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
- Congratulations, Jaeyoung!
Congratulations to Jaeyoung on defending his PhD thesis!
- Congratulations to Cherie on being named an MRS Fellow!
MRS Fellows are honored for their distinguished research accomplishments and outstanding contributions to the advancement of materials research (more).
- Congratulations, Sarah!
Congratulations to Sarah on defending her PhD thesis!
- Welcome, Ilia!
Ilia Geints has joined our group as a first-year PhD student in the Electrical and Systems Engineering (ESE) department.
- Welcome, Gary!
Gary Chen has joined our group as a first-year PhD student in the chemistry department.
- Welcome, Anamika!
Anamika Singh has joined our group as a postdoctoral researcher.
Research Highlights
Lynch, Jason; Smith, Evan; Alfieri, Adam; Song, Baokun; Klein, Matthew; Stevens, Christopher E.; Chen, Cindy Yueli; Lawrence, Chavez FK.; Kagan, Cherie R.; Gu, Honggang; Liu, Shiyuan; Peng, Lian-Mao; Vangala, Shivashankar; Hendrickson, Joshua R.; Jariwala, Deep
Gate-Tunable Optical Anisotropy in Wafer-Scale, Aligned Carbon Nanotube Films Journal Article
In: Nature Photonics, 2024.
@article{Lynch2024b,
title = {Gate-Tunable Optical Anisotropy in Wafer-Scale, Aligned Carbon Nanotube Films},
author = {Jason Lynch and Evan Smith and Adam Alfieri and Baokun Song and Matthew Klein and Christopher E. Stevens and Cindy Yueli Chen and Chavez FK. Lawrence and Cherie R. Kagan and Honggang Gu and Shiyuan Liu and Lian-Mao Peng and Shivashankar Vangala and Joshua R. Hendrickson and Deep Jariwala},
doi = {10.1038/s41566-024-01504-0},
year = {2024},
date = {2024-08-14},
urldate = {2024-08-14},
journal = {Nature Photonics},
abstract = {Telecommunications and polarimetry both require the active control of the polarization of light. Currently, this is done by combining intrinsically anisotropic materials with tunable isotropic materials into heterostructures using complicated fabrication techniques owing to the lack of scalable materials that possess both properties. Tunable birefringent and dichromic materials are scarce and rarely available in high-quality thin films over wafer scales. Here we report semiconducting, highly aligned, single-walled carbon nanotubes (SWCNTs) over 4″ wafers with normalized birefringence and dichroism values of 0.09 and 0.58, respectively. The real and imaginary parts of the refractive index of these SWCNT films are tuned by up to 5.9% and 14.3% in the infrared at 2,200 nm and 1,660 nm, respectively, using electrostatic doping. Our results suggest that aligned SWCNTs are among the most anisotropic and tunable optical materials known and open new avenues for their application in integrated photonics and telecommunications.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Telecommunications and polarimetry both require the active control of the polarization of light. Currently, this is done by combining intrinsically anisotropic materials with tunable isotropic materials into heterostructures using complicated fabrication techniques owing to the lack of scalable materials that possess both properties. Tunable birefringent and dichromic materials are scarce and rarely available in high-quality thin films over wafer scales. Here we report semiconducting, highly aligned, single-walled carbon nanotubes (SWCNTs) over 4″ wafers with normalized birefringence and dichroism values of 0.09 and 0.58, respectively. The real and imaginary parts of the refractive index of these SWCNT films are tuned by up to 5.9% and 14.3% in the infrared at 2,200 nm and 1,660 nm, respectively, using electrostatic doping. Our results suggest that aligned SWCNTs are among the most anisotropic and tunable optical materials known and open new avenues for their application in integrated photonics and telecommunications.
Liu, Chang; Jung, Wonil; Jeon, Sungho; Johnson, Grayson; Shi, Zixiao; Xiao, Langqiu; Yang, Shengsong; Chen, Cheng-Yu; Xu, Jun; Kagan, Cherie R.; Zhang, Sen; Muller, David A.; Stach, Eric A.; Murray, Christopher B.; Mallouk, Thomas E.
Stabilizing alkaline fuel cells with a niobium-doped brookite titanium dioxide catalyst support Journal Article
In: Cell Reports Physical Science, 2024.
@article{Liu2024,
title = {Stabilizing alkaline fuel cells with a niobium-doped brookite titanium dioxide catalyst support},
author = {Chang Liu and Wonil Jung and Sungho Jeon and Grayson Johnson and Zixiao Shi and Langqiu Xiao and Shengsong Yang and Cheng-Yu Chen and Jun Xu and Cherie R. Kagan and Sen Zhang and David A. Muller and Eric A. Stach and Christopher B. Murray and Thomas E. Mallouk},
doi = {10.1016/j.xcrp.2024.102090},
year = {2024},
date = {2024-07-08},
urldate = {2024-07-08},
journal = {Cell Reports Physical Science},
abstract = {Anion-exchange membrane fuel cells represent a promising and scalable approach for hydrogen energy utilization. However, their development is hindered by the weak bonding between metal catalysts and carbon supports, along with challenges in fabricating electronically/ionically conductive electrodes. Here, we report a composite cathode of Nb-doped brookite TiO2 nanorods that have robust stability when combined with Pt nanoscale catalysts in an alkaline fuel cell. The composite cathode, fabricated without the addition of an ionomer, delivers a power density of 419 mW cm−2 at a current density of 650 mA cm−2 and a voltage retention of 81% at 100 mA cm−2 after 25 h, substantially outperforming a cathode fabricated from commercial Pt/C. Further investigations of the chemical structure, anion exchange capacity, and mass transfer resistance reveal that a solvent residue derived from N-methylpyrrolidone plays an important role in charge transfer and mass transport in the alkaline fuel cell.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Anion-exchange membrane fuel cells represent a promising and scalable approach for hydrogen energy utilization. However, their development is hindered by the weak bonding between metal catalysts and carbon supports, along with challenges in fabricating electronically/ionically conductive electrodes. Here, we report a composite cathode of Nb-doped brookite TiO2 nanorods that have robust stability when combined with Pt nanoscale catalysts in an alkaline fuel cell. The composite cathode, fabricated without the addition of an ionomer, delivers a power density of 419 mW cm−2 at a current density of 650 mA cm−2 and a voltage retention of 81% at 100 mA cm−2 after 25 h, substantially outperforming a cathode fabricated from commercial Pt/C. Further investigations of the chemical structure, anion exchange capacity, and mass transfer resistance reveal that a solvent residue derived from N-methylpyrrolidone plays an important role in charge transfer and mass transport in the alkaline fuel cell.
Shulevitz, Henry J.; Amirshaghaghi, Ahmad; Ouellet, Mathieu; Brustoloni, Caroline; Yang, Shengsong; Ng, Jonah J.; Huang, Tzu-Yung; Jishkariani, Davit; Murray, Christopher B.; Tsourkas, Andrew; Kagan, Cherie R.; Bassett, Lee C.
Nanodiamond emulsions for enhanced quantum sensing and click-chemistry conjugation Journal Article
In: ACS Applied Nano Materials, 2024.
@article{Shulevitz2024,
title = {Nanodiamond emulsions for enhanced quantum sensing and click-chemistry conjugation},
author = {Henry J. Shulevitz and Ahmad Amirshaghaghi and Mathieu Ouellet and Caroline Brustoloni and Shengsong Yang and Jonah J. Ng and Tzu-Yung Huang and Davit Jishkariani and Christopher B. Murray and Andrew Tsourkas and Cherie R. Kagan and Lee C. Bassett},
url = {https://pubs.acs.org/doi/10.1021/acsanm.4c01699},
doi = {10.1021/acsanm.4c01699},
year = {2024},
date = {2024-06-29},
urldate = {2023-12-04},
journal = {ACS Applied Nano Materials},
abstract = {Nanodiamonds containing nitrogen-vacancy (NV) centers can serve as colloidal quantum sensors of local fields in biological and chemical environments. However, nanodiamond surfaces are challenging to modify without degrading their colloidal stability or the NV center's optical and spin properties. Here, we report a simple and general method to coat nanodiamonds with a thin emulsion layer that preserves their quantum features, enhances their colloidal stability, and provides functional groups for subsequent crosslinking and click-chemistry conjugation reactions. To demonstrate this technique, we decorate the nanodiamonds with combinations of carboxyl- and azide-terminated amphiphiles that enable conjugation using two different strategies. We study the effect of the emulsion layer on the NV center's spin lifetime, and we quantify the nanodiamonds' chemical sensitivity to paramagnetic ions using T1 relaxometry. This general approach to nanodiamond surface functionalization will enable advances in quantum nanomedicine and biological sensing.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Nanodiamonds containing nitrogen-vacancy (NV) centers can serve as colloidal quantum sensors of local fields in biological and chemical environments. However, nanodiamond surfaces are challenging to modify without degrading their colloidal stability or the NV center's optical and spin properties. Here, we report a simple and general method to coat nanodiamonds with a thin emulsion layer that preserves their quantum features, enhances their colloidal stability, and provides functional groups for subsequent crosslinking and click-chemistry conjugation reactions. To demonstrate this technique, we decorate the nanodiamonds with combinations of carboxyl- and azide-terminated amphiphiles that enable conjugation using two different strategies. We study the effect of the emulsion layer on the NV center's spin lifetime, and we quantify the nanodiamonds' chemical sensitivity to paramagnetic ions using T1 relaxometry. This general approach to nanodiamond surface functionalization will enable advances in quantum nanomedicine and biological sensing.
Xu, Jun; Zhao, Tianshuo; Zaccarin, Anne-Marie; Du, Xingyu; Yang, Shengsong; Ning, Yifan; Xiao, Qiwen; Kramadhati, Shobhita; Choi, Yun Chang; Murray, Christopher B.; III, Roy H. Olsson; Kagan, Cherie R.
Chemically Driven Sintering of Colloidal Cu Nanocrystals for Multiscale Electronic and Optical Devices Journal Article
In: ACS Nano, 2024.
@article{Xu2024,
title = {Chemically Driven Sintering of Colloidal Cu Nanocrystals for Multiscale Electronic and Optical Devices},
author = {Jun Xu and Tianshuo Zhao and Anne-Marie Zaccarin and Xingyu Du and Shengsong Yang and Yifan Ning and Qiwen Xiao and Shobhita Kramadhati and Yun Chang Choi and Christopher B. Murray and Roy H. Olsson III and Cherie R. Kagan},
url = {https://pubs-acs-org.proxy.library.upenn.edu/doi/10.1021/acsnano.4c02007},
year = {2024},
date = {2024-06-25},
urldate = {2024-06-25},
journal = {ACS Nano},
abstract = {Emerging applications of Internet of Things (IoT) technologies in smart health, home, and city, in agriculture and environmental monitoring, and in transportation and manufacturing require materials and devices with engineered physical properties that can be manufactured by low-cost and scalable methods, support flexible forms, and are biocompatible and biodegradable. Here, we report the fabrication and device integration of low-cost and biocompatible/biodegradable colloidal Cu nanocrystal (NC) films through room temperature, solution-based deposition, and sintering, achieved via chemical exchange of NC surface ligands. Treatment of organic-ligand capped Cu NC films with solutions of shorter, environmentally benign, and noncorrosive inorganic reagents, namely, SCN– and Cl–, effectively removes the organic ligands, drives NC grain growth, and limits film oxidation. We investigate the mechanism of this chemically driven sintering by systemically varying the Cu NC size, ligand reagent, and ligand treatment time and follow the evolution of their structure and electrical and optical properties. Cl–-treated, 4.5 nm diameter Cu NC films yield the lowest DC resistivity, only 3.2 times that of bulk Cu, and metal-like dielectric functions at optical frequencies. We exploit the high conductivity of these chemically sintered Cu NC films and, in combination with photo- and nanoimprint-lithography, pattern multiscale structures to achieve high-Q radio frequency (RF) capacitive sensors and near-infrared (NIR) resonant optical metasurfaces.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Emerging applications of Internet of Things (IoT) technologies in smart health, home, and city, in agriculture and environmental monitoring, and in transportation and manufacturing require materials and devices with engineered physical properties that can be manufactured by low-cost and scalable methods, support flexible forms, and are biocompatible and biodegradable. Here, we report the fabrication and device integration of low-cost and biocompatible/biodegradable colloidal Cu nanocrystal (NC) films through room temperature, solution-based deposition, and sintering, achieved via chemical exchange of NC surface ligands. Treatment of organic-ligand capped Cu NC films with solutions of shorter, environmentally benign, and noncorrosive inorganic reagents, namely, SCN– and Cl–, effectively removes the organic ligands, drives NC grain growth, and limits film oxidation. We investigate the mechanism of this chemically driven sintering by systemically varying the Cu NC size, ligand reagent, and ligand treatment time and follow the evolution of their structure and electrical and optical properties. Cl–-treated, 4.5 nm diameter Cu NC films yield the lowest DC resistivity, only 3.2 times that of bulk Cu, and metal-like dielectric functions at optical frequencies. We exploit the high conductivity of these chemically sintered Cu NC films and, in combination with photo- and nanoimprint-lithography, pattern multiscale structures to achieve high-Q radio frequency (RF) capacitive sensors and near-infrared (NIR) resonant optical metasurfaces.
Marino, Emanuele; Vo, Thi; Gonzalez, Cristian; Rosen, Daniel J.; Neuhaus, Steven J.; Sciortino, Alice; Bharti, Harshit; Keller, Austin W.; Kagan, Cherie R.; Cannas, Marco; Messina, Fabrizio; Glotzer, Sharon C.; Murray, Christopher B.
Porous Magneto-Fluorescent Superparticles by Rapid Emulsion Densification Journal Article
In: Chemistry of Materials, 2024.
@article{Marino2024,
title = {Porous Magneto-Fluorescent Superparticles by Rapid Emulsion Densification},
author = {Emanuele Marino and Thi Vo and Cristian Gonzalez and Daniel J. Rosen and Steven J. Neuhaus and Alice Sciortino and Harshit Bharti and Austin W. Keller and Cherie R. Kagan and Marco Cannas and Fabrizio Messina and Sharon C. Glotzer and Christopher B. Murray},
url = {https://pubs.acs.org/doi/full/10.1021/acs.chemmater.3c03209},
doi = {10.1021/acs.chemmater.3c03209},
year = {2024},
date = {2024-04-01},
urldate = {2024-04-01},
journal = {Chemistry of Materials},
abstract = {Porous superstructures are characterized by a large surface area and efficient molecular transport. Although methods aimed at generating porous superstructures from nanocrystals exist, current state-of-the-art strategies are limited to single-component nanocrystal dispersions. More importantly, such processes afford little control over the size and shape of the pores. Here, we present a new strategy for the nanofabrication of porous magneto-fluorescent nanocrystal superparticles that are well controlled in size and shape. We synthesize these composite superparticles by confining semiconductor and superparamagnetic nanocrystals within oil-in-water droplets generated using microfluidics. The rapid densification of these droplets yields spherical, monodisperse, and porous nanocrystal superparticles. Molecular simulations reveal that the formation of pores throughout the superparticles is linked to repulsion between nanocrystals of different compositions, leading to phase separation during self-assembly. We confirm the presence of nanocrystal phase separation at the single superparticle level by analyzing the changes in the optical and photonic properties of the superstructures as a function of nanocrystal composition. This excellent agreement between experiments and simulations allows us to develop a theory that predicts superparticle porosity from experimentally tunable physical parameters, such as nanocrystal size ratio, stoichiometry, and droplet densification rate. Our combined theoretical, computational, and experimental findings provide a blueprint for designing porous, multifunctional superparticles with immediate applications in catalytic, electrochemical, sensing, and cargo delivery applications.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Porous superstructures are characterized by a large surface area and efficient molecular transport. Although methods aimed at generating porous superstructures from nanocrystals exist, current state-of-the-art strategies are limited to single-component nanocrystal dispersions. More importantly, such processes afford little control over the size and shape of the pores. Here, we present a new strategy for the nanofabrication of porous magneto-fluorescent nanocrystal superparticles that are well controlled in size and shape. We synthesize these composite superparticles by confining semiconductor and superparamagnetic nanocrystals within oil-in-water droplets generated using microfluidics. The rapid densification of these droplets yields spherical, monodisperse, and porous nanocrystal superparticles. Molecular simulations reveal that the formation of pores throughout the superparticles is linked to repulsion between nanocrystals of different compositions, leading to phase separation during self-assembly. We confirm the presence of nanocrystal phase separation at the single superparticle level by analyzing the changes in the optical and photonic properties of the superstructures as a function of nanocrystal composition. This excellent agreement between experiments and simulations allows us to develop a theory that predicts superparticle porosity from experimentally tunable physical parameters, such as nanocrystal size ratio, stoichiometry, and droplet densification rate. Our combined theoretical, computational, and experimental findings provide a blueprint for designing porous, multifunctional superparticles with immediate applications in catalytic, electrochemical, sensing, and cargo delivery applications.