Contamination of TEM Holders Quantified and Mitigated with Open-Hardware, High-Vacuum Bakeout System

TL;DR

This paper introduces an open-hardware high-vacuum system for TEM holders that significantly reduces hydrocarbon contamination and improves vacuum conditions, enhancing high-resolution electron microscopy.

Contribution

The authors present a novel open-source high-vacuum manifold with bakeout capabilities for TEM holders, effectively reducing contaminants and enabling cleaner, more reliable microscopy experiments.

Findings

Overnight storage reduces contaminants by 10-100 times.

Bakeout lowers contaminant pressure below 10^-10 Torr.

Bakeout of loaded TEM holders is the most effective cleaning method.

Abstract

Hydrocarbon contamination plagues high-resolution and analytical electron microscopy by depositing carbonaceous layers onto surfaces during electron irradiation, which can render carefully prepared specimens useless. Increased specimen thickness degrades resolution with beam broadening alongside loss of contrast. The large inelastic cross-section of carbon hampers accurate atomic species detection. Oxygen and water molecules pose problems of lattice damage by chemically etching the specimen during imaging. These constraints on high-resolution and spectroscopic imaging demand clean, high-vacuum microscopes with dry pumps. Here, we present an open-hardware design of a high-vacuum manifold for transmission electron microscopy (TEM) holders to mitigate hydrocarbon and residual species exposure. We quantitatively show that TEM holders are inherently dirty and introduce a range of unwanted chemical species. Overnight storage in our manifold reduces contaminants by 1-2 orders of magnitude and promotes 2-4 times faster vacuum recovery. A built-in bakeout system further reduces contaminants partial pressure to below $10^{-10}$ Torr (~4 orders of magnitude down from ambient storage) and alleviates monolayer adsorption during a typical TEM experiment. We determine that bakeout of TEM holder with specimen held therein is the optimal cleaning method. Our high-vacuum manifold design is published with open-source blueprints, parts list, and cost.