Si1-xGex anode synthesis on plastic films for flexible rechargeable batteries

SiGe is a promising anode material for replacing graphite in next generation thin-film batteries owing to its high theoretical charge/discharge capacity. Metal-induced layer exchange (LE) is a unique technique used for the low-temperature synthesis of SiGe layers on arbitrary substrates. Here, we demonstrate the synthesis of Si_1-xGe_x (x = 0-1) layers on plastic films using Al-induced LE. The resulting SiGe layers exhibited high electrical conductivity (up to 1200 S cm^-1), reflecting the self-organized doping effect of LE. Moreover, the Si_1-xGe_x layer synthesized by the same process was adopted as the anode for the lithium-ion battery. All Si_1-xGe_x anodes showed clear charge/discharge operation and high coulombic efficiency (≥ 97%) after 100 cycles. While the discharge capacities almost reflected the theoretical values at each x at 0.1 C, the capacity degradation with increasing current rate strongly depended on x. Si-rich samples exhibited high initial capacity and low capacity retention, while Ge-rich samples showed contrasting characteristics. In particular, the Si_1-xGe_x layers with x ≥ 0.8 showed excellent current rate performance owing to their high electrical conductivity and low volume expansion, maintaining a high capacity (> 500 mAh g^-1) even at a high current rate (10 C). Thus, we revealed the relationship between SiGe composition and anode characteristics for the SiGe layers formed by LE at low temperatures. These results will pave the way for the next generation of flexible batteries based on SiGe anodes.

Impact of the carbon membrane inserted below Ni in the layer exchange of multilayer graphene

High-quality multilayer graphene on glass is achieved at a low temperature (400 °C).

Fabrication of SrGe2 thin films on Ge (100), (110), and (111) substrates

Semiconductor strontium digermanide (SrGe₂) has a large absorption coefficient in the near-infrared light region and is expected to be useful for multijunction solar cells. This study firstly demonstrates the formation of SrGe₂ thin films via a reactive deposition epitaxy on Ge substrates. The growth morphology of SrGe₂ dramatically changed depending on the growth temperature (300-700 °C) and the crystal orientation of the Ge substrate. We succeeded in obtaining single-oriented SrGe₂ using a Ge (110) substrate at 500 °C. Development on Si or glass substrates will lead to the application of SrGe₂ to high-efficiency thin-film solar cells.

Self-organization of Ge(111)/Al/glass structures through layer exchange in metal-induced crystallization

Al-induced crystallization enabled the self-organization of high-quality Ge/Al/glass structures through layer exchange at a low temperature of 325 °C.