Growth Of Nanocrystallites Research Articles

Boundary processes in the electrolyte–silicon interface area during the self-organization of the mosaic structure of 3D islets of porous silicon nanocrystallites in the long-term anode etching of p-Si (100) in electrolyte with an internal current source

The formation and self-organization of a porous silicon (por-Si) surface mosaic structure in the long-term anodic etching of p-type conductivity Si (100) (p-Si) in electrolytes with an internal power source is considered. We show that the formation of 3D islets of mosaic structure nanocrystallites of por-Si occurs with the participation of the adsorbed deposited silicon atoms formed as a result of disporportionation reactions during the etching of silicon single crystals, as in the case of the epitaxial growth of nanocrystallites by molecular beam deposition of silicon atoms on the AIIIBV and Si semiconductor surface and their further spontaneous self-organization. The quantum-size effects occurring in the local areas of the atomically rough surfaces of a real silicon crystal are taken into account. We note the significant role of oxidation of the silicon surface in the formation and self-organization of a mosaic structure of por-Si during long-term anodic etching of p-Si (100) in the HF: H2O2 electrolyte.

Single-Pot Synthesis of ⟨001⟩-Faceted N-Doped Nb2O5/Reduced Graphene Oxide Nanocomposite for Efficient Photoelectrochemical Water Splitting.

Due to exciting catalytic activity and selectivity, tailoring of nanocatalysts consisting of preferred crystal facets and desired structural properties remains at the forefront of materials engineering. A facile one-step nonhydrolytic solvothermal synthesis of a nanocomposite of reduced graphene oxide and one-dimensional nitrogen-doped Nb2O5 (N-NbOx) with exposed ⟨001⟩ facet is described. Triethylamine performed the dual role as nitrogen source and capping agent to control the size and unidirectional growth of Nb2O5 nanocrystallites. The nanocomposite showed efficient visible-light-mediated (λ > 420 nm) water splitting in a photoelectrochemical cell. A plausible mechanism for the formation of N-NbOx nanorods and improved photoelectrochemical efficacy in terms of their oriented growth is proposed.

Size Induced Structural and Magnetic Properties of Nanostructured Cobalt Ferrites Synthesized by Co-precipitation Technique

Cobalt ferrite (CoFe2O4), a well-known hard magnetic material high frequency applications and high-density recording media. Due to their good chemical and thermal stability, high permeability, high electrical resistivity, high saturation magnetization and coercivity etc. they found wide technological applications. Size dependent properties of CoFe2O4 include catalytic properties, electrochemical properties, magnetic properties and optical properties. Thermally induced changes in nanocrystalline CoFe2O4spinel ferrites were synthesized by co-precipitation technique. Unlike other techniques, co-precipitation is reported to be the most economical and successful technique for synthesizing ultrafine CoFe2O4powders having narrow particle size distribution. Their structural and magnetic properties were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM) and vibrating sample magnetometer (VSM) measurements. The average crystallite size of CoFe2O4was observed to increase from 23 to 65 nm as the annealing temperature was increased from 300 to 900°C. The lattice parameters were observed to increase due to increase in the crystallite size. The activation energy (E) of nanostructured CoFe2O4 was observed to be 11.6 kJ/mol. The annealing temperature has a prominent effect on the nanocrystallite growth. The saturation magnetization, coercivity and remanence were observed to increase with increasing crystalite size. In our future work, we plan to synthesize nanocrystalline CoFe2O4 using different techniques in order to understand the role of synthesis techniques on the structural and magnetic properties.

Graphene oxides-guided growth of ultrafine Co3O4 nanocrystallites from MOFs as high-performance anode of Li-ion batteries

This work presents the self-assembly growth of metal organic frameworks (ZIF-67) dodecahedrons on graphene oxides (GO) nanosheets. Ultrafine Co3O4 nanocrystallites with size of less than 10nm are uniformly spread on graphene nanosheets through pyrolysis of GO/ZIF-67. The relative mass ratio of graphene to Co3O4 is controlled by adjusting the repeated numbers of GO in precursor solutions. For application as anode material of Li-ion batteries, graphene/Co3O4 manifests good high rate behavior (877mAhg−1 at the current density of 5000mAg−1) and long-term cycling stability (714mAhg−1 after 200 cycles).

BOUNDARY PROCESSES IN ELECTROLYTE — SILICON INTERFACE AREA DURING SELF–ORGANIZATION OF MOSAIC STRUCTURE OF 3D–ISLANDS OF POROUS SILICON NANOCRYSTALLITES AT LONG–TERM ANODE ETCHING OF P–SI (100) IN ELECTROLYTE WITH AN INTERNAL SOURCE OF CURRENT

The formation and self−organization of porous silicon (por-Si) surface mosaic structure at long anodic etching of p -type conductivity Si (100) ( p -Si) in electrolytes with an internal power source has been considered. We show that the formation of 3D islets of mosaic structure nanocrystallites of por-Si occurs with the participation of the adsorbed deposited silicon atoms formed as a result of disproportioning reactions at etching of silicon single crystals, as is the case for epitaxial growth of nanocrystallites with molecular beam deposition of silicon atoms on А 3 В 5 and Si semiconductor surface and their further spontaneous self−organization. We note the significant role of oxidation of the silicon surface in the formation and self−organization of a mosaic structure of por-Si during long-term anodic etching of p -Si (100) in HF : H2O2 electrolyte quantum−size and effects occurring in local areas of atomic rough surfaces real crystal silicon.

The pivotal role of oxygen interstitials in the dynamics of growth and movement of germanium nanocrystallites

An unusual “symbiotic” chain reaction is activated by oxygen interstitials acting in concert with Ge and Si interstitials, inducing the coalescence of sparsely-distributed Ge nanocrystallites and their autonomous migration within SiO2/Si3N4layers.

Unusual Rh nanocrystal morphology control by hetero-epitaxially growing Rh on Au@Pt nanowires with numerous vertical twinning boundaries

Simultaneously growing multiple nanocrystallites in a crowded space can cause a shortage of precursors, and this can lead to a vertical growth of nanocrystallites on a given substrate. The presence of surfactant-surfactant interactions among adjacent nanocrystals can also place a unique structural constraint on the growing nanocrystallites, resulting in novel nanocrystal facet control. Herein, we report the growth of Rh on Au@Pt nanowires with multiple twinning boundaries, which are found along the entire nanowire length. The Au@Pt nanowires exhibit numerous bead-like structures, resulting from the preferred Pt deposition on the twinning boundaries, which can serve as nucleation sites for Rh. The heteroepitaxial growth of Rh on the Au@Pt nanowires results in unusual crystal growth behaviours. First, novel morphologies of Rh nanorods, nanoplates, and tangled manes are obtained temperature-dependently, which are not obtained in the absence of the Au@Pt nanowire substrate. Secondly, the thickness of vertically grown nanorods and nanoplates is tightly controlled. We also report the structure-catalytic activity relationship on the catalytic hydrogenation of phthalimides by the new Rh nanostructures.

Impurity induced crystallinity and optical emissions in ZnO nanorod arrays

We report the growth of ZnO nanocrystallites doped with impurities such as B, N and S by green chemistry route using ultrasound. The effect of intrinsic defects and impurity doping on the structural and optical properties of ZnO nanostructures has been studied and discussed. Characterization studies carried out using x-ray diffraction (XRD) reveal the change in lattice parameters and crystallinity of ZnO in the presence of dopant. This has been explained on the basis of the dopant substitution at regular anion and interstitial sites. Study on surface morphology by field emission scanning electron microscopy (FESEM) shows a change from particle-like structure to aligned nanorods nucleated at definite sites. Elemental analysis such as x-ray photon electron spectroscopy (XPS) has been carried out to ascertain the dopant configuration in ZnO. This has been corroborated by the results obtained from FTIR and Raman studies. UV–vis light absorption and PL studies show an expansion of the band gap which has been explained on the basis of Moss–Burstein shift in the electronic band gap of ZnO by impurity incorporation. The optical emissions corresponding to excitonic transition and defect centres present in the band gap of ZnO is found to shift towards lower/higher wavelength sides. New PL bands observed have been assigned to the transitions related to the impurity states present in the band gap of ZnO along with intrinsic defects.

The structural evolution of multi-layer graphene stacks in carbon fibers under load at high temperature – A synchrotron radiation study

Single carbon fibers were directly heated and tensile tested in vacuum in a specially designed in-situ X-ray testing device. We followed the structural evolution by diffraction of synchrotron radiation X-rays and determined the effect of time, temperature and applied stress on the growth of nanocrystallites as well as their orientational change with respect to the fiber axis. As the nanocrystallites are stacks of graphene sheets, this is a direct measurement of the development of multi-layer graphene with temperature. In the same experiment, size and orientation of pores within the material were obtained from simultaneous in-situ small-angle X-ray scattering. It turned out that the final temperature is decisive for structural evolution, significantly more than time or load. The multi-layer graphene network structure in fibers after heat treatment without stress is stable, whereas this is not the case in fibers without heat treatment, no matter if the carbon fibers were produced from polyacrylonitrile or from mesophase pitch precursor.

CTAB and acetic acid effect in the nanocrystallite growth of spray deposited CdO thin films

CdO thin films were deposited on glass substrates from cadmium acetate dihydrate along with precursor additives, acetic acid and CTAB using home built splay pyrolysis unit. XRD studies imply that the CdO thin films to be preferably oriented in the (111) plane. The Williamson–Hall plot indicates the presence of microstrain, especially high with acetic acid additive. Surface morphology was found to be closely packed spherical crystallite with precursor additives. Optical studies reveal a considerable change in the transmittance and band gap. Peak position is shifted in the Raman spectra, due to precursor additives.

Influence of the pH on the ZnO nanoparticle growth in supercritical water: Experimental and simulation approaches

In order to improve the knowledge on the nucleation and the growth mechanisms of metal oxides nanoparticles produced in supercritical water domain, ZnO was used as a “model” material. A continuous process of hydrothermal synthesis was employed to synthesize ZnO nanopowders (T=410°C and P=305bar) from Zn(NO3)2 and KOH solutions with different values of [KOH]/[Zn(II)] ratio from 0 to 8 in order to investigate the pH effect on the growth of ZnO nanocrystallite in terms of size and morphology. The samples were characterized by X-Ray Diffraction and Transmission Electronic Microscopy. ZnO crystal was considered as a cylindrical crystallite with a diameter D and height H. Especially, the aspect ratio D/H was already used to observe the change of ZnO nanoparticle shape correlated with TEM observations and results from a CFD simulation model. A schematic synoptic of the ZnO growth in supercritical domain is also presented.

Seeking to quantify the ferromagnetic-to-antiferromagnetic interface coupling resulting in exchange bias with various thin-film conformations

Ni3Fe/(Ni, Fe)O thin films with bilayer and nanocrystallite dispersion morphologies are prepared with a dual ion beam deposition technique permitting precise control of nanocrystallite growth, composition, and admixtures. A bilayer morphology provides a Ni3Fe-to-NiO interface, while the dispersion films have different mixtures of Ni3Fe, NiO, and FeO nanocrystallites. Using detailed analyses of high resolution transmission electron microscopy images with Multislice simulations, the nanocrystallites' structures and phases are determined, and the intermixing between the Ni3Fe, NiO, and FeO interfaces is quantified. From field-cooled hysteresis loops, the exchange bias loop shift from spin interactions at the interfaces are determined. With similar interfacial molar ratios of FM-to-AF, we find the exchange bias field essentially unchanged. However, when the interfacial ratio of FM to AF was FM rich, the exchange bias field increases. Since the FM/AF interface ‘contact’ areas in the nanocrystallite dispersion films are larger than that of the bilayer film, and the nanocrystallite dispersions exhibit larger FM-to-AF interfacial contributions to the magnetism, we attribute the changes in the exchange bias to be from increases in the interfacial segments that suffer defects (such as vacancies and bond distortions), that also affects the coercive fields.

The role of Si interstitials in the migration and growth of Ge nanocrystallites under thermal annealing in an oxidizing ambient.

We report a unique growth and migration behavior of Ge nanocrystallites mediated by the presence of Si interstitials under thermal annealing at 900°C within an H2O ambient. The Ge nanocrystallites were previously generated by the selective oxidation of SiGe nanopillars and appeared to be very sensitive to the presence of Si interstitials that come either from adjacent Si3N4 layers or from within the oxidized nanopillars. A cooperative mechanism is proposed, wherein the Si interstitials aid in both the migration and coarsening of these Ge nanocrystallites through Ostwald ripening, while the Ge nanocrystallites, in turn, appear to enhance the generation of Si interstitials through catalytic decomposition of the Si-bearing layers.

Effect of Annealing Temperature on ZnO Nanorods Prepared by Hydrothermal Process

We presented the effect of annealing temperature on nanocrystallite growth toward zinc oxide (ZnO) nanorods based on the hydrothermal process. The hydrothermal growths of the ZnO nanorods were prepared with zinc nitrate hexahydrate and hexamethylenetetramine solution at 90°C for 6 hours. The structural, morphological, optical, and anti-bacterial properties of the ZnO nanorods, prepared at different annealing temperatures, were characterized by grazing-incidence X-ray diffraction (GIXRD), field-emission scanning electron microscopy (FE-SEM), and UV-Vis spectrophotometer. The GIXRD patterns of the ZnO nanorods corresponded to the wurtzite structure. The FE-SEM results showed that the prepared ZnO nanorods were in the form of the hexagonal shape. The anti-bacterial behaviors of suspension of ZnO nanorods against Escherichia coli (gram-negative) would be discussed in this paper.

Electrodeposition and sol–gel derived nanocrystalline N–ZnO thin films for photoelectrochemical splitting of water: Exploring the role of microstructure

Nanocrystalline thin films of nitrogen (N)-incorporated ZnO, deposited on glass substrate by sol–gel (SG) and electrodeposition (ED) routes, have been investigated for their possible relevance to photoelectrochemical (PEC) splitting of water. XRD pattern established dominant evolution of hexagonal wurtzite ZnO. SEM analysis indicated continuous and homogenous growth of particles, while AFM analysis revealed favored growth of nanocrystallites along the c-axis. SG-derived films were denser with reduced film thickness. ED-derived samples were fluffy with relatively rougher top surface. All the samples exhibited broad absorption threshold at ∼400 nm with only marginal dip to the band gap on N incorporation. By comparing the performance of SG- and ED-derived samples, results of the study highlight crucial role of semiconductor microstructure, viz. film thickness, density, particle size and distribution, and film surface characteristics on their PEC response.

Effect of structural transition in an amorphous Ni80P20 alloy on the wetting by a eutectic Sn–Bi solder

Annealing-induced structural transition from amorphous to nanocrystalline states is believed to have a significant effect on the wettability of metallic glass alloys. In this study, an amorphous Ni80P20 alloy was pre-annealed at various temperatures to yield different structures and then wetted by a eutectic Sn–Bi solder at 473 K in a high vacuum using a dispensed sessile drop method. The results show that the structural relaxation and primary crystallization in the amorphous substrates greatly deteriorate the wettability while large-scale eutectic crystallization and the growth of nanocrystallites after high-temperature annealing improve it primarily due to the formation of a precursor film ahead of triple line. Moreover, the amorphous Ni–P substrates are more reactive with the molten Sn–Bi solder than the crystallized ones. The interfacial reaction yields Ni3Sn4 and a P-rich crystalline layer consisting mainly of Ni3P and Ni2SnP intermetallics. The presence of this layer dramatically retards the subsequent growth of the Ni3Sn4 phase.

Synthesis and photocatalytic activity of Eu3+-doped nanoparticulate TiO2 sols and thermal stability of the resulting xerogels

The synthesis of nanoparticulate TiO2 sols without and with Eu3+ doping (1, 2, or 3 mol%) by the colloidal sol–gel method in aqueous media was investigated, with emphasis on the effect of the Eu3+ doping on the peptization time and rheological properties of the sols. It was found that the addition of Eu3+ increasingly retards the peptization process, and also results in sols with greater aggregate sizes which are therefore more viscous, although in all cases the distributions of aggregate sizes are unimodal and the flow behavior is Newtonian. The shifting of the isoelectric point of the sols toward greater pH with increasing Eu3+ doping indicates that the aforementioned trends are due to the chemical adsorption of europium ionic complexes in the form of solvated species. Furthermore, the effect of Eu3+ doping on the ultraviolet–visible spectrum and photocatalytic activity of the peptized sols was also explored. It was found that the Eu3+ doping increasingly shifts slightly the absorption edge from the ultraviolet to the visible range, and that its effect on the photocatalytic activity is certainly complex because this is enhanced only if the Eu3+ cations have some electronic transition (charge transfer transition or transitions between the ground state and the excited states) at the wavelength of the incident radiation, in which case the photocatalytic activity first increases with increasing Eu3+ content and then decreases perhaps due to occurrence of Eu–Eu interactions or simply to the greater aggregation state. Finally, the influence of the Eu3+ doping on the thermal stability of the nanoparticulate xerogels resulting from the drying of the peptized sols was also examined by X-ray thermo-diffractometry together with transmission electron microscopy, selected area electron diffractometry, and X-ray energy-dispersive spectrometry. It was found that although the xerogels crystallize all as anatase phase, this is increasingly more thermally stable with increasing Eu3+ doping, displaying a slowed down nanocrystallite growth, delayed onset temperature of the anatase-to-rutile phase transformation, and extended retention temperature of anatase phase.

Production and Properties of Nanostructured Metal-Oxide Lead Zirconate–Titanate Piezoceramics

Compact ceramic samples of lead zirconate–titanate are sintered from nanocrystalline (d av = = 25 nm) Pb(Zr0.52Ti0.48)O3 powder synthesized by thermal decomposition of an oxalate precursor. Conditions of nanopowder compaction have been found and kinetics of sintering and growth of nanocrystallites and coarser grains formed during consolidation have been studied. The lead zirconate–titanate ceramic samples consolidated from nanopowders are sintered at lower (by 300–350°C) temperatures and have higher (by 25–45%) dielectric and piezoelectric properties as compared to samples fabricated by conventional solid-state technology. Two-level grain structure is formed during sintering: nanocrystallites divided by low-angle boundaries and descending from initial nanocrystalline particles and consolidated coarser micrograins divided by high-angle boundaries. Sintering of the lead zirconate–titanate ceramics from nanocrystalline powders permits controlling the nanoscale size of crystallites and thus the nanostructured features of consolidated material.

Preparation and thermal analysis kinetics of the core–nanoshell composite materials doped with Sm

The core–nanoshell composite materials with magnetic fly-ash hollow cenosphere as core and nano SmFeO3 as shell were synthesized by high-energy ball milling method. The magnetic fly-ash hollow cenosphere, samarium nitrate, and iron nitrate were used as raw materials. The synthesis and growth kinetics of the composite materials were investigated using the thermogravimetry and differential thermal analysis (TG–DTA) at different heating rates. The results show that the precursor of the composite materials decomposes in three steps. The apparent activation energy of each stage was calculated using the Doyle–Ozawa and Kissinger methods. The reaction order, frequency factor, and rate equations were also determined. The activation energy of the nano crystallite growth is calculated to be 16.12 kJ mol−1 according to kinetics theory of nano crystallite growth. It can be inferred that the crystallite grows primarily by means of an interfacial reaction during the thermal treatment. The magnetic properties and microwave absorbing properties of samples were analyzed by the vibrating sample magnetometer analysis and vector network analyzer. The results indicated that the exchange coupling interaction happens between ferrite of magnetic fly-ash hollow cenosphere and nanosized ferrite coating, which cause outstanding magnetic properties. In the frequency between 1 MHz and 1 GHz, the absorbing effectiveness of the composite absorbers can achieve −32 dB. The magnetic properties of the composite material are better than those of single phase. So it is consistent with requirements of the microwave absorbing material at the low-frequency absorption.

Crystallite growth kinetics of TiO2 surface modification with 9 mol% ZnO prepared by a coprecipitation process

The nanocrystallite growth of TiO2 surface modification with 9mol% ZnO prepared by a coprecipitation process has been studied. Thermogravimetric and differential thermal analysis (TG/DTA), X-ray diffraction (XRD), transmission electron microscopy (TEM), selected area electron diffraction (SAED) and UV–VIS–NIR spectrophotometry have been utilized to characterize the TiO2 nanocrystallites surface modification with 9mol% ZnO (denoted by T-9Z). The DTA result shows that the anatase TiO2 first formed at 533K and the completion of anatase TiO2 crystallization occurred at 745K for the T-9Z freeze-dried precursor powders. XRD results reveal that the anatase and rutile TiO2 coexist when the T-9Z freeze-dried precursor powders were calcined at 523–973K for 2h. When the T-9Z freeze-dried precursor powders were calcined at 973K for 2h, rutile TiO2 was the major phase, and the minor phases were anatase TiO2 and Zn2Ti3O8. The phase was composed of the rutile TiO2 and Zn2TiO4 for the T-9Z freeze-dried precursor powders after calcination at 1273K for 2h. The growth kinetics of TiO2 nanocrystallites in T-9Z powders were described as: DA,92=2.42×105×exp(-39.9×103/RT)and DR,92=8.49×105×exp(-47.6×103/RT) for anatase and rutile TiO2 nanocrystallites respectively. The analysis results of UV/VIS/NIR spectra reveal that the T-9Z freeze-dried precursor powders after calcination have a red-shifted effect with increasing calcination temperature and can be used as a UVA-attenuating agent.