Germanium Sub-Microspheres Synthesized by Picosecond Pulsed Laser Melting in Liquids: Educt Size Effects

Abstract

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 (200~1000 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 (200~1000 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.

Directional Scattering in a Germanium Nanosphere in the Visible Light Region

“…Besides, as shown in Figure f, the X‐ray diffraction (XRD) pattern with clear, shaped, strong peaks also indicates that Ge nanospheres have good crystallinity. These peaks are consistent with cubic structure (Fd3m) of Ge . Raman spectroscopy is commonly used to provide a fingerprint of the compound.…”

Ultrasmall Yttrium Iron Garnet Nanoparticles with High Coercivity at Low Temperature Synthesized by Laser Ablation and Fragmentation of Pressed Powders

“…Laser ablation synthesis and fragmentation of colloids has emerged as as ynthesis route that combines ah igh level of versatility [1][2][3] with manufacturing flexibility. [4,5] This flexibility is not only related to the flexible designs pace consisting of laser parameters, [6] liquid properties, [7] and target composition, [6] but also to target shape [8] and target assembly.…”

Recent Advances in Surfactant‐Free, Surface‐Charged, and Defect‐Rich Catalysts Developed by Laser Ablation and Processing in Liquids

“…LML is a technique that allows particle fusion to evolve into submicrospheres (SMSs) [66] and enables the particle/powder to be reshaped into SMSs . The mechanisms for LML have been summarized in ref.…”

“…The selectable educt of LML includes LAL‐synthesized colloids, Chem NPs, or microscale powders . It is often considered that NP agglomeration is a prerequisite to achieve SMSs by LML, but the groups of Gökce and Liang showed that laser irradiation of nanocolloids in liquids can directly trigger particle growth without the need for particle agglomeration pretreatment. This phenomenon should benefit from the formation of laser‐induced bubbles and subsequent bubble‐collapse‐induced shockwaves, which push the particles into agglomeration .…”

“…Nanosecond lasers are often used for LML owing to the instinctive heating effect, but recently Zhang et al. demonstrated the possibility of synthesizing germanium SMSs by using a picosecond laser (10 ps) . This work indicates that picosecond lasers are also suitable for LML if the pulse duration is longer than that of the electron–phonon coupling time of the irradiated materials (5 ps for Ge).…”