Environmental Scanning Electron Microscopy: Probing Ultrafast Solvation Dynamics at Interfaces Ding-Shyue (Jerry) Yang FEIS 2013, Key West Dec. 12 th, 2013

Acknowledgement Prof. Ahmed Zewail Dr. Omar Mohammed Prof. Samir Pal Dr. Brett Barwick Dr. Xing He Napat Punpongjareorn Karjini Rajagopal

Ultrafast Transmission Electron Microscopy: TEM with an ultrashort temporal resolution Flannigan and Zewail, Acc. Chem. Res. 45, 1828 (2012) Pulsed-electron source: currently, front-illuminated thermionic emitters with a small active surface Pulsed-electron source: currently, front-illuminated thermionic emitters with a small active surface generation of single-electron pulses to reduce Boersch effect, or pulses that contain many electrons for single-shot experiments Pulsed-electron source: currently, typically front-illuminated thermionic emitters with a small active surface generation of single-electron pulses to reduce Boersch effect, or pulses that contain many electrons for single-shot experiments Clocking by fs/ns excitation pulse: stroboscopic or single-shot measurements Detection of primary electrons

Why SUEM? obtaining 3D-like images for materials surfaces Scanning Ultrafast Electron Microscopy: SEM with an ultrashort temporal resolution Reimer, Scanning Electron Microscopy, 2 nd ed., Springer, Berlin (1998)

Why SUEM? obtaining 3D-like images for materials surfaces detected signals exhibiting surface sensitivity easier sample preparation and handling existence of the bulk for better energy dissipation environmental microscopy Scanning Ultrafast Electron Microscopy: SEM with an ultrashort temporal resolution

Reimer, Scanning Electron Microscopy, 2 nd ed., Springer, Berlin (1998) Environmental Scanning Electron Microscopy Elimination of charging artifacts: Imaging specimens at native states: ionization of gas molecules neutralizing surface charges; minimal sample preparation Imaging specimens at native states: imaging of hydrated samples study of solid-gas interactions

Instrumentation of Scanning Ultrafast Electron Microscopy Mohammed, Yang, Pal and Zewail, J. Am. Chem. Soc. 133, 7708 (2011)

Instrumentation of Scanning Ultrafast Electron Microscopy Yang, Mohammed and Zewail, Proc. Natl. Acad. Sci. USA 107, (2010) Schottky emitter: ZrO coated W(100) tip electrostatic field strength: ~10 7 V/cm

Time-Resolved Imaging by SUEM Silicon single crystal

Time-Resolved Imaging by SUEM Apparent laser fluence: ~0.5 mJ/cm 2

Time (ps) (Publication in preparation) Apparent laser fluence: 55  J/cm 2 Time-Resolved Imaging by SUEM

Mechanism for bright contrast at positive times Contrast change Carrier dynamics

Time-Resolved Environmental Imaging Yang, Mohammed, and Zewail, Angew. Chem. Int. Ed. 52, 2897 (2013)

Solvation dynamics at surfaces depend on the local atomic structures and properties of the gas molecules

Asay and Kim, J. Phys. Chem. B 109, (2005) Bohr, Wogelius, Morris, and Stipp, Geochim. Cosmochim. Acta 74, 5985 (2010) Glover, Miller, and Hutchison, ACS Nano 5, 8950 (2011) Multiple layers of water molecules adsorbed on different surfaces in a humid ambient

Manna, Wang, Cingolani, and Alivisatos, J. Phys. Chem. B 109, 6183 (2005) Rempel, Trout, Bawendi, and Jensen, J. Phys. Chem. B 110, (2006) Binding of adsorbate molecules to Cd sites on different CdSe surfaces

change in the work function due to the adsorbate dynamical change due to motions of the adsorbate The Helmholtz Equation

Yang, Mohammed, and Zewail, Angew. Chem. Int. Ed. 52, 2897 (2013) 1.42D 1.85D 3.92D

Structural Solvation Dynamics at Solid-Gas Interfaces

Conclusion  SUEM (TR-SEM): a technique for real-space imaging to study carrier/structural dynamics  Time-resolved environmental imaging reveals the solvation dynamics and motions of the adsorbate at different surfaces. Combination of TR-ED and TR-SEM for investigation of electronic and structural dynamics in condensed matter and at surfaces

Mohammed, Yang, Pal and Zewail, J. Am. Chem. Soc. 133, 7708 (2011) Current Temporal Resolution of SUEM