Muallem Merav, Palatnik Alex, Nessim Gilbert D, Tischler Yaakov R
The Department of Chemistry and the Bar-Ilan Institute for Nanotechnology and Advanced Materials, Bar-Ilan University , Ramat Gan 52900, Israel.
ACS Appl Mater Interfaces. 2015 Jan 14;7(1):474-81. doi: 10.1021/am506531p. Epub 2014 Dec 29.
We describe the design, fabrication, and characterization of mechanically stable, reproducible, and highly reflecting distributed Bragg reflectors (DBR) composed of thermally evaporated thin films of calcium fluoride (CaF2) and zinc sulfide (ZnS). CaF2 and ZnS were chosen as the low and high refractive index components of the multilayer DBR structures, with n = 1.43 and n = 2.38 respectively, because neither material requires substrate heating during the deposition process in order to produce optical quality thin films. DBRs consisting of seven pairs of CaF2 and ZnS layers, were fabricated with thicknesses of 96 and 58 nm, respectively, as characterized by high-resolution scanning electron microscopy (HR-SEM), and exhibited a center wavelength of λc = 550 nm and peak reflectance exceeding 99%. The layers showed good adhesion to each other and to the glass substrate, resulting in mechanically stable DBR coatings. Complete optical microcavities consisting of two such DBR coatings and a CaF2 spacer layer between them could be fabricated in a single deposition run. Optically, these structures exhibited a resonator quality factor of Q > 160. When a CaF2/ZnS DBR was grown, without heating the substrate during deposition, on top of a thin film containing the fluorescent dye Rhodamine 6G, the fluorescence intensity showed no degradation compared to an uncoated film, in contrast to a MgF2/ZnS DBR coating grown with substrate heating which showed a 92% reduction in signal. The ability to fabricate optical quality CaF2/ZnS DBRs without substrate heating, as introduced here, can therefore enable formation of low-loss high-reflectivity coatings on top of more delicate heat-sensitive materials such as organics and other nanostructured emitters, and hence facilitate the development of nanoemitter-based microcavity device applications.
我们描述了由热蒸发的氟化钙（CaF2）和硫化锌（ZnS）薄膜组成的机械稳定、可重复且高反射的分布式布拉格反射器（DBR）的设计、制造和表征。选择CaF2和ZnS作为多层DBR结构的低折射率和高折射率成分，其折射率分别为n = 1.43和n = 2.38，因为在沉积过程中这两种材料都不需要对衬底进行加热就能制备出光学质量的薄膜。由七对CaF2和ZnS层组成的DBR，其厚度分别为96和58 nm，通过高分辨率扫描电子显微镜（HR-SEM）表征，中心波长为λc = 550 nm，峰值反射率超过99%。这些层之间以及与玻璃衬底之间显示出良好的附着力，从而形成了机械稳定的DBR涂层。由两个这样的DBR涂层以及它们之间的CaF2间隔层组成的完整光学微腔可以在一次沉积过程中制备出来。在光学上，这些结构表现出品质因数Q > 160。当在含有荧光染料罗丹明6G的薄膜上生长CaF2/ZnS DBR且沉积过程中不加热衬底时，与未涂层的薄膜相比，荧光强度没有下降，而在衬底加热条件下生长的MgF2/ZnS DBR涂层的信号强度则下降了92%。因此，如本文所介绍的，在不加热衬底的情况下制备光学质量的CaF2/ZnS DBR的能力，可以在诸如有机物和其他纳米结构发射体等更脆弱的热敏材料上形成低损耗高反射率涂层，从而促进基于纳米发射体的微腔器件应用的发展。
