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At least 163 records · Page 9

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DOE OSTI2020

Solid-state organic intermediate-band photovoltaic devices

In one aspect, solid-state organic intermediate-band photovoltaic devices are provided. A solid-state organic intermediate-band photovoltaic device, in some embodiments, comprises an organic electron donor and an organic electron acceptor, wherein the organic electron donor comprises a singlet energy level separated from a triplet energy level by an energy gap. The device also comprises a triplet sensitizer comprising singlet and triplet energy levels falling within the singlet-triplet energy gap of the electron donor.

14 SOLAR ENERGY↗

DOE OSTI2021

Solid-state organic intermediate-band photovoltaic devices

Rand, Barry P.↗

DOE OSTI2017

Why X(3872) is not a molecule

We discuss the scenario where the X(3872) resonance is the c c-bar = χ{sub c1}(2P) charmonium which “sits on” the D*{sup 0} D-bar {sup 0} threshold. We explain the shift of the mass of the X(3872) resonance with respect to the prediction of a potential model for the mass of the χ{sub c1}(2P) charmonium by the contribution of the virtual D* D-bar + c.c. intermediate states into the self energy of the X(3872) resonance. This allows us to estimate the coupling constant of the X(3872) resonance with the D*{sup 0} D-bar {sup 0} channel, the branching ratio of the X(3872) → D*{sup 0} D-bar {sup 0} + c.c. decay, and the branching ratio of the X(3872) decay into all non-D*{sup 0} D-bar {sup 0} + c.c. states. We predict a significant number of unknown decays of X(3872) via two gluon: X(3872) → gluongluon → hadrons. We suggest a physically clear program of experimental researches for verification of our assumption.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2014

Pathway structure determination in complex stochastic networks with non-exponential dwell times

Analysis of complex networks has been widely used as a powerful tool for investigating various physical, chemical, and biological processes. To understand the emergent properties of these complex systems, one of the most basic issues is to determine the structure and topology of the underlying networks. Recently, a new theoretical approach based on first-passage analysis has been developed for investigating the relationship between structure and dynamic properties for network systems with exponential dwell time distributions. However, many real phenomena involve transitions with non-exponential waiting times. We extend the first-passage method to uncover the structure of distinct pathways in complex networks with non-exponential dwell time distributions. It is found that the analysis of early time dynamics provides explicit information on the length of the pathways associated to their dynamic properties. It reveals a universal relationship that we have condensed in one general equation, which relates the number of intermediate states on the shortest path to the early time behavior of the first-passage distributions. Our theoretical predictions are confirmed by extensive Monte Carlo simulations.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2014

Zero kinetic energy photoelectron spectroscopy of triphenylene

We report vibrational information of both the first electronically excited state and the ground cationic state of jet-cooled triphenylene via the techniques of resonantly enhanced multiphoton ionization (REMPI) and zero kinetic energy (ZEKE) photoelectron spectroscopy. The first excited electronic state S{sub 1} of the neutral molecule is of A{sub 1}′ symmetry and is therefore electric dipole forbidden in the D{sub 3h} group. Consequently, there are no observable Franck-Condon allowed totally symmetric a{sub 1}′ vibrational bands in the REMPI spectrum. All observed vibrational transitions are due to Herzberg-Teller vibronic coupling to the E′ third electronically excited state S{sub 3}. The assignment of all vibrational bands as e′ symmetry is based on comparisons with calculations using the time dependent density functional theory and spectroscopic simulations. When an electron is eliminated, the molecular frame undergoes Jahn-Teller distortion, lowering the point group to C{sub 2v} and resulting in two nearly degenerate electronic states of A{sub 2} and B{sub 1} symmetry. Here we follow a crude treatment by assuming that all e′ vibrational modes resolve into b{sub 2} and a{sub 1} modes in the C{sub 2v} molecular frame. Some observed ZEKE transitions are tentatively assigned, and the adiabatic ionization threshold is determined to be 63 365 ± 7 cm{sup −1}. The observed ZEKE spectra contain a consistent pattern, with a cluster of transitions centered near the same vibrational level of the cation as that of the intermediate state, roughly consistent with the propensity rule. However, complete assignment of the detailed vibrational structure due to Jahn-Teller coupling requires much more extensive calculations, which will be performed in the future.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2017

Raman Scattering of Light by Quantum Rings in a Magnetic Field

The effect of the Coulomb interaction in the intermediate state on the inelastic resonant process of light scattering by electrons in quantum rings in a magnetic field normal to the ring plane is investigated theoretically. By way of examples, one- and two-electron quantum rings are considered.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2016

Preliminary Insights on Potential Transitions to Closed Thorium-Based Fuel Cycles

Closed fuel cycles with comprehensive recycle strategies are often regarded as the logical and desired end-states of long-term nuclear energy strategies; such options offer potential improvements in terms of resource supply and sustainability, waste management, and potentially nuclear security. In the DOE-NE Fuel Cycle Option Campaign report, systems with closed recycle strategies (both uranium- and thorium-based) generally dominated strategies with less comprehensive recycle approaches across many performance metrics. That being said, developing momentum to transition from the current global implementation of once-through fuel cycles has proven challenging. Intermediate paths en route to closed fuel cycles have not been readily elucidated; this is especially true for thorium-based options. A comparatively extensive amount of work has been conducted on transitions to closed fuel cycles based on uranium and plutonium, generally based on an endpoint of sodium-cooled fast reactors (SFRs). In contrast, corresponding analyses for thorium-based options are limited. Early estimates, without the benefit of full-scale modeling, were performed in conjunction with the Molten Salt Fast Reactor (MSFR) design. There is some transition analysis work associated with the Japanese THORIMS-NES molten salt design, but the scope of this work was not directly comparable with the SFR-oriented analyses and considered the thorium fission reactors as an intermediate state en route to the global deployment of accelerator-driven systems. Others have considered thorium recently, but not in a closed-recycle context. To begin to resolve this gap, this paper describes a high-level analysis and initial perspectives on the topic of transitions to closed thorium-based cycles. The emphasis on this paper is not on the specific quantitative results that are described, although some of the overall takeaways from these trends may still be useful. Instead, this paper describes the need for such analyses to be conducted, describes the methodologies by which this can be accomplished, and reports an initial demonstration of these methodologies for a specific transition candidate scenario. (authors)

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗

DOE OSTI2016

Puzzles in quarkonium hadronic transitions with two pion emission

The anomalously large rates of some hadronic transitions from quarkonium are studied using QCD multipole expansion (QCDME) in the framework of a constituent quark model which has been successful in describing hadronic phenomenology. The hybrid intermediate states needed in the QCDME method are calculated in a natural extension of our constituent quark model based on the Quark Confining String (QCS) scheme. Some of the anomalies are explained due to the presence of an hybrid state with a mass near the mass of the decaying resonance whereas other are justified by the presence of molecular components in the wave function. Some unexpected results are pointed out.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2014

Enhancement of current collection in epitaxial lift-off InAs/GaAs quantum dot thin film solar cell and concentrated photovoltaic study

We report the fabrication of a thin film InAs/GaAs quantum dot solar cell (QD cell) by applying epitaxial lift-off (ELO) approach to the GaAs substrate. We confirmed significant current collection enhancement (∼0.91 mA/cm{sup 2}) in the ELO-InAs QD cell within the wavelength range of 700 nm–900 nm when compared to the ELO-GaAs control cell. This is almost six times of the sub-GaAs bandgap current collection (∼0.16 mA/cm{sup 2}) from the wavelength range of 900 nm and beyond, we also confirmed the ELO induced resonance cavity effect was able to increase the solar cell efficiency by increasing both the short circuit current and open voltage. The electric field intensity of the resonance cavity formed in the ELO film between the Au back reflector and the GaAs front contact layer was analyzed in detail by finite-differential time-domain (FDTD) simulation. We found that the calculated current collection enhancement within the wavelength range of 700 nm–900 nm was strongly influenced by the size and shape of InAs QD. In addition, we performed concentrated light photovoltaic study and analyzed the effect of intermediate states on the open voltage under varied concentrated light intensity for the ELO-InAs QD cell.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2013

EVOLUTION OF THE CROSS-CORRELATION AND TIME LAG OF 4U 1735-44 ALONG THE BRANCHES

We analyze the cross-correlation function between the soft and hard X-rays of atoll source 4U 1735-44 with RXTE data, and find anti-correlated soft and hard time lags of about a hecto-second. In the island state, the observations do not show any obvious correlations, and most observations of the banana branch show a positive correlation. However, anti-correlations are detected in the upper banana branch. These results are different from those of Z-sources (Cyg X-2, GX 5-1), where anti-correlations are detected in the horizontal branch and upper normal branch. In this case, the lag timescales of both this atoll and Z-sources are found to be similar, at a magnitude of several tens to hundreds of seconds. As a comparison, it is noted that anti-correlated lags lasting thousands of seconds have been reported from several black hole candidates in their intermediate states. In addition, for an observation containing four segments that show positive or anti-correlation, we analyze the spectral evolution with the hybrid model. In the observation, the anti-correlation is detected at the highest flux. The fitting results show that the Comptonized component is not the lowest at the highest flux, which suggests that the anti-correlation corresponds to the transition between the soft and hard states. Finally, we compare the corresponding results of atoll source 4U 1735-44 with those observed in Z-sources and black hole candidates, and the possible origins of the anti-correlated time lags are discussed.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2015

Some problems in heavy-quarkonium decays

Problems proposed by the present authors for studies at c-τ, b, super-c-τ, and super-b factories are formulated. First, a comparison of the mechanisms of light-scalar-meson production in the process D{sub s}{sup +}→ss̄e{sup +}ν→[σ(600)+f{sub 0}(980)]e{sup +}ν→π{sup +}π{sup −}e{sup +}ν with the mechanisms of light-pseudoscalar-meson production in the process D{sub s}{sup +}→ss̄e{sup +}ν→(η/η{sup ′})e{sup +}ν reveals that the transition ss̄→σ(600) is negligible in relation to the transition ss̄→f{sub 0}(980). As for f{sub 0}(980), ss̄→f{sub 0}(980) is not more than 30% of ss̄→η{sub s}(η{sub s}=ss̄). It is proposed to study light scalar mesons in the semileptonic decays of D{sup +}(D{sup −}) D{sup 0}(D̄{sup 0}), B{sup +}(B{sup −}), and B{sup 0}(B̄{sup 0}). Second, interference phenomena observed in the ψ(3770)-resonance region in the reaction e{sup +}e{sup −}→DD̄ are described on the basis of models satisfying the elastic-unitarity requirement. As a model, we propose the model of mixed ψ(3770) and ψ(2S) resonances. In order to select theoretical models, it is proposed to employ non-DD̄ decay channels such as e{sup +}e{sup −} → ψ(3770) → γχ{sub c0}, J/ψη, and ϕη. Third, branching ratios are calculated for ψ(3770) and ϒ(10580) decays proceeding to light (non-DD̄ and non-BB̄) hadrons owing to the contributions of real DD̄ and BB̄ intermediate states. The predictions obtained for these branching ratios lie in the range of 1% ≲ BR ≲ 15%. The lower boundary of this range is ten times higher than the branching ratio for annihilation to three gluons.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2018

3D Burgers Equation in Relativistic Plasma in the Presence of Electron and Negative Ion Trapping: Evolution of Shock Wave

The characteristics of shock waves in a relativistic plasma in the presence of nonisothermal electrons and nonisothermal negative ions is investigated by deriving the evolution equation in terms of a modified 3D Burgers equation, or trapped 3D Burgers equation. The solution of this equation is examined analytically to study the salient characteristics of shock waves in such plasma. The nonlinear coefficient is found to have the lowest (highest) value when the negative ions move toward thermal equilibrium with a dip-shaped electron distribution (when both electrons and negative ions follow a dip-shaped distribution) for a particular value of relativistic factor, and it remains in an intermediate state when both electrons and negative ions follow a flat-topped distribution. On the other hand, the dissipative coefficient is found to decrease (increase) with increasing relativistic parameter (viscous parameter). A profound effect of the trapped state of both electrons and negative ions and the temperature ratio between positive ions and electrons (negative ions and electrons) on the structure of the shock wave is also seen. However, it has been noticed that the trapped parameter of electrons has a dominating control over the shock potential profile than the trapped parameter of negative ions.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2019

Microscopic Description of the Mechanism of Transition between the 2H and 4H Polytypes of Silicon Carbide

Abstract—: The mechanism of displacement of one close-packed SiC layer from one minimum position to another on the example of SiC polytype transition 2H → 4H has been studied by ab initio methods. It has been shown that the intermediate state with monoclinic symmetry Cm greatly facilitates this displacement breaking it into two stages. Initially, the Si atom chiefly moves, only then—mainly the C atom. In this case, the Si–C bond is significantly tilted in comparison with the initial position, which allows the reducing of the compression of the SiC bonds in the (11 2-bar 0) plane. Two transition states of this process, which also possess the Cm symmetry, have been computed. It has been found that the height of the activation barrier of the process of moving the close-packed layer of SiC from one position to another is equal to 1.8 eV. The energy profile of this movement has been calculated.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2014

Chiral magnetization textures stabilized by the Dzyaloshinskii-Moriya interaction during spin-orbit torque switching

We study the effect of the Dzyaloshinskii-Moriya interaction (DMI) on current-induced magnetic switching of a perpendicularly magnetized heavy-metal/ferromagnet/oxide trilayer both experimentally and through micromagnetic simulations. We report the generation of stable helical magnetization stripes for a sufficiently large DMI strength in the switching region, giving rise to intermediate states in the magnetization and confirming the essential role of the DMI on switching processes. We compare the simulation and experimental results to a macrospin model, showing the need for a micromagnetic approach. The influence of the temperature on the switching is also discussed.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2015

Composition dependent multiple structural transformations of myoglobin in aqueous ethanol solution: A combined experimental and theoretical study

Experimental studies (circular dichroism and ultra-violet (UV) absorption spectra) and large scale atomistic molecular dynamics simulations (accompanied by order parameter analyses) are combined to establish a number of remarkable (and unforeseen) structural transformations of protein myoglobin in aqueous ethanol mixture at various ethanol concentrations. The following results are particularly striking. (1) Two well-defined structural regimes, one at x{sub EtOH} ∼ 0.05 and the other at x{sub EtOH} ∼ 0.25, characterized by formation of distinct partially folded conformations and separated by a unique partially unfolded intermediate state at x{sub EtOH} ∼ 0.15, are identified. (2) Existence of non-monotonic composition dependence of (i) radius of gyration, (ii) long range contact order, (iii) residue specific solvent accessible surface area of tryptophan, and (iv) circular dichroism spectra and UV-absorption peaks are observed. Interestingly at x{sub EtOH} ∼ 0.15, time averaged value of the contact order parameter of the protein reaches a minimum, implying that this conformational state can be identified as a molten globule state. Multiple structural transformations well known in water-ethanol binary mixture appear to have considerably stronger effects on conformation and dynamics of the protein. We compare the present results with studies in water-dimethyl sulfoxide mixture where also distinct structural transformations are observed along with variation of co-solvent composition.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2014

Direct observation of ballistic Andreev reflection

An overview is presented of experiments on ballistic electrical transport in inhomogeneous superconducting systems which are controlled by the process of Andreev reflection. The initial experiments based on the coexistence of a normal phase and a superconducting phase in the intermediate state led to the concept itself. It was followed by a focus on geometrically inhomogeneous systems like point contacts, which provided a very clear manifestation of the energy and direction dependence of the Andreev reflection process. The point contacts have recently evolved towards the atomic scale owing to the use of mechanical break-junctions, revealing a very detailed dependence of Andreev reflection on the macroscopic phase of the superconducting state. In present-day research, the superconducting in homogeneity is constructed by clean room technology and combines superconducting materials, for example, with low-dimensional materials and topological insulators. Alternatively, the superconductor is combined with nano-objects, such as graphene, carbon nanotubes, or semiconducting nanowires. Each of these “inhomogeneous systems” provides a very interesting range of properties, all rooted in some manifestation of Andreev reflection.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2018

The type II Weyl semimetals at low temperatures: Chiral anomaly, elastic deformations, zero sound

We consider the properties of the type II Weyl semimetals at low temperatures basing on the particular tight-binding model. In the presence of electric field directed along the line connecting the Weyl points of opposite chirality the occupied states flow along this axis giving rise to the creation of electron–hole pairs. The electrons belong to a vicinity of one of the two type II Weyl points while the holes belong to the vicinity of the other. This process may be considered as the manifestation of the chiral anomaly that exists without any external magnetic field. It may be observed experimentally through the measurement of conductivity. Next, we consider the modification of the theory in the presence of elastic deformations. In the domain of the considered model, where it describes the type I Weyl semimetals the elastic deformations lead to the appearance of emergent gravity. In the domain of the type II Weyl semimetals the form of the Fermi surface is changed due to the elastic deformations, and its fluctuations represent the special modes of the zero sound. We find that there is one to one correspondence between them and the sound waves of the elasticity theory. Next, we discuss the influence of the elastic deformations on the conductivity. The particularly interesting case is when our model describes the intermediate state between the type I and the type II Weyl semimetal. Then without the elastic deformations there are the Fermi lines instead of the Fermi points/Fermi surface, while the DC conductivity vanishes. However, even small elastic deformations may lead to the appearance of large conductivity.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2018

Measurement of the e{sup +}e{sup −} → ηK{sup +}K{sup −} Cross Section by Means of the SND Detector

The cross section for the process e{sup +}e{sup −} → ηK{sup +}K{sup −} wasmeasured at c.m. energies in the range between 1.56 and 2.00 GeV in an experiment with the SND detector at the VEPP-2000 e{sup +}e{sup −} collider. The invariant-mass distribution of kaon pairs is consistent with the hypothesis that the transition through the ηφ intermediate state makes a dominant contribution to the transition in question.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗