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•Room temperature rapid detection of hydrogen with novel memristor based Pt/TiO2/Pt structure.•The Pt/TiO2 diffusion occurs more efficiently at bottom electrode than top ...electrode.•The sensor response improves in the presence of 50% relative humidity at room temperature.•The sensor response toward 1vol.% H2 is independent of operating temperature in the range of 24–100°C.
In this paper, a sensor with memristor electrode geometry (Pt/TiO2/Pt) was fabricated by a simple and cost-effective method yielding 106 orders of resistance change with short reaction times (Tres∼19 and Trec∼118s) when exposed to 1vol.% H2. Under wet conditions an increase in sensor response toward 1vol.% H2 independent of operating temperature RT–100°C (Tres∼5s) and a reasonable H2-selectivity was observed in the presence of CO and NO2. Such sensor characteristics with lower power consumption offer great advantages and are highly suitable for fuel cell and hydrogen safety applications. Despite the knowledge that hydrogen atoms accumulate at Pt/TiO2 interface reducing Schottky barrier height (i.e. decreasing the resistance of the Pt/TiO2 interface by several orders of magnitude) the details of the involved sensing mechanisms, especially under humidity, is still incomplete. The results confirm the existence of both electronic and ionic conductivity within TiO2 sensing layer and their significant alteration under hydrogen exposure. Thus a sensing model is proposed that fit exceptionally well with the memristor-type resistance variation principle. The understanding gained by the proposed model will allow the fabrication of innovative sensors for stable, selective and robust H2 detection.
Highlights
Two-dimensional materials including TMDCs, hBN, graphene, non-layered compounds, black phosphorous, Xenes and other emerging materials with large lateral dimensions exceeding a hundred ...micrometres are summarised detailing their synthetic strategies.
Crystal quality optimisations and defect engineering are discussed for large-area two-dimensional materials synthesis.
Electronics and optoelectronics applications enabled by large-area two-dimensional materials are explored.
.
Large-area and high-quality two-dimensional crystals are the basis for the development of the next-generation electronic and optical devices. The synthesis of two-dimensional materials in wafer scales is the first critical step for future technology uptake by the industries; however, currently presented as a significant challenge. Substantial efforts have been devoted to producing atomically thin two-dimensional materials with large lateral dimensions, controllable and uniform thicknesses, large crystal domains and minimum defects. In this review, recent advances in synthetic routes to obtain high-quality two-dimensional crystals with lateral sizes exceeding a hundred micrometres are outlined. Applications of the achieved large-area two-dimensional crystals in electronics and optoelectronics are summarised, and advantages and disadvantages of each approach considering ease of the synthesis, defects, grain sizes and uniformity are discussed.
Nanocrystalline Ni–Zn ferrites with different neodymium contents (Ni0.5Zn0.5NdxFe2-xO4) were synthesized by sol-gel route combined with self-propagating combustion (SPC) method. The presence of ...surface functional groups, crystal structure and morphology of the samples were studied by FT-IR, XRD and SEM. The results show that the prepared samples are composed of spinel phase under the condition of low neodymium content, like the pure Ni–Zn ferrite. While neodymium oxide appears after the content of Nd3+ exceeds a certain limit (x > 0.04) and there exist two phases in the ferrite. The results of vibrating sample magnetometer (VSM) and vector network analyzer (VNA) show that adjusting the content of Nd is significant in improving the dielectric properties and microwave absorption capacity of the materials, specifically at low frequencies. When x < 0.04, the enhancement of dielectric loss ability of spinel ferrites by doping Nd3+ is the dominant factor affecting microwave absorption ability of samples. The secondary phase Nd2O3 hardly appears under this condition, thus the weakening effect of Nd3+ addition on magnetic loss ability is not obvious. When x = 0.04, the optimal absorption peak of the material reaches −20.8 dB at 4.4 GHz with a thickness of 8.5 mm and the effective absorption bandwidth (RL < −10 dB) was 3.2 GHz. On the contrary, when x > 0.04, the magnetic loss ability decreases rapidly (e.g., Ms decreases from 82.47 emu/g to 59.77 emu/g). Meanwhile, the dielectric loss increases slowly and the microwave absorption capacity decreases.
This study presents the systematic potential effects of reaction parameters on the synthesis of Co-doped ZnNi ferrite/polyaniline composites prepared
novel interfacial polymerization. Through ...intensive experiments and analysis, optimum reaction conditions including the polymerization temperature and reaction time are proposed so that the performance of the material is significantly improved. The structure, functional groups and morphologies of composites are investigated by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Fourier transform-infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HRTEM). In addition, the electromagnetic properties and microwave absorption properties of Co-doped ZnNi ferrite/polyaniline composites are examined by a vibrating sample magnetometer (VSM), Quantum Design (MPMS-VSM and MPMS-XL), the superconducting quantum interference device (SQUID) magnetometer and vector network analysis. Based on these analyses, it is found that by tuning the reaction conditions,
, polymerization temperature and reaction time, microwave absorption capabilities in terms of the maximum reflection loss (
) value and absorber thickness can be readily optimized. The results show that the composite with an optimized polymerization condition of 20 °C for 12 h displays remarkable microwave absorption properties with maximum reflectivity of -54.3 dB, and the effective bandwidth (
< -10 dB) is about 6.02 GHz at a thickness of 6.8 mm. Furthermore, the discussion shows that the promising microwave absorption may be due to the uniform urchin-like structure of the composites.
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•Ag modified TiO2 porous NPs were successfully synthesized by one-pot hydrothermal method for acetone sensing applications.•Enhanced sensing performance of Ag modification was ...observed.•The sensing response can be significantly increased by reducing crystal sizes.
Titanium dioxide, owing to its manifold characteristics, specifically excellent sensitivity and stability under harsh environment, is considered as one of the probable replacements for VOCs gas sensing applications. The response of TiO2 is significantly influenced by its porosity and metal doping. To this context, this report demonstrates a facile one-pot hydrothermal method to synthesize porous TiO2 nanoparticles (NPs) modified with sliver (1–5 mol%). The gas sensing performance of the sensors was investigated by testing their gas response to acetone, which is proved of highly effective for sensor applications. For instance, the sensor based on 2 mol % Ag-TiO2 showed high response (SR ~ 13.9), fast response (11 s) and recovery (14 s) time, good long-term stability (30 days) and good selectivity (SF ~ 12.6) toward 100 ppm acetone against other VOCs. To understand and authenticate the sensing mechanism, the structure and morphology of synthesized NPs was performed by XRD, XPS, SEM, EDS, TEM and HRTEM. Furthermore, a plausible sensing mechanism is discussed on basis of the obtained results.
•The sandwich-like multilayer structure rGO/ZNCF/PANI composite is synthesized.•The uniform structure of composite has enhanced microwave absorption ability.•The composite prepared by in-situ ...polymerization has best microwave absorption.
The rise of modern communication devices has seriously imperiled human health due to electromagnetic (EM) pollution. In this context, the aim of this work is to develop novel reduced graphene oxide/Co-doped ZnNi ferrite/polyaniline ternary composites that exhibit enhanced microwave absorption properties. It is observed that the ternary composite prepared by in-situ polymerization show best EM absorption. The maximum reflection loss (RL) reaches −24.2 dB and the efficient bandwidth (RL < −10 dB) is more than 3 GHz with an absorbed thickness of 1.7 mm. The in-depth analysis based on complex permittivity and permeability reveals that the improved microwave absorption ability is related to the uniform sandwich-like multilayer structure and impedance compatibility of the ternary composites. The results and analysis show that these ternary composites with small thickness and wide absorption band are the potential candidates for microwave absorption applications.
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•Mathematical prediction of current density values up to 10 k cycles on the basis of experimentally measured 1000 cycles data.•Selection of most suitable linear or quadratic ...regression model used.•Using minimum percentage difference models between experimental and predicted curves.
A comparison is made among the peak current density values of 1000 cycles of experimental chronoamperometry for WO3-Nb2O5 films with the simulated values. Quadratic and linear regression models are developed by using MATLAB standard function ‘fitlm’ to get least MSE and ‘predict’ method to extrapolate the current density values. Initial 400, 500, and 600 experimental cycles are used as starting references for predictions. Predicted model having −0.09 percent change with the experimental curve is followed to predict 10,000 cyclic values with −4.73 % difference. Binding energy values for W6+ (35.9, 38.05 eV), W5+ (36.8, 34.65 eV) and Nb5+ (210.35, 207.55 eV) are measured.
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•Very simple and cost-effective strategy to fabricate H2-sensors based on nanocrystalline TiO2.•The sensor performance is excellent in terms of sensitivity, selectivity, stability, ...and reaction times.•It is found that the sensors can operate at low applied voltage (0.1 V) and can reduce the power consumption effectively.•The critical points for response inversion are defined as critical concentration (Cc), temperature (Tc) and voltage (VC).•This work also unveils the physics and chemistry of response inversion of TiO2 gas sensors.
In this report, we demonstrate a simple and cost-effective strategy to prepare polycrystalline rutile TiO2 based gas sensors with tunable n/p type response inversion depending on gas concentration, operating temperature, and applied voltage. The effect of surface modification by Ag and Ni thin film on structural, morphological, and gas sensor characteristics is studied in detail. The sensors show excellent sensing performance in terms of sensitivity (sensor response∼25 for 0.1 vol. % H2 diluted in technical air), selectivity (selectivity factor for 0.1 vol. % H2 is about ∼24 against NH3, CH4, and NO2 and ∼8 for CO in the same concentration range), stability (both long-term and short-term), and reaction times (∼0.7 min for 0.1 vol. % H2). The aforementioned performance is recorded at 300 °C with applied voltage of 0.1 V. Excluding the power consumption of sensor heater (typically ∼5 × 10−5 watt), this applied voltage 0.1 V can reduce the power consumption to 3 × 10−10 watt. For the first time, we found a critical point, defined with critical-concentration (Cc), critical-temperature (Tc) and critical-voltage (VC), at which the response inverses from one kind to another, something intriguing to novel sensing phenomena that can be exploited to tailor the selectivity of the sensors. A physical-chemical sensing model is presented to understand the aforesaid peculiar occurrence.
The paper demonstrated cost-effective one-step hydrothermal process to synthesize TiO
2
microrods modified with Cr
2
O
3
nanoparticles. The crystal structure, microstructure and chemical composition ...of the obtained materials were characterized by XRD, SEM, TEM and EDS analysis. Subsequently, for gas sensor tests the sensors were fabricated onto a ceramic tube having a designed pair of Au electrodes with four Pt wires. The results indicate that the sensors based on the optimal content of Cr
2
O
3
nanoparticles modified TiO
2
microrods possess excellent gas-sensing performance to acetone. Specifically, the sensor based on optimal 3% Cr
2
O
3
modified TiO
2
microrods exhibited high response (15), fast response/recovery time (5/28 s), outstanding selectivity (against 100 ppm ethanol, methanol and formaldehyde) and good stability (1–40 days) towards 100 ppm acetone at 300 °C. Relying on the analysis, we infer that performance can be controlled by varying the Cr
2
O
3
contents. A plausible sensing mechanism is also discussed to explain the reasons for the enhanced acetone sensing with Cr
2
O
3
–TiO
2
heterostructures.
Atomically thin two-dimensional (2D) metal oxides exhibit unique optical, electrical, magnetic, and chemical properties, rendering them a bright application prospect in high-performance smart ...devices. Given the large variety of both layered and non-layered 2D metal oxides, the controllable synthesis is the critical prerequisite for enabling the exploration of their great potentials. In this review, recent progress in the synthesis of 2D metal oxides is summarized and categorized. Particularly, a brief overview of categories and crystal structures of 2D metal oxides is firstly introduced, followed by a critical discussion of various synthesis methods regarding the growth mechanisms, advantages, and limitations. Finally, the existing challenges are presented to provide possible future research directions regarding the synthesis of 2D metal oxides. This work can provide useful guidance on developing innovative approaches for producing both 2D layered and non-layered nanostructures and assist with the acceleration of the research of 2D metal oxides.
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Applied sciences; Materials synthesis; Nanomaterials
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