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QUANTITATIVE MICROANALYSIS OF SOLID SAMPLES WITH THE LASER PROBE MASS
SPECTROMETRY II (L.P.M.S. II)
J. Eloy
To cite this version:
J. Eloy. QUANTITATIVE MICROANALYSIS OF SOLID SAMPLES WITH THE LASER PROBE
MASS SPECTROMETRY II (L.P.M.S. II). Journal de Physique Colloques, 1984, 45 (C2), pp.C2-265-
C2-269. �10.1051/jphyscol:1984259�. �jpa-00223972�
QUANTITATIVE MICROANALYSIS OF S O L I D SAMPLES WITH T H E LASER PROBE MASS SPECTROMETRY I I (L,P,M,s, 11)
J . F . E l o y
DERDCA-SEA-S.ZAPC
-
CEN. GrenobZe, 85 X , 38041 GrenobZe Cedex, FranceResume
La spectrographie de masse a sonde laser est capable d'analyser directement des micro-volumes d'echantillons isolants ou conducteurs, mineraux ou organiques.
Cette methode permet des etudes analytiques
:- d'inclusions solides superficielles ou internes
- des releves de profils de concentration multi6lementaire
- d'inhomogeneites superficielles de matgriau - de phase
La methode de quantification des resultats par le modele d'ionisation de SAHA-EGGERT a et6 appliquee a differents problemes geologiques et sur des produits nouveaux en electronique du type monocristaux tel que fluorure, oxyde, etc.
Abstract
The laser probe mass spectrograph (L.P.M.S. 11) is able to analyse directly micro-volumes of insolator or, conductor, minerals or organical samples.
his method permits to study
:- the solid inclusions inside of material - the multielementary profiles of concentration - the superficial homogeneity of material
S- the phasis
For geological and electronical materials (fluorine, oxide
...)analysis, the vali- dity of the SAHA-EGGERT model to determine the ionization factors has been tested successfully.
PRINCIPE and DESCRIPTION
Like a1 l classical mass spectrometers, this apparatus comprises (figure 1)
:- an ion source
- a mass analyzor - a detector.
However, it presents together three original features (ELOY,
1980) (1)- ionization source
=l aser p1 asma created by refl exion absorption mode - mass separator
="time of flight" mode combined with magnetic deviation
- panorama high sensitivity detector (10-16 g)
=electro-optical system.
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1984259
JOURNAL DE PHYSIQUE
Power pulsiaser
E z I l
_ - Mogneltc held
-F---
-
monrtor
- Recofder .
L ASER PROBE MASS SECTROGRAPH (L PMS)
C E A - C E N - G r e n o b l e - GSF Munchen-Neuherberg
Figure 1 : schema o f L.P.M.S. I1
The i o n i z a t i o n o f t h e m a t e r i a l : conductor o r no, mineral o r organic, i s obtained by t h e successive v a p o r i z a t i o n and c r e a t i o n o f a micro-plasma w i t h a focused and pulsed h i g h power l a s e r beam (Nd/YAG l a s e r w i t h frequency t r i p l e r ; X = 0,355 ].[m).
The a n a l y t i c a l l a s e r c o n d i t i o n s are :
-
sampling diameter : a d j u s t a b l e bgtween 3 t o 100 um-
sampling thickness : 200-
2000 A per l a s e r shot impinging b u l k m a t e r i a l s-
f l u x o f focused l a s e r : 1 0 ~ - 1 0 1 0 ~ / c r n z-
l a s e r p u l s e t i m e : 3-4 ns.-
l a s e r energy spread : 0.1 t o 10 u J-
l a s e r plasma temperature : 7.103 - 2.104 K-
l a s e r plasma e l e c t r o n i c d e n s i t y : 1018-
1oZ0 ;/cm3For t h e sample observations, t h e i o n source i s equipped w i t h a b i n o c u l a r and Cassegrain i n v e r t e d o b j e c t i v e combination which provides a m a g n i f i c a t i o n o f G : 300-400 X.
b) !ass-separator
To separate t h e d i f f e r e n t masses i n t h e i o n i c beam, t h e device combines t h e magne- t i c d e v i a t i o n and t h e "time o f f l i g h t " mode. The
L.P.M.S.
system l a y s down c i r c u l a r t r a j e c t o r i e s t o t h e i o n s . I n f i r s t order, t h e "time o f f l i g h t " i s p r o p o r t i o n n a l t o the mass of ions ( t M (us.) = a.M (amu)+
b m+
c,
where a = aiB and b =6.2
and c = c s t e ) .
I t comprises :
-
a long (30 cm) Cu-Be e l e c t r o d e f o r t h e i o n - e l e c t r o n conversion-
a p l a s t i c s c i n t i l l a t o r f o r the electron-photon conversion-
a l i g h t guide f o r t h e photons t r a n s f e r t-
a speady photomul t i p l i e rI t s f a s t g a i n i s about 10 w i t h a time delay o f 2-3 ns. 7
The d e l i v e r e d a n a l y t i c a l s i g n a l s a r e s t o r e d by a t r a n s i e n t recorder (Biomation 6.500 : 1024 channels). A t t h e r e p e t i t i o n r a t e ( 1 shot/sec.) o f t h e l a s e r head the spectra a r e dispatched on v i s u a l scanning and simultaneously i n t o i n t h e memory ( 5 meoabytes) o f a computer.
QUANTITATIVE ANALYTICAL APPLICATIONS
The c a p a b i l i t i e s o f t h i s method t o determine t h e c a r t o g r a p h i c ( d e f i n i t i o n : 2 um) and the l o c a l i z a t i o n o f mineral elements in..depth i n organic o r mineral b u l k samples have a1 ready been demonstrated (UNSOLD, ELOY, 1983) ( 2 ) .
a)
:_tandar!-samele
F i r s t , we w i l l present an example o f organic samples a n a l y s i s ( p o l y e s t e r r e s i n ) charged w i t h a mineral used as standard which p e r m i t s t o measure the d e t e c t i o n l i m i t s . The recorded spectra show ( f i g u r e 2) t h e weak i n t e r f e r e n c e s brought about by t h e p a r t i a l l y i o n i z e d o r g a n i c fragments (CHAMEL, ELOY, 1983) ( 3 ) .
L . P . M S. Ll lb
M ~ S S - s p e c t r a l
S a m p l e : polycsler r e s i n
+ C o ( 3 0 p p m a t . )
Figure 2 : Mass spectrum of CO i n p o l y e s t e r r e s i n (30 ppm a t )
The r e s u l t s o f the s e n s i b i l i t y study are summarized on t h e f i g u r e 3 f o r CO and CS i n t o a p o l y e s t e r r e s i n .
b
~uagtjtatlve-ana~ysis~saeabi1it1~~_
Another o r i g i n a l aspect o f t h i s a n a l y t i c a l method (L.P.M.S. 11) i s i t s p o s s i b i l i t y t o c o r r e c t t h e spectra r e s u l t s and improve t h e i r accuracy.
Indeed t h e o r e t i c a l s t u d i e s of l a s e r i n t e r a c t i o n by LEISING (1973) (4) and TONON (1973) ( 5 ) i n d i c a t e t h a t under our l a s e r i n t e r a c t i o n c o n d i t i o n s , t h e plasma can be considered i n l o c a l thermal e q u i l i b r i u m (L.T.E. ) (Venugopalan, 1970 ( 6 ) . Thus, t h e i o n i z a t i o n y i e l d s f o r a l l elements are t h e o r e t i c a l l y governed by the SAHA-EGGERT law (DELOULE-ELOY, 1982) ( 7 ) . These approximations then p e r m i t an "ELOGET" program c a l - c u l a t e f o r a l l p o s s i b l e cases the e l e c t r o n i c temperature and d e n s i t y o f t h e plasma and the d i s t r i b u t i o n o f each atomic and i o n i c species i n d i f f e r e n t s t a t e s o f charge.
JOURNAL DE PHYSIQUE
5 9
Figure 3 : S e n s i t i v i t y c a l i b r a t i o n curve : ( CO) peak h e i g h t versus t h e concen- t r a t i o n o f CO and CS i n p o l y e s t e r r e s i n .
Also, knowing .the experimental number o f X' ions, the t o t a l atomic q u a n t i t i e s f o r each element can be c a l c u l a t e d . L a s t l y , knowing the r a t i o o f two elements i n c l u d e d i n t o the sampling volume, t h i s program resolves the SAHA-EGGERT equation f o r o n l y one c a l c u l a t e d e l e c t r o n i c temperature and d e n s i t y . These values o f temperature and d e n s i t y f o r the l a s e r plasma p e r m i t then t o c a l c u l a t e t h e c o r r e c t i o n s f a c t o r s f o r a l l o t h e r elements simultaneously detected.
Previously, these above c a l c u l a t i o n s were checked using the mass s p e c t r a o b t a i n e d f o r a s y n t h e t i c and a n a t u r a l c r y s t a l , thereby c o n f i r m i n g t h e v a l i d i t y o f o u r experimen- t a l data. Thus, i t was p o s s i b l e t o c a l c u l a t e the c o r r e c t e d r e s u l t s f o r f l u i d i n - c l usions l i b e r a t e d from n a t u r a l samples ( 7 ) .
The p r e c i s i o n o f t h i s method can be estimated w i t h the f o l l o w i n g example (see f i g u r e 4) concerning t h e p o l y e s t e r r e s i n sample charged w i t h c o b a l t (atomic concen- t r a t i o n : 30 ppm). The measured uncorrected value i s CO = 1534 ppm a t . The correc- t e d c a l c u l a t e d values (see f i g u r e 4) are comprised between 20 t o 40 ppm a t . because the reproduci b i l i t y of t h e l a s e r i o n i z a t i o n c o n d i t i o n s p e r m i t s t o c o n t r o l t h i s tem- p e r a t u r e a t
+
800 K, and then the e r r o r can be reduced t o+
30 % i n t h i s case.CORRECTED AT. C O N C . [CO]
PROG: ELOGET
Figure 4 : V a r i a t i o n of c o r r e c t e d c o b a l t concentrations versus t h e l a s e r plasma temperature
A second c i t e d example, concerned a p o l i s h e d i n d u s t r i a l known glass analyzed a f t e r the 5 f i r s t micrometers o f depth (see corresponding t a b l e o f uncorrected and correc- t e d r e s u l t s ) . The announced composition was obtained w i t h chemical a n a l y s i s .
These c o r r e c t e d r e s u l t s are c a l c u l a t e d w i t h determined e l e c t r o n i c temperature and density, as regard t h e known s t o e c h i o m e t r i c r a t i o f o r 0, Si, Ca, i n the glass sample I n l o o k i n g a t the r e s u l t i n g p r e c i s i o n values, we observe a b e t t e r i n f l u e n c e o f the
TABLE
-
Results o f q u a n t i t a t i v e a n a l y s i s o f i n d u s t r i a l glass w i t h L.P.M.S. I 1 stoechiometric reference : oxygen = 40 ; s i l i c o n = l 0 ; calcium = l-
averages o f twenty mass spectra.p r e c i s i o n %
c o r r e c t i o n program on t h e major elements than on the minor elements (except f o r Cr and MO) concentrations. The heterogeneity o f t h e glass can e x p l a i n these d i f f e r e n - ces.
CONCLUSION
The o r i g i n a l features o f t h i s Laser Probe Mass Spectrograph and t h e e s p e c i a l l y deve- lopped c o r r e c t i o n program a l l o w t h e use o f the L.P.M.S. technique f o r q u a n t i t a t i v e elementary a n a l y s i s . Without sample p r e p a r a t i o n o r any standard analysis, t h i s technique p e r m i t s t o evaluate i m p u r i t i e s concentrations i n m i c r o q u a n t i t i e s o f s o l i d m a t e r i a l s w i t h a s u f f i c i e n t approximation. The obtained a n a l y t i c a l r e s u l t s are n o t r e s t r i c t e d t o t h e s o l i d m a t e r i a l s since t h a t we have a p p l i e d t h i s method t o t h e a n a l y s i s o f gazeous o r f l u i d m i c r o - i n c l u s i o n s ( 7 ) .
4
REFERENCES
( 1 ) J.F. ELOY, Proc. 5 t h I n t e r n a t i o n a l Symposium i n High P u r i t y M a t e r i a l s i n Science and Technology. Dresden (GDR), May 1980, pp 96-110.
( 2 ) E. UNSOLD, J.F. ELOY, Proc. 2nd I n t . Workshop on Trace Element A n a l y t i c a l Che- m i s t r y i n Medicine and Biology, Neuherberg/Munich, Trace element
-
A n a l y t i c a l Chemistry i n Medicine and Biology, Vol. 2, 1983 by Walter de Gruyter and Co., B e r l i n . New York( 3 ) A. CHAMEL, J.F. ELOY
-
J. o f S.E.P. (1983) ( i n p r e s s ) .l
(4) LEISING h!., Laser prepulse v a p o r i z a t i o n o f aluminium w i r e t a r g e t s . Ph.D. Thesis.
Univ. o f Rochester, Rochester N.Y. ( a v a i l a b l e from Univ. M i c r o f i l m . Ann Arbor, Mich. No 73-14, p. 822 (1973).
( 5 ) G.F. TONON, Doct-Ing. Thesis, No 107 Univ. Claude Bernard, LYON (1973) ( 6 ) VENUGOPALAN "Reactions under plasma c o n d i t i o n s " Vol. I, Wiley
-
INterscience,(1970).
( 7 ) DELOULE E. and ELOY J.F.
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Chemical Geology, 37 (1982) 191-202.13 42 10 20 28 65 86 35 53 47 80 24
