Tunable Aspect Ratio Research Articles

Formation of flake-like DAAF crystals with tunable size realized on a microfluidic platform for binder-free initiator explosives

Flake-like energetic crystal has a great potential to achieve initiator explosive with high reactivity, low initiation threshold, high safety, and facile post-processing, but it has been limited for 3,3′-diamino-4,4′-azoxyfurazan (DAAF) by the difficulties in controlling crystal morphology. Here reported is a microfluidic preparation of flake-like DAAF crystals (f-DAAF) with tunable size by combined effect of the adding of facet-controlling agent (nigrosin alcohol soluble) and tuning of the external crystallization conditions. The results show that the crystal system of f-DAAF belong to monoclinic system, the (−201) facet is the largest exposed face. The f-DAAF possess high crystallinity, tunable flake aspect ratio from 6.15 to 66.8 and specific surface area from 2.57 to 5.67 m2·g−1. Molecular dynamics simulations were performed to investigate the selective interactions between the two molecules (facet-controlling agent and solvent) and different crystal faces of DAAF in a real experiment environment. Combined with the experimental results, a possible growth mechanism of the flake-like morphology was discussed. It is found that the f-DAAF not only possess lower impact sensitivity itself, but also can reduce the impact sensitivity of other explosives with high impact sensitivity. The electric explosion derived flyer initiation experiments show that the initiation sensitivity of f-DAAF is much lower than that of raw DAAF in micron size, and comparable to that of ultrafine DAAF. This work demonstrates the promising application potential of f-DAAF as high-performance initiator explosives with low initiation threshold and high safety, and also provides an effective way for their preparation.

Catalyst-free MBE growth of PbSnTe nanowires with tunable aspect ratio

Topological crystalline insulators (TCIs) are interesting for their topological surface states, which hold great promise for scattering-free transport channels and fault-tolerant quantum computing. A promising TCI is SnTe. However, Sn-vacancies form in SnTe, causing a high hole density, hindering topological transport from the surface being measured. This issue could be relieved by using nanowires with a high surface-to-volume ratio. Furthermore, SnTe can be alloyed with Pb reducing the Sn-vacancies while maintaining its topological phase. Here we present the catalyst-free growth of monocrystalline PbSnTe in molecular beam epitaxy. By the addition of a pre-deposition stage before the growth, we have control over the nucleation phase and thereby increase the nanowire yield. This facilitates tuning the nanowire aspect ratio by a factor of four by varying the growth parameters. These results allow us to grow specific morphologies for future transport experiments to probe the topological surface states in a Pb1–x Sn x Te-based platform.

Ring‐opening metathesis polymerization for synthesizing molecular bottlebrushes via the grafting‐through strategy

AbstractMolecular bottlebrush (MBB) has been considered as an important type of unimolecular nanomaterial for widespread applications ranging from energy to biomedicine, due to its typical one‐dimensional molecular conformation with tunable aspect ratio and chemical composition. In the recently decades, the ring‐opening metathesis polymerization (ROMP) combined with the grafting‐through strategy has emerged as a powerful tool for synthesizing MBBs with various architecture, including (multi)block MBBs, core‐shell MBBs, random MBBs and Janus MBBs et al. In this review, the recent advances on the synthesis of MBBs including the rational preparation of NB terminated macromonomers (MMs) and the grafting‐through ROMP are briefly summarized. Moreover, the emerging progress on the grafting‐through ROMP performed in the aqueous media is also highlighted.

Designer peptide–DNA cytoskeletons regulate the function of synthetic cells

The bottom-up engineering of artificial cells requires a reconfigurable cytoskeleton that can organize at distinct locations and dynamically modulate its structural and mechanical properties. Here, inspired by the vast array of actin-binding proteins and their ability to reversibly crosslink or bundle filaments, we have designed a library of peptide–DNA crosslinkers varying in length, valency and geometry. Peptide filaments conjoint through DNA hybridization give rise to tactoid-shaped bundles with tunable aspect ratios and mechanics. When confined in cell-sized water-in-oil droplets, the DNA crosslinker design guides the localization of cytoskeletal structures at the cortex or within the lumen of the synthetic cells. The tunable spatial arrangement regulates the passive diffusion of payloads within the droplets and complementary DNA handles allow for the reversible recruitment and release of payloads on and off the cytoskeleton. Heat-induced reconfiguration of peptide–DNA architectures triggers shape deformations of droplets, regulated by DNA melting temperatures. Altogether, the modular design of peptide–DNA architectures is a powerful strategy towards the bottom-up assembly of synthetic cells.

High yield seedless synthesis of mini gold nanorods: partial silver decoupling allows effective nanorod elongation with tunable surface plasmon resonance beyond 1000 nm and CTAB-free functional coating for mTHPC conjugation.

Gold nanorods with small dimensions demonstrate better cellular uptake and absorption efficiency. The ability to synthesize gold nanorods while maintaining a tunable high aspect ratio is challenging as it requires careful control of reaction conditions, often employing additional steps such as pH modification or the use of polymeric additives. We demonstrate a seedless approach for the synthesis of mini (width < 10 nm) gold nanorods with tunable longitudinal surface plasmon resonance from ∼700 nm to >1000 nm and aspect ratios ranging from ∼3 to ∼7 without the use of any polymeric additives or pH modification. A single mild reducing agent, hydroquinone, allowed for up to ∼98% reaction yield from a gold precursor. A mechanism for elongation is proposed based on partial silver decoupling from the reaction. Finally, the particles were coated with various capping agents to allow functionalization and conjugation of mTHPC drug molecules, which are used in photodynamic treatments, and cytotoxic CTAB was removed to increase their biocompatibility.

Fabrication of high-aspect-ratio fused silica microstructures with large depths using Bessel-beam femtosecond laser-assisted etching

We propose a facile method for the fabrication of high-aspect-ratio (HAR) fused silica microstructures with large depths using Bessel-beam femtosecond laser direct writing followed by selective chemical etching. First, laser-modified micropatterns with tunable aspect ratios are created in glass using backside Bessel laser irradiation. Then, surface and embedded glass microstructures are formed by selective removal of laser-modified regions through chemical etching. To demonstrate the capability of the proposed method, a vertical surface trench with an aspect ratio of ∼98, a depth of 2.82 mm, and a tapered angle of only ∼0.16°, and a series of periodic column array structures with 3D tunable feature sizes have been processed. Moreover, 3D multi-layer fabrication of embedded microchannels with HAR features has been demonstrated. Compared with conventional Gaussian-beam laser pulses, the proposed Bessel-beam method exhibits superior performance for ultrafast laser manufacturing of HAR glass microstructures with large depths.

Uniform Colloidal Polymer Rods by Stabilizer-Assisted Liquid-Crystallization-Driven Self-Assembly.

The synthesis of anisotropic colloidal building blocks is essential for their self-assembly into hierarchical materials. Here, a highly efficient stabilizer-assisted liquid-crystallization-driven self-assembly (SA-LCDSA) strategy was developed to achieve monodisperse colloidal polymer rods. This strategy does not require the use of block copolymers, but only homopolymers or random copolymers. The resulting rods have tunable size and aspect ratios, as well as well-defined columnar liquid crystal structures. The integrated triphenylene units enable the rods to exhibit unusual photo-induced fluorescence enhancement and accompanying irradiation memory effect, which, as demonstrated, are attractive for information encryption/decryption of paper documents. In particular, unwanted document decryption during delivery can be examined by fluorescence kinetics. This SA-LCDSA-based approach can be extended to synthesize other functional particles with desired π-molecular units.

Uniform Colloidal Polymer Rods by Stabilizer‐Assisted Liquid‐Crystallization‐Driven Self‐Assembly

AbstractThe synthesis of anisotropic colloidal building blocks is essential for their self‐assembly into hierarchical materials. Here, a highly efficient stabilizer‐assisted liquid‐crystallization‐driven self‐assembly (SA‐LCDSA) strategy was developed to achieve monodisperse colloidal polymer rods. This strategy does not require the use of block copolymers, but only homopolymers or random copolymers. The resulting rods have tunable size and aspect ratios, as well as well‐defined columnar liquid crystal structures. The integrated triphenylene units enable the rods to exhibit unusual photo‐induced fluorescence enhancement and accompanying irradiation memory effect, which, as demonstrated, are attractive for information encryption/decryption of paper documents. In particular, unwanted document decryption during delivery can be examined by fluorescence kinetics. This SA‐LCDSA‐based approach can be extended to synthesize other functional particles with desired π‐molecular units.

Anisotropic Growth of Centimeter-Size CsCu2 I3 Single Crystals with Ultra-Low Trap Density for Aspect-Ratio-Dependent Photodetectors.

Low-dimensional ternary copper iodide metal halide with strong quantum confinement effects has made great progress in optoelectronic fields. However, efficient regulation of anisotropic growth of metal halides single crystal still remains a great challenge. Herein, 2cmsize CsCu2 I3 single crystals with tunable aspect ratio and the trap states (ntrap ) as low as 5.38×109 cm-3 are fabricated by optimized anti-solvent vapor-assisted method, in which the growth cycle is shortened by half. Evidenced by real-time observation and the LaMer growth model, the rapid and anisotropic growth mechanism is ascribed to preferential 1D growth, promoted by high concentration and fast vapor rate. Furthermore, the aspect-ratio-dependent optoelectronic performance is observed, the on-off ratio for 2cm CsCu2 I3 single crystal are enhanced 350 times compared with those of short and thick single crystal, which shows ultrahigh on-off ratio of 1570, D* of 1.34×1012 Jones, Rλ of 276.94mAW-1 , t rise /t decay of 0.37 and 1.08ms, and EQE of 95.53%, which are clearly at very high level among lead-free perovskite-based photodetectors. This study not only provides a new strategy for overcoming anisotropic growth limitations of low-dimensional metal halides, but also paves a way for high-performance optoelectronic applications.

Postsynthetic Thiol-Induced Reshaping of Copper Sulfide Nanoparticles

Nanoparticles of copper sulfide, including roxbyite Cu1.8S, are important materials for many applications, and they also serve as versatile templates for cation exchange reactions that transform them into derivative metal sulfide compounds and complex heterostructures. The sizes and shapes of roxbyite nanoparticles are generally determined during synthesis, and their morphologies are retained during postsynthetic modifications such as cation exchange. Here, we demonstrate postsynthetic morphological modification of roxbyite nanoparticles by treating them with 1-dodecanethiol (1-DDT) and tert-dodecanethiol (t-DDT) at temperatures ranging from 90 to 160 °C. These thiols, which are typically used as ligands and/or sulfur reagents in nanoparticle synthesis, induce morphological reshaping while maintaining composition, crystal structure, and particle volume. For example, 56 nm × 21 nm roxbyite nanorods transform to 32 nm spherical particles in the presence of 1-DDT at 130 °C for two or more hours. The nanorods progressively decrease in length and increase in width, forming a series of ellipsoids having tunable aspect ratios at intermediate time points. Control experiments point to a single-crystal-to-single-crystal pathway that involves material diffusion and migration, which can be accelerated by increasing the density of cation vacancies in the nanoparticles. Because of this pathway, the thiol-induced morphology changes are selective to the copper sulfide regions of heterostructured nanorods containing roxbyite and ZnS, Co9S8, or CuInS2 made using partial cation exchange reactions, providing access to a library of derivative nanoparticles having otherwise inaccessible morphologies.

Magnetism Engineering in Antiferromagnetic β-FeOOH Nanostructures via Chemically Induced Lattice Defects

Elongated akaganéite (β-FeOOH) nanostructures were synthesized through a simple hydrothermal route, in which a careful selection of the experimental conditions allows for a tunable length and aspect ratio and concomitantly predetermines the magnetic response. An in-depth structural characterization using transmission electron microscopy, X-ray diffraction, and Raman spectroscopy, jointly with DC magnetic measurements, reveals a complex scenario where the interstitial Cl– content dictates the β-FeOOH thermal stability and leads to the formation of bulk uncompensated spins along the inner channels. The coexistence of different magnetic contributions is observed to result in a non-monotonic dependence of the coercivity and exchange bias field on both temperature and size, posing major limitations for the archetypical magnetic core–shell model generally assumed for nanostructured antiferromagnets. As a proof of concept, we further show how the β-FeOOH internal microstructure can be chemically manipulated through Cl– anion exchange, giving rise to a superparamagnetic component that comes along with an almost 20-fold increase in the coercivity at low temperature. The evaluation of these results reveals the potential of controlling the interplay between the crystal and magnetic structure via intercalation chemistry in antiferromagnets, expanding fundamental science knowledge and supporting practical applications, given their huge role in the technological fields of spintronics and magnonics.

Enhanced formation of nanometric titanium cones by incorporation of titanium, tungsten and/or iron in a helium ion beam

Surface patterning of bio-compatible titanium (Ti) shows a growing interest in the medical field. The engineering of material surfaces can achieve bactericidal properties and osteointegration improvements in order to develop medical implants. Spikes-like surface morphologies have already demonstrated the development of promising bactericidal properties. A barely new method to produce nanometric-sized cones on titanium consists of helium (He) ion irradiation using low energies (≈100eV) and temperatures comprised between 0.25<T/Tm<0.5 (with Tm being the melting temperature of the material). Ti, iron (Fe) and/or tungsten (W) were incorporated in a He beam, and their amounts were quantified using X-ray Photoelectron Spectroscopy (XPS). The He ion energy was varied from 70 and 120eV, the surface temperatures from 571 to 651K for fluences approximately equal to 1024m−2. After irradiation, the surface morphology was characterized using Scanning Electron Microscopy (SEM) and Focused Ion Beam (FIB). This study demonstrated the capability for irradiated Ti surfaces to form cones with tunable density, aspect ratio, and heights with the incorporation of Ti, Fe and/or W in a He ion. Additionally, the growth rate of the cones was enhanced by about 30 times in comparison to pure He irradiation as a function of the chosen materials introduced in the He beam.

Design and analysis of electrothermal metasurfaces

Electrothermal metasurfaces have attracted extensive attention due to their ability to dynamically control thermal infrared radiation. Although previous studies were mainly focused on the metasurfaces with infinite unit cells, the finite-size effect can be a critical design factor for developing thermal metasurfaces with fast response and broad temperature uniformity in practice. Here, we study the thermal metasurfaces consisting of gold nanorods with a finite array size, which, with only several periods, can achieve a resonance close to that of the infinite case. More importantly, such a small footprint due to the finite array size results in the response time down to a nanosecond level. Furthermore, the number of the unit cells in the direction perpendicular to the axis of the nanorods is found to be insensitive to the resonance and response time, thus providing a tunability in aspect ratio that can boost the temperature uniformity in the sub-Kelvin level.

Facile Fabrication of Starch-Based Microrods by Shear-Assisted Antisolvent-Induced Nanoprecipitation and Solidification.

Rod-like particles have attracted increasing attention because of their unique shape-dependent properties, which enable their superior performance compared to their isotropic counterparts. Thus, rod-like particles have potential applications in many fields, especially in biomedicine. However, the fabrication of uniform rod-like particles is challenging because of the principle of interfacial energy minimization. Herein, we present a facile, rapid, and cost-effective strategy for preparing starch-based microrods with tunable aspect ratios via shear-assisted antisolvent-induced nanoprecipitation and solidification. The preformed spherical particles swollen by the mixed solvent were elongated by the shear force and solidified in rod-like shape by antisolvent induction. The resulting starch-based microrods can encapsulate hydrophobic active substances and be modified with functional groups, indicating their potential applications as drug carriers and biologically active materials. The formation mechanism of the starch-based microrods discovered in this study provides a new perspective on the fabrication of rod-like polymer particles.

An effective one-step aqueous-phase synthesis of finely controllable Ag nanorods with tunable short aspect ratios and electronic dynamics properties

Ag nanorods with finely controllable aspect ratios (especially 1–5) were synthesized in high yield via an effective one-step aqueous-phase method, in which the longitudinal plasmon modes in visible and infrared regions of short Ag nanorods were well adjustable. Meanwhile, excitation wavelength- and excitation fluence-dependent electronic dynamics of short Ag nanorods were acquired and were found to be regular. This suggested that short Ag nanorods would have great potential in plasmonic and photoelectronic fields.

Site-selective doping induced synergistic effect of midgap states and aspect ratio-related charge transfer in Ag2S-ZnS heterostructure toward H2 photoproduction

Ag2S-ZnS (AZ) heterostructures with tunable aspect ratio (AR) and band structure were successfully synthesized by site-selective doping of metal ions. TEM and XPS results showed that by doping Cu, Mn and Cd ions in AZ heterostructures (Cu: AZ, Mn: AZ and Cd: AZ), respectively, the morphology of AZ heterostructures changed from tadpole-shape (Cu: AZ with AR of 1.2) to matchstick-shape (Cd: AZ with AR of 3.9) due to the selective doping of Cu ions in Ag2S head and Cd ions in ZnS tail as well as the doping of Mn ions both in Ag2S head and ZnS tail (Mn: AZ with AR of 2.7). All the UV-Vis spectra of doped AZ showed Urbach tail absorption, suggesting the existence of midgap-states created by metal ion dopants, which was confirmed by PL results. Cd: AZ with the largest AR values and Cd-doping induced midgap states showed the highest photocatalytic H2-production rate of 1443.55 μmol h−1 g−1. The catalytic activity of the Cd: AZ can be ascribed to the synergistic effect of midgap states and aspect ratio-dependent charge transfer, which all originate from the site-selective doping of metal ions. This investigation demonstrates a facile way to manipulate the charge carrier dynamics of semiconductor heterostructures by synergistic effects through simultaneously tuning and optimizing the electronic and morphological structures.

Chemically Tunable Aspect Ratio Control and Laser Refrigeration of Hexagonal Sodium Yttrium Fluoride Upconverting Materials

Chemically Tunable Aspect Ratio Control and Laser Refrigeration of Hexagonal Sodium Yttrium Fluoride Upconverting Materials

Templated electrodeposition as a scalable and surfactant-free approach to the synthesis of Au nanoparticles with tunable aspect ratios.

A high-throughput method for the fabrication of ordered arrays of Au nanoparticles is presented. It is based on pulsed electrodeposition into porous anodic alumina templates. In contrast to many synthesis routes, it is cyanide-free, prior separation of the alumina template from the aluminium substrate is not required, and the use of contaminating surfactants/capping agents often found in colloidal synthesis is avoided. The aspect ratio of the nanoparticles can also be tuned by selecting an appropriate electrodeposition time. We show how to fabricate arrays of nanoparticles, both with branched bases and with hemispherical bases. Furthermore, we compare the different morphologies produced with electron microscopies and grazing-incidence synchrotron X-ray diffraction. We find the nanoparticles are polycrystalline in nature and are compressively strained perpendicular to the direction of growth, and expansively strained along the direction of growth. We discuss how this can produce dislocations and twinning defects that could be beneficial for catalysis.

Phase-Controlled Synthesis of Pd-Sn Nanocrystal Catalysts of Defined Size and Shape.

Bimetallic Pd-based nanoparticles (NPs) are of interest as electrocatalysts for formic acid electrooxidation (FAEO) because of their higher initial catalytic activity and CO tolerance when compared to Pt. Intermetallic NPs (i-NPs) with specific geometric and electronic structures generally exhibit superior catalytic activity, selectivity, and durability when compared to their disordered (random alloy) counterparts; however, the colloidal synthesis of i-NPs remains a challenge. Here, a one-pot method was demonstrated as a facile route to obtain monodisperse Pd-Sn NPs with phase control, including intermetallic hexagonal Pd3Sn2 (P63/mmc), intermetallic orthorhombic Pd2Sn (Pnma), and alloy cubic Pd3Sn (FCC, Fm3m) as size-controlled NPs with quasi-spherical shapes. Initial metal precursor ratios and reaction temperature were critical parameters to achieving phase control. Also, slight modifications of synthetic conditions resulted in either Pd2Sn nanorhombohedra or nanorods with tunable aspect ratios. A systematic evaluation of the Pd-Sn NPs for FAEO showed that most presented higher specific activities when compared to commercial Pd/C, in which Pd2Sn quasi-spheres and nanorhombohedra showed the highest catalytic activity for FAEO. These results highlight the benefits of phase-controlled Pd-based nanocatalysts with defined nanocrystal size and shape, with use of trioctylphospine (TOP) and oleic acid (OA) central to shape and size control.

Three-step seedless synthesis of ultralong gold nanorods

Ultralong gold nanorods with an average aspect ratio up to 77 and average length up to 1.6 μm were obtained by using the three-step seedless wet chemistry growth method. The prepared ultralong gold nanorods were pentatwinned. The effects of the amount transferred from flask B to C, and the pH value in the growth solution C on the synthesized ultralong gold nanorods were investigated by using the scanning electron microscopy images. Results showed that ultralong gold nanorods with tunable average aspect ratio from 24 to 77 were obtained by changing the amount transferred from flask B to C and the pH value in the growth solution C. Due to the large aspect ratio of the prepared gold nanorods, the longitudinal surface plasmon resonance wavelength of the ultralong gold nanorods was expected in the infrared wavelength region. Moreover, 2 μm mid-infrared pulsed laser output was achieved in a passively Q-switched solid-state laser by using the prepared ultralong gold nanorods as the saturable absorber. Our method offers a new facile strategy to obtain ultralong gold nanorods with tunable aspect ratios, which have wide applications in areas such as photonics and optoelectronics.