At North Carolina State University, Yin Liu and his team discovered something counterintuitive: the weakest forces holding materials together might be the key to building smaller, more energy-efficient electronics. The researchers found that van der Waals forces—the gentle electromagnetic attractions between molecules that seem almost negligible at the atomic scale—can be harnessed to precisely tune the properties of ferroelectric thin films, opening a path toward a new generation of engineered materials for electronic devices.
The question driving their work was deceptively simple: how much does the strength of van der Waals bonding actually matter? Most materials science focuses on chemical bonds, which are comparatively strong and rigid. But van der Waals forces, while weaker, offer something different—flexibility. When two crystalline layers are chemically bonded, their atomic structures must align perfectly. When bonded by van der Waals forces instead, Liu explains, "the layers can have different orientations." This flexibility opens design possibilities that chemical bonding doesn't allow.
To test whether this flexibility translates into tuneable material properties, Liu's team deposited a thin film of tin selenide (SnSe) onto a monolayer of molybdenum disulfide (MoS₂). They chose SnSe because it's a ferroelectric material widely studied in research, and MoS₂ because it integrates easily into existing electronic devices. Crucially, MoS₂ has nearly perfect lattice matching with SnSe—their crystalline structures align closely—creating a relatively strong van der Waals force between them. This allowed them to compare their results against previous studies where SnSe was deposited on graphene, which had much weaker van der Waals bonding.
What they found was striking: the strength of the van der Waals force, combined with lattice matching, directly influences three critical properties of the resulting ferroelectric material. The first is thickness—the number of crystalline layers. The second is strain state—how the material is stretched or compressed at the atomic level. The third is domain architecture—the orientation of polarization in different sections of the material. Each of these characteristics fundamentally affects how the material behaves electronically and physically. In essence, by choosing substrates with different van der Waals force strengths, researchers can tune the material's performance without changing its chemical composition.
The practical benefits were immediate and impressive. Using a monolayer of MoS₂ as a substrate, the team grew larger thin films of SnSe—in terms of lateral size and surface area—than had ever been demonstrated on previous substrates. The films were also higher quality, with fewer structural defects that typically compromise electronic performance.
"This substrate is promising, and merits future investigation," Liu reflected, understating what amounts to a significant shift in how materials engineers might approach ferroelectric design. Rather than viewing van der Waals forces as negligible background effects, the research suggests they deserve careful attention as powerful tuning tools. As electronics demand smaller size and lower energy consumption, the ability to engineer materials at such a fundamental level—controlling thickness, strain, and domain architecture through substrate selection—could prove transformative across a range of applications, from sensors to memory devices to energy conversion systems.