Determination of energy barrier profiles for high-k dielectric materials utilizing bias-dependent internal photoemission

We utilize bias-dependent internal photoemission spectroscopy to determine the metal/dielectric/silicon energy barrier profiles for Au/HfO2/Si and Au/Al2O3/Si structures. The results indicate that the applied voltage plays a large role in determining the effective barrier height and we attribute much of the variation in this case to image potential barrier lowering in measurements of single layers. By measuring current at both positive and negative voltages, we are able to measure the band offsets from Si and also to determine the flatband voltage and the barrier asymmetry at 0 V. Our SiO2 calibration sample yielded a conduction band offset value of 3.03+/-0.1 eV. Measurements on HfO2 give a conduction band offset value of 2.7+/-0.2 eV (at 1.0 V) and Al2O3 gives an offset of 3.3+/-0.1 (at 1.0 V). We believe that interfacial SiO2 layers may dominate the electron transport from silicon for these films. The Au/HfO2 barrier height was found to be 3.6+/-0.1 eV while the Au/Al2O3 barrier is 3.5+/-0.1 eV

ROTSE All Sky Surveys for Variable Stars I: Test Fields

The ROTSE-I experiment has generated CCD photometry for the entire Northern sky in two epochs nightly since March 1998. These sky patrol data are a powerful resource for studies of astrophysical transients. As a demonstration project, we present first results of a search for periodic variable stars derived from ROTSE-I observations. Variable identification, period determination, and type classification are conducted via automatic algorithms. In a set of nine ROTSE-I sky patrol fields covering about 2000 square degrees we identify 1781 periodic variable stars with mean magnitudes between m_v=10.0 and m_v=15.5. About 90% of these objects are newly identified as variable. Examples of many familiar types are presented. All classifications for this study have been manually confirmed. The selection criteria for this analysis have been conservatively defined, and are known to be biased against some variable classes. This preliminary study includes only 5.6% of the total ROTSE-I sky coverage, suggesting that the full ROTSE-I variable catalog will include more than 32,000 periodic variable stars.Comment: Accepted for publication in AJ 4/00. LaTeX manuscript. (28 pages, 11 postscript figures and 1 gif

The ROTSE-III Robotic Telescope System

The observation of a prompt optical flash from GRB990123 convincingly demonstrated the value of autonomous robotic telescope systems. Pursuing a program of rapid follow-up observations of gamma-ray bursts, the Robotic Optical Transient Search Experiment (ROTSE) has developed a next-generation instrument, ROTSE-III, that will continue the search for fast optical transients. The entire system was designed as an economical robotic facility to be installed at remote sites throughout the world. There are seven major system components: optics, optical tube assembly, CCD camera, telescope mount, enclosure, environmental sensing & protection and data acquisition. Each is described in turn in the hope that the techniques developed here will be useful in similar contexts elsewhere.Comment: 19 pages, including 4 figures. To be published in PASP in January, 2003. PASP Number IP02-11

Observations of the Optical Counterpart to XTE J1118+480 During Outburst by the ROTSE-I Telescope

The X-ray nova XTE J1118+480 exhibited two outbursts in the early part of 2000. As detected by the Rossi X-ray Timing Explorer (RXTE), the first outburst began in early January and the second began in early March. Routine imaging of the northern sky by the Robotic Optical Transient Search Experiment (ROTSE) shows the optical counterpart to XTE J1118+480 during both outbursts. These data include over 60 epochs from January to June 2000. A search of the ROTSE data archives reveal no previous optical outbursts of this source in selected data between April 1998 and January 2000. While the X-ray to optical flux ratio of XTE J1118+480 was low during both outbursts, we suggest that they were full X-ray novae and not mini-outbursts based on comparison with similar sources. The ROTSE measurements taken during the March 2000 outburst also indicate a rapid rise in the optical flux that preceded the X-ray emission measured by the RXTE by approximately 10 days. Using these results, we estimate a pre-outburst accretion disk inner truncation radius of 1.2 x 10^4 Schwarzschild radii.Comment: 9 pages, 1 table, 2 figure

Silicon optical nanocrystal memory

We describe the operation of a silicon optical nanocrystal memory device. The programmed logic state of the device is read optically by the detection of high or low photoluminescence intensity. The suppression of excitonic photoluminescence is attributed to the onset of fast nonradiative Auger recombination in the presence of an excess charge carrier. The device can be programmed and erased electrically via charge injection and optically via internal photoemission. Photoluminescence suppression of up to 80% is demonstrated with data retention times of up to several minutes at room temperature

Low-energy structure of the even-A 96−104 Ru isotopes via g-factor measurements

The transient-field-perturbed angular correlation technique was used with Coulomb excitation in inverse kinematics to perform a systematic measurement of the g factors of the first excited 21+ states in the stable even-A isotopes Ru96-104. The measurements have been made relative to one another under matched kinematic conditions and include a measurement of g(21+)=+0.47(3) in Ru96

Transparent Anomalous Dispersion and Superluminal Light Pulse Propagation at a Negative Group Velocity

Anomalous dispersion cannot occur in a transparent passive medium where electromagnetic radiation is being absorbed at all frequencies, as pointed out by Landau and Lifshitz. Here we show, both theoretically and experimentally, that transparent linear anomalous dispersion can occur when a gain doublet is present. Therefore, a superluminal light pulse propagation can be observed even at a negative group velocity through a transparent medium with almost no pulse distortion. Consequently, a {\it negative transit time} is experimentally observed resulting in the peak of the incident light pulse to exit the medium even before entering it. This counterintuitive effect is a direct result of the {\it rephasing} process owing to the wave nature of light and is not at odds with either causality or Einstein's theory of special relativity.Comment: 12 journal pages, 9 figure

Spectroscopic studies of Dy-168,170 using CLARA and PRISMA

Preliminary results from an experiment aiming at Dy-170. Submitted to the LNL Annual Report 2008.Comment: 2 pages, 4 figures, Submitted to the LNL Annual Report 200