Depth profiling cross‐linked poly(methyl methacrylate) films: a time‐of‐flight secondary ion mass spectrometry approach Journal Articles uri icon

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abstract

  • RationaleIn order to determine the degree of cross‐linking on the surface and its variations in a nanometer‐scale depth of organic materials, we developed an approach based on time‐of‐flight secondary ion mass spectrometry (TOF‐SIMS), which provides rich chemical information in the form of fragment ions. TOF‐SIMS is extremely surface‐sensitive and capable of depth profiling with the use of a sputter ion beam to remove controllable amounts of substance.MethodsPoly(methyl methacrylate) (PMMA) films spin‐coated on a Si substrate were cross‐linked using a recently developed, surface sensitive, hyperthermal hydrogen projectile bombardment technique. The ion intensity ratio between two ubiquitous hydrocarbon ions, C6H– and C4H–, detected in TOF‐SIMS, denoted as ρ, was used to assess the degree of cross‐linking of the PMMA films. The cross‐linking depth of the PMMA films was revealed by depth profiling ρ into the polymer films using a C60+ sputter beam.ResultsThe control PMMA film spin‐coated on a Si substrate was characterized by ρ = 32% on its surface when using a 25 keV Bi3+ primary ion beam. This parameter on the PMMA films subjected to HHIC treatment for 10, 100 and 500 s increased to 45%, 56% and 65%, respectively. The depth profiles of ρ obtained using a 10 keV C60+ ion beam resembled an exponential decay, from which the cross‐linking depth was estimated to be 3, 15 and 39 nm, respectively, for the three cross‐linked PMMA films.ConclusionsWe demonstrated that the ion intensity ratio of C6H– to C4H– detected in TOF‐SIMS provides a unique and simple means to assess the degree of cross‐linking of the surface of PMMA films cross‐linked by the surface sensitive hyperthermal hydrogen projectile bombardment technique. With a C60+ sputter beam, we were able to depth profile the PMMA films and determine cross‐linking depths of the cross‐linked polymer films at nanometer resolutions. Copyright © 2017 John Wiley & Sons, Ltd.

authors

  • Naderi‐Gohar, Soheila
  • Huang, Kevin MH
  • Wu, Yiliang
  • Lau, Woon Ming
  • Nie, Heng‐Yong

publication date

  • February 28, 2017