Surface strain mediated dipole alignment of ClAlPc on Au(111)

In this letter, we demonstrate the control of dipole alignment of monolayer chloroaluminum phthalocyanine (ClAlPc) molecules via the strain in Au(111) substrates. Local ordering of ClAlPc dipole comprising alternate Cl-up and Cl-down configurations is found on the tensile-strained Au(111)/mica as a result of strain-enhanced absorption of Cl-down ClAlPc's and the dipole-dipole interaction. In contrast, the strain-released single crystal Au(111) substrate shows negligible coupling to Cl-down ClAlPc, therefore, facilitating the formation of unidirectionally aligned Cl-up ClAlPc dipole array. The dipole-dipole interaction becomes less prominent at low ClAlPc coverage where ClAlPc molecules can find their favorable absorption sites more easily according to their inherent dipole orientation. Our results emphasize the superior role of molecule-substrate interaction in functional molecular engineering on metal surface hence provide fundamental insight into the potential applications in molecular nanodevices with tunable and controllable properties.