Nanoscale tunable reduction of graphene oxide for graphene electronics

International audienceGraphene is now recognized as the most likely carbon-based successor material for CMOS electronics. Recently, interest in graphene oxide (GO) has risen for producing large-scale flexible conductors and for its potential to open an electronic gap in graphene structures. We report on a means to tune the topographical and electrical properties of graphene-based materials with nanoscopic resolution by local thermal reduction of GO with a nano-size tip. The reduced GO nanostructures show an increase in conductivity up to four orders of magnitude as compared to pristine GO. No sign of tip wear or sample tearing was observed. Variably conductive nanoribbons with dimensions down to 12 nm have been produced in oxidized epitaxial graphene films in a single step that is clean, rapid and reliable

Atomic-scale characterization of hydrogenated amorphous-silicon films and devices. Annual subcontract report, 14 February 1995--14 April 1996

The research is concerned with improving the electronic properties of hydrogenated amorphous silicon (a-Si:H) films and of photovoltaic (PV) cells that use these films. Two approaches toward this goal are being taken. One is to establish the character of silicon particle growth in the rf glow discharges that are used to make the films and PV cells, and to understand the particle incorporation into the films. The ultimate goal of this effort is to find mitigation techniques that minimize the particle incorporation. During this contract period, the authors have developed a novel particle light-scattering technique that provides a very detailed and sensitive diagnostic of the particles suspended in the discharge. The second program is directed toward measuring the electronic properties of these thin-film PV cells, as a function of depth within the cell. The approach being taken is to use a scanning tunneling microscope (STM) to measure the depth-dependent electronic properties of cross-sectioned PV cells. During the present period, cell cleaving and cross section locating methods, both in a UHV environment, have been successfully developed

Atomic-scale characterization of hydrogenated amorphous-silicon films and devices. Annual subcontract report, 14 February 1994--14 April 1995

Properties of the hydrogenated amorphous silicon (a-Si:H) films used in photovoltaic (PV) panels are reported. The atomic-scale topology of the surface of intrinsic a-Si:H films, measured by scanning tunneling microscopy (STM) as a function of film thickness, are reported and diagnosed. For 1-500-nm-thick films deposited under normal device-quality conditions from silane discharges, most portions of these surfaces are uniformly hilly without indications of void regions. However, the STM images indicate that 2-6-nm silicon particulates are continuously deposited into the growing film from the discharge and fill approximately 0.01% of the film volume. Although the STM data are not sensitive to the local electronic properties near these particulates, it is very likely that the void regions grow around them and have a deleterious effect on a-Si:H photovoltaics. Preliminary observations of particulates in the discharge, based on light scattering, confirm that particulates are present in the discharge and that many collect and agglomerate immediately downstream of the electrodes. Progress toward STM measurements of the electronic properties of cross-sectioned a-Si:H PV cells is also reported

Atomic-scale characterization of hydrogenated amorphous-silicon films and devices. Annual subcontract report, 15 April 1994--14 March 1998

The research is concerned with improving the electronic properties of hydrogenated amorphous silicon (a-Si:H) films and of photovoltaic (PV) cells that use these films. Two approaches toward this goal are being taken. One is to establish the character of silicon particle growth in the rf glow discharges that are used to make the films and PV cells, and to understand the particle incorporation into the films. The ultimate goal of this effort is to find mitigation techniques that minimize the particle incorporation. During this contract period the authors have developed a novel particle light-scattering technique that provides a detailed and sensitive diagnostic of small (8-60 nm diameter) particles suspended in the discharge. The authors have used this to measure the particle growth rates and densities, versus conditions in pure-silane discharges. The second program is directed toward measuring the electronic properties of thin-film PV cells, as a function of depth within the cell. The approach being taken is to use a scanning tunneling microscope (STM) to measure the depth-dependent electronic properties of cross-sectioned PV cells. During the present period, measurements on single and tandem amorphous silicon cells have been carried out. Using STM current-voltage spectroscopy, these measurements distinguish the boundaries between the highly-conducting and intrinsic layers, as well as the chemical potential versus depth in the cell

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Ramie (Boehmeria nivea (L.) Gaudich) was evaluated at 20-, 40-, and 60- day growth stages in three trials for chemical composition, yield, and intake with Holstein steers, respectively. Crude protein and ash contents decreased while crude fiber and nitrogen free extract contents increased as ramie advanced in maturity from 20 to 60 days of age. The ether extract content remained about the same between 20- and 40-day stages but decreased at the 60 day stage. Significant differences (P < .01) were obtained in green forage yields between 20- and 40- or 60-day ramie, and in dry forage and crude protein yields between 20- and 40-day, 20- and 60-day, and 40- and 60-day ramie. Significant differences (P < .01) were also obtained in green forage intakes between 20- and 40-day, 20- and 60-day, and 40- and 60-day ramie, and in dry forage intakes between 20- or 40- and 60-day ramie. Although ramie has a high crude protein content, its yields and intakes are very low in comparison to those of tropical grasses and alfalfa. It may be utilized as a feed or feed ingredient for livestock, principally monogastrics or small ruminants.El ramio (Boehmeria nivea (L.) Gaudich) es una planta textil de excelente calidad, rica en proteína y con un potencial como alimento para animales domésticos. Se evaluó en 3 pruebas a etapas de crecimiento de 20, 40 y 60 días de edad en la Subestación Experimental de Gurabo, con respecto a composición química, producción y consumo por novillos Holstein castrados. Los contenidos en proteína bruta y ceniza disminuyeron mientras los de fibra bruta y extracto libre de nitrógeno aumentaron de los 20 a los 60 días de edad. El contenido en extracto etéreo permaneció igual en nuestras cosechadas a los 20 y 40 días pero disminuyó en la de 60 días. Se obtuvieron diferencias significativas (P < .01) en producción de forraje verde entre ramio de 20 y de 40 ó 60 días de edad, y en producción de forraje seco y de proteína bruta entre ramio de 20 y 40 días, 20 y 60 días y 40 y 60 días de edad. Los consumos de forraje verde entre las edades de 20 y 40 días, 20 y 60 días y 40 y 60 días y de forraje seco entre las edades de 20 ó 40 y 60 días fueron significativos (P < .01 ). Se puede concluir que, aunque el ramio es rico en proteína bruta, su producción y consumo son bajos, al compararse con gramíneas tropicales y alfalfa. Sin embargo, su utilización como alimento o como ingrediente en raciones de alimentos para animales, principalmente monogástricos o rumiantes pequeños, es una posibilidad

Analysis of Driver Behavior in Dilemma Zones at Signalized Intersections

A field study evaluated the stopping characteristics of vehicles 2.5 to 5.5 s upstream of signalized intersections at the start of a yellow interval, a region typically considered drivers’ indecision zone or dilemma zone. Characteristics included brake-response times for first-to-stop vehicles, deceleration rates for first-to-stop vehicles, distinguishing characteristics and prediction of first-to-stop versus last-to-go events, and distinguishing characteristics and prediction of red-light-running events. Consumer-grade video cameras temporarily installed at four high-speed and two low-speed intersections in the Madison, Wisconsin, area recorded dilemma zone vehicles. Several factors were measured for each last-to-go (n = 435) and first-to-stop (n = 463) vehicle in each lane during each yellow interval, including approach speed; distance upstream at start of yellow; brake-response time; deceleration rate; vehicle type; headway; tailway; action of vehicles in adjacent lanes; presence of side-street vehicles, pedestrians, bicycles, or opposing vehicles waiting to turn left; flow rate; length of yellow interval; and cycle length. The observed 15th, 50th, and 85th percentile brake-response times for first-to-stop vehicles were 0.7, 1.0, and 1.6 s, respectively; their observed deceleration rates were 7.2, 9.9, and 12.9 ft/s², respectively. Vehicles were more likely to go through than to stop under the following conditions: shorter estimated travel time to intersection at start of yellow; longer yellow interval; the subject was a heavy vehicle (truck, bus, recreational vehicle); absence of side-street vehicles, bicycles, pedestrians, and opposing left-turn vehicles; and presence of vehicles in adjacent lanes that went through. Heavy vehicles were more likely than passenger vehicles to run a red light. Vehicles were more likely to run a red light when vehicles in adjacent lanes that also went through were present and when side-street vehicles, bicycles, pedestrians, and opposing left-turn vehicles were absent

Absence of HIV transmission from an infected dentist to his patients. An epidemiologic and DNA sequence analysis

OBJECTIVE: To determine if a general dentist with human immunodeficiency virus (HIV) infection transmitted HIV to any of his patients. DESIGN: A cohort study in which all patients treated by a dentist who developed the acquired immunodeficiency syndrome (AIDS) were identified and attempts were made to contact all patients for HIV antibody testing. SETTING: A general dentistry clinic operated by the Department of Veterans Affairs in southeastern Florida. PARTICIPANTS: All patients treated by a dentist during the 5 3/4 years before he developed AIDS were identified in a computerized registry of dental care. MAIN OUTCOME MEASURES: Attempts were made to contact all living patients for counseling and HIV antibody testing. Living patients with newly identified HIV infection were interviewed, and DNA sequence analysis was performed to compare genetic relatedness of their HIV to that of the dentist. Death certificates were obtained for decreased patients, and the medical records of those with diagnoses suggestive of HIV disease or drug abuse and those dying under the age of 50 years were reviewed in detail. RESULTS: There were 1192 patients who had undergone 9267 procedures, of whom 124 were deceased. A review of the death certificates of the deceased patients identified five who had died with HIV infection, all of whom were either homosexuals or users of illicit intravenous drugs. We were able to locate 962 (92%) of the remaining 1048 patients, and 900 agreed to be tested. Infection with HIV was documented in five of the 900 patients, including four who had clear evidence of risk factors for acquiring HIV infection. One patient who had only a single evaluation by the dentist denied high-risk behavior. Comparative DNA sequence analysis demonstrated that the viruses from the dentist and these five patients were not closely related. CONCLUSION: This study indicates that the risk for transmission of HIV from a general dentist to his patients is minimal in a setting in which universal precautions are strictly observed. Programs to ensure compliance with universal precautions would appear preferable to programs for widespread testing of dentists