Cherie R Kagan Research Group

Electrical and Systems Engineering - Chemistry - Materials Science and Engineering

Group Photo 2018

Welcome

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

http://kagan.seas.upenn.edu/index.php 9/26/2018:
Nanoimprinted chiral plasmonic substrates with three-dimensional nanostructures

Chiral plasmonic metamaterials can have giant optical chirality and be used in bio-sensing and light manipulation. We report a large-area fabrication method to prepare chiral substrates patterned with arrays of multilayer, three-dimensional nanostructures using a combination of nanoimprint lithography and glancing angle deposition. As one typical example, arrays of L-shaped chiral plasmonic nanostructures exhibit giant optical chirality in the infrared region with an experimentally achieved g-factor as high as 0.38. To demonstrate scalability, we fabricated a 1 cm2 chiral substrate with uniform chiral optical property.

9/24/2018:
Ultrasensitive, Mechanically Responsive Optical Metasurfaces via Strain Amplification

We report a structurally-reconfigurable, optical metasurface constructed by integrating a plasmonic lattice array in the gap between a pair of symmetric microrods that serve to locally amplify the strain created on an elastomeric substrate by an external mechanical stimulus. The strain on the metasurface is amplified by a factor of 1.5 to 15.9 relative to the external strain by tailoring the microrod geometry. The demonstrated mechano-sensitivity of the optical responses of the plasmonic lattice array is a factor of 10 greater than that of state-of-the-art stretchable plasmonic resonator arrays

9/12/2018:
Flexible colloidal nanocrystal electronics

Kagan reviews the physics and chemistry of colloidal semiconductor nanocrystals (NCs) that have lead to recent leaps forward in the performance of their field-effect transistors and the device design and fabrication that have allowed the demonstration of flexible colloidal NC integrated circuits. Taking stock of the advances made in the science and engineering of NC systems, challenges and opportunities are presented to develop next-generation, colloidal NC electronic materials and devices, important to their potential in future computational and in Internet of Things applications.

4/15/2018:
3D Nanofabrication via Chemo-Mechanical Transformation of Nanocrystal/Bulk Heterostructures

High yield, functional 3D cell-sized machines are achieved by ligand-chemistry-induced folding of planar nanocrystal/bulk hetero-structures. Design rules have been established to fabricate various 3D architectures and unique physical functions can be incorporated through careful selection of nanocrystals. This technique promises to find applications in a variety of fields including artificial motors, nano-robots, and chiral optical metasurfaces.

3/6/2018:
Angle-Independent Optical Moisture Sensors Based on Hydrogel-Coated Plasmonic Lattice Arrays

We construct an angle-independent optical sensor to measure soil moisture by coating hydrogel on top of an ultrathin, plasmonic Au nanorod lattice array. Refractive index changes of the hydrogel upon exposure to moisture are transduced into spectra shifts on the resonances of the array.

2/26/2018:
Electrons, Excitons, and Phonons in Two-Dimensional Hybrid Perovskites: Connecting Structural, Optical, and Electronic Properties

2D hybrid perovskites are widely tailorable in composition, structure, and dimensionality and provide an intriguing playground for the solid-state chemistry and physics communities to uncover structure-property relationships. In this Perspective, we correlate the unique structural and optoelectronic properties in semiconducting 2D perovskites and discuss current and future applications for this diverse class of materials. We describe the role of the heavy atoms in the inorganic framework; the geometry and chemistry of organic cations; and the "softness" of the organic-inorganic lattice on the electronic structure and dynamics of electrons, excitons, and phonons that govern the physical properties of these materials.

1/18/2018:
The Effect of Dielectric Environment on Doping Efficiency in Colloidal PbSe Nanostructures

We show dielectric confinement effects limit the doping efficiency of lead chalcogenide nanostructures in low dielectric constant media. As the dielectric mismatch between the nanostructure and its surrounding environment decreases, the doping efficiency is enhanced, consistent with our theoretical model.

Announcements

9/30/18:
Congratulations Martin!

Congratulations to Martin Sarott on completing and outstanding Masters thesis during his 6 month visiting research term from ETHZ. Best wishes, Martin!

9/10/18:
Congratulations Scott!

Congratulations and best wishes to Scott Stinner as he starts his new job at Seren IPS.

9/4/18:
Congratulations Eric!

Eric Wong has successfully defended his thesis, and is happily on his way to a fellowship in Seattle. Conrats, Eric!

9/1/18:
Congratulations Qinghua!

Qinghua Zhao has been selected as a VEIST Graduate Fellow. Congrats, Qinghua!

2/5/18:
Congratulations Nuri!

Congratulations and best wishes to Nuri Oh, now Professor of Materials Science and Engineering, Hanyang University.

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