Real-Time Compositional Monitoring of Sputtered Li₃PO₄ Electrolyte Films via In Situ Optical Emission Spectroscopy.

Area of Science:

• Materials Science
• Electrochemistry
• Analytical Chemistry

Background:

• Lithium phosphate (Li₃PO₄) is vital for all-solid-state thin-film batteries.
• Precise compositional control of Li₃PO₄ films is critical for ionic conductivity.
• Sputtering is a high-throughput method for film deposition, but requires strict stoichiometry management.

Purpose of the Study:

• To implement optical emission spectroscopy (OES) for real-time compositional analysis of Li₃PO₄ films during sputtering.
• To establish correlations between OES spectral line intensities and film stoichiometry.
• To demonstrate a method for in situ process control in thin-film battery manufacturing.

Main Methods:

• Utilized optical emission spectroscopy (OES) for real-time monitoring.
• Acquired emission spectra under varying sputtering powers (20-40 W) and pressures (1-5 Pa).
• Correlated OES data with atomic ratios from inductively coupled plasma mass spectrometry (ICP-MS) and field-emission electron probe microanalysis (FE-EPMA).

Main Results:

• Identified strong correlations between specific atomic emission lines (Li I, P I, O I) and film composition (e.g., P I 253.5 nm vs. O I 777.3 nm, R²=0.977).
• Demonstrated that selected emission line pairs show identical input power dependence, serving as a validation criterion.
• Confirmed the suitability of OES for in situ monitoring of Li- and P-containing films.

Conclusions:

• Optical emission spectroscopy provides a viable method for real-time compositional control of Li₃PO₄ films during sputtering.
• This technique is essential for achieving the precise stoichiometry needed for high-performance solid-state batteries.
• Offers a promising pathway for advanced process control in thin-film battery fabrication.