High‐Resolution ESR Imaging of N@C₆₀ Radicals on a Surface

Abstract

Electron Spin Resonance Microcopy (ESRM) is an imaging method capable of observing stable free radicals in small samples with a spatial resolution of ∼1 micron. Currently this technique is pursued mainly for biological applications at room temperature and at relatively low static magnetic fields. Future progress, which involves the use of higher magnetic fields at cryogenic temperatures, could significantly improve sensitivity and resolution and thus make this method attractive to many solid‐state and physical science applications. Here we consider a possible application of ESRM to the field of quantum computing employing Endohedral Nitrogen fullerene (N@C60) molecules. In order to fully address the challenges of quantum computing, the resolution should be significantly improved to ∼10 nm and the sensitivity should approach the single spin level. In the present work we show some preliminary results conducted with diluted N@C60 samples. A 2D image of N@C60 dispersed on a surface was obtained at a field of ∼0.6 T and at room temperature. Under these conditions the current sensitivity of the ESRM system is around 107−108 spins, and due to the low enrichment factor of the N@C60 sample (∼10−6), we were able to reach image resolution of only ∼50 m̈m. Future steps that are taken in order to significantly improve resolution and sensitivity of the system are discussed. These include the use of highly concentrated samples to be measured at ∼4 K and at a field of more than 1 T, which would lead to a resolution of ∼100 nm and a sensitivity of ∼100 spins.

ESR imaging in solid phase down to sub-micron resolution: methodology and applications

“…1, and its detailed description is provided elsewhere. 18 Briefly, the system is constructed from the following main components: (a) A PC that supervises the image acquisition process and is equipped with four PCI cards with the following functionalities: (b) A timing card with time resolution of 2.5 ns and a minimum pulse length of 2.5 ns. This card generates control signals for the microwave (MW) and gradient pulses of the imaging sequence (Fig.…”

Optically detected magnetic resonance imaging

“…The fluorescence emission is collected by the same fiber and goes to a detector, via a long-pass optical filter. (b and c) The imaging probehead is similar to the one described in ref [9][10][11] , based on a compact MW dielectric resonator into which we insert the diamond sample (with the 111 crystal orientation along the direction of the static field). Panel (c)…”

“…This ability is of importance for quantum information processing applications. "home-made" ESR pulsed microimaging system (described in detail in [9][10][11] ) comprised of a pulsed 6-18-GHz microwave bridge and fast pulse gradient drivers is combined with an ODMR optical setup. The sample is positioned at a static magnetic field of 0.27 T, perpendicular to its face, applied by an electromagnet.…”