Technical Chemistry I and Center for Nanointegration Duisburg-Essen (CENIDE), University of Duisburg-Essen, Universitätsstraße 7, 45141, Essen, Germany.
Sci Rep. 2017 Jan 13;7:40355. doi: 10.1038/srep40355.
Pulsed laser melting in liquid (PLML) has emerged as a facile approach to synthesize submicron spheres (SMSs) for various applications. Typically lasers with long pulse durations in the nanosecond regime are used. However, recent findings show that during melting the energy absorbed by the particle will be dissipated promptly after laser-matter interaction following the temperature decrease within tens of nanoseconds and hence limiting the efficiency of longer pulse widths. Here, the feasibility to utilize a picosecond laser to synthesize Ge SMSs (2001000 nm in diameter) is demonstrated by irradiating polydisperse Ge powders in water and isopropanol. Through analyzing the educt size dependent SMSs formation mechanism, we find that Ge powders (2001000 nm) are directly transformed into SMSs during PLML via reshaping, while comparatively larger powders (1000~2000 nm) are split into daughter SMSs via liquid droplet bisection. Furthermore, the contribution of powders larger than 2000 nm and smaller than 200 nm to form SMSs is discussed. This work shows that compared to nanosecond lasers, picosecond lasers are also suitable to produce SMSs if the pulse duration is longer than the material electron-phonon coupling period to allow thermal relaxation.
脉冲激光在液相中熔化（PLML）已成为一种简便的方法，可用于合成用于各种应用的亚微米级球体（SMSs）。通常使用纳秒级长脉冲持续时间的激光。然而，最近的研究结果表明，在熔化过程中，颗粒吸收的能量会在激光与物质相互作用后迅速耗散，随后在几十纳秒内温度下降，从而限制了更长脉宽的效率。在这里，通过在水中和异丙醇中辐照多分散 Ge 粉末，证明了可以利用皮秒激光来合成 Ge SMSs（直径为 2001000nm）。通过分析反应物尺寸依赖性 SMSs 形成机制，我们发现 Ge 粉末（2001000nm）在 PLML 过程中通过重塑直接转化为 SMSs，而相对较大的粉末（1000~2000nm）通过液滴二分法分裂成子 SMSs。此外，还讨论了大于 2000nm 和小于 200nm 的粉末对形成 SMSs 的贡献。这项工作表明，与纳秒激光相比，如果皮秒激光的脉冲持续时间长于材料电子-声子耦合周期以允许热弛豫，那么皮秒激光也适合于产生 SMSs。
