Electron-beam evaporation, metal deposition onto

Reproducibility of film preparation and stability of the resulting films are important issues for practical applications. Cleanliness of the IRE before metal deposition can play a decisive role in determining reproducibility. Depending on the conditions, metal films may not be stable and may peel off (36,37). The stability and reproducibility of metal films can be enhanced by evaporating a metal oxide support material (such as AI2O3) prior to evaporation of the desired metal. Contaminants on the IRE are covered or displaced by evaporation of the metal oxide. It was reported that a 50-100-nm-thick AI2O3 layer deposited on a Ge IRE by electron beam physical vapor deposition hardly affected the reflectivity in an ATR experiment. Thin platinum films directly deposited onto it were found to be rather stable under catalytic reaction conditions (26,38). 

Thin layers of catalyst can be deposited onto the surface of silicon microchannels by physical vapour deposition. Silicon is the preferred material, because the equipment for physical vapour deposition is available at microelectronics fabrication sites, which can also produce silicon microreactors. Physical vapour deposition such as cathodic sputtering, electron beam evaporation and pulsed laser deposition but also chemical vapour deposition create uniform metal surfaces with thicknesses in the nm range. Such coatings are rarely suitable as catalysts. However, a few exceptions such as hydrogen oxidation [145] and reactions in the very high temperature range do exist. 

Figure 26. Arrays of Cu islands patterned using photolithography and deposited by electron beam evaporation (10 nm height) on a thin films of Al (200 nm) evaporated onto Si substrates. Reprinted with permission from Journal of Metals, 53 (2001) 34, Copyright 2001 The Minerals, Metals Materials Society (TMS), Warrendale.

ZnO films can be prepared by many techniques, including chemical vapour deposition (CVD) [135], electron beam evaporation [136], molecular beam epitaxy (MBE) [137], pulsed laser deposition (PLD) [138], sol-gel [139], spray pyrolysis [140], sputtering [141] and chemical bath deposition [142]. Thermal oxidation of metallic Zn [143-149], ZnS or ZnSe [150-153] films has been used to prepare ZnO films. The Zn precursor films were deposited onto the substrates (glass, sapphire or Si) by magnetron sputtering, thermal/ electron-beam evaporation or filtered cathodic vacuum arc technique. Oxidation treatment was normally conducted in air or oxygen atmospheres in a wide temperature range typically from 300 to 1000°C. 

It corresponds to the condensation of a gaseous species onto a suitable substrate. In this process, the molten metal is evaporated from single or multiple bath co-deposition and allowed to condense on a substrate (possibly a rotating collector). Heat sources which have been used include electron-beam and induction techniques. 

For the formation of a metallic film in addition to thick film silk-screen technique, thin film metallization is another means for the film deposition. Deposition of thin film can be accomplished by either physical or chemical means, and thin film technology has been extensively used in the microelectronics industry. Physical means is basically a vapor deposition, and there are various methods to carry out physical vapor deposition. In general, the process involves the following 1) the planned deposited metal is physically converted into vapor phase and 2) the metallic vapor is transported at reduced pressure and condensed onto the surface of the substrate. Physical vapor deposition includes thermal evaporation, electronic beam assisted evaporation, ion-beam and plasma sputtering method, and others. The physical depositions follow the steps described above. In essence, the metal is converted into molecules in the vapor phase and then condensed onto the substrate. Consequently, the deposition is based on molecules and is uniform and very smooth. 

For thin-film metallization, a thin metallic film is first deposited onto the surface of the substrate. The deposition can be accomplished by thermal evaporation, electronic-beam- or plasma-assisted sputtering, or ion-beam coating techniques, all standard microelectronic processes. A silicon wafer is the most commonly used substrate for thin-film sensor fabrication. Other substrate materials such as glass, quartz, and alumina can also be used. The adhesion of the thin metallic film to the substrate can be enhanced by using a selected metallic film. For example, the formation of gold film on silicon can be enhanced by first depositing a thin layer of chromium onto the substrate. This procedure is also a common practice in microelectronic processing. However, as noted above, this thin chromium layer may unintentionally participate in the electrode reaction. 

Physical vapor deposition = PVD (electron beam assisted evaporation of aluminum oxide onto a metal) [96]... 

The first method is physical vapor deposition (PVD) divided into subcategories of evaporation and sputtering. Evaporation is used primarily for deposition of metals. A metal sample is held in a container (crucible) and heated by a resistive coil made of a refractory metal, an inductive coil, or an electron (e-) beam. The metal sample is heated and evaporated as a result. A flux of the metal vapor thus reaches the substrate, where it cools and deposits a thin film of the metal onto the substrate. 

Metallization occurs in high vacuum deposition systems using electron beam, flash, and resistive heating systems to evaporate the metal onto the substrate. Sputtering systems perform the same function under partial vacuum. Etching, either dry (plasma) or wet etching, processes remove... 

The simplest way to prepare a plasmonic nanostructure is thermal and electron beam deposition in vacuum on a flat substrate that is either hydrophilic or hydrophobic. Even though the roughness of the structure depends on the contact angle between the metal and substrate, which is less controllable, the method can be well applied to some metals. DUV plasmonic nanostructures were readily formed by thermal deposition of indium onto a glass substrate. The size of indium nanostructures can be controlled from 15 to 50 nm by the evaporation speed, pressure, and the deposited thickness. The resulting extinction peaks due to the dipole resonance were tuned to between 260 and 600 nm, which were used for surface enhancement of Raman spectroscopy by DUV excitation [7]. Self-assembled arrays of hemispherical gallium nanoparticles were deposited by molecular beam epitaxy on a sapphire support as a substrate for UV plasmonics. The mean NanoParticle radii of 23, 26, and 70 nm were fabricated at LSPR frequencies... 

The typical polymer LED structure is shown in Figure 7.3. In order to fit in the quartz finger dewar which is inserted in the microwave cavity (see Section 1.3.1 below), the width of the devices was limited to 4.5 mm. They were all fabricated on ITO-coated glass, which was the positive electrode. The active area of the devices was 7 mm. PPV layers were deposited by spin coating the appropriate precursor and thermally converting it CN-PPV was spin-cast directly from solution [3]. The deposition of the polymers was followed by evaporation of the metal electrode from which electrons were injected into the devices [3,9,25,26,28,29]. In the case of the PPV- and PPE-based devices, that electrode was Al-encapsulated Ca, which yielded a higher device efficiency than an A1 electrode [9,25,26,28,29]. The thickness of the emissive PPV and PPE layers was 600 and 300 nm, respectively. Derivatives of PPE dissolved in toluene were spin-coated onto the ITO substrates, followed by e-beam or thcnnal evaporation of A1 or Ca/Al electrodes in a base chamber pressure of 10 torr. The PPV/CN-PPV diodes used A1 as the electron-injecting electrode [3], The thickness of the PPV layer was 120 nm, and that of the CN-PPV layer was 100-200 nm. Finally, copper wires were bonded to the A1 and no layers with silver paint. 

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