Thermal stability and electronic structure of atomically uniform Pb films on Si(111)

Atomically uniform Pb films are successfully prepared on Si(111), despite a large lattice mismatch. Angle-resolved photoemission measurements of the electronic structure show layer-resolved quantum well states which can be correlated with dramatic variations in thermal stability. The odd film thicknesses N = 5, 7, and 9 monolayers show sharp quantum well states. The even film thicknesses N = 6 and 8 do not, but are much more stable than the odd film thicknesses. This correlation is discussed in terms of a total energy calculation and Friedel-like oscillations in properties.     

Spin dynamics in the carrier-doped S=1/2 triangular lattice of NaxCoO2.yH2O

We probed the local electronic properties of the mixed-valent Co+4-x triangular lattice in NaxCoO2.yH(2)O by 59Co NMR. We observed two distinct types of Co sites for x > or =1/2, but the valence seems averaged out for x approximately 1/3. Local spin fluctuations exhibit qualitatively the same trend down to approximately 100 K regardless of the carrier concentration x, and hence the nature of the electronic ground state. A canonical Fermi-liquid behavior emerges below approximately 100 K only for x approximately 1/3.     

Determining the hydrographic parameters of the surface of water from the image sequences of a CCD camera

Water surface fluctuations were analyzed using image sequences from a CCD (charge coupled device) camera. Both regular and irregular waves were used for the study. A transfer function is obtained by comparing the gray scales of the image and results of in-situ wave gauge array measurements. The effects of non-uniform illumination within the wave basin are imbedded in the transfer function. Thus, the obtained transfer function is directly applicable to all other areas of interests within the wave basin. Estimated wave heights are all in qualitative agreement with those obtained through direct measurements. It is shown that the averaged relative error between these two wave heights is less than 16%.     

Alternating layer and island growth of Pb on Si by spontaneous quantum phase separation

Real-time in situ x-ray studies of continuous Pb deposition on Si(111)-(7x7) at 180 K reveal an unusual growth behavior. A wetting layer forms first to cover the entire surface. Then islands of a fairly uniform height of about five monolayers form on top of the wetting layer and grow to fill the surface. The growth then switches to a layer-by-layer mode upon further deposition. This behavior of alternating layer and island growth can be attributed to spontaneous quantum phase separation based on a first-principles calculation of the system energy.     

Improved direct measurement of the parity-violation parameter Ab using a mass tag and momentum-weighted track charge

We present an improved direct measurement of the parity-violation parameter A(b) in the Z boson-b-quark coupling using a self-calibrating track-charge technique applied to a sample enriched in Z-->bb events via the topological reconstruction of the B hadron mass. Manipulation of the Stanford Linear Collider electron-beam polarization permits the measurement of A(b) to be made independently of other Z-pole coupling parameters. From the 1996-1998 sample of 400,000 hadronic Z decays, produced with an average beam polarization of 73.4%, we find A(b)=0.906+/-0.022(stat)+/-0.023(syst).     

Synthesis and characterization of luminescent osmium(II) carbonyl complexes based on chelating dibenzoylmethanate and halide ligands

Octahedral Os(II) complexes 1-5 with formula [Os(CO)3X(dbm)] are prepared through utilization of both solid-state pyrolysis and ligand exchange reactions. These complexes exhibit prominent 3pi-pi* phosphorescence with unusually long lifetimes (29-64 micros) and high quantum yields (0.08-0.13).     

Furan-containing oligoaryl cyclophanene

[structure: see text] Furan-containing oligoaryl cyclophanene 1 and the corresponding cyclophane 2 were synthesized from propargylic dithioacetal 3. The electrochemical and photophysical properties and the fluxional behavior of these molecules have been examined. The emission of 1 appeared at 499 nm whereas that of 2 appeared at 389 nm.     

Mixed finite volume methods on nonstaggered quadrilateral grids for elliptic problems

We construct and analyze a mixed finite volume method on quadrilateral grids for elliptic problems written as a system of two first order PDEs in the state variable (e.g., pressure) and its flux (e.g., Darcy velocity). An important point is that no staggered grids or covolumes are used to stabilize the system. Only a single primary grid system is adopted, and the degrees of freedom are imposed on the interfaces. The approximate flux is sought in the lowest-order Raviart-Thomas space and the pressure field in the rotated- nonconforming space. Furthermore, we demonstrate that the present finite volume method can be interpreted as a rotated- nonconforming finite element method for the pressure with a simple local recovery of flux. Numerical results are presented for a variety of problems which confirm the usefulness and effectiveness of the method.

     

Wavenumber Measurements of CO(2) Transitions in 1.5-µm Atmospheric Window Using an External-Cavity Diode Laser

Using an external-cavity diode laser (ECDL) as the light source, we have observed the spectrum of CO(2) in the 1.5-μm atmospheric window including the (30(0)1)(I) <-- (00(0)0) and (31(1)1)(I) <-- (01(1)0)(I) bands. Good signal-to-noise ratio allowed us to lock the frequency of our ECDL to the absorption line centers. Wavenumber measurements of the transitions with accuracy about 6.6 x 10(-4) cm(-1) are made with the help of a precision wavemeter calibrated to the accurate C(2)H(2) frequency references in the 1.5-μm wavelength region. Molecular constants are obtained by making the least-squares fits of the measured transition wavenumbers. The rotational and centrifugal distortion constants are consistent with the previous results using high-resolution Fourier transform spectroscopy. However, the band centers are different with previous results by several thousandth reciprocal centimeters. Copyright 2001 Academic Press.