Ultrafine particles produced by plasma enhanced chemical vapor deposition -from SiH4, CH4, NH3 and B2H6 gas mixtures- for nanostructured ceramics applications

[eng] Ultrafine particles of silicon and related binary and ternary alloys of the Si-B-C-N system produced in our research group from silane, methane, diborane, ammonia and nitrogen precursor gases by plasma enhanced chemical vapor deposition at low pressure and room temperature are reviewed. The in-situ techniques of plasma analysis and surface characterization (quadrupolar mass spectrometry, optical emission spectroscopy and ellipsometry) providing evidence of powder formation and the polymerization reactions based on the SinH2n- negative radicals electrically confined in the plasma sheath are described. The square wave modulation (SQWM) of the rf power is discussed as an efficient method of controlling the powder particle production with low particle-size dispersion. The properties of the powder particles determined by different structural characterization techniques providing their size and distribution, crystalline order and morphology, chemical composition and chemical bond vibrational characteristics, are analyzed and discussed[cat] Hom presenta una revisió sobre les partícules ultrafines de silici i els seus aliatges binaris i ternaris del sistema Si-B-C-N, produïdes en el nostre grup de recerca a partir dels gasos precursors silà, metà, diborà, amoníac i nitrogen, per dipòsit químic en fase vapor (CVD) reforçat per plasma, a baixa pressió i temperatura ambient. És descrita també la utilització de tècniques in situ d'anàlisi per plasma i de caracterització de superfícies (espectroscòpia de masses quadripolar, espectroscòpia òptica d’emissió i el·lipsometria), que donaren l’evidència de formació de partícules de pols i de reaccions de polimerització basades en radicals negatius SinH2n– confinats elèctricament en l’embolcall del plasma. La modulació d’ona quadrada (SQWM) de la font de rf és estudiada com un eficient mètode de control de la producció de partícules amb una petita dispersió de llurs dimensions. Finalment, hom analitza i discuteix les propietats de les partícules produïdes, determinades per diferents tècniques de caracterització, que permeteren obtenir llurs dimensions i distribució, ordre cristal·lí i morfologia, composició química i les característiques vibracionals dels enllaços químic

Effect of a Balanced Concentration of Hydrogen on Graphene CVD Growth

The extraordinary properties of graphene make it one of the most interesting materials for future applications. Chemical vapor deposition (CVD) is the syntheticmethod that permits obtaining large areas ofmonolayer graphene. To achieve this, it is important to find the appropriate conditions for each experimental system. In our CVD reactor working at low pressure, important factors appear to be the pretreatment of the copper substrate, considering both its cleaning and its annealing before the growing process.The carbon precursor/hydrogen flow ratio and its modification during the growth are significant in order to obtain large area graphene crystals with few defects. In this work, we have focused on the study of the methane and the hydrogen flows to control the production of single layer graphene (SLG) and its growth time. In particular, we observe that hydrogen concentration increases during a usual growing process (keeping stable the methane/hydrogen flow ratio) resulting in etched domains. In order to balance this increase, a modification of the hydrogen flow results in the growth of smooth hexagonal SLG domains. This is a result of the etching effect that hydrogen performs on the growing graphene. It is essential, therefore, to study the moderated presence of hydrogen

Laser induced nanostructuration of vertically aligned carbon nanotubes coated with nickel oxide nanoparticles

A facile method is explored to decorate vertically aligned multi-walled carbon nanotubes (VACNTs) with NiO nanostructures. Multi-walled VACNTs are grown by plasma enhanced chemical vapor deposition and coated with NiO nanoparticles (NPs) by drop casting and submitted to pulsed UV laser irradiation. Laser irradiation provokes rapid heating-melting-cooling processes which lead to the recrystallization of NiO NPs on the outer walls of VACNTs'. In this way, and depending on the laser fluence and the number of accumulated pulses, different nano-architectures such as continuous NiO coatings and spiny features are obtained. High resolution scanning and transmission electron microscopies and Raman spectroscopy, corroborated with photothermal simulations, suggest that the grown nanostructures are mainly created by the laser-induced high temperatures and catalytic action of NiO NPs

Homogeneous Fe2O3 coatings on carbon nanotube structures for supercapacitors

The combination of carbon nanotubes with transition metal oxides can exhibit complementary charge storage properties for use as electrode materials for next generation energy storage devices. One of the biggest challenges so far is to synthesize homogeneous oxide coatings on carbon nanotube structures preserving their integrity. Here we present the formation of conformal coatings of Fe2O3 on vertically aligned carbon nanotubes obtained by atomic layer deposition. We investigate the effect of pristine, nitrogen plasma and water plasma treated carbon nanotube surfaces on the ALD-growth of Fe2O3 using ferrocene and ozone precursors. The surface morphology, coating thickness, microstructure and surface chemistry of iron oxide-carbon nanotube composites and their ultimate influence on the electrochemical behavior of the composites are evaluated. The most effective surface functionalization is that achieved by H2O plasma treatment, whereas untreated carbon nanotubes, despite the lack of active sites in the starting pristine surface, can be coated with an inhomogeneous Fe2O3 film

Nanostructured DLC coatings for self-assembly applications

The singular characteristics of diamond-like carbon (DLC) thin films, concerning tribological and surfaces properties, are suitable for self-assembly applications. Usually, DLC thin films have been developed as protective coatings for sliding surfaces with relative motion. But, DLC coatings deposited on nanostructured surfaces also provide new potential for self-assembly applications. In particular, the addition of fluorine during the deposition of DLC deposited by pulsed DC plasma enhanced chemical vapor deposition (PECVD) has a significant effect on the surface energy and tribological characteristics, which accelerates the mechanisms involved in self-assembly processes. Among the multiple applications of DLC coatings we also found their biocompatibility and antithrombogenicity. Such properties make them candidates for a number of medical applications where wear-resistant coatings, such as prosthesis, or simply biocompatible parts are required

European contribution to the study of ROS: A summary of the findings and prospects for the future from the COST action BM1203 (EU-ROS).

The European Cooperation in Science and Technology (COST) provides an ideal framework to establish multi-disciplinary research networks. COST Action BM1203 (EU-ROS) represents a consortium of researchers from different disciplines who are dedicated to providing new insights and tools for better understanding redox biology and medicine and, in the long run, to finding new therapeutic strategies to target dysregulated redox processes in various diseases. This report highlights the major achievements of EU-ROS as well as research updates and new perspectives arising from its members. The EU-ROS consortium comprised more than 140 active members who worked together for four years on the topics briefly described below. The formation of reactive oxygen and nitrogen species (RONS) is an established hallmark of our aerobic environment and metabolism but RONS also act as messengers via redox regulation of essential cellular processes. The fact that many diseases have been found to be associated with oxidative stress established the theory of oxidative stress as a trigger of diseases that can be corrected by antioxidant therapy. However, while experimental studies support this thesis, clinical studies still generate controversial results, due to complex pathophysiology of oxidative stress in humans. For future improvement of antioxidant therapy and better understanding of redox-associated disease progression detailed knowledge on the sources and targets of RONS formation and discrimination of their detrimental or beneficial roles is required. In order to advance this important area of biology and medicine, highly synergistic approaches combining a variety of diverse and contrasting disciplines are needed.The EU-ROS consortium (COST Action BM1203) was supported by the European Cooperation in Science and Technology (COST). The present overview represents the final Action dissemination summarizing the major achievements of COST Action BM1203 (EU-ROS) as well as research news and personal views of its members. Some authors were also supported by COST Actions BM1005 (ENOG) and BM1307 (PROTEOSTASIS), as well as funding from the European Commission FP7 and H2020 programmes, and several national funding agencies

Photonic characteristics of Langmuir-Blodgett self-assembled monolayers of colloidal silica particles

Monodispersed colloidal crystals based on silica sub-micrometric particles were synthesized using the Stöber-Fink-Bohn process. The control of nucleation and coalescence result in improved characteristics such as high sphericity and very low size dispersion. The resulting silica particles show characteristics suitable for self-assembling across large areas of closely-packed 2D crystal monolayers by an accurate Langmuir-Blodgett deposition process on glass, fused silica and silicon substrates. Due to their special optical properties, colloidal films have potential applications in fields including photonics, electronics, electro-optics, medicine (detectors and sensors), membrane filters and surface devices. The deposited monolayers of silica particles were characterized by means of FESEM, AFM and optical transmittance measurements in order to analyze their specific properties and characteristics. We propose a theoretical calculation for the photonic band gaps in 2D systems using an extrapolation of the photonic behavior of the crystal from 3D to 2D. In this work we show that the methodology used and the conditions in self-assembly processes are decisive for producing high-quality two-dimensional colloidal crystals by the Langmuir-Blodgett technique

Homogeneous Fe2O3 coatings on carbon nanotube structures for supercapacitors

The combination of carbon nanotubes with transition metal oxides can exhibit complementary charge storage properties for use as electrode materials for next generation energy storage devices. One of the biggest challenges so far is to synthesize homogeneous oxide coatings on carbon nanotube structures preserving their integrity. Here we present the formation of conformal coatings of Fe2O3 on vertically aligned carbon nanotubes obtained by atomic layer deposition. We investigate the effect of pristine, nitrogen plasma and water plasma treated carbon nanotube surfaces on the ALD-growth of Fe2O3 using ferrocene and ozone precursors. The surface morphology, coating thickness, microstructure and surface chemistry of iron oxide–carbon nanotube composites and their ultimate influence on the electrochemical behavior of the composites are evaluated. The most effective surface functionalization is that achieved by H2O plasma treatment, whereas untreated carbon nanotubes, despite the lack of active sites in the starting pristine surface, can be coated with an inhomogeneous Fe2O3 film.The authors acknowledge financial support from the Spanish MINECO (Severo Ochoa Programme for Centres of Excellence in R&D SEV-2015-0496 and MAT2017-83169-R, ENE2014-56109-C3-1-R, ENE2014-56109-C3-3-R, ENE2017-89210-C2-1-R, ENE2017-89210-C2-2-R AEI/FEDER), and by AGAUR of Generalitat de Catalunya, grant numbers 2017SGR1086 and 2017SGR1519 We also thank the China Scholarship Council for CSC fellowship No. 201606920073 to P.Y. IA and FP acknowledge the financial support of their PhD studies from MICINN and SENESCYT of the Ecuadorian Government, which provided financial support through its scholarship program for 2014, respectively. The authors would also like to thank the CCiT-UB for help with the surface analysis and the structural and morphological characterization of the samples.Peer reviewe

Laser-driven coating of vertically aligned carbon nanotubes with manganese oxide from metal organic precursors for energy storage

Carbon nanotubes-transition metal oxide systems are intensively studied due to their excellent properties for electrochemical applications. In this work, an innovative procedure is developed for the synthesis of vertically aligned multi-walled carbon nanotubes (VACNTs) coated with transition metal oxide nanostructures. VACNTs are grown by plasma enhanced chemical vapor deposition and coated with a manganese-based metal organic precursor (MOP) film based on manganese acetate solution. Subsequent UV pulsed laser irradiation induces the effective heating-decomposition of the MOP leading to the crystallization of manganese oxide nanostructures on the VACNT surface. The study of the morphology, structure and composition of the synthesized materials shows the formation of randomly oriented MnO2 crystals, with few nanometers in size, and to their alignment in hundreds of nm long filament-like structures, parallel to the CNT's long axis. Electrochemical measurements reveal a significant increase of the specific capacitance of the MnO2-VACNT system (100 F g−1) as compared to the initial VACNT one (21 F g−1).The authors acknowledge the financial support of the Spanish Ministry of Economy, Industry and Competitiveness under the projects MAT2010-20468, ENE2014-56109-C3-1-R and ENE2014-56109-C3-3-R, as well as AGAUR (Generalitat de Catalunya) under the project 2014SGR984. ICMAB acknowledges financial support from the Spanish Ministry of Economy, Industry and Competitiveness, through the 'Severo Ochoa' Programme for Centres of Excellence in R&D (SEV- 2015-0496). IA and FP acknowledge finantial support of their PhD studies to MICINN and SENESCYT of the Ecuadorian Government, which provided financial support through its scholarship program for 2014, respectively. The authors would also like to thank the CCiT-UB for help with the structural and morphological characterization.Peer reviewe