PUBLICATIONS

Sahil Dagli, Jiyong Shim, Hamish Carr Delgado, Halleh B Balch, Sajjad Abdollahramezani, Chih-Yi Chen, Varun Dolia, Elissa Klopfer, Jefferson Dixon, Jack Hu, Babatunde Ogunlade, Jung-Hwan Song, Mark L Brongersma, David Barton, Jennifer A Dionne. DOI

Electrically tunable metasurfaces that control the amplitude and phase of light through biasing of nanoscale antennas present a route to compact, sub-micron thick modulator devices. However, most platforms face limitations in bandwidth, absolute optical efficiency, and tuning response. Here, we present electro-optically tunable metasurfaces capable of both GHz amplitude modulation and transmissive wavefront shaping in the telecom range. Our resonant electro-optic nanoantenna design consists of a silicon nanobar atop thin-film lithium niobate, with gold electrodes. The silicon nanobar is a periodically perturbed optical waveguide that supports high quality factor (Q >1000) guided mode resonances excited with free space light. Applying a voltage bias to the lithium niobate tunes its refractive index, modulating the resonant behavior of the silicon nanobar through evanescent mode overlap. We demonstrate an absolute transmittance modulation of 7.1% with ±5 V applied voltage, and show the dependence of this modulation behavior on the resonance quality factor. We additionally study the electrode limitations on modulation bandwidth, demonstrating bandwidths exceeding 800 MHz. Finally, we show how this resonant antenna platform can be used to design wavefront shaping metasurfaces. We demonstrate a beamsplitting metasurface device, whose diffraction efficiency can be modulated with a bandwidth of 1.03 GHz. The high-speed modulation and wavefront control capabilities of this platform provide a foundation for compact, high bandwidth free space communications and sensing devices.

Varun Dolia, Halleh B. Balch, Sahil Dagli, Sajjad Abdollahramezani, Hamish Carr Delgado, Parivash Moradifar, Kai Chang, Ariel Stiber, Fareeha Safir, Mark Lawrence, Jack Hu, Jennifer A. Dionne. arXiv / PDF

Metasurfaces provide a versatile and compact approach to free-space optical manipulation and wavefront shaping. Comprised of arrays of judiciously-arranged dipolar resonators, metasurfaces precisely control the amplitude, polarization, and phase of light, with applications spanning imaging, sensing, modulation, and computing. Three crucial performance metrics of metasurfaces and their constituent resonators are the quality-factor (Q-factor), mode volume (Vm), and ability to control far-field radiation. Often, resonators face a trade-off between these parameters: a reduction in Vm leads to an equivalent reduction in Q, albeit with more control over radiation. Here, we demonstrate that this perceived compromise is not inevitable – high-Q, sub-wavelength Vm, and controlled dipole-like radiation can be achieved, simultaneously. We design high-Q, very-large-scale-integrated silicon nanoantenna pixels – VINPix – that combine guided mode resonance waveguides with photonic crystal cavities. With optimized nanoantennas, we achieve Q-factors exceeding 1500 with Vm less than 0.1 (λ/nair )3 . Each nanoantenna is individually addressable by free-space light, and exhibits dipole-like scattering to the far-field. Resonator densities exceeding a million nanoantennas per cm2 can be achieved, as demonstrated by our fabrication of an 8 mm × 8 mm VINPix array. As a proof-of-concept application, we demonstrate spectrometer-free, spatially localized, refractive-index sensing utilizing a VINPix array. Our platform provides a foundation for compact, densely multiplexed devices such as spatial light modulators, computational spectrometers, and in-situ environmental sensors.

Jack Hu, Fareeha Safir, Kai Chang, Sahil Dagli, Halleh B. Balch, John M. Abendroth, Jefferson Dixon, Parivash Moradifar, Varun Dolia, Malaya K. Sahoo, Benjamin A. Pinsky, Stefanie S. Jeffrey, Mark Lawrence & Jennifer A. Dionne. DOI / PDF

Genetic analysis methods are foundational to advancing personalized medicine, accelerating disease diagnostics, and monitoring the health of organisms and ecosystems. Current nucleic acid technologies such as polymerase chain reaction (PCR) and next-generation sequencing (NGS) rely on sample amplification and can suffer from inhibition. Here, we introduce a label-free genetic screening platform based on high quality (high-Q) factor silicon nanoantennas functionalized with nucleic acid fragments. Each high-Q nanoantenna exhibits average resonant quality factors of 2,200 in physiological buffer. We quantitatively detect two gene fragments, SARS-CoV-2 envelope (E) and open reading frame 1b (ORF1b), with high-specificity via DNA hybridization. We also demonstrate femtomolar sensitivity in buffer and nanomolar sensitivity in spiked nasopharyngeal eluates within 5 minutes. Nanoantennas are patterned at densities of 160,000 devices per cm2, enabling future work on highly-multiplexed detection. Combined with advances in complex sample processing, our work provides a foundation for rapid, compact, and amplification-free molecular assays.

Halleh B. Balch†, Allister F. Mcguire†, Jason Horng†, Hsin-Zon Tsai, Kevin Li, Yi-Shiou Duh, Michael F. Crommie, Bianxiao Cui, Feng Wang. DOI / PDF / Berkeley News Coverage

The measurement of electrical activity across networks of excitable cells underlies current progress in neuroscience, cardiology, pharmacology, and neurotechnology. From microvolts to millivolts and microns to millimeters, the activity of electrogenic networks spans over three orders of magnitude of intensity, space, and time, which poses substantial technological challenge. As a result, the development of non-invasive, parallel, and scalable methods that permit network-scale recordings with single-cell spatial resolution remains key to enabling studies of electrogenic cells, emergent networks, and bioelectric computation. Here, we demonstrate a new technique capable of label-free imaging of extracellular potentials with high spatial resolution across an electrogenic network. The critically coupled waveguide-amplified graphene electric field (CAGE) sensor leverages the unique electric field-sensitive optical transitions in graphene to convert extracellular potentials into the optical regime, permitting simultaneous single-shot spatially resolved readout of electrogenic firing across a wide field of view. As a proof-of-concept, we demonstrate noninvasive label-free detection of native electrical activity from cardiac action potentials, simultaneously map the propagation of these potentials across a cellular network, and sensitively monitor their modification by pharmacological agents. This platform is robust, scalable to highly parallel detection, and directly compatible with existing microscopy techniques for multi-modal correlative imaging.

Halleh B. Balch, Austin M. Evans†, Raghunath R. Dasari†, Hong Li†, Ruofan Li†, Simil Thomas, Danqing Wang, Ryan P. Bisbey, Kaitlin Slicker, Ioannina Castano, Sangni Xun, Lili Jiang, Chenhui Zhu, Nathan Gianneschi, Daniel C. Ralph, Jean-Luc Brédas, Seth R. Marder, William R. Dichtel, Feng Wang. DOI / PDF / JACS Spotlight / Berkeley Lab ALS Highlight

Emergent quantum phenomena in electronically coupled two-dimensional heterostructures are central to next-generation optical, electronic, and quantum information applications. Tailoring electronic band gaps in coupled heterostructures would permit control of such phenomena and is the subject of significant research interest. Two-dimensional polymers (2DP) offer a compelling route to tailored band structures through the selection of molecular constituents. However, despite this promise of synthetic flexibility and electronic design, fabrication of 2DPs that form electronically coupled 2D heterostructures remains an outstanding challenge. Here, we report the rational design and optimized synthesis of an electronically coupled semiconducting 2DP/2D transition metal dichalcogenide (TMDC) heterostructure, demonstrate direct exfoliation of the highly crystalline and oriented 2DP films down to a few nanometers, and present the first thickness-dependent study of 2DP/TMDC vdW heterostructures. Control over the 2DP layers reveals enhancement of the 2DP photoluminescence by two orders of magnitude in ultra-thin sheets and an unexpected thickness-dependent modulation of the ultrafast excited state dynamics in the 2DP/TMDC heterostructure. These results provide fundamental insight into the electronic structure of 2DPs and present a route to tune emergent quantum phenomena in 2DP hybrid vdW heterostructures.

Alisha Geldert†, Halleh B. Balch†, Anjali Gopal, Alison Su, Samantha M. Grist, Amy E. Herr Berkeley News / Web

Ultraviolet-C decontamination holds promise in combating the COVID-19 pandemic, particularly with its potential to mitigate the N95 respirator shortage. Safe, effective, and reproducible decontamination depends critically on UV-C dose, yet dose is frequently measured and reported incorrectly, which results in misleading and potentially harmful protocols. Understanding best practices in UV-C dose measurement for N95 respirator decontamination is essential to the safety of medical professionals, researchers, and the public. Here, we outline the fundamental optical principles governing UV-C irradiation and detection, as well as the key metrics of UV-C wavelength and dose. In particular, we discuss the technical and regulatory distinctions between UV-C N95 decontamination and other applications of germicidal UV-C, and highlight the unique considerations required for UV-C N95 decontamination. Together,this discussion will inform best practices for UV-C dose measurement for N95 respirator decontamination during crisis-capacity conditions.

Austin M. Evans, Ashutosh Giri, Vinod K. Sangwan, Sangni Xun, Matthew Bartnof, Carlos G. Torres-Castanedo, Halleh B. Balch, Matthew S. Rahn, Nathan P. Bradshaw, Edon Vitaku, David W. Burke, Hong Li, Michael J. Bedzyk, Feng Wang, Jean-Luc Brédas, Jonathan A. Malen, Alan J. H. McGaughey, Mark C. Hersam, William R. Dichtel, Patrick E. Hopkins DOI

Covalent organic frameworks (COFs) are crystalline polymers with covalent bonds in two or three dimensions, providing pores 1–5 nm in diameter. COFs are typically isolated as microcrystalline powders, which are unsuitable for many applications that would leverage their tunable structures, such as opto- electronic devices and nanofiltration membranes. Here, we report the interfa- cial polymerization of polyfunctional amine and aldehyde monomers with a Lewis acid catalyst, Sc(OTf)3. Immiscible solutions segregate the catalyst from the monomers, confining polymerization to the solution interface. This method provides large-area, continuous COF films (several cm2) with a thickness tuned from 100 mm to 2.5 nm. Relatively thick films were crystalline, whereas the films that are a few nanometers thick were presumably amorphous. The COF films were transferred onto polyethersulfone supports, and the resulting membranes showed enhanced rejection of Rhodamine WT, a model water contaminant. The large area, tunable pore size, and tailored molecular composition show promise for nanofiltration applications

Michio Matsumoto, Lauren Valentino, Gregory M. Stiehl, Halleh B. Balch, Amanda R. Corcos, Feng Wang, Daniel C. Ralph, Benito J. Marinas, and William R. Dichtel. DOI / PDF

Covalent organic frameworks (COFs) are crystalline polymers with covalent bonds in two or three dimensions, providing pores 1–5 nm in diameter. COFs are typically isolated as microcrystalline powders, which are unsuitable for many applications that would leverage their tunable structures, such as opto- electronic devices and nanofiltration membranes. Here, we report the interfa- cial polymerization of polyfunctional amine and aldehyde monomers with a Lewis acid catalyst, Sc(OTf)3. Immiscible solutions segregate the catalyst from the monomers, confining polymerization to the solution interface. This method provides large-area, continuous COF films (several cm2) with a thickness tuned from 100 mm to 2.5 nm. Relatively thick films were crystalline, whereas the films that are a few nanometers thick were presumably amorphous. The COF films were transferred onto polyethersulfone supports, and the resulting membranes showed enhanced rejection of Rhodamine WT, a model water contaminant. The large area, tunable pore size, and tailored molecular composition show promise for nanofiltration applications

 Jason Horng†, Halleh B. Balch†, Allister F. McGuire, Hsin-Zon Tsai, Patrick R. Forrester, Michael F. Crommie, Bianxiao Cui, Feng Wang DOI / PDF / arXiv / Berkeley Lab

The use of electric fields for signalling and control in liquids is widespread, spanning bioelectric activity in cells to electrical manipulation of microstructures in lab-on-a-chip devices. However, an appropriate tool to resolve the spatio-temporal distribution of electric fields over a large dynamic range has yet to be developed. Here we present a label-free method to image local electric fields in real time and under ambient conditions. Our technique combines the unique gate-variable optical transitions of graphene with a critically coupled planar waveguide platform that enables highly sensitive detection of local electric fields with a voltage sensitivity of a few microvolts, a spatial resolution of tens of micrometres and a frequency response over tens of kilohertz. Our imaging platform enables parallel detection of electric fields over a large field of view and can be tailored to broad applications spanning lab- on-a-chip device engineering to analysis of bioelectric phenomena.