University of Twente Student Theses


Rotating a gold nanorod using optically induced torque

Hendrickx, Nico and Hond, Kit de (2014) Rotating a gold nanorod using optically induced torque.

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Abstract:In this thesis the possible torque on a gold nanoparticle with an aspect ratio of 7 is investigated using the discrete dipole approximation (DDA). For the different plasmon resonance modes the extinction and torque spectra are computed and the electric field is visualised together with the charge distribution. We found that the torque is at a maximum for particles oriented at 45◦ relative to the polarization and k-vector of the incident light. Furthermore the dipole resonance rendered the largest torque. For a particle with a short radius of 19 nm this maximum torque was determined to be 1.15 × 10−18 Nm. This torque is compared to the Brownian motion and it was found that the rotational energy associated with this torque is not enough to overcome the Brownian motion. However, experimental results show that for a similar torque alignment may be possible. This suggests there might be invalidities in the energy analysis used in this report. The dipole and octupole modes behave as expected, since a change in the charge distribution was observed causing the torque to oscillate. However, the quadrupole exhibits a static charge distribution, contradicting the torque oscillation that was visible in the quadrupole torque spectrum. A fitting explanation for this phenomenon is not yet found.
Item Type:Essay (Bachelor)
Faculty:TNW: Science and Technology
Subject:33 physics
Programme:Applied Physics BSc (56962)
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