Добірка наукової літератури з теми "Nanofils III-As"

Introduction Acetone in exhaled breath is a biomarker of diabetes. However, since it is a very stable substance, its detection by chemical sensors has been a challenging task. Alloy nanoparticles have attracted great attention because of their great catalytic performance, and it has been reported that the response to acetone can be improved by functionalizing oxide semiconductors (In2O3) with PtAu nanoparticles [1]. However, the mechanism of better response to acetone has not been fully understood, which is partly because the effects of alloying and supporting materials cannot be separated in the composite material systems. In this study, we demonstrate that PtAu-alloy nanofilms, where the effect of supporting materials is eliminated, show a greater response to acetone than Pt nanofilms. Furthermore, the impact of alloying on sensing performance was studied by high-throughput atomistic simulation with neural network potentials. Method First, we fabricated Pt and PtAu nanofilm sensors. As the Pt and PtAu nanofilms, Pt and Pt/Au were deposited, respectively, by electron beam evaporation method. The thickness of Pt film is 3 nm, whereas Pt/Au thicknesses are 2.5 nm/0.5 nm. The electrodes consisted of 40-nm Pt and 40-nm Au layers, and they were annealed in N2 ambient for 1 hour at 300 oC. XRD measurements were performed to evaluate the alloy states for three samples: Pt (20nm), Au (20 nm), and PtAu (18 nm). The PtAu film for XRD was fabricated by repeating sequential depositions of 5-nm Pt and 1-nm Au three times. All the films were annealed for 1 hour at 300 oC in N2 ambient. The sensor responses to acetone were evaluated by measuring the resistance of Pt and PtAu at 260 oC under the following sequences. i) Dry air (15 min) ii) 1-ppm acetone in dry air (2 min) iii) Dry air (3 min) We applied DC current of 100 µA and the voltage difference between the terminals were measured. To examine the factors that contribute to the difference in sensing performance of PtAu and Pt nanofilms, we calculated the reaction pathway using the nudged elastic band method. All calculations were carried out with PFP version 2.0.0 on Matlantis [2]. DFT-D3 was used to describe the van der Waals interaction [3]. Results Pt, Au, and PtAu samples showed (111) peaks in the XRD analysis. The position of (111) peak of PtAu located between those of Pt and Au peaks, suggesting that PtAu was successfully alloyed. By applying the Vegard’s law, the composition of PtAu was determined to be 0.823:0.177, which is consistent with the thickness ratio. When acetone was exposed, the resistance of the devices decreased. The response of PtAu to acetone was greater than that of Pt. In addition, the responses of Pt and PtAu devices were proportional to the square root of the concentration of acetone. The limit of detections (LOD) determined by 3σ method were 76 ppb for Pt and 14 ppb for PtAu. Discussion We considered that H atoms introduced by CH dissociation of acetone prevent the adsorption of oxygens from the atmosphere and reduce the surface scattering of electrons, leading to a decrease in the resistance of Pt nanofilms. The Nudged Elastic Band method was used to calculate the activation energy of CH dissociation of acetone on the surface of Pt and PtAu. PtAu slab was prepared by replacing Pt atoms partly with Au atoms. The calculations showed that the activation energy for PtAu was 64-meV lower than that of Pt. In the transition state, the dissociated H atom stayed at the bridge site of Pt. When Pt atoms are substituted with Au atoms, the distance between Pt’s at the bridge site expands due to the large lattice constant of Au. As a result, the transition state became more stable on PtAu surface than on Pt surface. In fact, we confirmed that the activation energy was lowered as the Pt-Pt distance increased. Conclusion We demonstrated, for the first time, that PtAu nanofilm sensors show a greater response to acetone than Pt nanofilm. The atomic simulation demonstrated that the dehydrogenation of methyl group of acetone is the fundamental mechanism of the acetone sensing, and that the lattice expansion induced by replacing Pt with Au contributed to stabilize the transition state and to reduce the activation energy. Further optimization of the alloy composition should be essential to achieve a more highly sensitive acetone sensor. References [1] N. Sui, et al., ACS Sens. 7, 2178-2187 (2022). [2] S. Takamoto, et al., Nat. Commun. 13, 2991 (2022). [3] S. Grimme, et al., J. Chem. Phys. 2010, 132, (2010).

The control of natural organic matter (NOM) in drinking water treatment plants is required in order to control (i) the formation of potentially harmful disinfection byproducts (DBPs), (ii) the regrowth of bacteria and (iii) pipe corrosion in the distribution system. Photocatalysis is a promising advanced oxidation technology due to its ability to mineralise chlorinated byproduct precursors such as humic acids (HAs) to carbon dioxide and water. In this study, the efficiency of HAs and NOM removal in terms of UV absorbance at 254 nm (UV254) was tested by means of a new photocatalytic reactor made of stacked polymethylmethacrylate (PMMA) rings coated by TiO2 nanofilm. Three different sets of rings were coated with TiO2 gel one, two and three times respectively to optimise the coating thickness according to UV254 removal efficiency. The titania sol was immobilised on the substrate by a low temperature procedure and after 8 months the reactors were reactivated by means of UV radiation before the experiments. The photocatalytic removal efficiency of humic acid in terms of UV254 was significantly higher after 1 hour for the reactor employed with high thickness TiO2 nanofilm (around 20%) compared to middle and low thickness reactors (6 and 1.4%, respectively). However, during the same reaction time only 10% of UV254 was removed with high thickness TiO2 nanofilm using raw surface water, probably owing to ionic species naturally occurring in the raw water sample. Finally, the activation of the TiO2 nanofilm may be effectively accomplished by means of UV radiation where calcination cannot be applied (e.g. thermally sensitive substrates).

SUMMARY Purpose: To evaluate the clinical performance of water, acetone, ethanol, and ethanol-water solvent-based dentin adhesives with nanofill or nanohybrid composites in Class III restorations. Methods and Materials: A total of 22 patients aged between 14 and 48 years (mean age: 25.2 years) participated in the study. Each patient received four Class III restorations, which were performed using water (Scotchbond Multipurpose), acetone (Prime&Bond NT), ethanol (XP Bond) and ethanol-water (Xeno V) solvent-based dentin adhesive systems with a nanofill (Filtek Supreme XT) or nanohybrid composite (CeramX Duo). Two experienced examiners evaluated the restorations with regard to retention, color match, marginal discoloration, wear/loss of anatomic form, caries formation, marginal adaptation, and surface texture at baseline and at one-, two-, three-, four-, and five-year recalls. Results: The five-year survival rates were 100% for Scotchbond Multipurpose, Prime&Bond NT, and XP Bond and 81.2% for Xeno V–bonded restorations. Only three Xeno V–bonded restorations failed. With the exception of marginal discoloration, there were no statistically significant differences among the four adhesive-bonded restorations in any of the evaluation periods in terms of the evaluation criteria. Conclusions: With the exception of marginal discoloration and marginal integrity deterioration of Xeno V–bonded restorations, all four adhesive-bonded restorations exhibited good long-term results. However, adhesion strategy (such as self-etch or etch-and-rinse) is more important than the solvent content of dentin adhesive systems in the success of Class III restorations.

To get high efficiency photodegradation on pollutants under visible light, Pr(III) doped Y2SiO5 upconversion materials and anatase TiO2 nanofilm coated Pr:Y2SiO5 composite have been prepared by using a sol-gel method. XRD and SEM test results indicated that TiO2 nanofilm was well coated on Pr:Y2SiO5 to form TiO2@Pr:Y2SiO5 composite particles with the sizes of 0.5–1.0 μm. To avoid secondary pollution resulting from incomplete recovery of catalyst particles, TiO2@Pr:Y2SiO5 was loaded on the glass fiber filters by using a dip-coating method. It is found that the catalyst particles were embedded into the carrier firmly, even after having been reused for 6 times. The luminescence intensities of TiO2@Pr:Y2SiO5 were getting down sharply with the coating contents of TiO2 increased, which was attributed to the adsorption of the luminescence by the TiO2 film in situ. As a result, TiO2@Pr:Y2SiO5 with 4% TiO2, which presented lowest luminescence intensity, showed the highest efficiency on the photodegradation of nitrobenzene wastewater. The catalysts loaded on glass fiber filters showed excellent reusability on the photodegradation of nitrobenzene and presented a photodegradation rate of 95% at the first time and up to 75.9% even after 6 times of reusing by the treatment time of 12 h.

In this work, Fe2O3 was investigated as a doping agent for poly(methyl methacrylate) (PMMA) in order to enhance the plasmonic effect in sensors based on D-shaped plastic optical fibers (POFs). The doping procedure consists of immerging a premanufactured POF sensor chip in an iron (III) solution, avoiding repolymerization and its related disadvantages. After treatment, a sputtering process was used to deposit a gold nanofilm on the doped PMMA in order to obtain the surface plasmon resonance (SPR). More specifically, the doping procedure increases the refractive index of the POF’s PMMA in contact with the gold nanofilm, improving the SPR phenomena. The doping of the PMMA was characterized by different analyses in order to determine the effectiveness of the doping procedure. Moreover, experimental results obtained by exploiting different water–glycerin solutions have been used to test the different SPR responses. The achieved bulk sensitivities confirmed the improvement of the plasmonic phenomenon with respect to a similar sensor configuration based on a not-doped PMMA SPR-POF chip. Finally, doped and non-doped SPR-POF platforms were functionalized with a molecularly imprinted polymer (MIP), specific for the bovine serum albumin (BSA) detection, to obtain dose-response curves. These experimental results confirmed an increase in binding sensitivity for the doped PMMA sensor. Therefore, a lower limit of detection (LOD), equal to 0.04 μM, has been obtained in the case of the doped PMMA sensor when compared to the one calculated for the not-doped sensor configuration equal to about 0.09 μM.

Naturally occurring Fe(III) films with rainbow reflection iridescence have been observed floating on the water surface of various spots covered with shallow water (e.g., edges of wetlands and creeks, standing water over soils). This natural phenomenon has become a scenic attraction and stimulated much curiosity. We pursued an experimental inquiry aimed at probing this interesting, curious natural wonder. As the first critical task, floating Fe(III) films were successfully generated in an assessable, controllable setting in our laboratory. This enabled us to establish this phenomenon reproducibly under controlled conditions and characterize the phenomenon over the entire span of the formation and transformation of the Fe(III) films. Our film generation method requires a few things: fresh soil (source for Fe(III) and microbes), glucose (energy source), and water in a container. The floating Fe(III) films as observed in the field occurred in ~1–3 day(s) on the water surface of the inundated soil mixed with the sugar. The Fe(III) films then grew from initial very thin, colorless, somewhat transparent films with rainbow reflection iridescence to colored thicker films and then to orange/orange-red/red crusts over the time. A comprehensive mechanistic picture was formulated to depict the formation of the Fe(III) films. Several sequential processes are operative. First, the Fe(III) (oxides, oxyhydroxides) in the soil is reduced to Fe(II) by the Fe(III)-reducing microbes during their anerobic respiration with Fe(III) as the electron (e−) acceptor after depletion of dissolved O2 in the water as a result of aerobic microbial respiration with O2 as the e− acceptor. The Fe(II), being soluble, then diffuses to the water surface where it is oxidized to Fe(III). Subsequently, the Fe(III) hydrolyzes and various Fe(III) hydrolysis products polymerize to stabilize. A polymeric model was created to account for the Fe(III) film transformation. The Fe(III) films are considered to transform from the dimers and trimers and linear polymers of Fe(OH)3 to Fe(III) polymer sheets (e.g., Fe(OH)3, FeOOH), to 3D Fe(III) polymers, and eventually to Fe2O3 colloid particles. This floating Fe(III) film phenomenon boasts an environmental chemical drama of redox cycling of Fe(III)/Fe(II) at soil/water and water/air interfaces coupled with Fe(II) transport from the inundated soil to the water surface followed by ultimate mineralization of the Fe(III) polymers. Our Fe(III) film generation method can be readily scaled up to supply Fe(III) films of rich varieties in thickness, size, morphology, and structure over the entire span of various stages of their formation and transformation as desired for various uses. This setup offers a platform needed for further controlled studies on the kinetics, mechanism, and process of abiotic and biotic nature involved in the Fe(III) film phenomenon and for exploration of versatile roles of the Fe(III) films as nanofilms in Fe(III)/Fe(II)-surface catalyzed chemical and photochemical reactions involving various natural and synthetic compounds.

GaN nanostructures are promising for a broad range of applications due to their 3D structure, thereby exposing non-polar crystal surfaces. The nature of the exposed crystal facets, i.e., whether they are a-, m-plane, or of mixed orientation, impacts the stability and performance of GaN nanostructure-based devices. In this context, it is of great interest to control the formation of well-defined side facets. Here, we show that we can control the crystal facet formation at the nanowire sidewalls by tuning the III–V ratio during selective area growth by molecular beam epitaxy. Especially, the N flux serves as a tool for controlling the growth kinetics. In addition, we demonstrate the growth of GaN nanofins with either a- or m-plane side facets. Based on our observations, we present the underlying nanostructure growth mechanisms. Low temperature photoluminescence measurements show a correlation of the formation of structural defects like stacking faults with the growth kinetics. This article demonstrates the controlled selective epitaxy of GaN nanostructures with defined crystal side facets on large-scale available AlN substrates.

Supramolecular metal-polyphenolic thin sensor films represent a unique class of composite materials. Their properties and sensitivity can be easily modified via controlled self-assembly of their molecular components. Among the different assembly methods, electrochemically triggered processes are extremely powerful because they allow spatial confinement of the film buildup via an electrical stimuli-controlled process. In this article, an approach to employ the electrochemically assisted self-assembly of a multicomponent supramolecular film based on a naturally occurring polyphenol, tannic acid (TA), is featured. Here, the capacity of polyphenolic compounds to form complexes with metal ions, as well as to act both as reducing agents and stabilizers in colloidal synthesis of metal nanoparticles (NPs) is utilized. The electrochemically triggered self-assembly can be coupled with the ion – printing method, in which the targeted metal ion, in this case Al(III), is incorporated into the film during the synthesis and chemically removed afterwards. This procedure results in a template-like structure of the film with openings ready to bind the same metal ion from the probed solution, thus significantly improving the selectivity of the sensor formed and enhancing its applicability for sensing of toxic metal ions in complex aqueous solutions, such as physiological fluids.

Results of experimental assessment of efficiency of use of low-temperature air plasma of the arc category of atmospheric pressure at treatment of burns of skin of the III degree in small laboratory animals are given. It is established that use of low-temperature air plasma of the arc-type discharge of atmospheric pressure allows to accelerate terms of final healing of wounds for 49% (p0,05), to reduce development frequency in them purulent inflammation by 45,5% (p0,01). Positive influence of air and plasma processing on dynamics of the area of a hem which after single influence by 35 days is reduced for 67% is revealed (p0,01). The analysis of a histologic picture confirms acceleration of formation of an extracellular matrix and epitelization against the background of impact of an air and plasma stream on wounds. Processing of a wound of low-temperature air plasma of the arc category of atmospheric pressure after an early surgical escharotomy allows to form on a wound surface a so-called nanofilm of a layer the coagulated proteins of wound exudate and cellular fragments which has selective vapor permeability, reduces an rate of wounds pathogenic infection, prevents drying and as a result, allows to reduce the frequency of development of purulent complications and extent of zones of a secondary necrosis. Influence of a stream of low-temperature air plasma of the arc-type discharge of atmospheric pressure allows to optimize significantly processes of reparative regeneration in a zone of a deep burn of skin at a stage of preparation for their surgical treatment.

Ce travail porte sur la croissance sélective (SAG) de nanofils (NFs) III-As par épitaxie en phase vapeur par la méthode aux hydrures (HVPE). Dans un premier temps, nous avons étudié la SAG de NFs de GaAs sur des substrats de GaAs. Des études systématiques portant sur les conditions de croissance ont mis en évidence une suppression de la croissance sous atmosphère riche en arsenic. Ces observations ont été appuyées par un modèle cinétique qui, pour la première fois en HVPE, prend en compte la diffusion des adatomes de Ga sur les facettes latérales des NFs. Puis, une étude préliminaire du dopage des NFs a été conduite, ainsi que des croissances de jonctions p-i-n dans des NFs. Les résultats sont encourageants quant à la réalisation de dispositifs à base de NFs par HVPE. Dans un second temps, nous avons étudié la SAG de NFs d’InAs et d’InGaAs sur des substrats de GaAs et Si. Il s’est avéré que la suppression de la croissance se produit également pour les NFs d’InAs. Concernant l’InGaAs, des réseaux de NFs de compositions variées ont été obtenus avec succès. Un modèle de croissance a été développé révélant que la composition des NFs est contrôlée par la cinétique de croissance plutôt que par des facteurs thermodynamiques. Cela simplifie considérablement le contrôle de la composition dans une large gamme de paramètres HVPE. Ces résultats montrent la capacité de la HVPE pour la fabrication de réseaux de NFs d’InGaAs homogènes avec des compositions facilement ajustables
This work focuses on the selective area growth (SAG) of III-As nanowires (NWs) by hydride vapor-phase epitaxy (HVPE). First, we have studied the SAG of GaAs NWs on GaAs substrates. Systematic studies according to growth conditions have demonstrated a growth suppression effect under arsenic-rich atmosphere. These observations were supported by a kinetic model which, for the first time in HVPE, takes into account the diffusion of Ga adatoms on the NWs side facets. Then, a preliminary study of the doping of NWs was carried out, as well as the growth of p-i-n junctions in NWs. The results are encouraging regarding the fabrication of NW-based devices by HVPE. Secondly, we have studied the SAG of InAs and InGaAs on GaAs and Si substrates. It turned out that growth suppression also occurs for InAs NWs. As for InGaAs, NW arrays with various compositions have been successfully obtained. A growth model was developed revealing that the NWs composition is controlled by growth kinetics rather than thermodynamic factors. This greatly simplifies the control of the composition across a wide range of HVPE parameters. These results show the capability of HVPE for the fabrication of homogeneous InGaAs NW arrays with widely tunable compositions