No abstract

The nitrogen-vacancy (NV) color center in diamond has demonstrated
great promise in a wide range of quantum sensing. Recently, there have been a series of
proposals and experiments using NV centers to detect spin noise of quantum materials
near the diamond surface. This is a rich complex area of study with novel nanomagnetism
and electronic behavior, that the NV center would be ideal for sensing.
However, due to the electronic properties of the NV itself and its host material,
getting high quality NV centers within nanometers of such systems is challenging.
Band bending caused by space charges formed at the metal-semiconductor interface
force the NV center into its insensitive charge states. Here, we investigate optimizing
this interface by depositing thin metal films and thin insulating layers on a series
of NV ensembles at different depths to characterize the impact of metal films on
different ensemble depths. We find an improvement of coherence and dephasing times
we attribute to ionization of other paramagnetic defects. The insulating layer of
alumina between the metal and diamond provide improved photoluminescence and
higher sensitivity in all modes of sensing as compared to direct contact with the metal,
providing as much as a factor of 2 increase in sensitivity, decrease of integration time
by a factor of 4, for NV T1 relaxometry measurements.

The recently-developed ability to control phosphorous-doping of silicon at an atomic level using scanning tunneling microscopy (STM), a technique known as atomic-precision-advanced-manufacturing (APAM), has allowed us to tailor electronic devices with atomic precision, and thus has emerged as a way to explore new possibilities in Si electronics. In these applications, critical questions include where current flow is actually occurring in or near APAM structures as well as whether leakage currents are present. In general, detection and mapping of current flow in APAM structures are valuable diagnostic tools to obtain reliable devices in digital-enhanced applications. In this paper, we used nitrogen-vacancy (NV) centers in diamond for wide-field magnetic imaging (with a few-mm field of view and micron-scale resolution) of magnetic fields from surface currents flowing in an APAM test device made of a P delta-doped layer on a Si substrate, a standard APAM witness material. We integrated a diamond having a surface NV ensemble with the device (patterned in two parallel mm-sized ribbons), then mapped the magnetic field from the DC current injected in the APAM device in a home-built NV wide-field microscope. The 2D magnetic field maps were used to reconstruct the surface current density, allowing us to obtain information on current paths, device failures such as choke points where current flow is impeded, and current leakages outside the APAM-defined P-doped regions. Analysis on the current density reconstructed map showed a projected sensitivity of ~ 0.03 A/m, corresponding to a smallest detectable current in the 200 μm-wide APAM ribbon of ~ 6 μA. These results demonstrate the failure analysis capability of NV wide-field magnetometry for APAM materials, opening the possibility to investigate other cutting-edge microelectronic devices.