Development at Glasgow of Medipix in Electron

Microscopy

Dr Damien McGrouther

Materials & Condensed Matter PhysicsSchool of Physics & Astronomy

damien.mcgrouther@glasgow.ac.uk

Transmission Electron Microscopy

SCREEN/

DETECTOR

CONDENSER

DIFFRACTIONPROJECTOR

SERIES

OBJECTIVE

OBJECTIVE

GUN

SAMPLE

Electrons -

60-300 keV kinetic energy

5 to 2 picometres wavelength

High vacuum in column

Modes -

TEM – Condenser illuminates, Objective

magnifies

STEM – Condenser/Objective focuses probe,

beam scanned

Sample rods, multiple functions

Sample thickness required < 100 nm

Traditional detectors:

TEM – Imaging camera – CCD or CMOS

STEM – scintillator:PMT solid, annular

DPC segmented pn diodes

Overview

Small, fast, high sensitivity direct detectors - Novel

capabilities for TEM & STEM imaging

• Development of Medipix/Timepix for TEM at

Glasgow since 2008

• Applications: 4D STEM, High speed imaging

• Commercial development with Quantum

Detectors Ltd

• Current & future research

Timepix on TEM circa 2010

• McMullan et al evaluated

performance with high energy

electrons [ McMullan G, et al.,

Ultramicroscopy 107, 401 (2007)]

• Also investigated Medipix2 as

scanning mode, STEM detector –

IWoRID 2010 [A. MacRaighne, et al.,

Journal Of Instrumentation 6, C01047

(2011) ]

• Focused on temporally resolved

imaging of magnetic

nanostructures

•Medipix2 + Fitpix readout card

Collaboration with PPE detectors group at Glasgow:

Circa 2010 – Medipix2 vs Indirect CCD

CCD images

From Gatan 794 MSC

1kx1k CCD binned 2x, using centre 1/2

Exposure times 4ms -> 1ms

1 ms image limited by shutter + noise

added by detector

Medipix2

Integral mode, single

exposures

1 ms -> 10ms

10ms image limited by

~1 nA beam current(~6200 electrons per ms)

Foucault contrast images

Domain wall pinned at an anti-notch

(Red arrows indicate direction of sensitivity)

5 0 0 n m 5 0 0 n m 5 0 0 n m

4 ms 2 ms 1 ms

1 ms 100 ms 50 ms 10 ms

First use of a

hybrid pixel

detector for

Differential

Phase

Contrast –

2011

Explanation

follows….

Electron-optical limitations on performance

Abbe spatial resolution ~l/2 =~ 1 picometre

Round electromagnetic lenses have

spherical aberration, CS –Scherzer, 1949

https://physics.aps.org/articles/v2/85

CS limits resolution to ~1Å

Last 10yrs, aberration correctors available to

induce negative CS

TEM – post-objective

STEM – pre-objective

Current spatial resolution, ~60 picometres

Detector technologies became the limitation!!

JEOL ARM200cF @ Glasgow

JEOL News, Vol 49, 2014

S. McVitie et al.,Ultramicroscopy 152, 57 (2015)

• 2011, installed JEOL ARM200cF STEM

• Study of magnetic structure in materials

- World-leading 0.7 nm spatial

resolution

• Differential Phase Contrast (DPC)

imaging, segmented detector

Medipix3, circa 2014 and onwards

MERLIN readout system - 1000’s fps

Simple static sled allowed

use of Medipix3 inside

vacuum of STEM detector

chamber

Development of Medipix3 as a STEM detector

Medipix3 data, 2ms exposuresKrajnak et al., Ultramicroscopy 165, June 2016

Pixelated DPC results

•Acquisition: 256x256 STEM scan, 1.9ms pixel

dwell time, 500fps

•Sub-pixel accuracy in measuring disc deflection

•Grain structure suppressed

•Enables full utilisation of 0.7nm spatial resolution

Krajnak et al., Ultramicroscopy

Volume 165, June 2016, Pages 42–50

4D-STEM

• Performing DPC in this

manner is “4D STEM”

• Focused electron beam

scans thin specimen (x , y)

• Detector records scattering

in reciprocal space (kx , ky)

• Wider range of techniques

including nano-diffraction,

VADF, ptychography…

4D-STEM for nanostructure

• 4D nano-diffraction (6nm, 0.4mrad) from X-section of FeRh island

– RC Temple, et al., Phys. Rev. Materials 2, 104406 (2018)

NiAl

FeRh

EBID Pt

MgO

Virtual DF - Chemical ordering

NiAl

FeRh

EBID Pt

Edge damage

from island

fabrication

Fe60Al40 alloy

• 4D STEM acquisition – simultaneous physical and magnetic structure

– 10mm CLA (6 nm FWHM, 415mrad)

– 4.4ms dwell time

– Typical scan area – 192 x 860 pixels (3.4 x 15.5mm2, 18 nm step size)

• 40nm thick film, B2 crystal structure – paramagnetic

• Irradiation, 26 keV Ne+, 6x1014 ions cm-2 – ferromagnetic

Ne+ irradiation of FeAl

• Irradiated rectangular strips,

– Widths from 3.9mm to 50nm, length 10mm

– Superlattice reflections extinguished

– Irradiated strips magnetically and structurally observable

VADF: 13.2-17.1 mrad

• Scan pixel diffraction pattern (from a 6 nm diameter region) :

– Important no saturation in central spot – DPC imaging

– Low index diffraction spots, lower intensity but well resolved

Contrast boosted

• Diffraction patterns

averaged over wide regions

of strip

• Resolve difference between

non-irradiated /irradiated– (110) B2 2.8931 Å

– (110) A2 2.9356 Å

• Slight elliptical distortion –

from diffraction optics –

tough to correct

Split Fan-blade

Distortion

• R. Bali,…,D. McGrouther et al., accepted for publication in Small,

September 2019

• Anisotropic lattice parameters from shape of irradiated feature

• => STRAIN ENGINEERING of MAGNETISM

High speed filming of Sk dynamics

Bloch type skyrmion

• 100 fps filming of

Skyrmion dynamics

• Replayed at 30fps

Commercial Product Development

Fast Pixel Detectors: a

paradigm shift in STEM

imaging, EP/M009963/1

Impact Acceleration

Account EP/K503903/1

MERLIN 1S & 4S MERLIN 1R MERLIN 4R

256x256 pixels

512x512 pixels

512x512 pixels256x256 pixels

MERLIN readout and motion

Diffraction pattern recording in TEM

• Cross-grating replica, Au nanocrystals on carbon

• 10mm CLA used to limit arrival rate in central spot to <1MHz

• Exposure = 16 secs

• Max intensity ~106 counts

• Min intensity ~ 3000 counts

J. Mir, D. McGrouther et al., Ultramicroscopy 182, 44 (2017)

MPX3: 300mm Si MTF & DQE

60 keV SPM

MTF

60 keV SPM

DQE

J. Mir, D. McGrouther et al., Ultramicroscopy 182, 44 (2017)

60 keV CSM

MTF

60 keV CSM

DQE

Electron stopping calculations

100mm

200mm

300mm

400mm

+55mm +110mm+55mm+110mm

100mm

200mm

300mm

400mm

+55mm +110mm+55mm+110mm

100mm

200mm

300mm

400mm

+55mm +110mm+55mm+110mm

Silicon, 200keV

Silicon, 60keV GaAs, 200keV

• MTF & DQE reflect localisation of

electron penetration

• Best performance with

– Low beam energies – 60keV

– Higher Z materials – e.g. GaAs:Cr,

CdTe being investigated

Comparing Si & GaAs:Cr Medipix3

Si – 200keV

GaAs:Cr – 200keV

Si

Mode: 4

Mean: 3.94

GaAs:Cr

Mode: 2

Mean: 2.32

• 500mm Si vs GaAs:Cr Medipix3

• Electron “hit” cluster statistics, based on

>50,000 hits

unpublished

MPX3: 500mm Si vs GaAs MTF

120keV 200keV

Single Pixel Mode

unpublished unpublished

MPX3: 500mm Si vs GaAs MTF

120keV 200keV

Charge Summing Mode

unpublished unpublished

Semiconductor defects

Raw: X-grating ImageFlat Field Exposure Flat-field corrected: X-grating

Have to take account of pixel distortions:

C. Ponchut et al 2017 JINST 12 C12023

Medipix3 - pixel circuitry

Modes:

• Single Pixel (SPM)

• Charge Summing Mode

(CSM)

• Spectroscopic

• Spectroscopic CSM

Pre-amp response to induced charge

t

Discriminated pulse to control logic

(two example thresholds shown)

X. Llopart et al., IEEE Trans. Nucl. Sci. 49, 2279 (2002)Medipix3 - R. Ballabriga et al., J. Instr. 6, C01052 (2011)

t ~ hundreds ns, dependent on settings

Counter pulse ~20ns

Medipix3 Time Resolution

G. Paterson, et al. in submission

https://arxiv.org/abs/1905.11884

Time resolution better than 80ns realisable!!

Summary

• Hybrid pixel detectors enabling on-chip single electron counting

for novel imaging and detection capabilities

• TEM: Adjustable MTF & DQE, best highest performance at

low-beam energies, but high-Z sensors improve high energy

performance. High speed filming for ms dynamics.

• STEM: High-frame rates and sensitivities enable novel 4D-

STEM detector applications with real-time or post-processing

• Detector developments - Time-resolved capabilities – direct

filming-> 80ns pump-probe with MPX3

• Timepix3 potential for further improvements but for limited

beam currents and with data load and computational cost.

Acknowledgements

• Nadia Bassiri, Michael Perreur-Lloyd, Dima Maneuski, Val O’Shea

– University of Glasgow

• Kirsty Paton, Fred Rendell, Magnus Nord, Gary Paterson, Ian MacLaren, Ray

Lamb, Matus Krajnak, Trevor Almeida, Stephen McVitie – University of

Glasgow

• Jamil Mir, Hidetaka Sawada (JEOL), Angus Kirkland – University of Oxford

• Rafael Ballabriga, Michael Campbell – CERN

• Ian Horswell, Nicola Tartoni, Diamond Light Source

• Olivia Sleator, olivia@quantumdetectors.com

• Eduardo Nebot, Liam O’Ryan, Roger Goldsbrough – Quantum Detectors