Thin Cr2O3 Film Research Articles

Optical response of green synthesized thin Cr2O3 films prepared via drop and spin coatings

This study investigated the impact of optical bandgap energy on the optical constants of Cr2O3 thin films, which were prepared via green synthesis method and deposited using drop and spin-coatings at 600, 800, 1000, and 1200 rpm onto Cu substrates. The deposited Cr2O3 thin films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectrometry (EDS), and UV–VIS-NIR spectroscopy. XRD revealed that the prepared nanocoating surfaces are pure eskolaite Cr2O3 phase. The grain size of the prepared Cr2O3 films decreased from 15 nm to 12 nm for the drop and spin coatings, respectively. The morphology of the drop and spin coated samples showed nanorods, mesospherical, and quasi-spherical shaped nanoparticles, respectively, along with the presence of O and Cr. The bandgap energy increased from 2.35 eV to 2.50 eV, with increasing Spin Coater rotational speeds (RS) from drop to 1200 rpm, respectively. As bandgap energy increase, the carriers' spatial dimension shrinks, resulting in grains smaller than or equal to the exciton's Bohr radius. Thicker film materials tend to have lower bandgap energies due to strain effects, whereas smaller grain sizes tend to have higher bandgap energies. The determined refractive index and extinction coefficient values vary as the bandgap energy varies for all prepared samples. These findings confirmed that differences in bandgap energy affect the refractive index (n) and extinction coefficient (k) of Cr2O3 thin films. These are attributed to quantum confinement, internal scattering, and interference effects of Cr2O3 thin film surfaces.

NV microscopy of thermally controlled stresses caused by thin Cr2O3 films.

Many modern applications, including quantum computing and quantum sensing, use substrate-film interfaces. Particularly, thin films of chromium or titanium and their oxides are commonly used to bind various structures, such as resonators, masks, or microwave antennas, to a diamond surface. Due to different thermal expansions of involved materials, such films and structures could produce significant stresses, which need to be measured or predicted. In this paper, we demonstrate imaging of stresses in the top layer of diamond with deposited structures of Cr2O3 at temperatures 19°C and 37°C by using stress-sensitive optically detected magnetic resonances (ODMR) in NV centers. We also calculated stresses in the diamond-film interface by using finite-element analysis and correlated them to measured ODMR frequency shifts. As predicted by the simulation, the measured high-contrast frequency-shift patterns are only due to thermal stresses, whose spin-stress coupling constant along the NV axis is 21±1 MHz/GPa, that is in agreement with constants previously obtained from single NV centers in diamond cantilever. We demonstrate that NV microscopy is a convenient platform for optically detecting and quantifying spatial distributions of stresses in diamond-based photonic devices with micrometer precision and propose thin films as a means for local application of temperature-controlled stresses. Our results also show that thin-film structures produce significant stresses in diamond substrates, which should be accounted for in NV-based applications.

Localized corrosion of 304 stainless steel triggered by embedded MnS

The present work investigated the localized corrosion of 304 stainless steel triggered by MnS in 3.5 wt% NaCl solution via multi-analytical approaches including in-situ and ex-situ techniques. The results suggested that the dissolution of MnS starts from boundary areas and directly releases elemental sulfur. The reoccurrence and disappearance of elemental sulfur during MnS dissolution indicated that sulfur was continuously consumed and converted. Copper-containing compounds were found deposited on residual MnS in the corrosion pit, whilst a thin Cr2O3 film covered the pit and thickened over time. Based on the evidence obtained, a more comprehensive MnS-induced localized corrosion mechanism was proposed.

Defect Nanostructure and its Impact on Magnetism of α-Cr2 O3 Thin Films.

Thin films of the magnetoelectric insulator α-Cr2 O3 are technologically relevant for energy-efficient magnetic memory devices controlled by electric fields. In contrast to single crystals, the quality of thin Cr2 O3 films is usually compromised by the presence of point defects and their agglomerations at grain boundaries, putting into question their application potential. Here, the impact of the defect nanostructure, including sparse small-volume defects and their complexes is studied on the magnetic properties of Cr2 O3 thin films. By tuning the deposition temperature, the type, size, and relative concentration of defects is tailored, which is analyzed using the positron annihilation spectroscopy complemented with electron microscopy studies. The structural characterization is correlated with magnetotransport measurements and nitrogen-vacancy microscopy of antiferromagnetic domain patterns. Defects pin antiferromagnetic domain walls and stabilize complex multidomain states with a domain size in the sub-micrometer range. Despite their influence on the domain configuration, neither small open-volume defects nor grain boundaries in Cr2 O3 thin films affect the Néel temperature in a broad range of deposition parameters. The results pave the way toward the realization of spin-orbitronic devices where magnetic domain patterns can be tailored based on defect nanostructures without affecting their operation temperature.

Synthesis and Gas Sensitivity of Thin Chromium Oxide Films

Thin polycrystalline Cr2O3 films were obtained using RF magnetron sputtering followed by annealing in air at T = 673 K. The obtained films had grain diameters within 40–70 nm and a bandgap width of 3.3 ± 0.2 eV. In a temperature range of 303–473 K, sensors based on these Cr2O3 films exhibited high response to NO2, H2, acetone and toluene vapors, while weakly responding to the presence of CH4 and CO and showing relatively weak dependence of the electric resistance on air humidity. A qualitative model of the influence of gases on the electrical properties of thin Cr2O3 films is proposed.

Синтез и газовая чувствительность тонких пленок оксида хрома

The thin polycrystal Cr2O3 films were synthesized by RF - magnetron sputtering with followed annealing at T = 673 K in an air atmosphere. The grains diameter in the thin Cr2O3 film is 40–70 nm, Eg = 3.3±0.2 eV. In the temperature range of 303–473 K, the Cr2O3 films show high response to NO2, Н2, vapors of acetone and toluene, weakly react to CH4 and CO and have the relatively weak dependence of resistance on humidity. The qualitative model of the gases influences on the thin Cr2O3 films electrical properties was proposed.

High temperature stability of aluminide-coated Inconel 617

Aluminum diffusion coatings were applied to the Inconel 617 by a pack cementation. The effect of coatings on the thermal stability and wear resistance of the Inconel alloy after heat-treatment under an air and a helium atmosphere at 1000°C, 48 h has been studied. The aluminide-coated Inconel specimens are prepared at 850°C and 1000°C for 1 h. An aluminiding layer indexed as AlxNi1-x(x = 0.4–0.6) was formed near the surface region and it played a role as a barrier layer against the surface diffusion of Cr . The thin Cr2O3film formed in situ on the alloy surface is protective inhibiting further oxidation at moderate temperatures. As the temperature increases further, the thermal stability of the Inconel alloy is limited by the instability of the Cr2O3scale. The aluminide-coated Inconel 617 samples showed the better performances, the enhanced thermal stability and improved wear resistance, most likely due to the barrier layer formation with the reduced amount of Cr2O3scale formation.

A Cr2O3-deposited Sm(Co0.68Fe0.22Cu0.08Zr0.02)7.5 magnet with increased oxidation resistance at 700 °C

A Sm(Co0.68Fe0.22Cu0.08Zr0.02)7.5 alloy was arc-ion-plated with a thin Cr2O3 film. It completely prevented the external oxidation and sufficiently suppressed the internal oxidation of the alloy in air at 700°C for 20h, causing the alloy to form only a very shallow layer where the Sm oxidation occurred. The mechanism for the effect of the Cr2O3 film on the oxidation of the alloy was proposed based on phase characterization of the oxidized layer.

Effect of a thin Cr2O3 film on oxidation at 600 °C of a Sm(CobalFe0.22Cu0.08Zr0.02)7.5 alloy

A Sm(CobalFe0.22Cu0.08Zr0.02)7.5 magnetic alloy, after having been arc-ion-plated with a thin Cr2O3 film, was dramatically increased in oxidation resistance. It formed an internal oxidation-affected zone (IOAZ) with a thickness only about 1.5μm at 600°C in air for 20h. TEM characterizations showed that the IOAZ was double-layered, consisting of an outer extremely thin Co-phase band and an inner oxidation zone with a matrix of Co-Fe solid solution dispersing Sm2O3 particles. The process for the formation of the IOAZ has been also presented in detail.

X-ray photoelectron spectroscopy studies of reactions on chromium metal and chromium oxide surfaces

This paper reports several interrelated XPS investigations of the Cr–O system that provide additional interpretation of the Cr 2p3/2 spectra, along with more detail on the reaction mechanisms between O2 gas and H2O vapour with metallic Cr. The Cr 2p3/2 spectra of polycrystalline Cr2O3 contain multiplet structures that bear a strong resemblance to those calculated by Gupta and Sen for the free Cr3+ ion. The O/Cr ratio derived from the corrected Cr3+ and substitutional O2− intensities for all polycrystalline Cr2O3 samples was 1.5. Annealing of freshly cleaved polycrystalline Cr2O3 surfaces above 550°C resulted in a sharpening of the multiplet structures that may be caused by the increased prevalence of the (0001) Cr2O3 orientation on the surface. The slight difference in binding energies between the low energy (0001) plane and the other major crystallographic orientations could contribute to the spectral broadening that is observed for the Cr 2p3/2 spectral line shapes. The Cr 2p3/2 spectrum for Cr(OH)3 was isolated from that produced by Cr2O3 and the multiplet structure was qualitatively re-assembled for that of the hydroxide. The Cr 2p3/2 and O 1s spectra of reaction products on polycrystalline metal surfaces were analysed using the above information. The oxidic portion of the Cr 2p3/2 spectra could be cleanly separated from the metallic substrate using spectral subtraction. Reactions of either O2 gas or H2O vapour both produced a thin Cr2O3 film that was deficient in Cr3+ and, depending on the reactant, showed varying concentrations of hypo-stoichiometric Cr moieties. The surface corrected O/Cr ratios calculated for all the oxidised surfaces were 1.7. There was little evidence to support the formation of Cr(OH)3 on these surfaces. For comparison, an aqueous reaction of a Ni–Cr (20%) alloy was studied where both Cr(OH)3 and Cr2O3 components could be analysed. For this example no sub-stoichiometric Cr oxide species were produced.

Integrated impedance based hydro‐carbon gas sensors with Na‐zeolite/Cr2O3 thin‐film interfaces: From physical modeling to devices

AbstractThe impedance at temperatures of some hundred degree Celsius of sodium ion conducting zeolites applied on planar interdigital gold electrodes covered with a thin Cr2O3 film changes very sensitively and selectively when exposed to hydrocarbons. In contrast to comparable ammonia sensors, it was found that the sensing effect occurs at the electrodes, namely at the zeolite/Cr2O3 interface. To explain the sensor effect, impedance spectra are calculated with a model that considers the zeolite conductivity, the semiconducting properties of Cr2O3, and the zeolite/Cr2O3 interface characteristics. A differential equation to describe the time‐dependent current through zeolite and Cr2O3 is derived. The impedance spectra are then extracted from the complex amplitude of the first harmonic I1 in the Fourier series associated with this periodic current function. The hydrocarbon concentration influences the charge carrier density in the Cr2O3 film, thus leading to the observed impedance changes. The simulated impedance spectra reproduce the important features of the measured spectra quite well.To avoid photolithographic and thin‐film processes for manufacturing a prototype sensor, the technology was transferred to the established industrial thick‐film hybrid technology. Electrodes and zeolites were screen‐printed and the Cr2O3 film was electroplated. Prototype sensors show a good and long‐term stable sensitivity toward hydrocarbons. Interfering gases like NO, CO, or H2 do not affect the sensor signal very strongly, but an unexpected pronounced response toward ammonia was observed.

Thin Cr2O3 Films for Magnetoelectric Data Storage Deposited by Reactive E-beam Evaporation

Magnetoelectric materials are proposed for use in magnetic memory applications. The main idea of the Magnetoelectric Random Access Memory (MERAM) is to enable electrical data writing in a magnetoelectric antiferromagnet, while the principle of the magnetoresistive data reading remains. As a possible medium for magnetoelectric data storage Cr 2 O 3 is proposed. Thin films of Cr 2 O 3 have been grown on a [0001] sapphire substrate by reactive e-beam evaporation of Cr 2 O 3 in an O 2 atmosphere. The out-of plane orientation of the thin Cr 2 O 3 films and the chemical environment of Cr 3+ ions are evidenced by X-Ray diffractometry and absorption spectroscopy. Surface characterization has been done by atomic force microscopy. At decreasing temperature the conductivity shows an exponentional decrease, which is probably due to hopping via small amounts of Cr 3 O 4 .

Determination of diffusion induced concentration profiles in Cr2O3 films on ceramic Al2O3 by Auger sputter depth profiling

Annealing induced interface and bulk effects in thin Cr2O3 films on aluminum oxide have been studied. The investigated samples have been prepared by reactive r.f. magnetron sputter deposition of Cr2O3 on ceramic Al2O3 substrates. Annealing at temperatures up to 1250° C have been carried out in situ under ultra high vacuum. Temperature induced compositional changes have been subsequently determined by AES sputter depth profiling without breaking the vacuum. The non-conducting substrates and the overlap of the Cr-(LMM)- and O-(KLL)-Auger peaks required special analysis parameters and spectra interpretation to obtain the concentration depth profiles of the different elements (Al, O, Cr).

Adsorption and reaction on oxide surfaces: NO, NO 2 on Cr 2O 3(111)/Cr(110)

Abstract We report results of electron spectroscopic measurements, i.e., LEED, EELS, ARUPS, XPS, and NEXAFS on NO, and NO2 adsorbed on a thin Cr2O3 film with (111) orientation grown on top of a Cr(110) single-crystal surface via an oxidation procedure. It is shown that the Cr2O3(111) surface is likely to consist of Cr-terminated and O-terminated terraces and that the Cr-atoms located within the oxide surface are in oxidation states different from the bulk. Our results indicate that these sites are involved in the dissociation of NO2 at rather low temperature to yield adsorbed NO and adsorbed oxygen.