V. Yu. Aristov

Electronic properties of potassium-doped CuPc

We have studied the electronic structure of potassium-doped copper phthalocyanine (CuPc) using photoemission spectroscopy. A detailed analysis of the core-level spectra allows us to propose possible lattice sites for the potassium ions. None of the films prepared in our studies showed a finite electronic density of states at the Fermi level (EF), which is in contrast to reports in the literature. Possible reasons for this discrepancy are discussed.

Alkali-Metal-Induced Highest Fermi-Level Pinning Position above Semiconductor Conduction Band Minimum

The room temperature deposition of small amounts of Cs on the InAs(110) surface induces the highest Fermi-level pinning position (~ 0.6 eV) above the conduction band minimum ever met for any semiconductor. The Fermi-level movement is monitored by core level photoemission spectroscopy using synchrotron radiation. This striking behaviour is explained in terms of donor-type surface states induced by few Cs atoms present on InAs(110) and suggests the existence of a two-dimensional electron gas at the surface.

Electronic structure of the organic semiconductor copper phthalocyanine: experiment and theory.

The electronic structure of the organic semiconductor copper-phthalocyanine (CuPc) has been determined by a combination of conventional and resonant photoemission, near-edge x-ray absorption, as well as by the first-principles calculations. The experimentally obtained electronic valence band structure of CuPc is in very good agreement with the calculated density of states results, allowing the derivation of detailed site specific information.

The unoccupied electronic structure of potassium doped copper phthalocyanine studied by near edge absorption fine structure

The unoccupied electronic structure of potassium doped copper-phthalocyanine thin films has been studied using x-ray absorption spectroscopy. The data reveal filling of the lowest unoccupied molecular orbital upon doping and related changes of the core level absorption spectra. The spectral changes can be rationalized taking into account the core level binding energies which also depend on doping.

Properties of hybrid organic-inorganic systems: Au nanoparticles embedded into an organic CuPc matrix

The evolution of the morphology and the electronic structure of the hybrid organic-inorganic system composed of gold nanoparticles (NPs) distributed in an organic matrix—copper phthalocyanine (CuPc)—as a function of nominal gold content was studied by transmission electron microscopy and by surface and bulk sensitive spectroscopic methods. The gold atoms deposited onto the CuPc surface diffuse into the organic matrix and self-assemble to NPs. There is no formation of a continuous metallic Au film on top of the CuPc film up to large nominal coverage of about 130 A considered in the present study. The gold is assembled in well defined NPs with metallic properties.

Consistent experimental determination of the charge neutrality level and the pillow effect at metal/organic interfaces

Experimental results for the interface dipoles at metal/organic and organis/organic interfaces have been analyzed on the basis of the induced density of interfaces states model. We demonstrate that a consistent analysis of a selected set of interfaces is possible, which allows the determination of all microscopic parameters of the model, and moreover enables the prediction of the electronic properties of further, yet unknown interfaces.

Photoemission measurements of quantum states in accumulation layers at narrow band gap III-V semiconductor surfaces

Abstract Tiny amounts of cesium adsorbed on cleaved InSb(110) surfaces result in a strong downward band bending (BB) and creates a two-dimensional (2D) electron channel in the sub-surface region. For the first time, electron emission arising from this channel was observed for this material. We compare it to the similar situation met previously with InAs(110). In this last case, new high-resolution measurements allow to determine the dispersions of the quantized energy levels, and to derive the average effective mass of the carriers in the channel. For both systems, self-consistent calculations and model-function curve fittings support the experimental results.

Morphology and properties of a hybrid organic-inorganic system: Al nanoparticles embedded into CuPc thin film

The evolution of the morphology and the electronic structure of the hybrid organic-inorganic system composed of aluminum nanoparticles (NPs) distributed in an organic semiconductor matrix—copper phthalocyanine (CuPc)—as a function of nominal aluminum content was studied by transmission electron microscopy and by photoemission spectroscopy methods. The aluminum atoms deposited onto the CuPc surface diffuse into the organic matrix and self-assemble to NPs in a well-defined manner with a narrow diameter distribution, which depends on the amount of aluminum that is evaporated onto the CuPc film. We find clear evidence of a charge transfer from Al to CuPc and we have been able to determine the lattice sites where Al ions sit. The finally at high coverage about 64 A the formation of metallic aluminum overlayer on CuPc thin film takes place.

Ultra-high vacuum cryomanipulators with liquid helium cooling for electron spectroscopy

Abstract The design of ultra-high vacuum cryomanipulators cooled by liquid heliumfor the use in surface studies is described. The main aspect of the design is a pumped low-temperature insert with a specialcopper felt heat exchanger mounted on the high-precision manipulator of electron spectrometer. The inserts can be cooled by a liquid helium flow from a fitted trans port Dewar through a standard transfer tube and pumped by a rotary pump of a helium recovery system. The design enables changing samples during UHV runs. Electrical microfeedthroughs (6- or 8-pins) mounted on the cryoinsert and changeable sample holders allow electrical measurements “in situ” under the UHV conditions.