- Email: [email protected]
Electronic coupling of quantized states in Ag nanofilm with fcc Fe(1 0 0) substrate
Applied Surface Science 169±170 (2001) 496±499
Electronic coupling of quantized states in Ag nano®lm with fcc Fe(1 0 0) substrate H. Sasaki, A. Tanaka*, K. Takahashi, W. Gondo, S. Suzuki, S. Sato Department of Physics, Graduate School of Science, Tohoku University, Aoba-ku, Sendai 980-8578, Japan Received 30 July 1999; accepted 21 October 1999
Abstract An angle-resolved photoemission study for the Ag nano®lm grown on the pseudomorphic fcc Fe(1 0 0) substrate has been carried out in order to investigate the detailed quantized electronic states. From the angle-resolved photoemission measurements, the dispersions of quantized electronic states in the present Ag nano®lms along the direction parallel to the nano®lm surface were directly determined. From these results, we discuss the electronic coupling of quantized electronic state in the Ag nano®lm with the electronic state of fcc Fe(1 0 0) substrate. # 2001 Elsevier Science B.V. All rights reserved. Keywords: Metallic nano®lm; Angle-resolved photoemission spectroscopy; Quantized electronic structure; In-plane dispersion; Hybridization effect
1. Introduction There is currently considerable interest in the physical properties of metallic nanostructures, where the various distinct physical properties are observed due to the quantum con®nement effects. In particular, the multilayers composed of alternating ferromagnetic and nonmagnetic metals show the interesting phenomena, e.g. an oscillatory magnetic coupling and a giant magnetoresistance [1]. From the reports of nonmagnetic noble-metal nano®lms deposited on the ferromagnetic transition-metal substrates, it has been suggested that the quantized electronic states in the nonmagnetic layers mediate the exchange coupling between the ferromagnetic layers [2,3]. In order to
*
Corresponding author. Tel.: 81-22-217-6418; fax: 81-22-217-6419. E-mail address: [email protected] (A. Tanaka).
fully elucidate the coupling mechanism in the metallic multilayers, it is also indispensable to consider the detailed electronic coupling between the nonmagnetic- and transition-metal layers. In this paper, we have carried out an angle-resolved photoemission study of Ag nano®lms deposited on the pseudomorphic metastable-phase fcc Fe(1 0 0). To our knowledge, there is no report that highlights the electronic coupling between the metallic nano®lms and pseudomorphic metastable substrates. From these results, we discuss the electronic coupling of the quantized electronic state in the Ag nano®lm with the electronic states of fcc Fe(1 0 0) substrate. 2. Experiment We prepared the Ag nano®lms and substrates by the molecular beam epitaxial (MBE) method using JPS100 (ANELVA Co.) MBE system connected directly
0169-4332/01/$ ± see front matter # 2001 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 9 - 4 3 3 2 ( 0 0 ) 0 0 7 4 5 - 5
H. Sasaki et al. / Applied Surface Science 169±170 (2001) 496±499
to ARUPS 10 (VG Scienti®c Co.) photoelectron spectrometer. The sample preparation procedures were described in detail previously [4]. The pseudomorphic fcc Fe(1 0 0) substrates were prepared on the hydrogen-terminated Si(1 0 0)-1 1 wafers using the Cu(1 0 0) seed layers. The Ag nano®lms were deposited on thus-prepared fcc Fe(1 0 0) substrates at room temperature. The cleanliness and structure of deposited layers were characterized by the Auger electron spectroscopy and low energy electron diffraction (LEED) observation. From the LEED patterns, an important point to note is that the present Ag nano®lm was grown in the peculiar direction of [1 1 1] on the fcc Fe(1 0 0) substrate. The prepared samples were transferred into the photoelectron spectrometer through the ultra-high vacuum chambers without exposure to air. The angle-resolved photoemission measurements were performed with the He I resonance line (hn 21:2 eV) as the excitation source. All photoemission measurements were recorded at 40 K using a closedcycle He refrigerator in order to decrease the photonassisted contributions to the spectra. A full acceptance angle of the hemispherical photoelectron analyzer was 0.48, and the total energy resolution was about 50 meV. 3. Results and discussion Fig. 1 shows the angle-resolved photoemission spectra measured for the Ag nano®lm with a thickness of 4.0 nm grown on the pseudomorphic fcc Fe(1 0 0) substrates, excited by He I resonance line at 40 K. The normal emission spectrum exhibits an intense peak just below Fermi level. This spectral feature originates from the Shockley surface state on Ag(1 1 1) reported previously [5], which is characteristic of Ag(1 1 1) clean surface. The existence of surface state indicates a good crystallinity and an orientation of the present Ag nano®lm. In addition, the ®ne-structures are observed in higher binding energy region than the surface state. From the nano®lm thickness dependence for the present system, we have concluded that these spectral features originate from the quantized states of Ag sp valence-electrons due to the quantum con®nement effect along the normal direction to surface [4]. In general, the Eigen values of these quantized states
497
Fig. 1. Angle-resolved photoemission spectra for the Ag nano®lm with a thickness of 4.0 nm excited by the He I resonance line. The polar emission angles with respect to the surface normal are indicated on each spectrum. The inset shows the spectra on an expanded scale.
are well characterized by the phase accumulation model which takes account the phase shift on the re¯ection of electron at both interfaces of the nano®lm [6,7]. From the theoretical calculation by the phase accumulation model, the observed features at lower and higher binding energies in Fig. 1 correspond to the quantized states with the quantum numbers n 1 and 2, respectively [4]. From the LEED observations, it is found that the present Ag(1 1 1) nano®lms are grown with the two domains rotated by 908 with respect to each other, like Ag deposited on Cu(1 0 0) reported by Hoyaz et al. [8]. Therefore, the present photoelectron detection plane in Fig. 1 includes the G-M and G-K symmetry lines of the surface Brillouin zone (SBZ). However, the in-plane dispersion around G point is expected to be isotropic, leading to the equivalent dispersions along the G-M and G-K symmetry lines, because the fcc Ag(1 1 1) surface exhibits a threefold symmetry. In fact, the in-plane dispersions of quantized states in our previous Ag/Cu(1 1 1) system along the G-M and G-K symmetry lines of the SBZ agree well each other [9]. Therefore, it is considered that the present angle-resolved photoemission spectra re¯ect the intrinsic in-plane dispersions of quantized states. In the inset of Fig. 1, the spectral features derived from
498
H. Sasaki et al. / Applied Surface Science 169±170 (2001) 496±499
Fig. 2. (a) In-plane dispersion of the quantized state in the Ag nano®lm with a thickness 2.5 nm. The solid lines represent the results for the least-squares ®ts to experimental data (see text). Open triangles and dashed lines represent our previous results of Ag nano®lm deposited on Cu(1 1 1) with a similar thickness and/or binding energy for a comparison; (b) same as (a) but for Ag nano®lm with a thickness of 4.0 nm.
the quantized states are shown on an expanded scale. As shown in the inset of Fig. 1, it is found that the quantized states shift toward Fermi level with increasing the photoelectron emission angle. This indicates that these quantized states have the in-plane energy dispersions. In order to see more clearly the in-plane dispersions of quantized states, we plot the binding energies of quantized states observed in the 2.5 and 4.0 nm-thick Ag nano®lms versus the wave vectors parallel to the surface in Fig. 2(a) and 2(b), respectively. The solid lines in Fig. 2 are results of least squares ®ts to each experimental data using parabolic function E E0 ÿ hkk2 =2mk , where E0 and mk are the binding energy at G point and the in-plane effective mass, respectively. From these least-square ®ts, we have obtained the in-plane effective masses of mk =me 1:20 0:02 for the quantized state with n 1 in the 2.5 nm-thick Ag nano®lm, and mk = me 1:81 0:02 and 0:62 0:02 for the quantized state with n 1 and 2 in the 4.0 nm-thick Ag nano®lm, respectively. We have also obtained the in-plane effective masses of mk =me 0:95 0:02 for the quantized state with n 1 in the 3.0 nm-thick Ag nano®lm, and mk =me 1:10 0:02 for the quantized state with n 1 (not given here). In Fig. 2, the results of our previous Ag nano®lm on Cu(1 1 1) with the similar thickness and/or binding energy are also shown by the open triangles and dashed lines for a
comparison. From our previous work, the in-plane effective masses of quantized states were about mk =me 0:3ÿ0:5 [9]. Moreover, it has been found that the dependence of the in-plane effective mass on the binding energy at G point is consistent with that derived from the bulk band calculation [10], which is independent of the nano®lm geometry. This means that the in-plane effective masses, that is, in-plane dispersions, of quantized states are equivalent to those of the parental valence-bands. However, as shown in Fig. 2, it is obvious that the present in-plane dispersions are considerably smaller than those of the previous Ag/Cu(1 1 1) system. One possible origin of this observation is related to the short lateral coherent length of the sample. However, a clear LEED pattern is observed for the present Ag nano®lm. Furthermore, the photoemission intensity of the surface state decreases with increasing the photoelectron emission angle, indicating that the surface state on the present Ag nano®lm surface disperses upward with increasing the wave vector parallel to the surface, as reported in the bulk Ag(1 1 1) surface [11]. Therefore, this contribution is considered to be negligible. Another possible candidate for such an effect is a hybridization effect with more localized states with larger effective mass. From the angle-resolved photoemission study for the present pseudomorphic fcc Fe(1 0 0) substrate, it is con®rmed that the Fe 3dderived valence-band with a small dispersion exists in the binding energy region where the quantized states are observed [12]. Therefore, it is considered that this enhancement in the in-plane effective mass of quantized state originates from the hybridization effect between the quantized state in Ag nano®lm and 3dderived electronic state in fcc Fe substrate at their interface. Similar enhancements of in-plane effective masses have been reported in the Cu/Co(1 0 0) [13] and Ag or Cu/V(1 0 0) systems [14]. These manybody problems due to the narrow partially ®lled bands are considered to be avoided in the previous Ag/ Cu(1 1 1) system, since the 3d-derived bands in Cu substrate are fully occupied. Therefore, no enhancement in the in-plane effective mass has been observed in the previous Ag/Cu(1 1 1) system. As mentioned above, the surface state on the present Ag nano®lm exhibits a signi®cant parabolic in-plane dispersion, similar to the bulk Ag(1 1 1) clean surface. While the wave function of quantized state extends over
H. Sasaki et al. / Applied Surface Science 169±170 (2001) 496±499
the whole nano®lm, that of surface state extends several atomic layers deep below the nano®lm surface. Therefore, the surface state cannot couple to the electronic states of substrate at Ag/fcc Fe (1 0 0) interface, consequently, it shows no contribution of hybridization effect to its in-plane effective mass. These conclusions indicate that the interfacial effects such as the hybridization with the substrate electronic state cannot be ignored in the consideration of the coupling in the metallic multilayers. The tight-binding analysis by Johnson et al. [13] has suggested that these hybridization effects are enhanced as the nano®lm becomes thinner. The preliminary results of the nano®lm thickness dependence as described above show the larger in-plane effective mass in the thinner Ag nano®lm. In order to discuss these hybridization effects quantitatively, the more detailed investigation of the nano®lm thickness dependence of the in-plane effective masses would be necessary. 4. Conclusion An angle-resolved photoemission study of Ag nano®lm grown on the fcc Fe(1 0 0) substrate has been carried out in order to investigate the electronic coupling of quantized electronic state in the metallic nano®lm with the substrate electronic state. From the angle-resolved photoemission measurements, the dispersions of quantized states in the Ag nano®lms on fcc Fe(1 0 0) along the direction parallel to the nano®lm surface were determined. It is found that the obtained in-plane effective masses of the quantized states in the present Ag nano®lms are larger than those in the previous Ag nano®lms on Cu(1 1 1) substrates. It is concluded that this in-plane effective mass enhancement of the quantized states originates from the hybridization effect between the quantized states in
499
Ag nano®lms and 3d-derived electronic states in the fcc Fe(1 0 0) substrates. Acknowledgements This work was supported by a Grant-in-Aid for Scienti®c Research from the Ministry of Education, Science and Culture of Japan, and also supported by the Core Research for Evolutional Science and Technology (CREST), Japan Science and Technology Corporation (JST).
References [1] S.S. Parkin, Phys. Rev. Lett. 67 (1991) 3598. [2] D.M. Edwards, J. Manthon, R.B. Muniz, M.S. Phan, Phys. Rev. Lett. 67 (1991) 493. [3] J.E. Ortega, F.J. Himpsel, Phys. Rev. Lett. 69 (1992) 844. [4] A. Tanaka, H. Sasaki, K. Takahashi, W. Gondo, S. Suzuki, S. Sato, J. Phys. Chem. Solids, in preparation. [5] S.D. Kavan, R.H. Gaylord, Phys. Rev. B 36 (1987) 5809. [6] N.V. Smith, Phys. Rev. B 32 (1985) 3549. [7] N.V. Smith, N.B. Brookes, Y. Chang, P.D. Johnson, Phys. Rev. B 49 (1994) 332. [8] J. Hoyaz, D. Naumovic, R. Fasel, P. Aebi, L. Schlapbach, Surf. Sci. 373 (1997) 153. [9] K. Takahashi, A. Tanaka, M. Hatano, H. Sasaki, S. Suzuki, S. Sato, J. Electron Spectrosc. Relat. Phenom. 88±91 (1998) 347. [10] K.-M. Ho, C.-L. Fu, S.H. Liu, D.M. Kolb, G. Paizza, J. Electroanal. Chem. 150 (1983) 235. [11] R. Paniago, R. Matzdorf, G. Meister, A. Goldmann, Surf. Sci. 336 (1995) 113. [12] H. Sasaki, A. Tanaka, K. Takahashi, W. Gondo, S. Suzuki, S. Sato, in preparation. [13] P.D. Johnson, K. Garrison, Q. Dong, N.V. Smith, L. Dongqi, J. Mattson, J. Pearson, S.D. Bader, Phys. Rev. B 50 (1994) 8954. [14] T. Valla, P. Pervan, M. Milun, A.B. Hayden, D.P. Woodruff, Phys. Rev. B 54 (1996) 11786.
Electronic coupling of quantized states in Ag nano®lm with fcc Fe(1 0 0) substrate H. Sasaki, A. Tanaka*, K. Takahashi, W. Gondo, S. Suzuki, S. Sato Department of Physics, Graduate School of Science, Tohoku University, Aoba-ku, Sendai 980-8578, Japan Received 30 July 1999; accepted 21 October 1999
Abstract An angle-resolved photoemission study for the Ag nano®lm grown on the pseudomorphic fcc Fe(1 0 0) substrate has been carried out in order to investigate the detailed quantized electronic states. From the angle-resolved photoemission measurements, the dispersions of quantized electronic states in the present Ag nano®lms along the direction parallel to the nano®lm surface were directly determined. From these results, we discuss the electronic coupling of quantized electronic state in the Ag nano®lm with the electronic state of fcc Fe(1 0 0) substrate. # 2001 Elsevier Science B.V. All rights reserved. Keywords: Metallic nano®lm; Angle-resolved photoemission spectroscopy; Quantized electronic structure; In-plane dispersion; Hybridization effect
1. Introduction There is currently considerable interest in the physical properties of metallic nanostructures, where the various distinct physical properties are observed due to the quantum con®nement effects. In particular, the multilayers composed of alternating ferromagnetic and nonmagnetic metals show the interesting phenomena, e.g. an oscillatory magnetic coupling and a giant magnetoresistance [1]. From the reports of nonmagnetic noble-metal nano®lms deposited on the ferromagnetic transition-metal substrates, it has been suggested that the quantized electronic states in the nonmagnetic layers mediate the exchange coupling between the ferromagnetic layers [2,3]. In order to
*
Corresponding author. Tel.: 81-22-217-6418; fax: 81-22-217-6419. E-mail address: [email protected] (A. Tanaka).
fully elucidate the coupling mechanism in the metallic multilayers, it is also indispensable to consider the detailed electronic coupling between the nonmagnetic- and transition-metal layers. In this paper, we have carried out an angle-resolved photoemission study of Ag nano®lms deposited on the pseudomorphic metastable-phase fcc Fe(1 0 0). To our knowledge, there is no report that highlights the electronic coupling between the metallic nano®lms and pseudomorphic metastable substrates. From these results, we discuss the electronic coupling of the quantized electronic state in the Ag nano®lm with the electronic states of fcc Fe(1 0 0) substrate. 2. Experiment We prepared the Ag nano®lms and substrates by the molecular beam epitaxial (MBE) method using JPS100 (ANELVA Co.) MBE system connected directly
0169-4332/01/$ ± see front matter # 2001 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 9 - 4 3 3 2 ( 0 0 ) 0 0 7 4 5 - 5
H. Sasaki et al. / Applied Surface Science 169±170 (2001) 496±499
to ARUPS 10 (VG Scienti®c Co.) photoelectron spectrometer. The sample preparation procedures were described in detail previously [4]. The pseudomorphic fcc Fe(1 0 0) substrates were prepared on the hydrogen-terminated Si(1 0 0)-1 1 wafers using the Cu(1 0 0) seed layers. The Ag nano®lms were deposited on thus-prepared fcc Fe(1 0 0) substrates at room temperature. The cleanliness and structure of deposited layers were characterized by the Auger electron spectroscopy and low energy electron diffraction (LEED) observation. From the LEED patterns, an important point to note is that the present Ag nano®lm was grown in the peculiar direction of [1 1 1] on the fcc Fe(1 0 0) substrate. The prepared samples were transferred into the photoelectron spectrometer through the ultra-high vacuum chambers without exposure to air. The angle-resolved photoemission measurements were performed with the He I resonance line (hn 21:2 eV) as the excitation source. All photoemission measurements were recorded at 40 K using a closedcycle He refrigerator in order to decrease the photonassisted contributions to the spectra. A full acceptance angle of the hemispherical photoelectron analyzer was 0.48, and the total energy resolution was about 50 meV. 3. Results and discussion Fig. 1 shows the angle-resolved photoemission spectra measured for the Ag nano®lm with a thickness of 4.0 nm grown on the pseudomorphic fcc Fe(1 0 0) substrates, excited by He I resonance line at 40 K. The normal emission spectrum exhibits an intense peak just below Fermi level. This spectral feature originates from the Shockley surface state on Ag(1 1 1) reported previously [5], which is characteristic of Ag(1 1 1) clean surface. The existence of surface state indicates a good crystallinity and an orientation of the present Ag nano®lm. In addition, the ®ne-structures are observed in higher binding energy region than the surface state. From the nano®lm thickness dependence for the present system, we have concluded that these spectral features originate from the quantized states of Ag sp valence-electrons due to the quantum con®nement effect along the normal direction to surface [4]. In general, the Eigen values of these quantized states
497
Fig. 1. Angle-resolved photoemission spectra for the Ag nano®lm with a thickness of 4.0 nm excited by the He I resonance line. The polar emission angles with respect to the surface normal are indicated on each spectrum. The inset shows the spectra on an expanded scale.
are well characterized by the phase accumulation model which takes account the phase shift on the re¯ection of electron at both interfaces of the nano®lm [6,7]. From the theoretical calculation by the phase accumulation model, the observed features at lower and higher binding energies in Fig. 1 correspond to the quantized states with the quantum numbers n 1 and 2, respectively [4]. From the LEED observations, it is found that the present Ag(1 1 1) nano®lms are grown with the two domains rotated by 908 with respect to each other, like Ag deposited on Cu(1 0 0) reported by Hoyaz et al. [8]. Therefore, the present photoelectron detection plane in Fig. 1 includes the G-M and G-K symmetry lines of the surface Brillouin zone (SBZ). However, the in-plane dispersion around G point is expected to be isotropic, leading to the equivalent dispersions along the G-M and G-K symmetry lines, because the fcc Ag(1 1 1) surface exhibits a threefold symmetry. In fact, the in-plane dispersions of quantized states in our previous Ag/Cu(1 1 1) system along the G-M and G-K symmetry lines of the SBZ agree well each other [9]. Therefore, it is considered that the present angle-resolved photoemission spectra re¯ect the intrinsic in-plane dispersions of quantized states. In the inset of Fig. 1, the spectral features derived from
498
H. Sasaki et al. / Applied Surface Science 169±170 (2001) 496±499
Fig. 2. (a) In-plane dispersion of the quantized state in the Ag nano®lm with a thickness 2.5 nm. The solid lines represent the results for the least-squares ®ts to experimental data (see text). Open triangles and dashed lines represent our previous results of Ag nano®lm deposited on Cu(1 1 1) with a similar thickness and/or binding energy for a comparison; (b) same as (a) but for Ag nano®lm with a thickness of 4.0 nm.
the quantized states are shown on an expanded scale. As shown in the inset of Fig. 1, it is found that the quantized states shift toward Fermi level with increasing the photoelectron emission angle. This indicates that these quantized states have the in-plane energy dispersions. In order to see more clearly the in-plane dispersions of quantized states, we plot the binding energies of quantized states observed in the 2.5 and 4.0 nm-thick Ag nano®lms versus the wave vectors parallel to the surface in Fig. 2(a) and 2(b), respectively. The solid lines in Fig. 2 are results of least squares ®ts to each experimental data using parabolic function E E0 ÿ hkk2 =2mk , where E0 and mk are the binding energy at G point and the in-plane effective mass, respectively. From these least-square ®ts, we have obtained the in-plane effective masses of mk =me 1:20 0:02 for the quantized state with n 1 in the 2.5 nm-thick Ag nano®lm, and mk = me 1:81 0:02 and 0:62 0:02 for the quantized state with n 1 and 2 in the 4.0 nm-thick Ag nano®lm, respectively. We have also obtained the in-plane effective masses of mk =me 0:95 0:02 for the quantized state with n 1 in the 3.0 nm-thick Ag nano®lm, and mk =me 1:10 0:02 for the quantized state with n 1 (not given here). In Fig. 2, the results of our previous Ag nano®lm on Cu(1 1 1) with the similar thickness and/or binding energy are also shown by the open triangles and dashed lines for a
comparison. From our previous work, the in-plane effective masses of quantized states were about mk =me 0:3ÿ0:5 [9]. Moreover, it has been found that the dependence of the in-plane effective mass on the binding energy at G point is consistent with that derived from the bulk band calculation [10], which is independent of the nano®lm geometry. This means that the in-plane effective masses, that is, in-plane dispersions, of quantized states are equivalent to those of the parental valence-bands. However, as shown in Fig. 2, it is obvious that the present in-plane dispersions are considerably smaller than those of the previous Ag/Cu(1 1 1) system. One possible origin of this observation is related to the short lateral coherent length of the sample. However, a clear LEED pattern is observed for the present Ag nano®lm. Furthermore, the photoemission intensity of the surface state decreases with increasing the photoelectron emission angle, indicating that the surface state on the present Ag nano®lm surface disperses upward with increasing the wave vector parallel to the surface, as reported in the bulk Ag(1 1 1) surface [11]. Therefore, this contribution is considered to be negligible. Another possible candidate for such an effect is a hybridization effect with more localized states with larger effective mass. From the angle-resolved photoemission study for the present pseudomorphic fcc Fe(1 0 0) substrate, it is con®rmed that the Fe 3dderived valence-band with a small dispersion exists in the binding energy region where the quantized states are observed [12]. Therefore, it is considered that this enhancement in the in-plane effective mass of quantized state originates from the hybridization effect between the quantized state in Ag nano®lm and 3dderived electronic state in fcc Fe substrate at their interface. Similar enhancements of in-plane effective masses have been reported in the Cu/Co(1 0 0) [13] and Ag or Cu/V(1 0 0) systems [14]. These manybody problems due to the narrow partially ®lled bands are considered to be avoided in the previous Ag/ Cu(1 1 1) system, since the 3d-derived bands in Cu substrate are fully occupied. Therefore, no enhancement in the in-plane effective mass has been observed in the previous Ag/Cu(1 1 1) system. As mentioned above, the surface state on the present Ag nano®lm exhibits a signi®cant parabolic in-plane dispersion, similar to the bulk Ag(1 1 1) clean surface. While the wave function of quantized state extends over
H. Sasaki et al. / Applied Surface Science 169±170 (2001) 496±499
the whole nano®lm, that of surface state extends several atomic layers deep below the nano®lm surface. Therefore, the surface state cannot couple to the electronic states of substrate at Ag/fcc Fe (1 0 0) interface, consequently, it shows no contribution of hybridization effect to its in-plane effective mass. These conclusions indicate that the interfacial effects such as the hybridization with the substrate electronic state cannot be ignored in the consideration of the coupling in the metallic multilayers. The tight-binding analysis by Johnson et al. [13] has suggested that these hybridization effects are enhanced as the nano®lm becomes thinner. The preliminary results of the nano®lm thickness dependence as described above show the larger in-plane effective mass in the thinner Ag nano®lm. In order to discuss these hybridization effects quantitatively, the more detailed investigation of the nano®lm thickness dependence of the in-plane effective masses would be necessary. 4. Conclusion An angle-resolved photoemission study of Ag nano®lm grown on the fcc Fe(1 0 0) substrate has been carried out in order to investigate the electronic coupling of quantized electronic state in the metallic nano®lm with the substrate electronic state. From the angle-resolved photoemission measurements, the dispersions of quantized states in the Ag nano®lms on fcc Fe(1 0 0) along the direction parallel to the nano®lm surface were determined. It is found that the obtained in-plane effective masses of the quantized states in the present Ag nano®lms are larger than those in the previous Ag nano®lms on Cu(1 1 1) substrates. It is concluded that this in-plane effective mass enhancement of the quantized states originates from the hybridization effect between the quantized states in
499
Ag nano®lms and 3d-derived electronic states in the fcc Fe(1 0 0) substrates. Acknowledgements This work was supported by a Grant-in-Aid for Scienti®c Research from the Ministry of Education, Science and Culture of Japan, and also supported by the Core Research for Evolutional Science and Technology (CREST), Japan Science and Technology Corporation (JST).
References [1] S.S. Parkin, Phys. Rev. Lett. 67 (1991) 3598. [2] D.M. Edwards, J. Manthon, R.B. Muniz, M.S. Phan, Phys. Rev. Lett. 67 (1991) 493. [3] J.E. Ortega, F.J. Himpsel, Phys. Rev. Lett. 69 (1992) 844. [4] A. Tanaka, H. Sasaki, K. Takahashi, W. Gondo, S. Suzuki, S. Sato, J. Phys. Chem. Solids, in preparation. [5] S.D. Kavan, R.H. Gaylord, Phys. Rev. B 36 (1987) 5809. [6] N.V. Smith, Phys. Rev. B 32 (1985) 3549. [7] N.V. Smith, N.B. Brookes, Y. Chang, P.D. Johnson, Phys. Rev. B 49 (1994) 332. [8] J. Hoyaz, D. Naumovic, R. Fasel, P. Aebi, L. Schlapbach, Surf. Sci. 373 (1997) 153. [9] K. Takahashi, A. Tanaka, M. Hatano, H. Sasaki, S. Suzuki, S. Sato, J. Electron Spectrosc. Relat. Phenom. 88±91 (1998) 347. [10] K.-M. Ho, C.-L. Fu, S.H. Liu, D.M. Kolb, G. Paizza, J. Electroanal. Chem. 150 (1983) 235. [11] R. Paniago, R. Matzdorf, G. Meister, A. Goldmann, Surf. Sci. 336 (1995) 113. [12] H. Sasaki, A. Tanaka, K. Takahashi, W. Gondo, S. Suzuki, S. Sato, in preparation. [13] P.D. Johnson, K. Garrison, Q. Dong, N.V. Smith, L. Dongqi, J. Mattson, J. Pearson, S.D. Bader, Phys. Rev. B 50 (1994) 8954. [14] T. Valla, P. Pervan, M. Milun, A.B. Hayden, D.P. Woodruff, Phys. Rev. B 54 (1996) 11786.