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Study of hydrogen content in solids by ERDA and radiation induced damage
839
Nuclear Instrumentsand Methods iu L’hysicsResearch B56/57 (1991) 839-842 North-Holland
Study of hydrogen context in solids by ERDA and ra~ation induced damage J. Tirira a, P. Trocellier ‘, M. Mosbah ’ and N. Metrich ’ ’ Laboratoire Pierre Siie, CEA/DSM/DPhG, b CNRS/Groupe
Saclay* 91191 Gif-sur- Yvette, France des Sciences de la Terre, Luboratoire Pierre Siie, CEA Saclay, 91191 Gif-mr-Yvette, France
A sjm~ation-opt~t~on algorithm (GABY code) is used for hydrogen dete~~~~ in elastic rewil detection analysis (ERDA) induced by 1.8-3 MeV 4He ions. ‘The scattering cross section and the effect of straggling muhiple scattering and geometricalspreadingare taken into account in the simulation.The capabilitiesof this absdute method (in transmissiongeometry} are briefly described in terms of se~iti~ty, probing depth and depth resolution. The hydrogen me~~ernen~ are interpreted in relation to the damage induced by the 4He microbeam. We show that the hydrogen ~st~bu~on can change during the 4He irradiation,dependingon the local structureof the target material. The influenceof large doses and the dose rate are &scussed.Th& procedurehas been appliedusing a nuckar microprobe to study the hydrogendistributionin thin polymer films irradiated by high energy heavy ions (Kr 230 MeV) and natural glasses.
I. Introduction An absolute method for quantitative hydrogen dete~~tion in near-surface regions of solids [1,2] using elastic recoil detection was recently proposed. The method is based on a simulation algorithm of proton elastic recoil induced by a low energy 4He’ beam (-z 3
MeV). Transmission geometry was shown to provide the best analytical conditions for ERDA. Iiowever, both experimental and simulation conditions have to be carefully chosen if an accurate hydrogen depth profile is to be obtained. The present paper includes a schematic description of the calculation procedure used to interpret the recoil spectra. The capabilities of this absolute method are briefly described in terms of sensitivity, probing depth and depth resolution. This procedure is applied using a nuclear mkroprobe to study the hydrogen distribution in thin polymer films irradiated by high energy heavy ions (Kr 2.30 MeV) and natural glasses. The hydrogen measurements are interpreted in terms of the optimal conditions to reduce the damage induced by the 4He microbeam.
2. Basic considerations The theoretical study to describe the 4He/H collision in solids and to interpret the recoil energy spectra has been presented in previous papers f3,4]. In these papers, we proposed an analytical formalism and developed a sim~ation algorithm. 0168~583X/91/$03.50
Since our goal is to carry out the absolute quantitative determination of hydrogen without any reference to a standard sample, we need accurate knowledge of all the parameters involved in both particle-solid interaction and experimental configuration (stopping powers, elastic-recoil cross section, kinematic and geometric factors, energy spreading). To simulate the recoil energy spectrum we built a software code “Gaby” which takes into account all the different parameters. Then the comparison between the simulated and experimental spectra provides quantitative results. The use of this procedure to determine hydrogen depth profiles requires the choice of an initial atomic hydrogen distribution and the knowledge of the relative quantity of the other constituents of the target. The ~ti~tian procedure is then performed according to a maximum likelihood &i-squared definition, so that the distribution of hydrogen and uncertainties can be calculated. The choice of the initial hydrogen ~st~bution is made in relation to the experiment@ spectrum. For exampfe, a Gaussian distribution in the case of hydrogen impl~tation in silicon crystal, or a step-like distribution when the depth profile is unknown. In this latter case, a constant hydrogen density is first chosen for the whole analysed region. This distribution allows an average simulated spectrum to be obtained. The next step consists of calculating the relationship between the experimental spectrum and the previous one; these normalised density v&es can thus be assigned as the initial hydrogen distribution. Some iterations must then be made to obtain a~~rnent between the experimental
@ 1991 - Eketier Science PublishersB.V. ~o~h-~oll~d)
IX. MATERIALS ANALYSIS
840
J. Tirira et al. / ~ete~tnatjon
and simulated spectra. The nonlinear least-squared algorithm employed permits rapid convergence for practical problems. This procedure allows the quantitative hydrogen distribution in near-surface regions of solids to be determined in absolute mode (without a standard).
of hydrogen conrent by ERDA
and the typical beam area was (50 x 50) pm*. The recoiled protons were recorded at O” with a surface barrier detector preceded by a 4 mm diameter cohimator leading to a solid angle of 1.48( kO.02) x 10v3 sr. The incident 4He+ energy is chosen as a function of the sample thickness so as to obviate the need of an absorber foil in front of the detector.
3. Analytical capabilities 4.2. Samples 3.1. Geometry
Around 8 = O” (detection angle), the variations of do/d9 are very smooth with respect to 8 in the usual energy range (EHe) < 4 MeV) [l]. For energies > 2.8 MeV the highest da/da values are reached for 8 = 0 O. Selectivity is optimized at this angle. These findings strongly suggest that transmission geometry at 0 = O” offers the best analytical conditions. 3.2. Probing depth The probing depth depends both on incident energy and sample thickness. For example, in polymer films, the total analysed depth varies from 2 to 6 pm between 1.8 and 3 MeV for 12.5 and 25 urn thickness respectively. This should be compared with the range 0.3-O-5 pm obtained in glancing geometry.
3.3. Depth resolution It should be pointed out that as the incident beam penetrates the sample, the energy of the projectiles decreases and the stopping power increases. On the other hand, the total energy resolution of the detection setup resolution, the geometrical resoiution, the energy straggling and the multiple scattering contribution does not vary as greatly as the stopping power [l]. Consequently, as depth increases, the energy decreases, but the depth resolution improves. For example, in a 25 pm thick polymer the depth resolution varies from 40 to 30 nm between the surface and 6 pm depth.
4. Experimental
The samples examined were, on one hand, thin Kapton films (Ca,H,,O,N,) rn~ufact~~ by DuPont de Nemours of 12.5 and 25 urn thickness. The sample surface (1 cm’) was coated with a 105( f5) nm gold layer. The 12.5 pm thick Kapton foil was irradiated (fluence 1.4 X lo9 cme2 s-l) by 230 MeV krypton ions. The samples were mounted on a target holder over a 1 mm diameter hole. In addition, both typical H,O-rich metaluminous rhyolite and submarine tholeiitic pillow-lava glasses have been studied for hydrogen. H,O was previously determined by weight loss or as OH- and molecular Ha0 by Fourier-transformed infrared spectrometry microanalysis. The OH- and Ha0 concentrations were obtained using a Bruker IFS 88 FT IR (CNRS-Nancy) equipped with a Brucker A590 microscope [S] and the absorptivity coefficients published by Newman et al. [6] for rhyolite and Stolper and Holloway [7] for basaltic compositions. The amounts of water in the samples are: (1) rhyolite from Valles Caldera in New Mexico [8], doped in H,O at 1 kbar and 830” C, (RCL56-6) Ha0 = 3.90 + 0.4 wt.% similar to all the previous published data [8,9]; (2) H,O-rich rhyolitic melt inclusion, (Guad) Ha0 = 4.3 + 0.3 wt.%; (3) submarine tholeiitic glass, Mid-Atlantic Ridge LEG2, (2nD45) Ha0 = 0.42 wt.% (whole rock analysis), Hz0 = 0.67 It 0.1 wt.% (FT-IR ~cro~~ysis), and (4) submarine tholeiitic glass from the East Pacific Rise (CY82 293V) Ha0 = 0.19 wt.% [lo]. Thin polished double-faced sections of these glasses were prepared. The mean thickness was 25 urn. They were polished with Also, (until 0.3 pm grain size), and then mounted on a target holder over a 1 mm diameter hole and gold coated (100 f 5 nm).
4.1. ERDA in transmission geometry
5. Results The hydrogen transmission measurements were conducted in the analysis chamber of the Bruyeres le Chltel French nuclear microprobe facility. The 4Het beam was delivered by a 4 MV Van de Graaff accelerator. The beam line is equipped with an adjustable object aperture and a magnetic quadruplet (Harwell system). The vacuum was maintained around 2 X 10T6 Torr. To minimize the hydrogen loss due to energy deposits, the beam intensity was set at the low value of 2 PA/cm2
5.1. Microbeam damage effects
The study of microbeam damage was carried out because the large dose and dose rates of 4He ions applied in microbeam analysis can result in significant damage for polymer and glass targets [3], affecting, for example, the variation of the composition in the sample. We particularly studied the variation of the hydrogen
J. Xirira et al. / Determination of hydrogen conks
00
841
by ERDA
pm (the range of 3 MeV 4He+ ions is roughly 14 urn) and the homogeneous hydrogen density is 2.5( kO.2) X 10” H/cm3 which agrees with the original composition (sto~~~omet~). The 12.5 pm thin Kapton foil previously irradiated with 200 MeV krypton ions was analysed with a 2.05 MeV 4He” microbeam. In contrast to the previous case, the shape of the hydrogen depth profile is not constant (fig. 2). Two main analysed regions appear: the first, flat, corresponding to a homogeneous hydrogen density of 2.05( iO.15) X 10” H’/cm3 from the surface to a depth of about 2 pm; and the second one corresponding to a double peak of high concentration located 2.5
Fig. 1. Hydrogen concentration in Kapton films as a function of charge per unit area for different beam currents: (a) 14.8 @/‘cmz; @) 7.8 ~A/cm2; and (c>2.6 pA,‘cm2_
content in the target films (Kapton, glass) as determined from the yield of the recoil protons. These measurements were performed with different doses and for different current densities. They can be used as an indication of damage rates in the target under microbeam irradiations with 3 MeV 4He. Fig” 1 shows hydrogen loss in Kapton film as a function of the dose per unit area. The irradiations were carried out at room temperature with the following beam intensities: (a) I= 14.8 uA/cm’; (b) I= 7.8 PA/Cm27 and (c) I= 2-6 PA/cm’. The beam was scanned over 400 pm X 400 pm. Rose rate effects are clearly significant for cases (a) and (b). However, the damage in Kapton for (c) may be minimised by either reducing the dose or the beam intensity. In the case of glass samples, the damage effects do not significantly change in reIation to the Kapton films for hydrogen measurements and the lowest beam intensity allows the largest dose without significant damage. Nevertheless high current density such as 20 PA/cm’ produces some damage in the analysed region: the beam impact is visible under the mmroscope and the concentration of some major elements varies. For examples Na,O content (measured using an electron microprobe) is significantly affected (10%) in rhyolite glasses, Based upon these observations, optimal beam density was set to get the low value of 2 pA,/cm2. Finally, the heating effects were minimised by reducing the diameter of the sample holder bole so that the distance between the beam spot position and the holeside is smaller ( < 1 mm). This consideration agrees well with Talmon and Thomas’ calculations for the heating effects [ll].
The 25 pm thick Kapton foil was analysed with a 3 MeV 4Hef microbeam. The total analysed depth is 6.2
and 2.8( fQ.1) Frn beneath the surface. In this case the primary damage due to the krypton bombardment left a metastable system and the 4He+ beam caused the high hydrogen distribution to evolve. It is difficult to study such an irradiated material in an absolute way, but a first approach can be made. The glass samples were analysed with a 3 MeV 4He’ microbeam. Hydrogen densities are presented as a function of water content in glasses (fig. 3), where each
Anatysed
\ sao
600
ENERGY
DEPiH
900
(Key)
(JW)
Fig. 2. (a) Recoil proton spectrum from krypton-irradiated Kapton foil, Dotted line: experimentaI spectrum; solid line: simulated spectrwn. A s&exnatic ERDA configuration is shown. &b)Hydrogen atomic density profaes derived from the above experimentatrecoil spectrum us&g the Gaby code. IX. MATERIALS ANALYSIS
842
.T. ‘II&a et al / Dete~m~n~io~of hydrogen content by ERDA
dose rates which can be applied over a small area. The damage effects are different for each material (structural, chemical) but the optimal beam conditions and dose rates enable us to minimise these effects. This study must be extended so that both the damage effects and their influence on the quantitative analysis can be interpreted. Finally, the semi-automatic simulation algorithm provides a powerful method of studying both the hydrogen content in solids and the role of each parameter in the ERDA configuration.
2.00 r
7
fj 0
“N 0 d
1.50 -
1.00 -
1 .
%‘0.00 0.00
L 1.00
’
( 2.00
’ 3.00
*
I
4.00
5.00
Hz0 wt.% Fig. 3. Hydrogen atomic densities of natural glasses (ERDA) as a function of water content (FT-IR).
point represents an average hydrogen density value obtained from different points of several fragments of the same glass sample. Reproductibility of the measurements is confirmed with an accuracy of 9% for concentration greater than 0.4 Hz0 wt.%. There is an apparent correlation between the determined H density and the total water content of the glasses. This work must be extended so that these results can be further interpreted. In particular a more complete range of I&O-rich samples must be investigated so that the relation between H and H,O in complex silicate glasses can be studied in more detail.
6. Conclusion Hydrogen distributions were determined by ERDA in absolute mode (without a standard) using the simulation-opti~ation algorithm “Gaby Code”. This procedure was applied to study Kapton foils and natural glasses. The results with a 4He microbeam show that upper limits exist for the size of doses and
Acknowledgements The authors would like to express special thanks and appreciation to Dr. J.P. Frontier for his hard work and valuable suggestions.
References [l] J. Tirira, P. Trocellier and J.P. Frontier, Nucl. Instr. and Meth. B45 (1990) 147. [2] J. Tirira., P. Trocellier, J.P. Frontier et al., Nucl. Instr. and Meth. B.50 (1990) 155. [3] J. Tirira, P. Trocellier, J.P. Frontier and P. Trouslard, Nucl. Ins&. and Meth. B45 (1990) 203. [4] J. Tirira, J.P. Frontier, P. Trocellier and P. Trouslard, Nucl. Instr. and Meth. B54 (1991) 328 (2nd Int. Conf. on Nuclear Microprobe Technology and Applications, Melbourne, Australia, 1990). [5] J. Pironon and 0. Barres, Geochim. Cosmocbim. Acta 54 (1990) 509. [6] S. Newman, E. Stolper and S. Epstein, Am. Mineral. 71 (1986) 1527. [7] E. St7ilper and J.R. Holloway, Earth Planet. Sci. Lett. 87 (1988) 397. [S] R. Fo8ge1, Ph.D. thesis, Brown Univ. (1989) p. 200. (91 H. Shaw, Carnegie Inst., Washington Pub. 634 (1977) 132. [lo] R. Hekinian and Y. Fouquet, Econ. Geol. 80 (1985) 221. [11] Y. Talmon and E.L. Thomas, J. Microsc. 111 (1977) 151.
Nuclear Instrumentsand Methods iu L’hysicsResearch B56/57 (1991) 839-842 North-Holland
Study of hydrogen context in solids by ERDA and ra~ation induced damage J. Tirira a, P. Trocellier ‘, M. Mosbah ’ and N. Metrich ’ ’ Laboratoire Pierre Siie, CEA/DSM/DPhG, b CNRS/Groupe
Saclay* 91191 Gif-sur- Yvette, France des Sciences de la Terre, Luboratoire Pierre Siie, CEA Saclay, 91191 Gif-mr-Yvette, France
A sjm~ation-opt~t~on algorithm (GABY code) is used for hydrogen dete~~~~ in elastic rewil detection analysis (ERDA) induced by 1.8-3 MeV 4He ions. ‘The scattering cross section and the effect of straggling muhiple scattering and geometricalspreadingare taken into account in the simulation.The capabilitiesof this absdute method (in transmissiongeometry} are briefly described in terms of se~iti~ty, probing depth and depth resolution. The hydrogen me~~ernen~ are interpreted in relation to the damage induced by the 4He microbeam. We show that the hydrogen ~st~bu~on can change during the 4He irradiation,dependingon the local structureof the target material. The influenceof large doses and the dose rate are &scussed.Th& procedurehas been appliedusing a nuckar microprobe to study the hydrogendistributionin thin polymer films irradiated by high energy heavy ions (Kr 230 MeV) and natural glasses.
I. Introduction An absolute method for quantitative hydrogen dete~~tion in near-surface regions of solids [1,2] using elastic recoil detection was recently proposed. The method is based on a simulation algorithm of proton elastic recoil induced by a low energy 4He’ beam (-z 3
MeV). Transmission geometry was shown to provide the best analytical conditions for ERDA. Iiowever, both experimental and simulation conditions have to be carefully chosen if an accurate hydrogen depth profile is to be obtained. The present paper includes a schematic description of the calculation procedure used to interpret the recoil spectra. The capabilities of this absolute method are briefly described in terms of sensitivity, probing depth and depth resolution. This procedure is applied using a nuclear mkroprobe to study the hydrogen distribution in thin polymer films irradiated by high energy heavy ions (Kr 2.30 MeV) and natural glasses. The hydrogen measurements are interpreted in terms of the optimal conditions to reduce the damage induced by the 4He microbeam.
2. Basic considerations The theoretical study to describe the 4He/H collision in solids and to interpret the recoil energy spectra has been presented in previous papers f3,4]. In these papers, we proposed an analytical formalism and developed a sim~ation algorithm. 0168~583X/91/$03.50
Since our goal is to carry out the absolute quantitative determination of hydrogen without any reference to a standard sample, we need accurate knowledge of all the parameters involved in both particle-solid interaction and experimental configuration (stopping powers, elastic-recoil cross section, kinematic and geometric factors, energy spreading). To simulate the recoil energy spectrum we built a software code “Gaby” which takes into account all the different parameters. Then the comparison between the simulated and experimental spectra provides quantitative results. The use of this procedure to determine hydrogen depth profiles requires the choice of an initial atomic hydrogen distribution and the knowledge of the relative quantity of the other constituents of the target. The ~ti~tian procedure is then performed according to a maximum likelihood &i-squared definition, so that the distribution of hydrogen and uncertainties can be calculated. The choice of the initial hydrogen ~st~bution is made in relation to the experiment@ spectrum. For exampfe, a Gaussian distribution in the case of hydrogen impl~tation in silicon crystal, or a step-like distribution when the depth profile is unknown. In this latter case, a constant hydrogen density is first chosen for the whole analysed region. This distribution allows an average simulated spectrum to be obtained. The next step consists of calculating the relationship between the experimental spectrum and the previous one; these normalised density v&es can thus be assigned as the initial hydrogen distribution. Some iterations must then be made to obtain a~~rnent between the experimental
@ 1991 - Eketier Science PublishersB.V. ~o~h-~oll~d)
IX. MATERIALS ANALYSIS
840
J. Tirira et al. / ~ete~tnatjon
and simulated spectra. The nonlinear least-squared algorithm employed permits rapid convergence for practical problems. This procedure allows the quantitative hydrogen distribution in near-surface regions of solids to be determined in absolute mode (without a standard).
of hydrogen conrent by ERDA
and the typical beam area was (50 x 50) pm*. The recoiled protons were recorded at O” with a surface barrier detector preceded by a 4 mm diameter cohimator leading to a solid angle of 1.48( kO.02) x 10v3 sr. The incident 4He+ energy is chosen as a function of the sample thickness so as to obviate the need of an absorber foil in front of the detector.
3. Analytical capabilities 4.2. Samples 3.1. Geometry
Around 8 = O” (detection angle), the variations of do/d9 are very smooth with respect to 8 in the usual energy range (EHe) < 4 MeV) [l]. For energies > 2.8 MeV the highest da/da values are reached for 8 = 0 O. Selectivity is optimized at this angle. These findings strongly suggest that transmission geometry at 0 = O” offers the best analytical conditions. 3.2. Probing depth The probing depth depends both on incident energy and sample thickness. For example, in polymer films, the total analysed depth varies from 2 to 6 pm between 1.8 and 3 MeV for 12.5 and 25 urn thickness respectively. This should be compared with the range 0.3-O-5 pm obtained in glancing geometry.
3.3. Depth resolution It should be pointed out that as the incident beam penetrates the sample, the energy of the projectiles decreases and the stopping power increases. On the other hand, the total energy resolution of the detection setup resolution, the geometrical resoiution, the energy straggling and the multiple scattering contribution does not vary as greatly as the stopping power [l]. Consequently, as depth increases, the energy decreases, but the depth resolution improves. For example, in a 25 pm thick polymer the depth resolution varies from 40 to 30 nm between the surface and 6 pm depth.
4. Experimental
The samples examined were, on one hand, thin Kapton films (Ca,H,,O,N,) rn~ufact~~ by DuPont de Nemours of 12.5 and 25 urn thickness. The sample surface (1 cm’) was coated with a 105( f5) nm gold layer. The 12.5 pm thick Kapton foil was irradiated (fluence 1.4 X lo9 cme2 s-l) by 230 MeV krypton ions. The samples were mounted on a target holder over a 1 mm diameter hole. In addition, both typical H,O-rich metaluminous rhyolite and submarine tholeiitic pillow-lava glasses have been studied for hydrogen. H,O was previously determined by weight loss or as OH- and molecular Ha0 by Fourier-transformed infrared spectrometry microanalysis. The OH- and Ha0 concentrations were obtained using a Bruker IFS 88 FT IR (CNRS-Nancy) equipped with a Brucker A590 microscope [S] and the absorptivity coefficients published by Newman et al. [6] for rhyolite and Stolper and Holloway [7] for basaltic compositions. The amounts of water in the samples are: (1) rhyolite from Valles Caldera in New Mexico [8], doped in H,O at 1 kbar and 830” C, (RCL56-6) Ha0 = 3.90 + 0.4 wt.% similar to all the previous published data [8,9]; (2) H,O-rich rhyolitic melt inclusion, (Guad) Ha0 = 4.3 + 0.3 wt.%; (3) submarine tholeiitic glass, Mid-Atlantic Ridge LEG2, (2nD45) Ha0 = 0.42 wt.% (whole rock analysis), Hz0 = 0.67 It 0.1 wt.% (FT-IR ~cro~~ysis), and (4) submarine tholeiitic glass from the East Pacific Rise (CY82 293V) Ha0 = 0.19 wt.% [lo]. Thin polished double-faced sections of these glasses were prepared. The mean thickness was 25 urn. They were polished with Also, (until 0.3 pm grain size), and then mounted on a target holder over a 1 mm diameter hole and gold coated (100 f 5 nm).
4.1. ERDA in transmission geometry
5. Results The hydrogen transmission measurements were conducted in the analysis chamber of the Bruyeres le Chltel French nuclear microprobe facility. The 4Het beam was delivered by a 4 MV Van de Graaff accelerator. The beam line is equipped with an adjustable object aperture and a magnetic quadruplet (Harwell system). The vacuum was maintained around 2 X 10T6 Torr. To minimize the hydrogen loss due to energy deposits, the beam intensity was set at the low value of 2 PA/cm2
5.1. Microbeam damage effects
The study of microbeam damage was carried out because the large dose and dose rates of 4He ions applied in microbeam analysis can result in significant damage for polymer and glass targets [3], affecting, for example, the variation of the composition in the sample. We particularly studied the variation of the hydrogen
J. Xirira et al. / Determination of hydrogen conks
00
841
by ERDA
pm (the range of 3 MeV 4He+ ions is roughly 14 urn) and the homogeneous hydrogen density is 2.5( kO.2) X 10” H/cm3 which agrees with the original composition (sto~~~omet~). The 12.5 pm thin Kapton foil previously irradiated with 200 MeV krypton ions was analysed with a 2.05 MeV 4He” microbeam. In contrast to the previous case, the shape of the hydrogen depth profile is not constant (fig. 2). Two main analysed regions appear: the first, flat, corresponding to a homogeneous hydrogen density of 2.05( iO.15) X 10” H’/cm3 from the surface to a depth of about 2 pm; and the second one corresponding to a double peak of high concentration located 2.5
Fig. 1. Hydrogen concentration in Kapton films as a function of charge per unit area for different beam currents: (a) 14.8 @/‘cmz; @) 7.8 ~A/cm2; and (c>2.6 pA,‘cm2_
content in the target films (Kapton, glass) as determined from the yield of the recoil protons. These measurements were performed with different doses and for different current densities. They can be used as an indication of damage rates in the target under microbeam irradiations with 3 MeV 4He. Fig” 1 shows hydrogen loss in Kapton film as a function of the dose per unit area. The irradiations were carried out at room temperature with the following beam intensities: (a) I= 14.8 uA/cm’; (b) I= 7.8 PA/Cm27 and (c) I= 2-6 PA/cm’. The beam was scanned over 400 pm X 400 pm. Rose rate effects are clearly significant for cases (a) and (b). However, the damage in Kapton for (c) may be minimised by either reducing the dose or the beam intensity. In the case of glass samples, the damage effects do not significantly change in reIation to the Kapton films for hydrogen measurements and the lowest beam intensity allows the largest dose without significant damage. Nevertheless high current density such as 20 PA/cm’ produces some damage in the analysed region: the beam impact is visible under the mmroscope and the concentration of some major elements varies. For examples Na,O content (measured using an electron microprobe) is significantly affected (10%) in rhyolite glasses, Based upon these observations, optimal beam density was set to get the low value of 2 pA,/cm2. Finally, the heating effects were minimised by reducing the diameter of the sample holder bole so that the distance between the beam spot position and the holeside is smaller ( < 1 mm). This consideration agrees well with Talmon and Thomas’ calculations for the heating effects [ll].
The 25 pm thick Kapton foil was analysed with a 3 MeV 4Hef microbeam. The total analysed depth is 6.2
and 2.8( fQ.1) Frn beneath the surface. In this case the primary damage due to the krypton bombardment left a metastable system and the 4He+ beam caused the high hydrogen distribution to evolve. It is difficult to study such an irradiated material in an absolute way, but a first approach can be made. The glass samples were analysed with a 3 MeV 4He’ microbeam. Hydrogen densities are presented as a function of water content in glasses (fig. 3), where each
Anatysed
\ sao
600
ENERGY
DEPiH
900
(Key)
(JW)
Fig. 2. (a) Recoil proton spectrum from krypton-irradiated Kapton foil, Dotted line: experimentaI spectrum; solid line: simulated spectrwn. A s&exnatic ERDA configuration is shown. &b)Hydrogen atomic density profaes derived from the above experimentatrecoil spectrum us&g the Gaby code. IX. MATERIALS ANALYSIS
842
.T. ‘II&a et al / Dete~m~n~io~of hydrogen content by ERDA
dose rates which can be applied over a small area. The damage effects are different for each material (structural, chemical) but the optimal beam conditions and dose rates enable us to minimise these effects. This study must be extended so that both the damage effects and their influence on the quantitative analysis can be interpreted. Finally, the semi-automatic simulation algorithm provides a powerful method of studying both the hydrogen content in solids and the role of each parameter in the ERDA configuration.
2.00 r
7
fj 0
“N 0 d
1.50 -
1.00 -
1 .
%‘0.00 0.00
L 1.00
’
( 2.00
’ 3.00
*
I
4.00
5.00
Hz0 wt.% Fig. 3. Hydrogen atomic densities of natural glasses (ERDA) as a function of water content (FT-IR).
point represents an average hydrogen density value obtained from different points of several fragments of the same glass sample. Reproductibility of the measurements is confirmed with an accuracy of 9% for concentration greater than 0.4 Hz0 wt.%. There is an apparent correlation between the determined H density and the total water content of the glasses. This work must be extended so that these results can be further interpreted. In particular a more complete range of I&O-rich samples must be investigated so that the relation between H and H,O in complex silicate glasses can be studied in more detail.
6. Conclusion Hydrogen distributions were determined by ERDA in absolute mode (without a standard) using the simulation-opti~ation algorithm “Gaby Code”. This procedure was applied to study Kapton foils and natural glasses. The results with a 4He microbeam show that upper limits exist for the size of doses and
Acknowledgements The authors would like to express special thanks and appreciation to Dr. J.P. Frontier for his hard work and valuable suggestions.
References [l] J. Tirira, P. Trocellier and J.P. Frontier, Nucl. Instr. and Meth. B45 (1990) 147. [2] J. Tirira., P. Trocellier, J.P. Frontier et al., Nucl. Instr. and Meth. B.50 (1990) 155. [3] J. Tirira, P. Trocellier, J.P. Frontier and P. Trouslard, Nucl. Ins&. and Meth. B45 (1990) 203. [4] J. Tirira, J.P. Frontier, P. Trocellier and P. Trouslard, Nucl. Instr. and Meth. B54 (1991) 328 (2nd Int. Conf. on Nuclear Microprobe Technology and Applications, Melbourne, Australia, 1990). [5] J. Pironon and 0. Barres, Geochim. Cosmocbim. Acta 54 (1990) 509. [6] S. Newman, E. Stolper and S. Epstein, Am. Mineral. 71 (1986) 1527. [7] E. St7ilper and J.R. Holloway, Earth Planet. Sci. Lett. 87 (1988) 397. [S] R. Fo8ge1, Ph.D. thesis, Brown Univ. (1989) p. 200. (91 H. Shaw, Carnegie Inst., Washington Pub. 634 (1977) 132. [lo] R. Hekinian and Y. Fouquet, Econ. Geol. 80 (1985) 221. [11] Y. Talmon and E.L. Thomas, J. Microsc. 111 (1977) 151.