Fast, Efficient Tailoring Growth of Nanocrystalline Diamond Films by Fine-Tuning of Gas-Phase Composition Using Microwave Plasma Chemical Vapor Deposition.

Nanocrystalline diamond (NCD) films are attractive for many applications due to their smooth surfaces while holding the properties of diamond. However, their growth rate is generally low using common Ar/CH4 with or without H2 chemistry and strongly dependent on the overall growth conditions using microwave plasma chemical vapor deposition (MPCVD). In this work, incorporating a small amount of N2 and O2 additives into CH4/H2 chemistry offered a much higher growth rate of NCD films, which is promising for some applications. Several novel series of experiments were designed and conducted to tailor the growth features of NCD films by fine-tuning of the gas-phase compositions with different amounts of nitrogen and oxygen addition into CH4/H2 gas mixtures. The influence of growth parameters, such as the absolute amount and their relative ratios of O2 and N2 additives; substrate temperature, which was adjusted by two ways and inferred by simulation; and microwave power on NCD formation, was investigated. Short and long deposition runs were carried out to study surface structural evolution with time under identical growth conditions. The morphology, crystalline and optical quality, orientation, and texture of the NCD samples were characterized and analyzed. A variety of NCD films of high average growth rates ranging from 2.1 µm/h up to 6.7 µm/h were successfully achieved by slightly adjusting the O2/CH4 amounts from 6.25% to 18.75%, while that of N2 was kept constant. The results clearly show that the beneficial use of fine-tuning of gas-phase compositions offers a simple and effective way to tailor the growth characteristics and physical properties of NCD films for optimizing the growth conditions to envisage some specific applications.

Biodegradation of e-waste microplastics by Penicillium brevicompactum.

Electronic and electric waste (e-waste) management strategies often fall short in dealing with the plastic constituents of printed circuit boards (PCB). Some plastic materials from PCB, such as epoxy resins, may release contaminants, but neither potential environmental impact has been assessed nor mitigation strategies have been put forward. This study assessed the biodegradation of microplastics (1-2 mm in size) from PCB by the fungus Penicillium brevicompactum over 28 days, thus contributing to the discussion of mitigation strategies for decreasing the environmental impact of such plastics in the environment. The capacity of P. brevicompactum to induce microplastic fragmentation and degradation has been determined by the increased the number of smaller-sized particles and microplastic mass reduction (up to 75 % within 14 days), respectively. The occurrence of chain scission and oxidation of microplastics exposed to P. brevicompactum when compared with the control conditions (which occurred only after 28 days of exposure) can be observed. Furthermore, Attenuated Total Reflectance-Fourier Transform Infrared (ATR-FTIR) spectroscopy performed in dried biomass put in evidence an increase in the absorption intensities in regions that could be attributed to functional groups associated with carbohydrates. The results underline the potential role of the genus Penicillium, particularly P. brevicompactum, in the biodegradation of microplastics from PCB, thus providing the basis for further exploration of its potential for e-waste bioremediation and research on the underlying mechanisms for sustainable approaches to mitigate e-waste pollution.

A Review on the Applications of Graphene in Mechanical Transduction.

A pressing need to develop low-cost, environmentally friendly, and sensitive sensors has arisen with the advent of the always-connected paradigm of the internet-of-things (IoT). In particular, mechanical sensors have been widely studied in recent years for applications ranging from health monitoring, through mechanical biosignals, to structure integrity analysis. On the other hand, innovative ways to implement mechanical actuation have also been the focus of intense research in an attempt to close the circle of human-machine interaction, and move toward applications in flexible electronics. Due to its potential scalability, disposability, and outstanding properties, graphene has been thoroughly studied in the field of mechanical transduction. The applications of graphene in mechanical transduction are reviewed here. An overview of sensor and actuator applications is provided, covering different transduction mechanisms such as piezoresistivity, capacitive sensing, optically interrogated displacement, piezoelectricity, triboelectricity, electrostatic actuation, chemomechanical and thermomechanical actuation, as well as thermoacoustic emission. A critical review of the main approaches is presented within the scope of a wider discussion on the future of this so-called wonder material in the field of mechanical transduction.

Comparative Study of γ- and e-Radiation-Induced Effects on FBGs Using Different Femtosecond Laser Inscription Methods.

This work presents an extensive, comparative study of the gamma and electron radiation effects on the behaviour of femtosecond laser-inscribed fibre Bragg gratings (FBGs) using the point-by-point and plane-by-plane inscription methods. The FBGs were inscribed in standard telecommunication single mode silica fibre (SMF28) and exposed to a total accumulated radiation dose of 15 kGy for both gamma and electron radiation. The gratings' spectra were measured and analysed before and after the exposure to radiation, with complementary material characterisation using Fourier transform infrared (FTIR) spectroscopy. Changes in the response of the FBGs' temperature coefficients were analysed on exposure to the different types of radiation, and we consider which of the two inscription methods result in gratings that are more robust in such harsh environments. Moreover, we used the FTIR spectroscopy to locate which chemical bonds are responsible for the changes on temperature coefficients and which are related with the optical characteristics of the FBGs.

Boron Doped Diamond for Real-Time Wireless Cutting Temperature Monitoring of Diamond Coated Carbide Tools.

Among the unique opportunities and developments that are currently being triggered by the fourth industrial revolution, developments in cutting tools have been following the trend of an ever more holistic control of manufacturing processes. Sustainable manufacturing is at the forefront of tools development, encompassing environmental, economic, and technological goals. The integrated use of sensors, data processing, and smart algorithms for fast optimization or real time adjustment of cutting processes can lead to a significant impact on productivity and energy uptake, as well as less usage of cutting fluids. Diamond is the material of choice for machining of non-ferrous alloys, composites, and ultrahard materials. While the extreme hardness, thermal conductivity, and wear resistance of CVD diamond coatings are well-known, these also exhibit highly auspicious sensing properties through doping with boron and other elements. The present study focuses on the thermal response of boron-doped diamond (BDD) coatings. BDD coatings have been shown to have a negative temperature coefficient (NTC). Several approaches have been adopted for monitoring cutting temperature, including thin film thermocouples and infrared thermography. Although these are good solutions, they can be costly and become impractical for certain finishing cutting operations, tool geometries such as rotary tools, as well as during material removal in intricate spaces. In the scope of this study, diamond/WC-Co substrates were coated with BDD by hot filament chemical vapor deposition (HFCVD). Scanning electron microscopy, Raman spectroscopy, and the van der Pauw method were used for morphological, structural, and electrical characterization, respectively. The thermal response of the thin diamond thermistors was characterized in the temperature interval of 20-400 °C. Compared to state-of-the-art temperature monitoring solutions, this is a one-step approach that improves the wear properties and heat dissipation of carbide tools while providing real-time and in-situ temperature monitoring.

Electrochemical Response of Glucose Oxidase Adsorbed on Laser-Induced Graphene.

Carbon-based electrodes have demonstrated great promise as electrochemical transducers in the development of biosensors. More recently, laser-induced graphene (LIG), a graphene derivative, appears as a great candidate due to its superior electron transfer characteristics, high surface area and simplicity in its synthesis. The continuous interest in the development of cost-effective, more stable and reliable biosensors for glucose detection make them the most studied and explored within the academic and industry community. In this work, the electrochemistry of glucose oxidase (GOx) adsorbed on LIG electrodes is studied in detail. In addition to the well-known electroactivity of free flavin adenine dinucleotide (FAD), the cofactor of GOx, at the expected half-wave potential of -0.490 V vs. Ag/AgCl (1 M KCl), a new well-defined redox pair at 0.155 V is observed and shown to be related to LIG/GOx interaction. A systematic study was undertaken in order to understand the origin of this activity, including scan rate and pH dependence, along with glucose detection tests. Two protons and two electrons are involved in this reaction, which is shown to be sensitive to the concentration of glucose, restraining its origin to the electron transfer from FAD in the active site of GOx to the electrode via direct or mediated by quinone derivatives acting as mediators.

Laser-Induced Graphene from Paper for Mechanical Sensing.

The ability to synthesize laser-induced graphene (LIG) on cellulosic materials such as paper opens the door to a wide range of potential applications, from consumer electronics to biomonitoring. In this work, strain and bending sensors fabricated by irradiation of regular filter paper with a CO2 laser are presented. A systematic study of the influence of the different process parameters on the conversion of cellulose fibers into LIG is undertaken, by analyzing the resulting morphology, structure, conductivity, and surface chemistry. The obtained material is characterized by porous electrically conductive weblike structures with sheet resistances reaching as low as 32 Ω sq-1. The functionality of both strain (gauge factor of ≈42) and bending sensors is demonstrated for different sensing configurations, emphasizing the versatility and potential of this material for low-cost, sustainable, and environmentally friendly mechanical sensing.

A new formaldehyde optical sensor: Detecting milk adulteration.

A sensor consisting of an optical fibre with the exposed tip coated with the polyoxometalate salt [(C4H9)4N]4H[PMo10V2O40], specially designed to be insoluble in water, which UV-Vis spectrum changed in contact with formaldehyde, is presented. The sensor limit of detection for formaldehyde was 0.2 mg L-1, and the limit of quantification was 0.6 mg L-1, which were close to the conventional spectrophotometric method values of 0.2 mg L-1 and 0.5 mg L-1, respectively, and lower than the tolerable limit for ingested food. The sensor was tested for formaldehyde quantification in milk, as its deliberate addition is a matter of concern. The results obtained analysing formaldehyde in milk samples by the optical sensor and by the conventional method were not statistically different (α = 0.05).

Physical Structure and Electrochemical Response of Diamond-Graphite Nanoplatelets: From CVD Synthesis to Label-Free Biosensors.

Hybrid diamond-graphite nanoplatelet (DGNP) thin films are produced and applied to label-free impedimetric biosensors for the first time, using avidin detection as a proof of concept. The DGNPs are synthesized by microwave plasma chemical vapor deposition through H2/CH4/N2 gas mixtures in a reproducible and rapid single-step process. The material building unit consists of an inner two-dimensional-like nanodiamond with preferential vertical alignment covered by and covalently bound to nanocrystalline graphite grains, exhibiting {111}diamond||{0002}graphite epitaxy. The DGNP films' morphostructural aspects are of interest for electrochemical transduction, in general, and for Faradaic impedimetric biosensors, in particular, combining enhanced surface area for biorecognition element loading and facile Faradaic charge transfer. Charge transfer rate constants in phosphate buffer saline/[Fe(CN)6]4- solution are shown to increase up to 5.6 × 10-3 cm s-1 upon N2 addition to DGNP synthesis. For the impedimetric detection of avidin, biotin molecules are covalently bound as avidin specific recognition elements on (3-aminopropyl)triethoxysilane-functionalized DGNP surfaces. Avidin quantification is attained within the 10-1000 µg mL-1 range following a logarithmic dependency. The limits of detection and of quantitation are 1.3 and 6.4 µg mL-1 (19 and 93 nM), respectively, and 2.3 and 13.8 µg mL-1 (33 and 200 nM) when considering the nonspecific response of the sensors.

ZnO decorated laser-induced graphene produced by direct laser scribing.

A scalable laser scribing approach to produce zinc oxide (ZnO) decorated laser-induced graphene (LIG) in a unique laser-processing step was developed by irradiating a polyimide sheet covered with a Zn/ZnO precursor with a CO2 laser (10.6 µm) under ambient conditions. The laser scribing parameters revealed a strong impact on the surface morphology of the formed LIG, on ZnO microparticles' formation and distribution, as well as on the physical properties of the fashioned composites. The ZnO microparticles were seen to be randomly distributed along the LIG surface, with the amount and dimensions depending on the used laser processing conditions. Besides the synthesis conditions, the use of different precursors also resulted in distinct ZnO growth's yields and morphologies. Raman spectroscopy revealed the existence of both wurtzite-ZnO and sp2 carbon in the majority of the produced samples. Broad emission bands in the visible range and the typical ZnO near band edge (NBE) emission were detected by photoluminescence studies. The spectral shape of the luminescence signal was seen to be extremely sensitive to the employed processing parameters and precursors, highlighting their influence on the composites' optical defect distribution. The sample produced from the ZnO-based precursor evidenced the highest luminescence signal, with a dominant NBE recombination. Electrochemical measurements pointed to the existence of charge transfer processes between LIG and the ZnO particles.

All-Diamond Microelectrodes as Solid State Probes for Localized Electrochemical Sensing.

The fabrication of an all-diamond microprobe is demonstrated for the first time. This ME (microelectrode) assembly consists of an inner boron doped diamond (BDD) layer and an outer undoped diamond layer. Both layers were grown on a sharp tungsten tip by chemical vapor deposition (CVD) in a stepwise manner within a single deposition run. BDD is a material with proven potential as an electrochemical sensor. Undoped CVD diamond is an insulating material with superior chemical stability in comparison to conventional insulators. Focused ion beam (FIB) cutting of the apex of the ME was used to expose an electroactive BDD disk. By cyclic voltammetry, the redox reaction of ferrocenemethanol was shown to take place at the BDD microdisk surface. In order to ensure that the outer layer was nonelectrically conductive, a diffusion barrier for boron atoms was established seeking the formation of boron-hydrogen complexes at the interface between the doped and the undoped diamond layers. The applicability of the microelectrodes in localized corrosion was demonstrated by scanning amperometric measurements of oxygen distribution above an Al-Cu-CFRP (Carbon Fiber Reinforced Polymer) galvanic corrosion cell.

Potentiometric chemical sensors from lignin-poly(propylene oxide) copolymers doped by carbon nanotubes.

Hardwood and softwood lignins obtained from industrial sulphite and kraft and laboratory oxygen-organosolv pulping processes were employed in co-polymerization with tolylene 2,4-diisocyanate terminated poly(propylene glycol). The obtained lignin-based polyurethanes were doped with 0.72 w/w% of multiwall carbon nanotubes (MWCNTs) with the aim of increasing their electrical conductivity to the levels suitable for sensor applications. Effects of the polymer doping with MWCNTs were assessed using electrical impedance (EIS) and UV-Resonance Raman (UV-RR) spectroscopy. Potentiometric sensors were prepared by drop casting of liquid polymer on the surface of carbon glass or platinum electrodes. Lignin-based sensors displayed a very low or no sensitivity to all alkali, alkali-earth and transition metal cations ions except Cr(VI) at pH 2. Response to Cr(VI) values of 39, 50 and 53 mV pX(-1) for the sensors based on kraft, organosolv and lignosulphonate lignins, respectively, were observed. Redox sensitivity values close to the theoretical values of 20 and 21 mV pX(-1) for organosolv and lignosulphonate based sensors respectively were detected in the Cr(III)/Cr(VI) solutions while a very low response was observed in the solutions containing Fe(CN)(6)(3-/4-). Conducting composite lignin-based polyurethanes doped with MWCNTs were suggested as being promising materials for Cr(VI)-sensitive potentiometric sensors.

The assessment of chromophores in bleached cellulosic pulps employing UV-Raman spectroscopy.

UV-Resonance Raman (UV-RR) coupled with UV-visible Diffuse Reflectance (UV-vis DR) spectroscopy was applied to a solid-state study of chromophores in Eucalyptus globulus kraft cellulosic pulps bleached by chlorine dioxide and hydrogen peroxide. The UV-RR spectra were acquired at 325nm laser beam excitation, which was shown to be appropriate for selective analysis of chromophore structures in polysaccharides. The proposed approach allowed the monitoring of chromophores in pulps and to track the extent of polysaccharide oxidation. However, precaution was suggested while performing a quantitative analysis of chromophores at the characteristic band of approximately 1600cm(-1) because of charge transfer complexes (CTCs) that exist in the pulp. These CTCs can affect the intensity of the aforementioned band by diminishing the conjugate state in the chromophore moieties. The amount of carbonyl and carboxyl groups in polysaccharides correlated with the intensity of the band at 1093cm(-1). The analysis of UV-RR spectra revealed xylan as an important source of chromophores in eucalypt kraft pulp.