Lifetime depth profiles

For now, the bimodal distribution may be an artifact. The two lifetimes can be considered as lower and upper bounds of the pore size distribution. This technique is the only one available that can provide non-destructive depth profiles without sample preparations other than mounting them in the vacuum system. Depth profiled lifetime data are currently being collected. This is practical due to the high data acquisition rate of 3TO3 to 104 lifetime events per second, depending on the implantation depth. 

Lifetime depth profiles will be useful for the detection of inhomogeneous pore size distributions and in tracking impurities. For microelectronic device fabrication it is crucial that subsequent processing steps do not alter the deposited porous layers. The case presented above of oxygen plasma treatment is just one example. A lifetime depth profile could provide direct evidence for the changes in pore sizes discussed in the work on HSSQ samples and oxygen plasma treatment [22]. Gidley et al have carried out similar depth profiles [74]. 

We can estimate the time scale in which the whole surface layer is affected by the primary ions. The lifetime of a surface may be simply estimated from the primary ion flux (Ip) and damage cross-section (er) generated by each impact. Ip is commonly measured in A cm-2 (1 A = 6.2 x 1018 charged particles per second). Assume that each primary ion generates a = 10-13 cm2. Then, 1013 primary ions cm-2 will affect the whole surface area of 1 cm2. It means that the lifetime of a surface with the flux density Ip= 1 pA cm-2 (= 6.2 x 1012 ions cm-2) is less than 1 second. Apparently, 1 p A cm-2 of flux density for primary ions is too high for static SIMS. Since it is commonly accepted for the static SIMS condition to limit the total amount of primary ions up to 1013 ions cm-2, for a 10-min duration of static SIMS examination a primary flux density of about 2.7 nA cm-2 is required to preserve the chemical structure of the surface top layer where the secondary ions are emitted. This flux is extremely low compared with that of dynamic SIMS, which requires a flux density of greater than 1 pA cm-2 to ensure a reasonable erosion rate of surface for depth profiling. 

The depth profile of free volume properties measured using variable energy PALS provides an opportunity to investigate the aging behavior as a function of depth from the free surface. The average o-Ps lifetime across a specific section of the film, t3 can be calculated by ... 

In addition to depth-profiling the active polymeric components of elertronic devices, IBA has proved to be a useful tool to study the diffusion of indium from the adjacent indium tin oxide (ETO) electrode into the polymer layers. Although the diffusion of In into active polymer layers does not predude the use of this comhination, the instability of the interface that was established by these experiments is certainly a cause for some concern when considering the operational lifetime of polymer LED devices. 

Based on predicted weathering and erosion rates of the region, we estimate the profile to be several million years old. Because the soil has developed in situ, the topmost grains have reacted with water for the greatest extent of time. With depth, the total "lifetime" of the particles as soil decreases. This implies that the topmost quartz surfaces should be "reactively mature" (all fines removed, deep grown-together etch pits) and the bottom-most quartz surfaces should be "reactively young" (plentiful fines, fresh surfaces). ... 

The vertical profile of DMS in marine air was first determined by Ferek et al (12), over the tropical Atlantic ocean. They found that under stable meteorological conditions, the mixing depth of DMS was about 1 km, with a rapid decline in concentration above this altitude. This distribution was considered consistent with the chemical lifetime of a few days predicted by... 

Meijer and Janssen [131] described tests to evaluate issues such as activity, selectivity, fouling lifetime of the catalyst, the surface composition and concentration profiles in depth of honeycomb catalysts. 

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