Emissivity of freestanding membranes with thin metal coatings

TL;DR

This paper demonstrates that adding ultra-thin metal coatings to freestanding silicon nitride membranes significantly enhances their emissivity, thereby improving their heat dissipation capabilities in vacuum environments, which is crucial for their application as TEM windows and X-ray filters.

Contribution

It introduces a method of using approximately 1 nm thick metal layers to substantially increase the emissivity of ultrathin membranes, aligning experimental results with classical scattering theory.

Findings

Emissivity of membranes increases by 100 to 300 times with metal coatings.

Enhanced emissivity improves thermal load capacity in vacuum environments.

Experimental results agree with adapted classical scattering models.

Abstract

Freestanding silicon nitride membranes with thicknesses down to a few tens of nanometers find use as TEM windows or soft X-ray spectral purity filters. As the thickness of a membrane decreases, emissivity vanishes, which limits radiative heat emission and resistance to heat loads. We show that thin metal layers with thicknesses in the order of 1 nm enhance the emissivity of thin membranes by two to three orders of magnitude close to the theoretical limit of 0.5. This considerably increases thermal load capacity of membranes in vacuum environments. Our experimental results are in line with classical theory in which we adapt thickness dependent scattering terms in the Drude and Lorentz oscillators.