title: An Optically Controlled Microscale Elevator Using Plasmonic Janus Particles.
abstract: In this article, we report how Janus particles, composed of a silica sphere with a gold half-shell, can be not only stably trapped by optical tweezers but also displaced controllably along the axis of the laser beam through a complex interplay between optical and thermal forces. Scattering forces orient the asymmetric particle, while strong absorption on the metal side induces a thermal gradient, resulting in particle motion. An increase in the laser power leads to an upward motion of the particle, while a decrease leads to a downward motion. We study this reversible axial displacement, including a hysteretic jump in the particle position that is a result of the complex pattern of a tightly focused laser beam structure above the focal plane. As a first application we simultaneously trap a spherical gold nanoparticle and show that we can control the distance between the two particles inside the trap. This photonic micron-scale "elevator" is a promising tool for thermal force studies, remote sensing, and optical and thermal micromanipulation experiments.
authors.affiliation: Photonics and Optoelectronics Group, Department of Physics and Center for Nanoscience (CeNS), Ludwig-Maximilians-Universität (LMU) , Amalienstaße 54, 80799 Munich, Germany ; Nanosystems Initiative Munich (NIM) , Schellingstraße 4, 80799 Munich, Germany.
authors.forename: Spas
authors.initials: S
authors.lastname: Nedev
authors.affiliation: Photonics and Optoelectronics Group, Department of Physics and Center for Nanoscience (CeNS), Ludwig-Maximilians-Universität (LMU) , Amalienstaße 54, 80799 Munich, Germany ; Nanosystems Initiative Munich (NIM) , Schellingstraße 4, 80799 Munich, Germany ; Instituto de Ciencia de Materiales de Sevilla (CSIC-Universidad de Sevilla) , C/Américo Vespucio 49, 41092 Sevilla, Spain.
authors.forename: Sol
authors.initials: S
authors.lastname: Carretero-Palacios
authors.affiliation: Photonics and Optoelectronics Group, Department of Physics and Center for Nanoscience (CeNS), Ludwig-Maximilians-Universität (LMU) , Amalienstaße 54, 80799 Munich, Germany ; Nanosystems Initiative Munich (NIM) , Schellingstraße 4, 80799 Munich, Germany.
authors.forename: Paul
authors.initials: P
authors.lastname: Kühler
authors.affiliation: Photonics and Optoelectronics Group, Department of Physics and Center for Nanoscience (CeNS), Ludwig-Maximilians-Universität (LMU) , Amalienstaße 54, 80799 Munich, Germany ; Nanosystems Initiative Munich (NIM) , Schellingstraße 4, 80799 Munich, Germany.
authors.forename: Theobald
authors.initials: T
authors.lastname: Lohmüller
authors.affiliation: Photonics and Optoelectronics Group, Department of Physics and Center for Nanoscience (CeNS), Ludwig-Maximilians-Universität (LMU) , Amalienstaße 54, 80799 Munich, Germany ; Nanosystems Initiative Munich (NIM) , Schellingstraße 4, 80799 Munich, Germany.
authors.forename: Alexander S
authors.initials: AS
authors.lastname: Urban
authors.affiliation: Photonics and Optoelectronics Group, Department of Physics and Center for Nanoscience (CeNS), Ludwig-Maximilians-Universität (LMU) , Amalienstaße 54, 80799 Munich, Germany ; Nanosystems Initiative Munich (NIM) , Schellingstraße 4, 80799 Munich, Germany.
authors.forename: Lindsey J E
authors.initials: LJ
authors.lastname: Anderson
authors.affiliation: Photonics and Optoelectronics Group, Department of Physics and Center for Nanoscience (CeNS), Ludwig-Maximilians-Universität (LMU) , Amalienstaße 54, 80799 Munich, Germany ; Nanosystems Initiative Munich (NIM) , Schellingstraße 4, 80799 Munich, Germany.
authors.forename: Jochen
authors.initials: J
authors.lastname: Feldmann
keywords: Janus particles; microswimmer; optical trapping; thermophoresis