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1 Supporting Information for Advanced Materials, adma Wiley-VCH Weinheim, Germany

2 High-Yield Synthesis of Rhombohedral BN Triangular Nanoplates Liqiang Xu, Jinhua Zhan*, Junqing Hu, Yoshio Bando, Xiaoli Yuan, Takashi Sekiguchi Masanori Mitome, and Dmitri Golberg Supporting information Table of Contents SI-1 SEM images of rhombohedral BN triangular nanoplates a) An overview SEM image; b) High-resolution SEM image showing the stacking of nanoplates; c) High-resolution SEM image showing the thickness of nanoplates; d) BN particle size distribution obtained by Zetasizer 000 particle size laser analyzer; e) Simulation of a triangular nanoplate viewed along various tilt angles. SI- Elemental maps collected from an individual r-bn nanoplate reveal that B and N atoms are homogeneously distributed in the nanostructures. SI- TEM image and electron diffraction pattern of flake-like BN particles generated in the absence of the metals. SI-4 TEM image and electron diffraction pattern of rhombohedral BN triangular nanoplates generated in the presence of metallic Ni. SI-5 a) Selected-area electron diffraction (SAED) patterns taken from an individual triangular nanoplate tilted inside the TEM suggesting its rhombohedral BN crystal structure; b) High-resolution TEM image taken from an individual triangular nanoplate along the [ 111] direction showing its one corner; c) SEM images taken from nickel sponge showing its surface. SI-6 a) -layer-stacking structural model of Ni (111); b) Configuration for one-monolayer BN/Ni (111). c) one possible configuration of a bended BN triangular monolayer. SI-7 a) The UV-Visible absorption spectrum of r-bn triangular nanoplates; b) plot of ( E photo ) vs. E photo; c) High-resolution CL spectrum taken from r-bn nanoplates at 14 K; d) Band-gap energy for III-V nitride semiconductors. SI-8 Formation process of rhombohedral BN triangular nanoplate. 1

SI-1 SEM images of rhombohedral BN triangular nanoplates and simulation of

image of as-obtained r-bn triangular nanoplates; b) High-resolution SEM

Size distribution(s) % in class 60 40 0 c) High-resolution SEM image

Diameter (nm) d) BN particle size distribution obtained by Zetasizer 000

The larger particles possibly originate from the agglomeration of

3 SI-1 SEM images of rhombohedral BN triangular nanoplates and simulation of a triangular nanoplate viewed along various tilt angles a) An overview SEM image of as-obtained r-bn triangular nanoplates; b) High-resolution SEM image showing the stacking of r-bn triangular nanoplates on each other; 80 Size distribution(s) % in class c) High-resolution SEM image showing the thickness of r-bn triangular nanoplates; Diameter (nm) d) BN particle size distribution obtained by Zetasizer 000 particle size laser analyzer. The larger particles possibly originate from the agglomeration of nanoplates in ethanol solution; [001] Tilt angle: e) simulation of a triangular nanoplate viewed along various tilt angles.

$SI- TEM image and electron diffraction pattern of flake-like BN particles generated in the absence of metallic powder intensity$ $SI-4 TEM images and electron diffraction pattern of rhombohedral BN triangular nanoplates generated in the presence of metallic$

4 SI- Elemental maps collected from an individual r-bn nanoplate reveal that B and N atoms are homogeneously distributed in the nanostructures. SI- TEM image and electron diffraction pattern of flake-like BN particles generated in the absence of metallic powder intensity (a.u.) q/nm -1 a) TEM image, inset is the ED pattern; b) electron-diffraction profile giving d-spacings consistent with h-bn (JCPDS card ). SI-4 TEM images and electron diffraction pattern of rhombohedral BN triangular nanoplates generated in the presence of metallic Ni sponge. intensity (a.u.) q/nm -1 a) TEM image, inset is the ED pattern; b) electron-diffraction profile giving d-spacings consistent with r-bn (JCPDS card ).

$SI-5 a) b) c) SI-5 a) Selected-area electron diffraction$ nanoplate with different tilting angles inside the TEM,

The angles between [ 011 ], [ 111 ] and [ 001 ] are 14 and.

an individual triangular nanoplate along the [ 111]

its corresponding Fourier-transform pattern.

r-bn crystal along the [ 111] direction, as shown in its

5 SI-5 a) b) c) SI-5 a) Selected-area electron diffraction (SAED) patterns taken from an individual triangular nanoplate with different tilting angles inside the TEM, suggesting its rhombohedral BN crystal structure. The angles between [ 011 ], [ 111 ] and [ 001 ] are 14 and.45, respectively; b) High-resolution TEM image taken from an individual triangular nanoplate along the [ 111] direction showing its one corner, the top-left inset is its corresponding Fourier-transform pattern. This HRTEM image is consistent with the projection of the r-bn crystal along the [ 111] direction, as shown in its top middle inset; c) SEM image and high-resolution SEM image showing the surfaces of nickel sponge. 4

SI-6 a) fcc hollow site b) hcp hollow site.49å H B N Ni c) SI-6 a) A -layer-stacking structural model of Ni (111).

for one-monolayer BN/Ni (111). The terminated N atoms are saturated with H atoms.

49å, whereas that of two adjacent N atoms in one BN monolayer is.50å.

6 SI-6 a) fcc hollow site b) hcp hollow site.49å H B N Ni c) SI-6 a) A -layer-stacking structural model of Ni (111). Its fcc hollow site and hcp hollow site are marked with black and yellow arrows, respectively; b) Configuration for one-monolayer BN/Ni (111). The terminated N atoms are saturated with H atoms. The interatomic distance of two adjacent Ni atoms is.49å, whereas that of two adjacent N atoms in one BN monolayer is.50å. The similar lattice parameter allows a perfect epitaxial growth of BN on Ni (111). N atoms sit on the top sites of the Ni atoms; c) one possible configuration of a bended BN triangular monolayer whose edges are terminated with H-saturated N atoms. 5

7 SI-7 a) b) absorbance (a.u.) ( E photo ) c) wavelength/nm CL intensity (a.u.) Wavelength/nm d) SI-7 a) The UV-Visible absorption spectrum of r-bn triangular nanoplates dispersed in ethanol solution; b) plot of ( E photo ) vs. E photo. An estimated optical band gap is obtained using the following equation for a semiconductor: h = A (h -E g ) m/, where A is a constant, is the absorption coefficient, E g is the band gap and m equals 1 for a direct transition. The intercept of a plot of ( E photo ) vs. E photo on the energy axis gives E g for a direct transition; c) High-resolution CL spectrum taken from r-bn nanoplates at 14 K; d) Band-gap energy for III-V nitride semiconductors, ZB = Zinc-blende, W= Wurtzite, H = Hexagonal. E g /ev Energy/eV ZB W H-BN BN AlN GaN InN 6

8 SI-8 Formation process of rhombohedral BN triangular nanoplates During the formation process of r-bn triangular nanoplates, the involved thermodynamic chemical reactions may possibly proceed as follows: NH NaNH 4 BF BF NH HF( g) Na 4 HF( g) NaNH NH HF( g) BF, Ni BN ( s) HF( g) N ( s) NaF ( s) NH Na N ( s) NH ( s) NaF ( s) NH NH 4BF4 4NaNH 4NaF ( s) BN ( s) 4NH At a temperature around 600, NH 4 BF 4 and NaNH may spontaneously decompose to produce BF and NH vapors (reaction 1 and ), respectively. 1, The reaction between BF (g) and NH (g) (reaction ) over the surface of metallic Ni powder generate regular sp -hybridzed BN triangular monolayers. BN crystal was also generated via means of a traditional chemical vapor deposition (CVD) from a BF /NH mixture system., 4 A scheme showing this assistant role is depicted in SI-6. Further reactions will drive the crystal growth of rhombohedral BN over these basal BN planes. The HF (g) produced by the reaction 1 and can instantly be consumed by Na N and NaNH to form NaF and NH, as described by the reaction 4 and 5, respectively. A total reaction between NH 4 BF 4 and NaNH can be described as the reaction 6. SI-References: [1] D. Göbbels; G. Z. Meyer, Anorg. Allg. Chem. 00, 68, [] a) H. Y. Leng, T. Ichikawa, S. Hino, N. Hanada, S. Isobe, H. Fujii, J. Power Sources 006, 156, 166; b) K. Jones, In Comprehensive Inorganic Chemistry (Ed.: A. F. Trotman-Dickinson), Pergamon Press, Oxford, 197, Vol., p147; (c) Advanced Inorganic Chemistry (Eds: F. A. Cotton, G. Wilkison) Interscience Publishers, London, 1966, p1. [] S. Prouhet, F. Langlais, A. Guette, R. Naslain, J. Rey, Euro. J. Solid State Inorg. Chem. 199, 0, 95. [4] A. G. Avent, P. B. Hitchcock, M. F. Lappert, D. S. Liu, G. Mignani, C. Richard, E. Roche, J. Chem. Soc., Chem. Commun., 1995, 855. (1) () () (4) (5) (6) 7

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