Materials Physics and Mechanics 42 (2019) 272-279

Received: October 6, 2018

STUDY OF HEAT DISSIPATING MATERIAL USING BORONNITRIDE FABRICATED BY LASER ABLATION
Atsushi Yamaguchi, Pankaj Koinkar, Akihiro Furube*
Graduate School of Technology, Industrial and Social Sciences, Tokushima University, Tokushima 770-8506,
Japan*e-mail: furube.akihiro@tokushima-u.ac.jp

Abstract. More research interest is developing rapidly on two dimensional (2D) materials
owing to their excellent electro-optic properties to develop next generation of electronics andhighly functional devices. Among well-known and widely used 2D materials, boron
nitride (BN) is an electrical insulator with a band gap of 5.5 eV, and attests high chemical
stability, outstanding mechanical properties, and high thermal conductivity. Accordingly, BN
is considered as a promising candidate to improve the heat dissipation material performance.
In this study, the cooling rate of composite materials of poly methyl methacrylate (PMMA),
hexagonal boron nitride (h-BN) and gold nanoparticles was investigated using femtosecond
transient absorption spectroscopy. The main objective of this study is to prepare the flexible
BN-PMMA films could have a significant impact on heat dissipation to enhance theperformance of electronics devices. BN nanostructures were prepared by nanosecond laser
ablation in acetone. The laser ablation was carried out at room temperature with laser ablation
time of 120 min. The SEM images of bulk BN and laser ablated BN were obtained forstructural and surface morphological characterization. Gold colloidal solution was preparedusing gold nano-particles with chloroauric acid and distilled water. For the preparation ofcomposite film, PMMA was dissolved in acetone solvent and then mixed with BN and gold
colloid solution. The prepared composite films were examined for cooling rate ofphotoexcited gold nanoparticles using femtosecond transient absorption spectroscopy. It isfound that the lifetime is shorter for composite films with Au and high BN content.
Keywords: boron nitride, laser ablation, X-ray diffraction, raman spectroscopy, scanningelectron microscopy, cooling process, transient absorption spectroscopy (TAS)

1. Introduction
During the past few years, (2D) materials have received a great deal of interest due to theirwide application in micro and nano optoelectronics, photocatalysis and energy conversion
device. Significant progress has been achieved in preparation of 2D materials using various
synthesis methods such as mechanical exfoliation, chemical exfoliation and hydrothermal or
solvothermal reactions, and chemical vapor deposition. These techniques are very effective tofabricate high quality nanosheets with limited efficiency [1-3]. A widely used 2D formof carbon is called as graphene. Graphene is well-known and one of the most extensively
studied materials because of its fascinating physical and chemical properties [4-6]. It can beexfoliated from graphite. Graphite, a base material for graphene, is relatively low cost andwidely used in our daily life such as lead of pencil. In the same way, besides graphene,
atomically thin transition-metal dichalcogenides (TMDs) also attracts enormous attention allover the world [7]. TMDs layered materials such as Molybdenum sulfide (MoS2), Tungsten
http://dx.doi.org/10.18720/MPM.4232019_2© 2019, Peter the Great St. Petersburg Polytechnic University© 2019, Institute of Problems of Mechanical Engineering RAS

Study of heat dissipating material using boron nitride fabricated by laser ablation

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sulfide (WS2) and Boron nitride (BN) exhibits unique features and characteristics,
establishing their significance in opto-electronic devices and applications. BN nanostructure
has greatly shown its potentials for applications in high performance devices like electrondevices, gas absorbents and reinforcing agents [8]. BN can be found in two forms; hexagonal
BN (h-BN) and cubic BN (c-BN). Among these, h-BN having similar structure to graphite is
new material for research as compared to widely studied c-BN. The h-BN is now widely usedin study. Recently, success in synthesis of Boron nitride nanotube (BNNT) has gaining muchattention because of their physicochemical properties. BNNT has similar nanostructure to thatof carbon nanotube (CNT) where boron and nitrogen atoms are arranged in hexagonal
network. BNNT displays comparable or even better characteristics as compared to CNT andis considered as a promising material for strengthening polymers, ceramics and metals
because of it has high rigidity and high chemical stability. It also exhibits superior properties
like antioxidant power and heat resistance, it is hard to oxidize up to 950oC and structurally
stable up to 900oC. It is reported that the h-BN can change to BNNTS and C-BN by using
laser ablation [2]. In the last decade, there have been few reports on the alternative routes forthe preparation of BN using the polymer as a precursor. In this context, few reports suggestthat poly methyl methacrylate (PMMA) and poly-styrene (PS) can be used as precursor tosynthesis BN-polymer composite film [3]. When BN coated with polymer, it shows
improvement in the properties such as thermal conductivity and mechanical strength due tothe interfacial adhesion in the composite films. Furthermore, previous reports suggest that thefabrication of new functional material combined with 2D materials and metal nanoparticle.
The formation of new composite materials exhibits superior performance as compared tonoble metal nanoparticle because of excellent characteristic of 2D material, the obtained large
surface area, chemical stability and prevention of aggregation of nanoparticles. Also,composite material of graphene and gold nanoparticle is emerging as a material with future
potential for high sensitivity electrochemical sensor [9-10]. In addition, composite material
like Au nanoparticle modified with of MoS2 nanostructure can be possible serve as an active
substrate to produce enhanced light absorption [11]. Most recently, advancement in
information and communication technologies accelerates the research activities for theproduction of innovative machines and devices. This creates increase in the demands ofelectronic parts such as CPU and memory. For the development of flexible electronic devices,a flexible material with superior heat dissipation are needed around the world [12]. The heatreleased from smaller electronic devices could alter the performance which results in overheat
or explosion. The heat dissipation is one factor which limits to develop electronic devices
such as mobile phones and batteries. Since BN produces high thermal conductivity, it can beeffectively used to control heat dissipation. Therefore, it is thought that BN could beconsidered as promising material to control heat dissipation to make smaller devices coolerand safer without causing damage.In the present work, we have prepared composite film ofBN with flexible PMMA and Au nanoparticle. The cooling process of BN and polymer
composite films were studied using femtosecond transient absorption spectroscopy.
2. Experimental
Chemicals and Materials. Chemicals and materials used were purchased and used asreceived; BN powder (Wako Chemical Japan), HAuCl4 4H2O (0.1 ml 2.5×10-5 mol) (Kishida
Chemical, Japan, 99.0 %), Na3C6H5O7 (Kanto Chemical, Japan: 0.100 g /10 ml,
294.1 g /mol), Poly-metylmetaclyl-acid (PMMA), Acetone (Kishida Chemical, Japan: 99.5%)
Preparation of 40 nm diameter gold nanoparticles by chemical synthesis. Goldnanoparticles are synthesized by the chemical method. HAuCl4 aqueous solution(0.1 ml: 2.5×10-5 mol) was added into deionized water (100 ml). The mixture was heated andstirred at 100ºC. Then, the Na3C6H5O7 (1 ml) solution was added into the mixture. After the274

Atsushi Yamaguchi, Pankaj Koinkar, Akihiro Furube

mixture was stirred at heating for 5 minutes and then kept for cooling at room temperature.
Finally, deionized water was added for total volume 100 ml. Au nanoparticle size wasdetermined by the experimentally observed peak position from UV-vis spectra.
Preparation of PMMA–Au–BN nanocomposite. PMMA solution was prepared asfollows: 4 g of PMMA (Mw = 100,000) was dissolved into 30 ml of Acetone. After this, 1 mg
and 5 mg laser ablated BN powder was added into PMMA mixture and stirred for 10 minutes
to prepare PMMA-Au-BN solution. Then, PMMA solution was mixed with 13 ml of
Au nanoparticle colloid. PMMA-Au-BN nanocomposite film was prepared transferring.
PMMA-Au-BN solution on glass substrate at room temperature for 3 hours. The PMMA-AuBN composite film with 1 g of BN and 5 g of BN hereafter referred as sample 1 and sample 2respectively. The preparation details of sample 1 and 2 is shown in Table 1.
Table 1. Synthesis of BN, PMMA and Au ColloidSample
BNAu
(mg)
(nm)
S1
140
S2
540

BN:Au
(Weight ratio)
16:1
78:1

Laser Ablation and characterization. The BN nanoparticle was prepared bynanosecond laser ablation using acetone as a solvent. We used analytical grade h-BN powder
about 100 mg mixed with 30 mL acetone into a glass bottle. The solution was kept undermagnetic stirring for 30 min prior to laser ablation. The laser ablation was carried out with
Nd:YAG laser (wavelength 532 nm, pulse duration 10 ns, pulse repetition frequency 10 Hz,
beam size 5 mm and laser power 56 mJ). During the laser ablation process, the solution wasrotated by magnetic stirrer and laser ablation time was 120 min. After laser ablation, BN
colloidal suspension was heated in air to obtain dry BN nanoparticle in the form of powder.
The laser ablated BN nanoparticles sample was characterized by X-ray diffraction (XRD) andscanning electron microscopy (SEM) to confirm the formation of nanostructure, surface
morphological changes as well as structural features.
Transient Absorption Spectroscopy (TAS) using femtosecond laser (coolingprocess of Au nanoparticle). Cooling process of the PMMA-Au-BN film was investigatedusing femtosecond transient absorption spectroscopy. The measurements were carried out
with an amplified Ti:sapphire laser (800 nm wavelength, 130 fs fwhm pulse width,
0.8 mJ/pulse intensity, 1 kHz repetition; Spectra Physics, Hurricane). The second harmonic of
400 nm wavelength at a 500 Hz modulation frequency was used for a pump light. On theother hand, the white-light continuum generated by focusing the fundamental beam fromTi:sapphire laser onto a sapphire plate (2 mm thick) was used for a probe light. The probe
light was focused at the center of the pump light (~0.3 mm diameter) on the sample, and thediffuse reflected probe light was detected by a Si photodiode after passing through a
monochromator (Acton Research, SpectraPro-150). Au nanoparticle of dispersion including
PMMA film was irradiated by the pump light (400 nm). Cooling effect of PMMA film
including BN was measured by probe light (850 nm).
3. Results and discussion
The spectroscopic data of bulk BN and laser treated BN were obtained using XRD diffraction,
Raman spectroscopy and SEM. Figures 1(a) and 1(b) display the XRD spectra of bulk BN
powder and laser-treated BN for 120 min. Figure 1(a) shows that the intensity of thediffraction peak (002) and (004) decreased for laser-treated BN with small shift as comparedto the bulk BN. It suggests that the bulk BN has been transformed into h-BN nanostructure
after the laser ablation while keeping its crystalline structure unchanged [13]. Figure 1(b)Study of heat dissipating material using boron nitride fabricated by laser ablation

275

shows that the intensity of the diffraction peaks (101), (100) and (102) slightly increases. It
indicates that the c-BN content is also observed after laser ablation.

Fig. 1. High resolution XRD spectra of (a) bulk BN powder and (b) laser ablated BN
The raman spectra of bulk BN powder and laser-treated BN for 120 is shown in Fig. 2.
In case of laser ablated BN, the spectra graph indicates that the signature peak assigned toh-BN is observed at 1364.4 cm-1 [7,14]. The increase in the intensity of peak at 1364.4 cm-1
confirms that h-BN nanostructure was still unchanged after the laser ablation.
Figure 3 illustrates SEM images of bulk BN powder and laser ablated BN for 120 min.
The SEM images show the formation of BN nanostructures upon laser ablation. Figure 3 (a)shows that the BN sheets having the diameter varies from 2 µm to 10 µm. In the case of laser
ablated BN sample, the formation of nanoparticle is observed with diameter of 30-70 nm andthe transformation of bulk BN powder into BN nanostructure might be due to the intensethermal activity produced during laser ablation.

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Fig. 2. Raman spectra of laser ablated BNFig. 3. SEM images of (a) Bulk BN, (b) 120 min laser ablated BNFigure 4 shows the UV-vis reflection spectra results of PMMA film, sample S1 andsample S2. The reflectances of sample S1 and sample S2 are noticeably lower around 550 to
570 nm, extending toward longer wavelength around 800 nm as compared to the nearly
constant reflectance of PMMA film. This lowering in the reflectance might be attributed toaggregation of Au nanoparticle in sample S1 and sample S2, because non-aggregated Au
nanoparticles could not show such a broad absorption band.

Fig. 4. Reflection spectra images of PMMA and Au-BN-PMMA composite films

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Figure 5 shows that transient absorption spectroscopy (TAS) using femto second laser(Probe light: 850 nm, Excitation light intensity: 3.0 mW). The summery of sample lifetime isshown in Table 2 from TAS measurement fitting graph result.

Fig. 5. TAS measurement of PMMA films including BN and Au
Cooling process of Au nanoparticle by photoexcitation was observed as reported
previously [15]. 400 nm excitation generates electron-hole pairs in the Au nanoparticle andelectron-electron scattering elevates the electron temperature within 100 fs. Thermal
equilibrium process happens by electron phonon scattering of the internal Au nanoparticle
from 100 fs to 1 ps. Thermal diffusion process happens by Au phonon – media phonon
scattering from 10 ps to 100 ps. It is seen that heat transfer occurs from Au nanoparticle tocircumference medium.
Table 2. Sumary of lifetime of sample S1 and S2Sample
tau 1
S10.45591 ± 0.0504
S20.15535 ± 0.0186

tau 215.396 ± 1.613.064 ± 2.23

Long wavelength area of plasmon band became broader by photoexcitation and theeffect was observed in this transient absorption experiment of using probe light of 850 nm.
Here the growth and decay of the transient signals correspond to temperature increase anddecrease. Figure 4 shows that sample including low BN (sample S1) has long lifetime better
than sample including more BN (sample S2) (see tau 2 vales in Table 2). That is, coolingprocess of Au nanoparticle after photoexcitation of including more BN is promoted by theeffect of efficient heat transfer property of BN.
4. Conclusions
We have successfully prepared the BN nanostructures using nanosecond laser ablation inacetone. The formation of BN nanostructure was confirmed by XRD, raman spectroscopy andSEM measurements. We prepared to PMMA composite films with the laser ablated BN andAu nanoparticle of a 40 nm diameter. The cooling process after exciting the Au nanoparticles
in the film was examined using femtosecond transient absorption spectroscopy and the effectof BN as an efficient heat dissipater was observed. Heat dissipation performance from BN278

Atsushi Yamaguchi, Pankaj Koinkar, Akihiro Furube

could play a crucial role in energy saving and enhance the overall performance of electronicdevices. Therefore, it is recommended that further research on heat dissipation is important toresolve a major challenge of high-temperature rise during the process which reduces theefficiency of future generation flexible electronic devices.
Acknowledgements. The authors sincerely acknowledge the cooperation and experimental
facilities provided by Prof. Shuichi Hashimoto, Prof .Toshihiro Moriga and Dr. Kei-ichiro
Murai, from Tokushima University, Japan.
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