Suresh Donthu

Controlled large-scale synthesis and magnetic properties of single-crystal cobalt nanorods

We report detailed synthesis studies of large-scale fabrication of single-crystalline cobalt nanorods using thermally evaporated gold as a conducting electrode on a nanoporous anodized aluminum oxide (AAO) template. By varying the time (i.e., adjusting the current density), it is possible to control the length of the nanorods and these rods grow in highly anisotropic face-centered (L10) phase. The large-scale isolation of these nanorods was achieved using a mild HF solution to dissolve the AAO membranes, leaving behind large scale ensemble of the isolated Co nanorods. Scanning electron microscopy and transmission electron microscopy examinations show clear evidence for metallic Co nanorods (about 100 nm in diameter) formed inside an array of AAO nanopores. We observe more uniform length of nanorods when an external magnetic field is applied during synthesis. A preferred perpendicular (shape) anisotropy is observed in these nanorod arrays. Magnetic properties indicate both coercivity and thermal activation...

Near-field scanning optical microscopy of ZnO nanopatterns fabricated by micromolding in capillaries

We report near-field scanning optical microscopy (NSOM) studies of 300‐nm-wide ZnO nanopatterns fabricated by micromolding in capillary technique using a sol-gel route. Atomic force microscopy and scanning electron microscopy show that the patterns are continuous with uniform linewidths. Simultaneous topography and optical signal collected in NSOM scans exhibit nanoscale photoluminescence intensity distribution in the ZnO nanopatterns. The nanoscale spectral mapping shows very broad defect-induced green-yellow-red luminescence bands, at room temperature, when excited with a 514.5‐nm Ar-ion laser. Our analyses demonstrate that spatially resolved ZnO luminescence features with an optical resolution of ⩽300nm can be obtained with NSOM while operating in collection mode, and underscore the need to couple nanoscale physical characterization with functional properties at the same scale.

Directed Fabrication of Ceramic Nanostructures on Fragile Substrates Using Soft-electron Beam Lithography (soft-eBL)

We demonstrate the use of a facile nanopatterning scheme known as soft electron beam lithography (soft-eBL) to fabricate and site specifically position a variety of functional ceramic nanostructures onto two fragile substrates: a 75-nm-thick electron-transparent silicon nitride membrane and suspended microhotplates with embedded heaters. The patterned nanostructures on nitride membranes can be readily probed with a variety of characterization tools without any postfabrication sample preparation, allowing observation of the nanostructures in near-pristine condition. We demonstrate this by characterizing the structural, chemical, and optical properties of several ceramic nanostructures patterned on membranes using electron microscopy and surface scanning probe tools such as atomic force microscopy and near- field scanning optical microscopy. We further demonstrate that such nanostructures, upon integration with microelectromechanical systems (MEMS) microhotplate platforms, can function as gas-sensing elements; we evaluate their sensing performance at micromoles per mole target analyte concentration levels.