Absorption Spectra Of Thin Films Research Articles

Influence of subphase temperature on Langmuir layers and thin films of A3B-type porphyrine derivative

The influence of aqueous subphase temperature on the formation and stability of floating layers of 5-(4-hydroxyphenyl)-10,15,20-tris(4-hexadecyloxyphenyl)porphyrin (P-OH) was investigated using the Langmuir technology. It was found that the increase in the subphase temperature from 1 to 40 °C leads to a loosening of floating layers (an increase in the area per molecule in the floating layer by ∼15% and a decrease in the surface compression modulus by more than two times). The stability of floating layers (i.e., the ability of a floating layer to maintain its area under the action of a constant compressive force) decreases with increasing subphase temperature. It has been shown that the most stable floating layers are formed at subphase temperatures lower than 30 °C. Monolayer films on solid substrates were obtained using the Langmuir-Schafer technique at subphase temperatures of 1, 10, 20, 30, and 40 °C. The surface relief of these films was studied by atomic force microscopy (AFM). The AFM analysis revealed that the films transferred from the aqueous subphase at a temperature of 20 °C had the highest continuity and the lowest roughness. The absorption spectra of the floating layers were obtained, in which a bathochromic shift of the Soret band and Q-bands were registered (by 19 nm at 20 °C) in comparison with chloroform solution spectrum. This shift is a consequence of the strong intermolecular π–π* interaction, resulting in the formation of J-type aggregates. The Soret band in the spectra of the floating layers shifted from 436 to 441 nm with an increase in subphase temperature from 1 to 40 °C. In the absorption spectra of thin films (8 transfers), the indicated shifts of absorption bands as well as a broadening of the Soret band are preserved. The results of this work can be used in the targeted creation of film samples with specific structure and properties.

Solid‐State Absorption, Luminescence, and Singlet Fission of Furanyl‐Substituted Diketopyrrolopyrroles with Different π‐Stacking Arrangements

AbstractSmall modifications of the diketopyrrolopyrrole (DPP) molecular structure induced remarkable changes in its spectral and photophysical behavior. Using furan (F) heterosubstitution instead of thiophene (T) substituent resulted in a small blue shift and decreased Huang‐Rhys factor of the absorption spectra in solution, irrespectively to N,N'‐alkyls. Branching of alkyl side chains by formal 2‐ethylation of n‐hexyl substituent (C6 to EH) switched the slipped‐stack arrangement, irrespectively on the heteroatoms. Consequent changes in steady‐state absorption spectra of thin films were interpreted using time dependent density functional theory calculations, carried out on model dimers. Solid‐state luminescence is weak and partially dependent on an excitation wavelength. Singlet fission was observed by femtosecond transient absorption spectroscopy, with considerably different yields for variously π‐stacked FDPP‐EH (30 %) and FDPP‐C6 (160 %). The shape of triplet‐triplet absorption spectra was also influenced by various π‐stacking. The results are discussed in terms of different mixing of both Frenkel and charge transfer states in model dimers and different excitonic and electronic coupling in both types of π‐stacks, visualized by natural transition orbitals.

Exciton absorption spectrum of thin films of ternary compounds in the CsCl–CuCl system

The absorption spectra of thin films (CsCl)1–x(CuCl)x were studied at T = 90 K in the spectral range 2–6 eV. From the analysis of the spectra, the formation of CsCu2Cl3 and Cs2CuCl3 compounds in the CsCl–CuCl system was created. The Cs2CuCl3 compound is stable only in a vacuum; in air, it apparently decomposes into CsCu2Cl3 with a disordered crystal lattice and CsCl. The exciton spectrum of both compounds is interpreted on the basis of transitions in the Cu+ ion. The one-dimensional character of excitons in CsCu2Cl3 and the two-dimensional character in Cs2CuCl3 were established.

Chế tạo màng mỏng có tính kị nước và siêu kị nước dựa trên vật liệu octadecylamin bằng các phương pháp hóa – lý khác nhau

Thin films based on octadecylamine (ODA) material have been successfully fabricated by different methods: Langmuir-Blodgett (LB) method, spin-coating, spray-coating and dip-coating methods. The films obtained on the glass substrate were investigated for their optical properties (Uv-vis), film morphology (digital microscope, SEM) and contact angle. The solution and thin film absorption spectra of ODA and the mixtures of ODA and polymer RTV/SR do not absorb in the wavelength of the visible light region. The SEM analysis results show that the film morphology of ODA strongly depends on the nature of the ODA solution and the method of film formation and these are important factors affecting the different hydrophobicity of ODA films. Comparison of the droplet contact angle of thin films obtained by the above methods shows that the films fabricated by LB, spin-coating and spray-coating all increase the hydrophobicity of the glass substrate with the droplet contact angle range from 100o-145o, while dip-coating it is possible to fabricate superhydrophobic films with contact angles up to 161o.

Growth of Hybrid Perovskite Films via Single-Source Perovskite Nanoparticle Evaporation.

Herein, we demonstrate a vacuum-based evaporation approach to fabricate organic-inorganic perovskite thin films by using phase-formed halide perovskite nanoparticles (NPs) as a precursor/source. We are able to consistently obtain MAPbX3 (MA=CH3 NH3 and X=Cl, Br or I) thin films at various substrates (e. g., glass, ITO, or plastic). The perovskite phase formation in thin film form is confirmed by x-ray diffraction (XRD) studies. Small micro-strain (tensile) values of 1.64×10-3 , 1.42×10-3 and 6.85×10-4 obtained for MAPbCl3 , MAPbBr3 and MAPbI3 films respectively from Williamson-Hall equation indicate low structural distortions in perovskite thin films. The absorption spectra of thin films show sharp band edge having direct band gap, which is followed by narrow full width at half maxima (FWHM ∼0.1 eV) of the emission peak. Thin films of MAPbCl3 , MAPbBr3 and MAPbI3 show direct band gap of 3.1 eV, 2.4 eV and 1.6 eV, respectively. Small Urbach energy values of 33 meV, 44 meV and 66 meV for MAPbCl3 , MAPbBr3 and MAPbI3 films respectively indicates low defect density in various perovskite films. Scanning electron microscopy (SEM) along with energy-dispersive X-ray spectroscopy (EDS) shows high surface coverage and uniform chemical composition of MAPbX3 (X=Cl, Br and I) thin films deposited by the present method. We have successfully controlled the film thickness from 250 nm to 1 μm by varying the nanoparticle precursor amount. The perovskite thin films deposited by the present method are highly stable against the degradation under ambient conditions. Systematic XRD studies along with absorption data demonstrate that the MAPbCl3 and MAPbBr3 films stored under ambient conditions remained stable for more than 30 days and MAPbI3 films for more than 7 days.

Fabrication of PMMA thin film and its optical and photocatalytic activity

In this study, the PMMA thin film is fabricated using drop casting method and its optical studies were done using UV/VIS/NIR spectroscopy. The absorption spectrum of thin film showed maximum absorption at 320 nm and the corresponding optical band-gap calculated is 2.83 eV. ATR-IR spectrum gives the different bond stretching and vibrational modes and confirms the presence of different bonds. Its Photoluminescence (PL) study gives a blue emission, observed at 432 nm also denoted by CIE 1931 curve. The optical band-gap calculated from PL is 2.87 eV. Further the effect of different excitation wavelength was examined and possible transitions were explained via transition diagram. The fabricated thin film was used in removal of hazardous dye Rhodamine B (RhB) from tap water. The PMMA thin film was able to photo-degrade 94 % of RhB was degraded in 50 min with reaction rate constant k equal to 0.0579 min−1. The thin film can be reused after oven drying for 2 h at 60⁰ C in hot air vacuum oven. The PMMA thin film was used up to 6 cycles and up to 90 % degradation was observed. Since no extra reducing agents (such as NaBH4) were used in this process hence it makes its possible use in environment friendly photocatalytic agent and waste water treatment.

Double Free: A Promising Route toward Moisture-Stable Hypotoxic Hybrid Perovskites

Double Free: A Promising Route toward Moisture-Stable Hypotoxic Hybrid Perovskites

Exciton absorption spectra of thin films of RbCu2Cl3 and Rb2Cu3Cl5 ternary compounds

The absorption spectra of RbCu2Cl3 and Rb2Cu3Cl5 thin films were studied in the 2−6 eV spectral and 90−450 K temperature ranges. The localization of excitons in CuCl43− structural elements of crystal lattice of compounds, three-dimensional nature of excitons in RbCu2Cl3 and two-dimensional nature of excitons in Rb2Cu3Cl5 were established. The exciton spectra of RbCu2Cl3 and Rb2Cu3Cl5 thin films were interpreted based on the transitions in the Cu+ ion.

Response of structural and optical properties against proton irradiation in AlN:Tm thin films

Thulium (Tm) doped aluminum nitride (AlN) thin films are deposited by radio frequency (RF) magnetron sputtering in a pure nitrogen atmosphere. As-deposited thin films are irradiated at room temperature with 335 keV protons and a fluence of 1 × 1014 ions/cm2. The effects of irradiation on the structural and optical properties of the deposited thin films are investigated. Rutherford backscattering (RBS) is performed to determine the thickness and stoichiometric properties of the films while the structural properties of the material before and after irradiation are investigated with x-ray diffraction (XRD). Non-ionizing energy loss (NIEL) study demonstrates that scattering events increase as the ions penetrate deep into the matrix and result in higher damage in the material. Fourier transform infrared spectroscopy (FTIR) is used to see the absorption spectra of thin films which reveals that the implanted films have great capabilities of solar energy storage. Bandgap of the film is determined using diffused reflection spectroscopy (DRS) technique, where a slight upwards shift in bandgap is observed due to irradiation induced material damages.

Multi-Stimuli-Responsive Field-Effect Transistor with Conjugated Polymer Entailing Spiropyran in the Side Chains

Multi-stimuli-responsive field-effect transistors (FETs) with organic/polymeric semiconductors have received increasing attention. Herein, we report a novel strategy for fabricating multi-stimuli-r...

Efficient Anti-solvent-free Spin-Coated and Printed Sn-Perovskite Solar Cells with Crystal-Based Precursor Solutions

Summary Tin-based perovskite solar cells (PSCs), with more consummate optical band gaps, lower exciton-binding energies, and higher charge-carrier mobility, have not attracted tremendous research efforts compared with the lead-based ones that have a record power conversion efficiency (PCE) of 24.2%. The major challenges for Sn-based research are significantly low open-circuit voltage, poor reproducibility, and environmental instability. It has been identified that the oxidation processes take place during the preparation of precursor solutions and fabrication of films, due to the low redox potential of the stannous absorption layer. Herein, we propose two strategies of crystal-resolving and recrystallization technology to reduce the oxidation process. As a result, PCEs of 8.9% (active area of 0.04 cm2) and 5.5% (active area = 1.01 cm2) are attained using the inverted p-i-n structure, which will lead to a revival of lead-free PSC research.

Spectral Features of Zinc Phthalocyanine: Optics, Stark Spectroscopy, and Photovoltaics

The results of spectral analysis of organic semiconductor, zinc phthalocyanine (ZnPc), which is one of the best donor materials for solar power engineering but is relatively rarely used in practice, are reported. The study of the ZnPc spectral features was performed in three different directions: optical measurements of the absorption spectra of thin films, Stark spectroscopy with information about dipole moments and polarizabilities of molecules in the solid phase, and investigation of the photovoltaic effect in simple ZnPc-based heterostructure with variation in the active-layer thickness.

PLAZMA POLİMERİZE D-LİMONENE İNCE FİLMLERİN ISLANABİLİRLİK, OPTİK VE KİMYASAL ÖZELLİKLERİ

In this study, organic based polymer thin films were obtained on various substrates using D-Limonene essential oil, which is an organic compound by radio frequency (RF) plasma polymerization technique. The optical band gap and absorption spectra of thin films were investigated by Uv-VIS spectra and depending on the increased RF power, the optical band gap of the thin films was found to be 3.19, 3.25 and 3.31 eV, respectively. WCA analyzes were also performed to determine the wettability properties of thin films and all thin films had hydrophilic properties and these properties were significantly affected by increased RF power. Considering both the morphological and optical properties of plasma polymerized (pp) D-Limonene thin films, it is thought that these films may be an alternative to those already used in current electronic applications due to their organic compound-based nature.

The exciton absorption spectrum of thin films of ternary compounds in the AgBr–PbBr2 system

Exciton absorption spectra of thin films of complex compounds AgPbBr3, AgPb2Br5, and AgPb3Br7 were studied in the photon energy range 2–6 eV. It was established that the compounds belong to the direct band dielectrics; low-frequency excitons are localized in the structural layers (PbBr8)6– of the crystal lattice and have a quasi-two-dimensional nature.

Studies on structural and optical properties of thermally evaporated nanocrystalline thin films of meso-Tetraphenylporphyrin manganese(III) chloride

Thin films of meso-Tetraphenylporphyrin manganese(III) chloride (MnTPPCl) were prepared by conventional thermal deposition technique, under vacuum (10−4 Pa), on glass and quartz substrates. X-ray diffraction (XRD) technique, Fourier-transform Infrared (FT-IR) technique and scanning electron microscope (SEM) were used to investigate crystalline and molecular structures, and morphology of MnTPPCl in powder form, and the as-deposited thin films. Absorption spectra of thin films were recorded in the wavelength range from 200 to 2500 nm by using Spectrophotometric measurements. Seven distinct absorptions were detected in MnTPPCl thin films in the range between 1.9 and 5 eV. The type of the optical transition and optical energy gap were estimated from the analysis of the absorption coefficient data. In the present work, dispersion parameters: oscillator energy, dispersion energy, optical dielectric constant at higher frequency, and Lattice dielectric constant were calculated as well as many other optical parameters. Nonlinear absorption coefficient spectrum of MnTPPCl thin film was obtained utilizing a linear optical parameter. The cyclic voltammetry measurements were employed to calculate HOMO-LUMO gap in the voltage range from − 2 to + 2 V.

Absorption spectrum of thin films of KPb2(Cl1-xBrx)5 solid solutions

The absorption spectra of thin films of KPb2(Cl1-xBrx)5 (0 ≤ x ≤ 1) are studied in the spectral range of 2–6 eV (T = 90 K). Solid solutions with a mixed monoclinic structure are formed at all concentrations 0 ≤ x ≤ 1 and a tetragonal structure is found for 0.9 ≤ x ≤ 1. The temperature of the tetragonal to monoclinic phase transition in the solid solutions increases with the amount of Cl additive. The concentration dependences of the spectral location and half width of the long-wavelength exciton bands are the result of small-scale and large-scale fluctuations in the composition of the solid solution.

Polymer Sensitive Elements for Gas Sensors of Ammonia

The influence of ammonia on the optical absorption spectra of thin films of polyaniline (PANI), poly-3,4-ethylenedioxythiophene (PEDOT), mixtures thereof, and the bilayer film structures based on PANI and PEDOT obtained by electrochemical method were studied. The kinetics of changes in the optical absorption of these structures under the action of ammonia was explored in the spectral range of 350 ... 900 nm. We proved that the thin-film structure of PANI / PEDOT significantly extends the spectral range of sensitivity to ammonia of individual PANI n PEDOT films by superposition of high gas sensitivity of PANI and PEDOT films in the range of wavelength of 500 ... 700 nm and 350... 550 nm respectively. It was shown that the area under the spectra of change of the optical absorption of thin-film structure of PANI / PEDOT is in 1.45 times larger than the area of the same for individual components of the layers, which is the key to increasing the sensitivity of the gas sensors. The results can be used to optimize ammonia gas sensors for monitoring biotechnological processes in food industry and the environment.

Organic high-sensitive elements of gas sensors based on conducting polymer films

ABSTRACTThe influence of ammonia on the optical absorption spectra of thin films of polyaniline (PANI), poly-3,4-ethylenedioxythiophene (PEDOT), mixtures thereof, and the bilayer film structures based on PANI and PEDOT obtained by electrochemical method were studied. The kinetics of changes in the optical absorption of these structures under the action of ammonia was explored in the spectral range of 350 … 900 nm. It was shown that thin film bilayer structure PANI / PEDOT significantly broaden the range of spectral sensitivity to ammonia compared to individual films.

Optical properties and mechanisms of current flow in Cu2ZnSnS4 films prepared by spray pyrolysis

Thin films Cu2ZnSnS4 (up to 0.9 μm thick) with p-type conductivity and band gap Eg = 1.54 eV have been prepared by the spray pyrolysis of 0.1 M aqueous solutions of the salts CuCl2 · 2H2O, ZnCl2 · 2H2O, SnCl4 · 5H2O, and (NH2)2CS at a temperature TS = 290°C. The electrophysical properties of the films have been analyzed using the model for polycrystalline materials with electrically active grain boundaries. The energy and geometric parameters of the grain boundaries have been determined as follows: the height of the barriers is Eb ≈ 0.045–0.048 eV, and the thickness of the depletion region is δ ≈ 3.25 nm. The effective concentrations of charge carriers p0 = 3.16 × 1018 cm–3 and their mobilities in crystallites μp = 85 cm2/(V s) have been found using the technique for determining the kinetic parameters from the absorption spectra of thin films at a photon energy hν ≈ Eg. The density of states at grain boundaries Nt = 9.57 × 1011 cm–2 has been estimated.

Measurements of absorption spectra of thin films by the waveguide technique

The waveguide technique for measuring the absorption spectra of thin films in spectral range of their transparency is considered. The error of measuring the absorption of a ∼0.1 μm thick film does not exceed 5% at an absorption coefficient of less than 50 cm–1. Capabilities and limitations of the method are discussed.