Dominik J. Bell

Artificial bacterial flagella: Fabrication and magnetic control

Inspired by the natural design of bacterial flagella, we report artificial bacterial flagella (ABF) that have a comparable shape and size to their organic counterparts and can swim in a controllable fashion using weak applied magnetic fields. The helical swimmer consists of a helical tail resembling the dimensions of a natural flagellum and a thin soft-magnetic “head” on one end. The swimming locomotion of ABF is precisely controlled by three orthogonal electromagnetic coil pairs. Microsphere manipulation is performed, and the thrust force generated by an ABF is analyzed. ABF swimmers represent the first demonstration of microscopic artificial swimmers that use helical propulsion. Self-propelled devices such as these are of interest in fundamental research and for biomedical applications.

Monolithically Fabricated Microgripper With Integrated Force Sensor for Manipulating Microobjects and Biological Cells Aligned in an Ultrasonic Field

This paper reports an electrostatic microelectromechanical systems (MEMS) gripper with an integrated capacitive force sensor. The sensitivity is more than three orders of magnitude higher than other monolithically fabricated MEMS grippers with force feedback. This force sensing resolution provides feedback in the range of the forces that dominate the micromanipulation process. A MEMS ultrasonic device is described for aligning microobjects suspended in water using ultrasonic fields. The alignment of the particles is of a sufficient accuracy that the microgripper must only return to a fixed position in order to pick up particles less than 100 mum in diameter. The concept is also demonstrated with HeLa cells, thus providing a useful tool in biological research and cell assays

Flagella-like Propulsion for Microrobots Using a Nanocoil and a Rotating Electromagnetic Field

A propulsion system similar in size and motion to the helical bacterial flagella motor is presented. The system consists of a magnetic nanocoil as a propeller (27 nm thick ribbon, 3 mun in diameter, 30-40 mum long) driven by an arrangement of macro coils. The macro coils generate a rotating field that induces rotational motion in the nanocoil. Viscous forces during rotation result in a net axial propulsion force on the nanocoil. Modeling of fluid mechanics and magnetics was used to estimate the requirements for such a system. The fabrication of the magnetic nanocoils and the system setup are explained. Experimental results from electromagnetic actuation of nanocoils as well as from their propulsion in both paraffin oil and water are presented. This is the first time a propulsion system of this size and motion-type has been fabricated and experimentally verified.

Piezoresistive InGaAs/GaAs Nanosprings with Metal Connectors

This paper presents the fabrication, assembly, and characterization of piezoresistive nanosprings for creating nanoelectromechanical systems. The fabrication process is based on conventional microfabrication techniques to create a planar pattern in a 27nm thick, n-type InGaAs/GaAs bilayer that self-forms into three-dimensional structures during a wet etch release. As the nanosprings have lower doped thin and flexible layers, small metal pads have been attached to both sides for achieving stable ohmic contact with electrodes. Nanorobotic manipulation is applied to assemble the nanosprings between electrodes using electron-beam-induced deposition inside a scanning electron microscope, and the bridged nanosprings were then characterized for electromechanical properties. With their strong piezoresistive response, low stiffness, large-displacement capability, and excellent fatigue resistance, they are well-suited to function as sensing elements in high-resolution, large-range electromechanical sensors.

Design of a Micro-Gripper and an Ultrasonic Manipulator for Handling Micron Sized Objects

This work reports on a system consisting of a MEMS (microelectromechanical system) gripper and an ultrasonic manipulator. The gripper is electrostatically actuated and includes an integrated force sensor measuring the gripping force. The device is monolithically fabricated using a silicon-on-insulator (SOI) fabrication process. The resolution of the force sensor is in the sub-micronewton range and, therefore, provides feedback of the forces that dominate the micromanipulation processes. A MEMS ultrasonic device is described which aligns small objects such as biological cells prior to manipulation with the gripper. The concept is demonstrated with polymer spheres, glass spheres and Hela cancer cells, thus providing a useful tool in micro-robotics and biological research

Ultra flexible SiGe/Si/Cr nanosprings

The electrical and mechanical properties of Si/SiGe rolled-up nanosprings have been investigated. Micromanipulation has been employed to investigate the mechanical properties. For nanosprings under investigation, a linear dependence between applied force and extention is found until the spring is extended to 91% of its original length, moreover, the springs could be reproducibly extended to more than 180% of their original length. An extremely small spring constant of 0.003N/m has been determined, which is an order of magnitude smaller than that of the most flexible available atomic force microscope (AFM) cantilever (~10-2N/m). Thus, it is expected that these springs can be used as ultra-sensitive force sensors. A simple estimation assuming an imaging resolution of approximately 1nm is adopted for displacement measurement and reveals that using a nanospring fabricated from a 300nm wide mesa as a visual-based force sensor, a resolution of 3pN/nm can be provided. The conductivity of nanospirals was analysed and current densities up to 530kA/cm2 were measured. Structures with metallic wires on top of the mesa structures were successfully employed to activate mechanical movements of the structure.

Micro and Nanorobotic Assembly Using Dielectrophoresis.

The contact phase of an assembly task involving micro and nano objects is complicated by the presence of surface and intermolecular forces such as electrostatic, surface-tension and Van der Waals forces. Assembly strategies must account for the presence of these forces in order to guarantee successful repeatable micro and nanoassemblies with high precision. A detailed model for this electrostatic interaction is developed and analyzed. Based on the results of this analysis, dielectrophoretic assembly principles of MEMS/NEMS devices are proposed and experimentally verified with microtweezers for micro Ni parts and with nanoelectrodes fabricated with electron-beam lithography for carbon nanotube assembly. The successful manipulation and assembly of single carbon nanotubes (CNTs) using dielectrophoretic forces produced by nanoelectrodes will lead to a higher integration of CNTs into both nanoelectronics and NEMS.

3-D InGaAs/GaAs Helical Nanobelts for Optoelectronic Devices

This article systematically characterizes conductometric InGaAs/GaAs helical nanobelts for use with optoelectronic sensing. The responsiveness, energy conversion efficiency, and external quantum efficiency are improved compared to conventional sensors by reducing the length of 3-D helical nanobelts without losing exposure area. Nanorobotic assembly and characterization of 3-D helical in/out-of-plane nanobelt photodetectors allowed for stable intrinsic property characterizations. When compared to nanotube bundles, impovement in properties such as energy conversion efficiency, responsiveness, and external quantum efficiency are experimentally demonstrated in both an optical microscope and scanning electron microscope. A probe-type photodetector was assembled using nanorobotic manipulation and in-situ gold nanoparticle ink soldering. The highly efficient and sensitive 3-D InGaAs/GaAs helical nanobelt photodetectors enable many optoelectronic device applications such as being the probes for the near field optical microscopy, confocal microscopy, fluorescence microscopy, or spatial detection with further characterizations.

Directed batch assembly of three-dimensional helical nanobelts through angular winding and electroplating

This paper presents a new technique for the directed batch assembly of rolled-up three-dimensional helical nanobelts. The wet etch time is controlled in order for the loose end of the self-formed SiGe/Si/Cr nanobelts to be located over an electrode by taking advantage of the additional angular winding motion in the lateral direction. In a subsequent Au electroplating step, contacts are electroformed and the batch assembly is completed, while at the same time the conductance of the structures is increased.

Nanorobotics for creating NEMS from 3D helical nanostructures

Robotic manipulation at the nanometer scale is a promising technology for structuring, characterizing and assembling nano building blocks into nanoelectromechanical systems (NEMS). Combined with recently developed nanofabrication processes, a hybrid approach to building NEMS from 3D SiGe/Si/Cr and Si/Cr nanostructures is presented. Nanosensors and nanoactuators are investigated from experimental, theoretical, and design perspectives.