Philip N. H. Nakashima
PhD Projects Offered
Metallic bonding in noble metals
What gives noble metals their “nobility” (low reactivity)? Chemical reactions involved the breakage and reformation of bonds between atoms. Quantitative convergent-beam electron diffraction (QCBED) will be applied to silver (Ag), gold (Au) and platinum (Pt) to characterise the metallic bonds in each of these noble metals.
Metallic bonding in refractory metals
A number of metals like molybdenum (Mo), tantalum (Ta) and tungsten (W) have extremely high melting points and have very high mechanical strengths. These properties are strongly correlated and are directly determined by the nature of the metallic bonds in these metals. Quantitative convergent-beam electron diffraction (QCBED) will be applied to quantitatively characterising the bonds in each of these refractory metals.
Metallic bonding in HCP metals
Why do atoms in metals like zinc (Zn), titanium (Ti) and magnesium (Mg) arrange themselves into a hexagonal close packed (HCP) structure instead of a face centred cubic (FCC) structure? Both structures are close packed and have the same number of octahedral and tetrahedral interstices. They only differ in the arrangements of these interstices due to the …ABCABC… packing sequence in the FCC structure and …ABABAB… sequence in the HCP structure. The answer lies in the nature of the metallic bonds. Quantitative convergent-beam electron diffraction (QCBED) will be applied to Zn, Ti and Mg to determine whether there are features in the bonding morphology that distinguish HCP metals from FCC metals.
Atomic and electronic structure determination in nano-composite materials
Composite materials owe their desirable properties to the hybridisation that occurs between the component materials. In the context of a nanometre-sized electron probe, multi-phased materials can be equated to layered structures. This project will apply quantitative convergent-beam electron diffraction (QCBED) to probing the atomic and chemical bonding structure of precipitates embedded in alloys. A focus of this research will be the investigation of bonding across precipitate/matrix interfaces and well as within the precipitates themselves.
Scanning quantitative convergent-beam electron diffraction
Recent developments in scanning convergent-beam electron diffraction (SCBED) have led to mapping polarisation domains at the nanometre scale in ferroelectrics (see Y.T. Shao, J.M. Zuo, Acta Cryst. B 73 (2017), 708). This project aims to combine SCBED with quantitative convergent-beam electron diffraction (QCBED) to produce a hybrid technique, scanning QCBED (SQCBED). This project will focus on mapping electronic structure variations in alloy solid solutions and will involve strong collaboration with the group of Prof. J.M. Zuo at the University of Illinois at Urbana-Champaign.
Experimental verification of the electron density domain theory
Recently, the electron density domain theory (EDDT) was proposed for explaining the electronic structure origins of precipitate nucleation and growth. This project will apply quantitative convergent-beam electron diffraction (QCBED) in scanning mode to alloy solid solutions as they are being heat treated in situ in the electron microscope. In this manner, electronic structure can be measured as a function of position and time during a precipitation process.
New generation quantitative convergent-beam electron diffraction
Quantitative convergent-beam electron diffraction (QCBED) has proven to be a very accurate method for measuring electronic structure in crystalline materials. It is, however, not a mainstream technique because of its technical complexity, lack of automation and the absence of a user-friendly front end. In addition, QCBED is currently based on the refinement of Fourier coefficients of the crystal potential rather than direct refinement of the real space electrostatic potential. This project is focussed largely on computer programming and software development with the aim of automating QCBED, giving it a user-friendly interface and making it a direct quantum crystallography measurement tool.
Measuring bonding as a function of position in nano-particles
Quantitative convergent-beam electron diffraction (QCBED) is capable of measuring the morphology of chemical bonds in crystalline materials with nanometre-scale spatial selectivity. This project aims to investigate the spatial variation of interatomic bonding within nanoparticles because bonding is the primary determinant of all materials properties and thus the key to understanding the exotic properties of nanoparticles and their strong shape and size dependence. This project was proposed by Prof. Joanne Etheridge, Director of the Monash Centre for Electron Microscopy and will be co-supervised by her.
More Project Opportunities:
The projects listed above are by no means exhaustive. Here is an additional list of subjects that would make for interesting PhD research projects:
- Alternatives to electron holography for measuring the mean inner potential of materials (both crystalline and non-crystalline).
- The measurement of electron momentum redistribution due to plasmon excitation using a new technique of spectrum diffraction.
- Exploring differential techniques in electron microscopy.
- Quantitative convergent-beam electron diffraction (QCBED) using plasmon-loss energy filtered CBED patterns.
- Time- and position-resolved electron density distributions using QCBED.
- Exploring new materials characterisation techniques using electron diffraction and electron energy loss spectroscopy (EELS).
If you have any ideas or interests of your own that are related to our group’s research, then please also feel free to propose your own project.