Exohedrally functionalised fullerenes have been inserted in single-walled carbon nanotubes (SWNTs) with the aid of supercritical carbon dioxide to form peapods; C(61)(COOEt)(2) are encapsulated in SWNTs in high yield, whereas C(61)(COOH)(2) aggregate via hydrogen bonding to form a supramolecular complex, which sterically hinders encapsulation and causes it to adhere to the exterior surface of the SWNTs.

We have investigated the use of supercritical fluids (SCFs) as carriers/solvents during the postsynthesis alumination of mesoporous silica. SCFs were found to be ideally suited for transport of Al into mesoporous silica and to lead to Al-grafted aluminosilicate materials that exhibit exceptional hydrothermal (steam) stability even for highly aluminated materials. The improvements in steam stability arising from the use of SCFs as grafting media (as compared to aqueous or organic solvents) are remarkable, especially for Al-grafted MCM-41 materials with high (Si/Al < or = 10) Al contents. It is proposed that under supercritical fluid conditions Al is sorbed on the surface of the pore walls of the host Si-MCM-41 with little penetration into the pore wall region, that is, the low solvating power of SCFs ensures the deposition of Al onto rather than into the silica framework. This is because the host silica framework cannot undergo any significant hydrolysis (to allow penetration of Al into the pore wall region) during the SCF-mediated alumination. Removal of the Al (i.e., dealumination) which occurs during steaming is therefore less detrimental to the structural integrity of SCF-grafted Al-MCM-41 materials since any dealumination that occurs will not involve removal of Al from deep within the pore walls.

The intercalation of ethane and ethene into the octahedral interstitial sites of the C60 lattice can be achieved by antisolvent precipitation, using supercritical C2H4 and C2H6. This method of crystallization (see picture), which has yielded unprecedented intercalation compounds with hydrocarbons once thought too large to form such species, should be applicable to other gases, solvents, and fullerenes.

High-purity conformal metal oxide films were deposited onto planar and etched silicon wafers by surface-selective precursor hydrolysis in supercritical carbon dioxide using a cold wall reactor. Continuous films of cerium, hafnium, titanium, niobium, tantalum, zirconium, and bismuth oxides between 21 and 263 nm thick were grown at temperatures between 250 and 300 °C using CO 2 soluble precursors. The as-deposited films were pure single-phase oxide in the cases of HfO 2 , ZrO 2 , and TiO 2 and composed of oxides of mixed oxidation states in the cases of cerium, tantalum, niobium, and bismuth oxides as determined by XPS. As-deposited films typically contained 5% carbon or less. Carbon contamination was eliminated in all cases by annealing at 400 °C. The films were characterized by XPS, profilometry, SEM, XRD, and AFM.

Supercritical fluids including carbon dioxide offer a combination of properties that are uniquely suited for device fabrication at the nanoscale. Liquid-like densities, favorable transport properties, and the absence of surface tension enable solution-based processing in an environment that behaves much like a gas. These characteristics provide a means for extending “top-down” processing methods including metal deposition, cleaning, etching, and surface modification chemistries to the smallest device features. The interaction of carbon dioxide with polymeric materials also enables complete structural specification of nanostructured metal oxide films using a “bottom-up” approach in which deposition reactions are conducted within sacrificial, pre-organized templates dilated by the fluid. The result is high-fidelity replication of the template structure in a new material. In particular, block copolymer templates yield well-ordered porous silica and titania films containing spherical or vertically aligned pores that can serve as device substrates for applications in microelectronics, detection arrays, and energy conversion. Finally, the synthesis of nanoparticles and nanowires in supercritical fluids is developing rapidly and offers promise for the efficient production of well-defined materials. In this review, we summarize these developments and discuss their potential for nextgeneration device fabrication.