5
Preparation of AlCuFe quasicrystalline film by pulsed laser-arc deposition Sedao a , Tianmin Shao a, T , Huiqing Mou a , Meng Hua b a State Key Lab. of Tribology, Tsinghua University, Beijing, PR China b Department of MEEM, City University of Hong Kong, Hong Kong Received 4 December 2003; accepted 1 November 2004 Available online 15 April 2005 Abstract Formation of stable AlCuFe quasicrystalline thin films by pulsed laser-arc deposition technique is reported in this paper. Using a single- source bulk AlCuFe quasicrystal as target material, AlCuFe film with ideal composition of quasicrystalline phase formation was deposited by suitably controlling the deposition parameters. The as-deposited film was basically in amorphous form. Icosahedral phase appeared after the films were annealed at elevated temperature. AlCuFe film was also deposited by pulsed laser ablation. Comparison of the quality of the films prepared using the two methods indicates that pulsed laser-arc deposition has greater ability in forming AlCuFe quasicrystalline structure. D 2005 Elsevier B.V. All rights reserved. PACS: 61.44.B; 81.15.F; 73.61.A Keywords: Quasicrystal; Thin films; Deposition; Laser-arc 1. Introduction Quasicrystals are compounds with unique chemical and physical properties. Their peculiar crystallographic structure generally provides them with good corrosion resistance, low thermal conductivity, high hardness and low friction coefficient [1,2]. Unfortunately, their brittle nature makes them unsuitable for being utilized as structural materials. Such limitation could be surmounted by using quasicrystals as surface materials. There are a variety of techniques, typically sputtering and evaporation, available for producing quasicrystalline films. Using pre-alloyed targets of different composition, Kreidler et al. [3] obtained metastable AlMn and AlMnSi quasicrys- talline films on glass substrates by sputtering deposition at temperatures ranging from 175 to 650 K. Haberkern et al. [4] used a co-sputtering technique with two magnetron sources to prepare AlRdRe icosahedral phase (i-phase) quasicrystalline thin films and finally achieved the antici- pated composition in quasicrystal by annealing the films at 950 K for 10 h in vacuum. One of the two-magnetron sources they used was Re target whilst the other was a sectional target of Al and Pd. Klein et al. prepared stable AlCuFe i-phase quasicrystalline films by solid state diffusion of sputtered Al, Cu and Fe layers [5]. Evaporation is another commonly used method for preparing thin films. Yoshioka et al. [6] firstly prepared AlCuFe i-phase quasicrystalline films from a single source of the alloy Al 40 Cu 5 Fe 55 by e-beam evaporation. The deposited films were then annealed in vacuum firstly at 623 K overnight and subsequently at 873 K for 2 h. They found that thin film samples prepared from a same mother alloy under similar conditions might not give the final composition as desired. Teghil et al. [7,8] studied and discussed pulsed laser ablation and deposition (PLD) of AlCuFe quasicrystalline films. They obtained the films of AlCuFe with composition almost similar to that of the target source when fluencies of the pulsed laser were beyond 6.5 J/cm 2 . Aiming at developing a two-step (deposition + subse- quent annealing) method for preparing i-phase quasicrystal- line thin films from bulk quasicrystal directly, we specifically investigated the possible formation of the stable AlCuFe i-phase quasicrystalline films by using pulsed laser- 0040-6090/$ - see front matter D 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.tsf.2005.01.007 T Corresponding author. Fax: +86 10 627 81379. E-mail address: [email protected] (T. Shao). Thin Solid Films 483 (2005) 1 – 5 www.elsevier.com/locate/tsf

Preparation of AlCuFe quasicrystalline film by pulsed laser-arc deposition

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www.elsevier.com/locate/tsf

Thin Solid Films 4

Preparation of AlCuFe quasicrystalline film by pulsed laser-arc deposition

Sedaoa, Tianmin Shaoa,T, Huiqing Moua, Meng Huab

aState Key Lab. of Tribology, Tsinghua University, Beijing, PR ChinabDepartment of MEEM, City University of Hong Kong, Hong Kong

Received 4 December 2003; accepted 1 November 2004

Available online 15 April 2005

Abstract

Formation of stable AlCuFe quasicrystalline thin films by pulsed laser-arc deposition technique is reported in this paper. Using a single-

source bulk AlCuFe quasicrystal as target material, AlCuFe film with ideal composition of quasicrystalline phase formation was deposited by

suitably controlling the deposition parameters. The as-deposited film was basically in amorphous form. Icosahedral phase appeared after the

films were annealed at elevated temperature. AlCuFe film was also deposited by pulsed laser ablation. Comparison of the quality of the films

prepared using the two methods indicates that pulsed laser-arc deposition has greater ability in forming AlCuFe quasicrystalline structure.

D 2005 Elsevier B.V. All rights reserved.

PACS: 61.44.B; 81.15.F; 73.61.A

Keywords: Quasicrystal; Thin films; Deposition; Laser-arc

1. Introduction

Quasicrystals are compounds with unique chemical and

physical properties. Their peculiar crystallographic structure

generally provides them with good corrosion resistance, low

thermal conductivity, high hardness and low friction

coefficient [1,2]. Unfortunately, their brittle nature makes

them unsuitable for being utilized as structural materials.

Such limitation could be surmounted by using quasicrystals

as surface materials.

There are a variety of techniques, typically sputtering and

evaporation, available for producing quasicrystalline films.

Using pre-alloyed targets of different composition, Kreidler

et al. [3] obtained metastable AlMn and AlMnSi quasicrys-

talline films on glass substrates by sputtering deposition at

temperatures ranging from 175 to 650 K. Haberkern et al.

[4] used a co-sputtering technique with two magnetron

sources to prepare AlRdRe icosahedral phase (i-phase)

quasicrystalline thin films and finally achieved the antici-

pated composition in quasicrystal by annealing the films at

0040-6090/$ - see front matter D 2005 Elsevier B.V. All rights reserved.

doi:10.1016/j.tsf.2005.01.007

T Corresponding author. Fax: +86 10 627 81379.

E-mail address: [email protected] (T. Shao).

950 K for 10 h in vacuum. One of the two-magnetron

sources they used was Re target whilst the other was a

sectional target of Al and Pd. Klein et al. prepared stable

AlCuFe i-phase quasicrystalline films by solid state

diffusion of sputtered Al, Cu and Fe layers [5].

Evaporation is another commonly used method for

preparing thin films. Yoshioka et al. [6] firstly prepared

AlCuFe i-phase quasicrystalline films from a single source

of the alloy Al40Cu5Fe55 by e-beam evaporation. The

deposited films were then annealed in vacuum firstly at

623 K overnight and subsequently at 873 K for 2 h. They

found that thin film samples prepared from a same mother

alloy under similar conditions might not give the final

composition as desired. Teghil et al. [7,8] studied and

discussed pulsed laser ablation and deposition (PLD) of

AlCuFe quasicrystalline films. They obtained the films of

AlCuFe with composition almost similar to that of the

target source when fluencies of the pulsed laser were

beyond 6.5 J/cm2.

Aiming at developing a two-step (deposition + subse-

quent annealing) method for preparing i-phase quasicrystal-

line thin films from bulk quasicrystal directly, we

specifically investigated the possible formation of the stable

AlCuFe i-phase quasicrystalline films by using pulsed laser-

83 (2005) 1–5

Sedao et al. / Thin Solid Films 483 (2005) 1–52

arc deposition technique (LAD) and PLD. In addition, we

also compared the quality of the films prepared by using the

two methods. This paper presents some of the relevant

findings and results from the study.

2. Experiment details

2.1. Preparation of film samples

The schematic arrangement of the LAD system is

illustrated in Fig. 1 [9,10]. The target, a piece of bulk

AlCuFe quasicrystal prepared by electromagnetic induction

melting, was mounted onto the target holder in the vacuum

chamber. A ring anode with inner hole-diameter of 5 mm

was placed parallel to the target surface and connected with

the target-cathode through a pulse current supply circuitry.

Substrate material was situated onto a substrate holder and

was facing the target material. A resistive heater was

embedded in the substrate holder for heating the substrate

to a desirable temperature in the range of 300–700 K. Laser

beam from a Nd-YAG pulsed laser (wavelength 1064 nm,

single pulse duration 160 ns and repetition rate 1.0 kHz) was

transmitted into the vacuum chamber. A focusing mirror

was used for focusing the laser beam on the target surface.

Under the action of the field established between the ring

anode and the target cathode, a laser-induced plasma was

emitted to initiate vacuum arc that further stimulate the

emission of more plasma from the nearby target. The arc

pulse duration was regulated by a specially designed pulse

arc source so as to obtain controllable ablation of the target.

As the erosion of cathode material due to emission was at

and around the near vicinity of the effective laser focusing

and arcing region, the target holder was designed to move in

a 2-dimensional plane for adjusting the emission locations

on the cathode material. This facilitated the even erosion of

target material and the achievement of desirable deposition

of arc induced plasma on substrate in the deposition process.

focusing

plasma

pump

holdertarget-cathode

arc sourcebias

anode

substrate

laser beammirror

+ _

Fig. 1. Schematic diagram of the LAD system.

For this specific study, the cathode–anode distance was 4

mm and the distance between the target and the substrate

was 50 mm. The laser power density was set at 6.5�108 W/

cm2. The deposition was performed with a laser-induced arc

repetition rate of 2 Hz for 18 min under a vacuum level of

2�10�4 Pa. The substrate holder was kept at room

temperature and supplied with a negative bias of �400 V.

A series of AlCuFe film samples were first deposited with

different arc source voltages and the elemental composition

of the deposited film samples was then identified by means

of energy dispersive analysis using X-ray spectroscopy

(EDAX). The analysis allowed the determination of the

optimal arc source voltage for achieving the deposition of

desirable composition of the films. The optimal arc source

voltage so evaluated was then used to deposit films, which

were then in situ annealed at 673 K for 4 h. Prior to the

annealing treatment, the vacuum chamber was filled with Ar

gas to 30 Pa and the Ar gas pressure was kept constant at

this level during the annealing process.

For the purpose of comparison, PLD film samples were

also deposited in the same vacuum chamber, under the same

setting of (i) laser power density, (ii) distance between the

target and the substrate and (iii) vacuum level as for the

LAD depositions. Two PLD film samples were prepared

separately. One of them was deposited for EDAX analysis.

The other was deposited and followed subsequent in situ

annealing treatment. Either of the deposition processes was

lasted for 90 min. The annealing condition of the PLD film

was similar to that used for annealing LAD films.

2.2. Measurements

A PHI-610 scanning Auger electron spectrometer, which

was coupled with a co-axial Ar+(3 keV) etching gun, was

used to obtain the depth profiles of the constituent elements

of Al, Cu and Fe. For each sputtering process, measure-

ments were performed over an Ar+sputtered surface area of

0.5�0.5 mm2. The sputtering rate of Ar+, as calibrated from

etching of SiO2/Si, was 20 nm/min. Auger electron

spectroscopy (AES) performed on the Ar+ etched film

surface was used to analyze the chemical composition of the

films. A D/MAX-IIIA X-ray diffractometer (Cu Ka source

k=1.596 2) was used to study the microstructure of the

films, which was further verified by a JEM-200CX trans-

mission electron microscope (TEM). The TEM was coupled

with an X-ray spectroscopy apparatus for EDAX analysis.

The substrate used for preparing films for TEM and EDAX

analyses was air-cleaved NaCl crystal, whilst samples

prepared on Si (111) wafer (pre-cleaned by fluorhydric acid

and ethanol) substrate were used for other analyses.

3. Results and discussion

The X-ray diffraction (XRD) pattern (Cu Ka) of the

target AlCuFe quasicrystal is shown in Fig. 2. Basically, the

4020 30 50 60 702Theta (degree)

Inte

nsity

(ar

b. u

nits

)

I I I I

II

I

β

Fig. 2. XRD pattern of the target material.

Sedao et al. / Thin Solid Films 483 (2005) 1–5 3

target material consisted of i-phase quasicrystal and some

crystalline phases [11,12]. Table 1 tabulates the elemental

composition of the films deposited by LAD under different

arc source voltages. It showed that: (i) the composition of

element Fe almost maintained in a relatively stable level

over the range of arc source voltages studied; (ii) the

composition of element Al decreased slightly (for arc

voltage no higher than 1020 V) and then remarkably (for

arc voltage beyond 1020 V) with the increase in arc voltage;

and (iii) the composition of element Cu increased remark-

ably with the increase in arc voltage. The film deposited at

low arc voltage was rich in Al whilst that at high ones was

rich in Cu (At arc voltage of 1100 V, the composition of

both element Al and Cu was almost in the same level. The

composition of film samples deposited at arc voltage in the

range of 950–1000 V were rather close to their target

material. Analysis of the data in Table 1 suggested that the

composition of the film deposited at the arc source voltage

of 980 V was ideal for the formation of quasicrystalline

phase. Additionally, results for the elemental composition of

the PLD film samples indicated that the films deposited by

PLD also met the elemental composition requirement for

forming quasicrystalline phase.

The as-deposited/annealed LAD films, which were

deposited by using 980 V arc source voltage (optimal arc

Table 1

EDAX analysis of the LAD and PLD film samples

# Arc source

voltage (V)

Film composition (at. %)

Al Cu Fe

1 900 73 16 11

2 950 65 25 10

3 980 65 23 12

4 1000 64 26 10

5 1020 60 28 12

6 1100 48 40 12

7(PLD) 65 21 14

Target 64 24 12

source voltage) and the as-deposited/annealed PLD films

were submitted to XRD analysis. The XRD patterns of these

films are shown in Fig. 3(a) and (b), respectively. The XRD

peaks of the silicon substrates were removed from these

results. Analysis of the obtained spectra for the as-deposited

LAD and PLD films (the XRD pattern of the as-deposited

PLD films was not shown here) suggested that the as-

deposited films were all in amorphous structure. The XRD

pattern of the annealed LAD film (the upper spectra in Fig.

3(a)) illustrated that the film consisted mainly of i-phase

quasicrystal with also crystalline cubic h-phase being

detected. The annealed PLD film consisted almost entirely

of amorphous (Fig. 3(b)). Only the peak at low angle hinted

to the existence of some crystalline phase [13–16].

The presence of i-phase quasicrystal in the LAD film,

which was deposited by using 980 V arc source voltage and

followed in situ annealing treatment was further verified by

TEM study. Fig. 4 shows the TEM image and the

corresponding pattern of its selected area electron diffraction

(SAED) of the annealed LAD film, which was separated

from its NaCl substrate. A typical TEM image (Fig. 4(a)) of

the in situ annealed LAD film seemed to suggest that the

film was smoothly and densely deposited. The SAED

pattern (Fig. 4(b)) clearly indicated the existence of i-phase

quasicrystal.

For estimating the thickness and comparing distribution

of the constituents in the films prepared by the two methods,

Auger depth profile analysis was performed. Elements Si,

Al, Cu and Fe were recorded. Fig. 5(a) shows the Auger

depth profile of the LAD film. The film was deposited by

using 980 V arc source voltage and then in situ annealed.

Fig. 5(b) shows the Auger depth profile of the annealed

PLD film. From the distance between the film surface and

interface of element Al, Cu, Fe and Si, the thickness of the

Fig. 3. XRD patterns of (a) the as-deposited (the lower curve) and in situ

annealed (the upper curve) LAD films. Both of the films were deposited by

using 980 V arc source voltage; and XRD pattern of (b) the annealed PLD

film. Annealing treatments were performed at 673 K for 4 h within Ar gas

ambient.

Fig. 6. After Ar+ etching for 2.5 min, AES spectra derived from (a) the

annealed LAD film and (b) the annealed PLD film.

100nm

(a) (b)

Fig. 4. (a) TEM image and (b) SAED pattern of the annealed LAD film.

The film was deposited on NaCl substrate by using 980 V arc source

voltage.

Sedao et al. / Thin Solid Films 483 (2005) 1–54

film samples is estimated to be 130 nm for LAD and 160 nm

for PLD films. It is observed that the constituents of the

LAD film were more evenly distributed than those of the

PLD film. This phenomenon might result from the differ-

Fig. 5. Auger depth profiles of (a) the annealed LAD film. The film was

deposited by using 980 V arc source voltage, and (b) the annealed PLD

film.

ence in ablation area and ablated particle energy of the two

deposition processes.

AES spectra of these annealed films were also measured.

Fig. 6(a) and (b) show the spectra of the annealed LAD and

PLD films, respectively. These AES spectra were obtained

from the film surfaces etched with Ar+ 2.5 min (50 nm

depth). From the energy window used, the following

elements can be identified: Al at 1396 eV, Cu at 920 eV,

Fe at 703 eV and O at 510 eV, respectively. The appearance

of oxygen Auger peak demonstrates that the oxygen is

present in the two films. According to these AES spectra the

concentration of oxygen in these films was calculated to be

12 at.% for LAD and 30 at.% for PLD films. The difference

in oxygen concentration could explain the difference in the

microstructure of the films by LAD and by PLD. As

reported in the literature [17,18], the forming ability of

AlCuFe i-phase quasicrystal is usually suppressed by the

presence of oxygen. In view of this, it is concluded that the

higher oxygen concentration in the films deposited by PLD

led to small or even absence of i-phase quasicrystal. The

different concentration level of oxygen in PLD and LAD

films is likely to result from different deposition rate. From

the film thickness estimated from the Auger depth profile

analysis and the deposition time, the deposition rate was

approximately 7.2 nm/min for the LAD film whilst 1.8 nm/

min for the PLD film. As deposition at low rate in the same

vacuum environment leads to more important oxygen

absorption in the film [19], the film deposited by PLD thus

had a higher concentration of oxygen.

4. Conclusions

Using LAD method, thin films deposited from a single

source, a bulk AlCuFe quasicrystal, were produced with

elemental composition close to the ideal ratio for

formation of AlCuFe quasicrystal. Arc source voltage

Sedao et al. / Thin Solid Films 483 (2005) 1–5 5

significantly influenced the composition of the films.

Structure of the as-deposited films by LAD was usually

in amorphous form. Such films after suitable annealing

treatment were likely to form quasicrystalline phase.

Compared with the PLD method, the preparation of

quasicrystalline films by LAD had more advantages. Such

advantageous films were produced because of the higher

deposition rate of LAD method than that of the PLD one,

which resulted in the decrease in the oxygen concentration

in the LAD films.

Acknowledgments

The work described in this paper was financially

supported by the National Natural Science Foundation of

China [Project No. 50075042 and Key Project No.

50135040].

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