Optical Absorption Coefficient Spectra Research Articles

Optical Characterization of Hydrogel and Silicone Hydrogel Soft Contact Lenses

Contact lenses are biomaterials that have emerged as an alternative to glasses in correcting vision defects. In this study, commercial nesofilcon A (hydrogel-Hy) and delefilcon A (silicone hydrogel-SiHy) daily disposable soft contact lenses were optically examined using UV-visible light spectroscopy. Optical absorption and transmittance measurements of the lenses were taken with a UV-visible spectrophotometer, and their properties of blocking the harmful part of the radiation to the eye and transmitting the harmless part were investigated. From the absorption spectrum, it was seen that the nesofilcon A lens absorbed ultraviolet light better. From the optical absorption coefficient spectra of nesofilcon A and delefilcon A lenses, the absorption edges were obtained as 386 and 325 nm, and the optical band gap values were 3.37 and 3.98 eV, respectively. Additionally, the refractive index profiles of the lenses were plotted. The refractive indices of the lenses at 550 nm wavelength were calculated as 1.55 and 1.77 for nesofilcon A and delefilcon A, respectively. While the delefilcon A lens transmitted visible light well, the nesofilcon A lens blocked UV light better and its refractive index was determined to be closer to the 1.40 the value specified by the manufacturer.

Optical and Recombination Parameters of CdS1−xTex Thin Films Obtained by the CMBD Method

This paper presents the results of the photoacoustic, SEM, and surface photovoltage experiments performed on the series of CdS1−xTex thin films. These CdS1−xTex (0 ≤ x ≤ 1) thin films were obtained on the glass substrate by the chemical molecular beam deposition (CMBD) method. The polycrystalline character of these films was revealed by SEM pictures. From the experimental optical characteristics, the optical absorption coefficient spectra of the samples and values of their energy gaps vs. their composition were determined. From the surface photovoltage characteristics, the diffusion lengths of the carriers were also determined.

The visible and near-infrared optical absorption coefficient spectrum of Parylene C measured by transmitting light through thin films in liquid filled cuvettes

Parylene C (PPXC) is a polymer deposited from the gas phase to form optically clear thin films used in devices including waveguides and sensors. The performance of these devices depends on the visible and near infrared absorption coefficient of PPXC. However, the absorption coefficient is difficult to measure. This is because PPXC films are typically too thin to exhibit detectable absorption in conventional transmittance measurements. To address this challenge, a method involving measuring the transmittance of multiple films immersed together in a liquid filled cuvette was devised. This increased the sensitivity to absorption by increasing the path length in PPXC, while also minimizing reflections and surface losses. Using 200-500 µm thick films, this method was applied to measure the absorption coefficient of PPXC at wavelengths in the range 330-3300 nm. The coefficient was found to vary spectrally by more than two orders of magnitude from 0.025 mm-1 at 1562 nm to 7.7 mm-1 at 3262 nm. These absorption measurements could aid the design of PPXC based sensors and waveguides. The method could be useful for measuring the absorption coefficient of other thin, low-loss materials, particularly those for which it is challenging to obtain thick samples such as other polymers deposited from the gas phase in a similar manner to PPXC.

Excellent properties of type-II van der Waals Janus-XM2X’/MX heterojunctions toward solar cell utilization

Constructing van der Waals (vdW) heterojunctions is an effective strategy for band engineering of two dimensional (2D) materials. The XM2X’/MX (M = Al, Ga, In; X = S, Se, Te) heterostructures are investigated by first-principles calculation. Five XM2X’/MX with less than 3% of lattice mismatch are found to be direct-band-gap type-II band structures with moderate band gap from 1.08 to 1.73 eV in HSE06 method, high optical absorption coefficient (∼105 cm−1) and broad absorption spectrum, which facilitates effective utilization of the solar visible light and separation of photo-generated electron-hole pairs. Intriguingly, the band gap and band offsets are tunable to achieve high power conversion efficiency by external electric field and vertical strain. These results indicate potential applications of the XM2X’/MX in solar energy conversion.

Spectral absorption coefficient extraction of an unknown layer from photoacoustic measurements of multilayered semiconductors

This paper reports on a theoretical relation for the normalized photoacoustic amplitude signal for use in determining the optical absorption coefficient spectrum of any layer of multilayered semiconductors’ samples. The derived relation is for use in gas-coupled photoacoustic cells. The model, unlike its predecessors so far reported in the literature that are usually for specific cases in dependence of the optical properties of the sample, takes into considerations the geometrical sample, the photoacoustic cell parameters, the thermal reflections as well as the light reflections at different interfaces. We present the results analysis on the effect of increasing the number of layers on the normalized photoacoustic response by considering particular applications in optoelectronic devices’ configurations. A computer program has been developed to extract the absorption coefficient spectral distribution of any particular layer. Three specific experimental applications are provided in evaluating the performance of the present model. Unlike conventional spectroscopic techniques, the photoacoustic method is known for high detectability in the region of weak absorption. Hence, the applications we present here include the cases of a single transparent sample, a thin solid single crystal and embedded layer in a three-layered sample.

Comparative studies of the optical absorption coefficient spectra in the implanted layers in silicon with the use of nondestructive spectroscopic techniques

Comparative studies of the optical absorption coefficient spectra in the implanted layers in silicon with the use of nondestructive spectroscopic techniques

Investigations and modeling aspects of the influence of the high energy and high dose implantation on the optical and transport parameters of implanted layers in silicon

This paper presents results of investigations and modeling aspects of the influence of Ge+ high energy (100 keV) and high dose (1014 cm−2) implantation on the optical and recombination parameters of implanted layers in silicon. The nondestructive and contactless MFCA (Modulated Free Carrier Absorption) method was used as it is sensitive to changes of these parameters expected for implanted layers. Several model cases describing the MFCA spectrum as a function of the energy of photons of the excitation laser light are presented, compared and discussed. The simplified one-layer model and the full two-layer model of the MFCA signal have been analyzed and compared. The possibility and correctness of determination of the optical absorption coefficient spectra of the implanted layers with the use of the one-layer simplified model has been discussed.

Determination of the Optical Absorption Coefficient Spectra of Thin Semiconductor Layers from Their Photoacoustic Spectra

This paper presents the new method of computation of the optical absorption coefficient spectra from the normalized photoacoustic amplitude spectra of thin semiconductor samples deposited on the optically transparent and thermally thick substrates. The simple equation for computations of the optical absorption coefficient spectrum from the normalized photoacoustic amplitude spectrum is derived and discussed. This model applied for computations of the optical absorption coefficient spectrum of thin germanium samples, deposited on the transparent glass substrate, from their photoacoustic spectra proved its correctness and usefulness.

Optical absorption spectra of perovskite thin films for defect estimation by photothermal bending spectroscopy

The measurement of the optical absorption coefficient spectra of perovskite thin films of CH3NH3PbI3 by resonant photothermal bending spectroscopy (resonant-PBS) and Fourier-transform photocurrent spectroscopy (FTPS) for the defect estimation of the material has been attempted. A fundamental absorption edge was observed in the photon energy ħω region of 1.5–1.6 eV by both techniques. In addition, extra absorption of about 102 cm−1 was detected at ħω < 1.5 eV only in the spectra measured by resonant-PBS. This extra absorption seems to indicate the existence of localized states in the bandgap of CH3NH3PbI3 films. The difference between resonant-PBS and FTPS profiles below the absorption edge is caused by the difference in measurement mechanism, that is, resonant-PBS utilizes a temperature rise of the sample by the nonradiative recombination of photoexcited carriers, while FTPS measures photocurrent arriving at electrodes by the electric field after the photoexcitation. These results seem to indicate that resonant-PBS is a useful tool for the defect estimation of CH3NH3PbI3.

Photoacoustic spectroscopy analysis of thin semiconductor samples

This paper is an analysis of determination possibility of the optical absorption coefficient spectra of thin semiconductor layers from their normalized photoacoustic amplitude spectra. Influence of multiple reflections of light in thin layers on their photoacoustic and optical absorption coefficient spectra is presented and discussed in detail. Practical formulae for the optical absorption coefficient spectrum as a function of the normalized photoacoustic amplitude spectrum are derived and presented. Next, they were applied for computations of the optical absorption coefficient spectra of thin In2S3 thin layers deposited on a glass substrate. This method was experimentally verified with the optical transmission method.

Determination of the optical absorption spectra of thin layers from their photoacoustic spectra

This paper presents a new method for computations of the optical absorption coefficient spectra from the normalized photoacoustic amplitude spectra of thin semiconductor samples deposited on the optically transparent and thermally thick substrates. This method was tested on CuIn(Te0.7Se0.3)2 thin films. From the normalized photoacoustic amplitude spectra, the optical absorption coefficient spectra were computed with the new formula as also with the numerical iterative method. From these spectra, the value of the energy gap of the thin film material and the type of the optical transitions were determined. From the experimental optical transmission spectra, the optical absorption coefficient spectra were computed too, and compared with the optical absorption coefficient spectra obtained from photoacoustic spectra.

Enhancement of photoconductive performance of CdSe via Yb nanosandwiching

In this work, we have explored the effects of the ytterbium nanosandwiching on the structural and optoelectronic properties of CdSe thin films. A ytterbium layer of thickness of 200 nm was sandwiched between two layers of CdSe (1.0 μm). The structural investigations have shown that the hexagonal structure of CdSe is deformed by 1.9% and 0.8% along the a and c-axes, respectively, by the inclusion of the Yb in the structure of CdSe. In addition, a systematic redshifts in the interference patterns of the optical transmittance and reflectance were observed. Accordingly, the optical absorption coefficient spectra of CdSe which displayed two energy gap values of 1.62 and 1.36 eV, are also redshifted. On the other hand, when exposed to blue light irradiation, the steady state and time dependent photocurrent analysis revealed a remarkable enhancement presented by a three orders of magnitude increase in the responsivity of CdSe upon Yb sandwiching. The photocurrent was observed to be limited by the saturation of the surface states and traps that causes longer relaxation constant compared to that of pure CdSe.

Optical and spectroscopic study of erbium doped calcium borotellurite glasses

In this study, 10CaF2 – (29.9–0.4x)CaO – (60-0.6x)B2O3 – xTeO2 – 0,1Er2O3 (x = 10, 16, 22, 30 and 50 mol %) glasses were synthesized, and their optical and spectroscopic properties were investigated. X-ray diffraction, density, glass transition temperature (Tg), crystallization temperature (Tx), refraction index, luminescence, radiative lifetime and optical absorption measurements were carried out. Molar volume (Vm), thermal stability (Tx-Tg), electronic polarizability (αm), optical bang gap energy (Eg) and Judd-Ofelt (JO) parameters Ωt (2,4,6) were also calculated. The results are discussed in terms of tellurium oxide content. The increase of TeO2 in the glasses composition increases density, refractive index and electronic polarizability. The optical band gap energy decreases varying from 3.37 to 2.71 eV for the glasses with 10 and 50 mol% of TeO2, respectively. The optical absorption coefficient spectra show characteristic bands of Er3+ ions. Furthermore, these spectra in NIR region show a decrease of hydroxyl groups as a function of TeO2 addition. Luminescence intensity and radiative lifetimes at 1530 nm show an increasing with the TeO2 content. The JO parameters of Er:CaBTeX glasses follow the trend Ω2 > Ω4 > Ω6 and the quality factor values (Ω4/Ω6) were between 1.37 and 3.07. By comparing the measured lifetime with the calculated radiative decay time, quantum efficiency was calculated. The luminescence emission intensity at 1530 nm decreases with the increase of temperature. The lifetime values show a slight trend to decrease with the temperature increase, from 300 to 420 K, for all the samples.

Hyperspectral photoacoustic spectroscopy of highly-absorbing samples for diagnostic ocular imaging applications

ABSTRACTPhotoacoustic spectroscopy has been used to measure optical absorption coefficient and the application of tens of wavelength bands in photoacoustic spectroscopy was reported. Using optical methods, absorption-related information is, generally, derived from reflectance or transmittance values. Hence measurement accuracy is limited for highly absorbing samples where the reflectance or transmittance is too low to give reasonable signal-to-noise ratio. In this context, this paper proposes and illustrates a hyperspectral photoacoustic spectroscopy system to measure the absorption-related properties of highly absorbing samples directly. The normalized optical absorption coefficient spectrum of the highly absorbing iris is acquired using an optical absorption coefficient standard. The proposed concepts and the feasibility of the developed diagnostic medical imaging system are demonstrated using fluorescent microsphere suspensions and porcine eyes as test samples.

Shape and size determination of plasmonic nano particles using particle swarm optimization algorithm based absorption coefficient

Plasmonic nano particles can be greatly enhancing the optical absorption coefficient spectrum. Since optical properties of these particles strongly depends on the size and shape of the nano particles, in this paper particle swarm optimization algorithm (PSO) is used to optimize the nano particles shape and size in order to amplification of the absorption coefficient. In PSO a swarm consists of a matrix with decimal numbers, controls the particles shape and size in order to increase the absorption coefficient in the visible part of light spectrum. It is found that significant plasmonic enhancement of above 100000 can be obtained by optimize selection of particle shapes and sizes.

Production of Ni(OH)2 Nanosheets By Liquid Phase Exfoliation: High Performance Oxygen Evolution Catalysts and Supercapacitor Electrodes

2D materials have generated much excitement in recent years.1-2 Although these can now be produced in a number of ways, many applications, particularly in the energy arena, require liquid dispersions of 2D nanosheets. Liquid phase exfoliation3-4(LPE) is a very simple processing method which allows layered crystals to be exfoliated in liquids to give suspensions of good quality nanosheets. One strength of this process is its versatility. It has been used to exfoliate graphene and a number of inorganic 2D materials such as BN, MoS2 and GaS. Another is its simplicity – it is straightforward and easy to replicate. Here we bring together these two strengths by demonstrating that LPE can be used to exfoliate a new family of 2D materials, the layered double hydroxides (LDHs). This family of materials have been exfoliated previously using chemical exfoliation techniques. These techniques work well but are time consuming, take multiple steps and use harsh chemicals. Here, LPE method method involves sonication of commercially available powders in aqueous surfactant solutions and so is mild and potentially scalable. More specifically, we demonstrate that LPE can be used to convert layered crystals of nickel hydroxide into Ni(OH)2 nanosheets in relatively large quantities. TEM, XPS and Raman spectroscopy show the exfoliated nanosheets to be relatively thin and of good quality. Size selection allowed the production of samples with mean nanosheet lengths ranging from 55 to 195 nm. Optical measurements showed the optical absorption coefficient spectra to be relatively invariant with nanosheet size while the scattering coefficient spectra varied strongly with size. The resulting strong size dependence allows the extinction spectra to be used to estimate nanosheet size as well as concentration. We used the exfoliated nanosheets to prepare thin film electrodes for use in supercapacitors and as oxygen evolution catalysts. Prior to use we perfomed an activation procedure of polarising the electrode at 10 mA/cm2 in 1 M NaOH which significantly increased both the capacitance and catalytic activity towards the oxygen evolution reaction (OER). While the resultant capacitance was reasonably high at ~1200 F/cm3 (20 mV/s), the catalytic performance was exceptional. We observed currents of 10 mA/cm2 at overpotentials as low as 297 mV for the OER, which is close to the state of the art. Fig 1 (a) A) Structure of nickel hydroxide, Ni(OH)2. Blue, Ni; yellow, O; silver, H. B) Photograph of typical Ni(OH)2 dispersion in surfactant solution (H2O + sodium cholate) showing distinctive green colour. C) Representative low resolution TEM image of Ni(OH)2 nanosheets (b) Polarisation curves, 1 M NaOH (1 mV/s), for OER from Ni(OH)2 electrodes fabricated from Ni(OH)2films on Ni foam current collector before and after activation with the equivalent curve for the bare Ni foam shown for comparison. 1. Chowalla, M.; Shin, H. S.; Eda, G.; Li, L.-J.; Loh, K. P.; Zhang, H., The chemistry of two-dimensional layered transition metal dichalcogenide nanosheets. Nature Chemistry 2013,5, (4), 263-275. 2. Wang, Q. H.; Kalantar-Zadeh, K.; Kis, A.; Coleman, J. N.; Strano, M. S., Electronics and optoelectronics of two-dimensional transition metal dichalcogenides. Nature Nanotechnology 2012,7, (11), 699-712. 3. Hernandez, Y.; Nicolosi, V.; Lotya, M.; Blighe, F. M.; Sun, Z.; De, S.; McGovern, I. T.; Holland, B.; Byrne, M.; Gun'ko, Y. K.; Boland, J. J.; Niraj, P.; Duesberg, G.; Krishnamurthy, S.; Goodhue, R.; Hutchison, J.; Scardaci, V.; Ferrari, A. C.; Coleman, J. N., High-yield production of graphene by liquid-phase exfoliation of graphite. Nature Nanotechnology 2008,3, (9), 563-568. 4. Coleman, J. N.; Lotya, M.; O'Neill, A.; Bergin, S. D.; King, P. J.; Khan, U.; Young, K.; Gaucher, A.; De, S.; Smith, R. J.; Shvets, I. V.; Arora, S. K.; Stanton, G.; Kim, H.-Y.; Lee, K.; Kim, G. T.; Duesberg, G. S.; Hallam, T.; Boland, J. J.; Wang, J. J.; Donegan, J. F.; Grunlan, J. C.; Moriarty, G.; Shmeliov, A.; Nicholls, R. J.; Perkins, J. M.; Grieveson, E. M.; Theuwissen, K.; McComb, D. W.; Nellist, P. D.; Nicolosi, V., Two-Dimensional Nanosheets Produced by Liquid Exfoliation of Layered Materials. Science 2011, 331, (6017), 568-571. Figure 1

Measurement and feature analysis of absorption spectra of four algal species

Two methods for particulate pigments (i.e., quantitative filter technique, QFT, and in vivo measurement, InVivo, respectively) and two methods for dissolved pigments (i.e., Acetone Extracts, AceEx, and high-performance liquid chromatography, HPLC, respectively) were used to obtain the optical absorption coefficient spectra for cultures of four typical algal species. Through normalization and analysis of the spectra, it is shown that (1) the four methods are able to measure optical absorption spectra of particulate and/or dissolved pigments; (2) that the optical absorption spectra of particulate and dissolved pigments were consistent in terms of the peak position in the blue wavelength, and the difference of the peak position in the near infrared wavelength was ~10 nm between each other; and (3) that the leveling effect of the absorption spectra of particulate pigments was significant. These four methods can all effectively measure the absorption coefficients of phytoplankton pigments, while each one has its unique advantages in different applications. Therefore, appropriate method should be carefully selected for various application due to their intrinsic difference.

Lamb wave acousto-optic modulator in ZnO/MgO multiple quantum wells and comparison with classical modulator.

An analysis of a ZnO/MgO multiple quantum well (MQW) acousto-optic modulator with Lamb waves is performed. With the MQW thickness in the range of 0.2 times the Lamb wavelength, the only observed Lamb modes are the lowest-order symmetric S0 and antisymmetric A0 modes. These modes induce strain and electric field components which influence the absorption coefficient of the modulator by the associated variation of the excitonic energies of MQW. The optical absorption coefficient spectra of the modulator as a function of the Lamb waves' power is presented. The Lamb-wave-based modulator gives a better absorption coefficient than the Rayleigh-wave-based one. An analysis of a classical acousto-optic modulator is also performed for comparison of performance.

The fundamental absorption edge in MnIn2Se4 layer semi-magnetic semiconductor

From the study of the optical absorption coefficient and photoluminescence spectra of the layer semi-magnetic semiconductor MnIn2Se4 the nature of its fundamental absorption edge is established. It is found that the lowest-energy-gap of this compound is allowed-indirect between parabolic bands that vary from about 1.55–1.43eV in the temperature range from 10K to room temperature. In addition, two allowed direct band-to-band transitions beginning at 1.72 and 1.85eV at 295K, and at 1.82 and 1.96eV at 10K which are related to optical absorption processes between the uppermost Γ4(z) and the middle Γ5(x) valence bands and the conduction band respectively, are observed in the high energy range. It is also found that the crystal field splitting parameter (Δcf) of MnIn2Se4 is of about 0.15eV nearly independent of the temperature. At energies around 2.2eVa photoluminescence band related to internal transitions between d-excited levels of Mn+2 ion to its 6A1 ground state is also observed in spectra.

Electrical characterization of hydrogenated amorphous silicon oxide films

The electrical characterization of hydrogenated amorphous silicon oxide (a-SiOx:H) films was performed by electron spin resonance (ESR) and electrical conductivity measurements. In the ESR spectra of the a-SiOx:H films, two ESR peaks with g-values of 2.005 and 2.013 were observed. The ESR peak with the g-value of 2.013 was not observed in the ESR spectra of a-Si:H films. The photoconductivity of the a-SiOx:H films decreased with increasing spin density estimated from the ESR peak with the g-value of 2.005. On the other hand, photoconductivity was independent of spin density estimated from the ESR peak with the g-value of 2.013. The optical absorption coefficient spectra of the a-SiOx:H films were also measured. The spin density estimated from the ESR peak with the g-value of 2.005 increased proportionally with increasing optical absorption owing to the gap-state defect.