Ambient  Pressure  X-­‐ray  Photoelectron  Spectroscopy:  Current  Status  and  Future  Trends  

Hendrik  Bluhm  Chemical  Sciences  Division,  Lawrence  Berkeley  Na8onal  Laboratory,  Berkeley,  CA.  

Goal:  InvesBgaBon  of  surfaces  under  realisBc  condiBons.  

under UV

no UV

©Scientific American.

Zhang et al., Nat. Mat. 2010.

Newberg et al., JPCC 2011.

Interfacial  Chemistry  of  Surfaces  Under  Ambient  Humidity  Studied  Using  XPS  

Interfacial  Chemistry  in  the  Environment  and  Atmosphere  Barbara Finlayson-Pitts, PCCP (2009)

Fundamental limit:

elastic and inelastic scattering of electrons in the gas phase

Ambient Pressure XPS: Obstacles

30x10-21

25

20

15

10

5

0

Ioni

zatio

n cr

oss

sect

ion

(m2 )

101

102

103

104

105

106

Electron kinetic energy (eV)

in situSEM in situ

TEM

in situEXAFSin situ

XPS

O2 exp. data from Schram et al. (1965) extrapolation of Schram's data

inelastic scattering is mostly due to ionization of gas phase molecules

For calculations of total ionization cross sections see: Kim&Rudd, Phys. Rev. A 50, 3954 (1994).

ionization cross section depends on molecule: H2 < He < O2 < CH3OH

( )pEzEII

vac

p )(exp)( σ−∝

Early Ambient Pressures XPS Designs

hν

gas, e-

R. Joyner, M.W. Roberts, Surf. Sci. 87, 501 (1979) M. Grunze et al., in: Surface Science of Catalysis (1987).

H. Siegbahn et al., JESRP 40, 163 (1986).

H. & K. Siegbahn et al., 1972 ff.

LBNL/FHI/Specs  Ambient  Pressures  XPS  Design  D.F. Ogletree, H. Bluhm, G. Lebedev, C.S. Fadley, Z. Hussain, M. Salmeron, Rev. Sci. Instrum. 73 (2002) 3872.

1 µm

to  pump   to  pump  

X-­‐rays  from  synchrotron  

p0   p1<<  p0     p2<<  p1    

hemispherical  analyzer  

LBNL/FHI  Berlin/Specs  

p0   p1   p2   p3   p4  

analyzer  input  lens  pre-­‐lens  

p0   p1   p2   p3   p4  

analyzer  input  lens  pre-­‐lens  

p0   p1   p2   p3   p4  

modified  analyzer  input  lens  

e-­‐  sample  

p0   p1   p2   p3   p4  

analyzer  input  lens  

electron  energy    analyzer  

p0   p1   p2   p3   p4  

analyzer  input  lens  pre-­‐lens  

DifferenBal  Pumping  Schemes  for  APXPS  

Uppsala,  Cardiff,  Maine,  Stanford  

Berkeley  (2000)  

Berlin,  Berkeley  (2002)  

VG  Scienta  HiPP  

Specs  NAP-­‐Phoibos  

Starr,  Liu,  Haevecker,  Knop-­‐Gericke,  Bluhm,  Chem.  Soc.  Rev.  (2013).  

Center for Fuel Cell Research

Ambient Pressure XPS Publications

Laboratory  X-­‐ray  source    

Synchrotron-­‐based  

Dia

mon

d

Upp

sala

Car

diff

U M

aine

ALS

9.3

.2

BE

SS

Y A

LS 1

1.0.

2

Not

re D

ame

U P

enn

Erla

ngen

D

ortm

und

Kor

ea

Poz

nan

MA

X-la

b S

SR

L

Pho

ton

Fact

ory

SO

LEIL

S

hang

hai

SLS

A

LBA

NS

LS

Ber

kele

y

Nov

osib

irsk

SP

ring-

8 Lo

ndon

D

uess

eldo

rf S

inga

pore

Laboratory-based

Synchrotron-based

Starr, Liu, Haevecker, Knop-Gericke, Bluhm, Chem. Soc. Rev. (2013).

What  is  the  Pressure  Limit  in  APXPS?  

Target  pressures:  Environmental  science:  20  Torr  Catalysis:    several  atm  

•  Photon  beam  size  à  sample-­‐aperture  distance  

•  KineBc  energy  of  photoelectrons  

•  Sca^ering  cross  secBon  of  gas  molecules  

•  Photoemission  cross  secBon  

Pressure  Limit:  Dependence  on  Photon  Beam  Size  

At  z~4d    p=0.99p0    Since  I/Ip~exp(-­‐z),  smaller  apertures  allow  for  higher  pressures.  

1st differential pumping

stage

sample cell

z

y

p0

d

p(y,z) β

p«p0 z

p/p0

-2

-1

0

1

2

-3 -2 -1 0 1 2 3 0.02

0.9

0.8

0

.7

0.3

0

.2

0.1

0.98

0.95 0.05

0.5

hv

e-

-­‐>  need  to  reduce  sample-­‐            aperture  distance  

Pressure Limit: Dependence on Kinetic Energy

54.7°

dia 0.3 mm

hv

e-

2

4

68

10

σ (

10-1

6 cm

2 )600400200

Kinetic Energy (eV)10-4

10-3

10-2

10-1

100

I/I0

543210

Water vapor pressure (Torr)

105 eV

200 eV

300 eV

450 eV

700 eV

H. Bluhm, JESRP (2010).

Water vapor

KineBc  energy:        930  eV  Aperture  size:        0.05  mm  Sample-­‐aperture  distance:    0.2  mm  AcquisiBon  Bme:        90  min  Kaya  et  al.,  Cat.  Today  (2012).  

Diverse  APXPS  Experiments  Demand  Wide  Array  of  in  situ  Cells  

1)  TradiBonal  surface  science  community:    in  situ  sample    preparaBon  (single  crystals),  including  thin  film  growth.      -­‐  PreparaBon  chamber,  load  lock,  <10-­‐9  Torr  base  pressure.  

 2)  Ex  situ  prepared  samples,  need  only  small  or  no  in  situ  

preparaBon  (catalysis,  environmental  science).      -­‐  Load  lock  but  no  preparaBon  chamber,  moderate  base      pressure.  

 3)  Complex  sample  environments,  ogen  not  compaBble  with  

standard  vacuum  procedures  (electrochemistry,  liquids,  catalysis).  -­‐  Exchangable,  taylored  sample  chambers.    

Examples  for  ApplicaBon  of  APXPS  (from  ALS  BL  11.0.2)  

ReacBon  of  water  with  oxides  and  metals  (Brown,  Salmeron,  Nilsson,  Held,  St.  Gobain  )  

Fuel  cells  (U  Maryland,  Sandia,  Stanford,  MIT)  

Chemistry  of  ice  surfaces  (PSI,  Newberg)  

HCl,  HNO3  

Chemistry  of  soluBon  surfaces    (Hemminger,  Ghosal,  Krisch)  

Heterogeneous  chemistry    of  soot  parBcles  (Wilson)  

+  OH*,  O3  mpch-­‐mainz.m

pg.de/~gth/  

Heterogeneous  catalysis  (Somorjai,  Salmeron,  Besenbacher,  de  Groot,    Lundgren,  Nilsson,  Starr)    

HydroxylaBon  and    Water  AdsorpBon    

on  Oxides  and  Metals  

Heterogeneous  Chemistry  of  Model  Mineral  Surfaces:  MgO(100)  

O  1s    hv=  750  eV  0.5  Torr  H2O  Isobar  RH=4x10-­‐4....  20%  

Oxide

OH H2O

H2O (v)

Model  system:  Epitaxial  MgO(100)/Ag(100)  films  

J.T. Newberg et al., Surf. Sci. (2011).

H2O(g)  O  1s  

5ML,  RH=20%  

Ag(100)  

MgO  

H2O(surf)  

Mg(OH)2  

AdsorpBon  Isobars  on  MgO(100)  

Isobars      0.5  Torr    0.15  Torr      0.02  Torr    0.005  Torr  

J.T. Newberg et al., Surf. Sci. (2011); JPCC (2011).

OH  

H2O  

RH  =  p/psaturaBon  

OH  

H2O  

RH  0.01%  

HydroxylaBon  Mechanism  on  MgO(100)  

0.15 Torr Isobar data

Hydroxylation proceeds through conversion of MgO top layer and addition of OH layer: MgO + H2O → Mg(OH)2

J.T. Newberg et al., Surf. Sci. (2011).

Comparison  of  Water  ReacBon  With  Different  Oxide  Surfaces  

α-Fe2O3(0001) Yamamoto et al., JPCC (2010).

Relative humidity (in %)

0 0.2

0.4 0.6

0.8 1

1.2 1.4 1.6

10-­‐4 10-­‐3 10-­‐2 0.1 1 10 100

Cov

erag

e (M

L)

Fe3O4(001) Kendelewicz et al., submitted (2012).

OH

H2O

MgO(001) Newberg et al., JPCC (2011).

OH

H2O

O/Al  raBo  

Al2O3 /NiAl(110) Shavorskiy et al., in preparation (2012).

RH  0.01%  

Hydroxylation preceeds water adsorption and starts at ~0.01% RH.

Molecular water is present at surfaces at RH < 1%

Cu(110)

Cu(111)

H2O OH

1 Torr H2O, 295 K

The  Role  of  Surface  Hydroxyls  for  Water  AdsorpBon  

Difference in the activation barrier for water dissociation

Edis (111) > Edis (110)

Yamamoto et al., JPCC (2008).

Future  work:    ReacBvity  of  Oxides  as  a  FuncBon  of  Humidity  J.

P. A

llen

et a

l., J

. Phy

s. C

hem

. C 1

16, 1

3240

(201

2).

p(H2 O

)

p(CO2)

MgO(100) MgO(310)

Systematic mapping of phase diagrams as a function of surface crystallography, temperature, and gas phase composition.

ApplicaBon  of  APXPS  to  Electrochemistry  

Center for Fuel Cell Research

XPS on Solid Oxide Fuel Cells Under Operating Conditions

Z. Liu, M.E. Grass, Z. Hussain, H. Bluhm

S.C. DeCaluwe, C. Zhang, G.S. Jackson, B. Eichhorn

A.H. McDaniel, K.F. McCarty, W. Chueh, R.L. Farrow, S. Nie, F. El Gabaly, M.A. Linne

Anode

Cathode

Electrolyte

air

fuel H2 H2O

e-

e- O2-

O2

Goal: Measurement of surface properties of CeOx anodes under operating conditions using XPS

Center for Fuel Cell Research

Measuring Local Electrical Potentials Using XPS

H. Siegbahn, M. Lundholm, JESRP 28, 135 (1982); H. Bluhm, JESRP 177, 71 (2010).

e-s

e-g

KE

surface gas

BE

apΦ

EF

Evac

EF

Evac

CL CL

Evac

samΦ

aperture sample gas

Center for Fuel Cell Research

Example: Change of Electrical Potential (Positive Bias)

H. Siegbahn, M. Lundholm, JESRP 28, 135 (1982); H. Bluhm, JESRP 177, 71 (2010).

apΦ

e-s

e-g

EF

Evac

CL

Evac KE

surface gas

BE

aperture sample gas

EF

Evac

CL

samΦ

Correlation of Local Electrical Potential and Surface Chemistry

Zhang  et  al.,  Nature  Materials  Nov  2010.  

H2:H2O=1:1,(0.5(Torr,~1000(K(

Single  chamber  experiment:    Cathode,  anode,  fuel  and                                                                                                              oxidizer  in  same  volume  

InvesBgaBon  of  Liquid/Solid  Interfaces  

The Electric Double Layer at Metal Oxide/Solution Interfaces

G.E. Brown et al., Chem. Rev. 1999.

G.E. Brown, Jr., Science 2001.

As(III) vs As(V): As(III) more toxic and mobile Cr(III) vs Cr(VI): Cr(VI) has higher toxicity

Oxidation state depends on redox potential and pH.

AP-HAXPES vs Vacuum-based HAXPES

0.9 mm

dia 0.3 mm

hv low KE e- 2

cm

σ(200 eV)

σ(104 eV) ~10-3...10-4

4

68

0.1

2

4

68

1

2

Ioni

zatio

n Cr

oss

Sect

ion

(10-1

6 c

m2 /m

ol.)

1022 4 6

1032 4 6

1042

Electron Kinetic Energy (eV)

electron scattering by water molecules

1.0

0.8

0.6

0.4

0.2

0.0

Tran

smiss

ion

1012 4 6

1022 4 6

1032 4 6

104

Photon Energy (eV)

20 Torr

2 Torr

200 Torr

Under ambient conditions: As in UHV, same reduction in signal due to small photoelectron cross section at high KE, but gain due to reduced scattering of incident photons and emitted electrons by gas molecules. Possible complication: high voltages in retarding lens may lead to gas dis-charge.

high KE e-

Inelastic Mean Free Path of Electrons in Water

Emfietzoglou & Nikjoo, Rad. Res. 2007.

20 nm~70 ML

Challenge: Control of Thermodynamic Conditions

101

102

103

104

Deso

rptio

n ra

te (M

L/se

c)

240230220210200190180Temperature (K)

High adsorption/desorption rates

D.R. Haynes, N.J. Tro, S.M. George, J. Phys. Chem. 96 (1992) 8502.

A.  Shavorskiy,  Z.  Liu,  S.  Axnanda,  E.  Crumlin,  Z.  Hussain,  P.N.  Ross,  H.  Bluhm,  in  preparaBon.  

Peltier sample holder (Ogletree, Bluhm, Hebenstreit, Salmeron, Nucl. Instr. Meth. A, 2009)

Peltier element

Thermionics sample holder

Mo

copper stage with thermocouple

O-ring seal

steel

Cu sample dock (heat sink)

Relative Humidity (%)

Film

Thi

ckne

ss (M

L)

0 100 0

2

4

Preparation of Thin Solution Films by Control of RH

Acknowledgements

LBNL E.R. Mysak J.T. Newberg J.D. Smith P.A. Ashby K.R. Wilson

PAH oxidation

LBNL/CSD D.E. Starr J.T. Newberg

PSI Villigen A. Krepelova M. Ammann

Univ Coll London D. Pan A. Michaelides

LBNL/MSD T. Pascal D. Prendergast

Ice surface experiments

LBNL D.F. Ogletree E. Hebenstreit C.S. Fadley G. Lebedev Z. Hussain E.K. Wong M. Salmeron

FHI Berlin K. Ihmann M. Haevecker A. Knop-Gericke E. Kleimenov R. Schloegl

APPES development

T. Tyliszczak M.K. Gilles A.L.D. Kilcoyne D.K. Shuh M.-L. Ng C. Rameshan A. Shavorskiy J.T. Newberg This work was supported by the Director, Office of Science,

Office of Basic Energy Sciences, under Contract No. DE-AC02-05CH11231.

U Maryland G. Jackson B. Eichorn C. Zhang S. de Caluwe

Sandia T. McDaniel F. El Gabaly K. McCarty M. Linne R. Farrow W. Chueh

LBNL Z. Liu M. Grass Z. Hussain A. Shavorskiy

Fuel cells

A. Shavorskiy Z. Hussain T. Tyliszczak

AP-SPEM

SSRL S. Yamamoto S. Kaya K. Andersson H. Ogasawara A. Nilsson

Stanford T. Kendelewicz G.E. Brown, Jr.

LBNL/MSD G. Ketteler X. Deng T. Herranz-Cruz S. Posgaard A. Verdaguer P. Jiang M. Salmeron

LBNL/CSD D.E. Starr J.T. Newberg E.R. Mysak

Water reaction with surfaces