NV– diamond laser

For the first time, lasing at NV− centers in an optically pumped diamond sample is achieved. A nanosecond train of 150-ps 532-nm laser pulses was used to pump the sample. The lasing pulses have central wavelength at 720 nm with a spectrum width of 20 nm, 1-ns duration and total energy around 10 nJ. In a pump-probe scheme, we investigate lasing conditions and gain saturation due to NV− ionization and NV0 concentration growth under high-power laser pulse pumping of diamond crystal.

Drilling of Sub-100 μm Hourglass-Shaped Holes in Diamond with Femtosecond Laser Pulses

A Micro holes in a diamond are presented by using a homemade femtosecond (fs) Yb:KGW laser. An fs laser source was used emitting pulse duration of 230 fs at 1030 nm wavelength, whereas the spot size amounted to 8.9 μm. Parameters like pulse energy, and pulse number were varied over a wide range in order to evaluate their influence both on the micro hole geometry like hole diameter, circularity, taper angle, and on the drilling quality. Hourglass-shaped micro holes whose diameters decrease and increase again after a certain depth have important applications. The results demonstrate the feasibility of extending the drilling of an hourglass-shaped hole in a diamond sample, which has similar diameters at the hole entrance (92 μm) and exit (95 μm), but a much smaller diameter (28 μm) at a certain waist section inside the hole.

Investigation of `glitches' in the energy spectrum induced by single-crystal diamond compound X-ray refractive lenses

Single-crystal diamond stands out among all the candidate materials that could be exploited to fabricate compound refractive lenses (CRLs) owing to its extremely stable properties. Among all related experimental features, beam divergence, χ-angles relative to the incoming beam in Eulerian geometry and different positions of the X-ray beam relative to the lens geometry may influence the transmission energy spectrum of CRLs. In addition, the orientation of the single-crystal diamond sample may also affect the glitches significantly. To verify these initial assumptions, two experiments, an energy scan and an ω-scan, were set up by employing a polished diamond plate consisting of five biconcave lenses. The results show that beam divergence does not affect the spectrum, nor do χ-angles when ω is set to zero. Nevertheless, different incident positions have an appreciable effect on the transmission spectrum, in particular the `strengths' of the glitches. This is attributed to absorption. The ω-scan setup is capable of determining the so-called orientation matrix, which may be used to predict both `energy positions' and `strengths' of the glitches.

Instrumental resolution as a function of scattering angle and wavelength as exemplified for the POWGEN instrument

The method of angular- and wavelength-dispersive (e.g.two-dimensional) Rietveld refinement is a new and emerging tool for the analysis of neutron diffraction data measured at time-of-flight instruments with large area detectors. Following the approach for one-dimensional refinements (using either scattering angle or time of flight), the first step at each beam time cycle is the calibration of the instrument including the determination of instrumental contributions to the peak shape variation to be expected for diffraction patterns measured by the users. The aim of this work is to provide the users with calibration files and – for the later Rietveld refinement of the measured data – with an instrumental resolution file (IRF). This article will elaborate on the necessary steps to generate such an IRF for the angular- and wavelength-dispersive case, exemplified for the POWGEN instrument. A dataset measured on a standard diamond sample is used to extract the profile function in the two-dimensional case. It is found that the variation of reflection width with 2θ and λ can be expressed by the standard equation used for evaluating the instrumental resolution, which yields a substantially more fundamental approach to the parameterization of the instrumental contribution to the peak shape. Geometrical considerations of the POWGEN instrument and sample effects lead to values for Δθ, Δtand ΔLthat yield a very good match to the extracted FWHM values. In a final step the refinement results are compared with the one-dimensional,i.e.diffraction-focused, case.

Measurements of Natural and Synthetic Diamond Samples Using Kelvin Probe, Surface Photovoltage and Ambient Pressure Photoemission Techniques

ABSTRACTDiamond is a promising wide band-gap semiconductor material for use in devices; therefore a thorough understanding of the surface electronic structure is important. The Kelvin Probe (KP), Surface Photovoltage / Surface Photovoltage Spectroscopy (SPV/SPS) and Ambient Pressure Photoemission Spectroscopy (APS) techniques are commonly applied to traditional and organic semiconductor materials. The application of these techniques to synthetic and natural diamond samples provides some challenges: surface charge on the samples and atypical capacitive interaction with the KP tip. In this study, measurements using a combination of KP, SPV/SPS and APS techniques are taken of samples of natural and synthetic diamond samples to investigate their surface electronic structure and compare their different properties. These techniques are all non-contact and non-destructive. The Fermi Level position of the diamond samples was found to vary, typically between 4.3 – 4.9 eV, depending on the light illumination. For example, when a natural diamond sample was illuminated with 400 nm light from a 150W Quartz Tungsten Halogen light source, there was a surface photovoltage response of ∼250 mV. The oxygen terminated synthetic diamond sample required near continuous illumination at low visible wavelengths in order to retain sufficient conductivity to allow measurement with the Kelvin Probe. By contrast, the natural diamond samples measured showed good conductivity in the layers underneath the top surface. In summary, the KP, SPV/SPS and APS measurement techniques provided some interesting information on the diamond samples and an initial investigation of their surface electronic states is performed.

Thermo-Chemical Dressing of Coarse Grained Diamond Grinding Wheels

This paper deals with a novel dressing method for coarse grained, single layered metal bonded grinding wheels based on the dynamic friction polishing. The diamond friction polishing technique utilizes the thermo-chemical reaction between a diamond sample and a metal tool rotating at high speed. Here, the tips of the diamond grains of a rapidly rotating grinding wheel are thermo-chemically flattened due to the contact with two slowly rotating steel calottes at predetermined friction pressure pd and grinding wheel velocity vsd. Dressing experiments have been carried out changing the friction pressure pd and the grinding wheel velocity vsd. The generated topography of the grinding wheel has been characterized by a confocal laser scanning microscope. Thus, the flattened grains with an average grain protrusion hk could be measured and the influence of the friction pressure and grinding wheel velocity on the dressing process is shown.

Effect of Growth Parameters on Single Crystal Diamond Deposition by DC Arc Plasma Jet CVD

Homoepitaxial diamond layers were grown on commercial 3.5 x 3.5 x 1.2 mm3 HPHT synthetic type Ib (100) single crystal diamond plates using a DC Arc Plasma Jet CVD operating at gas recycling mode. The effects of substrate temperature and CH4/H2 ratio on the surface morphology, the growth rate and the quality of the synthesized diamond have been studied using optical microscopy and Raman spectroscopy. With no intentional nitrogen added, the growth rate up to 12.3µm/h has been obtained in the single crystal diamond sample deposited at 1000 °C with CH4/H2=0.625%, exhibiting relatively smooth surface morphology without any growth hillocks nor non-epitaxial crystallites, and presenting the typical feature of the epitaxial step-flow growth. The full width at half maximum (FWHM) of the Raman spectra was 2.08 cm-1, which was close to that of the natural type IIa single crystal diamond.