Silicon and germanium nanostructures : synthesis and in situ TEM study

textA variety of chemical routes exist for a wide range of nanomaterials with tunable size, shape, composition and surface chemistry. Of these materials, silicon (Si) and germanium (Ge) nanomaterials have been some of the most challenging to synthesize. Solution-liquid-solid (SLS) growth of Si was studied using tin (Sn) as the seeding metal. Si nanorods with narrow diameters can be grown by the decomposition of trisilane in hot squalane in the presence of Sn nanocrystals. Photoluminescence could be obtained from the Si nanorods by thermal hydrosilylation passivation. This colloidal synthesis could be further simplified to a single-step reaction procedure by the in situ formation of Sn seed particles. In addition to trisilane as a Si source, isotetrasilane, neopentasilane and cyclohexasilane were studied for Si nanorod growth: all three reactants enabled nanorod formation at lower growth temperatures. A monophenylsilane (MPS) enhanced growth was discovered for supercritical fluid-liquid-solid (SFLS) growth of Ge nanowires that enables the Ge conversion of ~100%. A variety of metalorganic compounds were studied for replacing pre-synthesized metal nanoparticles to induce Ge nanowire growth. Si and Ge nanowires are some of the most promising anode materials in lithium ion batteries (LIBs) because of their high lithium storage capacity. However, the significant chemical and physical changes that occur during cycling hamper their practical uses. In situ transmission electron microscopy (TEM) techniques were conducted to observe and understand structural and interfacial changes of the Si and Ge nanowires during electrochemical cycling; and, therefore, resolving the problems with current anodes by materials modification. The in situ TEM experiments showed that the incorporation of Sn into Si nanowires can enhance their rate capability. But the enhanced Li diffusion leads to the premature pore formation in Si nanowires. Ge nanowires has been discovered the potential as sodium ion battery anodes after an initial activation with a lithiation step to amorphize the nanowires.Materials Science and Engineerin

Colloidal Silicon-Germanium Nanorod Heterostructures

Colloidal nanorods with axial Si and Ge heterojunction segments were produced by solution-liquid-solid (SLS) growth using Sn as a seed metal and trisilane and diphenylgermane as Si and Ge reactants. The low solubility of Si and Ge in Sn helps to generate abrupt Si-Ge heterojunction interfaces. To control the composition of the nanorods, it was also necessary to limit an undesired side reaction between the Ge reaction byproduct tetraphenylgermane and trisilane. High-resolution transmission electron microscopy reveals that the Si-Ge interfaces are epitaxial, which gives rise to a significant amount of bond strain resulting in interfacial misfit dislocations that nucleate stacking faults in the nanorods

Silicon nanoparticles as Raman scattering enhancers

[EN] In this communication we demonstrate the large amplification values of the Raman signal of organic molecules attached to silicon nanoparticles (SiNPs). Light induced Mie resonances of high refractive index particles generate strong evanescent electromagnetic (EM) fields, thus boosting the Raman signal of species attached to the nanoparticles. The interest of this process is justified by the wide range of experimental configurations that can be implemented including photonic crystals, the sharp spectral resonances easily tuneable with the particle size, the biocompatibility and biodegradability of silicon, and the possibility of direct analysis of molecules that do not contain functional groups with high affinity for gold and silver. Additionally, silicon nanoparticles present stronger field enhancement due to Mie resonances at larger sizes than gold.The authors acknowledge financial support from the following projects FIS2009-07812, MAT2012-35040, Consolider 2007-0046 Nano light, PROMETEO/2010/043, CTQ2011-23167, and Cross-SEAS, FP7 MC-IEF 329131. L. S. thanks the financial support from the MINECO (Estancias de profesores e investigadores extranjeros en centros espanoles) fellowship program.Rodríguez, M.; Shi, L.; Lu, X.; Korgel, B.; Alvarez -Puebla, R.; Meseguer Rico, FJ. (2014). Silicon nanoparticles as Raman scattering enhancers. Nanoscale. 6(11):5666-5670. https://doi.org/10.1039/c4nr00593gS5666567061

Wogonin induces cell cycle arrest and erythroid differentiation in imatinib-resistant K562 cells and primary CML cells

Wogonin, a flavonoid derived from Scutellaria baicalensis Georgi, has been demonstrated to be highly effective in treating hematologic malignancies. In this study, we investigated the anticancer effects of wogonin on K562 cells, K562 imatinib-resistant cells, and primary patient-derived CML cells. Wogonin up-regulated transcription factor GATA-1 and enhanced binding between GATA-1 and FOG-1, thereby increasing expression of erythroid-differentiation genes. Wogonin also up-regulated the expression of p21 and induced cell cycle arrest. Studies employing benzidine staining and analyses of cell surface markers glycophorin A (GPA) and CD71 indicated that wogonin promoted differentiation of K562, imatinib-resistant K562, and primary patient-derived CML cells. Wogonin also enhanced binding between GATA-1 and MEK, resulting in inhibition of the growth of CML cells. Additionally, in vivo studies showed that wogonin decreased the number of CML cells and prolonged survival of NOD/SCID mice injected with K562 and imatinib-resistant K562 cells. These data suggested that wogonin induces cycle arrest and erythroid differentiation in vitro and inhibits proliferation in vivo

Monodisperse silicon nanocavities and photonic crystals with magnetic response in the optial region

[EN] It is generally accepted that the magnetic component of light has a minor role in the light-matter interaction. The recent discovery of metamaterials has broken this traditional understanding, as both the electric and the magnetic field are key ingredients in metamaterials. The top-down technology used so far employs noble metals with large intrinsic losses. Here we report on a bottom-up approach for processing metamaterials based on suspensions of monodisperse full dielectric silicon nanocavities with a large magnetic response in the near-infrared region. Experimental results and theory show that silicon-colloid-based liquid suspensions and photonic crystals made of two-dimensional arrays of particles have strong magnetic response in the near-infrared region with small optical losses. Our findings might have important implications in the bottom-up processing of large-area low-loss metamaterials working in the near-infrared region.We acknowledge financial support from the following projects FIS2009-07812, Consolider 2007-0046 Nanolight, the PROMETEO/2010/043 and the Robert A. Welch Foundation (F-1464). L.S. thanks the financial support from the MINECO (Estancias de profesores e investigadores extranjeros en centros espanoles) fellowship program.Shi, L.; Harris, JT.; Fenollosa Esteve, R.; Rodríguez, M.; Lu, X.; Korgel, B.; Meseguer Rico, FJ. (2013). Monodisperse silicon nanocavities and photonic crystals with magnetic response in the optial region. Nature Communications. 4:419041-419047. https://doi.org/10.1038/ncomms29344190414190474Landau, L. D. & Lifshitz, E. M. . Electrodynamics of Continuous Media Oxford, UK (1960) .Smith, D. R., Pendry, J. B. & Wiltshire, M. C. K. . Metamaterials and negative refractive index. Science 305, 788–792 (2004) .Soukoulis, C. M., Kafesaki, M. & Economou, E. N. . Negative-index materials: new frontiers in optics. Adv. Mater. 18, 1941–1952 (2006) .Soukoulis, C. M. & Wegener, M. . Past achievements and future challenges in the development of three-dimensional photonic metamaterials. Nat. Photon. 5, 523–531 (2011) .Linden, S., Enkrich, C., Wegener, M., Zhou, J., Koschny, T. & Soukoulis, C. M. . Magnetic response of metamaterials at 100 Terahertz. Science 306, 1351–1353 (2004) .Enkrich, C. et al. Focused-Ion-Beam nanofabrication of near-infrared magnetic metamaterials. Adv. Mater. 17, 2547–2549 (2005) .Liu, N., Guo, H., Fu, L., Kaiser, S., Schweizer, H. & Giessen, H. . Three dimensional photonic metamaterials at optical frequencies. Nat. Mater. 7, 31–37 (2008) .Grigorenko, A. N. et al. Nanofabricated media with negative permeability at visible frequencies. Nature 438, 335–338 (2005) .Liu, N., Fu, L., Kaiser, S., Schweizer, H. & Giessen, H. . Plasmonic building blocks for magnetic molecules in three dimensional optical metamaterials. Adv. Mater. 20, 3859–3865 (2008) .Shelby, R. A., Smith, D. R. & Schultz, S. . Experimental verification of a negative index of refraction. Science 292, 77–79 (2001) .Zhang, X. & Liu, Z. . Superlenses to overcome the diffraction limit. Nat. Mater. 7, 435–441 (2008) .Schurig, D. et al. Metamaterials electromagnetic cloak at microwave frequencies. Science 314, 977–980 (2006) .Zheludev, N. I. . The road ahead of metamaterials. Science 328, 582–583 (2010) .Zheludev, N. I. . A roadmap of metamaterials. Opt. Photon. News 22, 30–35 (2011) .Zhao, Q., Zhou, J., Zhang, F. & Lippens, D. . Mie resonance-based dielectric metamaterials. Mater. Today 12, 60–69 (2009) .O’Brien, S. & Pendry, J. B. . Photonic band-gap effects and magnetic activity in dielectric composites. J. Phys. Condens. Mater. 14, 4035–4044 (2002) .Gansel, J. K. et al. Gold helix photonic metamaterials as broadband circular polarizer. Science 325, 1513–1515 (2009) .Radke, A., Gissibl, T., Klotzbucher, T., Braun, P. V. & Giessen, H. . Three-dimensional bichiral plasmonic crystals fabricated by direct laser writing and electroless silver plating. Adv. Mater. 23, 3018–3021 (2011) .Chanda, D. et al. Large-are flexible 3D optical negative index metamaterial formed by nanotransfer printing. Nat. Nanotech. 6, 402–407 (2011) .Blanco, A. et al. Large scale synthesis of a silicon photonic crystal with a complete three dimensional band gap near 1.5 microns. Nature 405, 437–440 (2000) .Xia, Y., Gates, B., Yin, Y. & Lu, Y. . Monodispersed colloidal spheres: old materials with new applications. Adv. Mater. 12, 693–713 (2000) .Garcia-Etxarri, A. et al. Strong magnetic response of submicron silicon particles in the infrared. Opt. Express 19, 4815–4826 (2011) .Miroshnichenko, A. E., Lukyanchuk, B. L., Maier, S. A. & Kivshar, Y. S. . Optically induced interaction of magnetic moments in hybrid metamaterials. ACS Nano 6, 837–842 (2012) .Shi, L., Xifre-Perez, E., Garcia de Abajo, F. J. & Meseguer, F. . Looking through the mirror: optical microcavity-mirror image photonic interaction. Opt. Express 20, 11247–11255 (2012) .Shi, L. & Meseguer, F. . Magnetic interaction in all silicon waveguide spherical coupler device. Opt. Express 20, 22617–22626 (2012) .Shi, L., Tuzer, T. U., Fenollosa, R. & Meseguer, F. . A new dielectric metamaterial building block with a strong magnetic response below 1.5 micrometers region. Silicon colloids nanocavities. Adv. Mater. 20, 5934–5938 (2012) .Evlyukhin, A. B., Reinhardt, C., Seidel, A., Lukyanchuk, B. S. & Chichkov, B. . Optical response features of Si-nanoparticle arrays. Phys. Rev. B 82, 045404 (2010) .Krasnok, A. E., Miroshnichenko, A. E., Belov, P. A. & Kivshar, Y. S. . Huygens optical elements and Yagi-Uda nanoantennas based on dielectric nanoparticles. JETP Lett. 94, 593–598 (2011) .Krasnok, A. E., Miroshnichenko, A. E., Belov, P. A. & Kivshar, Y. S. . All-dielectric optical nanoantennas. Opt. Express 20, 20599 (2012) .Evlyukhin, A. B. et al. Demonstration of magnetic dipole resonances of dielectric nanospheres in the visible region. Nano. Lett. 12, 3749–3755 (2012) .Kuznetsov, A. I., Miroshnichenko, A. E., Fu, Y. H., Zhang, J. & Lukyanchuk, B. . Magnetic light. Sci. Rep. 2, 492 (2012) .Miroshnichenko, A. E. et al. Magnetic light: optical magnetism of dielectric nanoparticles. Opt. Photon. News 23, 35 (2012) .Fu, Y. H., Kuznetsov, A. I., Miroshnichenko, A. E., Yu, Y. F. & Lukyanchuk, B. . Directional visible light scattering by silicon nanoparticles. Nat. Commun. 4, 1527 (2013) .Person, S., Jain, M., Lapin, Z., Saenz, J. J., Wicks, G. & Novotny, L. . Demonstration of zero optical backscattering from single nanoparticles. Nano. Lett. 13, 1806–1809 (2013) .Geffrin, J. M. et al. Magnetic and electric coherenece in forward- and back-scattered electromagnetic waves by a single dielectric subwavelength sphere. Nat. Commun. 3, 1171 (2012) .Pell, L. E., Schricker, A. D., Mikulec, F. V. & Korgel, B. A. . Synthesis of amorphous silicon colloids by trisilane thermolysis in high temperature supercritical solvents. Langmuir 20, 6546–6548 (2004) .Harris, J. T., Hueso, J. L. & Korgel, B. A. . Hydrogenated amorphous silicon (a-Si:H) colloids. Chem. Mater. 22, 6378–6383 (2010) .Alvarez-Puebla, R., Liz-Marzan, L. M. & Garcia de Abajo, F. J. . Light concentration at the nanometer scale. J. Phys. Chem. Lett. 1, 2428–2434 (2010) .Meseguer, F. . Colloidal crystals as photonic crystals. Colloids Surfaces A. 270, 1–7 (2005) .Zhan, P. et al. The anomalous infrared transmission of gold films on two-dimensional colloidal crystals. Adv. Mater. 18, 1612–1616 (2006) .Splinelli, P., Verschuuren, M. A. & Polman, A. . Broadband omnidirectional antireflection coating based on subwavelength surface Mie resonators. Nat. Commun. 3, 692 (2012) .Palik E. D. (ed.) Handbook of Optical Constants of Solids Academic Press: USA, (1998) .Doicu, A., Wriedt, T. & Eremin, Y. A. . Light Scattering by Systems of Particles Springer: Berlin, (2006)

Multiplexed volumetric CLEM enabled by scFvs provides insights into the cytology of cerebellar cortex.

Mapping neuronal networks is a central focus in neuroscience. While volume electron microscopy (vEM) can reveal the fine structure of neuronal networks (connectomics), it does not provide molecular information to identify cell types or functions. We developed an approach that uses fluorescent single-chain variable fragments (scFvs) to perform multiplexed detergent-free immunolabeling and volumetric-correlated-light-and-electron-microscopy on the same sample. We generated eight fluorescent scFvs targeting brain markers. Six fluorescent probes were imaged in the cerebellum of a female mouse, using confocal microscopy with spectral unmixing, followed by vEM of the same sample. The results provide excellent ultrastructure superimposed with multiple fluorescence channels. Using this approach, we documented a poorly described cell type, two types of mossy fiber terminals, and the subcellular localization of one type of ion channel. Because scFvs can be derived from existing monoclonal antibodies, hundreds of such probes can be generated to enable molecular overlays for connectomic studies

Cleaning up nitrogen pollution may reduce future carbon sinks

Biosphere carbon sinks are crucial for reducing atmospheric carbon dioxide (CO2) concentration to mitigate global warming, but are substantially affected by the input of reactive nitrogen (Nr). Although the effects of anthropogenic CO2 emission and nitrogen deposition (indicated by Nr emission to atmosphere) on carbon sink have been studied, it is unclear how their ratio (C/N) changes with economic development and how such change alters biosphere carbon sinks. Here, by compiling datasets for 132 countries we find that the C/N ratio continued to increase despite anthropogenic CO2 and Nr emissions to atmosphere both showing an asymmetric para-curve with economic growth. The inflection points of CO2 and Nr emissions are found at around $15,000 gross domestic product per capita worldwide. Economic growth promotes the use of Nr and energy, while at the same time increases their use efficiencies, together resulting in occurrences of inflection points of CO2 and Nr emissions. Nr emissions increase slower but decrease faster than that of CO2 emissions before and after the inflection point, respectively. It implies that there will be relatively more anthropogenic CO2 emission but less N deposition with economic growth. This may limit biosphere carbon sink because of relative shortage of Nr. This finding should be integrated/included in global climate change modelling. Efforts, such as matching N deposition with carbon sequestration on regional scale, to manage CO2 and Nr emissions comprehensively to maintain a balance are critical

Progress on improving Agricultural Nitrogen use efficiency: UK-China viortual joint centers on Nitrogen Agronomy

Two virtual joint centers for nitrogen agronomy were established between the UK and China to facilitate collaborative research aimed at improving nitrogen use efficiency (NUE) in agricultural production systems and reducing losses of reactive N to the environment. Major focus areas were improving fertilizer NUE, use of livestock manures, soil health, and policy development and knowledge exchange. Improvements to fertilizer NUE included attention to application rate in the context of yield potential and economic considerations and the potential of improved practices including enhanced efficiency fertilizers, plastic film mulching and cropping design. Improved utilization of livestock manures requires knowledge of the available nutrient content, appropriate manure processing technologies and integrated nutrient management practices. Soil carbon, acidification and biodiversity were considered as important aspects of soil health. Both centers identified a range of potential actions that could be taken to improve N management, and the research conducted has highlighted the importance of developing a systemslevel approach to assessing improvement in the overall efficiency of N management and avoiding unintended secondary effects from individual interventions. Within this context, the management of fertilizer emissions and livestock manure at the farm and regional scales appear to be particularly important targets for mitigation

Orientationally ordered silicon nanocrystal cuboctahedra in superlattices

This is an open access article published under an ACS AuthorChoice License. See Standard ACS AuthorChoice/Editors' Choice Usage Agreement - https://pubs.acs.org/page/policy/authorchoice_termsofuse.htmlUniform silicon nanocrystals were synthesized with cuboctahedral shape and passivated with 1-dodecene capping ligands. Transmission electron microscopy, electron diffraction, and grazing incidence wide-angle and small-angle X-ray scattering show that these soft cuboctahedra assemble into face-centered cubic superlattices with orientational order. The preferred nanocrystal orientation was found to depend on the orientation of the superlattices on the substrate, indicating that the interactions with the substrate and assembly kinetics can influence the orientation of faceted nanocrystals in superlattices

Oroxylin A promotes PTEN-mediated negative regulation of MDM2 transcription via SIRT3-mediated deacetylation to stabilize p53 and inhibit glycolysis in wt-p53 cancer cells

Introduction p53 plays important roles in regulating the metabolic reprogramming of cancer, such as aerobic glycolysis. Oroxylin A is a natural active flavonoid with strong anticancer effects both in vitro and in vivo. Methods wt-p53 (MCF-7 and HCT116 cells) cancer cells and p53-null H1299 cancer cells were used. The glucose uptake and lactate production were analyzed using Lactic Acid production Detection kit and the Amplex Red Glucose Assay Kit. Then, the protein levels and RNA levels of p53, mouse double minute 2 (MDM2), and p53-targeted glycolytic enzymes were quantified using Western blotting and quantitative polymerase chain reaction (PCR), respectively. Immunoprecipitation were performed to assess the binding between p53, MDM2, and sirtuin-3 (SIRT3), and the deacetylation of phosphatase and tensin homolog (PTEN). Reporter assays were performed to assess the transcriptional activity of PTEN. In vivo, effects of oroxylin A was investigated in nude mice xenograft tumor-inoculated MCF-7 or HCT116 cells. Results Here, we analyzed the underlying mechanisms that oroxylin A regulated p53 level and glycolytic metabolism in wt-p53 cancer cells, and found that oroxylin A inhibited glycolysis through upregulating p53 level. Oroxylin A did not directly affect the transcription of wt-p53, but suppressed the MDM2-mediated degradation of p53 via downregulating MDM2 transcription in wt-p53 cancer cells. In further studies, we found that oroxylin A induced a reduction in MDM2 transcription by promoting the lipid phosphatase activity of phosphatase and tensin homolog, which was upregulated via sirtuin3-mediated deacetylation. In vivo, oroxylin A inhibited the tumor growth of nude mice-inoculated MCF-7 or HCT116 cells. The expression of MDM2 protein in tumor tissue was downregulated by oroxylin A as well. Conclusions These results provide a p53-independent mechanism of MDM2 transcription and reveal the potential of oroxylin A on glycolytic regulation in both wt-p53 and mut-p53 cancer cells. The studies have important implications for the investigation on anticancer effects of oroxylin A, and provide the academic basis for the clinical trial of oroxylin A in cancer patients