Point Defects in crystals as sensors
We investigate point defects in crystals e.g. single impurtiy atoms: such defects absorb and emit light similar to atoms, however, they are trapped in the solid ("artificial atoms"). High densities of such defects lead to a coloration of transparent crystal leading to the term color centers. Electrons bound to the centers give them a magnetic moment (spin). Color centers are long term stable even at room temperature. Their emission is so bright that we observe single centers in our confocal laser-fluorescence microscopes. The most investigated color centers is the NV center in dimond, consisting of a nitrogen atom and a vacancy in the diamond lattice (see figure).
Color centers are versatile, sensitive sensors: The react to magnetic field, temperature, electric fields, optical near-fields and strain in the crystal. Depending on the orientation of the electronic spin, the brightness of the color center emission changes. Using this effect, we measure the color center's spin orientation.
We especially investigate color center as stomic-scale sensors allowing for high resolution imaging. In paralle, we harness quantum properties of the centers, e.g. theirs coherence, to realize highly sensitive measurements.
Review on sensing with color centers: M. Radtke, E. Bernardi, A. Slablab, R. Nelz and E. Neu, Nanoscale sensing based on nitrogen vacancy centers in single crystal diamond and nanodiamonds: achievements and challenges, Nano Futures 3(4), 042004 (2019), View the review online
BMBF-Project DiaNanoRa: Scanning Probes for the Life Sciences
To optimize using our color centers as sensors, we embed them into scanning probe devices made of single crystal diamond. Such a scanning probe consists of a diamond nanowire (diameter 200 nm) on a platform. We create color centers close to the end facet of the wire. Like this, we can bring the color center very close to the sample under investigation while the nanowire efficiently channels the color center's emission into our microscope optics.
We manufacture our scanning probes using nanofabrication in high-purity, synthetic diamond. To raster scan a sample with the color center in close proximity, we use a custom-build setup combining a confocal microscope and an atomic force microscope. Using this technology, color centers are promising sensors for electrical signals in the life sciences as well as for near-fields of fluorescent markers.
To investigate, how NV centers interact with other fluorescent systems, we placed a fluorescent 2dimensional material on our diamond and investigated the exchange of energy between those systems.
Technology of Diamond Scanning Probes: M. Radtke, R. Nelz, A. Slablab and E. Neu, Reliable Nanofabrication of Single-Crystal Diamond Photonic Nanostructures for Nanoscale Sensing, Micromachines 10(11), 718 (2019),
Near-Field interaction of NV centers: R. Nelz, M. Radtke, A. Slablab, Z.‐Q. Xu, M. Kianinia, C. Li, C. Bradac, I. Aharonovich and E. Neu, Near‐Field Energy Transfer between a Luminescent 2D Material and Color Centers in Diamond, Advanced Quantum Technologies 1900088 (2019),