Trapping of Hydrogen in Carbon Nitride Films During or After High Temperature Heat Treatment
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Trapping of Hydrogen in Carbon Nitride Films During or After High Temperature Heat Treatment David C. Ingram1, Asghar Kayani1, William C. Lanter2, Charles A. DeJoseph3. 1 Department of Physics and Astronomy, Ohio University, Athens, OH, USA. 2 Innovative Scientific Solutions, Corp., Beavercreek, OH, USA. 3 Air Force Research Laboratory (AFRL/PRPE), Wright-Patterson AFB, Dayton, OH, USA.
ABSTRACT Thin films of carbon nitride deposited by ion beam assisted deposition or by magnetron sputter deposition typically contain a significant fraction of hydrogen, 1-30 atomic percent (at.%). In order to improve the thermal stability of the properties of the films, attempts have been made to minimize the hydrogen trapped during deposition. Such films typically have less than 5 at.% hydrogen. On heating these films in ultra high purity (99.999%) argon, it has been found that above 600o C they start to absorb significant amounts of hydrogen, this despite retaining their mechanical integrity. The composition of the films is determined using Rutherford Backscattering Spectroscopy in combination with Elastic Recoil Spectroscopy for detecting the hydrogen isotopes. In this paper, the possible sources of the hydrogen have been investigated by exposing the samples to deuterated water or deuterium gas during or immediately after the heat treatment.
INTRODUCTION In previous work, we have shown that carbon nitride (CNx) can be fabricated with less than 5 atomic percent (at.%) hydrogen. However when these films are heated to 600o C or higher they contain hydrogen at 20 at.% or higher.1 This work is part of a study of methods to produce carbon nitride films, C3N4, which are predicted by Liu and Cohen to have extreme properties, including a hardness greater than diamond and a wide band gap.2,3 It had originally been expected that heating the films would have reduced the hydrogen content through diffusion and desorption. The purpose of this part of the study is to try to identify the source of the hydrogen that is present in these films after heat treatment. To do this films were heat treated and exposed to deuterium to determine the mechanism of hydrogen uptake. The hypothesis being tested is that the source of the hydrogen found in the films after the heat treatment is water vapor or hydrogen gas, both of which are known to be present in gas handling systems and vacuum systems. The hydrogen isotope content of the films is found using the MeV ion beam technique known as Elastic Recoil Spectroscopy (ERS) which is complementary to Rutherford Backscattering Spectrometry (RBS), and can give similar information to RBS in terms of mass identification and concentration as a function of depth.
EXPERIMENTAL Samples of carbon nitride films (CNx where x is approximately 0.6) were deposited using ion beam sputtering of a graphite target with a 1000 eV nitrogen beam while the growing film
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Graphite Sputtering Target
Water Cooled Substrate Holder
Broad Beam Ion Source 50 eV - 1 keV Direct Source
Sputtering Ion Source
Broad Beam Ion
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