Papers by Fernando Echeverrigaray
Frontiers in chemical engineering, Aug 31, 2022
Frontiers in chemical engineering, Aug 31, 2022
Journal of Materials Research and Technology, 2021
Abstract Owing to its singular and (to some extend) adaptable characteristics, titanium oxynitrid... more Abstract Owing to its singular and (to some extend) adaptable characteristics, titanium oxynitride (TixOyNz) represents an exceptional choice in the realm of new materials aiming at the development of practical devices. However, the effective use of TixOyNz in photovoltaic and (photo)catalysis applications, for example, relies on a refined production−properties balance. Accordingly, this paper reports on the physico-chemical properties of TixOyNz films as investigated by means of the Raman scattering and X-ray photoelectron spectroscopy (XPS) techniques – the former shedding light on the structural characteristics of the films, and the latter providing the state of oxidation of the film's constituents. The films were prepared by sputtering TiO2 and Ti targets in a plasma comprising different mixtures of Ar and N2. Because of the deposition method and conditions, the films exhibit Raman spectra that are consistent with a combination of TiO2 and TiN or, more properly, TixOyNz under the amorphous and (nano/micro-)crystalline structures. In fact, the experimental data indicate the presence of four TiO2- and two TiN-related phonon modes, whose relative scattering features scale with the oxygen and nitrogen contents of the films. A similar concentration dependence was verified with the percentage of Ti4+, Ti3+, and Ti2+ chemical states of oxidation. This mutual concentration dependence was explored thoroughly and the results clearly indicate the suitability of the Raman data to estimate the typical atom composition and distribution of the Ti-related chemical states of TixOyNz.
Advanced Materials Interfaces
O atrito e originado por eventos de dissipacao de energia devido ao trabalho realizado de forcas ... more O atrito e originado por eventos de dissipacao de energia devido ao trabalho realizado de forcas nao conservativas. Os mecanismos nanotribologicos por meio dos quais a dissipacao pode ocorrer englobam deformacao molecular e efeitos fononicos, eletricos (eletronicos e eletrostaticos) e magneticos. Apesar de sua importância fundamental, esses mecanismos fisico-quimicos que governam o atrito sao pouco compreendidos. Embora a literatura forneca uma riqueza de informacoes sobre a eficiencia energetica no estado de baixo atrito, tambem denominado de superlubricidade estrutural, algumas previsoes associadas so puderam ser confirmadas quantitativamente em poucos sistemas sob condicoes especificas. Sistemas nanoestruturados a base de carbono, tais como filmes finos de carbono amorfo hidrogenado (a-C:H), possuem uma combinacao unica de propriedades com potencial tecnologico-industrial para aplicacoes na area de mecânica e eletromecânica. Nesta tese, busca-se entender o papel das interacoes el...
Os biofilmes constituem uma nova forma de vida que oferece maior resistencia aos micro-organismos... more Os biofilmes constituem uma nova forma de vida que oferece maior resistencia aos micro-organismos, protegendo-os contra agressoes fisicas e quimicas do meio envolvente, o que facilita a sua adaptacao em condicoes adversas. O desenvolvimento de biofilmes patogenicos em superficies de contato nas areas da saude (proteses e instrumentos cirurgicos) e alimenticia (equipamentos e tubulacoes) e a principal causa do acrescimo de contaminacoes que podem, eventualmente, originar problemas de saude publica e de ordem economica. Para prevenir, controlar ou erradicar biofilmes, alternativas tecnologicas vem sendo desenvolvidas e testadas em materiais com propriedades antimicrobianas. Dentro deste contexto, este trabalho teve por objetivo avaliar as propriedades antimicrobianas dos ions prata (Ag+) implantados no aco inoxidavel austenitico AISI 304 a baixa energia (4 keV) no equipamento Ion Plating Diversified (IPD). As bacterias estudadas foram Escherichia coli (IBEc 101) e Staphyloccocus aureu...
Scientia cum Industria, Aug 1, 2014
Na medicina moderna, os biomateriais têm sido largamente utilizados como implantes. Dentre os bio... more Na medicina moderna, os biomateriais têm sido largamente utilizados como implantes. Dentre os biomateriais, o titânio de classe medicinal destaca-se pelo seu elevado grau de biocompatibilidade. Entretanto,órteses e próteses infectadas com microrganismos pós-implantadas requerem cirurgias e intervenções médicas que são dispendiosas e o tratamento pode levar meses. Para combater infecções associadas a implantes, a melhor estratégiaé prevenir que elas ocorram. Uma das estratégiasé a implantação deíons de prata no titânio. Neste trabalho,íons de prata foram implantados a baixas energias (4 keV) no titânio de uso medicinal com o objetivo de tornar a superfície do titânio bactericida e, assim, inibir a formação de biofilme. A implantação foi realizada em um equipamento do tipo Ion Plating. As amostras foram analisadas por espectrometria de Retroespalhamento de Rutherford (RBS), espectroscopia de emissãoótica por descarga luminescente (GD-OES) e difração de raios X (XRD). Os resultados obtidos mostram que a prata está implantada em profundidade de até 10 nm, corroborando com os dados da simulação realizada previamente. Além disso, a estratégia utilizada neste trabalho pode ser aplicada em escala industrial, devido ao tipo de equipamento utilizado para o tratamento da superfície.
Journal of Non-Crystalline Solids, 2022
Scientia cum Industria, 2014
Na medicina moderna, os biomateriais tem sido largamente utilizados como implantes. Dentre os bio... more Na medicina moderna, os biomateriais tem sido largamente utilizados como implantes. Dentre os biomateriais, o titânio de classe medicinal destaca-se pelo seu elevado grau de biocompatibilidade. Entretanto, orteses e proteses infectadas com microrganismos pos-implantadas requerem cirurgias e intervencoes medicas que sao dispendiosas e o tratamento pode levar meses. Para combater infeccoes associadas a implantes, a melhor estrategia e prevenir que elas ocorram. Uma das estrategias e a implantacao de ions de prata no titânio. Neste trabalho ions de prata foram implantados a baixas energias (4 keV) no titânio de uso medicinal com o objetivo de tornar a superficie do titânio bactericida e, assim, inibir a formacao de biofilme. A implantacao foi realizada em um equipamento do tipo Ion Plating. As amostras foram analisadas por espectrometria de Retroespalhamento de Rutherford (RBS), espectroscopia de emissao otica por descarga luminescente (GD-OES) e difracao de raios X (XRD). Os resultado...
ACS Applied Materials & Interfaces, 2021
In dry sliding, the coefficient of friction depends on the material pair and contact conditions. ... more In dry sliding, the coefficient of friction depends on the material pair and contact conditions. If the material and operating conditions remain unchanged, the coefficient of friction is constant. Obviously, we can tune friction by surface treatments, but it is a nonreversible process. Here, we report active control of friction forces on TiO2 thin films under UV light. It is reversible and stable and can be tuned/controlled with the light wavelength. The analysis of atomic force microscopy signals by wavelet spectrograms reveals different mechanisms acting in the darkness and under UV. Ab initio simulations on UV light-exposed TiO2 show a lower atomic orbital overlapping on the surface, which leads to a friction reduction of up to 60%. We suggest that photocontrol of friction is due to the modification of atomic orbital interactions from both surfaces at the sliding interface.
Journal of Materials Research and Technology, 2021
Optical properties of hydrogenated TiO 2 thin films deposited by the ion beam sputtering method a... more Optical properties of hydrogenated TiO 2 thin films deposited by the ion beam sputtering method are reported. By reducing the oxide by hydrogenation in situ (during deposition) and ex situ (by means of posterior thermal annealing) a controlled phase modification allows to manipulate optical properties to improve photoactivity for solar energy conversion and catalytic applications. The hydrogenation procedure prompts remarkable structural changes and optical properties of the TiO 2 hierarchical thin films. Photoemission electron spectroscopy (XPS) results show the presence of titanium in Ti 4þ into Ti 3þ state of oxidation, i.e., compatible with oxygen vacancies and titanium interstitials. Vibrational properties inspected by IR absorption and Raman spectroscopy allowed identifying potentially catalytic sites and vibration modes associated with hydrogen. The vibrational spectra show that both in situ and ex situ hydrogenation routes contribute to prompt (dis)order in the films, involving the presence of anatase crystalline phase embedded in an amorphous matrix or mixed-phase (anatase þ rutile) crystalline TiO 2. To avoid debate about the TiO 2 theoretical (indirect) and expected and measured (direct, normally reported) optical gap (E gap), the absorption coefficient spectra were analyzed by a recently developed method based on the Boltzmann sigmoidal function. From these analyses, conclusions about defects states prompted by the hydrogenation processes are presented.
Tribology International, 2020
Abstract In this study, the electro-tribological performance of hydrogenated amorphous carbon coa... more Abstract In this study, the electro-tribological performance of hydrogenated amorphous carbon coatings against bearing steel in different experimental conditions was continuously monitored by means of coefficient of friction (CoF) and electrical contact resistance (ECR). The influence of tribosystem variables such as humidity, velocity and lifetime on frictional and electrical response were also compared with specific wear energy calculation method. The main findings of both tribological and electrical behaviors include the dissipated energy and the micro-slip dielectric failures that can be linked to the properties of self-lubricating layers, which depend also on the working media. In this framework, the electro-tribological evaluation provides an electrical monitoring tool for coating premature wear detection in real time.
Thin Solid Films, 2018
Abstract Fundamental understanding of friction forces at the micro/nanoscale continues being a ch... more Abstract Fundamental understanding of friction forces at the micro/nanoscale continues being a challenge in tribology. This work reports on the friction behavior of the outermost magnetite layers grown on a nitrided ferrous alloy studied by two different and independent experimental methods: nanoindentation followed by unidirectional sliding and friction force microscopy. Macroscopic mechanical properties involving hardness (H) and Young modulus (E), such as the plastic deformation parameter (H3/E2) and the elastic strain to failure (H/E), as well as surface roughness cannot explain the lack of influence of the friction coefficient on the outermost magnetite layer thickness. Moreover, the observed energy dissipation phenomenon is consistent with phononic non-conservative damping forces.
Applied Surface Science, 2018
Hydrogenated amorphous carbon thin films (a-C:H) do not show good adhesion on ferrous alloys. Whe... more Hydrogenated amorphous carbon thin films (a-C:H) do not show good adhesion on ferrous alloys. When a silicon-containing intermediate thin film is chosen, deposition temperatures of at least 300 0 C are necessary to provide adequate adhesion. However, a new approach is introduced to achieve similar results at lower temperatures: a selective chemical hydrogen plasma etching before the carbonaceous film deposition. The effect is known but its physicochemical mechanism and kinetics remain open. We have investigated the role of hydrogen etching in the modification of the outermost and innermost interfaces of a-SiCx:H 2 interlayers. The results show that hydrogen radically modifies the interlayer thickness in the outermost region and increases the C/Si ratio in the innermost. Moreover, the hydrogen etching allows the formation of more CC bonds at the outermost interface, which is correlated to better adhesion. Finally, we proposed a mechanism in order to explain physical and chemical changes of the hydrogen etching.
Physical chemistry chemical physics : PCCP, Jan 9, 2018
Hydrogenated amorphous carbon (a-C:H) thin films have a unique combination of properties that are... more Hydrogenated amorphous carbon (a-C:H) thin films have a unique combination of properties that are fundamental in mechanical and electromechanical devices aimed at energy efficiency issues. The literature brings a wealth of information about the ultra-low friction (superlubricity) mechanism in a-C:H thin films. However, there is persistent controversy concerning the physicochemical mechanisms of contact mechanics at the atomic/molecular level and the role of electrical interactions at the sliding interface is still a matter of debate. We find that the hydrogenation of the outermost nanostructured surface atomic layers of a-C:H thin films is proportional to the surface potential and also to the friction forces arising at the sliding interface. A higher hydrogen-to-carbon ratio reduces the surface potential, directly affecting frictional forces by a less effective long-term interaction. The structural ultra-low friction (superlubricity) is attributed to a lower polarizability at the ou...
Surface and Coatings Technology, 2016
Abstract Biofilm formations on contact surfaces is one of the main causes in several health and f... more Abstract Biofilm formations on contact surfaces is one of the main causes in several health and food industries due the high incidence of pathogenic contaminations. An approach to reduce problems is to modify the surface properties with antibacterial or antibiofilm agents. The surface modification before biofilm formation reveals to be an effective technological alternative to prevent or eradicate bacterial adhesion in biomedical devices and surgical instruments, as well as food contaminations from process equipments. In this paper we evaluated the antibacterial properties of silver atoms incorporated on stainless steel surfaces by ion implantation at low energy (4 keV) using a reactive low voltage ion plating-type equipment. The simulations by the Monte Carlo method contributed to establish the minimum self-bias voltage used in the implantation process and to provide an ideal distribution estimate of the silver dose in-depth. The surface modifications in all samples were analyzed by RBS, GD-OES and XPS. The microbiological assays were conducted using Escherichia coli and Staphylococcus aureus , and the results demonstrated an initial reduction on bacterial adhesion, and delay of the biofilm formation. The results help clarify the physicochemical conditions required to obtain a surface resistant to bacteria colonization.
Scripta Materialia, 2010
ABSTRACT The effect of hydrogen on plasma post-oxidation following plasma nitriding of a ferrous ... more ABSTRACT The effect of hydrogen on plasma post-oxidation following plasma nitriding of a ferrous alloy was investigated. The increase in the hydrogen concentration in the plasma progressively reduces the hematite/magnetite concentration ratio in the outermost oxide layer down to zero at 25% H(2) concentration. Atomic hydrogen originating from scission of hydrogen molecules in the plasma leads to reduction of Fe(III) in hematite into Fe(II) in magnetite by controlling the gas mixture reduction potential. (C) 2010 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
AIP Advances
Lateral force microscopy (LFM) is an established technique to assess friction forces at the nanos... more Lateral force microscopy (LFM) is an established technique to assess friction forces at the nanoscale. Nanoindentation followed by unidirectional sliding (NUS) is also used to evaluate friction forces at the micro/nanoscale. However, comparative studies between NUS and LFM evaluating the experimental results at different scales are still missing. In this work, a-C:D/H and a-C:H thin films with different [D]/[C] and [H]/[C] contents were used to analyze the friction forces by NUS and LFM. The results show that the friction behavior assessed by these two techniques in different scales is the same. The correlation between friction forces measured by NUS and LFM depends mainly on a contact area factor that makes invariant the friction force from nanoscale to microscale. Such behavior suggests a similar damping mechanism, probably phonon-coupling phenomena, for the friction force origin.
Phys. Chem. Chem. Phys., , 2018
Hydrogenated amorphous carbon (a-C:H) thin films have a unique combination of properties that are... more Hydrogenated amorphous carbon (a-C:H) thin films have a unique combination of properties that are fundamental in mechanical and electromechanical devices aimed at energy efficiency issues. The literature brings a wealth of information about the ultra-low friction (superlubricity) mechanism in a-C:H thin films. However, there is persistent controversy concerning the physicochemical mechanisms of contact mechanics at the atomic/molecular level and the role of electrical interactions at the sliding interface is still a matter of debate. We find that the hydrogenation of the outermost nanostructured surface atomic layers of a-C:H thin films is proportional to the surface potential and also to the friction forces arising at the sliding interface. A higher hydrogen-to-carbon ratio reduces the surface potential, directly affecting frictional forces by a less effective long-term interaction. The structural ultra-low friction (superlubricity) is attributed to a lower polarizability at the outermost nanostructured layer of a-C:H thin films due to a higher hydrogen density, which renders weaker van der Waals forces, in particular London dispersion forces. More hydrogenated nanodomains at the surface of a-C:H thin films are proposed to be used to tailor superlubricity.
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Papers by Fernando Echeverrigaray