Nanocrystalline and Hard, Boron-Alloyed Be Coatings
- PDF / 1,193,058 Bytes
- 4 Pages / 417.6 x 639 pts Page_size
- 7 Downloads / 210 Views
magnetrons, i.e. minisources. Each minisource is used to sputter a different target material as appropriate to each deposition. The center of each minisource is located along the circumference of a 7 cm diameter circle at a 120' separation. The boron targets are fully dense powder The compacts. Synthesis of the boron sputter targets is described in detail elsewhere.[10l beryllium, alloy, and other metal targets are produced by conventional methods. The deposition chamber is cryogenically pumped to a 5x10 6 Pa base pressure. A 0.25-0.4 Pa sputter gas pressure of argon is maintained using a using a 25-35 cm 3 min' total flow rate. Nominal deposition rates from the boron and beryllium targets are 0.07 and 0.16 nm (W min)', respectively. The silicon substrates are located 6 cm beneath the center of the minisource array for the TEM study. The substrates are positioned at 60' separation along the circumference of a 4 cm diameter circle as concentric to the minisource array for the SEM study. The nominal composition of each alloy coating is computed from calibrated deposition rates as confirmed through measurements using a contact profilometer. The thin coatings are prepared for bright field TEM imaging in plan view by thinning the reverse side of the substrate my mechanical polishing then ion milling at glancing incidence. Specimen tilting at 30' is used to reveal any evidence of columnar growth.
Selected-area
diffraction patterns (SADPs) are used to determine crystalline phase. In addition to SEM imaging using secondary electrons to reveal surface morphology, energy dispersive spectrometry (EDS) of the boron-alloy Be coatings may reveal composition fluctuations that arise from the source-to-substrate geometry. The sequence of sampling composition starts at position #1 and is completed at position #6. In reference to sample position, the B source is located intermediate to positions #1 and #2, the metal dopant source (as e.g. Fe) intermediate positions to #3 and #4, and the Be source intermediate to positions #5 and #6. The intensities of the 0.72 eV Fe LI1 and 0.19 keV B K peaks are collected at each position using a 500 sec. live-count period. The coating hardness is measured using nanoindentation. In this instrument a Berkovitz diamond tip that has three-sides, each at 65.3Y to the base, is used to indent the coatings. Force measurements at various depths are repeated then averaged, and the standard deviations are used to derive the probable errors. Hardness (HO) is then defined as the average pressure under the indenter tip. Hardness can be calculated from the load divided by the projected area of contact between the tip and the sample. The projected area is determined from the depth of penetration using the known profile of the tip. Although there are limitations imposed by analyzing inhomogeneous and hard materials, hardness is computed using a standard Doerner-Nix procedure.1111 HF values are reported at a penetration depth equivalent to 20% the coating thickness. RESULTS Bright field images of Be.99, Be.94Cu06,
Data Loading...
