Alfredo Carlos Peterlevitz

Enhancement of diamond nucleation using the solid-liquid-gas interface energy

We demonstrate the enhancement of diamond nucleation through the use of the equilibrium forces at the solid-liquid-gas interface on a substrate wetted with droplets of an oil of low vapor pressure. Such a process is shown to produce well-faceted grains with densities of roughly 107 nuclei cm−2 (boundary), 105 nuclei cm−2 (oil-coated area), and 104 nuclei cm−2 (uncoated area) without the need for scratching or seeding the substrate. Diamond deposition was undertaken on silicon using ethanol and hydrogen in the feed of a hot-filament chemical vapor deposition reactor. The oil-covered regions, in addition to showing higher nucleation densities, have the merit that the intergrain spaces are covered with diamond structures, while the parts uncovered with oil exhibit intergrain spaces covered with diamond-like carbon.

Nitrogen-doped diamond films

We found that very high concentrations (up to 20% vol) of nitrogen in the ethanol/hydrogen gas mixture do not prejudice the diamond quality as determined by Raman spectroscopy. Nitrogen addition also increases the diamond growth rate, as was previously reported at low nitrogen concentrations. We observed that after a second heating cycle in air at temperatures between 300 and 673 K the electrical resistance versus temperature curves of the as-grown films presented a bulk semiconductor behavior. This stabilization was due to the oxidation of the as-grown hydrogenated surface. The electrical ionization energy Ed was found to be in the range of 1.62–1.90 eV corresponding to films produced with 0 to 20% vol nitrogen in the feed. The room temperature photoluminescence spectra of films produced at low nitrogen concentration suggest that Ed results from pure electronic transitions in the nitrogen-vacancy neutral defects; for samples produced with nitrogen concentrations in the range 15–20% vol the Ed values may ...

Field emission properties of porous diamond-like films produced by chemical vapor deposition

The field emission properties of “porous diamond-like” carbon structures have been characterized. A hot filament chemical vapor deposition system fed with ethyl alcohol vapor diluted in helium was used to deposit the samples. Morphological analysis by field emission scanning electron microscopy revealed that they had a highly porous structure, which was attributed to the modification of the kinetics of the carbon deposition process due to the presence of helium as a buffer gas. Micro-Raman spectroscopy showed two peaks in the graphene and microcrystalline graphite frequencies and a new peak at 1620 cm−1. Low threshold fields (Et) and hysteresis in the current versus voltage characteristic have been observed, and a model to explain the hysteresis is proposed.

Effects of argon dilution of an ethanol/hydrogen gas feed on the growth of diamond by hot-filament chemical vapor deposition

Abstract We studied the effects on the growth kinetics and properties of diamond and carbon-like diamond films obtained by the introduction of argon at low to high concentrations (0–85 vol.% Ar) into the feed mixture (ethanol and hydrogen) of a hot-filament chemical vapor deposition (CVD) reactor. Scanning electron microscopy (SEM) analysis revealed that the addition of argon induces an increase in the diamond grain size, and increases the flaws between the grains and the density of vacancy defects. Well-faceted diamond films of good quality (measured by Raman spectroscopy) have been obtained using up to 65 vol.% of argon in the gaseous mixture, while higher concentrations (85 vol.% Ar) produce diamond-like carbon or other complex carbon structures. We also observed an increase in the diamond growth rate with argon addition that was associated with an increase in carbon free radicals (up to ∼40 vol.% Ar) or to the increase in the filament temperature necessary to keep the substrate temperature constant at higher Ar concentrations (above ∼40 vol.% Ar). Room temperature photoluminescence spectroscopy also confirmed that argon addition increases the density of vacancy defects in the diamond structure.

QSPR Study of Passivation by Phenolic Compounds at Platinum and Boron-Doped Diamond Electrodes

= 0.851, and standard error of validation SEV = 0.097. A BDD model with one latent variable and four descriptors was built and validated in the same way; however, the statistical parameters Q2 = 0.333, R2 = 0.586, and SEV = 0.159 were of inferior quality with respect to the model for the Pt electrode. Both models were applied for prediction of 10 phenolic compounds. The Pt model showed to be suitable for predictive purposes. It was observed that passivation was much weaker on the BDD electrode than on the Pt electrode. Different interactions and reactions involving phenolics at the electrodes are the main reasons for such large differences between the models. Exploratory analyses were also performed and interpreted in terms of chemical concepts, such as phenolic reactivity, size/shape, hydrogen bonding, and electronic features. These findings can be useful to explore the possibility to predict phenolic passivation and to design electrochemical experiments involving different phenolic compounds. Furthermore, these PLS models aid in understanding electrode inactivation by phenolic compounds.

Measurement of the substitutional nitrogen activation energy in diamond films

We show that the electrical properties of nitrogen-doped nominally undoped polycrystalline chemical vapor deposited diamond films are modified by post-deposition heating in an oxidizing atmosphere. We found that the first heating cycle in air in the temperature range of 300–673 K decreased the graphitization content still present in the diamond surface and that after the second heating cycle the electrical resistance versus temperature curves became stabilized. Using a flow of argon with residues of oxygen over the surface of the sample during the heating cycles, the stabilization of the resistance-temperature dependence also occurred but only after the fourth heating cycle. The results suggest the existence of an oxidation mechanism of the nondiamond carbon atoms present at the diamond surface. After stabilization, the deep donor ionization energy was found to be Ed=1.62±0.02 eV. All results brought together strongly suggest that this level is due to single nitrogen atoms that occupy substitutional latti...

Up-regulation of T lymphocyte and antibody production by inflammatory cytokines released by macrophage exposure to multi-walled carbon nanotubes

Our data demonstrate that multi-walled carbon nanotubes (MWCNTs) are internalized by macrophages, subsequently activating them to produce interleukin (IL)-12 (IL-12). This cytokine induced the proliferative response of T lymphocytes to a nonspecific mitogen and to ovalbumin (OVA). This increase in the proliferative response was accompanied by an increase in the expression of pro-inflammatory cytokines, such as interferon-gamma (IFNγ), tumor necrosis factor-alpha (TNFα) and IL-6, in mice inoculated with MWCNTs, whether or not they had been immunized with OVA. A decrease in the expression of transforming growth factor-beta (TGFβ) was observed in the mice treated with MWCNTs, whereas the suppression of the expression of both TGFβ and IL-10 was observed in mice that had been both treated and immunized. The activation of the T lymphocyte response by the pro-inflammatory cytokines leads to an increase in antibody production to OVA, suggesting the important immunostimulatory effect of carbon nanotubes.

The Suppressive Effect of IL‐27 on Encephalitogenic Th17 Cells Induced by Multiwalled Carbon Nanotubes Reduces the Severity of Experimental Autoimmune Encephalomyelitis

Both Th1 and Th17 cells specific for neuroantigen are described as encephalitogenic in the experimental autoimmune encephalomyelitis (EAE) model.

Characterization of diamond fluorinated by glow discharge plasma treatment

Abstract The surface fluorination of diamond by treatment in glow discharge plasmas of CF4 for different times has been investigated. High quality diamond films were deposited onto silicon substrates using hot filament chemical vapor deposition (HFCVD). Subsequently, the films were exposed to a radiofrequency glow discharge plasma of CF4 for times ranging from 5 min to 1 h. The effects of the plasma treatment on the surface morphology, diamond quality and elemental composition were investigated using atomic force microscopy (AFM), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS), respectively. Differences in film roughness caused by the plasma treatment were detected by AFM and confirmed by scanning electron microscopy (SEM). Raman spectroscopic analyses showed that the original diamond was of high quality and that the bulk of each film was unchanged by the plasma treatment. Analyses using XPS revealed increased surface fluorination of the films at longer treatment times. In addition, the density of free radicals in the films was probed using electron paramagnetic resonance spectroscopy (EPRS), revealing that untreated diamond possesses an appreciable density of free radicals (6×1012 g−1) which initially falls with treatment time in the CF4 plasma but increases for long treatment times.

Structure and properties of diamond films deposited on porous silicon

Abstract Thick porous silicon (PS) layers, made by anodic etching of crystalline Si wafers, have been coated with diamond films using the hot-filament chemical vapor deposition (CVD) technique. Ethanol diluted in hydrogen was used as the carbon source for diamond deposition. We observed that diamond nucleation occurs predominantly on the top of the PS spikes, creating individual islands of growth. Nucleation is apparently homogeneous over the PS surface and the islands grow independently until the complete coalescence of the diamond film. Although the diamond film is polycrystalline, it does not have the usual columnar structure of diamond deposited on c-Si. A good adherence between diamond and PS was observed in diamond–PS and diamond–PS–diamond structures. The problems of the intrinsic and thermal stresses have been addressed. Samples were characterized by atomic force microscopy (AFM), scanning electron microscopy (SEM), Auger electron spectroscopy (AES), Raman and photoluminescence spectroscopy.