In situ high temperature X-ray diffraction, nitrogen porosimetry and gas adsorption at room temperature were used to elucidate the effect of the degassing or activation temperature on the long-range and micropore textural properties of a series of coordination polymers with pillared-layer structures. Ramp-and-soak thermal gravimetric analysis performed at selected activation temperatures were used to verify the thermal stability of a CPL-n series [Cu(2)(pzdc)(2)L; pzdc = pyrazine-2,3-dicarboxylate; L = 4,4-azopyridine (apy) for CPL-4, 1,2-di-(4-pyridil)-ethylene (bpe) for CPL-5, N-(4-pyridyl)-isonicotinamide (pia) for CPL-6, and 1,2-di-(4-pyridyl)-glycol (dpyg) for CPL-7]. Although the activation temperatures were far below the decomposition point of the complexes, these resulted in significant and unique changes in micropore surface area and volume, even for CPL-4, -5 and -6, which contained pillar ligands with similar dimensions and similar structural long-range order. For the case of CPL-7, however, the framework appeared to be non-porous at any given activation temperature. Pure component equilibrium adsorption data gathered for CO(2), CH(4), and N(2) were used to elucidate the CPL-n materials potential for storage and separations at room temperature. All of the materials exhibited considerable selectivity toward CO(2), particularly at moderate pressures. Meanwhile, CO(2) isosteric heats of adsorption indicated that the pore functionalities arising from the pillar ligands provided similar interactions with the adsorbate in the cases of CPL-4 and -5. For CPL-6, the presence of the carbonyl (C[double bond, length as m-dash]O) group appeared to enhance interactions with CO(2) at low loadings.

No abstract

Silicon nanomembranes are suspended single-crystal sheets of silicon, tens of nanometers thick, with areas in the thousands of square micrometers. Challenges in fabrication arise from buckling due to strains of over 10−3 in the silicon-on-insulator starting material. In equilibrium, the distortion is distributed across the entire membrane, minimizing the elastic energy with a large radius of curvature. We show that flat nanomembranes can be created using an elastically metastable configuration driven by the silicon-water surface energy. Membranes as thin as 6 nm are fabricated with vertical deviations below 10 nm in a central 100 μm × 100 μm area.

The lattice mismatch between SiGe and Si in heteroepitaxial Si/SiGe/Si trilayers leads to buckling when confined nanomembrane windows formed from these heterostructures are released from silicon-on-insulator substrates. We demonstrate that large areas in which the curvature and curvature-induced strain are reduced by an order of magnitude can be produced by patterning the windows to concentrate buckling in narrow arms with low flexural rigidity supporting a flat central region. Synchrotron x-ray thermal diffuse scattering shows that the improved flatness of patterned windows permits fundamental studies with fidelity similar to what can be achieved with flat single-component Si nanomembranes.