Victor Neto

Promoting secondary nucleation using methane modulations during diamond chemical vapor deposition to produce smoother, harder, and better quality films

In this paper, we present results obtained from a comparison study relating to the deposition of diamond films using two processes, namely, time-modulated chemical vapor deposition (TMCVD) and conventional CVD. Polycrystalline diamond films were deposited onto silicon substrates using both hot-filament CVD and microwave plasma CVD systems. The key feature of TMCVD is that it modulates methane (CH 4 ) flow during diamond CVD, whereas in conventional CVD the CH 4 flow is kept constant throughout the deposition process. Films grown using TMCVD were smoother, harder, and displayed better quality than similar films grown using constant CH 4 flow during CVD. The advantage of using TMCVD is that it promotes secondary nucleation to occur on existing diamond crystals. Pulsing CH 4 , consecutively, at high and low concentrations allows the depositing film to maintain its quality in terms of diamond-carbon phase. Films grown under constant CH 4 flow during diamond CVD displayed a columnar growth mode, whereas with the time modulated films the growth mode was different. The mechanism of film growth during TMCVD is presented in this paper. The growth rate of films obtained using the hot filament CVD system with constant CH 4 flow was higher than the growth rate of time modulated films. However, using the microwave-plasma CVD system, the effect was the contrary and the time-modulated films were grown at a higher rate. The growth rate results are discussed in terms of substrate temperature changes during TMCVD.

The impacts of emergent pollutants on Ruditapes philippinarum : biochemical responses to carbon nanoparticles exposure

Multi-walled carbon nanotubes (MWCNTs) are one of the most important carbon Nanoparticles (NPs). The production and use of these NPs are increasing rapidly and, therefore, the need to assess their presence in the environment and associated risks has become of prime importance. Recent studies demonstrated the impacts of different NPs on bivalves, a taxonomic group where species tolerance to anthropogenic stressors, such as pollutants, is widely variable. The Manila clam Ruditapes philippinarum is one of the most commonly used bivalve species in environmental monitoring studies and ecotoxicology tests, however, to our knowledge, no information is available on biochemical alterations on this species due to MWCNTs exposure. Thus, the present study aimed to assess the toxic effects of different MWCNT concentrations (0.01; 0.10 and 1.00mg/L) in R. philippinarum biochemical (energy reserves, metabolic capacity, oxidative status and neurotoxicity) performance, after 28days of exposure. The results obtained revealed that exposure to MWCNTs altered energy-related responses, with higher metabolic capacity and lower glycogen and protein concentrations in clams exposed to these carbon NPs. Moreover, R. philippinarum exposed to MWCNTs showed oxidative stress expressed in higher lipid peroxidation and lower ratio between reduced and oxidized glutathione, despite the activation of defence mechanisms in exposed clams. Additionally, neurotoxicity was observed by inhibition of cholinesterases activity in organisms exposed to MWCNTs. The present study provides valuable information regarding how these emerging pollutans could become a potential risk for the environment and living organisms.

Physiological and biochemical responses of two keystone polychaete species: Diopatra neapolitana and Hediste diversicolor to Multi-walled carbon nanotubes.

&NA; Multi‐walled carbon nanotubes (MWCNTs) are one of the most important carbon Nanomaterials (NMs). The production and use of these carbon NMs is increasing rapidly and, therefore, the need to assess their presence in the environment and associated risks has become increasingly important. However, limited literature is available regarding the impacts induced in aquatic organisms by this pollutant, namely in invertebrate species. Diopatra neapolitana and Hediste diversicolor are keystone polychaete species inhabiting estuaries and shallow water bodies intertidal mudflats, frequently used to evaluate the impact of environmental disturbances in these systems. To our knowledge, no information is available on physiological and biochemical alterations on these two species due to MWCNTs exposure. Thus, the present study aimed to assess the toxic effects of different MWCNTs concentrations (0.01; 0.10 and 1.00 mg/L) in both species physiological (regenerative capacity and respiration rate) and biochemical (energy reserves, metabolic activities, oxidative stress related biomarkers and neurotoxicity markers) performance, after 28 days of exposure. The results obtained revealed that exposure to MWCNTs induced negative effects on the regenerative capacity of D. neapolitana. Additionally, higher MWCNTs concentrations induced increased respiration rates in D. neapolitana. MWCNTs altered energy‐related responses, with higher values of electron transport system activity, glycogen and protein concentrations in both polychaetes exposed to this contaminant. Furthermore, when exposed to MWCNTs both species showed oxidative stress with higher lipid peroxidation, lower ratio between reduced and oxidized glutathione, and higher activity of antioxidant (catalase and superoxide dismutase) and biotransformation (glutathione‐S‐transferases) enzymes in exposed organisms. Graphical abstract Figure. No caption available. HighlightsMWCNTs induced negative effects on the regenerative capacity of Diopatra neapolitana.Diopatra neapolitana and Hediste diversicolor exposed to MWCNTs showed oxidative stress.Both species under MWCNTs increased their metabolic capacity.Inhibition of cholinesterases confirmed neurotoxicity of MWCNTs in both species.D. neapolitana and H. diversicolor are potential bioindicators to monitor carbon NMs pollution.

Polycrystalline diamond coatings on steel substrates

The usage of polycrystalline diamond onto steel substrates for potential usage in cutting tools, plastic injection moulds and biomedical tools, would be of great importance. In this paper, a review of the different approaches used to improve coating adhesion has been presented. Before this, the major problems hindering the successful nucleation and growth of diamond on steel and a layout criteria for interlayer selection to give optimum results in producing adherent diamond coatings on steel are highlighted. Finally, the paper presents the challenges that need to be met, which relate to the successful implementation of diamond coatings on steel components.

The impacts of seawater acidification on Ruditapes philippinarum sensitivity to carbon nanoparticles

In the present study, the impacts of multi-walled carbon nanotubes (MWCNTs), one of the most important NMs used in broad industrial and biomedical applications, on the clam Ruditapes philippinarum were evaluated under actual and predicted ocean acidification conditions. For this, oxidative stress, metabolic capacity and neurotoxicity related biomarkers were measured after a long-term exposure of the clams to different conditions. The results obtained revealed that under low pH conditions the toxicity of MWCNTs was similar to the impacts measured under control pH. In both cases the energy-related responses in contaminated clams were altered with an increase of their metabolism which resulted in the expenditure of their energy reserves (lower glycogen content). Moreover, R. philippinarum showed oxidative stress when exposed to MWCNTs expressed by higher lipid peroxidation activity, a lower ratio between reduced and oxidized glutathione and activation of antioxidant defences and biotransformation mechanisms. Additionally, neurotoxicity was observed by inhibition of cholinesterase activity in organisms exposed to MWCNTs at both pH conditions.

An overview of graphene materials: Properties, applications and toxicity on aquatic environments

Due to unique chemical and physical properties, nanomaterials from the Graphene family are being increasingly introduced in all fields of science. The specific roles they can occupy within different applications are attracting increased attention by several industrial sectors. These carbon nanoparticles are released into the environment especially accumulating in aquatic systems. Since the discovery of graphene, a number of research actives are being conducted to find out the toxic potential of the Graphene family materials to different organisms models. Although their toxicity effects are well described for biomedical applications, few data were produced with the specific aim of assessing the toxic effects of these carbon nanomaterials in the aquatic environment. The purpose of this review is to compile up-to-date information on properties, applications and characterization methods of graphene family materials in aquatic environments and identified biological toxic impacts of these NMs, with special focus on graphene oxide based on the most recent literature.

Physiological and biochemical impacts of graphene oxide in polychaetes: The case of Diopatra neapolitana

Graphene oxide (GO) is an important carbon nanomaterial (NM) that has been used, but limited literature is available regarding the impacts induced in aquatic organisms by this pollutant and, in particular in invertebrate species. The polychaete Diopatra neapolitana has frequently been used to evaluate the effects of environmental disturbances in estuarine systems due to its ecological and socio-economic importance but to our knowledge no information is available on D. neapolitana physiological and biochemical alterations due to GO exposure. Thus, the present study aimed to assess the toxic effects of different concentrations of GO (0.01; 0.10 and 1.00mg/L) in D. neapolitana physiological (regenerative capacity) and biochemical (energy reserves, metabolic activity and oxidative stress related biomarkers) performance, after 28days of exposure. The results obtained revealed that the exposure to GO induced negative effects on the regenerative capacity of D. neapolitana, with organisms exposed to higher concentrations regenerating less segments and taking longer periods to completely regenerate. GO also seemed to alter energy-related responses, especially glycogen content, with higher values in polychaetes exposed to GO which may result from a decreased metabolism (measured by electron transport system activity), when exposed to GO. Furthermore, under GO contamination D. neapolitana presented cellular damage, despite higher activities of antioxidant and biotransformation enzymes in individuals exposed to GO.

Nanodiamond coated Bragg gratings for sensing applications

In this paper, the coating of optical Bragg gratings with nanocrystalline diamond, obtained by hot filament chemical vapor deposition (HFCVD), is described. Due to the high temperature coating process, uniform fiber Bragg gratings (FBG) were erased during the diamond deposition. However, in the case of regenerated fiber Bragg gratings (RFBG), although attenuated, the optical signal is maintained. The results of the thermal and mechanical characterization of diamond coated RFBG (D-RFBG) suggest that they may be an important tool in the sensing field, including monitoring of high temperatures under harsh environments.

Microinjection Molding of Enhanced Thermoplastics

Injection molding is, nowadays, a well known and wildly used manufacturing process to produce both thermoplastic and thermosetting polymeric material components, in a large scale, with accuracy and at low prices. Even though the electronics industry provides an economy of scale for the silicon industry, polymer devices can be produced in huge volumes maintaining the requested features and quality, with a great variety of material characteristics, a fact that has considerably open the market to injection molding of microcomponents.

Performance of sub-micron diamond films coated on mould inserts for plastic injection moulding

In this article, results obtained from an investigation focusing on the application of diamond coatings on inserts for thermoplastic injection moulding applications are reported. The injection moulding industry can potentially benefit significantly from the use of diamond coatings on moulds typically employed in the injection moulding systems. Diamond films were coated on steel and onto silicon inserts and subsequently tested in real operating conditions. The moulded objects were analysed and the results were compared between bare steel and silicon inserts. The as-grown diamond coatings were characterised prior to and post the routine injection cycles using a number of techniques, such as Raman spectroscopy and SEM. Furthermore, the polymer finishing quality was assessed by optical microscopy for each material and coating used, and the results are presented and discussed in this article.