Publications

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    ABSTRACT: We have fabricated and tested two-dimensional arrays of YBa2Cu3O7−δ superconducting quantum interference devices. The arrays contain over 36 000 nano Josephson junctions fabricated from ion irradiation of YBa2Cu3O7−δ through narrow slits in a resist-mask that was patterned with electron beam lithography and reactive ion etching. Measurements of current-biased arrays in magnetic field exhibit large voltage modulations as high as 30 mV.
    Applied Physics Letters 01/2014; 104(6):062601-062601-3. · 3.79 Impact Factor
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    ABSTRACT: We report room-temperature electric field noise measurements combined with in-situ surface characterization and cleaning of a microfabricated ion trap. We used a single-ion electric field noise sensor in combination with surface cleaning and analysis tools, to investigate the relationship between electric field noise from metal surfaces in vacuum and the composition of the surface. These experiments were performed in a novel setup that integrates ion trapping capabilities with surface analysis tools. We find that surface cleaning of an aluminum-copper surface significantly reduces the level of electric field noise, but the surface does not need to be atomically clean to show noise levels comparable to those of the best cryogenic traps. The post-cleaning noise levels are low enough to allow fault-tolerant trapped-ion quantum information processing on a microfabricated surface trap.
    07/2013;
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    ABSTRACT: The authors demonstrate a low pressure reactive ion etching process capable of patterning nanometer scale angled sidewalls and three dimensional structures in photoresist. At low pressure, the plasma has a large dark space region where the etchant ions have very large highly directional mean free paths. Mounting the sample entirely within this dark space allows for etching at angles relative to the cathode with minimal undercutting, resulting in high-aspect ratio nanometer scale angled features. By reversing the initial angle and performing a second etch, the authors create three-dimensional mask profiles.
    Journal of Vacuum Science & Technology B Microelectronics and Nanometer Structures 01/2013; 31(1):0604-. · 1.36 Impact Factor
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    ABSTRACT: To mitigate the ever worsening bandwidth crisis of current data communication architectures, here we present nanoscale integrated optoelectronics devices including multiplexed nanolasers and high speed graphene optical modulators for future photonic integrations with high density.
    Communications and Photonics Conference (ACP), 2012 Asia; 01/2012
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    ABSTRACT: We demonstrated the parallel maskless plasmonic nanolithography at 10 meter/second. This is a low-cost high-throughput nano-fabrication scheme which has the potential of a few orders of magnitude higher throughput than current maskless techniques.
    Joint International Symposium on Optical Memory and Optical Data Storage; 07/2011
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    ABSTRACT: Integrated optical modulators with high modulation speed, small footprint and large optical bandwidth are poised to be the enabling devices for on-chip optical interconnects. Semiconductor modulators have therefore been heavily researched over the past few years. However, the device footprint of silicon-based modulators is of the order of millimetres, owing to its weak electro-optical properties. Germanium and compound semiconductors, on the other hand, face the major challenge of integration with existing silicon electronics and photonics platforms. Integrating silicon modulators with high-quality-factor optical resonators increases the modulation strength, but these devices suffer from intrinsic narrow bandwidth and require sophisticated optical design; they also have stringent fabrication requirements and limited temperature tolerances. Finding a complementary metal-oxide-semiconductor (CMOS)-compatible material with adequate modulation speed and strength has therefore become a task of not only scientific interest, but also industrial importance. Here we experimentally demonstrate a broadband, high-speed, waveguide-integrated electroabsorption modulator based on monolayer graphene. By electrically tuning the Fermi level of the graphene sheet, we demonstrate modulation of the guided light at frequencies over 1 GHz, together with a broad operation spectrum that ranges from 1.35 to 1.6 µm under ambient conditions. The high modulation efficiency of graphene results in an active device area of merely 25 µm(2), which is among the smallest to date. This graphene-based optical modulation mechanism, with combined advantages of compact footprint, low operation voltage and ultrafast modulation speed across a broad range of wavelengths, can enable novel architectures for on-chip optical communications.
    Nature 06/2011; 474(7349):64-7. · 38.60 Impact Factor
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    ABSTRACT: Optical imaging and photolithography promise broad applications in nano-electronics, metrologies, and single-molecule biology. Light diffraction however sets a fundamental limit on optical resolution, and it poses a critical challenge to the down-scaling of nano-scale manufacturing. Surface plasmons have been used to circumvent the diffraction limit as they have shorter wavelengths. However, this approach has a trade-off between resolution and energy efficiency that arises from the substantial momentum mismatch. Here we report a novel multi-stage scheme that is capable of efficiently compressing the optical energy at deep sub-wavelength scales through the progressive coupling of propagating surface plasmons (PSPs) and localized surface plasmons (LSPs). Combining this with airbearing surface technology, we demonstrate a plasmonic lithography with 22 nm half-pitch resolution at scanning speeds up to 10 m/s. This low-cost scheme has the potential of higher throughput than current photolithography, and it opens a new approach towards the next generation semiconductor manufacturing.
    Scientific Reports 01/2011; 1:175. · 5.08 Impact Factor
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    Sung Hyun Nam, Erick Ulin-Avila, Guy Bartal, Xiang Zhang
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    ABSTRACT: We present general properties of surface modes in binary metal-dielectric metamaterials. We show mechanism for surface mode formation and analyze their existence conditions for semi-infinite metamaterials in the frame of couple mode theory.
    Optics Express 12/2010; 18(25):25627-32. · 3.55 Impact Factor
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    Sung Hyun Nam, Erick Ulin-Avila, Guy Bartal, Xiang Zhang
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    ABSTRACT: We present what we believe to be the first study of deep subwavelength surface modes in binary metal-dielectric metamaterials. By employing anomalous coupling in binary periodicity, peculiar properties of band structure and eigenmode symmetry are obtained. We show that strongly confined plasmonic Tamm-like and Shockley-like surface modes can be formed at the termination of the array. We clarify the character of each surface mode and analyze its unique symmetry with the corresponding band structure.
    Optics Letters 06/2010; 35(11):1847-9. · 3.39 Impact Factor
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    ABSTRACT: Optical lithography has been the key for continuous size reduction of semiconductor devices and circuits manufacturing. Although the industry is continually improving the resolution, optical lithography becomes more difficult and less cost effective in satisfying the ever increasing demands in nano-manufacturing. Besides manufacturing, the dramatic advancements in nanoscale science and engineering also call an urgent need for high-throughput nano-fabrication technologies that are versatile to frequent design changes. Here we experimentally demonstrated the capability of patterning with 50 nm linewidth with a high flying speed at 10 meter/second. This low-cost nano-fabrication scheme has the potential of a few orders of magnitude higher throughput than current maskless techniques, and promises a new route towards the next generation nano-manufacturing. Besides its application in nanolithography, this technique can also be used for nanoscale metrology, imaging and data storage.© (2010) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
    03/2010;
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    ABSTRACT: Surface plasmon polaritons (SPPs) are electron density waves excited at the interfaces between metals and dielectric materials. Owing to their highly localized electromagnetic fields, they may be used for the transport and manipulation of photons on subwavelength scales. In particular, plasmonic resonant cavities represent an application that could exploit this field compression to create ultrasmall-mode-volume devices. A key figure of merit in this regard is the ratio of cavity quality factor, Q (related to the dissipation rate of photons confined to the cavity), to cavity mode volume, V (refs 10, 11). However, plasmonic cavity Q factors have so far been limited to values less than 100 both for visible and near-infrared wavelengths. Significantly, such values are far below the theoretically achievable Q factors for plasmonic resonant structures. Here we demonstrate a high-Q SPP whispering-gallery microcavity that is made by coating the surface of a high-Q silica microresonator with a thin layer of a noble metal. Using this structure, Q factors of 1,376 +/- 65 can be achieved in the near infrared for surface-plasmonic whispering-gallery modes at room temperature. This nearly ideal value, which is close to the theoretical metal-loss-limited Q factor, is attributed to the suppression and minimization of radiation and scattering losses that are made possible by the geometrical structure and the fabrication method. The SPP eigenmodes, as well as the dielectric eigenmodes, are confined within the whispering-gallery microcavity and accessed evanescently using a single strand of low-loss, tapered optical waveguide. This coupling scheme provides a convenient way of selectively exciting and probing confined SPP eigenmodes. Up to 49.7 per cent of input power is coupled by phase-matching control between the microcavity SPP and the tapered fibre eigenmodes.
    Nature 02/2009; 457(7228):455-8. · 38.60 Impact Factor
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    ABSTRACT: We report a direct experimental evidence of stimulated emission of surface plasmon polaritons (SPPs) at telecom wavelengths (1532 nm) with erbium doped glass as a gain medium. We observe an increase in the propagation length of signal surface plasmons when erbium ions are excited optically using pump SPP. The design, fabrication, and characterization of SPP waveguides, thin gold metal strips, embedded in erbium (Er) doped phosphate glass is presented. Such systems can be suitable as integrated devices coupling electronic and photonic data transmissions as well as SPP amplifiers and SPP lasers.
    Nano Letters 11/2008; 8(11):3998-4001. · 13.03 Impact Factor
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    ABSTRACT: We report experimental realization of the first bulk optical negative index metamaterial. The index is determined by measuring the refractive angle at the exiting side of a prism, demonstrating negative phase propagation in the metamaterial.
    Plasmonics and Metamaterials; 10/2008
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    ABSTRACT: Metamaterials are artificially engineered structures that have properties, such as a negative refractive index, not attainable with naturally occurring materials. Negative-index metamaterials (NIMs) were first demonstrated for microwave frequencies, but it has been challenging to design NIMs for optical frequencies and they have so far been limited to optically thin samples because of significant fabrication challenges and strong energy dissipation in metals. Such thin structures are analogous to a monolayer of atoms, making it difficult to assign bulk properties such as the index of refraction. Negative refraction of surface plasmons was recently demonstrated but was confined to a two-dimensional waveguide. Three-dimensional (3D) optical metamaterials have come into focus recently, including the realization of negative refraction by using layered semiconductor metamaterials and a 3D magnetic metamaterial in the infrared frequencies; however, neither of these had a negative index of refraction. Here we report a 3D optical metamaterial having negative refractive index with a very high figure of merit of 3.5 (that is, low loss). This metamaterial is made of cascaded 'fishnet' structures, with a negative index existing over a broad spectral range. Moreover, it can readily be probed from free space, making it functional for optical devices. We construct a prism made of this optical NIM to demonstrate negative refractive index at optical frequencies, resulting unambiguously from the negative phase evolution of the wave propagating inside the metamaterial. Bulk optical metamaterials open up prospects for studies of 3D optical effects and applications associated with NIMs and zero-index materials such as reversed Doppler effect, superlenses, optical tunnelling devices, compact resonators and highly directional sources.
    Nature 09/2008; 455(7211):376-9. · 38.60 Impact Factor
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    ABSTRACT: We report experimental realization of the first three-dimensional (3-D) optical negative index metamaterial. We measure the bulk refractive index using a 3-D prism and Snell’s Law, unambiguously demonstrating negative phase propagation in the material.
    Quantum Electronics and Laser Science Conference; 05/2008
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    ABSTRACT: Active plasmonics describes the interaction between an active medium and surface plasmons, and it offers a foundation for fundamental studies and an opportunity to expand surface plasmon based applications. In order to overcome the challenges posed by surface plasmons - primarily the metal losses - recent studies have focused extensively on surface plasmon amplification; however, there has been very limited headway from the experimental front. We present an experimental evidence of the amplification of long range surface plasmon polaritons (SPPs) by stimulated emission at telecom frequencies. We design SPP waveguides - thin gold metal strips - embedded in a gain medium, erbium doped phosphate glass. We confirm SPP amplification by showing an increase in the propagation length of surface plasmons in both pulsed and continuous modes. We present the design, fabrication and measurements of the gold SPP waveguides in erbium doped glass. Such structures will be suitable as integrated coupling devices as well as for the study of plasmon-exciton interface in cavity quantum electrodynamics.
    03/2008;
  • Abstracts of Papers of the American Chemical Society. 01/2006; 232.
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    ABSTRACT: We present data on the coverage and nearest-neighbor dependences of the diffusion of CO on Cu(111) by time-lapsed scanning tunneling microscope (STM) imaging. Most notable is a maximum in diffusivity of CO at a local coverage of one molecule per 20 substrate atoms and a repulsion between CO molecules upon approach closer than three adsites, which in combination with a less pronounced increase in potential energy at the diffusion transition state, leads to rapid diffusion of CO molecules around one another. We propose a new method of evaluating STM-based diffusion data that provides all parameters necessary for the modeling of the dynamics of an adsorbate population.
    The Journal of Chemical Physics 11/2005; 123(20):201102-201102-4. · 3.12 Impact Factor

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