Microscopic Particle Manipulation via Optoelectronic Devices

The optoelectronic tweezers (or optically induced dielectrophoresis (DEP)) have showed the ability to parallelly position a large number of colloidal microparticles without any template. The microparticles can be trapped and driven by the dielectrophoretic forces induced by the optical micropatterns in OET devices. In this chapter, the design and fabrication of flat optoelectronic devices (FOD) and hybrid optoelectronic device (HOD) are described. In the typical FOD, the manipulation modes including filtering, transporting, concentrating and focusing controlling regimes are experimentally demonstrated and analyzed. The controllable rotation of self-assembled microparticle chains in FOD has also been investigated, and a method incorporating the optically induced electrorotation (OER) and AC electroosmotic (ACEO) effects is numerically and experimentally implemented for manipulating microparticle chains. Based on the above research of FOD, a hybrid DEP microdevice HOD is conceptually and experimentally proposed. The HOD integrates with metallic microelectrode layer and the underneath photoconductive layer with projected optical virtual electrodes. FOD and HOD hybrid device enables the active driving, large-scale patterning and local position adjustment of microparticles. These techniques make up the shortcoming of low flexibility of traditional metallic microelectrodes and integrate the merits of both the metal electrode-induced and microimage-induced DEP techniques

Field induced assembly of particulate systems

The primary focus of the first part of this dissertation is to study the AC field-driven assembly of monodisperse silica and glass particles on liquid - liquid interface and forming a liquid film of uniform thickness having arrangement of particles on it. This liquid film with arrangement of regular particles can be converted into a solid film by curing top UV curable liquid. Here, electric field is used as a tool to facilitate AC field-driven assembly. The work describes the assembly of different size of regular particles and effective development of solid film. It is also shown that particles of two dissimilar sizes and dielectric properties can be assembled on Air-liquid interface and form assembly of dual particles with ring structure. In this work, two dissimilar particles are trapped between an interface and AC electric field is applied to particle suspensions in a gap between the top and bottom electrodes. In order to exploit the concept of dual particle assembly, mixture of glass particles and plastic latex particles are studied. It is noticeable that the lateral dipolar force leads two particles to either repel or attract. This force of repulsion and attraction between particles depend on their polarizabilities and the intensity of the force. Finally, rapid and effective formation of ring structure of dual particles is shown. The study is also extended for mixture of particles that are less than 10 μm. In all cases, it is observed that smaller particles act as the binder for larger particles and form dual particle ring structure since they have a reverse polarizability. In the third part of this dissertation, AC electric field is used to assemble the particles on the freely suspended single floating droplet on immiscible liquid. Particles on the droplet can be levitated and assembled at the pole or equator due to dielectric properties and conductivity of particles and liquid medium when low frequency is applied. Under high frequency, particles drag towards the pole or equator due to Clausius Mossotti factor of particle and droplet. The high and low frequency are distinguished by crossover frequency. Here, crossover frequency is investigated experimentally and assembly of the different particles at the pole or equator of the droplet is shown. At any initial location of the particle and considering the very low frequency, flow deceases with increase in frequency - this is studied experimentally. A diffusing particle is subjected to a variety of collisions that leads to a random or Brownian motion. Assembly of particles of various sizes with various viscous media are studied in the first and second part. It is experimentally observed that Brownian motion decreases with increase in particle size. The aim of this study is to highlight the visualization of Brownian motion and compute the transmission probability from inner to outer region under the conditions of varying viscosity, particle size and temperature. The obtained results are validated with Stokes-Einstein equation and Fang and Ning’s experimental and theoretical work. It is shown that the transmission probability increases with decrease in viscosity and particle size and increase in temperature

Optoelectronic tweezers for microparticle and cell manipulation

An optical image-driven light induced dielectrophoresis (DEP) apparatus and method are described which provide for the manipulation of particles or cells with a diameter on the order of 100 .mu.m or less. The apparatus is referred to as optoelectric tweezers (OET) and provides a number of advantages over conventional optical tweezers, in particular the ability to perform operations in parallel and over a large area without damage to living cells. The OET device generally comprises a planar liquid-filled structure having one or more portions which are photoconductive to convert incoming light to a change in the electric field pattern. The light patterns are dynamically generated to provide a number of manipulation structures that can manipulate single particles and cells or groups of particles/cells. The OET preferably includes a microscopic imaging means to provide feedback for the optical manipulation, such as detecting position and characteristics wherein the light patterns are modulated accordingly

Optoelectronic Tweezers for Microparticle and Cell Manipulation

An optical image-driven light induced dielectrophoresis (DEP) apparatus and method are described which provide for the manipulation of particles or cells with a diameter on the order of 100 micromillimeters or less. The apparatus is referred to as optoelectric tweezers (OET) and provides a number of advantages over conventional optical tweezers, in particular the ability to perform operations in parallel and over a large area without damage to living cells. The OET device generally comprises a planar liquid-filled structure having one or more portions which are photoconductive to convert incoming light to a change in the electric field pattern. The light patterns are dynamically generated to provide a number of manipulation structures that can manipulate single particles and cells or group of particles/cells. The OET preferably includes a microscopic imaging means to provide feedback for the optical manipulation, such as detecting position and characteristics wherein the light patterns are modulated accordingly

Additive nanomanufacturing: a review

Additive manufacturing has provided a pathway for inexpensive and flexible manufacturing of specialized components and one-off parts. At the nanoscale, such techniques are less ubiquitous. Manufacturing at the nanoscale is dominated by lithography tools that are too expensive for small- and medium-sized enterprises (SMEs) to invest in. Additive nanomanufacturing (ANM) empowers smaller facilities to design, create, and manufacture on their own while providing a wider material selection and flexible design. This is especially important as nanomanufacturing thus far is largely constrained to 2-dimensional patterning techniques and being able to manufacture in 3-dimensions could open up new concepts. In this review, we outline the state-of-the-art within ANM technologies such as electrohydrodynamic jet printing, dip-pen lithography, direct laser writing, and several single particle placement methods such as optical tweezers and electrokinetic nanomanipulation. The ANM technologies are compared in terms of deposition speed, resolution, and material selection and finally the future prospects of ANM are discussed. This review is up-to-date until April 2014

The Response of an Ellipsoidal Colloid Particle in an AC Field

The quest for new smart materials with engineered properties and desired functionalities has driven scientists into the domain of nanotechnology over the past 30 years. Particles with anisotropic properties as a result of their geometry, chemical patterning or surface functionality have been envisioned as building blocks for advanced materials. By tuning the anisotropic interactions engendered by anisotropic particles, one potentially could manipulate the dynamic pathways for assembly.The work described in this thesis considers the response of an ellipsoidal colloid particle to a nearby AC electrode polarized at ~0.1 – 4 kV/m and ~0.1 – 3 kHz. The ellipsoidal particle, which had a surface sulfate functional group, was dispersed in 10^-6M NaCl. The particle experienced typical electric-field induced responses, including electro-rotation and electro-orientation at low frequency - 100Hz - with an electric field intensity of 2500V/m. For instance, the particle (lying) was observed to frequently try to align its longer axis parallel to the electric field. We quantified the ellipsoid’s response by tracking its position and orientation with and without an electric field. The translational diffusion coefficient without and with electric field was calculated to be in the range of (7.625 – 39.2750) × 10^-3µm2/s and (0.725 – 305.525) × 10^-3µm2/s respectively. Surprisingly, the ellipsoid was also observed to propel in the direction normal to the electric field, which we believe to be a first for such a system. We proposed that the propulsion is a result of broken symmetry in the electrohydrodynamic (EHD) flow due to non-symmetric ellipsoid shape of our particle

Trapping of nanoparticles with dielectrophoretic nano-probes.

Dielectrophoresis (DEP) is an electrokinetic force capable of attracting or repelling neutrally charged particles due to a non-uniform electric field [1, 2]. Positive dielectrophoresis attracts particles in the region of the highest electric field gradient; negative dielectrophoresis repels particles from the region of the highest electric field gradient. The dielectrophoretic force is directly proportional to the square of the electric field gradient, as well as the cube of the radius of the particles involved. As particles decrease in size, the gradient of the electric field must increase rapidly in order to capture or repel the particles. The intense electric field gradients were produced using fabricated silver gallium (Ag2Ga) nano-probes electrodes in conjunction with indium tin oxide (ITO) coated microscope cover slips, which served as the opposite electrode. The silver gallium nano-probes ranged from approximately 100-500 nm in diameter and were typically positioned less than 40 ?m above the ITO cover slips. Positive and negative dielectrophoretic forces were able to dominate the other electrokinetic forces acting on sub-micron particles, which were suspended in deionized water and aqueous potassium chloride, using the nano-probes and ITO cover slips as electrodes. Colloidal quantum dots of gold, as small as 5 nm in diameter, were captured using positive DEP forces, as were sub-micron fluorescent polystyrene particles. Negative DEP forces repelled sub-micron fluorescent polystyrene particles suspended in a low conductivity solution

TEMPLATE-ASSISTED FABRICATION AND DIELECTROPHORETIC MANIPULATION OF PZT MICROTUBES

Mesoscopic high aspect ratio ferroelectric tube structures of a diverse range of compositions with tailored physical properties can be used as key components in miniaturized flexible electronics, nano- and micro-electro-mechanical systems, nonvolatile FeRAM memories, and tunable photonic applications. They are usually produced through advanced “bottom-up” or “topdown” fabrication techniques. In this study, a template wetting approach is employed for fabrication of Pb(Zr0.52Ti0.48)O3 (PZT) microtubes. The method is based on repeated infiltration of precursor solution into macroporous silicon (Si) templates at a sub-atmospheric pressure. Prior to crystallization at 750°C, free-standing tubes of a 2-μm outer diameter, extending to over 30 μm in length were released from the Si template using a selective isotropic-pulsed XeF2 reactive ion etching. To facilitate rapid electrical characterization and enable future integration process, directed positioning and aligning of the PZT tubes was performed by dielectrophoresis. The electric field-assisted technique involves an alternating electric voltage that is applied through pre-patterned microelectrodes to a colloidal suspension of PZT tubes dispersed in isopropyl alcohol. The most efficient biasing for the assembly of tubes across the electrode gap of 12 μm was a square wave signal of 5 Vrms and 10 Hz. By varying the applied frequency in between 1 and 10 Hz, an enhancement in tube alignment was obtained

Assembly of Ceramic Particles in Aqueous Suspensions Induced by High-Frequency AC Electric Field

Ceramic materials processed using colloidal methods have been the focus of a great deal of research aimed at tailoring the final structure and microstructure of the finished ceramic sample. To this end, various external field effects have been investigated to modify the suspension microstructure without manipulating the ceramic particles directly. In a previous work in the field of ice templating it has been shown that AC electric fields are able to produce microstructural changes in ice templated ceramics that have significantly improved the final mechanical properties. However, the mechanisms for this process are still not well understood in ceramics. To better understand the mechanisms that are present in colloidal processing of ceramics using AC field, this thesis investigates the role of high frequency alternating current (AC) electric field in the assembly of alumina and barium titanate particles in aqueous media. Field-particle interactions were in situ investigated via optical microscope for coarse and fine alumina as well as fine barium titanate powder particles in very dilute suspensions. In the first half of the work with both coarse and fine alumina particles, AC field-induced assembly led to the formation of chains aligned in the field direction. Chain length increased with both field strength and field duration. Chain formation was attributed to mutual dielectrophoretic (DEP) interaction forces. Threshold field strength for chain formation suggested stronger interactions for finer particles. In the second half of the work, fine alumina and fine barium titanate powders of similar size were compared to study the effect of the particle type on the formation of chains. The inter-chain distance was also measured suggesting that the particle type had a strong effect on how the chain structure developed. The effect of frequency on chain formation showed that decreasing the frequency of the AC field resulted in fluid motion that impeded the formation of chains. Darvan-C dispersant was added to the medium of the solution improving the formation of chains for both alumina and barium titanate. SEM images were used to confirm these findings by preserving the chains using a binder