# Germanene

**Germanene** is a two-dimensional material made of a single layer of germanium atoms arranged in a honeycomb lattice, the germanium analog of graphene. Theory predicts, and experiment has largely confirmed, that unlike flat graphene its lattice is low-buckled: the two interpenetrating triangular sublattices are displaced slightly with respect to each other in the direction normal to the sheet. Despite this buckling, the low-energy bands at the K and K′ points of the surface [Brillouin zone](https://www.edgepedia.org/brillouin-zone) retain a linear dispersion, so germanene hosts Dirac fermions like graphene, while its much larger spin-orbit coupling (interaction linking electron spin with its motion) gives it properties graphene lacks, including a quantum spin Hall phase.<sup>[1](https://www.sciencedirect.com/science/article/pii/B9780128238240000034)</sup>

| Key fact | Detail |
|---|---|
| Structure | Low-buckled honeycomb lattice; two triangular sublattices displaced vertically; mixed sp²–sp³ hybridization rather than graphene's pure sp²<sup>[1](https://www.sciencedirect.com/science/article/pii/B9780128238240000034)</sup><sup> • </sup><sup>[2](https://pmc.ncbi.nlm.nih.gov/articles/PMC9268513/)</sup> |
| Lattice parameters | Free-standing lattice constant predicted at 0.392–0.405 nm; measured values on Au(111), Pt(111), Al(111), Cu(111), Ag(111), and MoS₂ range from 0.38 to 0.43 nm<sup>[3](https://www.sciencedirect.com/science/article/abs/pii/S0039602823001358)</sup> |
| Spin-orbit gap | About 24 meV, versus a few μeV in graphene, owing to germanium's larger atomic number<sup>[1](https://www.sciencedirect.com/science/article/pii/B9780128238240000034)</sup> |
| Topological phase | A two-dimensional topological insulator of Kane-Mele type with helical edge states; an electric field perpendicular to the layer can drive a transition to a trivial band insulator<sup>[4](https://pmc.ncbi.nlm.nih.gov/articles/PMC11871225/)</sup><sup> • </sup><sup>[5](https://www.sciencedirect.com/science/article/pii/S0039602824000943)</sup> |
| First synthesis | 2014, on Pt(111) by Gao and colleagues and on Au(111) by Lay and colleagues<sup>[6](https://onlinelibrary.wiley.com/doi/10.1002/inf2.12365)</sup> |
| Synthesis routes | Molecular beam epitaxy, electrochemical synthesis, plasma-assisted synthesis, and liquid-phase exfoliation<sup>[6](https://onlinelibrary.wiley.com/doi/10.1002/inf2.12365)</sup> |
| Chemical stability | Highly reactive with oxygen; stable in ultrahigh vacuum or inert atmosphere, unlike its hydrogenated derivative germanane (GeH), which is stable in ambient conditions<sup>[7](https://pubs.acs.org/doi/10.1021/acs.nanolett.8b04207)</sup> |

## Structure and electronic properties

Germanene belongs to the [Xenes](https://www.edgepedia.org/xenes), the family of mono-elemental two-dimensional materials named after the group 14 elements. All graphene-like lattices of the heavier group 14 elements (silicene, germanene, stanene, and plumbene) are buckled rather than planar, and the buckling increases with atomic number; the corrugation of a free-standing germanene sheet is about 0.64 Å, with a predicted buckling parameter of 0.635 Å in early first-principles work.<sup>[2](https://pmc.ncbi.nlm.nih.gov/articles/PMC9268513/)</sup><sup> • </sup><sup>[8](https://arxiv.org/abs/1111.6333)</sup> The buckling reflects mixed sp²–sp³ hybridization of the electronic states, in contrast to the purely sp² bonding of graphene.<sup>[2](https://pmc.ncbi.nlm.nih.gov/articles/PMC9268513/)</sup>

The buckling is not merely a structural curiosity. Because the two sublattices sit at different heights, a perpendicular electric field transfers charge from one triangular sublattice to the other and opens a band gap, allowing the electronic structure to be tuned externally. Combined with the sizable spin-orbit gap of roughly 24 meV, this makes germanene a candidate for observing the quantum spin [Hall effect](https://www.edgepedia.org/hall-effect), in which topologically protected helical edge states carry current along the boundary of the sample while the bulk remains insulating.<sup>[1](https://www.sciencedirect.com/science/article/pii/B9780128238240000034)</sup> Germanene is classified as a Kane-Mele-type topological insulator (class AII), and its topological properties have been experimentally confirmed.<sup>[4](https://pmc.ncbi.nlm.nih.gov/articles/PMC11871225/)</sup>

## Synthesis

The first successful synthesis was reported in 2014. Gao and colleagues deposited germanium on Pt(111) by electron-beam physical vapor deposition and obtained a (√19 × √19) superstructure relative to the substrate, which corresponds to a (3 × 3) superlattice of a buckled honeycomb germanene sheet; in the same year, Lay and colleagues grew germanene with several phases on Au(111), one of which was identified as a √3 × √3 reconstructed germanene layer on a √7 × √7 Au(111) supercell.<sup>[6](https://onlinelibrary.wiley.com/doi/10.1002/inf2.12365)</sup> In the following years, germanene with various superstructures was grown on Ge₂Pt, Al(111), Sb(111), MoS₂, AlN/Ag(111), Cu(111), Ag(111), highly oriented pyrolytic graphite, and Ag(111)/Ge(111) substrates.<sup>[6](https://onlinelibrary.wiley.com/doi/10.1002/inf2.12365)</sup> A segregation method, in which annealing an Ag(111) thin film on a Ge(111) substrate produces monolayer germanene reproducibly, has also been demonstrated.<sup>[9](https://doi.org/10.1021/acs.chemmater.5c03462)</sup>

**Substrate identity is a recurring issue.** Surface x-ray diffraction combined with density functional theory showed that the (√7 × √7)R±19.1° reconstruction formed after room-temperature germanium deposition on Al(111) is a mixed Ge-Al honeycomb layer on top of an Al(111) plane, not a pure germanene layer.<sup>[10](https://journals.aps.org/prb/abstract/10.1103/PhysRevB.106.045412)</sup> More broadly, it has been speculated that germanium may form alloys with substrate surfaces, casting doubt on some reported syntheses.<sup>[6](https://onlinelibrary.wiley.com/doi/10.1002/inf2.12365)</sup> On Ag(111), angle-resolved photoemission, STM, and low-energy electron diffraction have confirmed a striped-phase germanene in the transition between the initial Ag₂Ge surface alloy at one-third monolayer coverage and the quasi-freestanding germanene phase at coverage of one monolayer or more.<sup>[11](https://journals.aps.org/prresearch/abstract/10.1103/PhysRevResearch.6.043190)</sup>

A well-characterized route uses Ge₂Pt nanocrystals. Depositing platinum on Ge(110) and annealing at about 1100 K forms three-dimensional Pt-Ge nanocrystals whose outermost layer is a buckled honeycomb germanene sheet with a lattice constant of 4.3 Å and a buckling of 0.2 Å; the nearest-neighbor distance of 2.5 ± 0.1 Å is close to the predicted 2.4 Å for germanene.<sup>[12](https://research.utwente.nl/en/publications/two-dimensional-dirac-signature-of-germanene/)</sup><sup> • </sup><sup>[13](https://pubmed.ncbi.nlm.nih.gov/25210978/)</sup> Germanene grows in multilayers on these crystals, with an interlayer spacing of about 3 Å indicating weak interaction between layers, and a work function of approximately 3.8 eV, substantially lower than that of pristine Ge(001) at 4.5 eV.<sup>[14](https://research.utwente.nl/files/451293665/1-s2.0-S235294072400249X-main.pdf)</sup>

## The substrate problem

Germanene shares a central practical difficulty with silicene: its predicted device properties are accessible only if a suitable substrate is found. Monolayer germanene has been synthesized mainly on metal surfaces, yet field-effect transistors require substrates with a large band gap, and common semiconducting substrates such as bare SiO₂ and GaAs interact strongly with germanene and destroy its Dirac cone.<sup>[15](https://pubs.rsc.org/en/content/articlehtml/2015/cp/c5cp02428e)</sup> The material is also structurally fragile: free-standing germanene changes from a Dirac material to a normal metal when tensile or compressive strain reaches 5%.<sup>[15](https://pubs.rsc.org/en/content/articlehtml/2015/cp/c5cp02428e)</sup>

[Density functional theory](https://www.edgepedia.org/density-functional-theory) studies of monolayer group III monochalcogenides ([GaS](https://www.edgepedia.org/gallium-sulfide), GaSe, GaTe, and InSe) as substrates found that the Dirac-cone-like band structure of germanene is preserved on them. On GaTe and InSe germanene is predicted to be semiconducting with a band gap above 0.1 eV, while effective masses at the Dirac point remain as small as 0.05–0.06 m₀ (the free [electron mass](https://www.edgepedia.org/electron-mass)), giving an estimated ultrahigh carrier mobility of around 1.5–2.2 × 10⁵ cm² V⁻¹ s⁻¹.<sup>[15](https://pubs.rsc.org/en/content/articlehtml/2015/cp/c5cp02428e)</sup> For ordinary field-effect devices, band gaps on the order of 400 meV are needed, motivating searches for gaps in defective and adatom-decorated germanene.<sup>[16](https://pmc.ncbi.nlm.nih.gov/articles/PMC10641765/)</sup>

## Topological electronics

The buckled structure gives germanene a device-relevant handle. A perpendicular electric field couples to the staggered sublattice potential and can induce a topological phase transition from a two-dimensional topological insulator to a trivial band insulator; together with the relatively large band gap, this makes germanene a candidate for a room-temperature topological field-effect transistor.<sup>[5](https://www.sciencedirect.com/science/article/pii/S0039602824000943)</sup><sup> • </sup><sup>[17](https://pmc.ncbi.nlm.nih.gov/articles/PMC11382626/)</sup> [Scanning tunneling spectroscopy](https://www.edgepedia.org/scanning-tunneling-spectroscopy) on germanene grown on Ge₂Pt(101) found metallic edge states that persist up to room temperature, decaying exponentially into the bulk over about 2–3 nm; proximity to the underlying platinum-containing layer increases the topological band gap to 100–150 meV, exceeding that of free-standing germanene.<sup>[17](https://pmc.ncbi.nlm.nih.gov/articles/PMC11382626/)</sup><sup> • </sup><sup>[4](https://pmc.ncbi.nlm.nih.gov/articles/PMC11871225/)</sup>

Narrow ribbons extend this control to zero dimensions. In ultranarrow germanene nanoribbons, combining scanning tunneling microscopy with tight-binding theory showed that tuning the electric field in the tunnel junction switches zero-dimensional topological end states reversibly on and off: increasing the field switches off the end modes of topological two-hexagon-wide ribbons while switching on zero-dimensional states in initially trivial three- and four-hexagon-wide ribbons. This demonstrates a proof of principle for a zero-dimensional topological field-effect device, with proposed uses in ultrasmall memory, controllable qubits, and neuromorphic architectures.<sup>[18](https://journals.aps.org/prl/abstract/10.1103/jx2x-fb5b)</sup>

## Related materials

Hydrogenation converts germanene into **germanane** (GeH), in which each germanium atom bonds to three neighboring germanium atoms in the plane and one hydrogen atom, giving sp³ hybridization. Germanane is stable in ambient conditions, in contrast to germanene itself, which is highly reactive with oxygen and normally stable only in ultrahigh vacuum or inert gas. Annealed [germanane](https://www.edgepedia.org/germanane) shows strong spin-orbit interaction signatures and, after annealing in argon, a resistivity of 1.6 × 10⁻⁷ Ω·m at room temperature, with the annealed product most likely multilayer germanene with a graphite-like structure.<sup>[7](https://pubs.acs.org/doi/10.1021/acs.nanolett.8b04207)</sup> Twisted bilayer germanene synthesized on Ge₂Pt(101) with a 21.8° twist angle shows a moiré-modulated band gap and a well-defined edge state, with tight-binding results suggesting topological properties regulable by an electric field.<sup>[19](https://arxiv.org/abs/2403.14560)</sup>

## References

1. [Germanene (Chapter 2), Xenes: 2D Synthetic Materials Beyond Graphene, Woodhead Publishing, 2022](https://www.sciencedirect.com/science/article/pii/B9780128238240000034)
2. [Single-Element 2D Materials beyond Graphene: Methods of Epitaxial Synthesis, PMC](https://pmc.ncbi.nlm.nih.gov/articles/PMC9268513/)
3. [Formation of germanene with free-standing lattice constant, Surface Science](https://www.sciencedirect.com/science/article/abs/pii/S0039602823001358)
4. [Realization of a one-dimensional topological insulator in ultrathin germanene nanoribbons, PMC](https://pmc.ncbi.nlm.nih.gov/articles/PMC11871225/)
5. [The renaissance of germanium, Surface Science 748, 122543 (2024)](https://www.sciencedirect.com/science/article/pii/S0039602824000943)
6. [Germanium-based monoelemental and binary two-dimensional materials, InfoMat (2022)](https://onlinelibrary.wiley.com/doi/10.1002/inf2.12365)
7. [Highly Conductive Metallic State and Strong Spin–Orbit Interaction in Annealed Germanane, Nano Letters](https://pubs.acs.org/doi/10.1021/acs.nanolett.8b04207)
8. [First-Principles Study of Structural and Electronic Properties of Germanene, arXiv](https://arxiv.org/abs/1111.6333)
9. [In Situ Study of Growth Mechanism of Germanene Segregated through Ag(111) Thin Films, Chemistry of Materials](https://doi.org/10.1021/acs.chemmater.5c03462)
10. [Combined surface x-ray diffraction and DFT study of the germanene/Al(111) structure, Phys. Rev. B 106, 045412 (2022)](https://journals.aps.org/prb/abstract/10.1103/PhysRevB.106.045412)
11. [Striped-phase germanene confirmed by photoemission final-state effect, Phys. Rev. Research 6, 043190 (2024)](https://journals.aps.org/prresearch/abstract/10.1103/PhysRevResearch.6.043190)
12. [Two-dimensional Dirac signature of germanene, Applied Physics Letters 107, 111605 (2015)](https://research.utwente.nl/en/publications/two-dimensional-dirac-signature-of-germanene/)
13. [Germanene termination of Ge2Pt crystals on Ge(110), J. Phys.: Condens. Matter 26, 442001 (2014)](https://pubmed.ncbi.nlm.nih.gov/25210978/)
14. [Image potential states of germanene and related Xenes, Applied Materials Today 39 (2024)](https://research.utwente.nl/files/451293665/1-s2.0-S235294072400249X-main.pdf)
15. [The electronic structure of quasi-free-standing germanene on monolayer MX (M = Ga, In; X = S, Se, Te), Phys. Chem. Chem. Phys. (2015)](https://pubs.rsc.org/en/content/articlehtml/2015/cp/c5cp02428e)
16. [Graphene-like emerging 2D materials: recent progress, challenges and future outlook, PMC](https://pmc.ncbi.nlm.nih.gov/articles/PMC10641765/)
17. [Tunability of topological edge states in germanene at room temperature, J. Mater. Chem. C (2024)](https://pmc.ncbi.nlm.nih.gov/articles/PMC11382626/)
18. [Electric-Field Control of Zero-Dimensional Topological States in Ultranarrow Germanene Nanoribbons, Phys. Rev. Lett. 135, 206601 (2025)](https://journals.aps.org/prl/abstract/10.1103/jx2x-fb5b)
19. [Moiré-modulated band gap and van Hove singularities in twisted bilayer germanene, arXiv](https://arxiv.org/abs/2403.14560)

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*Topic: Encyclopedia › Physical world and mathematics › Physics › Matter and radiation physics › Condensed matter physics › Electronic and magnetic properties*

*Initially written Oct 15, 2026*

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