UW-Stevens Point1, Chemisty, Stevens Point, WI 54481 Argonne National Laboratory2, Argonne, IL 60439
Transmission electron microscopy (TEM) is a commonly used technique to study the morphology and crystal structure of very thin materials, such as metal and semiconducting nanowires. These nano- and microwires may be produced easily via Electroplate and Lift (E&L) Lithography, a fundamental advance in electrochemical synthesis which was developed in 2010 through collaboration between students at UW-Stevens Point and researchers at Argonne National Laboratory. E&L uses photolithographically patterned electrodes made of ultrananocrystalline diamond (UNCD)TM as templates for electrochemical deposition. The UNCD film structure consists of a very thin (~ 50 nm) layer of conductive nitrogen-incorporated UNCD (NUNCD) in between two equally thin insulating layers of UNCD. Lithographically defined patterns are etched through the UNCD/NUNCD/UNCD film to expose edges of the conductive NUNCD, which serve as the sites for nanowire nucleation and growth. In the original E&L experiments, nanowires were produced on one substrate, and later transferred to a separate TEM grid for analysis. At best, the transfer process was time-consuming and labor-intensive; at worst, nanowires were often either damaged during the transfer, or failed to adhere to the grid. Thus, the development of a substrate which would permit direct nanowire growth upon a TEM grid is desirable for the rapid, immediate, easy characterization of the deposits. In this work, we report the fabrication of TEM grids which incorporate suspended UNCD films with areas up to 1x1 mm, supported only at the edges by a silicon frame, with a layered structure similar to the classic E&L templates. Within a circular area 3 mm in diameter, each TEM grid contains six independent, electrically addressable electrical contacts. Each contact permits the selective E&L-style growth of metal nanowires only upon exposed NUNCD connected to the active contact, at the edges of the one or more lithographically patterned small holes. The lithographic patterns may be varied to allow the deposition of different metals in different holes on the same TEM grid, or, in holes which span more than one circuit, different metals in different regions of the same hole. All of the small holes are etched through the layered UNCD in fully suspended areas of the film, where the underlying silicon has been removed. This allows thin wires to be electroplated which are completely supported by the UNCD, but free of obstruction by the substrate, ready to be analyzed in the TEM with no need for any further sample preparation. In preliminary experiments, permanent wire bonds have been made to several TEM grids, and electrochemical depositions of copper and platinum have been performed. Given their adaptability, these UNCD TEM grids have great potential for use as substrates in research fields as diverse as materials science and medical technology.
[Abstract (DOCX)]