Cu-phthalocyanine Films Research Articles

Growth and characterization of thin Cu-phthalocyanine films on MgO(001) layer for organic light-emitting diodes.

Surface morphology and thermal stability of Cu-phthalocyanine (CuPc) films grown on an epitaxially grown MgO(001) layer were investigated by using atomic force microscope and X-ray diffractometer. The (002) textured β phase of CuPc films were prepared at room temperature beyond the epitaxial MgO/Fe/MgO(001) buffer layer by the vacuum deposition technique. The CuPc structure remained stable even after post-annealing at 350°C for 1 h under vacuum, which is an important advantage of device fabrication. In order to improve the device performance, we investigated also current-voltage-luminescence characteristics for the new top-emitting organic light-emitting diodes with different thicknesses of CuPc layer.

Electronic properties of a zinc oxide surface modified by ultra-thin layers of conjugated organic molecules

Thin films of Cu-phthalocyanine (CuPc), perylene and 3,4,9,10-perylenetetracarboxylic acid dianhydride (PTCDA) were thermally deposited in situ in UHV on ZnO(0 0 0 −1) surface. The surface potential, the surface work function Φ and the structure of density of unoccupied electron states (DOUS) located 5–25 eV above the Fermi level ( E F) were monitored during the film deposition, using an incident beam of low-energy electrons according to the total current electron spectroscopy (TCS) method. Auger electron spectroscopy (AES) was used to monitor atomic composition of the surfaces under study. The deposition of the perylene and PTCDA films resulted in formation of the DOUS structure typical for these films while the deposition of CuPc films of less than 2 nm thickness resulted in formation of an intermediate DOUS structure which was replaced by a stable DOUS of CuPc along with a further increase of the deposit thickness. Migration of the substrate atoms into the intermediate layer was observed. The electronic work function Φ of the organic films changed during the film deposition until it reached stable values at a film thickness of 8–10 nm. Width of the interface dipole charge transfer layer and formation of intermediate TCS spectra during the film deposition are selected as relevant parameters for further comparison of the features of the interfaces studied.

Unoccupied electronic band structure of conjugated molecular films interfacing polycrystalline gold surface

Thin films of Cu-phthalocyanine (CuPc) and of tri-oligo(phenylene–vinylene) end terminated by di-butyl-thiole (tOPV) were thermally deposited in situ in UHV on polycrystalline Au substrate surfaces. The surface potential, the surface work function and the structure of density of unoccupied electron states (DOUS) located 5–25 eV above the Fermi level ( E F) were monitored during the film deposition, using an incident beam of low-energy electrons according to the total current electron spectroscopy (TCS) method. Auger electron spectroscopy (AES) was used to monitor atomic composition of the surfaces under study. The deposition of the CuPc films resulted in formation of the DOUS structure typical for these films while the deposition of tOPV films of less than 2 nm thickness resulted in formation of an intermediate DOUS structure which was replaced by a stable DOUS of tOPV along with a further increase of the deposit thickness. The electronic work function of the CuPc and the tOPV films changed during the film deposition until it reached a stable value of 4.4 ± 0.1 and 4.3 ± 0.1 eV, respectively, at a film thickness of 8–10 nm. The width of the interface dipole layer in the CuPc and the tOPV films interfacing with the Au surface did not exceed 2 nm. Analysis of the TCS data allowed us to assign the major DOUS features of the CuPc and tOPV films under study.

Interface formation between Cu-phthalocyanine films and CdS and GaAs semiconductor surfaces

Total current electron spectroscopy (TCS) is applied as a key experimental technique to studies of electronic structure of organic semiconductor films interfacing inorganic semiconductors. Thin films of Cu-phthalocyanine (CuPc) were thermally deposited in UHV on CdS(0 0 0 −1) and GaAs(1 0 0) substrates. The surface potential, the surface work function and the structure of unoccupied electron states (DOUS) located 5–25 eV above the Fermi level ( E F ) was monitored during the film deposition, using an incident beam of low-energy electrons according to the TCS method. Auger electron spectroscopy (AES) was used to monitor atomic composition of the surfaces under study. Electronic work function of the CuPc films changed during the film deposition until it reached a stable value 4.5±0.1 eV at the film thickness 8–10 nm. The deposition of the CuPc under 1.5 nm resulted in formation of the intermediate DOUS structures that were different for the cases of the two substrates used in the study. Fragments of the CuPc molecules were found to constitute mainly the intermediate deposit layers. Along with the increase of the deposit thickness to 8–10 nm, the intermediate DOUS structures were replaced by the DOUS structure typical for the CuPc film, although the S, Ga and As atoms migrated from the substrates were present in the CuPc film. Electron charge transfer layer at the CuPc/GaAs interface extended more than 5 nm from the GaAs surface, while the interaction at the CuPc/CdS interface resulted in band bending in the CdS subsurface region.

Interface formation between Cu-phthalocyanine films and CdS and GaAs semiconductor surfaces

Total current electron spectroscopy (TCS) is applied as a key experimental technique to studies of electronic structure of organic semiconductor films interfacing inorganic semiconductors. Thin films of Cu-phthalocyanine (CuPc) were thermally deposited in UHV on CdS(0 0 0 −1) and GaAs(1 0 0) substrates. The surface potential, the surface work function and the structure of unoccupied electron states (DOUS) located 5–25 eV above the Fermi level ( E F) was monitored during the film deposition, using an incident beam of low-energy electrons according to the TCS method. Auger electron spectroscopy (AES) was used to monitor atomic composition of the surfaces under study. Electronic work function of the CuPc films changed during the film deposition until it reached a stable value 4.5±0.1 eV at the film thickness 8–10 nm. The deposition of the CuPc under 1.5 nm resulted in formation of the intermediate DOUS structures that were different for the cases of the two substrates used in the study. Fragments of the CuPc molecules were found to constitute mainly the intermediate deposit layers. Along with the increase of the deposit thickness to 8–10 nm, the intermediate DOUS structures were replaced by the DOUS structure typical for the CuPc film, although the S, Ga and As atoms migrated from the substrates were present in the CuPc film. Electron charge transfer layer at the CuPc/GaAs interface extended more than 5 nm from the GaAs surface, while the interaction at the CuPc/CdS interface resulted in band bending in the CdS subsurface region.

Electronic charge distribution at interfaces between Cu-phthalocyanine films and semiconductor surfaces

Total current electron spectroscopy (TCS) that uses a probing beam of low energy electrons was applied to study electronic charge transfer at interfaces between Cu-phthalocyanine (CuPc) films thermally deposited in situ onto ZnO, oxidized and crystalline silicon substrates. Analysis of the TCS data provided us also with new data on the density of unoccupied electron states (DOUS) of the CuPc films at 0–25 eV above E F. A most significant electronic charge transfer from the CuPc film to SiO 2/n-Si and n-Si(1 0 0) was observed and the polarization layer extended up to 10 nm into the CuPc film bulk. The electronic structure of the CuPc molecules on n-Si(1 0 0) and on ZnO(0 0 0 1) was perturbed within 1–2 nm of the deposit due to interaction with the substrates. Admission of O 2 and NO 2 at 10 −5 Pa and 300 K resulted in a reversible decrease and increase of the film surface potential, respectively. Formation of TC peaks related to O-orbitals on the gas adsorption on the CuPc surface was also registered.

Unoccupied electronic states and energy level alignment at interfaces between Cu-phthalocyanine films and semiconductor surfaces

Thin films of Cu-phthalocyanine (CuPc) were thermally deposited in UHV on silicon, on highly ordered pyrolytic graphite (HOPG) and on ZnO substrates. The surface potential and the density of unoccupied electron states (DOUS) located 1–25 eV above vacuum level were measured during the film deposition using an incident beam of low-energy electrons according to the total current electron spectroscopy (TCS) method. Analysis of the TCS data allowed us to obtain DOUS features of the CuPc and to study charge transfer during the interface formation. A significant electron transfer from the CuPc film to SiO 2/n-Si and n-Si(1 0 0) was observed and the charge transfer layer in the film extended up to 10 nm. Band bending in the substrates due to the electron transfer was also monitored. A less significant charge transfer was observed at the interfaces between the CuPc film and the ZnO(0 0 0 1), SiO 2/p-Si and HOPG substrates. A model for the extended charge-transfer layer (extended interface dipole) is suggested to explain the observed spectroscopic features of the interfaces.

Interface formation between thin Cu-phthalocyanine films and crystalline and oxidized silicon surfaces

Thin films of Cu-phthalocyanine (CuPc) were thermally deposited in UHV on n-Si(1 0 0) and SiO 2/ n-Si substrates. Evolution of the surface potential and density of unoccupied electronic states located 0–25 eV above vacuum level were measured during the film deposition using an incident beam of low energy electrons using total current electron spectroscopy (TCS), and a new approach based on TCS analysis was developed and applied to studies of charge transfer at the interfaces. The analysis showed that a negative electric charge was transferred from the film to the substrate. A positively charged layer was registered in the CuPc films, which extends over a range from the substrate level and up to 10 nm. At a higher film thickness, bulk CuPc films were formed that have a workfunction of 4.5±0.1 eV. CuPc molecules decompose on the n-Si(1 0 0) substrate due to interaction with the crystalline surface while the film thickness is less than 3 nm. The features of the interfaces observed during formation of the interfaces are analyzed and a model for the extended charge-transfer layer (extended interface dipole) is applied.

Photo and gas sensitivity of thin Cu-phthalocyanine films studied by spectroscopy of unoccupied electron states

Thin films of Cu-phthalocyanine were thermally deposited in UHV on pyrolytic graphite, n-Si(1 0 0), SiO 2/n-Si, and SiO 2/p-Si substrates. Atomic composition of the films was tested by Auger electron spectroscopy. Evolution of surface potential and density of electron states located 0–25 eV above vacuum level were monitored during the film deposition by means of total current electron spectroscopy (TCS). The resulting spectra of the 2–3 nm thick CuPc films on the different substrates were however identical. Admission of 10 −5 Pa O 2 and NO 2 resulted in a reversible decrease and increase of the film surface potential, respectively. A new peak in the TCS appeared and the spectrum was attenuated on the admission of the gases. These changes were attributed to the interaction between the film and the gas molecules adsorbed. The changes were reversible on the gas evacuation. White light illumination reduced (increased) surface potential of the Cu-phthalocyanine film on SiO 2/n-Si (SiO 2/p-Si) substrate. The gas sensitivity is attributed to the processes at the gas/CuPc film interface, while the photovoltaic properties are attributed to the processes at the CuPc film/substrate interface.

00/02000 STM investigation of the growth structure of Cu-phthalocyanine films with submolecular resolution

00/02000 STM investigation of the growth structure of Cu-phthalocyanine films with submolecular resolution

STM investigation of the growth structure of Cu-phthalocyanine films with submolecular resolution

In this study Cu-phthalocyanine (CuPc) films have been investigated by scanning tunneling microscopy to get quantitative insight into the morphology of the films from the micrometer range down to nanometer resolution to see the arrangement of the molecules. The molecules on the surface have been found to be arranged in a slipped stacking order rather than in the expected zig-zag orientation normally found for CuPc crystals. The cystal structure could be identified to be an α-polymorph. The STM image of the individual molecules on the surface is in good agreement with calculations of the charge density of the LUMO for an isolated molecule. A model for the growth of the crystals was derived from this study.

Characterization of Gas Sorption of Plasma-Polymerized Cu-Phthalocyanine Film

The molecular recognition part of a gas sensor on a piezoelectric quartz crystal is prepared by the plasma polymerization technique. Cu-phthalocyanine (CuPc) was used as the monomer for plasma polymerization. The sorption of gases by the plasma-polymerized CuPc film coated on piezoelectric quartz crystal was measured. The intermolecular interactions between plasma-polymerized CuPc and a series of various gases were characterized on the basis of physicochemical parameters, i.e., the partition coefficient and modified Small's number. A specific interaction other than hydrophobicity occurs in the presence of double bonds, cyclorings, and aromatics. It results from the π-π interaction, because CuPc has a number of double bonds.

α型銅フタロシアニンの電気伝導に与える結晶性の影響

α型銅フタロシアニンの電気伝導に与える結晶性の影響

The Orientation Overgrowth of Metal-phthalocyanines on the Surface of Single Crystals. I. Vacuum-condensed Films on Muscovite

Abstract When substrate muscovite is preliminarily heated at 300°C for one hour and then kept at 150°C to 200°C during deposition in vacuo, Cu-phthalocyanine films condensed on it show parallel b-axis orientations, including single- and triple-directional orientations. The b-axis of the crystal runs parallel to the substrate face. On the other hand, when the substrate is preliminarily heated at 400°C and then kept at 150°C, films vacuum-condensed on it occur in a standing b-axis orientation. The high-resolution electron-diffraction pattern of the film reveals that the a-, b- and c-axes of the crystal are inclined to the normal of the substrate face at angles of about 75°, 32° and 118° respectively. An electron micrograph of the film shows that as discrete crystals grow they orient themselves in either of two different directions. The crystal which assumes the standing b-axis orientation has its (31\bar3) plane almost parallel to the substrate face. Pt-phthalocyanine film also assumes the standing b-axis orientation, in which the a-, b- and c-axes of the crystal are inclined to the normal of the substrate face at angles of about 74°, 35° and 120° respectively. It turns out that the molecular plane comes in contact with the muscovite surface in the case of the standing b-axis orientation. A plausible explanation of the origin of these orientations is presented in terms of the dehyroxylation of the surface mica layer caused by the thermal treatment.