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Ultrasonic control over nanorod orientation in evaporative assembly

Boulogne, T. and Derkink, F. (2015) Ultrasonic control over nanorod orientation in evaporative assembly.

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Abstract:In this thesis the effect of ultrasonic agitation on the orientation and self-assembly of gold nanoparticles was investigated on both SiO2 and HOPG substrates using scanning electron microscopy (SEM) and atomic force microscopy (AFM). For SiO2 substrates, the effect was analyzed using two different solutions; one (solution R) containing gold nanorods (GNRs) while the other (solution RS) contained both GNRs and gold nanospheres all with approximately equal dimensions. For HOPG substrates, only the solution containing GNRs was used. After synthesis of the solutions containing gold nanoparticles using the seed-mediated method, the solutions were investigated using UV-VIS spectroscopy in order to characterize them and verify the aspect ratio (AR) of the GNRs. Furthermore, the absorption spectra were simulated to determine the ARs of the GNRs more correctly by taking into account that the ARs follow a normal distribution. Droplets were deposited on both types of substrates, of which some where left to dry undisturbed while others were placed in an ultrasonic bath. Evaporation of the solvent let to coffee-stain rings which were then further investigated using SEM and AFM. SEM images were used to measure the lengths and widths of GNRs to determine their ARs, to measure the lengths of chains of side-by-side assembled GNRs and to measure the angles of GNRs with respect to the step edges of HOPG. AFM images were used to determine the position of GNRs when aligned to step edges. For SiO2 substrates, results suggest that ultrasonic agitation did not have a significant effect on solution R during evaporation even though some of the assembled chains of GNRs were longer, but this is probably attributed to an unintentional rise in temperature of the ultrasonic bath during evaporation. For solution RS, ultrasonic agitation did seem to have a tremendous effect. Instead of a neat phase separation with side-by-side assembled GNRs interspersed by regions of gold nanospheres which was seen in the undisturbed case, the gold nanospheres seem to have disappeared from the edge of the ring and GNR chains seem to be shorter. Results on HOPG also suggest that ultrasonic agitation has an effect, since GNRs are less often aligned parallel to step edges and seem to be near step edges less often in general. Further research should be done in order to rule out that the observations that were made were not caused by a rise in temperature during evaporation or other factors that had an influence that were not kept constant.
Item Type:Essay (Bachelor)
Faculty:TNW: Science and Technology
Subject:33 physics
Programme:Applied Physics BSc (56962)
Link to this item:http://purl.utwente.nl/essays/67607
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