G.J. Weisel

Systematic study of microwave absorption, heating, and microstructure evolution of porous copper powder metal compacts

We present a systematic study of the absorption, heating behavior, and microstructure evolution of porous copper powder metal compacts subjected to 2.45 GHz microwave radiation and explain our observations using known physical mechanisms. Using a single-mode microwave system, we place the compacts in pure electric (E) or magnetic (H) fields and compare the heating trends. We also investigate the effect of particle size on the same. The observed trends and the differences between E- and H-field heating are reflected in the dramatic changes in the conductivity, permittivity, and permeability of the samples. These property changes are effected by the microstructure evolution during heating in the two types of fields. We also find that the observed dependence of the initial microwave heating on particle size is suggestive of single-particle behavior.

Shallow boron‐doped junctions in silicon

Shallow boron‐doped junctions in silicon have been investigated by means of secondary ion mass spectrometry, scanning electron microscopy, transmission electron microscopy, spreading resistance profiling, and four‐point probe techniques. The junctions were formed by implanting BF+2 ions into n‐type Si at the dose range of 1–5×1015 ions/cm2, through a thin (25‐nm) screen layer of silicon dioxide. We have emphasized the higher dose range (3–5×1015 ions/cm2) as it is more relevant to processes in the current level of device integration. The use of BF+2 species and the screen oxide layer is necessary in order to form junctions whose depths xj≤0.4 μm, when conventional annealing techniques are employed. We have also examined junctions that were activated in a rapid thermal annealing system that utilizes an incoherent light source. One of the main objectives of this study is to compare conventional and rapid thermal annealing techniques. We thus evaluate the results obtained by these two methods of annealing fo...

The low-energy neutron-deuteron analyzing power and the 3P0,1,2 interactions of nucleon-nucleon potentials

Data for the analyzing power Ay(θ) for the elastic scattering of neutrons from deuterons have been measured at 5.0, 6.5 and 8.5 MeV to an accuracy of ±0.0035. Surprisingly large differences have been observed at these low energies between the data and rigorous Faddeev calculations using the Paris and Bonn B nucleon-nucleon potentials. The Ay(θ) data provide a stringent test for our present understanding of the on-shell and off-shell 3P0,1,2 nucleon-nucleon interactions.

Microwave absorption in percolating metal-insulator composites

We measure several electromagnetic properties of tungsten-Teflon composites as a function of metal volume concentration. The electric (E) and magnetic (H) loss tangents at 2.45GHz and the dc conductivity each exhibits a percolation transition at a different critical value of the metal volume fraction p. Moreover, the transition behavior depends on the average particle size and size distribution of the metal component. We explain the variation in each case by a schematic model derived from established percolation theory and the distinct response of conducting particles to microwave electric and magnetic fields.

Energy dependence of the three-nucleon analyzing power puzzle

We report on the energy dependence of the three-nucleon analyzing power puzzle in proton–deuteron elastic scattering. It was found that the relative difference between calculations and data remains nearly constant at the 25% level up to about 25 MeV incident proton energy. Above this energy the relative difference decreases, approaching zero near 40 MeV.

Techniques for vector analyzing power measurements of the 2H(n, np)n breakup reaction at low energies

Abstract Experimental methods to measure the vector analyzing powers over a broad range of kinematic configurations in the n-d breakup reaction have been developed at TUNL. These techniques employ the polarized beam facilities at TUNL and use the 2H( d , n )3He reaction as a source of low-energy polarized neutrons. Our methods permit measurements to a high statistical accuracy over a large fraction of three-nucleon phase space. The techniques are described and experimental spectra along with kinematic calculations are presented.

Analytical solution of dispersion relations for the nuclear optical model

Analytical solutions of dispersion integral relations, linking the real and imaginary parts of the nuclear optical model, have been derived. These are displayed for some widely used forms of the volume- and surface-absorptive nuclear potentials. When the analytical solutions are incorporated into the optical-model search code GENOA, replacing a numerical integration, the code runs three and a half to seven times faster, greatly aiding the analysis of direct-reaction, elastic scattering data.

Neutron–proton analyzing power at 12 MeV and inconsistencies in parametrizations of nucleon–nucleon data

Abstract We present the most accurate and complete data set for the analyzing power A y ( θ ) in neutron–proton scattering. The experimental data were corrected for the effects of multiple scattering, both in the center detector and in the neutron detectors. The final data at E n = 12.0 MeV deviate considerably from the predictions of nucleon–nucleon phase-shift analyses and potential models. The impact of the new data on the value of the charged pion–nucleon coupling constant is discussed in a model study.

Tunable plasmonic response of metallic nanoantennna heterodimer arrays modified by atomic-layer deposition

Abstract. We present a systematic study of tunable, plasmon extinction characteristics of arrays of nanoscale antennas that have potential use as sensors, energy-harvesting devices, catalytic converters, in near-field optical microscopy, and in surface-enhanced spectroscopy. Each device is composed of a palladium triangular-prism antenna and a flat counter-electrode. Arrays of devices are fabricated on silica using electron-beam lithography, followed by atomic-layer deposition of copper. Optical extinction is measured by employing a broadband light source in a confocal, transmission arrangement. We characterize the plasmon resonance behavior by examining the dependence on device length, the gap spacing between the electrodes, material properties, and the device array density, all of which contribute in varying degrees to the measured response. We employ finite-difference time-domain simulations to demonstrate good qualitative agreement between experimental trends and theory and use scanning electron microscopy to correlate plasmonic extinction characteristics with changes in morphology.

The Role of Geometry in Nanoscale Rectennas for Rectification and Energy Conversion

We have previously presented a method for optical rectification that has been demonstrated both theoretically and experimentally and can be used for the development of a practical rectification and energy conversion device for the electromagnetic spectrum including the visible portion. This technique for optical frequency rectification is based, not on conventional material or temperature asymmetry as used in MIM or Schottky diodes, but on a purely geometric property of the antenna tip or other sharp edges that may be incorporated on patch antennas. This “tip” or edge in conjunction with a collector anode providing connection to the external circuit constitutes a tunnel junction. Because such devices act as both the absorber of the incident radiation and the rectifier, they are referred to as “rectennas.” Using current nanofabrication techniques and the selective Atomic Layer Deposition (ALD) process, junctions of 1 nm can be fabricated, which allow for rectification of frequencies up to the blue portion of the spectrum (see Section 2).