Brongersma Group Plasmonics and Photonics at Stanford University

@article{shinomiya2022enhancedb,

title = {Enhanced Light Emission from Monolayer MoS2 by Doubly Resonant Spherical Si Nanoantennas},

author = {Hiroto Shinomiya and Hiroshi Sugimoto and Tatsuki Hinamoto and Yan Joe Lee and Mark L. Brongersma and Minoru Fujii},

doi = {10.1021/acsphotonics.2c00142},

year  = {2022},

date = {2022-04-19},

journal = {ACS Photonics},

volume = {9},

issue = {5},

pages = {1741-1747},

abstract = {Optical antennas provide a powerful tool to control local photonic environments and enhance light emission from two-dimensional transition-metal dichalcogenides. Dielectric nanoantennas with multipolar Mie resonances bring unique advantages for achieving simultaneous enhancement of the absorption and emission processes. Here, we achieve a strong modification of the photoluminescence (PL) behavior of monolayer MoS2 by a spherical nanoparticle (NP) of crystalline silicon (Si) that works as a double resonance nanoantenna. From theoretical calculations for in-plane dipoles placed beneath a Si NP nanoantenna with different sizes, we explore optimal conditions for the double resonances. Then, we develop a heterostructure composed of a Si NP and a monolayer MoS2 sheet with a comparable diameter and investigate the scattering, PL, and PL excitation spectra across a wide Si NP size range. We show that the spectral shape is significantly modified and PL intensity is enhanced up to ∼10-fold due to the coupling of the excitation process to the magnetic quadrupole resonance and the emission process to the magnetic dipole resonance.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nassiri2021highb,

title = {High-specific-power flexible transition metal dichalcogenide solar cells},

author = {Koosha Nassiri Nazif and Alwin Daus and Jiho Hong and Nayeun Lee and Sam Vaziri and Aravindh Kumar and Frederick Nitta and Michelle E Chen and Siavash Kananian and Raisul Islam and Kwan-Ho Kim and Jin-Hong Park and Ada SY Poon and Mark L. Brongersma and Eric Pop and Krishna C. Saraswat},

doi = {10.1038/s41467-021-27195-7},

year  = {2021},

date = {2021-12-09},

journal = {Nature Communications},

volume = {12},

issue = {1},

pages = {1-9},

abstract = {Semiconducting transition metal dichalcogenides (TMDs) are promising for flexible high-specific-power photovoltaics due to their ultrahigh optical absorption coefficients, desirable band gaps and self-passivated surfaces. However, challenges such as Fermi-level pinning at the metal contact\textendashTMD interface and the inapplicability of traditional doping schemes have prevented most TMD solar cells from exceeding 2% power conversion efficiency (PCE). In addition, fabrication on flexible substrates tends to contaminate or damage TMD interfaces, further reducing performance. Here, we address these fundamental issues by employing: (1) transparent graphene contacts to mitigate Fermi-level pinning, (2) MoOx capping for doping, passivation and anti-reflection, and (3) a clean, non-damaging direct transfer method to realize devices on lightweight flexible polyimide substrates. These lead to record PCE of 5.1% and record specific power of 4.4 W g−1 for flexible TMD (WSe2) solar cells, the latter on par with prevailing thin-film solar technologies cadmium telluride, copper indium gallium selenide, amorphous silicon and III-Vs. We further project that TMD solar cells could achieve specific power up to 46 W g−1, creating unprecedented opportunities in a broad range of industries from aerospace to wearable and implantable electronics.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{braun2021photochemistry,

title = {Photochemistry democratizes 3D nanoprinting},

author = {Paul V. Braun and Mark L. Brongersma},

doi = {10.1038/s41566-021-00911-x},

year  = {2021},

date = {2021-11-29},

journal = {Nature Photonics},

volume = {15},

number = {12},

pages = {871-873},

abstract = {For 20 years, nanoscale 3D printing has been based on two-photon absorption, requiring expensive pulsed lasers. Now, via a two-step absorption process, such printing has been demonstrated using a low-cost, low-power continuous-wave laser diode, showing the potential for dramatic cost reductions in 3D nanoprinting.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{aslan2021excitons,

title = {Excitons in strained and suspended monolayer WSe2},

author = {Burak Aslan and Colin Yule and Yifei Yu and Yan Joe Lee and Tony F. Heinz and Linyou Cao and Mark L. Brongersma},

doi = {10.1088/2053-1583/ac2d15},

year  = {2021},

date = {2021-10-21},

urldate = {2021-10-21},

journal = {2D Materials},

volume = {9},

number = {1},

pages = {015002},

abstract = {We study suspended membranes of atomically thin WSe2 as hosts of excitons. We perform optical reflectance measurements to probe the exciton physics and obtain the peak energies for the 1$s$, 2$s$, and 3$s$ states of the $A$ exciton in suspended WSe2 and consider supported membranes as a reference. We find that elimination of the influence of the dielectric environment enables a strong electron\textendashhole interaction and a concomitant increase in the exciton binding energy in suspended monolayer (1L) WSe2. Based on the experimental results, we calculate the excitonic binding energies by employing the recently developed quantum electrostatic heterostructure model and the commonly employed Rytova\textendashKeldysh potential model. We see that the binding energy of the ground state $A$ exciton increases from about 0.3 eV (on a substrate) to above 0.4 eV (suspended). We also exploit the tunability of the excitons in suspended samples via mechanical strain. By applying external gas pressure of 2.72 atm to a 1L suspended over a circular hole of 8 μm diameter, we strain the WSe2 and obtain a reversible 0.15 eV redshift in the exciton resonance. The linewidth of the $A$ exciton decreases by more than half, from about 50 to 20 meV under 1.5% biaxial strain at room temperature. This line narrowing is due to the suppression of intervalley exciton\textendashphonon scattering. By making use of the observed strain-dependent optical signatures, we infer the two-dimensional (2D) elastic moduli of 1L and 2L WSe2. Our results exemplify the use of suspended 2D materials as novel systems for fundamental studies, as well as for strong and dynamic tuning of their optical properties.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}