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Graphene's advantages for sensor applications are offset by its low electric impedance and consequently low signal-to-noise ratio. We have improved the sensitivity of graphene based photosensors by integrating an energy filtering barrier as an amplifying element. The resulting graphene devices exhibit the highest reported photosensitivity (Ion/Ioff∼4000, gain∼10 A/W) while retaining broad band detection and high speed response. In addition to this unprecedented photosensitivity, the proposed device structure renders the complete graphene photosensitive which enables large scale and flexible photodetectors. The presented approach represents a universal route to enhancing the performance of graphene sensors. [ABSTRACT FROM AUTHOR]

The strong interest in graphene has motivated large effort in the scalable production of high-quality material. The potential of chemical vapor deposition on Cu foil to produce such graphene is impeded by lacking understanding of the relation between catalyst properties and graphene performance. We here present a systematic analysis of the catalyst morphology and its effect on electrical properties of graphene. We find that nanometer sized particles increase the density of bilayer regions but have no significant effect on carrier transport. Long wavelength roughness (waviness), on the other hand, generates defective graphitic regions that deteriorate carrier mobility. These findings shed light on the graphene formation process on Cu substrates and open a route to improve graphene quality for electronics applications. [ABSTRACT FROM AUTHOR]

Raman spectroscopy and in situ Raman spectroelectrochemistry have been used to study the influence of defects on the Raman spectra of semiconducting individual single-walled carbon nanotubes (SWCNTs). The defects were created intentionally on part of an originally defect-free individual semiconducting nanotube, which allowed us to analyze how defects influence this particular nanotube. The formation of defects was followed by Raman spectroscopy that showed D band intensity coming from the defective part and no D band intensity coming from the original part of the same nanotube. It is shown that the presence of defects also reduces the intensity of the symmetry-allowed Raman features. Furthermore, the changes to the Raman resonance window upon the introduction of defects are analyzed. It is demonstrated that defects lead to both a broadening of the Raman resonance profile and a decrease in the maximum intensity of the resonance profile. The in situ Raman spectroelectrochemical data show a doping dependence of the Raman features taken from the defective part of the tested SWCNT. [ABSTRACT FROM AUTHOR]

Objective: We designed the current study to assess the rates of risky sexual behavior among women bar drinkers, as well as differences in predictors of risky sexual behavior, based on partner type-new or regular. Method: We conducted comprehensive, in-person interviews with 241 young women who reported weekly drinking in bars. Several constructs (e.g., individual characteristics, social and sexual behavior, substance use) that we hypothesized would predict risky sexual behavior were assessed in two separate hierarchical regression models for new and regular sexual partners. Results: Rates of risky sexual behavior were significantly higher with regular partners compared with new partners. Increased risky sexual behavior with new partners was significantly associated with having had a riskier regular partner in the past 6 months, lower sexually transmitted disease (STD)/pregnancy prevention assertiveness, increased expectations of sexual disinhibition when drinking, a greater history of prior sexual risk taking, and more frequent drinking in bars. Increased risky sexual behavior with a regular partner was significantly associated with being older, the use of oral contraceptives, lower assertiveness for STD/pregnancy prevention, a greater history of prior sexual risk taking, and increased drug use. Conclusions: Among young women who regularly drink in bars, sexual risk taking was significantly higher with regular partners than with new partners. The predictors of risky sexual behavior differed based on partner type. These findings have implications for including information about the role of alcohol, drinking context, and drug use, as well as individual difference characteristics and partner type in targeted prevention strategies to reduce sexual risk taking. [ABSTRACT FROM AUTHOR]

Raman spectra of isolated single-walled carbon nanotubes (SWNTs) were obtained for a wide range of laser excitation energies to study the resonance excitation window of the radial breathing mode feature for members of (2n+m) families. A chiral angle (θ) dependence of the resonance window width (Γ) was observed, which is much stronger than the diameter dependence. The implications of this work on nanotube metrology are discussed. [ABSTRACT FROM AUTHOR]

The production of large-scale, single crystalline graphene is a requirement for enhancing its electronic, mechanical, and chemical properties. Chemical vapor deposition (CVD) has shown the potential to grow high quality graphene but the simultaneous nucleation of many grains limits their achievable domain size. We report here that ultralow nucleation densities can be achieved through multi-step optimization of the catalyst morphology. First, annealing in a hydrogen-free environment is required to retain a surface copper oxide which decreases the nucleation density. Second, CuO was found to be the relevant copper species for this process and air oxidation of the copper foil at 200 °C maximizes its concentration. Both pre-treatment steps were found to affect the morphology of the catalyst and a direct correlation between nucleation density and surface roughness was found which indicates that the primary role of the oxidation step is the decrease in catalyst roughness. To further enhance this determining parameter, confined CVD was carried out after sample oxidation and hydrogen-free annealing. Each of these three steps reduces the grain density by approximately one order of magnitude resulting in ultralow nucleation densities of 1.23 grains/mm2 and high quality, single-crystalline graphene grains of several millimeter sizes were grown using this method. [ABSTRACT FROM AUTHOR]

A self-powered photodetector with ultrahigh sensitivity, fast photoresponse, and wide spectral detectivity covering from 1000 nm to 400 nm based on graphene/ZnO/Si triple junctions has been designed, fabricated, and demonstrated. In this device, graphene serves as a transparent electrode as well as an efficient collection layer for photogenerated carriers due to its excellent tunability of Fermi energy. The ZnO layer acts as an antireflection layer to trap the incident light and enhance the light absorption. Furthermore, the insertion of the ZnO layer in between graphene and Si layers can create build-in electric field at both graphene/ZnO and ZnO/Si interfaces, which can greatly enhance the charge separation of photogenerated electron and hole pairs. As a result, the sensitivity and response time can be significantly improved. It is believed that our methodology for achieving a high-performance self-powered photodetector based on an appropriate design of band alignment and optical parameters can be implemented to many other material systems, which can be used to generate unique optoelectronic devices for practical applications. [ABSTRACT FROM AUTHOR]

The material and optical properties of ZnO thin film samples grown on different buffer layers on sapphire substrates through a two-step temperature variation growth by molecular beam epitaxy were investigated. The thin buffer layer between the ZnO layer and the sapphire substrate decreased the lattice mismatch to achieve higher quality ZnO thin film growth. A GaN buffer layer slightly increased the quality of the ZnO thin film, but the threading dislocations still stretched along the c-axis of the GaN layer. The use of MgO as the buffer layer decreased the surface roughness of the ZnO thin film by 58.8% due to the suppression of surface cracks through strain transfer of the sample. From deep level emission and rocking curve measurements it was found that the threading dislocations play a more important role than oxygen vacancies for high-quality ZnO thin film growth. [ABSTRACT FROM AUTHOR]

Graphene nanoribbons can exhibit either quasi-metallic of semiconducting behavior, depending on the atomic structure of their edges. Thus, it is important to control the morphology and crystallinity of these edges for practical purposes. We demonstrated an efficient edge-reconstruction process, at the atomic scale, for graphitic nanoribbons by Joule heating. During Joule heating and electron beam irradiation, carbon atoms are vaporized, and subsequently sharp edges and step-edge arrays are stabilized, mostly with either zigzag- or armchair-edge configurations. Model calculations show that the dominant annealing mechanisms involve point defect annealing and edge reconstruction. [ABSTRACT FROM AUTHOR]

Objective: The Current study assessed women's risk for victimization during the first year at college, based on Changes in drinking during the transition from high school to college. We were specifically interested in differential risk for victimization based on women's change in drinking status over the transition to college. We compared continued abstainers with women who began drinking ("new" drinkers) and women who continued drinking but either decreased, increased, or did not change their level of weekly drinking. Method: Data were collected using a Web-based survey each fall for the first 2 years at college with one cohort (N = 886) of incoming freshmen women at a large state university in New York. Women reported on their alcohol and other drug use, psychological symptoms, number of sexual partners, and experiences with physical and sexual victimization for the year before entering college (Year 1 survey) and for the first year at college (Year 2 survey). Results: Abstainers were significantly less likely to experience physical or sexual victimization during the first year at college, compared with drinkers. Logistic regression indicated that there were differences in the predictors of physical and sexual victimization during the first year at college. These differences included history of victimization, psychological symptoms, and number of sexual partners, as well as the type of change in drinking over the transition. Conclusions: In comparison with abstainers, having a history of physical victimization, greater psychological symptoms, and being a "new" drinker increased the odds of physical victimization, whereas having a greater number of current psychological symptoms, sexual partners, and increasing weekly drinking increased the odds of sexual victimization during the first year at college. These findings have implications for prevention efforts targeting young women entering college. [ABSTRACT FROM AUTHOR]

In 3 quasi-experiments using intact classrooms and 1 true experiment using random assignment, students completed partially complete graphic organizers (GOs) or studied complete GOs that covered course content. The partial task led to increased overall examination performance in all experiments. Also, the authors measured students' note-taking style (linear vs. graphic) at the beginning and end of the course. In all experiments, GO note taking increased. The increases were greatest when the authors presented the partial task in a computer environment with a timed, forced-choice task. Implications for using the partial GO task in the classroom, as well as future note-taking research directions are discussed. [ABSTRACT FROM AUTHOR]

The authors examined intervention studies that appeared in 4 educational psychology journals (Cognition & Instruction, Contemporary Educational Psychology, Journal of Educational Psychology, Journal of Experimental Education) and the American Educational Research Journal (AERJ) in 1983 and from 1995 to 2004. The majority of studies included adults (age 18 and older) as participants, administered brief (less than 1 day) interventions, assessed intervention effects immediately following the intervention, and did not report treatment integrity. Most studies included multiple outcome measures and exhibited an increase in effect-size reporting from 4% in 1995 to 61% in 2004. The percentage of total articles based on randomized experiments decreased over the 21-year period in both the educational psychology journals (from 40% in 1983 to 34% in 1995 to 26% in 2004) and AERJ (from 33% to 17% to 4%). Limitations of the study and future research issues are discussed. [ABSTRACT FROM AUTHOR]

The synthesis of graphene with controllable electronic and mechanical characteristics is of significant importance for its application in various fields ranging from drug delivery to energy storage. Electrochemical exfoliation of graphite has yielded graphene with widely varying behavior and could be a suitable approach. Currently, however the limited understanding of the exfoliation process obstructs targeted modification of graphene properties. We here investigate the process of electrochemical exfoliation and the impact of its parameters on the produced graphene. Using in situ optical and electrical measurements we determine that solvent intercalation is the required first step and the degree of intercalation controls the thickness of the exfoliated graphene. Electrochemical decomposition of water into gas bubbles causes the expansion of graphite and controls the functionalization and lateral size of the exfoliated graphene. Both process steps proceed at different time scales and can be individually addressed through application of pulsed voltages. The potential of the presented approach was demonstrated by improving the performance of graphene-based transparent conductors by 30times. [ABSTRACT FROM AUTHOR]