Nonvolatile memories using deep traps formed in HfO₂ by Nb ion implantation

We report nonvolatile memories (NVMs) based on deep-energy trap levels formed in HfO₂ by metal ion implantation. A comparison of Nb- and Ta-implanted samples shows that suitable charge-trapping centers are formed in Nb-implanted samples, but not in Ta-implanted samples. This is consistent with density-functional theory calculations which predict that only Nb will form deep-energy levels in the bandgap of HfO₂. Photocurrent spectroscopy exhibits characteristics consistent with one of the trap levels predicted in these calculations. Nb-implanted samples showing memory windows in capacitance–voltage (V) curves always exhibit current (I) peaks in I–V curves, indicating that NVM effects result from deep traps in HfO₂. In contrast, Ta-implanted samples show dielectric breakdowns during the I–V sweeps between 5 and 11 V, consistent with the fact that no trap levels are present. For a sample implanted with a fluence of 10¹³Nb cm⁻², the charge losses after 10⁴ s are ∼9.8 and ∼25.5% at room temperature (RT) and 85°C, respectively, and the expected charge loss after 10 years is ∼34% at RT, very promising for commercial NVMs

Strong enhancement of ultraviolet emission from ZnO films by V implantation

ZnOfilms were prepared on Si(100) wafers by rf sputtering and subsequently implanted with V ions to fluences of (1,2.5,5,10)×10¹⁵ cm¯². The room-temperature ultraviolet photoluminescence(PL) intensity of the implantedfilms is shown to increase with increasing fluence up to 2.5×1015 cm−2, becoming ∼37 times more intense than the emission from the unimplanted ZnOfilm, before decreasing at higher fluences. The increase in PL intensity is correlated with improved crystallinity of ZnO, accompanied by a reduction in the concentration of deep-level native defects by V incorporation into the ZnO lattice, as verified by x-ray diffraction, x-ray photoelectron spectroscopy, and low-temperature PL. The subsequent reduction in PL intensity at fluences higher than 2.5×10¹⁵ cm¯² is shown to result from the deterioration of the crystal quality and the precipitation of V secondary phase possibly introducing defects in the films

An all-electron density functional theory study of the structure and properties of the neutral and singly charged M-12 and M-13 clusters: M = Sc-Zn

The electronic and geometrical structures of the M 12 and M 13 clusters where M = Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Zn along with their singly negatively and positively charged ions are studied using all-electron density functional theory within the generalized gradient approximation. The geometries corresponding to the lowest total energy states of singly and negatively charged ions of V13, Mn12, Co12, Ni 13, Cu 13, Zn 12, and Zn 13 are found to be different from the geometries of the corresponding neutral parents. The computed ionizationenergies of the neutrals, vertical electron detachment energies from the anions, and energies required to remove a single atom from the M 13 and M 13 + clusters are in good agreement with experiment. The change in a total spin magnetic moment of the cation or anion with respect to a total spin magnetic moment of the corresponding neutral is consistent with the one-electron model in most cases, i.e., they differ by ±1.0 μ B. Exceptions are found only for Sc12 −, Ti12 +, Mn12 −, Mn12 +, Fe12 −, Fe13 +, and Co12 +

Human Prion Diseases in the United States

BACKGROUND: Prion diseases are a family of rare, progressive, neurodegenerative disorders that affect humans and animals. The most common form of human prion disease, Creutzfeldt-Jakob disease (CJD), occurs worldwide. Variant CJD (vCJD), a recently emerged human prion disease, is a zoonotic foodborne disorder that occurs almost exclusively in countries with outbreaks of bovine spongiform encephalopathy. This study describes the occurrence and epidemiology of CJD and vCJD in the United States. METHODOLOGY/PRINCIPAL FINDINGS: Analysis of CJD and vCJD deaths using death certificates of US residents for 1979-2006, and those identified through other surveillance mechanisms during 1996-2008. Since CJD is invariably fatal and illness duration is usually less than one year, the CJD incidence is estimated as the death rate. During 1979 through 2006, an estimated 6,917 deaths with CJD as a cause of death were reported in the United States, an annual average of approximately 247 deaths (range 172-304 deaths). The average annual age-adjusted incidence for CJD was 0.97 per 1,000,000 persons. Most (61.8%) of the CJD deaths occurred among persons >or=65 years of age for an average annual incidence of 4.8 per 1,000,000 persons in this population. Most deaths were among whites (94.6%); the age-adjusted incidence for whites was 2.7 times higher than that for blacks (1.04 and 0.40, respectively). Three patients who died since 2004 were reported with vCJD; epidemiologic evidence indicated that their infection was acquired outside of the United States. CONCLUSION/SIGNIFICANCE: Surveillance continues to show an annual CJD incidence rate of about 1 case per 1,000,000 persons and marked differences in CJD rates by age and race in the United States. Ongoing surveillance remains important for monitoring the stability of the CJD incidence rates, and detecting occurrences of vCJD and possibly other novel prion diseases in the United States

Optimization of process parameters for the synthesis of geopolymer binders

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Effect of (O, As) dual implantation on p-type doping of ZnO films

Optical and electrical characteristics of ZnOfilms co-implanted with O and As ions have been investigated by photoluminescence(PL), Hall-effect, and current-voltage (I-V) measurements. 100-nm-thick ZnOfilms grown on n-type Si (100) wafers by RF sputtering have been implanted with various fluences of 30 keV O and 100 keV As ions at room temperature, and subsequently annealed at 800 °C for 20 min in a N2 ambient. The dually-implanted ZnOfilms show stable p-type characteristics for particular implant combinations, consistent with the observation of dominant PL peaks at 3.328 and 3.357 eV that are associated with the acceptor levels. For these dually-implanted p-type ZnO films/n-type Si diodes, the I-V curves show rectifying p-n junction behavior. Other singly (As)- or dually-implanted samples show n-type or indeterminable doping characteristics. These results suggest that O implantation plays a key role in forming p-type ZnOfilms by reducing the oxygen vacancy concentration and facilitating the formation of As-related acceptors in ZnO.This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MEST) (No. 2011-0017373)

Educator Perceptions of Conflict Interactions Among Young Children in Inner-city Elementary and Middle Schools

A study that investigated the perceptions of educational professionals regarding the rising issue of aggressive and disruptive behaviors among young children in inner-city schools is discussed in this article. A convenient sample of 14 professionals were selected and interviewed from educators in an inner-city located in the northeast region of Ohio. Evidence of this investigation suggests that young children’s aggressive behaviors are increasing in both occurrence and complexity. While these behaviors are perceived to be a function of certain environmental exposures, a case can be made for the effectiveness in conflict management and life skill application in young children as many children seem to display more problems in collective and social settings

Variant Creutzfeldt-Jakob Disease Death, United States

Reports of secondary bloodborne transmission of vCJD add to the uncertainty about the future of the vCJD outbreak

Towards optimization-safe systems: analyzing the impact of undefined behavior

This paper studies an emerging class of software bugs called optimization-unstable code: code that is unexpectedly discarded by compiler optimizations due to undefined behavior in the program. Unstable code is present in many systems, including the Linux kernel and the Postgres database. The consequences of unstable code range from incorrect functionality to missing security checks. To reason about unstable code, this paper proposes a novel model, which views unstable code in terms of optimizations that leverage undefined behavior. Using this model, we introduce a new static checker called Stack that precisely identifies unstable code. Applying Stack to widely used systems has uncovered 160 new bugs that have been confirmed and fixed by developers.United States. Defense Advanced Research Projects Agency (DARPA Clean-slate design of Resilient, Adaptive, Secure Hosts (CRASH) program under contract #N66001-10-2-4089)National Science Foundation (U.S.) (NSF award CNS-1053143