Complex Refractive Index Function Research Articles

Combining Infrared Refraction and Attenuated Total Reflection Spectroscopy.

We have specified and obtained a ZnSe prism with an unconventional face angle cut to 30°. This prism, with internal incidence angles ranging from 30° to 48°, allows users to record internal reflection spectra below the critical angle and attenuated total reflection (ATR) spectra above the critical angle without the need to change optics or move or replace the sample. We demonstrate its capabilities using 102 spectra of benzyl benzoate taken with s- and p-polarization at different angles of incidence. The subcritical spectra were analyzed to obtain n∞, a key parameter for correcting the ATR spectra. These corrected spectra were subsequently used to determine the complex refractive index for all ATR measurements. The averaged complex refractive index function shows excellent agreement with that obtained through ATR spectroscopic ellipsometry.

Sophisticated Attenuated Total Reflection Correction Within Seconds for Unpolarized Incident Light at 45°.

The most common mid-infrared (MIR) attenuated total reflection (ATR) accessory has a nominal angle of incidence of 45° and does not have a polarizer. A spectrum recorded with such an accessory does not hold enough information for the sophisticated ATR correction of MIR spectra with strong peaks, which are often strongly affected by refractive index changes due to anomalous dispersion. Here we show that a 45° ATR spectrum recorded without a polarizer and the polarization angle for the same ATR Fourier transform infrared spectroscopy system provide enough information to determine the ATR s-polarized spectrum. Further analysis with an improved non-iterative Kramers-Kronig analysis immediately yields the complex refractive index function. The analysis is about two orders of magnitude faster than iterative formalism and runs within seconds on a typical office PC. The effectiveness of our advanced ATR correction formalism is showcased through its application to water, employing diamond, ZnSe, and Ge ATR crystals, along with two distinct ATR accessories. Additionally, the formalism is applied to octadecane spectra. Potential sources of errors such as incidence angle spread, dispersion of the polarization angle, and the influence of reflection at the air/ATR crystal interface are investigated by simulations.

Deep learning-enabled Inference of 3D molecular absorption distribution of biological cells from IR spectra

Infrared spectroscopy delivers abundant information about the chemical composition, as well as the structural and optical properties of intact samples in a non-destructive manner. We present a deep convolutional neural network which exploits all of this information and solves full-wave inverse scattering problems and thereby obtains the 3D optical, structural and chemical properties from infrared spectroscopic measurements of intact micro-samples. The proposed model encodes scatter-distorted infrared spectra and infers the distribution of the complex refractive index function of concentrically spherical samples, such as many biological cells. The approach delivers simultaneously the molecular absorption, sample morphology and effective refractive index in both the cell wall and interior from a single measured spectrum. The model is trained on simulated scatter-distorted spectra, where absorption in the distinct layers is simulated and the scatter-distorted spectra are estimated by analytic solutions of Maxwell’s equations for samples of different sizes. This allows for essentially real-time deep learning-enabled infrared diffraction micro-tomography, for a large subset of biological cells.

First-Principles Study on the Magnetoelectric and Optical Properties of Novel Magnetic Semiconductor Li(Mg, Cr)P With Decoupled Spin and Charge Doping.

The electronic structures, magnetic and optical properties of Li1±y(Mg1−xCrx) P (x, y = 0.125) are calculated by using the first principles method based on density functional theory. We find that the incorporation of Cr causes the strong hybridization between Li-2s, P-2p, and Cr-3d orbitals, resulting in a spin-polarized impurity band and forming stronger Cr-P polar covalent bonds. Li(Mg0.875Cr0.125)P becomes half-metallic ferromagnetism. The properties of the doped systems can be regulated by Li off-stoichiometry. When Li is deficient, the narrower impurity band and stronger p-d orbital hybridization enhance the half-metallicity. While the half-metallicity disappears, the band gap becomes wider, and the conductivity decreases for Li excess system, but its magnetic moments increase. Comparing optical properties show that the imaginary part of dielectric and complex refractive index function and optical absorption spectrum all have a new peak in the low energy region after Cr doping, and the new peaks are significantly enhanced when Li is deficient. The absorption range of low frequency electromagnetic wave is enlarged, and the energy loss functions show obvious red-shift effect for the doped systems. The results indicate that the properties of Li(Mg,Cr)P can be controlled by Cr doping and Li off-stoichiometry independently, which will benefit potential spintronics applications.

Electronic structures and optical properties of Mn-doped LiCaN new diluted magnetic semiconductors

Using the first-principle density functional theory based on the full potential linearized augmented plane wave method, the geometric structures of new diluted magnetic semiconductor Li1± y (Ca1− x Mn x )N ( x =0, 0.125; y =0, 0.125) were optimized. The electronic structures and optical properties were calculated and discussed in detail. The results show that the magnetic and electrical properties of the doped system can be separately regulated by Mn doping and Li off-stoichiometry. When Mn doped in the system, the electrons of the Mn 3d split into triply degenerate t 2g and double degenerate e g energy levels. Meanwhile, the Mn 3d states hybridize with Ca 4s and N 2p states, leads to the systems display half-metallic ferromagnetism. In Li excess and insufficient compounds, the band gaps and magnetic moments decrease, while the Curie temperature and electrical conductivity increase, and they exhibit 100% spin injection. In addition, the half-metallicity of Li insufficient system enhances significantly. In Li excess compound, Jahn-Teller effect leads to the highest Curie temperature and the lowest formation energy. Comparing optical properties indicates that the imaginary part of dielectric function, complex refractive index function, optical absorption function and the imaginary part of photoconductivity are all affected by Li stoichiometry. The energy loss functions of the doped systems show obvious blue-shift effect and much stronger plasma resonant frequency, and the oscillating range of plasma is wider in Li excess and insufficient compounds.

Photoelectric properties of Ag and Cr co-doped LiZnP new diluted magnetic semiconductors

Spintronic devices utilize the electron charge and spin degree of freedom to achieve novel quantum functionalities. Diluted magnetic semiconductors (DMS) constitute an important category of spintronic materials that have the potential to be successfully incorporated into the existing semiconductor industry. The prototypical DMS (Ga,Mn) As, discovered in the 1990s, accomplishes spin and charge doping simultaneously through the heterovalent substitution of the magnetic ion Mn2+ for Ga3+. Two challenges have presented themselves in this material. First, the heterovalent nature of this integrated spin/charge doping results in severely limited chemical solubility in (Ga,Mn) As, restricting specimen fabrication to metastable thin films by molecular beam epitaxy; second, the simultaneous spin and charge doping precludes the possibility of individually tuning the spin and charge degree of freedom. A new type of ferromagnetic DMS based on I-Ⅱ-V group can overcome both of these challenges. Li(Zn,Mn) As utilizes excess Li concentration to introduce hole carriers, while independently making the isovalent substitution of Mn2+ for Zn2+ in order to achieve local spin doping. With no heterovalent substitution to restrict chemical solubility, bulk samples of Li(Zn,Mn) As are successfully fabricated. However, one drawback of Li(Zn,Mn) As is its use of the toxic element As. The isostructural direct-gap semiconductor LiZnP also undergoes a ferromagnetic transition upon Mn doping, and its bulk magnetic properties are very similar to those of LiZnAs. In this paper, the geometric structure of pure LiZnP, Ag doped, Cr doped, and Ag-Cr co-doped LiZnP new diluted magnetic semiconductor are optimized by using the first-principles plane wave ultra-soft pseudo-potential technology based on the density function theory. Then we calculate the electronic structure, magnetism, formation energy, differential charge density, and optical properties of the doped systems. The results show that the material is a paramagnetic metal after single doping of the nonmagnetic element Ag. When magnetic element Cr is doped with LiZnP, sp-d orbital hybridization makes the peak of density of state nearly EF-split, leading the system to become metallic ferromagnetism. However, Ag-Cr co-doped LiZnP changes into half-metallic ferromagnetism, which is completely different from the single doping system. The band gap decreases slightly, and the electrical conductivity is enhanced. Meanwhile, the formation energy of the system becomes lower, the bond between atoms strengthens, and the stability of the unit cell becomes stronger. A comparison of the optical properties indicate that the imaginary part of dielectric function and the optical absorption spectrum both present new peaks in low energy region in the doped systems. Ag-Cr co-doped LiZnP has the highest dielectric peak. Meanwhile, the complex refractive index function changes obviously in a low energy region, and the absorption edge extends to the low energy direction. The system enhances the absorption of low-frequency electromagnetic waves.

Photoelectric properties of Mn-doped LiMgP new diluted magnetic semiconductor

We optimized the geometry structures of Li1± y (Mg1− x Mn x )P for ( x =0.125; y =0, 0.125) by adopting the first-principles calculation of plane wave ultra-soft pseudo-potential technology based upon the density function theory (DFT). Then we calculated the electronic structures, formation energies, electric density difference and optical properties. The results reveal that spin polarization impurity bands were produced in Mn doped system. The properties of system and the orbits of participate in hybridization could be changed by dominating the amount of Li. The Mn doped system still revealed semiconductor properties, and the width of impurity band is 0.461 eV, and the magnetic moment is 4.98 μ в. The Li overdose system revealed metallicity, and the width of impurity bands increased to 0.890 eV, and the magnetic moment decreased to 4.10 μ в. Meanwhile the total energies and the formation energies reduced, the conductive capability increased. The Li deficient system revealed half metallicity, and the half-metallic band gap is 0.478 eV, and the magnetic moment is 4.02 μ в. Most of the charge overlap populations of LiMgP system are positive. It means all the chemical bonds of LiMgP are covalent bonds. Magnetism element Mn doped into the system creates Mn-P covalent bonds that are stronger than Mg-P bonds. In the Mn doped system, the quantity of share electron increased and the deviation of share electron decreased. The charge overlap population of Li-P bond is −0.02 which reveals ionic bonds. In the Li overdose system, the charge overlap population of Mn-P bonds reach the minimum value of 0.52. The density of states of Mn3 d and P3 p at the Fermi level is larger than that of single doped Mn, but at the same time, the interaction of the Mn-P bonds is weakened due to the participation of Li2 s in orbital hybridization. Formation energy and total energy become lower. And in the Li deficient system, the charge overlap population of Mn-P bonds reached the maximum value of 0.69, and the bonds lengths reached the minimum value. The electron cloud of Mn atoms and P atoms is the densest, and the deviation of the share electron is the weakest. The results reveal that p-d hybridization happened in Mn3 d and P3 p , and the hybridization was the strongest. The deficiency of the electron cloud of P atoms of charge density difference was caused by the deficiency of Li atoms. Analyzing images of optical properties can find that the imaginary part of dielectric function and the optical spectroscopy appeared a new peak at low energy region in Mn doped system. And the complex refractive index functions have a significant change at the same time. It means the system has an augment optical absorption range, and energy loss get lower.

新型稀磁半导体Cu掺杂LiMgN的电子结构和光学性质

Using first-principles density functional theory based on the full potential linearized augmented plane wave method and the local spin density approximation (LSDA), the geometric structures of pure LiMgN, Cu-doped LiMgN, and Cu-doped LiMgN with either excess Li or Li deficiency are optimized, and their electronic structures, half-metallic properties, formation energies and optical properties are calculated. The results indicate that Cu doping makes the Cu3d states hybridize with the Li2s and N2p states simultaneously, and this leads to sp-d orbital hybridization. The resulting system produces spin polarization impurity bands, displays half-metallic behavior and has a net magnetic moment. Li(Mg 0.9375 Cu 0.0625 )N is still a direct band gap semiconductor like LiMgN. The bottom of its conduction band and the top of its valance band are both at the G point in the Brillouin zone. The band gap of the material is 2.41 eV, which is slightly narrower than the value of 2.47 eV for LiMgN. There are a total of six impurity bands in the band gap. Three of these bands are in the spin-up band, and the other three are in the spin-down band. In the spin-down band, the Fermi level goes through the impurity bands, and thus the material shows half-metallic properties. The half-metallic energy gap is 0.09 eV. The strong sp-d orbital hybridization causes the energy level to split, and the t2g energy level of the Cu3d state electrons in the spin-down band is pushed above the Fermi level, which leads to half-filled states. The number of spin-up electrons is slightly more than that of the spin-down electrons, and the Li(Mg 0.9375 Cu 0.0625 )N system has a 1.04 μ в net magnetic moment. The properties of the Li-deficient or Li-excess systems are affected by the stoichiometric number of Li in each case. In the Li-deficient compounds, the Li vacancies strengthen the sp-d orbital hybridization, and make the impurity band width, the half-metallic properties, the net magnetic moment, and the Curie temperature increase, while the formation energy decreases from 2.23 to 1.50 eV. In contrast, the half-metallic behavior of the Li-excess Cu-doped LiMgN vanishes, and the system becomes an indirect band gap semiconductor, although its band gap narrows to 2.13 eV, and its conductive properties become stronger. These results show that the LiMgN semiconductor is a realistic candidate diluted magnetic semiconductor material with decoupled charge and spin doping, in which the charge and the spin can be injected separately via Li off-stoichiometry and Cu isovalent doping. The calculated dielectric function indicates that these Cu-doped systems have a new dielectric peak in the low-energy region. The Li deficiency enhances both the dielectric peak and the absorption of low-frequency electromagnetic waves, while there is an obvious change in the complex refractive index function.

First-priciples study on Mn-doped LiZnAs, a new diluted magnetic semiconductor

The electronic structures, half-metallic and optical properties, as well as formation energy of pure LiZnAs, Mn-doped LiZnAs and Mn-doped LiZnAs with excess and deficient of Li are geometrically optimized and calculated by using the first principle density functional theory based on the full potential linearized augumented plane wave method. Results show that in the systems of Li(Zn0.875Mn0.125)As, Li1.1(Zn0.875Mn0.125) As and Li0.9(Zn0.875Mn0.125)As a 100% spin injectors is revealed, and the materials exhibit half metallic. The half metallic materials with excess and deficient of Li are more stable than Mn-doped LiZnAs. Excess of Li could improve the Curie temperature and conductivity of the material, and cause the formation energy of the system decrease. So the separation of spin and charge injection mechanisms may be achieved in LiZnAs semiconductor, and the magnetic and electrical properties of diluted magnetic semiconductor may be regulated respectively by Mn doping and Li stoichiometry. In addition, the dielectric function and the complex refractive index function in the low-energy region are found to be influenced by the stoichiometry of Li.

Doped with Ag and Zn effects on electronic structure and optical properties of CdS

The geometry structure, electronic structure and optical properties of zinc bende CdS:M (M = Ag,Zn) were studied systemically using density functional theory based on first-principles ultrasoft pseudopotential method and GGA.The relationship between the distribution of the electronic states and their structures has been analyzed. The dielectric function and the complex refractive index function on doping CdS system have been obtained. The calculation results showed that the hole concentration of Ag-doped CdS is increased, enhanced the conductivity of the material. But the carrier concentration of Al-doped CdS was not changed; the optical band gap were narrowed for Ag-doping, Zn-doping CdS. The mechanism of luminescence has been explained in terms of an analysis of the dielectric function and the complex refractive index function.

Size dependence of complex refractive index function of growing nanoparticles

The evidence of the change of the complex refractive index function E(m) of carbon and iron nanoparticles as a function of their size was found from two-color time-resolved laser-induced incandescence (TiRe-LII) measurements. Growing carbon particles were observed from acetylene pyrolysis behind a shock wave and iron particles were synthesized by pulse Kr–F excimer laser photo-dissociation of Fe(CO)5. The magnitudes of refractive index function were found through the fitting of two independently measured values of particle heat up temperature, determined by two-color pyrometry and from the known energy of the laser pulse and the E(m) variation. Small carbon particles of about 1–14 nm in diameter had a low value of E(m)∼0.05–0.07, which tends to increase up to a value of 0.2–0.25 during particle growth up to 20 nm. Similar behavior for iron particles resulted in E(m) rise from ∼0.1 for particles 1–3 nm in diameter up to ∼0.2 for particles >12 nm in diameter.

First-principles study on electronic structure and optical properties of Al and Mg doped GaN

The electronic structure and optical properties of pure and Al_and Mg-doped cubic-blende GaN have been studied based on the density functional theory and the generalized gradient approximation method. The relationship between the distribution of the electronic states and their structures has been analyzed.The dielectric function and the complex refractive index function on the doping GaN system have been obtained. The calculation results indicate that the hole concentration of Mg-doped GaN is increased and the Mg-doping markedly enhanced the conductivity of the material.But the carrier concentration of Al-doped GaN is not changed and optical bandgap is broadened.The mechanism of luminescence has been explained in terms of an analysis of the dielectric function and the complex refractive index function. It offers theoretical data for the design and application of GaN optoelectronic materials. By comparison, our results are in good agreement with that published in the literatures.

Tropospheric aerosol optical properties derived from lidar, sun photometer, and optical particle counter measurements

Tropospheric aerosols have been observed for the period from November 1990 to April 1992 with a lidar, a sun photometer, and an optical particle counter. Variations of aerosol optical thickness derived from the lidar and the sun photometer data and measurements are presented. The simultaneous measurements of these instruments also allowed us to estimate the extinction-to-backscatter ratio (S(1)), which ranged from 20 to 70. Comparison of optical thicknesses derived from both instruments clearly shows the effect of Mt. Pinatubo's eruption and the temporal variation of optical thickness in the stratosphere over 12 km. The possible range of the complex refractive index for the columnar mean aerosols can be deduced from the probable range of S(1) derived by the use of an S(1) diagram as a function of complex refractive index (m). The imaginary part of m can be estimated provided that the real part of m is known.