Research Projects

Flexible Nanomembrane-Based, Thermal-Transport Biosensor for Living Cells:

Knowledge of a living cell thermal transport properties is beneficial to a plethora of applications. Designed a novel thermal transport bio-sensing technique based on GaN nanomembranes. I studied the effect of phonon-boundary scattering within gallium nitride nanomembranes on excitation-laser induced local-heating. Then, I attached these nanomembranes to different types of cells (HeLa cervical cancer, MCF-7, SK-BR-3 ductal breast cancers and MDA-MB-231 basal breast cancer) and measured the changes in their photoluminescence. Developed an analytical model to calculate the thermal transport properties of the cancer cells based on the spectral shifts within the photoluminescence emission of nanomembranes attached to them. Built COMSOL simulation models to support the experimental data. Successfully measured the thermal transport properties and differentiated between the four different cell types. (Small (2016) doi:10.1002/smll.201603080.)

Indium rich Red Emitting Indium Gallium Nitride Quantum Dots for Solid State lighting:

Indium-rich, red-light emitting InGaN LEDs, suffer from decreased internal quantum efficiency (IQE), due to the high threading dislocation density and the presence of micron-sized indium clusters. The incorporation of quantum dots increases IQE through 3D carrier localization. I determined the effect of 3D and 2D localization of carriers within indium rich (27%) InGaN QDs and their underlying wetting layer, respectively, on their photoluminescence properties. I then demonstrated how QDs exhibited a reduced thermal quenching in their temperature dependent photoluminescence emission. Finally, I used XRD data, accompanied with quantum confinement and piezoelectric field MATLAB calculations, to shed light on the physical origin of the spectral difference between the QDs and their wetting layers. (J. Appl. Phys. 112, 063506 (2012)).

Gallium Nitride Nanomembranes Exfoliation for Flexible Devices:

The technology for exfoliating and transferring threading dislocation-free GaN single crystal nanomembrane to other rigid and flexible substrates will enable an entirely new technological platform for flexible GaN based devices. I developed a new technique for exfoliating GaN nanomembranes. Careful characterization revealed that the non-radiative cores of threading dislocation were etched during the exfoliation process. The technique relied on engineering the epitaxial growth kinetics of GaN combined with electroless etching carrier dynamics to exfoliate nanometer sized nanomembranes. I transferred these freestanding nanomembranes on different substrates and performed several optical (Photoluminescence and Raman), structural (TEM and SEM) and chemical (EDS and XPS) characterizations. (Adv. Funct. Mater. 24, 16, 2305 (2013)). (Cover page)

Carrier Lifetimes within InGaN Nanowires on Molybdenum:

Measured the temperature and power dependent time resolved photoluminescence (TRPL) emission from InGaN/GaN nanowires on molybdenum and titanium substrates. Using modified exponential model and temperature dependent external quantum efficiency measurement, calculated the radiative and non-radiative lifetimes of carriers within the nanowires. (Nano Letters 16 (7), 4616 (2016)).

Strain-Induced Bandgap Modulations of Gallium Nitride Nanomembranes

The extremely low flexural rigidity of nanomembranes allows them to twist, stretch and wrinkle in ways that are impossible for their bulk counterparts. As strain builds up within the nanostructure, modifications occur to the structure's electronic and optical properties. I have fabricated stretching devices for measuring the electron and hole changes in mobilities due to the application of external strain................ (More to come after publication).

Flexible Artificial Leaf for Solar Water Splitting:

Solar hydrogen generation is a novel potential field for clean energy where solar photons are absorbed within a semiconductor structure and then used to split the water molecule into hydrogen and oxygen gases. While nanowires lack the flexibility of nanomembranes and nanomembranes lack the high indium compositions of nanowires, I merged ......................... (More to come after publication).

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