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Quantum Limited Atomic Force Microscopy

Periodic Reporting for period 1 - Q-AFM (Quantum Limited Atomic Force Microscopy)

Reporting period: 2019-01-01 to 2019-12-31

The field of Atomic Force Microscopy (AFM) is limited by the sensitivity of the resonant mechanical force sensor. Our vision is a radical new design of the force sensor, which will result in radical improvement of the AFM. The AFM is important to society. Being one of the most important tools of nanotechnology, the AFM offers very high resolution, quantitative images of surfaces, helping scientists and engineers to design better materials, catalysts, and understand fundamental physical and chemical process at the nanometer scale.

We will adopt a new paradigm for the resonant mechanical force sensor used in Low Temperature Atomic Force Microscopy (LT-AFM). Our ultimate goal is a Quantum-limited Atomic Force Microscope (Q-AFM), where the force sensor is working at the fundamental limit of action and reaction set by quantum physics. Achieving this limit will result in three orders of magnitude improvement in force sensitivity, and five orders of magnitude in measurement bandwidth, beyond the current state-of-the-art. This gain in performance will translate to a radical increase in imaging speed and in the information content of images. Our sensors will lead to a revolution in SPM, where multi-dimensional data sets are acquired in seconds, as opposed to several days as is the current practice.
In the first year we spent a lot of time on literature study, to better understand what has been done and to find inspiration for our sensor design. We do not recount on this study here. After much reading and discussion, we settled on a design concept and have worked to build up simulations tools and calculate basic design parameters. We identified the critical dimensions and features of the design and we have begun fabrication to see what we can achieve in a real device. We developed a classical nonlinear model to simulate and study the dynamics of our sensor and readout concept. We have also made preparations for low temperature and high-frequency measurements. This work was carried out in WP1, and a detailed description is given in the technical report part B.

In the first year we also worked to adapt the multifrequency AFM methodology to the case of very high Q resonance, typical of AFM in vacuum and at low temperature. We wrote simulation code and checked out different drive and measurement schemes in simulation. We have also worked on the theory force reconstruction and have checked our ideas using simulated data. We made a deeper analysis of qPlus sensor readout using an RF tank circuit. Our analysis should that this scheme will not work, so we have scratched this idea in our original proposal. Our experiments with Intermodulation AFM and the qPlus sensor pointed to unforeseen difficulties with the traditional multifrequency feedback method. We have therefore defined a new task; to implement a fully programable and very flexible approach to AFM feedback. This work was carried out in WP2, and a detailed description is given in the technical report part B.
We are trying to solve a problem in the LT-AFM community and not by an incremental amount. By introducing a new measurement paradigm to the LT-AFM community, our project has the potential to result in enormous advancement. We are merging ideas from the superconducting quantum circuit community, augmenting these with designs and techniques from the MEMS sensors and actuators community, and applying them to LT-AFM. Implementing our sensor requires expertise in microwave analog electronics. In order to use the massive improvement in sensitivity and bandwidth, multifrequency digital acquisition techniques using Field Programmable Gate Arrays (FPGA) is required. Achieving our goals requires an interdisciplinary team with skills in diverse areas of applied physics and cutting-edge technology.

The social and economic impacts of our research are direct for a smaller community of scientist, but far reaching in their indirect impact. If we are successful, a smaller community of LT-AFM scientists will get a much better instrument. To the larger society who daily use high-tech electronic devices, sensors, which rely advanced materials and measurement techniques, our project will have impact by pushing the development of signal transduction to the quantum limit. Our approach of measuirng in the frequency domain brings the technical advantage of advanced signal processing methods which are in daily use for communication technology (both radio and optical fiber). Our research adapts and brings these methods to sensing and actuating.
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