Versatile technique for assessing thickness of 2D layered materials by XPS

Abstract

X-ray photoelectron spectroscopy (XPS) has been utilized as a versatile method for thickness characterization of various two-dimensional (2D) films. Accurate thickness can be measured simultaneously while acquiring XPS data for chemical characterization of 2D films having thickness up to approximately 10 nm. For validating the developed technique, thicknesses of few-layer graphene (FLG), MoS and amorphous boron nitride (a-BN) layer, produced by microwave plasma chemical vapor deposition (MPCVD), plasma enhanced chemical vapor deposition (PECVD), and pulsed laser deposition (PLD) respectively, were accurately measured. The intensity ratio between photoemission peaks recorded for the films (C 1s, Mo 3d, B 1s) and the substrates (Cu 2p, Al 2p, Si 2p) is the primary input parameter for thickness calculation, in addition to the atomic densities of the substrate and the film, and the corresponding electron attenuation length (EAL). The XPS data was used with a proposed model for thickness calculations, which was verified by cross-sectional transmission electron microscope (TEM) measurement of thickness for all the films. The XPS method determines thickness values averaged over an analysis area which is orders of magnitude larger than the typical area in cross-sectional TEM imaging, hence provides an advanced approach for thickness measurement over large areas of 2D materials. The study confirms that the versatile XPS method allows rapid and reliable assessment of the 2D material thickness and this method can facilitate in tailoring growth conditions for producing very thin 2D materials effectively over a large area. Furthermore, the XPS measurement for a typical 2D material is non-destructive and does not require special sample preparation. Therefore, after XPS analysis, exactly the same sample can undergo further processing or utilization.

Enhancing Interconnect Reliability and Performance by Converting Tantalum to 2D Layered Tantalum Sulfide at Low Temperature

“…XPS Analysis : Monochromatic XPS was employed in this work using a system described elsewhere . The AAnalyzer software was used for XPS peak analysis .…”

Epitaxial growth of monolayer PdTe2 and patterned PtTe2 by direct tellurization of Pd and Pt surfaces

“…XPS thickness model is discussed in detail elsewhere. 25,26 This derivation follows the approach by Fadley. 27 The equation for the overlayer thickness, t, can be written as…”

“…We point out that our thickness calculation based on XPS was crosschecked by transition electron microscopy (TEM) for TMDC materials such as MoS2. 26 Chemical sensitivity of XPS characterizations also helps to confirm the formation of PdTe2 and PtTe2. After deposition at room temperature, the centroids of the Pd 3d5/2 and Pd 3d3/2 peaks are 335.6 eV and 340.9 eV, respectively, which shift towards higher binding energies (BEs) by 0.5 eV with respect to those of Pd(111) (Figure 3a (Figure 3b and 3d), which are higher by ~0.5 eV than those of bulk materials.…”

Structure-Controlled Chemical Properties of PdZn Near-Surface Alloys

“…The procedure to calculate film thickness using XPS data is described in detail elsewhere, − and brief details are provided in the Supporting Information. The thickness calculation procedure was adopted from ref , giving the ratio between the photoemission peaks of a substrate and an overlayer.…”