Dr. Sang Pham

Profile

I joined the University of Leeds in February 2022 as a Postdoctoral Research Fellow working with Dr. Sean Collins on a project aimed at linking atomic structure and optoelectronic properties at defects and interfaces in polymer, small organic molecule, and hybrid semiconductors under active investigation for optoelectronic applications. I work mainly at the Leeds Electron Microscopy and Spectroscopy Centre (LEMAS) in the School of Chemical and Process Engineering and the chemical synthesis lab in the School of Chemistry. I also often use microscopy facilities at SuperSTEM (the EPSRC National Research Facility for Advanced Electron Microscopy), and the Electron Physical Sciences Imaging Centre (ePSIC) at the Diamond Light Source. 

I completed my undergraduate degree in 2017 at the Ho Chi Minh City University of Technology (HCMUT) in Vietnam, pursuing a degree in chemical engineering focusing on petroleum chemical processes. I then moved to Australia for my PhD at the University of Wollongong in the School of Mechanical, Materials, Mechatronic and Biomedical Engineering where I was awarded a PhD degree with Examiners’ Commendation for an Outstanding Thesis on February 2022. I was nominated as a school nominee for the best 2021 PhD thesis of the Faculty of Engineering and Information Sciences, University of Wollongong. During my PhD, I developed a multi-functional microcapsule that significantly improves the lubrication and anti-oxidation performances of melt lubricants under high-temperature steel manufacturing conditions. I also led the development of the correlative technique combining the advantages of in-situ TEM mechanical compression, aberration-corrected STEM, and in-situ TEM and TOF-SIMS heating to elucidate the structure-property relationship of materials from the nanoscale to the macroscale, especially the effect of nanoscale structural transformation at high temperatures on the mechanical properties of the hierarchical structures (e.g. multi-layered tribofilms and double-shell microcapsules).

In parallel with the position at the University of Leeds, I am holding the Visiting Honorary Research Fellow at the University of Wollongong, Australia, carrying out PhD supervision and collaborative research into the development of advanced surface analytical technique – Nanoindentation/Raman/Heating – to unravel the tribology enigma of the Carbon-based tribofilms under practical tribological conditions.

As an international researcher, I value equality and diversity and I am committed to making research environments more inclusive for those under-represented groups. 

Responsibilities

• Academic Research Staff

Research interests

Electron Microscopy of Structural Defects and Interfaces in Organic Semiconductors

Organic semiconductors (OSCs) are core components in advanced organic light-emitting diodes (OLEDs), organic photovoltaics, organic transistors, organic solar cells, and organic sensors. The promise of low-cost manufacturing, ease of processing, mechanical flexibility, and versatility in chemical synthesis make organic semiconductors very attractive for future electronic and optoelectronic devices. The key scientific challenges of OSCs are from materials’ low charge carrier mobility which depends intrinsically on different factors. Structural dislocations and defects, where atomic structure and electronic structure change significantly due to a disruption in the periodicity of the crystal structure, serve as trapping sites that hamper the charge transport and cause the interfacial energetic disorder in planar heterojunction devices. Yet direct structural characterization of these defects and their spatial distribution and variation at the nanoscale are limited due to the dose-damage constraints of OSCs under conventional electron microscopy conditions. As a result, the mechanisms by which particular defect types and molecular packing disorders as well as interface structures hinder charge transport remain ambiguous. The aim of my research is to link the structure and charge transport property at the nanoscale in these types of materials by advanced low-dose electron microscopy to elucidate which defects or dislocations play a major role in controlling charge transport. This will advance the fundamentals of photo-physic at the nanoscale in OSCs while paving a pathway to efficiently control the defects/dislocations for next-generation designs of advanced materials technologies. 

Tribology Mechanisms of the High-Performance Tribofilms

Extreme pressure (EP) lubricant additives are one of the important additives in fully formulated oil-based lubricants which helps to prevent excessive wear of the sliding components under severe lubrication conditions. Tribochemical reactions between EP additives and sliding surfaces often lead to the formation of the solid “tribofilms” which can prevent direct asperities contact between the sliding surfaces, thus, reducing damages from friction and wear. These additives become more important for the wear protection of critical components in modern engines or transmission of modern vehicles during the multiple stops/starts process due to the preference for using low-viscosity oil-based lubricants. Reducing friction and wear of the moving machinery components in transportation vehicles can result in considerable energy and material savings. Recent emission legislation requires the development of new high-performance tribofilm systems to partially/completely replace conventional zinc dialkyl dithiophosphate (ZDDP) tribofilm. Many recent efforts have sought to develop a strategy to form high-performance Carbon-based tribofilms, one of several promising candidates, on the sliding surfaces of modern vehicles. Unlike ZDDP tribofilms underpinned by decades of research on the mechanisms underlying the growth and anti-wear properties, research on fundamental mechanisms of the new generation of high-performance tribofilms, e.g. Carbon-based tribofilms, is still immature. Many questions remain unresolved for these tribofilms regarding the growth kinetics, formation mechanisms, dynamic structural changes during sliding, and the bonding strength of the multilayered tribofilms on different substrates. My research seeks to answer these questions by the combination of advanced electron microscopy (i.e. 4D-STEM) and advanced surface analytical tools (i.e. Nanoindentation/Raman/Heating multi-modal correlative system). The findings are expected to unpack the microscopic mechanisms of these high-performance tribofilms to improve tribofilm design for future vehicles. 

Qualifications

• PhD (Material, Mechanical, and Manufacturing Engineering)
• B. Eng. Chemical Engineering

Professional memberships

• Member of Bragg Centre for Materials Research