David D. Allred received Alumni Professorship Award

Over the last few years many ion beam techniques have been reported for the profiling of hydrogen in materials. We have evaluated nine of these using similar samples of hydrogen ion-implanted into silicon. When possible the samples were analysed using two or more techniques to confirm the ion-implanted accuracy. We report the results of this work which has produced a consensus profile of H in silicon which is useful as a calibration standard. The analytical techniques used have capabilities ranging from very high depth resolution (≈50Å) and high sensitivity (< 1 ppm) to deep probes for hydrogen which can sample throughout thin sheets (up to 0.2 mm thick).

Magnesium fluoride on xenon difluoride passivated aluminum (Al+XeMgF₂) mirrors have high reflectance encompassing the H Lyman-α at 121.6 nm. Al+XeMgF₂ is a key candidate for space telescopes and satellites that demand far-UV (FUV) measurements coupled with high reflectance at longer wavelengths. Contamination can significantly reduce FUV reflectance, so Al+XeMgF₂ mirrors must be as clean as possible. Protecting the surfaces while in storage is also desirable. We investigated the suitability of four different formulations of Photonic Cleaning Technologies' First Contact Polymer for cleaning and protecting Al+XeMgF₂ coatings by repeatedly cleaning test samples. These were cleaved from a silicon wafer coated with 300 nm of chemical vapor deposited (CVD) silicon nitride (Si₃N₄). All the formulations could clean samples at least once. Using Variable-Angle, Spectroscopic Ellipsometry (VASE), we determined that two (S2 and S3) of the four tested formulations were able to clean and protect the Al+XeMgF₂ surfaces multiple times (>20) over 5 months without detectable alumina growth on the Al in a low humidity environment. There were also no changes to the thickness of 'apparent' MgF₂. Apparent MgF₂ includes the deposited MgF₂, the 2–3 nm AlF₃ layer produced by the XeF₂ passivation step, and contributions from surface roughening. There was also no detectable alumina growth for the controls. The fact that the samples were stored between tests in a desiccator with their First Contact overcoat provides evidence that Al+XeMgF₂ samples can successfully be protected and stored under some First Contact formulations for at least five months in a dry environment. Far-ultraviolet reflectance is not reported here.

We investigated the growth of carbon nanotubes (CNTs) directly on stainless steel substrates. The CNTs were grown using a two-step process: oxidation of the stainless steel surface and CNT growth. The samples were oxidized in an 800 °C furnace fed with a flow of air for 4 min. CNTs were grown by switching the flow to ethylene, which both reduces the oxide and initializes CNT growth. The time of CNT growth was varied to understand how the samples evolved over time. To better understand the growth mechanisms, we isolated cross-sections of the CNT-substrate interface using a focused ion beam. These cross-sections were investigated with transmission electron microscopy and energy dispersive X-ray spectroscopy. CNTs were seen to grow from iron-rich nanoparticles embedded in the oxide layer. The oxide layer was also seen to lose iron over time, suggesting that these iron nanoparticles were reduced out of the oxide. The base particles were embedded in the oxide layer, leaving cavities when the CNTs were removed. The diameters of the nanotubes were also seen to grow over time as a result of carbon infiltration. The effects of the embedded particle and infiltration quickly isolate the catalyst, leading to short CNTs (1–10 µm).