We report on the first through-wafer silicon-based Electrostatic Quadrupole Array (ESQA) to focus high energy ion beams. This device is a key enabler for a wafer-based accelerator architecture that lends itself to orders-of-magnitude reduction in cost, volume and weight of charged particle accelerators. ESQs are a key building block in developing compact Multiple Electrostatic Quadrupole Array Linear Accelerator (MEQALAC) [1]. In a MEQALAC electrostatic forces are used to focus ions, and electrostatic field scaling permits high beam current densities by decreasing the beam aperture size for a given peak electric field set by breakdown limitations. Using multiple parallel beams, each totaling to an area A, can result in higher total beam current compared to a single aperture beam of the same area. Smaller dimensions also allow for higher focusing electric field gradients and therefore higher average beam current density. Here we demonstrate that Deep Reactive Ion Etching (DRIE) micromachined pillar electrodes, electrically isolated by silicon-nitride thin films enable higher performance ESQA with waferscale scalability. The fabricated ESQA are able to hold up toi kV in air. A 3×3 array of 12 keV argon ion beams are focused in a wafer accelerator unit cell to pave the way for multiple wafer accelerator.

Pulsed ESR experiments are reported for ensembles of negatively-charged nitrogen-vacancy centers (NV −) in diamonds at X-band magnetic fields (280–400 mT) and low temperatures (2–70 K). The NV − centers in synthetic type IIa diamonds (nitrogen impurity concentration  <1 ppm) are prepared with bulk concentrations of 2 ⋅ 1013 cm −3 to 4 ⋅ 1014 cm −3 by high-energy electron irradiation and subsequent annealing. We find that a proper post-radiation anneal (1000°C for 60 min) is critically important to repair the radiation damage and to recover long electron spin coherence times for NV −s. After the annealing, spin coherence times of T2 = 0.74ms at 5 K are achieved, being only limited by 13C nuclear spectral diffusion in natural abundance diamonds. By measuring the temperature dependence of T2 in the under-annealed diamonds (900°C) we directly extract the density (1014 −16 cm −3) and activation energy (2.5 meV) of unannealed defects responsible for the faster NV − decoherence. At X-band magnetic fields, strong electron spin echo envelope modulation (ESEEM) is observed originating from the central 14N nucleus, and we extract accurate 14N nuclear hypefine and quadrupole tensors. In addition, the ESEEM effects from two proximal 13C sites (second-nearest neighbor and fourth-nearest neighbor) are resolved and the respective 13C hyperfine coupling constants are extracted.

Exposure to beams of low-energy electrons (2-30 keV) in a scanning electron microscope locally induces formation of NV-centers without thermal annealing in diamonds that have been implanted with nitrogen ions. We find that non-thermal, electron-beam-induced NV-formation is about four times less efficient than thermal annealing. But NV-center formation in a consecutive thermal annealing step (800 °C) following exposure to low-energy electrons increases by a factor of up to 1.8 compared to thermal annealing alone. These observations point to reconstruction of nitrogen-vacancy complexes induced by electronic excitations from low-energy electrons as an NV-center formation mechanism and identify local electronic excitations as a means for spatially controlled room-temperature NV-center formation. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.

In this work, we demonstrate the use of frequency-tunable superconducting NbTiN coplanar waveguide microresonators for multi-frequency pulsed electron spin resonance (ESR) experiments. By applying a bias current to the center pin, the resonance frequency (∼7.6 GHz) can be continuously tuned by as much as 95 MHz in 270 ns without a change in the quality factor of 3000 at 2 K. We demonstrate the ESR performance of our resonators by measuring donor spin ensembles in silicon and show that adiabatic pulses can be used to overcome magnetic field inhomogeneities and microwave power limitations due to the applied bias current. We take advantage of the rapid tunability of these resonators to manipulate both phosphorus and arsenic spins in a single pulse sequence, demonstrating pulsed double electron-electron resonance. Our NbTiN resonator design is useful for multi-frequency pulsed ESR and should also have applications in experiments where spin ensembles are used as quantum memories.