Nanosecond resolution time-resolved x-ray study of silicon during pulsed-laser irradiation

Abstract

We have used the pulsed time structure of the Cornell High-Energy Synchrotron Source (CHESS) to carry out a nanosecond resolution time-resolved x-ray study of silicon during pulsed-laser irradiation. Time-resolved temperature distributions and interfacial overheating and undercooling were measured on 〈111〉 and 〈100〉 silicon during 25 ns UV laser pulses through the analysis of thermal expansion induced strain. The temperature gradients were found to be > 107 K/cm at the liquid-solid interface and the temperature distributions have been shown to be in agreement with numerical heat flow calculations for these laser conditions. The combined overheating and undercooling (during ∼ 10 m/s melting and ∼ 6 m/s regrowth) was measured to be 110 ± 30 K on 〈111〉 oriented silicon and 50 ± 25 K on 〈100〉 silicon. These values have been interpreted in terms of velocity coefficients of overheating and undercooling.

A ballistic-diffusive heat conduction model extracted from Boltzmann transport equation

“…The variations of q * | x * =0 with respect to the time which are obtained from equation (5.6), the ballistic-diffusive equations (Chen 2001(Chen , 2002 and the Fourier law, are displayed in figure 2 (the horizontal axis is for the logarithm of time to base 10) for the case Kn = 10.0. One can see that the non-dimensional heat flux at the boundary x * = 0 expressed by equation (5.6) is lower than the result obtained by the classical heat conduction equation, which agrees with the experimental observation (Larson et al 1986). In comparison with the result obtained by Chen (2001Chen ( , 2002, our result is larger at earlier time and smaller at later time.…”

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

“…The undercooling was also found to be orientation and regrowth velocity dependent: ∼5 K/m s on (100)Ge and ∼20 K/m s on (111)Ge. 23,24 Basharin et al 16 have estimated the temperature dependence of Gibbs free energy of graphite, metastable liquid carbon and diamond at a low pressure of 120 MPa of helium and found that free energy of liquid carbon can be equal to that of diamond at 4160 ± 50 K, which is considerably lower than melting point of liquid graphite, at a pressure of 120 MPa of helium. 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.…”

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“…Undercooling during nanosecond laser (KrF laser λ = 0.248 µm) melting has been measured in crystalline Ge and Si using nanosecond resolution time-resolved x-ray diffraction in a synchrotron. 25,26 These results showed undercooling as high as 110 ± 30 K on (111) Si during ∼10 ms −1 melting and ∼6 ms −1 regrowth velocity. Thus, the undercooling is crystalline Ge and Si is roughly half that predicted theoretically for amorphous Ge and Si.…”