Ship engines in the open ocean and Arctic typically combust heavy fuel oil (HFO), resulting in light-absorbing particulate matter (PM) emissions that have been attributed to black carbon (BC) and conventional, soluble brown carbon (brC). We show here that neither BC nor soluble brC is the major light-absorbing carbon (LAC) species in HFO-combustion PM. Instead, "tar brC" dominates. This tar brC, previously identified only in open-biomass-burning emissions, shares key defining properties with BC: it is insoluble, refractory, and substantially absorbs visible and near-infrared light. Relative to BC, tar brC has a higher Angstrom absorption exponent (AAE) (2.5-6, depending on the considered wavelengths), a moderately-high mass absorption efficiency (up to 50% of that of BC), and a lower ratio of sp 2-to sp 3-bonded carbon. Based on our results, we present a refined classification of atmospheric LAC into two sub-types of BC and two sub-types of brC. We apply this refined classification to demonstrate that common analytical techniques for BC must be interpreted with care when applied to tar-containing aerosols. The global significance of our results is indicated by field observations which suggest that tar brC already contributes to Arctic snow darkening, an effect which may be magnified over upcoming decades as Arctic shipping continues to intensify.

Heavy fuel oil (HFO) particulate matter (PM) emitted by marine engines is known to contain toxic heavy metals, including vanadium (V) and nickel (Ni). The toxicity of such metals will depend on the their chemical state, size distribution, and mixing state. Using online soot-particle aerosol mass spectrometry (SP-AMS), we quantified the mass of five metals (V, Ni, Fe, Na, and Ba) in HFO-PM soot particles produced by a marine diesel research engine. The in-soot metal concentrations were compared to in-PM2.5 measurements by inductively coupled plasma-optical emission spectroscopy (ICP-OES). We found that <3% of total PM2.5 metals was associated with soot particles, which may still be sufficient to influence in-cylinder soot burnout rates. Since these metals were most likely present as oxides, whereas studies on lower-temperature boilers report a predominance of sulfates, this result implies that the toxicity of HFO PM depends on its combustion conditions. Finally, we observed a 4-to-25-fold enhancement in the ratio V:Ni in soot particles versus PM2.5, indicating an enrichment of V in soot due to its lower nucleation/condensation temperature. As this enrichment mechanism is not dependent on soot formation, V is expected to be generally enriched within smaller HFO-PM particles from marine engines, enhancing its toxicity.

The lack of cost-effective systems for the extensive assessment of air pollutants is a concern for health and safety in urban and industrial areas. The use of polymer thin films as labelfree colorimetric sensors featuring specific interactions with pollutants would then represent a paradigm shift in environmental monitoring and packaging technologies, allowing to assess air quality, formation of byproducts in closed environment, and the barrier properties of the polymer themselves. To this end, all-polymer distributed Bragg reflectors promises reliable transducers for chemical stimuli, and effective colorimetric label-free selective detectors. We show selectivity attained by specific interaction of the polymeric components with the analytes. Such interactions drive the analyte intercalation trough the polymer structure and its kinetics, converting it in a dynamic optical response which is at the basis of the Flory-Huggins photonic sensors. Additionally, we demonstrate that such optical response can be used to esteem the diffusion coefficients of small molecules within the polymer media via simple UV-Vis spectroscopy retrieving data comparable to those obtained with state of the art gravimetric procedures. These results pave the way to an innovative, simple, and lowcost detection method integrable to in-situ assessment of barrier polymers used for the encapsulation of optoelectronic devices, food packaging, and goods storage in general. Currently, barrier properties of polymer thin films to vapors and gas are assessed via gravimetric 1 and pressure decay methods, 2-4 or by optical techniques based on microscopy 5 and infrared absorption, 6 which remained substantially unchanged for the last few decades. These methods need dedicated equipment and cannot be performed in-situ. In this scenario, research for new low-cost, simpler, and portable technologies to gather lab-on-chip devices is strongly pursued. In these regards, sensors based on the optical response of polymer distributed Bragg reflectors (DBR) represent a possible revolution in the field due to the high responsivity to analytes in the vapor phase. 7-9 DBRs are planar photonic crystals made of media with different refractive index stacked to form a dielectric lattice. The interaction between light and DBRs induces frequency regions where light propagation is forbidden. These frequencies are called photonic band gaps (PBGs), and are easily detectable via simple reflectance or transmittance spectroscopy. 10 In analogy with the energy-gap of semiconductors, the PBG properties depend on the lattice structure. Then, dielectric contrast among the lattice components, lattice parameters, and the number of layers affect the optical features generated by the DBR photonic structure. 11 Intuitively, a perturbation of

Manipulating the anisotropy in 2D nanosheets is a promising way to tune or trigger functional properties at the nanoscale. Here, a novel approach is presented to introduce a one-directional anisotropy in MoS nanosheets via chemical vapor deposition (CVD) onto rippled patterns prepared on ion-sputtered SiO /Si substrates. The optoelectronic properties of MoS are dramatically affected by the rippled MoS morphology both at the macro- and the nanoscale. In particular, strongly anisotropic phonon modes are observed depending on the polarization orientation with respect to the ripple axis. Moreover, the rippled morphology induces localization of strain and charge doping at the nanoscale, thus causing substantial redshifts of the phonon mode frequencies and a topography-dependent modulation of the MoS workfunction, respectively. This study paves the way to a controllable tuning of the anisotropy via substrate pattern engineering in CVD-grown 2D nanosheets.

MoS and generally speaking, the wide family of transition-metal dichalcogenides represents a solid nanotechnology platform on which to engineer a wealth of new and outperforming applications involving 2D materials. An even richer flexibility can be gained by extrinsically inducing an in-plane shape anisotropy of the nanosheets. Here, the synthesis of anisotropic MoS nanosheets is proposed as a prototypical example in this respect starting from a highly conformal chemical vapor deposition on prepatterend substrates and aiming at the more general purpose of tailoring anisotropy of 2D nanosheets by design. This is envisioned to be a suitable configuration for strain engineering as far as strain can be spatially redistributed in morphologically different regions. With a similar approach, both the optical and electronic properties of the 2D transition-metal dichalcogenides can be tailored over macroscopic sample areas in a self-organized fashion, thus paving the way for new applications in the field of optical metasurfaces, light harvesting, and catalysis.

We study the optical properties of an anisotropic ripple-shaped two-dimensional molybdenum disulfide (MoS2) nanosheet deposited by chemical vapor deposition onto a nanopatterned silica (SiO2) substrate. We unveil a giant anisotropic optical response in the linear and nonlinear regime by a combination of optical extinction measurements, ultrafast broadband transient absorption experiments, and finite element method numerical simulations. In steady state optical measurements, such anisotropy appears as a polarization-dependent extinction in correspondence with the characteristic excitonic peaks (A, B, C, and D) of MoS2. Along with spectral changes, ultrafast measurements strikingly exhibit the onset of an anisotropic relaxation dynamic in the region of the C exciton. Numerical simulations indicate that the observed polarization-dependent optical response is dictated by the nanopattering of MoS2, with peculiar features belonging to the out-of-plane component of the dielectric tensor of MoS2 that is made effective through the rippled configuration. Our findings give a rationale to the anisotropic exciton response and show that morphology manipulation represents a valuable option for the tuning of optical and electronic properties in transition-metal dichalcogenides.

Nanofabrication of flat optic silica gratings conformally layered with two-dimensional (2D) MoS 2 is demonstrated over large area (cm 2 ), achieving a strong amplification of the photon absorption in the active 2D layer. The anisotropic subwavelength silica gratings induce a highly ordered periodic modulation of the MoS 2 layer, promoting the excitation of Guided Mode Anomalies (GMA) at the interfaces of the 2D layer. We show the capability to achieve a broadband tuning of these lattice modes from the visible (VIS) to the near-infrared (NIR) by simply tailoring the illumination conditions and/or the period of the lattice. Remarkably, we demonstrate the possibility to strongly confine resonant and nonresonant light into the 2D MoS 2 layers via GMA excitation, leading to a strong absorption enhancement as high as 240% relative to a flat continuous MoS 2 film. Due to their broadband and tunable photon harvesting capabilities, these large area 2D MoS 2 metastructures represent an ideal scalable platform for new generation devices in nanophotonics, photo- detection and -conversion, and quantum technologies.

We report on the optical photomodulation properties of all-polymer planar microcavities in which the photochromic poly((4-pentyloxy-3'-methyl-4'-(6-methacryloxyhexyloxy))azobenzene) (PMA4) acts as photoresponsive cavity layer. We induce the trans-cis isomerization process of the azobenzene group by polarized 405 nm CW-laser irradiation, while the backward process is driven by unpolarized CW-laser irradiation at 442 nm. The all-optical photoisomerization process induces a remarkable in-plane anisotropic spectral shift of the cavity modes for the first and second order photonic band gaps. The spectral and intensity modulation effects for these flexible all-polymer microcavities are discussed with respect to those so far reported in literature for analogous systems