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Biomedical subjects

John L Grazul

Publications and source records attributed to John L Grazul.

4 recordsLinked to original sources
PubMed2006

Room design for high-performance electron microscopy.

Aberration correctors correct aberrations, not instabilities. Rather, as spatial resolution improves, a microscope's sensitivity to room environment becomes more noticeable, not less. Room design is now an essential part of the microscope installation process. Previously ignorable annoyances like computer fans, desk lamps and that chiller in the service corridor now may become the limiting factors in the microscopes performance. We discuss methods to quantitatively characterize the instrument's response to magnetic, mechanical, acoustical and thermal disturbances and thus predict the limits that the environment places on imaging and spectroscopy.

Journal Article↗
PubMed2004

Atomic-scale imaging of nanoengineered oxygen vacancy profiles in SrTiO3.

At the heart of modern oxide chemistry lies the recognition that beneficial (as well as deleterious) materials properties can be obtained by deliberate deviations of oxygen atom occupancy from the ideal stoichiometry. Conversely, the capability to control and confine oxygen vacancies will be important to realize the full potential of perovskite ferroelectric materials, varistors and field-effect devices. In transition metal oxides, oxygen vacancies are generally electron donors, and in strontium titanate (SrTiO3) thin films, oxygen vacancies (unlike impurity dopants) are particularly important because they tend to retain high carrier mobilities, even at high carrier densities. Here we report the successful fabrication, using a pulsed laser deposition technique, of SrTiO3 superlattice films with oxygen doping profiles that exhibit subnanometre abruptness. We profile the vacancy concentrations on an atomic scale using annular-dark-field electron microscopy and core-level spectroscopy, and demonstrate absolute detection sensitivities of one to four oxygen vacancies. Our findings open a pathway to the microscopic study of individual vacancies and their clustering, not only in oxides, but in crystalline materials more generally.

Journal Article↗
PubMed2003

Direct fabrication of large micropatterned single crystals.

Micropatterning of single crystals for technological applications is a complex, multistep process. Nature provides alternative fabrication strategies, when crystals with exquisite micro-ornamentation directly develop within preorganized frameworks. We report a bio-inspired approach to growing large micropatterned single crystals. Micropatterned templates organically modified to induce the formation of metastable amorphous calcium carbonate were imprinted with calcite nucleation sites. The template-directed deposition and crystallization of the amorphous phase resulted in the fabrication of millimeter-sized single calcite crystals with sub-10-micron patterns and controlled crystallographic orientation. We suggest that in addition to regulating the shape, micropatterned frameworks act as sites for stress and impurity release during the amorphous-to-crystalline transition. The proposed mechanisms may have direct biological relevance and broad implications in materials synthesis.

Animals↗