ev-tem: transmission electron microscopy at leem energies
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eV-TEM: Transmission Electron Microscopy at LEEM Energies
Imaging in LEEM and eV-TEM• Comparison of the same area in eV-TEM and LEEM• gold nanoparticles on graphene• Silicon Nitride support grid (2.5 µm holes)
eV-TEM Setup
References[1] P.S. Neu, D. Geelen et al., arxiv.org, 2009.09856 (2020, preprint)[2] D. Geelen et al., Ultramicroscopy. 159, 482–487 (2015)[3] D. Geelen, doctoral dissertation, Casimir PhD Series (2018)[4] M. Seah & W. Dench, Surface and interface analysis 1, 2–11 (1979)[5] Gatta-AFM, http://www.gattaquant.com/products/ gatta-afm.html[6] D. Geelen et al., Phys. Rev. Lett. 123, 86802 (2019)
P.S. Neu1, D. Geelen1, A. Thete1, R.M. Tromp2,1 & S.J. van der Molen1
1Leiden University, 2IBM Yorktown Heights [email protected]
contrast aperture
electron gun-15 kV
detector
prism 1
deector 3
deector 1
sample-15 kV + V0
objective lens
electron mirrorprism 2
TEM gun-15 kV
80%
20%
3.0 eV3.0 eV3.0 eVeV-TEM
2.5 eV
4.0 eV
Resonant Transmission and Re�ection in Graphene• Transmissivity minimum, i.e. Mean Free Path minimum, at ~30 eV -> matches ‘universal curve’ prediction [4]
• Transmissivity maxima (corresponding reflectivity minima) caused by the interference of electrons reflected from different layers [6]
• Insets: splitting of the minima is characteristic of the layer count
Resolution• ~10 nm resolution measured from 20% to 80% intensity increase• Limited by size & coherence of electron emitter
• Electron gun behind sample - barium-oxide emitter - 0.8 eV energy spread• 0-100 eV landing energy• Extension of fully-operational aberration corrected LEEM
DNA Origami• DNA origami rectangles[5] on graphene oxide• no visible degradation over one hour
[2]
4.0 eV 2.5 eVeV-TEM LEEM
3.0 eV
2.0 eV
LEEM
eV-TEM
long axis, 70 nm short axis, 50 nm
Inte
nsity
pro
files
alo
ng a
rrow
s of
cor
resp
ondi
ng c
olor
0 10 20 30 40 50 60 70
Energy [eV]
10−4
10−3
10−2
10−1
100
Refl
ectivi
ty
One layer
Two layers
Three layers
0 10 20 30 40 50 60 70
Energy [eV]
10−4
10−3
10−2
10−1
100
Tra
nsm
issivi
ty
One layer
Two layers
Three layers
0 2 4 6
Energy [eV]
0.2
0.4
Refl
ectivity
16 18 20 22 24
Energy [eV]
0.06
0.12
7.0 eV
2.0 eV
500 nm
500 nm
0 10 20 30 40 50 60 70
Energy [eV]
10−4
10−3
10−2
10−1
100
Refl
ectivi
ty
One layer
Two layers
Three layers
10−2
10−1
100
Tra
nsm
issivi
ty
One layer
Two layers
Three layers
0 2 4 6
Energy [eV]
0.2
0.4
Refl
ectivity
16 18 20 22 24
Energy [eV]
0.06
0.12
7.0 eV
2.0 eV
500 nm
500 nm