CVD-Wachstum von Diamantspitzen mit Stickstoff-Vakanz-Zentren für die Raster-Sonden-Magnetometrie

CVD Growth of Diamond Tips for Scanning Probe Magnetometry In this thesis an investigation on the CVD growth of diamond for the fabrication of AFM tips containing nitrogen vacancy centers (NV centers) is presented. Acting as probes in a scanning probe magnetometer they enable the measurement of magnetic fields with a spatial resolution in the order of nanometers. Established manufacturing techniques for this kind of probes include the ion implantation of nitrogen and etching of diamond tips, both of which are known to induce crystal damage reducing the sensitivity of the NV centers as magnetic sensors. A novel method to manufacture diamond tips with NV centers, which is presented in this thesis, is based on the CVD growth of diamond with the aim of circumventing above mentioned, detrimental mechanisms. In a first step, the CVD growth process of diamond on microstructures is investigated. When observing the growth mechanisms, a deviation from the established geometric growth model has to be taken into account: the growth speed of diamond is increasing with the dimensions of the diamond microstructures. The acquired knowledge about the anisotropic diamond growth enables the fabrication of diamond tips with a radius of curvature of 20 nm, suitable for AFM measurements. The second step involves the creation of NV centers within the microstructures. A nitrogen doped CVD process is presented that enables the creation of NV centers with a spatial accuracy of approximately 1 μm and with preferential alignment of the NV axes. DEER measurements reveal a high crystal quality with a low density of paramagnetic spins other than the intentionally doped substitutional nitrogen atoms, enabling long dephasing times of the NV center electron spins. Both of the above mentioned processes are combined to produce a diamond tip with NV centers for use in a scanning probe magnetometer. A magnetic sensitivity of the NV centers of 60 μT√Hz−1 is achieved. The detection of current density magnitude and direction through the metal lines of a high electron mobility transistor by performing a NV center based scanning probe magnetometry measurement serves as an application example. The noise present in the acquired magnetic field maps and its amplification along the path of data processing towards the current density is investigated. The presented experiments on the CVD growth of diamond microstructures enable a better understanding of the subprocesses involved in diamond growth and extend the capabilities of CVD diamond growth as a tool for quantum computing and quantum sensing.