Environmental Scanning Electron Microscopy:
Probing Ultrafast Solvation Dynamics at
Interfaces
Ding-Shyue (Jerry) Yang
FEIS 2013, Key West
Dec. 12th, 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
Pulsed-electron source:
currently, typically
front-illuminated
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
Flannigan and Zewail, Acc. Chem. Res. 45, 1828 (2012)
Scanning Ultrafast Electron Microscopy:
SEM with an ultrashort temporal resolution
Why SUEM?

obtaining 3D-like images for materials surfaces
Reimer, Scanning Electron Microscopy, 2nd ed., Springer, Berlin (1998)
Scanning Ultrafast Electron Microscopy:
SEM with an ultrashort temporal resolution
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
Environmental Scanning Electron Microscopy
Elimination of charging artifacts:
ionization of gas molecules
neutralizing surface charges;
minimal sample preparation
Imaging specimens at native states:
imaging of hydrated samples
study of solid-gas interactions
Reimer, Scanning Electron Microscopy, 2nd ed., Springer, Berlin (1998)
Instrumentation of Scanning
Ultrafast Electron Microscopy
Mohammed, Yang, Pal and Zewail, J. Am. Chem. Soc. 133, 7708 (2011)
Instrumentation of Scanning
Ultrafast Electron Microscopy
Schottky
emitter:
ZrO coated
W(100) tip
electrostatic
field
strength:
~107 V/cm
Yang, Mohammed and Zewail, Proc. Natl. Acad. Sci. USA 107, 14993 (2010)
Time-Resolved Imaging by SUEM
Silicon single crystal
Time-Resolved Imaging by SUEM
Silicon single crystal
Apparent laser fluence: ~0.5 mJ/cm2
Time-Resolved Imaging by SUEM
Apparent laser fluence:
55 mJ/cm2
Time (ps)
(Publication in preparation)
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
Multiple layers of water molecules adsorbed on
different surfaces in a humid ambient
Asay and Kim, J. Phys. Chem. B 109, 16760 (2005)
Glover, Miller, and Hutchison, ACS Nano 5, 8950 (2011)
Bohr, Wogelius, Morris, and Stipp,
Geochim. Cosmochim. Acta 74, 5985 (2010)
Binding of adsorbate molecules to Cd sites on
different CdSe surfaces
Manna, Wang, Cingolani, and Alivisatos,
J. Phys. Chem. B 109, 6183 (2005)
Rempel, Trout, Bawendi, and Jensen,
J. Phys. Chem. B 110, 18007 (2006)
The Helmholtz Equation
change in the work function due to the adsorbate
1
0
ΔΦstatic  ε  σ  μ cosθ
dynamical change due to motions of the adsorbate
ΔΦdyn  ε  σ  Δμ cosθ  0
1
0
1.42D
1.85D
3.92D
Yang, Mohammed, and Zewail, Angew. Chem. Int. Ed. 52, 2897 (2013)
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
Current Temporal Resolution of SUEM
Mohammed, Yang, Pal and Zewail, J. Am. Chem. Soc. 133, 7708 (2011)