Letter pubs.acs.org/NanoLett
Imaging Intra- and Interparticle Acousto-plasmonic Vibrational Dynamics with Ultrafast Electron Microscopy David T. Valley, Vivian E. Ferry, and David J. Flannigan* Department of Chemical Engineering and Materials Science, University of Minnesota, 421 Washington Avenue SE, Minneapolis, Minnesota 55455, United States S Supporting Information *
ABSTRACT: We report real-space, time-resolved imaging of coherently excited acoustic phonon modes in plasmonic nanoparticles via femtosecond electron imaging with an ultrafast electron microscope. The particles studied were cetyl trimethylammonium bromide stabilized Au nanorods (40 × 120 nm), and the particular specimen configurations for which photoinduced vibrational modes were visualized consisted of a single, isolated nanocrystal and a cluster of four irregularly arranged and randomly oriented particles, all supported on an amorphous Si3N4 membrane. In both configurations, we are able to resolve discrete intraparticle acoustic phonon modes via diffraction-contrast modulation with bright-field femtosecond electron imaging. For the single nanorod, we spatiotemporally mapped the intraparticle vibrational energy distribution and decay times. With Fourier filtering, acoustic phonons ranging from 4 to 30 GHz (250 to 33 ps periods, respectively) were visualized, corresponding to bending, extensional, and higher-order modes. Furthermore, heterogeneously distributed intraparticle decay times, ranging from 3 to 10 ns, were spatially mapped, indicating a strong dependence on coupling of the mode to the underlying substrate. For a cluster of four randomly oriented nanorods, we are able to image acoustic phonon modes that are strongly localized to particular particle−particle contact regions within the aggregate. A vibrational mode occurring at 27 GHz (37 ps period) was observed to occur at a 10 nm side-to-end contact region, with other intraparticle points at distances of 20 and 50 nm from the region showing no such dynamics, although the initial few-picosecond diffraction-contrast response was observed changing sign in moving from the end to the center of the particle. Excellent agreement is found between the spatiotemporally mapped vibrational-mode symmetries and finite-element simulations of supported modes in a polymer-coated Au nanorod supported on a Si3N4 membrane. This experiment resolves both the structure and dynamic properties of the plasmonic assembly, providing insight into the characteristics of complex plasmonic assemblies that ultimately determine their response to ultrafast excitation. KEYWORDS: Gold nanorods, lattice vibrations, pump−probe, ultrafast structural dynamics
P
several picoseconds following photoexcitation via electronatom scattering. This results in the excitation, launch, and decay of coherent intraparticle acoustic phonons and, ultimately, to diffusion of heat to the surroundings on the nanosecond time scale.21 Although the eigenfrequencies of vibrational modes in isolated nanoparticles can be well-predicted with continuum mechanical modeling, determination of transient responses and mode-coupling dynamics is typically accomplished via ultrafast spectroscopic measurements.10,17,20 Owing to the complexities of excitation of multiple modes and of ill-defined interparticle and particlesubstrate contacts, identification and assignment of vibrational frequencies typically requires the probing of either single
lasmonic nanostructures, which exhibit high absorption cross-sections and strongly localized electromagnetic fields, offer a route to couple light into nanomechanical motion at subdiffraction-limited length scales. Controlled interactions between photons and phonons have been explored for application in mass sensing, optical buffering, reconfigurable metamaterials, and medical therapies and for understanding hot-electron relaxation in photochemical reactions.1−5 Coupling can be achieved via ultrafast photoexcitation of electrons and subsequent energy transfer to the lattice.6−19 More specifically, coherent acoustic modes in metallic nanoparticles can be excited through initial femtosecond optical excitation of a surface plasmon, which decays in approximately 10 fs via electron−electron scattering and radiation damping.14,17 This produces a hot electron distribution with a significantly higher average temperature than the crystal lattice.20 Equilibration of charge-carriers with the lattice then follows and occurs within © XXXX American Chemical Society
Received: September 22, 2016 Revised: October 10, 2016 Published: October 24, 2016 A
DOI: 10.1021/acs.nanolett.6b03975 Nano Lett. XXXX, XXX, XXX−XXX
Letter
Nano Letters particles or highly monodisperse ensembles.8,9,11,13,14,19,22,23 Despite such challenges, optical pump−probe techniques have been used to study a wide range of phenomena in plasmonic nanostructures, including influence of the surrounding environment and of adhesion layers in evaporated structures, constitutive nanomechanical properties, and selective excitation of specific vibrational modes.7,13,15,18 As advances have been made in experimental methodologies, extraction of meaningful quantitative information about photon to acoustic-mode coupling in complex assemblies of plasmonic nanoparticles has become increasingly important. For configurations of this type, it is reasonable to expect that the precise arrangement will strongly influence the vibrational lifetimes, the particular acoustic modes supported, and the preferred energytransport pathways. However, probing dynamics in plasmonic nanostructures with diffraction-limited optics is challenging because the detection is based on spectral shifts in plasmon resonance, which can also be influenced by electromagnetic coupling.24 Furthermore, previous studies on nanoparticle aggregates suggest optical-detection methods likely sample only subregions of the overall assembly, making it challenging to elucidate subaggregate structure−dynamics relationships.25−28 Therefore, phenomena in complex assemblies might best be studied with structural imaging techniques. The development and rapid growth of ultrafast structural pump−probe methodologies has led to insight into structure− function relationships at the atomic and nanoscale levels.29,30 Improved spatial resolutions over diffraction-limited optical methods, and especially the possibility to capture full morphological and crystallographic information, is increasingly being recognized as a powerful means to probe micro- to subnanoscale structural dynamics. Of particular relevance here, ultrafast Bragg coherent diffraction imaging with X-ray free-electron lasers has
been used to probe structural dynamics, including photoinitiated acoustic phonons in few-hundred-nanometer Au particles.31−33 Also, femtosecond X-ray scattering has been used to conduct reciprocal-space studies of photoinduced anisotropic structural responses of ensembles of in-contact CdS and CdSe nanoparticles, and ultrafast electron diffraction has been used to study the collective structural dynamics of clusters of surface-passivated Au nanoparticles.34,35 An especially promising laboratory-scale approach for such studies is ultrafast electron microscopy (UEM), which enables the extension of the capabilities of conventional transmission electron microscopy down to femtosecond time scales.36−40 Furthermore, ease of electron-trajectory manipulation and switching between imaging and diffraction modes enables comprehensive single-particle studies.40−42 Importantly, it was recently demonstrated that femtosecond electron imaging with UEM at relatively low laser-repetition rates (e.g., 25 kHz) enables the direct visualization of individual acoustic-phonon wavefronts and discrete vibrational and dispersion dynamics on an atomic-scale defect-by-defect basis in thin, semiconducting crystals.43 Here, we report the first direct, real-space imaging of nanoscale intra- and interparticle acoustic-phonon dynamics in single and few-particle clusters (here, a tetramer) of plasmonic nanocrystals. To gain access to a variety of vibrational modes and irregularly arranged few-particle clusters, specimens composed of singlecrystal Au nanorods were prepared (see the Supporting Information for specimen preparation methods and crystallographic and morphological characterization). Figure 1 summarizes the results of bright-field UEM imaging of the ultrafast structural response of a single Au nanorod supported on an amorphous Si3N4 membrane. The UEM stroboscopic approach used here (Figure 1a and the Supporting Information) consisted of 270 fs (full width at half-maximum, fwhm) optical pump pulses (1030 or 515 nm)
Figure 1. UEM pump−probe schematic, specimen overview, and ultrafast structural response. (a) Simplified schematic of the UEM experimental configuration, with wavevectors of the incoming pump photon pulse (hv, green) and probe photoelectron packet (e−, blue) labeled. (b) Bright-field TEM image of a single gold nanorod, the intraparticle dynamics of which are summarized in (c) and also in Figures 2 and 3. Scale bar: 50 nm. (c) Select UEM and false-colored difference images. The time relative to the first-observed t0.5 response (defined as the experiment time of 0 ps) is labeled in the upper-left corner of each frame. The t = −20 ps frame is a representative bright-field UEM image (scale bar: 50 nm). Subsequent difference images (i.e., t = −15 ps, −10 ps, etc.) isolate the intraparticle diffraction-contrast dynamics, displayed as percent signal change. The pump wavelength was 1030 nm. The reader is encouraged to view the UEM video in the Supporting Information to get a clear sense of the dynamics summarized in this figure. B
DOI: 10.1021/acs.nanolett.6b03975 Nano Lett. XXXX, XXX, XXX−XXX
Letter
Nano Letters with a 100 μm spot size (fwhm) and sub-picosecond 200 keV photoelectron probe packets. The specimens were spatially centered within the pump pulse, thus ensuring a uniform excitation profile for each particle. In bright-field TEM imaging (Figure 1b), diffraction contrast is extremely sensitive to changes in nanocrystal orientation and intraparticle strain-field distributions, thus providing a direct link to ultrafast structural dynamics with UEM.43−46 In Figure 1c, the photoinduced picosecond diffraction-contrast response of a single Au nanorod is shown, with emphasis placed on the emergence and evolution of intraparticle structural dynamics via difference images (in this case, from −20 to 50 ps at 5 ps steps). Analysis reveals an apparent diffraction-contrast oscillation occurring during the first 50 ps following photoexcitation, with signal change evolving from being initially concentrated at the rod ends (0 to 20 ps) to spanning the entire rod (20 to 40 ps) and back again (40 to 50 ps), indicative of a coherent acoustic mode. The intraparticle dynamics summarized in Figure 1 were isolated and spatiotemporally quantified via pixel-by-pixel image analysis (see the Supporting Information), the results of which are summarized in Figure 2. Because the difference images revealed strong contrast modulation localized to the ends of the nanorod, single-pixel analysis is displayed at the center of one of the lobes of largest intensity change, the results of which are compiled in Figure 2a. At the magnifications used here, one pixel corresponds to 0.6 nm. For this particular spot, the image intensity initially decreased in approximately 3 ps, followed by oscillations superimposed over a relatively slow, single-exponential decay (a time constant of approximately 4 ns) back to the initial state. Here, because visualization of intra- and interparticle acoustic modes is the focus, systematic studies of the initial photoinduced dynamics and deconvolution from the UEM instrument response will be the subject of a future study. The observed oscillations arise from excitation of intraparticle acoustic modes (analyzed below), and the overall decay is due to energy transfer mainly to the Si3N4 membrane. As expected from the results shown in Figure 1, examination of the spatial dependence of the signal amplitude shows that the greatest modulation occurs within two lobes of intensity centered at each end of the nanorod (Figure 2b). Note that the signal-amplitude modulation is uniformly at (or near) zero outside the specimen. Furthermore, a similar analysis reveals the spatially dependent decay rates, ranging from 2 to 3 ns near the rod ends to 10 ns and longer, predominantly within the central region (Figure 2c). This decay-rate heterogeneity is attributed to a combination of the mechanical action of the excited acoustic modes and the resulting intraparticle modulation of coupling to the underlying thin support membrane. The measured nanosecond time constants are consistent with previous all-optical studies of substrate-supported single Au nanorods of similar sizes and aspect ratios and is indicative of diffusive energy transfer to the surroundings.13,23 Isolation and analysis of the intraparticle acoustic oscillations was done by quantifying the image-intensity modulation at all points along the rod length in the frequency domain; single-point analysis is displayed for four distinct points in Figure 3. Oscillations were isolated by first subtracting the Gaussian-convolved exponential fit (Figure 3a) and then applying a Fourier transform to the result (Figure 3b). Fourier-filtered spatial maps were then generated for frequencies from 0.8 to 35.2 GHz at 0.8 GHz steps, and a select set displaying particularly strong responses is collected in Figure 3c. Spatially resolved maps of modulated contrast strength from all of the sampled frequencies are collected in the Supporting Information.
Figure 2. Spatiotemporal mapping of intraparticle structural dynamics. (a) Single-pixel transient response at the particle position denoted with the blue-outlined white dot in (b). The red dots are modulated imageintensity values compiled from six individual UEM scans obtained with randomized time points, the blue trace is the average of the six scans at each time point, and the black curve is a least-squares fit to the blue trace composed of an initial Gaussian peak function convoluted with a single exponential decay. (b) Contour map of the modulated signal amplitude generated from a pixel-by-pixel analysis of the spatiotemporal intraparticle response. The contour map is overlaid onto a representative UEM brightfield image for reference. (c) Contour map of the primary decay (i.e., the time constant of the single exponential decay) generated from a pixel-bypixel analysis using a filter to exclude signal-amplitude changes of less than 0.25%. Again, the contour map is overlaid onto a representative UEM bright-field image for reference.
As can be seen from the Fourier transforms and frequency maps, strong intraparticle oscillations are observed at approximately 4 and 10 GHz at all four points in the particle and between 20 and 30 GHz for points one, two, and three. Importantly, the presence of signal at discrete frequencies in the spectra, in addition to the absence of contrast modulation outside the particles in the spatial maps, indicates the observed modes do not arise from experimental artifacts, noise, or fitting errors. From a comparison to finite element simulations and continuum mechanics calculations (see the Supporting Information), the lowest frequency (3.9 GHz) is assigned to a bending mode, and the next-lowest (9.4 and 10.2 GHz) are attributed to the fundamental extensional mode, consistent with single-particle optical pump−probe measurements on nanorods of comparable dimensions.11,16,23 The observed C
DOI: 10.1021/acs.nanolett.6b03975 Nano Lett. XXXX, XXX, XXX−XXX
Letter
Nano Letters
Figure 3. Spatiotemporal mapping of intraparticle acoustic vibrational dynamics. (a) UEM image-intensity responses of four distinct locations within a single Au nanorod [labeled 1 through 4 in the first frame of (c)]. The raw data from each location is shown in black and is overlaid with a black curve corresponding to a least-squares fit composed of an initial Gaussian peak function convoluted with a single exponential decay. The result of subtracting the fit curve from the raw data is shown in red to isolate vibrational dynamics. Each response is labeled (1 through 4) with the corresponding nanorod location from which it was measured. The data are offset for clarity. (b) FFTs (modulus) of the isolated oscillatory responses [i.e., the red traces in (a)] for the four distinct nanorod locations; each spectrum is labeled with the corresponding location. (c) Bright-field UEM image and corresponding Fourier filtered spatial frequency maps. Warmer colors represent regions within the nanorod displaying responses at the frequencies labeled in the upper-left corner of each frame (e.g., 3.9 or 9.4 GHz, etc.). The cooler colors indicate no response. The nanorod is outlined for clarity. Scale bar: 50 nm.
bright-field UEM imaging relies on variation in diffraction contrast for these studies.40,43−46 Accordingly, observation of dynamics may depend upon the initial lattice orientation with respect to the fixed Ewald sphere despite enabling access to modes not strictly reliant on distortion of optical dipoles. This effect is applicable to single, isolated particles and to clusters (Figures 3c, 4f, and S4 and S5). Such a hypothesis could be tested by performing a systematic study of observed diffraction-contrast dynamics on crystallographic orientation. Further, real-space contrast dynamics could be correlated to UEM convergent-beam diffraction studies to determine preferential wave vectors and atomic-scale scattering mechanisms. In conclusion, intra- and interparticle ultrafast vibrational dynamics have been spatiotemporally resolved and mapped for a single Au nanorod and a few-particle assembly with ultrafast electron microscopy. With nanometer real-space resolution, fundamental acoustic modes were visualized, corresponding to bending and extensional motions. In randomly arranged assemblies, the effects of contact regions on localization of oscillations was observed, and the discrete vibrational frequencies were spatially mapped, thus establishing full spatiotemporal dynamics of subassembly motions. It is expected that these results will open new avenues of research into acousto-plasmonic materials, structures, and dynamics. For example, understanding dynamics at subassembly length scales could ultimately point toward the design of nanostructures for efficient coupling of photons to mechanical motion, and particularly of structures that selectively excite targeted acoustic modes. Furthermore, these studies provide a new means to probe fundamental processes of energy nucleation and evolution in a host of nanocrystal-based structures and systems for a wide range of applications (e.g., catalysis, optoelectronics, energy transduction, etc.).
responses at 24.2 and 27.3 GHz likely originate from the next highest symmetric extensional mode. In addition to direct visualization of nanoscale single-particle dynamics, localization and subaggregate spatiotemporal mapping of vibrational modes was performed on a nonordered, few-particle assembly. Figure 4 displays the results of bright-field UEM imaging of photoinduced acoustic-mode dynamics in a cluster of four Au nanorods of random arrangement (see the Supporting Information). Unlike the single particle, both increases and decreases in relative signal amplitude were observed within the cluster. This is likely a consequence of a variety of well-known factors in diffraction-contrast imaging, including local lattice strain, orientation of the specimen with respect to the incoming probe electron wavevector, and subsequent motion of the reciprocal lattice on the fixed Ewald sphere.45,46 In particular, three points within one of the nanorods and in the vicinity of an interparticle contact region (Figure 4a,b), displayed distinct dynamics (Figure 4c,d); Point One showed a decrease in image intensity, Point Two (nearest the contact region) mainly showed strong oscillations about the pretime-zero intensity, and Point Three showed an increase in image intensity. Fourier analysis of the oscillations observed at each point reveal the strongestamplitude motions occur nearest the contact region (Figure 4e), and spatial maps of five selected frequencies confirm localization of the structural dynamics within the single nanorod (Figure 4f). It is reasonable to expect that there will generally be significant perturbation to the dynamics within the contact region; interparticle dynamics could either excite additional oscillations or damp fundamental single-particle modes, depending upon the orientation, the nature of the particle−particle contact, the assembly size, geometry, etc. In addition, it is important to again note that the detection of structural dynamics with D
DOI: 10.1021/acs.nanolett.6b03975 Nano Lett. XXXX, XXX, XXX−XXX
Letter
Nano Letters
Figure 4. Spatiotemporal mapping of interparticle vibrational mode coupling. (a) Bright-field image of a Au-nanorod tetramer. The particular region of interest, containing a distinct end-to-side contact between two rods, is contained within the red corner brackets. Scale bar: 100 nm. (b) Magnified view of the contact region highlighted in (a). Scale bar: 10 nm. (c) Contour map of the modulated signal amplitude generated from a pixel-by-pixel analysis of the spatiotemporal intra- and interparticle response. The map is overlaid onto a representative UEM bright-field image for reference. The pump wavelength was 515 nm. (d) UEM single-pixel image-intensity responses of three distinct locations within the contacted Au nanorod [labeled 1 through 3 in the first frame of (f)]. The raw data from each location is shown in black and is overlaid with a black curve corresponding to a leastsquares fit composed of an initial Gaussian peak function convoluted with a single exponential decay. The result of subtracting the fit curve from the raw data is shown in red to isolate vibrational dynamics. Each response is labeled (1 through 3) with the corresponding nanorod location from which it was measured. The data are offset for clarity. (e) Fourier transforms (modulus) of the isolated oscillatory responses [i.e., the red traces in (d)] for the three distinct nanorod locations; each spectrum is labeled with the corresponding location. (f) Bright-field UEM image and corresponding Fourier filtered spatial frequency maps. Warmer colors represent regions within the contacted nanorod displaying responses at the frequencies labeled in the lower-left corner of each frame. The cooler colors indicate no response. The nanorods are outlined for clarity. Scale bar: 50 nm. The reader is encouraged to view the UEM videos in the Supporting Information to get a clear sense of the dynamics summarized in this figure.
E
DOI: 10.1021/acs.nanolett.6b03975 Nano Lett. XXXX, XXX, XXX−XXX
Letter
Nano Letters
■
(12) Cardinal, M. F.; Mongin, D.; Crut, A.; Maioli, P.; RodríguezGonzález, B.; Pérez-Juste, J.; Liz-Marzán, L. M.; Del Fatti, N.; Vallée, F. J. Phys. Chem. Lett. 2012, 3, 613−619. (13) Yu, K.; Zijlstra, P.; Sader, J. E.; Xu, Q.-H.; Orrit, M. Nano Lett. 2013, 13, 2710−2716. (14) Major, T. A.; Lo, S. S.; Yu, K.; Hartland, G. V. J. Phys. Chem. Lett. 2014, 5, 866−874. (15) O’Brien, K.; Lanzillotti-Kimura, N. D.; Rho, J.; Suchowski, H.; Yin, X.; Zhang, X. Nat. Commun. 2014, 5, 4042. (16) Mahmoud, M. A.; O’Neil, D.; El-Sayed, M. A. Nano Lett. 2014, 14, 743−748. (17) Crut, A.; Maioli, P.; Del Fatti, N.; Vallée, F. Phys. Rep. 2015, 549, 1−43. (18) Chang, W.-S.; Wen, F.; Chakraborty, D.; Su, M.-N.; Zhang, Y.; Shuang, B.; Nordlander, P.; Sader, J. E.; Halas, N. J.; Link, S. Nat. Commun. 2015, 6, 7022. (19) Kirschner, M. S.; Lethiec, C. M.; Lin, X.-M.; Schatz, G. C.; Chen, L. X.; Schaller, R. D. ACS Photonics 2016, 3, 758−763. (20) Hartland, G. V. Annu. Rev. Phys. Chem. 2006, 57, 403−430. (21) Brongersma, M. L.; Halas, N. J.; Nordlander, P. Nat. Nanotechnol. 2015, 10, 25−34. (22) Lo, S. S.; Devadas, M. S.; Major, T. A.; Hartland, G. V. Analyst 2013, 138, 25−31. (23) Zijlstra, P.; Tchebotareva, A. L.; Chon, J. W. M.; Gu, M.; Orrit, M. Nano Lett. 2008, 8, 3493−3497. (24) Thijssen, R.; Verhagen, E.; Kippenberg, T. J.; Polman, A. Nano Lett. 2013, 13, 3293−3297. (25) Grant, C. D.; Schwartzberg, A. M.; Norman, T. J.; Zhang, J. Z. J. Am. Chem. Soc. 2003, 125, 549−553. (26) Jain, P. K.; Qian, W.; El-Sayed, M. A. J. Phys. Chem. B 2006, 110, 136−142. (27) Eah, S.-K.; Jaeger, H. M.; Scherer, N. F.; Lin, X.-M.; Wiederrecht, G. P. Chem. Phys. Lett. 2004, 386, 390−395. (28) Ruello, P.; Ayouch, A.; Vaudel, G.; Pezeril, T.; Delorme, N.; Sato, S.; Kimura, K.; Gusev, V. E. Phys. Rev. B: Condens. Matter Mater. Phys. 2015, 92, 174304. (29) Chergui, M.; Zewail, A. H. ChemPhysChem 2009, 10, 28−43. (30) Miller, R. J. D. Science 2014, 343, 1108−1116. (31) Clark, J. N.; Beitra, L.; Xiong, G.; Higginbotham, A.; Fritz, D. M.; Lemke, H. T.; Zhu, D.; Chollet, M.; Williams, G. J.; Messerschmidt, M.; Abbey, B.; Harder, R. J.; Korsunsky, A. M.; Wark, J. S.; Robinson, I. K. Science 2013, 341, 56−59. (32) Miao, J. W.; Ishikawa, T.; Robinson, I. K.; Murnane, M. M. Science 2015, 348, 530−535. (33) Bostedt, C.; Boutet, S.; Fritz, D. M.; Huang, Z. R.; Lee, H. J.; Lemke, H. T.; Robert, A.; Schlotter, W. F.; Turner, J. J.; Williams, G. J. Rev. Mod. Phys. 2016, 88, 015007. (34) Szilagyi, E.; Wittenberg, J. S.; Miller, T. A.; Lutker, K.; Quirin, F.; Lemke, H.; Zhu, D. L.; Chollet, M.; Robinson, J.; Wen, H. D.; Sokolowski-Tinten, K.; Lindenberg, A. M. Nat. Commun. 2015, 6, 6577. (35) Mancini, G. F.; Latychevskaia, T.; Pennacchio, F.; Reguera, J.; Stellacci, F.; Carbon, F. Nano Lett. 2016, 16, 2705−2713. (36) Zewail, A. H. Science 2010, 328, 187−193. (37) Flannigan, D. J.; Zewail, A. H. Acc. Chem. Res. 2012, 45, 1828− 1839. (38) LaGrange, T.; Reed, B. W.; Santala, M. K.; McKeown, J. T.; Kulovits, A.; Wiezorek, J. M. K.; Nikolova, L.; Rosei, F.; Siwick, B. J.; Campbell, G. H. Micron 2012, 43, 1108−1120. (39) Piazza, L.; Masiel, D. J.; LaGrange, T.; Reed, B. W.; Barwick, B.; Carbone, F. Chem. Phys. 2013, 423, 79−84. (40) Plemmons, D. A.; Suri, P. K.; Flannigan, D. J. Chem. Mater. 2015, 27, 3178−3192. (41) Yurtsever, A.; van der Veen, R. M.; Zewail, A. H. Science 2012, 335, 59−64. (42) van der Veen, R. M.; Kwon, O.-H.; Tissot, A.; Hauser, A.; Zewail, A. H. Nat. Chem. 2013, 5, 395−402. (43) Cremons, D. R.; Plemmons, D. A.; Flannigan, D. J. Nat. Commun. 2016, 7, 11230.
ASSOCIATED CONTENT
S Supporting Information *
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.nanolett.6b03975. Descriptions of the experimental methods, results of static characterization of crystallinity and orientation of the singleand multiparticle specimens, descriptions and summaries of UEM bright-field image and data analysis of the single- and multiparticle experiments, and results of finite element simulations of eigenmodes . (PDF) UEM bright-field imaging of single-particle diffractioncontrast dynamics and corresponding transient signal modulation. (AVI) UEM bright-field imaging of multiparticle diffractioncontrast dynamics and corresponding transient signal modulation. (AVI)
■
AUTHOR INFORMATION
Corresponding Author
*E-mail: fl
[email protected]. Author Contributions
D.T.V. prepared the specimens, conducted the experiments, and analyzed the data. D.T.V., V.E.F., and D.J.F. conceived of the studies, designed the experiments, and interpreted the results. D.J.F. supervised the work. D.T.V., V.E.F., and D.J.F. wrote the manuscript. Notes
The authors declare no competing financial interest.
■
ACKNOWLEDGMENTS This work was supported partially by the National Science Foundation through the University of Minnesota MRSEC under award no. DMR-1420013 and partially by the Arnold and Mabel Beckman Foundation through a Beckman Young Investigator Award. Additional support was provided by a Ray D. and Mary T. Johnson/Mayon Plastics Professorship through the University of Minnesota Department of Chemical Engineering and Materials Science.
■
REFERENCES
(1) Li, M.; Tang, H. X.; Roukes, M. L. Nat. Nanotechnol. 2007, 2, 114− 120. (2) Safavi-Naeini, A. H.; Alegre, T. P. M.; Chan, J.; Eichenfield, M.; Winger, M.; Lin, Q.; Hill, J. T.; Chang, D. E.; Painter, O. Nature 2011, 472, 69−73. (3) Zheludev, N. I.; Plum, E. Nat. Nanotechnol. 2016, 11, 16−22. (4) Jain, P. K.; Huang, X.; El-Sayed, I. H.; El-Sayed, M. A. Acc. Chem. Res. 2008, 41, 1578−1586. (5) Harutyunyan, H.; Martinson, A. B. F.; Rosenmann, D.; Khorashad, L. K.; Besteiro, L. V.; Govorov, A. O.; Wiederrecht, G. P. Nat. Nanotechnol. 2015, 10, 770−774. (6) Link, S.; Burda, C.; Mohamed, M. B.; Nikoobakht, B.; El-Sayed, M. A. Phys. Rev. B: Condens. Matter Mater. Phys. 2000, 61, 6086−6090. (7) Hu, M.; Hillyard, P.; Hartland, G. V.; Kosel, T.; Perez-Juste, J.; Mulvaney, P. Nano Lett. 2004, 4, 2493−2497. (8) Pelton, M.; Sader, J. E.; Burgin, J.; Liu, M. Z.; Guyot-Sionnest, P.; Gosztola, D. Nat. Nanotechnol. 2009, 4, 492−495. (9) Marty, R.; Arbouet, A.; Girard, C.; Mlayah, A.; Paillard, V.; Lin, V. K.; Teo, S. L.; Tripathy, S. Nano Lett. 2011, 11, 3301−3306. (10) Hartland, G. V. Chem. Rev. 2011, 111, 3858−3887. (11) Ruijgrok, P. V.; Zijlstra, P.; Tchebotareva, A. L.; Orrit, M. Nano Lett. 2012, 12, 1063−1069. F
DOI: 10.1021/acs.nanolett.6b03975 Nano Lett. XXXX, XXX, XXX−XXX
Letter
Nano Letters (44) Barwick, B.; Park, H. S.; Kwon, O. H.; Baskin, J. S.; Zewail, A. H. Science 2008, 322, 1227−1231. (45) Kwon, O.-H.; Barwick, B.; Park, H. S.; Baskin, J. S.; Zewail, A. H. Nano Lett. 2008, 8, 3557−3562. (46) Flannigan, D. J.; Zewail, A. H. Nano Lett. 2010, 10, 1892−1899.
G
DOI: 10.1021/acs.nanolett.6b03975 Nano Lett. XXXX, XXX, XXX−XXX
