Progress in Crystal Growth and Characterization of Materials最新文献

Hydroxyapatite (HAp), ideal formula Ca₁₀(PO₄)₆(OH)₂, has unique physicochemical properties, including an excellent adsorption ability for functional biomolecules (e.g. nucleic acids, proteins) thanks to its specific large crystal surface. This property can be further improved with cationic and anionic replacements within the HAp framework. The adsorption of such biomolecules, indeed, can cause changes in the electric properties of the HAp surface in terms of resistivity and capacitance, generating the conditions for an improvement of the materials targeted for sensor applications. This work relates to the multiple routes for the synthesis of HAp materials, their electrochemical and structural investigations, and a short overview on the most well-known applications in sensor design. Moreover, with the aim of finding new promising HAp-based materials tailored for bioreceptor immobilization in biosensing, we underwent some doped-hydroxyapatite materials, specifically Sr-HAp, Gd-HAp, and Er-HAp, to a complete characterization. Electrochemical analyses, based on differential pulse voltammetry and cyclic voltammetry, evidenced improved analytical performances of HAp in terms of signal enhancement, repeatability, reproducibility, and reusability, in particular concerning the Er-HAp phase. A multi-methodological structural study, based on powder X-ray diffraction analysis, microscopy techniques (optical, electron, and fluorescence), energy dispersive X-ray spectroscopy (for chemical analyses), Fourier transform infrared spectroscopy, and absorption/fluorescence spectroscopies, showed the mechanism of doping replacement in HAp crystallographic sites, owing to the results of the Rietveld refinement from powder X-ray data, and a strong fluorescence for Sr-HAp.

This review presents a comprehensive discussion of the electrospray crystallization process, which represents a combination of electrospraying and crystallization through solvent evaporation, offering an efficient and cost-effective approach for the synthesis of submicrometric and nanosized crystals. Electrospray crystallization has demonstrated a multitude of advantages, including the generation of smaller crystals, enhanced dispersion, and the creation of diverse product morphologies, such as planar and cubic tetragonal structures. These benefits surpass those of conventional electrospraying methods and traditional crystallization mechanisms. This review also provides a historical context of works and highlights the wide array of potential applications. It explores the mechanisms and fundamental concepts related to both electrospraying and crystallization processes. Moreover, it presents an experimental process development proposal, with the aim of charting a course for future applications of advanced crystals, including drug delivery, catalysis, and energy storage.

Defect-selective etching methods are commonly used for a quick assessment of crystallographic and chemical inhomogeneities in various semiconductors, including nitrides. Because of the stability of GaN, "extreme" etchants such as molten bases and hot phosphoric/sulfuric acids are required for chemical etching. Photoetching provided an alternative and attractive path for room temperature etching of GaN. In this comprehensive review the introduction and subsequent modification of the photoetching method used for revealing defects and inhomogeneities in GaN are described in detail. The initial etchant, a KOH-based aqueous solution, was subsequently modified by addition of potassium peroxydisulphate (K₂S₂O₈), and later trisodium phosphate (Na₃PO₄) was added. The mechanism of photoetching in these solutions is presented and the advantages of using two- and three-component solutions are considered. This mechanism is based on generation of charge carriers (electrons and holes) by illumination of GaN with supra-bandgap light and was named photo-electrochemical (PEC) method. A correlation has been established between the carrier concentration in n-type GaN and the photoetch rate. A model is outlined that allows interpretation of large differences in the photoetch rate of inhomogeneous samples. Numerous examples of defects revealed by photoetching of GaN bulk crystals and homo- or hetero-epitaxial layers are described. The corresponding models for the formation of etch features are discussed and the results are compared with those obtained from other structural methods used for analysis of novel defects found in ammonothermally grown GaN crystals. The range of defects revealed by photoetching in GaN includes dislocations, inversion domains, nano-pipes, nano-scale and extended inhomogeneities. The importance of using photoetching for analysis of potentially new types of defect in recently grown ammonothermally GaN bulk crystals is emphasized. Future prospects of the PEC method for analysis of defects are considered.

The origin of life has been marked by existing chemical, physical and atmospheric conditions in the primeval era of Earth. In this sense, experiments have been carried out that emulate the conditions of the Precambrian era, where organic blocks such as amino acids, sugars, organic compounds and O₂ have been synthesized from the elements of this condition. Nevertheless, even while these results have been disruptive, allowing a significant advance in the origin of life, no functional biomolecules have been synthesized. Considering the work done previously, as a starting point and the evidences of the synthesis of biomorphs in the presence of biomolecules, the objective of this study was the synthesis of barium silico-carbonate biomorphs, based on biomolecules in Precambrian conditions. The purpose of this is to identify if it is possible to obtain functional biomolecules. The results showed that the barium biomorphs synthesized in conditions that emulate the primitive era present spherical or circular morphology, with a chemical composition that corresponds to the polymorphs of witherite, goethite and carbonaceous material (CM) such as protein, carbohydrate and phosphate group bonds. However, the synthesis of an active or functional biomolecule was not possible. The results therefore show that to be able to obtain a functional biomolecule that could be considered a sign of life springing from organic and inorganic compounds, it is necessary to involve other factors heretofore not considered. This is due to the fact that chemical elements per se, together with some atmospheric factors that have been described which apparently permitted the formation of the protocell in the primitive era of Earth, are not sufficient to obtain functional biomolecules. In this way, the origin of life may be understood from the equation of life (L = amc²), considering all involved factors and not only the chemical composition of elements that make up various organisms in combination with only some atmospheric factors.

Since the beginning of humanity, man has generated various theories to explain the formation of the Universe, and the origin of life on Earth. However, even while these theories coincide sometimes, they are also subject to controversy, but it was Albert Einstein who postulated the theory of special and general relativity, in the understanding of the formation and functioning of the Universe. Meanwhile, for decades, experiments have been carried out regarding the origin of life in our planet. While these experiments have made relevant contributions in obtaining essential chemical blocks of life, obtaining a functional biomolecule as authoritative proof of how life began has not been found. This shows that not all variables implicated in the origin of life have been considered. For a better comprehension of the origin of life, the objective of this work was to synthesize calcium carbonate biomorphs in the presence of various biomolecules in atmospheric conditions that emulate the Precambrian era and also in the conditions of our current atmosphere. Our results show that both in the conditions that emulate the Precambrian era and in the current atmosphere, biomorphs show a spherical morphology, which is compatible with life forms. But a functional biomolecule that could indicate a beginning of life was not obtained. For the purpose of explaining the reason for which it has not been possible to obtain a pioneer organism, such as occurred in the primeval era, I have proposed a theory of life in which I have considered the interaction of the various lengths of wave of the electromagnetic spectrum, the magnetic fields of the various atoms, the energy and the physical laws that rule the Universe. The proposed equation for the origin of life (L = amc²) is grounded in the equation of special relativity (E = mc²) and general relativity for the Universe, equations that specify how the local density of matter and energy determine the geometry of space-time. For this aforementioned equation: L represents life, the letter “a” stands for absorption of a specific type of equivalent to the Higgs Boson, “m” corresponds to matter and finally “c” is the light speed. Considering the four factors of space-time-matter-energy that participated in the origin of life in the equation that I propose, the absorption that matter should have been also incorporated, which should be generated based on the Higgs Boson, also known as the particle of God, or perhaps, on another particle equivalent to that of the Higgs. The origin of life therefore fulfills the four factors of space-time-matter-energy in the aforementioned equation L = amc².