THIN FILM TECHNOLOGY STRATEGIC RESEARCH PROGRAMME
1.
Introduction
The Thin Film Technology Strategic Research Programme (or Thin Films SRP) was officially launched in
April 2001 to keep pace with the technological advancement in thin film related application areas. These
areas include substrate patterning, bump metallurgy, thin film filters and coatings for fibre optic
telecommunication systems, medical implants and wear protection, etc. Thin film technology is also closely
linked with nanotechnology, which is becoming one of the main areas in the new-generation manufacturing
and precision engineering industries. Thin Films SRP is currently involved in the processing and
characterisation of nano composite thin films for electronics and nano tribological applications, thin films for
MEMS application, biomedical application, thin film fuel cells and batteries.
2.
Objectives
The objectives of the thin film strategic research program are
To coordinate the thin films related research and development effort in the school
To understand fundamental aspects of the thin film hardness, toughness, adhesion and functionality
To fabricate high performance thin films and coatings for precision engineering, MEMS and biological
applications
To aspire to be a center of excellence in thin films research and development and a training ground for
high caliber thin film researchers and application experts
3.
Research and Development
Currently the thin film strategic research program is concentrating on the following aspects of research:
Nanocomposite Thin Films
Tribology of Thin Films
Diffusion Barriers
Biological Thin Films
Thin Film Shape Memory Alloys
Thin Film Fuel Cells
Thin Film Batteries
Thin Film Resistors
Listed below is a part of our research project highlights:
STRENGTHENING MECHANISM FOR SUPERHARD NANOCOMPOSITE COATINGS WITH HIGH
TOUGHNESS
Principle Investigator:
SAM ZHANG
Research Student:
SUN DEEN
Nanotechnology is one of the key technologies of the near future. Nanocomposite coatings represent a new
class of materials which exhibit improved mechanical properties owing to the size effect. This project studies
the strengthening mechanism for superhard and high toughness nanocomposite coatings prepared by
magnetron sputtering technique. The as-deposited coatings are expected to provide a good combination
between high hardness and at the same time high toughness. Some of the research groups have fabricated
the superhard nanocomposite coatings, which hardness arrived to 100 GPa. But the coatings have very low
toughness. In most of the wear resistant applications, hardness is only one of many properties. The other
important properties include high hot hardness and toughness (up to 800°C), oxidation resistance, chemical
stability and a low coefficient of friction against the material to be machined, high adherence, and
compatibility with the substrate and low thermal conductivity, which such a material has to meet.
In this project, superhard multiphase nanocomposite coatings with high toughness will be prepared by
magnetron sputtering. The emphasis will be put on the studying of strengthening mechanism for asdeposited multiphase nanocomposite coatings combined with superior hardness and high toughness.
A further increase of the hardness with decreasing crystallite size can be achieved only if grain boundary
sliding can be blocked by appropriate design of the material. Multiphase systems display many similarities
with composite materials and often display higher hardness and toughness values than single-phase
materials The different phase exhibits different slide systems and provide complex boundary to
accommodate the coherency strain without forming voids or other flaws. Accordingly, superhard coatings
with high toughness can be achieved though optimal designing of multiphase.
TRIBOLOGY OF NANO-COMPOSITE AS PROTECTIVE COATINGS FOR PISTON RINGS IN INTERNAL
COMBUSTION ENGINES
Principle Investigator:
SAM ZHANG
Research Student:
BUI XUAN LAM
Fossil fuel sources are running out. The alternative fuels are under research or with very limited applications
(except the “dangerous source”- the nuclear energy). Therefore, saving is the best policy. It is estimated that
a reduction of friction losses by 10 % results in 4% fuel saving at 50 % of engine load. In this project, we are
developing a new generation of coating to be utilised for piston ring protection in an internal combustion
engine. This type of coatings is a combination of two hard phases: hard crystalline particles of nitrides and/or
carbides embedded in a hard (more than 30 GPa) Diamond-Like Carbon (DLC) matrix. A harmonious scale
of these phases results in a hard and tough coating. Main tasks of the project include producing DLC(Al,Ti)CxNy and DLC-(Cr,Ti)CxNy nano-composite coatings by reactive magnetron sputtering; Investigating
the influence of parameters to mechanical and tribological properties of the coatings; Depositing the coatings
on piston rings; Designing the experiments for test rig tests and engine tests. Evaluating the feasibility of
applying nano-composite DLC as protective coatings for piston rings in internal combustion engines.
DEVELOPMENT OF MEMBRANE-ELECTRODE-ASSEMBLIES FOR POLYMER ELECTROLYTE
FUEL CELLS
Principle Investigator:
JIANG SAN PING
Co-investigators:
SAM ZHANG
Research Student:
MINDY GU
Polymer electrolyte fuel cells (PEFC) are attracting wide attention as a clean, high efficiency, low pollution
and low temperature power generation technology. They have wide range applications in areas such as
transportation, portable power sources, and remote area power supply and distributed power supply.
Membrane-electrode-assembly (MEA) is the heart of PEFC and the performance of PEFC is largely
determined by the structure and the performance of MEA. Conventionally, MEA is prepared by sandwiching
electro-catalyst layer, electrolyte membrane and gas diffusion layer together under heat and pressure. The
electro-catalyst layer usually has high Pt loading and the thickness of the catalyst layer is in the range of 30
to 100 µm. However, it has been well known that less than 10% of the Pt catalysts in the catalyst layer is
actually useful for the fuel cell reactions as the reaction primarily occurs at the electrode/electrolyte interface
region, a region of only a few microns thick. This indicates that Pt catalysts in other parts of the catalyst layer
away from the thin electrode/electrolyte region would not be utilized and are wasted. On the other hand, the
conventional techniques in the preparation of separate Pt/C catalyst layer by rolling or screen printing
method are particularly difficulty in the control of uniform distribution of Pt catalysts at the interface region.
Sputtering is a reliable and a highly commercialised technique for thin film deposition and has been used in
industry for large scale production of reflective coatings, such as glass-coatings etc. It is a process that
energetic particles bombard a surface (target) and erode it. The atoms of the surface material are gradually
dislodged by momentum transfer from energetic particles to atoms. The sputtered atoms land on a substrate
and form a layer of thin film. This technique has the potential for creating the membrane electrode assembly
structure and for large-scale manufacture of fuel cell electrodes, with uniform layers containing low or ultralow Pt or Pt/Ru catalysts. It is expected that MEA prepared would have special characteristics of localized
distribution of electro-catalyst near the electrode/electrolyte interface and very low level of Pt (≤ 0.1 mg/cm2).
This project will explore the magnetron sputtering thin film techniques in the fabrication and development of
new MEA for polymer electrolyte fuel cells with low Pt loading and high performance. The aim of the project
is to establish the relationship between the microstructure of MEA and the performance and finally the
feasibility of the fabrication of micro PEFC using methanol as fuel.
Shape Memory Alloy Thin Films
Principle Investigator: Liu Yong
Research student: Huang Xu
Thin film SMAs have the potential to become a primary actuating mechanism for devices with dimension from microto-millimeter range requiring large forces over large displacements. The most promising applications of SMA thin films
are MEMS and medical devices. The unique property of SMAs is due to a unique deformation mechanism, i.e.
detwinning process. As typically shown in Fig. 1a, SMA consists of 100% lattice twins in its martensitic state and,
under stresses, the mirror-plane symmetry can be removed without introducing significant amount of dislocations (Fig.
1b). The detwinning can lead to about 6% deformation that can be fully restored upon heating to above a critical
temperature.
a
b
(1
00
)
(101)
(001)
15 Å
Figure 1. (a) TEM micrograph of typical NiTi martensite consisting of 100% lattice twins. (b) HRTEM image of an
area along detwinned region showing the details of the atomistic rearrangement during detwinning process.
We are currently working on understanding the performance of SMA thin films. In our research, the factors that affect
the phase transformation characteristics, mechanical and thermal mechanical properties of sputter-deposited thin films,
melt spun ribbons and rolled thin sheets are systematically investigated. It is found that the substrate condition strongly
affects the properties of sputter-deposited thin films as typically shown in Fig. 2a. In the case of SMA melt-spun ribbon,
through suitable annealing treatment, a high superelasticity (about 9%) is found to exist in Ti50Ni25Cu25 with very low
hysteresis (Fig. 2b). This result sheds new light on its applications. The effect of rolling texture and annealing condition
on both the superelasticity and shape memory effect is also under investigation, which is expected to provide useful
guidelines on the fabrication and effective utilization of the SMA thin sheets.
1.5
(a)
As
1.2
Deposited on (100) Si
Deposited on SiO2
750
(b)
TiNi25Cu25 melt-spun ribbon
600
o
tested at 123 C
layer on top of (100) Si
0.9
450
0.3
As
0.0
-30
150
Af
Rf
Ms
Rs
0
3
300
Ms
30
Residual Strain, %
0.6
0
Af
60
90
120
2
1
0
0
3
6
9
12
Deformation Strain, %
0
2
4
6
8
10
12
Temperature, C
Figure 2. (a) Effect of substrate condition on the shape recovery of deposited NiTi thin films. (b) Cyclic
deformation of a TiNi25Cu25 melt spun ribbon showing a high superelasticity with low hysteresis. It is
further found that the superelasticity stabilizes gradually with increasing number of cycles under constant
deformation amplitude.
CERAMIC NANOCOMPOSITE COATINGS FABRICATED BY MAGNETRON SPUTTERING
Principle Investigator:
LIU ERJIA
Research Fellow:
GAO JIANXIA
The primary objective is to fabricate and characterise ceramic nanocomposite coatings and thin
films, such as AlN, TiCN, AlTiN, ZrN, SiC, and metal-containing diamondlike carbon (a-C:M), etc.,
for applications in the areas of precision engineering (both optical and mechanical parts) as well
as electronic packaging and biomaterials. The coatings to be developed will have high wear and
corrosion resistance, low friction, high durability, and good thermal stability. The coatings will be
deposited with r.f. & d.c. magnetron sputtering technique under different deposition conditions,
such as varying substrate bias, substrate temperature, gas flow rate, vacuum partial pressure,
and surface etching or finishing effect, etc. The coating structure, chemical stoichiometry, surface
morphological characteristics, mechanical, tribological, chemical and thermal properties will be
evaluated using different characterisation techniques. Both multi-layer and single-layer films will
be developed. It is believed that each of these ceramic materials has its own characteristics.
Some may have high hardness and low wear rate and friction, some may have superior thermal
or optical properties, and others may be bioactive as biomaterials. The metal alloy coatings +
TiAlN & AlTiN are at their beginning. They appear to be specially interesting.
The objectives are as follows:
a. Deposition of ceramic nanocomposite coatings
b. Characterisation of structure and various properties such as mechanical, tribological,
chemical, optical and thermal characteristics of the coatings.
Promising applications are in the areas of precision engineering such as moulds (DVD lens
inserts), dies, cutting tools, bearings, seals, automotive and aerospace parts, printer parts,
optical parts, and biomedical applications such as orthopaedic implants, pacemakers, surgical
instruments, orthodontic devices and dental instruments.
MULTICOMPONENT DIAMONDLIKE CARBON THIN FILMS
Principle Investigator:
LIU ERJIA
Research Fellow:
GAO JIANXIA
By testing multicomponent diamondlike carbon (DLC) films deposited on different substrates in
different aqueous chemical solutions, the information concerning corrosion resistance of DLC
materials and chemical interaction between films and chemical solutions is to be acquired, which
could help improve the corrosion resistance of these materials as protective layers on tools,
biomaterials, and so on.
Pure bulk diamonds are, in general, inert to most organic and inorganic chemical solutions as well
as acids, although they are metastable in ambient atmosphere and at room temperature.
Diamondlike carbon (DLC) materials with a high content of sp3 carbon bonding may also be able
to resist most chemical solutions. However, DLC materials containing certain elements may be
reactive with some chemical species under certain conditions. The aim of this project is to
investigate the chemical properties of multicomponent DLC materials and to improve their
corrosion resistance.
The following tests will be conducted:
1. Open circuit to measure corrosion potential and corrosion rate in aqueous solutions
2. Electrochemical impedance spectroscopy to measure the electrical equivalent circuits of
multicomponent DLC electrode/solution interface.
3. Potentiodynamic and potentialstat polarization to give the oxidation and reduction reactions in
DLC electrode/solution system
4. SEM/EDX, AFM and XRD to reveal microstructural and composition changes before and
after corrosion testing.
5. Effect of different elements and their concentrations in DLC on chemical behavior of DLC
materials.
Adhesion mechanics of thin-layered systems and nanotribology
Principle Investigator:
Idapalapati Sridhar
Nano-probe instruments like Surface Force Apparatus (SFA) or Atomic Force Microscope
(SFM) are routinely used to extract the mechanical properties of thin-layers by subjecting
them to indentation process. Inadvertently at these micro or nano indentation loads, the
adhesive surface forces operating between the indenter and the thin-layer will contribute
to the deformation. The well-established JKR (Johnson-Kendal-Roberts) theory is
applied to extract the surface energy of the contacting solids. For this thin-layer system
JKR theory should be an error as it is based on the indentation of an elastic half-space
with an elastic sphere. From the tribological point of view, under sliding contact, it has
been suggested that experimental values of friction in nano-contacts can be correlated
with the area predicted by the JKR theory.
A novel method based on linear elastic fracture mechanics principles coupled with nondimensional analysis and finite element (FE) method are employed to extract the surface
energy of the contacting layered system(s) or thin layer and indenter. Both SFM and AFM
geometries are considered. The effect of indenter elasticity was included in the study of
deformation field. Computations of contact size and contact stiffness each as a function of
load are presented for a range of values of adhesion energy and elastic modulus ratio of
layer and substrate.
Current work focuses on developing useful emperical relations between the contact load
versus contact area for flat punch and spherical probe geometries based on the parametric
study conducted (numerical results) for the layered systems and also extend the work to ratedependent viscoelastic layered systems (to understand the indentation behavior of polymers)
and to biological tissues.
4.
Facilities
Microforce testing system with temperature chamber (from -70C to 200C)
Magnetic Susceptibility Meter (from -196C to 900C)
Magnetron sputter system (E303A, Penta Vacuum, RF: upto 1kW, DC: upto 1kW, Bias:
upto 600W, Uniformity:5%)
AFM (SPM-9500 J2, Shimadzu (Asia Pacific) Pte. Ltd., from 1nm to 30µm, Resolution:
1,280×1,024 pixels)
Ultra-micro hardness tester (DUH-W201S, Shimadzu (Asia Pacific) Pte. Ltd., from 0.1µm
to 200µm, high precision: <1%)
Scratch tester (SST-101, Shimadzu (Asia Pacific) Pte. Ltd., from 0 to 1000mN, accuracy
10%)
Raman spectroscope (Ranishaw-RM1000, ITS Science & Medical Pte. Ltd., spectral
range:-1000cm-1~9000cm-1, resolution:1cm-1, CCD array detector: 576x384 pixels, spatial
resolution:1µmx1000)
Contact angle goniometer (FTA 200, Analytical Technologies Pte. Ltd., from 3° to 160°,
accuracy ±1°)
Multimeter (Agilent 34401A, Agilent Technologies, Inc., for voltage from 100mV to 1000V,
accuracy 100nV (on 100mV range), for resistance from 100Ω to 100MΩ, accuracy
100µΩ (on 100Ω range), for current from 10mA to 3A, accuracy 10nA (on 10mA range),
for frequency from 3Hz to 300kHz)
XPS (Ultra, Kratos company, UK, X-ray energy: 1486.6 eV, Vacuum:4×10-10 Torr,
Minimum spot for detection: 15µm)
Contact–Start–Stop (CSS) tests
Optical Surface Analyzer (OSA) system (Candela OSA-5100)
5.
Future Plans
The thin film strategic research program will continue to concentrate on the following aspects of
thin film research in the following areas with emphasis on both fundamental understanding in
combination with industrial applications:
Nanocomposite Thin Films
Tribology of Thin Films
Diffusion Barriers
Biological Thin Films
Thin Film Shape Memory Alloys
Thin Film Fuel Cells
Thin Film Batteries
Thin Film Resistors
.
6.
Publications
1. Zheng QS and Y Liu (2002). Prediction of the detwinning anisotropy in textured NiTi shape
memory alloy, Philosophical Mag. A 82, 665-683.
2. Liu Y, YL Li and KT Ramesh (2002). Rate dependence of deformation mechanisms in shape
memory alloy, Philosophical Mag. A, accepted.
3. Liu Y, YL Li, ZL Xie and KT Ramesh (2002). Dynamic deformation of shape memory alloy:
evidence of domino detwinning? Philosophical Mag. Let., accepted.
4. J. H. Hsieh, W. Wu, and C. Li, "Deposition and characterization of Ti(C,N,O) coatings by
unbalanced magnetron sputtering" . SURFACE AND COATING TECHNOLOGY, to be
published.
5. C. Q. Sun, Y. Q. Fu, B. B. Yan, and J. H. Hsieh, "Improving diamond-metal adhesion with
graded TiCN interlayers". JOURNAL OF APPLIED PHYSICS, 91 (2002) 2051.
6. Sam Zhang , Xianting Zeng, Zhenggui Tang, Ming Jen Tan, Exploring the antisticking
properties of solid lubricant thin films in transfer molding, International Journal of Modern
Physics B, 16 (6&7) 2002, pp. 1080-1085.
7. Zeng Xianting, Sam Zhang, L. S. Tan, Multilayered (Ti, Al) Ceramic Coating for High Speed
Machining Applications, J. Vac. Sci. Technol. A, Vol. 19, No. 4, Jul/Aug 2001 pp. 1919-1922.
8. J. H. Hsieh, W. H. Zhang, and C. Li, "Characterization of (Tix Cr0.6-x)N0.4 coatings and their
tribological behaviors against an epoxy molding compound", SURFACE AND COATING
TECHNOLOGY, 146-147 (2001) 331.*
9. Sam Zhang, Tan Ming Jen, Xianting Zeng, Hong Xie, Peter Hing: Raman and PEELS studies
of magnetron sputtered a-C, International Journal of Modern Physics B, 14 (2&3) 2000 pp.
268-273.
10. X. T. Zeng, S. Zhang, and T. Muramatsu: Comparison of three advanced hard coatings for
stamping applications, Surface and Coatings Technology, 2000, Vol. 127 No. 1 (2000) pp.
38-42.
11. S. Zhang, X.T. Zeng, H. Xie, P. Hing: A phenomenological approach for Id/Ig and sp3 of
magnetron sputtered a-C, Surface and Coatings Technology, Surface and Coatings
Technology, Jan 2000, Vol. 123 No. 2-3 pp. 256-260
12. S. Yi, J. K. Kim, and J. H. Hsieh, “Bonding Strengths at Plastic Encapsulant-gold-plated
Copper Leadframe”, MICROELECTRONICS RELIABILITY, 40 (2000) 1207.
13. S. Yi, J. K. Kim, and J. H. Hsieh, “Adhesion Strengths of Epoxy Molding Compounds to Goldplated Copper Leadframes”, JOURNAL OF ADHESION, 73 (2000) 1.
14. W. H. Zhang and J. H. Hsieh, “Tribological Behavior of TiN and CrN Coatings Sliding Against
Epoxy Molding Compound”, SURFACE AND COATING TECHNOLOGY, 130 (2000) 240.*
15. Sam Zhang, Tan Ming Jen, Xianting Zeng, Hong Xie, Peter Hing: Raman and PEELS studies
of magnetron sputtered a-C, International Journal of Modern Physics B, 14(2&3)2000 268273.
16. X. T. Zeng, S. Zhang, and T. Muramatsu: Comparison of three advanced hard coatings for
stamping applications, Surface and Coatings Technology, 2000, Vol. 127 No. 1 (2000) pp.
38-42.
17. J. H. Hsieh, S,Yi, and L. Fong,”Plasma Cleaning of Copper Leadframe with Ar and Ar/H
Gases”, SURFACE AND COATING TECHNOLOGY, 112 (1999) 245.*
18. Zhang, S., Xie, H., Hing, P., Mo. Z.: Adhesion and Raman Studies of Magnetron Sputtered
Amorphous Carbon on WC/Co, Surface Engineering, 1999, Vol. 15, No. 4. pp. 341-346.
19. S. Zhang, H. Xie, X.T. Zeng and P. Hing: Residual Stress Characterization of Diamond-like
Carbon Coatings by X-ray Diffraction Method, Surface and Coatings Technology, 1999, Vol.
122 pp. 219-224.
20. Zhang, S., Xie, H., Hing, P., Mo. Z.: Adhesion and Raman Studies of Magnetron Sputtered
Amorphous Carbon on WC/Co, Surface Engineering, 1999, Vol. 15, No. 4. pp. 341-346.
21. S. Zhang, H. Xie, X.T. Zeng and P. Hing: Residual Stress Characterization of Diamond-like
Carbon Coatings by X-ray Diffraction Method, Surface and Coatings Technology, 1999, Vol.
122 pp. 219-224
22. S. Zhang and H. Xie: Improving Adhesion of Amorphous Carbon on Cemented Carbide
Through Plasma Cleaning, Surface and Coatings Technology, (113)1-2 (1999) pp. 120-125.
23. S. Zhang, M.J. Tan, P. Hing, H. Xie, H.L. Wong , W.L. Ng: Nitrogenated Carbon Layer on
Magnetic Recording Disks. Journal of Materials Processing Technology, Vol. 89-90, 1999 pp.
556-560.
24. Liu Y, YL Li, KT Ramesh and J Van Humbeeck (1999). High rate deformation of martensitic
NiTi shape memory alloy, Scripta Materialia, 41, 89-95.
25. Liu Y, ZL Xie, J Van Humbeeck and L Delaey (1999). Effect of texture orientation on the
martensite deformation of NiTi shape memory alloy, Acta Materialia, 47/2, pp. 645-660.
26. Liu YN, Y Liu and J Van Humbeeck (1999). Two-way memory effect developed by martensite
deformation in NiTi, Acta Materialia, 47/1, pp. 199-209.
27. Liu Y, ZL Xie, J Van Humbeeck and L Delaey (1999). Deformation of shape memory alloys
via twinned domain re-configurations, Mater. Sci. Eng. A 273-275, 679-684.
28. Liu Y, ZL Xie and J Van Humbeeck (1999). Cyclic deformation of NiTi shape memory alloys,
Mater. Sci. Eng. A 273-275, 673-678.
29. Liu Y, ZL Xie, J Van Humbeeck and L Delaey (1999). Some results on the detwinning
process in NiTi shape memory alloys, Scripta Materialia 41, 1273-1281.
30. Van Humbeeck J and Y Liu (2000). The high damping capacity of shape memory alloys, in
Shape Memory Implants, ed. L Yahia, Springer-Verlag Berlin, pp. 46 - 60.
31. Liu Y, ZL Xie, J Van Humbeeck, L Delaey and YN Liu (2000). On the deformation of twinned
domain in NiTi shape memory alloys, Philosophical Mag. A 80, 1935-1953.
32. Huang X and Y Liu (2001). Effect of Annealing on the Transformation Behavior and
Superelasticity of NiTi Shape Memory Alloy, Scripta Materialia, 45/2, 153-160.
33. Zheng QS and Y Liu (2002). Prediction of the detwinning anisotropy in textured NiTi shape
memory alloy, Philosophical Mag. A 82, 665-683.
34. Liu Y, YL Li and KT Ramesh (2002). Rate dependence of deformation mechanisms in shape
memory alloy, Philosophical Mag. A, accepted.
35. Liu Y, YL Li, ZL Xie and KT Ramesh (2002). Dynamic deformation of shape memory alloy:
evidence of domino detwinning? Philosophical Mag. Let., accepted.
36. Huang X and Y Liu (2002). Substrate-induced Stress and Transformation Behavior of
Sputter-Deposited NiTi Thin Films, Scripta Materialia, submitted.
37. Liu Y. and WK, Kow (2002). Superelasticity of A TiNi25Cu25 Shape Memory Alloy Melt Spun
Ribbon, J. de Physique, submitted and to be presented in ICOMAT'02, Helsinki, Finland.
38. Xie ZL, Y Liu and E Stach (2002). In-Situ TEM Study of the Shape Recovery Process in
Predeformed NiTi Shape Memory Alloy, J. de Physique, submitted and to be presented in
ICOMAT'02, Helsinki, Finland.
39. A. Zeng, E. Liu, I. F.Annergren, S. N. Tan, S. Zhang, P. Hing, J. Gao, ‘EIS Capacitance
Diagnosis of Nanoporosity Effect on the Corrosion Protection of DLC Films’, Diamond and
Related Materials 11 (2002) 160-168.
40. E. Liu, J.X. Gao, A.P. Zeng, B.K. Tay, X. Shi, “Tribological Behavior of Nanocomposite
Diamondlike Carbon-Aluminum Films”, Mat. Res. Soc. Symp. Proc. Vol. 695 (2002) Materials
Research Society, L.5.10.1.
41. Jianxia Gao, Xiangrong Zhu, Weili Liu, Zhibin Zhang, Jianqing Cao, Chenglu Lin, Dezhang
Zhu, and E. Liu, 'Ferroelectricity and ferromagnetism in (Pb,La)(Ca,Ti)O3 – La0.67Sr0.33MnOx
multilayers', Applied Physics Letters 78 (2001) 11.
42. J.R. Shi, X. Shi, Z. Sun, E.Liu, B.K. Tay, and X.Z. Jin, ‘Structural and mechanical-properties
of amorphous silicon-carbon alloy films deposited by filtered cathodic vacuum arc technique’,
Int. J. Modern Phys. B, 14 (2000) p.315-320.
43. J.R. Shi, X. Shi, Z. Sun, E.Liu, B.K. Tay, and S. P. Lau, ‘Ultraviolet and visible Raman studies
of nitrogenated tetrahedral amorphous carbon films’, Thin Solid Films, 366 (2000) p.169-174.
44. D. Sheeja, B.K. Tay, S.P Lau, X. Shi, J. Shi, Y. Li, X. Ding, E. Liu, Z. Sun, ‘Characterisation of
ta-C films prepared by a two-step filtered vacuum arc deposition technique’, Surface and
Coatings Technology, Elsevier, Netherlands, 127 (2000) p.247-251.
45. E. Liu, X. Shi, H.S. Tan, L.K. Cheah, Z. Sun, B.K. Tay, and J.R. Shi, ‘The Effect of Nitrogen
on the Mechanical Properties of Tetrahedral Amorphous Carbon Films Deposited with a
Filtered Cathodic Vacuum Arc’, Surface and Coatings Technology, Elsevier, Netherlands,
120-121 (1999) p.601-606.
46. E. Liu, X. Shi, B.K. Tay, L.K. Cheah, H.S. Tan, J.R. Shi, and Z. Sun, ‘Micro-Raman
spectroscopic analysis of tetrahedral amorphous carbon films deposited under varying
conditions’, Journal of Applied Physics, USA, 86 (1999) p.6078-6083.
47. E. Liu, X. Shi, L.K. Cheah, Y.H. Hu, H.S. Tan, J.R. Shi, and B.K. Tay, ‘Electrical Behaviour of
Metal/Tetrahedral Amorphous Carbon/Metal (MSM) Structure’, Solid State Electronics,
Elsevier, Netherlands, 43 (1999) p.427-434.
48. K.L. Johnson and I. Sridhar, “Adhesion between a spherical indenter and an elastic solid with
a compliant elastic coating”, Journal of Physics D: Applied Physics, 34(5):683-689, (2001).
7.
Selected Abstracts of Key Publications
Liu Y, ZL Xie, J Van Humbeeck and L Delaey (1999). Effect of texture orientation on the
martensite deformation of NiTi shape memory alloy, Acta Materialia, 47/2, pp. 645-660.
For a cold rolled NiTi sheet, the tensile stress-strain curves show a flat stress-plateau during
tension along the rolling direction, while under tension along the transverse direction the
specimens are quickly strain-hardened and no flat stress-plateau occurred. This shows that the
deformation mechanisms of martensite twins are different when loading along different directions.
TEM observations show that, in the as-annealed condition, the major type of twins in the
martensite phase is <011> type II twins in the present material. (001) compound twins and a
small amount of (11 1 ) type I twins are also present. Deformation details of these three types of
twins under deformation along both rolling and transverse directions are different. After deforming
along the rolling direction to 6% strain, reorientation and de-twinning of the <011> type II twins
have occurred, while after deforming along the transverse direction to 6% strain, no significant
reorientation and de-twinning of <011> type II twins have been observed. In stead, a high density
of dislocations has been generated inside the <011> type II twins and de-twinning of the (001)
compound twins has been observed. A further crystallographic analysis shows that the shear
direction of each type of martensite twins relative to the loading direction is different, which may
explain the different deformation behaviour of the twins. This may also account for the
macroscopical deformation behaviour of the material.
Liu Y, ZL Xie, J Van Humbeeck, L Delaey and YN Liu (2000). On the deformation of twinned
domain in NiTi shape memory alloys, Philosophical Mag. A 80, 1935-1953.
Owing to its importance in understanding the mechanical and thermomechanical behaviors of
shape memory alloys (SMAs), the deformation mechanism of martensitic twins has been of
continuous research interest. Several deformation steps have been distinguished in accordance
with the stress-strain curves, and some explanations have been proposed based on
microstructural studies. However, various experimental observations have suggested that a
complete understanding of the macroscopic deformation behavior of the twinned martensitic NiTi
SMAs from a microscopic scale is yet to be established. The present research aims at providing a
further insight into the microstructural variations under tension within each deformation stages
and trying to correlate these changes to the observed mechanical behavior. As a result, the
understanding of the deformation behaviour of NiTi martensite under tension is refined.
Zheng QS and Y Liu (2002). Prediction of the detwinning anisotropy in textured NiTi shape
memory alloy, Philosophical Mag. A 82, 665-683.
Deformation of shape memory alloys via detwinning of thermally formed martensite twins is a
unique microstructural process, which leads to a macroscopic stress-plateau in the stress-strain
curves. Since this type of deformation mechanism involves insignificantly the dislocation
processes, the original shape of the shape memory alloys can be partially or even fully recovered
upon subsequent heating to a critical temperature. The response of twinned domains under
stresses plays a critical role in the anisotropy of both the mechanical (stress-strain curve) and the
thermomechanical (stress-strain-temperature curve) behavior of textured shape memory alloys.
Recent results (Acta Mater. 1999, 47, 645) have shown that the relation between the shear
direction of texturally distributed martensite twins and the loading direction plays a critical role in
the anisotropy of both microscopic and macroscopic deformation processes. Based on this
observation, the present research is to analyze the orientation-dependence of the detwinning
process from a crystallographic approach and using mechanics of heterogeneous materials. The
obtained results are found to agree with the experimental observations. Specifically, for a NiTi
sheet with given textures, the predicted response of two types of martensite twins, namely, <011>
type II and (001) compound twins as a function of loading direction, agrees well with the major
features of experimental observations.
Sam Zhang , Xianting Zeng, Zhenggui Tang, Ming Jen Tan, Exploring the antisticking properties
of solid lubricant thin films in transfer molding, International Journal of Modern Physics B, 16
(6&7) 2002, pp. 1080-1085.
Abstract
In the plastic molding industry, plastic parts like pager and handphone cases, plastic
containers, etc. are formed in a mold by applying temperature and pressure. The transfer
molding is the standard workhorse for the electronics industry. Although the transfer
molding is widely used, it is far from being optimized. Mold sticking is a serious practical
problem in this industry. A solution to the problem is to apply mold-releasing agents on
the mold to act as a lubricant layer between the plastic and the mold. This easily results
in stains and degraded surface finish. This paper investigates the effectiveness of solid
thin films on reducing the adhesion between polymer and mold steel of different surface
roughness. WS2, MoS2, and DLC coatings are deposited on test surfaces via unbalanced
magnetron sputtering before polymer blocks are molded on and pulled apart using an
Instron Machine. The force required to separate the plastic part and the mold steel is
used as an indication of the stickiness. After the separation, the coating surface is also
examined under microscope for stains and polymer residues. The coatings are
characterized using Raman spectroscopy and contact angle measurements. Generally,
the stickiness increases with initial surface roughness for all coatings. Initial test indicates
that the DLC coating has the highest contact angle with water (100°) and the best antisticking properties among the samples tested, and could reduce the stickiness by 80% as
compared to bare steel.
YQ Fu, HJ Du and S Zhang, Curvature method as a tool to evaluate shape memory effects for
TiNiCu thin films,SURFACE ENGINEERING: SCIENCE AND TECHNOLOGY II, Edited by: Ashok
Kumar, Yip-Wah Chung, John J. Moore, Gary L. Doll, Kyoshi Yatsui, D.S. Misra, Feb 2002, pp
293-303.
Abstract
TiNiCu films were prepared by co-sputtering of a Ti55Ni45 target with a separated Cu target.
Curvature method was used to measure residual stress and evaluate shape memory effects.
Results showed that for samples deposited at room temperature, large tensile stress was found in
the deposited films. Post-annealing of the above samples at 923 K for 1 hour could significantly
reduce the residual stress. The residual stress of samples deposited at 723 K was quite low.
Upon heating, TiNiCu films generated large tensile stress when transforming from martensite to
austenite, whereas during cooling, the stress relaxed significantly when the films transformed
back to the ductile martensite phase. Effects of film thickness, heating rate, annealing process
and cyclic heating/cooling process on martensite phase transformation were investigated.
Zeng Xianting, Sam Zhang, L. S. Tan, Multilayered (Ti, Al) Ceramic Coating for High Speed
Machining Applications, J. Vac. Sci. Technol. A, Vol. 19, No. 4, Jul/Aug 2001 pp. 1919-1922.
Abstract
A multilayered (Ti, Al) ceramic hard coating was deposited on tunsten-carbide ball-nose end mills
for high-speed machining using an unbalanced magnetron-sputtering system. The process
parameter dependence of the coating properties was studied. X-ray diffractometry, x-ray
photoelectron spectroscopy, nanoindentation, and scratch tests were used to characterize the
structural, compositional, and mechanical properties of the coatings. High hardness, up to 40
GPa; good adhesion strength, up to 100 N in scratch critical load; and high-oxidation resistance
were achieved, leading to excellent performance in high-speed milling on hardened tool steel at a
speed of 260 m/min. The results show that the tool life with this coating is improved by a factor of
4 or better under the testing conditions used compared to the uncoated tools. The surface finish
of the machined steel achieved with this coating is also significantly better.
S. Zhang, H. Xie, X.T. Zeng and P. Hing: Residual Stress Characterization of Diamond-like
Carbon Coatings by X-ray Diffraction Method, Surface and Coatings Technology, 1999, Vol. 122
pp. 219-224
Abstract
This paper presents residual stress measurements of amorphous diamond-like carbon (DLC)
coatings obtained by studying the stress conditions of the substrate surface layer immediately
adjacent to the coating via X-ray diffraction ( XRD) with a thin film attachment. In such a set-up,
the incidence angle a at which the primary beam strikes the specimen is fixed at a glancing angle
(2° in our experiments) relative to the sample surface while the detector rotates to collect the
diffracted X-rays. The amorphous carbon coatings were deposited on single-crystal silicon wafers
and on polycrystalline KBr substrates in an unbalanced magnetron sputtering system. The effects
of substrate material and deposition parameters on the internal stresses of the coatings are
discussed in detail. XRD with thin film attachment provides a new and more precise way to
determine the residual stresses in amorphous coatings. Increasing the relative nitrogen flow
reduces the compressive stress level of the hydrogenated amorphous carbon coatings. Under the
experimental conditions studied, higher substrate bias power and sputter power densities both
increased the compressive stress level. © 1999 Elsevier Science S.A. All rights reserved.
S. Zhang and H. Xie: Improving Adhesion of Amorphous Carbon on Cemented Carbide Through
Plasma Cleaning, Surface and Coatings Technology, (113)1-2 (1999) pp. 120-125.
Abstract
Diamond-like amorphous carbon coatings 1 µm thick were deposited onto cemented carbide
substrates by magnetron sputtering of a graphite target in argon under different substrate bias
powers and chamber pressures. Scratch testing was used to assess the coating adhesion. X-ray
photoelectron spectroscopy depth profiling was employed to quantify cobalt loss at the substrate
surface as a function of bias power during plasma cleaning. It was found that under the same
deposition conditions, the scratch adhesion strength increased with the bias power during plasma
cleaning and reached a maximum at about 200 W or -210 V in terms of induced voltage. After
that, further increases in bias power led to a decrease in adhesion. The increase was attributed to
better cleaning of the sample surface and removal of surface cobalt while the decrease in
adhesion was linked to an increase in residual stress which resulted in a different failure
mechanism. Thus, an increase in the deposition power density, and therefore more severe ion
bombardment, led to higher residual stress and lower adhesion. Under constant bias and
deposition power, however, it was established that below a certain minimum chamber pressure
spontaneous coating detachment occurs.
8.
Contact Persons & Web-site address
The Thin Films SRP welcomes collaboration with industries, research entities and researchers
home and abroad. Please direct queries to Associate Professor Sam Zhang, Director of Thin
Films SRP, School of MPE at 6790 4400 or msyzhang@ntu.edu.sg. Details of the program
information and its research activities and capabilities can be found at its website at
http://www.ntu.edu.sg/MPE/Research/Programmes/Thinfilms/