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Morphology transition of Ag ultrathin films on Pt (1 1 1): Kinetic Monte Carlo simulation
Applied Surface Science 301 (2014) 289–292
Contents lists available at ScienceDirect
Applied Surface Science journal homepage: www.elsevier.com/locate/apsusc
Morphology transition of Ag ultrathin films on Pt (1 1 1): Kinetic Monte Carlo simulation Shuhan Chen ∗ , Jingming Luo, Shouliang Bu School of Physics and Optical Information Sciences, Jia Ying University, Meizhou 514015, People’s Republic of China
a r t i c l e
i n f o
Article history: Received 11 November 2013 Received in revised form 8 February 2014 Accepted 12 February 2014 Available online 22 February 2014 Keywords: Ultrathin film KMC simulation Competing process Transition temperature
a b s t r a c t Kinetic Monte Carlo simulations are carried out to explore the growth of the Ag ultrathin film on Pt (1 1 1) in the early growth stage. With increasing temperature, the island shapes are demonstrated to transform from fractal to compact and resemble the surface crystal structure at high temperature. The transition temperature of the island evolution is demonstrated to increase with the deposition rate. The competing mechanism between nucleation and growth is pursued. The transition temperature of island evolution is deduced by the average island density distributions and demonstrated by the island morphology evolutions. In addition, the extent of a non-ideal substrate surface is explored. As the interaction energy between adatom and defect point increases, the island shape becomes small and irregular. The effect of surface defect on the nucleation and growth is demonstrated. © 2014 Elsevier B.V. All rights reserved.
1. Introduction Thin films perform a very important role in new materials and are extensively used for electronic devices and optical components [1–4]. Thin films grown under nonequilibrium condition have attracted considerable interest among researchers [5–7]. It is very important to achieve a quantitative understanding of the morphology evolution which evolves when atoms are deposited onto a solid substrate for fundamental and practical reasons. In many cases, the property of the film is determined in the early growth stage. The film growth processes can be strongly affected by fabrication conditions, such as substrate temperature, deposition rate, surface microstructure of substrate, etc. Many theoretical and experimental works have been performed to investigate the role of these factors. Despite considerable work done in recent years analyzing ultrathin film growth, many questions remain unanswered. Many experiments have been performed to observe the fractal islands resembling the diffusion-limited aggregation (DLA) mode at lower substrate temperature [8–10]. The island becomes more compact at high substrate temperature [9]. The competing processes between nucleation and growth are demonstrated by experiment [11]. However, some experiments have observed compact islands at lower temperature [12]. In order to reveal the basic reason for the effect of the fabrication conditions on the growth
∗ Corresponding author. Tel.: +86-753-2186837. E-mail address: [email protected] (S. Chen). http://dx.doi.org/10.1016/j.apsusc.2014.02.066 0169-4332/© 2014 Elsevier B.V. All rights reserved.
morphology of thin film, a variety of kinetic Monte Carlo (KMC) simulation works have been performed [13–20]. These studies provided insight into the structure evolution during thin film growth. We should note that the use of a pure two dimensional (2D) model is correct only if the shape relaxation time is large [21]. In this work, we perform a two dimensional (2D) kinetic Monte Carlo simulation to study the growth of the ultrathin Ag film on Pt (1 1 1) under physical vapor deposition in the early growth stage. The morphologies at different substrate temperatures with different deposition rates are explored. Our results are not only in agreement with the observations of Ag films growth [11], but also predict the morphologies evolution with different temperatures and deposition rates. The competing processes between nucleation and growth are demonstrated. In addition, by introducing a surface factor to represent the extent of a non-ideal substrate surface, the effect of surface defect at different surface factor is discussed. By changing these factors, we obtain different island morphologies. The effect of the energy between surface defect and adatom on the growth of ultrathin film is demonstrated. 2. Simulation model Simulations are performed on a fcc (1 1 1) surface, with a system size of 200 × 200. An atom depositing on the substrate becomes adatom and diffuses randomly along six directions on the hexagonal surface. We assume that the adatom diffuses only to the nearest-neighbor sites. Diffusing to next-nearest-neighbor sites is forbidden because higher activation energy is needed [22]. The
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simulation increment for any given event to occur t is given time n by t = v (− ln R), where vi is the rate of the event i to occur, i i=1 and R is a random number between 0 and 1. The possible events are simplified as follows.
After a diffusion event, the diffusion rates for the affected atoms are updated. We stop the simulation when the coverage value is obtained (and thus neglect the adatom evaporation in our model).
(i) Procedure for a deposition event. An Ag atom deposits at a user-defined deposition rate and becomes an adatom adsorbed on the surface. The adsorption site can be chosen randomly to imitate the film growth on hexagonal substrate (ii) Procedure for a diffusion event. A diffusion event is selected randomly. The selecting probability is proportional to its rate. The atom moves to the new site specified by a diffusion event.
The diffusion rate is given by Arrhenius rate equation vij→i j = v0 exp(−E/kB T ), where v0 = 1 × 1012 is attempt frequency, E is activation barrier, kB is Boltzmann’s constant, and T is the substrate temperature. For fcc metals simple bond-counting arguments usually give the correct answer when searching for optimum structure [23]. We note that using bond-counting kinetics is reasonable for Ag (1 1 1) [24]. So simple bond-counting kinetics in our simulation
Fig. 1. The morphologies of Ag island formation on Pt (1 1 1) at different substrate temperature (F = 1.7 × 10−5 ML/s, = 0.1 ML).
Fig. 2. The morphologies of Ag island formation on Pt (1 1 1) at different temperatures (F = 1.7 ML/s, = 0.1 ML).
S. Chen et al. / Applied Surface Science 301 (2014) 289–292
model is used, with activation barrier to any transition being given by E = (1 + ˇ)Es + nEb , where n is the number of nearest-neighbor atoms, which have bond energy Eb . Here we only consider the interaction energy between adatom and near-neighbor atoms, but the effect of the next near-neighbor atoms is not taken into account. We set Eb = 0.18 eV [25]. In our work, the effects of non-ideal surface, such as surface defects steps, terraces are considered by introducing a surface parameter ˇ. The barrier Es = 0.16 eV represents the interaction energy between adatom and ideal substrate surface [26]. The surface factor ˇ = 0 represents the substrate is ideal. The interaction energy between adatom and defect increases with the factor . First, we have checked the reasonableness of parameters in this model. By using these parameters which were accurately estimated by first principle calculations or experiments [25,26] in our model, the morphologies we simulated generally agree with the experiment [11] at 110 K and 280 K with almost the same deposition rate, as is shown in Fig. 1.
291
Fig. 3. The island density distributions for different temperatures at the deposition rate of 1.7 × 10−5 ML/s and 1.7 ML/s respectively ( = 0.1 ML).
3. Results and discussion With the simulation scheme described above, we simulate the evolution of Ag ultrathin films with different substrate temperatures at the deposition flux F = 1.7 × 10−5 ML/s and the coverage = 0.1 ML, as is shown in Fig. 1. These simulation results are in general agreement with the experiment at 110 K and 280 K [11]. In addition, we investigate the island evolution with different substrate temperatures. It is obvious that the island morphologies are strongly affected by the substrate temperature. At lower temperature (T = 110 K), the island morphology is fractal and the fractal arm of the island is small. As substrate temperature increases (T = 130–170 K), the island morphologies still maintain fractal, but the arms of the fractal island become thick. As the temperature continually increases (T = 190–280 K), the shapes of island transform to compact and begin to resemble the surface crystal structure (hexagonal) at high temperature (i.e. T = 280 K). In order to understand the competing mechanism between nucleation and growth, “fast” deposition rate (F = 1.7 ML/s) is also
used in our simulation. Fig. 2 shows the island morphologies evolution with different substrate temperatures at the deposition rate F = 1.7 ML/s and the coverage = 0.1 ML. The result shows that the island morphology is also strongly affected by the temperature of substrate at a fast deposition rate. However, the arm of the fractal island is much thinner than that at “slow” deposition rate (F = 1.7 × 10−5 ML/s). The results also show that the transition temperature of island shapes from fractal to compact is about 280 K at the deposition rate of 1.7 ML/s, which is much larger than 190 K at the deposition rate of 1.7 × 10−5 ML/s. The reason is that the morphological transition is a result of a competition between nucleation and growth. This competition is determined by the surface diffusion and the deposition rate. At a “slow” deposition rate, the adatom can migrate on the substrate sufficiently before encountering the new adsorbed adatom. However, it is difficult for the adatom to nucleate due to a much smaller diffusion length at a “fast” deposition rate. Therefore, in order to form a compact island, one should extend diffusion length by increasing substrate temperature.
Fig. 4. The island morphologies evolution at different surface defect factors ˇ with the temperature of 280 K and the coverage of 0.1 ML (F = 1.7 ML/s).
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To quantitatively examine the temperature dependence of the island morphologies at two kinds of deposition rates, we plot the island density (which represents the average numbers of the adatom per site in an island) distributions for different temperatures, as is shown in Fig. 3. The results show that the average island density increases with the temperature. At the same temperature, the average island density with a “fast” deposition rate is larger than that with a “slow” deposition rate. We can conclude that the shapes of island transform to compact from fractal while the average island density D > 0.5. This conclusion can be demonstrated by the island morphologies evolution in Fig. 1 (T > 190 K) and Fig. 2 (T > 280 K) well. In real thin film growth, it is necessary to study the kinetic process on defect substrate since the substrate cannot be of ideal smoothness. Meanwhile, certain defect modes can be considered as special structure substrates, which can be made into unique devices, such as low dimensional systems (quantum wells and quantum wires) [27]. The kinetic process of thin film growth on a tetragonal lattice with defect mode is discussed in our previous work [28]. In this work, we investigate the island growth on a hexagonal lattice surface with different surface factor ˇ with the substrate temperature of 280 K and the deposition rate of 1.7 ML/s, as is shown in Fig. 4. As the factor ˇ increases, the shape of island becomes small and irregular. The shape of island is compact at lower ˇ. However, the effect of the substrate lattice structure on the island morphology is weaker. The shape of island cannot resemble the surface crystal structure even at high temperature. Since the interaction energy between adatom and defect point is usually larger than that between the adatom and ideal substrate surface, the adatoms prefer to nucleate at the defect point and hardly diffuse on the surface. So it is difficult for the adatoms to unite to form critical nuclei, which subsequently grow to islands by attachment of further adatoms. 4. Conclusions In summary, we have performed a 2D kinetic Monte Carlo simulation to study the growth of the Ag ultrathin film on Pt (1 1 1) in the early growth stage. The morphologies at different substrate temperatures with different deposition rates have been explored. The transition temperature of island growing from compact to fractal is deduced by the average island density distributions and demonstrated by the island morphology evolutions. The competition processes between nucleation and growth are demonstrated. The average diffusion length is small and thus the transition
temperature of island evolution is increased greatly at a “fast” deposition rate. In addition, by introducing a surface factor to represent the extent of a non-ideal substrate surface, the effect of energy between substrate defect and adatom on the nucleation and growth is demonstrated. For future work, using the probability classes we would be able to simulate very large systems with the ones reported (in the micro meter scale any beyond) [29]. Acknowledgements This work is supported by the Natural Science Foundation of Guangdong Province, China (Grant no. S2012010010976), and the Special Fund for Guangdong Province Higher Education Disciplines and Majors Construction (No. 2013LYM 0084). References [1] D.H. Lowndes, D.B. Geohegan, A.A. Puretzky, D.P. Norton, C.M. Rouleau, Science 273 (1996) 898. [2] J.W. Matthews, Epitaxial Growth, Academic Press, New York, 1975. [3] I. Ohkubo, H.M. Christen, S.V. Kalinin, G.E. Jellison Jr., C.M. Rouleau, D.H. Lowndes, Appl. Phys. Lett. 84 (2004) 1350. [4] Y.J. Park, C.S. Oh, T.H. Yeom, Y.M. Yu, J. Cryst. Growth 264 (2004) 1. [5] F. Family, T. Vicsek (Eds.), Dynamics of Fractal Surfaces, World Scientific, Singapore, 1991. [6] A.-L. Barabási, H.E. Stanley, Fractal Concepts in Surface Growth, Cambridge, England, Cambridge University, 1995. [7] P. Meakin, Fractals, Scaling, and Growth Far from Equilibrium, Cambridge University Press, Cambridge, England, 1998. [8] R.Q. Hwang, J. Schröder, C. Günther, R.J. Behm, Phys. Rev. Lett. 67 (1991) 3279. [9] T. Michely, M. Hohage, M. Bott, G. Comsa, Phys. Rev. Lett. 70 (1993) 3943. [10] R. Nishitani, A. Kasuya, S. Kubota, Y. Nishina, J. Vac. Sci. Technol. B 9 (1991) 806. [11] H. RÖder, E. Hahn, H. Brune, J.P. Bucher, K. Kern, Nature 366 (1993) 141. [12] H. Brune, H. Roder, C. Boragno, K. Kern, Phys. Rev. Lett. 73 (1994) 1955. [13] T.A. Witten, L.M. Sander, Phys. Rev. Lett. 47 (1981) 1400. [14] X. Tan, X.J. Zheng, Y.C. Zhou, Surf. Coat. Technol. 197 (2005) 288. [15] X. Tan, Y.C. Zhou, X.J. Zheng, Surf. Sci. 588 (2005) 175. [16] C.X. Liu, Y.Q. Yang, X. Luo, R.J. Zhang, B. Huang, Appl. Surf. Sci. 255 (2008) 3342. [17] Y.Y. Huang, Y.C. Zhou, Y. Pan, Physica E 41 (2009) 1673. [18] P. Bruschi, P. Cagnoni, A. Nannini, Phys. Rev. B 55 (1997) 7955. [19] Y.Y. Huang, Y.C. Zhou, Y. Pan, Physica B 405 (2010) 1335. [20] H. Wei, Z. Liu, K. Yao, Vacuum 56 (2000) 185. [21] A.L. Magna, Surf. Sci. 601 (2007) 308. [22] H.L. Wei, Z.L. Liu, K.L. Yao, Vacuum 56 (2000) 185. [23] M. Schmid, A. Garhofer, J. Redinger, F. Wimmer, P. Scheiber, P. Varga, Phys. Rev. Lett. 107 (2011) 016102. [24] J.M. Warrender, M.J. Aziz, Phys. Rev. B 75 (2007) 085433. [25] M.Z. Li, P.W. Chung, E. Cox, C.J. Jenks, P.A. Thiel, J.W. Evans, Phys. Rev. B 77 (2008) 033402. [26] P.J. Feibelman, Surf. Sci. 313 (1994) L801. [27] H.J. Qi, J.D. Shao, D.P. Zhang, K. Yi, Z.X. Fan, Appl. Surf. Sci. 249 (2005) 85. [28] Z.Y. Chen, Y. Zhu, S.H. Chen, Z.R. Qiu, S.J. Jiang, Appl. Surf. Sci. 257 (2011) 6102. [29] A.L. Magna, S. Coffa, Comput. Mater. Sci. 17 (2000) 21.
Contents lists available at ScienceDirect
Applied Surface Science journal homepage: www.elsevier.com/locate/apsusc
Morphology transition of Ag ultrathin films on Pt (1 1 1): Kinetic Monte Carlo simulation Shuhan Chen ∗ , Jingming Luo, Shouliang Bu School of Physics and Optical Information Sciences, Jia Ying University, Meizhou 514015, People’s Republic of China
a r t i c l e
i n f o
Article history: Received 11 November 2013 Received in revised form 8 February 2014 Accepted 12 February 2014 Available online 22 February 2014 Keywords: Ultrathin film KMC simulation Competing process Transition temperature
a b s t r a c t Kinetic Monte Carlo simulations are carried out to explore the growth of the Ag ultrathin film on Pt (1 1 1) in the early growth stage. With increasing temperature, the island shapes are demonstrated to transform from fractal to compact and resemble the surface crystal structure at high temperature. The transition temperature of the island evolution is demonstrated to increase with the deposition rate. The competing mechanism between nucleation and growth is pursued. The transition temperature of island evolution is deduced by the average island density distributions and demonstrated by the island morphology evolutions. In addition, the extent of a non-ideal substrate surface is explored. As the interaction energy between adatom and defect point increases, the island shape becomes small and irregular. The effect of surface defect on the nucleation and growth is demonstrated. © 2014 Elsevier B.V. All rights reserved.
1. Introduction Thin films perform a very important role in new materials and are extensively used for electronic devices and optical components [1–4]. Thin films grown under nonequilibrium condition have attracted considerable interest among researchers [5–7]. It is very important to achieve a quantitative understanding of the morphology evolution which evolves when atoms are deposited onto a solid substrate for fundamental and practical reasons. In many cases, the property of the film is determined in the early growth stage. The film growth processes can be strongly affected by fabrication conditions, such as substrate temperature, deposition rate, surface microstructure of substrate, etc. Many theoretical and experimental works have been performed to investigate the role of these factors. Despite considerable work done in recent years analyzing ultrathin film growth, many questions remain unanswered. Many experiments have been performed to observe the fractal islands resembling the diffusion-limited aggregation (DLA) mode at lower substrate temperature [8–10]. The island becomes more compact at high substrate temperature [9]. The competing processes between nucleation and growth are demonstrated by experiment [11]. However, some experiments have observed compact islands at lower temperature [12]. In order to reveal the basic reason for the effect of the fabrication conditions on the growth
∗ Corresponding author. Tel.: +86-753-2186837. E-mail address: [email protected] (S. Chen). http://dx.doi.org/10.1016/j.apsusc.2014.02.066 0169-4332/© 2014 Elsevier B.V. All rights reserved.
morphology of thin film, a variety of kinetic Monte Carlo (KMC) simulation works have been performed [13–20]. These studies provided insight into the structure evolution during thin film growth. We should note that the use of a pure two dimensional (2D) model is correct only if the shape relaxation time is large [21]. In this work, we perform a two dimensional (2D) kinetic Monte Carlo simulation to study the growth of the ultrathin Ag film on Pt (1 1 1) under physical vapor deposition in the early growth stage. The morphologies at different substrate temperatures with different deposition rates are explored. Our results are not only in agreement with the observations of Ag films growth [11], but also predict the morphologies evolution with different temperatures and deposition rates. The competing processes between nucleation and growth are demonstrated. In addition, by introducing a surface factor to represent the extent of a non-ideal substrate surface, the effect of surface defect at different surface factor is discussed. By changing these factors, we obtain different island morphologies. The effect of the energy between surface defect and adatom on the growth of ultrathin film is demonstrated. 2. Simulation model Simulations are performed on a fcc (1 1 1) surface, with a system size of 200 × 200. An atom depositing on the substrate becomes adatom and diffuses randomly along six directions on the hexagonal surface. We assume that the adatom diffuses only to the nearest-neighbor sites. Diffusing to next-nearest-neighbor sites is forbidden because higher activation energy is needed [22]. The
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S. Chen et al. / Applied Surface Science 301 (2014) 289–292
simulation increment for any given event to occur t is given time n by t = v (− ln R), where vi is the rate of the event i to occur, i i=1 and R is a random number between 0 and 1. The possible events are simplified as follows.
After a diffusion event, the diffusion rates for the affected atoms are updated. We stop the simulation when the coverage value is obtained (and thus neglect the adatom evaporation in our model).
(i) Procedure for a deposition event. An Ag atom deposits at a user-defined deposition rate and becomes an adatom adsorbed on the surface. The adsorption site can be chosen randomly to imitate the film growth on hexagonal substrate (ii) Procedure for a diffusion event. A diffusion event is selected randomly. The selecting probability is proportional to its rate. The atom moves to the new site specified by a diffusion event.
The diffusion rate is given by Arrhenius rate equation vij→i j = v0 exp(−E/kB T ), where v0 = 1 × 1012 is attempt frequency, E is activation barrier, kB is Boltzmann’s constant, and T is the substrate temperature. For fcc metals simple bond-counting arguments usually give the correct answer when searching for optimum structure [23]. We note that using bond-counting kinetics is reasonable for Ag (1 1 1) [24]. So simple bond-counting kinetics in our simulation
Fig. 1. The morphologies of Ag island formation on Pt (1 1 1) at different substrate temperature (F = 1.7 × 10−5 ML/s, = 0.1 ML).
Fig. 2. The morphologies of Ag island formation on Pt (1 1 1) at different temperatures (F = 1.7 ML/s, = 0.1 ML).
S. Chen et al. / Applied Surface Science 301 (2014) 289–292
model is used, with activation barrier to any transition being given by E = (1 + ˇ)Es + nEb , where n is the number of nearest-neighbor atoms, which have bond energy Eb . Here we only consider the interaction energy between adatom and near-neighbor atoms, but the effect of the next near-neighbor atoms is not taken into account. We set Eb = 0.18 eV [25]. In our work, the effects of non-ideal surface, such as surface defects steps, terraces are considered by introducing a surface parameter ˇ. The barrier Es = 0.16 eV represents the interaction energy between adatom and ideal substrate surface [26]. The surface factor ˇ = 0 represents the substrate is ideal. The interaction energy between adatom and defect increases with the factor . First, we have checked the reasonableness of parameters in this model. By using these parameters which were accurately estimated by first principle calculations or experiments [25,26] in our model, the morphologies we simulated generally agree with the experiment [11] at 110 K and 280 K with almost the same deposition rate, as is shown in Fig. 1.
291
Fig. 3. The island density distributions for different temperatures at the deposition rate of 1.7 × 10−5 ML/s and 1.7 ML/s respectively ( = 0.1 ML).
3. Results and discussion With the simulation scheme described above, we simulate the evolution of Ag ultrathin films with different substrate temperatures at the deposition flux F = 1.7 × 10−5 ML/s and the coverage = 0.1 ML, as is shown in Fig. 1. These simulation results are in general agreement with the experiment at 110 K and 280 K [11]. In addition, we investigate the island evolution with different substrate temperatures. It is obvious that the island morphologies are strongly affected by the substrate temperature. At lower temperature (T = 110 K), the island morphology is fractal and the fractal arm of the island is small. As substrate temperature increases (T = 130–170 K), the island morphologies still maintain fractal, but the arms of the fractal island become thick. As the temperature continually increases (T = 190–280 K), the shapes of island transform to compact and begin to resemble the surface crystal structure (hexagonal) at high temperature (i.e. T = 280 K). In order to understand the competing mechanism between nucleation and growth, “fast” deposition rate (F = 1.7 ML/s) is also
used in our simulation. Fig. 2 shows the island morphologies evolution with different substrate temperatures at the deposition rate F = 1.7 ML/s and the coverage = 0.1 ML. The result shows that the island morphology is also strongly affected by the temperature of substrate at a fast deposition rate. However, the arm of the fractal island is much thinner than that at “slow” deposition rate (F = 1.7 × 10−5 ML/s). The results also show that the transition temperature of island shapes from fractal to compact is about 280 K at the deposition rate of 1.7 ML/s, which is much larger than 190 K at the deposition rate of 1.7 × 10−5 ML/s. The reason is that the morphological transition is a result of a competition between nucleation and growth. This competition is determined by the surface diffusion and the deposition rate. At a “slow” deposition rate, the adatom can migrate on the substrate sufficiently before encountering the new adsorbed adatom. However, it is difficult for the adatom to nucleate due to a much smaller diffusion length at a “fast” deposition rate. Therefore, in order to form a compact island, one should extend diffusion length by increasing substrate temperature.
Fig. 4. The island morphologies evolution at different surface defect factors ˇ with the temperature of 280 K and the coverage of 0.1 ML (F = 1.7 ML/s).
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To quantitatively examine the temperature dependence of the island morphologies at two kinds of deposition rates, we plot the island density (which represents the average numbers of the adatom per site in an island) distributions for different temperatures, as is shown in Fig. 3. The results show that the average island density increases with the temperature. At the same temperature, the average island density with a “fast” deposition rate is larger than that with a “slow” deposition rate. We can conclude that the shapes of island transform to compact from fractal while the average island density D > 0.5. This conclusion can be demonstrated by the island morphologies evolution in Fig. 1 (T > 190 K) and Fig. 2 (T > 280 K) well. In real thin film growth, it is necessary to study the kinetic process on defect substrate since the substrate cannot be of ideal smoothness. Meanwhile, certain defect modes can be considered as special structure substrates, which can be made into unique devices, such as low dimensional systems (quantum wells and quantum wires) [27]. The kinetic process of thin film growth on a tetragonal lattice with defect mode is discussed in our previous work [28]. In this work, we investigate the island growth on a hexagonal lattice surface with different surface factor ˇ with the substrate temperature of 280 K and the deposition rate of 1.7 ML/s, as is shown in Fig. 4. As the factor ˇ increases, the shape of island becomes small and irregular. The shape of island is compact at lower ˇ. However, the effect of the substrate lattice structure on the island morphology is weaker. The shape of island cannot resemble the surface crystal structure even at high temperature. Since the interaction energy between adatom and defect point is usually larger than that between the adatom and ideal substrate surface, the adatoms prefer to nucleate at the defect point and hardly diffuse on the surface. So it is difficult for the adatoms to unite to form critical nuclei, which subsequently grow to islands by attachment of further adatoms. 4. Conclusions In summary, we have performed a 2D kinetic Monte Carlo simulation to study the growth of the Ag ultrathin film on Pt (1 1 1) in the early growth stage. The morphologies at different substrate temperatures with different deposition rates have been explored. The transition temperature of island growing from compact to fractal is deduced by the average island density distributions and demonstrated by the island morphology evolutions. The competition processes between nucleation and growth are demonstrated. The average diffusion length is small and thus the transition
temperature of island evolution is increased greatly at a “fast” deposition rate. In addition, by introducing a surface factor to represent the extent of a non-ideal substrate surface, the effect of energy between substrate defect and adatom on the nucleation and growth is demonstrated. For future work, using the probability classes we would be able to simulate very large systems with the ones reported (in the micro meter scale any beyond) [29]. Acknowledgements This work is supported by the Natural Science Foundation of Guangdong Province, China (Grant no. S2012010010976), and the Special Fund for Guangdong Province Higher Education Disciplines and Majors Construction (No. 2013LYM 0084). References [1] D.H. Lowndes, D.B. Geohegan, A.A. Puretzky, D.P. Norton, C.M. Rouleau, Science 273 (1996) 898. [2] J.W. Matthews, Epitaxial Growth, Academic Press, New York, 1975. [3] I. Ohkubo, H.M. Christen, S.V. Kalinin, G.E. Jellison Jr., C.M. Rouleau, D.H. Lowndes, Appl. Phys. Lett. 84 (2004) 1350. [4] Y.J. Park, C.S. Oh, T.H. Yeom, Y.M. Yu, J. Cryst. Growth 264 (2004) 1. [5] F. Family, T. Vicsek (Eds.), Dynamics of Fractal Surfaces, World Scientific, Singapore, 1991. [6] A.-L. Barabási, H.E. Stanley, Fractal Concepts in Surface Growth, Cambridge, England, Cambridge University, 1995. [7] P. Meakin, Fractals, Scaling, and Growth Far from Equilibrium, Cambridge University Press, Cambridge, England, 1998. [8] R.Q. Hwang, J. Schröder, C. Günther, R.J. Behm, Phys. Rev. Lett. 67 (1991) 3279. [9] T. Michely, M. Hohage, M. Bott, G. Comsa, Phys. Rev. Lett. 70 (1993) 3943. [10] R. Nishitani, A. Kasuya, S. Kubota, Y. Nishina, J. Vac. Sci. Technol. B 9 (1991) 806. [11] H. RÖder, E. Hahn, H. Brune, J.P. Bucher, K. Kern, Nature 366 (1993) 141. [12] H. Brune, H. Roder, C. Boragno, K. Kern, Phys. Rev. Lett. 73 (1994) 1955. [13] T.A. Witten, L.M. Sander, Phys. Rev. Lett. 47 (1981) 1400. [14] X. Tan, X.J. Zheng, Y.C. Zhou, Surf. Coat. Technol. 197 (2005) 288. [15] X. Tan, Y.C. Zhou, X.J. Zheng, Surf. Sci. 588 (2005) 175. [16] C.X. Liu, Y.Q. Yang, X. Luo, R.J. Zhang, B. Huang, Appl. Surf. Sci. 255 (2008) 3342. [17] Y.Y. Huang, Y.C. Zhou, Y. Pan, Physica E 41 (2009) 1673. [18] P. Bruschi, P. Cagnoni, A. Nannini, Phys. Rev. B 55 (1997) 7955. [19] Y.Y. Huang, Y.C. Zhou, Y. Pan, Physica B 405 (2010) 1335. [20] H. Wei, Z. Liu, K. Yao, Vacuum 56 (2000) 185. [21] A.L. Magna, Surf. Sci. 601 (2007) 308. [22] H.L. Wei, Z.L. Liu, K.L. Yao, Vacuum 56 (2000) 185. [23] M. Schmid, A. Garhofer, J. Redinger, F. Wimmer, P. Scheiber, P. Varga, Phys. Rev. Lett. 107 (2011) 016102. [24] J.M. Warrender, M.J. Aziz, Phys. Rev. B 75 (2007) 085433. [25] M.Z. Li, P.W. Chung, E. Cox, C.J. Jenks, P.A. Thiel, J.W. Evans, Phys. Rev. B 77 (2008) 033402. [26] P.J. Feibelman, Surf. Sci. 313 (1994) L801. [27] H.J. Qi, J.D. Shao, D.P. Zhang, K. Yi, Z.X. Fan, Appl. Surf. Sci. 249 (2005) 85. [28] Z.Y. Chen, Y. Zhu, S.H. Chen, Z.R. Qiu, S.J. Jiang, Appl. Surf. Sci. 257 (2011) 6102. [29] A.L. Magna, S. Coffa, Comput. Mater. Sci. 17 (2000) 21.