Oxidation-Based Continuous Laser Writing in Vertical Nano-Crystalline Graphite Thin Films

Nano and femtosecond laser writing are becoming very popular techniques for patterning carbon-based materials, as they are single-step processes enabling the drawing of complex shapes without photoresist. However, pulsed laser writing requires costly laser sources and is known to cause damages to the surrounding material. By comparison, continuous-wave lasers are cheap, stable and provide energy at a more moderate rate. Here, we show that a continuous-wave laser may be used to pattern vertical nano-crystalline graphite thin films with very few macroscale defects. Moreover, a spatially resolved study of the impact of the annealing to the crystalline structure and to the oxygen ingress in the film is provided: amorphization, matter removal and high oxygen content at the center of the beam; sp2 clustering and low oxygen content at its periphery. These data strongly suggest that amorphization and matter removal are controlled by carbon oxidation. The simultaneous occurrence of oxidation and amorphization results in a unique evolution of the Raman spectra as a function of annealing time, with a decrease of the I(D)/I(G) values but an upshift of the G peak frequency

In-situ preparation of ultra-small Pt nanoparticles within rod-shaped mesoporous silica particles: 3-D tomography and catalytic oxidation of n-hexane

The shape and porous configuration of supports are key parameters to design outstanding catalysts. However, the selection of a proper mesoporous support, such as SBA-15, by itself does not guarantee accessibility to catalytic sites. The distribution of the active phase and its stability are strongly related to the procedure used to deposit it on the catalytic substrate. Herein, we have prepared rod-shaped SBA-15 silica supports functionalized with amine groups to facilitate the electrostatic attraction and a good distribution of the resulting Pt-based catalytic nanoparticles along the pore walls. Additionally, the use of tetrakis-(hydroxymethyl)-phosphonium chloride (THPC) as both reductant and stabilizer is presented as a novel alternative for Pt nanoparticle synthesis. The behaviour of this catalyst in the total oxidation of n-hexane demonstrates high activity and excellent stability after 70 h on reaction stream. STEM-HAADF and 3-D tomography were used to confirm the presence of the metallic nanoparticles within the mesochannels and to corroborate their reduced sintering after reaction

On-chip monitoring of toxic gases: capture and label-free SERS detection with plasmonic mesoporous sorbents

AThe detection of the spread of toxic gas molecules in the air at low concentration in the field requires a robust miniaturized system combined with an analytical technique that is portable and able to detect and identify the molecules, as is the case with surface enhanced Raman scattering (SERS). This work aims to address capability gaps faced by first responders in real-time detection, identification and monitoring of neurotoxic gases by developing robust, reliable and reusable SERS microfluidic chips. Thus, the key performance attributes of a portable SERS detection system that must be addressed in detail are its limit of detection, response time and reusability. To this purpose, we integrate a 3D plasmonic architecture based on closely packed mesoporous silica (MCM48) nanospheres decorated with Au nanoparticle arrays, denoted as MCM48@Au, into a Si microfluidic chip designed and used for preconcentration and label-free detection of gases at a trace concentration level. The SERS performance of the plasmonic platform is thoroughly analyzed using DMMP as a model neurotoxic simulant over a 1 cm2 SERS active area and over a range of concentrations from 100 ppbV to 2.5 ppmV. The preconcentration-based SERS signal amplification by the mesoporous silica moieties is evaluated against dense silica counterparts, denoted as Stöber@Au. To assess the potential for applications in the field, the microfluidic SERS chip has been interrogated with a portable Raman spectrometer, evaluated with temporal and spatial resolution and subjected to several gas detection/regeneration cycles. The reusable SERS chip shows exceptional performance for the label-free monitoring of 2.5 ppmV gaseous DMMP

Wafer-scale pulsed laser deposition of ITO for solar cells: reduced damage vs. interfacial resistance

Transparent conducting oxides (TCOs) used in solar cells must be optimized to achieve minimum parasitic absorption losses while providing sufficient lateral conductivity. Low contact resistance with the adjacent device layers and low damage to the substrate during deposition of the TCO are also important requirements to ensure high solar cell efficiencies. Pulsed laser deposition (PLD) has been proposed as an alternative low-damage TCO deposition technique on top of sensitive layers and interfaces in organic and perovskite solar cells but is yet to be studied for the more mature silicon technology. Focusing on the PLD deposition pressure as the key parameter to reduce damage, we developed tin-doped indium oxide (ITO) with a sheet resistance of 60 Ω □−1 at different pressures and implemented it in silicon heterojunction (SHJ) solar cells. Buffer-free semi-transparent perovskite cells with the same PLD ITO electrodes were also fabricated for comparison. While in the perovskite cells increased ITO deposition pressure leads to an improved open circuit voltage and fill factor indicative of damage reduction, SHJ cells with PLD ITO at all conditions maintained a high passivation quality, but increased pressures lead to high series resistance. Transmission electron microscopy and time-of-flight secondary ion mass spectrometry confirmed the formation of a parasitic SiOx at the ITO/a-Si:H interface of the SHJ cell causing a transport barrier. The optimized ITO films with the highest carrier density were able to obtain >21% SHJ efficiency with 75 nm-thick PLD ITO. Moreover, reducing the ITO thickness to ∼45 nm and using TiOx for optical compensation enables fabrication of SHJ devices with reduced indium consumption and efficiencies of >22%

Kinked silicon nanowires: Superstructures by metal assisted chemical etching

We report on metal assisted chemical etching of Si for the synthesis of mechanically-stable, hybrid crystallographic orientation Si superstructures with high aspect ratio, above 200. This one-pot-type method sustains high etching rates and facilitates reproducible results. The protocol enables the control of the number, angle and location of kinks via successive etch-quench sequences. We analysed relevant Au mask catalyst features to systematically assess their impact on a wide spectrum of etched morphologies that can be easily attained and customized by fine tuning of the critical etching parameters. For instance, the designed kinked Si nanowires can be internalized in biological cells, without affecting their viability. An accessible numerical model is provided to explain the etch profiles and the physico-chemical events at the Si-Au-electrolyte interface and offers guidelines for the development of finite-element modeling of metal assisted Si chemical etching

The reflexiv personal and possessive pronouns in Czech and in Romanian

In the diploma work, we have treated of the problems concerning retlexive and possessive pronouns "se" (oneself) and "svůj" (my, yOUf, and so on) above aH. In the introduction, we have orientated our attention first to deictic words, and successively we got the general description of pronouns in Czech language, where we came principally to possessive and retlexive pronouns. We have concluded that these pronouns are very difficult for foreign student s learning Czech language. We stopped at personal retlexive pronoun "se" (oneself) and "si" (to oneself), pronoun expressing that a person or a thing, this is indicating, is identical with the originator of an action. This originator of an action is usually expressed by the subject and the action by a definite verb but it is possible that it can be expressed by another way as object or infinitive for instance. (see l.2.) From the point of view of the delimitation of lexical language it is necessary to give attention to the ambiguity of the retlexive pronoun ,,se" (oneself). If this is fulfilling the function of an article of object in a sentence construction (myl se - he washed himselj), it is real retlexive pronoun, and consequently an independent lexical unit. If it is part of a retlexive verb (přiznat se - to confess himselj), ifthe case may be of a retlexive..

The reflexiv personal and possessive pronouns in Czech and in Romanian

In the diploma work, we have treated of the problems concerning retlexive and possessive pronouns "se" (oneself) and "svůj" (my, yOUf, and so on) above aH. In the introduction, we have orientated our attention first to deictic words, and successively we got the general description of pronouns in Czech language, where we came principally to possessive and retlexive pronouns. We have concluded that these pronouns are very difficult for foreign student s learning Czech language. We stopped at personal retlexive pronoun "se" (oneself) and "si" (to oneself), pronoun expressing that a person or a thing, this is indicating, is identical with the originator of an action. This originator of an action is usually expressed by the subject and the action by a definite verb but it is possible that it can be expressed by another way as object or infinitive for instance. (see l.2.) From the point of view of the delimitation of lexical language it is necessary to give attention to the ambiguity of the retlexive pronoun ,,se" (oneself). If this is fulfilling the function of an article of object in a sentence construction (myl se - he washed himselj), it is real retlexive pronoun, and consequently an independent lexical unit. If it is part of a retlexive verb (přiznat se - to confess himselj), ifthe case may be of a retlexive..

Electron tomography of the nano-objects

Ce travail a été consacré au développement dans le domaine de nanomatériaux de différents modes de travail en microscopie électronique compatibles avec une approche tomographique. Il s'agit du mode champ clair parallèle, des modes champ sombre annulaire et champ clair en mode balayage du faisceau, du mode imagerie filtrée (qui apporte la sélectivité chimique) ou encore de la tomographie à froid. Pour un système donné, le choix du mode est dicté par la nature de l'échantillon et l'information qu'on souhaite obtenir. Un ajustement approprié et pointu de tous les paramètres intervenant dans les différentes étapes de l'analyse a été nécessaire pour chacun de ces modes Une attention particulière a été donnée au couplage des méthodes tomographiques avec les autres modes de microscopie électronique, en particulier la haute résolution qui est plus sensible à la structure cristallographique. Ceci nous a permis d'obtenir une description complète des nano-objets en termes de morphologie, structure cristalline et composition chimique. Une grande partie du travail a été dédiée à l'étude de nanomatériaux d'intérêt en catalyse, où les applications exploitant les effets nanométriques sont multiples : les nanomatériaux carbonés (SiC, nanotubes de carbone dopés), nanoparticules individuelles ou organisées en super-réseaux (Ce02, Pt), nanostructures coeur-couronne (Au-Ag). Finalement, l'implémentation de la tomographie analytique s'est révélée être d'un intérêt crucial pour l'étude de ces systèmes: elle nous a permis de dépasser la simple acquisition d'images à 3D en nous donnant la possibilité de distinguer dans l'espace la distribution des éléments chimiques qui constituent l'échantillon étudié.In the general frame of studying nanomaterials, this thesis is devoted to the exploration of the various electron microscopy modes that allow tomographie recording. These recording modes range from the parallel bright field mode to the bright and dark field annular scanning modes. Filtered imaging as well as low temperature recording have been explored in depth. Strong attention has been paid to the determination of the optimized parameters and procedures that must be used in each mode according to the nature of the sample under study and ta the nature of the properties to be characterized. lt was shown that a synergy could be obtained from the concomitant use of other microscopy modes with the tomographie ones. The 3D reconstruction of nano-objects allowed reaching very rich descriptions of the objects, up to the point of quantitatively measuring parameters otherwise not reachable, such as porosities or specifie surfaces. Because of this ability, various materials of interest in the fields of catalysis have been studied, carbon based materials: Sic, doped carbon nano-tubes; isolated or self-organized nano-particles: CeO2 Pt; core-shell nano-particles: Au-Ag. The use of filtered imaging for reconstructing 3D images of nano-objects paved the way for the chemical analysis of nano-objects with a 3D chemical resolution of the order of 5nm

Electron tomography of the nano-objects

Ce travail a été consacré au développement dans le domaine de nanomatériaux de différents modes de travail en microscopie électronique compatibles avec une approche tomographique. Il s'agit du mode champ clair parallèle, des modes champ sombre annulaire et champ clair en mode balayage du faisceau, du mode imagerie filtrée (qui apporte la sélectivité chimique) ou encore de la tomographie à froid. Pour un système donné, le choix du mode est dicté par la nature de l'échantillon et l'information qu'on souhaite obtenir. Un ajustement approprié et pointu de tous les paramètres intervenant dans les différentes étapes de l'analyse a été nécessaire pour chacun de ces modes Une attention particulière a été donnée au couplage des méthodes tomographiques avec les autres modes de microscopie électronique, en particulier la haute résolution qui est plus sensible à la structure cristallographique. Ceci nous a permis d'obtenir une description complète des nano-objets en termes de morphologie, structure cristalline et composition chimique. Une grande partie du travail a été dédiée à l'étude de nanomatériaux d'intérêt en catalyse, où les applications exploitant les effets nanométriques sont multiples : les nanomatériaux carbonés (SiC, nanotubes de carbone dopés), nanoparticules individuelles ou organisées en super-réseaux (Ce02, Pt), nanostructures coeur-couronne (Au-Ag). Finalement, l'implémentation de la tomographie analytique s'est révélée être d'un intérêt crucial pour l'étude de ces systèmes: elle nous a permis de dépasser la simple acquisition d'images à 3D en nous donnant la possibilité de distinguer dans l'espace la distribution des éléments chimiques qui constituent l'échantillon étudié.In the general frame of studying nanomaterials, this thesis is devoted to the exploration of the various electron microscopy modes that allow tomographie recording. These recording modes range from the parallel bright field mode to the bright and dark field annular scanning modes. Filtered imaging as well as low temperature recording have been explored in depth. Strong attention has been paid to the determination of the optimized parameters and procedures that must be used in each mode according to the nature of the sample under study and ta the nature of the properties to be characterized. lt was shown that a synergy could be obtained from the concomitant use of other microscopy modes with the tomographie ones. The 3D reconstruction of nano-objects allowed reaching very rich descriptions of the objects, up to the point of quantitatively measuring parameters otherwise not reachable, such as porosities or specifie surfaces. Because of this ability, various materials of interest in the fields of catalysis have been studied, carbon based materials: Sic, doped carbon nano-tubes; isolated or self-organized nano-particles: CeO2 Pt; core-shell nano-particles: Au-Ag. The use of filtered imaging for reconstructing 3D images of nano-objects paved the way for the chemical analysis of nano-objects with a 3D chemical resolution of the order of 5nm

Electron tomography of the nano-objects

Ce travail a été consacré au développement dans le domaine de nanomatériaux de différents modes de travail en microscopie électronique compatibles avec une approche tomographique. Il s'agit du mode champ clair parallèle, des modes champ sombre annulaire eIn the general frame of studying nanomaterials, this thesis is devoted to the exploration of the various electron microscopy modes that allow tomographie recording. These recording modes range from the parallel bright field mode to the bright and dark fi