Vacuum deposition techniques

Gas phase (ultra high) vacuum deposition is expensive and time-consuming but clean. It can be employed for most oligothiophene oligomers up to octithiophene (a-8T) and also for polythiophene with a polymerization degree of 20-25 monomeric units. An exception are molecules with thermally unstable substituents. 

The molecules are filled into Knudsen- or Langmuir-type evaporation cells and heated up to their sublimation temperature. Mass spectra show that the materials are usually clean or can be cleaned by sublimation and sublime without destruction, even above the temperature at which the maximum evaporation rate is obtained. The subhmation conditions remain constant and reproducible in contrast to many other stable organic materials like phthalocyanines. Usually no residuents remain in the cell. This shows the excellent processability of oligothiophenes for thin film formation from the gas phase. Typical evaporation conditions will be summarized in Tables 7 and 8 for a-5T and a-bT, respectively (see below). 

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The quartz crystal microbalance has a long history of application as a means of determining film thickness in vacuum deposition techniques and more recently as a means of detecting trace constituents in the gas phase. In essence, it is an extremely sensitive sensor capable of measuring mass changes in the nanogram range. 

The first step in sample preparation is the deposition of a thin metal film on an insulating substrate (e.g. a glass microscope slide). This base electrode is deposited by conventional vacuum deposition techniques with the electrode geometry defined by a shadow mask. Next, this electrode is oxidized either by exposing the film to room air or oxygen, or by establishing an oxygen plasma within the vacuum chamber. In the case of Al-electrodes, a remarkably uniform oxide layer is formed, typically 1-2 nm thick. The oxide film may then be dosed with the compound of interest this is achieved in one of three ways. 

Vacuum deposition techniques, such as sputtering, electron beam evaporation, and plasma deposition are common. Photopolymerization and laser-assisted depositions are used for preparation of specialized layers, particularly in the fabrication of sensing arrays. Most commercial instruments have thickness monitors (Chapter 4) that allow precise control of the deposition process. 

The most widely used vacuum deposition techniques are evaporation and sputtering, often employed for smaller substrates. In the evaporation process, heating the metal by an electron beam or by direct resistance produces the vapours. The system is operated at a very high vacuum (between 10-5 and 10 6 Torr) to allow a free path for the evaporant to reach the substrate. The rate of metal deposition by evaporation processes varies from 100 to 250,000 A min h These processes can be operated on a batch or a continuous scale. On the other hand, in the case of the sputtering technique, the reaction chamber is first evacuated to a pressure of about 10-5 Torr and then back-filled with an inert gas up to a pressure of 100 mTorr. A strong electric field in the chamber renders ionisation of the inert gas. These inert gas ions... 

ATR studies of the biocorrosion of submerged copper surfaces have been reported. The IRE of a cylindrical internal reflectance cell (CIRCLE) was coated with a thin copper layer via a vacuum deposition technique (105). The copper layer reduces the sampling depth of the radiation outward from the surface of the IRE. Therefore, the intensity of the water bending band will vary with copper layer thicknesses of 4.1 nm or less. The copper layers were shown to be stable to exposure to water alone, but the presence of acidic polysaccahrides in the water caused a reduction in the copper layer thicknesses (106.107). The adsorption of a model compound, Gum Arabic, onto the coated IRE was detected by increases in the C-O stretching band of the pyranose units near 1050 cm"1 (106). 

Numerous methods have been described in the literature for depositing coatings onto piezoelectric acoustic sensors. They generally fall into three categories solvent casting techniques, vacuum deposition techniques, and vapor-phase deposition techniques. 

G. K. Hubler, Comparison of vacuum deposition techniques, Pulsed Laser Deposition Thin Films 327-55, 327, 1994. 

The phosphorescent organic light emitting diodes (PHOLEDs) based on Ir(dmp>py)3 complexes were fabricated by the vacuum deposition technique with the following configuration ITO/copper phthalocyanine (CuPc, 10 nm) as hole injection layer/4,4 -bis[(l-naphthyl)(phenyl)-amino]-l,l -biphenyl (NPD, 40 nm) as hole transport layer/CBP Ir(dmppy)3 (8%) (20 nm) as emissive layer/2,9-dimethyl-4,7-diphenyl-l,10-phenanthroline (BCP, 10 nm) as a hole blocking layer/ tris-(8-hydroxyquinoline)aluminum (Alqs, 40 nm) as an electron transport layer/LiF (1 nm) as electron injection layer/ A1 (100... 

D. Peterson, Non-Vacuum Deposition Techniques for use in Fabrication Thin Film Circuits, No. Noobsr 91336, Final Rep., 1967. 

A vacuum deposition technique where the material to be deposited is heated until it vaporizes. This condenses on the substrate and forms a thin film. 

As with most vacuum deposition techniques, film growth on the substrate occurs according to the following sequence atom arrival and physical adsorption, migration on the surface or... 

The intermittent plasma-assisted vacuum deposition technique has been found to introduce the effective electrocatalytic activity and stability for CO2 reduction into metal phthalocyanine thin films formed on a glassy carbon. The films properties are significantly influenced by the chemical state of the Aim. It has been suggested that the electrode process is determined by the surface chemical reaction involving adsorbed H and/or H+ and a carbon containing intermediate ". ... 

A thin film might be prepared by means of either ion sputtering" or vacuum deposition techniques. In both cases, the thin-fihn electrode is binder free that is, there is no parasite mass lowering its capacity. Moreover, the silicon layer is strongly attached to the copper substrate. 

Thin layers of solids like chalcogenides may also be deposited on a metal surface by electrolysis or by vacuum deposition techniques. These electrodes are closer to solid ISEs than to traditional electrodes of the second kind. 

INEOS chlor offers both precious metal and nickel alloy coatings [192]. The precious metal coatings are deposited on a nickel substrate, and the electrocatalytically active layers are applied to the smface by thermal deposition or electroplating. Thermal spraying or vacuum deposition techniques form the nickel-alloy coating. These materials have been used in the FM 21 electrolyzers for over four membrane cycles. 

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