Some Critical Materials and Processing Issues in SiC Power Devices

There has been a rapid improvement in SiC materials and power devices during the last few years. However, the materials community has overlooked some critical issues, which may threaten the emergence of SiC power devices in the coming years. Some of these pressing materials and processing issues will be presented in this paper. The first issue deals with the possibility of process-induced bulk traps in SiC immediately under the SiC/SiO₂ interface, which may be involved in the reduction of effective inversion layer electron mobility in SiC metal–oxide–semiconductor field-effect transistor (MOSFETs). The second issue addresses the effect of recombination-induced stacking faults (SFs) in majority carrier devices such as MOSFETs, Schottky diodes, and junction field-effect transistors (JFETs). In the past it was assumed that the SFs only affect the bipolar devices such as PiN diodes and thyristors. However, most majority carrier devices have built-in p–n junction diodes, which can become forward biased during operation in a circuit. Thus, all high-voltage SiC devices are susceptible to this phenomenon.     

An Overlay Photonic Layer Security Approach Scalable to 100 Gb/s [Topics in Optical Communications]

As data rates outpace the capabilities of electronic encryption schemes, photonic layer security may fill the gap in providing a communication security solution at high data rates. In this article we review and highlight the advantages of our proposed optical code-division multiplexed (OCDM)-based photonic layer security (PLS) system based on high-resolution control of the optical phase of tightly spaced phase locked laser lines. Such a PLS system is scaleable to 100 Gb/s and provides a protocol independent security solution. We review the use of high-resolution control of the optical phase of mode-locked laser frequency combs as an enabling technology for a new class of OCDM systems. A network based on such systems is compatible with and can have comparable spectral efficiency to existing DWDM networks. Through inverse multiplexing of 10 Gb/s tributaries, we have already demonstrated optical transmission of a 40 Gb/s aggregate OCDM signal over 400 km. Such a PLS solution is achieved through shared phase scrambling of the individual OCDM codes assigned to each of the tributaries using an integrated micro-ring resonator-based phase coder/ scrambler. The confidentiality of OCDM-based PLS is robust against exhaustive, known plain text, and archival/forensic attacks, and can complement digital encryption operating at higher layers. Moreover, the integrity of the PLS solution is ensured through the inherent coupling to confidentiality, since knowledge of the key is needed in order to easily alter the transmitted data stream without introducing observable errors. This system can leverage advances in optical integration to support new applications where electronic encryption is impractical because of space, weight, power, availability, and cost requirements. Such applications range from timely security support for the emerging 100 GbE standards to all-optical multilevel security offered through the compatibility of PLS with transparent DWDM networks.     

Chitin-Derived AVR-48 Prevents Experimental Bronchopulmonary Dysplasia (BPD) and BPD-Associated Pulmonary Hypertension in Newborn Mice

Bronchopulmonary dysplasia (BPD) is the most common complication of prematurity and a key contributor to the large health care burden associated with prematurity, longer hospital stays, higher hospital costs, and frequent re-hospitalizations of affected patients through the first year of life and increased resource utilization throughout childhood. This disease is associated with abnormal pulmonary function that may lead to BPD-associated pulmonary hypertension (PH), a major contributor to neonatal mortality and morbidity. In the absence of any definitive treatment options, this life-threatening disease is associated with high resource utilization during and after neonatal intensive care unit (NICU) stay. The goal of this study was to test the safety and efficacy of a small molecule derivative of chitin, AVR-48, as prophylactic therapy for preventing experimental BPD in a mouse model. Two doses of AVR-48 were delivered either intranasally (0.11 mg/kg), intraperitoneally (10 mg/kg), or intravenously (IV) (10 mg/kg) to newborn mouse pups on postnatal day (P)2 and P4. The outcomes were assessed by measuring total inflammatory cells in the broncho-alveolar lavage fluid (BALF), chord length, septal thickness, and radial alveolar counts of the alveoli, Fulton’s Index (for PH), cell proliferation and cell death by immunostaining, and markers of inflammation by Western blotting and ELISA. The bioavailability and safety of the drug were assessed by pharmacokinetic and toxicity studies in both neonatal mice and rat pups (P3-P5). Following AVR-48 treatment, alveolar simplification was improved, as evident from chord length, septal thickness, and radial alveolar counts; total inflammatory cells were decreased in the BALF; Fulton’s Index was decreased and lung inflammation and cell death were decreased, while angiogenesis and cell proliferation were increased. AVR-48 was found to be safe and the no-observed-adverse-effect level (NOAEL) in rat pups was determined to be 100 mg/kg when delivered via IV dosing with a 20-fold safety margin. With no reported toxicity and with a shorter half-life, AVR-48 is able to reverse the worsening cardiopulmonary phenotype of experimental BPD and BPD-PH, compared to controls, thus positioning it as a future drug candidate.     

Experiential household food insecurity in an urban underserved slum of North India

One-third of India’s urban population resides in extreme poverty, in slums and squatters. Food insecurity remains a visible reality among this segment. Yet, it is scarcely documented. This paper describes levels and determinants of experiential household food insecurity (HFI) in an underserved urban slum of Delhi (India) and reports the internal validity and reliability of the measure used to assess experiential HFI. A four-item scale was adapted from the U.S. six-item short-form food security scale and was administered in Hindi through household interviews with 410 female adults. Association of HFI with household economic and socio-demographic characteristics were examined using multiple logistic regression. Cronbach’s alpha and Rasch-model-based item fit statistics were used to assess reliability and internal validity. Fifty-one percent of households were food insecure. Significant HFI predictors were unemployed to employed family members’ ratio of > 3:1 (Odds Ratio 2.1, Confidence Interval 1.2 – 3.4) and low household standard of living (OR 4.9, C.I. 2.7 – 8.9). Cronbach’s alpha was 0.8. Item severities as estimated under Rasch model assumptions spanned 9.7 logits. Item infit statistics (0.77 – 1.07) indicated that the Rasch model fit the data well. Item outfit statistics suggested that one item was inconsistently understood by a small proportion of respondents. For improving HFI among the urban poor, in addition to improving behaviors/entitlement access, programs should consider linkage of urban poor to existing employment schemes, upgrading of their skills and linkage to potential employers. The adapted scale was reliable and easy to administer. However, being a subjective assessment, its sensitivity to social expectation and its association with nutrition security require examination.     

Grain growth and crack formation in NiO thin films by swift heavy ion irradiation

NiO thin films grown on Si(1 0 0) substrates by electron beam evaporation and sintered at 700 °C, were irradiated by 120 MeV Au⁹⁺ ions. Though irradiation is known to induce lattice disorder and suppression of crystallinity, we observe grain growth at some fluences of irradiation. Associated with the growth of grains, the films develop cracks at a fluence of 3 × 10¹² ions cm⁻². The width of the cracks increased at higher fluences. Swift heavy ion irradiation induced atomic diffusion and strain relaxation in nanoparticle thin films, which are not in thermodynamic equilibrium, seem to be responsible for the observed grain growth. This phenomenon along with the tensile stress induced surface instability lead to crack formation in the NiO thin films.     

Codon 4 ACT-->ACA, codon 5 CCT-->TCT, and codon 6 GAG-->TAG mutations in cis position: a form of thalassemia trait

A female of Uttar Pradesh, of Indian origin, who had a transfusion-dependent child, carried codon 4 ACT-->ACA, codon 5 CCT-->TCT, and codon 6 GAG-->TAG mutations at the cis position. The mutation was detected through sequencing of the amplified beta-globin gene. Heterozygosity is expressed as a thalassemia trait with moderate anemia, low MCV (57 fl), raised HbA2 (6.7%), and normal fetal hemoglobin (1.4%).     

Determination of the relative surface areas of PVD coatings by electrochemical impedance spectroscopy

The application of electrochemical methods for the determination of the real surface area of PVD coatings is explored. Titanium and chromium coatings with different growth morphologies and surface topographies were fabricated by magnetron sputtering. The morphology was characterized by SEM and its effect on the electrochemical polarization behavior of the coatings was studied by linear sweep voltammetry in 5 M HCl and 0.66 M NaCl. The nominal current densities measured were consistently higher for coatings having a coarse microstructure. Impedance spectroscopy was used to determine the real surface area of the films relative to a flat surface produced by mechanical polishing. When corrected for the real surface area, the polarization current density at a given potential did not depend on film morphology, both for titanium and chromium. The present paper demonstrates that electrochemical impedance spectroscopy is a useful method for the estimation of the surface area of PVD coatings.     

Growth of Nb3Sn in multifilamentary bronze composites

Growth of Nb₃Sn layers in multifilamentary composites has been investigated and their superconducting critical temperatures are measured using both resistive and inductive techniques. The growth parameters are discussed in the light of the analytical models of Reddi et al. Results show that for the composites studied, the rate controlling step for Nb₃Sn growth is diffusion of tin through grain boundaries of Nb₃Sn with the time exponent n determined by both the initial grain size and grain growth. T _c measurements show that for composites with a higher filament number, the width of superconducting transition is broader with no significant change in the onset T _c.     

Growth conditions and structural characterization of molybdenum sulphoselenide single crystals: (MoSxSe2−x, 0≦x≦2)

Single crystals of layer compounds with composition MoS_xSe_2?x, where x varies within the range 0 to 2, have been grown by the direct vapour transport technique to the maximum size of 15 mm × 10 mm × 0.3 mm. The series forms a complete range of isomorphous solid solutions, showing good agreement with Vegard's law. The composition of the above crystals was examined by ESCA (Electron Spectroscopy for Chemical Analysis). Crystal lattice parameters have been determined for the series with an X-ray diffractometer.