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Structure-dependent growth control in nanowire synthesis via on-film formation of nanowires.

Shim W, Ham J, Noh JS, Lee W - Nanoscale Res Lett (2011)

Bottom Line: In this study, we investigated various experimental growth parameters such as deposition rate, deposition area, and substrate structure which modulate the microstructure and the magnitude of stress in the films, and thus significantly affect the nanowire density.We found that Bi nanowire growth is favored in thermodynamically unstable films that facilitate atomic mass flow during annealing.A large film area and a large thermal expansion coefficient mismatch between the film and the substrate were found to be critical for inducing large compressive stress in a film, which promotes Bi nanowire growth.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Materials Science and Engineering, Yonsei University, 134 Shinchon, Seoul 120-749, Korea. wooyoung@yonsei.ac.kr.

ABSTRACT
On-film formation of nanowires, termed OFF-ON, is a novel synthetic approach that produces high-quality, single-crystalline nanowires of interest. This versatile method utilizes stress-induced atomic mass flow along grain boundaries in the polycrystalline film to form nanowires. Consequently, controlling the magnitude of the stress induced in the films and the microstructure of the films is important in OFF-ON. In this study, we investigated various experimental growth parameters such as deposition rate, deposition area, and substrate structure which modulate the microstructure and the magnitude of stress in the films, and thus significantly affect the nanowire density. We found that Bi nanowire growth is favored in thermodynamically unstable films that facilitate atomic mass flow during annealing. A large film area and a large thermal expansion coefficient mismatch between the film and the substrate were found to be critical for inducing large compressive stress in a film, which promotes Bi nanowire growth. The OFF-ON method can be routinely used to grow nanowires from a variety of materials by tuning the material-dependent growth parameters.

No MeSH data available.


SEM images of Bi nanowires grown on Bi films with different areas: (a) (104 μm)2, (b) (103 μm)2, (c) (102 μm)2, and (d) (10 μm)2. Insets show optical microscope images of the samples before annealing. (e) Histograms of Bi nanowire densities depending on the Bi film areas.
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Figure 3: SEM images of Bi nanowires grown on Bi films with different areas: (a) (104 μm)2, (b) (103 μm)2, (c) (102 μm)2, and (d) (10 μm)2. Insets show optical microscope images of the samples before annealing. (e) Histograms of Bi nanowire densities depending on the Bi film areas.

Mentions: Compressive stress stored in Bi films is thought to be the driving force for spontaneous Bi nanowire growth by the OFF-ON method. In order to check the appropriateness of this hypothesis and to study the effect of another parameter on Bi nanowire growth, we investigated the effect of Bi film areas. For this, we fabricated Bi thin film patterns with four different size of areas: (104 μm)2, (103 μm)2, (102 μm)2, and (10 μm)2. Figure 3a,b,c,d shows SEM images of Bi nanowire grown on different Bi film areas (A), where the Bi films were deposited on SiO2/Si substrates at a rate of 32.7 Å/s. If the compressive stress hypothesis is reasonable, then a larger Bi film area should result in a higher density of Bi nanowires, because the compressive stress is generally less relieved at the center of a film and more released at the edges of the film. Indeed, we found that the density of Bi nanowires at the edge is higher in the factor of 1.3 than that at the center, and the total density increased as the Bi film area increased after annealing at 270°C for 10 h (see Figure 3e). This indirectly shows that compressive stress is a driving force for Bi nanowire growth by the OFF-ON method, and preventing stress relief is another key factor for promoting nanowire growth. In this sense, Bi film area is another parameter that determines the Bi nanowire density. The magnitude of stress and its correlation with the nanowire density is discussed in detail elsewhere [16]. In addition, the above result proves that Bi nanowire growth is not driven by the thermal evaporation of Bi atoms during annealing; if this were the case, then Bi nanowire density should be independent of Bi film area.


Structure-dependent growth control in nanowire synthesis via on-film formation of nanowires.

Shim W, Ham J, Noh JS, Lee W - Nanoscale Res Lett (2011)

SEM images of Bi nanowires grown on Bi films with different areas: (a) (104 μm)2, (b) (103 μm)2, (c) (102 μm)2, and (d) (10 μm)2. Insets show optical microscope images of the samples before annealing. (e) Histograms of Bi nanowire densities depending on the Bi film areas.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
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getmorefigures.php?uid=PMC3211252&req=5

Figure 3: SEM images of Bi nanowires grown on Bi films with different areas: (a) (104 μm)2, (b) (103 μm)2, (c) (102 μm)2, and (d) (10 μm)2. Insets show optical microscope images of the samples before annealing. (e) Histograms of Bi nanowire densities depending on the Bi film areas.
Mentions: Compressive stress stored in Bi films is thought to be the driving force for spontaneous Bi nanowire growth by the OFF-ON method. In order to check the appropriateness of this hypothesis and to study the effect of another parameter on Bi nanowire growth, we investigated the effect of Bi film areas. For this, we fabricated Bi thin film patterns with four different size of areas: (104 μm)2, (103 μm)2, (102 μm)2, and (10 μm)2. Figure 3a,b,c,d shows SEM images of Bi nanowire grown on different Bi film areas (A), where the Bi films were deposited on SiO2/Si substrates at a rate of 32.7 Å/s. If the compressive stress hypothesis is reasonable, then a larger Bi film area should result in a higher density of Bi nanowires, because the compressive stress is generally less relieved at the center of a film and more released at the edges of the film. Indeed, we found that the density of Bi nanowires at the edge is higher in the factor of 1.3 than that at the center, and the total density increased as the Bi film area increased after annealing at 270°C for 10 h (see Figure 3e). This indirectly shows that compressive stress is a driving force for Bi nanowire growth by the OFF-ON method, and preventing stress relief is another key factor for promoting nanowire growth. In this sense, Bi film area is another parameter that determines the Bi nanowire density. The magnitude of stress and its correlation with the nanowire density is discussed in detail elsewhere [16]. In addition, the above result proves that Bi nanowire growth is not driven by the thermal evaporation of Bi atoms during annealing; if this were the case, then Bi nanowire density should be independent of Bi film area.

Bottom Line: In this study, we investigated various experimental growth parameters such as deposition rate, deposition area, and substrate structure which modulate the microstructure and the magnitude of stress in the films, and thus significantly affect the nanowire density.We found that Bi nanowire growth is favored in thermodynamically unstable films that facilitate atomic mass flow during annealing.A large film area and a large thermal expansion coefficient mismatch between the film and the substrate were found to be critical for inducing large compressive stress in a film, which promotes Bi nanowire growth.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Materials Science and Engineering, Yonsei University, 134 Shinchon, Seoul 120-749, Korea. wooyoung@yonsei.ac.kr.

ABSTRACT
On-film formation of nanowires, termed OFF-ON, is a novel synthetic approach that produces high-quality, single-crystalline nanowires of interest. This versatile method utilizes stress-induced atomic mass flow along grain boundaries in the polycrystalline film to form nanowires. Consequently, controlling the magnitude of the stress induced in the films and the microstructure of the films is important in OFF-ON. In this study, we investigated various experimental growth parameters such as deposition rate, deposition area, and substrate structure which modulate the microstructure and the magnitude of stress in the films, and thus significantly affect the nanowire density. We found that Bi nanowire growth is favored in thermodynamically unstable films that facilitate atomic mass flow during annealing. A large film area and a large thermal expansion coefficient mismatch between the film and the substrate were found to be critical for inducing large compressive stress in a film, which promotes Bi nanowire growth. The OFF-ON method can be routinely used to grow nanowires from a variety of materials by tuning the material-dependent growth parameters.

No MeSH data available.