Adriana F. Azevedo

Nanodiamond Films for Applications in Electrochemical Systems

The purpose of the present paper is to give an overview on the current development status of nanocrystalline diamond electrodes for electrochemical applications. Firstly, we describe a brief comparison between the general properties of nanocrystalline diamond (undoped and boron-doped) and boron-doped microcrystalline diamond films. This is followed by a summary of the nanodiamond preparation methods. Finally, we present a discussion about the undoped and boron-doped nanocrystalline diamond and their characteristics, electrochemical properties, and practical applications.

Chemical vapor deposition diamond thin films growth on Ti6AL4V using the Surfatron system

Diamond films with small grain size, good quality and high grain density were deposited on Ti6Al4V substrates using a technique assisted by surface wave-guide microwave discharge, the Surfatron system. The grain density was studied as a function of the film growth time in order to compare two different substrate preparation techniques: conventional ultrasonic bath in hexane and diamond powder only, and carbon ion sub-implantation with the same ultrasonic bath. The titanium carbide (TiC) interface formation as a function of the grain density was evaluated using X-ray diffraction (XRD) and scanning electron microscopy (SEM). Diamond quality was also analyzed by Raman scattering spectroscopy.

Filmes de nanodiamantes para aplicações em sistemas eletroquímicos e tecnologia aeroespacial

NANODIAMOND FILMS FOR APPLICATIONS IN ELECTROCHEMICAL SYSTEMS AND AERONAUTICS AND SPACE TECHNOLOGY. The goal of this work is to show the use of undoped nanodiamond films as a new material for electrochemical and aerospace applications. Correlation between the applications and physico-chemical features of nano and conventional CVD polycrystalline diamond films are presented. An important and innovative application of these nanodiamonds is organic electrosynthesis, including pharmaceutical and water disinfection products, as well as electroanalytical applications, for example, development of biosensors for detection of glucose, glutamate and dopamine. In aeronautics and space developments, these nanodiamonds could be used as electrodes in rechargable batteries and in tribological investigations.

Raman analyses of residual stress in diamond thin films grown on Ti6Al4V alloy

The stress evolution in diamond films grown on Ti6Al4V was investigated in order to develop a comprehensive view of the residual stress formation. Residual stress is composed of intrinsic stress induced during diamond film growth and extrinsic stress caused by the different thermal expansion coefficients between the film and substrate. In the coalescence stage it has been observed that the residual stress is dominated by the microstructure, whereas on continuous films, the thermal stress is more important. In this work diamond thin films with small grain size and good size and good quality were obtained in a surface wave-guide microwave discharge, the Surfatron system, with a negative bias voltage applied between the plasma shell and substrate. For above of -100V applied bias, the ratio of carbon sp3/sp2 bond may increase and the nucleation rate increase arising the high value at the -250V applied bias. Stress measurements and sp3 content in the film were studied by Raman scattering spectroscopy. The total residual stress is compressive and varied from -1.52 to -1.48 GPa between 0 and -200 V applied bias, respectively, and above the -200 V, the compressive residual stress increased drastically to -1.80 GPa. The diamond nucleation density was evaluated by top view SEM images.

Fourier Transform Infrared Spectroscopic Study of Boron-Doped Micro/Nano/Ultrananocrystalline Diamond Prepared by Chemical Vapor Deposition

Boron-doped diamond (BDD) films were grown with different grain sizes. The films were deposited on silicon substrate after a suitable pre-treatment in a hot filament assisted by chemical vapor deposition (CVD) reactor in Ar/H2/CH4 gas mixtures. The addition of argon to the growth gas mixture clearly revealed the transition from nanocrystalline (BDND) to ultrananocrystalline (BDUND) diamond films. Raman spectroscopy results of BDD, BDND and BDUND exhibited a good quality diamond films considering the diamond defined peak. Fourier Transform Infrared Spectroscopy (FTIR) spectra indicated carbonyl groups and B-C in BDND and BDUND films, while the microcrystalline BDD films showed only C-H bonds and boron-carbon (B-C), without the presence of oxygen and unsaturated species. Therefore, the carbonyl presence in the nanocrystalline films is mainly due to oxidation of transpolyacetylene present at the film grain boundaries. The transition became pronounced in the gas mixture with 60% of Ar, and the microcrystalline films were totally transformed in nanocrystalline diamond at 70% of Ar.

Electrodeposition of Te and Cu Thin Films on Boron Doped Diamond (BDD) Electrode

This study was motivated by the relevance of Cu-Te system applications such as, highly efficient solar cells, photo-diode devices and various hetero-junction electronic components where they are used as p-type semiconductors [1]. Copper tellurides also exhibit technological interest due to their potential application in thermoelectric devices [2]. However, these compounds have rarely been the subject of study, and have been prepared only through dry methods, such as, sputtering and chemical vapor deposition. In this work the electrodeposition method was used to obtain the Cu, Te and Cu-Te thin films. The advantages of electrodeposition include the fact that most compound semiconductor is obtained at or near room temperature, which is considered low temperature deposition. Electrodeposition also promotes controlled growth and it is generally a low cost methodology when compared to the dry methods. Besides, BDD electrodes have received great attention due to its unique characteristics such as, inert surface with low adsorption properties, remarkable corrosion stability (even in strong acidic media), and wide working potential window in aqueous and non-aqueous electrolytes. In this way, the aim of this work is to study the electrodeposition process of Te, Cu, as well as Cu–Te system on BDD electrodes. The electrolytes were prepared with HClO4, CuSO4, TeO2 and water purified by reverse osmosis. Prior to the experiments, the solutions were dearated with N2 for 10 min. BDD films were grown on Si substrate by chemical vapor deposition (CVD) in a hot filament reactor during 6 hours. It was utilized a gaseous mixture of 99% vol. H2 and 1% vol. CH4 with a pressure of 50 torr. The boron doping was obtained from H2 forced to pass through a bubbler containing B2O3 dissolved in CH3OH. The H2 and B2O3/CH3OH/H2 were controlled in order to obtain the desired B/C ratio in CH3OH. From the Mott Schottky plot, the doping level was estimated to approximately 10 boron atoms.cm [3]. BDD films were used as working electrode. A platinum wire serves as a counter electrode and Ag/AgCl electrode was used as reference. The cyclic voltammetric experiments were performed using a potentiostat/galvanostat Autolab PGSTAT 302.

Investigation of Boron Doped Nanocrystalline Diamond Films Grown on Porous Silicon Substrate under Different Doping Concentrations

The production and characterization of porous silicon (PS) samples were studied as well as their use as substrates to grow boron doped nanocrystalline diamond (NCD) films. PS represents a suitable material for diamond growth due to its large number of nucleation sites and surface area, becoming an excellent material for porous electrodes. NCD films were grown by chemical vapor deposition (CVD) technique by balancing H2/CH4/Ar gas mixture, at two different boron levels. Doping was conducted by an additional hydrogen line passing through a bubbler containing B2O3 dissolved in methanol. Two ratios of boron/carbon were used of 2000 and 20000 ppm in the bubbler solution. Scanning electron microscopy, Raman spectroscopy and X-ray diffraction were used to characterize the films as well as the PS substrate. Results showed that it is possible to obtain NCD films on PS substrate with good quality at different doping levels.

Nanocrystalline Diamond Films Prepared with Different Diamond Seeding Processes of 4 Nm and 0.25 Μm Diamond Powders

The growth of diamond films in metastable condition occurs in two steps: nucleation and growth of crystals. Studies have shown that the nucleation process is the most critical step and essential to optimize the properties of the diamond, but its understanding is still very limited. Furthermore, the nucleation process is directly related to the pretreatment applied to the surface of the substrate: cleaning the surface and seeding. When the substrate is silicon, it is cleaned with acetone and scratching with diamond particles dispersed in a suitable solvent followed by ultrasonic agitation (nucleation rate = 109 part/cm2). However, research has demonstrated that the use of diamond nanoparticles (ND) prepared with the use of a powerful ultrasound (750W) provides nucleation density much higher (1012 part/cm2) compared to that processed with larger size particles. This work demonstrates that diamond films prepared with ND different solutions exhibit differences in relation to diamond films prepared using diamond particle dispersed in an organic solvent. Morphological analysis and the quality of the films were evaluated by Scanning Electron Microscopy, Optical Perfilometry and Raman Scattering Spectroscopy.

Boron-Doped Ultra/Nanocrystalline Diamond Films Obtained with Different Growth Times and Boron Doping Levels

In this work, the achievement and characterization of boron-doped nanocrystalline diamond films is presented. A series of experiments varying boron doping levels from 2,000 to 30,000 ppm and film growth times during 6, 10 and 16 h were performed. These films were analyzed by Scanning Electron Microscoy (SEM), Atomic Force Microscopy (AFM), Raman spectroscopy and Cyclic Voltammetry (CV) measurements. The results showed that the films presented two morphologies: ultra and nanocrystalline diamond. From Raman spectroscopy, the doping level increase for all the films, independent of growth time, increased the boron acceptor number and it was confirmed by Mott-Schottky plot (MSP). Electrochemical response showed the influence of boron content in the work potential window, mainly for films grown during 6 h. However, the reversibility was almost independent on the boron content for samples grown during 16 h.