Parallel processes for patterning densely packed nanometre-scale structures are critical for many diverse areas of nanotechnology. Thin films of diblock copolymers can self-assemble into ordered periodic structures at the molecular scale (approximately 5 to 50 nm), and have been used as templates to fabricate quantum dots, nanowires, magnetic storage media, nanopores and silicon capacitors. Unfortunately, perfect periodic domain ordering can only be achieved over micrometre-scale areas at best and defects exist at the edges of grain boundaries. These limitations preclude the use of block-copolymer lithography for many advanced applications. Graphoepitaxy, in-plane electric fields, temperature gradients, and directional solidification have also been demonstrated to induce orientation or long-range order with varying degrees of success. Here we demonstrate the integration of thin films of block copolymer with advanced lithographic techniques to induce epitaxial self-assembly of domains. The resulting patterns are defect-free, are oriented and registered with the underlying substrate and can be created over arbitrarily large areas. These structures are determined by the size and quality of the lithographically defined surface pattern rather than by the inherent limitations of the self-assembly process. Our results illustrate how hybrid strategies to nanofabrication allow for molecular level control in existing manufacturing processes.

Epitaxial self-assembly of block copolymers on lithographically defined nanopatterned substrates

Nanochemistry: Synthesis in diminishing dimensions

The present invention provides systems, methods, screens, reagents and kits for optical system analysis of cells to rapidly determine the distribution, environment, or activity of fluorescently labeled reporter molecules in cells for the purpose of screening large numbers of compounds for those that specifically affect particular biological functions.

A system for cell-based screening

An exact hard-spheres scattering model for the mobilities of polyatomic ions

Electrochemistry of Fullerenes and Their Derivatives

The ionization potentials (IPs) of several large carbon clusters Cn (n≥48), including the enhanced abundance (‘‘magic number’’) clusters C50, C60, and C70, have been determined by Fourier transform ion cyclotron resonance (FTICR) mass spectrometric charge transfer bracketing experiments. The IPs of C50, C60, and C70 were bracketed by the same two charge transfer compounds, leading to a common value of 7.61±0.11 eV. The IPs of even numbered clusters adjacent to these magic number clusters were found to be lower by as much as 0.5 eV and all clusters between C50 and C200 were determined to have IPs greater than 6.20 eV. The reaction rates of C+60 and C+70 with metallocenes were anomalously slow in comparison to the other large carbon cluster ions. IP and reactivity results suggest that C50, C60, and C70 may indeed have different or more stable structures than neighboring clusters, which supports the hypothesis of closed‐shell, spherical species. The implications of these results for the mechanism of C+n formation by direct laser vaporization are also discussed.

‘‘Magic number’’ carbon clusters: Ionization potentials and selective reactivity

The availability of macroscopic quantities of fullerenes has resulted in a vast number of physical and chemical studies of these new materials. However, the mechanisms that lead to the formation of these spherical carbon allotropes are not well understood. Mass spectral evidence has been obtained for the size-selective growth of fullerenes through the coalescence of cyclo[n] carbons, molecular carbon allotropes consisting of monocyclic rings with n carbon atoms. Whereas coalescence of cyclo[30]carbon (cyclo-C30) produces predominantly buckminsterfullerene (C60), the smaller rings cyclo-Cl8 and cyclo-C24 preferentially produce fullerene C70 through distinct intermediates. The present studies not only provide new insights into fullerene formation mechanisms but also raise the possibility of tailoring the size distributions of fullerenes by variation of the appropriate properties of the precursors.

http://science.sciencemag.org/content/sci/259/5101/1594.full.pdf

Cyclocarbon Coalescence: Mechanisms for Tailor-Made Fullerene Formation

The ion/molecule chemistry of laser‐generated carbon cluster ions (C+n; n=3–19) has been studied using Fourier transform mass spectrometry. The ion/molecule reactions of mass‐selected carbon cluster ions with D2 and O2 have been studied and reaction rates measured. Reactions of the primary product ions with D2 and O2 were also studied. The change in reactivity observed as a function of cluster size suggests a structural change from linear to monocyclic rings in the cluster ions between n=9 and 10. Evidence for the presence of two structural isomers for the C+7 cluster ion has also been observed and has been attributed to the existence of both a linear and cyclic form of the ion. MNDO calculations have also been used to obtain structural and thermodynamic information on possible reactant and product ions in an attempt to explain the differences observed in the ion/molecule reactions. The results from collision induced dissociation studies of the carbon cluster ions are also discussed.

Ion molecule reactions of carbon cluster ions with D2 and O2

The purpose of this account is to describe some of the key, early mass spectrometric studies of gas-phase carbon clusters, which served as a prelude to the Huffman-Kratschmer discovery as well as some of the more recent investigations of fullerene properties in the gas phase. The authors concentrate on analytical investigations of fullerene structure and chemistry as studied by mass spectrometry.

Stephen W. McElvany

Papers

‘‘Magic number’’ carbon clusters: Ionization potentials and selective reactivity

Cyclocarbon Coalescence: Mechanisms for Tailor-Made Fullerene Formation

Ion molecule reactions of carbon cluster ions with D2 and O2

Characterization of fullerenes by mass spectrometry

FTMS studies of mass-selected, large cluster ions produced by direct laser vaporization