Interface formation between two organic films based on phthalocyanine and perylene derivatives

The process of interface formation between two organic films composed of donor (copper phthalocyanine, CuPc) and acceptor (perylene-3,4,9,10-tetracarboxylic dianhydride, PTCDA) molecules has been studied in situ using the total current spectroscopy technique. It is established that the donor-acceptor interaction between CuPc and PTCDA molecules do not distort the energy structure of the density of electron states. The main π*, σ*₁, and σ*₂ bands of antibonding (unoccupied) electron states are identified, which are determined both by C-C bonds in the aromatic rings and by additional C-N and C-O bonds. The width of the interface potential barrier is evaluated and its relation to the limiting polarizability of molecules is demonstrated. The interface potential barrier is formed in the course of negative charge transfer between donor (CuPc) and acceptor (PTCDA) molecules.     

Photovoltaic properties of interfaces in organic molecular film-silicon structures

A photovoltaic effect was discovered and studied in the structures comprising thin films of perylenetetracarboxylic acid dianhydride (PTCDA) and oligo(phenylene-vinylene) (OPV) deposited in vacuum onto a silicon surface, as well as in the OPV/PTCDA/Si structure. A change in the surface potential under illumination in the visible spectral range was detected in situ using the electron probe technique. The spectra and the relaxation characteristics of the photoinduced potential were measured. The fast and slow components of the photopotential were revealed, which corresponded to the photoabsorption and relaxation processes in the silicon substrate (fast component) and in the organic film (slow component). These components have opposite signs, which accounts for the photopotential sign change on the passage from the short-wavelength (350–600 nm) to long-wavelength (700–905 nm) spectral regions.     

Vacant electron state manifestations in the electron-beam-induced current spectra of macromolecular films

The vacuum-deposited films of corbatin (CRB) and perylene tetracarboxy dianhydride (PTCDA) were studied in situ by method of total electron-beam-induced current (EBIC) spectroscopy. The results are interpreted within the framework of the model of vacant electron states (VES) above the energy level of vacuum. For PTCDA samples, the VES density determined from the EBIC measurements shows a good agreement with the available NEXAFS data. For CRB films, the VES density above the vacuum level is reported for the first time.     

Effect of nitrogen-containing substituents on fragmentation of perylene derivatives under laser irradiation

The effect of nitrogen-containing substituents such as phenyl imide and actyl imide on the character of fragmentation of perylene derivative molecules under laser irradiation has been studied by laser desorption (LD) mass spectrometry. Replacement of the central oxygen atom by a nitrogen atom in anhydride carboxy groups in perylene tetracarboxylic dianhydride (PTCDA) molecule results in the suppression of CO2 desorption and predominant desorption of CO. The LD mass spectrum exhibits peaks that correspond to fragments of the perylene nucleus and those of the aromatic and aliphatic substituents. Intact PTCDA molecules are present in the desorbed flux in insignificant amounts.     

Formation and electron properties of the interface between organic (TPD) and inorganic (ZnO) materials

The initial stage of formation of an organic coating of N,N′-bis(3-methylphenyl)-N,N′-diphenylbenzidine (TPD) on a crystalline (ZnO) surface in the course of thermal deposition in high vacuum has been studied using the low-energy total current spectroscopy technique. A change in the work function and the density of unoccupied electron states in an energy interval of 0–20 eV above the vacuum level was traced as the organic coating thickness increased up to 8 nm. The energy positions of the bands of unoccupied electron states in the TPD film have been determined, including π* band (7–9 eV above the Fermi level), σ₁* band (10–12 eV), σ₂* band (14–16 and 18–20 eV).     

Evolution of Acid–Base Properties of the Surface of Zinc Oxide Powders Obtained by the Method of Grinding in an Attritor

The evolution of the acid–base properties of the surface of zinc oxide powders during mechanical grinding in an attritor is studied. The study is performed using the methods of the adsorption of acid–base indicators and X-ray photoelectron spectroscopy. Correlations between the results obtained by these methods are established. It is shown that a monotonic decrease in the particle size of ZnO powders is accompanied by a nonmonotonic change in the surface acid–base properties.     

Characteristic electron energy losses in organic PTCDA films

Studies are made of the characteristic energy losses of slow electrons during the formation of thin PTCDA films on a ZnO(0001) surface. It is shown that at low primary electron energies (<100 eV) the energy loss spectrum ( _n =3.0, 6.3, and 15 eV) reflects the structure of the transitions between the valence band and the conduction band. As the primary electron energy increases, energy losses to the excitation of plasma oscillations become dominant (ħω ₁=6 eV — excitation of a π-plasmon and ħω ₂=25 eV — excitation of a σ-plasmon). Pis’ma Zh. Tekh. Fiz. 25, 19–24 (October 26, 1999)