Experimental setup Surface-extended X-ray absorption fine structure
1 experimental setup
1.1 synchrotron radiation sources
1.2 electron detectors
1.3 signal-to-noise ratio
experimental setup
synchrotron radiation sources
normally, sexafs work done using synchrotron radiation has highly collimated, plane-polarized , precisely pulsed x-ray sources, fluxes of 10 10 photons/sec/mrad/ma , improves signal-to-noise ratio on obtainable conventional sources. experimental setup conventional exafs shown here in figure 2. bright source x-ray source illuminating sample , transmission being measured absorption coefficient as
μ
=
ln
(
i
)
ln
(
i
o
)
,
{\displaystyle {\begin{aligned}\mu ={\frac {\ln(i)}{\ln(i_{o})}},\end{aligned}}}
where transmitted , io incident intensity of x-rays. plotted against energy of incoming x-ray photon energy.
electron detectors
in sexafs, electron detector , high-vacuum chamber required calculate auger yields instead of intensity of transmitted x-ray waves. detector can either energy analyzer, in case of auger measurements, or electron multiplier, in case of total or partial secondary electron yield. energy analyzer gives rise better resolution while electron multiplier has larger solid angle acceptance.
signal-to-noise ratio
the equation governing signal-to-noise ratio is
s
n
=
(
Ω
4
π
ϵ
n
μ
a
)
(
1
+
i
b
i
n
(
μ
t
+
n
)
)
(
δ
μ
a
μ
a
i
o
1
/
2
)
,
{\displaystyle {\frac {s}{n}}={\sqrt {\frac {({\frac {\omega }{4\pi }}\epsilon _{n}\mu _{a})}{(1+{\frac {i_{b}}{i_{n}}}(\mu _{t}+n))}}}\left({\frac {\delta \mu _{a}}{\mu _{a}}}i_{o}^{1/2}\right),}
where
μa absorption coefficient;
in nonradiative contribution in electron counts/sec;
ib background contribution in electron counts/sec;
μa absorption sexafs-producing element;
μt total absorption elements;
io incident intensity;
n attenuation length;
Ω/(4π) solid angle acceptance detector;
εn nonradiative yield probability electron not decay radiatively , emitted auger electron.
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