Orientation Of Nanocrystals Research Articles

Orientation of Cellulose Nanocrystals Controlled in Perpendicular Directions by Combined Shear Flow and Ultrasound Waves Studied by Small-Angle X-ray Scattering

The combined effect of shear flow and ultrasound (US) waves on the dynamical structural orientations of cellulosic cholesteric liquid crystals was investigated by time-resolved, in situ small-angle X-ray scattering (SAXS). A dedicated channel-type shear flow/ultrasound cell for SAXS characterization was developed to simultaneously generate a shear flow-induced horizontal stress force and a US-induced vertical acoustic radiation force. The control of the alignment of anisometric cellulose nanocrystals (CNCs), with their director parallel to the ultrasonic wave direction of propagation, was revealed at an unprecedented nanometer scale. Concurrently, the application of shear flow induced a horizontal orientation of CNCs with their directors aligned along the velocity direction. By adjusting the level of simultaneously applied shear flow and US intensity to the CNC suspensions, it was possible to tune the direction and the level of orientation of the CNCs during a period of time. For a specific ratio of the applied shear rate to acoustic power, some transient orientation of the CNCs at an intermediate angle between horizontal and vertical directions was evidenced. Relaxation of these orientations’ phenomena upon cessation of flow and/or US was also highlighted.

Effect of Different Polyethylene Glycol (PEG) and Ethyl Cellulose on Impedance Spectroscopy of CuGaO2 Film

Delafossite materials (CuIMIIIO2) are p-type metal oxides which can be used as hole transport layers in a wide range of heterojunction solar cells. These materials are interesting because of their crystal structure that can facilitate hole diffusion through the valance band. Maximizing the interfacial capacitance within porous nanocrystalline films of CuGaO2 is a primary goal for enhancing their performance in solar cells. The electrochemistry of CuGaO2 can reveal much information about the capacitance of the material and therefore the electronic density of valance band states. Here we have investigated the structural and electrochemical properties of CuGaO2 nanocrystalline thin films in acetonitrile solution with LiClO4 electrolyte. Nanocrystalline films are produced by dispersion of CuGaO2 nanocrystals in a polymer solution designed to control the porosity of the resulting film. We have used different molecular weights of polyethylene glycol and two different chain lengths of ethyl cellulose polymers to understand their impact on film morphology. As the film capacitance is related to surface area, a more porous film is expected to increase the film capacitance. In addition, we have also varied the CuGaO2 : polymer ratio to find the optimum condition for enhanced film capacitance. The films were characterized by powder XRD where peak ratios for (003)/(006) and (012)/(006) planes were calculated to understand the orientation of nanocrystals within the film. Electrochemical Impedance Spectroscopy (EIS) was used to probe the electrochemical behavior and capacitance of the films. We are particularly observing the Creal values at low frequency for comparative study of various films. These studies find that Creal is maximized for the ethyl cellulose polymers and a 2:1 ratio of CuGaO2 : polymer mixture.

Toward revealing full atomic picture of nanoindentation deformation mechanisms in Li2O-2SiO2 glass-ceramics

Obtaining full understanding of deformation mechanisms in Li2O-2SiO2 glass-ceramics subjected to sharp contact loading is a pressing need for many industrial applications. We herein conduct systematic molecular dynamics simulations to reveal atomic details that are otherwise extremely challenging to probe experimentally. Our study shows that glass-ceramics exhibit a dramatically different plastic deformation map compared to glass, where the nanocrystalline phase dictates the plastic zone shape. Shear flow preferentially nucleates and travels along the interfaces before moving to the surrounding glass and nanocrystals. Dislocations, amorphization zones around the indenter, and shear flow at glass and crystal interfaces help to dissipate contact energy and deconcentrate the deformation, thereby increasing fracture toughness and discouraging the development of catastrophic cracks. Additionally, extensive discussions on the effect of LS2 nanocrystal aspect ratio, location and orientation with respect to indenter in shaping the plastic zone also help to establish a solid knowledge in understanding surface damage behaviors of glass-ceramics as observed in many real applications.

Controllable wettability tuning of the stainless steel surface through successive ionic layer deposition of Zn-Fe layered double hydroxysulfate

An efficient and scalable technique was proposed to control the wettability of stainless steel through successive ionic layer deposition (SILD) of ZnFe layered double hydroxysulfate (LDHS). The composition, structure, and surface characteristics of the coatings were investigated by EDS, XRD, SEM, Raman spectroscopy, and contact angle (CA) analysis. It was found that the coatings consisted of 2D nanocrystals with a thickness of 5–17 nm and a planar size of 55–416 nm, depending on the number of SILD cycles (n = 1–15). It was shown that their growth was accompanied by substrate-relative orientation change: 2D nanocrystals oriented horizontally at n = 1–2 and vertically at n = 3–15. The vertical orientation occurs due to the positive charge of substrate and nanocrystals surface during the SILD which results in their electrostatic repulsion. The SILD modification also leads to a change in surface wettability from weakly hydrophobic (n = 2, CA = 64.7 ± 0.6°) to superhydrophilic (n = 15, CA = 9.2 ± 0.3°). It correlates with established nanocrystals orientation since hydrophilic sulfate groups became more accessible for interaction with water in case of vertical orientation and practically inaccessible for horizontally directed nanocrystals.

Direct Assembly of Vertically Oriented, Gold Nanorod Arrays

AbstractAlthough many nanoscale materials such as quantum dots and metallic nanocrystals exhibit size dependent optical properties, it has been difficult to incorporate them into optical or electronic devices because there are currently no methods for precise, large‐scale deposition of single nanocrystals. Of particular interest is the need to control the orientation of single nanocrystals since the optical properties are usually strongly anisotropic. Here a method based on electrophoretic deposition (EPD) is reported to precisely assemble vertically oriented, single gold nanorods. It is demonstrated that the orientation of gold nanorods during deposition is controlled by the electric dipole moment induced along the rod by the electric field. Dissipative particle dynamics simulations indicate that the magnitude of this dipole moment is dominated by the polarizability of the solution phase electric double layer around the nanorod. The resulting vertical gold nanorod arrays exhibit reflected colors due to selective excitation of the transverse surface plasmon mode. The EPD method allows assembly of arrays with a density of over one million, visually resolvable, vertical nanorods per square millimeter.

Space-Selective Control of Functional Crystals by Femtosecond Laser: A Comparison between SrO-TiO2-SiO2 and Li2O-Nb2O5-SiO2 Glasses

We report on space-selective crystallization of congruent and polar Sr2TiSi2O8 crystals in a stoichiometric SrO-TiO2-SiO2 glass induced by (1030 nm, 300 fs) femtosecond laser irradiation. This allows us to compare with non-congruent laser-induced crystallization of polar LiNbO3 in non-stoichiometric Li2O-Nb2O5-SiO2 glass and gain information on the mechanism of nanocrystals orientation with the laser polarization that we pointed out previously. Using scanning electron microscopy (SEM), second harmonic generation (SHG), and electron backscattered diffraction (EBSD), we studied the laser-induced crystallization according to the laser processing parameters (pulse energy, pulse repetition rate, scanning speed). We found (1) a domain where the laser track is filled with crystals not perfectly textured (low energy), (2) a domain where an amorphous volume remains surrounded by a crystallized shell (high energy). This arises from Sr out-diffusion and may give rise to the crystallization of both SrTiO3 and Sr2TiSi2O8 phases at low speed. In the one-phase domain (at higher speed), the possibility to elaborate a tube with a perfect Fresnoite texture is found. A significant difference in size and morphology whereas the crystallization threshold remains similar is discussed based on glass thermal properties. Contrarily to Li2O-Nb2O5-SiO2 (LNS) glass, no domain of oriented nanocrystallization controlled by the laser polarization has been found in SrO-TiO2-SiO2 (STS) glass, which is attributed to the larger crystallization speed in STS glass. No nanogratings have also been found that is likely due to the congruency of the glass.

Nonclassical Recrystallization.

Applications in the fields of materials science and nanotechnology increasingly demand monodisperse nanoparticles in size and shape. Up to now, no general purification procedure exists to thoroughly narrow the size and shape distributions of nanoparticles. Here, we show by analytical ultracentrifugation (AUC) as an absolute and quantitative high‐resolution method that multiple recrystallizations of nanocrystals to mesocrystals is a very efficient tool to generate nanocrystals with an excellent and so‐far unsurpassed size‐distribution (PDIc=1.0001) and shape. Similar to the crystallization of molecular building blocks, nonclassical recrystallization removes “colloidal” impurities (i.e., nanoparticles, which are different in shape and size from the majority) by assembling them into a mesocrystal. In the case of nanocrystals, this assembly can be size‐ and shape‐selective, since mesocrystals show both long‐range packing ordering and preferable crystallographic orientation of nanocrystals. Besides the generation of highly monodisperse nanoparticles, these findings provide highly relevant insights into the crystallization of mesocrystals.

A multiscale study of structural and compositional changes in a natural nanocomposite: Osteoporotic bone with chronic endogenous steroid excess.

Glucocorticoid (or steroid) induced osteoporosis (GIOP) is the leading form of secondary osteoporosis, affecting up to 50% of patients receiving chronic glucocorticoid therapy. Bone quantity (bone mass) changes in GIOP patients alone are inadequate to explain the increased fracture risk, and bone material changes (bone quality) at multiple levels have been implicated in the reduced mechanics. Quantitative analysis of specific material-level changes is limited. Here, we combined multiscale experimental techniques (scanning small/wide-angle X-ray scattering/diffraction, backscattered electron imaging, and X-ray radiography) to investigate these changes in a mouse model (Crh-120/+) with chronic endogenous steroid production. Nanoscale degree of orientation, the size distribution of mineral nanocrystals in the bone matrix, the spatial map of mineralization on the femoral cortex, and the microporosity showed significant changes between GIOP and the control, especially in the endosteal cortex. Our work can provide insight into the altered structure-property relationship leading to lowered mechanical properties in GIOP. SIGNIFICANCE STATEMENT: As a natural nanocomposite with a hierarchical structure, bone undergoes a staggered load transfer mechanism at the nanoscale. Disease and age-related deterioration of bone mechanics are caused by changes in bone structure at multiple length scales. Although clinical tools such as dual-energy X-ray absorptiometry (DXA) can be used to assess the reduction of bone quantity in these cases, little is known about how altered bone quality in diseased bone can increase fracture risk. It is clear that high-resolution diagnostic techniques need to be developed to narrow the gap between the onset and diagnosis of fracture-related changes. Here, by combining several scanning probe methods on a mouse model (Crh-120/+) of glucocorticoid-induced osteoporosis (GIOP), we developed quantitative and spatially resolved maps of ultrastructural changes in collagen fibrils and mineral nanocrystals, mineralization distribution (microscale), and morphology (macroscale) across femoral osteoporotic bone. Our results indicate that the altered bone remodelling in GIOP leads to 1) heterogeneous bone structure and mineralization, 2) reduced degree of orientation of collagen fibrils and mineral nanocrystals, and 3) reduced length and increased thickness of mineral nanocrystals, which contribute to mechanical abnormalities. The combined multiscale experimental approach presented here will be used to understand musculoskeletal degeneration in aging and osteoporosis.

Mapping the 3D orientation of nanocrystals and nanostructures in human bone: Indications of novel structural features.

Bone is built from collagen fibrils and biomineral nanoparticles. In humans, they are organized in lamellar twisting patterns on the microscale. It has been a central tenet that the biomineral nanoparticles are co-aligned with the bone nanostructure. Here, we reconstruct the three-dimensional orientation in human lamellar bone of both the nanoscale features and the biomineral crystal lattice from small-angle x-ray scattering and wide-angle x-ray scattering, respectively. While most of the investigated regions show well-aligned nanostructure and crystal structure, consistent with current bone models, we report a localized difference in orientation distribution between the nanostructure and the biomineral crystals in specific bands. Our results show a robust and systematic, but localized, variation in the alignment of the two signals, which can be interpreted as either an additional mineral fraction in bone, a preferentially aligned extrafibrillar fraction, or the result of transverse stacking of mineral particles over several fibrils.

Faceting and Nanostructuring of Gold Surfaces through Cathodic Corrosion: Role of Cationic Electrolyte Species and Water

Gold is one of the most frequently employed electrode materials in electrochemistry due to its exceptional properties such as chemical inertness and high resistance to oxidation and dissolution [1-3]. According to Pourbaix diagrams, gold is regarded stable against degradation under cathodic polarization [4]. In contrast, applying relatively high negative potentials in the presence of alkali metal cations induce notable changes on Au electrode surfaces [5].In this study, cathodic corrosion of polycrystalline gold in different electrolytes of alkali metal hydroxides has been systemically investigated. In comparison to the recent work [5,6], this study provides new findings as a function of the applied parameters for the nanostructuring of gold surfaces. Cell design and the distance between the electrodes have carefully been controlled and optimized. The progression of surface restructuring and corrosion features was investigated using cyclic voltammetry (CV) and scanning electron microscopy (SEM). The results show different corrosion features depending on the nature and the concentration of alkali metal hydroxides, on the applied voltage, and on time. Current-potential curves for the modified electrodes in 0.1 M H2SO4 show characteristic features in the double-layer and oxidation regions. Analyzing the cyclic voltamogramms of the corroded electrodes provides evidence about the preferential orientation of facets and the electrochemical active surface area as a function of the applied parameters. The SEM micrographs show that polarizing the gold surfaces at relatively high negative potentials generates different size and orientation of octahedral nanocrystals using NaOH, spherical nanoparticles and triangular pits using KOH and triangular pits using LiOH. Besides the alkali metal cations, the electrolyte concentration and the applied voltage are important parameters. Furthermore, the role of water in cathodic corrosion of gold has been investigated using mixtures of different mole fraction of water and non-aqueous electrolytes. The absence of corrosion features using water-free non-aqueous electrolytes reveal that water plays a key role in the cathodic corrosion process.In addition, various aqueous mixed electrolytes have been systemically investigated. The results show combined corrosion features according to the mole fraction of different cations. For example, a 1:1 NaOH + LiOH mixture leads to the formation of rectangular pits which are attributed to (100)-facets compared to a 1:1 KOH + LiOH mixture which leads to triangular pits revealing the formation of (111)-facets.By applying alternating current (AC) to Au electrodes in contact with the same electrolytes, colloidal gold nanoparticles could successfully be synthesized. These nanoparticles have been used for the functionalization of water-soluble carbon nitride to enhance its activity for specific photocatalytic reactions such as alcohol oxidation.

Controlling the Nucleation and Growth Orientation of Nanocrystalline Carbon Films during Plasma-Assisted Deposition: A Reactive Molecular Dynamics/Monte Carlo Study.

Nanocrystalline carbon films containing preferentially oriented graphene-based nanocrystals within an amorphous carbon matrix have attracted significant theoretical and experimental interest due to their favorable chemical and physical properties. At present, there are intense efforts to study the grain size and growth orientation of the graphene-based nanocrystals to achieve a controllable growth of nanocrystalline carbon films. However, despite the frequent use of plasma-assisted deposition techniques, the atomistic-scale mechanisms, including the effects of plasma density and energy on the nucleation process and growth orientation of the graphene-based nanocrystals, as well as associated dynamic processes involved in deposition processes, have not yet been thoroughly studied. In this paper, the plasma-assisted growth of nanocrystalline carbon thin films with preferentially oriented nanocrystals was systematically studied by hybrid molecular dynamics-Monte Carlo simulations using a recently developed force field, the charge-implicit ReaxFF. By combining the experimental data with the atomistic simulations, we reveal that plasma ion bombardments, in suitable ranges of energies and densities, allow the highest nucleation density in the nanocrystalline carbon films. Theoretically optimum windows of the plasma energy and density are first presented in the form of crystallization phase diagrams. Furthermore, to investigate the relationship between the growth orientation and the plasma ion energy, simulations of graphene irradiated with Ar ions from different incident angles were also performed. On the basis of the mechanism of "survival of the fittest", we proposed using the critical energy of generating the Stone-Thrower-Wales defects to design the growth orientation of graphite-like nanocrystals by controlling the plasma ion energy.

Preferred crystallographic orientation of nanocrystals embedded inside nanopores

The preferred crystallographic orientation of nanocrystals plays a significant role in determining their properties. From the wide variety of nanocrystal growth techniques, we focus in this paper on crystal growth by precipitation from liquid solutions inside porous substrates, and discuss the progress that has been made during the last decade concerning the control of crystal growth direction through this method. In this overview, the motivation and principal mechanisms of achieving highly oriented nanocrystals are presented. Moreover, different experimental challenges within the described growth technique are probed. The paper presents the thermodynamic and kinetic considerations for favoring crystal growth inside pores rather than bulk growth. A special focus is made on the origin of obtaining preferred crystallographic orientations in various types of materials, including varying perspectives of thermodynamic and kinetic driving forces. The paper ends with technological application of crystal growth with preferred crystallographic orientation inside nano-pores.

Controlling Nanoparticle Orientations in the Self-Assembly of Patchy Quantum Dot-Gold Heterostructural Nanocrystals.

Self-assembly of nanocrystals is a promising route for creating macroscale materials that derive function from the properties of their nanoscale building blocks. While much progress has been made assembling nanocrystals into different superlattices, controlling the relative orientations of nanocrystals in those lattices remains a challenge. Here, we combine experiments with computer simulations to study the self-assembly ofpatchy heterostructural nanocrystals (HNCs), consisting of near-spherical quantum dots decorated with regular arrangements of small gold satellites, into close-packed superlattices with pronounced orientational alignment of HNCs. Our simulations indicate that the orientational alignment is caused by van der Waals interactions between gold patches and is sensitive to the interparticle distance in the superlattice. We demonstrate experimentally that the degree and type of orientational alignment can be controlled by changing ligand populations on HNCs. This study provides guidance for the design and fabrication of nanocrystal superlattices with enhanced structural control.

Controlling the Spatial Direction of Hydrothermally Grown Rutile TiO2 Nanocrystals by the Orientation of Seed Crystals

Hydrothermally grown TiO2 nanorods are a key material for several electronic applications. Due to its anisotropic crystal structure, the electronic properties of this semiconductor depend on the crystallographic direction. Consequently, it is important to control the crystal orientation to optimize charge carrier pathways. So far, the growth on common polycrystalline films such as fluorine tin oxide (FTO) results in randomly distributed growth directions. In this paper, we demonstrate the ability to control the growth direction of rutile TiO2 nanocrystals via the orientation of the seed crystals. The control of the orientation of such nanocrystals is an important tool to adjust the electronic, mechanical, and chemical properties of nanocrystalline films. We show that each employed macroscopic seed crystal provides the growth of parallel nanofingers along the [001] direction under specific angles. The parallel growth of these nanofingers leads to mesocrystalline films whose thickness and surface structure depends on the crystal orientation of the seed crystal. In particular, the structure of the films is closely linked with the known inner structure of hydrothermally grown rutile TiO2 nanorods on FTO. Additionally, comprehensive 1D structures on macroscopic single-crystals are generated by branching processes. These branched nanocrystals form expanded 2D defect planes, which provide the opportunity of defect doping-induced two-dimensional electronic systems (2DES).

Magnetoelectric coupling tailored by the orientation of the nanocrystals in only one component in percolative multiferroic composites.

Novel 1–3 type multiferroic composite thin films were prepared via a simple 0–3 composite fabrication process. The orientation of the Ni0.5Zn0.5Fe2O4 (NZFO) nanocrystals in the BaTiO3–Ni0.5Zn0.5Fe2O4 (BTO–NZFO) composite thin films was controlled by magnetron sputtering, and the controlling effect of such orientation on magnetoelectric coupling was investigated in detail. The NZFO lattice in the BTO–NZFO composite thin films grew with (100) orientation under the induction of the (111) plane of Si. The transfer of substrate stress between the closely contacted grains also contributes to the orientation of the NZFO nanocrystals. The 0.6BTO–0.4(100)NZFO multiferroic composite thin film exhibited a magnetization strength of 9.2% at the Curie point of the BTO phase, showing extremely strong magnetoelectric coupling characteristics. This work provides an effective strategy for the development of high-performance multiferroic composites, and brings about new conception of realizing strong magnetoelectric coupling effect from the perspective of physical chemistry.

Effects of aspect ratio and crystal orientation of cellulose nanocrystals on properties of poly(vinyl alcohol) composite fibers

This work reports a study on the effects of different types and aspect ratios of cellulose nanocrystals (CNCs) on properties of poly (vinyl alcohol) (PVA) composite fibers. CNCs were extracted from wood pulp and cotton and reinforced into PVA to produce fibers by dry-jet-wet spinning. The fibers were collected as-spun and with the first stage drawing up to draw ratio 2. The elastic modulus and tensile strength of the fibers improved with increasing CNC content (5–15 wt. %) at the expense of their strain-to-failure. It was also observed that the mechanical properties of fibers reinforced with cotton CNC were higher than the fibers with wood CNC at the same amount of CNCs due to their higher aspect ratio. The degree of orientation along the spun fiber axis was quantified by 2D X-ray diffraction. As expected, the CNC orientation correlates to the mechanical properties of the fibers. Micromechanical models were used to predict the fiber performance and compare with experimental results. Finally, surface and cross-sectional morphologies of fibers were analyzed by scanning electron microscopy and optical microscopy.

Ultrafine heat-induced structural perturbations of bone mineral at the individual nanocrystal level

The nanoscale characteristics of the mineral phase in bone tissue such as nanocrystal size, organization, structure and composition have been identified as potential markers of bone quality. However, such characterization remains challenging since it requires combining structural analysis and imaging modalities with nanoscale precision. In this paper, we report the first application of automated crystal orientation mapping using transmission electron microscopy (ACOM-TEM) to the structural analysis of bone mineral at the individual nanocrystal level. By controlling the nanocrystal growth of a cortical bovine bone model artificially heated up to 1000 °C, we highlight the potential of this technique. We thus show that the combination of sample mapping by scanning and the crystallographic information derived from the collected electron diffraction patterns provides a more rigorous analysis of the mineral nanostructure than standard TEM. In particular, we demonstrate that nanocrystal orientation maps yield valuable information for dimensional analysis. Furthermore, we show that ACOM-TEM has sufficient sensitivity to distinguish between phases with close crystal structures and we address unresolved questions regarding the existence of a hexagonal to monoclinic phase transition induced by heating. This first study therefore opens new perspectives in bone characterization at the nanoscale, a daunting challenge in the biomedical and archaeological fields, which could also prove particularly useful to study the mineral characteristics of tissue grown at the interface with biomaterials implants. Statement of SignificanceIn this paper, we propose a new approach to assess the mineral properties of bone at the individual nanocrystal level, a major challenge for decades. We use a modified Transmission Electron Microscopy acquisition mode to perform an Automated Crystal Orientation Mapping (ACOM-TEM) by analyzing electron diffraction patterns. We tune the mineral nanocrystal size by heating a model bovine bone system and show that this method allows precisely assessing the mineral nanocrystal size, orientation and crystallographic phase. ACOM-TEM therefore has sufficient sensitivity to solve problems that couldn't be answered using X-ray diffraction. We thus revisit the fine mechanisms of bone nanocrystal growth upon heating, a process currently used for bone graft manufacturing, also of practical interest for forensic science and archaeology.

Immobilized Seed-Mediated Growth of Two-Dimensional Array of Metallic Nanocrystals with Asymmetric Shapes.

Bottom-up fabrication of such arrays with specific orientation of nanoparticles remains a challenge. In this paper, we report an immobilized seed-mediated growth strategy for the fabrication of two-dimensional (2D) arrays of mono- and bimetallic polyhedral nanocrystals with well-defined shapes and orientations on a substrate. This method relies on the controlled solution-phase deposition of metals (i.e., Au and Pd) on a selectively exposed surface of self-assembled seed nanoparticles that are immobilized on a substrate through collapsed polymer brushes. By using this approach, we demonstrated the preparation of various 2D arrays of shaped Au nanocrystals and Au core/Pd shell nanocrystals with asymmetric geometry of two halves and controlled orientations with respect to the substrate. The shape evolution of seeds to final nanocrystals was systematically monitored and evaluated by electron microscopic imaging. Our study suggests that the shape and orientation of nanocrystals within arrays is determined by the preferential orientation of assembled seed nanoparticles on the substrate and controllable deposition of metals on exposed crystal facets of immobilized seeds. The synthetic approach we developed presents an important addition to current tools for the fabrication of substrate-supported functional nanostructures.

Parrotfish Teeth: Stiff Biominerals Whose Microstructure Makes Them Tough and Abrasion-Resistant To Bite Stony Corals.

Parrotfish (Scaridae) feed by biting stony corals. To investigate how their teeth endure the associated contact stresses, we examine the chemical composition, nano- and microscale structure, and the mechanical properties of the steephead parrotfish Chlorurus microrhinos tooth. Its enameloid is a fluorapatite (Ca5(PO4)3F) biomineral with outstanding mechanical characteristics: the mean elastic modulus is 124 GPa, and the mean hardness near the biting surface is 7.3 GPa, making this one of the stiffest and hardest biominerals measured; the mean indentation yield strength is above 6 GPa, and the mean fracture toughness is ∼2.5 MPa·m1/2, relatively high for a highly mineralized material. This combination of properties results in high abrasion resistance. Fluorapatite X-ray absorption spectroscopy exhibits linear dichroism at the Ca L-edge, an effect that makes peak intensities vary with crystal orientation, under linearly polarized X-ray illumination. This observation enables polarization-dependent imaging contrast mapping of apatite, a method to quantitatively measure and display nanocrystal orientations in large, pristine arrays of nano- and microcrystalline structures. Parrotfish enameloid consists of 100 nm-wide, microns long crystals co-oriented and assembled into bundles interwoven as the warp and the weave in fabric and therefore termed fibers here. These fibers gradually decrease in average diameter from 5 μm at the back to 2 μm at the tip of the tooth. Intriguingly, this size decrease is spatially correlated with an increase in hardness.

Comparable study of vermiculites from four commercial deposits prepared with fixed ceria nanoparticles

Four commercial macroscopic vermiculites (Ver) from different exploited deposits were investigated regarding their chemistry and structural transformation stage from mica (phlogopite), and compared with selected raw vermiculites and “hydrobioties” known from literature, in which the chemical analyzes verified the existence of iron as Fe3+ and Fe2+. Subsequently prepared vermiculite/ceria (Ver/CeO2) nanoparticles composites were compared from the point of view of the fixation of ceria nanoparticles by using stability test and regarding their photocatalytic activity in the decomposition of N2O. The experimental methods used for these studies were X-ray fluorescence spectrometry, atomic emission spectrometry, X-ray powder diffraction, infrared (FR-IR) and Raman spectroscopy and transmission electron microscopy with high resolution (HRTEM). Negative layer charge of vermiculites produced by the local charge balance and distribution of Fe3+ in tetrahedral and octahedral sheets were related to the CeO2 nanocrystals fixation and orientation. Among the four Ver/CeO2 nanoparticles composite samples, the vermiculite in sample Ver-C/CeO2 exhibited the highest negative layer charge. The CeO2 crystallites were the smallest among all four samples. HRTEM found separated CeO2 nanocrystallites and CeO2 agglomerates of differently oriented nanocrystallites. Such forms of CeO2 nanocrystals influenced the position of the Raman CeO2 F2g and suppressed ability for photocatalytic N2O conversion.