Fabrication and physical properties of thin TixOy membranes from single crystal TiO2

ABSTRACT:

Utilizing focused ion beam (FIB) milling, we have fabricated thin membranes (also referred to as nanowalls) of TixOy of 100–300 nm thickness starting from rutile titania bulk single crystals. Low probe currents (∼80 pA) in conjunction with XeF2-assisted milling enables minimal contamination during the fabrication process. Transmission electron microscopy studies indicated polycrystallinity and presence of nano-twins in the FIB-milled nanowalls. Formation of such nanoscale twinned structures may be related to high degree of nonstoichiometry, i.e., reduction as a result of milling in TiO2 that is consistent with observations in other oxides in the literature. Compositional analysis in the transmission electron microscope also showed reduced content of oxygen, confirming nonstoichiometry after milling. The authors have studied the temperature dependence of the electrical conductivity behavior in such ultra-thin walls in the temperature range of 300 K < T <520 K as a first effort. Temperature dependence of the electrical resistivity of the nanowall showed semiconducting behavior with an activation energy different from that corresponding to TiO2 single crystal and was attributed to formation of reduced TixOy phases after FIB processing. The results suggest a pathway to fabricate oxide structures for probing mesoscopic conduction phenomena.

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