A Low-Energy Electron Microscope for the Study of Growth and Dynamics of Surfaces in Spain

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Instituto de Química-Física “Rocasolano” http://surfmoss.iqfr.csic.es/leem

A Low-Energy Electron Microscope for the Study of Growth and Dynamics of

Surfaces in Spain

Juan de la Figuera

Instituto de Química Física “Rocasolano”, CSIC

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Low energy electron microscopy

Reflectivity of W(110)

Enough Electrons?

Yes!

Electrons at low energy:

sensitive to the last nm of the material

Is it a “low energy” counterpart to the transmission electron microscope:

- Why low energy? Optimized for surfaces

- Use reflected electrons (problem to separate them from incoming electrons).

- Prototype in the 60’s (Ernst Bauer)

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What is a Low-Energy Electron Microscope?

Illumination

column Imaging column

Objective

Contrast aperture

Image

Illumination aperture

Electron emitter

-

+

V s

HV

LEED pattern

Sample V = HV + Vs

Beam separator

STEP/FRESNEL

MIRROR REFLECTIVITY

QUANTUM

INTERFERENCE LEED

DARK FIELD

polarizer

SPLEEM

Kevin F. McCarty & Juan de la Figuera. in Surf. Sci. Tech.51, 531 (Springer 2013) http://surfmoss.iqfr.csic.es/leem

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Position (nm)

Refectivity (arb. units)

Phase contrast:

how to see atomic steps

W(110) 10 μm

Step height ~ 0.25 nm

Wavelength for 5 eV ~ 0.5 nm

W. L. Ling et al., Phys. Rev. Lett. 93 (2004) 166101

Enhanced self-

diffusion on Cu(111)

by trace amounts of S

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Measuring the density of a 2D gas in equilibrium with a solid

θ

T

600 K

670 K

J. de la Figuera et al., Surf. Sci. 600 (2006) L105

Coverage (θ)

T em pe ra tu re ( K ) 2D

gas 2D

condensate

Coexistence Region

n

_s₀

= n

₀

e

^−W^s^/^KT

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Measuring the density of a 2D gas in equilibrium with a solid

Coverage (θ)

T em pe ra tu re ( K ) 2D

gas 2D

condensate

Coexistence Region

n

_s₀

= n

₀

e

^−W^s^/^KT

θ

T

2D adatom gas

Coexistence region:

gas+condensate

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Phase contrast: thickness of films

In a thin film interference between the electron reflected on each

boundary.

4-7 ML Co/Ru(0001)

If the thickness differs, the reflected intensity will differ

10 μm

If we change the energy, we change the electron wavelenght and the

reflected intensity will also change.

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Growth studies

Step-flow:

Cr/W(110)

B. Santos et al., New J. Phys.

10 (2008) 013005

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Growth studies

Step-flow:

Cr/W(110)

Island nucl.

Co/Ru(0001)

g)

10 (2008) 013005

F. El Gabaly et al., Phys Rev Lett 96 (2006) 147202

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Growth studies

Step-flow:

Cr/W(110)

Island nucl.

Co/Ru(0001)

g)

10 (2008) 013005

N. Rougemaille et al.

Phys. Rev. Lett.

99 (2007) 106101

Kinetic labyrinth:

Pd/Ru(0001)

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Growth studies

Step-flow:

Cr/W(110)

Island nucl.

Co/Ru(0001)

g)

10 (2008) 013005

N. Rougemaille et al.

Phys. Rev. Lett.

99 (2007) 106101

Oxide growth:

Fe3O4/Ru(0001)

M. Monti et al., Phys. Rev. B

85 (2012) 020404(R)

Kinetic labyrinth:

Pd/Ru(0001)

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Doing (low-energy) electron diffraction

100 150 200 250 300 350

Energy (eV)

In te ns ity (a .u .) (00)

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fit experiment

Measuring the diffraction pattern

changing the energy: Crystallography (beware multiple scattering)

B. Santos et al., New J. Phys. 10 (2008) 013005

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Ts= 454 ºC

c(2x2)

p(1x1)

Following the surface order-disorder transition on Fe3O4(100)

Reversible, no hysteresis

It does not coincide with bulk Tc

430 440 450 460 470 480 490

0.0 0.2 0.4 0.6 0.8 1.0

Temperature (ºC)

A m pl itu de ( ar b. u n its )

N.C. Bartelt et al., Phys. Rev. B 88 (2013) 235436

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Ts= 454 ºC

Following the surface order-disorder transition on Fe3O4(100)

Reversible, no hysteresis

It does not coincide with bulk Tc

0.0 0.1 0.2 0.3 0.4 0.5

F W H M ( / k

0

)

430 440 450 460 470 480 490

0.0 0.2 0.4 0.6 0.8 1.0

Temperature (ºC)

A m pl itu de ( ar b. u n its )

T/T

_c

= 0.98

0 5 10 15 20 25 30

T/T

_c

= 1.02

0.4 0.2 0

1 2 3

0.0 0.2 0.4

k/k

₀

N.C. Bartelt et al., Phys. Rev. B 88 (2013) 235436

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Mixing LEED and LEEM:

 LEED and dark field

A

A B

B

Ru(0001)

Limiting the beam size down to a fraction of a micrometer by means of an aperture give micro-LEED:

Take LEED data on a single terrace!

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Mixing LEED and LEEM:

 LEED and dark field

2  m

Limiting the beam size down to a fraction of a micrometer by means of an aperture give micro-LEED:

Take LEED data on a single terrace!

A

A B

B

Ru(0001)

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Dark Field

E=46.7 eV

Dark field imaging

5 µm FOV

LEEM STM

FFT of selected areas

F. El Gabaly, W. Ling, K.F. McCarty, J. de la Figuera, Science 308 (2005) 1303

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LEEM take home points

●

Time resolution:

–

milliseconds in LEEM mode (video taped)

●

Real-space resolution:

–

10 nanometers resolution (2 nm with ab. corr.)

–

Typical field of view 3-25 µm

–

Atomic steps can be detected, thickness using QSE

●

Diffraction data (no energy filtering):

–

µLEED ,Nanometer scale LEED (in imaging mode)

–

Dark field imaging

●

Limitations:

–

In-situ UHV (ultra-high vacuum) technique (not a post-mortem characterization technique)

–

Only for flat, (poly or mono) crystalline

–

An electric field of ~10 kV/mm is applied while imaging

~70 worldwide 2

1 1*

1 3

1

>5

1

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A LEEM at the Rocasolano

Received 3

^rd

July 2017

Expected start operating in September 2017

The only LEEM instrument in Spain outside of the Alba synchrotron (which is mostly devoted to PEEM).

Infrastructure call CSIC15-EE-3056

A. Quesada A. Mascaraque

E. G. Michel

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We The People

Andreas K. Schmid

SPLEEM

Jose F. Marco

Gong Chen

Norm C. Bartelt

Laura Martin

Arantzazu Mascaraque, Sandra Ruiz Gómez Beatriz Martínez Pabón Lucas Pérez

Oscar Rodriguez dela Fuente

LEEM/PEEM

Lucia Aballe Michael Foerster

Adrian Quesada Carmen Munuera Christian Tusche

Halle

Spin-PEEM

Tirma Herranz

Former members of our group

Farid El Gabaly

Raquel Gargallo

Benito Santos

Lucía Vergara Former members of SPLEEM group

Adrian Quesada, Christoph Klein, Farid el Gabaly, Nicolai Rougemaille

Kevin F. McCarty Former members of LEEM group

Andrea Locatelli, Tevfik Onur Mentes Benito Santos

Yaiza Montaña

Anna Mandziak

LEEM

Guiomar Delgado María Sanchez

Pilar Prieto Jose E. Prieto