In this review the basic principles of interference lithography (IL) are described. IL is emerging as one of the most powerful yet relatively inexpensive methodologies for creating large-area patterns with micron-to sub-micron periodicities.-dimensional periodic structures ( ) can be obtained by interfering ( ) non-coplanar beams in a photoresist. The symmetry and shape of the "unit cell" can be conveniently controlled by varying the intensities, geometries, polarizations, and phases of the beams involved. IL done with shorter wavelength lasers and/or liquid immersion lithography can create features with sub-50 nm dimensions. Such periodic structures are beginning to find wide use in photonic crystal science, optical telecommunications, data storage, and the integrated circuit industry. Newer innovations such as diffraction element assisted lithography or DEAL and phase-controlled IL for making twodimensional structures are also discussed.SEM images of two-dimensional patterns created by three-beam non-coplanar interference lithography. The upper left hand image corresponds to the case when the phases of the three beams used to make the exposure are equal. The remaining images correspond to situations where one laser beam has been given a different phase relative to the other two beams when making the exposure.

Transition-metal (TM)-doped boron clusters have received considerable attention in recent years, in part, because of their remarkable size-dependent structural and electronic properties. However, the structures of medium-sized boron clusters doped with TM atoms are still not well-known because of the much increased complexity of the potential surface as well as the rapid increase in the number of low-energy isomers, which are the challenges in cluster structural searches. Here, by means of an unbiased structure search, we systematically investigated the structural evolution of medium-sized tantalum-doped boron clusters, TaB (n = 10-20). The results revealed that TaB (n = 10-15) clusters adopt half-sandwich molecular geometries, with the notable exception of TaB, while for n = 16-18 and 19-20, the lowest-energy clusters are characterized by drum-type geometries and tubular molecules with two B atoms on the top, respectively. Good agreement between the calculated and experimental photoelectron spectra strongly support the validity of our global minimum structures. Molecular orbital and adaptive natural density partitioning analyses indicate that the enhanced stability of half-sandwich TaB is due to the strong interaction of the Ta atom (5d orbitals) with surrounding B atoms (2p orbitals) and σ B-B bonds in the B moiety.

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Using an efficient structure search method based on a particle swarm optimization algorithm, we study the structural evolution of solid carbon dioxide (CO2) under high pressure. Our results show that, although it undertakes many structural transitions under pressure, CO2 is quite resistive to structures with C beyond 4-fold coordination. For the first time, we are able to identify two 6-fold structures of solid CO2 with Pbcn and Pa3 symmetries that become stable at pressures close to 1 TPa. Both structures consist of a network of C-O octahedra, showing hypervalence of the central C atoms. The C-O bond length varies from 1.30 to 1.34 Å at the 4-fold to 6-fold transition, close to the C-O distance in the transition state of a corresponding S(N)2 reaction. It has been a longstanding and challenging objective to stabilize C in a hypervalent state, particularly when it is bonded with nonmetallic elements. Most of the work so far has focused on synthesizing organic molecules with a high coordination number of C. Our results provide a good measure of the resistivity of C toward forming hypervalent compounds with nonmetallic elements and of the barrier of reaction involving C-O bonds.