PIE: Perpendicular-incidence ellipsometry—application to the determination of the optical properties of uniaxial and biaxial absorbing crystals

Perpendicular-incidence ellipsometry (to be given the acronym PIE) is simpler than oblique-incidence conventional or generalized ellipsometry as a tool for the characterization of optically anisotropic surfaces. To illustrate the potential usefulness and simplicity of PIE, we present an example of its application to the determination of the optical properties of uniaxially and biaxially anisotropic crystals.     

椭偏与光度法联用精确测定吸收薄膜的光学常数与厚度

介绍了一种同时利用椭偏仪和分光光度计精确测量薄膜光学常数的方法, 并详细比较了该方法与使用单一椭偏仪拟合结果的可靠性.采用可变入射角光谱型椭偏仪（VASE）表征了250—1700 nm波段辉光放电法沉积的类金刚石薄膜,研究发现当仅用椭偏参数拟合时,由于厚度与折射率、消光系数的强烈相关性,无法得到吸收薄膜光学常数的准确解.如果加入分光光度计测得的透射率同时拟合,得到的结果具有很好的惟一性.该方法无需设定色散模型即可快速拟合出理想的结果,特别适合于确定透明衬底上较薄吸收膜的光学常数. 关键词： 光学常数 光谱型椭偏仪 吸收薄膜 透射率     

椭偏与光度法联用精确测定吸收薄膜的光学常数与厚度

介绍了一种同时利用椭偏仪和分光光度计精确测量薄膜光学常数的方法, 并详细比较了该方法与使用单一椭偏仪拟合结果的可靠性.采用可变入射角光谱型椭偏仪（VASE）表征了250—1700 nm波段辉光放电法沉积的类金刚石薄膜,研究发现当仅用椭偏参数拟合时,由于厚度与折射率、消光系数的强烈相关性,无法得到吸收薄膜光学常数的准确解.如果加入分光光度计测得的透射率同时拟合,得到的结果具有很好的惟一性.该方法无需设定色散模型即可快速拟合出理想的结果,特别适合于确定透明衬底上较薄吸收膜的光学常数.     

椭偏精确测定透明衬底上吸收薄膜的厚度及光学常数

椭偏仪难以精确测量透明衬底上吸收薄膜光学常数的原因:1)衬底的背面反射光为非相干光, 它的存在会极大的增加拟合难度; 2)衬底光学常数(折射率和消光系数)的差异会影响测量的准确性, 而且会在吸收薄膜的光学常数中表现出来, 需要单独测量其光学常数; 3)厚度与光学常数之间呈现强烈的关联性. 针对以上三个问题, 选择石英玻璃、载玻片、盖玻片和普通浮法玻璃作为研究对象. 采用折射率匹配法消除上述衬底背面反射光的影响. 结果显示, 折射率匹配法能够有效消除折射率在1.43-1.64、波长范围为190-1700 nm波段的石英、浮法玻璃等透明衬底的背面反射光. 之后, 通过拟合椭偏参数ψ和垂直入射时的透过率T₀ 分别得到以上衬底的折射率和消光系数. 拟合得到的结果与文献报道的趋势一致. 最后, 采用椭偏参数和透过率同时拟合的方法(SE+T法)得到类金刚石薄膜(沉积在石英玻璃上)和非晶硅薄膜(沉积在载玻片、盖玻片上)光学常数和厚度的准确解.     

Generalized ellipsometric method for the determination of all the optical constants of the system: Optically absorbing film on an absorbing substrate

A numerical method has been developed to evaluate all the optical parameters of the system of an optically absorbing film on an absorbing substrate using ellipsometric measurements. The generality and validity of the algorithm has been investigated for different ideal cases. In addition the effects of the actual limited precision of ellipsometric measurements as well as the problem of multiple solutions have been studied.     

Immersion transmission ellipsometry (ITE) for the determination of orientation gradients in photoalignment layers

The capability of the method of immersion transmission ellipsometry (ITE) (Jung et al. Int Patent WO, 2004/109260) to not only determine three-dimensional refractive indices in anisotropic thin films (which was already possible in the past), but even their gradients along the z-direction (perpendicular to the film plane) is investigated in this paper. It is shown that the determination of orientation gradients in deep-sub-μm films becomes possible by applying ITE in combination with reflection ellipsometry. The technique is supplemented by atomic force microscopy for measuring the film thickness. For a photo-oriented thin film, no gradient was found, as expected. For a photo-oriented film, which was subsequently annealed in a nematic liquid crystalline phase, an order was found similar to the one applied in vertically aligned nematic displays, with a tilt angle varying along the z-direction. For fresh films, gradients were only detected for the refractive index perpendicular to the film plane, as expected.     

Soft-template synthesis and optical Properties of Sb2S3 semiconductor quasi-nanospheres

The reverse micelle system composed of four phases of Hexamethylene/Triton-100/n-pentanol/water (containing 1 ml 0.1 M Sb³⁺ or 1 ml 0.1 M S²⁻), which ratio is 28:3:1:1, is prepared. Sb₂S₃ quasi-nanospheres with diameters between 160 and 240 nm are synthesized by above reverse micelle soft-template system. The result shows that the fluorescence peaks have a blue shift about 19 nm when it is excited at 219 nm, and the UV–Vis absorption peaks shift about 453 nm (2.74 eV).     

Measurement of the optical functions of uniaxial materials by two-modulator generalized ellipsometry: rutile (TiO(2))

Two-modulator generalized ellipsometry is applied to determination of the optical functions of uniaxial rutile. For a nondepolarizing sample the two-modulator generalized ellipsometer determines all the elements of the normalized Jones matrix with one measurement and thereby totally characterizes light reflecting from the sample. If a uniaxial crystal is appropriately aligned, then determining its optical functions requires only a single measurement. We have used this new instrument to obtain optical functions of rutile that are the most accurate available for optical energies above the band edge.     

Ellipsometric determination of the optical constants of glassy As2S3 thin films in the weak absorption region

The optical constants (the complex refractive index tensor and the geometrical thickness) of thin freshly prepared unannealed films from glassy chalcogenide As-S semiconductors with the stoichiometric formula As₂S₃ are calculated in the weak absorption region (λ = 0.6328 μm) based on multiangle ellipsometric measurements and taking into account the birefringence of optical waves in such films. The advantage of the approximation of an anisotropic uniaxial film is shown, the values of the ordinary and extraordinary refractive indices are determined, and the difference between them is found to be ∼5 × 10⁻³. Original Russian Text ? M.I. Kozak, V.N. Zhikharev, I.P. Studenyak, I.D. Seĭkovskĭ, 2006, published in Optika i Spektroskopiya, 2006, Vol. 101, No. 4, pp. 602–604.     

Polarized spectral analysis of Er3+ ions in biaxial Bi2(MoO4)3 crystal

An Er³⁺:Bi₂(MoO₄)₃ single crystal has been grown by the Czochralski technique. The Stark sublevels of the ⁴I_15/2 and ⁴I_13/2 multiplets of Er³⁺ ions in the crystal were determined. The polarized absorption spectra, polarized fluorescence spectra, and fluorescence decay curve of the crystal were measured at room temperature and the relevant spectroscopic parameters, including the Judd–Ofelt intensity parameters, spontaneous emission probability, fluorescence branching ratio, radiative lifetime, and stimulated emission cross section, were estimated. The effect of re-absorption on the spectroscopic parameters was discussed. When the crystal was excited at 977 nm, up-conversion green fluorescence was observed and discussed.     

Pyroelectric properties of a ferroelectric single crystal [NH2(CH3)2]3Sb2Cl9 (DMACA)

The pyroelectric properties of DMACA single crystals have been measured in the range 135–293 K, revealing the existence of ferroelectric second order phase transition at T_c = 243 K. The saturation value of spontaneous polarization P_s along a-axis amounts to 6.8 × 10⁻³ Cm⁻² at about 203 K. Critical exponent β = 0.5 has been found in the region 0.5–10 K away from T_c.     

Determination and analysis of the optical constants of thin films of nickel(II) and copper(II) hydrazone complexes by spectroscopic ellipsometry

Thin films of four nickel(II) and copper(II) hydrazone complexes, which will hopefully be used as recording layers for the next-generation of high-density recordable disks, were prepared by using the spin-coating method. Absorption spectra of the thin films on K9 optical glass substrates in the 300–700 nm wavelength region were measured. Optical constants (complex refractive indices N) and thickness d of the thin films prepared on single-crystal silicon substrates in the 275–675 nm wavelength region were investigated on a rotating analyzer-polarizer scanning ellipsometer by fitting the measured ellipsometric angles (Ψ(λ) and Δ(λ)) with a 3-layer model (Si/dye film/air). The dielectric functions ε and absorption coefficients α as a function of the wavelength were then calculated. Additionally, a design to achieve high reflectivity and optimum dye film thickness with an appropriate reflective layer was performed with the Film Wizard software using a multilayered model (PC substrate/reflective layer/dye film/air) at 405 nm wavelength. PACS 81.05.L; 78.20.Ci; 78.20.-e     

Magnetic Properties of Sb2S3 and Bi2S3 as Evidenced by 121,123Sb and 209Bi NQR Spectra

Journal of Experimental and Theoretical Physics -     

c(2 x 2)CO ON Ni(100): Photoemission orientation determination

Angular resolved photoemission studies of c(2 x 2)CO adsorbed on Ni(100) show that the molecule is bound to the surface with the molecular axis normal to the surface. The uncertainty of this determination is approximately 15°, which is consistent with the expected angular broadening due to vibrational modes. This is in distinct contrast to a bend of 34° proposed to explain LEED data on this system.     

用光谱和EPR谱确定CsMgBr3:Ni2+的局域结构

本文采用半自洽场(semi-SCF)自由Ni2 的3d轨道波函数、点电荷—偶极子模型和Ni2 -6X-(X=F,Cl,Br,I)络合物的μ-κ-α模型,建立了结构参数与光谱、EPR谱之间的定量关系,利用完全对角化方法,由光谱和电子顺磁共振(EPR)谱,确定了CsMgBr3:Ni2 晶体在77K温度时的局域结构参数,统一解释了CsMgBr3:Ni2 晶体的局域结构、光谱和EPR谱。所得理论结果与实验值符合得很好。此外,还讨论了晶体局域结构发生畸变的原因。     

Structural and optical properties of amorphous Sb2S3 thin films deposited by vacuum thermal evaporation method

Sb₂S₃ thin films have been deposited by vacuum thermal evaporation onto glass substrates at various substrate temperatures in the range of 30–240 °C. Crushed powder of the synthesized Sb₂S₃ was used as raw material for the vacuum thermal evaporation. The structural investigation performed by means of X-ray diffraction (XRD) showed that the all as-deposited films present an amorphous structure and all the films were highly resistive. The reflectance and transmittance of the films are measured in the incident wavelength range 300–1800 nm. The absorption coefficient spectral analysis revealed the existence of long and wide band tails of the localized states in the low absorption region. The band tails width is calculated and found to be varying between 0.024 and 0.032 eV. The analysis of the absorption coefficient in the high absorption region revealed two direct forbidden band gaps between 1.78–1.98 eV and 1.86–2.08 eV.     

Thickness dependence of the forbidden energy gap in stibnite (Sb2S3) thin films

The increase in the energy gap with decreasing film thickness has been observed and studied in case of thin films of stibnite (Sb₂S₃). Such an increase in energy gap, which is inversely proportional to the square of the film thickness, is attributed to quantum effects. The effective mass of electrons has been estimated to be ((0.5±1.0) m₀ from this study.     

Z-scan determination of the third-order optical nonlinearity of L-asparaginium picrate (LASP) crystal

The NLO properties of L-asparaginium picrate (LASP) crystals have been measured. The measurements were performed using a SHG diode-pumped laser at 532-nm wavelengths by employing the Z-scan technique. The nonlinear refractive index is found to be on the order of 10^?8 cm²/W. The magnitude of the third-order susceptibility is on the order of 10^?5 esu.     

Conductivity studies on LiX–Li2S–Sb2S3–P2S5 (X = LiI or Li3PO4) glassy system

New sulfide glasses in the Li₂S–Sb₂S₃–P₂S₅ system have been prepared by classical quenching technique where glassy domain remains up to 50% molar addition of Li₂S and electrical conductivities have been determined by impedance spectroscopy. Room temperature DC conductivity vs Li₂S content exhibits two regions implying different conductivity mechanisms. The compositions of low lithium content presented low electronic conductivities close to 0.01 μS/cm at room temperature (due to Sb₂S₃ semiconducting properties). The compositions of medium lithium content could result to mixed ionic–electronic conductors with predominant ionic conductivity with a maximum close to 1 μS/cm; Arrhenius behavior is found between 25 °C and T _g for all glasses, but activation energy is found to be somehow above most similar systems. A comparative study with glasses belonging to the other chalcogenide systems has been undertaken and values of the decoupling index are reported, and in order to validate conductivity data, a circuit equivalent circuit was proposed and fitted parameters were calculated with good agreement.