Near Ambient Pressure Photoemission at SOLEIL

Transcription

1 Near Ambient Pressure Photoemission at SOLEIL F. Rochet Laboratoire de Chimie Physique Matière et Rayonnement (LCPMR) 11 rue Pierre et Marie Curie Paris cedex 05 Research group at LCPMR: «Functionalized (and environmental) Surfaces» F. Bournel J.-J. Gallet F. Rochet R. Benbalagh (IR-UPMC) A. Naitabdi (ANR) H. Tissot (PhD) 1

2 Origin of the project and fundings ANR SAPRES «Surface under ambient pressure with electron spectroscopies (36%) LCPMR (project leader) UCCS Lille (J F Paul) IRCELYON (Y Jugnet) SESAME Ile de France (44%) UPMC Consortium «Photoémission environnementale en Ile de France» UPMC (20%) EQUIPMENT COST 1.27 M (VAT included) SOLEIL (beamline upgrade beam entrance device) ~100 k 2

3 Surfaces under ambient pressures (around 1 mbar) Dense layers of molecules, weak binding energy under NAP and ROOM temperature Dense layers under UHV and cryogenic temperatures, BUT equilibrium structures (Ea matters)? -10 Gibbs Free Energy kt lnp matters i.e. 0.3 ev between 10 mbar (UHV) and 1 bar (300 K) Metals readily oxidize under AP (several ML) Why near ambient? See the saturation water vapor pressure around 300 K 3

4 Saturation water pressure as a function of temperature Relative humidity RH(p,T)=p/p0(T)x100 Under typical environmental and atmospheric temperatures and relative humidities (10 100%) the water vapor pressure is in the millitorr to Torr range, orders of magnitude higher than under typical ultra-high vacuum conditions. 4

5 Principle of XPS & ARXPS Photoelectric effect XPS is surface sensitive spectroscopy small values of the photoelectron inelastic mean free path in SOLIDS (a few Å to a few tens of Å) 5

6 What information is learned from XPS? Elemental Identification Chemical State Identification Quantification Depth profile - Angular Resolved XPS - Changing the electron inelastic mean free path (escape depth), needs synchrotron radiation

7 objective: With a gas phase over the surface one wishes to collect photoelectrons from the sample hν Photoelectrons from gas phase Analysis chamber gas sample To pumping ter ons e r am lect e r a e s y p of p ha e K fp s Im e ga th t h ug o hr ct e l E an n ro er z y al

8 Electron elastic mean free path through an oxygen gas environment as a function of kinetic energy (1 mbar) 8

9 The NAP-XPS concept Attenuation of electrons in the gas phase implies: 1. small distance (~1mm) between sample surface and a differentially pumped aperture (ø 0.3 mm) 2. series of differential pumping stages to protect the detection 9

10 The NAP-XPS analyzer principle Differentially pumped electrostatic lenses Electron focused onto the apertures between the pumping stages reduced aperture sizes= improved pumping 10

11 Other design with a wide acceptance (44 ) pre-lens 11

12 Introducing the synchrotron beam into the reaction chamber: Al or SiNx window Schematic diagram of the x-ray insertion tube (blue), tapered off to bring the end as close to the surface as possible to avoid absorption by the gas. A 100 nm thick Si3N4 or Al membrane closes the end of the tube to prevent gas from entering the x-ray source. Source (Salmeron) Transmission of 100-nm thick SiNx and Al membranes for X-rays up to a photon energy of 1500 ev. The sharp drop in transmission at ev corresponds to the Si and Al L-edges, whereas the decrease in intensity for SiNx at around 400 ev is due to the N K-edge. 12

13 Introducing the synchrotron beam into the reaction chamber: a windowless setup (SOLEIL) 13

14 Attenuation by the gas phase Water Vapor Path length through the gas 3 cm 14

15 Illustrative application cases Catalysis Surfaces in «wet» conditions (environmental chemistry) Processes: oxidation of surfaces, CVD etc. Non conventional surfaces e.g. liquid water surfaces 15

16 An illustrative example of NAP-XPS: methanol oxidation on Cu foils O 1s photoemission spectra mesured at hν=720 ev of the CH3OH :O2 mixture (1 mbar) reacting over a copper foil at 400 C. Methanol oxidation on a copper catalyst investigated using in situ X-ray photoelectron spectroscopy, H.Bluhm et al, J. Phys. Chem. B 108, (2004). 16

17 Surfaces in wet conditions Miquel Salmeron website Water droplets analyzer Nozzle 17

18 Surfaces in wet conditions: alkali halides Br 3d et K 3p are recorded with the same KE (160 ev) (two different hν, SR) Same λ, same probed depth Same KE same spectrometer transmission At RH 5% K:Br = 1:1 At deliquescence K:Br=1:2! Electron spectroscopy reveals surface enhancement of halides, S. Ghosal et al. Science 307, 563 (2005) 18

19 Surfaces in wet conditions water on Cu(110) under 1 Torr 19 Klas Andersson, et al. J. AM. CHEM. SOC. 2008, 130,

20 Oxidation of silicon Y. Enta, B.S. Mun, Y. Enta, M. Rossi, P.N. Ross, Z. Hussain, C.S. Fadley, K.S. Lee, S.-K. Kim, Appl. Phys. Lett. 92 (2008)

21 The NAP setup at SOLEIL Gold-coated analysis chamber (3-5 l) (CO compatible) Vertical manipulator Single crystals Polycrystalline foils Pressed powders (pellets) 21

22 SOLEIL setup NAP-XPS spectrometer Beam entrance UHV chamber mbar Distribution chamber Analysis chamber 20 mbar 1bar chamber

23 NAP setup at SOLEIL Sample environment Laser Heating Button heater (600 C) Peltier cooler (-35 ) 23

24 The NAP setup at SOLEIL 24

25 Our agenda Delivery september 2012 First tests 2nd semester months following the NAP-XPS installation Commissioning : 100 shifts, Expert Users: 150 shifts (1 shift = 8 hours) 25

26 COMMUNAUTÉ SCIENTIFIQUE CONCERNÉE PAR LE SYSTÈME NAP-XPS Les chercheurs de l ANR SAPRES LCPMR (UPMC) IRCELYON UCCS (LILLE) Le Consortium UPMC Institut de Minéralogie et de Physique des Milieux Condensés (IMPMC) Institut des Nanosciences de Paris (INSP) Institut des Matériaux de Paris Centre de l UPMC (IMPC). Laboratoire Interfaces et Systèmes Électrochimiques (LISE) «Projet LABEX UPMC» De la molécule unique aux nano-édifices IPCM (Institut parisien de chimie moléculaire) PECSA (Physicochimie des Electrolytes, Colloïdes et Sciences Analytiques) analyses de surfaces de polymères et d argiles en conditions humides. 26

27 Future developments: XPS spectroscopy of liquid microjets? NAP-XPS analyzer 27

28 Applications in biological Molecules N1s PE spectral of 0.5m lysine at diff. ph Biological molecules in water environment. Microscopic structure sensitive to ph D. Nolting, E.F. Aziz, N. Ottosson, M. Faubel, I.V. Hertel, B. Winter, J. Am. Chem. Soc. 129 (2007)