Lifshitz analysis of dispersion forces based on quantitative reflection electron energy loss spectroscopy

HYPOTHESIS

The energy loss experienced by an electron while moving through a solid is determined by the optical properties of the surrounding. Hence, quantitative Reflection Electron Energy Loss Spectroscopy (REELS) should allow the determination of optical data required for the calculation of Hamaker coefficients using Lifshitz theory. This approach might improve the accuracy of calculated Hamaker coefficients and should also enable to harness the unique capabilities of REELS to analyse nanostructured surfaces and thin-films with great spatial resolution and surface sensitivity.

EXPERIMENTS

REELS spectra of a survey of insulating polymers and of metal-like Ti_0.23Al_0.32N_0.44 (TiAlN) were measured, the complex dielectric functions determined and the corresponding Hamaker coefficients across vacuum and water calculated. The sensitivity of the quantification procedure towards typical systematic errors was investigated. For polystyrene the results were comparatively analysed using vacuum ultraviolet spectroscopy (VUV).

FINDINGS

The accuracy especially of the non-retarded vacuum Hamaker constants of the polymers was increased when compared to VUV reflectance spectroscopy due to the higher spectral range of REELS. Furthermore, a new correction procedure for the intricate case of unresolved inelastic losses in the REELS spectrum, such as encountered in the case of TiAlN, could be developed using spectroscopic ellipsometry as a complementary mean.

Analysis of dispersive interactions at polymer/TiAlN interfaces by means of dynamic force spectroscopy

The structural and electronic origins of the interactions between polycarbonate and sputter deposited TiAlN were analysed using a combined electron and force spectroscopic approach. Interaction forces were measured by means of dynamic force spectroscopy and the surface polarizability was analysed by X-ray photoelectron valence band spectroscopy. It could be shown that the adhesive interactions between polycarbonate and TiAlN are governed by van der Waals forces. Different surface cleansing and oxidizing treatments were investigated and the effect of the surface chemistry on the force interactions was analysed. Intense surface oxidation resulted in a decreased adhesion force by a factor of two due to the formation of a 2 nm thick Ti_0.21Al_0.45O surface oxide layer. The origin of the residual adhesion forces caused by the mixed Ti_0.21Al_0.45O surface oxide was clarified by considering the non-retarded Hamaker coefficients as calculated by Lifshitz theory, based on optical data from Reflection Electron Energy Loss Spectroscopy. This disclosed increased dispersion forces of Ti_0.21Al_0.45O due to the presence of Ti(iv) ions and related Ti 3d band optical transitions.

New amidinate complexes of indium(iii): promising CVD precursors for transparent and conductive In2O3 thin films

Heteroleptic and homoleptic In(iii)-amidinate complexes as promising CVD precursors for In₂O₃ thin films.