Evaporated molecular films

With evaporated molecular films, one observes a similar situation [38]. Figure 8.58 gives the characteristic of the unipolar electron current in an Alq3 film at room temperature. The contacts are Ca as electron injector and aluminium as counter electrode. The difference in their work functions generates a built-in voltage Vbi 1V. Only when V> -Vbi does current begin to flow. In the pass direction, at V 4 V, it is already a factor of 10 larger than in the inhibited direction. 

THE USE OF LB INSULATING LAYERS TO IMPROVE THE EFFICIENCY OF LIGHT EMITTING DIODES BASED ON EVAPORATED MOLECULAR FILMS... 

We report on the use of insulating Langmuir-Blodgett films of arachidic acid (AA) to improve the quantum efficiency of light emitting devices based on evaporated molecular films of 8-hydroxyquinoline aluminium (Alq) and N,N -diphenyl-N,N -(3-methylphenyl)-l,l -biphenyl-4,4 -diamine (TPD). Devices based on indium-tin oxide (ITO)/TPD/Alq/Al structures were found to emit green visible electroluminescence (peak at 517 nm) when a positive bias was applied to the ITO electrode. The external quantum efficiency was approximately 0.13 %. The incorporation of an arachidic acid LB film between the Alq and the A1 electrode was found to increase both the forward current and light output of the LED and to produce a threefold increase in efficiency - to 0.4 %. 

The Use of LB Insulating Layers to Improve the Efficiency of Light Emitting Diodes Based on Evaporated Molecular Films... 

Haick H, Niitsoo O, Ghabboun J, Cahen D (2007) Electrical contacts to organic molecular films by metal evaporation effect of contacting details. J Phys Chem C 111 2318-2329... 

In the first monolayer of conjugated model material, a model molecular solid or a polymer adsorbate, assume that no chemistry (covalent bonding) occurs, since, in the absence of, for example, mechanical rupturing, the bonds at the surface of the molecular film are completely satisfied. This assumption is supported by the fact that, at least for condensed molecular solids, vapor-deposited films may be re-evaporated (removed) from the surface by gentle heating in UHV. 

Thin semiconductor films (and other nanostructured materials) are widely used in many applications and, especially, in microelectronics. Current technological trends toward ultimate miniaturization of microelectronic devices require films as thin as less than 5 nm, that is, containing only several atomic layers [1]. Experimental deposition methods have been described in detail in recent reviews [2-7]. Common thin-film deposition techniques are subdivided into two main categories physical deposition and chemical deposition. Physical deposition techniques, such as evaporation, molecular beam epitaxy, or sputtering, involve no chemical surface reactions. In chemical deposition techniques, such as chemical vapor deposition (CVD) and its most important version, atomic layer deposition (ALD), chemical precursors are used to obtain chemical substances or their components deposited on the surface. 

Fig. 8. Schematic of the procedure used for fabrication of nanoscale molecular-switch devices by imprint lithography [62]. (a) Deposition of a molecular film on Ti/Pt nanowires and their micron-scale connections to contact pads, (b) Blanket evaporation of a 7.5 nm Ti protective layer, (c) Imprinting of 10 nm Pt layers with a mold that was oriented perpendicular to the bottom electrodes and aligned to ensure that the top and bottom nanowires crossed, (d) Reactive ion etching with CF4 and O2 (4 1) to remove the blanket Ti protective layer.

Analogous to the supramolecular TRPyP systems, the tetramthenated porphyr-azine species also form homogeneous molecular films on solid substrates, by the slow evaporation of the solvent. Such films are suitable for the preparation of modified electrodes displaying versatile electrochemical and photoelectrochem-ical properties. The spectrum of a TRPyPz film on ITO is analogous to the solution spectrum exhibiting the Soret band at 390 and a broad Q band at 705 nm, respectively and the peripheral ruthenium complexes n-n and CT bands at 300 and 500 nm (125, 126). 

Figure 3.8 Molecular absorption of a PTCD derivative, surface plasmon of the evaporated silver film. Excimer fluorescence of an LB monolayer on glass and SERRS with the background SEF of the LB monolayer on the silver island film.

Hu, W.S. et al.. Molecular orientation of evaporated pentacene films on gold Alignment effect of self-assembled monolayer, Langmuir 21, 2260-2266, 2005. 

Polyisobutene with a terminal amino group is extremely efficient to clean the inner surfaces of cylinders in motors of cars. If this polymer is added in minute amounts to gasoline, it is sprayed into the cylinders in the form of tiny droplets upon evaporation of the gasoline. Here it forms a molecular film on the metal surface, which prevents the formation of deposits. The polymer film sticks for a short time and then moves slowly to the burning room, where it is de-... 

The study of surface films of the Langmuir type covers an extremely diverse group of phenomena. Measurements of film viscosity, diffusion on the surface, diffusion through the surface film, surface potentials, the spreading of monolayers, and chemical reactions in monolayers are just a few of the topics that have been studied. One interesting application is the use of long-chain alcohols to retard evaporation from reservoirs and thus conserve water. The phrase to pour oil on the troubled waters reflects the ability of a mono-molecular film to damp out ripples, apparently by distributing the force of the wind more evenly. There are also several different types of surface films only the simplest was discussed in this section. 

The most flexible methods, which can be applied in principle to nearly all molecules and which provide the most important techniques for the preparation of organic molecular films, are vacuum evaporation and molecular-beam epitaxy (cf [14]). In both methods, the substance required is evaporated or sublimed and captured on a substrate which is cooled as necessary. In molecular-beam epitaxy, the substrate must be an (inorganic) single crystal. The nature of the substrate s surface, its temperature and the velocity of evaporation or sublimation, adjustable... 

Fig. 14 Molecular structure and geometry of LB monolayer of 1 sandwiched between Au electrodes with direction of enhanced electron flow. The substrate was glass. 50 mmx50 mm j0.4mm, covered either by a Cr adhesion layer or by a hydrophobic xylene covering, followed by an evaporated Au film 50 mm x50 mm x 50 nm. then the LB monolayer or multilayer, then by 48 cylindrical Au pads. 17 nm thick and with an area of 0.283 mm. (From Ref. [34].)...

It was found, however, that devices having 1,3,4,-oxadiazole derivatives, or other low molecular weight molecules, as electron transporters in the form of a vacuum evaporated thin film, have a short lifetime, a feature probably associated with recrystallisation or aggregation phenomena [107]. 

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