Cluster secondary ion mass spectrometry of polymers and related materials

Abstract

Cluster secondary ion mass spectrometry (cluster SIMS) has played a critical role in the characterization of polymeric materials over the last decade, allowing for the ability to obtain spatially resolved surface and in-depth molecular information from many polymer systems. With the advent of new molecular sources such as C(60)(+), Au(3)(+), SF(5)(+), and Bi(3)(+), there are considerable increases in secondary ion signal as compared to more conventional atomic beams (Ar(+), Cs(+), or Ga(+)). In addition, compositional depth profiling in organic and polymeric systems is now feasible, without the rapid signal decay that is typically observed under atomic bombardment. The premise behind the success of cluster SIMS is that compared to atomic beams, polyatomic beams tend to cause surface-localized damage with rapid sputter removal rates, resulting in a system at equilibrium, where the damage created is rapidly removed before it can accumulate. Though this may be partly true, there are actually much more complex chemistries occurring under polyatomic bombardment of organic and polymeric materials, which need to be considered and discussed to better understand and define the important parameters for successful depth profiling. The following presents a review of the current literature on polymer analysis using cluster beams. This review will focus on the surface and in-depth characterization of polymer samples with cluster sources, but will also discuss the characterization of other relevant organic materials, and basic polymer radiation chemistry.

Systematic Temperature Effects in the Argon Cluster Ion Sputter Depth Profiling of Organic Materials Using Secondary Ion Mass Spectrometry

“…The sputtering yield had doubled at 140°C and tripled at 180°C. All these effects are discussed clearly with the models in the review by Mahoney [16] and relate to polymers, their cross linking, depolymerisation, and other polymer-related behavior.…”

“…In a detailed survey of the SIMS of polymers and related materials by cluster primary ions, Mahoney [16] notes that at high temperatures, polymers show ion-induced depolymerisation and, at low temperatures, reduced crosslinking. Below the glass transition temperature, T g , free radicals becomes trapped and their reaction rate is reduced.…”

Polymer surface structures determined using ToF-SIMS

“…For example, a better understanding of the sputtering mechanisms of polymeric materials has been gained using molecular dynamics simulations (Delcorte et al 2003), multivariate analysis methods have been employed to interpret data (Lee et al 2008), and new techniques such as clusterion beams and metal-assisted SIMS have been developed (Delcorte et al 2002, Winograd 2005. Not only have these advances improved the SIMS capabilities for polymer analysis, but they have also opened up new application perspectives such as molecular depth profiling, which allows polymeric materials to be analyzed along the depths as wells as at the surface (Ninomiya et al 2009, Mahoney 2010, Wucher and Winograd 2010, Shard et al 2013.…”

Development of a Primary Ion Column for Mass Spectrometry-Based Surface Analysis

“…Dynamic SIMS also provides enhanced sputter and ionization yields, maximizing sensitivity for trace analysis 10 . However, advances in projectiles have allowed for Dynamic SIMS to become widely applicable by incurring significantly reduced damage 19,20 . Other advances capitalize on the DC-nature of the beam in this mode, allowing for nanoscale analyses to be performed with ease (>250 nm) 15 .…”

“…Sputtering of this nature is regarded as kinetically assisted potential sputtering, where the initial impact to generate the concerted, non-linear motion leading to emission contributes energy to generate the thermal spike [30][31] . Factors influencing the occurrence of such elastic or inelastic collisions have been strongly correlated to the projectile cross-section, the energy per constituent distributed on the projectile upon impact (if considering clusters), and the molecular forces holding these projectiles together 32,33,20 . …”