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- Electrochemical quartz microbalance (2)
- Gold (2)
- S-layers crystallization (2)
- Scanning force microscopy (2)
- XPS (2)
- Band structure (1)
- Diamond growth & characterization (1)
- Electron Spectroscopy (1)
- FTIR Ellipsometry (1)
- Nanoindentation (1)
Amorphous carbon (a-C) multilayered films consisting of sequential layers rich in sp2 (A) and sp3 (B) content have been developed by magnetron sputtering. We study here the effect of thickness d of the A layer in developing stable thick films with controllable stress and elastic properties. In situ spectroscopic ellipsometry is used to calculate the thickness and the composition of the individual layers. The latter were compared with those obtained by depth profiling X-ray photoelectron spectroscopy, which also provides the different chemical bonding of the multilayers in depth. The stress and hardness of the deposited a-C films were found to be related to the thickness of the Aj layers and the relative ratio dAj/dB of thicknesses. The possible mechanisms for the stress control, stability and enhancement of elastic properties of multilayered a-C films are discussed.
The mechanism of the recrystallization of nano-scale bacterial surface protein layers (S-layers) on solid substrates is of fundamental interest in the understanding and engineering of biomembranes and e.g. biosensors. In this context, the influence of the charging state of the substrate had to be clarified. Therefore, the electrochemical behaviour of the S-layers on gold electrodes has been investigated by in-situ electrochemical quartz microbalance (EQMB) measurements, scanning force microscopy (SFM) and small-spot X-ray photoelectron spectroscopy (SS-XPS) of potentiostatically emersed substrates. It was shown that the negatively charged bonding sites of the S-layer units (e.g. carboxylates) can bond with positively charged Au surface atoms in the positively charged electrochemical double layer region positive of the point of zero charge (not, vert, similar-0.8 V vs. saturated mercury-mercurous sulphate electrode). Surface conditions in other potential regions decelerated the recrystallization and fixation of S-layers. Time-resolved in-situ and ex-situ measurements demonstrated that two-dimensional S-layer crystal formation on gold electrodes can occur within few minutes in contrast to hours common in self-assembled monolayer (SAM) generation. These results proved that the recrystallization and fixation of 2D-crystalline S-layers on an electronic conductor can be influenced and controlled by direct electrochemical manipulation.
A study on the bonding structure and mechanical properties of magnetron sputtered CNx thin films
(2001)
Carbon nitride (CNx) films have been deposited by reactive (RF) magnetron sputtering, in order to investigate the effect of the energetic ion bombardment during deposition (IBD), in terms of applied Vb, on their bonding structure. Fourier Transform IR Ellipsometry (FTIRE) and X-ray photoelectron spectroscopy (XPS) were used for the investigation of the films bonding structure, while their mechanical properties were evaluated by nanoindentation measurements. At films grown with low negative Vb, (low energy IBD) the N atoms are distributed homogeneously in substitutional sites in graphitic rings through both sp2 and sp3 bonds and in linear chains, through sp2 bonds. In contrast, the high negative Vb (high energy IBD) has been suggested to promote the non-homogeneous N distribution at localized regions in the films where the formation of sp3 C---N bonds is favored. This behavior was also evidenced by the C1s and N1s XPS peak components, assigned to the sp3 and sp2 carbonnitrogen bonds. Also, high energy IBD films revealed increased values of hardness and elasticity, while hardness values up to 45 GPa were measured at localized regions.
A complementary study of composition and bonding of sputtered a-C films, deposited on Si(001) substrates with various bias voltages (Vb) applied to the substrate during deposition is presented. The sp3 and sp2 fractions in the films were calculated by deconvolution of the X-ray photoelectron spectroscopy (XPS) C1s peak and studied by the differential auger electron spectroscopy (AES) CKLL peak signal. The results of this analysis are compared with the estimation of sp3 fraction calculated by spectroscopic ellipsometry (SE) and validated using density measurements by X-ray reflectivity. It was observed a considerable increase of sp3 content in films deposited with negative Vb. The respective sp3 and sp2 fractions and Ar concentration with respect to the Vb and the depth profile analysis give valuable information on the deposition mechanism of the sputtered a-C films. XPS valence band spectra provided the electron density of states in the a-C films valence band. The characteristic broad p band of diamond was prominent in most of the films. The valence band structure of the films was correlated with their optical response measured by SE.