Deformation twin traces on gold surfaces: A pathway to tailored epitaxial growth of 1D semiconductors.

The field of one-dimensional semiconducting materials holds a wide variety of captivating applications, such as photovoltaic cells, electronic devices, catalysis cells, lasers, and more. The tunability of electrical, mechanical, or optical attributes of a semiconductor crystal relies on the ability to control and pattern the crystal's growth direction, orientation, and dimensions. In this study, we harvest the unique properties of crystallographic defects in Au substrates, specifically twin boundaries, to fabricate selective epitaxial growth of semiconducting nanocrystals. Different crystallographic defects were previously shown to enhance materials properties, such as, screw dislocations providing spiral crystal growth, dislocation outcrops, and vacancies increasing their catalytic activity, dislocation strengthening, and atomic doping changing the crystal's electrical properties. Here, we present a unique phenomenon of directed growth of semiconductor crystals of gold(I)-cyanide (AuCN) on the surface of thin Au layers, using traces of deformation twins on the surface. We show that emergence of deformation twins to the {111} Au surface leads to the formation of ledges, exposing new {001} and {111} facets on the surface. We propose that this phenomenon leads to epitaxial growth of AuCN on the freshly exposed {111} facets of the twin boundary trace ledges. Specific orientations of the twin boundaries with respect to the Au surface allow for patterned growth of AuCN in the <110> orientations. Nano-scale patterning of AuCN semiconductors may provide an avenue for property tuning, particularly the band gap acquired.

High-Mg calcite nanoparticles within a low-Mg calcite matrix: A widespread phenomenon in biomineralization.

During the process of biomineralization, organisms utilize various biostrategies to enhance the mechanical durability of their skeletons. In this work, we establish that the presence of high-Mg nanoparticles embedded within lower-Mg calcite matrices is a widespread strategy utilized by various organisms from different kingdoms and phyla to improve the mechanical properties of their high-Mg calcite skeletons. We show that such phase separation and the formation of high-Mg nanoparticles are most probably achieved through spinodal decomposition of an amorphous Mg-calcite precursor. Such decomposition is independent of the biological characteristics of the studied organisms belonging to different phyla and even kingdoms but rather, originates from their similar chemical composition and a specific Mg content within their skeletons, which generally ranges from 14 to 48 mol % of Mg. We show evidence of high-Mg calcite nanoparticles in the cases of six biologically different organisms all demonstrating more than 14 mol % Mg-calcite and consider it likely that this phenomenon is immeasurably more prevalent in nature. We also establish the absence of these high-Mg nanoparticles in organisms whose Mg content is lower than 14 mol %, providing further evidence that whether or not spinodal decomposition of an amorphous Mg-calcite precursor takes place is determined by the amount of Mg it contains. The valuable knowledge gained from this biostrategy significantly impacts the understanding of how biominerals, although composed of intrinsically brittle materials, can effectively resist fracture. Moreover, our theoretical calculations clearly suggest that formation of Mg-rich nanoprecipitates greatly enhances the hardness of the biomineralized tissue as well.

Self-catalytic growth of one-dimensional materials within dislocations in gold.

Dislocations in metals affect their properties on the macro- and the microscales. For example, they increase a metal's hardness and strength. Dislocation outcrops exist on the surfaces of such metals, and atoms in the proximity of these outcrops are more loosely bonded, facilitating local chemical corrosion and reactivity. In this study, we present a unique autocatalytic mechanism by which a system of inorganic semiconducting gold(I) cyanide nanowires forms within preexisting dislocation lines in a plastically deformed Au-Ag alloy. The formation occurs during the classical selective dealloying process that forms nanoporous Au. Nucleation of the nanowire originates at the surfaces of the catalytic dislocation outcrops. The nanowires are single crystals that spontaneously undergo layer-by-layer one-dimensional growth. The continuous growth of nanowires is achieved when the dislocation density exceeds a critical value evaluated on the basis of a kinetic model that we developed.

On the mechanism of calcium carbonate polymorph selection via confinement.

Organisms deposit various biominerals in the course of their biomineralisation. The most abundant of these is calcium carbonate, which manifests itself in several polymorphs. While organisms possess the ability to control the specific polymorph deposited, the exact mechanism by which polymorph selection takes place is not yet fully understood. Because biominerals often grow within confined spaces, one of the suggested possibilities was that polymorph selection might be an outcome of confinement. Confining conditions have indeed been extensively shown to have a strong impact on the nucleation and crystal growth of calcium carbonate and, in particular, on its polymorph selection. However, despite numerous studies on the crystal growth of calcium carbonate in confined spaces, the mechanism of polymorph selection under confinement has not been elucidated. Herein, we discuss previously reported results and suggest a mechanistic explanation of the observed selective formation of calcite or aragonite or vaterite. We consider the possible effects of charged confining inner surfaces and of the sizes of the confining pores, and discuss whether the predominantly precipitating phase is amorphous calcium carbonate. We also discuss two possible scenarios of crystallization from amorphous calcium carbonate under conditions of confinement: via solid-state transformation or via a mechanism of dissolution-reprecipitation.

Retention of surface structure causes lower density in atomic layer deposition of amorphous titanium oxide thin films.

Size effects and structural modifications in amorphous TiO2 films deposited by atomic layer deposition (ALD) were investigated. As with the previously investigated ALD-deposited Al2O3 system we found that the film's structure and properties are strongly dependent on its thickness, but here, besides the significant change in the density of the films there is also a change in their chemical state. The thin near-surface layer contained a significantly larger amount of Ti+3 species and oxygen vacancies relative to the sample's bulk. We attribute this change in chemistry to the ALD specific deposition process wherein each different atomic species is deposited in turn, thereby forming a "corundum-like" structure of the near-surface layer resembling that found in the Al2O3 system. This, combined with the fact that each deposited layer starts out as a surface layer and maintains the surface structure over the next several following deposition cycles, is responsible for the overall decrease in the film density. This is the first time this effect has been shown in detail for TiO2, expending the previously discovered phenomenon to a new system and demonstrating that while similar effects occur, they can present in different ways for oxide systems with different structures and symmetries.

Acidic Monosaccharides become Incorporated into Calcite Single Crystals*.

Carbohydrates, along with proteins and peptides, are known to represent a major class of biomacromolecules involved in calcium carbonate biomineralization. However, in spite of multiple physical and biochemical characterizations, the explicit role of saccharide macromolecules (long chains of carbohydrate molecules) in mineral deposition is not yet understood. In this study, we investigated the influence of two common acidic monosaccharides (MSs), the two simplest forms of acidic carbohydrates, namely glucuronic and galacturonic acids, on the formation of calcite crystals in vitro. We show here that the size, morphology, and microstructure of calcite crystals are altered when they are grown in the presence of these MSs. More importantly, these MSs were found to become incorporated into the calcite crystalline lattice and induce anisotropic lattice distortions, a phenomenon widely studied for other biomolecules related to CaCO3 biomineralization, but never before reported in the case of single MSs. Changes in the calcite lattice induced by MSs incorporation were precisely determined by high-resolution synchrotron powder X-ray diffraction. We believe that the results of this research may deepen our understanding of the interaction of saccharide polymers with an inorganic host and shed light on the implications of carbohydrates for biomineralization processes.

Reliability of Smartphone-Based Instant Messaging Application for Diagnosis, Classification, and Decision-making in Pediatric Orthopedic Trauma.

OBJECTIVE: Smartphones have the ability to capture and send images, and their use has become common in the emergency setting for transmitting radiographic images with the intent to consult an off-site specialist. Our objective was to evaluate the reliability of smartphone-based instant messaging applications for the evaluation of various pediatric limb traumas, as compared with the standard method of viewing images of a workstation-based picture archiving and communication system (PACS). METHODS: X-ray images of 73 representative cases of pediatric limb trauma were captured and transmitted to 5 pediatric orthopedic surgeons by the Whatsapp instant messaging application on an iPhone 6 smartphone. Evaluators were asked to diagnose, classify, and determine the course of treatment for each case over their personal smartphones. Following a 4-week interval, revaluation was conducted using the PACS. Intraobserver agreement was calculated for overall agreement and per fracture site. RESULTS: The overall results indicate "near perfect agreement" between interpretations of the radiographs on smartphones compared with computer-based PACS, with κ of 0.84, 0.82, and 0.89 for diagnosis, classification, and treatment planning, respectively. Looking at the results per fracture site, we also found substantial to near perfect agreement. CONCLUSIONS: Smartphone-based instant messaging applications are reliable for evaluation of a wide range of pediatric limb fractures. This method of obtaining an expert opinion from the off-site specialist is immediately accessible and inexpensive, making smartphones a powerful tool for doctors in the emergency department, primary care clinics, or remote medical centers, enabling timely and appropriate treatment for the injured child. This method is not a substitution for evaluation of the images in the standard method over computer-based PACS, which should be performed before final decision-making.

Treatment of Adolescent Hallux Valgus With Percutaneous Distal Metatarsal Osteotomy.

Background. Hallux valgus is a complex deformity of the first ray of the foot, and a significant number of adolescents develop this deformity. More than 130 surgical procedures have been described to treat hallux valgus, but there is no compelling evidence to prefer one method over another. Minimal invasive techniques have been proposed and reported to be successful and cost-effective. The objective of this study was to describe the clinical course of adolescent patients treated with percutaneous distal metatarsal osteotomy. Methods. A retrospective study included patients who had a percutaneous hallux valgus correction during the years 2008 to 2015. The following measurements were compared before surgery up to last follow-up: AOFAS Hallux-Metatarsophalangeal-Interphalangeal questionnaire and radiological measurements (HVA, IMA, DMAA). Any postoperative complications were extracted from the medical records. Results. The procedure was performed on 32 feet (27 patients). All patients were <18 years of age. There were 10 male patients (12 feet) and 17 female patients (20 feet). Average age at surgery was 15.8 years (range = 13-18 years). Average follow-up time was 43 months (range= 24-94 months). The average AOFAS score before surgery was 66, and after surgery, at last follow-up was 96. This difference was significant (P value <.0001). Most patients were pain free after the procedure and returned to appropriate age functioning. Significant improvement was noted in all radiological criteria. Conclusions. Percutaneous distal metatarsal osteotomy is safe, reliable, and effective for the correction of mild to moderate symptomatic hallux valgus in adolescents.Levels of Evidence: Level IV.

Structural and chemical variations in Mg-calcite skeletal segments of coralline red algae lead to improved crack resistance.

The calcareous alga Jania sp. is an articulated coralline red seaweed that is abundant in the shallow waters of oceans worldwide. We have previously demonstrated that its structure is highly intricate and exhibits hierarchical organization across multiple length scales from the macro to the nano scale. Moreover, we have proven that the inner pores of its structure are helical, conveying the alga greater compliance as compared to a cylindrical configuration. Herein, we reveal new insights into the structure of Jania sp., particularly, its crystallographic variations and the internal elemental distribution of Mg and Ca. We show that the high-Mg calcite cell wall nanocrystals of Jania sp. are arranged in layers with alternating Mg contents. Moreover, we show that this non-homogenous elemental distribution assists the alga in preventing fracture caused by crack propagation. We further reveal that each one of the cell wall nanocrystals in Jania sp. is not a single crystal as was previously thought, but rather comprises Mg-rich calcite nanoparticles demonstrating various crystallographic orientations, arranged periodically within the layered structure. We also show that these Mg-rich nanoparticles are present in yet another species of the coralline red algae, Corallina sp., pointing to the generality of this phenomenon. To the best of our knowledge this is a first report on the existence of Mg-rich nanoparticles in algal mineralized tissue. We envisage that our findings on the bio-strategy found in the algae to enhance their fracture toughness will have an impact on the design of structures with superior mechanical properties. STATEMENT OF SIGNIFICANCE: Understanding the structure-property relation in biomineralized tissues is of great importance in unveiling Nature's material design strategies, which form the basis for the development of novel structural materials. Crystallographic and elemental variations in the skeletal parts of the coralline red algae and their cumulative contribution to prevention of mechanical failure are yet poorly studied. Herein, we reveal that the high-Mg calcite cell wall nanocrystals of Jania sp. are arranged in layers with alternating Mg concentrations and that this organization facilitates crack deflection, thereby preventing catastrophic fracture. We further discovered that the nanocrystals contain incoherent Mg-rich nanoparticles and suggest that they form via spinodal decomposition of the Mg-ACC precursor and self-arrange periodically throughout the alga's mineralized cell wall, a phenomenon most likely to be widespread in high-Mg calcite biomineralization.

A fungal mycelium templates the growth of aragonite needles.

Fungi live within diverse environments and survive well under extreme conditions that are usually beyond the tolerance of most other organisms. In different environments fungi are known to induce precipitation of a wide range of minerals. Various species of fungi have been shown to facilitate calcium carbonate mineralization. Here, inspired by examples of needle-fiber calcite formed via fungus-induced biomineralization typically observed in soils and sediments, we utilized inactivated fungus to synthetically induce precipitation of CaCO3 needles. To our knowledge, the feasibility of growing aragonitic needles within fungal mycelium in vitro has not been previously demonstrated. The needles we obtained were curved, displayed hexagonal facets, and demonstrated high-aspect ratios close to 60. The size and shape of these synthetic needles matched those of the mycelium of the natural fungus. Utilizing high-resolution characterization techniques, we studied the morphology and the micro- and nanostructures of the aragonitic needles. Our findings showed that even inactivated fungal mycelium, if present in the crystallization environment, can serve as a template for the formation of high-aspect ratio fibers and can stabilize metastable polymorphs.