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Nanomaterials, Volume 12, Issue 6 (March-2 2022) – 143 articles

Cover Story (view full-size image): The rapidly advancing technology of wearable and miniaturized electronics has increased the demand for low-cost high-performance flexible Ultraviolet (UV) sensors. Hiroaki Komatsu et al. developed translucent freestanding films consisting of cellulose nanofibers (CNFs) and ZnO nanoparticles (NPs), which exhibit a stable response over on/off cycles of UV light exposure. The responsivity and sensitivity of nanocomposite film with 60 wt.% ZnO were 36.5 mA/W and 247, respectively. The developed nanocomposite films are expected to be applied as environmentally friendly flexible UV sensors. View this paper
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Article
Experimental Study on the Quenching Behavior of a Copper Cube in the Cellulose Nanofiber Solution
Nanomaterials 2022, 12(6), 1033; https://doi.org/10.3390/nano12061033 - 21 Mar 2022
Viewed by 600
Abstract
This study investigates the quenching behavior and heat transfer characteristics of a copper cube immersed in cellulose nanofiber (CNF) solutions. The heat transfer performance of CNF solutions during boiling has been examined in several studies, but the quenching behavior of CNF solutions, which [...] Read more.
This study investigates the quenching behavior and heat transfer characteristics of a copper cube immersed in cellulose nanofiber (CNF) solutions. The heat transfer performance of CNF solutions during boiling has been examined in several studies, but the quenching behavior of CNF solutions, which is an important heat transfer method, has not been evaluated. In this study, four copper cubes with the same dimensions and four different quenchants (deionized water and 0.01%, 0.1% and 0.5% CNF solutions) were prepared. A copper cube heated to greater than 600 °C was submerged three times in the quenchant. This was repeated with different copper cubes in each of the quenchants. The time at which the heated copper cube convectively transferred heat to the surroundings was recorded. The cooling time was shortest when the cube was immersed in a 0.5% CNF solution for the first time. The average cooling time for quenching in the 0.5% CNF solution was 30.3% shorter than that in DI water. In this study, film boiling during quenching was thoroughly observed and analyzed to explain the cause of enhancement in heat transfer efficiency. Full article
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Article
Application of Mini-LEDs with Microlens Arrays and Quantum Dot Film as Extra-Thin, Large-Area, and High-Luminance Backlight
Nanomaterials 2022, 12(6), 1032; https://doi.org/10.3390/nano12061032 - 21 Mar 2022
Viewed by 863
Abstract
The demand for extra-thin, large-area, and high-luminance flat-panel displays continues to grow, especially for portable displays such as gaming laptops and automotive displays. In this paper, we propose a design that includes a light guide layer with a microstructure above the mini-light-emitting diode [...] Read more.
The demand for extra-thin, large-area, and high-luminance flat-panel displays continues to grow, especially for portable displays such as gaming laptops and automotive displays. In this paper, we propose a design that includes a light guide layer with a microstructure above the mini-light-emitting diode light board. The light control microstructure of concave parabel-surface microlens arrays on a light-emitting surface increases the likelihood of total internal reflection occurring and improved the uniformity merit function. We used a 17 in prototype with quantum-dot and optical films to conduct our experiments, which revealed that the thickness of the module was only 1.98 mm. When the input power was 28.34 watts, the uniformity, average luminance, and CIE 1931 color space NTSC of the prototype reached 85%, 17,574 cd/m2, and 105.37%, respectively. This module provided a flat light source that was extra thin and had high luminance and uniformity. Full article
(This article belongs to the Special Issue Quantum Dots and Micro-LED Display 2.0)
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Article
Dispersion of Multi-Walled Carbon Nanotubes into White Cement Mortars: The Effect of Concentration and Surfactants
Nanomaterials 2022, 12(6), 1031; https://doi.org/10.3390/nano12061031 - 21 Mar 2022
Cited by 5 | Viewed by 748
Abstract
Multi-wall carbon nanotubes (MWCNTs) exhibit exceptional mechanical and electrical properties and can be used to improve the mechanical and piezoelectric properties of cement-based materials. In the present study, the effect of different MWCNT concentrations as well as different types of surfactants and a [...] Read more.
Multi-wall carbon nanotubes (MWCNTs) exhibit exceptional mechanical and electrical properties and can be used to improve the mechanical and piezoelectric properties of cement-based materials. In the present study, the effect of different MWCNT concentrations as well as different types of surfactants and a superplasticizer were examined to reinforce, at the nanoscale, a white cement mortar typically used for the restoration of monuments of cultural heritage. It was shown that sodium dodecylbenzenesulfonate (SDBS) and Triton X-100 surfactants slightly decreased the white cement mortars’ electrical resistivity (by an average of 10%), however, the mechanical properties were essentially decreased by an average of 60%. The most suitable dispersion agent for the MWCNTs proved to be the superplasticizer Ceresit CC198, and its optimal concentration was investigated for different MWCNT concentrations. Carboxylation of the MWCNT surface with nitric acid did not improve the mechanical performance of the white cement nanocomposites. The parametric experimental study showed that the optimum combination of 0.8 wt% of cement superplasticizer and 0.2 wt% of cement MWCNTs resulted in a 60% decrease in the electrical resistivity; additionally, the flexural and compressive strengths were both increased by approximately 25% and 10%, respectively. Full article
(This article belongs to the Special Issue Hybrid Porous Nanomaterials for Energy and Environment)
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Article
Simulation and Experimental Study of the Multisized Silver Nanoparticles Sintering Process Based on Molecular Dynamics
Nanomaterials 2022, 12(6), 1030; https://doi.org/10.3390/nano12061030 - 21 Mar 2022
Viewed by 698
Abstract
Multisized nanoparticles (MPs) are widely employed as electronic materials to form conductive patterns, benefitting from their excellent sintering properties and mechanical reliability. However, due to the lack of effective detection methods for the real-time sintering process, it is difficult to reveal the sintering [...] Read more.
Multisized nanoparticles (MPs) are widely employed as electronic materials to form conductive patterns, benefitting from their excellent sintering properties and mechanical reliability. However, due to the lack of effective detection methods for the real-time sintering process, it is difficult to reveal the sintering behavior during the MPs sintering process. In this work, a molecular dynamics method is used to track the trajectory of silver atoms. The melting behavior of a single nanoparticle (SP) is first discussed. The structural evolution of equally sized nanoparticles (EPs) and unequally sized nanoparticles (UPs) during the sintering process is analyzed alongside morphology changes. It is proposed that the UPs sintering process benefits from the wetting behavior of small-sized nanoparticles on the surface of large-sized nanoparticles, and the sintering angle (θ) is proposed as an index to estimate the sintering result of UPs. Based on the works above, three basic sintering modes and one advanced sintering mode in the MP sintering process are analyzed emphatically in this paper, and the roles of different-sized nanoparticles in MPs are concluded from simulation and experimental results. This work provides theoretical support for conductive ink composition design and sintering process optimization. Full article
(This article belongs to the Section Theory and Simulation of Nanostructures)
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Article
Improved Performance of NbOx Resistive Switching Memory by In-Situ N Doping
Nanomaterials 2022, 12(6), 1029; https://doi.org/10.3390/nano12061029 - 21 Mar 2022
Cited by 1 | Viewed by 696
Abstract
Valence change memory (VCM) attracts numerous attention in memory applications, due to its high stability and low energy consumption. However, owing to the low on/off ratio of VCM, increasing the difficulty of information identification hinders the development of memory applications. We prepared N-doped [...] Read more.
Valence change memory (VCM) attracts numerous attention in memory applications, due to its high stability and low energy consumption. However, owing to the low on/off ratio of VCM, increasing the difficulty of information identification hinders the development of memory applications. We prepared N-doped NbOx:N films (thickness = approximately 15 nm) by pulsed laser deposition at 200 °C. N-doping significantly improved the on/off ratio, retention time, and stability of the Pt/NbOx:N/Pt devices, thus improving the stability of data storage. The Pt/NbOx:N/Pt devices also achieved lower and centralized switching voltage distribution. The improved performance was mainly attributed to the formation of oxygen vacancy (VO) + 2N clusters, which greatly reduced the ionic conductivity and total energy of the system, thus increasing the on/off ratio and stability. Moreover, because of the presence of Vo + 2N clusters, the conductive filaments grew in more localized directions, which led to a concentrated distribution of SET and RESET voltages. Thus, in situ N-doping is a novel and effective approach to optimize device performances for better information storage and logic circuit applications. Full article
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Article
Borophene and Pristine Graphene 2D Sheets as Potential Surfaces for the Adsorption of Electron-Rich and Electron-Deficient π-Systems: A Comparative DFT Study
Nanomaterials 2022, 12(6), 1028; https://doi.org/10.3390/nano12061028 - 21 Mar 2022
Cited by 1 | Viewed by 1091
Abstract
The versatility of striped borophene (sB), β12 borophene (β12), and pristine graphene (GN) to adsorb π-systems was comparatively assessed using benzene (BNZ) and hexafluorobenzene (HFB) as electron-rich and electron-deficient aromatic π-systems, respectively. Using the density functional theory (DFT) method, [...] Read more.
The versatility of striped borophene (sB), β12 borophene (β12), and pristine graphene (GN) to adsorb π-systems was comparatively assessed using benzene (BNZ) and hexafluorobenzene (HFB) as electron-rich and electron-deficient aromatic π-systems, respectively. Using the density functional theory (DFT) method, the adsorption process of the π-systems on the investigated 2D sheets in the parallel configuration was observed to have proceeded more favorably than those in the vertical configuration. According to the observations of the Bader charge transfer analysis, the π-system∙∙∙sB complexes were generally recorded with the largest contributions of charge transfer, followed by the π-system∙∙∙β12 and ∙∙∙GN complexes. The band structures of the pure sheets signaled the metallic and semiconductor characters of the sB/β12 and GN surfaces, respectively. In the parallel configuration, the adsorption of both BNZ and HFB showed more valence and conduction bands compared to the adsorption in the vertical configuration, revealing the prominent preferentiality of the anterior configuration. The density-of-states (DOSs) results also affirmed that the adsorption process of the BNZ and HFB on the surface of the investigated 2D sheets increased their electrical properties. In all instances, the sB and β12 surfaces demonstrated higher adsorptivity towards the BNZ and HFB than the GN analog. The findings of this work could make a significant contribution to the deep understanding of the adsorption behavior of aromatic π-systems toward 2D nanomaterials, leading, in turn, to their development of a wide range of applications. Full article
(This article belongs to the Special Issue Graphene and Related 2D Materials)
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Review
Metamaterials and Metasurfaces: A Review from the Perspectives of Materials, Mechanisms and Advanced Metadevices
Nanomaterials 2022, 12(6), 1027; https://doi.org/10.3390/nano12061027 - 21 Mar 2022
Cited by 6 | Viewed by 1433
Abstract
Throughout human history, the control of light, electricity and heat has evolved to become the cornerstone of various innovations and developments in electrical and electromagnetic technologies. Wireless communications, laser and computer technologies have all been achieved by altering the way light and other [...] Read more.
Throughout human history, the control of light, electricity and heat has evolved to become the cornerstone of various innovations and developments in electrical and electromagnetic technologies. Wireless communications, laser and computer technologies have all been achieved by altering the way light and other energy forms act naturally and how to manage them in a controlled manner. At the nanoscale, to control light and heat, matured nanostructure fabrication techniques have been developed in the last two decades, and a wide range of groundbreaking processes have been achieved. Photonic crystals, nanolithography, plasmonics phenomena and nanoparticle manipulation are the main areas where these techniques have been applied successfully and led to an emergent material sciences branch known as metamaterials. Metamaterials and functional material development strategies are focused on the structures of the matter itself, which has led to unconventional and unique electromagnetic properties through the manipulation of light—and in a more general picture the electromagnetic waves—in widespread manner. Metamaterial’s nanostructures have precise shape, geometry, size, direction and arrangement. Such configurations are impacting the electromagnetic light waves to generate novel properties that are difficult or even impossible to obtain with natural materials. This review discusses these metamaterials and metasurfaces from the perspectives of materials, mechanisms and advanced metadevices in depth, with the aim to serve as a solid reference for future works in this exciting and rapidly emerging topic. Full article
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Article
Highly Sensitive and Stable Humidity Sensor Based on the Bi-Layered PVA/Graphene Flower Composite Film
Nanomaterials 2022, 12(6), 1026; https://doi.org/10.3390/nano12061026 - 21 Mar 2022
Cited by 4 | Viewed by 779
Abstract
Two-dimensional (2D) materials and their composites have gained significant importance as the functional layer of various environmental sensors and nanoelectronics owing to their unique properties. This work reports for the first time a highly sensitive, fast, and stable humidity sensor based on the [...] Read more.
Two-dimensional (2D) materials and their composites have gained significant importance as the functional layer of various environmental sensors and nanoelectronics owing to their unique properties. This work reports for the first time a highly sensitive, fast, and stable humidity sensor based on the bi-layered active sensing area composed of graphene flower (GF) and poly (vinyl alcohol) PVA thin films for multifunctional applications. The GF/PVA humidity sensor exhibited stable impedance response over 15 days, for a relative humidity (RH) range of (40–90% RH) under ambient operating conditions. The proposed bi-layered humidity sensor also exhibited an ultra-high capacitive sensitivity response of the 29 nF/%RH at 10 kHz and fast transient response of 2 s and 3.5 s, respectively. Furthermore, the reported sensor also showed a good response towards multi-functional applications such as non-contact skin humidity and mouth breathing detection. Full article
(This article belongs to the Special Issue Electrochemical Properties and Applications of Nanomaterials)
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Article
Simultaneously Enhancing the Strength, Plasticity, and Conductivity of Copper Matrix Composites with Graphene-Coated Submicron Spherical Copper
Nanomaterials 2022, 12(6), 1025; https://doi.org/10.3390/nano12061025 - 21 Mar 2022
Viewed by 694
Abstract
In this study, Cu matrix composites reinforced with reduced graphene oxide-coated submicron spherical Cu ([email protected]) exhibiting both high-strength plastic product (UT) and high electrical conductivity (EC) were prepared. [email protected] results in the formation of Cu4O3 and Cu2O nanotransition [...] Read more.
In this study, Cu matrix composites reinforced with reduced graphene oxide-coated submicron spherical Cu ([email protected]) exhibiting both high-strength plastic product (UT) and high electrical conductivity (EC) were prepared. [email protected] results in the formation of Cu4O3 and Cu2O nanotransition layers to optimize the interface combination. In addition, as a flow carrier, [email protected] can also render graphene uniformly dispersed. The results show that [email protected] has a significant strengthening effect on the Cu matrix composites. The relative density (RD) of the [email protected]/Cu composites exceeds 95%, and the hardness, UT, and yield strength (YS) reach 106.8 HV, 14,455 MPa% (tensile strength (TS) 245 MPa, elongation (EL) 59%), and 119 MPa; which are 21%, 72%, and 98% higher than those of Cu, respectively. Furthermore, EC is 95% IACS (International Annealed Copper Standard), which is also higher than that of Cu. The strength mechanisms include transfer load strengthening, dislocation strengthening, and grain refinement strengthening. The plastic mechanisms include the coordinated deformation of the interface of the Cu4O3 and Cu2O nanotransition layers and the increase in the fracture energy caused by graphene during the deformation process. The optimized EC is due to [email protected] constructing bridges between the large-size Cu grains, and graphene on the surface provides a fast path for electron motion. This path compensates for the negative influence of grain refinement and the sintering defects on EC. The reduced graphene oxide-reinforced Cu-matrix composites were studied, and it was found that the comprehensive performance of the [email protected]/Cu composites is superior to that of the rGO/Cu composites in all aspects. Full article
(This article belongs to the Topic Metal Matrix Composites: Recent Advancements)
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Article
Resonant Tunneling Diodes: Mid-Infrared Sensing at Room Temperature
Nanomaterials 2022, 12(6), 1024; https://doi.org/10.3390/nano12061024 - 21 Mar 2022
Viewed by 967
Abstract
Resonant tunneling diode photodetectors appear to be promising architectures with a simple design for mid-infrared sensing operations at room temperature. We fabricated resonant tunneling devices with GaInAsSb absorbers that allow operation in the 24 μm range with significant electrical responsivity of [...] Read more.
Resonant tunneling diode photodetectors appear to be promising architectures with a simple design for mid-infrared sensing operations at room temperature. We fabricated resonant tunneling devices with GaInAsSb absorbers that allow operation in the 24 μm range with significant electrical responsivity of 0.97 A/W at 2004 nm to optical readout. This paper characterizes the photosensor response contrasting different operational regimes and offering a comprehensive theoretical analysis of the main physical ingredients that rule the sensor functionalities and affect its performance. We demonstrate how the drift, accumulation, and escape efficiencies of photogenerated carriers influence the electrostatic modulation of the sensor’s electrical response and how they allow controlling the device’s sensing abilities. Full article
(This article belongs to the Special Issue Semiconductor and Nanophotonic Devices)
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Article
Highly Selective Removal of Cationic Dyes from Wastewater by MgO Nanorods
Nanomaterials 2022, 12(6), 1023; https://doi.org/10.3390/nano12061023 - 21 Mar 2022
Cited by 3 | Viewed by 794
Abstract
The organic synthetic dyes employed in industries are carcinogenic and harmful. Dyes must be removed from wastewater to limit or eliminate their presence before dumping into the natural environment. The current study aims to investigate the use of MgO nanoparticles to eliminate basic [...] Read more.
The organic synthetic dyes employed in industries are carcinogenic and harmful. Dyes must be removed from wastewater to limit or eliminate their presence before dumping into the natural environment. The current study aims to investigate the use of MgO nanoparticles to eliminate basic fuchsine (BF), as a model cationic dye pollutant, from wastewater. The MgO nanorods were synthesized through a coprecipitation method. The obtained nanocomposite was characterized using various techniques such as X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), Brunauer–Emmett–Teller (BET), and FTIR spectroscopy. It was found that the variation of dye concentration and pH influenced the removal of BF by MgO. The adsorption capacity of 493.90 mg/g is achieved under optimum operating conditions (pH = 11, contact time = 236 min, and initial BF concentration = 200 ppm). Pseudo-second-order adsorption kinetics and Freundlich isotherm models best fitted BF sorption onto MgO nanorods. The BF sorption mechanism is associated with the electrostatic attractions and hydrogen bond between the O–H group of MgO and the NH2 groups of BF, as indicated by the pH, isotherms, and FTIR studies. The reusability study indicates that MgO was effectively used to eliminate BF in at least four continuous cycles. The investigation of MgO with different dyes suggests the high adsorption selectivity of BF, crystal violet (CV), and malachite green (MG) dyes compared with methyl orange (MO) dye. Overall, MgO nanorods can act as a potential and promising adsorbent for the efficient and rapid removal of cationic dyes (CV, MG, and BF) from wastewater. Full article
(This article belongs to the Special Issue Nanomaterials for Sustainable Energy and Environmental Protection)
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Article
Deformation Mechanism of Depositing Amorphous Cu-Ta Alloy Film via Nanoindentation Test
Nanomaterials 2022, 12(6), 1022; https://doi.org/10.3390/nano12061022 - 21 Mar 2022
Cited by 2 | Viewed by 758
Abstract
As a representative of immiscible alloy systems, the Cu-Ta system was the research topic because of its potential application in industry, military and defense fields. In this study, an amorphous Cu-Ta alloy film was manufactured through magnetron sputter deposition, which was characterized by [...] Read more.
As a representative of immiscible alloy systems, the Cu-Ta system was the research topic because of its potential application in industry, military and defense fields. In this study, an amorphous Cu-Ta alloy film was manufactured through magnetron sputter deposition, which was characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Mechanical properties of Cu-Ta film were detected by the nanoindentation method, which show that the elastic modulus of Cu3.5Ta96.5 is 156.7 GPa, and the hardness is 14.4 GPa. The nanoindentation process was also simulated by molecular dynamic simulation to indicate the deformation mechanism during the load-unload stage. The simulation results show that the structure <0,2,8,4> and <0,2,8,5> Voronoi cells decreased by 0.1% at 50 Ps and then remained at this value during the nanoindentation process. In addition, the number of dislocations vary rapidly with the depth between indenter and surface. Based on the experimental and simulation results, the Voronoi structural changes and dislocation motions are the key reasons for the crystallization of amorphous alloys when loads are applied. Full article
(This article belongs to the Special Issue Nanotechnologies and Nanomaterials: Selected Papers from CCMR)
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Article
Rheological and Thermal Conductivity Study of Two-Dimensional Molybdenum Disulfide-Based Ethylene Glycol Nanofluids for Heat Transfer Applications
Nanomaterials 2022, 12(6), 1021; https://doi.org/10.3390/nano12061021 - 21 Mar 2022
Viewed by 702
Abstract
The rheological behavior of two-dimensional (2D) MoS2-based ethylene glycol (EG) nanofluids (NFs) was investigated at low volume concentrations (0.005%, 0.0075%, and 0.01%) in a wide temperature range of 0–70 °C and at atmospheric pressure. A conventional two-step method was followed to [...] Read more.
The rheological behavior of two-dimensional (2D) MoS2-based ethylene glycol (EG) nanofluids (NFs) was investigated at low volume concentrations (0.005%, 0.0075%, and 0.01%) in a wide temperature range of 0–70 °C and at atmospheric pressure. A conventional two-step method was followed to prepare NFs at desired volume concentrations. Based on the control rotational (0.1–1000 s−1 shear rate) and oscillation (0.01–1000% strain) methods, the viscoelastic flow curves and thixotropic (3ITT (three interval thixotropic) and hysteresis loop) characteristics of NFs were examined. Shear flow behavior revealed a remarkable reduction (1.3~14.7%) in apparent dynamic viscosity, which showed concentration and temperature dependency. Such remarkable viscosity results were assigned to the change in activation energy of the ethylene glycol with the addition of MoS2. However, the nanofluids exhibited Newtonian behavior at all temperatures for concentrations below 0.01% between 10 and 1000 s−1. On the other hand, strain sweep (@1Hz) indicated the viscoelastic nature of NFs with yielding, which varied with concentration and temperature. Besides, 3ITT and hysteresis loop analysis was evident of non-thixotropic behavior of NFs. Among all tested concentrations, 0.005% outperformed at almost all targeted temperatures. At the same time, ~11% improvement in thermal conductivity can be considered advantageous on top of the improved rheological properties. In addition, viscosity enhancement and reduction mechanisms were also discussed. Full article
(This article belongs to the Special Issue Thermal Properties of Nanomaterials: Fundamentals and Applications)
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Article
Nonlinear Optical Rectification in an Inversion-Symmetry-Broken Molecule near a Metallic Nanoparticle
Nanomaterials 2022, 12(6), 1020; https://doi.org/10.3390/nano12061020 - 21 Mar 2022
Cited by 1 | Viewed by 628
Abstract
We study the nonlinear optical rectification of an inversion-symmetry-broken quantum system interacting with an optical field near a metallic nanoparticle, exemplified in a polar zinc–phthalocyanine molecule in proximity to a gold nanosphere. The corresponding nonlinear optical rectification coefficient under external strong field excitation [...] Read more.
We study the nonlinear optical rectification of an inversion-symmetry-broken quantum system interacting with an optical field near a metallic nanoparticle, exemplified in a polar zinc–phthalocyanine molecule in proximity to a gold nanosphere. The corresponding nonlinear optical rectification coefficient under external strong field excitation is derived using the steady-state solution of the density matrix equations. We use ab initio electronic structure calculations for determining the necessary spectroscopic data of the molecule under study, as well as classical electromagnetic calculations for obtaining the influence of the metallic nanoparticle to the molecular spontaneous decay rates and to the external electric field applied to the molecule. The influence of the metallic nanoparticle to the optical rectification coefficient of the molecule is investigated by varying several parameters of the system, such as the intensity and polarization of the incident field, as well as the distance of the molecule from the nanoparticle, which indirectly affects the molecular pure dephasing rate. We find that the nonlinear optical rectification coefficient can be greatly enhanced for particular incident-field configurations and at optimal distances between the molecule and the metallic nanoparticle. Full article
(This article belongs to the Special Issue Metallic-Nanoparticle Structures and Quantum-Emitters)
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Article
Double-Focusing Gradient-Index Lens with Elastic Bragg Mirror for Highly Efficient Energy Harvesting
Nanomaterials 2022, 12(6), 1019; https://doi.org/10.3390/nano12061019 - 21 Mar 2022
Cited by 1 | Viewed by 819
Abstract
The applicability of piezoelectric energy harvesting is increasingly investigated in the field of renewable energy. In improving harvester efficiency, manipulating elastic waves through a geometric configuration as well as upgrading harvester elements is important. Periodic structures, such as phononic crystals and metamaterials, are [...] Read more.
The applicability of piezoelectric energy harvesting is increasingly investigated in the field of renewable energy. In improving harvester efficiency, manipulating elastic waves through a geometric configuration as well as upgrading harvester elements is important. Periodic structures, such as phononic crystals and metamaterials, are extensively employed to control elastic waves and enhance harvesting performance, particularly in terms of wave localization and focusing. In this study, we propose a double-focusing flexural energy harvesting platform consisting of a gradient-index lens and elastic Bragg mirror. Based on the design process, the frequency and time response of the harvesting platform are analyzed. The results indicate that the output voltage and power calculated at 1800 Ω are 7.9 and 62 times higher than those observed in the bare plate, respectively. Even when compared to the existing gradient-index system, they are 1.5 and 2.3 times higher, respectively. These findings can facilitate the usage of periodic structures as geometric stimuli to significantly enhance harvesting performance. Full article
(This article belongs to the Special Issue Properties and Applications of Metamaterials)
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Article
Scalable Production of High-Quality Silver Nanowires via Continuous-Flow Droplet Synthesis
Nanomaterials 2022, 12(6), 1018; https://doi.org/10.3390/nano12061018 - 21 Mar 2022
Viewed by 744
Abstract
Silver nanowires (Ag NWs) have shown great potential in next-generation flexible displays, due to their superior electronic, optical, and mechanical properties. However, as with most nanomaterials, a limited production capacity and poor reproduction quality, based on the batch reaction, largely hinder their application. [...] Read more.
Silver nanowires (Ag NWs) have shown great potential in next-generation flexible displays, due to their superior electronic, optical, and mechanical properties. However, as with most nanomaterials, a limited production capacity and poor reproduction quality, based on the batch reaction, largely hinder their application. Here, we applied continuous-flow synthesis for the scalable and high-quality production of Ag NWs, and built a pilot-scale line for kilogram-level per day production. In addition, we found that trace quantities of water could generate sufficient vapor as a spacer under high temperature to efficiently prevent the back-flow or mixed-flow of the reaction solution. With an optimized synthetic formula, a mass production of pure Ag NWs of 36.5 g/h was achieved by a multiple-channel, continuous-flow reactor. Full article
(This article belongs to the Topic Synthesis and Applications of Nanowires)
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Article
Room-Temperature, Ionic-Liquid-Enhanced, Beta-Cyclodextrin-Based, Molecularly Imprinted Polymers for the Selective Extraction of Abamectin
Nanomaterials 2022, 12(6), 1017; https://doi.org/10.3390/nano12061017 - 20 Mar 2022
Cited by 1 | Viewed by 757
Abstract
To ensure environmental protection and food quality and safety, the trace level detection of pesticide residues with molecularly imprinted polymers using a more economic, reliable, and greener approach is always demanded. Herein, novel, enhanced, imprinted polymers based on beta-cyclodextrin, using room-temperature, ionic liquid [...] Read more.
To ensure environmental protection and food quality and safety, the trace level detection of pesticide residues with molecularly imprinted polymers using a more economic, reliable, and greener approach is always demanded. Herein, novel, enhanced, imprinted polymers based on beta-cyclodextrin, using room-temperature, ionic liquid as a solvent for abamectin were developed with a simple polymerization process. The successful synthesis of the polymers was verified, with morphological and structural characterization performed via scanning electron microscope analysis, nitrogen adsorption experiments, and thermogravimetric analysis. The imprinted polymers showed good adsorption ability, which was confirmed with a pseudo-second-order kinetic model and a Langmuir isotherm model, as they exhibit a theoretical adsorption of 15.08 mg g−1 for abamectin. The polymers showed high selectivity for abamectin and significant reusability without significant performance loss. The MIPs were used to analyze abamectin in spiked apple, banana, orange, and grape samples, and as a result, a good recovery of 81.67−101.47%, with 1.26−4.36% relative standard deviation, and limits of detection and quantitation of 0.02 µg g−1 and 0.05 µg g−1, respectively, was achieved within a linear range of 0.03−1.50 µg g−1. Thus, room-temperature, ionic-liquid-enhanced, beta-cyclodextrin-based, molecularly imprinted polymers for the selective detection of abamectin proved to be a convenient and practical platform. Full article
(This article belongs to the Special Issue Advances in Molecularly Imprinted Polymer Nanomaterials)
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Article
Majorana Anyon Composites in Magneto-Photoluminescence Spectra of Natural Quantum Hall Puddles
Nanomaterials 2022, 12(6), 1016; https://doi.org/10.3390/nano12061016 - 20 Mar 2022
Viewed by 600
Abstract
In magneto-photoluminescence (magneto-PL) spectra of quasi two-dimensional islands (quantum dots) having seven electrons and Wigner–Seitz radius rs~1.5, we revealed a suppression of magnetic field (B) dispersion, paramagnetic shifts, and jumps of the energy of the emission components for filling [...] Read more.
In magneto-photoluminescence (magneto-PL) spectra of quasi two-dimensional islands (quantum dots) having seven electrons and Wigner–Seitz radius rs~1.5, we revealed a suppression of magnetic field (B) dispersion, paramagnetic shifts, and jumps of the energy of the emission components for filling factors ν > 1 (B < 10 T). Additionally, we observed B-hysteresis of the jumps and a dependence of all these anomalous features on rs. Using a theoretical description of the magneto-PL spectra and an analysis of the electronic structure of these dots based on the single-particle Fock–Darwin spectrum and many-particle configuration-interaction calculations, we show that these observations can be described by the rs-dependent formation of the anyon (magneto-electron) composites (ACs) involving single-particle states having non-zero angular momentum and that the anyon states observed involve Majorana modes (MMs), including zero-B modes having an equal number of vortexes and anti-vortexes, which can be considered as Majorana anyons. We show that the paramagnetic shift corresponds to a destruction of the equilibrium self-formed ν~5/2 AC by the external magnetic field and that the jumps and their hysteresis can be described in terms of Majorana qubit states controlled by B and rs. Our results show a critical role of quantum confinement in the formation of magneto-electrons and implies the liquid-crystal nature of fractional quantum Hall effect states, the Majorana anyon origin of the states having even ν, i.e., composite fermions, which provide new opportunities for topological quantum computing. Full article
(This article belongs to the Special Issue Quantum Dots)
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Article
Carbon Nanotubes Interconnected NiCo Layered Double Hydroxide Rhombic Dodecahedral Nanocages for Efficient Oxygen Evolution Reaction
Nanomaterials 2022, 12(6), 1015; https://doi.org/10.3390/nano12061015 - 20 Mar 2022
Cited by 1 | Viewed by 857
Abstract
Proper control of a 3d transition metal-based catalyst with advanced structures toward oxygen evolution reaction (OER) with a more feasible synthesis strategy is of great significance for sustainable energy-related devices. Herein, carbon nanotube interconnected NiCo layered double hydroxide rhombic dodecahedral nanocages (NiCo-LDH [...] Read more.
Proper control of a 3d transition metal-based catalyst with advanced structures toward oxygen evolution reaction (OER) with a more feasible synthesis strategy is of great significance for sustainable energy-related devices. Herein, carbon nanotube interconnected NiCo layered double hydroxide rhombic dodecahedral nanocages (NiCo-LDH [email protected]) were developed here with the assistance of a feasible zeolitic imidazolate framework (ZIF) self-sacrificing template strategy as a highly efficient OER electrocatalyst. Profited by the well-fined rhombic dodecahedral nanocage architecture, CNTs’ interconnected characteristic and structural feature of the vertically aligned nanosheets, the as-synthesized NiCo-LDH [email protected] integrated large exposed active surface areas, enhanced electron transfer capacity and multidimensional mass diffusion channels, and thereby collaboratively afforded the remarkable electrocatalytic performance of the OER. Specifically, the designed NiCo-LDH [email protected] exhibited a distinguished OER activity, which only required a low overpotential of 255 mV to reach a current density of 10 mA cm−2 for the OER. For the stability, no obvious current attenuation was detected, even after continuous operation for more than 27 h. We certainly believe that the current extraordinary OER activity combined with the robust stability of NiCo-LDH [email protected] enables it to be a great candidate electrocatalyst for economical and sustainable energy-related devices. Full article
(This article belongs to the Special Issue Electrocatalysts for Fuel Cell Reactions in Alkaline Media)
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Article
Effect of Radial Stress on the Nanoparticle-Based Electrolyte Layer in a Center-Wound Roll with Roll-to-Roll Systems
Nanomaterials 2022, 12(6), 1014; https://doi.org/10.3390/nano12061014 - 20 Mar 2022
Viewed by 955
Abstract
Recently, slot-die coating based on the roll-to-roll process has been actively used to fabricate nanoparticle-based electrolyte layers because it is advantageous for high-speed processes and mass production of uniformly thick electrolyte layers. In this process, the fabricated electrolyte layer is stored as a [...] Read more.
Recently, slot-die coating based on the roll-to-roll process has been actively used to fabricate nanoparticle-based electrolyte layers because it is advantageous for high-speed processes and mass production of uniformly thick electrolyte layers. In this process, the fabricated electrolyte layer is stored as a wound roll throughout the rewinding process. We analyzed the defects and geometric changes in an electrolyte layer, i.e., gadolinium-doped cerium oxide (GDC), due to the radial stress in the wound roll. We found that the thickness of the coated layer could be decreased by increasing the radial stress, i.e., cracks can be generated in the coated layer if excessively high radial stress is applied to the wound-coated layer. More thickness changes and crack defects were generated with time due to the residual stress in the wound roll. Finally, we analyzed the effects of taper tension profiles on the defects of the coated layer in the wound roll and determined the taper tension profile to minimize defects. Full article
(This article belongs to the Special Issue Nanomaterials for Printed Electronics and Bioelectronics)
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Article
WC-High Entropy Alloy Reinforced Long Life Self-Grinding Silage Knife Prepared by Laser Cladding
Nanomaterials 2022, 12(6), 1013; https://doi.org/10.3390/nano12061013 - 19 Mar 2022
Cited by 1 | Viewed by 780
Abstract
The working environment of agricultural knives is bad, which makes the knives wear out easily. A wear resistant layer of AlCoCrFeNi high entropy alloy (HEA) reinforced by tungsten carbide (WC) was prepared by laser cladding on one side of the cutting edge of [...] Read more.
The working environment of agricultural knives is bad, which makes the knives wear out easily. A wear resistant layer of AlCoCrFeNi high entropy alloy (HEA) reinforced by tungsten carbide (WC) was prepared by laser cladding on one side of the cutting edge of a 65 Mn silage knife. Both the effects of WC addition on the microstructure and mechanical properties of AlCoCrFeNi (WC)x (x = 0, 0.1, 0.2 and 0.3 in mass percentage) alloys were investigated. All experimental alloys displayed a crystalline structure of simple body centered cubic (BCC). The hardness of the cladding layer increases with the increase of WC content, and the hardness value enhances from 740 HV0.2 to 1060 HV0.2. A self-grinding edge was formed during working for the cladded knives. The cutting quality can be improved and the service life of agricultural knives can be increased meanwhile. The weight loss rate of untreated knives was about 2.64 times that of the cladded knives after a 76 h field experiment. Full article
(This article belongs to the Special Issue Modern Nanomaterials: Structure, Properties and Applications)
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Article
Widely Tuneable Composition and Crystallinity of Graded Na1+xTaO3±δ Thin Films Fabricated by Chemical Beam Vapor Deposition
Nanomaterials 2022, 12(6), 1012; https://doi.org/10.3390/nano12061012 - 19 Mar 2022
Viewed by 531
Abstract
Combinatorial approach has been widely recognized as a powerful strategy to develop new-higher performance materials and shed the light on the stoichiometry-dependent properties of known systems. Herein, we take advantage of the unique features of chemical beam vapor deposition to fabricate compositionally graded [...] Read more.
Combinatorial approach has been widely recognized as a powerful strategy to develop new-higher performance materials and shed the light on the stoichiometry-dependent properties of known systems. Herein, we take advantage of the unique features of chemical beam vapor deposition to fabricate compositionally graded Na1+xTaO3±δ thin films with −0.6 < x < 0.5. Such a varied composition was enabled by the ability of the employed technique to deliver and combine an extensive range of precursors flows over the same deposition area. The film growth occurred in a complex process, where precursor absolute flows, flow ratios, and substrate temperature played a role. The deviation of the measured Na/Ta ratios from those predicted by flow simulations suggests that a chemical-reaction limited regime underlies the growth mechanism and highlights the importance of the Ta precursor in assisting the decomposition of the Na one. The crystallinity was observed to be strongly dependent on its stoichiometry. High under-stoichiometries (e.g., Na0.5TaO3−δ) compared to NaTaO3 were detrimental for the formation of a perovskite framework, owing to the excessive amount of sodium vacancies and oxygen vacancies. Conversely, a well-crystallized orthorhombic perovskite structure peculiar of NaTaO3 was observed from mildly under-stoichiometric (e.g., Na0.9TaO3−δ) to highly over-stoichiometric (e.g., Na1.5TaO3+δ) compositions. Full article
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Article
Conversion of Carbon Dioxide into Methanol Using Cu–Zn Nanostructured Materials as Catalysts
Nanomaterials 2022, 12(6), 999; https://doi.org/10.3390/nano12060999 - 18 Mar 2022
Cited by 5 | Viewed by 825
Abstract
Nowadays, there is a growing awareness of the great environmental impact caused by the enormous amounts of carbon dioxide emitted. Several alternatives exist to solve this problem, and one of them is the hydrogenation of carbon dioxide into methanol by using nanomaterials as [...] Read more.
Nowadays, there is a growing awareness of the great environmental impact caused by the enormous amounts of carbon dioxide emitted. Several alternatives exist to solve this problem, and one of them is the hydrogenation of carbon dioxide into methanol by using nanomaterials as catalysts. The aim of this alternative is to produce a value-added chemical, such as methanol, which is a cheaply available feedstock. The development of improved materials for this conversion reaction and a deeper study of the existing ones are important for obtaining higher efficiencies in terms of yield, conversion, and methanol selectivity, in addition to allowing milder reaction conditions in terms of pressure and temperature. In this work, the performance of copper, zinc, and zinc oxide nanoparticles in supported and unsupported bimetallic systems is evaluated in order to establish a comparison among the different materials according to their efficiency. For that, a packed bed reactor operating with a continuous gas flow is used. The obtained results indicate that the use of bimetallic systems combined with porous supports, such as zeolite and activated carbon, is beneficial, thus improving the performance of unsupported materials by four times. Full article
(This article belongs to the Special Issue Metallic and Metal Oxide Nanoparticles and Their Applications)
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Article
Effect of Graphene Oxide and Nanosilica Modifications on Electrospun Core-Shell PVA–PEG–SiO2@PVA–GO Fiber Mats
Nanomaterials 2022, 12(6), 998; https://doi.org/10.3390/nano12060998 - 18 Mar 2022
Cited by 1 | Viewed by 797
Abstract
Electrospinning is a well-established method for the fabrication of polymer biomaterials, including those with core-shell nanofibers. The variability of structures presents a great range of opportunities in tissue engineering and drug delivery by incorporating biologically active molecules such as drugs, proteins, and growth [...] Read more.
Electrospinning is a well-established method for the fabrication of polymer biomaterials, including those with core-shell nanofibers. The variability of structures presents a great range of opportunities in tissue engineering and drug delivery by incorporating biologically active molecules such as drugs, proteins, and growth factors and subsequent control of their release into the target microenvironment to achieve therapeutic effect. The object of study is non-woven core-shell PVA–PEG–SiO2@PVA–GO fiber mats assembled by the technology of coaxial electrospinning. The task of the core-shell fiber development was set to regulate the degradation process under external factors. The dual structure was modified with silica nanoparticles and graphene oxide to ensure the fiber integrity and stability. The influence of the nano additives and crosslinking conditions for the composite was investigated as a function of fiber diameter, hydrolysis, and mechanical properties. Tensile mechanical tests and water degradation tests were used to reveal the fracture and dissolution behavior of the fiber mats and bundles. The obtained fibers were visualized by confocal fluorescence microscopy to confirm the continuous core-shell structure and encapsulation feasibility for biologically active components, selectively in the fiber core and shell. The results provide a firm basis to draw the conclusion that electrospun core-shell fiber mats have tremendous potential for biomedical applications as drug carriers, photocatalysts, and wound dressings. Full article
(This article belongs to the Special Issue Materials Science and Nanoengineering (ICMSN-2022))
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Article
Nanoarchitectonics of Illite-Based Materials: Effect of Metal Oxides Intercalation on the Mechanical Properties
Nanomaterials 2022, 12(6), 997; https://doi.org/10.3390/nano12060997 - 18 Mar 2022
Viewed by 582
Abstract
Clay minerals inevitably interact with colloidal oxides (mainly iron and aluminum oxides) in the evolution of natural geomaterials. However, the interaction between the clay minerals and the colloidal oxides affecting the stability and the strength of geotechnical materials remains poorly understood. In the [...] Read more.
Clay minerals inevitably interact with colloidal oxides (mainly iron and aluminum oxides) in the evolution of natural geomaterials. However, the interaction between the clay minerals and the colloidal oxides affecting the stability and the strength of geotechnical materials remains poorly understood. In the present work, the interaction between the clay minerals and the colloidal oxides was investigated by reaction molecular dynamics simulations to explore the mechanical properties of illite-based materials. It was found that the metal atoms of the intercalated amorphous iron and aluminum oxides interact with oxygen atoms of the silica tetrahedron at the interface generating chemical bonds to enhance the strength of the illite-based materials considerably. The deformation and failure processes of the hybrid illite-based structures illustrated that the Al–O bonds were more favorable to the mechanical properties’ improvement of the hybrid system compared with Fe–O bonds. Moreover, the anisotropy of illite was greatly improved with metal oxide intercalation. This study provides new insight into the mechanical properties’ improvement of clay-based materials through metal oxides intercalation. Full article
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Article
Thermophysical Properties of Nanofluid in Two-Phase Fluid Flow through a Porous Rectangular Medium for Enhanced Oil Recovery
Nanomaterials 2022, 12(6), 1011; https://doi.org/10.3390/nano12061011 - 18 Mar 2022
Cited by 1 | Viewed by 821
Abstract
It is necessary to sustain energy from an external reservoir or employ advanced technologies to enhance oil recovery. A greater volume of oil may be recovered by employing nanofluid flooding. In this study, we investigated oil extraction in a two-phase incompressible fluid in [...] Read more.
It is necessary to sustain energy from an external reservoir or employ advanced technologies to enhance oil recovery. A greater volume of oil may be recovered by employing nanofluid flooding. In this study, we investigated oil extraction in a two-phase incompressible fluid in a two-dimensional rectangular porous homogenous area filled with oil and having no capillary pressure. The governing equations that were derived from Darcy’s law and the mass conservation law were solved using the finite element method. Compared to earlier research, a more efficient numerical model is proposed here. The proposed model allows for the cost-effective study of heating-based inlet fluid in enhanced oil recovery (EOR) and uses the empirical correlations of the nanofluid thermophysical properties on the relative permeability equations of the nanofluid and oil, so it is more accurate than other models to determine the higher recovery factor of one nanoparticle compared to other nanoparticles. Next, the effect of nanoparticle volume fraction on flooding was evaluated. EOR via nanofluid flooding processes and the effect of the intake temperatures (300 and 350 K) were also simulated by comparing three nanoparticles: SiO2, Al2O3, and CuO. The results show that adding nanoparticles (<5 v%) to a base fluid enhanced the oil recovery by more than 20%. Increasing the inlet temperature enhanced the oil recovery due to changes in viscosity and density of oil. Increasing the relative permeability of nanofluid while simultaneously reducing the relative permeability of oil due to the presence of nanoparticles was the primary reason for EOR. Full article
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Article
Compound Heat Transfer Augmentation of a Shell-and-Coil Ice Storage Unit with Metal-Oxide Nano Additives and Connecting Plates
Nanomaterials 2022, 12(6), 1010; https://doi.org/10.3390/nano12061010 - 18 Mar 2022
Cited by 5 | Viewed by 872
Abstract
Due to the high enthalpy of fusion in water, ice storage systems are known as one of the best cold thermal energy storage systems. The phase change material used in these systems is water, thus it is inexpensive, accessible, and completely eco-friendly. However, [...] Read more.
Due to the high enthalpy of fusion in water, ice storage systems are known as one of the best cold thermal energy storage systems. The phase change material used in these systems is water, thus it is inexpensive, accessible, and completely eco-friendly. However, despite the numerous advantages of these systems, the phase change process in them is time-consuming and this leads to difficulties in their practical application. To solve this problem, the addition of nanomaterials can be helpful. This study aims to investigate the compound heat transfer enhancement of a cylindrical-shaped unit equipped with double helically coiled coolant tubes using connecting plates and nano additives as heat transfer augmentation methods. Complex three-dimensional numerical simulations are carried out here to assess the best heat exchanger material as well as the impact of various nanoparticle types, including alumina, copper oxide, and titania, and their concentrations in the PCM side of the ice storage unit. The influence of these parameters is discussed on the charging rate and the temperature evolution factor in these systems. The results suggest that using nano additives, as well as the connecting plates, together is a promising way to enhance the solidification rate by up to 29.9%. Full article
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Article
Selective Mid-IR Metamaterial-Based Gas Sensor System: Proof of Concept and Performances Tests
Nanomaterials 2022, 12(6), 1009; https://doi.org/10.3390/nano12061009 - 18 Mar 2022
Cited by 1 | Viewed by 692
Abstract
In this paper, we propose a highly selective and efficient gas detection system based on a narrow-band IR metasurface emitter integrated with a resistive heater. In order to develop the sensor for the detection of specific gases, both the microheater and metasurface structures [...] Read more.
In this paper, we propose a highly selective and efficient gas detection system based on a narrow-band IR metasurface emitter integrated with a resistive heater. In order to develop the sensor for the detection of specific gases, both the microheater and metasurface structures have been optimized in terms of geometry and materials. Devices with different metamaterial structures and geometries for the heater have been tested. Our prototype showed that the modification of the spectral response of metasurface-based structures is easily achieved by adapting the geometrical parameters of the plasmonic micro-/nanostructures in the metasurface. The advantage of this system is the on-chip integration of a thermal source with broad IR radiation with the metasurface structure, obtaining a compact selective radiation source. From the experimental data, narrow emission peaks (FWHM as low as 0.15 μm), corresponding to the CO2, CH4, and CO absorption bands, with a radiant power of a few mW were obtained. It has been shown that, by changing the bias voltage, a shift of a few tens of nm around the central emission wavelength can be obtained, allowing fine optimization for gas detection applications. Full article
(This article belongs to the Special Issue Nanomaterials for Photonics: Advances and Applications)
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Article
Influence of the Micro-Nanostructuring of Titanium Dioxide Films on the Photocatalytic Degradation of Formic Acid under UV Illumination
Nanomaterials 2022, 12(6), 1008; https://doi.org/10.3390/nano12061008 - 18 Mar 2022
Cited by 2 | Viewed by 644
Abstract
Surface micro-nanostructuring can provide new functionalities and properties to coatings. For example, it can improve the absorption efficiency, hydrophobicity and/or tribology properties. In this context, we studied the influence of micro-nanostructuring on the photocatalytic efficiency of sol-gel TiO2 coatings during formic acid [...] Read more.
Surface micro-nanostructuring can provide new functionalities and properties to coatings. For example, it can improve the absorption efficiency, hydrophobicity and/or tribology properties. In this context, we studied the influence of micro-nanostructuring on the photocatalytic efficiency of sol-gel TiO2 coatings during formic acid degradation under UV illumination. The micro-nanostructuring was performed using the UV illumination of microspheres deposited on a photopatternable sol-gel layer, leading to a hexagonal arrangement of micropillars after development. The structures and coatings were characterized using Raman spectroscopy, ellipsometry, atomic force microscopy and scanning electron microscopy. When the sol-gel TiO2 films were unstructured and untreated at 500 °C, their effect on formic acid’s degradation under UV light was negligible. However, when the films were annealed at 500 °C, they crystallized in the anatase phase and affected the degradation of formic acid under UV light, also depending on the thickness of the layer. Finally, we demonstrated that surface micro-nanostructuring in the form of nanopillars can significantly increase the photocatalytic efficiency of a coating during the degradation of formic acid under UV light. Full article
(This article belongs to the Special Issue Laser Fabrication of Functional Micro/Nanomaterials)
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Article
Interface Formation during the Growth of Phase Change Material Heterostructures Based on Ge-Rich Ge-Sb-Te Alloys
Nanomaterials 2022, 12(6), 1007; https://doi.org/10.3390/nano12061007 - 18 Mar 2022
Cited by 3 | Viewed by 795
Abstract
In this study, we present a full characterization of the electronic properties of phase change material (PCM) double-layered heterostructures deposited on silicon substrates. Thin films of amorphous Ge-rich Ge-Sb-Te (GGST) alloys were grown by physical vapor deposition on Sb2Te3 and [...] Read more.
In this study, we present a full characterization of the electronic properties of phase change material (PCM) double-layered heterostructures deposited on silicon substrates. Thin films of amorphous Ge-rich Ge-Sb-Te (GGST) alloys were grown by physical vapor deposition on Sb2Te3 and on Ge2Sb2Te5 layers. The two heterostructures were characterized in situ by X-ray and ultraviolet photoemission spectroscopies (XPS and UPS) during the formation of the interface between the first and the second layer (top GGST film). The evolution of the composition across the heterostructure interface and information on interdiffusion were obtained. We found that, for both cases, the final composition of the GGST layer was close to Ge2SbTe2 (GST212), which is a thermodynamically favorable off-stoichiometry GeSbTe alloy in the Sb-GeTe pseudobinary of the ternary phase diagram. Density functional theory calculations allowed us to calculate the density of states for the valence band of the amorphous phase of GST212, which was in good agreement with the experimental valence bands measured in situ by UPS. The same heterostructures were characterized by X-ray diffraction as a function of the annealing temperature. Differences in the crystallization process are discussed on the basis of the photoemission results. Full article
(This article belongs to the Special Issue Synthesis, Properties and Applications of Germanium Chalcogenides)
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