Calculation Of Optical Absorption Research Articles

Structural, electronic, and optical-absorption properties of 2D Si thin films

AbstractRecent experimental studies highlighted the potential of thin-film crystalline silicon (Si) for high-efficiency solar cells. Using density functional theory, we investigated 2D Si thin films across various orientations, thicknesses, and surface structures to elucidate their structure–property relationships. Through surface-energy calculations and Wulff construction, we determined the crystal habit of Si, which aligns with available experimental observations. Electronic-structure calculations underscored the critical role of valence saturation on surfaces in enabling semiconducting behavior in Si thin films, essential for optical applications. From optical-absorption calculations, we identified the surface index exhibiting the highest absorption coefficients for thin films Si solar cell applications. Graphical abstract

Contact engineering for graphene nanoribbon devices

Graphene nanoribbons (GNRs), when synthesized with atomic precision by bottom–up chemical approaches, possess tunable electronic structure, and high theoretical mobility, conductivity, and heat dissipation capabilities, which makes them an excellent candidate for channel material in post-silicon transistors. Despite their immense potential, achieving highly transparent contacts for efficient charge transport—which requires proper contact selection and a deep understanding of the complex one-dimensional GNR channel-three-dimensional metal contact interface—remains a challenge. In this study, we investigated the impact of different electron-beam deposited contact metals—the commonly used palladium (Pd) and softer metal indium (In)—on the structural properties and field-effect transistor performance of semiconducting nine-atom wide armchair GNRs. The performance and integrity of the GNR channel material were studied by means of a comprehensive Raman spectroscopy analysis, scanning tunneling microscopy (STM) imaging, optical absorption calculations, and transport measurements. We found that, compared to Pd, In contacts facilitate favorable Ohmic-like transport because of the reduction of interface defects, while the edge structure quality of GNR channel plays a more dominant role in determining the overall device performance. Our study provides a blueprint for improving device performance through contact engineering and material quality enhancements in emerging GNR-based technology.

Stability, electronic, thermodynamic, and optical aspects of CsPbI3-xBrx(x=0, 1, 2, 3) compounds: An ab-initio study

All organic metal halide perovskite, due to tunable band gap and stability, has great potential for use in optoelectrical devices. So, we investigate the structural, mechanical, dynamic stability, and electronic, thermodynamic, and optical properties of CsPbI3−xBrx(x=0.1.2.3) compounds. All studied compounds are mechanically stable in the equilibrium temperature and pressure. The phonon dispersion curve of these compounds confirms their dynamical stability. Replacing the halide position with the Br atom is associated with a structural change from cubic to tetragonal, which in turn leads to an increase in stability, hardness, and the value of the direct band gap of CsPbI3−xBrx compounds. Moreover, this structural deformation gives rise to a significant increase of carrier mobility in the asymmetric direction z of the tetragonal structure compared to other symmetric x and y directions.Optical properties calculations show high absorption in the blue-purple frequency region of visible light. The optical conductivity of the deformed structures along the asymmetric z direction is higher than along the symmetric x or y direction, which is in agreement with the charge carrier mobility results. The optical absorption calculations show that the increase of Br concentration in the CsPbI3−xBrx compounds cause the main peak of the absorption to move to a larger amount of energy. The static refractive index of these compounds is comparable to the light-absorbing semiconductor materials in solar cells, and their first peak of refractive index is within the visible energy spectrum of the electromagnetic beam.The direct bandwidth behavior with structural, electronic, and optically adjustable properties makes these compounds attractive for use in optoelectronic devices.

Mycosynthesis of silver nanoparticles using psychrotrophic strains of Tulasnella albida Bourdot & Galzin from the South Orkney Islands (Antarctica)

This study is the first report on mycosynthesis of silver nanoparticles (NPs) using psychrotrophic Antarctic filamentous fungi, and the first report regarding Tulasnella (Basidiomycota). In this work, the ability to synthesize silver NPs from cell free filtrates of strains of Tulasnella albida isolated from Antarctica was assessed. All fungal filtrates were capable of synthesizing silver NPs with the addition of AgNO3. UV–vis spectroscopy, TEM and SEM microscopy analyses were performed to characterize the synthesized NPs. ATR-FTIR and Micro Raman spectroscopy analyses were conducted to find functional groups responsible for the reduction of AgNO3 and to detect the presence of silver oxide on the AgNPs. Theoretical calculations of optical absorption based on core-shell Ag–Ag2O were used to characterize the experimental absorption spectra of silver NPs colloids. Spherically shaped silver NPs, typically 2–3nm in diameter, were obtained. The largest ones showed a capping shell around them, which could be associated with the formation of small silver NPs. Functional groups corresponding to amides and alcohols were detected, confirming the presence of proteins as possible intermediates in the synthesis of AgNPs. On the other hand, the Micro Raman analysis confirms the presence of silver oxide on the surface of the AgNPs. This work presents a simple procedure for the synthesis of silver NPs using a psychrotrophic organism that could be interesting for the industry.

Surface Effects on Anisotropic Photoluminescence in One‐Dimensional Organic Metal Halide Hybrids

1D organic metal halide hybrids (OMHHs) exhibit strongly anisotropic optical properties, highly efficient light emission, and large Stokes shift, holding promise for novel photodetection and lighting applications. However, the fundamental mechanisms governing their unique optical properties and in particular the impacts of surface effects are not understood. Herein, 1D C4N2H14PbBr4 by polarization‐dependent time‐averaged and time‐resolved photoluminescence (TRPL) spectroscopy, as a function of photoexcitation energy, is investigated. Surprisingly, it is found that the emission under photoexcitation polarized parallel to the 1D metal halide chains can be either stronger or weaker than that under perpendicular polarization, depending on the excitation energy. The excitation‐energy‐dependent anisotropic emission is attributed to fast surface recombination, supported by first‐principles calculations of optical absorption in this material. The fast surface recombination is directly confirmed by TRPL measurements, when the excitation is polarized parallel to the chains. The comprehensive studies provide a more complete picture for a deeper understanding of the optical anisotropy in 1D OMHHs.

Implementation of real‐time TDDFT for periodic systems in the open‐source PySCF software package

We present a new implementation of real-time time-dependent density functional theory (RT-TDDFT) for calculating excited-state dynamics of periodic systems in the open-source Python-based PySCF software package. Our implementation uses Gaussian basis functions in a velocity gauge formalism and can be applied to periodic surfaces, condensed-phase, and molecular systems. As representative benchmark applications, we present optical absorption calculations of various molecular and bulk systems and a real-time simulation of field-induced dynamics of a (ZnO)4 molecular cluster on a periodic graphene sheet. We present representative calculations on optical response of solids to infinitesimal external fields as well as real-time charge-transfer dynamics induced by strong pulsed laser fields. Due to the widespread use of the Python language, our RT-TDDFT implementation can be easily modified and provides a new capability in the PySCF code for real-time excited-state calculations of chemical and material systems.

Theoretical investigations of optoelectronic and transport properties of Rb2YInX6 (X = Cl, Br, I) double perovskite materials for solar cell applications

The double perovskite-based materials have attracted considerable attention of scientists owing to their potential applications in optoelectronic and transport properties. Here, we report the optoelectronic and transport properties of Rb2YInX6 (X = Cl, Br, I) double perovskites by DFT computations. By computing tolerance factor (tG), enthalpy of formation (ΔHf) and lattice constant (ao), the thermodynamic and structural stabilities are verified. The energy bandgap computations for Rb2YInX6 gives direct bandgap having values 3.05, 2.60 and 2.20 eV for Cl, Br and I based compositions respectively. Optical absorption calculations executed within the energy range of 2–8 eV which validate its use in optoelectronic applications like solar cells. Using semi classical Boltzmann theory computed values of ZT illustrates that Rb2YInBr6 is fairly good candidate for transport applications. These compounds may attain consideration in optoelectronic and thermoelectric properties.

Near-Infrared II Thermoplasmonics of Cuprous Selenide Multilayer Nanoshells: The Role of the Plasmonic Core.

We present a numerical investigation of the plasmonic and photothermal properties of two different types of cuprous selenide (Cu2-xSe) concentric multilayer nanoshells (CMNSs), heteroCMNSs and homoCMNSs, comprising an outer Cu2-xSe nanoshell and an intermediate silica layer but with a different nanoparticle core of either Au or Cu2-xSe. Numerical calculations of optical absorption, near-field enhancement, and local temperature increase are performed with varied dimensions. The plasmon modes from both types of CMNSs are interpreted by combining the plasmon hybridization theory with the surface charge distribution. The two CMNSs exhibit remarkable near-infrared II (NIR-II) plasmonic properties tunable by controlling the interaction between the inner core and the Cu2-xSe nanoshell. The distinct temperature increase distributions between the two CMNSs are identified at their NIR-II resonance wavelengths. The correlation between the partial absorption and the temperature increase of the inner core and Cu2-xSe nanoshell suggests the thermal interplay between the components.

LiCl monolayer for UV detection: First principles prediction

Abstract Two-dimensional (2D) materials design for nanoscience and nanotechnology has attracted continuously the researchers' attention because of the important role in the next generation of optoelectronics. In this paper, we report results concerning the prediction of a new 2D material, Lithium Chloride LiCl, using first-principles calculations. This material is proposed for the detection and absorption of ultraviolet (UV) radiation. Our calculations assert that the pristine LiCl monolayer, which crystallizes in the D3h symmetry (space group P 6 ‾ 2 m) is dynamically stable. The monolayer at hand is an indirect gap insulator with a band gap of 6.048(7.212) eV predicted by WC(HSE06) functional. The external strains effect on the electronic structure of LiCl monolayer is also investigated. Optical absorption calculations show a wide absorption band in the UV region and high absorption coefficients. Results suggest that the LiCl monolayer may be a promising candidate for optoelectronic applications in the UV-detection and absorption. We believe that results presented in this work should pave a solid way for the applications of alkaline halides monolayers with a wide electronic band gap in optoelectronic devices.

Optical and morphological properties of Au@Ag core-shell nanoparticles: Influence of different reducing agents

Colloidal suspensions of gold coated with silver core-shell nanoparticles in poly vinyl alcohol were prepared by the seed-mediated growth approach and a comparative study of optical and morphological properties was conducted. Two types of gold seeds were considered. For the first type, a strong reducing agent (NaBH4) and for the second one, a weak reducing agent (Na3C6H5O7) were used. Four volumes of AgNO3 solution were used to obtain silver coatings with different thicknesses. In each case, morphological and optical properties were investigated by transmission electron microscopy and ultraviolet–visible spectroscopy, respectively. Also, numerical calculations of optical absorption were performed with Matlab toolbox for the simulation of metallic nanoparticles, using a boundary element method approach. This study offers practical considerations useful as a route of synthesis at room temperature of this type of nanoparticles, in such a way that a good homogeneity and reproducibility can be achieved. Results here presented show practical details useful in the synthesis of this type of nanoparticles for applications such as catalysis.

First principles prediction of the elastic, electronic and optical properties of Sn3X4 (X = P, As, Sb, Bi) compounds: Potential photovoltaic absorbers

We report a first-principles study of structural, mechanical and optoelectronic properties of the Sn3X4 (X = P, As, Sb, Bi) compounds. The calculations were performed using the full-potential linearized augmented plane wave approach (FP-LAPW). The structural and mechanical properties of Sn3X4 (X = P, As, Sb, Bi) compounds were obtained using GGA-PBE. In addition, The Tran-Blaha modified Becke-Johnson exchange potential (TB-mBJGGA) technique was used to calculated the optoelectronic properties. The calculated electronic band structures and density of states reveal a direct band gap at Γ points varied from 0.11 eV to 1.23 eV for X = P, As, Sb, Bi. The optical absorption calculations show that all compounds have high absorption coefficients about twenty times greater than that of CuInSe2 and CdTe in the visible region. The high absorption of these materials could be attributed to the localized p-states of cation (X = P, As, Sb, Bi) in the lower region of the conduction band.

UV-active plasmons in alkali and alkaline-earth intercalated graphene

The interband pi and pi+sigma plasmons in pristine graphene and the Dirac plasmon in doped graphene are not applicable, since they are broad or weak, and weakly couple to an external longitudinal or electromagnetic probe. Therefore, the ab initio Density Function Theory is used to demonstrate that the chemical doping of the graphene by the alkali or alkaline earth atoms dramatically changes the poor graphene excitation spectrum in the ultra-violet frequency range (4 - 10 eV). Four prominent modes are detected. Two of them are the intra-layer plasmons with the square-root dispersion, characteristic for the two-dimensional modes. The remaining two are the inter-layer plasmons, very strong in the long-wavelength limit but damped for larger wave-vectors. The optical absorption calculations show that the inter-layer plasmons are both optically active, which makes these materials suitable for small organic molecule sensing. This is particularly intriguing because the optically active two-dimensional plasmons have not been detected in other materials.

First principles electron-correlated calculations of optical absorption in magnesium clusters

In this paper, we report large-scale configuration interaction (CI) calculations of linear optical absorption spectra of various isomers of magnesium clusters Mg$_{n}$ (n=2--5), corresponding to valence transitions. Geometry optimization of several low-lying isomers of each cluster was carried out using coupled-cluster singles doubles (CCSD) approach, and these geometries were subsequently employed to perform ground and excited state calculations using either the full-CI (FCI) or the multi-reference singles-doubles configuration interaction (MRSDCI) approach, within the frozen-core approximation. Our calculated photoabsorption spectrum of magnesium dimer (Mg$_{2}$) isomer is in excellent agreement with the experiments both for peak positions, and intensities. Owing to the sufficiently inclusive electron-correlation effects, these results can serve as benchmarks against which future experiments, as well as calculations performed using other theoretical approaches, can be tested.

Effect of Doping in Controlling the Structure, Reactivity, and Electronic Properties of Pristine and Ca(II)-Intercalated Layered Silicene

Hybrid two-dimensional (2D) materials composed of carbon- and germanium-doped silicene monolayers, denoted as Si1–xCx, Si1–xGex, and Si1–2xCxGex (0 ≤ x ≤ 1), were investigated by first-principles calculations. Their structural features can be understood on the basis of Vegard’s law. The lattice parameters were found to correlate well with the arithmetic mean of the percentage doping of the individual constituents. The electronic band gap showed an interesting bell-shaped behavior for Si1–xCx with respect to doping, wherein Eg increased from 0 (for x = 0) to a maximum (for x = 0.5) and eventually decreased again to 0 (for x = 1). Clearly controlled carbon doping of the silicene monolayer was found to open up the band gaps and also provides a means of harvesting solar energy for semiconductor and photovoltaic applications. In addition to pristine monolayer silicene, we also investigated the effects of Ca(II)-intercalated multilayer silicene/germanene as available in the van der Waals mineral phases of CaSi2 and CaGe2. The stabilities and reaction energies for hydrogenation, fluorination, and mixed hydrogenation–fluorination for these Ca(II)-intercalated structures were compared with those of pristine and doped monolayer silicene. Optical absorption calculations demonstrated that doped monolayers and Ca(II)-intercalated multilayer silicene/germanene have strong photoabsorption in the visible light region. The presence of Ca(II) stabilizes the silicene/germanene layers, and the Ca(II) also affects the electronic structures of these 2D materials.

Optical absorption and conductivity in quasi-two-dimensional crystals from first principles: Application to graphene

This paper gives a theoretical formulation of the electromagnetic response of the quasi-two-dimensional (Q2D) crystals suitable for investigation of optical activity and polariton modes. The response to external electromagnetic field is described by current-current response tensor $\Pi_{\mu\nu}$ calculated by solving the Dyson equation in the random phase approximation (RPA), where current-current interaction is mediated by the photon propagator $D_{\mu\nu}$. The irreducible current-current response tensor $\Pi^0_{\mu\nu}$ is calculated from the {\em ab initio} Kohn-Sham (KS) orbitals. The accuracy of $\Pi^0_{\mu\nu}$ is tested in the long wavelength limit where it gives correct Drude dielectric function and conductivity. The theory is applied to the calculation of optical absorption and conductivity in pristine and doped single layer graphene and successfully compared with previous calculations and measurements.

Triple Surface Plasmon Resonances in Zn Nanoparticles in Silica

Theoretical calculations of optical absorption (OA) spectra of Zn nanoparticles (NPs) in silica glass, using a simple model, have been resulted in appearance of three OA bands, all of which are found to blueshift with decrease in NP radius due to quantum confinement effects of free electrons. The intensities of the OA bands are seen to increase with increase in incident light energy. Importantly, all the three OA bands have been found to satisfy, accurately, the surface plasmon resonance (SPR) condition. All these observations clearly indicate that the observed OA bands are originated from the SPR absorptions in Zn NPs, but not due to inter-band absorption.

Effects of vacancy point defects and phase transitions on optical properties of shocked Al2O3

The velocity interferometer system for any reflector (VISAR) and pyrometric measurements in dynamic highpressure experiments require the use of an optical window, and Alumina (Al2O3) or sapphires is often considered as a window material due to its high shock impedance and excellent transparency. Consequently, understanding the characteristics of its transparency and refractive index change under shock loading is crucial for explaining such experimental data. Experimental studies indicate optical transparency loss in shocked Al2O3. The mechanisms for the phenomenon are some interesting issues. A first-principles study suggests that shock-induced VO+2 (the +2 charged O vacancy) defects in Al2O3 could be an important factor causing the transparency loss. Recently, the red shift of the extinction curve (i.e., the wavelength dependence of the extinction coefficient) with increasing shock pressure has been observed. It is needed to ascertain whether this behavior is also related to shock-induced vacancy point defects. In addition, up to now, information about Al2O3 refractive index at a wavelength of 532 nm under strong shock compression (the optical source wavelength in VISAR measurement is usually set at 532 nm) has been unknown, and neither the effects of structural transitions nor vacancy point defects on the refractive index of shocked Al2O3 are determined. Here, to investigate the above-mentioned questions, we perform first principles calculations of optical absorption and refractive index properties of Al2O3 crystal without and with VO+2 and VAl3 (the -3 charged Al vacancy) defects in a pressure range of 180 GPa (the calculations in CASTEP are carried out by the plane-wave pseudo potential method in the framework of the density functional theory). Our absorption data show that the observed optical extinction in shocked Al2O3 cannot be explained by only considering pressure and temperature factors, but shock-induced VO+2 should be an important source for this behavior. On the basis of these results, we may judge that 1) the transparency loss explanation for shocked Al2O3 in the view of vacancy point defects is reasonable; 2) the absorption extinction should dominate the extinction phenomenon observed in shocked Al2O3. Our calculations find that high-pressure structural transition in Al2O3 causes an obvious enhancement of its refractive index. The refractive index decreases with increasing shock pressure in corundum and Rh2O3 regions, and decreases slightly below 172 GPa and increases slowly above 172 GPa with increasing shock pressure in CalrO3 region. The VO+2 and VAl3 defects in Al2O3 have apparent influences on the shock pressure dependence of its refractive index. These results mean that the information about Al2O3 refractive index under strong shock loading cannot be obtained simply by extrapolating its low pressure data. Our prediction could be of importance for future experimental study and new window-material development.

Predicting a quaternary tungsten oxide for sustainable photovoltaic application by density functional theory

A quaternary oxide, CuSnW2O8 (CTTO), has been predicted by density functional theory (DFT) to be a suitable material for sustainable photovoltaic applications. CTTO possesses band gaps of 1.25 eV (indirect) and 1.37 eV (direct), which were evaluated using the hybrid functional (HSE06) as a post-DFT method. The hole mobility of CTTO was higher than that of silicon. Further, optical absorption calculations demonstrate that CTTO is a better absorber of sunlight than Cu2ZnSnS4 and CuInxGa1−xSe2 (x = 0.5). In addition, CTTO exhibits rigorous thermodynamic stability comparable to WO3, as investigated by different thermodynamic approaches such as bonding cohesion, fragmentation tendency, and chemical potential analysis. Chemical potential analysis further revealed that CTTO can be synthesized at flexible experimental growth conditions, although the co-existence of at least one secondary phase is likely. Finally, like other Cu-based compounds, the formation of Cu vacancies is highly probable, even at Cu-rich growth condition, which could introduce p-type activity in CTTO.

Two-dimensional silicon-carbon hybrids with a honeycomb lattice: New family for two-dimensional photovoltaic materials

We predict a series of new two-dimensional (2D) inorganic materials made of silicon and carbon elements (2D SixC1x) based on density functional theory. Our calculations on optimized structure, phonon dispersion, and finite temperature molecular dynamics confirm the stability of 2D SixC1x sheets in a two-dimensional, graphene-like, honeycomb lattice. The electronic band gaps vary from zero to 2.5 eV as the ratio x changes in 2D SixC1x changes, suggesting a versatile electronic structure in these sheets. Interestingly, among these structures Si0.25C0.75 and Si0.75C0.25 with graphene-like superlattices are semimetals with zero band gap as their  and * bands cross linearly at the Fermi level. Atomic structural searches based on particle-swarm optimization show that the ordered 2D SixC1x structures are energetically favorable. Optical absorption calculations demonstrate that the 2D silicon-carbon hybrid materials have strong photoabsorption in visible light region, which hold promising potential in photovoltaic applications. Such unique electronic and optical properties in 2D SixC1x have profound implications in nanoelectronic and photovoltaic device applications.

Wannier interpolation of the electron-phonon matrix elements in polar semiconductors: Polar-optical coupling in GaAs

We generalize the Wannier interpolation of the electron-phonon matrix elements to the case of polar-optical coupling in polar semiconductors. We verify our methodological developments against experiments, by calculating the widths of the electronic bands due to electron-phonon scattering in GaAs, the prototype polar semiconductor. The calculated widths are then used to estimate the broadenings of excitons at critical points in GaAs and the electron-phonon relaxation times of hot electrons. Our findings are in good agreement with available experimental data. Finally, we demonstrate that while the Fr\"ohlich interaction is the dominant scattering process for electrons/holes close to the valley minima, in agreement with low-field transport results, at higher energies, the intervalley scattering dominates the relaxation dynamics of hot electrons or holes. The capability of interpolating the polar-optical coupling opens new perspectives in the calculation of optical absorption and transport properties in semiconductors and thermoelectrics.