CuPc Monolayer Research Articles

Noncontact atomic force microscopy study of copper-phthalocyanines: Submolecular-scale contrasts in topography and energy dissipation

Copper-phthalocyanine (CuPc) thin films on MoS2 surfaces were investigated by noncontact atomic force microscopy (NC-AFM). Submolecular resolution was successfully obtained in both topographic and dissipation images of CuPc monolayers. For topographic contrasts, the influence of short-range chemical interactions is particularly considered while the dissipation contrasts are discussed in relation to the tip-induced molecular fluctuations. Molecularly-resolved NC-AFM image was also obtained on CuPc multilayer, which revealed the structural difference between the monolayer and multilayer surfaces. The energy dissipation measured on these surfaces showed distinctive difference reflecting the different structural stabilities in the films. Furthermore, local surface modification of CuPc monolayer was demonstrated by NC-AFM. This is a direct evidence for the existence of energy transfer from the vibrating cantilever to the molecules through dissipative tip–sample interactions.

Ordered binary monolayer composed of two organic molecules: Copper-phthalocyanine and 3,4,9,10-perylene-tetra-carboxylic-dianhydride on Cu(111)

The two planar organic molecules copper-phthalocyanine (CuPc) and 3,4,9,10-perylene-tetracarboxylic-dianhydride (PTCDA) are found to form an ordered mixed monolayer on Cu(111). The layers have been prepared by exposing the surface to an equivalent of a little bit more than half of a monolayer of CuPc and the same amount of PTCDA followed by thermal annealing. The investigations by scanning tunneling microscopy reveal regular patterns with a commensurate unit cell which contains one CuPc and two PTCDA molecules.

Electronic structure of copper phthalocyanine monolayer: a first-principles study

The electronic structure of copper phthalocyanine (CuPc) monolayer was investigated by the first-principles all-electron full-potential linearized augmented plane wave (FLAPW) energy band method. The magnetic properties of the CuPc monolayer were investigated with spin-polarized calculation. It was found that the Cu atom has a magnetic moment of 0.56 μ B, but it does not affect strongly the paramagnetic properties of the monolayer. The ground-state electronic structure of the CuPc monolayer found in spin-polarized calculation is indistinguishable from the paramagnetic case in the energy range from −10 to −1.5 eV and above 1.0 eV, with respect to the Fermi level ( E F), but taking into account the magnetic properties of the open-shell Cu atom results with the splitting of bands near E F . The obtained total density of states and the calculated values of work function (4.66 eV) and ionization potential (5.23 eV) of the CuPc monolayer were found to be in a good agreement with the experimental data concerned CuPc thin films.

Metal d-Orbital Occupation-Dependent Images in the Scanning Tunneling Microscopy of Metal Phthalocyanines

A strong d-orbital dependence in the scanning tunneling microscopy image of metal phthalocyanines is demonstrated. Unlike copper phthalocyanine (CuPc) wherein the central metal appears as a hole in the molecular image, the cobalt atom in CoPc is the highest point (about 0.3 nm) in the molecular image. On the other hand, the benzene ring regions of CoPc and CuPc appear to have the same height. These data are consistent with theoretical calculations that predict a large contribution of cobalt d-orbitals near the Fermi energy. An intriguing aspect of this work is that it may be possible to chemically identify the different metal phthalocyanines simply by their appearance. This is demonstrated for the case of a mixed monolayer of CuPc and CoPc on Au(111).

Organic-Inorganic Hetero Nanosystems as an Approach to Molecular Optoelectronics

A concept of organic-inorganic hetero nanosystems has been proposed as an approach to molecular optoelectronics. The direct use of the optical function of an individual organic molecule in a solid state is anticipated through the electronic function of inorganic materials. Basic information on the formation of hetero nanostructures by vacuum thin film technology was discussed. Various types of organic-inorganic hetero nanostructures consisting of copperphthalocyanine (CuPc) molecular crystals and metal oxides of TiOx and SiO2 were fabricated by evaporation and reactive evaporation techniques. Cross sectional transmission electron microscopy (TEM) directly revealed that the thickness of the mixing layer at the ceramics interface on a CuPc molecular crystal is at most a monolayer of CuPc in superlattice structures. The formation of nanoboxes of CuPc molecular crystal in a ceramic matrix which had been fabricated using the multilayer technique, was confirmed by observations of in-plane TEM and atomic force microscopy. Optoelectronic functions in organic-inorganic hetero nanosystems were discussed from the viewpoints of carrier generation at the interface, size effects, and molecular orientation.

STM-Investigations on Heteroepitaxially Grown Over-Layers of Cu-Phthalocyanine on AU(111) Surfaces

6855bHeteroepitaxial growth of copper phthalocyanine (CuPc) on Au(111) surfaces has been confirmed for the first time by Scanning Tunneling Microscopy (STM). The combination of in situ electron diffraction (RHEED) with STM allows direct studies of heterogeneous layer growth, revealing a novel commensurable superstructure of the organic overlayer with the Au(111) surface. The organic molecular beam epitaxy (OMBE) technique has demonstrated that molecular orderings of CuPc monolayers can be controlled, resulting in artificial lattice structures in organic ultrathin films being different from those in bulk

The topography of isolated molecules of copper–phthalocyanine adsorbed on GaAs(110)

Single molecules of Cu–phthallocyanine (CuPc) have been investigated on a GaAs (110) substrate under UHV conditions. Prior to the measurement, a tunneling experiment on a silver substrate covered with about one monolayer of CuPc was performed. By this procedure a few molecules are transferred to the tunneling tip. When tunneling on GaAs some of these molecules can be redeposited on the freshly cleaved (110) surface. The ring structure and the fourfold symmetry of the molecule can be clearly recognized on the atomic flat surface of GaAs. In a few cases, a deep dip in the middle of the molecule is visible.

Observation of Heteroepitaxially Grown Organic Ultrathin Layers on Inorganic Substrates by In Situ RHEED and by STM

ABSTRACTAn organic molecular beam epitaxy (OMBE) system has been designed and constructed with in situ reflection high-energy electron diffraction (RHEED) specifically for the deposition of organic molefelar layers under ultrahigh vacuum (UHV), the order of 10–10 torr. The system is equipped with a portable UHV chamber which allows easy transfer of the OMBE film samples to a separate UHV scanning tunneling microscopy (STM) system. A structural investigation of heteroepitaxially grown organic ultrathin layers of copper phthalocyanine (CuPc) on inorganic substrates was carried out by the combined UHV system from less than a monolayer of CuPc.