Vibrational Spectroscopy of Water with High Spatial Resolution

Abstract

The ability to examine the vibrational spectra of liquids with nanometer spatial resolution will greatly expand the potential to study liquids and liquid interfaces. In fact, the fundamental properties of water, including complexities in its phase diagram, electrochemistry, and bonding due to nanoscale confinement are current research topics. For any liquid, direct investigation of ordered liquid structures, interfacial double layers, and adsorbed species at liquid-solid interfaces are of interest. Here, a novel way of characterizing the vibrational properties of liquid water with high spatial resolution using transmission electron microscopy is reported. By encapsulating water between two sheets of boron nitride, the ability to capture vibrational spectra to quantify the structure of the liquid, its interaction with the liquid-cell surfaces, and the ability to identify isotopes including H O and D O using electron energy-loss spectroscopy is demonstrated. The electron microscope used here, equipped with a high-energy-resolution monochromator, is able to record vibrational spectra of liquids and molecules and is sensitive to surface and bulk morphological properties both at the nano- and micrometer scales. These results represent an important milestone for liquid and isotope-labeled materials characterization with high spatial resolution, combining nanoscale imaging with vibrational spectroscopy.

Vibrational electron energy loss spectroscopy in truncated dielectric slabs

“…Recent instrumentation advances in electron energy loss spectroscopy (EELS) in the scanning transmission electron microscope (STEM) 1 have made it possible to record energy losses in the infrared (IR) energy range. 2 These developments have stimulated both experimental and theoretical investigations of the vibrational response of various organic [3][4][5] and inorganic [6][7][8][9][10] compounds probed locally by a tightly focused electron beam.…”

“…In such an arrangement, one can avoid radiation damage caused by direct electron beam penetration, which is especially crucial for organic and other radiation sensitive samples. 3,10,22,23 The long-range interaction contributing to the EEL signal can be even more pronounced, when the beam interacts with samples supporting collective polaritonic excitations, such as plasmons or optical phonons strongly coupled with electromagnetic waves (volume and surface plasmon polaritons and phonon polaritons, respectively 24,25 ). Analogously to EELS studies of plasmon polariton excitations in the visible spectral range, [26][27][28][29][30] spatially-resolved EELS characterization of propagating 8 or localized 7 phonon polaritons has been recently performed in the IR spectral range, showing a slow spatial intensity decay of polaritonic losses as a function of the electron beam distance to the sample.…”

Liquid-Phase STEM-EDS in Graphene and Silicon Nitride Cells

“…LP-STEM EELS and EDS provide a means to study the physical and chemical properties of the liquid layer, giving insight into local thickness variations, solution chemistry and effects resulting from the electron beam's interaction with the liquid [4]- [6]. By accurate measurement of these parameters it should be possible to account for the artefacts they produce in both imaging and spectroscopy techniques in order to achieve meaningful quantitative information [7].…”

Damage-Free Nanoscale Isotopic Analysis of Biological Materials with Vibrational Electron Spectroscopy

“…Moreover, at these low energies the vibrational EELS can be acquired in 'aloof' mode where the beam is positioned 10s of nm away from the sample and the interactions are carried through the evanescent field of fast electrons [3]. As a result, the vibrational response of organic materials can now be accessed with high spatial resolution in the STEM, which is enabled by the ability to collect aloof EELS with a high signal-to-noise ratio and without directly irradiating the sample [4].…”