Precursor layer

The preparation of MCM-36 involves a lamellar Intermediate, designated MCM-22 precursor, produced in a hydrothermal process. The layers in MCM-22 precursor are approximately 25 A thick and upon calcination condense with the formation of T-O-T moieties producing the zeolite MCM-22. This relationship indicates that the internal structure of the MCM-22 precursor layers matches that of zeolite MCM-22, which is also reflected in the similarity of their X-ray diffraction patterns (XRD) shown in Figure 1. 

Several methods are used to deposit the films onto molybdenum-coated soda-lime glass substrates. Coevaporation of Cu, In, Se, and Ga from elemental sources onto a heated substrate, with careful control of the deposition rate of each, has achieved the highest efficiency. Another common method is selenization. A metal precursor layer of Cu, In, and Ga is deposited by, for example, sputtering and reacted in H2Se or Se vapor. For layers without Ga, the final reaction in a series is... 

Steitz, R., Gutberlet, T., Hauss, T., Klosgen B., Krastev, R., Schemmel, S., Simonsen, A.C., and Eindenegg, G.H. Nanobubbles and their precursor layer at the interface of water against a hydrophobic substrate, Langmuir, 19, 2409, 2003. 

Fig. 25. A schematic diagram of surface diffusion processes (l) diffusion in a weakly held precursor layer, (2) diffusion of a chemisorbed atom or molecule, and (3) diffusion of surface atoms of the solid.

The ED and EL deposition processes are simple and fast, and they can synthesize binary or multinary precursors for subsequent processing into high-quality CIGS thin-film absorbers for solar cells. The device fabricated using ED precursor layers resulted in efficiencies as high as 15.4%. The quality of CIGS-based films and devices prepared from ED precursors is very promising. This may lead to novel, fast, and low-cost methods for solar-cell absorber fabrication. 

A typical experimental setup is sketched in Scheme 5. Organic precursor layers are deposited on the atomically clean surfaces by sublimation of the molecular linkers, typically present in high-purity powder form. The temperature of the substrate is controllably varied from cryogenic conditions ( 10 K) to elevated temperatures ( 500K) in order to achieve thermodynamically metastable or equilibrated products. In the surface-assembled systems the coordination centers are evaporated using electron beam or re-... 

As can be seen in Fig. 2, the precursor layer thickness goes below the molecular dimensions already at moderately small values of x, so the approximation... 

A contact line can be defined as a transition between a precursor film and a droplet , or a film of macroscopic thickness. Eor a straight contact line normal to the X axis, it is convenient to use a phase plane representation of this equation obtained by taking the nominal layer thickness h as the independent, and the squared slope y = h x)) as the dependent variable. The boundary condition y = 0 is set at the precursor layer thickness ho ... 

For a finite droplet, the contact line can be nominally defined as the locus of the inflection point of the profile h x). The slope at the inflection point coincides with the apparent contact angle one would measure in a macroscopic experiment, which does not resolve a strongly curved transitional region separating the bulk fluid and the precursor layer. The profile in the transitional region can be easily matched to a macroscopic solution defining the equilibrium shape of the droplet bulk. 

Quasistationary equahons can be solved numerically [23, 26] or with the help of analyhcal matehing teehniques [27-29] for standard setups, such as advancing or receding menisei or macroscopic droplets on a precursor layer. An example of analytieal solution based on integral mobihty relahons [28] is given in the next Seehon. 

Integrating this term leads therefore to a contour integral n T ds, where n is the normal to the boundary of the integration region. As this boundary lies on a flat precursor layer, the contour integral vanishes. 

This leads to a contour integral expressing the driving force due to a weak gradient of the disjoining potential in the precursor layer ... 

Figure 1.27 Grazing incidence XRD pattern of sulfurized Cu/Sn/Cu/Zn precursor layer. The asterisks indicate a secondary phase assigned to copper sulfide. Cu/(Zn + Sn) = 0.70 0.07, Zn/Sn = 1.06 0.12. Reproduced from reference [11].

The effect of chemical bath composition, electrodeposition potential, etc., on film composition was determined [317]. The precursor films were loaded in a physical evaporation chamber and additional In or Cu and Se were added to the films to adjust the final composition of CIS. The device fabricated using electrodeposited Cu-In-Se precursor layers had a solar cell efficiency of 9.4%. CIS thin films have also been obtained from different precursors prepared by direct or sequential electrodeposition processes [303]. The results showed that thin crystalline chalcopyrite CIS films with the desired composition can be obtained after annealing, whether directly or sequentially electrodeposited precursors at 400 °C. An improvement in film quality was obtained by using an electrodeposited Cu layer as the growth surface for CIS formation. If elemental Se was also added during the heat treatment, then a higher recrystalHzation of the films was observed. A new approach for CIS formation by sequential electrodeposition of Cu and In-Se layers and subsequent heat treatment with elemental selenium in Ar + H2 flows has been presented [304]. An increase in the film crystallinity was achieved... 

Akkahat, ., Mekboonsonglarp, W., Kiatkamjornwong, S., Hoven, V. P. (2012). Surface-grafted Poly(acrylic acid) brushes as a precursor layer for biosensing applications effect of graft density and swellability on the detection efficiency. Langmuir, 28, 5302-5311. 

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