M. Lampimäki - Academia.edu (original) (raw)

Papers by M. Lampimäki

Surface Science Spectra, 2008

In this work, polycrystalline Cu͑Ag͒ bulk alloy ͑1 wt.% Ag͒ and Ag/Cu͑100͒ surface alloy ͑0.9 ML ... more In this work, polycrystalline Cu͑Ag͒ bulk alloy ͑1 wt.% Ag͒ and Ag/Cu͑100͒ surface alloy ͑0.9 ML Ag͒ have been characterized by x-ray photoelectron spectroscopy ͑XPS͒ employing Al K ␣ and Mg K ␣ radiation. XPS spectra of the principal core levels ͑Cu, Ag͒ are presented together with XAES ͑x-ray induced Auger electron spectroscopy͒ spectra of the Cu LMM transition. The samples were prepared in situ by argon ion sputtering at room temperature and subsequent annealing at 700 K. Ag overlayer was deposited on the Cu͑100͒ surface by a resistively heated Ag evaporator. The absence of contaminants such as C or O was confirmed by XPS. Together, the industrial Cu͑Ag͒ alloy and the well defined Ag/Cu͑100͒ model system serve as a template for studies of nanoscale surface oxidation and segregation phenomena.

Surface Science, 2005

In this work we have investigated in situ the nanoscale oxide formation on Cu{1 0 0}, Ag/Cu{1 0 0... more In this work we have investigated in situ the nanoscale oxide formation on Cu{1 0 0}, Ag/Cu{1 0 0} surface alloy and polycrystalline Cu(Ag) alloy. The experiments were conducted in pure oxygen atmosphere ($2 mbar) as a function of surface temperature (320-473 K). The concentration of metallic Cu, Cu 2 O and CuO in the surface region was quantified by X-ray photoelectron spectroscopy (XPS). Oxygen induced segregation of the alloy constituents in the near-surface region, as well as the diffusion of oxygen towards the bulk, were investigated using depth-profiles obtained by employing Ar + ion sputtering and Auger electron spectroscopy (AES). We observed only Cu 2 O formation on all three surfaces under the oxidation conditions used in these experiments. The formation of Cu 2 O was found to be strikingly similar on both Ag/Cu{1 0 0} and Cu{1 0 0}. Our depth-profiling experiments indicate that this is due to a rapid oxygen induced segregation of Cu to the surface and subsequent formation of Cu oxides on top of the Ag overlayer. Evidence of a similar oxidation mechanism was also found on Cu(Ag).

Journal of Electron Spectroscopy and Related Phenomena, 2007

Surface oxidation ranging from initial stages to the onset of passive oxide layer formation have ... more Surface oxidation ranging from initial stages to the onset of passive oxide layer formation have been investigated on Fe-20Cr-18Ni{1 1 1} single crystal surface by X-ray photoelectron spectroscopy (XPS). Surface segregation of the alloying elements and the morphology of the surface oxide nanostructure were characterized quantitatively by inelastic electron background analysis. Our results demonstrate that by increasing the oxidation temperature the relative concentrations of Fe 2+ and Fe 3+ cations increase due to their enhanced mobility. Higher temperature also improves the mobility of chromium, thus enhancing its segregation to the oxygen-rich surface and thereby reinforcing the passive layer on the alloy. This is in agreement with the results showing the sudden decrease in oxide film thickness at the oxidation temperatures exceeding 600 K. Additionally, a pronounced segregation of metallic nickel is found in the interface between the surface oxide layer and the bulk alloy.

The Journal of Chemical Physics, 2008

Surface oxidation of Cu͑100͒ has been investigated by variable temperature scanning tunneling mic... more Surface oxidation of Cu͑100͒ has been investigated by variable temperature scanning tunneling microscopy and quantitative x-ray photoelectron spectroscopy as a function of O 2 pressure ͑8.0 ϫ 10 −7 and 3.7ϫ 10 −2 mbar͒ at 373 K. Three distinct phases in the initial oxidation of Cu͑100͒ have been observed: ͑1͒ the formation of the mixed oxygen chemisorption layer consisting of Cu͑100͒-c͑2 ϫ 2͒-O and Cu͑100͒-͑2 ͱ 2 ϫ ͱ 2͒R45°-O domains, ͑2͒ the growth of well-ordered ͑2 ͱ 2 ϫ ͱ 2͒R45°-O islands, and ͑3͒ the onset of subsurface oxide formation leading to the growth of disordered Cu 2 O. We demonstrate that the ͑2 ͱ 2 ϫ ͱ 2͒R45°-O reconstruction is relatively 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 scanning tunneling microscopy experiments up to 0.5 ML of oxygen. The formation of these islands and their nanostructure appear to be critical to the onset of further migration of oxygen atoms deeper into copper and subsequent Cu 2 O formation in the high pressure regime. The reactivity of each phase is correlated with the surface morphology and the role of the various island structures in the oxide growth is discussed.

Journal of Electron Spectroscopy and Related Phenomena, 2007

Substrate-induced effects in the creation and decay of 2p core excitations of K + and Cl − in ult... more Substrate-induced effects in the creation and decay of 2p core excitations of K + and Cl − in ultrathin films of KCl on Cu(1 0 0) surface have been studied using photoelectron, photoabsorption and resonant Auger spectra, excited by synchrotron radiation. The measurements were performed on different overlayers ranging from sub-monolayer coverages up to continuous thick films. It is demonstrated that the formation and decay of core excitations in thin films of KCl at Cu(1 0 0) surface is strongly influenced by the hybridization of excited states of K + or Cl − origin with the metal substrate, which leads to the delocalization of the excited electron from the absorption site.

Surface and Interface Analysis, 2008

Surface oxidation of Fe-19Cr-17Ni, Fe-19Cr-18Ni-1Al and TiC-enriched Fe-19Cr-18Ni-1Al alloys was ... more Surface oxidation of Fe-19Cr-17Ni, Fe-19Cr-18Ni-1Al and TiC-enriched Fe-19Cr-18Ni-1Al alloys was investigated by photoelectron spectroscopy (PES). The experiments were conducted at 323 K in pure O 2 (2.7 × 10 −6 mbar). Composition and morphology of the nanoscale surface oxides were determined quantitatively by inelastic electron background analysis. Moreover, use of synchrotron radiation facilities were necessary to obtain improved sensitivity for studying minor alloying elements such as Al and Si. The results indicate oxygen-induced segregation of Al, which significantly hinders the oxidation of the major alloying elements Fe and Cr. Ti remains in its inert carbide form. The relative concentration of Fe within the oxide layer was found to increase with the oxide-layer thickness, indicating greater mobility of Fe relative to other alloying elements.

Review of Scientific Instruments, 2006

The design and performance of an x-ray photoelectron spectroscopy ͑XPS͒-scanning tunneling micros... more The design and performance of an x-ray photoelectron spectroscopy ͑XPS͒-scanning tunneling microscopy ͑STM͒ surface analysis system for studying nanostructured materials are described. The analysis system features electron spectroscopy methods ͑XPS and Auger electron spectroscopy͒ in addition to a variable temperature STM. With the analytical methods of the system, surface chemical analysis as well as surface morphology down to atomic resolution can be obtained. The system also provides facilities for sample cleaning, annealing, gas dosing, depth profiling, and surface modifications by sputtering and evaporation. Controlled gas exposures from ultrahigh vacuum to atmospheric pressures in the adjustable temperature range of 120-1100 K can be carried out in different chambers. A fast entry air lock allows the transfer of samples and STM tips into the system without air exposures. The surface analysis system uses a common sample holder in all five chambers which are independently pumped and separated from each other by gate valves. Thus, it is possible to make all sample preparations and experiments in situ under well-defined conditions as illustrated by the formation and characterization of strained, self-assembled nano-oxides on Cu͑100͒.

Surface Science Spectra, 2008

In this work, polycrystalline Cu͑Ag͒ bulk alloy ͑1 wt.% Ag͒ and Ag/Cu͑100͒ surface alloy ͑0.9 ML ... more In this work, polycrystalline Cu͑Ag͒ bulk alloy ͑1 wt.% Ag͒ and Ag/Cu͑100͒ surface alloy ͑0.9 ML Ag͒ have been characterized by x-ray photoelectron spectroscopy ͑XPS͒ employing Al K ␣ and Mg K ␣ radiation. XPS spectra of the principal core levels ͑Cu, Ag͒ are presented together with XAES ͑x-ray induced Auger electron spectroscopy͒ spectra of the Cu LMM transition. The samples were prepared in situ by argon ion sputtering at room temperature and subsequent annealing at 700 K. Ag overlayer was deposited on the Cu͑100͒ surface by a resistively heated Ag evaporator. The absence of contaminants such as C or O was confirmed by XPS. Together, the industrial Cu͑Ag͒ alloy and the well defined Ag/Cu͑100͒ model system serve as a template for studies of nanoscale surface oxidation and segregation phenomena.

Surface Science, 2005

In this work we have investigated in situ the nanoscale oxide formation on Cu{1 0 0}, Ag/Cu{1 0 0... more In this work we have investigated in situ the nanoscale oxide formation on Cu{1 0 0}, Ag/Cu{1 0 0} surface alloy and polycrystalline Cu(Ag) alloy. The experiments were conducted in pure oxygen atmosphere ($2 mbar) as a function of surface temperature (320-473 K). The concentration of metallic Cu, Cu 2 O and CuO in the surface region was quantified by X-ray photoelectron spectroscopy (XPS). Oxygen induced segregation of the alloy constituents in the near-surface region, as well as the diffusion of oxygen towards the bulk, were investigated using depth-profiles obtained by employing Ar + ion sputtering and Auger electron spectroscopy (AES). We observed only Cu 2 O formation on all three surfaces under the oxidation conditions used in these experiments. The formation of Cu 2 O was found to be strikingly similar on both Ag/Cu{1 0 0} and Cu{1 0 0}. Our depth-profiling experiments indicate that this is due to a rapid oxygen induced segregation of Cu to the surface and subsequent formation of Cu oxides on top of the Ag overlayer. Evidence of a similar oxidation mechanism was also found on Cu(Ag).

Journal of Electron Spectroscopy and Related Phenomena, 2007

Surface oxidation ranging from initial stages to the onset of passive oxide layer formation have ... more Surface oxidation ranging from initial stages to the onset of passive oxide layer formation have been investigated on Fe-20Cr-18Ni{1 1 1} single crystal surface by X-ray photoelectron spectroscopy (XPS). Surface segregation of the alloying elements and the morphology of the surface oxide nanostructure were characterized quantitatively by inelastic electron background analysis. Our results demonstrate that by increasing the oxidation temperature the relative concentrations of Fe 2+ and Fe 3+ cations increase due to their enhanced mobility. Higher temperature also improves the mobility of chromium, thus enhancing its segregation to the oxygen-rich surface and thereby reinforcing the passive layer on the alloy. This is in agreement with the results showing the sudden decrease in oxide film thickness at the oxidation temperatures exceeding 600 K. Additionally, a pronounced segregation of metallic nickel is found in the interface between the surface oxide layer and the bulk alloy.

The Journal of Chemical Physics, 2008

Surface oxidation of Cu͑100͒ has been investigated by variable temperature scanning tunneling mic... more Surface oxidation of Cu͑100͒ has been investigated by variable temperature scanning tunneling microscopy and quantitative x-ray photoelectron spectroscopy as a function of O 2 pressure ͑8.0 ϫ 10 −7 and 3.7ϫ 10 −2 mbar͒ at 373 K. Three distinct phases in the initial oxidation of Cu͑100͒ have been observed: ͑1͒ the formation of the mixed oxygen chemisorption layer consisting of Cu͑100͒-c͑2 ϫ 2͒-O and Cu͑100͒-͑2 ͱ 2 ϫ ͱ 2͒R45°-O domains, ͑2͒ the growth of well-ordered ͑2 ͱ 2 ϫ ͱ 2͒R45°-O islands, and ͑3͒ the onset of subsurface oxide formation leading to the growth of disordered Cu 2 O. We demonstrate that the ͑2 ͱ 2 ϫ ͱ 2͒R45°-O reconstruction is relatively 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 scanning tunneling microscopy experiments up to 0.5 ML of oxygen. The formation of these islands and their nanostructure appear to be critical to the onset of further migration of oxygen atoms deeper into copper and subsequent Cu 2 O formation in the high pressure regime. The reactivity of each phase is correlated with the surface morphology and the role of the various island structures in the oxide growth is discussed.

Journal of Electron Spectroscopy and Related Phenomena, 2007

Substrate-induced effects in the creation and decay of 2p core excitations of K + and Cl − in ult... more Substrate-induced effects in the creation and decay of 2p core excitations of K + and Cl − in ultrathin films of KCl on Cu(1 0 0) surface have been studied using photoelectron, photoabsorption and resonant Auger spectra, excited by synchrotron radiation. The measurements were performed on different overlayers ranging from sub-monolayer coverages up to continuous thick films. It is demonstrated that the formation and decay of core excitations in thin films of KCl at Cu(1 0 0) surface is strongly influenced by the hybridization of excited states of K + or Cl − origin with the metal substrate, which leads to the delocalization of the excited electron from the absorption site.

Surface and Interface Analysis, 2008

Surface oxidation of Fe-19Cr-17Ni, Fe-19Cr-18Ni-1Al and TiC-enriched Fe-19Cr-18Ni-1Al alloys was ... more Surface oxidation of Fe-19Cr-17Ni, Fe-19Cr-18Ni-1Al and TiC-enriched Fe-19Cr-18Ni-1Al alloys was investigated by photoelectron spectroscopy (PES). The experiments were conducted at 323 K in pure O 2 (2.7 × 10 −6 mbar). Composition and morphology of the nanoscale surface oxides were determined quantitatively by inelastic electron background analysis. Moreover, use of synchrotron radiation facilities were necessary to obtain improved sensitivity for studying minor alloying elements such as Al and Si. The results indicate oxygen-induced segregation of Al, which significantly hinders the oxidation of the major alloying elements Fe and Cr. Ti remains in its inert carbide form. The relative concentration of Fe within the oxide layer was found to increase with the oxide-layer thickness, indicating greater mobility of Fe relative to other alloying elements.

Review of Scientific Instruments, 2006

The design and performance of an x-ray photoelectron spectroscopy ͑XPS͒-scanning tunneling micros... more The design and performance of an x-ray photoelectron spectroscopy ͑XPS͒-scanning tunneling microscopy ͑STM͒ surface analysis system for studying nanostructured materials are described. The analysis system features electron spectroscopy methods ͑XPS and Auger electron spectroscopy͒ in addition to a variable temperature STM. With the analytical methods of the system, surface chemical analysis as well as surface morphology down to atomic resolution can be obtained. The system also provides facilities for sample cleaning, annealing, gas dosing, depth profiling, and surface modifications by sputtering and evaporation. Controlled gas exposures from ultrahigh vacuum to atmospheric pressures in the adjustable temperature range of 120-1100 K can be carried out in different chambers. A fast entry air lock allows the transfer of samples and STM tips into the system without air exposures. The surface analysis system uses a common sample holder in all five chambers which are independently pumped and separated from each other by gate valves. Thus, it is possible to make all sample preparations and experiments in situ under well-defined conditions as illustrated by the formation and characterization of strained, self-assembled nano-oxides on Cu͑100͒.