In situ study of erosion and deposition of amorphous hydrogenated carbon films by exposure to a hydrogen atom beam

This paper reports on the first dual-beam experiment employing a hydrogen atom beam for sample exposure and an ion beam for analysis, enabling in situ and real-time studies of hydrogen atom interaction with materials. The erosion of an amorphous hydrogenated carbon (a-C:H) layer by deuterium atoms at 580K sample temperature was studied and the uptake of deuterium during the erosion process was measured in real time. The deuterium areal density increased at the beginning to 7.3 X 10(15) D cm(-2), but then stabilized at a constant value of 5.5 X 10(15) D cm(-2). Formation of a polymer-like deposit on an a-C: H layer held at room temperature and subjected to the deuterium atom beam was observed and also studied in situ. For both erosion and deposition studies an a-C-13:H layer on top of an Si substrate was used as a sample, making the experiments isotopically fully specified and thereby differentiating the deposited from the original layer and the interacting D atoms from H atoms present in the layer and in the residual vacuum. From the deposition study it was shown that carbon in the deposited layer originates from carbon-carrying species in the background vacuum that interact with hydrogen atoms. The areal density of the carbon at the surface was determined from the energy shift of the Si edge in the Rutherford backscattering spectrum. The cross section for Li-7 on D at 4.3 MeV Li ion energy and at a recoil angle of 30 degrees was also determined to be (236 +/- 16) X 10(-27) cm(2)/sr. This is a factor of 3 +/- 0.2 times higher than the Rutherford elastic cross section. (C) 2012 American Vacuum Society. [http://dx.doi.org/10.1116/1.4723637]