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X-ray line broadening in electrodeposited gold coatings
139
Electrodeposition and Surface Treatment, 3 (1975) 139 - 144 0 ElsevierSequoia S.A., Lausanne- Printedin Switzerland
X-RAY LINE BROADENING COATINGS
IN ELECTRODEPOSITED
GOLD
L. REVAY Materials
Labomtory,
LM Ericsson
Telephone
Company,
S-126 25 Stockholm
(Sweden)
(Received December 13, 1974)
Summary X-ray line broadening studies of electrodeposited gold coatings with different deposition variables and annealing treatments have been made. Dislocation densities estimated from X-ray data on domain size and lattice strains have been shown to increase with increasing cobalt content and deposition rate; an annealing treatment reduced the dislocation level in the deposits.
Introduction Analysis of X-ray line broadening has been shown to be a useful tool in studying the structure of electrodeposited metals. Although this technique is indirect it has the advantage of being able to yield quantitative structural information not obtainable by microscopy. X-ray (or electron) diffraction is the only other way to measure microstrain. The analysis reveals the microstructure of crystalline materials in terms of coherently diffracting domain sizes and microstrains within these domains. Few studies employing X-ray techniques have been made in electrodeposited gold coatings to obtain information regarding the microstructure. X-ray line broadening analysis of gold films of 2700 and 6500 A has been made by Wook and Witt [ 11. Analysis of the broadened X-ray reflections in epitaxial electrodeposits (< 1500 A) of gold on (lOO)-faces of single crystal copper substrates was used to obtain the microstrain by Thompson and Lawless [ 21. Determination of crystallite size and non-uniform microstrains in gold films by X-ray analysis was reported by Atasagum and Wook [ 31. Recently, structure and properties of electrodeposited gold and gold alloy coatings have been investigated by Dettke and Riedel [4] who exploited 10 gold reflexes for the line broadening analysis; a method similar to that employed by Fischer and Binder [ 51. The microstrain and effective domain size values reported here are based on analysis only of the profiles of the (111)-(222) gold reflexes. The present investigation aims to demonstrate the use of a relatively simple
140
analysis of the line broadening in an X-ray diffraction pattern from the gold deposits. The gold layers were deposited on different polycrystalline metal substrates or interposed layers which caused complications due to the overlapping reflexes from the substrates. Measurements were therefore performed only on reflexes (111 and 222) which are not disturbed by reflexes from the substrate. Despite this analysis limitation this technique is very sensitive to small changes in the structure of electrodeposits. Experimental
procedures
The measurements were made using a commercially available Philips X-ray diffractometer equipped with a lithium-fluoride monochromator in the diffracted beam and a scintillation detector with pulse height discriminator in the counting circuit. For excitation of Cu-Koc radiation a highly stabilised Philips X-ray generator operating at 40 kV and 20 mA was used. To get appreciable intensity 1” divergent and scatter slits were employed. The profiles of the gold reflexes were chart recorded at room temperature at a scanning speed of l/8 (28 ) per minute and a recorder speed of 800 mm/h. For all samples the higher order reflections were relatively weak and only the first two reflections (ill)-(222) could be considered for line broadening measurements. For determination of Kol, integral breadths a graphical a-doublet correction was applied [6, 71. It was considered that the method should be as simple as possible, thus the integral breadth was taken as a measure of the broadening rather than fitting a Fourier series to the peak. The diffraction line half width B’ is related to the integral breadth B as follows: B = %nB’. B’ was measured and B calculated. The pure diffraction integral breadths (0) were obtained by using the parabolic equation as suggested by Anantharaman [8] : /3 = B -
b2/B
(1)
where B is the observed integral breadth and b is representative of the instrumental conditions. The use of this equation has been justified by satisfactory agreement with Fourier data. The required b values at appropriate 20 values were taken from a plot of b us. 20 obtained with annealed gold, zinc and silicon standards. The measured values of B and calculated values of p for two reflections in gold are given in Table I. Analysis
of X-ray line broadening
A separation of domain size and lattice strain contribution to X-ray line broadening can be effected by assuming a relation analogous to the parabolic equation (1) used for elimination of instrumental broadening [8]. This principle can be written in the following way [9, lo] : PD
=P-6:/b
(2)
141 TABLE I Integral breadth of X-ray reflections in electrodeposited Sample
(222)
(111) b
B
B
b
P
X lo3 radians Standard A B C D E F G H I J K L M N 0 P
gold
X
P
lo3 radians
2.62
2.41 9.63 11.12 12.03 10.68 12.44 7.71 6.82 8.15 7.05 8.99 7.05 8.94 8.62 9.15 6.56 6.74
9.03
10.70 11.52 10.28 11.99 6.98 5.99 7.45 6.23 8.36 6.23 8.60 8.05 8.52 5.50 5.85
17.09 19.55 21.45 17.72 23.53 13.44 10.04 13.96 10.56 17.00 12.46 15.48 14.76 16.46 8.92 11.38
16.67 19.22 21.15 17.33 23.24 12.95 9.35 13.49 9.93 16.61 11.92 15.04 14.31 16.06 8.16 10.81
where po is the integral breadth related to the effective domain size D, and p, is the integral breadth related to the non-uniform lattice strain (microstrain) E. Substituting in equation (2) the formulae h PD = D, cost9
(3)
p, = 4E tane
(4)
and gives case fly =‘+
16e2sin20
(5) m0se . e In the above equations X is the wavelength of X-ray radiation used and 0 is the Bragg angle. A plot of (p cos 0 /X) us. (16 e2sin2B/PX cos 0) gives a straight line with a slope of e2 and an intercept of l/D,. Consequently by plotting these expressions for two orders of the same reflection, it is possible to separate D, from E. The integral breadth method for separation of microstrain and effective domain size is also dependent on the fact that the strain is a function of the order of reflection while the effective domain size is not.
142
D, includes broadening effects due to both the domain size and faulting [ll] respectively. In this particular case the fault-unaffected (111) reflex was used and consequently the intercept in the above plot will be l/D, = l/D, where D is the true domain size. Results and discussion The plotted data of (/3 cos e/h) uersus (16 e2 sin2 19//3X cos 0) (Fig. 1) show the influence of deposition conditions on strained domain size and are representative of a large number of diffraction profiles recorded in this study. Table II presents the type of electrodeposited layers for which this technique is applied. A rough estimate of the dislocation density Nd (lines/cm2) in electrodeposited gold layers was made from the measured domain size and lattice strain values (see Table II) by using an equation deduced from the work of Williamson and Smallman [ 121. The equation is strictly valid only if some restricting assumptions are satisfied: N
(7)
d
K is a constant depending on strain distribution function (as here assumed = 12), $= Burgers vector (= a/J2), a = gold lattice parameter. It is interesting to observe (Table II) that both the microstrain and the estimated dislocation density values varied in a way similar to the variation of microhardness. It is thus considered that microstrain measurement may be a substitute for hardness determination in the case of thin electrodeposits for which an accurate determination of hardness is difficult.
430
OJO
p.xlisin’0 16
450 in
070
i-;’
Fig. 1. Plots of (p cos e/h) us. (16 E2sin2e/flx cos 0) for electrodeposited
gold coatings.
(g/I)
(g/I)
0.30
0.15
0.15 0.30
x
20 mm2.
alkaline “soft gold” same
acid “hard gold” same same
SSllle
0.30 0.05
same
3.8 3.6 3.5 3.8 3.6 acid “hard gold”
PH
Bath character,
0.15
0.05
0.24 0.15 0.10 0.60 0.32
Deposition rate Wmin)
* Thickness 4 pm; dimension for specimens 20
-
-
-
0
P
-
-
-
-
M N
L
-
0.10 1.12 2.38 0.10 1.12 -
Cobalt additive
Gold concentration
Deposition conditions
A 10.4 B 4.1 C 3.0 D 10.4 E 4.7 F as deposited G annealed (200 “C: 1 hour in air) H as deposited _ I annealed J as deposited _ K annealed
Specimens
Deposition variables and measured structural parameters
TABLE II
2
2
2 2
2
10
2
2
5.4 5.2 4.2 5.7 6.5
(pm)
Gold coating thickness
238 192 188 192 204 328 303 290 298 322 370
-.\.___
same
same
392
322
.____
D (A)
Domain size,
Ni inter244 mediate layer* same 263 same 274
NiFe same same same same Ni intermediate layer* Cu intermediate layer* Ag intermediate layer*
Substrate
2.30
1.10
3.15 3.67
2.90
3.34 3.67 4.24 3.08 5.00 2.68 1.41 2.68 1.59 3.74 2.52
Micro strain (E x 103)
1.22
0.71
2.50 2.79
-
105
-
-
180 149 183 154 178 152
1.71 0.97 1.93 1.11 2.42 1.42 2.48
-
Hardness HK 0.005 (kg/mm2)
2.92.10’1 3.98 4.70 3.34 5.10
Eetimated dislocation densities Nd x 1011 (iines/cm2)
Measured structural properties
144
A detailed analysis of the structure is limited by the substrate overlapping effects and weak reflexes. The techniques described can therefore be expected to give only an approximate picture of the microstrain and average domain size. The estimated dislocation density of electrodeposited gold layer is typical for electrodeposits and also corresponds to that in the cold worked state. Despite their approximate nature, the measured values have correlated with electrodeposition parameters. Acknowledgements The author thanks Dr. U. Lindborg for suggesting these investigations, and department manager E. Edman for support of the work. References 1 2 3 4 5 6 7 8 9 10
R. W. Wook and F. Witt, J. Vat. Sci. Technol., (1965) 243. E. R. Thompson and K. R. Lawless, Electrochim. Acta, 14 (1969) 269. M. Atasagum and R. W. Wook, J. Vat. Sci. Technol., 362 (1970). M. Dettke and W. Riedel, Oberfhache-Surface, 14 (5) (1973) 130. H. Binder and H. Fischer, Metalloberfltiche, 17 (10) (1963) 295. A. Taylor, X-ray Metallography, Wiley, London, 1961. H. P. Klug and L. E. Alexander, X-ray Diffraction Procedures, Wiley, London, 1954. T. R. Anantharaman and P. Rama Rao, Z. Metallk., 54 (11) (1963) 658. N. C. Halder and C. N. J. Wagner, Acta Cry&, 20 (1966) 312. C. N. J. Wagner, Local atomic arrangements studied by X-ray diffraction, Metallurgical Sot. Conf. Chicago (1965) p. 217. 11 B. E. Warren, X-ray Diffraction, Addison-Wesley, 1969. 12 G. K. Williamson and R. E. Smallman, Phil. Mag., 1 (1956) 34.
Electrodeposition and Surface Treatment, 3 (1975) 139 - 144 0 ElsevierSequoia S.A., Lausanne- Printedin Switzerland
X-RAY LINE BROADENING COATINGS
IN ELECTRODEPOSITED
GOLD
L. REVAY Materials
Labomtory,
LM Ericsson
Telephone
Company,
S-126 25 Stockholm
(Sweden)
(Received December 13, 1974)
Summary X-ray line broadening studies of electrodeposited gold coatings with different deposition variables and annealing treatments have been made. Dislocation densities estimated from X-ray data on domain size and lattice strains have been shown to increase with increasing cobalt content and deposition rate; an annealing treatment reduced the dislocation level in the deposits.
Introduction Analysis of X-ray line broadening has been shown to be a useful tool in studying the structure of electrodeposited metals. Although this technique is indirect it has the advantage of being able to yield quantitative structural information not obtainable by microscopy. X-ray (or electron) diffraction is the only other way to measure microstrain. The analysis reveals the microstructure of crystalline materials in terms of coherently diffracting domain sizes and microstrains within these domains. Few studies employing X-ray techniques have been made in electrodeposited gold coatings to obtain information regarding the microstructure. X-ray line broadening analysis of gold films of 2700 and 6500 A has been made by Wook and Witt [ 11. Analysis of the broadened X-ray reflections in epitaxial electrodeposits (< 1500 A) of gold on (lOO)-faces of single crystal copper substrates was used to obtain the microstrain by Thompson and Lawless [ 21. Determination of crystallite size and non-uniform microstrains in gold films by X-ray analysis was reported by Atasagum and Wook [ 31. Recently, structure and properties of electrodeposited gold and gold alloy coatings have been investigated by Dettke and Riedel [4] who exploited 10 gold reflexes for the line broadening analysis; a method similar to that employed by Fischer and Binder [ 51. The microstrain and effective domain size values reported here are based on analysis only of the profiles of the (111)-(222) gold reflexes. The present investigation aims to demonstrate the use of a relatively simple
140
analysis of the line broadening in an X-ray diffraction pattern from the gold deposits. The gold layers were deposited on different polycrystalline metal substrates or interposed layers which caused complications due to the overlapping reflexes from the substrates. Measurements were therefore performed only on reflexes (111 and 222) which are not disturbed by reflexes from the substrate. Despite this analysis limitation this technique is very sensitive to small changes in the structure of electrodeposits. Experimental
procedures
The measurements were made using a commercially available Philips X-ray diffractometer equipped with a lithium-fluoride monochromator in the diffracted beam and a scintillation detector with pulse height discriminator in the counting circuit. For excitation of Cu-Koc radiation a highly stabilised Philips X-ray generator operating at 40 kV and 20 mA was used. To get appreciable intensity 1” divergent and scatter slits were employed. The profiles of the gold reflexes were chart recorded at room temperature at a scanning speed of l/8 (28 ) per minute and a recorder speed of 800 mm/h. For all samples the higher order reflections were relatively weak and only the first two reflections (ill)-(222) could be considered for line broadening measurements. For determination of Kol, integral breadths a graphical a-doublet correction was applied [6, 71. It was considered that the method should be as simple as possible, thus the integral breadth was taken as a measure of the broadening rather than fitting a Fourier series to the peak. The diffraction line half width B’ is related to the integral breadth B as follows: B = %nB’. B’ was measured and B calculated. The pure diffraction integral breadths (0) were obtained by using the parabolic equation as suggested by Anantharaman [8] : /3 = B -
b2/B
(1)
where B is the observed integral breadth and b is representative of the instrumental conditions. The use of this equation has been justified by satisfactory agreement with Fourier data. The required b values at appropriate 20 values were taken from a plot of b us. 20 obtained with annealed gold, zinc and silicon standards. The measured values of B and calculated values of p for two reflections in gold are given in Table I. Analysis
of X-ray line broadening
A separation of domain size and lattice strain contribution to X-ray line broadening can be effected by assuming a relation analogous to the parabolic equation (1) used for elimination of instrumental broadening [8]. This principle can be written in the following way [9, lo] : PD
=P-6:/b
(2)
141 TABLE I Integral breadth of X-ray reflections in electrodeposited Sample
(222)
(111) b
B
B
b
P
X lo3 radians Standard A B C D E F G H I J K L M N 0 P
gold
X
P
lo3 radians
2.62
2.41 9.63 11.12 12.03 10.68 12.44 7.71 6.82 8.15 7.05 8.99 7.05 8.94 8.62 9.15 6.56 6.74
9.03
10.70 11.52 10.28 11.99 6.98 5.99 7.45 6.23 8.36 6.23 8.60 8.05 8.52 5.50 5.85
17.09 19.55 21.45 17.72 23.53 13.44 10.04 13.96 10.56 17.00 12.46 15.48 14.76 16.46 8.92 11.38
16.67 19.22 21.15 17.33 23.24 12.95 9.35 13.49 9.93 16.61 11.92 15.04 14.31 16.06 8.16 10.81
where po is the integral breadth related to the effective domain size D, and p, is the integral breadth related to the non-uniform lattice strain (microstrain) E. Substituting in equation (2) the formulae h PD = D, cost9
(3)
p, = 4E tane
(4)
and gives case fly =‘+
16e2sin20
(5) m0se . e In the above equations X is the wavelength of X-ray radiation used and 0 is the Bragg angle. A plot of (p cos 0 /X) us. (16 e2sin2B/PX cos 0) gives a straight line with a slope of e2 and an intercept of l/D,. Consequently by plotting these expressions for two orders of the same reflection, it is possible to separate D, from E. The integral breadth method for separation of microstrain and effective domain size is also dependent on the fact that the strain is a function of the order of reflection while the effective domain size is not.
142
D, includes broadening effects due to both the domain size and faulting [ll] respectively. In this particular case the fault-unaffected (111) reflex was used and consequently the intercept in the above plot will be l/D, = l/D, where D is the true domain size. Results and discussion The plotted data of (/3 cos e/h) uersus (16 e2 sin2 19//3X cos 0) (Fig. 1) show the influence of deposition conditions on strained domain size and are representative of a large number of diffraction profiles recorded in this study. Table II presents the type of electrodeposited layers for which this technique is applied. A rough estimate of the dislocation density Nd (lines/cm2) in electrodeposited gold layers was made from the measured domain size and lattice strain values (see Table II) by using an equation deduced from the work of Williamson and Smallman [ 121. The equation is strictly valid only if some restricting assumptions are satisfied: N
(7)
d
K is a constant depending on strain distribution function (as here assumed = 12), $= Burgers vector (= a/J2), a = gold lattice parameter. It is interesting to observe (Table II) that both the microstrain and the estimated dislocation density values varied in a way similar to the variation of microhardness. It is thus considered that microstrain measurement may be a substitute for hardness determination in the case of thin electrodeposits for which an accurate determination of hardness is difficult.
430
OJO
p.xlisin’0 16
450 in
070
i-;’
Fig. 1. Plots of (p cos e/h) us. (16 E2sin2e/flx cos 0) for electrodeposited
gold coatings.
(g/I)
(g/I)
0.30
0.15
0.15 0.30
x
20 mm2.
alkaline “soft gold” same
acid “hard gold” same same
SSllle
0.30 0.05
same
3.8 3.6 3.5 3.8 3.6 acid “hard gold”
PH
Bath character,
0.15
0.05
0.24 0.15 0.10 0.60 0.32
Deposition rate Wmin)
* Thickness 4 pm; dimension for specimens 20
-
-
-
0
P
-
-
-
-
M N
L
-
0.10 1.12 2.38 0.10 1.12 -
Cobalt additive
Gold concentration
Deposition conditions
A 10.4 B 4.1 C 3.0 D 10.4 E 4.7 F as deposited G annealed (200 “C: 1 hour in air) H as deposited _ I annealed J as deposited _ K annealed
Specimens
Deposition variables and measured structural parameters
TABLE II
2
2
2 2
2
10
2
2
5.4 5.2 4.2 5.7 6.5
(pm)
Gold coating thickness
238 192 188 192 204 328 303 290 298 322 370
-.\.___
same
same
392
322
.____
D (A)
Domain size,
Ni inter244 mediate layer* same 263 same 274
NiFe same same same same Ni intermediate layer* Cu intermediate layer* Ag intermediate layer*
Substrate
2.30
1.10
3.15 3.67
2.90
3.34 3.67 4.24 3.08 5.00 2.68 1.41 2.68 1.59 3.74 2.52
Micro strain (E x 103)
1.22
0.71
2.50 2.79
-
105
-
-
180 149 183 154 178 152
1.71 0.97 1.93 1.11 2.42 1.42 2.48
-
Hardness HK 0.005 (kg/mm2)
2.92.10’1 3.98 4.70 3.34 5.10
Eetimated dislocation densities Nd x 1011 (iines/cm2)
Measured structural properties
144
A detailed analysis of the structure is limited by the substrate overlapping effects and weak reflexes. The techniques described can therefore be expected to give only an approximate picture of the microstrain and average domain size. The estimated dislocation density of electrodeposited gold layer is typical for electrodeposits and also corresponds to that in the cold worked state. Despite their approximate nature, the measured values have correlated with electrodeposition parameters. Acknowledgements The author thanks Dr. U. Lindborg for suggesting these investigations, and department manager E. Edman for support of the work. References 1 2 3 4 5 6 7 8 9 10
R. W. Wook and F. Witt, J. Vat. Sci. Technol., (1965) 243. E. R. Thompson and K. R. Lawless, Electrochim. Acta, 14 (1969) 269. M. Atasagum and R. W. Wook, J. Vat. Sci. Technol., 362 (1970). M. Dettke and W. Riedel, Oberfhache-Surface, 14 (5) (1973) 130. H. Binder and H. Fischer, Metalloberfltiche, 17 (10) (1963) 295. A. Taylor, X-ray Metallography, Wiley, London, 1961. H. P. Klug and L. E. Alexander, X-ray Diffraction Procedures, Wiley, London, 1954. T. R. Anantharaman and P. Rama Rao, Z. Metallk., 54 (11) (1963) 658. N. C. Halder and C. N. J. Wagner, Acta Cry&, 20 (1966) 312. C. N. J. Wagner, Local atomic arrangements studied by X-ray diffraction, Metallurgical Sot. Conf. Chicago (1965) p. 217. 11 B. E. Warren, X-ray Diffraction, Addison-Wesley, 1969. 12 G. K. Williamson and R. E. Smallman, Phil. Mag., 1 (1956) 34.