Methods for color center preserving hydrogen-termination of diamond

TL;DR

This paper investigates low-damage hydrogenation techniques for diamond surfaces, using annealing in nitrogen-hydrogen mixtures and microwave plasma exposure, to preserve near-surface color centers crucial for device applications.

Contribution

It introduces alternative hydrogenation methods that reduce damage compared to traditional plasma treatments, supported by spectroscopic and modeling analyses.

Findings

Annealing in nitrogen-hydrogen mixtures effectively hydrogenates diamond surfaces.

Microwave hydrogen plasma exposure without stage heating preserves nitrogen-vacancy centers.

Surface oxygen ligands limit the quality of hydrogen termination.

Abstract

Chemical functionalization of diamond surfaces by hydrogen is an important method for controlling the charge state of near-surface fluorescent color centers, an essential process in fabricating devices such as diamond field-effect transistors and chemical sensors, and a required first step for realizing families of more complex terminations through subsequent chemical processing. In all these cases, termination is typically achieved using hydrogen plasma sources which can etch or damage the diamond as well as deposited materials or embedded colour centers. This work explores alternative methods for lower-damage hydrogenation of diamond surfaces, specifically the annealing of diamond samples in high-purity, non-explosive mixtures of nitrogen and hydrogen gas, and the exposure of samples to microwave hydrogen plasmas in the absence of intentional stage heating. The effectiveness of these methods are characterized by x-ray photoelectron spectroscopy, and comparison of the results to density-functional modelling of the surface hydrogenation energetics implicates surface oxygen ligands as the primary factor limiting the termination quality of annealed samples. Finally, photoluminescence spectroscopy is used to verify that both the annealing and reduced sample temperature plasma methods are non-destructive to near-surface ensembles of nitrogen-vacancy centers, in stark contrast to plasma treatments which use heated sample stages.