Morphology-Controlled Synthesis of Hexagonal Boron Nitride Crystals

Subscriber access provided by CORNELL UNIVERSITY LIBRARY

Article

Morphology controlled synthesis of hexagonal boron nitride crystals by chemical vapor deposition Subash Sharma, Kamal Sharma, Mohamad Saufi Rosmi, Yazid Yaakob, Mona Ibrahim Araby, Hajime Ohtani, Golap Kalita, and Masaki Tanemura Cryst. Growth Des., Just Accepted Manuscript • DOI: 10.1021/acs.cgd.6b01110 • Publication Date (Web): 29 Sep 2016 Downloaded from http://pubs.acs.org on October 4, 2016

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

Crystal Growth & Design is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 23

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Crystal Growth & Design

Morphology‐controlled synthesis of hexagonal boron nitride crystals by chemical vapor deposition Subash Sharma†*, Kamal Sharma†, Mohamad Saufi Rosmi†‡, Yazid Yaakob†§, Mona Ibrahim Araby†, Hajime Ohtani#, Golap Kalita†, Masaki Tanemura† †

Department of Physical Science and Engineering, Nagoya Institute of Technology Gokiso-cho, Showa-ku, Nagoya 466-8555, Japan ‡

Department of Chemistry, Faculty of Science and Mathematics, Universiti Pendidikan Sultan Idris, 35900 Tanjong Malim, Perak, Malaysia

§

Department of Physics, Faculty of Science, Universiti Putra Malaysia, 43400 UPM Serdang, Selangor, Malaysia #

Department of Life Science and Applied Chemistry, Nagoya Institute of Technology Gokiso-cho, Showa-ku, Nagoya 466-8555, Japan

Keywords: hexagonal boron nitride, morphology control, crystal growth, chemical vapor deposition

ACS Paragon Plus Environment

1


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 2 of 23

Abstract

Synthesis of hexagonal boron nitride (hBN) crystals with controlled morphology is a major challenge due to various kinetic and thermodynamic factors at the edge. Supplying BN building blocks by heating precursor Ammonia Borane at a temperature of 90ºC produced triangular crystals, whereas at higher heating (130ºC) hBN crystals with hexagonal morphology were observed. The Shape of crystals could also be modulated from hexagonal to triangular under continuous reduced supply of BN building blocks. We attributed these phenomena to a different growth mechanism dependent on the concentration of BN radicals in the growth region. With a low supply of BN building blocks, crystal growth is the edge attachment limited, producing triangles, whereas under higher concentration of BN building blocks, crystal growth is limited by diffusion producing hexagons. Presence of alternating B and N terminated vertices in hexagonal hBN crystals offers the possibility of hBN/graphene inplane heterostructure synthesis with B-C and N-C bonding at the interface which is not possible with N terminated triangular crystals. Supplying the controlled amount of BN building blocks to synthesize triangular, hexagonal crystal and modulation from hexagons to triangles is major achievement (in the present work) due to single parameter control over the experiment.


2

Page 3 of 23

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Introduction The advent of graphene in 2004 opened the unexplored field of two-dimensional (2D) materials.1 Due to atomic level thickness, 2D materials are attractive for nanoscale device fabrications.2 These materials demonstrate a wide range of electronic properties ranging from conductor (graphene), insulator (hBN) and semiconductor (MoS2).3–5 2D materials with a variety of electronic and optoelectronic properties offer the possibility of synthesizing engineered materials by layer-by-layer stacking or fabricating in-plane heterostructures.6–8 Recently, hexagonal boron nitride (hBN) has attracted considerable attention due its closer lattice resemblance with graphene.9 In hBN lattice, B and N are atoms arranged in honeycomb form while C atoms are the sole constituent of graphene. hBN has demonstrated many novel properties such as high transparency, thermal conductivity, anti-oxidation behavior and UV emission.10–12 Absence of dangling bonds and charge traps also makes hBN a better substrate than the conventionally used SiO2. The highest recorded mobility of graphene has been reported on hBN substrate, mimicking the property of freestanding graphene. 13 Exfoliation has been popular in extracting monolayer graphene from highly oriented pyrolytic graphite (HOPG).14 Exfoliating hBN layers from bulk hBN crystal, however, is not very effective due to the presence of chemical bonding between neighboring layers.15 Recent development in chemical vapor deposition (CVD) has made large‐area synthesis of high quality hBN film possible with high controllability over the quality and number of layers.16–19 In the CVD method, precursor is supplied to a high temperature growth zone and hBN films are


3


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 4 of 23

synthesized on transition metal substrates such as Cu, Ni, Pt, Co, Ru and Mo.20–24Generally temperature above 1000ºC is taken as growth temperature. Low and atmospheric pressure CVD has been employed for the synthesis of hBN. Growth conditions, such as precursor flow rate, growth temperature and pressure inside the CVD chamber etc., affect the growth mechanism. 25, 26

For a graphene case, the shape evolution of graphene crystal has been studied extensively with shapes ranging from hexagonal, triangle, round shape, flower‐shaped and fractals. 27–31 Crystals with different morphology offer different catalytic, magnetic and electronic behavior due to different edge orientations.32,

33

Experimental factors, such as use of H2, pressure inside the

growth chamber and surface orientation of underlying substrates, has been shown to play a vital role in determining the shape of graphene crystal.27 By contrast, few hBN studies have been reported on morphological studies of hBN crystal and their experimental manipulation. Previously, we revealed the etching mechanism of triangular hBN crystals in the presence of H2 in CVD study.34

In the present work we report the synthesis of high‐quality hBN on Cu foil

using atmospheric pressure CVD (APCVD) with the controlled shape of hBN crystals ranging from conventional triangular to hexagonal shape. Very recently, we noticed that the precursor heating temperature has a decisive role in the control of

the morphology of synthesized hBN

crystal on Cu foil in the atmospheric CVD process. Tuning the supply rate of BN building blocks by manipulating precursor-heating temperature, even the transformation of hexagonal hBN crystal to triangular symmetry was controllable. Hexagon‐shaped hBN crystal is believed to have alternating B and N terminated in vertices contrast with N terminated triangular crystals. Magnetic, catalytic and electronic properties in 2D crystals are found to be highly dependent on edge termination. In this regard, different properties can be expected from hexagonal compared


4

Page 5 of 23

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


to triangular crystals. Recent studies on synthesis of Inplane heterostructure of hBN and graphene can also benefit from morphology‐tuned synthesis of hBN. Only N-C bond can be expected on interface during synthesis of triangular hBN crystals followed by graphene growth, whereas on hexagonal hBN crystal surrounded by graphene, both B-C and N-C bonding is expected on interface providing rich variety of edge-related properties. These B-C and N-C edges can be cut into nanoribbons and their properties explored for device fabrications.

Experimental Section In the present investigation atmospheric pressure chemical vapor deposition (APCVD) is used for the synthesis of hBN on Cu substrate using ammonia borane (H3NBH3) as precursor. Our CVD system consists of a single-zone split furnace with a quartz tube as the reactor zone. Ammonia borane was placed in a magnetic boat, which can be dragged towards and away from a furnace with an external magnet as shown in Figure 1a. As ammonia borane is solid, it is easy to handle and less hazardous compared to gaseous precursors. The rate of sublimation of the precursor is controlled by varying the distance between the precursor-boat and furnace. Before hBN synthesis, the Cu foil was annealed in H2 (100 SCCM) atmosphere for 30 min at 1020ºC. During growth H2 was replaced with 84 SCCM of Ar. Ammonia borane was heated by dragging the magnetic boat with the precursor towards growth furnace. Temperature of the precursor was examined with an infrared thermometer. Growth period was around 10 min for both temperatures (90ºC and 130ºC) for the synthesis of triangular and hexagonal crystals respectively. The synthesized hBN on Cu substrate was characterized using an optical microscope, SEM, XPS. A sacrificial layer of PMMA was spin coated on hBN/Cu to transfer film to a quartz substrate and TEM grid after wet etching in Fe(No3)3.9.H2O) solution.


5


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 6 of 23

Absorbance of hBN on the quartz substrate was measured with UV-Vis. hBN film was characterized with transmission electron microscope JEM ARM-200F TEM at 200 KV. Under thermal treatment, ammonia borane decomposes to borazine and amino borane with production of H2 (Figure 1b).35 Borazine is the main building block for hBN synthesis, which dehydrogenates on catalytic substrate to produce hBN flake. Prior to growth, the Cu foil was annealed at 1020ºC in 100 SCCM H2 for 30 min. Annealing in H2 serves to get rid of organic impurities, oxide layer and surface oxygen as well as makes the surface flat with reduced roughness. During growth H2 was replaced with 84 SCCM of Ar. The magnetic boat with precursor was maintained at a distance of 15 cm from the furnace. Precursor temperature increased slowly from room temperature to 90ºC as observed by an external Infrared thermometer. After growth of 10 min, the furnace was cooled under atmospheric conditions. Results and discussion Figure 1c, d, e shows optical and SEM images of as-synthesized triangular hBN crystals. hBN triangles are found to be almost equiangular with sharp edges with the size of 5~10 µm. At some places, multiple triangular crystals overlap to form polygonal structures as seen in Figure 1d. For optical characterization, hBN on Cu foil was slightly annealed at 170ºC under atmospheric condition to partially oxidize the Cu substrate. Oxidized Cu substrate helps easier identification of hBN crystals due to its distinct pinkish contrast with an ordinary optical microscope.

This method can be applied to grow larger and perfect BN-microplates by

extending growth time. With growth as long as 30 min, individual hBN crystals merged to form continuous film as shown in Figure 1f. Some reddish patches are partially oxidized bare Cu surface.


6

Page 7 of 23

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


As-synthesized continuous hBN film on Cu was characterized with XPS. Figure 2a shows binding energy values of B and N at 190.6 eV and 398.23 eV which are close to reported values for hBN. Polymethyl methacrylate (PMMA) was spin coated on hBN/Cu to transfer film to transmission electron microscope (TEM) grid. Cu was etched using Iron (III) Nitrate Nonahydrate (Fe (NO3 )3.9.H2O ) solution. As-transferred hBN was characterized with TEM. Figure 2a, b shows the presence of monolayer and bilayer hBN film. The hBN film was also transferred to quartz substrate to study optical properties. Transferred hBN film is found to be highly transparent as shown by Figure 2e. In case of graphene, different experimental conditions affect the growth mechanism.

Parameters, such as carrier gas and its flow rate, substrate

treatment, background pressure and synthesis temperatures, have been found to play a major role during graphene nucleation and growth. It is also the case for hBN growth. Understanding the effect of these parameters, especially kinetic and thermodynamical factors, will be crucial for the synthesis of hBN with desired attributes such as the thickness and morphology and size of crystals. Growth temperature is a major thermodynamic parameter. Gas flow rate, supply rate of precursor and the constituent carrier gas are kinetic factors. In what follows, the effect of precursor heating temperature on morphology of crystals will be discussed. Analogous to with CVD synthesis of graphene, hBN synthesis on Cu involves the following major steps: (1) Adsorption of BN building blocks on Cu substrate, (2) dehydrogenation of BN radicals, (3) surface diffusion, and (4) edge attachment. Beside these steps, etching of hBN during growth is also a major phenomenon necessary to understand the overall crystal growth phenomenon. Since growth and etching occur simultaneously in the APCVD, crystal growth is regular attachment of atoms to the crystal edge atoms

after certain atoms are etched. Our

previous study revealed H2 as a highly efficient etching agent of hBN at high temperature,


7


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 8 of 23

similar to the graphene case where H2 plays an important role in determining the shape of graphene crystal by etching the weak carbon-carbon bond on crystal edges.36 To avoid H2 induced etching, only Ar was used as carrier gas during crystal growth in this study. Some previous work has shown the role of evaporating Cu in determining the morphology of hBN crystal in low pressure CVD.37 To avoid major Cu evaporation during synthesis of hBN, we use an APCVD system at the comparatively lower temperature of (1020ºC). After avoiding etching of hBN and evaporation of Cu during growth, we studied the role of precursor heating temperature on crystal growth and morphology while all other experimental conditions remained the same. As demonstrated above, regular sharp edge triangular hBN crystals were obtained with a precursor heating temperature 90ºC; we designed a second set of experiments in which the precursor boat was placed closer (10 cm) to the furnace for rapid decomposition and increased supply of borazine. Temperature of around 130ºC was maintained on the precursor boat. The growth was carried for 10 min and subjected to cooling. hBN crystals with hexagonal morphology were observed in contrast to triangular crystals as shown in Figure 3. Hexagonal crystals were almost same size as the triangular type. Bigger crystals along with smaller hBN crystals have roughly adopted hexagonal morphology with irregular edge. Some hBN crystals (Figure 3(c) and 3(d)) showed a wrinkled surface due to negative thermal expansion coefficient of hBN. During cooling of hBN/Cu after growth, Cu substrate shrinks whereas hBN expands leading to formation of wrinkles. Since grain boundaries are defective sites, much hBN nucleation can be observed around the Cu grain boundary (Figure 3(c)). Due to the chemical potential difference between B and N species, triangles are the equilibrium shapes for hBN crystals.38 In the present work, by maintaining a high concentration of precursors in growth zone, more homogeneous crystal growth occurs, leading to formation of


8

Page 9 of 23

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


hexagonal hBN crystals. Tay et al. mentioned surface oxygen on Cu foil as a contributing factor for hexagonal crystal.39

In this work, we have avoided the presence of oxygen by high

temperature annealing in H2 atmosphere. To further prove the role of borazine concentration, we designed a 10-min experiment, in which in the first half of the experiment we grew hexagonal crystals by a high supply rate of precursors (at 130ºC) and rapidly reducing in the second half of the experiment (at 90ºC). Samples were cooled in the atmospheric condition and characterized with optical microscope and SEM. Figure 4 shows the modulation of hexagonal crystals under the decreased supply rate of precursors. It is observed that under a low concentration of precursor, one may observe that the growth dynamic is abruptly shifted from isotropic to directional. Figures 4a, b, c and d show crystals with unidirectional and bidirectional growth. As seen in Figures 4h, 4i and 4j, the low precursor supply drastically reduces the crystal growth velocity and crystal adopts one or two particular growth directions in the other half of the experiment. Interestingly, under continuous supply of low precursor (at 90ºC), double-lobed hBN crystal is transformed into triangular hBN crystal with almost the same angles (60º). Figures 4i and 4j show the intermediate stage of transformation and almost transformed hBN crystal to adopt triangular morphology with clear bump feature from earlier hexagonal crystal, respectively. Figure 4k presents the schematics for transformation of the hexagonal hBN crystal into a triangular form with different shape evolutions. The effect of the precursor supply rate on the morphology of synthesized graphene has been observed in past reports.29 Since all other experimental conditions remained identical in the present study, it is obvious that the concentration of BN building blocks played a key role in


9


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 10 of 23

determining the morphology of crystal. In the present work, triangular hBN crystals demonstrated sharp interface synthesized under precursor heating temperature (90ºC) whereas hexagonal crystals had irregular and curved vertices. Crystals with straight edges in the zigzag direction were synthesized when edge attachment is the limiting factor for crystal growth.40 In addition, irregular edges would be attributed to a growth mechanism in which the diffusion is the as-synthesized rate-limiting factor.41,42 With knowledge of the graphene synthesis process on Cu substrate, formation of triangular, hexagonal crystals and transformation of hexagonal to triangular crystal can be explained as follows. Triangles with zigzag edges are the equilibrium shape for hBN crystal under low supply of precursor due to edge attachment as the rate-limiting phenomenon. During a high concentration supply of BN radicals, kinetics at edge would be changed, with diffusion becoming the rate-limiting phenomenon for crystal growth. Increased diffusion and availability of free B and N radicals makes crystal growth favorable for both B and N terminated edges for maintaining hexagonal morphology.

In fact, hBN synthesis under

LPCVD, the edges of hBN crystal are known to be modulated from straight edges to curved morphology by heating ammonia borane at different temperatures.43 In this work we tuned the growth mechanism from edge attachment limited to diffusion limited by drastic reduction in the supply of BN building blocks thereby modulating the crystal morphology. To further analyze volumetric evolution of Borazine at different temperature, evolved gas analysis (EGA) followed by gas chromatography was done for the decomposition of ammonia borane at 90 and 130ºC under Ar atmosphere. Figure 5a shows EGA spectra of ammonia borane decomposition at 130ºC where the highest volume of gases is evolved around 9thmin. Figure 5b presents mass spectra compiled at the 9th min showing relative abundance of main building block borazine (atomic mass 80.5) around 30%. Similarly, Figure 5c shows the decomposition of


10

Page 11 of 23

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


ammonia borane at 90ºC with the main evolution of gas largely around 13.5th min. Follow-up mass spectra was compiled at 13.5th min as shown in Figure 5d. Relative abundance of borazine was found to be around 2%. Thus, it can be concluded that by changing the precursor heating temperature, borazine concentration can be significantly varied, leading to a different growth mechanism of hBN crystals. In summary, we developed a method for CVD synthesis of triangular and hexagonal-shaped hBN crystals. The synthesized method was highly controllable with the transformation of hexagonal to triangular shape by controlling heating temperature of ammonia borane. The different modes of crystal growth were attributed to the concentration of BN building block in growth region as proved by EGA and gas chromatography analysis. This work is a promising milestone for synthesis of crystals with variety of morphologies with different edge-related electronic, magnetic and catalytic properties.

Conclusions In summary, we developed a new method for CVD synthesis of triangular and hexagonal-shaped hBN crystals. The method for this synthesis was highly controllable with the transformation of hexagonal to triangular shape by controlling the heating temperature of ammonia borane. The different modes of crystal growth were attributed to the concentration of BN building blocks in growth region as proved by EGA and gas chromatography analysis. This work may be a promising as milestone for synthesis of crystals with a variety of morphologies with different edge-related electronic, magnetic and catalytic properties.

AUTHOR INFORMATION Corresponding Author


11


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 12 of 23

*[email protected] Notes The authors declare no competing financial interest. Funding Sources The work was supported by a Grant-in-Aid for Young Scientists (B) from the Japan Society for the Promotion of Science (Grant No. 15K21076).

References 1.

Novoselov, K. S.; Geim, A. K.; Morozov, S. V.; Jiang, D.; Zhang, Y.; Dubonos, S. V.;

Grigorieva, I. V.; Firsov, A. A. Science 2004, 306, 666-669. 2.

Mas-Balleste, R.; Gomez-Navarro, C.; Gomez-Herrero, J.; Zamora, F. Nanoscale 2011,

3, 20-30. 3.

Castro Neto, A. H.; Guinea, F.; Peres, N. M. R.; Novoselov, K. S.; Geim, A. K. Reviews

of Modern Physics 2009, 81, 109-162. 4.

Watanabe, K.; Taniguchi, T.; Kanda, H. Nat Mater 2004, 3, 404-409.

5.

Mak, K. F.; Lee, C.; Hone, J.; Shan, J.; Heinz, T. F. Phys Rev Lett 2010, 105, 136805.

6.

Liu, Z.; Ma, L.; Shi, G.; Zhou, W.; Gong, Y.; Lei, S.; Yang, X.; Zhang, J.; Yu, J.;

Hackenberg, K. P.; Babakhani, A.; Idrobo, J. C.; Vajtai, R.; Lou, J.; Ajayan, P. M. Nat Nanotechnol 2013, 8, 119-124. 7.

Ci, L.; Song, L.; Jin, C.; Jariwala, D.; Wu, D.; Li, Y.; Srivastava, A.; Wang, Z. F.; Storr,

K.; Balicas, L.; Liu, F.; Ajayan, P. M. Nat Mater 2010, 9, 430-435.


12

Page 13 of 23

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


8.

A. Azizi, S. E., G. Geschwind, K. Zhang, B. Jiang, D. Mukherjee, L. Hossain, A. F.

Piasecki, B. Kabius, J. A. Robinson. ACS Nano 2015, 9, 4882-4890. 9.

Liu, L.; Feng, Y. P.; Shen, Z. X. Physical Review B 2003, 68, 104102.

10. Lipp, A.; Schwetz, K. A.; Hunold, K. Journal of the European Ceramic Society 1989, 5, 3-9. 11. Ouyang, T.; Chen, Y.; Xie, Y.; Yang, K.; Bao, Z.; Zhong, J. Nanotechnology 2010, 21, 245701. 12. Watanabe, K.; Taniguchi, T.; Niiyama, T.; Miya, K.; Taniguchi, M. Nature Photonics 2009, 3, 591-594. 13. Dean, C. R.; Young, A. F.; Meric, I.; Lee, C.; Wang, L.; Sorgenfrei, S.; Watanabe, K.; Taniguchi, T.; Kim, P.; Shepard, K. L.; Hone, J. Nat Nanotechnol 2010, 5, 722-726. 14. Hernandez, Y.; Nicolosi, V.; Lotya, M.; Blighe, F. M.; Sun, Z.; De, S.; McGovern, I.; Holland, B.; Byrne, M.; Gun'Ko, Y. K. Nature Nanotechnology 2008, 3, 563-568. 15. Pakdel, A.; Bando, Y.; Golberg, D. Chem Soc Rev 2014, 43, 934-959. 16. Bae, S.; Kim, H.; Lee, Y.; Xu, X.; Park, J. S.; Zheng, Y.; Balakrishnan, J.; Lei, T.; Kim, H. R.; Song, Y. I.; Kim, Y. J.; Kim, K. S.; Ozyilmaz, B.; Ahn, J. H.; Hong, B. H.; Iijima, S. Nat Nanotechnol 2010, 5, 574-578. 17. Zhan, Y.; Liu, Z.; Najmaei, S.; Ajayan, P. M.; Lou, J. Small 2012, 8, 966-971. 18. Lee, Y. H.; Zhang, X. Q.; Zhang, W.; Chang, M. T.; Lin, C. T.; Chang, K. D.; Yu, Y. C.; Wang, J. T.; Chang, C. S.; Li, L. J.; Lin, T. W. Adv Mater 2012, 24, 2320-2325.


13


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 14 of 23

19. Song, L.; Ci, L.; Lu, H.; Sorokin, P. B.; Jin, C.; Ni, J.; Kvashnin, A. G.; Kvashnin, D. G.; Lou, J.; Yakobson, B. I.; Ajayan, P. M. Nano Lett 2010, 10, 3209-3215. 20. Kim, K. K.; Hsu, A.; Jia, X.; Kim, S. M.; Shi, Y.; Hofmann, M.; Nezich, D.; RodriguezNieva, J. F.; Dresselhaus, M.; Palacios, T.; Kong, J. Nano Lett 2012, 12, 161-166. 21. Shi, Y.; Hamsen, C.; Jia, X.; Kim, K. K.; Reina, A.; Hofmann, M.; Hsu, A. L.; Zhang, K.; Li, H.; Juang, Z. Y.; Dresselhaus, M. S.; Li, L. J.; Kong, J. Nano Lett 2010, 10, 4134-4139. 22. Kim, G.; Jang, A. R.; Jeong, H. Y.; Lee, Z.; Kang, D. J.; Shin, H. S. Nano Lett 2013, 13, 1834-1839. 23. Orofeo, C. M.; Suzuki, S.; Kageshima, H.; Hibino, H. Nano Research 2013, 6, 335-347. 24. Sutter, P.; Lahiri, J.; Albrecht, P.; Sutter, E. ACS Nano 2011, 5, 7303-7309. 25. Tay, R. Y.; Wang, X.; Tsang, S. H.; Loh, G. C.; Singh, R. S.; Li, H.; Mallick, G.; Teo, E. H. T. Journal of Materials Chemistry C 2014, 2, 1650-1657. 26. Koepke, J. C.; Wood, J. D.; Chen, Y.; Schmucker, S. W.; Liu, X.; Chang, N. N.; Nienhaus, L.; Do, J. W.; Carrion, E. A.; Hewaparakrama, J. Chemistry of Materials 2016, 28, 4169-4179. 27. Geng, D.; Wang, H.; Yu, G. Adv Mater 2015, 27, 2821-2837. 28. Geng, D.; Wu, B.; Guo, Y.; Huang, L.; Xue, Y.; Chen, J.; Yu, G.; Jiang, L.; Hu, W.; Liu, Y. Proc Natl Acad Sci U S A 2012, 109, 7992-7996. 29. Sharma, S.; Kalita, G.; Hirano, R.; Shinde, S. M.; Papon, R.; Ohtani, H.; Tanemura, M. Carbon 2014, 72, 66-73.


14

Page 15 of 23

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


30. Chen, X.; Liu, S.; Liu, L.; Liu, X.; Liu, X.; Wang, L. Applied Physics Letters 2012, 100, 163106. 31. Kumar, K.; Yang, E. H. Sci Rep 2013, 3, 2571. 32. Mukherjee, R.; Bhowmick, S. Journal of Chemical Theory and Computation 2011, 7, 720-724. 33. Barone, V.; Peralta, J. E. Nano Letters 2008, 8, 2210-2214. 34. Sharma, S.; Kalita, G.; Vishwakarma, R.; Zulkifli, Z.; Tanemura, M. Scientific Reports 2015, 5, 10426. 35. Frueh, S.; Kellett, R.; Mallery, C.; Molter, T.; Willis, W. S.; King’ondu, C.; Suib, S. L. Inorganic Chemistry 2010, 50, 783-792. 36. Vlassiouk, I.; Regmi, M.; Fulvio, P.; Dai, S.; Datskos, P.; Eres, G.; Smirnov, S. Acs Nano 2011, 5, 6069-6076. 37. Yin, J.; Yu, J.; Li, X.; Li, J.; Zhou, J.; Zhang, Z.; Guo, W. Small 2015, 11, 4497-4502. 38. Liu, Y.; Bhowmick, S.; Yakobson, B. I. Nano Lett 2011, 11, 3113-3116. 39. Tay, R. Y.; Griep, M. H.; Mallick, G.; Tsang, S. H.; Singh, R. S.; Tumlin, T.; Teo, E. H. T.; Karna, S. P. Nano Lett 2014, 14, 839-846. 40. Artyukhov, V. I.; Liu, Y.; Yakobson, B. I. Proc Natl Acad Sci U S A 2012, 109, 1513615140. 41. Bartelt, N.; McCarty, K. MRS Bulletin 2012, 37, 1158.


15


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 16 of 23

42. Witten Jr, T.; Sander, L. M. Physical Review Letters 1981, 47, 1400. 43. Wang, L.; Wu, B.; Chen, J.; Liu, H.; Hu, P.; Liu, Y. Adv Mater 2014, 26, 1559-1564.


16

Page 17 of 23

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 1. a) Schematics of CVD system b) Decomposition mechanism of ammonia borane c,d) Optical images of triangular hBN crystal of size 5~10 µm. e) SEM image of hBN crystal with strips demonstrating negative thermal expansion of hBN f) Continuous hBN film synthesized with growth time around 30 min


17


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 18 of 23

Figure 2. XPS spectra of a) B and b) N core edges at 190.6 eV and 398.2 eV, respectively. TEM image showing presence of c) monolayer and d) bilayer hBN film. e) hBN film on quartz showing negligible absorbance (less than 0.01)


18

Page 19 of 23

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 3. a,b) Optical image of hexagonal hBN crystals synthesized at precursor heating temperature of 130oC c,d) SEM images of hexagon-shaped hBN crystal


19


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 20 of 23

Figure 4. a,b,c,d) Evolution of single-lobed and bi-lobed structures from hexagon-shaped hBN crystal. Closeup view of e) hexagonal crystal f) single and g) bilobed crystal h) Optical image of hexagonal crystal and its modulation to i) intermediate state and almost j) modulated triangle, showing little bump. k) Schematics representing transformation of hexagonal to triangular crystal with decreased supply of borazine to growth zone.


20

Page 21 of 23

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 5. a) EGA thermogram of ammonia borane heated at 1300C showing maximum decomposition around 9th min b) Mass spectra complied at 9th min, showing relative abundance of borazine around 30% c) EGA thermogram of ammonia borane heated at 90ºC showing maximum decomposition around 13.5th min d) Mass spectra compiled at 13.5th min, showing relative abundance of borazine around 2%.

For Table of Contents Use Only ACS Paragon Plus Environment

21


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 22 of 23

Morphology‐controlled synthesis of hexagonal boron nitride crystals by chemical vapor deposition

Subash Sharma†*, Kamal Sharma†, Mohamad Saufi Rosmi†‡, Yazid Yaakob†§, Mona Ibrahim Araby†, Hajime Ohtani#, Golap Kalita†, Masaki Tanemura†

Synthesis of hBN crystals with controlled morphology is a major challenge due to various kinetic and thermodynamic factors at edge. Supplying controlled amount of BN building blocks to synthesize triangular, hexagonal crystal and modulation from hexagons to triangles is major achievement due to the single parameter control throughout the experiment. Diffusion and edge attachment determine the morphology of hBN during crystal growth.


22

Page 23 of 23


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 ACS Paragon Plus Environment

23

Morphology-Controlled Synthesis of Hexagonal Boron Nitride Crystals

Recommend Documents