DHA - Assembly of components into structures Fabrication of components
The main aim of this project is to make materials which can be assembled using the DHA into some
form of micro- or nano-tool. These tools are currently under development, with increasing
functionality and complexity, with the obvious goal of producing more complex structures and devices.
Initially components for fabrication were produced by template based electrodeposition. Cadmium
sulphide nanowires of varying sizes were produced from a cadmium sulphate/sodium thiosulphate
solution, using potentiostatic electrodeposition into PCTE (Polycarbonate Track Etched) membranes.
Typical diameters of the wires were 200-800 nm and lengths 4-10 μm. These were then successfully
treated with the protein biotin and used in the DHA in combination with streptavidin coated silica
beads.
Figure 4. TEM images of CdS nanorods using electrodeposition. |
Although electrodepostion is a relatively simple procedure, there are limitations in that only one
semiconductor can be deposited onto the membrane. Metallic multi-deposition is simple, whereas
combinations of non-metals aren't possible. In addition the process leaves behind a mixture which
contains nanowires, polycarbonate membrane and pieces of gold (used as the contact in the
electrodeposition process).
Nanowire components have since been produced using chemical vapour deposition. (CVD) CdS powder
under Argon gas flow in a tube furnace is evaporated. Silicon wafers coated with a thin (approx 10 nm)
gold layer catalyst act as the site for nanostructure growth. By altering growth conditions such as
flow rate, temperature, run time and gold layer thickness differing nanocomponents such as plates,
ribbons and wires can be formed. The cadmium sulphide content has been confimed by EDX.
Figure 5(a). Optical image showing CdS platelets. |
Figure 5(b). Optical image showing CdS nanowires (fine structures). |
Figure 6. EDX results of the CdS nanorods. The copper peak is due to the use of a copper test substrate. |
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Figure 7. TEM images of CdS nanorods produced using chemical vapour deposition.
In addition nanocomponents by photolithography is being investigated to mass produce different forms of components made from silica.
Photonic band gap materials Photonic Bad Gap (PBG) materials are likely to be useful in a wide range of devices, including: low threshold lasing, optical computation, and optical data transferral. Using the DHA PBG materials can be built which are difficult or impossible to do with bulk techniques.
DHA linksThe links below provide information on other areas of the DHA project.