Anal. Chem. 2005, 77, 6969-6975

X-ray Absorption Fine Structure Combined with
X-ray Fluorescence Spectrometry. Improvement ofSpectral Resolution at the Absorption Edges of
9-29 keV
Yasuo Izumi,*,† Hiroyasu Nagamori,† Fumitaka Kiyotaki,† Dilshad Masih,† Taketoshi Minato,†
Eric Roisin,‡ Jean-Pierre Candy,‡ Hajime Tanida,§ and Tomoya Uruga*,§

Interdisciplinary Graduate School of Science and Engineering, Tokyo Institute of Technology, Nagatsuta 4259-G1-16,
Midori-ku, Yokohama 226-8502, Japan, Laboratoire de Chimie Organometallique de Surface, UMR CNRS-CPE 9986,
France, and Japan Synchrotron Radiation Research Institute, Kohto 1-1-1, Mikazuki-cho, Sayo 679-5198, Japan

X-ray absorption near-edge structure (XANES) suffersfrom core-hole lifetime broadening at a higher energy
absorption edge, such as Sn K (29 keV, ΓK ) 8.49 eV).
To overcome this problem, emitted Sn Kr1 fluorescencefrom sample was counted using high-energy-resolution
fluorescence spectrometer in the XANES measurements.
Experimental energy resolution (5.0 eV) was consistent
with theoretical values based on the Rowland configuration of the spectrometer. The absorption edge became
steeper compared to conventional spectra. The white-line
peak due to SnII species became remarkably sharper andmore intense in the Sn Kr1-detecting Sn K-edge XANES
for Pt-Sn/SiO2. To support the semiclassical theory ofresonant Raman scattering for the explanation of observed
elimination of lifetime width, more resolved XANES data
at Cu K, Pb L3, and Sn K in this work were convoluted(filtered) with a Lorentzian of each core-hole lifetime
width. The processed data resembled generally wellcorresponding XANES spectrum measured in transmission mode. The verification based on ab initio XANES
calculations was also performed.
X-ray absorption near-edge structure (XANES) is the fluctuation of X-ray absorption intensity in the range of ∼100 eV including
the absorption edge. It has been widely applied to analysis andspeciation for surface,1 macromolecules,1 life science,2 environmental science,3 and catalysis.2,4 Among various spectroscopic
methods, XANES is advantageous to sensitively monitor thechemical state of an X-ray absorbing element. In addition, it often* To whom correspondence should be addressed. E-mail; yizumi@
chemenv.titech.ac.jp; urugat@spring8.or.jp.
†
Tokyo Institute of Technology.
‡
CNRS.
§
Japan Synchrotron Radiation Research Institute.
(1) Stöhr, J. NEXAFS Spectroscopy; Springer: Berlin-Heidelberg, 1992.
(2) Koningsberger, D. C., Prins, R., Eds. X-ray Absorption-Principles, Applications, Techniques of EXAFS, SEXAFS, and XANES; John Wiley & Sons: New
York, 1988.
(3) Van Grieken, R. E., Markowicz, A. A., Eds. Handbook of X-ray Spectrometry,
2nd ed.; Marcel Dekker: New York, 2002.
(4) Iwasawa, Y., Ed. X-ray Absorption Fine Structure for Catalysts and Surfaces;
World Scientific: Singapore, 1996.
10.1021/ac0512453 CCC: $30.25
Published on Web 09/24/2005© 2005 American Chemical Society

reflects the site symmetry and the type of coordinated atom(s)for an X-ray absorbing element.1,2 Geometric information deduced
from XANES is complementary to bonding distance and thecoordination number extracted from extended X-ray absorption
fine structure (EXAFS) that ranges ∼1000 eV beyond the absorption edge.
The chemical state and the site symmetry are primarilyreflected within (10 eV range from the absorption edge as
preedge peak(s), absorption-edge energy shift, and “white-line”
peak above the absorption edge.1,2 In principle, all the XANES
spectra are affected by the core-hole lifetime broadening. This
broadening is especially serious at higher energy absorption edge
due to the increase of core-hole lifetime width (Γ).5,6
The elimination of lifetime broadening was first reported forthe Dy L3-edge XANES by using a secondary high-energyresolution (∆E ) 0.3 eV) fluorescence spectrometer in combination with synchrotron wiggler beamline.7 The resolved preedge
peaks due to 2p f 4f transition and sharper, more intense whiteline peak were observed for Dy metal, oxide, and nitride when
the Dy LR1 fluorescence was detected with energy bandwidth
smaller than ΓL3 (4.17 eV; Table 1).8 More resolved Pt L3- (ΓK )5.31 eV) and Cu K-edge (ΓK ) 1.55 eV) spectra were also reportedby the detection of Pt LR19 and Cu KR1,10 respectively.
We have developed and applied this XAFS technique combinedwith X-ray fluorescence (XRF) spectrometry at V,11-13 Cr,10
Cu,10,14,15 and As K-edges16 and Pb L3-edge.17,18 The Γ values for
Cu K, Dy L3, Pt L3, Pb L3, and Sn K increase starting from 1.55 to(5) Nishihata, Y.; Emura, S.; Maeda, H.; Kubozono, Y.; Harada, M.; Uruga, T.;
Tanida, H.; Yoneda, Y.; Mizuki, J.; Emoto, T. J. Synchrotron Radiat. 1999,
6, 149-151.
(6) Nishihata, Y.; Kamishima, O.; Kubozono, Y.; Maeda, H.; Emura, S. J.
Synchrotron Radiat. 1998, 5, 1007-1009.
(7) Hämäläinen, K.; Siddons, D. P.; Hastings, J. B.; Berman, L. E. Phys. Rev.
Lett. 1991, 67, 2850-2853.
(8) Krause, M. O.; Oliver, J. H. J. Phys. Chem. Ref. Data 1979, 8, 329-338.
(9) de Groot, F. W. F. Top. Catal. 2000, 10, 179-186.
(10) Izumi, Y.; Nagamori, H. Bull. Chem. Soc. Jpn. 2000, 73, 1581 - 1587.
(11) Izumi, Y.; Kiyotaki, F.; Yagi, N.; Vlaicu, A.; Nisawa, A.; Fukushima, S.;
Yoshitake, H.; Iwasawa, Y. J. Phys. Chem. B 2005, 109, 14884-14891.
(12) Izumi, Y.; Kiyotaki, F.; Yoshitake, H.; Aika, K.; Sugihara, T.; Tatsumi, T.;
Tanizawa, Y.; Shido, T.; Iwasawa, Y. Chem. Lett. 2002, 1154-1155.
(13) Izumi, Y.; Kiyotaki, F.; Yoshitake, H.; Aika, K.; Sugihara, T.; Tatsumi, T.;
Tanizawa, Y.; Shido, T.; Iwasawa, Y. Chem. Commun. 2002, 2402-2403.

Analytical Chemistry, Vol. 77, No. 21, November 1, 2005 6969

Table 1. Energy Values for Absorption Edges and Emission Peaks, Lifetime Widths for the Core Hole and Emission
Peaks, and Energy Resolution of Fluorescnece-detecting XAFS
absorption
edge
V
Cr
Mn
Fe
Cu
As
Sn
Dy
Pt
Pb

K

L3

E (eV)aΓK or L3(eV)8emission
detected

E
(eV)a

Γ
(eV)8

∆E
(eV)b

5463.95988.86537.6
7111.28980.311865
29194.7
7789.711562
13040.6

1.01
1.08
1.16
1.25
1.55
2.14
8.49
4.17
5.31
5.81

KR1
Kβ1,3
Kβ1,3
Kβ1,3
KR1
KR1
KR1
LR1

4952.25946.76490.57058.08047.810543.7
25271.3
6495.29442.310551.5

1.26
∼1.08
∼1.16
∼1.25
2.01
3.08
11.24
5.6

2.0
2.0
0.8
1.6
1.1
1.3
5.0
0.8
5.0

refs
11-13
10, 1529
30
this work, 10, 14
16
this work
7
9
this work, 17, 18

a Energy values for metal.20 b Energy resolution including the contribution of beamline.

Scheme 1. Schematic View of Our Fluorescence
Spectrometer Combined with XAFS Beamline

8.49 eV (Table 1). This work reports experimental trials to
overcome the problem of core-hole lifetime broadening at the
Sn K-edge. The feasibility of this technique at the edge isdemonstrated. The improvement of spectral resolution was foundto be more significant at higher energy edges utilizing thistechnique.
Further, the XANES data obtained combining with XRF wereconvoluted (filtered) with a Lorentzian and compared to XANES
data obtained in transmission mode at the edges of 9-29 keV(Cu K, Pb L3, and Sn K). The ∆E/E (E, photon energy) for the
beam incident on the sample was ∼10-4. The ∆E of our
fluorescence spectrometer was theoretically estimated to 1.1, 1.9,
and 4.0 eV at Cu K-, Pb L3-, and Sn K-edges, respectively, including
the contribution of beamline.14 Comparable values were experimentally achieved when the vertical openings of slits 1 and 2
equipped in the spectrometer (Scheme 1) were set to 0.5, 2.0,
and 2.0 mm, respectively.
METHODS
Samples. Standard samples CuCl2 (>95%, Wako), 2PbCO3‚
Pb(OH)2 (first grade, Wako), Sn metal (>99.5%, Wako), SnO(14) Izumi, Y.; Kiyotaki, F.; Nagamori, H.; Minato, T. J. Electron Spectrosc. Relat.
Phenom. 2001, 119, 193-199.
(15) Izumi, Y.; Oyanagi, H.; Nagamori, H. Bull. Chem. Soc. Jpn. 2000, 73, 20172023.
(16) Izumi, Y.; Masih, D.; Aika, K.; Seida, Y. J. Phys. Chem. B 2005, 109, 32273232.
(17) Izumi, Y.; Kiyotaki, F.; Minato, T.; Seida, Y. Anal. Chem. 2002, 74, 38193823.
(18) Izumi, Y.; Kiyotaki, F.; Seida, Y. J. Phys. Chem. B 2002, 106, 1518-1520.

6970

Analytical Chemistry, Vol. 77, No. 21, November 1, 2005(>99.9%, Wako), and SnO2 (>99.9%, Aldrich) were used asreceived. The samples were diluted to metal (X-ray absorbing
element) 1.5-5.0 wt % by thorough mixing with boron nitride(special grade, Wako).
The Pt-Sn/SiO2 catalyst was prepared by the following
procedure.19 The slurry of Pt(NH3)4(OH)2 (Strem) was reactedwith the surface hydroxyl groups of silica (specific surface area
200 m2 g-1, Degussa) for 10 h. After filtration, the obtained powder
was calcined in flowing O2 + N2 (1:4) and then reduced in flowing
H2 at 673 K (Pt/SiO2). Sn(n-C4H9)4 was introduced to the reduced
Pt/SiO2 powder in the presence of H2 (3.0 kPa) and reacted at
373 K. The Pt-Sn/SiO2 sample was treated under flowing H2 at
673 K before it was introduced and sealed in a glass cell. Since
the X-ray data were acquired a few weeks later than the cell wassealed, the possibility of contamination by air of the sample could
not be excluded. The Pt loading was 2.5 wt % as metal and theatomic ratio Sn/Pt was 1.0.
Operating Conditions of Synchrotron Ring, Beamline, andthe Fluorescence Spectrometer. The X-ray measurements were
performed at the undulator beamline BL10XU at SPring-8, Japan.
The storage ring energy was 8.0 GeV, and the ring current was
100-71 mA. A Si(111) double-crystal monochromator was used.
A rhodium-coated double mirror was inserted in the incident X-ray
beam path in order to suppress higher harmonics except for the
Sn K-edge study. The X-ray fluorescence from the sample wasanalyzed by a homemade Rowland-type spectrometer equippedwith a Johansson-type Ge crystal (Saint-Gobain) and a NaI(Tl)scintillation counter (SC; Oken).
The arrangement of the spectrometer is depicted in Scheme
1. The Rowland radius was set to 220 mm and the higher-orderreflections of Ge(111) were used. The size of slit 0 in front of I0
ionization chamber was fixed to 1.0 × 1.0 mm2. The sample wasset in a plane tilted from a horizontal plane toward the directionof the incident X-ray by an angle θ and also toward the direction
perpendicular to incident X-ray in the same horizontal plane byan angle χ. The values θ and χ were set to 6-13 and 7-13 deg,
respectively. The horizontal opening of receiving slit 1 (100 mm
apart from the center of sample) and of slit 2 in front of SC was
fixed at 8.0 mm. The vertical opening of the two slits was varied
between 0.5 and 7.5 and between 0.5 and 2.0 mm, respectively,
as the compromise between ∆E and photon counts.10,15(19) Humblot, F.; Didillon, D.; Lepeltier, F.; Candy, J. P.; Corker, J.; Clause, O.;
Bayard, F.; Basset, J. M. J. Am. Chem. Soc. 1998, 120, 137-146.

All the X-ray measurements were performed at 290 K.
Maximum incident photon flux at the BL10XU was ∼1013 s-1.
Throughout the XANES spectrum measurements, the undulator
gap and the parallelism of the monochromator crystals were
optimized to maximize the X-ray beam flux at each data point.
The average If counts at SC were 2 × 102 s-1 for copper(II)chloride (Cu K-edge), 6 × 103 s-1 for 2PbCO3‚Pb(OH)2 (Pb L3edge), and 3 × 10 s-1 for Pt-Sn/SiO2 (Sn K-edge). The energy
values of monochromator and fluorescence spectrometer werereproduced within (0.1 and (0.2 eV, respectively.
X-ray Emission and Absorption Spectrum Measurements.
The Cu KR1 emission spectra were measured for copper(0) metal
and copper(II) chloride with the excitation energy set at 9000.1
eV. The Ge(444) reflection was used. The emission energy for
Cu metal was calibrated to 8047.8 eV20 (Bragg angle θB ) 70.630
deg). The fluorescence spectrometer was tuned to the Cu KR1
peak top and Cu K-edge XANES spectrum was measured. The
scan step of monochromator was ∼0.28 and ∼0.56 eV in theenergy range 8957-9021 and 9021-9063 eV, respectively. The
dwell time of each data point was 10-15 s.
The Pb LR1 emission spectra were measured for Pb0 metal
and 2PbIICO3‚PbII(OH)2 with the excitation energy set at 13064.3
eV. The Ge(555) reflection was used. The emission energy for
Pb metal was calibrated to 10551.5 eV20 (θB ) 64.083 deg). The
fluorescence spectrometer was tuned to the Pb LR1 peak top, andPb L3-edge XANES spectrum was measured. The scan step ofmonochromator was ∼0.30 and ∼0.60 eV in the energy range
13 016-13 077 and 13 077-13 125 eV, respectively. The dwell timeof each data point was 40 s.
The Sn KR1 emission spectra were measured for Sn0 metaland Pt-Sn/SiO2 catalyst with the excitation energy set at 29 235.0
eV. The Pt-Sn/SiO2 catalyst was sealed in Pyrex glass cell
equipped with a Kapton film window of 12.5-µm thickness. The
cell was purged with 81 kPa of hydrogen and placed in a sample
holder. The Ge(13,13,13) reflection was used. The emission
energy for Sn metal was calibrated to 25 271.3 eV20 (θB ) 77.527
deg). The fluorescence spectrometer was tuned to the Sn KR1
peak top, and Sn K-edge XANES spectrum was measured. The
scan step of monochromator was ∼0.45 and ∼1.9 eV in the energy
range 29 137-29 227 and 29 227-29 303 eV, respectively. The
dwell time of each data point was 20-100 s. All the absorption
edge energy values were calibrated to each reference value (Table1).20
The signal/background ratio was >1.2 × 102 for copper(II)chloride (Cu K-edge), >1.7 × 102 for 2PbCO3‚Pb(OH)2 (Pb L3edge), and >1.8 for Pt-Sn/SiO2 (Sn K-edge). To suppress thedetection of scattered X-rays (via air and parts of spectrometer),sample and SC were thoroughly covered with lead plates of 1-5mm thickness except for the incident beam entrance, the exit of
X-ray fluorescence from sample, and the entrance of X-ray
fluorescence reflected via Ge crystal (Scheme 1) in the Pb L3and Sn K-edges study.
Analysis. Background subtraction of the raw XANES spectrum
was performed using a Victoreen parameter. A smooth spline
function was calculated in the postedge region, and the spectrum
was normalized at k ≈ 4 Å-1 from the edge (derivative maximum).
In a procedure similar to data smoothing, normalized XANES data
(20) Bearden, J. A. Rev. Mod. Phys. 1967, 39, 78-124.

were convoluted using Lorentzian.21
N

Ii(convoluted) ) Ii(data) +∑ {Ι (Lorentzian) ×jj*1

Ij (neighboring data) × energy intervalj (eV) ×
weighting constant} (1)The convolution using a Gaussian or pseudo-Voigt function
was also performed. As these operations were performed fornormalized data and thus the summation in eq 1 included more
preedge zero intensity data as the data i above the absorption
edge approached nearer the edge, the convoluted XANES spectrum came to be tilted slightly upward as a function of energy.
Therefore, the background subtraction was performed again fromthe convoluted spectrum. Thus obtained data was renormalized.
The effect of experimental energy resolution was also verified
by ab initio caluculations.13 A code FEFF version 8.122 was applied
to generate theoretical XANES spectra in self-consistent field andmultiple scattering calculation modes. The energy shift of pure
imaginary “optical” potential was varied to evaluate the eliminationof the lifetime broadening effect.
RESULTS
Cu K-Edge. The full width at a half-maximum (fwhm) of the
Cu KR1 emission peak was 2.3 eV measured for CuCl2.14 The
natural width of Cu KR1 is 2.01 eV.8 Under the condition that the
convolution of ∆E (1.1 eV) is smaller than the ΓK value for copper(1.55 eV), Cu KR1-detecting Cu K-edge XANES spectrum wasmeasured for CuCl2 (Figure 1a). The more resolved peaks at 8989
and 8979.5 eV23-27 are justified by convolution in the Analysis
section compared to conventional XANES (Figure 1b).
Pb L3-Edge. The fwhm of the Pb LR1 emission peak was 8.8
eV measured for 2PbCO3‚Pb(OH)2. The lifetime width of Pb L3 is
5.81 eV.8 The width of 82Pb M5 may be similar to that for 66Dy
(1.4 eV).7 Thus, the ∆E of the fluorescence spectrometer was
estimated to 5.0 eV including the contribution of beamline. Thisvalue is worse than theoretical estimation28 (1.9 eV). The major
reason of this discrepancy is that the vertical opening of receiving
slit 1 (Scheme 1) was set to as much as 7.5 mm to know the lower
detection limit of Pb contained in a sample under a fixed conditionof the fluorescence spectrometer.17,18
Under the condition that the ∆E is smaller than the ΓL3 value
for lead (5.81 eV), Pb LR1-detecting Pb L3-edge XANES spectrum(21) In eq 1, the Lorentzian was centered at the energy of each data point i. The
maximum intensity of Lorentzian was one. The width of Lorentzian wasvaried around the Γ value for the absorption edge. The weighting constant
was optimized for each edge to better fit the processed data to theconventional experimental XANES data (1.0, 0.15, and 1.0 for Cu K-, Pb L3-,and Sn K-edges, respectively).
(22) Ankudinov, A. L.; Ravel, B.; Rehr, J. J.; Condradson, S. D. Phys. Rev. B 1998,
58, 7565-7576.
(23) Kau, L.; Spira-Solomon, D. J.; Penner-Hahn, J. E.; Hodgson, K. O.; Solomon,
E. I. J. Am. Chem. Soc. 1987, 109, 6433-6442.
(24) Pickering, I. J.; George, G. N. Inorg. Chem. 1995, 34, 3142-3152.
(25) Shadle, S. E.; Penner-Hahn, J. E.; Schugar, H. J.; Hedman, B.; Hodgson, K.
O.; Solomon, E. I. J. Am. Chem. Soc. 1993, 115, 767-776.
(26) Kuroda, Y.; Yoshikawa, Y.; Konno, S.; Hamano, H.; Maeda, H. J. Phys. Chem.
1995, 99, 10621-10628.
(27) Saini, N.; Lanzara, A.; Bianconi, A.; Oyanagi, H. Phys. Rev. B 1998, 58,
11768-11773.
(28) Georgopoulos, P.; Knapp, G. S. J. Appl. Crystallogr. 1981, 14, 3-7.

Analytical Chemistry, Vol. 77, No. 21, November 1, 2005

6971

Figure 1. Normalized Cu K-edge XANES spectrum for CuCl2
measured by detecting Cu KR1 fluorescence (a) or in transmission
mode (b). The data a were convoluted by a Lorentzian of core-hole
lifetime width for Cu K level (1.55 eV) to be a′ (dotted line). (Inset)
Magnified preedge and absorption edge region.

Figure 3. Sn KR1 emission spectrum for Sn metal. Each data pointis presented as a dot. Broader and narrower dotted lines are the Sn
KR1 lifetime width (11.24 eV) and the energy resolution of fluorescence spectrometer (5.0 eV) including the contribution of beamline.

metal (Figure 4A(a)), the first intense peak at 29 201.7 eV became
sharper and more intense compared to that measured in thetransmission mode (Figure 4A(b)). The absorption edge became
steeper by selective detection of Sn KR1 based on the firstderivative data (Figure 4A, inset). For the Sn K-edge data of PtSn/SiO2, the improvement of spectral resolution was remarkably
pronounced for the white-line peak at 29 206.3 eV (Figure 4B(a)). The absorption edge became also steeper at 29 200.3 eV(Figure 4B, inset).

Figure 2. Normalized Pb L3-edge XANES spectrum for 2PbCO3‚
Pb(OH)2 measured by detecting Pb LR1 fluorescence (a) or intransmission mode (b). The data a were convoluted by a Lorentzianof core-hole lifetime width for Pb L3 level (5.81 eV) to be a′ (dottedline). (Inset) First-derivative spectra of normalized XANES (a, b).

was measured for 2PbCO3‚Pb(OH)2 (Figure 2a). The more
resolved peaks at 13 048 and 13 037 eV are justified by convolution
in the Analysis section compared to conventional XANES (b). The
resolution improvements are clearly demonstrated in their firstderivative spectra (Figure 2, inset). Essentially, the absorption
edge became far steeper with this method.
Sn K-Edge. The fwhm of the Sn KR1 emission peak was 12.3
eV for Sn metal (Figure 3, dots). The natural width of Sn KR1 line
is 11.24 eV.8 The ∆E of the fluorescence spectrometer was
estimated to 5.0 eV including the contribution of beamline. Thisvalue is essentially consistent with theoretical estimation28 (4.0
eV).
Under the condition that the ∆E is smaller than the ΓK value
for tin (8.49 eV), Sn KR1-detecting Sn K-edge XANES spectra were
measured for Sn metal and Pt-Sn/SiO2. In the spectrum for Sn
6972 Analytical Chemistry, Vol. 77, No. 21, November 1, 2005

ANALYSIS
Cu K-Edge. The Cu KR1-detecting XANES data in Figure 1a
was convoluted using Lorentzian, Gaussian, or both. Lorentzian
convolution nicely transformed the data to the one similar toconventional data if adequate Lorentzian width was chosen. When
Gaussian was used, the spectrum did not change substantiallyfrom original data because the feet of the Gaussian peak rapidly
diminish to the bottom and thus the effective number of data
points for convolution with Gaussian in eq 1 were very limited
compared to the convolution using Lorentzian. When the pseudoVoigt function was used, data were transformed essentially due
to the Lorentzian portion only. Thus, the fwhm value for Lorentzian was systematically varied around 1.55 eV.
The convoluted spectrum using a Lorentzian of 1.55-eV width
was depicted in Figure 1a′. The processed data were essentially
identical with conventional spectrum b except for the minor
difference in the preedge region 8975-8985 eV (vide supra forthe reason).
Pb L3-Edge. The fwhm value of the Lorentzian was varied
around 5.81 eV. The Pb LR1-detecting XANES was effectivelytransformed into data similar to a conventional spectrum when
convoluted with a Lorentzian of 5.81-eV width (Figure 2a′). The
processed data were nearly identical with conventional spectrumb except for a minor difference in the region below 13 040 eV.
Sn K-Edge. When the fwhm value of the Lorentzian varied
for Sn KR1-detecting XANES measured for Pt-Sn/SiO2, the whiteline peak became less intense and broader as the Lorentzian width
progressively grew from 5.00 to 11.24 eV. The processed datamode using a Lorentzian. However, the coincidence was notcomplete in the case of Sn K-edge data for Pt-Sn/SiO2.

Figure 4. Normalized Sn K-edge XANES spectra for Sn metal (A)and Pt-Sn/SiO2 catalyst (2.5 wt % Pt; Sn/Pt atomic ratio, 1.0) (B)measured by detecting Sn KR1 fluorescence (a) or in transmission
mode (b). The data a were convoluted by a Lorentzian of core-hole
lifetime width for Sn K level (8.49 eV) to be a′ (dotted line). (Inset)
First-derivative spectra of normalized XANES (a, b). (C) Sn K-edge
XANES for SnIIO (a) and SnIVO2 (b) measured in transmission mode.

when the fwhm value was 8.49 eV [Figure 4A(a′) and 4B(a′)]
resembled most corresponding conventional spectra A(b) (Snmetal) and B(b) (Pt-Sn/SiO2), respectively, except for thedifferences in the region below 29190 eV for both samples andthe postedge region between 29 245 and 29 260 eV for Pt-Sn/
SiO2.
In summary, convolution of XANES data combined with XRF
nicely reproduced conventional XANES obtained in transmission

DISCUSSION
Reason for the Improvement of XANES Profile Resolution. The improvement of spectral resolution was pronounced in
the region of (10 eV from the absorption edges of Cu K, Pb L3,
and Sn K by detecting Cu KR1, Pb LR1, and Sn KR1, respectively,
with smaller ∆E (1.1, 5.0, and 5.0 eV, respectively) than theircore-hole lifetime width (1.55, 5.81, and 8.49 eV, respectively).
The XANES method combined with XRF was found to beadvantageous at higher energy absorption edges because theincrease of lifetime width is greater than the increase of instrumental ∆E (Table 1). At the lower energy K-edges of V,11-13 Cr,10,15
and Mn,29 the ∆E only due to beamline was similar/larger thaneach ΓK value (Table 1).
The steepness of the absorption edge was significantly improved for Pb L3- and Sn K-edges (Figures 2 and 4) in selective
fluorescence detection mode compared to transmission mode. The
improvement was directly visualized as their first-derivative data
(derivative peak sharpness and intensity) in Figures 2 (inset) and
4A and B(inset), respectively.
The theoretical basis of enhanced resolution observed in
Figures 1, 2, and 4 was formulated in the Appendix section.7,30
The X-ray fluorescence is considered associated with dipole
transition from shell B to A, e.g., from L3 to K (KR1) or from M5
to L3 (LR1). Based on eq A1, when the energy resolution tomonitor the fluorescence, B(ω2), is smaller than ΓA, Lorentzian
lifetime broadening will be suppressed by B(ω2), and sharperfeatures near the absorption edge can be observed.
This theoretical prediction was in accord with the data in thiswork (Figures 1, 2, and 4) using a high-∆E Rowland-type
spectrometer to satisfy the condition B(ω2) < ΓA. To confirm thiseffect, the Cu KR1-, Pb LR1-, and Sn KR1-detecting XANES data
were convoluted using a Lorentzian with each core-hole lifetime
width. All the processed data resembled fairly well corresponding
XANES spectra measured in transmission mode except for a minor
discrepancy of Sn K-edge data for Pt-Sn/SiO2. In summary, thesedata convolution tests supported the theoretical rationale ofresolution improvement for XANES in the condition B(ω2) < ΓA.
This effect was also confirmed based on the energy shift ofpure imaginary “optical” potential in ab initio calculations. A similar
spectrum was calculated to conventional XANES (Figure 4A(b))
when the shift was set to zero (Figure 5c) whereas the profile of
Sn KR1-detecting XANES measured in the condition B(ω2) < ΓA
was well reproduced when the shift was set to -2.0 eV (Figure
5a, b).
Feasible Applications of Fluorescence-Selecting XANESSatisfying the Condition B(ω2) < ΓA. (1) Cu K-Edge. The weak
preedge peak at ∼8979 eV has been reported for CuII compounds
due to 1s f 3d transition.23-27 The shoulder peak on theabsorption edge between 8986 and 8988 eV was also reported forCuII(2,5-dithiahexane)2(ClO4)2, [creatinium]2+[CuIICl4]2-, and CuII(imidazole)4(ClO4)2, but no shoulder peak was found for CuIISO4‚
5H2O.23 The peak was assigned to shakedown transition. The 1s
f 4p transition (the final state (1s)1‚‚‚(3d)9(4p)1) and ligand-to(29) Grush, M. M.; Christou, G.; Hämäläinen, K.; Cramer, S. P. J. Am. Chem.
Soc. 1995, 117, 5895-5896.
(30) Glatzel, P.; Bergmann, U. Coord. Chem. Rev. 2005, 249, 65-95.

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Figure 5. Normalized Sn K-edge XANES spectrum for Sn metal
measured by detecting Sn KR1 fluorescence (a) and corresponding
Sn K-edge XANES generated by FEFF in SCF and FMS modes (b,c). The energy shift to pure imaginary “optical” potential was set to-2.0 (b) and 0 eV (c). The edge energy for spectra b and c wascorrected to spectrum a.

metal charge transfer (LMCT) take place at the same time. In
total, the final state is (1s)1‚‚‚(3d)10L(4p)1, where L means ligand
hole.23-25
Polarized XAFS studies were performed to discuss the Cu site
symmetry utilizing the anisotropy of 1s f 3d and 1s f 4p peakintensity for CuIICl2 24 and Bi2Sr2CaCu2O8+δ single crystals.27
Utilizing the improvement of spectral resolution depicted in Figure
1a, type of ligand atom and site symmetry will be discussed into
more detail also for powder samples.
(2) Pb L3-Edge. Due to the difference between ΓK for copperand ΓL3 for lead (Table 1), conventional Pb L3 absorption edge
(Figure 2b) was apparently broader than that of Cu K-edge (Figure1b). Pb LR1-detecting Pb L3-edge XANES spectrum was measured
satisfying the condition B(ω2) < ΓL3. Due to the effect to makesteeper the absorption edge, two shoulder peaks at the foot (13 037 eV) and the end (13 048 eV) of the absorption edge came tobe resolved (Figure 2a).
The presence/absence of the peak at 13 048 eV was reported
to judge the speciation of PbII.31-33 The shoulder peak was
observed for coordinatively saturated PbII sites (e.g., 2PbCO3‚Pb(OH)2) but not for unsaturated PbII species (e.g., ion-exchanged
Pb2+ on the surface). The resolved Pb LR1-detecting Pb L3-edge
data were reported for the more accurate speciation in theapplication of environmental chemistry.17,18(3) Sn K-Edge. Due to the difference of ΓL3 for lead and ΓK fortin (Table 1), convenitonal Sn K-edge data were even broader(Figure 4b). Sn KR1-detecting Sn K-edge XANES spectrum wasmeasured, satisfying the condition B(ω2) < ΓL3 for Sn metal(Figure 4A(a)) and Pt-Sn/SiO2 (Figure 4B(a)). The intense peakenergy above the edge for Pt-Sn/SiO2 (29206.3 eV) corresponded(31) Rouff, A. A.; Elzinga, E. J.; Reeder, R. J. Environ. Sci. Technol. 2004, 38,
1700-1707.
(32) Huang, F.; Jao, H.; Hung, W.; Chen, K.; Wang, C. J. Phys. Chem. B 2004,
108, 20458-20464.
(33) Rose, J.; Moulin, I.; Hazemann, J.; Masion, A.; Bertsch, P. M.; Bottero, J.;
Mosnier, F.; Haehnel, C. Langmuir 2000, 16, 9900-9906.

6974 Analytical Chemistry, Vol. 77, No. 21, November 1, 2005

to the SnII state compared to values for standard Sn0 (Figure 4A),
SnII, and SnIV (Figure 4C). The postedge pattern of Figure 4B(a)was similar to that for SnIIO (Figure 4C(a)). Thus, the major Sn
species in Pt-Sn/SiO2 was concluded to be SnII.34
In a comparison between Figure 4A(a) and B(a), the intense
peak above the edge was more pronounced for the SnII species.
The convoluted spectrum with a Lorentzian did not completely
reproduce corresponding conventional data only in the case of
Sn K-edge for Pt-Sn/SiO2 (Figure 4B(a′)) among all spectra
processed in this paper. The reason is unclear, but the resonant
excitation effect may be enhanced for the electronic transition tobound/semibound state, such as the π* state and empty state ofCu 3d. A minor discrepancy was also detected in the preedge
region between convoluted and conventional Cu K-edge (Figure
1a′, b). This effect was proposed for the increase of 1s f 3d preedge peak intensity in the Fe Kβ1,3-detecting Fe K-edge for FeII/III
species.35 The contribution of resonance excitation effect for
specific peaks near the edge is not included in eq 1 for convolution.
In a reverse point of view to utilize this data discrepancy for
Sn, valence-selective peak enhancement may be enabled andapplied to Sn K-edge studies for such as heterogeneous catalysts,36
gas sensor,37 and environmental samples,38,39 where lifetime
broadening has hampered quantitative analysis.
CONCLUSIONS
X-ray fluorescence-detecting XAFS method was successfully
applied to the Sn K-edge in combination with a highly brilliant,
low-emittance synchrotron beam. At higher energy absorption
edges, the effect to detect the X-ray fluorescence with an energy
bandwidth smaller than each core-hole lifetime width was more
remarkable to obtain steeper absorption edge. Preedge peak, peakon the absorption edge, and white-line peak hidden in the
broadened absorption edge in conventional spectra became
revealed. The improvement of energy resolution by this method
was supported by the data convolution with a Lorentzian of eachcore-hole lifetime width and also by ab initio XANES calculations(energy shift of pure imaginary “optical” potential). As applicationsof this method, improved speciation of low concentrations of Pb2+
was enabled to determine the surface reaction mechanism of
Pb2+.17,18 Selective detection of enhanced SnII or SnIV white-line
peak will enable more quantitative characterization of redox
catalysis sites and oxidic Sn sites for supported Pt-Sn catalysts.
In situ population ratio change of coexisting Sn0, SnII, and SnIV
species for Pt-Sn catalysts was suggested based on 119SnMössbauer measurements.40(34) The Sn-O bonds at 2.06 Å (the coordination number N ) 3-4) based on
the curve fit analysis of Sn K-edge EXAFS supported this conclusion. SnPt shell was also given at a bond distance 2.70 Å with the N of 8-10. Onceformed Pt-Sn alloy on SiO2 surface may be partially oxidized.
(35) Heijboer, W. M.; Glatzel, P.; Sawant, K. R.; Lobo, R. F.; Bergmann, U.; Barrea,
R. A.; Konongsberger, D. C.; Weckhuysen, B. M.; de Groot, F. M. F. J. Phys.
Chem. B 2004, 108, 10002-10011.
(36) Onda, A.; Komatsu, T.; Yashima, T. J. Catal. 2004, 221, 378-385.
(37) Grandjean, D.; Benfield, R. E.; Nayral, C.; Maisonnat, A.; Chaudret, B. J.
Phys. Chem. B 2004, 108, 8876-8887.
(38) Sakakibara, N.; Takahashi, Y.; Yamaguchi, Y.; Shibata, K.; Uruga, T. Chem.
Lett. 2004, 33, 264-265.
(39) Takahashi, Y.; Sakakibara, N.; Nomura, M. Anal. Chem. 2004, 76, 43074314.
(40) Stievano, L.; Wagner, F. E.; Calogero, S.; Recchia, S.; Dossi, C.; Psaro, R.
Stud. Sur. Sci. Catal. 2000, 130D, 3903-3908 (Corma, A., Melo, F. V.,
Mendioroz, S., Fierro, J. L. G., Eds.).

ACKNOWLEDGMENT
The experiments were performed under the approval of theSPring-8 Program Review Committee, 2004A0122-NX-np and2003B0386-NXa-np at the Sn K-edge, 2001B0004-CX-np and2001A0022-NX-np at the Pb L3-edge, and 1999B0220-NX-np and1998A0295-NX-np at the Cu K-edge. Y.I. is thankful for financial
support from the Grant-in-Aid for Scientific Research (B13555230),
Encouragement of Young Scientists (B14740401, A12740376), andExploratory Research (08874066) from the Ministry of Education,
Culture, Sports, Science, and Technology, Toray Science Foundation (98-3901), and Yamada Science Foundation (2000). This paper
is part 16 in the series.
APPENDIX
X-ray fluorescence is considered associated with dipole transition from shell B to A. When incident photon energy pω1 isenough above the absorption edge, the fwhm of the fluorescenceis ΓA + ΓB. When pω1 is set in the vicinity of the absorption
edge, the cross section σ(ω1) for the fluorescence is formulated

based on semiclassical interpretation of resonant Raman scattering,7,30

σ(ω1) ∝(ω2)∫ d(pω ) ∫ dB
∞

0

∞

2

0

ΓA
ω2 EB - EA + pω1 - pω2
ω1
EB - EA(pω1 + EA - )2 + ΓA2/4
ΓB(pω1 + EB - pω2 - )2 + ΓB2/4

σA ( - EA) (A1)

where pω1 is scattered photon energy,  is the kinetic energy ofphotoelectron, EB and EA are the B and A shell binding energies,and σA is the total A-shell photoabsorption cross section.
Received for review July 13, 2005. Accepted August 24,
2005.
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