Electron beam-induced deposition

A third class of catalysts was prepared by electron beam induced deposition of XiCl4 on a polycrystalhne Au foil. Deposition of TiCU at 300 K leads to films which comprise Ti + and Ti species as inferred from XPS measurements [90]. Depending on the experimental parameters (background pressure of TiCU, electron flux, electron energy) different composition of Ti oxidation states are observed [23]. From angular-dependent measurements it was concluded that the Ti + centers are more prominent at the surface of the titanium chloride film, while the Xp+ centers are located in the bulk [90]. 

Iron carbonyls have been also used to fabricate nanostructures of potential use in catalysis. In this context, the preparation at room temperature of nano-sized a-Fe single crystals over carbon micro-grid films has been reported. The particles were prepared by electron beam induced deposition using Fe(CO)s as precursor [77]. The use of a focused electron beam to induce metal deposition from carbonyl compounds opens a new route for the preparation of nano-sized metal particles. 

Rather than investigating hot spots by removing molecules from a surface, Chen et al. were able to deposit amorphous carbonaceous nanoparticles into a localized hot spot using a modified electron-beam-induced deposition method (EBID) [120]. The carbon nanoparticles were deposited within a nanoslit cavity structure which was coated with gold to create a SERS active surface where hot spots exist [121]. 

Silvis-Cividjian, N., C.W. Hagen, L.H.A. Leunissen and R Kruit. 2002. The role of secondary electrons in electron-beam-induced-deposition spatial resolution. Microelectron Eng 61-62 693-699. 

Yang X, Simpson ML, Randolph SJ, Rack PD, Baylor LR, Cui H, et al. Integrated tungsten nanofiber field emission cathodes selectively grown by nanoscale electron beam-induced deposition. Appl Phys Lett 2005 86 183106. 

Chemical alternation of the surface layer and deposition of a new layer on top of the silicone mbber can be achieved by physical techniques. For the inert surface of silicone rubber, the former requires the generation of high-energy species, such as radicals, ions, or molecules in excited electronic states. In the latter case, coatings of atoms or atomic clusters are deposited on polymer surfaces using technique such as plasma (sputtering and plasma polymerization) or energy-induced sublimation, like thermal or electron beam-induced evaporation. 

Ordered multilayer deposits of phthalocyanine molecules could be observed by low-energy electron diffraciton with no apparent electron beam induced chemical effects. This appears consistent with the general trend for molecules with highly conjugated electron systems to be more stable under electron bombardment than other organic molecules. 

Electron-beam-induced evaporation, in which a stream of electrons is emitted from a hot filament and accelerated into a target of the material to be deposited, is an effective means to deposit Al, Au, Cr, Ti, and most any other metal, again in a high-vacuum system. The added complexity of e-beam systems makes them considerably more expensive than comparable thermal deposition apparatus. 

Schottky contacts on ZnO were realized by the thermal evaporation of Ag, Au, Ni, or Pd, respectively. We used different surface preparation techniques prior to the deposition of the contact metal. For the single crystals a front-back contact configuration was used while a front-front configuration has to be used for thin films grown on insulating sapphire substrates. The homogeneity of the Schottky contacts depends on the surface preparation as revealed by electron beam induced current (EBIC) measurements (Fig. 6). 

Figure 6. Electron beam induced current scans on a) a sample treated with N2O plasma and b) a sample treated with HCl prior to the metal deposition.

Other Reactions on Zeolites. - Coke deposits on USHY, H-OFF, and HZSM-5 zeolites were characterized by EELS. The EELS spectra were taken on small areas during a short period of time to minimize specimen drift and electron beam-induced damages. Because of this, the spectra were too noisy to proceed with a data reduction, and therefore no quantitative treatment of the EELS spectra was attempted. A qualitative analysis was carried out, comparing the spectra taken on the coked zeolite (or on the insoluble coke) with the EELS spectra taken on reference carbon compounds of known structure. Figure 5 shows the results. It was found that in HZSM-5 and H-OFF the coke forms an external envelope around the zeolite crystal and stands as an empty mold after zeolite extraction. Its structure is similar to that of coronene (polyaromatic-pregraphitic). In USHY zeolite, the coke has a structure more like pentacene (linear polyaromatic). 

Deposition of metals can be accomplished using various methods. However, thermal evaporation, electron-beam-induced evaporation, and sputtering are the most used methods. 

Fig. 7.12. Electron-beam-induced current (EBIC) images showing the plan view of (a) GeSi deposited on unpatterned Si substrates and (b) GeSi deposited on patterned Si substrates. The figures reveal changes in misfit dislocation densities in a Geo.19Sio.8i alloy on a (001) Si substrate. Adapted from Fitzgerald et al. (1991) and Fitzgerald (1995). Reproduced with permission from E.A. Fitzgerald, Massachusetts Institute of Technology.

New promising technologies for future electron-beam lithography applications based on pyroelectrically induced electron emission from LiNbOs ferroelectrics [22] were recently proposed [23], The developed system possessing micrometer scale resolution used 1 1 electron beam projection. The needed electron pattern was obtained by means of deposited micrometer-size Ti-spots on the polar face of LiNbOs. Another solution for the high resolution electron lithography may be found in nanodomain patterning of a ferroelectric template. 

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