## 1 Introduction  
This is well known that thin (no thicker than a few tens of nanometers) metal layers sandwiched between two dielectrics having the same refraction indices (RI) support the propagation of long-range surface plasmon polaritons (LRSPP) appearing as a result of the interference of SPP pertinent to the two neighboring metal-dielectric interfaces [1; 2; 3]. (For brevity, below we will usually omit the word polariton speaking simply about surface plasmons). Besides fundamental researches, during previous years this effect has been used also for sensing purposes, somewhat analogously (but with certain advantages caused by the long propagation distances in the case) to more standard surface plasmon resonance (SPR)-based sensors (see e.g., [4; 5] for general reviews of the field). Both (almost) free-standing thin metal layers, and such layers working in water and deposited onto an appropriate substratum made from material having the same RI as the water (e.g., particular Teflon) were exploited [6; 7]. However, certainly, the necessity to construct a symmetric \"sandwich\" structure to support the LRSPP propagation poses a serious problem to be overcome and limits further development of the method. This is true even when the exploitation of such an approach in water is at stake (water's relatively low refraction index \(n=1.33\) drastically limits the choice of appropriate supports) and makes the work almost impossible in gases is their RI is very close to unity.  
The situation has changed completely when it was recognized that somewhat similar situation occurs when one of the dielectrics of a symmetrical sandwich structure is replaced with a specially designed Photonic Crystal (PC) [8]. This enabled the launch and use of surface plasmons (in the red spectral region) for such \"non-plasmonic\" materials as palladium [9; 10; 11] and cobalt [12], as well as launch and use blue (at 405 nm [13]) surface plasmons for gold. Note, that in all of the above cases, without the properly designed Photonic Crystal supporting LRSPP, there is simply no point in speaking about surface plasmons at all: their propagation distances would then be just of the order of the wavelength.  
Another big topic is the use of PC-supported surface electromagnetic waves without any metal layer, which has numerous implications in sensors, electromagnetic field control at the surface and so forth. This topic is relatively far from the research under discussion now, but for completeness, we still would like to indicate a few corresponding essential papers and reviews [14; 15; 16; 17; 18; 19; 20; 21; 22], see further references therein.  
In this paper, we report on the realization of PC-supported long-range surface plasmons for silver at the red wavelength of He-Ne laser, \(\lambda\) = 632.8 nm. Quite narrow plasmon resonances, attesting to the ultralong SPP propagation and high quality of silver films, were observed. From one point of view, silver is always considered as the best surface plasmon-supporting metal in the red and near-infrared spectral ranges. However, from another point of view, the difficulties in the preparation of high-quality thin layers of silver and rapid degradation of this material exposed to the atmosphere make its exploitation quite tricky. To the best of our knowledge, up to date LRSPP with thin silver nanofilms have been realized only with the (almost) symmetrical sandwich structures composed of silica and (very) thick layers of an index matching oil or polymer [23; 24], so that their exploitation as sensors seems not possible.  
We also profit a lot from the extensive experience of preparation of thin silver layers onto different dielectrics gained by the Australian team, especially in the course of the researches aiming at the optimization of thin film coatings for solar and thermal radiation control, see e.g., [25; 26]. Important peculiarity here is the use of materials, which are not oxide materials, as adjacent layers for silver. Detailed discussion of this point is given in the next Section.