Oxygen plasma treatment

Fig. 26. Surface morphology of a platinum sample after 4 h of oxygen plasma treatment. The platinum surface is partially covered by faceted particles 5 pm in diameter (245).

A significant number of papers take advantage of the fact that oxidation of PDMS (either by exposure to UV-ozone or to oxygen plasma) can create a stiff silica-like material [17, 40, 43], During the oxidation process, up to 50% of PDMS in the topmost layer is converted into silica [40], Oxygen plasma treatment was first applied by B owden and coworkers [ 16] to create such a surface layer and use a thermal shrinkage process to create wrinkles. They found patterns with wavelengths between fractions of a micron and 10 p.m. They also reported the appearance of cracks which arise due to the brittle nature of the silica material. 

Figure 2.15 Schematic representation for the process of immobilization of the stationary phase in the channel, (a) Microfabricated quartz chip with cross channel design (b) PDMS slab bonded reversibly to the quartz, defining the location of the stationary phase (c) quartz with stationary phase particles immobilized in the separation channel after removing the PDMS cover (d) bonding of PDMS and quartz after oxygen plasma treatment [71].

Conventional photolithography with a negative photoresist SU-8 on a silicon wafer was used for manufacture [56], PDMS pre-polymer and a curing agent were mixed and poured on this master. The PDMS replica was separated and inlet and outlet holes were punched into the replica. The PDMS micro structure was bonded to glass slides by oxygen plasma treatment. 

Fig. 26. Cyclic voltajnmograms for a polycrystalline diamond electrode before (broken line) and after (solid line) oxygen plasma treatment for 1 min, taken in 0.1 M Na2S04 + ImM Fe(CN)63-/4" solution. Scan rate 100 mV s 1. Reprinted from [115]. Copyright (1999), with permission from Elsevier Science.

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]. 

Polymer substrates are often coated with metals for a wide variety of reasons. In many cases, the chemical condition of the surface has been found Q) to alter the adhesion of the metal film to the substrate. In particular, oxygen plasma treatment of polymer surfaces before metal deposition has been found (, 4)... 

Figure 11 shows an RBS spectrum of a PBTMSS film after O2 RIE (1 min, —800 V, 20 mTorr). The substrate signal in this and other spectra is markedly lower and it is similar to the simulated spectrum which indicates that oxygen plasma treatment makes the film more radiation resistant. In addition, the surface layer of plasma treated films does not contain measurable amounts of sulfur. The thickness of this sulfur-free layer, estimated by comparison with simulated spectra, is about 50 A after RIE and SME and 25 A after the barrel etching. The data also show that the same layer is enriched in oxygen and silicon which was confirmed by simulation. These results compare favorably with those obtained from AES spectra. 

The effect of the oxygen plasma treatment in the presence of the contaminant is again seen in the fluorine traee from the depth profile, showing the inerease... 

The decrease of Si due to F-containing contaminants and the role of the oxygen plasma treatment can be explained by the principle of CAP. The key factor to explain the change of elementary composition at the interface is the plasma sensitivity of elements involved on the surface and in the plasma phase. The ablation of materials exposed to plasmas appears to follow the plasma sensitivity series of the elements involved, which is in the order of the electronegativity of the elements, i.e., elements with higher electronegativity in the condensed phase are more prone to ablate in plasma that contains elements with lower electronegativity [5]. 

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