Gene Siegel

Enzymatic glucose sensor based on Au nanoparticle and plant-like ZnO film modified electrode.

A novel electrochemical glucose sensor was developed by employing a composite film of plant-like Zinc oxide (ZnO) and chitosan stabilized spherical gold nanoparticles (AuNPs) on which Glucose oxidaze (GOx) was immobilized. The ZnO was deposited on an indium tin oxide (ITO) coated glass and the AuNPs of average diameter of 23 nm were loaded on ZnO as the second layer. The prepared ITO/ZnO/AuNPs/GOx bioelectrode exhibited a low value of Michaelis-Menten constant of 1.70 mM indicating a good bio-matrix for GOx. The studies of electrochemical properties of the electrode using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) showed that, the presence of AuNPs provides significant enhancement of the electron transfer rate during redox reactions. The linear sweep voltammetry (LSV) shows that the ITO/ZnO/AuNPs/GOx based sensor has a high sensitivity of 3.12 μA·mM(-1)·cm(-2) in the range of 50 mg/dL to 400 mg/dL glucose concentration. The results show promising application of the gold nanoparticle modified plant-like ZnO composite bioelectrode for electrochemical sensing of glucose.

Robust longitudinal spin-Seebeck effect in Bi-YIG thin films

In recent years, the coupling of magnetic insulators (bismuth-doped yttrium iron garnet, Bi-YIG) with platinum has garnered significant interest in spintronics research due to applicability as spin-current-driven thermoelectric coatings. These coatings bridge the gap between spintronics technologies and thermoelectric materials, providing a novel means of transforming waste heat into electricity. However, there remain questions regarding the origins of the spin-Seebeck effect (SSE) as well as claims that observed effects are a manifestation of magnetic proximity effects, which would induce magnetic behavior in platinum. Herewith we provide support that the voltages observed in the Bi-YIG/Pt films are purely SSE voltages. We reaffirm claims that magnon transport theory provides an ample basis for explaining SSE behavior. Finally, we illustrate the advantages of pulsed-laser deposition, as these Bi-YIG films possess large SSE voltages (even in absence of an external magnetic field), as much as twice those of films fabricated via solution-based methods.

Growth of centimeter-scale atomically thin MoS2 films by pulsed laser deposition

We are reporting the growth of single layer and few-layer MoS2 films on single crystal sapphire substrates using a pulsed-laser deposition technique. A pulsed KrF excimer laser (wavelength: 248 nm; pulse width: 25 ns) was used to ablate a polycrystalline MoS2 target. The material thus ablated was deposited on a single crystal sapphire (0001) substrate kept at 700 °C in an ambient vacuum of 10−6 Torr. Detailed characterization of the films was performed using atomic force microscopy (AFM), Raman spectroscopy, UV-Vis spectroscopy, and photoluminescence (PL) measurements. The ablation of the MoS2 target by 50 laser pulses (energy density: 1.5 J/cm2) was found to result in the formation of a monolayer of MoS2 as shown by AFM results. In the Raman spectrum, A1g and E12g peaks were observed at 404.6 cm−1 and 384.5 cm−1 with a spacing of 20.1 cm−1, confirming the monolayer thickness of the film. The UV-Vis absorption spectrum exhibited two exciton absorption bands at 672 nm (1.85 eV) and 615 nm (2.02 eV), with a...

Magnetic characteristics of phase-separated CeO2: Co thin films

Herewith, we are reporting the magnetic properties of phase-separated Co-doped CeO2 films (with a Ce:Co atomic-ratio of 0.97:0.03) grown on single-crystal SrTiO3 (001) substrates. A comparison of the magnetic characteristics of these films with those of homogenously doped CeO2:Co films of the same composition illustrates the significant differences in their magnetic behavior. These behavioral characteristics provide a model for determining if the magnetic behavior observed in this, as well as in other diluted magnetic dielectric systems, is due to homogeneous doping, a mixture of doping and transition metal cluster formation, or exists purely as a result of transition metal clustering.

A simple and selective colorimetric mercury (II) sensing system based on chitosan stabilized gold nanoparticles and 2,6-pyridinedicarboxylic acid

The development of simple and cost-effective methods for the detection and treatment of Hg2+ in the environment is an important area of research due to the serious health risk that Hg2+ poses to humans. Colorimetric sensing based on the induced aggregation of nanoparticles is of great interest since it offers a low cost, simple, and relatively rapid procedure, making it perfect for on-site analysis. Herein we report the development of a simple colorimetric sensor for the selective detection and estimation of mercury ions in water, based on chitosan stabilized gold nanoparticles (AuNPs) and 2,6-pyridinedicarboxylic acid (PDA). In the presence of Hg2+, PDA induces the aggregation of AuNPs, causing the solution to change colors varying from red to blue, depending on the concentration of Hg2+. The formation of aggregated AuNPs in the presence of Hg2+ was confirmed using transmission electron microscopy (TEM) and UV-Vis spectroscopy. The method exhibits linearity in the range of 300nM to 5μM and shows excellent selectivity towards Hg2+ among seventeen different metal ions and was successfully applied for the detection of Hg2+ in spiked river water samples. The developed technique is simple and superior to the existing techniques in that it allows detection of Hg2+ using the naked eye and simple and rapid colorimetric analysis, which eliminates the need for sophisticated instruments and sample preparation methods.

Spintronic detection of interfacial magnetic switching in a paramagnetic thin film of tris(8-hydroxyquinoline)iron(III)

Dali Sun,1,* Christopher M. Kareis,2 Kipp J. van Schooten,1 Wei Jiang,3 Gene Siegel,3 Marzieh Kavand,1 Royce A. Davidson,2 William W. Shum,2 Chuang Zhang,1 Haoliang Liu,1 Ashutosh Tiwari,3 Christoph Boehme,1 Feng Liu,3 Peter W. Stephens,4 Joel S. Miller,2 and Z. Valy Vardeny1,† 1Department of Physics & Astronomy, University of Utah, Salt Lake City, Utah 84112, USA 2Department of Chemistry, University of Utah, Salt Lake City, Utah 84112, USA 3Department of Material Science & Engineering, University of Utah, Salt Lake City, Utah 84112, USA 4Department of Physics & Astronomy, Stony Brook University, Stony Brook, New York 11794, USA (Received 26 May 2016; revised manuscript received 11 November 2016; published 17 February 2017)

Temperature dependence of the spin relaxation in highly degenerate ZnO thin films

Zinc oxide is considered a potential candidate for fabricating next-generation transparent spintronic devices. However, before this can be achieved, a thorough scientific understanding of the various spin transport and relaxation processes undergone in this material is essential. In the present paper, we are reporting our investigations into these processes via temperature dependent Hanle experiments. ZnO thin films were deposited on c-axis sapphire substrates using a pulsed laser deposition technique. Careful structural, optical, and electrical characterizations of the films were performed. Temperature dependent non-local Hanle measurements were carried out using an all-electrical scheme for spin injection and detection over the temperature range of 20–300 K. From the Hanle data, spin relaxation time in the films was determined at different temperatures. A detailed analysis of the data showed that the temperature dependence of spin relaxation time follows the linear-in-momentum Dyakonov-Perel mechanism.

Spin Current Response in Bi-YIG/Pt Thin Film Heterostructures Induced by Gamma Radiation

Most of the present solid-state nuclear radiation detectors require cooling to low temperatures for their operation. Herewith, we are reporting the observation of a room temperature spin current response to gamma radiation from a novel Bi-YIG/Pt thin film hetero-structure device. A pulsed laser deposition technique was used to fabricate a 45-nm thick Bi-YIG film over which a 5-nm thick Pt film was deposited by an e-beam technique. Films were thoroughly characterized using energy dispersive X-ray spectroscopy and atomic force microscopy. Sensitivity of the Bi-YIG/Pt thin film device to gamma radiation was tested by investigating the strength of the inverse spin Hall effect voltage generated in the Pt layer on exposing the device to gamma radiation flux. Our results show that even for a very small flux source, a room-temperature spin current response is detectable.