Impact of irradiation conditions on the magnetic field sensitivity of spin defects in hBN nano flakes

Abstract We study <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msubsup> <mml:mi>V</mml:mi> <mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">B</mml:mi> </mml:mrow> </mml:mrow> <mml:mo>−</mml:mo> </mml:msubsup> </mml:mrow> </mml:math> centres generated by 25 keV helium focused ion beam (FIB) irradiation in thin (∼70 nm) hexagonal boron nitride (hBN) nanoflakes, to investigate the effect of implantation conditions on the key parameters that influence the magnetic field sensitivity of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msubsup> <mml:mi>V</mml:mi> <mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">B</mml:mi> </mml:mrow> </mml:mrow> <mml:mo>−</mml:mo> </mml:msubsup> </mml:mrow> </mml:math> quantum sensors. Using a combination of photoluminescence, optically detected magnetic resonance, and Raman spectroscopy we examine the competing factors of maximising signal intensity through larger <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msubsup> <mml:mi>V</mml:mi> <mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">B</mml:mi> </mml:mrow> </mml:mrow> <mml:mo>−</mml:mo> </mml:msubsup> </mml:mrow> </mml:math> concentration against the degradation in spin coherence and lattice quality at high ion fluences. Both the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msubsup> <mml:mi>V</mml:mi> <mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">B</mml:mi> </mml:mrow> </mml:mrow> <mml:mo>−</mml:mo> </mml:msubsup> </mml:mrow> </mml:math> spin properties and hBN lattice parameters are largely preserved up to an ion fluence of 10 14 ions cm −2 , and beyond this significant degradation occurs in both. Our measurements give an inferred AC magnetic field sensitivity of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mrow> <mml:mo>∼</mml:mo> </mml:mrow> <mml:mn>1</mml:mn> <mml:mstyle scriptlevel="0"/> <mml:mtext>μ</mml:mtext> <mml:mtext>T</mml:mtext> <mml:mrow> <mml:mo>/</mml:mo> </mml:mrow> <mml:msqrt> <mml:mtext>Hz</mml:mtext> </mml:msqrt> </mml:mrow> </mml:math> at the optimal implantation dose. Using the patterned implantation enabled by the FIB, the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msubsup> <mml:mi>V</mml:mi> <mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">B</mml:mi> </mml:mrow> </mml:mrow> <mml:mo>−</mml:mo> </mml:msubsup> </mml:mrow> </mml:math> centres and the associated lattice damage are well localised to the implanted regions. This work demonstrates how careful selection of fabrication parameters optimises the properties of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msubsup> <mml:mi>V</mml:mi> <mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">B</mml:mi> </mml:mrow> </mml:mrow> <mml:mo>−</mml:mo> </mml:msubsup> </mml:mrow> </mml:math> centres in hBN, supporting their application as quantum sensors based in 2D materials.