The growth and structure of oxide films formed on single crystal (100) and polycrystalline Cr between 550 and 900 °C

Hussey, R. J.; Mitchell, D. F.; Graham, M. J.

doi:10.1002/maco.19870381005

Cited by 41 publications

(4 citation statements)

References 17 publications

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“…That this region was comparatively thin, indicates that the oxide layer grew predominantly via outward chromium cation diffusion. This is consistent with previous studies that have found that chromium diffusion is more important than oxygen diffusion for chromia scale growth at 900 °C …”

Section: Discussionsupporting

confidence: 94%

Oxidation‐led decomposition of hexagonal boron nitride coatings on alloy substrates at 900 °C: Chromia‐formers

Fleming

2019

Materials & Corrosion

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In contrast to a mass of powder in air at 900 °C, the oxidation rate of hexagonal boron nitride does not tend to a plateau when present as a coating on austenitic stainless steel type 304 and type 310, and a real‐world hot forming tool alloy. As with a mass of powder, a molten boron trioxide diffusion barrier encapsulates each hexagonal boron nitride grain around the basal plane. These subsequently merge to form a dispersion of remnant grains throughout a molten matrix. Boron trioxide is semipermeable, and as such, the substrate oxidizes concurrently. As it does so, outwardly diffusing chromium (III) ions react with boron trioxide to form chromium borate, which depletes the diffusion barrier. This causes the oxidation of hexagonal boron nitride to be sustained at an enhanced rate and the overlayer ultimately undergoes complete decomposition. During this process, the scale comprises chromium borate and chromia only. While manganese chromium spinel and iron chromium spinel form readily at the oxide‐atmosphere interface of equivalently heat‐treated uncoated substrates, they do not form until after the coating has completely decomposed.

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Section: Discussionsupporting

confidence: 94%

Oxidation‐led decomposition of hexagonal boron nitride coatings on alloy substrates at 900 °C: Chromia‐formers

Fleming

2019

Materials & Corrosion

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“…First, partial thermal oxidation of the Cr layer may increase the oxide thickness, since during the fabrication procedure the chromium layer undergoes two heating processes: an elevated temperature in the evaporator chamber during the evaporation process, and PMMA baking for second step lithography (180 • C, 2 min). Thermal oxide growth of Cr x O y primarily takes place through outward cation diffusion; thus new oxide forms mainly on top of the existing scale [21], increasing the resulting oxide layer overhang and gap size. Second, internal stresses generated within the (primarily) Cr layer due to inward diffusion of oxygen [22] may lead to elastic deformation of the underlying Cr.…”

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confidence: 99%

Nanogaps with very large aspect ratios for electrical measurements

Fursina

Lee

Sofin

et al. 2008

Applied Physics Letters

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For nanoscale electrical characterization and device fabrication it is often desirable to fabricate planar metal electrodes separated by large aspect ratio gaps with interelectrode distances well below 100 nm. We demonstrate a self-aligned process to accomplish this goal using a thin Cr film as a sacrificial etch layer. The resulting gaps can be as small as 10 nm and have aspect ratios exceeding 1000, with excellent interelectrode isolation. Such Ti/Au electrodes are demonstrated on Si substrates and are used to examine a voltage-driven transition in magnetite nanostructures. This shows the utility of this fabrication approach even with relatively reactive substrates.PACS numbers: 81.07. -b,81.16.-c,85.35.-p There is much interest in the electronic characterization of nanoscale materials and the creation of working molecular-based devices [1]. Both goals demand the fabrication of metallic electrodes separated by a distance comparable with the targeted length, i.e. a few nanometers. Much recent progress has been made in nanogap fabrication, and several techniques were proposed, including electromigration [2,3,4], electrodeposition [5,6], mechanically controlled break junctions [7], advanced ebeam lithography methods [8,9,10,11,12], on-wire lithography [13], etc. Interelectrode distances down to 1-2 nm may be achieved [4,6,9] by some of these methods, though without much control of gap aspect ratio.A significant challenge is fabricating two electrodes separated by a nanometer gap running parallel over a macroscopic width (high-aspect-ratio (HAR) nanogaps). HAR nanogap fabrication has been demonstrated based on a selective etching of cleaved GaAs/AlGaAs heterostructures [14,15]. However, this method requires particular substrates and allows only restricted gap geometries. A much simpler technique was proposed recently [16] with potentially no limitations on the width of the gap. Two separate lithographic patterning steps are used to define first and second electrodes, while the interelectrode separation is controlled by the oxidation of an Al sacrificial layer deposited upon the first electrode. The native aluminum oxide layer, Al 2 O 3 , overhangs the underlying metal and serves as a mask during the deposition of the second electrode. This layer must be removed afterwards, but since Al 2 O 3 , corundum, is one of the most chemically inert materials [17], removal by direct chemical etching is very difficult. In a refinement, the authors deposited an additional sacrificial layer of SiO 2 and subsequently used etchant for SiO 2 to remove the SiO 2 and Al/Al 2 O 3 layers [16]. The use of SiO 2 etchant greatly limits the use of this approach in conjunction with conventional silicon electronics. While this method potentially allows fabrication of HAR nanogaps, the reported aspect ratios are less than 10 [16].In this letter we report a highly reproducible and flexible method for nanometer-sized (10-20 nm) gap fabrication with aspect ratios exceeding 1000. Modifying the original method [16] by replacing the Al layer wi...

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“…Results for Cr2O3 formed on chromium at 900°C indicate that two independent oxygen diffusion processes occur during oxide growth (12). The first is isotropic oxygen selfdiffusion occurring a t the interface between the 160-and l 8 0 -oxide layers.…”

Section: Chromium Oxidementioning

confidence: 97%

Recent advances in oxide film characterization

Graham¹

1992

Pure and Applied Chemistry

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-This paper considers the application of surface-analytical techniques to characterize both thin (-2 nm) passive oxide films and thick (up to 1 pm) oxides formed on metals and alloys a t high temperature. Auger electron spectroscopy (AES), X-ray photoelectron spectroscopy (XPS), Mossbauer spectroscopy, X-ray absorption near edge spectroscopy (XANES), secondary ion mass spectrometry (SIMS) and electron energy-loss (EEL) microscopy are considered. Emphasis is placed on the use of SIMS and EEL microscopy to provide chemical information a t high spatial resolution. Characterization of oxide films on an atomic scale leads to a better understanding of the processes which take place during corrosion and oxidation.

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The growth and structure of oxide films formed on single crystal (100) and polycrystalline Cr between 550 and 900 °C

Cited by 41 publications

References 17 publications

Oxidation‐led decomposition of hexagonal boron nitride coatings on alloy substrates at 900 °C: Chromia‐formers

Oxidation‐led decomposition of hexagonal boron nitride coatings on alloy substrates at 900 °C: Chromia‐formers

Nanogaps with very large aspect ratios for electrical measurements

Recent advances in oxide film characterization

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