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We determined the optimal composition of reactive magnetron-sputtered mixed layers of Titanium oxide and Tin oxide (TiO2-SnO2) for electrochromic purposes. We determined and mapped the composition and optical parameters using Spectroscopic Ellipsometry (SE). Ti and Sn targets were put separately from each other, and the Si-wafers on a glass substrate (30 cm × 30 cm) were moved under the two separated targets (Ti and Sn) in a reactive Argon-Oxygen (Ar-O2) gas mixture. Different optical models, such as the Bruggeman Effective Medium Approximation (BEMA) or the 2-Tauc–Lorentz multiple oscillator model (2T–L), were used to obtain the thickness and composition maps of the sample. Scanning Electron Microscopy (SEM) with Energy-Dispersive X-ray Spectroscopy (EDS) has been used to check the SE results. The performance of diverse optical models has been compared. We show that in the case of molecular-level mixed layers, 2T–L is better than EMA. The electrochromic effectiveness (the change of light absorption for the same electric charge) of mixed metal oxides (TiO2-SnO2) that are deposited by reactive sputtering has been mapped too.

We determined the optimal composition of reactive magnetron sputtered TiO2-SnO2 mixed layers for electrochromic purposes. We determined and mapped the composition and optical parameters by Spectroscopic Ellipsometry (SE). The Ti‐ and Sn‐ targets have been placed separately, and the Si-wafers on glass substrate (30 cm× 30 cm) were moved under the two separated targets (Ti and Sn) in Ar‐O2 plasma. Different (Effective Medium Approximation (EMA) and oscillator-type) op-tical models were used to obtain the composition maps and thickness of the sample layer. Scanning Electron Microscopy (SEM) with Energy-Dispersive X-ray Spectroscopy (EDS) has been used to check the SE results. The ’goodness’ of diverse optical models have been compared, according to the conditions of sample preparation. We show that in the case of molecular-level mixed layers 2‐Tauc‐Lorentz oscillator model is better than the Bruggeman Effective Medium Approximation (BEMA). The electrochromic properties of mixed metal oxides that deposited by reactive sputtering have been mapped, too.

Quantum confinement of the charge carriers of graphene is an effective way to engineer its properties. This is commonly realized through physical edges that are associated with the deterioration of mobility and strong suppression of plasmon resonances. Here, we demonstrate a simple, large-area, edge-free nanostructuring technique, based on amplifying random nanoscale structural corrugations to a level where they efficiently confine charge carriers, without inducing significant inter-valley scattering. This soft confinement allows the low-loss lateral ultra-confinement of graphene plasmons, scaling up their resonance frequency from the native terahertz to the commercially relevant visible range. Visible graphene plasmons localized into nanocorrugations mediate much stronger light–matter interactions (Raman enhancement) than previously achieved with graphene, enabling the detection of specific molecules from femtomolar solutions or ambient air. Moreover, nanocorrugated graphene sheets also support propagating visible plasmon modes, as revealed by scanning near-field optical microscopy observation of their interference patterns. A scalable soft nanoengineering technique enables the realization of visible plasmons in corrugated graphene.

Spectroscopic ellipsometry is a sensitive and optical model-supported quantitative tool to monitor interfaces. In this work, solid-liquid interfaces are studied using the Kretschmann-Raether configuration for biosensing applications. The interface layers support two purposes simultaneously: (i) chemical suitability for the adsorption of molecules to be detected and (ii) the optical enhancement of the signal to increase the sensitivity. Ellipsometry is not only used as a sensor but also as a quantitative measurement tool to study and understand the interface phenomena, and to develop the sensing layers for the largest possible optical sensitivity. Plasmonic and structured layers are of primary importance in terms of optical sensitivity. Layers structured both in lateral and vertical directions have been studied. Optical models based on both the transfer matrix and the finite element method were developed and used for the structural analysis where the material and geometrical derivatives are used in the inverse fitting process of the model data to the measurement. Structures utilizing plasmonic, diffraction, multilayer field enhancement, and other methods were analyzed as possible candidates for the improvement of the optical performance of the cell. Combinatorial and periodic plasmonic surface structures were developed to enhance the sensitivity of in-situ ellipsometry at solid-liquid interfaces utilizing the Kretschmann-Raether (KR) geometry. Ag$_x$Al$_{1-x}$ layers with variable compositions and Au layers with changing periods and critical dimensions were investigated to improve the performance of sensors based on the KR arrangement., Comment: 9 pages, 3 figures, SPIE Photonics West conference contribution

Mid-infrared (IR) ellipsometry of thin films and molecule layers at solid–liquid interfaces has been a challenge because of the absorption of light in water. It has been usually overcome by using c...

The optical parameters of hydrogenated amorphous a- $$\hbox {Si}_{1-x}\,\hbox {Ge}_{{x}}$$ Si 1 - x Ge x :H layers were measured with focused beam mapping ellipsometry for photon energies from 0.7 to 6.5 eV. The applied single-sample micro-combinatorial technique enables the preparation of a- $$\hbox {Si}_{1-x}\,\hbox {Ge}_{{x}}$$ Si 1 - x Ge x :H with full range composition spread. Linearly variable composition profile was revealed along the 20 mm long gradient part of the sample by Rutherford backscattering spectrometry and elastic recoil detection analysis. The Cody-Lorentz approach was identified as the best method to describe the optical dispersion of the alloy. The effect of incorporated H on the optical absorption is explained by the lowering of the density of localized states in the mobility gap. It is shown that in the low-dispersion near infrared range the refractive index of the a- $$\hbox {Si}_{1-x}\,\hbox {Ge}_x$$ Si 1 - x Ge x alloy can be comprehended as a linear combination of the optical parameters of the components. The micro-combinatorial sample preparation with mapping ellipsometry is not only suitable for the fabrication of samples with controlled lateral distribution of the concentrations, but also opens new prospects in creating databases of compounds for optical and optoelectonic applications.

CrAlN alloys can play an important role in the improvement of next generation piezoelectric MEMS devices. However, enhanced piezoelectric constants require high degree of uniaxial orientation in the polycrystalline thin film. In this work, CrxAl1−xN thin films with varying compositions were deposited at different substrate temperatures by reactive DC co-sputtering technique and compared with respect to their microstructure and optical properties. The relationship between the atomic composition of the layers and the plasma powers over the Al and Cr targets during co-sputtering was revealed accurately by Rutherford backscattering spectrometry. As it was found by X-ray and selective area electron diffraction methods, thin films in the range of x = 0–0.23 show hexagonal wurtzite-type phase, which changes to cubic rock-salt-type structure between 0.23

Silicon is absorbed as uncharged mono-silicic acid by plant roots through passive absorption of Lsi1, an influx transporter belonging to the aquaporin protein family. Lsi2 then actively effluxes silicon from root cells towards the xylem from where it is exported by Lsi6 for silicon distribution and accumulation to other parts. Recently, it was proposed that silicon nanoparticles (SiNPs) might share a similar route for their uptake and transport. SiNPs then initiate a cascade of morphophysiological adjustments that improve the plant physiology through regulating the expression of many photosynthetic genes and proteins along with photosystem I (PSI) and PSII assemblies. Subsequent improvement in photosynthetic performance and stomatal behaviour correspond to higher growth, development, and productivity. On many occasions, SiNPs have demonstrated a protective role during stressful environments by improving plant-water status, source-sink potential, reactive oxygen species (ROS) metabolism, and enzymatic profile. The present review comprehensively discusses the crop improvement potential of SiNPs stretching their role during optimal and abiotic stress conditions including salinity, drought, temperature, heavy metals, and ultraviolet (UV) radiation. Moreover, in the later section of this review, we offered the understanding that most of these upgrades can be explained by SiNPs intricate correspondence with phytohormones, antioxidants, and signalling molecules. SiNPs can modulate the endogenous phytohormones level such as abscisic acid (ABA), auxins (IAAs), cytokinins (CKs), ethylene (ET), gibberellins (GAs), and jasmonic acid (JA). Altered phytohormones level affects plant growth, development, and productivity at various organ and tissue levels. Similarly, SiNPs regulate the activities of catalase (CAT), ascorbate peroxidase (APX), superoxide dismutase (SOD), and ascorbate-glutathione (AsA-GSH) cycle leading to an upgraded defence system. At the cellular and subcellular levels, SiNPs crosstalk with various signalling molecules such as Ca

Regular monitoring of arsenic concentrations in water sources is essential due to the severe health effects. Our goal was to develop a rapidly responding, sensitive and stable sensing layer for the detection of arsenic. We have designed flagellin-based arsenic binding proteins capable of forming stable filament structures with high surface binding site densities. The D3 domain of Salmonella typhimurium flagellin was replaced with an arsenic-binding peptide motif of different bacterial ArsR transcriptional repressor factors. We have shown that the fusion proteins developed retain their polymerization ability and have thermal stability similar to that of wild-type filament. The strong arsenic binding capacity of the monomeric proteins was confirmed by isothermal titration calorimetry (ITC), and dissociation constants (Kd) of a few hundred nM were obtained for all three variants. As-binding fibers were immobilized on the surface of a gold electrode and used as a working electrode in cyclic voltammetry (CV) experiments to detect inorganic arsenic near the maximum allowable concentration (MAC) level. Based on these results, it can be concluded that the stable arsenic-binding flagellin variant can be used as a rapidly responding, sensitive, but simple sensing layer in a field device for the MAC-level detection of arsenic in natural waters.

The environmental monitoring of Ni is targeted at a threshold limit value of 0.34 mu M, as set by the World Health Organization. This sensitivity target can usually only be met by time-consuming and expensive laboratory measurements. There is a need for inexpensive, field-applicable methods, even if they are only used for signaling the necessity of a more accurate laboratory investigation. In this work, bioengineered, protein-based sensing layers were developed for Ni detection in water. Two bacterial Ni-binding flagellin variants were fabricated using genetic engineering, and their applicability as Ni-sensitive biochip coatings was tested. Nanotubes of mutant flagellins were built by in vitro polymerization. A large surface density of the nanotubes on the sensor surface was achieved by covalent immobilization chemistry based on a dithiobis(succimidyl propionate) cross-linking method. The formation and density of the sensing layer was monitored and verified by spectroscopic ellipsometry and atomic force microscopy. Cyclic voltammetry (CV) measurements revealed a Ni sensitivity below 1 mu M. It was also shown that, even after two months of storage, the used sensors can be regenerated and reused by rinsing in a 10 mM solution of ethylenediaminetetraacetic acid at room temperature.

In this work, amorphous hydrogen-free silicon nitride (a-SiNx) and amorphous hydrogenated silicon nitride (a-SiNx:H) films were deposited by radio frequency (RF) sputtering applying various amounts of hydrogen gas. Structural and optical properties were investigated as a function of hydrogen concentration. The refractive index of 1.96 was characteristic for hydrogen-free SiNx thin film and with increasing H2 flow it decreased to 1.89. The hydrogenation during the sputtering process affected the porosity of the thin film compared with hydrogen-free SiNx. A higher porosity is consistent with a lower refractive index. Fourier-transform infrared spectroscopy (FTIR) confirmed the presence of 4 at.% of bounded hydrogen, while elastic recoil detection analysis (ERDA) confirmed that 6 at.% hydrogen was incorporated during the growing mechanism. The molecular form of hydrogen was released at a temperature of ~65 &deg, C from the film after annealing, while the blisters with 100 nm diameter were created on the thin film surface. The low activation energy deduced from the Arrhenius method indicated the diffusion of hydrogen molecules.

Ion implantation has been a key technology in microelectronics and generally, for the controlled surface modification of materials for tribology, biocompatibility, corrosion resistance and many more. In this work in-situ spectroscopic ellipsometry was used for accurately tracking and on-line evaluating the accumulation of voids and damage in crystalline Ge during implantation of 200-keV Sb+ ions at a total fluence of 1016 cm− 2 using an ion flux of 2.1 × 1012 cm− 2s− 1. The phases of damage accumulation were identified using unique optical multi-layer models describing the layer structure and composition. The formation of initial partial disorder was followed by complete amorphization and void formation occurring at the fluence of 1 × 1015 cm− 2, reaching a high volume fraction of voids and a layer thickness of ≈ 200 nm by the end of the process. This agrees with numerical simulations and results of complementary measurements including ion beam analysis and electron microscopy. The developed in-situ method for controlling the dynamics of structural damage accumulation is a versatile ion-implantation tool for avoiding adverse void formation and for controlled evolution of subsurface nanocavities or cellular surface texture alike.

Mid-infrared (IR) ellipsometry of thin films and molecule layers at solid–liquid interfaces has been a challenge because of the absorption of light in water. It has been usually overcome by using configurations utilizing illumination through the solid substrate. However, the access to the solid–liquid interface in a broad spectral range is also challenging due to the limited transparency of most structural materials in the IR wavelength range. In this work, we propose a concept of a microfabricated analysis cell based on an IR-transparent Si membrane with advantages of a robust design, flexible adaptation to existing equipment, small volume, multiple-angle capabilities, broad wavelength range, and opportunities of multilayer applications for adjusted ranges of high sensitivity. The chamber was prepared by 3D micromachining technology utilizing deep reactive ion etching of a silicon-on-insulator wafer and bonded to a polydimethylsiloxane microfluidic injection system resulting in a cell volume of approximately 50 μL. The mechanical stability of the 2 and 5 μm-thick membranes was tested using different “backbone” reinforcement structures. It was proved that the 5 μm-thick membranes are stable at lateral cell sizes of 5 mm by 20 mm. The cell provides good intensity and adjustment capabilities on the stage of a commercial mid-IR ellipsometer. The membrane configuration also provides optical access to the sensing interfaces at a broad range of incident angles, which is a significant advantage in many potential sensing structure configurations, such as plasmonic, multilayer, 2D, or metamaterial applications.

The optical parameters of hydrogenated amorphous a-$$\hbox {Si}_{1-x}\,\hbox {Ge}_{{x}}$$ Si 1 - x Ge x :H layers were measured with focused beam mapping ellipsometry for photon energies from 0.7 to 6.5 eV. The applied single-sample micro-combinatorial technique enables the preparation of a-$$\hbox {Si}_{1-x}\,\hbox {Ge}_{{x}}$$ Si 1 - x Ge x :H with full range composition spread. Linearly variable composition profile was revealed along the 20 mm long gradient part of the sample by Rutherford backscattering spectrometry and elastic recoil detection analysis. The Cody-Lorentz approach was identified as the best method to describe the optical dispersion of the alloy. The effect of incorporated H on the optical absorption is explained by the lowering of the density of localized states in the mobility gap. It is shown that in the low-dispersion near infrared range the refractive index of the a-$$\hbox {Si}_{1-x}\,\hbox {Ge}_x$$ Si 1 - x Ge x alloy can be comprehended as a linear combination of the optical parameters of the components. The micro-combinatorial sample preparation with mapping ellipsometry is not only suitable for the fabrication of samples with controlled lateral distribution of the concentrations, but also opens new prospects in creating databases of compounds for optical and optoelectonic applications.

Accurate reference dielectric functions play an important role in the research and development of optical materials. Libraries of such data are required in many applications in which amorphous semiconductors are gaining increasing interest, such as in integrated optics, optoelectronics or photovoltaics. The preparation of materials of high optical quality in a reproducible way is crucial in device fabrication. In this work, amorphous Ge (a-Ge) was created in single-crystalline Ge by ion implantation. It was shown that high optical density is available when implanting low-mass Al ions using a dual-energy approach. The optical properties were measured by multiple angle of incidence spectroscopic ellipsometry identifying the Cody-Lorentz dispersion model as the most suitable, that was capable of describing the dielectric function by a few parameters in the wavelength range from 210 to 1690 nm. The results of the optical measurements were consistent with the high material quality revealed by complementary Rutherford backscattering spectrometry and cross-sectional electron microscopy measurements, including the agreement of the layer thickness within experimental uncertainty.

Group IV semiconductor nanoclusters/nanocrystals attract a great interest because of substantial transformation of their optical, electrical and luminescent properties due to quantum confinement effects. During last decades significant attention was paid to the Si nanocrystals (ncs) embedded in Si oxide or nitride, and later, to the Ge-ncs embedded in these matrices. The mechanism of these 'ncs' formation was investigated in details. Recently we have reported on the Si-ncs formation in hafnia and alumina thin films. This work will present the results obtained for the Ge-rich Al2O3 films. The effect of Ge content and annealing conditions on the evolution of optical and structural properties of these materials and formation of Ge-ncs will be addressed. The films with different Ge content were grown on quarts substrates by magnetron co-sputtering of Ge and Al2O3 targets in argon plasma. After deposition, they were annealed in nitrogen atmosphere and analyzed by means of spectroscopic ellipsometry, FTIR, Raman scattering, XRD and photoluminescence methods. It is observed that suitable thermal treatment leads to the decomposition of nonstoichiometric films and results in the Ge-ncs formation. The formation of Ge-ncs via phase separantion requires lower temperatures (600-700°C) than that for Si-ncs production in alumina host (1050-1100ºC). An annealing at 800-950ºC results in the Ge out-diffusion from the films via formation of volatile GeO. This process results in the significant depletion of the near-surface regions in germanium that was confirmed by an appearance of gradient in the refractive index via film volume. Decomposition process stimulates also an appearance of visible and near-infrared photoluminescence. The shape of luminescent spectrum depends significantly on both Ge content and the excitation wavelength. It is observed that exciton recombination inside nanocrystals dominates at longer wavelength excitation, whereas the UV-blue excitation results in the radiative recombination via interface or host defects in the materials. This result was found to be caused by the competition of different radiative channels in the films. The evolution of optical and luminescent properties will be discussed in details.

International audience; Thermally-stimulated evolution of optical and structural properties of Ge-rich-Al2O3 films with different Ge contents was investigated. As-deposited films and films annealed at TA ≤ 550 °C were found to be amorphous whatever the Ge content. The formation of amorphous Ge clusters occurs at TA = 550 °C, whereas their crystallization is prominent at TA = 600 °C requiring a shorter annealing time for the higher Ge content. The films annealed at TA = 550 °C showed broad photoluminescence spectrum. Its shape and intensity depend on Ge content and excitation energy. Annealing at TA = 600 °C results in the appearance of additional UV bands originated from the formation of GeOx phase covered Ge clusters. An analysis of excitation spectra was performed to distinguish the mechanism of light emission in these films as well as to discriminate contribution of carrier recombination in the Ge phase (amorphous clusters and/or nanocrystals) as well as via interface or host defects. The concentration and mobility of free carriers was also estimated.

The change of optical and structural properties of Ge nanoclusters in ZrO 2 matrix have been investigated by spectroscopic ellipsometry versus annealing temperatures. Radio-frequency top-down magnetron sputtering approach was used to produce the samples of different types, i.e. single-layers of pure Ge, pure ZrO 2 and Ge-rich-ZrO 2 as well as multi-layers stacked of 40 periods of 5-nm-Ge-rich-ZrO 2 layers alternated by 5-nm-ZrO 2 ones. Germanium nanoclusters in ZrO 2 host were formed by rapid-thermal annealing at 600–800 °C during 30 s in nitrogen atmosphere. Reference optical properties for pure ZrO 2 and pure Ge have been extracted using single-layer samples. As-deposited multi-layer structures can be perfectly modeled using the effective medium theory. However, annealed multi-layers demonstrated a significant diffusion of elements that was confirmed by medium energy ion scattering measurements. This fact prevents fitting of such annealed structure either by homogeneous or by periodic multi-layer models.

Aluminum nitride (AlN) films were synthesized onto Si(100) substrates by pulsed laser deposition (PLD) in vacuum or nitrogen, at 0.1, 1, 5, or 10 Pa, and substrate temperatures ranging from RT to 800 &deg, C. The laser parameters were set at: incident laser fluence of 3&ndash, 10 J/cm2 and laser pulse repetition frequency of 3, 10, or 40 Hz, respectively. The films&rsquo, hardness was investigated by depth-sensing nanoindentation. The optical properties were studied by FTIR spectroscopy and UV-near IR ellipsometry. Hardness values within the range of 22&ndash, 30 GPa and Young&rsquo, s modulus values of 230&ndash, 280 GPa have been inferred. These values were determined by the AlN film structure that consisted of nanocrystallite grains, strongly dependent on the deposition parameters. The values of optical constants, superior to amorphous AlN, support the presence of crystallites in the amorphous film matrix. They were visualized by TEM and evidenced by FTIR spectroscopy. The characteristic Reststrahlen band of the h-AlN lattice with component lines arising from IR active phonon vibrational modes in AlN nanocrystallites was well detectable within the spectral range of 950&ndash, 500 cm&minus, 1. Control X-ray diffraction and atomic force microscopy data were introduced and discussed. All measurements delivered congruent results and have clearly shown a correlation between the films&rsquo, structure and the mechanical and optical properties dependent on the experimental conditions.

We used numerical simulations based on the finite element method (FEM) to calculate both the amplitude and phase information of the scattered electric field from random rough surfaces, which can be directly compared to ellipsometric measurements and effective medium approximation (EMA) calculations. FEM can serve as an exploration tool for the relationship between the thickness of the surface roughness evaluated by Bruggeman EMA and the morphological parameters of the surface, such as the root mean square height, the lateral auto-correlation length and the typical average slope. These investigations are of high interest in case of poly-crystalline and amorphous materials. The paper focuses on the simulations of rough Si surfaces. The ellipsometric calculations from FEM and EMA simulations match for wavelengths of illumination much shorter than the typical feature size of the surface. Furthermore, for these cases, the correlation between the EMA thickness and the root mean square height of the roughness for a given auto-correlation length is quadratic, rather than linear, which is in good agreement with experimental measurements and analytical calculations presented in recent reports., 4 fugires

Due to its remarkable switching effect in electrical and optical properties, VO2 is a promising material for several applications. However, the stoichiometry control of multivalent vanadium oxides, especially with a rational deposition technique, is still challenging. Here, we propose and optimize a simple fabrication method for VO2 rich layers by the oxidation of metallic vanadium in atmospheric air. It was shown that a sufficiently broad annealing time window of 3.0&ndash, 3.5 h can be obtained at an optimal oxidation temperature of 400 &deg, C. The presence of VO2 was detected by selected area diffraction in a transmission electron microscope. According to the temperature dependent electrical measurements, the resistance contrast (R30 &deg, C/R100 &deg, C) varied between 44 and 68, whereas the optical switching was confirmed using in situ spectroscopic ellipsometric measurement by monitoring the complex refractive indices. The obtained phase transition temperature, both for the electrical resistance and for the ellipsometric angles, was found to be 49 &plusmn, 7 &deg, C, i.e., significantly lower than that of the bulk VO2 of 68 &plusmn, 6 &deg, C.

Nuclear fuel claddings can balloon and rupture at high temperatures under internal gas pressure in case of design basis accidents like loss-of-coolant-accident (LOCA). The thermal phenomena surrounding the ballooning and cracking was investigated in a series of experiments performed using zirconium alloy cladding tubes at the Centre for Energy Research in Hungary. The experiments were recorded using a high-speed infrared camera in the intermediate infrared range and the temperatures were measured in-situ. It was found that before the rupture of the cladding tube, the ballooned cladding surface forms a bulge and heats up locally, a hot spot appears. During crack propagation, the crack tip temperature is significantly warmer than the rest of the tube. The hot spot temperature and the rate of temperature increase was determined. The infrared emission coefficient of the slightly oxidized zirconium cladding samples in the intermediate infrared range was also determined. The emissivity coefficient that fit our measurements was found to be around e = 0.89.

We designed a Bragg mirror structure with an SiO2 top layer to create a resonance in the ultraviolet wavelength range, near the absorption peak position of various proteins. We demonstrate that the wavelength of enhanced sensitivity can be adjusted by proper design of the 1D photonic structure. The possibility to design the wavelength of enhanced sensitivity supports measurements of better selectivity, optimized for the absorption of the target material. Since the width of the resonant peak in the reflectance spectra can be sharper than those of plasmonics, and they can be positioned at more favourable regions of the instrument and material (e.g., in terms of intensity or selectivity), the sensitivity can exceed those of plasmon-enhanced measurements. In this study we demonstrate the main features of the concept at the example of in situ spectroscopic ellipsometry of fibrinogen adsorption in the Kretschmann-Raether configuration. We realized a resonant peak with a full width at half maximum of 3 nm near the wavelength of 280 nm, which coincides with the absorption maximum of fibrinogen. The influence of depolarization and surface roughness on the measurements, and the potential for improving the current experimental detection limit of 45 pg/mm2 is also discussed.

This paper suggests the evaluation of morphological parameters of porous silicon layers (PSL) using spectroscopic ellipsometry from UV to mid-infrared optical range. PSL were prepared by electrochemical etching of monocrystalline silicon wafers in hydrofluoric acid-based electrolyte. Measuring with an optical and an infrared ellipsometer with a wide spectral range permits an accurate characterization of PSL properties from the top surface to the bottom of the layer with thicknesses from several hundred nanometers up to a few tens of micrometers. Several different optical models for ellipsometric evaluations were developed to determine the thickness, the average porosity, the in-depth porosity gradient, the oxidation level and the surface roughness of the PSL. Porosity was modeled with multiple effective medium layers by varying ratio of crystalline silicon, void and oxidized silicon wherever needed. Thin PSL (

Protective SiC-rich nano layer was created by ion beam mixing of Si/C multilayers. The transformation of the Si and C layers into a homogeneous SiC layer was analyzed using complementary depth profiling by spectroscopic ellipsometry (SE) and Auger electron spectroscopy (AES). The distribution of elements and their chemical states was revealed by AES, whereas SE measured the accurate thicknesses, density, crystallinity, and the distribution of different phases. The optical properties of the created SiC layer determined by SE were almost identical to that of ion implantation-amorphized SiC. Amorphous Si and void formations were revealed by SE. The void profile determined by SE correlated well with the Xe distribution measured by AES. The complementary capabilities of SE and AES for a detailed chemical investigation were pointed out, such as the atomic (AES), structural (AES and SE) and non-destructive depth profiling (SE) features. It was shown that besides the synergism that the two methods reveal, SE is capable of a quick, sensitive and non-destructive testing of such layer structures and materials.

NbO2 is a promising candidate for resistive switching devices due to an insulator-metal transition above room temperature, which is related to a phase transition from a distorted rutile structure to an undistorted one. However, the electrical resistivity of the NbO2 thin films produced so far has been too low to achieve high on-off switching ratios. Here, we report on the structural, electrical, and optical characterization of single-crystalline NbO2 (001) thin films grown by pulsed laser deposition on MgF2 (001) substrates. An annealing step reduced the full width at half maximum of the NbO2 (004) x-ray Bragg reflection by one order of magnitude, while the electrical resistivity of the films increased by two orders of magnitude to about 1 kΩcm at room temperature. Temperature-dependent resistivity measurements of an annealed sample revealed that below 650 K, two deep-level defects with activation energies of 0.25 eV and 0.37 eV dominate the conduction, while above 650 K, intrinsic conduction prevails. Optical characterization by spectroscopic ellipsometry and by absorption measurements with the electric field vector of the incident light perpendicular to the c-axis of the distorted rutile structure indicates the onset of fundamental absorption at about 0.76 eV at room temperature, while at 4 K, the onset shifts to 0.85 eV. These optical transitions are interpreted to take place across the theoretically predicted indirect bandgap of distorted rutile NbO2.

Usually, HfO2 and ZrO2 are considered as twin-oxides that have to demonstrate similar reaction on their doping with group IV elements as well as stable tetragonal “high-k” phase. However, in most cases the films produced with different approaches were compared. In this work, both Ge doped HfO2 and Ge-doped ZrO2 films were prepared using the same equipment that allows the same Ge content in both materials to be achieved via monitoring of deposition conditions. Thus, the effect of Ge content and thermal treatment on optical and structural properties of these films was studied to obtain direct experimental confirmation whether the formation of corresponding solid solutions and their phase separation stimulated by thermal treatment is similar for both oxides. The films were grown on 6-inch Si wafers by confocal magnetron sputtering using the deposition unit with installed Ge, HfO2 and ZrO2 targets simultaneously. After the deposition, the wafers with the films were cut on smaller samples and rapid thermal annealing in nitrogen atmosphere was performed at 300-900ºC during 30 s. The samples were investigated by means of spectroscopic ellipsometry, Raman scattering, FTIR and TEM methods. As-deposited pure ZrO2 and Ge-ZrO2 films as well as those annealed at TA≤600°C were found to be amorphous and homogeneous. Annealing at higher TA stimulates a phase separation and a formation of Ge nanoclusters (Ge-ncs). They crystallize at TC=640-700°C showing the tendency to the TC decrease with Ge content rise. An appearance of tetragonal ZrO2 phase in Ge-rich films was observed at TC=680-700°C. Such behavior of ZrO2 host shows the possibility to form Ge-ncs in amorphous matrix at TA=640-680°C that offers success application of such films. Contrary to pure ZrO2 films, as-deposited pure HfO2 films were found to be crystalline. Their doping with [Ge]≥5at% reduces the degree of film crystallinity towards amorphous structure that was found to be stable for TA£600°C. At higher TA the formation of Ge-ncs and tetragonal HfO2 phase was detected. However, this latter was found to be formed at TC=600-670 °C, while the Ge-ncs crystallize at TC=700-800°C. Note that the formation of larger Ge-ncs in Ge-ZrO2 films than that in Ge-HfO2 ones at the same annealing conditions was observed. Obtained results support the theoretical consideration about stability of tetragonal “high-k” phases in annealed films. However, they show also the difference in the reaction of Ge-HfO2 and Ge-ZrO2 materials on thermal treatment followed by phase separation. Its mechanism will be discussed in details.

For most thin film structures, by changing the wavelength range to fit ellipsometric spectra, the values of the fitted parameters also change to a certain extent. The reason is that compared with the ellipsometric sensitivity many thin films are vertically non-uniform. In absorbing films with significant dispersion in the used wavelength range, the penetration depth of probing light can show large variations depending on the wavelength. Consequently, the value of a fitted parameter for a certain wavelength range is a weighted sum of structural information over different depth ranges corresponding to the different wavelengths. By changing the wavelength range, the range of penetration depths can be adjusted, and the fitted values can be plotted as a function of the probed depth range calculated directly from the determined or tabulated extinction coefficients. We demonstrate the results on deposited polycrystalline thin films. The advantage of this approach over the parameterization of structural properties as a function of depth is that the wavelength scan approach requires no parameterized depth distribution model for the vertical dependence of a layer property. The difference of the wavelength scan method and the vertical parameterization method is similar to the difference between the point-by-point and the parameterized dielectric function methods over the used wavelength range. The lateral structures strongly influence the ellipsometric response, as well. One of the most remarkable effects is when the lateral feature sizes approach the wavelength of the probing light. In this case the effective medium method is not valid any more, since scattering and depolarization occurs. By scanning the wavelength range, the limit wavelength of the onset of scattering can be found, and used for the determination of the corresponding critical lateral period length.

Indium-tin-oxide (ITO) thin films were prepared by reactive magnetron sputtering; their optical constants and thickness were determined by spectral reflectometry (SR) in the wavelength range from 400 nm to 800 nm and spectroscopic ellipsometry (SE) in the wavelength range from 191 nm to 1690 nm. A comparative evaluation of the measured data from SR and SE has been made using the same single layer optical model based on the Cauchy dispersion relation. The introduction of a surface roughness layer into the optical model considerably improved the fit quality during evaluation of SE data. Vertical inhomogeneity of the ITO thin films was assessed using a multilayer optical model describing porosity gradient and the three-layer optical model suggested by Jung [Y.S. Jung, Thin Solid Films 467, 36 (2004)] from the SE data. Copyright � 2014 Materials Research Society.

Bioinspired 1+2D nanoarchitectures inspired by the quasi-ordered structures occurring in photonic nano-architectures of biological origin, like for example butterfly scales, were produced by depositing a layer of SiO2 nanospheres (156 nm and 292 nm in diameter) on Si wafers, over which a regular multilayer composed from three alternating layers of SiO2 and TiO2 was deposited by physical vapor deposition. Flat multilayers were deposited in the same run on oxidized Si (324 nm SiO2 thickness) for comparison. Different types of disorder (in plane and out of plane) were purposefully allowed in the 1+2D nanoarchitectures. The positions of the specular reflection maxima for the flat multilayer and for the two different bioinspired nanoarchitectures were found to be similar. Additionally to this, the bioinspired nanoarchitectures exhibited angle independent diffuse reflection too, which was absent in the flat multilayer. Different model calculations were made to explain the specular and diffuse optical properties...

A novel technique for rare-earth doping in silica is developed with femtosecond laser plasma processing and record high concentration of erbium in silica/silica-on-silicon platforms to realize compact optical amplifiers for silicon photonics are achieved.

Titanate nanotubes were synthesized from TiO{sub 2} in alkaline medium by a conventional hydrothermal method (150 Degree-Sign C, 4.7 bar). To obtain hydrogen titanates, the as-prepared sodium titanates were treated with either HCl or H{sub 3}PO{sub 4} aqueous solutions. A simple synthesis procedure was devised for stable titanate nanotube sols without using any additives. These highly stable ethanolic sols can readily be used to prepare transparent titanate nanotube thin films of high quality. The resulting samples were studied by X-ray diffraction, N{sub 2}-sorption measurements, Raman spectroscopy, transmission and scanning electron microscopy, X-ray photoelectron spectroscopy and spectroscopic ellipsometry. The comparative results of using two kinds of acids shed light on the superior thermal stability of the H{sub 3}PO{sub 4}-treated titanate nanotubes (P-TNTs). X-ray photoelectron spectroscopy revealed that P-TNTs contains P in the near-surface region and the thermal stability was enhanced even at a low ({approx}0.5 at%) concentration of P. After calcination at 500 Degree-Sign C, the specific surface areas of the HCl- and H{sub 3}PO{sub 4}-treated samples were 153 and 244 m{sup 2} g{sup -1}, respectively. The effects of H{sub 3}PO{sub 4} treatment on the structure, morphology and porosity of titanate nanotubes are discussed. - Graphical Abstract: TEM picture (left) showsmore » P-TNTs with diameters about 5-6 nm. Inset shows a stable titanate nanotube sol illuminated by a 532 nm laser beam. Due to the presence of the nanoparticles the way of the light is visible in the sol. Cross sectional SEM picture (right) as well as ellipsometry revealed the formation of optical quality P-TNT films with thicknesses below 50 nm. Highlights: Black-Right-Pointing-Pointer H{sub 3}PO{sub 4} treatment led to TNTs with high surface area even after calcination at 500 Degree-Sign C. Black-Right-Pointing-Pointer H{sub 3}PO{sub 4}-treated TNTs preserved their nanotube morphology up to 500 Degree-Sign C. Black-Right-Pointing-Pointer Stable TNT sols can be prepared by the peptization of TNT gels. Black-Right-Pointing-Pointer High-transparency TNT thin films of high quality were fabricated.« less

Biodegradable polyesters such as poly(lactic-co-glycolic acid) copolymers (PLGA) are preferred materials for drug carrier systems although their surface hydrophobicity greatly limits their use in controlled drug delivery. PLGA thin films on a solid support blended with PEG-containing compound (Pluronic) were used as model systems to study the interfacial interactions with aqueous media. Degree of surface hydrophilization was assessed by wettability, and X-ray photoelectron spectroscopy (XPS) measurements. Protein adsorption behavior was investigated by in situ spectroscopic ellipsometry. The degree of protein adsorption showed a good correlation with the hydrophilicity, and surface composition. Unexpectedly, the layer thickness was found to have a great impact on the interfacial characteristics of the polymer films in the investigated regime (20-200 nm). Thick layers presented higher hydrophilicity and great resistance to protein adsorption. That special behavior was explained as the result of the swelling of the polymer film combined with the partial dissolution of Pluronic from the layer. This finding might promote the rational design of surface modified biocompatible nanoparticles.