A recent American Chemical Society's Weekly PressPac briefly describes an important advance toward industrial-scale production of nanodevices (scroll down to item #4). With this new technique, 'zinc oxide nanowires are grown in the exact positions where nanodevices later will be fabricated, in a way that involves a minimum number of fabrication steps and is suitable for industrial-scale applications.' In fact, this technique only needs only three photolithographic steps. It could soon be used for mass fabrication of nanowire-based transistors and sensors.
You can see on the left a schematic of the photolithography process used for this new scalable fabrication of nanowire devices. "(a) Gold pads and fiducial marks are deposited on the surface. (b) Nanowires (NWs) are grown selectively from the two sides of the gold pads. (c) Metal electrodes and bonding pads are placed exactly on NWs by alignment of fiducial marks." (Credit: Babak Nikoobakht, National Institute of Standards and Technology) Here is a link to a larger version of this picture.
This new way of producing nanodevices at the industrial scale has been conceived by Babak Nikoobakht, a research chemist working for the National Institute of Standards and Technology (NIST) in the Surface and Interface research group.
This research work is published in the American Chemical Society's Chemistry of Materials journal under the name "Toward Industrial-Scale Fabrication of Nanowire-Based Devices." Here are two links to the HTML version and to the PDF version of this paper, from which the above figure has been extracted.
Here is the beginning of the abstract. "Although optical lithography is suited for producing intricate architectures, its combination with 'bottom-up' approaches becomes a very challenging issue. The challenge is to electrically address the coordinates of millions of nanoparticles (e.g., nanowires) on a given surface. Here, we describe a method that controls the registries of horizontally grown nanowires (NWs) and advances the current state-of-the-art NW device assembly technology. In this architecture, NWs are grown where the nanodevices will later be fabricated on. There is no need to transfer NWs to a different surface or align them."
This technique only needs only three photolithographic steps. "The first is defining the starting coordinates of horizontally grown NWs. Since the growth direction of NWs is known, the end point coordinates of NWs become known as well. Therefore, the devices would be exactly fabricated where horizontal NWs are residing. Second, this method allows control over the number of NWs in each device. This is because each NW is grown from a gold nanodroplet, thus controlling this number results in control over the number density of NWs. Third, this is a scalable technique capable of industrial-scale applications in its current status."
Here is the conclusion from the researchers. "In comparison to other available techniques this method requires a minimum number of fabrication steps. The chemical method provides the horizontal growth of NWs from individual gold nanodroplets, and their alignment is dictated by lattice match with the underlying substrate. Locations of NWs, with a submicrometer precision, are controlled by the position of gold patterns made by photolithography. NWs are grown where the devices will be fabricated, and there is no need to transfer NWs to a different substrate. This approach in its current state seems to be a promising methodology for parallel nanodevice fabrication at technologically relevant scales."
Sources: American Chemical Society, November 7, 2007; and various websites
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