Imagine trying to photograph a soap bubble with a blast of radiation: the picture might be sharp, but the subject vanishes first. That is the problem researchers face with these promising, fragile materials. These porous crystal materials are promising for gas storage and separation, energy storage and conversion, chemical sensing, water adsorption, and lithium-ion storage.

Their usefulness depends on structure–activity relationships: how a material’s detailed structure controls what it can do. Atomic-scale determination of the crystal structures is a prerequisite for understanding those relationships. Surfaces, interfaces, defects, and guest species directly affect the properties of these materials, while growth and transformation under working conditions also matter.

But using electron microscopy is challenging because these materials are extremely sensitive to electron-beam irradiation. That sensitivity comes from their organic components and the bonds linking organic parts to metals, so the structure can decompose before detection is complete.

Several advanced approaches were developed for beam-sensitive materials, including three-dimensional diffraction, more sensitive cameras, and imaging that records weak signals. The central idea is simple: reduce the electron dose, since beam damage in MOFs depends on dose regardless of the damage mechanism.

Shorter exposure times and lower beam intensity can achieve low electron doses, the practical settings used to reduce irradiation during TEM measurements. Before imaging, assess whether the low-dose conditions remain acceptable so the material’s crystallinity stays stable instead of disappearing under the beam.

A preliminary assessment determines whether the low-dose conditions preserve the crystal structure. Electron diffraction helps measure how much exposure the material can withstand, because its pattern changes as damage appears. Watching a material change in real time requires longer irradiation, so these observations need an electron dose well below the damage threshold.

Three-dimensional electron diffraction collects diffraction patterns from a single crystal at different tilt angles. Those patterns produce diffraction peaks that can be used for structure determination and analysis. The data collection has evolved from stepwise methods to faster continuous strategies.

In liquid, chemical interactions generate many tiny intermediates that quickly reach an equilibrium. By directly visualizing their nucleation, growth, and self-assembly dynamics, in situ liquid-cell electron microscopy provides insight into how these materials are synthesized in solution.

In liquid-cell TEM, the contrast, morphology, and growth behavior of MOFs can directly reveal liquid-phase synthesis conditions and underlying mechanisms. Those synthesis conditions—including concentration, temperature, and node-to-linker ratio—can later be checked and verified by ex situ TEM as well.

Freezing the material preserves a direct glimpse of what is normally hidden: gas molecules sit inside the framework’s tiny repeating spaces, while protein-grown versions can contain both ordered regions and disordered patches. That makes the method a way to connect atomic structure with how these materials form and function.

The review’s central finding is that advanced electron microscopy is overcoming the limits imposed by beam damage, using low electron dose and low temperature to protect structural integrity. These advances reveal surfaces, interfaces, defects, and interactions between the framework and the things inside it.

They also make it possible to study formation, phase changes, pore breathing, and structural modification caused by electron irradiation. These real-time images reveal that the structures do not appear all at once: small groups first gather in solution, then organize, and finally lock into an ordered solid.

That makes the hidden, step-by-step birth of these materials visible. Future improvements may reveal details that current methods cannot observe, including the atomic-scale structure of a framework together with the species inside it. Other developing approaches may also provide information about stress, strain, and electric and magnetic fields, in addition to structure.

For people who depend on better storage, sensing, separation, or energy materials, the practical promise is a clearer path from what a material looks like to what it can do. Advanced electron microscopy is making it possible to inspect these porous materials without destroying them, and even watch them form and change.

That can help connect their tiny structures to uses in storage, sensing, separation, and energy.