Key parameters to enhance the antibacterial effect of graphene oxide in solution.

Graphene oxide (GO) has lately become an interesting biomaterial due to its stunning properties and versatility, its claimed antimicrobial activity holds promise for potential health applications. Nonetheless, multiple reports investigating GO antibacterial activity lack rigor and uniformity on several aspects which are crucial when evaluating this effect. In this work, we highlight and address these parameters: morphology of the materials, exposure time, exposure methodology and concentration. We investigate the effect of GO and GO-based metallic composites observing these parameters on two pathogenic bacteria. Our nanomaterials have been characterized by means of SEM, EDX, DLS, FTIR and Raman spectroscopies. Escherichia coli and Salmonella Typhimurium suspended in saline solutions (no growth medium) have been exposed to GO (lateral size = 100 nm), silver nanoparticles, ceria nanoparticles, GO/silver and GO/ceria aqueous solutions for 0, 5, 15, 30, 60 and 90 minutes, before plating. Our experiments indicate that no prior exposure of the materials to bacteria (0 min) results in poor inactivation rates independently of concentration, while increasing times of interaction enhance inactivation. Moreover, our experiments show concentration-dependent results showing higher activity for concentrations of 100 µg mL-1; and prove that 30 minutes of exposure are sufficient to deploy the antimicrobial effects of these materials. GO possesses the lowest inactivation rate, and the presence of silver and ceria nanoparticles in the GO surface boosts its antimicrobial effect. Thus, the enhancement of the antibacterial activity of graphene oxide relies on 30 minutes of interaction in water, concentration of 100 µg mL-1, and its decoration by silver/ceria nanoparticles.

Microstructure and selected mechanical properties of aged Ti-15Zr-based alloys for biomedical applications.

In this study, Ti-15Zr-xMo (5, 10, 15, and 20 wt%) alloys were submitted to solution and aging treatments and their effects evaluated in terms of phase composition and selected mechanical properties (Vickers microhardness and Young's modulus) for use as biomedical implants. The solution treatment was performed at 1123 K for 2 h, while aging treatments were carried out at 698 K for 4, 8, and 12 h, followed by water quenching. Phase composition and microstructure were dependent of the heat treatments, with Ti-15Zr-5Mo (α +â€¯ß type) and Ti-15Zr-10Mo (metastable ß type) alloys exhibiting intense α phase precipitation. The α-phase precipitates were related to α″ → α and ß → α phase decompositions. The Ti-15Zr-10Mo alloy exhibited an intermediary isothermal ω-phase precipitation after aging for 4 h. Vickers microhardness and Young's modulus values changed gradually with the amount of α phase. Aged Ti-15Zr-15Mo and Ti-15Zr-20Mo alloys presented better combinations of hardness and Young's modulus than CP-Ti and Ti-64 ELI for biomedical applications.

Nucleation, Growth Mechanism, and Controlled Coating of ZnO ALD onto Vertically Aligned N-Doped CNTs.

Zinc oxide thin films were deposited on vertically aligned nitrogen-doped carbon nanotubes (N-CNTs) by atomic layer deposition (ALD) from diethylzinc and water. The study demonstrates that doping CNTs with nitrogen is an effective approach for the "activation" of the CNTs surface for the ALD of metal oxides. Conformal ZnO coatings are already obtained after 50 ALD cycles, whereas at lower ALD cycles an island growth mode is observed. Moreover, the process allows for a uniform growth from the top to the bottom of the vertically aligned N-CNT arrays. X-ray photoelectron spectroscopy demonstrates that ZnO nucleation takes place at the N-containing species on the surface of the CNTs by the formation of the Zn-N bonds at the interface between the CNTs and the ZnO film.

Heat Dissipation Interfaces Based on Vertically Aligned Diamond/Graphite Nanoplatelets.

Crystalline carbon-based materials are intrinsically chemically inert and good heat conductors, allowing their applications in a great variety of devices. A technological step forward in heat dissipators production can be given by tailoring the carbon phase microstructure, tuning the CVD synthesis conditions. In this work, a rapid bottom-up synthesis of vertically aligned hybrid material comprising diamond thin platelets covered by a crystalline graphite layer was developed. A single run was designed in order to produce a high aspect ratio nanostructured carbon material favoring the thermal dissipation under convection-governed conditions. The produced material was characterized by multiwavelength Raman spectroscopy and electron microscopy (scanning and transmission), and the macroscopic heat flux was evaluated. The results obtained confirm the enhancement of heat dissipation rate in the developed hybrid structures, when compared to smooth nanocrystalline diamond films.

Micro-arc oxidation as a tool to develop multifunctional calcium-rich surfaces for dental implant applications.

Titanium (Ti) is commonly used in dental implant applications. Surface modification strategies are being followed in last years in order to build Ti oxide-based surfaces that can fulfill, simultaneously, the following requirements: induced cell attachment and adhesion, while providing a superior corrosion and tribocorrosion performance. In this work micro-arc oxidation (MAO) was used as a tool for the growth of a nanostructured bioactive titanium oxide layer aimed to enhance cell attachment and adhesion for dental implant applications. Characterization of the surfaces was performed, in terms of morphology, topography, chemical composition and crystalline structure. Primary human osteoblast adhesion on the developed surfaces was investigated in detail by electronic and atomic force microscopy as well as immunocytochemistry. Also an investigation on the early cytokine production was performed. Results show that a relatively thick hybrid and graded oxide layer was produced on the Ti surface, being constituted by a mixture of anatase, rutile and amorphous phases where calcium (Ca) and phosphorous (P) were incorporated. An outermost nanometric-thick amorphous oxide layer rich in Ca was present in the film. This amorphous layer, rich in Ca, improved fibroblast viability and metabolic activity as well as osteoblast adhesion. High-resolution techniques allowed to understand that osteoblasts adhered less in the crystalline-rich regions while they preferentially adhere and spread over in the Ca-rich amorphous oxide layer. Also, these surfaces induce higher amounts of IFN-γ cytokine secretion, which is known to regulate inflammatory responses, bone microarchitecture as well as cytoskeleton reorganization and cellular spreading. These surfaces are promising in the context of dental implants, since they might lead to faster osseointegration.

The High performance of nanocrystalline CVD diamond coated hip joints in wear simulator test.

The superior biotribological performance of nanocrystalline diamond (NCD) coatings grown by a chemical vapor deposition (CVD) method was already shown to demonstrate high wear resistance in ball on plate experiments under physiological liquid lubrication. However, tests with a close-to-real approach were missing and this constitutes the aim of the present work. Hip joint wear simulator tests were performed with cups and heads made of silicon nitride coated with NCD of ~10 µm in thickness. Five million testing cycles (Mc) were run, which represent nearly five years of hip joint implant activity in a patient. For the wear analysis, gravimetry, profilometry, scanning electron microscopy and Raman spectroscopy techniques were used. After 0.5 Mc of wear test, truncation of the protruded regions of the NCD film happened as a result of a fine-scale abrasive wear mechanism, evolving to extensive plateau regions and highly polished surface condition (Ra<10nm). Such surface modification took place without any catastrophic features as cracking, grain pullouts or delamination of the coatings. A steady state volumetric wear rate of 0.02 mm(3)/Mc, equivalent to a linear wear of 0.27 µm/Mc favorably compares with the best performance reported in the literature for the fourth generation alumina ceramic (0.05 mm(3)/Mc). Also, squeaking, quite common phenomenon in hard-on-hard systems, was absent in the present all-NCD system.

Nanoscale mapping of carbon oxidation in pyrogenic black carbon from ancient Amazonian anthrosols.

Understanding soil organic matter is necessary for the development of soil amendments, which are important for sustaining agriculture in humid tropical climates. Ancient Amazonian anthrosols are uniquely high in black recalcitrant carbon, making them extremely fertile. In this study, we use high-resolution electron microscopy and spectroscopy to resolve the oxidation process of carbon in the nanoscale crystallites within the black carbon grains of this special soil. Most alkali and acid chemical extraction methods are known to cause chemical modifications in soil organic matter and to give poor or no information about the real spatial structure of soil aggregates. However, here we show that carbon-oxygen functional groups such as phenol, carbonyl, and carboxyl dominate over different spatial regions, with areas varying from over tens to hundreds of nm(2). The chemical maps show that in the nanoscale grain, the surface has a tendency to be less aromatic than the grain core, where higher oxidative-degradation levels are indicated by the presence of carbonyl and carboxyl groups. A deep understanding of these structures could allow artificial reproduction of these natural events.

The use of a Ga+ focused ion beam to modify graphene for device applications.

In this work, we clarify the features of the lateral damage of line defects in single layer graphene. The line defects were produced through well-controlled etching of graphene using a Ga(+) focused ion beam. The lateral damage length was obtained from both the integrated intensity of the disorder induced Raman D band and the minimum ion fluence. Also, the line defects were characterized by polarized Raman spectroscopy. It was found that graphene is resilient under the etching conditions since the intensity of the defect induced Raman D peak exhibits a dependence on the direction of the lines relative to the crystalline lattice and also on the direction of the laser polarization relative to the lines. In addition, electrical measurements of the modified graphene were performed. Different ion fluences were used in order to obtain a completely insulating defect line in graphene, which was determined experimentally by means of charge injection and electric force microscopy measurements. These studies demonstrate that a Ga+ ion column combined with Raman spectroscopy is a powerful technique to produce and understand well-defined periodic arrays of defects in graphene, opening possibilities for better control of nanocarbon devices.

Ion beam nanopatterning and micro-Raman spectroscopy analysis on HOPG for testing FIB performances.

This work reports Ga(+) focused ion beam nanopatterning to create amorphous defects with periodic square arrays in highly oriented pyrolytic graphite and the use of Raman spectroscopy as a new protocol to test and compare progresses in ion beam optics, for low fluence bombardment or fast writing speed. This can be ultimately used as a metrological tool for comparing different FIB machines and can contribute to Focused Ion Beam (FIB) development in general for tailoring nanostructures with higher precision. In order to do that, the amount of ion at each spot was varied from about 10(6) down to roughly 1 ion per dot. These defects were also analyzed by using high resolution scanning electron microscopy and atomic force microscopy. The sensitivities of these techniques were compared and a geometrical model is proposed for micro-Raman spectroscopy in which the intensity of the defect induced D band, for a fixed ion dose, is associated with the diameter of the ion beam. In addition, the lateral increase in the bombarded spot due to the cascade effect of the ions on graphite surface was extracted from this model. A semi-quantitative analysis of the distribution of ions at low doses per dot or high writing speed for soft modification of materials is discussed.

Quantifying defects in graphene via Raman spectroscopy at different excitation energies.

We present a Raman study of Ar(+)-bombarded graphene samples with increasing ion doses. This allows us to have a controlled, increasing, amount of defects. We find that the ratio between the D and G peak intensities, for a given defect density, strongly depends on the laser excitation energy. We quantify this effect and present a simple equation for the determination of the point defect density in graphene via Raman spectroscopy for any visible excitation energy. We note that, for all excitations, the D to G intensity ratio reaches a maximum for an interdefect distance ∼3 nm. Thus, a given ratio could correspond to two different defect densities, above or below the maximum. The analysis of the G peak width and its dispersion with excitation energy solves this ambiguity.

Quartz microbalance device for transfer into ultrahigh vacuum systems.

An uncomplicated quartz microbalance device has been developed which is transferable into ultrahigh vacuum (UHV) systems. The device is extremely useful for flux calibration of different kinds of material evaporators. Mounted on a commercial specimen holder, the device allows fast quartz microbalance transfer into the UHV and subsequent positioning exactly to the sample location where subsequent thin film deposition experiments shall be carried out. After backtransfer into an UHV sample stage, the manipulator may be loaded in situ with the specimen suited for the experiment. The microbalance device capability is demonstrated for monolayer and submonolayer vanadium depositions with an achieved calibration sensitivity of less the 0.001 ML coverage.