Soft X-ray Spectromicroscopy

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1 Soft X-ray Spectromicroscopy oncept of x-ray spectromicroscopy Instrumentation in spectromicroscopy Transmission spectromicroscopy examples Polymers and polymer composites Wet cell studies of bio-inorganic interfaces Photoemission spectromicroscopy examples Transition-metal silicides Microelectronics applications Natural materials X-ray Absorption surface spectromicroscopy examples Magnetic materials Future prospects

2 What is an X-ray microscope? omputer D detector, Photodiode Zone-plate X-ray lenses Specimen on SiN membranes X-ray beam Ultra-smooth grazing incidence mirrors

3 The oncept of Spectro-Microscopy Y Energy Ti edge x Fe edge A multidimensional multidimensional map: map: Spectral Spectral intensity intensity as as a function function of of energy energy and and position. position.

4 Micro-organisms at inorganic interfaces Mineral interface 1 nm thickness Microbe 1 µm long ell wall 10 nm Biomineral nm Exopolymer 100 nm thick

5 Four types of x-ray spectromicroscopy (a) TXM (transmission x-ray microscopy) (b) STXM (scanning TXM) e - (c) SPEM (scanning Photoemission Microscopy) (d) XPEEM (X-ray Photelectron Emission Microscopy)

6 Improvement in resolution over time: X-ray photoemission spectromicroscopy (nano-esa) 1E+5 1E+4 XPS introduced 1 micron 0.1 micron 100 Angstroms Spatial Resolution (microns) 1E+3 1E+2 1E+1 1E+0 1E-1 1E-2 XPS with Synch. Radiation Magnetic Projection PESM (lab) SR-PESM, microxafs X1A SPEM, MAXIMUM Spectro-LEEM Lab limit (until table top laser) Grazing optics limit Zone-plate optics limit. 10 Angstroms 1E-3 1E-4 Aberration orrected XPEEM Electron optics limit

7 Micro Zone-Plate Optics Pinhole positions st order focus 3rd order focus mm central stop 60 µm pinhole detector y x zone plate X ray hν = 375 ev order sorting aperture (OSA)

8 Scanning Transmission X-ray Microscope (STXM) STXM at BL 7.0.1

9 STXM of poly-acrylonitrile fibres (bond-type imaging) B fresh Absorption (arb. units) A early 1st stage later 3rd stage A π* (=N) B π* ( N) σ* (-O) edge center Photon Energy (ev) 300 air furnace heating to > two-phase structure Model: Exothermic oxidation reaction at the outer edge accumulates heat in the core Fiber center melts and loses orientation order of N bonding along the fiber H H 2 H H 2 N N H OH - Jun Kikuma, B. P. Tonner, H. Shin, J. Denlinger, J. Zhang, A. Warwick, 1997 N H O N

10 Wet-cell Soft X-ray Spectromicroscopy Seal Spacer X-ray Zone-plate Lens Detector or Imaging system Water or solvent SiN window

11 MnOOH (manganite) mineral particles and micro-organisms µm ev 517 ev 1 µm

12 The Marine Bacillus, strain SG-1 Mn-Reduction Vegetative ycle Vegetative ell Mn-Oxidation Dormant spore Mn 2+, O 2? Sporulation ycle? Mn-Oxides Rosson & Nealson, 1982 De Vrind et al., 1986 Hastings & Emerson, 1986 Mandernack et al., 1995 Bargar et al., 2000 clay minerals Surface Enhancement Kepkay & Nealson, 1982

13 hemical Oxidation of Mn(II) in the Presence of Water, O 2, and atalytic Iron (Hydr)Oxide Particles homogenous solution ph 8.4 Goethite ph 8.4 from: Wehrli, B.: Aquatic hemical Kinetics (Ed.: W. Stumm), 1990, p 311ff, data from: Diem, D., Stumm, W., Geochim. osmochim. Acta, 52,1984, 1571 and Davies, S. & Morgan, J., J. olloid. Interface Sci., 129, 1989, 63

14 Spore Incubation: Stagnant Batch STXM contrast at ev 2 µm d Imaging c single spore cells a R: Mn(II) G: Mn(III) B: Mn(IV) Mn(II) tot =10 mm ph = 7.5 b Optical Density (a.u.) a b c d * in % n.d. < 5% XANES Mn II Mn III Mn IV* n.d n.d Red-Green-Blue-charge state map Photon Energy (ev) Pecher, K. et al. (2001) Quantitative charge state analysis of manganese biominerals in aqueous suspension using Scanning Transmission X-ray Microscopy (STXM) submitted to Geochimica et osmochimica Acta

15 ontinuously Agitated Batch Incubation Optical Density [a.u.] t 1 = 6 h t 2. t 6 t 7 = 186 h Photon Energy [ev] % Mn ph=7.8 (10 mm HEPES, 50 mm Nal) [Mn(II)] tot =10ìM = const. Mn(II) Mn(III) Mn(IV) Time [h]

16 Surface and bulk composition of Fe-oxide nanoparticles Goethite (α-feooh) II Magnetite (Fe 3 O 4 ) III norm. intensity TEY XANES TEY XANES photon energy (ev) STXM microxanes (stack mode) STXM microxanes (stack mode) Figs. A and B compare total electron yield (TEY) XANES and STXM µ-xanes of two iron oxide minerals. Magnetite which also contains structural Fe(II) seems to be oxidized within a surface near region compared to its bulk composition. In addition, the bulk Fe(II)/Fe(III) ratio varies among single particles of magnetite.

17 Zone-plate X-ray Photoemission Microscope: SPEM Micro-zone plate Raster Multi-channel Spectrometer Electrons u 3p Image Sample Surface 10µm

18 1 µm Pyrite surface micro-analysis 1 µm S LMM O1s 1s OSA 1s S2s S2p u3p? Si2p? Fe3p Fe3s O 1s contrast 5 µm 1 µm clean region a2p U4f As3p As3d Photoemission Intensity (arb. units) 1 µm 1 µm no zone plate U-4f contrast Binding Energy (ev)

19 Future Prospects for X-ray Spectromicroscopy Opportunities for PhD research Improved spatial resolution by understanding the physics of imaging Zone-plates slowly improve to nm Electron imaging using aberration correction to 5 nm Near-field and other scanning probe techniques to 1 nm Increased use in applied science and technology Micro and nano-electronics development Environmental applications Biomedical research Novel experiments in basic research Time and space domain; kinetics of surface reactions Nonlinear optical effects Nano-spectroscopy ; quantum effects in objects of small size