Interpretation Of Depth Profiles Research Articles

Interpretation of Depth Profiles Obtained by DC-Glow Discharge Sputtering

Penetration profiles obtained by dc-glow discharge sputtering are interpreted. An analytical formula is proposed that accounts for the influence of knock-on effect upon the observed shape of the profile and enables the evaluation of the coefficient of volume diffusion at low temperatures. For the illustration of the theoretical conclusions, some chosen experimental curves obtained for the case of 63 Ni diffusion in Ni3Al are processed.

Improving the interpretation of x-ray photoelectron and Auger electron spectra using numerical methods

X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) have long been used for sputter depth profiling for the determination of sample chemical composition as a function of depth. Often in XPS and AES, peak overlap or a subtle change in chemistry makes the chemical analysis of the elements in a material difficult. By using a variety of numerical methods, such as linear least squares fitting and target factor analysis, it is possible to improve the analysis and interpretation of depth profiles. The use of numerical methods can aid in the interpretation of chemical state information and in most cases significantly improves the detection limits of specific elements. An XPS sputter depth profile of tantalum silicide on silicon and an AES profile of a multilayer structure of gold, tantalum, and silicon carbide are shown as examples of the improvements offered by applying numerical methods.

Transformation of amorphous glassy metal/zirconium alloys into CO2 hydrogenation catalysts: an XPS, SIMS, and SNMS investigation

Active catalysts for hydrogenation reactions starting from CO2 have been obtained from amorphous Cu70Zr30, Au25Zr75, Pd25Zr75 and Ni64Zr36 alloys. During in situ activation of these metallic glasses, oxidation and segregation phenomena are occurring, which lead to dispersed metal/zirconia catalysts. A combination of XPS and SNMS depth profiling is applied to examine changes in the oxidation state, as well as in the relative concentrations of the metal and of the zirconium components. From the chemical shifts of the metal 3d/Zr3p doublets analyzed as a function of sputtering time, the removal of an inactive surface ZrO2 layer by Ar ion bombardment, and the concomitant appearance of metallic Zr are demonstrated. Experiments on model substrates with defined layer structures show that the interpretation of depth profiles is most straightforward from the SNMS data. For Au25Zr75 and Pd25Zr75, the ZrO/Zr ratio at sputtering equilibrium increases significantly during transformation of the precursors into the respective metal/zirconia catalysts. The Ni64Zr36 alloy is not fully activated under identical conditions of pretreatment, such that the composition of the original bulk alloy is reached after prolonged sputtering. In situ activation experiments with Cu70Zr30 reveal a pronounced surface enrichment of metallic copper during exposure to CO2 hydrogenation conditions.