X-ray Spectrometry - Advanced Analytical Chemistry - Lecture Slides, Slides of Analytical Chemistry

Download X-ray Spectrometry - Advanced Analytical Chemistry - Lecture Slides and more Slides Analytical Chemistry in PDF only on Docsity! Notes e This lecture covers both atomic a applications of X-ray spectrometi e X-ray diffraction is only briefly dis covered in its own lecture along crystallography and solid-state st         !  "#    $  % &'  %"  & ()"%*  + (! & ()+%*   ,!& &  -&! &&& & !'    &, . /'     0  1    )  * !   )  $  * docsity.com     ! "  #"    ! " ! $% &"   % &  '!"  () "'* + #",-  . "/ 010 "  $2342567 8 9: ;;<= >> ?@ABCBD75EFABBGB8FCH6388BGBC3F56IJHGF3IBK docsity.com X-ray Generation: Characte e The characteristics lines in X-ray spectra result from electronic transitions between inner atomic 100 (edge 1s) e The X-ray spectra for most heavy elements are much simpler than the UV/Vis spectra observed in ICP-OES, for example. Big difference between X-ray and UV- 40} Atomic number, Z ot 1 0 10 20 30 40 50 doesn’t just excite electrons to higher SS Frequency x 10-8 Figure 12-3 Relationship between X-ray emission fre- Predicts the basic quency and atomic number for Kay and Ly lines. relationship of atom number and the frequency of the characteristic lines [i _ where Z is the atomic number, and K and o are v= 1404 a) constants that vary with the spectral series. Incident X-ray Photoelectron (Exi) (Epe = Exi- Ex) X-ray fluorescence Auger electron (Exrr = Ex- Ex) (Ene = Ex- EL- Em) docsity.com       !"!#$!%& !'! ()*+ ,-./"012034 $54 $61042034 $50 $60112034 $74 $81142034 $71 $80 9:;<=>?=@A<BCD:AEFGHIJJKLMNHO:APQRSTUVSWUXYZZY[: docsity.com Amptek K and L Emission Line Lookup Chart nets, XR-100CR / XR-100T-CZT / ROVER nergy Values in keV X-Ray and Gamma Ray Detectors : Pryy v cr Fe Nt 9 2 | 2 2 2 ze | ND | Mo Pa 3 a | a so | 5 82 cs . Gahan Oe oo agon|ense|save a agan[anse|anse sa | 60 | 6 ez | 63 seis | sas seer | sat or | 8 ante | essim | i880 25/0738) pam 0y881955 se a,00m709) docsity.com  e X-ray tubes: fire electrons at targets that emission properties as well as their robu etc... e (Note — modern tubes are more efficient, X-ray Generation: X Cooling-water inlet ‘Tungsten target Beryllium window Fig. 21.9 Schematic diagram of an X-ray tube. X rays are generated in a target (in this tube, a tungsten insert in a copper anode) when it is bombarded by an electron beam. This beam is generated by thermionic emission from the cathode and accelerated through the large potential difference between it and the anode. The latter is kept at ground potential for reasons of safety while the cathode is made strongly ne} geat deal of heat is dissipated at the anode and carried away by circulating water. The X-ray beam emerges through the beryllium window placed well to the side. It is important for the window to be out of the line of strongly scattered electrons as well as materials sputtered from the target so that it will suffer minimum thermal stress and plated layers, which would reduce its trans- mission. Air is removed from inside the tube to reduce absorption of long wavelength X rays. The beam is brought to a focus on the cathode by making the cylindrical electrode around the cathode sufficiently more negative than the cathode      ! ""#"!"$%&'() $! *"+,- ,() #"""".)! *$ ""/! 0 "10 "2"## ! ""#34+- ! 5/"  #0! () $/#%". 0'5# 6$ 0() $/!#() $#"! #$ $04+,7/1 " 0".#. ".#"1"01 1$,60.!() $" 50$8/00 9#"! ". ".% $0'#+ docsity.com       ! 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X-ray fluorescence and incident electron y a (Exrr = Ex- Ev) Incident electron © auger electron (Ene = Ex- E,- Ew) docsity.com   !"!##$"%&' !( !&' )!*+#%'%,!, -%'./' !0*+-%,!,-%! !*+%%#) !1.  !%! '.&%#"2 3456789:;<=>?8@@@A7BBABCD<A;ECFAGC9HI@@@AE79>9AE9J9AK9;>7A:?AKBLMNNOP docsity.com X-ray Emission: e APXS: e Alpha particles better for exciting light elements: e X-rays better in exciting heavier elements Cr a a TI acy] ree soy Can Alpha-Particle-X-ray-Spectrometer Results Silicon |- After grinding with the Rock Abrasion Rool — Clovis outcrop Humphrey basalt rock ‘Sulfur Chlorine * background Potassium Chromium Manganese Bromine 3 c ° °o 3 z ¥ < 2 2 oO T T T T T T T 4000 6000 8000 10000 12000 14000 16000 Energy eV ree soy Ca) docsity.com       !"#!"$ %& %$'()*+$#$  ,$-$ !.#,/0$$-" 1 $"$2!$"$"-3$ ,$&$.$3$.!"-!"2$"$2!$# ,  14*$&!#!&.5()*! ,$1-%. !"#" 160 !"!.! -%$  ,$&,$1!&."-,!&.  $# ,$ 14()*$& $$"! !3$  ,$0!- !"  $5&-!" !"&,$1! 5"- ,$-! "&$5&-!" !""%1$"-$&!$# ,$ 1!11$-! $.%%"-!"2 ,$ 1#!" $$ 4()*"$$-"!" $"$5$"$2 %".$%&$#'"&, "+4 docsity.com X-ray Absorption Fine St eTwo regions of the XAFS spectrum: ee | — EXAFS (extended x-ray gus [Vi __ ae absorption fine ost} | h(a ret) os cl | — XANES (X-ray Sensitive to oxidation : state and coordination Bey) (CePA chte-lal Tole VCs Figure 6: XAFS j:(E) for FeO. On top, the measured XAFS spectrum is shown octahedral coordination with the XANES and EXAFS regions identified. On the bottom, ji() is shown with smooth background function jio{ 2) and the edge-step Ayip( y). of an atom). Derae Ty eB NCAT ITC CNT MAROTTA SSR MONT RPAUE) FeO has a rock-salt structure. To model the FeO EXAFS, we calculate the scattering am- plitude f(k) and phase-shift 6(k), based on a guess of the structure, with Fe-O distance R = 2.14.A (a regular octahe- dral coordination). We’ll use these functions to refine the values R, N, o’, and Eo so our model EXAFS function matches our data. T T T T T Fit results: N =58+1.8 R = 2.10 + 0.02A AEp =-3.1425eV ao? ~~ = 0.015 + 0.005 A’. R(A) |x(R)| for FeO (blue), and a 1* shell fit (red). SIC SCORER ATI CM TUTE TE RD. ¢U TMM OLIN ROMO eT} 3 docsity.com