  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.
