Defu

Job CategoryMaterials Engineering
Location Anywhere in the U.S.
Authorized to Work Here Yes

Experience
 Skilled at general materials characterization such as XRD, EDS, SEM and TEM;
 Skilled at electrochemical characterization, such as CV, EQCM;
 Skilled at materials property characterization, such as magnetic, electrical and mechanical properties characterization;
Education
 Sep 2008- present Ph.D. candidate (5th year), Department of Materials Science
and Engineering (MSE), University of Virginia.
Advisor: Prof. Giovanni Zangari
 Jul 2008 Bachelor of Engineering, MSE (Ranking No.1 out of 91 students),
Harbin Institute of Technology (HIT), China
Advisor: Prof. Dechang Jia
Thesis on inorganic and ceramic materials: Microstructure and
mechanical properties of Cf /α-Al2O3p reinforced geopolymer matrix
composite.
Current research
o Electroplating and characterization of various alloy thin film systems: Au-Ni, Cu-Au, Cu-In, Ag-Ni, Ag-Cu, Fe-Te, Ni-Fe, Ni-Fe-Pt, Ni-Mn, Cu-Mn and Cu-Zn-Sn-S, specially Cu, Au, Ag and their alloys, focusing on magnetic, electrical, mechanical and catalytic properties;
o Fundamental study on the thermodynamics and kinetics of electroplating of metals and alloys;
o Deposition by plating and testing of thin film of metals and alloys;
o Metal coordination with various organic agents or additives and its effect on thin film plating.
Techniques
 Scanning Electron Microscope (SEM); Energy Dispersive X-Ray Spectroscopy (EDS)
 Transmission Electron Microscope (TEM), High Resolution TEM (HRTEM) and
corresponding sample preparation skills (Ion Milling, etc.);
 X-Ray Diffraction (XRD);
 Vibrating Sample Magnetometer (VSM);
 Focused Ion Beam (FIB);
 Mechanical properties measurements, such as tensile strength, bending strength, hardness;
 Optical profilometer; four-point probe resistivity measurement;
 Potentiostat-galvanostat;
 Electrochemical Impedance Spectroscopy (EIS);
 Electrochemical Quartz Crystal Microbalance (EQCM);
 Atomic Force Microscope (AFM);
 Data analysis softwares: Origin; Matlab; Mathematica.

Selected Project Experience
 Internship in IBM (T. J. Watson Center)
May-Aug2011, Advanced Metallization and Plating Processes: electroplating of Cu interconnects with focus on additive effects, and superfilling of Invar alloys.
 Fe-Pt (Four years of electroplating of magnetic Fe-Pt alloys)
Developing a novel alkaline solution for electroplatingof Fe-Pt magnetic alloys: 1) for the commonly used solutions usually with acidic pH using Pt chloride and Fe2+ chloride or sulfate, high impurity (oxygen) content due to the interfacial pH increase as a result of hydrogen generation, and rough or porous morphology due to the diffusion deposition of Pt, in the deposited films are observed; 2) we solved the morphology issue by using Pt complexing to bring closer the deposition potentials of Pt and Fe, so that Pt is no longer under diffusion deposition; 3) to reduce the oxygen in the deposits, we complexed Fe3+ using organics (citrate + glycine), which also serve as buffers for the pH change; 4) the use of Fe3+ instead of Fe2+ is good for practical applications due to the fact that Fe2+ tends to oxidize to Fe3+ or else, making the Fe2+ solution unstable without long duration; 5) we obtained this alkaline solution with more than 6 months of stability, comparing with about 2 days for the acidic solutions with Fe2+ by others; 6) we showed in the deposits the oxygen content was reduced to less than 6at.% comparing with 30at.% from acidic solutions; 7) smooth morphology in the compact deposits were achieved confirmed using AFM and SEM; 8) we were able to get the phase transformation in these deposits at much lower annealing temperatures, which is beneficial for applications, especially for patterning deposition that cannot stand high temperatures; 9) the phase transformed deposits showed very high coercivity, making them promising for hard magnetic material applications; 10) we found that phase transformation occurs at lower temperatures for thicker films; 11) we also found that magnetic properties can be tuned by making multilayer structures with various thicknesses and compositions, and this can be easily done just by setting different deposition current densities in a single experiment; 12) TEM and HRTEM were used to better understand the microstructure and crystal structure of the deposits as-deposited and after annealing.
 Ag-Ni (A collaboration project with TE Connectivity (Harrisburg, PA)).
Developing a complexing solution for electroplating of Ag-Ni alloys, focusing on the electrical property of Ag rich Ag-Ni alloys for electrical contacts: 1) currently, the majority of electrical contacts are Au rich hard gold alloys with Co/ Ni; 2) the fact that gold price is stably high makes it more and more cost ineffective to use Au alloys; 3) Ag rich Ag alloys with Co/Ni has been proposed as substitution; 4) cyanide solutions are usually used for the electroplating of Ag-Ni alloys with reasonable stability and good morphology, however they are environmentally unacceptable due to the high toxicity of cyanide; 5) alternative complexing agents are needed, and here we selected thiourea; 6) we showed that thiourea can bring closer the deposition of Ag and Ni predicted by chemical stability calculation and confirmed by experimental data, which is highly desirable to obtain deposits with good morphology; 7) solutions with appropriate chemicals are stable more than three weeks; 8) Ag bright and smooth deposits were obtained for Ag rich alloys; 9) TEM and HRTEM showed that the grain sizes of the Ag rich alloys are ~20nm, much lower than pure Ag usually ~1m, and the reduction in grain size is very important to obtain reasonable wear resistance and hardness due to the fact that the hardening mechanism for such alloys is a grain size effect; 10) phase structure of the deposits with increasing Ni content was resolved by XRD, TEM nad HRTEM, and it was observed that low Ni content alloys with Ag, while phase separation occurs with high Ni contents.
 Au-Ni (A typical system for metastable solid solutions and phase separation)
Microstructural analysis and theoretical study on the metastable Au-Ni solid solutions:
1) Thermodynamic equilibrium structures for Au-Ni at room temperature are separate phases of Au and Ni; 2) electroplating by tuning the deposition conditions far away from equilibrium was shown to obtain metastable phases; 3) we found in the deposits in our study the existence of metastable solid solutions by XRD, confirmed by performing TEM, HRTEM and X-ray Photoelectron spectroscopy (XPS); 4) we also found that micr...

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