Nanotechnology in wood science: Innovations and applications.

Application of nanomaterials is gaining tremendous interest in the field of wood science and technology for value addition and enhancing performance of wood and wood-based composites. This review focuses on the use of nanomaterials in improving the properties of wood and wood-based materials and protecting them from weathering, biodegradation, and other deteriorating agents. UV-resistant, self-cleaning (superhydrophobic) surfaces with anti-microbial properties have been developed using the extraordinary features of nanomaterials. Scratch-resistant nano-coatings also improve durability and aesthetic appeal of wood. Moreover, nanomaterials have been used as wood preservatives for increasing the resistance against wood deteriorating agents such as fungi, termites and borers. Wood can be made more resistant to ignition and slower to burn by introducing nano-clays or nanoparticles of metal-oxides. The use of nanocellulose and lignin nanoparticles in wood-based products has attracted huge interest in developing novel materials with improved properties. Nanocellulose and lignin nanoparticles derived/synthesized from woody biomass can enhance the mechanical properties such as strength and stiffness and impart additional functionalities to wood-based products. Cellulose nano-fibres/crystals find application in wide areas of materials science like reinforcement for composites. Incorporation of nanomaterials in resin has been used to enhance specific properties of wood-based composites. This review paper highlights some of the advancements in the use of nanotechnology in wood science, and its potential impact on the industry.

Epidermal Inspired Flexible Sensor with Buckypaper/PDMS Interfaces for Multimodal and Human Motion Monitoring Applications.

The advancements in the areas of wearable devices and flexible electronic skin have led to the synthesis of scalable, ultrasensitive sensors to detect and differentiate multimodal stimuli and dynamic human movements. Herein, we reveal a novel architecture of an epidermal sensor fabricated by sandwiching the buckypaper between the layers of poly(dimethylsiloxane) (PDMS). This mechanically robust sensor can be conformally adhered on skin and has the perception capability to detect real-time transient human motions and the multimodal mechanical stimuli of stretching, bending, tapping, and twisting. The sensor has feasibility for real-time health monitoring as it can distinguish a wide range of human physiological activities like breathing, gulping, phonation, pulse monitoring, and finger and wrist bending. This multimodal wearable epidermal sensor possesses an ultrahigh gauge factor (GF) of 9178 with a large stretchability of 56%, significant durability for 5000 stretching-releasing cycles, and a fast response/recovery time of 59/88 ms. We anticipate that this novel, simple, and scalable design of a sensor with outstanding features will pave a new way to consummate the requirements of wearable electronics, flexible touch sensors, and electronic skin.

Structural, magnetic, and dielectric properties of solution combustion synthesized LaFeO3, LaFe0.9Mn0.1O3, and LaMnO3 perovskites.

Nanocrystalline LaFeO3, LaFe0.9Mn0.1O3, and LaMnO3 perovskites have been synthesized by a novel solution combustion route, in which oxalyl dihydrazide (ODH) has been used as a fuel. These materials have been characterized using several physicochemical techniques. LaFeO3 and LaFe0.9Mn0.1O3 adopt an orthorhombic structure and LaMnO3 crystallizes in a rhombohedral structure as demonstrated by X-ray diffraction (XRD) patterns. The microporous character of the materials due to huge gas evolution during preparation has been revealed by field emission scanning electron microscopy (FESEM) images. Corresponding elements are present in stoichiometric amounts in all perovskites as revealed by energy dispersive X-ray spectroscopy (EDXS) analyses. X-ray photoelectron spectroscopy (XPS) studies demonstrate the presence of La3+, Fe2+, Fe3+, Mn3+, and Mn4+ species in the respective materials. Absorption bands in the frequency range of 500-600 cm-1 related to Fe-O/Mn-O bonds in FeO6/MnO6 octahedra are observed in Fourier transform infrared (FTIR) spectra. Raman spectroscopy depicts symmetric modes related to metal-oxygen bonds in orthorhombic and rhombohedral structures. Weak ferromagnetism has been observed in LaFeO3 and LaFe0.9Mn0.1O3 which is due to superexchange interaction between the magnetic cations. However, LaMnO3 shows paramagnetic behavior. The electrical characteristics exhibit the lowest dielectric loss for magnetic LaFeO3 among the LaFeO3, LaFe0.9Mn0.1O3, and LaMnO3 perovskites studied here.

Solution combustion synthesis, characterization, magnetic, and dielectric properties of CoFe2O4 and Co0.5M0.5Fe2O4 (M = Mn, Ni, and Zn).

Nanocrystalline CoFe2O4 and Co0.5M0.5Fe2O4 (M = Mn, Ni, and Zn) ferrites were prepared by the solution combustion method using oxalyl dihydrazide as a fuel. These materials were characterized by several physicochemical techniques. X-ray diffraction (XRD) patterns indicate the cubic spinel structure of these ferrites. Field emission scanning electron microscopy (FESEM) images demonstrate the microporous nature of the materials because of the large amount of gas production during their synthesis. High resolution transmission electron microscopy (HRTEM) images show lattice fringes corresponding to the {220} and {311} planes of the spinel structure. Fourier transform infrared (FTIR) spectra exhibit absorption bands around the 500-600 cm-1 wavenumber region which are related to metal-oxygen bonds with tetrahedral coordination. Symmetric and asymmetric stretching and symmetric bending modes associated with tetrahedral and octahedral cations present in the spinel structures have been assessed by Raman spectroscopy. X-ray photoelectron spectroscopy (XPS) studies demonstrate the presence of Co2+, Mn2+, Ni2+, Zn2+, and Fe3+ in tetrahedral and octahedral coordinations in these ferrites. Co0.5Zn0.5Fe2O4 is observed to show the highest saturation magnetization among all these materials. The dielectric measurements reveal that the dielectric constant and loss values decrease with an increase in frequency and the ac conductivity increases at higher frequencies due to mobilization of the charge carriers.

Engineering the Microstructure of Silicon Nanowires by Controlling the Shape of the Metal Catalyst and Composition of the Etchant in a Two-Step MACE Process: An In-Depth Analysis of the Growth Mechanism.

In this work, slanted, kinked, and straight silicon nanowires (SiNWs) are fabricated on Si(111) and (100) substrates using a facile two-step metal-assisted chemical etching nanofabrication technique. We systematically investigated the effect of crystallography, morphology of Ag catalyst, and composition of etchant on the etch profile of Ag catalyst on Si(111) and (100) substrates. We found that the movement of AgNPs inside the Si is determined by physiochemical events such as Ag/Ag interaction, Ag/Si contact, and diffusion kinetics. Further, from detailed TEM and micro-Raman spectroscopy analyses, we demonstrate that the metal catalyst moves in the crystallographically preferred etching direction (viz., <100>) only when the interface effect is not predominant. Further, the metal-assisted chemical etching (MACE) system is highly stable at low-concentration plating and etching solutions, but at high concentrations, the system loses its stability and becomes highly random, leading to the movement of Ag catalyst in directions other than ⟨100⟩. In addition, our studies reveal that Ag nanostructures growth on Si(111) and (100) substrates through galvanic displacement is controlled by substrate symmetry and surface bond density. Finally, we demonstrate that by using an optimized balance between the Ag morphology and concentration of the etchant, the angle in slanted SiNWs, kink position in kinked SiNWs, and aspect ratio of straight SiNWs can be controlled judiciously, leading to enhanced optical absorption in the broadband solar spectrum.

Sub-wavelength waveguide properties of 1D and surface-functionalized SnO2 nanostructures of various morphologies.

One-dimensional (1D) SnO2 sub-wavelength waveguides are a critical contribution to advanced optoelectronics. Further understanding of the surface defects and role of morphology in 1D SnO2 nanowires can help to better utilize these nanostructures more efficiently. For this purpose, three different nanowires (NWs), namely belts, cylindrical- and square-shaped structures were grown using SnO2 quantum dots as a precursor material. The growth process of these NWs is discussed. The nanobelts were observed to grow up to 3 mm in length. Morphological and structural studies of the nanostructures were also carried out. All NWs showed waveguide behavior with visible photoluminescence (PL) upon excitation with a 325 nm laser. This behavior was also demonstrated in tapered and surface-functionalized SnO2 NWs. While the tapered waveguide can allow for easy focusing of light, the simple surface chemistry offers selective light propagation by tuning the luminescence. Defect-related PL in NWs is studied using temperature-dependent measurements and a band diagram is proposed.

Enhanced microwave absorption properties of PMMA modified MnFe2O4-polyaniline nanocomposites.

A manganese based spinel ferrite, chemically modified with polymethyl methacrylate (PMMA) and polyaniline (PANI) are synthesized and their composites are used as electromagnetic interference (EMI) shielding materials. X-ray diffraction studies show that the as-prepared manganese ferrite crystallizes in a cubic spinel structure. The particles are highly agglomerated and nanocrystalline as indicated by transmission electron microscopy. Manganese exists in +2 and +4 oxidation states and Fe in +2 and +3 oxidation states. Modified manganese ferrite and polyaniline composites in different weight ratios are evaluated for their EMI shielding properties. It is observed that composites containing the PMMA modified ferrite show enhanced total shielding effectiveness (SET) compared to those containing the unmodified ferrite in the X band frequency range (8-12 GHz). The optimized ratio of the PMMA modified ferrite and PANI demonstrates SET values as high as ∼44 dB in the X band frequency range.

Nanocolumnar Crystalline Vanadium Oxide-Molybdenum Oxide Antireflective Smart Thin Films with Superior Nanomechanical Properties.

Vanadium oxide-molybdenum oxide (VO-MO) thin (21-475 nm) films were grown on quartz and silicon substrates by pulsed RF magnetron sputtering technique by altering the RF power from 100 to 600 W. Crystalline VO-MO thin films showed the mixed phases of vanadium oxides e.g., V2O5, V2O3 and VO2 along with MoO3. Reversible or smart transition was found to occur just above the room temperature i.e., at ~45-50 °C. The VO-MO films deposited on quartz showed a gradual decrease in transmittance with increase in film thickness. But, the VO-MO films on silicon exhibited reflectance that was significantly lower than that of the substrate. Further, the effect of low temperature (i.e., 100 °C) vacuum (10-5 mbar) annealing on optical properties e.g., solar absorptance, transmittance and reflectance as well as the optical constants e.g., optical band gap, refractive index and extinction coefficient were studied. Sheet resistance, oxidation state and nanomechanical properties e.g., nanohardness and elastic modulus of the VO-MO thin films were also investigated in as-deposited condition as well as after the vacuum annealing treatment. Finally, the combination of the nanoindentation technique and the finite element modeling (FEM) was employed to investigate yield stress and von Mises stress distribution of the VO-MO thin films.

Thermally stable plasmonic nanocermets grown on microengineered surfaces as versatile surface enhanced Raman spectroscopy sensors for multianalyte detection.

Noble metal nanoparticle-based plasmonic sensors, fabricated by top-down and colloidal routes, are widely used for high sensitivity detection of diverse analyte molecules using surface enhanced Raman spectroscopy (SERS). However, most of these sensors do not show stability under harsh environments, which limits their use as versatile SERS substrates. In this work, we report the first use of plasmonic nanocermets, grown on microengineered Si surfaces, as potential candidates for a highly robust SERS sensor. The robustness of the sensor is attributed to the anchoring of the nanoparticles in the nanocermet, which is an important factor for exploiting its reusability. The fairly uniform distribution of nanoparticles in the sensor led to high enhancement factors (10(6)-10(7)) and enabled the detection of low concentrations of a wide range of analytes, including differently charged biomolecules, which is extremely difficult for other SERS sensors. With more precise control over the particle geometry and distribution, plasmonic nanocermets may play an important role in ultrasensitive SERS measurements in adverse conditions such as high temperature.

Anomalous enhancement in interfacial perpendicular magnetic anisotropy through uphill diffusion.

We observed interfacial chemical sharpening due to uphill diffusion in post annealed ultrathin multilayer stack of Co and Pt, which leads to enhanced interfacial perpendicular magnetic anisotropy (PMA). This is surprising as these elements are considered as perfectly miscible. This chemical sharpening was confirmed through quantitative energy dispersive x-ray (EDX) spectroscopy and intensity distribution of images taken on high angle annular dark field (HAADF) detector in Scanning Transmission Electron Microscopic (STEM) mode. This observation demonstrates an evidence of miscibility gap in ultrathin coherent Co/Pt multilayer stacks.

Carbon nanotube-based tandem absorber with tunable spectral selectivity: transition from near-perfect blackbody absorber to solar selective absorber.

CVD grown CNT thin film with a thickness greater than 10 µm behaves like a near-perfect blackbody absorber (i.e., α/ε = 0.99/0.99). Whereas, for a thickness ≤ 0.4 µm, the CNT based tandem absorber acts as a spectrally selective coating (i.e., α/ε = 0.95/0.20). These selective coatings exhibit thermal stability up to 650 °C in vacuum, which can be used for solar thermal power generation.

Wettability of Y2O3: A Relative Analysis of Thermally Oxidized, Reactively Sputtered and Template Assisted Nanostructured Coatings.

The wettability of reactively sputtered Y2O3, thermally oxidized Y-Y2O3 and Cd-CdO template assisted Y2O3 coatings has been studied. The wettability of as-deposited Y2O3 coatings was determined by contact angle measurements. The water contact angles for reactively sputtered, thermally oxidized and template assisted Y2O3 nanostructured coatings were 99°, 117° and 155°, respectively. The average surface roughness values of reactively sputtered, thermally oxidized and template assisted Y2O3 coatings were determined by using atomic force microscopy and the corresponding values were 3, 11 and 180 nm, respectively. The low contact angle of the sputter deposited Y2O3 and thermally oxidized Y-Y2O3 coatings is attributed to a densely packed nano-grain like microstructure without any void space, leading to low surface roughness. A water droplet on such surfaces is mostly in contact with a solid surface relative to a void space, leading to a hydrophobic surface (low contact angle). Surface roughness is a crucial factor for the fabrication of a superhydrophobic surface. For Y2O3 coatings, the surface roughness was improved by depositing a thin film of Y2O3 on the Cd-CdO template (average roughness = 178 nm), which resulted in a contact angle greater than 150°. The work of adhesion of water was very high for the reactively sputtered Y2O3 (54 mJ/m²) and thermally oxidized Y-Y2O3 coatings (43 mJ/m²) compared to the Cd-CdO template assisted Y2O3 coating (7 mJ/m²).