Department of Physics, Chemistry and Biology

Master’s Thesis

Combinatorial Thin Film Synthesis of Cr2AlC; a

Comparison of Two Sputtering Methods

Peter CarlssonLiTH-IFM-EX--12/2573--SE

Department of Physics, Chemistry, and BiologyLinköpings universitet

SE-581 83 Linköping, Sweden

Master’s ThesisLiTH-IFM-EX--12/2573--SE

Combinatorial Thin Film Synthesis of Cr2AlC; a

Comparison of Two Sputtering Methods

Peter Carlsson

Supervisors: Per Eklund

IFM, Linköpings universitetMarcela M. M. Bilek

The University of SydneyDavid R. McKenzie

The University of Sydney

Examiner: Johanna Rosén

IFM, Linköpings universitet

Linköping, 13 April, 2012

Avdelning, InstitutionDivision, Department

Thin Film Physics Division

Department of Physics, Chemistry and Biology

Linköpings universitet

SE-581 83 Linköping, Sweden

DatumDate

2012-04-13

SpråkLanguage

Svenska/Swedish

Engelska/English

RapporttypReport category

Licentiatavhandling

Examensarbete

C-uppsats

D-uppsats

Övrig rapport

URL för elektronisk version

ISBN—

ISRNLiTH-IFM-EX--12/2573--SE

Serietitel och serienummerTitle of series, numbering

ISSN—

TitelTitle

Svensk titel

Combinatorial Thin Film Synthesis of Cr2AlC; a Comparison of Two Sputtering

Methods

FörfattareAuthor

Peter Carlsson

SammanfattningAbstract

MAX phase materials have unique properties that combine metals and ceramics.

These properties stems from the complex structure with extremely strong M-X

bonds and weaker M-A bonds. Physical vapor deposition in form of magnetron

sputtering is widely used for thin film syntheses. High Power Impulse Magnetron

Sputtering (HIPIMS) was introduced in the mid-90s, today it is a state of the art

thin film deposition method for researchers all over the world.

Combinatorial sputter deposition of Cr2AlC with HIPIMS and direct current

magnetron sputtering of the chromium target were compared. Aluminum and

carbon were sputtered from individual targets with a shield in between of the

three targets, making the combinatorial method possible.

X-ray diffraction showed that Cr2AlC was present at 550o

C and scanning elec-

tron microscopy showed that there was not big difference in the morphology. Elec-

trical measurements indicated that the film deposited with HIPIMS had a signif-

icant higher electrical conductivity compared to the film deposited with direct

current. x-ray photoelectron Spectroscopy gives an idea of the composition of the

film, in one position there were oxygen through the film, the rest were dense films.

By using a combinatorial approach Cr2Al was also found in the films. The two

films compared deposited with different methods, showed small differences but not

the ones expected.

NyckelordKeywords key1, key2

Abstract

MAX phase materials have unique properties that combine metals and ceramics.These properties stems from the complex structure with extremely strong M-Xbonds and weaker M-A bonds. Physical vapor deposition in form of magnetronsputtering is widely used for thin film syntheses. High Power Impulse MagnetronSputtering (HIPIMS) was introduced in the mid-90s, today it is a state of the artthin film deposition method for researchers all over the world.

Combinatorial sputter deposition of Cr2AlC with HIPIMS and direct currentmagnetron sputtering of the chromium target were compared. Aluminum andcarbon were sputtered from individual targets with a shield in between of thethree targets, making the combinatorial method possible.

X-ray diffraction showed that Cr2AlC was present at 550oC and scanning elec-tron microscopy showed that there was not big difference in the morphology. Elec-trical measurements indicated that the film deposited with HIPIMS had a signif-icant higher electrical conductivity compared to the film deposited with directcurrent. x-ray photoelectron Spectroscopy gives an idea of the composition of thefilm, in one position there were oxygen through the film, the rest were dense films.By using a combinatorial approach Cr2Al was also found in the films. The twofilms compared deposited with different methods, showed small differences but notthe ones expected.

v

Acknowledgments

I would like to thank the following people for making this thesis possible:Dr. Johanna Rosén for giving me the opportunity to do this Master’s Thesis.Dr. Per Eklund for advising me on the writing of this Master’s Thesis.Prof. Marcela Bielek and Prof. David McKenzie for giving me the oppor-tunity to do this project at The University of Sydney.Dr. Mark Tucker for guiding and discussing all experimental techniques andthank you for the support during all the experimental work.Alice Poppleton and Ben Treverrow for training me in the AJA sputteringsystem.Dr. Cenk Kocer for the help to setup the camera instruments for photographyof the samples.Prof. Dougal Mcculloch for doing the XPS measurements.Matthew Field for analysing and summarize the XPS data.And Jasmine Öberg for supporting me all the time during my work.

vii

Contents

1 Introduction 3

1.1 Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31.2 Outline . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

2 Theory 7

2.1 MAX Phase Materials . . . . . . . . . . . . . . . . . . . . . . . . . 72.1.1 Cr2AlC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

2.2 Thin Film Deposition . . . . . . . . . . . . . . . . . . . . . . . . . 82.3 Thin Film Deposition of MAX Phases . . . . . . . . . . . . . . . . 102.4 Combinatorial Thin Film Deposition . . . . . . . . . . . . . . . . . 10

3 Experimental Details 11

4 Results and Discussion 15

4.1 Analyses of the Sample Regions . . . . . . . . . . . . . . . . . . . . 154.1.1 Position 16,5 . . . . . . . . . . . . . . . . . . . . . . . . . . 184.1.2 Position 11,-11 . . . . . . . . . . . . . . . . . . . . . . . . . 184.1.3 Position 0,0 . . . . . . . . . . . . . . . . . . . . . . . . . . . 194.1.4 Position -4,-19 . . . . . . . . . . . . . . . . . . . . . . . . . 224.1.5 Position -5,15 . . . . . . . . . . . . . . . . . . . . . . . . . . 26

4.2 Lower Temperature Samples . . . . . . . . . . . . . . . . . . . . . . 27

5 Summary and Conclusions 31

5.1 Recommendations . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

Bibliography 33

ix

Acronyms

HIPIMS High Power Impulse Magnetron Sputtering

DC Direct Current

DCMS Direct Current Magnetron Sputtering

PVD Physical Vapor Deposition

CVD Chemical Vapor Deposition

XRD X-ray Diffraction

SEM Scanning Electron Microscopy

XPS X-Ray Photoelectron Spectroscopy

FEG Field Emission Gun

RF Radio Frequency

1

Chapter 1

Introduction

This Master’s Thesis is the result of a collaboration between the University ofSydney, Linköping University and the Royal Melbourne Institute of Technology.The main project work has been done at the University of Sydney, where thedepositions of the films, scanning electron microscopy and x-ray diffraction havebeen done. Colleagues at the Royal Melbourne Institute of Technology have doneelectrical measurements and x-ray photoelectron spectroscopy. The examinationis at Linköping University.

1.1 Background

During the 60s and early 70s, Hans Nowotny’s group at Vienna University foundover 100 of new solids. These solids were ternary compounds of either carbonor nitrogen combined with an early transition metal and a third element, usuallysilicon or aluminum. Many of these phases were H-phases, Cr2AlC-structuredmaterials, and also Ti3SiC2-structured materials. Nowotny’s group were able toidentify the complex unit cell of these materials [1].

Nowotny’s discovery was remarkable, but it took until the mid-90s before thesematerials were further investigated. Barsoum & El-Raghy fabricated Ti3SiC2 anddiscovered some of the superb properties these materials have [2]. When Ti4AlN3

was discovered [3], it was realized that these three categories of phases have thesame basic structure and therefore also similar properties. The name Mn+1AXn

(MAX) phases (n=1, 2, or 3) was introduced.The properties of MAX phases are a combination of ceramics and metals. They

can be thermal shock resistant, have high stiffness and be corrosion resistant [4]and at the same time they can have high electrical and thermal conductivities andbe machinable [5]. These unique properties give MAX phase materials potentialto be used in applications like protective coatings, sensors, low friction surfaces,electrical contacts, high temperature devices and many more [6]. Because of thispotential, research on MAX phase materials has grown in the last decade. Tobe able to commercialize MAX phases as coatings, low deposition temperature isneeded and the market for low temperature coatings is big.

3

4 Introduction

Using Chemical Vapor Deposition (CVD), Nickl was the first to deposit a MAXphase thin film in 1972, when a Ti3SiC2 thin film was synthesized [7]. The firstdeposition of thin film MAX phases with Physical Vapor Deposition (PVD) wasmade by Palmquist et al in 2002. Ti3SiC2 was synthesized by sputtering bothfrom a compound target and from three individual elemental targets [8]. Since2002, there have been many reports on MAX phase syntheses by PVD.

Bulk syntheses of MAX phases typically occur close to thermodynamic equi-librium, while sputter deposition allow synthesis of phases that are not thermody-namically stable. It is known that sputtering can stabilize and grow metastablephases. Also bulk synthesis of MAX phases generally need higher temperature.Palmquist et al were able to synthesize a new MAX phase Ti4SiC3 by using thenon thermodynamic equilibrium conditions that is possible with sputtering. Dueto these conditions, Palmquist et al discovered Ti5Si2C3 and Ti7Si2C5 with prop-erties similar to MAX phases. Sputtering may be able to lower the depositiontemperature and also grow new MAX phases, not possible to synthesize with bulksynthesis [9, 10].

This project will investigate thin film synthesis of the MAX Phase Cr2AlC,using High Power Impulse Magnetron Sputtering (HIPIMS) and find the lowestpossible deposition temperature, in comparison with Direct Current MagnetronSputtering (DCMS) deposition. There are no published reports on the synthesisof Cr2AlC using HIPIMS deposition to date. HIPIMS is known to provide amore highly ionized deposition flux to the substrate compared to conventional DCsputtering [6]. Therefore it is of interest to investigate if HIPIMS can be used tosynthesize MAX phase materials at lower temperatures than have been reported.Deposition of Cr2AlC has been reported at the lowest temperature of any MAXphase synthesis; it has been reported that Cr2AlC has been deposited using DCsputtering at 550oC [11] and at 370oC for 10 µm thick films [12]. Investigationswill be done to study if HIPIMS synthesis can lower these temperatures further.Questions to be investigated in this project are listed below:

• How will the growth of Cr2AlC films be affected by the use of HIPIMSdeposition, compared to DC sputtering?

• Can Cr2AlC be synthesized at lower temperatures using HIPIMS than arepossible using DC sputtering? What is the lowest possible deposition tem-perature for Cr2AlC when HIPIMS is used?

• What phases will appear on the sample when using a combinatorial ap-proach, and is there a difference in using DCMS compared to HIPIMS forthe combinatorial approach and why/why not?

1.2 Outline

This chapter is an introduction to the thesis with the background to the subject. Itcontinues with a theoretical chapter (chapter 2), where the theory of MAX phasematerials, thin film deposition, thin film deposition of MAX phases, combinatorial

1.2 Outline 5

thin film deposition and Cr2AlC is discussed. In chapter 3, the experimentaldetails are described and there is a review of the equipment that was used. Thefollowing chapter (chapter 4) explains and discusses the results. The last chapter(chapter 5) is a summary of the project with some conclusions; there is also asuggestion of further work.

Chapter 2

Theory

2.1 MAX Phase Materials

There are three classes of Mn+1AXn (MAX) phases, for n=1,2 or 3. M is anearly transition metal, A is an A-group element and X is either C and/or N. Thedifferent stoichiometries are referred to as 211, 312 and 413. The elements forMAX phase are shown in Figure 2.1 [13, 14].

Figure 2.1: MAX phase groups [14].

MAX phase materials have a hexagonal structure, the unit cells for 211, 312and 413 MAX phases are shown in Figure 2.2a. In the unit cell, there are octahedra(M6X) with A layers in between. The A layers act as a mirror plane so a zigzagstructure arises, shown in Figure 2.2b. The three MAX phase structures havedifferent stacking sequence. There are two M layers in 211 phases, three in 312phases and four in 413 phases.

MAX phase materials have been reported to have unique properties, combiningthese of metals and ceramics. They can be easy machinable, thermally and electri-cally conductive, resistant to thermal shock and plastic at elevated temperatures.They can also be oxidation resistant, refractory, have a high specific stiffness andlow density. The reason for these properties is the unique structure of the materi-als. The M-X bonds are an extremely strong mixture of metallic-covalent bonds,

7

8 Theory

(a) (b)

Figure 2.2: (a)The MAX phase unit cells, red is a M atom, blue is a A atom andblack is a X atom [6]. (b) A TEM image of the structure of Ti3SiC2, showing thestacking sequence and the zigzag structure for MAX phases [14].

while the M-A bonds are relative weak. This combination of bonds in a layeredstructure is the explanation for MAX phase materials unique properties. Thestrong M-X bonds contribute to the damage tolerance, while the weaker M-Abonds contribute to the MAX phases machinability [6, 14].

2.1.1 Cr2AlC

The MAX phase Cr2AlC was discovered in the 1960s by Jeitschko et al, andlater studies have shown that Cr2AlC has excellent resistance to oxidation andhot corrosion. The structure can be described as single layers of aluminum atomsseparating the chromium carbides into nanolaminates of Cr2AlC. At elevated tem-peratures the aluminum atoms will diffuse to the surface and form a protectiveoxide [12, 15].

2.2 Thin Film Deposition

Physical Vapor Deposition (PVD) and Chemical Vapor Deposition (CVD) arewidely used techniques for thin film deposition. CVD uses gases to chemicallyreact to each other at a specific temperature. In PVD atoms are transferred froma solid target to a substrate where they form a film. It is possible to control theformation and the growth of the film. In evaporation, the target is heated to acertain degree where the material is evaporated and condensed on the substrate.In sputtering, an ionized gas is used to bombard the target so the target materialis ejected to form a film on the substrate. [16]

In magnetron sputtering the target is a cathode and the substrate is an anode.An inert gas, generally argon, is ionized and accelerated to the negatively charged

2.2 Thin Film Deposition 9

Substrate

Target

Ar+

Figure 2.3: General sputtering

target. The ions will knock out atoms from the target and these atoms will thenform a film on the substrate, see figure 2.3. Magnetrons are used to trap electronsclose to the target and therefore the probability of ion collision is enhanced. Acircular field of plasma over the target called the "race track” is formed. More ionsare created and the sputter deposition rate is increased. The amount of electronsis also increased, therefore a lower working pressure can be used while the plasmais self-sustained. This leads to a higher mean free path for the sputtered atomsand thereby the deposition rate is enhanced [16, 17].

High Power Impulse Magnetron Sputtering (HIPIMS) is a sputtering techniquewhere high power is applied to the cathode in pulses. The time-average targetpower is the same as in DCMS, but during a short pulse the power is very high.This results in a much higher plasma density and a higher ionization degree ofthe target material. The pulse-on time is short to avoid the target to melt. Thinfilms deposited with HIPIMS can generate a denser and smother film compared toDCMS. Therefore, HIPIMS can acquire unique morphologies for low temperaturedeposition. The energetic bombardment of HIPIMS increases the surface diffusionof the substrate and may cause a different preferred growth orientation comparedto DCMS [17, 18].

Radio Frequency (RF) sputtering is mainly used for insulating material to avoidcharge build up. An alternating potential in the MHz region and typically 5 to30 MHz is used. That high frequency makes only the electrons mobile enough tofollow the periodic change. The outcome is that the target is self-biased negativelyby the electrons in the chamber and positive ions will be accelerated to the targetso sputtering can occur.

Reactive sputtering is another method of sputtering. A gas (usually togetherwith a inert gas) is introduced to the sputtering chamber during the deposition ofa metallic target. The gas and the metallic compound will together form a filmon the substrate. Reactive sputtering is good for creating e.g. oxides, nitrides andcarbides[16].

10 Theory

2.3 Thin Film Deposition of MAX Phases

PVD is commonly used for thin film deposition of MAX phases, and DC sputteringis the method mostly used for MAX phase carbides. MAX phase nitrides have notbeen as much investigated, but reactive sputtering is the method used for thenitrides. Using reactive sputtering for MAX nitrides need an exact amount ofnitrogen, else unwanted phases will be included in the film. Because of that,relatively little work has been done on reactive sputtering of MAX phases.

CVD has been used for thin film Ti3SiC2 MAX phase deposition. The re-quired temperature for the process is between 1000-1300oC. It is possible to de-posit Ti3SiC2 with PVD at a lower temperature. With magnetron sputtering, itis also easier to get a single phase of the MAX phase compared to CVD. Whenusing CVD extra phases occurs such as TiC, SiC, TiSi2 and Ti3Si2Cx [6].

2.4 Combinatorial Thin Film Deposition

If a large number of samples are produced and investigated in the same experiment,it is called combinatorial. Thereby a composition gradient is produced over thesample and a large number of compositions can be analyzed easily, without makinga large number of different samples [10].

In the 1960’s co-evaporating and co-sputtering of two or more targets lead toa film composition continuum, thereby it was easier to investigate a large numberof compositions in one sample and the possibility to find new materials increased[19].

An article by Mertens et al has been published on a combinatorial thin filmdeposition of Cr2AlC. Four different phases were found in the sample, one pureCr2AlC phase. In the other three phases Cr23C and Cr2Al were mixed with Cr2AlC[20].

Lofland et al used magnetron sputtering to synthesis combinatorial thin filmsof the MAX phase (Ti1-xNbx)

2AlC in 2009. They were able to identify a Nb-rich

region with enhanced elastic stiffness by using Raman Spectroscopy [21].

Chapter 3

Experimental Details

A combinatorial sputtering approach was used to investigate a large field of com-positions. A shield was mounted between the three targets and the substrate,yielding a gradient of thickness for each material during sputtering. To be able toget the 211 stoichiometry in the middle of the sample the deposition parametersfor each target needed to be calibrated. Chromium, aluminum and carbon filmswere deposited separately on three 50x50mm silicon substrate with parallel linesof ink at a 5mm interspaces. The ink and the film was removed by ultrasonicationin isopropanol after the deposition. The thicknesses of the films were measuredwith a contact surface profiler at a grid of points with a 5mm distance across thesurface of each sample, which resulted in 81 points. The density of the films wereapproximated to the bulk density, the expected error is not significant given thearea of the composition space covered by the sample. By calculating the number ofatoms deposited on the substrate per second for the 81 points, the power appliedto the target could be determined to acquire the 211 stoichiometry in the center ofthe sample. Figure 3.1 shows the calculated incident composition space that thedeposition should cover and the calculated thickness gradient.

Depositions were made with a AJA, Inc. magnetron sputtering system and sixsamples were synthesized with different temperatures and with the incident 211stoichiometry in the middle of the sample (0,0). Polished Al2O3 (0001)-orientedwafers with a diameter of 50 mm and a thickness of 0.5 mm were used. Figure3.2 shows the coordinate system and where the targets are located in relation tothe substrate. Aluminum was deposited with a DC power supply at 70 W, carbonwith a RF power supply at 577 W and chromium with both DC at 87 W andHIPIMS. The HIPIMS deposition was made with a pulse of 70 µs at 150 Hz and avoltage of 750 V and a maximum current of 39A which is shown in figure 3.3. Theparameters for the HIPIMS deposition of chromium were influenced by Hecimovic& Ehiasarian [22]. It was only possible to use the HIPIMS power supply on onetarget. To maximize the fraction of the deposited species produced by HIPIMS,the chromium target was chosen to be used as the HIPIMS target. RF sputteringof the carbon target was chosen as it produced the most reliable operation of thecarbon target in the deposition system used. The different depositions are shown

11

12 Experimental Details

in table 3.1.The chamber had a base pressure less than 2.5 ·10−6 Torr after the sample was

heated. Argon gas was used during sputtering with a rate of 20 sccm (cm3 min−1

at STP). The pressure in the chamber during deposition was kept at 2.7 mTorr.

0

1

0.25

Carbon0.5

0.75

0.75

1

Aluminium0.5

0

0.25

0.25

0.5Chro

mium

0.75

0 1400

450

500

550

600

650Thickness[nm]

Figure 3.1: The incident composition area and thickness of the deposited samples,shown in a ternary phase diagram.

y

x

(0,0)

Al

C

Cr

Figure 3.2: The coordinate system of the samples in units of mm.

To be able to calibrate the deposition temperature of the samples, an infraredpyrometer was used. First the emissivity of an oxidised titanium metal samplewas measured. Thereafter the surface temperature of the titanium sample wasmeasured by using the Infrared pyrometer. Because the titanium sample had ansimilar size, thickness and thermal conductivity as the Al2O3 wafer, the surfacetemperature was assumed to be the same as the deposited film.

13

-20 0 20 40 60 80 100-200

0

200

400

600

800

1000

1200

Vol

tage

(V)

Time (µs)

0

20

40

Cur

rent

(A)

Figure 3.3: Voltage (left, black) and current (right, blue) as a function of timeduring a single HIPIMS pulse on the chromium target.

Table 3.1: Deposited samples.

Sample no. Surface temp. (oC) Cr Power supply1 350 HIPIMS2 450 HIPIMS3 500 HIPIMS4 550 HIPIMS5 550 DC

X-Ray Diffraction (XRD) was used with a PANalytical X’pert MRD diffrac-tometer, equipped with a 6-axis sample stage. A Nickel filter and a 10 mm verticalslit was used between the source and the sample. Measurements were made in aθ − 2θ geometry to find the different phases on the sample. Grazing incidence wasused to increase the counts of the sample compared to the substrate.

Both frosted and mirror-like regions on the sample surface were visible to thenaked eye. To be able to get images of this, a camera set up was made with aflash from the side, perpendicular to the camera. Scattered light from the frostyareas are lighter in the pictures and the mirror like areas are black.

Scanning Electron Microscopy (SEM) was used to investigate the surface mor-phology of the samples, using a Zeiss EVO 50 SEM operating at 20kV with a LaB6

filament. Higher resolution SEM images were acquired by a Hitachi S-4500 FieldEmission Gun (FEG) SEM, operating at 15kV.

Sample 4 and 5 were separated into pieces, five of these pieces contained thepoints of interest. This was made because further analysis needed smaller samples.

14 Experimental Details

Four-point probe electrical measurements were performed using a SignametricsPCI source meter, thermally evaporated NiCr contact pads and NiCr probes. Aconstant current I=1mA was applied between the outer contacts, the voltage Vwas measured between the inner contacts. The resistance R was calculated withequation (3.1).

R = V/I (3.1)

The thickness, length and width of the samples were measured with a FEG-SEMand are expected to be accurate to within 5%. The resistivity ρ was calculatedwith equation (3.2).

ρ = R · T · W

L(3.2)

Where R is the resistance, T the thickness, W the width and L the length. Re-sistance versus length and current-voltage measurements were also performed toconfirm the low-resistance, ohmic properties of the NiCr contacts on the films.

X-Ray Photoelectron Spectroscopy (XPS) was performed on the films using aThermo Scientific K-Alpha spectrometer with an Al anode x-ray source. A XPSdepth profile was acquired by etching the surface for a total time of 750 seconds.

Chapter 4

Results and Discussion

After XRD measurements, it was decided to further analyze sample 4 and 5, tocompare HIPIMS and DCMS at 550oC.

The frosty regions on the samples seemed interesting, therefore further analysestook place at these positions. Figure 4.1 presents these regions and the five pointsof interest with the coordinates in millimeter from the center.

Figure 4.1: The samples synthesized at 550oC and the five analyzed areas with thecoordinates in millimeter from the center. To the left synthesized with HIPIMSand to the right synthesized with DCMS.

4.1 Analyses of the Sample Regions

The five positions, 0,0; 16,5; 11,-11; -4,-19; -5,15 of the HIPIMS sample and theDCMS sample, both synthesized at 550oC shown in figure 4.1, will be analyzed in

15

16 Results and Discussion

0 100 200 300 400 500 600 7000

5

10

15

20

25

30

35

40

45

50

Con

cent

ratio

n (a

t%)

Etch Time (s)

Al C Cr O

(a) HIPIMS

0 100 200 300 400 500 600 7000

5

10

15

20

25

30

35

40

45

50

Con

cent

ratio

n (a

t%)

Etch Time (s)

Al C Cr O

(b) DCMS

Figure 4.2: XPS at position 0,0.

0 100 200 300 400 500 600 7000

5

10

15

20

25

30

35

40

45

50

Con

cent

ratio

n (a

t%)

Etch Time (s)

Al C Cr O

(a) HIPIMS

0 100 200 300 400 500 600 7000

5

10

15

20

25

30

35

40

45

50

Con

cent

ratio

n (a

t%)

Etch Time (s)

Al C Cr O

(b) DCMS

Figure 4.3: XPS at position 16,5.

this section.The result from the depth profile XPS is shown in figure 4.2-4.6. The XPS

was uncalibrated due to the absence of an Al/Cr/C/O standard. Therefore theactual percentage value is not to be considered, but it is of interest to look at thetendency of the curves to compare the films at different positions. In position 16,5,the HIPIMS film have a high amount of oxygen through the film, figure 4.3a. Thiscould be due to that the film is porous in this location and thereby will oxygen getinto the material and oxidize all through the film. In the other positions there isa clear drop of oxygen, this denotes that the film is denser in this positions. TheXPS depth profile has not reached a steady state, a longer etching time wouldreach that state and a better result for the film composition would have beenshown.

Table 4.1 shows the electrical measurements that was made on the samples.The conductivity is better for HIPIMS in three positions and it is the same as theDCMS film in one position.

4.1 Analyses of the Sample Regions 17

0 100 200 300 400 500 600 7000

5

10

15

20

25

30

35

40

45

50

Con

cent

ratio

n (a

t%)

Etch Time (s)

Al C Cr O

(a) HIPIMS

0 100 200 300 400 500 600 7000

5

10

15

20

25

30

35

40

45

50

Con

cent

ratio

n (a

t%)

Etch Time (s)

Al C Cr O

(b) DCMS

Figure 4.4: XPS at position 11,-11.

0 100 200 300 400 500 600 7000

5

10

15

20

25

30

35

40

45

50

55

Con

cent

ratio

n (a

t%)

Etch Time (s)

Al C Cr O

(a) HIPIMS

0 100 200 300 400 500 600 7000

5

10

15

20

25

30

35

40

45

50

55

Con

cent

ratio

n (a

t%)

Etch Time (s)

Al C Cr O

(b) DCMS

Figure 4.5: XPS at position -4,19.

0 100 200 300 400 500 600 7000

5

10

15

20

25

30

35

40

45

Con

cent

ratio

n (a

t%)

Etch Time (s)

Al C Cr O

(a) HIPIMS

0 100 200 300 400 500 600 7000

5

10

15

20

25

30

35

40

45

Con

cent

ratio

n (a

t%)

Etch Time (s)

Al C Cr O

(b) DCMS

Figure 4.6: XPS at position -5,15.

18 Results and Discussion

Table 4.1: Electrical measurements, where R is the resistance, T is the thickness,L is the the length and W is the width.

Position R T L W Resistivity Conductivity

Units Ω nm mm mm Ω·m 1/(Ω·m)0,0 HIPIMS 4.1 390 3.5 1.5 7.0·10−7 1.4·106

16,5 HIPIMS 1.5 380 1.3 2.4 1.0·10−6 9.6·105

16,5 DCMS 11 400 2.7 3.0 4.9·10−6 2.0·105

11,-11 HIPIMS 8.2 370 7 2.1 9.3·10−7 1.1·106

11,-11 DCMS 2.5 330 6 6 8.3·10−7 1.2·106

-4,-19 HIPIMS 1.4 400 2.5 2 4.5·10−7 2.2·106

-4,-19 DCMS 5.2 420 2 1.8 2.0·10−6 5.1·105

-5,15 HIPIMS 0.7 430 1.5 2.5 4.9·10−7 2.0·106

-5,15 DCMS 4.5 410 2.2 2.3 1.9·10−6 5.2·105

4.1.1 Position 16,5

The coordinate 16,5 from the center is a carbon rich area. The XRD grazingincidence is shown in figure 4.7 and the XRD θ − 2θ is shown in figure 4.8. Thediffraction pattern shows only Cr2AlC MAX phase peaks at this position, but thepeak to background ratio is very low and the 002 peak is weak. This indicatesthat the MAX phase crystals are only a small fraction of the films and the restis probably amorphous. The film deposited with HIPIMS looks similar with someminor differences compared to the film deposited with DCMS. The 002 peak isbigger for DCMS and the 100 and 110 peaks is bigger for HIPIMS, this mightdenote that there is a difference in the preferred orientations between the twomethods. On the contrary the intensity variation could just be an instrumentalfactor and the films could have the same orientation.

SEM images in figure 4.9 shows the morphology of the films deposited withHIPIMS and DCMS, the morphology looks similar for the both deposition meth-ods. Figure 4.10 is an image with higher resolution indicating the narrow crystal-lites that exist at this region.

4.1.2 Position 11,-11

11,-11 is the position analyzed with lowest amount of chromium. The XRD grazingincidence is shown in figure 4.11 and the XRD θ − 2θ is shown in figure 4.12. Thediffraction pattern shows that the Cr2AlC MAX phase is present in the film. Thereare other small peaks indicating the presence of another phase, but there are notenough peaks to be sure of which phase. The grazing incidence and the θ − 2θindicates a larger intensity of the 002 peak for DCMS, while the 100 peak is largerfor HIPIMS.

The SEM images in figure 4.13 shows that there is no significant difference inthe morphology of the two compared films. Figure 4.14 is a SEM image with higher

4.1 Analyses of the Sample Regions 19

10 20 30 40 50 60 70 80 90

2 position (o)

Intensity (a.u.)

Cr2AlC (002)

Cr2AlC (100)

Cr2AlC (110)

Cr2AlC (116)

HIPIMS

DC

Cr2AlC (103)

Cr2AlC (106)

Cr2AlC (109)

Figure 4.7: XRD grazing incidence at the position 16,5.

resolution of the HIPIMS film, showing a leaf like structure of the morphology.

4.1.3 Position 0,0

The position 0,0 is the center of the sample, where the incident composition wasprepared to be the 211 stoichiometry for the MAX phase. The XRD grazingincidence is shown in figure 4.11 and the XRD θ − 2θ is shown in figure 4.12.The diffraction pattern shows the Cr2AlC MAX phase peaks, but they are shifted0.5, this could suggest the formation of (Cr,Al)

2Cx with a=2.843 Å and c=4.285

Å [23].The Cr2Al phase is also present in this region and the peaks are larger for

the HIPIMS film compared to the DCMS film, indicating that there is a higherfraction of Cr2Al in the HIPIMS film. The Cr2Al peaks are not shifted.

The grazing incidence and the θ − 2θ shows a bigger 100 peak for the HIPIMSfilm. The MAX phase 002 peak is not present in the scans for the DCMS film,but there is a small 002 peak for the HIPIMS film in grazing incidence. There isa large peak at 65.341o in the θ − 2θ scan that is not identified.

20 Results and Discussion

1010 20 30 40 50 60 70 80 90

2 position (o)

Intensity (a.u.)

Substrate

Substrate

Substrate

Cr2AlC (002)

Cr2AlC (100)

Cr2AlC (110)

Cr2AlC (116)

HIPIMS

DC

Figure 4.8: XRD θ − 2θ at the position 16,5.

Figure 4.9: SEM images from the 16,5 position deposited with HIPIMS (left) anddeposited with DCMS (right).

The SEM images in figure 4.17 shows that there is no significant difference inthe morphology of the two compared films. Figure 4.18 shows the morphology

4.1 Analyses of the Sample Regions 21

Figure 4.10: SEM image from the 16,5 position.

10 20 30 40 50 60 70 80 90

2 position (o)

Intensity (a.u.)

Cr2AlC (002)

Cr2AlC (100)

Cr2AlC (110)

Cr2AlC (116)

HIPIMS

DC

Cr2AlC (103)

Cr2AlC (106)

Cr2AlC (109)

Cr9Al 17 (300)

Figure 4.11: XRD grazing incidence at the position 11,-11.

from the HIPIMS film with higher resolution, showing a leaf like structure of themorphology, similar to the morphology at the position 11,-11.

22 Results and Discussion

10 20 30 40 50 60 70 80 90

2 position (o)

Intensity (a.u.)

Substrate

Substrate

Substrate

Cr2AlC (002)

Cr2AlC (100)

Cr2AlC (110)

Cr2AlC (116)

HIPIMS

DC

Cr2AlC (109)

Cr2AlC (106)

Figure 4.12: XRD θ − 2θ at the position 11,-11.

Figure 4.13: SEM images from the 11,-11 position deposited with HIPIMS (left)and deposited with DCMS (right).

4.1.4 Position -4,-19

The position -4,-19 is a aluminum rich area. The grazing incident diffractionpattern in figure 4.19 indicates the presence of Cr2Al in the HIPIMS film, while

4.1 Analyses of the Sample Regions 23

Figure 4.14: SEM image from the 11,-11 position.

10 20 30 40 50 60 70 80 90

2 position (o)

Intensity (a.u.)

Cr2AlC (100)

Cr2AlC (110)

Cr2AlC (116)

HIPIMS

DC

Cr2AlC (103)

Cr2AlC (106)

Cr2AlC (109)

Cr2Al (002)

0.5o Shiftof Cr

2AlC

Cr2Al (103)

Figure 4.15: XRD grazing incidence at the position 0,0.

the DCMS sample shows no peaks at all. There is a shift in the Cr2AlC peaksfrom the diffraction pattern in figure 4.19, that could suggest the formation of(Cr,Al)

2Cx [23]. In the XRD θ − 2θ in figure 4.20 five huge peaks are present in

24 Results and Discussion

10 20 30 40 50 60 70 80 90

2 position (o)

Intensity (a.u.)

Substrate

Substrate

Substrate

Cr2AlC (100)

Cr2AlC (116)

HIPIMS

DC

65.341o

Figure 4.16: XRD θ − 2θ at the position 0,0.

Figure 4.17: SEM images from the 0,0 position deposited with HIPIMS (left) anddeposited with DCMS (right).

the DCMS sample, which have not been identified.The SEM image in figure 4.21 shows no different in the two samples morphol-

4.1 Analyses of the Sample Regions 25

Figure 4.18: SEM image from the 0,0 position.

ogy.

10 20 30 40 50 60 70 80 90

2 position (o)

Intensity (a.u.)

Cr2AlC (100)

Cr2AlC (110)

Cr2AlC (116)

HIPIMS

DC

Cr2AlC (103)

Cr2AlC (106)

Cr2AlC (109)

Cr2AlC (002) 0.5o Shift

of Cr2AlC

Cr2Al (002)

Cr2Al (103)

Cr2Al (200/105)

Figure 4.19: XRD grazing incidence at the position -4,-19.

26 Results and Discussion

10 20 30 40 50 60 70 80 90

2 position (o)

Intensity (a.u.)

Substrate

Substrate

Substrate

Cr2AlC (100)

Cr2AlC (116)

HIPIMS

DC

Cr2AlC (002)

Cr2AlC (109)

65.332o

Figure 4.20: XRD θ − 2θ at the position -4,-19.

Figure 4.21: SEM images from the -4,-19 position deposited with HIPIMS (left)and deposited with DCMS (right).

4.1.5 Position -5,15

The position -5,15 is a chromium rich area. Figure 4.22 shows the XRD grazingincident data and figure 4.23 shows the XRD θ − 2θ. The 002 peak is not present

4.2 Lower Temperature Samples 27

and the Cr2AlC peaks are shifted, therefore is it hard to tell if the MAX phaseis present or not. There are small peaks in the diffraction pattern that is notidentified.

The SEM image in figure 4.24 shows the morphology of the films.

10 20 30 40 50 60 70 80 90

2 position (o)

Intensity (a.u.)

Cr2AlC (100)

Cr2AlC (110)

Cr2AlC (116)

HIPIMS

DC

Cr2AlC (103)

Cr2AlC (106)

Cr2AlC (109)

Cr2AlC (002) 0.3-0.6o Shift

of Cr2AlC

Figure 4.22: XRD grazing incidence at the position -5,15.

4.2 Lower Temperature Samples

For the samples deposited at lower temperatures, the XRD diffraction patterndid not clearly show that the MAX phase was precent. Figure 4.25 shows theXRD data for 350oC, 450oC and 500oC synthesized with HIPIMS. 350oC clearlyshows an amorphous structure of the sample. 450oC shows that a phase is weaklypresent. 500oC shows a phase that is similar to the MAX phase, but it could alsobe the (Cr,Al)

2Cx phase, previously reported for this temperature [23].

There is a big different between 450oC and 500oC, so this is the temperaturewere crystallization starts to take place. At 450oC small peaks are visible, soonly a small fraction has crystallized, while at 500oC the peaks are of the same

28 Results and Discussion

10 20 30 40 50 60 70 80 90

2 position (o)

Intensity (a.u.)

Substrate

Substrate

Substrate

Cr2AlC (116)

HIPIMS

DC

65.419o

Cr2AlC (106)

75.909o

Figure 4.23: XRD θ − 2θ at the position -5,15.

Figure 4.24: SEM images from the -5,15 position deposited with HIPIMS (left)and deposited with DCMS (right).

magnitude as they are at 550oC.

4.2 Lower Temperature Samples 29

Intensity (a.u.)

350oC

450oC

500oC

50 6010 20 30 40 70 80 902 position (o)

Figure 4.25: XRD for the samples deposited with HIPIMS at 350oC (blue), 450oC(red) and 500oC (green).

Chapter 5

Summary and Conclusions

To easily investigate a large number of compositions, a combinatorial method wasused.

In this project two films, deposited at 550oC and synthesized with HIPIMSand DCMS were compared. Analyses with Scanning Electron Microscopy showedthat the films had similar morphology at the same positions. X-Ray Diffractionindicated that the MAX phase Cr2AlC was synthesized. X-Ray PhotoelectronSpectroscopy verified that the films consists of chromium, aluminum, carbon andoxygen. Electrical measurements revealed that the HIPIMS film had better con-ductivity than the DCMS film in three of four positions.

Over the combinatorial area different structures and phases are present. Inposition 0,0 and -4,-19 Cr2Al was synthesized. The DCMS film at position -4,-19 shows some peaks that were not possible to identify. More analyses on thisposition would have been required to understand these phases. There are otherpeaks in the films that have not been identified, indicating that there are morephases present.

To be certain that the MAX phase is present, the XRD data need to containthe 002 peak and no peak shift can exist. Position 11,-11 is a position that satisfythese requirements. Position 16,5 is in the border zone for these conditions, butfor the other three positions it is not possible to tell which phase is present withthe data acquired in this project.

Synthesis of the MAX phase Cr2AlC by HIPIMS does not change the lowestdeposition temperature compared to DCMS. The lowest possible temperature fordepositing Cr2AlC is 550oC for both HIPIMS and DCMS. The XRD data from thetwo methods have intensity variations for different orientations, this might stemfrom a different preferred orientation when using HIPIMS.

31

32 Summary and Conclusions

5.1 Recommendations

HIPIMS is only used on the chromium target in this project, that might not beenough to get an effect, if HIPIMS would be used on all three targets there couldbe a different result. It would be interesting to try different HIPIMS parameters,by using a higher power more energy could be transferred to the substrate to allowMAX phase formation at lower temperatures.

To be sure if the MAX phase was synthesized in all positions, transmissionelectron microscopy of each sample and position need to be done. In such a imagethere would be obvious if the zigzag structure from MAX phases is present or not.

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