Fabrication of magnetic disks and gold waveguide onto a small diamond chip In my research I use nitrogen vacancy (NV) defect centers in diamond as quantum sensors to study magnons in magnetic disks. This is a thread to explain how I fabricated magnetic disks and a gold coplanar waveguide (CPW) onto a small diamond chip containing NV defect centers, to use for my experiments. The diamond material is electronic grade single crystal diamond from @ElementSix_ . We grow an additional layer of diamond onto the chip and engineer a layer of NV defect centers 15 nm below the sample surface through facilities at @qnextquantum . (I’ll describe this process in a future thread). To fabricate the magnetic disks on the diamond we use electron beam lithography (EBL) and electron beam evaporation, while the gold CPW is patterned through photo-lithography and thermal evaporation. To the extent possible we employed standard processes to carry out the fabrication. However, due to the small dimensions of the diamond chip (2 mm x 2 mm x 180 μm), we encountered a number of engineering challenges. Standard lithography and material deposition processes are typically carried out on substrates with lateral dimensions of 10s of mm. Anything smaller can’t be affixed to the fabrication equipment (spin coaters, deposition/EBL stages etc.) and requires mounting to a larger substrate. To account for this, we mount the diamond to a glass slide using CrystalBond 590 wax. The dimensions of the glass slide are about 60 x 30 mm. The first image is the diamond sample held by tweezers next to a nickel for size comparison. The second image is a schematic of the diamond chip mounted to the glass for fabrication processing. @PhysicsCWRU

Materials and methods A layer of isotopically pure 12C was grown on an electronic-grade single crystal diamond (from @ElementSix_) via plasma enhanced chemical vapor deposition, through facilities at @qnextquantum. 15N2 gas was introduced into the growth process at the appropriate time to achieve a 15 nm deep delta-doped layer of nitrogen. A subsequent electron irradiation (2 MeV, 1e14 dose) was used to create the vacancies followed by annealing of the sample at 850 ◦C under forming gas (H2/Ar) for 2 hours to form the NV centers. A triacid (HClO4:HNO3:H2SO4) clean was then used to remove residual contaminants from the sample surface. An array of 2.1-μm-diameter and 37-nm-thick Py disks were then fabricated atop the NV center-containing diamond film by electron beam lithography, electron beam evaporation and liftoff. This results in a 15 nm vertical separation between the surface of the disks and the NV centers. A subsequent photo-lithography process was used to pattern a 125 nm thick gold co-planar waveguide (CPW) over the disk array. Figure 3(a) shows a schematic of the sample and setup. A 100X oil immersion microscope with 1.25 numerical aperture focuses 532-nm-wavelength excitation onto the sample from the back side of the diamond. Photoluminescence (PL) is collected back through the objective, and detected by a single photon counting module. Figure 3(b) shows a scanning PL image of four Py disks (blue), with several NV centers (bright spots) in the diamond ≈ 15 nm above the disks. The NV/disk pair studied in this paper is indicated by the red arrow.

The interaction between defect spin qubits and magnons (the quasiparticles of spin waves) in a magnetic material offers opportunities both for control and coupling of qubit states, and for use of the spin qubit as a probe to study magnon phenomena. In the prototypical system, negatively charged nitrogen vacancy (NV) defects in diamond are placed in proximity to a ferromagnetic structure. An AC magnetic field is then used to drive dynamics of the NV spin, the magnon modes of the ferromagnet, or both. Meanwhile, the NV spin state can be initialized and monitored optically. I’ll be posting about my research using NV defect centers as quantum sensors to study the magnetization dynamics of ferromagnetic disks in a vortex state in future posts. This is a short thread to introduce you to the sample I use for this research. This is a picture of the diamond sample I use for my research. It is electronic grade single crystal diamond from @ElementSix_. We grew an additional layer of diamond onto the sample and engineered a layer of NV defect centers 15 nm below the sample surface (through facilities at @qnextquantum @argonne @doescience). On the surface of the sample I fabricated an array of magnetic disks in a vortex state, as well as a gold waveguide. (I will also be posting about the fabrication processes used to make these samples). @PhysicsCWRU