Investigation of the mechanism for current induced network failure for spray deposited silver nanowires.

Silver nanowires are one of the prominent candidates for the replacement of the incumbent indium tin oxide in thin and flexible electronics applications. Their main drawback is their inferior electrical robustness. Here, the mechanism of the short duration direct current induced failure in large networks is investigated by current stress tests and by examining the morphology of failures. It is found that the failures are due to the heating of the film and they initiate at the nanowire junctions, indicating that the main failure mechanism is based on the Joule heating of the junctions. This failure mechanism is different than what has been seen in literature for single nanowires and sparse networks. In addition, finite element heating simulations are performed to support the findings. Finally, we suggest ways of improving these films, in order to make them more suitable for device applications.

Coherent quantum transport features in carbon superlattice structures.

Whilst resonant transmission is well understood and can be fully harnessed for crystalline superlattices, a complete picture has not yet emerged for disordered superlattices. It has proven difficult to tune resonant transmission in disordered diamond-like carbon (DLC) superlattices as conventional models are not equipped to incorporate significant structural disorder. In this work, we present concurrent experimental and theoretical analysis which addresses resonant transmission in DLC superlattices. Devices were fabricated by growing alternate layers of DLC with different percentages of sp3 hybridized carbon.Coherent quantum transport effects were demonstrated in these structurally disordered DLC superlattices through distinct current modulation with negative differential resistance (NDR) in the current-voltage (I-V) measurements. A model was developed using tight-binding calculations assuming a random variation of the hopping integral to simulate structural (bond-length) disorder. Calculations of the I-V characteristics compliment the interpretation of the measurements and illustrate that while DLC superlattice structures are unlike their classical counterparts, the near-field structural order will help with the confinement of quantised states. The present model provides an empirical guide for tailoring the properties of future devices, giving rise to much hope that carbon electronics operating at high frequencies over large areas can now be developed.

Dispersive hole transport in polymer:carbon nanotube composites.

The hole transport properties of poly(2-methoxy, 5-(2'-ethyl-hexoxy)-p-phenylene vinylene) (MEH-PPV) blended with acid oxidized multiwall carbon nanotubes (COOH-MWCNTs) were investigated in a diode configuration using the time-of-flight (TOF) photocurrent method. While the room temperature hole mobility in pure MEH-PPV films was non-dispersive with positive field dependent mobility, MEH-PPV:COOH-MWCNT blended devices exhibited dispersive transport and negative field dependent mobility. This indicates that the hole mobility in this composite is influenced by positional disorder caused by the presence of COOH-MWCNTs in the MEH-PPV matrix. These results strongly suggest that the distribution of COOH-MWCNTs optimising in the organic matrix is important for charge transport in the high mobility nanotube component to be activated, when used in hybrid material systems.

Laser-assisted hydrothermal growth of size-controlled ZnO nanorods for sensing applications.

Pulsed laser irradiation is used to seed the low-temperature hydrothermal growth of ZnO nanorods. UV laser irradiation produces ZnO nanoparticles in solution that act as nucleation seeds for the subsequent hydrothermal growth of the nanorods. By systematically varying the seed density and/or the concentration of the reactants, the diameter of the nanorods can be controlled over a wide range with a narrow size distribution. The nanorods are linked into multi-pod structures, due to nucleation at a central seed, but ultrasonic processing of the solutions is shown to yield isolated nanorods. Three-dimensional networks of these multi-pod structures are fabricated by drop-casting the solutions onto inter-digitated electrodes. These devices are used to detect ethanol, water vapour and UV light exposure.

The growth of silica and silica-clad nanowires using a solid-state reaction mechanism on Ti, Ni and SiO(2) layers.

A large area compatible and solid-state process for growing silica nanowires is reported using nickel, titanium and silicon dioxide layers on silicon. The silica nanowires also contain silicon, as indicated by Raman spectroscopy. The phonon confinement model is employed to measure the diameter of the Si rich tail for our samples. The measured Raman peak shift and full width at half-maximum variation with the nanowire diameter qualitatively match with data available in the literature. We have investigated the effect of the seedbed structure on the nanowires, and the effect of using different gas conditions in the growth stages. From this, we have obtained the growth mechanism, and deduced the role of each individual substrate seedbed layer in the growth of the nanowires. We report a combined growth mechanism, where the growth is initiated by a solid-liquid-solid process, which is then followed by a vapour-liquid-solid process. We also report on the formation of two distinct structures of nanowires (type I and type II). The growth of these can be controlled by the use of titanium in the seedbed. We also observe that the diameter of the nanowires exhibits an inverse relation with the catalyst thickness.

Continuous-flow laser synthesis of large quantities of iron oxide nanowires in solution.

Large quantities of iron oxide nanowires are rapidly synthesized at room temperature by pulsed-laser (248 nm) ablation of iron powder under methanol. By introducing a stream of methanol, a continuous flow of nanoscale products is collected. Through control of the flow rate, and hence the residence time of the products within the growth vessel, their morphology can be controlled. At high collection rates a lamellate 'nanobelt' morphology is observed, whereas at low collection rates nanowires dominate. Chemical and structural characterization suggests that the as-synthesized products have the stoichiometry of the goethite [FeO(OH)] phase. Annealing at temperatures above 400 °C crystallizes the products as hematite (α-Fe(2)O(3)).

Energy loss spectroscopic profiling across linear interfaces: the example of amorphous carbon superlattices.

Energy loss spectroscopic profiling is a way to acquire, in parallel, spectroscopic information across a linear feature of interest, using a Gatan imaging filter (GIF) fitted to a transmission electron microscope (TEM). This technique is capable of translating the high spatial resolution of a bright field image into a sampling of the spectral information with similar resolution. Here we evaluate the contributions of chromatic aberration and the various acquisition parameters to the spatial sampling resolution of the spectral information, and show that this can reach 0.5 nm, in a system not ordinarily capable of forming electron probes smaller than 2 nm. We use this high spatial sampling resolution to study the plasmon energy variation across amorphous carbon superlattices, in order to extract information about their structure and electronic properties. By modelling the interaction of the relativistic incident electrons with a dielectric layer sandwiched between outer layers, we show that, due to the screening of the interfaces and at increased collection angles, the plasmon energy in the sandwiched layer can still be identified for layer thicknesses down to 5 A. This allows us to measure the change in the well bandgap as a function of well width and to interpret it in terms of the changes in the sp2 -fractions due to the deposition method, as measured from the carbon K-edges, and in terms of quantum confinement of the well wavefunction by the adjacent barriers.

Cigarette smoking and colorectal cancer mortality in the cancer prevention study II.

BACKGROUND: Recent studies suggest that long-term cigarette smoking is associated with an increased risk of colorectal cancer. Whether the association is causal or due to confounding remains unclear. METHODS: We examined cigarette smoking in relation to colorectal cancer mortality, evaluating smoking duration and recency and controlling for potential confounders in the Cancer Prevention Study II. This prospective nationwide mortality study of 1 184 657 adults (age > or =30 years) was begun by the American Cancer Society in 1982. After exclusions, our analytic cohort included 312 332 men and 469 019 women, among whom 4432 colon or rectal cancer deaths occurred between 1982 and 1996 among individuals who were cancer free in 1982. Rate ratios (RRs) and 95% confidence intervals (CIs) were estimated by fitting Cox proportional hazards models. All statistical tests were two-sided. RESULTS: Multivariate-adjusted colorectal cancer mortality rates were highest among current smokers, were intermediate among former smokers, and were lowest in lifelong nonsmokers. The multivariate-adjusted RR (95% CI) for current compared with never smokers was 1.32 (1.16-1.49) among men and 1.41 (1.26-1.58) among women. Increased risk was evident after 20 or more years of smoking for men and women combined as compared with never smokers. Risk among current and former smokers increased with duration of smoking and average number of cigarettes smoked per day; risk in former smokers decreased significantly with years since quitting. If the multivariate-adjusted RR estimates in this study do, in fact, reflect causality, then approximately 12% of colorectal cancer deaths among both men and women in the general U.S. population in 1997 were attributable to smoking. CONCLUSIONS: Long-term cigarette smoking is associated with increased risk of colorectal cancer mortality in both men and women. Clear reduction in risk is observed with early smoking cessation.

Smoking vs other risk factors as the cause of smoking-attributable deaths: confounding in the courtroom.

CONTEXT: The surgeon general estimates that more than 400,000 deaths are attributable to smoking annually in the United States. The tobacco industry has criticized the surgeon general's estimates because they do not control for the lower educational and socioeconomic status of modern-day smokers. OBJECTIVE: To determine whether controlling for education, occupation, race, alcohol consumption, and various dietary factors, in addition to age and sex, substantially alters the relative and attributable risk estimates associated with tobacco smoking. DESIGN, SETTING, AND PARTICIPANTS: Nationwide American Cancer Society prospective cohort study of 974, 150 US adults aged 30 years or older, enrolled in 1982 and followed up through 1988. (The same study is used for the surgeon general and Centers for Disease Control and Prevention [CDC] estimates of smoking-attributable deaths in the United States.) MAIN OUTCOME MEASURES: Death from each of the chronic diseases considered in the CDC's estimate of smoking-attributable mortality (cancers of the lung, oropharynx, larynx, esophagus, pancreas, kidney, bladder, and cervix; ischemic heart disease, arterial disease, and other heart conditions; stroke; chronic obstructive pulmonary disease; and other respiratory conditions). Estimates adjusted for multiple covariates were compared with those adjusted for age only among current and former vs never smokers. RESULTS: Adjusting for multiple covariates slightly decreased the relative and attributable risk estimates for current smoking in both men and women, but slightly increased the estimates for former smoking in women. Multivariate adjustment decreased the overall estimate of deaths attributable to smoking in the United States by approximately 1%, from 401,109 to 396,741 per year. CONCLUSIONS: Our study suggests that federal estimates of deaths caused by smoking are not substantially altered by adjustment for behavioral and demographic factors associated with smoking beyond the current adjustment for age and sex. JAMA. 2000;284:706-712

Deaths from hematopoietic and other cancers in relation to permanent hair dye use in a large prospective study (United States).

OBJECTIVES: To assess in a large prospective study whether women who used permanent hair dye, especially dark dye for many years, experienced increased death rates from hematopoietic and other cancers that have been associated with hair dye use in some previous reports. METHODS: In 1982, 547,586 women provided information on use of permanent hair dye and other lifestyle factors when enrolled in an American Cancer Society (ACS) prospective study. We extended mortality follow-up from 7 to 12 years. Using Cox proportional hazards modeling we compared death rates from hematopoietic and other cancers among women according to their hair dye use at baseline with death rates in unexposed women. RESULTS: The adjusted death rate from all cancers combined was marginally lower among women who ever used hair dye than nonusers (relative risk [RR] = 0.9; 95% confidence interval [CI] = 0.9-1.0). Mortality from all hematopoietic cancers was marginally higher among users than nonusers (RR = 1.1; CI = 1.0-1.2), and increased with an index that combined duration of use and darker coloration (test of trend p = 0.02). Women who used black or brown dye for 10 or more years experienced somewhat higher death rates from non-Hodgkin's lymphoma and (for black dye only) multiple myeloma. The temporal increase in death rates from non-Hodgkin's lymphoma and multiple myeloma between 1982-88 and 1989-94 was similar for women in our study who never used hair dyes to the increase among all US women. CONCLUSIONS: If prolonged use of dark permanent hair dyes contributes to death rates from non-Hodgkin's lymphoma and multiple myeloma, then the increase is small and difficult to detect reliably even in large prospective studies. The use of permanent hair dye is unlikely to be a major contributor to the temporal rise in non-Hodgkin's lymphoma and multiple myeloma in the US.

Alcohol consumption and mortality among middle-aged and elderly U.S. adults.

BACKGROUND: Alcohol consumption has both adverse and beneficial effects on survival. We examined the balance of these in a large prospective study of mortality among U.S. adults. METHODS: Of 490,000 men and women (mean age, 56 years; range, 30 to 104) who reported their alcohol and tobacco use in 1982, 46,000 died during nine years of follow-up. We compared cause-specific and rates of death from all causes across categories of base-line alcohol consumption, adjusting for other risk factors, and related drinking and smoking habits to the cumulative probability of dying between the ages of 35 and 69 years. RESULTS: Causes of death associated with drinking were cirrhosis and alcoholism; cancers of the mouth, esophagus, pharynx, larynx, and liver combined; breast cancer in women; and injuries and other external causes in men. The mortality from breast cancer was 30 percent higher among women reporting at least one drink daily than among nondrinkers (relative risk, 1.3; 95 percent confidence interval, 1.1 to 1.6). The rates of death from all cardiovascular diseases were 30 to 40 percent lower among men (relative risk, 0.7; 95 percent confidence interval, 0.7 to 0.8) and women (relative risk, 0.6; 95 percent confidence interval, 0.6 to 0.7) reporting at least one drink daily than among nondrinkers, with little relation to the level of consumption. The overall death rates were lowest among men and women reporting about one drink daily. Mortality from all causes increased with heavier drinking, particularly among adults under age 60 with lower risk of cardiovascular disease. Alcohol consumption was associated with a small reduction in the overall risk of death in middle age (ages 35 to 69), whereas smoking approximately doubled this risk. CONCLUSIONS: In this middle-aged and elderly population, moderate alcohol consumption slightly reduced overall mortality. The benefit depended in part on age and background cardiovascular risk and was far smaller than the large increase in risk produced by tobacco.