Tuneable exchange-spring stiffness in amorphous magnetic trilayer structures.

We investigate the magnetic properties of amorphous Sm10Co90/Co60(Al70Zr30)40/Co85(Al70Zr30)15exchange-spring magnet trilayers. The magnetically soft Co85(Al70Zr30)15layer is coupled to the magnetically hard Sm10Co90layer through the weakly magnetic low-TcCo60(Al70Zr30)40spacer layer. The strength of the coupling can be controlled with temperature and the coupling persists above the intrinsicTcof the spacer layer due to a long-range magnetic proximity effect. Polarized neutron reflectivity is used to examine the magnetic profile of the trilayers during magnetization reversal. A two-step switching occurs, with the switching angle of the soft layer strongly dependent on the strength of the coupling. In the strong coupling regime a magnetic state can be achieved where the soft layer magnetization is perpendicular to the hard layer whereas in the weak coupling regime the soft layer reverses fully.

Shrinking of silicon nanocrystals embedded in an amorphous silicon oxide matrix during rapid thermal annealing in a forming gas atmosphere.

We report the effect of hydrogen on the crystallization process of silicon nanocrystals embedded in a silicon oxide matrix. We show that hydrogen gas during annealing leads to a lower sub-band gap absorption, indicating passivation of defects created during annealing. Samples annealed in pure nitrogen show expected trends according to crystallization theory. Samples annealed in forming gas, however, deviate from this trend. Their crystallinity decreases for increased annealing time. Furthermore, we observe a decrease in the mean nanocrystal size and the size distribution broadens, indicating that hydrogen causes a size reduction of the silicon nanocrystals.

Identification of vibrational signatures from short chains of interlinked molecule-nanoparticle junctions obtained by inelastic electron tunnelling spectroscopy.

Short chains containing a series of metal-molecule-nanoparticle nanojunctions are a nano-material system with the potential to give electrical signatures close to those from single molecule experiments while enabling us to build portable devices on a chip. Inelastic electron tunnelling spectroscopy (IETS) measurements provide one of the most characteristic electrical signals of single and few molecules. In interlinked molecule-nanoparticle (NP) chains containing typically 5-7 molecules in a chain, the spectrum is expected to be a superposition of the vibrational signatures of individual molecules. We have established a stable and reproducible molecule-AuNP multi-junction by placing a few 1,8-octanedithiol (ODT) molecules onto a versatile and portable nanoparticle-nanoelectrode platform and measured for the first time vibrational molecular signatures at complex and coupled few-molecule-NP junctions. From quantum transport calculations, we model the IETS spectra and identify vibrational modes as well as the number of molecules contributing to the electron transport in the measured spectra.

Improved gas sensing activity in structurally defected bilayer graphene.

Graphene is a two-dimensional material with a capability of gas sensing, which is here shown to be drastically improved by inducing gentle disorder in the lattice. We report that by using a focused ion beam technique, controlled disorder can be introduced into the graphene structure through Ga(+) ion irradiation. This disorder leads to an increase in the electrical response of graphene to NO(2) gas molecules by a factor of three in an ambient environment (air). Ab initio density functional calculations indicate that NO(2) molecules bind strongly to Stone-Wales defects, where they modify electronic states close to the Fermi level, which in turn influence the transport properties. The demonstrated gas sensor, utilizing structurally defected graphene, shows faster response, higher conductivity changes and thus higher sensitivity to NO(2) as compared to pristine graphene.

Enabling measurements of low-conductance single molecules using gold nanoelectrodes.

A high resistance nanogap platform was used to trap and electrically characterize 30 nm thiolated double-stranded DNA molecules. High resolution scanning electron microscopy was also used to image the trapped DNA strands. It was found that the surface state of the electrodes and underlying substrate could influence the measurements of trapped molecules when the measured resistances were on the order of TΩ or greater. Hydrophilic surfaces gave rise to larger leakage currents that could potentially mask the underlying signals from molecules positioned in the nanogap. Finally, the careful handling of the samples and control of the environment is essential to avoid surface charging of the oxide substrate layer as these parasitic charges affect electrical measurements of the nanogap. The presented results thus outline some important considerations when making low-conductance measurements on molecules and should prove useful for the characterization of molecules in molecular electronics or sensors employing nanogap platforms.

Assessment of a nanoparticle bridge platform for molecular electronics measurements.

A combination of electron beam lithography, photolithography and focused ion beam milling was used to create a nanogap platform, which was bridged by gold nanoparticles in order to make electrical measurements and assess the platform under ambient conditions. Non-functionalized electrodes were tested to determine the intrinsic response of the platform and it was found that creating devices in ambient conditions requires careful cleaning and awareness of the contributions contaminants may make to measurements. The platform was then used to make measurements on octanethiol (OT) and biphenyldithiol (BPDT) molecules by functionalizing the nanoelectrodes with the molecules prior to bridging the nanogap with nanoparticles. Measurements on OT show that it is possible to make measurements on relatively small numbers of molecules, but that a large variation in response can be expected when one of the metal-molecule junctions is physisorbed, which was partially explained by attachment of OT molecules to different sites on the surface of the Au electrode using a density functional theory calculation. On the other hand, when dealing with BPDT, high yields for device creation are very difficult to achieve under ambient conditions. Significant hysteresis in the I-V curves of BPDT was also observed, which was attributed primarily to voltage induced changes at the interface between the molecule and the metal.

Asymmetry of the two-beam geometry in EMCD experiments.

We analyse theoretically the influence of the asymmetry of the two-beam geometry on quantitative measurements of the energy-loss magnetic chiral dichroism. Our simulations indicate that this asymmetry is not very strong inside or close to the Thales circle, but in other regions of the diffraction plane it can hinder an accurate extraction of the orbital to spin moment ratio.

Mechanisms of quantum dot energy engineering by metalorganic vapor phase epitaxy on patterned nonplanar substrates.

A novel technique for tuning the strength of quantum confinement in site-controlled semiconductor quantum dots (QDs) is introduced and investigated theoretically and experimentally. The method makes use of controlled local growth rates during metalorganic vapor phase epitaxy on patterned arrays of inverted pyramids. A model accounting for precursor migration and adatom incorporation predicts the tuning in QD thickness as a function of the pattern parameters. The results are in good agreement with experimental findings. This technique offers means for designing QD photonic structures with potential applications in QD-based cavity quantum electrodynamics and quantum information processing.

Analytical electron microscopy as a tool for accessing colloid formation process in natural waters.

Analytical electron microscopy was used to characterize aquatic iron-rich colloids. We focused our attention on a redox transition medium in the drainage water of a peat soil. In the anoxic peat water, observations by transmission electron microscopy and associated energy dispersive analyses (TEM-EDS) highlight the presence of spherical entities (approximately 100-600 nm), containing only traces of iron. The increase of dissolved oxygen concentration favours the formation of iron oxy(hydr)oxides. In the oxygenated drain, particles with the same morphology and size range are present. Statistical TEM-EDS analyses show that they represent the only colloidal form of iron in the drain samples. Nevertheless, although Fe-K peaks appear clearly on EDS spectra, the proportion of iron in these colloids reaches at most 4% at. (whereas C + O > 90% at.). Structural information completes this study. Both electron spectroscopic imaging (ESI) and electron energy-loss spectroscopy (EELS) reveal the disparity between element distributions within the drain entities. Iron and calcium are preferably distributed on the outer sphere of the particle, whereas carbon and oxygen follow the theoretical variation of the signal intensity within a plain sphere. The implication of organic matter as nucleation site for iron precipitation is spectacularly demonstrated by the presence of nanometre-sized iron-rich phases highlighted by EELS line scans.

Theoretical and experimental limits of the analysis of III/V semiconductors using EELS

The optimisation of acquisition conditions for EELS spectroscopy of Al(x)Ga(1-x)As heterostructures permits one to find the absolute concentration with a precision of better than delta = +/-0.02 and to detect changes in concentration of +/-0.01 for x = 0-0.5. In order to achieve this concentration precision, we investigated ways to reduce the influence of three major sources on the inaccuracies of the measurement: the effect of electron channelling which biases the ionisation probabilities on the different atomic sites, the contribution of the sample surface layers and the accuracy in the spectral analysis. An optimal specimen orientation that maximises the stability of the electron densities on Al and As sites without introducing an unacceptable loss of spatial resolution due to sample tilt is found by computing the electron channelling intensity as a function of the specimen tilt angle. The influence of a Ga enriched surface layer on the analysis is demonstrated. Two methods for the extraction of the edge intensity from the spectra are compared. These methods are shown to give the upper and the lower limit of the Ga concentration.

Experimental method for high-accuracy reflectivity-spectrum measurements.

An experimental method for accurate measurements of the reflectivity spectrum of mirrors is presented. It combines the noise reduction obtained with multiple beam reflections on two identical mirrors; high-beam quality, owing to the use of single-mode optical fibers; and high immunity against intensity variations of the beam. This method is demonstrated for characterizing a 30-period GaAs/Al(0.65)Ga(0.35)As distributed Bragg reflector designed for long-wavelength vertical-cavity surface-emitting lasers. Its peak reflectivity is found to be 99.43 ? 0.04% at 1.562 mum, and an optical absorption coefficient of alpha = 36 ? 6 cm(-1) is derived. The peak internal reflectivity of this distributed Bragg reflector used as the top mirror in a wafer-fused vertical-cavity surface-emitting laser is calculated to be 98.87 ? 0.12%, and the transmission is 0.28%.

Risk factors for the development of allergic disease: analysis of 2,190 patient records.

Records of 2,190 patients with demonstrable allergic disease, including 1,148 patients with asthma and 557 patients with allergic rhinitis, were analyzed for the impact of certain risk factors on age of onset of allergic disease and on sensitization to certain specific antigens. The risk factors examined included race, sex, maternal age, family structure, life style, feeding history, environmental factors and heredity of allergic disease. Age of onset was significantly earlier (P less than 0.001) in males, blacks, children of younger mothers, bottle-fed babies, children of rural origin, children of smoking parents and children with a bilateral family history of allergy.

Flunisolide aerosol in the treatment of perennial allergic rhinitis.

A double-blind, crossover study was performed with a new topical aerosol steroid, flunisolide, administered every 12 hours over a period of eight weeks to 36 adult patients with perennial allergic rhinitis. During the treatment period the majority of patients had significant relief of symptoms as compared with the placebo period. Most prominent improvement occurred with the symptoms of nasal stuffiness, sneezing, rhinorrhea and the number of times patients had to blow their noses. Best results were obtained in patients with higher degrees of atopy. Side effects were minimal and limited to nasal irritation in some patients. Criteria for optimal patient selection are discussed and an explanation for the lack of systemic effects of aerosolized use of the newer corticosteroids is given.

Unreliability of maximum mid-expiratory flow rate as sole index of bronchodilator response in chronic asthma.

Analysis of individual patterns of response to bronchodilation in asthmatics, rather than group averages, emphasizes the varying types of "asthma" as well as the need to examine all parameters of lung function when evaluating any new therapeutic agent. The often praised maximum mid-expiratory flow rate may be very misleading as a parameter of drug response.

Differing patterns of pulmonary function response to bronchodilators in asthmatics.

An analysis of the patterns of pulmonary function response to bronchodilators in 20 adult asthmatics reveal distinct categories of response. It is suggested that the pattern of response is related primarily to the degree of baseline abnormality in pulmonary function rather than to other characteristics of the disease or patient. Thus, one may predict pulmonary function response to bronchodilators in adult asthmatics based solely upon baseline function.

Spirometric comparison of carbuterol and isoproterenol aerosol therapy in bronchial asthma. A double blind, matched-pair study of 28 adults and a double blind crossover study of 18 children.

Two adrenergic aerosols were compared in a double blind, matched-pair study of 6 months' duration in 28 adult patients with chronic bronchial asthma, and in a double blind, crossover, short-term study in 18 children with severe asthma. In the adult study, one member of each pair was given either 150 mug of isoproterenol or 200 mug of carbuterol 4 times per day, by inhalation, for 6 months. In the childhood study, 18 children, 6 to 12 years of age, with moderate to severe asthma were studied in a double blind, crossover therapeutic trial in which high or low doses of aerosolized carbuterol or isoproterenol were given 4 times daily for 5 days each. Treatment results were evaluated by measuring forced vital capacity, 1-sec forced expiratory volume, and maximal mid-expiratory flow (FEF25-75%) at regulat intervals before and after administration of the respective test drugs. In the adult study, there was a significant difference between carbuterol and isoproterenol for forced vital capacity (P less than 0.02), for 1-sec forced expiratory volume (P less than 0.02), and for FEF25-75% (P less than 0.01) in favor of carbuterol. In the pediatric study, the difference between carbuterol and isoproterenol was significant (P less than 0.05) only for the FEF25-75% on the fifth day of treatment with the high dose administration of carbuterol. There was no associated toxicity of either drug with respect to electrocardiogram, blood chemistry, or subjective complaints. Tachyphylaxis (tolerance with time) to isoproterenol appeared to develop in one patient.

Annals of allergy.

A review of the world literature regarding the relative efficacy, duration and toxicity of the available beta-adrenergic bronchodilator aerosols for the treatment of asthma is presented. Many of these agents will soon become available in the United States and some familiarity with their actions is necessary for optimal care of asthmatic patients.

Suppression of histamine-induced pruritus by three antihistaminic drugs.

A double-blind crossover study of inhibition of histamine-induced pruritus by three commonly prescribed antihistamines was conducted on 28 normal subjects. Drugs used included diphenhydramine HCl (Benadryl), cyproheptadine (Periactin), hydroxyzine HCl (Atarax), and a lactose placebo in identical capsules. Intradermal histamine dose-response thresholds of pruritus were obtained before and after pretreatment with the three antihistamines and placebo in each subject. Analysis of data revealed a fivefold increase above baseline of the histamine dose required to produce pruritus following both cyproheptadine and placebo. This compared to a tenfold increase following diphenhydramine and a 750-fold increase following hydroxyzine HCl. The most common side effect was drowsiness, which occurred with all three drugs.