We present a theoretical model describing the collective behavior of molecules in nanoscale direct deposition processes such as dip-pen nanolithography.We show that strong intermolecular interactions combined with nonuniform substrate-molecule interactions can produce various shapes of molecular patterns including fractal-like structures.Computer simulations reveal circular and starlike patterns at low and intermediate densities of preferentially attractive surface sites,respectively.At large density of such surface sites,the molecules form a two-dimensional invasion percolation cluster.Previous experimental results showing anisotropic patterns of various chemical and biological molecules correspond to the starlike regime [P.Manandhar et al,Phys.Rev.Lett.90,115505 (2003);J.-H.Lim and C.A.Mirkin,Adv.Mater.(Weinheim,Ger.)14,1474 (2002);D.L.Wilson et al,Proc.Natl.Acad.Sci.U.S.A.98,13660 (2001);M.Su et al,Appl.Phys,Lett.84,4200 (2004);R.McKendry et al,Nano Lett.2,713 (2002);H.Zhou et al,Appl.Surf.Sci.236,18 (2004);G.Agarwal et al,J.Am.Chem.Soc.125,580 (2003)].
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机译：我们提出了一个理论模型来描述分子在纳米级直接沉积工艺（例如浸笔式纳米光刻）中的集体行为。我们表明，强大的分子间相互作用与不均匀的底物-分子相互作用可以产生各种形状的分子图案，包括分形结构。模拟显示分别在低密度和中等密度的优先吸引的表面位点处存在圆形和星形图案。在这样的表面位点处具有较大密度时，分子形成二维入侵渗流簇。先前的实验结果显示了各种化学和生物分子的各向异性模式[P.Manandhar et al。，Phys.Rev.Lett.90,115505（2003）; J.-H.Lim and CAMirkin，Adv.Mater。（Weinheim，Ger。）14,1474（2002） ）; DLWilson等人，Proc.Natl.Acad.Sci.USA98,13660（2001）; M.Su等人，Appl.Phys，Lett.84,4200（2004）; R.McKendry等人，Nano Lett .2,713（2002）; H.Zhou等，Ap S.Surf.Sci.236，18（2004）; G.Agarwal等人，J.Am.Chem.Soc.125，580（2003）]。
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