I conducted this research as a PhD candidate at the University of Victoria, British Columbia. Beyond contributing valuable insights to the field of surface science, this project allowed me to refine my expertise in instrumentation, data analysis, and scientific communication.
This study challenges the conventional approach in molecular surface analysis by demonstrating that Sum-Frequency Generation (SFG) spectroscopy can extract electronic structure information without requiring molecular orientation data. Key findings showed that interfacial electronic structures differ from bulk solutions, impacting environmental science, pharmaceuticals, and materials engineering.
When studying molecules at surfaces—such as those found in biological membranes, industrial coatings, or environmental interfaces—scientists typically rely on techniques that assume a fixed molecular orientation. This poses a significant challenge because:
Our study challenges the conventional approach by showing that we can extract critical molecular information from nonlinear optical signals without knowing molecular orientation. To demonstrate this, we investigated p-cyanophenol at the air-water interface, using SFG spectroscopy and Raman depolarization ratio measurements.
10 September, 2021 - Ongoing
Research
Research Assistant
Novel technique to analyze surfaces
The figure shows the basic principle of Sum-Frequency Generation(SFG). Sum-Frequency Generation spectroscopy is a nonlinear optical technique where a fixed visible laser and a tunable infrared (IR) laser interact at a surface, generating a sum-frequency signal that reveals molecular structure and orientation. Sum Frequency Generation (SFG) occurs only when the material's centro-symmetry is broken.
To understand how we solved this problem, we need to look at how light interacts with molecules at interfaces.
SFG spectroscopy is a nonlinear optical technique used to study surfaces and interfaces. It works by:
To test our hypothesis, we designed an experiment where we could separate molecular orientation effects from electronic structure measurements.
We prepared a solution of p-cyanophenol (75 mM) in water and studied its behavior at the air-water interface.
We performed Raman depolarization ratio measurements to analyze the molecular polarizability. We then used SFG spectroscopy with three different laser polarization schemes (SPS, SSP, PPP). This allowed us to isolate signals related to molecular environment and electronic structure while removing orientation-dependent effects.
Using established optical models, we analyzed how refractive index variations at the surface influenced the measurements. We applied a surface volume mixing model to determine how molecular interactions affected electronic properties.
Our results demonstrated that we could successfully extract electronic structure information without needing molecular orientation data.
By removing the need for molecular orientation analysis, our approach can revolutionize several scientific fields.
Our findings can be used to accurately study protein interactions at interfaces, investigate water structure at biological and environmental surfaces, and analyze molecular behavior in coatings, membranes, and nanomaterials.
Our work opens new doors for future research. Next steps include:
Images courtesy: macrovector & fatmawatilauda
