The interaction of thin NiO layers with single crystalline α-Al2O3(112̄0) substrates

The behaviour upon thermal annealing of ultrathin nickel oxide films formed on yttria-stabilized ZrO 2 (100) (YSZ) and a-Al 2 O 3 (0001) (sapphire) by in situ oxidizing vapour-deposited Ni films of 0.2-5 ML thickness, was investigated by XPS/x-ray-induced Auger electron spectroscopy (XAES). The sapphire substrate was also used following room-temperature argon ion sputtering to create a defective surface. Heating the nickel oxide films in ultrahigh vacuum (UHV) leads to decomposition in a temperature range strongly dependent on the substrate. On YSZ, the oxide decomposes towards metallic Ni at ∼200 K lower temperature compared with sapphire, where the decomposition temperature is close to the estimated thermodynamic stability limit for nickel oxide in the UHV chamber (∼900 K). This result supports the previously conjectured substrate-mediated nickel oxide decomposition on YSZ. Furthermore, upon oxide decomposition on sapphire, a chemical interaction with the substrate is evidenced, especially by XAES. This interaction, which appears to exist already at 580 K on the sputtered sapphire substrate, is attributed to the formation of an NiAl 2 O 4 spinel-like interfacial compound.

Section: Resultsmentioning

confidence: 91%

Section: Introductionmentioning

confidence: 95%

Interaction of ultrathin nickel oxide films with single‐crystal zirconia and alumina surfaces

Sygellou

Zafeiratos

Tsud

et al. 2002

“…The difference E B = 781.0 eV between the Al 2p C peak and the main Ni 2+ peak (Table 1) suggests the formation of a mixed Ni-Al hydroxide layer (Ni x Al y (OH) z ). [24,27] …”

Section: Reactivity In Chloride-containing Liquid Watermentioning

confidence: 98%

“…However, the Ni 2p core level, fully attenuated after 240 min, is now characterized by two peaks at 856.8 eV and 862.6 eV assigned to Ni 2+ and to a shake-up satellite, respectively. [24] The satellite to main peak intensity ratio is ∼0.56-0.58, suggesting the presence of a nickel-aluminium mixed compound (typical ratio of 0.6-0.7 for spinels [25] ) rather than nickel hydroxide (typical ratio of ∼0.3). [26] The presence of nickel in the surface hydroxide layer evidences the loss of the corrosion protection property provided by the thermal oxide film.…”

Section: Reactivity In Chloride-containing Liquid Watermentioning

confidence: 98%

X‐ray photoelectron spectroscopy study of the interaction of ultra‐thin alumina films on NiAl alloys with NaCl solutions

Bennour

Maurice

Marcus

2010

We report a XPS study of the reactivity in 0.5 M NaCl aqueous solution of NiAl(100) surfaces covered by ultra-thin aluminium oxide films grown by thermal oxidation of the alloy at 900• C. Detailed analysis of the film thickness, the oxide stoichiometry and the alloy composition below the oxide was performed to characterize the drastic modifications induced by chloride exposure. Chloride entry in the oxide was observed by AR-XPS that revealed the existence of two chemical states of chlorides, one associated to aluminium oxide, the other one to aluminium hydroxide. The film modifications were initiated in the inner part and characterized by the formation of chloride-containing hydroxide species. The growth of these species spread later to the entire film, accompanied by a marked thickening of the modified alumina layer by selective oxidation of the alloy. Longer immersion times (>20 h) led to the formation of mixed nickel-aluminium chloride-containing hydroxide species, indicating the loss of corrosion protection.

“…1 Typically, the initial stages of the growth of thin films have been analysed by transmission electron microscopy (TEM) or scanning electron microscopy (SEM) 2 and, more recently, by atomic force microscopy (AFM) and similar tip probes. 3,4 However, depending on the system, the use of these methods may have important limitations. This is particularly evident when the materials of the substrate and the deposited layer do not permit a clear differentiation by electron microscopy (e.g.…”

Section: Introductionmentioning

confidence: 99%

Study of the first nucleation steps of thin films by XPS inelastic peak shape analysis

Мансилла

Martín-Concepción

Espinós

et al. 2006

The initial steps in the formation of thin films have been investigated by analysis of the peak shape (both inelastic background and elastic contributions) of X-ray photoelectron spectra. Surface coverage and averaged height of the deposited particles have been estimated for several overlayers (nanometre range) after successive deposition cycles. This study has permitted the assessment of the type of nucleation and growth mechanisms of the films. The experiments have been carried out in situ in the preparation chamber of an XPS spectrometer. To check the performance of the method, several materials (i.e. cerium oxide, vanadium oxide and cadmium sulfide) have been deposited on different substrates using a variety of preparation procedures (i.e. thermal evaporation, ion beam assisted deposition and plasma enhanced chemical vapour deposition). It is shown that the first deposited nuclei of the films are usually formed by three-dimensional particles whose heights and degree of surface coverage depend on the chemical characteristics of the growing thin film and substrate materials, as well as the deposition procedure. It is concluded that XPS peak shape analysis can be satisfactorily used as a general method to characterize morphologically the first nanometric moieties that nucleate a thin film.