Spontaneous formation of ordered patterns in Al films deposited on silicone oil surfaces

Abstract

We report the spontaneous formation of large spatial ordered patterns in a continuous aluminum ͑Al͒ film system deposited on silicone oil surfaces by a thermal evaporation method. The growth mechanism of the ordered patterns can be traced to a three-stage process, the first of which involves nucleation and growth of strips with a characteristic domain structure in the films. In the subsequent stage, triangle-shaped domains with different sizes appear in the strips. Then the domains grow and finally form the ordered and band-shaped patterns. The experiment shows that the ordered patterns result from the spontaneous ordered organization of the Al atoms and atomic clusters driven by the internal stress in this nearly free sustained film system.Spontaneous generation of complex order in apparently simple systems is of long-standing and continuing interest not only for its aesthetic appeal, but also for its fundamental and technological relevance. [1][2][3][4][5][6][7][8][9] In natural systems there are large varieties of self-organized phenomena that potentially span a wide range of scales, from macroscopic ground surface morphologies 1 and granular materials 2 to nanometerscale structures such as microporous materials, 3 nanocrystals ͑including nanoclusters, nanowires, nanotubes, etc.͒ in semiconductors, 4 nanostructure arrays on strained crystal surfaces, 5 and complex biological and nonbiological structures organized with supramolecules ͑or molecules͒. 6,7 Some previous studies demonstrated that the ordered patterns existing in thin films deposited both on solid substrates 5,10,11 and on soft polymer substrates 8,9 are induced by the buckling of the films owing to the relief of the internal stress.Vapor phase deposition of metals on liquid substrates was studied in a number of recent investigations. 12-15 It is observed that atoms, atomic compact clusters, and branched islands on liquid substrates possess large mobility and they can diffuse, rotate, and aggregate on the liquid surfaces freely. In principle, the phenomena resulted from the internal stress in continuous thin films deposited on liquid surfaces can emerge obviously because of the weak interaction between the films and the liquid substrates. Therefore it is expected that various characteristic patterns caused by the internal stress relief may appear apparently in these nearly free sustained films. 12 Here we report the spontaneous formation of large spatial ordered stress relief patterns existing in continuous aluminum ͑Al͒ films deposited on silicone oil surfaces. We anticipate that this nearly free sustained metallic film system subjected to the distinctive effect of the underlying liquid layers will provide a test bed not only for the fundamental research on the internal stress in the films, but also for the technological application of various free sustained films on liquid substrates.The samples were prepared by thermal evaporation of 99.999% pure Al in a vacuum of 6ϫ10 Ϫ4 Pa at room temperature. Commercial silicone oil ͑Dow Corning 705 Diffusion ...

Experimental Observations of Orderly Structures in Copper Films Deposited on Liquid Substrates

“…The experiment shows that the interaction in the tangent direction between the metallic film and the liquid substrate is very small, compared with the case that thin films on solid or soft polymer substrates. [3][4][5][6][7][8] In addition, corrugated surface morphology, periodic cracks and orderly patterns were observed in these nearly free sustained films, [11][12][13][14] which mainly originated from the relaxation of the internal stress created during or after deposition.…”

Characteristic mechanical properties and complex ordered structures in metal films on liquid substrates

“…The film systems on liquid substrates always possess special growth mechanisms, distinctive microstructures and anomalous physical properties. In addition, they also generally exhibit large varieties of characteristic surface morphologies and structures such as chrysanthemum-shaped wrinkles in silver films [6] , parallel sinusoidal cracks in nickel films [7] , band-shaped structures composed of rectangular domains in metal (including iron, aluminum and gold) films [8][9][10] , large spatially molecular organic crystals in thin liquid films [11] , etc.The band-shaped structures in iron, aluminum and gold film systems are a totally new form of ordered patterns, which have never been observed in the film systems on solid and polymer substrates. Furthermore, the fact that a same type of ordered structures can form in various thin films sufficiently indicates that these structures are not closely dependent on the film materials, but may be related to the special physical system of a stiff solid film on a mobile liquid layer.…”

“…The film systems on liquid substrates always possess special growth mechanisms, distinctive microstructures and anomalous physical properties. In addition, they also generally exhibit large varieties of characteristic surface morphologies and structures such as chrysanthemum-shaped wrinkles in silver films [6] , parallel sinusoidal cracks in nickel films [7] , band-shaped structures composed of rectangular domains in metal (including iron, aluminum and gold) films [8][9][10] , large spatially molecular organic crystals in thin liquid films [11] , etc.…”

“…The metal film systems deposited on soft polymer substrates have also been of great interest in the past years [3,4] . Because the difference in thermal expansion coefficient between the polymer substrate and the film is quite large, characteristic ordered structures at the nanometer scale are frequently observed, which can be well controlled and tuned by changing the experimental parameters such as the substrate temperature, film thickness, etc.In the last decade, an experimental group in Zhejiang University attempted to use liquid surfaces as the film substrates, and has successfully fabricated various metal film systems [5][6][7][8][9][10] . The experimental results showed that the metal atoms, atomic clusters, ramified aggregates and even a whole film piece can motion freely on the liquid surfaces, indicating that the interaction between the solid films and the liquid substrates in the tangent direction is very small [5] , which is quite different from the films on solid and polymer substrates [1][2][3][4] .…”

“…In the last decade, an experimental group in Zhejiang University attempted to use liquid surfaces as the film substrates, and has successfully fabricated various metal film systems [5][6][7][8][9][10] . The experimental results showed that the metal atoms, atomic clusters, ramified aggregates and even a whole film piece can motion freely on the liquid surfaces, indicating that the interaction between the solid films and the liquid substrates in the tangent direction is very small [5] , which is quite different from the films on solid and polymer substrates [1][2][3][4] .…”