A5063437174- Quantum Dots Synthesis And Properties
- Silicon Nanostructures and Photoluminescence
- Chalcogenide Semiconductor Thin Films
- Diamond and Carbon-based Materials Research
- Nanowire Synthesis and Applications
- Semiconductor materials and devices
- Molecular Junctions and Nanostructures
- High-pressure geophysics and materials
- Perovskite Materials and Applications
- Semiconductor materials and interfaces
- Quantum and electron transport phenomena
- Advanced Chemical Physics Studies
- Force Microscopy Techniques and Applications
- Advancements in Battery Materials
- Nanocluster Synthesis and Applications
- Semiconductor Quantum Structures and Devices
- Laser-Ablation Synthesis of Nanoparticles
- Physics of Superconductivity and Magnetism
- Advanced Battery Materials and Technologies
- Advanced Physical and Chemical Molecular Interactions
- 2D Materials and Applications
- Ion-surface interactions and analysis
- Advanced Thermoelectric Materials and Devices
- Advanced ceramic materials synthesis
- Photovoltaic Systems and Sustainability
Samsung (United States)
2021-2023
Argonne National Laboratory
2016-2021
Material Sciences (United States)
2019-2021
University of Chicago
2014-2019
University of California, Davis
2009-2015
Budapest University of Technology and Economics
2009-2014
University of California System
2014
Abstract Band edge positions of semiconductors determine their functionality in many optoelectronic applications such as photovoltaics, photoelectrochemical cells and light emitting diodes. Here we show that band lead sulfide (PbS) colloidal semiconductor nanocrystals, specifically quantum dots (QDs), can be tuned over 2.0 eV through surface chemistry modification. We achieved this remarkable control the development simple, robust scalable solution-phase ligand exchange methods, which...
In this Letter, the photoinduced switching of single nitrogen-vacancy (NV) center between two different charge states, negative (NV(-)) and neutral (NV(0)), is studied under resonant excitation at liquid helium temperature. We show that conversion NV(0) to NV(-) significantly improves spectral stability defect allows high fidelity initialization spin qubit. Based on density functional theory calculations a novel mechanism involving an Auger ionization transfer electron from valence band...
NiFe oxyhydroxide materials are highly active electrocatalysts for the oxygen evolution reaction (OER), an important process carbon-neutral energy storage. Recent spectroscopic and computational studies increasingly support iron as site of catalytic activity but differ with respect to relevant redox state. A combination hybrid periodic density functional theory calculations spectroelectrochemical experiments elucidate electronic structure thermodynamics Ni-only mixed thin-film...
Lithium-CO2 batteries are attractive energy-storage systems for fulfilling the demand of future large-scale applications such as electric vehicles due to their high specific energy density. However, a major challenge with Li-CO2 is attain reversible formation and decomposition Li2 CO3 carbon discharge products. A fully battery developed overall neutrality using MoS2 nanoflakes cathode catalyst combined an ionic liquid/dimethyl sulfoxide electrolyte. This combination materials produces...
Abstract Due to their exceptional high energy density, lithium-ion batteries are of central importance in many modern electrical devices. A serious limitation, however, is the slow charging rate used obtain full capacity. Thus far, there have been no ways increase without losses density and electrochemical performance. Here we show that a cathode can be dramatically increased via interaction with white light. We find direct exposure light an operating LiMn 2 O 4 during leads remarkable...
Silicon exhibits a large variety of different bulk phases, allotropes, and composite structures, such as, e.g., clathrates or nanostructures, at both higher lower densities compared with diamond-like Si-I. New Si structures continue to be discovered. These novel forms offer exciting prospects create based materials, which are non-toxic earth-abundant, properties tailored precisely towards specific applications. We illustrate how materials either in the as nanostructures may used...
We present density functional and many body perturbation theory calculations of the electronic, optical, impact ionization properties Si nanoparticles (NPs) with core structures based on high-pressure bulk phases. particles a BC8 structure exhibit significantly lower optical gaps multiple exciton generation (MEG) thresholds, an order magnitude higher MEG rate than diamondlike ones same size. Several mechanisms are discussed to further reduce gap, including surface reconstruction chemistry,...
Generating multiple excitons by a single high-energy photon is promising third-generation solar energy conversion strategy. We demonstrate that exciton generation (MEG) in PbS|CdS Janus-like heteronanostructures enhanced over of single-component and core/shell nanocrystal architectures, with an onset close to two times the PbS band gap. attribute MEG asymmetric nature heteronanostructure results increase effective Coulomb interaction drives reduction competing hot cooling rate. Slowed occurs...
Interactions between light and matter are of fundamental interest in a variety fields, such as solar-energy conversion. A new, accurate method, based on first principles, is used to predict the absorption emission properties range organic inorganic molecules.
Abstract The development of theories and methods devoted to the accurate calculation electronic quasi-particle states levels molecules, clusters solids is prime importance interpret experimental data. These quantum systems are often modelled by using Born–Oppenheimer approximation where coupling between electrons vibrational modes not fully taken into account, treated as pure quasi-particles. Here, we show that in small diamond cages, called diamondoids, electron–vibration leads breakdown...
Abstract The optimization of traditional electrocatalysts has reached a point where progress is impeded by fundamental physical factors including inherent scaling relations among thermokinetic characteristics different elementary reaction steps, non‐Nernstian behavior, and electronic structure the catalyst. This indicates that currently utilized classes may not be adequate for future needs. study reports on synthesis characterization new class materials based 2D transition metal...
Absorption spectrum of small nanodiamonds, i.e., diamondoids has been recently measured exhibiting features that are not understood. Previous calculations, even beyond standard density-functional theory (DFT), failed to obtain the experimental optical gaps $({E}_{\text{g}})$ diamondoids. We show all-electron time-dependent DFT (TD-DFT) calculations including hybrid functional in TD-DFT kernel able provide quantitatively accurate results. Our demonstrate Rydberg transitions characteristic for...
The electronic properties and charge recombination dynamics of oxidized Si nanoparticles containing surface dangling bonds are investigated using first principles calculations.
We studied the optical absorption enhancement in colloidal suspensions of PbS quantum dots (QD) upon ligand exchange from oleate to a series cinnamate ligands. By combining experiments and ab initio simulations, we elucidate physical parameters that govern enhancement. find that, within cinnamate/PbS QD system, scales linearly with electronic gap ligand, indicating ligand/QD coupling occurs equally efficient between HOMO their respective LUMO levels. Disruption conjugation connects aromatic...
In this paper, we analyze the numerical aspects of inherent multireference density matrix renormalization group (DMRG) calculations on top periodic Kohn–Sham functional theory using complete active space approach. The potential framework is illustrated by studying hexagonal boron nitride nanoflakes embedding a charged single vacancy point defect revealing vertical energy spectrum with prominent character. We investigate consistency DMRG from perspective sample size, basis and selection...
The optical gap of nanometer sized diamond cages, i.e., diamondoids, lies in the ultraviolet spectral region. Here we show by hybrid functional based time-dependent density-functional calculations that, varying number $\mathrm{C}\mathrm{S}$ double bonds at surface absorption onset can be tuned toward infrared Our finding has an important implication for vivo biological applications where toxic and unstable dye molecules may substituted luminescent sulfurized diamondoids.
The Intermediate Band (IB) solar cell concept is a promising idea to transcend the Shockley-Queisser limit. Using results of first-principles calculations, we propose that colloidal nanoparticles (CNPs) are viable and efficient platform for implementation IB concept. We focused on CdSe CNPs showed intragap states present in isolated with reconstructed surfaces combine form an arrays CNPs, which well separated from valence conduction band edges. demonstrated optical transitions active. also...
The in silico design of novel complex materials for energy conversion requires accurate, ab initio simulation charge transport. In this work, we present an implementation constrained density functional theory (CDFT) the calculation parameters transport hopping regime. We verify our against literature results molecular systems, and discuss dependence on numerical choice localization potentials. addition, compare CDFT with those other commonly used methods simulating between nanoscale building...
Defects at the surface of semiconductor quantum dots (QDs) give rise to electronic states within gap, which are detrimental charge transport properties QD devices. We investigated in silicon with deep and shallow defect levels, using ab initio calculations constrained density functional theory. found that defects may be more than ones, associated transfer rates differing by up 5 orders magnitude for small (1–2 nm) considered here. Hence, our results indicate common assumption, ability trap...
We analyze the performance of recently proposed screened exchange constant functional (SX) ( Brawand et al. Phys. Rev. X 2016 , 6 041002 ) on GW100 test set, and we discuss results obtained at different levels self-consistency. The SX is a generalization dielectric dependent hybrid functionals to finite systems; it nonempirical depends average screening interaction. compare for ionization potentials with those CCSD(T) calculations experiments, find excellent agreement, par recent state art...
We have investigated high energy excitations in ∼1−2 nm Si nanoparticles (NPs) by ab initio time-dependent density functional calculations, focusing on the influence excitation spectra, of surface reconstruction, passivation alkyl groups, and interaction between NPs. found that reconstruction may change spectra dramatically at both low energies above gap; absorption be enhanced nonlinearly presence compared to unreconstructed, hydrogenated NPs, Our findings can help interpret recent...
The electronic structure and absorption spectrum of hydrogenated silicon carbide nanocrystals (SiC NCs) have been determined by first principles calculations. We show that the reconstructed surface can significantly change not just onset but shape at higher energies. compare our results with two recent experiments on ultrasmall SiC NCs.
Diamondoids are small diamond nanoparticles (NPs) that built up from cages. Unlike usual semiconductor NPs, their atomic structure is exactly known, thus they ideal test-beds for benchmarking quantum chemical calculations. Their usage in spintronics and bioimaging applications requires a detailed knowledge of electronic optical properties. In this paper, we apply density functional theory (DFT) based methods to understand the properties few selected pure modified diamondoids which accurate...
Multiple Exciton Generation (MEG) in nanoparticle-based solar cells promises to increase the cell-efficiency above Shockley–Queisser limit. However, utilizing MEG is hampered by Quantum Confinement Dilemma (QCD): quantum confinement advantageously increases effective Coulomb interaction, but at same time disadvantageously electronic gap. Using ab initio calculations we showed that germanium nanoparticles with core structures of high pressure phases bulk Ge can transcend QCD, simultaneously...