Growth Of Anodic Oxide Films Research Articles

Isotopic Tracer Study of Initiation of Porosity in Anodic Alumina Formed in Chromic Acid.

In this paper, we focused on the initiation of porosity in the anodic alumina under galvanostatic conditions in chromic acid, using an 18O isotope tracer. The general concept of the initiation and growth of porous anodic oxide films on metals has undergone constant development over many years. A mechanism of viscous flow of the oxide from the barrier layer to the pore walls has recently been proposed. In this work, two types of pre-formed oxide films were analysed: pure Al2O3 formed in chromic acid, and a film containing As ions formed in a sodium arsenate solution. Both were anodized in chromic acid for several different time durations. Both pre-formed films contained the oxygen isotope 18O. The locations and quantities of 18O and As were analysed by means of ion accelerator-based methods supported by transmission electron microscopy. The significant difference observed between the two oxide films is in the 18O distribution following the second step of anodization, when compared with galvanostatic anodization in phosphoric or sulfuric acid reported in previous works. From the current experiment, it is evident that a small amount of As in the pre-formed barrier layer appears to alter the ionic conductivity of the film; thus, somehow, it inhibits the movement of oxygen ions ahead of advancing pores during anodization in chromic acid. However, anodising pure alumina film under these conditions does not enhance oxygen movement within the oxide layer. In addition, the tracer stays in the outer part of the growing porous oxide film. A lower-than-expected value for pure alumina enrichment in 18O in the pre-formed films suggests, indirectly, that the pre-formed film may contain hydrogen species, as well as trapped electrons, since no Cr is detected. This may lead to the presence of space charge distribution, which has a dual effect: it both retards the ejection of Al3+ ions and prevents O2- ions from migrating inward. Thus, the negative- and positive-charge distributions might play a role in the initiation of pores via a flow mechanism.

Electro-chemo-mechanical properties of anodic oxide (passive) films formed on Cu, Ni and Fe

Abstract Electro-chemo-mechanical properties of anodic oxide (passive) films formed on metals have been reviewed focusing on the results of stress variations caused by anodic oxidation of Cu, Ni, and Fe thin film electrodes in deaerated pH 8.4 borate buffer solution at 25 °C. The surface stress varies toward compressive direction due to adsorption of OH on Cu from aqueous solution as well as adsorption of oxygen on metals from gas phase. The stresses are generated with the growth of three-dimensional anodic oxide films on metals. The magnitude and sign (tensile or compressive) of the intrinsic film stress were determined by taking the residual stress of the substrate and the dielectrostriction into consideration. The tensile or compressive intrinsic film stress depends on p-type or n-type semiconductive properties of the anodic oxide films, which is explained in terms of the void formation or oxide formation in the metal side at the metal/film interface. Furthermore, the stress variation toward compressive direction during cathodic reduction of the anodic oxide films is explained in terms of the volume expansion due to the formation of intermediate species.

Element Distribution in Porous Ga Oxide Obtained by Anodizing Ga in Phosphoric Acid

A STEM/EDS study of a porous Ga oxide film formed by an anodization process was conducted in this study to examine the crystalline structure of the film and the elemental distribution in the oxide film before and after heat treatment. The as-formed anodic film with a morphology resembling the well-known porous anodic Al oxide film was amorphous, crystallizing after heat treatment at 600 °C without changing the morphology and elemental distribution. The EDS elemental maps disclosed the duplex nature of the pore wall oxide; the phosphate anion was contaminated in the outer oxide layer next to the pores, and the inner layer consisted of relatively pure Ga oxide, practically free from phosphate. The similarity of morphology and elemental distributions between the porous anodic Al and Ga oxides suggests that the growth of both anodic oxide films proceeds under the same mechanism. In addition, crystallized porous Ga oxides are expected to be applied to fabricate various functional devices requiring geometrically controlled semiconductor nanohole arrays, such as devices for hydrogen formation.

The effect of electrolyte temperature on the growth, morphology, and properties of porous anodic tin oxide films

The effect of electrolyte temperature on the anodic formation of nanoporous tin oxide layers, their morphology and properties was studied in detail. Electrochemical synthesis of SnOx films was carried out in both acidic (H2C2O4) and alkaline (NaOH) electrolytes at various potentials. Differences in morphological features of as-generated films and the kinetics of their formation were carefully investigated from FE-SEM images. The effect of anodizing temperature was successfully verified revealing its undeniable importance when designing the anodization procedure. For instance, both in acidic and alkaline electrolytes, applying too low temperatures results in formation of cracked oxide layers with the least open pores or compact surface, while too high temperatures (≥40 °C) leads to obtaining films with clogged pores due to the partial etching of the material by the electrolyte. Anodizing temperature was also found to be a crucial parameter responsible for the type of morphology of the synthesized materials (compact or porous layers or even crater-like hierarchical structures) when the process is carried out at higher potentials (here 9 V). Finally, we have proved that the impact of electrolyte temperature on the crystallinity of the anodic tin oxide layers is negligible, whereas the photoelectrochemical activity is significantly influenced due to the tight relation with the morphology of as-synthesized materials.

Микро/наноструктурированные анодно-оксидные покрытия на монокристаллах ниобия

The paper discusses the results of studying of the growth of anodic oxide films (AOFs) by anodizing of niobium single crystals in a fluorine-containing electrolyte (aqueous solution of 10 % H2SO4 + 1 % HF), as well as the effect of saturation of the niobium surface with oxygen on the structure and properties of AOF.

Dynamic evolution of structure–activity of anode on lead release and overpotential change in zinc electrowinning

Anode is the main source of lead (Pb) contaminations in zinc (Zn) electrowinning, also greatly affects the energy consumption due to the high dependence of overpotential for the oxygen evolution reaction (OER) on anodic oxide film (AOF). Herein, continuous tracking of the Pb-based anode was conducted for 60 d to reveal the evolution of structure–activity relationship with the growth of AOF. Results showed that three competitive reactions including Pb corrosion reaction, Mn2+ oxidation reaction and OER on the anode had complex interactive influences on the characteristic evolution of AOF as time increased periodically. With the continuous formation and coverage of AOF (PbSO4/ PbO2/MnO2) during the early 15 d, the Pb-based anode exhibited obvious self-protection effects of less Pb released and less MnO2-containing waste generated, which were attributed to the physically blocking effect of AOF against the excessive exposure of Pb surface by the dense and reticular structure and the electrochemically inhibiting effect for the Mn2+ oxidation by abundant Mn3+ and oxygen vacancy (Ov) of MnO2. Density-Functional-Theory (DFT) calculation indicated that the PbSO4 with higher energy band gap (4.19 eV) and lower formation energy (-1.51 eV atom−1) was prone to form and accumulate, which caused increasing voltage and accelerating release of Pb in the late stage due to over-thickness and structure instability of AOF. This study can provide inspiration for the future design or reconstruction of highly effective AOF structure to synergistically reduce pollution generation of Pb and anode slime and decrease OER overpotential.

The effect of argon ion etching treatments on anodic oxide film growth and the electrochemical properties of tantalum

The aim of present paper was to improve the anticorrosive properties of tantalum. Herein, the formation of tantalum oxide film via an argon ion etching pretreatment step and anodic oxidation is reported. The surface morphologies of etched tantalum investigated using scanning electron microscopy. The composition and corrosion resistance of the tantalum oxide film was characterized using X-ray photoelectron spectroscopy and an electrochemical workstation, respectively. The effects of vacancy defects and O atom adsorption on the on Ta (110), (200) and (211) surfaces have been investigated based on first-principles calculations to simulate the etched surface. The experimental results showed that the etched tantalum had a relatively clean surface with fine pores, which promoted the formation of an anodization film to 131.53 nm. The corrosion resistance of tantalum was obviously improved by etching followed by anodization, and the highest corrosion potential of 0.133 V and relatively low corrosion current density of 1.016 μA cm–2 were observed. Furthermore, first principle calculations revealed that vacancy defects increased the activity of the tantalum surface and enhanced the adsorption of oxygen, thereby promoting the formation of oxide film. Among all these defective surfaces, O atom adsorption on the (110) surface exhibited relatively a high adsorption energy of −519.66 kJ/mol and charge transfer of −1.310 e, followed by O atoms on the (200) and (211) surfaces showing an enhanced adsorption energy of −487.33 and −494.27 kJ/mol, and charge transfer of 1.255 and 1.194 |e |, respectively. This work demonstrated an effective argon ion etching pretreatment step to promote the formation of oxide film, which improved the corrosion behavior of tantalum.

Anodization of titanium in reduced graphene oxide-citric acid electrolyte

Crystalline oxide film coated pure titanium has been fabricated by anodizing in citric acid (C6H8O7) solution containing reduced graphene oxide (RGO) electrolyte. The voltages ranging from 10 to 90 V were used during the anodization process. The results demonstrate that the growth rate and thickness of barrier layer decrease with the increase of applied voltage. The anodic oxide film mainly consists of anatase TiO2. The sample anodized at 50 V has the highest crystallinity, which is caused by the high lattice oxygen (OL2−) content on the sample surface. When the applied voltages are 10–50 V, the samples exhibit excellent corrosion resistances.Combiningmicrostructure characteristics, it is concluded that the growth of anodic oxide film in the uniformly mixed C6H8O7 and RGO electrolyte is more favorable under low voltages 10–50 V.

Similarity and Difference in the Plating Pretreatment for Mg and Al Alloys

Mg and Al are light-weight less-noble metals and are expected as a key material for potential applications in the fields of transportation to save energy. Especially for Mg alloys, the addition of corrosion resistance is essentially important for outside use. Plating has been used to provide various functionalities to metals such as good appearance, wear resistance, sliding performance, wettability or repellency, and corrosion resistance. Both Mg and Al have similar difficulty in the plating process because the surface of metals is always covered with the passive film (Al) or corrosion film (Mg) that prevents the plating process as the electron transfer and the metal-to-metal bonding. In the plating process, therefore, such surface films should be removed before or during the treatment process. The zincate pretreatment has been applied to these metals in which the surface was replaced with Zn layer that provides a good substrate for the subsequent plating process. In the zincate process, Al or Mg surface is dissolved, and Zn is deposited simultaneously by the substitution reaction in the zincate bath containing Zn(II) ions to cover the substrate. In the case of Al, this substitution reaction proceeds rapidly, and the substrate surface is almost completely covered with Zn layer. In the case of Mg, however, the coverage with Zn is more important than Al because Mg can be rapidly dissolved in the zincating bath. Excess dissolution of Mg substrate causes the undesired poor adhesion of the plating film to the substrate. Therefore, the zincating condition for Mg alloys should be optimized to take a balance between the Mg dissolution and the substitutional deposition of Zn. On the other hand, a complicated structure composed of the area where dense pillars are formed and a bank surrounding this area is sometimes found on AZ31 alloy after the zincate treatment, as shown in Fig. 1. Such a structure is formed by the combination of the continuous dissolution of Mg substrate and the local deposition of Zn that protects Mg substrate from the dissolution. A bank is formed on the grain boundary of AZ31 surface, where initial Zn deposition preferentially proceeded. Such micro-structure can be compared with a well-known ordered porous alumina film formed on Al by the dynamic process of the continuous growth of anodic oxide film and mass transportation of ions in the growing film. Figure 1

Anodisation of aluminium alloy AA7075 – Influence of intermetallic particles on anodic oxide growth

Microstructure and Volta-potential analyses were conducted to characterise intermetallic-particles (IMPs) in AA7075-T5. EIS and AFM were applied under operando-conditions to investigate anodisation processes. IMPs have pronounced influence on the growth of anodic aluminium oxide (AAO) films resulting in low charge-transfer resistance. Cu-bearing constituents show cathodic-character, whereas Mg2Si and MgZn2 particles show anodic-character. During anodisation, Al7Cu2Fe remain stable with peripheral-dissolution around boundary. De-alloying of S-phase particles leads to the detachment. Mg2Si undergoes de-alloying at low potential, and re-passivation at high potential. MgZn2 dissolves entirely upon anodization. Localised-dissolution in large-IMPs boundaries or nanometre-sized IMPs facilitates bubble evolution, confirming local breakdown of barrier-layer.

Hard anodization of copper in potassium carbonate aqueous solution

Anodization of copper was performed in potassium carbonate aqueous solution. Registered current curves allowed to claim that the anodic oxide film growth occurs according to the hard anodization mechanism. Detailed investigation of the anodization products revealed formation of nanowires made of crystalline phases including various oxides and complex phases containing hydroxyl anions and carbonates. It was found that the diameter of the nanowires grows linearly with the anodizing voltage between 30 (10 V) and 47 nm (50 V). The major, crystalline components of the anodically grown nanowires were: paramelaconite (Cu4O3), cuprite (Cu2O) and tenorite (CuO). The presence of malachite, Cu2CO3(OH)2 was also reported and meant effective incorporation of the electrolyte anions into the growing anodic film.

Determining the electric-field strength in a passive film via photo-induced electric fields

The nature of the electric-field strength in the passive film on tungsten is explored using photo-electrochemical techniques. A theoretical expression for the photo-stimulated growth of the film has been derived. Rotating ring-disk electrode (RRDE) experiments indicate that photo-corrosion of a tungsten electrode is negligible under super-band gap light illumination. XPS results show that tungsten is in the maximum possible oxidation state (VI) in the film and hence no higher oxidation state is available. The photo-stimulated transient film growth of tungsten in pH 8.5 ± 0.1 boric-borax buffer was recorded as a function of film formation potential (1 VSCE, 2 VSCE, 3 VSCE, 4 VSCE, 5 VSCE, 6 VSCE) and light intensities (50, 200, 1000 mW/cm2). Steady state passive film thickness measurements of the passive film on tungsten indicate that super band gap, UV light suppresses the electric field in the barrier layer, and hence stimulates anodic oxide film growth. The data obtained in this study demonstrate that the electric field strength in the steady state is independent of the applied potential and film thickness, as postulated in the Point Defect Model.

Integration of electrochemical and synchrotron-based X-ray techniques for in-situ investigation of aluminum anodization

Anodization of aluminum alloys AA 6082 and AA 7075 was investigated in-situ with integrated electrochemical and synchrotron-based X-ray reflectivity (XRR) methods providing complementary information about the anodic processes taking place on the alloys. The stepwise potentiostatic polarization measurements reveal dynamic processes of the anodic oxide formation and dissolution, and the following electrochemical impedance spectroscopy measurements detect the break of the native oxide and the growth of typical two-layer anodic oxide film, while the XRR measurements show the growth of entire anodic oxide film whose thickness increases linearly with the increasing applied potential. The results indicate that while a stable anodic oxide can be formed on the both alloys with a similar growth factor, AA 7075 shows a thinner thickness of the barrier layer and a lower resistance of the oxide film. The electrochemical results suggest both localized and uniform anodic dissolution processes, which are more pronounced on AA 7075, demonstrating the effect of alloying elements on the growth of anodic oxides.

Flow Instability Mechanism for Formation of Self-Ordered Porous Anodic Oxide Films

Experimental studies have suggested that oxide flow plays an important role in the growth of porous anodic oxide films on reactive metals. Here a mathematical model for anodic oxide formation is presented that includes viscous flow of oxide, along with high-field ionic conduction and interfacial oxygen transfer and metal dissolution reactions. Flow is driven by near-surface compressive stress, as has been detected by measurements of residual stress distributions in anodic alumina. Linear stability analysis of the model shows that pattern formation at the solution interface is possible near the critical value of a parameter expressing competition between stabilizing electrochemical oxide formation and destabilizing flow. According to the critical parameter value, pattern formation requires that the Faradaic efficiency for oxygen transfer at the solution interface must be close to the transport number for electrical migration of oxygen ions across the film. This relationship between efficiency and transport number is indeed suggested by experimental data. A scaling ratio of pore separation to voltage, as characteristically found in anodic films, is predicted by the wavelength at the critical point.

Transient Relaxations of Ionic Conductance during Growth of Porous Anodic Alumina Films: Electrochemical Impedance Spectroscopy and Current Step Experiments

Transient electrochemical relaxations during growth of anodic oxide films can provide insight into mechanisms of transport processes. Few such studies have focused on porous anodic oxides, which are of significant interest as functional materials. Conductance relaxations during anodizing of aluminum in acidic porous anodic oxide-forming solutions are investigated, using high voltage impedance spectroscopy and constant current reanodizing experiments. Both experiments follow phenomenology demonstrated in prior studies of anodic barrier films. Low-frequency inductive loops in impedance spectra exhibit time constants with inverse proportionality to current density and characteristic resistances nearly equal to those of high-frequency capacitive features. Potential decays during reanodizing depend on charge passed instead of time. Both sets of experiments are analyzed with a model including conductance relaxations due to electric field-dependent generation and removal of bulk charge-carrying defects. The model is found to be quantitatively consistent with nearly all aspects of experimental behavior; the inverse current density dependence of the inductive time constant and the charge parameterization of potential decays both arise because of exponential electric field dependence of ionic conduction and defect generation/removal rates. Oxide volume changes accompanying defect relaxations may help explain mechanical stress generation during anodizing, which is thought to drive pore formation.

(Invited) Characterization of Thin Passive Film-Electrolyte Junctions. Amorphous Semiconductor (a-SC) Schottky Barrier Approach

The knowledge of the solid-state properties of passive film is a preliminary task for a full understanding of the electron and ion transfer processes at the metal/oxide and oxide/electrolyte interface. Both processes are of paramount importance in determining the mechanism of film growth and dissolution as well as in determining the nature of the breakdown during the growth of anodic oxide films or the onset of generalized or localized corrosion process (1-2). With very few exceptions, it is a common belief, that most of anodic oxide films, grown on metals and alloys in aqueous solutions, display a semiconducting or insulating behaviour. It is also very well known that in many cases the initial air-formed or electrochemically grown films have a highly defective or amorphous structure. In any case the location of the characteristic energy levels of the metal/passive-film/electrolyte junction is a necessary task to reach a deeper understanding of the mechanism of charge transfer at the metal/oxide/electrolyte interface so that it is not surprising that in-situ electrochemical techniques like electrochemical impedance spectroscopy (EIS) and differential admittance (DA) have been routinely employed to get information both on the electrical properties as well as on the mechanism of growth of thin and thick oxide films. In order to account for the amorphous or scarcely crystalline nature of anodic oxide films we have suggested, in several papers (3-5), an approach to the description of physicochemical properties of semiconducting passive films based on the theory of amorphous semiconductors. We have stressed in previous papers that the characterization of semiconducting passive film/electrolyte junction based on the use of simple M-S theory to get information on the solid state properties of anodic films presents some drawbacks in terms of assumptions as well as for a correct location of the characteristics energy levels of the passive film/electrolyte junction: flat band potential, Ufb, and the nearest characteristic level of the semiconductor EC (n-type SC) or EV (p-type SC). In an attempt to overcome the intrinsic limits of this traditional approach we advocated the use of the theory of a-SC Schottky barrier as developed in (6-10). In more recent papers (4-5) we try to extend the results of the a-SC Schottky barrier theory to the case of thin film amorphous semiconductors, i.e. when the space charge region of the semiconductor reaches an extension near to the 70% of the film thickness. In the last paper (5b) we introduced also a new parameter directly related to the series resistance of the space charge region which allows to extract information on the homogeneity of the DOS distribution within the space charge region as well as on the relative weight of the volumetric charge presents in the semiconductor with respect to the surface charge located on the metal. Although some very preliminary results strongly supported the novel proposed approach to the use of a-SC theory for thin semiconducting film, a more detailed experimental study was undertaken in order to exploit the robustness of our approach to the case of thin semiconducting anodic films. In this work the results of an extensive characterization, by means of EIS and DA technique, of thin semiconducting passive films grown on Ti metal will be presented in order to highlight the validity of the proposed approach. Further information on the amorphous nature and on the possible dependence of the dielectric constant on the electric field will be taken into account in an attempt to rationalize the complex behaviour of barrier-like passive film on Ti. References 1 - F. Di Quarto, M. Santamaria, Corrosion Eng. Sci. Tech. 39 (2004) 71. 2 - Harrington, S.P. and Devine, T.M., J. Electrochem.Soc. 155 (2008) C381. 3 - F. Di Quarto, F. La Mantia, M. Santamaria, Electrochim. Acta 50 (2005) 5090. 4 - F. La Mantia, H. Habazaki, M. Santamaria, F. Di Quarto, Russ. J. Electrochem 46 (2010) 1306. 5 - a) F. La Mantia, J. Stojadinovic, M. Santamaria, F. Di Quarto, ChemPhysChem, 13 (2012) 2910; b) F. La Mantia, M. Fan, J. Stojadinovic, M. Santamaria, S. Miraghaei, F. Di Quarto, Electrochim. Acta 179 (2015) 460. 6 - R.A. Abram, P.J. Doherty, Phil. Mag. B 45 (1982) 167. 7 - I.W. Archibald, R.A. Abram, Phil. Mag. B 48 (1983) 111. 8 - I.W. Archibald, R.A. Abram, Phil. Mag. B 54 (1986) 421. 9 - J.D. Cohen, D.V. Lang, Phys. Rev. B 25 (1982) 5321. 10 - D.V. Lang, J.D. Cohen, J.P. Harbison, Phys. Rev. B 25 (1982) 5285.

Characterization of anodic oxide film growth on Ti6Al4V in NaTESi electrolyte with associated adhesive bonding behaviour

The formation of anodic oxide films on the Ti6Al4V alloy in the NaTESi electrolyte has been studied in the present paper. An anodic film with a shallow pore-like texture was formed after anodizing to 10V. Porous anodic films with increased porosity were generated after anodizing from 20 to 40V, and the pores were developed mainly within the α phase. Significant amounts of sodium species were incorporated in the films, and the amount increased with increasing anodizing voltage. The current efficiency for the anodic film growth increased from 10 to 30V, but decreased from 30 to 40V due to the occurrence of more oxygen evolution. The film thicknesses determined by RBS were 15nm, 65nm, 115nm and 250nm at 10, 20, 30 and 40V respectively. The film thickness generated at 10V showed good agreement with the thickness of 11nm revealed by transmission electron microscopy. The Raman spectra indicated that the degree of crystallinity of the anodic film increased at higher voltages. The dielectric permittivity of the film was estimated as ∼118 according to the results from transmission electron microscopy and electrochemical impedance spectroscopy. Single-lap shear bonding tests were employed to compare the strength of adhesively joined titanium alloy anodized to different voltages. The results revealed appreciable increase in bond strength with increasing anodic film thickness.

Diagnosis of the Mechanism of Anodic Oxide Film Growth on Platinum in KOH

Abstract Diagnostic criteria for growth of the anodic oxide film on platinum in KOH are reported. In this work, the analytical analysis of oxide film growth demonstrated that the electric field in the passive film formed anodically on platinum in KOH is constant, independent of the applied voltage and barrier layer thickness. This criterion intrinsically distinguishes the Point Defect Model (PDM) from the High Field Model (HFM). Unequivocally, the PDM provides a superior theoretical framework than does the HFM for interpreting oxide film growth on platinum. Importantly, we argue that the diagnostic criteria also apply to metal interstitial conduction, which is the mechanism proposed in the HFM for formation of the PtO oxide film on platinum, but with film growth occurring at the film/solution interface and with a thickness-dependent electric field, rather than being restricted to oxygen vacancy conductors alone, as originally derived for the PDM. Thus, the ability of the diagnostic criteria to differentiate between the HFM and the PDM, in this case, is a direct assessment of the dependence of the electric field strength on the applied voltage and barrier layer thickness, with the experimental results coming down unequivocally on the side of the PDM.

Evolution of insoluble eutectic Si particles in anodic oxidation films during adipic-sulfuric acid anodizing processes of ZL114A aluminum alloys

The effects of insoluble eutectic Si particles on the growth of anodic oxide films on ZL114A aluminum alloy substrates were investigated by optical microscopy (OM) and scanning electron microscopy (SEM). The anodic oxidation was performed at 25°C and a constant voltage of 15 V in a solution containing 50 g/L sulfuric acid and 10 g/L adipic acid. The thickness of the formed anodic oxidation film was approximately 7.13 μm. The interpore distance and the diameters of the major pores in the porous layer of the film were within the approximate ranges of 10–20 nm and 5–10 nm, respectively. Insoluble eutectic Si particles strongly influenced the morphology of the anodic oxidation films. The anodic oxidation films exhibited minimal defects and a uniform thickness on the ZL114A substrates; in contrast, when the front of the oxide oxidation films encountered eutectic Si particles, defects such as pits and non-uniform thickness were observed, and pits were observed in the films.

Ellipsometric in situ diagnostics of the growth of porous anodic oxide films on aluminum

An ellipsometric in situ study of the growth of porous aluminum anodic oxide films on aluminum substrate has been performed. Theoretical calculations have been carried out to interpret the experimental dependences of ellipsometric parameters; they made it possible to identify the most characteristic details of anodic oxidation. It is shown that the ellipsometric method allows one to control in situ in real time a number of important layer parameters: growth rate, porosity, depth uniformity, and the state of interface. The ellipsometric measurements have also revealed high sensitivity to the presence of metal nanoparticles both in the bulk of a layer and on its surface.