High-quality single crystalline diamond has useful properties beyond its extreme hardness that have led to its use in a wide variety of applications from ultra sharp knives for surgery to nanotechnology. For nanotechnology applications, processing single-crystal diamond into tiny functional structures is a critical but difficult step.

Now Barbara Fairchild from the University of Melbourne and colleagues1 have produced ultrathin membranes of diamond using ion implantation and etching of damaged layers.

The researchers exploited a technique that employs ion implantation and annealing of bulk single-crystal diamond. Namely, when bulk diamond is bombarded with a high density of ions moving with the same high energy, they create a highly damaged layer at the maximum penetration depth within the material. Notably, the higher the energy of the ions, the deeper is the location of the damaged layer. Once annealed, this highly damaged region becomes a sacrificial layer that can be etched away, so the undamaged material above it can be removed in the form of a thin film.

In spite of the successful use of this method, technical difficulties such as strain leading to cracking have precluded the realization of ultra-thin films. Fairchild and colleagues therefore set out to produce extremely thin films by a novel ‘sandwich’ technique.

Fig. 1: A scanning electron microscopy image of a curved Bragg stack mirror created from the processed film.

The researchers used ion bombardment to create not one, but two layers within the bulk diamond sample. By creating upper and lower damaged layers sandwiched by ~200nm of crystalline diamond, they were able to create ultrathin, high-quality diamond films—the thinnest was 210nm. Further processing enables the films to be shaped into tiny rings and other structures such as Bragg gratings (Fig. 1).

“Thinner films have already been made in polycrystalline diamond. However we’re interested in single-crystal diamond because of its superb optical properties,” says Fairchild.

In the future, “we hope to harness these properties for microscale optical and opto-mechanical devices,” says Fairchild. “We are currently refining our technique and intend to make photonic crystals, waveguides, cavities and cantilever devices.”