Van der Waals heterostructures

This Nature article by A. K. Geim and I. V. Grigorieva is a forward-looking review of “van der Waals (vdW) heterostructures”: artificial materials assembled by stacking atomically thin two-dimensional (2D) crystals in a chosen sequence with one-atomic-plane precision. The central research question is not a single hypothesis tested experimentally, but rather: why vdW heterostructures matter, how they work in practice, what materials are realistically available for assembly, and what directions are most promising for future fundamental physics and applications.

The importance of the topic is framed by the trajectory of graphene research. Graphene has matured from a discovery phase into a vast application-driven field (the authors note on the order of 10,000 papers per year), and they argue that “simple graphene” has passed its peak. At the same time, the fundamental physics of graphene is still not exhausted, and device quality continues to improve. However, the authors emphasize that progress is now increasingly driven by using graphene as a platform and by expanding to other 2D crystals such as hexagonal boron nitride (hBN) and transition-metal dichalcogenides (e.g., MoS a). The review’s broader context is therefore the shift from studying a single material to engineering designer “layer-by-layer” systems where the interface itself becomes a tunable component.

Methodologically, the paper is a synthesis of the emerging experimental literature rather than a new study with a defined sample size. The “method” is the conceptual and practical workflow of vdW heterostructure fabrication: (i) isolate micrometre-sized exfoliated 2D flakes (often via the Scotch tape method), (ii) transfer them face-down onto a target using optical alignment and micromanipulators, (iii) remove the supporting polymer/film, and (iv) repeat until the desired stack is built. For device fabrication, the authors describe subsequent lithography and plasma etching into Hall-bar geometries, plus metal contact evaporation. They also discuss an alternative “vertical” device route where thin hBN, MoS a, or WS a layers act as tunnel barriers between graphene electrodes.

A key practical theme is that vdW heterostructures work “exceptionally well” because interfaces can be made atomically sharp and clean despite ubiquitous contamination on exposed 2D surfaces. The authors explain this using the physics of vdW adhesion: when two layers are brought into contact, vdW forces can squeeze out trapped contaminants or expel them into micrometre-scale “bubbles,” yielding interfaces that are clean and sharp on the scale relevant for electronic transport. They cite cross-sectional imaging work showing clean buried interfaces and note that contamination can be effectively removed at interfaces.

The review’s key findings are presented as concrete empirical benchmarks and device demonstrations from the literature. For materials quality and device performance, the authors highlight that encapsulated graphene on hBN can reach mobilities on the order of 100,000 cm${}^2$V${}^{-1}$s${}^{-1}$, and up to about 500,000 cm${}^2$V${}^{-1}$s${}^{-1}$ at low temperature. They also cite room-temperature ballistic transport in encapsulated graphene, including negative bend resistance and magnetic focusing signatures. For quantum capacitance, they mention that capacitors larger than 100 $\mu$m${}^2$ can show quantum oscillations at magnetic fields as low as about 0.2 T.

For heterostructure functionality beyond encapsulation, the authors summarize several “evolutionary steps.” First, hBN’s role as a high-quality substrate for graphene is credited as a major enabling advance. Second, encapsulation with thin hBN is described as stabilizing device quality against ambient degradation. Third, vertical tunnelling devices are described as a major step: by using few-layer hBN (or other 2D crystals) as tunnel barriers, one can realize field-effect tunnelling transistors where the tunnel current is controlled by gate-tuned changes in graphene’s Fermi energy. The authors report on-off switching ratios exceeding $10^6$ at room temperature for these vertical tunnelling devices.

For more complex stacks, the review points to a graphene–hBN superlattice consisting of six alternating bilayers (the largest number of 2D crystals reported at the time). It also discusses double-layer graphene devices where two graphene sheets are separated by as little as three hBN layers, corresponding to a separation of roughly 1 nm. The authors emphasize that even at this separation, tunnelling is suppressed while interlayer Coulomb interactions remain strong, enabling exploration of many-body states. They report that the measurements in zero magnetic field have not yet shown evidence of interlayer excitonic superfluidity, despite the expectation that the Coulomb energy scale could be large (they state it can exceed 0.1 eV). They also note that the most promising route for coherent states may be in quantizing magnetic fields, which at the time had not been fully explored in this context.

A particularly important “result” for the review is the role of crystallographic alignment and moir patterns. The authors cite graphene on hBN superlattices where alignment accuracy better than about 1${}^{\circ }$ can be achieved. In these systems, moir potentials reconstruct the electronic spectrum, producing additional Dirac cones at high carrier densities. They state that the Hall effect can change sign and that the new Dirac cones show their own Landau levels. The authors interpret these strong spectral effects as evidence that interfacial contamination is negligible and that vdW heterostructures can be used for band-structure engineering.

The review also provides a “reality check” on what 2D crystals can actually survive and be used. The authors argue that many theoretically imaginable 2D materials are unlikely to be stable when exfoliated because melting temperature decreases with decreasing thickness and because monolayers have no bulk to protect them from surface reactions. They give specific stability examples: MoS${}_2$ begins oxidizing in moist air around 85${}^{\circ }$C, and they note that graphene would not survive if room temperatures were doubled to around 300${}^{\circ }$C. They also discuss that many materials stable in bulk corrode or decompose when thinned (e.g., GaSe, TaS${}_2$, Bi${}_2$Se${}_3$). They highlight that contamination is trapped between layers unless it can be cleared; vdW adhesion and annealing can mitigate this.

Limitations are acknowledged implicitly through the review’s emphasis on practical constraints: (i) the available library of stable 2D crystals is limited, (ii) fabrication requires months to master even though the conceptual stacking is simple, (iii) scalable manufacturing is not yet solved, and (iv) many speculative “big dreams” may fail because the field is still early and parameter space is vast. The authors also note that knowledge about oxide and hydroxide monolayers is limited largely to microscopy observations, with few electrical measurements.

Finally, the review discusses practical implications. Who should care includes condensed-matter physicists interested in many-body phenomena (e.g., Wigner crystallization, excitonic superfluidity, itinerant magnetism), device engineers seeking new transistor and tunnelling architectures, and materials scientists focused on scalable production. The authors argue that vdW heterostructures can accelerate the application roadmap already associated with graphene by enabling new device architectures (encapsulation, vertical tunnelling, superlattices, and proximity effects). For industrial scale, they discuss several approaches—vdW epitaxy, Langmuir–Blodgett-like layer deposition, and self-assembly from suspensions—but conclude that the most feasible route at the time is to grow mono- and few-layer sheets on catalytic substrates, then isolate and transfer them to build stacks. They predict a “snowball effect” as more groups adopt the technology and explore the combinatorial parameter space of materials, sequences, and alignments.

Overall, the paper’s contribution is to consolidate the field’s enabling principles (materials stability, contamination control, and atomic-scale assembly), to report key performance benchmarks from representative experiments, and to chart a roadmap for future physics and scalable engineering of vdW heterostructures.