Upload
sedao
View
217
Download
2
Embed Size (px)
Citation preview
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].
References
[1] P.D. Bloom, K.G. Baikerikar, J.U. Otaigbe, Mater. Sci. Eng., A Struct.
Mater.: Prop. Microstruct. Process. 294/296 (2000) 156.
[2] T. Grenet, F. Giroud, A. Bergman, G. Safran, J. Labar, P. Barnar,
J.L. Joulaud, M. Capitan, J. Alloys Compd. 342 (2002) 2.
[3] K.G. Kreidler, F.S. Biancaniello, M.J. Kaufmann, Scr. Metal. 21
(1987) 657.
[4] R. Haberkern, R. Rosenbaum, H. Bekar, M. Pilosof, A. Milner,
A. Gerber, P. Haussler, Mater. Sci. Eng., A Struct. Mater.: Prop.
Microstruct. Process. 294/296 (2000) 613.
[5] T. Klein, O.G. Symko, Appl. Phys. Lett. 64 (1994) 431.
[6] A. Yoshioka, K. Edagawa, K. Kimura, S. Takeuchi, Jpn. J. Appl.
Phys. 34 (1995) 1606.
[7] R. Teghil, L. D’Alessio, M.A. Simone, M. Zaccagnino, D. Ferro,
D.J. Sordelet, Appl. Surf. Sci. 168 (2000) 267.
[8] R. Teghil, L. D’Alessio, A. Santagata, M. Zaccagnino, D. Ferro,
D.J. Sordelet, Appl. Surf. Sci. 210 (2003) 307.
[9] D. Se, T.M. Shao, W.D. Yuan, Appl. Laser Technol. 2 (2002) 132, (in
Chinese).
[10] X.K. Cao, T.M. Shao, S.Z. Wen, Tribol. Trans. 47 (2004) 227.
[11] W. Pompe, H.-J. Scheibe, P. Siemroth, R. Wilberg, D. Schulze,
B. Buecken, Thin Solid Films 208 (1992) 11.
[12] A. Haugeneder, T. Eisenhammer, A. Mahr, J. Schneider, M. Wendel,
Thin Solid Films 307 (1997) 120.
[13] A. Kanjilal, U. Tiwari, R. Chatterjee, Mater. Res. Bull. 37 (2002) 343.
[14] D.J. Sordelet, M.F. Besser, J.L. Logsdon, Mater. Sci. Eng., A Struct.
Mater.: Prop. Microstruct. Process. 255 (1998) 54.
[15] P. Brunet, L. Zhang, D.J. Sordelet, M. Besser, J.M. Dubois, Mater.
Sci. Eng., A Struct. Mater.: Prop. Microstruct. Process. 294/296
(2000) 74.
[16] T. Grenet, F. Giroud, C. Loubet, J.L. Joulaud, M. Capitan, Mater. Sci.
Eng., A Struct. Mater.: Prop. Microstruct. Process. 294/296 (2000)
838.
[17] G.S. Song, K.B. Kim, E. Fleury, W.T. Kim, D.H. Kim, J. Mater. Sci.
Lett. 20 (2001) 1293.
[18] N. Bonasso, P. Pigeat, D. Rouxel, B. Weber, Thin Solid Films 409
(2002) 165.
[19] D. Nesheva, I. Bineva, Z. Levi, T.S. Merdzhanova, J.C. Pivin,
Vacuum 68 (2003) 1.