{ "id": "ep8caj9k3j", "slug": "germanene", "title": "Germanene", "updated": "2026-10-15", "topic_path": [ { "id": "physical", "label": "Physical world and mathematics", "api_url": "https://www.edgepedia.org/api/v1/topics/physical" }, { "id": "physical.physics", "label": "Physics", "api_url": "https://www.edgepedia.org/api/v1/topics/physical.physics" }, { "id": "physical.physics.matter-and-radiation", "label": "Matter and radiation physics", "api_url": "https://www.edgepedia.org/api/v1/topics/physical.physics.matter-and-radiation" }, { "id": "physical.physics.matter-and-radiation.condensed-matter", "label": "Condensed matter physics", "api_url": "https://www.edgepedia.org/api/v1/topics/physical.physics.matter-and-radiation.condensed-matter" }, { "id": "physical.physics.matter-and-radiation.condensed-matter.cm-electronic", "label": "Electronic and magnetic properties", "api_url": "https://www.edgepedia.org/api/v1/topics/physical.physics.matter-and-radiation.condensed-matter.cm-electronic" } ], "geo": [ { "id": "geo.weu.t2001.physical.physics.matter-and-radiation.condensed-matter.cm-electronic", "label": "Western Europe · 2001 to 2020: Electronic and magnetic properties", "api_url": "https://www.edgepedia.org/api/v1/geo/geo.weu.t2001.physical.physics.matter-and-radiation.condensed-matter.cm-electronic", "path": [ { "id": "geo.weu", "label": "Western Europe", "api_url": "https://www.edgepedia.org/api/v1/geo/geo.weu" }, { "id": "geo.weu.t2001", "label": "Western Europe · 2001 to 2020", "api_url": "https://www.edgepedia.org/api/v1/geo/geo.weu.t2001" }, { "id": "geo.weu.t2001.physical", "label": "Physical world and mathematics", "api_url": "https://www.edgepedia.org/api/v1/geo/geo.weu.t2001.physical" }, { "id": "geo.weu.t2001.physical.physics", "label": "Physics", "api_url": "https://www.edgepedia.org/api/v1/geo/geo.weu.t2001.physical.physics" }, { "id": "geo.weu.t2001.physical.physics.matter-and-radiation", "label": "Matter and radiation physics", "api_url": "https://www.edgepedia.org/api/v1/geo/geo.weu.t2001.physical.physics.matter-and-radiation" }, { "id": "geo.weu.t2001.physical.physics.matter-and-radiation.condensed-matter", "label": "Condensed matter physics", "api_url": "https://www.edgepedia.org/api/v1/geo/geo.weu.t2001.physical.physics.matter-and-radiation.condensed-matter" }, { "id": "geo.weu.t2001.physical.physics.matter-and-radiation.condensed-matter.cm-electronic", "label": "Electronic and magnetic properties", "api_url": "https://www.edgepedia.org/api/v1/geo/geo.weu.t2001.physical.physics.matter-and-radiation.condensed-matter.cm-electronic" } ] } ], "excerpt": "Germanene is a two-dimensional material made of a single honeycomb layer of germanium atoms, the germanium analog of graphene, first synthesized in 2014. Unlike flat graphene, its lattice is low-buckled.", "snippet": "Germanene is a two-dimensional material made of a single honeycomb layer of germanium atoms, the germanium analog of graphene, first synthesized in 2014. Unlike flat graphene, its lattice is low-buckled.", "node": "physical.physics.matter-and-radiation.condensed-matter.cm-electronic", "markdown": "# Germanene\n\n**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.[1](https://www.sciencedirect.com/science/article/pii/B9780128238240000034)\n\n| Key fact | Detail |\n|---|---|\n| Structure | Low-buckled honeycomb lattice; two triangular sublattices displaced vertically; mixed sp²–sp³ hybridization rather than graphene's pure sp²[1](https://www.sciencedirect.com/science/article/pii/B9780128238240000034) • [2](https://pmc.ncbi.nlm.nih.gov/articles/PMC9268513/) |\n| 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[3](https://www.sciencedirect.com/science/article/abs/pii/S0039602823001358) |\n| Spin-orbit gap | About 24 meV, versus a few μeV in graphene, owing to germanium's larger atomic number[1](https://www.sciencedirect.com/science/article/pii/B9780128238240000034) |\n| 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[4](https://pmc.ncbi.nlm.nih.gov/articles/PMC11871225/) • [5](https://www.sciencedirect.com/science/article/pii/S0039602824000943) |\n| First synthesis | 2014, on Pt(111) by Gao and colleagues and on Au(111) by Lay and colleagues[6](https://onlinelibrary.wiley.com/doi/10.1002/inf2.12365) |\n| Synthesis routes | Molecular beam epitaxy, electrochemical synthesis, plasma-assisted synthesis, and liquid-phase exfoliation[6](https://onlinelibrary.wiley.com/doi/10.1002/inf2.12365) |\n| 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[7](https://pubs.acs.org/doi/10.1021/acs.nanolett.8b04207) |\n\n## Structure and electronic properties\n\nGermanene 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.[2](https://pmc.ncbi.nlm.nih.gov/articles/PMC9268513/) • [8](https://arxiv.org/abs/1111.6333) The buckling reflects mixed sp²–sp³ hybridization of the electronic states, in contrast to the purely sp² bonding of graphene.[2](https://pmc.ncbi.nlm.nih.gov/articles/PMC9268513/)\n\nThe 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.[1](https://www.sciencedirect.com/science/article/pii/B9780128238240000034) Germanene is classified as a Kane-Mele-type topological insulator (class AII), and its topological properties have been experimentally confirmed.[4](https://pmc.ncbi.nlm.nih.gov/articles/PMC11871225/)\n\n## Synthesis\n\nThe 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.[6](https://onlinelibrary.wiley.com/doi/10.1002/inf2.12365) 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.[6](https://onlinelibrary.wiley.com/doi/10.1002/inf2.12365) A segregation method, in which annealing an Ag(111) thin film on a Ge(111) substrate produces monolayer germanene reproducibly, has also been demonstrated.[9](https://doi.org/10.1021/acs.chemmater.5c03462)\n\n**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.[10](https://journals.aps.org/prb/abstract/10.1103/PhysRevB.106.045412) More broadly, it has been speculated that germanium may form alloys with substrate surfaces, casting doubt on some reported syntheses.[6](https://onlinelibrary.wiley.com/doi/10.1002/inf2.12365) 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.[11](https://journals.aps.org/prresearch/abstract/10.1103/PhysRevResearch.6.043190)\n\nA 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.[12](https://research.utwente.nl/en/publications/two-dimensional-dirac-signature-of-germanene/) • [13](https://pubmed.ncbi.nlm.nih.gov/25210978/) 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.[14](https://research.utwente.nl/files/451293665/1-s2.0-S235294072400249X-main.pdf)\n\n## The substrate problem\n\nGermanene 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.[15](https://pubs.rsc.org/en/content/articlehtml/2015/cp/c5cp02428e) 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%.[15](https://pubs.rsc.org/en/content/articlehtml/2015/cp/c5cp02428e)\n\n[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.[15](https://pubs.rsc.org/en/content/articlehtml/2015/cp/c5cp02428e) 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.[16](https://pmc.ncbi.nlm.nih.gov/articles/PMC10641765/)\n\n## Topological electronics\n\nThe 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.[5](https://www.sciencedirect.com/science/article/pii/S0039602824000943) • [17](https://pmc.ncbi.nlm.nih.gov/articles/PMC11382626/) [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.[17](https://pmc.ncbi.nlm.nih.gov/articles/PMC11382626/) • [4](https://pmc.ncbi.nlm.nih.gov/articles/PMC11871225/)\n\nNarrow 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.[18](https://journals.aps.org/prl/abstract/10.1103/jx2x-fb5b)\n\n## Related materials\n\nHydrogenation 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.[7](https://pubs.acs.org/doi/10.1021/acs.nanolett.8b04207) 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.[19](https://arxiv.org/abs/2403.14560)\n\n## References\n\n1. [Germanene (Chapter 2), Xenes: 2D Synthetic Materials Beyond Graphene, Woodhead Publishing, 2022](https://www.sciencedirect.com/science/article/pii/B9780128238240000034)\n2. [Single-Element 2D Materials beyond Graphene: Methods of Epitaxial Synthesis, PMC](https://pmc.ncbi.nlm.nih.gov/articles/PMC9268513/)\n3. [Formation of germanene with free-standing lattice constant, Surface Science](https://www.sciencedirect.com/science/article/abs/pii/S0039602823001358)\n4. [Realization of a one-dimensional topological insulator in ultrathin germanene nanoribbons, PMC](https://pmc.ncbi.nlm.nih.gov/articles/PMC11871225/)\n5. [The renaissance of germanium, Surface Science 748, 122543 (2024)](https://www.sciencedirect.com/science/article/pii/S0039602824000943)\n6. [Germanium-based monoelemental and binary two-dimensional materials, InfoMat (2022)](https://onlinelibrary.wiley.com/doi/10.1002/inf2.12365)\n7. [Highly Conductive Metallic State and Strong Spin–Orbit Interaction in Annealed Germanane, Nano Letters](https://pubs.acs.org/doi/10.1021/acs.nanolett.8b04207)\n8. [First-Principles Study of Structural and Electronic Properties of Germanene, arXiv](https://arxiv.org/abs/1111.6333)\n9. [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)\n10. [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)\n11. [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)\n12. [Two-dimensional Dirac signature of germanene, Applied Physics Letters 107, 111605 (2015)](https://research.utwente.nl/en/publications/two-dimensional-dirac-signature-of-germanene/)\n13. [Germanene termination of Ge2Pt crystals on Ge(110), J. Phys.: Condens. Matter 26, 442001 (2014)](https://pubmed.ncbi.nlm.nih.gov/25210978/)\n14. [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)\n15. [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)\n16. [Graphene-like emerging 2D materials: recent progress, challenges and future outlook, PMC](https://pmc.ncbi.nlm.nih.gov/articles/PMC10641765/)\n17. [Tunability of topological edge states in germanene at room temperature, J. Mater. Chem. C (2024)](https://pmc.ncbi.nlm.nih.gov/articles/PMC11382626/)\n18. [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)\n19. [Moiré-modulated band gap and van Hove singularities in twisted bilayer germanene, arXiv](https://arxiv.org/abs/2403.14560)\n\n---\n*Topic: Encyclopedia › Physical world and mathematics › Physics › Matter and radiation physics › Condensed matter physics › Electronic and magnetic properties*\n\n*Initially written Oct 15, 2026*\n\n*Copyright 2026 EdgeChat AI, a subsidiary of Biostate AI.*\n\nLicense: Edgepedia Community License 1.0, https://www.edgepedia.org/edgepedia/license\n", "same_as": [], "url": "https://www.edgepedia.org/germanene", "markdown_url": "https://www.edgepedia.org/germanene.md", "license": { "name": "Edgepedia Community License 1.0", "url": "https://www.edgepedia.org/edgepedia/license", "summary": "Free with credit, commercial use included. AI training is open to everyone. For other uses, organizations over USD 100M in revenue or 100M monthly users license separately.", "spdx": "LicenseRef-Edgepedia-Community-1.0" }, "credit": "\"Germanene\", Edgepedia (EdgeChat), https://www.edgepedia.org/germanene. Edgepedia Community License 1.0.", "credit_md": "\"[Germanene](https://www.edgepedia.org/germanene)\", Edgepedia (EdgeChat), [https://www.edgepedia.org/germanene](https://www.edgepedia.org/germanene). [Edgepedia Community License 1.0](https://www.edgepedia.org/edgepedia/license).", "credit_html": "\"Germanene\", Edgepedia (EdgeChat), https://www.edgepedia.org/germanene. Edgepedia Community License 1.0.", "speakable": "Germanene is a two-dimensional material made of a single honeycomb layer of germanium atoms, the germanium analog of graphene, first synthesized in 2014. Unlike flat graphene, its lattice is low-buckled." }