Abstract
Single crystal zinc particles, 1–2 μm in diameter, were observed in situ with transmission electron microscopy during sublimation. The rate of sublimation is strongly dependent on the presence of a surface oxide layer. Near 375 °C, minimally oxidized Zn surfaces sublime in tens of seconds, consistent with a model in which the particle behaves similarly to an isolated microscale effusion cell. By contrast, zinc particles fully enclosed by oxide sublime less than one-tenth as quickly. These results provide new insight into the synthesis mechanisms of hollow ZnO microspheres and related structures formed from metallic zinc at elevated temperatures.
Highlights
The TEM is fitted with a Gatan imaging filter, images were acquired in bright-field mode with the energy filtering window set at 20 eV to filter out inelastically scattered electrons
TEM grids were pressed against the upper surface of the furnace by means of a thin tantalum spring attached to a copper stalk
For particle BFigs. 2͑cand 2͑d, the orientation of the largest visible opening in the oxide shellFig. 2͑dis consistent with the sublimation pattern; the particle erodes not from a point at the edge but rather from a surface which is oriented such that all edges visible in profile erode at similar rates
Summary
A. Wall1 1Lawrence Livermore National Laboratory, 7000 East Avenue, Livermore, California 94550, USA 2Epimedia, Inc., 42 Norman Ct, Walnut Creek, California 94595, USAReceived 31 January 2011; accepted 6 May 2011; published online 14 June 2011͒ Zinc particles were formed by condensation of vapor in argon and subsequent deposition onto copper TEM grids. Observe a progressive increase in the thickness of the oxide shell as a function of the time since the start of sublimation.
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