Diamond collaboration observes 2D water behaviour

New research conducted on Diamond’s B22 MIRIAM beamline in the Soft Condensed Matter science group, has revealed how water behaves differently when confined to into small spaces, that is down to just few or one molecule thick. For the first time, scientists have directly measured via an InfraRed microbeam the vibrational signatures of truly two-dimensional water. In a study now published in Nature Communications, researchers used ultra-thin channels made into microdevices to trap water in isolated layers: an InfraRed microscope then probes locally how the hydrogen-bonding network changes under extreme confinement (2D) and gradually up to bulk water (3D).

Professor Radha Boya from The University of Manchester

Researchers from Professor Radha Boya’s team in The University of Manchester’s Department of Physics and the National Graphene Institute, working in collaboration with Diamond Light Source and Freie Universität Berlin scientists, found that water reorganises in surprising ways at the smallest molecular scales. Hydrogen-bonds give bulk water many of its familiar properties (from liquid to ice phases), but until now it has been extremely difficult to directly test what happens when water is forced into a flat, single-layer arrangement, also because the amount of material is so small to be experimentally measured.

By combining atomically precise nanochannels with the ultra-bright Synchrotron InfraRed microbeam on the B22 beamline at Diamond, the team was able to measure the vibrational modes of confined water, going down to a single molecular layer, and step by step up to several layers, until reaching bulk water.

Professor Radha Boya from The University of Manchester said: “You can think of bulk water as a three-dimensional network where each molecule is constantly forming and breaking hydrogen bonds in all directions. When you squash water into a single layer, that network simply cannot hold together in the same way. For the first time, we were able to directly see how those bonds rearrange in this extreme limit.”

Manchester University researchers created Angstrom-scale slit channels using stacks of two-dimensional materials on silicon chips, including graphite spacers and hexagonal boron nitride top layer. These materials acted as both atomically-smooth confining walls as well as optical amplifiers, in a so-called waveguide effect which boosts the IR absorption from just a single layer of water to a measurable signal.

Dr Gianfelice Cinque from Diamond Light Source

InfraRed spectroscopy is a highly sensitive and non-destructive method to probe molecules. In particular, all vibrational modes of the water molecule are strongly IR active: here the focus has been on the so-called stretching mode or O-H bond. By comparing water in channels of different heights with water in bulk regions of the same microdevice, the researchers tracked how that IR vibrational frequency changed as the water layer became thinner and thinner, which is linked to the molecule bond changes.

Dr Gianfelice Cinque at Diamond Light Source said: “My first excitement during the beamtimes at beamline B22 was being able to experimentally measure the vibrational fingerprint of a single monolayer of water. To our knowledge, this is the first time that the molecular changes from bulk (3D) to confined (2D) water has been directly detected by an InfraRed microprobe. We then measured that thinner water layers - reaching a monolayer - have O-H stretching mode progressively shifting to higher frequencies (blue shift): this is a clear sign that the hydrogen-bonding network is disrupted toward 2D water formation.”

Professor Roland Netz of Freie Universität Berlin

“Our measurements show that monolayer water does not resemble a flat version of ordinary liquid water,” added Professor Boya. “Instead, it forms a fragmented, mosaic-like structure made up of small hydrogen-bonded clusters surrounded by poorly bound or free molecules.”

The study also showed that this behaviour is specific to the monolayer limit. Once the channels exceeded around one nanometre (10 Angstroms) in height, equivalent to roughly three molecular layers of water, the vibrational signatures began to move back towards those of bulk water, indicating recovery of a more conventional hydrogen-bond network.
To understand the origin of these spectral changes, the experiments were supported by atomistic simulations to model the water behaviour.

Professor Roland Netz of Freie Universität Berlin said: “Despite the disrupted bonding, monolayer water is unexpectedly dense and structurally distinct from both bulk water and simple interfacial water at surfaces.”

The findings provide direct experimental evidence for long-standing theoretical predictions about two-dimensional water and offer a benchmark for future studies of confined fluids.

Dr Marcos Martins, first author of the study from The University of Manchester

Dr Marcos Martins, first author of the study at The University of Manchester, said: “Water confined at this scale plays a role in everything from nanofluidic devices to biological channels and energy technologies. Having a direct experimental picture of how its structure changes at the single-layer limit helps us understand the physical rules that govern these systems.”

The ability to directly measure how water re-organises at the single-layer limit could help researchers design better Angstrom-scale technologies, including nanofluidic devices, selective membranes, and electrochemical and energy devices where confined water shapes interfacial behaviour. The same platform could also be used to study other ultrathin liquids and solvated ions, expanding experimental access to extreme confinement in materials science and biology.

Martins, M.V.S., Jyothilal, H., Becker, M.R. et al. Sub-diffractional infrared absorption of two-dimensional water. Nat Commun (2026). https://doi.org/10.1038/s41467-026-72629-9

Phys.org: Scientists observe water's behavior in a single molecular layer