Growth Process Of Nanocrystals Research Articles

Nucleation and Growth of Nanocrystals Investigated by In Situ Transmission Electron Microscopy.

Nanocrystals play a key role in the modern energy, catalysis, semiconductor, and biology industries due to their unique structures and performances. However, controllable fabrication of ideal nanocrystals with the desired structures and properties is still challenging, which needs a deep understanding of their nucleation and growth process. Here, the research on nucleation and growth of nanocrystals studied by in situ transmission electron microscopy (TEM) is reviewed, mainly focusing on the atomic migration dynamics, interface evolution, and structure transformation. In addition, the challenges in the study of nanocrystal growth by TEM are discussed and the perspective on the future development of advanced in situ TEM techniques is provided. It is hoped that the review can give a deep insight into the nanocrystal nucleation and growth process, and further contribute to the rational design and precise fabrication of high-performance functional nanocrystals.

Digitizing protocols into single reactors for the one-pot synthesis of nanomaterials

Digitizing protocols into single reactors for the one-pot synthesis of nanomaterials

Intrafibrillar Growth of Hydroxyapatite Nanocrystals in Multiscale Collagen

Collagen fibrils hierarchically assemble from microscale to macroscale, which endows the natural composite bone with good mechanical properties and remodeling functions. Revealing the intrafibrillar growth process of hydroxyapatite nanocrystals of collagen will guide the research of bone repair or collagen-based composites. Herein, we investigated the mineralization of multiscale collagen matrices and strongly proved the intrafibrillar hydroxyapatite nanocrystals in the collagen fibrils. The hydroxyapatite nanocrystals were deposited within collagen fibrils with co-orientation along the (002) crystal plane, which is the longitude of the fibril. The whole growth process was captured by TEM to demonstrated the five stages of the intrafibrillar growth process of hydroxyapatite nanocrystals. The infiltration and transformation of amorphous calcium phosphate in isolated collagen fibrils are both demonstrated. The intrafibrillar growth process of hydroxyapatite nanocrystals in collagen film was also investigated, showing that the growth area of collagen films increased linearly with time and the growth process. By studying the in situ mineralization under different reaction conditions, the kinetic equation of the mineralized area of collagen film under each condition was obtained, and the optimal hydroxyapatite mineralized solution was proved to be a solution with polyacrylic acid of 50 μG/mL and a pH of 7.5. Our work provides more detailed information of the growth process of HAP nanocrystals during the mineralization of collagen at different scales and would contribute to future research on the formation process of more minerals in collagen.

A facile route to metal-oxide nanocrystals by direct pyrolysis of metal-organic frameworks

Metal-oxide nanoparticles (NPs) are of particular interest in various industrial applications. However, current liquid-phase synthetic routes for metal-oxide NPs generally involve complicated processes. Herein, we demonstrate a simple direct route to metal-oxide NPs through the pyrolysis of their metal–organic frameworks (MOFs). As illustrated by the synthesis of ZrO2 and CeO2 NPs, we employed Zr(IV)- and Ce(IV)-based CAU-24 MOFs as precursors, and pyrolysis was performed in both air and molten NaCl environments. Pure oxide NPs with sizes of less than 200 nm were obtained via both routes. Compared with direct pyrolysis in air, the use of molten salt as a liquid reaction medium leads to much smaller ZrO2 NPs but facilitates the growth of CeO2 NPs. The results can be explained by the presence of different phases in the nanocrystal growth process.

A Kinetic Isotope Effect in the Formation of Lanthanide Phosphate Nanocrystals.

Mechanisms of nucleation and growth of crystals are still attracting a great deal of interest, in particular with recent advances in experimental techniques aimed at studying such phenomena. Studies of kinetic isotope effects in various reactions have been useful for elucidating reaction mechanisms, and it is believed that the same may apply for crystal formation kinetics. In this work, we present a kinetic study of the formation of europium-doped terbium phosphate nanocrystals under acidic conditions, including a strong H/D isotope effect. The nanocrystal growth process could be quantitatively followed through monitoring of the europium luminescence intensity. Hence, such lanthanide-based nanocrystals may serve as unique model systems for studying crystal nucleation and growth mechanisms. By combining the luminescence and NMR kinetics data, we conclude that the observed delayed nucleation occurs due to initial formation of pre-nucleation clusters or polymers of the lanthanide and phosphate ions, which undergo a phase transformation to crystal nuclei and further grow by cluster attachment. A scaling behavior observed on comparison of the H2O and D2O-based pre-nucleation and nanocrystal growth kinetics led us to conclude that both pre-nucleation and nanocrystal growth processes are of similar chemical nature.

Synthesis of small-sized hexagonal NaREF4 (RE = Yb, Lu) nanocrystals through accelerating phase transformation

Heavy lanthanide element-based NaREF4 nanocrystals have recently been proposed as a promising replacement of classical hexagonal NaYF4 for their efficient luminescence and excellent X-ray attenuation property. However, synthetic control over their particle size remains challenging due to the fast growth and slow nucleation. Herein, a simple and robust approach for the controlled synthesis of small NaYbF4 and NaLuF4 nanocrystals is presented as well as a mechanistic investigation of the nanocrystal growth process. The injection order of NaOH and NH4F plays critical role in controlling the nanocrystal growth by accelerating phase transformation from cubic phase to hexagonal phase. We also verify experimentally that control of the hexagonal-phase nucleation rather than growth process is crucial for controlling the final particle size of NaYbF4 and NaLuF4. After coating an inert shell, we found enhanced downshifting emission of NaYbF4:Er nanocrystals compared with less Yb3+ doping. The results shown here provide a reliable method for preparing small-sized hexagonal NaYbF4 nanocrystals with enhanced downshifting emission, which favors their further applications in bioscience.

Single-parameter-tuned synthesis for shape-controlled gold nanocrystals stimulated by iron carbonyl

Shape-controlled synthesis is essential for functional nanomaterials, allowing deeper insights intothe relationship between the structures and the catalytic properties. Synthesis of nanocrystals with particular morphologies are usually studied independently among various synthetic methods, those underline that different surface capping ligands or shape-directing agents bring about disparate shapes. However, a single quantitative parameter method is still lacking to realize precise control of well-defined morphology nanocrystals, especially anisotropic structures, which is essential to understanding the growth process of nanocrystals. Herein, we proposed a single-parameter-tuned synthesis strategy for preparation of shape-controlled gold nanocrystals by regulating the amount of iron carbonyl, by which we produced highly monodisperse Au nanocrystals with various shapes in organic phase including nanoplates (diameter of 16.02 ± 1.13 nm and thickness of 5.35 ± 0.58 nm), nanorods (length of 37.53 ± 3.73 nm and width of 5.26 ± 0.37 nm) and nanospheres (diameter of 8.26 ± 0.38 nm). The single-parameter-tuned method reveals the dual roles of iron carbonyl for controlling the shapes of gold nanocrystals including reductant and oxidative etchant and empowers versatility in synthetic methodology for other noble metals. Moreover, catalytic activity shifting in shapes of nanocrystals was revealed based on the reduction of 4-nitrophenol, showing that the as-synthesized Au nanoplates displayed the enhanced catalytic performance with the lowest activation energy. Our work provides a brand-new pathway for shape-controlled synthesis of noble-metal nanocrystals and has a strong practical value in application fields.

Synthesis of Ultrathin Perovskite Nanowires via a Postsynthetic Transformation Reaction of Zero-Dimensional Perovskite Nanocrystals

The synthesis of lead-halide perovskite (LHP) thin nanowires (NWs) has been a challenging task that requires delicate control of nanocrystal (NC) nucleation and growth processes. Herein, we present...

Crystal growth by ordered coalescence of lattice arrays in ZrO2-based nanocomposites at the early stage of crystallization

Amorphous ZrO2-based nanocomposite powder synthesized by sol-gel method is often used as the raw material for preparing advanced ZrO2-based ceramics. The crystal growth process of the amorphous ZrO2-based nanocomposite powder during heat treatment has a crucial influence on the final microstructure and thus the achieved performance of ZrO2-based ceramics. However, the crystal growth process of ZrO2 nanocrystals (NCs), especially at the early stage, was ambiguous due to the lack of detailed investigation. To illustrate this issue, ZrO2-based nanocomposite powder was prepared by sol-gel method, followed by annealing at elevated temperatures. Transmission electron microscopy (TEM) was used to observe the growth process of ZrO2 NCs. Results showed that tiny ZrO2 lattice arrays without definite morphology were formed after the completion of nucleation. Nucleation might follow the classic nucleation mechanism of epitaxial growth by utilizing atoms as building blocks. Then, the randomly-oriented ZrO2 lattice arrays adopt an ordered coalescence mechanism to grow to large ZrO2 NCs. ZrO2 lattice arrays acted as building blocks and they grew rapidly by unifying their crystallography orientations. Self-perfecting, including elimination of dislocations and adjustment of lattice spacing, occurred during the growth process. Ordered coalescence of ZrO2 lattice arrays contributed to the rapid growth of ZrO2 NCs. This study deepens our fundamental understanding of the growth mechanism of amorphous ZrO2-based nanocomposite powder during heat treatment and may offer guidelines for tailoring the final microstructure and performance of ZrO2-based ceramics.

A low-dimensional crystal growth model on an isotropic and quasi-free sustained substrate**Project supported by the National Natural Science Foundation of China (Grant Nos. 11374082 and 51671048) and the Ten Thousand Talents Plan of Zhejiang Province of China (Grant No. 2018R52003).

A new crystal growth theoretical model is established for the low-dimensional nanocrystals on an isotropic and quasi-free sustained substrate. The driven mechanism of the model is based on the competitive growth among the preferential growth directions of the crystals possessing anisotropic crystal structures, such as the hexagonal close-packed and wurtzite structures. The calculation results are in good agreement with the experimental findings in the growth process of the low-dimensional Zn nanocrystals on silicone oil surfaces. Our model shows a growth mechanism of various low-dimensional crystals on/in the isotropic substrates.

Metal-organic frameworks-derived hollow-structured iron-cobalt bimetallic phosphide electrocatalysts for efficient oxygen evolution reaction

The oxygen evolution reaction (OER) is a cornerstone reaction for many renewable energy technologies. Developing low-cost and durable alternatives to precious-metal catalysts with high activity for OER are highly desirable to reduce the processing cost and complexity of renewable energy systems. Recently, metal phosphides based on earth-abundant transition metals, especially bimetallic phosphates have emerged as promising candidates for efficient OER catalysts. The rational design of nanostructured bimetallic phosphates is critical for the practical applications of these electrocatalysts, which requires a well understanding of the composition control and nanocrystal growth process. Herein, we report a facile strategy for the synthesis of novel iron-cobalt bimetallic phosphides (FeCoP) with hollow structures by phosphating Fe (Co)-centered metal-organic frameworks (MOFs). The resultant FeCoP hollow polyhedron, which have large specific surface area providing rich catalytic active sites, show excellent electrocatalytic activity towards OER with low overpotential, small Tafel slope, and remarkable stability. This work provides a new strategy for exploring efficient phosphide catalysts and opens up new avenues for the development of OER catalysts.

Roles of ion irradiation and thermal annealing in inducing crystallization in metallic glass

We studied the crystallization behavior of metallic glass Ni50Nb10Zr15Ti15Pt7.5Cu2.5 under different ion irradiation and thermal annealing conditions. The results show that although the room temperature ion irradiation would not introduce observable structural defects in metallic glass, the excess free volume induced by ion irradiation would promote the formation of nanocrystals under thermal annealing. Meanwhile, the interstitial atoms induced by high temperature ion irradiation may act as an important role in the enhancement of atomic diffusivity and nanocrystals growth process. Our study shows that the combination of ion irradiation and thermal annealing may help to achieve controllable structural modification of metallic glass.

Modulation ferromagnetism in multiferroic BiFeO3 nanocrystals via bandgap engineering

In addition to electric fields and currents, light can also provide an approach to modulate the ferromagnetism with low energy consumption. BiFeO3, with features of relatively small bandgap and large polarization, provides an opportunity for investigating the optical modulation of magnetism. In this work, pure-phase BiFeO3 nanocrystals embedded in Al2O3 films are synthesized. It is demonstrated that the strain generated and accumulated during the growth process of BiFeO3 nanocrystals can lead to the modification of the atomic structure and thus produce a strain engineered bandgap. A distinguished light-modulated ferromagnetism is observed in BiFeO3 nanocrystals. Contributed by the strain engineered bandgap, the ferromagnetism of BiFeO3 nanocrystals can be modulated and enhanced more efficiently by light irradiation. It paves the way for modulating the ferromagnetic properties of BiFeO3 nanocrystals via bandgap engineering, which has promising applications in modern information technology.

Multicomponent Doped Sugar-Coated Haws Stick-like Nanofibers as Efficient Oxygen Reduction Reaction Catalysts for the Zn–Air Battery

In this work, unique sugar-coated haws stick-like core–shell ZIF-67@PAN-HCCP-MIM-FeCl3 nanofibers were successfully prepared by electrospinning and an in situ nanocrystal growth process. After carbonization of the as-synthesized nanofibers at various temperatures, the resulting sample Fe/Co-N/P-9 (carbonized at 900 °C) retained the presented a sugar-coated haws stick-like structure. The internal carbon nanofiber acts like a “stick” as a support, the “haws” composed of Co2P and Fe5C2 nanoparticles act as catalytic active sites, and the graphite carbon acts as “sugar” to protect particles from detachment. The channel gap between inner core and outer layer can improve the mass transfer process. Owing to these special structure and unique composition features, Fe/Co-N/P-9 exhibited excellent oxygen reduction reaction (ORR) performance with an onset potential of 0.96 V (vs RHE) and a half wave potential of 0.85 V (vs RHE) in 0.1 M KOH solution. Fe/Co-N/P-9 also showed good catalytic stability and methanol tole...

Morphology-Controlled Metal Sulfides and Phosphides for Electrochemical Water Splitting.

Because H2 is considered a promising clean energy source, water electrolysis has attracted great interest in related research and technology. Noble-metal-based catalysts are used as electrode materials in water electrolyzers, but their high cost and low abundance have impeded them from being used in practical areas. Recently, metal sulfides and phosphides based on earth-abundant transition metals have emerged as promising candidates for efficient water-splitting catalysts. Most studies have focused on adjusting the composition of the metal sulfides and phosphides to enhance the catalytic performance. However, morphology control of catalysts, including faceted and hollow structures, is much less explored for these systems because of difficulties in the synthesis, which requires a deep understanding of the nanocrystal growth process. Herein, representative synthetic methods for morphology-controlled metal sulfides and phosphides are introduced to provide insights into these methodologies. The electrolytic performance of morphology-controlled metal sulfide- and phosphide-based nanocatalysts with enhanced surface area and intrinsically high catalytic activity is also summarized and the future research directions for this promising catalyst group is discussed.

Dot–Wire–Platelet–Cube: Step Growth and Structural Transformations in CsPbBr3 Perovskite Nanocrystals

While the classical mechanism for the growth of colloidal chalcogenide nanocrystals is largely understood, fundamental insights for the growth of perovskite nanocrystals still remain elusive. Using nanoclusters of ∼0.6 nm diameter as monomers and growing to more than 25 nm in a single reaction, herein, the step growth process of perovskite CsPbBr3 nanocrystals is reported. This is performed with a step-rise of the reaction temperature with correlating annealing time. The growth is so precise that ∼0.6 nm (nearly one unit cell) increments were successively monitored in parallel with the conversion of clusters to nanowires and then to thickness tunable platelets and finally to size-tunable cube-shaped nanostructures. The entire reaction was monitored optically and microscopically, and their step growths were correlated. From these observations, the possible growth mechanism for perovskite nanocrystals along with their shape transformations was proposed.

An investigation into nanohybrid states of europium (III) complex with hydroxyapatite nanocrystals

We synthesized the novel inorganic-organic nanohybrid systems in hydroxyapatite (HA) nanocrystal growth processes under the presence of tris(2,2,6,6-tetramethyl-3,5-heptanedionato)europium (III) (EuTH) complex for the first time. The nanohybrid states were successfully controlled by the EuTH concentration to Ca ions in HA. The morphology of the HA was observed by a transmission electron microscope and the nanocrystalline aspect ratios were estimated to be 2.5–4.8. The segregated EuTH molecules on the HA nanocrystals covered over the a-plane in HA, leading to the effective crystal growth along with the uncovered c-plane. The luminescence properties of the nanohybrids were different from that of the EuTH itself in the solution and solid states, indicating the unique Eu3+ ion states on the HA nanocrystals because of the different ligand field symmetry. Moreover, the relative luminescence intensity ratio based on the 5D0 → 7F1 and 5D0 → 7F2 transitions in the nanohybrid became lower with increasing the EuTH concentration, suggesting that the hybridization lowered the coordination environment symmetry of Eu3+ ion. The luminescence intensity and quantum efficiency of the nanohybrids were higher than that of the EuTH itself. Therefore, the interaction at EuTH–HA interface as well as between EuTH–EuTH molecules significantly changed by the inorganic-organic hybridization under different EuTH concentrations. In future, the present hybridization technique can be applied for preparing the nanohybrids with various metallic complexes.

General Strategy for Synthesis of Pd3M (M = Co and Ni) Nanoassemblies as High‐Performance Catalysts for Electrochemical Oxygen Reduction

AbstractNanoassemblies have attracted considerable attention because of their unique structural advantages, such as the high porosity, abundant surface defects, and low‐coordinated atomic steps, which are of importance to improve electrocatalytic activity and stability. However, developing effective and general synthetic methods for preparation of well‐defined Pd‐based nanoassemblies remains a challenge. Herein, a facile, effective, and general synthetic strategy for fabrication of high‐quality Pd3M (M = Co and Ni) nanoassemblies is developed. It is identified that arginine is pivotal for control of the nucleation and growth process of nanocrystals, where there is strong self‐assembly capacity between arginine molecules as well as effective coordination interaction between guanidine group of arginine with metal ions, endowing its unique dual‐function for the structure‐controllable synthesis of Pd3M alloy. The electrocatalytic performances of Pd3M nanoassemblies for the oxygen reduction reaction are studied through the rotating ring‐disk electrode technique. As expected, both Pd3Co and Pd3Ni nanoassemblies exhibit the more positive onset reduced‐overpotentials and the better catalytic stabilities compared to their counterparts. This work opens a new and general guideline for designing PdM alloy nanoassemblies with exclusive active sites for boosting energy electrocatalysis.

Identifying multi-stage nanocrystal growth using in situ TEM video data

ABSTRACTThe in situ transmission electron microscopy technique is receiving considerable attention in material science research, as its in situ nature makes possible discoveries that ex situ instruments are unable to make and provides the capability of directly observing nanocrystal growth processes. As incresing amounts of dynamic transmission electron microscopy (TEM) video data become available, one of the bottlenecks appears to be the lack of automated, quantitative, and dynamic analytic tools that can process the video data efficiently. The current processing is largely manual in nature and thus laborious, with existing tools focusing primarily on static TEM images. The absence of automated processing of TEM videos does not come as a surprise, as the growth of nanocrystals is highly stochastic and goes through multiple stages. We introduce a method in this article that is suitable for analyzing the in situ TEM videos in an automated and effective way. The method learns and tracks the normalized particle size distribution and identifies the phase-change points delineating the stages in nanocrystal growth. Using the outcome of the change-point detection process, we propose a hybrid multi-stage growth model and test it on an in situ TEM video, made available in 2009 by Science.

Decoupling and elucidation of surface-driven processes during inorganic mineralization on virus templates

There is a lack of fundamental information about the molecular processes governing biomineralization of inorganic materials to produce nanostructures on biological templates. This information is essential for the directed synthesis of high quality nanomaterials via biotemplating. We characterized palladium (Pd) mineralization via the individual adsorption, reduction, and nanocrystal growth processes, which simultaneously occur during the hydrothermal synthesis on the Tobacco mosaic virus (TMV). The adsorption of precursor and reduction of palladium were decoupled through UV–vis Spectroscopy and in situ X-ray absorption spectroscopy studies. The role of additional cysteine (Cys) residues, ionic strength, and coating density on the fundamental parameters describing these processes were quantitatively evaluated. Primary nanocrystal growth and structural orientation of Pd nanoparticles was characterized using in situ small angle X-ray scattering. The adsorption, reduction of Pd species, and nanocrystal sizes were significantly changed on addition of Cys residues to the amino terminus of the TMV coat protein. Reduction of Pd on an already coated virion was dependent on the Pd surface area, and was hindered by the presence of residual salt. Furthermore, trends in Pd adsorption intensity and capacity suggested that chloride ions affected the adsorption equilibrium. Application of this fundamental approach with further optimization of parameters dictating biomineralization would facilitate directed synthesis and scale up of bioinorganic systems.