Efficient photo-induced dielectrophoretic particle trapping on Fe:LiNbO_3 for arbitrary two dimensional patterning

Abstract

ID and 2D patterning of uncharged micro-and nanoparticles via dielectrophoretic forces on photovoltaic z-cut Fe:LiNb0 3 have been investigated for the first time. The technique has been successfully applied with dielectric micro-particles of CaC0 3 (diameter d = 1-3 urn) and metal nanoparticles of Al (d = 70 nm). At difference with previous experiments in x-and >>-cut, the obtained patterns locally reproduce the light distribution with high fidelity. A simple model is provided to analyse the trapping process. The results show the remarkably good capabilities of this geometry for high quality 2D light-induced dielectrophoretic patterning overcoming the important limitations presented by previous configurations.

Recent Achievements on Photovoltaic Optoelectronic Tweezers Based on Lithium Niobate

“…They used charged particles because they assumed that dielectrophoretic (DEP) forces acting on neutral particles were too weak in this configuration. Nevertheless, using highly doped crystals our group has demonstrated in a number of recent papers an excellent performance for 2D trapping with neutral inorganic micro-and nano-particles [19,29] and biological objects [22]. As previously mentioned, the experimental results have been accompanied with the development of a simple theoretical model for this configuration [28,29] that satisfactorily explains the experimental patterns.…”

“…Nevertheless, using highly doped crystals our group has demonstrated in a number of recent papers an excellent performance for 2D trapping with neutral inorganic micro-and nano-particles [19,29] and biological objects [22]. As previously mentioned, the experimental results have been accompanied with the development of a simple theoretical model for this configuration [28,29] that satisfactorily explains the experimental patterns. The comparison between electrophoretic and dielectrophoretic patterning which deals with charged and neutral particles respectively, is deeply investigated in reference [19] by theory and z-cut experiments.…”

“…A recent work [27] includes a theoretical study for the same x-/y-cut geometry and using a very similar model than that of reference [26] but applied to a cylindrical light beam. Additionally, since 2013 another configuration with the polar axis normal to the surface, i.e., z-cut, (see Figure 2c) has been often employed in relation to 2D patterning (see Section 3) and a simple model to describe it has been already reported [28,29]. Micro-and nano-particles placed in the vicinity of the crystal sample experience dielectrophoretic forces fDEP for neutral particles and electrophoretic forces fEP for charged particles.…”

Diffractive optical devices produced by light-assisted trapping of nanoparticles

“…For 2D gratings, we use a twodimensional distribution of light intensity generated by a spatial light modulator (HOLOEYE, LC-R 1080). This light distribution is projected on a Z-cut Fe:LiNbO3 substrate (perpendicular configuration) that allows an accurate reproduction of the 2D light pattern [11,20]. Light comes from a frequency doubled Nd:YAG, operating at 532 nm with typical intensities in the range 1-100 mW/cm 2 .…”

“…After the pattern fabrication the initial bulk photorefractive charge grating is erased by thermal heating [18] during about 10 min at T ~ 250ºC to avoid its competition with the particle grating. The deposition and light-assisted patterning procedures are described in more detail in [8,19] and [20] for 1D and 2D, respectively. Finally, it is worthwhile remarking that the method can be considered reconfigurable in the sense that the same substrate can be reused by simply removing the particles and repeating the fabrication process.…”