Arrangement Of Nanocrystals Research Articles

Influence of chromium concentration on the structural, optical, magnetical, and thermal properties of ZnS nanocrystals

Pure ZnS and Zn1-xCrxS nanoparticles were successfully prepared using the coprecipitation method, where x represents the concentration (x = 0.00, 0.10, and 0.05). There are many analytical methods used, such as X-ray diffraction (XRD), scanning electron microscopy (SEM), and Spectroscopy of energy dispersive (EDS). The magnetism structure of the catalysts was investigated using spectrophotometry (VSM), thermogravimetric analysis (TGA), and differential thermal analysis (DTA). X-ray diffraction studies determine the nanocrystal arrangement and size of microcrystals. As seen in SEM analysis, the particles are agglomerated. The coordination of sulfur ions around zinc ions was examined using FTIR analysis. The energy band gap of the Cr-doped sample increases. Photoluminescence spectroscopy showed that the violet emission around 424 nm could be attributed to the excitation process of electrons from the low energy of the conduction band to the valence band of sulfur intermediate atoms. The front amplitude of doped ZnS nanocrystals remains constant regardless of the amount of Cr present. The results show that the ZnS nanocrystals were replaced by dilute Cr3+ ions. Cr-doped ZnS exhibits diamagnetic properties under hightemperature conditions. The results show that these materials are improved by the Cr doping process, making them suitable for many applications.

Langmuir-Blodgett Transfer of Nanocrystal Monolayers: Layer Compaction, Layer Compression, and Lattice Stretching of the Transferred Layer.

Grazing incidence small angle X-ray scattering (GISAXS) was used to study the structure and interparticle spacing of monolayers of organic ligand-stabilized iron oxide nanocrystals floating at the air-water interface on a Langmuir trough, and after transfer to a solid support via the Langmuir-Blodgett technique. GISAXS measurements of the nanocrystal arrangement at the air-water interface showed that lateral compression decreased the interparticle spacing of continuous films. GISAXS also revealed that Langmuir-Blodgett transfer of the nanocrystal layers to a silicon substrate led to a stretching of the film, with a significant increase in interparticle spacing.

Formation and properties of spindle-shaped aragonite mesocrystals from Mg-bearing solutions.

The formation of aragonite under ambient conditions is typically linked to Mg-rich aqueous environments. The grains that form in such environments show peculiar properties such as aggregate-like appearance and mesocrystalline character. We tested the effect of dissolved Mg2+ ions on the formation of aragonite mesocrystals by synthesizing aragonite with an automatic titrator at constant pH and at different dissolved Mg : Ca ratios, and by studying the properties of the precipitated material with various scanning transmission electron microscopy (STEM) techniques. At all studied Mg : Ca ratios the firstly condensed carbonate phase was Mg-bearing amorphous calcium carbonate (Mg-ACC) that transformed into aragonite during the synthesis experiments. The aragonite grains had typically aggregate-like appearance and spindle shapes, with the external morphologies of the spindles unaffected by variation in solution chemistry. The alignment of the nanocrystals within the aggregates was crystallographically highly coherent, the [001] directions of nanocrystals showing only a small misorientation with respect to one another; however, both parallel and twin assembly of neighbouring crystals occurred. An increase in the dissolved Mg concentration decreased the crystallographic coherence between the aragonite nanocrystals, suggesting an important role of Mg2+ ions in the assembly of aragonite spindles. Whereas the mesoscale-ordered arrangement of nanocrystals implies a particle-mediated assembly, the observed differences in particle size and composition between the amorphous precursor and the crystalline end-product suggest that the crystallization includes at least partial dissolution and re-precipitation. These findings provide insight into the formation of aragonite and could contribute to the understanding of important aspects of the formation of mesocrystals and hierarchically structured biogenic minerals.

Targeted Approach to Enhance the Solubility of Weakly Soluble Drugs by Nanocrystal Technology.

About 90% of the newly discovered drugs are poorly soluble in water, to overcome this problem, nanocrystal technology is used. Nanocrystal technology is a modern technique that is specially used to increase the solubility of less soluble drugs. Production of a nanocrystal on a large scale can be done by techniques like homogenization (high-pressure), precipitation, and milling methods. Using this technique, saturation solubility, the adhesiveness of a drug molecule to the surface cell, and the dissolution velocity is enhanced. This technology is better than the traditional method because it provides certain other benefits like increased drug loading capability, fantastic reproducibility of oral retention, further developed proportionality of portion bioavailability and expanded patient compliance. This audit makes sense of the various kinds of techniques for the arrangement of nanocrystals, benefits, drawbacks, a system of solvency improvement, clinical applications, and future imminent. This review article also provides further guidelines for studies about nanocrystal technology.

The Silver Ion and Nanocrystalline Pattern in the Glass Substrate, the Electric Field-Induced Thermal Transfer and Ink Absorption Layer Structure and Printing Performance

People’s research on nanocrystals is getting more in-depth with the development of science and technology, and the patterned arrangement of nanocrystals can greatly improve the performance of our equipment in related fields, allowing people to control the patterning of nanocrystals. Research on thermal transfer is also increasing. Glass materials doped with patterned metal nanocrystals have great application potential, and the search for a simple and efficient patterned preparation method has attracted great attention of many researchers. Using the directional induced migration effect of the high temperature and high voltage DC electric field, combined with the subsequent heat treatment process, the distribution of silver nanocrystals corresponding to the surface silver film pattern can be formed in the silicate glass substrate, to realize the electric field-induced thermal transfer of the nanocrystal pattern print. This article aims to study the patterned thermal transfer of silver ions and nanocrystals on the glass substrate by applying an electric field to induce and analyze the ink absorption layer structure and printing performance. On this basis, an electron beam-induced thermal transfer method and Maxwell’s equation are proposed to investigate and calculate the structure of the ink absorption layer. The experimental structure shows that using this method increases the success rate of the preparation of silver ions and nanocrystal patterns on the glass substrate by 30%, which improves the ink absorption layer and printing performance to different degrees.

Direct Observation Techniques Using Scanning Electron Microscope for Hydrothermally Synthesized Nanocrystals and Nanoclusters

Metal oxide nanocrystals have garnered significant attention owing to their unique properties, including luminescence, ferroelectricity, and catalytic activity. Among the various synthetic methods, hydrothermal synthesis is a promising method for synthesizing metal oxide nanocrystals and nanoclusters. Because the shape and surface structure of the nanocrystals largely affect their properties, their analytical methods should be developed. Further, the arrangement of nanocrystals should be studied because the properties of nanoclusters largely depend on the arrangement of the primary nanocrystals. However, the analysis of nanocrystals and nanoclusters remains difficult because of their sizes. Conventionally, transmission electron microscopy (TEM) is widely used to study materials in nanoscale. However, TEM images are obtained as the projection of three-dimensional structures, and it is difficult to observe the surface structures and the arrangement of nanocrystals using TEM. On the other hand, scanning electron microscopy (SEM) relies on the signals from the surface of the samples. Therefore, SEM can visualize the surface structures of samples. Previously, the spatial resolution of SEM was not enough to observe nanoparticles and nanomaterials with sizes of between 10 and 50 nm. However, recent developments, including the low-landing electron-energy method, improved the spatial resolution of SEM, which allows us to observe fine details of the nanocluster surface directory. Additionally, improved detectors allow us to visualize the elemental mapping of materials even at low voltage with high solid angle. Further, the use of a liquid sample holder even enabled the observation of nanocrystals in water. In this paper, we discuss the development of SEM and related observation technologies through the observation of hydrothermally prepared nanocrystals and nanoclusters.

3-D hierarchical micro/nano-structures of porous Bi2WO6: Controlled hydrothermal synthesis and enhanced photocatalytic performances

As one of the simplest aurivillius layered materials, Bi2WO6 is a promising photocatalyst with a wide range of applications. The construction of 3-D hierarchical micro/nano-structures (3-D HMNSs) can be considered as an excellent strategy to improve the photocatalytic activity. In this paper, a series of porous Bi2WO6 photocatalysts with 3-D HMNSs were synthesized by hydrothermal method via adjusting the concentration of reactants. All kinds of characterization methods (XRD, SEM, TEM, BET, UV–Vis, etc.) were used to characterize the as-synthesized samples. Taking tetracycline as a model pollutant, the photocatalytic properties of these Bi2WO6 photocatalysts were investigated, and the mechanism of its photocatalytic degradation was also proposed. The Bi2WO6-4# sample showed the highest visible-light photocatalytic activity, with tetracycline removal rate of 99.9% in 1 h irradiation and a kinetic reaction rate constant of 0.06071 min−1. The catalytic mechanism analysis shows that the active radicals of ·OH and ·O2− produced by the photoelectron hole have strong oxidizing property, which can quickly decompose tetracycline. Bi2WO6-4# with oriented arrangement of nanocrystals and increased Eg have the advantage of promoting the separation of electron-hole pair, accounting for the high photocatalytic activity.

Elasticity of Cross-Linked Titania Nanocrystal Assemblies Probed by AFM-Bulge Tests.

In order to enable advanced technological applications of nanocrystal composites, e.g., as functional coatings and layers in flexible optics and electronics, it is necessary to understand and control their mechanical properties. The objective of this study was to show how the elasticity of such composites depends on the nanocrystals’ dimensionality. To this end, thin films of titania nanodots (TNDs; diameter: ~3–7 nm), nanorods (TNRs; diameter: ~3.4 nm; length: ~29 nm), and nanoplates (TNPs; thickness: ~6 nm; edge length: ~34 nm) were assembled via layer-by-layer spin-coating. 1,12-dodecanedioic acid (12DAC) was added to cross-link the nanocrystals and to enable regular film deposition. The optical attenuation coefficients of the films were determined by ultraviolet/visible (UV/vis) absorbance measurements, revealing much lower values than those known for titania films prepared via chemical vapor deposition (CVD). Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images showed a homogeneous coverage of the substrates on the µm-scale but a highly disordered arrangement of nanocrystals on the nm-scale. X-ray photoelectron spectroscopy (XPS) analyses confirmed the presence of the 12DAC cross-linker after film fabrication. After transferring the films onto silicon substrates featuring circular apertures (diameter: 32–111 µm), freestanding membranes (thickness: 20–42 nm) were obtained and subjected to atomic force microscopy bulge tests (AFM-bulge tests). These measurements revealed increasing elastic moduli with increasing dimensionality of the nanocrystals, i.e., 2.57 ± 0.18 GPa for the TND films, 5.22 ± 0.39 GPa for the TNR films, and 7.21 ± 1.04 GPa for the TNP films.

Tuning Chiral Nematic Pitch of Bioresourced Photonic Films via Coupling Organic Acid Hydrolysis

AbstractControlling the iridescent photonic film generated by self‐assembly of colorless cellulose nanocrystal (CNC) from the nanoscale to macroscale is challenging. This study combines experimental and computational approaches to systematically investigate the correlation between electrostatic interactions and chiral nematic structures. The chiral nematic order of the CNC colloidal is preserved in solid films after the evaporation of water. The cross‐sections of the iridescent film show a clear left‐handed helical arrangement of nanocrystals. The helical structure with the aid of acrylic acid exhibits longer organized patterns. This work reveals that compared to CNC prepared by pure sulfuric acid (zeta potential −37.1 mV), the CNC prepared using coupled mineral sulfuric and organic acrylic acid has a higher zeta potential (−67.2 mV), which induces the increase of helical pitch of the cholesteric nematic phase from 312 to 409 nm and a red shift of the iridescent film. Consequently, the tuning of reflected light wavelength lies in the variation of chiral nematic pitch inside the layered structure, which gives rise to different iridescent colors. The bioresourced photonic film is appealing to both academia and industry where optical and photonic components are essential.

Effect of low NiO doping on anomalous light scattering in zinc aluminosilicate glass-ceramics

The effect of low NiO doping (0–0.15mol%) on the extinction coefficient of zinc aluminosilicate glass-ceramics prepared by five different two-stage heat treatments was studied experimentally. Extinction coefficient vs wavelength presented as a log-log plot was separated into scattering and absorption coefficients. The NiO addition drastically changes not only values of the scattering coefficient at a given wavelength of visible light (effect 1), but also the type of wavelength dependence of this coefficient (effect 2). These effects do not correlate with variation of sizes and volume fractions of nanocrystals determined by Rietveld refinement of X-ray diffraction data. They cannot be described in the model of independent Rayleigh scatterers. These effects are characteristic features of anomalous light scattering by inhomogeneous glasses and can be explained by interference of light scattered by different nanocrystals. To calculate interference effects, the detailed information on mutual arrangement of nanocrystals is required, which unlikely can be determined experimentally for multiphase polydisperse system of nanocrystals. Instead, simplified models for systems of nanocrystals in glass-ceramics can be considered. And finally, we cannot explain the mechanism of the effect of small NiO additions on light scattering and hence, on structure of glass-ceramics.

Cellular interfaces with hydrogen-bonded organic semiconductor hierarchical nanocrystals

Successful formation of electronic interfaces between living cells and semiconductors hinges on being able to obtain an extremely close and high surface-area contact, which preserves both cell viability and semiconductor performance. To accomplish this, we introduce organic semiconductor assemblies consisting of a hierarchical arrangement of nanocrystals. These are synthesised via a colloidal chemical route that transforms the nontoxic commercial pigment quinacridone into various biomimetic three-dimensional arrangements of nanocrystals. Through a tuning of parameters such as precursor concentration, ligands and additives, we obtain complex size and shape control at room temperature. We elaborate hedgehog-shaped crystals comprising nanoscale needles or daggers that form intimate interfaces with the cell membrane, minimising the cleft with single cells without apparent detriment to viability. Excitation of such interfaces with light leads to effective cellular photostimulation. We find reversible light-induced conductance changes in ion-selective or temperature-gated channels.

Revealing the nanostructure of calcium phosphate coatings using HRTEM/FIB techniques

Herein, we report on the micro- and nanostructure of the calcium phosphate coating produced by pulsed laser deposition (PLD), using focused ion beam (FIB) lamella sample preparation and transmission electron microscopy (TEM) as the characterization technique. The initial selected area electron diffraction (SAED) data demonstrated the presence of hydroxyapatite (HA) over any other possible calcium phosphate crystalline structure and the polycrystalline nature of the coating. Moreover, the SAED analyses showed clear textured ring patterns coherent with the presence of a preferred orientation in the HA nano-crystal growth. The SAED data also indicated that the coating appears to be textured in the 〈002〉 crystalline direction. Dark-field images obtained using 002 as the working reflection showed a clear oriented crystal growth in columns, from bottom to top. These columns have a peculiar arrangement of nano-crystals since, in some cases, the preferred orientation appears to start at a certain distance from the substrate. Direct d-spacing measurements on high-resolution TEM images provided further proof of the presence of an HA nano-crystal structure. The reported data may be of interest in the future to adjust the microstructure of the HA coatings.

Confinement-induced nanocrystal alignment of conjugated polymer by the soft-stamped nanoimprint lithography**Project supported by the National Natural Science Foundation of China (Grant No. 21204058).

Soft-stamped nanoimprint lithography (NIL) is considered as one of the most effective processes of nanoscale patterning because of its low cost and high throughput. In this work, this method is used to emboss the poly (9, 9-dioctylfluorene) film. By reducing the linewidth of the nanogratings on the stamp, the orientations of nanocrystals are confined along the grating vector in the nanoimprint process, where the confinement linewidth is comparable to the geometrical size of the nanocrystal. When the linewidth is about 400 nm, the poly (9, 9-dioctylfluorene) (PFO) nanocrystals could be orderly arranged in the nanogratings, so that both pattern transfer and well-aligned nanocrystal arrangement could be achieved in a single step by the soft-stamped NIL. The relevant mechanism of the nanocrystalline alignment in these nanogratings is fully discussed. The modulation of nanocrystal alignment is of benefit to the charge mobilities and other performances of PFO-based devices for the future applications.

Nanocrystal Superlattice Embedded within an Inorganic Semiconducting Matrix by in Situ Ligand Exchange: Fabrication and Morphology

The authors carry out ligand exchange reaction replacing bulky insulating org. ligands with inorg. chalcogenidometallate clusters in nanocrystal assemblies floating at the gas-liq. interface. The mobility of the nanocrystals allows lattice contraction without significantly diminishing the ordering obsd. by grazing incidence X-ray scattering and transmission electron microscopy (TEM). This approach produces inorg. nanocomposite films one to a few nanocrystals in thickness with highly regular arrangements of nanocrystals. Anal. of free-standing nanocrystal membranes by low-dose, aberration-cor. TEM allows direct visualization of the nanocrystal-matrix interface.

An attempt to cast light into starch nanocrystals preparation and cross-linking

Potato starch was hydrolyzed with 2.2 or 3.7M hydrochloric acid in order to obtain the nanocrystals which afterwards were chemically cross-linked with sodium hexametaphosphate. The stronger acidity resulted in smaller nanocrystals with mean size of 48nm in a shorter time. X-ray diffraction confirmed the dominant crystalline nature of particles and Fourier transform infrared spectroscopy suggested the presence of lower number of free hydroxyl groups in nanocrystals after cross-linking. Starch nanocrystals showed two distinctive differential scaning colorimetry endotherms at 26 and 125°C, attributed to destruction of nanocrystals lattice and moblizing of each nanocrystal’s structure, respectively. Cross-linking resulted in a tenacious spatial arrangement of nanocrystals, strengthening the crystals lattice against phase transitions induced by heating. Scanning electron microscopy images confirmed the particle size measured for nanocrystals by light scattering. Atomic force microscopy topographic images suggested that starch nanocrystals were originated from small amylopectin blocklets in granular assembly of starch.

SEM imaging of chiral nematic films cast from cellulose nanocrystal suspensions

The chiral nematic self-assembly of aqueous suspensions of cellulose nanocrystals is partially preserved on evaporation of water, but the ordering of the rod-like nanoparticles may become distorted by changes in volume, ionic strength and surface and convective forces during evaporation, thus affecting the morphology and optical properties of the dried film. Proposed applications for these solids with chiral nematic order require confirmation of their structure. A SEM examination of the fracture surface of a slowly-dried film showed a surprisingly regular fan-like pattern which is shown to be characteristic of cross-sections of the left-handed helicoidal arrangement of nanocrystals, where the helicoidal axis was almost perpendicular to the film surfaces. Superimposed on this pattern was what appeared to be a regular porosity, which is postulated to result from pull-out of the nanocrystals oriented orthogonal to the fracture surface.

Early stage mineralization in tissue engineering mapped by high resolution X-ray microdiffraction

The specific routes of biomineralization in nature are here explored using a tissue engineering approach in which bone is formed in porous ceramic constructs seeded with bone marrow stromal cells and implanted in vivo. Unlike previous studies this model system reproduces mammalian bone formation, here investigated at high temporal resolution. Different mineralization stages were monitored at different distances from the scaffold interface so that their spatial analysis corresponded to temporal monitoring of the bone growth and mineralization processes. The micrometer spatial resolution achieved by our diffraction technique ensured highly accurate reconstruction of the different temporal mineralization steps and provided some hints to the challenging issue of the mineral deposit first formed at the organic–mineral interface. Our results indicated that in the first stage of biomineralization organic tissue provides bioavailable calcium and phosphate ions, ensuring a constant reservoir of amorphous calcium phosphate (ACP) during hydroxyapatite (HA) nanocrystal formation. In this regard we suggest a new role of ACP in HA formation, with a continuous organic–mineral transition assisted by a dynamic pool of ACP. After HA nanocrystals formed, the scaffold and collagen act as templates for nanocrystal arrangement on the microscopic and nanometric scales, respectively.

Optimizing non-radiative energy transfer in hybrid colloidal-nanocrystal/silicon structures by controlled nanopillar architectures for future photovoltaic cells

To optimize colloidal nanocrystals/Si hybrid structures, nanopillars are prepared and organized via microparticle patterning and Si etching. A monolayer of CdSe nanocrystals is then grafted on the passivated oxide-free nanopillar surfaces, functionalized with carboxy-alkyl chain linkers. This process results to a negligible number of non-radiative surface state defects with a tightly controlled separation between the nanocrystals and Si. Steady-state and time-resolved photoluminescence measurements confirm the close-packing nanocrystal arrangement and the dominance of non-radiative energy transfer from nanocrystals to Si. We suggest that radially doped p-n junction devices based on energy transfer offer a viable approach for thin film photovoltaic devices.

Self assembly of inorganic nanocrystals in 3D supra crystals: Intrinsic properties

Here we describe how arrangements of nanocrystals can self-organize in 3D arrays called supra crystals. The 3D arrays can fall into the familiar categories of face centered cubic (fcc), hexagonal compact packing (hcp) crystals, and body centered (bcc) crystals. Intrinsic collective properties of these 3D arrangements are different from the properties of individual nanoparticles and from particles in bulk. We demonstrate by two various processes and with two types of nanocrystals (silver and cobalt) that when nanocrystals are self ordered in 3D superlattices, they exhibit a coherent breathing mode vibration of the supra crystal, analogous to a breathing mode vibration of atoms in a nanocrystal. Comparison between the approaches to saturation of the magnetic curve for supra crystals and disordered aggregates produced from the same batch of nanocrystals is similar to that observed with films or nanoparticles either highly crystallized or amorphous.

Effect of silk sericin on assembly of hydroxyapatite nanocrystals into enamel prism-like structure

Taking the inspiration from the biomineral, the silk sericin was selected to modulate the assembly of nanosized hydroxyapatite crystals via a modified co-precipitation method. The effect of silk sericin concentration and mineralization time on the formation of hydroxyapatite nanocrystals, including their nucleation, growth, aggregation, especially assembly dynamics, were investigated using the transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM), X-ray diffraction (XRD) and Fourier transform infrared (FT-IR) spectroscopy. The results revealed that both the concentration of silk sericin and the mineralization time could affect the size, morphology and assembly of hydroxyapatite crystals. Higher concentration of silk sericin in the reaction system was apt to form the larger hydroxyapatite crystals and longer mineralization time helped to improve the crystallinity of hydroxyapatite crystals together with an increase of crystal size. More interested thing was that an arrangement of nanocrystals in order was observed when the concentration of silk sericin was kept at 1(w/v)% in the reaction system. The larger rod-like hydroxyapatite crystals of 300–500 nm in length and 50–80 nm in diameter were assembled along the c-axis by the smaller crystals of ca. 20 nm under the control of silk sericin, whose arrangement method was similar to the natural enamel. A proposed formation mechanism of the special structure was elucidated. In addition, the biocompatibility of obtained crystals was evaluated in vitro and their strong ability to promote the cell differentiation and proliferation was proved in the paper, which may be important for the biomedical applications and also for the fundamental studies of cell–matrix interactions.