Borophene, a boron analogue of graphene, exhibits a rich variety of chemical and physical properties. Here, we provide an intensive overview of recent progress in theoretical modeling and experimental synthesis of borophene. In particular, we analyze the influence of substrate, growth temperature, and precursor on the selectivity of boron nucleation. While three-dimensional (3D) bulk boron is more stable than a two-dimensional (2D) boron sheet, the nucleation barrier determined by the growth process controls the formation of the material and it depends on the specific growth environment. Theoretical studies have shown that a metal substrate can play an important role in stabilizing 2D boron clusters over their 3D form, resulting in the kinetically favored growth of 2D boron on the substrate even though the 2D boron clusters will be overwhelmingly less stable than the 3D form with increasing cluster size. Ag and Cu substrates have proven to be particularly suitable for achieving this preference. Guided by theoretical works and perhaps original insights, experimentalists from two independent groups have successfully synthesized 2D boron sheets on silver substrates by depositing ultra-high purity boron onto a clean Ag (111) surface under high vacuum conditions. Moreover, the borophene samples were found to exhibit the same atomic structure previously predicted to be preferred on this substrate. Besides the substrate, the growth temperature is also key to the final product. When the temperature is too low, boron growth cannot overcome the nucleation barrier of the 2D structure. As a result, boron clusters or amorphous boron structures are likely to be formed. In contrast, an excessively high growth temperature will steer the growth to overcome the nucleation barrier of 3D boron, possibly yielding boron nanofilms with finite thickness. Therefore, the growth temperature needs to be carefully controlled, so that the free energy of boron growth will be located between the nucleation barriers of the 3D and 2D forms. Some impurity elements found in synthetic source materials, such as hydrogen and oxygen, can also impact boron nucleation. The existence of these elements may alter the competition between 2D and 3D structures during the nucleation process. More importantly, hydrogen and oxygen can passivate the dangling bonds on the surface of a 3D boron structure, lowering its surface energy, and therefore, impairing the nucleation of 2D boron structures. At present, molecular beam epitaxy (MBE) is the only method with which borophene has been successfully synthesized. Yet this method is very expensive, suffers from low yield, and is constrained to small sample sizes. Thus, exploring the growth of borophene via chemical vapor deposition (CVD) on different substrates is critically important for realizing the great potential of borophene in various applications. By discussing possible growth conditions and atomistic mechanisms of borophene nucleation as well as theoretical methods for modeling and simulations, we suggest prospects for chemical vapor deposition growth of borophene on selected substrates. This work aims to offer useful guidance for chemical synthesis of large-area, high-quality borophenes and promote their practical applications.
Fig 1 The parallel of chemistry between carbon and boron (a) Carbon can form sp3, sp2 and sp bonds, thus can form a variety of nanostructures, such as 1D atomic chains, nanotubes and diamond. (b) Because of electronic deficiency, boron can form a vast number of multicenter chemical bonds, forming a typical B12 icosahedron in bulk phases as well as planar, fullerene molecules and nanotube structure at nanoscale.
Fig 2 Theoretical and experimental synthesis of two-dimensional borophene (a) Historical evolution of theoretical models of borophene, from the initial triangular structure to the combined structure of triangular lattice and hollow hexagons, to the polymorphism of borophene, and then to the energetically preferred borophene on substrates. (b) High resolution scanning electron microscope (SEM) image of stripe borophene (S1) synthesized by molecular beam epitaxy, compared to simulated SEM image using the v1/6 model on Ag substrate. (c) SEM image of homogeneous phase borophene (S2), compared to simulated SEM image based on the v1/5 model. (b) is adopted from American Association for the Advancement of Science publisher and (c) is adopted from Springer Nature publisher 11, 12.
Fig 3 The nucleation selectivity of borophene (a) Schematic diagram of the free energy of boron growth on a substrate along two- and three-dimensional routes. The range of temperature corresponding to the energy range of yellow shaded area should benefit boron nucleation along the 2D route. (b) A schematic diagram of nucleation and growth of 3D boron along a step of metal substrate. (c) The same as
(b) but for 2D boron. (a) is adopted from Springer Nature publisher 44.
Mannix A. J. ; Kiraly B. ; Hersam M. C. ; Guisinger N. P. Nat. Rev. Chem. 2017, 1, 0014.
Molle A. ; Goldberger J. ; Houssa M. ; Xu Y. ; Zhang S. C. ; Akinwande D. Nat. Mater. 2017, 16, 163.
Oganov A. R. ; Solozhenko V. L. J. Superhard Mater. 2009, 31, 285.
Huang W. ; Sergeeva A. P. ; Zhai H. J. ; Averkiev B. B. ; Wang L. S. ; Boldyrev A. I. Nat. Chem. 2010, 2, 202.
Sergeeva A. P. ; Popov I. A. ; Piazza Z. A. ; Li W. L. ; Romanescu C. ; Wang L. S. ; Boldyrev A. I. Acc. Chem. Res. 2014, 2, 1349.
Zhai H. J. ; Zhao Y. F. ; Li W. L. ; Chen Q. ; Bai H. ; Hu H. S. ; Piazza Z. A. ; Tian W. J. ; Lu H. G. ; Wu Y. B. ; et al Nat. Chem. 2014, 6, 727.
Ciuparu D. ; Klie R. F. ; Zhu Y. M. ; Pfefferle L. J. Phys. Chem. B 2004, 108, 3967.
Liu F. ; Shen C. M. ; Su Z. J. ; Ding X. L. ; Deng S. Z. ; Chen J. ; Xu N. S. ; Gao H. J. J. Mater. Chem. 2010, 20, 2197.
Tai G. A. ; Hu T. S. ; Zhou Y. G. ; Wang X. F. ; Kong J. Z. ; Zeng T. ; You Y. C. ; Wang Q. Angew. Chem. Int. Ed. 2015, 54, 15473.
Sun X. ; Liu X. F. ; Yin J. ; Yu J. ; Li Y. ; Hang Y. ; Zhou X. C. ; Yu M. L. ; Li J. D. ; Tai G. A. ; et al Adv. Funct. Mater. 2017, 27, 1603300.
Mannix A. J. ; Zhou X. F. ; Kiraly B. ; Wood J. D. ; Alducin D. ; Myers B. D. ; Liu X. L. ; Fisher B. L. ; Santiago U. ; Guest J. R. ; et al Science 2015, 350, 1513.
Feng B. J. ; Zhang J. ; Zhong Q. ; Li W. B. ; Li S. ; Li H. ; Cheng P. ; Meng S. ; Chen L. ; Wu K. H. Nat. Chem. 2016, 8, 563.
Zhang Z. H. ; Penev E. S. ; Yakobson B. I. Chem. Soc. Rev. 2017, 46, 6746.
Feng B. J. ; Sugino O. ; Liu R. Y. ; Zhang J. ; Yukawa R. ; Kawamura M. ; Iimori T. ; Kim H. ; Hasegawa Y. ; Li H. ; et al Phys. Rev. Lett. 2017, 118, 096401.
Huang Y. F. ; Shirodkar S. N. ; Yakobson B. I. J. Am. Chem. Soc. 2017, 139, 17181.
Zhang Z. H. ; Yang Y. ; Penev E. S. ; Yakobson B. I. Adv. Funct. Mater. 2017, 27, 1605059.
Boustani I. ; Quandt A. ; Hernandez E. ; Rubio A. J. Chem. Phys. 1999, 110, 3176.
Boustani I. Phys. Rev. B 1997, 55, 16426.
Yang X. B. ; Ding Y. ; Ni J. Phys. Rev. B 2008, 77, 041402.
Tang H. ; Ismail-Beigi S. Phys. Rev. Lett. 2007, 99, 115501.
Szwacki N. G. ; Sadrzadeh A. ; Yakobson B. I. Phys. Rev. Lett. 2007, 98, 166804.
Penev E. S. ; Bhowmick S. ; Sadrzadeh A. ; Yakobson B. I. Nano Lett. 2012, 12, 2441.
Wu X. ; Dai J. ; Zhao Y. ; Zhuo Z. ; Yang J. ; Zeng X. C. ACS Nano 2012, 6, 7443.
Lu H. ; Mu Y. ; Bai H. ; Chen Q. ; Li S. J. Chem. Phys. 2013, 138, 024701.
Yu X. ; Li L. ; Xu X. ; Tang C. J. Phys. Chem. C 2012, 116, 20075.
Xu S. ; Li X. ; Zhao Y. ; Liao J. ; Xu W. ; Yang X. ; Xu H. J. Am. Chem. Soc. 2017, 139, 17233.
Zhou X. F. ; Dong X. ; Oganov A. R. ; Zhu Q. ; Tian Y. J. ; Wang H. T. Phys. Rev. Lett. 2014, 112, 085502.
Ma F. ; Jiao Y. ; Gao G. ; Gu Y. ; Bilic A. ; Chen Z. ; Du A. Nano Lett. 2016, 16, 3022.
Liu Y. ; Penev E. S. ; Yakobson B. I. Angew. Chem. Int. Ed. 2013, 52, 3156.
Liu H. S. ; Gao J. F. ; Zhao J. J. Sci. Rep. 2013, 3, 3238.
Zhang Z. H. ; Yang Y. ; Gao G. Y. ; Yakobson B. I. Angew. Chem. Int. Ed. 2015, 54, 13022.
Meng X. M. ; Hu J. Q. ; Jiang Y. ; Lee C. S. ; Lee S. T. Chem. Phys. Lett. 2003, 370, 825.
Cao L. M. ; Zhang Z. ; Sun L. L. ; Gao C. X. ; He M. ; Wang Y. Q. ; Li Y. C. ; Zhang X. Y. ; Li G. ; Zhang J. ; et al Adv. Mater. 2001, 13, 1701.
Cao L. M. ; Hahn K. ; Wang Y. Q. ; Scheu C. ; Zhang Z. ; Gao C. X. ; Li Y. C. ; Zhang X. Y. ; Sun L. L. ; Wang W. K. ; et al Adv. Mater. 2002, 14, 1294.
Ni H. ; Li X. D. J. Nano Res. 2008, 1, 10.
Xu J. Q. ; Chang Y. Y. ; Gan L. ; Ma Y. ; Zhai T. Y. Adv. Sci. 2015, 2, 1500023.
Tian J. F. ; Xu Z. C. ; Shen C. M. ; Liu F. ; Xu N. S. ; Gao H. J. Nanoscale 2010, 2, 1375.
Yang J. K. ; Yang Y. ; Waltermire S. W. ; Wu X. X. ; Zhang H. T. ; Gutu T. ; Jiang Y. F. ; Chen Y. F. ; Zinn A. A. ; Prasher R. ; et al Nat. Nanotechnol. 2012, 7, 91.
Zhong Q. ; Kong L. J. ; Gou J. ; Li W. B. ; Sheng S. X. ; Yang S. ; Cheng P. ; Li H. ; Wu K. H. ; Chen L. Phys. Rev. Mater. 2017, 1, 021001.
Zhang Z. H. ; Mannix A. J. ; Hu Z. L. ; Kiraly B. ; Guisinger N. P. ; Hersam M. C. ; Yakobson B. I. Nano Lett. 2016, 16, 6622.
Shirodkar S. N. ; Penev E. S. ; Yakobson B. I. Sci. Bull. 2018, 63, 270.
Li W. B. ; Kong L. J. ; Chen C. Y. ; Gou J. ; Sheng S. X. ; Zhang W. F. ; Li H. ; Chen L. ; Cheng P. ; Wu K. H. Sci. Bull. 2018, 63, 282.
N?rskov J. K. ; Bligaard T. ; Rossmeisl J. ; Christensen C. H. Nat. Chem. 2009, 1, 37.
Zhang Z. ; Penev E. S. ; Yakobson B. I. Nat. Chem. 2016, 8, 525.
Xu S. G. ; Zhao Y. J. ; Liao J. H. ; Yang X. B. ; Xu H. Nano Res. 2016, 9, 2616.
Tibbetts G. G. J. Cryst. Growth 1984, 66, 632.
Ding F. ; Harutyunyan A. R. ; Yakobson B. I. Proc. Nat. Acad. Sci. USA 2009, 106, 2506.
Artyukhov V. I. ; Liu Y. Y. ; Yakobson B. I. Proc. Natl. Acad. Sci. USA 2012, 109, 15136.
Zhang Z. H. ; Liu Y. Y. ; Yang Y. ; Yakobson B. I. Nano Lett. 2016, 16, 1398.