Cherie R Kagan Research Group

Electrical and Systems Engineering - Chemistry - Materials Science and Engineering

Group Photo 2014


The Kagan group explores the chemical and physical properties of nanostructured and organic materials and integrates these materials in electronic, optoelectronic, optical, thermoelectric and bioelectronic devices. We combine the flexibility of chemistry and bottom-up assembly with top-down fabrication techniques to design novel materials and devices. We explore the structure and function of these materials and devices using spatially- and temporally-resolved optical spectroscopies, AC and DC electrical techniques, electrochemistry, scanning probe and electron microscopies and analytical measurements.

Research Highlights

Electron and hole transport in ambipolar, thin film pentacene transistors

We fabricated solution-processed, ambipolar, thin-film pentacene field-effect transistors to study both electron and hole transport simultaneously in a single, organic solid-state device. We show that the lower electron than hole mobility is consistent with greater energetic disorder and therefore a greater density of localized tail states for electrons than holes.

Post-Synthesis Processing of CdSe NCs and Nc Solids: Correlation Between Surface Chemistry and Optoelectronic Properties

We show that post-synthesis washing and ligand exchange of CdSe nanocrystals (NCs) and NC solids using methanol removes ligands and Cd from the NC surface, creating localized charge carrier trap states. We correlate the photocurrent through CdSe NC solids with such trap states and show that the photocurrent can be increased by passivation of the traps through treatment with CdCl2.

Engineering Charge Injection and Transport in PbSe NC Devices and Circuits

By engineering the contact metallurgy and nanocrystal ligand exchange chemistry and surface passivation in PbSe nanocrystal thin film transistors, we tune the polarity and magnitude of charge injection and transport and demonstrate an insulator-to-metal transition as we strengthen the nanocrystal coupling and increase the carrier concentration in the nanocrystal channel. Using n-type and p-type PbSe nanocrystal transistors realized by selecting the contact metallurgy, we construct complementary, integrated nanocrystal circuits from a single nanocrystal material.

Low-Frequency (1/f) Noise in Nanocrystal FETs

We investigate the origins and magnitude of low-frequency noise in high-mobility nanocrystal field-effect transistors and show the noise is of 1/f-type. We show that 1/f noise relates to NC thin-film electronic structure, where the McWhorter model describes 1/f noise in the subthreshold regime and the Hooge model describes 1/f noise in the device linear and saturation regimes.

Plasmon-Enhanced Upconversion in Individual Self-Assembled Heterodimers

We utilized template-assisted self-assembly to form discrete nanocrystal heterodimers consisting of a single upconversion nanophosphor and a single gold nanorod. By matching the surface plasmon resonance of the nanorods with the excitation wavelength of the phosphors and by spatially localizing the phosphors in the intense near-fields surrounding the rod tips, several-fold luminescence enhancements were achieved.

Gate Induced Carrier Delocalization in QD FETs

Our DOE SISGR team used gate-dependent, low temperature resistance and magnetotransport measurements to study indium-doped CdSe QD FETs. We showed that with increasing gate voltage the localization product (localization length times dielectric transport) describing transport of accumulated carriers, suggests the localization length increases significantly beyond the QD diameter.


Congratulations to Yuming!

Congratulations to Yuming on his PhD graduation and wishing him the best in Michigan, at the Dow Chemical Company!

Welcome Lizzie and Pil Sung

Welcome to Pil sung, our new post-doc, and Lizzie Dresselhaus, our new undergrad!

Congratulations to SJ!

Congratulations to SJ on his PhD graduation and wishing him the best during his postdoc in the Rogers group. Also a congratulations to SJ for winning the SJ Stein Prize from the University of Pennsylvania, recognizing his PhD work for its "superior achievement in the field of new or unique materials or applications for materials in electronics," and the MRS Graduate Student Silver Award at the Spring, 2014 meeting.

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Electrical & Systems Engineering, Moore Building
200 South 33rd Street, Philadelphia, PA 19104