J. O. Orwa

The Raman spectrum of nanocrystalline diamond

Abstract Nanometre sized diamond powder has been purified by centrifugation to remove contamination from sp2 bonded carbon. The purified powder has been characterized using electron energy loss spectroscopy (EELS) and Raman spectroscopy. The EELS spectra confirmed the absence of sp2 bonded carbon and showed strong contributions from surface plasmons. Strong relatively sharp peaks are observed in the Raman spectra at 500, 1140, 1132 and 1630 cm −1 . By comparing the Raman spectra of the nanodiamond clusters with that of amorphized diamond and with calculations of the vibrational density of states we are able to suggest the origin of features in the vibrational spectrum from nanocrystalline diamond.

Diamond in tellurite glass: a new medium for quantum information.

M. R. Henderson, B. C. Gibson, H. Ebendorff-Heidepriem, K. Kuan , S. Afshar V., J. O. Orwa, I. Aharonovich ,S. Tomljenovic-Hanic, A. D. Greentree, S. Prawer, and T. M. Monro

Diamond nanocrystals formed by direct implantation of fused silica with carbon

We report synthesis of diamond nanocrystals directly from carbon atoms embedded into fused silica by ion implantation followed by thermal annealing. The production of the diamond nanocrystals and other carbon phases is investigated as a function of ion dose, annealing time, and annealing environment. We observe that the diamond nanocrystals are formed only when the samples are annealed in forming gas (4% H in Ar). Transmission electron microscopy studies show that the nanocrystals range in size from 5 to 40 nm, depending on dose, and are embedded at a depth of only 140 nm below the implanted surface, whereas the original implantation depth was 1450 nm. The bonding in these nanocrystals depends strongly on cluster size, with the smaller clusters predominantly aggregating into cubic diamond structure. The larger clusters, on the other hand, consist of other forms of carbon such as i-carbon and n-diamond and tend to be more defective. This leads to a model for the formation of these clusters which is based o...

Thermally induced sp2 clustering in tetrahedral amorphous carbon (ta-C) films

Tetrahedral amorphous carbon films with 70%–88% sp3 content are studied by atomic force microscopy (AFM), transmission electron microscopy (TEM), and Raman spectroscopy as a function of annealing temperature in the range 25–1100°C. Using a high-resolution AFM current imaging, we directly image the formation and growth of conducting graphitic (sp2-bonded) nanoclusters in the ta-C films. Overall results from all the techniques used show that the structural and electronic changes in the films depend sensitively on the initial sp3 content. Cross-sectional TEM confirms that the clusters appear not only at the surface of the films but in the bulk as well. The growth and, perhaps, the partial orientation of the sp2-bonded nanoclusters in the size range of 1–3nm is accompanied by a large reduction in the film stress, which decreases sharply in the temperature range 500–600°C.

Engineering of nitrogen-vacancy color centers in high purity diamond by ion implantation and annealing

The negatively-charged nitrogen-vacancy (NV) center is the most studied optical center in diamond and is very important for applications in quantum information science. Many proposals for integrating NV centers in quantum and sensing applications rely on their tailored fabrication in ultra pure host material. In this study, we use ion implantation to controllably introduce nitrogen into high purity, low nitrogen chemical vapor deposition diamond samples. The properties of the resulting NV centers are studied as a function of implantation temperature, annealing temperature, and implantation fluence. We compare the implanted NV centers with native NV centers present deep in the bulk of the as-grown samples. The results for implanted NV centers are promising but indicate, at this stage, that the deep native NV centers possess overall superior optical properties. In particular, the implanted NV centers obtained after annealing at 2000 °C under a stabilizing pressure of 8 GPa showed an ensemble linewidth of 0....

Bulk and surface thermal stability of ultra nanocrystalline diamond films with 10-30 nm grain size prepared by chemical vapor deposition

The thermal stability of nanocrystalline diamond films with 10–30 nm grain size deposited by microwave enhanced chemical vapor deposition on silicon substrate was investigated as a function of annealing temperature up to 1200 °C. The thermal stability of the surface-upper atomic layers was studied with near edge x-ray absorption fine structure (NEXAFS) spectroscopy recorded in the partial electron yield mode. This technique indicated substantial thermally induced graphitization of the film within a close proximity to the surface. While in the bulk region of the film no graphitization was observed with either Raman spectroscopy or NEXAFS spectroscopy recorded in total electron yield mode, even after annealing to 1200 °C. Raman spectroscopy did detect the complete disappearance of transpolyacetylene (t-PA)-like ν1 and ν3 modes following annealing at 1000 °C. Secondary ion mass spectroscopy, applied to investigate this relative decrease in hydrogen atom concentration detected only a ∼ 30% decrease in the bulk content of hydrogen atoms. This enhanced stability of sp3 hybridized atoms within the bulk region with respect to graphitization is discussed in terms of carbon bond rearrangement due to the thermal decomposition of t-PA-like fragments.

Nickel related optical centres in diamond created by ion implantation.

Ni-related optical centres in diamond are promising as alternatives to the nitrogen vacancy (NV) centre for quantum applications and biomarking. In order to achieve the reliability and reproducibility required, a method for producing the Ni-related centres in a controllable manner needs to be established. In this study, we have attempted this control by implanting high purity CVD diamond samples with Ni and N followed by thermal annealing. Samples implanted with Ni show a new Ni-related PL peak centered at 711 nm and a well known doublet at 883/885 nm along with weak NV luminescence. The optical properties of the two Ni-related defects are investigated. In particular, an excited state lifetime of the 883/885 nm peak is measured to be 11.6 ns.

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.

Growth of c-diamond, n-diamond and i-carbon nanophases in carbon-ion-implanted fused quartz

Abstract Combined high-resolution transmission electron microscopy, selected-area electron diffraction and parallel electron-energy-loss spectroscopy are used to characterize nanophases of carbon found embedded in fused quartz. These appear after implantation of 1 MeV carbon ions, followed by annealing in argon, oxygen and forming gas for lh at 1100°C. For argon, virtually all the carbon diffuses out of the substrate with no observable carbon clusters for all doses studied. After annealing in oxygen, a crystalline CO x phase is identified at the end of range, following a dose of 5 × 1017 carbon ions cm−2. Three nanocrystalline carbon phases, including diamond, appear after annealing in forming gas; these form a layer 170 nm beneath the fused quartz surface for all ion doses. The average size of these clusters and the corresponding phases depend on the ion dose; the smallest clusters of 5-7 nm diameter crystallize as fcc Fd3m diamond following a dose of 0.5 × 1017 carbon ions cm−2, whereas clusters of 8–13 nm diameter, for a higher dose of 2 × 1017 carbon ions cm−2, have a Fm3m modified phase of diamond known as n-diamond. The largest clusters (diameter, 15–40nm) for a dose of 5 × 10 17 carbon ions cm−2, have the cubic P213 (or P4232) structure known as i-carbon. These buried layered diamond-related materials may have applications for field emission devices.

NANO-CRYSTALS OF c-DIAMOND, n-DIAMOND AND i-CARBON GROWN IN CARBON-ION IMPLANTED FUSED QUARTZ

Combined high-resolution transmission electron microscopy, selected area electron diffraction and parallel electron energy loss spectroscopy are used to characterise carbon nano-phases found embedded in fused quartz. These appear after implantation of 1 MeV carbon ions, followed by annealing in argon, oxygen and forming gas for 1 hour at 1100°C. For Ar, virtually all of the carbon diffuses out of the substrate with no observable carbon clusters for all doses studied. After annealing in oxygen, a crystalline COx phase is identified at the end of range, following a dose of 5×1017C/cm2. Three nano-crystalline carbon phases, including diamond, appear after annealing in forming gas: these form a layer 170 nm beneath the fused quartz surface for all ion doses. The average size of these clusters and the corresponding phases depend on the ion dose; the smallest size of 5–7 nm diameter crystallise as fcc diamond following a dose of 0.5× 1017C/cm2, whereas clusters of 8–13 nm diameter, for a higher dose of 2× 1017C/cm2, have a modified phase of diamond known as n-diamond. The largest clusters, diameter 15–40 nm, for a dose of 5× 1017C/cm2, have the cubic P213 (or P4232) structure known as i-carbon. These buried layered diamond and diamond-related materials may have applications for field emission and optical waveguide type devices.