ToF‐SIMS characterisation of methane‐ and hydrogen‐plasma‐modified graphite using principal component analysis

Abstract

Time of flight secondary ion mass spectrometry (ToF-SIMS) has been used to determine the extent of surface modification of highly ordered pyrolytic graphite (HOPG) samples that were exposed to radio-frequency methane and hydrogen plasmas. The ToF-SIMS measurements were examined with the multivariate method of principal component analysis (PCA), to maximise the amount of spectral information retained in the analysis. This revealed that the plasma (methane or hydrogen plasma) modified HOPG exhibited greater hydrogen content than the pristine HOPG. The hydrogen content trends observed from the ToF-SIMS studies were also observed in elastic recoil detection analysis measurements. The application of the ToF-SIMS PCA method also showed that small hydrocarbon fragments were sputtered from the hydrogen-plasma-treated sample, characteristic of the formation of a plasma-damaged surface, whereas the methane-plasma-treated surface sputtered larger hydrocarbon fragments, which implies the growth of a polymer-like coating. Scanning tunnelling microscopy measurements of the modified surfaces showed surface features that are attributable to either etching or film growth after exposure to the hydrogen or methane plasma.

Stamping Nanoparticles onto the Electrode for Rapid Electrochemical Analysis in Microfluidics

“…Similarly, Figure 3 e,f are ToF-SIMS 2D maps of hydrocarbon fragment peaks C 4 H 10 + m/z + 58.0604 and C 5 H 9 + m/z + 69.0462 from the graphite mixing and stamping WE surface. Identification of these fragments as graphite fragments has been reported previously [ 30 , 31 ]. Additional SIMS spectral plots show dominant counts of these two peaks in supporting information (SI) Figure S1b .…”

Hydrogenation of sp2-bonded carbon surfaces using methane plasma

“…1(c) shows peak intensities extracted from the mean spectra (calculated from the 10 normalised spectra for each sample), for the peaks with dominant loadings as determined from the PCA results. We have previously shown that the C 2 H 3 + and C 3 H 3 + fragments are symptomatic of pristine graphite [6]. The yields of these fragments are observed to decrease as the plasma exposure time is increased, which shows the nature of the surface becomes less like HOPG.…”

“…The details of the chamber have been described elsewhere [6]. High purity methane (99.95% from Linde) was added to the chamber using a motorised automatic pressure controller, with chamber pressure monitored by a Baratron capacitive pressure gauge.…”

“…It has been reported that sp 2 forms of carbon are etched upon exposure to hydrogen plasma [5], and this increase in roughness can be detrimental for electrochemical applications, as rough surfaces are expected to exhibit large background currents [2]. In contrast, when sp 2 carbon is exposed to methane plasma the surface is hydrogenated [6], however with less degree of etching and resulting in a comparatively less-damaged surface than the hydrogen plasma treatment.…”

Matrix and primary ion‐related aspects of tryptophan SIMS analysis

“…Chiba et al investigated the carbon cluster emission from graphite . Deslandes et al determined the effect of surface modification of HOPG . Detter et al examined the matrix effect of granulated graphite on the Ag and Cu complex emission …”