Highly (100)-oriented thin films of PbTiO3 were prepared on (100)-textured LNO/Pt/Ti/SiO2/Si substrates by rf magnetron sputtering at temperatures ≥480 °C, while randomly oriented PbTiO3 films were obtained on Pt/Ti/SiO2/Si substrates. The textured LNO layer can help to control the orientation of PbTiO3 thin films, and reduce their surface roughness quite significantly. The dielectric constant (εT) of PbTiO3 films deposited on LNO was lower than that of films on Pt and the dielectric loss (tan δ) increased when a higher deposition temperature or longer time was used. The highly (100)-textured PbTiO3 films also showed different ferroelectric hysteresis characteristics, i.e., a higher coercive field and a lower remanent polarization, from that of randomly oriented films deposited on Pt.
The Ir nano particle thin film was grown by dcrect current magnetron sputtering at room temperature. Microstructure of thin films grown at different sputtering pressures were measured by scanning electron microscopy. The results show that the particle size of the films depends on the deposition rate in the nucleation stage of Ir films and the deposition rate can be well controlled by sputtering pressure. A new kind of cathodes are fabricated from 25% porous tungsten impregnated with 6∶1∶2-type barium calcium aluminate and coated with the nano particulate Ir thin film. The coating processes produces a film thickness of 200—500 nm and the cathodes are fired in hydrogen atmosphere for ten minutes at 1200℃ to further improve the coating microstructure. The cathodes have been studied with thermal electron microscope by which the electron-optical picture of a thermal emission cathode could be obtained. Time of flight mass spectrometer (ToFMS) has been used in a study of evaporation from impregnated cathodes. The chemical composition of evaporation of various impregnated cathodes have been measured by ToFMS. The variation of ion current of evaporants from S-type cathode and M-type cathode (coated with iridium) and n-type cathode (coated with iridium nano-particle thin film) with temperature and time have been studied and discussed. Emission current characteristics have been measured as a function of voltage and temperature.
The development of modern satellite communication technologies is imposing higher demands on the lifetime and reliability of the microwave vacuum electronic devices, which directly depend on the evaporation properties of the extensively used Monel and stainless steel. Therefore, it is of vital importance to study the evaporation properties of these two types of metallic materials. For the first time, as far as we know, this paper proposes to study the evaporation properties of metallic materials using time-of-flight mass spectrometer (TOFMS). The components and the contents of the vacuum background, the evaporants from the Monel and from the stainless steel have been measured using the TOFMS, respectively. After the pressure of the measurement chamber is below 4.010-8 Pa, the TOFMS is used for the metallic materials working at different temperatures. They are respectively acquired when the Monel and stainless steel are at room temperature on operate between 750 to 900 ℃ under a pressure of 1.010-6 Pa. The measurements are carried out rapidly and in high sensitivity. As disclosed by the measurements, Mn and Cu began to evaporate when the Monel and the stainless steel are heated to 800 ℃, which is still far below the melting points of the two alloys (1243 ℃ and 1080 ℃). When the Monel and the stainless steel are further heated to 900 ℃, the evaporation of Mn, Cu, and Cr becomes quite considerable. Once the evaporated Mn, Cu, or Cr deposit on the ceramics for the insulation in an electron gun, its insulation will be deteriorated. Hence, the Monel and the stainless steel are not suitable to be use as the components in cathode electron guns, especially those used in the devices that are to work a long lifetime in high vacuum. Moreover, the Monel and the stainless steel are not suitable for used as the components that are often under the electron bombardment, e.g., anodes and collectors, either. The SEM images and XRD of the heat treated surface structures of the Monel and the stainless steel in ultrahigh vacuum (1.010-6 Pa) have also been studied. On heating at 900 ℃ for 30 and 120 min the surface structure and composition change remarkably and a significant reduction in Mn and Cr is visible, and also a large number of holes and crystal boundaries emerge on the surfaces of the two metallic alloys. With increasing heating time, the boundaries will grow larger and larger. As a result, the strength of the two metallic materials becomes weaker and gas permeation and leakage even occur. Therefore, it can be concluded that the components made from Monel and stainless steel, especially those with thin walls, should not be heated to high temperatures in ultrahigh vacuum for a long time. The above phenomena are analyzed in detail theoretically and the proper and feasible application methods of the metallic materials are explored in device design and technological process control. These works are expected to contribute to the prolonging of the lifetimes of the satellites, and will lead to tremendous economic benefits.
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