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The realization of vertical GaN devices requires deep plasma etching and is contingent on high mask selectivity. In this work, we show that SiO2 can be an effective mask material for deep etching GaN with GaN:SiO2 selectivities greater than 40—higher than the conventionally reported 15 for metal hard masks such as nickel. Ultrahigh SiO2 selectivities were achieved by introducing Al and AlCl into the Cl2-Ar inductively coupled plasma, which reacts with the SiO2 mask surface to form an etch-resistant aluminum silicate surface layer. This mechanism provides a low-contamination pathway to etch deep GaN microdevices.

B $$_{12}$$ P $$_{2}$$ , a wide bandgap semiconductor, has been previously reported to self-heal from high-energy electron bombardment as determined from transmission electron microscopy. However, the effect of irradiation on the electronic transport properties of B $$_{12}$$ P $$_{2}$$ has not been studied. We report electrical transport measurements on B $$_{12}$$ P $$_{2}$$ after $$\alpha $$ irradiation. The temperature-dependent Hall effect was measured on p-type B $$_{12}$$ P $$_{2}$$ after successive $$\alpha $$ irradiation from $$^{210}$$ Po over a fluence range of $$1\times \,10^{11}{-}1\times 10^{13}\,\alpha /\hbox {cm}^{2}$$ to test for self-healing of B $$_{12}$$ P $$_{2}$$ to $$\alpha $$ bombardment. Prior to irradiation, B $$_{12}$$ P $$_{2}$$ displayed electrical transport characteristics of both hopping and impurity/defect band conduction due to background impurities and growth-induced defects. Fluences of $$5\times 10^{12}\,\alpha /\hbox {cm}^{2}$$ or greater caused a decrease in the hole mobility and an increase in defect band conduction, suggesting defect accumulation in B $$_{12}$$ P $$_{2}$$ .

Shrinking the volumetric footprint of gas sensors is desirable as it allows for nonintrusive, nonperturbing gas mixture analysis and access to tight enclosures. Micro-resonators are a perfect candidate for these sensors as their size parameter (~micron) is minimal, and the typical surface propagating whispering gallery modes can interact with an analyte without disrupting the environment. The large, quality factor (Q) of these resonant cavity modes enables long interaction lengths on the order of 100s of centimeters between the optical field and analyte. Thus, the presence of a gas different than the nominal environment will result in a shift of the resonant properties, including the resonant wavelength, amplitude, and quality factor, that can be detected in real-time. To illustrate this effect, we utilized a spherical micro resonator on the end of a piece of optical fiber, formed using standard ball lens fabrication, and excited the resonant modes using a tapered optical fiber connected to tunable Infrared laser. The resonator was fixed in contact with the tapered region of fiber, and the assembly was placed inside an in-house, optically coupled, vacuum-tight vessel for gas testing. We compared the spectral response of air, pure CO2, and pure N2 gas, observing spectral shifting and broadening of the cavity resonances. In addition, the effect of vessel temperature on resonance peak position due to the thermo-optic effect was investigated and quantified. Lastly, a feedback arm was added to the setup to reduce signal noise and automated data analysis was implemented to improve data clarity.

This paper presents the design of a SiC-based photoconductive semiconductor switch (PCSS) in which a picosecond laser pulse generates excess free electrons and holes that are rapidly separated by applying a lateral electric field across the switch. Due to the high velocity and low recombination rate of carriers in high-quality, semi-insulating SiC, the PCSS can potentially operate at terahertz frequency at 10's of watts of output power, thereby improving the frequency-power-size tradeoff of high-electron mobility transistors and traveling wave tubes. The key contributions of this paper are as follows. First, we quantify the impact of material properties, doping, traps, laser spot size, and electric field on the transient response of the switch. Second, we develop a new compact model that can describe the performance of the PCSS over broad operating conditions. Excellent agreement of the model against numerical data is demonstrated. Finally, we identify an upper bound on the frequency of operation of the switch and obtain “frequency versus length” and “frequency versus laser spot size” scaling under low optical generation conditions.

This paper discusses ongoing research at Lawrence Livermore National Laboratory (LLNL) that investigates the effectiveness of a whispering gallery mode micro-resonator as a biosensor. Whispering Gallery mode resonators have properties such as ultrahigh quality factors (Q factors up to 1011), very high power density, and small mode volume that make them suitable for sensing applications1. In this work, silica microspheres (spheres on the order of 250μm) are used as resonators. These resonators are coupled to a tapered optical fiber connected to an infrared laser. Using critical coupling techniques, resonant wavelengths (wavelengths of zero power transmission) are produced. The resonant wavelengths of the coupled system are dependent upon properties of the microsphere such as diameter and index of refraction. Conjugation of biological organisms to the sphere causes a small change in these properties and thus creates a shift in resonant wavelengths (free spectral range) which can be characterized and used as a sensor. This paper will discuss microsphere and taper fabrication, the tested functionalization process, and the effect conjugation has on the microsphere Q factors. Future work includes real time analysis of biological organism conjugation and bringing the sensor down to the chip sized scale.

This paper discusses ongoing research at Lawrence Livermore National Laboratory (LLNL) that investigates the effectiveness of spherical micro-resonators, coupled to a symmetrically tapered optical fiber, as a gas sensor. We will discuss silica-based microspheres and optimized tapered fiber coupling systems to detect greenhouse gases, i.e. CO2 in this context. The coupling setup is designed to be portable and amenable to different controlled environments, from constrained and controlled geometries to open and flexible enclosures. 3D-printed spherical resonator and tapered-fiber holders were made to satisfy different requirements. We produced microspheres for absorption spectroscopy of targeted gas and fabricated tapers by HF etching, using an HF-resistant fixture for safer handling and reduced waste. Detection within loose enclosures was performed as a preliminary study, where we observed spectral shift and broadening in the cavity resonances induced by the gaseous environments. Optically coupled vacuum-tight vessels have been designed and built to understand environmental effects.

For quantum computing to become fault tolerant, the underlying quantum bits must be effectively isolated from the noisy environment. It is well known that including an electromagnetic bandgap around the qubit operating frequency improves coherence for superconducting circuits. However, investigations of bandgaps to other environmental coupling mechanisms remain largely unexplored. Here we present a method to enhance the coherence of superconducting circuits by introducing a phononic bandgap around the device operating frequency. The phononic bandgaps block resonant decay of defect states within the gapped frequency range, removing the electromagnetic coupling to phonons at the gap frequencies. We construct a multi-scale model that derives the decrease in the density of states due to the bandgap and the resulting increase in defect state $T_1$ times. We demonstrate that emission rates from in-plane defect states can be suppressed by up to two orders of magnitude. We combine these simulations with theory for resonators operated in the continuous-wave regime and show that improvements in quality factors are expected by up to the enhancement in defect $T_1$ times. Furthermore, we use full master equation simulation to demonstrate the suppression of qubit energy relaxation even when interacting with 200 defects states. We conclude with an exploration of device implementation including tradeoffs between fabrication complexity and qubit performance., The following article has been submitted to Applied Physics Letters

This publication arises from research funded by the John Fell Oxford University Press (OUP) Research Fund and the Research Complex at Harwell is acknowledged for their hospitality. SEH acknowledges partial financial support from a DARPA MESO Project (No. N66001-11-1-4105) and the VPGE (Stanford University) and LCM partial financial support from EPSRC (UK) through a Doctoral Training Award. We investigate the magnetic properties of Ho-doped Bi2Te3 thin films grown by molecular beam epitaxy. Analysis of the polarized X-ray absorption spectra at the Ho M5 absorption edge gives an effective 4f magnetic moment which is ∼45% of the Hund's rule ground state value. X-ray magnetic circular dichroism (XMCD) shows no significant anisotropy, which suggests that the reduced spin moment is not due to the crystal field effects, but rather the presence of non-magnetic or antiferromagnetic Ho sites. Extrapolating the temperature dependence of the XMCD measured in total electron yield and fluorescence yield mode in a field of 7 T gives a Curie-Weiss temperature of θ CW ≈ -30 K, which suggests antiferromagnetic ordering, in contrast to the paramagnetic behavior observed with SQUID magnetometry. From the anomaly of the XMCD signal at low temperatures, a Néel temperature TN between 10 K and 25 K is estimated. Postprint

Gallium nitride (GaN) has excellent material properties for power switching applications. The availability of low-defect density bulk GaN substrates has generated increased interest in vertically-structured devices [1]–[2]. By defining the electric field vertically, devices can sustain higher voltages within a smaller device footprint when compared to lateral topologies [2]. Despite record performance in vertical bulk-based devices, vertical heteroepitaxial devices remain attractive as a low-cost alternative [3]–[7]. A key design parameter is the drift layer thickness which, to first order, determines the maximum achievable breakdown voltage. For GaN-on-Si, drift layers have been limited to $\sim 3\ \mu \mathrm{m}$ due to film quality issues from lattice and thermal mismatches [4], [6]. For growth on sapphire, films $> 10\ \mu \mathrm{m}$ can be achieved. To date, drift layers $\leq 7\ \mu \mathrm{m}$ -thick and hard breakdown voltages $ have been reported for p-i-n GaN-on-sapphire [3], [5]. This may be due to difficulties with high-quality deep mesa etching. Recently, we reported exceptionally smooth $> 10\ \mu \mathrm{m}$ -deep GaN etching which enables the use of thicker drift layers and simplified processing [8]. Here, vertical p-i-n GaN-on-sapphire diodes with $a 10\ \mu m$ -thick drift layer are demonstrated with 1.1 kV soft breakdown (defined at 0.1 A/cm2) and irreversible hard breakdown $at > 1.3\ kV$ . These results are, to our knowledge, the highest breakdown voltage reported for $GaN$ diodes on foreign substrates and were achieved without edge termination techniques due to our high-quality mesa isolation etch.

The local electrical characteristics on the surface of MBE-grown Bi2Te3 are probed under ambient conditions by conductive atomic force microscopy. Nanoscale mapping reveals a 10–100× enhancement in current at step-edges compared to that on terraces. Analysis of the local current–voltage characteristics indicates that the transport mechanism is similar for step-edges and terraces. Comparison of the results with those for control samples shows that the current enhancement is not a measurement artifact but instead is due to local differences in electronic properties. The likelihood of various possible mechanisms is discussed. The absence of enhancement at the step-edges for graphite terraces is consistent with the intriguing possibility that spin–orbit coupling and topological effects play a significant role in the step-edge current enhancement in Bi2Te3.

We present the catalyst-free growth of binary Bi2Te3 topological insulator nanostructures on c-plane sapphire substrates by molecular beam epitaxy. Dense arrays of single-crystalline nanostructures, growing along the [110] direction, are obtained for substrate temperatures ranging from ∼180 °C to 260 °C. The growth rate and shape of the nanostructures are highly temperature-dependent. The microscopic study of the nanostructures and their relationship to the underlying Bi2Te3 thin film gives an insight into the growth mechanism.

The breaking of time-reversal symmetry (TRS) in topological insulators is a prerequisite for unlocking their exotic properties and for observing the quantum anomalous Hall effect (QAHE). The incorporation of dopants which exhibit magnetic long-range order is the most promising approach for TRS-breaking. REBiTe3, wherein 50% of the Bi is substitutionally replaced by a RE atom (RE = Gd, Dy, and Ho), is a predicted QAHE system. Despite the low solubility of REs in bulk crystals of a few %, highly doped thin films have been demonstrated, which are free of secondary phases and of high crystalline quality. Here we study the effects of exposure to atmosphere of rare earth-doped Bi2(Se, Te)3 thin films using x-ray absorption spectroscopy. We demonstrate that these RE dopants are all trivalent and effectively substitute for Bi3+ in the Bi2(Se, Te)3 matrix. We find an unexpected high degree of sample oxidation for the most highly doped samples, which is not restricted to the surface of the films. In the low-doping limit, the RE-doped films mostly show surface oxidation, which can be prevented by surface passivation, encapsulation, or in-situ cleaving to recover the topological surface state.

Breaking the time-reversal symmetry (TRS) in topological insulators (TIs) through ferromagnetic doping is an essential prerequisite for unlocking novel physical phenomena and exploring potential device applications. Here, we report the successful growth of high-quality (Dy(x)Bi(1-x))2Te3 thin films with Dy concentrations up to x = 0.355 by molecular beam epitaxy. Bulk-sensitive magnetisation studies using superconducting quantum interference device magnetometry find paramagnetic behaviour down to 2 K for the entire doping series. The effective magnetic moment, μeff, is strongly doping concentration-dependent and reduces from ∼12.6 μ(B) Dy(-1) for x = 0.023 to ∼4.3 μ(B) Dy(-1) for x = 0.355. X-ray absorption spectra and x-ray magnetic circular dichroism (XMCD) at the Dy M4,5 edge are employed to provide a deeper insight into the magnetic nature of the Dy(3+)-doped films. XMCD, measured in surface-sensitive total-electron-yield detection, gives μ(eff )= 4.2 μ(B) Dy(-1). The large measured moments make Dy-doped films interesting TI systems in which the TRS may be broken via the proximity effect due to an adjacent ferromagnetic insulator.

© 2014 AIP Publishing LLC. We report on the controlled removal of an amorphous Se capping layer from Bi2Te3 and Bi2Se3 topological insulators. We show that the Se coalesces into micron-sized islands before desorbing from the surface at a temperature of ∼150°C. In situ Auger Electron Spectroscopy reveals that Se replaces a significant fraction of the Te near the top surface of the Bi2Te3. Rutherford Backscattering Spectrometry and Transmission Electron Microscopy show that after heating, Se has been incorporated in the Bi2Te3 lattice down to ∼7 nm from its top surface while remaining iso-structural.

A high-throughput system to rapidly assess the intracellular replication of Staphylococcus aureus has been developed utilizing S. aureus transformed with a dual gfp-luxABCDE reporter operon under the control of a growth-dependent promoter. Replication of tagged bacteria internalized into bovine mammary epithelial cells (MAC-T) could be measured by monitoring fluorescence and bioluminescence from the reporter operon following removal of extracellular bacteria from the plates. Bacterial replication inside cells was confirmed by a novel ex vivo time-lapse confocal microscopic method. This assay of bacterial replication was used to evaluate the efficacy of antibiotics which are commonly used to treat staphylococcal infections. Not all antibiotics tested were able to prevent intracellular replication of S. aureus and some were ineffective at preventing replication of intracellular bacteria at concentrations above the MIC determined for bacteria in broth culture. Comparison of the fluorescence and bioluminescence signals from the bacteria enabled effects on protein synthesis and metabolism to be discriminated and gave information on the entry of compounds into the eukaryotic cell, even if bacterial replication was not prevented. Elevated resistance of S. aureus to antibiotics inside host cells increases the likelihood of selecting S. aureus strains which are resistant to commonly used antimicrobial agents within the intracellular niche. The approach presented directly assesses intracellular efficacy of antibiotics and provides an evidence-based approach to antibiotic selection for prescribing physicians and medical microbiologists.

Ferromagnetically doped topological insulators with broken time-reversal symmetry are a prerequisite for observing the quantum anomalous Hall effect. Cr-doped ${(\mathrm{Bi},\mathrm{Sb})}_{2}{(\mathrm{Se},\mathrm{Te})}_{3}$ is the most successful materials system so far, as it combines ferromagnetic ordering with acceptable levels of additional bulk doping. Here, we report a study of the local electronic structure of Cr dopants in epitaxially grown ${\mathrm{Bi}}_{2}{\mathrm{Se}}_{3}$ thin films. Contrary to the established view that the Cr dopant is trivalent because it substitutionally replaces ${\mathrm{Bi}}^{3+}$, we find instead that Cr is divalent. This is evidenced by the energy positions of the Cr $K$ and ${L}_{2,3}$ absorption edges relative to reference samples. The extended x-ray absorption fine structure at the $K$ edge shows that the Cr dopants substitute on octahedral sites with the surrounding Se ions contracted by $\ensuremath{\Delta}d=\ensuremath{-}0.36$ \AA{}, in agreement with recent band structure calculations. Comparison of the Cr ${L}_{2,3}$ x-ray magnetic circular dichroism at $T=5$ K with multiplet calculations gives a spin moment of $3.64 {\ensuremath{\mu}}_{\mathrm{B}}/{\mathrm{Cr}}_{\mathrm{bulk}}$, which is close to the saturation moment for ${\mathrm{Cr}}^{2+} {d}^{4}$. The reduced Cr oxidation state in doped ${\mathrm{Bi}}_{2}{\mathrm{Se}}_{3}$ is ascribed to the formation of a covalent bond between Cr $d({e}_{g})$ and Se $p$ orbitals, which is favored by the contraction of the Cr-Se distances.

Thin film GdBiTe3 has been proposed as a candidate material in which to observe the quantum anomalous Hall effect. As a thermal non-equilibrium deposition method, molecular beam epitaxy (MBE) has the ability to incorporate large amounts of Gd into Bi2Te3 crystal structures. High-quality rhombohedral (GdxBi1-x)2Te 3 films with substitutional Gd concentrations of x ≤ 0.4 were grown by MBE. Angle-resolved photoemission spectroscopy shows that the topological surface state remains intact up to the highest Gd concentration. Magnetoresistance measurements show weak antilocalization, indicating strong spin orbit interaction. Magnetometry reveals that the films are paramagnetic with a magnetic moment of 6.93 μB per Gd3+ ion. © 2013 AIP Publishing LLC.

Discharge from hospital follow-up is a key time point in the cancer journey. With recommendations for earlier discharge of cancer survivors, attention to the discharge process is likely to become increasingly important. This study explored cancer survivors' experiences of discharge from hospital follow-up. Survivors of breast, colorectal and prostate cancer (n= 1275), 5-16 years post diagnosis were approached to take part in a questionnaire survey. The questionnaire included questions about discharge status, provision of time/information prior to discharge, feelings at discharge and satisfaction with how discharge was managed. Completed questionnaires were returned by 659 survivors (51.7%). Approximately one-third of respondents were not discharged from follow-up 5-16 years post diagnosis. Of those discharged, a substantial minority reported insufficient time (27.9%), information (24.5-45.0%) or adverse emotions (30.9%) at the time of discharge. However, 90.6% of respondents reported satisfaction with how discharge from hospital follow-up was managed. Despite high levels of satisfaction, discharge of cancer survivors from hospital follow-up could be improved with the provision of additional time, information and support. Better structuring of the final hospital appointment or a review appointment in primary care at this time could help to ensure that discharge from hospital follow-up is managed optimally for cancer survivors.

Atomically resolved scanning tunneling microscope images of carbon ridge defects found in few-layer graphene formed on the C-face (0001) of 4H-silicon carbide reveal a striated exterior surface formed from out-of-plane distortions of the hexagonal graphene lattice. While ridge formation is likely explained by compressive in-plane stresses coupled with the small values of the bending modulus for few-layer graphene, the striated structure along the ridges argues for a localized unidirectional stress in the material directed along the ridge length.

Six gamma-emitting isotopes, Se-75, Hg-203, Cs-134, Fe-59, Zn-65 and Co-60, were introduced simultaneously in a single epilimnetic addition to an oligotrophic lake on the Precambrian Shield of northwestern Ontario, Canada. Accumulation of each isotope was monitored in fathead minnow (Pimephales promelas) for 274 days. Isotope accumulation in blood, gill, gut, liver, kidney, spleen, gonad, brain, muscle and gut contents of lake trout (Salvelinus namaycush) was monitored for 352 days. Fish accumulated only traces of Fe-59. Isotopes which occured in water primarily in the charcoal-extracted fraction (Se-75 and Zn-65) were most readily accumulated by fish. Fathead minnow accumulated higher concentrations of all isotopes than lake trout. In lake trout, the highest concentrations of isotopes were found in the following tissues: Se-75, liver; Hg-203 and Co-60, kidney; Cs-134, muscle; Zn-65, gut. Food seemed to be the primary source of all isotopes to fish. Ratios of isotope concentrations in fish to those in water were higher for both fathead minnow and lake trout than ratios reported from laboratory studies using aqueous exposures. Concentration ratios for Cs-134 in both fathead minnow and lake trout from oligotrophic Lake 224 were over an order of magnitude greater than published data for fish from eutrophic lakes.

Northern pike (Esox lucius Linnaeus), white sucker (Catostomus commersoni Lacepede) and sediment cores were obtained from 13 lakes located 4.5 to 84 km from the base metal smelter at Flin Flon, Manitoba, Canada. Zn, Cu, Cd, Hg, Se, Pb and As concentrations were determined in liver and muscle of fish. Depth profiles of Zn, Cu, Cd, Hg and Se concentrations were determined in sediment cores. The area receiving significant metal deposition from the smelter is smaller than previously estimated. Increases in metal concentrations in depth profiles of sediment cores appear to coincide with the onset of smelting operations at Flin Flon. Metal concentrations in fish from two lakes near the smelter dropped between 1976 and 1982, after a tall stack (250 m) was installed on the smelter. Metal concentrations in muscle were poor indicators of metal concentrations in sediments. Concentrations of Cd and Se in liver of northern pike, and concentrations of Zn, Cu, Cd and Se in liver of white sucker were greatest in the most contaminated lakes. Concentrations of Hg in fish declined with increased proximity to the smelter. Limnological variables seemed to have little influence on metal concentrations in fish.

Breaking the time-reversal symmetry (TRS) in topological insulators (TIs) through ferromagnetic doping is an essential prerequisite for unlocking novel physical phenomena and exploring potential device applications. Here, we report the successful growth of high-quality (DyxBi1−x)2Te3 thin films with Dy concentrations up to x = 0.355 by molecular beam epitaxy. Bulk-sensitive magnetisation studies using superconducting quantum interference device magnetometry find paramagnetic behaviour down to 2 K for the entire doping series. The effective magnetic moment, μeff, is strongly doping concentration-dependent and reduces from ~12.6 μB Dy−1 for x = 0.023 to ~4.3 μB Dy−1 for x = 0.355. X-ray absorption spectra and x-ray magnetic circular dichroism (XMCD) at the Dy M4,5 edge are employed to provide a deeper insight into the magnetic nature of the Dy3+-doped films. XMCD, measured in surface-sensitive total-electron-yield detection, gives μeff = 4.2 μB Dy−1. The large measured moments make Dy-doped films interesting TI systems in which the TRS may be broken via the proximity effect due to an adjacent ferromagnetic insulator.

We report the growth of Mn-doped Bi2Se3 thin films by molecular beam epitaxy (MBE), investigated by x-ray diffraction (XRD), atomic force microscopy (AFM), SQUID magnetometry and x-ray magnetic circular dichroism (XMCD). Epitaxial films were deposited on c-plane sapphire substrates by co-evaporation. The films exhibit a spiral growth mechanism typical of this material class, as revealed by AFM. The XRD measurements demonstrate a good crystalline structure which is retained upon doping up to ∼7.5 atomic-% Mn, determined by Rutherford backscattering spectrometry (RBS), and show no evidence of the formation of parasitic phases. However an increasing interstitial incorporation of Mn is observed with increasing doping concentration. A magnetic moment of 5.1 μB/Mn is obtained from bulk-sensitive SQUID measurements, and a much lower moment of 1.6 μB/Mn from surface-sensitive XMCD. At ∼2.5 K, XMCD at the Mn L2,3 edge, reveals short-range magnetic order in the films and indicates ferromagnetic order below 1.5 K.

Materials with layered van der Waals crystal structures are exciting research topics in condensed matter physics and materials science due to outstanding physical properties associated with their strong two dimensional nature. Prominent examples include bismuth tritelluride and triselenide topological insulators (TIs), which are characterized by a bulk bandgap and pairwise counter-propagating spin-polarized electronic surface states. Angle-resolved photoemission spectroscopy (ARPES) of ex-situ grown thin film samples has been limited by the lack of suitable surface preparation techniques. We demonstrate the shortcomings of previously successful conventional surface preparation techniques when applied to ternary TI systems which are susceptible to severe oxidation. We show that in-situ cleaving is a simple and effective technique for preparation of clean surfaces on ex-situ grown thin films for high quality ARPES measurements. The method presented here is universally applicable to other layered van der Waals systems as well.

We report the structural and magnetic study of Cr-doped Bi2Se3 thin films using x-ray diffraction (XRD), magnetometry and polarized neutron reflectometry (PNR). Epitaxial layers were grown on c-plane sapphire by molecular beam epitaxy in a two-step process. High-resolution XRD shows the exceptionally high crystalline quality of the doped films with no parasitic phases up to a Cr concentration of 12% (in % of the Bi sites occupied by substitutional Cr). The magnetic moment, measured by SQUID magnetometry, was found to be per Cr ion. The magnetic hysteresis curve shows an open loop with a coercive field of . The ferromagnetic transition temperature was determined to be analyzing the magnetization-temperature gradient. PNR shows the film to be homogeneously ferromagnetic with no enhanced magnetism near the surface or interface.

Incorporation of magnetic dopants into topological insulators to break time-reversal symmetry is a prerequisite for observing the quantum anomalous Hall (QAHE) effect and other novel magnetoelectric phenomena. GdBiTe3 with a Gd:Bi ratio of 1:1 is a proposed QAHE system, however, the reported solubility limit for Gd doping into Bi2Te3 bulk crystals is between ∼0.01 and 0.05. We present a magnetic study of molecular beam epitaxy grown (GdxBi1-x)2Te 3 thin films with a high Gd concentration, up to x ≈ 0.3. Magnetometry reveals that the films are paramagnetic down to 1.5 K. X-ray magnetic circular dichroism at the Gd M4,5 edge at 1.5 K reveals a saturation field of ∼6 T, and a slow decay of the magnetic moment with temperature up to 200 K. The Gd3 ions, which are substitutional on Bi sites in the Bi2Te3 lattice, exhibit a large atomic moment of ∼7 μB, as determined by bulk-sensitive superconducting quantum interference device magnetometry. Surface oxidation and the formation of Gd2O3 lead to a reduced moment of ∼4 μB as determined by surface-sensitive x-ray magnetic circular dichroism. Their large atomic moment makes these films suitable for incorporation into heterostructures, where interface polarization effects can lead to the formation of magnetic order within the topological insulators. © 2014 AIP Publishing LLC.

Large-area topological insulator Bi2Te3 thin films were grown on Al2O3 (0001) using a two-temperature step molecular beam epitaxy growth process. By depositing a low temperature nucleation layer to serve as a template for high temperature epitaxial film growth, a high quality terrace-step surface morphology with a significant reduction in three-dimensional defect structures was achieved. X-ray diffraction measurements indicate that high crystalline quality Bi2Te3 layers were grown incoherently by van der Waals epitaxy using this technique. Angle resolved photoemission spectroscopy measurements verified the integrity of this growth method by confirming the presence of metallic surface states on cleaved two-step Bi2Te3 samples.

Rainbow trout (Salmo gairdneri) and lake whitefish (Coregonus clupeaformis) were exposed for 72 d to 109Cd in pelletized commercial trout food or in the water in a continuous-flow water exposure system. Blood, gill, gut, liver, kidney, muscle, skin, feces and gut contents were sampled from 40 fish in each group during the exposure phase and from 20 fish in each group during the subsequent 56-d depuration period. Gill accumulated the highest cadmium concentrations. After 56 d of depuration, most of the cadmium in food-exposed fish of both species was in the kidney, gut and liver, but water-exposed fish retained most of the cadmium in gill and kidney. Whole-body concentration factors (L/kg wet weight tissue) after 72 d of exposure for water-exposed fish were 55 for rainbow trout and 42 for whitefish. Whole-body bioconcentration factors after 72 d of exposure for food-exposed fish were less than 1 (kg food/kg dry weight tissue). Both species accumulated significantly greater proportions of the cadmium dose from food than from water. The percentages of the cadmium dose accumulated after 72 d of water exposure were 0.15% for trout and 0.11% for whitefish, while for food exposure the values were 1.03% for trout and 1.01% for whitefish. A simple two-compartment kinetic model was fitted to the data. Equilibrium cadmium bioconcentration factors for aqueous exposure were estimated to be 161 for rainbow trout and 51 for lake whitefish. Biological half-times for depuration ranged from 24 to 63 d.

In laboratory experiments, lake whitefish (Coregonus clupeaformis) were exposed to acidified water of pH 5.0 4.7, 4.4, and 4.1 for 2 wk; controls were held at pH 7.6. Continuous recordings of locomotor activity over 4 days and nights at the end of each treatment showed a consistent trend towards reduced daytime activity and loss of diel rhythmicity with increasing ambient acidity. Feeding was observed to decrease at pH 4.7, and to cease at pH 4.4 and 4.1. Associated with these behavioral effects were changes of blood plasma variables. Plasma cortisol and glucose levels increased with lowered pH; sodium, chloride, and their fractional contribution to osmolality decreased.

The generation of photocarriers in copper and metal‐free phthalocyanines (CuPc and H2Pc, respectively) is shown to be an extrinsic process, i.e., the result of absorbed oxygen impurities. ir Photoconduction found in CuPc is absent in H2Pc. This suggests that the ir response may arise from the singlet–triplet absorption which is enhanced by the spin–orbit coupling of the Cu ion. The photocurrent is proportional to (light intensity)s, where s is the same constant for ir and visible (intrinsic) absorptions. This constancy supports the interpretation that both singlet and triplet excitons generate carriers via interaction with the same trapping centers.

The electron mobility of charge carriers in copper phthalocyanine has been determined to be approximately two orders of magnitude greater than that in metal‐free phthalocyanine. This difference can be interpreted in terms of the electron spin resonance results and the intermolecular copper‐nitrogen overlap. The electron spin resonance of copper phthalocyanine magnetically diluted in metal‐free phthalocyanine has been measured in single crystals. The hyperfine structure of the nitrogen ligands, as well as that of the copper hyperfine structure, is clearly resolved. An analysis of the data in terms of molecular orbitals suggests a scheme of strong out‐of‐plane π bonding with the π orbitals of the phthalocyanine ring and almost no in‐plane π bonding. This brings about an inversion of the usual positions of the copper Eg and B2g orbitals. This strong π bonding predicts that in metallo‐organic compounds of this type, the organic π‐electron delocalization is increased to include the central metal atom, and properties dependent on this delocalization should be altered when copper is used. The increased delocalization of the π‐electron orbitals gives rise to larger intermolecular π wavefunction overlap resulting in a greater mobility for charge carriers in copper phthalocyanine.

The crystal phase transition in phthalocyanines is shown to have no influence on the electrical conductivity; the intrinsic conductivities are identical. The changes in intermolecular overlap are too small to be discerned. The stronger propensity of the α phase to absorb oxygen is the source of the apparently higher conductivity of the α phase.

An electron spin resonance study of vanadyl phthalocyanine magnetically diluted in metal‐free and zinc phthalocyanine salts, and in sulfuric acid solution, confirms the placement of the 3d unpaired electron in the dxy singlet orbital of the vanadium ion. An improved method of synthesis for vanadyl phthalocyanine which increased the yield to 64% is described. The infrared spectrum of vanadyl phthalocyanine indicates that this complex exists in only one polymorphic modification.

The complex initial permeability of a series of polycrystalline manganese-rich manganese ferrites (${\mathrm{Mn}}_{1+x}{\mathrm{Fe}}_{2\ensuremath{-}x}{\mathrm{O}}_{4}$) has been measured between 20 Mc/sec and 2000 Mc/sec. Three resonances are detected; the two lower-frequency resonances, which occur below 200 Mc/sec, are associated with domain wall motion. The higher-frequency resonance, which varies between 300 and 600 Mc/sec depending on the composition, allows the calculation of an effective polycrystalline anisotropy constant, ${K}_{e}$. Microwave resonance measurements on single crystals of the same composition give the real anisotropy constant ${K}_{1}$. Comparison of these two experiments show that ${K}_{e}\ensuremath{\approx}2{K}_{1}$. Measurement of the magnetic moment indicates that in these compounds the ${\mathrm{Mn}}^{3+}$ ion assumes a value of approximately two Bohr magnetons instead of the expected four Bohr magnetons.

Excess conductivities induced by steady-state sources of gamma rays and by pulsed sources of neutrons and gamma rays in polyethylene, polystyrene, polypropylene, Nylon, polyisobutylene (impregnated paper), mylar, Teflon, diallylphthalate, H-film, cellulose acetate, reconstituded mica, tantalum oxide, and an epoxy formulation have been measured. The measurements were made at steady-state gamma-ray dose rates within the interval from 1.0 × 10-3 rads(H2O)/sec to 1.0 × 104 rads(H2O)/sec, and at combined pulsedneutron and gamma-ray dose rates less than 2.0 × 108 rads(H2O)/sec. All measurements were made at controlled temperatures between 25°C and 71°C. With steady-state gamma-ray irradiation, an excess conductivity is induced which has distinct features in three time intervals denoted as A, B, and C. In interval A, induced conductivity (? - ?o) is responding to a step increase in gamma-ray dose rate. The conductivity response is exponential (? - ?o) = A(1 - e-t/?o), with the time constant (?o) decreasing with increased gamma-ray dose rare (?). The change in time constant as a function of gamma-ray dose rate at a fixed temperature is approximated by ?o = ko?-? where ko and ? are empirical constants. In interval B the induced conductivity has arrived at an equilibrium value whose magnitude as a function of gamma-ray dose rate at a fixed temperature is characterized to a good approximation by (? - ?o) = A???, where A? and ? are empirical constants. In interval C the conductivity is recovering upon removal of the sample from the radiation environment.

The evaluation of phthalocyanine as a photoconductive material has lead to the unusual result that the photocurrent varies as the one‐third power of the light intensity. In this paper, this effective desensitization is analyzed in terms of diffusion effects involving the surface.

Electron spin resonance of a water solution and of the pure powder of K3[Cr(CN)5NO]·H2O reveal a single sharp resonance line at room temperature. The water solution resonance gives a Cr53 hyperfine structure which is further split by a ``superhyperfine'' structure due to the nitrogen in the NO ligand. From the electron spin resonance the Cr1+ ion appears to be in a spin quenched (de5) orbital singlet ground state. The optical absorption data allows the determination of the splittings of the d levels in concordance with the ESR spectrum.

The triplet‐state lifetime of metal‐free phthalocyanine has been found to vary from 10−6 sec at room temperature to 150×10−6 sec at 77°K. Decay from the first excited state proceeds via the triplet state. Excitation by a giant‐pulse ruby laser completely empties the ground state. Luminescence is quenched in metallic phthalocyanines by the extremely rapid intersystem crossing.

Results were obtained which demonstrate that calcium accumulation in the rabbit lens may suppress glycolysis, not only by its inhibitory effect on cation transport but by its direct effect on glycolytic enzymes. In lenses cultured in calcium-enriched medium, lactate production declined in proportion to the increase in free and bound levels of calcium. In lens homogenates to which varying amounts of calcium were added, lactate production also decreased. To insure that excess calcium was not simply chelating ATP, homogenates were exposed to calcium and then dialyzed against a calcium-free buffer prior to addition of ATP. Under these conditions, lactate production diminished maximally by approximately 50% as bound calcium increased five-fold.

Calcium-sensitive microelectrodes have been employed to determine that the free, intracellular concentration of calcium in the lens is approximately 30 microM. Additionally, active extrusion of intracellular calcium has been demonstrated.

Chondroitin sulfate (CDS) has been found to serve as an excellent protective coating for intraocular lens (IOL) implantation to avoid any damage to the corneal endothelium; the protection is total. Using a new vital dye, acid violet 49, as a stain, a series of possible coatings including albumin and hyaluronic acid was evaluated in vitro and in vivo. Some 600 animal corneas were trephined, and the sample buttons submitted to the dragging of variously coated lenses across the endothelium. The animal species were rabbit, pig, cow, dog, cat, and monkey. IOLs were traumatically inserted in rabbits and monkeys. Chondroitin sulfate surpassed by far the protective qualities of other compounds: albumin was second best; hyaluronic acid third, the latter two yielding substantial damage in our tests. Comparisons with the commercially available Healon still revealed chondroitin sulfate to be the most efficacious protective agent. The material was eliminated from the anterior chamber in periods less than 40 hours. Monitoring of postoperative intraocular pressures revealed only normal pressures in our animals.