Professor Vardeny is an experimental physicist interested in transient and steady state optical, electronic and spintronic properties of organic semiconductors in the time domain from femtoseconds to minutes. In his laboratory Prof. Vardeny synthesizes a variety of semiconducting polymers and grows various single crystals from pi-conjugated oligomers and molecules. Using a variety of pulsed laser excitations he studies the transient response of photoexcitations in doped and undoped semiconducting polymer films, molecular organic crystals, fullerenes, single walled nanotubes and dielectric and metallic photonic crystals. The transient response also includes laser action in the form of amplified spontaneous emission, random lasers, and lasing in fabricated microcavities, including microring, microdisk, opal photonic crystals and asymmetric cavities that support chaotic ray behavior. The transient dynamic investigations are complemented using steady state optical measurements such as absorption, emission and photomodulation spectroscopies, as well as optical detected magnetic resonance, photoconductivity and Raman scattering spectroscopies. In addition, the charge and spin injection from external electrodes into organic semiconductors is also investigated using a variety of metallic, ferromagnetic, and half metallic electrodes. Also being studied are the nonlinear optical spectra of these materials using the technique of four-wave-mixing, Z-scan and two-photon-absorption. The optical studies also include a variety of organic photonic crystals made out of polymers and oligomers infiltrated into synthetic opals, as well as 2D and 3D metallic photonic crystals.
On a more applicative note, solid-state devices made out of the organic semiconductors, such as field-effect-transistors, organic light emitting diodes, organic photovoltaic cells, and spin-valve devices are engineered, fabricated and tested in the laboratory.
“Two-Dimensional Electronic Excitations in Self-Assembled Conjugated Polymer Nanocrystals” (with R. Österbacka, C. P. An, and X. M. Jiang), Science 287, 839 (2000).
“Formation Cross-Sections of Singlet and Triplet Excitons in Pi-Conjugated Polymers” (with M. Wohlgenannt et al.), Nature 409, 494 (2001).
“A Boost for Fiber Optics”, Z. V. Vardeny, Nature 416, 489 (2002).
“Ultrafast Dynamics of Excitons and Solitons in Disubstituted Polyacetylene” (with O. J. Korovyanko, I. I. Gontia, T. Masuda, and K. Yoshino), Phys. Rev. B 67, 035114 (2003).
“Conjugation-Length Dependence of Spin-Dependent Polaron Recombination in pi-Conjugated Materials” (with M. Wohlgenannt, X. M. Jiang, and R. A. J. Janssen), Phys. Rev. Lett. 88, 197401 (2002).
“Photoinduced Quantum Interference Antiresonances in Pi-Conjugated Polymers” (with R. Österbacka, X. M. Jiang, C. P. An, and B. Horovitz), Phys. Rev. Lett. 88, 226401 (2002).
“Universal Properties of Random Lasers” (with R. C. Polson, and M. E. Raikh), IEEE Quantum Electronics 9, 120 (2003).
“Linear and Nonlinear Photoexcitation Dynamics in p-Conjugated Polymers” (with O. Epshtein, Y. Eichen, E. Ehrenfreund, and M. Wohlgenannt), Phys. Rev. Lett. 90, 046804 (2003).
Vladimir Burtman email: burtman at physics dot utah dot edu
Research Areas: Experimental organic condensed matter physics, nanometer-scale physics, molecular electronics, transoprt in low-dimensional structures. Current Research:
V. Burtman, A. Zelichenok and S. Yitzchaik, " Organic Quantum-Confined Structures via Molecular Layer Epitaxy" Angewandte Chemie International Edition, (1999), 38, 2041-2045;
- Organic Solid State, Nano-technologies, Optoelectronic
- Transport in disordered media. Charge Transport and Energy Transfer in organic devices, Redox reactions in transport mechanism (polaron transport).
- 1D and 2D structures by Self-assembling and Epitaxial growth. Interface phenomena. Molecular bandgap engineering. Hybrid Integration of Molecular Electronic.
- Molecular wires and macromolecules as conductive media. Transport of charge, spin and phonons through molecular wires.
- Molecular Photovoltaic and artificial photosynthesis
- Magnetism in Organics, Spintronics, organic SAM spin-based devices, Spin injection and transport, Ferromagnet-organic semiconductor hybrid structures
- Molecular FET like switching. Self-assembly avenue to molecular FET devices
K. I. Pokhodnya, V. Burtman, A. J. Epstein, J. W. Raebiger, J. S. Miller Control of Coercivity in Organic-based Solid Solution VxCo1-x[TCNE]2*zCH2Cl2 Room Temperature Magnets, Adv. Mater. 15, 1211-1214 (2003).
A. Pakolev, D. Zaslavsky and V. Burtman "From Electron Transfers to Electric Currents: Light-induced in-plane Currents in Monomolecular Films" cond-mat/0404240. April 2004.
Tatsunosuke Matsui email: matsui at physics dot utah dot edu
Research projects: metallic photonic crystal (MPC)
"Fabrication of Flexible Distributed Feedback Laser Using Photoinduced Surface Relief Grating on Azo-Polymer Film as a Template", T. Matsui, M. Ozaki, K. Yoshino and F. Kajzar: Jpn. J. Appl. Phys., 41 (2002) L1386-L1388.
- modification of blackbody radiation utilizing 3D metallic opal PC for efficient lamp. references: "Modification of Planck blackbody radiation by photonic band-gap structures", C. M. Cornelius et.al. PRA 59 (1999) 4736. "Enhancement and suppression of thermal emission by a three-dimensional photonic crystal", S.-Y. Lin et.al. PRB rapid comm. 62 (2000) R2243. "Experimantal observation of photonic-crystal emission near a photonic band edge", S.-Y. Lin et.al. APL 83 (2003) 593.
- ultra-fast (femto-sec) spectroscopy of surface plasmon in 2D MPC. references: "Surface plasmons on smooth and rough surfaces and on gratings", H. Raether (Springer, Berlin, 1988). "Surface plasmon subwavelength optics", W. L. Barnes et.al. Nature 424 (2003) 824.
- observation of anomalous transmission trough 2D MPC. references: "Extraordinary optical transmission through sub-wavelength hole arrays", T. W. Ebbesen et.al. Nature 391 (1998) 667. "Surface-plasmon-enhanced transmission through hole arrays in Cr films", T. Thio et.al. JOSAB 16 (1999) 1743.
"Electro-tunable laser action in a dye-doped nematic liquid crystal waveguide under holographic excitation", T. Matsui, M. Ozaki and K. Yoshino: Appl. Phys. Lett., 83 (2003) 422-424.
"Single-Mode Operation of Electro-Tunable Laser in a Dye-Doped Nematic Liquid Crystal Waveguide Under Holographic Excitation", T. Matsui, M. Ozaki and K. Yoshino: Jpn. J. Appl. Phys., 42 (2003) L1462-L1464.
Chuanzhen Liu email: cliu at physics dot utah dot edu
My research includes two parts:
- I research spin enhanced PLED (polymer light emitting diodes) by using a nanoparticle blended with polymer to improve the quantum efficiency.
- I research on photovoltaic devices and try to improve power conversion efficiency of polymer solar cells.
Xiaomei Jiang email: xmj at physics dot utah dot edu
Introduction of my research field: “Optical and electronic properties of pi-conjugated polymers” My primary area of research lays in the optical and electronic properties of organic electronic materials (OEM), and their potential optoelctronic applications including light emitting diodes(OLED), solar cells (OSC) and field-effect transistors(FET). My exploration about OEM went along the line of orders, from the conventional one dimensitional pi-conjugated polymers to polymers with two dimensional lamellae structure and then to single crystals of oligomers. The principle experimental technique used in the studies has been the continuous wave (cw) photomodulation technique. Two polymers have been the focus of the interest: poly(3-alkyl substituted) thiophene(P3AT) with different regioregularities, and substituted poly(p-phenylene-ethynylene)(PPE). Films of both polymers have morphology variations, which give rise to different photophysics. It is found out that the optical properties are very sensitive to the film morphology. Organic solar cells is one of the major applications of pi-conjugated polymers. However, the underlying mechanisms to improve their quantum efficiency are still unclear. One major concern is to reduce current losses due to geminate recombination. Various efforts to increase the energy conversion efficiency of organic solar cells have been done and promising results have been obtained.
- “ Optical studies of Photoinexcitations in regioregular and regiorandom Polythiophene Films”, X.M. Jiang, R. Österbacka, O.J. Korovyanko, C.P. An, B. Horovitz, R.A.J. Janssen and Z.V.Vardeny, Adv. Funct. Mater, 12(9), 587-597(2002).
- “Conjugation-length dependence of spin-dependent Exciton Formation Rates in pi-conjugated oligomers and polymers”, M. Wohlgenannt, X.M. Jiang, Z.V.Vardeny, R.A.J. Janssen, Phys. Rev. Lett, 88, 197401-1(2002).
- “ Two-dimentional electronic excitations in self-assembled conjugated polymer nanocrystals”, R. Österbacka, C.P. An, X.M. Jiang, and Z.V.Vardeny, Science, 287, 739 (2000).
Chuanxiang Sheng email: cxsheng at physics dot utah dot edu
fs two-color pump-probe for the transient PM spectroscopy. Our ultrafast laser system was a 100 fs titanium-sapphire oscillator operating at a repetition rate of about 80 MHz(Tsunami, Spectra-Physics), which pumped an optical parametric oscillator (OPO) (Opal, Spectra-Physics).
Ultrafast spectroscopy of excitons in single-walled carbon nanotubes Korovyanko, O.J.; Sheng, C.-X.; Vardeny, Z.V.; Dalton, A.B.; Baughman, R.H. Physical Review Letters, v 92, 017403/1-4
Alexandre Ndobe email: ndobe at physics dot utah dot edu
I am studying the transport properties of Organic materials through Organic Field effect transistors and photovoltaic effect.
Cungeng Yang email: cgyang at physics dot utah dot edu
My area is magnetic resonance study of electron spin dynamics in organic materials through optical and electrical detection. I also do some continuous wave spectroscopy and device physics.
Joshua Kennedy email: wjk at physics dot utah dot edu
Carbon nanotube spectroscopy
Minghong Tong email: minghong at physics dot utah dot edu
femtosecond polymer spectroscopy
Chenchun Wu email: chenchun at physics dot utah dot edu
di-styryl benzene studies
Abdullah Tulek email: tulek at physics dot utah dot edu
Fujian Wang email: fujian at physics dot utah dot edu
Giant magnetoresistance in organic spin-valves: a spin valve is a layered structure of magnetic and non-magnetic(spacer) materials whose electrical resistance depends on the spin state of electrons passing through the device and so can be controlled by an external magnetic field. The discoveries of giant magnetoresistance and tunnelling magnetoresistance in metallic spin valves have revolutionized applications such as magnetic recording and memory, and launched the new field of spin electronics--spintronics. Intense research efforts are now devoted to extending the spin-dependent effects to semiconducor materials. Our group uses the PI-conjugated organic semiconductor as the spacer. Due to the relatively strong electron-phonon coupling and large spin coherence, organic semiconductors are the promising alternative approach to semiconductor spintronics. We have obtained spin valve effect in LSMO/ALQ/Co structure and reported the results in Nature. Now we are working on Fe/ALQ/Co structure.
reference: "Giant magnetoresistance in organic spin-valves " Z. H. Xiong, Di Wu, Z. Valy Vardeny & Jing Shi, Nature vol 427 page 821 (2004)