Allotropes of silicon

Allotropes of silicon are structurally varied forms of silicon.

## Contents

* 1 Amorphous
* 2 Crystalline
* 2.1 Silicene
* 2.2 Si24
* 2.3 4H silicon
* 2.4 Silicyne
* 3 References

## Amorphous

Amorphous silicon takes the form of a brown powder.[1]

## Crystalline

Crystalline silicon has a metallic luster and a grayish color. Single crystals can be grown with the Czochralski process. Crystalline silicon can be doped with elements such as boron, gallium, germanium, phosphorus or arsenic. Doped silicon is used in solid-state electronic devices, such as solar cells, rectifiers and computer chips.[1]

Silicon crystallizes in the same pattern as diamond, viewable as two interpenetrating face-centered cubic primitive lattices. The cube measures 0.543 nm on a side.[2]

### Silicene

Silicene is a two-dimensional system with a hexagonal honeycomb structure similar to that of graphene. Silicene has different characteristics than graphene. It has a periodically buckled topology; interlayer coupling is much stronger; and its oxidized form, 2D silica, has a different chemical structure from graphene oxide. It was first created in 2010.

Penta-silicene is a two-dimensional system with pentagonal structure similar to that of penta-graphene. The structure was first synthesized in 2005.[3][4]

### Si24

Si24 is an orthorhombic crystalline Si allotrope. It was first synthesized in 2014.[5][6] Creating the allotrope involved forming Na4Si24, a polycrystalline compound with help from a tantalum capsule, high temperature, and a 1,500 ton multi-anvil press that gradually reached a pressure of 10 gigapascals (1,500,000 psi). Next it was "degassed" in a vacuum at 400 K (127 °C; 260 °F) for eight days. The result was a zeolite-type structure.[7]

Si24 has a quasi-direct band gap (specifically a small and almost flat indirect band gap). It can conduct electricity more efficiently than diamond-structured silicon. It can absorb and emit light. It is composed of five-, six-, and eight-membered rings. Small atoms and molecules could pass through the associated holes.[7]

Si24 can be doped as both p- and n-type, and the dopants are readily ionized. Boron and phosphorus the most likely dopants.[8]

Potential applications include energy storage and filtering.[7]

### 4H silicon

4H silicon is a bulk, highly ordered hexagonal 4-layer crystalline form of Si24. Optical absorption measurements revealed an indirect band gap near 1.2 eV, in agreement with first principles calculations.[5][6]

### Silicyne

Main article: Chemistry:Silicyne

1-dimensional silicyne is analogous to the carbon allotrope carbyne, being a long chain of silicons, instead of carbons.[9] 2-dimensional silicyne is analogous to the carbon allotrope graphyne.[10]

## References

1. ↑ 1.0 1.1 "Silicon | Si (Element) - PubChem". https://pubchem.ncbi.nlm.nih.gov/element/Silicon#section=Description.
2. ↑ "Silicon and Germanium". http://hyperphysics.phy-astr.gsu.edu/hbase/Solids/sili2.html.
3. ↑ Leandri, C.; Lay, G. Le; Aufray, B.; Girardeaux, C.; Avila, J.; Dávila, M.E.; Asensio, M.C.; Ottaviani, C. et al. (2005). "Self-aligned silicon quantum wires on Ag(110)" (in en). Surface Science 574 (1): L9–L15. doi:10.1016/j.susc.2004.10.052. https://linkinghub.elsevier.com/retrieve/pii/S0039602804013895.
4. ↑ Sahaf, H.; Masson, L.; Léandri, C.; Aufray, B.; Le Lay, G.; Ronci, F. (2007-06-25). "Formation of a one-dimensional grating at the molecular scale by self-assembly of straight silicon nanowires" (in en). Applied Physics Letters 90 (26): 263110. doi:10.1063/1.2752125. ISSN 0003-6951. http://aip.scitation.org/doi/10.1063/1.2752125.
5. ↑ 5.0 5.1 Irving, Michael (2021-06-07). "Scientists create strange new form of silicon" (in en-US). https://newatlas.com/materials/4h-silicon-allotrope/.
6. ↑ 6.0 6.1 Shiell, Thomas B.; Zhu, Li; Cook, Brenton A.; Bradby, Jodie E.; McCulloch, Dougal G.; Strobel, Timothy A. (2021-05-25). "Bulk Crystalline $4H$-Silicon through a Metastable Allotropic Transition". Physical Review Letters 126 (21): 215701. doi:10.1103/PhysRevLett.126.215701. PMID 34114875. https://link.aps.org/doi/10.1103/PhysRevLett.126.215701.
7. ↑ 7.0 7.1 7.2 "New type of silicon could find use in solar cells and LEDs" (in en-US). 2014-11-20. https://newatlas.com/new-zeolite-type-silicon-synthesized/34851/.
8. ↑ Linghu, Jiajun; Shen, Lei; Yang, Ming; Xu, Shuyan; Feng, Yuan Ping (2017-07-27). "Si24: An Efficient Solar Cell Material". The Journal of Physical Chemistry C 121 (29): 15574–15579. doi:10.1021/acs.jpcc.7b04032. ISSN 1932-7447. https://doi.org/10.1021/acs.jpcc.7b04032.
9. ↑ Phillip F. Schewe; Ben Stein (3 September 1998). "Silicyne, A New Form Of Silicon". Inside Science Research - Physics News Update (American Institute of Physics) (388): p. Story #3. Archived from the original on 6 August 2007. https://web.archive.org/web/20070806184852/http://www.aip.org/pnu/1998/split/pnu388-3.htm. Retrieved 2013-10-12.
10. ↑ Pei Yang (裴 洋) and Wu Hai-Bin (武海斌) (2013). "Optimized geometry and electronic structure of graphyne-like silicyne nanoribbons". Chinese Physics B 22 (5): 057303. doi:10.1088/1674-1056/22/5/057303.

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