Decorating defects

HC1 etching at 1350°C has been used to study defects [10] and decorated defects in a similar way to that of molten salts. 

The nucleation behavior of transition metal particles is determined by the ratio between the thermal energy of the diffusing atoms and the interaction of the metal atoms at the various nucleation sites. To create very small particles or even single atoms, low temperatures and metal exposures have to be used. The metal was deposited as metal atoms impinging on the surface. The metal exposure is given as the thickness (in monolayer ML) of a hypothetical, uniform, close-packed metal layer. The interaction strength of the metals discussed here was found to rise in the series from Pd < Rh < Co ( Ir) < V [17,32]. Whereas Pd and Rh nucleate preferentially at line defects at 300 K and decorate the point defects at 90 K, point defects are the predominant nucleation center for Co and V at 300 K. At 60 K, Rh nucleates at surface sites between point defects [16,33]. 

Figure 8.6 summarizes our current knowledge of the appearance of point defects in STM images. The most prevalent point defects on sputtered/annealed Ti02(l 1 0) lxl surfaces have been identified as Ob-vacs, OHb, and OHb pairs and these are shown in a ball model together with an STM image decorated with a number of all three types of defects. 

IR Studies of Lattice Defects Decorated with Hydrogen. 158... 

The implantation of hydrogen into silicon or crystal growth in a hydrogen atmosphere introduces vibrational bands that have been ascribed to lattice defects decorated with hydrogen. While IR experiments were begun —10 years before similar studies of passivated shallow impurities, the structures of the complexes that result from H+ implantation are not well understood. This subject has been reviewed previously by Pearton et al. (1987, 1989). Here, the central experimental results will be summarized. A recent uniaxial stress study (Bech Nielsen etal., 1989) of several of the vibrational features will be discussed in Section IV.3. 

To make further progress in the assignment of the hydrogen decorated lattice defects, additional structural or chemical information is required. 

Figure 3.1 Electron micrograph showing a dislocation in silver, imaged as a dark line. The small triangular features that decorate the dislocation are stacking faults formed by the aggregation of point defects. [From W. Sigle, M. L. Jenkins, and J. L. Hutchison, Phil. Mag. Lett., 57 267 (1988). Reproduced by permission of Taylor and Francis, http //www.informa world.com.]...

Defects in a SCR, which is present under reverse bias, can be tested in a similar way. Figure 10.6 c shows the same wafer as in Fig. 10.6 e after removal of the oxide and under cathodic polarization in the dark. Hydrogen bubbles caused by the dark current now decorate nickel silicide precipitates that short-circuit the SCR. Nickel precipitates are known to increase the dark current of a p-type Si electrode under reverse bias by orders of magnitude [Wa4]. If the bias is increased the copper silicide precipitates also become visible, as shown in Fig. 10.6 d. This method, like defect etching (Fig. 10.4f), is only sensitive to precipitated metals. Metals that stay in solution, like iron, do not show up in defect mapping and have to be determined by other methods, for example diffusion length mapping. 

If mapping of the defects is dispensable and only the average contamination level is of interest, measurements of the reverse dark current are sufficient to provide this information [Wi2]. This method is also applicable to n-type samples, which is in contrast to decoration of SCR defects by hydrogen bubbles, which is not possible in the anodic regime. 

Fig. 10.6 A p-type Si wafer with a 20 nm thick thermal oxide has been contaminated by scratching the backside with metal wires (Ni, Cu, Fe), according to the pattern shown in (a) and later annealed at 1200°C for 30 s. (e) Under cathodic bias in acetic acid, oxide defects become decorated by hydrogen bubbles. (c, d) After oxide removal junction defects caused by metal precipitates are decorated by hydrogen bubbles, if sufficient catho...

Figure 9.5(d) gives an impression about the topo-chemical nature of the hydrogen atom s attack on carbon. Even these highly reactive species attack carbon not in an isotropic form but react from the edges and thus decorate, after some extent of conversion, the planar shape of the BSU as stacks of graphene layers with uneven but identical outer shapes. The rounded protrusions into the edge structure arise from defect clusters that would manifest themselves in a perpendicular view as etch pits . 

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