This video was made by Captain Corrosion OÜ for the Group of Sensor Technologies (Institute of Physics, University of Tartu) to show the working principle of pulsed laser deposition (PLD), where a pulsing laser beam extracts matter from the target. This extracted matter is then deposited to the substrate. By tuning the level of vacuum in the deposition chamber and the intensity of the laser it is possible to use PLD technology to introduce different modifications into graphene. The Group of Sensor Technologies uses this method to create novel graphene-based gas sensors that can be used for instance for measuring the level of pollution in air.
Read more: http://dx.doi.org/10.1063/1.4962959
Silver nanorods / nanowires with well defined length (up to tens micrometers) and diameter (around 10 nanometers) can easily be prepared by template synthesis method.
First a template is created by anodizing aluminum. In this process a porous oxide layer is created on top of the metal. The distribution, diameter and length of the pores depends on the anodizing solution and electrical parameters.
In the next step the pores are filled with silver by electrochemical deposition. The growth starts at the bottom of the pores where the pores are connected to the conductive metal. Eventually the whole pore is filled with silver and the deposition is stopped.
In order to get the silver nanorods out of the aluminum oxide matrix, the oxide needs to be etched away. The oxide matrix is removed almost instantly when dipping the substrate into an alkaline solution. As a result the silver nanorods escape into the solution. The amount, diameter and length of the nanorods depends on the oxide template that was used in the preparation process.
Large quantities of silver nanorods can be prepared in that way since in the pores in the oxide matrix are very close to each other which means that after deposition the substrate surface mostly consists of silver in the pores. Also in the etching process only the thin oxide layer is removed from the substrate to extract the nanowires and this means one can easily tune the amount of silver nanorods in a solution by the amount of substrates dipped into the same solution. For example for preparing a solution with a small concentration of silver nanowires only one sample is dipped into the solution. All the nanorods on that sample then go into the solution. By dipping the next sample into the same solution all of the nanowires on the second sample also go into the solution and the concentration is doubled. This process can be repeated as long as aluminium oxide etching is still possible. Note that the sample needs to be removed from the solution once its oxide layer is removed (this may take only a few seconds).
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