Cryogenic transmission electron microscopy (cryo-TEM) has become a powerful tool for probing the structures of soft-matter materials at nanometer or sub-nanometer scale. For many complex molecular fluids (CMFs), the limiting factor in such studies is the preparation of a cryo-TEM specimen that represents the native structure. Plunge freezing of electron-transparent thin films has been widely used, but it is often influenced or even dominated by surface effects and mechanical disturbances of the CMF. In this article, we use liquid crystals as model CMF systems and present the general procedures and typical results of cryo-ultramicrotomy of rapidly frozen “bulk” samples.

Lithium sulfur (Li–S) batteries have the potential to provide higher energy storage density at lower cost than conventional lithium ion batteries. A key challenge for Li–S batteries is the loss of sulfur to the electrolyte during cycling. This loss can be mitigated by sequestering the sulfur in nanostructured carbon–sulfur composites. The nanoscale characterization of the sulfur distribution within these complex nanostructured electrodes is normally performed by electron microscopy, but sulfur sublimates and redistributes in the high-vacuum conditions of conventional electron microscopes. The resulting sublimation artifacts render characterization of sulfur in conventional electron microscopes problematic and unreliable. Here, we demonstrate two techniques, cryogenic transmission electron microscopy (cryo-TEM) and scanning electron microscopy in air (airSEM), that enable the reliable characterization of sulfur across multiple length scales by suppressing sulfur sublimation. We use cryo-TEM and airSEM to examine carbon–sulfur composites synthesized for use as Li–S battery cathodes, noting several cases where the commonly employed sulfur melt infusion method is highly inefficient at infiltrating sulfur into porous carbon hosts.

Direct imaging of nanoscale objects suspended in liquid media can be accomplished using cryogenic transmission electron microscopy (cryo-TEM). Cryo-TEM has been used with particular success in microbiology and other biological fields. Samples are prepared by plunging a thin film of sample into an appropriate cryogen, which essentially produces a snapshot of the suspended objects in their liquid medium. With successful sample preparation, cryo-TEM images can facilitate elucidation of aggregation and self-assembly, as well as provide detailed information about cells and viruses. This work provides an explanation of sample preparation, detailed examples of the many artifacts found in cryo-TEM of aqueous samples, and other key considerations for successful cryo-TEM imaging.

It has been shown, by imaging gold (200) planes, that it is possible to achieve better than 0.20-nm structural resolution in cryo-transmission electron microscopy (cryo-TEM). This has been done using commercially available cryo equipment and using a 300-kV field emission gun (FEG) TEM. The images of 15-nm gold particles embedded in amorphous frozen water clearly show the (111) planes (separated by 0.235 nm) in gold. Fourier transform demonstrates the presence of (200) planes in the image, proving a resolution of better than 0.20 nm. The experimental results are supported by image simulations using the multislice method. These simulations suggest that it should be possible to achieve the same resolution even in smaller particles and particles of lighter elements. The crucial experimental problem to overcome is keeping the thickness of the amorphous film low and to work at low electron dose conditions.