Search

We discuss the effect of topological inhomogeneity of very thin metallic conductometric sensors on their response to external stimuli, such as pressure, intercalation, or gas absorption, that modify the material's bulk conductivity. The classical percolation model was extended to the case in which several independent scattering mechanisms contribute to resistivity. The magnitude of each scattering term was predicted to grow with the total resistivity and diverge at the percolation threshold. We tested the model experimentally using thin films of hydrogenated palladium and CoPd alloys where absorbed hydrogen atoms occupying the interstitial lattice sites enhance the electron scattering. The hydrogen scattering resistivity was found to grow linearly with the total resistivity in the fractal topology range in agreement with the model. Enhancement of the absolute magnitude of the resistivity response in the fractal range thin film sensors can be particularly useful when the respective bulk material response is too small for reliable detection. [ABSTRACT FROM AUTHOR]

In this study, the authors demonstrate the fabrication, calibration, and testing of a piezoresistive microcantilever‐based sensor for biomedical microelectromechanical system (BioMEMS) application. To use any sensor in BioMEMS application requires surface modification to capture the targeted biomolecules. The surface alteration comprises self‐assembled monolayer (SAM) formation on gold (Au)/chromium (Cr) thin films. So, the Au/Cr coating is essential for most of the BioMEMS applications. The fabricated sensor uses the piezoresistive technique to capture the targeted biomolecules with the SAM/Au/Cr layer on top of the silicon dioxide layer. The stiffness (k) of the cantilever‐based biosensor is a crucial design parameter for the low‐pressure range and also influence the sensitivity of the microelectromechanical system‐based sensor. Based on the calibration data, the average stiffness of the fabricated microcantilever with and without Au/Cr thin film is 141.39 and 70.53 mN/m, respectively, which is well below the maximum preferred range of stiffness for BioMEMS applications. The fabricated sensor is ultra‐sensitive and selective towards Hg2+ ions in the presence of other heavy metal ions (HMIs) and good enough to achieve a lower limit of detection 0.75 ng/ml (3.73 pM/ml). [ABSTRACT FROM AUTHOR]

Thin film thermocouples were embedded in vertically to the rake face of cutting tools for better durability in temperature monitoring during titanium alloy cutting processes. • Tools embedded with thin film sensors to monitor cutting temperature. • Thin film thermocouples are embedded vertically to the tool face for protection. • Annealing treatment improved the quality of laterally deposited films. • Good sensitivity and fast responses are validated by experimental tests. • The vertically embedded sensors show good performance and reliability. Smart tools instrumented with thin film thermocouples for online cutting temperature measurement are promising in intelligent manufacturing. However, the surface-mounted planar devices are easily damaged through delamination and abrasion due to the high temperature, great stresses and harsh friction. This paper reports a novel approach to embed the thin film thermocouples in vertical direction to the tool rake face for protection. Attention is also paid to improve the quality of the vertically deposited thin films on the lateral walls of the micro-grooves. Experimental tests have been done to obtain the sensitivity and response of the sensors in the tool. The embedded sensors function well in monitoring the cutting temperature in cutting tests of a titanium alloy. [ABSTRACT FROM AUTHOR]

Highlights • Organic vapor phase deposition of perylene diimide monolayers significantly reduces surface recombination of InP wafers. • Conformal coating allows for passivation of 3D surfaces such as mesas. • Passivation leads to improved photoconductivity in InP detectors. Abstract We demonstrate the surface passivation of InP using thin layers of a perylenetetracarboxylic diimide derivative (PTCDI-C 9) applied via organic vapor phase deposition (OVPD). The organic layer forms a conformal crystalline film on the InP surface, which is confirmed by atomic force microscopy and X-ray diffraction. Area-dependent photoluminescence measurements indicate that the coating reduces surface recombination. The organic thin film deposited by OVPD exhibits improved photoconductivity compared to an unpassivated InP sample, and to a layer deposited via vacuum thermal evaporation. Our results suggest that semiconductor surface passivation using organic thin films deposited by OVPD has applications to a variety of optoelectronic devices, particularly with structures requiring sidewall or conformal coatings. [ABSTRACT FROM AUTHOR]

The authors report quartz crystal microbalance (QCM) integrated with hexagonal boron nitride–graphene (hg) monolayer heterostructure as a sensor to detect mass flow of sulphur hexafluoride (SF6), an important electrical insulating gas, under humid conditions. Their recent work demonstrated an enhancement in QCM sensing characteristics upon attaching monolayer 2D materials onto the QCM electrode surface and its application for improved relative humidity measurement. Here, they extend this approach to detect flow of SF6 gas causing variation in relative humidity. They fabricated a hg-QCM sensor by transferring the heterostructure thin film onto the QCM electrode surface using a standard wet transfer technique and measured return loss of the QCM under SF6 gas flow at a selected RH condition. The mass flow of the humid SF6 gas effects perturbation in damping at the QCM surface as indicated by changes in the motional resistance of the QCM. The motional resistance changes introduced significant variation in loaded Q-factor, the magnitude of which was gas species-dependent, thus allowing to distinguish SF6 from other common electronics gases. [ABSTRACT FROM AUTHOR]

Superconducting titanium thin films are good candidates for transition edge sensors. In this paper, we deposit titanium thin films on cooled silicon-on-insulator substrates by using electron-beam evaporation. The deposition rate dependence of the film stress, resistivity, and superconducting transition temperature are presented and analyzed. The relationship between film electrical properties and thickness is discussed. For investigating the heating influence on thin Ti films, a depth profile of oxygen diffusion in the films is also analyzed by X-ray photoelectron spectroscopy. [ABSTRACT FROM AUTHOR]

Surface plasmon resonance (SPR)-based differential phase analysis has been presented. Real as well as complex plane analysis of resonance parameters have been undertaken for the optimum selection of metal thicknesses in a bimetallic SPR configuration working under both angular and spectral regime. Theoretically, we can characterize the aqueous solution in terms of this differential phase variation due to the variation of sample parameters such as concentration and temperature. In this respect, two case studies, namely, concentration of hemoglobin in human blood and sensing of temperature of water have been demonstrated and proposed theoretically. By monitoring the change of differential phase, proposed approach leads to a very sensitive measurement of concentration and temperature. [ABSTRACT FROM AUTHOR]

This study reports the synthesis, characterization and gas sensing applications of N-cyclohexylmethacrylamide (NCMA) monomer material using FT-IR,1H and13C NMR, UV-visible spectroscopy, Quartz Crystal Microbalance (QCM) and Langmuir-Blodgett (LB) thin film deposition techniques. The thin film deposition conditions of NCMA monomer material, which are prepared by LB film technique, are characterized by UV-visible spectroscopy and QCM system. The sensing behaviors of the LB film with respect to volatile organic compounds (VOCs) at room temperature are investigated. Surface pressure change as a function of surface area of NCMA molecule at the water surface shows a well-organized and stable monolayer at 18 mN m−1surface pressure value for LB film deposition. Transfer ratio values are found to be ≥ 0.94 for quartz glass and ≥ 0.93 for quartz crystal substrate. The typical frequency shift per layer is obtained 20.10 Hz/layer and the deposited mass onto a quartz crystal is calculated as 824.62 ng/layer. The sensing responses of the LB films against chloroform, dichloromethane, acetone, toluene, benzene and ethanol are measured by QCM system. The sensitivities of the NCMA LB film sensor are determined between 0.085 and 0.029 Hz ppm−1. Sensitivities with detection limits are between 35.29 and 100.33 ppm against organic vapors. These results can be concluded that the monomer LB film sample is found to be significantly more sensitive to chloroform and dichloromethane vapors than others organic vapors used in this work. This material may find potential applications in the development of room temperature organic vapor sensing. [ABSTRACT FROM AUTHOR]

This paper deals with the development of an accurate and precise humidity sensor, which is based on the extension of Thompson and Lampard theorem and a sol–gel-based thermally and chemically stable metal oxide thin film. In light of the extension of the theorem, most appropriate conductors are shaped around the material and the resulting sensor has cross conductance, which is the function of thickness only. It is fabricated and tested for different ranges of humidity. It is found that the fabricated sensor has outstanding static and dynamic characteristics. [ABSTRACT FROM PUBLISHER]

The sterilization of packages in aseptic food processes is highly significant to maintain a consumer-safe product with extended shelf-life. Today, the sterilization of food packages is predominantly accomplished by gaseous hydrogen peroxide (H 2 O 2 ) in combination with heat. In order to monitor this sterilization process, calorimetric gas sensors as differential set-up of two platinum temperature sensors representing a catalytically active (additionally deposition of MnO 2 ) and a passive segment have been recently developed. The temperature rise of the exothermic decomposition serves as an indicator of the present H 2 O 2 concentration. In the present work, a theoretical approach considering the sensor’s thermochemistry and physical transport phenomena was formulated to evaluate the temperature rise based on the energy content of gaseous H 2 O 2 . In a further part of this work, three polymers have been analyzed with respect to their application as passivation materials. The examined polymers are photoresist SU-8, perfluoroalkoxy (PFA) and fluorinated ethylene propylene (FEP). Thermal analyses by means of differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) have been conducted to determine the operation limits of the polymers. The overall chemical resistance and stability of the polymers against the harsh environmental conditions during the sterilization process have been examined by attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR). [ABSTRACT FROM AUTHOR]

Purpose – The purpose of this paper is to focus on the technology and performance of the miniature microfluidic module for urea determination. The presented module was made using low-temperature co-fired ceramics (LTCC). It shows the possibility for the integration of the bioreceptor layers with structures that have been fabricated using modern microelectronic technology. Design/methodology/approach – The presented microfluidic module was fabricated using LTCC technology. The possibility for the fabrication of an enzymatic microreactor in a multilayer ceramic substrate, made of CeramTec glass ceramic (GC) material systems with an integrated thick-film heater, is studied. Different configurations of the LTCC/heater materials (gold, silvers and palladium-silver) are taken into account. The performance of the LTCC-based microfluidic module with the integrated heater and immobilized enzyme was examined experimentally. Findings – A compatible material for the heater embedded in the CeramTec GC-based structures was found. The preliminary measurements made for the test solution containing various concentrations of urea have shown stability (for seven days of operation) and a relatively high signal-to-noise ratio (above 3 pH units) for the microreactor’s output signal. Research limitations/implications – The presented research is a preliminary work which is focused on the fabrication of the LTCC-based microfluidic module, with an integrated heater and immobilized enzyme for urea determination. The device was positively tested using a model reaction of the hydrolysis of urea. However, urea concentration in real (biological) fluid should also be measured. Practical implications – The development of the LTCC-based microfluidic module for urea determination provides opportunity for the construction of a lab-on-chip, or μTAS-type system, for fast medical diagnoses and the continuous monitoring of various biochemical parameters, e.g. for estimating the effectiveness of hemodialysis. Originality/value – This paper shows the design, fabrication and performance of the novel microfluidic module for urea determination, made with LTCC technology. [ABSTRACT FROM AUTHOR]

Present paper reports the fabrication of zinc ferrite thin film sensor having two different types of surface morphologies (mixed shaped nanorods and vertically aligned nanorods) and their growth mechanism. The LPG sensing properties of the vertically aligned assembled nanorods are found improved significantly in comparison to mixed shaped nanorods. When we compare our sensor performance with other thin film sensors, it is found that the sensor performance obtained in this work is definitely better than that of others. Thus our investigation demonstrates the potential application of aligned nanorods in the fabrication of LPG sensor operable at room temperature. [ABSTRACT FROM AUTHOR]

The development of carbon nanotube (CNT)‐based sensors remains an active area of research. Towards this end, a new method for manipulating CNTs, assembling CNT networks and fabricating CNT‐based nanosensors was demonstrated in this study. CNTs were collected and concentrated by optically‐induced dielectrophoresis (ODEP) forces and aligned between a pair of electrodes. This assembly was then used directly as a temperature sensor and a hot‐film anemometer, which detects changes in windspeed. By offering efficient CNT collection and ready‐to‐use sensor fabrication, this ODEP‐based approach presents a promising method for the development of CNT‐based sensing applications and massively parallel assembly of CNT‐lines. The developed CNT‐based nanosensors may be used to measure the temperature and the flow velocity of bio‐samples in the near future. [ABSTRACT FROM AUTHOR]

A composite optical waveguide sensor, consisting of lithium iron phosphate (LiFePO 4 , LFP) as the sensing material, was constructed and utilized for the detection of volatile organic compound gases. Nano-LFP powder was prepared via the hydrothermal method and was subsequently utilized in a dip-coating procedure for the fabrication of LFP thin films. The effect of heat treating temperature on the refractive index of the thin films was studied. A glass optical waveguide gas sensor was fabricated by coating an LFP thin film on the surface of single-mode tin-diffused glass optical waveguide. The sensor was found to exhibit a linear response to xylene in the range of 50–1000 ppm, with response times of less than 5 s. [ABSTRACT FROM AUTHOR]

Preparation of transparent sol-gel thin film immobilized with bromocresol purple (BCP) pH-sensitive indicator was made via the acid catalyzed sol-gel reaction of tetraethylorthosilicate and the bromocresol purple indicator (BCP). Different surfactants include cationic cetyl trimethyl ammonium bromide (CTAB), anionic sodium dodecyl sulfate (SDS), and nonionic Triton X-100 (TX-100) were used to improve the mesostructure of the host material and to increase its porosity. The color change behavior of the immobilized bromocresol purple indicator affected significantly in presence of SDS comparing with its free counterpart in aqueous solution. In presence of CTAB and Triton-X 100, the immobilized bromocresol purple indicator shows similar behavior as its free counterpart in aqueous solution. The BCP retains its structure during the sol-gel reactions in terms of response to pH. Different parameters including concentration of indicator and surfactant, temperature, number of layers, response time, life time, and the number of measurements were investigated. The pKa values of the different prepared BCP immobilized thin films were determined. The BCP thin film sensor showed stability, repeatability, reproducibility, fast response, and long life time behavior. The polarized light microscopy indicated that the bromocresol purple indicator molecules are distributed uniformly within the host silica network. [ABSTRACT FROM AUTHOR]

Abstract: This paper introduces a novel approach to the detection and accurate measurement of extremely small signals, produced by bilayer thin films without the use of sophisticated hardware. The implementation of this measuring system is based on the LabVIEW graphical programming. This general purpose, robust and low-cost signal detector, provides an excellent way to evaluate magnetostrictive materials and their application in magnetic sensors. Initially the complete system was first simulated in LabVIEW software with the simulated signal superimposed with noise signals and the correct performance of the program was successfully confirmed. Later the software was incorporated together with the simple modulating circuit of the sensor. The results from the acquisition proved that the system provides a quick and excellent way to evaluate magnetostrictive materials and their application in magnetic sensors. [Copyright &y& Elsevier]

A thin film semiconductor sensor array has been employed to discriminate several aromatic compounds in water, ethanol and wine. These compounds are aromas or off-odours usually found in wines: acetic acid, ethyl acetate, acetaldehyde, trichloroanisole (TCA) and SO2. The concentrations of these compounds were in the range of mg/l except in the case of TCA that was in the ng/l range. Principal component analysis (PCA) and radial basis neural networks (RB-NN) were performed in the data. The results showed that despite the strong influence of ethanol the system could discriminate correctly the compounds. [Copyright &y& Elsevier]

• Ag-CNT nanocomposite sensor showed a better temperature coefficient of resistance. • Ag-CNT nanocomposite sensors have higher sensitivity compared to conventional counterparts. • Ag-CNT nanocomposite TFS has a higher TCR compared to the only Ag TFS by 46.4%. Thin film sensor (TFS) is one of the most promising candidates for instantaneous temperature measurements owing to their extremely small response time (~milliseconds) aided with fair accuracy. Since they are capable of making quick and precise temperature measurements, they can be also used as heat flux gauges to measure surface heat fluxes in dynamic environments like high speed aerospace applications, gas turbine blades etc. Usual TFS are made by depositing a thin metallic film over insulating substrate. In this work we developed an Ag-Carbon nanotube (CNT) nanocomposite film as the sensing element of a TFS and compare it with pure Ag TFS, both having Macor as substrate. Static calibration established a better temperature coefficient of resistance (TCR) value i.e. better sensitivity, for the nanocomposite TFS. X-ray diffraction (XRD) and Energy Dispersive X-ray (EDX) studies are done to probe behind the increase in sensitivity of the nanocomposite TFS compared to its conventional metallic counterpart. [ABSTRACT FROM AUTHOR]

In this paper, we present the fabrication of an efficient thin film temperature sensor utilizing chemical vapor deposited carbon nanotube (CNT) film as the sensing element on Si substrates, with diamond-like carbon (DLC):Ni as a catalyst in assisting CNT growth. The fabricated sensor showed good electrical response with change in temperature. Relative linear change in resistance of 18.4% for an increase in temperature from 22 °C to 200 °C was achieved. Various characterizing techniques, such as scanning electron microscopy (SEM) and Raman spectroscopy, were used to characterize the films. In an effort to study device performance, van der Pauw and Hall measurements were carried out to study the dependence of resistance on temperature and magnetic fields. Temperature coefficient of resistance of the sensor was calculated as 1.03 × 10−3/°C. All implications arising from the study are presented. The results establish the aptness of the as-grown CNT film to be used as an active sensing material in thin film temperature sensors. [ABSTRACT FROM AUTHOR]