We describe kinetic control of DNA hybridization: loop complexes are used to inhibit the hybridization of complementary oligonucleotides; rationally designed DNA catalysts are shown to be effective in promoting their hybridization. This is the basis of a strategy for using DNA as a fuel to drive free-running artificial molecular machines.

To investigate the viability of large scale manufacture of SCALPEL masks, key components of the SCALPEL mask process have been performed by commercial suppliers. SCALPEL mask blanks have been fabricated by MCNC to specifications supplied by Lucent and have been delivered, patterned, and utilized. Patterning, inspection, and metrology have been performed by DuPont Photomask and Photronics using the standard set of tools used for photomasks. A wet chemical pattern transfer process has been developed that is compatible with the processing tools in the mask shops and is extensible to the 0.1 m generation of integrated circuits. SCALPEL masks that have been fabricated using these processes and tools exhibit excellent pattern fidelity and feature edge quality.

Intersubband electroluminescence is reported in a quantum-cascade structure based on asymmetric superlattice active regions and designed for emission in the THz range ͑Ϸ80 m͒. Comparison with a structure based on a ''vertical transition'' in a single quantum well shows an increased full width at half maximum ͑2.8 vs 0.9 meV͒ of the emission line. In both cases the dependence of the optical power on the injected current is linear or sublinear and remains in the pW range.

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A process for high-resolution patterning of the membrane-type masks used in the SCALPEL1 (SCattering with Angular Limitation in Projection Electron-beam Lithography) lithography system is described. SCALPEL is a 4X projection electron beam lithography tool with the potential to extend commercial lithographic capability well into the deep sub-micron range: the recently-completed SCALPEL proof-ofconcept (SPOC) system has printed 0.08 j.tm lines in thick resist on Si. The details of the patterning process we currently employ and metrology results from the first series of masks are presented here.The SPOC mask blank2 consists of a segmented W-coated SiN (Si-rich) membrane, fabricated on a 4' Si wafer. The blank is patterned with 45 different test chips using a vector-scanned e-beam lithography tool. Metrology is performed on completed masks, and results from measurements of line-edge roughness, CD linearity, and pattern unifonnity are presented. We examine the need for proximity effect correction of the pattern data, and compare the effect of correction on pattern data file size for a variety of mask technologies.