| Popis: |
A real time observation of the growth of agglomerates of pyramidal crystallites of mercuric iodide on a porous glass surface using tapping mode atomic force microscopy is reported. Crystallites are observed to grow from the pores (5.0 nm diameter) onto the surface of the porous glass impregnated with mercuric iodide. Immediately after fracturing the impregnated porous glasses, topographical images reveal a surface with a root mean square roughness of 75–130 nm over a 5 μm×5 μm area, which is typical for surfaces of fractured porous glass. After 3 h, 60–90 nm pyramidal structures with a high aspect ratio (pyramid base to height) begin to appear on the surface. Some of the pyramidal structures agglometrate and form structures much larger and higher than the surrounding ones. The bottom of some of these agglomerated pyramids form equilateral triangles with dimensions of 300–500 nm, exhibiting a preferred orientation on the surface. 6 h after fracturing, micrometer‐size crystallites are observed. Most of the pyramidal structures are no longer observed and mostly needlelike features are covering the surface. Step heights consistent with multiples of the c axis of α‐mercuric ioide are observed on the micrometer‐sized crystallites. Some pyramidal structures are observed between the large crystallites, with sizes comparable to the early stage pyramidal structures. Raman and electronic spectra are also reported for mercuric iodide confined in porous glasses. The Raman spectra have peaks located at 39 and 141 cm−1, indicating that the confined mercuric iodide is stabilized in the yellow, orthorhombic (β phase) at room temperature. Confinement of mercuric iodide in pores with radii smaller than 3.75 nm results in the appearance of a new band at 145 cm−1 in the Raman spectra, suggesting the presence of a new or modified β phase of mercuric iodide. Further evidence supporting the presence of a new phase of mercuric iodide is found in the electronic spectra where an energy gap of 2.7 eV is observed, and lies between the energy gaps of the red, tetragonal, α phase (2.2 eV) and the yellow, orthorhombic β phase (3.1 eV) of mercuric iodide. The atomic force microscopy measurements provide a unique method for real time monitoring of the crystal growth and morphology changes of nanocrystalline mercuric iodide, while the spectroscopy provides insight to the phonon structure and energy gaps of the confined material. |
