Optical microstructures, processing

Dr. Li earned a B.S. (1982) in optics from the Beijing Institute of Technology, China, and a Ph.D. in physics from the Laboratoire d Optique Electronique du C.N.R.S., Toulouse, France. Since joining the DuPont Company, he has worked on many industrially important projects, including the research and development of new OLEDs. His main interest is to establish the relationship of the process conditions, microstructures, and performances of these devices. 

Experiments using the DCC approach aimed at the discovery of improved phosphor materials have also been described. [9] In this case, samples are evaluated optically, an approach well suited to direct comparisons of large numbers of samples, although it is somewhat difficult to compare the results to the optical properties of bulk materials. Further spectroscopic evaluations of individual elements of the sample array are also easily accomplished by a variety of approaches including scanning fiber techniques. One concern in studies of phosphors is the sensitivity of the optical behavior including fluorescence intensity to processing effects such as details of the microstructure or surface preparation. 

Another technological breakthrough in optical hber technology, however, allows one to upgrade established 100 fs-class laser systems for broadband applications and even surpass the bandwidth of dedicated short-pulse Ti sapphire lasers. Key to this is the use of novel microstructured optical hbers, which are designed to exhibit extremely high optical nonlinearities. If nanojoule femtosecond laser pulses are launched into such a hber, the combination of different nonlinear optical processes leads to the creation of new frequency components. Therefore, the laser bandwidth can be increased dramatically by orders of magnitude. 

In fact, even in pure block copolymer (say, diblock copolymer) solutions the self-association behavior of blocks of each type leads to very useful microstructures (see Fig. 1.7), analogous to association colloids formed by short-chain surfactants. The optical, electrical, and mechanical properties of such composites can be significantly different from those of conventional polymer blends (usually simple spherical dispersions). Conventional blends are formed by quenching processes and result in coarse composites in contrast, the above materials result from equilibrium structures and reversible phase transitions and therefore could lead to smart materials capable of responding to suitable external stimuli. 

The magnetic, optical, and electrical properties of materials often depend on the microstructural details and the morphology of materials. Even if the final state is not a colloid, many products pass through colloidal processing routes prior to the final stage. The availability of methods to produce model particles allows us to study and control the desired properties of the final product. 

As has been discussed above, there is a strong influence of grain size on the electrical and optical properties of ZnO films. Take as a first example, ZnO films grown by the LP-CVD process in the substrate temperature range between 155 and 180°C they have a microstructure as described in Sect. 6.2.2.1 with conical crystallites that form pyramids at the surface (see Fig. 6.6). This microstructure has, via the pyramidal structure of the surface, a pronounced influence on the optoelectronic properties of the films, specifically on their light scattering capability. 

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