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616 Matching Results

Start Over Access Open Access Year 1998 Day 13th

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Results: 1 - 24 of 616 next

(open access)

W and WSi(x) Ohmic Contacts on p- And n-Type GaN

W and WSi ohmic contacts on both p- and n-type GaN have been annealed at temperatures from 300-1000 *C. There is minimal reaction (< 100 ~ broadening of the metal/GaN interface) even at 1000 *C. Specific contact resistances in the 10-5 f2-cm2 range are obtained for WSiX on Si-implanted GaN with a peak doping concentration of- 5 x 1020 cm-3, after annealing at 950 `C. On p-GaN, leaky Schottky diode behavior is observed for W, WSiX and Ni/Au contacts at room temperature, but true ohmic characteristics are obtained at 250 - 300 *C, where the specific contact resistances are typically in the 10-2 K2-cm2 range. The best contacts for W and WSiX are obtained after 700 *C annealing for periods of 30- 120 sees. The formation of &WzN interracial phases appear to be important in determining the contact quality.

Date: October 13, 1998

Creator: Abernathy, C. R.; Cao, X. A.; Eizenberg, M.; Han, J.; Lothian, J. R.; Pearton, S. J. et al.

Object Type: Article

System: The UNT Digital Library

(open access)

New Neutron Rich Nuclei Near {sup 208}Pb

The level properties near the stable doubly-magic nuclei formed the experimental grounds for the theoretical description of nuclear structure. However with a departure from the beta-stability line, the classical well-established shell structure might be modified. In particular, it may even vanish for extremely exotic neutron-rich nuclei near the neutron-drip line. Presently, it is impossible to verify such predictions by a direct experimental studies of these exotic objects. However, one may try to observe and understand the evolution of the nuclear structure while departing in the experiment as far as possible from the stable nuclei. An extension of experimental nuclear structure studies towards the nuclei characterized by high neutron excess is crucial for such verifications as well as for the {tau}-process nucleosynthesis scenario. Heavy neutron-rich nuclei, south-east of doubly-magic {sup 208}Pb, were always very difficult to produce and investigate. The nuclei like {sup 218}Po and {sup 214}Pb or {sup 210}Tl marked the border line of known nuclei from the beginning of the radioactivity era for over ninety years. To illustrate the difficulties, one can refer to the experiments employing the on-line mass separator technique. A spallation of heavy targets like {sup 232}Th and {sup 238}U by high-energy protons was proven as …

Date: November 13, 1998

Creator: Aeystoe, J.; Andreyev, A.; Evensen, A.-H.; Hoff, P.; Huhta, M.; Huyse, M. et al.

Object Type: Article

System: The UNT Digital Library

(open access)

Proton Radioactivity Measurements at HRIBF: Ho, Lu, and Tm Isotopes

Two new isotopes, {sup 145}Tm and {sup 140}Ho and three isomers in previously known isotopes, {sup 141m}Ho, {sup 150m}Lu and {sup 151m}Lu have been discovered and studied via their decay by proton emission. These proton emitters were produced at the Holifield Radioactive Ion Beam Facility (HRIBF) by heavy-ion fusion-evaporation reactions, separated in A/Q with a recoil mass spectrometer (RMS), and detected in a double-sided silicon strip detector (DSSD). The decay energy and half-life was measured for each new emitter. An analysis in terms of a spherical shell model is applied to the Tm and Lu nuclei, but Ho is considerably deformed and requires a collective model interpretation.

Date: November 13, 1998

Creator: Akovali, Y.; Batchelder, J. C.; Bingham, C. R.; Davinson, T.; Ginter, T. N.; Gross, C. J. et al.

Object Type: Article

System: The UNT Digital Library

(open access)

Highest energy phenomena in the universe

One of the most enduring and frustrating mysteries in astrophysics is the nature of the cosmic gamma-ray burst (GRB). GRB` s were first reported in the 1970` s, and since then have been observed from over a dozen different satellites. Two recently launched satellites have revolutionized this field. One, the most sensitive, is known as the Compton Gamma-Ray Observatory (CGRO). This orbiting observatory carries an experiment known as the Burst and Transient Source Experiment (BATSE), which was intended to help elucidate the nature and origin of GRB` s. The other is the Italian-Dutch satellite Beppo-SAX, which is substantially less sensitive than BATSE, but can provide greatly superior positional accuracy for the GRBs it detects. The purpose of this LDRD project was to maximize the combined return of these satellites and two ground-based programs (MACHO [Massive Compact Halo Objects] and LOTIS [Livermore Optical Transient Imaging System]), which LLNL largely controls. We have been successful in designing and implementing real-time response systems, and have successfully responded to GRBs with the MACHO Telescope System.

Date: May 13, 1998

Creator: Alcock, C. R., LLNL

Object Type: Report

System: The UNT Digital Library