A5062272137- Quantum Dots Synthesis And Properties
- Graphene research and applications
- Spectroscopy and Quantum Chemical Studies
- Molecular Junctions and Nanostructures
- Carbon Nanotubes in Composites
- Chalcogenide Semiconductor Thin Films
- Photochemistry and Electron Transfer Studies
- Energetic Materials and Combustion
- Thermal properties of materials
- Mechanical and Optical Resonators
- Perovskite Materials and Applications
- 2D Materials and Applications
- Advanced Thermodynamics and Statistical Mechanics
- Quantum and electron transport phenomena
- Thermal and Kinetic Analysis
- Advanced Chemical Physics Studies
- Combustion and Detonation Processes
- Plasmonic and Surface Plasmon Research
- Nanopore and Nanochannel Transport Studies
- High-pressure geophysics and materials
- Semiconductor Quantum Structures and Devices
- thermodynamics and calorimetric analyses
- Diamond and Carbon-based Materials Research
- Silicon Nanostructures and Photoluminescence
- Topological Materials and Phenomena
Los Alamos National Laboratory
2014-2023
Center for Integrated Nanotechnologies
2014-2015
University of Arizona
2014
New Mexico State University
2008-2010
Nonlinear Control Strategies (United States)
2010
Florida State University
2009
Novosibirsk State University
2004-2006
Russian Academy of Sciences
2001
The optical response of semiconducting monolayer transition-metal dichalcogenides (TMDCs) is dominated by strongly bound excitons that are stable even at room temperature. However, substrate-related effects such as screening and disorder in currently available specimens mask many anticipated physical phenomena limit device applications TMDCs. Here, we demonstrate these undesirable suppressed suspended devices. Extremely robust (photogain > 1,000) fast (response time < 1 ms) photoresponse...
We report 65 tesla magneto-absorption spectroscopy of exciton Rydberg states in the archetypal monolayer semiconductor WSe$_2$. The strongly field-dependent and distinct energy shifts 2s, 3s, 4s excited neutral excitons permits their unambiguous identification allows for quantitative comparison with leading theoretical models. Both sizes (via low-field diamagnetic shifts) energies $ns$ agree remarkably well detailed numerical simulations using non-hydrogenic screened Keldysh potential 2D...
Quantum dots (QDs) of ternary I–III–VI2 compounds such as CuInS2 and CuInSe2 have been actively investigated heavy-metal-free alternatives to cadmium- lead-containing semiconductor nanomaterials. One serious limitation these nanostructures, however, is a large photoluminescence (PL) line width (typically >300 meV), the origin which still not fully understood. It remains even unclear whether observed broadening results from considerable sample heterogeneities (due, e.g., size polydispersity)...
Luminescent solar concentrators (LSCs) can be utilized as both large-area collectors of radiation supplementing traditional photovoltaic cells well semitransparent "solar windows" that provide a desired degree shading and simultaneously serve power-generation units. An important characteristic an LSC is concentration factor (C) thought coefficient effective enlargement (or contraction) the area cell when it coupled to LSC. Here we use analytical numerical Monte Carlo modeling in addition...
One process limiting the performance of solar cells is rapid cooling (thermalization) hot carriers generated by higher-energy photons. In principle, thermalization losses can be reduced converting kinetic energy energetic into additional electron-hole pairs via carrier multiplication (CM). While being inefficient in bulk semiconductors this enhanced quantum dots, although not sufficiently high to considerably boost power output practical devices. Here we demonstrate that thick-shell...
Understanding the pathways of hot exciton relaxation in photoexcited semiconductor nanocrystals, also called quantum dots (QDs), is paramount importance multiple energy, electronics and biological applications. An important nonradiative channel originates from nonadiabatic (NA) coupling electronic degrees freedom to nuclear vibrations, which QDs depend on confinement effects complicated surface chemistry. To elucidate role ligands processes we study dynamics NA Cd(33)Se(33) passivated by...
Photoluminescent defect states introduced by sp3 functionalization of semiconducting carbon nanotubes are rapidly emerging as important routes for boosting emission quantum yields and introducing new functionality. Knowledge the relaxation dynamics these is required understanding how functionalizing agents (molecular dopants) may be designed to access specific behaviors. We measure photoluminescence (PL) decay aryl nanotube surface. Results given five different chiralities, each doped with a...
Fluorescent defects have opened up exciting new opportunities to chemically tailor semiconducting carbon nanotubes for imaging, sensing, and photonics needs such as lasing, single photon emission, upconversion. However, experimental measurements on the trap depths of these show a puzzling energy mismatch between optical gap (difference in emission energies native exciton defect states) thermal detrapping determined by application van 't Hoff equation. To resolve this fundamentally important...
The influence of ligands on electronic structure small gold clusters (Au2, Au4) has been investigated by density functional theory (DFT). Specifically, we study the effect bonding four donor (NH3, NMe3, PH3, and PMe3) cluster geometries energetics in gas phase solution. Performance five generations DFT functionals different basis sets is assessed. Our results benchmark importance model polarization functions set for calculations ligated systems. We obtain NMe3 ≈ NH3 < PH3 PMe3 order ligand...
The detonation of carbon-rich high explosives yields solid carbon as a major constituent the product mixture, and depending on thermodynamic conditions behind shock front, variety allotropes morphologies may form evolve. We applied time-resolved small-angle X-ray scattering (TR-SAXS) to investigate dynamics clustering during PBX 9502, an explosive composed 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) 5 wt % fluoropolymer binder. Solid formation was probed from 0.1 2.0 μs front revealed rapid...
The unique optical properties exhibited by visible emitting core/shell quantum dots with especially thick shells are the focus of widespread study, but have yet to be realized in infrared (IR)-active nanostructures. We apply an effective-mass model identify PbSe/CdSe as a promising system for achieving this goal. then synthesize colloidal shell thicknesses up 4 nm that exhibit unusually slow hole intraband relaxation from core states, evidenced emergence dual emission, i.e., IR...
One of the most striking features novel two-dimensional semiconductors (e.g., transition metal dichalcogenide monolayers or phosphorene) is a strong Coulomb interaction between charge carriers resulting in large excitonic effects. In particular, this leads to formation multicarrier bound states upon photoexcitation excitons, trions, and biexcitons), which could remain stable at near-room temperatures contribute significantly optical properties such materials. present work we have used path...
Photoluminescent sp3 defect states introduced to single wall carbon nanotubes (SWCNTs) through low-level covalent functionalization create new photophysical behaviors and functionality as a result of sites acting exciton traps. Evaluation relaxation dynamics in varying dielectric environments can aid advancing more complete description defect-state pathways electronic structure. Here, we exploit helical wrapping polymers route suspending (6,5) SWCNTs covalently functionalized with...
An Arrhenius–Wescott–Stewart–Davis (AWSD) reactive flow model for high explosive PBX 9404 is developed. We specifically calibrate an AWSD by fitting equations of state reactants and detonation products to the results thermochemical calculations experimental data from multiple sources. The calibrated are then coupled with Arrhenius rate law based on shock temperature that describes reaction progress during detonation. parameter values in gas-gun diameter effect results. strong agreement...
Landauer's formula is the standard theoretical tool to examine ballistic transport in nano- and meso-scale junctions, but it necessitates that any variation of junction with time must be slow compared characteristic times system, e.g., relaxation local excitations. Transport through structurally dynamic junctions is, however, increasingly interest for sensing, harnessing fluctuations, real-time control. Here, we calculate steady-state current when electrons reservoirs present demonstrate...
DNA denaturation has been a subject of intense study due to its relationship transcription and fundamental importance as nonlinear structural transition. Many aspects this phenomenon, however, remain poorly understood. Existing models fit quite well with experimental results on the fraction unbound base pairs versus temperature, but yield incorrect for other essential quantities such pair fluctuation time scales. Here we demonstrate that nanoscale thermal transport can serve sensitive probe...
We propose a novel method to probe electronic excitations in graphene by monitoring the fluorescence quenching of semiconductor quantum dot (or dye molecule) due resonance energy transfer sheet. show how dispersion relation plasmons (as well as other excitations) can be accurately extracted controlling backgate voltage and distance between graphene.
We discuss fundamental differences in electronic structure as reflected one- and two-photon absorption spectra of semiconductor quantum dots organic molecules by performing systematic experimental theoretical studies the size-dependent colloidal dots. Quantum-chemical effective-mass calculations are used to model compare them with results. Currently, quantum-chemical limited only small-sized (nanoclusters) but allow one study various environmental effects on optical such solvation surface...
Close-packed assemblies of ligand-passivated colloidal nanocrystals can exhibit enhanced photoluminescent stability, but the origin this effect is unclear. Here, we use experiment, simulation, and ab initio computation to examine influence interparticle interactions on stability silicon nanocrystal aggregates. The time-dependent photoluminescence emitted by structures ranging in size from a single quantum dot agglomerates more than thousand compared with Monte Carlo simulations...
This study describes variational energy expressions and analytical excited state gradients for time-dependent self-consistent field methods with polarizable solvent effects. Linear response, vertical excitation, state-specific models are examined. Enforcing a ground expression in the model is found to reduce it excitation model. Variational then provided linear response formulated. Using semiempirical chemistry, verified by numerical differentiation respect static external electric field....
We implement and examine three excited state solvent models in time-dependent self-consistent field methods using a consistent formalism which unambiguously shows their relationship. These are the linear response, specific, vertical excitation models. Their effects on energies calculated with equivalent of COSMO/CIS/AM1 given for set test molecules varying charge transfer character. The resulting explained qualitatively dipole approximation. It is shown that fundamental differences between...
Recent demonstration of room temperature, telecommunication wavelength single photon generation by sp3 defects wall carbon nanotubes established these as a new class quantum materials. However, their practical utilization in development light sources calls for significant improvement imperfect yield (QY∼10-30%). PL intensity fluctuations observed with some also need to be eliminated. Aiming toward attaining fundamental understanding necessary addressing critical issues, we investigate...