Charge Transfer In Thin Films Research Articles

Mechanism of Transverse Charge Transfer in Thin Films of Hexagonal Boron Nitride

A mechanism of transverse charge transfer through hexagonal boron nitride (h-BN) in a MIS structure has been studied. Experimental data for charge transfer have been analyzed in terms of different models of charge transfer in insulators. It has been shown that charge transfer in h-BN is described by the model of phonon-assisted tunneling between neutral traps. The thermal and optical energies of phonon-coupled traps in h-BN have been determined. Based on charge transfer measurements, XPS spectra, and the ab initio electronic structure of intrinsic defects in h-BN it has been found that boron–nitrogen divacancies are most probably responsible for charge transfer in h-BN and transfer is provided by electrons.

Mechanism of Transverse Charge Transfer in Thin Films of Hexagonal Boron Nitride

Mechanism of Transverse Charge Transfer in Thin Films of Hexagonal Boron Nitride

Charge transfer in thin films of donor–acceptor complexes studied by infrared spectroscopy

The degree of charge transfer in thin films of organic charge transfer (CT)-complexes, which are deposited via thermal evaporation, is examined via infrared-spectroscopy. We demonstrate a linear relationship between the shift in the excitation energy of the CN-stretching mode of CT-complexes with the acceptor 7,7,8,8-tetracyanoquinodimethane (TCNQ) and the charge transfer. The measured correlation corresponds very well with DFT calculations. For Na-TCNQ we observe a splitting in the peak of the CN-stretching mode, which can be explained by the coupling of two modes and was confirmed by the calculations. In CT-complexes with partial charge transfer the appearance of an electronic excitation is demonstrated.

Metal-to-ligand and ligand-to-metal charge transfer in thin films of Prussian blue analogues investigated by X-ray absorption spectroscopy

A series of thin films of Prussian blue analogues is investigated by X-ray absorption spectroscopy (XAS) at the Fe, Co and Mn L(2,3)-edges. The ligand field multiplet theory enables us to examine accurately the electronic structure of these materials. Experimental XAS spectra of CoFe Prussian blue analogues are successfully reproduced using a ground state configuration including metal-to-ligand (MLCT) and ligand-to-metal charge transfer (LMCT) at the Co and Fe L(2,3)-edges. In particular, a huge improvement is achieved for satellite peaks at the Co(iii) L(2,3)-edges compared to previous calculations in the literature based on LMCT effects only. On the other hand, XAS spectra of MnFe analogues synthesized for the first time, can be reproduced conveniently by taking into account either MLCT or LMCT depending on the conditions of the sample preparation. For each thin film, the proportion of the different oxidation states of Co, Fe and Mn is evaluated. Unexpectedly, this analysis reveals the presence of a significant amount of a reduced phase, which turns out to be strongly dependent on the sample synthesis and storage conditions.

The microstructure of and charge transfer in thin films based on metal-polymer nanocomposites

Charge transfer in nanostructured metal-polymer composites was studied. The frequency dependences of film conductance and susceptance were obtained at various metal concentrations. The susceptance of samples above the percolation threshold was negligibly small, which corresponded to the purely metallic conductivity type. For samples below the percolation threshold, susceptance and conductance were comparable in magnitude, which was evidence of an important role played by susceptance mechanisms. At low frequencies, the samples behaved as quasi-linear RC circuits and both the active and reactive impedance components increased linearly as the frequency grew. At high frequencies, the dispersion of susceptance, which was inversely proportional to frequency, was observed. The conclusion was drawn that the hopping conductivity mechanism through polymeric matrix surface states prevailed in films below the percolation threshold. At high frequencies, when the applied voltage period was shorter than the characteristic time of surface state recharging, these states began to be eliminated from charge transfer processes. It was suggested that a decrease in the reactive impedance component with an increase in frequency might be the reason for the dispersion observed experimentally.

The microstructure of and charge transfer in thin films based on metal-polymer nanocomposites

Charge transfer in nanostructured metal-polymer composites was studied. The frequency dependences of film conductance and susceptance were obtained at various metal concentrations. The susceptance of samples above the percolation threshold was negligibly small, which corresponded to the purely metallic conductivity type. For samples below the percolation threshold, susceptance and conductance were comparable in magnitude, which was evidence of an important role played by susceptance mechanisms. At low frequencies, the samples behaved as quasi-linear RC circuits and both the active and reactive impedance components increased linearly as the frequency grew. At high frequencies, the dispersion of susceptance, which was inversely proportional to frequency, was observed. The conclusion was drawn that the hopping conductivity mechanism through polymeric matrix surface states prevailed in films below the percolation threshold. At high frequencies, when the applied voltage period was shorter than the characteristic time of surface state recharging, these states began to be eliminated from charge transfer processes. It was suggested that a decrease in the reactive impedance component with an increase in frequency might be the reason for the dispersion observed experimentally.