Differential sputtering

Ion implantation also has promise in other tields involv ino surface technology for example, new metallurgical phases w ith prior unknown properties can be I untied. In some eases. Mich as heav y implantations of tantalum irt copper of phosphorus in iron, amorphous or glassy phases can be formed. Or. if the implanted atoms ore mobile, inclusions and precipitates can he formed as. for example, implanted argon and helium atoms are insoluble in metals and may form bobbles. The composition of a surface layer can be changed by differential sputtering caused by the implanted ions. 

Figure 17.3.11 AES depth profiles for GaAs anodized in H3PO4 solutions. Ordinate has been corrected for relative Auger intensities and differential sputtering rates. Abscissa is sputtering time. Thickness scales are approximate. Roman numerals indicate different compositional regions in the oxide layer. Bulk GaAs is at rightmost limit, (a) From electrochemical treatment only.

To avoid artifacts created by, for example, differential sputtering rates, Wucher et al. developed protocols for 3D molecular imaging [394]. A procedure for establishing correct depth scales in samples with nonuniform... 

Figure 3.20 Measured differential sputter yields (normalized steady-state values) versus apparent depth for (a) 0.25 keV, (b) 0.5 keV, (c) 1.0 keV, and (d) 2.5 keV Cs impact on Silicon at the listed angles. Reproduced with permission from van der Heide et al. (2003) Copyright 2003 Elsevier.

Sputter rate variations in multicomponent substrates, often referred to as differential sputtering, have long been recognized as one of the potential issues that can result in erroneous quantification (quantification is covered in Sections 5.4.2 and 5.2.3). This is realized as differential sputtering alters the sputter yield, and thereby the surface composition of deeper layers. As will be discussed in Section 3.2, the surface chemistry is one of the primary factors governing secondary ion yields. In short, severe complications are introduced as a result of the fact that sputter yields and ionization yields are usually intrinsically intertwined. 

Understanding the dynamics of the differential sputtering process that is in effect for the substrate of interest under the analytical conditions applied. Note This is a potentially complex undertaking in condensed matter physics (for a review, see Gnaser 1999) requiring the delineation of the sputtering and ionization phenomena. 

Also shown in this Figure 5.20 are the secondary ion yield variations noted. These stem from the differential uptake of Cesium within the respective grains, which, in turn, results from the differential ionization yields as well as differential sputter rates. Note As discussed in Section 3.2.2.2.2, increased Cesium uptake occurs with decreasing sputter rates, hence the greater signal intensities noted from the shallower regions in Figure 5.20. 

Other recent investigations involving AES, often with depth profiling, deal with the surface segregation of Ag in Al-4.2 % Ag [2.163], of Sn in Cu and formation of superficial Sn-Cu alloy [2.164], of Mg in Al-Mg alloy [2.165], and of Sb in Ee-4% Sb alloy [2.166]. Note the need to differentiate between, particularly, segregation, i. e. original sample properties, from the artifact of preferential sputtering. 

In Sigmund s theory, steps 2-4 were accomplished by deriving a differential equation for the sputtering yield based on methods similar to those outlined for reflection of energetic particles in Sect. 2.2.3 (see Ref. 35 for more detail). The sputtering yield from Sigmund s theory is given by... 

Spectra taken during the Auger sputter profile were transformed into a data matrix and treated by the PHI-MATLAB , version 4.0, software. Each element was treated separately, that is the number of matrices was the same as the number of significant elements, and each matrix was completely independent of the others. The number of factors used for reconstruction was the one predicted by the minimum of the indicator function (IND). Unless specified, no mathematical treatment was performed on the data (differentiation, smoothing). 

Table 26.1 Number of factors (NF) detected as a function of the number of points used to differentiate the spectra (Ndif) for the treatment of the Auger sputter profile of a J3-WC, film deposited on tungsten. (Ndif = 0 means no differentiation)...

All XPS or ESCA measurements were performed using a Perkin Elmer 5300 ESCA spectrometer equipped with a dual anode (Mg, Al) X-ray source, differentially pumped Ar+ sputter gun, and the variable angle measurement set-up for angle-resolved photoelectron spectroscopic measurements. The data collection and treatment, e.g. smoothing, curve-fitting, intensity measurements, were accomplished by a Perkin Elmer 7500 dedicated computer system using PHI software package. 

A molecularly imprinted polypyrrole film coating a quartz resonator of a QCM transducer was used for determination of sodium dodecyl sulphate (SDS) [147], Preparation of this film involved galvanostatic polymerization of pyrrole, in the presence of SDS, on the platinum-film-sputtered electrode of a quartz resonator. Typically, a 1-mA current was passed for 1 min through the solution, which was 0.1 mM in pyrrole, 1 mM in SDS and 0.1 M in the TRIS buffer (pH = 9.0). A carbon rod and the Pt-film electrode was used as the cathode and anode, respectively. The SDS template was then removed by rinsing the MlP-film coated Pt electrode with water. The chemosensor response was measured in a differential flow mode, at a flow rate of 1.2 mL min-1, with the TRIS buffer (pH = 9.0) as the reference solution. This response was affected by electropolymerization parameters, such as solution pH, electropolymerization time and monomer concentration. Apparently, electropolymerization of pyrrole at pH = 9.0 resulted in an MIP film featuring high sensitivity of 283.78 Hz per log(conc.) and a very wide linear concentration range of 10 pM to 0.1 mM SDS. 

Tong et al. [98] prepared Pd and Pd77Ag23 membranes by applying a similar procedure to that of Franz et al. [93], The membranes introduced on the support by sputtering had a thickness between 500 and 1 000 nm. They were stable against a differential pressure up to 4 bar and were operated at 450 °C for more than 1000 h. A hydrogen flux up to 90 Ndm3 m 2 s 1 and a separation factor of 1 500 for H2/He were determined for these membranes. 

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