Elastic properties of boron carbide films via surface acoustic waves measured by Brillouin light scattering

Abstract

Surface acoustic wave (SAW) velocity has been determined by high resolution Brillouin light scattering to study the mechano‐elastic properties of boron carbide films prepared by radio frequency (RF) sputtering. The comparison of experimentally observed elastic behaviour with simulations made by considering film composition obtained from elastic recoil detection analysis‐time of flight (ERDA‐ToF) spectroscopy allows establishing that elastic properties are determined by that of crystalline boron carbide with a lessening of the SAW velocity values due to surface oxidation.

Elastic properties of B-C-N films grown by N2-reactive sputtering from boron carbide targets

“…22 Raman spectroscopy is an ideal non-destructive technique to check carbon structures 35 and FTIR spectroscopy is especially indicated to study boron-type vibrations in this BCN system, because their signals are not masked by the sp 2 -carbon modes, which are IR-forbidden. Fig.…”

“…In this way, it is easier to establish comparisons with velocities previously measured in "A"-type samples. 22 These kh values were selected in a narrow range delimited by the sufficient SAW velocity variation respect to the substrate and by keeping good optical quality. The kh values were tuned by the appropriate incident angle h s in order to improve the signal to noise ratio and regarding the films thickness of 29 nm and 80 nm, respectively.…”

“…40 This is unlike to the experimental findings showing an increase of v SAW as kh increases, but analogue to that found in "A"-samples, explained by the existence of a B 2 O 3 layer on the top of the "A" type thin films. 22 Moreover, regarding the atomic and chemical composition differences between the "N"-and "A"-type films, it becomes clear that in the case of the "N"-type films, BCN ternary compounds are not present to explain the elastic behavior and, contrary to the "A"-type films, BC compounds are present only in a small amount. Thus, the "N"-type films are mainly formed by graphitic amorphous carbon and smaller amounts of h-BN and boron carbide.…”

“…The study of the v SAW dependence on film thickness and on the phonon propagation direction may deliver information about the compounds that actually determine the elastic properties of the coating. 22 In this sense, Brillouin scattering is a non-destructive contactless technique that measures directly the thickness dependence of v SAW as well as the substrate influence to obtain information about the elastic behavior of a coated substrate.…”

“…A thorough explanation of the experimental setup was provided elsewhere. 22 The chemical composition of the obtained films was characterized by using the Fourier Transform detection of infrared absorption spectroscopy (FTIR) (Varian 660 FTIR model spectrophotometer) and a homemade micro-Raman system, consisting on a Jobin-Yvon HR 460 monochromator, a cooled CCD detection system and Kaiser Super-NotchPlus filters to suppress the elastic scattered light. The excitation light (514.5 nm line of an Ar þ laser) was focused on the samples with an Olympus microscope and a Â100 objective that collects also the scattered light.…”