Bonding in Liquid Carbon Studied by Time-Resolved X-Ray Absorption Spectroscopy

Abstract

Even the most basic properties of liquid carbon have long been debated due to the challenge of studying the material at the required high temperature and pressure. Liquid carbon is volatile and thus inherently transient in an unconstrained environment. In this paper we use a new technique of picosecond time-resolved x-ray absorption spectroscopy to study the bonding of liquid carbon at densities near that of the solid. As the density of the liquid increases, we see a change from predominantly sp-bonded atomic sites to a mixture of sp, sp2, and sp3 sites and compare these observations with molecular dynamics simulations.

Probing the hydrogen-bond network of water via time-resolved soft X-ray spectroscopy

“…A possible explanation is that the silicon nitride windows may act as tamping layers, thereby slowing down the expansion dynamics. 64 Other experiments monitored water expansion by interferometric surface height changes upon overtone excitation of water vibrations and found water to expand on multiple timescales ranging from nano-to microseconds 65 . We can exclude cooling of the excited sample volume on nanosecond timescales because the thermal diffusivity of neither water nor the window material (silicon nitride) is large enough to allow heat to be dissipated faster than on micro-to millisecond timescales.…”

Direct synthesis of sp-bonded carbon chains on graphite surface by femtosecond laser irradiation

“…13 According to the thermal diffusion length l = ͑D a ͒ 1/2 , where D Ϸ͑1/3͒ F 2 is the thermal diffusivity, is electron relaxation time, a = M ion / M e electron-lattice interaction time, and F =8ϫ 10 5 m / s the Fermi velocity. Assuming = 2 fs, 24 one can deduce l = 134 nm, in good harmony with experimental value of 139 nm.…”

“…11,22 Different SERS modes dependent on the laser intensity agree with theoretical calculation and experiments showing that bonding in liquid carbon progresses from sp to sp 3 with increasing liquid density. 23,24 In the crater, the incident fluence is so strong that the thermal effect significantly results in much liquid ͑evident in Fig. 1͒.…”

Research Update: Direct conversion of amorphous carbon into diamond at ambient pressures and temperatures in air

“…Thus, it is possible that diamond can be nucleated from super undercooled state at 4160 K. However, Basharin et al 17 tried to quench diamond using 1-ms pulsed laser melting (wavelength of λ = 1.06 µm and a power of 10 kW) of HOPG graphite with limited success due to lower undercooling with 1 ms lasers on a crystalline graphite substrate. 16,17 Bonding and structure of liquid carbon have been studied using time-resolved x-ray absorption spectroscopy 25 and results compared with first-principles molecular dynamics simulations. 26 These results suggest that local bonding structure of the liquid can be varied from a mixture of twofold and threefold coordinated atoms at low density (1.27 g cm −3 ) to fourfold coordinated atoms at high density (3.02 g cm −3 ).…”