The embedded atom method (EAM) was applied to calculate the energy on Mg doping in polycrystalline Ni3Al. The EAM predicted the energy of Mg in Al site in grain boundary is lower than that of Mg in Ni site and much lower than that of Mg in Al or Ni site in bulk and in free surface. It means that Mg would segregate to grain boundary rather than bulk and free surface and Mg will favor to be the substitute of Al rather than of Ni in grain boundary. These results were consistent with the experiments that Mg segregated to grain boundaries with Al depletion and Ni enrichment.

Pulsed grid-controlled traveling-wave tubes (TWTs) are widely used in the field of space and defense for navigation and directing of radars, aircrafts, satellites, and guided missiles. In order to attain even higher frequency and power requirements, gun designs for modern microwave tubes have utilized grids, which are very close to cathode. However, during the course of the TWTs work, electron emission substances such as Ba and BaO on the cathode can be evaporated and deposited on the counter electrode. Harmful electron emission from the grid, namely, grid emission, is very likely triggered, this in turn destroys the working condition of the controlled traveling-wave tube, making it necessary to suppress the electron emission properties of the grid. Pt films as an anti-emission material have been widely used, but little is known about its electron emission suppression characteristics and surface composition at high temperature when grids works. In our investigation, Pt films were deposited onto the surface of the molybdenum grids by ion-beam-assisted deposition (IBAD). The mechanism for electron emission suppression of the molybdenum grid coated with Pt films is discussed.

Platinum (Pt) and Carbon (C) was coated on the substrate of silicon and molybdenum by ion beam assisted deposition (IBAD). The structure of the as-deposited Pt-C film was studied by XRD and Raman spectroscopy. The XRD results show that Pt exhibits mixed strong (111) and weak (200) orientations. The Raman spectrum show that the carbon exists in the form of amorphous. The electron emission suppression characteristics of Pt-C thin film were measured using analogous diode method. The results show that electron-emission from Mo anode coated with Pt-C film is much less than that from the Mo anode without Pt-C film.

Platinum and carbon were deposited onto the surface of molybdenum grids simultaneously by ion beam assisted deposition. The structure of the Pt–C films was studied by XRD and Raman spectroscopy. The XRD results showed that Pt exhibited mixed strong (111) and weak (200) orientations. The Raman spectra showed that the carbon existed in the form of graphite-like phase. Electron emission characteristics from the Mo grid with and without Pt–C films were measured using analogous diode method. The results showed that electron emission from the Mo grid coated with Pt–C films was much less than that from the Mo grid without Pt–C films. The obtained results demonstrated that the Pt–C films are effective grid-coating materials for the application of suppression thermo-electron emission.

Low energy ion beam assisted deposition(IBAD)was employed to prepare Cu,Ag or Pt films on Mo/Si(100)substrate.When the film deposition was performed with simultaneous bombardment of 500 eV Ar ion beam normal to the film surface at ion/atom arrival ratio of 0.2,the prepared Cu films were(111)preferred orientation, Ag and Pt films were(111)and(200)mixed orientations.When the Ar ion beam was off-normal direction of the film surface 45°,the prepared Cu,Ag and Pt films all exhibited highly preferred(111)orientation.Monte Carlo method was used to calculate the sputtering yields of Ar ions incident on single crystal Ag(100)and(111)plane at various in- cident angles and azimuth angles respectively.The effects of channeling effects and surface free energy on the crys- tallographic texture of Cu,Ag and Pt films are discussed.

Low energy ion beam assisted deposition (IBAD) was employed to prepare Ag films on Mo/Si (100) substrate. It was found that Ag films deposited by sputtering method without ion beam bombardment were preferred (111) orientation. When the depositing film was simultaneously bombardment by Ar+ beam perpendicular to the film surface at ion/atom arrival ratio of 0.18, the prepared films exhibited weak (111) and (200) mixed orientations. When the direction of Ar+ beam was off-normal direction of the film surface, Ag films showed highly preferred (111) orientation. Monte Carlo method was used to calculate the sputtering yields of Ar+ ions at various incident and azimuth angles. The effects of channeling and surface free energy on the crystallographic orientation of Ag films were discussed.

Plasma-enhanced chemical vapor deposition (PECVD) was used to grow Fe-catalyzed carbon nanotubes (CNTs). The nanotubes had a uniform diameter in the range of about 10–20nm. A base growth mode was responsible for the CNTs growth using a mixture of H2 (60sccm) and C2H2 (15sccm). For a mixture of H2 (100sccm) and C2H2 (25sccm), a complicated growth mechanism took place involving both the base growth and the tip growth. X-ray photoelectron spectroscopy measurements revealed that the grown CNTs contained C–H covalent bonds and Fe–C bonds located at the interface between them and the substrates. The factors determining the growth mechanism of CNTs are discussed and their growth mechanisms with the different gas ratios are suggested.

Plasma-enhanced chemical vapor deposition (PECVD) method was employed to synthesize the Fe-catalyzed carbon nanotubes (CNTs). Hf films were deposited onto the synthesized CNTs, followed by heat treatment at 1200°C which could form HfC. Field emission properties indicate that the HfC-coated CNTs have good emission current density due to low work function of HfC and also keep stable emission characteristics under poor vacuum owing to the chemical inertness of HfC. Consequently, field emission characteristics of the CNTs can be improved by the HfC-coated surface treatment compared with the synthesized CNTs.

Hf was deposited onto the surface of Mo grids by ion-beam-assisted deposition. The electron-emission characteristics of the grids with and without Hf, which were contaminated by active electron-emission substances (Ba, BaO) of the cathode, were measured using an analogous-diode method. The surfaces of the grids were analyzed by x-ray diffraction and x-ray photoelectron spectroscopy. The results showed that electron-emission current from the Mo grid coated with Hf film was less than that from the Mo grid without Hf. During the course of the testing, active electron-emission substances from the cathode were deposited continuously onto the surface of the grid. Due to BaHfO3 compounds and Ba-Hf diffusion, the Mo grid coated with Hf effectively reduced the electron-emission substances on the grid from the cathode, which reduced grid electron emission.

Low energy ion beam assisted deposition (IBAD) was employed to prepare Ag films on Mo/Si(100) substrate. It was found that Ag films deposited by the sputtering method were with (111) preferred orientation. Ag films exhibited mixed (111) and (100) orientations if the growing films were bombarded by 500 eV Ar{sup +} beam along normal direction with Ion/Atom arrival ratio of 0.18. Ag films exhibited highly preferred (111) orientation at incidence angle of 54.7 degree. (authors)

Platinum was deposited onto molybdenum grid by ion beam assisted deposition (IBAD). Electron emission behavior from molybdenum grids with and without Platinum contaminated by active electron emission substances (Ba, BaO) of the cathode were measured using analogous diode method. The characteristics on molybdenum grid coated with platinum film were analyzed by X-ray diffraction (XRD), energy dispersive X-ray (EDX) and X-ray photoelectron spectroscopy (XPS). The results show that the electron emission from the grid coated with platinum film is less than that without Platinum film, and the mechanism far suppression of the electron emission of molybdenum grid coated with Platinum film was discussed.

Plasma-enhanced chemical vapor deposition (PECVD) method was employed to grow the Fe-catalyzed carbon nanotubes (CNTs). The grown CNTs with a uniform diameter in the range of about 10–20nm and the typical lengths beyond 1μm resulted in a very high aspect ratio. The Raman and TEM results showed that the grown CNTs contained a large amount of carbonaceous particles and crystal defects, such as pentagon–heptagon pair defects. XPS measurement indicated that the CNTs had CH covalent bonds. Field emission characteristics exhibited the low turn-on threshold field of 2.75V/μm and the maximum emission current density of 7.75mA/cm2 at 6.5V/μm. The growth mechanism of CNTs and the effects of hydrogen plasma on their structure were discussed.

Hafnium (Hf) films with different preferred crystalline orientation have been prepared on Si(111) by ion beam assisted deposition (IBAD) at room temperature. The effects of the Ar+ ion incidence angle and the ion/atom arrival ratio on the texture were investigated. Hf films deposited by vacuum electron-beam evaporation have polycrystalline orientations. Hf films deposited by sputtering method, with the deposition rate about 0.15 nm/s, have weak (110) orientations. Hf films have preferred (110) orientation when the growing films were bombarded by 500 eV Ar+ ions with the incidence angle of 75° and current density of 90 μA/cm2 with the ion/atom arrival ratio about 0.21. However, as the current density was beyond 120 μA/cm2 with the ion/atom arrival ratio about 0.43, the Hf films exhibited mixed (002) and (100) orientations and which were independent of the ion incident angle. The preferred orientation of Hf films is determined by the competition between the surface energy and the strain energy.

Pt films were deposited on Mo/Si(100) substrate by low energy ion beam assisted deposition (IBAD). The ion/atom arrival ratios were 0.1,0.2, and 0.3, respectively. Pt films had mixed (111) and (200) orientations deposited with simultaneous 500eV Ar~+ ion bombardment at incidence angle of 0o and had highly preferred (111) orientation at incidence angle of 45o. Therefore, it is a good method to prepare highly oriented Pt(111) films on Mo/Si(100) substrate by off-normal incidence ion bombardment during film growth. The reason for the preferred orientation of Pt films was also discussed. It was considered that the orientation of Pt films did not simply depend on the channeling effects of ions, or the grain surface free energy, but it was the results of mutual competition of surface free energy and channeling effects.

Hf films were synthesized by ion beam assisted deposition(IBAD). The influence of ion bombardment during deposition on the preferred orientation of films was studied. Hf film grains exhibit preferred (110) orientation when the growing film is bombarded by 500 eV Ar~+ions at an incident angle of 75° and a current density of 0.9 A/m~2. When the current density is beyond 1.2 A/m~2, the Hf films exhibit mixed (002) and (100) orientation and which is not concerned with the ion incident angle. The reason for the preferred orientation of Hf film was discussed. It is considered that the preferred orientation of Hf films does not simply depend on the channeling effects of ions, or the grain surface energy, but it is the result of mutual competition and actions of several factors, which influences the crystallographic orientation of thin films in the non-equilibrium growth conditions.

Monte Carlo simulation with the energetics described by the embedded atom method (EAM) has been employed to calculate not only grain boundary concentration profiles of Ni, Mg and Al, but also dependence of the grain boundary cohesion on the Mg bulk concentration, for the Ni3Al-x at.% Mg (100%Ni\100%Ni)[001]/Sigma5(210)/36.87degrees grain boundary, at equilibrium. We suggest that the bulk effects of Mg on the grain boundary include the primarily positive effect on the Ni enrichment at the grain boundary, i.e. the Mg atoms induce Ni atoms to substitute into Al sites, the secondarily positive effect on it, i.e. the Mg atoms substitute into Al sites, and the negative effect on it, i.e. the Mg atoms substitute into Ni sites. For the Ni3Al-x at.% Mg grain boundary, at the equilibrium, the calculations show that when x (the Mg bulk concentration) increases from 0.1 to 0.5, the Mg enrichment increases, both the Ni enrichment and the Al depletion maximizes at x = 0.2. The calculations also show the best cohesion of the grain boundary at x = 0.2. (C) 2003 Elsevier B.V. All rights reserved.

The Monte Carlo simulation with the energetics described by the embedded atom method has been employed to mainly study physical behaviors of boron atoms during relaxation of the Ni3Al-x at.% B grain boundary.During relaxation of impure Ni3Al grain boundaries,we suggest that for different types of impure atoms(Mg,B,Cr and Zr atoms etc.),as the segregating species,they have the different behaviors,but as the inducing species,they have the same behaviors,i.e.they all induce Ni atoms to substitute Al atoms.Calculations show that at the equilibrium.when x(the B bulk concentration) increases from 0.1 to 0.9,the peak concentration of B increases,correspondently,the peak concentration of Ni maximizes but the valley concentration of Al minimizes,at x=0.5,The calculations also show the approximate saturation of Ni at the grain boundary at x=0.5.

The embedded atom method (EAM) has been used to calculate boundary concentration distributions of Ni, Al, and B, and B probabilities in the "interstitial" and the "substitutional" sites, at the Ni3Al-x at.% B (100% Ni/100% Ni) [001]/Sigma5(210)/36.87degrees grain boundary at the equilibrium. It has been proposed by us that the bulk effects of B on the grain boundary include the main effect, that is, the B atoms induce Ni atoms to substitute into Al sites, and the sub-effect, that is, the B atoms substitute into Ni sites. In this work, it is found that at as x increases from 0.1 to 1.0, the B probability in the "interstitial" sites decreases from 97.3% to 38.8%, while that in the "substitutional" sites increases from 2.7% to 61.2%. It is also found that owing to combination of the main effect and the sub-effect, corresponding to B enrichment increasing, the Ni enrichment and the Al depletion become more and more obvious when x increases from 0.1 to 0.5. Then, corresponding to B enrichment decreasing, the Ni enrichment and the Al depletion also become more and more obvious when x decreases from 0.9 to 0.5. Thus, between low (x = 0.1) and high (x = 0.9) B bulk concentrations, there is a B bulk concentration (x = 0.5), at which the Ni enrichment and the Al depletion become the most obvious, and Ni is approximately saturated. (C) 2002 Elsevier Science B.V All rights reserved.

PIC method was used to study the dose uniformity in plasma immersion ion implantation of circular plate. The results of simulations show that the lateral length of the plate is the main factor that affects the dose uniformity, and the other factors, like the depth, the shape of the boundary, and the insulator shroud, only have weak effects on the dose uniformity.