Subscriber access provided by University of Newcastle, Australia
Article
Plasmonic-photonic hybrid modes excited on titanium nitride nanoparticle array in the visible region Ryosuke Kamakura, Shunsuke Murai, Satoshi Ishii, Tadaaki Nagao, Koji Fujita, and Katsuhisa Tanaka ACS Photonics, Just Accepted Manuscript • DOI: 10.1021/acsphotonics.6b00763 • Publication Date (Web): 16 Feb 2017 Downloaded from http://pubs.acs.org on February 17, 2017
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 free 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 accessible to all readers and 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.
ACS Photonics 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 9
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
ACS Photonics
Plasmonic−photonic hybrid modes excited on titanium nitride nanoparticle array in the visible region Ryosuke Kamakura,† Shunsuke Murai,†‡* Satoshi Ishii,§⊥ Tadaaki Nagao,§⊥ Koji Fujita,† and Katsuhisa Tanaka† †
Department of Material Chemistry, Graduate School of Engineering, Kyoto University, Katsura, Nishikyo-ku, Kyoto 6158510, Japan ‡ PRESTO, Japan Science and Technology Agency (JST), Kawaguchi, Saitama 332-0012, Japan §
International Center for Material Nanoarchitectonics (WPI-MANA), National Institute for Materials Science (NIMS), Tsukuba, Ibaraki 305-0044, Japan
⊥
CREST, Japan Science and Technology Agency, 4-1-8 Honcho, Kawaguchi, Saitama 332-0012, Japan
Supporting Information ABSTRACT: Conventionally used plasmonic materials generally have low thermal stability, low chemical durability (except gold) and are incompatible with complementary metal−oxide−semiconductor processes. However, titanium nitride (TiN), an emerging plasmonic material, possesses gold-like optical properties and displays relatively large ohmic losses. We fabricated a periodic array of TiN nanoparticles to effectively reduce these losses by coupling the localized surface plasmon resonance with light diffraction. The height of the nanoparticle and the periodicity of the array were designed to match the excitation conditions of both the localized surface plasmon resonance and light diffraction. As a result, the array supported a plasmonic–photonic hybrid mode in the visible region. To assess the loss mitigation effect, photoluminescence (PL) from the light emitting layer on the array was measured. The PL intensity was larger than that from the same layer on a TiN thin film, demonstrating the reduced loss. The angular and spectral profiles of the PL could be controlled by the hybrid mode. Our results therefore pave the way toward plasmonic devices that can be fabricated using traditional complementary metal−oxide−semiconductor processes. KEYWORDS: titanium nitride, localized surface plasmon resonance, periodic nanoparticle array.
Metallic nanoparticles possess large polarizability and can strongly manipulate light. This characteristic originates from localized surface plasmon resonances (LSPRs), which are plasma oscillations coupled with light at the metal’s surface. With rapid progress in nanofabrication techniques, various metallic nanostructures1-4 such as bow ties5,6, Yagi−Uda antennas7, and periodic particle arrays8−11 have been explored to utilize the responses of LSPRs for optical applications12−17. An important trend in plasmonics is a search for better materials. Conventionally, gold, silver, and copper have been used as plasmonic materials in the visible region. Although they show reasonably good optical properties, they suffer from low thermal stability, low chemical durability (except gold), and incompatibility with complementary metal−oxide−semiconductor (CMOS) processes. These limitations have hindered the implementation of plasmonic components in a number of applications. Therefore, the possibilities of using alternative materials such as transition metal nitrides and transparent conducting oxides18−20, which can function effectively in the visible and infrared regions, respectively, have been explored21−25. Among the above-mentioned alternative materials, titanium nitride (TiN) is an attractive material that is plasmonic in the visible and near-infrared. It shows optical properties similar to those of gold26, possesses a high thermal stability and high chemical durability, and is compatible with CMOS processes27. Plasmonic nanostructures have been fabricated by combining thin-film deposition techniques such as sputtering28,
pulsed laser deposition22, and atomic layer deposition27 with lithographic techniques and lift off or etching processes29−31. These attractive properties and mature fabrication techniques have boosted the exploration of TiN-based plasmonics. TiN has already been applied to create highly efficient local heat transducers31, broadband absorbers in the visible and nearinfrared range29, and hyperbolic metamaterials32. A major drawback of using TiN is that it has a larger ohmic loss than gold32. This is beneficial for efficient light−heat conversion, but detrimental for optical applications such as sensing and photoluminescence (PL) control, where heat is a byproduct of the intended phenomena. That is one reason why TiN-based plasmonic application has been mainly limited to optical absorbers and light−heat converters. To mitigate the intrinsic losses, we focused on a periodic array of nanoparticle, which can support lattice plasmons8,9. In such a structure, light diffraction in the plane of the array can mediate radiative coupling between the LSPRs on each nanoparticle10,33−38. Due to its hybrid nature this plasmonic−photonic hybrid mode accompanies the spatial distribution of light energy that is not concentrated near the nanoparticle but extends in the plane of the array, thus reducing the energy dissipation to the nanoparticle39. This characteristic distribution of light energy has been demonstrated to be useful for molecular sensing40, intensified fluorescence41−43, plasmonic lasers44, and increasing the efficiency of solar cells45,46. Our group previously reported the fabrication of periodic arrays of TiN nanoparticles with a height of 30 nm22. Although the plasma frequency of TiN was in the visible region, the height of the nanoparticle restricted
ACS Paragon Plus Environment
ACS Photonics
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 excitation of the hybrid mode only in the near-infrared region, and limits the application of the TiN array to the nearinfrared region. If the TiN array could support the hybrid mode in the visible region, the better overlap between the solar spectrum and absorption, lower work function (4.2–4.5 eV)47, and higher chemical and thermal stabilities of TiN compared with noble metals would enable their application to practical and feasible devices operating in the visible region48,49. In this study, we made an array composed of taller nanoparticles (height: 160 nm) to elucidate the full potential of TiN and excite the hybrid mode in the visible region36,50. We experimentally observed the hybrid mode in the visible region, and the simulation confirmed that the distribution of the energy of light extends in the plane of the array. We further demonstrated a PL enhancement in the visible region. The present study experimentally verifies that the periodic TiN array is an excellent platform for plasmonic and photonic devices in the visible and near-infrared region.
SAMPLE FABRICATION A TiN thin film (thickness: 160 nm) was grown on a sapphire substrate (GEOMATEC, Japan). The deposition was done by using DC magnetron sputtering under an Ar and N2 atmosphere at the substrate temperature of 250 ºC and the chamber pressure of 5×10-4 Pa. The X-ray diffraction patterns show the -oriented growth of the thin film, and the spectroscopic ellipsometry shows that the dielectric function is comparable to that of the thin film prepared via pulsed laser deposition22 (supporting information Fig. S1). The thin film was then patterned with a combination of nanoimprint lithography (EntreTM3, Obducat) and reactive ion etching (RIE) (RIE-101iPH, Samco) to form a periodic array of nanoparticles. Fig. 1(a) shows the process flow. First, the resist (TU2170, thickness: 200 nm) was coated onto the TiN thin film and prebaked for 5 min at 95 °C. As a master mold for nanoimprint lithography, a silicon mold consisting of a square array of nanopillars (diameter: 150 nm; height: 200 nm; and periodicity: 400 nm) was fabricated by electron beam lithography (F7000s-KYT01, Advantest) and silicon deep etching (RIE800iPB-KU, Samco). Then, the surface structure of the silicon mold was transferred to the resist by nanoimprint lithography. The square array of TiN nanoparticles was structured by RIE under a chamber pressure of 2 Pa, radio frequency power of 700 W, and Ar, BCl3, and Cl2 gas flow rates of 8, 5, and 15 sccm51, respectively. After being processed by RIE for 90 s, the residual resist was removed by O2 plasma etching (RIE10NR, Samco). For the demonstration of PL enhancement, poly (methyl methacrylate) (PMMA) containing 0.8 wt% rhodamine 6G (R6G) was spin coated on the sample. This light emitting layer will be referred to as the PMMA + R6G layer.
CHARACTERIZATION The surface structure of the TiN array was examined using scanning electron microscopy (SEM) (SU8000, Hitachi). The dispersive refractive index and the thickness of the TiN film and the PMMA + R6G layer were examined using a spectroscopic ellipsometry setup (FE-5000, Otsuka Electronics). The optical transmittance was measured as functions of incident angle (θin) and wavelength (λ). The sample was put on a rotation stage to vary θin on the sample surface. Si- and InxGa1xAs-based detectors were used to obtain spectra in the visible
Page 2 of 9
and infrared regions, respectively. The zeroth-order transmittance was obtained by normalizing the transmission intensity of the sample to that of the substrate. For the transmittance of the TiN array embedded in the PMMA + R6G layer, the transmission intensity was normalized to the transmission of the layer on the substrate. The PL spectra were measured as follows: a diode pumped solid state laser (λ = 473 nm, Shanghai Dream laser) was incident from the backside of the sample tilted by 5° from the normal. An optical fiber coupled to the spectrometer was rotated around the frontside of the sample to obtain the PL spectra as a function of emission angle (θem). The PL decay curve was examined using a confocal laser microscope combined with a time resolved detector. The excitation pulse at λ = 470 nm from a picosecond pulsed diode laser (PicoQuant model LDH-D-C-470B with a PDL 828 ‘Sepia II’ driver) was focused on the sample by a ×50 objective lens (0.8 NA-Olympus). The PL was collected by a timecorrelated photon counting system (WITec, StrobeLock) through a long pass color glass filter. The laser repetition rate was 10 MHz and the PL decay curve was collected with 0.2 s (integration time) and accumulated 100 times.
RESULTS AND DISCUSSION Exciting the plasmonic–photonic hybrid modes. The SEM image of the fabricated TiN nanoparticle array is shown in Fig. 1(b). The array is composed of TiN nanoparticles with diameters of 250 nm and heights of 160 nm, arranged in a square lattice with a pitch of a = 400 nm.
Fig. 1 (a) Schematic of the process flow of the TiN nanoparticle array. (b) A SEM top-view image of the TiN nanoparticle array. The size of the nanoparticles was ca. 250 (diameter) × 160 nm (height); they were periodically arranged in a square lattice with a pitch of 400 nm. The coordinate axes used in optical measurements and numerical simulations are also indicated. The inset of (b) shows an enlarged and oblique (30° to vertical) image.
Figure 2(a) displays the experimental transmittance spectra of the TiN array as a function of θin using a color scale. The conditions of light diffraction in the plane of the array, i.e., Rayleigh anomalies, are plotted using the refractive index of the substrate (n = 1.79) and air (n = 1.00) as black and red
ACS Paragon Plus Environment
Page 3 of 9
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
ACS Photonics
Fig. 3 Dip position of the transmittance of TiN nanoparticle array for this study (red circle, diameter: 250 nm, height: 160 nm) and a previous report (blue circle, diameter: 260 nm, height: 30 nm; green circle, diameter: 180 nm, height: 30 nm) as a function of incident angle. The dotted line represents the Rayleigh anomalies with the refractive index of a sapphire substrate (n = 1.79).
Fig. 2 (a) Experimental and (b) simulated transmittance spectra (p-polarized component) of the TiN nanoparticle array as a function of θin. Black and red dotted lines in (a) and (b) are the Rayleigh anomalies with the refractive indices of a sapphire substrate (n = 1.79) and air (n = 1.00), respectively. Panels (c)–(e) show the calculated spatial distribution of the normalized intensity, |E|2/|E0|2, in the zx-plane, at a y position intersecting the middle of a nanoparticle. The conditions of irradiation are λ = 900 nm and θin = 0° (c), λ = 900 nm and θin = 26° (d), λ = 700 nm and θin = 48° (e). The symbols in (b) denote the conditions of the calculation in (c)–(e). The white lines represent the boundaries of the materials.
dotted lines, respectively. Rayleigh anomalies satisfy the relation 2π k 2 = k 2 + m2 out inc 1a x
2 + m 2 2π 2 a y
2 2π + 2 k inc m1 a x
(1)
where kout and kinc [= sin ] are the wave vectors of the scattered and incident light; ax and ay are the pitch in the x and y directions; and m1 and m2 are the diffraction orders, respect-
tively42. The spectra clearly show the dips in transmittance, and the angular profiles of the dips vary along the diffraction lines. This indicates the coupling of the LSPRs via in-plane diffraction to generate the plasmonic−photonic hybrid modes35−39. The experimental transmittance spectra were reproduced by a simulation using the finite elemental method (COMSOL Multiphysics). The simulation model comprised from bottom to top the following elements: the sapphire substrate (n = 1.79), TiN particles (each with a diameter of 250 nm, height of 160 nm, and values for n and the extinction coefficient k that were obtained from spectroscopic ellipsometry data), and air (n = 1.00). The size of the unit cell was 400 nm × 400 nm × 2000 nm in the x, y, and z directions, with the periodic boundary conditions being applied to the x and y directions, port node on the top, and perfectly matched layer on the bottom. The coordinate axes were selected in accordance with the experiment (see the SEM image in Fig. 1(b)). The incident light was projected from the top and was linearly polarized in the x direction. The calculated transmittance is shown in Fig. 2(b). The angular profiles of the spectral features in the visible and near-infrared regions are reproduced satisfactorily. To elucidate the characteristics of the hybrid modes, the distributions of the light energy in the visible and near-infrared regions were calculated at conditions typical for light incident on the samples (see Figs. 2(c)−(e)). Under the conditions for exciting LSPRs (λ = 900 nm and θin = 0°, Fig. 2(c)), the light energy is most intense around the TiN nanoparticle because of the localized nature of LSPRs bound on the surface of TiN nanoparticle. Here the incident light energy is transferred to LSPRs and the dip appears in transmittance. Conversely, under the conditions to excite hybrid modes in the near-infrared (λ = 900 nm and θin = 26°, Fig. 2(d)) and the visible (λ = 700 nm and θin = 48°, Fig. 2(e)) regions, the energy is accumulated not only around the particle but also between the particles owing to the simultaneous excitations of the LSPRs and the inplane diffraction33−39. In Fig. 2(d), where the condition corresponds to the diffraction with n = 1.79, the light energy is concentrated at the substrate side, while in Fig. 2(e), where the
ACS Paragon Plus Environment
ACS Photonics
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 4 of 9
Fig. 4 Experimental (a) and simulated (b) transmittance spectra (p-polarized components) of the TiN nanoparticle array embedded in the PMMA layer with R6G as a function of θin. The transmittance was deduced by normalizing the transmittance of the sample to that of the layer on the substrate. The black and red dotted lines in (a) and (b) are the Rayleigh anomalies with n = 1.45 (PMMA + R6G layer) and 1.79 (sapphire substrate), respectively. (a) and (b) are plotted using different color scales for a clear comparison of the spectral features.
condition corresponds to that with n = 1.00, the light energy is concentrated at the air side. From the experiments and the simulations, we confirm that the fabricated TiN nanoparticle array shows plasmonic−photonic hybrid modes in the visible and near-infrared regions. As the incident angle approaches the diffraction condition, the in-plane radiative coupling of LSPRs via diffraction is excited and leads to the reduction of transmittance along with the diffraction lines 39 (supporting information Fig. S2). Spectral tuning of the hybrid modes by the nanoparticle height. When the height of the TiN nanoparticle is 30 nm, the hybrid mode is only observed in the near-infrared region (λ = ~1100 nm)22 (see supporting information Fig. S3). In this study, the TiN nanoparticles (height: 160 nm) are taller and the LSPRs blueshift because the increase in height is accompanied by an increase in the number of free electrons contributing to the plasmonic oscillation. Figure 3 compares the dip positions in near-infrared in this study and those in the previous report. It clearly demonstrates that the dip position can be tuned by the height and diameter of the nanoparticle. In addi-
Fig. 5 (a) Emission spectra (p-polarized component) of the PMMA + R6G layer on a sapphire substrate (black line) and that on the TiN nanoparticle array (red line) at θem = 0°. The excitation wavelength was 473 nm. (b) The transmittance and PL enhancement of the TiN array embedded in the layer were normalized with respect to the layer on the substrate. Transmittance (c) and the PL enhancement (d) of the TiN arrays embedded in the layer as functions of θin and θem, respectively. The PL enhancement is referenced to the PMMA + R6G layer on a sapphire substrate. The black dotted line in panels (c) and (d) is the Rayleigh anomaly with n = 1.45.
ACS Paragon Plus Environment
Page 5 of 9
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
ACS Photonics
Fig. 6 (a) Simulated transmittance (p-polarized component) and the integrated light energy in the PMMA + R6G layer on the TiN array normalized by that of the layer on the substrate, ∫|Efilm|2/∫|Efilmref|2, at θin = 0°. Panels (b) and (c) show the calculated spatial distribution of the normalized intensity, |E|2/|E0|2, in the zyplane, at the x-position intersecting the middle of a nanoparticle. The irradiation conditions were λ = 549 nm (b) and λ = 592 nm (c) at θin = 0°. The symbols in (a) denote the wavelengths used for the calculations in (b) and (c).
tion, the dip position is varied with θin for the taller particle along the diffraction condition, indicating the stronger in-plane coupling caused by (i) the blueshift of LSPRs to achieve spectral overlap with the diffraction condition and (ii) the larger scattering cross section of the taller nanoparticle that enhances the diffraction. The dip positions for the arrays with the height of 30 nm are almost constant with θin because of the small spectral overlap between the dip position and the diffraction condition below θin = 60°. PL enhancement. As a demonstration of optical functionality using the TiN nanoparticle array, we examined the PL enhancement from the PMMA + R6G layer on the TiN array. The optical transmittance is shown in Fig. 4(a). The dip in the transmittance, observed at around λ = 700 nm for the array before the coating in Fig. 2(a), redshifts to around λ = 800 nm because the PMMA + R6G layer has a higher refractive index than air. New dips can be found in the visible region. The lines of the Rayleigh anomalies with n = 1.79 and 1.45 are plotted as red and black dotted lines, respectively. A narrow dip ap-
pears at λ = 580 nm and θin = 0°, which extends along the (0, ±1) diffraction line with n = 1.45 with increasing θin. This angular profile indicates that this dip is caused by the in-plane diffraction into the PMMA + R6G layer (supporting information Fig. S4). We conducted a simulation using a model where a layer of PMMA + R6G (thickness = 800 nm, n and k values calculated using spectroscopic ellipsometry) on the array. The spectral features in the angular profile of transmittance can be reproduced by the simulation, as shown in Fig. 4(b), although the dips are deeper in the simulation. The deviation is caused by the difference between the shape of the particle during the experiment and the simulation (supporting information Fig. S5). Figure 5(a) displays the PL spectra (θem = 0°) for the PMMA + R6G layer on the TiN array as well as that for the reference with the layer on a sapphire substrate. The reference shows a PL peak centered at λ = 555 nm, which is typical for R6G52. Surprisingly, the PMMA + R6G layer on the array shows additional peak at λ = 585 nm, and the overall PL intensity is increased compared with that of the reference prepared on a flat sapphire substrate. To analyze this interesting behavior, the PL enhancement, defined as the PL intensity normalized by the reference PL intensity from the layer on a sapphire substrate, is compared with the transmittance at normal incidence in Fig. 5(b). The PL enhancement at λ = 555 and 585 nm was 1.5× and 2.8×, respectively. It is noteworthy that these peaks are associated with the dips in transmittance. Figures 5(c) and 5(d) compare the transmittance and the PL enhancement as a function of θin and θem, respectively. It is obvious that the angular profile of the dips in transmittance and that of the PL enhancement follow the Rayleigh anomaly reflecting n = 1.45 (shown by dotted lines). In other words, the direction of the PL is manipulated along with the Rayleigh anomaly. Figure 6(a) shows the simulated transmittance and the integrated light energy in the PMMA + R6G layer at θin = 0°. The latter denotes the energy stored inside the layer. Two peaks of the integrated light energy (λ = 549 and 592 nm) slightly redshift from the dips in transmittance (λ = 547 and 591 nm). This relation is similar to the redshift of the PL enhancement with respect to the dips in transmittance as observed in Fig. 5(b). The redshift originates from the difference between the nearfield enhancement and the far-field radiation, i.e., the maximum field enhancement on the surface of the nanoparticle occurs at wavelengths longer than the wavelength of the extinction peak42,43. Moreover, the values of the local maxima of the integrated light energy at λ = 549 and 592 nm are 1.38× and 3.62×, which are comparable to the values of the PL enhancement at λ = 555 and 585 nm (1.5 and 2.8), respectively. To evaluate the origin of the local maxima of the light energy stored in the polymer layer, the light energy distributions at the peaks (λ = 549 and 592 nm) are visualized in Figs. 6(b) and 6(c). The spatial distributions show a concentration of light energy in the layer, indicating the waveguiding nature of these modes36,41. Given the higher refractive index of the substrate (n = 1.79) compared with that of the PMMA + R6G layer (n = 1.45), the waveguide is clearly leaky at the bottom interface with the substrate. A closer look at the energy distribution reveals that the energy is also concentrated in the vicinity of the particle (supporting information Fig. S6). This means that the excited mode is a hybrid between LSPRs and the quasi-guided mode, although the contribution of LSPRs is limited.
ACS Paragon Plus Environment
ACS Photonics
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
Fig. 7 Normalized PL decay curves of the PMMA + R6G layer on the sapphire substrate (black line), the TiN film (blue line), and the TiN arrays (red line). The inset shows the PL decay curves before the normalization.
Figure 7 shows the PL decay curves for the PMMA + R6G layers deposited on the TiN array (red line), on the TiN film (blue line), and on the sapphire substrate (black line) as reference. The inset shows the decay curves before the normalization, showing the order in the PL intensity from the three samples, i.e., from the array > the film > the reference. The decay curves can be fitted by a single exponential function, and the lifetimes (τobs) were calculated; the reference showed longest τobs of 2.34 ns, and τobs of the layer on the array was 2.15 ns. The lifetime for the layer on TiN film was the shortest (τobs = 1.99 ns). The decrease in τobs with respect to the reference is attributable to the increase in the radiative and/or nonradiative decay rates. Although they are indistinguishable only from the PL decay curve, we assume that in the worst case scenario the TiN acts as an energy dissipation channel and increases only the nonradiative decay rate41,53. Using a crude estimation where the quantum yield of the reference is unity, the quantum yields of R6G molecules in the layer on the TiN array and thin film are calculated by the relation τobs/2.34. They are decreased by 15% and 8% for the layer on the TiN film and the TiN array, respectively. The dissipation is notably reduced by using an array structure, because the nanoparticle array has a smaller TiN volume compared with thin film. The simulation shows that optical absorption of the array is less than that of the TiN thin film (supporting information Fig. S7). In addition to the smaller volume of TiN, the spatial distribution of the light energy contributes to the mitigation effect (see Figs. 6(b) and 6(c)). The energy is concentrated not near the nanoparticle but extends into the layer. This characteristic distribution of the light energy helps avoid a severe dissipation of the energy. Let us briefly discuss the origin of the PL enhancement in the present system. First, the change in absorption at the excitation, λ = 473 nm, owing to the presence of the array is negligibly small (see supporting information Fig. S8). This means that the PL enhancement is not due to increased absorption. Second, the change in quantum yield of R6G by the array is not dominant: in the worst scenario, the quantum yield only dropped by 8%. These observations lead to the conclusion that the PL enhancement occurs via outcoupling, i.e., the efficiency
Page 6 of 9
of the light extraction from the structure into free space is drastically increased through the excitation of the hybrid modes. As depicted in Fig. 6, the energy of incident light is effectively transferred into the layer when λ = 549 and 592 nm. This means that by reciprocity, when light of the corresponding wavelength is generated in the layer via PL, it efficiently couples outside via the excitation of the hybrid modes. Because of the large energy distribution of the hybrid modes in the PMMA + R6G layer as shown in Figs. 6(b) and (c), a large fraction of the excited dye molecules emits into the hybrid modes, and these modes are preferentially coupled out at θem that corresponds to θin to excite the same mode. The correspondence between the values of the PL enhancement (1.5× and 2.8× at λ = 555 and 585 nm) and the calculated integrated intensity (1.38× and 3.62× at λ = 549 and 592 nm) supports that the enhancement is dominated by outcoupling. We numerically compare the optical performance of TiN nanoparticle array with the Au nanoparticle array by simulating the integrated light energy for the same geometry used for calculation in Fig. 6 and with the nanoparticle of Au instead of TiN. The value of integrated light energy is 2.3 times smaller for the TiN than that for the Au nanoparticle array (supporting information Fig. S9). Nevertheless, superior material properties such as higher chemical and thermal stabilities with the acceptable optical performance would rationalize the usage of TiN nanoparticle array to applications in the visible region.
CONCLUSION We have fabricated a periodic array of TiN nanoparticles to elucidate the full potential of TiN to excite the plasmonic– photonic hybrid mode in the visible spectrum. The array can enhance the PL intensity of an emitting layer deposited on top of the array. The results show that fabricating periodic nanoparticle arrays is a sensible strategy to mitigate the effects of the ohmic losses of TiN, while utilizing the properties of LSPRs. Given the high thermal stability of TiN, it is beneficial to apply the TiN nanoparticle array to explore the field where high-power irradiation is involved, such as high harmonic generation and upconversion.
ASSOCIATED CONTENT Supporting Information. The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsphotonics.XXXXXXX Dielectric function and X-ray diffraction pattern, simulated reflectance and absorptance spectra of air/TiN array/sapphire, transmittance spectra of the array with the particle height of 30 nm in the visible region, simulated reflectance and absorptance spectra of air/PMMA + R6G/TiN array/sapphire, simulated transmittance spectra with changing shape of the nanoparticle, simulated light energy distribution, simulated absorptance spectra of the PMMA + R6G layer on the TiN thin film and TiN array, ∆Extinction of the PMMA + R6G layer on the TiN array and sapphire substrate, and comparing the performance of nanoparticle array made of TiN and Au (PDF).
ACS Paragon Plus Environment
Page 7 of 9
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
ACS Photonics
AUTHOR INFORMATION Corresponding Author *E-mail:
[email protected] (S. M.)
Notes The authors declare no competing financial interest.
Acknowledgments This work was partly supported by Nanotechnology Hub, Kyoto University and National Institute for Material Science (NIMS) Nanofabrication Platform, in the “Nanotechnology Platform Project” sponsored by the Ministry of Education, Culture, Sports, Science and Technology (MEXT), Japan. Financial support from Grant-in-Aids for Scientific Research (B, No.16H04217) from MEXT is acknowledged. SM gratefully acknowledges the support from “the construction project for the consortium of the fostering of science and technology personnel,” Nanotech Career-up Alliance (Nanotech CUPAL). The authors would like to thank Enago (www.enago.jp) for the English language review.
REFERENCES (1) Vercruysse, D.; Sonnefraud, Y.; Verellen, N.; Fuchs, F. B.; Martino, G. D.; Lagae, L.; Moshchalkov, V. V.; Maier, S. A.; Dorpe, P. V. Undirectional Side Scattering of Light by a SingleElement Nanoantenna. Nano Lett. 2013, 13, 3843-3849. (2) Aouani, H.; Mahboub, O.; Devaux, E. Rigneault, H.; Ebbesen, T. W.; Wenger, J. Plasmonic Antennas for Directional Sorting of Fluorescence Emission. Nano Lett. 2011, 11, 2420-2406. (3) Murai, S.; Uno, S.; Kamakura, R.; Fujita, K.; Tanaka, K. Plasmonic Mesostructures Prepared by Oriented Mesoporous Materials as a Template. ECS Transactions 2015, 69, 117-121. (4) Christ, A.; Tikhodeev, S. G.; Gippius, N. A.; Kuhl, J.; Giessen, H. Waveguide-Plasmon Polaritons: Strong Coupling of Photonic and Electronic Resonances in a Metallic Photonic Crystal Slab. Phys. Rev. Lett. 2003, 91, 183901. (5) Kinkhabwala, A.; Yu, Z.; Fan, S.; Avlasevich, Y.; Müllen, K.; Moerner, W. E. Large Single-Molecule Fluorescence Enhancements Produced By A Bowtie Nanoantenna. Nat. Photon. 2009, 3, 654-657. (6) Muskens, O. L.; Giannini, V.; Sánchez-Gil, J. A.; Rivas, J. G. Strong Enhancement of the Radiative Decay Rate of Emitters by Single Plasmonic Nanoantennas. Nano Lett. 2007, 7, 2871-2875. (7) Coenen, T.; Vesseur, E. J. R.; Polman, A.; Koenderink, F. Directional Emission from Plasmonic Yagi-Uda Antennas Probed by Angle-Resolved Cathodoluminescence Spectroscopy. Nano Lett. 2011, 11, 2779-3784. (8) Kravets, V. G.; Schedin, F.; Grigorenko, A. N. Extremely Narrow Plasmon Resonances Based on Diffraction Coupling of Localized Plasmons in Arrays of metallic Nanoparticles. Phys. Rev. Lett. 2008, 101, 087403. (9) Zou, S.; Schatz, G. C. Narrow Plasmonic/Photonic Extinction And Scattering Line Shapes For One And Two Dimensional Silver Nanoparticle Arrays. J. Chem. Phys. 2004, 121, 12606. (10) Zhou, W.; Odom, T. W. Tunable Subradiant Lattice Plasmons by Out-of-Plane Dipolar Interactions. Nature Nanotech. 2011, 6, 423-427. (11) Hicks, E. M.; Zou, S.; Schatz, G. C.; Spears, K. G.; Duyne, R. P. V.; Gunnarsson, L.; Rindzevicius, T.; Kasemo, B.; Käll, M. Controlling Plasmon Line Shapes through Diffractive Coupling in Linear Arrays of Cylindrical Nanoparticles Fabricated by Electron Beam Lithography. Nano Lett. 2005, 5, 1065-1070 (12) Kauranen, M.; Zayats, A. V. Nonlilnear plasmonics. Nat. Photon. 2012, 6, 737-748. (13) Clavero, C. Plasmon-induced Hot-Electron Generation at Nanoparticle/Metal-Oxide Interfaces for Photovoltaic And Photocatalytic Devices. Nat. Photon. 2014, 8, 95-103.
(14) Sorger, V. J.; Oulton, R. F.; Ma, R.-M.; Zhang, X. Toward Integrated Plasmonic Circuits. MRS Bull. 2012, 37, 728-738. (15) Oshikiri, T.; Ueno, K.; Misama, H. Plasmon-Induced Ammonia Synthesis through Nitrogen Photofixation with Visible Light Irradiation. Angew. Chem. Int Ed. 2014, 53, 9802-9805. (16) Tateishi, K.; Funato M.; Kawakami, Y.; Okamoto K.; Tamada K. Highly Enhanced Green Emission from InGaN Quantum Wells Due To Surface Plasmon Resonance on Aluminum Films. Appl. Phys. Lett. 2015, 106, 121112. (17) Okamoto, K.; Niki, I.; Shvartser, A.; Maltezos, G.; Narukawa, Y.; Mukai, T.; Kawakami, Y.; Schere, A. Surface Plasmon Enhanced Bright Light Emission From InGaN/GaN. Physica Status Solidi (a) 2007, 204, 2103-2107. (18) Boltassaeva, A.; Atwater, H. A. Low-Loss Plasmonic Metamaterials, Science 2011, 331, 290. (19) Naik, G. V.; Kim, J.; Bolatasseva, A. Oxides and Nitrides as Alternative Plasmonic Materials In The Optical Range. Opt. Mat. Express 2011, 1, 1090-1099. (20) Kinsey, N.; Syed, A. A.; Courtwright, D.; Vault, C. D.; Bonner, C. E.; Gavrilenko, V. I.; Shalaev, V. M.; Hagan, D. J.; Stryland, E. W. V.; Boltasseva, A. Effective Third-Order Nonlinearities In Metallic Refractory Titanium Nitride Thin Films. Opt. Mat. Express 2015, 5, 2395-2403. (21)Kamakura, R.; Fujita, K.; Murai, S.; Tanaka, K. Controlling Plasmonic Properties of Epitaxial Thin Films of Indium Tin Oxide In The Near-Infrared Region. Journal of Physics: Conference Series 2015, 619, 012056. (22) Murai, S.; Fujita, K.; Daido, Y.; Yasuhara, R.; Kamakura, R.; Tanaka, K. Plasmonic Arrays of Titanium Nitride Nanoparticles Fabricated from Epitaxial Thin Films. Opt. Express 2016, 24, 1143-1153. (23) Naik, G. V.; Saha, B.; Liu, J.; Saber, S. M.; Stach, E. A.; Irudayaraj, J. M. K.; Sands, T. D.; Shalaev, V. M.; Boltasseva, A. Epitaxial Superlattices With Titanium Nitride As A Plasmonic Component For Optical Hyperbolic Metamaterials. Proc. Natl. Acad. Sci. USA 2014, 111, 7546-7551. (24) Guo, P.; Schaller, R. D.; Ketterson, J. B.; Chang, R. P. H. Ultrafast Switching of Tunable Infrared Plasmons In Indium Tin Oxide Nanorod Arrays With Large Absolute Amplitude. Nat. Photon. 2016, 10, 267-273. (25) Srinivasan, V.; Ramamurthy, S. S. Purcell Factor: A Tunable Metric for Plasmon-Coupled Fluorescence Emission Enhancements in Cermet Nanocavities. J. Phys. Chem. C. 2016, 120, 2908-2913. (26) Patsalas P.; Logothetidis S. Optical, Electronic, and Transport Properties of Nanocrystalline Titanium Nitride Thin Films. J. Appl. Phys. 2001, 90, 4725-4734. (27) Briggs, J. A.; Naik, G. V.; Petach, T. A.; Baum, B. K.; Goldhaber-Gordon, D.; Dionne, J. A. Fully CMOS-compatible titanium nitride nanoantennas. Appl. Phys. Lett. 2016, 108, 051110. (28) Naik, G. V.; Schroeder, J. L.; Ni, X.; Kildishev, A. V.; Sands, T. D.; Boltasseva, A. Titanium Nitride as a Plasmonic Material for Visible and Near-Infrared Wavelengths. Opt. Mat. Express 2012, 2, 478-489. (29) Li, W.; Guler, U.; Kinsey, N.; Naik, G. V.; Boltasseva, A.; Guan, J.; Shalaev, V. M.; Kildishev, A. V. Refractory Plasmonics with Titanium Nitride: Broadband Metamaterial Absorber. Adv. Mater. 2014, 26, 7959-7965. (30) Bagheri, S.; Zgrabik, C. M.; Gissibl, T.; Tittl, A.; Sterl, F.; Walter, R.: Zuani, S. D.; Berrier, A.; Stauden, T.; Richter, G.; Hu, E. L.; Giessen, H. Large-area Fabrication of TiN Nanoantenna Arrays for Refractory Plasmonics in the Mid-Infrared by Femtosecond Direct Laser Writing And Interference Lithography. Opt. Mater. Express 2015, 5, 2625-2633. (31) Guler, U.; Ndukaife, J. C.; Naik, G. V.; Nnanna, A. G.; Kildishev, A. V.; Shalaev, V. M.; Boltasseva, A. Local Heating
ACS Paragon Plus Environment
ACS Photonics
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
with Lithographically Fabricated Plasmonic Titanium Nitride Nanoparticles. Nano Lett. 2013, 13, 6078-6083. (32) Ishii, S.; Sugavaneshwar, R. P.; Nagao, T. Titanium Nitride Nanoparticles as Plasmonic Solar Heat Transducers. J. Phys. Chem. C. 2016, 120, 2343-2348. (33) Auguie, B.; Barnes, W. L. Collective Resonances in Gold Nanoparticle Arrays. Phys. Rev. Lett. 2008, 101, 143902. (34) Vesshi, G.; Giannini, V.; Ribas, J. G. Shaping the Fluorescent Emission by Lattice Resonances in Plasmonic Crystals of Nanoantenna. Phys. Rev. Lett. 2009, 102, 146807. (35) Zinenko, T. L.; Byelobrov, V. O.; Marciniak, M.; Ctyroky, J.; Nosich, A. I. Grating Resonances on Periodic Arrays of SubWavelength Wires and Strips: From Discoveries to Photonic Device Applications. In Contemporary Optoelectronics: Materials, Metamaterials and Device Applications; Shulika, O., Sukhoivanov, I., Eds.; Springer Series in Optical Sciences, 2015; pp 65– 79. (36) Rodriguez, S. R. K. Coupling light and matter in metallic nanoparticle arrays. Technische Universiteit Eindhoven: Eindhoven, 2014; pp 25–66. (37) Linden, S.; Kuhl, J.; Gissen, H.; Controlling the Interaction between Light and Gold Nanoparticles: Selective Suppression of Extinction. Phys. Rev. Lett. 2001, 86, 4688-4691. (38) Väkeväinen, A. I; Moerland, R. J.; Rekola, H. T.; Eskelinen, A.-P.; Martikainen, J.-P.; Kim, D.-H.; Törmä, P. Plasmonic Surface Lattice Resonances at the Strong Coupling Regime. Nano Lett. 2014, 14, 1721-1727. (39) Abass, A.; Rodriguez, S.R.K.; Rivas, J.G.; Maes, B. Tailoring Dispersion and Eigenfield Profiles of Plasmonic Surface Lattice Resonances. ACS Photonics. 2014, 1, 61-68. (40) Brolo, A. G.; Gordon, R.; Leathem, B. Kavanagh, K. L. Surface Plasmon Sensor Based on the Enhanced Light Transmission thorough Arrays of Nanoholes in Gold Films. Langmuir 2004, 20, 4813-4815. (41) Lozano, G.; Louwers, D. J.; Rodriguez, S. RK.; Murai, S.; Jansen, O. TA.; Verschuuren, M. A.; Rivas, J. G. Plasmonics for Solid-State Lighting: Enhanced Excitation and Directional Emission of Highly Efficient Light Sources. Light: Science & Applications 2013, 2, e66. (42) Murai, S.; Verschuuren, M. A.; Lozano, G.; Pirruccio, G. Rodriguez, S. R. K.; Rivas, J. G. Hybrid Plasmonic-Photonic Modes in Diffractive Arrays of Nanoparticles Couples to LightEmitting Optical Waveguides. Opt. Express 2013, 21, 4250-4262. (43) Giannini, V.; Vecchi, G.; Rivas, J. G. Lightning Up Multipolar Surface Plasmon Polaritons by Collective Resonances in Arrays of Nanoantennas. Phys. Rev. Lett. 2010, 105, 266801. (44) Yang, A.; Li, Z.; Knudson, M. P.; Hryn, A. J.; Wang, We.; Aydin, K.; Odom, T. W.; Unidirectional Lasing from TemplateStripped Two-Dimensional Plasmonic Crystals. ACS Nano, 2015, 9, 11582-11588. (45) Mokkapati, S.; Beck, F. J.; Polman, A.; Catchpole, K. R. Designing Periodic Arrays of Metal Nanoparticles for LightTrapping Applications in Solar Cells. Appl. Phys. Lett. 2009, 95, 053115. (46) Munday, J. N.; Atwater, H. A. Large Integrated Absorption Enhancement in Plasmonic Solar Cells by Combining Metallic Gratings and Antireflection Coatings. Nano Lett. 2011, 11, 21952201. (47) Lima, L. P. B.; Diniz, J. A.; Doi, I.; Godoy, F. J. Titanium Nitride as Electrode for MOS Technology and Schottky Diode: Alternative Extraction Method of Titanium Nitride Work Function. Microelectronic Engineering. 2012, 92, 86-90. (48) Skriver, H. L; Rosengaard, N. M. Surface Energy and Work Function of Elemental Metals. Phys. Rev. B. 1992, 46, 7157-7168. (49) Ishii, S.; Shinde, S. L.; Jevasuwan, W.; Fukuda, N.; Nagao, T. Hot Electron Excitation from Titanium Nitride Using Visible Light. ACS Photonics, 2016, 3, 1552-1557.
Page 8 of 9
(50) Savoia, S.; Ricciardi, A.; Crescitelli, A.; Granata, C.; Esposito, E.; Galdi, V.; Cusano, A. Surface Sensitivity of Rayleigh Anomalies in Metallic Nanogratings. Opt. Express 2016, 21, 23531-23542. (51) Tonotani, J.; Iwamoto, T.; Sato, F.; Hattori, K.; Ohmi, S.; Iwai, H. Dry Etching Characteristics of TiN Film Using Ar/CHF 3, Ar/Cl2 and Ar/BCl3 Gas Chemistries in an Inductively Couples Plasma. J. Vac. Sci. Technol. B 2003, 21, 2163. (52) Ritchie, G.; Burstein, E. Luminescence of Dye Molecules Adsorbed at a Ag Surface. Phys. Rev. B 1981, 24, 4843. (53) Gregory, S.; Khurgin, J. B.; Soref, R. A. Practical Enhancement of Photoluminescence by Metal Nanoparticles. Appl. Phys. Lett. 2009, 94, 101103.
ACS Paragon Plus Environment
Page 9 of 9
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
ACS Photonics
Insert Table of Contents artwork here
ACS Paragon Plus Environment
