This paper presents a method of constructing a single signal subspace for high-resolution estimation of the angles of arrival of multiple wide-band plane waves. The technique relies on an approximately coherent Combination of the spatial signal spaces of the temporally narrow-band decomposition of the received signal vector from an array of sensors. The algorithm is presented, and followed by statistical simulation examples. The performance of the technique is contrasted with other suggested methods and statistical bounds in terms of the determination of the correct number of sources (detection), bias, and variance of estimates of the angles.

We have observed collective spin-wave modes in inhomogeneously magnetized Ni 0.81 Fe 0.19 thin-film stripes. The stripes, 18 nm thick and 2 m wide, are studied in an in-plane magnetic field oriented along their short axes. When the magnetic field is on the order of the shape anisotropy field, the equilibrium magnetization near the stripe edges rotates 90 deg over a length scale of order 100 nm-1 m. Time-resolved Kerr microscopy is used to detect a hierarchy of spin-wave modes in these edge regions. Using a combination of semianalytical theory and micromagnetic simulations, we show that these modes span the entire stripe but can only be detected near the edges, where the effective wave vector is small.

Thiolate self-assembled monolayers (SAMs) on metal surfaces have been explored recently to address the assembly and connection issue in molecular electronics. In these systems, the molecule-metal contact is detrimental to electron transport. This is manifested not only in contact resistance, but also in the nature of the molecular device, which depends on the extent of wave function mixing between the molecule and the metal surface. We probe interfacial electronic structure, particularly unoccupied electronic states, in thiolate SAMs on Cu(111) using laser two-photon photoemission spectroscopy, in conjunction with ab initio calculations of model molecules. We find that the interfacial electronic structure is dominated by two virtual orbitals localized to the thiolate anchor and strongly coupled to the metal substrate. The shapes and energies of these interfacial σ*-like orbitals are independent of the nature of the hydrocarbon group (conjugated aromatics or saturated alkyls). As low-lying acceptor orbitals, they may play important roles in electron transport through self-assembled molecular wires.

No abstract