Clear-field mask

The first step involving the preparation of master is spin coating of silicon wafer with SU-8 negative resist. Subsequently, UV exposure is carried out with a clear field mask. This is followed by the development of SU-8 master. Glass posts are placed on SU-8 master to define the inlets and reservoirs. PDMS is mixed with prepolymers having weight ratio of the base and... 

Note masks are either comprised of soda-lime glass (coated with either a photographic emulsion, Pe203, or Cr films), or quartz (with a Cr film). Due to the absorption of UV light by glass, the latter is required for deep UV (DUV) photolithography. Masks may be classified as either light-field or dark-field whereas the former is mostly clear with opaque patterns, the latter is an opaque mask, with transparent features. 

Figure 13.16 shows a SiNW 4 p.m in length and 9.5 nm in width. Figure 13.16a shows the silicon oxide mask. The thickness of the fabricated mask is about 3 nm. After etching, the SiNW is contacted to two platinum electrodes (Fig. 13.16b). The fabricated SiNW is the main element of a field-effect transistor formed by introducing a gate electrode. Here, the gate electrode is situated at the back of a silicon-on-insulator wafer. The output and transfer characteristics of the transistor formed with the SiNW described above are shown in Fig. 13.16d. The output curve (left panel) shows a clear dependence on the gate voltage. The off-state drain current leakage is about 10 A. The device shown above has an on/off current ratio of 10, and it can be used to develop very sensitive biomolecular sensors.

Thus, a comparison between HPLC-derived lipophilicity indices and calculated log P values for a series of 8-substituted xanthines showed a clear influence of conformational effects. 8 In this case, Rekker s method was unable to take 3D effects into account, but the difference between experimental and predicted values was structure dependent rather than constant. Conformational analyses confirmed that a smaller than predicted lipophilicity was associated with folded conformers stabilized by hydrophobic and van der Waals forces and having part of their nonpolar surface masked from the aqueous phase. A 4D theoretical approach (log P calculations by MLP for conformers generated by high temperature molecular dynamics) suggests that these effects should be lower in an w-octanol/water system than in RP-HPLC. Indeed, the n-octanol/water system is not the most suitable model to study intramolecular interactions in nonpolar media because a surprisingly high proportion of water is dissolved in the w-octanol. Recall, however, that w-octanol, despite some limitations, was selected by many workers in the field as a model for biological membranes. 

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