Nanoscale oxidation of Cu(100): Oxide morphology and surface reactivity

Abstract

Surface oxidation of Cu(100) in O(2) has been investigated in situ by x-ray photoelectron spectroscopy, x-ray induced Auger electron spectroscopy (XAES), and scanning tunneling microscopy (STM) as a function of surface temperature (T(S)=303-423 K) and O(2) pressure (p(O(2) )=3.7 x 10(-2)-213 mbars). Morphology of the oxide on the surface and in the near surface layers is characterized by utilizing STM and the inelastic electron background of the XAES O KLL signal. Analysis of the peak shape of the XAES Cu LMM facilitates the quantification of Cu, Cu(2)O, and CuO surface concentrations. The authors conclude that the surface oxidation of Cu(100) proceeds in three distinct steps: (1) Dissociative adsorption of O(2) and the onset of Cu-(2 square root 2 x square root 2)R45 degrees -O (theta(O)=0.5 ML) surface reconstruction, (2) initial formation of Cu(2)O and the appearance of 1.8 A high elongated islands that also adopt the Cu-(2 square root 2 x square root 2)R45 degrees -O structure, and (3) formation of highly corrugated Cu-O islands which together with the surface reconstruction strongly enhance the reactivity of the surface towards further oxide formation. Both Cu(2)O and CuO formations are enhanced by increased surface temperature, but no pressure dependence can be seen.

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

“…It shows the O KLL spectrum from Cu͑100͒ after 6.0ϫ 10 5 L exposure and the optimized surface morphology as obtained by extrinsic electron background analysis. 60,67 The structure consists of 20 and 3 Å thick oxide layers covering 20% and 80% of the surface, respectively. The O KLL transition is optimal for the analysis, because its background is not perturbed by spectral features of other transitions.…”

“…[62][63][64][65] The former technique is described in detail in our previous studies. 60,61,66,67 The latter analysis was conducted with QUASES software package 68 and it yielded concentration of oxides and their in-depth distribution. The analysis process is based on computational morphology models using known information of the initial electron energy, inelastic electron mean free paths ͑IMFPs͒, ionization cross section, measurement geometry, energy dependence of the spectrometer transmission function, and attenuation described by the Beer-Lambert law.…”

“…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. The nucleation and growth of well-ordered two-dimensional Cu-O islands between two ͑2 ͱ 2 ϫ ͱ 2͒R45°-O domains is revealed by time-resolved STM experiments up to 0.5 ML of oxygen.…”

Catalyst preparation for CMOS-compatible silicon nanowire synthesis

“…Oxidation of copper is a long standing subject 21 as metal oxide is usually undesirable for good electrical contacts. Studies at the nanoscale were recently conducted since copper oxide may have interesting applications in photovoltaics and chemistry 22,23 . At low oxygen exposure, a Cuprous oxide (Cu 2 O) forms until, at higher exposure, a Cupric (CuO) phase nucleates 22 and eventually forms nanowires 24 .…”

“…Upon exposure to SiH 4 , the very reactive Cuprous oxide 23 [3][4][5] . The size of the catalyst particle being larger than ten nanometres, a reduction to 400°C of their melting temperature is not expected 25 and nanowire growth should occur in the VSS regime.…”