@article{Chae2017,

title = {Nanophotonic Atomic Force Microscope Transducers Enable Chemical Composition and Thermal Conductivity Measurements at the Nanoscale},

author = {Jungseok Chae and Sangmin An and Georg Ramer and Vitalie Stavila and Glenn Holland and Yohan Yoon and A. Alec Talin and Mark Allendorf and Vladimir A. Aksyuk and Andrea Centrone},

doi = {10.1021/acs.nanolett.7b02404},

issn = {1530-6992},

year  = {2017},

date = {2017-09-13},

urldate = {2017-09-13},

journal = {Nano Lett.},

volume = {17},

number = {9},

pages = {5587--5594},

publisher = {American Chemical Society (ACS)},

abstract = {The atomic force microscope (AFM) offers a rich observation window on the nanoscale, yet many dynamic phenomena are too fast and too weak for direct AFM detection. Integrated cavity-optomechanics is revolutionizing micromechanical sensing; however, it has not yet impacted AFM. Here, we make a groundbreaking advance by fabricating picogram-scale probes integrated with photonic resonators to realize functional AFM detection that achieve high temporal resolution (<10 ns) and picometer vertical displacement uncertainty simultaneously. The ability to capture fast events with high precision is leveraged to measure the thermal conductivity (η), for the first time, concurrently with chemical composition at the nanoscale in photothermal induced resonance experiments. The intrinsic η of metal–organic-framework individual microcrystals, not measurable by macroscale techniques, is obtained with a small measurement uncertainty (8%). The improved sensitivity (50×) increases the measurement throughput 2500-fold and enables chemical composition measurement of molecular monolayer-thin samples. Our paradigm-shifting photonic readout for small probes breaks the common trade-off between AFM measurement precision and ability to capture transient events, thus transforming the ability to observe nanoscale dynamics in materials.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Strelcov2017,

title = {CH3NH3PbI3 perovskites: Ferroelasticity revealed},

author = {Evgheni Strelcov and Qingfeng Dong and Tao Li and Jungseok Chae and Yuchuan Shao and Yehao Deng and Alexei Gruverman and Jinsong Huang and Andrea Centrone},

doi = {10.1126/sciadv.1602165},

issn = {2375-2548},

year  = {2017},

date = {2017-04-07},

urldate = {2017-04-07},

journal = {Sci. Adv.},

volume = {3},

number = {4},

publisher = {American Association for the Advancement of Science (AAAS)},

abstract = {Ferroelectricity has been proposed as a plausible mechanism to explain the high photovoltaic conversion efficiency in organic-inorganic perovskites; however, convincing experimental evidence in support of this hypothesis is still missing. Identifying and distinguishing ferroelectricity from other properties, such as piezoelectricity, ferroelasticity, etc., is typically nontrivial because these phenomena can coexist in many materials. In this work, a combination of microscopic and nanoscale techniques provides solid evidence for the existence of ferroelastic domains in both CH3NH3PbI3 polycrystalline films and single crystals in the pristine state and under applied stress. Experiments show that the configuration of CH3NH3PbI3 ferroelastic domains in single crystals and polycrystalline films can be controlled with applied stress, suggesting that strain engineering may be used to tune the properties of this material. No evidence of concomitant ferroelectricity was observed. Because grain boundaries have an impact on the long-term stability of organic-inorganic perovskite devices, and because the ferroelastic domain boundaries may differ from regular grain boundaries, the discovery of ferroelasticity provides a new variable to consider in the quest for improving their stability and enabling their widespread adoption.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Chae2015b,

title = {Engineering Near-Field SEIRA Enhancements in Plasmonic Resonators},

author = {Jungseok Chae and Basudev Lahiri and Andrea Centrone},

doi = {10.1021/acsphotonics.5b00466},

issn = {2330-4022},

year  = {2016},

date = {2016-01-20},

urldate = {2016-01-20},

journal = {ACS Photonics},

volume = {3},

number = {1},

pages = {87--95},

publisher = {American Chemical Society (ACS)},

abstract = {Engineering of the optical resonances in plasmonic resonator arrays is achieved by virtue of the intrinsic properties of the constituent structures such as composition, size, and shape and by controlling the inter-resonator interactions by virtue of the array’s geometrical arrangement. The nanoscale confinement of the plasmonic field enhances light–matter interactions, enabling, for instance, the surface-enhanced infrared absorption (SEIRA) effect. However, the subwavelength confinement also poses an experimental challenge for discriminating the response stemming from the individual resonators and from the collective response in densely packed arrays. In this work, the photothermal induced resonance technique is leveraged to obtain nanoscale images and spectra of near-field SEIRA hot spots observed in isolated plasmonic resonators of different shapes and in selected resonators within closely packed plasmonic arrays, informing on whether the interactions with neighboring resonators are beneficial or otherwise. Results are correlated with far-field spectra and theoretical calculations.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Chae2015,

title = {Chloride Incorporation Process in CH_{3}NH_{3}PbI_{3–\textit{x}}Cl_{\textit{x}} Perovskites via Nanoscale Bandgap Maps},

author = {Jungseok Chae and Qingfeng Dong and Jinsong Huang and Andrea Centrone},

doi = {10.1021/acs.nanolett.5b03556},

issn = {1530-6992},

year  = {2015},

date = {2015-12-09},

urldate = {2015-12-09},

journal = {Nano Lett.},

volume = {15},

number = {12},

pages = {8114--8121},

publisher = {American Chemical Society (ACS)},

abstract = {CH3NH3PbI3–xClx perovskites enable fabrication of highly efficient solar cells. Chloride ions benefit the morphology, carrier diffusion length, and stability of perovskite films; however, whether those benefits stem from the presence of Cl– in the precursor solution or from their incorporation in annealed films is debated. In this work, the photothermal-induced resonance, an in situ technique with nanoscale resolution, is leveraged to measure the bandgap of CH3NH3PbI3–xClx films obtained by a multicycle coating process that produces high efficiency (∼16%) solar cells. Because chloride ions modify the perovskite lattice, thereby widening the bandgap, measuring the bandgap locally yields the local chloride content. After a mild annealing (60 min, 60 °C) the films consist of Cl-rich (x < 0.3) and Cl-poor phases that upon further annealing (110 °C) evolve into a homogeneous Cl-poorer (x < 0.06) phase, suggesting that methylammonium-chrloride is progressively expelled from the film. Despite the small chloride content, CH3NH3PbI3–xClx films show better thermal stability up to 140 °C with respect CH3NH3PbI3 films fabricated with the same methodology.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Yuan2015,

title = {Photovoltaic Switching Mechanism in Lateral Structure Hybrid Perovskite Solar Cells},

author = {Yongbo Yuan and Jungseok Chae and Yuchuan Shao and Qi Wang and Zhengguo Xiao and Andrea Centrone and Jinsong Huang},

doi = {10.1002/aenm.201500615},

issn = {1614-6840},

year  = {2015},

date = {2015-06-05},

journal = {Advanced Energy Materials},

volume = {5},

number = {15},

publisher = {Wiley},

abstract = {Long range electromigration of methylammonium ions (MA+) in methyl ammonium lead tri-iodide (MAPbI3) film is observed directly using the photo­thermal induced resonance technique. The electromigration of MA+ leads to the formation of a lateral p-i-n structure, which is the origin of the switchable photovoltaic effect in MAPbI3 perovskite devices.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}