Microstructure evolution in zirconium carbide thin films at different substrate temperatures

Subject Areas : Journal of Theoretical and Applied Physics

Ali Heidarnia ¹ , Hamid Ghomi ²

1 - Laser and Plasma Research Institute, Shahid Beheshti university
2 - Laser and Plasma Research Institute, Shahid Beheshti University

Received: 2022-02-20 Accepted : 2022-05-04 Published : 2022-06-01

Keywords:

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Microstructure Evolution in Zirconium Carbide Thin Films at different Substrate Temperatures 

A. Heidarnia and H. Ghomi

Laser and Plasma Research Institute, Shahid Beheshti University, Evin 1983963113, Tehran, Iran

 

 

Abstract

Zirconium carbide (ZrC) is promising candidate materials in advanced nuclear reactors as fuel cladding and plasma facing materials. It can employ to increase ductility and fracture toughness of tungsten as prominent candidate of plasma facing materials in ITER and DEMO future fusion reactors. In this study, ZrC thin films are were deposited through DC magnetron sputtering at different substrate temperatures. Sputtering gas of Argon and reactive gas of acetylene are respectively employed as the sputtering gas and reaction gas to produce ZrC from the a Zr target. The phase and structure, crystallite size, displacement density, microstrain, and lattice's constant of the produced thin films were determined using X-ray diffraction (XRD) analysis. Raman spectroscopy was also used to identify various structures and chemical bonds. Furthermore, the analysis of Raman peaks associated with amorphous carbon bonds revealed that the ratio of sp3/sp2 carbon bonds increases by increasing temperature from 100°C to 180°C, which has a substantial impact on substantially affects the hardness of the thin films. Field Emission Scanning electron microscopy (FESEM) was used to measure the cross-sectional area and thickness of the thin films, and it was discovered that increasing temperature increases enhances the thickness of the thin films. The elemental analysis of ZrC thin films that was performed using X-ray energy dispersive spectroscopy (EDS) demonstrated the atoms that constitute the thin film, and their changes with temperature variations.

 Keywords: Microstructure, Zirconium carbide, Thin film deposition, Substrate temperature, Plasma facing materials.

 

1. Introduction

ZrC is a member of the high-temperature ceramic family. This ceramic is used in a wide range of industries, including cutting tools, hypersonic vehicles, high-temperature nuclear reactors, electronics, and other applications, due to its important and prominent properties, including such as a high melting point (approximately 3500 oC), low cross-sectional absorption of thermal neutrons, high hardness, a low working function of electron emission, metal behavior in electrical and optical properties, and etc so on. [1-4].

Various techniques are have been used to produce ZrC thin films, including e.g., electron beam evaporation(Wang et al., 2015), chemical vapor deposition (CVD) [5, 6], pulsed laser ablation [7], and magnetron sputtering [8]. Various Numerous investigations have also been carried out on various the different potentials and properties of ZrC thin films, and the various a number of parameters that influence affecting their the development of the films. R. Liu et al. [9] reviewed the development of the W-ZrC alloy for plasma facing materials for fusion devices. They perceived that ZrC operating as Oxygen getter at grain boundaries of tungsten and improved the strength, ductility, high temperature stability and resistance to neutron and ions irradiation. Also, the grain boundaries strengthening of tungsten reviewed by X. Wu et al. [10] and they realized by adding second phase ameliorated performance of tungsten. S. Biira et al. [11] studied the influence effect of thermal behavior of ZrC thin films produced by chemical vapor deposition at various annealing temperatures on their performance. After annealing, the researchers they discovered that the lattice's constant and the crystallite size increased. In addition Furthermore, depending on the crystalline preference, the surface morphology and hardness of the produced thin film vary depending on the annealing temperature. J. Xu et al. [12] used a twin cathode glow discharge to create a ZrC nanocrystalline film on a titanium-aluminum-vanadium (Ti-6Al-4V) alloy in order to improve its corrosion resistance. In their research, they discovered They revealed that the corrosion resistance of the coating decrease by increasing temperature, the corrosion resistance of the coating decreased. According to Meng et al. [13], who investigated the a coating of ZrC coating by magnetron sputtering at different methane to argon ratios, the transition from the crystalline to the amorphous phase occurs when the carbon concentration is greater than exceeds 86% percent, the transition from the crystalline to the amorphous phase occurs. Additionally, a high proportion of carbon reduces hardness, and improves the friction coefficient and corrosion resistance of the coating.

In this paper the current research for further investigate the ZrC thin film properties, studies focused on the structure, amorphous carbon bonds, and element composition evolution of ZrC thin films produced by DC magnetron sputtering at the substrate temperatures of 100°C, 150°C, and 180°C. XRD analysis and the Scherer method were used to investigate the crystallite size, microstrain, displacement density, and lattice's constant at the aforementioned temperatures are were estimated using XRD analysis and Scherer method. Besides, the chemical bonds in ZrC coatings, as well as the evolution of amorphous carbon bonds, are were investigated examined using Raman analysis. And the evolution of elemental composition at different temperatures is was observed detected using EDS analysis.

 

 

 

2. Experimental Method

DC magnetron sputtering was used to deposit ZrC coatings on Si substrates at the temperatures of 100°C, 150°C, and 180°C. This method used utilized a Zr target with a diameter of 5 cm, a thickness of 3 mm, and a purity of 99.95% percent, argon as the sputtering gas (Ar, 5N), and acetylene as the reactive gas (C2H2, 5N) in the process. The substrates are were first cleaned through washing by soap and water, followed by before ultrasonic washing in acetone and ethanol solutions for a total of 20 minutes in each solution. After the samples substrates are were dried in dry air, the substrates they are were placed inside the vacuum chamber. Rotary and turbomolecular vacuum pumps evacuated the chamber to a pressure of 10-4 mbar. Pre-sputtering operations are were carried out for 15 minutes to eliminate the possibility of contamination of the target surface by introducing Ar to the chamber and regulating the pressure in the range of 10-1 mbar. Then, The system is was then drained, and the argon-acetylene gas mixture is was introduced into the chamber in the a proportion of equal to C2H2/ C2H2+Ar=15, after which the chamber pressure is was adjusted to a value of 4×10-2 mbar. By applying a voltage to the electrodes of the sputtering device, the gas inside the chamber is was ionized and argon ions are were generated and accelerated to the Zr target by an electric field between the electrodes and sputter the zirconium atoms. These atoms are were scattered in all directions and reacted with carbon atoms due to the decomposition of acetylene gas. Finally, the ZrC coating deposit was formed on silicon substrates. The experimental conditions are shown in Table 1.

Table 1. Zirconium carbide coating conditions on silicon substrates. 

Sample code	Substrate temperature (0C)		Power (W)	Working pressure (mbar)	Deposition time (h)	Substrate-target distance (cm)	Gas ratio C2H2 / C2H2+ Ar
ZrC1		100	150	4×10-2	1	8	15
ZrC2		150	150	4×10-2	1	8	15
ZrC3		180	150	4×10-2	1	8	15

 

Then, To study the microstructure of ZrC thin films, the an XRD device manufactured by STOE with a Cu kα X-ray generator with having a wavelength of 1.54060 A°, and a voltage of 40 kV and a current of 40 mA in the range of 20-80 ° were was used employed. A Takram P50C0R10 Raman spectrometer manufactured by Teksan with a laser having a wavelength of 532 nm and a power of 0.5-70 mW laser was used utilized to study the structure and chemical bonds between carbon-zirconium and carbon-carbon. Additionally, a field emission scanning electron microscope (FESEM) equipped with X-ray energy dispersive spectroscopy (EDS) was used to evaluate the cross section and thickness of the produced thin films produced, and X-ray energy dispersive spectroscopy (EDS) was used as well as to analyze their elemental composition.

3. Results and discussion

3.1. X-ray diffraction

As illustrated in Fig. 1, the X-ray diffraction pattern of ZrC thin films generated at various substrate temperatures was investigated. The peaks in this diffraction pattern It shows that the produced thin films are composed of two different phases of metal and ceramic. In ZrC, the ceramic phase can be detected at the diffraction angles of approximately (2q) 32.52 and 68.7, which correspond to the two crystal planes of (111) and (222). In accordance with Based on the standard International Commission on Crystallographic Data (ICCD), this pattern is in accordance with the standard X-ray diffraction pattern of the zirconium carbide card with the reference code of 01-074-1221, this pattern indicating that the ZrC thin films have an FCC structure. Another finding is that, the peak of the diffraction pattern found at an angle of approximately (2q) 34.09 is associated with the metal phase of zirconium phase, which corresponds to the crystal plane (111) and has an FCC lattice structure (ICCD standard zirconium X-ray diffraction card with the reference code of 01- 088-2329). As shown in Fig. 1, the peak intensity of the (111) crystal plane (111) of zirconium carbide grows as temperature increases, indicating that the crystallization of thin films is rising in this direction as the temperature increases. In this experiment, the crystal size (D) of ZrC in the direction of the (111) crystal plane (111) is was estimated at three different temperatures using the Scherer equation [14]. The Scherer relationship is given in Eq. (1).

                                                                                                                      (1)

Where k denotes the crystal shape factor constant (which has a value of around  0.9), b denotes the full width at half maximum (FWHM) in radians, q denotes the Bragg's angle in degrees, and l denotes the wavelength of the X-ray source (1.5406 Ao). Figure 2 shows how the crystallite size of zirconium carbide thin films changes as the temperature of the substrate increases.

 

Fig. 1. The XRD pattern of ZrC thin films at three different substrate temperatures.

 

 

Fig. 2. Crystallite size and FWHM changes along the (111) ZrC (111) crystal plane.

 

As the substrate temperature increases from 100°C to 180°C, the FWHM decreases along the (111) ZrC (111) crystal plane, increasing which increases the crystallite size (from 8.5 nm to 14 nm) (see Fig. 2). This result is in agreement with [15]. As the substrate temperature increases from 100°C to 150°C, the crystallite size also slightly increases, i.e., slightly and increases from 8.5 nm to 8.6 nm. In this temperature range, the energy increase resulting from temperature increase is mostly used to add the metal phase of Zr to the ceramic phase of ZrC This range of temperatures sees the majority of the increase in energy spent on the addition of zirconium metal to zirconium carbide ceramic. When the temperature is further increased At higher temperatures (up to 180oC), the phase structure is maintained at 150oC, and the additional heat generated causes the energy released as a result of temperature increase grows the crystallite growth from 8.6 to 14 nm to occur. Another parameter that depends on the crystallite size is the displacement density (), which is defined as the length of dislocation lines per unit volume of the crystal and may be approximated using Eq. (2) [14, 16, 17].

                                                                                                                           (2)

In Eq. (2), Where D is the crystallite size estimated using Eq. (1). Therefore, the lower is the displacement density along the (111) crystal plane, the better the crystallization would be better. Displacement densities along the (111) ZrC (111) crystal plane for three different temperatures are given in Table 2 for three different temperatures. Also Similarly, the microstrain of ZrC thin films along the (111) crystal plane is determined at different temperatures according to the basis of Eq. (3) [14]. The microstrain values calculated are shown in Table 2.

                                                                                                                      (3)

Considering the X-ray diffraction patterns of ZrC discussed above, their crystal lattice is cubic. Therefore, Eq. (4) is used to determine the cubic lattice's constant along the (111) ZrC (111) crystal plane [18].

                                          (4)

In Eq. (4), acubic is the cubic lattice's constant in Ao, dhkl is the distance between crystal planes, and hkl is the miller index. The lattice's constant calculated along the (111) ZrC (111) crystal plane at three different temperatures is given in Table 2.

 

Table 2. The estimated Parameters resulting from the analysis of ZrC thin film structures along the (111) crystal plane using the Scherer method.

 

 

Therefore, as the temperature increases, the microstrain and displacement density decrease, and but the lattice's constant increases. Therefore Consequently, minimum microstrain, minimum displacement density, and maximum crystallite size are obtained at 180oC, indicating the best mode of crystallization at this temperature.

 

3.2. Raman spectroscopy

Figure 3 depicts the Raman spectrum of ZrC thin films that were grown on the substrates at the temperatures of 100oC, 150oC and 180oC. The Raman active peaks observed in ZrC are located in the frequency range of 190-620 cm-1, and amorphous carbons (a-C) are responsible for the Raman active peaks observed in ZrC in the frequency range of 1300-1600 cm-1 [19]. ZrC peaks are observed in at 210 cm-1 and 615 cm-1, demonstrating that ZrC is polycrystalline and is assigned to TA (transverse acoustic) and LO (longitudinal acoustic) [19]. The Raman peaks observed at 301, 456, and 767 cm-1 are assigned to ZrO2 [20, 21]. The amorphous carbon (a-C) Raman peaks, which are known as D-peak (diamond or disorder peak) and G-peak (graphite peak), is are located in at 1300-1400 cm-1 and 1550-1600 cm-1.

 

 

Fig. 3. The Raman spectrum of ZrC thin films at the substrate temperatures of a)100oC, b) 150oC, and c) 180oC.

 

In the thin films containing carbon atoms, the position and FWHM of G-peak, and ID/IG (the ratio of D-peak to G-peak Intensity) are important parameters providing information about the structure and type of their chemical bond and the sp2/sp3 hybridization ratio. The value of ID/IG, which is proportional to the ratio of sp2/sp3 carbon bonds, is obtained using the area under the D-peak to G-peak fitting curve [22], and its value at the substrate temperature of 100oC is equal to 4.6 at the substrate temperature of 100oC and decreases as temperature increases in such a way that it reaches 2.52 at 180oC (see Fig. 4). Therefore Hence, by increasing as temperature increase, the ratio of sp2/sp3 decreases (the ratio of sp3/sp2 increases). This result is in agreement with the research conducted by X. Zhao et al. [23], indicating that an increase in the substrate temperature plays an essential a pivotal role in producing hard carbon coatings (with having more sp3 carbon bonds). It should be mentioned that the G-peak position depends on the amount of sp2 carbon and its FWHM depends on the amount of sp3 carbon [24]. The position and FWHM changes of G-peak are shown in Fig. 5, indicating signifying that the increase in disorder by increasing as temperature increases, the disorder also increases. These changes in the range of 100-180oC are in agreement with the research of Mingming Li et al. [24] conducted in the range of 100-200oC.

 

 

Fig. 4. Changes of D to G peak Intensity at different substrate temperatures.

 

 

Fig. 5. The variations of position and FWHM of G-peak at different substrate temperatures.

 

3.3. Field-Emission Scanning Electron Microscopy (FESEM)

Figure 6 shows the cross-sectional images of ZrC thin films at three distinct substrate temperatures of 100°C, 150°C, and 180°C. It is shown that the thickness of ZrC thin films increases from 1.52 µm to 2.01 µm as temperature increases. This result is in agreement with the XRD results (see Fig. 2), which revealed that the crystallite size grows by increasing temperature.

The changes in of the thin film thickness in the range of 100-150oC are lower than in the range of 150-180oC. The reason can be found in the XRD pattern of thin films at three different temperatures. As shown in Fig. 1, the diffraction pattern at 100oC includes only the ceramic phase, but at 150oC and 180oC, it includes both ceramic and metal phases. Therefore For that reason, in the first temperature range, a major part of the energy resulting from increased the increase in temperature is used to change the phase structure of the thin film, but in the second temperature range, the whole energy resulting from the increase in temperature increase is used to grow the crystallite and increase the film thickness.

 

 

 

Fig. 6. The cross-sectional FESEM images of ZrC thin films on Si substrate at temperatures a)100oC, b) 150oC, c) 180oC.

 

According to the thickness of the ZrC thin films measured by FESEM, and the deposition duration (1 hour), the deposition rate at three different temperatures is obtained at three different temperatures as shown in Fig. 7.

 

Fig. 7. ZrC deposition rate at different temperatures.

 

3.4.        X-ray Energy Dispersive Spectroscopy (EDS)

To evaluate the elements comprising the thin film, X-ray EDS is was used. The EDS spectrum of ZrC thin films at three different temperatures of 100oC, 150oC, and 180oC are shown in Fig. 8.

The results of EDS (see Table 3) verify the presence of Zr, C, and Si elements, where Zr and C constitute the thin films, and Si constitutes the substrate. Despite that All the same, the gas ratio used in the ZrC deposition is the same at three different temperatures, but the concentration and atomic percentage of the elements are different at three different temperatures. By increasing The concentration of carbon reduces as the temperature rises from 100oC to 180oC, while the concentration of zirconium increase the carbon density decreases and Zr density increases. This result is in agreement with variations of Si and C in SiC coating while changing Temperature variations from 100oC to 200oC in Mingming Li et al. [24] show that silicon and carbon components in the silicon carbide coating vary.

 

Table 3. EDS analysis of ZrC thin films at the different temperatures.

Sample code	Substrate temperature (0C)	Crystallite size (nm)	Lattice's constant (Ao)	Dislocation density (×10 12 cm-2)	Microstrain (×10 -5)
ZrC1	100	8.5	4.77	1.37	1.45
ZrC2	150	8.6	4.77	1.34	1.43
ZrC3	180	14	4.81	0.5	0.89

Sample code	Substrate temperature (0C)	Elemental composition (in weight%)		Elemental composition (in atomic%)
		C	Zr	C	Zr
ZrC1	100	15.13	80.23	54.66	38.16
ZrC2	150	9.79	85.32	42.35	48.61
ZrC3	180	3.34	91.22	18.92	67.94

 

 

 

 

Fig. 8. The EDS spectrum of ZrC thin films at three different temperatures of a) 100oC, b) 150oC, and c) 180oC

4.       Conclusion

ZrC thin films are were deposited on Silicon substrate at three different temperatures of 100oC, 150oC, and 180oC at the gas ratio of C2H2/Ar+C2H2=15. The With the help of XRD patterns and using Scherer method for the peak along the ZrC (111) crystal plane, it was specified identified that the produced thin films have a cubic lattice, and as temperature increased from 100oC to 180oC, both the lattice's constant and the crystallite size increased from 4.7708 Ao to 4.8140 Ao, and from 8.6nm to 14nm, respectively. Also Moreover, as temperature increased, the displacement density and microstrain of the thin films decreased, such that so minimum displacement density (0.5×1012 cm-2) and minimum microstrain (0.89×10-5) are were obtained at 180oC. Raman spectroscopy verified the presence of TA and LO modes in ZrC at 210 cm-1 and 615 cm-1 , respectively. Also Furthermore, the D-peak and G-peak analyses of carbon bonds showed that ID/IG decreases as temperature increases. The FESEM images also showed that the thickness of the thin films increases from 1.52µm to 2.01µm as temperature increases. The EDS results also showed that by increasing temperature, the carbon density of carbon and Zr decreases and increases, respectively. 

 

Acknowledgment

This work was supported by the Lasers, Photonics, Advanced Materials and Manufacturing Technologies Development Headquarter, Iran 

 

References

[1] J. Aihara, S. Ueta, M. Honda, N. Mizuta, M. Goto, Y. Tachibana, K. Okamoto, J. Nucl. Mater. 522 32 (2019).

[2] V.V. Chayeuski, V.V. Zhylinski, P.V. Rudak, D.P. Rusalsky, N. Višniakov, O. Černašėjus, Appl. Surf. Sci. 446 18 (2018).

[3] M.-h. Ding, H.-S. Zhang, C. Zhang, X. Jin, Surf. Coat. Technol. 224 34 (2013).

[4] D.D. Kumar, G.S. Kaliaraj, A.M.K. Kirubaharan, K. Alagarsamy, V. Vishwakarma, R. Baskaran, Surf. Coat. Technol. 374 569 (2019).

[5] S.-L. Wang, K.-z. Li, H.-J. Li, Y.-L. Zhang, W.-Y. Zhang, Int. J. Refract. Met. Hard Mater. 48 108 (2015).

[6] Y. Zhu, L. Cheng, B. Ma, S. Gao, W. Feng, Y. Liu, L. Zhang, Appl. Surf. Sci. 332 591 (2015).

[7] D. Craciun, G. Socol, E. Lambers, E.J. McCumiskey, C.R. Taylor, C. Martin, N. Argibay, D.B. Tanner, V. Craciun, Appl. Surf. Sci. 352 28 (2015).

[8] A. Gilewicz, K. Mydłowska, J. Ratajski, Ł. Szparaga, P. Bartosik, P. Kochmański, R. Jędrzejewski, Vacuu 169 (2019).

[9] R. Liu, Z.M. Xie, J.F. Yang, T. Zhang, T. Hao, X.P. Wang, Q.F. Fang, C.S. Liu, Nucl. Mater. Energy 16 191 (2018).

[10] X. Wu, X. Li, Y. Zhang, Y. Xu, W. Liu, Z. Xie, R. Liu, G.-N. Luo, X. Liu, C.S. Liu, J. Fusion Energy 39 342 (2021).

[11] S. Biira, T.T. Thabethe, T.T. Hlatshwayo, H. Bissett, T. Ntsoane, J.B. Malherbe, J. Alloys Compd. 834 (2020).

[12] J. Xu, Z. Li, S. Xu, P. Munroe, Z.-H. Xie, J. Power Sources 297 359 (2015).

[13] Q.N. Meng, M. Wen, F. Mao, N. Nedfors, U. Jansson, W.T. Zheng, Surf. Coat. Technol. 232 876 (2013).

[14] R. Rai, T. Triloki, B.K. Singh, Appl. Phys. A 122 (2016).

[15] L.C. Agudelo-Morimitsu, J. De La Roche, D. Escobar, R. Ospina, E. Restrepo-Parra, Ceram. Int. 39 7355 (2013).

[16] A.R. Bushroa, R.G. Rahbari, H.H. Masjuki, M.R. Muhamad, Vacuu 86 1107 (2012).

[17] S. Habashyani, A. Özmen, S. Aydogan, M. Yilmaz, Vacuu 157 497 (2018).

[18] N.K. Das, J. Chakrabartty, S.F.U. Farhad, A.K. Sen Gupta, E.M.K. Ikball Ahamed, K.S. Rahman, A. Wafi, A.A. Alkahtani, M.A. Matin, N. Amin, Results Phys. 17 (2020).

[19] S. Pellegrino, P. Trocellier, L. Thomé, S. Miro, J.M. Costantini, E. Jouanny, Nucl. Instrum. Methods Phys. Res., Sect. B 454 61 (2019).

[20] S.N. Basahel, T.T. Ali, M. Mokhtar, K. Narasimharao, Nanoscale Res. Lett. 10 73 (2015).

[21] H. Zegtouf, N. Saoula, M. Azibi, L. Bait, N. Madaoui, M.R. Khelladi, M. Kechouane, Surf. Coat. Technol. 393 (2020).

[22] Z. Li, H. Zhang, W. He, C. Ma, N. Xiangfan, G.a. Zhang, Y. Li, Ceram. Int. 47 5730 (2021).

[23] X. Zhao, X. He, Y. Sun, J. Yi, P. Xiao, Acta Mater. 57 893 (2009).

[24] M. Li, L. Jiang, Y. Sun, T. Xiao, P. Xiang, X. Tan, J. Non·Cryst. Solids 503-504 252 (2019).

 

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