Ray Reflectivity Research Articles

Nanoscale effect on the formation of the amorphous Ni silicide by rapid thermal annealing from crystalline and pre-amorphized silicon

The Ni monosilicide alloyed with Pt is widely used as contact material in advanced microelectronics devices and a good knowledge of silicide formation kinetics is required for the process control. In this work, the nature, and the growth kinetics of the first silicide obtained during the solid-state reaction between the Ni0.9Pt0.1 and the Si are studied for different pre amorphization implant (PAI) conditions as well as for a reference sample without PAI. Reactions between a 10 nm thick Ni0.9Pt0.1 film and Si (100) substrate are analyzed after several rapid thermal anneals (RTA). The nature of the first silicide is determined by Fourier Transform of TEM images and by chemical TEM-EDX analyses. The silicide growth behavior is determined by measuring the silicide thickness by X ray reflectivity (XRR) after the partial reaction induced by RTAs at different temperatures and times. To determine the growth law, the linear parabolic model is first considered but a nonlinear reactive diffusion model must be developed to accurately reproduce the experimental results. From this model, the effective diffusion coefficient as well as its activation energy were determined for the three samples with PAI and the reference sample without PAI. The influence of the driving force on the nonlinear diffusion for thin films is proved, and the impact of the amorphous substrate on the kinetics parameters is quantified and compared to the literature.

Determination of layer morphology of rough layers in organic light emitting diodes by X‐ray reflectivity

AbstractX‐ray reflectivity (XRR) has been proven to be a useful tool to investigate thin layers as well as buried interfaces in stacks built of very thin layers. Nevertheless, x‐ray reflectivity measurements are limited by the roughness of the layers and interfaces as the roughness destroys the interference structure, the so‐called Kiessig fringes. As investigations of thin layers in organic light emitting devices (OLEDs) are still subject of research and development, the focus of this paper is the investigation of a layer of indium tin oxide (ITO) which serves as transparent anode material in OLEDs. Due to the fabrication process, ITO shows rough surface structures, so‐called spikes, hindering the determination of the ITO layer thickness and roughness in XRR measurements. In this paper, it is theoretically and experimentally proven that a smoothing layer on the ITO enables the determination of the buried ITO layer thickness and roughness as well as the density of the spikes. Furthermore, a sputtered aluminum layer (e.g. cathode material) showing spikes in atomic force microscopy covered with a smoothing layer reveals Kiessig fringes allowing the determination of the density of buried spikes. In general, it is shown that a smoothing layer on a rough surface enhances the sensitivity of x‐ray reflectivity measurements.

Curvature modulated structural and magnetic properties of CoO/Co thin films deposited onto 2-D nanosphere array

The importance and applications of nanoscale magnetic storage devices has been of current interest owing to the extensive research interest in magnetic nanocaps. Continuing their research trend, we have attempted to synthesize and characterize an important isolated magnetic nanocaps system constituting Co and its oxide. CoO/Co thin films were deposited onto self-assembled arrays of polystyrene (PS) nanospheres (∼600 nm diameter) under ultra-high vacuum environment using electron beam evaporation technique. The magnetic and structural properties of these nanostructures were then compared with those of simultaneously deposited films on bare Si substrate (referred to as reference film). The studied film and the reference film were grown in polycrystalline manner as observed from X-ray diffraction measurements while their roughnesses as observed from X- ray reflectivity were quite different. X- ray reflectivity showed that for the reference films well defined Kiessig oscillations appeared suggesting low roughness in the deposited films, while the films on PS followed the curvature of underlying nanospheres and thus have very high roughness resulting in the disappearance of Kiessig oscillations. Magnetic measurements exhibited a drastically high coercivity when the substrate was changed from flat (Si) to curved one (PS). As the film thickness was increased, the coercivity first showed a slight decrement (4.92 kA/m) and beyond 40 nm film thickness, it showed some enhancement (14.2 kA/m). The exchange bias measurements also showed interesting results with variation in film thickness. Co 10 nm film deposited on PS showed negative exchange bias of −127 kA/m which decreased to −26 kA/m in 100 nm film. The overall results were explained by correlating the magnetic and microstructural properties of the thin films as a function of thickness.

Structure and morphology of bovine serum albumin–lysozyme (BSA–Lys) complex films at air–water interface

The heteroprotein complex formed between the two globular proteins, bovine serum albumin and lysozyme was studied at the air–water interface by varying the subphase pH condition (pH ≈ 4.0–12.0). The surface pressure–mean molecular area isotherms of bovine serum albumin–lysozyme complex monolayers showed that relatively lower value of area per molecule was obtained at pH ≈ 9.2 in contrast to the other subphase pH conditions. Stability of the complex monolayers were analyzed from the normalized molecular area–time curves, which validated the formation of a relatively more stable film at pH ≈ 9.2. The in – situ study of the complex films were explored from Brewster angle microscopy and the corresponding images showed the evolution of elongated and compact circular domains at pH ≈ 7.0 and 9.2 respectively, at a higher surface pressure of 18 mN/m, while mostly homogenous films were visible at all the other pH conditions. The complex films were transferred from the water subphase on to the silicon substrates at a surface pressure of 18 mN/m for further study. The out–of–plane structure and in–plane morphology were obtained from X–ray reflectivity and atomic force microscopy analysis respectively, which showed the formation of a relatively thicker film deposited at pH ≈ 9.2. This unique pH value, i.e., pH ≈ 9.2, which is located in between the isoelectric point of bovine serum albumin and lysozyme, is the preferred pH condition for complex formation through electrostatic attraction of the two protein molecules. The biofilm of this stable protein complex formed at the air–water interface may have potential applications in thin film technology. • Bovine serum albumin–lysozyme complex films are formed on water surface. • Lower value of area per molecule for initial rising of pressure is obtained at pH ≈ 9.2. • Mostly elongated and compact circular domains are found at pH ≈ 7.0 to 9.2. • Relatively thicker film is formed at pH ≈ 9.2 where complex formation is maximum. • Stability of such complex film is maximum at pH ≈ 9.2.

Refined extreme ultraviolet mask stack model.

A refined model of an extreme ultraviolet (EUV) mask stack consisting of the Mo/Si multilayer coated by a Ru protective layer and a TaBN/TaBO absorber layer was developed to facilitate accurate simulations of EUV mask performance for high-NA EUV photo-lithography (EUVL) imaging. The model is derived by combined analysis of the measured EUV and x ray reflectivity of an industry-representative mask blank. These two sets of measurements were analyzed using a combined free-form analysis procedure that delivers high-resolution x ray and EUV optical constant depth profiles based on self-adapted sets of sublayers as thin as 0.25 nm providing a more accurate description of the reflectivity than obtained from only EUV reflectivity. "Free-form analysis" means that the shape of the layer interfaces in the model is determined experimentally and is not given a priori by the structure model. To reduce the numerical effort for EUV imaging simulations, a low-resolution model of the multilayer and absorber stack with sublayer thicknesses larger than 2 nm, that fits to only the EUV reflectance, was derived from the high-resolution model. Rigorous high-NA EUVL simulations were done to compare the performance of the new model to our previous work [Proc. SPIE8886, 88860B (2013)PSISDG0277-786X10.1117/12.2030663].

Effects of the Potassium Titanate Functional Filler Types on the Thermal Protection Performance of Heat Resistant Ablative Coated Fabrics

Considering sub-micron potassium titanate whiskers (BX-101), nanoscale potassium titanate whiskers (AX-301), sub-micron potassium titanate whiskers (AX-316) and high strength potassium titanate crystal (AX-319) as functional fillers, heat resistant ablative coated fabrics which have high radiant heat reflectivity were prepared. The effect of the type of functional filler on the thermal protection performance of heat resistant ablative coated fabrics was mainly discussed. Research showed that the microstructure of potassium titanate functional filler had a significant impact on the radiant heat reflectivity and thermal insulation performance of the prepared coated fabric. The coated fabric which took nanoscale potassium titanate whiskers (AX-301) with a minimum diameter and greater length-diameter ratio as functional filler has the highest thermal reflectivity and the best insulation property. Heat ray reflectivity of potassium titanate coated fabrics had positive correlation with their crystallinities. The higher the coated fabric crystallinity was, the greater the heat ray reflectivity. Thermogravimetric analysis results showed that after adding four kinds of potassium titanate fillers, the thermal stability of the prepared coated fabrics was enhanced, and the nanoscale potassium titanate whiskers (AX-301) coated fabrics had the best thermal stability.

Design, fabrication and characterization of TiO2-SiO2 multilayer with tailored color glazing for thermal solar collectors

The paper reports on the design, fabrication, and characterization of a 7-layer SiO2-TiO2 colored coating for solar thermal façades. A combined theoretical and experimental approach was employed for designing the colored coating by using optical modeling and individual layers characterization, targeting for high solar transmittance and pronounced yellow-green reflected color. SiO2-TiO2 multilayers were deposited on glass and silicon substrates by using the reactive RF magnetron sputtering of stoichiometric oxide targets. The coatings were investigated by UV–Vis spectrophotometric methods for optical properties, surface profilometry, X ray reflectivity and SEM for the thickness of individual layers composing the multilayer and AFM for surface roughness. Hardness H, reduced modulus Er, and adhesion were determined by nanoindentation and scratch tests. The deposited colored glazing exhibited a prominent reflectivity peak of ~54% centered at 574nm, specific visible reflectance of ~45.39% and an integrated solar transmittance of about 80.3%. Its optical properties were preserved in the ambient for temperatures up to 200°C and the color was not modified for incidence angles up to 45°. H values of 7.18GPa, Er of 88.31GPa, H/Er ratio of about 0.081 and good scratch resistance up to 13mN were measured.

Annealing temperature dependence of structural and electrical properties of Sb2Te and GeInSbTe thin films

In this paper, we report on annealing temperature dependence of structural and electrical properties of the Sb2Te and GeInSbTe thin films. X-ray diffraction shows an amorphous phase for the as-deposited films, while single crystalline hexagonal Sb2Te phase for Sb2Te films and mixed crystalline phases (rhombohedral Sb, cubic In2Te3 and hexagonal Sb2Te) for the GeInSbTe films annealed above 150 °C. X ray reflectivity and room temperature resistivity measurements of the annealed films revealed the higher thermal stability of the GeInSbTe than Sb2Te thin films at higher annealing temperatures. The electrical and optical measurements showed the minor role of the grain boundary scattering to the charge transport in both type of films. However, increase in annealing temperature lead to large increase in mobility of charge carriers in p-type films. This mobility improvement can be easily related to increase in scattering time of charge carriers attributed to better crystallization and thereby reduced scattering. The annealing of the Sb2Te films above 225 °C results in partial evaporation of the material and increase in resistivity.

Effect of deposition technique of Ni on the perpendicular magnetic anisotropy in Co/Ni multilayers

The perpendicular magnetic anisotropy (PMA) of Si/Pt 3.5/(Co 0.3/Ni 0.6)n /Co 0.3/ Pt 3 (all thicknesses are nm) multilayers were investigated for two different sample sets by using ferromagnetic resonance (FMR) and magnetooptic Kerr effect (MOKE) techniques. In the first sample set all layers (buffer, cap, Co and Ni) were grown by magnetron sputtering technique while in the second sample set Ni sub-layers were grown by molecular beam epitaxy (MBE) at high vacuum. Apart from deposition technique of Ni, all other parameters like thicknesses and growth rates of each layers are same for both sample sets. Multilayers in these two sample sets display PMA in the as grown state until a certain value of bilayer repetition (n) and the strength of PMA decreases with increasing n. Magnetic easy axis's of the multilayered samples switched from film normal to the film plane when n is 9 and 5 for the first and second sample sets, respectively. The reason for that, PMA was decreased due to increasing roughness with increasing n. This was confirmed by X Ray Reflectivity (XRR) measurements for both sample sets. Moreover, in the first sample set coercive field values are smaller than the second sample set, which means magnetic anisotropy is lower than the latter one. This stronger PMA is arising due to existence of stronger Pt (111) and Co/Ni (111) textures in the second sample set.

APPLICATION OF IN SITU X–RAY REFLECTIVITY FOR DETERMINING PARAMETERS OF NANOSCALE SILICON FILMS

At present special importance attaches monitoring methods to measure the parameters of film structures directly during their formation — in situ methods. Application of these methods helps to ensure a film with desired characteristics, allowing quickly adjust process conditions. The paper describes the possibilities of the in situ X -ray reflectivity to determine the parameters of nanoscale films in real time of their formation. Experimental results on the magnetron deposition of nanoscale Si films and other materials on silicon substrates are presented.

Structures and Polymorphic Transitions of Triacylglycerols, SOS and POS Thin Films: A Study on Temperature Dependence

AbstractX‐ray reflectivity (XR) and scanning probe microscopy (SPM) were used to examine the structures, polymorphic transitions, and surface morphologies of triacylglycerol (TAG), 1,3‐stearin‐2‐olein (SOS) and 1‐palmitin‐2‐olein‐3‐stearin (POS) thin films supported on Si substrates. The structural parameters: thickness, electron density, and surface/interface roughnesses of TAG thin films were determined by the nonlinear least‐squares regression of XR profiles to reveal their temperature dependences. In the lower temperature regimes, we observed Bragg peaks without significant interference fringe patterns in the XR profiles. SPM at room temperature displayed isolated islands on TAG thin films with surface undulations. Whereas in the higher temperature regimes in which the Bragg peaks disappeared, the interference fringe patterns became prominent. The analyses of the XR profiles indicated the structural change in thin films from three layers to single layer on Si substrates with increasing temperature. However, the temperatures at which the structural change occurred were obviously different between SOS and POS thin films.

Elucidating the Molecular Details of Phosphatidylserine Membrane Recognition in Immune Response

The immune system recognizes a vast array of chemical signatures as antigens although historically most research has focused more exclusively on protein/protein recognition. More recently it has been appreciated that lipid membranes can also provide important immunological signals as demonstrated in both phosphatidylserine (PS) recognition in apoptotic cell clearance and transient PS exposure in T Cell activation. Despite the clear immunological importance of PS exposure and recognition, there remain very few molecular details regarding the mechanisms of PS membrane recognition. Even more fundamentally, it remains unclear if all PS exposing membranes are immunologically equal or if there exists a sensitivity to additional membrane properties beyond simply the presence or absence of PS. To address this gap in our understanding we have made use of a novel combination of biophysical and biochemical techniques to elucidate the molecular mechanisms by which Tim4 (an immune related PS receptor) recognizes PS containing membranes. Tryptophan fluorescence binding assays have revealed that Tim4 binding is sensitive to membrane PS composition suggesting that there is more to the story than a single PS to single protein interaction. By utilizing a combination of x ray reflectivity measurements to determine membrane bound protein orientation and depth of penetration, as well as molecular dynamics simulations to support the experimental results, we have developed a protein/membrane binding model that provides structural evidence to explain the unique complexities of Tim4 mediated PS membrane recognition. Most significantly, these results provide a standard against which other immunologically related PS receptors can be compared, thereby allowing us to begin to address the more fundamental question of just how important lipid membrane recognition is for our bodies' immunological defense mechanisms.

Study Of Co90Fe10 Magnetic thin Film On MgO Substrate Using In-situ Moke Technique

Growth behavior of Co90Fe10 film on MgO substrate has been studied. In-situ magneto-optical Kerr effect measurements have been used to study evolution of the magnetic properties of the film with increasing film thickness. Extrapolating linear variation of Kerr signal with film thickness provides the evidence of a magnetic dead layer of thickness 2.2 nm at the interface with MgO substrate. X- ray reflectivity fitting confirms presence of an intermixed layer of about 2 nm.

Study of focused-ion-beam–induced structural and compositional modifications in nanoscale bilayer systems by combined grazing incidence x ray reflectivity and fluorescence

A detailed analysis of the structural and compositional changes in NiFe/Au bilayers induced by a focused ion beam (FIB) is presented. NiFe/Au bilayers with different thickness were irradiated with a focused 30 keV Ga+ ion beam, and the evaluation of the individual layers and interfaces were investigated systematically as a function of a broad range of irradiation fluence using grazing incidence x ray reflectivity (GIXRR) and angular dependent x ray fluorescence (ADXRF) techniques carried out at synchrotron radiation sources. Experimental data were collected from 1.3 mm × 4.5 mm structures, and irradiation of such a broad areas with a 100-nm-wide focused ion beam is a challenging task. Two irradiation regimes were identified: For Ga+ fluences < 15.6 × 1014 ion/cm2 (low dose regime), the main influence of the focused ion beam is on the interface and, beyond this dose (high dose regime), sputtering effects and ion implantation becomes significant, eventually causing amorphization of the bilayer system. The broadening of the NiFe/Au interface occurs even at the lowest dose, and above a critical fluence (Φ = 1.56 × 1014 ion/cm2) can be represented by an interfacial-intermixed layer (NixFeyAu(1-x-y); x = 0.5-0.6, y = 0.1-0.15) formed between the NiFe and Au layers. The thickness of this layer increases with irradiation fluence in the low dose regime. A linear relationship is found between the squared intermixing length and irradiation fluence, indicating that FIB-induced mixing is diffusion controlled. The ballistic model fails to describe FIB-induced intermixing, indicating that thermodynamical factors, which might be originated from FIB specific features, should be taken into account. Despite the complexity of the chemical and structural formation, good agreement between the experiment and theory highlights the functionality of the combined GIXRR and ADXRF techniques for studying intermixing in high resolution.

Densification of chemical vapor deposition silicon dioxide film using oxygen radical oxidation

Silicon dioxide (SiO2) films formed by chemical vapor deposition (CVD) were treated with oxygen radical oxidation using Ar/O2 plasma excited by microwave. The mass density depth profiles, carrier trap densities, and current-voltage characteristics of the radical-oxidized CVD-SiO2 films were investigated. The mass density depth profiles were estimated with x ray reflectivity measurement using synchrotron radiation of SPring-8. The carrier trap densities were estimated with x ray photoelectron spectroscopy time-dependent measurement. The mass densities of the radical-oxidized CVD-SiO2 films were increased near the SiO2 surface. The densities of the carrier trap centers in these films were decreased. The leakage currents of the metal-oxide-semiconductor capacitors fabricated by using these films were reduced. It is probable that the insulation properties of the CVD-SiO2 film are improved by the increase in the mass density and the decrease in the carrier trap density caused by the restoration of the Si-O network with the radical oxidation.

On determination of properties of ultrathin and very thin silicon oxide layers by FTIR and X - ray reflectivity

ABSTRACTWe analyze properties of ultra-thin SiO2 + very thin SiOx double layer structure formed on high-doped n-type Si (100) wafers using FTIR, X-ray reflectivity and AFM methods. The observed absorption band around 1230 cm−1 is attributed to the longitudinal optical mode of SiOx precipitates incorporated in silicon matrix. In particular, the corresponding peak positions indicate that there are precipitates of SiOx with x >1.8. The absorption band around 1070 cm−1 is attributed to the Si–O–Si stretching bond. This position is characteristic for stoichiometric SiO2. From the results it can be concluded that differently shaped particles co-exist in the samples. This assumption is supported by the oxide density measurements performed by FTIR and X-ray reflectivity. We determined density of oxide layers, roughness of corresponding interfaces, and surface roughness by the X-ray reflectivity. The obtained values were compared with those determined by FTIR and AFM. Additionally, we present the results of multifractal analysis on a complete set of six samples.

Ray tracing and reflectivity measurements in nematic hybrid cells

We propose an experimental procedure to show that an optical beam may propagate in a planar-homeotropic hybrid nematic crystal cell for incidence angles i larger than the critical one. Its effect on the reflectance coefficient R as a function of i is accounted for by using total internal reflection techniques. We model the propagation of a linearly polarized Gaussian beam of finite diameter through the cell and the reflectance curves R vs. i are calculated theoretically in the total internal reflection regime by using an analytical description. The experimental procedure, cell assembling and methodology are designed so that there is reasonable consistency with the model assumptions. In the optical limit approximation this model allows us to calculate analytically the phase shift, the trajectory and the reflectivity curves of a beam traveling with an extraordinary polarization (P-polarization) inside the cell. Since only some parts of the reflected beams will interfere, Berreman’s method is not suitable for the physical situation considered. The possibility of leakage through the tunneling effect across the cell is also considered and estimated quantitatively. The comparison between the theoretical results and the experimental data shows good agreement between our experimental results and the theoretical curves R vs. i. We compare our results with other measurements reported in the literature and find that the behavior of the reflectance curve is highly affected by the cell thickness-beam waist ratio. The values of this parameter can produce different behaviors of the reflectivity measurements. The analysis of the model predictions and experimental results suggest a possible interpretation of the physical origin of the reflectivity curves and give a qualitative insight into the phenomena behind the total internal reflection regime. Finally, we emphasize the limitations and advantages of the model and of the experimental results presented.

ZrC Thin Films Grown by Pulsed Laser Deposition

AbstractZrC thin films were grown on Si substrates by the pulsed laser deposition (PLD) technique. X- ray photoelectron spectroscopy, x-ray diffraction and reflectivity, variable angle spectroscopic ellipsometry, and four point probe measurements were used to investigate the composition, density, thickness, surface morphology, optical and electrical properties of the grown structures. It has been found that crystalline films could be grown only by using fluences above 6 J/cm2 and substrate temperatures in excess of 500 °C. For a fluence of 10 J/cm2 and a substrate temperature of 700 °C, highly (100)-textured ZrC films exhibiting a cubic structure (a=0.469 nm) and a density of 6.7 g/cm3 were deposited. The use of a low-pressure atmosphere of C2H2 had a beneficial effect on crystallinity and stoichiometry of the films. All films contained high levels of oxygen contamination, especially in the surface region, because of the rather reactive nature of Zr atoms.

THE USE OF SEISMIC MODELLING WHEN DESIGNING ONSHORE 3D AND 4D SURVEYS

There are many parameters to consider when designing acquisition geometries for onshore 3D and 4D seismic surveys. Plots of attributes, such as fold and offset distribution, are necessary in the design process but they are not always sufficient. For instance, they fail to predict the bandwidth and signal-to-noise ratios associated with various candidate designs. Properly crafted synthetic seismograms, however, can be used to yield these predictions. Downhole and surface seismic measurements are needed to drive this. The downhole measurements— primarily well logs—are used to create stratified earth models for input to ray trace calculations and reflectivity modelling. The surface seismic measurements-including finely sampled noise tests-are needed to derive intraarray statics distributions, ambient noise distributions, ground roll characterisations and other descriptions. These empower modelling routines to contaminate and perturb the synthetic signal in prospect-specific fashions. Results from Middle East studies typically show that survey designs that are best suited for addressing one particular issue might not be best for addressing others. Incorporation of digital group forming algorithms within the modelling process allows prediction of results that would be obtained from new high channel-count, singlesensor systems.

Unsuccessful initial search for a midmantle chemical boundary with seismic arrays

Compositional layering of the midmantle has been proposed to account for seismic and geochemical patterns [van der Hilst and Karason, 1999], and inferred radiogenic heat source concentrations [Kellogg et al., 1999]. Compositional layering would require thermal boundary layers both above and below an interface. We construct a minimal 1‐D model of a mid‐mantle boundary consistent with the observed nearly adiabatic compressional velocity structure [Dziewonski and Anderson, 1981] and the proposed high heat flow from the lower mantle [Albarede and van der Hilst, 1999; Kellogg et al., 1999]. Ray tracing and reflectivity synthetic seismograms show that a distinct triplication is predicted for short‐period P waves. Although topography on a boundary would cause uncertainty in the strength and the range of the triplication, many clear observations would be expected. We examine data from the US West Coast regional networks in the most likely distance range of 60° to 70° for a 1770‐km‐depth boundary, and find no evidence for P wave triplications.