We extend our theoretical description of optical excitations in binary plasmonic supercrystals made of two types of metal nanoparticles to three common cubic structures: sodium chloride (NaCl), zinc blende (ZnS), and auricupride (Cu3Au). Our microscopic model of plasmon polaritons in supercrystals incorporates dipole and quadrupole nanoparticle excitations, their interactions, and their coupling with photons. We calculate the plasmon-polariton dispersion for the three cubic structures starting from the dipole and quadrupole energies obtained in the quasistatic approximation. The bands depend on the properties of the nanoparticles as well as the symmetry and the lattice parameters of the supercrystals. To gain further insight into the coupling of different excitations and develop a set of symmetry selection rules for each structure, we complement our calculations with an extensive group theory analysis. Comparing the results across various structures makes our symmetry analysis more general, enabling us to observe selection rules that apply to multiple structures.

This work investigated the charge transport behavior at the interface between a Pt-Ir metal contact and transparent zinc oxide (ZnO) electrodes with one, four, and eight ZnO layers. Electrostatic force microscopy (EFM), Kelvin probe force microscopy (KPFM), and conducting atomic force microscopy (c-AFM) techniques were employed to explore the nanoscale surface electrical properties. The variation in thickness led to changes in the type of contact formed between metal and semiconductor, which went from ohmic to rectifier with the increase in the number of layers. The modulation in the type of contact formed was mainly due to the presence of grain boundaries (GB) during film formation. The influence of the thickness synthesis parameter on the optoelectronic and charge transport properties of conductive and transparent ZnO electrodes is demonstrated, and its importance in the formation of metal- semiconductor (M-S) contacts that make zinc oxide a versatile semiconductor.

Separating charge carriers in low-mobility materials presents a considerable challenge for organic photovoltaic devices. This study addresses this issue by producing CoFe2O4 nanoparticles via the proteic sol-gel method and incorporating them into the heterojunction mixture of regioregular poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C-61-butyric acid methyl ester (PCBM) at a concentration of 7%. The addition of these nanoparticles led to a suppression of photoluminescence, indicating that the thin films were successfully decorated with magnetic ferrite nanoparticles (NPs). Our analysis demonstrated that incorporating NPs into the bulk heterojunction (BHJ) of P3HT:PCBM blends resulted in a notable reduction in photoluminescence compared to films without decoration. This suppression suggests an increase in the density of free charge carriers and a decrease in recombination events. Moreover, atomic force microscopy revealed a higher transverse current in the BHJ:NP film when compared to both the BHJ and P3HT films without NPs. This increase implies that the nanoparticles may serve as nucleation centers for forming conductive pathways, thereby facilitating charge transport within the film. Consequently, the presence of nanoparticles can enhance the interfacial area between the film materials, promoting improved charge transfer and reducing the recombination of charge carriers.

Metal-halide perovskites (MHPs) emerged as a family of novel semiconductors with outstanding optoelectronic properties for applications in photovoltaics and light emission. Recently, they also attract interest as promising candidates for spintronics. In materials lacking inversion symmetry, spin-orbit coupling (SOC) leads to the Rashba-Dresselhaus effect, offering a pathway for spin current control. Therefore, inversion symmetry breaking in MHPs, which are characterized by strong SOC, has crucial implications. Yet, in complex low-dimensional hybrid organic-inorganic perovskites (HOIPs), the presence of and structural contributions to inversion symmetry breaking remain elusive. Here, employing intense THz fields, lattice dynamics carrying spectroscopic fingerprints of inversion symmetry breaking are coherently driven and observed in Ruddlesden-Popper (PEA)2(MA)n -1PbnI3 n +1 perovskites, which are globally assigned to a centrosymmetric space group. We demonstrante coherent control by THz pulses over specific phonons, which are assigned to either purely inorganic or highly anharmonic hybridized cage-ligand vibrations. By developing a general polarization analysis for THz-driven phonons, linear and nonlinear driving mechanisms are pinpointed. From this, simultaneous IR- and Raman-activity of inorganic cage modes below 1.5 THz is identified, indicating mode-selective inversion symmetry breaking. By exploring the driving pathways of these coherent phonons, the groundwork is laid for simultaneous ultrafast control of optoelectronic and spintronic properties in 2D HOIPs.

The inhibitory performance of three distinct protic ionic liquids (PILs), namely, 2-hydroxyethyl ammonium formate (PIL 01), 2-hydroxyethyl ammonium propionate (PIL 02), and 2-hydroxyethyl ammonium pentanoate (PIL 03), was evaluated to determine their suitability as eco-friendly corrosion inhibitors for carbon steel (ASTM A36) in a 3.5 wt. % NaCl aerated neutral electrolyte solution. Standard corrosion inhibitor assessment methods, including electrochemical impedance spectroscopy (EIS), potentiodynamic polarization (PDP), weight loss measurements, and microscopic techniques (SEM and optical microscopy), were employed to examine the steel surface and corrosion rate. There is a general agreement that the inhibition efficacy is directly associated with the adsorption capacity of substances on the surface of an investigated material, normally stainless or carbon steel. The standard free energies of adsorption were approximately -22 kJ mol-1, indicating a physical adsorption type of interaction between ionic liquids and the electrode surface. The adsorption behavior of protic ionic liquids on an A36 steel surface conforms to a Langmuir-type isotherm. In conclusion, PIL 01 demonstrated an inhibition efficiency exceeding 80%, while PILs 02 and 03 exhibited efficacies in the 50-60% range. The inhibition efficiency was observed to be proportional to the inhibitor's concentration. These results suggest that PIL 01, PIL 02, and PIL 03 exhibit significant corrosion inhibition properties.

The optical excitation of close-by molecules can couple into collective states giving rise to phenomena such as ultrafast radiative decay and superradiance. Particularly intriguing are one-dimensional molecular chains that form inside nanotube templates, where the tubes align molecules into single- and multifile chains. The resulting collective excitations have strong fluorescence and shifted emission/absorption energies compared to the molecular monomer. We study the optical properties of α-sexithiophene chains inside boron nitride nanotubes by combining fluorescence with far- and near-field absorption spectroscopy. The inner nanotube diameter determines the number of encapsulated molecular chains. A single chain of α-sexithiophene molecules has an optical absorption and emission spectrum that is red-shifted by almost 300 meV compared to the monomer emission, which is much larger than expected from dipole-dipole coupling. For two or more parallel chains, the collective state splits into excitation and emission channels with a Stokes shift of 200 meV due to the chain-chain interaction. Our study emphasizes the formation of a delocalized collective state through Coulomb coupling of the molecular transition moments in one-dimensional molecular lattices. They show a remarkable tunability in the transition energy, which makes encapsulated molecules promising candidates for components in future optoelectronic devices and for analytic spectroscopy.

Ultrastrong light-matter coupling has traditionally been studied in optical cavities, where it occurs when the light-matter coupling strength reaches a significant fraction of the transition frequency. This regime fundamentally alters the ground and excited states of the particle-cavity system, unlocking new ways to control its physics and chemistry. However, achieving ultrastrong coupling in engineered cavities remains a major challenge. Here, we show that ultra- and deep-strong coupling naturally occur in bulk materials without the need for external cavities. By analyzing experimental data from over 70 materials, we demonstrate that phonon-, exciton-, and plasmon-polaritons in many solids exhibit ultrastrong coupling, systematically surpassing the coupling strengths achieved in cavity-based systems. To explain this phenomenon, we introduce a dipole lattice model based on a generalized Hopfield Hamiltonian, which unifies photon-matter, matter-matter, and photon-photon interactions. The complete overlap between the photonic and collective dipole modes in the lattice enables ultrastrong coupling, leading to excited-state mixing, radiative decay suppression, and potential phase transitions into collective ground states. Applying our model to real materials, we show that it reproduces light-matter coupling across broad material classes and may underlie structural phase transitions that give rise to emergent phenomena such as ferroelectricity, insulator-to-metal transitions, and exciton condensation. Recognizing ultrastrong coupling as an intrinsic property of solids reshapes our understanding of light-matter interactions and opens new avenues for exploring quantum materials and exotic phases of matter.

Nanotubes align molecules into one dimensional chains creating collective states through the coupling of the molecular transition dipole moments. These collective excitations have strong fluorescence, narrow bandwidth, and shifted emission/absorption energies. We study the optical properties of α-sexithiophene chains in boron nitride nanotubes by combining fluorescence with far- and near-field absorption spectroscopy. The inner nanotube diameter determines the number of encapsulated molecular chains. A single chain of α-sexithiophene molecules has an optical absorption and emission spectrum that is red-shifted by almost 300 meV compared to the monomer emission, which is much larger than expected from dipole-dipole coupling. The collective state splits into excitation and emission channels with a Stokes shift of 200 meV for chains with two or more files. Our study emphasises the formation of a delocalized collective state through Coulomb coupling of the transition moments that shows a remarkable tuneability in transition energy.

The industry's principal objective is to comprehend the optimal application of each metal alloy in terms of corrosion resistance. A key focus lies in exploring alternative approaches to address this corrosive process in a manner that is both sustainable and economically feasible. The major strategy to mitigate this contest involves the utilization of inhibitors. However, it is imperative to note that certain inhibitors pose environmental risks. This study explores the effect of the addition of protic ionic liquids (PILs) on the corrosion of carbon steel (A36) in a saline solution (3.5 wt% NaCl), considering variations in pH and temperature. It focuses on understanding the effects of pH and temperature on the PILs' ability to protect the steel surface. Notably, changes in pH do not affect the protective capacity of the inhibitors. Efficiency values exceeding 72% were achieved under both acidic conditions tested. The study reveals two scenarios: At 40 °C, the PILs effectively protect the steel, with an efficiency of approximately 74% at concentrations of 500 and 1000 ppm. However, at 60 °C, efficiency decreases notably, reaching a maximum of 51% at a concentration of 500 ppm. Afterward, to evaluate the protective effectiveness of these compounds, gravimetric and electrochemical impedance spectroscopy (EIS) serve as the main methods, accompanied by optical and atomic force microscopy (AFM) for evaluating the surface. In electrochemical tests, PILs 1 and 2 exhibit superior efficiency, with film formation, while PILs 3 to 6 demonstrate comparatively lower values.

The amino acid L-histidine, which has an imidazole ring, was investigated as a corrosion inhibitor for AISI 1018 carbon steel in chloride solution based on the effectiveness of inhibitors containing imidazole in their composition. A neutral environment was chosen for this study due to the scarcity of research on this amino acid in this environment type. Concentrations of 250, 500, and 1000 ppm were evaluated. Various methods were used to determine inhibition effectiveness, including mass loss, open circuit potential, linear potentiodynamic polarization, and electrochemical impedance spectroscopy. For mass loss, the inhibition efficiency varied from 83 to 88% according to the increase in concentration. For the electrochemical tests, the efficiency variation ranged from 62 to 90% with increasing amino acid concentration. Furthermore, a simulation analysis using quantum chemical calculations within the scope of Density Functional Theory (DFT) revealed that histidine’s nucleophilic character is crucial for its corrosion inhibitory capacity in an aqueous medium at pH 7. The inhibition efficiency increased with increasing concentration in a neutral medium, following the Langmuir isotherm for the adsorption of L-histidine. Additional studies were carried out using Fourier transform infrared spectroscopy (FTIR) and thermogravimetry (TGA). Analysis of the substrate surface by scanning electron microscopy (SEM) showed greater preservation with the addition of L-histidine, confirming its adsorption on the steel. Atomic Force Microscopy (AFM) also demonstrated an improvement in surface roughness in the presence of amino acids compared to the medium without an inhibitor.

The collective excitations of solids are classified as longitudinal and transverse depending on their relative polarization and propagation direction. This seemingly formal classification results in surprisingly distinct types of excitations if calculated within the Coulomb gauge. Transverse modes couple to free-space photons and hybridize into polaritons for strong light-matter coupling. Longitudinal modes, in contrast, are seen as pure matter excitations that produce a dynamic polarization inside the material without photon coupling. Here we show that both longitudinal and transverse modes manifest as polaritons in the explicitly covariant Lorenz gauge. Longitudinal excitations couple to longitudinal and scalar photons, which have been considered elusive so far. We show that the dipolar excitations become systematically threefold degenerate in the long-wavelength limit when including all photonic degrees of freedom, as expected from symmetry. Our findings demonstrate how choosing a gauge determines our thinking about materials excitations and how gauge fixing reveals new pathways for tailoring polaritons in crystals, metamaterials, and surfaces. Longitudinal polaritons will interact with longitudinal near fields located at surfaces, which provides additional excitation channels to engineer scanning near-field microscopy and surface-enhanced spectroscopy.

We pursue the premise that plasmon-phonon coupling and hybrid plasmon-phonon modes can be broadly tailored in van der Waals (vdW) heterostructures. While the coupling between optical plasmons in graphene and phonons of substrate materials has already been widely investigated, the coupling of acoustic plasmons to phonons has remained elusive to date. Here we demonstrate that double-layer graphene intercalated with a transition-metal dichalcogenide (TMD) can harbor acoustic plasmon-phonon resonances with particularly high coupling strength. Using the quantum-electrostatic heterostructure method, which takes into account the contribution of each vdW monolayer at the ab initio level, we present the dependence of the plasmon-phonon coupling strength on the thickness of the TMD, as well as on the graphene doping. Our results reveal optimal and experimentally feasible conditions to achieve ultrastrong plasmon-phonon coupling, and thus enable further advances in nanoscale thermal and optical devices of high sensitivity.

The collective excitations of solids are classified as longitudinal and transverse depending on their relative polarization and propagation direction. This seemingly subtle difference results in surprisingly distinct types of excitations if calculated within the Coulomb gauge. Transverse modes couple to free-space photons and hybridize into polaritons for strong light-matter coupling. Longitudinal modes, in contrast, are seen as pure matter excitations that produce a dynamic polarization inside the material. Here we show that both longitudinal and transverse modes become polaritons in the explicitly covariant Lorenz gauge. Longitudinal excitations couple to longitudinal and scalar photons, which have been considered elusive so far. We show that the dipolar excitations become three-fold degenerate in the long-wavelength limit when including all photonic degrees of freedom, as expected from symmetry. Our findings demonstrate how choosing a gauge determines our thinking about materials excitations and how gauge fixing reveals new pathways for tailoring polaritons in crystals, metamaterials, and surfaces. Longitudinal polaritons will interact with longitudinal near fields located at surfaces, which provides additional excitation channels in scanning near-field microscopy and surface-enhanced spectroscopy.

In this chapter, we discuss the basic concepts of resonance Raman scattering and photoluminescence and how these optical spectroscopies are key for accessing the electronic states of condensed matter systems. In particular, we used carbon nanotubes as a model system for discussing how Raman spectroscopy and photoluminescence are powerful for determining with high resolution the energy of the confined electronic states. These techniques are among the most promising for advancing the science of nanomaterials because they are noninvasive, contactless, readily available, and allow one to characterize materials incorporated in devices.

We present a theory of optical excitations in binary plasmonic supercrystals that are made out of two types of metal nanoparticles. Compared to monodisperse supercrystals, binary crystals have a larger number of plasmonic bands. Their dispersion is governed by the lattice symmetry, unit cell parameters, and shape and material composition of the nanoparticle building blocks. We develop a quantum description of the plasmon polaritons in supercrystals that starts from the dipole and quadrupole excitations of the nanoparticles, their interaction, and their coupling to photons. We show how to use group theory to analyze the plasmon- and photon-induced supercrystal states and their interaction. Plasmon-polaritons of binary metallic supercrystals are in the regime of ultrastrong and deep strong light-matter interaction; i.e., the coupling strength is on the same order as the photon energy. One consequence of the strong interaction is that quadrupolar plasmon modes and photons with energies well above the plasmon energies have to be taken into account to calculate the polariton dispersion. A cesium chloride crystal of two nanoparticles with different dipole and quadrupole energies serves as the example structure to show how the plasmon-polariton dispersion depends on the properties of the nanoparticles and supercrystal structure. The tools presented here can be used to predict and analyze any type of optically active excitation in supercrystals. The results show how to differentiate the optical properties of binary nanoparticle supercrystals into properties that inflexibly depend on lattice symmetry and properties that can be finely tuned by choosing the nanoparticle composition and shape.

The presence of defect states, such as grain boundaries (GBs), can interfere with the charge transport properties of various semiconductor oxides. In this research, electrostatic force microscopy (EFM) and conducting atomic force microscopy (c-AFM) techniques were used to explore the nanoscale surface electrical properties of zinc oxide (ZnO) thin films deposited on a conductive fluorine-doped tin oxide (FTO) substrate. Films like these are often used as anode materials in photovoltaic and other optoelectronic devices. EFM measurements revealed the presence of charge trapping within the grain boundary region, suggesting localized band-bending effects. Furthermore, a current map obtained through c-AFM indicated that the grain regions exhibited higher conductivity, validating the observations made with EFM. By combination of c-AFM and Kelvin probe force microscopy (KPFM), it was possible to obtain experimental confirmation of band bending at grain boundaries. Data extracted from current-voltage (I-V) curves allowed the quantification of local saturation currents of 1.29 and 0.75 nA at the grain and GB. It was also possible to calculate the difference in potential barrier height between grain and GB as 50.40 meV. Urbach energy calculations identified the existence of defect states within the band gap. These defect states shifted the Fermi level toward the conduction band, reducing the local work functions to 3.93 and 3.89 eV for the grain and GB. These findings align with the thermionic emission (TE) model and Schottky-Mott theory, contributing to a deeper understanding of nanoscale charge transport within ZnO-based anodes and paving the way for the development of transparent conductive oxide-based optoelectronic devices and other applications.

In this work, we study theoretically the structural, electronic and transport properties of oxidized stanene using a combination of density functional theory (DFT), quantum molecular dynamics and the Landauer-Buttiker theory for the ballistic transport. Our results clearly show that oxygen adsorb onto stanene surface in both molecular or atomic forms, thus causing considerable modifications to its electronic structure and transport properties. Nevertheless, our quantum conductance calculations reveal that, in spite of oxidation, stanene still remains a good conductor that might be applied as field effect transistors, gas sensors and other devices.

Crystals of plasmonic metal nanoparticles have intriguing optical properties. They reach the regimes of ultrastrong and deep strong light-matter coupling, where the photonic states need to be included in the simulation of material properties. We propose a quantum description of the plasmon polaritons in supercrystals that starts from the dipole and quadrupole excitations of the nanoparticle building blocks and their coupling to photons. Our model excellently reproduces results of finite difference time domain simulations. It provides detailed insight into the emergence of the polariton states. Using the example of a face centered cubic crystals we show that the dipole and quadrupole states mix in many high symmetry directions of the Brilouin zone. A proper description of the plasmon and plasmon-polariton band structure is only possible when including the quadrupole-derived states. Our model leads to an expression of the reduced coupling strength in nanoparticle supercrystals that we show to enter the deep strong coupling regime for metal fill fractions above 0.8. In addition to the plasmon-polariton energies we analyse the relative contributions of the dipole, quadrupole, and photonic states to their eigenfunctions and are able to demonstrate the decoupling of light in the deep strong coupling regime. Our results pave the way for a better understanding of the quantum properties of metallic nanoparticle supercrystals in the ultrastrong and deep-strong coupling regime.

In this work, we investigate the transverse transport properties of few-layers MoS(2)using a Conductive Atomic Force Microscopy based technique. We find that the system changes between a low-force regime, characterized by a nearly-ideal contact between the MoS(2)flake and the substrate, and a high-force regime, for which this contact starts to become highly non-ideal. We propose a 3-diode model that effectively describes the current-voltage characteristics of few-layers MoS2. From this model, we estimate how fast the energy gaps of two-dimensional MoS(2)materials change as a function of the applied force. From our analysis, we estimate that MoS2-Au Schottky barrier heights change at the rate of 0.21, 0.23, and 0.78 meV nN(-1)for the few-layers, three-layers, and two-layers MoS2, respectively. Our work opens up new possibilities of investigating and controlling the electronic properties of 2D semiconducting materials.

In the regime of deep strong light–matter coupling, the coupling strength exceeds the transition energies of the material1–3, fundamentally changing its properties4,5; for example, the ground state of the system contains virtual photons and the internal electromagnetic field gets redistributed by photon self-interaction1,6. So far, no electronic excitation of a material has shown such strong coupling to free-space photons. Here we show that three-dimensional crystals of plasmonic nanoparticles can realize deep strong coupling under ambient conditions, if the particles are ten times larger than the interparticle gaps. The experimental Rabi frequencies (1.9 to 3.3 electronvolts) of face-centred cubic crystals of gold nanoparticles with diameters between 25 and 60 nanometres exceed their plasmon energy by up to 180 per cent. We show that the continuum of photons and plasmons hybridizes into polaritons that violate the rotating-wave approximation. The coupling leads to a breakdown of the Purcell effect—the increase of radiative damping through light–matter coupling—and increases the radiative polariton lifetime. The results indicate that metallic and semiconducting nanoparticles can be used as building blocks for an entire class of materials with extreme light–matter interaction, which will find application in nonlinear optics, the search for cooperative effects and ground states, polariton chemistry and quantum technology4,5. Photons and plasmons hybridize into polaritons in three-dimensional crystals of plasmonic nanoparticles, leading to deep strong light–matter coupling and the breakdown of the Purcell effect.