Diamond Nanocrystallites Research Articles

Chemical Functionalization of Nanodiamond by Amino Groups: An X-Ray Photoelectron Spectroscopy Study

The development of chemical functionalization techniques for diamond nanocrystallites opens up ways with a view to altering their solubility in different solvents, improve interfacial adhesion of nanodiamonds with a composite matrix in new materials, and provide new possibilities for the modification of the electronic properties of nanodiamond crystallites. In this work, we present results on the chemical functionalization of nanodiamonds by amino groups using ammonia as a nitrogenation agent. Nanodiamond material used was formed by the detonation technique with average crystallite sizes of 4-5 nm. The final materials and intermediates products were characterized by Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). Chemical functionalization of nanodiamonds by amino groups could enable the preparation of new nylon nano-composite materials. Presence of surface amino groups could alter pH of nanodiamond colloids towards basic values and improve colloidal stability of nanodiamond suspensions at pH close to 7. This could enable syntheses of new drug delivery systems based on nanodiamonds.

SYNTHESIS OF NANOCRYSTALLINE DIAMOND FILMS ON MOLYBDENUM SUBSTRATE BY FLAME COMBUSTION METHOD

The flame combustion method enables the synthesis of diamond using acetylene-oxygen gas flame combustion in ambient atmosphere. It has various advantages over other methods. In this study, to obtain nanocrystalline diamond films and to achieve good adhesion, diamond films were synthesized by flame combustion using a mixture of commercial or high purity acetylene and oxygen gas with the addition of nitrogen gas. Nitrogen gas added as the nanocrystalline diamond promotion agent; nitrogen flow rate was varied. According to the results, at the mixture of commercial acetylene and oxygen gas, as nitrogen flow rate was increased, the diamond nanocrystallites was high density on the microcrystallites. At the mixture of high purity acetylene and oxygen gas, the optimal nitrogen flow rate was 0.500 cm3/s, and the diamond nanocrystallites was synthesized continuously on the diamond microcrystallites. They sowed very high density.

Preparation of Diamond Nanocrystallites in Powder by Using a Coaxial Arc Plasma Gun

ABSTRACTWe suggest a new method for fabricating diamond nanoclusters by employing a coaxial arc plasma gun. Diamond powder comprised of diamond nanoclusters and amorphous carbon was fabricated in vacuum and a hydrogen atmosphere, and the diamond crystallite sizes were estimated to be 1.8, 2.3, and 2.3 nm for the powders prepared at hydrogen pressures of 0, 53.3, and 159.6 Pa respectively, from the X-ray diffraction peaks. The hydrogen ambient gas is not necessarily required for the diamond nanoclusters formation. We consider that this method enables us to form diamond nanoclusters in nucleation owing to a supersaturated condition at a facing plate located in front of an arc plasma gun.

Nanodiamond crystallites embedded in carbon films prepared by thermionic vacuum arc method

Nanostructured carbon films with thicknesses of 100 and 200 nm have been deposited from pure vapour carbon plasma using an original thermionic vacuum arc method. Silicon single crystalline wafers, glass and stainless steel held at 400 °C were used for substrates. The films consist of diamond nanoparticles of 5 nm diameter on the average embedded in a disordered graphite matrix as revealed by HRTEM, XPS and visible Raman measurements. The graphitic cluster diameters L a range from 1.5 to 2.3 nm. Thicker films (200 nm) on stainless steel exhibit the largest clusters.

UNCD/a-C nanocomposite films for biotechnological applications

Ultrananocrystalline diamond/amorphous carbon nanocomposite films (UNCD/a-C) have been deposited by microwave plasma chemical vapor deposition from a 17% CH4/N2 mixture. The films consist of diamond nanocrystallites of 3–5nm embedded in an amorphous carbon matrix of 1–1.5nm width. In a first series of experiments it is shown that as-grown UNCD/a-C films are hydrogen-terminated, conductive and very stable. Furthermore, by plasma- and photochemical treatments the H-termination can either be improved or replaced by terminating OH or F functionalities, whereas chemical room temperature processes to change the termination failed. A second set of investigations concerns the functionalization of differently terminated UNCD surfaces. Processes are discussed to bind DNA on H-terminated UNCD and to deposit an anti-fouling poly(ethylene glycol) layer on OH-terminated films. A third series of experiments shows that UNCD surfaces are not prone to unspecific interactions with highly-fouling proteins such as bovine serum albumin (BSA) but nevertheless some interaction will take place. However, the amount of adsorption and also the ratio of BSA and fibrinogen adsorption, which is of importance for the hemocompatibility of a surface, can be adjusted by the surface termination. Finally, it will be shown that continuous as-grown UNCD surfaces are bioinert and not cytotoxic for a variety of different cell lines.

Influence of CH4 on the morphology of nanocrystalline diamond films deposited by Ar rich microwave plasma

The influences of the process gases, such as methane and nitrogen concentration on the morphology of nanocrystallites diamond films are assessed. It has been found that the concentration of CH4 in the reactant gases is important to control the morphology of diamond nanocrystallites. The morphology of nanocrystallites changes from granular to rodlike shape by changing methane concentration in Ar/H2/CH4 microwave plasma. The addition of nitrogen is considered to be helpful in the formation of graphite content and for increasing the deposition rate. No considerable changes in the morphology of diamond nanocrystallites were observed by varying nitrogen concentration in the feed gases as observed by scanning electron microscopy. Although Raman spectroscopy indicated that the amount of sp2-bonded carbon increased by the addition of nitrogen in the plasma. The high concentration of methane in the gas mixture due to the presence of argon rich environment is suggested to be responsible for the formation of diamond nanorods.

Electrical properties of ultrananocrystalline diamond/amorphous carbon nanocomposite films

The electrical surface properties of ultrananocrystalline diamond/amorphous carbon composite films have been investigated by four-point probe I/V and Hall measurements, whereas impedance spectroscopy has been used to establish the electrical bulk properties of the films. It turned out that the surface is p-type conductive with a resistivity of 0.14 Ω cm and a sheet carrier concentration of 7.6 × 10 13 cm − 2. The bulk resistivity is higher by almost seven orders of magnitude (1.3 × 10 6 Ω cm). The bulk conduction is thermally activated with an apparent activation energy of 0.17 eV. From Cole–Cole plots of the impedance spectra it can be concluded that there are three different contributions to the bulk conductivity. In order to try to identify these three components contributing to the electrical bulk conduction, Raman spectra have been recorded at five different wavelengths from the IR to UV region. These measurements showed that the UNCD/a-C films consist of at least three components: diamond nanocrystallites, an amorphous carbon matrix, and trans-polyacetylene-like structures probably at the interface between these two.

Ultrananocrystalline Diamond / Amorphous Carbon Composite Films – Deposition, Characterization and Applications

UNCD/a-C composite films have been deposited by microwave plasma chemical vapour deposition from methane/nitrogen mixtures with 17% CH4 in the temperature range 500-770°C on various substrates such as monocrystalline silicon wafers, polycrystalline diamond, c-BN, TiN, GaAs, and other materials of technological interest. The resulting films have been thoroughly characterized with respect to their morphology, crystallinity, composition, and bonding structure. It was found that they are composed of diamond nanocrystallites (3-5 nm in diameter) surrounded by 1-1.5 nm amorphous carbon grain boundary material; the ratio of the volume fractions of crystalline and amorphous phase is close to unity. The investigations of the application-relevant properties of the UNCD/a-C films revealed that they are attractive for a number of mechanical, tribological, structural, and biomedical applications.

Spectroscopic characterisation and discussion of nanocarbon ensembles in electrical applications

Nanocarbon ensembles (NCE) composed of ultrananocrystalline diamond (UNCD) powders by reacting with methane at 1200 K are complementarily characterised by optical microscope (OM), Raman, fourier transform infrared spectroscopy (FT-IR), x-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). The porous bulk material of NCE are further confirmed to be composed of nanodiamond crystallites surrounded and networked by nanographite-like phases. The Raman scattering overtone of nanographite phases in NCE is newly observed. H inclusion in NCE is also shown by FT-IR. The XPS results first reveal the disorderliness of the sp2- and sp3-C bonding environment in NCE. The AFM morphology of NCE is shown for the first time in this work. The porosity and H inclusion may contribute to the low thermoelectric power factor of NCE. However, NCE may be another good nanocarbon material for field emission applications. An alternative one-step synthesis of NCE by spark plasma sintering (SPS) is suggested to prepare the inhomogeneous B-doped NCE nanocarbon materials for thermoelectric applications.

Electron spin resonance detection and identification of nitrogen centers in nanodiamonds

Individual nitrogen centers N0 and nitrogen pairs N2+ have been detected and identified in natural diamond nanocrystals by means of the high-frequency electron spin resonance method. The N0 nitrogen centers have been observed in synthetic diamond nanocrystallites with a size of less than 10 nm produced by high-temperature high-pressure sintering of detonation nanodiamonds. Thus, the possibility of the stable state of impurity nitrogen atoms in diamond nanoparticles has been demonstrated.

Preparation and characterization of green fluorescent nanodiamonds for biological applications

Green fluorescent nanodiamonds (denoted as gFNDs) have been produced and characterized for use as cellular markers and/or labels. The gFND particles, containing a high concentration of N–V–N (or H3) centers, were prepared by radiation damage of type Ia natural diamond nanocrystallites with either a home-built 40-keV He + beam or a research-grade 3-MeV H + beam, followed by thermal annealing at 800 °C. Prior to the irradiation treatment, infrared spectroscopy of C–N stretches (at 1282 cm − 1 ) of natural diamond single crystals revealed a nitrogen concentration in the range of 900 ppm. Irradiation and annealing of the specimens led to the emergence of a broad absorption band at ~ 470 nm, corresponding to the phonon sideband of the electronic transition of the H3 center. Measuring the integrated absorption coefficient of the zero-phonon line (at 503 nm) of this center at liquid nitrogen temperature suggested a H3 density of 1.7 × 10 18 centers/cm 3 (or 10 ppm). A similarly high concentration of the defect centers was estimated for natural diamond nanocrystallites treated under the same experimental conditions. The centers emitted green light ( λ em = 530 nm) upon illumination by a blue laser ( λ ex = 473 nm or 488 nm). Applications of this novel nanomaterial as fluorescent cellular markers were demonstrated with both confocal fluorescence microscopy and flow cytometry of 70-nm-sized gFND particles uptaken by live HeLa cells through endocytosis.

Mass production and dynamic imaging of fluorescent nanodiamonds

Fluorescent nanodiamond is a new nanomaterial that possesses several useful properties, including good biocompatibility, excellent photostability and facile surface functionalizability. Moreover, when excited by a laser, defect centres within the nanodiamond emit photons that are capable of penetrating tissue, making them well suited for biological imaging applications. Here, we show that bright fluorescent nanodiamonds can be produced in large quantities by irradiating synthetic diamond nanocrystallites with helium ions. The fluorescence is sufficiently bright and stable to allow three-dimensional tracking of a single particle within the cell by means of either one- or two-photon-excited fluorescence microscopy. The excellent photophysical characteristics are maintained for particles as small as 25 nm, suggesting that fluorescent nanodiamond is an ideal probe for long-term tracking and imaging in vivo, with good temporal and spatial resolution.

Stability of hydrogenated nanodiamonds under extreme ultraviolet irradiation

It is generally accepted that diamond is resistant to a wide spectrum of electromagnetic radiation from the ultraviolet through to the soft X-ray range, which makes it very attractive for the fabrication of diamond-based photodetectors. However the effect of photon radiation on the diamond structure has not yet been examined. In the work presented here, photoelectron spectroscopy has been used to study the graphitization of nanodiamond crystallites exposed to extreme ultraviolet radiation. Under such irradiation, the surface hydrogen groups and graphite species are found to prevent graphitization. The mechanism of radiation-induced nanodiamond graphitization is discussed.

Structure and Field Emission Study of Hot Filament Chemical Vapor Deposited Nanocrystalline Diamond Films

Grain sizes of the hot filament chemical vapor deposited diamond films were found to decrease from 3 µm to 15 nm with increase in substrate temperature during deposition from 1023 K to 1173 K respectively. These films were deposited on p‐type silicon (100) substrate using methane and hydrogen as reactant gases. Surface scanning electron micrographs of the deposited films confirmed that diamond grain size was strongly dependent on the substrate temperature. High resolution transmission electron microscope studies of the nanodiamond films showed lattice fringes corresponding to graphitic planes in the interface region between two diamond nanocrystallites. Field emission studies carried out in a diode geometry revealed that nanodiamond films were better emitters than microcrystalline films, which is attributed to increase in graphitic grain boundaries with decrease in grain size.

Synthesis of nanocrystalline diamonds by microwave plasma

Nanocrystalline diamonds, varying in size from 40 to 400 nm, with random faceting were grown without the help of initial nucleation sites on nickel substrates as seen by scanning electron micrographs. These carbonaceous films were deposited in a microwave plasma reactor using hexane/nitrogen based chemical vapour deposition. The substrate temperatures during deposition were varied from 400 to 600 °C. The morphological investigations obtained by scanning electron micrographs and atomic force microscopy revealed the presence of nanocrystallites with multifaceted structures. Micro Raman investigations were carried out on the deposited films, which conclusively inferred that the growth of nanodiamond crystallites seen in the scanning electron micrographs correlate with clear Raman peaks appearing at 1120 and 1140 cm−1. Nanoindentation analysis with atomic force microscopy has revealed that the carbonaceous deposition identified by the Raman line at ∼1140 cm−1, in fact, is related to nanodiamond on account of its hardness which was ∼30 GPa. X-ray diffraction data supported this fact.

Adsorption and hydrolytic activity of lysozyme on diamond nanocrystallites

Oxidative-acid-treated nanodiamonds exhibit high affinity for proteins, a property well suited for immobilization of enzymes for biotechnological application. Using lysozyme as an example, this work demonstrates that the enzyme can retain much of its activity after physical adsorption to the surfaces of 100-nm diamond crystallites. The activity relative to that of free lysozyme in solution is ∼ 60% at the maximum surface coverage of 50% and pH 5. While the enzymatic activity decreases as the surface coverage is lowered, it can be recovered by blocking the empty sites on the surface with supplementary proteins such as cytochrome c to create a more “crowded” environment. A relative activity up to 70% can be attained at a partial coverage of 20%.

Diamond nanocrystals and amorphous SiO x nanowires formed by rapid thermal annealing of carbon film

Rapid thermal annealing (RTA) has been performed on the carbon films prepared by radio frequency plasma-enhanced chemical vapor deposition on Si substrate. The RTA at 800 °C for 60 s leads to the formation of many diamond nanocrystallites agglomerating on the film surface. Higher temperature RTA at 1100 °C for 60 s induces the high-density amorphous SiO x ( x = 1.2) nanowires on the film surface without diamond nanocrystallites. At both the RTA temperatures, a well-oriented SiC interlayer is also formed simultaneously. The sp 3 sites in the carbon film and the oxygen during the RTA treatment as well as the RTA temperature are considered to play important roles in determining the final reaction products.

Influence of the substrate nature on the properties of nanocrystalline diamond films

Nanocrystalline diamond/amorphous carbon (NCD/a-C) nanocomposite films have been deposited by microwave plasma CVD from CH 4/N 2 mixtures on a variety of substrates such as polycrystalline diamond, cubic boron nitride, silicon, titanium nitride, and Ti–6Al–4V. The study aimed to investigate the influence of the chemical nature of the substrate, the surface roughness, and the pretreatment of the substrate on the nucleation, the bulk structure, and the mechanical and tribological properties of the NCD/a-C films. The present paper is especially devoted to the bulk structure of the films. By means of X-ray diffraction (XRD), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) it is shown that the bulk properties of the films are not affected by the properties of the substrate although these have a strong influence on the nucleation behaviour. XRD measurements show that – irrespective of the substrate used – the films contain diamond nanocrystallites of 3–5 nm diameter. From the Raman spectra it can be inferred that the crystallite/matrix ratio does not vary. The XPS measurements, finally, show that there are no great changes in the sp 2/sp 3 ratio of the matrix. These findings are discussed in view of possible growth mechanisms of NCD/a-C nanocomposite films.

Self-organization of diamond nanocrystallites in a low-pressure microwave plasma

The self-organization effect is found in diamond nanocrystallites that arise in polymer-like hydrocarbon films growing in the nonequilibrium microwave plasma of volatile carboniferous materials at a low substrate temperature. The nature of this effect (specifically, the conditions of formation of the hydrocarbon substrate, its role during diamond nanocrystallite growth, and ways of controlling the size and concentration of the crystallites) is studied.

Chemical vapour deposition of oriented diamond nanocrystallites by a bias-enhancednucleation method

A microwave plasma chemical vapour deposition (MPCVD) system hasbeen used to deposit nanometre-sized single-crystalline diamonds on1 × 1 cm2 Si(100) substrates. The distribution of deposited diamonds has good uniformity over thewhole Si substrate surface by using a dome-shaped Mo anode which allows the applicationof bias-enhanced nucleation. The morphology and crystallinity of the deposits on Si werecharacterized by scanning electron microscopy (SEM) and transmission electron microscopy(TEM) with electron diffraction and lattice images. SEM and TEM observations show thatoriented diamond nuclei as single crystals with facets can form on self-formed Si conesthrough epitaxial SiC within a short bias period. After a longer bias time, it has beenobserved that polycrystalline diamonds formed as a result of secondary nucleation.