High Speed Atomic Force Microscope Design Using Dvd Optics PDF Download

This thesis presents the design, control and instrumentation of a novel atomic force microscope (AFM). This AFM is capable of high-speed imaging while maintaining large out-of-plane and lateral scan ranges. The primary contributions of this thesis include the design and implementation of a high-speed and large-range AFM; design, implementation and control of a multi-actuated nano-positioner; development of a general direct data-based control design scheme for redundantly actuated nano-positioners; design and implementation of a non-linear amplitude demodulation method for tapping mode imaging; and development of a parameter estimation methodology for piezo actuator hysteresis modeling and compensation. Atomic force microscopes can provide nano-scale resolution images of sample surface topography in air, vacuum or in liquid. This instrument operates by scanning a micro-mechanical probe on a sample. A measurement of the probe-sample interaction is used to control the AFM scanner and also form a 3D image of the sample surface topography. The mechanical nature and the serial-point-collection bases of operation of this instrument significantly limits its speed and constrains its application to the study of static samples. Unlocking the high-speed performance capability of AFM enables study of dynamic nano-scale processes and opens up the possibility of novel scientific discoveries. Improving the speed performance of AFM however, should not compromise imaging range so that the instrument can accommodate imaging experiments with diverse lateral and out-of-plane scan range requirements. In addition to high-speed and large-range performance, instrument flexibility and ease of use are very important. An AFM should allow samples of different sizes, and provide a simple platform for setting up the imaging experiment. In this work all the components of the AFM are designed to meet these specifications. A multi-actuated scanner is designed and built that is composed of five nano-positioners with different range and bandwidth characteristics. Through redundant actuation this nano-positioner is capable of operating at high speeds and over large lateral and out-of-plane scan ranges. A general data-based compensator design methodology for the control of redundantly actuated nano-positioners is developed. In the proposed approach the compensators are obtained directly from the measured scanner actuator response, without any intermediate modeling. This feature makes updating or tuning the associated parameters easier. The flexibility of AFM control is maintained by designing these compensators auxiliary to a PID control unit. It is shown that in this form, a PID controller suffices to meet the needs of high-speed atomic force microscopy. This approach to control design is also used in the thesis to retroactively enhance existing AFMs operating on both flexure-based scanners and piezo-tubes. To improve the positioning accuracy of the scanner we proposed a more accurate parameter estimation scheme for the Maxwell model of hysteresis extended to the full hysteresis loop. Finally, to enable operation of AFMs with probe arrays in tapping mode a non-linear demodulation method based on the Teager Energy Operator is designed and implemented in both analog and digital forms. The main advantage of this technique is simplicity, enabling implementation of hundreds of these operators in digital form on FPGAs (Field Programmable Gate Arrays) or in ASIC (Application-Specific Integrated Circuit) form on AFM probe arrays for parallel sensing. The developments of this thesis form the bases for the design and implementation of a novel AFM. The implemented instrument is capable of high-speed imaging and simultaneously achieves 6 [mu]m out-of-plane and 120 [mu]m lateral scan ranges making it the largest range high-speed AFM reported to this date. This instrument also features a modular design with a laser spot size of 3.5 [mu]m compatible with small cantilevers, an optical view of the sample and probe for site selection and laser adjustment, a conveniently large (15 mm) waterproof sample stage that accommodates samples with various sizes and a data logging and plotting system with 20 MHz throughput for high resolution image acquisition at high imaging speeds. The designed AFM is used to visualize etching of calcite in a solution of sulfuric acid. Layer-by-layer dissolution along the crystalline lines in a low pH environment is observed in real time and the corresponding dissolution rate is estimated. The designed AFM is also used to visualize in real time the nucleation, growth and striping of copper on gold for the first time.