Joanna M. Atkin

University of Colorado, Denver, Colorado, United States

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Publications (25)146.53 Total impact

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    ABSTRACT: Vibrational spectroscopy can provide information about structure, coupling, and dynamics underlying the properties of complex molecular systems. While measurements of spectral line broadening can probe local chemical environments, the spatial averaging in conventional spectroscopies limits insight into underlying heterogeneity, in particular in disordered molecular solids. Here, using femtosecond infrared scattering scanning near-field optical microscopy (IR s-SNOM), we resolve in vibrational free-induction decay (FID) measurements a high degree of spatial heterogeneity in polytetrafluoroethylene (PTFE) as a dense molecular model system. In nanoscopic probe volumes as small as 10(3) vibrational oscillators, we approach the homogeneous response limit, with extended vibrational dephasing times of several picoseconds, i.e., up to 10 times the inhomogeneous lifetime, and spatial average converging to the bulk ensemble response. We simulate the dynamics of relaxation with a finite set of local vibrational transitions subject to random modulations in frequency. The combined results suggest that the observed heterogeneity arises due to static and dynamic variations in the local molecular environment. This approach thus provides real-space and real-time visualization of the sub-ensemble dynamics that define the properties of many functional materials.
    Journal of Physical Chemistry Letters 11/2015; DOI:10.1021/acs.jpclett.5b02093 · 7.46 Impact Factor
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    ABSTRACT: We extended the characterization of photoinduced quantum phase transitions into the nanoscale. We demonstrate this for VO2 by accessing spatial inhomogeneities in the insulator-tometal transition due to local strain and defects.
  • V. Kravtsov · R. Ulbricht · J.M. Atkin · M.B. Raschke ·
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    ABSTRACT: We demonstrate efficient and broadband nonlinear nano-optics in plasmonic nanofocusing with nanometer localized four-wave mixing. We achieve deterministic optical control and nano-spectroscopic imaging of graphene as the basis for extension of multidimensional spectroscopy to the nanoscale.
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    ABSTRACT: Tip-enhanced Raman spectroscopy at cryogenic temperatures probes the intrinsic linewidths of vibrational modes. Temperature dependent investigation of small ensembles reveals ultrafast vibrational relaxation dynamics, conformational heterogeneity, and single molecule fluctionality on the time scale of seconds.
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    ABSTRACT: We study the micro-Raman spectra of colloidal silicon nanocrystals as a function of size, excitation wavelength, and excitation intensity. We find that the longitudinal (LO) phonon spectrum is asymmetrically broadened towards the low energy side and exhibits a dip or anti-resonance on the high-energy side, both characteristics of a Fano lineshape. The broadening depends on both nanocrystal size and Raman excitation wavelength. We propose that the Fano lineshape results from interference of the optical phonon response with a continuum of electronic states that become populated by intraband photoexcitation of carriers. The asymmetry exhibits progressive enhancement with decreasing particle size and with increasing excitation energy for a given particle size. We compare our observations with those reported for p- and n-doped bulk Si, where Fano interference has also been observed, but we find opposite wavelength dependence of the asymmetry for the bulk and nanocrystalline Si. Our results have important implications for potentially controlling carrier energy relaxation channels in strongly confined Si nanocrystals.
    Nano Letters 01/2015; 15(3). DOI:10.1021/nl503671n · 13.59 Impact Factor
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    ABSTRACT: The insulator-to-metal transition (IMT) of the simple binary compound of vanadium dioxide VO$_2$ at $\sim 340$ K has been puzzling since its discovery more than five decades ago. A wide variety of photon and electron probes have been applied in search of a satisfactory microscopic mechanistic explanation. However, many of the conclusions drawn have implicitly assumed a {\em homogeneous} material response. Here, we reveal inherently {\em inhomogeneous} behavior in the study of the dynamics of individual VO$_2$ micro-crystals using a combination of femtosecond pump-probe microscopy with nano-IR imaging. The time scales of the photoinduced bandgap reorganization in the ultrafast IMT vary from $\simeq 40 \pm 8$ fs, i.e., shorter than a suggested phonon bottleneck, to $\sim 200\pm20$ fs, with an average value of $80 \pm 25$ fs, similar to results from previous studies on polycrystalline thin films. The variation is uncorrelated with crystal size, orientation, transition temperature, and initial insulating phase. This together with details of the nano-domain behavior during the thermally-induced IMT suggests a significant sensitivity to local variations in, e.g., doping, defects, and strain of the microcrystals. The combination of results points to an electronic mechanism dominating the photoinduced IMT in VO$_2$, but also highlights the difficulty of deducing mechanistic information where the intrinsic response in correlated matter may not yet have been reached.
    Nature Communications 12/2014; 6. DOI:10.1038/ncomms7849 · 11.47 Impact Factor
  • Vasily Kravtsov · Samuel Berweger · Joanna M. Atkin · Markus B Raschke ·
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    ABSTRACT: With nanosecond radiative lifetimes, quenching dominates over enhancement for conventional fluorescence emitters near metal interfaces. We explore the fundamentally distinct behavior of photoluminescence (PL) with few-femtosecond radiative lifetimes of a coupled plasmonic emitter. Controlling the emitter-surface distance with sub-nanometer precision by combining atomic force and scanning tunneling distance control, we explore the unique behavior of plasmon dynamics at the transition from long range classical resonant energy transfer to quantum coupling. Because of the ultrafast radiative plasmon emission, classical quenching is completely suppressed. Field-enhanced behavior dominates until the onset of quantum coupling dramatically reduces emission intensity and field enhancement, as verified in concomitant tip-enhanced Raman measurements. The entire distance behavior from 10's nm to sub-nm can accurately be described using a phenomenological rate equation model and highlights the new degrees of freedom in radiation control enabled by an ultrafast emitter near surfaces.
    Nano Letters 08/2014; 14(9). DOI:10.1021/nl502297t · 13.59 Impact Factor
  • Joanna M. Atkin · Paul Sass · Jonas Allerbeck · Markus B. Raschke ·
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    ABSTRACT: We demonstrate ultrafast infrared vibrational free-induction decay probing in scattering-scanning near-field microscopy. We observe long-lived few picosecond vibrational coherences, far in excess of the far-field ensemble response.
    CLEO: QELS_Fundamental Science; 06/2014
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    ABSTRACT: Since its first experimental realization, tip-enhanced Raman spectroscopy (TERS) has emerged as a potentially powerful nanochemical analysis tool. However, questions about the comparability and reproducibility of TERS data have emerged. This interlaboratory comparison study addresses these issues by bringing together different TERS groups to perform TERS mea-surements on nominally identical samples. Based on the spectra obtained, the absolute and relative peak positions, number of bands, peak intensity ratios, and comparability to reference Raman and surface-enhanced Raman spectroscopy (SERS) data are discussed. Our general findings are that all research groups obtained similar spectral patterns, irrespective of the setup or tip that was used. The TERS (and SERS) spectra consistently showed fewer bands than the conventional Raman spectrum. When comparing these three methods, the spectral pattern match and substance identification is readily possible. Absolute and relative peak positions of the three major signals of thiophenol scattered by 19 and 9 cm À1 , respectively, which can prob-ably be attributed to different spectrometer calibrations. However, within the same group (but between different tips), the signals only scattered by 3 cm À1 on average. This study demonstrated the suitability of TERS as an analytical tool and brings TERS a big step forward to becoming a routine technique.
  • Vasily Kravtsov · Joanna M. Atkin · Markus B. Raschke ·
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    ABSTRACT: We demonstrate broadband slow light through adiabatic nanofocusing of surface plasmon polaritons (SPPs) on a conical tip. A few femtosecond group delay for nanofocused pulses is found, corresponding to an SPP velocity of less than 0.2c at the apex of the tip.
    CLEO: QELS_Fundamental Science; 06/2013
  • Joanna M Atkin · Markus B Raschke ·
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    ABSTRACT: Optical spectroscopic imaging has taken a leap into the intramolecular regime with an approach that achieves subnanometre spatial resolution. The technique should find applications in photochemistry and nanotechnology. See Letter p.82
    Nature 06/2013; 498(7452):44-5. DOI:10.1038/498044a · 41.46 Impact Factor
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    Vasily Kravtsov · Joanna M Atkin · Markus B Raschke ·
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    ABSTRACT: We study the decrease in group velocity of broadband surface plasmon polariton propagation on a conical tip, using femtosecond time-domain interferometry. The group delay of (9±3) fs measured corresponds to a group velocity at the apex of less than 0.2c. The result agrees in general with the prediction from adiabatic plasmonic nanofocusing theory, yet is sensitive with respect to the exact taper geometry near the apex. This, together with the sub 25 fs<sup>2</sup> second-order dispersion observed, provides the fundamental basis for the use of plasmons for broadband slow-light applications.
    Optics Letters 04/2013; 38(8):1322-4. DOI:10.1364/OL.38.001322 · 3.29 Impact Factor
  • Samuel Berweger · Joanna M. Atkin · Xiaoji G. Xu · Markus B. Raschke ·
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    ABSTRACT: We demonstrate a generalized route to generate nanometer spatially confined ultrafast optical pulses with arbitrary deterministic femtosecond waveform control using surface plasmon polarition nanofocusing in 3D tapered noble metal tips.
    The European Physical Journal Conferences 03/2013; 41:09010-. DOI:10.1051/epjconf/20134109010
  • Markus B. Raschke · Samuel Berweger · Joanna M. Atkin ·
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    ABSTRACT: The interaction of light with a metal mediated by surface plasmon polaritons provides for sub-diffraction limited optical confinement and control. While the relationship of the linear plasmon response to the underlying elementary electronic excitations of the metal is well understood in general, the corresponding ultrafast and nonlinear plasmon interactions could provide further enhanced functionalities. However, while the ultrafast and nonlinear optics of metals is an advanced field, the understanding of the related plasmonic properties is less developed. Here we discuss ultrafast and nonlinear wave-mixing properties of metals and metallic nanostructures in terms of the elementary optical interactions related to electronic band structure, plasmon resonances, and geometric selection rules. These properties form the fundamental basis of the nonlinear plasmonic light-matter interaction. The understanding of these fundamental properties, together with the ability to measure and control the typically fast femtosecond intrinsic and extrinsic dephasing times, is important for the development of applications such as enhanced nano-imaging, coherent control of individual quantum systems, strong light-matter interaction and extreme nonlinear optics, and nano-photonic devices.
    Plasmonics: Theory and Applications, 01/2013: pages 237-281; , ISBN: 978-94-007-7804-7
  • Joanna M. Atkin · Samuel Berweger · Andrew C. Jones · Markus B. Raschke ·
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    ABSTRACT: The structure of our material world is characterized by a large hierarchy of length scales that determines material properties and functions. Increasing spatial resolution in optical imaging and spectroscopy has been a long standing desire, to provide access, in particular, to mesoscopic phenomena associated with phase separation, order, and intrinsic and extrinsic structural inhomogeneities. A general concept for the combination of optical spectroscopy with scanning probe microscopy emerged recently, extending the spatial resolution of optical imaging far beyond the diffraction limit. The optical antenna properties of a scanning probe tip and the local near-field coupling between its apex and a sample provide few-nanometer optical spatial resolution. With imaging mechanisms largely independent of wavelength, this concept is compatible with essentially any form of optical spectroscopy, including nonlinear and ultrafast techniques, over a wide frequency range from the terahertz to the extreme ultraviolet. The past 10 years have seen a rapid development of this nano-optical imaging technique, known as tip-enhanced or scattering-scanning near-field optical microscopy (s-SNOM). Its applicability has been demonstrated for the nano-scale investigation of a wide range of materials including biomolecular, polymer, plasmonic, semiconductor, and dielectric systems. We provide a general review of the development, fundamental imaging mechanisms, and different implementations of s-SNOM, and discuss its potential for providing nanoscale spectroscopic including femtosecond spatio-temporal information. We discuss possible near-field spectroscopic implementations, with contrast based on the metallic infrared Drude response, nano-scale impedance, infrared and Raman vibrational spectroscopy, phonon Raman nano-crystallography, and nonlinear optics to identify nanoscale phase separation (PS), strain, and ferroic order. With regard to applications, we focus on correlated and low-dimensional materials as examples that benefit, in particular, from the unique applicability of s-SNOM under variable and cryogenic temperatures, nearly arbitrary atmospheric conditions, controlled sample strain, and large electric and magnetic fields and currents. For example, in transition metal oxides, topological insulators, and graphene, unusual electronic, optical, magnetic, or mechanical properties emerge, such as colossal magneto-resistance (CMR), metal-insulator transitions (MITs), high-T C superconductivity, multiferroicity, and plasmon and phonon polaritons, with associated rich phase diagrams that are typically very sensitive to the above conditions. The interaction of charge, spin, orbital, and lattice degrees of freedom in correlated electron materials leads to frustration and degenerate ground states, with spatial PS over many orders of length scale. We discuss how the optical near-field response in s-SNOM allows for the systematic real space probing of multiple order parameters simultaneously under a wide range of internal and external stimuli (strain, magnetic field, photo-doping, etc.) by coupling directly to electronic, spin, phonon, optical, and polariton resonances in materials. In conclusion, we provide a perspective on the future extension of s-SNOM for multi-modal imaging with simultaneous nanometer spatial and femtosecond temporal resolution.
    Advances In Physics 12/2012; 61(6):745-842. DOI:10.1080/00018732.2012.737982 · 20.83 Impact Factor
  • Samuel Berweger · Joanna M. Atkin · Robert L. Olmon · Markus B. Raschke ·
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    ABSTRACT: The efficiency of plasmonic nanostructures as optical antennas to concentrate optical fields to the nanoscale has been limited by intrinsically short dephasing times and small absorption cross sections. We discuss a new optical antenna concept based on surface plasmon polariton (SPP) nanofocusing on conical noble metal tips to achieve efficient far- to near-field transformation of light from the micro- to the nanoscale. The spatial separation of the launching of propagating SPPs from their subsequent apex confinement with high energy concentration enables background-free near-field imaging, tip-enhanced Raman scattering, and nonlinear nanospectroscopy. The broad bandwidth and spectral tunability of the nanofocusing mechanism in combination with frequency domain pulse shaping uniquely allow for the spatial confinement of ultrashort laser pulses and few-femtosecond spatiotemporal optical control on the nanoscale. This technique not only extends powerful nonlinear and ultrafast spectroscopies to the nanoscale but can also generate fields of sufficient intensity for electron emission and higher harmonic generation.
    Journal of Physical Chemistry Letters 03/2012; 3(7):945–952. DOI:10.1021/jz2016268 · 7.46 Impact Factor
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    ABSTRACT: The simultaneous control of optical fields on both nanometer spatial and femtosecond time scales would enable direct spectroscopic access to the elementary electronic and vibrational excitations in matter. Here, we utilize adiabatic surface plasmon polariton (SPP) nanofocusing on free-standing 3D tapered metal tips in order to generate nanometer confined field localization at the tip apex. Using the second harmonic generation (SHG) at the tip apex we perform MIIPS pulse optimization and frequency-resolved optical gating (FROG) characterization of the nanofocused pulses. With the combination of high bandwidth coupling using a chirped grating, pulse-shaping, and low-dispersion nanofocusing, we can achieve full optical control on the nanoscale, from < 16 fs pulse duration to arbitrary optical waveforms. This technique enables linear and non-linear plasmon-enhanced spectroscopy, with the simultaneous temporal control over ultrashort pulses opening the possibility for true time-resolved scanning-probe imaging. We demonstrate this capability for background-free probing of individual molecular and nanocrystalline systems.
  • Molly May · Joanna Atkin · Markus Raschke ·
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    ABSTRACT: Strongly correlated electron materials display diverse complex phenomena such as metal-insulator transitions and ferroelectric and ferromagnetic ordering, with characteristic lengths on the nanometer scale. In order to directly access and study the associated nano-phase behavior and domains for a wide range of materials, we have developed a low temperature tip-enhanced scattering-type scanning near-field optical microscope (s-SNOM). A microscopy flow cryostat reservoir is coupled to a shear-force atomic force microscope, with illumination of electrochemically etched Au tips provided by an on-axis high numerical aperture parabolic mirror. We will discuss the use of this system for the study and imaging of ferroic ordering in multiferroic and ferroelectric materials through the symmetry selectivity provided by tip-enhanced second harmonic generation (SHG) and nano-Raman crystallography via the tensor based selection rules.
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    ABSTRACT: In addition to its metal-insulator transition (MIT), VO2 exhibits a rich phase behavior of insulating monoclinic (M1,M2) and triclinic (T) phases. By using micro-Raman spectroscopy and independent control of temperature and uniaxial strain in individual single-crystal microbeams, we map these insulating phases with their associated structural changes as represented by their respective phonon frequencies. The competition between these structural forms is dictated by the internal strain due to differing lattice constants, the experimentally applied external strain, and the temperature-dependent phase stability. We identify the nature of the triclinic phase as a continuously distorted variant of the M1 monoclinic phase, while a discontinuous transition into the M2 phase occurs from both the M1 and T phases. The results suggest that understanding the driving forces that determine the interplay between M1, M2, and T phases near the MIT could be critical for the identification of the underlying mechanism behind the MIT itself.
    Physical review. B, Condensed matter 01/2012; 85(2). DOI:10.1103/PhysRevB.85.020101 · 3.66 Impact Factor
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    ABSTRACT: We demonstrate the simultaneous and independent nanometer-femtosecond spatiotemporal control of optical fields through the intrinsic adiabatic surface plasmon polariton nanofocusing ability of tapered Au tips combined with femtosecond pulse shaping.
    Frontiers in Optics; 10/2011

Publication Stats

259 Citations
146.53 Total Impact Points


  • 2015
    • University of Colorado
      • Department of Physics
      Denver, Colorado, United States
  • 2014
    • University of North Carolina at Chapel Hill
      • Department of Chemistry
      North Carolina, United States
  • 2011-2014
    • University of Colorado at Boulder
      • • Department of Chemistry and Biochemistry
      • • Department of Physics
      Boulder, Colorado, United States
  • 2010
    • University of Washington Seattle
      • Department of Chemistry
      Seattle, Washington, United States