pubs.acs.org/journal/apchd5 Letter Room-Temperature Silicon Platform for GHz-Frequency Nanoelectro-Opto-Mechanical Systems Daniel Navarro-Urrios, Martín F. Colombano, Guillermo Arregui, Guilhem Madiot, Alessandro Pitanti, Amadeu Griol, Tapani Makkonen, Jouni Ahopelto, Clivia M. Sotomayor-Torres, and Alejandro Martínez* Cite This: ACS Photonics 2022, 9, 413−419 Read Online ACCESS * See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles. Metrics & More Article Recommendations sı Supporting Information ABSTRACT: Nanoelectro-opto-mechanical systems enable the synergistic coexistence of electrical, mechanical, and optical signals on a chip to realize new functions. Most of Downloaded via 79.152.129.231 on May 11, 2023 at 12:07:07 (UTC). the technology platforms proposed for the fabrication of these systems so far are not fully compatible with the mainstream CMOS technology, thus, hindering the mass-scale utilization. We have developed a CMOS technology platform for nanoelectro-opto- mechanical systems that includes piezoelectric interdigitated transducers for electronic driving of mechanical signals and nanocrystalline silicon nanobeams for an enhanced optomechanical interaction. Room-temperature operation of devices at 2 GHz and with peak sensitivity down to 2.6 cavity phonons is demonstrated. Our proof-of-principle technology platform can be integrated and interfaced with silicon photonics, electronics, and MEMS devices and may enable multiple functions for coherent signal processing in the classical and quantum domains. KEYWORDS: cavity optomechanics, nanoelectro-opto-mechanical systems (NEOMS), silicon photonics, interdigitated transducers, microwave-to-optics conversion R ecent advances in nanotechnology have enabled the generation, manipulation, and detection of coherent motion in nanoscale devices using both optical and electrical regime is highly relevant for classical and quantum applications, since most wireless networks deployed so far operate at GHz frequencies and superconducting qubits have signals. Such devices, usually termed nanoelectro-opto- frequencies in that range. Therefore, microwave-to-optics mechanical systems (NEOMS),1 hold the promise for conversion (and vice versa) using NEOMS has become a disruptive applications in the classical and quantum realms, hot scientific topic in recent years. including, for example, microwave photonics,2 sensing,3 Microwave-to-optics conversion in on-chip NEOMS has electro-optical modulation,4 and coherent microwave-to-optics been demonstrated in several technological platforms such as interfaces.5 The realization of on-chip NEOMS requires several aluminum nitride (AlN),11,12 gallium arsenide (GaAs),13−16 features to be simultaneously fulfilled. To ensure strong lithium niobate (LN),17−19 and gallium phosphide (GaP).20,21 optomechanical (OM) interaction, transparent materials able However, in order to ensure coexistence and interoperation of to confine photons and phonons in the same small volumes are NEOMS with mainstream electronic, photonic, and MEMS needed. This usually requires released high refractive index devices, it is highly desirable to implement them on a silicon films properly structured to form either waveguides or cavities platform and using CMOS-compatible fabrication processes. with enough overlapping of the photonic and phononic The realization of silicon NEOMS has a major roadblock, fields.4,6,7 In such optomechanical crystals,8 cavities designed which is that silicon is not piezoelectric. This means that other to confine light at telecom wavelength typically support alternatives must be explored to perform the electromechanical mechanical modes at several GHz frequencies. (EM) operations. Some approaches make use of the low- The conversion of mechanical waves from electrical signals frequency electric fields between metallic strips to exert a force can be achieved by means of metal-contacted piezoelectric that leads to mechanical motion.22,23 However, this approach is materials. Forming interdigitated transducers (IDT) enables generation of surface acoustic waves (SAW), the frequency of which depends on the IDT period.9 The generated SAWs can Received: October 21, 2021 be further converted to volume mechanical vibrations and vice Published: February 1, 2022 versa10 and interact with optical fields confined in the cavity. IDTs with submicrometer periods can excite SAWs at frequencies of several GHz, which can couple to the mechanical modes in the OM crystals cavities. This microwave © 2022 American Chemical Society https://doi.org/10.1021/acsphotonics.1c01614 413 ACS Photonics 2022, 9, 413−419 ACS Photonics pubs.acs.org/journal/apchd5 Letter Figure 1. Experimental setup and NEOMS platform. A tunable fiber is linearly polarized and connected to a tapered fiber loop that is brought into contact with an adiabatic integrated waveguide, enabling the optical excitation of an optical resonance of an OM cavity. Reflection and transmission can be collected with near-IR photodiodes PD1 and PD2, respectively. The laser power is set to be on the order of the hundreds of μW so that radiation pressure forces can be neglected and the optical signal is only used for transducing the mechanical motion. The RF spectrum of the reflected signal can be extracted with a Spectrum Analyzer (SA). Coherent piezo-electrical excitation is performed with of a Vector Network Analyzer (VNA), which is connected to the input Interdigitated Transducers (IDT) through port 1. In this case, the reflected signal is connected to port 2 of the VNA, so that S21 provides the coherent response of an OM cavity optical resonance to the piezo-electrical excitation. The top SEM image shows a device consisting of two focusing Al IDTs (with contact pads connected to metallic characterization tips) on the AlN layer (left and right parts of the image) and a released nc-Si OM circuit between them. The OM cavity is also connected to the input and output IDTs for electrical injection of coherent phonons. The bottom SEM image shows a zoom of the OM cavity coupled to a waveguide with a mirror. Details of the fiber-waveguide coupling are also shown. The top left inset shows typical transmission (black) and reflection (red) optical spectra of one of the test devices when coupled to the tapered waveguide. highly inefficient, requires very large electric powers to operate, insulator wafers (SOI) typically used in the fabrication of and cannot reach the microwave frequency regime. Increasing silicon OM circuitry. Here, we demonstrate microwave-to- the efficiency by bringing the metal strips closer would result in optics transduction using 2 GHz mechanical mode excited by higher optical losses. A different technique consists of the SAW and coupled to a 200 THz optical mode in a nc-Si integration of piezoelectric material, such as AlN, on a silicon fishbone optomechanical nanobeam.31−33 Our platform paves wafer. This approach has been recently used to demonstrate the way toward realization of room-temperature NEOMS EM and OM interaction in silicon waveguides, leading to compatible based-on CMOS technology for a wide variety of broadband nonreciprocal behavior.24 More recently, combina- applications. ■ tion of either AlN and IDTs25 or microwave resonators26 with released crystalline silicon nanobeams has resulted in DESCRIPTION OF THE TECHNOLOGY PLATFORM successful demonstration of microwave-to-optics conversion at cryogenic temperatures. Indeed, it has been suggested27 that Figure 1 shows the experimental setup for characterizing the AlN on Si NEOMS reunite the best of both worlds, NEOMS a scanning electron microscope (SEM) images of one piezoelectric and optomechanical behavior, provided that the of the tested devices (top right inset) and a zoom of the OM performance of each component is kept when building the cavity and the waveguide for evanescent light coupling devices. (bottom right inset). The design of the OM crystal is based In this work, we demonstrate an alternative silicon platform on the corrugated unit cell described elsewhere that displays a for NEOMS using Al IDTs on piezoelectric AlN layer to full phononic bandgap around 4 GHz and several additional generate coherent GHz frequency mechanical waves that phononic pseudogaps in the GHz region,31 as experimentally efficiently interact with optical fields in released OM cavities demonstrated in refs33 and 34. The cavity region is operating at room temperature. The core material to guide and constructed with 12 central cells in which the pitch, the radius confine both photons and phonons is nanocrystalline-silicon of the hole, the stubs length and the stubs width are varied in a (nc-Si), which has shown optical and mechanical properties quadratic way toward the center. The first three geometrical similar to those of crystalline silicon (c-Si).28 Advantages over parameters progressively decrease while the latter increases. c-Si include (i) the optical, mechanical, and thermal properties This OM cavity, in contrast to one in which the stubs width is of nc-Si can be tuned by annealing when transforming the constant, allows bringing down in energy the phononic amorphous Si film to nanocrystalline (for details, see SI) as the breathing modes so that those in the 2.0−2.5 GHz region properties depend on the grain size,28−30 (ii) the thickness, coming from the Γ point of the second even−even band are stress, grain size, and doping can be tuned independently, placed in a pseudogap for modes of similar spatial parity.31 adding extra degrees of freedom in the material and device This leads to two improved features in comparison with the design, and (iii) nc-Si NEOMS are processed on standard standard design. On the one hand, the breathing modes silicon wafers, which are less expensive than silicon-on- appearing now close to 2.0 GHz, being protected by the 414 https://doi.org/10.1021/acsphotonics.1c01614 ACS Photonics 2022, 9, 413−419 ACS Photonics pubs.acs.org/journal/apchd5 Letter Figure 2. Microwave-to-optics transduction from electro-opto-mechanical characterization. The black curve shows a RF spectrum measured by the Spectrum Analyzer (SA) of thermally activated modes. The red curve shows a piezo-optical S21 coherent spectrum measured with the Vector Network Analyzer (VNA). Both curves are transduced optically by coupling light into the 1560 nm optical resonance of the OM cavity. The inset shows FEM simulations of supported optical and mechanical modes displaying OM coupling rates (gOM/2π) of 200 kHz obtained by importing the geometrical profile from a SEM image of the measured device. The resolution bandwidth of the coherent measurement is 400 kHz, which limits the line width of the mechanical resonances. pseudogap, enhance their Q-factors otherwise dominated by scattering. The top left inset to Figure 1 displays characteristic leakage through the mirrors. In this regard, it is also worth transmission (black trace) and reflection (red trace) spectra of noticing that material losses of GHz modes in optimized nc-Si one of the test devices. The coupling spectral bandwidth of the OM cavities are a factor of 2−3 lower than those made of c-Si waveguide adiabatic coupler is about 50 nm and its central thanks to nc-Si material tensile stress.28−30 On the second wavelength for maximum coupling depends on the specific hand, since the IDTs are designed to operate at 2 GHz with an position the tapered fiber contacts the tapered region of the average bandwidth of about 0.2 GHz (see Figures S1 and S2 in the Supporting Information), they can resonantly excite those waveguide, thus enabling tunability over the whole spectral breathing modes effectively. Finally, FEM simulations of the range of the tunable laser. The transmission spectrum also actual cavities realized by their contour retrieved from SEM shows an oscillatory behavior associated with optical modes of images resulted in vacuum OM coupling rates g0/2π ≈ 200 the fiber loop and a minimum at around 1560, where all the kHz, which is a large enough value to observe a wide range of input light has effectively being coupled into the waveguide. OM phenomena and comparable with what is obtained in the Indeed, the contact position is chosen to maximize the optical standard design.31 fiber-to-waveguide coupling in the spectral range where the The displacement readout of the mechanical cavity mode OM cavity modes appear. The latter become apparent in the amplitude is done by coupling light into the optical cavity reflection spectrum as resonant dips in the signal reflected by using an integrated waveguide that can be accessed by a the waveguide mirror. In the upper left inset, two OM cavity tapered fiber via an adiabatic coupler. It consists of a region in which the waveguide smoothly increases its width by 90 nm in resonances appear around 1560 and 1590 nm with Q-factors a region placed before a 90° bend, so that its effective index ≈104. It is worth noticing that the transmitted signal does not matches that of the tapered fiber loop placed on top of the contain any information from the OM cavity, which is only guide.35 The bottom SEM picture in Figure 1 shows also embedded in the reflected signal. details of the final part of the input integrated waveguide, The IDTs were circular to electrically excite and focus the which is terminated with a photonic crystal mirror based on a SAW, which was converted into guided mechanical waves at unit cell with an optical band gap for TE modes similar to that the entrance of the released nanobeam. Simulation results of the outer cells of the OM cavity. The waveguide mirror suggest that conversion efficiencies close to 1% at 2 GHz are region contains a tapered region of holes of increasing achievable using realistic parameters.10 Experimental laser diameter that reduces the losses associated with the optical Doppler vibrometry results using 1 GHz IDTs confirmed that a mode mismatch between the propagating and the mirror SAW is generated by the IDTs and is focused into a released regions. These characteristics, together with an optimized relative positioning of the waveguide and mirror region with nanobeam, where high intensities of mechanical guided waves respect to the OM cavity, enables the coupling of about 50% of are observed.37 This implies that such mechanical waves the waveguide input light into the optical modes of the OM should strongly interact with optical waves if an OM cavity is cavity.36 The missing half of the power that does not reflect inserted in the mechanical path and if both mechanical and back is likely lost in the mirror of the waveguide due to optical waves resonate in the cavity. 415 https://doi.org/10.1021/acsphotonics.1c01614 ACS Photonics 2022, 9, 413−419 ACS Photonics pubs.acs.org/journal/apchd5 Letter Figure 3. Electro-mechanical efficiency estimation. Number of coherent phonons as a function of the VNA output electrical power for a mechanical mode at Ωm/2π = 2.058 GHz. The right vertical axis indicates the corresponding average squared deformation. The top inset shows the RF spectra of the thermal noise when the VNA electrical driving is off (red curve) and on with a power of 1nW (black curve). The bottom inset shows the piezo-optical coherent response as a function of the VNA electrical driving power. ■ ELECTRO-OPTO-MECHANICAL CHARACTERIZATION of the mechanical excitation of the specific OM cavity mechanical modes. In fact, we have observed substantial spectral differences in S21 depending on which IDT is used for Thermally activated mechanical modes can be optically SAW excitation (see Figure S4 in the Supporting Information). transduced and observed in the Spectrum Analyzer (SA) It is also worth mentioning that the actual values of S21 reflect when the excitation laser wavelength is in resonance with an just the ratio between the power output by port 1 of the VNA optical cavity mode and the modes have a minimum degree of and the incoming electrical power provided by the photo- OM coupling rate to overcome the experimental noise level. detector to port 2, so it does not provide a quantitative The radiofrequency (RF) spectrum measured with the SA is measure of the energy efficiency of the electro-optomechanical shown in the black curve of Figure 2 and displays a set of process occurring in the device. ■ mechanical breathing modes of interest for this work appearing slightly above 2 GHz. Mechanical Q-factors, measured at room temperature, reach 4 × 103. This value is an order of ELECTRO-MECHANICAL EFFICIENCY ESTIMATION magnitude higher than the values measured from samples The average phonon number of a given mode of eigenfre- fabricated using nc-Si with all the stubs identical on cavity quency Ωm in the high temperature (T) regime can be modes of similar origin but not placed in a pseudo gap.29 approximated by n̅th ≈ κBT/ℏΩm, where κB and ℏ are the Moreover, the Q-factors are about a factor of 2 larger than the Boltzmann and Planck constants, respectively. It is then modes appearing at GHz range, placed either in pseudo or full straightforward to quantify, in the SA, the average number of gaps, in c-Si OM cavities, thus, confirming the beneficial role of coherent OM cavity phonons driven by the IDT(Ncoh ph ) by tensile stress in reducing mechanical losses by attenuating the comparing the RF overall power contained in the coherent thermo-elastic coupling.28,33 peak at the excitation frequency (Scoh(Ωcoh)) with that Before interpreting the measurements of optically trans- contained in the thermally activated one (Sth(Ωm)) for duced coherently driven motion, it is important to state that equivalent experimental conditions. The latter magnitudes when the optical excitation is not in resonance with an OM are calculated by just integrating the areas beneath the RF cavity mode, S21 gives values below −120 dB without peaks. The expression for evaluating Ncoh ph , which is propor- significant spectral features (see Figure S1 in the Supporting tionally related to the averaged squared deformation ⟨x2coh⟩, Information). On the contrary, when the laser is in resonance reads as the follows: with an optical mode such as the displayed in the lower part of the inset to Figure 2, the piezo-optic S21 response (red curve of coh Scoh(Ωcoh) Nph = nth ̅ S (Ω ) Figure 2) exhibits a rich structure of coherent peaks which, in th m (1) some cases, overcome the noise level by 60 dB in a region consistent with the central operating frequency and bandwidth In Figure 3 we estimate the electro-mechanical conversion of the IDTs. Several peaks match the frequencies of the efficiency by showing the evaluation of Ncoh ph using eq 1 for the thermally activated mechanical modes (highlighted with case of a mechanical mode at Ωm/2π = 2.058 GHz as a vertical dashed lines), an example of which is illustrated in function of the VNA output electrical power. The data follow a the upper part of the inset to Figure 2. The relative height of linear trend, the slope of which allows extracting an electro- the different peaks does not match in the two experiments mechanical conversion efficiency of 228 coherent phonons/ because, in the case of S21, the spectral response is not only μW, which is limited by the ohmic losses at the contacts determined by the OM coupling rate as in the SA spectrum, between the metallic tips and the Al pads. This value is of the but also by the spectral response of the IDT and the efficiency same order of magnitude reported in ref 13 using an IDT with 416 https://doi.org/10.1021/acsphotonics.1c01614 ACS Photonics 2022, 9, 413−419 ACS Photonics pubs.acs.org/journal/apchd5 Letter an order of magnitude narrower bandwidth than in our device. possibility to, for example, fabricate multilayer systems. Besides Indeed, thanks to the broad IDT bandwidth, we obtain similar application in quantum networks to transfer qubits via optical responses with power on the various mechanical modes that links,10 the possibility to have interacting microwave and appear in the black curve of Figure 2. The linear dependence of optical signals in CMOS silicon chips operating at room Ncoh ph with VNA output power is consistent with the observation temperature opens new avenues in integrated microwave of the invariability of the S21 spectral response plotted in the photonics,2 with prospects for application in all-optical lowest inset to Figure 3, thus, implying a linear mechanical processing in wireless networks.38 Finally, these results are response with injected electrical power. We have also very encouraging to advance the use of multistate variables in a quantified the minimum number of coherent phonons that single chip for optimal information transmission and can be detected, that is, the peak sensitivity, which is about 2.6 processing. coherent phonons using a resolution bandwidth of 3 kHz (0.05 coherent phonons/Hz1/2) and a VNA output power slightly below 1 nW. The top inset in Figure 3 shows this ■ * ASSOCIATED CONTENT sı Supporting Information measurement, where the red and black curves display the RF The Supporting Information is available free of charge at spectrum around the mechanical resonance when the electrical https://pubs.acs.org/doi/10.1021/acsphotonics.1c01614. driving is off and on, respectively. A narrow peak at Ωcoh in the center of the mechanical resonance of the black curve stands Device fabrication; Experimental setup; Piezo-optical out of the thermal background, thus, enabling the quantifica- coherent response: noise level, IDT bandwidth, phase tion of Ncoh response, injected power dependence, and IDT depend- ph . Considering the electro-mechanical conversion efficiency and the sensitivity values reported above we can also ence; RF spectra vs VNA output power (PDF) compute the minimum electrical power that can be converted in a measurable optical signal, that is, the peak sensitivity for electro-mechanical conversion, which is about 10 nW using a ■ AUTHOR INFORMATION Corresponding Author RBW of 3 kHz (0.2 nW/Hz1/2). Finally, it is worth noting that, Alejandro Martínez − Nanophotonics Technology Center, when performing the coherent piezo-optical measurement of Universitat Politècnica de Valencia, 46022 Valencia, Spain; S21 with the VNA, the peak sensitivity improves dramatically, orcid.org/0000-0001-5448-0140; Email: amartinez@ decreasing its value by several orders of magnitude thanks to a ntc.upv.es much lower noise level. ■ CONCLUSIONS In summary, we have presented a new platform for on-chip Authors Daniel Navarro-Urrios − Catalan Institute of Nanoscience and Nanotechnology (ICN2), CSIC and BIST, 08193 NEOMS which is completely compatible with CMOS Barcelona, Spain; MIND-IN2UB, Departament technology. Microwave-to-optical conversion at room temper- d’Electrònica, Facultat de Física, Universitat de Barcelona, ature has been demonstrated with a peak sensitivity below 3 08028 Barcelona, Spain; orcid.org/0000-0001-9055- phonons. Electro-mechanical conversion efficiencies have been 1583 evaluated, leading to values of more than 200 coherent cavity Martín F. Colombano − Catalan Institute of Nanoscience and phonons per microwatt of electrical power. The latter value can Nanotechnology (ICN2), CSIC and BIST, 08193 Barcelona, be greatly improved by reducing the ohmic losses in the IDT Spain contacts, by means of wire bonding the contacts of the IDTs to Guillermo Arregui − Catalan Institute of Nanoscience and the electric signal source. Our platform, which so far is a proof- Nanotechnology (ICN2), CSIC and BIST, 08193 Barcelona, of-concept, compares very well in performance to the Spain competition10−19 in terms of mechanical frequency and OM Guilhem Madiot − Catalan Institute of Nanoscience and coupling rate. The key and crucial advantages are room Nanotechnology (ICN2), CSIC and BIST, 08193 Barcelona, temperature operation and complete compatibility with Si Spain; orcid.org/0000-0003-2662-4324 technologies, which enables coexistence with silicon elec- Alessandro Pitanti − NEST, Istituto Nanoscienze − CNR and tronics, photonics, and MEMS. The use of nc-Si instead of its Scuola Normale Superiore, I-56127 Pisa, Italy crystalline counterpart adds flexibility in tuning optical, Amadeu Griol − Nanophotonics Technology Center, mechanical, and thermal properties of the system. The Universitat Politècnica de Valencia, 46022 Valencia, Spain performance can be easily improved by perfectly matching Tapani Makkonen − VTT Technical Research Centre of the mechanical frequency of the OM cavity with the IDTs Finland Ltd., FI-02044 Espoo, Finland response. The frequency of the IDTs depends on the pitch of Jouni Ahopelto − VTT Technical Research Centre of Finland the electrode fingers and can be increased up to at least 10 Ltd., FI-02044 Espoo, Finland GHz. At higher frequencies, series resistances and the coupling Clivia M. Sotomayor-Torres − Catalan Institute of coefficient may become limiting factors. In addition to the Nanoscience and Nanotechnology (ICN2), CSIC and BIST, novelty of combining AlN with Si, we have unambiguously 08193 Barcelona, Spain; Catalan Institute for Research and demonstrated the possibility to excite mechanical vibrations in Advances Studies ICREA, 08010 Barcelona, Spain; nanobeams using focusing of the SAWs, leading to enhanced orcid.org/0000-0001-9986-2716 oscillation amplitudes. The integration of AlN with a Complete contact information is available at: nonpiezoelectric material such as silicon represents a https://pubs.acs.org/10.1021/acsphotonics.1c01614 technological breakthrough in designing and realizing NOEMS components. Furthermore, the platform developed Funding here is based on nanocrystalline silicon, which is more This research has received funding from the European Union affordable than crystalline silicon and more versatile, with the H2020 FET Open Project PHENOMEN (No. 713450). The 417 https://doi.org/10.1021/acsphotonics.1c01614 ACS Photonics 2022, 9, 413−419 ACS Photonics pubs.acs.org/journal/apchd5 Letter ICN2 authors acknowledge support by the Severo Ochoa (18) Shao, L.; Yu, M.; Maity, S.; Sinclair, N.; Zheng, L.; Chia, C.; program from Spanish MINECO (Grant No. SEV-2019- Shams-Ansari, A.; Wang, C.; Zhang, M.; Lai, K.; Lončar, M. 0706), the MCIN project SIP (PGC2018-101743-B-100), and Microwave-to-optical conversion using lithium niobate thin-film by the CERCA Programme Generalitat de Catalunya. G.A. was acoustic resonators. Optica 2019, 6, 1498−1505. (19) Jiang, W.; Sarabalis, C. J.; Dahmani, Y. D.; Patel, R. N.; Mayor, supported by a BIST and MFC by a S. Ochoa Project Ph.D. F. M.; McKenna, T. P.; Van Laer, R.; Safavi-Naeini, A. H. Efficient studentships. G. M. acknowledges support from the EU ERC bidirectional piezo-optomechanical transduction between microwave project LEIT (GA Nr. 885689). A.M. acknowledges support and optical frequency. Nat. 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(38) Mercadé, L.; Morant, M.; Griol, A.; Llorente, R.; Martínez, A. Photonic frequency conversion of OFDM microwave signals in a wavelength-scale optomechanical cavity. Laser & Photon. Rev. 2021, 15, 2100175. Recommended by ACS Monolithically Integrated Ultralow Threshold Topological Corner State Nanolasers on Silicon Taojie Zhou, Zhaoyu Zhang, et al. NOVEMBER 08, 2022 ACS PHOTONICS READ Subwavelength Control of Photons and Phonons in Release- Free Silicon Optomechanical Resonators Jianhao Zhang, Carlos Alonso Ramos, et al. DECEMBER 06, 2022 ACS PHOTONICS READ Light Modulation in Silicon Photonics by PZT Actuated Acoustic Waves Irfan Ansari, Dries Van Thourhout, et al. MAY 20, 2022 ACS PHOTONICS READ Dual Band Computational Infrared Spectroscopy via Large Aperture Meta-Optics Johannes E. Fröch, Arka Majumdar, et al. SEPTEMBER 19, 2022 ACS PHOTONICS READ Get More Suggestions > 419 https://doi.org/10.1021/acsphotonics.1c01614 ACS Photonics 2022, 9, 413−419