Surfaces

Electron transport measurements on Co/TiN multilayers are employed to explore the effect of TiN layers on Co resistivity. For this, 50 nm thick multilayer stacks containing N = 1–10 individual Co layers that are separated by 1 nm thick TiN layers are sputter deposited on SiO₂/Si(001) substrates at 400 °C. X-ray diffraction and reflectivity measurements indicate a tendency for a 0001 preferred orientation, an X-ray coherence length of 13 nm that is nearly independent of N, and an interfacial roughness that increases with N. The in-plane multilayer resistivity ρ increases with increasing N = 1–10, from ρ = 14.4 to 36.6 µΩ-cm at room temperature and from ρ = 11.2 to 19.4 µΩ-cm at 77 K. This increase is due to a combination of increased electron scattering at interfaces and grain boundaries, as quantified using a combined Fuchs–Sondheimer and Mayadas–Shatzkes model. The analysis indicates that a decreasing thickness of the individual Co layers d_Co from 50 to 5 nm causes not only an increasing resistivity contribution from Co/TiN interface scattering (from 9 to 88% with respect to the room-temperature bulk resistivity) but also an increasing (39 to 154%) grain boundary scattering contribution, which exacerbates the resistivity penalty due to the TiN liner. These results are supported by Co/TiN bilayer and trilayer structures deposited on Al₂O₃ (0001) at 600 °C. Interfacial intermixing causes Co₂Ti and Co₃Ti alloy phase formation, an increase in the contact resistance, a degradation of the Co crystalline quality, and a 2.3× higher resistivity for Co deposited on TiN than Co directly deposited on Al₂O₃(0001). The overall results show that TiN liners cause a dramatic increase in Co interconnects due to diffuse surface scattering, interfacial intermixing/roughness, and Co grain renucleation at Co/TiN interfaces.

This study investigates the optimization of sol–silicate façade coatings modified with colloidal silica and a silane-based hydrophobizing additive to enhance hydrophobicity while maintaining a high water-vapor transmission rate (V). The effects of the binder ratio between potassium water glass (WG) and colloidal silica (CS), the type of colloidal silica (unmodified or epoxy-silanized), and the concentration of the hydrophobizing additive (HA) were systematically evaluated. Water-vapor transmission was determined according to EN ISO 7783, and surface wettability was measured before and after accelerated UV-A aging. Dynamic viscosity was monitored for two years to assess long-term storage stability. The optimized formulation contained 7 wt % potassium water glass, 15 wt % colloidal silica, and 1 wt % hydrophobizing additive. It exhibited stable viscosity over time (≈19,000 mPa·s after six months), high water-vapor transmission (V > 6700 g·m⁻²·d⁻¹, class V1), and an initial contact angle of 118°, which decreased only moderately after UV-A exposure. Coatings containing epoxy-silanized colloidal silica showed slightly lower transmission but still remained within the high V range suitable for vapor-open façade systems. The results confirm that balanced sol–silicate systems can combine durable hydrophobicity with long-term rheological and functional stability.

In recent years, porous carbon-based materials have demonstrated their potential as electrode materials, particularly as supercapacitors for energy storage. The specific capacitance of a carbon-based material is strongly influenced by its porosity. Herein, activated biochar (BCA) from millet was prepared using ZnCl₂ as an activator at temperatures of 400, 700, and 900 °C. Activation was achieved through wet and dry impregnation of millet bran powder particles. The porosity of BCAs was assessed by determining the iodine and methylene blue numbers (N_I and N_MB, respectively), which provide information on microporosity and mesoporosity, respectively. Characterization of the BCAs was carried out using Raman spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and cyclic voltammetry. The data show that the BCA prepared at 700 °C following dry impregnation, P700(p), has the highest N_I and the highest geometric mean value ($ñ=\sqrt{N_I\times N_{MB}}$), a descriptor we introduce to characterize the overall porosity of the biochars. P700(p) biochar exhibited remarkable electrochemical properties and a maximum specific capacitance of 440 F g⁻¹ at a current density of 0.5 A g⁻¹, in the three-electrode configuration. This value drops to 110 F g⁻¹, in the two-electrode configuration. The high specific capacitance is not due to ZnO, but essentially to the textural properties of the biochar (represented by ñ descriptor), and possibly but to a lesser extent to small amounts of Zn₂SiO₄ left over in the biochar. Moreover, the capacitance retention increases with cycling, up to 130%, thus suggesting electrochemical activation of the biochar during the galvanostatic charge-discharge process. To sum up, the combination of pyrolysis temperature and the method of impregnation permitted to obtaining of a porous biochar with excellent electrochemical properties, meeting the requirements of supercapacitors and batteries.