Open Access
Add to BibSonomy
Abstract
We measured the photoelectron emission efficiency of aluminum (Al) nanohole arrays fabricated by colloidal lithography and demonstrated the enhancement of photoelectron emission in the deep-UV region via surface plasmon resonances. The Al nanohole arrays for increasing absorption in the deep-UV region were designed using the finite-difference time-domain method and used as photocathodes to enhance the photoelectron emission efficiency. The enhancement factor improved by up to 3.5 times for the optimized nanohole array. Using a two-dimensional mapping system, we demonstrated that the photoelectron emission depended on the uniformity of the sample and diameter of the nanohole arrays. Al nanohole arrays fabricated by colloidal lithography can be used to develop highly sensitive surface-detecting optical sensors and highly efficient surface-emitting electron sources. The two-dimensional mapping system can facilitate the development of highly efficient photocathodes.
© 2024 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement
1. Introduction
The confinement and field enhancement effects of surface plasmon resonance have been applied to optical waveguides [1,2], surface-enhanced Raman scattering [3–7], tip-enhanced Raman scattering [8,9], biosensors [10–12], photodetectors [13–15] and photocatalysis [16–18]. Various applications of plasmonics have been reported for photoelectric effects, such as the enhancement of photoelectric conversion efficiency and control of photoelectron emission trajectories [19–38]. Photoelectrons are emitted when the incident energy exceeds the work function of a material. Photoelectron emission is proportional to the probability of light absorption according to Fermi's golden rule. In the case of a transmission photocathode, the suppression of energy losses inside the photocathode requires a lower thickness. Surface plasmon resonances have been extensively studied for improving the optical absorption efficiency of thin photoelectric films [31–34]. Most studies utilized multiphoton or tunnel ionization induced by ultrashort laser pulses. The electric field-enhancing effect of surface plasmons excited by ultrashort laser pulses accelerates the emitted electrons and produces higher-energy electrons. Dombi et al. have demonstrated that plasmon-enhanced fields accelerate the electrons emitted by ultrashort laser pulses and that the control of the energy and trajectory of photoelectrons depends on the plasmonic nanostructures [35].
Photocathode electron guns can control the spatiotemporal information of the electron beam using the excitation light. Ultrashort pulsed electron beams are generated using ultrashort laser pulses as an excitation source and are applied to electron microscopes and diffraction instruments with high temporal resolution. Vogelsang et al. demonstrated that ultrashort pulsed electrons are emitted by the optical confinement effect of surface plasmons excited at the tip of gold nanotapers by point-projection microscopy (PPM) imaging [26].
Photocathode electron guns have a high demand for increasing brightness, that is, photoelectron emission efficiency. We previously reported the enhancement of photoelectron emission efficiency by surface plasmons [36–38]. Due to the high photon energy associated with deep-ultraviolet (DUV) light, many materials such as Al, Ni, Al2O3, TiO2, and Si3N4 emit photoelectrons upon DUV light irradiation [39]. Deep-UV (DUV) light at a wavelength of 266 nm has a work function of 4.28 eV higher than that of aluminum (Al); thus, photoelectrons in Al are emitted into the vacuum. Recently, nanodisk and nanohole arrays have improved the photoelectron emission efficiency by up to four times [38]. Surface plasmon resonance on the periodic arrays in metal films is excited by normal incidence [40,41]. The plasmon coupling effect combining the nanodisk and nanohole arrays enhanced the electric field intensity, resulting in more efficient photoelectron emission. This technology can be applied in surface-detecting optical sensors and surface-emitting electron sources. In this study, Al nanohole arrays were fabricated using colloidal lithography [42–44] based on the self-assembly of polystyrene (PS) latex beads to increase the photocathode area. Two-dimensional mapping and structural parameter dependence were evaluated using photoelectron emission efficiency measurements of the fabricated devices.
2. Optimization of the nanohole array for DUV surface plasmon excitation
An Al nanohole array was used for surface plasmon excitation at normal incidence and also as an electrode. Hole arrays can be easily fabricated using colloidal lithography, which makes them suitable for large-area applications. Figure 1(a) shows a schematic of photoelectron emission enhancement by the Al nanohole array, which acts as a plasmonic photocathode. When DUV light is incident on it, a surface plasmon resonance is excited, and absorption is greatly enhanced. This enhancement effect increases the photoelectron emission efficiency. Figure 1(b) shows the simulation model. The holes were arranged in a triangular lattice and periodic boundary conditions were assigned. The excitation wavelength was set to 266 nm (fourth harmonic of the Nd:YAG laser). The finite-difference time-domain (FDTD) method (FullWAVE, Synopsis Inc.) was used to optimize the structural parameters, period, diameter, and film thickness of the Al nanohole array. Electromagnetic field analysis showed that the optimal structural parameters of the Al nanohole array for surface plasmon excitation at a wavelength of 266 nm were a period of 150 nm, diameter of 105 nm, and Al film thickness of 20 nm. Figure 2(a) shows the diameter dependence of the reflectance. In the calculations, the period and thickness were set to 150 nm and 20 nm, respectively. A reflection dip is observed at a wavelength of 266 nm and diameter of 105 nm, which shifts toward shorter wavelengths with increasing diameter. The optimized structural parameters were used to calculate the electric field intensity and absorption distribution in the x-z cross section, as shown in Figures 2(b) and 2(c), respectively. At the edge of the nanohole array, enhancement of the electric field intensity owing to the surface plasmon resonance was clearly observed. In the absorption distribution, enhancement of the electric field clearly enhances the absorption in the Al area.
Fig. 1. (a) Schematic of photoemission enhancement using an Al nanohole array. (b) Simulation model for the structural design of the nanohole array.
Fig. 2. (a) Simulation results of the dependence of the reflectance spectral map on the hole diameter. (b) Electric field intensity and (c) absorption distributions in the x-z cross section. (d) Dependence of the electric field intensity and absorption efficiency on the hole diameter. Absorption distributions on the hole array surface (x-y plane) for diameters of (e) 80 nm, (f) 105 nm, and (g) 120 nm.
Figure 2(d) shows the dependence of the electric field intensity and absorption on the hole diameter. The electric field intensity and absorption were averaged at the top of the hole array surface, and they peaked at a diameter of 105 nm. Figures 2(e)–2(g) show the absorption distribution on the hole array surface for hole diameters of 80, 105, and 120 nm, respectively. In all cases, absorption is enhanced at the edges of the holes, and a comparing of the distributions shows that the highest absorption occurs at 105 nm. This result indicates that the enhancement of the efficiency of photoelectron emission attributed to surface plasmons necessitates optimization of the hole diameter as a structural parameter.
3. Fabrication by colloidal lithography and optical characterization of the nanohole array
A nanohole array was fabricated using colloidal lithography [42,43]. Figure 3 shows a schematic of the fabrication process of the nanohole array. First, PS latex beads with a diameter of 155 nm were dropped onto a quartz (SiO2) substrate. The beads self-assembled during drying and formed triangular lattice aggregates that were miniaturized by reactive ion etching (RIE). In this study, the etching time was set from 40 s to 70 s for proper fabrication of the hole arrays. The etching conditions were O2: 20 sccm, RF power: 100 W, and pressure: 50 Pa. After RIE etching, an Al thin film was deposited via vacuum evaporation on the substrate on which PS beads self-assembled. The film thickness, as measured using a surface profiler, was 23 nm. It is acknowledged that aluminum surfaces are naturally oxidized by approximately 3 nm, thereby the actual aluminum film thickness is assumed to be 20 nm [45]. Finally, the PS beads were removed using the tape lift-off method to obtain the nanohole array.
Fig. 3. Schematic of fabrication of nanohole array by colloidal lithography. (a) Alignment of PS beads by self-assembly. (b) Beads size control by RIE etching. (c) Al thin film deposition. (d) Beads removal by tape lift-off.
Figure 4(a) shows the control of the size of PS beads size by RIE etching. Before etching, the periods and diameters of the self-assembled beads were equal. After etching, only the diameter decreased whereas the period remained unchanged. Figure 4(b) shows the secondary electron images of the aluminum nanohole arrays at RIE etching times of 40, 50, 60, and 70 s. The holes were aligned in a triangular lattice, and their size increased with the RIE etching time. Figure 4(c) shows a low-magnification SEM image taken at an etching time of 40 sec. The hole arrays fabricated by colloidal lithography exhibited large-area periodicity. Figure 4(d) shows the radial distribution function. The peak is located at 150 nm, which is consistent with the design value. Figure 4(e) shows the etching time dependence of the diameter, which indicates that the diameter decreases with increasing etching time. Diameters of 107, 102, 85, and 83 nm were obtained for the etching times of 40, 50, 60, and 70 s, respectively. Figure 4(f) shows the reflection spectra of the fabricated hole array, in which the resonance wavelength shifts to longer wavelength as the diameter decreases. This trend is consistent with the calculated results shown in Figure 4(g). Considering the reflection spectra, the surface plasmons can be excited by DUV light with a wavelength of 266 nm for a period of 150 nm, a diameter of 107 nm, and an Al film thickness of 23 nm (corresponding to the purple color in the reflection spectrum). The reflectance of samples with a diameter of 107 nm exhibited a broader bandwidth and lower values over the DUV-to-visible wavelength range than expected from the simulation. There are two possible reasons for the low reflectance: The first is a structural defect in which the surface roughness scatters incident light at the edges of the holes. The other is a decrease in the Al thickness owing to oxidation, which weakens the resonance efficiency and increases transmittance. Figure 4(h) shows the simulated reflectance, transmittance, and absorption spectra for an Al hole array with a period of 150 nm, a diameter of 107 nm, and a thickness of 20 nm, which are the same parameters as those of the measured device for photoelectron emission. An absorption peak was observed around 266 nm excitation wavelength, indicating enhanced photoelectron emission. On the other hand, a low absorption of approximately 10% was observed in the spectra for a 20 nm-thick Al thin film (Fig. 4(i)).
Fig. 4. (a) Schematic of the control over the diameter via RIE etching. (b) SEM images of the fabricated nanohole arrays for etching times of 40, 50, 60, and 70 s, respectively. The scale bar corresponds to 100 nm. (c) Low magnification SEM image for etching time of 40 s. The scale bar corresponds to 1 µm. (d) Radial distribution function. (e) Etching time dependence of the diameter of the holes. (f) Reflection spectra of the fabricated nanohole array. (g) Simulated reflection spectra with different diameters. Simulated reflectance, transmittance, and absorption spectra (h) for Al hole array and (i) for Al thin film.
4. Design and implementation of a two-dimensional mapping system for photoelectric emission efficiency
We constructed the measurement system shown in Figure 5 to evaluate the photoelectron emission efficiency of the photocathodes. The fourth harmonic of an Nd:YAG laser was used as the light source, and the optical power was adjusted using an ND filter. The photocathode samples were placed in a vacuum chamber at 10−5 Pa. An electric field of 25 V/mm was applied between the sample and electrode. Beam incidence on the samples was controlled using a galvanometer scanner system. A telecentric fθ lens placed after the galvanometer scanner collimated the incident light and ensured perpendicular incidence at all positions of the photocathode. The galvanometer system facilitated measurements at any position on the sample and two-dimensional mapping of the photoelectron emission. The sample size that could be evaluated was 16 × 16 mm2.
Figure 6 shows the two-dimensional maps of the photoelectron emission efficiency of the Al thin films with different thicknesses obtained using the experimental system. Figures 6(a) and 6(b) show the thickness distribution model and photocurrent measured distribution result of the Al thin-film sample with film thicknesses 0, 13, and 35 nm. The photocurrent varies at the boundaries of different film thicknesses, whereas it remains a constant value in the region of constant film thickness. The photocurrent decreases as the film thickness increases. Figure 6(c) shows the reference laser light power distribution, in which results in uniform. Figure 6(d) shows the transmitted photoelectron emission efficiency distribution corresponding to the photocurrent divided by the reference laser light power. Further, Figure 6(d) shows that the photoelectron emission efficiency varies with the film thickness, indicating proper two-dimensional mapping. Figure 6(e) shows the line profile corresponding to the dotted line in Figure 6(d), and a clear difference in the efficiency values is observed. Figure 6(f) shows the dependence of the Al thin film thickness on the photoelectron emission efficiency obtained from the two-dimensional mapping results, where the triangles and circles correspond to samples without and with Al deposition, respectively. Because the sample without the Al film did not emit photoelectrons, its efficiency was approximately zero. The efficiency of the Al thin film decreased exponentially with increasing film thickness because of the mean free path of the excited photoelectrons.
Fig. 6. Two-dimensional mapping measurements for the Al thin film. (a) Thickness distribution of the Al thin film. (b) Photocurrent distribution. (c) Reference laser light power distribution. (d) Photoelectron emission efficiency distribution. The scale bars in (a)−(c) correspond to 5 mm. (e) Line profile corresponding to the dotted line in Figure 6(d). (f) Dependence of the photoelectron emission efficiency on the Al thin film thickness.
5. Two-dimensional mapping and the diameter dependence of photoelectron emission efficiency
The issue with colloidal lithography is the uniformity of the sample surface. In this study, two-dimensional mapping images of the photoelectron emission efficiency were obtained to evaluate the relationship between sample uniformity and photoelectron emission efficiency. Figure 7(a) shows a transmission image of a nanohole array (period: 150 nm, diameter: 107 nm, thickness: 23 nm) optimized for the incident wavelength, which was observed using an optical microscope. Figure 7(b) presents a two-dimensional mapping image of the photoelectron emission efficiency. The spatial distribution obtained by efficiency mapping is consistent with that of the optical image. Figure 7(c) shows the SEM images corresponding to areas (1), (2), and (3) in Figure 7(a). In Area (1), the uniform distribution of nanoholes indicates a high efficiency owing to the enhancement effect of the surface plasmons. In contrast, Area (2) shows the boundary between the stacked PS area owing to aggregation and the nanohole array. The efficiency in the stacked area was lower than that in the hole array area. In Area (3), a clear difference in efficiency was observed at the boundary between the nanohole array and hole defect region. Figure 7(d) shows the line profile of the dotted line in Figure 7(b). The photoelectron emission efficiencies of the stacked and defective structures were 30% and 60% lower than those of the hole array, respectively. Therefore, maximizing photoelectron emission efficiency necessitates a uniform structure. The higher efficiency of the stacked structure compared to the defective structure may be attributed to the three-dimensional formation of the nanostructure during the aggregation of the beads. This two-dimensional photoelectron emission efficiency mapping system can be used to evaluate the photocathode surfaces of surface-emitting electron sources and photodetectors because it can determine the relationship between the photoelectron emission efficiency and uniformity of the surface structure.
Fig. 7. Two-dimensional mapping and diameter dependence of the photoelectron emission efficiency of the sample optimized for a resonance wavelength of 266 nm. (a) Image of the sample surface obtained by optical microscopy. (b) Two-dimensional mapping image of photoelectron emission efficiency. (c) SEM images (1)−(3) corresponding to the numbers in Figure 5(a). The scale bars in (a) and (b) correspond to 100 µm, while that in (1) corresponds to 100 nm. The scale bars in (2) and (3) correspond to 1 µm. (d) Line profile corresponding to the dotted line in Figure 7(b). (e) Diameter dependence of the enhancement factor.
Figure 7(e) shows the dependence of the enhancement factor on the diameter. The point and curve data represent the experimental values and calculated absorption efficiency, respectively. The enhancement factor, which is defined as the ratio of the efficiency of the nanohole array to that of an Al thin film without nanostructures, increases with the diameter. As shown in Figure 4(e), the resonance wavelength shifts toward the incident wavelength of 266 nm as the diameter increases. Therefore, the enhancement of the resonance effect improves the photoelectron emission efficiency. The experimental results indicate that increasing the excitation efficiency of the surface plasmons by optimizing the diameter of the nanohole arrays results in highly efficient photoelectron emission. The enhancement factor improved by up to 3.5 times, which is comparable to that reported previously [35]. The results demonstrate that the bottom-up approach can be adopted as a fabrication method to improve photoelectron emission efficiency over a large area.
6. Conclusion
Al nanohole arrays were designed using the FDTD method to increase the absorption at a wavelength of 266 nm. The optimized structural parameters of the Al-nanohole array for surface plasmon excitation at 266 nm were a period of 150 nm, a diameter of 105 nm, and an Al film thickness of 20 nm. Al nanohole arrays were fabricated by colloidal lithography based on the self-assembly effect of PS latex beads and analyzed using a two-dimensional mapping system to demonstrate the photoelectron emission efficiency enhancement. The photoelectron emission depended on the sample uniformity and diameter of the nanohole arrays, and the enhancement factor improved by up to 3.5 times for the optimized diameter. Al nanohole arrays fabricated by colloidal lithography can realize highly sensitive surface-detecting optical sensors and highly efficient surface-emitting electron sources owing to the high absorption induced by surface plasmons. A two-dimensional photoelectron emission efficiency mapping system can reveal the relationship between the photoelectron emission efficiency and uniformity of the sample surface, thereby facilitating the development of highly efficient photocathodes.
Funding
Core Research for Evolutional Science and Technology (JPMJCR2003).
Disclosures
The authors declare no conflicts of interest.
Data availability
The data that support the findings of this study are available from the corresponding author upon reasonable request.
References
1. P. Neutens, P. Van Dorpe, I. De Vlaminck, et al., “Electrical detection of confined gap plasmons in metal insulator metal waveguides,” Nat. Photonics 3(5), 283–286 (2009). [CrossRef]
2. D. Gramotnev and S. Bozhevolnyi, “Plasmonics beyond the diffraction limit,” Nat. Photonics 4(2), 83–91 (2010). [CrossRef]
3. S. Nie and S. Emory, “Probing single molecules and single nanoparticles by surface-enhanced Raman scattering,” Science 275(5303), 1102–1106 (1997). [CrossRef]
4. A. Campion and P. Kambhampati, “Surface-enhanced Raman scattering,” Chem. Soc. Rev. 27(4), 241–250 (1998). [CrossRef]
5. S. Bai, X. Ren, K. Obata, et al., “Label-free trace detection of bio-molecules by liquid-interface assisted surface-enhanced Raman scattering using a microfluidic chip,” Opto-Electron. Adv. 5(10), 210121 (2022). [CrossRef]
6. Z. Pei, J. Li, C. Ji, et al., “Flexible cascaded wire-in-cavity-in-bowl structure for high-performance and polydirectional sensing of contaminants in microdroplets,” J. Phys. Chem. Lett. 14(25), 5932–5939 (2023). [CrossRef]
7. M. Shao, C. Ji, J. Tan, et al., “Ferroelectrically modulate the Fermi level of graphene oxide to enhance SERS response,” Opto-Electron. Adv. 6(11), 230094 (2023). [CrossRef]
8. N. Hayazawa, Y. Inouye, Z. Sekkat, et al., “Metallized tip amplification of near-field Raman scattering,” Opt. Commun. 183(1-4), 333–336 (2000). [CrossRef]
9. A. Taguchi, “Plasmonic tip for nano Raman microcopy: structures, materials, and enhancement,” Opt. Rev. 24(3), 462–469 (2017). [CrossRef]
10. W. Li, K. Ren, and J. Zhou, “Aluminum-based localized surface plasmon resonance for biosensing,” TrAC, Trends Anal. Chem. 80, 486–494 (2016). [CrossRef]
11. V. Chabot, C. Cuerrier, E. Escher, et al., “Biosensing based on surface plasmon resonance and living cells,” Biosens. Bioelectron. 24(6), 1667–1673 (2009). [CrossRef]
12. L. R. Hirsch, R. J. Stafford, J. A. Bankson, et al., “Nanoshell-mediated near-infrared thermal therapy of tumors under magnetic resonance guidance,” Proc. Natl. Acad. Sci. U. S. A. 100(23), 13549–13554 (2003). [CrossRef]
13. M. Knight, H. Sobhani, P. Nordlander, et al., “Photodetection with active optical antennas,” Science 332(6030), 702–704 (2011). [CrossRef]
14. A. Sobhani, M. Knight, Y. Wang, et al., “Narrowband photodetection in the near-infrared with a plasmon-induced hot electron device,” Nat. Commun. 4(1), 1643 (2013). [CrossRef]
15. M. Tanzid, A. Ahmadivand, R. Zhang, et al., “Combining plasmonic hot carrier generation with free carrier absorption for high-performance near-infrared silicon-based photodetection,” ACS Photonics 5(9), 3472–3477 (2018). [CrossRef]
16. P. Zilio, M. Dipalo, F. Tantussi, et al., “Hot electrons in water: injection and ponderomotive acceleration by means of plasmonic nanoelectrodes,” Light: Sci. Appl. 6(6), e17002 (2017). [CrossRef]
17. L. Shen, G. Gibson, N. Poudel, et al., “Plasmon resonant amplification of hot electron-driven photocatalysis,” Appl. Phys. Lett. 113(11), 113104 (2018). [CrossRef]
18. Y. Wang, I. Aravind, Z. Cai, et al., “Hot electron driven photocatalysis on plasmon-resonance grating nanostructures,” ACS Appl. Mater. Interfaces 12(15), 17459–17465 (2020). [CrossRef]
19. J. Bösenberg, “Photoelectrons from optically excited nonradiative surface plasma oscillations,” Phys. Lett. A 37(5), 439–440 (1971). [CrossRef]
20. H. W. Rudolf and W. Steinmann, “Two photon photoelectric effect in the surface plasma resonance of aluminium,” Phys. Lett. A 61(7), 471–472 (1977). [CrossRef]
21. T. Tsang, T. Srinivasan-Rao, and J. Fischer, “Surface-plasmon-enhanced multiphoton photoelectric emission from thin silver films,” Opt. Lett. 15(15), 866–868 (1990). [CrossRef]
22. T. Tsang, T. Srinivasan-Rao, and J. Fischer, “Surface-plasmon field-enhanced multiphoton photoelectric emission from metal films,” Phys. Rev. B 43(11), 8870–8878 (1991). [CrossRef]
23. H. Chen, J. Boneberg, and P. Leiderer, “Surface-plasmon-enhanced multiple-photon photoemission from Ag and Al films,” Phys. Rev. B 47(15), 9956–9958 (1993). [CrossRef]
24. K. Iwami, A. Iizuka, and N. Umeda, “Electron field emission from a gold tip under laser irradiation at the plasmon-resonant wavelength,” J. Vac. Sci. Technol., B: Nanotechnol. Microelectron.: Mater., Process., Meas., Phenom. 29(2), 02B103 (2011). [CrossRef]
25. R. Hobbs, W. Putnam, A. Fallahi, et al., “Mapping photoemission and hot-electron emission from plasmonic nanoantennas,” Nano Lett. 17(10), 6069–6076 (2017). [CrossRef]
26. J. Vogelsang, J. Robin, B. Nagy, et al., “Ultrafast electron emission from a sharp metal nanotaper driven by adiabatic nanofocusing of surface plasmons,” Nano Lett. 15(7), 4685–4691 (2015). [CrossRef]
27. Y. Shen, H. Chen, N. Xu, et al., “A plasmon-mediated electron emission process,” ACS Nano 13(2), acsnano.8b08444 (2019). [CrossRef]
28. F. Medeghini, J. Pettine, S. M. Meyer, et al., “Regulating and directionally controlling electron emission from gold nanorods with silica coatings,” Nano Lett. 22(2), 644–651 (2022). [CrossRef]
29. M. Müller, V. Kravtsov, A. Paarmann, et al., “Nanofocused plasmon-driven sub-10 fs electron point source,” ACS Photonics 3(4), 611–619 (2016). [CrossRef]
30. B. Schröder, M. Sivis, R. Bormann, et al., “An ultrafast nanotip electron gun triggered by grating-coupled surface plasmons,” Appl. Phys. Lett. 107(23), 231105 (2015). [CrossRef]
31. Z. Jiang, X. Li, D. Huang, et al., “Effect of plasmonic near field on the emittance of plasmon-enhanced photocathode,” Nucl. Instrum. Methods Phys. Res., Sect. A 897, 14–17 (2018). [CrossRef]
32. S. E. Irvine and A. Y. Elezzabi, “Surface-plasmon-based electron acceleration,” Phys. Rev. A 73(1), 013815 (2006). [CrossRef]
33. P. Dombi, P. Rácz, and B. Bódi, “Ultrafast monoenergetic electron source by optical waveform control of surface plasmons,” Opt. Express 16(5), 2887–2893 (2008). [CrossRef]
34. P. Dombi, P. Rácz, and B. Bódi, “Surface plasmon enhanced electron acceleration with few-cycle laser pulses,” Laser Part. Beams 27(2), 291–296 (2009). [CrossRef]
35. P. Dombi, A. Hörl, P. Rácz, et al., “Ultrafast strong-field photoemission from plasmonic nanoparticles,” Nano Lett. 13(2), 674–678 (2013). [CrossRef]
36. Y. Watanabe, W. Inami, and Y. Kawata, “Deep-ultraviolet light excites surface plasmon for the enhancement of photoelectron emission,” J. Appl. Phys. 109(2), 023112 (2011). [CrossRef]
37. A. Ono, N. Shiroshita, M. Kikawada, et al., “Enhanced photoelectron emission from aluminum thin film by surface plasmon resonance under deep-ultraviolet excitation,” J. Phys. D: Appl. Phys. 48(18), 184005 (2015). [CrossRef]
38. H. Morisawa, A. Ono, W. Inami, et al., “Hot–electron emission enhancement by deep UV surface plasmon resonance on an aluminum periodic disk–hole array,” Opt. Mater. Express 11(7), 2278–2287 (2021). [CrossRef]
39. G. Gervinskas, G. Seniutinas, and S. Juodkazis, “Control of surface charge for high-fidelity nanostructuring of materials,” Laser Photonics Rev. 7(6), 1049–1053 (2013). [CrossRef]
40. H. F. Ghaemi, T. Thio, D. E. Grupp, et al., “Surface plasmons enhance optical transmission through subwavelength holes,” Phys. Rev. B 58(11), 6779–6782 (1998). [CrossRef]
41. S.-H. Chang, S. K. Gray, and G. C. Schatz, “Surface plasmon generation and light transmission by isolated nanoholes and arrays of nanoholes in thin metal films,” Opt. Express 13(8), 3150–3165 (2005). [CrossRef]
42. P. Hanarp, D. S. Sutherland, J. Gold, et al., “Control of nanoparticle film structure for colloidal lithography,” Colloids Surf., A 214(1-3), 23–36 (2003). [CrossRef]
43. A. B. Dahlin, T. Sannomiya, R. Zahn, et al., “Electrochemical crystallization of plasmonic nanostructures,” Nano Lett. 11(3), 1337–1343 (2011). [CrossRef]
44. J. Junesch, T. Sannomiya, and A. B. Dahlin, “Optical properties of nanohole arrays in metal–dielectric double films prepared by mask-on-metal colloidal lithography,” ACS Nano 6(11), 10405–10415 (2012). [CrossRef]
45. F. P. Fehlner and N. F. Mott, “Low-temperature oxidation,” Oxid. Met. 2(1), 59–99 (1970). [CrossRef]
