Rimantas Brucas

Gold Nanowire Based Electrical DNA Detection Using Rolling Circle Amplification

We present an electrical sensor that uses rolling circle amplification (RCA) of DNA to stretch across the gap between two electrodes, interact with metal nanoparticle seeds to generate an electrically conductive nanowire, and produce electrical signals upon detection of specific target DNA sequences. RCA is a highly specific molecular detection mechanism based on DNA probe circularization. With this technique, long single-stranded DNA with simple repetitive sequences are produced. Here we show that stretched RCA products can be metalized using silver or gold solutions to form metal wires. Upon metallization, the resistance drops from TΩ to kΩ for silver and to Ω for gold. Metallization is seeded by gold nanoparticles aligned along the single-stranded DNA product through hybridization of functionalized oligonucleotides. We show that combining RCA with electrical DNA detection produces results in readout with very high signal-to-noise ratio, an essential feature for sensitive and specific detection assays. Finally, we demonstrate detection of 10 ng of Escherichia coli genomic DNA using the sensor concept.

Self-organized MnAs quantum dots formed during annealing of GaMnAs under arsenic capping

Formation of MnAs quantum dots in a regular ring-like distribution has been found on molecular beam epitaxy grown (GaMn)As(100) surfaces after low-temperature annealing under As capping. The appearance of the dots depends on the thickness and Mn concentration in the (GaMn)As layer. With 5 at. % substitutional Mn the quantum dots showed up for layers thicker than 100 nm. For thinner layers the surfaces of the annealed samples are smooth and well ordered with 1×2 surface reconstruction, just as for as-grown (GaMn)As. The annealed surfaces are Mn rich, and are well suited for continued epitaxial growth.

Exponentially decaying magnetic coupling in sputtered thin film FeNi/Cu/FeCo trilayers

Magnetic coupling in trilayer films of FeNi/Cu/FeCo deposited on Si/SiO2 substrates have been studied. While the thicknesses of the FeNi and FeCo layers were kept constant at 100 angstrom, the thic ...

On the realization of artificial XY spin chains

Spin chains are the most elementary entities in the study of magnetic ordering behavior. The authors describe a route toward the realization of artificial XY spin chains. Using thin-film deposition ...

Tailoring the magnetodynamic properties of nanomagnets using magnetocrystalline and shape anisotropies

Magnetodynamical properties of nanomagnets are affected by the demagnetizing fields created by the same nanoelements. In addition, magnetocrystalline anisotropy produces an effective field that also contributes to the spin dynamics. We show how the dimensions of magnetic elements can be used to balance crystalline and shape anisotropies, and that this can be used to tailor the magnetodynamic properties. We study ferromagnetic ellipses patterned from a 10-nm-thick epitaxial Fe film with dimensions ranging from 50×150 to 150×450 nm. The study combines ferromagnetic resonance (FMR) spectroscopy with analytical calculations and micromagnetic simulations, and proves that the dynamical properties can be effectively controlled by changing the size of the nanomagnets. We also show how edge defects in the samples influence the magnetization dynamics. Dynamical edge modes localized along the sample edges are strongly influenced by edge defects, and this needs to be taken into account in understanding the full FMR spectrum.

Magnetic and transport properties of Ni81Fe19∕Al2O3 granular multilayers approaching the superparamagnetic limit

The magnetic and transport properties of Ni81Fe19∕Al2O3 granular multilayer films were studied in relation to their structural properties as the nominal thickness t of the permalloy (Ni81Fe19) layer was varied near the percolation limit: in the range of 8⩽t⩽16A while keeping the nominal thickness of the Al2O3 layers constant at 16A. A good structural quality of the multilayers was demonstrated by low angle x-ray reflectivity measurements, and transmission electron microscopy showed the transition from continuous permalloy layers separated by aluminium oxide layers for t=16A to metal grains dispersed in the insulator at t=8A. Magnetization measurements showed the gradual transition from ferromagnetic layers to superparamagnetic clusters and grains that successively become blocked as the temperature decreases. A strong correlation between transport and structural properties was observed in the temperature (T) dependence of the electrical resistance measured with the current in the plane in the range of 2⩽T⩽...

Temperature-dependent Gilbert damping of Co2FeAl thin films with different degree of atomic order

Half-metallicity and low magnetic damping are perpetually sought for spintronics materials, and full Heusler compounds in this respect provide outstanding properties. However, it is challenging to ...

Static and dynamic magnetic properties of bcc Fe49Co49V2 thin films on Si(1?0?0) substrates

Thin films of Fe49Co49V2 have been grown on Si(1?0?0) substrates by dc magnetron sputtering varying the substrate temperature in the range from room temperature (RT) to 600??C. The static magnetic properties of the films were studied using a superconducting quantum interference device and magneto-optic Kerr effect magnetometry, while x-ray diffraction and reflectivity measurements have been used for the evaluation of the structural properties and thickness of the prepared samples. The easy axis coercivity decreases from 60?Oe for the sample grown at RT to 15?Oe for the one grown at 400??C. We also studied the dynamic magnetic properties of the samples by using the high-frequency vector network analyser ferromagnetic resonance (FMR) technique. Results from FMR measurements show that the extrinsic linewidth decreases with increasing growth temperature up to 450??C and then increases with further increase of growth temperature. The source of the extrinsic linewidth is two-magnon scattering by small, weak inhomogeneities. The intrinsic Gilbert damping (?) follows a similar trend to the extrinsic linewidth, with the lowest damping constant ????0.005 found at a growth temperature of 450??C.

Magnetic coupling in asymmetric FeCoV/Ru/FeNi trilayers

We have investigated the magnetic anisotropy and interlayer coupling in trilayer films of permendur(100 \AA)/Ru/permalloy(100 \AA), with the thickness of the Ru spacer varying from 0 to 200 \AA. Wh ...

Positive correlation between coercivity and ferromagnetic resonance extrinsic linewidth in FeCoV/SiO2 films

Dynamic magnetic properties of Fe49Co49V2 thin films grown on Si/SiO2 substrates have been studied by using ferromagnetic resonance technique. The effective Lande g-factor, extrinsic linewidth, and Gilbert relaxation rate are all found to decrease in magnitude with increasing sample growth temperature from 20 °C to about 400–500 °C and then on further increase of the growth temperature to increase in magnitude. Samples grown at about 400–450 °C display the smallest coercivity, while the smallest value of the Gilbert relaxation rate of about 0.1 GHz is obtained for samples grown at 450–500 °C. An almost linear relation between extrinsic linewidth and coercivity is observed, which suggests a positive correlation between magnetic inhomogeneity, coercivity, and extrinsic linewidth. The Gilbert relaxation is found to decrease with increasing lattice constant, which is ascribed to the degree of structural order in the films.