S. Prawer

Thermal stability and relaxation in diamond-like-carbon. A Raman study of films with different sp3 fractions (ta-C to a-C)

The thermal stability and relaxation processes in hydrogen free diamond-like-carbon films with different sp3 fractions (40%, 60%, and 80%) are comparatively studied for the first time by visible Raman spectroscopy. The 80% sp3 film is very stable under annealing in the entire temperature region investigated (300–1270 K) and shows only a minor change of the optical transmission, most likely due to a mild sp2 clustering, but no graphitization. This is very important for practical applications requiring a high thermal stability. The films with lower sp3 fraction show a thermal stability which decreases with the decreasing sp3. Graphitization starts at 700 K for the 40% sp3 film.

Growth-sector dependence of fine structure in the first-order Raman diamond line from large isolated chemical-vapor-deposited diamond crystals

The growth‐sector dependence of fine structure in the first‐order Raman diamond line is investigated for the first time in high resolution spectra taken from large isolated diamond single crystals grown using microwave plasma chemical vapor deposition on tungsten wire tips. The volumes of crystal beneath the (100) and (111) surfaces of these crystals were sampled using a high resolution Raman microprobe from which the line shape of the 1332 cm−1 diamond line was found to be distinctly different. A splitting of the diamond line into two components of up to 7 cm−1 was observed for (100) growth sectors. This splitting may be caused by the buildup of directional strain fields caused by the different fundamental growth processes occurring on the (100) and (111) growth surfaces. An additional third peak near 1326 cm−1 was only observed in (111) growth sectors and may be attributable to the presence of stacking faults.

Diamond chemical-vapor deposition on optical fibers for fluorescence waveguiding

A technique has been developed for depositing diamond crystals on the endfaces of optical fibers and capturing the fluorescence generated by optically active defects in diamond into the fiber. This letter details the diamond growth on optical fibers and transmission of fluorescence through the fiber from the nitrogen-vacancy color center in diamond. Control of the concentration of defects incorporated during the chemical vapor deposition growth process is also demonstrated. These are critical steps in developing a fiber coupled single-photon source based on optically active defect centers in diamond.

Effect of surface roughness on field emission from chemical vapor deposited polycrystalline diamond

The effect of surface roughness on electron emission from hydrogenated polycrystalline diamond films is reported. Field emission measurements were performed with both millimeter and nanometer spatial resolution using scanning probe techniques. Surface asperities were removed by ion beam treatment, which resulted in a reduction of the rms roughness from 198 to 94 nm, leading to an increase in the threshold field required for electron emission by about a factor of 2. These results suggest that surface asperities, rather than grain boundaries, are the dominant influence on electron emission in polycrystalline diamond films.

Nanoscale electrical characterization of trap-assisted quasibreakdown fluctuations in SiO2

Conductive atomic force microscopy has been used to electrically image quasibreakdown sites in thin, native SiO2 films. Local current–voltage spectroscopy reveals, at individual sites, fluctuations in the breakdown current between well-defined conductivity states. Theoretical modeling has been performed to show that conduction through the film is governed by local trap-assisted tunneling, with typically one or two charge traps contributing to conduction through a quasibreakdown site. Our study provides a semiquantitative analysis to characterize the effective trap states that give rise to local random telegraph signals in the oxide film.

He+ and H+ mubeam damage, swelling and annealing in diamond

Abstract The effects of scanned 2 MeV He + and 1.4 MeV H + mubeam irradiation on unimplanted and P implanted diamond were characterized. Although diamond was found to be resistant to lattice defect production, it was found to swell very rapidly in comparison with other materials, giving rise to serious swelling induced dechanneling at scan edges at relatively low doses (10 17 /cm 2 for 2 MeV He + ). mubeams annealed the damage due to a 1.5 μm deep phosphorus implantation at a dose of 10 15 P + /cm 2 . The implantation damage was reduced at a dose of (1.6 × 10 17 /cm 2 ) by up to 21% for 2 MeV He + irradiation, up to 16% for high flux 1.4 MeV H + irradiation and 12% for low flux H + irradiation. For the choice of analysis beam, all these beam effects were found to be most significant for He + mubeams, so H + mubeams should be used for analysis of diamond unless high depth resolution is required.

Thin film resists for registration of single-ion impacts

We demonstrate registration of the location of the impact site of single ions using a thin film polymethyl methacrylate resist on a SiO2/Si substrate. Carbon nanotube-based atomic force microscopy is used to reveal craters in the surface of chemically developed films, consistent with the development of latent damage induced by single-ion impacts. The responses of thin PMMA films to the implantation of He+ and Ga+ ions indicate the role of electronic and nuclear energy loss mechanisms at the single-ion level.

THE EFFECT OF ION-BEAM INDUCED STRAIN ON THE NUCLEATION DENSITY OF CHEMICAL VAPOUR DEPOSITED DIAMOND.

The effect of ion implantation on the nucleation of CVD diamond on silicon and diamond substrates has been investigated. The strategy employed is to create laterally confined regions of strain in the substrates by focused MeV implantation of light ions. Raman Microscopy has been employed to obtain spatially resolved maps of the strain in these implanted regions. On diamond substrates a homo-epitaxial CVD diamond film was grown on top of both the implanted and unimplanted regions of the substrate. Raman analysis of the film grown on top of the implanted region revealed it to be under slightly tensile strain as compared to that grown on the unimplanted diamond substrate. The film deposited on the implanted portion of the diamond showed a lower fluorescence background; indicating a lower concentration of incorporated defects. These results suggest that the strain and defects in the diamond substrate material have an important influence on the quality of the homo-epitaxially grown diamond films.

Nitrogen Ion Implantation into Glassy Carbon and Diamond.

High dose N ion implantations into glassy carbon (GC) and diamond were performed at energies of 160 and 300 keV respectively. Target temperatures of the GC and diamond substrates were −100° C and room temperature respectively. Maximum N concentrations of 30 and 17 at.% were achieved for the GC and diamond respectively. Atomic force microscopy (AFM) and scanning electron microscopy (SEM) revealed unusual surface modifications for both substrates.

STUDIES OF DEFECTS ON ION IRRADIATTED DIAMOND

Based on previous work, a knowledge of the defect structures created in diamond is crucial for optimizing the doping of diamond by ion irradiation. In the present work, type Ha diamond has been irradiated with 320keV Xe ions at room temperature. It was found that up to a dose of 1×10 14 ions/cm 2 , the diamond remains single crystalline, with no evidence of graphitization. TEM results are supplemented with EELS, Raman spectroscopy, ESR and electrical conductivity measurements, to provide a comprehensive picture of the defect structure in the ion implanted layer.