Cherie R Kagan Research Group
The Kagan group’s research is focused on studying the chemical and physical properties of nanostructured materials and in integrating materials with optical, electrical, magnetic, mechanical, and thermal properties for (multi-)functional devices. We combine the flexibility of chemistry and bottom-up assembly with top-down fabrication techniques to design materials and devices. We explore the properties of materials and measure the characteristics of devices using spatially- and temporally-resolved optical spectroscopies, AC and DC electrical techniques, electrochemistry, scanning probe and electron microscopies, and analytical measurements.
Announcements
- Welcome, Akhila!
Akhila Mallavarapu has joined our group as a postdoctoral researcher.
- Congratulations, Jun!
Jun has won the the SEAS Masters Award for Research and joined our group as a first-year PhD student in the Electrical and Systems Engineering Department.
- Congratulations, Qinghua!
Congratulations to Qinghua on defending her PhD thesis!
- Congratulations, Han!
Congratulations to Han on defending his PhD thesis!
- Congratulations, Yiyu!
Congratulations to Yiyu Cai on receiving the John L. Margrave Thesis Award in recognition of an outstanding doctoral thesis in the Department of Chemistry from Rice University.
- Welcome, Yun Chang!
Yun Chang Choi has joined our group as a first-year PhD student in the Chemistry department.
Research Highlights
Zhao, Qinghua; Yang, Shengsong; Ng, Jonah J.; Xu, Jun; Choi, Yun Chang; Murray, Christopher B.; Kagan, Cherie R.
Impurities in Nanocrystal Thin-Film Transistors Fabricated by Cation Exchange Bachelor Thesis
2021.
@bachelorthesis{Zhao2021b,
title = {Impurities in Nanocrystal Thin-Film Transistors Fabricated by Cation Exchange},
author = {Qinghua Zhao and Shengsong Yang and Jonah J. Ng and Jun Xu and Yun Chang Choi and Christopher B. Murray and Cherie R. Kagan},
url = {https://doi.org/10.1021/acs.jpclett.1c01551},
doi = {10.1021/acs.jpclett.1c01551},
year = {2021},
date = {2021-07-09},
journal = {The Journal of Physical Chemistry Letters},
volume = {12},
number = {28},
pages = {6514–6518},
abstract = {Cation exchange is a versatile tool used to alter the composition of nanostructures and thus to design next-generation catalysts and photonic and electronic devices. However, chemical impurities inherited from the starting materials can degrade device performance. Here, we use a sequential cation-exchange process to convert PbSe into CdSe nanocrystal thin films and study their temperature-dependent electrical properties in the platform of the thin-film transistor. We show that residual Pb impurities have detrimental effects on the device turn-on, hysteresis, and electrical stability, and as the amount increases from 2% to 7%, the activation energy for carrier transport increases from 38(3) to 62(2) meV. Selection and surface functionalization of the transistor’s gate oxide layer and low-temperature atomic-layer deposition encapsulation of the thin-film channel suppress these detrimental effects. By conversion of the nanocrystal thin films layer upon layer, impurities are driven away from the gate–oxide interface and mobilities improve from 3(1) to 32(3) cm2 V–1 s–1.},
keywords = {},
pubstate = {published},
tppubtype = {bachelorthesis}
}
Cation exchange is a versatile tool used to alter the composition of nanostructures and thus to design next-generation catalysts and photonic and electronic devices. However, chemical impurities inherited from the starting materials can degrade device performance. Here, we use a sequential cation-exchange process to convert PbSe into CdSe nanocrystal thin films and study their temperature-dependent electrical properties in the platform of the thin-film transistor. We show that residual Pb impurities have detrimental effects on the device turn-on, hysteresis, and electrical stability, and as the amount increases from 2% to 7%, the activation energy for carrier transport increases from 38(3) to 62(2) meV. Selection and surface functionalization of the transistor’s gate oxide layer and low-temperature atomic-layer deposition encapsulation of the thin-film channel suppress these detrimental effects. By conversion of the nanocrystal thin films layer upon layer, impurities are driven away from the gate–oxide interface and mobilities improve from 3(1) to 32(3) cm2 V–1 s–1.
Guo, Jiacen; Kim, Ji-Young; Yang, Shengsong; Xu, Jun; Choi, Yun Chang; Stein, Aaron; Murray, Christopher B.; Kotov, Nicholas A.; Kagan, Cherie R.
Broadband Circular Polarizers via Coupling in 3D Plasmonic Meta-Atom Arrays Journal Article
In: ACS Photonics, 2021.
@article{Guo2021,
title = {Broadband Circular Polarizers via Coupling in 3D Plasmonic Meta-Atom Arrays},
author = {Jiacen Guo and Ji-Young Kim and Shengsong Yang and Jun Xu and Yun Chang Choi and Aaron Stein and Christopher B. Murray and Nicholas A. Kotov and Cherie R. Kagan},
url = {https://pubs.acs.org/doi/abs/10.1021/acsphotonics.1c00310},
doi = {10.1021/acsphotonics.1c00310},
year = {2021},
date = {2021-04-13},
journal = {ACS Photonics},
abstract = {We report broadband circular polarizers achieved by engineering the electromagnetic coupling between 3D meta-atoms in large-area arrays. The 3D meta-atoms are composed of bulk Au/Au nanocrystal (NC) bilayer helical arms, tailored in their number, length, and curvature through a one-step patterning process and postfabrication chemical and thermal treatments. By tuning the meta-atom array periodicity, hybridization originating from dipole–dipole and quadrupole–quadrupole interactions broadens the chiral response. We demonstrate circular polarizers operating at wavelengths spanning 2.5 to 5 μm, with a maximal transmission difference between left- and right-hand circularly polarized light of 43%.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
We report broadband circular polarizers achieved by engineering the electromagnetic coupling between 3D meta-atoms in large-area arrays. The 3D meta-atoms are composed of bulk Au/Au nanocrystal (NC) bilayer helical arms, tailored in their number, length, and curvature through a one-step patterning process and postfabrication chemical and thermal treatments. By tuning the meta-atom array periodicity, hybridization originating from dipole–dipole and quadrupole–quadrupole interactions broadens the chiral response. We demonstrate circular polarizers operating at wavelengths spanning 2.5 to 5 μm, with a maximal transmission difference between left- and right-hand circularly polarized light of 43%.
Zhao, Qinghua; Gouget, Guillaume; Guo, Jiacen; Yang, Shengsong; Zhao, Tianshuo; Straus, Daniel B.; Qian, Chengyang; Oh, Nuri; Wang, Han; Murray, Christopher B.; Kagan, Cherie R.
Enhanced Carrier Transport in Strongly Coupled, Epitaxially Fused CdSe Nanocrystal Solids Journal Article
In: Nano Letters, 21 (7), pp. 3318–3324, 2021.
@article{Zhao2021,
title = {Enhanced Carrier Transport in Strongly Coupled, Epitaxially Fused CdSe Nanocrystal Solids},
author = {Qinghua Zhao and Guillaume Gouget and Jiacen Guo and Shengsong Yang and Tianshuo Zhao and Daniel B. Straus and Chengyang Qian and Nuri Oh and Han Wang and Christopher B. Murray and Cherie R. Kagan},
url = {https://pubs.acs.org/doi/abs/10.1021/acs.nanolett.1c00860},
doi = {10.1021/acs.nanolett.1c00860},
year = {2021},
date = {2021-04-01},
journal = {Nano Letters},
volume = {21},
number = {7},
pages = {3318–3324},
abstract = {Strongly coupled, epitaxially fused colloidal nanocrystal (NC) solids are promising solution-processable semiconductors to realize optoelectronic devices with high carrier mobilities. Here, we demonstrate sequential, solid-state cation exchange reactions to transform epitaxially connected PbSe NC thin films into Cu2Se nanostructured thin-film intermediates and then successfully to achieve zinc-blende, CdSe NC solids with wide epitaxial necking along {100} facets. Transient photoconductivity measurements probe carrier transport at nanometer length scales and show a photoconductance of 0.28(1) cm2 V–1 s–1, the highest among CdSe NC solids reported. Atomic-layer deposition of a thin Al2O3 layer infiltrates and protects the structure from fusing into a polycrystalline thin film during annealing and further improves the photoconductance to 1.71(5) cm2 V–1 s–1 and the diffusion length to 760 nm. We fabricate field-effect transistors to study carrier transport at micron length scales and realize high electron mobilities of 35(3) cm2 V–1 s–1 with on–off ratios of 106 after doping.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Strongly coupled, epitaxially fused colloidal nanocrystal (NC) solids are promising solution-processable semiconductors to realize optoelectronic devices with high carrier mobilities. Here, we demonstrate sequential, solid-state cation exchange reactions to transform epitaxially connected PbSe NC thin films into Cu2Se nanostructured thin-film intermediates and then successfully to achieve zinc-blende, CdSe NC solids with wide epitaxial necking along {100} facets. Transient photoconductivity measurements probe carrier transport at nanometer length scales and show a photoconductance of 0.28(1) cm2 V–1 s–1, the highest among CdSe NC solids reported. Atomic-layer deposition of a thin Al2O3 layer infiltrates and protects the structure from fusing into a polycrystalline thin film during annealing and further improves the photoconductance to 1.71(5) cm2 V–1 s–1 and the diffusion length to 760 nm. We fabricate field-effect transistors to study carrier transport at micron length scales and realize high electron mobilities of 35(3) cm2 V–1 s–1 with on–off ratios of 106 after doping.
Kagan, Cherie R.; Arnold, David P.; Allen, Mark G.; Olsson, Roy H.
2021 IEEE 34th International Conference on Micro Electro Mechanical Systems (MEMS), IEEE 2021.
@conference{Kagan2021,
title = {IoT4Ag: MEMS-Enabled Distributed Sensing, Communications, And Information Systems for The Internet Of Things For Precision Agriculture},
author = {Cherie R. Kagan and David P. Arnold and Mark G. Allen and Roy H. Olsson},
url = {https://ieeexplore.ieee.org/abstract/document/9375346},
doi = {10.1109/MEMS51782.2021.9375346},
year = {2021},
date = {2021-03-15},
booktitle = {2021 IEEE 34th International Conference on Micro Electro Mechanical Systems (MEMS)},
organization = {IEEE},
abstract = {We introduce the US NSF Engineering Research Center for the Internet of Things for Precision Agriculture (IoT4Ag). IoT4Ag aims to improve agricultural outcomes using highly distributed sensor technologies that monitor the soil and microclimate where plants are grown. MEMS will be a key technology enabler of this application, which requires sensing diverse measurands over large physical areas. We describe example optical and RF sensors that use large-area, low-cost fabrication technologies, are biocompatible or biodegradable, communicate from above or below the soil surface, require zero or near-zero power, and/or are powered from biodegradable batteries, wireless power, and energy harvesting.},
keywords = {},
pubstate = {published},
tppubtype = {conference}
}
We introduce the US NSF Engineering Research Center for the Internet of Things for Precision Agriculture (IoT4Ag). IoT4Ag aims to improve agricultural outcomes using highly distributed sensor technologies that monitor the soil and microclimate where plants are grown. MEMS will be a key technology enabler of this application, which requires sensing diverse measurands over large physical areas. We describe example optical and RF sensors that use large-area, low-cost fabrication technologies, are biocompatible or biodegradable, communicate from above or below the soil surface, require zero or near-zero power, and/or are powered from biodegradable batteries, wireless power, and energy harvesting.
Kagan, Cherie R.; Bassett, Lee C.; Murray, Christopher B.; Thompson, Sarah M.
Colloidal Quantum Dots as Platforms for Quantum Information Science Journal Article
In: Chemical Reviews, 121 (5), pp. 3186–3233, 2020.
@article{Kagan2020,
title = {Colloidal Quantum Dots as Platforms for Quantum Information Science},
author = {Cherie R. Kagan and Lee C. Bassett and Christopher B. Murray and Sarah M. Thompson},
url = {https://pubs.acs.org/doi/abs/10.1021/acs.chemrev.0c00831},
doi = {10.1021/acs.chemrev.0c00831},
year = {2020},
date = {2020-12-29},
journal = {Chemical Reviews},
volume = {121},
number = {5},
pages = {3186–3233},
abstract = {Colloidal quantum dots (QDs) are nanoscale semiconductor crystals with surface ligands that enable their dispersion in solvents. Quantum confinement effects facilitate wave function engineering to sculpt the spatial distribution of charge and spin states and thus the energy and dynamics of QD optical transitions. Colloidal QDs can be integrated in devices using solution-based assembly methods to position single QDs and to create ordered QD arrays. Here, we describe the synthesis, assembly, and photophysical properties of colloidal QDs that have captured scientific imagination and have been harnessed in optical applications. We focus especially on the current understanding of their quantum coherent effects and opportunities to exploit QDs as platforms for quantum information science. Freedom in QD design to isolate and control the quantum mechanical properties of charge, spin, and light presents various approaches to create systems with robust, addressable quantum states. We consider the attributes of QDs for optically addressable qubits in emerging quantum computation, sensing, simulation, and communication technologies, e.g., as robust sources of indistinguishable, single photons that can be integrated into photonic structures to amplify, direct, and tune their emission or as hosts for isolated, coherent spin states that can be coupled to light or to other spins in QD arrays.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Colloidal quantum dots (QDs) are nanoscale semiconductor crystals with surface ligands that enable their dispersion in solvents. Quantum confinement effects facilitate wave function engineering to sculpt the spatial distribution of charge and spin states and thus the energy and dynamics of QD optical transitions. Colloidal QDs can be integrated in devices using solution-based assembly methods to position single QDs and to create ordered QD arrays. Here, we describe the synthesis, assembly, and photophysical properties of colloidal QDs that have captured scientific imagination and have been harnessed in optical applications. We focus especially on the current understanding of their quantum coherent effects and opportunities to exploit QDs as platforms for quantum information science. Freedom in QD design to isolate and control the quantum mechanical properties of charge, spin, and light presents various approaches to create systems with robust, addressable quantum states. We consider the attributes of QDs for optically addressable qubits in emerging quantum computation, sensing, simulation, and communication technologies, e.g., as robust sources of indistinguishable, single photons that can be integrated into photonic structures to amplify, direct, and tune their emission or as hosts for isolated, coherent spin states that can be coupled to light or to other spins in QD arrays.