[原分所演講] IAMS Lecture on October 28, 10:00am, Dr. Poe Lecture Hall, Dr.Ming-Fu Lin
消息來源：化學系辦公室
截止日期：2016-10-28
IAMS Lecture Announcement
中研院原分所演講公告
Title: Probing Ultrafast Dynamics of Small Molecules, Photocatalysts and Semiconductors by Using Time-Resolved Femtosecond Pump-Probe Techniques
Speaker: Dr.Ming-Fu Lin (SLAC National Accelerator Lab, USA)
Time: 10:00 AM, October 28 (Friday)
Place: Dr. Poe Lecture Hall, IAMS (本所浦大邦講堂 臺大校園內)
Contact: Dr. Jung-Chi Liao 廖仲麒博士
Abstract:
In this seminar, I will present ultrafast dynamics of molecules, organic metallic photocatalysts and semiconductors from using several frontier pump-probe techniques. At first, I use a tabletop broadband extreme ultraviolet (XUV) light source from high-harmonic generation (HHG) to measure dissociative ionization dynamics of vinyl bromide (CH2=CHBr) associated with different ionic states. This broad XUV photon source allows us to observe real-time ultrafast CBr bond dissociation from the first ionic excited à state,1 demonstrating the ability of XUV transient absorption spectroscopy for element and chemical specificities with femtosecond temporal resolution.
Secondly, we further use this tabletop XUV light source to investigate ultrafast electronic dynamics of photocatalysts and semiconductors. Photocatalysts such as coordination complexes play a very important role in solar energy conversion and water splitting. We are able to measure the inner-shell M-edge absorption spectra from several thin-film organic metallic compounds containing cobalt and iron ions by using tabletop XUV light source. From these studies we demonstrate that the XUV absorption spectroscopy has sensitivities of oxidation state, spin state and ligand field of molecules.2 This is an important step toward future time-resolved studies of electronic dynamics in these materials.
Finally, I will present our current studies of charge carrier relaxation dynamics of multilayered PbI2 and bilayered MoSe2, respectively, using a combination of time-resolved XUV3, UV-VIS and Mega-eV ultrafast electron diffraction (MeV-UED)4 techniques. Lead iodide (PbI2) is a layered material and an important precursor for hybrid organic-inorganic perovskite solar cell. In brief, PbI2 is optically excited at 400 nm (3.1 eV), followed by a broadband XUV light source which measures carrier-specific relaxation dynamics in both conduction and valence bands. We observe a real-time formation of electron and hole pairs that recombines very quickly and this energy goes to lattice heat with a lifetime of 5.6±0.6 ps. From MeV-UED experiment, we further confirm that the lattice heat comes from a full 3.1 eV photon energy instead of excess energy over the band gap. This UED technique allows us to measure lattice temperature of thin film with ~200 fs temporal resolution. Optical transient absorption spectroscopy also supports the observation of bimolecular e-h recombination dynamics through efficient emission of longitudinal acoustic phonon. We proceed to study carrier dynamics of nanoscale MoSe2 bilayer with pump energies near the band edge (i.e. 800 nm) and above the band edge that produces hot carriers (i.e. 400 nm), respectively. The preliminary UED results both indicate that carrier energy coverts very efficiently to lattice heat in the time scale of sub-picosecond. We will carry out an optical transient microscopy to demonstrate that the bimolecular recombination results in efficient acoustic phonon emission in nano-bilayered MoSe2. From our current studies of bulk PbI2 and MoSe2 bilayer, we discover that at high carrier density electron-hole plasma recombines with nearly 100% efficiency to produce lattice heat through longitudinal acoustic phonon emission (i.e. nonradiative bimolecular recombination). These results provide us with threshold values of carrier density for the applications of layered materials in efficient optoelectronics and solar cells.
1. Lin, M.-F., Neumark, D. M., Gessner, O. & Leone, S. R. Ionization and dissociation dynamics of vinyl bromide probed by femtosecond extreme ultraviolet transient absorption spectroscopy. J. Chem. Phys. 140, 64311 (2014).
2. Zhang, K. et al. Shrinking the Synchrotron: Tabletop Extreme Ultraviolet Absorption of Transition Metal Complexes. J Phys Chem Lett 7, 3383–3387 (2016).
3. Lin, M.-F., Verkamp, M. A., Ryland, E. S., Zhang, K. & Vura-Weis, J. Impact of spatial chirp on high harmonic extreme ultraviolet absorption spectroscopy of thin films. J. Opt. Soc. Am. B 33, 1986–1992 (2016).
4. Weathersby, S. P. et al. Mega-electron-volt ultrafast electron diffraction at SLAC National Accelerator Laboratory. Rev. Sci. Instrum. 86, 1–7 (2015).
中研院原分所演講公告
Title: Probing Ultrafast Dynamics of Small Molecules, Photocatalysts and Semiconductors by Using Time-Resolved Femtosecond Pump-Probe Techniques
Speaker: Dr.Ming-Fu Lin (SLAC National Accelerator Lab, USA)
Time: 10:00 AM, October 28 (Friday)
Place: Dr. Poe Lecture Hall, IAMS (本所浦大邦講堂 臺大校園內)
Contact: Dr. Jung-Chi Liao 廖仲麒博士
Abstract:
In this seminar, I will present ultrafast dynamics of molecules, organic metallic photocatalysts and semiconductors from using several frontier pump-probe techniques. At first, I use a tabletop broadband extreme ultraviolet (XUV) light source from high-harmonic generation (HHG) to measure dissociative ionization dynamics of vinyl bromide (CH2=CHBr) associated with different ionic states. This broad XUV photon source allows us to observe real-time ultrafast CBr bond dissociation from the first ionic excited à state,1 demonstrating the ability of XUV transient absorption spectroscopy for element and chemical specificities with femtosecond temporal resolution.
Secondly, we further use this tabletop XUV light source to investigate ultrafast electronic dynamics of photocatalysts and semiconductors. Photocatalysts such as coordination complexes play a very important role in solar energy conversion and water splitting. We are able to measure the inner-shell M-edge absorption spectra from several thin-film organic metallic compounds containing cobalt and iron ions by using tabletop XUV light source. From these studies we demonstrate that the XUV absorption spectroscopy has sensitivities of oxidation state, spin state and ligand field of molecules.2 This is an important step toward future time-resolved studies of electronic dynamics in these materials.
Finally, I will present our current studies of charge carrier relaxation dynamics of multilayered PbI2 and bilayered MoSe2, respectively, using a combination of time-resolved XUV3, UV-VIS and Mega-eV ultrafast electron diffraction (MeV-UED)4 techniques. Lead iodide (PbI2) is a layered material and an important precursor for hybrid organic-inorganic perovskite solar cell. In brief, PbI2 is optically excited at 400 nm (3.1 eV), followed by a broadband XUV light source which measures carrier-specific relaxation dynamics in both conduction and valence bands. We observe a real-time formation of electron and hole pairs that recombines very quickly and this energy goes to lattice heat with a lifetime of 5.6±0.6 ps. From MeV-UED experiment, we further confirm that the lattice heat comes from a full 3.1 eV photon energy instead of excess energy over the band gap. This UED technique allows us to measure lattice temperature of thin film with ~200 fs temporal resolution. Optical transient absorption spectroscopy also supports the observation of bimolecular e-h recombination dynamics through efficient emission of longitudinal acoustic phonon. We proceed to study carrier dynamics of nanoscale MoSe2 bilayer with pump energies near the band edge (i.e. 800 nm) and above the band edge that produces hot carriers (i.e. 400 nm), respectively. The preliminary UED results both indicate that carrier energy coverts very efficiently to lattice heat in the time scale of sub-picosecond. We will carry out an optical transient microscopy to demonstrate that the bimolecular recombination results in efficient acoustic phonon emission in nano-bilayered MoSe2. From our current studies of bulk PbI2 and MoSe2 bilayer, we discover that at high carrier density electron-hole plasma recombines with nearly 100% efficiency to produce lattice heat through longitudinal acoustic phonon emission (i.e. nonradiative bimolecular recombination). These results provide us with threshold values of carrier density for the applications of layered materials in efficient optoelectronics and solar cells.
1. Lin, M.-F., Neumark, D. M., Gessner, O. & Leone, S. R. Ionization and dissociation dynamics of vinyl bromide probed by femtosecond extreme ultraviolet transient absorption spectroscopy. J. Chem. Phys. 140, 64311 (2014).
2. Zhang, K. et al. Shrinking the Synchrotron: Tabletop Extreme Ultraviolet Absorption of Transition Metal Complexes. J Phys Chem Lett 7, 3383–3387 (2016).
3. Lin, M.-F., Verkamp, M. A., Ryland, E. S., Zhang, K. & Vura-Weis, J. Impact of spatial chirp on high harmonic extreme ultraviolet absorption spectroscopy of thin films. J. Opt. Soc. Am. B 33, 1986–1992 (2016).
4. Weathersby, S. P. et al. Mega-electron-volt ultrafast electron diffraction at SLAC National Accelerator Laboratory. Rev. Sci. Instrum. 86, 1–7 (2015).