Laser Writing of Bright Colors on Near-Percolation Plasmonic

Subscriber access provided by University of Winnipeg Library

Article

Laser Writing of Bright Colors on Near-Percolation Plasmonic Reflector Arrays Alexander Sylvester Roberts, Sergey M Novikov, Yuanqing Yang, Yiting Chen, Sergejs Boroviks, Jonas Beermann, N. Asger Mortensen, and Sergey I Bozhevolnyi ACS Nano, Just Accepted Manuscript • DOI: 10.1021/acsnano.8b07541 • Publication Date (Web): 07 Dec 2018 Downloaded from http://pubs.acs.org on December 7, 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 21 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 Nano

Laser Writing of Bright Colors on Near-Percolation Plasmonic Reflector Arrays Alexander S. Roberts,† Sergey M. Novikov,†, Yuanqing Yang,† Yiting Chen,† Sergejs Boroviks,† Jonas Beermann,† N. Asger Mortensen,†,¤ and Sergey I. Bozhevolnyi†,¤,* †Centre

for Nano Optics, University of Southern Denmark, Campusvej 55, DK-5230 Odense M,

Denmark ¤Danish

Institute for Advanced Study, University of Southern Denmark, Campusvej 55, DK-

5230 Odense M, Denmark E-mail: [email protected]

ABSTRACT: Coloration by surface nanostructuring has attracted a great deal of attention by the virtue of making use of environment-friendly recyclable materials and generating non-bleaching colors. Recently, it was found possible to delegate the task of color printing to laser postprocessing that modifies carefully designed and fabricated nanostructures. Here we take the next crucial step in the development of structural color printing by dispensing with preformed nanostructures and using instead near-percolation metal films atop dielectric-metal sandwiches, i.e., near-percolation plasmonic reflector arrays. Scanning rapidly (~ 20 μm/s) across 4-nm-thin island-like gold films supported by 30-nm-thin silica layers atop 100-nm-thick gold layers with a strongly focused Ti-sapphire laser beam, while adjusting the average laser power from 1 to 10

ACS Paragon Plus Environment

1

ACS Nano 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 21

mW, we produce bright colors varying from green to red by laser-heating-induced merging and reshaping of gold islands. Selection of strongly heated islands and their reshaping, both originating from excitation of plasmonic resonances, are strongly influenced by the polarization direction of laser illumination, so that the colors produced are well pronounced only when viewed with the same polarization. Conversely, the laser color writing with circular polarizations results in bright polarization-independent color images. The fabrication procedure for nearpercolation reflector arrays is exceedingly simple and scalable to mass production, while the laser-induced modification occurs inherently with the subwavelength resolution. This combination of features makes the approach developed for laser color writing readily amenable for practical implementation and use in diverse applications ranging from nanoscale patterning for security marking to large-scale color printing for decoration.

KEYWORDS: structural colors, plasmonic colors, gap surface plasmons, semi-continuous metal films, plasmonic reflector arrays, laser color writing Ultrafast laser processing of materials holds important implications for both applied and fundamental

research,1

including

possibilities

for

post-processing

and

reconfiguring

nanophotonic structures.2,3 Laser processing at the nanoscale often involves resonant (local) field enhancement and photo-thermal effects, for example, to modify the morphology of individual plasmonic resonators4 or dielectric nanoparticles (NPs).5 Fascinating applications range from the ultrafast delivery of heat at the nanoscale6 to laser writing of plasmonic colors with subdiffraction-limit resolution.7 Laser ablation, achieved typically at high radiation fluences, can also be used for coloration of plasmonic surfaces,8,9 although with considerably lower spatial resolutions. Previous works on plasmonic colors10,11 have extensively utilized progress in


2

Page 3 of 21 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 Nano

nanofabrication technologies to accurately pattern surfaces with carefully designed plasmonic nanostructures,12–14 using also replication techniques oriented towards mass production.15,16 Considering a very large body of research conducted in the field of structural colors,5-16 it seems unavoidable that high-resolution color printing requires high-resolution fabrication of designed nanostructures, which would result in appropriate colors either immediately12-16 or after postprocessing by laser writing.5,7 In this work, we demonstrate a conceptually different approach to high-resolution laser printing of structural colors (Fig. 1) that eliminates the need for preformed nanostructures, using instead near-percolation metal films atop dielectric-metal sandwiches, i.e., near-percolation plasmonic reflector arrays (NPPRAs). The main idea is to take advantage of scatteringabsorption properties of gap-surface plasmon (GSP) resonators17,18 (that make these particularly attractive for the environment-protected color printing)13 and laser-induced modification of local resonance properties in near-percolation metal films.19-21 Here, the GSP back-reflector configuration is pivotal for improving the color vibrancy, which is generally recognized as a common challenge for plasmonic colors,11 while a very high NP surface-density in nearpercolation metal films ensures high spatial resolution in laser-heating-induced NP reshaping and thereby in color writing. Furthermore, due to inherent stability of GSP resonators with respect to surfactants, the fabricated color prints can be protected with a transparent dielectric overlay (deposited before or after color printing) for ambient use without destroying its coloring.13 Finally, the NPPRA fabrication is exceedingly simple and requires only three consecutive material depositions, producing an optically thick metal back-reflector, a thin dielectric spacer and a very thin semi-continuous metal film.


3

ACS Nano 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 21

Figure 1. Schematic of laser-heating-induced reshaping of gold islands of near-percolation thin gold films atop silica-gold sandwiches. The island-like film shown represents three-dimensional rendering of an actual SEM image (1132821 nm2) taken from a sample (consisting of a 4-nmthin gold film supported by a 30-nm-thin silica layer atop a 100-nm-thick gold layer), whose right half acquired red color after illumination with a strongly focused 10-mW laser beam as shown on the inset to the left. Both laser beam and left inset are shown not to scale. The lateral dependence of the filling ratio was calculated from the extended (in the other direction) version of the same SEM image (11323621 nm2), reflecting the fact that reshaping by local melting produces island in-plane shrinking and merging. RESULTS AND DISCUSSION Laser Color Writing Configuration. The NPPRA-based laser-writing platform (Fig. 1) is amenable to a variety of modifications through the rich physics involved in thermally and locally induced NP reshaping and associated dependencies on interfacial energies, surface tensions and laser (pulse) characteristics, among others, and is thus intimately dependent on material and geometric choices as well as spatial and temporal properties of the laser. The thermally induced NP merging and reshaping can, in general, be viewed as a part of dewetting that describes the


4

Page 5 of 21 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 Nano

rupture of a thin (melted) film on the substrate and the formation of droplets. Thermally induced dewetting of a top metal film (as a whole) in metal-insulator-metal structures has been found suitable for fabrication of plasmonic broadband visible absorbers22 and solar absorbers,23 replacing typically slow and expensive lithographic nano-patterning step with a straightforward and cost-effective heating procedure. Similar global dewetting of a silver film on glass has been used to fabricate a layer of plasmonic NPs producing dichroic colors when viewed in transmission/reflection24 as in the famous Lycurgus cup. Local laser-heating-induced NP reshaping in NPPRAs pioneered in our work allows one not only to realize laser color writing with subwavelength resolution but also to achieve polarization selectivity by controlling the illumination polarization, a fascinating and very important feature that might be useful for polarization multiplexing and stereoscopic imaging. The NPPRA-based configuration investigated in detail in this work comprises 4-nm-thin (on average) gold films evaporated on 30-nm-thick silica (SiO2) layers atop optically thick (100 nm) gold films supported by silicon substrates (Fig. 1). The laser color writing is performed with a strongly focused Ti-sapphire laser (750 nm wavelength) beam with linear polarization and average powers ranging from 1 to 11 mW with the power level maintained in a closed feedback loop and controlled synchronously with beam positioning via a computer interface (see Supplementary Section 1). The top island-like gold film contains differently sized NPs that are gradually merged and reshaped due to local laser-induced heating, changing thereby the color of reflected light (Fig. 1). We found that the color perceived depends not only on the writing laser beam power but also on its polarization. Color Writing with Linear Polarization. First experiments were conducted using the constant-power laser writing within square regions. Viewing through an analyzer that is co-


5

ACS Nano

a

11

b

c

d

11

6.6

6.6

f

g

h

Power (mw)

e

Power (mw)

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 6 of 21

2.8

0

2.8

0

Figure 2. Color and spectral analyses of anisotropic laser color writing. Bright-field optical microscopy images (50 magnification, NA = 0.80) of (a, d) 15  15 m2 color squares produced with different average laser powers increasing gradually from 0 to 11 mW and (b, c) a 90  90 m2 color print of the SDU logo viewed with an analyzer (a, b) co-polarized and (c, d) cross-polarized with respect to the polarization of writing laser beam. Scale bars: 10 m. e, f Optical reflectance spectra and (g, h) their representations in a standard CIE-1931 and linear sRGB color spaces corresponding to the color squares shown in (a) and (d), respectively. Panels (b, c) are adapted with permission colorized versions of the logo of the University of Southern Denmark.


6

Page 7 of 21 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 Nano

polarized with the polarization of the writing beam reveals bright and deeply saturated colors that span from yellow for the pristine sample and low-power exposures to green (for intermediate powers) and red for the largest powers (Fig. 2a). Notably, the colors are uniform even when viewed through diffraction-limited optics, indicating that the density of reshaped NPs is sufficiently high to average out local variations in the optical response on scales comparable to the diffraction limit as observed in a color print of the University of Southern Denmark (SDU) logo (Fig. 2b) fabricated using a computerized script.13 Comparing these images with those viewed through a cross-polarized analyzer (Figs. 2c and 2d) demonstrates a high degree of polarization selectivity for colors obtained at powers up to ~ 4 mW, indicating thereby the color range that can be accessed independently in both linear polarizations. At higher powers, the colors seen in the cross-polarized configuration start to divert from the pristine NPPRA color and begin to exhibit colors seen in the co-polarized configuration for lower powers. Different colors observed in the co- and cross-polarized configurations are associated with different bright-field reflectance spectra (Figs. 2e and 2f) that can in turn be mapped on a standard CIE-1931 and linear sRGB color spaces (Figs. 2g and 2h). The colors observed without using an analyzer and the reflection spectra obtained with unpolarized light represent an intermediate case as expected (see Supplementary Section 4). In general, even though the cross talk in the images written and viewed with orthogonal polarizations is substantial, the degree of their differences is still appreciable and can further be enhanced using image processing methods and recognition techniques. We believe that this interesting and important feature might be found useful for polarization multiplexing (see Supplementary Section 4). Color Writing Resolution. Local laser-heating-induced NP reshaping in NPPRAs and ensuing surface coloration introduced in our work is expected to feature subwavelength


7

ACS Nano 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 8 of 21

resolution because of very high densities of NPs (>> 100 m-2) typical for near-percolation metal films. Similarly to the color laser printing on preformed nanostructures,5,7 the NP reshaping requires a certain level of the writing laser power, a feature that allows to achieve, in general, deep subwavelength resolutions by properly adjusting the writing laser power. On the other hand, in the absence of well-defined unit cells (that one can immediately judge as being modified or not), it is difficult to quantify the achieved resolution using non-optical characterization, such as SEM imaging. Using optical images, even with high magnifications and numerical apertures, allows one to determine the resolution only up to the diffraction limit of half of the wavelength used. In this respect, the optical image shown in Fig. 2b indicates that the spatial resolution is close to or even better than the wavelength when imaging with the co-polarized (with respect to the writing polarization) illumination. Environmentally protected colors. In the course of our investigations, we have used for color printing different NPPRA configurations, i.e., having thicknesses of both spacer SiO2 layers and thin island-like gold films, and found the effect of polarization-selective laser color printing to be remarkably robust (see Supplementary Section 6). The practical applicability of color printing schemes hinges on the endurance of the printed colors under often chemically and mechanically corrosive influences of the environment. While colors in the simple configuration with a laserreshaped gold top layer can simply be wiped off with a light touch, the presented approach suggests various schemes of protection with a dielectric overlay due to the inherent stability of GSP resonators with respect to surfactants.13 Thus, we have demonstrated both that the fabricated color prints can be protected with a transparent dielectric (polymer) overlay for ambient use without destroying its coloring, and the possibility for laser color printing on SiO2protected NPPRAs (see Supplementary Section 7).


8

Page 9 of 21 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 Nano

Physical Origin of Laser Color Writing. Laser-heating induced morphological changes in near-percolation metal films have recently been considered using two-photon luminescence (TPL) imaging19,20 and scanning (amplitude-phase resolved) near-field optical micrscopy20 as well as bright-field optical microscopy along with electron energy-loss spectroscopy (EELS).21 In general, highly localized heating, which results in NP merging and reshaping upon laser light exposure, originates from the excitation of strongly enhanced and confined (dipolar) resonant surface plasmon (SP) excitations, whose existence for thin near-percolation (island-like) metal films illuminated with practically any wavelength is well documented.20,21,25-27 For example, the apparent blue shift in the reflectance minimum when increasing the laser writing power (Fig. 2e,f) has previously been noted in laser-modified near-percolation metal films21 and attributed to the reshaping of heated elongated particles into more spherical ones due to the surface tension.20,21 Somewhat similar laser-induced reshaping of gold nanorods has been used for fivedimensional optical recording with TPL readout.28 However, the presence of an optically thick metal back-reflector changes drastically both underlying physical mechanisms involved and their optical manifestation. Thus, in the case of plasmonic metasurfaces, we established that the presence of a back reflector enhances dramatically the scattering contribution from induced magnetic dipoles18 and opens thereby the possibility for controlling the reflected field phase within the whole 2 range.29 In the current case of laser color writing with NPPRAs, we have experimentally established using TPL imaging of colored NPPRA areas intimate relationship between plasmonic resonances (see Supplementary Section 8).


9

ACS Nano 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 10 of 21

Figure 3. Modelling of anisotropic laser color writing. a SEM images of a pristine 4-nm-thin gold island-like film (yellow frame) and those exposed to the laser color writing with an xpolarized 3.9 mW (green frame) and 7.3 mW (red frame) beam. Scale bars: 100 nm. The insets represent optical bright-field microscopy images of the corresponding film areas (~ 15 m2 in size). b Simulated reflectance spectra of island-like films shown in (a) for the co- and crosspolarized illumination (solid and dashed lines, respectively), revealing anisotropy in the optical properties of laser-modified films, and (c) their representations in a standard CIE-1931 and linear sRGB color spaces. d Electric (Ex) and magnetic (Hy) field magnitude distributions calculated for the red-frame surface morphology (illuminated with the x-polarized light at 740 nm) in the middle spacer plane (left and middle panels) and in the cross section (right panels) along the dashed line indicated in the panels with plane distributions. Scale bars: 100 nm. Further understanding of underlying physical mechanisms involved in the proposed approach for color printing requires constructing an adequate physical system amenable to modelling of its optical properties. To this end, we have verified the correlation between the surface morphology reconstructed using the SEM images and the optical reflectance spectra calculated using threedimensional finite-difference time-domain (FDTD) simulations.30 Using the SEM images of three different areas (pristine and illuminated with a linearly polarized 3.9 and 7.3 mW beam) of


10

Page 11 of 21 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 Nano

a 4-nm-thin gold island-like film showing three distinct colors, yellow, green and red (Fig. 3a), we calculated the reflectance spectra for the co- and cross-polarized illumination (Fig. 3b) and their color representations (Fig. 3c). It is seen that the simulations reproduce qualitatively the experimental observations of spectra and colors, including the effect of polarization sensitivity (cf. Fig. 2e-h and Fig. 3b,c) that is apparently introduced by the melting-induced anisotropy in NP shapes.20,21 The electric (Ex) and magnetic (Hy) field magnitude distributions (Fig. 3d) indicate the occurrence of localized SP modes (hot spots) typical for near-percolation metal films25-27 revealed by the electric field distributions as well as relatively weakly localized GSP modes (due to their scattering by random nanostructures) revealed by the magnetic field distributions. These underlying physical mechanisms responsible for both selection of strongly heated NPs and their merging and reshaping were further revealed by simulating the absorption spectra for different material compositions based on the same random nanostructure reconstructed from the SEM image of the red-colored surface (see Supplementary Section 2). We found the absorption spectra originate from the interband absorption in the thick bottom gold layer for short (< 500 nm) wavelengths, while the direct absorption in the top gold nanostructured film contributes primarily to the total absorption for long (> 700 nm) wavelengths. In the intermediate wavelength range (500 nm <  < 700 nm), the absorption due to the strongly localized SP and weakly localized GSP modes becomes dominant. Finally, a special role played by the circumstance that NP shapes are different from spherical ones for the observed polarization sensitivity20,21 was further emphasized using simulations of reflectance spectra from regular arrays of gold ellipsoidal NPs supported by dielectric-metal sandwiches (see Supplementary Section 3).


11

ACS Nano 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 12 of 21

Figure 4. Color writing with circularly polarized light. a Bright-field optical microscopy (50 magnification, NA = 0.80) image of a 90  90 m2 color print of the SDU logo written with circularly polarized and viewed with unpolarized light. b Zoom (15  15 m2) of the optical microscope image shown in (a). c, d SEM images (3.2  3.2 m2) of the area contoured in (b) with the boundaries of differently colored regions indicated with white dotted lines in (c) and the lower half of the SEM image being covered with the corresponding zoom of the optical microscope image shown in (b). Insets in (d) are 200200 nm2. Panel (a) is an adapted with permission colorized version of the logo of the University of Southern Denmark. Polarization invariant color writing. The polarization selectivity discussed at length in the previous sections becomes detrimental when targeting conventional color printing with prints to be viewed with ambient (unpolarized) light. In order to produce polarization-independent color images we employed circularly polarized light for laser color printing. We found that the corresponding color prints look identical for all polarizations as well as for unpolarized light (see Supplementary Section 5) and even exhibit a bit brighter and more intense colors than those observed with the co-polarized writing and viewing, although the difference being admittedly small (cf. Fig. 2b and Fig. 4a). Polarization insensitive printing with circularly polarized light is a


12

Page 13 of 21 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 Nano

nontrivial feature, when taking into account the demonstration of chiral SP multiple scattering by random surface nanostructures exploited for on-chip spectro-polarimetry.31 In the current configuration, random NPs involved in scattering of various SP modes as discussed above are significantly smaller, and the regime of strong multiple scattering (resulting in strong localization) required for chiral sensitivity31 is apparently not accessible. We further used the printed image for determination of the spatial resolution by superimposing optical microscopy and SEM images and highlighting thereby the correlation between structural colors and the morphology of island-like film (Fig. 4). Analyzing the SEM zoom shown in Fig. 4c, one infers that the width of transition between modified (by laser writing) and pristine film surface is at the level of 400 nm, or even smaller, justifying thereby our claim of the subwavelength resolution in the considered approach for laser color printing. The estimated resolution is considerably smaller than the writing laser spot size (~ 750 nm, see Methods) because the strongest modification of particles occurs in the very center of the laser beam, resulting in the nonlinear response similar to that found in the TPL microscopy that also exhibits a similar resolution (~ 350 nm, see Methods). CONCLUSION In summary, we have demonstrated the usage of near-percolation plasmonic reflector arrays for laser printing of structured colors. Scanning rapidly (~ 20 μm/s) across 4-nm-thin island-like gold films supported by 30-nm-thin silica layers atop 100-nm-thick gold layers with a strongly focused Ti-sapphire laser beam, while adjusting the average laser power from 1 to 10 mW, we have produced bright colors varying from green to red by laser-heating-induced merging and reshaping of gold islands. Both polarization sensitive and independent color writing were demonstrated using linearly and circularly polarized light, respectively. In the case of linearly


13

ACS Nano 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 14 of 21

polarized writing, the difference between cross-polarized images is substantial, suggesting important perspectives for polarization multiplexing. Although the currently realized gamut of colors32 takes a modest 4.4% area of the sRGB triangle (Fig. 2g), further gamut extension can be expected with optimized sample configurations and laser writing procedures. The fabrication procedure for near-percolation reflector arrays is exceedingly simple requiring only three consecutive material depositions (to produce an optically thick metal back-reflector, a thin dielectric spacer and a very thin semi-continuous metal film) and thereby truly scalable to mass production. At the same time, the laser-induced modification occurs inherently with the subwavelength resolution, while the fabricated color prints can be protected with a transparent dielectric overlay for ambient use without destroying its coloring. Moreover, we have also demonstrated the possibility for laser color printing on polymer-protected near-percolation plasmonic reflector arrays, a procedure that allows one to separate the process of pristine sample fabrication and that of laser color printing. Finally, preliminary experiments indicated that the laser color writing can also be performed with our laser operating without mode locking, i.e., operating practically in a continuous-wave mode (see Supplementary Section 9), a feature that is very important for transferring this technology into the domain of practical applications. The combination of aforementioned features makes the approach developed for laser color writing readily amenable for practical implementation and use in diverse applications ranging from nanoscale patterning for security marking to large-scale color printing for decoration. METHODS Optical Spectra Measurement. Linear reflection spectroscopy is performed on a BX51 research microscope (Olympus) equipped with a halogen light source, polarizers and a fibrecoupled grating spectrometer (Ocean Optics QE65000, wavelength resolution: 1.6 nm). The


14

Page 15 of 21 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 Nano

reflected light is collected using an MPlanFL objective (Olympus) with ×100 magnification (NA = 0.9). Through use of a pinhole placed in a conjugated image plane, we collect spectra from an area with a diameter of ~ 20 μm. The experimental reflectance data shown in the main manuscript (Figure 2e and 2f), as well as in Supplementary Information, represent the reflection spectra calculated as the ratio Rstr/Rref, where Rstr is the reflection measured from colorized areas, and Rref is the reference obtained from a protected silver mirror (Thorlabs, PF10-03-P01) that exhibits an average reflection of 99% in the wavelength range between 350 and 1100 nm. Two-Photon

Photoluminescence

Microscopy.

The

two-photon

photoluminescence

microscopy (TPL) characterization relies on the previously described approach18,19. The experimental setup consists of a scanning optical microscope in reflection geometry built on the basis of a commercial microscope and a computer-controlled translation stage. The linearly polarized light beam from a mode-locked pulsed (pulse duration ~200 fs, repetition rate ~80 MHz) Ti-Sapphire laser (wavelength λ: 730 nm to 860 nm, Δλ  10 nm, average power ~300 mW) is used as an illumination source at the fundamental harmonic (FH) frequency. After passing an optical isolator (to suppress back-reflection into the laser cavity), half-wave plate, polarizer, red color filter, and wavelength selective beam splitter, the laser beam is focused on the sample surface at normal incidence with a Mitutoyo infinity-corrected long working distance objective (×100 magnification, NA = 0.70). The half-wave plate and polarizer allow accurate adjustment of the incident power. TPL radiation generated in reflection and the reflected FH beam are collected simultaneously with the same objective, separated by the wavelength selective beam splitter, directed through the appropriate filters and detected with two photomultiplier tubes (PMTs). The tube for TPL photons (within the transmission band of 350 nm to 550 nm) is connected with a photon counter giving typically only ~20 dark counts per


15

ACS Nano 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 16 of 21

second (cps). The FH and TPL spatial resolution at full-width-half- maximum is ~ 0.75 μm and ~ 0.35 μm, respectively, which means no individual clusters are resolved in the TPL images. In this work, we used the following scan parameters: the integration time (at one point) of 50 ms, scanning speed (between the measurement points) of 20 μm/s, and scanning step sizes of ~ 360 nm. The TPL images are obtained with the incident power of 0.3 mW. For writing, we used an incident power of 1 to 11 mW. For the reference bulk gold sample, we confirmed that the TPL signals obtained depend quadratically on the incident power. During these measurements, we kept for simplicity the excitation wavelength fixed at 740 nm, since there are no specific resonances close to this wavelength, and 740 nm is more visible and convenient to focus. Laser Color Writing. The printing of colored images with power modulation for individual pixels is based on the setup used for TPL microscopy, with an additional electronically controllable optical attenuator (Thorlabs, EVOA800A) inserted in the beam path prior to the microscope. The fiber-coupled optical attenuator can be inserted and removed from the beam path by means of flip-mirrors, which guide the laser beam towards an objective (collimator) for in-coupling (out-coupling). Polarization-maintaining single-mode fibres are used to maintain control of the polarization state. For the exposure with a circularly polarized beam, an additional Glan-Taylor polarizer and subsequent achromatic quarter-wave plate (Thorlabs SAQWP05M700) with a flat retardation response in the spectral region from 300 – 1100 nm are inserted after the optical attenuator. The scanning speed of 20 μm/s used throughout for color printing represents the largest speed, which is limited due to relatively slow operations of the variable optical attenuator (VOA) and closed-feedback loop control used for precise coordinate determination in the computer-controlled scanning stage. ASSOCIATED CONTENT


16

Page 17 of 21 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 Nano

The authors declare no competing financial interests. Supporting Information. The Supporting Information (PDF), containing Experimental setup, Computer simulations of realistic near-percolation arrays, Coupled dipole analysis, Polarization selectivity, cross-talk and multiplexing, Polarization invariant color printing, Robustness of the near-percolation plasmonic reflector array configuration, Printing of environmentally protected colors, Correlation between optical color and two-photon luminescence images, and Influence of mode locking on laser color writing, is available free of charge on the ACS Publications website. AUTHOR INFORMATION Corresponding Author *E-mail: [email protected] Present Addresses Center

for Photonics and 2D Materials, Moscow Institute of Physics and Technology, 9

Institutsky Lane, Dolgoprudny 141700, Russia. Author Contributions S. I. B. conceived the idea. A. S. R. and S. M. N. contributed equally to this work. A. S. R. and Y. C. fabricated the substrates. Y. C. did the SEM characterization, while A. S. R. and S. M. N. performed the laser writing and optical characterization. J. B. performed characterization by twophoton induced photoluminescence microscopy. Y. Y. conducted the analysis of underlying physical effects involved in NPPRA coloring. S. B. evaluated contributions to the reflection spectra of differently sized NPs using a semi-analytic model. S. I. B., J. B., and N. A. M. supervised the project and provided feedback on the experiments. All authors contributed to the interpretation of results and participated in the preparation of manuscript.


17

ACS Nano 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 18 of 21

ACKNOWLEDGMENT S. I. B. acknowledges the European Research Council, Grant 341054 (PLAQNAP). N. A. M. is a VILLUM Investigator supported by VILLUM FONDEN (grant No. 16498). Centre for Nano Optics is financially supported by the University of Southern Denmark (SDU 2020 funding). REFERENCES 1. Malinauskas, M.; Žukauskas, A.; Hasegawa, S.; Hayasaki, Y.; Mizeikis, V.; Buividas, R.; Juodkazis, S. Ultrafast Laser Processing of Materials: from Science to Industry. Light Sci. Appl. 2016, 5, e16133. 2. Makarov, S. V.; Zalogina, A. S.; Tajik, M.; Zuev, D. A.; Rybin, M. V.; Kuchmizhak, A. A.; Juodkazis, S.; Kivshar, Y. Light-Induced Tuning and Reconfiguration of Nanophotonic Structures. Laser Photon. Rev. 2017, 11, 1700108. 3. Zhua, X.; Hedayatia, M. K.; Raza, S.; Levy, U.; Mortensen, N. A.; Kristensen, A. Digital Resonant Laser Printing: Bridging Nanophotonic Science and Consumer Products. Nano Today 2018, 19, 7-10. 4. Chen, X.; Chen, Y.; Yan, M.; Qiu, M. Nanosecond Photothermal Effects in Plasmonic Nanostructures. ACS Nano 2012, 6, 2550–2557. 5. Zhu, X.; Yan, W.; Levy, U.; Mortensen, N. A.; Kristensen, A. Resonant-Laser-Printing of Structural Colors on High-Index Dielectric Metasurfaces. Sci. Adv. 2017, 3, e1602487. 6. Baffou, G. & Quidant, R. Thermo-Plasmonics: Using Metallic Nanostructures as NanoSources Of Heat. Laser Photon. Rev. 2013, 7, 171–187. 7. Zhu, X.; Vannahme, C.; Højlund-Nielsen, E.; Mortensen, N. A.; Kristensen, A. Plasmonic Colour Laser Printing. Nat. Nanotech. 2016, 11, 325–329. 8. Guay, J-M.; Lesina, A. C.; Côté, G.; Charron, M.; Poitras, D.; Ramunno, L.; Berini, P.; Weck, A. Laser-Induced Plasmonic Colours on Metals. Nat. Commun. 2017, 8, 16095. 9. Hu, D.; Lu, Y.; Cao, Y.; Zhang, Y.; Xu, Y.; Li, W.; Gao, F.; Cai, B.; Guan, B.-O.; Qiu, C.-W.; Li. X. Laser-Splashed Three-Dimensional Plasmonic Nanovolcanoes for Steganography in Angular Anisotropy. ACS Nano 2018, 12, 9233-9239. 10. Gu, Y.; Zhang, L.; Yang, J. K.W.; Yeo, S. P.; Qiu, C.-W. Color Generation via Subwavelength Plasmonic Nanostructures. Nanoscale 2015, 7, 6409–6419.


18

Page 19 of 21 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 Nano

11. Kristensen, A.; Yang, J.; Bozhevolnyi, S. I.; Link, S.; Nordlander, P.; Halas, N.; Mortensen, N. A. Plasmonic Colour Generation. Nat. Rev. Mater. 2017, 2, 16088. 12. Kumar, K.; Duan, H.; Hegde, R. S.; Koh, S. C. W.; Wei, J. N.; Yang, J. K. W. Printing Colour at the Optical Diffraction Limit. Nat. Nanotechnol. 2012, 7, 557–561. 13. Roberts, A. S.; Pors, A.; Albrektsen, O.; Bozhevolnyi, S. I. Subwavelength Plasmonic Color Printing Protected for Ambient Use. Nano Lett. 2014, 14, 783–787. 14. Tan, S. J.; Zhang, L.; Zhu, D.; Goh, X. M.; Wang, Y. M.; Kumar, K.; Qiu, C.-W.; Yang, J. K. W. Plasmonic Color Palettes for Photorealistic Printing with Aluminum Nanostructures. Nano Lett. 2014, 14, 4023–4029. 15. Clausen, J. S.; Højlund-Nielsen, E.; Christiansen, A. B.; Yazdi, S.; Grajower, M.; Taha, H.; Levy, U.; Kristensen, A.; Mortensen, N. A. Plasmonic Metasurfaces for Coloration of Plastic Consumer Products. Nano Lett. 2014, 14, 4499–4504. 16. Højlund-Nielsen, E.; Clausen, J.; Mäkela, T.; Thamdrup, L. H.; Zalkovskij, M.; Nielsen, T.; Li Pira, N.; Ahopelto, J.; Mortensen, N. A.; Kristensen, A. Plasmonic Colors: Toward Mass Production of Metasurfaces. Adv. Mater. Technol. 2016, 1, 1600054. 17. Bozhevolnyi, S. I.; Søndergaard, T. General Properties of Slow-Plasmon Resonant Nanostructures: Nanoantennas and Resonators. Opt. Express 2007, 15, 10869-10877. 18. Pors, A.; Bozhevolnyi, S. I. Plasmonic Metasurfaces for Efficient Phase Control in Reflection. Opt. Express 2013, 21, 27438-27451. 19. Novikov, S. M.; Beermann, J.; Frydendahl, C.; Stenger, N.; Coello, V.; Mortensen, N. A.; Bozhevolnyi, S. I. Enhancement of Two-Photon Photoluminescence and SERS for LowCoverage Gold Films. Opt. Express 2016, 24, 16743–16751. 20. Novikov, S. M.; Frydendahl, C.; Beermann, J.; Zenin, V. A.; Stenger, N. Coello, V.; Mortensen, N. A.; Bozhevolnyi, S. I.; White Light Generation and Anisotropic Damage in Gold Films Near Percolation Threshold. ACS Photonics 2017, 4, 1207–1215. 21. Frydendahl, C.; Repän, T.; Geisler, M.; Novikov, S. M.; Beermann, J.; Lavrinenko, A. V.; Xiao, S.; Bozhevolnyi, S. I.; Mortensen, N. A.; Stenger, N. Optical Reconfiguration and Polarization Control in Semi-Continuous Gold Films Close to the Percolation Threshold. Nanoscale 2017, 9, 12014–12024. 22. Yan, M.; Dai, J.; Qiu, M. Lithography-Free Broadband Visible Light Absorber Based on a Mono-Layer of Gold Nanoparticles. J. Opt. 2014, 16, 025002.


19

ACS Nano 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 20 of 21

23. Berean, K. J.; Sivan, V.; Khodasevych, I.; Boes, A.; Gaspera, E. D.; Field, M. R.; KalantarZadeh, K.; Mitchell, A.; Rosengarten, G. Laser-Induced Dewetting for Precise Local Generation of Au Nanostructures for Tunable Solar Absorption. Adv. Opt. Mater. 2016, 4, 1247–1254. 24. Yu, R.; Mazumder, P.; Borrelli, N. F.; Carrilero, A.; Ghosh, D. S.; Maniyara, R.A.; Baker, D.; García de Abajo, F. J.; Pruneri, V. Structural Coloring of Glass Using Dewetted Nanoparticles and Ultrathin Films of Metals. ACS Photonics 2016, 3, 1194–1201. 25. Ducourtieux, S.; Podolskiy, V. A.; Grésillon, S.; Buil, S.; Berini, B.; Gadenne, P.; Boccara, A. C.; Rivoal, J. C.; Bragg, W. D.; Banerjee, K.; Safonov, V. P.; Drachev, V. P.; Ying, Z. C.; Sarychev, A. K.; Shalaev, V. M. Near-Field Optical Studies of Semicontinuous Metal Films. Phys. Rev. B 2001, 64, 165403. 26. Seal, K.; Genov, D. A.; Sarychev, A. K.; Noh, H.; Shalaev, V. M.; Ying, Z. C.; Zhang, X.; Cao, H. Coexistence of Localized and Delocalized Surface Plasmon Modes in Percolating Metal Films. Phys. Rev. Lett. 2006, 97, 206103. 27. Losquin, A.; Camelio, S.; Rossouw, D.; Besbes, M.; Pailloux, F.; Babonneau, D.; Botton, G. A.; Greffet, J.-J.; Stéphan, O.; Kociak, M.

Experimental Evidence of Nanometer-Scale

Confinement of Plasmonic Eigenmodes Responsible for Hot Spots in Random Metallic Films. Phys. Rev. B 2013, 88, 115427. 28. Zijlstra, P.; Chon, J. W. M.; Gu, M. Five-Dimensional Optical Recording Mediated by Surface Plasmons in Gold Nanorods. Nature 2009, 459, 410-413. 29. Pors, A.; Bozhevolnyi, S. I. Efficient and Broadband Quarter-Wave Plates by Gap-Plasmon Resonators. Opt. Express 2013, 21, 2942-2952. 30. Chettiar, U.K.; Nyga, P.; Thoreson, M.D.; Kildishev, A. V.; Drachev, V. P.; Shalaev, V. M. FDTD Modeling of Realistic Semicontinuous Metal Films. Appl. Phys. B-Lasers Opt. 2010, 100, 159-168. 31. Chen, Y.; Ding, F.; Coello, V.; Bozhevolnyi, S. I. On-Chip Spectropolarimetry by Fingerprinting with Random Surface Arrays of Nanoparticles. ACS Photonics 2018, 5, 1703– 1710. 32. Dong, Z.; Ho, J.; Yu, Y. F.; Fu, Y. H.; Paniagua-Dominguez, R.; Wang, S.; Kuznetsov, A. I.; Yang, J. K. W. Printing Beyond sRGB Color Gamut by Mimicking Silicon Nanostructures in Free-Space. Nano Lett. 2017, 17, 7620-7628.


20

Page 21 of 21 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 Nano

Graphical TOC Entry


21

Laser Writing of Bright Colors on Near-Percolation Plasmonic

Recommend Documents