Influence of magnetic field on electron beam-induced Coulomb explosion of gold microparticles in transmission electron microscopy.

In this work we instigated the fragmentation of Au microparticles supported on a thin amorphous carbon film by irradiating them with a gradually convergent electron beam inside the Transmission Electron Microscope. This phenomenon has been generically labeled as "electron beam-induced fragmentation" or EBIF and its physical origin remains contested. On the one hand, EBIF has been primarily characterized as a consequence of beam-induced heating. On the other, EBIF has been attributed to beam-induced charging eventually leading to Coulomb explosion. To test the feasibility of the charging framework for EBIF, we instigated the fragmentation of Au particles under two different experimental conditions. First, with the magnetic objective lens of the microscope operating at full capacity, i.e. background magnetic field B=2 T, and with the magnetic objective lens switched off (Lorenz mode), i.e. B=0 T. We observe that the presence or absence of the magnetic field noticeably affects the critical current density at which EBIF occurs. This strongly suggests that magnetic field effects play a crucial role in instigating EBIF on the microparticles. The dependence of the value of the critical current density on the absence or presence of an ambient magnetic field cannot be accounted for by the beam-induced heating model. Consequently, this work presents robust experimental evidence suggesting that Coulomb explosion driven by electrostatic charging is the root cause of EBIF.

Hybrid tungsten-carbon 2D nanostructures viain situgasification of carbon substrates driven by ebeam irradiation of WO2.9microparticles.

Since the transmission electron microscope (TEM) has the capacity to observe the atomic structure of materials,in situTEM synthesis methods are uniquely suited to advance our fundamental understanding of the bottom-up dynamics that drive the formation of nanostructures. E-beam induced fragmentation (potentially identified as a manifestation of Coulomb explosion) and electron stimulated desorption are phenomena that have received attention because they trigger chemical and physical reactions that can lead to the production of various nanostructures. Here we report a simple TEM protocol implemented on WO2.9microparticles supported on thin amorphous carbon substrates. The method produces various nanostructures such as WC nanoparticles, WC supported films and others. Nevertheless, we focus on the gradual graphitization and gasification of the C substrate as it interacts with the material expelled from the WO2.9microparticles. The progressive gasification transforms the substrate from amorphous C down to hybrid graphitic nanoribbons incorporating W nanoparticles. We think these observations open interesting possibilities for the synthesis of 2D nanomaterials in the TEM.

Operation Mechanism in Hybrid Mg-Li Batteries with TiNb2O7 Allowing Stable High-Rate Cycling.

We studied the structural evolution and cycling behavior of TiNb2O7 (TNO) as a cathode in a nonaqueous hybrid dual-salt Mg-Li battery. A very high fraction of pseudocapacitive contribution to the overall specific capacity makes the material suitable for ultrafast operation in a hybrid battery, composed of a Mg-metal anode, and a dual-salt APC-LiCl electrolyte with Li and Mg cations. Theoretical calculations show that Li intercalation is predominant over Mg intercalation into the TNO in a dual-salt electrolyte with Mg2+ and Li+, while experimentally up to 20% Mg cointercalation was observed after battery discharge. In hybrid Mg-Li batteries, TNO shows capacities which are about 40 mA h g-1 lower than in single-ion Li batteries at current densities of up to 1.2 A g-1. This is likely due to a partial Mg cointercalation or/and location of Li cations on alternative crystallographic sites in the TNO structure in comparison to the Li-intercalation process in Li batteries. Generally, hybrid Mg-Li cells show a markedly superior applicability for a very prolonged operation (above 1000 cycles) with 100% Coulombic efficiency and a capacity retention higher than 95% in comparison to conventional Li batteries with TNO after being cycled either under a low (7.75 mA g-1) or high (1.55 A g-1) current density. The better long-term behavior of the hybrid Mg-Li batteries with TNO is especially pronounced at 60 °C. The reasons for this are an appropriate cathode electrolyte interface containing MgCl2 species and a superior performance of the Mg anode in APC-LiCl electrolytes with a dendrite-free, fast Mg deposition/stripping. This stable interface stands in contrast to the anode electrolyte interface in Li batteries with a Li anode in conventional carbonate-containing electrolytes, which is prone to dendrite formation, thus leading to a battery shortcut.

Synthesis of (Li2Fe1-yMny)SO Antiperovskites with Comprehensive Investigations of (Li2Fe0.5Mn0.5)SO as Cathode in Li-ion Batteries.

A series of solid solutions (Li2Fe1-yMny)SO with a cubic antiperovskite structure was successfully synthesized. The composition (Li2Fe0.5Mn0.5)SO was intensively studied as a cathode in Li-ion batteries showing a reversible specific capacity of 120 mA h g-1 and almost a 100% Coulombic efficiency after 50 cycles at 0.1C meaning extraction/insertion of 1 Li per formula unit during 10 h. Operando X-ray absorption spectroscopy confirmed the redox activity of both Fe2+ and Mn2+ cations during battery charge and discharge, while operando synchrotron X-ray diffraction studies revealed a reversible formation of a second isostructural phase upon Li-removal and insertion at least for the first several cycles. In comparison to (Li2Fe)SO, the presence of Mn stabilizes the crystal structure of (Li2Fe0.5Mn0.5)SO during battery operation, although post mortem TEM studies confirmed a gradual amorphization after 50 cycles. A lower specific capacity of (Li2Fe0.5Mn0.5)SO in comparison to (Li2Fe)SO is probably caused by slower kinetics, especially in the two-phase region, as confirmed by Li-diffusion coefficient measurements.

Evaluation of bezafibrate, gemfibrozil, indomethacin, sulfamethoxazole, and diclofenac removal by ligninolytic enzymes.

The laccase (Lac), manganese peroxidases (MnP), and lignin peroxidase enzymes produced by basidiomycete have been studied due to their potential in bioremediation, therefore, in this study, degradation of diclofenac (DCF), sulfamethoxazole (SMX), indomethacin (IND), gemfibrozil (GFB), and bezafibrate (BZF) by enzymes produced by Trametes maxima, Pleurotus sp., and Pycnosporus sanguineus grown in culture was evaluated. The degradation of drugs can mainly be attributed to MnP because a correlation between the activity of this enzyme and the degree of removal was found. The specific activity of Lac did not show correlation with drug removal, while lignin peroxidase was not expressed. Trametes maxima showed the highest specific activity of MnP (387.6 ± 67.4 U/mg) and efficiency removal 90.2% of DCF, 72.62% of SMX, 60.76% of IND, 43.39% of GFB, and 32.59% of BZF) followed by Pleurotus sp. with specific activity of MnP of 55.9 ± 8.5 U/mg and 89.47% of DCF, 47.61% of GFB and 73% of IND were removed, P. sanguineus had the lowest specific activity of 18 ± 1.3 U/mg and was able to remove only 42% of SMX and 10.59% of IND. In order to prove that MnP remove drugs instead of Lac, the pure Lac was tested and only degraded DCF.

Room temperature single-step synthesis of metal decorated boron-rich nanowires via laser ablation.

Hybrid nanostructures, such as those with nanoparticles anchored on the surface of nanowires, or decorated nanowires, have a large number of potential and tested applications such as: gas sensing, catalysis, plasmonic waveguides, supercapacitors and more. The downside of these nanostructures is their production. Generally, multi-step synthesis procedures are used, with the nanowires and the nanoparticles typically produced separately and then integrated. The few existent single-step methods are lengthy or necessitate highly dedicated setups. In this paper we report a single-step and rapid (ca. 1 min) laser ablation synthesis method which produces a wide variety of boron-rich decorated nanowires. Furthermore, the method is carried at room temperature. The synthesis process consists on a filamentary jet ejection process driven by pressure gradients generated by the ablation plume on the rims of the irradiation crater. Simultaneously nanoparticles are nucleated and deposited on the filaments thus producing hybrid decorated nanowires.

Bioactivities and Extract Dereplication of Actinomycetales Isolated From Marine Sponges.

In the beginning of the twenty-first century, humanity faces great challenges regarding diseases and health-related quality of life. A drastic rise in bacterial antibiotic resistance, in the number of cancer patients, in the obesity epidemics and in chronic diseases due to life expectation extension are some of these challenges. The discovery of novel therapeutics is fundamental and it may come from underexplored environments, like marine habitats, and microbial origin. Actinobacteria are well-known as treasure chests for the discovery of novel natural compounds. In this study, eighteen Actinomycetales isolated from marine sponges of three Erylus genera collected in Portuguese waters were tested for bioactivities with the main goal of isolating and characterizing the responsible bioactive metabolites. The screening comprehended antimicrobial, anti-fungal, anti-parasitic, anti-cancer and anti-obesity properties. Fermentations of the selected strains were prepared using ten different culturing media. Several bioactivities against the fungus Aspergillus fumigatus, the bacteria Staphylococcus aureus methicillin-resistant (MRSA) and the human liver cancer cell line HepG2 were obtained in small volume cultures. Screening in higher volumes showed consistent anti-fungal activity by strain Dermacoccus sp. #91-17 and Micrococcus luteus Berg02-26. Gordonia sp. Berg02-22.2 showed anti-parasitic (Trypanosoma cruzi) and anti-cancer activity against several cell lines (melanoma A2058, liver HepG2, colon HT29, breast MCF7 and pancreatic MiaPaca). For the anti-obesity assay, Microbacterium foliorum #91-29 and #91-40 induced lipid reduction on the larvae of zebrafish (Danio rerio). Dereplication of the extracts from several bacteria showed the existence of a variety of secondary metabolites, with some undiscovered molecules. This work showed that Actinomycetales are indeed good candidates for drug discovery.

New Frontiers in Electron Beam-Driven Chemistry in and around Graphene.

Modern aberration corrected transmission electron microscopes offer the potential for electron beam sensitive materials, such as graphene, to be examined with low energy electrons to minimize, and even avoid, damage while still affording atomic resolution, and thus providing excellent characterization. Here in this review, the exploits in which the electron beam interactions, which are often considered negative, are explored to usefully drive a wealth of chemistry in and around graphene, importantly, with no other external stimuli. After introducing the technique, this review covers carbon phase reactions between amorphous carbon, graphene, fullerenes, carbon chains, and carbon nanotubes. It then explores different studies with clusters and nanoparticles, followed by coverage of single atom and molecule interactions with graphene, and finally concludes and highlights the anticipated exciting future for electron beam driving chemistry in and around graphene.

In-situ Quasi-Instantaneous e-beam Driven Catalyst-Free Formation Of Crystalline Aluminum Borate Nanowires.

The catalyst-assisted nucleation and growth mechanisms for many kinds of nanowires and nanotubes are pretty well understood. At times, though, 1D nanostructures form without a catalyst and the argued growth modes have inconsistencies. One such example is the catalyst-free growth of aluminium borate nanowires. Here we develop an in-situ catalyst-free room temperature growth route for aluminium nanowires using the electron beam in a transmission electron microscope. We provide strong experimental evidence that supports a formation process that can be viewed as a phase transition in which the generation of free-volume induced by the electron beam irradiation enhances the atomic mobility within the precursor material. The enhanced atomic mobility and specific features of the crystal structure of Al5BO9 drive the atomic rearrangement that results in the large scale formation of highly crystalline aluminium borate nanowires. The whole formation process can be completed within fractions of a second. Our developed growth mechanism might also be extended to describe the catalyst-free formation of other nanowires.

Room temperature in situ growth of B/BOx nanowires and BOx nanotubes.

Despite significant advances in the synthesis of nanostructures, our understanding of the growth mechanisms of nanowires and nanotubes grown from catalyst particles remains limited. In this study we demonstrate a straightforward route to grow coaxial amorphous B/BOx nanowires and BOx nanotubes using gold catalyst particles inside a transmission electron microscope at room temperature without the need of any specialized or expensive accessories. Exceedingly high growth rates (over 7 µm/min) are found for the coaxial nanowires, and this is attributed to the highly efficient diffusion of B species along the surface of a nanowire by electrostatic repulsion. On the other hand the O species are shown to be relevant to activate the gold catalysts, and this can occur through volatile O species. The technique could be further developed to study the growth of other nanostructures and holds promise for the room temperature growth of nanostructures as a whole.