- Email: [email protected]
Rectification and resistive switching in mesoscopic heterostructures based on Bi2Se3
Materials Letters 158 (2015) 403–405
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Rectification and resistive switching in mesoscopic heterostructures based on Bi2Se3 N.А. Тulina n, А.N. Rossolenko, I.М. Shmytko, N.N. Кolesnikov, D.N. Borisenko, S.I. Bozhko, A.M. Ionov Institute of Solid State Physics RAS, Chernogolovka, Russia
art ic l e i nf o
a b s t r a c t
Article history: Received 5 June 2015 Accepted 15 June 2015 Available online 16 June 2015
We fabricated mesoscopic heterostructures based on topological insulator Bi2Se3 which exhibit a bipolar resistive switching (BRS) effect. The BRS effect could be related to the interface effect and the current transfer in such junctions exhibits a diode character with Schottky-like barriers in heavily doped semiconductors. It was shown that the deviation of the current–voltage characteristics (CVC) from the classic current transport Schottky-like diode behavior is due to the influence of the electric field on spreading resistance Rs that is temperature dependent and modified in strong electric fields. & 2015 Published by Elsevier B.V.
Keywords: Heterostructures Bithmus selenide Diode Resistive switching
1. Indroduction Resistive switching (RS) in heterostructures based on various compounds is a phenomenon that is intensively studied in nanotechnology to produce elements of a new generation of twoterminal nonvolatile memory with record breaking sizes and data transfer (nano-scale memristor matrices as ultra-low energy memory with an ultra-high density for mobile applications) [1–3]. There are two types of resistive switching: unipolar and bipolar. The first type is used to create phase change memory and is based on amorphous/crystalline phase changes (amorphous chalcogenide glasses, amorphous oxides of transition metals), which involve release of electric field energy for heating of the junction region. The current–voltage characteristics of such structures are unipolar. The problem was thoroughly studied and theoretically substantiated although it is not yet completely understood [4,5]. Phase change memory technology has recently made considerable advances and found application in mass production of phase change memory elements and other practical devices [6]. The other type, bipolar resistive switching effects, exhibits either an ionic bond character or electronic transition. Ionic switching is related to ionic transport in solid dielectrics where several scenarios are feasible. A new phase is forming as a response to the electric field in the percolation channel (the electroforming process). In the frame of another scenario a junction-specific region is generated in the heterojunction near the electrodes, for instance, a Schottky barrier, its properties n
Corresponding author. E-mail address: [email protected] (N.А.
Тulina).
http://dx.doi.org/10.1016/j.matlet.2015.06.060 0167-577X/& 2015 Published by Elsevier B.V.
determined by those of the material, controlled by the electric field and modified by the ionic transport. The situation allows a methodical investigation of the switching process and creating theoretical models for their comparison with the experimental data as well as for a directed design of real junctions. Most compounds exhibiting the BRS effect are oxides, namely, high temperature superconductors (HTSC), doped manganites (colossal magnetoresistance compounds) and binary oxides. The investigation of the BRS effect in Bi2Se3-based heterostructures is of interest mostly from the viewpoint of observing the BRS effect in non-oxide structures. On the other hand, topological insulator (TI) Bi2Se3, a novel material with unusual properties, is now the subject of intensive theoretical and experimental studies [7]. The influence of the defect state on the resistive properties of Bi2Se3 is attractive to researchers in view of solving the problem of the topological insulator [7]. By varying the external parameters, it is possible to realize different metastable “Off” (high resistance state) and “On” (low resistance state) states that are proposed to be used in electronic memory devices. Therefore, heterostructures based on a topological insulator are interesting from the viewpoint of the TI problems and understanding the BRS mechanism.
2. Results Film heterojunctions based on thermally evaporated Bi2Se3 films were made. Two types of junctions were studied: mesoscopic film junctions with amorphous bismuth selenide (as-deposited Bi2Se3 thin film), mesoscopic junctions which were subjected to
404
N.А.
Тulina et al. / Materials Letters 158 (2015) 403–405
Fig. 1. Examples of influence of annealing on CVC of mesoscopic Ag–BiSe–Nb structures. Ag – top electrode (TE), Nb – bottom electrode (BE), grounded. Upper left corner: a chip with mesoscopic structures. Center: the СVC of the structures with amorphous bismuth selenide (solid squares) annealed at 200 °С for 1 h (solid circles). In the bottom right corner shown are the x-ray diffraction spectra of asdeposited Bi2Se3 films (a), and films after annealing at 200 °С for 1 h (b).
postmetallization annealing (PMA). The 1.4 mkm Bi2Se3 films were studied by x-ray photoelectron spectroscopy and x-ray analysis using a D500 (Siemens) diffractometer. The topological surface microstructure of the thermally evaporated Bi2Se3 films was studied by means of a SUPRA II scanning microscope and an atomicforce microscope Solver PROM (NT MDT). The mesoscopic heterostructures were produced by photolithography, the formed Ag–BiSe–Nb structure had a contact window 50 50 mkm2 or 10 10 mkm2 in size. The heterostructures were subjected to postmetallization annealing at 200 °С, 400 °С and 500 °С for 1 h. The structures annealed at 400 °С and 500 °С were investigated to reveal BRS effects. The CVC and the temperature dependences of the metastable state resistance were measured. Figs. 1–3 show the main results obtained. Fig. 1 presents examples of the influence of annealing on the CVC of the mesoscopic Ag–BiSe–Nb structures. From the x-ray spectra it is seen that the Bi2Se3 structure was realized in the samples in question by annealing at 200 °С [8,9]. Fig. 2 shows the temperature dependences of the CVC of the Ag–BiSe–Nb diodes. Fig. 3 presents examples of the BRS effect in the mesoscopic structures based on nanostructured Bi2Se3 films produced by postmetallization annealing. x-ray structural analysis reveals that PMA transfers the film into a multi-phase nanocrystalline state.
3. Discussion As it is seen from Fig. 1, the CVC of the mesoscopic structures based on the amorphous bismuth selenide films are symmetrical. The СVС of the structures after crystallization annealing demonstrate a diode character of the conductivity (Figs. 1 and 2). Based on the diode nature of the СVС of the heterostructures, we assume that they are Schottky-like diodes. In the case of perfect Schottky barriers the current is carried through the structure by a thermally stimulated carrier flow (relationship (1))
Fig. 2. СVС of Ag–BiSe–Nb diodes: open circles-T ¼ 297 K, solid squares-T ¼325 K, solid circles-T ¼336 K, solid squares-T¼ 386 K; solid line: a classic Schottky behavior, relationship (1); stars-relationship (2) Upper left corner: the change of the СVС of the heavily doped semiconductor from the diode to ohmic behavior with increasing number of carriers [10]. 1-N ¼1018 cm 3; 2-N ¼ 1*1019 cm 3; 3-N ¼2*1019 cm 3. Bottom right corner: example of temperature dependence of mesoscopic Ag–BiSe–Nb structures resistance.
Fig. 3. BRS effect in mesoscopic structures based on nanostructured Bi2Se3 films produced by postmetallization annealing: open circles – the CVC of the mesoscopic Al–BiSe–Nb structures; solid circles-Ag–BiSe–Nb. Upper left corner: the x-ray spectra of the samples subjected to PMA (500 °С for 1 h). Bottom right corner: CVC approximation, the СVС with resistive switching exhibit Poole–Frenkel-type current contributions (Ln(I/V)–V1/2). Bottom left corner: the microphotograph of the annealed film (500 °С for 1 h).
I = I0[exp(eV /n*kT ) − 1} ,
where I0
= A*T2*S*exp( − (eфв − ev)/kT ),
(1)
A* is the Richardson number, n is the imperfection factor, фв is the barrier height, S is the contact area. In heavily doped defect structures the height and width of the barrier depend on its charge system. The inset to Fig. 2 shows the СVС of the Schottky barriers as a function of the number of carriers in the semiconductor [10]. The СVС of the structures for the direct and indirect voltage in
N.А.
Тulina et al. / Materials Letters 158 (2015) 403–405
the structures in question are nearly linear functions, which suggests the presence of series resistance Rs, spreading resistance, which should be taken into account when modeling the transport properties of the structures by the relationship
I = I0[exp((eV − I*Rs)/n*kT ) − 1}
(2)
The calculated СVС are shown in Fig. 2, n ¼1, Rs ¼1800 Ω, barrier height ф ¼0.46 eV. The specific feature of the structures obtained is the high resistivity of the bismuth selenide in the mesoscopic structure which is about 5 Ω сm (Fig. 2). The influence of the defect state on the resistance properties of Bi2Se3 is attractive to researchers in view of solving the problem of the topological insulator. The original Bi2Se3 sample must be an insulator with a gap of the order of 0.3 eV and a 2D surface layer with a specific linear dispersion of the density state. So far all the samples obtained had metallic conduction of ρ ¼10 4 Ω сm [6], which is due to the influence of the selenium vacancies that have low formation energy [11,12]. In our case post-metallization annealing transfers the amorphous bismuth selenide film to a multi-phase nanostructured state, which is evidenced by the wide reflexes of the x-ray structure spectra (inset to Fig. 3) and the microphotograph of the annealed films. It has been recently shown in Refs. [13,14] that the physical properties of nanostructured oxides are essentially dependent on intergranular boundary defects. It may be assumed that in our case PMA also increases the number of the defects in the grain boundaries which are responsible for the high resistance of the annealed samples and enhance the BRS effect (Fig. 3). As it is seen from Fig. 3, at large bias the high resistance СVС branches of the structures with a BRS effect have a Poole–Frenkel (current) contribution (Ln(I/V)–V1/2). At the same time the low resistance СVС branch is linear in the logarithmic current–voltage coordinates, which is typical of Schottky thermionic emission with transition to dependence I¼CUk, the mode of spatial charge-limited currents. The development of the Poole–Frenkel mechanism during current transfer points to the existence of localized donor centers, and selenium vacancies are considered to be such donors in bismuth selenide. They may create levels as well as small zones in the dielectric gap. A sufficiently strong electric field (about 105 V/сm) stimulates the process of electrodiffusion of mobile defects (selenium vacancies) thus modulating a barrier during current transfer. This scenario accomplishes a reversible switching process. In work [10] it is shown that the diode properties of the metal–semiconductor junction are dependent on the number of carriers in the semiconductor (Fig. 2) and observed in semiconductors with a number of carriers less than1019 сm 3. The number of carriers and spreading resistance are temperature dependent. The change in the СVС of the diodes is related to
405
the decrease of Rs(Т) as well as the change in the number of carriers activated from the local centers by the temperature and the electric field. Thus, the BRS effects observed in the annealed structures are associated with the influence of the electric field on the number of carriers near the Schottky barrier in heavily doped semiconductors and transition of the contact to the ohmic regime. This also changes spreading resistance Rs(Т), which, in turn, affects the CVC making them a linear function of voltage. However, reversible bipolar resistive switching may originate from several processes, probably trapping–detrapping in nanostructured bismuth selenide. In conclusion, for the first time the diode properties have been realized and the BRS effect has been investigated in mesoscopic structures based on nanostructured Bi2Se3 films. The BRS effects observed in the annealed samples are related to the influence of the electric field on the number of carriers near the Schottky barrier in heavily doped semiconductors and transition of the contact from the diode to the ohmic regime.
Acknowledgments The work was supported by the Russian Foundation for Basic Research, Grant no. 14-07-00951, and the programs of the Physical Sciences Division RAS “Physics of Novel Materials and Structures”.
References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14]
R. Waser, M. Aono, Nat. Mater. 6 (2007) 833. Y.V. Pershin, M.D. Ventra, Adv. Phys. 60 (2011) 145. N.A. Tulina, Phys.-Uspekhi 50 (2007) 1171. M. Nardone, M. Simon, I.V. Karpov, V.G. Karpov, J. Appl. Phys. 112 (2012) 071101. N.A. Bogoslovskiy, K.D. Tsendin, Fiz. Tverd. Tela 46 (2012) 577 (in Russian). G.W. Burr, M.J. Breitwisch, M. Franceschini, et al., J. Vac. Sci. Technol. B 28 (2010) 223. M.Z. Hasan, C.L. Kale, Rev. Mod. Phys. 82 (2012) 3045. T.E. Manjulavalli, T. Balassubramanian, D. Nataraj, Chalcogenide Lett. 5 (2008) 297. L.I. Soliman, M.M. Nassary, H.T. Shaban, A.S. Salwa, Vacuum 85 (2010) 358. D. Schroeder, Adv. Solid State Phys. 36 (1996) 26. L. Xue, P. Zhou, C.X. Zhang, C.Y. He, G.L. Hao, L.Z. Sun, J.X. Zhong, arXiv: 1207.0103v1 [cond-mat.mtrl-sci], 2012. Zhi Ren, A.A. Taskin, Satoshi Sasaki, Kouji Segawa, Yoichi Ando, Phys. Rev. B 82 (2010) 241306. B.B. Straumal, S.G. Protasova, A.A. Mazilkin, et al., Beilstein J. Nanotechnol. 4 (2013) 361. N.A. Tulina, A.N. Rossolenko, I.Yu Borisenko, A.M. Ionov, I.M. Shmytko, A. A. Ivanov, Mater. Lett. 136 (2014) 404.
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Rectification and resistive switching in mesoscopic heterostructures based on Bi2Se3 N.А. Тulina n, А.N. Rossolenko, I.М. Shmytko, N.N. Кolesnikov, D.N. Borisenko, S.I. Bozhko, A.M. Ionov Institute of Solid State Physics RAS, Chernogolovka, Russia
art ic l e i nf o
a b s t r a c t
Article history: Received 5 June 2015 Accepted 15 June 2015 Available online 16 June 2015
We fabricated mesoscopic heterostructures based on topological insulator Bi2Se3 which exhibit a bipolar resistive switching (BRS) effect. The BRS effect could be related to the interface effect and the current transfer in such junctions exhibits a diode character with Schottky-like barriers in heavily doped semiconductors. It was shown that the deviation of the current–voltage characteristics (CVC) from the classic current transport Schottky-like diode behavior is due to the influence of the electric field on spreading resistance Rs that is temperature dependent and modified in strong electric fields. & 2015 Published by Elsevier B.V.
Keywords: Heterostructures Bithmus selenide Diode Resistive switching
1. Indroduction Resistive switching (RS) in heterostructures based on various compounds is a phenomenon that is intensively studied in nanotechnology to produce elements of a new generation of twoterminal nonvolatile memory with record breaking sizes and data transfer (nano-scale memristor matrices as ultra-low energy memory with an ultra-high density for mobile applications) [1–3]. There are two types of resistive switching: unipolar and bipolar. The first type is used to create phase change memory and is based on amorphous/crystalline phase changes (amorphous chalcogenide glasses, amorphous oxides of transition metals), which involve release of electric field energy for heating of the junction region. The current–voltage characteristics of such structures are unipolar. The problem was thoroughly studied and theoretically substantiated although it is not yet completely understood [4,5]. Phase change memory technology has recently made considerable advances and found application in mass production of phase change memory elements and other practical devices [6]. The other type, bipolar resistive switching effects, exhibits either an ionic bond character or electronic transition. Ionic switching is related to ionic transport in solid dielectrics where several scenarios are feasible. A new phase is forming as a response to the electric field in the percolation channel (the electroforming process). In the frame of another scenario a junction-specific region is generated in the heterojunction near the electrodes, for instance, a Schottky barrier, its properties n
Corresponding author. E-mail address: [email protected] (N.А.
Тulina).
http://dx.doi.org/10.1016/j.matlet.2015.06.060 0167-577X/& 2015 Published by Elsevier B.V.
determined by those of the material, controlled by the electric field and modified by the ionic transport. The situation allows a methodical investigation of the switching process and creating theoretical models for their comparison with the experimental data as well as for a directed design of real junctions. Most compounds exhibiting the BRS effect are oxides, namely, high temperature superconductors (HTSC), doped manganites (colossal magnetoresistance compounds) and binary oxides. The investigation of the BRS effect in Bi2Se3-based heterostructures is of interest mostly from the viewpoint of observing the BRS effect in non-oxide structures. On the other hand, topological insulator (TI) Bi2Se3, a novel material with unusual properties, is now the subject of intensive theoretical and experimental studies [7]. The influence of the defect state on the resistive properties of Bi2Se3 is attractive to researchers in view of solving the problem of the topological insulator [7]. By varying the external parameters, it is possible to realize different metastable “Off” (high resistance state) and “On” (low resistance state) states that are proposed to be used in electronic memory devices. Therefore, heterostructures based on a topological insulator are interesting from the viewpoint of the TI problems and understanding the BRS mechanism.
2. Results Film heterojunctions based on thermally evaporated Bi2Se3 films were made. Two types of junctions were studied: mesoscopic film junctions with amorphous bismuth selenide (as-deposited Bi2Se3 thin film), mesoscopic junctions which were subjected to
404
N.А.
Тulina et al. / Materials Letters 158 (2015) 403–405
Fig. 1. Examples of influence of annealing on CVC of mesoscopic Ag–BiSe–Nb structures. Ag – top electrode (TE), Nb – bottom electrode (BE), grounded. Upper left corner: a chip with mesoscopic structures. Center: the СVC of the structures with amorphous bismuth selenide (solid squares) annealed at 200 °С for 1 h (solid circles). In the bottom right corner shown are the x-ray diffraction spectra of asdeposited Bi2Se3 films (a), and films after annealing at 200 °С for 1 h (b).
postmetallization annealing (PMA). The 1.4 mkm Bi2Se3 films were studied by x-ray photoelectron spectroscopy and x-ray analysis using a D500 (Siemens) diffractometer. The topological surface microstructure of the thermally evaporated Bi2Se3 films was studied by means of a SUPRA II scanning microscope and an atomicforce microscope Solver PROM (NT MDT). The mesoscopic heterostructures were produced by photolithography, the formed Ag–BiSe–Nb structure had a contact window 50 50 mkm2 or 10 10 mkm2 in size. The heterostructures were subjected to postmetallization annealing at 200 °С, 400 °С and 500 °С for 1 h. The structures annealed at 400 °С and 500 °С were investigated to reveal BRS effects. The CVC and the temperature dependences of the metastable state resistance were measured. Figs. 1–3 show the main results obtained. Fig. 1 presents examples of the influence of annealing on the CVC of the mesoscopic Ag–BiSe–Nb structures. From the x-ray spectra it is seen that the Bi2Se3 structure was realized in the samples in question by annealing at 200 °С [8,9]. Fig. 2 shows the temperature dependences of the CVC of the Ag–BiSe–Nb diodes. Fig. 3 presents examples of the BRS effect in the mesoscopic structures based on nanostructured Bi2Se3 films produced by postmetallization annealing. x-ray structural analysis reveals that PMA transfers the film into a multi-phase nanocrystalline state.
3. Discussion As it is seen from Fig. 1, the CVC of the mesoscopic structures based on the amorphous bismuth selenide films are symmetrical. The СVС of the structures after crystallization annealing demonstrate a diode character of the conductivity (Figs. 1 and 2). Based on the diode nature of the СVС of the heterostructures, we assume that they are Schottky-like diodes. In the case of perfect Schottky barriers the current is carried through the structure by a thermally stimulated carrier flow (relationship (1))
Fig. 2. СVС of Ag–BiSe–Nb diodes: open circles-T ¼ 297 K, solid squares-T ¼325 K, solid circles-T ¼336 K, solid squares-T¼ 386 K; solid line: a classic Schottky behavior, relationship (1); stars-relationship (2) Upper left corner: the change of the СVС of the heavily doped semiconductor from the diode to ohmic behavior with increasing number of carriers [10]. 1-N ¼1018 cm 3; 2-N ¼ 1*1019 cm 3; 3-N ¼2*1019 cm 3. Bottom right corner: example of temperature dependence of mesoscopic Ag–BiSe–Nb structures resistance.
Fig. 3. BRS effect in mesoscopic structures based on nanostructured Bi2Se3 films produced by postmetallization annealing: open circles – the CVC of the mesoscopic Al–BiSe–Nb structures; solid circles-Ag–BiSe–Nb. Upper left corner: the x-ray spectra of the samples subjected to PMA (500 °С for 1 h). Bottom right corner: CVC approximation, the СVС with resistive switching exhibit Poole–Frenkel-type current contributions (Ln(I/V)–V1/2). Bottom left corner: the microphotograph of the annealed film (500 °С for 1 h).
I = I0[exp(eV /n*kT ) − 1} ,
where I0
= A*T2*S*exp( − (eфв − ev)/kT ),
(1)
A* is the Richardson number, n is the imperfection factor, фв is the barrier height, S is the contact area. In heavily doped defect structures the height and width of the barrier depend on its charge system. The inset to Fig. 2 shows the СVС of the Schottky barriers as a function of the number of carriers in the semiconductor [10]. The СVС of the structures for the direct and indirect voltage in
N.А.
Тulina et al. / Materials Letters 158 (2015) 403–405
the structures in question are nearly linear functions, which suggests the presence of series resistance Rs, spreading resistance, which should be taken into account when modeling the transport properties of the structures by the relationship
I = I0[exp((eV − I*Rs)/n*kT ) − 1}
(2)
The calculated СVС are shown in Fig. 2, n ¼1, Rs ¼1800 Ω, barrier height ф ¼0.46 eV. The specific feature of the structures obtained is the high resistivity of the bismuth selenide in the mesoscopic structure which is about 5 Ω сm (Fig. 2). The influence of the defect state on the resistance properties of Bi2Se3 is attractive to researchers in view of solving the problem of the topological insulator. The original Bi2Se3 sample must be an insulator with a gap of the order of 0.3 eV and a 2D surface layer with a specific linear dispersion of the density state. So far all the samples obtained had metallic conduction of ρ ¼10 4 Ω сm [6], which is due to the influence of the selenium vacancies that have low formation energy [11,12]. In our case post-metallization annealing transfers the amorphous bismuth selenide film to a multi-phase nanostructured state, which is evidenced by the wide reflexes of the x-ray structure spectra (inset to Fig. 3) and the microphotograph of the annealed films. It has been recently shown in Refs. [13,14] that the physical properties of nanostructured oxides are essentially dependent on intergranular boundary defects. It may be assumed that in our case PMA also increases the number of the defects in the grain boundaries which are responsible for the high resistance of the annealed samples and enhance the BRS effect (Fig. 3). As it is seen from Fig. 3, at large bias the high resistance СVС branches of the structures with a BRS effect have a Poole–Frenkel (current) contribution (Ln(I/V)–V1/2). At the same time the low resistance СVС branch is linear in the logarithmic current–voltage coordinates, which is typical of Schottky thermionic emission with transition to dependence I¼CUk, the mode of spatial charge-limited currents. The development of the Poole–Frenkel mechanism during current transfer points to the existence of localized donor centers, and selenium vacancies are considered to be such donors in bismuth selenide. They may create levels as well as small zones in the dielectric gap. A sufficiently strong electric field (about 105 V/сm) stimulates the process of electrodiffusion of mobile defects (selenium vacancies) thus modulating a barrier during current transfer. This scenario accomplishes a reversible switching process. In work [10] it is shown that the diode properties of the metal–semiconductor junction are dependent on the number of carriers in the semiconductor (Fig. 2) and observed in semiconductors with a number of carriers less than1019 сm 3. The number of carriers and spreading resistance are temperature dependent. The change in the СVС of the diodes is related to
405
the decrease of Rs(Т) as well as the change in the number of carriers activated from the local centers by the temperature and the electric field. Thus, the BRS effects observed in the annealed structures are associated with the influence of the electric field on the number of carriers near the Schottky barrier in heavily doped semiconductors and transition of the contact to the ohmic regime. This also changes spreading resistance Rs(Т), which, in turn, affects the CVC making them a linear function of voltage. However, reversible bipolar resistive switching may originate from several processes, probably trapping–detrapping in nanostructured bismuth selenide. In conclusion, for the first time the diode properties have been realized and the BRS effect has been investigated in mesoscopic structures based on nanostructured Bi2Se3 films. The BRS effects observed in the annealed samples are related to the influence of the electric field on the number of carriers near the Schottky barrier in heavily doped semiconductors and transition of the contact from the diode to the ohmic regime.
Acknowledgments The work was supported by the Russian Foundation for Basic Research, Grant no. 14-07-00951, and the programs of the Physical Sciences Division RAS “Physics of Novel Materials and Structures”.
References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14]
R. Waser, M. Aono, Nat. Mater. 6 (2007) 833. Y.V. Pershin, M.D. Ventra, Adv. Phys. 60 (2011) 145. N.A. Tulina, Phys.-Uspekhi 50 (2007) 1171. M. Nardone, M. Simon, I.V. Karpov, V.G. Karpov, J. Appl. Phys. 112 (2012) 071101. N.A. Bogoslovskiy, K.D. Tsendin, Fiz. Tverd. Tela 46 (2012) 577 (in Russian). G.W. Burr, M.J. Breitwisch, M. Franceschini, et al., J. Vac. Sci. Technol. B 28 (2010) 223. M.Z. Hasan, C.L. Kale, Rev. Mod. Phys. 82 (2012) 3045. T.E. Manjulavalli, T. Balassubramanian, D. Nataraj, Chalcogenide Lett. 5 (2008) 297. L.I. Soliman, M.M. Nassary, H.T. Shaban, A.S. Salwa, Vacuum 85 (2010) 358. D. Schroeder, Adv. Solid State Phys. 36 (1996) 26. L. Xue, P. Zhou, C.X. Zhang, C.Y. He, G.L. Hao, L.Z. Sun, J.X. Zhong, arXiv: 1207.0103v1 [cond-mat.mtrl-sci], 2012. Zhi Ren, A.A. Taskin, Satoshi Sasaki, Kouji Segawa, Yoichi Ando, Phys. Rev. B 82 (2010) 241306. B.B. Straumal, S.G. Protasova, A.A. Mazilkin, et al., Beilstein J. Nanotechnol. 4 (2013) 361. N.A. Tulina, A.N. Rossolenko, I.Yu Borisenko, A.M. Ionov, I.M. Shmytko, A. A. Ivanov, Mater. Lett. 136 (2014) 404.