João Roberto Moro

Very adherent CVD diamond film on modified molybdenum surface

In this work, studies have been carried out on surface modification on a pure molybdenum surface to enhance CVD diamond adherence. Pure molybdenum exhibits a phase transformation temperature close to that of diamond growth, but it is possible to obtain a surface modification by ion sub-implantation at an appropriate lower temperature without phase transformation. In this study, it was possible to create an appropriate interface by using appropriate ion compounds and impact energy on the substrate surface at a very narrow window of working temperature. This interface efficiently avoided carbon diffusion during diamond growth and also improved the chemical bond density between atoms from the interface and carbon from the onset of diamond nucleation. Diamond films from a few micrometers up to millimeters have been obtained with very good adherence. Characterization by XPS and small angle X-ray diffraction of this interface prior to diamond growth and after diamond nucleation reveals different compound contributions to the chemical bonds. Indentation and SEM analyses were also carried out.

CVD Diamond Films Growth on Silicon Nitride Inserts (Si3N4) with High Nucleation Density by Functionalization Seeding

Silicon Nitride is largely used as the base material to manufacture cutting tools. Due to its low thermal expansion coefficient it is ideal candidate for CVD diamond deposition. In this work, we functionalized the surface of silicon nitride inserts (Si3N4) with a polymer (PDDA Poly (diallyldimethylamonium chloride - Mw 40000)) to promote seeding with nanodiamond particles. The seeding was performed in water slurry containing 4 nm diamond particles dispersed by PSS Poly (sodium4-styrenesulfonate) polymer. CVD diamond films, with high nucleation density, were deposited in a hot filament reactor. Film morphology was characterized by Atomic Force Microscopy (AFM) and Scanning Electron Microscopy (SEM). Diamond film quality was determined by Raman Spectroscopy. CVD diamond film adherence was evaluated using Rockwell C indentation.

Studies of molybdenum surface modification for growth of adherent CVD diamond film

Surfaces with very poor mechanical and frictional properties can be improved, or even, acquire new properties similar to diamond if good adherent CVD diamond film is obtained on it. In this work, nitrogen ions were sub-implanted on pure molybdenum as a means to enhance CVD diamond film adherence. Deposition time from 2 up to 60 h were used for deposition of 10 to 400 µm thick CVD diamond films with very good adherence on sub-implanted molybdenum substrate. Characterizations were carried out by XPS, X-ray diffraction and nano indentation on prepared surfaces prior to diamond growth and after the onset nucleation. The ionic sub-implantation with nitrogen possibly assists in adhesion, with the creation of a thin layer of nitrates and complexes.

Taxa de crescimento de filmes de diamante CVD em superfícies de molibdênio

The substrate preparation for CVD diamond growth is of basic importance due to several reasons. A new molybdenum substrate preparation method, the aluminum oxide abrasion jetting, is introduced and compared with the traditional ones. Raman Scattering Spectroscopy (RSS) and Scanning Electron Microscopy (SEM) characterize CVD diamond films. CVD diamond films of good quality and uniformity were obtained. The substrate preparation by aluminum oxide blasting allowed for a higher nucleation rate.

Activation energies in diamond films evaluated using admittance spectroscopy and resistivity measurements

This article reports on the study of high-quality boron-doped diamond films using admittance techniques. We have found two well-defined energy states at 74 and 340 meV, indicating that the doping procedure has induced defects and consequently provoked the localization of carriers. This is a direct indication that there are different coexisting conduction mechanisms for the transport of carriers. Additionally, we perform complementary resistivity experiments showing the presence of the variable range hopping as the dominant transport mechanism.