Physicochemical Characterization of Passive Films and Corrosion Layers by Differential Admittance and Photocurrent Spectroscopy

Bocchetta

Santamaria

et al. 2010

Electrochimica Acta

a b s t r a c tThe photoelectrochemical polymerization of poly(3,4-ethylenedioxythiophene), PEDOT, was successfully realized on anodic film grown to 50 V on magnetron sputtered niobium. Photocurrent Spectroscopy was employed to study the optical properties of Nb/Nb 2 O 5 /PEDOT/electrolyte interface in a large range of potential, and to get an estimate of the band gap and flat band potential of both the oxide and the polymer. Scanning Electron Microscopy was used to study the morphology of PEDOT. Both the optical and morphological features of the photoelectrochemically grown polymer were compared with those showed by PEDOT electropolymerized on gold conducting substrate.

Section: Methodsmentioning

confidence: 99%

Light induced electropolymerization of poly(3,4-ethylenedioxythiophene) on niobium oxide

Bocchetta

Santamaria

et al. 2010

Electrochimica Acta

“…As assumed in previous works, [3][4][5][6]8,9 in so far as the term is constant, Eq. 2c predicts that the bandgap of semiconducting compounds is linearly dependent on the square of the difference of electronegativity between the most electronegative element (oxygen in the case of oxides) and the metallic element.…”

Section: Theoretical Backgroundmentioning

confidence: 99%

Critical Review—Photocurrent Spectroscopy in Corrosion and Passivity Studies: A Critical Assessment of the Use of Band Gap Value to Estimate the Oxide Film Composition

Quarto

Zaffora

et al. 2017

J. Electrochem. Soc.

Self Cite

A critical assessment of the Photocurrent Spectroscopy (PCS) Technique for the semi-quantitative characterization of passive film and corrosion layers composition is carried out. We take into account more than three decades of PCS usage as "in-situ" analytical technique and related results as well as the criticism of the underlying semi-empirical correlation relating the measured optical bandgap (E g ) to the passive film composition. The discrepancies between the experimental data, gathered by PCS measurements, and E g estimates originating from recently developed Density Functional Theory based modeling of solid state properties are stressed with particular emphasis on the case of anodic passive film grown on technologically important alloys (Fe-Cr and stainless steels). The extension of this correlation to mixed oxides and its use for relating the oxide composition to the bandgap values is critically reviewed by comparing the predicted E g of mixed oxides with the experimental values. Suggestions on how to account for different bandgap values of oxide polymorphs and how to correlate the E g values to the composition of mixed s,p-d-metal oxides are presented and discussed on the basis of experimental results reported in the literature. On the basis of this assessment, the ability of PCS in providing quantitative information on the composition of passive film and corrosion layer is generally confirmed. Fujimoto (fujimoto@mat.eng.osaka-u.ac.jp) and HeeJin Jang (heejin@chosun.ac.kr). . This paper is a Critical Review in Electrochemical and Solid State Science and Technology (CRES 3 T). This article was reviewed by ShinjiPhotocurrent Spectroscopy (PCS) is currently employed for the characterization of solid-state properties of semiconducting and insulating materials, since the knowledge of their bandgap is a prerequisite to any possible application in different fields such as solar energy conversion (photoelectrochemical and photovoltaic solar cells, photocatalysis) and microelectronics (high-k, high band-gap materials). 1,2In the last 20-30 years an increasing number of electrochemists working in the field of corrosion have been attracted by this technique owing to its versatility and ability to scrutinize "in-situ" corrosion layers and passive films having semiconducting or insulating behavior. In previous as well as in very recent works 3-7 we have shown that PCS is able to provide detailed information on characteristic energy levels of passive film/electrolyte junctions (flatband potential: U FB ; internal photoemission threshold: E th ; bandgap value: E g ). Such information is necessary for a deeper understanding of the possible mechanisms of charge transfer (electrons and ions) at the metal/corrosion layer/electrolyte interface. Further advantages stem from the fact that the PCS technique does not require particular surface finishing control, it can be used both on large areas as well as in microscopic regions of the electrode, and can reach high sensitivity by using a lock-in amplifier coupled to a mec...

“…11 As shown in Fig. 4 for the anodic film grown on Ta-66at.%Nb, from the photocurrent spectra corrected for the efficiency of the lamp-monochromator system, 9 according to eq. 3 we can estimate the optical band gap of the investigated oxides by extrapolating to zero the (I ph hν) 0.5 vs hν plot.…”

Section: +mentioning

confidence: 99%

Characterization of the Solid State Properties of Anodic Oxides on Magnetron Sputtered Ta, Nb and Ta-Nb Alloys

Zampardi

Santamaria

et al. 2011

J. Electrochem. Soc.

Tantalum oxide, niobium oxide and Ta-Nb containing mixed oxides were grown by anodizing sputter-deposited Ta, Nb and Ta-Nb alloys of different compositions. A photoelectrochemical investigation was performed in order to estimate the band gap and the flat band potential of the oxides as a function of their composition. The band gap of the investigated Ta-Nb containing mixed oxides changed monotonically between those estimated for Ta 2 O 5 (4.1 eV) and Nb 2 O 5 (3.4 eV) and in agreement with a proposed correlation between the Band gap of an oxide and the difference of electronegativity of the oxide constituents. From the differential capacitance curves recorded in a wide range of electrode potential and for several frequencies of the alternative signal, the dielectric constant of the investigated oxides were estimated. © 2011 The Electrochemical Society. [DOI: 10.1149/2.031201jes] All rights reserved. Microelectronics is very important for almost all kinds of technology evolutions in the past four decades. In this area, the dielectrics science occupies a prominent place in providing the dominant technology in integrated capacitors or gate insulators. In the last years the main challenge has been to scale down the insulating oxide thickness keeping low values of the leakage current. This task has been partially achieved for metal-oxide-semiconductor field effect transistor thanks to the use of hafnium based dielectrics, while less has been done for dynamic random access memory and metal-insulator-metal capacitors (DRAM MIMCAP). To the last generation DRAM, very low (from 0.5 to 0.35 nm) equivalent thickness is required with the constraint to maintain a very low leakage current. This implies the use of material having high dielectric constant (∼50) and high band gap (>4 eV), which can be obtained by post formation thermal treatment and tuning of the oxide composition. Owing to their high value of dielectric constant, Ta 2 O 5 and Nb 2 O 5 are quite attractive oxides for the development of the next generation of DRAM. Tantalum oxide is a wide band gap (∼4 eV) material with a high dielectric constant (ε = 27 -30) if properly crystallized (T > 750• C). Niobium oxide has a higher dielectric constant (ε = 53) with respect to Ta 2 O 5 but a lower band gap (∼3.3 eV). In recent papers, 1-3 it has been shown that the addition of small amount of Nb in tantalum based oxide decreases the crystallization temperature with small effect on the band gap value of the material. Thus, (Nb (1−x) Ta x ) 2 O 5 have been introduced in the International Technology Roadmap for Semiconductors (ITRS).Tantalum-niobium mixed oxides for microelectronic components are usually prepared by high vacuum techniques (physical and chemical vapour depositions, atomic layer deposition). [4][5][6][7] In this work we propose to prepare these oxides by anodizing in suitable solutions sputter-deposited Nb-Ta alloys. This electrochemical room temperature process allows to grow oxides of controlled thickness and composition, even if a detailed investigation on t...