Daresbury Laboratory

1
Requirements in Particle Science
Science in which Electrons and Ions are detected
Michele Siggel-King
Daresbury Laboratory
Low Energy Detector Roadmap Workshop
Michele Siggel-King
30 June 1 July 2005
2
Questionnaires and Input Received for Particle
Science
from 32 groups
Chris Binns (Leicester) Tony Cafolla (DCU) Fred
Currell (Belfast) Vin Dhanak (Liverpool) John
Dyke (Southampton) John Eland (Oxford) Andrew
Evans (Aberystwyth) Leszek Frasinski
(Reading) David Holland (Daresbury) Rob Jones
(Nottingham) Ottmar Jugutzki (Frankfurt) George
King (Manchester) David Langstaff
(Aberystwyth) Rob Lindsay (Manchester) Andrew
Malins (Daresbury) Philip Moriarty
(Nottingham) Sunil Patel (Daresbury)
Maria-Novella Piancastelli (Uppsala) Erwin
Poliakoff (Louisiana) Ivan Powis
(Nottingham) Katharine Reid (Nottingham) H
Schmidt-Bocking (Frankfurt) Sven Schroeder
(Manchester) David Shaw (Daresbury) Michele
Siggel-King (Daresbury) Emma Sokell
(UCD) Giovanni Stefani (Roma-III) Svante Svensson
(Uppsala) Geoff Thornton (UCL) Mike Towrie
(RAL) Richard Tuckett (Birmingham) Gerrit van der
Laan (Daresbury) Peter Weightman (Liverpool) Phil
Woodruff (Warwick)
Michele Siggel-King
3
Particle Detection
overview
target sample
Michele Siggel-King
4
Photoelectron Spectroscopy w/ Deflection-type
Analyser
basic experiment/measurement
eg 180 HMA (hemispherical mirror analyser)
outer hemisphere
inner hemisphere
Particle Sensor
lens
Sample/Target
Michele Siggel-King
5
Photoelectron Spectroscopy w/ Deflection-type
Analyser
Measurements at Realistic Pressures
Rob Lindsay (Manchester) Robert Jones
(Nottingham) John Purton et al (Daresbury)
Most surface studies at UHV --- have given
lots of useful information --- even though
10,000,000,000,000 x diff in P
Ruthenium is the very best catalyst CO oxidation
catalyst at atmospheric pressure --- but is not
active in vacuum
Limitations detector must be at reasonable
vacuum mean free path of
electrons high background
lots of counts s/n poor Potential higher
pressures, snap shot spectroscopy, pump-probe
Michele Siggel-King
6
Snap-shot Photoelectron Spectroscopy
Following a Reaction in Real Time Snapshot PES
Particle Sensor
Sample/Target
Michele Siggel-King
7
Snap-shot Photoelectron Spectroscopy
Following a Reaction in Real Time Snapshot PES
Evans et al. Aberystwyth
Real-time monitoring of an organic semiconductor
thin film (tin phthalocyanine) growing on a GaAs
surface. data not corrected or smoothed
photon energy 100 eV pass energy 100 eV KE
range at hma exit 59-65 eV 15 sec / pes 550
spectra in image 768 discrete anodes
(points/spectra)
As 3d
Michele Siggel-King
8
Snap-shot Photoelectron Spectroscopy
Following a Reaction in Real Time Snapshot PES
Evans et al. Aberystwyth
Particle Sensor
Sample/Target
Michele Siggel-King
9
Angle-Resolved Photoelectron Spectroscopy
Traditional Method
eg, rotate sample normal with respect to the
light propagation direction and/or spectrometer
acceptance direction
-or- move spectrometer with respect light
propagation angle and/or surface normal
-or- move light propagation direction (or
polarisation vector) with respect to surface
normal and/or spectrometer acceptance direction
(not SR)
Sample/Target
Michele Siggel-King
10
Angle-Resolved Photoelectron Spectroscopy
Traditional Method

• Who
• Rob Lindsay (Manchester)
• Chris Binns (Leicester)
• Rob Jones (Nottingham)
• Phil Woodruff (Warwick)
• Michele Siggel-King (Daresbury)
• George King (Manchester)
• and others

• Science
• Gas-Phase dipole asymmetry (b) parameters
• Gas-Phase non-dipole phenomena
• Surfaces photoelectron diffraction
• Surfaces at realistic pressures snapshot
• Surfaces spin polarised core levels
• Surfaces SR-based structural and electronic
• structure studies

Limitations time consuming (limited beam
time, surface contamination ... detector
countrates (0D vs- 1D vs- 2D) hv or uhv
ke limit (3keV possible up to 10keV)
Michele Siggel-King
11
Angle-Resolved Photoelectron Spectroscopy
The TEARES Project Extending the Capabilities of
Electron Detection Systems
state-of-the-art versatile electron spectroscopy
system large horizontal angular acceptance
Michele Siggel-King
12
Angle-Resolved Photoelectron Spectroscopy
TEARES non-dipole effects
important at high photon energies recently shown
to be important for energies below 100eV

• Current controversy over some systems -- eg CO

Michele Siggel-King
13
Angle-Resolved Photoelectron Spectroscopy
TEARES non-dipole effects
Michele Siggel-King
14
Angle-Resolved Photoelectron Spectroscopy
TEARES photoelectron diffraction

• Limitations on Toroidal System
• Count-rate particle sensor saturates at 1
  MHz must limit angular and/or energy
  through-put
• Source size limit on resolution angular
  resolution limited by 2GLS source size
• Potential
• angle-resolved studies of dilute systems
• at high resolution
• studies at realistic pressures
• snap-shot studies energy angle, f(t)
• pump-probe

Michele Siggel-King
15
Threshold Photoelectron Spectroscopy
Something interesting will often happen when you
excite a reaction close to its threshold
eg Penetrating Field Technique
Michele Siggel-King
16
Threshold Photoelectron Spectroscopy
Who?
George King et al. (Manchester) John Dyke et al.
(Southampton) Andrew Yencha (New York) Andrew
Malins (Daresbury)
Michele Siggel-King
17
Time of Flight
Basic Experiment-I
Michele Siggel-King
18
Time of Flight
Charged Particle Imaging Velocity Mapping of
Electrons
characterisation of a train of attosecond pulses
Who? (CPVM) Frasinski/Hatherley Holland/Shaw G.
King R. Tuckett
S(n,?) ? ?P2(cos?) ?P4(cos?)
Michele Siggel-King
19
Time of Flight
Basic Experiment-II
ions
Times of flight 2dim positions ? 3 dim
momentum vector
Michele Siggel-King
20
Time of Flight
Charged Particle Imaging Velocity Mapping of
Ions Electrons
1st Photon (pump) aligns and excites the molecule
to a specified excited neutral state
2nd Photon (probe) probes the excited state
4? SR - collects all e-s and all
ions excellent collection efficiency
enables many of the quantum numbers to be
specified
enables access to different ionization channels
2-D position flight time can give very
detailed information on the system. Velocity
Mapping
angular distributions from such a prepared state
cannot be described by a simple ? parameter
delay between pump and probe photons can be
varied to study time-dependent interactions and
dynamics
Michele Siggel-King
21
Time of Flight
Charged Particle Imaging Velocity Mapping of
Ions Electrons
Michele Siggel-King
22
Time of Flight
Charged Particle Imaging Velocity Mapping of
Ions Electrons
Technique has been utilised by R. Doerner
3 Nature Publications
Complete Photo-Fragmentation of the Deuterium
Molecule 431 (2004) 437.
4? SR - collects all e-s and all
ions excellent collection efficiency
Three-Dimensional Imaging of Atomic Four-Body
Processes 422 (2003) 48.
Correlated Electron Emission in Multiphoton
Double Ionization 405 (2000) 658.
2-D position flight time can give very
detailed information on the system. Velocity
Mapping
10s of PRLs
Michele Siggel-King
23
Time of Flight
Charged Particle Imaging Requirements
Limitations
Michele Siggel-King
24
Areas in which Detector Development is Required
based on questionnaire feedback
Improvements required high countrate 1D 2D
detectors
Improvements required 2D detectors spatial
resolution timing resolution multi-hit
capabilities
Michele Siggel-King