Joseph

LaiHe/His

Decades of measurements of the thermophysical properties of hot metals show that pulsed Joule heating is an effective method to heat solid and liquid metals that are chemically reactive or difficult to contain. To extend such measurements to hundreds of GPa pressure, pulsed heating methods have recently been integrated with diamond anvil cells. The recent design used a low-side switch and active electrical sensing equipment that was prone to damage and measurement error. Here, we report the design and characterization of new electronics that use a high-side switch and robust, passive electrical sensing equipment. The new pulse amplifier can heat similar to 5 to 50 mu m diameter metal wires to thousands of kelvin at tens to hundreds of GPa using diamond anvil cells. Pulse durations and peak currents can each be varied over three orders of magnitude, from 5 mu s to 10 ms and from 0.2 to 200 A. The pulse amplifier is integrated with a current probe. Two voltage probes attached to the body of a diamond anvil cell are used to measure voltage in a four-point probe geometry. The accuracy of four-point probe resistance measurements for a dummy sample with 0.1 Omega resistance is typically better than 5% at all times from 2 mu s to 10 ms after the beginning of the pulse.

Decades of measurements of the thermophysical properties of hot metals show that pulsed Joule heating is an effective method to heat solid and liquid metals that are chemically reactive or difficult to contain. To extend such measurements to hundreds of GPa pressure, pulsed heating methods have recently been integrated with diamond anvil cells. The recent design used a low-side switch and active electrical sensing equipment that was prone to damage and measurement error. Here, we report the design and characterization of new electronics that use a high-side switch and robust, passive electrical sensing equipment. The new pulse amplifier can heat 5 to 50 mum diameter metal wires to thousands of kelvin at tens to hundreds of GPa using diamond anvil cells. Pulse durations and peak currents can each be varied over three orders of magnitude, from 5 s to 10ms and from 0.2 to 200A. The pulse amplifier is integrated with a current probe. Two voltage probes attached to the body of a diamond anvil cell are used to measure voltage in a four-point probe geometry. The accuracy of four-point probe resistance measurements for a dummy sample with 0.1 Omega resistance is typically better than 5% at all times from 2 s to 10ms after the beginning of the pulse.

A 75 kW, 915 MHz microwave plasma-assisted chemical vapor deposition system was adapted and utilized to scale up production of high-quality single-crystal diamonds at high growth rates. A 300 mm diameter plasma discharge was achieved with uniform temperature distributions of +/- 250 degrees C on up to 300 single-crystal diamond substrates. Diamond single crystals were synthesized from H-2/CH4/N-2 gas mixtures at pressures between 90 and 180 Torr, with recorded growth rates from 10 to 30 mu m/h. The source of N-2 was from vacuum chamber leakage, and it greatly affected synthesis chemistry. Optical emission spectroscopy was used to probe the localized plasma chemistry and plasma uniformity at different gas pressures. Production rates of up to 100 g/day of single-crystal diamonds were demonstrated, with 25% of the material categorized as colorless. Crystals up to 3.5 mm in thickness could be produced during a single deposition run. The quality of the crystals produced was assessed by photoluminescence and UV-visible absorption spectroscopies.

Single crystal diamond synthesis by microwave plasma chemical vapor deposition at rapid growth rate has considerably advanced in the past few years. Developments have been made in growth, optical quality, and mechanical properties. Of the various types of single crystal diamond that can be produced using these techniques, high quality single crystal CVD diamond can be routinely produced, and this material is playing an increasing role in research on materials under extreme conditions. This article highlights recent developments in single crystal CVD diamond synthesis and characterization, as well as various applications in high-pressure materials research.

Small-angle X-ray scattering (SAXS) was performed on single-crystal chemical vapor deposition (CVD) diamonds with low nitrogen concentrations, which were fabricated by microwave plasma-assisted chemical vapor deposition at high growth rates. High optical quality undoped 500 mm-thick single-crystal CVD diamonds grown without intentional nitrogen addition proved to be excellent as windows on SAXS cells, yielding parasitic scattering no more intense than a 7.5 mm-thick Kapton film. A single-crystal CVD diamond window was successfully used in a high-pressure SAXS cell.