Polaritons Defy Symmetry
Nanoscale polaritons are crucial for nanophotonic devices. Hyperbolic polaritons (HPs) in high-symmetry crystals often lack directionality. In a recent eLight publication, scientists led by Profs. Zhang, Li, and Dai introduced a technique for anisotropic HP excitation and propagation. They discovered hyperbolic shear polaritons in low-symmetry crystals with enhanced directional propagation. This approach allows control of HPs' mirror symmetry without needing low crystalline symmetry. It enables tunable asymmetric polariton propagation, expanding possibilities for nanoscale light control and reconfigurable polaritonic devices.Introduced method breaks mirror symmetry in crystal polaritons, enabling control of asymmetry in HP responses. Offers nanoscale light manipulation and potential applications in nanoimaging, photonics, and quantum physics.
Coating Protects Ancient Pottery
Neolithic Cucuteni ceramic pottery is a valuable artifact that requires proper protection to ensure its preservation for future generations. In this study, polymer nanostructured material is used as protective coatings for the conservation of such ancient artefacts against UV ageing. In the context of comparative evaluation of the protective efficiency, this article reports the use of a functional coating that operates via specific photochemical transformations at the coating-air interface as a UV resistant protection coating for cultural heritage artefacts. An important finding was related to the decrease of the carbonyl band from 1739 cm-1 and to the appearance of other two additional bands located at 1718 (saturated aliphatic ketone) and 1712 cm-1 (carboxylic acid dimer). In addition, the loss of ester groups may be considered the main degradation process, as illustrated by the decrease of the intensity and area of the 1739 cm-1 main carbonyl stretching band.
This study reports the first investigation of the photodegradation behaviour of protective coatings through nano-FTIR technique.
Nanoscale Negative Refraction
Refraction is a familiar effect in which a light beam alters direction as it propagates from one medium to another. Negative refraction is a nonintuitive but well-established effect in which the light beam is bent in the “wrong” direction. Two groups now independently demonstrate negative refraction at the interface of two-dimensional van der Waal materials. Hu et al. used molybdenum trioxide with a graphene MoO3 / Graphene overlayer to show that in-plane negative refraction of mid-infrared (mid-IR) polaritons occurs at the interface and is gate tunable. Sternbach et al. used molybdenum trioxide/hexagonal boron nitride MoO3 / hBN bicrystals to show that negative refraction of mid-IR polaritons occurs for propagation normal to the interface.
Polaritonic negative refraction in the mid-IR provides opportunities for optical and thermal applications such as IR super-resolution imaging, nanoscale thermal manipulation, and chemical sensing devices with enhanced sensitivity.
Non-Aqueous Lithium–Air Cells
Metal–air batteries, such as Li–air, may be the key for large-scale energy storage as they have the highest energy density among all electrochemical devices. However, these devices suffer from irreversible side reactions leading to battery failure, especially when ambient air is used as the O2 source. This study uses nano-FTIR to track the chemical composition changes at the nanoscale of electrode surface during cell discharge. The results obtained here open an instructive operando chemical analysis of the Li–Air battery development. The authors observed a high sensitivity to humidity and CO2 in atmospheric conditions, and that the interaction between DMSO and carbon nanotubes (CNT) generates formate species. From 140 s of operation, the DMSO presented a low decomposition rate that remained the same until the end of the discharge.
nano-FTIR is an important tool to study complex discharge processes typically found in conversion batteries, as the case studied here for Lithium–Air.
Molecular Identity of Catalytic Agent
Unambiguous identification of catalytic poisoning species requires experimental methods simultaneously delivering accurate information regarding adsorption sites and adsorption geometries of adsorbates with nanometer-scale spatial resolution, as well as their detailed chemical structure and surface functional groups. However, to date, it has not been possible to study catalytic sulfur poisoning of metal/metal-oxide interfaces at the nanometer scale without sacrificing chemical identity. In this study, nano-FTIR & s-SNOM identify the chemical nature, adsorption sites, and adsorption geometries of sulfur-based catalytic poisons on a Pd(nanodisk)/Al2O3 (thin-film) planar model catalyst surface at the nanometer scale. In addition, this study reveals striking variations between sulfate species from one nanoparticle to another and even vast alterations of sulfur poisoning on a single Pd nanoparticle.
s-SNOM & nano-FTIR provide critical molecular-level insights crucial for the development of high-performance heterogeneous catalysts with extended lifetimes.
1D Luttinger-liquid plasmons formed inside carbon nanotubes (CNTs) are long-lived excitations with extreme electromagnetic field confinement. In the past, s-SNOM amplitude studies were limited to semiconducting CNTs which require additional doping. This s-SNOM phase study, allows investigation of metallic carbon nanotubes as they support strong tip-launched Luttinger-liquid plasmons at ambient conditions. The Authors extracted the dispersion relation of the hybrid Luttinger-liquid plasmon–phonon polaritons. The dispersion shows pronounced mode splitting, and an ultrastrong coupling regime with phonons of both investigated substrates, i.e., native silica and hBN. Such strong coupling of quasiparticles allows now applications like induced transparency, polariton lasing, changing of the rate of chemical reactions, or enhanced sensitivity in infrared and Raman spectroscopy
s-SNOM studies of Luttinger-liquid plasmons is an essential application to develop novel low-loss plasmonic circuits for the sub-wavelength manipulation of light.
Solid-state batteries possess the potential to significantly impact energy storage industries by enabling diverse benefits, such as increased safety and energy density. However, challenges persist with physicochemical properties and processes at electrode/electrolyte interfaces. Thus, there is great need to characterize such interfaces in situ and unveil scientific understanding that catalyzes engineering solutions. In this study, the authors conduct multiscale in situ microscopies (optical, atomic force, and infrared near-field) and nano-FTIR of intact and electrochemically operational graphene/solid polymer electrolyte interfaces. They find nanoscale structural and chemical heterogeneities intrinsic to the solid polymer electrolyte initiate a cascade of additional interfacial nanoscale heterogeneities during Li plating and stripping; including Li-ion conductivity, electrolyte decomposition, and interphase formation.
nano-FTIR applies to buried interfaces and interphases in their native environment and readily adaptable to a number of other electrochemical systems and battery chemistries.
Plasmon in Suspended Graphene
Plasmons in 2D graphene have been invariably studied in supported samples so far. The substrate provides stability for graphene but often causes undesired interactions (such as dielectric losses, phonon hybridization, and impurity scattering) that compromise the quality and limit the intrinsic flexibility of graphene plasmons. This s-SNOM study demonstrate the visualization of plasmons in suspended graphene and introduces the graphene suspension height as an effective plasmonic tuning knob that enables in situ change of the dielectric environment and substantially modulates the plasmon wavelength, propagation length, and group velocity. Such active control of micrometer plasmon propagation facilitates near-unity-order modulation of nanoscale energy flow that serves as a plasmonic switch with an on-off ratio above 14.
The suspended graphene plasmons possess long propagation length, high tunability, and controllable energy transmission simultaneously, opening up broad horizons for application in nano-photonic devices.
Semiconductors based on organic polymers have several advantages over their conventional, mostly silicon-based cousins. They are simpler and cheaper to manufacture, and can be produced in the form of thin, flexible layers, which allows them to be attached to diverse substrates and surfaces. Their electrical conductivity and energy efficiency are a function of the properties of the materials of which they are made. This degree of molecular order affects the mobility and transport of the charge carriers within them. Up until now, it has been very difficult to access these structures experimentally. s-SNOM and nano-FTIR make a valuable contribution to our understanding of these layered systems and to organic electronics in general.
s-SNOM & nano-FTIR is ideally suited for monitoring and optimize growth parameters to get highly ordered organic films and thus faster devices with crucial impact in development of optoelectronic devices such as OLED technology, or organic solar cells.
Enzymatical Biocatalytic Reactions
Biocatalytic transformations in living organisms, such as multi-enzyme catalytic cascades, proceed in different cellular membrane-compartmentalized organelles with high efficiency. Nevertheless, it remains challenging to mimic biocatalytic cascade processes of natural systems. One method to mimic natural enzymes is the use of multi-shelled metal-organic frameworks (MOFs). Such MOFs can be used as a hierarchical scaffold to spatially organize enzymes on nanoscale to enhance cascade catalytic efficiency. In this study, the authors employed s-SNOM and nano-FTIR technology, which resolves nanoscale heterogeneity of vibrational activity associated to enzymes encapsulated in multi-shelled MOFs. This work provides important insights into developing complex multi-spatial compartmental systems for multi-enzyme catalytic cascades that hold great promise in many industrial processes.
Infrared nanoscale analysis reveals molecular identity of nm-small materials. Method which can be applied in many chemical and pharmaceutical industrial processes.
Phonon Polaritons & Organic Molecules
Light plays an essential role in modern science and technology, with applications ranging from fast optical communication to medical diagnosis and laser surgery. In many of these applications, the interaction of light with matter is of fundamental importance. The images obtained in this work reveal that the interaction between infrared light and molecular vibrations can be so strong that eventually the material properties are modified, such as conductivity and chemical reactivity. This effect, called vibrational strong coupling, could be used in the future for development of ultrasensitive spectroscopy devices or to study quantum aspects of strong vibrational coupling that have been not accessible so far.
Infrared s-SNOM imaging reveals vibrational strong coupling between propagating phonon polaritons and small organic molecules. A phenomenon with high potential to control fundamental physical and chemical material properties.
Secondary Structure of Single Proteins
The secondary structure of a proteins is highly relevant in the pathogenous mechanism leading to Alzheimer, Parkinson, and other neuro-degenerative diseases. Although a variety of methods have been developed to study the protein chemistry and structure, recognizing and mapping the secondary structure on the nanometer scale, or even with single protein sensitivity, is still a major challenge. nano-FTIR technology is used in this study to enabled nanoscale chemical imaging and probing of protein’s secondary structure with enormous sensitivity. In short, a sharp metalized tip is illuminated with a broadband infrared laser beam, and the backscattered light is analyzed with a specially designed Fourier transform spectrometer.
nano-FTIR probes the infrared spectroscopy and resolves the secondary structure of proteins complexes with diameter of 12 nm, 6 nm protein monolayer and even of 3 nm thin fibrils.