M.A. Neto

Three‐dimensional printed PCL‐hydroxyapatite scaffolds filled with CNTs for bone cell growth stimulation

A three-phase [nanocrystalline hydroxyapatite (HA), carbon nanotubes (CNT), mixed in a polymeric matrix of polycaprolactone (PCL)] composite scaffold produced by 3D printing is presented. The CNT content varied between 0 and 10 wt % in a 50 wt % PCL matrix, with HA being the balance. With the combination of three well-known materials, these scaffolds aimed at bringing together the properties of all into a unique material to be used in tissue engineering as support for cell growth. The 3D printing technique allows producing composite scaffolds having an interconnected network of square pores in the range of 450-700 μm. The 2 wt % CNT scaffold offers the best combination of mechanical behaviour and electrical conductivity. Its compressive strength of ∼4 MPa is compatible with the trabecular bone. The composites show typical hydroxyapatite bioactivity, good cell adhesion and spreading at the scaffolds surface, this combination of properties indicating that the produced 3D, three-phase, scaffolds are promising materials in the field of bone regenerative medicine.

Free-standing diamond films grown on cobalt substrates

Abstract Diamond films were grown directly on cobalt substrates, using microwave plasma-assisted chemical vapour deposition. Although cobalt is known to inhibit the nucleation of diamond and enhancing the formation of graphite, we were able to grow relatively thick films (∼190 μm). The films were easily detached from the substrates. The poor adhesion allows the possibility of obtaining free-standing diamond films without chemical etching. Micro-Raman spectroscopy showed the 1332 cm −1 characteristic Raman peak of diamond and the 1580 cm −1 , 1360 cm −1 bands of graphite, on the growth surface and backside of the films, respectively. Through scanning electron microscopy and X-ray diffraction we were able to monitor film thickness and morphology with growth evolution. The results showed the (111) preferential growth morphology for the film with higher growth rate. By energy dispersive X-ray spectroscopy it was only possible to detect cobalt in the back of the films, but not in the surface. The role of cobalt in the film growth is discussed.

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.

Interfacing metallic ohmic contacts in biocompatible ceramic substrates with diamond surfaces for biosensing applications

The development of biosensors for in vivo applications requires the deposition of metallic contacts on biofunctionalized, biocompatible surfaces. For improved performance the metallic contacts should not interfere with the biosensing zone of the sensors. Owing to their biological compatibility with human tissues and fluids, diamond, titanium and silicon nitride ceramics (Si3N4) are potential candidates to be incorporated in implantable biosensors. The easy formation of titanium carbide under carbon saturated atmospheres, make titanium the right choice for diamond nucleation and growth. The same applies to the well studied Si3N4 ceramics used as substrates for diamond growth. The fabrication of biocompatible ceramic substrates with incorporated titanium contacts and chemically vapour deposited low resistivity boron doped diamond surfaces is the aim of the present work.

Diamond / SiC heterojunctions

Diamond and SiC are wide bandgap (WBG) materials which can be used to fabricate high power devices with improved performance. The combination of these materials into one single device is expected to bring some benefits, like a better thermal management with a corresponding increase in the operating power. Diamond films deposited by Chemical Vapor Deposition (CVD) can be doped with boron, making them p-type semiconductors. Diamond films deposited on foreign substrates are intrinsically polycrystalline, so the quality of the interface, determined by deposition conditions and seeding method, plays a critical role in the heterojunction characteristics, impacting both reverse current and breakdown voltage. This work reports the fabrication and characterization of p-diamond / n-SiC heterojunctions. P-type polycrystalline diamond (PCD) films were deposited directly on the surface on n-type SiC commercial wafers by Hot Filament CVD (HFCVD) using different seeding techniques. I-V characteristics of the obtained heterojunctions were measured at room temperature and the quality and morphology of the diamond films were assessed by scanning electronic microscopy (SEM) and Raman spectroscopy. The influence of the different seeding techniques on the I-V characteristics is discussed.