Surface-Enhanced Dual-Frequency Two-Dimensional Vibrational

Subscriber access provided by UCL Library Services

C: Plasmonics, Optical Materials, and Hard Matter

Surface-Enhanced Dual-Frequency Two-Dimensional Vibrational Spectroscopy of Thin Layers at an Interface Robert T. Mackin, Bar Cohn, Andrey Gandman, Joel D Leger, Lev Chuntonov, and Igor V Rubtsov J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/acs.jpcc.8b02436 • Publication Date (Web): 27 Apr 2018 Downloaded from http://pubs.acs.org on April 27, 2018

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 22 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

The Journal of Physical Chemistry

Surface-Enhanced Dual-Frequency Two-Dimensional Vibrational Spectroscopy of Thin Layers at an Interface Robert T. Mackin,a Bar Cohn,b Andrey Gandman,b Joel D. Leger,a Lev Chuntonov,b* Igor V. Rubtsova* a

Department of Chemistry, Tulane University, New Orleans, LA 70118, U.S.A.

b

Schulich Faculty of Chemistry and Solid State Institute, Technion, Haifa, Israel [email protected], [email protected]

ABSTRACT Development of spectroscopic approaches to study molecules at interfaces is important as the molecular properties often differ from those in the bulk. Implementation of surface-enhanced two-dimensional infrared (SE 2DIR) spectroscopy using lithographically fabricated plasmonic nanoarrays is demonstrated for nanometer-thick films. The sample, 4-azidobutyrate-Nhydroxysuccinimide ester (azNHS), dispersed in polystyrene was deposited onto the nanoarray. Raw enhancements in the SE 2DIR spectra exceeding 5×104 and 1.3×103 fold were achieved for the CO and NN peaks, respectively. The field enhancement provided by the nanoarray was sufficient to record cross peaks in 1nm-thick samples under dilute conditions for azNHS (~0.1M). Note that the cross peaks were recorded for vibrational modes frequency-separated by ~350 cm-1 with the enhancement factor of 4.1×104. The effective electric field enhancement factors, measured for NN and CO modes via linear and two nonlinear IR techniques, have similar sample-thickness dependences, which permits using linear spectroscopy for enhancement evaluation. High-quality cross-peak waiting-time dependences were recorded for samples as thin as 1nm involving several IR reporters demonstrating applicability of an arsenal of 2DIR approaches, including spectral diffusion, chemical exchange, relaxation-assisted 2DIR, to interrogate samples in nm-thick films. The study opens new opportunities in analyzing structures and dynamics of molecules at interfaces.

ACS Paragon Plus Environment

1

The Journal of Physical Chemistry 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 2 of 22

INTRODUCTION Electromagnetic radiation is enhanced locally near the surface of noble-metal nanostructures owing to excitation of the localized plasmon resonances. Nanodevices utilizing plasmon resonances as key functional elements emerge in a variety of fields, including sensors, molecular machines, plasmon-assisted chemistry and medicine, etc.1-3 Enhancement of the nearfield upon the excitation of the plasmon resonances leads to enhancement of the spectroscopic transitions in molecules on the nanostructure surfaces – a phenomenon that is extensively used in several sensitive spectroscopic techniques,4-6 including surface enhanced infrared absorption (SEIRA) spectroscopy.4,7-14 SEIRA is capable of studying very thin layers of a sample and providing valuable data for molecules at interfaces.13 Rational engineering of the plasmonic fields via the design of metal nanostructure’s shape and size allows measurements with sensitivity down to a single monolayer of molecules self-assembled on metallic structures.8,15,16 It is appealing to use such plasmonic nanostructures for enhancing sensitivity in nonlinear measurements. A powerful time-resolved technique, two-dimensional infrared (2DIR) spectroscopy, reports on correlations of vibrational modes in the sample. These correlations, measured via detection of diagonal and cross peaks, can be linked to the molecular structures and their dynamics.17 2DIR spectroscopy of molecules at interfaces has shown that their structure and dynamics can differ from those in the bulk.18-24 Rough metal surfaces are actively used to achieve enhancements in 2DIR measurements.18-27 The raw-signal enhancement of 470 fold was reported, providing opportunities of SE 2DIR diagonal-peak measurements of monolayers.22,28,29 SE 2DIR spectroscopy based on the enhanced fields of plasmonic half-wavelength infrared antennas has recently been demonstrated on diagonal peaks.28,30 In addition, progress has been made in theoretical approach to quantum dynamics of molecules on plasmonic structures studied by ultrafast 2D spectroscopy.31,32 It is attractive to expand SE 2DIR into cross-peak measurements for thin film samples, which would unleash the full power of 2DIR. Note that cross peaks are typically several orders of magnitude weaker than diagonal peaks. Furthermore, the typical plasmon spectrum of the infrared antenna is rather narrow (fwhm~200 cm-1), which adds the challenge of cross-peak measurements. Therefore, the signal enhancement depends strongly on the frequency mismatch between the molecular and plasmonic transitions. In addition, because the strength of the


2

Page 3 of 22 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


plasmon-enhanced near-field is known to drop fast with the distance from the nanoantenna surface,10,33 the signal enhancement depends also on the sample thickness. In this work we demonstrate that despite of such unfavorable settings, robust systematic measurements of the enhanced signals are possible even with moderate enhancements by mid-IR antenna, which are significantly lower than those routinely obtained in the visible.4-6 A range of SE 2DIR techniques were performed, including diagonal and cross peak measurements on dilute samples of various thicknesses (1 – 85 nm). Cross peaks between vibrational labels spatially separated by over 10Å and frequency separated by over 350 cm-1 were recorded. In addition, relaxation-assisted 2DIR (RA 2DIR) measurements reporting on the energy transport within molecules and between the sample film and the gold nanoantenna were successfully performed. The magnitudes of signal enhancements that made such measurements possible were determined using heterodyned three-pulse photon echo, vibrational pump-probe, and linear FTIR techniques as well as by numerical simulations (FDTD). The work demonstrates that large arsenal of 2DIR approaches, including RA 2DIR, spectral diffusion, and other waiting time dependent methods, is now applicable to samples as thin as 1 nm, opening an avenue of measuring structural and dynamics properties of molecules at interfaces.

EXPERIMENTAL METHODS Electron beam lithography. The gold antennas were fabricated on solvent-cleaned CaF2 windows. A double layer PMMA coating (495-A2 and 950-A3 MicroChem) was used to make a negative slope template by the electron beam. A 20 nm layer of chromium (Cr) was deposited in order to have good conductivity for the EBL. The CaF2/PMMA/Cr samples were exposed to a pre-designed pattern using an EBL instrument (RAITH, EBPG 5200). The total area of the array was 5mm×5mm. During the development the Cr layer was removed by etchant (Micro Chemicals); the exposed PMMA was removed by methyl isobutyl ketone–isopropanol solution (MicroChem). A 5 nm Cr adhesion layer and 80 nm layer of gold were evaporated and the liftoff was done with acetone. Linear spectroscopy. Linear FTIR measurements were performed in a transmission mode with a Tensor 27 spectrometer (Bruker). A wire-grid polarizer was placed in the sample cell compartment to measure polarized FTIR spectra allowing measuring spectra with different


3


Page 4 of 22

polarizations without having to move the sample. Additionally, an aperture of ca. 3 mm in diameter was placed in front of the sample to limit the sampled area to the location of the array. Dual-frequency 2DIR and Pump-Probe IR spectroscopies. A fully automated dual-frequency three-pulse 2DIR spectrometer with heterodyned detection is described in detail elsewhere.34,35 To prevent nanoarray degradation, a neutral density filter, OD=1, was placed on all three beams before the sample. To increase the signal, this filter was removed during perpendicular polarization measurements of nanoarray and in off gold measurements. An additional ND filter was placed on the first and second beams (OD=0.3) resulting in a pulse energy at the sample of ca. 70 nJ/pulse for each beam. The third (probe) beam was further suppressed for both 2DIR and pump-probe experiments resulting in ca. 8 nJ pulse energy. The signals in the 2DIR measurements on CaF2 and on gold under perpendicular polarization were scaled down to correspond to the same pulse energies used in the measurements on the gold array under parallel polarization. Note that the non-collinear laser beam geometry used in 2DIR measurements permits collecting only the 3rd-order signals in a given direction/measurement. FDTD simulations. Numerical electromagnetic FDTD calculations were done using Lumerical software. Transmission spectrum was calculated by integration of the flux of the Pointing vector of the light passing through the sample. We used a plane wave excitation and a non-uniform mesh in order to increase sampling in the vicinity of the antenna; grid size down to 0.25 nm was used for thin layers. The simulation space involved a three-dimensional box with dimensions matching those of the array’s unit and extending to 10 micrometers along the light propagation dimension. The 2D array was modeled using a periodic boundary condition. Absorbing boundary conditions were imposed for the propagating light. All the calculations were performed with an effective refractive index of the environment of n=1.21, which represented a combined effect of the CaF2 substrate and Cr adhesion layer under the gold structures. The gold dielectric constants from Johnson and Christy were used,36 while the vibrational transitions were modeled by a collection of Lorentz oscillators with the permittivity function ε (ω ) = n02 + ∑ k

ω0,2 k

f k ω02 , − ω 2 − iωγ k

where n0 = 1.58 represents the refractive index of the polystyrene matrix (assumed to be constant across the relevant frequency range), and the summation is over three CO and NN transitions of azNHS, such that ω0,k is the corresponding transition frequency, fk is the oscillator strength, and

γk is the associated linewidth. We used ω0,1 =1742 cm-1, ω0,2 =1788 cm-1, ω0,3 =1818 cm-1, ω0,4


4

Page 5 of 22 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


=2103 cm-1. The oscillator strengths were calibrated in a series of linear absorption experiments with thick polymer layers resulting in f1 =0.0205, f 2 =0.0033, f3 =0.0025, f 4 =0.0089; the same width, γ = 25 cm-1, was used for all transitions. RESULTS AND DISCUSSION The magnitude of the signal enhancement is the key quantity in assessing the feasibility of surface-enhanced spectroscopy. We evaluated the signal enhancement in a series of experiments, where we have systematically varied the amount of molecules contributing to the signal and their location within the enhanced near-field. Our studies were conducted with 4azidobutyrate-N-hydroxysuccinimide ester compound (azNHS, Fig. 1b, inset) dispersed in a polystyrene (PS) polymer film. The linear and 2DIR measurements were focused predominantly on two vibrational modes of azNHS, an asymmetric C=O stretching mode of succinimide (νCO) centered at 1742 cm-1 and a stretching mode of the azido moiety (νNN) centered at 2103 cm-1. Figure 1b (green line) shows the linear absorption (FTIR) spectrum of azNHS in a PS film measured under light polarized perpendicular to the long axis of the gold bars, which matches the absorption spectrum of azNHS in solution. The samples were made by spin coating of an azNHS/polystyrene solution onto the gold nanoarray (see SEM image in Fig. 1a) and on a bare CaF2 window. The extinction spectrum of the bare plasmonic array collected with the light polarization parallel to the long axis of the gold bars (Fig. 1b, black line) is broad (fwhm~200 cm-1) and intense (Dmax~1.8). The extinction spectrum of the nanoarray coated with 32 nm thick azNHS in polystyrene ([azNHS]=2.45 M) is shown with a blue line. The deposition of the polystyrene film leads to shift of the plasmon resonance to lower frequencies. Such sensitivity to change of the environment’s refractive index is often used in plasmonic sensing of binding dynamics;37-39 here, we used this shift as a gauge of the thickness of the deposited film (Fig. S2).

Surface Enhanced Linear FTIR Spectroscopy. As a reference point for signal enhancement in 2DIR measurements we first determined enhancements in linear SIERA measurements. To isolate the extinction associated with the vibrational transitions of azNHS, the shifted spectrum of the empty gold nanoantennas was subtracted from the spectrum of azNHS on the gold array. Typical Fano lineshapes are obtained for both νNN and νCO but their phases are different because of the corresponding blue and red detuning from the plasmon resonance.8 The optical density


5


Page 6 of 22

difference between the maximum and minimum in the Fano lineshape was taken as the FTIR ). To evaluate the enhancement provided by the amplitude of the molecular peak ( D Au

FTIR nanoantenna, the D Au values were compared to the signals generated from the sample of the

same thickness but lacking the plasmon enhancement. Three reference samples were tested to ensure that the sample thickness on the array is represented well by the reference sample. Those included a bare CaF2 region of the CaF2 window bearing the gold array (off the gold), on a different CaF2 window spin coated under the same conditions as for the nanoarray, and on the nanoarray with light polarization perpendicular to the gold bars. The film thickness was evaluated by the plasmon shift (see SI) as well as by the absorption peak of polystyrene in the CH stretching region (2924 cm-1). The analysis suggests that the thickness of the spin coated layer on CaF2 and off the gold array is essentially the same, in agreement with the conclusion of our previous study.30 Note that the spin coated layer essentially conforms to the surface, covering the gold bars from all directions.30 Comparison of the νCO absorption peaks for the film on the array measured with perpendicular polarization with that of the film off the array showed slight enhancement for the former by an average factor of 1.69. An enhancement was also predicted by the modeling (see SI). This experimental factor was applied to the data sets measured with FTIR as a reference resulting in a good match between different series. D Ref FTIR FTIR The resulting ratios, D Au , are shown in Table S3 along with the effective field / D Ref

FTIR FTIR enhancement ξ lin = (D Au / D Ref ) . The left panel of Figure 2b shows the electric field 1/ 2

enhancement as a function of film thickness in the FTIR measurements for the νCO and νNN transitions. Both curves show a drastic increase of the enhancement towards very small thicknesses with field enhancements exceeding 22 fold. The enhancement for νCO is essentially constant between 10 nm and 25 nm thicknesses at ca. 8.5; it decreases slowly for thicker films. The enhancement curve for νNN does not show a plateau but decreases monotonically towards larger thicknesses. Two effects play an important role for these dependences. First, the near-field decays away from the gold bar surface (Fig. S4), resulting in a reduction of the effective field enhancement experienced by molecules in thicker films. Since thicker films have a greater contribution to the signal generated from the sample located farther away from the antennas,30,33 as the film thickness increases, the average electric field felt by the sample decreases, which is most apparent at small thicknesses (40 ps, is caused by residual heating of the sample impinged by the excitation pulses, which results in a thermal grating


12

Page 13 of 22 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


diffracting the third beam in the phase-matched direction, producing cross peaks.48 Note that at time delays exceeding 40 ps, the local vibrational energy equilibration (thermalization) is mostly complete. The transient grating can vanish due to cooling, which can occur in two directions, along the substrate and perpendicular to the grating grooves. Under the experimental conditions, the period of the transient grating is ca. 17 µm; thermalization in this direction takes microseconds. Thermalization into the substrate (gold) can occur rapidly for nanometer thick films. As the signals are generated mostly in the vicinity of the gold bars, the cooling into the gold bars should dominate the thermalization dynamics. Therefore, the waiting time dynamics at delays >40 ps can report on the cooling of the transient grating into the substrate, providing data on the thermal conductivity at the interface.

CONCLUSIONS Successful implementation of SE 2DIR spectroscopy using plasmonic arrays is demonstrated for nanometer-thick films. The sample, azNHS compound dispersed in a dilute fashion in polystyrene film, was deposited onto a plasmonic nanostructure, fabricated lithographically on a CaF2 window. Raw enhancements of the SE 2DIR diagonal spectra exceeding 5×104 and 1.3×103 fold were achieved for the CO and NN peaks, respectively. The latter value is small because of the frequency mismatch between the molecular transition and the plasmon maximum, ∆Ω. Selig et al. recently reported SE 2D pump-probe measurements on the CO stretching mode of PMMA enhanced by a randomized gold nanoarray.28 A raw-signal enhancement of 6×103 was obtained for a 5 nm thick film deposited on an array under conditions of ∆Ω ~ 0.28 The enhancement of 5×104 obtained in our work for the CO peak suffers from the frequency mismatch and would be several fold larger under ∆Ω ~ 0 conditions. However, one of the objectives of this work was to quantify the enhancement for cross peaks, where the ∆Ω ~ 0 condition cannot be satisfied simultaneously for both vibrational modes involved. Nevertheless, the field enhancement was sufficient to record cross peaks in a 1 nm thick sample at ca. 0.1 M azNHS concentration. Note that under these conditions there are only ca. 1250 molecules of azNHS per side of a single bar (w×h = 0.021 µm2) with a rather low density with one molecule per ~1700 Å2 (~40Å×40Å) area. The corresponding surface density of 0.06 molecules per nm2 is ca. 100 fold smaller than the surface density of small molecules in a monolayer.


13


Page 14 of 22

High-quality waiting-time dependences for such cross peaks were demonstrated. It was confirmed that the observed dependences are characteristic to the compound (azNHS) and were not noticeably affected by the plasmon transition that served to enhance them. The ability of measuring waiting time dependences makes a range of 2DIR techniques, such as spectral diffusion, chemical exchange, and RA 2DIR, available for interrogating samples in nm-thick films.49 Raw signal enhancements were recorded for two vibrational reporters (νNN, νCO) via several techniques, including IR pump-probe, 2DIR three-pulse echo, and linear FTIR methods. It was found that the effective electric field enhancement factors for a given vibrational reporter, measured via different techniques, have similar sample-thickness dependences allowing for simplified evaluation of the enhancements achievable in the 3rd-order techniques using linear FTIR spectroscopy. Consequently, we have shown that classical electrodynamics modeling of thickness dependences of linear signals allows prediction of the enhancement magnitude also for the non-linear signals. Note, that the cross peaks were recorded for vibrational modes with central frequencies separated by over 350 cm-1, while the width of the plasmon transition is rather small (fwhm~200 cm-1). Even under such unfavorable conditions, the raw enhancement factor of 4.1×104 was obtained for 1-nm thick films. Development of more elaborate plasmonic structures with wider spectral response and higher near field enhancements is an important next step, which would allow measuring SE 2DIR spectra of thin samples covering larger frequency regions with numerous structural reporters, as available for thick samples.50 Thermal conduction in thin layers, including self-assembled monolayers, is highly important in nano-scale devices, where molecules play important structural and functional roles, and in particular in those devices made of noble metals.1 We demonstrated that SE RA 2DIR permits recording transport of the excess energy in thin films on an ultrafast time scale. Detailed understanding of the excess energy relaxation pathways in nano-devices2,3 can lead to optimal ways of microscopic heat management. The implementation of plasmonic nanoarrys to 2DIR spectroscopy opens a route to studies of structural dynamics in minute amounts of analyte molecules on the nanoscale. It allows to fully benefiting from the techniques of multi-dimensional ultrafast spectroscopy and nano-fabrication methods developed to steer and localize plasmonic fields on the sub-wavelength scale. While further developments of more efficient plasmonic arrays are expected, immediate


14

Page 15 of 22 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


applications of SE 2DIR cross-peaks measurements are anticipated for studies of structural dynamics of molecules at interfaces.51

Supporting Information. Procedure for determination of the film thickness, signal referencing, and supplementary tables and figures. This information is available free of charge via the Internet at http://pubs.acs.org

Acknowledgement. This work is supported by a grant 2016167 from the United States – Israel Binational Science Foundation (BSF). Plasmonic arrays were prepared at the Micro- and NanoFabrication Unit, Technion, with support from the Russell Berrie Nanotechnology Institute. Support by the United States National Science Foundation (CHE-1462075) and by Israel Science Foundation (1118/15) is gratefully acknowledged.

References (1) Van Delden, R. A.; Ter Wiel, M. K.; Pollard, M. M.; Vicario, J.; Koumura, N.; Feringa, B. L. Unidirectional Molecular Motor on a Gold Surface, Nature 2005, 437, 1337-1340 (2) Kudernac, T.; Ruangsupapichat, N.; Parschau, M.; Macia, B.; Katsonis, N.; Harutyunyan, S. R.; Ernst, K.-H.; Feringa, B. L. Electrically Driven Directional Motion of a Four-Wheeled Molecule on a Metal Surface, Nature 2011, 479, 208-211 (3) Panman, M. R.; Bodis, P.; Shaw, D. J.; Bakker, B. H.; Newton, A. C.; Kay, E. R.; Brouwer, A. M.; Buma, W. J.; Leigh, D. A.; Woutersen, S. Operation Mechanism of a Molecular Machine Revealed Using Time-Resolved Vibrational Spectroscopy, Science 2010, 328, 12551258 (4) Wang, H.; Kundu, J.; Halas, N. J. Plasmonic Nanoshell Arrays Combine SurfaceEnhanced Vibrational Spectroscopies on a Single Substrate, Angew. Chem., Int. Ed. 2007, 46, 9040-9044 (5) Kneipp, K.; Wang, Y.; Kneipp, H.; Perelman, L. T.; Itzkan, I.; Dasari, R. R.; Feld, M. S. Single Molecule Detection Using Surface-Enhanced Raman Scattering (Sers), Phys. Rev. Lett. 1997, 78, 1667-1670 (6) Nie, S.; Emory, S. R. Probing Single Molecules and Single Nanoparticles by Surface-Enhanced Raman Scattering, Science 1997, 275, 1102-1106 (7) Enders, D.; Pucci, A. Surface Enhanced Infrared Absorption of Octadecanethiol on Wet-Chemically Prepared Au Nanoparticle Films, Appl. Phys. Lett. 2006, 88, 184104


15


Page 16 of 22

(8) Neubrech, F.; Pucci, A.; Cornelius, T. W.; Karim, S.; García-Etxarri, A.; Aizpurua, J. Resonant Plasmonic and Vibrational Coupling in a Tailored Nanoantenna for Infrared Detection, Phys. Rev. Lett. 2008, 101, 157403 (9) Bochterle, J.; Neubrech, F.; Nagao, T.; Pucci, A. Angstrom-Scale Distance Dependence of Antenna-Enhanced Vibrational Signals, Acs Nano 2012, 6, 10917-10923 (10) Neubrech, F.; Beck, S.; Glaser, T.; Hentschel, M.; Giessen, H.; Pucci, A. Spatial Extent of Plasmonic Enhancement of Vibrational Signals in the Infrared, Acs Nano 2014, 8, 6250-6258 (11) Adato, R.; Yanik, A. A.; Amsden, J. J.; Kaplan, D. L.; Omenetto, F. G.; Honge, M. K.; Erramilli, S.; Altug, H. Ultra-Sensitive Vibrational Spectroscopy of Protein Monolayers with Plasmonic Nanoantenna Arrays, Proc. Natl. Acad. Sci. U.S.A. 2009, 106, 19227-19232 (12) Adato, R.; Altug, H. In-Situ Ultra-Sensitive Infrared Absorption Spectroscopy of Biomolecule Interactions in Real Time with Plasmonic Nanoantennas, Nature Comm. 2013, 4, 3154 (13) Neubrech, F.; Huck, C.; Weber, K.; Pucci, A.; Giessen, H. Surface-Enhanced Infrared Spectroscopy Using Resonant Nanoantennas, Chem. Rev. 2017, 117, 5110–5145 (14) Vogt, J.; Huck, C.; Neubrech, F.; Pucci, A. Plasmonic Light Scattering and Infrared Vibrational Signal Enhancement. In Frontiers of Plasmon Enhanced Spectroscopy Volume 2; ACS Publications, 2016; pp 1-19. (15) Brown, L. V.; Yang, X.; Zhao, K.; Zheng, B. Y.; Nordlander, P.; Halas, N. J. FanShaped Gold Nanoantennas above Reflective Substrates for Surface-Enhanced Infrared Absorption (Seira), Nano Letters 2015, 15, 1272-1280 (16) Aouani, H.; Šípová, H.; Rahmani, M.; Navarro-Cia, M.; Hegnerová, K. i.; Homola, J. i.; Hong, M.; Maier, S. A. Ultrasensitive Broadband Probing of Molecular Vibrational Modes with Multifrequency Optical Antennas, ACS Nano 2012, 7, 669-675 (17) Hochstrasser, R. M. Two-Dimensional Spectroscopy at Infrared and Optical Frequencies., Proc. Natl. Acad. Sci. U.S.A. 2007, 104, 14190-14196 (18) Yan, C.; Yuan, R.; Pfalzgraff, W. C.; Nishida, J.; Wang, L.; Markland, T. E.; Fayer, M. D. Unraveling the Dynamics and Structure of Functionalized Self-Assembled Monolayers on Gold Using 2d Ir Spectroscopy and Md Simulations, Proc. Natl. Acad. Sci. U.S.A. 2017, 113, 4929-4934 (19) Donaldson, P. M.; Hamm, P. Gold Nanoparticle Capping Layers: Structure, Dynamics, and Surface Enhancement Measured Using 2dir Spectroscopy, Angew. Chem. Int.Ed. 2013, 52, 634-638 (20) Selig, O.; Siffels, R.; Rezus, Y. L. A. Ultrasensitive Ultrafast Vibrational Spectroscopy Employing the near Field of Gold Nanoantennas, Phys. Rev. Lett. 2015, 114, 233004 (21) Kraack, J. P.; Hamm, P. Surface-Sensitive and Surface-Specific Ultrafast TwoDimensional Vibrational Spectroscopy, Chem. Rev. 2017, 117, 10623–10664 (22) Kraack, J. P.; Kaech, A.; Hamm, P. Surface Enhancement in Ultrafast 2d Atr Ir Spectroscopy at the Metal-Liquid Interface, J. Phys. Chem. C 2016, 120, 3350-3359 (23) Yan, C.; Thomaz, J. E.; Wang, Y.-L.; Nishida, J.; Yuan, R.; Breen, J. P.; Fayer, M. D. Ultrafast to Ultraslow Dynamics of a Langmuir Monolayer at the Air/Water Interface Observed with Reflection Enhanced 2d Ir Spectroscopy, J. Am. Chem. Soc. 2017, 139, 1651816527


16

Page 17 of 22 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(24) Li, J.; Qian, H.; Chen, H.; Zhao, Z.; Yuan, K.; Chen, G.; Miranda, A.; Guo, X.; Chen, Y.; Zheng, N.et al. Two Distinctive Energy Migration Pathways of Monolayer Molecules on Metal Nanoparticle Surfaces, Nat. Comm. 2016, 7, 10749 (25) Kraack, J. P.; Lotti, D.; Hamm, P. Ultrafast, Multidimensional Attenuated Total Reflectance Spectroscopy of Adsorbates at Metal Surfaces, J. Phys. Chem. Lett. 2014, 5, 23252329 (26) Kraack, J. P.; Lotti, D.; Hamm, P. 2d Attenuated Total Reflectance Infrared Spectroscopy Reveals Ultrafast Vibrational Dynamics of Organic Monolayers at Metal-Liquid Interfaces, J. Chem.Phys. 2015, 142, 212413 (27) Lotti, D.; Hamm, P.; Kraack, J. P. Surface-Sensitive Spectro-Electrochemistry Using Ultrafast 2d Atr Ir Spectroscopy, J. Phys. Chem. C 2016, 120, 2883-2892 (28) Selig, O.; Siffels, R.; Rezus, Y. L. A. Ultrasensitive Ultrafast Vibrational Spectroscopy Employing the near Field of Gold Nanoantennas, Phys. Rev. Lett. 2015, 114, 233004 (29) Kraack, J. P.; Hamm, P. Vibrational Ladder-Climbing in Surface-Enhanced, Ultrafast Infrared Spectroscopy, Phys. Chem. Chem. Phys. 2016, 18, 16088-16093 (30) Gandman, A.; Mackin, R.; Cohn, B.; Rubtsov, I. V.; Chuntonov, L. TwoDimensional Fano Lineshapes in Ultrafast Vibrational Spectroscopy of Thin Molecular Layers on Plasmonic Arrays, J. Phys. Chem. Lett. 2017, 8, 3341-3346 (31) Finkelstein-Shapiro, D.; Calatayud, M.; Atabek, O.; Mujica, V.; Keller, A. Nonlinear Fano Interferences in Open Quantum Systems: An Exactly Solvable Model, Phys. Rev. A 2016, 93, 063414 (32) Finkelstein-Shapiro, D.; Poulsen, F.; Pullerits, T.; Hansen, T. Coherent TwoDimensional Spectroscopy of a Fano Model, Phys. Rev. B 2016, 94, 205137 (33) Dregely, D.; Neubrech, F.; Duan, H.; Vogelgesang, R.; Giessen, H. Vibrational near-Field Mapping of Planar and Buried Three-Dimensional Plasmonic Nanostructures, Nature Comm. 2013, 4, 3237 (34) Leger, J.; Nyby, C.; Varner, C.; Tang, J.; Rubtsova, N. I.; Yue, Y.; Kireev, V.; Burtsev, V.; Qasim, L.; Rubtsov, G. I.et al. Fully Automated Dual-Frequency Three-Pulse-Echo 2dir Spectrometer Accessing Spectral Range from 800 to 4000 Wavenumbers, Rev. Sci. Instr. 2014, 85, 083109, 1-16. (35) Nyby, C. M.; Leger, J. D.; Tang, J.; Varner, C.; Kireev, V. V.; Rubtsov, I. V. Mid-Ir Beam Direction Stabilization Scheme for Vibrational Spectroscopy, Including DualFrequency 2dir, Opt. Express 2014, 22, 6801-6809 (36) Johnson, P. B.; Christy, R. W. Optical Constants of the Noble Metals, Phys. Rev. B 1972, 6, 4370-4379 (37) Anker, J. N.; Hall, W. P.; Lyandres, O.; Shah, N. C.; Zhao, J.; Van Duyne, R. P. Biosensing with Plasmonic Nanosensors, Nat Mater 2008, 7, 442-453 (38) Willets, K. A.; Van Duyne, R. P. Localized Surface Plasmon Resonance Spectroscopy and Sensing, Annu. Rev. Phys. Chem. 2007, 58, 267-297 (39) Reinhard, B. M.; Sheikholeslami, S.; Mastroianni, A.; Alivisatos, A. P.; Liphardt, J. Use of Plasmon Coupling to Reveal the Dynamics of DNA Bending and Cleavage by Single Ecorv Restriction Enzymes, Proc. Natl. Acad. Sci. U.S.A. 2007, 104, 2667-2672 (40) Neuman, T.; Huck, C.; Vogt, J.; Neubrech, F.; Hillenbrand, R.; Aizpurua, J.; Pucci, A. Importance of Plasmonic Scattering for an Optimal Enhancement of Vibrational Absorption in Seira with Linear Metallic Antennas, J. Phys. Chem. C 2015, 119, 26652-26662


17


Page 18 of 22

(41) Lovera, A.; Gallinet, B.; Nordlander, P.; Martin, O. J. F. Mechanisms of Fano Resonances in Coupled Plasmonic Systems, ACS Nano 2013, 7, 4527-4536 (42) Taubert, R.; Ameling, R.; Weiss, T.; Christ, A.; Giessen, H. From near-Field to Far-Field Coupling in the Third Dimension: Retarded Interaction of Particle Plasmons, Nano Lett. 2011, 11, 4421-4424 (43) Hein, S. M.; Giessen, H. Retardation-Induced Phase Singularities in Coupled Plasmonic Oscillators, Phys. Rev. B 2015, 91, 205402 (44) Alonso-GonzÃ¡lez, P.; Albella, P.; Neubrech, F.; Huck, C.; Chen, J.; Golmar, F.; Casanova, F.; Hueso, L. E.; Pucci, A.; Aizpurua, J.et al. Experimental Verification of the Spectral Shift between near- and Far-Field Peak Intensities of Plasmonic Infrared Nanoantennas, Phys. Rev. Lett. 2013, 110, 203902 (45) Rubtsova, N. I.; Qasim, L., N.; Kurnosov, A. A.; Burin, A. L.; Rubtsov, I. V. Ballistic Energy Transport in Oligomers, Acc. Chem.Res. 2015, 48, 2547-2555 (46) Rubtsova, N. I.; Rubtsov, I. V. Vibrational Energy Transport in Molecules Studied by Relaxation-Assisted Two-Dimensional Infrared Spectroscopy, Ann. Rev. Phys. Chem. 2015, 66, 717-738 (47) Lin, Z.; Rubtsov, I. V. Constant-Speed Vibrational Signaling Along Polyethyleneglycol Chain up to 60-Å Distance, Proc. Natl. Acad. Sci. U.S.A. 2012, 109, 14131418 (48) Lin, Z.; Keiffer, P.; Rubtsov, I. V. A Method for Determining Small Anharmonicity Values from 2dir Spectra Using Thermally Induced Shifts of Frequencies of High-Frequency Modes., J. Phys. Chem. B 2011, 115, 5347-5353 (49) Love, J. C.; Estroff, L. A.; Kriebel, J. K.; Nuzzo, R. G.; Whitesides, G. M. SelfAssembled Monolayers of Thiolates on Metals as a Form of Nanotechnology, Chem. Rev. 2005, 105, 1103-1170 (50) Naraharisetty, S. G.; Kasyanenko, V. M.; Rubtsov, I. V. Bond Connectivity Measured Via Relaxation-Assisted Two-Dimensional Infrared Spectroscopy, J. Chem. Phys. 2008, 128, 104502 (51) Cohn, B.; Prasad, A. K.; Chuntonov, L. Communication: Probing the Interaction of Infrared Antenna Arrays and Molecular Films with Ultrafast Quantum Dynamics, J. Chem. Phys. 2018, 148, 131101 Figures a)

b)

LII d

L⊥ .


18

Page 19 of 22

Figure 1. a) Scanning electron microscope image of gold plasmonic array with d=1.95 µm, L⊥ × L|| = 2.2 µm × 2.95 µm (see Fig. S1). b) Linear extinction spectra of a bare plasmonic nanoarray (black line) and plasmonic array with a deposited ca. 32 nm thick azNHS/polystyrene ([azNHS] = 2.45 M) film (blue). The extinction spectrum associated with the molecular transitions (red) was obtained by subtraction of the shifted and scaled spectrum of the bare nanoarrays from the spectrum of the film on the nanoarrays. The absorption spectrum of the film measured with light polarized perpendicular to the bars is shown with green line (scaled 30-fold).

.

Fig. 2. Thickness dependence of the effective electric field enhancement for (a) linear, (b) pumpprobe (PP) and diagonal 2DIR (HPE), and (c) cross peak measurements. The error bars show the standard deviation determined for multiple experiments for the same thicknesses. The dashed cross HPE HPE line (c) shows cross peak enhancement evaluated as ξ NN/CO = ( ξ NN ξ CO ) 0 . 5 . Lines of matching colors represent electromagnetic simulations for the respective experiments. 1800

15 1800

1750

1750

ωτ / cm-1

0.08

b)

a)

0.06

10 1700

1700 0.04

5 1650

1650 0.02 1650 1700 1750 1800 -1

c)

1650 1700 1750 1800 7 6

2150

5

-1

ωτ / cm

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


4

2100

d)

1

2150

0.8 2100

0.6

3

0.4

2 2050

2050

1 2050

2100

ω / cm-1 t

2150

1.2

0.2 2050

2100

2150

ωt / cm-1

Figure 3. SE 2DIR diagonal CO spectra of 5.9 nm thick azNHS/polystyrene film (a) on gold array and (b) on CaF2. SE 2DIR diagonal NN spectra of 14.5 nm thick film (c) on gold array and (d) on CaF2 measured at T = 0.1 ps.


19


Page 20 of 22

.

Figure 4. SE 2DIR magnitude νNN/νCO cross peak spectrum of 1 nm thick azNHS/PS on gold array measured at T = 3.8 ps. The attached panels show the total linear absorption of the sample on the nano array under parallel (blue) and perpendicular (green, ×3000) polarizations. Note that the broad plasmon absorption (blue) is significantly detuned from both molecular transitions.

.

.

Figure 5. FDTD simulations of the nanoarray spectra. Extinction spectra (left axis) are shown with solid lines for the bare gold array (black), array with a polystyrene film of 30 nm without azNHS (blue) and with azNHS embedded (red). Near-field spectra (right axis) calculated at the point located on the line passing through the antenna center, at the height of 20 nm, and at the distance of 1 nm from the antenna edge (see also Fig. S4) are shown with dashed lines for the bare array (black) and array with 30 nm film (blue). The near-field of the bare array spectrum was scaled down by a factor of 2.6 for easier comparison.


20

Page 21 of 22

0.6 0.3 0

OD

a)

1.5

ω / cm-1 τ

2150 1 2100 0.5 2050 1700

1750

1800

1850

ωt / cm-1

b)

Cross peak amplitude (norm.)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


1.0

On nanoarray: -1 1742 cm -1 1785 cm -1 1815 cm In CDCl3:

0.8 0.6

-1

1742 cm 0.4 0.2 0.0 0

10

20

30

40

50

100 200 300 400

Waiting Time (ps)

Figure 6. SE 2DIR cross peaks (a) between νNN and three carbonyl transitions at 1742, 1785, and 1815 cm-1 for the 39.5 nm thick sample and (b) their waiting-time dependences. Waiting time dependence for νNN/1742 cm-1 of azNHS in CDCl3 solution at 0.06 M concentration in 50 µm sample cell is also shown (green).


21


Page 22 of 22

TOC Graphic


22

Surface-Enhanced Dual-Frequency Two-Dimensional Vibrational

Recommend Documents