Molecular resolution friction microscopy of Cu phthalocyanine thin films on dolomite (104) in water

Abstract

The reliability of ultrathin organic layers as active components for molecular electronic devices depends ultimately on an accurate characterization of the layer morphology and ability to withstand mechanical stresses on the nanoscale. To this end, since the molecular layers need to be electrically decoupled using thick insulating substrates, the use of AFM becomes mandatory. Here, we show how friction force microscopy (FFM) in water allows us to identify the orientation of copper(ii)phthalocyanine (CuPc) molecules previously self-assembled on a dolomite (104) mineral surface in ultra-high vacuum. The molecular features observed in the friction images show that the CuPc molecules are stacked in parallel rows with no preferential orientation with respect to the dolomite lattice, while the stacking features resemble well the single CuPc crystal structure. This proves that the substrate induction is low and makes friction force microscopy in water a suitable alternative to more demanding dynamic AFM techniques in ultra-high vacuum.

Molecular-scale shear response of the organic semiconductor β -DBDCS (100) surface

“…However, lattice resolution is difficult to achieve in ambient conditions due to the formation of a water meniscus between the probing tip and surface because of capillary condensation. A costly alternative is to measure the friction in ultrahigh-vacuum conditions [12,18], but as shown by some of us [19][20][21][22], this obstacle can also be overcome if the tip is completely immersed in a liquid (e.g., water), so that capillary bridges between the tip and surface are not formed. In this way, we were able to relate the strong friction anisotropy observed on the (104) cleavage surface of calcite and dolomite to the pathways followed by the tip driven along different scan directions [21].…”

“…Furthermore, the formation of grain boundaries, which control the microtexture and thus, to a large extent, charge and exciton transport in the devices [38,39], is directly related to the nanomechanical properties at the surface of the crystallites, where AFM provides again nanoscale structural information [28,30]. This equally holds for thin films and crystal surfaces [19,20], where, for instance, the quality of lasing in the crystal is controlled by habit (relative shape) and tracht (size, shape, and homogeneity of the facets) of the crystal as well as by the orientation of the molecules with respect to the crystal facets [40,41]. All these parameters are controlled by the molecular electronic and steric demands.…”

Facile fabrication of multilayer films of graphene oxide/copper phthalocyanine with high dielectric properties

“…Alternatively, graphene oxide (GO) appears as a very important precursor of graphene, possessing a similar anisotropic nature and comparable mechanical strength with graphene 15 , and can be easily reduced into graphene [16][17][18] . With the inherent π-π stacking property of phthalocyanine, special architectures (column, microsphere and nanofiber) have been fabricated by self-assembly of CuPc, [20][21][22][23] and their potential applications in solar cell, fuel cells, opticallimiting materials, gas sensors and field-effect transistors have been shown. As a result, the asymmetric GO can form nematic and lamellar liquid crystals (LC) in water and polar organic solvents.…”

CuPc:C60 nanocomposite: A pathway to control organic microstructure and phase transformation

“…These line scans show step heights of approximately 1.5 and 1.7 nm, both of which correspond reasonably well with the known van der Waals radius of the CuPc molecule ($1.45 nm). [24] The explanation for this end-on adsorption of CuPc on the hexagonally ordered C 60 phase is twofold. Firstly, the different 2D symmetries of the hexagonal C 60 lattice, and the oblique lattice of the flat lying CuPc [as found in the monolayer CuPc films on Cu(111)] will result in lattice mismatch between the two structures and will not permit commensurate registration of an ordered phase of flat lying CuPc on the hexagonal C 60 [this is presumably the origin of the disorder observed in the C 60 films on the Cu(111)-CuPc surface].…”