Morphological control of nanostructured Ge films in high Ar-gas-pressure plasma sputtering process for Li ion batteries

Abstract

We present a study on morphological control of nanostructured Ge films by the Ar gas pressure in plasma sputtering deposition. In the low Ar-gas-pressure range, aggregated islands of amorphous grains are formed on the film surface, while in the high-pressure range of 500 mTorr monodisperse nano-grains of about 30 nm in size are orderly arranged without aggregation. The film porosity shows a high value of over 10%. We tested the charge/discharge cycle performance of Li-ion batteries with nanostructured Ge films as anodes. The battery cell with an ordered arrangement structure maintained a high capacity of 434 mAh g−1 after 40 charge/discharge cycles, while that with an aggregated structure exhibited a rapid degradation of capacity to 5.08–183 mAh g−1. An ordered arrangement of Ge nano-grains with a high porosity, which is realized in a simple one-step procedure using high Ar-gas-pressure plasma sputtering, is effective for the stable cycling of high-capacity metal anodes.

Low-Temperature and High-Speed Fabrication of Nanocrystalline Ge Films on Cu Substrates Using Sub-Torr-Pressure Plasma Sputtering

“…The shorter target-substrate distance leads to the larger amount of highly reactive Ge atoms impinging to the substrate surface, which results in the rapid growth of grains on the substrate and the high deposition rate. On the other hand, at high pressures such as 0.5 Torr, Ge nanoparticles could be synthesized in a gas-phase plasma because a higher-density plasma is produced locally in front of the cathode sputtering target [1], [14]. The shorter collision mean free path for Ge species would cause nucleation of nanograins in the gas phase [12], [15].…”

“…The Ge films were fabricated on an n-type Si wafer and Cu disk using 13.56 MHz radio-frequency (RF) magnetron sputtering, as schematically shown in Fig. 1 [14]. The diameter and thickness of the Cu disk were 15 mm and 80 µm, respectively.…”

Single-step fabrication of fibrous Si/Sn composite nanowire anodes by high-pressure He plasma sputtering for high-capacity Li-ion batteries

“…Some of the following explanations of methods overlap with descriptions in our previous papers 68,69 . The Si anode films were fabricated on a Cu disk using 13.56 MHz radiofrequency (rf) magnetron sputtering.…”

Fabrication of amorphous LiPON, LiAlGePO, and GeSn films in low-temperature plasma sputtering process for all-solid-state Li+-ion battery

“…1 in Ref. 34), and the sputtering target was changed from Ge to a GeSn (6 at%) disk 1 inch in diameter in the present study. The rf input power was varied at 3.94 (20 W) and 11.8 W cm −2 (60 W), where the Ar gas pressure was 500 mTorr, the target-substrate distance was 20 mm, and substrate was not heated or cooled.…”

“…22,32,33) We have already successfully generated a dispersed arrangement of monodisperse nanograins without aggregation using an Ar high-pressure plasma process in the sub-Torr range. 34,35) In the present study, we used Ar highpressure sputtering to fabricate GeSn nanomaterials for Li + -ion battery anodes.…”