Optical Absorption Properties Research Articles

In-Plane Strain Tuned Electronic and Optical Properties in Germanene-MoSSe Heterostructures.

DFT calculations are performed to investigate the electronic and optical absorption properties of two-dimensional heterostructures constructed by Janus MoSSe and germanene. It is found that a tiny gap can be opened up at the Dirac point in both Ge/SMoSe and Ge/SeMoS heterostructures, with intrinsic high-speed carrier mobility of the germanene layer being well preserved. An n-type Schottky contact is formed in Ge/SMoSe, while a p-type one is formed in Ge/SeMoS. Compared to corresponding individual layers, germanene-MoSSe heterostructures can exhibit extended optical absorption ability, ranging from ultraviolet to infrared light regions. The position of the Dirac cone, the Dirac gap value as well as the position of the optical absorption peak for both Ge/SMoSe and Ge/SeMoS heterostructures can be tuned by in-plane biaxial strains. It is also predicted that a Schottky–Ohmic transition can occur when suitable in-plane strain is imposed (especially tensile strain) on heterostructures. These results can provide a helpful guide for designing future nanoscale optoelectronic devices based on germanene-MoSSe vdW heterostructures.

Role of electron-electron interaction in the plasmon modes of twisted bilayer graphene

The unconventional properties of magic angle twisted bilayer graphene (TBG), such as correlated insulator states and superconductivity, have drawn significant attention to areas where electron-electron interactions play an important role. However, the role of electron-electron interactions on the plasmon properties of TBG has rarely been studied. In this study, we focus on TBG with a twist angle near the magic angle (1.32 \ifmmode^\circ\else\textdegree\fi{}), and examine the plasmon and optical absorption properties using the continuum model involving Hartree potentials that describe the electron-electron interaction. We find that the Hartree potentials decrease the energy of the intraband plasmon due to the band flattening driven by the interaction between electrons, whereas the energy of the interband plasmon is slightly increased by the Hartree potentials. Moreover, the splitting of the interband absorption peak occurs due to the effects of the Hartree potentials, which can be verified in experiments. Interestingly, the ultrahigh wave location (${\ensuremath{\lambda}}_{\mathrm{air}}/{\ensuremath{\lambda}}_{p}\ensuremath{\sim}2000$) of the intraband plasmon enables TBG to be a superior platform for future terahertz optoelectronic devices.

High-performance electron mobility and photoabsorption in Bi2O2Se nanoribbons

Two-dimensional (2D) Bi2O2Se has attracted much attention as a promising candidate for electronic and optoelectronic applications. However, the transport and optical properties in Bi2O2Se nanoribbons (NRs) are not yet fully understood. In this work, by using first-principles calculations, the intrinsic carrier mobility (μ) and the optical absorption properties of Bi2O2Se NRs are investigated. In contrast to the dramatic deterioration of μ in graphene upon the formation of NRs, the magnitude of μ in Bi2O2Se NRs can reach up to 3600 cm2 V−1 s−1 at a width ranging from 3.3 to 4.5 nm, which is about ten times higher than its sheet counterpart. Such a high intrinsic electron mobility of Bi2O2Se NRs can be attributed to the weaker edge state perturbations due to external strain inherent in Bi2O2Se NRs. Moreover, in Bi2O2Se NRs, the optical absorption at the visible (2.4–3.1 eV) and ultraviolet (4.3 eV) region reaches 5%–10% and 19.2%, respectively. Furthermore, the optical absorption properties can be well tuned by the width of NRs. In addition, the relatively small stretching modulus ranging from 0.40 to 2.24 × 10−7 J/m and the moderate critical strain ranging from 0.04 to 0.14 guarantee its moderate flexibility and ductility. Our results indicate that width modulation provides a potential approach for improving the transport and optical properties of Bi2O2Se nanostructures.

Microstructural, Optical, and Work Function Tuning of Fullerene (C60) Modified Zinc Oxide Films for Optoelectronic Devices

Here, we report the synthesis of pristine and fullerene (C60) modified zinc oxide (ZnO) films by the sol-gel method. Various compositions of C60 ranging from pristine to 0.25 wt%, 0.50 wt%, and 1.00 wt% have been chosen for the modification of ZnO film. The incorporation of C60 in pristine ZnO films modifies its structural, surface morphological, optical, and electrical properties. Structural characterization suggests that pristine and C60 modified ZnO films exhibit Wurtize crystal structure. Surface morphological characterization demonstrates that incorporation of C60 into ZnO leads to the formation of spherical nano-particles which varies on the doping of C60. The properties of C60 doped ZnO films show a reduction in the bandgap values from 3.11 eV to 2.73 eV with enhanced optical absorption and photoluminescence properties. Further, the surface potential and work function of pristine and C60 incorporated ZnO films, as investigated by Kelvin probe force microscopy (KPFM) show tuning of Fermi level in pristine and C60 modified ZnO films. The work function of the ZnO films changes from −4.38 eV to −4.46 eV on the incorporation of C60. The variations in work function may be due to reduced microstructural and localized defects offered during the incorporation of C60. Also, C60 modified ZnO Schottky diodes exhibited enhanced carrier mobility with better charge transport properties.

Array‐Based Discrimination of Phenolic Acids in Water at Near‐Neutral pH with Chromogenic and Fluorescent Cyclodextrin‐Based Supramolecular Sensors

AbstractPhenolic acids are a class of poorly water‐soluble organic compounds with antioxidant properties that contain a carboxylic acid and a phenol group, common in plants. We used hydroxypropyl‐β‐cyclodextrin (HP‐β‐CD) as a supramolecular host to sense phenolic acids in water near physiological pH. The analytes’ complexation was monitored through changes in the optical absorption and emission properties of a series of six organic dyes, acting as indicators in a displacement assay, that were selected from screening a panel of 17 candidates. Binding constants between these dyes and the HP‐β‐CD were in the 102–104 range. We showed that the nuanced differences in the dyes’ optical signatures associated with this displacement process, when analyzed and summarized using multivariate analysis algorithms such as principal component analysis (PCA), can be used to successfully discriminate among six phenolic acids, and to identify six unknown samples of such acids, down to a 0.02 mM concentration.

A Simple Expression for the Refractive Index of Distilled Water

Water is conceivably the most important material in the universe and most essential to the functioning of all the known life-forms. A simple expression for the real part of refractive index of water was investigated and proposed a new equation as a function of temperature between 0 oC and 100 oC and also wavelength in the range of 200 to 1100 nm. Water is transparent in the visible light and has a complex optical absorption property in the infrared and ultraviolet ranges. The refractive index highly depends on wavelength and temperature. The expression for refractive index is useful for different applications in biomedical optics. The proposed sample has accurate expression, has good agreement, as well as demonstrates increased performance with experimental measurements for calculations of knowledge of the refractive index of water at given ranges.

Tunable perfect optical absorption in truncated photonic crystals with lossy defects

We theoretically investigate tunable optical absorption properties of photonic crystals containing lossy materials as defects. It is found that a lossy defect can induce one or multiple perfect absorption peaks in the bandgap of photonic crystals and the number of the peaks mainly depends on the thickness of the defect layer. On the one hand, multiple complete absorption peaks can also emerge in the photonic bandgap when multiple lossy defects are inserted within the photonic crystals, and the resonant wavelengths of absorption peaks can be modulated by changing the distances among the defects. On the other hand, the optical absorption away from resonant wavelengths is nearly zero in the whole visible range. Such nanostructures can be used to engineer novel optical devices such as tunable single-channel and multi-channel perfect optical absorbers.

A first principle comparison of arsenic-based double halide perovskite materials for photovoltaic and optoelectronic application

The comparison study of arsenic-based double halide perovskite materials concentrated on the physical properties is initiated based on first principle. The structure stability is confirmed by the tolerance factor, formation energy and elastic constant. The materials are ductile and ionic compounds through elastic properties. The range of band gap is from 0.882eV to 2.125eV, close to the recommended values for optoelectronic and photovoltaic application. The halogen atoms have great effects on electronic band structures while alkali metal does rarely. All small effective masses for the studied materials indicate high mobilities, favorable for carrier transport. The excellent light absorption properties corresponding to ultraviolet–visible–infrared region reveal great applicable potential for solar energy utilization. Among these materials, K2AgAsBr6 is the most suitable for use as a solar cell material and photocatalytic material because it has an ideal band gap value, high dielectric constant and good optical absorption properties.

Enhanced light absorption of kinked nanowire arrays for high-performance solar cells

A kinked InP nanowire array solar cell architecture is proposed for high-performance solar cells. Coupled three-dimensional optoelectronic simulations are performed to investigate the optical absorption and photovoltaic conversion properties. The results show that the kinked morphology significantly enhances the absorption by increasing the optical path, exciting more resonance modes, and reducing the transmission into the substrate. Moreover, the kinked morphology also increases the absorption in the intrinsic region by suppressing the absorption loss in the top doped region. For short nanowires with a total length of 1–1.5 μm, the kinked structures exhibit remarkable efficiency exceeding 14%, significantly higher than the vertical nanowires. Nanowires with different kinked angles are studied, and a moderate kinked angle is beneficial for obtaining optimal performance. This work demonstrates the potential of kinked nanowires in ultra-thin low-cost high-efficiency solar cells.

Photothermal excitation and Thomson impact in a semiconductor microelongated thermoelastic medium with microtemperatures in the gravity

AbstractThe heating of solids occurs due to the absorbed light from the heat source. Photothermal spectroscopy is a method of measuring the optical absorption and thermal properties of semiconductor materials using high‐sensitivity spectroscopic techniques. In the present paper, the harmonic solution as an analytical solution is provided to describe the semiconductor photothermal microelongated medium with microtemperatures in the gravity field. The proposed photothermal microelongated model is subjected to an induced magnetic field to observe the Thomson effect. The numerical calculations for the components of thermal stresses, displacement, temperature field, and carrier density are obtained using the harmonic solution approach. The propagation of heat, elastic, and plasma waves, as well as the distributions of each investigated field, were examined and explained. The comparison is also used to see how the gravity, Thomson effect, and the photo‐excitation have more observable effects on the distribution of the medium fields during their values changes. With the development of technologies, the semiconducting materials were used widely in modern engineering. The study of wave propagation in a semiconducting medium will have important academic significance and application value.

Surface Photovoltage Study of GaAsSbN and GaAsSb Layers Grown by LPE for Solar Cells Applications

The properties of GaAsSbN and GaAsSb layers grown by liquid-phase epitaxy on n-GaAs substrates were investigated in a comparative plan with a view of their possible application in multi-junction solar cells. To avoid non-uniformity effects in the composition of these compounds with two or three different group-V volatile elements, the crystallization was carried out from finite melt with a thickness of 0.5 mm at low (<560 °C) temperatures. X-ray microanalysis and X-ray diffraction were used to determine the composition, lattice mismatch, and crystalline quality of the epitaxial layers. The morphology and surface roughness were examined by atomic force microscopy. Surface photovoltage (SPV) spectroscopy at room temperature was applied to study the optical absorption properties and the photocarrier transport in the samples. The long-wavelength photosensitivity of the GaAsSbN and GaAsSb layers, determined from their SPV spectra, is extended down to 1.2 eV. Although GaAsSb has a slightly larger lattice mismatch with the GaAs substrate compared to GaAsSbN, it presents a higher photoresponse, since, in GaAsSbN, the incorporation of N induces additional recombination centres. Therefore, GaAsSb could be an alternative to GaAsSbN for solar cell applications.

Dielectric screening versus geometry deformation in two-dimensional allotropes of silicon and germanium

The search for connections between electronic and structural features is a key factor in the synthesis of artificial materials for on-demand applications, with graphene and analogous elemental semimetals playing a distinguished role as building blocks of photonic and plasmonic systems. In particular, a diversity of arrangements and electronic-state dispersions is offered by currently synthesized two-dimensional allotropes of silicon and germanium, respectively known as silicene and germanene. These monolayers make the ideal playground to understand how their collective and single-particle electronic states, excited by electron or light beams, may be controlled by geometry rather than doping or gating. Here, we provide such a study using time-dependent density-functional theory, in the random-phase approximation, to identify the structural dependent properties of charge-density plasmon oscillations and optical absorption in flat to buckled silicene and germanene lattices. We further single out flat germanene as an unprecedented two-dimensional conductor, hosting Dirac cone fermions in parallel with metal-like charge carriers, which contribute to strong intraband plasmon modes and one-electron excitations in the far-infrared limit. Finally, we show how this atypical scenario can be tuned by external stress or strain.

A Cost-Effective Long-Wave Infrared Detector Material Based on Graphene@PtSe2/HfSe2 Bidirectional Heterostructure: A First-Principles Study

The Graphene@PtSe2 heterostructure is an excellent long-wave infrared detection material. However, the expensive cost of PtSe2 prevents its widespread use in infrared detection. In this paper, Hf was used to partially replace Pt to form Graphene@(PtSe2)n(HfSe2)4−n (n = 1, 2, and 3) bidirectional heterostructures consisting of graphene and lateral PtSe2/HfSe2 composites based on first-principles calculations. Then, the new bidirectional heterostructures were compared with heterostructures formed by graphene with pure MSe2 (M = Pt, Hf). It was found that the band gaps of the bidirectional heterostructures were between those of Graphene@PtSe2 and Graphene@HfSe2. Among these heterostructures, the Graphene@(PtSe2)3(HfSe2)1 bidirectional heterostructure has almost the same optical absorption properties in the infrared wavelength region of 1.33~40 µm as the Graphene@PtSe2 heterostructure, and it improves the absorption in the near-infrared wavelength region of 0.75~1.33 µm. Such a designment may bring the material costs down (since PtSe2 costs approximately five times more than HfSe2). This study on the designment of the bidirectional Graphene@(PtSe2)3(HfSe2)1 heterostructure also illustrates a cost-effective design method for Pt-based IR detectors.

Encapsulated layer induces boundary effect and twist angle adjust absorption in h-BN/graphene/h-BN heterostructure

This work studied the optical absorption properties and electronic properties of graphene nanosheets encapsulated in h-BN at different twisted angles based on first principles. UV–Vis spectrum shows that compared with the monolayer graphene nanosheets, the absorption’s peak of the encapsulated graphene nanosheets show a red shift and its molar absorption coefficient decreased significantly. The molar absorption coefficients of h-BN/graphene/h-BN heterostructures show an increasing trend when the graphene nanosheets are twisted relative to the packaging layer (twisted angles are 0°, 15°, 21.8°, 27.8° and 30°, respectively). More curiously, charge density difference (CDD) indicates that the region of electron aggregation in excited state mainly occurs at the centre of graphene nanosheets due to the introduction of h-BN packaging layer. The smoothed isosurface diagram of electron hole pairs shows that the distribution breadth of electron hole pair density decreases compared with that before encapsulation, and the distribution breadth of electron increase is larger than that of hole. With the increase of twisted angles, the distribution breadth of electron hole pair density increases gradually. Both CDD and smoothed isosurface diagram show that the system has strong boundary effect. This provides a method to adjust the photoelectric properties of graphene nanosheets by using different twisted angles, and provides a theoretical basis for its application in the field of micro-nano optoelectronics.

Copper Phthalocyanine MWCNTs Composites: Characterization and Evaluation for Sensor and Solar Cells interlayer

Copper Phthalocyanine (CuPc) thin film with and without multi-walled carbon nanotubes (MWCNTs) is prepared using the solution based method and used in gas sensor and solar cell applications. The structural characteristics of the CuPc thin films showed a single peak around 7o with the preferred orientation for charge transportation. Using atomic force microscopy (AFM), morphological properties show a rough surface with some aggregates and ribbons. The optical absorption properties were determined using UV-Visible absorption spectroscopy; the optical band gap has varied after adding MWCNTs to CuPc. Electrical conductivity of CuPc:MWCNTs composite is higher than that of the pure CuPc. The CuPc thin film sensr have shown good response properties to ammonia gas. The solar cell performance of the P3HT:PCBM based solar cell was enhanced.

Structure and tunable broadband near-infrared luminescence of Cr3+ in borophosphate glass

In this work, a series of Cr3+ ion-doped borophosphate glasses were prepared by the melt-quenching method. The structure, optical absorption, and near-infrared luminescence properties of the borophosphate glasses were investigated in detail. The results showed that Cr2O3 plays a modifier role in borophosphate glass consisting of borate and phosphate groups. The indirect optical bandgap and Urbach energy were found to vary in the range of 3.293–3.344 eV and 0.290–0.394 eV, respectively. Meanwhile, the Cr3+ ions located in a weak crystal field environment were confirmed by a Dq/B value of less than 2.3. Under the excitation of 440 nm, the as-prepared glasses exhibit broadband near-infrared (NIR) luminescence with an FWHM of about 210 nm and demonstrate a significant spectral red-shift from 858 nm to 894 nm. When the Cr2O3 content is greater than 0.30 mol%, the fluorescence intensity appears obvious concentration quenching. This work illustrates the potential application prospects of Cr3+ ion-doped glass materials as broadband NIR fluorescent devices.

Enhanced photocatalytic Hg0 removal over Z-scheme CeO2/Bi5O7I nanorod composite under fluorescent light irradiation

Novel CeO2 modified Bi5O7I nanorod composites were synthesized via a coprecipitation subsequent calcination method, which were employed to oxidize gaseous Hg0 in a photocatalytic bubbling reactor. The porosity properties, crystal structures, morphologies, elemental composition and optical absorption properties of the composites were investigated using various characterization methods. CeO2/Bi5O7I showed a significantly improved photoactivity of Hg0 removal under fluorescent light irradiation. The optimal mass percentage of CeO2 to CeO2–Bi5O7I was 10% and its photocatalytic removal efficiency of Hg0 reached as high as 97%. In comparison to NO, SO2 exhibited significant inhibition on Hg0 removal because of its easy reactivity with active species. The XRD, HRTEM and XPS results indicated the tight contact between Bi5O7I and CeO2, implying that a heterojunction between Bi5O7I and CeO2 was produced. The UV–vis DRS, PL and transient photocurrent test demonstrated that an enhanced activity of 10% CeO2/Bi5O7I for Hg0 removal could be assigned to the broad visible-light-absorption property, much superior separation of photoexcited electron-hole pairs. The scavenging experiments exhibited the superoxide radicals (•O2−) was the major oxidants in the process of Hg0 removal. Moreover, a proposed Z-scheme charge transfer path in CeO2/Bi5O7I nanorod composite was put forward according to the characterization and DFT calculation results.

Local control of optical absorption properties of glass using precipitation of gold nanoparticles via gold sphere movement driven by laser

Glass embedded with metal nanoparticles is a promising material necessary for optical devices because of its absorption properties associated with the surface plasmon resonance (SPR) of metal nanoparticles. We demonstrated that continuous-wave laser illumination of the metal sphere in glass migrates the metal sphere and dopes the migration trajectory. In this study, we have attempted to locally control the absorption properties of borosilicate glass via gold nanoparticle precipitation using gold sphere migration. The gold sphere was moved in the glass via laser illumination, and the gold nanoparticles were precipitated in the movement trajectory. The trajectory was colored in red and purple gradations because of the SPR of gold nanoparticles. The particle size of the precipitated gold nanoparticles and the absorption peak wavelength increased with increasing velocity of the gold sphere. The absorption properties of the trajectory depend on the velocity of the gold sphere migration, which enabled local control of the absorption properties of the glass.

THEORETICAL INVESTIGATIONS OF THE OPTOELECTRONIC PROPERTIES OF SOME 2, 4, 5-TRIPHENYL IMIDAZOLE BASED DYES FOR PROBABLE USE AS DYE-SENSITIZED SOLAR CELLS

The fast growing global demand for energy and the diminishing negative environmental effects associated with the burning of fossil fuels have forced the rapid development of renewable energy technology. In comparison to silicon-based semiconductor solar cells, dye-sensitized solar cells (DSSCs) offer a fascinatingly low cost of photovoltaic energy conversion, which has attracted a lot of attention. This work focuses on the investigation of photovoltaic, optical, and electronic absorption properties of some 2, 4, 5-triphenyl imidazole based dyes using Time Dependent-Den-sity Functional Theory (TD-DFT) via a Donor-π-Acceptor (D-π-A) framework. Results obtained show that most compounds with a cyanoacetic acceptor unit are much more favoured for Dye-Sensitive Solar Cells (DSSCs) applications than those without. Also, the electronic injection free energy (ΔGinject) was observed to have the highest value in TPI6 (-0.86 eV) due to the presence of a cyanoacetic acceptor. Furthermore, Absorbance data revealed how dyes containing cyanoacetic acceptor units tend to absorb both visible and UV light while dyes lacking the strong cyanoacetic acceptor groups absorbed only at the electromagnetic spectrum.

Distinct absorption transducing features of silica supported MoO3/PANI hybrid coated optical fiber towards Malathion monitoring in food samples

This work will show, for the first time, the absorptive silica-supported polyaniline (PANI) molybdenum trioxide (MoO3) semiconductor hybrid coating onto the optical fiber realizing the concept of lossy mode resonance (LMR) incorporated with molecular imprinting (MIP)-based sensors. The unique optical absorptive and imprinting (IP) properties and possessing a proper refractive index, introducing a versatile optical transducer, were assessed in the detection of Malathion (MAL) to address the rising concern of pesticide residue in crops. The accurate structural and morphological characterization confirmed the rough crystalline and spherical particles for a ternary composite of PANI, SiO2, and MoO3 onto an optical fiber curved surface while spectroscopic analysis confirms the formation of imprinting polymer and desirable absorbance characteristics. The experimental and numerical sensing studies revealed that the proposed sensing probe allows the rapid adsorption/desorption of MAL to the sensing films and highly permeable coating under studying the effective parameters influence. The optimized probe exhibits an excellent performance with the maximum sensitivity of within 14–224 µM with the linearity coefficient of R2 = 0.99 possessing a low limit of detection of 9.1 nM. Additionally, this sensor selectively detects. in the presence of other real species and also showed good recovery in the various corps samples.