ACS PRF | ACS
All e-Annual Reports
43924-G10
Plasmonics of Composite Materials: New Avenues of Light Management on the Nanoscale
Original PRF proposal contained four major tasks:
[1]. Reflection/refraction of surface waves
[2]. Surface waves and material anisotropy
[3]. Nonlinear response of surface modes
[4]. Localization of surface modes and applicability of effective-medium descriptions
Over past year, ACS-PRF funding has enabled us to initiate several new projects on designing fundamentally new types of materials for optical sensing, imaging, and lithography, developing analytical theories of their optical response, and understanding the limitations of applicability of these theories. Relating to the major tasks (see above), we have almost completed tasks [2] and [4], and performed a substantial part of task [1]. We have also extended the goals of original PRF proposal to materials with active (gain) component and obtained several fundamental results concerning plasmonics in these structures. Below we describe our major PRF-funded achievements in more details.
A. Anisotropic plasmonic metamaterials
Although this topic was originally listed as task 2 of PRF proposal, our discovery of negative refraction in strongly anisotropic systems (funded by OSU and NSF), provided our group with a unique opportunity to gain one of the leading positions in the rapidly developing field of metamaterials, and thus made this topic a priority. PRF funding has provided a partial support for the following projects:
I. Understanding the optical properties of nanowire composites
This project was motivated by the lack of fundamental understanding of optical response of these systems as demonstrated by a number of controversies.
On one hand, it has been expected that the coupling of the SPPs on nanowire surfaces to free-space incident radiation will result in reversal of phase velocity of the coupled modes and in appearance of the negative refraction.
On the other hand, several groups working on microwave analogs of plasmonic nanowire arrays have indicated that finite-length of nanowires in nanowire-filled waveguides prevent the onset of negative refraction.
Our PRF-funded results, published in Appl.Phys.Lett. have resolved the above controversy and unambiguously demonstrated the existence of optical negative refraction in nanowire arrays.
At the same time, we have developed an analytical description of optical behavior of nanowire systems, and demonstrated that these unique metamaterials can be used for a number of exciting applications apart from negative refraction. In particular, we have shown that the transparency of nanowire systems can be essentially reversed by minor mechanical modulation of composite geometry (i.e. compression/stretching). The limits of applicability of the developed effective-medium theories were also analyzed. These results can be utilized in a number of novel optical sensing/detecting/fabricating devices.
This research partially completes tasks 2 and 4 of original PRF proposal.
We have also demonstrated that nanowire-based negative refractive systems can be used to build planar lenses with far-field resolution exceeding free-space diffraction limit. This part of the project partially completes task 1 of the proposal.
II. Nanolayered systems
In another PRF-supported project, we have analyzed the interplay between coupled SPPs in metal-dielectric multilayers. We have demonstrated, that in contrast to the widely accepted belief, the optical behavior of multilayered systems is rarely described by well-known quasistatic effective medium theories (EMTs). We have identified the origin of the discrepancy between EMTs and real optical response of the multilayers, and liked this discrepancy with metamaterial analog of spatial dispersion of dielectric permittivity.
We have developed a nonlocal EMT which adequately describes optics in even few-layer composites and demonstrated the convergence of nonlocal EMT to its quasistatic counterpart in the limit of infinitely long composites with infinitely thin layers. Our results provide a solid foundation for design of new generations of metamaterials and (more importantly) for assessing the performance of microscale layered systems based on the performance of few-layer prototypes.
These results are summarized in publications in J.Nanomaterials and in Appl.Phys.Lett.
This project partially completes tasks 2, and 4 of the PRF proposal.
B. Gain in metamaterials
Absorption of electromagnetic waves in metals is considered to be the major fundamental constraint of plasmonic structures, limiting their sensitivity, size, and efficiency. It has been recently suggested that effects of plasmonic absorption can be compensated by material gain in the adjacent dielectric layers. We have developed the analytical description of this phenomenon. The experimental verification of our results has been carried out by group of Prof. Noginov at Norfolk State University. The manuscript detailing our work is currently under review in Phys.Rev.Lett
In a different project, we have developed an approach to manipulation of dispersion properties of negative-index composites using material gain. We have demonstrated that relatively weak material gain can be utilized to achieve broadband coupling and/or broadband processing in active negative-index structures. Our results are accepted for publication in Appl.Phys.Lett.
This part of the project is an extension of Task 3 of original PRF proposal
C. Next steps
Next, we are planning to analyze nonlinear properties of SPP, mainly focusing on competing task 3 of the proposal.
