Results in Optics最新文献

Silicon, traditionally known as an indirect band gap semiconductor, unveils intriguing properties at the nanoscale, stemming from deviations from k-conservation rules within nanostructures. In our study, we scrutinized four hydrogenated Si 0D-nanostructures—Si₁₀H₁₆, Si₁₄H₂₀, Si₁₈H₂₄, and Si₂₂H₂₈—to unravel their dynamic stability under thermal fluctuations and optical characteristics. We initiated our exploration by employing the TD-DFT framework to generate and analyze the optical properties of these geometrically optimized nanostructures. Simultaneously, we conducted ab initio molecular dynamics simulations to examine the structural robustness and thermal stability of the four structures. Leveraging the Car-Parrinello molecular dynamics approach within the Quantum ESPRESSO open software suite, we observed temperature evolution and stability differences among the nanostructures at targeted temperatures 40 and 300 K. Our subsequent investigation delved into the Turbo-Lanczos time-dependent DFT method, unraveling the optical properties and excited-state dynamics of hydrogenated Si nanostructures. The results unveiled shifts towards higher energy absorption edges E₀, accompanied by alterations in the permittivity tensor, complex refractive index, oscillator strength, and reflectivity. Notably, the analysis revealed an enlarged HOMO-LUMO gap, distinctive from bulk Si. Furthermore, our models predicted the elimination of phase-dependent E₁/E₂ optical transition peaks in the imaginary part of the dielectric function, and a gradual decrease in the low-frequency dielectric response with increased hydrogenation of the amorphous structures. These findings underscore the promising applications of hydrogenating Si nanostructures in diverse technological domains such as optoelectronics, memristors, sensors, and quantum computing. Their tunable optical properties, size-dependent behaviors, and compatibility with existing silicon-based devices make them particularly appealing for next-generation technologies.

In this study, WO₃/Ag/W/WO₃ (WAWW) films were deposited at room temperature on a B270 glass substrate from W and Ag targets using a radiofrequency magnetron reactive sputtering system. The influence of the thin tungsten interlayer on the electrical and optical properties of the WAWW layer structure was investigated through ellipsometry, a four-point probe and a spectrophotometer. It was determined that the thin tungsten interlayer effectively prevented the oxidation of the silver film. The WAWW film had a dielectric-metal-dielectric (DMD) layered structure with good electrical conductivity and high visible transmittance. The tungsten layer was no more than 2-nm thick. The sheet resistance and luminous transmittance of the WO₃(29.5 nm)/Ag(14.2 nm)/W(2 nm)/WO₃(68.6 nm) film were 4.64 Ω/sq and 65.4 %, respectively. Based on the WAWW four-layer structure, stacked WO₃(29.5 nm)/Ag(14.2 nm)/W(2 nm)/WO₃(68.6 nm)/Ag(16.9 nm)/W(2 nm)/WO₃(30.4 nm) seven-layer structures deposited on B270 glass substrates were used for both ITO-free electrochromic and hot mirror applications. The visible (400–700 nm) and NIR (700–1200 nm) transmittance values of the bleached WAWW seven-layer structure were 71.5 % and 9.9 %, respectively. The visible transmittance of the colored WAWW seven-layer structure was 23.6 %. Finally, the bi-layer WAWW films were used to obtain an ITO-free WAWW seven-layer structure with a good electrochromic and optical performance.

Titanium dioxide (TiO₂) has attracted much attention because of their desirable physicochemical properties especially in the water splitting process. In this work pure and Fe-doped TiO₂ compounds are studies theoretically with the help of Generalized Gradient Approximation with the revised Pardew–Burke–Ernzerh (RPBE) exchange–correlation scheme. Total Density of States (TDOS) and Partial Density of States (DOS) were analyzed in detail which show that iron (Fe) and oxygen (O) orbitals hybridize, especially in the region of the doping system conduction band minima for both modes. Additionally, this interaction produces an energy level that effectively reduces the bandgap of the adsorbed system. Optical properties were elucidated which shows that Fe-doped TiO₂ system results in high absorption and photoconductivity. Moreover, the results demonstrate low bandgap energy which is suitable for the reduction in water splitting without the need for external energy. Magnetic properties demonstrated that Fe-doped TiO₂ systems show very low diamagnetic responses. The calculated elastic properties of Fe-doped TiO₂ indicate ductile nature of the material with a strong average bond strength. Fe-doped TiO₂ exhibited less microcracks with a mechanically stable composition.

Sb₂Se₃ has a high absorption coefficient of 10⁵ cm⁻¹ in the visible light range, which is an excellent absorber layer material. Currently, a better band alignment between conventional CdS and Sb₂Se₃ has led to the widespread adoption of CdS as the electron transport layer (ETL) in Sb₂Se₃ solar cells. However, CdS is toxic, necessitating the exploration of alternative ETL materials that are eco-friendly and possess an appropriate energy band with Sb₂Se₃. In this study, we endeavor to pioneer an all-inorganic, green solar cell structure of Au/MoS₂/Sb₂Se₃/WS₂/ITO by employing MoS₂ as the hole transport layer (HTL) and WS₂ as the ETL. We primarily optimized Sb₂Se₃ thickness and its hole doping concentration (N_A) by SCAPS-1D numerical simulation. Based on the analysis of built-in electric field and carrier recombination rate along Sb₂Se₃, the optimal thickness and N_A ranges of Sb₂Se₃ are determined, which are 0.9–1.1 μm and 10¹⁶-10¹⁸ cm⁻³ respectively. Through a series of optimization, the structure achieves the highest power conversion efficiency (PCE) of about 25.3 % in the current simulation of Sb₂Se₃ solar cells. After comparing the novel WS₂ ETL with the conventional CdS ETL, we find that WS₂ has a larger built-in potential (V_bi) and charge recombination resistance (R_rec). In addition, from the analysis of energy band structure, the spike-like band at Sb₂Se₃/WS₂ interface can effectively inhibit the carrier recombination, which makes the device obtain a larger open circuit voltage (V_OC) of 0.69 V. This study can provide theoretical reference for the development of non-toxic and efficient Sb₂Se₃ solar cells.

We investigated the optical properties and thermal conductivity of blade-coated graphene quantum dots (GQDs)/PEDOT:PSS hybrid thin films by varying the content of GQDs. The optical properties were determined by spectroscopic ellipsometry in the range of 1.2–5.5 eV. Two dispersion models were used to analyze the optical properties of the films: the Bruggeman effective medium approximation (BEMA) for the hybrid films, and the Drude model combined with a Lorentzian oscillator for both the pure and the hybrid films, which provides insight into their electrical properties. As a novel finding, we observed that the optical anisotropy of PEDOT:PSS (Aldrich 483095) films is reduced after incorporating GQDs. Moreover, dedoping of the PEDOT chains is demonstrated upon increasing the content of GQDs within the hybrid films. Furthermore, the thermal conductivity shows a two-fold decrease as the GQDs fraction increases from 0 to 10 wt%. This result is understood considering that the GQDs act as local scattering centers, resulting in a decrease of the thermal conductivity.

The most important goal of quantum communication is to distribute the encryption key between the transmitter and the receiver. The optimal situation in Quantum Key Distribution (QKD) between transmitter and receiver is to increase the key distribution rate per second, increase the transmission distance, and reduce the error in key distribution. Several protocols used for QKD. The most important of QKD protocols is the BB84. One of the challenges leading to errors in quantum protocols is generating error pulses in single-photon detectors. These pulses caused by the inherent effects of quantum devices. They can cause wrong detection in the receiver. Many measures have been taken in the design and construction of single-photon detectors to reduce this error pulses, but it is not possible to eliminate all of them. Afterpulse and dark counts are two types of unwanted pulses that occur with single-photon detectors. In this paper, a new QKD protocol is proposed. It is an upgrade of the BB84 protocol and can reduce the effects of unwanted pulses such as afterpulse and dark counts in QKD avalanche detectors.