Direct layer deposition

FIG. 21. SEM micrographs of two deposits, each formed with 50 cycles and the same deposition hardware, but with differing ECALE programs. The conditions are as follows (a) deposit atomic layer of Te at —1.25 V directly (b) deposit bulk Te at —0.8 V first, followed by rinsing out excess HTe02, and subsequently stripping off the excess Te in the corresponding blank. (Erom Ref. 158.)... 

As previously mentioned, the first atomic layer, in contact with the substrate, appears to be the most critical. Electrochemically there are three different ways to form the first atomic layer of Se, and graphs depicting each are displayed in Fig. 56. The first method is straightforward—the direct reductive deposition of Se atomic layers from a HSeOs" solution. The voltammetry for Se deposition is shown in Fig. 57 and displays two feature, Ci and Cj. Ci could be thought of as a UPD feature because it... 

Although the sputter deposition technique can provide a cheap and directly controlled deposition method, the performance of PEM fuel cells with sputtered CLs is still inferior to that of conventional ink-based fuel cells. In addition, other issues arise related to the physical properties of sputtered catalyst layers, such as low lateral electrical conductivity of the thin metallic films [96,108]. Furthermore, the smaller particle size of sputter-deposited Ft can hinder water transport because of the high resistance to water transport in a thick, dense, sputtered Ft layer [108]. Currently, the sputter deposition method is not considered an economically viable alternative for large-scale electrode fabrication [82] and further research is underway to improve methods. 

Reproducibility of film preparation and stability of the resulting films are important issues for practical applications. Cleanliness of the IRE before metal deposition can play a decisive role in determining reproducibility. Depending on the conditions, metal films may not be stable and may peel off (36,37). The stability and reproducibility of metal films can be enhanced by evaporating a metal oxide support material (such as AI2O3) prior to evaporation of the desired metal. Contaminants on the IRE are covered or displaced by evaporation of the metal oxide. It was reported that a 50-100-nm-thick AI2O3 layer deposited on a Ge IRE by electron beam physical vapor deposition hardly affected the reflectivity in an ATR experiment. Thin platinum films directly deposited onto it were found to be rather stable under catalytic reaction conditions (26,38). 

Fig. 12 a and b. Variation of dope concentration over the deposit thickness for single layer deposition (schematic)13 (a) moving the reactor with the gas flow, (b) moving the reactor toward the direction of the gas flow. (Reproduced by permission of The Electrochemical Society)... 

Fig. 8 b In this approach, a DETA-coated silicon surface is coated with SMPD and 254 nm light is used to direct the deposition of photoresist. Here, thiolated DNAs bound to the SMPD layer are not covered by photoresist... 

Compositions of the pervasive layered deposits seen in Mars Global Surveyor imagery (Malin and Edgett, 2000) have not been measured directly. However, TES spectra, which are dominated by sand-sized particles, indicate that igneous minerals (pyroxenes and plagioclase) are abundant on the martian surface. Quartz, which should be readily detectable in TES spectra, has not been observed. Deconvolutions of the spectra of soils and dust are dominated by framework silicates, either plagioclase or zeolites (Bandfield and Smith, 2003 McSween et aL, 2003). 

A fresh interfacial area needs to be created directly before depositing the mono-layer material. This can be achieved by sweeping the surface remnants of a previous experiment or inadvertant surface-active Impurities are collected by compressing the area, followed by suction of the reduced area. This manipulation can be repeated several times. Preferably after compression the surface pressure should be 0.1 mN m". In most cases, some tens of a pf of the spreading solution Is supplied by using a micrometer syringe. In the case of a liquid-gas interface, a drop of the spreading solution may Just be deposited on the surface, provided the monolayer material is insoluble in the liquid phase. However, in the case of... 

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