Showing 1–23 of 23 results for author: Ilic, B

A lateral nanoflow assay reveals nanoplastic fluorescence heterogeneity

Authors: Kuo-Tang Liao, Andrew C. Madison, Adam L. Pintar, B. Robert Ilic, Craig R. Copeland, Samuel M. Stavis

Abstract: Plastic nanoparticles present technological opportunities and environmental concerns, but measurement challenges impede product development and hazard assessment. To meet these challenges, we advance a lateral nanoflow assay that integrates complex nanofluidic replicas, optical localization microscopy, and novel statistical analyses. We apply our sample-in-answer-out system to measure polystyrene… ▽ More Plastic nanoparticles present technological opportunities and environmental concerns, but measurement challenges impede product development and hazard assessment. To meet these challenges, we advance a lateral nanoflow assay that integrates complex nanofluidic replicas, optical localization microscopy, and novel statistical analyses. We apply our sample-in-answer-out system to measure polystyrene nanoparticles that sorb and carry hydrophobic fluorophores. An elegant scaling of surface forces automates advection and dominates diffusion to drive the analytical separation of colloidal nanoparticles by their steric diameters. Reference nanoparticles, with a mean of 99 nm and a standard deviation of 8.4 nm, test the unknown limits of silicone replicas to function as separation matrices. New calibrations correct aberrations from microscope and device, improving the accuracy of reducing single micrographs to joint histograms of steric diameter and fluorescence intensity. A dimensional model approaches the information limit of the system to discriminate size exclusion from surface adsorption, yielding errors of the mean ranging from 0.2 nm to 2.3 nm and errors of the standard deviation ranging from 2.2 nm to 4.2 nm. A hierarchical model accounts for metrological, optical, and dimensional variability to reveal a fundamental structure-property relationship. Intensity scales with diameter to the power of 3.6 +/- 0.5 at 95 % coverage, confounding basic concepts of surface adsorption or volume absorption. Distributions of fluorescivity - the product of the number density, absorption cross section, and quantum yield of an ensemble of fluorophores - are ultrabroad and asymmetric, limiting any inference from fluorescence intensity. This surprising characterization of common nanoplastics resets expectations for optimizing products, applying standards, and understanding byproducts. △ Less

Submitted 17 May, 2022; v1 submitted 29 December, 2020; originally announced January 2021.

Fabrication of micro fluidic cavities using Si-to-glass anodic bonding

Authors: N. Zhelev, T. S. Abhilash, R. G. Bennett, E. N. Smith, B. Ilic, J. M. Parpia, L. V. Levitin, X. Rojas, A. Casey, J. Saunders

Abstract: We demonstrate the fabrication of $\sim$1.08 $μ$m deep microfluidic cavities with characteristic size as large as 7 mm $\times$ 11 mm or 11 mm diameter, using a silicon$-$glass anodic bonding technique that does not require posts to act as separators to define cavity height. Since the phase diagram of $^3$He is significantly altered under confinement, posts might act as pinning centers for phase b… ▽ More We demonstrate the fabrication of $\sim$1.08 $μ$m deep microfluidic cavities with characteristic size as large as 7 mm $\times$ 11 mm or 11 mm diameter, using a silicon$-$glass anodic bonding technique that does not require posts to act as separators to define cavity height. Since the phase diagram of $^3$He is significantly altered under confinement, posts might act as pinning centers for phase boundaries. The previous generation of cavities relied on full wafer-bonding which is more prone to failure and requires dicing post-bonding, whereas the these cavities are made by bonding a pre-cut piece of Hoya SD-2 glass to a patterned piece of silicon in which the cavity is defined by etching. Anodic bonding was carried out at 425 $^{\circ}$C with 200 V, and we observe that pressurizing the cavity to failure ($>$ 30 bar pressure) results in glass breaking, rather than the glass-silicon bond separation. In this article, we discuss the detailed fabrication of the cavity, its edges, and details of the junction between the coin silver fill line and the silicon base of the cavity that enables a low internal-friction joint. This feature is important for mass coupling torsional oscillator experimental assays of the superfluid inertial contribution where a high quality factor ($Q$) improves frequency resolution. The surface preparation that yields well-characterized smooth surfaces to eliminate pinning sites, the use of transparent glass as a cover permitting optical access, low temperature capability and attachment of pressure-capable ports for fluid access may be features that are important in other applications. △ Less

Submitted 12 June, 2018; v1 submitted 2 May, 2018; originally announced May 2018.

Comments: 10 figures

Measuring frequency fluctuations in nonlinear nanomechanical resonators

Authors: Olivier Maillet, Xin Zhou, Rasul R. Gazizulin, Bojan R. Ilic, Jeevak M. Parpia, Olivier Bourgeois, Andrew D. Fefferman, Eddy Collin

Abstract: Advances in nanomechanics within recent years have demonstrated an always expanding range of devices, from top-down structures to appealing bottom-up MoS$_2$ and graphene membranes, used for both sensing and component-oriented applications. One of the main concerns in all of these devices is frequency noise, which ultimately limits their applicability. This issue has attracted a lot of attention r… ▽ More Advances in nanomechanics within recent years have demonstrated an always expanding range of devices, from top-down structures to appealing bottom-up MoS$_2$ and graphene membranes, used for both sensing and component-oriented applications. One of the main concerns in all of these devices is frequency noise, which ultimately limits their applicability. This issue has attracted a lot of attention recently, and the origin of this noise remains elusive up to date. In this Letter we present a very simple technique to measure frequency noise in nonlinear mechanical devices, based on the presence of bistability. It is illustrated on silicon-nitride high-stress doubly-clamped beams, in a cryogenic environment. We report on the same $T/f$ dependence of the frequency noise power spectra as reported in the literature. But we also find unexpected {\it damping fluctuations}, amplified in the vicinity of the bifurcation points; this effect is clearly distinct from already reported nonlinear dephasing, and poses a fundamental limit on the measurement of bifurcation frequencies. The technique is further applied to the measurement of frequency noise as a function of mode number, within the same device. The relative frequency noise for the fundamental flexure $δf/f_0$ lies in the range $0.5 - 0.01~$ppm (consistent with literature for cryogenic MHz devices), and decreases with mode number in the range studied. The technique can be applied to {\it any types} of nano-mechanical structures, enabling progresses towards the understanding of intrinsic sources of noise in these devices. △ Less

Submitted 8 June, 2018; v1 submitted 20 February, 2018; originally announced February 2018.

Comments: Published 7 may 2018

Journal ref: ACS Nano 2018

Topological quantization of energy transport in micro- and nano-mechanical lattices

Authors: Chih-Chun Chien, Kirill A. Velizhanin, Yonatan Dubi, B. Robert Ilic, Michael Zwolak

Abstract: Topological effects typically discussed in the context of quantum physics are emerging as one of the central paradigms of physics. Here, we demonstrate the role of topology in energy transport through dimerized micro- and nano-mechanical lattices in the classical regime, i.e., essentially "masses and springs". We show that the thermal conductance factorizes into topological and non-topological com… ▽ More Topological effects typically discussed in the context of quantum physics are emerging as one of the central paradigms of physics. Here, we demonstrate the role of topology in energy transport through dimerized micro- and nano-mechanical lattices in the classical regime, i.e., essentially "masses and springs". We show that the thermal conductance factorizes into topological and non-topological components. The former takes on three discrete values and arises due to the appearance of edge modes that prevent good contact between the heat reservoirs and the bulk, giving a length-independent reduction of the conductance. In essence, energy input at the boundary mostly stays there, an effect robust against disorder and nonlinearity. These results bridge two seemingly disconnected disciplines of physics, namely topology and thermal transport, and suggest ways to engineer thermal contacts, opening a direction to explore the ramifications of topological properties on nanoscale technology. △ Less

Submitted 21 March, 2018; v1 submitted 20 July, 2017; originally announced July 2017.

Comments: 6 pages, 3 figures; Supplemental information included as an ancillary file

Journal ref: Phys. Rev. B 97, 125425 (2018)

Dynamics of impurity attraction and repulsion of an intrinsic localized mode in a driven 1-D cantilever array

Authors: M. Sato, Y. Sada, W. Shi, S. Shige, T. Ishikawa, Y. Soga, B. E. Hubbard, B. Ilic, A. J. Sievers

Abstract: Both low frequency and high frequency impurity modes have been produced in a SiN micromechanical cantilever array by illumination with either an infrared or visible laser. When such laser-induced impurities are placed near a driven intrinsic localized mode (ILM) it is either repelled or attracted. By measuring the linear response spectrum for these two cases it was found that vibrational hopping o… ▽ More Both low frequency and high frequency impurity modes have been produced in a SiN micromechanical cantilever array by illumination with either an infrared or visible laser. When such laser-induced impurities are placed near a driven intrinsic localized mode (ILM) it is either repelled or attracted. By measuring the linear response spectrum for these two cases it was found that vibrational hopping of the ILM takes place when the natural frequency of the ILM and an even symmetry linear local mode are symmetrically located about the driven ILM frequency so that parametric excitation of these two linear modes is enhanced, amplifying the lateral motion of the ILM. Numerical simulations are consistent with these signature findings. It is also demonstrated that the correct sign of the observed interaction can be found with a harmonic lattice-impurity model but the magnitude of the effect is enhanced in a nonlinear lattice. △ Less

Submitted 20 December, 2014; originally announced December 2014.

Comments: to be published in CHAOS

Evanescent field optical readout of graphene mechanical motion at room temperature

Authors: Robin M. Cole, George A. Brawley, Vivek P. Adiga, Roberto De Alba, Jeevak M. Parpia, Bojan Ilic, Harold G. Craighead, Warwick P. Bowen

Abstract: Graphene mechanical resonators have recently attracted considerable attention for use in precision force and mass sensing applications. To date, readout of their oscillatory motion has typically required cryogenic conditions to achieve high sensitivity, restricting their range of applications. Here we report the first demonstration of evanescent optical readout of graphene motion, using a scheme w… ▽ More Graphene mechanical resonators have recently attracted considerable attention for use in precision force and mass sensing applications. To date, readout of their oscillatory motion has typically required cryogenic conditions to achieve high sensitivity, restricting their range of applications. Here we report the first demonstration of evanescent optical readout of graphene motion, using a scheme which does not require cryogenic conditions and exhibits enhanced sensitivity and bandwidth at room temperature. We utilise a high $Q$ microsphere to enable evanescent readout of a 70 $μ$m diameter graphene drum resonator with a signal-to-noise ratio of greater than 25 dB, corresponding to a transduction sensitivity of $S_{N}^{1/2} = $ 2.6 $\times 10^{-13}$ m $\mathrm{Hz}^{-1/2}$. The sensitivity of force measurements using this resonator is limited by the thermal noise driving the resonator, corresponding to a force sensitivity of $F_{min} = 1.5 \times 10^{-16}$ N ${\mathrm{Hz}}^{-1/2}$ with a bandwidth of 35 kHz at room temperature (T = 300 K). Measurements on a 30 $μ$m graphene drum had sufficient sensitivity to resolve the lowest three thermally driven mechanical resonances. △ Less

Submitted 7 August, 2014; v1 submitted 6 August, 2014; originally announced August 2014.

Comments: Fixed formatting errors in bibliography

Study of superfluid $^3$He under nanoscale confinement. A new approach to the investigation of superfluid $^3$He films

Authors: Lev Levitin, Robert Bennett, Andrew Casey, Brian Cowan, John Saunders, Dietmar Drung, Thomas Schurig, Jeevak Parpia, Bojan Ilic, Nikolay Zhelev

Abstract: We review recent experiments in which superfluid $^3$He has been studied under highly controlled confinement in nanofluidic sample chambers. We discuss the experimental challenges and their resolution. These methods open the way to a systematic investigation of the superfluidity of $^3$He films, and the surface and edge excitations of topological superfluids. We review recent experiments in which superfluid $^3$He has been studied under highly controlled confinement in nanofluidic sample chambers. We discuss the experimental challenges and their resolution. These methods open the way to a systematic investigation of the superfluidity of $^3$He films, and the surface and edge excitations of topological superfluids. △ Less

Submitted 23 December, 2013; originally announced December 2013.

Comments: 15 pages, 10 figures, submitted to special MicroKelvin edition of Journal of Low Temperature Physics

Simultaneous Electrical and Optical Readout of Graphene-Coated High Q Silicon Nitride Resonators

Authors: V. P. Adiga, R. De Alba, I. R. Storch, P. A. Yu, B. Ilic, R. A. Barton, S. Lee, J. Hone, P. L. McEuen, J. M. Parpia, H. G. Craighead

Abstract: We have fabricated and tested mechanical resonators consisting of a single-atomic-layer of graphene deposited on suspended silicon nitride membranes. With the addition of the graphene layer we retain the desirable mechanical properties of silicon nitride but utilize the electrical and optical properties of graphene to transduce resonant motion by both optical and electrical means. By positioning t… ▽ More We have fabricated and tested mechanical resonators consisting of a single-atomic-layer of graphene deposited on suspended silicon nitride membranes. With the addition of the graphene layer we retain the desirable mechanical properties of silicon nitride but utilize the electrical and optical properties of graphene to transduce resonant motion by both optical and electrical means. By positioning the graphene-on-silicon-nitride drums in a tunable optical cavity we observe position dependent damping and resonant frequency control of the devices due to optical absorption by graphene. △ Less

Submitted 9 July, 2013; originally announced July 2013.

Graphene Metallization of High-Stress Silicon Nitride Resonators for Electrical Integration

Authors: Sunwoo Lee, Vivekananda P. Adiga, Robert A. Barton, Arend van der Zande, Gwan-Hyoung Lee, B. Rob Ilic, Alexander Gondarenko, Jeevak M. Parpia, Harold G. Craighead, James Hone

Abstract: High stress stoichiometric silicon nitride resonators, whose quality factors exceed one million, have shown promise for applications in sensing and signal processing. Yet, electrical integration of the insulating silicon nitride resonators has been challenging, as depositing even a thin layer of metal degrades the quality factor significantly. In this work, we show that graphene used as a conducti… ▽ More High stress stoichiometric silicon nitride resonators, whose quality factors exceed one million, have shown promise for applications in sensing and signal processing. Yet, electrical integration of the insulating silicon nitride resonators has been challenging, as depositing even a thin layer of metal degrades the quality factor significantly. In this work, we show that graphene used as a conductive coating for Si3N4 membranes reduces the quality factor by less than 30 % on average, which is minimal when compared to the effect of conventional metallization layers such as chromium or aluminum. The electrical integration of Si3N4-Graphene (SiNG) heterostructure resonators is demonstrated with electrical readout and electro-static tuning of the frequency by up to 1 % per volt. These studies demonstrate the feasibility of hybrid graphene/nitride mechanical resonators in which the electrical properties of graphene are combined with the superior mechanical performance of silicon nitride. △ Less

Submitted 21 May, 2013; originally announced May 2013.

Comments: 8 pages, 5 figures, journal

Journal ref: Nano Letters vol 13, pp. 4275-4279 (2013)

Synchronous imaging for rapid visualization of complex vibration profiles in electromechanical microresonators

Authors: Yoav Linzon, Daniel J. Joe, Slava Krylov, Bojan Ilic, Juraj Topolancik, Jeevak M. Parpia, Halrod G. Craighead

Abstract: Synchronous imaging is used in dynamic space-domain vibration profile studies of capacitively driven, thin n+ doped poly-silicon microbridges oscillating at rf frequencies. Fast and high-resolution actuation profile measurements of micromachined resonators are useful when significant device nonlinearities are present. For example, bridges under compressive stress near the critical Euler value ofte… ▽ More Synchronous imaging is used in dynamic space-domain vibration profile studies of capacitively driven, thin n+ doped poly-silicon microbridges oscillating at rf frequencies. Fast and high-resolution actuation profile measurements of micromachined resonators are useful when significant device nonlinearities are present. For example, bridges under compressive stress near the critical Euler value often reveal complex dynamics stemming from a state close to the onset of buckling. This leads to enhanced sensitivity of the vibration modes to external conditions, such as pressure, temperatures, and chemical composition, the global behavior of which is conveniently evaluated using synchronous imaging combined with spectral measurements. We performed an experimental study of the effects of high drive amplitude and ambient pressure on the resonant vibration profiles in electrically-driven microbridges near critical buckling. Numerical analysis of electrostatically driven post-buckled microbridges supports the richness of complex vibration dynamics that are possible in such micro-electromechanical devices. △ Less

Submitted 31 October, 2011; originally announced October 2011.

Comments: 7 pages, 8 figure, submitted to Physical Review A

MSC Class: PACS - 87.64.-t; 07.10.Cm; 85.85.+j; 05.45.-a

High-Q Nanomechanics via Destructive Interference of Elastic Waves

Authors: I. Wilson-Rae, R. A. Barton, S. S. Verbridge, D. R. Southworth, B. Ilic, H. G. Craighead, J. M. Parpia

Abstract: Mechanical dissipation poses an ubiquitous challenge to the performance of nanomechanical devices. Here we analyze the support-induced dissipation of high-stress nanomechanical resonators. We develop a model for this loss mechanism and test it on silicon nitride membranes with circular and square geometries. The measured Q-values of different harmonics present a non-monotonic behavior which is suc… ▽ More Mechanical dissipation poses an ubiquitous challenge to the performance of nanomechanical devices. Here we analyze the support-induced dissipation of high-stress nanomechanical resonators. We develop a model for this loss mechanism and test it on silicon nitride membranes with circular and square geometries. The measured Q-values of different harmonics present a non-monotonic behavior which is successfully explained. For azimuthal harmonics of the circular geometry we predict that destructive interference of the radiated waves leads to an exponential suppression of the clamping loss in the harmonic index. Our model can also be applied to graphene drums under high tension. △ Less

Submitted 11 October, 2010; originally announced October 2010.

Comments: 8 pages, 1 figure

Journal ref: Phys. Rev. Lett. 106, 047205 (2011)

On-chip nano-manipulation of magnetic particles via domain walls conduits

Authors: P. Vavassori, M. Gobbi, M. Donolato, V. Metlushko, B. Ilic, M. Cantoni, D. Petti, S. Brivio, R. Bertacco

Abstract: The manipulation of geometrically constrained magnetic domain walls (DWs) in nanoscale magnetic strips has attracted much interest recently, with proposals for prospective memory and logic devices. Here we propose to use the high controllability of the motion of geometrically constrained DWs for the manipulation of individual nanoparticles on a chip with an active control of position at the nano… ▽ More The manipulation of geometrically constrained magnetic domain walls (DWs) in nanoscale magnetic strips has attracted much interest recently, with proposals for prospective memory and logic devices. Here we propose to use the high controllability of the motion of geometrically constrained DWs for the manipulation of individual nanoparticles on a chip with an active control of position at the nanometer scale. The proposed method exploits the fact that magnetic nanoparticles in solution can be captured by a DW, whose position can be manipulated with nanometric accuracy in a specifically designed magnetic nanowire structure. We show that the high control over DW nucleation, displacement, and annihilation processes in such structures can be used to capture, transport and release magnetic nanoparticles. As magnetic particles with functionalized surfaces are commonly used as molecule labels in several applications - including single molecule manipulation, separation, cells manipulation and biomagnetic sensing, the accurate control over the handling of the single magnetic nanoparticles becomes crucial as it may reflect the handling of the single molecules. The approach described here opens the path to the implementation and design of nano-transport lines, with application to single molecule study and lab-on-chip devices. In perspective, the easy integration on chip with sensors of domain walls and particles will allow for the realization of programmable circuits for molecular manipulation with continuous control of the desired process. △ Less

Submitted 20 March, 2009; originally announced March 2009.

Journal ref: J. Appl. Phys. 107, 09B301 (2010); Adv. Mater. 22, 2706 (2010)

On-chip manipulation of magnetic nanoparticles through domain walls conduits

Authors: P. Vavassori, M. Gobbi, M. Donolato, V. Metlushko, B. Ilic, M. Cantoni, D. Petti, S. Brivio, R. Bertacco

Abstract: The manipulation of geometrically constrained magnetic domain walls (DWs) in nanoscale magnetic strips has attracted much interest recently, with proposals for prospective memory and logic devices. Here we propose to use the high controllability of the motion of geometrically constrained DWs for the manipulation of individual nanoparticles on a chip with an active control of position at the nano… ▽ More The manipulation of geometrically constrained magnetic domain walls (DWs) in nanoscale magnetic strips has attracted much interest recently, with proposals for prospective memory and logic devices. Here we propose to use the high controllability of the motion of geometrically constrained DWs for the manipulation of individual nanoparticles on a chip with an active control of position at the nanometer scale. The proposed method exploits the fact that magnetic nanoparticles in solution can be captured by a DW, whose position can be manipulated with nanometric accuracy in a specifically designed magnetic nanowire structure. We show that the high control over DW nucleation, displacement, and annihilation processes in such structures can be used to capture, transport and release magnetic nanoparticles. As magnetic particles with functionalized surfaces are commonly used as molecule carriers or labels, the accurate control over the handling of the single magnetic nanoparticle is crucial for several applications including single molecule manipulation, separation, cells manipulation and biomagnetic sensing. △ Less

Submitted 20 March, 2009; originally announced March 2009.

Journal ref: Adv. Mater. 22, 2706-2710 (2010),J. Appl. Phys. 107, 09B301 (2010)

Vortex dynamics in confined stratified conditions

Authors: Farkhad G. Aliev, Juan F. Sierra, Ahmad A. Awad, Gleb N. Kakazei, Dong-Soo Han, Sang-Koog Kim, Vitali Metlushko, Bojan Ilic, Konstantin Y. Guslienko

Abstract: We report on linear spin dynamics in the vortex state of the Permalloy dots subjected to stratified (magnetic) field. We demonstrate experimentally and by simulations the existence of two distinct dynamic regimes corresponding to the vortex stable and metastable states. Breaking cylindrical symmetry leads to unexpected eigenmodes frequency splitting in the stable state and appearance of new eige… ▽ More We report on linear spin dynamics in the vortex state of the Permalloy dots subjected to stratified (magnetic) field. We demonstrate experimentally and by simulations the existence of two distinct dynamic regimes corresponding to the vortex stable and metastable states. Breaking cylindrical symmetry leads to unexpected eigenmodes frequency splitting in the stable state and appearance of new eigenmodes in the metastable state above the vortex nucleation field. Dynamic response in the metastable state strongly depends on relative orientation of the external rf pumping and the bias magnetic fields. These findings may be relevant for different vortex states in confined and stratified conditions. △ Less

Submitted 29 December, 2008; originally announced December 2008.

Self organized mode locking effect in superconductor / ferromagnet hybrids

Authors: J. Van de Vondel, A. V. Silhanek, V. Metlushko, P. Vavassori, B. Ilic, V. V. Moshchalkov

Abstract: The vortex dynamics in a low temperature superconductor deposited on top of a rectangular array of micrometer size permalloy triangles is investigated experimentally. The rectangular unit cell is such that neighboring triangles physically touch each other along one direction. This design stabilizes remanent states which differ from the magnetic vortex state typical of individual non-interacting… ▽ More The vortex dynamics in a low temperature superconductor deposited on top of a rectangular array of micrometer size permalloy triangles is investigated experimentally. The rectangular unit cell is such that neighboring triangles physically touch each other along one direction. This design stabilizes remanent states which differ from the magnetic vortex state typical of individual non-interacting triangles. Magnetic Force Microscopy images have revealed that the magnetic landscape of the template can be switched to an ordered configuration after magnetizing the sample with an in-plane field. The ordered phase exhibits a broad flux flow regime with relatively low critical current and a highly anisotropic response. This behavior is caused by the spontaneous formation of two separated rows of vortices and antivortices along each line of connected triangles. The existence of a clear flux flow regime even for zero external field supports this interpretation. The density of induced vortex-antivortex pairs is directly obtained using a high frequency measurement technique which allows us to resolve the discrete motion of vortices. Strikingly, the presence of vortex-antivortex rows gives rise to a self organized synchronized motion of vortices which manifests itself as field independent Shapiro steps in the current-voltage characteristics. △ Less

Submitted 5 November, 2008; originally announced November 2008.

Comments: 9 pages, 11 figures

Magnetic dipole induced guided vortex motion

Authors: N. Verellen, A. V. Silhanek, V. Metlushko, W. Gillijns, F. Gozzini, B. Ilic, V. V. Moshchalkov

Abstract: We present evidence of magnetically controlled guided vortex motion in a hybrid superconductor/ferromagnet nanosystem consisting of an Al film on top of a square array of permalloy square rings. When the rings are magnetized with an in-plane external field H, an array of point-like dipoles with moments antiparallel to H, is formed. The resulting magnetic template generates a strongly anisotropic… ▽ More We present evidence of magnetically controlled guided vortex motion in a hybrid superconductor/ferromagnet nanosystem consisting of an Al film on top of a square array of permalloy square rings. When the rings are magnetized with an in-plane external field H, an array of point-like dipoles with moments antiparallel to H, is formed. The resulting magnetic template generates a strongly anisotropic pinning potential landscape for vortices in the superconducting layer. Transport measurements show that this anisotropy is able to confine the flux motion along the high symmetry axes of the square lattice of dipoles. This guided vortex motion can be either re-routed by 90 degrees by simply changing the dipole orientation or even strongly suppressed by inducing a flux-closure magnetic state with very low stray fields in the rings. △ Less

Submitted 19 May, 2008; originally announced May 2008.

Comments: 5 pages, 3 figures

Dipole-induced vortex ratchets in superconducting films with arrays of micromagnets

Authors: C. C. de Souza Silva, A. V. Silhanek, J. Van de Vondel, W. Gillijns, V. Metlushko, B. Ilic, V. V. Moshchalkov

Abstract: We investigate the transport properties of superconducting films with periodic arrays of in-plane magnetized micromagnets. Two different magnetic textures are studied: a square array of magnetic bars and a close-packed array of triangular microrings. As confirmed by MFM imaging, the magnetic state of both systems can be adjusted to produce arrays of almost point-like magnetic dipoles. By carryin… ▽ More We investigate the transport properties of superconducting films with periodic arrays of in-plane magnetized micromagnets. Two different magnetic textures are studied: a square array of magnetic bars and a close-packed array of triangular microrings. As confirmed by MFM imaging, the magnetic state of both systems can be adjusted to produce arrays of almost point-like magnetic dipoles. By carrying out transport measurements with ac drive, we observed experimentally a recently predicted ratchet effect induced by the interaction between superconducting vortices and the magnetic dipoles. Moreover, we find that these magnetic textures produce vortex-antivortex patterns, which have a crucial role on the transport properties of this hybrid system. △ Less

Submitted 18 January, 2007; originally announced January 2007.

Comments: 4 pages, 4 figures

Journal ref: Phys. Rev. Lett. 98, 117005 (2007)

Tunable pinning in superconducting films with magnetic micro-loops

Authors: A. V. Silhanek, W. Gillijns, V. V. Moshchalkov, V. Metlushko, B. Ilic

Abstract: We study the flux pinning properties of superconductor/magnetic micro-rings lattice hybrid structures. The used open triangular micromagnets represent an eight-fold degree of freedom system, with six polarized and two flux-closure possible states. By conveniently choosing the magnetic state of the underlying rings it is possible to induce different pinning potentials. We show that the magnetic v… ▽ More We study the flux pinning properties of superconductor/magnetic micro-rings lattice hybrid structures. The used open triangular micromagnets represent an eight-fold degree of freedom system, with six polarized and two flux-closure possible states. By conveniently choosing the magnetic state of the underlying rings it is possible to induce different pinning potentials. We show that the magnetic vortex state with minimum stray field produces a weaker pinning in comparison with the polarized states. △ Less

Submitted 7 November, 2006; originally announced November 2006.

Journal ref: Appl. Phys. Lett. 89, 182505 (2006)

Anisotropy of Magnetization Reversal and Magnetoresistance in Square Arrays of Permalloy Nano-Rings

Authors: A. V. Goncharov, A. A. Zhukov, V. V. Metlushko, G. Bordignon, H. Fangohr, C. H. de Groot, J. Unguris, W. C. Uhlig, G. Karapetrov, B. Ilic, P. A. J. de Groot

Abstract: Magnetization reversal mechanisms and impact of magnetization direction are studied in square arrays of interconnected circular permalloy nanorings using MOKE, local imaging, numerical simulations and transport techniques. Magnetization reversal mechanisms and impact of magnetization direction are studied in square arrays of interconnected circular permalloy nanorings using MOKE, local imaging, numerical simulations and transport techniques. △ Less

Submitted 5 April, 2006; originally announced April 2006.

Commensurability effects induced by a periodic array of nanoscale anti-dots in Nb superconductor

Authors: A. A. Zhukov, E. T. Filby, P. A. J. de Groot, V. V. Metlushko, B. Ilic

Abstract: We study the interactions of the vortex lattice with a periodic square array of holes in a superconducting Nb film using magnetic and resistive measurements. Three different temperature regions have been observed. They are governed by interplay between vortex-vortex interactions and pinning by holes. At low temperatures flux jumps suppress the commensurability anomalies. In all measurements a pe… ▽ More We study the interactions of the vortex lattice with a periodic square array of holes in a superconducting Nb film using magnetic and resistive measurements. Three different temperature regions have been observed. They are governed by interplay between vortex-vortex interactions and pinning by holes. At low temperatures flux jumps suppress the commensurability anomalies. In all measurements a peak has been observed close to commensurate states 5-7. The Cole-Cole plot reveals significant changes in the flux penetration mechanism at this point. △ Less

Submitted 22 October, 2003; originally announced October 2003.

Comments: 12 pages, 5 figures

Extraction of domain-specific magnetization reversal for nanofabricated periodic arrays using soft x-ray resonant magnetic scattering

Authors: D. R. Lee, J. W. Freeland, G. Srajer, S. K. Sinha, V. Metlushko, B. Ilic

Abstract: A simple scheme to extract the magnetization reversals of characteristic magnetic domains on nanofabricated periodic arrays from soft x-ray resonant magnetic scattering (SXRMS) data is presented. The SXRMS peak intensities from a permalloy square ring array were measured with field cycling using circularly polarized soft x-rays at the Ni L$_3$ absorption edge. Various SXRMS hysteresis loops obse… ▽ More A simple scheme to extract the magnetization reversals of characteristic magnetic domains on nanofabricated periodic arrays from soft x-ray resonant magnetic scattering (SXRMS) data is presented. The SXRMS peak intensities from a permalloy square ring array were measured with field cycling using circularly polarized soft x-rays at the Ni L$_3$ absorption edge. Various SXRMS hysteresis loops observed at different diffraction orders enabled the determination of the magnetization reversal of each magnetic domain using a simple linear algebra. The extracted domain-specific hysteresis loops reveal that the magnetization of the domain parallel to the field is strongly pinned, while that of the perpendicular domain rotates continuously. △ Less

Submitted 29 September, 2003; originally announced September 2003.

Comments: 4 pages, 4 figures

Lock-in to commensurate states induced by a periodic array of nanoscale anti-dots in Nb superconductor

Authors: A. A. Zhukov, P. A. J. de Groot, V. V. Metlushko, B. Ilic

Abstract: We study the interactions of the vortex lattice with a periodic square array of holes in a superconducting Nb film. Using high resolution magnetic field measurements of electrical losses, extremely narrow states with a magnetic field width reaching 1% of the matching field value are found at the commensurate points. They are accompanied by pronounced harmonic generation in response to ac modulat… ▽ More We study the interactions of the vortex lattice with a periodic square array of holes in a superconducting Nb film. Using high resolution magnetic field measurements of electrical losses, extremely narrow states with a magnetic field width reaching 1% of the matching field value are found at the commensurate points. They are accompanied by pronounced harmonic generation in response to ac modulation of the magnetic field or current. We relate these sharp anomalies to a locked commensurate state of the Mott insulator type. △ Less

Submitted 25 July, 2002; originally announced July 2002.

Comments: 7 pages, 4 figures

Vortex configurations, matching, and domain structure in large arrays of artificial pinning centers

Authors: S. B. Field, S. S. James, J. Barentine, V. Metlushko, G. Crabtree, H. Shtrikman, B. Ilic, S. R. J. Brueck

Abstract: High-resolution scanning Hall probe microscopy has been used to image vortex configurations in very large periodic arrays of artificial pinning sites. Strong matching effects are seen at fields where either one or two vortices can sit at a site; with three vortices per site, however, no clear matching is observed. Matching effects have been also been observed at several fractional multiples of t… ▽ More High-resolution scanning Hall probe microscopy has been used to image vortex configurations in very large periodic arrays of artificial pinning sites. Strong matching effects are seen at fields where either one or two vortices can sit at a site; with three vortices per site, however, no clear matching is observed. Matching effects have been also been observed at several fractional multiples of the matching field, including 1/5, 1/4, 1/3, 1/2, and 3/4. These fractional values are characterized by striking domain structure and grain boundaries. △ Less

Submitted 25 March, 2000; originally announced March 2000.

Comments: 4 pages, 5 figures