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 as-

deposited 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 ultra-

low 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 micro-to-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

15 Å

(001)

(100)

(101)

b

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.

-30 0 30 60 90 120

0.0

0.3

0.6

0.9

1.2

1.5(a)

Af

As

Ms

Af

As

Ms

Rf

Rs

Deposited on (100) Si Deposited on SiO2

layer on top of (100) Si

Temperature, C 0 2 4 6 8 10 12

0

150

300

450

600

750(b)

TiNi25Cu25 melt-spun ribbon

tested at 123oC

0 3 6 9 12

0

1

2

3

Deformation Strain, %

Re

sid

ua

l Str

ain

, %

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 non-dimensional 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 rate-dependent 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 Gold-

plated 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 268-273.

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 (111 ) 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 anti-sticking 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/