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Large-scale fabrication of nanopatterned sapphire substrates by annealing of patterned Al thin films by soft UV-nanoimprint lithography.

Cui L, Han JC, Wang GG, Zhang HY, Sun R, Li LH - Nanoscale Res Lett (2013)

Bottom Line: The first comprised a low-temperature oxidation anneal at 450°C for 24 h.This was followed by a high-temperature annealing in the range of 1,000°C and 1,200°C for 1 h to induce growth of the underlying sapphire single crystal to consume the oxide layer.The SEM results indicate that the patterns were retained on sapphire substrates after high-temperature annealing at less than 1,200°C.

View Article: PubMed Central - HTML - PubMed

Affiliation: Shenzhen Graduate School, Harbin Institute of Technology, Shenzhen 518055, People's Republic of China. cuilin0512@gmail.com.

ABSTRACT
Large-scale nanopatterned sapphire substrates were fabricated by annealing of patterned Al thin films. Patterned Al thin films were obtained by soft UV-nanoimprint lithography and reactive ion etching. The soft mold with 550-nm-wide lines separated by 250-nm space was composed of the toluene-diluted polydimethylsiloxane (PDMS) layer supported by the soft PDMS. Patterned Al thin films were subsequently subjected to dual-stage annealing due to the melting temperature of Al thin films (660°C). The first comprised a low-temperature oxidation anneal at 450°C for 24 h. This was followed by a high-temperature annealing in the range of 1,000°C and 1,200°C for 1 h to induce growth of the underlying sapphire single crystal to consume the oxide layer. The SEM results indicate that the patterns were retained on sapphire substrates after high-temperature annealing at less than 1,200°C. Finally, large-scale nanopatterned sapphire substrates were successfully fabricated by annealing of patterned Al thin films for 24 h at 450°C and 1 h at 1,000°C by soft UV-nanoimprint lithography.

No MeSH data available.


SEM and AFM images of Al patterns after annealing. SEM images of the morphology of the Al patterns on sapphire substrates after annealing for 24 h at 450 °C and 1 h at 1,200°C (a) and 1,000°C (b). AFM image of Al patterns after dual-stage annealing for 24 h at 450°C and 1 h at 1,000°C (c).
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Figure 4: SEM and AFM images of Al patterns after annealing. SEM images of the morphology of the Al patterns on sapphire substrates after annealing for 24 h at 450 °C and 1 h at 1,200°C (a) and 1,000°C (b). AFM image of Al patterns after dual-stage annealing for 24 h at 450°C and 1 h at 1,000°C (c).

Mentions: Dramatic changes in the pattern morphology were observed following high-temperature annealing applied to induce grain growth of the sapphire. Figure 4a shows a SEM image of the morphology of the patterned surface after annealing for 24 h at 450°C and 1 h at 1,200°C. For nanopatterned Al thin films that subsequently experienced an annealing temperature of 1,200°C, it was found that smoothing and coalescence of the line features had occurred to such an extent that the patterning was no longer discernible. The phenomenon of surface diffusion-driven smoothing of surface features is well established in the literature [19-22] and occurs due to surface energy considerations [23,24]. The kinetics of the smoothing of the line patterns can be used to derive information on the diffusion mechanism. Therefore, for the successful fabrication of NPSS, the relative kinetics of smoothing versus grain growth of the underlying sapphire is critical. Fortunately, for high-temperature annealing at 1,000°C and 1,100°C, the patterns were retained on sapphire substrates. Figure 4b shows a SEM image of the morphology of the patterned surface after high-temperature annealing for 1 h at 1,000°C. Figure 4c shows the AFM image of nanopatterned Al thin films with 250-nm-wide lines separated by 550-nm space after dual-stage annealing for 24 h at 450°C and 1 h at 1,000°C. Using this technique, it can be seen that the upper surfaces of the patterns are not flat; instead, the center of the patterns is higher than the edges. Moreover, the height of the patterns following the high-temperature annealing of 1 h at 1,000°C was approximately150 nm. Our experimental results reveal that the consistency of line patterns fabricated by dual-stage annealing of patterned Al thin films for 24 h at 450°C and 1 h at 1,000°C and the orientation were the same as those of the sapphire (0001) substrates [14].


Large-scale fabrication of nanopatterned sapphire substrates by annealing of patterned Al thin films by soft UV-nanoimprint lithography.

Cui L, Han JC, Wang GG, Zhang HY, Sun R, Li LH - Nanoscale Res Lett (2013)

SEM and AFM images of Al patterns after annealing. SEM images of the morphology of the Al patterns on sapphire substrates after annealing for 24 h at 450 °C and 1 h at 1,200°C (a) and 1,000°C (b). AFM image of Al patterns after dual-stage annealing for 24 h at 450°C and 1 h at 1,000°C (c).
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Figure 4: SEM and AFM images of Al patterns after annealing. SEM images of the morphology of the Al patterns on sapphire substrates after annealing for 24 h at 450 °C and 1 h at 1,200°C (a) and 1,000°C (b). AFM image of Al patterns after dual-stage annealing for 24 h at 450°C and 1 h at 1,000°C (c).
Mentions: Dramatic changes in the pattern morphology were observed following high-temperature annealing applied to induce grain growth of the sapphire. Figure 4a shows a SEM image of the morphology of the patterned surface after annealing for 24 h at 450°C and 1 h at 1,200°C. For nanopatterned Al thin films that subsequently experienced an annealing temperature of 1,200°C, it was found that smoothing and coalescence of the line features had occurred to such an extent that the patterning was no longer discernible. The phenomenon of surface diffusion-driven smoothing of surface features is well established in the literature [19-22] and occurs due to surface energy considerations [23,24]. The kinetics of the smoothing of the line patterns can be used to derive information on the diffusion mechanism. Therefore, for the successful fabrication of NPSS, the relative kinetics of smoothing versus grain growth of the underlying sapphire is critical. Fortunately, for high-temperature annealing at 1,000°C and 1,100°C, the patterns were retained on sapphire substrates. Figure 4b shows a SEM image of the morphology of the patterned surface after high-temperature annealing for 1 h at 1,000°C. Figure 4c shows the AFM image of nanopatterned Al thin films with 250-nm-wide lines separated by 550-nm space after dual-stage annealing for 24 h at 450°C and 1 h at 1,000°C. Using this technique, it can be seen that the upper surfaces of the patterns are not flat; instead, the center of the patterns is higher than the edges. Moreover, the height of the patterns following the high-temperature annealing of 1 h at 1,000°C was approximately150 nm. Our experimental results reveal that the consistency of line patterns fabricated by dual-stage annealing of patterned Al thin films for 24 h at 450°C and 1 h at 1,000°C and the orientation were the same as those of the sapphire (0001) substrates [14].

Bottom Line: The first comprised a low-temperature oxidation anneal at 450°C for 24 h.This was followed by a high-temperature annealing in the range of 1,000°C and 1,200°C for 1 h to induce growth of the underlying sapphire single crystal to consume the oxide layer.The SEM results indicate that the patterns were retained on sapphire substrates after high-temperature annealing at less than 1,200°C.

View Article: PubMed Central - HTML - PubMed

Affiliation: Shenzhen Graduate School, Harbin Institute of Technology, Shenzhen 518055, People's Republic of China. cuilin0512@gmail.com.

ABSTRACT
Large-scale nanopatterned sapphire substrates were fabricated by annealing of patterned Al thin films. Patterned Al thin films were obtained by soft UV-nanoimprint lithography and reactive ion etching. The soft mold with 550-nm-wide lines separated by 250-nm space was composed of the toluene-diluted polydimethylsiloxane (PDMS) layer supported by the soft PDMS. Patterned Al thin films were subsequently subjected to dual-stage annealing due to the melting temperature of Al thin films (660°C). The first comprised a low-temperature oxidation anneal at 450°C for 24 h. This was followed by a high-temperature annealing in the range of 1,000°C and 1,200°C for 1 h to induce growth of the underlying sapphire single crystal to consume the oxide layer. The SEM results indicate that the patterns were retained on sapphire substrates after high-temperature annealing at less than 1,200°C. Finally, large-scale nanopatterned sapphire substrates were successfully fabricated by annealing of patterned Al thin films for 24 h at 450°C and 1 h at 1,000°C by soft UV-nanoimprint lithography.

No MeSH data available.