Post-Synthetic Anisotropic Wet-Chemical Etching of Colloidal Sodalite ZIF Crystals

Controlling the shape of metal-organic framework (MOF) crystals is important for understanding their crystallization and useful for myriad applications. However, despite the many advances in shaping of inorganic nanoparticles, post-synthetic shape control of MOFs and, in general, molecular crystals remains embryonic. Herein, we report using a simple wet-chemistry process at room temperature to control the anisotropic etching of colloidal ZIF-8 and ZIF-67 crystals. Our work enables uniform reshaping of these porous materials into unprecedented morphologies, including cubic and tetrahedral crystals, and even hollow boxes, by an acid-base reaction and subsequent sequestration of leached metal ions. Etching tests on these ZIFs reveal that etching occurs preferentially in the crystallographic directions richer in metal-ligand bonds; that, along these directions, the etching rate tends to be faster on the crystal surfaces of higher dimensionality; and that the etching can be modulated by adjusting the pH of the etchant solution

Magnetic correlations and quantum criticality in the insulating antiferromagnetic, insulating spin liquid, renormalized Fermi liquid, and metallic antiferromagnetic phases of the Mott system V_2O_3

Magnetic correlations in all four phases of pure and doped vanadium sesquioxide V_2O_3 have been examined by magnetic thermal neutron scattering. While the antiferromagnetic insulator can be accounted for by a Heisenberg localized spin model, the long range order in the antiferromagnetic metal is an incommensurate spin-density-wave, resulting from a Fermi surface nesting instability. Spin dynamics in the strongly correlated metal are dominated by spin fluctuations in the Stoner electron-hole continuum. Furthermore, our results in metallic V_2O_3 represent an unprecedentedly complete characterization of the spin fluctuations near a metallic quantum critical point, and provide quantitative support for the SCR theory for itinerant antiferromagnets in the small moment limit. Dynamic magnetic correlations for energy smaller than k_BT in the paramagnetic insulator carry substantial magnetic spectral weight. However, the correlation length extends only to the nearest neighbor distance. The phase transition to the antiferromagnetic insulator introduces a sudden switching of magnetic correlations to a different spatial periodicity which indicates a sudden change in the underlying spin Hamiltonian. To describe this phase transition and also the unusual short range order in the paramagnetic state, it seems necessary to take into account the orbital degrees of freedom associated with the degenerate d-orbitals at the Fermi level in V_2O_3.Comment: Postscript file, 24 pages, 26 figures, 2 tables, accepted by Phys. Rev.

Stress-Strain Studies by Means of a Non-Focusing X-Ray Diffraction Camera

The distortion of the crystal lattices in a metal under stress has provided a valuable means of studying these stresses. The best method of non-destructive study is through x-ray diffraction techniques. The stress-strain relationships have been thoroughly studied by many investigators, each using his own modifications of the basic principles involved. This thesis presents another method of studying the stress-strain relationships in metals by means of x-ray diffraction. The investigation was carried out with non-focused x-ray diffraction cameras. The stress distortions in metals are easily found on x-ray patterns, but the accurate measurement of the small changes is rather difficult. It was hoped that some inherent non-focused features of the camera would magnify or offer some definite photographic indication of the stresses. All of this work was carried out using a series of aluminum alloys. These alloys were photographed while under various stresses by means of x-rays. Special calibrated jigs were devised to facilitate the photographing of the specimens

Phlebotomy : worktext and procedures manual, 4th ed./ Warekois

xv, 363 p.: ill, tab.; 24 cm

Phlebotomy : worktext and procedures manual, 4th ed./ Warekois

xv, 363 p.: ill, tab.; 24 cm