Sonya Roberson

Preliminary evaluation of an SF5+ polyatomic primary ion beam for analysis of organic thin films by secondary ion mass spectrometry

Organic vapor deposited thin films of pure biomolecules, polymer films and biomolecules dispersed in gelatin and biological tissue have been analyzed in a magnetic sector secondary ion mass spectrometer using an SF5+ primary ion beam at keV impact energies. In comparison to Ar+ bombardment under identical conditions, bombardment with SF5+ gives a 10 to 50 fold enhancement in the secondary ion yields for characteristic molecular ions. The SF5+ primary ion beam can be focussed to a small spot allowing molecular ion images to be obtained at micrometer spatial resolution with enhanced sensitivity. More importantly, the decay in molecular ion signal as a function of primary ion dose commonly observed in SIMS using monoatomic primary ions is either eliminated or greatly reduced, allowing molecular depth profiles to be obtained of organic thin films. By continuing to sample intact molecules as sputtering proceeds into the sample, the total number of detected characteristic secondary ions is increased by as much as a factor of approximately 700 for SF5+ bombardment as compared to Ar+ bombardment under identical analytical conditions. This effect is thought to be a result of the high erosion rate and the low penetration depth inherent in the use of a polyatomic primary projectile.

Multifunctional ToF-SIMS: combinatorial mapping of gradient energy substrates

Abstract We present a simple method for chemical modification of chlorosilane self-assembled monolayers (SAMs) on Si surfaces by exposure to a gradient of UV-ozone radiation to create stable substrates with a range of contact angles ( θ H 2 O ≈5–95°) and surface energies on a single substrate. These gradient energy substrates are developed to potentially generate libraries for combinatorial studies of thin film phenomenology, where a systematic variation of interfacial surface energy represents one of the significant parameters along one axis. The graded oxidation process presents a systematic variation of surface chemical composition. We have utilized contact angle measurements and time-of-flight secondary ion mass spectrometry (ToF-SIMS) to investigate this variation for a series of ions, among which are SiCH 3 + , SiOH + and COOH − . We show that the macroscopic measurements of surface free energy/contact angle correlate with the detailed analysis of surface chemistry (as assessed by ToF-SIMS) on these test substrates.

Time-Of-Flight Secondary Ion Mass Spectrometry (Tof-SIMS) For High-Throughput Characterization Of Biosurfaces

A graded oxidation process, involving UV-ozone (UVO) treatment, was used to create a poly(e-caprolactone) (PCL) surface with a systematic variation in surface chemistry. Time-of-flight secondary ion mass spectrometry (TOF-SIMS) has proved useful in characterizing the chemical composition of these surfaces and in monitoring the oxidation process. The TOF-SIMS data correlates with contact angle data and the results of the binding studies performed with mouse calvarial cells. UVO treatment resulted in a PCL surface with improved wettability and cellular adhesion.

Cluster Primary Ion Beam Secondary Ion Mass Spectrometry for Semiconductor Characterization

We are evaluating the use of polyatomic and cluster primary ion beams for characterization of semiconductor materials by secondary ion mass spectrometry using both magnetic sector and time-of-flight SIMS instruments. Primary ion beams of SF5+, C8− and CsC6− have been used to analyze low energy arsenic implants in silicon, boron delta-doped structures, thin gate oxides, metal multilayers, organic surface contamination and photoresist thin films. Compared to monoatomic bombardment under the same conditions, cluster ion beams offer improved depth resolution for silicon depth profiling and a reduction in sputter-induced topography for metals. For organic materials, the use of a cluster ion beam can give large improvements in yield for characteristic secondary ions and can minimize beam-induced degradation in some materials.

Preparation and Certification of K-411 Glass Microspheres.

The production and characterization of NBS K-411 glass microspheres in the 2-40 µm range for certification as NIST Standard Reference Material(R) 2066 (SRM(R)) are described. Quantitative analysis and heterogeneity testing of the microspheres were done with an electron probe microanalyzer-X-ray energy dispersive spectrometry (EPMA-EDS) automated particle analysis procedure. Results for the trimmed and normalized data produced mean compositions for the elements Mg, Si, Ca, Fe, and O (calculated from stoichiometry) that are in good agreement with the certified values for the K-411 bulk glass (NBS SRM 470 Glasses for Mineral Analysis), but with uncertainties about twice as large as those for the bulk material. Differences from the bulk are attributable to microsphere geometry as well as mass and size effects.