Tip-state control of rates and branching ratios in atomic manipulation

We report the atomic manipulation properties of two distinct, stable, and reproducible states of a scanning tunneling microscope tip applied to chlorobenzene/Si(111)-(7x7). We show that the tip state influences the rates of (current-driven) molecular desorption and C-Cl dissociation as well as the branching ratio between these processes, but does not change the mediating electronic channel or the required number of electrons. These manipulation properties combined with the imaging properties of the two tip-states suggest the major difference between tip-states is their coupling efficiency to the pi-states of the chlorobenzene molecule.     

Magnetic Anisotropies and (Ga,Mn)As‐based Spintronic Devices

In this Review, we discuss the rich anisotropic properties of the ferromagnetic semiconductor (Ga,Mn)As, and their implications in transport studies. We review the various sources and types of anisotropy seen in the material, discuss its magnetization reversal process, and demonstrate how basic transport properties, such as resistivity and Hall measurements, can be used as very sensitive tools to investigate the magnetization properties of the material. We also discuss how the magnetic anisotropy, coupled with large spin–orbit coupling, leads to an anisotropy in the transport density of states, which in turn leads to fundamentally novel behavior such as tunneling anisotropic magnetoresistance (TAMR).     

Photonic crystals,amorphous materials,and quasicrystals

Photonic crystals consist of artificial periodic structures of dielectrics, which have attracted much attention because of their wide range of potential applications in the field of optics. We may also fabricate artificial amorphous or quasicrystalline structures of dielectrics, i.e. photonic amorphous materials or photonic quasicrystals. So far, both theoretical and experimental studies have been conducted to reveal the characteristic features of their optical properties, as compared with those of conventional photonic crystals. In this article, we review these studies and discuss various aspects of photonic amorphous materials and photonic quasicrystals, including photonic band gap formation, light propagation properties, and characteristic photonic states.     

Nanopatterning the electronic properties of gold surfaces with self-organized superlattices of metallic nanostructures

The self-organized growth of nanostructures on surfaces could offer many advantages in the development of new catalysts, electronic devices and magnetic data-storage media. The local density of electronic states on the surface at the relevant energy scale strongly influences chemical reactivity, as does the shape of the nanoparticles. The electronic properties of surfaces also influence the growth and decay of nanostructures such as dimers, chains and superlattices of atoms or noble metal islands. Controlling these properties on length scales shorter than the diffusion lengths of the electrons and spins (some tens of nanometres for metals) is a major goal in electronics and spintronics. However, to date, there have been few studies of the electronic properties of self-organized nanostructures. Here we report the self-organized growth of macroscopic superlattices of Ag or Cu nanostructures on Au vicinal surfaces, and demonstrate that the electronic properties of these systems depend on the balance between the confinement and the perturbation of the surface states caused by the steps and the nanostructures' superlattice. We also show that the local density of states can be modified in a controlled way by adjusting simple parameters such as the type of metal deposited and the degree of coverage.     

Negative binomial states of the quantized radiation field

Abstract

Negative binomial states of a single field mode are introduced and their properties are compared with those of the (positive) binomial states. We find that the two types of state have similar properties if the roles of the creation and annihilation operators are interchanged.     

Electronic states of graphene nanoribbons and analytical solutions

Abstract

Graphene is a one-atom-thick layer of graphite, where low-energy electronic states are described by the massless Dirac fermion. The orientation of the graphene edge determines the energy spectrum of π-electrons. For example, zigzag edges possess localized edge states with energies close to the Fermi level. In this review, we investigate nanoscale effects on the physical properties of graphene nanoribbons and clarify the role of edge boundaries. We also provide analytical solutions for electronic dispersion and the corresponding wavefunction in graphene nanoribbons with their detailed derivation using wave mechanics based on the tight-binding model. The energy band structures of armchair nanoribbons can be obtained by making the transverse wavenumber discrete, in accordance with the edge boundary condition, as in the case of carbon nanotubes. However, zigzag nanoribbons are not analogous to carbon nanotubes, because in zigzag nanoribbons the transverse wavenumber depends not only on the ribbon width but also on the longitudinal wavenumber. The quantization rule of electronic conductance as well as the magnetic instability of edge states due to the electron–electron interaction are briefly discussed.     

Structures and magnetic properties of ZnO nanoislands

Using first-principles calculations, we systematically study the atomic structures and electronic properties for two dimensional triangular ZnO nanoislands that are graphite-like with monolayer and bilayer thickness. We find that the monolayer ZnO nanoisland with oxygen-terminated zigzag-edges is magnetic at its ground state, and the magnetism comes from the oxygen-edge states. The other monolayer and bilayer ZnO nanoislands with different edge structures are all nonmagnetic at their ground states. It is further revealed that for different ZnO nanoislands, their magnetic properties are quite dependent on their sizes, with larger nanoislands having larger magnetic moments.     

Viscosity of defined and undefined hydrocarbon liquids calculated using an extended corresponding-states model

We predict the viscosity of petroleum fractions using extended corresponding states. Our model builds upon the TRAPP procedure, which is the most advanced approach to predict transport properties of straight-chain nonpolar hydrocarbons and their mixtures. We perform comparisons with experimental viscosity data for pure hydrocarbons, treating them as nonstandard components; we find deviations of 10–15%. We also extend the model to predict the transport properties of petroleum fractions and compare with an experimental database of more than 80 crude oils, including highly aromatic petroleum fractions. The model predicts the viscosity of the crude oil fractions within experimental uncertainty.Paper presented at the Twelfth Symposium on Thermophysical Properties, June 19–24, 1994, Boulder, Colorado, U.S.A.     

Luminescent properties of YAlO3:Mn single crystalline films

The YAP:Mn single crystalline films (SCF) have been crystallized by liquid phase epitaxy (LPE) method onto YAP substrates. The cathode- (CL) and photo-luminescence (PL) spectra of the YAP:Mn SCF were analyzed for determination of the preferable valence states of manganese ions which are realized in these SCF depending on Mn content in the 0.01–0.81 at.% range. The thermoluminescence (TL) properties of YAP:Mn SCF with the different Mn content above the RT range were also examined in comparison with the properties of YAP:Mn single crystal counterpart. We show that YAP:Mn (0.01 at.%) SCF possesses effective TL properties both under α-particle and γ-quanta excitation with main TSL peaks at 130 and 195 °C. We assume that the different valence states of Mn ions are responsible for their TL properties, e.g. both emission and trapping centers in YAP:Mn are formed mainly by the different valence states of Mn ions.     

Quantum phase measurements and non-classical polarization states of light

Abstract

In our paper we consider the non-classical behaviour of both the Hermitian (observable) Stokes parameters of light and the phase difference of two modes that describe the quantum polarization states of optical field. To characterize the degree of polarization of light we introduce a new quantity taking into account the quantum properties of different quantum states of two orthogonally polarized modes. The problem of determination of the phase difference in two modes of optical field for the quantum polarization states of light is discussed. To describe in general such a quantum field we introduce two pairs of the phase operators: the phase angles for the Stokes parameters of light in a three-dimensional picture of the Poincaré sphere. We also consider a special type of the eight-port polarization interferometer (polarimeter) for simultaneous homodyne detection of both the Stokes parameters of light and the polarization phase operators and their fluctuations as well. Using an anisotropic (spatioperiodic) Kerr-like nonlinear medium associated with the polarization interferometer we could generate and also observe the polarization-squeezed phase states of light. The fluctuations in the phase difference between two orthogonally polarized modes for these non-classical states are less than the fluctuations for light in coherent state.     

Phase Fluctuations and Squeezing

Abstract

We investigate the relationship between squeezing and reduced phase fluctuations for various states of the single-mode electromagnetic field, including the strongly-squeezed vacuum and phase states. We find that, although squeezing the fluctuations of the electric field that arise from the vacuum guarantees a more well-defined phase, reducing phase fluctuations does not guarantee a squeezed electric field. We also investigate the evolution of the electric field and its fluctuations for a phase state. Our results show that even though the electric field fluctuations never vanish for a phase state, the times when the electric field changes sign are precisely defined. We also discuss why it is not always possible to attribute physical properties to certain states, such as simple superpositions of phase states.     

Prediction of the viscosity and thermal conductivity coefficients of mixtures

A corresponding states procedure to predict the viscosity and thermal conductivity coefficients of a pure fluid or mixture is discussed. We show the transport properties of a fluid or mixture can be calculated to within experimental error given only corresponding values for a reference fluid and equation of state data. With methane, as the reference fluid, we consider nitrogen, ethane, propane, butane, carbon dioxide, and mixtures of these fluids. LNG is also included. It is shown that the conventional corresponding states approach is not sufficient to predict correctly the transport properties. The effect of internal degrees of freedom on the thermal conductivity coefficient and the enhancement in the critical region for this coefficient is discussed briefly.     

Effect of quantum and dielectric confinement on the exciton-exciton interaction energy in type II core/shell semiconductor nanocrystals

We study theoretically two electron-hole pair states (biexcitons) in core/shell hetero-nanocrystals with type II alignment of energy states, which promotes spatial separation of electrons and holes. To describe Coulomb interactions in these structures, we apply first-order perturbation theory, in which we use an explicit form of the Coulomb-coupling operator that takes into account interface-polarization effects. This formalism is used to analyze the exciton-exciton interaction energy as a function of the core and shell sizes and their dielectric properties. Our analysis shows that the combined contributions from quantum and dielectric confinement can result in strong exciton-exciton repulsion with giant interaction energies on the order of 100 meV. Potential applications of strongly interacting biexciton states include such areas as lasing, nonlinear optics, and quantum information.     

Complex dynamics variables for molecules and molecular clusters

We describe a method to analyse dynamic properties of molecules and molecular clusters. The model involves the change in lifetimes of collective, quasi-stationary excited states of the system under consideration by low energy electron local excitations. Probabilities of desorption-ionisation processes and cluster decomposition are also estimated. The model is based on the quantum multi-particle theory and the exciton or excimol theory for condensed matter and molecules. The energies of excitation have complex values which permit us to take into account the unharmonic character of bond vibrations and the relaxation process. We apply a perturbation theory for excitation analysis describing the possible deviation of molecules or molecular clusters from regular structures. The wave-functions can be taken in their asymptotic form and the dilatation method is used for the complex energy states.     

Reflectance spectra of individual single-walled carbon nanotubes

We report backscattering spectroscopic measurements on individual single-walled carbon nanotubes (SWNTs). The reflectance spectra show geometry-dependent resonant peaks corresponding to optical transitions between Van Hove singularities in the SWNTs' joint density of states. All nanotubes display certain colours as their reflectance spectra demonstrate strong energy dependence. This approach was proved to be an effective tool for probing the geometric structures and optical properties of individual SWNTs.     

A study on the photoconductivity of a set of horizontal Bridgman semi-insulating GaAs ingots

We report in this paper a study of the photoconductivity of a set of Horizontal Bridgman semi-insulating GaAs samples. In order to obtain steady-state photoconductivity spectra, we measure the photocurrent by a procedure that consists in thermally erasing the typical GaAs photomemory. The thermal evolution, between 80 and 300 K, of the photoconductivity is also obtained. The data so obtained allow us to distinguish clearly a diversity of behaviours between the photoelectronic properties of the different samples, which could not be observed with the conventional photoconductivity technique. The way in which chromium and oxygen impurities are introduced in GaAs, as well as their charge states, seem to be strongly influenced by native defects and background impurities, which play an important role in the compensation mechanism.     

Mechanisms for laser control of chemical reactions

During the past several years, a new technique for realistic simulations of the interaction of light with matter has been developed and employed. Recent simulations of laser pulses interacting with molecules clearly demonstrate the potential for control of chemical reactions through various mechanisms, which include the following: (i) excitation of electrons to states that have different bonding properties; (ii) control of electron populations through a coherent pump-pulse, control-pulse sequence; and (iii) control of molecular vibrations through a pump-control sequence. Significant chemical insights are gained when one can watch a realistic animation of species interacting and reacting. One can monitor the time evolution of electronic states and their occupancy, as well as the motion of the atoms. One can also observe the evolution from reactants to products through transition states. Finally, one can determine how this evolution is affected by the various properties of the laser pulses, including intensity, duration, phase, and the interval between pulses.     

From heat to entropy

Milestones in the development of thermodynamics are the discovery of the absolute temperature scale and the recognition that differential “heat” is a form of energy given as the product of absolute temperature and differential entropy. Following a new path, the last statement results from a careful analysis of the heat transfer applying the first theorem without reference to the usual cycles in thermodynamics. This confirms also characteristic properties of entropy. In particular, the total entropy can never decrease in a process. In thermal equilibrium, the differential thermal energy is proportional to the differential entropy with the constant of proportionality being the temperature of the heat and entropy. Hence, thermal energy and entropy are transferred simultaneously into the same storage facilities, some of which are mentioned. However, the issue which one is the superior quantity is obsolete. The entropy is maximum for a given amount of exchanged thermal energy and, vice versa, for a given amount of exchanged entropy the concomitant energy is minimum. We calculate the thermal energy and entropy of phonons (as bosons) in oscillators and of electrons (as fermions) in their states of solids and melts as examples from statistical thermodynamics. The thermal energy or heat is the sum of the energies of all bosons and fermions in their elementary states or quantum states according to Bose Einstein and Fermi Dirac statistics in thermal equilibrium minus the total energy in the limit T→0 K. The entropy can be written as mixing entropy of all of these quantum states weighted with their occupancies, in agreement with an earlier publication. Thus, entropy is a logarithmic metrics of the number of all possible variants to distribute the respective total energy over all elementary states in thermal equilibrium.     

Estimation of nonclassical properties of multiphoton coherent states from optical tomograms

We have examined both single and entangled two-mode multiphoton coherent states and shown how the ‘Janus-faced’ properties between two partner states are mirrored in appropriate tomograms. Entropic squeezing, quadrature squeezing and higher-order squeezing properties for a wide range of nonclassical states are estimated directly from tomograms. We have demonstrated how squeezing properties of two-mode entangled states produced at the output port of a quantum beamsplitter are sensitive to the relative phase between the reflected and transmitted fields. This feature allows for the possibility of tuning the relative phase to enhance squeezing properties of the state. Finally, we have examined the manner in which decoherence affects squeezing and the changes in the optical tomogram of the state due to interaction with the environment.