Quantification of van der Waals forces in bimodal and trimodal AFM.

The multifrequency formalism is generalized and exploited to quantify attractive forces, i.e., van der Waals interactions, with small amplitudes or gentle forces in bimodal and trimodal atomic force microscopy (AFM). The multifrequency force spectroscopy formalism with higher modes, including trimodal AFM, can outperform bimodal AFM for material property quantification. Bimodal AFM with the second mode is valid when the drive amplitude of the first mode is approximately an order of magnitude larger than that of the second mode. The error increases in the second mode but decreases in the third mode with a decreasing drive amplitude ratio. Externally driving with higher modes provides a means to extract information from higher force derivatives while enhancing the range of parameter space where the multifrequency formalism holds. Thus, the present approach is compatible with robustly quantifying weak long range forces while extending the number of channels available for high resolution.

Who Does the Job? How Copper Can Replace Noble Metals in Sustainable Catalysis by the Formation of Copper-Mixed Oxide Interfaces.

Following the need for an innovative catalyst and material design in catalysis, we provide a comparative approach using pure and Pd-doped LaCu x Mn1-x O3 (x = 0.3 and 0.5) perovskite catalysts to elucidate the beneficial role of the Cu/perovskite and the promoting effect of Cu y Pd x /perovskite interfaces developing in situ under model NO + CO reaction conditions. The observed bifunctional synergism in terms of activity and N2 selectivity is essentially attributed to an oxygen-deficient perovskite interface, which provides efficient NO activation sites in contact with in situ exsolved surface-bound monometallic Cu and bimetallic CuPd nanoparticles. The latter promotes the decomposition of the intermediate N2O at low temperatures, enhancing the selectivity toward N2. We show that the intelligent Cu/perovskite interfacial design is the prerequisite to effectively replace noble metals by catalytically equally potent metal-mixed-oxide interfaces. We have provided the proof of principle for the NO + CO test reaction but anticipate the extension to a universal concept applicable to similar materials and reactions.