Dataset Paper High-Yield Synthesis of Cubic and Hexagonal Boron Nitride Nanoparticles by Laser Chemical Vapor Decomposition of Borazine

We report a new method for the synthesis of boron nitride nanostructures (nBN) using laser chemical vapor decomposition (LCVD). Borazine was used as precursor and excited with two simultaneous radiations, the fundamental and second YAG laser harmonics. If only one of the two radiations is employed, no reaction takes place. Abundant BNpowder is obtained aer one hour of laser radiation. e BN yield obtained with the LCVD technique is about 83% by weight. e BNmaterial was characterized using scanning electron microscopy, transmission electron microscopy, electron energy loss spectroscopy, Raman spectroscopy, Fourier transform infrared spectroscopy, and X-ray diffraction. ey all indicate that the BN powder consists of a mixture of hexagonal and cubic BN nanostructures. No other BN phases or stoichiometries were found. e size of the resulting BN nanostructures is in the range of 20–100 nm and their B : N composition is 1 : 1. A simpli�ed mechanism involving laser-excited states followed by photoinduced removal of hydrogen is proposed to understand the synthesis of BN nanopowder by LCVD of borazine.


Introduction
e cubic and hexagonal allotropes of boron nitride (BN) are structurally analogous to diamond and graphite, respectively.Moreover, BN nanostructures are structural analogues of carbon nanostructures, such as fullerenes.However, unlike carbon nanostructures, BN nanostructures are electrically insulating, with energy gap of ∼5.5 eV [1][2][3], and resistant to oxidation up to 800 ∘ C [4,5].Due to these key characteristics, BN nanostructures are more useful in structural applications, such as reinforcing industrial ceramics (e.g., quartz, alumina, and silicon nitride) to improve their tolerance to thermal shocks [6,7].
e application of the pulsed laser radiation for deposition of different materials is a very active area, where highpower pulsed laser radiation is used [21][22][23].e borazine molecule (B 3 N 3 H 6 ) is isostructural and isoelectronic with benzene and has high vapor pressure, the exact 1 : 1 proportion of B : N, and three B-N bonds, all of which favor the stoichiometric synthesis of BN nanostructures [24].In this paper, we report the high-yield synthesis of cubic and hexagonal BN nanostructures by the LCVD technique using borazine as precursor.

Methodology
e reactor employed is schematically represented in Figure 1.e reactor body comprises a quartz tube with an external diameter of 1.5 �� and wall thickness of 0.04 �� .is tube was installed on stainless steel frames and connected to a vacuum system.In the input side of reactor, the quartz lens with focus length of 10 cm was installed.e laser radiation was focused by this lens in the reactor center.e total reactor volume is about 211 cm 3 .e reactor was evacuated by a mechanical pump to about 10 −2 Torr, and then it was evacuated by turbopump down to 10 −6 Torr.It was �lled with high-purity nitrogen (99.99%) to atmospheric pressure and evacuated again to the base pressure 10 −6 Torr.is process was repeated three times.e fundamental YAG laser harmonic (1064 nm) and second laser harmonic (532 nm) radiations were used to decompose the borazine (Boro Science, Canada, Inc.) gas.e relationship between radiation energy density of both these YAG laser harmonics is 8.9 : 0.051 (=175 = 12).e repetition laser rate was 10 Hz; the beam diameter was 3 mm; the pulse duration was about 10 ns.e borazine purity was analyzed using time-of-�ight mass spectrometry (TOFMS) by multiphoton photoionization of borazine molecule by radiation of the excimer ArF laser (193 nm; PSL-100; MPB Inc.).A mixture of Ar and Borazine (1%) at the input pressure of 760 Torr was passed through the pulsed electrodynamics valve and supersonic nozzle (diameter is 0.5 mm).e gas jet was expanded to the vacuum chamber and collimated by skimmer with an inlet diameter of 1.5 mm.e collimated molecular beam was passed through the ionization area of the commercial TOFMS machine (TOF Electronics Inc.), where the borazine molecules were photoionized by radiation of the ArF excimer laser.e positive ions were detected by a multichannel plate detector (MCP-Hamamatsu), signal from which was collected by the digital oscilloscope (LeCroy-9310A).e averaged waveform was transferred from oscilloscope to PC computer using the Scope Explorer commercial soware (LeCroy).e original TOFMS is represented in the time scale, which can be converted to ion mass scale using the relationship  = 3 2 , where 93 is the empirical machine's constant.
e Raman spectra were measured using micro-Raman spectrometer with triple monochromator (ISA Jobin Yvon Model T64000) with 1 cm −1 spectral resolution and 514.5 nm Ar-ion laser excitation.e spectra were recorded using the 80X objective that gives a probe area of 1-2 m 2 .FTIR spectroscopy was carried out on a standard FTIR spectrometer (Bruker, Tensor 27 Helios).e X-ray diffraction patterns were measured using a Siemens D5000 X-Ray spectrometer.Images of the BN materials were obtained by Scanning Electron Microscopy (JSM-5800LV JEOL) and Energy-Filtered Transmission Electron Microscopy (LEO 922 OMEGA).

Dataset Description
e dataset associated with this Dataset Paper consists of 7 items which are described as follows.
Dataset Item 1 (Table).TOFMS of borazine.e time scale can be converted to ion mass scale using the relationship  = 3 2 , where 93 is the empirical machine's constant.We employed TOFMS to analyze the purity of the borazine gas to be used as raw material to synthesize BN powder.e TOFMS spectrum (Figure 2  is more than 99.9% pure.e LCVD reactor was �lled with borazine vapor to an initial pressure of 40 mbar.When either the fundamental YAG laser harmonic radiation (1064 nm) or second laser harmonic radiation (532 nm) was used, no decomposition of borazine took place aer waiting for one hour.Only when the two radiations were passed simultaneously, the pressure increased indicating that decomposition of borazine was taking place.e pressure increased to about 70 mbar in 30 min, but the reaction was le to continue for 60 min and the pressure remained essentially constant.e walls of the reactor were covered with BN white dust.e BN white powder was collected from the reactor walls for further characterization.We estimated the yield of BN to be about 0.83 ± 0.02 by taking the pressure change, the total reactor volume, and mass of the BN product.e ideal gas equation is employed.Notice that this yield is relatively high [25].From this result, it appears that the synthesis of BN from borazine involves a primary process for the electronic excitation of borazine molecules and borazine fragments, followed by a secondary process for the photoinduced removal of H from the excited borazine and borazine fragments.e process goes on until all hydrogen is detached, leaving behind BN powder and increasing the chamber pressure.is is a simpli�ed mechanism that captures the essential features that a computational model of the LCVD of borazine should contain.

Column 1: Time (𝜇𝜇s)
Column 2: Relative Intensity Dataset Item 2 (Image).SEM image of the BN powder.e structure of the BN material was analyzed by SEM and TEM microscopy.From the SEM image, it can be seen that the BN material is covering the whole substrate and has a powdered appearance.
Dataset Item 3 (Image).TEM image of the BN nanostructures.e TEM images show that the BN powder consists of BN nanostructures with sizes in the 20 to 100 nm range.
Dataset Item 4 (Image).A close-up TEM image of the BN nanostructures.e interplanar spacing was measured to be 0.35 nm, very close to that of cubic zinc blende BN, which is 0.36 nm [26], and the EELS mapping (not shown) reveals a homogenous distribution of B and N atoms in 1 : 1 in all sampled materials Dataset Item 5 (Table ).Raman spectrum of the BNnanostructured material.e Raman spectrum (Figure 3) consists of two characteristic bands at 803 and 1356 cm −1 , which correspond to hexagonal BN. e A 2 (805 cm −1 ) mode is near 803 cm −1 and the E 1 (1367 cm −1 ) mode is near 1356 cm −1 [22,23].In addition, there are two broad bands at around 1000 cm −1 and 1400 cm −1 that can be assigned to cubic BN [27] with a large defect density that causes band broadening.Together, these bands indicate that the nanostructured BN material obtained from LCVD is a mixture of hexagonal and cubic BN nanostructures.a.u.means arbitrary units.
Column 1: Wavenumber (cm −1 ) Column 2: Intensity (a.u.) Dataset Item 6 (Table ).FTIR spectrum of the BNnanostructured material.e FTIR spectrum (Figure 4) consists of bands at 802.23 and 1367.19 cm −1 , which can also be related to hexagonal BN-nanostructured materials, and the c-BN absorption band at ∼1068 cm −1 that can be related to cubic BN-nanostructured materials [22,23,28,29].Other bands observed in the FTIR spectrum have much lower intensity.e FTIR data give additional proof that the product obtained is a mixture of cubic and hexagonal BN material.

Concluding Remarks
We developed a new method for the synthesis of cubic and hexagonal boron nitride nanostructures (nBN).is method involves the irradiation of borazine with the fundamental and second YAG laser harmonics simultaneously.is technique gives high yields up to 83% by weight.e multilateral characterizations done to the BN nanopowder indicate that it consists of a mixture of hexagonal and cubic BN nanostructures with sizes in the range of 20-100 nm and 1 : 1 B : N composition.e essential aspects of the synthesis mechanism to be consistent with the experimental facts should involve laser-excited states followed by photoinduced removal of hydrogen.�on�ict of �nterests e authors declare that they have no competing �nancial interests.

F 1 :
Schematic representation of the LCVD reactor.

F 2 :
TOFMS of borazine showing four bands corresponding to different combinations of the B isotopes in the borazine molecule.Below each band is the corresponding molecular mass in atomic mass units.

F 3 :F 4 :
cBN LO LO LO LO LO LO LO LO LO LO Wavenumber (cm −1 ) Raman spectrum of the BN-nanostructured material showing the bands corresponding to a mixture of hexagonal and cubic BN particles.FTIR spectrum of the BN-nanostructured material showing the bands corresponding to a mixture of hexagonal and cubic BN particles.

F 5 :
X-ray diffractogram of the BN-nanostructured material showing the peaks corresponding to a mixture of hexagonal and cubic BN particles.Dataset Availabilitye dataset associated with this Dataset Paper is dedicated to the public domain using the CC0 waiver and is available at http://dx.doi.org/10.7167/2013/281672/dataset.
) consists of 4 lines corresponding to ion masses of 78, 79, 80, and 81, which correspond to B 3 N 3 H + 6 ions with different B isotopes.B has two stable isotopes 10 B and 11 B. eir relative abundance is 19:81.e relationship among the intensities of the TOFMS lines is in good agreement with what is expected from the natural abundance of B isotopes.No other lines were detected from 10 to 400 a.m.u.We can conclude that the borazine employed