Immunity of nanoscale magnetic tunnel junctions with perpendicular magnetic anisotropy to ionizing radiation

Spin transfer torque magnetic random access memory (STT-MRAM) is a promising candidate for next generation memory as it is non-volatile, fast, and has unlimited endurance. Another important aspect of STT-MRAM is that its core component, the nanoscale magnetic tunneling junction (MTJ), is thought to be radiation hard, making it attractive for space and nuclear technology applications. However, studies on the effects of ionizing radiation on the STT-MRAM writing process are lacking for MTJs with perpendicular magnetic anisotropy (pMTJs) required for scalable applications. Particularly, the question of the impact of extreme total ionizing dose on perpendicular magnetic anisotropy, which plays a crucial role on thermal stability and critical writing current, remains open. Here we report measurements of the impact of high doses of gamma and neutron radiation on nanoscale pMTJs used in STT-MRAM. We characterize the tunneling magnetoresistance, the magnetic field switching, and the current-induced switching before and after irradiation. Our results demonstrate that all these key properties of nanoscale MTJs relevant to STT-MRAM applications are robust against ionizing radiation. Additionally, we perform experiments on thermally driven stochastic switching in the gamma ray environment. These results indicate that nanoscale MTJs are promising building blocks for radiation-hard non-von Neumann computing

Full vectorial analysis of polarization effects in optical nanowires

We develop a full theoretical analysis of the nonlinear interactions of the two polarizations of a waveguide by means of a vectorial model of pulse propagation which applies to high index subwavelength waveguides. In such waveguides there is an anisotropy in the nonlinear behavior of the two polarizations that originates entirely from the waveguide structure, and leads to switching properties. We determine the stability properties of the steady state solutions by means of a Lagrangian formulation. We find all static solutions of the nonlinear system, including those that are periodic with respect to the optical fiber length as well as nonperiodic soliton solutions, and analyze these solutions by means of a Hamiltonian formulation. We discuss in particular the switching solutions which lie near the unstable steady states, since they lead to self-polarization flipping which can in principle be employed to construct fast optical switches and optical logic gates

Mode-locked picosecond pulse generation from an octave-spanning supercontinuum

We generate mode-locked picosecond pulses near 1110 nm by spectrally slicing and reamplifying an octave-spanning supercontinuum source pumped at 1550 nm. The 1110 nm pulses are near transform-limited, with 1.7 ps duration over their 1.2 nm bandwidth, and exhibit high interpulse coherence. Both the supercontinuum source and the pulse synthesis system are implemented completely in fiber. The versatile source construction suggests that pulse synthesis from sliced supercontinuum may be a useful technique across the 1000 - 2000 nm wavelength range

Terahertz All-Optical Modulation in a Silicon-Polymer Hybrid System

Although Gigahertz-scale free-carrier modulators have been previously demonstrated in silicon, intensity modulators operating at Terahertz speeds have not been reported because of silicon's weak ultrafast optical nonlinearity. We have demonstrated intensity modulation of light with light in a silicon-polymer integrated waveguide device, based on the all-optical Kerr effect - the same ultrafast effect used in four-wave mixing. Direct measurements of time-domain intensity modulation are made at speeds of 10 GHz. We showed experimentally that the ultrafast mechanism of this modulation functions at the optical frequency through spectral measurements, and that intensity modulation at frequencies in excess of 1 THz can be obtained in this device. By integrating optical polymers through evanescent coupling to high-mode-confinement silicon waveguides, we greatly increase the effective nonlinearity of the waveguide for cross-phase modulation. The combination of high mode confinement, multiple integrated optical components, and high nonlinearities produces all-optical ultrafast devices operating at continuous-wave power levels compatible with telecommunication systems. Although far from commercial radio frequency optical modulator standards in terms of extinction, these devices are a first step in development of large-scale integrated ultrafast optical logic in silicon, and are two orders of magnitude faster than previously reported silicon devices.Comment: Under consideration at Nature Material

A full vectorial model for pulse propagation in emerging waveguides with subwavelength structures part I: Kerr nonlinearity

The propagation of pulses through waveguides with sub-wavelength features, inhomogeneous transverse structure, and high index contrast cannot be described accurately using existing models in the presence of nonlinear effects. Here we report the development of a generalised full vectorial model of nonlinear pulse propagation and demonstrate that, unlike the standard pulse propagation formulation, the z-component of guided modes plays a key role for these new structures, and results in generalised definitions of the nonlinear coefficient gamma, Aeff , and mode orthognality. While new definitions reduce to standard definitions in some limits, significant differences are predicted, including a factor of approximately 2 higher value for gamma, for emerging waveguides and microstructured fibers

Hybrid integration of III/V lasers on a silicon-on-insulator (SOI) optical board

Abstract: Heterogeneous integration of III-V semiconductor materials on a silicon-on-insulator (SOI) platform has recently emerged as one of the most promising methods for the fabrication of active photonic devices in silicon photonics. For this integration, it is essential to have a reliable and robust bonding procedure, which also provides a uniform and ultra-thin bonding layer for an effective optical coupling between III-V active layers and SOI waveguides. A new process for bonding of III-V dies to processed siliconon-insulator waveguide circuits using divinylsiloxane-bis-benzocyclobutene (DVS-BCB) was developed using a commercial wafer bonder. This "cold bonding" method significantly simplifies the bonding preparation for machine-based bonding both for die and wafer-scale bonding. High-quality bonding, with ultra-thin bonding layers (<50 nm) is demonstrated, which is suitable for the fabrication of heterogeneously integrated photonic devices, specifically hybrid III-V/Si lasers. K. Mayora, "Novel three-dimensional embedded SU-8 microchannels fabricated using a low temperature full wafer adhesive bonding," J. Micromech. Microeng. 14(7), 1047-1056 (200

Pneumoconiosis and respiratory problems in dental laboratory technicians: Analysis of 893 dental technicians

Objectives: To explore the rate of pneumoconiosis in dental technicians (DTP) and to evaluate the risk factors. Material and Methods: Data of 893 dental technicians, who were admitted to our hospital in the period January 2007–May 2012, from 170 dental laboratories were retrospectively examined. Demographic data, respiratory symptoms, smoking status, work duration, working fields, exposure to sandblasting, physical examination findings, chest radiographs, pulmonary function tests and high-resolution computed tomography results were evaluated. Results: Dental technicians’ pneumoconiosis rate was 10.1% among 893 cases. The disease was more common among males and in those exposed to sandblasting who had 77-fold higher risk of DTP. The highest profusion subcategory was 3/+ (according to the International Labour Organization (ILO) 2011 standards) and the large opacity rate was 13.3%. Conclusions: To the best of our knowledge, it was the largest DTP case series (N = 893/90) in the literature in English. Health screenings should be performed regularly for the early diagnosis of pneumoconiosis, which is an important occupational disease for dental technicians

Cord blood adipokines and lipids and adolescent nonalcoholic fatty liver disease

© 2016 by the Endocrine Society. Context: Maternal adiposity in pregnancy is associated with offspring adiposity and metabolic dysfunction postnatally, including greater risk of nonalcoholic fatty liver disease (NAFLD). Recent genetic analyses suggest a causal effect of greater maternal body mass index on offspring birth weightandponderal index, but the relative roles of the environment in utero or later in life remains unclear. Objective: We sought to determine whether markers of infant adiposity (birth weight, umbilical cord blood leptin, adiponectin, and lipids) were associated with markers of NAFLD in adolescence. Design, Setting, and Participants: This was aUK prospective birth cohort with 17 years of follow-up with liver function tests (aspartate aminotransferase, alanine aminotransferase, gamma-glutamyltransferase) (n = 1037 participants), and ultrasound scan assessed liver fat, volume, and sheer velocity at age 17 (n = 541 participants). Missing covariate data were imputed. Main Outcomes: Ultrasound and biochemical measures of NAFLD were measured. Results: Birth weight, cord blood leptin, and adiponectin were not associated with a diagnosis of NAFLD. In adjusted analyses, 2 of 42 associations attained conventional 5% levels of significance. Birth weight was positively associated with liver volume (1.0% greater per 100 g [95% confidence interval 0.5%-2.0%]). Cord high-density lipoprotein-cholesterol was positively associated with alanine aminotransferase (11.6% higher per 1 mmol/L [95% confidence interval 0.3, 23.4]); however, this association was primarily mediated via offspring adiposity. Conclusions: In this extensive analysis, we found little evidence measurements of infant fat mass and birth size were related to adolescent markers of NAFLD. The association between birth weight and adolescent liver volume may indicate the contribution of greater organ size to birth weight and tracking of organ size