Glaphynes: 2D Silica–Graphyne Heterostructures

• Glaphynes are hybrid 2D heterostructures formed by stacking a silica glass monolayer on graphyne, exhibiting topology-dependent electronic properties.
• The design leverages interfacial Si–O–C bonding to modulate band structures, with gaps ranging from nearly zero (α-glaphyne) to 1.51 eV (γ-glaphyne).
• Precise stacking registry and pore alignment drive charge redistribution and bond distortion, offering tunable transport properties for nanoelectronic applications.

Searching arXiv for the cited glaphyne/glaphyne-related papers to ground the article in current records. arxiv_search(query="glaphyne graphyne silica glass 2D heterostructures", max_results=10, sort_by="relevance") arxiv_search(query="(Fabris et al., 17 Sep 2025)", max_results=5, sort_by="relevance") arxiv_search(query="From Glaphene to Glaphynes", max_results=10, sort_by="relevance") arxiv_search(query="(Solis et al., 2018) OR (Popov et al., 2013) OR (Autreto et al., 2015) OR (Do et al., 2013) OR (Kanegae et al., 2024)", max_results=10, sort_by="relevance") Glaphynes are hybrid two-dimensional heterostructures formed by vertically stacking a monolayer of 2D silica glass, $\mathrm{SiO_2}$, onto graphyne monolayers. The class was proposed in direct analogy to glaphene, the experimentally realized $\mathrm{SiO_2}$/graphene hybrid, with the aim of testing whether interfacial hybridization and electronic proximity effects can similarly reconfigure the electronic structure of graphynes (Fabris et al., 17 Sep 2025). In the initial study, three variants were examined: $\alpha$-, $\beta$-, and $\gamma$-glaphyne, corresponding to silica stacked on $\alpha$-, $\beta$-, and $\gamma$-graphyne. Because graphynes are porous mixed $sp/sp^2$ carbon allotropes containing acetylenic linkers, they provide a topologically richer substrate than graphene for interface-driven band engineering (Solis et al., 2018).

1. Definition and materials context

Graphynes are two-dimensional carbon allotropes in which benzenoid rings are interconnected by acetylenic groups, producing the coexistence of $sp$- and $\mathrm{SiO_2}$0-hybridized carbon atoms (Solis et al., 2018). Within the hexagonal $\mathrm{SiO_2}$1-, $\mathrm{SiO_2}$2-, and $\mathrm{SiO_2}$3-graphyne series, the acetylenic insertion pattern governs pore topology, atomic density, and electronic structure. Prior work identified $\mathrm{SiO_2}$4-graphyne as a zero-gap material with a Dirac cone at $\mathrm{SiO_2}$5, $\mathrm{SiO_2}$6-graphyne as a zero-gap material with a Dirac crossing displaced from the graphene-like location, and $\mathrm{SiO_2}$7-graphyne as a gapped semiconductor (Popov et al., 2013).

Against that background, glaphynes were introduced as silica–graphyne analogues of glaphene. The reference point is important: glaphene was reported to exhibit strong interlayer hybridization and a sizable band gap of approximately $\mathrm{SiO_2}$8 eV, converting graphene’s semimetallic spectrum through proximity-induced $\mathrm{SiO_2}$9-orbital coupling (Fabris et al., 17 Sep 2025). Glaphynes probe whether the same general mechanism survives when the carbon layer is no longer a dense $\alpha$0 sheet but a porous graphyne network with topology-dependent frontier states.

The proposal therefore sits at the intersection of two established research directions: graphyne physics, where acetylenic topology controls Dirac features, gaps, and chemical reactivity, and hybrid 2D heterostructures, where interfacial registry and orbital overlap can induce new electronic phases (Fabris et al., 17 Sep 2025).

2. Interface construction and structural chemistry

The glaphyne structures were built by combining graphyne supercells with commensurate $\alpha$1 supercells chosen to minimize lattice mismatch, followed by full relaxation within SCC-DFTB (Fabris et al., 17 Sep 2025). For $\alpha$2- and $\alpha$3-glaphyne, a $\alpha$4 graphyne supercell was stacked with a $\alpha$5 $\alpha$6 supercell. For $\alpha$7-glaphyne, a $\alpha$8 $\alpha$9-graphyne cell was stacked with a $\beta$0 $\beta$1 supercell; an alternative larger model, $\beta$2 $\beta$3 on $\beta$4 $\beta$5-graphyne, reduced mismatch to $\beta$6 (Fabris et al., 17 Sep 2025).

After relaxation, all three heterostructures adopted P6MM symmetry. Their relaxed structural parameters and principal electronic outcomes are summarized below.

Variant	Relaxed cell	Electronic outcome
$\beta$7-glaphyne	264 atoms; $\beta$8 Å; $\beta$9	Dirac-like cone at $\gamma$0; $\gamma$1 eV
$\gamma$2-glaphyne	66 atoms; $\gamma$3 Å; $\gamma$4	Direct gap at $\gamma$5; $\gamma$6 eV
$\gamma$7-glaphyne	300 atoms; $\gamma$8 Å; $\gamma$9	Direct gap at $\alpha$0; $\alpha$1 eV

The initial interlayer spacing was set to approximately $\alpha$2 Å. Relaxation yielded separations of $\alpha$3 Å for $\alpha$4-, $\alpha$5 Å for $\alpha$6-, and $\alpha$7 Å for $\alpha$8-glaphyne. The isolated silica monolayer thickness was $\alpha$9 Å and became approximately $\beta$0 Å after stacking, consistent with the experimental thickness of about $\beta$1 nm reported for glaphene (Fabris et al., 17 Sep 2025).

A central structural feature is the emergence of interfacial Si–O–C bonding. In the phonon density of states, modes between approximately $\beta$2 and $\beta$3 were assigned to interfacial Si–O–C signatures, analogous to the $\beta$4 feature reported for glaphene. In $\beta$5-glaphyne, peaks near $\beta$6 and $\beta$7 are consistent with Si–O and C–O stretching and coupled Si–O–C modes, while $\beta$8-glaphyne shows a distinct peak at $\beta$9 (Fabris et al., 17 Sep 2025).

Hybridization perturbs the acetylenic chains unevenly across the three topologies. The bond-length changes are small in $\gamma$0- and $\gamma$1-glaphyne, but pronounced in $\gamma$2-glaphyne, where the graphyne chain sequence changes from $\gamma$3, $\gamma$4, $\gamma$5 Å in pristine $\gamma$6-graphyne to $\gamma$7, $\gamma$8, $\gamma$9 Å after stacking. This is the largest reported single-bond elongation among the three variants and was attributed to mismatch-induced strain combined with interlayer coupling (Fabris et al., 17 Sep 2025).

3. Computational treatment and stability indicators

The reported glaphyne calculations used self-consistent-charge density-functional tight binding, SCC-DFTB, as implemented in DFTB+ (Fabris et al., 17 Sep 2025). The matsci-0-3 Slater–Koster parameter set was employed for carbon and silica. Brillouin-zone sampling used a Monkhorst–Pack $sp/sp^2$0 mesh, nonbonded interactions were included through a Lennard–Jones potential combined with UFF parameters, and geometry optimization used the conjugate-gradient method with SCC convergence of $sp/sp^2$1 a.u. and force tolerance of $sp/sp^2$2 a.u. (Fabris et al., 17 Sep 2025).

Stability was assessed structurally, energetically, and vibrationally. Structurally, the relaxed geometries retained their intended symmetry and showed bond lengths and silica thicknesses consistent with prior literature. Vibrationally, the phonon density of states showed the interfacial Si–O–C region without reported imaginary modes. Molecular dynamics was not performed in the study, so thermal stability under finite-temperature trajectories remains unresolved (Fabris et al., 17 Sep 2025).

Energetically, all glaphynes were more stable per atom than their pristine graphyne parents when measured by cohesive energy. The reported cohesive energies were $sp/sp^2$3 eV/atom for $sp/sp^2$4-glaphyne, $sp/sp^2$5 eV/atom for $sp/sp^2$6-glaphyne, and $sp/sp^2$7 eV/atom for $sp/sp^2$8-glaphyne, compared with $sp/sp^2$9, $sp$0, and $sp$1 eV/atom for pristine $sp$2-, $sp$3-, and $sp$4-graphyne, respectively (Fabris et al., 17 Sep 2025). The corresponding interpretation in the source is that more negative values indicate stronger binding and enhanced stability.

A binding-energy expression,

$sp$5

was also defined, although no numerical values were reported. The qualitative stability argument therefore rests primarily on cohesive-energy trends, relaxed geometries, and phonon signatures rather than on an explicit interlayer binding-energy dataset (Fabris et al., 17 Sep 2025).

4. Electronic structure and topology-dependent proximity effects

The defining result of the glaphyne study is that the electronic proximity effect from silica is real but not universal in its consequences. The same silica overlayer produces markedly different band-structure outcomes depending on graphyne topology and interfacial registry (Fabris et al., 17 Sep 2025).

In pristine form, $sp$6-graphyne has a Dirac cone at $sp$7 and $sp$8. After hybridization, $sp$9-glaphyne remains nearly gapless, with a Dirac-like cone shifted to $\mathrm{SiO_2}$00 and a band gap of approximately $\mathrm{SiO_2}$01 eV. Near the Fermi level, the density of states is dominated by C $\mathrm{SiO_2}$02 states; Si $\mathrm{SiO_2}$03 states contribute to the conduction band, while O states lie deeper in energy (Fabris et al., 17 Sep 2025).

Pristine $\mathrm{SiO_2}$04-graphyne is also semimetallic, with a Dirac cone along $\mathrm{SiO_2}$05–$\mathrm{SiO_2}$06 and $\mathrm{SiO_2}$07. By contrast, $\mathrm{SiO_2}$08-glaphyne develops a direct gap of $\mathrm{SiO_2}$09 eV at $\mathrm{SiO_2}$10. The bands also show slight flattening, implying reduced mobility. Its valence- and conduction-band edges are primarily C $\mathrm{SiO_2}$11, with Si $\mathrm{SiO_2}$12 participation in the conduction band and O states deeper in the conduction region (Fabris et al., 17 Sep 2025).

Pristine $\mathrm{SiO_2}$13-graphyne is already semiconducting, with a direct gap at $\mathrm{SiO_2}$14 of $\mathrm{SiO_2}$15 eV in the reported calculation, consistent with prior reports placing it in the approximate $\mathrm{SiO_2}$16–$\mathrm{SiO_2}$17 eV range (Fabris et al., 17 Sep 2025). In $\mathrm{SiO_2}$18-glaphyne, the direct gap at $\mathrm{SiO_2}$19 increases slightly to $\mathrm{SiO_2}$20 eV. Carbon $\mathrm{SiO_2}$21 states still dominate near $\mathrm{SiO_2}$22, while Si and O contributions remain largely confined to lower-lying states (Fabris et al., 17 Sep 2025).

The comparison across the three heterostructures establishes a restrictive conclusion: the formation of Si–O–C bonds does not by itself guarantee gap opening. The strongest case, $\mathrm{SiO_2}$23-glaphyne, combines aligned pores, stronger interfacial coupling, and substantial acetylenic bond distortion; $\mathrm{SiO_2}$24-glaphyne retains a nearly gapless Dirac-like spectrum; and $\mathrm{SiO_2}$25-glaphyne remains semiconducting with only a modest gap increase (Fabris et al., 17 Sep 2025). A common simplification is therefore incorrect: glaphynes are not uniformly “glaphene-like” wide-gap materials.

5. Charge redistribution, orbital character, and registry

The interfacial electronic response was further characterized through Mulliken populations and frontier-orbital isosurfaces. Relative to pristine graphynes, the overlap population increased by approximately $\mathrm{SiO_2}$26 for $\mathrm{SiO_2}$27-, $\mathrm{SiO_2}$28 for $\mathrm{SiO_2}$29-, and $\mathrm{SiO_2}$30 for $\mathrm{SiO_2}$31-glaphyne, indicating modified C $\mathrm{SiO_2}$32 distributions and enhanced interlayer coupling, with $\mathrm{SiO_2}$33-glaphyne as the clear outlier (Fabris et al., 17 Sep 2025).

The charge-density-difference quantity was defined as

$\mathrm{SiO_2}$34

Although the study did not provide layer-resolved numerical charge transfer, work-function shifts, or interface potential barriers, the HOCO/LUCO isosurfaces showed qualitative charge redistribution from graphyne to $\mathrm{SiO_2}$35, again strongest for $\mathrm{SiO_2}$36-glaphyne (Fabris et al., 17 Sep 2025).

Registry is the crucial structural correlate of this electronic behavior. In $\mathrm{SiO_2}$37-glaphyne, the pores of the silica and $\mathrm{SiO_2}$38-graphyne lattices are periodically aligned, and that registry correlates with localized frontier orbitals and with the opening of the direct gap. The same section of the study explicitly links the $\mathrm{SiO_2}$39 eV gap in $\mathrm{SiO_2}$40-glaphyne to aligned pores, Si–O–C coupling, and the strong elongation of the acetylenic single bonds (Fabris et al., 17 Sep 2025).

By contrast, the weaker electronic perturbation in $\mathrm{SiO_2}$41- and $\mathrm{SiO_2}$42-glaphyne is consistent with frontier states that remain more carbon-dominated and more delocalized near the Fermi level. Effective masses were not explicitly reported, but the source notes that the band flattening in $\mathrm{SiO_2}$43-glaphyne suggests increased effective masses and potentially lower mobility (Fabris et al., 17 Sep 2025). This suggests that glaphyne band engineering is inseparable from a transport tradeoff: stronger interfacial perturbation can open a technologically relevant gap, but may also reduce band dispersion.

6. Relation to glaphene, prospective uses, and open problems

Relative to glaphene, glaphynes display a weaker and far more topology-sensitive proximity response. Glaphene was reported to show very strong hybridization and a large gap of approximately $\mathrm{SiO_2}$44 eV, whereas glaphynes range from nearly gapless ($\mathrm{SiO_2}$45) to moderately gapped ($\mathrm{SiO_2}$46) to slightly modified semiconductor ($\mathrm{SiO_2}$47) (Fabris et al., 17 Sep 2025). Their vibrational evidence for Si–O–C bonding is nonetheless analogous: glaphene exhibits a characteristic mode near $\mathrm{SiO_2}$48, while glaphynes show related signatures across $\mathrm{SiO_2}$49–$\mathrm{SiO_2}$50 (Fabris et al., 17 Sep 2025).

The immediate application space identified for glaphynes is nanoelectronics and heterostructure band-gap engineering. In that context, $\mathrm{SiO_2}$51-glaphyne is the most notable case because its direct gap of $\mathrm{SiO_2}$52 eV places it in a regime relevant to transistor channels and optoelectronics (Fabris et al., 17 Sep 2025). The same source also points to sensors and membranes, where pore alignment and interfacial Si–O–C chemistry could enable selective transport and surface-mediated catalysis. These are prospective uses rather than experimentally demonstrated functions.

Experimental feasibility is argued indirectly. The successful synthesis of glaphene suggests that related vapor-phase growth strategies might be adapted to graphyne substrates, and the prior synthesis of $\mathrm{SiO_2}$53-graphyne makes that allotrope a particularly plausible platform (Fabris et al., 17 Sep 2025). This does not establish that glaphynes have been synthesized, but it places them within a credible experimental trajectory.

Several limitations remain explicit. Quantitative interlayer binding energies, work-function alignment, effective masses, and mobilities were not provided. Systematic studies of applied strain, twist angle, stacking alternatives, and electric fields were not performed, even though the reported dependence on registry already indicates that such variables are likely central to future band engineering (Fabris et al., 17 Sep 2025). The source also notes that complementary DFT or many-body calculations would refine band-edge positions and interfacial charge-transfer predictions. A plausible implication is that glaphynes are best viewed not as a single material with a fixed proximity effect, but as a registry-sensitive heterostructure family in which topology determines whether silica acts as a weak perturbation, a gap-opening overlayer, or only a modest band-edge modifier.