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<i>In situ</i> spectroelectrochemical ellipsometry using super continuum white laser: Study of the anodization of magnesium alloy
摘要： This work shows the interest to use a real time, white laser-based ellipsometer to characterize a complex electrolyte|electrode interface during an electrochemical process in an aqueous-based medium. This method is proposed to probe electrochemical interfaces that are usually not suitable to the full extent application of ellipsometry due to great disturbance of the re?ected light ?ux provoked by gas evolution or roughness. In situ spectroelectrochemical ellipsometry combining such a visible super continuum ?ber laser-band source was not previously reported to the best of the authors’ knowledge. The setup was employed to monitor an electrochemical process whose mechanism was previously incompletely described: the prespark anodization regime of the plasma electrolytic oxidation process of the Mg alloy AZ91D in the 3M KOH electrolyte. Above the anodization voltage of 4 V, the side water oxidation reaction induced light diffusion that reduces re?ected light beam intensity. The process is monitored in an extended voltage range from 4 to 40 V and in an extended spectral range (495–800 nm). In the presented case, the use of a visible super continuum ?ber laser-band source enhanced the signal-to-noise ratio giving access to a deeper picture of the triplex layer structure during surface repassivation by monitoring the evolution of the outer, inner, and interfacial layers.
关键词： AZ91D,anodization,super continuum white laser,spectroelectrochemical ellipsometry,magnesium alloy
更新于2025-09-11 14:15:04
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Two-dimensional plasmonic biosensing platform: Cellular activity detection under laser stimulation
摘要： Combining biosensors with nanoscience provides great advantages such as being label-free and real time, highly sensitive, and small in size, as well as providing a low limit of detection and integration to other systems. That is why plasmonics finds various applications in drug detection, food safety, agriculture, photothermal therapy, etc. In this paper, we have fabricated a two-dimensional plasmonic grating biosensor using a soft lithography technique, which has eliminated some disadvantages of conventional plasmonic structures like expensive fabrication cost, inflexibility, and lack of mass production. On the other hand, we benefited from infrared neural stimulation for regulating membrane depolarization, which was based on photothermal mechanism and provided a contact-free and high spatial/temporal resolution. Eventually, the membrane depolarization of two different cell types of Hep G2 and mesenchymal stem cells cultured on two-dimensional plasmonic structure has been investigated under infrared neural stimulation. After preparing the soft plasmonic crystal, its reflection spectra and respective ellipsometry parameters were analyzed before and after cell culture with/without stimulation (near-infrared immune region ～1450 nm). By comparing the obtained ellipsometry results for HEP G2 and mesenchymal stem cells, it is observed that the behavior of two cell types with respect to IR stimulation was the same as well as providing us the possibility of distinguishing the level of membrane depolarization under various stimulating frequencies. The strength of this integrated system for membrane depolarization detection has been shown experimentally, which can open new avenues toward neuroplasmonic application in the future.
关键词： infrared neural stimulation,membrane depolarization,ellipsometry,soft lithography,plasmonic biosensor
更新于2025-09-11 14:15:04
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Vacuum-annealed and oxygen plasma treated ellipsometric investigations on molybdenum bronzes and measurements of their thermo optic coefficients and electronic polarizability coefficients
摘要： In this investigation, we have measured the optical constants (n, k) of vacuum evaporated MoO3 thin films and of ZxMoO3 (Z = H+, Li+) bronze thin films being annealed at different temperatures and with different concentrations (x) over the range 298–453 K without and within an oxygen plasma environment using manual ellipsometry. We have also measured mass densities, thermo optic coefficients (TOCs), electronic polarizability coefficients (EPCs) and the coefficients of temperature dependence of density of MoO3 thin film and of its bronzes over the same temperature range. It was found that the change in density and porosity of MoO3 thin film (when annealed at 453 K for 36 h) was not more than 6.4% and 15% respectively from the room temperature data. In the case of bronzes, when the samples H0.203MoO3, Li0.076MoO3 and Li0.133MoO3 were annealed at 453 K within an oxygen plasma over different periods of times, it was found that the overall increase in mass density and decrease in the porosity was not more than 4% and 11%, respectively from the initial data at room temperature. Comparably, when the samples H0.211MoO3 and Li0.27MoO3 were annealed at 453 K within an oxygen plasma over different periods of time, the respective decrease in density and increase in porosity was found not more than 3.4% and 6% from the room temperature data. All these results are mostly due to evolution of H2O which causes diffusion of oxygen leading to shallow and deep localised states in the oxide bronze layers. TOCs and EPCs of samples HxMoO3 (x = 0.203) and LixMoO3(x = 0.076, 0.133) upon annealing at 453 K (without and within an oxygen plasma) over different periods of times have an increase in TOCs and in EPCs, and that increase is from 0.10 × 10?4 K?1 to 13.5 × 10?4 K?1 and 0.13 × 10?27 cm3 K?1 to 3.2 × 10?27 cm3 K?1, respectively. On the other hand, the thermo optic coefficient and the coefficient of temperature dependence of density of MoO3 thin films decrease from ? 1.2 × 10?4 K?1 to ? 8.86 × 10?4 K?1 and ? 1.86 × 10?4 g cm?3 K?1 to ? 15.13 × 10?4 g cm?3 K?1, respectively. In the case of H0.211MoO3 and Li0.27MoO3 when annealed at 453 K over different periods of time within oxygen plasma, the overall decrease in TOC is from ? 0.3 × 10?4 K?1 to ? 4.62 × 10?4 K?1, and the decrease in coefficient of temperature dependence of density is from ? 0.45 × 10?4 g cm?3 K?1 to ? 8.9 × 10?4 g cm?3 K?1. These results are due to linear thermal expansion effect.
关键词： ellipsometry,thermo optic coefficients,electronic polarizability coefficients,MoO3 thin films,molybdenum bronzes
更新于2025-09-11 14:15:04
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Modelling of Optical Damage in Nanorippled ZnO Produced by Ion Irradiation
摘要： Here, we report on the production of nanoripples on the surface of ZnO bulk substrates by ion beam erosion with 20 keV Ar+ ions at an oblique incidence (60°). The ripple patterns, analyzed by atomic force microscopy, follow a power law dependence for both the roughness and the wavelength. At high fluences these ripples show coarsening and asymmetric shapes, which become independent of the beam direction and evidence additional mechanisms for the pattern development. The shallow damaged layer is not fully amorphized by this process, as confirmed by medium energy ion scattering. A detailed study of the damage-induced changes on the optical properties was carried out by means of spectroscopic ellipsometry. Using a 3-layer model based on Tauc-Lorenz and critical point parameter band oscillators, the optical constants of the damaged layer were determined. The results showed a progressive reduction in the refractive index and enhanced absorption below the bandgap with the fluence.
关键词： ripples,ZnO,patterning,sputtering,damage,spectroscopic ellipsometry
更新于2025-09-11 14:15:04
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Thickness-Dependent Swelling Behavior of Vapor-Deposited Smart Polymer Thin Films
摘要： In this contribution, the temperature-dependent swelling behavior of vapor-deposited smart polymer thin films is shown to depend on cross-linking and deposited film thickness. Smart polymers find application in sensor and actuator setups and are mostly fabricated on delicate substrates with complex nanostructures that need to be conformally coated. As initiated chemical vapor deposition (iCVD) meets these specific requirements, the present work concentrates on temperature-dependent swelling behavior of iCVD poly(N-isopropylacrylamide) thin films. The transition between swollen and shrunken state and the corresponding lower critical solution temperature (LCST) was investigated by spectroscopic ellipsometry in water. The films’ density in the dry state evaluated from X-ray reflectivity could be successfully correlated to the position of the LCST in water and was found to vary between 1.1 and 1.3 g/cm3 in the thickness range 30?330 nm. This work emphasizes the importance of insights in both the deposition process and mechanisms during swelling of smart polymeric structures.
关键词： X-ray reflectivity,spectroscopic ellipsometry,vapor-deposited,smart polymers,iCVD,LCST,film thickness,swelling behavior,cross-linking
更新于2025-09-11 14:15:04
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Refractive Index Variation of Magnetron-Sputtered a-Si1?xGex by “One-Sample Concept” Combinatory
摘要： Gradient a-Si1?xGex layers have been deposited by "one-sample concept" combinatorial direct current (DC) magnetron sputtering onto one-inch-long Si slabs. Characterizations by electron microscopy, ion beam analysis and ellipsometry show that the layers are amorphous with a uniform thickness, small roughness and compositions from x = 0 to x = 1 changing linearly with the lateral position. By focused-beam mapping ellipsometry, we show that the optical constants also vary linearly with the lateral position, implying that the optical constants are linear functions of the composition. Both the refractive index and the extinction coefficient can be varied in a broad range for a large spectral region. The precise control and the knowledge of layer properties as a function of composition is of primary importance in many applications from solar cells to sensors.
关键词： SiGe,optical properties,spectroscopic ellipsometry
更新于2025-09-10 09:29:36
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Layer-Dependent Dielectric Function of Wafer-Scale 2D MoS <sub/>2</sub>
摘要： Wafer-scale, high-quality, and layer-controlled 2D MoS2 films on c-sapphire are synthesized by an innovative two-step method. The dielectric functions of MoS2 ranging from the monolayer to the bulk are investigated by spectroscopic ellipsometry over an ultra-broadband (0.73–6.42 eV). Up to five critical points (CPs) in the dielectric function spectra are precisely distinguished by CP analysis, and their physical origins are identified in the band structures with the help of first-principles calculations. Results demonstrate that the center energies of these CPs exhibit intriguing layer dependency, which are interpreted by the intrinsic layer-dependent transitions in MoS2. Specially, the change in the imaginary part of the dielectric functions versus the thickness exhibits a “W” like curve, and the two valley bottoms appear at about four-layer and 10-layer respectively. These complex fluctuations are attributed to the alternating domination of the decreasing excitonic effect, the increasing joint density of states, and the mass density increase in relative thick MoS2 samples.
关键词： layer-dependent dielectric function,two-step method,spectroscopic ellipsometry,wafer-scale 2D MoS2
更新于2025-09-10 09:29:36
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Temperature dependence of the dielectric function of monolayer MoS2
摘要： An analytic expression of the dielectric function of monolayer molybdenum disulfide (MoS2) ε = ε1 + iε2 is presented for energies from 1.4 to 6.0 eV and temperatures from 35 to 350 K. The dielectric function parametric model is used to express ε as a sum of polynomials, which naturally includes asymmetry of critical-point lineshapes. The temperature dependence is achieved by fitting model parameters. In this way the dielectric function of MoS2 for arbitrary temperature can be calculated. We observed the fundamental absorption peak, which occurs at the K point of the Brillouin zone. These results are expected to be useful in designing and understanding applied-device technologies based on monolayer MoS2.
关键词： Monolayer MoS2,Ellipsometry,Dielectric function parametric model,Dielectric function
更新于2025-09-10 09:29:36
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Charge transient behaviour and spectroscopic ellipsometry characteristics of TiN/HfSiO MOS capacitors
摘要： A combination of two powerful techniques, namely, charge Deep level transient spectroscopy and spectroscopic ellipsometry is employed on atomic layer deposited Si-metal oxide semiconductor capacitors (MOSCAPs) to investigate the energy ef?ciency of the physical process. Ultra-thin TiN/HfSiO acted as gate-dielectric stack on Si substrate was carefully subjected to rapid thermal processing and subsequent spectroscopic measurements to determine the transient behaviour of charges and electro-optical characteristics. Some key parameters such as trap concentration, activation energy required to surmount the traps, capture cross section, refractive index and extinction coef?cient are found to play an important role in order to assess the energy ef?ciency of the devices both in terms of post-process quality of the retained surface and residual ef?ciency of the process by virtue of dynamics at atomistic scales. The results may provide a useful insight to the Si manufacturing protocols at ever decreasing nodes with desirable energy ef?ciency.
关键词： energy efficiency,charge Deep level transient spectroscopy,MOSCAPs,spectroscopic ellipsometry,TiN/HfSiO
更新于2025-09-10 09:29:36
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Thermal hysteresis measurement of the VO <sub/>2</sub> dielectric function for its metal-insulator transition by visible-IR ellipsometry
摘要： The real and imaginary parts of the dielectric function of VO2 thin films, deposited on r-plane sapphire via pulsed laser deposition, are measured by means of visible-infrared ellipsometry for wavelengths ranging from 0.4 to 15 μm and temperatures within its phase transition. For both the insulator-to-metal (heating) and metal-to-insulator (cooling) transitions, it is shown that the two ellipsometric signals exhibit three temperature-driven behaviors, which are well described by appropriate combinations of the Tauc-Lorentz, Gaussian, and Drude oscillator models. By fitting Bruggeman’s effective medium model for the dielectric function to the corresponding measured experimental values, using the volumetric fraction of the VO2 metallic domains as a fitting parameter for different temperatures within the VO2 phase transition, we have found that this model is suitable for describing the dielectric function in visible and near-infrared wavelengths (～0.4 to ～3.0 μm), but it generally fails for longer infrared ones. Furthermore, the hysteresis loop of the VO2 emissivity averaged over a relevant interval of wavelengths is determined and shown to vary from ～0.49, in the insulator phase, to ～0.16, in the metallic one. These values, based on the VO2 dielectric function, are consistent with previous measurements reported in the literature, and therefore, our measured data are expected to be useful for describing the behavior of VO2 films involved in optical and radiative applications.
关键词： metal-insulator transition,ellipsometry,emissivity,VO2,dielectric function
更新于2025-09-10 09:29:36