Recent progress in ultrafast spectroscopy and semiconductor technology is enabling unique applications in screening, detection, and diagnostics in the Terahertz (T‐ray) regime. The promise of ...efficaciously operation in this spectral region is tempered by the lack of devices that can spectrally analyze samples at sufficient temporal and spatial resolution. Real‐time, multispectral T‐ray (Mul‐T) imaging is reported by designing and demonstrating hyperspectral metamaterial focal plane array (MM‐FPA) interfaces allowing multiband (and individually tunable) responses without compromising on the pixel size. These MM‐FPAs are fully compatible with existing microfabrication technologies and have low noise when operating in the ambient environment. When tested with a set of frequency switchable quantum cascade lasers (QCLs) for multicolor illumination, both MM‐FPAs and QCLs can be tuned to operate at multiple discrete THz frequencies to match analyte “fingerprints.” Versatile imaging capabilities are presented, including unambiguous identification of concealed substances with intrinsic and/or human‐engineered THz characteristics as well as effective diagnosis of cancerous tissues without notable spectral signatures in the THz range, underscoring the utility of applying multispectral approaches in this compelling wavelength range for sensing/identification and medical imaging.
A real‐time, multispectral T‐ray (Mul‐T) imager based on multispectral metamaterial focal plane array and frequency switchable quantum cascade lasers is reported. Non‐destructive material identification and defect inspection for concealed tablets based on the Mul‐T imager are implemented successfully.
van der Waals nanomaterials supporting phonon polariton quasiparticles possess extraordinary light confinement capabilities, making them ideal systems for molecular sensing, thermal emission, and ...subwavelength imaging applications, but they require defect-free crystallinity and nanostructured form factors to fully showcase these capabilities. Here we introduce bottom-up-synthesized α-MoO3 structures as nanoscale phonon polaritonic systems that feature tailorable morphologies and crystal qualities consistent with bulk single crystals. α-MoO3 nanoribbons serve as low-loss hyperbolic Fabry–Pérot nanoresonators, and we experimentally map hyperbolic resonances over four Reststrahlen bands spanning the far- and mid-infrared spectral range, including resonance modes beyond the 10th order. The measured quality factors are the highest from phonon polaritonic van der Waals structures to date. We anticipate that bottom-up-synthesized polaritonic van der Waals nanostructures will serve as an enabling high-performance and low-loss platform for infrared optical and optoelectronic applications.
We employ synchrotron-based near-field infrared spectroscopy to image the phononic properties of ferroelectric domain walls in hexagonal (
) Lu
Sc
FeO
, and we compare our findings with a detailed ...symmetry analysis, lattice dynamics calculations, and prior models of domain-wall structure. Rather than metallic and atomically thin as observed in the rare-earth manganites, ferroelectric walls in
-Lu
Sc
FeO
are broad and semiconducting, a finding that we attribute to the presence of an
-site substitution-induced intermediate phase that reduces strain and renders the interior of the domain wall nonpolar. Mixed Lu/Sc occupation on the
site also provides compositional heterogeneity over micron-sized length scales, and we leverage the fact that Lu and Sc cluster in different ratios to demonstrate that the spectral characteristics at the wall are robust even in different compositional regimes. This work opens the door to broadband imaging of physical and chemical heterogeneity in ferroics and represents an important step toward revealing the rich properties of these flexible defect states.
Supramolecular Electronic Crystals
The cooperative tuning of a supramolecular electronic crystal enables access to a long‐lived hidden conducting phase with a broad temperature range from 2 to 360 K, ...through a pulsed electromagnetic field. In article number 2103000, Shenqiang Ren and co‐workers demonstrate a a dynamic and cooperative phase in K‐TCNQ, with the control of pulsed electromagnetic excitation. A dedicated charge–spin–lattice decoupling is required to activate and subsequently stabilize the non‐equilibrium phase.
A class of well‐defined, complex protein‐based 2D and 3D nanostructures with shape and function on demand is manufactured and assembled via “Protein Bricks” by precisely patterning on genetically ...engineered spider silk using ion and electron beams, as reported by Xiaoxia Xia, Tiger H. Tao, and co‐workers in article number 1705919. This approach provides a facile method for excellent biocompatibility, ease of functionalization, heterogeneous nanostructuring, and controllable 3D assembly, shedding light on a wide range of applications such as biosensing for structure enhanced fluorescence and biomimetic microenvironments for controlling cell fate.
The strong electron-lattice interactions in correlated electron systems provide unique opportunities for altering the material properties with relative ease and flexibility. In this Rapid ...Communication, we use localized strain control via a focused-ion-beam patterning of TiO2 substrates to demonstrate that one can selectively engineer the insulator-to-metal transition temperature, the fractional component of the insulating and metallic phases, and the degree of optical anisotropy down to the length scales of the intrinsic phase separation in VO2 thin films without altering the quality of the films. The effects of localized strain control on the strongly correlated electron system are directly visualized by state-of-the-art IR near-field imaging and spectroscopy techniques and x-ray microdiffraction measurements.
Ultrafast optical pump–optical probe and optical pump–terahertz probe spectroscopy were performed on vanadium dioxide (VO2) and vanadium sesquioxide (V2O3) thin films over a wide temperature range. A ...comparison of the experimental data from these two different techniques and two different vanadium oxides, in particular a comparison of the spectral weight oscillations generated by the photoinduced longitudinal acoustic modulation, reveals the strong electron-phonon coupling that exists in both materials. The low-energy Drude response of V2O3 appears more amenable than VO2 to ultrafast strain control. Additionally, our results provide a measurement of the temperature dependence of the sound velocity in both systems, revealing a four- to fivefold increase in VO2 and a three- to fivefold increase in V2O3 across the insulator-to-metal phase transition. Our data also confirm observations of strong damping and phonon anharmonicity in the metallic phase of VO2, and suggest that a similar phenomenon might be at play in the metallic phase of V2O3. More generally, our simple table-top approach provides relevant and detailed information about dynamical lattice properties of vanadium oxides, paving the way to similar studies in other complex materials.
Mid‐infrared (MIR) spectroscopy has been used with great success to quantitatively determine the mineralogy of geologic samples. It has been employed in a variety of contexts from determining bulk ...composition of powdered samples to spectroscopic imaging of rock thin sections via micro‐Fourier transform infrared (micro‐FTIR) imaging spectroscopy. Recent advances allow for IR measurements at the nanoscale. Near field nanoscale infrared imaging and spectroscopy with a broadband source (nano‐FTIR) enable understanding of the spatial relationships between compositionally distinct materials within a sample. This will be of particular use when analyzing returned samples from Bennu and Ryugu, which are thought to be compositionally like CI or CM1/2 carbonaceous chondrites. Returned samples will likely contain olivine/pyroxene chondrules that have been transformed into hydrous phyllosilicates, sulfides, carbonates, and other alteration phases. The use of near‐field infrared techniques to probe the boundaries between once pristine chondrules and alteration phases at the nanoscale is a novel approach to furthering our understanding of the compositional evolution of carbonaceous asteroids and the processes that drive their evolution. Here we report the results of nano‐FTIR spectroscopy and imaging measurements performed on the carbonaceous chondrite Allan Hills (ALH) 83100 (CM1/2). We show with nanoscale resolution that spatially resolved Fe‐Mg variations exist within the phyllosilicates around a chondrule rim. We also present effects of crystal orientation on the nano‐FTIR spectra to account for the spectral differences between the meteorite and mineral spectra.
Plain Language Summary
National Aeronautics and Space Administration's OSIRIS‐REx mission will return a sample of near‐Earth asteroid Bennu to Earth in September 2023. Based on remote sensing analyses of the asteroid, it is expected that the sample will be similar to CI or CM chondrite meteorites. Key remote sensing analyses of Bennu included thermal infrared emission spectroscopy. In this work, we conduct infrared spectral analyses of Allan Hills (ALH) 83100, a CM1/2 chondrite that shares spectral similarities to Bennu. We use synchrotron near‐field infrared nano‐infrared (nano‐IR) measurements to analyze the sample at scales of about 30 nm/pixel. This allows us to capture the spectra of very fine‐grained components in meteorites that contribute to their overall bulk spectra measured from remote sensing platforms. While nano‐IR spectra do not directly translate to remote‐sensing infrared measurements, identification of mineral and organic components in analog extraterrestrial materials provides key constraints on models of Bennu's composition from orbital infrared spectroscopy. We document the chemical alteration of a chondrule and show strong alteration gradients in the sample over length scales smaller than 10 microns. The variability in Fe and Mg in the phyllosilicate‐rich matrix of the meteorite over small spatial scales may indicate aqueous alteration in the ALH 83100 parent body as well as in the solar nebula.
Key Points
Nano‐Fourier transform infrared (nano‐FTIR) spectroscopy provides extremely fine‐scale (∼20 nm) spatially resolved mineralogic compositional information
Phyllosilicate spectra in Allan Hills (ALH) 83100 show Fe‐Mg variations around a chondrule rim
Effects of crystallographic orientation on the nano‐FTIR spectra are shown
Plume volcanism may sample mantle sources deeper than mid-ocean ridge and arc volcanism. Ocean island basalts (OIBs) are commonly related to plume volcanism, and their diverse isotopic and elemental ...compositions can be described using a limited number of mantle endmembers. However, the origins and depths of these mantle endmembers are highly debated. Here we show that the HIMU (high μ, μ =238U/204Pb) endmember may reside in the transition zone. Specifically, we report the geochemical signature of a high-pressure multiphase diamond inclusion, entrapped at 420–440 km depth and 1450 ±50 K, which matches exactly the geochemical patterns of the HIMU-rich OIBs. Since the HIMU component is variably sampled by almost all OIBs, our finding implies that the transition zone causes a major overprint of the geochemical features of mantle plumes. Furthermore, some mantle plumes, like those feeding Bermuda, St Helena, Tubuai and Mangaia, appear to be dominated by this source. Furthermore, our finding highlights the importance of the transition zone in highly incompatible element budget of the mantle.
Recent theoretical studies have suggested that transition metal perovskite oxide membranes can enable surface phonon polaritons in the infrared range with low loss and much stronger subwavelength ...confinement than bulk crystals. Such modes, however, have not been experimentally observed so far. Here, using a combination of far-field Fourier-transform infrared (FTIR) spectroscopy and near-field synchrotron infrared nanospectroscopy (SINS) imaging, we study the phonon-polaritons in a 100 nm thick freestanding crystalline membrane of SrTiO3 transferred on metallic and dielectric substrates. We observe a symmetric-antisymmetric mode splitting giving rise to epsilon-near-zero and Berreman modes as well as highly confined (by a factor of 10) propagating phonon polaritons, both of which result from the deep-subwavelength thickness of the membranes. Theoretical modeling based on the analytical finite-dipole model and numerical finite-difference methods fully corroborate the experimental results. Our work reveals the potential of oxide membranes as a promising platform for infrared photonics and polaritonics.
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