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Optical and Magneto-Optical Properties of Multilayer Nanosized [Co/TiO2]n Films
摘要： The optical and magneto-optical properties of the metal–dielectric multilayer [Co/TiO2]n structures with 2–4-nm-thick layers prepared on a silicon substrate Si(001) by ion-beam deposition have been studied. The complex permittivity of multilayer [Co/TiO2]n structures has been measured by the optical ellipsometry technique in the spectral range of 0.6–5.6 eV and analyzed using the optical reflection matrices for isotropic multilayer dielectric structures taking into account the optical losses and also using the method of anisotropic effective medium. The magneto-optical Kerr effect has been measured by the polarimetric technique in the spectral range of 1.2–4.5 eV in the polar and longitudinal geometries. The magnetic anisotropy type is determined on the base of the field dependences of the magneto-optical Kerr effect. It is found that the nanosized [Co/TiO2]n structures can be considered as artificial optically uniaxial media with a strong magnetic and optical anisotropy at room temperature.
关键词： silicon substrate,Co/TiO2,magneto-optical properties,multilayer nanosized films,optical properties,complex permittivity,magneto-optical Kerr effect,magnetic anisotropy,optical ellipsometry,ion-beam deposition
更新于2025-09-10 09:29:36
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(TiO <sub/>2</sub> ) <sub/>1?x</sub> (TaON) <sub/>x</sub> Solid Solution for Band Engineering of Anatase TiO <sub/>2</sub>
摘要： Band engineering of anatase TiO2 was achieved by means of an anatase (TiO2)1?x(TaON)x (TTON) solid solution. Epitaxial thin films of TTON (0.1 ≤ x ≤ 0.9) were synthesized by nitrogen plasma-assisted pulsed laser deposition on (LaAlO3)0.3(SrAl0.5Ta0.5O3)0.7 substrates. Epitaxial growth of anatase TTON was confirmed by X-ray diffraction. The lattice constants of the TTON thin films increased with TaON content in accordance with Vegard’s law, indicating formation of a complete solid solution. The bandgaps, band alignment, and refractive indices of the TTON thin films were investigated by combination of spectroscopic ellipsometry and X-ray photoelectron spectroscopy. The bandgap of the anatase TTON systematically decreased with increasing x, mainly because of an upward shift in the valence band maximum caused by broadening of the valence band as a result of hybridization of the shallow N 2p orbital. The position of the conduction band minimum was rather insensitive to chemical composition, which makes the band alignment of anatase TTON suitable for photocatalytic water splitting with visible light. The refractive index of anatase TTON monotonically increased with an increase in x.
关键词： Epitaxial thin films,Vegard’s law,X-ray photoelectron spectroscopy,TTON solid solution,Band engineering,Photocatalytic water splitting,Spectroscopic ellipsometry,Nitrogen plasma-assisted pulsed laser deposition,Anatase TiO2
更新于2025-09-10 09:29:36
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Thermal Atomic Layer Etching of Silicon Using O2, HF and Al(CH3)3 as the Reactants
摘要： The thermal atomic layer etching (ALE) of silicon was performed using O2, HF and Al(CH3)3 as the reactants at temperatures from 225-290°C. This thermal etching process is based on Si oxidation using O2 and conversion of SiO2 to Al2O3 using trimethylaluminum (TMA). Al2O3 is then fluorinated by HF to produce AlF3 prior to removal of AlF3 by a ligand-exchange reaction with TMA. Thermal Si ALE was studied using silicon-on-insulator (SOI) wafers. In situ spectroscopic ellipsometry was employed to monitor simultaneously both the thickness of the top SiO2 layer and the underlying silicon film during Si ALE. These studies observed that the silicon film thickness decreased linearly with the number of reaction cycles while the thickness of the SiO2 layer remained constant. Using an O2-HF-TMA exposure sequence, the Si ALE etch rate was 0.4 ?/cycle at 290°C. This etch rate was obtained using static reactant pressures of 250, 1.0 and 1.0 Torr, and exposure times of 10, 5 and 5 s, for O2, HF and TMA, respectively. The SiO2 thickness was 10-11 ? under these reaction conditions at 290°C. The Si ALE etch rate increased with O2 and TMA pressure before reaching a limiting etch rate at higher O2 and TMA pressures. The order of the reactants affected the Si etch rate. Changing the exposure sequence from O2-HF-TMA to O2-TMA-HF reduced the etch rate from 0.4 to 0.2 ?/cycle at 290°C. Lowering the etch temperature below 290oC also resulted in the reduction of the Si etch rate. Atomic force microscopy (AFM) measurements determined that the root-mean-squared (RMS) roughness of the surface was 2.0 ± 0.2 ? before and after the Si ALE using the optimum reaction conditions. Lowering the static O2 pressures below 250 Torr reduced the etch rate and also increased the RMS surface roughness. There was no evidence for any change in the Si ALE process for ultrathin Si films with thicknesses <100 ? in the quantum confinement regime. Thermal Si ALE should be useful for silicon applications in many areas including electronics, optoelectronics, thermoelectrics and photonics.
关键词： silicon,HF,thermal atomic layer etching,spectroscopic ellipsometry,Al(CH3)3,O2,atomic force microscopy
更新于2025-09-10 09:29:36
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Effect of deposition rate on the growth mechanism of microcrystalline silicon thin films using very high frequency PECVD
摘要： The intrinsic microcrystalline silicon thin films were deposited by very high frequency plasma enhanced chemical vapor deposition (VHF-PECVD). Two series of films with different deposition rate 0.30 nm/s and 1.94 nm/s were prepared. The film surface and gas phase reaction growth processes were monitored with real-time spectroscopic ellipsometry and optical emission spectroscopy. The effect of deposition rate on the microcrystalline silicon thin film growth mechanism has been studied. The microcrystalline silicon surface growth was analyzed with KPZ model. The results show that the growth exponent of β is 0.448 for the films with low deposition rate, and the growth exponent of β is 0.302 for the films with high deposition rate. The growth exponent does not increase with deposition rate, but declines. And the reasons for this phenomenon were explained.
关键词： Real time spectroscopic ellipsometry,Microcrystalline silicon,High rate deposition,Optical emission spectrum,Growth mechanism
更新于2025-09-09 09:28:46
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Investigation of optical and dielectric properties of CsPbI3 inorganic lead iodide perovskite thin film
摘要： This experimental work reports refractive index, extinction coe?cients, and dielectric functions at different incident angles in visible range for the ?rst time. The refractive index of CsPbI 3 thin ?lm is 2.46 at 435 nm with this result implies that Cs based lead halide solar cells may be, ideal antire?ection coating for many tandem solar cells. Thus lower refractive index of CsPbI 3 inorganic perovskite material is bene?cial for perovskite device fabrications because of the minimum light looses to re?ection at the front of the active layer. Furthermore microstructure of the cubic phase Pm-3 m was investigated by X-ray di?raction. CsPbI 3 perovskite thin ?lm showed the sharp absorption edge and PL emission near infrared region with direct band gap of 1.67 eV with high color purity of red emission. In addition, the higher dielectric function value of CsPbI 3 , will helps to many optoelectronic devices.
关键词： Ellipsometry,Dielectric function,Inorganic perovskite,Refractive index
更新于2025-09-09 09:28:46
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Ellipsometry - Principles and Techniques for Materials Characterization || Achromatic Ellipsometry: Theory and Applications
摘要： In the present chapter, the theory and some applications of Achromatic Ellipsometry, including transmittance, absorbance, and emission, are presented. The new methodology introduced here comprises the calculation of Stokes parameters using Fourier series analysis. Light polarization was determined by calculating the polarization degree, anisotropy, asymmetry parameters, and rotational and ellipsometry angles. The nematic liquid crystal E7? doped with 4,7-bis{2-[4-(4-decylpiperazin-1-yl)phenyl]ethynyl}-[2,1,3]-benzothiadiazole (5A) within twisted and parallel structures, was used to illustrate the applications for this technique, that has been shown to be an innovative and versatile tool to correlate the photophysics with materials structure.
关键词： ellipsometry,Stokes parameters,optical spectroscopy
更新于2025-09-09 09:28:46
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Ellipsometry - Principles and Techniques for Materials Characterization || Spectroscopic Ellipsometry Study of Organic-Inorganic Halide: FAPbIxBr3?x Perovskite Thin Films by Two-Step Method
摘要： Spectroscopic ellipsometry (SE) was used to investigate the role of isopropyl alcohol (IPA) solvent in the synthesis of organic-lead-halide perovskite CH(NH2)2PbIxBr3?x [FAPbIxBr3?x] thin films including the effect of I/Br composition ratio by the two-step reaction of an amorphous (a-)PbIxBr2?x layer and FAIxBr1?x solution diluted in IPA. An optical dispersion model was developed to extract the complex refractive index N (=n + ik), optical transition, and film thickness of FAPbIxBr3?x perovskites by SE analysis at different I/Br composition ratio as a function of immersion time in a solution of FAIxBr1?x diluted in IPA. SE combined with X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM) revealed that Br incorporation into films promoted the densification of FAPbIxBr3?x perovskite network along with increased film thickness and volume fraction of void. IPA promoted film crystallization of a-PbIxBr2?x accompanied by the formation of surface roughness, grain boundaries, and voids, followed by enhanced diffusion of FAIxBr1?x into the grain boundaries/voids in the mesoporous crystallized PbIxBr2?x network. These processes contribute synergistically to the growth of the perovskite structure.
关键词： growth mechanism,two-step reaction,ellipsometry,role of isopropyl alcohol (IPA) solvent,organic-lead-halide perovskite
更新于2025-09-09 09:28:46
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Structural, optical and electrical properties of reactively sputtered CrxNy films: Nitrogen influence on the phase formation
摘要： The properties of various CrxNy films grown by direct current (DC) reactive sputtering process with different values of nitrogen partial pressures (0, 2×10-4, 3.5×10-4 and 5×10-4 mbar) were studied. The structural analysis of the samples was performed by using X-ray diffraction and transmission electron microscopy (TEM), while an elemental analysis was realized by means of Rutherford backscattering spectrometry. By varying nitrogen partial pressure the pure Cr layer, mixture of Cr, Cr2N and CrN phases, or single-phase CrN was produced. TEM analysis showed that at pN2 = 2×10-4 mbar the layer has dense microstructure. On the other hand, the layer deposited at the highest nitrogen partial pressure exhibits pronounced columnar structure. The optical properties of CrxNy films were evaluated from spectroscopic ellipsometry data by the Drude or combined Drude and Tauc-Lorentz model. It was found that both refractive index and extinction coefficient are strongly dependent on the dominant phase formation (Cr, Cr2N, CrN) during the deposition process. Finally, the electrical studies indicated the metallic character of Cr2N phase and semiconducting behaviour of CrN.
关键词： spectroscopic ellipsometry,thin films,chromium nitrides,electrical properties,microstructure
更新于2025-09-09 09:28:46
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ion bombardment effect on the band gap of anatase TiO2 ultrathin films
摘要： We report a study of the effect of nitrogen ion bombardment on the optical properties of anatase TiO2 ultrathin films, particularly the band gap energy. The TiO2 films were prepared by a sol-gel method and dip-coating process. The as-prepared TiO2 films were then exposed to a +N2 low-energy ion beam from a microwave electron cyclotron resonance (ESR) ion source. Raman and spectroscopic ellipsometry (SE) analysis were performed on TiO2 films prepared at different +N2 exposure times. The Raman measurements reveal the conservation of the anatase TiO2 crystalline structure after the ion beam exposure. From a detailed ellipsometric study, the thickness of layers, the dielectric function, the band gap and the Urbach energies were determined. The obtained results show an increase of the TiO2 band gap with the decrease of thickness of films during +N2 exposure time. The band gap energy was blue shifted from 20 meV to 140 meV as the exposure time was increased from 5 min to 20 min when the thickness was decreased from 30 nm to 21 nm. This increasing of band gap energy could be explained by the thickness effect. From the band tail, the Urbach energy was also affected by +N2 ion beam. These results are in good agreement with the observed broadending of the Raman band the OeTieO bending vibration mode, as the exposure time increases.
关键词： +N2 ion bombardment,TiO2,Urbach energy,Band gap energy,Raman,Ellipsometry
更新于2025-09-09 09:28:46
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Dynamic SIMS, spectroscopic ellipsometry and x-ray diffractometry analysis of SiGe HBTs with Ge grading
摘要： In this paper, SiGe heterojunction bipolar transistors (HBTs) with Ge concentrations up to 40 atomic percent (at%) and different slopes of Ge gradients are characterized by comparing dynamic secondary ion mass spectrometry (D-SIMS) and multi-angle spectroscopic ellipsometry (SE). X-ray diffractometry (XRD) was used as reference. D-SIMS results show that sputter rate and Ge content calibration have major impact on depth pro?le measurements of HBTs with graded SiGe. Strained and relaxed SiGe show differences in Ge content calibration and no difference in sputter rate calibration. Jiang’s protocol was used for Ge content calibration and proven to be valid up to ～50 at% Ge. SE with a combination of 3 angles of incidence (AOIs) (59, 65, 71°) in comparison with the single AOI (71°) realized in industrial setup for semiconductor manufacturing environment was analyzed to ?nd a more stable solution for revealing the thickness of plateau and gradient parts of SiGe base. SE with 71° AOI and rotating compensator is the best choice for in-line HBT with Ge grading characterization. The determination of gradient shape continues to be a challenging task for SE, due to high parameter correlations and the need to use some ?xed parameters within the ?tting procedure. D-SIMS remains the favorite for graded pro?le determination. Results of D-SIMS and SE with ?xed parameters are in good agreement with XRD for HBTs with Ge grading.
关键词： SiGe,XRD,spectroscopic ellipsometry,SIMS,HBT
更新于2025-09-09 09:28:46