 and 0.83% for reproducibility and repeatability, are assessed, along with a rapid response time of ≈3.0 min. The constructed optode is stable in wet circumstances and should be kept for at least four weeks without detecting any variation in its sensitivity. The recommended sensor was successfully performed to estimate Mn(II) in food, saline effluents, tea leaves, biological and water samples, and the results were established by the GFAAS method.

High-sensitive humidity sensor based on MoS2/graphene oxide quantum dot nanocomposite

In this work, a high sensitivity humidity sensor based on Molybdenum disulfide/graphene oxide quantum dot (MoS2/GOQD) composite film was proposed. The humidity sensitive thin film of MoS2/GOQD was deposited on Au interdigitated microelectrodes via a facile drop-coating technique. The sensing characteristics of the MoS2/GOQD composite film sensor were investigated against various relative humidity (RH) at room temperature. The experimental results indicated that MoS2/GOQD composite film sensor possessed a high sensitivity of 369 pF/%RH, which is about twenty times larger than that of pure MoS2 based humidity sensor. Moreover, the sensor exhibited a good repeatability, rapid response/recovery speed, low hysteresis, and good long-term stability. Furthermore, the underlying humidity sensitivity enhancement mechanism of the fabricated sensor was analyzed and discussed in detail. This research demonstrates that the MoS2/GOQD composite film is a promising sensitive material for fabricating a high sensitivity humidity sensor.

High sensitive samarium-doped ZnS thin films for photo-detector applications

We developed the ZnS and samarium-doped ZnS thin films for photo-detector applications via a simple Nebulizer Spray Pyrolysis technique. The structural, morphological, optical, and photo-detecting behavior of ZnS and Sm-doped (0.5, 1.0, and 1.5%) ZnS thin films were characterized by XRD, Raman, AFM, UV–Vis, and Keithley analyzer measurements. The XRD analysis confirms the hexagonal wurtzite structure with the polycrystalline nature of all the samples. This wurtzite nature of ZnS:Sm was also confirmed by E1 (LO) phonon mode present at 346 cm −1 in the Raman spectrum. AFM images and thickness measurement depicted enrichment of particles on the surface. The presence of constituents in the samples was identified by EDX analysis. The semiconducting nature of the prepared films was exhibited by optical studies and it shows the lowest optical band gap ( E g ) value for the 0.5% Sm-doped ZnS (3.35 eV) thin film. Photo-sensing measurements was carried out by Keithley analyzer and showed the enhancement of sensing parameters up to 0.5% of Sm doping and then decreases for higher concentrated ZnS:Sm. The highest value of Responsivity ( R) , EQE, and Detectivity ( D *) was 8.30x10 −2 AW −1 , 28.26%, and 2.42 × 10 10 Jones, respectively for as-prepared 0.5% Sm-doped ZnS. Hence, it clearly depicts that the doping of a small amount of samarium highly alters the host lattice and their photoconducting mechanism. • Development of high-performance photodetector based on Sm@ZnS has been presented. • The grown films are of good crystallinity. • Surface morphology of the pure and Sm-doped ZnS samples was identified by AFM. • Good optical transparency and variation in bandgap values of Sm:ZnS films was noticed. • Responsivity ( R) , EQE and Detectivity ( D *) are highest for 0.5% of Sm-doped ZnS film.

Hydrogen-induced optical properties of FC/Pd/Mg films: Roles of grain size and grain boundary

Nanomodification is an effective method to solve the thermodynamic and kinetics limitation of Magnesium (Mg)-based materials, which shows promising application prospects in hydrogen energy field. However, the role of the grain size of pure Mg on the hydrogen-induced performance of the hydrogen sensitive thin film under cyclic hydrogen loading/unloading process at room temperature has rarely been studied systematically. To study the relationship between the structure of Mg layer and the hydrogen-induced optical performance of fluorocarbon (FC)/Pd/Mg films, a series of Mg with different internal structures were prepared by changing the velocity of sputtered atoms under different sputtering powers. The FC/Pd/Mg (40 W) film with fine nanostructure showed faster hydrogenation/dehydrogenation kinetics as well as a larger optical conversion range, which can be attributed to the large population of grain boundaries with high grain boundary energy and more hydrogen diffusion path. As sputtering power gradually increased from 40 W to 300 W, the grain inside films grew larger. The FC/Pd/Mg (300 W) film had more columnar-like regions inside and less grain boundaries with lower energy contributing to slower hydrogen absorption/desorption kinetics and lower optical conversion range.

A novel dew point measurement system based on the thermal effect of humidity sensitive thin film

A novel dew point measurement method has been developed by using a temperature sensor covered by humidity sensitive thin film (referred as HSTF). The measurement mechanism is that the mutation of the temperature-time curve caused by the thermal effect of the HSTF can be used to detect dew points. The automatic measurement system of dew point and relative humidity (RH) based on LabVIEW is built. Compared with the existing dew point detection methods, the technique has the advantages of simple device and anti-interference. The experimental data were compared with the reference values with the satisfactory results, relative humidity deviations are less than 1%, the working range is 0–30 °C within 25–85% humidity environment and the maximum response time are less than 65 s which can be further shortened by software. The research provides an effective way for the construction of a simple and automatic dew point measurement system.