Passivity of Metals, Alloys, and Semiconductors

Schultze, J.W.; Hassel, Achim Walter

doi:10.1002/9783527610426.bard040302

Cited by 28 publications

(32 citation statements)

References 127 publications

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“…This phenomenon is already intensively discussed by the authors [21] and can be explained according to literature. [16,18,33] The oxide growth does not start before the time t max , which is defined by the following:…”

Section: Resultsmentioning

confidence: 99%

TEM investigation of barrier‐like anodic oxide films on aluminum

Schneider

Lämmel

Hübner

et al. 2015

Surface & Interface Analysis

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The present study focuses mainly on non-electrochem. investigation of thin barrier-like oxide films formed under different pulse frequencies. The TEM investigation principally shows amorphous oxide films, which are dense and free of pores. The various pulse expts. have no influence on these film properties. The oxide growth factor was calcd. to 1.06 nmV-1 in all cases. The microstructure (crystallog. orientation, grain boundaries) of the underlying substrate does not affect the oxide films. Independent of the pulse frequency, electrolyte species are not incorporated into the oxide films. The evidenced differences in the film thickness are caused by intrinsic peculiarities of the high-field mechanism of growing oxide

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Section: Resultsmentioning

confidence: 99%

TEM investigation of barrier‐like anodic oxide films on aluminum

Schneider

Lämmel

Hübner

et al. 2015

Surface & Interface Analysis

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“…27 From this linear dependence, the so-called formation factor dz ox /dE f was found to be in the range 1.3-2.4 nm/V for TaO x (Ref. 19) and 1.3-3.3 nm/V for TiO x .…”

Section: Sample Preparationmentioning

confidence: 97%

Charge Transport Through Thin Amorphous Titanium and Tantalum Oxide Layers

Stella¹,

Kovacs²,

Diesing³

et al. 2011

J. Electrochem. Soc.

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Heterosystems of metal/insulator/gold type with titanium oxide and tantalum oxide as internal barriers are studied using internal photoemission (IPE), field induced current transport (current transients after voltage steps) and chemical reaction induced current transport (chemicurrent). IPE investigations over a broad energy range from 0.8 to 4.5 eV allow a determination of the interstitial layers band gap and the maximum height of the internal tunnel barrier. The built-in field of the heterosystem is derived by the evaluation of the slope in the photoyield versus photon energy plot. Current transients recorded after voltage steps allow the determination of the heterosystems time constants which generally have a value of some milli seconds. In titanium oxide systems additional time constants with values of several 100 s appear for bias voltages >0.5 V. These time constants are assigned to slow processes altering the height of the titanium oxide barriers. and electron sources in spin polarized tunneling. 5 In the present work we present a comparative investigation of charge transport induced by different methods through thin oxide films. Charges are driven through the oxide by: i) application of a device voltage ii) illumination of the samples with monochromatic light at variable photon energies, leading to spectra of internal photoemission, iii) non adiabatic chemical surface reactions. All three methods are combined since it is possible to derive the nature of excited carriers transport through heterosystems.6 For aluminum and tantalum oxide heterosystems it was found, that they form a high pass filter for excited electrons and holes (defect electrons). 4,6 Since the height of the internal barriers for electrons and holes can be modified by an applied bias voltage, it became possible to characterize the spectra of excited charge carriers with energies below the vacuum barrier. Bias voltages of up to 1 V could be applied to the system which had an internal barrier height of 3 eV.To increase the detection efficiency for excited electrons travelling from the surface of a metal towards the bulk, one can either decrease the thickness of the top metal film of a heterosystem or one can reduce the height of the internal barrier. But with a decrease of the internal barrier the method of applying a bias voltage for tuning this barrier might become problematic, since tunnel currents become larger with lower barrier heights. Additionally, the influence of midgap states, impurities and remanent changes of the internal barrier might become more relevant for lower barriers.8,9 These problems are adressed in the present work.A comparison of metal/insulator/metal heterojunctions is presented with potentiostatically formed titanium and tantalum oxide as interjacent insulating layer. Titanium and tantalum oxide were chosen since both have bandgaps smaller than 4.5 eV.10 For amorphous tantalum oxide values of 4.2 eV are typical 11,12 whereas crystalline samples show values of 3.9-4.5 eV.12,13 Bulk titanium oxide values are for rut...

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“…This valve-like behaviour led to naming this group of metals (including Al, Nb and to some extent Mo, W and Zr) valve metals [3]. The valve metal oxides grow following the high-field mechanism [4] and are very difficult to reduce under cathodic polarization [5]. They are able to withstand an electric field equal to the film formation field strength [6], may be amorphous (glassy Ta) [7] and are used in various applications including orthopaedic implants and mesoporous materials [8, 9].…”

Section: Introductionmentioning

confidence: 99%

Properties of anodic oxides grown on a hafnium–tantalum–titanium thin film library

Mardare

Ludwig

Savan

et al. 2014

Science and Technology of Advanced Materials

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A ternary thin film combinatorial materials library of the valve metal system Hf–Ta–Ti obtained by co-sputtering was studied. The microstructural and crystallographic analysis of the obtained compositions revealed a crystalline and textured surface, with the exception of compositions with Ta concentration above 48 at.% which are amorphous and show a flat surface. Electrochemical anodization of the composition spread thin films was used for analysing the growth of the mixed surface oxides. Oxide formation factors, obtained from the potentiodynamic anodization curves, as well as the dielectric constants and electrical resistances, obtained from electrochemical impedance spectroscopy, were mapped along two dimensions of the library using a scanning droplet cell microscope. The semiconducting properties of the anodic oxides were mapped using Mott–Schottky analysis. The degree of oxide mixing was analysed qualitatively using x-ray photoelectron spectroscopy depth profiling. A quantitative analysis of the surface oxides was performed and correlated to the as-deposited metal thin film compositions. In the concurrent transport of the three metal cations during oxide growth a clear speed order of Ti > Hf > Ta was proven.

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Passivity of Metals, Alloys, and Semiconductors

Abstract: The sections in this article are Introduction Definition of Passivity Survey of Systems General Principles of Passivity Thermodynamics and Bond Polarity Experimental Techniques for Characterization of Passive Films Thickness and Stoichiometry of Passive Films … Show more

Cited by 28 publications

References 127 publications

TEM investigation of barrier‐like anodic oxide films on aluminum

TEM investigation of barrier‐like anodic oxide films on aluminum

Charge Transport Through Thin Amorphous Titanium and Tantalum Oxide Layers

Properties of anodic oxides grown on a hafnium–tantalum–titanium thin film library

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