© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Adv. Mater. 2011, XX, 1–5 1 www.advmat.de www.MaterialsViews.com COMMUNICATION wileyonlinelibrary.com Mady Elbahri,* Mehdi Keshavarz Hedayati, Venkata Sai Kiran Chakravadhanula, Mohammad Jamali, Thomas Strunkus, Vladimir Zaporojtchenko, and Franz Faupel An Omnidirectional Transparent Conducting-Metal-Based Plasmonic Nanocomposite DOI: 10.1002/adma.201003811 The task to produce a transparent metal, with conductivity comparable to indium tin oxide (ITO) while retaining high transparency through the visible region has so far proven to be challenging. In this regard, metal–polymer nanocomposites have traditionally been excluded from investigation due to their strong absorption and reflection of visible light. Here, we present the first transparent conducting metal (TCM) composed of a stack of a gold film and a silver/polymer nanocomposite fabricated by sputtering on a glass substrate. In this plasmonic device, the reflection is minimized by means of symmetric plas- monic coupling under impedance matching condition in the vis- ible range. Additionally the magnetic optical resonance, which is induced by dipole–image interaction lowers the absorption and scattering of the whole structure. Since both phenomena occur in the same wavelength range, the optical transmission of the device is significantly enhanced. The plasmonic metama- terial shows an omnidirectional optical transmission up to 80% in the visible wavelength range, which is comparable to that of ITO, and an electrical conductivity that is one order of magni- tude higher than that of ITO. In the field of plasmonics, much attention is paid to new approaches for the concentration and manipulation of light to improve the absorption and/or transmission of energy. [1] For instance, a combination of noble metal nanoparticles and a metal film has been used to diminish the reflection by plasmonic coupling. [2] Applying the same idea, recently a per- fect absorber was realized with a structure consisting of a gold metal film separated from gold nanoparticles with MgF 2 as an interlayer. [3] Other plasmonic devices, which show high absorbance, were fabricated by structuring a metal surface in different manners such as a nanostructure layer [4] or micro- cavities on the top surface. [5] Light propagation normal to the metal film is an interesting issue. When the film is optically thin, i.e., in the range of the skin depth, the energy transfer can be enhanced by the surface plasmon polariton (SPP) mode and super-resolution imaging can be achieved. [6] These unique features have generated the rapidly growing field of SPP-based photonics or plasmonics. Plasmonics combines both the capacity of photonics and the miniaturization capability of electronics and is thus an out- standing candidate for future optoelectronic applications. [7] Transparent conductors (TCs), which are integral compo- nents in flat panel displays, solar cells, and smart windows, deliver electrons to or collect them from the active part of the device while at the same time allowing visible photons to pass through relatively unimpeded. At present, ITO and other trans- parent conductive oxides (TCO) are used. Efforts to produce a transparent metal with conductivity superior to ITO that retains high transparency through the visible region has so far proved to be challenging. [8] Metal/polymer nanocomposites, which show some attractive optical properties, seem to be the worst candidates for TC development owing to their strong absorp- tion and reflection in the visible region. Here, we report the first experimental realization of the omnidirectional TCM by coating a metal film on a glass substrate with a thin layer of metal/polymer nanocomposite. The strategy is based on using the nanocomposite as a random plasmonic coupler, refractive index ( n) tuner, and matching layer to minimize the reflection of the gold film by establishing a symmetric plasmonic coupling on the gold film. For that purpose the dielectric constant of the air/metal inter- face is tuned by changing the filling factor of the coating layer (nanocomposite) while maintaining that of the glass/metal interface constant. It works along with lowering the absorption and scattering of the metal film by inducing a transfer magnetic resonance that is attributed to the interaction between nano- particle plasmon resonances in the composite and their dipole images on the gold mirror. This reduction in the reflection and scattering/absorption of the system consequently leads to a strong transmission enhancement of the gold film. Since the dielectric constant of (sputtered) polytetrafluoroeth- ylene (PTFE) is lower than that of glass it was used as the host matrix for composite deposition. [9] To have a high electrical con- ductivity, a base layer was fabricated by sputtering of a 25-nm gold film onto fusion glass, although the film is highly reflec- tive in the near-IR to mid-IR range. 20-nm silver/PTFE nano- composites with different volume filling factors in the range of ≈7–23%, determined by in situ quartz microbalance monitoring Prof. M. Elbahri, M. Keshavarz Hedayati, M. Jamali Nanochemistry and Nanoengineering Institute for Materials Science Faculty of Engineering University of Kiel, Kaiserstrasse 2, 24143 Kiel, Germany E-mail: me@tf.uni-kiel.de Prof. M. Elbahri Institute of Polymer Research Helmholtz-Zentrum Geesthacht Max-Planck-Str. 1, 21502 Geesthacht, Germany E-mail: mady.elbahri@hzg.de V. S. K. Chakravadhanula, Dr. T. Strunkus, Dr. V. Zaporojtchenko, Prof. F. Faupel Multicomponent Materials Institute for Materials Science Faculty of Engineering University of Kiel, Kaiserstrasse 2, 24143 Kiel, Germany