Abstract: Li-air batteries are an exciting class of energy storage devices with exceptional theoretical capacities which could facilitate longer-range electrical vehicles if fully optimised systems are realised. 1 Energy storage in Li-air batteries proceeds via different mechanisms to those associated with conventional Li-ion batteries, necessitating detailed studies into the fundamental processes associated with discharge and charge. Recently, increasing attention has been devoted to understanding the role of the electrolyte in determining the performance of Li-air batteries. It has been conclusively shown that carbonate based electrolytes are not suitable for rechargeable systems due to the rapid accumulation of carbonate based species on the cathode. 2 These carbonates are particularly prevalent during the charging process due to decomposition of the electrolyte and reactions between the electrolyte, the primary discharge product Li 2 O 2 and its intermediates. Numerous reports have revealed that characteristic Li 2 O 2 toroids often form on the cathode surface during discharge in a variety of cathode/electrolyte systems. 3 , 4 Recently, Nazar et al. showed that the formation of these toroids is strongly related to the applied current for a given system (TEGDME/LiTFSI electrolyte and Super P carbon cathode). 5 Their results show that at low applied currents, large crystalline Li 2 O 2 toroids form on the cathode surface with a clear change to quasi-amorphous Li 2 O 2 films at higher applied currents. They also found that the toroids were much more difficult to decompose during charge than the thin films, indicating that the nature of the Li 2 O 2 formed on discharge plays a key role in determining rechargeability. In this work we have investigated the morphology and composition of discharge products formed on Super P cathodes using various different electrolyte solvent and salt combinations. We demonstrate that even at high applied currents (250 μA), electrolytes containing sulfolane as the electrolyte solvent show preferential Li 2 O 2 toroid formation (Figure 1 a,b). In comparison, electrolytes using TEGDME (Figure 1 c,d) as the electrolyte solvent do not lead to the formation of Li 2 O 2 toroids at the same applied currents. The comparative performance of cells using the various electrolytes determined using galvanostatic charge-discharge methods were demonstrated to be linked to the morphology and areal coverage of the Li 2 O 2 formed on the cathodes. The decomposition of these particles and films is visualized by conducting ex-situ SEM analysis at various stages of the charge process. The influence of catalyst addition (Pd, MnO 2, Co 3 O 4 ) to Super P carbon cathodes on the morphology of Li 2 O 2 formed on cathodes and thus their electrochemical performance was also probed. This report gives insight into the importance of understanding the formation and decomposition of Li 2 O 2 on cathodes for realizing rechargeable high capacity Li-O 2 battery systems. Figure 1: SEM images of Super P cathodes discharged with an applied current of 250 μA using different electrolyte solvent/salt combinations. 1. Bruce, P. G.; Freunberger, S. A.; Hardwick, L. J.; Tarascon, J. M. Nature materials 2011, 11, (1), 19-29. 2. McCloskey, B. D.; Bethune, D. S.; Shelby, R. M.; Girishkumar, G.; Luntz, A. C. The Journal of Physical Chemistry Letters 2011, 2, (10), 1161-1166. 3. Fan, W.; Cui, Z.; Guo, X. The Journal of Physical Chemistry C 2013 . 117 (6), pp 2623–2627 4. Mitchell, R. R.; Gallant, B. M.; Shao-Horn, Y.; Thompson, C. V. The Journal of Physical Chemistry Letters 2013 , 1060-1064. 5. Adams, B. D.; Radtke, C.; Black, R.; Trudeau, M. L.; Zaghib, K.; Nazar, L. F. Energy & Environmental Science 2013, 6, (6), 1772-1778. Acknowledgements: Financial support was provided by the European Union Seventh Framework Programme (FP7/2007-2013) project STABLE.

Abstract: New types of transparent conducting materials (TCMs) are being sought due to the increase in demand for their use in next generation electronics and photovoltaics. Methods to improve transparency be inferred by controlling porosity (graded refractive index), or from a change in the crystal structure of some materials that are not inherently transparent at visible frequencies. Transparent materials with tunable optical properties are important in conductive and capacitive displays, tandem solar cells, organic PVs and other devices. In thin film oxide deposition, where non-uniformities and porosity are not ideal, diffusion from glass substrates into oxide thin films during thermal treatment has previously been considered detrimental and was suppressed using diffusion barriers such as thick coatings of SiO 2 . In this work, we show how the transparency and conductivity of a dip-coated thin film of vanadium oxide can be markedly improved by substrate diffusion during thermal treatment, resulting in a completely transparent thin film of vanadium oxide-based material with an order of magnitude increase in electrical conductivity. The phase change and stoichiometry variation during thermal annealing of the vanadium oxide dip-coated from liquid precursors is elucidated using X-Ray photoelectron spectroscopy (XPS) and Raman scattering spectroscopy. Angle-resolved transmission spectra correlated the transparency to the changes in optical properties of the thin films and electron microscopy confirms no formal structural change contributes to the change in transparency. Hall probe measurements demonstrate improved conductivity with transparency due to diffusion of cations from the substrate into the host material lattice. References: C. M. Eliason and M. D. Shawkey, Opt. Express, 22, A642 (2014). C. O’Dwyer, M. Szachowicz, G. Visimberga, V. Lavayen, S. B. Newcomb and C. M. S. Torres, Nature Nanotechology , 4 , 239 (2009). J. Q. Xi, M. F. Schubert, J. K. Kim, E. F. Schubert, M. Chen, S. Y. Lin, W. Liu and J. A. Smart, Nature Photonics , 1 , 176 (2007). C. O'Dwyer and C. M. S. Torres, Front. Physics , 1 , 18 (2013). C. Glynn, D. Creedon, H. Geaney, J. O'Connell, J. D. Holmes and C. O'Dwyer, ACS Appl. Mater. Interfaces , 6 , 2031 (2014). K. K. Banger, Y. Yamashita, K. Mori, R. L. Peterson, T. Leedham, J. Rickard and H. Sirringhaus, Nature Materials , 10 , 45 (2011). J. Mannhart and D. G. Schlom, Science , 327 , 1607 (2010). F. Nicholas, M. P. Sean, W. H. Mark and S. S. N. Bharadwaja, Journal of Physics D: Applied Physics , 42 , 055408 (2009). T. Manning, I. Parkin, Polyhedron, 23 , 3087 (2004).

Abstract: Photonic crystals (PhCs) are types of colloidal crystals which demonstrate a host of exciting optical phenomena, the nature of which can lend insight into their structure and enable a range of potential applications in fields such as optics and optoelectronics, 1 energy storage, 2-6 and sensors for environmental monitoring, biomedicine and food preservation. 7 Artificial opals 8 are PhCs which can be formed easily using low-cost self-assembly methods and their structures are composed of highly ordered, close-packed, polymeric sphere arrays. While the optical behaviour of opals has received significant attention over the last number of decades, there is limited information on the effect of crystal thickness on the optical properties they display. Most studies focus their attention on the lattice parameters and refractive index contrast within the materials. 9,10 Here, the relationship between volume fraction and crystal thickness using an evaporation-induced self-assembly (EISA) method of formation is established. 11-13 The extent to which thickness can be used to manipulate the optical properties of the crystals is explored, focusing on the change in the photonic band gap (PBG). Specifically, the thickness-induced changes in the properties which define the PBG for a range of volume fractions. Through meticulous structural and optical characterization, primarily in the form of scanning electron microscopy (SEM) images and angle-resolved ultraviolet-visible (UV-Vis) spectroscopy, the quality of the crystals formed is examined, with thicknesses exceeding 40 layers grown from volume fractions below 0.15 %, for the first time, to our knowledge. Crystal structure is correlated to optical fingerprint, shown in the form of transmission spectra in the UV-Vis region. We expect this work to provide our colleagues in the scientific community with a direct correlation between crystal thickness and the optical fingerprint of opal PhCs. Our analysis also stands as a manual to aid any future attempts at the growth of ultra-thick colloidal crystals. Such research may act as a precursor to further developments in materials employed in the photonics, sensing, energy storage and related communities. References 1 M. I. Shalaev, W. Walasik, A. Tsukernik, Y. Xu, and N. M. Litchinitser, Nature Nanotechnology 14, 31 (2019). 2 D. McNulty, A. Lonergan, S. O'Hanlon, and C. O'Dwyer, Solid State Ionics 314, 195 (2018). 3 D. McNulty, H. Geaney, D. Buckley, and C. O'Dwyer, Nano Energy 43, 11 (2018). 4 D. McNulty, E. Carroll, and C. O'Dwyer, Advanced Energy Materials 7, 1602291 (2017). 5 E. Armstrong, D. McNulty, H. Geaney, and C. O’Dwyer, ACS Applied Materials & Interfaces 7, 27006 (2015). 6 D. McNulty, H. Geaney, Q. Ramasse, and C. O'Dwyer, Adv. Funct. Mater. 30, 2005073 (2020). 7 J. Hou, M. Li, and Y. Song, Nano Today 22, 132 (2018). 8 E. Armstrong and C. O'Dwyer, Journal of Materials Chemistry C 3, 6109 (2015). 9 D. R. Solli and J. M. Hickmann, Optical Materials 33, 523 (2011). 10 S. G. Romanov, Physics of the Solid State 59, 1356 (2017). 11 Q. Jiang, C. Li, S. Shi, D. Zhao, L. Xiong, H. Wei, and L. Yi, Journal of Non-Crystalline Solids 358, 1611 (2012). 12 J. Zhang, Y. Li, X. Zhang, and B. Yang, Advanced Materials 22, 4249 (2010). 13 A. Lonergan, C. Hu, and C. O'Dwyer, Phys. Rev. Materials 4, 065201 (2020). 14 S. O'Hanon, D. McNulty, R. Tian, J. Coleman, and C. O'Dwyer, J. Electrochem. Soc. 167, 140532 (2020). Figure 1. Optical and structural analysis for 350 nm PS opals formed by EISA. Analysis presented in the form of transmission spectra obtained for samples formed from a range of five volume fractions, labelled by their dilution factors (a,d,g), sample plan view SEM images (b,e,f), and sample cross-sectional SEM images (c,f,i). (a-c) correspond to regions of maximum opal thickness, (d-f) to regions of lesser thickness, (g-i) to regions of minimal thickness. Figure 1

Abstract: In bulk form the thermoelectric material bismuth telluride (Bi 2 Te 3 ) has a high figure of merit (ZT) at room temperature. When bulk Bi 2 Te 3 is exfoliated to smaller dimensions, such as its 2D form (nanosheets), its thermoelectric effects are improved by reduction in thermal conductivity due to phonon confinement and scattering, thus increasing the ZT. The difficulty involved in incorporating nanosheets into energy harvesting systems motivated the search for a form of Bi 2 Te 3 that retains the high ZT apparent at the nanoscale with the capability of being deposited or painted onto device infrastructures. This work highlights a method whereby solvent exfoliation of Bi 2 Te 3 into solution-dispersible 2D nanosheets can form a practical thin film that can be distributed across a surface. Optical transmission measurements quantify the relationship between efficient and stable exfoliation and the reduction in optical density. Optimized exfoliated suspension are also shown to form smooth, uniform blends when mixed with poly ethylene glycol and other polymers to produce a paintable Bi 2 Te 3 film that can be applied to surfaces using an innovative painting technique. Atomic force microscopy, transmission electron spectroscopy, Raman spectroscopy and scanning electron spectroscopy are used to examine the structure of the 2D nanosheets and the highly reproducible Bi 2 Te 3 thin films. Electrical transport studies show that the films have conductive pathways over a range of surfaces and various structural formations, linking the conductivity to the percolating conduction through the nanosheet ensemble. The combination of the facile preparation method and the scope for diverse surface coating as a cohesive and conductive thin film offers a methods for integration with heat producing devices for energy harvesting applications. References K. M. F. Shahil, M. Z. Hossain, D. Teweldebrhan and A. A. Balandin, Applied Physics Letters , 96 (2010). B. Poudel, Q. Hao, Y. Ma, Y. Lan, A. Minnich, B. Yu, X. Yan, D. Wang, A. Muto, D. Vashaee, X. Chen, J. Liu, M. S. Dresselhaus, G. Chen and Z. Ren, Science , 320 , 634 (2008). M. Saleemi, M. S. Toprak, S. Li, M. Johnsson and M. Muhammed, Journal of Materials Chemistry , 22 , 725 (2012). L. E. Bell, Science , 321 , 1457 (2008). S. Li, M. S. Toprak, H. M. A. Soliman, J. Zhou, M. Muhammed, D. Platzek and E. Müller, Chemistry of Materials , 18 , 3627 (2006). Y. Hernandez, N. Valeria, L. Mustafa, B. F. M., S. Zhenyu, S. De, M. T., B. Holland, M. Byrne, Y. K. Gun'Ko, J. J. Boland, P. Niraj, G. Duesberg, S. Krishnamurthy, R. Goodhue, J. Hutchison, V. Scardaci, A. C. Ferrari and J. N. Coleman, Nature Nanotechnology , 3 , 1748 (2008). V. Nicolosi, M. Chhowalla, M. G. Kanatzidis, M. S. Strano and J. N. Coleman, Science , 340 (2013). L. D. Hicks and M. S. Dresselhaus, Physical Review B , 47 , 12727 (1993).

Abstract: Transition Metal Dichalcogenindes (TMD) have considerable potential for applications spanning electronics, sensors and optoelectronics due to the wide ranging electronic and optical properties which are displayed by this class of 2D layered materials [1]. Research is focused on issues such as: large area growth [2, 3] , stable approaches to doping [4] and achieving required values of specific contact resistivity [5] . We are contributing to the research effort by investigating the structural, optical and electronic properties of crystalline molybdenum disulfide (MoS 2 ) grown by chemical vapour deposition (CVD) in a commercial 300mm atomic layer deposition reactor. In this work we report on the properties of monolayer and multilayer MoS 2 growth at 550 o C using Mo(CO) 6 and H 2 S precursors on a number of different substrates, including SiO 2 , sapphire and amorphous alumina. This work focuses on the topology, Raman response and electronic properties of the CVD grown MoS 2 thin films. Figure 1 (a) shows the Raman spectrum for an as-grown 10nm MoS 2 on a SiO 2 /Si substrate. MoS 2 can be determined by the peaks at approximately 385cm -1 (E 1 2g ) and 410cm -1 (A 1g ). There are two other peak characteristics of MoS 2 which cannot be seen due to back-scattering at 286cm -1 (E 1g ), and lack of sensitivity below 200cm -1 at 32cm -1 (E 2 2g )[6]. Additional peaks are detected at wavenumbers between 2000-3000cm -1 , seen in Fig. 1 (b). Further investigation is needed to establish if these peaks are from photoluminescence, contaminants within the structure or purely a surface effect. Fig. 1 (c) shows an AFM image of an annealed 1.2nm MoS 2 sample on a SiO 2 /Si substrate. The blue marks indicate areas on the material that are above a height of 0.6nm. Further results will be presented as a function of the number of MoS 2 monolayers using Conductive AFM (C-AFM) and Kelvin Probe analysis. XTEM images seen in Fig. 1 (d), (e) show MoS 2 grown on SiO 2 /Si and sapphire substrates respectively. They show that polycrystalline and layered MoS 2 is formed at the growth temperature of 550 o C, with no subsequent post growth annealing . There is no interfacial layer formed at the MoS 2 /SiO 2 interface, but an amorphous interfacial layer of ~0.5nm is observed between MoS 2 and sapphire, which is still being investigated. Plan view TEM analysis (not shown) confirms aligned MoS 2 with grain sizes (over a local area of around 100 nm x 100nm) in the range 5nm to 20nm. The carrier concentration, carrier type and carrier mobility were studied with Hall measurements carried out at room temperature using a Van der Pauw structure (1cm x 1 cm). Excellent ohmic behavior is achieved on MoS 2 (nominally 10nm) deposited on both sapphire and a-Al 2 O 3 /sapphire substrates. Table 1 provides a summary of the Hall analysis, showing that the non-intentionally doped MoS 2 grown by CVD is n -type with very low carrier concentrations on the order of ~10 14 cm -3 , electron mobility in the range 3.3-16.7cm 2 /V.s. Mobility values up to ~ 15 cm 2 /Vs for a grain size in the 10nm to 60nm range, is an interesting result, as in the work of K. Kang et al., [3], the monolayer grain size is around 1 mm with an associated electron mobility of 30 cm 2 /V. These results suggests that grain boundary defects in 2D MoS 2 may not be the main factor limiting carrier mobility, as is typically the case in polycrystalline 3D semiconductors (see for example [7]). In addition, the unintentional n type doping in the CVD grown MoS 2 is low, with values around 1-3x10 14 cm -3 . This low value of unintentional doping provides a useful baseline in-situ for doping studies with elements such as Nb [8] and Re [9] . References [1] Geim,A.K. & Grigorieva,I.V. Van der Waals Heterostructures. Nature 499,419–425 (2013). [2] Lin,Y.-C.etal. Wafer-scale MoS 2 thin layers prepared by MoO 3 sulfurization. Nanoscale 4, 6637–6641(2012). [3] Kang et al., Nature , 2015, 520, 656–660 [4] C. Zhou, Y. Zhao, S. Raju, Y. Wang, Z. Lin, M. Chan, Y. Chai, Adv. Funct. Mater. 2016, 26, 4223 [5] Gioele Mirabelli, Michael Schmidt, Brendan Sheehan, Karim Cherkaoui, Scott Monaghan, Ian Povey, Melissa McCarthy, Alan P Bell, Roger Nagle, Felice Crupi, Paul K Hurley, Ray Duffy, “Back-gated Nb-doped MoS2 junctionless field-effect-transistors” AIP Advances, 6, 2 , 025323 (2016) [6] Li et al, From Bulk to Monolayer MoS 2 : Evolution of Raman Scattering, Advanced Functional Materials , 22 (2012) [7] John Y. W. Seto, The electrical properties of polycrystalline silicon films, Journal of Applied Physics 46, 5247 (1975) [8] Saptarshi Das et al., Nb-doped single crystalline MoS 2 field effect transistor, Appl. Phys. Lett. 106, 173506 (2015) [9] T. Hallam et al., Rhenium-doped MoS 2 films Appl. Phys. Lett. 111, 203101 (2017) Figure 1

Abstract: Research in lithium-ion batteries is often focused on optimising the electrode performance of either the anode 1 or cathode 2 . One common research strategy is to explore alternative electrode material candidates for use as both the anode 3 and cathode 4 . Another approach involves optimising the performance of existing electrode materials through structured electrode architectures with nano-sized features. Incorporating nanostructure into electrode design has reported advantages of shorter ion diffusion lengths and improved rate capability during cycling 5 . A common and simple technique for introducing nanostructure to electrodes is the use of a photonic crystal template, particularly inverse opal photonic crystals. The porous geometry, highly interconnected material and nano-sized features of the pore walls are all believed to contribute to improved electrochemical performance in inverse opal electrodes 6 7 . Photonic crystal materials are more than just a structural template and are renowned for their ability to tune the wavelengths of light propagating in the structure 8 9 . The repeating dielectric material comprising the structure reflects specific wavelengths, known as the photonic bandgap or stopband, depending on the size of the repeating lattice and the refractive index contrast between the composite materials. Tuning the photonic stopband of various inverse opal materials has been extensively studied 10 11 . Inverse opal battery electrodes have yet to exploit the optical potential of the photonic stopband. Here, we showcase a fundamentally new operando analysis technique for lithium-ion battery electrodes adopting a photonic crystal structure. Visible spectroscopy is used to monitor the presence and position of the photonic stopband of the electrode material during battery cycling, see Figure 1. Capitalizing on the sensitivity of the photonic stopband to lattice size and refractive index contrast, shifts or changes in the optical spectrum can be correlated to the electrode environment and material performance. Several optical effects are observed throughout the cycling process and linked back to the battery performance of the anode. A TiO 2 inverse opal anode is reported on here, yet the technique is versatile and should be applicable to a wide range of electrode materials possessing a photonic crystal structure. References Kim, H.; Choi, W.; Yoon, J.; Um, J. H.; Lee, W.; Kim, J.; Cabana, J.; Yoon, W.-S., Exploring Anomalous Charge Storage in Anode Materials for Next-Generation Li Rechargeable Batteries. Chemical Reviews 2020, 120 (14), 6934-6976. Xu, J.; Dou, S.; Liu, H.; Dai, L., Cathode materials for next generation lithium ion batteries. Nano Energy 2013, 2 (4), 439-442. Liang, B.; Liu, Y.; Xu, Y., Silicon-based materials as high capacity anodes for next generation lithium ion batteries. Journal of Power Sources 2014, 267 , 469-490. Manthiram, A.; Song, B.; Li, W., A perspective on nickel-rich layered oxide cathodes for lithium-ion batteries. Energy Storage Materials 2017, 6 , 125-139. Mahmood, N.; Tang, T.; Hou, Y., Nanostructured Anode Materials for Lithium Ion Batteries: Progress, Challenge and Perspective. Advanced Energy Materials 2016, 6 (17), 1600374. McNulty, D.; Carroll, E.; O'Dwyer, C., Rutile TiO2 Inverse Opal Anodes for Li-Ion Batteries with Long Cycle Life, High-Rate Capability, and High Structural Stability. Advanced Energy Materials 2017, 7 (12), 1602291. McNulty, D.; Geaney, H.; Buckley, D.; O'Dwyer, C., High capacity binder-free nanocrystalline GeO2 inverse opal anodes for Li-ion batteries with long cycle life and stable cell voltage. Nano Energy 2018, 43 , 11-21. John, S., Strong localization of photons in certain disordered dielectric superlattices. Phys. Rev. Lett. 1987, 58 (23), 2486-2489. Yablonovitch, E., Inhibited spontaneous emission in solid-state physics and electronics. Phys. Rev. Lett. 1987, 58 (20), 2059-2062. Schroden, R. C.; Al-Daous, M.; Blanford, C. F.; Stein, A., Optical Properties of Inverse Opal Photonic Crystals. Chemistry of Materials 2002, 14 (8), 3305-3315. Lonergan, A.; Hu, C.; O’Dwyer, C., Filling in the gaps: The nature of light transmission through solvent-filled inverse opal photonic crystals. Physical Review Materials 2020, 4 (6), 065201. Figure 1 (a) Schematic diagram of simultaneous electrochemical and optical characterisation techniques for photonic crystal electrodes. (b) Galvanostatic charge/discharge data for a TiO 2 inverse opal electrode. (c) Optical spectrum for a TiO 2 inverse opal submerged in LiPF 6 electrolyte. (d) SEM image showing the ordered structure of a pristine TiO 2 inverse opal. (e) Operando optical spectra obtained at 0.5 V intervals during discharge of the TiO 2 inverse opal electrode. Figure 1

Abstract: Photonic crystals are periodic dielectric structures which selectively tune the wavelengths of light propagating through the material 1 2 . The highly ordered, repeating structural lattice induces a photonic bandgap or stopband which inhibits or partially attenuates certain frequencies of light, similar to the electronic bandgap with forbidden energies present in semiconductor materials 3 . These forbidden frequencies are blocked in transmission and reflected from the material surface. The inherent sensitivity of this photonic response to repeating lattice size dimensions and the magnitude of the refractive index contrast between the constituent materials allows for tailored optical behaviour by adjusting the photonic crystal structural parameters or environment 4 5 . A range of interesting applications using both the photonic bandgap and material porosity have emerged, predicated on the ability to accurately forecast the wavelength position of the photonic response. Colorimetric sensors 6 7 , photocatalysts 8 9 and solar cells 10 are prime examples of these types of applications; the porosity of the photonic crystal facilitates greater material infiltration and reactions, while the photonic bandgap acts to enhance the optical component of the process. Critically, the use of these structures is tied to our ability to predict and interpret the signature optical response. Here, we examine several techniques which can be used modify the photonic bandgap/stopband for photonic crystal structures. For TiO 2 and SnO 2 inverse opal photonic crystals, we explore how solvent infiltration into the highly porous network red-shifts the observed photonic response. Using solvents with different refractive indices, we apply the shifted photonic stopband data to determine the fill fraction of solid material comprising the photonic crystal network. We also examine functionalization of artificial opal and inverse opal photonic crystals with metal films. We detail the emergence of a consistent photonic stopband blue-shift with increasing metal content and propose a reduction in the effective refractive index of the entire photonic crystal introduced by the specific properties of the metal film. Importantly, the effects investigated here are broadly applicable to a range of realistic operating conditions across many disciplines where an understanding of the photonic stopband is paramount to the application. References Yablonovitch, E., Inhibited Spontaneous Emission in Solid-State Physics and Electronics. Physical Review Letters 1987, 58 (20), 2059-2062. John, S., Strong localization of photons in certain disordered dielectric superlattices. Physical Review Letters 1987, 58 (23), 2486-2489. Joannopoulos, J. D.; Villeneuve, P. R.; Fan, S., Photonic crystals: putting a new twist on light. Nature 1997, 386 (6621), 143-149. Blanford, C. F.; Schroden, R. C.; Al-Daous, M.; Stein, A., Tuning Solvent-Dependent Color Changes of Three-Dimensionally Ordered Macroporous (3DOM) Materials Through Compositional and Geometric Modifications. Advanced Materials 2001, 13 (1), 26-29. Aguirre, C. I.; Reguera, E.; Stein, A., Tunable Colors in Opals and Inverse Opal Photonic Crystals. Advanced Functional Materials 2010, 20 (16), 2565-2578. Zhang, Y.; Qiu, J.; Hu, R.; Li, P.; Gao, L.; Heng, L.; Tang, B. Z.; Jiang, L., A visual and organic vapor sensitive photonic crystal sensor consisting of polymer-infiltrated SiO2 inverse opal. Physical Chemistry Chemical Physics 2015, 17 (15), 9651-9658. Li, H.; Chang, L.; Wang, J.; Yang, L.; Song, Y., A colorful oil-sensitive carbon inverse opal. Journal of Materials Chemistry 2008, 18 (42), 5098-5103. Chen, J. I. L.; von Freymann, G.; Choi, S. Y.; Kitaev, V.; Ozin, G. A., Amplified Photochemistry with Slow Photons. Advanced Materials 2006, 18 (14), 1915-1919. Collins, G.; Lonergan, A.; McNulty, D.; Glynn, C.; Buckley, D.; Hu, C.; O'Dwyer, C., Semiconducting Metal Oxide Photonic Crystal Plasmonic Photocatalysts. Advanced Materials Interfaces 2020, 7 (8), 1901805. Liu, L.; Karuturi, S. K.; Su, L. T.; Tok, A. I. Y., TiO2 inverse-opal electrode fabricated by atomic layer deposition for dye-sensitized solar cell applications. Energy & Environmental Science 2011, 4 (1), 209-215. Figure 1 SEM images and optical transmission spectra for (a) TiO 2 and (b) SnO 2 inverse opals. In each case the wavelength position of the photonic stopband is red-shifted significantly when a solvent infiltrates the porous photonic crystal network. SEM images and optical transmission spectra for (c) artificial polystyrene opals coated with a gold film and (d) TiO 2 inverse opals coated with a copper film. Metal film incorporation into the photonic crystal network acts to consistent blue-shift the observed photonic stopband. Figure 1