Catálogo de publicaciones - libros

We describe a way of combining, in the same technological cycle, the nanodiamond particle injection from a suspension and the growth of diamond films by microwave plasma chemical vapor deposition (MPCVD). The breaking of injected nanodiamond aggregates into particles of about 100 nm in size when they hit a substrate provides a nucleation density over 10 cm. The films produced from a CH+H mixture with a periodic injection of ND particles during the film growth are found to consist of diamond nanocrystallites with the traces of -hybridized carbon on them.

The density functional theory and non-empirical pseudopotentials were implemented to study the stabilization of ultra nanoclusters (C and C) of diamond by alkali (Li and K) and noble (Cu, Ag and Au) metals. It has been shown that copper is the best candidate to keep the diamond-like cluster geometries. Calculations show that epitaxial diamond films can be grown on copper substrates with geometry parameters closed to those of bulk diamond. The mean cohesive energy for the C(100) films is larger than that for the C(111) films; however, the C(100) films are more stable against the separation from the copper substrate. The latter fact explains why the preferable observed orientation of diamond microcrystallites on copper is the <111> direction.

We report experimental data on small angle X-ray scattering behind the detonation wave front in the high pressure zone, obtained using synchrotron radiation. A series of detonation experiments with ultradisperse diamond in oxygen and oxygen-free media have led us to the conclusion that diamond cannot be produced immediately behind the wave front. We believe that here there is a diamond-free zone and zones of diamond formation. Additional information on this region was derived from the electrical conductivity measurements. It was found that the time (as well as the site) of nanodiamond nucleation coincided with the beginning of unloading. The shock compression initiates the adamantan-diamond transition. These findings indicate that it is the C-H bonds, rather than the C-C bonds, which break up in the adamantan structure and that there is a fast diffusion of hydrogen through adamantan and explosives. A new model of detonation nanodiamond formation is suggested on the basis of our experimental results.

To analyse the process of detonation nanodiamond (UDD) synthesis, the positions of the melting and phase equilibrium curves in the carbon phase diagram were calculated for UDD particles of 1–10 nm in size. We also found the position of a set of triple points in the ranges of = 13.5–16.5 GPa and = 2210–4470K. This set of points indicates the area of liquid nanocarbon. The diamond area in the phase diagram was subdivided into three regions, depending on the nature of the nanoparticles: UDD and diamond, liquid nanocarbon, and amorphous nanoparticles. The parameters of explosives used in the UDD synthesis are found to lie within the liquid nanocarbon region. Therefore, the reaction zone of the detonation wave is the site of formation of carbon nanodroplets, which then crystallize to form UDD particles along a segment of the isotropic line of the detonation product spreading through the UDD area at = 16–10 GPa and = 3400–2900K. The curve for the detonation rate vs. the density of the explosive charge exhibits breaks that can be interpreted as being due to the onset and termination of nanocarbon melting rather than to UDD formation in the reaction zone.

Nanodiamond (ND) reactivity and the ease of graphitization limits the temperature range where it may be effectively used. At the same time new nanocarbons (NC) can be produced using controlled ND graphitization (namely: onion-like carbon (OLC), / nanocomposites, and nanographite). Here we briefly review data on the graphitization of diamond with emphasis on the low temperature graphitization at 1370–1870K and the properties of OLC.

A wide application of detonation nanodiamonds is hampered by their low purity and difficulties of making stable nanodiamond suspensions. These problems have not been adequately dealt with in available publications. Here we present an integrated conception of the nanodiamond structure and offer a practical solution to some of these problems. A detailed description and a schematic illustration of the detonation nanodiamond structure are presented. The structure-forming effect of nanodiamond particles on the ambient is interpreted. The pH of an aqueous suspension of nanodiamonds is determined and their behavior as a function of the pH is shown. We also analyse the mechanism of a prolonged water washing to remove excessive acidity, a factor determining the chemical purification time. A method is offered to improve essentially the quality of nanodiamonds and the stability of their aqueous suspensions by treating them with ammonia water (to an alkalescent medium), followed by heating to 200–240°C under pressure (so called “thermolysis”).

The long overdue disintegration/purification work of detonation nanodiamond (discovered 40 years ago) is in good progress. Here are described features of two novel processes adopted, stirred media milling and diamond carbon analysis. Contamination with bead material provides serious problem in the milling and preventive ways are discussed. Black color that appears as the disintegration proceeds is introduced. Necessity and principles of diamond analysis by integrated X-ray diffraction intensities and theoretically attainable highest purity are discussed.

This paper briefly discusses the advantages of commercial nanodiamond and analyses its structural and chemical impurities, polyfunctional surface termination, agglomeration, and other features that may restrict the ND application in academic research and industrial practice. We have designed and tested a novel approach to detonation nanodiamond purification and surface functionalization, using a high temperature treatment in gaseous media containing hydrogen and chlorine. A drastic change in the hydrophily (by a factor of 20) due to thermal treatment at 450’C in a CC14/Ar mixture is demonstrated. The characterization techniques employed (chemical analyses; Raman, FTIR, and ESR spectroscopy; chromatomass spectrometry) can provide a profound nanodiamond modification and its prescribed functionalization.

A combination of N(E) Auger spectroscopy, X-ray excitation (XAES), electron energy loss spectroscopy (EELS), and valence band (VB) XPS have been used to study nanodiamond (ND) particles. These methods have different information depths of 1–2, 5–7, and 10–12 monolayers (ML), respectively, and an inherent spectral structure in the identification of – -bonds. Our data show that the upper 1–2 ML of a ND particle consists of carbon atoms with -bonds, which differ from those in well- known carbon compounds. The ND core is made up of diamond. Chemical reactions of the carbon atoms with the particle have been studied in-situ and ex-situ. The crutial role of the upper monolayer in the diamond growth has been established for both cases.

A unique technology of nanodiamond surface modification is suggested which allows to separation of commercial nanodiamond powders into two fractions (F1 and F2), each possessing absolutely new properties as compared to the initial powder. Fl and F2 differ in size characteristics. Initial and modified nanodiamonds contain iron impurities and two types of nondiamond carbon. The color of the powders and hydrosols does not correlate with the content of non-diamond carbon. According to the EPR data, modified nanodiamonds possess a high level of diamond matrix shielding, and the extracted fractions differ in width of the basic transition area and in the SHF energy adsorption ratio. Due to this, Fl can be applied as precursors for CVD growth of nanocrystalline diamond and as field electron emission tips.