We review the principles of formation, physical properties, and current or envisaged applications for a wide range of carbon allotropic forms. We discuss experimental and theoretical advances relating to staple zero-, one-, and two-dimensional carbon structures, such as fullerenes, carbon nanotubes, and graphene. In addition we emphasize research on emerging carbon allotropes (carbon nanoscrolls, funnels, etc) that result from combining or deforming allotropic forms with well-defined dimensionality. Such materials fall in-between clearly delineated dimensional categories and consequently exhibit unique characteristics that are promising for electronic, optical, and mechanical applications. We also consider other approaches to tuning properties of carbon-based materials, such as chemical functionalization, intentional introduction of structural disorder, and placement of guest atoms or molecules inside hollow structures. Finally, we discuss the properties of and experimental methods for studying zero-dimensional systems (paramagnetic nitrogen impurity atoms) in diamond matrix. The review emphasizes the interplay between the various material properties of carbon-based nanostructures and the designs for nanoscale devices that rely on synergistic combinations of these properties. For example, an electromechanical vibrator, a strain sensor, a nanodynamometer, and a nanoelectromechanical memory cell that we describe exploit both electronic and nanomechanical properties of low-dimensional carbon structures, a reed switch and a magnetic field sensor use magnetic and nanomechanical properties, a maser based on nitrogen-doped diamond uses thermal and optoelectronic properties, etc. All presented device concepts have been validated by calculations, and some have been implemented experimentally.

A quasi-classical model of ionization equilibrium in the p-type diamond between hydrogen-like acceptors (boron atoms which substitute carbon atoms in the crystal lattice) and holes in the valence band (v-band) is proposed. The model is applicable on the insulator side of the insulatormetal concentration phase transition (Mott transition) in p-Dia:B crystals. The densities of the spatial distributions of impurity atoms (acceptors and donors) and of holes in the crystal are considered to be Poissonian, and the fluctuations of their electrostatic potential energy are considered to be Gaussian. The model accounts for the decrease in thermal ionization energy of boron atoms with increasing concentration, as well as for electrostatic fluctuations due to the Coulomb interaction limited to two nearest point charges (impurity ions and holes). The mobility edge of holes in the v-band is assumed to be equal to the sum of the threshold energy for diffusion percolation and the exchange energy of the holes. On the basis of the virial theorem, the temperature T j is determined, in the vicinity of which the dc band-like conductivity of holes in the v-band is approximately equal to the hopping conductivity of holes via the boron atoms. For compensation ratio (hydrogen-like donor to acceptor concentration ratio) K % 0.15 and temperature T j , the concentration of "free" holes in the v-band and their jumping (turbulent) drift mobility are calculated. Dependence of the differential energy of thermal ionization of boron atoms (at the temperature 3T j /2) as a function of their concentration N is calculated. The estimates of the extrapolated into the temperature region close to T j hopping drift mobility of holes hopping from the boron atoms in the charge states (0) to the boron atoms in the charge states (À1) are given. Calculations based on the model show good agreement with electrical conductivity and Hall effect measurements for p-type diamond with boron atom concentrations in the range from 3 Â 10 17 to 3 Â 10 20 cm À3 , i.e., up to the Mott transition. The model uses no fitting parameters. Published by AIP Publishing.

No abstract

No abstract

For nondegenerate bulk semiconductors, we have used the virial theorem to derive an expression for the temperature Tj of the transition from the regime of “free” motion of electrons in the c-band (or holes in the υ-band) to their hopping motion between donors (or acceptors). Distribution of impurities over the crystal was assumed to be of the Poisson type, while distribution of their energy levels was assumed to be of the Gaussian type. Our conception of the virial theorem implementation is that the transition from the band-like conduction to hopping conduction occurs when the average kinetic energy of an electron in the c-band (hole in the υ-band) is equal to the half of the absolute value of the average energy of the Coulomb interaction of an electron (hole) with the nearest neighbor ionized donor (acceptor). Calculations of Tj according to our model agree with experimental data for crystals of Ge, Si, diamond, etc. up to the concentrations of a hydrogen-like impurity, at which the phase insulator-metal transition (Mott transition) occurs. Under the temperature Th ≈ Tj /3, when the nearest neighbor hopping conduction via impurity atoms dominates, we obtained expressions for the electrostatic field screening length Λh in the Debye-Hückel approximation, taking into account a nonzero width of the impurity energy band. It is shown that the measurements of quasistatic capacitance of the semiconductor in a metal-insulator-semiconductor structure in the regime of the flat bands at the temperature Th allow to determine the concentration of doping impurity or its compensation ratio by knowing Λh.