Ain Thin Films Prepared by Reactive Ion Beam Coating
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deposited AIN thin films on Si (100) by low energy reactive ion beam deposition. non-RBS and AES were used to study the composition of these films, and the AFM was applied to study the morphology. UV-Visible light transmittance spectra were used to analyze the optical band gap of AIN thin films. More and more research work has been focused on the electron field emission process. Chen et al [10] have studied the relationship between the morphology and the electron emission properties of SiC/Si heterostructures. In this paper, we studied the surface structures and the electron emission characteristics of stoichiometric AIN thin films prepared under appropriate conditions. As it has been reported that aluminum tips formed due to aluminum condensation, we have also prepared AIN films with excessive Al and studied their surface topography and electron emission behavior to reveal the relationship between them. EXPERIMENT In our work, AIN thin films were deposited on Si(100) and silica substrates by low energy ion beam deposition from an aluminum target sputtered by a mixture of argon ions and nitrogen ions. Our system has been described in detail elsewhere [11]. The aluminum target is of high purity (99.999%) and 5 inches in diameter. The vacuum chamber was evacuated by a mechanical pump and a molecular pump to about 6.58x 10-4 Pa before deposition. The target 251 Mat. Res. Soc. Symp. Proc. Vol. 585 © 2000 Materials Research Society
was pre-sputtered for about 10 min to remove the surface oxide layer. The total pressure was kept 1.995x10 2 Pa during the deposition process, with the Ar/N2 ratio 1:1. The Si(100) substrates were not heated. The beam energy ranges from 450 eV to 850 eV. In this paper, we discuss two samples deposited under beam energies of 450 eV, 40 mA and 750 eV, 65 mA, which represents the stoichiometric and non-stoichiometric films, respectively. Auger electron spectroscopy of the films was recorded on a Perkin-Elmer PH1550 ESCA/SAM system. Non-Rutherford elastic backscattering experiments were done on a system capable of accelerating ion beams to greater than 4 MeV. We also used atomic force microscopy (Nanoscope III, Digital Instruments) to study the morphology of the films. The optical band gap of the films was determined by Tauc plots from the UV-Vis transmittance spectra. The films used in such measurements were ion beam coated onto silica substrates that are transparent in the UV-Vis range (190-700nm). The electron field emission experiments were performed in an ultrahigh vacuum chamber with a base pressure better than 2.63x 10-6 Pa. The current density field (J-E) characteristics were measured using a diode structure with a copper plate as the anode. The sample under test was separated from the anode by a mica spacer with a circular opening of various diameters. The typical thickness of the mica spacers used is 20 ýtm measured by a precision thickness gauge with an accuracy of ±ljim. The nominal current density is defined as the total emitted current divided by the area of the circular opening o
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