The type and concentration of hydroxy groups in MCM-41 as a function of the Si : A1 ratio have been investigated and compared with amorphous Si/Al oxide. Three hydroxy groups at 3745, 3715 and 3530 cm-' were observed in the IR spectra of siliceous MCM-41. For Al-containing samples the intensity of the bands at 3715 and 3530 cm-' increased with increasing A1 concentra-Paper 6/01807F;

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Magnesium silicides can be used for thermoelectric energy conversion, as high values of figure of merit zT were obtained for n-type (1.4 at 500 °C) and p-type (0.55 at 350 °C) materials. This, however, needs to be complemented by low resistive and stable contacting to ensure long-term thermogenerator operation and minimize losses. In this study, we selected Cu and Ni 45 Cu 55 as contacting electrodes for their high electrical conductivity, similar coefficient of thermal expansion (CTE) and good adhesion to Mg 2 (Si,Sn). Both electrodes were joined to Mg 2 Si 0.3 Sn 0.7 pellets by hot pressing in a current-assisted press. Microstructural changes near the interface were analyzed using SEM/EDX analysis, and the specific electrical contact resistance r c was estimated using a travelling potential probe combined with local Seebeck scanning. Good contacting was observed with both electrode materials. Results show low r c with Cu, suitable for application, for both n-type and p-type silicides (< 10 µΩ•cm 2 ), with the occurrence of wide, highly conductive diffusion regions. Ni 45 Cu 55 joining also showed relatively low r c values (~ 30 µΩcm 2 ) for n-and p-type, but had a less inhomogeneous reaction layer. We also performed annealing experiments with Cu-joined samples at 450 °C for one week to investigate the evolution of the contact regions under working temperatures. r c values increased (up to ~ 100 µΩcm 2 ) for annealed n-type samples, but remained low (< 10 µΩcm 2 ) for p-type. Therefore, Cu is a good contacting solution for p-type Mg 2 (Si,Sn), and a potential one for n-type if the diffusion causing contact property degradation can be prevented.

Solid-state nanopores constitute a versatile platform for study of ion transport in nanoconfinement. The electrical double layer (EDL) plays a vital role in such nanoconfinements, but effects of induced surface charge on the EDL in the presence of an external transmembrane electric field are yet to be characterized. Here, the formation of induced charge on the nanopore sidewall surface and its effects, via modulation of the EDL and electroosmotic flow, on the ionic current are elucidated using a novel experimental setup with solid-state truncated-pyramidal nanopores. This study consists of three complementary approaches, i.e., an analytical model for induced surface charge, numerical simulation of induced surface charge, electroosmotic flow, and ionic current, and experimental validation with respect to the ionic current. The induced surface charge is generated by polarization in the dielectric membrane as a response to the applied electric field. This charge generation results in a nonuniform density of surface charge along the nanopore sidewall. It further causes ions in the electrolyte to redistribute, leading to a massive accumulation of single-polarity ions in the EDL and their counterions near the smaller opening of the nanopore. It also alters electrohydrodynamic properties in the nanopore, giving rise to the formation of electroosmotic vortexes in the vicinity of the smaller opening of the nanopore. Finally, the pattern of the electroosmotic flow can significantly influence the transport properties of the nanopore.

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