Formulation of zinc foliar sprays for wheat grain biofortification: a review of current applications and future perspectives

Agronomic biofortification of wheat grain with zinc can improve the condition of about one billion people suffering from zinc (Zn) deficiency. However, with the challenge of cultivating high-yielding wheat varieties in Zn-deficient soils and the global need to produce higher-quality food that nourishes the growing population, innovation in the strategies to deliver Zn directly to plants will come into play. Consequently, existing foliar formulations will need further refinement to maintain the high agronomic productivity required in competitive global grain markets while meeting the dietary Zn intake levels recommended for humans. A new generation of foliar fertilisers that increase the amount of Zn assimilated in wheat plants and the translocation efficiency of Zn from leaves to grains can be a promising solution. Research on the efficacy of adjuvants and emerging nano-transporters relative to conventional Zn forms applied as foliar fertilisers to wheat has expanded rapidly in recent years. This review scopes the range of evidence available in the literature regarding the biofortification of bread wheat (Triticum aestivum L.) resulting from foliar applications of conventional Zn forms, Zn nanoparticles and novel Zn-foliar formulations. We examine the foliar application strategies and the attained final concentration of grain Zn. We propose a conceptual model for the response of grain Zn biofortification of wheat to foliar Zn application rates. This review discusses some physiological aspects of transportation of foliarly applied Zn that need further investigation. Finally, we explore the prospects of engineering foliar nano-formulations that could effectively overcome the physicochemical barrier to delivering Zn to wheat grains.

Stratum-Confined Solid-State Reaction (SC-SSR) toward Colloidal Silicon-Based Hollow Nanostructures for Bioapplications

Silicon nanostructures (SiNSs) can provide multifaceted bioapplications; but preserving their subhundred nm size during high-temperature silica-to-silicon conversion is the major bottleneck. The SC-SSR utilizes an interior metal-silicide stratum space at a predetermined radial distance inside silica nanosphere to guide the magnesiothermic reduction reaction (MTR)-mediated synthesis of hollow and porous SiNSs. In depth mechanistic study explores solid-to-hollow transformation encompassing predefined radial boundary through the participation of metal-silicide species directing the in-situ formed Si-phase accumulation within the narrow stratum. Evolving thin-porous Si-shell remains well protected by the in-situ segregated MgO emerging as a protective cast against the heat-induced deformation and interparticle sintering. Retrieved hydrophilic SiNSs (<100 nm) can be conveniently processed in different biomedia as colloidal solutions and endocytosized inside cells as photoluminescence (PL)-based bioimaging probes. Inside the cell, rattle-like SiNSs encapsulated with Pd nanocrystals can function as biorthogonal nanoreactors to catalyze intracellular synthesis of probe molecules through C-C cross coupling reaction.

Jellybean Quantum Dots in Silicon for Qubit Coupling and On-Chip Quantum Chemistry

The small size and excellent integrability of silicon metal-oxide-semiconductor (SiMOS) quantum dot spin qubits make them an attractive system for mass-manufacturable, scaled-up quantum processors. Furthermore, classical control electronics can be integrated on-chip, in-between the qubits, if an architecture with sparse arrays of qubits is chosen. In such an architecture qubits are either transported across the chip via shuttling or coupled via mediating quantum systems over short-to-intermediate distances. This paper investigates the charge and spin characteristics of an elongated quantum dot-a so-called jellybean quantum dot-for the prospects of acting as a qubit-qubit coupler. Charge transport, charge sensing, and magneto-spectroscopy measurements are performed on a SiMOS quantum dot device at mK temperature and compared to Hartree-Fock multi-electron simulations. At low electron occupancies where disorder effects and strong electron-electron interaction dominate over the electrostatic confinement potential, the data reveals the formation of three coupled dots, akin to a tunable, artificial molecule. One dot is formed centrally under the gate and two are formed at the edges. At high electron occupancies, these dots merge into one large dot with well-defined spin states, verifying that jellybean dots have the potential to be used as qubit couplers in future quantum computing architectures.

Liquid-Modulated Photothermal Phenomena in Porous Silicon Nanostructures Studied by μ-Raman Spectroscopy

In the present study, the effect of liquid filling of the nanopore network on thermal transport in porous Si layers was investigated by μ-Raman spectroscopy. The values of thermal conductivity of porous Si and porous Si-hexadecane composites were estimated by fitting the experimentally measured photoinduced temperature rise with finite element method simulations. As a result, filling the pores with hexadecane led to (i) an increase in the thermal conductivity of the porous Si-hexadecane composite in a wide range of porosity levels (40-80%) and (ii) a suppression of the characteristic laser-induced phase transition of Si from cubic to hexagonal form.

Synergistic Solar-Driven Freshwater Generation and Electricity Output Empowered by Wafer-Scale Nanostructured Silicon

Electricity generation triggered by the ubiquitous water evaporation process provides an intriguing way to harvest energy from water. Meanwhile, natural water evaporation is also a fundamental way to obtain fresh water for human beings. Here, a wafer-scale nanostructured silicon-based device that takes advantage of its well-aligned configuration that simultaneously realizes solar steam generation (SSG) for freshwater collection and hydrovoltaic effect generation for electricity output is developed. An ingenious porous, black carbon nanotube fabric (CNF) electrode endows the device with sustainable water self-pumping capability, excellent durable conductivity, and intense solar spectrum harvesting. A combined device based on the CNF electrode integrated with nanostructured silicon nanowire arrays (SiNWs) provided an aligned numerous surface-to-volume water evaporation interface that enables a recorded continuous short-circuit current 8.65 mA and a water evaporation rate of 1.31 kg m^-2 h^-1 under one sun illumination. Such wafer-scale SiNWs-based SSG and hydrovoltaic integration devices would unchain the bottleneck of the weak and discontinuous electrical output of hydrovoltaic devices, which inspires other sorts of semiconductor-based hydrovoltaic device designs to target superior performance.

Application of the Photoacoustic Approach in the Characterization of Nanostructured Materials

A new generation of sensors can be engineered based on the sensing of several markers to satisfy the conditions of the multimodal detection principle. From this point of view, photoacoustic-based sensing approaches are essential. The photoacoustic effect relies on the generation of light-induced deformation (pressure) perturbations in media, which is essential for sensing applications since the photoacoustic response is formed due to a contrast in the optical, thermal, and acoustical properties. It is also particularly important to mention that photoacoustic light-based approaches are flexible enough for the measurement of thermal/elastic parameters. Moreover, the photoacoustic approach can be used for imaging and visualization in material research and biomedical applications. The advantages of photoacoustic devices are their compact sizes and the possibility of on-site measurements, enabling the online monitoring of material parameters. The latter has significance for the development of various sensing applications, including biomedical ones, such as monitoring of the biodistribution of biomolecules. To extend sensing abilities and to find reliable measurement conditions, one needs to clearly understand all the phenomena taking place during energy transformation during photoacoustic signal formation. Therefore, the current paper is devoted to an overview of the main measurement principles used in the photoacoustic setup configurations, with a special focus on the key physical parameters.

When Silicon Materials Meet Natural Sources: Opportunities and Challenges for Low-Cost Lithium Storage

The manipulation of progressive lithium-ion batteries (LIBs) with high energy density, low cost, and long-term cycling stability is of high priority to meet the growing demands for next-generation energy storage devices. Silicon (Si) has been receiving marvelous attention as a promising anode material for rechargeable LIBs, due to its high theoretical gravimetric capacity and low cost. Si is the second most abundant element in the earth crust in the form of silicates, so it is the most cost-effective element as an anode material in next-generation LIBs. In this review, different natural sources such as rice husk, sugar cane bagasse, bamboo, reed plant, sand, halloysite, and different waste sources such as waste of the solar power industry, fly ash, straw ash, and other industrial waste that can give rise to different nanostructured Si are systematically summarized. In addition, different synthesis methods of fabricating nanostructured Si are reviewed as well as including magnesiothermic reduction, etching methods, ball milling, and chemical vapor deposition. The advantages and disadvantages of these kind of synthesis methods are discussed as well. Furthermore, the opportunities and challenges of nano-Si are also discussed.

Low-Load Metal-Assisted Catalytic Etching Produces Scalable Porosity in Si Powders

The recently discovered low-load metal-assisted catalytic etching (LL-MACE) creates nanostructured Si with controllable and variable characteristics that distinguish this technique from the conventional high-load variant. LL-MACE employs 150 times less metal catalyst and produces porous Si instead of Si nanowires. In this work, we demonstrate that some of the features of LL-MACE cannot be explained by the present understanding of MACE. With mechanistic insight derived from extensive experimentation, it is demonstrated that (1) the method allows the use of not only Ag, Pd, Pt, and Au as metal catalysts but also Cu and (2) judicious combinations of process parameters such as the type of metal, Si doping levels, and etching temperatures facilitate control over yield (0.065-88%), pore size (3-100 nm), specific surface area (20-310 m²·g^-1), and specific pore volume (0.05-1.05 cm³·g^-1). The porous structure of the product depends on the space-charge layer, which is controlled by the Si doping and the chemical identity of the deposited metal. The porous structure was also dependent on the dynamic structure of the deposited metal. A distinctive comet-like structure of metal nanoparticles was observed after etching with Cu, Ag, Pd, and, in some cases, Pt; this structure consisted of 10-50 nm main particles surrounded by smaller (<5 nm) nanoparticles. With good scalability and precise control of structural properties, LL-MACE facilitates Si applications in photovoltaics, energy storage, biomedicine, and water purification.

Deep Learning Meets Nanophotonics: A Generalized Accurate Predictor for Near Fields and Far Fields of Arbitrary 3D Nanostructures

Deep artificial neural networks are powerful tools with many possible applications in nanophotonics. Here, we demonstrate how a deep neural network can be used as a fast, general purpose predictor of the full near-field and far-field response of plasmonic and dielectric nanostructures. A trained neural network is shown to infer the internal fields of arbitrary three-dimensional nanostructures many orders of magnitude faster compared to conventional numerical simulations. Secondary physical quantities are derived from the deep learning predictions and faithfully reproduce a wide variety of physical effects without requiring specific training. We discuss the strengths and limitations of the neural network approach using a number of model studies of single particles and their near-field interactions. Our approach paves the way for fast, yet universal, methods for design and analysis of nanophotonic systems.

Interplay Between Silicon Nanocrystal Size and Local Environment Within Porous Silicon on the Analyte-Dependent Photoluminescence Response

Porous silicon (pSi) exhibits strong photoluminescence (PL) and its PL is often exploited for chemical sensor development. However, the sensor response is not uniform across a pSi specimen. We use co-localized confocal PL and Raman scattering mapping to establish a relationship between the analyte-induced PL response and the silicon nanocrystallite size, size distribution, and amorphous silicon (aSi) contribution across a pSi specimen. Using toluene as a model analyte, high analyte-induced PL response is associated with areas within the specimen that have (i) low aSi content, (ii) silicon nanocrystallites having diameters between 2 and 5 nm, and (iii) silicon nanocrystallites that exhibit a narrow size distributions (≤1% relative standard deviation).

Light Trapping in Conformal Graphene/Silicon Nanoholes for High-Performance Photodetectors

Hybrid graphene/silicon heterojunctions have been widely utilized in photodetectors because of their unique characteristics of high sensitivity, fast response, and CMOS compatibility. However, the photoresponse is restricted by the high reflectance of planar silicon (up to 50%). Herein, an improved graphene/Si detector with excellent light absorption performance is proposed and demonstrated by directly growing graphene on the surface of silicon nanoholes (SiNHs). It is shown that the combination of SiNHs with conformal graphene provides superior interfaces for efficient light trapping and transport of the photoexcited carriers. A high absorption of up to 90% was achieved, and the conformal graphene/SiNH-based photodetectors exhibited a higher photoresponsivity (2720 A/W) and faster response (∼6.2 μs), compared with the counterpart of the planar graphene/Si, for which the corresponding values are 850 A/W and 51.3 μs. These results showcase the vital role of the material morphology in optoelectronic conversion and pave the way to explore novel high-performance heterojunction photodetectors.

Printing Beyond sRGB Color Gamut by Mimicking Silicon Nanostructures in Free-Space

Localized optical resonances in metallic nanostructures have been increasingly used in color printing, demonstrating unprecedented resolution but limited in color gamut. Here, we introduce a new nanostructure design, which broadens the gamut while retaining print resolution. Instead of metals, silicon nanostructures that exhibit localized magnetic and electric dipole resonances were fabricated on a silicon substrate coated with a Si₃N₄ index matching layer. Index matching allows a suppression of substrate effects, thus enabling Kerker's conditions to be met, that is, sharpened transitions in the reflectance spectra leading to saturated colors. This nanostructure design achieves a color gamut superior to sRGB, and is compatible with CMOS processes. The presented design could enable compact high-resolution color displays and filters, and the use of a Si₃N₄ antireflection coating can be readily extended to designs with nanostructures fabricated using other high-index materials.

Ordered Silicon Pillar Arrays Prepared by Electrochemical Micromachining: Substrates for High-Efficiency Cell Transfection

Ordered arrays of silicon nano- to microscale pillars are used to enable biomolecular trafficking into primary human cells, consistently demonstrating high transfection efficiency can be achieved with broader and taller pillars than reported to date. Cell morphology on the pillar arrays is often strikingly elongated. Investigation of the cellular interaction with the pillar reveals that cells are suspended on pillar tips and do not interact with the substrate between the pillars. Although cells remain suspended on pillar tips, acute local deformation of the cell membrane was noted, allowing pillar tips to penetrate the cell interior, while retaining cell viability.

Sub-10 nm Silicon Nanopillar Fabrication Using Fast and Brushless Thermal Assembly of PS-b-PDMS Diblock Copolymer

A new approach to obtaining spherical nanodomains using polystyrene-block-polydimethylsiloxane (PS-b-PDMS) is proposed. To reduce drastically the process time, we blended a copolymer with cylindrical morphology with a PS homopolymer. Adding PS homopolymer into a low-molar-mass cylindrical morphology PS-b-PDMS system drives it toward a spherical morphology. Besides, by controlling the as-spun state, spherical PDMS nanodomains could be kept and thermally arranged. This PS-homopolymer addition allows not only an efficient, purely thermal arrangement process of spheres but also the ability to work directly on nontreated silicon substrates. Indeed, as shown by STEM measurements, no PS brush surface treatment was necessary in our study to avoid a PDMS wetting layer at the interface with the Si substrate. Our approach was compared to a sphere-forming diblock copolymer, which needs a longer thermal annealing. Furthermore, GISAXS measurements provided complete information on PDMS sphere features. Excellent long-range order spherical microdomains were therefore produced on flat surfaces and inside graphoepitaxy trenches with a period of 21 nm, as were in-plane spheres with a diameter of 8 nm with a 15 min thermal annealing. Finally, direct plasma-etching transfer into the silicon substrate was demonstrated, and 20 nm high silicon nanopillars were obtained, which are very promising results for various nanopatterning applications.

Nanostructured Silicon-Based Fingerprint Dusting Powders for Enhanced Visualization and Detection by Mass Spectrometry

Porous silicon microparticles (pSi MPs) functionalized with fluorescent dyes (lissamine and carboxy-5-fluorescein) and intrinsically luminescent pSi MPs were explored as novel fingerprint dusting powders. The versatility of luminescent pSi MPs is demonstrated through time-gated imaging of their long-lived (lifetime>28 μs) near-IR emission, and mass spectrometry analysis of fingerprints dusted with luminescent pSi MPs to provide further information on exogenous small molecules present in latent fingerprints.

High-efficiency nanostructured silicon solar cells on a large scale realized through the suppression of recombination channels

Nanostructured silicon solar cells show great potential for new-generation photovoltaics due to their ability to approach ideal light-trapping. However, the nanofeatured morphology that brings about the optical benefits also introduces new recombination channels, and severe deterioration in the electrical performance even outweighs the gain in optics in most attempts. This Research News article aims to review the recent progress in the suppression of carrier recombination in silicon nanostructures, with the emphasis on the optimization of surface morphology and controllable nanostructure height and emitter doping concentration, as well as application of dielectric passivation coatings, providing design rules to realize high-efficiency nanostructured silicon solar cells on a large scale.

Synchrotron soft X-ray absorption spectroscopy study of carbon and silicon nanostructures for energy applications

Carbon and silicon materials are two of the most important materials involved in the history of the science and technology development. In the last two decades, C and Si nanoscale materials, e.g., carbon nanotubes, graphene, and silicon nanowires, and quantum dots, have also emerged as the most interesting nanomaterials in nanoscience and nanotechnology for their myriad promising applications such as for electronics, sensors, biotechnology, etc. In particular, carbon and silicon nanostructures are being utilized in energy-related applications such as catalysis, batteries, solar cells, etc., with significant advances. Understanding of the nature of surface and electronic structures of nanostructures plays a key role in the development and improvement of energy conversion and storage nanosystems. Synchrotron soft X-ray absorption spectroscopy (XAS) and related techniques, such as X-ray emission spectroscopy (XES) and scanning transmission X-ray microscopy (STXM), show unique capability in revealing the surface and electronic structures of C and Si nanomaterials. In this review, XAS is demonstrated as a powerful technique for probing chemical bonding, the electronic structure, and the surface chemistry of carbon and silicon nanomaterials, which can greatly enhance the fundamental understanding and also applicability of these nanomaterials in energy applications. The focus is on the unique advantages of XAS as a complementary tool to conventional microscopy and spectroscopy for effectively providing chemical and structural information about carbon and silicon nanostructures. The employment of XAS for in situ, real-time study of property evolution of C and Si nanostructures to elucidate the mechanisms in energy conversion or storage processes is also discussed.

Pulsed transfer etching of PS-PDMS block copolymers self-assembled in 193 nm lithography stacks

This work presents the graphoepitaxy of high-χ block copolymers (BCP) in standard industry-like lithography stacks and their transfer into the silicon substrate The process includes conventional 193 nm photolithography, directed self-assembly of polystyrene-block-polydimethylsiloxane (PS-b-PDMS) and pulsed plasma etching to transfer the obtained features into the substrate. PS-b-PDMS has a high Flory-Huggins interaction parameter (high-χ) and is capable of achieving sub-10 nm feature sizes. The photolithography stack is fabricated on 300 mm diameter silicon wafers and is composed of three layers: spin-on-carbon (SoC), silicon-containing anti-reflective coating (SiARC) and 193 nm photolithography resist. Sixty-nanometer-deep trenches are first patterned by plasma etching in the SiARC/SoC stack using the resist mask. The PS-b-PDMS is then spread on the substrate surface. Directed self-assembly (DSA) of the BCP is induced by a solvent vapor annealing process and PDMS cylinders parallel to the substrate surface are obtained. The surface chemistry based on SoC permits an efficient etching process into the underlying silicon substrate. The etching process is performed under dedicated pulsed plasma etching conditions. Fifteen nanometer half-pitch dense line/space features are obtained with a height up to 90 nm.

Broadband antireflective silicon nanostructures produced by spin-coated Ag nanoparticles

We report the fabrication of broadband antireflective silicon (Si) nanostructures fabricated using spin-coated silver (Ag) nanoparticles as an etch mask followed by inductively coupled plasma (ICP) etching process. This fabrication technique is a simple, fast, cost-effective, and high-throughput method, making it highly suitable for mass production. Prior to the fabrication of Si nanostructures, theoretical investigations were carried out using a rigorous coupled-wave analysis method in order to determine the effects of variations in the geometrical features of Si nanostructures to obtain antireflection over a broad wavelength range. The Ag ink ratio and ICP etching conditions, which can affect the distribution, distance between the adjacent nanostructures, and height of the resulting Si nanostructures, were carefully adjusted to determine the optimal experimental conditions for obtaining desirable Si nanostructures for practical applications. The Si nanostructures fabricated using the optimal experimental conditions showed a very low average reflectance of 8.3%, which is much lower than that of bulk Si (36.8%), as well as a very low reflectance for a wide range of incident angles and different polarizations over a broad wavelength range of 300 to 1,100 nm. These results indicate that the fabrication technique is highly beneficial to produce antireflective structures for Si-based device applications requiring low light reflection.

Antireflective silicon nanostructures with hydrophobicity by metal-assisted chemical etching for solar cell applications

We present broadband antireflective silicon (Si) nanostructures with hydrophobicity using a spin-coated Ag ink and by subsequent metal-assisted chemical etching (MaCE). Improved understanding of MaCE, by conducting parametric studies on optical properties, reveals a design guideline to achieve considerably low solar-weighted reflectance (SWR) in the desired wavelength ranges. The resulting Si nanostructures show extremely low SWR (1.96%) and angle-dependent SWR (<4.0% in the range of 0° to 60°) compared to that of bulk Si (SWR, 35.91%; angle-dependent SWR, 37.11%) in the wavelength range of 300 to 1,100 nm. Relatively large contact angle (approximately 102°) provides a self-cleaning capability on the solar cell surface.

Picosecond carrier dynamics induced by coupling of wavefunctions in a Si-nanodisk array fabricated by neutral beam etching using bio-nano-templates

The picosecond carrier dynamics in a closely packed Si-nanodisk (Si-ND) array with ultrathin potential barrier fabricated by neutral beam etching using bio-nano-templates was investigated by time-resolved photoluminescence (PL). The PL decay curves were analyzed as a function of photon energy by the global fitting method. We show three spectral components with different decay times, where the systematic energy differences of the spectral peaks are clarified: 2.03 eV for the fastest decaying component with a decay time τ = 40 ps, 2.02 eV for τ = 300 ps, and 2.00 eV for τ = 1.6 ns. These energy separations ranging from 10 to 30 meV among the emissive states can be attributed to the coupling of wavefunctions of carriers between neighboring NDs.

Paradox of low field enhancement factor for field emission nanodiodes in relation to quantum screening effects

We put forward the quantum screening effect in field emission [FE] nanodiodes, explaining relatively low field enhancement factors due to the increased potential barrier that impedes the electron Fowler-Nordheim tunneling, which is usually observed in nanoscale FE experiments. We illustratively show this effect from the energy band diagram and experimentally verify it by performing the nanomanipulation FE measurement for a single P-silicon nanotip emitter (Φ = 4.94eV), with a scanning tungsten-probe anode (work function, Φ = 4.5eV) that constitutes a 75-nm vacuum nanogap. A macroscopic FE measurement for the arrays of emitters with a 17-μm vacuum microgap was also performed for a fair comparison.

Morphology Analysis of Si Island Arrays on Si(001)

The formation of nanometer-scale islands is an important issue for bottom-up-based schemes in novel electronic, optoelectronic and magnetoelectronic devices technology. In this work, we present a detailed atomic force microscopy analysis of Si island arrays grown by molecular beam epitaxy. Recent reports have shown that self-assembled distributions of fourfold pyramid-like islands develop in 5-nm thick Si layers grown at substrate temperatures of 650 and 750°C on HF-prepared Si(001) substrates. Looking for wielding control and understanding the phenomena involved in this surface nanostructuring, we develop and apply a formalism that allows for processing large area AFM topographic images in a shot, obtaining surface orientation maps with specific information on facets population. The procedure reveals some noticeable features of these Si island arrays, e.g. a clear anisotropy of the in-plane local slope distributions. Total island volume analysis also indicates mass transport from the substrate surface to the 3D islands, a process presumably related to the presence of trenches around some of the pyramids. Results are discussed within the framework of similar island arrays in homoepitaxial and heteroepitaxial semiconductor systems.

Size-dependent Fano Interaction in the Laser-etched Silicon Nanostructures

Photo-excitation and size-dependent Raman scattering studies on the silicon (Si) nanostructures (NSs) prepared by laser-induced etching are presented here. Asymmetric and red-shifted Raman line-shapes are observed due to photo-excited Fano interaction in the quantum confined nanoparticles. The Fano interaction is observed between photo-excited electronic transitions and discrete phonons in Si NSs. Photo-excited Fano studies on different Si NSs show that the Fano interaction is high for smaller size of Si NSs. Higher Fano interaction for smaller Si NSs is attributed to the enhanced interference between photo-excited electronic Raman scattering and phonon Raman scattering.