Fabrication and Assembly Behavior of Square Microcapsules

Template methods have been extensively investigated for
the preparation of a number of one-dimensional (1D) nano-
structures, including chemical sensors, high-density data stor-
age, and microdevices.[1–11] Alumina and polymer membranes
with channel diameters ranging from tens of nanometers to
several micrometers are commonly used in these methods,
leading to various wire and tube structures by both chemical
and electrochemical routes.[6–8,12–15] In addition, porous silicon
membranes have been prepared with features in the hundreds
of nanometers to micrometer range.[16,17] As with some alumi-
na membranes,[18] silicon membranes can be formed with non-
circular channels.[17] While Si membranes have been exten-
sively studied as photonic crystals,[19–21] their use as templates
has been relatively limited.[22–26] Herein we report the use of
silicon membranes in the fabrication of micrometer-sized
square tubes and capsules. The Si pores of a membrane are
modified with a polymer component such that a gap is created
along the wall of the channel. Electrochemical deposition
within this modified structure creates square metal tubes. The
tubes can be released from the membrane, or with further
processing, be converted to buoyant microcapsules with inter-
esting assembly properties.