High-Sensitivity LEIS Principles & Applications

46
ION-TOF GmbH Heisenbergstr. 15 D-48149 Münster / Germany www.iontof.com Lehigh University November 06,, 2014 High-Sensitivity LEIS Principles & Applications Hidde Brongersma TU/e, Imperial College, ION-TOF [email protected] 1

Transcript of High-Sensitivity LEIS Principles & Applications

Page 1: High-Sensitivity LEIS Principles & Applications

ION-TOF GmbH

Heisenbergstr. 15

D-48149 Münster / Germany

www.iontof.com

Lehigh University

November 06,, 2014

High-Sensitivity LEIS

Principles & Applications

Hidde Brongersma TU/e, Imperial College, ION-TOF

[email protected]

1

Page 2: High-Sensitivity LEIS Principles & Applications

Introduction to LEIS

Miscellaneous Applications

Imaging, NPs, segregation, surface modification, anti-wetting, NPs

Outer surface oxides

SOFC, membranes

Growth

Summary

Outline

Page 3: High-Sensitivity LEIS Principles & Applications

Low Energy Ion Scattering

Ef (eV)

Energy spectrum of an

alloy

0 1000 2000 3000

S (

a.u

. ) 192Ir

103Rh

55Mn

51V

59Co 39K

Atomic composition of outermost

atomic layer

Energy 1 – 8 keV

Lateral resolution 0.01 – 1 mm

In-depth (0 – 10 nm)

No matrix effects

Characteristics of the technique

Example: 3 keV Ne alloy

Energy

LE

IS S

ign

al

θ

3He+, 4He+, Ne+, Ar+

1- 8 keV

Detector for Energy of Ions

1 3

2

1 2 3

Studying the outermost surface of any material

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LEIS Enables Simple Quantification

Example: Coverage of Bromine adsorbed on Tungsten

100

200

300

400

500

600

0

0 100 200 50 150

SBr ( a.u. )

SW

(

a.u

.)

LEIS ‘sees’ only 1st atomic layer

No matrix effect !

θ w = 1

θ Br = 1

Bromine

Tungsten

Bromine

Tungsten

Bromine

Bromine Tungsten

LEIS can quantify the surface coverage θ in the 1st atomic layer

θ W + θ Br = 1

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Noble gas ion source

Pulsing system

Position sensitive detector

Energy analyser

Focussing optics

Large acceptance angle ( 360o )

Parallel energy detection

only low ion fluence needed

STATIC LEIS

“ Analysis before Damage ”

“ Hit same place only once “

( Core/shell nanoclusters ! )

ToF filtering eliminates SIMS ions

Qtac: Unique new Analyser High – Sensitivity LEIS

Sample

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LEIS Technique

Features of Low Energy Ion Scattering (LEIS)

He+, Ne+, Ar+, Kr+

1 - 8 keV

Reviews

Brongersma et al., Surf. Sci. Rep. 62 (2007) 63

H.H. Brongersma, Low-Energy Ion Scattering in: Characterization of

Materials, Ed. E.N. Kaufmann, pp. 2024-2044, Wiley (2012).

LEIS Features for elemental surface analysis:

Ultra-high surface sensitivity, top atomic layer

Reliable and straight-forward quantification

Non destructive (static) analysis

Detection limits:

Li - O ≥ 1 % of 1 ML

F - Cl 1 % - 0.05 % of 1 ML

K - U 500 ppm - 10 ppm of 1 ML

Static depth profiling (up to 10 nm)

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LE

IS s

ignal

0.75 0.80 0.85 0.90 0.95

Pd

Pt

Ef / Ei

0.75 0.80 0.85 0.90 0.95

Pt

Pd

LE

IS s

ignal

Ef / Ei

4He 10,000 nC 4He 5.4 nC

NIM B 68 (1992) 207

Conventional LEIS High-Sensitivity LEIS

Promoters visible, but removed from spectrum

Conventional LEIS vs HS - LEIS

Pd / Pt-C ( 1000 m2/g )

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Sample Cleaning

Atom Source for O- and H-atoms

O2 or H2

O or H atoms

Sample

CO CO2

H2O

CxHyOz

O atoms remove organics, coke

Chemical energy: no sputtering

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Two possibilities:

1. Static LEIS + Sputter depth profiling with dual ion beam

( advantage of quantification, depth resolution LEIS)

2. Static LEIS (non destructive) for heavier elements

(analogous to RBS and MEIS, but better depth resolution)

In – Depth profiling

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Depth info; non-destructive

Si

ZrO2

He+

Ef

3 keV

Heo

Zrsurf

Zrbck

Osurf

Sibck

Sisurf Fin

al E

ne

rgy

Depth resolution better for lower primary E !

He+

∆E

160 eV /nm

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1st atom and Static Depth Profile

ZrO2 Atomic Layer Deposition on Silicon

Detection / quantification pinholes (still present after 70 cycles)

Thickness distribution ZrO2 layer (160 eV/nm)

No matrix effect

Example: calibration / quantification for a 2 component system

70 cycles

2 4

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1 %

10 ppm

0.01 %

Depth Resolved

LEIS

SIMS

AES XPS

0.1 1 10 100

Information Depth ( Atomic Layers )

100 %

10 %

0.1 %

1 ppm

D

ete

ctio

n R

an

ge

Detection range vs Information Depth

for AES, LEIS, SIMS and XPS

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Imaging

Surface segregation, anti wetting

Interdiffusion

Surface modification

Nano particles

Miscellaneous Applications

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Surface Imaging

Lateral Resolution and Sensitivity required

Field of view: 2 mm

Ti

C

u

Imaging in surface analysis:

Probe or detector needs sufficient lateral resolution

Data rate has to be high enough (acquisition time)

Detection must be sensitive enough

sufficient information from each pixel before damage

detection sensitivity “useful lateral resolution”

With new ion source

lateral resolution

~ 10 um

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Surface segregation: universal process

Example: Acrylonitrile-Butadiene-Styrene (ABS)

0 1000 2000 30000

1

2

3

4

ZnCa

O

N

LE

IS S

ignal (C

ts/n

C)

Energy (eV)

C

Na

Pb

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Anti wetting

Fluorine density vs surface energy

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.45

10

15

20

25

30

35

40

45

Su

rfa

ce

en

erg

y (

mN

/m)

Fluorine density (*1015

/cm2)

P(MMA-co-F1MA) P(MMA-co-F6MA) P(MMA-co-F10MA) C

8F

17-PMMA/PMMA blend

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Metal - polymer interface in ultra - thin layers

PLED: Ba evaporation on PPV

LE

IS S

ign

al (C

ts/n

C)

1500 2000 2500 3000

0

2

4

6

8

10

12

7 nm

During evaporation of

barium on PPV, most of

the Ba diffuses into the

PPV.

Compare the peakshape

of a sub-monolayer of Ba

(blue) with the actual

peak (red)

Peak shape ↔ depth

distribution

Measured

Ba for < 1 ML

Energy (eV)

PLED: higher light output

for narrow depth distribution

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Surface modification

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Aging of plasma oxidized HDPE

Aging (LEIS) faster than aging (XPS) !

“Straight line” diffusion process

Time1/2 (min)

1 .2 5

1 .7 5

2 .2 5

0 2 0 4 0 6 0 8 0 1 0 0 1 2 0

Tim e½

log

(O s

ign

al)

0 .2 5

0 .7 5

1 .2 5

log

(O i

n a

t%)

XP S

L E IS

Lo

g(O

in

at%

)

XPS

LEIS

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Nano particles (supported catalyst)

Average size

Core / Shell

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TEM:

excellent catalyst characterisation

detailed info, but local

contrast required ( high Z cluster on low Z support )

Chemisorption:

requires known probe / surface interaction

HS - LEIS:

new technique; any material; clusters: 1 atom - 10 nm

Comparison: Richard A. P. Smith (J&M) et al., ECASIA 2009

T. Tanabe et al. (Toyota), Appl. Catal. A370 (2009) 108

Particle Size on Supported Catalysts

Diameter TON; size often related to failure

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Example: Three-Way catalyst (exhaust)

Pt clusters on CeO2/ …../ γ-alumina

Loading = 0.004 g Pt / γ-alumina

Cluster diameter: 1.6 nm (average)

Accurate for d < 10 nm

Important / unique applications for catalysis

4. Nanoclusters

Average diameter nanoclusters

Surface segregation in alloy clusters

Core/shell particles

(verification, closure, thickness shell)

The diameter is derived from the ratio of the bulk loading (volume) to the

LEIS signal (surface area)

This method is possible where TEM fails ( d ≤ 2 nm; high Z support)

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Low Energy Ion Scattering

Characterisation of Functionalised Core/Shell Nanoparticles

Courtesy of

M. Fuchs et al., Surf. Interface

Anal. 42 (2010) 1131

4 nm

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The outer surface

of

mixed oxides

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O Al

Zn

Energy

Inte

nsity

ZnAl2O4

ZnO

Zn in tetrahedral site below surface

LEIS of spinels AB2O4

LEIS reveals surface composition powders

Al

O

Zn

Powders: preferential exposure plane with B cations

(octahedral sites)

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Important / unique applications for catalysis

Mixed oxides and catalysis

0

1

2

0 5 1 0 1 5

0

1

2

0 5 1 0 1 5

2

00

1

Yie

ld

15105

Co LEIS signal

CoAl2O4

ZnCo2O4

The atomic composition of the 1st atom layer controls catalysis.

In a spinel ( AB2O4 ) only the B-cations (octahedral site) are catalytically

active and visible for LEIS (1st at.).

The A-cations (tetrahedral sites) are in 2nd layer (not active, no LEIS peak).

Co3O4 = CoCo2O4

Test reaction:

only Co catalytically active

Co signals:

XPS: 1 : 2 : 3

LEIS: 0.3 : 1.9 : 2.0

LEIS Catalysis XPS

Page 27: High-Sensitivity LEIS Principles & Applications

Cations in octahedral sites at surface ( B in normal spinel )

LEIS

Chemistry } 1 : 1 !

Cations in tetrahedral sites below surface ( A in normal spinel )

Chemistry

LEIS

----------------------------------------------------------------------------------

Perovskites, other oxides: more complicated !

Kilner et al.: LaSrCo oxides ….

Alumina: difference α – γ !

Spinels (AB2O4)

LEIS and chemistry

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Performance relies on oxygen transport

Performance: “ Hampered by the surface ”

Why ? What is the surface ??

M. de Ridder et al., J. Appl. Phys. 92 (2002) 3056 - 3064

M. de Ridder et al., Solid State Ionics 156 (2003) 255 – 262

J.A. Kilner et al., J. Solid State Electrochem. 15 (2011) 861 - 876

Fuel Cells and Oxygen Membranes

Importance of the outer surface

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0 1000 2000 30000

100

200

300

Hf/Ba

(Y,Zr)

Ca

SiNa

FO

LE

IS s

igna

l (a

.u.)

Energy (eV)

sample 2

sample 4

Calcination for 5 hours

at 1000 oC in an

oxygen flow of 1.5 bar.

Segregation of

monolayer of

impurities

For T > 700 C: No Y, Zr in 1st atom !

Fuel Cells

Yttria stabilized Zirconia (YSZ) after calcination

XPS: Ca not visible ( ↔ Zr )

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0.0 0.2 0.4 0.6 0.8 1.00.0

0.2

0.4

0.6

0.8

1.0

0.0

0.2

0.4

0.6

0.8

1.0

YS

Z c

ove

rag

e

Iso

top

ic f

ractio

n 1

8O

CaO Coverage

M. de Ridder et al., Solid State Ionics 156 (2003) 255 - 262

Fuel Cells

CaO coverage blocks 16O –18O exchange

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H. Téllez, R. J. Chater, S. Fearn, E. Symianakis, H. H. Brongersma, J.A. Kilner Appl. Phys. Lett. 101, 151602 (2012)

Isotopic exchange 16O – 18O

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Growth of Ultra thin

LEIS and Microelectronics

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Layer thickness versus cycle #

Max

Average

Min

Cycles

Thic

kness

Linear growth

Transient

Closure

The transient regime determines the uniformity of the layer

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Width of the transient regime depends on nucleation of ALD

reaction, precursors and growth mode

- 2D growth: Preferential growth on substrate

CrOx/Al2O3, ZrO2/SiO2, HfO2/Si

- Random growth AlN/Al2O3, AlN/SiO2, Fe2O3/ZrO2

- 3D growth: Preferential growth on pre-deposited matter

Ni/Al2O3, HfO2/Ge, WNC/SiO2/Si, Ta(CN)/SiO2/Si, Ta(Si)/SiO2/Si, TiN/SiO2,

Al2O3/Si-H, ZrO2/Si-H

Controlling the transient regime is fundamental for continuity of

ultrathin ALD films. ALD + LEIS !!

Transient regime (growth before closure)

( 6 up to > 150 cycles !)

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7 keV He+ LEIS 3.0 nm TiN / Si(100) nominal

0

1

1

2

2

3

3

4

0 1000 2000 3000 4000 5000 6000

Yie

ld

Ef (eV)

TRBS-I simulations

1. TiN (bulk) brown

2. TiO2 (bulk) green

3. 2.8 nm TIN / Si black

4. TiO2/TiO2+TiN /TiN /TIN+ Si red

5. LEIS (surf. peaks corr.) blue

Page 36: High-Sensitivity LEIS Principles & Applications

Growth of Ultra-thin layers

LEIS: 1st atom + in-depth, quantitative, sensitive

Initial growth

Poisoning, activation

Pinholes

Diffusion

Thickness uniformity

Use LEIS in the optimization of growth processes (ALD!)

Page 37: High-Sensitivity LEIS Principles & Applications

Sensitivity

1st atom + in-depth

Surf. segr. / anti wetting / M – polymer / surf. Modific. / NPs

/ graphene

Outer surface of oxides

SOFC , membranes

ALD growth

Summary

Page 38: High-Sensitivity LEIS Principles & Applications

Miscellaneous applications

Catalysts, microelectronics, polymers, (bio-) sensors, ....

But also:

Candy wrappers

F 16 dome, windows of planes

Bone tissue, dental implants, stents, …...

Aging of linoleum ( “ Linowonder” )

Anti-wetting (watches, diapers, …..)

Floor wax

Page 39: High-Sensitivity LEIS Principles & Applications
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IBA 2013 – Seattle, WA – slide 41 [email protected]

Graphene analysis with LEIS ??

Wishes:

Determination layer thickness, layer integrity

Distinguish and Quantify carbon allotropes

Detection contaminants / dopants on/in and below the film (intercalation)

LEIS ??

Carbon: low Z Low sensitivity

Monolayer depth info? Carbon atoms very small

Distinguish allotropes ? No matrix effects (in general)

LEIS seems useless for studying graphene, but : ..........

Author: AlexanderAlUS, wikipedia Author: Mstroeck, wikipedia

Page 42: High-Sensitivity LEIS Principles & Applications

Energy (eV)

Annealing time

5 nm

Yie

ld (

cts

/nA

)

Diffusion study with in-situ heating

Mo/Si layer – quantification of diffusion constant

FOM

5 nm Si

10 nm Mo

SiO2

Si Wafer

B4C

V. de Rooij-Lohmann, Appl. Phys. Lett. 94 063107 (2009)

V. de Rooij-Lohmann, J. Appl. Phys. 108 014314 (2010)

5 nm Si / 1.6 nm B4C / 10 nm Mo, annealing @ 500 deg. C

Diffusion coefficient without B4C : (8 2) • 10-20 m2/s

Diffusion coefficient with 1.6 nm B4C: (4 1) • 10-21 m2/s

Page 43: High-Sensitivity LEIS Principles & Applications

High-energy edge of SAMs on Au

2200 2375 2550 2725 29000

4

8

12

16

20

Au

Norm

alised inte

nsity (

Cts

/nC

)

Energy (eV)

Au (x 0.02) Au (dirty) + C11 - thiols Au (clean) + C11 - thiols

11Å

overlayer

thickness

Fluorinated thiol on dirty Au surface

Fluorinated thiol on clean Au surface

11Å

Page 44: High-Sensitivity LEIS Principles & Applications

0 5 10 15 20 25 300.0

0.5

1.0

1.5

2.0

Re

mo

ve

d la

ye

r th

ickn

ess (

nm

)

Oxidation time (minutes)

Erosion rate for atomic oxygen treatment

Erosion rate: 0.64 nm/min

C20 SAM on Au

Page 45: High-Sensitivity LEIS Principles & Applications

Quantification of F with LiF(100)

LiF (100)750 1500 2250 3000

0

40

80

120

160

Au

C

F

LE

IS S

ignal (C

ts/n

C)

Energy (eV)

LiF

Teflon

F8 - thiol (*1/20)

LiF(100) : Teflon : s.-a. ML = 1.23 : 1.24 : 1.48 *1015 at./cm2

Page 46: High-Sensitivity LEIS Principles & Applications

Outer and Near surface of Perovskites

by LEIS ( for Fuel Cells and Oxygen Membranes )

Outer surface: A-site termination (LEIS: no other cations)

Subsurface: Layered oxide (LEIS depth profiling)

Examples: Structure

La0.6 Sr0.4 Co0.2 Fe0.8 O3-δ Perovskite

Gd Ba Co2 O5-δ Double Perovskite

La2 Ni O4-δ Ruddlesden - Popper

John Druce, Helena Tellez, 2014