Graduation Committee Parallel Probe Readout for Data Storage

In this thesis techniques are developed to read out nanoscale probes and arrays of probes. e main targeted application area is probe-based data storage. e work also contributes to other areas, such as metrology, biological sensing, materials research and nano-electro-mechanical switches. First, an exhaustive literature review of the accomplishments within probe storage is presented. It is found that optical readout techniques are used extensively in applications using probes; however, the very demanding application probe storage is not amongst them. Optical readout of probes ošers reliability, high-speed, low noise and low complexity. It has to be extended to operation on arrays of probes for successful implementation in probe storage. e rst technique that is developed in this work is parallel frequency readout of an array of cantilever probes, demonstrated using optical beam dežection with a single laser-diode pair. Multi-frequency addressing makes the individual nanomechanical response of each cantilever distinguishable within the received signal. Addressing is accomplished by exciting the array with the sum of all cantilever resonant frequencies. is technique requires considerably less hardware compared to other parallel optical readout techniques. Readout is demonstrated in beam dežectionmode and interferencemode. Many cantilevers can be readout in parallel, limited by the oscillators’ quality factor and available bandwidth. e proposed technique facilitates parallelism in applications at the nanoscale, including probebased data storage and biological sensing. A second technique to perform parallel optical readout of probes makes use of dišraction patterns that result if a laser spot is incident on an array of probes. e cantilevers form an optical grating and the state of dežection of each cantilever within the array determines the dišraction pattern, which is captured by a 1-dimensional array of photodiodes. Each cantilever can be regarded as a slit in a traditional multiple-slit dišraction experiment. In our situation the phase of the režected light is a function of the amount of dežection of the cantilever, in contrast to a slit dišraction experiment, where the slits are assumed to contain light sources of equal phase. e developed technique is straightforward applicable when two discrete levels are permitted in cantilever bending. A novel fabrication process is developed to produce probe arrays with sharp tips that are self-aligned on the cantilever. e focus is on achieving an array that gives rise to a highly uniform tip-medium distance. In order to accomplish this we make