Synthesis and characterisation of thin film MAX phase alloys Mathew Guenette , Mark Tucker, Yongbai Yin, Marcela Bilek, David McKenzie Applied and Plasma Physics, University of Sydney 2006, Australia. [email protected] Introduction MAX phases are a family of ternary alloys that exhibit a unique combination of metallic and ceramic properties. That is, machinablility, resistance to thermal shock, high thermal and electrical conductivity combined with stiffness, oxidation resistance and high temperature (T>1400°C) stability. The nanolaminate crystal structure of the MAX phases consists of single hexagonal layers of the A element between metal-carbide or metal-nitride (M n+1 X n ) layers. http:// www.materials.drexel.edu/max H. Högberg et al. Surface & Coatings Technology 193: 6–10, 2005 Figure 1. General M n+1 AX n phase composition (n=1,2,3) and unit cell Deposition of Ti 2 AlC thin film on Al 2 O 3 (0001) at a temperature of 900°C was carried out using a high current, centre triggered, pulsed cathodic arc fitted with three cathodes (Ti, Al and C) (Fig. 2). The film composition can be accurately controlled by varying the number of pulses of each element. A linear relationship between the number of pulses from the cathodes and the composition of the film is observed over the order of 10 000 to 100 000 pulses (Fig. 4). Pulsed cathodic arc MAX phase synthesis and SNMS composition analysis Due to cathode erosion with deposition, long term drift in the composition of deposited films occurs. Film composition is affected by changes in substrate temperature and bias due to different mass and volatility between elements. Correct stoichiometry is vital to successfully synthesise MAX phases and a method for rapid tuning of film composition is required. Secondary Neutral Mass Spectrometry (SNMS) is a fast and convenient plasma technique which can be used to analyse the composition of a thin film. The film is sputtered with an argon plasma and the composition of the emerging neutral particles is measured with a mass spectrometer. The elemental ratio within the sample is directly proportional to the ratio of the SNMS signal intensities. Quantitative analysis of films is possible by comparison to standards of known composition. P u lse ra tio v s S N M S in te n sity ra tio y = 0.4228x R 2 = 0.9503 0 0.5 1 1.5 2 2.5 3 3.5 4 0 2 4 6 8 A l/C p u lses A l/ C co u n ts Figure 2. Pulsed cathodic arc at the University of Sydney Figure 3. SNMS chamber Figure 4. Al/C pulse ratio vs the Al/C film composition ratio from SNMS. The linear relationship establishes a quick and reliable method for accurately controlling and quantifying the composition of thin film MAX phases. X-ray Diffraction XRD scans of near stoichiometric Ti 2 AlC reveal a highly oriented, relatively phase pure thin film. The θ/2θ scan in Fig.5 shows strong reflections only from Ti 2 AlC(00ℓ) planes demonstrating preferred c-axis oriented film growth. Oriented TiC(hhh) reflections are also observed. The glancing angle scan reveals only Ti 2 AlC peaks demonstrating a highly phase pure film. Conclusion • A method for accurately controlling and quantifying the composition of thin films grown in the pulsed cathodic arc has been established. • This method has been used for the growth of highly oriented and phase pure Ti 2 AlC suitable for measurement of non-isotropic properties such as elastic constants and electrical conductivity. Figure 5. a) θ/2θ XRD scan b) glancing angle XRD scan (incident angle = 0.6°) a) b)

Synthesis and characterisation of thin film MAX phase alloys Mathew Guenette, Mark Tucker, Yongbai Yin, Marcela Bilek, David McKenzie Applied and Plasma

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Synthesis and characterisation of thin film MAX phase alloys

Mathew Guenette, Mark Tucker, Yongbai Yin, Marcela Bilek, David McKenzieApplied and Plasma Physics, University of Sydney 2006, Australia.

[email protected]

Introduction

MAX phases are a family of ternary alloys that exhibit a unique combination of metallic and ceramic properties. That is, machinablility, resistance to thermal shock, high thermal and electrical conductivity combined with stiffness, oxidation resistance and high temperature (T>1400°C) stability.The nanolaminate crystal structure of the MAX phases consists of single hexagonal layers of the A element between metal-carbide or metal-nitride (Mn+1Xn) layers. http://www.materials.drexel.edu/max H. Högberg et al. Surface & Coatings

Technology 193: 6–10, 2005

Figure 1. General Mn+1AXn phase composition (n=1,2,3) and unit cell

Deposition of Ti2AlC thin film on Al2O3(0001) at a temperature of 900°C was carried out using a high current, centre triggered, pulsed cathodic arc fitted with three cathodes (Ti, Al and C) (Fig. 2). The film composition can be accurately controlled by varying the number of pulses of each element. A linear relationship between the number of pulses from the cathodes and the composition of the film is observed over the order of 10 000 to 100 000 pulses (Fig. 4).

Pulsed cathodic arc MAX phase synthesis and SNMS composition analysis

Due to cathode erosion with deposition, long term drift in the composition of deposited films occurs. Film composition is affected by changes in substrate temperature and bias due to different mass and volatility between elements. Correct stoichiometry is vital to successfully synthesise MAX phases and a method for rapid tuning of film composition is required.

Secondary Neutral Mass Spectrometry (SNMS) is a fast and convenient plasma technique which can be used to analyse the composition of a thin film. The film is sputtered with an argon plasma and the composition of the emerging neutral particles is measured with a mass spectrometer. The elemental ratio within the sample is directly proportional to the ratio of the SNMS signal intensities. Quantitative analysis of films is possible by comparison to standards of known composition.

Pulse ratio vs SNMS intensity ratio

y = 0.4228xR2 = 0.9503

00.5

11.5

22.5

33.5

0 2 4 6 8Al/ C pulses

Al/

C c

nts

Figure 2. Pulsed cathodic arc at the University of Sydney

Figure 3. SNMS chamber

Figure 4. Al/C pulse ratio vs the Al/C film composition ratio from SNMS. The linear relationship establishes a quick and reliable method for accurately controlling and quantifying the composition of thin film MAX phases.

X-ray Diffraction

XRD scans of near stoichiometric Ti2AlC reveal a highly oriented, relatively phase pure thin film. The θ/2θ scan in Fig.5 shows strong reflections only from Ti2AlC(00ℓ) planes demonstrating preferred c-axis oriented film growth. Oriented TiC(hhh) reflections are also observed. The glancing angle scan reveals only Ti2AlC peaks demonstrating a highly phase pure film.

Conclusion

• A method for accurately controlling and quantifying the composition of thin films grown in the pulsed cathodic arc has been established.

• This method has been used for the growth of highly oriented and phase pure Ti2AlC suitable for measurement of non-isotropic properties such as elastic constants and electrical conductivity.

Figure 5. a) θ/2θ XRD scan b) glancing angle XRD scan (incident angle = 0.6°)