Nanothermodynamics as a tool to describe small objects of nature

An apparatus based on a thermodynamic method is developed to determine the parameters of nanoparticles. The essence of the applied approaches is an optimization procedure. In terms of this procedure, the sizes and structures of the objects are determined using the potential energy and Helmholtz energy as objective functions for solid and liquid particles, respectively. To find the thermodynamic functions of nanoparticles, the generally accepted frame of reference, the concept of supramolecule, and the main points of statistical thermodynamics are used. It is shown that the energy stored in nanoparticles is much higher than in macroscopic objects and also that the number of atomic and molecular species entering into nanoparticles should be considered as a state variable. Using the notion of phase as applied to nanoparticles, phase transformations are considered and an analogue of the capillary pressure is found in the frame of the classical approach.     

Nanowire formation by coalescence of small gold clusters inside carbon nanotubes

The coalescence of Au₁₃, Au₅₅ and Au₁₄₇ icosahedral clusters encapsulated inside single walled carbon nanotubes (CNTs) of different diameters are investigated using molecular dynamics simulation with semi-empirical potentials. Three steps needed for the formation of encapsulated nanowires are followed in detail, namely, the penetration of clusters in CNTs, the coalescence between two clusters inside CNTs and their accumulation to form wires. It is suggested that no significant energy barrier is encountered during the penetration of free clusters into CNTs provided the CNT radius is large enough, that is, about 0.3 nm larger than the cluster radius. The relative orientation of clusters imposed by the CNT favors their spontaneous coalescence. After coalescence of two clusters, the Au atoms are rearranged to form new structures of cylindrical symmetry that may be seven fold, six fold, five fold, helical or fcc depending on the CNT diameter. The thermal stability of these structures is discussed and the structural properties of nanowires formed by accumulation of many clusters in CNTs are analyzed in detail. A geometrical method is presented which allows the prediction of the structure of multi-shell helical wires, when knowing only the CNT radius. These modeling results suggest the possibility of synthesizing metallic nanowires with controlled diameter and structure by embedding clusters into nanotubes with suitable diameters.     

Like particle correlations as a tool to study the multiple production mechanism

The measurement of correlations between like pions in the inclusive processes a + b → π^± + π^± + X permits us to study the space-time mechanism of multiple production. Similar measurements for neutrons evaporated from highly excited nuclei give the shape of nuclei and their mean lives; for pions from the resonance decay - the mean resonance life.     

Fragmentation of highly excited small neutral carbon clusters

We present a combined experimental and theoretical study of fragmentation of small Cn clusters (n = 5,7,9) produced in charge transfer collisions of fast (nu = 2.6 a.u.) singly charged Cn+ clusters with He. Branching ratios for all possible fragmentation channels have been measured. Comparison with microcanonical Metropolis Monte Carlo simulations based on quantum chemistry calculations allows us to determine the energy distribution of the excited clusters just after the collision.     

Desorption of small ionic fragments from oligonucleotides induced by low energy carbon ions

The degradation of oligonucleotide films containing differing base sequences induced by 4 keV C⁺ ions has been studied experimentally. The oligonucleotides were deposited onto a gold coated stainless steel substrate and the anions and cations released from the films were analyzed by a quadrupole mass spectrometer. The total ion desorption yield was recorded as a function of time using a constant C⁺ ion flux of 6 × 10¹⁴ ions cm^-2 s^-1. At low fluences the formation of small ionic fragments was observed, whilst for fluences greater than 1.2 × 10¹⁸ ions cm^-2 molecules were sputtered from the substrate. In addition to studies of the influence of a particular base to the total cation desorption yield, the effect of base substitution with bromine was measured for negative ion desorption. These results showed a strong degradation of oligonucleotide films during ion bombardment.     

Triboluminescence,a new tool to investigate fracture-initiation time of crystals under stress

The present paper reports that triboluminescence (TBL) does not appear at the instant of impact of the load but a certain time lag is required for its appearance which depends on the value of the stress applied to the crystal. Since TBL appears in sugar crystals during the creation of new surfaces, the fracture-initiation time of the crystal has been taken to be the delay time in observing TBL pulse after the application of stress. The dependence of fracture-initiation time,t _f ^σ , of crystals on the stress, σ, may be expressed ast _f ^σ =t _o exp (− ασ), wheret _o and α are constants. The values of the lattice energy, and the change in lattice energy per unit stress, of sugar crystals have been calculated from TBL measurements and they have been found to be 21·2 kcal mole⁻¹ and 0·41 × 10⁻⁸ kcal mole⁻¹ dyne⁻¹ cm² respectively.     

Conductivity of a small metallic particle

The size-dependent ac-conductivity of a small metallic particle is studied for electrons enclosed in a box with random impurities. The exact wave functions and energies are calculated numerically up to 500 electrons, then the Kubo-formula is evaluated, and an ensemble average is performed. A strong size- and frequency dependence of the conductivity is found which is in good agreement with random matrix results. The size dependence of the dc-conductivity agrees qualitatively with microwave absorption measurements on submicron particles.     

Gasification of porous carbon particle by steam

Diffusive-kinetic model of porous carbon particle gasification by steam is developed. The model considers the processes of heat and mass transfer both inside the porous particle and above it. Heat losses by radiation to the particle from furnace wall are taken into account. Heterogeneous reactions of carbon with steam and carbon with carbon dioxide and homogeneous reaction of carbon monoxide with steam are considered. Pressure variation caused by gas mass increasing inside the particle is considered too. The analysis of the model inside the porous particle made possible determining the correlation between the reaction rate of carbon with steam and the reaction rate of carbon with carbon dioxide. The homogeneous reaction is supposed to be equilibrium. It is considered that the kinetics of heterogeneous reactions is known, than the equations of the model may be solved; and consequently the dependences of the particle gasification rate and the composition of the gasification products vs. composition, pressure and temperature of ambient gas and the internal surface of the porous particle are determined.     

Scattering of Hawking photons as a barrier to particle absorption by black holes

Electromagnetic scattering interactions between photons emanating from a Schwarzschild black hole and an incident charged particle should generate a repulsive force between the particle and black hole. The net scattering cross-section is calculated here as a function of the mass M of the black hole and the mass m of the particle for scenarios in which the particle is point-like and initially stationary, with proper energy ε=m, at some location far from the black hole. It follows from comparing the repulsive scattering force to the corresponding gravitational force that, in order for the particle to be drawn to the black hole, ε/Tbh must be greater than a certain lower bound that is of the order ¹⁰−3 for spin-1/2 or spin-0 particles with unit-charge. Although the scattering restriction is weaker than the requirement ε/Tbh?1 obtained independently from field-theoretic and thermodynamic treatments, the recurrence of a lower bound on the Boltzmann factor ε/Tbh in limitations on particle absorption suggests a physical unity whose nature is fundamentally thermodynamic.     

Single particle spectra in deep inelastic scattering as a probe of small x dynamics

We study the transverse momentum () spectrum of charged particles produced in deep inelastic scattering (DIS) at small Bjorken x in the central region between the current jet and the proton remnants. We calculate the spectrum at large with the BFKL ln (1/x) resummation included and then repeat the calculation with it omitted. We find that data favour the former. We normalize our BFKL predictions by comparing with HERA data for DIS containing a forward jet. The shape of the x distribution of DIS + jet data is also well described by BFKL dynamics. Received: 4 May 1998 / Published online: 21 August 1998     

Interatomic interaction potentials and their application to the description of particle scattering by a surface

The data on interatomic interaction potentials obtained from experiments are compared with the well-known theoretical models of potentials. A new analytical form of a potential that provides the best fit for experiments is proposed. The accuracy of its application is estimated as a function of the internuclear distance under consideration. Individual potentials for systems consisting of inert gases are discussed, and an algorithm for constructing potentials is proposed for cases not yet studied.     

Calculation of the electromagnetic absorption by a small metal particle with a two-parameter kinetic equation

The behavior of the magnetic dipole absorption cross section in a small metal particle is considered. A modified kinetic equation with the collision integral taking into account the deviation of the properties of metals at low temperatures from the Wiedemann-Franz law is solved. Diffuse reflection of electrons from the sample surface is considered. The dependence of the absorption cross section of a particle on the parameter describing the deviation from the Wiedemann-Franz law is analyzed.