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TiN bilayers deposited by laser molecular beam epitaxy
Vacuum 85 (2011) 1037e1041
Contents lists available at ScienceDirect
Vacuum journal homepage: www.elsevier.com/locate/vacuum
Microstructure and optical properties of cubic AlN/TiN bilayers deposited by laser molecular beam epitaxy Fu Yuechun*, Meng Xianghai, Yang Weijia, He Huan, Shen Xiaoming Key Laboratory of New Processing Technology for Materials and Nonferrous Metal, Ministry of Education, College of Materials Science and Engineering, Guangxi University, Nanning, Guangxi 530004, China
a r t i c l e i n f o
a b s t r a c t
Article history: Received 14 October 2010 Accepted 1 March 2011
AlN/TiN bilayers were deposited on Si(100) substrates with varying laser pulse energy by laser molecular beam epitaxy (LMBE) technique, and their growth mode, crystal structure and optical properties were investigated. The results indicated that atomically flat TiN single films and AlN/TiN bilayers with layerby-layer growth mode were successfully grown on Si(100) substrates at optimal laser pulse energy. Both TiN and AlN in the grown bilayers exhibited the NaCl-type cubic structure with the same (200) preferred orientation, showing an excellent epitaxial relationship. TiN single film was more reflective in the infrared range and presented a small transparent window centered at wavelength of 404 nm. Reflectance spectrum of AlN film on top of TiN indicated the sharp absorption at about 246 nm, yielding a bandgap energy of 5.04 eV comparable to the theoretical calculation of bulk cubic AlN, but scarcely reported by the experimental data. Ó 2011 Elsevier Ltd. All rights reserved.
Keywords: Cubic AlN/TiN bilayers Laser molecular beam epitaxy Microstructure Optical properties
1. Introduction AlN/TiN multilayer films are extensively studied as hard coatings due to the high hardness and thermal stability of TiN and the elevated thermal conductivity and bending strength of AlN [1e3]. Moreover, AlN has large bandgap and high dielectric constant, and TiN is an excellent contact material for AlN for its high electrical conductivity and low contact resistance. So the AlN/TiN structures are potential materials in a number of optoelectronic and electronic applications. It is well known that AlN has two crystal structures, a stable wurtzite structure with hexagonal symmetry and a metastable zincblende or NaCl structure with cubic symmetry. Though NaCl-type cubic AlN has higher lattice matching with TiN, investigations of AlN/TiN multilayers showed that cubic AlN films with a critical thickness of 2e3 nm could be stabilized on TiN templates. Beyond this range, the AlN phase was found to exhibit the hexagonal crystallite [4e6]. As for AlN/TiN bilayers with larger thickness, hexagonal AlN phases were favored on TiN films, and a mixed hexagonal and cubic AlN phases were also observed depending on the growth conditions [7e9]. Laser molecular beam epitaxy (LMBE) technique is now popularly used to deposit thin films for the precise controlling of film
* Corresponding author. Tel.: þ86 771 3270152. E-mail address: [email protected] (F. Yuechun). 0042-207X/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.vacuum.2011.03.014
growth [10,11]. The nonequilibrium nature of the LMBE process is desirable for the synthesis of metastable cubic AlN, and thus cubic AlN/TiN bilayers and multilayers would present significant differences in the physical and electronic properties as compared with those of hexagonal phases. In this paper, cubic AlN/TiN bilayers were prepared on Si(100) substrates with varying laser pulse energy by LMBE technique. The growth mode, crystal structure and optical properties of TiN single films and AlN/TiN bilayers were examined.
2. Experiments A series of TiN single films and AlN/TiN bilayers were deposited on Si(100) substrates using LMBE technique. KrF excimer laser (l ¼ 248 nm, s ¼ 10 ns) with the repetition rate of 5 Hz was focused on the nominally stoichiometric targets of AlN (99.9% purity) and TiN (99.9% purity) which were mounted 5 cm apart from the substrate. A base pressure less than 105 Pa was achieved by using a turbo-molecular pump, and the working pressure was 103 Pa for TiN and 101 Pa for AlN by controlling the gas flow of N2 (99.999% purity). For TiN depositions, the substrate temperature was kept at 700 C and the laser pulse energy was in the range of 100e200 mJ. As for AlN depositions, the substrate temperature and laser pulse energy range were 750 C and 80e150 mJ, respectively. During depositions, the growth mode and thickness of films were characterized by in situ reflection high-energy electron diffraction
1038
F. Yuechun et al. / Vacuum 85 (2011) 1037e1041
(RHEED), and the typical thickness of AlN and TiN under study was 70e100 nm and 10e70 nm, respectively. The crystal structures of TiN and AlN/TiN films were characterized by X-ray diffraction (XRD) (Rigaku D/MAX-RB), and scanning electron microscopy (SEM) (Hitachi S-3400N) equipped with electron backscattered diffraction (EBSD). Optical reflectance spectra of the films were acquired using UVeVIS spectrometer (PerkineElmer Lambda950). 3. Results and discussion 3.1. TiN depositions The initial study was carried out to deposit TiN films with good surface and crystalline qualities on Si(100) substrates. Fig. 1 shows the RHEED patterns of TiN films prepared under different laser pulse energy. At energy of 100 mJ, the RHEED pattern exhibits a clear spotty pattern, indicating the three-dimensional growth mode and rough surface. When deposited at 150 mJ, the diffraction spots become streaky, which reveals that the growth of TiN film is changing from the island mode to the layer-by-layer mode. Atomically flat TiN film with layer-by-layer growth mode was obtained at laser energy of 200 mJ, which is evidenced by the distinct streaky pattern as shown in Fig. 1(c). It is generally accepted that the high kinetic energies of the ablated species impinging on a growing film enhance the surface mobility and thereby improve the crystalline quality [12]. The present study confirms that the high kinetic energy can be imparted to the deposited Ti and N atoms/ions at higher laser energy, and hence the film surface is rearranged under equilibrium to get the higher quality. The XRD patterns of corresponding TiN films are shown in Fig. 2. All films in the investigated laser energy range only show the TiN(200) reflex, which is to be expected from the RHEED results.
Fig. 2. XRD patterns of TiN films prepared as a function of laser pulse energy.
The EBSD scan of TiN film deposited at 200 mJ is shown in Fig. 3. A single-crystal film has been detected which is confirmed by the pole figure only exhibiting the (100) orientation. Therefore, it is deduced that TiN films could be grown on Si(100) substrates with strong orientation. 3.2. AlN/TiN bilayers depositions Firstly, highly orientated TiN films were deposited on Si(100) substrates at laser pulse energy of 200 mJ, and then investigations were proceeded to prepare optimal AlN films on these TiN films with varying laser energy. The RHEED patterns of AlN films
Fig. 1. The RHEED patterns of TiN films deposited under different laser pulse energy (a) 100 mJ, (b) 150 mJ, (c) 200 mJ.
F. Yuechun et al. / Vacuum 85 (2011) 1037e1041
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Fig. 3. (a) EBSD pattern and (b) (001) pole figure of TiN film deposited at laser pulse energy of 200 mJ.
are shown in Fig. 4. Weak streaky pattern is observed for AlN film deposited at 80 mJ, while the streaks become intensive at laser energy of 110 mJ, showing that AlN film with good crystallinity has been achieved on the TiN film. However, the RHEED pattern of AlN film grown at 150 mJ is ring and halo pattern, indicating that the crystalline structure is random and the film is polycrystalline. XRD patterns of AlN/TiN bilayers denote two important points as shown in Fig. 5. First, AlN presents the NaCl-type cubic structure on TiN(200) in all bilayers, and shows the (200) preferred orientation. No traces of hexagonal AlN were detected for the films deposited at 80 mJ and 110 mJ even if the principal structure of AlN films is believed to be the wurtzite structure. However, a little amount of hexagonal AlN phases appear in the AlN film deposited at 150 mJ. It is supposed that increased
number of collisions at higher laser energy may lead to a variation in the growth direction of AlN films. Second, the AlN film deposited at 110 mJ exhibits the sharp and strong cubic AlN(200) diffraction peak, indicating the high crystalline quality. The XRD results agree well with the RHEED observations and thus the optimal laser energy for AlN deposition is determined as 110 mJ. Fig. 6 shows the pole figure of AlN film deposited at 110 mJ by EBSD. It is clearly seen that the AlN film consists of a cubic phase without the inclusion of a wurtzite phase, and it shows the same (100) orientation as that of the TiN film. This excellent epitaxial relationship between TiN and cubic AlN in this study is partly because of the small lattice mismatch (4.6%) between them, and partly due to the high crystallinity of TiN film with atomically flat surface and large thickness. The terminating atomic layer of TiN(200) could enhance the surface migration and nucleation of
Fig. 4. The RHEED patterns of AlN films deposited under different laser pulse energy (a) 80 mJ, (b) 110 mJ, (c) 150 mJ.
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F. Yuechun et al. / Vacuum 85 (2011) 1037e1041
Fig. 5. XRD patterns of AlN/TiN bilayers fabricated as a function of laser pulse energy.
AlN, and thus cubic AlN can stably exist in wide thickness range. As for AlN/TiN multilayers, thin TiN films could only stabilize the cubic AlN in a few nanometers [4e6]. The present AlN/TiN bilayers are expected to play a significant role on the applications in electronics and optoelectronics. 3.3. Optical properties The reflective performances of TiN single film and AlN/TiN bilayers deposited at desirable conditions are shown in Fig. 7. TiN film is more reflective in the infrared range and exhibits a minimum reflectance centered at wavelength of 404 nm. It was reported that stoichiometric TiN yielded a small transparent window at the transmittance peak of 411 nm [13], which is comparable to the present result. For AlN/TiN bilayers, light rays pierce through a 100 nm thick AlN film and then are reflected by a mirror-like conducting TiN template. In the near ultraviolet region, the reflectance of AlN film declines sharply, indicating the strong absorption at about 246 nm. This absorption yields a bandgap energy of 5.04 eV, which is consistent with the theoretical calculation of bulk cubic AlN [14], but scarcely reported by the experimental data. However, no interference pattern is observed in the visible region probably due to the thin thickness of AlN film.
Fig. 7. Reflectance spectra of (a)TiN single film and (b) AlN/TiN bilayers.
4. Conclusions Atomically flat TiN single films and AlN/TiN bilayers with layer-bylayer growth mode were successfully grown on Si(100) substrates at optimal laser pulse energy using LMBE technique. In the grown bilayers, TiN and AlN films showed an excellent epitaxial relationship evidenced by the same NaCl-type cubic structure with (200) preferred orientation. Reflectance spectra showed that TiN single film was more reflective in the infrared range and exhibited a small transparent window centered at wavelength of 404 nm. The AlN film deposited on top of TiN possessed a bandgap energy of 5.04 eV, which is consistent with the theoretical calculation of bulk cubic AlN. Acknowledgments This work was financially supported by the Open Foundation of the Key Lab of New Processing Technology for Nonferrous Metals and Materials under Project No. GXKFJ09-24 and GXKFZ-05. References
Fig. 6. Pole figure of AlN film deposited at laser pulse energy of 110 mJ.
[1] Thobor A, Rousselot C, Clement C, Takadoum J, Martin N, Sanjines R, et al. Enhancement of mechanical properties of TiN/AlN multilayers by modifying the number and the quality of interfaces. Surf Coat Technol 2000;124:210e21. [2] Lim JW, Lee SH, Lee JJ. Preparation and properties of nanoscale multilayered TiN/AlN coatings deposited by plasma enhanced chemical vapor deposition. Surf Coat Technol 2003;169e170:460e3. [3] Mei FH, Shao N, Dai JW, Li GY. Coherent growth and superhardness effect of AlN/TiN nanomultilayers. Mater Lett 2004;58:3477e80.
F. Yuechun et al. / Vacuum 85 (2011) 1037e1041 [4] Chen D, Ma XL, Wang YM. Thickness-dependent structural transformation in the AlN film. Acta Mater 2005;53:5223e7. [5] Kim IW, Li Q, Marks LD, Barnett SA. Critical thickness for transformation of epitaxially stabilized cubic AlN in superlattices. Appl Phys Lett 2001;78: 892e4. [6] Pankov V, Evstigneev M, Prince RH. Role of substrate in the pseudomorphic stabilization of rocksalt-type AlN phase in AlN/TiN superlattices. Appl Phys Lett 2002;80:4142e4. [7] Auger MA, Sanchez O, Ballesteros C, Jergel M, Aguilar-Frutis M, Falcony C. TiN/ AlN bilayers and multilayers grown by magnetron co-sputtering. Thin Solid Films 2003;433:211e6. [8] Vasco Boutos T, Sanjinés R, Karimi A. Effects of deposition temperature and bilayer thickness on the mechanical properties of AlN/TiN multilayer thin films. Surf Coat Technol 2004;188e189:409e14.
1041
[9] Talyansky V, Vispute RD, Ramesh R, Sharma RP, Venkatesan T, Li YX, et al. Fabrication and characterization of epitaxial AlN/TiN bilayers on sapphire. Thin Solid Films 1998;323:37e41. [10] Wang XQ, Yoshikawa A. Molecular beam epitaxy growth of GaN, AlN and InN. Prog Cryst Growth Charact Mater 2004;48e49:42e103. [11] Joyce BA, Joyce TB. Basic studies of molecular beam epitaxy-past, present and some future directions. J Cryst Growth 2004;264:605e19. [12] Willmott PR, Timm R, Huber JR. RHEED analysis of interface growth modes of TiN films on Si(100) produced by crossed beam laser ablation. Appl Surf Sci 1998;127e129:105e10. [13] Smith GB, Swift PD. TiNx films with metallic behavior at high N/Ti ratios for better solar control windows. Appl Phys Lett 1999;75:630e2. [14] Rubio A, Corkill JL, Cohen ML, Shirley EL, Louie SG. Quasiparticle band structure of AlN and GaN. Phys Rev B 1993;48:11810e6.
Contents lists available at ScienceDirect
Vacuum journal homepage: www.elsevier.com/locate/vacuum
Microstructure and optical properties of cubic AlN/TiN bilayers deposited by laser molecular beam epitaxy Fu Yuechun*, Meng Xianghai, Yang Weijia, He Huan, Shen Xiaoming Key Laboratory of New Processing Technology for Materials and Nonferrous Metal, Ministry of Education, College of Materials Science and Engineering, Guangxi University, Nanning, Guangxi 530004, China
a r t i c l e i n f o
a b s t r a c t
Article history: Received 14 October 2010 Accepted 1 March 2011
AlN/TiN bilayers were deposited on Si(100) substrates with varying laser pulse energy by laser molecular beam epitaxy (LMBE) technique, and their growth mode, crystal structure and optical properties were investigated. The results indicated that atomically flat TiN single films and AlN/TiN bilayers with layerby-layer growth mode were successfully grown on Si(100) substrates at optimal laser pulse energy. Both TiN and AlN in the grown bilayers exhibited the NaCl-type cubic structure with the same (200) preferred orientation, showing an excellent epitaxial relationship. TiN single film was more reflective in the infrared range and presented a small transparent window centered at wavelength of 404 nm. Reflectance spectrum of AlN film on top of TiN indicated the sharp absorption at about 246 nm, yielding a bandgap energy of 5.04 eV comparable to the theoretical calculation of bulk cubic AlN, but scarcely reported by the experimental data. Ó 2011 Elsevier Ltd. All rights reserved.
Keywords: Cubic AlN/TiN bilayers Laser molecular beam epitaxy Microstructure Optical properties
1. Introduction AlN/TiN multilayer films are extensively studied as hard coatings due to the high hardness and thermal stability of TiN and the elevated thermal conductivity and bending strength of AlN [1e3]. Moreover, AlN has large bandgap and high dielectric constant, and TiN is an excellent contact material for AlN for its high electrical conductivity and low contact resistance. So the AlN/TiN structures are potential materials in a number of optoelectronic and electronic applications. It is well known that AlN has two crystal structures, a stable wurtzite structure with hexagonal symmetry and a metastable zincblende or NaCl structure with cubic symmetry. Though NaCl-type cubic AlN has higher lattice matching with TiN, investigations of AlN/TiN multilayers showed that cubic AlN films with a critical thickness of 2e3 nm could be stabilized on TiN templates. Beyond this range, the AlN phase was found to exhibit the hexagonal crystallite [4e6]. As for AlN/TiN bilayers with larger thickness, hexagonal AlN phases were favored on TiN films, and a mixed hexagonal and cubic AlN phases were also observed depending on the growth conditions [7e9]. Laser molecular beam epitaxy (LMBE) technique is now popularly used to deposit thin films for the precise controlling of film
* Corresponding author. Tel.: þ86 771 3270152. E-mail address: [email protected] (F. Yuechun). 0042-207X/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.vacuum.2011.03.014
growth [10,11]. The nonequilibrium nature of the LMBE process is desirable for the synthesis of metastable cubic AlN, and thus cubic AlN/TiN bilayers and multilayers would present significant differences in the physical and electronic properties as compared with those of hexagonal phases. In this paper, cubic AlN/TiN bilayers were prepared on Si(100) substrates with varying laser pulse energy by LMBE technique. The growth mode, crystal structure and optical properties of TiN single films and AlN/TiN bilayers were examined.
2. Experiments A series of TiN single films and AlN/TiN bilayers were deposited on Si(100) substrates using LMBE technique. KrF excimer laser (l ¼ 248 nm, s ¼ 10 ns) with the repetition rate of 5 Hz was focused on the nominally stoichiometric targets of AlN (99.9% purity) and TiN (99.9% purity) which were mounted 5 cm apart from the substrate. A base pressure less than 105 Pa was achieved by using a turbo-molecular pump, and the working pressure was 103 Pa for TiN and 101 Pa for AlN by controlling the gas flow of N2 (99.999% purity). For TiN depositions, the substrate temperature was kept at 700 C and the laser pulse energy was in the range of 100e200 mJ. As for AlN depositions, the substrate temperature and laser pulse energy range were 750 C and 80e150 mJ, respectively. During depositions, the growth mode and thickness of films were characterized by in situ reflection high-energy electron diffraction
1038
F. Yuechun et al. / Vacuum 85 (2011) 1037e1041
(RHEED), and the typical thickness of AlN and TiN under study was 70e100 nm and 10e70 nm, respectively. The crystal structures of TiN and AlN/TiN films were characterized by X-ray diffraction (XRD) (Rigaku D/MAX-RB), and scanning electron microscopy (SEM) (Hitachi S-3400N) equipped with electron backscattered diffraction (EBSD). Optical reflectance spectra of the films were acquired using UVeVIS spectrometer (PerkineElmer Lambda950). 3. Results and discussion 3.1. TiN depositions The initial study was carried out to deposit TiN films with good surface and crystalline qualities on Si(100) substrates. Fig. 1 shows the RHEED patterns of TiN films prepared under different laser pulse energy. At energy of 100 mJ, the RHEED pattern exhibits a clear spotty pattern, indicating the three-dimensional growth mode and rough surface. When deposited at 150 mJ, the diffraction spots become streaky, which reveals that the growth of TiN film is changing from the island mode to the layer-by-layer mode. Atomically flat TiN film with layer-by-layer growth mode was obtained at laser energy of 200 mJ, which is evidenced by the distinct streaky pattern as shown in Fig. 1(c). It is generally accepted that the high kinetic energies of the ablated species impinging on a growing film enhance the surface mobility and thereby improve the crystalline quality [12]. The present study confirms that the high kinetic energy can be imparted to the deposited Ti and N atoms/ions at higher laser energy, and hence the film surface is rearranged under equilibrium to get the higher quality. The XRD patterns of corresponding TiN films are shown in Fig. 2. All films in the investigated laser energy range only show the TiN(200) reflex, which is to be expected from the RHEED results.
Fig. 2. XRD patterns of TiN films prepared as a function of laser pulse energy.
The EBSD scan of TiN film deposited at 200 mJ is shown in Fig. 3. A single-crystal film has been detected which is confirmed by the pole figure only exhibiting the (100) orientation. Therefore, it is deduced that TiN films could be grown on Si(100) substrates with strong orientation. 3.2. AlN/TiN bilayers depositions Firstly, highly orientated TiN films were deposited on Si(100) substrates at laser pulse energy of 200 mJ, and then investigations were proceeded to prepare optimal AlN films on these TiN films with varying laser energy. The RHEED patterns of AlN films
Fig. 1. The RHEED patterns of TiN films deposited under different laser pulse energy (a) 100 mJ, (b) 150 mJ, (c) 200 mJ.
F. Yuechun et al. / Vacuum 85 (2011) 1037e1041
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Fig. 3. (a) EBSD pattern and (b) (001) pole figure of TiN film deposited at laser pulse energy of 200 mJ.
are shown in Fig. 4. Weak streaky pattern is observed for AlN film deposited at 80 mJ, while the streaks become intensive at laser energy of 110 mJ, showing that AlN film with good crystallinity has been achieved on the TiN film. However, the RHEED pattern of AlN film grown at 150 mJ is ring and halo pattern, indicating that the crystalline structure is random and the film is polycrystalline. XRD patterns of AlN/TiN bilayers denote two important points as shown in Fig. 5. First, AlN presents the NaCl-type cubic structure on TiN(200) in all bilayers, and shows the (200) preferred orientation. No traces of hexagonal AlN were detected for the films deposited at 80 mJ and 110 mJ even if the principal structure of AlN films is believed to be the wurtzite structure. However, a little amount of hexagonal AlN phases appear in the AlN film deposited at 150 mJ. It is supposed that increased
number of collisions at higher laser energy may lead to a variation in the growth direction of AlN films. Second, the AlN film deposited at 110 mJ exhibits the sharp and strong cubic AlN(200) diffraction peak, indicating the high crystalline quality. The XRD results agree well with the RHEED observations and thus the optimal laser energy for AlN deposition is determined as 110 mJ. Fig. 6 shows the pole figure of AlN film deposited at 110 mJ by EBSD. It is clearly seen that the AlN film consists of a cubic phase without the inclusion of a wurtzite phase, and it shows the same (100) orientation as that of the TiN film. This excellent epitaxial relationship between TiN and cubic AlN in this study is partly because of the small lattice mismatch (4.6%) between them, and partly due to the high crystallinity of TiN film with atomically flat surface and large thickness. The terminating atomic layer of TiN(200) could enhance the surface migration and nucleation of
Fig. 4. The RHEED patterns of AlN films deposited under different laser pulse energy (a) 80 mJ, (b) 110 mJ, (c) 150 mJ.
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F. Yuechun et al. / Vacuum 85 (2011) 1037e1041
Fig. 5. XRD patterns of AlN/TiN bilayers fabricated as a function of laser pulse energy.
AlN, and thus cubic AlN can stably exist in wide thickness range. As for AlN/TiN multilayers, thin TiN films could only stabilize the cubic AlN in a few nanometers [4e6]. The present AlN/TiN bilayers are expected to play a significant role on the applications in electronics and optoelectronics. 3.3. Optical properties The reflective performances of TiN single film and AlN/TiN bilayers deposited at desirable conditions are shown in Fig. 7. TiN film is more reflective in the infrared range and exhibits a minimum reflectance centered at wavelength of 404 nm. It was reported that stoichiometric TiN yielded a small transparent window at the transmittance peak of 411 nm [13], which is comparable to the present result. For AlN/TiN bilayers, light rays pierce through a 100 nm thick AlN film and then are reflected by a mirror-like conducting TiN template. In the near ultraviolet region, the reflectance of AlN film declines sharply, indicating the strong absorption at about 246 nm. This absorption yields a bandgap energy of 5.04 eV, which is consistent with the theoretical calculation of bulk cubic AlN [14], but scarcely reported by the experimental data. However, no interference pattern is observed in the visible region probably due to the thin thickness of AlN film.
Fig. 7. Reflectance spectra of (a)TiN single film and (b) AlN/TiN bilayers.
4. Conclusions Atomically flat TiN single films and AlN/TiN bilayers with layer-bylayer growth mode were successfully grown on Si(100) substrates at optimal laser pulse energy using LMBE technique. In the grown bilayers, TiN and AlN films showed an excellent epitaxial relationship evidenced by the same NaCl-type cubic structure with (200) preferred orientation. Reflectance spectra showed that TiN single film was more reflective in the infrared range and exhibited a small transparent window centered at wavelength of 404 nm. The AlN film deposited on top of TiN possessed a bandgap energy of 5.04 eV, which is consistent with the theoretical calculation of bulk cubic AlN. Acknowledgments This work was financially supported by the Open Foundation of the Key Lab of New Processing Technology for Nonferrous Metals and Materials under Project No. GXKFJ09-24 and GXKFZ-05. References
Fig. 6. Pole figure of AlN film deposited at laser pulse energy of 110 mJ.
[1] Thobor A, Rousselot C, Clement C, Takadoum J, Martin N, Sanjines R, et al. Enhancement of mechanical properties of TiN/AlN multilayers by modifying the number and the quality of interfaces. Surf Coat Technol 2000;124:210e21. [2] Lim JW, Lee SH, Lee JJ. Preparation and properties of nanoscale multilayered TiN/AlN coatings deposited by plasma enhanced chemical vapor deposition. Surf Coat Technol 2003;169e170:460e3. [3] Mei FH, Shao N, Dai JW, Li GY. Coherent growth and superhardness effect of AlN/TiN nanomultilayers. Mater Lett 2004;58:3477e80.
F. Yuechun et al. / Vacuum 85 (2011) 1037e1041 [4] Chen D, Ma XL, Wang YM. Thickness-dependent structural transformation in the AlN film. Acta Mater 2005;53:5223e7. [5] Kim IW, Li Q, Marks LD, Barnett SA. Critical thickness for transformation of epitaxially stabilized cubic AlN in superlattices. Appl Phys Lett 2001;78: 892e4. [6] Pankov V, Evstigneev M, Prince RH. Role of substrate in the pseudomorphic stabilization of rocksalt-type AlN phase in AlN/TiN superlattices. Appl Phys Lett 2002;80:4142e4. [7] Auger MA, Sanchez O, Ballesteros C, Jergel M, Aguilar-Frutis M, Falcony C. TiN/ AlN bilayers and multilayers grown by magnetron co-sputtering. Thin Solid Films 2003;433:211e6. [8] Vasco Boutos T, Sanjinés R, Karimi A. Effects of deposition temperature and bilayer thickness on the mechanical properties of AlN/TiN multilayer thin films. Surf Coat Technol 2004;188e189:409e14.
1041
[9] Talyansky V, Vispute RD, Ramesh R, Sharma RP, Venkatesan T, Li YX, et al. Fabrication and characterization of epitaxial AlN/TiN bilayers on sapphire. Thin Solid Films 1998;323:37e41. [10] Wang XQ, Yoshikawa A. Molecular beam epitaxy growth of GaN, AlN and InN. Prog Cryst Growth Charact Mater 2004;48e49:42e103. [11] Joyce BA, Joyce TB. Basic studies of molecular beam epitaxy-past, present and some future directions. J Cryst Growth 2004;264:605e19. [12] Willmott PR, Timm R, Huber JR. RHEED analysis of interface growth modes of TiN films on Si(100) produced by crossed beam laser ablation. Appl Surf Sci 1998;127e129:105e10. [13] Smith GB, Swift PD. TiNx films with metallic behavior at high N/Ti ratios for better solar control windows. Appl Phys Lett 1999;75:630e2. [14] Rubio A, Corkill JL, Cohen ML, Shirley EL, Louie SG. Quasiparticle band structure of AlN and GaN. Phys Rev B 1993;48:11810e6.