Ultrafast lasers create new phase of carbon

Conversion of abundant, common carbon into bulk diamond is typically accomplished through volcanic action or laboratory environments at very high temperatures and pressures, while diamond thin films require chemical vapor deposition (CVD) processes at moderate temperatures in the presence of hydrogen. But an alternate method from researchers at North Carolina State University (Raleigh, NC) converts amorphous carbon films to a new state of carbon called Q-carbon through irradiation with a 193 nm argon fluoride (ArF) excimer laser pulse, with photon energy of 6 eV and pulse duration of 20 ns.

After illumination with 0.6 J/cm² pulses from the laser, a variety of different diamond forms is possible depending upon exposure times and pulse frequency, including nanodiamonds, microdiamonds, mixtures of nano- and microdiamonds, and large-area single-crystal diamond thin films on metal/semiconducting epitaxial substrates. Using this nanosecond pulsed laser melting approach, the researchers can also create nano- and microneedle diamonds for biomedical applications. The Q-carbon forms are not only fabricated at ambient temperatures without catalysts or gases, but also have unique chemical properties such as room-temperature ferromagnetism and enhanced hardness, field emission, and electrical conductivity. Reference: J. Narayan and A. Bhaumik, J. Appl. Phys., 118, 21, 215303 (Dec. 2015).