History of very thick film and bulk sample group IIIB, IVB, VB, and rare earth materials for various vacuum applications

Abstract

Thick occluder film and bulk hydride materials are extremely hard to produce without flaking or cracking. This paper discusses methods of how to prepare thick films and bulk samples (i.e., rods and wires) that have reduced stress for many applications. These include accelerator research for cancer therapy, intense neutron sources, particle-beam fusion diagnostic beam focusing studies, and mass spectrometer calibration. Thick films of ∼(≥3000 to 150 000 nm thickness of various hydrides are sensitive to oxidation and are easily contaminated by improper handling. They must be specially prepared to reduce internal stresses due to temperature variations during processing, stresses due to hydriding, and substrate configuration (i.e., curved surfaces). Discussed are techniques developed at the General Electric Neutron Devices Department, in Largo, FL, in the mid-1970s to the late 1990s to produce flaking and crack free samples of thick films and bulk samples. Items studied include Er, Sc, and Ti thick film hydrides on a Cr underlay, on various substrates, Er and Sc bulk rod samples for the first basic material heat capacity and thermal diffusivity studies as a function of hydride loading, Nb and V wires in bundles of ∼30 wires, for the first tritide neutron vibration spectra studies, and Ti wires for mass spectrometer calibration studies. Film samples were prepared by standard E-beam evaporation techniques and then non-air-exposure loaded. Bulk samples were loaded with a Sievert's precise gas quantity loading system. To produce reduced intrinsic stress (strain) in samples of Er, Sc, and Ti thick films, and bulk samples of Er, Sc, Nb, V, and Ti, special processing employing slow bakeout heating and cool down rates, slow film deposition rates, slow leak in pressure hydriding rates, followed by slow cooling rates to room temperature were used. Using the process described, very successful results were obtained.