Promising properties of ALD boron nitride nanotube mats for water purification

International audienc

Photonic hyperuniform networks obtained by silicon double inversion of polymer templates

Hyperuniform disordered networks belong to a peculiar class of structured materials predicted to display isotropic complete photonic bandgaps for a refractive index contrast larger than 3. The practical realization of such photonic designer materials is challenging, however, as it requires control over a multi-step fabrication process on optical length scales. Here we report the direct-laser writing of three-dimensional hyperuniform polymeric templates followed by a silicon double inversion procedure leading to high-quality network structures made of polycrystalline silicon. We observe a pronounced gap in the shortwave infrared centered at a wavelength of Gap≃2.5  μm, in good agreement with numerical simulations. In the experiments the typical structural length scale can be varied between 2 and 1.54 μm, leading to a blueshift of the gap accompanied by an increase of the silicon filling fraction

Silicon hyperuniform disordered photonic materials with a pronounced gap in the shortwave infrared

The mesoscale fabrication of silicon hyperuniform disordered materials with a broad and pronounced photonic gap in the shortwave infrared is reported. Due to their unique structure and their high refractive index, these fascinating materials are predicted to possess a complete photonic bandgap in the absence of any long-range order

Deposição de camadas atómicas de óxido de metais por sol-gel não-aquoso

Doutoramento em QuímicaO trabalho apresentado neste manuscrito foi desenvolvido no âmbito do programa doutoral intitulado “Deposição de Camadas Atómicas (ALD) de óxido de metais por sol-gel não-aquoso”. O objectivo deste trabalho foi a preparação de hetero-estruturas funcionais por ALD e a sua caracterização. Foi desenvolvido um novo processo de deposição de óxido de estanho a temperatura baixa-moderada, utilizando um método ALD não-aquoso, o qual foi aplicado com sucesso ao revestimento controlado das paredes internas e externas de nanotubos de carbono. Uma vez que a preparação de nanomateriais funcionais requer uma elevada exatidão do processo de deposição, foi demonstrada a deposição precisa de filmes que se adaptem à forma do substrato ou de filmes nano-estruturados constituídos por partículas em vários substratos. Além disso, foram depositados com grande exatidão vários óxidos de metal em nanotubos de carbono e demonstrou-se a possibilidade de ajustar o revestimento feito por ALD através do controlo da funcionalização da superfície do substrato nano-estruturado de carbono. As hetero-estruturas obtidas foram posteriormente aplicadas como sensores de gases. O melhoramento verificado na sensibilidade foi atribuído à formação de heterojunções p-n entre o filme de óxido de metais e o suporte. O trabalho desenvolvido tendo como objetivo o controlo do revestimento por ALD através da funcionalização da superfície do suporte é certamente de interesse para o design de hetero-estruturas funcionais baseadas em substratos de carbono. De facto, durante o último período do programa de doutoramento, este conceito foi alargado à funcionalização e revestimento com óxidos de metal de fibras de carbono preparadas por “electrospinning”, de forma a melhorar a estabilidade e a atividade eletrocatalítica de catalisadores à base de Pt. Este trabalho foi realizado maioritariamente na Universidade de Aveiro mas também na Universidade Nacional de Seul e beneficiou de várias colaborações internacionais devido à natureza multidisciplinar da área de investigação em que está inserido.The studies discussed in this manuscript have been carried out under the PhD program entitled “Atomic Layer Deposition of metal oxide by non-aqueous solgel chemistry”. The aim of this work was the elaboration by ALD and characterization of functional heterostructures. A novel low-mild temperature tin dioxide deposition process has been developed using a non-aqueous ALD approach and successfully applied to the conformal and controlled coating of the inner and outer walls of carbon nanotubes. Because a high deposition accuracy is required for the elaboration of functional nanomaterials, the precise deposition of conformal or nanostructured films made of particles onto various substrates was demonstrated. Moreover, various metal oxides have been deposited onto carbon nanotubes in an accurate manner and we have demonstrated the capability to tailor the ALD coating by controlled surface functionalization of the nanostructured carbon-based substrate. The heterostructures obtained were subsequently applied to gas sensing. The improvement of the sensitivity recorded was attributed to the formation of a p-n heterojunction between the metal oxide thin film and its support. The work aimed to control the ALD coating through the surface functionalization is certainly of interest for designing functional heterostructures based on carbonbased substrates. As a matter of fact, during the last period of the PhD program, this concept was extended to the metal oxide functionalization and coating of electrospun carbon fibers for the enhancement of Pt-based electrocatalyst activity and stability. This work was mainly carried out at the University of Aveiro, but also at the Seoul National University, and benefits of several international collaborations due to the multidisciplinar nature of the research field

Influence of the Lattice Mismatch on the Atomic Ordering of ZnO Grown by Atomic Layer Deposition onto Single Crystal Surfaces with Variable Mismatch (InP, GaAs, GaN, SiC)

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ISOLASI, KARAKTERISASI DAN UJI AKTIVITAS ANTIBIOTIK BAKTERI ENDOFIT DARI TUMBUHAN ECENG GONDOK [Eichhornia crassipes (Mart.)] DI DANAU MANINJAU, SUMATERA BARAT

Penelitian tentang isolasi, karakterisasi, dan uji aktivitas antibiotik bakteri endofit dari tumbuhan eceng gondok [Eichhornia crassipes (Mart.)] di Danau Maninjau, Sumatera Barat telah dilaksanakan. Penelitian ini bertujuan untuk memperoleh isolat bakteri endofit tumbuhan eceng gondok Eichhornia crassipes yang dapat menghasilkan antibiotik dan mengetahui kelompok bakteri endofit tumbuhan Eichhornia crassipes (Mart.) sebagai penghasil antibiotik. Penelitian ini menggunakan metode eksperimen dengan analisis data secara deskriptif. Aktivitas antibiotik bakteri endofit diuji menggunakan metode kertas cakram dengan bakteri uji Escherichia coli dan Staphylococcus aureus serta jamur Candida albicans. Identifikasi bakteri endofit tumbuhan Eichhornia crassipes (Mart.) dilakukan secara makroskopis, mikroskopis, dan biokimia. Dari hasil penelitian ini didapatkan sebelas isolat bakteri penghasil antibiotik dengan sensitivitas antibiotik yang berbeda, dimana terdapat dua isolat bakteri yang paling potensial sebagai penghasil antibiotik, yaitu isolat BEE-11 dan BEE-13. Hasil karakterisasi isolat bakteri penghasil antibiotik dikelompokkan kedalam 1 genus yang sama yaitu Bacillus, dengan 8 spesies, diantaranya Bacillus sp. 1, Bacillus sp. 2, Bacillus sp. 3, Bacillus sp. 4, Bacillus sp. 5, Bacillus sp. 6, Bacillus sp. 7, dan Bacillus sp. 8. Kata Kunci: Bakteri endofit, Eichhornia crassipes, Antibioti

High-quality photonic crystals with a nearly complete band gap obtained by direct inversion of woodpile templates with titanium dioxide

Photonic crystal materials are based on a periodic modulation of the dielectric constant on length scales comparable to the wavelength of light. These materials can exhibit photonic band gaps; frequency regions for which the propagation of electromagnetic radiation is forbidden due to the depletion of the density of states. In order to exhibit a full band gap, 3D PCs must present a threshold refractive index contrast that depends on the crystal structure. In the case of the so-called woodpile photonic crystals this threshold is comparably low, approximately 1.9 for the direct structure. Therefore direct or inverted woodpiles made of high refractive index materials like silicon, germanium or titanium dioxide are sought after. Here we show that, by combining multiphoton lithography and atomic layer deposition, we can achieve a direct inversion of polymer templates into TiO₂ based photonic crystals. The obtained structures show remarkable optical properties in the near-infrared region with almost perfect specular reflectance, a transmission dip close to the detection limit and a Bragg length comparable to the lattice constant

Labeling and monitoring the distribution of anchoring sites on functionalized CNTs by atomic layer deposition

The chemical inertness of graphite and, in the case of tubes, of rolled up few layer graphene sheets, requires some degree of “defect engineering” for the fabrication of carbon based heterostructured materials. It is shown that atomic layer deposition provides a means to specifically label anchoring sites and can be used to characterize the surface functionality of differently treated carbon nanotubes. Direct observation of deposited titania by analytical transmission electron microscopy reveals the location and density of anchoring sites as well as structure related concentrations of functional groups on the surface of the tubes. Controlled functionalization of the tubes therefore allows us to tailor the distribution of deposited material and, hence, fabricate complex heterostructures