Nano-Oxidation of Cu(100) Investigated by In situ UHV-TEM

Abstract

The initial stages of the oxide formation were investigated by oxidizing Cu(100) thin films in a specialized in situ ultra-high vacuum (UHV) TEM at oxygen partial pressure of 5x10 -4 torr and a temperature range of 150°C to 1000°C. Epitaxial Cu 2 O islands formed on Cu(100) where the morphology can be either triangular, huts, rods or pyramids depending only on the oxidation temperature. Of particular focus was the formation of nanorods at 600°C, that was observed to change from initially square shaped islands to elongated islands at a critical size of 114nm. The experimental data on the elongation of Cu 2 O islands agree with the energetic calculations based on the balance between surface/interface energies and the elastic strain relief in the three dimensional islands.

Oxygen adsorption-induced nanostructures and island formation on Cu{100}: Bridging the gap between the formation of surface confined oxygen chemisorption layer and oxide formation

“…8,59 This suggests that adsorption of O 2 on Cu͑100͒ is only kinetically limited to 0.5 ML coverage and, as the present investigation demonstrates, by increasing the oxygen impingement rate on the surface ͑i.e., oxygen partial pressure͒, new surface structures leading to subsurface oxide formation can be obtained. The onset and growth of oxide on Cu͑100͒ and vicinal surfaces consisting of Cu͑100͒ terraces have been studied extensively by in situ TEM ͑above 423 K͒, [36][37][38][39][40][41][42][43][44][45] and by utilizing combinations of HREELS/XPS, [24][25][26] hyperthermal O 2 molecular beam ͑HOMB͒/XPS, 27,28 NEXAFS, 29 and MBSS. 17 All previous STM investigations [9][10][11][12][13][14][15][16] on Cu͑100͒ have been limited to oxygen coverages below 0.5 ML except our recent XPS/STM study that focused on the formation of subsurface Cu 2 O and CuO in the temperature range of 300-423 K. 60 In this paper we investigate physicochemical phenomena leading to oxide island nucleation on Cu͑100͒ by means of variable temperature scanning tunneling microscopy ͑VT-STM͒ and quantitative XPS as a function of O 2 pressure ͑8.0ϫ 10 −7 and 3.7ϫ 10 −2 mbar͒ at 373 K. We revisit the extensively studied surface confined oxygen adlayer and demonstrate that the ͑2 ͱ 2 ϫ ͱ 2͒R45°-O reconstruction is inert in the low pressure regime.…”

“…Cu͑100͒ is reactive towards O 2 dissociation, and adsorption of O 2 and oxide formation have been extensively investigated on it by a wide array of techniques: low-energy electron diffraction ͑LEED͒, 8 scanning tunneling microscopy ͑STM͒/LEED, 9-16 molecular beam surface scattering ͑MBSS͒/reflection highenergy electron diffraction ͑RHEED͒/Auger electron spectroscopy ͑AES͒/thermal desorption mass spectrometry ͑TDMS͒/LEED, 17,18 surface stress change by crystal curvature technique/density functional theory ͑DFT͒/LEED, 19 LEED multiple-scattering analysis, 20 time-resolved verylow-energy electron diffraction ͑VLEED͒, 21 spot profile analysis low-energy electron diffraction/helium diffraction ͑HED͒, 22 high-resolution electron energy-loss spectroscopy ͑HREELS͒/LEED/AES, 23 HREELS/x-ray photoelectron spectroscopy ͑XPS͒, [24][25][26] hyperthermal O 2 molecular beam ͑HOMB͒/XPS, 27,28 near edge x-ray absorption fine structure ͑NEXAFS͒, 29 normal-emission photoelectron diffraction/NEXAFS/LEED, 30 surface-extended x-ray absorption fine structure ͑SEXAFS͒, 31 angle-and temperaturedependent SEXAFS, 32 angle-dependent NEXAFS and SEXAFS/LEED/XPS/AES/TDMS, 33 surface x-ray diffraction, 34 in situ synchrotron x-ray scattering, 35 transmission electron microscopy ͑TEM͒, [36][37][38][39][40][41][42][43][44][45] analytical electron microscopy ͑AEM͒, 46,47 and ab initio calculations. [48][49][50][51][52]…”

On the Development and the Oxidation of Novel Ni-Cr and Ni-Al Nanocoatings by Composite Electrodeposition

“…High density of the grain boundaries in ENCs will significantly enhance the "short-circuit" diffusion of Cr or Al towards the oxidation front [12], leading to reduction of the transient time for sealing the Cr 2 O 3 or Al 2 O 3 nuclei. This is evidenced by recent work [34], which shows that the critical content of Al for the formation of alumina layer is largely reduced when the Al mricoparticles codeposited are replaced by the equivalent nanoparticles. Thus, ENCs Ni-Cr or Ni-Al may be served as Cr 2 O 3 or Al 2 O 3 former for the metallic materials with a poor oxidation performance, instead of other Cr 2 O 3 or Al 2 O 3 -forming coatings fabricated by other techniques, such as pack cementation, thermal spraying and sputtering as well.…”