Hirohito Ogasawara, Dennis Nordlund, Anders Nilsson

Transcription

1 Pump-probe Ultrafast Surface Chemistry (PES, XES) station for Real Time Electronic Structure Mapping of Catalytic Reactions: Instrumentation Hirohito Ogasawara, Dennis Nordlund, Anders Nilsson Stanford Synchrotron Radiation Lightsource (SSRL) & Stanford Institute for Materials & Energy Science (SIMES) SSRL LCLS?

2 Catalytic reactions on surfaces are used for Conversion of chemicals N 2 + H 2 NH 3 NH 3 + O 2 HNO 3 CO + H 2 O CO 2 + H 2 R-CO-R, R-CHO RCHOH CO, HC, NO x N 2, H 2 O, CO 2 etc Clean fuel H 2 O, electricity H 2, O 2 H + + O 2 H 2 O, electricity etc On the surface catalyst, reactions occur efficiently and selectively.

3 Catalsyt surface provides a mechanism to lower the activation energy activation barrier Gibbs free energy reactant H + + O 2 product H O 2

4 Catalsyt surface provides a mechanism to lower the activation energy Gibbs free energy reactant H + + O 2 Pt catalyst product O, electricity H 2

5 Catalsyt surface provides a mechanism to lower the activation energy Gibbs free energy reactant H + + O 2 Pt catalyst product O, electricity H 2 Catalyst can perform the reaction faster or at lower temperatures Catalyst can perform the reaction selectively

6 Catalyt surface provides a mechanism to lower the activation energy Gibbs free energy reactant H + + O 2 bad catalyst Harmful to the fuel cell assembly H 2 O 2 H 2 product O, electricity Catalyst can perform the reaction efficiently Catalyst can perform the reaction selectively

7 SXR: Observe the surface reaction mechanism in the time domain Understand the origin of catalytic efficiency and selectivity dissociation adsorption hydrogenation desorption Laser temperature jump Photodissociation X-ray emission (XES) Photoemission (PES)

8 Plan under the SXR consortium FY2009 Customize the XES/PES endstation at BL 13-2 new sample holder, new manipulator, remote operation, DAQ, valve position sensors, pump interlocks Test this complete setup at SSRL BL13-2 FY2010 Ready for first experiments. After first experiments: Design a complete new instrument, dedicated for SXR in-situ study, THz pump etc 2011 Static study at SSRL Ultrafast study at LCLS

9 PES/XES station at BL13-2 X-ray emission spectrometer XES beam photoemission spectrometer Requirements: Power 1 x 208V, 30A, 3-phase or 3 x 115V, 30A, 2-phase Ducting for pump exhaust Pressurized air line Nitrogen line PES

10 PES/XES station at BL13-2 X-ray emission spectrometer This part is mainly used at LCLS XES beam photoemission spectrometer Requirements: Power 1 x 208V, 30A, 3-phase or 3 x 115V, 30A, 2-phase Ducting for pump exhaust Pressurized air line Nitrogen line PES

11 PES/XES station for SXR Sample manipulator XES elliptically shaped grating LCLS DAQ digital camera beam beam PES VG-Scienta R3000 LCLS DAQ digital camera Side view Lens acceptance: +/- 15 degrees Energy window(single-shot): 24 ev, 12% of E pass Top view

12 PES and XES performance molecular oxygen heat atomic oxygen O1s XPS taken during Temperature ramp time per spectrum = 7 sec at SSRL BL13-2 Analyzer: Scienta SES-100 (+ digital camera, ~50fps) Photon Flux: ~10 11 photons/sec Lens acceptance: +/- 6 degrees New analyzer was installed in Sep 2008 Lens acceptance: +/- 15 degrees Energy window(single-shot): 24 ev Plan to install 120fps digital camera VG-Scienta R3000

13 PES and XES performance C, N and O Kedges Illumination selector Revolver place for 3 gratings Elliptical grating: L=10 cm Ni coating: less grazing incidenc Sample X,Y stage Grating Selector rotation+lock Under commission at BL13 2 MCP + digital camera Incidence angle

14 PES/XES station for SXR Sample manipulator Preparation level beam Spectroscopy level 10 mm Side view

15 PES/XES station for SXR When the sample is at the preparation level.. Gas doser Users can operate the Ne sputter gun, the EB heating system (up to 1100 K) and the gas doser to prepare sample. Preparation levelsputter gun Users can operate the gas line system to adjust the pressure.

16 PES/XES station for SXR When the sample is at the spectroscopy level.. If FEL beam is used in the hatch 2, users may not enter the hatch 2. The gas doser can be operated remotely. A filament for radiative heating can be controlled remotely. XES power supply can be turn on and off remotely. Spectroscopy level PES power supply can be controlled remotely. beam Gas doser Pulsed gas beam is delivered. Pulse width: ~300 microseconds, Repetition rate ~250 Hz

17 PES/XES station for SXR Beam position monitor? Beam dump TV cameras The position of reflected soft x-ray beam may be monitored. Side view Top view (PES) Top view (XES)

18 - Grazing incidence e 1 deg. reflectivity [%] X-ray interaction with matter calculator deg. 80 Ni 60 5 deg. Cu Photon Energy [ev] e- e- 5 deg. Advantage: large foot print on the sample: 2 mm x 10 micron less power density reflectivity [%] X-ray interaction with matter calculator deg. 40 Ni Cu Photon Energy [ev] angle of incidence <0.5 degree gives, reflectivity: >90% attenuation length: ~5 atomic layers, less photoionization of bulk atoms

19 Scan the sample to avoid X-ray irradiation induced damages Each FEL pulse hits a fresh spot SSRL BL13-2 Without scanning, the sample is seriously damaged! LCLS One shot seriously damages the sample. SSRL LCLS Scanning is necessary: 10 micron/sec SSRL Scanning is necessary: 10 micron/shot =1 mm/sec. LCLS Sample scan bea m

20 PES and XES count rate: SSRL and LCLS SSRL BL13-2: PES: a few sec accumulation (~10 11 photons/sec) XES: ~1000 sec accumulation (~10 12 photons/sec) LCLS SXR: same amount of photons/pulse PES: one-shot XES: ~10 sec accumulation

21 First experiments Ultrafast temperature jump Hot Oxygen Atom Hot Nitrogen Atom NIR laser: 780nm, short pulse width, small spot size: 10micron hot atom Photodissociation Dissociation of O 2 Dissociation of NO UV laser: 260nm, short pulse width, small spot size: 10 micron * *

22 Pump-probe Ultrafast Surface Chemistry Station: Understand the origin of catalytic efficiency and selectivity Main Point of Contact for the Project: Anders Nillsson Point of Contact for the Instrumentation: Dennis Nordlund Hirohito Ogasawara SSRL LCLS reactant(ads) product(ads)? intermediates(ads) intermediates(ads) reactant(ads) product(ads) Time [fs]