This was published on Materials Today on 16 December 2014 – you can read this story in-situ here: http://www.materialstoday.com/biomaterials/news/bacteriaenabled-nanofiber-fets/
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US scientists demonstrate that microbially-synthesized chalcogenide nanofibers can be used to build functional field-effect transistors (FETs)
There are many routes to synthesizing nanomaterials, but biological processes offer a number of advantages over traditional chemical strategies, thanks to their use of lower temperatures and pressures. Chalcogenide compounds (which combine group VI elements such as sulphur, with electropositive elements such as arsenic) are of particular relevance to biogenic synthesis. Their remarkable versatility means that depending on their composition and synthesis techniques, they can be crystalline, glassy, metallic, semiconductive or ionic conductors. A team of researchers from the University of Southern California have used a strain of the bacteria Shewanella to produce these tunable materials, and demonstrated their potential for use in fully-functional field-effect transistors (FETs).
The study, appearing in Acta Biomaterialia [DOI:10.1016/j.actbio.2014.11.005], focuses on the microbial synthesis and characterization of individual arsenic sulphide nanofibers. Using a previously unstudied strain of the bacteria, the team found that they could produce the yellow As2S3 nanofibers significantly faster, and at a much higher yield, than previously observed with other Shewanella strains. In fact, the team found that the bacterial synthesis of As-S nanofibers was faster and more effective than the non-biological precipitation of already-reduced arsenic and sulphur.
The structural, crystallographic, electronic and band gap properties of these nanofibers were also characterized. In this analysis, a wide range of fiber diameters were found (20-600 nm), with many fibers arranged into bundles. The precipitate itself was found to be primarily amorphous, but with a small fraction of crystalline material also present. The measured optical band gap of the nanofibers suggested that they are indirect band gap semiconductors. In addition, using individual fibers, the team also constructed nanofiber-FETs. In almost two-thirds of cases, these devices exhibited p-type behavior, consistent with the behavior of amorphous chalcogenide glasses. Almost 25% of the FETs demonstrated the reverse characteristics, reflecting the complexity of the bacterial growth medium.
Chalcogenides have already found commercial applications as rewritable optical storage disks and infrared devices. But these results add a better understanding of how such materials can be microbially-synthesized, thus avoiding the use of the toxic solvents and harsh reaction conditions typical of well-established chemical strategies. The authors believe that this work may help to realize the potential of these nanomaterials in a range of sensors, waveguides, photovoltaics and storage devices.
– Acta Biomaterialia, Article in press, “Field effect transistors based on semiconductive microbially synthesized chalcogenide nanofibers.” DOI:10.1016/j.actbio.2014.11.005