Silicene is a two-dimensional allotrope of silicon, with a hexagonal honeycomb structure similar to that of graphene
Contrary to graphene, silicene is not flat, but has a periodically buckled topology; the coupling between layers in silicene is much stronger than in multilayered graphene; and the oxidized form of silicene, 2D silica, has a very different chemical structure from graphene oxide.
History
Although theorists had speculated about the existence and possible properties of free-standing silicene, researchers first observed silicon structures that were suggestive of silicene in 2010. Using a scanning tunneling microscope they studied self-assembled silicene nanoribbons and silicene sheets deposited onto a SILVER crystal, Ag(110) and Ag(111), with atomic resolution. The images revealed HEXAGONS in a honeycomb structure similar to that of graphene, which, however, were shown to originate from the silver surface mimicking the hexagons. Density functional theory (DFT) calculations showed that silicon atoms tend to form such HONEYCOMB structures on SILVER, and adopt a slight curvature that makes the graphene-like configuration more likely. However, such a model has been invalidated for Si/Ag(110): the Ag surface displays a missing-row reconstruction upon Si adsorption and the honeycomb structures observed are tip artifacts.
- Takeda, K.; Shiraishi, K. (1994). “Theoretical possibility of stage corrugation in Si and Ge analogs of graphite”. Physical Review B. 50 (20): 14916–14922. Bibcode:1994PhRvB..5014916T. doi:10.1103/PhysRevB.50.14916. PMID 9975837.
- Guzmán-Verri, G.; Lew Yan Voon, L. (2007). “Electronic structure of silicon-based nanostructures”. Physical Review B. 76 (7): 075131. arXiv:1107.0075. Bibcode:2007PhRvB..76g5131G. doi:10.1103/PhysRevB.76.075131. S2CID 54532311.
- Cahangirov, S.; Topsakal, M.; Aktürk, E.; Şahin, H.; Ciraci, S. (2009). “Two- and One-Dimensional Honeycomb Structures of Silicon and Germanium”. Physical Review Letters. 102 (23): 236804. arXiv:0811.4412. Bibcode:2009PhRvL.102w6804C. doi:10.1103/PhysRevLett.102.236804. PMID 19658958. S2CID 22106457.
- Aufray, B.; Kara, A.; Vizzini, S. B.; Oughaddou, H.; LéAndri, C.; Ealet, B.; Le Lay, G. (2010). “Graphene-like silicon nanoribbons on Ag(110): A possible formation of silicene”. Applied Physics Letters. 96 (18): 183102. Bibcode:2010ApPhL..96r3102A. doi:10.1063/1.3419932.
- Lalmi, B.; Oughaddou, H.; Enriquez, H.; Kara, A.; Vizzini, S. B.; Ealet, B. N.; Aufray, B. (2010). “Epitaxial growth of a silicene sheet”. Applied Physics Letters. 97 (22): 223109. arXiv:1204.0523. Bibcode:2010ApPhL..97v3109L. doi:10.1063/1.3524215. S2CID 118490651.
- Lay, G. Le; Padova, P. De; Resta, A.; Bruhn, T.; Vogt, P. (2012-01-01). “Epitaxial silicene: can it be strongly strained?”. Journal of Physics D: Applied Physics. 45 (39): 392001. Bibcode:2012JPhD…45M2001L. doi:10.1088/0022-3727/45/39/392001. ISSN 0022-3727. S2CID 122247004.
- Bernard, R.; Leoni, T.; Wilson, A.; Lelaidier, T.; Sahaf, H.; Moyen, E.; Assaud, L. C.; Santinacci, L.; Leroy, F. D. R.; Cheynis, F.; Ranguis, A.; Jamgotchian, H.; Becker, C.; Borensztein, Y.; Hanbücken, M.; Prévot, G.; Masson, L. (2013). “Growth of Si ultrathin films on silver surfaces: Evidence of an Ag(110) reconstruction induced by Si”. Physical Review B. 88 (12): 121411. Bibcode:2013PhRvB..88l1411B. doi:10.1103/PhysRevB.88.121411.
- Colonna, S.; Serrano, G.; Gori, P.; Cricenti, A.; Ronci, F. (2013). “Systematic STM and LEED investigation of the Si/Ag(110) surface”. Journal of Physics: Condensed Matter. 25 (31): 315301. Bibcode:2013JPCM…25E5301C. doi:10.1088/0953-8984/25/31/315301. PMID 23835457. S2CID 29137834.
This was followed in 2013 by the discovery of DUMBELL reconstruction in silicene that explains the formation mechanisms of layered silicene and silicene on Ag.
- Özçelik, V. Ongun; Ciraci, S. (2013-12-02). “Local Reconstructions of Silicene Induced by Adatoms”. The Journal of Physical Chemistry C. 117 (49): 26305–26315. arXiv:1311.6657. Bibcode:2013arXiv1311.6657O. doi:10.1021/jp408647t. S2CID 44136093.
- Cahangirov, Seymur; Özçelik, V. Ongun; Rubio, Angel; Ciraci, Salim (2014-08-22). “Silicite: The layered allotrope of silicon”. Physical Review B. 90 (8): 085426. arXiv:1407.7981. Bibcode:2014PhRvB..90h5426C. doi:10.1103/PhysRevB.90.085426. S2CID 19795635.
- Cahangirov, Seymur; Özçelik, Veli Ongun; Xian, Lede; Avila, Jose; Cho, Suyeon; Asensio, María C.; Ciraci, Salim; Rubio, Angel (2014-07-28). “Atomic structure of the 3×3 phase of silicene on Ag(111)”. Physical Review B. 90 (3): 035448. arXiv:1407.3186. Bibcode:2014PhRvB..90c5448C. doi:10.1103/PhysRevB.90.035448. S2CID 42609103.
In 2015, a silicene field-effect transistor was tested that opens up opportunities for two-dimensional silicon for fundamental science studies and electronic applications.
- Tao, L.; Cinquanta, E.; Chiappe, D.; Grazianetti, C.; Fanciulli, M.; Dubey, M.; Molle, A.; Akinwande, D. (2015). “Silicene field-effect transistors operating at room temperature”. Nature Nanotechnology. 10 (3): 227–31. Bibcode:2015NatNa..10..227T. doi:10.1038/nnano.2014.325. hdl:10281/84255. PMID 25643256.
- Peplow, Mark (2 February 2015) “Graphene’s cousin silicene makes transistor debut”. Nature News & Comment.
- Iyengar, Rishi (February 5, 2015). “Researchers Have Made Computer-Chip Transistors Just One Atom Thick”. TIME.com.
- Davenport, Matt (February 5, 2015). “Two-Dimensional Silicon Makes Its Device Debut”. acs.org.
In 2022, it was found that silicene/Ag(111) growth on top of a Si/Ag(111) surface alloy, functions as a foundation and scaffold for the two-dimensional layer. This, however, raises questions of whether silicene can be truly regarded as two-dimensional material at all, due to its strong chemical bonds to the surface alloy.
- Küchle, Johannes T.; Baklanov, Aleksandr; Seitsonen, Ari P.; Ryan, Paul T.P.; Feulner, Peter; Pendem, Prashanth; Lee, Tien-Lin; Muntwiler, Matthias; Schwarz, Martin; Haag, Felix; Barth, Johannes V.; Auwärter, Willi; Duncan, David A.; Allegretti, Francesco (2022). “Silicene’s pervasive surface alloy on Ag(111): a scaffold for two-dimensional growth”. 2D Materials. 9 (4): 045021. Bibcode:2022TDM…..9d5021K. doi:10.1088/2053-1583/ac8a01.
Similarities and differences with graphene
SILICON and CARBON are similar atoms. They lie above and below each other in the same group on the periodic table, and both have an s2 p2 electronic structure. The 2D structures of silicene and graphene also are quite similar, but both have important differences. While both form hexagonal structures, graphene is completely flat, while silicene forms a buckled hexagonal shape. Its buckled structure gives silicene a tuneable band gap by applying an external electric field. Silicene’s hydrogenation reaction is more exothermic than graphene’s. Another difference is that since silicon’s COVALENT BONDS do not have pi-stacking, silicene does not cluster into a GRAPHITE-like form. The formation of a buckled structure in silicene unlike planar structure of GRAPHENE has been attributed to strong Pseudo Jahn–Teller distortions arising due to vibronic coupling between closely spaced filled and empty electronic states.
- Garcia, J. C.; de Lima, D. B.; Assali, L. V. C.; Justo, J. F. (2011). “Group IV Graphene- and Graphane-Like Nanosheets”. J. Phys. Chem. C. 115 (27): 13242. arXiv:1204.2875. doi:10.1021/jp203657w. S2CID 98682200.
- Jose, D.; Datta, A. (2014). “Structures and Chemical Properties of Silicene: Unlike Graphene”. Accounts of Chemical Research. 47 (2): 593–602. doi:10.1021/ar400180e. PMID 24215179.
Silicene and graphene have similar electronic structures. Both have a Dirac cone and linear electronic dispersion around the Dirac points. Both also have a quantum spin Hall effect. Both are expected to have the characteristics of massless Dirac fermions that carry charge, but this is only predicted for silicene and has not been observed, likely because it is expected to only occur with free-standing silicene which has not been synthesized. It is believed that the substrate on which the silicene is made has a substantial effect on its electronic properties.
- Jose, D.; Datta, A. (2014). “Structures and Chemical Properties of Silicene: Unlike Graphene”. Accounts of Chemical Research. 47 (2): 593–602. doi:10.1021/ar400180e. PMID 24215179.
Unlike carbon atoms in graphene, silicon atoms tend to adopt sp3 hybridization over sp2 in silicene, which makes it highly chemically active on the surface and allows its electronic states to be easily tuned by chemical functionalization.
- Du, Yi; Zhuang, Jincheng; Liu, Hongsheng; Zhuang, Jincheng; Xu, Xun; et al. (2014). “Tuning the Band Gap in Silicene by Oxidation”. ACS Nano. 8 (10): 10019–25. arXiv:1412.1886. Bibcode:2014arXiv1412.1886D. doi:10.1021/nn504451t. PMID 25248135. S2CID 14692606.
Compared with graphene, silicene has several prominent advantages: (1) a much stronger spin–orbit coupling, which may lead to a realization of quantum spin Hall effect in the experimentally accessible temperature, (2) a better tunability of the band gap, which is necessary for an effective field effect transistor (FET) operating at room temperature, (3) an easier valley polarization and more suitability for valleytronics study.
- Zhao, Jijun; Liu, Hongsheng; Yu, Zhiming; Quhe, Ruge; Zhou, Si; Wang, Yangyang; Zhong, Hongxia; Han, Nannan; Lu, Jing; Yao, Yugui; Wu, Kehui (2016). “Rise of silicene: A competitive 2D material”. Progress in Materials Science. 83: 24–151. doi:10.1016/j.pmatsci.2016.04.001.
Unlike graphene, it has been shown that, at least silicene supported by Ag(111) grows on a surface alloy. Hence, decoupling silicene is much less trivial, if possible at all, than decoupling graphene.
- Küchle, Johannes T.; Baklanov, Aleksandr; Seitsonen, Ari P.; Ryan, Paul T.P.; Feulner, Peter; Pendem, Prashanth; Lee, Tien-Lin; Muntwiler, Matthias; Schwarz, Martin; Haag, Felix; Barth, Johannes V.; Auwärter, Willi; Duncan, David A.; Allegretti, Francesco (2022). “Silicene’s pervasive surface alloy on Ag(111): a scaffold for two-dimensional growth”. 2D Materials. 9 (4): 045021. Bibcode:2022TDM…..9d5021K. doi:10.1088/2053-1583/ac8a01.
Surface alloying
Silicene on Ag(111) grows on top of a Si/Ag(111) surface alloy, which has been shown by a combination of different measurement techniques. The surface alloy precedes the growth of silicene, acting both as foundation and as scaffold for the two-dimensional layer. Upon further increase of silicon coverage, the alloy is covered by silicene, yet pervasivley exists for all coverages. This implies that the properties of the layer are strongly influenced by its alloy.
- Küchle, Johannes T.; Baklanov, Aleksandr; Seitsonen, Ari P.; Ryan, Paul T.P.; Feulner, Peter; Pendem, Prashanth; Lee, Tien-Lin; Muntwiler, Matthias; Schwarz, Martin; Haag, Felix; Barth, Johannes V.; Auwärter, Willi; Duncan, David A.; Allegretti, Francesco (2022). “Silicene’s pervasive surface alloy on Ag(111): a scaffold for two-dimensional growth”. 2D Materials. 9 (4): 045021. Bibcode:2022TDM…..9d5021K. doi:10.1088/2053-1583/ac8a01.
Band gap
Early studies of silicene showed that different dopants within the silicene structure provide the ability to tune its band gap. Very recently, the band gap in epitaxial silicene has been tuned by oxygen adatoms from zero-gap-type to semiconductor-type. With a tunable band gap, specific electronic components could be made-to-order for applications that require specific band gaps. The band gap can be brought down to 0.1 eV, which is considerably smaller than the band gap (0.4 eV) found in traditional field effect transistors (FETs).
- Ni, Z.; Zhong, H.; Jiang, X.; Quhe, R.; Luo, G.; Wang, Y.; Ye, M.; Yang, J.; Shi, J.; Lu, J. (2014). “Tunable band gap and doping type in silicene by surface adsorption: Towards tunneling transistors”. Nanoscale. 6 (13): 7609–18. arXiv:1312.4226. Bibcode:2014Nanos…6.7609N. doi:10.1039/C4NR00028E. PMID 24896227. S2CID 8924184.
- Du, Yi; Zhuang, Jincheng; Liu, Hongsheng; Zhuang, Jincheng; Xu, Xun; et al. (2014). “Tuning the Band Gap in Silicene by Oxidation”. ACS Nano. 8 (10): 10019–25. arXiv:1412.1886. Bibcode:2014arXiv1412.1886D. doi:10.1021/nn504451t. PMID 25248135. S2CID 14692606.
Inducing n-type doping within silicene requires an alkali metal dopant. Varying the amount adjusts the band gap. Maximum doping increases the band gap 0.5eV. Due to heavy doping, the supply voltage must also be c. 30V. Alkali metal-doped silicene can only produce n-type semiconductors; modern day electronics require a complementary n-type and p-type junction. Neutral doping (i-type) is required to produce devices such as light emitting diodes (LEDs). LEDs use a p-i-n junction to produce light. A separate dopant must be introduced to generate p-type doped silicene. IRIDIUM (Ir) doped silicene allows p-type silicene to be created. Through platinum (Pt) doping, i-type silicene is possible. With the combination of n-type, p-type and i-type doped structures, silicene has opportunities for use in electronics.
- Ni, Z.; Zhong, H.; Jiang, X.; Quhe, R.; Luo, G.; Wang, Y.; Ye, M.; Yang, J.; Shi, J.; Lu, J. (2014). “Tunable band gap and doping type in silicene by surface adsorption: Towards tunneling transistors”. Nanoscale. 6 (13): 7609–18. arXiv:1312.4226. Bibcode:2014Nanos…6.7609N. doi:10.1039/C4NR00028E. PMID 24896227. S2CID 8924184.
Power dissipation within traditional metal oxide semiconductor field effect transistors (MOSFETs) generates a bottleneck when dealing with nano-electronics. Tunnel field-effect transistors (TFETs) may become an alternative to traditional MOSFETs because they can have a smaller subthreshold slope and supply voltage, which reduce power dissipation. Computational studies showed that silicene based TFETs outperform traditional silicon based MOSFETs. Silicene TFETs have an on-state current over 1mA/μm, a sub-threshold slope of 77 mV/decade and a supply voltage of 1.7 V. With this much increased on-state current and reduced supply voltage, power dissipation within these devices is far below that of traditional MOSFETs and its peer TFETs.
- Ni, Z.; Zhong, H.; Jiang, X.; Quhe, R.; Luo, G.; Wang, Y.; Ye, M.; Yang, J.; Shi, J.; Lu, J. (2014). “Tunable band gap and doping type in silicene by surface adsorption: Towards tunneling transistors”. Nanoscale. 6 (13): 7609–18. arXiv:1312.4226. Bibcode:2014Nanos…6.7609N. doi:10.1039/C4NR00028E. PMID 24896227. S2CID 8924184.
Properties
2D silicene is not fully planar, apparently featuring chair-like puckering distortions in the rings. This leads to ordered surface ripples. Hydrogenation of silicenes to silicanes is exothermic. This led to the prediction that the process of conversion of silicene to silicane (hydrogenated silicene) is a candidate for HYDROGEN STORAGE. Unlike graphite, which consists of weakly held stacks of graphene layers through dispersion forces, interlayer coupling in silicenes is very strong.
The buckling of the hexagonal structure of silicene is caused by pseudo Jahn–Teller distortion (PJT). This is caused by strong vibronic coupling of unoccupied molecular orbitals (UMO) and occupied molecular orbitals (OMO). These orbitals are close enough in energy to cause the distortion to high symmetry configurations of silicene. The buckled structure can be flattened by suppressing the PJT distortion by increasing the energy gap between the UMO and OMO. This can be done by adding a LITHIUM ion.
- Jose, D.; Datta, A. (2014). “Structures and Chemical Properties of Silicene: Unlike Graphene”. Accounts of Chemical Research. 47 (2): 593–602. doi:10.1021/ar400180e. PMID 24215179.
In addition to its potential compatibility with existing semiconductor techniques, silicene has the advantage that its edges do not exhibit oxygen reactivity.
- Padova, P. D.; Leandri, C.; Vizzini, S.; Quaresima, C.; Perfetti, P.; Olivieri, B.; Oughaddou, H.; Aufray, B.; Le Lay, G. L. (2008). “Burning Match Oxidation Process of Silicon Nanowires Screened at the Atomic Scale”. Nano Letters. 8 (8): 2299–2304. Bibcode:2008NanoL…8.2299P. doi:10.1021/nl800994s. PMID 18624391.
In 2012, several groups independently reported ordered phases on the Ag(111) surface. Results from scanning tunneling spectroscopy measurements and from angle-resolved photoemission spectroscopy (ARPES) appeared to show that silicene would have similar electronic properties as graphene, namely an electronic dispersion resembling that of relativistic Dirac fermions at the K points of the Brillouin zone, but the interpretation was later disputed and shown to arise due to a substrate band. A band unfolding technique was used to interpret the ARPES results, revealing the substrate origin of the observed linear dispersion.
- Vogt, P.; De Padova, P.; Quaresima, C.; Avila, J.; Frantzeskakis, E.; Asensio, M. C.; Resta, A.; Ealet, B. N. D.; Le Lay, G. (2012). “Silicene: Compelling Experimental Evidence for Graphenelike Two-Dimensional Silicon” (PDF). Physical Review Letters. 108 (15): 155501. Bibcode:2012PhRvL.108o5501V. doi:10.1103/PhysRevLett.108.155501. PMID 22587265.
- Lin, C. L.; Arafune, R.; Kawahara, K.; Tsukahara, N.; Minamitani, E.; Kim, Y.; Takagi, N.; Kawai, M. (2012). “Structure of Silicene Grown on Ag(111)”. Applied Physics Express. 5 (4): 045802. Bibcode:2012APExp…5d5802L. doi:10.1143/APEX.5.045802. S2CID 96026790.
- Feng, B.; Ding, Z.; Meng, S.; Yao, Y.; He, X.; Cheng, P.; Chen, L.; Wu, K. (2012). “Evidence of Silicene in Honeycomb Structures of Silicon on Ag(111)”. Nano Letters. 12 (7): 3507–3511. arXiv:1203.2745. Bibcode:2012NanoL..12.3507F. doi:10.1021/nl301047g. PMID 22658061. S2CID 6522717.
- Chen, L.; Liu, C. C.; Feng, B.; He, X.; Cheng, P.; Ding, Z.; Meng, S.; Yao, Y.; Wu, K. (2012). “Evidence for Dirac Fermions in a Honeycomb Lattice Based on Silicon” (PDF). Physical Review Letters. 109 (5): 056804. arXiv:1204.2642. Bibcode:2012PhRvL.109e6804C. doi:10.1103/PhysRevLett.109.056804. PMID 23006197. S2CID 22876885.
- Guo, Z. X.; Furuya, S.; Iwata, J. I.; Oshiyama, A. (2013). “Absence of Dirac Electrons in Silicene on Ag(111) Surfaces”. Journal of the Physical Society of Japan. 82 (6): 063714. arXiv:1211.3495. Bibcode:2013JPSJ…82f3714G. doi:10.7566/JPSJ.82.063714. S2CID 118438039.
- Wang, Yun-Peng; Cheng, Hai-Ping (2013-06-24). “Absence of a Dirac cone in silicene on Ag(111): First-principles density functional calculations with a modified effective band structure technique”. Physical Review B. 87 (24): 245430. arXiv:1302.5759. Bibcode:2013PhRvB..87x5430W. doi:10.1103/PhysRevB.87.245430. S2CID 119263023.
- Arafune, R.; Lin, C. -L.; Nagao, R.; Kawai, M.; Takagi, N. (2013). “Comment on “Evidence for Dirac Fermions in a Honeycomb Lattice Based on Silicon””. Physical Review Letters. 110 (22): 229701. Bibcode:2013PhRvL.110v9701A. doi:10.1103/PhysRevLett.110.229701. PMID 23767755.
- Lin, C. L.; Arafune, R.; Kawahara, K.; Kanno, M.; Tsukahara, N.; Minamitani, E.; Kim, Y.; Kawai, M.; Takagi, N. (2013). “Substrate-Induced Symmetry Breaking in Silicene”. Physical Review Letters. 110 (7): 076801. Bibcode:2013PhRvL.110g6801L. doi:10.1103/PhysRevLett.110.076801. PMID 25166389.
- Gori, P.; Pulci, O.; Ronci, F.; Colonna, S.; Bechstedt, F. (2013). “Origin of Dirac-cone-like features in silicon structures on Ag(111) and Ag(110)”. Journal of Applied Physics. 114 (11): 113710–113710–5. Bibcode:2013JAP…114k3710G. doi:10.1063/1.4821339.
- Xu, Xun; Zhuang, Jincheng; Du, Yi; Feng, Haifeng; Zhang, Nian; Liu, Cheng; Lei, Tao; Wang, Jiaou; Spencer, Michelle; Morishita, Tetsuya; Wang, Xiaolin; Dou, Shixue (2014). “Effects of oxygen adsorption on the surface state of epitaxial silicene on Ag(111)”. Scientific Reports. Nature Publishing Group. 4: 7543. arXiv:1412.1887. Bibcode:2014NatSR…4E7543X. doi:10.1038/srep07543. PMC 4269890. PMID 25519839.
- Mahatha, S.K.; Moras, P.; Bellini, V.; Sheverdyaeva, P.M.; Struzzi, C.; Petaccia, L.; Carbone, C. (2014-05-30). “Silicene on Ag(111): A honeycomb lattice without Dirac bands”. Physical Review B. 89 (24): 201416. arXiv:2306.17524. Bibcode:2014PhRvB..89t1416M. doi:10.1103/PhysRevB.89.201416. S2CID 124891489.
- Chen, M.X.; Weinert, M. (2014-08-12). “Revealing the Substrate Origin of the Linear Dispersion of Silicene/Ag(111)”. Nano Letters. 14 (9): 5189–93. arXiv:1408.3188. Bibcode:2014NanoL..14.5189C. doi:10.1021/nl502107v. PMID 25115310. S2CID 5277372.
Besides silver, silicene has been reported to grow on ZrB
2, and iridium. Theoretical studies predicted that silicene is stable on the Al(111) surface as a honeycomb-structured monolayer (with a binding energy similar to that observed on the 4×4 Ag(111) surface) as well as a new form dubbed “polygonal silicene”, its structure consisting of 3-, 4-, 5- and 6-sided polygons.
- Fleurence, A.; Friedlein, R.; Ozaki, T.; Kawai, H.; Wang, Y.; Yamada-Takamura, Y. (2012). “Experimental Evidence for Epitaxial Silicene on Diboride Thin Films”. Physical Review Letters. 108 (24): 245501. Bibcode:2012PhRvL.108x5501F. doi:10.1103/PhysRevLett.108.245501. PMID 23004288.
- Meng, L.; Wang, Y.; Zhang, L.; Du, S.; Wu, R.; Li, L.; Zhang, Y.; Li, G.; Zhou, H.; Hofer, W. A.; Gao, H. J. (2013). “Buckled Silicene Formation on Ir(111)”. Nano Letters. 13 (2): 685–690. Bibcode:2013NanoL..13..685M. doi:10.1021/nl304347w. PMID 23330602.
- Morishita, T.; Spencer, M. J. S.; Kawamoto, S.; Snook, I. K. (2013). “A New Surface and Structure for Silicene: Polygonal Silicene Formation on the Al(111) Surface”. The Journal of Physical Chemistry C. 117 (42): 22142. doi:10.1021/jp4080898.
The p-d hybridisation mechanism between Ag and Si is important to stabilise the nearly flat silicon clusters and the effectiveness of Ag substrate for silicene growth explained by DFT calculations and molecular dynamics simulations. The unique hybridized electronic structures of epitaxial 4 × 4 silicene on Ag(111) determines highly chemical reactivity of silicene surface, which are revealed by scanning tunneling microscopy and angle-resolved photoemission spectroscopy. The hybridization between Si and Ag results in a metallic surface state, which can gradually decay due to oxygen adsorption. X-ray photoemission spectroscopy confirms the decoupling of Si-Ag bonds after oxygen treatment as well as the relative oxygen resistance of Ag(111) surface, in contrast to 4 × 4 silicene [with respect to Ag(111)].
- Gao, J.; Zhao, J. (2012). “Initial geometries, interaction mechanism and high stability of silicene on Ag(111) surface”. Scientific Reports. 2: 861. Bibcode:2012NatSR…2E.861G. doi:10.1038/srep00861. PMC 3498736. PMID 23155482.
- Xu, Xun; Zhuang, Jincheng; Du, Yi; Feng, Haifeng; Zhang, Nian; Liu, Cheng; Lei, Tao; Wang, Jiaou; Spencer, Michelle; Morishita, Tetsuya; Wang, Xiaolin; Dou, Shixue (2014). “Effects of oxygen adsorption on the surface state of epitaxial silicene on Ag(111)”. Scientific Reports. Nature Publishing Group. 4: 7543. arXiv:1412.1887. Bibcode:2014NatSR…4E7543X. doi:10.1038/srep07543. PMC 4269890. PMID 25519839.
Functionalized silicene
Beyond the pure silicene structure, research into functionalized silicene has yielded successful growth of organomodified silicene – oxygen-free silicene sheets functionalized with phenyl rings.[40] Such functionalization allows uniform dispersion of the structure in organic solvents and indicates the potential for a range of new functionalized silicon systems and organosilicon nanosheets.
- Sugiyama, Y.; Okamoto, H.; Mitsuoka, T.; Morikawa, T.; Nakanishi, K.; Ohta, T.; Nakano, H. (2010). “Synthesis and Optical Properties of Monolayer Organosilicon Nanosheets”. Journal of the American Chemical Society. 132 (17): 5946–7. doi:10.1021/ja100919d. PMID 20387885.
Silicene transistors
The U.S. Army Research Laboratory has been supporting research on silicene since 2014. The stated goals for research efforts were to analyze atomic scale materials, such as silicene, for properties and functionalities beyond existing materials, like graphene. In 2015, Deji Akinwande, led researchers at the University of Texas, Austin in conjunction with Alessandro Molle’s group at CNR, Italy, and collaboration with U.S. Army Research Laboratory and developed a method to stabilize silicene in air and reported a functional silicene field effect transistor device. An operational transistor’s material must have bandgaps, and functions more effectively if it possesses a high mobility of electrons. A bandgap is an area between the valence and conduction bands in a material where no electrons exist. Although graphene has a high mobility of electrons, the process of forming a bandgap in the material reduces many of its other electric potentials.
- Botari, T.; Perim, E.; Autreto, P. A. S.; van Duin, A. C. T.; Paupitz, R.; Galvao, D. S. (2014). “Mechanical properties and fracture dynamics of silicene membranes”. Phys. Chem. Chem. Phys. 16 (36): 19417–19423. arXiv:1408.1731. Bibcode:2014PCCP…1619417B. doi:10.1039/C4CP02902J. ISSN 1463-9076. PMID 25102369. S2CID 36269763.
- Quhe, Ru-Ge; Wang, Yang-Yang; Lü, Jing (August 2015). “Silicene transistors— A review”. Chinese Physics B (in Chinese). 24 (8): 088105. Bibcode:2015ChPhB..24h8105Q. doi:10.1088/1674-1056/24/8/088105. ISSN 1674-1056. S2CID 250764469.
Therefore, there have been investigations into using graphene analogues, such as silicene, as field effect transistors. Despite silicene’s natural state also having a zero-band gap, Akinwande and Molle and coworkers in collaboration with U.S. Army Research Laboratory have developed a silicene transistor. They designed a process termed “silicene encapsulated delamination with native electrodes” (SEDNE) to overcome silicene’s instability in the air. The stability that resulted has been claimed to be due to Si-Ag’s p-d hybridization. They grew a layer of silicene on top of a layer of Ag via epitaxy and covered the two with alumina (Al2O3). The silicene, Ag, and Al2O3 were stored in a vacuum at room temperature and observed over a tracked period of two months. The sample underwent Raman spectroscopy to be inspected for signs of degradation, but none were found. This complex stack was then laid on top of a SiO2 substrate with the Ag facing up. Ag was removed in a thin strip down the middle to reveal a silicene channel. The silicene channel on the substrate had a life of two minutes when exposed to air until it lost its signature Raman spectra. A bandgap of approximately 210 meV was reported. The substrate’s effects on silicene, in developing the bandgap, have been explained by the scattering of grain boundaries and limited transport of acoustic phonons, as well as by symmetry breaking and hybridization effect between silicene and the substrate. Acoustic phonons describe the synchronous movement of two or more types of atoms from their equilibrium position in a lattice structure.
- Quhe, Ru-Ge; Wang, Yang-Yang; Lü, Jing (August 2015). “Silicene transistors— A review”. Chinese Physics B (in Chinese). 24 (8): 088105. Bibcode:2015ChPhB..24h8105Q. doi:10.1088/1674-1056/24/8/088105. ISSN 1674-1056. S2CID 250764469.
- Tao, Li; Cinquanta, Eugenio; Chiappe, Daniele; Grazianetti, Carlo; Fanciulli, Marco; Dubey, Madan; Molle, Alessandro; Akinwande, Deji (2015-02-02). “Silicene field-effect transistors operating at room temperature”. Nature Nanotechnology. 10 (3): 227–231. Bibcode:2015NatNa..10..227T. doi:10.1038/nnano.2014.325. hdl:10281/84255. ISSN 1748-3387. PMID 25643256.
- Chen, M.X.; Zhong, Z.; Weinert, M. (2016). “Designing substrates for silicene and germanene: First-principles calculations”. Physical Review B. 94 (7): 075409. arXiv:1509.04641. Bibcode:2016PhRvB..94g5409C. doi:10.1103/PhysRevB.94.075409. S2CID 118569302.
Silicene nanosheets
2D silicene nanosheets are used in high-voltage symmetric supercapacitors as attractive electrode materials.
- Guo, Q.; Bai, C.; Gao, C.; Chen, N.; Qu, L. (September 1, 2022). “New Horizons Toward Supercapacitor Energy Devices”. ACS Applied Materials & Interfaces. 14 (34): 39014–39021. doi:10.1021/acsami.2c13677. PMID 35983748. S2CID 251670349. Retrieved September 7, 2022.
See also

- Stanene
- Not to be confused with stanine.
- Stanene is a topological insulator, which may display dissipationless currents at its edges near room temperature. It is composed of tin atoms arranged in a single layer, in a manner similar to graphene. Stanene got its name by combining stannum (the Latin name for tin) with the suffix -ene used by graphene. Research is ongoing in Germany and China, as well as at laboratories at Stanford and UCLA.
- DOE/SLAC National Accelerator Laboratory (2013-11-21). “Will 2-D tin be the next super material?”. Sciencedaily.com. Retrieved 2014-01-10.
- Garcia, J. C.; de Lima, D. B.; Assali, L. V. C.; Justo, J. F. (2011). “Group IV Graphene- and Graphane-Like Nanosheets”. J. Phys. Chem. C. 115: 13242. arXiv:1204.2875. doi:10.1021/jp203657w.
- “Will 2-D tin be the next super material?”. Phys.org. 21 November 2013. Retrieved 2014-01-10.
- Xu, Yong; Yan, Binghai; Zhang, Hai-Jun; Wang, Jing; Xu, Gang; Tang, Peizhe; Duan, Wenhui; Zhang, Shou-Cheng (2013-09-24). “Large-Gap Quantum Spin Hall Insulators in Tin Films”. Physical Review Letters. 111 (13): 136804. arXiv:1306.3008. doi:10.1103/PhysRevLett.111.136804. ISSN 0031-9007. PMID 24116803. S2CID 11310025.
- Singh, Ritu (November 24, 2013). “Tin could be the next super material for computer chips”. Zeenews.
- Markoff, John (January 9, 2014). “Designing the Next Wave of Computer Chips”. New York Times. Retrieved January 10, 2014.
- The addition of fluorine atoms to the tin lattice could extend the critical temperature up to 100 °C. This would make it practical for use in integrated circuits to make smaller, faster and more energy efficient computers.
- “Will 2-D Tin be the Next Super Material?” (Press release). Stanford University: SLAC National Accelerator Laboratory. November 21, 2013.
- See also
- Graphene
- Silicene
- Boron
- Stannenes (Similar name to Stanene)
- Stannane (similar name as Stanene, too)
- Semiconductors
- Topological Insulator
- Superconductivity
- Superconductors
- 2D silica
- Two-dimensional silica (2D silica) is a layered polymorph of silicon dioxide. Two varieties of 2D silica, both of hexagonal crystal symmetry, have been grown so far on various metal substrates. One is based on SiO4 tetrahedra, which are covalently bonded to the substrate. The second comprises graphene-like fully saturated sheets, which interact with the substrate via weak van der Waals bonds. One sheet of the second 2D silica variety is also called hexagonal bilayer silica (HBS); it can have either ordered or disordered (amorphous) structure.
- Björkman, T; Kurasch, S; Lehtinen, O; Kotakoski, J; Yazyev, O. V.; Srivastava, A; Skakalova, V; Smet, J. H.; Kaiser, U; Krasheninnikov, A. V. (2013). “Defects in bilayer silica and graphene: common trends in diverse hexagonal two-dimensional systems”. Scientific Reports. 3: 3482. Bibcode:2013NatSR…3E3482B. doi:10.1038/srep03482. PMC 3863822. PMID 24336488.
- 2D silica has potential applications in electronics as the thinnest gate dielectric. It can also be used for isolation of graphene sheets from the substrate.[1] 2D silica is a wide band gap semiconductor, whose band gap and geometry can be engineered by external electric field. It was shown to be a member of the auxetics materials family with a negative Poisson’s ratio.
- Özçelik, V. Ongun; Cahangirov, S.; Ciraci, S. (2014-06-20). “Stable Single-Layer Honeycomblike Structure of Silica”. Physical Review Letters. 112 (24): 246803. arXiv:1406.2674. Bibcode:2014PhRvL.112x6803O. doi:10.1103/PhysRevLett.112.246803. PMID 24996101.
- Two-dimensional silica (2D silica) is a layered polymorph of silicon dioxide. Two varieties of 2D silica, both of hexagonal crystal symmetry, have been grown so far on various metal substrates. One is based on SiO4 tetrahedra, which are covalently bonded to the substrate. The second comprises graphene-like fully saturated sheets, which interact with the substrate via weak van der Waals bonds. One sheet of the second 2D silica variety is also called hexagonal bilayer silica (HBS); it can have either ordered or disordered (amorphous) structure.
- Germanene
- Germanene is a material made up of a single layer of germanium atoms. The material is created in a process similar to that of silicene and graphene, in which high vacuum and high temperature are used to deposit a layer of germanium atoms on a substrate. High-quality thin films of germanene have revealed unusual two-dimensional structures with novel electronic properties suitable for semiconductor device applications and materials science research.
- Dávila, María Eugenia; Le Lay, Guy (2016). “Few layer epitaxial germanene: A novel two-dimensional Dirac material”. Scientific Reports. 6: 20714. Bibcode:2016NatSR…620714D. doi:10.1038/srep20714. PMC 4748270. PMID 26860590.
- “Graphene gets a ‘cousin’ in the shape of germanene”. Phys.org. Institute of Physics. 10 September 2014.
- Derivaz, Mickael and Dentel, Didier and Stephan, Regis and Hanf, Marie-Christine and Mehdaoui, Ahmed and Sonnet, Philippe and Pirri, Carmelo (2015). “Continuous germanene layer on Al (111)”. Nano Letters. ACS Publications. 15 (4): 2510–2516. Bibcode:2015NanoL..15.2510D. doi:10.1021/acs.nanolett.5b00085. PMID 25802988.
- Li, Linfei; Shuang-zan Lu; Jinbo Pan; Zhihui Qin; Yu-qi Wang; Yeliang Wang; Geng-yu Cao; Shixuan Du; Hong-Jun Gao (2014). “Buckled Germanene Formation on Pt(111)”. Advanced Materials. 26 (28): 4820–4824. Bibcode:2014AdM….26.4820L. doi:10.1002/adma.201400909. PMID 24841358. S2CID 1951633.
- In September 2014, G. Le Lay and others reported the deposition of a single atom thickness, ordered and two-dimensional multi-phase film by molecular beam epitaxy upon a gold surface in a crystal lattice with Miller indices (111). The structure was confirmed with scanning tunneling microscopy (STM) revealing a nearly flat honeycomb structure.
- Dávila, M. E. (2014). “Germanene: a novel two-dimensional germanium allotrope akin to graphene and silicene”. New Journal of Physics. 16 (9): 095002. arXiv:1406.2488. Bibcode:2014NJPh…16i5002D. doi:10.1088/1367-2630/16/9/095002. S2CID 53453703.
- We have provided compelling evidence of the birth of nearly flat germanene—a novel, synthetic germanium allotrope which does not exist in nature. It is a new cousin of graphene.— Guy Le Lay from Aix-Marseille University, New Journal of Physics
- Additional confirmation was obtained by spectroscopic measurement and density functional theory calculations. The development of high quality and nearly flat single atom films created speculation that germanene may replace graphene if not merely add an alternative to the novel properties of related nanomaterials.
- Dávila, M. E. (2014). “Germanene: a novel two-dimensional germanium allotrope akin to graphene and silicene”. New Journal of Physics. 16 (9): 095002. arXiv:1406.2488. Bibcode:2014NJPh…16i5002D. doi:10.1088/1367-2630/16/9/095002. S2CID 53453703.
- Clifford, Jonathan (10 September 2014). “Aix-Marseille University Researchers Produce Germanium Allotrope Germanene”. Uncover California Online Media. Archived from the original on 17 February 2020. Retrieved 11 September 2014.
- “Gold Substrate Used To Synthesize Graphene’s Cousin Germanene”. Capital OTC. 10 September 2014. Archived from the original on 11 September 2014. Retrieved 11 September 2014.
- Spickernell, Sarah (10 September 2014). “Germanene: Have scientists just created the new graphene?”. City A.M.
- Leathers, Jason (10 September 2014). “New Member In The Family ‘Germanene'”. Capital Wired. Archived from the original on 3 June 2016. Retrieved 11 September 2014.
- “Graphene gets a ‘cousin’ in the shape of germanene”. Phys.org. Institute of Physics. 10 September 2014.
- Bampoulis and others have reported the formation of germanene on the outermost layer of Ge2Pt nanocrystals. Atomically resolved STM images of germanene on Ge2Pt nanocrystals reveal a buckled honeycomb structure. This honeycomb lattice is composed of two hexagonal sublattices displaced by 0.2 Å in the vertical direction with respect to each other. The nearest-neighbor distance was found to be 2.5±0.1 Å, in close agreement with the Ge-Ge distance in germanene.
- Bampoulis, P.; Zhang, L.; Safaei, A.; van Gastel, R.; Poelsema, B.; Zandvliet, H. J. W. (2014). “Germanene termination of Ge2Pt crystals on Ge(110)”. Journal of Physics: Condensed Matter. 26 (44): 442001. arXiv:1706.00697. Bibcode:2014JPCM…26R2001B. doi:10.1088/0953-8984/26/44/442001. PMID 25210978. S2CID 36478002.
- Based on STM observations and density functional theory calculations, formation of an apparently more distorted form of germanene has been reported on platinum. Epitaxial growth of germanene crystals on GaAs(0001) has also been demonstrated, and calculations suggest that the minimal interactions should allow germanene to be readily removed from this substrate.
- Li, Linfei; Shuang-zan Lu; Jinbo Pan; Zhihui Qin; Yu-qi Wang; Yeliang Wang; Geng-yu Cao; Shixuan Du; Hong-Jun Gao (2014). “Buckled Germanene Formation on Pt(111)”. Advanced Materials. 26 (28): 4820–4824. Bibcode:2014AdM….26.4820L. doi:10.1002/adma.201400909. PMID 24841358. S2CID 1951633.
- Kaloni, T. P.; Schwingenschlögl, U. (13 November 2013). “Weak interaction between germanene and GaAs(0001) by H intercalation: A route to exfoliation”. Journal of Applied Physics. 114 (18): 184307–184307–4. arXiv:1310.7688. Bibcode:2013JAP…114r4307K. doi:10.1063/1.4830016.
- Dávila, M. E. (2014). “Germanene: a novel two-dimensional germanium allotrope akin to graphene and silicene”. New Journal of Physics. 16 (9): 095002. arXiv:1406.2488. Bibcode:2014NJPh…16i5002D. doi:10.1088/1367-2630/16/9/095002. S2CID 53453703.
- Germanene’s structure is described as “a group-IV graphene-like two-dimensional buckled nanosheet”. Adsorption of additional germanium onto the graphene-like sheet leads to formation of “dumbbell” units, each with two out-of-plane atoms of germanium, one on either side of the plane. Dumbbells attract each other. Periodically repeating arrangements of dumbbell structures may lead to additional stable phases of germanene, with altered electronic and magnetic properties.
- Ye, Xue-Sheng; Zhi-Gang Shao; Hongbo Zhao; Lei Yang; Cang-Long Wang (2014). “Intrinsic carrier mobility of germanene is larger than graphene’s: first-principle calculations”. RSC Advances. 4 (41): 21216–21220. Bibcode:2014RSCAd…421216Y. doi:10.1039/C4RA01802H.
- Özçelik, V. Ongun; E. Durgun; Salim Ciraci (2014). “New Phases of Germanene”. The Journal of Physical Chemistry Letters. 5 (15): 2694–2699. arXiv:1407.4170. doi:10.1021/jz500977v. PMID 26277965. S2CID 40693268.
- In October 2018, Junji Yuhara and others reported that germanene is easily prepared by a segregation method, using a bare Ag thin film on a Ge substrate and achieved in situ its epitaxial growth. The growth of germanene, akin to graphene and silicene, by a segregation method, is considered to be technically very important for the easy synthesis and transfer of this highly promising 2D electronic material.
- Yuhara, Junji; Hiroki Shimazu; Kouichi Ito; Akio Ohta; Masaaki Araidai; Masashi Kurosawa; Masashi Nakatake; Guy Le Lay (2018). “Germanene Epitaxial Growth by Segregation through Ag(111) Thin Films on Ge(111)”. ACS Nano. 12 (11): 11632–11637. doi:10.1021/acsnano.8b07006. PMID 30371060. S2CID 53102735.
- Germanene’s electronic and optical properties have been determined from ab initio calculations, and structural and electronic properties from first principles. These properties make the material suitable for use in the channel of a high-performance field-effect transistor and have generated discussion regarding the use of elemental monolayers in other electronic devices. The electronic properties of germanene are unusual, and provide a rare opportunity to test the properties of Dirac fermions. Germanene has no band gap, but attaching a hydrogen atom to each germanium atom creates one. These unusual properties are generally shared by graphene, silicene, germanene, stanene, and plumbene.
- Ni, Zeyuan; Qihang, Liu; Tang, Kechao; Zheng, Jiaxin; Zhou, Jing; Qin, Rui; Gao, Zhengxiang; Yu, Dapeng; Lu, Jing (2012). “Tunable Bandgap in Silicene and Germanene”. Nano Letters. 12 (1): 113–118. Bibcode:2012NanoL..12..113N. doi:10.1021/nl203065e. PMID 22050667.
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- Garcia, J. C.; de Lima, D. B.; Assali, L. V. C.; Justo, J. F. (2011). “Group IV graphene- and graphane-like nanosheets”. J. Phys. Chem. C. 115 (27): 13242–13246. arXiv:1204.2875. doi:10.1021/jp203657w. S2CID 98682200.
- Kaneko, Shiro; Tsuchiya, Hideaki; Kamakura, Yoshinari; Mori, Nobuya; Ogawa, Matsuto (2014). “Theoretical performance estimation of silicene, germanene, and graphene nanoribbon field-effect transistors under ballistic transport”. Applied Physics Express. 7 (3): 035102. Bibcode:2014APExp…7c5102K. doi:10.7567/APEX.7.035102. S2CID 95179181.
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- Berger, Andy (17 July 2015). “Beyond Graphene, a Zoo of New 2-D Materials”. Discover Magazine. Retrieved 19 September 2015.
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- Yuhara, J.; He, B.; Le Lay, G. (2019). “Graphene’s Latest Cousin: Plumbene Epitaxial Growth on a “Nano WaterCube””. Advanced Materials. 31 (27): 1901017. Bibcode:2019AdM….3101017Y. doi:10.1002/adma.201901017. PMID 31074927. S2CID 149446617
- Scientists Use Gold Substrate to Grow Graphene’s Cousin, Germanene (and germanene to grow gold?). Lead author Guy Le Lay, from Aix-Marseille University, said that the research was an accident. ‘Following our synthesis of graphene’s other cousin, silicene, we thought it natural to try and produce germanene in the same way, by depositing germanium onto a silver substrate,’ Le Lay said in a statement. ‘This attempt failed, so I decided to switch to a gold substrate, having remembered my old work from my PhD thesis, in which gold was grown onto a germanium substrate. I thought it would be worth trying the other way around,’ Le Lay said in a news release. The study was published in the Journal of Physics
- Nichols, Mary, Scientists Use Gold Substrate to Grow Graphene’s Cousin, Germanene, Design & Trend, September 10, 2014 Wayback Machine
- Germanene is a material made up of a single layer of germanium atoms. The material is created in a process similar to that of silicene and graphene, in which high vacuum and high temperature are used to deposit a layer of germanium atoms on a substrate. High-quality thin films of germanene have revealed unusual two-dimensional structures with novel electronic properties suitable for semiconductor device applications and materials science research.
- Borophene
- Borophene is a crystalline atomic monolayer of boron, i.e., it is a two-dimensional allotrope of boron and also known as boron sheet. First predicted by theory in the mid-1990s, different borophene structures were experimentally confirmed in 2015.
- Boustani, Ihsan (January 1997). “New quasi-planar surfaces of bare boron”. Surface Science. 370 (2–3): 355–363. Bibcode:1997SurSc.370..355B. doi:10.1016/S0039-6028(96)00969-7.
- Mannix, A. J.; Zhou, X.-F.; Kiraly, B.; Wood, J. D.; Alducin, D.; Myers, B. D.; Liu, X.; Fisher, B. L.; Santiago, U.; Guest, J. R.; et al. (December 17, 2015). “Synthesis of borophenes: Anisotropic, two-dimensional boron polymorphs”. Science. 350 (6267): 1513–1516. Bibcode:2015Sci…350.1513M. doi:10.1126/science.aad1080. PMC 4922135. PMID 26680195.
- Feng, Baojie; Zhang, Jin; Zhong, Qing; Li, Wenbin; Li, Shuai; Li, Hui; Cheng, Peng; Meng, Sheng; Chen, Lan; Wu, Kehui (March 28, 2016). “Experimental realization of two-dimensional boron sheets”. Nature Chemistry. 8 (6): 563–568. arXiv:1512.05029. Bibcode:2016NatCh…8..563F. doi:10.1038/nchem.2491. PMID 27219700. S2CID 19475989.
- Experimentally various atomically thin, crystalline and metallic borophenes were synthesized on clean metal surfaces under ultrahigh-vacuum conditions. Its atomic structure consists of mixed triangular and hexagonal motifs, such as shown in Figure 1. The atomic structure is a consequence of an interplay between two-center and multi-center in-plane bonding, which is typical for electron deficient elements like boron.
- Mannix, A. J.; Zhou, X.-F.; Kiraly, B.; Wood, J. D.; Alducin, D.; Myers, B. D.; Liu, X.; Fisher, B. L.; Santiago, U.; Guest, J. R.; et al. (December 17, 2015). “Synthesis of borophenes: Anisotropic, two-dimensional boron polymorphs”. Science. 350 (6267): 1513–1516. Bibcode:2015Sci…350.1513M. doi:10.1126/science.aad1080. PMC 4922135. PMID 26680195.
- Feng, Baojie; Zhang, Jin; Zhong, Qing; Li, Wenbin; Li, Shuai; Li, Hui; Cheng, Peng; Meng, Sheng; Chen, Lan; Wu, Kehui (March 28, 2016). “Experimental realization of two-dimensional boron sheets”. Nature Chemistry. 8 (6): 563–568. arXiv:1512.05029. Bibcode:2016NatCh…8..563F. doi:10.1038/nchem.2491. PMID 27219700. S2CID 19475989.
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- Borophenes exhibit in-plane elasticity and ideal strength. It can be stronger than graphene, and more flexible, in some configurations. Boron nanotubes are also stiffer than graphene, with a higher 2D Young’s modulus than any other known carbon and noncarbon nanostructures. Since borophene is theoretically predicted to have metallic electronic structures and boron is lighter than most elements, borophene is expected to be the lightest experimentally realizable 2D metal. As with most 2D materials, borophene is expected to have anisotropic properties. In terms of mechanical properties, v1/6 (where the fraction denotes the hollow hexagon density) borophene is theoretically predicted to have an in-plane modulus of up to 210 N/m, Poisson’s ratio of up to 0.17. Furthermore, the modulus is predicted to be relatively invariant to phase as v varies from 1/5 to 1/9. This is a particularly salient point because borophenes undergo novel structural phase transition under in-plane tensile loading instead of fracturing due to the fluxional nature of their multi-center in-plane bonding. v1/6 borophene is also predicted to have an out-of-plane bending stiffness of 0.39 eV, smaller than any reported 2D material. The ratio of the modulus to the stiffness (a.k.a. the Foppl–von Karman number per unit area) which effectively characterizes a material’s flexibility is around 570 nm−2 for the v1/6 phase. These predicted properties are partially supported by experimental work, where v1/6 borophene was synthesized on a surface reconstructed Ag(111) substrate. Instead of growing as flat, planar borophene sheets as expected for flat Ag(111) substrates, the borophene took on an undulating configuration closely following the protruding rows arising from the surface reconstructed Ag(111) substrate. Ideal flexible electronics require the ability to be stressed, compressed, and even twisted into a wide array of geometries; however, most 2D materials reported to date are unable to meet all of these criteria since they are stiff against in-plane deformation. Undulated borophene is a promising material for flexible electronics as undulated 2D materials adhered to elastomeric substrates should remain easy to bend and afford large in-plane deformations. The undulated borophene’s mechanical properties were studied using first principles calculations and were found to have similar values for the aforementioned mechanical properties. Comparing these values to graphene, the prototypical 2D material, the modulus and bending stiffness of borophene is lower while the Poisson’s ratio is similar. Notably, the Foppl-von Karman number for the v1/6 phase is more than twice that of graphene, indicating that borophenes are flexible atomic layers. Thus, borophenes may have applications such as reinforcing elements for composites and in flexible electronic interconnects, electrodes, and displays.
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- Borophene also has potential as an anode material for batteries due to high theoretical specific capacities, electronic conductivity, and ion transport properties. Hydrogen easily adsorbs to borophene, offers potential for hydrogen storage – over 15% of its weight. Borophene can catalyze the breakdown of molecular hydrogen into hydrogen ions, and reduce water.
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- Computational studies by I. Boustani and A. Quandt showed that small boron clusters do not adopt icosahedral geometries like boranes, instead they turn out to be quasi-planar (see Figure 2). This led to the discovery of a so-called Aufbau principle that predicts the possibility of borophene (boron sheets), boron fullerenes (borospherene) and boron nanotubes.
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- Additional studies showed that extended, triangular borophene (Figure 1(c)) is metallic and adopts a non-planar, buckled geometry. Further computational studies, initiated by the prediction of a stable B80 boron fullerene, suggested that extended borophene sheets with honeycomb structure and with partially filled hexagonal holes are stable. These borophene structures were predicted to be metallic. The so-called γ sheet (a.k.a. β12 borophene or υ1/6 sheet) is shown in Figure 1(a).
- Boustani, Ihsan; Quandt, Alexander; Hernández, Eduardo; Rubio, Angel (February 8, 1999). “New boron based nanostructured materials”. The Journal of Chemical Physics. 110 (6): 3176–3185. Bibcode:1999JChPh.110.3176B. doi:10.1063/1.477976.
- Kunstmann, Jens; Quandt, Alexander (July 12, 2006). “Broad boron sheets and boron nanotubes: An ab initio study of structural, electronic, and mechanical properties”. Physical Review B. 74 (3): 035413. arXiv:cond-mat/0509455. Bibcode:2006PhRvB..74c5413K. doi:10.1103/PhysRevB.74.035413. S2CID 73631941.
- Gonzalez Szwacki, Nevill; Sadrzadeh, Arta; Yakobson, Boris I. (April 20, 2007). “B80 Fullerene: An Ab Initio Prediction of Geometry, Stability, and Electronic Structure”. Physical Review Letters. 98 (16): 166804. Bibcode:2007PhRvL..98p6804G. doi:10.1103/PhysRevLett.98.166804. PMID 17501448.
- Tang, Hui & Ismail-Beigi, Sohrab (2007). “Novel Precursors for Boron Nanotubes: The Competition of Two-Center and Three-Center Bonding in Boron Sheets”. Physical Review Letters. 99 (11): 115501. arXiv:0710.0593. Bibcode:2007PhRvL..99k5501T. doi:10.1103/PhysRevLett.99.115501. PMID 17930448. S2CID 30421181.
- Özdoğan, C.; Mukhopadhyay, S.; Hayami, W.; Güvenç, Z. B.; Pandey, R.; Boustani, I. (March 18, 2010). “The Unusually Stable B100 Fullerene, Structural Transitions in Boron Nanostructures, and a Comparative Study of α- and γ-Boron and Sheets”. The Journal of Physical Chemistry C. 114 (10): 4362–4375. doi:10.1021/jp911641u.
- The planarity of boron clusters was first experimentally confirmed by the research team of L.-S. Wang. Later they showed that the structure of B36 (see Figure 2) is the smallest boron cluster to have sixfold symmetry and a perfect hexagonal vacancy, and that it can serve as a potential basis for extended two-dimensional boron sheets.
- Zhai, Hua-Jin; Kiran, Boggavarapu; Li, Jun; Wang, Lai-Sheng (November 9, 2003). “Hydrocarbon analogues of boron clusters — planarity, aromaticity and antiaromaticity”. Nature Materials. 2 (12): 827–833. Bibcode:2003NatMa…2..827Z. doi:10.1038/nmat1012. PMID 14608377. S2CID 23746395.
- Piazza, Z. A.; Hu, H. S.; Li, W. L.; Zhao, Y. F.; Li, J.; Wang, L. S. (2014). “Planar hexagonal B36 as a potential basis for extended single-atom layer boron sheets”. Nature Communications. 5: 3113. Bibcode:2014NatCo…5.3113P. doi:10.1038/ncomms4113. PMID 24445427.
- After the synthesis of silicene, multiple groups predicted that borophene could potentially be realized with the support of a metal surface. In particular, the lattice structure of borophene was shown to depend on the metal surface, displaying a disconnect from that in a freestanding state.
- Zhang, L. Z.; Yan, Q. B.; Du, S. X.; Su, G.; Gao, H.-J. (August 15, 2012). “Boron Sheet Adsorbed on Metal Surfaces: Structures and Electronic Properties”. The Journal of Physical Chemistry C. 116 (34): 18202–18206. doi:10.1021/jp303616d.
- Liu, Yuanyue; Penev, Evgeni S.; Yakobson, Boris I. (March 11, 2013). “Probing the Synthesis of Two-Dimensional Boron by First-Principles Computations”. Angewandte Chemie International Edition. 52 (11): 3156–3159. arXiv:1312.0656. doi:10.1002/anie.201207972. PMID 23355180. S2CID 44779429.
- Liu, Hongsheng; Gao, Junfeng; Zhao, Jijun (November 18, 2013). “From Boron Cluster to Two-Dimensional Boron Sheet on Cu(111) Surface: Growth Mechanism and Hole Formation”. Scientific Reports. 3 (1): 3238. Bibcode:2013NatSR…3E3238L. doi:10.1038/srep03238. PMC 3831238. PMID 24241341.
- Zhang, Z.; Yang, Y.; Gao, G.; Yakobson, B.I. (September 2, 2015). “Two-Dimensional Boron Monolayers Mediated by Metal Substrates”. Angewandte Chemie International Edition. 54 (44): 13022–13026. doi:10.1002/anie.201505425. PMID 26331848.
- In 2015 two research teams succeeded in synthesizing different borophene phases on silver (111) surfaces under ultrahigh-vacuum conditions. Among the three borophene phases synthesized (see Figure 1), the v1/6 sheet, or β12, was shown by an earlier theory to be the ground state on the Ag(111) surface, while the χ3 borophene was previously predicted by Zeng team in 2012. So far, borophenes exist only on substrates; how to transfer them onto a device-compatible substrate is necessary, but remains a challenge.
- Zhang, Z.; Yang, Y.; Gao, G.; Yakobson, B.I. (September 2, 2015). “Two-Dimensional Boron Monolayers Mediated by Metal Substrates”. Angewandte Chemie International Edition. 54 (44): 13022–13026. doi:10.1002/anie.201505425. PMID 26331848.
- Wu, Xiaojun; Dai, Jun; Zhao, Yu; Zhu, Zhiwen; Yang, Jinlong; Zeng, Xiao Cheng (July 20, 2012). “Two-Dimensional Boron Monolayer Sheets”. ACS Nano. 6 (8): 7443–7453. doi:10.1021/nn302696v. PMID 22816319.
- Zhang, Z.; Penev, E.S.; Yakobson, B.I. (October 31, 2017). “Two-dimensional boron: structures, properties and applications”. Chemical Society Reviews. 46 (22): 6746–6763. doi:10.1039/c7cs00261k. PMID 29085946.
- Mannix, A. J.; Zhou, X.-F.; Kiraly, B.; Wood, J. D.; Alducin, D.; Myers, B. D.; Liu, X.; Fisher, B. L.; Santiago, U.; Guest, J. R.; et al. (December 17, 2015). “Synthesis of borophenes: Anisotropic, two-dimensional boron polymorphs”. Science. 350 (6267): 1513–1516. Bibcode:2015Sci…350.1513M. doi:10.1126/science.aad1080. PMC 4922135. PMID 26680195.
- Feng, Baojie; Zhang, Jin; Zhong, Qing; Li, Wenbin; Li, Shuai; Li, Hui; Cheng, Peng; Meng, Sheng; Chen, Lan; Wu, Kehui (March 28, 2016). “Experimental realization of two-dimensional boron sheets”. Nature Chemistry. 8 (6): 563–568. arXiv:1512.05029. Bibcode:2016NatCh…8..563F. doi:10.1038/nchem.2491. PMID 27219700. S2CID 19475989.
- Molecular beam epitaxy is the main approach for the growth of high-quality borophene. The high melting point of boron and the growth of borophenes at moderate temperatures posed a significant challenge for the synthesis of borophenes. Utilizing diborane (B2H6) pyrolysis as a pure boron source, a group of researchers reported the growth of atomic-thickness borophene sheets via chemical vapor deposition (CVD) for the first time. The CVD-borophene layers display an average thickness of 4.2 Å, χ3 crystalline structure, and metallic conductivity.
- Mazaheri, Ali; Javadi, Mohammad; Abdi, Yaser (February 24, 2021). “Chemical Vapor Deposition of Two-Dimensional Boron Sheets by Thermal Decomposition of Diborane”. ACS Applied Materials & Interfaces. 13 (7): 8844–8850. doi:10.1021/acsami.0c22580. ISSN 1944-8244. PMID 33565849. S2CID 231862792.
- Atomic-scale characterization, supported by theoretical calculations, revealed structures reminiscent of fused boron clusters consisting of mixed triangular and hexagonal motives, as previously predicted by theory and shown in Figure 1. Scanning tunneling spectroscopy confirmed that the borophenes are metallic. This is in contrast to bulk boron allotropes, which are semiconducting and marked by an atomic structure based on B12 icosahedra.[citation needed]
- In 2021 researchers announced hydrogenated borophene on a silver substrate, dubbed borophane. The new material was claimed to be far more stable than its component. Hydrogenation reduces oxidation rates by more than two orders of magnitude after ambient exposure.
- Lavars, Nick (April 6, 2021). “2D “borophane” offers new building block for advanced electronics”. New Atlas. Archived from the original on April 6, 2021. Retrieved April 9, 2021.
- ^ Li, Qiucheng; Kolluru, Venkata Surya Chaitanya; Rahn, Matthew S.; Schwenker, Eric; Li, Shaowei; Hennig, Richard G.; Darancet, Pierre; Chan, Maria K. Y.; Hersam, Mark C. (March 12, 2021). “Synthesis of borophane polymorphs through hydrogenation of borophene”. Science. 371 (6534): 1143–1148. Bibcode:2021Sci…371.1143L. doi:10.1126/science.abg1874. ISSN 0036-8075. PMID 33707261. S2CID 232199843.
- Multilayer borophene
- Experimental evidence supporting the formation of stacked bilayer and trilayer borophene sheets was first observed in CVD-grown borophene layers.[28] Soon after that, the creation of two-layer borophene was announced in August 2021.
- Liu, Xiaolong; Li, Qiucheng; Ruan, Qiyuan; Rahn, Matthew S.; Yakobson, Boris I.; Hersam, Mark C. “Borophene synthesis beyond the single-atomic-layer limit.” Nature Materials (26 August 2021). https://doi.org/10.1038/s41563-021-01084-2
- Mazaheri, Ali; Javadi, Mohammad; Abdi, Yaser (February 24, 2021). “Chemical Vapor Deposition of Two-Dimensional Boron Sheets by Thermal Decomposition of Diborane”. ACS Applied Materials & Interfaces. 13 (7): 8844–8850. doi:10.1021/acsami.0c22580. ISSN 1944-8244. PMID 33565849. S2CID 231862792.
- Experimental evidence supporting the formation of stacked bilayer and trilayer borophene sheets was first observed in CVD-grown borophene layers.[28] Soon after that, the creation of two-layer borophene was announced in August 2021.
- See also
- Borophene is a crystalline atomic monolayer of boron, i.e., it is a two-dimensional allotrope of boron and also known as boron sheet. First predicted by theory in the mid-1990s, different borophene structures were experimentally confirmed in 2015.
- Plumbene
- Plumbene is a material made up of a single layer of lead atoms. The material is created in a process similar to that of graphene, silicene, germanene, and stanene, in which high vacuum and high temperature are used to deposit a layer of lead atoms on a substrate. High-quality thin films of plumbene have revealed two-dimensional honeycomb structures. First researched by Indian scientists, further investigations are being done around the world.
- Das, Dhiman Kumar; Sarkar, Jit; Singh, S. K. (2018-08-01). “Effect of sample size, temperature and strain velocity on mechanical properties of plumbene by tensile loading along longitudinal direction: A molecular dynamics study”. Computational Materials Science. 151: 196–203. doi:10.1016/j.commatsci.2018.05.006. S2CID 139217230.
- Wang, Pei-ji; Ping Li; Zhang, Bao-min; Yan, Shi-shen; Sheng-shi Li; Zhang, Run-wu; Ji, Wei-xiao; Yan, Shi-shen; Zhang, Chang-wen (2016-02-02). “Unexpected Giant-Gap Quantum Spin Hall Insulator in Chemically Decorated Plumbene Monolayer”. Scientific Reports. Nature. 6: 20152. Bibcode:2016NatSR…620152Z. doi:10.1038/srep20152. PMC 4735859. PMID 26833133.
- Zhang, Liang; Zhao, Hui; Ji, Wei-xiao; Zhang, Chang-wen; Li, Ping; Wang, Pei-ji (2018). “Discovery of a new quantum spin Hall phase in bilayer plumbene”. Chemical Physics Letters. 712: 78–82. Bibcode:2018CPL…712…78Z. doi:10.1016/j.cplett.2018.09.016. ISSN 0009-2614. S2CID 105573942.
- In April 2019, J. Yuhara and others reported the deposition of a single atom thickness by molecular beam epitaxy with a segregation method upon a palladium surface in a crystal lattice with Miller indices (111). The structure was confirmed with scanning tunneling microscopy (STM) revealing a nearly flat honeycomb structure. There is no evidence of any three-dimensional islands, but one notices a unique nanostructured tessellation all over the terraces looking like a space-filling polyhedral foam reduced to dimension 2.
- Yuhara, J.; He, B.; Le Lay, G. (2019). “Graphene’s Latest Cousin: Plumbene Epitaxial Growth on a “Nano WaterCube””. Advanced Materials. 31 (27): 1901017. Bibcode:2019AdM….3101017Y. doi:10.1002/adma.201901017. PMID 31074927. S2CID 149446617.
- Plumbene’s electronic and optical properties have been determined from ab initio calculations, indicating a band gap of 0.4 eV
- Yu, X.-L.; Huang, L.; Wu, J. (2017), “From a normal insulator to a topological insulator in plumbene”, Physical Review B, 95 (12): 125113, arXiv:1702.07447, Bibcode:2017PhRvB..95l5113Y, doi:10.1103/PhysRevB.95.125113, S2CID 119076198
- Das, Dhiman Kumar; Sarkar, Jit; Singh, S. K. (2018-08-01). “Effect of sample size, temperature and strain velocity on mechanical properties of plumbene by tensile loading along longitudinal direction: A molecular dynamics study”. Computational Materials Science. 151: 196–203. doi:10.1016/j.commatsci.2018.05.006. S2CID 139217230.
- Plumbene is a material made up of a single layer of lead atoms. The material is created in a process similar to that of graphene, silicene, germanene, and stanene, in which high vacuum and high temperature are used to deposit a layer of lead atoms on a substrate. High-quality thin films of plumbene have revealed two-dimensional honeycomb structures. First researched by Indian scientists, further investigations are being done around the world.
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External links
Wikimedia Commons has media related to Silicene.
- Yamada-Takamura, Y.; Friedlein, R. (2014). “Progress in the materials science of silicene”. Science and Technology of Advanced Materials. 15 (6): 064404. Bibcode:2014STAdM..15f4404Y. doi:10.1088/1468-6996/15/6/064404. PMC 5090386. PMID 27877727.
- Anthony, Sebastian (April 30, 2012). “Silicene discovered: Single-layer silicon that could beat graphene to market”.
- Choi, Charles Q. (December 4, 2013). “Could Atomically Thin Tin Transform Electronics?”. Scientific American.
- Johnson, R. Colin (3 December 2013). “Stanene May Be Better Than Graphene”. EE Times.
- Myslewski, Rik (4 December 2013). “OHM MY GOD! Move over graphene, here comes ‘100% PERFECT’ stanene”. The Register.
- “Tin-based stanene could conduct electricity with 100 percent efficiency”. gizmag. 2013-12-01. Retrieved 2013-12-05.
- Vandenberghe, William (2013-10-25). “Quantum Transport for future Nano-CMOS Applications : TFETs and 2D topological insulators” (PDF). University of Texas at Dallas. Retrieved 2014-01-03.
- Meet Graphene’s Sexy New Cousin Germanene
- Scientists Use Gold Substrate to Grow Graphene’s Cousin, Germanene
- Graphene Family Tree? Germanene Makes Its Appearance
- Liu, Cheng-Cheng (1 January 2011). “Quantum Spin Hall Effect in Silicene and Two-Dimensional Germanium”. Physical Review Letters. 107 (7): 076802. arXiv:1104.1290. Bibcode:2011PhRvL.107g6802L. doi:10.1103/PhysRevLett.107.076802. PMID 21902414. S2CID 16967564.
- Liu, Cheng-Cheng (1 January 2011). “Low-energy effective Hamiltonian involving spin-orbit coupling in silicene and two-dimensional germanium and tin”. Physical Review B. 84 (19): 195430. arXiv:1108.2933. Bibcode:2011PhRvB..84s5430L. doi:10.1103/PhysRevB.84.195430. S2CID 44216872.
- CNRS Website (2015)
- CNRS Website (2017)