A5048766371- Organic Electronics and Photovoltaics
- Conducting polymers and applications
- Organic Light-Emitting Diodes Research
- Perovskite Materials and Applications
- Molecular Junctions and Nanostructures
- Photonic Crystals and Applications
- Photonic and Optical Devices
- Thin-Film Transistor Technologies
- Luminescence and Fluorescent Materials
- Photoreceptor and optogenetics research
- Mechanical and Optical Resonators
- Solid-state spectroscopy and crystallography
- Silicon Nanostructures and Photoluminescence
- Plasmonic and Surface Plasmon Research
- Quantum and electron transport phenomena
- Spectroscopy and Quantum Chemical Studies
- Random lasers and scattering media
- Fullerene Chemistry and Applications
- Photochemistry and Electron Transfer Studies
- Phase-change materials and chalcogenides
- Organic and Molecular Conductors Research
- Terahertz technology and applications
- Silicon and Solar Cell Technologies
- Graphene research and applications
- Analytical Chemistry and Sensors
University of Utah
2016-2025
University of Chicago
2021
Center for Integrated Nanotechnologies
2021
Los Alamos National Laboratory
2021
Argonne National Laboratory
2021
North Carolina State University
2021
Salt Lake Regional Medical Center
2013-2020
University of Maryland, College Park
2013
University of Georgia
2013
Technion – Israel Institute of Technology
1984-2010
Several spectroscopic methods were applied to study the characteristic properties of electronic excitations in thin films regioregular and regiorandom polythiophene polymers. In polymers, which form two-dimensional lamellar structures, increased interchain coupling strongly influences traditional one-dimensional polymer chains. The photogenerated charge (polarons) show delocalization that results a relatively small polaronic energy, multiple absorption bands gap where lowest energy band...
Using the picosecond pump and probe technique we have detected oscillations of photoinduced transmission reflection in thin films $a$-${\mathrm{As}}_{2}$${\mathrm{Te}}_{3}$ cis-polyacetylene. These are due to generation propagation coherent acoustic phonons film. We discuss detection mechanism, use this effect measure sound velocity a film $a$-Si${\mathrm{O}}_{2}$.
Spin injection sans magnetism Light-emitting diodes (LEDs) that emit circularly polarized light (spin-LEDs) have potential applications in three-dimensional displays, bioencoding, and tomography. The requisite spin polarization of the charge carriers is usually achieved with ferromagnetic contacts applied magnetic fields, but Kim et al. report on a room-temperature spin-LED relies instead chiral-induced selectivity organic layer. This layer selectively injected spin-polarized holes into...
A random collection of scatterers in a gain medium can produce coherent laser emission lines dubbed “random lasing.” We show that biological tissues, including human support lasing when infiltrated with concentrated dye solution. To extract typical resonator size within the tissue we average power Fourier transform spectra collected from many excitation locations tissue; verified this procedure by computer simulation. Surprisingly, found malignant tissues more compared to healthy taken same...
Chiral molecules in Pb-halide 2D-layered films achieve up to 86% spin-polarized transport, enabling novel spintronic applications.
The resonant Raman scattering (RRS) from the three ${A}_{g}$ modes of trans-polyacetylene and charged-induced ir are analyzed with use amplitude- phase-mode theories. It is shown that observed phonon frequencies relative intensities all obtained at various laser excitation energies \ensuremath{\Elzxh}${\ensuremath{\omega}}_{L}$ accounted for by a single propagator which also describes charge-induced infrared-active modes. dispersion RRS exhibits inhomogeneity sample in turn provides...
Two-dimensional (2D) layered hybrid organic-inorganic halide perovskite semiconductors form natural "multiple quantum wells" that have strong spin-orbit coupling due to the heavy elements in their building blocks. This may lead "Rashba splitting" close extrema electron bands. We used a plethora of ultrafast transient, nonlinear optical spectroscopies and theoretical calculations study primary (excitons) long-lived (free carriers) photoexcitations thin films 2D perovskite, namely,...
Abstract Translation of chirality and asymmetry across structural motifs length scales plays a fundamental role in nature, enabling unique functionalities contexts ranging from biological systems to synthetic materials. Here, we introduce transfer the organic–inorganic interface two-dimensional hybrid perovskites using appropriate chiral organic cations. The preferred molecular configuration spacer cations, R -(+)- or S -(−)-1-(1-naphthyl)ethylammonium their asymmetric hydrogen-bonding...
Recently the hybrid organic-inorganic trihalide perovskites have shown remarkable performance as active layers in photovoltaic and other optoelectronic devices. However, their spin characteristic properties not been fully studied, although due to relatively large spin-orbit coupling these materials may show great promise for spintronic applications. Here we demonstrate spin-polarized carrier injection into methylammonium lead bromide films from metallic ferromagnetic electrodes two...
The spin-polarized organic light-emitting diode (spin-OLED) has been a long-sought device within the field of spintronics. We designed, fabricated, and studied spin-OLED with ferromagnetic electrodes that acts as bipolar spin valve (OSV), based on deuterated derivative poly(phenylene-vinylene) small hyperfine interaction. In double-injection limit, shows ~1% magneto-electroluminescence (MEL) response, which follows electrode coercive fields originates from space charge-limited current. stark...
We have studied the interplay between photophysics and film morphology of poly(9,9-dioctyl)fluorene (PFO) using a variety optical probes. Upon slowly warming spin-cast PFO from 80 to 300 K, fraction sample is transformed into different solid phase, $\ensuremath{\beta}$ phase. Absorption electroabsorption measurements show that phase has more extended conjugation than glassy As consequence, excited states are redshifted higher polarizability. The photoinduced absorption spectrum dominated by...
We have studied electronic excited states in films of poly(p-phenylenevinylene) using picosecond transient and cw photomodulation, photoluminescence, their excitation spectra, as well electroabsorption spectroscopy. determined all the important energy levels singlet excitons with odd even parity, onset continuum band, two-electron (biexciton) states, two relevant triplet show that good agreement exists models involving electron correlation.
Picosecond dynamics of exciton emission and absorption have been studied in neat thin films a variety poly (phenylene vinylene) derivatives. We found that the stimulated band 120 nm width $\ensuremath{\sim}1\mathrm{ns}$ duration, which is observed at low density $n$, collapses $n>{10}^{17}{\mathrm{cm}}^{\ensuremath{-}3}$ into much narrower 7 lifetime $\ensuremath{\tau}\ensuremath{\ll}10\mathrm{ps}$. Based on its excitation intensity dependence, polarization, lifetime, illuminated area,...
We show that one-electron band theory fails to describe optical absorption in PPV and the spectrum can be described only within a Coulomb-correlated model. The lowest state is an exciton, whose binding energy estimated theoretically 0.90\ifmmode\pm\else\textpm\fi{}0.15 eV. Measurements of photoconductivity quantum efficiency poly[2-methoxy,5-(${2}^{\mathcal{'}}$-ethyl-hexyloxy)-1,4 phenylenevinylene] reveal good agreement with theoretical value.
From photoinduced absorption and light-induced electron-spin resonance, we demonstrate that the dominant photocarriers generated in polythiophene with excitation above energy gap (${E}_{g}$) are charged bipolarons (spin 0). The observation of (${B}^{2\ifmmode\pm\else\textpm\fi{}}$) rather than polarons (${P}^{\ifmmode\pm\else\textpm\fi{}}$) as photoexciations demonstrates Coulomb contribution to bipolaron (${U}_{B}$) is sufficiently small...
Stimulated emission was studied in various scattering gain media, including thin \ensuremath{\pi}-conjugated polymer films, organic dyes-doped gel and opal crystals saturated with laser dye solutions. We found that at high excitation intensities a featureless amplified spontaneous band transforms into finely structured spectrum having features as narrow 0.1 nm. this regime is directional characterized by linear laserlike intensity dependence. speculate phenomenon due to optical feedback...