hydrogen interaction with aromatic carbon systems...

Hydrogen interaction with

aromatic carbon systems

-Experimental techniques

Liv Hornekær

Aromatic carbon systems

Interstellar Catalysis

Graphene electronics

H chemisorbed on graphite

Eva Rauls

Jeloica & Sidis, Chem. Phys. Lett. 300, 157 (1999)

Sha et al, Surface Science 496, 318 (2002)

V

Tip

Z S

erv

o

STM – 2

Surface

Tunnel current I

Tip

V

Z S

erv

o

Surface

STM – 3

Tunnel current

Tip

V

X Servo

I

Tip movement

Computer

Z S

erv

o

Surface

STM – 4

STM

κ=

STM Princip

Prøve Tantal-holder

Invar-top

Kvartskugle Wolfram tip

Isolator

Skannerør

Invar hus

Fjeder

Aksel InchWorm

Holder

Al-hus

5 mm

Aarhus STM

5 mm

Typiske data for ScannerRør

Afbøjning i X og Y: 5 nm/V

Afbøjning i Z: 1.3 nm/V

Resonansfrekvens: 10 kHz

Skannerør

Aarhus STM

5 mm

1 nm

Forstørrelse

5000000 gange!

Aarhus STM

Typiske data for InchWorm

Skridtlængde: 1 nm

Hastighed: 0.01 mm/sek

10000 skridt/sek!

5 mm

InchWorm

Aarhus STM

The Inchworm

Center Rod – ZrO2

Clamp 1 Clamp 2

Center

Electrode

STM and vibrations

STM tip: ~ 3 cm

Tip-sample: 0.1 nm

Eiffeltower 320 m

Eiffeltower – ground: 0.1 mm

Tip-sample vibration < 0.01 nm

Eiffeltower – ground vib. < 1 μm !!

STM and Vacuum

STM on graphite

2.46 Å

Hydrogen on graphite –

Monomers

Zeljko Sljivancanin

Vt~ -710mV, I

t~ -0.16nA

155 x 171 Å2 , 180 K

H-Dimers on graphite

A: Ortho–dimer

B: Para-dimer

103 x 114 Å2

Vt = 884 mV, I

t = 0.16 nA

Dimers: Theory vs. Experiment

Vt = 884 mV, I

t = 0.16 nA

Vt=0.9 V, LDOS=1x10

-6 (eV)

-1 Å

-3

e. f.

Ortho dimer Para dimer Hornekær et al.

Phys. Rev. Lett.

96, 156104

(2006)

Similar results for

ortho dimer:

Ferro et al. Chem.

Phys. Lett. 368,

609 (2003).

Y. Miura et al. J.

Appl. Phys. 93,

3395 (2003).

Dimer formation

Hornekær et al. Phys. Rev. Lett. 97, 186102 (2006)

Zero barrier sticking into para-dimer also found by:

Rougeau et al. Chem. Phys. Lett. 431, 135 (2006)

Kinetic Monte Carlo Simulations

-Experimental benchmarks

Cuppen & Hornekær, J. Chem. Phys. 128, 174707 (2008)

All D abstracted

at long H exposure

Thomas et al,

Surf. Sci. 602, 2311 (2008)

Ortho/para ratio ~0.15

Abstraction Mechanisms

J. Chem. Phys. 128, 174707 (2008)

Diffusion

Barrier to diffusion for an isolated H atom: 1.15 eV

Barrier to desorption for an isolated H atom: 0.9 eV

H-Dimers on graphite

A: Ortho–dimer

B: Para-dimer

103 x 114 Å2

Vt = 884 mV, I

t = 0.16 nA

n=1 => First order

desorption

490 K => 1.4 eV

580 K => 1.6 eV

dQ

dt = -k0 e

- / T Qn kB EB

Zecho et al, J. Chem. Phys. 117, 8486 (2002)

H2 formation on graphite - TDS

Dimers after Anneal

103 x 114 Å2

Vt = 884 mV, I

t = 0.19 nA

Vt = 884 mV, I

t = 0.36 nA

80 x 72 Å2

Recombination pathways


Ortho Meta Para

Ortho-dimer - high barrier

E. Rauls

Para-dimer - low barrier

E. Rauls

Recombination pathways


Ortho Meta Para

Measuring the kinetic energy of

formed molecules

Laser Induced

Thermal Desorption

(LITD)

Alexandrite Laser

760 nm

150 mJ/cm2

/ 400 mJ/cm2

150 ns pulse

Time of Flight Measurement

D

QMS

Laser

D2

Kinetic energy distribution

Baouche et al., J. Chem. Phys. 125, 084712 (2006 )

Atom detection - REMPI

REMPI

detector

LAAD

Laser

REMPI

Laser

2+1 REMPI

Frequency tripled

Nd:YAG pumped Dye laser

~202-210 nm

~0.5 mJ, d=0.1 mm spot

5 ns pulse, 0.1-0.2 cm-1

Atom: 1S1/2

-> 1S1/2

Molecules: X1S

g

+ X-> E,F

1Sg

+

Dv=0, DJ=0

v=0, J=2 and v=1, J=2

Atom desorption

Baouche et al., J. Chem. Phys. 131, 244707 (2009)

Desorption flux

Baouche et al., J. Chem. Phys. 131, 244707 (2009)

Kerwin & Jackson, JCP 128, 084702 (2008)

H on HOPG

High Coverage

Medium Coverage

80 x 72 Å2

171 x 155 Å2

Low Coverage

103 x 114 Å2

Vt~800mV, I

t~0.15-0.2nA

Preferential sticking and clustering

Diffusion

Barrier to diffusion for an isolated H atom: 1.15 eV

Eley Rideal - Abstraction

Sha et al. (2002)

Zecho et al. (2002)

Matinazzo & Tantardini (2006)

Morisset et al. (2004)

Jeloaica & Sidis (2001)

Meijer et al. (2001)

Bachellerie et al. (2007)

Thomas et al. (2008)

Random adsorption and cluster formation

171 x 155 Å2

In accord with LEED and UPS measurements:

Neumann et al. Appl. Phys. A 55, 489 (1992)

Guttler et al. Chem. Phys. Lett. 395, 171 (2004)

Large cluster formation also found in HREELS and DFT studies:

Allouche et al, JCP 123, 124701 (2005)

Trimer Configurations

Sljivancanin et al.,

PRB 83, 205426 (2011)

Vt = -1051 mV, I

t = -0.53 nA

High coverage

171 x 155 Å2

High Coverage

Vt = -1.05 V, I

t = -0.55 nA

80 x 72 Å2

Vt = -1.05 V, I

t = -0.18 nA,

171 x 155 Å2

Ferro et al., Chem. Phys. Lett.

478, 42 (2009) Hornekær et al., Chem. Phys. Lett. 446, 237 (2007)

525K anneal

RT

Status:

Astrochemistry: H2 formation on

graphitic grains possible under

PDR conditions - Good

Energy partitioning dependent on

small scale surface structure – smooth

surface ~1/3 into translation

Graphene electronics: No ordered

structures - Bad

Hydrogen induced band gap

opening

STM desorption of H

70 x 70 Å2

Vt = -1.25 V, I

t = -0.37 nA,

Templated H adsorption by a

SAM of CyA on graphite

A

B • Red = Oxygen

• Blue = Nitrogen

• Black = Carbon

• White = Hydrogen

100 Å

Vt = -1.25 V, I

t = -0.39 nA,

Formation of linear H

adsorbate structures

100 Å

Vt = -1.25 V, I

t = -0.37 nA,

30 Å

Vt = -1.25 V, I

t = -0.37 nA,

Formation of linear H

adsorbate structures

Model structure

30 Å

Vt = -1.25 V, I

t = -0.37 nA,

Dark areas between lines – local

band gap opening?

Would this work on graphene?

Graphene on SiC

30x30Å,

V= -0.41V,

I= -0.39nA

Bi-layer graphene

showing

triangular pattern

100x100Å, V= -0.41V, I= -0.36nA

step edge height 3.1Å

30x30Å,

V= -0.41V,

I= -0.38nA

Mono-layer graphene

showing

honeycomb structure

Hydrogen dose at 1600K, F=3x1012

atoms/cm2 s, t=5s

200x200Å, V= -0.245V, I= -0.26nA

H on graphene/SiC

Balog et al. JACS 131, 8741 (2009)

H on graphene/SiC

200x200Å, V= -0.36V, I= -0.32nA

Hydrogenation: T=1600K,

F=3x1012

atoms/cm2 s, t=90s

De-hydrogenation: Anneal to 800°C

Balog et al. JACS 131, 8741 (2009)

Graphene/Ir

Wavevector kx (Å-1)

STM of H/Graphene/Ir

Balog et al., Nat. Mat. 9, 315 (2010)

XPS:

M. L. Ng, R. Balog, L. Hornekær,

B. Preobrajenski, K. Schulte, N. A.

Vinogradov, and N. Mårtensson.

Adsorbate structures


Global bandgap opening

Pedersen et al. PRL 100, (2008)

ARUPS of H/Graphene/Ir

– bandgap opening


XPS-doping

80 meV 20 meV 20 meV

450 meV

BG=940mV

Band gap opening by patterned H adsorption


STM of H/Graphene/Ir

Global bandgap opening

Thermal stability - TDS

Challenges

Chemical stability

Substrate

Generality of method

What is important – confinement, order/disorder

Mobility – shape of dispersion

Hydrogenation of

Graphene/Pt(100) - STM

5s, 300x300Å2

25s, 500x500Å2

1 min, 200x200Å2

Pt(100) - TDS

Hydrogenation of

Graphene/Pt(100) - STM

5s, 300x300Å2

25s, 500x500Å2

1 min, 200x200Å2

Conclusions – graphite/graphene

•High diffusion barrier prevents formation of ordered H

adsorbate structures on graphite

•Pre-pairing of H atoms on the surface => unusual desorption kinetics

•H2 formation under PDR conditions

•Hydrogen induced substrate interactions =>

increased binding – and in some cases

nano-patterning

•H nano-patterns on graphite =>

~1 eV band gap opening.

How is interstellar H2 produced ?

Hgas

+Hgas

H2

H + H + H

2

H + H + H

2

H-PAH interaction

Density Functional Theory (DFT) calculations

reveal low barrier routes to

H-PAH formation and PAH catalyzed H2 formation

Rauls and Hornekær, Astrophys. J. 679, 531 (2008)

H-PAH interaction

Rauls and Hornekær, Astrophys. J. 679, 531 (2008)

Density Functional Theory (DFT) calculations

reveal low barrier routes to

H-PAH formation and PAH catalyzed H2 formation

Experimental procedure

HPAH TDS/TPD

H-PAH formation

C24

H22

Hydrogenation: STM images

70 x 70 Å

Coronene Coronene exposed to D

Substrate: Cu(100)

H – aromatic carbon

Very reactive defect/edge sites

Basal plane: Coverage effects

Curvature effects

Substrate can play an active role

Low mobility in chemisorbed state

Outlook

Frame 1

Frame 2

Frame 3

In situ Hydrogen dosing

HPAH-UV/IR interaction

Graphene – deeper understanding

other substrates

HPAH – H beam energy

People involved

Richard Balog

Bjarke Jørgensen

Louis Nilsson

Saoud Baouche

Emil Friis

John Thrower

Arnd Baurichter

Victor Petrunin

Marco Bianchi

Emil Rienks

Philip Hofmann

Mie Andersen

Bjørk Hammer

Thomas G. Pedersen

Eva Rauls

Zeljko Sljivancanin

Alan Luntz

Erik Lægsgaard

Ivan Steensgaard

Flemming Besenbacher

Silvano Lizzit

Mattia Fanetti

Allessandro Baraldi

Rosanna Laciprete

Dept. Phys. and Astron. and iNANO, University of Aarhus

Funding

StG HPAH

hydrogen interaction with aromatic carbon systems...

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