Zixiao Pan

Nanopatterning of multiferroic BiFeO3 using “soft” electron beam lithography

The authors report fabrication of multiferroic BiFeO3 (BFO) by the soft electron beam lithography technique. BiFeO3 nanopatterns with less than 100nm characteristic dimension are fabricated from its liquid-phase precursor on diverse substrates. The chemical constituents and phase purity are characterized by transmission electron microscopy. The ferroelectric behavior is confirmed by piezoresponse force microscopy. A saturation magnetization of about 10emu∕cm3 is observed, demonstrating the multiferroic characteristic of the BFO nanopatterns. Furthermore, the BFO nanolines pattened on SrTiO3 substrate exhibit a bamboolike structure, which can serve as an excellent model system for investigating the contribution of grain boundaries to the leakage current.

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.

Patterning-controlled morphology of spatially and dimensionally constrained oxide nanostructures

This letter reports a facile approach for morphologic control of complex oxide nanostructures patterned by “soft” electron beam lithography (soft-eBL). The authors demonstrate fabrication of epitaxial nanofrustum and nanopyramidal morphologies of ferroelectric BaTiO3 and magnetic CoFe2O4 lines, with controlled zig-zag or smooth edges. The dimensional and shape control is achieved by simply tuning the patterning parameters such as resist thickness and patterning directions with respect to underlying substrate orientation. The crystal orientation, element distribution, and piezoelectric behavior of BaTiO3 nanofrustums are evaluated with analytical transmission electron microscopy and piezoresponse force microscopy. It is argued that soft-eBL allows for exquisite control over morphology, shape evolution, and orientation of zero- and one-dimensional nanostructures akin to what has been possible in the past with semiconductor heterostructures by thin film approaches.

A convenient and rapid sample repositioning approach for atomic force microscopy

A novel repositioning approach is described for repeated observations of a specimen at a close proximal location in the atomic force microscope. The approach is similar to keystone architecture, whereby the repositioning is achieved by forming a male structured base for the specimen, and a corresponding female counterpart as the frame. For the combination of an acrylic acid frame and a metal base, 90% translation shifts are less than 10 µm, and almost all angular disorientations are within +3° to −3°. Nanometre‐scale surface features can be relocated easily and reliably even after 40 imaging–removal–imaging cycles, dipping the specimen in solutions or heating up to 500 °C.

High-sensitivity strain mapping around epitaxial oxide nanostructures using scanning x-ray nanodiffraction

The generation and presence of strain around nanostructures of oxides is a key to their growth, properties, and functions, but it has been a challenge to experimentally measure its sign, magnitude, and spatial distribution. Combining diffuse scattering with scanning x-ray nanodiffraction, we have mapped the strain distribution in an oxide-on-oxide nanopatterned structure with a high sensitivity (10−4) and a submicrometer spatial resolution. An edge-induced strain distribution is observed from a sample of CoFe2O4 nanolines epitaxially grown on MgO substrate, which agrees quantitatively with the numerical simulations.