V.M. Zhilin

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.

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.

Unoccupied electronic states in an organic semiconductor probed with x-ray spectroscopy and first-principles calculations

High-quality films of copper phthalocyanine (CuPc) prepared in situ were used as a model to characterize unoccupied states of organic molecular semiconductors. We demonstrate that a combination of high-resolution near-edge x-ray absorption together with first-principles calculations constitutes a reliable tool for the detection and identification of particular molecular orbitals.

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.

One-dimensional random walk of nanosized liquid Pb inclusions on dislocations in Al

Migration of nanosized liquid Pb inclusions attached to dislocations in Al has been observed during in-situ transmission electron microscopy heating experiments and monitored by real-time video recordings. The movements of the inclusions can be separated into two independent components parallel to and perpendicular to the dislocations respectively. Movements parallel to the dislocation lines display properties of partially confined one-dimensional random walks where smaller inclusions can be seen to move over distances that are many times their own sizes. In contrast, the trajectories perpendicular to the dislocation lines are within narrowly confined spaces. Frame-by-frame analysis of digitized video sequences recorded at different temperatures for the same inclusion attached to a nearly horizontal dislocation illustrates the two types of movement. The step lengths parallel to the dislocation increase rapidly with increasing temperature while the step lengths in the transverse movement only display a weak temperature dependence. A detailed statistical analysis of the inclusion trajectories documents that both patterns of movement are random. The activation enthalpy of the one-dimensional movement parallel to the dislocation was found to be 2.72 ± 0.10 eV at lower temperatures and 1.44 ± 0.07 eV at higher temperatures with a transition temperature around 650–660 K.

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.

CESIUM-INDUCED QUANTIZED 2D ELECTRON CHANNEL ON THE InAs(110) SURFACE

We present the first clear evidence of electron emission arising directly from a quantized two-dimensional electron channel from the InAs(110) surface covered by a few Cs atoms (≈ 0.01 Cs ML). Spectral features observed by photoemission spectroscopy using synchrotron radiation reveal discrete-energy electronic states resulting from quantization in the direction normal to the surface. The electron photoemission originates from the vicinities of points in the first and second surface Brillouin zones corresponding to the bottom of the conduction band. These findings are in agreement with self-consistent theoretical energy-level calculations using a jellium-like model.

Sb or Cs covered InAs(110) surfaces: moving EF into conduction band and quantized 2D electron channel

With the study of the formation of Sb/InAs interface by synchrotron radiation photoemission, we add a new piece of evidence that a two-dimensional free electron gas can be created at room temperature, on the (110) cleaved surface of InAs upon adsorption of few metal atoms. In the case of Cs, we demonstrate that this very interesting feature results from 2D channels quantized in the direction normal to the surface.

In Situ TEM Investigation of Diffusion of Nano-Scale Liquid Pb Inclusions on Dislocations and in Bulk Aluminum

Diffusion of nano-sized liquid Pb inclusions in thin aluminum foils is investigated using in-situ transmission electron microscopy (TEM). Free diffusion of the inclusions in the bulk and diffusion constrained by dislocations trapping is studied. The motion of trapped Pb inclusions is spatially confined in close proximity to the dislocations. The diffusion coefficients of free motion of the inclusions are determined using Einsteins equation. The diffusion coefficients of trapped inclusions were obtained using an equation based on Smoluchowskis analysis of the Brownian motion of particle in a harmonic potential. The agreement of the diffusion coefficients of free and trapped inclusions indicates the same underlying microscopic mechanism, and no strong influence from dislocations. The microscopic mechanism controlling the mobility is discussed.