Assefa Tadesse A, Cao Yue, Banerjee Soham, Kim Sungwon, Kim Dongjin, Lee Heemin, Kim Sunam, Lee Jae Hyuk, Park Sang-Youn, Eom Intae, Park Jaeku, Nam Daewoog, Kim Sangsoo, Chun Sae Hwan, Hyun Hyojung, Kim Kyung Sook, Juhas Pavol, Bozin Emil S, Lu Ming, Song Changyong, Kim Hyunjung, Billinge Simon J L, Robinson Ian K
Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, Upton, NY 11793, USA.
Department of Applied Physics and Applied Mathematics, Columbia University, New York, NY 10027, USA.
Sci Adv. 2020 Jan 17;6(3):eaax2445. doi: 10.1126/sciadv.aax2445. eCollection 2020 Jan.
Melting is a fundamental process of matter that is still not fully understood at the microscopic level. Here, we use time-resolved x-ray diffraction to examine the ultrafast melting of polycrystalline gold thin films using an optical laser pump followed by a delayed hard x-ray probe pulse. We observe the formation of an intermediate new diffraction peak, which we attribute to material trapped between the solid and melted states, that forms 50 ps after laser excitation and persists beyond 500 ps. The peak width grows rapidly for 50 ps and then narrows distinctly at longer time scales. We attribute this to a melting band originating from the grain boundaries and propagating into the grains. Our observation of this intermediate state has implications for the use of ultrafast lasers for ablation during pulsed laser deposition.
熔化是物质的一个基本过程，在微观层面上仍未被完全理解。在这里，我们使用时间分辨X射线衍射来研究多晶金薄膜的超快熔化过程，先用光学激光泵浦，然后用延迟的硬X射线探测脉冲。我们观察到一个中间新衍射峰的形成，我们将其归因于被困在固态和熔化态之间的物质，该峰在激光激发后50皮秒形成，并持续超过500皮秒。峰宽在50皮秒内迅速增加，然后在更长的时间尺度上明显变窄。我们将此归因于起源于晶界并传播到晶粒中的熔化带。我们对这种中间状态的观察对在脉冲激光沉积过程中使用超快激光进行烧蚀具有重要意义。
