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Seebeck effect in disordered low dimensional interface structures
Journal of Non-Crystalline Solids 250±252 (1999) 776±780
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Seebeck eect in disordered low dimensional interface structures J. Barzola-Quiquia *, C. Lauinger, P. H aussler Institut f ur Physik, Technische Universit at Chemnitz, D-09107 Chemnitz, Germany
Abstract We have studied the physical and chemical interaction at the interface of amorphous Sb and Cu, by means of measurements of the Seebeck coecient, S, and the resistance per square, R . The solid interfaces were prepared in situ using a quenching technique near liquid He temperature. We have observed a thickness as well as temperature dependence of S of the Cu/Sb interface at Cu thickness <3 nm. In this thickness range the low temperature (<150 K) slope of S, S=T jT !0 , increases when reducing the Cu coverage. For thicknesses >3 nm an opposite eect is observed. In this region S=T jT !0 increases with increasing Cu thickness, but the Ss are much smaller than for thicknesses <3 nm. These dependences of S=T jT !0 are discussed taking into account the thermopower of three-dimensional Cux Sb1ÿx alloys and polycrystalline Cu ®lms. Evidence has been found that for Cu thickness <3 nm the chemical interaction at the interface forms a homogeneous amorphous CuSb alloy. Ó 1999 Elsevier Science B.V. All rights reserved.
1. Introduction Few systematic investigations have been performed to determine the physical and chemical interaction of the interface of ®lms [1,2]. The Seebeck coecient is a probe to study such interface reactions due to its sensitivity to electronic properties. If two dierent conductors are joined together at both ends and the two junctions kept at dierent temperatures with small temperature difference (DT Tsample , an electromotive force is set up which is proportional to the temperature difference. The thermoelectromotive force per degree is called the Seebeck coecient. In a previous paper [3] we reported structural and chemical eects in bilayers consisting of an
* Corresponding author. Tel.: +49 371 531 3109; fax: +49 371 531 3555; e-mail: [email protected]
amorphous Sb ®lm and an Au ®lm by measuring the Seebeck coecient, S, and the resistance per square, R . To reduce eects due to diusion at the interface as far as possible we performed in situ preparation and measurements at liquid He temperature. Our investigation showed that in the ®rst stages of the formation of the Au/Sb interface chemical interaction as well as percolation are responsible for the temperature and thickness dependence of both S and R . These eects are observable up to a critical Au thickness, dAu;c 2 nm. In this region the properties of the Au are not independent of the Sb underlayer. Instead, an amorphous AuSb alloy with a thickness of a few atomic layers is formed. The thickness of the amorphous AuSb alloy is given by d dAu dSb;eff , where dSb;eff is that part of the Sb ®lm which contributes to the amorphous mixture. The results obtained from transport measurements were supported by the results of
0022-3093/99/$ ± see front matter Ó 1999 Elsevier Science B.V. All rights reserved. PII: S 0 0 2 2 - 3 0 9 3 ( 9 9 ) 0 0 1 7 7 - 5
J. Barzola-Quiquia et al. / Journal of Non-Crystalline Solids 250±252 (1999) 776±780
photoemission spectroscopy both ultraviolet light and X-ray (UPS, XPS) [4]. The UPS/XPS investigations showed that the thickness which is attributable to the entire amorphous mixture is a maximum at a thickness of approximately 7 atomic layers [4]. The dependence of S and R at thicknesses less than dAu;c , i.e. in the regime of chemical interaction, has a similarity to the transport coecients of three-dimensional (3D) amorphous Aux Sb1ÿx alloys [5]. Increasing the thickness of the Au coverage on the Sb corresponds to an increasing Au content in an amorphous alloy. The UPS/XPS spectra [4] show that the bilayer with the critical Au coverage, dAu;c , is equivalent to an amorphous Aux Sb1ÿx alloy with x 0:8. At Au coverages, dAu > dAu;c a similarity with the properties of S and R of polycrystalline Au ®lms (without Sb underlayer) is observed, which we suggest is due to the growth of an Au polycrystalline state. x 0:8 also marks the transition from the amorphous to the polycrystalline phase in quenched 3D Aux Sb1ÿx [6] which demonstrates that the same stabilization eects are essential in the two dimensional metastable interfaces. It is the goal of this paper to study the properties of S and R of Cu/Sb bilayers with ®xed Sb thickness and Cu thicknesses ranging from approximately 0.5±5 nm, and polycrystalline Cu (without Sb underlayer).
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also deposited a series of Cu ®lms directly onto a glass substrate without an amorphous Sb underlayer. It is well known [6] that Cu ®lms prepared in this way are polycrystalline even with substrate temperatures of 20 K during deposition. The random errors of S and R are approximately 10% [9]. Further experimental details are given in Refs. [5,8]. 3. Results Fig. 1 shows the temperature dependence of S for four dierent Cu/Sb bilayers with dCu ranging between 0.5 and 5 nm. The most important feature is the increase of S with decreasing Cu thickness. In addition, the temperature dependence of S above approximately 150 K has opposite curvatures for the bilayers with low (dCu 0:5 nm) and large (dCu 1:5 nm) Cu thickness. Furthermore, S of the sample with the greatest Cu thickness, dCu 5 nm, has a nearly linear temperature dependence. In the following we give an explanation for the dependence on the Cu thickness of S of the bilayers.
2. Experiment The experiments were performed in a 4 Hecryostat in the temperature range between 1.7 and 250 K. The ®lms were prepared by quench condensation of the vapour onto a glass substrate in a vacuum with a base pressure of 3 10ÿ8 mbar. First Sb with a thickness of 7 nm was deposited onto a glass substrate. Sb quenched at low temperatures has an amorphous structure and it is an electrical insulator [7]. After that Cu was deposited on top of the amorphous Sb. The Cu thickness was varied between 0.5 and 5 nm. During the deposition of the Cu the substrate temperature increased to 20 K. To compare the properties of Cu on amorphous Sb with that of polycrystalline Cu we
Fig. 1. Temperature dependence of the Seebeck coecient S of Cu/Sb bilayers with dierent Cu coverages dCu in nm.
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J. Barzola-Quiquia et al. / Journal of Non-Crystalline Solids 250±252 (1999) 776±780
4. Discussion 4.1. Seebeck coecient For a discussion of the thickness dependence we perform a comparison of the low temperature slope of S, S=T jT !0 , of the Cu/Sb bilayers with that of polycrystalline Cu ®lms. In Fig. 2 S=T jT !0 is depicted as a function of dCu , together with the data of polycrystalline Cu ®lms. At smaller dCu , S=T jT !0 of the bilayers increases when reducing the Cu thickness. On the other hand S=T jT !0 of the bilayer with dCu 5 nm agrees with the data of polycrystalline Cu. A minimum in the thickness dependence of S=T jT !0 of the Cu/Sb bilayers at dCu 3 nm occurs. S=T jT !0 of polycrystalline Cu is thickness independent in the region dCu > 20 nm, whereas it decreases with decreasing dCu below 20 nm. In the region dCu < 5 nm the polycrystalline ®lms are discontinuous and S as well as R are not measurable near the percolation threshold. We will discuss the properties of S and R near the percolation threshold in a following paper. From the theoretical point of view the thickness depen-
Fig. 2. Thickness dependence of the low temperature slopes of S of Cu/Sb bilayers () and polycrystalline Cu ®lms (s).
dence of S in percolating ®lms is not understood. As outlined in Refs. [9,10] one has to know the energy dependence of the electron mean free path, details of the Fermi surface and also microscopic properties of the grains, e.g. grain size, to perform a detailed analysis of the thickness dependence of S. Since these quantities are not known further analysis is not possible. As in the case of Au/Sb bilayers we ascribe the increase of S=T jT !0 below dCu;c to the formation of an amorphous Cu/Sb phase at the interface. To support this hypothesis we have plotted S=T jT !0 of 3D Cux Sb1ÿx alloys versus x in the whole concentration range, see Fig. 3. x 0.8 marks the maximum limit of the amorphous phase of 3D Cux Sb1ÿx . Alloys with x > 0.8 are partly polycrystalline even after quench condensation at 4 K, for x < 0.8 they are amorphous [6]. The most striking feature of the x-dependence of S=T jT !0 is the increase in the region x < 0.2. We have analysed this increase [11] and we ascribe it to the appearance of a disorder-driven metal±insulator transition at a critical Cu concentration, xc 0:08.
Fig. 3. Concentration dependence of the low temperature slope of S of 3D Cux Sb1ÿx alloys. The vertical dashed line marks the upper limit of the amorphous phase. The solid line is a guide to the eye.
J. Barzola-Quiquia et al. / Journal of Non-Crystalline Solids 250±252 (1999) 776±780
However, we have to mention that the dependence of S=T jT !0 near xc is not understood [11]. In the following we compare S(T) of the Cu/Sb bilayers, shown in Fig. 1, with that of 3D Cux Sb1ÿx alloys. As mentioned above, three dierent temperature dependences of S are seen. If we compare this with 3D alloys these dependences can be summarized as follows: S(T ) of the bilayer with dCu 0:5 nm is comparable with a 3D sample with x 0:2, that of the bilayers with dCu 1:5 nm and 1.6 nm corresponds to a 3D alloy with x near the phase boundary at 0.8. In contrast S(T ) of the bilayer with dCu 5 nm is similar to that of a polycrystalline CuSb alloy with x > 0.8. In summary both S=T jT !0 and the temperature dependence of S support our idea of a strong similarity between Cu/Sb bilayers and 3D amorphous Cux Sb1ÿx alloys below the critical Cu coverage, dCu;c . In our model an increase of the Cu thickness in the bilayer is equivalent to an increasing Cu content in a Cux Sb1ÿx alloy. As in the case of Au/ Sb bilayers the transition from an amorphous to a polycrystalline interface leads to a minimum in the thickness dependence of S=T jT !0 . The critical Cu thickness, dCu;c 3 nm, is larger than the corresponding dAu;c 2 nm. Since the bilayer with dCu;c 3 nm corresponds to an alloy with x 0:8 an estimate of the thickness, dSb;eff , of that part of the Sb ®lm which contributes to the interface is possible, yielding dSb;eff 1:5 nm. This dSb;eff is about a factor 2 larger compared with the corresponding dSb;eff 0:8 nm determined for Au/Sb bilayers [3]. We cannot give an explanation for the dierent dSb;eff s. In future studies investigations of the crystallization temperatures of Cu/Sb bilayers will be performed. Comparing with the corresponding thickness of 3D amorphous Cux Sb1ÿx alloys [6] may give more information about the characteristic parameters of the amorphous interface. 4.2. Resistance per square Finally we discuss the low temperature dependence of R of Cu/Sb bilayers and polycrystalline Cu ®lms. We observe a logarithmic temperature dependence of R below 4 K. The reason for this log T-dependence are quantum corrections due to
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weak antilocalization and electron±electron interaction [12], and it is valid in 2D, hence showing the reduced dimension of our ®lms. From the temperature dependence of R , electronic parameters describing these eects can be determined. These are a p (weak antilocalization) and (1ÿF ) (electron±electron interaction) [12] which can be separated from a combined measurement of R and the Hall coecient, RH . However, since no Hall measurements were possible in our case, we could only determine the sum of both, i.e. a p + (1ÿF ). We ®nd the surprising result a p 1 ÿ F 0:8 independent of dCu for bilayers and polycrystalline ®lms (as far as dCu < 10 nm). However, due to the dierent properties of the bilayers and the polycrystalline ®lms as described above we expected dierences in the electronic properties of both. Hence, further investigations of RH and the magneto-resistance are necessary.
5. Conclusions The seebeck coecient, S, and its low temperature slope, S=T jT !0 , have been used to investigate the formation of an homogeneously amorphous CuSb alloy at the interface of Cu on top of amorphous Sb at low temperatures (T 20 K). The interface reaction is restricted to Cu coverages smaller than the critical value dCu;c 3 nm. The total thickness of the amorphous interface was determined and it has a maximum of approximately 4.5 nm which corresponds to an CuSb alloy with 80 at.% Cu. If the Cu coverages is larger than dCu;c the Cu grows as a polycrystalline ®lm on the amorphous interface.
References [1] M. Seyert, A. Siber, P. Ziemann, Phys. Rev. Lett. 67 (1991) 3792. [2] H.-G. Boyen, G. Indlekofer, G. Gantner, H. Stupp, A. Cossy-Favre, P. Oelhafen, Phys. Rev. B 51 (1995) 17096. [3] C. Lauinger, F. Baumann, H.-G. Boyen, J. Phys.: Condens. Matter 8 (1996) 6653. [4] H.-G. Boyen, A. Cossy-Favre, P. Oelhafen, A. Siber, P. Ziemann, C. Lauinger, T. Moser, P. H aussler, F. Baumann, Phys. Rev. B 51 (1995) 1791.
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J. Barzola-Quiquia et al. / Journal of Non-Crystalline Solids 250±252 (1999) 776±780
[5] C. Lauinger, F. Baumann, J. Phys.: Condens. Matter 7 (1995) 1305. [6] P. Haussler, Phys. Rep. 222 (1995) 65. [7] J.J. Hauser, Phys. Rev. B 9 (1974) 2623. [8] E. Compans, Rev. Sci. Instrum. 60 (1989) 2715.
[9] R.I. Boughton, J. Low Temp. Phys. 37 (1979) 31. [10] J.R. Sambles, T.W. Priest, J. Phys. F 14 (1984) 1693. [11] C. Lauinger, T. Hunger, J. Barzola-Quiquia, P. H aussler, H.-G. Boyen, these Proceedings, p. 791. [12] G. Bergmann, Phys. Rep. 107 (1984) 1.
www.elsevier.com/locate/jnoncrysol
Seebeck eect in disordered low dimensional interface structures J. Barzola-Quiquia *, C. Lauinger, P. H aussler Institut f ur Physik, Technische Universit at Chemnitz, D-09107 Chemnitz, Germany
Abstract We have studied the physical and chemical interaction at the interface of amorphous Sb and Cu, by means of measurements of the Seebeck coecient, S, and the resistance per square, R . The solid interfaces were prepared in situ using a quenching technique near liquid He temperature. We have observed a thickness as well as temperature dependence of S of the Cu/Sb interface at Cu thickness <3 nm. In this thickness range the low temperature (<150 K) slope of S, S=T jT !0 , increases when reducing the Cu coverage. For thicknesses >3 nm an opposite eect is observed. In this region S=T jT !0 increases with increasing Cu thickness, but the Ss are much smaller than for thicknesses <3 nm. These dependences of S=T jT !0 are discussed taking into account the thermopower of three-dimensional Cux Sb1ÿx alloys and polycrystalline Cu ®lms. Evidence has been found that for Cu thickness <3 nm the chemical interaction at the interface forms a homogeneous amorphous CuSb alloy. Ó 1999 Elsevier Science B.V. All rights reserved.
1. Introduction Few systematic investigations have been performed to determine the physical and chemical interaction of the interface of ®lms [1,2]. The Seebeck coecient is a probe to study such interface reactions due to its sensitivity to electronic properties. If two dierent conductors are joined together at both ends and the two junctions kept at dierent temperatures with small temperature difference (DT Tsample , an electromotive force is set up which is proportional to the temperature difference. The thermoelectromotive force per degree is called the Seebeck coecient. In a previous paper [3] we reported structural and chemical eects in bilayers consisting of an
* Corresponding author. Tel.: +49 371 531 3109; fax: +49 371 531 3555; e-mail: [email protected]
amorphous Sb ®lm and an Au ®lm by measuring the Seebeck coecient, S, and the resistance per square, R . To reduce eects due to diusion at the interface as far as possible we performed in situ preparation and measurements at liquid He temperature. Our investigation showed that in the ®rst stages of the formation of the Au/Sb interface chemical interaction as well as percolation are responsible for the temperature and thickness dependence of both S and R . These eects are observable up to a critical Au thickness, dAu;c 2 nm. In this region the properties of the Au are not independent of the Sb underlayer. Instead, an amorphous AuSb alloy with a thickness of a few atomic layers is formed. The thickness of the amorphous AuSb alloy is given by d dAu dSb;eff , where dSb;eff is that part of the Sb ®lm which contributes to the amorphous mixture. The results obtained from transport measurements were supported by the results of
0022-3093/99/$ ± see front matter Ó 1999 Elsevier Science B.V. All rights reserved. PII: S 0 0 2 2 - 3 0 9 3 ( 9 9 ) 0 0 1 7 7 - 5
J. Barzola-Quiquia et al. / Journal of Non-Crystalline Solids 250±252 (1999) 776±780
photoemission spectroscopy both ultraviolet light and X-ray (UPS, XPS) [4]. The UPS/XPS investigations showed that the thickness which is attributable to the entire amorphous mixture is a maximum at a thickness of approximately 7 atomic layers [4]. The dependence of S and R at thicknesses less than dAu;c , i.e. in the regime of chemical interaction, has a similarity to the transport coecients of three-dimensional (3D) amorphous Aux Sb1ÿx alloys [5]. Increasing the thickness of the Au coverage on the Sb corresponds to an increasing Au content in an amorphous alloy. The UPS/XPS spectra [4] show that the bilayer with the critical Au coverage, dAu;c , is equivalent to an amorphous Aux Sb1ÿx alloy with x 0:8. At Au coverages, dAu > dAu;c a similarity with the properties of S and R of polycrystalline Au ®lms (without Sb underlayer) is observed, which we suggest is due to the growth of an Au polycrystalline state. x 0:8 also marks the transition from the amorphous to the polycrystalline phase in quenched 3D Aux Sb1ÿx [6] which demonstrates that the same stabilization eects are essential in the two dimensional metastable interfaces. It is the goal of this paper to study the properties of S and R of Cu/Sb bilayers with ®xed Sb thickness and Cu thicknesses ranging from approximately 0.5±5 nm, and polycrystalline Cu (without Sb underlayer).
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also deposited a series of Cu ®lms directly onto a glass substrate without an amorphous Sb underlayer. It is well known [6] that Cu ®lms prepared in this way are polycrystalline even with substrate temperatures of 20 K during deposition. The random errors of S and R are approximately 10% [9]. Further experimental details are given in Refs. [5,8]. 3. Results Fig. 1 shows the temperature dependence of S for four dierent Cu/Sb bilayers with dCu ranging between 0.5 and 5 nm. The most important feature is the increase of S with decreasing Cu thickness. In addition, the temperature dependence of S above approximately 150 K has opposite curvatures for the bilayers with low (dCu 0:5 nm) and large (dCu 1:5 nm) Cu thickness. Furthermore, S of the sample with the greatest Cu thickness, dCu 5 nm, has a nearly linear temperature dependence. In the following we give an explanation for the dependence on the Cu thickness of S of the bilayers.
2. Experiment The experiments were performed in a 4 Hecryostat in the temperature range between 1.7 and 250 K. The ®lms were prepared by quench condensation of the vapour onto a glass substrate in a vacuum with a base pressure of 3 10ÿ8 mbar. First Sb with a thickness of 7 nm was deposited onto a glass substrate. Sb quenched at low temperatures has an amorphous structure and it is an electrical insulator [7]. After that Cu was deposited on top of the amorphous Sb. The Cu thickness was varied between 0.5 and 5 nm. During the deposition of the Cu the substrate temperature increased to 20 K. To compare the properties of Cu on amorphous Sb with that of polycrystalline Cu we
Fig. 1. Temperature dependence of the Seebeck coecient S of Cu/Sb bilayers with dierent Cu coverages dCu in nm.
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J. Barzola-Quiquia et al. / Journal of Non-Crystalline Solids 250±252 (1999) 776±780
4. Discussion 4.1. Seebeck coecient For a discussion of the thickness dependence we perform a comparison of the low temperature slope of S, S=T jT !0 , of the Cu/Sb bilayers with that of polycrystalline Cu ®lms. In Fig. 2 S=T jT !0 is depicted as a function of dCu , together with the data of polycrystalline Cu ®lms. At smaller dCu , S=T jT !0 of the bilayers increases when reducing the Cu thickness. On the other hand S=T jT !0 of the bilayer with dCu 5 nm agrees with the data of polycrystalline Cu. A minimum in the thickness dependence of S=T jT !0 of the Cu/Sb bilayers at dCu 3 nm occurs. S=T jT !0 of polycrystalline Cu is thickness independent in the region dCu > 20 nm, whereas it decreases with decreasing dCu below 20 nm. In the region dCu < 5 nm the polycrystalline ®lms are discontinuous and S as well as R are not measurable near the percolation threshold. We will discuss the properties of S and R near the percolation threshold in a following paper. From the theoretical point of view the thickness depen-
Fig. 2. Thickness dependence of the low temperature slopes of S of Cu/Sb bilayers () and polycrystalline Cu ®lms (s).
dence of S in percolating ®lms is not understood. As outlined in Refs. [9,10] one has to know the energy dependence of the electron mean free path, details of the Fermi surface and also microscopic properties of the grains, e.g. grain size, to perform a detailed analysis of the thickness dependence of S. Since these quantities are not known further analysis is not possible. As in the case of Au/Sb bilayers we ascribe the increase of S=T jT !0 below dCu;c to the formation of an amorphous Cu/Sb phase at the interface. To support this hypothesis we have plotted S=T jT !0 of 3D Cux Sb1ÿx alloys versus x in the whole concentration range, see Fig. 3. x 0.8 marks the maximum limit of the amorphous phase of 3D Cux Sb1ÿx . Alloys with x > 0.8 are partly polycrystalline even after quench condensation at 4 K, for x < 0.8 they are amorphous [6]. The most striking feature of the x-dependence of S=T jT !0 is the increase in the region x < 0.2. We have analysed this increase [11] and we ascribe it to the appearance of a disorder-driven metal±insulator transition at a critical Cu concentration, xc 0:08.
Fig. 3. Concentration dependence of the low temperature slope of S of 3D Cux Sb1ÿx alloys. The vertical dashed line marks the upper limit of the amorphous phase. The solid line is a guide to the eye.
J. Barzola-Quiquia et al. / Journal of Non-Crystalline Solids 250±252 (1999) 776±780
However, we have to mention that the dependence of S=T jT !0 near xc is not understood [11]. In the following we compare S(T) of the Cu/Sb bilayers, shown in Fig. 1, with that of 3D Cux Sb1ÿx alloys. As mentioned above, three dierent temperature dependences of S are seen. If we compare this with 3D alloys these dependences can be summarized as follows: S(T ) of the bilayer with dCu 0:5 nm is comparable with a 3D sample with x 0:2, that of the bilayers with dCu 1:5 nm and 1.6 nm corresponds to a 3D alloy with x near the phase boundary at 0.8. In contrast S(T ) of the bilayer with dCu 5 nm is similar to that of a polycrystalline CuSb alloy with x > 0.8. In summary both S=T jT !0 and the temperature dependence of S support our idea of a strong similarity between Cu/Sb bilayers and 3D amorphous Cux Sb1ÿx alloys below the critical Cu coverage, dCu;c . In our model an increase of the Cu thickness in the bilayer is equivalent to an increasing Cu content in a Cux Sb1ÿx alloy. As in the case of Au/ Sb bilayers the transition from an amorphous to a polycrystalline interface leads to a minimum in the thickness dependence of S=T jT !0 . The critical Cu thickness, dCu;c 3 nm, is larger than the corresponding dAu;c 2 nm. Since the bilayer with dCu;c 3 nm corresponds to an alloy with x 0:8 an estimate of the thickness, dSb;eff , of that part of the Sb ®lm which contributes to the interface is possible, yielding dSb;eff 1:5 nm. This dSb;eff is about a factor 2 larger compared with the corresponding dSb;eff 0:8 nm determined for Au/Sb bilayers [3]. We cannot give an explanation for the dierent dSb;eff s. In future studies investigations of the crystallization temperatures of Cu/Sb bilayers will be performed. Comparing with the corresponding thickness of 3D amorphous Cux Sb1ÿx alloys [6] may give more information about the characteristic parameters of the amorphous interface. 4.2. Resistance per square Finally we discuss the low temperature dependence of R of Cu/Sb bilayers and polycrystalline Cu ®lms. We observe a logarithmic temperature dependence of R below 4 K. The reason for this log T-dependence are quantum corrections due to
779
weak antilocalization and electron±electron interaction [12], and it is valid in 2D, hence showing the reduced dimension of our ®lms. From the temperature dependence of R , electronic parameters describing these eects can be determined. These are a p (weak antilocalization) and (1ÿF ) (electron±electron interaction) [12] which can be separated from a combined measurement of R and the Hall coecient, RH . However, since no Hall measurements were possible in our case, we could only determine the sum of both, i.e. a p + (1ÿF ). We ®nd the surprising result a p 1 ÿ F 0:8 independent of dCu for bilayers and polycrystalline ®lms (as far as dCu < 10 nm). However, due to the dierent properties of the bilayers and the polycrystalline ®lms as described above we expected dierences in the electronic properties of both. Hence, further investigations of RH and the magneto-resistance are necessary.
5. Conclusions The seebeck coecient, S, and its low temperature slope, S=T jT !0 , have been used to investigate the formation of an homogeneously amorphous CuSb alloy at the interface of Cu on top of amorphous Sb at low temperatures (T 20 K). The interface reaction is restricted to Cu coverages smaller than the critical value dCu;c 3 nm. The total thickness of the amorphous interface was determined and it has a maximum of approximately 4.5 nm which corresponds to an CuSb alloy with 80 at.% Cu. If the Cu coverages is larger than dCu;c the Cu grows as a polycrystalline ®lm on the amorphous interface.
References [1] M. Seyert, A. Siber, P. Ziemann, Phys. Rev. Lett. 67 (1991) 3792. [2] H.-G. Boyen, G. Indlekofer, G. Gantner, H. Stupp, A. Cossy-Favre, P. Oelhafen, Phys. Rev. B 51 (1995) 17096. [3] C. Lauinger, F. Baumann, H.-G. Boyen, J. Phys.: Condens. Matter 8 (1996) 6653. [4] H.-G. Boyen, A. Cossy-Favre, P. Oelhafen, A. Siber, P. Ziemann, C. Lauinger, T. Moser, P. H aussler, F. Baumann, Phys. Rev. B 51 (1995) 1791.
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J. Barzola-Quiquia et al. / Journal of Non-Crystalline Solids 250±252 (1999) 776±780
[5] C. Lauinger, F. Baumann, J. Phys.: Condens. Matter 7 (1995) 1305. [6] P. Haussler, Phys. Rep. 222 (1995) 65. [7] J.J. Hauser, Phys. Rev. B 9 (1974) 2623. [8] E. Compans, Rev. Sci. Instrum. 60 (1989) 2715.
[9] R.I. Boughton, J. Low Temp. Phys. 37 (1979) 31. [10] J.R. Sambles, T.W. Priest, J. Phys. F 14 (1984) 1693. [11] C. Lauinger, T. Hunger, J. Barzola-Quiquia, P. H aussler, H.-G. Boyen, these Proceedings, p. 791. [12] G. Bergmann, Phys. Rep. 107 (1984) 1.