scholarly journals Morphology-driven gas sensing by fabricated fractals: A review

2021 ◽  
Vol 12 ◽  
pp. 1187-1208
Author(s):  
Vishal Kamathe ◽  
Rupali Nagar
Keyword(s):  
Fractal Dimension ◽  
Gas Sensors ◽  
Fractal Geometry ◽  
Gas Sensing ◽  
Network Connectivity ◽  
Hybrid Structure ◽  
Controlled Growth ◽  
Length Scales ◽  
Comprehensive Review ◽  
Gas Response

Fractals are intriguing structures that repeat themselves at various length scales. Interestingly, fractals can also be fabricated artificially in labs under controlled growth environments and be explored for various applications. Such fractals have a repeating unit that spans in length from nano- to millimeter range. Fractals thus can be regarded as connectors that structurally bridge the gap between the nano- and the macroscopic worlds and have a hybrid structure of pores and repeating units. This article presents a comprehensive review on inorganic fabricated fractals (fab-fracs) synthesized in labs and employed as gas sensors across materials, morphologies, and gas analytes. The focus is to investigate the morphology-driven gas response of these fab-fracs and identify key parameters of fractal geometry in influencing gas response. Fab-fracs with roughened microstructure, pore-network connectivity, and fractal dimension (D) less than 2 are projected to be possessing better gas sensing capabilities. Fab-fracs with these salient features will help in designing the commercial gas sensors with better performance.

A Strategy to Improve O2 Gas Response of La-SnO2 Nanofibers Based Sensor through Temperature Modulation

2019 ◽  
Vol 944 ◽  
pp. 657-665
Author(s):  
Ya Xiong ◽  
Hui Li ◽  
Tian Chao Guo ◽  
Qing Zhong Xue
Keyword(s):  
Gas Sensors ◽  
Gas Sensing ◽  
Operation Mode ◽  
Temperature Modulation ◽  
Oxide Semiconductors ◽  
Oxygen Ions ◽  
Isothermal Test ◽  
Sensor Temperature ◽  
Heating Energy Consumption ◽  
Gas Response

Generally sensing mechanisms of gas sensors based on metal-oxide semiconductors greatly depend on temperature, suggesting temperature modulation can be applied as a vital method to effectively enhance the sensor response. In this paper, we reported a strategy of quick-cooling operating temperature mode in the course of gas sensing process to elevate the O2 gas response while maintaining low heating energy consumption. La-SnO2 nanofibers synthesized by electrospinning were chosen as gas sensing materials. The O2 gas responses by employing quick-cooling operation mode are significantly improved compared with those obtained by traditional isothermal test. The improved O2 response is contributed to a higher coverage of negatively charged oxygen ions as a result of quick cooling. Our research offers a facile route to detect gas at low temperature with high response. More importantly, the strategy demonstrated here could also be extended to other gas sensor as long as its gas response is related to the sensor temperature.

Effect of Au Doped WO3 Gas Sensors for NO2 Detection

2011 ◽  
Vol 492 ◽  
pp. 308-311 ◽  
Author(s):  
Wu Bin Gao ◽  
Cheng Dong ◽  
Xu Liu ◽  
Yun Han Ling ◽  
Jia Lin Sun
Keyword(s):  
Gas Sensors ◽  
Gas Sensing ◽  
Point Contact ◽  
X Ray ◽  
Sensing Properties ◽  
Gas Sensing Properties ◽  
Tungsten Filaments ◽  
Gas Response ◽  
Contact Sensors

Gas sensor based on point contact tungsten trioxide (WO3) was prepared by in-situ induction-heating thermal oxidation of tungsten filaments. X-ray diffractometry (XRD) and field emission scanning electron microscopy (FESEM) were employed to analyze the phase and the morphology of the fabricated thin films. The results showed that the WO3films exhibited a monoclinic phase and were composed of hierarchical micro and nano crystals. The NO2(1-8 ppm) sensing properties of the point contact sensors based on Pure and Au-sputtering doped (2.5 at%) WO3films were investigated. The results showed that the gas sensing properties of the Au (2.5 at%) doped WO3sensors were superior to those of the undoped. The obtained point contact WO3sensor exhibited the maximum NO2gas response at 100°C.

Enhanced Gas Sensing of Tin Dioxide Based Sensor for Indoor Formaldehyde Application

2021 ◽  
Vol 16 (2) ◽  
pp. 337-342
Author(s):  
Gaoqi Zhang ◽  
Fan Zhang ◽  
Kaifang Wang ◽  
Shanyu Liu ◽  
Ying Wang ◽  
...  
Keyword(s):  
Gas Sensors ◽  
Tin Dioxide ◽  
Gas Sensing ◽  
Fast Response ◽  
Sensing Material ◽  
Gas Sensing Properties ◽  
Recovery Times ◽  
Response And Recovery ◽  
Formaldehyde Sensing ◽  
Gas Response

Indoor formaldehyde detection is of great important at present. Using efficient solvothermal method, nanosheet-constructed and nanorod-constructed hierarchical tin dioxide (SnO2) microspheres were successfully synthesized in this work and used for the gas sensing material for indoor formaldehyde application. The as-prepared two kinds of SnO2 gas sensing materials were applied to fabricate the gas sensors and formaldehyde gas sensing experiments were carried out. The HCHO gas sensing tests indicate that the gas response of the nanosheet-constructed SnO2 microspheres is about 1.7 times higher than that of the nanorod-constructed SnO2 microspheres. In addition, both of the two SnO2 based gas sensors show almost fast response and recovery time to HCHO gas. For the nanosheet-constructed microspheres, the response value is estimated to be 32.0 at 350 °C to 60 ppm formaldehyde gas, while the response and recovery times are 7 and 5 s, respectively. The simple and efficient preparation method and improved gas sensing properties show that the as-synthesized hierarchical SnO2 microsphere that is constructed by a large amount of nanosheets exhibits significant potential application for the indoor formaldehyde sensing.

scholarly journals ppb-Level Selective Hydrogen Gas Detection of Pd-Functionalized In2O3-Loaded ZnO Nanofiber Gas Sensors

Sensors ◽  
2019 ◽  
Vol 19 (19) ◽  
pp. 4276 ◽  
Author(s):  
Jae-Hyoung Lee ◽  
Jae-Hun Kim ◽  
Jin-Young Kim ◽  
Ali Mirzaei ◽  
Hyoun Woo Kim ◽  
...  
Keyword(s):  
Gas Sensors ◽  
Gas Sensing ◽  
Hydrogen Gas ◽  
Strong Response ◽  
Pd Nanoparticle ◽  
Highly Sensitive ◽  
Hydrogen Gas Sensors ◽  
Zno Nanofibers ◽  
Gas Response ◽  
Hydrogen Gas Detection

Pd nanoparticle-functionalized, xIn2O3 (x = 0.05, 0.1, and 0.15)-loaded ZnO nanofibers were synthesized by an electrospinning and ultraviolet (UV) irradiation method and assessed for their hydrogen gas sensing properties. Morphological and chemical analyses revealed the desired morphology and chemical composition of the synthesized nanofibers. The optimal gas sensor namely Pd-functionalized, 0.1In2O3-loaded ZnO nanofibers showed a very strong response to 172–50 ppb hydrogen gas at 350 °C, which is regarded as the optimal sensing temperature. Furthermore, the gas sensors showed excellent selectivity to hydrogen gas due to the much lower response to CO and NO2 gases. The enhanced gas response was attributed to the excellent catalytic activity of Pd to hydrogen gas, and the formation of Pd/ZnO and In2O3/ZnO heterojunctions, ZnO–ZnO homojunction, as well as the formation of PdHx. Overall, highly sensitive and selective hydrogen gas sensors can be produced based on a simple methodology using a synergistic effect from Pd functionalization and In2O3 loading in ZnO nanofibers.

Role of Fractal Geometry in Roughness Characterization and Contact Mechanics of Surfaces

1990 ◽  
Vol 112 (2) ◽  
pp. 205-216 ◽  
Author(s):  
A. Majumdar ◽  
B. Bhushan
Keyword(s):  
Fractal Dimension ◽  
Size Distribution ◽  
Power Law ◽  
Magnetic Tape ◽  
Fractal Geometry ◽  
Rough Surfaces ◽  
Statistical Parameters ◽  
Length Scales ◽  
Imperfect Contact ◽  
Contact Spots

A proper characterization of the multiscale topography of rough surfaces is very crucial for understanding several tribological phenomena. Although the multiscale nature of rough surfaces warrants a scale-independent characterization, conventional techniques use scale-dependent statistical parameters such as the variances of height, slope and curvature which are shown to be functions of the surface magnification. Roughness measurements on surfaces of magnetic tape, smooth and textured magnetic thin film rigid disks, and machined stainless steel surfaces show that their spectra follow a power law behavior. Profiles of such surfaces are, therefore, statistically self-affine which implies that when repeatedly magnified, increasing details of roughness emerge and appear similar to the original profile. This paper uses fractal geometry to characterize the multiscale self-affine topography by scale-independent parameters such as the fractal dimension. These parameters are obtained from the spectra of surface profiles. It was observed that surface processing techniques which produce deterministic texture on the surface result in non-fractal structure whereas those producing random texture yield fractal surfaces. For the magnetic tape surface, statistical parameters such as the r.m.s. peak height and curvature and the mean slope, which are needed in elastic contact models, are found to be scale-dependent. The imperfect contact between two rough surfaces is composed of a large number of contact spots of different sizes. The fractal representation of surfaces shows that the size-distribution of the multiscale contact spots follows a power law and is characterized by the fractal dimension of the surface. The surface spectra and the spot size-distribution follow power laws over several decades of length scales. Therefore, the fractal approach has the potential to predict the behavior of a surface phenomenon at a particular length scale from the observations at other length scales.

scholarly journals Effect of Growth Temperature and Time on Morphology and Gas Sensitivity of Cu2O/Cu Microstructures

2016 ◽  
Vol 2016 ◽  
pp. 1-10 ◽  
Author(s):  
Ling Wu ◽  
Lun Zhang ◽  
Zhipeng Xun ◽  
Guili Yu ◽  
Liwei Shi
Keyword(s):  
Electron Microscopy ◽  
Gas Sensors ◽  
Gas Sensing ◽  
Spherical Particles ◽  
X Ray Diffraction ◽  
Gas Sensitivity ◽  
X Ray ◽  
Transmission Electron ◽  
Wide Range ◽  
Gas Response

A facile hydrothermal synthesis with CuSO4as the copper source was used to prepare micro/nano-Cu2O. The obtained samples have been characterized by X-ray diffraction, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). With increasing the reaction temperature and time, the final products were successively Cu2O octahedron microcrystals, Cu2O/Cu composite particles, and a wide range of Cu spherical particles. The gas sensitivity of products towards ethanol and acetone gases was studied. The results showed that sensors prepared with Cu2O/Cu composites synthesized at 65°C for 15 min exhibited optimal gas sensitivity. The gas sensing mechanism and the effect of Cu in the enhanced gas response were also elaborated. The excellent gas sensitivity indicates that Cu2O/Cu composites have potential application as gas sensors.

Quantitative topographic analysis of fractal surfaces by scanning tunneling microscopy

1990 ◽  
Vol 5 (10) ◽  
pp. 2244-2254 ◽  
Author(s):  
Morgan W. Mitchell ◽  
Dawn A. Bonnell
Keyword(s):  
Brownian Motion ◽  
Fractal Dimension ◽  
Fracture Surface ◽  
Fourier Analysis ◽  
Scanning Tunneling Microscopy ◽  
Fractal Geometry ◽  
Scanning Tunneling ◽  
Tunneling Microscopy ◽  
Length Scales ◽  
Fractal Models

The applicability of models based on fractal geometry to length scales of nanometers is confirmed by Fourier analysis of scanning tunneling microscopy images of a sputter deposited gold film, a copper fatigue fracture surface, and a single crystal silicon fracture surface. Surfaces are characterized in terms of fractal geometry with a Fourier profile analysis, the calculations yielding fractal dimensions with high precision. Fractal models are shown to apply at length scales to 12 Å, at which point the STM tip geometry influences the information. Directionality and spatial variation of the topographic structures are measured. For the directions investigated, the gold and silicon appeared isotropic, while the copper fracture surface exhibited large differences in structure. The influences of noise in the images and of intrinsic mathematical scatter in the calculations are tested with profiles generated from fractal Brownian motion and the Weierstrass-Mandelbrot function. Accurate estimates of the fractal dimension of surfaces from STM data result only when images consist of at least 1000–2000 points per line and 1/f-type noise has amplitudes two orders of magnitude lower than the image signal. Analysis of computer generated ideal profiles from the Weierstrass-Mandelbrot function and fractional Brownian motion also illustrates that the Fourier analysis is useful only in determining the local fractal dimension. This requirement of high spatial resolution (vertical information density) is met by STM data. The fact that fractal models can be used at lengths as small as nanometers implies that continued topographic structural analyses may be used to study atomistic processes such as those occurring during fracture of elastic solids.

scholarly journals Improving Ammonia Detecting Performance of Polyaniline Decorated rGO Composite Membrane with GO Doping

Materials ◽  
2021 ◽  
Vol 14 (11) ◽  
pp. 2829
Author(s):  
Yubin Yuan ◽  
Haiyang Wu ◽  
Xiangrui Bu ◽  
Qiang Wu ◽  
Xuming Wang ◽  
...  
Keyword(s):  
Gas Sensors ◽  
Gas Sensing ◽  
Response Process ◽  
Ammonia Gas ◽  
Adsorption Sites ◽  
Nh3 Adsorption ◽  
Doped Polyaniline ◽  
Ammonia Gas Sensors ◽  
Gas Response ◽  
Sensing Performance

Gas-sensing performance of graphene-based material has been investigated widely in recent years. Polyaniline (PANI) has been reported as an effective method to improve ammonia gas sensors’ response. A gas sensor based on a composite of rGO film and protic acid doped polyaniline (PA-PANI) with GO doping is reported in this work. GO mainly provides NH3 adsorption sites, and PA-PANI is responsible for charge transfer during the gas-sensing response process. The experimental results indicate that the NH3 gas response of rGO is enhanced significantly by decorating with PA-PANI. Moreover, a small amount of GO mixed with PA-PANI is beneficial to increase the gas response, which showed an improvement of 262.5% at 25 ppm comparing to no GO mixing in PA-PANI.

NOx Gas Sensing Properties of Fe-Doped ZnO Nanoparticles

2020 ◽  
Vol 12 (6) ◽  
pp. 908-914 ◽  
Author(s):  
Ahmad Umar ◽  
M. Alduraibi ◽  
Omar Al-Dossary
Keyword(s):  
Gas Sensors ◽  
Zno Nanoparticles ◽  
Gas Sensing ◽  
Hydrothermal Process ◽  
Gas Sensing Properties ◽  
Recovery Times ◽  
Different Temperatures ◽  
Response And Recovery ◽  
Doped Zno ◽  
Gas Response

Herein, NOx, i.e., nitric oxide (NO) and nitrogen dioxide (NO2), gas sensors were fabricated using iron (Fe)-doped ZnO nanoparticles prepared via the facile hydrothermal process. The synthesized Fe-doped ZnO nanoparticles were analyzed through several techniques that revealed the well-crystallinity and dense growth of nanoparticles with the typical diameters of 25 ± 5 nm. The synthesized nanoparticles were utilized as a prospective material for the fabrication of NOx gas sensors operating at different temperatures, i.e., 350 °C, 400 °C, and 450 °C. The detailed sensing performances revealed that the optimum and most suitable sensing temperature for the fabricated sensors is 400 °C. In presence of 10 ppm NO gas, the fabricated sensor exhibited the highest gas response of 1.35 with a response (tresponse) and recovery (trecovery) time of 44 s and 402 s, respectively. Similarly, the fabricated NO2 gas sensor, in presence of 10 ppm gas shows the highest gas response of 1.33 with a response and recovery times of 50 s and 281 s, respectively. The presented results demonstrate that Fe-doped ZnO nanomaterials are capable to fabricate efficient NOx gas sensors.

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