A. T. Dideikin

Ultradisperse Diamond Cluster Aggregation Studied by Atomic Force Microscopy

The structure of ultradisperse diamond (UDD) conglomerates was studied by scanning atomic-force microscopy (AFM). The UDD layers were prepared from a detonation carbon obtained by synthesis in an aqueous medium. The finest details in the AFM images of UDD layers are of the order of 10 nm, which does not allow individual 4.5-nm diamond clusters to be distinguished. The UDD conglomerates deposited and dried on a silicon substrate surface, exhibit certain deformation and differ from the initial (apparently, spherical) shape. This may imply that cohesion between the UDD nanoparticles is comparable with their adhesion to the silicon substrate.

Effect of hydrogen on the structure of ultradisperse diamond

The paper reports on a study of the effect of annealing in hydrogen on the structural phase transition in clusters of ultradisperse diamond (UDD) obtained by the detonation method. The samples studied were of two types, namely, prepared by the “dry” and “wet” techniques, which differ in the cooling rate of the detonation products and, accordingly, in the structure of the diamond nanocluster shell. It is shown that, irrespective of the type of synthesis, the relative content of the diamond (sp3) phase increases within the anneal temperature range of 450 to 750°C, the increase being more pronounced in the samples prepared by “dry” synthesis. A model accounting for the observed structural transformation processes is discussed. A hypothesis of the possibility of compacting UDD clusters into bulk single crystals is put forward.

Electrosurface properties of single-crystalline detonation nanodiamond particles obtained by air annealing of their agglomerates

A complex study of electrosurface properties has been performed for single-crystalline detonation nanodiamond particles with sizes of 4–5 nm obtained by air annealing of their agglomerates. FTIR spectroscopy and X-ray photoelectron spectroscopy data indicate that the investigated properties result from the presence of two types of ionogenic functional groups on the particle surface, i.e., acidic carboxyl and amphoteric hydroxyl groups. Acid-base potentiometric titration, laser Doppler electrophoresis, and conductometry have been employed to measure the ΓH+(pH) and ΓOH-(pH) adsorption isotherms of potential-determining ions, as well as the pH dependences (in a pH range of 3.5–10.5) of the surface charge density, electrophoretic mobility, and specific surface conductivity of detonation nanodiamond particles in aqueous 0.0001–0.01 M KCl solutions.

Small-angle scattering from polydisperse particles with a diffusive surface

Particles with a diffusive surface, characterized by a deviation from the Porod power-law asymptotic behavior in small-angle scattering towards an exponent below −4, are considered with respect to the polydispersity problem. The case of low diffusivity is emphasized, which allows the description of the scattering length density distribution within spherically isotropic particles in terms of a continuous profile. This significantly simplifies the analysis of the particle-size distribution function, as well as the change in the scattering invariants under contrast variation. The effect of the solvent scattering contribution on the apparent exponent value in power-law-type scattering and related restrictions in the analysis of the scattering curves are discussed. The principal features and possibilities of the developed approach are illustrated in the treatment of experimental small-angle neutron scattering data from liquid dispersions of detonation nanodiamond. The obtained scattering length density profile of the particles fits well with a transition of the diamond states of carbon inside the crystallites to graphite-like states at the surface, and it is possible to combine the diffusive properties of the surface with the experimental shift of the mean scattering length density of the particles compared with that of pure diamond. The moments of the particle-size distribution are derived and analyzed in terms of the lognormal approximation.

Single-layer graphene oxide films on a silicon surface

A method is proposed to produce large-area single-layer graphene oxide films on the surface of semiconductor silicon wafers by precipitation from aqueous suspensions. Graphene oxide is synthesized from natural crystalline graphite during chemical oxidation and represents a wide-gap insulator. Single-layer graphene with a homogeneous-fragment size up to 50 μm can be formed by the reduction of graphene oxide films, and this size is significantly larger than those achieved to date.

Free graphene films obtained from thermally expanded graphite

A method of obtaining free graphene films using intercalation and subsequent thermal expansion of crystalline graphite is suggested. Thermally expanded graphite prepared by microwave irradiation is examined under a scanning electron microscope. It is found that it contains fragments of free graphene films. The conclusion is drawn that this method is promising for obtaining graphene suitable for experimental research.

Photodetectors based on metal-tunnel insulator-semiconductor structures

Abstract The photoelectrical effects in metal-insulator-semiconductor (MIS) structures with tunnelling-transparent insulator are reviewed. It is shown that, based on such structures, photodetectors of the following types can be created: photodetectors with the lowest value of the dark current; two types of photodetectors with internal photocurrent multiplication (on the majority-carrier tunnelling through the insulator and on the avalanche-current multiplication); and light-controlled switching devices. The parameters of all these types of photodetectors so far achieved are analysed and the physical processes that determine the main characteristics of such detectors are considered. It is shown that the considered photodetectors can be realized not only with tunnelling but also with different mechanisms of the insulator conduction. The considered photoelectrical effects can be used as the basis of photodetectors using different semiconductor materials.

Formation of nanodiamond films from aqueous suspensions during spin coating

The formation of multifunctional ordered arrays of detonation diamond particles is studied during self-assembling in spin coating of films of evaporating microdroplets. It is shown that the most homogeneous layer of diamond particles on a crystalline silicon substrate forms at a rate of substrate rotation of 8000 min–1, whereas a relation between the distribution of particles and the radius is clearly detected at rates of about 2000 min–1. As the rate of substrate rotation increases from 2500 to 8000 min–1, the density of the coating of a silicon substrate with diamond nanoparticles decreases approximately threefold. A model is proposed to estimate the increase in the number of individual diamond “points” with the substrate rotation frequency.

Formation of detonation diamond layers on silicon by the aerosol method

An aerosol method for deposition of nanometer-thick layers of detonation diamonds has been developed. Application of a suspension of deagglomerated diamond particles onto substrates from an aerosol provides deposition of small-size drops, with the ultrasonic spraying of the suspension precluding formation of secondary agglomerates of nanodiamond particles in the course of sample drying. The layers are promising for high-precision studies of the structure and chemical composition of the surface of isolated nanodiamond particles.

Counterion condensation in hydrosols of single-crystalline detonation nanodiamond particles obtained by air annealing of their agglomerates

The pattern of previously recorded dependences of the specific surface charge and electrophoretic mobility of monodisperse detonation nanodiamond particles on pH of aqueous KCl solutions suggests that counterions are condensed on the particle surface. Counterion condensation is considered in terms of the Levin model, and the experimental ratios between the densities of the electrokinetic and surface charges of dispersed particles, as well as the fractions of condensed counterions, are calculated as depending on pH and KCl concentration in nanodiamond hydrosols. The obtained dependences lead to the conclusion that counterion condensation on the surface of detonation nanodiamond particles does indeed take place.