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

Abstract

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. V C 2015 AIP Publishing LLC. [http://dx.doi.org/10.1063/1.4918989]Manipulating the two-dimensional (2D) arrangement of functional molecules on a substrate at atomic scale represents one of the most challenging aspects of molecular nanodevice fabrication. 1-4 By tuning the intermolecular, 5-9 molecule-substrate interfacial, 10-13 or substrate-mediated intermolecular interactions, 14,15 one is able to engineer the local ordering of 2D molecular assemblies. Dipolar phthalocyanine molecules, such as chlorogallium phthalocyanine (ClGaPc), 16,17 chloroaluminum phthalocyanine (ClAlPc), 18 vanadyl phthalocyanine (VOPc), 19 titanyl phthalocyanine (TiOPc), 20 and tin phthalocyanine (SnPc), 21 a class of large p-conjugated molecules with intrinsic dipole moment perpendicular to the p-plane, 22 have attracted intensive attention for their prospective applications in molecular nanoelectronics and organic electronics. 23-25 For instance, unidirectionally aligned molecular dipoles can effectively modify the substrate work function and stimulate the charge injection or collection at the molecule-electrode interface. 26,27 Reversible molecular switching (i.e., dipole-up versus dipole-down orientation) has been realized in monolayer ClAlPc, VOPc on graphite, 28,29 VOPc in hydrogen-bonded networks on graphite, 30 and SnPc on Cu(111), 31 which might fuel ultrahigh density information storage eventually. 32 To further expand their applications in molecular nanodevice, it is necessary to develop novel interfacial engineering techniques to manipulate the molecular dipoles on a solid surface. In this letter, the strain mediated dipole alignment of nonplanar ClAlPc on the tensile-strained Au(111)/mica and the strain-released single crystal Au(111) was investigated in situ by low-temperature scanning tunneling microscopy (LT-STM). The tensile strain in Au(111)/mica shifts the metal d bands towards the Fermi level and adjusts the interfacial coupling between ClAlPc and gold. Local ordering of dipole al...

Chiral Organization and Charge Redistribution in Chloroaluminum Phthalocyanine on Au(111) Beyond the Monolayer

“…28 In the frame of a substrate strain related dipole alignment interpretation, differences between lattice parameters measured in STM for the same molecule-substrate system were attributed to diverse degrees of surface strain, which can be dependent on sample preparation conditions. 23 As depicted in the pictorial cartoon of Figure 1e, the ClAlPc molecules are slightly rotated within the unit cell by ≈ 10° and, outstandingly, show a pinwheel rather than symmetric intramolecular shape. This local-point chirality is similar to that found in other achiral phtalocyanines, as CuPc on Ag(100), 36 and interpreted as due to asymmetric charge transfer between molecules and substrate leading to orbital specific chirality.…”

“…[3][4][5] Some examples of interest are chlorogallium phthalocyanine (ClGaPc), 6,7 vanadyl phthalocyanine (VOPc), [8][9][10][11] titanyl phthalocyanine (TiOPc), 4,[12][13][14][15][16] tin phthalocyanine (SnPc) [17][18][19][20][21][22] and chloroaluminum phthalocyanine (ClAlPc). 9,[23][24][25][26][27][28][29][30] When adsorbed on surfaces, depending on coverage and interaction with the substrate, these non-planar molecules can adopt configurations either with the dipole pointing up or down.…”

“…The ClAlPc/Au(111) system has been previously studied by ultraviolet photoemission spectroscopy (UPS) and low temperature scanning tunneling microscopy (STM) in UHV conditions. 23,28,29 It was found that the molecules, deposited with the substrate kept at room temperature, ordered in a square structure with  99% or only  60% in the Cl-up configuration depending on the strain degree of the reconstructed topmost surface of the Au(111) substrate.…”

Material descriptors for photocatalyst/catalyst design

“…Such tuning of the surface d-band center can influence the adsorption of adsorbates, and thereby change the dipole-dipole interaction. For example, this effect has been confirmed by studying adsorption of ClAlPc on Au (111) (Niu, 2015). Furthermore, by applying an external electric field, the external voltage can tune the E F level, providing a way for manipulating the work function (Yu et al, 2009).…”

Probing the Properties of Quasi‐Isolated ClAlPc by Using Polycrystalline h‐BN on Pt(111) as a Testbed

“…A particular system is Gr/Pt(111), [16] where the as-grown samples form preferentially MLs in which all the molecules always adopt a Cl-up configuration. In contrast, on noble metal substrates, [14,[17][18][19][20][21][22][23][24] ClAlPc molecules interact stronger with the support, and molecules with Cl-up or Cl-down configuration are commonly found to coexist within the as-grown MLs, although upon annealing, single layers with molecules in a Cl-up configuration can be obtained. The interaction with the substrate also influences the electronic structure of ClAlPc.…”