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

AcknowledgementAcknowledgement

Prof. Ahmed Zewail

Dr. Omar MohammedProf. Samir PalDr. Brett Barwick

Dr. Xing HeNapat PunpongjareornKarjini Rajagopal

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

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)

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

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

Instrumentation of ScanningInstrumentation of ScanningUltrafast Electron MicroscopyUltrafast Electron Microscopy

Mohammed, Yang, Pal and Zewail, J. Am. Chem. Soc. 133, 7708 (2011)

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

Time-Resolved Imaging by SUEMTime-Resolved Imaging by SUEM

Silicon single crystal

Silicon single crystal

Time-Resolved Imaging by SUEMTime-Resolved Imaging by SUEM

Apparent laser fluence: ~0.5 mJ/cm2

Time (ps)(Publication in preparation)

Apparent laser fluence:55 J/cm2

Time-Resolved Imaging by SUEMTime-Resolved Imaging by SUEM

Mechanism for bright contrast at Mechanism for bright contrast at positive timespositive times

Contrast change

Carrier dynamics

Time-Resolved Environmental Time-Resolved Environmental ImagingImaging

Yang, Mohammed, and Zewail, Angew. Chem. Int. Ed. 52, 2897 (2013)

Solvation dynamics atSolvation dynamics atsurfaces depend on thesurfaces depend on thelocal atomic structureslocal atomic structuresand properties of theand properties of thegas moleculesgas molecules

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

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

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

Yang, Mohammed, and Zewail, Angew. Chem. Int. Ed. 52, 2897 (2013)

1.42D1.85D3.92D

Structural Solvation Dynamics atStructural Solvation Dynamics atSolid-Gas InterfacesSolid-Gas Interfaces

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

Mohammed, Yang, Pal and Zewail, J. Am. Chem. Soc. 133, 7708 (2011)

Current Temporal Resolution Current Temporal Resolution of SUEMof SUEM