Soft X-ray radiation-damage studies in PMMA using a cryo-STXM

Area of Science:

• Materials Science
• Radiation Physics
• Spectroscopy

Background:

• Ionizing radiation studies are limited by material damage.
• Cryo-methods can mitigate radiation damage.
• Poly(methylmethacrylate) (PMMA) is a model polymer for radiation studies.

Purpose of the Study:

• To quantify mass loss and C=O bond density changes in PMMA films under varying radiation doses and temperatures.
• To compare the effectiveness of cryo-methods versus room temperature studies in preserving PMMA.
• To determine the critical dose for C=O bond breaking in PMMA.

Main Methods:

• Thin films of PMMA were studied under vacuum.
• Oxygen-edge X-ray absorption near edge structure (XANES), also known as near-edge X-ray fine structure (NEXAFS) spectroscopy, was used to measure C=O bond density.
• Mass loss was measured at different radiation doses.
• Experiments were conducted at both room temperature (298 K) and cryogenic temperature (113 K).

Main Results:

• Cryo-methods preserved over 95% of PMMA mass at doses up to 10^7 Gy.
• No significant difference in C=O bond density decrease was observed between 298 K and 113 K sample temperatures.
• The critical dose for C=O bond breaking was approximately 15 x 10^6 Gy at both temperatures.

Conclusions:

• While cryo-methods significantly reduce mass loss in PMMA during irradiation, they do not substantially alter the dose-dependent decrease in C=O bond density.
• The fundamental limit for C=O bond breaking in PMMA is reached at a critical dose of approximately 15 x 10^6 Gy, irrespective of temperature (298 K vs. 113 K).
• These findings highlight the specific benefits of cryo-methods for mass preservation but indicate that chemical bond stability is less temperature-dependent within this range.