Barbara A. Fairchild

Fabrication of Ultrathin Single-Crystal Diamond Membranes†

A method for preparing ultrathin single-crystal diamond membranes suitable for post-processing and liftout, is reported. The proposed method used single-crystal diamond substrates and two-energy ion implant process for the fabrication of thin diamond membranes. Two ion-implant process was used in this method to prepare two different damage layers within diamond sample. This method can be used for preparing integrated quantum-photonic structure based on color center in diamond. This method can also be used for fabricating various structures including Bragg gratings and whispering gallery mode resonators. A significant application of the diamond nanostructures is to fabricate the micro- and nanoscale cantilevers. It was also observed that the fabricated single-crystal diamond are suitable for another FIB processing.

Diamond integrated quantum photonics

Diamond is a leading contender as the material of choice for the quantum computer industry. This potential arises mainly from the quantum properties of color centers in diamond. However, before diamond can realize its full potential, the technology to fabricate and sculpt diamond as well as, if not better than, silicon must be developed. A comprehensive processing capability for diamond that will allow the fabrication of qubits and their associated photonic structures is required. Here we describe the remarkable properties of diamond color centers, and the techniques being developed to engineer qubits and sculpt monolithic structures around them. Finally we outline some of the new proposals that use engineered diamond to realize tasks not possible with existing technologies.

Fabrication and electrical characterization of three-dimensional graphitic microchannels in single crystal diamond

We report on the systematic characterization of conductive micro-channels fabricated in single-crystal diamond with direct ion microbeam writing. Focused high-energy ( MeV) helium ions are employed to selectively convert diamond with micrometric spatial accuracy to a stable graphitic phase upon thermal annealing, due to the induced structural damage occurring at the end-of-range. A variable-thickness mask allows the accurate modulation of the depth at which the microchannels are formed, from several µm deep up to the very surface of the sample. By means of cross-sectional transmission electron microscopy (TEM), we demonstrate that the technique allows the direct writing of amorphous (and graphitic, upon suitable thermal annealing) microstructures extending within the insulating diamond matrix in the three spatial directions, and in particular, that buried channels embedded in a highly insulating matrix emerge and electrically connect to the sample surface at specific locations. Moreover, by means of electrical characterization at both

Mechanism for the Amorphisation of Diamond

The breakdown of the diamond lattice is explored by ion implantation and molecular dynamics simulations. We show that lattice breakdown is strain-driven, rather than damage-driven, and that the lattice persists until 16% of the atoms have been removed from their lattice sites. The figure shows the transition between amorphous carbon and diamond, with the interfaces highlighted with dashed lines.

Diamond-based structures to collect and guide light

We examine some promising photonic structures for collecting and guiding light in bulk diamond. The aim of this work is to optimize single photon sources and single spin read-out from diamond color centers, specifically NV centers. We review the modeling and fabrication (by focused ion beam and reactive ion etching) of solid immersion lenses, waveguides and photonic crystal cavities in monolithic diamond.

Splitting of photoluminescent emission from nitrogen?vacancy centers in diamond induced by ion-damage-induced stress

We report a systematic investigation on the spectral splitting of negatively charged, nitrogen?vacancy (NV?) photoluminescent emission in single-crystal diamond induced by strain engineering. The stress fields arise from MeV ion-induced conversion of diamond to amorphous and graphitic material in regions proximal to the centers of interest. In low-nitrogen sectors of a high-pressure?high-temperature diamond, clearly distinguishable spectral components in the NV? emission develop over a range of ?4.8?THz corresponding to distinct alignment of sub-ensembles which were mapped with micron spatial resolution. This method provides opportunities for the creation and selection of aligned NV? centers for ensemble quantum information protocols.

Tailoring the optical constants of diamond by ion implantation

We study the effect of 30 keV gallium ion implantation on the optical properties of diamond, as determined using spectroscopic ellipsometry. We find that the refractive index of the implanted layer can be either lower, or higher, than that of pristine diamond, depending on the implantation dose. This observation provides a new route to optical device fabrication in diamond using focused ion beam methods. In particular, in the low dose regime, lowering of the refractive index would allow for core-cladding type structures to be defined where the core has not interacted with the beam, and is hence undamaged by the implantation.

Surface damage on diamond membranes fabricated by ion implantation and lift-off

Thin membranes with excellent optical properties are essential elements in diamond based photonic systems. Due to the chemical inertness of diamond, ion beam processing must be employed to carve photonic structures. One method to realize such membranes is ion-implantation graphitization followed by chemical removal of the sacrificial graphite. The interface revealed when the sacrificial layer is removed has interesting properties. To investigate this interface, we employed the surface sensitive technique of grazing angle channeled Rutherford backscattering spectroscopy. Even after high temperature annealing and chemical etching a thin layer of damaged diamond remains, however, it is removed by hydrogen plasma exposure.

Producing optimized ensembles of nitrogen-vacancy color centers for quantum information applications

Quantum information applications place stringent demands on the development of platforms that can host them. Color centers in diamond have been identified as important media for quantum information processing. Accordingly, the photoluminescence properties of nitrogen-vacancy (N-V) centers in diamond created by implantation and annealing are studied at cryogenic temperatures (below 10 K). We examine high pressure high temperature and chemical vapor deposition synthetic diamonds with varying nitrogen concentration and present an accurate method to estimate the concentration of the (N-V) centers created by ion implantation. The ion irradiation route produced up to 6 ppm of optically active (N-V) centers, while nitrogen implantation yielded up to 3 ppm of optically active (N-V) with 8% conversion efficiency. However, a broadening of the (N-V)− zero phonon line was observed in all samples.

Improved diamond surfaces following lift-off and plasma treatments as observed by x-ray absorption spectroscopy

We have investigated the nature of the residual damage in diamond crystals following the ion implantation/graphitization “lift-off” process, using near-edge x-ray absorption fine structure spectroscopy and transmission electron microscopy. A defective but crystalline interface is found, which displays dense pre-edge unoccupied states and an almost complete loss of the core-level C 1s exciton signature. This residual crystalline damage is resistant to standard chemical etching, however a hydrogen plasma treatment is found to completely recover a pristine diamond surface. Analysis and removal of residual ion-induced damage is considered crucial to the performance of many diamond device architectures.