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Fabrication and in situ X-ray photoelectron spectroscopy of granular metal thin films
264
Thin Solid
Fabrication and in situ X-ray photoelectron granular metal thin films
spectroscopy
Films,
206
( 1991)
264&268
of
S. I. Shah and B. A. Doele
I. Weerasekera
and K. M. Unruh
Abstract A series of Fe,(SiO,), , , Co,, 5( SiOZ),, 5. and Ni,, 5( SiO>),, 5 transition metal based granular films were prepared by r.f. sputter deposition. Owing to their novel magnetic properties, and possible application as magnetic storage media, the iron based granular films were studied over a range of compositions from s =0.3 to .\- =0.9 atomic fraction. X-ray diffraction and transmission electron microscopy measurements indicated that these films consist of small metal particles embedded in an amorphous SiO, matrix. In the case of the Fe,(SiO,), ~, films. mean particle sizes from several nanometers to about IO nm could be obtained by varying the relative metal composition. The mean particle size was also observed to decrease, and the particle size distribution to become more uniform. with decreasing metal composition. In situ X-ray photoelectron spectroscopy measurements were carried out to determine the kind and relative composition of metal oxides associated with the metal particles. The metal oxides FeO, Fe?O,, Fe,O,. COO, NiO. and Ni,O, were identified in the case of the iron. cobalt and nickel particles respectively.
1. Introduction It is now well known that the apparently intensive bulk properties of macroscopic matter are actually size dependent [ 11. In order to observe experimentally these finite size effects, however, it is necessary to prepare systems in which at least one sample dimension is very small, typically in the range from several nanometers to several hundreds of nanometers. Small particles are well suited for these studies and have been successfully prepared by a variety of chemical and physical techniques [2, 31. In particular, vapor deposition methods have been widely used to prepare small particles in the form of discontinuous thin films, “smoke”, and granular metals. The last class of materials, usually consisting of small metal particles embedded in an insulating matrix, offer a number of advantages for the study of basic materials properties. These include control of the particle size over several orders of magnitude, relatively uniform particle size distributions. environmental protection of often reactive metals, and mechanical durability. Small magnetic particles in general, and small iron particles in particular, have been previously shown to exhibit novel size dependent magnetic properties [4, 51. While several explanations have been offered for these properties, a lack of detailed information on the chemical composition of the small particles has limited theo-
0040~6090/9 I /$3.50
retical treatments. In this work we report the results of a structural and compositional study of small iron, cobalt and nickel particles embedded in an insulating SiO, matrix. In addition to X-ray diffraction (XRD) and transmission electron microscopy (TEM) measurements, emphasis was placed on an X-ray photoelectron spectroscopy (XPS) study of the chemical composition of the granular iron, cobalt and nickel particles.
2. Experimental
details
All of the films studied in this work were prepared by r.f. magnetron deposition. Base system pressures were typically better than 1 x 10e7 Torr prior to backfilling the deposition chamber with high purity argon to a sputtering pressure of 5 x 10-j Torr. Composite sputtering targets were fabricated at each desired composition by cold pressing thoroughly mixed 325 mesh metal and SiO, powders into copper target pans. Films were deposited onto room temperature and water cooled carbon-coated copper microscopy grids for the TEM measurements and glass or quartz substrates for the XRD and XPS studies. After deposition, selected samples were immediately transferred under vacuum from the sputtering chamber to an attached analytical chamber for XPS measurements using a SSI 310 X-ray photoelectron spectrometer.
,’ 1991
Elsevier
Sequoia.
Lausanne
S. I. Shah et ul. 1 XPS
of‘grunuiur
A 1 mm diameter beam of monochromatic Al K, radiation at 1487 eV was used to obtain photoelectrons from the largest possible sample area. In addition to the Fe, peaks, Co, and Ni 2p,,,, 2p,,,, and 3p photoelectron the 0 Is, and Si 2p peaks were recorded. The C 1s peak at 285 eV, due to the unavoidable presence of small amounts of carbon, was used as an internal calibration standard for correcting possible peak position errors arising from, for example, charging of the sample surface. In order to extract quantitative chemical information, the XPS spectra were fitted to sums of 80% gaussian and 20% lorentzian line profiles following a background subtraction. XRD and TEM measurements were carried out to determine the structure of the granular metal particles and the SiOZ matrix. Mean metal particle size estimates were also obtained directly from the TEM micrographs and from a simple Scherrer line broadening analysis of
Fig, I. TEM x = 0.9.
bright
field images
and diffraction
patterns
of Fe,(SiOh),
me~ul fhin J&m
265
the X-ray scattering peaks. In the latter case, linewidths were determined by fitting measured diffraction profiles to a lorentzian lineshape and subtracting the instrumental linewidth [6].
3. Results and discussion Bright field TEM micrographs and electron diffraction patterns obtained from representative Fe., (SiO*), ~, granular films are shown in Fig. 1. As is characteristic of all granular metal films [3], the ironrich films can be seen to consist of a connected network of small metal particles and isolated SiO, inclusions, while metal-deficient films consist of isolated metal particles in a continuous SiO, matrix. The TEM images indicate a decrease in the mean ion particle size from about 12 nm in the x = 0.9 granular films to less than
~ granular
films for (a) x = 0.3, (b) x = 0.5. Cc) .Y = 0.7, and (d)
266
S. I. Shah et al. / XPS of grunuiur
2 nm in the x = 0.3 films. The corresponding particle sizes based on a Scherrer analysis were about 17 nm and 2 nm, in reasonable agreement with the TEM results. The TEM micrographs of the Co,,(SiO,),,, and Ni,,,( SiO,),,, granular films were qualitatively indistinguishable from those of Fig. 1. It can also be seen from the electron diffraction patterns of Fig. 1 that relatively well defined b.c.c. diffraction patterns for iron compositions at x = 0.9 and x = 0.7 were obtained. With reduced iron composition and decreasing particle size, the electron diffraction rings become increasingly diffuse, as expected, based on the very small particle size seen in the TEM images. Similar behavior was found in the case of the XRD patterns shown in Fig. 2, although a distinct b.c.c. diffraction pattern was only observed in the x = 0.9 granular film. X-ray photoelectron spectra covering the 2p energy range for granular (Fe, Co, Ni)0.5(Si02)0.5 films are presented in Fig. 3. In each case an unresolved XPS signal, arising from the presence of metal oxides, was observed as a high energy shoulder to the primary metal peak. By deconvoluting the measured spectra as described above, Fe 2p,,, and 2p,,, peaks at 707.4 and 720.4 eV were identified. These peak energies are close
metal
thin films
20
Fe 2p 16
4t
co 2p 16 -
4-
822.7
812.7
802.7
2or---
864.0
792.7
782.7
772 7
NI 20
861 0
857.9
854.9
851.8
a46.6
Blndlng Energy (N, Fig. 3. 2p X-ray granular films.
Fig. 2. X-ray diffraction x = 0.9, 0.7, and 0.5.
patterns
of Fe,(SiO,),
_ , granular
films for
photoelectron
spectra
of (Fe, Co, Ni),,,(SQ),,.,
to their expected values [7]. In addition, the XPS signals associated with the formation of Fe,O, at 711.0 and 724.2 eV, Fe0 at 709.7 eV, and Fe,O, at 708.3 eV were observed. The Fe0 and Fe,O, 2p,,, peaks were not resolved. These values are also in good agreement with the reported values for the peak energies of these iron oxides [8]. The broad satellite peak centered around 715 eV is characteristic of paramagnetic Fe0 [8,9]. The presence of these oxides was also confirmed by the deconvolution of the Fe 3p peak envelope. Based on the relative intensities of the iron and iron oxide 2p,,, peaks, about 44O/oof the XPS signal was found to arise from metallic iron, 12% from iron in the form of Fe,O,, 11% from FeO, and 33% from Fe,O,. Figure 3 also shows the XPS spectrum of a Co,,, (SiO,),,, film. The two peaks at 777.8 and 792.8 eV arise from the Co 2~,,~ and 2p,,, core levels, and again are in good agreement with previously reported values [7]. The peaks at 780.5 and 795.9 eV correspond to the presence of COO. Satellite peaks at 783.5 and 801.9 eV also confirm the presence of paramagnetic Co0 [lo]. It is worth noting that the cobalt oxide Co,O, produces a peak at 779.3 eV and does not have any satellite peaks
261
S. I. Shah et al. / XPS of granulur mrtul thin films
[ 111. The presence of Co,O, can, therefore, be excluded. Based on their integrated peak intensities, about 45% of the cobalt XPS signal was due to metallic cobalt while 55% of the signal originated from COO. The XPS spectrum of the Ni,,,( SiOZ)0.5 granular film is the most complex of the three materials studied. The Ni 2p,,, and 2p ,,z peaks at 852.4 and 869.8 eV are consistent with previous studies [ 121. In addition, an Ni 2P,,, energy loss peak is observed at 857.7 eV with a characteristically large peak width [ 131. The high energy shoulders to the Ni 2p,,, and 2p,,, peaks arise from the presence of NiO at 854.2, 856.6, and 873.5 eV while the peak at 856.8 eV is due to N&O,. Metallic nickel accounted for about 66% of the XPS signal with about 21% of the signal arising from Ni,O, and 13% from NiO. As mentioned earlier, Fe,( SiO,), _ _~granular films with x = 0.3 to x = 0.9 atomic fraction were prepared and studied over a wide range of compositions owing to the novel magnetic properties of these materials. The Fe 2p XPS region is shown in Fig. 4 for several selected compositions, while the results of a peak deconvolution and intensity analysis are summarized in Table 1. Based on these data, the iron fraction of the total XPS signal is seen to increase as the size of the iron particles
TABLE I. Iron concentration x, iron mean particle size, and iron and iron oxide fractions based on the relative intensities of the XPS 2p,,, .Y
spectra Particle diameter
Fe fraction
Fe,Q fraction
Fe0 fraction
Fe,% fraction
0.32 0.44 0.62 0.67
0.1 I 0.12 0.1 I 0.13
0.21 0.1 I 0.03 0.05
0.36 0.33 0.23 0.14
(nm) 0.3 0.5 0.7 0.9
1.6 3.5 8.5 I2
increases. As also indicated in Table I, the relative Fe,O, concentration appears to be essentially independent of particle size, while the relative Fe0 and Fe,O, concentrations decrease with increasing particle size. In addition to the presence of the metal oxides discussed above, evidence for the presence of metal silitides was also sought. The Si 2p XPS peak was invariably found at 103.6 eV, corresponding to silicon in the form of SiO,. Pure silicon, silicides, and silicates result in an Si 2p peak between about 99 and 101 eV which was not observed. Based on these observations, we conclude that little, if any, silicide or silicate formation occurs during film growth.
Fe 20
4. Summary
and conclusions
Granular (Fe, Co,, Ni)., ( SiO,), _ ,. films were prepared by r.f. sputter deposition and studied by X-ray and electron diffraction, TEM, and XPS measurements. The TEM and XRD measurements indicated that these materials consist of small metal particles embedded in an amorphous SiO, matrix. Smaller mean particle sizes and a more uniform particle size distribution were associated with reduced metal concentration. In addition to the elemental metals, the XPS measurements identified the metal oxides FeO, Fe,O,, Fe,O,, COO, NiO, and N&O, in the case of the iron, cobalt and nickel particles respectively. No evidence for metal silitide or silicate formation was found. In the case of the granular iron films, the relative concentration of metallic iron was found to increase with increasing particle size. In addition, while the Fe,O, fraction was essentially independent of the particle size, the Fe0 and FezO, fractions were both found to decrease with increasing particle size.
4 730.0 Binding
Fig. 4. Fe 2p X-ray films.
720.0 Energy (eV)
photoelectron
710.0
700.0
spectra
of Fe,( SiO,),
Acknowledgments ~,
granular
We acknowledge C. L. Chien and G. C. Hadjipanayis for a number of helpful discussions. The TEM work
268
S. I. Shah et cd. 1 XPS of grcmulcrr mefd
was carried out by M. L. van Kavelaar and M. J. Kavelaar. The work of KMU was supported in part under ONR contract N00014-8%K003.
5 6
References 7 I T. L. Hill, Thermodynamics of Smull Systems. W. A. Benjamin. New York, 1963. 2 MRS BUN., Vol. XIV, 1989, MRS Bull., Vol. XV, 1990 and references cited therein, Materials Research Society, Pittsburgh. PA. 3 B. Abeles, P. Sheng, M. D. Coutts and Y. Arie, Ado. P/zy.s., 24
8 9 IO
( 1975) 407.
47 (1976)
1I
and C. P. Bean, in G. T. Rado and H. Suhl (eds.). Academic Press, New York, 1963, Chapter 6. Y.-W. Du, J. Wu, H.-X. Wang, Z.-Q. Qui, H. Tang and J. C. Walker, J. Appl. Phys., 61 ( 1987) 33 14.
12
C. G. Granqvist
2200. 4 I. S. Jacobs Magneiism
III,
and R. A. Buhrman,
J. Appl.
Phys.,
thin ,jilm.s
V. Papaefthymiou, A. Kostikas. A. Simopoulos. D. Niarchos, S. Gangopadyay, G. C. Hadjipanayis, C. M. Sorensen and K. J. Klabunde, J. Appl. Ph_vs.. 67 ( 1990) 4487. G. Xiao and C. L. Chien, Arm/. Phw. Leff., 51 (1987) 1280. S. H. Liou and C. L. Chien: &I/. Ph_rs. Letf., 52 (1988) 512. H. P. Klug and L. E. Alexander, X-Ruy D~flcrction Procedures ,/iw Polycrysrdline cd Amorphous Moterids. Wiley. New York. 1974. C. D. Wagner. W. M. Riggs, L. E. Davis, J. F. Moulder and G. E. Muilenberg (eds.), Hundbook of X-R(r) Photoelectron Spectroscopy, Perkin-Elmer Corp., Eden Prairie. MN, 1978. p. 76. C. R. Brundle. T. J. Chuang and K. Wandet, Surf: Sci.. 68 ( 1977) 459. N. S. McIntyre and D. G. Zetaruk, And. Chem.. 49 ( 1977) 1521. J. Haber and L. Ungier, J. Elecrron Spectrosc. Rekrr. Phenom., I2 (1977) 305. D. C. Frost. C. A. McDowell and I. S. Woolsey. Mol. Phys.. 27 (1974) 1473. K. S. Kim and R. E. Davis, J. Electron Spectrosc. Relrrt. Phenom.. I (1972-1973)
13 K. S. Kim. Electron
251.
W. E. Baitinger,
Specrrosc.
Relut.
J. W. Amy
Phenom..
5
and
( 1974)
N. Winograd.
35 I.
J.
Thin Solid
Fabrication and in situ X-ray photoelectron granular metal thin films
spectroscopy
Films,
206
( 1991)
264&268
of
S. I. Shah and B. A. Doele
I. Weerasekera
and K. M. Unruh
Abstract A series of Fe,(SiO,), , , Co,, 5( SiOZ),, 5. and Ni,, 5( SiO>),, 5 transition metal based granular films were prepared by r.f. sputter deposition. Owing to their novel magnetic properties, and possible application as magnetic storage media, the iron based granular films were studied over a range of compositions from s =0.3 to .\- =0.9 atomic fraction. X-ray diffraction and transmission electron microscopy measurements indicated that these films consist of small metal particles embedded in an amorphous SiO, matrix. In the case of the Fe,(SiO,), ~, films. mean particle sizes from several nanometers to about IO nm could be obtained by varying the relative metal composition. The mean particle size was also observed to decrease, and the particle size distribution to become more uniform. with decreasing metal composition. In situ X-ray photoelectron spectroscopy measurements were carried out to determine the kind and relative composition of metal oxides associated with the metal particles. The metal oxides FeO, Fe?O,, Fe,O,. COO, NiO. and Ni,O, were identified in the case of the iron. cobalt and nickel particles respectively.
1. Introduction It is now well known that the apparently intensive bulk properties of macroscopic matter are actually size dependent [ 11. In order to observe experimentally these finite size effects, however, it is necessary to prepare systems in which at least one sample dimension is very small, typically in the range from several nanometers to several hundreds of nanometers. Small particles are well suited for these studies and have been successfully prepared by a variety of chemical and physical techniques [2, 31. In particular, vapor deposition methods have been widely used to prepare small particles in the form of discontinuous thin films, “smoke”, and granular metals. The last class of materials, usually consisting of small metal particles embedded in an insulating matrix, offer a number of advantages for the study of basic materials properties. These include control of the particle size over several orders of magnitude, relatively uniform particle size distributions. environmental protection of often reactive metals, and mechanical durability. Small magnetic particles in general, and small iron particles in particular, have been previously shown to exhibit novel size dependent magnetic properties [4, 51. While several explanations have been offered for these properties, a lack of detailed information on the chemical composition of the small particles has limited theo-
0040~6090/9 I /$3.50
retical treatments. In this work we report the results of a structural and compositional study of small iron, cobalt and nickel particles embedded in an insulating SiO, matrix. In addition to X-ray diffraction (XRD) and transmission electron microscopy (TEM) measurements, emphasis was placed on an X-ray photoelectron spectroscopy (XPS) study of the chemical composition of the granular iron, cobalt and nickel particles.
2. Experimental
details
All of the films studied in this work were prepared by r.f. magnetron deposition. Base system pressures were typically better than 1 x 10e7 Torr prior to backfilling the deposition chamber with high purity argon to a sputtering pressure of 5 x 10-j Torr. Composite sputtering targets were fabricated at each desired composition by cold pressing thoroughly mixed 325 mesh metal and SiO, powders into copper target pans. Films were deposited onto room temperature and water cooled carbon-coated copper microscopy grids for the TEM measurements and glass or quartz substrates for the XRD and XPS studies. After deposition, selected samples were immediately transferred under vacuum from the sputtering chamber to an attached analytical chamber for XPS measurements using a SSI 310 X-ray photoelectron spectrometer.
,’ 1991
Elsevier
Sequoia.
Lausanne
S. I. Shah et ul. 1 XPS
of‘grunuiur
A 1 mm diameter beam of monochromatic Al K, radiation at 1487 eV was used to obtain photoelectrons from the largest possible sample area. In addition to the Fe, peaks, Co, and Ni 2p,,,, 2p,,,, and 3p photoelectron the 0 Is, and Si 2p peaks were recorded. The C 1s peak at 285 eV, due to the unavoidable presence of small amounts of carbon, was used as an internal calibration standard for correcting possible peak position errors arising from, for example, charging of the sample surface. In order to extract quantitative chemical information, the XPS spectra were fitted to sums of 80% gaussian and 20% lorentzian line profiles following a background subtraction. XRD and TEM measurements were carried out to determine the structure of the granular metal particles and the SiOZ matrix. Mean metal particle size estimates were also obtained directly from the TEM micrographs and from a simple Scherrer line broadening analysis of
Fig, I. TEM x = 0.9.
bright
field images
and diffraction
patterns
of Fe,(SiOh),
me~ul fhin J&m
265
the X-ray scattering peaks. In the latter case, linewidths were determined by fitting measured diffraction profiles to a lorentzian lineshape and subtracting the instrumental linewidth [6].
3. Results and discussion Bright field TEM micrographs and electron diffraction patterns obtained from representative Fe., (SiO*), ~, granular films are shown in Fig. 1. As is characteristic of all granular metal films [3], the ironrich films can be seen to consist of a connected network of small metal particles and isolated SiO, inclusions, while metal-deficient films consist of isolated metal particles in a continuous SiO, matrix. The TEM images indicate a decrease in the mean ion particle size from about 12 nm in the x = 0.9 granular films to less than
~ granular
films for (a) x = 0.3, (b) x = 0.5. Cc) .Y = 0.7, and (d)
266
S. I. Shah et al. / XPS of grunuiur
2 nm in the x = 0.3 films. The corresponding particle sizes based on a Scherrer analysis were about 17 nm and 2 nm, in reasonable agreement with the TEM results. The TEM micrographs of the Co,,(SiO,),,, and Ni,,,( SiO,),,, granular films were qualitatively indistinguishable from those of Fig. 1. It can also be seen from the electron diffraction patterns of Fig. 1 that relatively well defined b.c.c. diffraction patterns for iron compositions at x = 0.9 and x = 0.7 were obtained. With reduced iron composition and decreasing particle size, the electron diffraction rings become increasingly diffuse, as expected, based on the very small particle size seen in the TEM images. Similar behavior was found in the case of the XRD patterns shown in Fig. 2, although a distinct b.c.c. diffraction pattern was only observed in the x = 0.9 granular film. X-ray photoelectron spectra covering the 2p energy range for granular (Fe, Co, Ni)0.5(Si02)0.5 films are presented in Fig. 3. In each case an unresolved XPS signal, arising from the presence of metal oxides, was observed as a high energy shoulder to the primary metal peak. By deconvoluting the measured spectra as described above, Fe 2p,,, and 2p,,, peaks at 707.4 and 720.4 eV were identified. These peak energies are close
metal
thin films
20
Fe 2p 16
4t
co 2p 16 -
4-
822.7
812.7
802.7
2or---
864.0
792.7
782.7
772 7
NI 20
861 0
857.9
854.9
851.8
a46.6
Blndlng Energy (N, Fig. 3. 2p X-ray granular films.
Fig. 2. X-ray diffraction x = 0.9, 0.7, and 0.5.
patterns
of Fe,(SiO,),
_ , granular
films for
photoelectron
spectra
of (Fe, Co, Ni),,,(SQ),,.,
to their expected values [7]. In addition, the XPS signals associated with the formation of Fe,O, at 711.0 and 724.2 eV, Fe0 at 709.7 eV, and Fe,O, at 708.3 eV were observed. The Fe0 and Fe,O, 2p,,, peaks were not resolved. These values are also in good agreement with the reported values for the peak energies of these iron oxides [8]. The broad satellite peak centered around 715 eV is characteristic of paramagnetic Fe0 [8,9]. The presence of these oxides was also confirmed by the deconvolution of the Fe 3p peak envelope. Based on the relative intensities of the iron and iron oxide 2p,,, peaks, about 44O/oof the XPS signal was found to arise from metallic iron, 12% from iron in the form of Fe,O,, 11% from FeO, and 33% from Fe,O,. Figure 3 also shows the XPS spectrum of a Co,,, (SiO,),,, film. The two peaks at 777.8 and 792.8 eV arise from the Co 2~,,~ and 2p,,, core levels, and again are in good agreement with previously reported values [7]. The peaks at 780.5 and 795.9 eV correspond to the presence of COO. Satellite peaks at 783.5 and 801.9 eV also confirm the presence of paramagnetic Co0 [lo]. It is worth noting that the cobalt oxide Co,O, produces a peak at 779.3 eV and does not have any satellite peaks
261
S. I. Shah et al. / XPS of granulur mrtul thin films
[ 111. The presence of Co,O, can, therefore, be excluded. Based on their integrated peak intensities, about 45% of the cobalt XPS signal was due to metallic cobalt while 55% of the signal originated from COO. The XPS spectrum of the Ni,,,( SiOZ)0.5 granular film is the most complex of the three materials studied. The Ni 2p,,, and 2p ,,z peaks at 852.4 and 869.8 eV are consistent with previous studies [ 121. In addition, an Ni 2P,,, energy loss peak is observed at 857.7 eV with a characteristically large peak width [ 131. The high energy shoulders to the Ni 2p,,, and 2p,,, peaks arise from the presence of NiO at 854.2, 856.6, and 873.5 eV while the peak at 856.8 eV is due to N&O,. Metallic nickel accounted for about 66% of the XPS signal with about 21% of the signal arising from Ni,O, and 13% from NiO. As mentioned earlier, Fe,( SiO,), _ _~granular films with x = 0.3 to x = 0.9 atomic fraction were prepared and studied over a wide range of compositions owing to the novel magnetic properties of these materials. The Fe 2p XPS region is shown in Fig. 4 for several selected compositions, while the results of a peak deconvolution and intensity analysis are summarized in Table 1. Based on these data, the iron fraction of the total XPS signal is seen to increase as the size of the iron particles
TABLE I. Iron concentration x, iron mean particle size, and iron and iron oxide fractions based on the relative intensities of the XPS 2p,,, .Y
spectra Particle diameter
Fe fraction
Fe,Q fraction
Fe0 fraction
Fe,% fraction
0.32 0.44 0.62 0.67
0.1 I 0.12 0.1 I 0.13
0.21 0.1 I 0.03 0.05
0.36 0.33 0.23 0.14
(nm) 0.3 0.5 0.7 0.9
1.6 3.5 8.5 I2
increases. As also indicated in Table I, the relative Fe,O, concentration appears to be essentially independent of particle size, while the relative Fe0 and Fe,O, concentrations decrease with increasing particle size. In addition to the presence of the metal oxides discussed above, evidence for the presence of metal silitides was also sought. The Si 2p XPS peak was invariably found at 103.6 eV, corresponding to silicon in the form of SiO,. Pure silicon, silicides, and silicates result in an Si 2p peak between about 99 and 101 eV which was not observed. Based on these observations, we conclude that little, if any, silicide or silicate formation occurs during film growth.
Fe 20
4. Summary
and conclusions
Granular (Fe, Co,, Ni)., ( SiO,), _ ,. films were prepared by r.f. sputter deposition and studied by X-ray and electron diffraction, TEM, and XPS measurements. The TEM and XRD measurements indicated that these materials consist of small metal particles embedded in an amorphous SiO, matrix. Smaller mean particle sizes and a more uniform particle size distribution were associated with reduced metal concentration. In addition to the elemental metals, the XPS measurements identified the metal oxides FeO, Fe,O,, Fe,O,, COO, NiO, and N&O, in the case of the iron, cobalt and nickel particles respectively. No evidence for metal silitide or silicate formation was found. In the case of the granular iron films, the relative concentration of metallic iron was found to increase with increasing particle size. In addition, while the Fe,O, fraction was essentially independent of the particle size, the Fe0 and FezO, fractions were both found to decrease with increasing particle size.
4 730.0 Binding
Fig. 4. Fe 2p X-ray films.
720.0 Energy (eV)
photoelectron
710.0
700.0
spectra
of Fe,( SiO,),
Acknowledgments ~,
granular
We acknowledge C. L. Chien and G. C. Hadjipanayis for a number of helpful discussions. The TEM work
268
S. I. Shah et cd. 1 XPS of grcmulcrr mefd
was carried out by M. L. van Kavelaar and M. J. Kavelaar. The work of KMU was supported in part under ONR contract N00014-8%K003.
5 6
References 7 I T. L. Hill, Thermodynamics of Smull Systems. W. A. Benjamin. New York, 1963. 2 MRS BUN., Vol. XIV, 1989, MRS Bull., Vol. XV, 1990 and references cited therein, Materials Research Society, Pittsburgh. PA. 3 B. Abeles, P. Sheng, M. D. Coutts and Y. Arie, Ado. P/zy.s., 24
8 9 IO
( 1975) 407.
47 (1976)
1I
and C. P. Bean, in G. T. Rado and H. Suhl (eds.). Academic Press, New York, 1963, Chapter 6. Y.-W. Du, J. Wu, H.-X. Wang, Z.-Q. Qui, H. Tang and J. C. Walker, J. Appl. Phys., 61 ( 1987) 33 14.
12
C. G. Granqvist
2200. 4 I. S. Jacobs Magneiism
III,
and R. A. Buhrman,
J. Appl.
Phys.,
thin ,jilm.s
V. Papaefthymiou, A. Kostikas. A. Simopoulos. D. Niarchos, S. Gangopadyay, G. C. Hadjipanayis, C. M. Sorensen and K. J. Klabunde, J. Appl. Ph_vs.. 67 ( 1990) 4487. G. Xiao and C. L. Chien, Arm/. Phw. Leff., 51 (1987) 1280. S. H. Liou and C. L. Chien: &I/. Ph_rs. Letf., 52 (1988) 512. H. P. Klug and L. E. Alexander, X-Ruy D~flcrction Procedures ,/iw Polycrysrdline cd Amorphous Moterids. Wiley. New York. 1974. C. D. Wagner. W. M. Riggs, L. E. Davis, J. F. Moulder and G. E. Muilenberg (eds.), Hundbook of X-R(r) Photoelectron Spectroscopy, Perkin-Elmer Corp., Eden Prairie. MN, 1978. p. 76. C. R. Brundle. T. J. Chuang and K. Wandet, Surf: Sci.. 68 ( 1977) 459. N. S. McIntyre and D. G. Zetaruk, And. Chem.. 49 ( 1977) 1521. J. Haber and L. Ungier, J. Elecrron Spectrosc. Rekrr. Phenom., I2 (1977) 305. D. C. Frost. C. A. McDowell and I. S. Woolsey. Mol. Phys.. 27 (1974) 1473. K. S. Kim and R. E. Davis, J. Electron Spectrosc. Relrrt. Phenom.. I (1972-1973)
13 K. S. Kim. Electron
251.
W. E. Baitinger,
Specrrosc.
Relut.
J. W. Amy
Phenom..
5
and
( 1974)
N. Winograd.
35 I.
J.