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Keeping pentacene in shape for microelectronic devices
Keeping pentacene in shape for microelectronic devices Pentecene - a chain-like aromatic molecule consisting of five benzene rings - is one of the most promising organic molecular semiconductors for microelectronic devices. Now researchers from IBM Watson Research Center have successfully imaged the formation of thin-films of pentacene in real time and understand how to control thinfilm growth on inorganic substrates [Nature (2 August 2001), 412, 517-520]. Using low-energy electron microscopy (LEEM) in photoelectron emission microscopy mode (PEEM),
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Frank Meyer zu Heringdorf and co-workers found that strongly bonded molecules inhibit nucleation and decrease the crystalline qual~ of the pentacene thin-film formed on a silicon substrate. The researchers believe this is because any bond breaking and reforming changes the shape of the organic molecule - particularly if bonding to a material like silicon. Any change in shape prevents the molecules packing together snugly, so reducing the overall crystalline quality of the resulting thin film. To test their observations, the
September/October ZOO1
researchers chemically treated silicon substrates to achieve an optimal interaction between the substrate and the pentscene molecules so that they are held on the surface, but allowed to diffuse and
rotate. Coating a silicon (100) substrate surface with an ordered array of non-nactive C-H groups prior to thin-film deposition dramatically improved the crystallinity of the pentacene thin films, to the point where perfect single crystals of 0.1 mm (20-100 times larger than achieved previously) were formed. Practical applications of
organic microelectmnic devices such as transistors, for integrated circuits, could now be made from a single crystal of pentecene - with all the advantages of single-crystal transport properties to be expected. Furthermore, understanding and controlling properties at the interface between organic and inorganic materials could lead to cheap and simple self-assembly processes for future devices. The similarities between organic thin-film growth and that of inorganic material bode well for future development of real devices.
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Frank Meyer zu Heringdorf and co-workers found that strongly bonded molecules inhibit nucleation and decrease the crystalline qual~ of the pentacene thin-film formed on a silicon substrate. The researchers believe this is because any bond breaking and reforming changes the shape of the organic molecule - particularly if bonding to a material like silicon. Any change in shape prevents the molecules packing together snugly, so reducing the overall crystalline quality of the resulting thin film. To test their observations, the
September/October ZOO1
researchers chemically treated silicon substrates to achieve an optimal interaction between the substrate and the pentscene molecules so that they are held on the surface, but allowed to diffuse and
rotate. Coating a silicon (100) substrate surface with an ordered array of non-nactive C-H groups prior to thin-film deposition dramatically improved the crystallinity of the pentacene thin films, to the point where perfect single crystals of 0.1 mm (20-100 times larger than achieved previously) were formed. Practical applications of
organic microelectmnic devices such as transistors, for integrated circuits, could now be made from a single crystal of pentecene - with all the advantages of single-crystal transport properties to be expected. Furthermore, understanding and controlling properties at the interface between organic and inorganic materials could lead to cheap and simple self-assembly processes for future devices. The similarities between organic thin-film growth and that of inorganic material bode well for future development of real devices.