Gil Cabral

Chemically functionalized carbon nanotubes and their characterization using thermogravimetric analysis, fourier transform infrared, and raman spectroscopy

This article reports key findings on the chemical functionalization of carbon nanotubes (CNT). The functionalization of chemical vapor-deposited CNT was carried out by treating tubes with polyvinyl alcohol through ultrasonication in water with the aid of a surfactant. The surfactant is expected to promote the unbundling of aggregated CNT. The characterization of functionalized samples using thermogravimetric analysis, Fourier transform infrared spectroscopy, and Raman spectroscopy revealed that the CNT were functionalized by the interaction of carboxylic acid and hydroxyl groups. From the characterization studies, it is apparent that there is a strong interaction between these functional groups and the covalently bonded carbon in the CNT network. The functionalization process enabled good CNT dispersion in the solution, and the CNT remained in suspension for many days. To support the effective functionalization of the tubes, the interaction of functionalized CNT with Ni ions is also demonstrated.

Surface engineered surgical tools and medical devices

Surface engineered surgical tools and medical devices / , Surface engineered surgical tools and medical devices / , کتابخانه دیجیتال جندی شاپور اهواز

Electron field emission from patterned nanocrystalline diamond coated a-SiO2 micrometer-tip arrays

We report the fabrication of patterned nanocrystalline diamond (NCD) submicrometer-tip arrays. This includes synthesis of silica (a-SiO2) templates by conventional vapor-liquid-solid method and conformal coating of the a-SiO2 nanowires with 5–10nm sized nanodiamond grains by microwave plasma chemical vapor deposition. Detailed structural investigations were carried out by high resolution transmission electron microscopy. Electron field emission of nanodiamond emitter arrays was observed with a threshold field of 5.5V∕μm. A high emission current density of 10mAcm−2 at 11V∕μm has been obtained. This value is comparable to those of high quality NCD films deposited on silicon substrates.We report the fabrication of patterned nanocrystalline diamond (NCD) submicrometer-tip arrays. This includes synthesis of silica (a-SiO2) templates by conventional vapor-liquid-solid method and conformal coating of the a-SiO2 nanowires with 5–10nm sized nanodiamond grains by microwave plasma chemical vapor deposition. Detailed structural investigations were carried out by high resolution transmission electron microscopy. Electron field emission of nanodiamond emitter arrays was observed with a threshold field of 5.5V∕μm. A high emission current density of 10mAcm−2 at 11V∕μm has been obtained. This value is comparable to those of high quality NCD films deposited on silicon substrates.

Simultaneous formation of silicon carbide and diamond on Si substrates by microwave plasma assisted chemical vapor deposition

Abstract The effects of several process parameters, such as substrate temperature, nucleation density, and substrate surface pretreatment, on the simultaneous formation of SiC and diamond under typical growth conditions of diamond by microwave plasma assisted chemical vapor deposition (MPCVD), have been investigated by scanning electron microscopy (SEM), X-ray diffraction, and Raman and Fourier-transfer infrared (FTIR) spectroscopy. Results show that no SiC can be detected in the diamond films grown with a high nucleation density, whereas, SiC is detected in the thick diamond films grown with a low nucleation density, with or without surface pretreatment of the Si substrates. SEM micrographs and FTIR spectra illustrate that SiC is formed on the Si substrate not covered by diamond nuclei or in void regions between diamond nuclei. The formation of SiC and diamond on Si substrates under the growth conditions of diamond by MPCVD is a concurrent competitive deposition process, especially at the initial stage of diamond nucleation and growth. This is an alternative method for the synthesis of diamond-SiC composites by MPCVD.

Modelling on the mechanical properties of nanocomposite hydroxyapatite/PMMA/ carbon nanotube coatings

A combination of Hydroxyapatite (HA), Polymethylmethacrylate (PMMA) and Carbon Nanotubes (CNTs) was used to synthesize a new composite material, which is superior in mechanical properties to the conventional HA as a biomedical scaffold in tissue engineering. PMMA is well-known as a bone cement highly compatible with HA and can act as a functionalising/linking and/or coupling agent with the HA-CNTs mixtures, while the unique and excellent structure and properties of CNTs, after functionalisation, are able to reinforce and strengthen the porous HA matrix. The evolution of the secondary phases of HA may impair the mechanical properties; however, the evolving species (calcium oxide, tetra-calcium and tri-calcium phosphates or amorphous calcium phosphates) are trapped in the CNTs-PMMA network yielding a nanocomposite with improved mechanical and longer lasting lifetime performance, based on preliminary observations, shows good biocompatibility, and a detailed study to evaluate its biocompatibility is underway. The experimental study was characterised by means of X-Ray Diffraction (XRD), vibrational Raman spectroscopy and Scanning Electron Microscopy (SEM).

Fabrication of vertically aligned carbon nanotubes for spintronic device applications

We report on the observation of coulomb blockade and coulomb staircase at room temperature in multiwalled carbon nanotube (MWCNT) based heterostructures. The hybrid structure consists of nickel ferromagnets separated by vertically aligned MWCNTs. The MWCNTs were grown vertically on a nickel substrate by a double plasma hot filament chemical vapour deposition technique. Deposition of ferromagnetic nickel nanoparticles on the top of MWCNTs was achieved for the first time using the laser chemical vapour deposition method. The fabrication technique is unique in that it is formed of many individual ferromagnetic tunnel junctions integrated into a single system. A well defined coulomb blockade and coulomb staircase was displayed in current–voltage characteristics obtained by scanning tunnelling spectroscopy. The capacitance (1. 6 × 10−18 F) in the system is determined from the spacing ΔV between peaks in the dI/dV curves.

Impact of surface roughness of diamond coatings on the cutting performance when dry machining of graphite

Time Modulated Chemical Vapour Deposition (TMCVD) process regime has been used to deposit diamond coatings onto commercially available tungsten carbide tool inserts. The TMCVD process was developed in our laboratories so that diamond films with fine grains could be deposited. It accomplishes this by promoting secondary nucleation during larger methane flow modulations. The average surface roughness of the diamond coatings were correlated with the cutting performance of the coatings when dry machining of graphite. Inserts coated were characterised by Scanning Electron Microscopy (SEM) and Raman spectroscopy and were tested for turning performance using graphite as the workpiece material. The cutting forces were measured by the DynoWareT™ data acquisition system. Polycrystalline Diamond (PCD) inserts were also used for comparison. Repeated turning tests showed that the surface roughness of the coatings is a limiting factor when achieving better chip flow during machining.

Characterization of diamond adhesion on micro-grain WC-Co substrates using Brinell indentations and micro-Raman spectroscopy

In this study, we investigate the adhesion of diamond coatings deposited on 0.8 µm WC–10% Co substrates using chemical vapour deposition (CVD). Polycrystalline diamond films were deposited using (i) constant methane (CH4) flow, at 3 and 4.5 sccm, and (ii) modulated CH4 flow at 4.5 and 3 sccm for 8 and 10 min, respectively. Constant CH4 flow into the vacuum chamber during diamond CVD is the conventional approach to deposit diamond onto a range of substrate materials. The timed CH4 modulations are an integral part of our recently proposed process called time-modulated CVD (TMCVD). The coating adhesion was characterized using indentation tests employing a Brinell indenter. In this study, we employ three indentation loads: 294, 490 and 612.5 N. In addition, micro-Raman spectroscopy was used to (i) characterize the deposited films for diamond-carbon phase purity and (ii) determine the biaxial stresses in the coating samples. In this paper, we correlate the adhesion strength of diamond films to biaxial stresses. No lateral cracking occurred in diamond films deposited by the TMCVD process after a 294 N load indentation. This result coupled with the complementary stress calculations indicates a higher film–substrate adhesion in time-modulated films. Our findings suggest that at higher indentation loads the response from and the behaviour of the substrate need to be considered in determining the coating adhesion strength. The TMCVD process promotes secondary nano-sized diamond crystallites during the higher timed methane modulations. It is expected that the mechanical interlock at the film/substrate interface is higher for film coatings deposited using TMCVD, thus resulting in the improved adhesion of the time-modulated coating on WC–Co.

Surface Engineering of Artificial Heart Valves to Using Modified Diamond-like Coatings

There are two types of artificial heart valves, namely, (i) biological valves and (ii) mechanical valves. biological heart valves are made from tissue taken from animals or human cadavers. They are treated with preservatives and sterilized for human implantation. On the other hand, mechanical heart valves are made of man-made materials. The advantage of mechanical valves over biological valves is that they normally last for a comparatively longer lifetime. The biological valves exhibit a shorter lifetime and tend to wear out with time in service. This chapter discusses mechanical heart valves and highlights the underlying problems faced with biomaterials used in the manufacture of such valves.

Biomaterial-cell tissue interactions in surface engineered carbon-based biomedical implants and devices

Implantable prosthesis and medical devices are subjected to several interacting forces whenever they come in contact with the physiologic systems (blood, immune, musculoskeletal, nervous, digestive, respiratory, reproductive and urinary) and organs of the human body. These interactions include the effects of core body temperature (and/or variable temperatures in the oral cavity), the body physiologic fluids containing several ions and biomolecules, proteins and cells of various progeny and functions. This chapter focuses on cell tissue–implant interactions and how carbon-based implants are being developed for next-generation implantable devices.