Langmuir-Blodgett , semiconductor

C. Langmuir-Blodgett Films Containing Semiconductor Nanoparticles... 

Formation of Semiconductor Nanoparticles Inside Langmuir-Blodgett Films... 

The application of Langmuir-Blodgett films as rectifiers and/or switches have been also proposed. Peterson [106] investigated two semiconductors polyparaphenylene 178 and polyphenylenevinylene 179 with these purposes in mind. These systems with the chain lengths of at least 20 units could also be used as photovoltaic devices since their electroluminescence should be readily detectable. The doping of such materials may be necessary but at present it is not clear whether they will form Langmuir-Blodgett films when doped. 

Semiconductor particle formation between Langmuir-Blodgett (LB) films is an alternative and promising approach to band-gap engineering [662-666]. The ease of formation of self-assembled (SA) films [183-185,203-246] promoted the incorporation of semiconductors into these media [663, 710]. 

Several examples of catenanes and rotaxanes have been constructed and investigated on solid surfaces.1 la,d f 12 13 26 If the interlocked molecular components contain electroactive units and the surface is that of an electrode, electrochemical techniques represent a powerful tool to study the behavior of the surface-immobilized ensemble. Catenanes and rotaxanes are usually deposited on solid surfaces by employing the Langmuir-Blodgett technique27 or the self-assembled monolayer (SAM) approach.28 The molecular components can either be already interlocked prior to attachment to the surface or become so in consequence of surface immobilization in the latter setting, the solid surface plays the dual role of a stopper and an interface (electrode). In most instances, the investigated compounds are deposited on macroscopic surfaces, such as those of metal or semiconductor electrodes 26 less common is the case of systems anchored on nanocrystals.29... 

However, the successful use of processes dependent on Langmuir-Blodgett films for semiconductor applications is in doubt due to the presence of water and other detrimental contaminants in the films produced. The internal dislocations required for switching by the molecules may not be facile since the molecules are expected to be packed into semicrystalline phases in the Langmuir-Blodgett films. In addition, new developments in the field may obviate the need for such films as part of the device. 

Contact mode hthography has been apphed most of all to hard materials mica [235], semiconductors [236, 237] and metals [238-240]. Langmuir-Blodgett films [241, 242] and thin polymer films [243-251] can also be structured in contact mode. 

Self-assembled monolayers have recently attracted much attention as a new methodology for molecular assembly [249, 342]. They enable highly organized chemical binding of molecules of interest to the surfaces of, e.g., metals, semiconductors, and insulators. The well-ordered structure of self-assembled monolayers is in sharp contrast with conventional Langmuir-Blodgett films and lipid bilayer membranes in terms of stability, uniformity, and manipulation. Functional molecules can be arranged unidirectionally at the molecular level on substrates when substituents which will self-assemble on the substrates are attached to a terminal of the molecules. The wide variety of examples reported to date include porphyrins and metalloporphyrins in self-assembled monolayers [299-339]. 

More recently, Fendler and coworkers have used surfactant vesicles as hosts for colloidal semiconductor particles [83]. For instance, dihexadecyl phosphate (DHP) and 2Ci8Br vesicles incorporating CdS, ZnS and mixed CdS-ZnS particles have been obtained and used for the realization of nanoscale photoelectric devices (see later). It is important to point out, however, that the presence of the closed vesicle does not appear, at least with these systems, to be of critical importance for the control of the size of the particles, as similar phenomena also occurs in Langmuir-Blodgett films [84], suggesting that a crucial role in nucleation is played mainly by the surface. 

High-resolution circuitry and active devices employing Langmuir-Blodgett film techniques or polymer-based transistors are being considered for the sophisticated electronics required in future vehicles. Temperature or energy balance in the vehicle could be controlled through conductive polymers or semiconductor deposits on electrochromic windows. Electroluminescent liquid crystals and fluorescent and electrochromic materials used for visual displays show promise for future development. 

Hu, W. et al.. The gas sensitivity of a metal-insulator-semiconductor field-effect-transistor based on Langmuir-Blodgett films of a new asymmetrically substituted phthalocyanine. Thin Solid Films, 360, 256, 2000. 

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