Paper TF2-TuA2
ALD-Based Fabrication and Chromatographic Separations on Binder-Free, Carbon Nanotube-Templated Thin Layer Chromatography Plates

Tuesday, October 30, 2012, 2:20 pm, Room 11

We recently reported the use of patterned carbon nanotube (CNT) forests as scaffolds for the microfabrication of silica-based thin-layer chromatography plates (TLC) (Advanced Functional Materials2011, 21(6), 1132 – 1139). In this fabrication, CNTs were infiltrated by low pressure chemical vapor deposition of silicon using SiH₄, which was then oxidized and hydrated. Thorough characterization by RBS, XPS, TEM, SEM, and ToF-SIMS has been performed on these materials, which has given us a considerable understanding of them, e.g., the structure of the Si/SiO₂/Al₂O₃(30 nm)/Fe(6 nm) stack deposited prior to CNT growth has been confirmed, multiwall CNTs are grown in our process, CNT growth is base (bottom up) and not tip (top down), the thickness of the Fe catalyst layer plays a key role in the fabrication of our plates – when the catalyst layer is too thick CNT structures are unstable, etc. Fast and efficient separations were demonstrated on these plates.

Nevertheless, the oxidation of silicon in these materials leads to a volume expansion of the support, which appears to affect the A-term of the van Deemter equation in our separations. That is, distortions in the material appear to adversely affect separations performed on them. Accordingly, we have now shown that TLC plates can be fabricated by (i) priming patterned nanotube forests with a few nanometers of amorphous carbon, followed by a layer of Al₂O₃ deposited by atomic layer deposition (ALD), (ii) deposition of SiO₂ in a fast (pseudo) ALD of this material, and (iii) oxidizing at a lower temperature (ca. 600 K) than was used previously to remove the CNTs. An amino bonded phase was created. The resulting TLC plates show 125,000 – 225,000 N/m in a baseline separation of four fluorescent dyes. An even more recent and newly developed microfabrication method in our laboratory of CNT-templated TLC plates also shows fast separations with 400,000 – 500,000 N/m in preliminary results. These separations rival (or exceed) those of HPLC/UPLC in both speed and efficiency. Separations of biological interest will be shown.