Highly thermally conductive nanocomposites synthesized by PVD for thermal management applications

Journal Pre-proof Highly thermally conductive nanocomposites synthesized by PVD for thermal management applications Xiaopeng Han, Ying Huang, Jin Yan, Yade Zhu, Xiaogang Gao PII:

S0925-8388(20)30280-2

DOI:

https://doi.org/10.1016/j.jallcom.2020.153917

Reference:

JALCOM 153917

To appear in:

Journal of Alloys and Compounds

Received Date: 3 November 2019 Revised Date:

11 January 2020

Accepted Date: 17 January 2020

Please cite this article as: X. Han, Y. Huang, J. Yan, Y. Zhu, X. Gao, Highly thermally conductive nanocomposites synthesized by PVD for thermal management applications, Journal of Alloys and Compounds (2020), doi: https://doi.org/10.1016/j.jallcom.2020.153917. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2020 Published by Elsevier B.V.

Highly thermally conductive nanocomposites synthesized by PVD for thermal management applications Xiaopeng Hana,b, Ying Huang*a,b, Jin Yana,b, Yade Zhua,b, Xiaogang Gaoa,b *Corresponding author. E-mail: [email protected]

a MOE Key Laboratory of Material Physics and Chemistry under Extrodinary Conditions, Ministry of Education, School of Science, Northwestern Polytechnical University, Xi'an 710072, PR China b Shaanxi Engineering Laboratory for Graphene New Carbon Materials and applications, Northwestern Polytechnical University, Xi'an 710072, PR China

*Corresponding author. E-mail: [email protected]

Highly thermally conductive nanocomposites synthesized by PVD for thermal management applications Xiaopeng Han, Ying Huang*, Jin Yan, Yade Zhu, Xiaogang Gao The address of all authors is the College of Science, Northwestern Polytechnical University. *Corresponding author. E-mail: [email protected] MOE Key Laboratory of Material Physics and Chemistry under Extrodinary Conditions, Ministry of Education, School of Science, Northwestern Polytechnical University, Xi'an 710072, PR China Shaanxi Engineering Laboratory for Graphene New Carbon Materials and applications, Northwestern Polytechnical University, Xi'an 710072, PR China Abstract Uniform Ag and Si layers were successfully prepared on the surface of graphite films(GF) to improve thermal conductivity(TC) by physical vapor deposition method(PVD). The results demonstrate that the unique cubic crystal structure of Ag layer with different deposition time show good interface bonding and no carbide product of Ag/GF composites. Meanwhile, the dense Si coating contribute to the enhancement of the thermal diffusion ability. The Ag/GF composites with the deposition time of 2 h possess the best comprehensive property with the TC of 9.93 (W/m·K), which is approximately 73.30% higher than untreated GF. The TC of Si/GF composites reach the maximum TC of 11.12 W/(m·K) and increase about 101.81% due to the nano-Si layer comparing with untreated GF. Those composites with high performance make them promising thermal management laminated materials. Key Words: thermal conductivity; Ag coating; Si coating; graphite film 1 Introduction With the continuous miniaturization of electronic device and lasher technology, thermal diffusion has to be necessary technological issue for a broad applications,

including spacecrafts, intelligent vehicles, smart phones, battery technologies, and electronic packaging as well as thumbnail-size chips. The effective thermal transport has recognized a critical challenge and urgent demand of high thermal conductivity materials to design thermal management system. Currently, ceramic, metals or composites display good thermal conductivity (TC). However, the ceramic material is eliminated due its high price, poor machinability and degraded crystal quality. The TC of metal materials, such as silver and copper, is excellent, but the density and the coefficient of thermal expansion is unsatisfactory. Composites, with its attractive properties, is a promising candidate material for thermal management because the performance can be scientifically designed. Common high-performance composites take advantages of carbon materials and metal composites with traditional process ways. Nowadays, common metal matrix composites applied in thermal export application are mainly carbon fibers/Al1, carbon nanotubes/Al2-4, graphene/Al5,6, SiC/Al7,8, diamond/Al9, graphite films/Al4,10,11 and so on. In other words, graphite materials have been widely used in composites for its high TC, low density, consistent orientation and low cost to improve the comprehensive properties12. However, with the limitation of processing methods, such as vacuum gas pressure, vacuum hot pressing as well as spark plasma sintering, relatively high cost and low TC of the metal-based composites prevent its application in thermal diffusion fields. As we all know, the challenge of poor wettability (the contact angle between mental and graphite materials more than 90°), which will result in weak bonding force, cracks and pores of the carbon/metal composites, followed by the deterioration of heat export property. The dispersion of carbon nanotube4,5,13-15 or graphene16-22 in the matrix have been recognized a problem to keep uniform dispersion and cannot widely used as heat export materials. The graphite film (GF)4,23-25 has excellent thermal properties of 1000-1500 W/m·K and has attracted much attention in the areas of heat dissipation. At the same time, all graphite materials react with molten metal under high temperature and infiltration pressure. In fact, graphite materials26-29 can be used as reinforcements to enhance performance of those composites, but the poor wettability

and interfacial reaction confine its application. Thus, various metal coatings, such as transition elements (such as Ti30, Cr16, Ni31, SiC27,32,33) and nitrides, have been prepared on the graphite materials to strength the surface properties. Furthermore, the high thermal-diffusion metal, consisting of Ag34,35, Cu11,36 or alloy, are recognized to be useful components for interface modification of graphite materials. Ag or Cu are used as reinforcement, due to their promising interface bonding and high TC. What’s more, those metal possessing lots of attractive performance, such as good oxidation resistance, high bending strength, and good ductility, are desirable thermal management materials. Presently, the metal coatings are produced by salt bath plating or chemical plating, but the coating and matrix cannot be strengthened effectively due to only chemical bonding. The chemical method always limited by oxidation or impurity, which will lead to defects and weak the function of coatings. The physical method is mainly including PVD or chemical vapor deposition (CVD), in which the experimental condition is relatively mild. Aluminum (Al) composites coating possessed with nitrides by PVD exhibited much increased properties37-39. A good matched layer of matrix, is used to solve the challenge of interfacial bonding and bad surface reaction10,11,31. In this study, a novel one-step method is proposed to strengthen thermal diffusion between the GF and Ag, GF and Si. The Ag and Si coating is fabricated by PVD method. Taking the advantage of high heat export performance between nano-layers and GF substrate, the nano-plating can be sued as thermal diffusion layer. This method has been successfully used to fabricate the nitriding of Al alloys to improve the interface microhardness and friction resistance properties

40,41

. Generally, the

promising interface layer is obtained, the thermal properties and mechanical performance of the coatings are studied. The heat performance is enhanced with Ag coating to improve the properties of substrate. The compact coating can act as protective coating to improve surface wettability between layer and substrate for enabling good TC contact between that, as well as effectively enhance the mechanical property of the composites. Combining with the microstructure morphology of SEM and AFM, the thermal properties of the as-obtained layers are studied and analyzed.

The results show that the nano-plating is contributed to improve the out-of-plane TC of the composites, effectively. 2 Experimental section 2.1Materials GF with 99.9% graphitization (in-plane and out-of-plane directions were measured to be about 1100 and 6 W/(m·K), respectively) with the average thickness of 0.3 mm and the size of 180 mm×180 mm were purchased from Qingdao Graphite Co. Ltd. Acetone. The high quality Ag target (99.999%, 60 mm×60 mm×5 mm) were utilized in the preparation of the nano-plating from Yipin Chuancheng (Beijing) technology Co. Ltd, China. 2.2 Preparation of Ag/GF composites by PVD All GF were heated to 1000

for 2 h in an Ar atmosphere with a flow rate of 15

sccm, and then were naturally cooled down to room temperature. GF (100×100 mm2) were cleared surface impurities by acetone solution and dried at 80

for next step.

Then, the nano-coatings were prepared by PVD system. An effective turbo molecular pump and mechanical pump were used to reduce deposition chamber pressure to reach the working pressure 5×10-3 Pa. The GF were fixed on a rotating platform at a speed of 10 rpm. The deposition procedure was carried out under optimal conditions: target power E=350.0 W, deposition pressure P=1.5 Pa, holding time from 30 min to 90 min, gas flow rate=80 sccm and at 30

.

2.3 Characterization After all the treatments, the X-ray diffraction (XRD) was employed to analysis the crystalline property and composition of the Ag/GF and Si/GF composites, which was equipped with Cu-Ka radiation at 40 kV using 100 mA in the 2θ range from 5° to 85°. X-ray photoelectron spectroscopy (XPS, Thermal Scientific K Alpha) equipped with

monochromatic Al Alpha photoelectron spectrometer was used to analyze the interfacial component. The three dimensional structure of prepared composites was analyzed by AFM (Dimension Fast Scan and Dimension Icon, Germany, Bruker).The surface morphology and elements distribution of the Ag/GF and Si/GF composites were observed using a scanning electron microscope (SEM, Helios G4 CX, American, FEI) equipped with effective scanning unit and an energy dispersive X-ray (EDX) spectrometer. The TC of prepared composites (out-of-plane) were performed with Laser Flash Apparatus (NETZSCH LFA447, Germany) at room temperature to 600

.

2.4 Results and discussion The layer-by-layer nano-plating composites with the Ag or Si as multideck reinforcement were fabricated by PVD, as shown in Figure 1.

Figure 1. Schematic drawing of the fabrication process of the Ag/GF composites (a) and the Si/GF composites (b). In order to improve the purity and graphitization degree, all GF were heated to 1000

and kept warm for 2 hours. To enhance the thermal diffusion property, the

Ag-coating or Si-coating was deposited on the surface of GF for different time by a PVD method. Generally, those different coatings were performed with same process besides different deposition parameters.

Figure 2. SEM images of Ag/GF composites obtained with different deposition time:(a,d) 0.5 h;(b,e) 1 h;(c,f) 2 h. Microstructure and morphology of Ag/GF composites with different deposition time from 0.5 h to 2 h are shown in Figure 2. As shown in Figure 2a, the treated interface of GF is relatively flat with some obvious cracks. As seen Figure 2d, further observation revealed that the surface formed Peanut-like silver particles, and some parts doesn’t form compact layer. When the deposition time of 1 h, as shown in Figure 2b, the dense coating with uniform Peanut-like granule are obviously formed on the surface of GF. As time increases, the coating forms an increasingly dense and multi-layer structure, as shown in Figure 2e. Larger and dense particles coated on the graphite surface compared to Figure 2a, further explanation that silver particles have constantly deposited with the increase of time. As the deposition time reach to 2 h (Figure 2a), it is observed that the GF are covered completely with three-dimensional nano-layer. In addition, Figure 2f shows the particles prepared in this condition with unique cubic crystal structure comparing with those Peanut-like granules in Figure 2d and e. The growth mechanism of silver particles can be analyzed and predicted by SEM photos of the three-dimensional structures. At first, the particles are gradually grown into a Peanut-like shape to cover the surface of GF, and then the Peanut-like granules are gradually developed into cubic particles due to the limited space. In summary, the coatings with various microscopic shape and dense exhibit different thermal diffusion property. The obtained unique particles with deposition time of 2 h

contribute to perform effective diffusion structures for the thermal management materials of GF matrix.

Figure3. Three-dimensional AFM images (5 µm×5 µm) of Ag-coated GF with different deposition time:(a,d) 0.5 h;(b,e)1 h;(c,f)2 h. AFM images of Ag-coated graphite films after PVD process are displayed in Figure3. The surface morphologies have obviously changed with increasing of deposition time. As shown in Figure 3a and d, the surface of GF becomes rough with increasing deposition time and exhibits “flower-like” structure. Meanwhile, the surface of GF displays numerous “flower” and the “flower” become larger due to enough deposition time. After 2 h deposition, the RMS value up to 242.9 nm, indicating that the coatings grow gradually after long deposition time. What’s more, the surface become flat and smooth due to the accumulation of Ag atmos. It is obvious that the surface of coatings displays more continuous surface morphology and outstanding stereochemical structure. It is worth nothing that “flower-like” coatings exiting on the GF play an important role in thermal transport due to three-dimensional structure.

Figure 4. The section SEM images of Ag/GF composites:(a) 0.5 h; (b) 1 h;(c) 2 h; elements mapping of the C (e) and Ag (f) EDX pattern of (d). The cross-section microstructure and elements distribution of Ag films deposited for o.5 h,1 h and 2 h are shown in Figure 4. As presented in Figure 4a, the Ag/GF composites have uniform coatings with the thickness of 3.10 µm. For Ag/GF composites (Figure 4b), we can observe that the dense layer about 6.02 µm on the surface of GF. After 2 h treatment, a continuous diffusion layer with much increased thickness is formed about 11.36 µm. Ag distribution is consistent with Figure 4d, indicating the strong bonding effect of prepared layers and GF matrix.

Figure 5. XRD patterns of Ag/GF composites with different deposition time. The XRD patterns of untreated and coated GF are also collected, and all details are shown in Figure 5, respectively. It is obvious that there are two obvious Ag peaks in all deposited samples. Two sharp diffraction peaks with the 2θ at 38° and 81° which can confirm the presence of elemental silver on the GF surface. No impurity peaks display in deposited samples, which shown that the high purity Ag have been successfully formed on matrix. With the extension of time, the peak of carbon gradually weakens. Finally, the carbon peak disappears when the deposition time is 2 hours. In summary, after the deposition of Ag on the surface of GF, obvious Ag peaks are observed in the Figure 5, showing that the coating fabricated by PVD have more dense structures and lower defects corresponding to SEM images (Figure 2).

Figure 6. XPS spectra of Ag/GF composites (wide scan) with different deposition time. Figure 6 displays the effects of increasing the deposition time on the thickness values, while comparing the Ag peaks with raw GF materials. It can be observed that by changing of deposition parameters, the intensity of the carbon peak gradually weakens. The main reason for this reduction is more dense Ag Peanut-like granules have been distributed on the surface of GF. The intensity of Ag peaks increases gradually with the extension of deposition time. It is evident that by increasing of deposition time, the coatings grow from point to Peanut-like granule until cover the whole surface. Generally, the results are consistent with the SEM photos. Further analysis shows that GF and silver are physically combined without metal carbide, which is a sign of proper wettability of GF and metal reinforcement by the process of PVD.

Figure 7. TC of Ag/GF composites in the vertical directions. Some literatures have been reported that existence of porosity in the samples and formation of carbide phase by chemical plating or bath plating caused significant drop in thermal property. According to XPS results, it can be seen that no carbide formation during the deposition process. For the laminated materials, the combination method is a key parameter to reflect the interface bonding property between the matrix and nano-plating. The TC of the prepared composites can be calculated as the formula: λ = αρC

(1)

where λ is the TC, α represents the thermal diffusivity, ρ represents the density, and C is the specific heat capacity of the composite. All prepared composites and GF are tested by the laser flash method to attain the parameter of thermal diffusivity.

Table 1. Thermal property of Ag/GF laminated composites GF

Ag0.5h

Ag1h

Ag2h

TD

TC

TD

TC

TD

TC

TD

TC

T( )

[cm2/s]

[W/(m·K)]

[cm2/s]

[W/(m·K)]

[cm2/s]

[W/(m·K)]

[cm2/s]

[W/(m·K)]

25

0.0544

5.73

0.0803

8.46

0.0851

8.96

0.0943

9.93

100

0.0430

4.53

0.0647

6.81

0.0713

7.51

0.0750

7.90

200

0.0335

3.53

0.0508

5.35

0.0536

5.64

0.0574

6.04

300

0.0269

2.83

0.0399

4.20

0.0442

4.65

0.0503

5.30

400

0.0225

2.37

0.0328

3.45

0.0376

3.96

0.0395

4.16

600

0.0179

1.88

0.0254

2.68

0.0288

3.03

0.0312

3.29

The lasher flash method is used to analyze thermal diffusivity of the GF and Ag/GF composites. According to the experiment results (Table 1), the out-of-plane direction TC of GF is 5.73 W/(m·K) in room temperature. With the increase of temperature, the TC of the GF decreases gradually according to different thermal diffusivity. As for the deposition time of 0.5 h, the TC of Ag/GF is 8.46 W/(m·K) in the 25

. TCs in xy

direction are much higher than those untreated GF materials. In Figure 7 it is discovered that TC of Ag/GF composites increase with the much longer deposition time. When the deposition time up to 2 h, the specimen has highest TC at 9.93 W/(m·K) at 25

. The main reason for this increase is electronic transmission rate of

Ag atoms which have been uniform distributed on the interfacial of GF. What’s more, the unique cubic crystal structure contributes to heat transport from inside of GF to the surface of the Ag/GF composites. Figure7 also reveals that the effect of increasing temperature on the TC values, while comparing the experimental results of untreated GF. It can be seen that by increasing the operation temperature, the TC of the composites decreases gradually.

Figure 8. Infrared thermal images of Ag/GF composites. Figure 8 shows the corresponding infrared thermal images of Ag/GF nanocomposites. The surface temperature of the composites is increased faster with the higher deposition time, indicating that a higher thermal transfer performance, which is also consistent with the results in Figure 7. What’s more, the temperature distribution on the surface of GF is uniform, revealing that the Ag layers maintains uniform dispersibility. In general, the uniform dispersion of nano Ag layers and low interface resistance are beneficial for forming effective heat transfer structure. The GF acts as thermally conductive layer, and the deposited coating acts as heat dissipation layer to form a thermal conductive-diffusion structure. 2.5 Conclusion In this section, all Ag/GF composites have been prepared by PVD method. It is demonstrated that the Ag layer with unique cubic crystal structure can be formed on the surface of GF, which further enhance the performance of laminated composites. The surface nano-plating of silver contributes to thermal diffusion with 73.30 % increase in the value under room temperature. In summary, an ideal laminated Ag/GF composite has been fabricated with high performance TC of 9.93 W/(m·K).

3 Experimental section 3.1 Materials and Preparation All of the raw materials and chemicals were used as Experimental section the Si target (99.99%). All GF were treated as section

except

. But the PVD parameters of

Si were carried in the following conditions: target power E=100.0 W, deposition pressure P=3.0 Pa, holding time 30 min to 90 min, gas flow rate=50 sccm, and the specimen temperature at room temperature. 3.2 Characterization All characterization devices are the same as chapter 2.2. 3.3 Result and discussion With the same methods in the previous chapter, the Si/GF composites were fabricated by PVD and the specific process is displayed in Figure 8.

Figure 9. SEM images of microstructure in the surface layer:(a,d) Si layer deposited for 0.5 h;(b,e) Si layer deposited for 1 h;(c,f) Si layer deposited for 2 h. The morphologies of Si films deposited for 0.5 h, 1 h and 2 h are shown in Figure 9, respectively. As shown in Figure 9a, the deposited coatings have dense structure without obvious grooves and defects. After further observation in Figure 9d, Si layers

have been formed on the surface of GF. At the beginning of the growth of the slice, part of layers are obtained. When the operation time of 1 h, as shown in Figure 9b, neat and large layer are deposited on the interfacial of GF in the argon gas components. In Figure 9b, with the increase of the operation time, the Si coating are obvious grown to compared with the operation time of 0.5 h. In this condition, grooves and defects can be evident observed due to the reaction time. As seen in Figure 9c, more dense and smooth layers exhibit on the surface of GF as the operation time reached to 2 h. In Figure 9f, the layered structure of Si coatings fabricated by PVD has been covered perfectly on GF. In summary, the Si layer with different morphology and thickness are controlled by adjusting the operation time under identical parameters. The growth mechanism can be proved that single Si atom increases to little layers and then little layers cover to the whole surface eventually.

Figure 10. Three-dimensional AFM images(5 µm×5 µm) of Si-coated graphite films after exposure to a variety of deposition time:(a,d) 0.5 h;(b,e)1 h;(c,f)2 h. As shown in Figure 10, the GF with different deposition time are presented. The value of RMS from 195.5 nm up to 319.6 nm, showing that the thick of Si layers increase gradually after much longer time. Meanwhile, the surface of GF is relatively flat under short deposition time for 0.5 h. By contrast, the interface of GF displays

numerous short cones and undulate patterns, and the short cons become larger with much longer deposition time. Thus a silicon-rich layer gradually formed, which can improve heat transport and decrease the interface resistance.

Figure 11. Microstructure and morphology of Si/GF composites：(a,b) 0.5 h; (c) 1 h; (d) 2 h; elements mapping of the C (e) and Si (f) EDX pattern of (d). The cross-section misctotructure and elements distribution of Si films deposited for o.5 h,1 h and 2 h are shown in Figure 11. Films, of 286.2 nm and 457.2 nm thick, are prepared on the matrix. As can be seen from the Figure11, the thickness of the coating gradually increases with deposition time. Diffusion of Si towars to the whole GF surface are obviously observed. The Si distribution indicates the prepared layer bonds well with the GF matrix.

Figure 12. X-ray diffraction patterns for Si / GF before and after plasma deposition. The performance of nano-plating not only depends on the layer distribution and consistency, but also depends on the phase structure of the layer. Figure 12 shows the XRD patterns for untreated GF, Si coated specimen. It can be seen that two obvious peaks exist in all treated specimens. The sharp diffraction peaks with the 2θ at 55° which can confirm the presence of elemental Si on the graphite surface.

A typical

carbon peak can also be seen at 26°. With the increase of operation time, the peak of carbon decrease gradually due to the thickness of Si plating. In fact, the surface property depends on the phase composition.

Figure 13. XPS spectra of Si/GF composite (wide scan) with different operation time. Figure 13 shows the influence of increasing the operation time on the XPS spectra, while comparing with the untreated GF. It is evident that by adjusting the operation time, the intensity of Si peak increased. Combined with the Figure 9, it should be noted that Si layers coat the whole GF gradually and improve surface property obviously. What’s more, the intensity of carbon peak reduced with the increase of deposition time, indicating that the dense of Si layers. Furthermore, only a good interface combination can improve the heat dissipation capability and minimize interfacial resistance.

Figure 14. TC of Si/GF composites in the vertical directions. In Figure 14, it is displayed that the TC of Si/GF composites decrease with the different operation temperature. Compared with raw materials, the TC of Si/GF increases with Si layer. According to the experiment results (Table 2), the xy direction TC of GF is 5.51 W/(m·K) in room temperature. The TC of Si/GF composites with deposition time of 2 h is 11.12 W/(m·K), which is improved by 101.81% comparing with raw materials in 30

. It is also indicated that the operation time of 0.5 h and 2 h

has almost the same effect on the value of TC. The improvement of TC of Si/GF composites are owed to the thermal resistance decreased due to the interface contact of Si coatings and GF. In other words, Si coating can accelerate thermal transfer. Moreover, no interfacial reaction form between layer and matrix, which is beneficial to heat conduction between layers and matrix. Detailed results of the composites are listed in table 2.

Table 2. Thermal property of Si/GF laminated composites GF

Si0.5h

Si1h

Si2h

TD

TC

TD

TC

TD

TC

TD

TC

T( )

[cm2/s]

[W/(m·K)]

[cm2/s]

[W/(m·K)]

[cm2/s]

[W/(m·K)]

[cm2/s]

[W/(m·K)]

25

0.0511

5.51

0.0863

9.32

0.0851

9.19

0.1030

11.12

100

0.0416

4.49

0.0752

8.12

0.0713

7.70

0.0754

8.10

200

0.0329

3.55

0.0548

5.92

0.0536

5.79

0.0572

6.16

300

0.0266

2.87

0.0442

4.77

0.0442

4.77

0.0503

5.43

400

0.0228

2.46

0.0378

4.08

0.0376

4.06

0.0396

4.28

600

0.0179

1.93

0.0296

3.20

0.0289

3.12

0.0312

3.37

According to the experiment results (Table 2), the out-of-plane direction TC of GF is 5.51 W/(m·K) in room temperature. With the increase of temperature, the TC of the GF decreases gradually due to different thermal diffusivity. As for the deposition time of 0.5 h, the TC of Ag/GF is 9.32 W/(m·K) in the 25

. TCs in xy direction are much

higher than those untreated GF materials. In Figure 14 it can be discovered that TC of Ag/GF composites increase with the much longer deposition time. When the deposition time up to 2 h, the specimen has highest TC at 11.12 W/(m·K) at 25

.

Figure 15. Infrared thermal images of Si/GF composites Figure15 displays the corresponding infrared thermal images of Si/GF nanocomposites. The higher thermal transfer performance is proved that the surface temperature of the composites increases faster with the longer deposition time. What’s more, the temperature distribution on the surface of GF is uniform, revealing that the Si coatings displays uniform dispersibility. In general, the uniform dispersion of nano Si layers and low interface resistance are beneficial to heat transfer performance. The novel fabrication method by PVD can further improve the distribution of coatings to strength thermal conductivity. 3.4 Conclusion In this section, a novel PVD way is adopted to prepare laminated Si/GF composites, no cracks and significant defects are discovered. The Si coating contributes to the surface thermal diffusion for the improvement of TC property of Si/GF composites. The TC of 11.12 W/(m·K) of the composites increases about 101.81% due to the unique Si layer. The excellent thermal property of Si/GF composites displays the huge potential in the application of thermal management area.

4 Conclusion In this study, a new strategy for preparing high TC laminated materials is presented using PVD method. Firstly, it was demonstrated that the Ag/GF composite with Ag layer can be performed with this process, which further enhance the performance of TC about 73.30%. The unique cubic crystal structure can be obviously contributed to improve thermal transport with increased TC of 9.93 W/(m·K). It can be also seen that by increasing the operation temperature, the TC of the composites decreased gradually. Secondly, Si/GF materials fabricated by the same way. The surface thermal diffusion is improved with Si coating to enhance TC property of Si/GF composites. The TC of 11.12 W/(m·K) of the composites increases about 101.81% due to the unique Si layer. In summary, Ag/GF and Si/GF composites will be served as promising thermal management materials. Acknowledge This

work

was

financially

supported

by

Innovation

Foundation

for

School-enterprise Collaboration of Northwestern polytechnical University (Grant No. XQ201912). We would like to thank the Analysis and Testing Center for Northwestern Polytechnical University for providing the test of scanning electron microscope. Reference

(1) Liu, T.T.；He, X.B.；Liu, Q.；Ren, S.B.；Kang, Q.P.；Zhang, L., and Qu, X.H., Effect of chromium carbide coating on thermal properties of short graphite fiber/Al composites. J MATER SCI. 2014, 49, 6705-6715. (2) Xiang, J.F.；Xie, L.J.；Meguid, S.A.；Pang, S.Q.；Yi, J.；Zhang, Y., and Liang, R., An atomic-level understanding of the strengthening mechanism of aluminum matrix composites reinforced by aligned carbon nanotubes. COMP MATER SCI. 2017, 128, 359-372. (3) Guo, B.S.；Song, M.；Yi, J.H.；Ni, S.；Shen, T., and Du, Y., Improving the mechanical

properties of carbon nanotubes reinforced pure aluminum matrix composites by achieving non-equilibrium interface. MATER DESIGN. 2017, 120, 56-65. (4) Chang, J.；Zhang, Q.；Lin, Y.F.；Zhou, C.；Yang, W.S.；Yan, L.W., and Wu, G.H., Carbon Nanotubes Grown on Graphite Films as Effective Interface Enhancement for an Aluminum Matrix Laminated Composite in Thermal Management Applications. ACS APPL MATER INTER. 2018, 10, 38350-38358. (5) Wozniak, J.；Jastrzębska, A.；Cygan, T., and Olszyna, A., Surface modification of graphene oxide nanoplatelets and its influence on mechanical properties of alumina matrix composites. J. Eur. Ceram. Soc. 2017, 37, 1587-1592. (6) Dixit, S.；Mahata, A.；Mahapatra, D.R.；Kailas, S.V., and Chattopadhyaya, K., Multi-layer graphene reinforced aluminum - Manufacturing of high strength composite by friction stir alloying. Compos. Pt. B-Eng. 2018, 136, 63-71. (7) Zhang, W.Y.；Du, Y.H.；Zhang, P., and Wang, Y.J., Air-isolated stir casting of homogeneous Al-SiC composite with no air entrapment and Al4C3. J. Mater. Process. Technol. 2019, 271, 226-236. (8) Marimuthu, S.；Dunleavey, J.；Liu, Y.；Smith, B.；Kiely, A., and Antar, M., Characteristics of hole formation during laser drilling of SiC reinforced aluminium metal matrix composites. J. Mater. Process. Technol. 2019, 271, 554-567. (9) Tan, Z.；Xiong, D.B.；Fan, G.；Chen, Z.；Guo, Q.；Guo, C.；Ji, G.；Li, Z., and Zhang, D., Enhanced thermal conductivity of diamond/aluminum composites through tuning diamond particle dispersion. J MATER SCI. 2018, 1-11. (10) Zheng, Q.；Braun, P.V., and Cahill, D.G., Thermal Conductivity of Graphite Thin Films Grown by Low Temperature Chemical Vapor Deposition on Ni (111). ADV MATER INTERFACES. 2016, 3. (11) Huang, Y.；Su, Y.；Guo, X.；Guo, Q.；Ouyang, Q.；Zhang, G., and Zhang, D., Fabrication and thermal conductivity of copper coated graphite film/aluminum composites for effective thermal management. J. Alloys Compd. 2017, 711, 22-30. (12) Han, X.P.；Huang, Y.；Gao, Q.；Yu, M., and Chen, X.F., High Thermal Conductivity and Mechanical Properties of Nanotube@Cu/Ag@Graphite/Aluminum Composites. IND ENG CHEM RES. 2018, 57, 10365-10371. (13) Han, X.；Huang, Y.；Gao, Q.；Fan, R., and Peng, X., Effects of nanotube content on thermal and mechanical properties of NT@Cu/Ag@GF/Al composites. J ALLOY COMPD. 2018, 766. (14) Yan, J.；Huang, Y.；Zhang, Z., and Liu, X.D., Novel 3D microsheets contain cobalt particles

and numerous interlaced carbon nanotubes for high-performance electromagnetic wave absorption. J. Alloys Compd. 2019, 785, 1206-1214. (15) Yan, J.；Huang, Y.；Han, X.P.；Gao, X.G., and Liu, P.B., Metal organic framework (ZIF-67)-derived hollow CoS2/N-doped carbon nanotube composites for extraordinary electromagnetic wave absorption. Compos. Pt. B-Eng. 2019, 163, 67-76. (16) Han, X.；Huang, Y.；Zhou, S.；Sun, X.；Peng, X., and Chen, X., Effects of graphene content on thermal and mechanical properties of chromium-coated graphite flakes/Si/Al composites. J MATER SCI-MATER EL. 2017, 1-11. (17) Zhang, L. ；Hou, G.； Zhai, W.；Ai, Q.； Feng, J.； Zhang, L. ； Si, P., and Ci, L., Aluminum/graphene composites with enhanced heat-dissipation properties by in-situ reduction of graphene oxide on aluminum particles. J ALLOY COMPD. 2018, 748, 854-860. (18) Ju, J.M.；Wang, G., and Sim, K.H., Facile synthesis of graphene reinforced Al matrix composites with improved dispersion of graphene and enhanced mechanical properties. J ALLOY COMPD. 2017, 704, 585-592. (19) Liu, P.B.；Zhang, Y.Q.；Yan, J.；Huang, Y.；Xia, L., and Guang, Z.X., Synthesis of lightweight N-doped graphene foams with open reticular structure for high-efficiency electromagnetic wave absorption. Chem. Eng. J. 2019, 368, 285-298. (20) Liu, P.B.；Yan, J.；Guang, Z.X.；Huang, Y.；Li, X.F., and Huang, W.H., Recent advancements of polyaniline-based nanocomposites for supercapacitors. J. Power Sources. 2019, 424, 108-130. (21) Li, C.；Zeng, X.L.；Tan, L.Y.；Yao, Y.M.；Zhu, D.L.；Sun, R.；Xu, J.B., and Wong, C.P., Three-dimensional interconnected graphene microsphere as fillers for enhancing thermal conductivity of polymer. Chem. Eng. J. 2019, 368, 79-87. (22) Lin, Z.D.；Shu, S.C.；Li, A.；Wu, M.L.；Yang, M.Y.；Han, Y.；Zhu, Z.X.；Chen, B.A.； Ding, Y. ； Zhang, Q. ； Wang, Q., and Dai, D., Preparation and Mechanical Property of Graphene-reinforced Copper Matrix Composites. J. Inorg. Mater. 2019, 34, 469-477. (23) Huang, Y.；Ouyang, Q.；Guo, Q.；Guo, X.；Zhang, G., and Zhang, D., Graphite film/aluminum laminate composites with ultrahigh thermal conductivity for thermal management applications. Mater. Des. 2016, 90, 508-515. (24) Huang, Y.；Su, Y.；Li, S.；Ouyang, Q.；Zhang, G.；Zhang, L., and Zhang, D., Fabrication of graphite film/aluminum composites by vacuum hot pressing: Process optimization and thermal conductivity. COMPOS PART B-ENG. 2016, 107, 43-50. (25) Ruiz, J.；Ganatra, Y.；Bruce, A.；Howarter, J., and Marconnet, A.M. Investigation of

aluminum foams and graphite fillers for improving the thermal conductivity of paraffin wax-based phase change materials. in Thermal and Thermomechanical Phenomena in Electronic Systems (ITherm), 2017 16th IEEE Intersociety Conference on. 2017. IEEE. (26) Zhang, X.；Shi, Z.；Zhang, X.；Wang, K.；Zhao, Y.；Xia, H., and Wang, J., Three dimensional AlN skeleton-reinforced highly oriented graphite flake composites with excellent mechanical and thermophysical properties. CARBON. 2018. (27) Xue, C.；Bai, H.；Tao, P.；Wang, J.；Jiang, N., and Wang, S., Thermal conductivity and mechanical properties of flake graphite/Al composite with a SiC nano-layer on graphite surface. MATER DESIGN. 2016, 108, 250-258. (28) Oddone, V.；Boerner, B., and Reich, S., Composites of aluminum alloy and magnesium alloy with graphite showing low thermal expansion and high specific thermal conductivity. SCI TECHNOL ADV MAT. 2017, 18, 180. (29) Muthazhagan, C.；Babu, A.G.；Bhaskar, G.B., and Rajkumar, K. Influence of graphite reinforcement on mechanical properties of aluminum-boron carbide composites. in 1st International Materials, Industrial, and Manufacturing Engineering Conference, MIMEC 2013, December 4, 2013 - December 6, 2013. 2014. Johor Bahru, Malaysia: Trans Tech Publications Ltd. (30) Zhang, J.B.；Liu, W.Y.；Jin, Y.M.；Wu, S.J.；Hu, T.T.；Li, Y., and Xiao, X.P., Study of the interfacial reaction between Ti3SiC2 particles and Al matrix. J. Alloys Compd. 2018, 738, 1-9. (31) Ishigaki, T.；Tatsuoka, S.；Sato, K.；Yanagisawa, K.；Yamaguchi, K., and Nishida, S., Influence of the Al content on mechanical properties of CVD aluminum titanium nitride coatings. Int. J. Refract. Met. Hard Mat. 2018, 71, 227-231. (32) Wang, C.；Bai, H.；Xue, C.；Tong, X.S.；Zhu, Y.B., and Jiang, N., On the influence of carbide coating on the thermal conductivity and flexural strength of X (X = SiC, TiC) coated graphite/Al composites. RSC ADV. 2016, 6, 107483-107490. (33) Tsai, W.Y.；Huang, G.R.；Wang, K.K.；Chen, C.F., and Huang, J.C., High Thermal Dissipation of Al Heat Sink When Inserting Ceramic Powders by Ultrasonic Mechanical Coating and Armoring. MATERIALS. 2017, 10. (34) Laghrib, F.；Ajermoun, N.；Hrioua, A.；Lahrich, S.；Farahi, A.；El Haimouti, A.；Bakasse, M., and El Mhammedi, M.A., Investigation of voltammetric behavior of 4-nitroaniline based on electrodeposition of silver particles onto graphite electrode. Ionics. 2019, 25, 2813-2821. (35) Sivasamy, P.；Harikrishnan, S.；Hussain, S.I.；Kalaiselvam, S., and Babu, L.G., Improved thermal characteristics of Ag nanoparticles dispersed myristic acid as composite for low temperature thermal energy storage. Mater. Res. Express. 2019, 6, 7.

(36) Rodriguez-Guerrero, A.；Sanchez, S.A.；Narciso, J.；Louis, E., and Rodriguez-Reinoso, F., Pressure infiltration of Al-12 wt.% Si-X (X = Cu, Ti, Mg) alloys into graphite particle preforms. Acta Mater. 2006, 54, 1821-1831. (37) Lu, C.；Wang, Y.X.；Zhu, Y.D.；Guo, J.H.；Wang, Y.；Fu, H.Y.；Chen, Z.B., and Yan, M.F., A novel anti-frictional multiphase layer produced by plasma nitriding of PVD titanium coated ZL205A aluminum alloy. Appl. Surf. Sci. 2017, 431. (38) Abdoos, M.；Yamamoto, K.；Bose, B.；Fox-Rabinovich, G., and Veldhuis, S., Effect of coating thickness on the tool wear performance of low stress TiAlN PVD coating during turning of compacted graphite iron (CGI). Wear. 2019, 422, 128-136. (39) Sullivan, S.P.；Leftwich, T.R.；Goodwin, C.M.；Ni, C.Y.；Teplyakov, A.V., and Beebe, T.P., Growth and chemical modification of silicon nanostructures templated in molecule corrals: Parallels with the surface chemistry of single crystalline silicon. Surf. Sci. 2019, 683, 38-45. (40) El-Ghazaly, A.；Anis, G., and Salem, H.G., Effect of graphene addition on the mechanical and tribological behavior of nanostructured AA2124 self-lubricating metal matrix composite. Compos. Pt. A-Appl. Sci. Manuf. 2017, 95, 325-336. (41) Hsieh, C.-C. and Liu, W.-R., Synthesis and characterization of nitrogen-doped graphene nanosheets/copper composite film for thermal dissipation. CARBON. 2017, 118, 1-7.

Highlights: 1. N,P-CNL-1:1 deliver an enhanced limiting current density of -5.97 mA cm-2 at 1600 rpm and outstanding initial potential (-0.004 V) and wave potential (- 0.144 V). 2.PAN can serve as a carbon source and produce graphene nitrogen, pyridinium, FeNx and other active sites. 3. The addition of phosphorus forms a rich active site Fe2P improve the electrochemical properties of the material greatly.

1. Preparation of coated thin films by physical vapor deposition to improve the thermal conductivity of the matrix. 2. Ag/GF composites with three-dimensional Ag layer enhance the performance of TC about 73.30% and Si/GF composites increases about 101.81% due to the unique Si layer. 3. Ag/GF composites and Si/GF composites can be served as flexible conductive material.

Declaration of interests ☒ The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. ☐The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: