Electrical Engineering
      and Computer Sciences

Electrical Engineering and Computer Sciences


UC Berkeley


2009 Research Summary

Nanowire Manipulation Using Lateral-Field Optoelectronic Tweezers

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Aaron Takami Ohta, Arash Jamshidi, Hsan-yin Hsu, Justin K Valley, Steven Neale and Ming C. Wu

NIH and Defense Advanced Research Projects Agency

Optoelectronic tweezers (OET) provide a non-invasive, low-power, optical manipulation tool for trapping, transporting, and sorting cells and other microparticles [1,2]. The OET device enables optically-controlled manipulation with optical intensities 100,000 times less than optical tweezers. Direct imaging and incoherent light sources (from a single LED or halogen lamp) can be projected on the OET device to create optical manipulation patterns in real time [3].

Optoelectronic tweezers produce light-induced dielectrophoresis. A photosensitive layer forms "virtual electrodes" upon exposure to light, creating non-uniformities in an applied electric field. The non-uniform electric field gives rise to a force known as dielectrophoresis: particles move as a result of the non-uniformities in the electric field imparting unequal forces on the induced dipole of the particle.

We have demonstrated a new OET device that creates lateral electric fields on a single-sided device (Figure 1). This lateral-field OET device (LOET) produces the same forces as conventional OET, but offers new functionality. The LOET device enables the manipulation of rod-shaped particles, like nanowires, with the long axis parallel to the plane of the device (Figure 2). This ability means that LOET can be used in applications such as the assembly of nanowires in nanoelectronic circuits.

Figure 1
Figure 1: Lateral-field optoelectronic tweezers device (LOET), which consists of a photosensitive interdigitated electrode array on a glass substrate

Figure 2
Figure 2: Trapping and transport of 100-nm diameter Si nanowires in the LOET device. (a) The initial position of a Si NW, with the electric field turned off. The laser spot is visible in the upper right. (b) The laser is moved closer to the nanowire. This frame is immediately before the electric field is switched on; after the electric field is applied, the nanowire is attracted towards the laser. (c) The trapped nanowire is transported by scanning the laser spot at up to 20 μm/s. (d) The laser is switched off to show the final position of the nanowire in greater clarity. The initial position is also indicated; the direction of the transport is shown by the arrow.

P. Y. Chiou, A. T. Ohta, and M. C. Wu, Nature, Vol. 436, 2005, pp. 370-372.
A. T. Ohta, P.-Y. Chiou, H. L. Phan, S. W. Sherwood, J. M. Yang, A. N. K. Lau, H.-Y. Hsu, A. Jamshidi, and M. C. Wu, IEEE Journal of Selected Topics in Quantum Electronics, Vol. 13, 2007, pp. 235-243.
A. T. Ohta, P. Y. Chiou, T. H. Han, J. C. Liao, U. Bhardwaj, E. R. B. McCabe, F. Yu, R. Sun, and M. C. Wu, IEEE Journal of Microelectromechanical Systems, Vol. 16, 2007, pp. 491-499.