Pulsed Laser Porosification of Silicon Thin Films

Abstract

We present a new and simple laser-based process to porosify thin film silicon using a pulsed laser. During deposition, we incorporate gas atoms or molecules into the Si thin film. Pulsed laser radiation of wavelength λ=5324ptnm heats up thin film Si beyond its melting point. Upon heating, gas atoms or molecules form nm-sized thermally expanding gas bubbles in the silicon melt, until they explosively exit the film, leaving pores behind. Rapid heating and fast cooling during pulsed laser processing enable re-solidification of the liquid Si before the created pores contract and pore closure occurs within the liquid phase. Optimized plasma-enhanced chemical vapor deposition or sputtering of amorphous Si thin films on stainless steel substrate incorporates the necessary concentration of gas atoms or molecules. We are able to tailor the pore size between 50 and 550 nm by changing laser pulse energy density and film deposition parameters. Evaporated silicon containing no gas atoms forms only a few very large μm-sized gas bubbles due to laser-induced vapor formation of evaporated solid material at the substrate–silicon interface.

Position-controlled laser-induced creation of rutile TiO2 nanostructures

“…As soon as the silicon melts, the absorption increases even faster causing a melting catastrophe leaving bubbles, tubes, and holes behind as demonstrated in figure 4. These structures prevent the creation of highly ordered crystallized TiO 2 on the surface and are a clear sign that a significant amount of silicon was molten [37].…”

A Rapid, Scalable Laser‐Scribing Process to Prepare Si/Graphene Composites for Lithium‐Ion Batteries

“…[41,45] Recent progress in laser processing of silicon-based materials for LIBs includes laser drying of electrode films, ultrafast laser ablation to create grid-structured silicon films, laser porosification of silicon thin films, and laser conversion of commercial silicone-based adhesive tapes to silicon oxide thin films. [46][47][48][49][50][51][52][53][54][55] Although the synthesis processes and battery performance such as rate capability have been improved, poor cycle life remains as a serious issue.…”

Laser Porosificated Silicon Anodes for Lithium Ion Batteries

“…In our previous study, we proved laser induced crystallization of the Si thin films during porosification by Raman spectroscopy. [31] Hence, plain Si is amorphous and porous Si is crystalline before the galvanostatic cycling. An initial lithiation and delithiation of the Si electrode once at C/20 current rate followed by one cycle at C/5 rate serve as formation of the silicon electrode using C charge = 932 mAh g −1 as rated capacity.…”

“…After the deposition, a laser porosification process uses the incorporated Ar as source for pore creation in the thin film. [31] Figure 1a-c schematically presents the Si anodes manufacturing steps. Figure 1a shows the laser porosification process.…”