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

Raman spectroscopy applied to early (ca. 1746-1754) English steatitic porcelains: a tentative study of compositions

Two pieces of unmarked English porcelainware, a vase and a coffee cup, were examined by Raman spectroscopy. The presence of both forsterite and enstatite was identified in the vase, and enstatite and diopside in the coffee cup, indicating that both articles contained magnesium. The glazes on the two objects were found to be different in chemical composition, as were the compositions of their on-glaze enamels used for their decoration. Residues of an organic binder were observed in the turquoise on-glaze enamels used to decorate both objects, indicating that either this colour was cold-painted onto these, or, more likely, a lead-based glaze fired at very low temperature was employed. From the data generated, together with the supporting historical information, it is now proposed that the two objects were decorated in different factories, most likely between ca. 1746 and 1754. The vase has been attributed to manufacture and decoration at Worcester during ca. 1753-1754, and the coffee cup is presently attributed to Bow manufacture and decoration in ca. 1746

Two-dimensional electron transport in selectively doped n-AlGaAs/InGaAs/GaAs pseudomorphic structures

The transport properties of the two-dimensional electron gas in selectively doped AlyGa1-yAs/InxGa1-xAs/GaAs pseudomorphic structures grown by molecular beam epitaxy are studied. The mobility in the temperature range from 1.7 to 300 K is reported based on the Hall effect and high-field magnetoconductance measurements. The relative strengths of various scattering mechanisms are assessed through a numerical iterative solution of the Boltzmann equation and compared with the experimental Hall mobility versus temperature data. Comparison shows that at low temperature, alloy scattering determines the low-field mobility with a suitable choice of alloy scattering potential. At room temperature, polar-optical phonon scattering is the dominant mechanism. However, alloy scattering also contributes in reducing the room-temperature mobility by approximately 20% compared to polar optical scattering alone

Forming in hydrogenated amorphous silicon metal-semiconductor-metal devices using bipolar pulse stressing

Because of the ability to deliver large voltage and current transients and limit power dissipation, a single bipolar pulse applied through a series capacitor results in forming at lower voltages with more uniformity compared to unipolar pulses. In addition, the on-resistances following bipolar pulse stressing are more uniform compared to unipolar pulses

Polarity-dependent forming in ion bombarded amorphous silicon memory devices

Polarity-dependent forming in ion bombarded metal-semiconductor-metal (MSM) memory devices of hydrogenated amorphous silicon is reported. It is shown that prior to ion bombardment, current transport in the MSM devices is asymmetric and is controlled by the Schottky barriers at two MS junctions. Upon bombardment, however, there is a bulk component to the current and the I-V characteristics of the devices become symmetric at low bias voltages. The forming voltage in the bombarded devices shows polarity dependence. For positive bias applied on the top contact, we find that devices form at the same electric field independent of the thickness of the amorphous silicon while for negative voltage on the top contact, the electric field needed for forming increases with the thickness. A model involving the difference in energy deposition and heat sinking for the two polarities is proposed

Carbon diffusion and nanocrystalline diamond formation in carbon ion-implanted oxides studied by nuclear elastic scattering

We have shown that MeV implantation of carbon into fused quartz and sapphire followed by thermal annealing in a suitable environment can result in the formation of diamond. Using cross-sectional transmission electron microscopy (TEM) and secondary ion mass spectroscopy (SIMS), we determined (in a previous paper) that, following annealing, there was a redistribution of carbon from the original implantation depth, depending on the annealing environment, annealing time and annealing temperature. In our search, for the optimum implantation and annealing parameters to maximize the yield of diamond, we have used backscattering spectrometry (BS), with MeV hydrogen, to profile the implanted carbon, taking advantage of the large C(p,p)C scattering cross-section at around 1.73 MeV. We studied samples of fused quartz and sapphire implanted with carbon to a range of doses and annealed in forming gas, oxygen and argon. We show that in an oxygen environment, there is significant carbon loss in fused quartz but not in sapphire while in the other environments no significant loss is reported. We conclude that redistribution of carbon, the formation of nanocrystalline diamond (as seen in cross-sectional TEM) and possible carbon loss is determined both by the mobility of carbon in the host matrix at the prevailing annealing temperatures and, most importantly, the annealing ambient

Effect of ion bombardment and annealing on the electrical properties of hydrogenated amorphous silicon metal-semiconductor-metal structures

The electrical properties of hydrogenated amorphous silicon (a-Si:H) metal-semiconductor-metal (MSM) devices are investigated as a function of Si bombardment dose prior to and after annealing. We observe that conduction in unbombarded devices is surface-barrier controlled whereas it is bulk controlled in bombarded devices. The resistance decreases with bombardment dose in a manner consistent with increased hopping conductivity in highly damaged structures. A relative permittivity of between 8 and 12, depending on dose, was calculated from experimental Poole-Frenkel plots for bombarded devices. These values compare closely with the theoretical relative permittivity for amorphous silicon of 11.7 and confirm that conduction is by Poole-Frenkel mechanism. For bulk-controlled conduction, we observe an increase in the zero-field Coulombic trap barrier height with decreasing dose, ranging from 0.53 for a Si dose of 5× 1013 cm-2 to 0.89 for a dose of 2× 1012 cm-2. We attribute this to a decrease in the concentration of charged defects with decreasing dose and find that the change in concentration of charged centers needs to be about 4× 1019 cm-3 to account for the change of 0.35 eV from the lower to the upper dose. Activation energies obtained from Arrhenius plots of current density against temperature varied with dose and temperature in a similar way as Coulombic barrier height. We explain these results in terms of the variation in the number of charged defect centers with dose and annealing temperature and a shift in the Fermi level

Raman investigation of damage caused by deep ion implantation in diamond

Raman microscopy has been employed to investigate the nature of damage created when natural type-IIa diamond is irradiated with MeV alpha particles. Three features appear in the Raman spectrum due to damage, viz., (i) the first-order diamond Raman line is broadened and downshifted, (ii) broad features appear which are a measure of the vibrational density of states of ion-beam-amorphized diamond, and (iii) the damage causes the appearance of sharp defect-induced Raman peaks at 1490 and 1630 cm-1. For damage below an amorphization threshold, a linear relationship exists between the full width at half maximum and frequency shift, which shows that these are Kramers-Kronig related. The annealing behavior of the sharp Raman feature at 1490 cm-1 suggests that this peak is associated with vacancies with an activation energy for annealing of 4.06 eV, while the 1630-cm-1 peak is due to an interstitial related defect with an activation energy of 1.2 eV. For sub-MeV ion irradiation, damage beyond the critical amorphization level usually leads to relaxation of the diamond structure to graphite upon thermal annealing. However, for MeV ion irradiation, it was found that annealing, even when the ion induced damage level is well above the amorphization threshold, could restore the original diamond structure. We attribute this result to the high internal pressure the damaged layer is subjected to which does not allow relaxation to graphitically bonded structures

Identification of the point defects in diamond as measured by Raman spectroscopy: comparison between experiment and computation

Raman spectroscopy and molecular dynamics (MD) simulations are used to identify the vibrational spectrum of simple point defects in diamond. Two local mode frequencies are found in ion irradiated diamond. The first (with an energy of 185 meV) is clearly identified as arising from the vacancy defect, whereas a mode at 202 meV is demonstrated to be due to the [100] split interstitial

Diamond-like carbon nanocrystals formed by implanting fused quartz and sapphire (α-Al2O3) with carbon ions

In an attempt to synthesize diamond nanocrystals 1 MeV carbon ions were implanted into fused quartz and sapphire to several different doses and annealed in a furnace at 1100°C for different durations in different annealing ambients. We observe a peak in the optical absorption spectrum at around 5 eV in carbon-implanted quartz and sapphire samples after thermal annealing. We studied the behaviour of the absorption peak as a function of carbon ion dose, annealing time and ambient. Raman spectroscopy using the 514.5 nm line of an argon ion laser was used to elucidate the nature of the chemical bonding in the carbon-implanted samples. Several sharp hitherto unknown Raman peaks are observed in carbon-implanted and annealed sapphire which are consistent with the presence of diamond-like carbon clusters