Nanomaterial Films Research Articles

Carbon-Based Nanomaterials Thin Film Deposited on a Flexible Substrate for Strain Sensing Application.

Hybrid nanomaterial film consisting of multi-walled carbon nanotubes (MWCNT) and graphene nanoplatelet (GNP) were deposited on a highly flexible polyimide (PI) substrate using spray gun. The hybridization between 2-D GNP and 1-D MWCNT reduces stacking among the nanomaterials and produces a thin film with a porous structure. Carbon-based nanomaterials of MWCNT and GNP with high electrical conductivity can be employed to detect the deformation and damage for structural health monitoring. The strain sensing capability of carbon-based hybrid nanomaterial film was evaluated by its piezoresistive behavior, which correlates the change of electrical resistance with the applied strain through a tensile test. The effects of weight ratio between MWCNT and GNP and the total amount of hybrid nanomaterials on the strain sensitivity of the nanomaterial thin film were investigated. Experimental results showed that both the electrical conductivity and strain sensitivity of the hybrid nanomaterial film increased with the increase of the GNP contents. The gauge factor used to characterize the strain sensitivity of the nanomaterial film increased from 7.75 to 24 as the GNP weight ratio increased from 0 wt.% to 100 wt.%. In this work, a simple, low cost, and easy to implement deposition process was proposed to prepare a highly flexible nanomaterial film. A high strain sensitivity with gauge factor of 24 was achieved for the nanomaterial thin film.

Co-Doped LaFeO3 Gas Sensor for Fast Low-Power Acetone Detection

Co-doped LaFe1−xCoxO3 (x = 0, 0.1, 0.2, 0.4, 0.6, 0.9) nanomaterial films were prepared via a citric acidassisted sol–gel method and characterized by various techniques. Compared with pure LaFeO3, the optimum operating temperature of the LaFe0.9Co0.1O3 gas sensor dropped to 110 °C from 140 °C. The response value to 100 ppm acetone was 35.89, with a fast response–recovery time of 14/9 s. The enhanced gas sensitivity may be attributed to the higher number of surface oxygen vacancies and larger specific surface area of LaFe0.9Co0.1O3. Doping with Co ions improved the moisture resistance of the LaFeO3 sensor at 18%–54% relative humidity. Appropriate doping of Co3+ into LaFeO3 nanofibers is a promising method for designing and fabricating an acetone sensor with high gas-sensing performance.

Proton transport over nanoparticle surface in insulating nanoparticle film-based humidity sensor

We study proton transport on the surface of insulating nanoparticles for humidity sensors. We use this approach to reveal proton transfer mechanisms in humidity-sensitive materials. Hydrophilic and hydrophobic ligand-terminated silica nanoparticle films are adopted for evaluating the temperature dependence of the ion conductivity. According to the activation energy of the conductivity, we explain that Grotthuss (H+ transfer) and vehicular (H3O+ transfer) mechanisms are mainly dominant on hydrophilic (−OH terminated) and hydrophobic (acrylate terminated) surfaces of the nanoparticles, respectively. This investigation gives us a clue to understanding the proton transfer mechanism in solution-processed flexible humidity-sensitive nanomaterial films.

Adjustable film properties of cellulose nanofiber and cellulose nanocrystal composites

A novel nanocomposite comprised of cellulose nanocrystals (CNCs) and 2,2,6,6-tetramethylpiperidine 1-oxyl (TEMPO) oxidized cellulose nanofibers (TOCNFs) was prepared through solution casting to evaluate potential improvements of the mechanical performance compared to individual reinforcements alone. Such materials can be implemented as mechanical reinforcements in polymer composites, especially when less weight is desired. Dissipative particle dynamics (DPD) simulations, in combination with polarized light microscopy and atomic force microscopy, were analyzed to evaluate the morphology of these combined cellulose nanomaterial (CNM) films. Our results indicate that TOCNFs provide enhanced translational mobility to CNCs which become incorporated near the crystalline domains of TOCNFs. This mobility enables CNCs to increase the rigidity of the network without sacrificing elongation and toughness. The combination of these materials provides improved ultimate tensile strength and elongation without sacrificing the Young's modulus. Therefore, a combination of these materials can be used to develop nanocomposites with enhanced mechanical properties.

Respiratory Monitoring by Ultrafast Humidity Sensors with Nanomaterials: A Review.

Respiratory monitoring is a fundamental method to understand the physiological and psychological relationships between respiration and the human body. In this review, we overview recent developments on ultrafast humidity sensors with functional nanomaterials for monitoring human respiration. Key advances in design and materials have resulted in humidity sensors with response and recovery times reaching 8 ms. In addition, these sensors are particularly beneficial for respiratory monitoring by being portable and noninvasive. We systematically classify the reported sensors according to four types of output signals: impedance, light, frequency, and voltage. Design strategies for preparing ultrafast humidity sensors using nanomaterials are discussed with regard to physical parameters such as the nanomaterial film thickness, porosity, and hydrophilicity. We also summarize other applications that require ultrafast humidity sensors for physiological studies. This review provides key guidelines and directions for preparing and applying such sensors in practical applications.

Recent Advances in Processing and Applications of Heterobimetallic Oxide Thin Films by Aerosol-Assisted Chemical Vapor Deposition.

The fabrication of smart, efficient, and innovative devices critically needs highly refined thin-film nanomaterials; therefore, facile, scalable, and economical methods of thin films production are highly sought-after for the sustainable growth of the hi-tech industry. The chemical vapor deposition (CVD) technique is widely implemented at the industrial level due to its versatile features. However, common issues with a precursor, such as reduced volatility and thermal stability, restrict the use of CVD to produce novel and unique materials. A modified CVD approach, named aerosol-assisted CVD (AACVD), has been the center of attention due to its remarkable tendency to fabricate uniform, homogenous, and distinct nano-architecture thin films in an uncomplicated and straightforward manner. Above all, AACVD can utilize any custom-made or commercially available precursors, which can be transformed into a transparent solution in a common organic solvent; thus, a vast array of compounds can be used for the formation of nanomaterial thin films. This review article highlights the importance of AACVD in fabricating heterobimetallic oxide thin films and their potential in making energy production (e. g., photoelectrochemical water splitting), energy storage (e. g., supercapacitors), and environmental protection (e. g., electrochemical sensors) devices. A heterobimetallic oxide system involves two metallic species either in a composite, solid solution, or metal-doped metal oxides. Moreover, the AACVD tunable parameters, such as temperature, deposition time, and precursor, which drastically affect thin films microstructure and their performance in device applications, are also discussed. Lastly, the key challenges and issues of scaling up AACVD to the industrial level and processing for emerging functional materials are also highlighted.

Time Evolution and Spatial Hierarchy of Crack Patterns.

Cracks generated due to desiccation of wet colloidal systems are ubiquitous, examples being nanomaterial films, painted walls, cemented floors, mud fields, river beds, and even giant rocks. In all such cases, crack patterns are often appreciably similar but for the length and time scales, which can be widely differing. In this work, we have examined the crack formation more closely to see if there exists some generality with regard to the length scale of parameters and the formation time. Specifically, using a commonly used colloidal dispersion and optimized conditions to form polygonal network patterns rather than isolated cracks (films of subcritical thickness), we have studied the time evolution of the pattern parameters, the area occupied by the cracks, their lengths, and the widths. As is well known, initially, a network of cracks forms, which we term as the primary generation, followed by interconnecting cracks inside the polygonal regions (secondary) and, later, cracks spreading in local regions (tertiary). We find that the area and the width increase nearly linearly with time with the change in the slope corresponding to the change in the generation. When normalized with respect to the final values, the trends obtained for different film thicknesses overlap, the only exception being the pattern containing unconnected cracks. Thus, the time evolution of cracks is shown to be predictable based on width filtering. Including the angle between cracks as further input into the recursive model, the possibility of identifying the hierarchy of crack segments is also shown. The approach may be useful in determining the age, authenticity, and details of old paintings, understanding the stress profile of geological rocks, and analyzing various natural and manmade hierarchical structures.

Strain-Induced Nonlinear Frictional Behavior of Graphene Nanowall Films.

Graphene nanowall (GNW) films, a representation of three-dimensional (3D) carbon nanomaterial films, are emerging as promising candidates for applications in electric devices and composites, on account of their 3D structures and exceptional properties of graphene sheets. However, the frictional responses of GNW films, which exhibit significant influence on their performances, have seldom been reported. Herein, we reported a growth process of a GNW film by the chemical vapor deposition method and studied the frictional behavior of the GNW film for the first time. The results demonstrated the nonlinearity between the frictional force of the GNW film and normal load. Based on the structural evolution of the GNW film with normal load and frictional tests on precompressed GNW films, the influence of the strain property of the GNW film, namely, the strengthening effect, could be confirmed. The results of molecular dynamics simulations show that the bending force of GNWs in front of the tip plays a determinate role in the frictional force of the GNW film. Furthermore, the bending force is proportional to the bending contact area, which increases nonlinearly with the normal load due to the strengthening effect of the GNW film. The result suggests that the nonlinear increase of the bending contact area induced by the strengthening effect of the GNW film is the key factor that leads to its nonlinear frictional force. This study provides a novel insight into the frictional responses of GNW films, which would be beneficial for the design and application of electric devices and composites made of GNW and other 3D carbon nanomaterial films.

Construction of biocomputing systems based on switchable bioelectrocatalysis and stimulus-responsive film electrodes

The construction of biocomputing platforms, particularly based on multiple stimulus-responsive film electrodes and switchable bioelectrocatalysis, is briefly overviewed. The bioelectrocatalysis mechanisms and switch principles for common redox biomacromolecules, such as horseradish peroxidase (HRP), glucose oxidase (GOD), natural deoxyribonucleic acid (DNA) and coenzyme nicotinamide adenine dinucleotide (NADH), are briefly introduced. Reversible switch systems are exemplified with smart hydrogel polymer films, functional nanomaterial composite films, inorganic coordination polymers and molecularly imprinted polymer (MIP) films modified on electrode surfaces, demonstrating different electrochemical and optical properties depending on external stimuli. This review highlights the various biomolecular logic gates, logic circuits and devices including sequential circuits achieved due to biocatalytic reactions combined with stimulus-responsive film electrodes. Future developments leading to intelligent multianalyte biosensing and information processing at the molecular level based on switchable and tunable bioelectrocatalysis properties are greatly expected as a research trend in this area.

Physical and chemical modifications of cellulose fibers for food packaging applications

Cellulose fibers have gained considerable interest for use as gas barriers and reinforcing fillers in food packaging materials because of their interesting properties, including biodegradability, low density, nontoxicity, and low cost. Although modifications of cellulose nanomaterials for reinforcing applications have been reviewed in the literature, they suffer from a lack of comparative results, and the modifications related to food packaging applications have not been covered yet. This study reviews physical and chemical methods used to improve oxygen and water barrier properties, water uptake, mechanical strength, and transparency of different food packaging films of cellulose nanomaterials, and provides comparative results. Heat treatment, esterification, and TEMPO-mediated and periodate oxidation are the most common methods used to improve the barrier properties of free-standing, bilayer, and composite films prepared from cellulose nanomaterials. Modification using silane compounds is a well-established method for improving the mechanical properties of cellulose fibers and polymer composite films.

Synthesis and study of thin films of (PbSe)100-xBix nanomaterials

Melt quenching technique has been applied for the synthesis of (PbSe)100-xBix alloys and its thin films have been deposited on the glass substrate at 100 K by Thermal evaporation technique. The structural studies confirm the formation of a higher density of aggregated cubic QDs and the polycrystalline nature of the samples. As compared to other metal-doped PbSe materials, our Bi-doped samples exhibit a faster reduction in the size of the particles. This extraordinary behavior has a high influence on its optical band structure for better response and performance. Emission spectra exhibit an influential blue shift and peak broadening effect with the rise in x values, which give rise to a change in its energy band structure. These effects may be due to quantum size effects with various size distributions. The optical absorption suggests a direct bandgap of an increasing trend with x values of Bi. These trends are the information about the growing confinement effect with the reduction in the size of the particles, which results in the discrete density of states of high filling factor and the comparatively higher density of localized states. The width of the Urbach tail proposes a reducing trend with an increase in Bi content in the base sample. Such a trend might be occurring due to a reduction in band tails that gives rise to the broadening of the bandgap.

Elaboration of TiO2/carbon of oil fly ash nanocomposite as an eco-friendly photocatalytic thin-film material

Titanium/carbon nanomaterial thin film nanocomposites are important components for green advanced technologies and the sustainable future. The aim of this research is to evaluate the photocatalytic activity of the titanium dioxide/carbon nanoparticles derived from oil fly ash (TiO2/COFA) nanocomposite as an eco-friendly photocatalytic material. Herein, the structural, morphological, and optical properties of TiO2/COFA thin films were investigated. Carbon-rich oil fly ash waste has been used as a precursor of carbon nanoparticles synthesised by high-energy ball-milling in nitric acid medium. TiO2/COFA thin films were fabricated by the spin-coating method. The doping of COFA with ratios of 4, 7, and 10 wt % in the TiO2 host were explored for the first time. The obtained results of these films successfully confirmed the presence of carbon nanoparticles in the TiO2 films. The surface morphology of the doped thin films improved as compared to that of the undoped films. XRD confirmed that the doped TiO2 films had a weakly crystalline structure. In addition, doping with COFA decreased the optical bandgap energy of the films from 3.6 to 3.3 eV, whereas it increased the refractive index and the extinction coefficient and significantly enhanced the optical conductivity to reach a value of 5 × 1014 S−1. The photoluminescence intensity of the doped films decreased drastically as the COFA content increased. The results indicated the enhancement of the light conversion and photocatalytic efficiency of doped films in the visible range, and their possible use as solar energy materials.

Coating of Conducting and Insulating Threads with Porous MOF Particles through Langmuir-Blodgett Technique.

The Langmuir-Blodgett (LB) method is a well-known deposition technique for the fabrication of ordered monolayer and multilayer thin films of nanomaterials onto different substrates that plays a critical role in the development of functional devices for various applications. This paper describes detailed studies about the best coating configuration for nanoparticles of a porous metal-organic framework (MOF) onto both insulating or conductive threads and nylon fiber. We design and fabricate customized polymethylmethacrylate sheets (PMMA) holders to deposit MOF layers onto the threads or fiber using the LB technique. Two different orientations, namely, horizontal and vertical, are used to deposit MIL-96(Al) monolayer films onto five different types of threads and nylon fiber. These studies show that LB film formation strongly depends on deposition orientation and the type of threads or fiber. Among all the samples tested, cotton thread and nylon fiber with vertical deposition show more homogenous monolayer coverage. In the case of conductive threads, the MOF particles tend to aggregate between the conductive thread’s fibers instead of forming a continuous monolayer coating. Our results show a significant contribution in terms of MOF monolayer deposition onto single fiber and threads that will contribute to the fabrication of single fiber or thread-based devices in the future.

Shelf-life, quality, safety evaluations of blueberry fruits coated with chitosan nano-material films

Chitosan coating (B/CH) in addition with nano-material films as silicon (B/CH/Nano-SiO2) and titanium (B/CH/Nano-TiO2) dioxides were developed and applied to detect potential changes on fresh blueberry fruits in commercial storage temperature. Physical, mechanical parameters (weight loss, decay rate, colour index and firmness), phytochemical contents (ascorbic acid, acidity, soluble solids concentration, titratable acidity, and repining index), phenolic enzymes (peroxidase and polyphenoloxidase), pigments (anthocyanin) and microbiological analysis (mesophilic aerobic, yeasts and molds populations) were detected every other day until the end of the experiment. Nano-coating based on (Nano-TiO2) established the most suitable values for weight loss (2.22%), titratable acidity (0.45% citric acid), and repining index. (B/CH/Nano-TiO2) reported a gradual increase in polyphenoloxidase and peroxidase enzyme activities (659.45 U/min g) and (20.39 U/min g), respectively. While, (B/CH/Nano-SiO2) established the slightest change in acidity (2.61), anthocyanin (105.19 cyanidin-3-O-glucoside mg/100 g FW) and minimized the growth of mesophilic aerobic, yeasts, and molds populations (3.73–3.98 log CFU/g), respectively. (B/CH) films maintained lightness (6.80% loss) and recorded the highest ascorbic acid content (7.34 g/100 g FW). Therefore, chitosan nano-material films can maintain nutrients and control the microbial growth for extending the shelf life of fresh blueberry fruits.

The technology of 3D curved glass hot-pressing film of new bionic nanomaterial

In order to solve the problems of uneven thickness, poor hardness and wear resistance of traditional curved glass coating technology, a new three-dimensional (3D) curved glass hot-pressing technology of bionic nanomaterials was studied. According to the principle of machine vision, whether the curved glass to be coated meets the requirements of hot-pressing was checked. In addition, a biomimetic nanomaterial film was prepared through the mixed-solvent method. According to the characteristics of 3D curved glass at different temperatures, the parameters of the hot-press film machine were set, and the hot-press film machine was used to complete the research on the 3D curved glass hot-press film technology. Compared with the traditional curved glass film technology, the experimental results show that the new bionic nanomaterial 3D curved glass hot-pressing film technology can achieve uniform coating on the glass surface, and the hardness and wear resistance of the film are better than those of films produced by the traditional coating technology, showing that the new technology has great practical application value.

Highly Sensitive D-Shaped Optical Fiber Surface Plasmon Resonance Refractive Index Sensor Based on Ag-α-Fe 2 O 3 Grating

This work proposed the simulation of a highly sensitive surface plasmon resonance (SPR) optical fibre sensor equipped with a hematite ( $\alpha -\textit {Fe}_{\sf 2}{O}_{\sf 3}$ ) layer coated with silver gratings on the surface of a D-shaped optical fibre. $\alpha -\textit {Fe}_{\sf 2}{O}_{\sf 3}$ nanomaterial film was utilised as the sensing layer. Free electrons on the metal surface were stimulated via evanescent waves on the fibre surface to generate surface plasmon waves. The resonance absorption peaks were monitored to determine the changes in refractive index (RI). The SPR fibre sensor was optimised using the finite element method to analyse the structural parameters of the D-shaped optical fibre and silver gratings. This method was also applied to examine the effect of the thickness of the hematite sensing layer on sensor sensitivity (S). The hematite-coated silver gratings significantly enhanced the sensor as revealed by the simulation outcomes. In this work, the maximum response S of the sensor can reach $6.4~\mu \text{m}$ /RIU when the external RI was changed from 1.33 to 1.39 with 45 nm thick silver grating, 50 nm width air gaps and 12 nm thick hematite ( $\alpha -\textit {Fe}_{\sf 2}{O}_{\sf 3}$ ). The results suggest the high potential of $\alpha -\textit {Fe}_{\sf 2}{O}_{\sf 3}$ nanomaterials in optical fibre-sensing applications.

Xurography-Enabled Thermally Transferred Carbon Nanomaterial-Based Electrochemical Sensors on Polyethylene Terephthalate-Ethylene Vinyl Acetate Films.

A novel benchtop approach to fabricate xurography-enabled thermally transferred (XTT) carbon nanomaterial-based electrochemical sensors is proposed. Filtered nanomaterial (NM) films were transferred from Teflon filters to polyethylene terephthalate-ethylene vinyl acetate (PET-EVA) substrates by a temperature-driven approach. Customized PET-EVA components were xurographically patterned by a cutting plotter. The smart design of PET-EVA films enabled us to selectively transfer the nanomaterial to the exposed EVA side of the substrate. Hence, the substrate played an active role in selectively controlling where nanomaterial transfer occurred allowing us to design different working electrode geometries. Counter and reference electrodes were integrated by a stencil-printing approach, and the whole device was assembled by thermal lamination. To prove the versatility of the technology, XTT materials were exclusively made of carbon black (XTT-CB), multiwalled carbon nanotubes (XTT-MWCNTs), and single-walled carbon nanotubes (XTT-SWCNTs). Their electrochemical behavior was carefully studied and was found to be highly dependent on the amount and type of NM employed. XTT-SWCNTs were demonstrated to be the best-performing sensors, and they were employed for the determination of l-tyrosine (l-Tyr) in human plasma from tyrosinemia-diagnosed patients. High analytical performance toward l-Tyr (linear range of 0.5-100 μM, LOD = 0.1 μM), interelectrode precision (RSD ip,a = 3%, n = 10; RSD calibration slope = 4%, n = 3), and accurate l-Tyr quantification in plasma samples with low relative errors (≤7%) compared to the clinical declared values were obtained. The proposed benchtop approach is cost-effective and straightforward, does not require sophisticated facilities, and can be potentially employed to develop pure or hybrid nanomaterial-based electrodes.

A novel SWCNT-amplified "signal-on" electrochemical aptasensor for the determination of trace level of bisphenol A in human serum and lake water.

Anovel "signal-on" electrochemical aptasensor was developed for ultrasensitive and specific detection of BPA, using single-walled carbon nanotubes (SWCNT) as the electro-catalytic probe for further signal amplification. The multi-walled carbon nanotubes (MWCNT), amino-functionalized magnetite, and gold nanoparticles (NH2-Fe3O4/Au NPs) were applied first to modify the glassy carbon electrode (GCE) surface and to form a nanomaterial film with satisfactory conductive properties, stability, and biocompatibility. The BPA aptamer was then loaded onto the sensing platform by hybridization with complementary DNA (CDNA). In the presence of BPA it combineswith theaptamer and the BPA-aptamer conjugate was released from the electrode;subsequently the added SWCNT and CDNA assembled quickly. Thus, the dual-amplification of the "signal-on" electrochemical aptasensor takes effect. The [Fe (CN)6]3-/4- redox probe signal (∆I) detected by DPV (differential pulse voltammetry) is proportional to the negative logarithm of BPA concentration between 10-19M and 10-14M. The detection limit is 0.08aM. Importantly, the proposed biosensor represents a successful application for determination of BPAin human serum and lake water. Schematic representation of SWCNT-amplified "signal-on" electrochemical aptasensor for the detection of trace level of bisphenol A in human serum and lake water.

Mobility Improvement of Sol-Gel Method Processed Transparent SnSx Thin Films by Na Doping.

The In-Ga-Zn-O oxide semiconductor (a-IGZO) is currently a well-researched and widely used material in the semiconductor industry; however, due to the shortage of indium, new transparent conducting films (TCFs) need to be developed as a substitute of a-IGZO. For this, a new TCF, SnSx (the compound of SnS₂ and SnS) nanomaterial using spin-coating method is processed. We systematically investigate the structure, electrical and optical properties of SnSx and the Na doped SnSx nanomaterial films. Through Na doping, Hall electron mobility of the processed material is increased to 59.6 cm²/Vs and its corresponding average transmittance is 62% in the range 400-800 nm, indicating the material's potential applications as a transparent conductor and in invisible thin film transistors (TFTs).

Langmuir Films of Layered Nanomaterials: Edge Interactions and Cell Culture Applications.

The application of nanomaterials in technology is limited by challenges in their processing into macroscopic structures with reliable and scalable methods. Herein, it is demonstrated that using scalable fabrication methods such as liquid-phase exfoliation, it is possible to produce dispersions of a wide variety of layered nanomaterials, including the first demonstration of boron nitride, with controllable and standardized size and thickness scaling. These can be used, as-produced, for Langmuir deposition, to create single layer films with tuneable density. Of particular importance, we show that the difference in edge chemistry of these materials dictates the film formation process, and therefore can be used to provide a generic fabrication methodology that is demonstrated for various layered nanomaterials, including graphene, boron nitride, and transition metal dichalcogenides. We show that this leads to controllable cancer cell growth on graphene substrates with different edge densities but comparable surface coverage, which can be produced on a statistically relevant cell study amount. This opens pathways for the generic fabrication of a range of layered nanomaterial films for various applications toward a commercially viable film fabrication technology.