Used in thin film deposition

ESA leads to an obstruction, for example, the ovens, Knudsen cells, etc. needed for deposition of thin films prevent a direct view of the substrate. This is one reason why RHEED is in rather widespread use in thin-film deposition systems—the electron gun and screen are remote and grazing incidence does not interfere with film deposition. Therefore, in many cases RHEED is a real in situ technique. By comparison, the conventional front view LEED system blocks essentially the full space and the rear view system blocks half of the space available. In this respect MEIS and RBS are also remote systems that do not take much space around the substrate or target. In some systems transport is installed as a solution (it is the only solution when adding STM to the tool box). 

In Situ Monitoring by Mass Spectrometry of Laser Ablation Plumes Used in Thin Film Deposition... 

Mirzamaani et al. [74, 75] point out that the earlier studies of the interrelationships between structure and magnetics have examined films substantially thicker than those now being used in thin-film disks. These authors have examined very thin CoP films and have studied the relative roles of shape anisotropy, stress anisotropy, and crystal anisotropy in determining the magnetic properties. For their CoP-deposition system, shape anisotropy dominated the other factors in determining the film magnetic properties. The shape anisotropy of a particular deposit was determined by the surface condition of the substrate on which the CoP was deposited. 

The main physicochemical processes in thin-film deposition are chemical reactions in the gas phase and on the film surface and heat-mass transfer processes in the reactor chamber. Laboratory deposition reactors have usually a simple geometry to reduce heat-mass transfer limitations and, hence, to simplify the study of film deposition kinetics and optimize process parameters. In this case, one can use simplified gas-dynamics reactor such as well stirred reactor (WSR), calorimetric bomb reactor (CBR, batch reactor), and plug flow reactor (PFR) models to simulate deposition kinetics and compare theoretical data with experimental results. 

The results presented in this section further illustrate that there is a considerable dependence of the band alignment at the CdS/ZnO interface on the details of its preparation. An important factor is the local structure of the ZnO film. There is considerable local disorder when the films are deposited at room temperature in pure Ar, deposition conditions that are often used in thin film solar cells. It is recalled that the disorder is only on a local scale and does not affect the long range order of the films, as obvious from clear X-ray diffraction patterns recorded from such films (see discussion in Sect. 4.2.3.3). Growth of sputter deposited ZnO on CdS always results in an amorphous nucleation layer at the interface. The amorphous nucleation layer affects the valence band offset. 

Solution-phase synthetic methods, as they were described for synthetic organic libraries, can also be applied to materials science and are devoid of the diffusion problems encountered in thin-film deposition. The reagent solutions are mixed and incubated following an appropriate procedure, and the final products are usually isolated by precipitation or crystallization. Automated liquid dispensing units with extreme precision and high rehabiUty can be used in synthetic protocols. No major differences are presented in respect to solution-phase organic library synthesis (see Section 8.2.4). Several examples are briefly illustrated below to provide a quick overview of the currently reported synthetic methods in solution for materials libraries. 

The WFg H2 System. The reaction WFg + 3H2 W + 6HF is possible from 300 to 800 °C and is also used in thin-film production. There are several disadvantages in comparison to the other reduction methods. The HF formed during the reaction may cause defects, like encroachment or wormholes. The layers show poor adhesion on native Si02, which is always present on Si. Therefore, tungsten is not directly deposited on Si but on a bilayer. One layer provides an ohmic contact with Si, and the other acts as an adhesion promotor for W. 

In practice, however, the attained sensitivity is in the 10 7 g cm 2 range. This accuracy of quartz-crystal microbalances for mass determination is by far sufficient for most requirements in thin-film deposition. Commercially available thickness and rate monitors use quartz crystals with a frequency of 5 or 6 MHz. Fig. 6a shows the Leybold IC/4 Plus thickness and rate monitor and Fig. 6b shows the various types of quartz crystal holders. 

Qiiartz crystal microbalances work best in contact with gases or vacuum and are used as deposition monitors in thin film deposition apparatus. They have been employed for chemical vapor sensing purposes by coating one of the crystal interfaces with a film that selectively binds the target molecule, detecting the consequent change in the mass of the film. 

The particle size distribution may be controlled in both laser ablation/vaporization techniques by manipulating the pulse energy/duration (usually in the timeframe of 10-50 ns/pulse). It should be noted that when laser ablation is used for thin-film deposition, the technique is referred to as pulsed-laser deposition (PLD). At lower operating pressures ca. <0.1 Torr), thin films will be favored however, at higher pressures ca. >1 Torr), nanoparticles will be formed due to a greater opportunity for gas-phase nucleation to occur. 

However, while the sputtering technique is not very commonly used to study interlace effects in ionically conducting multilayer heterostructures, there are mmierous examples of thin film deposition. Actually, sputtering was the primary technique used for thin film deposition in the SOFC field, such as for Zr02 [84] and Ce02-based films [85]. The conducting properties were interpreted in terms of substrate-induced space charge effects, strain, or microstructure. 

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