Current Research Activities

 (Updated Oct 6, 2015)
The research in our group mainly focuses on using advanced Scanning Probe Microscopy (SPM) techniques to characterize the coupling phenomena of various functional properties in 
advanced materials, such as energy storage materials, transitional metal oxide materials,   piezo-/ferroelectric materials, or biomaterials. 

For these studies, we are mainly using the advanced SPM techniques, including, Piezoresponse Force Microscopy (PFM), Spectroscopy Switching PFM, Kelvin Probe Force Microscopy 
(KPFM), Conductive Atomic Force Microscopy (c-AFM), Electrochemical Strain Microscopy (ESM); Electrochemical Atomic Force Microscopy (EC-AFM), Contact Resonance Atomic 
Force Microscopy (CR-AFM) or Atomic Force Acountic Microscopy (AFAM) and so on, in such a way, we can perform fundamental studies of various functional properties such as resistive 
switching, polarization switching, local I-V characteristics, ferroelectric hysteresis loop, ion and electron conductivity in batteries, local elasticity and viscoelasticity etc.

Following poster shows what we are doing at NUS:

Coupling properties and SPM techniques

Current on-going projects are:  
1. Multifunctional Properties of Oxide Materials
This research is to use the state-of-arts Scanning Probe Microscopy techniques, including Piezoresponse Force Microscopy (PFM); Kelvin Probe Force Microscopy (KPFM); Conductive 
AFM (c-AFM); Contact Resonance Force Microscopy (CR-FM) and Magnetic Force Microscopy (MFM) to study the multifunctional properties: including electrical, magnetic and mechanical 
coupling phenomena, in various oxide materials as well as ferroelectric, piezoelectric and multiferroics materials and thin films, including doped and undoped ZnO thin films, doped and 
undoped BiFeO3 thin films, and PVDF thin films, TiOthin films as well as patterned films. 

This project was initially started with Dr. Wong Meng Fei on characterization of ZnO thin films using PFM and KPFM techniques, the project was then continued by Dr. Amit Kumar on 
studying the functionality of ZnO films. It was further continued by Dr. Xiao Juanxiu on ZnO and NiO thin films, as well as Ms. Lu Wanheng on TiO2 and VO2 thin films. From August 2016,
Ms. Yu Bingxue joint the group to continue this project.
Some Recent Publications:
1. J.X.Xiao, T.S.Herng, J.Ding, K.Y.Zeng, "Polarization rotation in copper doped zinc oxide (ZnO:Cu) thin films studied by Piezoresponse Force MIcroscopy (PFM) techniques"
    Acta Materialia, 123, 2017, 394-403. 
2. W.H.Lu, L.-M. Wong, S.J.Wang, K.Y.Zeng, "Correlation of electrochemical effects and resistive switching in TiO2 thin films"
     Journal of The Electrochemical Society, 163, 2016, E147-153.
3. J.X.Xiao, K.Y.Zeng, L.-M.Wong, S.J.Wang, "Correlation of the resistive switching and polarization switching in zinc oxide thin films using scanning probe microscopy techniques".
     Journal of Materials Research, 30, 2015, 3431-3442.
4.  J.X.Xiao, W.L.Ong, Z.M.Guo, G.W.Ho, K.Y.Zemg, "Resistive switching and polarization reversal of hydrothermal-method-growth undoped zinc oxide nanorods by using scannning probe microscopy techniques".
     ACS Applied Materials & Interfaces, 7, (2015), 11412-11422.
5.  Y.M.Du, A.Kumar, H.Pan, K.Y.Zeng, S.J.Wang, P.Yang, A.T.S.Wee, "The resisitve switching in TiO2 films studied by conductive atomic force microscopy and Kelvin probe force microscopy"
     AIP Advances, 3, (2013), 082107.
6.  K.Sun, B.M.Zhao, V.Murugesan, A.Kumar, K.Y.Zeng, J.Subbiah, W.W.H.Wong, D.J.Jones, J.Y.Ouyang, "High-performance polymer solar cells wioth a conjugated
     zwitterion by solution processing or thermal deposition as the electron-collection interlayer", Journal of Materials Chemistry, 22, (2012), 24155.
7.  A.Kumar, T.S.Herng, K.Y.Zeng, J.Ding, "Bipolar charge storage characteristics in copper and cobalt co-doped Zinc Oxide (ZnO) thin film", ACS Applied Materials &
     Interfaces, 4, (2012), 5276-5280.
8.  T.S.Herng, A.Kumar, C.S.Ong, Y.P.Feng, Y.H.Lu, K.Y.Zeng, J.Ding, "Investigation of the non-volatile resistance change in noncentrosymmetric compounds".
     Scientific Reports, 2: (2012), 587.
9 Q.Q.Ke, X.J.Lou, H.Yang, A. Kumar, K.Y.Zeng, J.Wang, "Negative capacitance induced by redistribution of oxygen vacancies in the fatigued BiFeO3 based thin film".
     Applied Physics Letters, 101, (2012), 022904.
10 K.Sun, B.M.Zhao, A.Kumar, K.Y.Zeng, J.Y.Ouyang, "Highly-efficient inverted polymer solar cells with indium tin oxide modified with solution-processed zwitterions as the transparent cathode",
      ACS APPLIED MATERIALS AND INTERFACES, 4, (2012), 2009-2017.
11.  S.T.Chen, X.Li, K.Yao, F.E.H.Tay, A. Kumar, K.Y.Zeng, "Self-polarized ferroelectric PVDF homopolymer ultra-thin films derived from Langmuir-Blodgett deposition".
      POLYMER, 53, (2012), 1404-1408. DOI: 10.1016/j.polymer.2012.01.058.
12.  Q.Q.Ke. A.Kumar, X.J.Lou, K.Y.Zeng, J.Wang, "Origin of the enhanced polarization in La and Mg co-substituted BiFeO3 thin film during the fatigue process ".
       APPLIED PHYSICS LETTERS, 100, (2012), 042902.
13. Q.Q.Ke. A.Kumar, X.J.Lou, K.Y.Zeng, J.Wang, "Oxygen-vacancy-mediated negative differential resistance in La and Mg co-substituted BiFeO3 thin film".
      JOURNAL OF APPLIED PHYSICS, 110, (2011), 124102.
14A.Kumar, F.Yan, K.Y.Zeng, and L.Lu, "Electric, magnetic and mechanical coupling effects on ferroelectric properties and surface potential of BiFeO3 thin film".
      FUNCTIONAL MATERIALS LETTERS - 4, (2011), 91-95.
15. T.S.Herng, M.F.Wong, D.C.Qi, J.B.Yi, A.Kumar, A.Huang, F.C.Kartawidjaja, S.Smadici, P.Abbamonte, C.Sanchez-Hanke, S.Shannigrahi, J.M.Xue, J.Wang, Y.P.Feng,
      A.Rusydi, K.Y.Zeng and J.Ding, "Mutual ferromagnetic-ferroelectric coupling in multiferroic copper doped ZnO",
      ADVANCED MATERIALS - 23, (2011), 1635-1640.
16. M.F.Wong, T.S.Herng, Z.Zhang, K.Y.Zeng, and J.Ding, "Stable bipolar surface potential behavior of copper-doped zinc oxide films studied by Kelvin probe force microscopy",
      APPLIED PHYSICS LETTERS, 97, (2010), 232103.

Ph.D Thesis:
1. Xiao Juanxiu, "Characterization of the Multifunctional Properties of Zinc Oxide based Materials by Scanning Probe Microscopy Techniques"Doctor of Philosophy.
    Department of Mechanical Engineering, NUS, 2015.
2. Amit Kumar: "Application of biased scanning probe microscopy techniques for multifunctional characterization of BiFeOand ZnO thin films", Doctor of Philosophy,
    Department of Mechanical Engineering, NUS, 2012. 

2. Reliability and properties of thin film solid state battery.
This research is to study the reliability and mechanical properties of Li-ion rechargable thin film solide state battery, especially the effects of charging/discharging cycles, using biased 
scanning probe microscopy techniques, including Electrostatic Force Microscopy (EFM), Kelvin Probe Force Microscopy and the newly-developed Electrochemical Strain Microscopy 

This project was started with Dr. Zhu Jing on using nanoindentation to study the mechanical properties of electrode materials for Li-ion battery. Following that, Dr. Zhu Jing was conducted 
the in-situ characterization of electrode materials by using Scanning Probe Microscopy techniques. This project was continued by Dr. Yang Shan on study of diffusion and deformation of 
Li-rich thin films, and Dr. Li Tao on study the stiffness, property, and composition changes in Li-rich nanoparticles. Mr. Wang Zhongting also join this project to provide the detail study by 
computer simulations. 
Some Recent Publications:
1. S.Yang, B.G.Yan, L.Lu, K.Y.Zeng, "Grain boundary effects on Li-ion diffusion in a Li1.2Co0.13Ni0.13Mn0.54O2 thin film cathode studied by scanning probe microscopy techniques".
    RSC ADVANCES, 6, (2016), 94000-94009. 
2. S.Yang, B.G.Yan, T.Li, J.Zhu, L.Lu, K.Y.Zeng, "In-situ studies of lithium-ion diffusion in a lithium-rich thin film cathode by scanning probe microscopy techniques",
    PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 17, (2015), 22235--22242.
3. T.Li, B.H.Song, L.Lu, K.Y.Zeng, "Voltage induced electrochemical reactions in the single lithium-rich-oxide nanoparticles".
    PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 17, (2015), 10257-20264.2. 
4. J.Zhu, K.Y.Zeng, and L.Lu, "Cycling effect on morphological and interfacial properties of RuO2 anode film in thin film lithium ion microbatteries",
    METALLURGICAL AND MATERIALS TRANSACTION A - Special issue: Materials For Energy Applications, 44A, (2013), S26-S34. DOI: 10.1007/s11661-011-0847-0.
5. J.Zhu, L.Lu, K.Y.Zeng, "Nanoscale mapping of Li-ion diffusion in cathode within all-solid-state Li-ion battery by advanced Scanning Probe Microscopy Techniques".
    ACS NANO, 7, (2013), 1666-1675. DOI: 10.1021/nn305648j.
6. J.Zhu, K.Y.Zeng, L.Lu, "Cycling effects on interfacial reliability of TiO2 anode film in thin film lithium-ion microbatteries",
    JOURNAL OF SOLID STATE ELECTROCHEMISTRY, 16, (2012), 1877 - 1881, DOI:10.1007/s10008-011-1545-y.
7. J.Zhu, J.K.Feng, L.Lu and K.Y.Zeng, "In-situ study of topography, phase and volume changes of TiO2 anode in all-solid-state thin film Li-ion battery by biased scanning probe microscopy".
    JOURNAL OF POWER SOURCES, 197, (2012), 224-230.
8. J.Zhu, K.Y.Zeng, and L.Lu, "In-situ nanoscale mapping of surface potential in all-solid-state thin film Li-ion battery using Kelvin probe force microscopy".
    JOURNAL OF APPLIED PHYSICS, 111, (2012), 063723,
9. J.Zhu, K.Y.Zeng, L.Lu, "Cycling effects on surface morphology, nanomechanical and interfacial reliability of LiMn2O4 cathode in thin film lithium ion batteries".
    ELECTROCHIMICA ACTA, 68, (2012), 52-59. DOI: 10.1016/j.electacta.2012.02.032.
10. J.Zhu, K.B.Yeap, K.Y.Zeng, and L.Lu, "Nanomechanical characterization of sputtered RuO2 thin film on silicon substrate for solid state electronic devices",
    THIN SOLID FILMS, 519, (2011), 1914 - 1922
Ph.D Thesis:
1. Yang Shan: Nanoscale Characterization of Thin Film Li1.2Mn0.54Ni0.13Co0.13O2 Cathode in Lithium Ion Batteries by using Scanning Probe Microscopy Techniques, Doctor of Philosophy, Department of Mechanical
    Engineering, NUS (2016)
2. Zhu Jing: Reliability and Aging Mechanisms of All-Solid-State Thin Film Lithium Ion Microbatteries, Doctor of Philosophy, Department of Mechanical Engineering, NUS (2013).
3. Biopiezoelectricity and Bioferroelectricity.
This project is to study the electromechanical coupling effects in seashell as well as other biological systems and to correlate the electromechanical coupling phenomena with the excellent 
mechanical properties, such as strength and toughness, of the seashells, using Piezoresponse Force Microscopy (PFM) and Kelvin Probe Force Microscopy (KPFM), as well as the Band 
Excitation (BE) Image and Analysis technique.
This project was started by Dr. Li Tao to study the electromechanical coupling phenomena in Abalone shell and clam shell, and Dr. Li Tao also conducted the study on bone samples from
oim/oim and wild mouse modes. This project was continued by Ms. Sun Yao on various bone samples from different mouse modes. 
Some Recent Publications:
1. T.Li, S.-W.Chang, N.Rodriguez-Florez, M.J.Buehler, S.Shefelbine, M.Dao, K.Y.Zeng, "Studies of chain substitution caused sub-fibril level differences in stiffness and ultrastructure of wildtype and oim/oim collagen fibers using 
    multifrequency-AFM and molecular modeling".
    BIOMATERIALS, 107 (2016), 15-22
2. T.Li and K.Y.Zeng, "Nanoscale elasticity mapping of micro-constituents of abalone shell by band excitation-contact resonance force microscopy".
     NANOSCALE, 6, (2014), 2177-2185.
3T.Li and K.Y.Zeng, "Nanoscale piezoelectric and ferroelectric behaviors of seashell by piezoresponse force microscopy",
    JOURNAL OF APPLIED PHYSICS, 113, (2013), 187202.
4. T.Li, L.Chen and K.Y.Zeng, "In-situ studies of nanoscale electromechanical behavior of nacre under flexural stresses by band excitation PFM",
    ACTA BIOMATERIALIA, 9, (2013), 5903-5912.
5. T.Li and K.Y.Zeng, "Nano-hierarchical structure and electromechanical coupling properties of calmshell", DOI: 10.1016/j/jsb.2012.06.004.
    JOURNAL OF STRUCTURE BIOLOGY, 180, (2012), 73-83.
6. T.Li and K.Y.Zeng, "Piezoelectric properties and surface potential of Green Abalone shell studied by Scanning Probe Microscopy techniques",
    ACTA MATERIALIA, 59, (2011), 3667-3679.
Ph.D Thesis:
1. Li Tao: Nanostructure, biopiezoelectric and Bioferroelectric Behaviors of Mollusk Shells studied by Scanning Probe Microscopy Techniques. Doctor of PhilosophyDepartment of Mechanical Engineering, NUS (2013).
4. Domain structure and dynamics of piezoelectric single crystal materials.
This research area is to characterize nanosctructure domain and domain dynamics of PZN-PT piezoelectric single crystals. The effects of in-plane and out-plane poling are also studied. 
Piezo-response Force Microscopy (PFM) will be used to study the piezoelectric properties before and after poling, as well as the domain structure and domain switch mechanisms in this 
materials. This project was started by Dr. Wang Meng Fei on the PZN-PT samples. The project is now continued by Ms. Wang Hongli. 

Some Recent Publications:
1. H.L.Wang, K.Y.Zeng, "Domain structure, local surface potential distribution and relaxation of Pb(Zn1/3Nb2/3)O3-9%PbTiO3 (PZN-PT) single crystals"
    Journal of Materiomics, 2, 2016, 309-315.

Ph.D Thesis:
1. Wong Meng Fei, Micromechanical Properties and Domain Structures of PZN-PT Piezoelectric Single Crystals, Doctor of Philosophy,.Department of Mechanical Engineering, NUS (2011).