Rhenium alloys as ductile substrates for diamond thin-film electrodes

Abstract

Molybdenum-rhenium (Mo/Re) and tungsten-rhenium (W/Re) alloys were investigated as substrates for thin-film, polycrystalline boron-doped diamond electrodes. Traditional, carbide-forming metal substrates adhere strongly to diamond but lose their ductility during exposure to the high-temperature (1000°C) diamond, chemical vapor deposition environment. Boron-doped semi-metallic diamond was selectively deposited for up to 20 hours on one end of Mo/Re (47.5/52.5 wt.%) and W/Re (75/25 wt.%) alloy wires. Conformal diamond films on the alloys displayed grain sizes and Raman signatures similar to films grown on tungsten; in all cases, the morphology and Raman spectra were consistent with well-faceted, microcrystalline diamond with minimal sp2 carbon content. Cyclic voltammograms of dopamine in phosphate-buffered saline (PBS) showed the wide window and low baseline current of high-quality diamond electrodes. In addition, the films showed consistently well-defined, dopamine electrochemical redox activity. The Mo/Re substrate regions that were uncoated but still exposed to the diamond-growth environment remained substantially more flexible than tungsten in a bend-to-fracture rotation test, bending to the test maximum of 90° and not fracturing. The W/Re substrates fractured after a 27° bend, and the tungsten fractured after a 21° bend. Brittle, transgranular cleavage fracture surfaces were observed for tungsten and W/Re. A tension-induced fracture of the Mo/Re after the prior bend test showed a dimple fracture with a visible ductile core. Overall, the Mo/Re and W/Re alloys were suitable substrates for diamond growth. The Mo/Re alloy remained significantly more ductile than traditional tungsten substrates after diamond growth, and thus may be an attractive metal substrate for more ductile, thin-film diamond electrodes.

Effects of copper interlayer on deposition and flexibility improvement of diamond microelectrode

“…Diamond film grown on copper [12,13] or rhenium [3,14] does not generate carbide, but the diamond film readily delaminated. Mo/Re alloy seems to be an appropriate substrate [3], which remains ductile after diamond film growth, while the cost increases to a much high level. The other approach is to sputter an interlayer as a diffusion barrier on the surface of substrate before diamond film deposition.…”

“…One is the chronically implantable electrode requires excellent flexibility for maintaining its performance and mechanical integrity in intact behaving animals for weeks or months [3]. The main reason of this trouble is that diamond films are often deposited on heterogeneous substrates and these conventional heterogeneous substrates [3][4][5][6][7][8] inevitably react with carbon under CVD condition. It is very easy to form a brittle carbide layer between the substrate and diamond film.…”

A Preliminary Study of Oxidation Behavior of Mo-50Re Alloy at Different Temperature Using Positron Annihilation Lifetime Spectroscopy

“…Molybdenum-base alloys have attracted considerable interest for use as structural materials in many engineering applications such as heating elements, thermocouple sheathings, vacuum furnace components and electron tube components due to their high thermal conductivity, high temperature strength and corrosion resistance [1,2]. The strength, creep resistance, and low temperature ductility of Mo are improved with increasing the rhenium content up to its solubility limit, which was first described as the "rhenium effect" in 1956 [3].…”