Cathodoluminescence and its causes

NIST is using atomically precise fabrication to develop electronic devices for use in quantum information processing and novel quantum materials. We are using hydrogen-based scanning probe lithography to enable deterministic placement of individual dopant atoms with atomically aligned contacts and gates to fabricate single atom transistors, devices for single electron spin manipulation, and arrayed devices for analog quantum simulation research. Atomic precision devices, where individual atoms or electrons fundamentally affect device performance, bring about a variety of new manufacturing and metrology challenges. Single atom defects and charge instability deeply change device performance, affecting reliable manipulation and sensing of individual electrons. Conventional metrology methods such as transmission electron and scanning electron microscopy often prove inadequate at this length scale and new, challenging electrical test methods are needed.

Possibilities for application of the theory of subspaces to determination of the energy of excited electronic states are studied in terms of density functional formalism. Specific features of computer implementation of the theory in a basis of spherical Gaussian functions, whose parameters are determined by minimizing the energy of the corresponding subspace of states, are discussed. The results of calculation of the energy of excited states and the excitation energies of simple atoms and molecules are presented to demonstrate the potential of the approach.

The paper reviews technique [1] and computed energies for various electronic states of many-electron multiply charged ions, molecular ions, and electronic phases of solids. The model used allows computation of the state energy for free many-electron multiply charged ions with relative accuracy ∼10−4 suitable for analysis of spectroscopy data.The paper reviews technique [1] and computed energies for various electronic states of many-electron multiply charged ions, molecular ions, and electronic phases of solids. The model used allows computation of the state energy for free many-electron multiply charged ions with relative accuracy ∼10−4 suitable for analysis of spectroscopy data.

In 1925, Erwin Schrodinger, drawing heavily on the experience of classical waves, introduced a wave equation for electrons, from which one could deduce their states and properties (energy, momentum, angular momentum, etc.). He applied this to the hydrogen atom with great success, determining the energy and angular momentum states of the hydrogen electron. From the energy states, one could determine the spectral frequencies; the decay of an excited state induced by heating to the ground state was accompanied by the emission of radiation of quanta whose energy was equal to that lost by the electron, and from this, the radiation frequency followed from Planck’s law. He thus correctly predicted the major spectral lines of hydrogen.

The behavior of NiO‐Al2O3 catalysts is strongly dependent on the preparation method, as well as on pretreatment conditions. In the present work we investigated the influences of Ni(II) ion on NiO‐Al2O3 catalysts properties due to the preparation by impregnation method. Based on experimental diffuse reflectance spectroscopy (DRS) data of electronic d‐d transitions of Ni (II) promoter ion the energies of electronic states in spinel‐like structure were calculated, and the most probable scheme of molecular orbital have been proposed.

We have generated a series of all 6561 unique, discrete three-state combinatorial switch models to describe the partitioning of the cooperative oxygen-binding free change among the 10 variously ligated forms of human hemoglobin tetramers. These models were inspired by the experimental observation of Smith and Ackers that the cooperative free energy of the intersubunit contact regions of the 10 possible ligated forms of human hemoglobin tetramers can be represented by a particular distribution of three distinct energy levels [Smith, F. R., & Ackers, G. K. (1985) Proc. Natl. Acad. Sci. U.S.A. 82, 5347-5351]. A statistical thermodynamic formulation accounting for both dimer-tetramer equilibria and ligand binding properties of hemoglobin solutions as a function of oxygen and protein concentrations was utilized to exhaustively test these thermodynamic models. In this series of models each of the 10 ligated forms of the hemoglobin tetramer can exist in one, and only one, of three possible energy levels; i.e., each ligated form was assumed to be associated with a discrete energy state. This series of models includes all possible ways that the 10 ligation states of hemoglobin can be distributed into three distinct cooperative energy levels. The mathematical models, as presented here, do not permit equilibria between energy states to exist for any of the 10 unique ligated forms of hemoglobin tetramers. These models were analyzed by nonlinear least-squares estimation of the free energy parameters characteristic of this statistical thermodynamic development.(ABSTRACT TRUNCATED AT 250 WORDS)

The density-of-states contributions to the negative field charge drift mobility effect in poly(3-hexylthiophene) organic semiconductor

Effects of intermolecular interactions on the occupied electronic structure of amorphous solid of a carbazole-based material were investigated under an assumption that the organic solid consists of randomly oriented assemblies of dimers. The electronic energy states were calculated on the ensemble of large number of random dimers, of which geometries are relaxed using semiempirical van der Waals density functional theory. Intermolecular interactions result in splitting of energy level, and further disorders occur by aggregation of randomly orientated molecules. As a result, frontier occupied energy states can be represented by a superposition of Gaussian distributions, including (i) a main distribution with full width at half maximum of 80-110 meV, depending on the methods of relaxation and (ii) shoulders separated from the center of the main distribution with a value as large as 150 meV. A possible origin for the appearance of these shoulders was ascribed to the presence of molecular assemblies consisting of more tightly bound dimers compared with the others.

In the efforts to develop novel active electrode materials for metal ion batteries, vanadium oxides are unique in that they have shown practically relevant performance characteristics for storage of several types of cations (such as Li, Na, Mg, K, and Al). Multiple experimentally accessible stoichiometries and phases, coupled with possibilities of modifications, create abundant design opportunities but require rational rather than ad hoc approaches. Because the mechanism of charge-discharge involves changes in occupancy and energies of electronic states, ab initio modeling is indispensable to understand limits of performance to which experiment can strive and to guide the design. We first summarize the theoretical basics of transition metal oxide chemistry and the fundamentals of first-principles investigations of battery materials and then review existing ab initio literature on vanadium oxides as active electrode materials for different classes of metal-ion batteries. We highlight the extent to which such modeling is able to describe or guide experiment and highlight the need for truly comparative computational studies among multiple phases and different active cations. Specifically, we discuss the computation of voltage-capacity curves as well as approaches to model cation diffusion kinetics in vanadia hosts from first principles. We describe how ab initio modeling can help design improved vanadia-based electrode materials by using doping and amorphization. We also highlight methodological and computational issues associated with modeling of vanadia or cation-intercalated vanadia, including the modeling of phase ordering, treatment of dispersion interactions, and application of the Hubbard correction especially in the context of comparing computed electrochemical performance of layered and non-layer phases and metallic and semiconductor phases. We also point out the inadequacy of the commonly used concept of formal oxidation states to understand the mechanism of charge-discharge.

We carry out a simulation of freely jointed ring polymers in the presence of uncorrelated blockers on a cubic three-dimensional lattice. The size of the polymer is shown to obey Lifshitz scaling at large polymer mass. The simulation results are compared with the predictions of the RISM polaron theory [D. Chandler, Y. Singh, and D. M. Richardson, J. Chem. Phys. 81, 1975 (1984)] derived for the nearly isomorphic problem of thermal excess electrons in simple fluids. Implications of the Gaussian density field treatment of the fluid in that theory are discussed. Further comparisons are drawn between the blocker model and the quantum percolation problem. This correspondence allows us to compare the values of mobility edge (the energy of electronic states at the bottom of the conduction band) in hard-sphere-like fluids with those in lattice models.

Describing electronically excited states of molecules accurately poses a challenging problem for theoretical methods. Popular second order techniques like Linear Response CC2 (CC2-LR), Partitioned Equation-of-Motion MBPT(2) (P-EOM-MBPT(2)), or Equation-of-Motion CCSD(2) (EOM-CCSD(2)) often produce results that are controversial and are ill-balanced with their accuracy on valence and Rydberg type states. In this study, we connect the theory of these methods and, to investigate the origin of their different behavior, establish a series of intermediate variants. The accuracy of these on excitation energies of singlet valence and Rydberg electronic states is benchmarked on a large sample against high-accuracy Linear Response CC3 references. The results reveal the role of individual terms of the second order similarity transformed Hamiltonian, and the reason for the bad performance of CC2-LR in the description of Rydberg states. We also clarify the importance of the T̂1 transformation employed in the CC2 procedure, which is found to be very small for vertical excitation energies.

Electronic structure of Mn-doped InAs nanowires in the magnetic field

Semiconductor research and applications have experienced a progressive reduction in dimensionality of structures from bulk, through quantum wells and wires to quantum dots (QDs). QDs provide an ultimate limit of charge carrier confinement. Their size is in the nanometer range, i.e. of the order of the exciton Bohr radius, giving rise to fully quantized confined electron and hole states. Their electronic properties differ significantly from those of systems with higher dimensionality and offer potential applications in novel optoelectronic devices. The most effective method for the fabrication of coherent, dislocation-free semiconductor QDs is the strained-layer epitaxy in the Stranski–Krastanow mode [1, 2]. Such self-organized transformation from two-dimensional layer-by-layer growth to a three-dimensional mode was found for many heterostructure systems. InAs quantum dots in GaAs matrix represent the best studied model system. The discrete energy states and the ease of integration into an optoelectronic device recently lead, e.g., to the presentation of electrically driven single photon sources [3]. Prerequisite for practical applications is the ability to control the electronic properties of the dot. Fabrication of quantum dots by applying Stranski-Krastanow growth is hampered by the action of entropy at growth temperature, usually leading to ensembles of dots which vary in size, shape, and composition. Consequently the energies of bound states vary within the ensemble. Since this growth mode still yields defect-free dots with superior electronic properties, the technique was recently advanced to improve the shape homogeneity within the ensemble and the integrity of the dot-matrix interfaces [4]. The development aimed to find a growth regime which simultaneously favors the formation of equilibrium-near dots with homogeneous composition and sharp interfaces. This chapter addresses the growth control of such particular kind of InAs dots in GaAs matrix and their electronic properties.

The oxygen reduction reaction (ORR) is of great importance in energy‐converting processes such as fuel cells and in metal–air batteries and is vital to facilitate the transition toward a nonfossil dependent society. The ORR has been associated with expensive noble metal catalysts that facilitate the O2 adsorption, dissociation, and subsequent electron transfer. Single‐ or few‐atom motifs based on earth‐abundant transition metals, such as Fe, Co, and Mo, combined with nonmetallic elements, such as P, S, and N, embedded in a carbon‐based matrix represent one of the most promising alternatives. Often these are referred to as single atom catalysts; however, the coordination number of the metal atom as well as the type and nearest neighbor configuration has a strong influence on the function of the active sites, and a more adequate term to describe them is metal‐coordinated motifs. Despite intense research, their function and catalytic mechanism still puzzle researchers. They are not molecular systems with discrete energy states; neither can they fully be described by theories that are adapted for heterogeneous bulk catalysts. Here, recent results on single‐ and few‐atom electrocatalyst motifs are reviewed with an emphasis on reports discussing the function and the mechanism of the active sites.

We have designed and fabricated hybrid nanodots structures, in which Si quantum dots (QDs) and either Ni-silicide or Pt-silicide nanodots (NDs) are stacked with ultrathin SiO2 interlayer, as a novel functional floating gate (FG) to satisfy both multiple valued capability and large capacity on charge storage. Multiple-step charge injection to sililcide NDs through discrete energy states in Si-QDs and stable storage of many charges in deep potential wells in silicide NDs have been confirmed from electrical characteristics of MOS capacitors and transistors measured at room temperature. A unique optical response of the hybrid NDs FG to near-infrared light irradiation, which is caused by the transfer of photo-excited electrons from silicide NDs to Si-QDs, has also been demonstrated.