Optomagnetically Controlled Microparticles Manufactured with Glancing Angle Deposition

Abstract

734 wileyonlinelibrary.com www.particle-journal.com www.MaterialsViews.comOptical trapping and magnetic trapping are common micromanipulation techniques for controlling colloids including micro-and nanoparticles. Combining these two manipulation strategies allows a larger range of applied forces and decoupled control of rotation and translation; each of which are benefi cial properties for many applications including force spectroscopy and advanced manufacturing. However, optical trapping and magnetic trapping have confl icting material requirements inhibiting the combination of these methodologies. In this paper, anisotropic microscaled particles capable of being simultaneously controlled by optical and magnetic trapping are synthesized using a glancing angle deposition (GLAD) technique. The anisotropic alignment of dielectric and ferromagnetic materials limits the optical scattering from the metallic components which typically prevents stable optical trapping in three dimensions. Compared to the current state of the art, the benefi ts of this approach are twofold. First, the composite structure allows larger volumes of ferromagnetic material so that larger magnetic moments may be applied without inhibiting the stability of optical trapping. Second, the robustness of the synthesis process is greatly improved. The dual optical and magnetic functionality of the synthesized colloids is demonstrated by simultaneously optically translating and magnetically rotating a magnetic GLAD particle using a custom designed optomagnetic trapping system.involves the application of an electric fi eld generated by a highly focused laser to impart forces upon micrometer and nanometer scaled particles. Magnetic trapping is a similar procedure that generates forces through the application of an external magnetic fi eld generated by a permanent or electromagnet. Both of these techniques are desirable for many manufacturing, sensor, and experimental procedures because the forces may be applied using externally generated fi elds that do not require direct access to the sample. The limitations preventing simultaneous application of optical and magnetic trapping (OMT) within a single probe particle is inherently a material compatability issue. Optical trapping requires dielectrics, which have minimal optical absorption, in order to maximize the OT applied force, prevent undesirable optical scattering forces, and limit thermal vibrations. Alternatively, MT requires the presence of ferromagnetic materials which are not optically transparent and therefore are generally not applicable for OT. In order to combine the benefi ts of each micromanipulation technique with a single probe particle, the dielectric and ferromagnetic materials must be aligned such that the optical scattering is minimized while still including ferromagnetic material. This paper describes the design and synthesis of particles using a glancing angle deposition (GLAD) process, which results in so-called patchy particles. Due to the material anisotropy, magnetic GLAD partic...

Optical trapping performance of dielectric-metallic patchy particles

“…The stiffness of the OT was observed to increase linearly with increasing optical power. This observation is consistent with OT theory for dielectric particles as well as empirical data for GLAD particle trapping [17]. Variations in the radial and axial stiffnesses occur based on the size of the patch for a tested particle allowing some degree of particle stiffness design.…”

“…A GLAD particle may be described by two surface patch parameters: substrate tilt and substrate rotation. Detailed discussion of these parameters may be found in [17]. Briefly, the substrate rotation controls the shape profile of the metallic patch while the substrate tilt controls the overall area of the patch.…”

“…cles due to their appearance [16]. The second fabrication method implemented a glancing angle deposition (GLAD) process, leading to a range of patch geometries [17]. These particles contained only a small patches covering less than 20% of the total surface area in every test case, enabling optical trapping on axis much like a pure dielectric, as shown in Fig.…”