- Email: [email protected]
LaAlO3 thin film deposited on Si(100) and MgO(100) substrates
SOLID STATE ELSEVIER
IONI
Solid State Ionics 101-103 (1997) 191-195
LaA10 3 thin film deposited on Si(100) and MgO(100) substrates ~
M.V. C a b a n a s
a
a
, C.V. R a g e l , F. C o n d e
a
~
, J.M. Gonzalez-Calbet
b c
" , M. Vallet-Regf a'c'*
~Departamento de Qu{mica lnorgrnica y Bioinorgcinica, Facultad de Farmacia, Universidad Complutense, 28040-Madrid, Spain 'Departamento de Qufmica lnorgdnica, Facultad de Qu[micas, Universidad Complutense, 28040-Madrid, Spain ~lnstituto de Magnetismo Aplicado. Apdo. 155. Las Rozas, 28230-Madrid, Spain
Abstract LaAIO 3 films have been deposited on Si(100) and MgO(100) substrates by a modified CVD process. Solutions of aluminum and lanthanum acetylacetonates were used as precursors. The influence of both deposition temperatures and substrates on the characteristics of these thin films has been studied. Keywords: Superconducting thin films; Buffer layers; Pyrosol method Materials: LaAIO3; Si; MgO
1. Introduction Since the discovery of superconductivity at high temperatures in copper-oxide perovskite systems, much effort has already been expended in preparing very high quality thin film superconductors for device applications. The film quality is affected by the processes which appear at high deposition temperatures (600-800°C) such as interdiffusion, difference between the thermal expansion constants and by the mismatch of the lattice constants. The deposition of high temperature superconductor (HTSC) films on substrates such as silica, silicon or sapphire requires buffer layers to prevent interdiffusion between YBazCu307_ 6 (YBCO) and the reactive substrate [1]. Different buffer layers such as Zr(Y)O 2, CeO 2, LaA10 3, etc., have been reported [2]. In this sense, for the well-known YBCO sys*Corresponding author. [email protected]
Fax:
+34-1
394
1786;
e-mail:
tems, the perovskites are preferred as substrates, since they present a related crystal structure and can exhibit good lattice match. LaAIO 3 has to date been evaluated to be one of the best substrates in supporting YBCO thin films [3-6]. It is rhombohedral, and belonging to space .group R3m with unit cell dimensions of a = 5.375 A and a = 60.1 ° [7]. It has small lattice mismatch ( - 0 . 4 3 and - 2.1% along the a and b axes of YBCO, respectively), good chemical stability at high temperatures and a reasonably low dielectric constant [8]. In this paper we report both synthesis and characterization of LaA10 3 films deposited on Si(100) and MgO(100) substrates by a modified CVD process.
2. Experimental The synthesis pathway used for film deposition has been the pyrosol method, which has been reported for the MgO and Fe203 films obtention
0167-2738/97/$17.00 © 1997 Elsevier Science B.V. All rights reserved. PII S 0 1 6 7 - 2 7 3 8 ( 9 7 ) 0 0 2 7 4 - 9
M.V. Cabatias et al. / Solid State lonics 101-103 (1997) 191-195
192
[9,10]. This method is based on the pyrolysis on a heated substrate of an aerosol produced by ultrahigh frequency spraying of a solution. This solution contained the reactants of the materials to be deposited. In our case, the reactants have been Al(acac) 3 and La(acac) 3 . 2 H 2 0 (acac = C 5 H 7 0 ~), which have been synthesized according to the following reaction schemes [11 ]: NH 3
The La/A1 ratio of the resultant films was determined by energy dispersive X-ray spectrometry (EDS) with a Link AN10000 System. Phase identification was made by X-ray diffraction (XRD) in a Philips X-Pert MPD diffractometer equipped with a thin film (grazing incidence) attachment and a flat monochromator placed between sample and detector and using Cu Kc~ radiation. Surface morphology and film thickness were examined by scanning electron microscopy (SEM) on a JEOL 6400 equipment.
AI(NO3) 3 • 9H20(aq) + 3acacH --~ Al(acac) 3, pH=8
La(NO3)3 • 6H20(aq) + 3acacH
3. Results and discussion
NH 3
--~ La(acac)3 • 2H20.
pH=5
6
The study of these complexes by elemental analysis, atomic absorption spectrophotometry, infrared spectroscopy, thermogravimetry, differentail thermal analysis and X-ray diffraction indicates the molecular formulas shown above. The solubility of the acac's so obtained was tested for different organic solvents. Al(acac)3 is soluble in acetylacetone but not La(acac)3.2H20. Both are soluble in butanol and ethanol, although the solubility of the aluminum complex is much higher than that of the lanthanum complex. Accordingly, we have generated an aerosol from a solution formed by acetylacetonates dissolved in butanol with different concentrations. The study of ethanol as a solvent is in progress. In order to know the deposition conditions for AI and La, the deposition behaviour of Al(acac) 3 and La(acac)3.2H20 were separately studied in detail. In all cases, argon was used as carrier gas (Qg=2.2 l/min) and Si(100) and MgO(100) as substrates. According to the low solubility of La(acac) 32H20 in butanol, the solution concentrations were 0.02 and 0.01 M for individual film deposition, and the temperature deposition varied between 500 and 900°C. From the results obtained, LaAIO 3 films were prepared using argon as carrier gas and the same substrates. In this case, different La/AI ratios (1:1 and 2:1) in the solution were used with AI solution concentrations ranging from 0.003 to 0.01 M. Two deposition temperatures of 600 and 800°C were used since attempts made with higher temperatures did not give significant improvements.
The films obtained from Al(acac)3 or La(acac) 3. 2H20 dissolved in butanol had good adherence and homogeneity. XRD data showed that the films were amorphous in the case of Al(acac) 3 deposition, independently of temperature. For La(acac)3.2H20 deposition at 900°C, a lanthanum oxide carbonate [12] was observed. At lower temperatures, amorphous or not well crystallized phases were found. The film growth rate varied between 0.2 and 0.6 nm/min, depending on the deposition temperature and solution concentration. The AI or La deposition showed similar results for temperatures above 500°C. At this temperature the film growth rate for La was twice that observed for A1 deposition. According to these results and since there was no significant difference between depositions at 800 or 900°C, the LaA103 films were obtained by deposition at 600 and 800°C. Although individual AI or La depositions showed similar behaviour at these temperatures, when a solution containing a 1:1 La/A1 ratio was used, the films so obtained showed a higher A1 content. On the other hand, when the AI concentration was lower than 0.003 M or La concentration lower than 0.005 M, these cations were not transported to the film. Then, a 1:1 La/A1 ratio in the films was obtained when a solution containing 0.013 M La and 0.0065 M of A1 was used. These results were obtained independently of temperature (600 and 800°C) or substrate (Si and MgO). In all cases, the film surfaces were highly homogeneous and a different deposition rate was obtained depending on temperature. Then, the film growth rate varied from 0.3 nm/min (at 600°C) to 0.4 nm/min (at 800°C). The films obtained contained carbon
M.V. CabaBas et al. / Solid State lonics 101-103 (1997) 191-195
193
which appeared in a larger amount at 800°C than at 600°C. This effect could be related to the higher deposition rates observed for higher temperatures [13]. On the other hand, all as-deposited films were amorphous according to XRD data, then an ulterior annealing of the films was necessary in order to obtain a LaAIO 3 film. Different results were obtained depending on the substrate used.
~: LaAI03 !
900°1;
"E
3.1. Si( lO0) substrate
£ LaAIO3 * La-il-$i-0
lOOOOC
La-il-Si-9
10
20
30
I0
50
60
[21]
Fig. 1. XRD patterns of a film deposited on Si(lO0) obtained at 800°C and annealed at different temperatures.
LaAIO 3 was obtained as the majority phase when the as-deposited films were annealed at 900°C (Fig. 1). Nevertheless, an ulterior reaction of La and A1 with the substrate could be observed by increasing the annealing temperature (Fig. 1). The film surface microstructure was also modified by the annealing temperature. Fig. 2 shows the surface of films obtained at 800°C (thickness 0.4 0,m) but annealed at different temperatures. These results show that the Si(100) is not a good substrate for LaAIO 3 deposition. This fact agrees with the results obtained by other authors in the elaboration of LaA103 films onto silicon using a laser evaporation method [2].
Fig. 2. Scanning electron micrographs of: (a) as-deposited film on Si(100) at 800°C and annealed at (b) 900°C, (c) 1000°C and (d) 1250°C.
194
M.V Caba~as et al. / Solid State lonics 101-103 (1997) 191-195
3.2. MgO(100) substrate When butanol was used as a solvent, the initial amorphous phase evolved to a single perovskite phase after a thermal treatment of 1000°C for 5 min, independent of the deposition temperature used for the as-deposited film. No reaction with the substrate was observed even when the film was annealed at ! 250°C. The surface morphology of the as-deposited films
and after annealing is shown in Fig. 3. In these micrographs, an evolution of the surface microstructure is observed with the thermal treatment. Also the deposition temperature plays a role in the microstructure of the films. On one side, films deposited at lower temperature are more closely packed and, on the other side, the film's grain size is also affected rising from 625 nm at 600°C to 1250 nm at 800°C (see Fig. 3b,d).
4. C o n c l u s i o n s
LaAIO 3 thin films have been obtained by a modified CVD process from aluminum and lanthanum acetylacetonates. The appropriate La/AI ratio in films was obtained when a 2:1 La/AI ratio in the solution was used. All as-deposited films are amorphous, then an ulterior annealing was necessary. After this treatment, a LaAIO 3 perovskite well-crystallized phase is obtained. When Si(100) is used as substrate, a reaction of the LaA103 film with the silicon is observed. Films highly homogeneous and compact can be obtained by the CVD method when MgO(100) is used as substrate. The LaAIO 3 films so obtained will be used as buffer layers for ulterior deposition of YBa2Cu307 films. +
+
+
+
Acknowledgements
+
~,'? ;,+,+++. +++;+"+, ,,+" ~ . • ++~:++0+++++++++"++;"++° ++ ,+ +, ,+++++:ft, +++ + .,+ ++++"+ + +, ~ +
+
+~ e ~ + +
+ m¢l~ +++ *~ _.,++ P+++,+ ++++ + p,d+ '~,~~+.++, .... +;=: "7"
i
+
Financial support of the European Community through the Brite-Euram Project (BRE2-CT940742), of CICYT (Spain) through Research Project MAT96-0919 and of Comunidad Autrnoma de Madrid (CAM, Spain) through research Project (0144/94) is acknowledged. A. Rodrfguez provided valuable technical assistance.
t
"2ja"nj[~+¢,¢
+
.,,+. -,,+
References
+ °.+, +.. ,+, ~+,,,'
Fig. 3. Scanning electron micrographs of: (a) as-deposited film on MgO(100) at 600°C and (b) after annealing at 1000°C, (c) asdeposited film at 800°C and (d) after annealing at 1000°C.
[1] T. Venkatesan, E.W. Chase, X.D. Wu, A. Inam, C.C. Chang, Appl. Phys. Lett. 53 (1988) 243. [2] V. Sandu, J. Jaklovszky, D. Miu, D. Dragulinscu, C. Grigoriu, M.C. Bunescu, J. Mater. Sci. Lett. 13 (1994) 122.
M.~ CabaBas et al. / Solid State lonics 101-103 (1997) 191-195
[31 R.W. Simon, C.E. Platt, A.E. Lee, G.S. Lee, K.P. Daly, M.S. Wire, J.A. Luine, M. Urbanick, Appl. Phys. Lett. 53 (1988) 2677. [4] M.R Siegal, J.M. Phillips, Y. Hsieh, J.H. Marshall, Physica C 172 (1990) 282. [5] D. Grischkowsky, S. Keiding, Appl. Phys. Lett. 57 (1990) 1055. [61 D.T. Morelli, J. Mater. Res. 7 (1992) 2492. [7[ G.W. Berkstresser, A.J. Valentino, C.D. Brandle, J. Cryst. Growth 109 (1991) 467. [8] G.D. Yao, S. Yun Hou, M. Dudley, J.M. Phillips, J. Mater. Res. 7 (1992) 1847.
195
[9] M. Vallet-Regf., M. Labeau, E. Garcfa, M.V. Cabafias, J.M. Gonzfilez-Calbet, G. Delabouglise, Physica C 180 (1991) 57. [10] A. Martfnez, J. Pefia, M. Labeau, J.M. Gonz~ilez-Calbet, M. Vallet-Regf, J. Mater. Res. 10 (1995) 1307. [111 E.W. Berg, J. Jaime Chinang, Anal. Chim. Acta 40 (1968) 101. [12] ASTM powder diffraction file 23-0320. 113] E. Fredriksson, J. Carlsson, J. Chem. Vap. Deposit. 1 (1993) 333.
IONI
Solid State Ionics 101-103 (1997) 191-195
LaA10 3 thin film deposited on Si(100) and MgO(100) substrates ~
M.V. C a b a n a s
a
a
, C.V. R a g e l , F. C o n d e
a
~
, J.M. Gonzalez-Calbet
b c
" , M. Vallet-Regf a'c'*
~Departamento de Qu{mica lnorgrnica y Bioinorgcinica, Facultad de Farmacia, Universidad Complutense, 28040-Madrid, Spain 'Departamento de Qufmica lnorgdnica, Facultad de Qu[micas, Universidad Complutense, 28040-Madrid, Spain ~lnstituto de Magnetismo Aplicado. Apdo. 155. Las Rozas, 28230-Madrid, Spain
Abstract LaAIO 3 films have been deposited on Si(100) and MgO(100) substrates by a modified CVD process. Solutions of aluminum and lanthanum acetylacetonates were used as precursors. The influence of both deposition temperatures and substrates on the characteristics of these thin films has been studied. Keywords: Superconducting thin films; Buffer layers; Pyrosol method Materials: LaAIO3; Si; MgO
1. Introduction Since the discovery of superconductivity at high temperatures in copper-oxide perovskite systems, much effort has already been expended in preparing very high quality thin film superconductors for device applications. The film quality is affected by the processes which appear at high deposition temperatures (600-800°C) such as interdiffusion, difference between the thermal expansion constants and by the mismatch of the lattice constants. The deposition of high temperature superconductor (HTSC) films on substrates such as silica, silicon or sapphire requires buffer layers to prevent interdiffusion between YBazCu307_ 6 (YBCO) and the reactive substrate [1]. Different buffer layers such as Zr(Y)O 2, CeO 2, LaA10 3, etc., have been reported [2]. In this sense, for the well-known YBCO sys*Corresponding author. [email protected]
Fax:
+34-1
394
1786;
e-mail:
tems, the perovskites are preferred as substrates, since they present a related crystal structure and can exhibit good lattice match. LaAIO 3 has to date been evaluated to be one of the best substrates in supporting YBCO thin films [3-6]. It is rhombohedral, and belonging to space .group R3m with unit cell dimensions of a = 5.375 A and a = 60.1 ° [7]. It has small lattice mismatch ( - 0 . 4 3 and - 2.1% along the a and b axes of YBCO, respectively), good chemical stability at high temperatures and a reasonably low dielectric constant [8]. In this paper we report both synthesis and characterization of LaA10 3 films deposited on Si(100) and MgO(100) substrates by a modified CVD process.
2. Experimental The synthesis pathway used for film deposition has been the pyrosol method, which has been reported for the MgO and Fe203 films obtention
0167-2738/97/$17.00 © 1997 Elsevier Science B.V. All rights reserved. PII S 0 1 6 7 - 2 7 3 8 ( 9 7 ) 0 0 2 7 4 - 9
M.V. Cabatias et al. / Solid State lonics 101-103 (1997) 191-195
192
[9,10]. This method is based on the pyrolysis on a heated substrate of an aerosol produced by ultrahigh frequency spraying of a solution. This solution contained the reactants of the materials to be deposited. In our case, the reactants have been Al(acac) 3 and La(acac) 3 . 2 H 2 0 (acac = C 5 H 7 0 ~), which have been synthesized according to the following reaction schemes [11 ]: NH 3
The La/A1 ratio of the resultant films was determined by energy dispersive X-ray spectrometry (EDS) with a Link AN10000 System. Phase identification was made by X-ray diffraction (XRD) in a Philips X-Pert MPD diffractometer equipped with a thin film (grazing incidence) attachment and a flat monochromator placed between sample and detector and using Cu Kc~ radiation. Surface morphology and film thickness were examined by scanning electron microscopy (SEM) on a JEOL 6400 equipment.
AI(NO3) 3 • 9H20(aq) + 3acacH --~ Al(acac) 3, pH=8
La(NO3)3 • 6H20(aq) + 3acacH
3. Results and discussion
NH 3
--~ La(acac)3 • 2H20.
pH=5
6
The study of these complexes by elemental analysis, atomic absorption spectrophotometry, infrared spectroscopy, thermogravimetry, differentail thermal analysis and X-ray diffraction indicates the molecular formulas shown above. The solubility of the acac's so obtained was tested for different organic solvents. Al(acac)3 is soluble in acetylacetone but not La(acac)3.2H20. Both are soluble in butanol and ethanol, although the solubility of the aluminum complex is much higher than that of the lanthanum complex. Accordingly, we have generated an aerosol from a solution formed by acetylacetonates dissolved in butanol with different concentrations. The study of ethanol as a solvent is in progress. In order to know the deposition conditions for AI and La, the deposition behaviour of Al(acac) 3 and La(acac)3.2H20 were separately studied in detail. In all cases, argon was used as carrier gas (Qg=2.2 l/min) and Si(100) and MgO(100) as substrates. According to the low solubility of La(acac) 32H20 in butanol, the solution concentrations were 0.02 and 0.01 M for individual film deposition, and the temperature deposition varied between 500 and 900°C. From the results obtained, LaAIO 3 films were prepared using argon as carrier gas and the same substrates. In this case, different La/AI ratios (1:1 and 2:1) in the solution were used with AI solution concentrations ranging from 0.003 to 0.01 M. Two deposition temperatures of 600 and 800°C were used since attempts made with higher temperatures did not give significant improvements.
The films obtained from Al(acac)3 or La(acac) 3. 2H20 dissolved in butanol had good adherence and homogeneity. XRD data showed that the films were amorphous in the case of Al(acac) 3 deposition, independently of temperature. For La(acac)3.2H20 deposition at 900°C, a lanthanum oxide carbonate [12] was observed. At lower temperatures, amorphous or not well crystallized phases were found. The film growth rate varied between 0.2 and 0.6 nm/min, depending on the deposition temperature and solution concentration. The AI or La deposition showed similar results for temperatures above 500°C. At this temperature the film growth rate for La was twice that observed for A1 deposition. According to these results and since there was no significant difference between depositions at 800 or 900°C, the LaA103 films were obtained by deposition at 600 and 800°C. Although individual AI or La depositions showed similar behaviour at these temperatures, when a solution containing a 1:1 La/A1 ratio was used, the films so obtained showed a higher A1 content. On the other hand, when the AI concentration was lower than 0.003 M or La concentration lower than 0.005 M, these cations were not transported to the film. Then, a 1:1 La/A1 ratio in the films was obtained when a solution containing 0.013 M La and 0.0065 M of A1 was used. These results were obtained independently of temperature (600 and 800°C) or substrate (Si and MgO). In all cases, the film surfaces were highly homogeneous and a different deposition rate was obtained depending on temperature. Then, the film growth rate varied from 0.3 nm/min (at 600°C) to 0.4 nm/min (at 800°C). The films obtained contained carbon
M.V. CabaBas et al. / Solid State lonics 101-103 (1997) 191-195
193
which appeared in a larger amount at 800°C than at 600°C. This effect could be related to the higher deposition rates observed for higher temperatures [13]. On the other hand, all as-deposited films were amorphous according to XRD data, then an ulterior annealing of the films was necessary in order to obtain a LaAIO 3 film. Different results were obtained depending on the substrate used.
~: LaAI03 !
900°1;
"E
3.1. Si( lO0) substrate
£ LaAIO3 * La-il-$i-0
lOOOOC
La-il-Si-9
10
20
30
I0
50
60
[21]
Fig. 1. XRD patterns of a film deposited on Si(lO0) obtained at 800°C and annealed at different temperatures.
LaAIO 3 was obtained as the majority phase when the as-deposited films were annealed at 900°C (Fig. 1). Nevertheless, an ulterior reaction of La and A1 with the substrate could be observed by increasing the annealing temperature (Fig. 1). The film surface microstructure was also modified by the annealing temperature. Fig. 2 shows the surface of films obtained at 800°C (thickness 0.4 0,m) but annealed at different temperatures. These results show that the Si(100) is not a good substrate for LaAIO 3 deposition. This fact agrees with the results obtained by other authors in the elaboration of LaA103 films onto silicon using a laser evaporation method [2].
Fig. 2. Scanning electron micrographs of: (a) as-deposited film on Si(100) at 800°C and annealed at (b) 900°C, (c) 1000°C and (d) 1250°C.
194
M.V Caba~as et al. / Solid State lonics 101-103 (1997) 191-195
3.2. MgO(100) substrate When butanol was used as a solvent, the initial amorphous phase evolved to a single perovskite phase after a thermal treatment of 1000°C for 5 min, independent of the deposition temperature used for the as-deposited film. No reaction with the substrate was observed even when the film was annealed at ! 250°C. The surface morphology of the as-deposited films
and after annealing is shown in Fig. 3. In these micrographs, an evolution of the surface microstructure is observed with the thermal treatment. Also the deposition temperature plays a role in the microstructure of the films. On one side, films deposited at lower temperature are more closely packed and, on the other side, the film's grain size is also affected rising from 625 nm at 600°C to 1250 nm at 800°C (see Fig. 3b,d).
4. C o n c l u s i o n s
LaAIO 3 thin films have been obtained by a modified CVD process from aluminum and lanthanum acetylacetonates. The appropriate La/AI ratio in films was obtained when a 2:1 La/AI ratio in the solution was used. All as-deposited films are amorphous, then an ulterior annealing was necessary. After this treatment, a LaAIO 3 perovskite well-crystallized phase is obtained. When Si(100) is used as substrate, a reaction of the LaA103 film with the silicon is observed. Films highly homogeneous and compact can be obtained by the CVD method when MgO(100) is used as substrate. The LaAIO 3 films so obtained will be used as buffer layers for ulterior deposition of YBa2Cu307 films. +
+
+
+
Acknowledgements
+
~,'? ;,+,+++. +++;+"+, ,,+" ~ . • ++~:++0+++++++++"++;"++° ++ ,+ +, ,+++++:ft, +++ + .,+ ++++"+ + +, ~ +
+
+~ e ~ + +
+ m¢l~ +++ *~ _.,++ P+++,+ ++++ + p,d+ '~,~~+.++, .... +;=: "7"
i
+
Financial support of the European Community through the Brite-Euram Project (BRE2-CT940742), of CICYT (Spain) through Research Project MAT96-0919 and of Comunidad Autrnoma de Madrid (CAM, Spain) through research Project (0144/94) is acknowledged. A. Rodrfguez provided valuable technical assistance.
t
"2ja"nj[~+¢,¢
+
.,,+. -,,+
References
+ °.+, +.. ,+, ~+,,,'
Fig. 3. Scanning electron micrographs of: (a) as-deposited film on MgO(100) at 600°C and (b) after annealing at 1000°C, (c) asdeposited film at 800°C and (d) after annealing at 1000°C.
[1] T. Venkatesan, E.W. Chase, X.D. Wu, A. Inam, C.C. Chang, Appl. Phys. Lett. 53 (1988) 243. [2] V. Sandu, J. Jaklovszky, D. Miu, D. Dragulinscu, C. Grigoriu, M.C. Bunescu, J. Mater. Sci. Lett. 13 (1994) 122.
M.~ CabaBas et al. / Solid State lonics 101-103 (1997) 191-195
[31 R.W. Simon, C.E. Platt, A.E. Lee, G.S. Lee, K.P. Daly, M.S. Wire, J.A. Luine, M. Urbanick, Appl. Phys. Lett. 53 (1988) 2677. [4] M.R Siegal, J.M. Phillips, Y. Hsieh, J.H. Marshall, Physica C 172 (1990) 282. [5] D. Grischkowsky, S. Keiding, Appl. Phys. Lett. 57 (1990) 1055. [61 D.T. Morelli, J. Mater. Res. 7 (1992) 2492. [7[ G.W. Berkstresser, A.J. Valentino, C.D. Brandle, J. Cryst. Growth 109 (1991) 467. [8] G.D. Yao, S. Yun Hou, M. Dudley, J.M. Phillips, J. Mater. Res. 7 (1992) 1847.
195
[9] M. Vallet-Regf., M. Labeau, E. Garcfa, M.V. Cabafias, J.M. Gonzfilez-Calbet, G. Delabouglise, Physica C 180 (1991) 57. [10] A. Martfnez, J. Pefia, M. Labeau, J.M. Gonz~ilez-Calbet, M. Vallet-Regf, J. Mater. Res. 10 (1995) 1307. [111 E.W. Berg, J. Jaime Chinang, Anal. Chim. Acta 40 (1968) 101. [12] ASTM powder diffraction file 23-0320. 113] E. Fredriksson, J. Carlsson, J. Chem. Vap. Deposit. 1 (1993) 333.