- Email: [email protected]
Incorporation of Mn atoms into the GaAs(110) surface
Journal of Crystal Growth ] (]]]]) ]]]–]]]
Contents lists available at SciVerse ScienceDirect
Journal of Crystal Growth journal homepage: www.elsevier.com/locate/jcrysgro
Incorporation of Mn atoms into the GaAs(110) surface Motoi Hirayama n, Shiro Tsukamoto Anan National College of Technology, 265 Aoki, Minobayashi, Anan, Tokushima 774-0017, Japan
a r t i c l e i n f o
abstract
Keywords: A1. Surface structure A3. Molecular beam epitaxy B1. Gallium compounds B1. Nanomaterials B3. Magnetic materials
We have investigated Mn atoms on a GaAs(110) surface prepared by molecular beam epitaxy. Atomicscale local structures have been observed at the temperature of 200 1C: single Mn atom and double Mn atoms exist in Ga row on scanning tunneling microscope (STM) images. We also show simulated STM images of Ga-substituted Mn atoms of GaAs(110), calculated from the first-principles calculations. Both experimental and theoretical STM images of single and double Mn configurations are in good agreement with each other. Therefore, the Mn atoms seems to be incorporated into the topmost Ga site due to STM images. & 2013 Elsevier B.V. All rights reserved.
1. Introduction Diluted magnetic semiconductors have been expected for materials of spin-memories or spin-operating devices, so-called spintronic devices. In particular, many Mn compounds in III–V semiconductors draw great attentions for materials of such devices [1]. A Mn doping into a III–V semiconductors, particularly GaAs, leads electronic properties to half-metallic [2]. A Mn atom interacts with the neighboring Mn atom through threedimensional hole states coupled with Mn 3d orbitals [3]. Behaviors of Mn atoms on GaAs surfaces are very important for well-controlled interfaces between semiconductors and magnetic materials including half-metals. Well-aligned interfacial structures of a hexagonal MnAs have been realized on the GaAs surfaces by a molecular beam epitaxy (MBE) method [4–6]. In particular, a GaAs(110) surface has surprisingly good epitaxial match with the hexagonal MnAs½1120 [6]. An initial growth of the MnAs on the GaAs(110) surface has been investigated, and MnAs nanocrystals with surprisingly ultrahigh density have been formed at the initial stage of MnAs formations [7]. Recently, the substitution of a Mn atom with the topmost Ga atom on the GaAs(110) surface can be realized, using the substitution technique by a scanning tunneling microscope (STM) tip [8]. A Mn pair substituted using such a technique exhibits the ferromagnetic coupling of Mn core spins [9]. Surface Mn atoms located at an interstitial and a substitutional position have been identified, using cross-sectional STM measurements and simulations of a STM image based on the density functional theory [10]. Theoretical calculations have also been clarified that one-dimensional alignments of the substitutional Mn atoms on
n
Corresponding author. Tel.: þ81 884 23 7100. E-mail address: [email protected] (M. Hirayama).
the GaAs(110) surface induce a strong magnetic coupling through anisotropic surface states [11]. We aim to confirm a structural realizability of the Mn atoms in the GaAs(110) surface using the STM. To verify Mn incorporations in the GaAs(110), we simulated the STM images calculated from first-principles calculations based on the spin-density functional theory. We also investigated a realizability of the atomic-scale halfmetallic systems by experimental and theoretical approaches.
2. Experimental and calculation details We perform MBE growth of the Mn atoms on the GaAs(110). A Mn flux is irradiated on the GaAs(110)-(1 1) surface at the temperature of 200 1C after growing a buffer layer at 550 1C. We estimate that an amount of the Mn atoms was 0.05 ML from Mn amounts in the case of MnSb. We observe Mn atoms on GaAs(110) at the temperature of 200 1C using a STM system without breaking the vacuum environment [12]. We also perform the first-principles calculations based on the pseudopotential method within the spin-density functional theory [13–15]. The generalized gradient approximation is used for the exchange-correlation potential [16]. The cutoff energy is set to be 36 Ry for a plane wave expansion. 64k points are used for the integration over the two-dimensional (1 1) Brillouin zone. The structural relaxation is carried out until the remaining forces acting on atoms are less than 103 Hartree=aB . The constantcurrent STM images are calculated from the local density of states, using Tersoff–Hamann approximation [17,18]. A slab for the clean GaAs(110)-(1 1) surface with a thickness of six atomic layers is prepared as a calculation model. Two layers of Ga and As atoms from the back side of the slab are fixed at the bulk position, and the back side surface is terminated with H atoms and their bond lengths are fixed at the optimized values.
0022-0248/$ - see front matter & 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.jcrysgro.2012.12.173
Please cite this article j.jcrysgro.2012.12.173i
as:
M.
Hirayama,
S.
TsukamotoJournal
of
Crystal
Growth
(2013),
http://dx.doi.org/10.1016/
2
M. Hirayama, S. Tsukamoto / Journal of Crystal Growth ] (]]]]) ]]]–]]]
Mn atoms are substituted with the topmost Ga atoms on the GaAs(110)-(1 1) reconstructed surface. One or two Mn atoms are substituted in the area of a (4 4) unit cell.
3. Results and discussions We have observed the Mn-irradiated GaAs(110) surface using STM. Fig. 1 shows the STM images of the Mn atoms on the GaAs(110) surface. We can see beautiful stripes of the Ga row along the /110S-direction, as shown in Fig. 1(a). Then, some bright areas superimposed on the Ga row intersperse on the surface. These features seem to be induced by a Mn atom on/in the surface, since these features disappear in the STM images of the clean GaAs(110) surface. The fact that the bright spots are just on the Ga-row indicates that the Mn atoms are not physisorbed on the surface [19]. The relationship between the tip bias and the brightness on the STM images is consistent with the crosssectional STM measurement [10]. Different features appear in other regions. A bright spot also appears in Fig. 1(b). The Mn-induced signs are superimposed on the Ga stripes, and the Mn atoms seem to be observed as the bright areas in the empty state images. This feature, at first glance, looks like a single Mn atom as in Fig. 1(a). However, this bright spot indicates a sign of double configuration of Mn atoms. Details of the analysis are explained below. We also demonstrate the simulated STM images calculated from the first-principles calculations. The origin of the tip bias is the Fermi energy in the majority spin band of a metallic nature. Fig. 2 shows the calculated STM images of Ga-substituted Mn atoms on GaAs(110). Periodically aligned bright dots correspond to the topmost Ga positions, namely the dots indicate the empty Ga 4p states. These dots can be observed as the stripes of the Ga row shown in Fig. 1. Although the Ga 4p states couple with the topmost As 4p states, the substituted Mn atoms form the p–d hybridized states with the topmost As atoms [11]. The bright areas in the vicinity of the Mn atoms seem to be reflected in the Mn 3d states hybridized with the valence band maximum of GaAs. A single Mn atom substituted in the Ga site appears as the brighter spot than that on the Ga sites, as shown in Fig. 2(a). This feature is qualitatively good agreement with the experimental STM image shown in Fig. 1(a). On the other hand, double Mn atoms induce a triangular alignment of bright spots, as shown in Fig. 2(b). Two of these spots correspond to the location at the Mn atoms substituted in the topmost Ga site and the other at the topmost As site. The location and the appearance of the bright spots agree with the experimental STM image except the bright spot at the As site.
<001>
<001>
<110>
<110>
<001> <110> Fig. 2. Calculated STM images of (a) single Mn atom and (b) double Mn atoms on GaAs(110) surface obtained at the tip bias of 2.0 V. The area of the STM images is set to be 3.2 nm 4.6 nm for /110S- and /001S-directions, respectively. This size corresponds to a (8 8) unit cell of GaAs(110)-(1 1).
We also evaluated line profiles of the experimental and the simulated STM images to discuss quantitatively. Fig. 3 shows the line profiles of the single and the double Mn configurations corresponding to Fig. 1(a) and (b), respectively. The experimental profiles are broader than the theoretical ones because the STM tip has a finite radius. Additionally, asymmetric profiles in the /110S-direction are also caused by the tip condition and the scan direction. The tip height on the single Mn atom, as shown in Fig. 3(a) and (b), is higher than that on the nearest neighbor by approximately 0.02 nm. This situation is consistent with the simulated profiles on which the difference on the constant-current height between in the single Mn atom and in the nearest neighbor is 0.02 nm. This difference mainly results from the atomic positions of the Mn and the Ga atoms located at the surface: the height difference between the Mn and the Ga atoms is 0.02 nm, which is much larger than the difference in the atomic radii [20]. If the Mn atom is located at an interstitial position, the height difference may be over 0.1 nm [21]. In the /110S-direction, as shown in Fig. 3(a), a breadth of the experimental profile near the Mn atom is relatively sharp more than near the Ga row. Furthermore, these features agree with the theoretical profiles. This means that the surface Mn atom is alone. We can conclude that the single Mn atom is substituted with the topmost Ga atom. In the case of the double Mn configuration shown in Fig. 1(b), the line profile of the experimental STM image shown in Fig. 3(c) and (d) indicates that the tip-height difference between on the Ga row including the Mn atoms and that on the nearest neighbor is approximately 0.02 nm. This value agrees well with the difference in the constant-current height of the simulated STM image shown in Fig. 3(d), and also the simulated profile of the single Mn atom, as shown in Fig. 3(b). In the /110S-direction, as shown in Fig. 3(c), a breadth of the experimental profile near the Mn atom is relatively broad in comparison with the single Mn configuration discussed above. These features agree well with the theoretical profiles. This means that the Mn atoms form pair configuration, and two Mn atoms located at the adjoining Ga sites. Thus, the double Mn atoms are also substituted with the topmost Ga atoms. To obtain more positive information, spin-polarized STM measurements or scanning tunneling spectroscopy measurements are needed.
4. Summary Fig. 1. Topographic STM images of Mn atoms on GaAs(110). The area of the STM images is 4 nm 4 nm, obtained at a tip bias of 1.0 V and a tunneling current of 0.8 nA.
Please cite this article j.jcrysgro.2012.12.173i
as:
M.
Hirayama,
S.
We have investigated the MBE prepared Mn atoms on the GaAs(110) surface, and succeeded to observe the atomic-scale features by STM measurements: the single Mn atom and the
TsukamotoJournal
of
Crystal
Growth
(2013),
http://dx.doi.org/10.1016/
M. Hirayama, S. Tsukamoto / Journal of Crystal Growth ] (]]]]) ]]]–]]]
0.03
0.03
0.02
0.02 0.01
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Height (nm)
0.01 0.00 -0.01 -0.02
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3
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Fig. 3. Comparison of line profiles between experimental (solid line) and theoretical (dashed line) STM images. The profiles are taken from (a) (b) Fig. 1(a) and (c) (d) Fig. 1(b), and drawn in (a) (c) /110S- and (b) (d) /001S-directions.
double Mn atoms exist in the Ga row. We also show the simulated STM images calculated from the first-principles calculations. For the single and double Mn configurations, both images from the experimental and the theoretical approaches are good agreement with each other. Therefore, the Mn atoms seem to be incorporated into the Ga row on STM images obtained at the temperature of 200 1C. We have succeeded to realize the local structures for the spintronic materials in an atomic-scale without extremely low temperature environments.
Acknowledgements The authors thank Dr. G. Bell for helpful discussion, and also thank Mr. T. Teraoka for assistance of experiments. References ˇ ´ , J. Fabian, S. Das Sarma, Reviews of Modern Physics 76 (2004) [1] I. Zutic 323–410, http://dx.doi.org/10.1103/RevModPhys.76.323. [2] H. Ohno, A. Shen, F. Matsukura, A. Oiwa, A. Endo, S. Katsumoto, Y. Iye, Applied Physics Letters 69 (3) (1996) 363–365, http://dx.doi.org/10.1063/1.118061. [3] T. Dietl, H. Ohno, F. Matsukura, Physical Review B 63 (2001) 195205, http://d x.doi.org/10.1103/PhysRevB.63.195205. ¨ [4] A. Trampert, F. Schippan, L. Daweritz, K.H. Ploog, Applied Physics Letters 78 (17) (2001) 2461–2463, http://dx.doi.org/10.1063/1.1367302. [5] N. Mattoso, M. Eddrief, J. Varalda, A. Ouerghi, D. Demaille, V.H. Etgens, Y. Garreau, Physical Review B 70 (2004) 115324, http://dx.doi.org/10.1103/ PhysRevB.70.115324.
Please cite this article j.jcrysgro.2012.12.173i
as:
M.
Hirayama,
S.
¨ [6] L. Daweritz, D. Kolovos-Vellianitis, A. Trampert, C. Herrmann, K.H. Ploog, E. Bauer, A. Locatelli, S. Cherifi, S. Heun, Journal de Physique IV France 132 (2006) 159–162, http://dx.doi.org/10.1051/jp4:2006132031. [7] M. Hirayama, G.R. Bell, S. Tsukamoto, Journal of Vacuum Science and Technology B 29 (4) (2011) 04D109, http://dx.doi.org/10.1116/1.3610963. [8] D. Kitchen, A. Richardella, A. Yazdani, Journal of Superconductivity 18 (2005) 23–28, http://dx.doi.org/10.1007/s10948-005-2144-x. [9] D. Kitchen, A. Richardella, J.-M. Tang, M.E. Flatte´, A. Yazdani, Nature 442 (2006) 436, http://dx.doi.org/10.1038/nature04971. [10] A. Stroppa, X. Duan, M. Peressi, D. Furlanetto, S. Modesti, Physical Review B 75 (2007) 195335, http://dx.doi.org/10.1103/PhysRevB.75.195335. [11] M. Hirayama, J. Nakamura, A. Natori, Journal of Vacuum Science and Technology B 27 (4) (2009) 2062–2065, http://dx.doi.org/10.1116/1.3153285. [12] S. Tsukamoto, T. Honma, G. Bell, A. Ishii, Y. Arakawa, Small 2 (3) (2006) 386–389, http://dx.doi.org/10.1002/smll.200500339. [13] M. Tsukada, et al., Computer Program Package TAPP, University of Tokyo, Tokyo, Japan, 1983–2012. [14] J. Yamauchi, M. Tsukada, S. Watanabe, O. Sugino, Physical Review B 54 (1996) 5586–5603, http://dx.doi.org/10.1103/PhysRevB.54.5586. [15] J. Yamauchi, M. Tsukada, S. Watanabe, O. Sugino, Surface Science 341 (3) (1995) L1037–L1041, http://dx.doi.org/10.1016/0039-6028(95)00826-8. [16] J.P. Perdew, K. Burke, M. Ernzerhof, Physical Review Letters 77 (1996) 3865–3868, http://dx.doi.org/10.1103/PhysRevLett.77.3865. [17] J. Bardeen, Physical Review Letters 6 (1961) 57–59, http://dx.doi.org/ 10.1103/PhysRevLett.6.57. [18] J. Tersoff, D.R. Hamann, Physical Review B 31 (1985) 805–813, http://dx.doi.org/ 10.1103/PhysRevB.31.805. [19] A. Stroppa, X. Duan, M. Peressi, Materials Science and Engineering: B 126 (2–3) (2006) 217–221, http://dx.doi.org/10.1016/j.mseb.2005.09.033. [20] J.C. Slater, The Journal of Chemical Physics 41 (10) (1964) 3199–3204, http:// dx.doi.org/10.1063/1.1725697. [21] J.X. Cao, X.G. Gong, R.Q. Wu, Physical Review B 72 (2005) 153410, http://dx.doi. org/10.1103/PhysRevB.72.153410.
TsukamotoJournal
of
Crystal
Growth
(2013),
http://dx.doi.org/10.1016/
Contents lists available at SciVerse ScienceDirect
Journal of Crystal Growth journal homepage: www.elsevier.com/locate/jcrysgro
Incorporation of Mn atoms into the GaAs(110) surface Motoi Hirayama n, Shiro Tsukamoto Anan National College of Technology, 265 Aoki, Minobayashi, Anan, Tokushima 774-0017, Japan
a r t i c l e i n f o
abstract
Keywords: A1. Surface structure A3. Molecular beam epitaxy B1. Gallium compounds B1. Nanomaterials B3. Magnetic materials
We have investigated Mn atoms on a GaAs(110) surface prepared by molecular beam epitaxy. Atomicscale local structures have been observed at the temperature of 200 1C: single Mn atom and double Mn atoms exist in Ga row on scanning tunneling microscope (STM) images. We also show simulated STM images of Ga-substituted Mn atoms of GaAs(110), calculated from the first-principles calculations. Both experimental and theoretical STM images of single and double Mn configurations are in good agreement with each other. Therefore, the Mn atoms seems to be incorporated into the topmost Ga site due to STM images. & 2013 Elsevier B.V. All rights reserved.
1. Introduction Diluted magnetic semiconductors have been expected for materials of spin-memories or spin-operating devices, so-called spintronic devices. In particular, many Mn compounds in III–V semiconductors draw great attentions for materials of such devices [1]. A Mn doping into a III–V semiconductors, particularly GaAs, leads electronic properties to half-metallic [2]. A Mn atom interacts with the neighboring Mn atom through threedimensional hole states coupled with Mn 3d orbitals [3]. Behaviors of Mn atoms on GaAs surfaces are very important for well-controlled interfaces between semiconductors and magnetic materials including half-metals. Well-aligned interfacial structures of a hexagonal MnAs have been realized on the GaAs surfaces by a molecular beam epitaxy (MBE) method [4–6]. In particular, a GaAs(110) surface has surprisingly good epitaxial match with the hexagonal MnAs½1120 [6]. An initial growth of the MnAs on the GaAs(110) surface has been investigated, and MnAs nanocrystals with surprisingly ultrahigh density have been formed at the initial stage of MnAs formations [7]. Recently, the substitution of a Mn atom with the topmost Ga atom on the GaAs(110) surface can be realized, using the substitution technique by a scanning tunneling microscope (STM) tip [8]. A Mn pair substituted using such a technique exhibits the ferromagnetic coupling of Mn core spins [9]. Surface Mn atoms located at an interstitial and a substitutional position have been identified, using cross-sectional STM measurements and simulations of a STM image based on the density functional theory [10]. Theoretical calculations have also been clarified that one-dimensional alignments of the substitutional Mn atoms on
n
Corresponding author. Tel.: þ81 884 23 7100. E-mail address: [email protected] (M. Hirayama).
the GaAs(110) surface induce a strong magnetic coupling through anisotropic surface states [11]. We aim to confirm a structural realizability of the Mn atoms in the GaAs(110) surface using the STM. To verify Mn incorporations in the GaAs(110), we simulated the STM images calculated from first-principles calculations based on the spin-density functional theory. We also investigated a realizability of the atomic-scale halfmetallic systems by experimental and theoretical approaches.
2. Experimental and calculation details We perform MBE growth of the Mn atoms on the GaAs(110). A Mn flux is irradiated on the GaAs(110)-(1 1) surface at the temperature of 200 1C after growing a buffer layer at 550 1C. We estimate that an amount of the Mn atoms was 0.05 ML from Mn amounts in the case of MnSb. We observe Mn atoms on GaAs(110) at the temperature of 200 1C using a STM system without breaking the vacuum environment [12]. We also perform the first-principles calculations based on the pseudopotential method within the spin-density functional theory [13–15]. The generalized gradient approximation is used for the exchange-correlation potential [16]. The cutoff energy is set to be 36 Ry for a plane wave expansion. 64k points are used for the integration over the two-dimensional (1 1) Brillouin zone. The structural relaxation is carried out until the remaining forces acting on atoms are less than 103 Hartree=aB . The constantcurrent STM images are calculated from the local density of states, using Tersoff–Hamann approximation [17,18]. A slab for the clean GaAs(110)-(1 1) surface with a thickness of six atomic layers is prepared as a calculation model. Two layers of Ga and As atoms from the back side of the slab are fixed at the bulk position, and the back side surface is terminated with H atoms and their bond lengths are fixed at the optimized values.
0022-0248/$ - see front matter & 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.jcrysgro.2012.12.173
Please cite this article j.jcrysgro.2012.12.173i
as:
M.
Hirayama,
S.
TsukamotoJournal
of
Crystal
Growth
(2013),
http://dx.doi.org/10.1016/
2
M. Hirayama, S. Tsukamoto / Journal of Crystal Growth ] (]]]]) ]]]–]]]
Mn atoms are substituted with the topmost Ga atoms on the GaAs(110)-(1 1) reconstructed surface. One or two Mn atoms are substituted in the area of a (4 4) unit cell.
3. Results and discussions We have observed the Mn-irradiated GaAs(110) surface using STM. Fig. 1 shows the STM images of the Mn atoms on the GaAs(110) surface. We can see beautiful stripes of the Ga row along the /110S-direction, as shown in Fig. 1(a). Then, some bright areas superimposed on the Ga row intersperse on the surface. These features seem to be induced by a Mn atom on/in the surface, since these features disappear in the STM images of the clean GaAs(110) surface. The fact that the bright spots are just on the Ga-row indicates that the Mn atoms are not physisorbed on the surface [19]. The relationship between the tip bias and the brightness on the STM images is consistent with the crosssectional STM measurement [10]. Different features appear in other regions. A bright spot also appears in Fig. 1(b). The Mn-induced signs are superimposed on the Ga stripes, and the Mn atoms seem to be observed as the bright areas in the empty state images. This feature, at first glance, looks like a single Mn atom as in Fig. 1(a). However, this bright spot indicates a sign of double configuration of Mn atoms. Details of the analysis are explained below. We also demonstrate the simulated STM images calculated from the first-principles calculations. The origin of the tip bias is the Fermi energy in the majority spin band of a metallic nature. Fig. 2 shows the calculated STM images of Ga-substituted Mn atoms on GaAs(110). Periodically aligned bright dots correspond to the topmost Ga positions, namely the dots indicate the empty Ga 4p states. These dots can be observed as the stripes of the Ga row shown in Fig. 1. Although the Ga 4p states couple with the topmost As 4p states, the substituted Mn atoms form the p–d hybridized states with the topmost As atoms [11]. The bright areas in the vicinity of the Mn atoms seem to be reflected in the Mn 3d states hybridized with the valence band maximum of GaAs. A single Mn atom substituted in the Ga site appears as the brighter spot than that on the Ga sites, as shown in Fig. 2(a). This feature is qualitatively good agreement with the experimental STM image shown in Fig. 1(a). On the other hand, double Mn atoms induce a triangular alignment of bright spots, as shown in Fig. 2(b). Two of these spots correspond to the location at the Mn atoms substituted in the topmost Ga site and the other at the topmost As site. The location and the appearance of the bright spots agree with the experimental STM image except the bright spot at the As site.
<001>
<001>
<110>
<110>
<001> <110> Fig. 2. Calculated STM images of (a) single Mn atom and (b) double Mn atoms on GaAs(110) surface obtained at the tip bias of 2.0 V. The area of the STM images is set to be 3.2 nm 4.6 nm for /110S- and /001S-directions, respectively. This size corresponds to a (8 8) unit cell of GaAs(110)-(1 1).
We also evaluated line profiles of the experimental and the simulated STM images to discuss quantitatively. Fig. 3 shows the line profiles of the single and the double Mn configurations corresponding to Fig. 1(a) and (b), respectively. The experimental profiles are broader than the theoretical ones because the STM tip has a finite radius. Additionally, asymmetric profiles in the /110S-direction are also caused by the tip condition and the scan direction. The tip height on the single Mn atom, as shown in Fig. 3(a) and (b), is higher than that on the nearest neighbor by approximately 0.02 nm. This situation is consistent with the simulated profiles on which the difference on the constant-current height between in the single Mn atom and in the nearest neighbor is 0.02 nm. This difference mainly results from the atomic positions of the Mn and the Ga atoms located at the surface: the height difference between the Mn and the Ga atoms is 0.02 nm, which is much larger than the difference in the atomic radii [20]. If the Mn atom is located at an interstitial position, the height difference may be over 0.1 nm [21]. In the /110S-direction, as shown in Fig. 3(a), a breadth of the experimental profile near the Mn atom is relatively sharp more than near the Ga row. Furthermore, these features agree with the theoretical profiles. This means that the surface Mn atom is alone. We can conclude that the single Mn atom is substituted with the topmost Ga atom. In the case of the double Mn configuration shown in Fig. 1(b), the line profile of the experimental STM image shown in Fig. 3(c) and (d) indicates that the tip-height difference between on the Ga row including the Mn atoms and that on the nearest neighbor is approximately 0.02 nm. This value agrees well with the difference in the constant-current height of the simulated STM image shown in Fig. 3(d), and also the simulated profile of the single Mn atom, as shown in Fig. 3(b). In the /110S-direction, as shown in Fig. 3(c), a breadth of the experimental profile near the Mn atom is relatively broad in comparison with the single Mn configuration discussed above. These features agree well with the theoretical profiles. This means that the Mn atoms form pair configuration, and two Mn atoms located at the adjoining Ga sites. Thus, the double Mn atoms are also substituted with the topmost Ga atoms. To obtain more positive information, spin-polarized STM measurements or scanning tunneling spectroscopy measurements are needed.
4. Summary Fig. 1. Topographic STM images of Mn atoms on GaAs(110). The area of the STM images is 4 nm 4 nm, obtained at a tip bias of 1.0 V and a tunneling current of 0.8 nA.
Please cite this article j.jcrysgro.2012.12.173i
as:
M.
Hirayama,
S.
We have investigated the MBE prepared Mn atoms on the GaAs(110) surface, and succeeded to observe the atomic-scale features by STM measurements: the single Mn atom and the
TsukamotoJournal
of
Crystal
Growth
(2013),
http://dx.doi.org/10.1016/
M. Hirayama, S. Tsukamoto / Journal of Crystal Growth ] (]]]]) ]]]–]]]
0.03
0.03
0.02
0.02 0.01
Height (nm)
Height (nm)
0.01 0.00 -0.01 -0.02
0.00 -0.01 -0.02 -0.03
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3
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Fig. 3. Comparison of line profiles between experimental (solid line) and theoretical (dashed line) STM images. The profiles are taken from (a) (b) Fig. 1(a) and (c) (d) Fig. 1(b), and drawn in (a) (c) /110S- and (b) (d) /001S-directions.
double Mn atoms exist in the Ga row. We also show the simulated STM images calculated from the first-principles calculations. For the single and double Mn configurations, both images from the experimental and the theoretical approaches are good agreement with each other. Therefore, the Mn atoms seem to be incorporated into the Ga row on STM images obtained at the temperature of 200 1C. We have succeeded to realize the local structures for the spintronic materials in an atomic-scale without extremely low temperature environments.
Acknowledgements The authors thank Dr. G. Bell for helpful discussion, and also thank Mr. T. Teraoka for assistance of experiments. References ˇ ´ , J. Fabian, S. Das Sarma, Reviews of Modern Physics 76 (2004) [1] I. Zutic 323–410, http://dx.doi.org/10.1103/RevModPhys.76.323. [2] H. Ohno, A. Shen, F. Matsukura, A. Oiwa, A. Endo, S. Katsumoto, Y. Iye, Applied Physics Letters 69 (3) (1996) 363–365, http://dx.doi.org/10.1063/1.118061. [3] T. Dietl, H. Ohno, F. Matsukura, Physical Review B 63 (2001) 195205, http://d x.doi.org/10.1103/PhysRevB.63.195205. ¨ [4] A. Trampert, F. Schippan, L. Daweritz, K.H. Ploog, Applied Physics Letters 78 (17) (2001) 2461–2463, http://dx.doi.org/10.1063/1.1367302. [5] N. Mattoso, M. Eddrief, J. Varalda, A. Ouerghi, D. Demaille, V.H. Etgens, Y. Garreau, Physical Review B 70 (2004) 115324, http://dx.doi.org/10.1103/ PhysRevB.70.115324.
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