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Liu X, Chanana A, Huynh U, Xue F, Haney P, Blair S, Jiang X, Vardeny ZV. Circular photogalvanic spectroscopy of Rashba splitting in 2D hybrid organic-inorganic perovskite multiple quantum wells. Nat Commun 2020; 11:323. [PMID: 31949152 PMCID: PMC6965620 DOI: 10.1038/s41467-019-14073-6] [Citation(s) in RCA: 44] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2019] [Accepted: 12/10/2019] [Indexed: 11/23/2022] Open
Abstract
The two-dimensional (2D) Ruddlesden−Popper organic-inorganic halide perovskites such as (2D)-phenethylammonium lead iodide (2D-PEPI) have layered structure that resembles multiple quantum wells (MQW). The heavy atoms in 2D-PEPI contribute a large spin-orbit coupling that influences the electronic band structure. Upon breaking the inversion symmetry, a spin splitting (‘Rashba splitting’) occurs in the electronic bands. We have studied the spin splitting in 2D-PEPI single crystals using the circular photogalvanic effect (CPGE). We confirm the existence of Rashba splitting at the electronic band extrema of 35±10 meV, and identify the main inversion symmetry breaking direction perpendicular to the MQW planes. The CPGE action spectrum above the bandgap reveals spin-polarized photocurrent generated by ultrafast relaxation of excited photocarriers separated in momentum space. Whereas the helicity dependent photocurrent with below-gap excitation is due to spin-galvanic effect of the ionized spin-polarized excitons, where spin polarization occurs in the spin-split bands due to asymmetric spin-flip. Hybrid organic-inorganic perovskites (HOIP) have high potential for spintronics applications. Using the circular photogalvanic effect the authors demonstrate the existence of Rashba-splitting in the continuum bands of a 2D layered HOIP that results from inversion symmetry breaking along the growth direction.
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Affiliation(s)
- Xiaojie Liu
- Department of Physics & Astronomy, University of Utah, Salt Lake City, UT, 84112, USA
| | - Ashish Chanana
- Department of Physics & Astronomy, University of Utah, Salt Lake City, UT, 84112, USA.,Department of Electrical Engineering, University of Utah, Salt Lake City, UT, 84112, USA
| | - Uyen Huynh
- Department of Physics & Astronomy, University of Utah, Salt Lake City, UT, 84112, USA
| | - Fei Xue
- Physical Measurement Laboratory, National Institute of Standards and Technology, Gaithersburg, MD, 20899, USA.,Institute for Research in Electronics and Applied Physics & Maryland Nanocenter, University of Maryland, College Park, MD, 20742, USA
| | - Paul Haney
- Physical Measurement Laboratory, National Institute of Standards and Technology, Gaithersburg, MD, 20899, USA
| | - Steve Blair
- Department of Electrical Engineering, University of Utah, Salt Lake City, UT, 84112, USA
| | - Xiaomei Jiang
- Department of Physics, University of South Florida, Tampa, FL, 33620, USA.
| | - Z V Vardeny
- Department of Physics & Astronomy, University of Utah, Salt Lake City, UT, 84112, USA.
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Sheng CX, Kim KH, Tong M, Yang C, Kang H, Park YW, Vardeny ZV. Ultrafast Transient Spectroscopy of Trans-Polyacetylene in the Midinfrared Spectral Range. Phys Rev Lett 2020; 124:017401. [PMID: 31976729 DOI: 10.1103/physrevlett.124.017401] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/18/2019] [Revised: 11/11/2019] [Indexed: 06/10/2023]
Abstract
Trans-polyacetylene [t-(CH)_{x}] possesses twofold ground state degeneracy. Using the Su-Schrieffer-Heeger Hamiltonian, scientists predicted charged solitons to be the primary photoexcitations in t-(CH)_{x}; this prediction, however, has led to sharp debate. To resolve this saga, we use subpicosecond transient photomodulation spectroscopy in the mid-IR spectral range (0.1-1.5 eV) in neat t-(CH)_{x} thin films. We show that odd-parity singlet excitons are the primary photoexcitations in t-(CH)_{x}, similar to many other nondegenerate π-conjugated polymers. The exciton transitions are characterized by two photoinduced absorption (PA) bands at 0.38 and 0.6 eV, and an associated photoluminescence band at ∼1.5 eV having similar polarization memory. The primary excitons undergo internal conversion within ∼100 fs to an even-parity (dark) singlet exciton with a PA band at ∼1.4 eV. We also find ultrafast photogeneration of charge polarons when pumping deep into the polymer continuum band, which are characterized by two other PA bands in the mid-IR and associated photoinduced IR vibrational modes.
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Affiliation(s)
- C X Sheng
- Department of Physics and Astronomy, University of Utah, Salt Lake City, Utah 84112, USA
- School of Electronic and Optical Engineering, Nanjing University of Science and Technology, Nanjing, Jiangsu 210094, China
| | - K H Kim
- Department of Physics and Astronomy, Seoul National University, Seoul 08826, Korea
- Department of Microtechnology and Nanoscience (MC2), Chalmers University of Technology, 412 96 Gothenburg, Sweden
| | - M Tong
- Department of Physics and Astronomy, University of Utah, Salt Lake City, Utah 84112, USA
| | - C Yang
- Department of Physics and Astronomy, University of Utah, Salt Lake City, Utah 84112, USA
| | - H Kang
- Department of Physics and Astronomy, Seoul National University, Seoul 08826, Korea
| | - Y W Park
- Institute of Applied Physics, Seoul National University, Seoul 08826, Korea
- Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
| | - Z V Vardeny
- Department of Physics and Astronomy, University of Utah, Salt Lake City, Utah 84112, USA
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Jiang W, Zhou M, Liu Z, Sun D, Vardeny ZV, Liu F. Structural, electronic, and magnetic properties of tris(8-hydroxyquinoline)iron(III) molecules and their magnetic coupling with ferromagnetic surface: first-principles study. J Phys Condens Matter 2016; 28:176004. [PMID: 27044670 DOI: 10.1088/0953-8984/28/17/176004] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
Using first-principles calculations, we have systematically investigated the structural, electronic, and magnetic properties of facial (fac-) and meridional (mer-) tris(8-hydroxyquinoline)iron(III) (Feq3) molecules and their interaction with ferromagnetic substrate. Our calculation results show that for the isolated Feq3, mer-Feq3 is more stable than the fac-Feq3; both Feq3 isomers have a high spin-state of 5 μB as the ground state when an on-site Hubbard-U term is included to treat the highly localized Fe 3d electrons; while the standard DFT calculations produce a low spin-state of 1 μB for mer-Feq3. These magnetic behaviors can be understood by the octahedral ligand field splitting theory. Furthermore, we found that fac-Feq3 has a stronger bonding to the Co surface than mer-Feq3 and an anti-ferromagnetic coupling was discovered between Fe and Co substrate, originating from the superexchange coupling between Fe and Co mediated by the interface oxygen and nitrogen atoms. These findings suggest that Feq3 molecular films may serve as a promising spin-filter material in spintronic devices.
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Affiliation(s)
- W Jiang
- Department of Materials Science & Engineering, University of Utah, Salt Lake City, UT 84112, USA
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Lafalce E, Vardeny ZV. Exceptional gain for the stimulated resonant Raman scattering in the π-conjugated polymer poly(dioctylfluorene). Opt Lett 2015; 40:4699-4702. [PMID: 26469598 DOI: 10.1364/ol.40.004699] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
Stimulated resonant Raman scattering (SRRS) is observed in slab waveguides formed in thin films of the π-conjugated polymer poly(dioctylfluorene) (PFO). The presence of two distinct morphological phases with different electronic bandgaps in these films allows the output frequency of this process to be observed over a much broader range than in other organic materials. In particular, the SRRS peak is pronounced when it is spectrally located in the vicinity of the amplified spontaneous emission bands of the films, which peak at 449 and 463 nm, respectively, for the two different phases, allowing selective tuning in the range of 440-470 nm. Furthermore, the superposition of the SRRS spectral location with that of electronic gain produces an overall gain of 269 cm(-1), making this material extremely attractive for use as an active material in compact Raman lasers.
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Malissa H, Kavand M, Waters DP, van Schooten KJ, Burn PL, Vardeny ZV, Saam B, Lupton JM, Boehme C. Room-temperature coupling between electrical current and nuclear spins in OLEDs. Science 2014; 345:1487-90. [DOI: 10.1126/science.1255624] [Citation(s) in RCA: 78] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
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Sheng CX, Singh S, Gambetta A, Drori T, Tong M, Tretiak S, Vardeny ZV. Ultrafast intersystem-crossing in platinum containing π-conjugated polymers with tunable spin-orbit coupling. Sci Rep 2014; 3:2653. [PMID: 24030602 PMCID: PMC3772376 DOI: 10.1038/srep02653] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/24/2013] [Accepted: 08/22/2013] [Indexed: 11/09/2022] Open
Abstract
The development of efficient organic light-emitting diodes (OLED) and organic photovoltaic cells requires control over the dynamics of spin sensitive excitations. Embedding heavy metal atoms in π-conjugated polymer chains enhances the spin-orbit coupling (SOC), and thus facilitates intersystem crossing (ISC) from the singlet to triplet manifolds. Here we use various nonlinear optical spectroscopies such as two-photon absorption and electroabsorption in conjunction with electronic structure calculations, for studying the energies, emission bands and ultrafast dynamics of spin photoexcitations in two newly synthesized π-conjugated polymers that contain intrachain platinum (Pt) atoms separated by one (Pt-1) or three (Pt-3) organic spacer units. The controllable SOC in these polymers leads to a record ISC time of <~1 ps in Pt-1 and ~6 ps in Pt-3. The tunable ultrafast ISC rate modulates the intensity ratio of the phosphorescence and fluorescence emission bands, with potential applications for white OLEDs.
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Affiliation(s)
- C-X Sheng
- 1] Department of Physics & Astronomy, University of Utah, Salt Lake City, Utah 84112, USA [2] School of Electronic and Optical Engineering, Nanjing University of Science and Technology, Nanjing, Jiangsu, 210094, China [3]
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Nguyen TD, Gautam BR, Ehrenfreund E, Vardeny ZV. Magnetoconductance response in unipolar and bipolar organic diodes at ultrasmall fields. Phys Rev Lett 2010; 105:166804. [PMID: 21230995 DOI: 10.1103/physrevlett.105.166804] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/21/2010] [Revised: 09/20/2010] [Indexed: 05/20/2023]
Abstract
We measured magnetoconductance (MC) response in a number of unipolar and bipolar organic diodes based on π-conjugated polymers and small molecules at fields |B|<100 mT and various bias voltages and temperatures. Similar to magneto-electroluminescence, the MC(B) response in bipolar diodes shows a sign reversal at ultrasmall |B|<1-2 mT due to interplay of hyperfine and Zeeman interactions in opposite-charge polaron pairs. Surprisingly, similar MC(B) response was also measured in unipolar devices, indicating the existence of like-charge polaron pairs, however, with a clear difference between the hyperfine interaction constants of electron polaron and hole polaron.
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Affiliation(s)
- T D Nguyen
- Department of Physics and Astronomy, University of Utah, 115 South 1400 East, Salt Lake City, Utah 84112, USA
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9
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Abstract
A mapping technique is developed to spatially resolve random laser-emission spectra from disordered solid media with an optical gain above the threshold excitation intensity for lasing; the technique is applied to pi-conjugated polymer 1 ms. By mapping the spatial extent of emission peaks in the random laser spectrum, bright areas that correspond to naturally formed lasing microcavities are unraveled. The size of the obtained microcavities matches the size extracted from the Fourier transform analysis of the laser-emission spectrum. Mapping at increased excitation intensities shows multiple resonant microcavities that lase at increasing threshold intensities.
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Affiliation(s)
- R C Polson
- Department of Physics and Astronomy, University of Utah, Salt Lake City, Utah 84112, USA.
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10
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Agrawal A, Matsui T, Zhu W, Nahata A, Vardeny ZV. Terahertz spectroscopy of plasmonic fractals. Phys Rev Lett 2009; 102:113901. [PMID: 19392201 DOI: 10.1103/physrevlett.102.113901] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/04/2008] [Revised: 01/27/2009] [Indexed: 05/27/2023]
Abstract
We use terahertz time-domain spectroscopy to study the transmission properties of metallic films perforated with aperture arrays having deterministic or stochastic fractal morphologies ("plasmonic fractals"), and compare them with random aperture arrays. All of the measured plasmonic fractals show transmission resonances and antiresonances at frequencies that correspond to prominent features in their structure factors in k space. However, in sharp contrast to periodic aperture arrays, the resonant transmission enhancement decreases with increasing array size. This property is explained using a density-density correlation function, and is utilized for determining the underlying fractal dimensionality, D(<2). Furthermore, a sum rule for the transmission resonances and antiresonances in plasmonic fractals relative to the transmission of the corresponding random aperture arrays is obtained, and is shown to be universal.
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Affiliation(s)
- A Agrawal
- Department of Electrical and Computer Engineering, University of Utah, Salt Lake City, Utah 84112, USA
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11
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Drori T, Sheng CX, Ndobe A, Singh S, Holt J, Vardeny ZV. Below-gap excitation of pi-conjugated polymer-Fullerene blends: implications for bulk organic heterojunction solar cells. Phys Rev Lett 2008; 101:037401. [PMID: 18764293 DOI: 10.1103/physrevlett.101.037401] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/01/2008] [Indexed: 05/26/2023]
Abstract
We used a variety of optoelectronic techniques such as broadband fs transient and cw photomodulation spectroscopies, electroabsorption, and short-circuit photocurrent in bulk heterojunctions organic solar cells for studying the photophysics in pi-conjugated polymer-fullerene blends with below-gap excitation. In contrast to the traditional view, we found that below-gap excitation, which is incapable of generating intrachain excitons, nevertheless efficiently generates polarons on the polymer chains and fullerene molecules. The polaron action spectrum extends deep inside the gap as a result of a charge-transfer complex state formed between the polymer chain and fullerene molecule. With appropriate design engineering the long-lived polarons might be harvested in solar cell devices.
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Affiliation(s)
- T Drori
- Department of Physics, University of Utah, Salt Lake City, Utah 84112, USA
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12
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Abstract
We have systematically measured epsilon(omega) of subwavelength aperture arrays fabricated in metal films as a function of aperture size and incidence angle using terahertz time-domain spectroscopy. This approach simultaneously yields both the real and imaginary epsilon(omega) components, enabling deeper insight into the underlying mechanism of the 'enhanced optical transmission' (EOT) phenomenon. For random aperture arrays we find that epsilon(omega) has a plasma response, with an effective plasma frequency that is determined by the waveguide mode cutoff frequency of the individual apertures. However epsilon(omega) in plasmonic lattices is strongly modulated at discrete resonant frequencies that correspond to the reciprocal vectors in the structure factor that are superposed on the plasma envelope response and appear as dips in the EOT spectrum. The existence of a sum rule for the discrete resonance oscillator strengths when the aperture size or incidence angle are changed validates our approach and allows for engineering of the individual resonances in the EOT spectrum.
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Affiliation(s)
- Amit Agrawal
- Department of Electrical and Computer Engineering, University of Utah, Salt Lake City, UT 84112, USA
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13
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Tong M, Kirakosyan AS, Shahbazyan TV, Vardeny ZV. Ultrafast response of surface electromagnetic waves in an aluminum film perforated with subwavelength hole arrays. Phys Rev Lett 2008; 100:056808. [PMID: 18352413 DOI: 10.1103/physrevlett.100.056808] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/29/2007] [Revised: 10/09/2007] [Indexed: 05/26/2023]
Abstract
The ultrafast dynamics of surface electromagnetic waves photogenerated on aluminum film perforated with subwavelength arrays of holes was studied in the visible spectral range by the technique of transient photomodulation with approximately 100 fs time resolution. We observed a pronounced blueshift of the resonant transmission band that reveals the important role of plasma attenuation in the optical response of nanohole arrays. The blueshift is inconsistent with plasmonic mechanism of extraordinary transmission and points to the crucial role of interference in the formation of transmission bands. The transient photomodulation spectra were successfully modeled within the Boltzmann equation approach for the electron-phonon relaxation dynamics, involving nonequilibrium hot electrons and quasiequilibrium phonons.
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Affiliation(s)
- M Tong
- Department of Physics, University of Utah, Salt Lake City, Utah 84112, USA
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14
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Yang CG, Ehrenfreund E, Vardeny ZV. Polaron spin-lattice relaxation time in pi-conjugated polymers from optically detected magnetic resonance. Phys Rev Lett 2007; 99:157401. [PMID: 17995211 DOI: 10.1103/physrevlett.99.157401] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/01/2007] [Indexed: 05/25/2023]
Abstract
We describe a method for obtaining the polaron spin-lattice relaxation time T{SL} in pi-conjugated polymers by measuring the optically detected magnetic resonance (ODMR) dynamics as a function of microwave power and laser intensity. The peculiar ODMR dynamics is well described by a spin dependent recombination model where both recombination and spin relaxation rates determine together the response dynamics. We apply this method to the spin 1/2 ODMR in films of pristine 2-methoxy-5-(2{'}-ethylhexyloxy) phenylene vinylene [MEH-PPV] polymer, as well as MEH-PPV doped with various concentrations of radical impurities. We obtained T{SL} approximately 30 micros in pristine MEH-PPV, but substantially shorter when the magnetic impurities are added.
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Affiliation(s)
- C G Yang
- Department of Physics, University of Utah, Salt Lake City, Utah 84112, USA
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Meyer RK, Benner RE, Vardeny ZV, Ding Y, Barton T. REχ(3), REχ(5), and REχ(7) Measured in Poly(Phenylene Ethynyl Silane)S by the Z Scan Technique. ACTA ACUST UNITED AC 2006. [DOI: 10.1080/10587259408039297] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
Affiliation(s)
- R. K. Meyer
- a Department of Electrical Engineering , University of Utah , Salt Lake City , Utah , 84112
| | - R. E. Benner
- a Department of Electrical Engineering , University of Utah , Salt Lake City , Utah , 84112
| | - Z. V. Vardeny
- b Department of Physics , University of Utah , Salt Lake City , Utah , 84112
| | - Y. Ding
- c Department of Chemistry , University of Iowa , Ames , Iowa , 50011
| | - T. Barton
- c Department of Chemistry , University of Iowa , Ames , Iowa , 50011
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Meyer RK, Benner RE, Vardeny ZV, Wei X, Lin JB, Barton T. Nonlinear Optical Susceptibilities Measured in Poly(Paraphenylene Cumulene[3]) by the Z Scan Technique. ACTA ACUST UNITED AC 2006. [DOI: 10.1080/10587259408039298] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
Affiliation(s)
- R. K. Meyer
- a Department of Electrical Engineering , University of Utah , Salt Lake City , Utah , 84112
| | - R. E. Benner
- a Department of Electrical Engineering , University of Utah , Salt Lake City , Utah , 84112
| | - Z. V. Vardeny
- b Department of Physics , University of Utah , Salt Lake City , Utah , 84112
| | - X. Wei
- b Department of Physics , University of Utah , Salt Lake City , Utah , 84112
| | - J. B. Lin
- c Department of Chemistry , University of Iowa , Ames , Iowa , 50011
| | - T. Barton
- c Department of Chemistry , University of Iowa , Ames , Iowa , 50011
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Affiliation(s)
- J. M. Leng
- a Department of Physics , University of Utah , Salt Lake City , Utah , 84112
| | - D. Dick
- a Department of Physics , University of Utah , Salt Lake City , Utah , 84112
| | - X. Wei
- a Department of Physics , University of Utah , Salt Lake City , Utah , 84112
| | - Z. V. Vardeny
- a Department of Physics , University of Utah , Salt Lake City , Utah , 84112
| | - F. Guo
- b Department of Physics , University of Arizona , Tucson , Arizona , 85721
| | - S. Mazumdar
- b Department of Physics , University of Arizona , Tucson , Arizona , 85721
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Affiliation(s)
- J. M. Leng
- a Department of Physics , John Dixon Laser Institute, University of Utah , Salt Lake City , Utah , 84112
| | - X. Wei
- a Department of Physics , John Dixon Laser Institute, University of Utah , Salt Lake City , Utah , 84112
| | - Z. V. Vardeny
- a Department of Physics , John Dixon Laser Institute, University of Utah , Salt Lake City , Utah , 84112
| | - Y. W. Ding
- b Department of Chemistry , Iowa State University , Ames , Iowa , 50011
| | - T. J. Barton
- b Department of Chemistry , Iowa State University , Ames , Iowa , 50011
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Affiliation(s)
- S. A. Jeglinski
- a University of Utah, Physics Department , Salt Lake City , UT , 84112
| | - M. E. Hollier
- a University of Utah, Physics Department , Salt Lake City , UT , 84112
| | - J. Gold
- a University of Utah, Physics Department , Salt Lake City , UT , 84112
| | - Z. V. Vardeny
- a University of Utah, Physics Department , Salt Lake City , UT , 84112
| | - Y. Ding
- b Iowa State University, Chemistry Department , Ames , IA , 50011
| | - T. Barton
- b Iowa State University, Chemistry Department , Ames , IA , 50011
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Affiliation(s)
- Z. V. Vardeny
- a Department of Physics , University of Utah , Salt Lake City , Utah , 84112
| | - Xing Wei
- a Department of Physics , University of Utah , Salt Lake City , Utah , 84112
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Affiliation(s)
- S. Frolov
- a Department of Physics , University of Utah , Salt Lake City , Utah , 84112
| | - J. M. Leng
- a Department of Physics , University of Utah , Salt Lake City , Utah , 84112
| | - Z. V. Vardeny
- a Department of Physics , University of Utah , Salt Lake City , Utah , 84112
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Greenwald Y, Poplawski J, Wei X, Ehrenfreund E, Speiser S, Vardeny ZV. Optical Excitations of Acceptor Substituted Poly-Thiophene Derivatives. ACTA ACUST UNITED AC 2006. [DOI: 10.1080/10587259408037747] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
Affiliation(s)
- Y. Greenwald
- a Department of Chemistry , Technion-Israel Institute of Technology , Haifa , 32000 , Israel
- b Solid State Institute, Technion-Israel Institute of Technology , Haifa , 32000 , Israel
| | - J. Poplawski
- b Solid State Institute, Technion-Israel Institute of Technology , Haifa , 32000 , Israel
| | - X. Wei
- c Department of Physics , University of Utah , Salt Lake City , UT , 84112
| | - E. Ehrenfreund
- b Solid State Institute, Technion-Israel Institute of Technology , Haifa , 32000 , Israel
| | - S. Speiser
- a Department of Chemistry , Technion-Israel Institute of Technology , Haifa , 32000 , Israel
| | - Z. V. Vardeny
- c Department of Physics , University of Utah , Salt Lake City , UT , 84112
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Yang CG, Eherenfreund E, Vardeny ZV. Comment on "Yield of singlet excitons in organic light-emitting devices: a double modulation photoluminescence-detected magnetic resonance study". Phys Rev Lett 2006; 96:089701; author reply 089702. [PMID: 16606240 DOI: 10.1103/physrevlett.96.089701] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/21/2005] [Indexed: 05/08/2023]
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Sheng CX, Vardeny ZV. Comment on "Large optical nonlinearity of semiconducting single-walled carbon nanotubes under resonant excitations". Phys Rev Lett 2006; 96:019705; discussion 019706. [PMID: 16486538 DOI: 10.1103/physrevlett.96.019705] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/03/2005] [Indexed: 05/06/2023]
Affiliation(s)
- C-X Sheng
- Physics Department, University of Utah, Salt Lake City, Utah 84112, USA
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Wu D, Xiong ZH, Li XG, Vardeny ZV, Shi J. Magnetic-field-dependent carrier injection at La2/3Sr1/3MnO3/ and organic semiconductors interfaces. Phys Rev Lett 2005; 95:016802. [PMID: 16090643 DOI: 10.1103/physrevlett.95.016802] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/08/2004] [Indexed: 05/03/2023]
Abstract
We have fabricated organic diodes utilizing several pi-conjugated organic semiconductors (OSEC) as spacer layers between La2/3Sr1/3MnO3 (LSMO) and various metallic electrodes, and measured their magnetoresistance (MR) and magnetoelectroluminescence (MEL) responses. The devices exhibit large negative high-field MR responses that resemble the MR response of the LSMO electrode, but amplified by approximately 3 orders in the resistance, and accompanied by a positive high-field MEL effect. These magnetic-field effects result from enhanced carrier injection at the LSMO-OSEC interface that is attributed to the anomalous field-dependent Fermi level shift in LSMO.
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Affiliation(s)
- D Wu
- Department of Physics, University of Utah, Salt Lake City, Utah 84112, USA
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Korovyanko OJ, Sheng CX, Vardeny ZV, Dalton AB, Baughman RH. Ultrafast spectroscopy of excitons in single-walled carbon nanotubes. Phys Rev Lett 2004; 92:017403. [PMID: 14754017 DOI: 10.1103/physrevlett.92.017403] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/29/2003] [Indexed: 05/24/2023]
Abstract
We studied the femtosecond dynamics of photoexcitations in films containing semiconducting and metallic single-walled carbon nanotubes (SWNTs), using various pump-probe wavelengths and intensities. We found that confined excitons and charge carriers with subpicosecond dynamics dominate the ultrafast response in semiconducting and metallic SWNTs, respectively. Surprisingly, we also found from the exciton excited state absorption bands and multiphoton absorption resonances in the semiconducting nanotubes that transitions between subbands are allowed; this unravels the important role of electron-electron interaction in SWNT optics.
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Affiliation(s)
- O J Korovyanko
- Department of Physics, University of Utah, Salt Lake City, Utah 84112, USA
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Österbacka R, Wohlgenannt M, Shkunov M, Chinn D, Vardeny ZV. Excitons, polarons, and laser action in poly(p-phenylene vinylene) films. J Chem Phys 2003. [DOI: 10.1063/1.1566937] [Citation(s) in RCA: 68] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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Epshtein O, Eichen Y, Ehrenfreund E, Wohlgenannt M, Vardeny ZV. Linear and nonlinear photoexcitation dynamics in pi-conjugated polymers. Phys Rev Lett 2003; 90:046804. [PMID: 12570443 DOI: 10.1103/physrevlett.90.046804] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/21/2002] [Indexed: 05/24/2023]
Abstract
Linear and nonlinear recombination kinetics with various lifetime distributions were identified for long-lived photoexcitations in a series of pi-conjugated polymer films using modulation frequency and excitation intensity dependencies of the photoinduced absorption. This includes monomolecular, bimolecular, and defect-limited recombination processes that lead to saturation. Using generalized kinetics parameters, we found characteristic plots for all recombination processes. Specifically, the bimolecular recombination process shows superlinear intensity dependence away from the steady state; on the contrary, dispersive bimolecular recombination leads to sublinear dependence.
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Affiliation(s)
- O Epshtein
- Department of Physics and Solid State Institute, Technion, Israel Institute of Technology, Haifa 32000, Israel
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Osterbacka R, Jiang XM, An CP, Horovitz B, Vardeny ZV. Photoinduced quantum interference antiresonances in pi-conjugated polymers. Phys Rev Lett 2002; 88:226401. [PMID: 12059436 DOI: 10.1103/physrevlett.88.226401] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/19/2001] [Indexed: 05/23/2023]
Abstract
We observed photoinduced quantum interference antiresonances between several discrete infrared-active vibrations and the lower-polaron continuous absorption band in a series of pi-conjugated polymer films having superior planar orders, where the polaron transition energy is relatively small. The photoinduced Fano-type antiresonances are well explained by extending the amplitude mode model beyond the adiabatic limit. The agreement between the data and the model confirms the presence of a continuous electronic band above the polaron state. We show that high frequency modes are strongly coupled to electrons, with implications for superconductivity.
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Affiliation(s)
- R Osterbacka
- Department of Physics, Abo Akademi University, Porthansgatan 3, FIN-20500 Turku, Finland
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Wohlgenannt M, Jiang XM, Vardeny ZV, Janssen RAJ. Conjugation-length dependence of spin-dependent exciton formation rates in pi-conjugated oligomers and polymers. Phys Rev Lett 2002; 88:197401. [PMID: 12005663 DOI: 10.1103/physrevlett.88.197401] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/14/2001] [Indexed: 05/23/2023]
Abstract
We have measured the ratio, r = sigma(S)/sigma(T) of the formation cross section, sigma of singlet and triplet excitons from polarons in pi-conjugated oligomer and polymer films, using a spectroscopic technique we developed recently. We discovered a universal relation between r and the conjugation length (CL): r(-1) depends linearly on CL-1, irrespective of the chain structure. Since r is directly related to the maximum possible electroluminescence quantum efficiency in organic light emitting diodes (OLED), our results indicate that polymers have an advantage over small molecules in OLED applications.
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Affiliation(s)
- M Wohlgenannt
- Department of Physics and Astronomy, The University of Iowa, Iowa City, Iowa 52242, USA
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Huang J, Eradat N, Raikh ME, Vardeny ZV, Zakhidov AA, Baughman RH. Anomalous coherent backscattering of light from opal photonic crystals. Phys Rev Lett 2001; 86:4815-4818. [PMID: 11384355 DOI: 10.1103/physrevlett.86.4815] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/28/2000] [Indexed: 05/23/2023]
Abstract
We studied coherent backscattering (CBS) of light from opal photonic crystals with incomplete band gaps. We observed a dramatic broadening of the CBS cone for incident angles close to the Bragg condition in the crystals. We modify the conventional CBS theory to incorporate Bragg attenuation resulting from the photonic band structure. By fitting the CBS data with the modified theory, we extract both the disorder-induced light mean-free path and the Bragg attenuation length of the inherent opal photonic crystal.
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Affiliation(s)
- J Huang
- Department of Physics, University of Utah, Salt Lake City, UT 84112, USA
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Wohlgenannt M, Tandon K, Mazumdar S, Ramasesha S, Vardeny ZV. Formation cross-sections of singlet and triplet excitons in pi-conjugated polymers. Nature 2001; 409:494-7. [PMID: 11206541 DOI: 10.1038/35054025] [Citation(s) in RCA: 393] [Impact Index Per Article: 17.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2000] [Accepted: 12/05/2000] [Indexed: 11/08/2022]
Abstract
Electroluminescence in organic light-emitting diodes arises from a charge-transfer reaction between the injected positive and negative charges by which they combine to form singlet excitons that subsequently decay radiatively. The quantum yield of this process (the number of photons generated per electron or hole injected) is often thought to have a statistical upper limit of 25 per cent. This is based on the assumption that the formation cross-section of singlet excitons, sigmaS, is approximately the same as that of any one of the three equivalent non-radiative triplet exciton states, sigmaT; that is, sigmaS/sigmaT approximately 1. However, recent experimental and theoretical work suggests that sigmaS/sigmaT may be greater than 1. Here we report direct measurements of sigmaS/sigmaT for a large number of pi-conjugated polymers and oligomers. We have found that there exists a strong systematic, but not monotonic, dependence of sigmaS/sigmaT on the optical gap of the organic materials. We present a detailed physical picture of the charge-transfer reaction for correlated pi-electrons, and quantify this process using exact valence bond calculations. The calculated sigmaS/sigmaT reproduces the experimentally observed trend. The calculations also show that the strong dependence of sigmaS/sigmaT on the optical gap is a signature of the discrete excitonic energy spectrum, in which higher energy excitonic levels participate in the charge recombination process.
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Affiliation(s)
- M Wohlgenannt
- Department of Physics, University of Utah, Salt Lake City 84112, USA
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Frolov SV, Bao Z, Wohlgenannt M, Vardeny ZV. Ultrafast spectroscopy of even-parity states in pi-conjugated polymers. Phys Rev Lett 2000; 85:2196-2199. [PMID: 10970496 DOI: 10.1103/physrevlett.85.2196] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/08/1999] [Indexed: 05/23/2023]
Abstract
Relaxation dynamics of even parity ( A(g)) states in poly( p-phenylene vinylene) derivatives are studied using a novel fsec transient spectroscopy, in which two different excitation pulses successively generate odd parity ( 1 (1)B(u)) excitons at 2.2 eV and then reexcite them to higher A(g) states. For reexcitation energies Planck's over 2piomega<1.1 eV ultrafast internal conversion back to 1 (1)B(u) takes place in accordance with Vavilov-Kasha's rule. However, for Planck's over 2piomega>1.1 eV the decay occurs in a nonemissive state identified as a polaron pair, showing that the A(g) states above 3.3 eV mediate charge transfer.
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Affiliation(s)
- SV Frolov
- Bell Laboratories, Lucent Technologies, 600 Mountain Avenue, Murray Hill, New Jersey 07974, USA
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Affiliation(s)
- M. Wohlgenannt
- Department of Physics, University of Utah, Salt Lake City, Utah 84112
| | - C. P. An
- Department of Physics, University of Utah, Salt Lake City, Utah 84112
| | - Z. V. Vardeny
- Department of Physics, University of Utah, Salt Lake City, Utah 84112
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Abstract
Several spectroscopic methods were applied to study the characteristic properties of the electronic excitations in thin films of regioregular and regiorandom polythiophene polymers. In the regioregular polymers, which form two-dimensional lamellar structures, increased interchain coupling strongly influences the traditional one-dimensional electronic properties of the polymer chains. The photogenerated charge excitations (polarons) show two-dimensional delocalization that results in a relatively small polaronic energy, multiple absorption bands in the gap where the lowest energy band becomes dominant, and associated infrared active vibrations with reverse absorption bands caused by electron-vibration interferences. The relatively weak absorption bands of the delocalized polaron in the visible and near-infrared spectral ranges may help to achieve laser action in nanocrystalline polymer devices using current injection.
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Affiliation(s)
- R Osterbacka
- Physics Department, University of Utah, Salt Lake City, UT 84112, USA
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Lane PA, Wei X, Vardeny ZV. Studies of Charged Excitations in pi -Conjugated Oligomers and Polymers by Optical Modulation. Phys Rev Lett 1996; 77:1544-1547. [PMID: 10063105 DOI: 10.1103/physrevlett.77.1544] [Citation(s) in RCA: 24] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
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Lane PA, Wei X, Vardeny ZV, Partee J, Shinar J. Optically detected magnetic-resonance study of triplet-state dynamics in C70. Phys Rev B Condens Matter 1996; 53:R7580-R7583. [PMID: 9982271 DOI: 10.1103/physrevb.53.r7580] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/12/2023]
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Wei X, Vardeny ZV, Sariciftci NS, Heeger AJ. Absorption-detected magnetic-resonance studies of photoexcitations in conjugated-polymer/C60 composites. Phys Rev B Condens Matter 1996; 53:2187-2190. [PMID: 9983706 DOI: 10.1103/physrevb.53.2187] [Citation(s) in RCA: 75] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/11/2023]
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Wei X, Vardeny ZV. Spin dynamics of triplet photoexcitations in C60: Evidence for a dynamic Jahn-Teller effect. Phys Rev B Condens Matter 1995; 52:R2317-R2320. [PMID: 9981400 DOI: 10.1103/physrevb.52.r2317] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/12/2023]
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Kanner GS, Frolov S, Vardeny ZV. Detection of electronic excited states in conjugated polymers by picosecond transient strain spectroscopy. Phys Rev Lett 1995; 74:1685-1688. [PMID: 10059091 DOI: 10.1103/physrevlett.74.1685] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
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Chandross M, Mazumdar S, Jeglinski S, Wei X, Vardeny ZV, Kwock EW, Miller TM. Excitons in poly(para-phenylenevinylene). Phys Rev B Condens Matter 1994; 50:14702-14705. [PMID: 9975714 DOI: 10.1103/physrevb.50.14702] [Citation(s) in RCA: 123] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/12/2023]
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Dick D, Wei X, Jeglinski S, Benner RE, Vardeny ZV, Moses D, Srdanov VI, Wudl F. Transient spectroscopy of excitons and polarons in C60 films from femtoseconds to milliseconds. Phys Rev Lett 1994; 73:2760-2763. [PMID: 10057185 DOI: 10.1103/physrevlett.73.2760] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
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Hess BC, Forgy EA, Frolov S, Dick DD, Vardeny ZV. High-pressure study of picosecond exciton dynamics in solid C60. Phys Rev B Condens Matter 1994; 50:4871-4874. [PMID: 9976799 DOI: 10.1103/physrevb.50.4871] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/12/2023]
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Wei X, Raikh M, Vardeny ZV, Yang Y, Moses D. Photoresponse of poly(para-phenylenevinylene) light-emitting diodes. Phys Rev B Condens Matter 1994; 49:17480-17483. [PMID: 10010940 DOI: 10.1103/physrevb.49.17480] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/12/2023]
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Leng JM, Jeglinski S, Wei X, Benner RE, Vardeny ZV, Guo F, Mazumdar S. Optical probes of excited states in poly(p-phenylenevinylene). Phys Rev Lett 1994; 72:156-159. [PMID: 10055590 DOI: 10.1103/physrevlett.72.156] [Citation(s) in RCA: 108] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
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47
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Leng JM, Wei X, Vardeny ZV, Khemani KC, Moses D, Wudl F. Magneto-optical studies of photoexcitations in C61. Phys Rev B Condens Matter 1993; 48:18250-18253. [PMID: 10008467 DOI: 10.1103/physrevb.48.18250] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/12/2023]
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Lee CH, Yu G, Moses D, Srdanov VI, Wei X, Vardeny ZV. Transient and steady-state photoconductivity of a solid C60 film. Phys Rev B Condens Matter 1993; 48:8506-8509. [PMID: 10007061 DOI: 10.1103/physrevb.48.8506] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/12/2023]
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Zheng LX, Hess BC, Benner RE, Vardeny ZV, Baker GL. Resonant Raman-scattering spectroscopy of polydiacetylene films at high pressure. Phys Rev B Condens Matter 1993; 47:3070-3077. [PMID: 10006386 DOI: 10.1103/physrevb.47.3070] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/12/2023]
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