Addendum: “Observation of Bragg reflection in photonic crystals synthesized from air spheres in a titania matrix” [Appl. Phys. Lett. 76, 1816 (2000)] A. Richel, N. P. Johnson, and D. W. McComb Citation: Applied Physics Letters 77, 1062 (2000); doi: 10.1063/1.1289056 View online: http://dx.doi.org/10.1063/1.1289056 View Table of Contents: http://scitation.aip.org/content/aip/journal/apl/77/7?ver=pdfcov Published by the AIP Publishing Articles you may be interested in Enhanced Bragg reflections from size-matched heterostructure photonic crystal thin films prepared by the Langmuir-Blodgett method Appl. Phys. Lett. 89, 093116 (2006); 10.1063/1.2339031 Erratum: “Bragg grating magnetic photonic crystal waveguides” [Appl. Phys. Lett.86, 251102 (2005)] Appl. Phys. Lett. 87, 269901 (2005); 10.1063/1.2153013 Emission in a SnS 2 inverted opaline photonic crystal Appl. Phys. Lett. 79, 731 (2001); 10.1063/1.1389825 Observation of Bragg reflection in photonic crystals synthesized from air spheres in a titania matrix Appl. Phys. Lett. 76, 1816 (2000); 10.1063/1.126175 Erratum: “Distributed Bragg reflectors based on AlN/GaN multilayers” [Appl. Phys. Lett. 74, 1036 (1999)] Appl. Phys. Lett. 74, 4070 (1999); 10.1063/1.123264
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APPLIED PHYSICS LETTERS
VOLUME 77, NUMBER 7
14 AUGUST 2000
ADDENDA Addendum: ‘‘Observation of Bragg reflection in photonic crystals synthesized from air spheres in a titania matrix’’ †Appl. Phys. Lett. 76, 1816 „2000…‡ A. Richel and N. P. Johnsona) Department of Electronics and Electrical Engineering, Optoelectronics Research Group, University of Glasgow, Glasgow G12 8QQ, Scotland, United Kingdom
D. W. McComb Department of Chemistry, University of Glasgow, Glasgow G12 8QQ, Scotland, United Kingdom
共Received 6 June 2000; accepted for publication 22 June 2000兲 关S0003-6951共00兲03533-6兴
We recently reported on the synthesis, detailed characterization by electron microscopy and angle-resolved optical reflectivity of photonic crystals consisting of air spheres in a titania matrix.1 Several errors in the initials and names of the authors whose work was cited in this letter have been brought to our attention. We apologize to the authors concerned and for the purpose of clarity reproduce the full list of references below.2–13 The synthesis method employed was based on two recently published methods that were cited in our letter. The method described in Ref. 7 utilizes vacuum filtration. However, the procedure is carried out in air. In Ref. 8, a different organometallic precursor, titanium 共IV兲 propoxide, is used. That procedure is carried out in a nitrogen-purged glove box and involves repeated cycles 共up to eight兲 of penetration, reaction with air, and drying. The penetration of the matrix with the organometallic species was carried out without use of vacuum filtration methods. In our work, we employed a combination of these approaches. The steps were as follows: 共1兲 a self-assembled array of latex microspheres was formed, 共2兲 the array was dried under an infrared lamp, 共3兲 the array was soaked with ethanol and placed in a nitrogen-filled glove box, and 共4兲 infiltration of the array with titanium 共IV兲 ethoxide was carried out using vacuum filtration. The advantages of our approach are that the instantaneous reaction of the organometallic precursor with air is avoided by use of a nitrogen-purged glove box and high-quality specimens are obtained in a single reaction cycle. We note that the authors of Ref. 7 have recently published a more detailed description of their experimental method.14 In this letter, they employ a solution of titanium 共IV兲 ethoxide in ethanol in an attempt to suppress the rapid reaction of the organometallic species with air. The overall result of the modified procedure described in our letter is to decrease the shrinkage of the lattice that occurs when the latex template is removed and to improve the uniformity of the photonic crystals obtained. In our work, the a兲
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average shrinkage observed was reported as 17.5%, compared with values of 26%–32% in Ref. 7 and around 33% in Ref. 8. Our scanning electron microscope images show a very regular lattice in which the ordering structure of the penultimate layer is also apparent. The transmission electron microscope 共TEM兲 images show details of the tetrahedral and octahedral sites and electron diffraction was used to establish the phase of TiO2 present, i.e., anatase. In the highresolution TEM image the individual crystallites that make up the ‘‘walls’’ of this remarkable structure are clearly observed, and detailed analysis of the defects observed may yield useful insight into the growth mechanism and structure–property relationship of this photonic material. Following publication of our letter, we learned of a letter by Thijssen and co-workers in which angle-resolved Bragg reflections from air spheres in titania were analyzed.15 Their letter appeared in print shortly before our work was submitted for publication, and we acknowledge the omission of this reference. While there are differences in the apparatus used, the experiments carried out and the results obtained are fairly similar. It is interesting to note that average volume fraction of titania in the air–sphere lattice does differ significantly between the various articles. In Ref. 8, the reported density of TiO2 is between 12 and 20 vol %, while in Ref. 15 authors from the same research group report a density between 6 and 12 vol %. In our letter, the angle-resolved Bragg spectra were used to estimate a volume fraction of TiO2 of 23%. In addition, the walls of the titania–air spheres appear to be significantly thinner 共14 nm兲 in our work than those reported in Ref. 14. This structural difference may account for the larger relative stopband width of ⌬E/E⫽0.15 observed in our work.
1
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