From Mechatronics Research Laboratory (MRL)
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Imaging at the Nano-scale: State of the Art and Advanced Techniques
Surface characteristics, such as topography and critical dimensions serve as important indicators of product quality and manufacturing process performance especially at the micrometer and the nanometer scales. This project focuses on different technologies used for obtaining high precision 3-D images of surfaces, along with some selected applications. Atomic Force Microscopy (AFM) is one of such methods. These images are commonly distorted by convolution effects, which become more prominent when the sample surface contains high aspect ratio features. In addition, data artifacts can result from poor dynamic response of the instrument used. In order to achieve reliable data at high throughput, dynamic interactions between the instrument's components need to be well understood and controlled, and novel image deconvolution schemes need to be developed. Our work aims at mitigating these distortions and achieving reliable data to recover metrology soundness.
Applications include:
AFM based DNA Sequencing
Investigator: Daniel J. Burns
A novel DNA sequencing method is developed based on the specific binding nature of nucleotides and measured by an atomic force microscope (AFM). A single molecule of DNA is denatured and immobilized on an atomically flat surface, and a force probe functionalized with a nucleotide is scanned along the molecule to detect locations of the nucleotide’s complement. The AFM's high resolution and control bandwidth allow sequence information to be obtained from single DNA molecules and orders of magnitude faster than current techniques.
To increase the spatial resolution of the atomic force microscope so that individual bases can be distinguished, a single-walled carbon nanotube is grown from the AFM probe and functionalized with a single DNA base. The carbon nanotube diameter is of the order as the nucleotide base spacing—providing the necessary spatial resolution for single molecule sequencing. The AFM’s calculated minimum detectable force is less than experimentally obtained nucleotide binding forces, indicating that the AFM is capable of directly measuring single nucleotide interactions. A model of the oscillating AFM probe dynamics provides a methodical approach to determining attractive forces with a chemically-specific sensor. This attractive force detection is performed by measuring the phase lag of the oscillating probe near the sample surface as compared to the resonating probe in free air.
As grown, the carbon nanotubes are too long to be used as reliable force probes, therefore a method for shortening carbon nanotubes is developed utilizing the AFM feedback to determine the final nanotube length. This shortening procedure is performed in conjunction with the nucleotide functionalization, creating a precise and chemically-specific force probe.
Atomic Force Microscopy Imaging Correction
Investigator: Khalid Elrifai
The control of AFM systems is the focus of this project. AFM has become a very popular tool in research and industries of Nano-technology, Bio-technology, semiconductors, MEMS, and life sciences. The image shown below is of a product of a thin-film deposition process using PVD sputtering collected for metrology purposes. AFM as a system is regulated through feedback with a piezotube actuator and a photodiode sensor, with the image created from the input voltage. AFM is particularly popular due to its high compatibility with vacuum, room, or fluid ambient conditions as well as its independence on particular optical or electrical properties of imaged samples. Yet this comes at the cost of high uncertainty and coupling between the controlled system dynamics and user defined scan parameters. This imposes challenges on the ability to acquire accurate, repeatable, artifact free images within an acceptable operation bandwidth. (Product of a thin-film deposition process using PVD sputtering collected for metrology purposes)
Design of Autonomous Robots for the Exploration of Complex and Unstructured Terrains
Investigators: Pablo Valdivia Y Alvarado and Adam Wahab
The aim of this initiative is to provide design methodologies with an emphasis on achieving compact, rough and energy efficient mechanisms that can navigate and adapt to changes in the environment. The primary focus is on underwater locomotion and the exploitation of natural physical phenomena to achieve robot tasks.
Control of Systems with Unknown Dynamics
The demand for high performance machines has introduced an increasingly challenging controller design problem. These systems are characterized by significant dynamic changes and are subjected to unpredictable disturbances.
Methods of estimating unknown system dynamics and unpredictable disturbances have been developed and were shown to be simple and very effective. These methods are designed to control linear and non-linear multi-input multi-output systems without the use of explicit system models or parameter estimation. A fundamental step in this approach is combining past observations with adaptation leading to direct estimation of system dynamics. These approaches introduce the concept of function estimation rather than parameter estimation.
Analytical and experimental studies have been conducted to demonstrate the effectiveness of these algorithms. The theoretical issues addressed include stability, convergence, accuracy, choice of sampling period and delay, feedback gain selection. The applications of interest to date have involved servo systems, robot manipulators, intelligent vehicle systems and high-speed high precision active magnetic bearings.
Modeling of Physical Systems
The analysis, design and synthesis of systems require not only a good understanding of basic principles but also their use in different physical domains. The study of existing and new systems is a prime concern in this project. The use of bond graphs for modeling has demonstrated its practicality and clear description of physical system behavior. This graphical representation along with its implication is used extensively. Examples of specific applications include automotive braking systems, 2 two-axis linear motors for robotic applications, magnetic bearing systems and, piezoelectric and magnetostrictive materials for atomic resolution systems. Other issues deal directly with the basics of feedback control systems. For instance, the relative degrees and zero dynamics are intrinsic system properties associated with a given input-output pair. Based on the understanding of physical systems and the bond graph notation, a set of rules have been proposed to determine such properties directly from a bond graph model.
Design and Control of Atomic Resolution Systems
This project focuses on the development of design and manufacturing methodologies for atomic resolution systems. These systems involve dimensions and tolerances of less than about 100 nanometers. This technology is of great importance to many sectors in particular mechanical and electronic industries. Several consumer products are expected to be significantly influenced by this technology. One can envision a hand-held engineering workstation, a thumbnail size digital audio system replacing the current portable audio devices, and a digital camcorder about ten times smaller than the current systems.
Our short-range interest is to design and build atomic resolution systems for advanced data storage systems. We expect our approach to increase the data storage capacity by several Tbytes in comparison to DVD's. This is achieved by the use of scanning tunneling microscope technology. Several issues are of concern:(1) electro-mechanical dynamic behavior of micro scale systems, (2) tribology, (3) high speed and high precision control algorithms for mechanical systems with about 10KHz resonance, and (4) high-performance sensors for nanoprecision applications.
Besides its potential technological breakthrough, this project leads the way for mechanical engineers to continue their contributions to the field of microelectronics rather than becoming simple users.
Applications include:
Programmable Filter for Macromolecules
Investigator: Mauricio Gutierrez
Current methods of separating biological materials are not adequate. Present methods are costly, time consuming, bulky, and can be toxic to humans. The objective of this project is to develop a smart filter using unconventional methods. Molecules to be separated range in size from 0.5 nm to 500 nm.
Design of Spectrometers for Noninvasive Glucose Measurement
Noninvasive measurement of blood glucose has been long envisioned. Such a method will provide an invaluable tool for the diagnosis and treatment of diabetes. With the current finger-prick technique, close glucose monitoring is difficult, as it is painful, inconvenient and expensive. This project focuses on the development of accurate and reliable noninvasive glucose sensors. Specifically, the sensitivity and specificity problems are addressed. Also, design parameters associated with the hardware such as throughput, integration time, spectral range, spectral resolution play an important role in the performance of the instrument.
