Eric W Moore

Cornell University, New York City, NY, United States

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Publications (18)37.53 Total impact

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    ABSTRACT: We introduce a spin-modulation protocol for force-gradient detection of magnetic resonance that enables the real-time readout of longitudinal magnetization in an electron spin resonance experiment involving fast-relaxing spins. We applied this method to observe a prompt change in longitudinal magnetization following the microwave irradiation of a nitroxide-doped perdeuterated polystyrene film having an electron spin-lattice relaxation time of [Formula: see text]. The protocol allowed us to discover a large, long-lived cantilever frequency shift. Based on its magnitude, lifetime, and field dependence, we tentatively attribute this persistent signal to deuteron spin magnetization created via transfer of polarization from nitroxide spins.
    Applied Physics Letters 04/2013; 102(13):132404. · 3.52 Impact Factor
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    ABSTRACT: Magnetic resonance force microscopy (MRFM), which combines magnetic resonance imaging with scanning probe microscopy together, is capable of performing ultra-sensitive detection of spin magnetization. In an attempt to observe dynamic nuclear polarization (DNP) in an MRFM experiment, which could possibly further improve its sensitivity towards a single proton spin, a film of perdeuterated polystyrene doped with a nitroxide electron-spin probe was prepared. A high-compliance cantilever with a 4-μm-diameter magnetic tip was brought near the film at a temperature of 7.3 K and in a background magnetic field of ~0.6 T. The film was irradiated with 16.7-GHz microwaves while the resulting transient change in cantilever frequency was recorded in real time. In addition to observing the expected prompt change in cantilever frequency due to saturation of the nitroxide's electron-spin magnetization, we observed a persistent cantilever frequency change. Based on its magnitude, lifetime, and field dependence, we tentatively attribute the persistent signal to polarized deuteron magnetization created via transfer of magnetization from electron spins. Further measurements of the persistent signal's dependence on the cantilever amplitude and tip-sample separation are presented and explained by the cross-effect DNP mechanism in high magnetic field gradients.
    IEEE Transactions on Magnetics 01/2013; 49(7):3528-3532. · 1.42 Impact Factor
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    ABSTRACT: In-plane to out-of-plane magnetization switching in a single nickel nanorod affixed to an attonewton-sensitivity cantilever was studied at cryogenic temperatures. We observe multiple sharp, simultaneous transitions in cantilever frequency, dissipation, and frequency jitter associated with magnetic switching through distinct intermediate states. These findings suggest a new route for detecting magnetic fields at the nanoscale.
    Journal of Applied Physics 04/2012; 111(8):83911-839117. · 2.21 Impact Factor
  • Sanggap Lee, Eric W Moore, John A Marohn
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    ABSTRACT: We report a unified framework describing all existing protocols for spin manipulation and signal creation in frequency-modulation magnetic resonance force microscopy using classical perturbation theory. The framework is well suited for studying the dependence of the frequency shift on the cantilever amplitude via numerical simulation. We demonstrate the formalism by recovering an exact result for a single spin signal and by simulating, for the first time as a function of cantilever amplitude, the frequency shift due to a volume of noninteracting spins inverted by an adiabatic rapid passage. We show that an optimal cantilever amplitude exists that maximizes the signal. Our findings suggest that understanding the amplitude dependence of the spin signal will be important for designing future high-sensitivity experiments.
    Physical Review B 04/2012; 85(16):165447-165453. · 3.66 Impact Factor
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    ABSTRACT: Mechanically detecting electron spin resonance has opened up new avenues of performing magnetic resonance detection and imaging to an individual spin-labeled macromolecule. The large gradient field from the magnetic tipped cantilever creates selective resonance conditions for each spin label in the macromolecule. The detection is made through the shifts in the cantilever self-oscillating frequency due to the back action on to the cantilever from the resonating spin polarization. In order to improving the detection sensitivity, great efforts have been made to transfer polarization of electron spins to nearby nuclear spins. Here, we reported an anomalous frequency shift in our mechanically detected ESR experiment. This ESR induced anomalous frequency shift, however is larger in amplitude and slower in relaxation time than ESR frequency shift. We will discuss that this anomalous polarization are potentially due to the dynamic nuclear polarization (DNP) mechanism.
    02/2012;
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    ABSTRACT: The authors report a method for rapidly prototyping attonewton-sensitivity cantilevers with custom-fabricated tips and illustrate the method by preparing tips consisting of a magnetic nanorod overhanging the leading edge of the cantilevers. Micron-long nickel nanorods with widths of 120-220 nm were fabricated on silicon chips by electron beam lithography, deposition, and lift-off. Each silicon chip, with its integral nanomagnet, was attached serially to a custom-fabricated attonewton-sensitivity cantilever using focused ion beam manipulation. The magnetic nanorod tips were prepared with and without an alumina capping layer, and the minimum detectable force and tip magnetic moment of the resulting cantilevers was characterized by cantilever magnetometry. The results indicate that this serial but high-yield approach is an effective way to rapidly prepare and characterize magnetic tips for the proposed single-electron-spin and single-proton magnetic resonance imaging experiments. The approach also represents a versatile route for affixing essentially any vacuum-compatible sample to the leading edge of an attonewton-sensitivity cantilever.
    Journal of vacuum science & technology. B, Microelectronics and nanometer structures: processing, measurement, and phenomena: an official journal of the American Vacuum Society 05/2011; 29(3):32001. · 1.36 Impact Factor
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    ABSTRACT: Magnetic resonance force microscopy offers exciting possibilities for imaging protons and electrons in native and spin-labeled biomolecules. The central component of a magnetic resonance force microscope experiment is a custom-fabricated attonewton-sensitivity cantilever with an overhanging magnetic-nanorod tip. We have recently developed a method for making precision tips which involves 1) fabricating overhanging magnetic tips on shortened mock cantilevers, 2) using focused ion beam milling and deposition (FIB/FID) to cut the mock cantilever (and attached tip) free from the substrate, and then 3) attaching the released structure to a full-length high-sensitivity cantilever. The resulting magnets have been characterized by cantilever magnetometry, high-resolution transmission electron microscopy (HR-TEM), and nanometer-resolution electron energy loss spectroscopy (EELS). This approach to fabrication and analysis is allowing us to optimize tips for proposed single-electron-spin imaging experiments in a very short time. Rapid access to such high-quality tips will significantly advance our ability to image individual biomolecules and macromolecular complexes.
    03/2011;
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    ABSTRACT: Torque magnetometry, using attonewton-sensitivity cantilevers, is extremely sensitive to both the average magnetic moment and magnetization fluctuations within a small magnetic tip. Operating at T = 4 : K with such a system, we study in-plane to out-of-plane magnetization switching in a single, electron beam lithographically defined nickel nanorod, of radius r 50 : nm. Numerous, simultaneous, peaks are visible in cantilever frequency, dissipation and jitter as well as Barkhausen like steps. A analytic model is developed that achieves order of magnitude agreement with the frequency and dissipation peaks.
    03/2011;
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    ABSTRACT: We present data and theoretical signal and noise calculations for a protocol using parametric amplification to evade the inherent tradeoff between signal and detector frequency noise in force-gradient magnetic resonance force microscopy signals, which are manifested as a modulated frequency shift of a high- Q microcantilever. Substrate-induced frequency noise has a 1/f frequency dependence, while detector noise exhibits an f^2 dependence on modulation frequency f. Modulation of sample spins at a frequency that minimizes these two contributions typically results in a surface frequency noise power an order of magnitude or more above the thermal limit and may prove incompatible with sample spin relaxation times as well. We show that the frequency modulated force-gradient signal can be used to excite the fundamental resonant mode of the cantilever, resulting in an audio frequency amplitude signal that is readily detected with a low-noise fiber optic interferometer. This technique allows us to modulate the force-gradient signal at a sufficiently high frequency so that substrate-induced frequency noise is evaded without subjecting the signal to the normal f^2 detector noise of conventional demodulation.
    03/2011;
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    ABSTRACT: We have batch-fabricated cantilevers with ∼100 nm diameter nickel nanorod tips and force sensitivities of a few attonewtons at 4.2 K. The magnetic nanorods were engineered to overhang the leading edge of the cantilever, and consequently the cantilevers experience what we believe is the lowest surface noise ever achieved in a scanned probe experiment. Cantilever magnetometry indicated that the tips were well magnetized, with a ≤ 20 nm dead layer; the composition of the dead layer was studied by electron microscopy and electron energy loss spectroscopy. In what we believe is the first demonstration of scanned probe detection of electron-spin resonance from a batch-fabricated tip, the cantilevers were used to observe electron-spin resonance from nitroxide spin labels in a film via force-gradient-induced shifts in cantilever resonance frequency. The magnetic field dependence of the magnetic resonance signal suggests a nonuniform tip magnetization at an applied field near 0.6 T.
    ACS Nano 11/2010; 4(12):7141-50. · 12.03 Impact Factor
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    ABSTRACT: We introduce and demonstrate a method of measuring small force gradients acting on a harmonic oscillator in which the force-gradient signal of interest is used to parametrically up-convert a forced oscillation below resonance into an amplitude signal at the oscillator's resonance frequency. The approach, which we demonstrate in a mechanically detected electron spin resonance experiment, allows the force-gradient signal to evade detector frequency noise by converting a slowly modulated frequency signal into an amplitude signal.
    Applied Physics Letters 07/2010; 97(4). · 3.52 Impact Factor
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    ABSTRACT: A straightforward way to enhance sensitivity and spatial resolution of magnetic resonance force microscopy is approaching an attonewton-sensitivity cantilever having a 100-nm diameter magnetic tip to closer than 50 nm proximity of spin samples. When one detects magnetic resonance via cantilever frequency-shift measurements, cantilevers experience a drastic increase of surface frequency noise at small tip-sample separations. Even along with lessening contribution of conducting tip charge to the noise, surface frequency noise remains as a remarkable obstacle. On the other hand, surface force noise was found to remain surprisingly unchanged up until about 10 nm with custom-fabricated overhanging magnetic nanorod tips. We thus developed a novel protocol, reading out a force-gradient (frequency-shift) spin signal as a force (amplitude change), harnessing spin-driven parametric amplification to evade surface noise and detector noise in force-gradient detected scanned probe magnetic resonance, presenting a demonstration on ESR from nitroxide spin probe in a thin film.
    03/2010;
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    ABSTRACT: Magnetic resonance force microscopy is a promising route to 3-dimensional nanoscale imaging of organic materials due to its high sensitivity and isotopic specificity. Labeling of proteins, DNA and biomolecular assemblies with free radical labels for inductive detection are well established techniques, although many of these radical's relaxation times are too short to support previously demonstrated techniques for single electron detection by magnetic resonance force microscopy. We report on our efforts toward sub-single electron sensitivity on organic radicals using batch fabricated 100 nm nickel nanorod tipped ultrasensitive cantilevers.
    03/2010;
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    ABSTRACT: We report an approach that extends the applicability of ultrasensitive force-gradient detection of magnetic resonance to samples with spin-lattice relaxation times (T (1)) as short as a single cantilever period. To demonstrate the generality of the approach, which relies on detecting either cantilever frequency or phase, we used it to detect electron spin resonance from a T (1) = 1 ms nitroxide spin probe in a thin film at 4.2 K and 0.6 T. By using a custom-fabricated cantilever with a 4 microm-diameter nickel tip, we achieve a magnetic resonance sensitivity of 400 Bohr magnetons in a 1 Hz bandwidth. A theory is presented that quantitatively predicts both the lineshape and the magnitude of the observed cantilever frequency shift as a function of field and cantilever-sample separation. Good agreement was found between nitroxide T (1) 's measured mechanically and inductively, indicating that the cantilever magnet is not an appreciable source of spin-lattice relaxation here. We suggest that the new approach has a number of advantages that make it well suited to push magnetic resonance detection and imaging of nitroxide spin labels in an individual macromolecule to single-spin sensitivity.
    Proceedings of the National Academy of Sciences 12/2009; 106(52):22251-6. · 9.81 Impact Factor
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    ABSTRACT: Nitroxide spin labels are widely used in electron spin resonance studies of biological and polymeric systems. Magnetic resonance force microscopy (MRFM) is a magnetic resonance technique that couples the high spatial resolution of a scanning probe microscope with the species selectivity of magnetic resonance. We report on our investigations of 4-amino TEMPO, a nitroxide spin label, by force-gradient MRFM. Our microscope operates at high vacuum in liquid helium, using a custom fabricated ultra-soft silicon cantilever in the magnet-on-cantilever geometry. An 18 GHz gap coupled microstripline resonator supplies the transverse field.
    03/2009;
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    ABSTRACT: Single Ni nanorods having 50 to 100 nm diameter were integrated as the tip of ultra-sensitive cantilevers, having a force sensitivity of 8 aN/Hz^1/2 at 4.2 K, designed for use in scanned-probe magnetic resonace force microscopy. We measured cantilever frequency, dissipation, and frequency fluctuations as a function of magnetic field, applied along both the easy axis and the hard axis of the nanorods while the cantilevers were self-oscillated. The nanorods exhibit bulk magnetization. Hard-axis magnetometry experiments show the nanorods have Bswitch˜ 300 mT, in which the magnetization switches from being orthogonal to being parallel to the applied field, and the three observables each show multiple sharp peaks. We find the cantilever frequency shift is well described by modeling the tip as a single-domain of uniformly-magnetized spins interacting with the applied field (the Stoner-Wohlfarth model).
    03/2009;
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    ABSTRACT: Magnetic resonance force microscopy (MRFM) is a technique that may one day allow us to acquire magnetic resonance images of single molecules. To date we have demonstrated that MRFM can achieve a sensitivity of ˜10^5 proton spins, using a custom-fabricated silicon cantilever with a 9 micron diameter magnet tip. By making improved magnetic tips and mitigating surface dissipation, it may be possible to achieve single-proton sensitivity. Achieving the attonewton force sensitivity necessary to image single proton spins requires custom-fabricating cantilevers with extreme dimensions. In MRFM the force exerted on the cantilever, per spin, is proportional to the field gradient from the cantilever's magnetic tip. Achieving single proton sensitivity therefore also requires dramatically reducing magnet size. We have developed an electron-beam-lithography(EBL) process for batch fabricating nanoscale tip magnets on ultrasensitive silicon cantilevers. Research by our group has shown that surface induced dissipation is a major source of noise, which can be minimized by fabricating the magnets overhanging the end of the cantilever. We will present 50-600 nm wide nickel overhanging magnets fabricated by EBL and isotropic plasma etching. With our designed cantilever, we expect a sensitivity of better than 10^3 protons.
    01/2009;
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    ABSTRACT: Nitroxide spin labels, such as 4-amino TEMPO can be used to as environmental, conformal and structural probes in biological and polymer systems. We report on our efforts to detect electron spin resonance of 4-amino TEMPO in a polymer matrix using the magnetic resonance force microscope as a proof of concept for future experiments on spin labeled proteins. Our microscope operates at high vacuum and low temperature, using a custom fabricated single crystal silicon cantilever in the magnet-on-cantilever geometry. The applied field is provided by a microstripline resonator at 18 GHz.
    03/2008;