Search query: Transition energy

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abstract: We study the influence of surface passivating ligands on the optical and structural properties of zinc blende CdSe nanoplatelets. Ligand exchange of native oleic acid with aliphatic thiol or phosphonic acid on the surface of nanoplatelets results in a large shift of exciton transition energy for up to 240 meV. Ligand exchange also leads to structural changes (strain) in the nanoplatelet's core analysed by wide angle X ray diffraction. By correlating the experimental data with theoretical calculations we demonstrate that the exciton energy shift is mainly caused by the ligand induced anisotropic transformation of the crystalline structure altering the well width of the CdSe core. Further the exciton reduced mass in these CdSe quantum wells is determined by a new method and this agrees well with the expected values substantiating that ligand strain induced changes in the colloidal quantum well thickness are responsible for the observed spectral shifts. Our findings are important for theoretical modeling of other anisotropically strained systems and demonstrate an approach to tune the optical properties of 2D semiconductor nanocrystals over a broad region thus widening the range of possible applications of AIIBVI nanoplatelets in optics and optoelectronics.
author_names: Artsiom Antanovich

Alexander W Achtstein

A S Matsukovich

Anatol V Prudnikau

Prashant Bhaskar

Vladimir N Gurin

Michael Molinari

Mikhail V Artemyev
title: A strain induced exciton transition energy shift in CdSe nanoplatelets: the impact of an organic ligand shell.
venue: Nanoscale
year: 2017

abstract: We use continuum mechanics to calculate an entire least energy pathway of membrane fusion, from stalk formation, to pore creation, and through fusion pore enlargement. The model assumes that each structure in the pathway is axially symmetric. The static continuum stalk structure agrees quantitatively with experimental stalk architecture. Calculations show that in a stalk, the distal monolayer is stretched and the stored stretching energy is significantly less than the tilt energy of an unstretched distal monolayer. The string method is used to determine the energy of the transition barriers that separate intermediate states and the dynamics of two bilayers as they pass through them. Hemifusion requires a small amount of energy independently of lipid composition, while direct transition from a stalk to a fusion pore without a hemifusion intermediate is highly improbable. Hemifusion diaphragm expansion is spontaneous for distal monolayers containing at least two lipid components, given sufficiently negative diaphragm spontaneous curvature. Conversely, diaphragms formed from single component distal monolayers do not expand without the continual injection of energy. We identify a diaphragm radius, below which central pore expansion is spontaneous. For larger diaphragms, prior studies have shown that pore expansion is not axisymmetric, and here our calculations supply an upper bound for the energy of the barrier against pore formation. The major energy requiring deformations in the steps of fusion are: widening of a hydrophobic fissure in bilayers for stalk formation, splay within the expanding hemifusion diaphragm, and fissure widening initiating pore formation in a hemifusion diaphragm.
author_names: Rolf J Ryham

Thomas Klotz

Lihan Yao

Fredric S Cohen
title: Calculating Transition Energy Barriers and Characterizing Activation States for Steps of Fusion.
venue: Biophysical journal
year: 2016

abstract: Abstract Germany has set ambitious policies for increasing renewable energy shares and decommissioning nuclear energy, but there are certain scientific gaps on how this transition should occur, especially when considering all energy sectors. The purpose of this study is to advance the knowledge of transitioning the German energy system to 100% renewable energy towards 2050. Taking into consideration renewable resource potentials, energy system costs and primary energy supply this study develops a path for transitioning the German energy system within the heating, industrial, transport and electricity sectors. The analysis demonstrates that it is possible to carry out this transition from a technical and economic perspective with some measures being vital for achieving this ambition in a cost effective manner. The most significant challenge in this transition is regarding resource potentials where especially biomass resources are constrained and under pressure. Finally, the most influential measures for achieving the renewable transition are discussed.
author_names: Kenneth Hansen

Brian Vad Mathiesen

Iva Ridjan Skov
title: Full energy system transition towards 100% renewable energy in Germany in 2050
venue: Renewable and Sustainable Energy Reviews
year: 2019

abstract: Owing to its low excitation energy and long radiative lifetime, the first excited isomeric state of thorium 229, 229mTh, can be optically controlled by a laser1,2 and is an ideal candidate for the creation of a nuclear optical clock3, which is expected to complement and outperform current electronic shell based atomic clocks4. A nuclear clock will have various applications such as in relativistic geodesy5, dark matter research6 and the observation of potential temporal variations of fundamental constants7 but its development has so far been impeded by the imprecise knowledge of the energy of 229mTh. Here we report a direct measurement of the transition energy of this isomeric state to the ground state with an uncertainty of 0.17 electronvolts (one standard deviation) using spectroscopy of the internal conversion electrons emitted in flight during the decay of neutral 229mTh atoms. The energy of the transition between the ground state and the first excited state corresponds to a wavelength of 149.7 3.1 nanometres, which is accessible by laser spectroscopy through high harmonic generation. Our method combines nuclear and atomic physics measurements to advance precision metrology, and our findings are expected to facilitate the application of high resolution laser spectroscopy on nuclei and to enable the development of a nuclear optical clock of unprecedented accuracy. The transition energy of the first excited state of 229Th to the ground state is determined through the measurement of internal conversion electrons to correspond to a wavelength of 149.7 3.1 nanometres.
author_names: Benedict Seiferle

Lars von der Wense

Pavlo V Bilous

Ines Amersdorffer

Christoph Lemell

Florian Libisch

Simon Stellmer

Thorsten Schumm

Christoph E Dullmann

Adriana P'alffy

Peter G Thirolf
title: Energy of the 229Th nuclear clock transition
venue: Nature
year: 2019

abstract: Abstract Is an energy transition currently in progress, where renewable energy sources are replacing fossil fuels? Previous changes in the proportion of energy produced by various sources such as in the nineteenth century when coal surpassed biomass in providing the largest share of the global energy supply and in the twentieth century when petroleum overtook coal could more accurately be characterized as energy additions rather than transitions. In both cases, the use of the older energy source continued to grow, despite rapid growth in the new source. Evidence from contemporary trends in energy production likewise suggest that as renewable energy sources compose a larger share of overall energy production, they are not replacing fossil fuels but are rather expanding the overall amount of energy that is produced. We argue that although it is reasonable to expect that renewables will come to provide a growing share of the global energy supply, it is misleading to characterize this growth in renewable energy as a "transition" and that doing so could inhibit the implementation of meaningful policies aimed at reducing fossil fuel use.
author_names: Richard York

Shannon Elizabeth Bell
title: Energy transitions or additions?
venue: Energy Research Social Science
year: 2019

abstract: In this paper, intersubband transition energy is computed for core shell (normal and inverted) quantum dots (CSQD) of cubic and spherical geometries by solving time independent Schrodinger equation using finite difference technique. Sparse, structured Hamiltonian matrices of order N3 x N3 for cubic and N x N for spherical dots are produced considering N discrete points in spatial direction. The matrices are diagonalized to obtain eigenstates for electrons. Computed results for the lowest three eigenstates and intersubband transitions are shown for different structural parameters taking GaAs/AlxGa1 xAs based CSQD as example. Transition energy decreases with increase in core thickness. When compared, spherical CSQDs show higher transition energy between two subbands than cubic CSQDs of similar size and same material composition. Also, in inverted configuration, transition energy decreases for a cubic dot while increases for a spherical dot as core size is increased. Wide tuning range for intersubband transition by tailoring dot dimensions indicates important applications for optical emitters/detectors.
author_names: Arpan Deyasi

S Bhattacharyya

Nikhil Ranjan Das
title: Computation of intersubband transition energy in normal and inverted core shell quantum dots using finite difference technique
year: 2013

abstract: The 1s2s (3)S(1) 1s(2) (1)S(0) relativistic magnetic dipole transition in heliumlike argon, emitted by the plasma of an electron cyclotron resonance ion source, has been measured using a double flat crystal x ray spectrometer. Such a spectrometer, used for the first time on a highly charged ion transition, provides absolute (reference free) measurements in the x ray domain. We find a transition energy of 3104.1605(77) eV (2.5 ppm accuracy) This value is the most accurate, reference free measurement done for such a transition and is in good agreement with recent QED predictions.
author_names: Pedro Amaro

Sophie Schlesser

Mauro Guerra

E-O Le Bigot

J M Isac

Pascal Travers

Jose Paulo Santos

Csilla I Szabo

Alexandre Gumberidze

Paul Indelicato
title: Absolute measurement of the relativistic magnetic dipole transition energy in heliumlike argon.
venue: Physical review letters
year: 2012

abstract: Abstract The effects of the doping level and the operating current on the transition energy of InGaN/GaN QW diodes have been studied through the self consistent solution of the Schrodinger and Poisson equations. Broad change in the transition energy is observed due to the doping variation. With increase in the current density the emission peak shifts toward higher energy. This shift, which is a major disadvantage of the lighting devices, is reduced significantly by increasing the doping concentration.
author_names: Siddhartha Panda

Dipankar Biswas
title: Effects of doping concentration on the transition energy of InGaN/GaN quantum well diodes
year: 2013

author_names: Pengbiao Geng

Shasha Zheng

Hao Tang

Rongmei Zhu

Li Zhang

Shuai Cao

Huaiguo Xue

Huan Pang
title: Transition Metal Sulfides Based on Graphene for Electrochemical Energy Storage
year: 2018

abstract: The calculation of vertical electronic transition energies of molecular systems in solution with accurate quantum mechanical methods requires the use of approximate and yet reliable models to describe the effect of the solvent on the electronic structure of the solute. The polarizable continuum model (PCM) of solvation represents a computationally efficient way to describe this effect, especially when combined with coupled cluster (CC) methods. Two formalisms are available to compute transition energies within the PCM framework: State Specific (SS) and Linear Response (LR) The former provides a more complete account of the solute solvent polarization in the excited states, while the latter is computationally very efficient (i.e. comparable to gas phase) and transition properties are well defined. In this work, I review the theory for the two formalisms within CC theory with a focus on their computational requirements, and present the first implementation of the LR PCM formalism with the coupled cluster singles and doubles method (CCSD) Transition energies computed with LR and SS CCSD PCM are presented, as well as a comparison between solvation models in the LR approach. The numerical results show that the two formalisms provide different absolute values of transition energy, but similar relative solvatochromic shifts (from nonpolar to polar solvents) The LR formalism may then be used to explore the solvent effect on multiple states and evaluate transition probabilities, while the SS formalism may be used to refine the description of specific states and for the exploration of excited state potential energy surfaces of solvated systems.
author_names: Marco Caricato
title: A comparison between state specific and linear response formalisms for the calculation of vertical electronic transition energy in solution with the CCSD PCM method.
venue: The Journal of chemical physics
year: 2013