Plasmon Energy Shifts Research Articles

Optoelectronic and thermoelectric properties of Sb2S3 under hydrostatic pressure for energy conversion

This study reports the optoelectronic and thermoelectric properties of antimony trisulfide (Sb2S3) under a hydrostatic pressure of up to 20.4 GPa. The properties were computed based on the full-potential linearized augmented plane wave using the generalized gradient approximation by Perdew, Burke, and Ernzerhof as the exchange-correlation potentials. It was shown that increasing the pressure from 0.00 to 20.4 GPa decreases the calculated bandgap from 1.44 to 0.84 eV. There was a discontinuity in the pressure range of 4.82–6.3 GPa due to the isostructural electronic phase transition. The applied pressure increases the inner electrical polarization. At high pressure, the energy of the negative value of ε1 becomes large, and ε1 itself always remains negative. We observed that the high absorption of Sb2S3 also increases with pressure and the plasmon energy shifts to high energy. The applied pressure increases the static dielectric constant and static refractive index. It was found that the Seebeck coefficients increase with increasing temperature and decrease with increasing pressure. The bipolar effect occurs at low doping levels and high pressure. The optical and thermoelectric properties of Sb2S3 obtained under pressure show that it is suitable for clean energy conversion and optoelectronic applications.

Surface and Bulk Plasmon Excitation on Aluminum Surface at Small to High Grazing Angles

We present a series of spectra measured by reflected electron energy loss spectroscopy on an aluminum sample using a cylindrical mirror analyzer. The measurements were performed in the energy range between 250 eV and 2000 eV and with various incident angles, including the grazing geometry of an 88° incident angle. The observed spectra were evaluated and decomposed for surface and bulk excitation. The determined surface plasmon excitations were compared to the elastic peak and to the bulk excitation. We found a slight surface plasmon energy shift with altering glancing angles. We show that this shift exists independently from the bulk plasmon interference.

Plasmon energy losses in shear bands of metallic glass

Shear bands resulting from plastic deformation in cold-rolled Al88Y7Fe5 metallic glass were observed to display alternating density changes along their propagation direction. Electron-energy loss spectroscopy (EELS) was used to investigate the volume plasmon energy losses in and around shear bands. Energy shifts of the peak centre and changes in the peak width (FWHM) reflecting the damping were precisely determined within an accuracy of a few meV using an open source python module (Hyperspy) to fit the shapes of the plasmon and zero-loss peaks with Lorentzian functions. The maximum bulk plasmon energy shifts were calculated for the bright and dark shear band segments relative to the matrix to be about 38 and 14 meV, respectively. The damping was observed to be larger for the denser regions. The analysis presented here suggests that the changes in the plasmons are caused by two contributions: (i) Variable damping in the shear band segments due to changes in the medium-range order (MRO). This affects the static structure factor S(k), which, in turn, leads to either reduced or increased damping according to the Ziman–Baym formula. (ii) The ionic density and the effective electron mass appearing in the zero-momentum plasmon frequency formula Ep(q=0) are coupled and give rise to small variations in the plasmon energy. The model predicts plasmon energy shifts in the order of meV.

Unveiling Photovoltaic Performance Enhancement Mechanism of Polymer Solar Cells via Synergistic Effect of Binary Solvent Additives

Binary solvent additive engineering is an effective strategy to optimize photoactive films for high‐efficiency organic solar cells, however, the effect of single components on device performance and the combination principle of binary solvent additives remain unclear. Herein, synchrotron‐based grazing incident X‐ray diffraction, Derjaguin–Muller–Toporov modulus imaging, and plasmon energy shift imaging acquired by scanning transmission electron microscopy to investigate the effect of new binary solvent additive of 1,8‐diiodooctane (DIO) and less‐toxic and p‐anisaldehyde (AA) on device performance of solar cells based on poly[(5,6‐difluoro‐2,1,3‐benzothiadiazol‐4,7‐diyl)‐alt‐(3,3‴‐di(2‐octyldodecyl)2,2′;5′,2″;5″,2‴‐quaterthio‐phen‐5,5‴‐diyl)] (PffBT4T‐2OD) and [6,6]‐phenyl‐C61‐butyric acid methyl ester (PC61BM) are used. It is found that AA mainly favors polymer order and high crystallinity of PffBT4T‐2OD. Differently, DIO mainly enables PC61BM diffusing into PffBT4T‐2OD polymer matrix, leading to enlarged donor–acceptor (D–A) interface. As expected, by combining AA and DIO, the composite film provides large D–A interface and more balanced charge carrier transport. Consequently, their beneficial synergistic effect results in enhanced short circuit current and fill factor, and thereby increased power conversion efficiency of 10.64%, improved by 16% with respect to the control device. Herein, a general mechanism of enhancing device performance via the combination of solvent additives with different contributions to photoactive film is unveiled.

Evolution of the charge carrier plasmon in the one-dimensional metal TTF-TCNQ as a function of temperature and momentum

We have investigated the charge carrier plasmon in the quasi one-dimensional metal TTF-TCNQ using electron energy-loss spectroscopy. Our data reveal a negative plasmon dispersion with a slope that is independent of temperature, which is in agreement to predictions from model calculations and previous room temperature data. A plasmon energy shift upon temperature is observed, and we discuss possible contributions to this shift. The spectral width of the plasmon is rather temperature independent, but increases clearly above a momentum value of about 0.3 Å−1.

(Invited) Plasmon−Plasmon Interactions and Radiative Damping of Plasmons in Graphene Nanoribbon Arrays

While graphene absorbs only 2.3% in the mid infra red (IR) spectral region, graphene plasmons have much stronger absorption in the far IR. Plasmons tunability by the external electric fields and by the spatial confinment offer a promising platform for opto-electronic and sensor applications. In this work [1], we demonstrate both theoretically and experimentally that the plasmon−plasmon and plasmon−radiation interactions modify strongly the plasmon resonance energy, radiative damping, and oscillator strength in graphene nanoribbon arrays. Even for the moderate filling factors of about 50%, plasmon radiative lifetime reduces to a ps time scale from a convetional ns time scale in the isolated graphene nanoribbon. We find scaling of plasmons with respect to the graphene doping level and filling factor, which both modify the strength of the long-range Coulomb and plamson-radiative interactions. The surprisingly large plasmon energy shift and radiative damping significantly affect the graphene-based plasmonic device performance. [1] Vyacheslav Semenenko, Simone Schuler, Alba Centeno, Amaia Zurutuza, Thomas Mueller, and Vasili Perebeinos, ACS Photonics 5, 3459–3465, 2018.

Doping dependent plasmon dispersion in2H-transition metal dichalcogenides

We report the behavior of the charge carrier plasmon of $2H$-transition metal dichalcogenides (TMDs) as a function of intercalation with alkali metals. Intercalation and concurrent doping of the TMD layers have a substantial impact on plasmon energy and dispersion. While the plasmon energy shifts are related to the intercalation level as expected within a simple homogeneous electron gas picture, the plasmon dispersion changes in a peculiar manner independent of the intercalant and the TMD materials. Starting from a negative dispersion, the slope of the plasmon dispersion changes sign and grows monotonously upon doping. Quantitatively, the increase of this slope depends on the orbital character $(4d$ or $5d)$ of the conduction bands, which indicates a decisive role of band structure effects on the plasmon behavior.

Ultrasensitive Characterization of Mechanical Oscillations and Plasmon Energy Shift in Gold Nanorods.

Mechanical vibrational resonances in metal nanoparticles are intensively studied because they provide insight into nanoscale elasticity and for their potential application to ultrasensitive mass detection. In this paper, we use broadband femtosecond pump-probe spectroscopy to study the longitudinal acoustic phonons of arrays of gold nanorods with different aspect ratios, fabricated by electron beam lithography with very high size uniformity. We follow in real time the impulsively excited extensional oscillations of the nanorods by measuring the transient shift of the localized surface plasmon band. Broadband and high-sensitivity detection of the time-dependent extinction spectra enables one to develop a model that quantitatively describes the periodic variation of the plasmon extinction coefficient starting from the steady-state spectrum with only one additional free parameter. This model allows us to retrieve the time-dependent elongation of the nanorods with an ultrahigh sensitivity and to measure oscillation amplitudes of just a few picometers and plasmon energy shifts on the order of 10(-2) meV.

Improved Temperature Determination from Plasmon Energy Shifts in Aluminum

Improved Temperature Determination from Plasmon Energy Shifts in Aluminum

Probing the Chemical Structure in Diamond-Based Materials Using Combined Low-Loss and Core-Loss Electron Energy-Loss spectroscopy

We report the analysis of the changes in local carbon structure and chemistry caused by the self-implantation of carbon into diamond via electron energy-loss spectroscopy (EELS) plasmon energy shifts and core-edge fine structure fingerprinting. These two very different EELS energy and intensity ranges of the spectrum can be acquired under identical experimental conditions and nearly simultaneously using specially designed deflectors and energy offset devices known as "DualEELS." In this way, it is possible to take full advantage of the unique and complementary information that is present in the low- and core-loss regions of the EELS spectrum. We find that self-implanted carbon under the implantation conditions used for the material investigated in this paper creates an amorphous region with significant sp 2 content that varies across the interface.

Multiscale Theoretical Modeling of Plasmonic Sensing of Hydrogen Uptake in Palladium Nanodisks.

We study theoretically the optical properties of palladium nanodisks during hydrogen uptake. A combination of an ab initio quantum mechanical description of the Pd-H dielectric properties and a full electrodynamical study of light scattering in the H-modified Pd nanodisks allows us to trace the shift of the localized surface plasmon as a function of the H concentration in the Pd-H disk. We follow the evolution of the plasmon peak energy for different admixtures of the Pd-H α and β phases and interpret quantitatively the experimental sensitivity of the plasmon energy shift to the structural inhomogeneity upon H absorption. Our multiscale theoretical framework provides a solid background for plasmonic sensing of structural domains, as well as for identifying H saturation conditions in metal hydride systems.

Plasmon hybridization in tubular metallic nanostructures

In this paper, the excitations of surface plasmons in tubular metallic nanostructures are investigated. More accurate dispersion relations for the frequencies of the modes, on the basis of the Drude and Lorentz models for the dielectric function of the systems, in the presence of damping effects, are obtained. Numerical results show that by considering the friction force, the plasmon energy shift to lower values and a broadening of the frequency for each energy mode is observed.

Composition fluctuations in dilute nitride (Ga,In)(N,As)/GaAs heterostructures measured by low-loss electron energy-loss spectroscopy

We report on the investigation of composition fluctuations in epitaxially grown (Ga,In)(N,As) epilayers on GaAs(001) substrates by using electron energy-loss spectroscopy (EELS). The N and In concentrations are determined locally with a probe size of about 8nm from the low-loss EELS measurements. We demonstrate that the small amount of N incorporating in dilute nitride alloys can be measured quantitatively by the plasmon energy shift with respect to a GaAs reference, and that the In content is analyzed simultaneously from the In 4d transitions, which have been isolated from the overlapping Ga 3d transitions. Our spatially resolved EELS results are utilized to discuss the origin of the inherent composition fluctuations and their influences on the morphological instabilities during epitaxial growth.

Toward Correlation of Conductance of RuO2 Nanowire with Plasmon Energy Shift

Toward Correlation of Conductance of RuO2 Nanowire with Plasmon Energy Shift

Thermal and adsorbate induced plasmon energy shifts in graphite

Electron-energy-loss spectroscopy has been used to study plasmon excitations in pristine and alkali metal (Na, K, Cs) dosed highly oriented pyrolitic graphite in the temperature range 85–400 K. The energy and line width of the π-band E∥ c plasmon in pristine graphite was found to be extremely sensitive to substrate temperature and to the presence of adsorbates in qualitative accord with previously reported observations and theoretical calculations. After increasing monotonously with coverage (following square root dependence) the plasmon energy levels off above specific alkali coverages ( θ Na≈1.45, θ K≈0.25, and θ Cs≈0.2) at a common plasmon energy ℏ ω≈250 meV. The results are interpreted as evidence for formation of alkali-like bands in the topmost graphite layers.

Dopant Effect on Local Dielectric Properties in Barium Titanate Based Electroceramics Determined by Transmission EELS

Local electronic excitations of Nb‐doped BaTiO3 electroceramic were investigated using low‐loss electron energy loss (EEL) spectroscopy with a transmission electron microscope. The variations in electronic structure of the BaTiO3 were monitored as a function of Nb content by using Kramers‐Krönig analysis of the low‐loss EEL spectra. We found that the valence state of Nb (+5) as compared with that of the Ti (+4) introduces changes in the valence and conduction band states of BaTi1−xNbxO3 samples. The real part of the dielectric function, Re(1/ɛ), displays an increasingly less negative character with higher amounts of dopant and the valence plasmon exhibits “quasi‐plasmon” characteristics with the addition of Nb (at 0.0–1.8 at.%). Further, the plasmon energy shifts (by about 0.5 eV) to higher values with Nb additions. Significant changes take place in oscillator strengths of excitations in local (nanometer‐scale) regions of the perovskite samples. This investigation demonstrates a method to quantitatively assess electronic properties, at the submicrometer scale, of doped ceramics used in electronic and electrooptical applications.

Plasmon energy shift in porous silicon measured by x-ray photoelectron spectroscopy

In order to provide experimental support for quantum confinement models describing electronic effects in porous silicon (p-Si), the Si 2s and Si 2p plasmon losses have been studied by x-ray photoelectron spectroscopy. The p-Si plasmon energy was found at a value 0.8÷1.6 eV higher than that of bulk Si (17.4 eV), as measured on the cleaned Si substrate as a reference. The magnitude of these shifts suggests possible quantum confinement effects ascribed to the p-Si nanostructures.

Collective excitations of thin films of disordered potassium adsorbed on Ag(110)

Collective electronic excitations of disordered potassium adsorbed on Ag(110) have been studied by energy loss spectroscopy–low-energy electron diffraction (ELS–LEED) for overlayer thicknesses varying from 0.3 to 2.3 monolayers. We find that, in the long-wavelength limit, the argon surface plasmon energy shifts upwards with increasing potassium coverage, contrary to the expectation of classical dielectric theory, while its dispersion decreases. The potassium-induced loss, connected to the 3s to 3p interband transition, sets in above half a monolayer coverage, indicating a filling of the K(3s) state. Above one monolayer coverage collective potassium-induced modes are observed as well.

Nanoscale Modification Of Amorphous Diamond-Like Carbon Film Surfaces

ABSTRACTScanning Tunneling and Atomic Force Microscopy (STM, AFM) of amorphous tetrahedral carbon films (a-tC) film surfaces grown by pulsed laser deposition indicate extreme flatness and uniform electronic properties.1 This is consistent with the observed predominance of sp3 (diamond-like) bonding in these materials.2 Potential applications of a-tC films may be enhanced with the ability to modify their surfaces on the nanoscale. Exploiting the metastable nature of the sp3 hybridized state of carbon, the high flux electron beam from an STM tip was used to modify ˜100 nm regions; processing in air or in vacuum produces similar results. STM and AFM maps of the modified regions indicate stable morphologic and electronic structures consistent with a local transformation to sp2 (graphitic) hybridization. Surface potentiometric mapping of these regions indicates a correlation between electron dose and a lowering of the surface potential. In addition, spatially-resolved electron energy loss spectroscopy of the modified areas performed with a Scanning Auger Microscope shows plasmon energy shifts that confirm an elevated sp2 content in the modified regions.3

Surface-plasmon energy shifts due to submonolayer molecular adsorption on silver and aluminum.

We have investigated the effect of submonolayer molecular adsorptions on the surface-plasmon spectrum of silver and aluminum surfaces using low-energy electron-loss spectroscopy. Plasmon energy shifts of about 200 and 500 meV for one-monolayer hydrocarbon coverage were observed on silver and aluminum films, respectively. In addition, a new loss peak appears upon adsorption, which we associate with a molecular electronic resonance. Its energy shifts with increasing coverage in the opposite direction to that of the plasmon. A classical dielectric model is presented in which the losses are attributed to two branches of a collective excitation in a system consisting of (adsorbate) oscillators on top of a semi-infinite metal surface.