Role of extended defected SiC interface layer on the growth of epitaxial graphene on SiC

An extended layer of defected SiC has been observed in SiC subjected to heat treatments at 850 and 1050 °C prior to growth of graphene by thermal decomposition. This layer is found to strongly affect the graphene thickness, surface morphology, and Raman spectrum of graphene grown on it. By comparing the strength of the XPS signal associated with this layer it was found that the samples with stronger defected layer signal had the least number of surface pits but also showed the increase in Raman D to G band ratio. The shifts in 2D and G peaks are associated with varying amounts of strain and unintentional doping induced by the SiC defected interface layer, respectively.     

The Role of the Nickel Catalyst and Its Chemical and Structural Evolution During Carbon Nanopearl Growth

The role of the nickel catalyst size and its chemical and structural evolution during the early stages of carbon nanopearl nucleation and growth, by chemical vapor deposition from acetylene/argon mixture, were investigated and correlated with the resulting nanopearls’ morphological and structural properties. Carbon nanopearls were grown using Ni nanoparticles that were 20 nm and 100 nm in size, at a growth temperature of 850°C, for the following growth times: 10 s, 30 s, 60 s, 90 s, 120 s, and 300 s. x-Ray diffraction, x-ray photoelectron spectroscopy, Raman spectroscopy, and transmission electron microscopy were performed on the carbon nanopearl samples. The x-ray diffraction and x-ray photoelectron spectra showed that the following chemical constituents were present during the growth of carbon nanopearls: NiO, Ni₂O₃, Ni₃C, Ni, CO, and C (both amorphous and graphite). Transmission electron microscopy showed an increase in carbon nanopearl size with larger Ni nanoparticles. Raman results concluded that the smaller catalyst resulted in a more crystalline graphitic structure. Finally, the results showed that the 20 nm Ni nanoparticles chemically reacted sooner than the 100 nm Ni nanoparticles.     

Positional control of catalyst nanoparticles for the synthesis of high density carbon nanofiber arrays

Precise arrangement of nanoscale elements within larger systems, is essential to controlling higher order functionality and tailoring nanophase material properties. Here, we present findings on growth conditions for vertically aligned carbon nanofibers that enable synthesis of high density arrays and individual rows of nanofibers, which could be used to form barriers for restricting molecular transport, that have regular spacings and few defects. Growth through plasma-enhanced chemical vapor deposition was initiated from precisely formed nickel catalyst dots of varying diameter and spacing that were patterned through electron beam lithography. Nanofiber growth conditions, including power, precursor gas ratio, growth temperature and pressure were varied to optimize fiber uniformity and minimize defects that result from formation and migration of catalyst particles prior to growth. It was determined that both catalyst dot diameter and initial plasma power have a considerable influence on the number and severity of defects, while growth temperature, gas ratio (C₂H₂:NH₃) and pressure can be varied within a considerable range to fine-tune nanofiber morphology.     

Expanding a performance improvement initiative in critical care from hospital to system

BACKGROUND: Concern about the expense and effects of intensive care prompted the development and implementation of a hospital-based performance improvement initiative in critical care at North Shore University Hospital, Manhasset, New York, a 730-bed acute care teaching hospital. THE HOSPITAL-BASED PERFORMANCE IMPROVEMENT INITIATIVE IN CRITICAL CARE: The initiative was intended to use a uniform set of measurements and guidelines to improve patient care and resource utilization in the intensive care units (ICUs), to establish and implement best practices (regarding admission and discharge criteria, nursing competency, unplanned extubations, and end-of-life care), and to improve performance in the other hospitals in the North Shore-Long Island Jewish Health System. In the medical ICU, the percentage of low-risk (low-acuity) patients was reduced from 42% to 22%. ICU length of stay was reduced from 4.6 days to 4.1 days. IMPLEMENTING THE CRITICAL CARE PROJECT SYSTEMWIDE: A system-level critical care committee was convened in 1996 and charged with replicating the initiative. By and large, system efforts to integrate and implement policies have been successful. The critical care initiative has provided important comparative data and information from which to gauge individual hospital performance. DISCUSSION: Changing the critical care delivered on multiple units at multiple hospitals required sensitivity to existing organizational cultures and leadership styles. Merging organizational cultures is most successful when senior leadership set clear expectations that support the need for change. The process of collecting, trending, and communicating quality data has been instrumental in improving care practices and fostering a culture of safety throughout the health care system.     

Thermally stimulated current spectroscopy of high-purity semi-insulating 4H-SiC substrates

High-purity semi-insulating (HPSI) 4H-SiC has been widely used as a substrate material for AlGaN/GaN high electron-mobility transistors because of its fairly good lattice match with GaN and its high thermal conductivity. To control material quality, it is important to understand the nature of the deep traps. For this purpose, we have successfully applied thermally stimulated current (TSC) spectroscopy to investigate deep traps in two HPSI 4H-SiC samples grown by physical vapor transport (PVT) and high-temperature chemical vapor deposition (HTCVD), respectively. Fundamentals of TSC spectroscopy, typical TSC spectra obtained on the two samples, and theoretical fittings of a boron-related trap (peaked at ∼ 150 K) will be presented. Based on literature data for deep traps in conductive 4H-SiC, the impurity and point-defect nature of several commonly observed TSC traps, peaked at ∼105 K (0.22 eV), ∼150 K (0.29 eV), ∼175 K (∼0.33 eV), ∼260 K (∼0.53 eV), ∼305 K (∼0.63 eV), and ∼360 K (0.91 eV), in the HPSI 4H-SiC will be discussed.     

Transport coefficients of AlGaN/GaN heterostructures

We have experimentally determined the effective mass (m*) of GaN, the classical (τ _c), and quantum (τ _q) scattering times for a two-dimensional electron gas residing at the interface of an AlGaN/GaN heterostructure, using the Shubnikovde Haas effect. The ratio of the two scattering times, τ _c/τ _q, suggests that, at low temperatures, the scattering mechanism limiting the mobility is due to remote ionized impurities located in AlGaN. This study should provide sample growers with information useful for improving the quality of the nitride heterostuctures.     

A clinical pathway for ostomy care in the home: process and development

Infusion of insulin directly into thyroid arterial blood perfusing the surgically isolated in situ pig thyroid gland produced an increase in the secretion rate of calcitonin (CT) measured by immunoassay in thyroid venous effluent blood. Insulin in concentrations ranging from approximately 1 to 400 ng/ml produced a maximal stimulation of 4-5 fold. The stimulatory effect of insulin on CT could not be duplicated by infusion of either IGF-I or amylin. Specific binding of radiolabeled insulin was demonstrated using isolated pig thyroid plasma membranes and both rat (6-23) and human (TT) medullary thyroid carcinoma C-cells. Increased CT release was observed from C-cells exposed to a high concentration of insulin. The administration of glucose iv to pigs in order to stimulate secretion of endogenous insulin produced an increase in circulating insulin, which was accompanied by an increase in the secretion of CT. The results show that insulin, delivered directly to the pig thyroid gland, can stimulate CT release. The in vitro binding and secretion studies indicate that C-cells can bind insulin and respond with an increase in CT secretion, and the iv glucose experiments suggest that endogenous insulin is capable of stimulating CT secretion. The findings imply that insulin is capable of acting as a CT secretagogue and suggest that changes in CT secretion may accompany altered states of insulin production such as diabetes or insulin-secreting tumors.