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Environmental Scanning Electron Environmental Scanning Electron Microscopy: Probing Ultrafast Microscopy: Probing Ultrafast
Solvation Dynamics at InterfacesSolvation Dynamics at Interfaces
Ding-Shyue (Jerry) Yang
FEIS 2013, Key WestDec. 12th, 2013
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AcknowledgementAcknowledgement
Prof. Ahmed Zewail
Dr. Omar MohammedProf. Samir PalDr. Brett Barwick
Dr. Xing HeNapat PunpongjareornKarjini Rajagopal
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Ultrafast Transmission Electron Ultrafast Transmission Electron Microscopy:Microscopy:
TEM with an ultrashort temporal TEM with an ultrashort temporal resolutionresolution
Flannigan and Zewail, Acc. Chem. Res. 45, 1828 (2012)
Pulsed-electron source:Pulsed-electron source:currently, front-illuminated thermionic emitters with a smallactive surface
Pulsed-electron source:Pulsed-electron source:currently, front-illuminated thermionic emitters with a smallactive surface
generation of single-electronpulses to reduce Boersch effect, orpulses that contain many electronsfor single-shot experiments
Pulsed-electron source:Pulsed-electron source:currently, typically front-illuminated thermionic emitters with a smallactive surface
generation of single-electronpulses to reduce Boersch effect, orpulses that contain many electronsfor single-shot experiments
Clocking by fs/ns excitation Clocking by fs/ns excitation pulse:pulse:stroboscopic or single-shotmeasurements
Detection of primary electronsDetection of primary electrons
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Why SUEM?
obtaining 3D-like images for materials
surfaces
Scanning Ultrafast Electron Microscopy:Scanning Ultrafast Electron Microscopy:SEM with an ultrashort temporal SEM with an ultrashort temporal
resolutionresolution
Reimer, Scanning Electron Microscopy, 2nd ed., Springer, Berlin (1998)
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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:Scanning Ultrafast Electron Microscopy:SEM with an ultrashort temporal SEM with an ultrashort temporal
resolutionresolution
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Reimer, Scanning Electron Microscopy, 2nd ed., Springer, Berlin (1998)
Environmental Scanning Electron Environmental Scanning Electron MicroscopyMicroscopy
Elimination of charging Elimination of charging artifacts:artifacts:ionization of gas molecules neutralizing surface charges;minimal sample preparation
Imaging specimens at native Imaging specimens at native states:states:imaging of hydrated samplesstudy of solid-gas interactions
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Instrumentation of ScanningInstrumentation of ScanningUltrafast Electron MicroscopyUltrafast Electron Microscopy
Mohammed, Yang, Pal and Zewail, J. Am. Chem. Soc. 133, 7708 (2011)
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Instrumentation of ScanningInstrumentation of ScanningUltrafast Electron MicroscopyUltrafast Electron Microscopy
Yang, Mohammed and Zewail, Proc. Natl. Acad. Sci. USA 107, 14993 (2010)
Schottkyemitter:
ZrO coatedW(100) tip
electrostaticfield
strength:~107 V/cm
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Time-Resolved Imaging by SUEMTime-Resolved Imaging by SUEM
Silicon single crystal
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Silicon single crystal
Time-Resolved Imaging by SUEMTime-Resolved Imaging by SUEM
Apparent laser fluence: ~0.5 mJ/cm2
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Time (ps)(Publication in preparation)
Apparent laser fluence:55 J/cm2
Time-Resolved Imaging by SUEMTime-Resolved Imaging by SUEM
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Mechanism for bright contrast at Mechanism for bright contrast at positive timespositive times
Contrast change
Carrier dynamics
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Time-Resolved Environmental Time-Resolved Environmental ImagingImaging
Yang, Mohammed, and Zewail, Angew. Chem. Int. Ed. 52, 2897 (2013)
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Solvation dynamics atSolvation dynamics atsurfaces depend on thesurfaces depend on thelocal atomic structureslocal atomic structuresand properties of theand properties of thegas moleculesgas molecules
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Asay and Kim, J. Phys. Chem. B 109, 16760 (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 Multiple layers of water molecules adsorbed on different surfaces in a adsorbed on different surfaces in a
humid ambient humid ambient
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Manna, Wang, Cingolani, and Alivisatos,J. Phys. Chem. B 109, 6183 (2005)
Rempel, Trout, Bawendi, and Jensen,J. Phys. Chem. B 110, 18007 (2006)
Binding of adsorbate molecules to Cd Binding of adsorbate molecules to Cd sites on different CdSe surfaces sites on different CdSe surfaces
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change in the work function due to the adsorbate
dynamical change due to motions of the adsorbate
θcosμσεΔΦ 10static
0θcosμΔσεΔΦ 10dyn
The Helmholtz Equation The Helmholtz Equation
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Yang, Mohammed, and Zewail, Angew. Chem. Int. Ed. 52, 2897 (2013)
1.42D1.85D3.92D
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Structural Solvation Dynamics atStructural Solvation Dynamics atSolid-Gas InterfacesSolid-Gas Interfaces
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ConclusionConclusion
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 forinvestigation of electronic and structuraldynamics in condensed matter andat surfaces
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Mohammed, Yang, Pal and Zewail, J. Am. Chem. Soc. 133, 7708 (2011)
Current Temporal Resolution Current Temporal Resolution of SUEMof SUEM