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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Structurally induced large changes of the energy level alignment in CuPc on Cu ( 110 ) - ( 2 × 1 ) O

While it is becoming apparent that organic semiconductor/metal interfaces may exhibit a variety of different structural phases, it is at present unclear to what extent these different thin-film structures determine the interfacial electronic structure. Here, we observe large changes in the interfacial electronic structure for the case of copper(II) phthalocyanine (CuPc) on Cu(110)–(2×1)O. This striking evolution of the interfacial electronic structure occurs beyond the first monolayer of CuPc and is particularly evident in the frontier orbital region. Using scanning tunneling microscopy in conjunction with photoemission spectroscopy, we characterize ultrathin films of CuPc grown on oxygen reconstructed Cu(110). We propose that the observed unique changes to the electronic structure result from an abrupt transition in film structure between the first and second layers: An interface layer of ordered, face-on molecules templates a largely vertical, edge-on orientation of molecules in the subsequent layer. The quadrupole moment of the molecule accounts for the sizable and unusual change in ionization energy between molecules in the two layers. Lastly, our results demonstrate that the precise structure of the organic semiconductor film exerts an important role in determining the interfacial electronic structure that must be considered and may be harnessed for tailoring energy level alignment at such interfaces.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2020

Modulating Energy Level on an A‐D‐A′‐D‐A‐Type Unfused Acceptor by a Benzothiadiazole Core Enables Organic Solar Cells with Simple Procedure and High Performance

Unfused‐ring acceptors (UFAs) have gained considerable research attention as they offer simple chemical structures through simplified synthesis methods, which would boost the commercialization of organic solar cells (OSCs). Recently, a new small molecule acceptor (SMA) named Y6 was reported, yielding high‐performance OSCs. Herein, the Y6‐like A‐DA′D‐A framework is developed to A‐D‐A′‐D‐A‐type backbone adopted in constructing UFAs. Two new Y6‐like UFAs are synthesized within four steps and the effect of noncovalent atoms at the central electron‐deficient core on material properties and device performances is studied. It is found that the introduction of fluorine atoms can bring larger red‐shift in the absorption spectra and better aggregation of the resulting UFA film states compared with those of oxygen atoms. Interestingly, the variations in the noncovalent interaction atoms induce different intermolecular charge transfer between donors and UFAs. When blended with another economical donor, PTQ10, F substitution at the benzothiadiazole ring is more effective than O substitution, leading to the increased short‐circuit current density ( J SC ) and higher efficiency of over 12%, among the best performances of UFA‐based OSCs. This contribution demonstrates the appropriate introduction of noncovalent interaction is a promising method for tuning energy levels, absorption, and aggregation of UFAs for high‐performance OSCs.

Yu, Han↗
DOE OSTI2014

A new accurate ground-state potential energy surface of ethylene and predictions for rotational and vibrational energy levels

In this paper we report a new ground state potential energy surface for ethylene (ethene) C{sub 2}H{sub 4} obtained from extended ab initio calculations. The coupled-cluster approach with the perturbative inclusion of the connected triple excitations CCSD(T) and correlation consistent polarized valence basis set cc-pVQZ was employed for computations of electronic ground state energies. The fit of the surface included 82 542 nuclear configurations using sixth order expansion in curvilinear symmetry-adapted coordinates involving 2236 parameters. A good convergence for variationally computed vibrational levels of the C{sub 2}H{sub 4} molecule was obtained with a RMS(Obs.–Calc.) deviation of 2.7 cm{sup −1} for fundamental bands centers and 5.9 cm{sup −1} for vibrational bands up to 7800 cm{sup −1}. Large scale vibrational and rotational calculations for {sup 12}C{sub 2}H{sub 4}, {sup 13}C{sub 2}H{sub 4}, and {sup 12}C{sub 2}D{sub 4} isotopologues were performed using this new surface. Energy levels for J = 20 up to 6000 cm{sup −1} are in a good agreement with observations. This represents a considerable improvement with respect to available global predictions of vibrational levels of {sup 13}C{sub 2}H{sub 4} and {sup 12}C{sub 2}D{sub 4} and rovibrational levels of {sup 12}C{sub 2}H{sub 4}.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Development of Fleet Energy Savings Evaluation Tools for Smart Mobility: Smart Vehicle Energy Technology (SVET) Model for Passenger Fleets and Freight Fleet Level Energy Estimation Tool (FFLEET) for Freight Fleets

As part of the U.S. Department of Energy’s (DOE) Systems and Modeling for Accelerated Research in Transportation (SMART) Mobility Initiative, the Oak Ridge National Laboratory (ORNL) led a study to develop web-based tools intended to enable vehicle fleet operators, including both passenger and freight fleets, to quantify the energy savings achievable by implementing advanced transportation technologies. By developing a profile of a fleet’s existing vehicle inventory and providing data about how and where the vehicles are driven, fuel consumption can be calculated for the entire fleet and users can perform “what if” scenarios to evaluate the energy savings that can be realized when replacing existing vehicles and implementing new technologies.

33 ADVANCED PROPULSION SYSTEMS↗
DOE OSTI2013

Composition dependence of the mercury vacancies energy levels in HgCdTe: Evolution of the “negative-U” property

HgCdTe films grown by liquid phase epitaxy with different Cd compositions were post-annealed to control the Hg vacancy concentration. Then temperature-dependent Hall measurements and photoluminescence measurements allowed us to study the evolution of the Hg vacancy acceptor levels with the cadmium composition. For Cd compositions below 33% the Hg vacancies in HgCdTe present a negative-U property with the ionized state V{sup −} stabilized compared to the neutral state V{sup 0}. For Cd compositions higher than 45%, the Hg vacancies in HgCdTe present a more standard level ordering with the ionized state V{sup −} at higher energy than the neutral state V{sup 0}.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Energy transfer and energy level decay processes in Tm{sup 3+}-doped tellurite glass

The primary excited state decay and energy transfer processes in singly Tm{sup 3+}-doped TeO{sub 2}:ZnO:Bi{sub 2}O{sub 3}:GeO{sub 2} (TZBG) glass relating to the {sup 3}F{sub 4}{yields}{sup 3}H{sub 6}{approx}1.85 {mu}m laser transition have been investigated in detail using time-resolved fluorescence spectroscopy. Selective laser excitation of the {sup 3}H{sub 4} manifold at 794 nm, the {sup 3}H{sub 5} manifold at 1220 nm, and {sup 3}F{sub 4} manifold at 1760 nm has established that the {sup 3}H{sub 5} manifold is entirely quenched by multiphonon relaxation in tellurite glass. The luminescence from the {sup 3}H{sub 4} manifold with an emission peak at 1465 nm suffers strong suppression due to cross relaxation that populates the {sup 3}F{sub 4} level with a near quadratic dependence on the Tm{sup 3+} concentration. The {sup 3}F{sub 4} lifetime becomes longer as the Tm{sup 3+} concentration increases due to energy migration and decreases to 2.92 ms when [Tm{sup 3+}] = 4 mol. % as a result of quasi-resonant energy transfer to free OH{sup -} radicals present in the glass at concentrations between 1 x 10{sup 18} cm{sup -3} and 2 x 10{sup 18} cm{sup -3}. Judd-Ofelt theory in conjunction with absorption measurements were used to obtain the radiative lifetimes and branching ratios of the energy levels located below 25 000 cm{sup -1}. The spectroscopic parameters, the cross relaxation and Tm{sup 3+}({sup 3}F{sub 4}) {yields} OH{sup -} energy transfer rates were used in a numerical model for laser transitions emitting at 2335 nm and 1865 nm.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Spectra of optical absorption and energy levels diagram of Er{sup 3+} ions in bulk crystals of aluminum nitride

The absorption spectra of the Er{sup 3+} ions embedded in the AlN matrix have been investigated. The admixture of erbium was introduced in bulk AlN crystals by diffusion. The absorption lines, which are associated with the intraconfigurational electronic f–f-transitions from the ground {sup 4}I{sub 15/2}-state to the levels of ion Er{sup 3+} excited states have been observed in the spectral range of 370–700 nm. The transitions to the state levels {sup 4}F{sub 9/2}, {sup 2}H{sub 11/2}, {sup 4}F{sub 7/2}, {sup 4}F{sub 5/2}, {sup 2}H{sub 9/2}, and {sup 4}G{sub 11/2} have been investigated in detail at the temperature T = 2 K. The number of the observed lines for these transitions coincides with the theoretically possible one for the electronic f–f-transitions in the ions Er{sup 3+}, which are in the crystal field with the symmetry below cubic. The narrowness of the observed lines and their number convincingly testify the replacement of preferably one regular crystalline position by erbium ions. The implementation of Er{sup 3+} in the Al{sup 3+} position with the local symmetry C{sub 3v} appears the most probable. The energy positions of the levels of excited states for the investigated transitions have been determined. The diagram of the Er{sup 3+} ion energy levels in the AlN crystals has been built.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Extended Calculations of Spectroscopic Data: Energy Levels, Lifetimes, and Transition Rates for O-like Ions from Cr xvii to Zn xxiii

Employing two state-of-the-art methods, multiconfiguration Dirac–Hartree–Fock and second-order many-body perturbation theory, the excitation energies and lifetimes for the lowest 200 states of the 2s{sup 2}2p{sup 4}, 2s2p{sup 5}, 2p{sup 6}, 2s{sup 2}2p{sup 3}3s, 2s{sup 2}2p{sup 3}3p, 2s{sup 2}2p{sup 3}3d, 2s2p{sup 4}3s, 2s2p{sup 4}3p, and 2s2p{sup 4}3d configurations, and multipole (electric dipole (E1), magnetic dipole (M1), and electric quadrupole (E2)) transition rates, line strengths, and oscillator strengths among these states are calculated for each O-like ion, from Cr xvii to Zn xxiii. Our two data sets are compared with the National Institute of Standards and Technology and CHIANTI compiled values, and previous calculations. The data are accurate enough for identification and deblending of new emission lines from the Sun and other astrophysical sources. The amount of high-accuracy data is significantly increased for the n = 3 states of several O-like ions of astrophysical interest, where experimental data are very scarce.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2011

FORBIDDEN AND INTERCOMBINATION LINES OF RR TELESCOPII: WAVELENGTH MEASUREMENTS AND ENERGY LEVELS

Ultraviolet and visible spectra of the symbiotic nova RR Telescopii are used to derive reference wavelengths for many forbidden and intercombination transitions of ions +1 to +6 of elements C, N, O, Ne, Na, Mg, Al, Si, P, S, Cl, Ar, K, and Ca. The wavelengths are then used to determine new energy values for the levels within the ions' ground configurations or first excited configuration. The spectra were recorded by the Space Telescope Imaging Spectrograph of the Hubble Space Telescope and the Ultraviolet Echelle Spectrograph of the European Southern Observatory in 2000 and 1999, respectively, and cover 1140-6915 A. Particular care was taken to assess the accuracy of the wavelength scale between the two instruments. An investigation of the profiles of the emission lines reveals that the nebula consists of at least two plasma components at different velocities. The components have different densities, and a simple model of the lines' emissions demonstrates that most of the lines principally arise from the high density component. Only these lines were used for the wavelength study.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

Rates of exponential decay in systems of discrete energy levels by Stieltjes imaging

An isolated bound state coupled to a continuum shows an exponential decay of its survival probability. Rates of the exponential decay occurring due to the bound-continuum coupling can be recovered from discretized continuum (L{sup 2}) calculations using a computational technique known as Stieltjes-Chebyshev moment theory or Stieltjes imaging. At the same time, some genuinely discrete level systems, e.g., Bixon-Jortner model, also show an exponential (or approximately exponential) decay of the initially populated level before the onset of quantum revivals. Here, we demonstrate numerically that Stieltjes imaging can be used for calculation of the rates of the exponential decay in such discrete level systems. We apply the Stieltjes imaging technique to the approximately exponential decay of inner-valence vacancies in trans-butadiene in order to show that the breakdown of the molecular orbital picture of ionization in the inner valence region can be physically interpreted as an energy-forbidden Coster-Kronig transition.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2013

Tailoring the energy level alignment at the Co/Alq{sub 3} interface by controlled cobalt oxidation

We have studied the influence of oxygen exposure at the prototypical interface between cobalt and the organic semiconductor tris(8-hydroxyquinoline)aluminum (III) (Alq{sub 3}) by photoemission spectroscopy. We find that oxidation of the cobalt leads to a gradual suppression of hybrid interface states, to a progressive change in the work function and to a continuous energetic shift of the molecular orbitals towards higher binding energies. Based on these observations, we propose controlled oxidation of the ferromagnetic electrode as an easy and effective possibility to tune the performance of organic spintronics devices.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Prediction of {sup 1}P Rydberg energy levels of beryllium based on calculations with explicitly correlated Gaussians

Benchmark variational calculations are performed for the seven lowest 1s{sup 2}2s np ({sup 1}P), n = 2…8, states of the beryllium atom. The calculations explicitly include the effect of finite mass of {sup 9}Be nucleus and account perturbatively for the mass-velocity, Darwin, and spin-spin relativistic corrections. The wave functions of the states are expanded in terms of all-electron explicitly correlated Gaussian functions. Basis sets of up to 12 500 optimized Gaussians are used. The maximum discrepancy between the calculated nonrelativistic and experimental energies of 1s{sup 2}2s np ({sup 1}P) →1s{sup 2}2s{sup 2} ({sup 1}S) transition is about 12 cm{sup −1}. The inclusion of the relativistic corrections reduces the discrepancy to bellow 0.8 cm{sup −1}.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2012

Concerning the energy levels of silver in Ge-Si alloys

The emission from impurity states of silver (an element of the IB subgroup) in a Ge-Si alloy, containing 18 at % Si, has been studied. The donor level of silver has been found in crystals doubly doped with gallium and silver, while its first acceptor level has been revealed in crystals doped with only silver. Single crystals were grown by pulling from a melt using a feeding rod. Doping with gallium was performed by introducing this element into the feeding rod, and silver was introduced into the crystals via diffusion. The positions of the donor and first acceptor Ag levels with respect to the top of the valence band were found by analyzing the temperature dependence of the Hall coefficient and the electroneutrality equation for the crystal: 0.06 and 0.29 eV, respectively.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Energy levels and far-infrared spectra of oval-shaped nanorings

The evolution of the Aharonov-Bohm oscillation of low-lying states and far infrared spectrum associated to variation of the path curvature for electron motion along nanorings with centerlines in a form of a set of Cassini ovals, whose shape is changed continuously from a single elongated loop to two separated loops is theoretically investigated.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2018

High-accuracy multi-configuration Dirac–Hartree–Fock calculations of the energy levels and transition properties of Ga-like to Br-like gadolinium ions

Highlights: • A complete and accurate data set of excitation energies, lifetimes, wavelengths and E1, M1, E2, M2 and E3 line strengths, transition rates, and oscillator strengths for Ga-like to Br-like Gd ions is reported. • The Multi-configuration Dirac–Hartree–Fock method is employed. • The effects of core–valence electron correlation from the deep subshells 3d and 3p have been investigated. • The computed excitation energies from the present MCDHF calculations of the VV+CV{sub 3d}+CV{sub 3p} model agree well with the experimental values. The differences are less than ±0.1% for most of the levels. - Abstract: Theoretical calculations of Ga-like to Br-like gadolinium ions were performed by using the fully relativistic multi-configuration Dirac–Hartree–Fock (MCDHF) method. Extensive lists of excitation energies, wavelengths, line and oscillator strengths, and E1, M1, E2, M2, and E3 transition rates are presented. The effects of core–valence electron correlation from the deep subshells 3d and 3p are investigated and the accuracy of the results is confirmed by comparing with available theoretical and experimental data sets.

74 ATOMIC AND MOLECULAR PHYSICS↗