Zoran Jakšić

A consideration of the use of metamaterials for sensing applications: field fluctuations and ultimate performance

We analysed some peculiarities of electromagnetic metamaterials convenient for plasmon-based chemical sensing with enhanced sensitivity. Owing to the vastly extended range of possible values of refractive index, a higher degree of design freedom is enabled in comparison to conventional surface plasmon sensors. After considering some possible approaches to use metamaterials as either surface or bulk adsorbents, we analysed the ultimate performance of such sensing devices which are limited by refractive index fluctuations caused by adsorption and desorption processes. We utilized an approach based on a parallel between the adsorption–desorption mechanism and the carrier generation–recombination in semiconductors. As a special case, we considered structures for the detection of a single gas and used our approach to calculate the spectral density of refractive index fluctuations. We believe that our analysis may be of importance in different practical fields, including e.g. environmental sensing, homeland security and biosensing.

Emittance and absorptance tailoring by negative refractive index metamaterial- based Cantor multilayers

We investigated electromagnetic wave propagation through one-dimensional stacks of alternating positive and negative refractive index layers arranged as truncated quasi-periodic (fractal) Cantor multilayers. We considered the occurrence of phase compensation in these structures. In our calculation we utilized the transfer matrix technique and applied the Kirchhoffs second law to calculate emittance and absorptance modification by negative index metamaterials. We took into account dispersion and absorptive losses and analysed both on-axis and off-axis radiation. We showed that Cantor structures formed by inserting negative refractive index layers as a substitution part in the multilayer lattices enable tailoring of both spectral and angular dependences of emittance/absorptance. We conclude that phase compensation could significantly extend the applicability of Cantor-type multilayers containing negative refractive index materials.

Functionalization of Artificial Freestanding Composite Nanomembranes

Artificial nanomembranes may be defined as synthetic freestanding structures with a thickness below 100 nm and a very large aspect ratio, of at least a few orders of magnitude. Being quasi-2D, they exhibit a host of unusual properties useful for various applications in energy harvesting, sensing, optics, plasmonics, biomedicine, etc. We review the main approaches to nanomembrane functionalization through nanocompositing, which ensures performance far superior to that of simple nanomembranes. These approaches include lamination (stacking of nanometer-thin strata of different materials), introduction of nanoparticle fillers into the nanomembrane scaffold, nanomembrane surface sculpting and modification through patterning (including formation of nanohole arrays and introduction of ion channels similar in function to those in biological nanomembranes). We also present some of our original results related to functionalization of metal matrix composite nanomembranes.

Oblique surface waves at an interface between a metal–dielectric superlattice and an isotropic dielectric

We investigate the existence and dispersion characteristics of surface waves that propagate at an interface between a metal–dielectric superlattice and an isotropic dielectric. Within the long-wavelength limit, when the effective-medium (EM) approximation is valid, the superlattice behaves like a uniaxial plasmonic crystal with the main optical axes perpendicular to the metal–dielectric interfaces. We demonstrate that if such a semi-infinite plasmonic crystal is cut normally to the layer interfaces and brought into contact with a semi-infinite dielectric, a new type of surface mode can appear. Such modes can propagate obliquely to the optical axes if favorable conditions regarding the thickness of the layers and the dielectric permittivities of the constituent materials are met. We show that losses within the metallic layers can be substantially reduced by making the layers sufficiently thin. At the same time, a dramatic enlargement of the range of angles for oblique propagation of the new surface modes is observed. This can lead, however, to field non-locality and consequently to failure of the EM approximation.

Performance limits to the operation of nanoplasmonic chemical sensors: noise-equivalent refractive index and detectivity

We considered figures of merit for chemical and biological sensors based on plasmonic structures and utilizing adsorption/desorption mechanism. The operation of these devices in general is limited by noise determining the minimum detectable refractive-index change. We dedicated our work to the intrinsic noise mechanisms connected with the plasmonic process itself. In contrast, most of the available literature is almost exclusively dedicated to the external noise sources (illumination source and photodetector). Reviewing the refractive-index fluctuations caused by thermal, adsorption-desorption and 1/f noise, we observed a striking analogy between the qualitative behavior of noise in (nano)plasmonic devices and that in semiconductor infrared detectors. The power spectral densities for noise in both of these have an almost identical shape; the adsorption-desorption noise corresponds to generation-recombination processes in detectors, while the other two mechanisms exist in the both types of the devices. Thus the large and mature existing apparatus for infrared detector noise analysis may be applied to the plasmonic sensors. Based on the observed analogy, we formulated the noise-equivalent refractive-index and the specific detectivity as the figures of merit to analyze the ultimate performance of plasmon sensors. The approach is valid for conventional surface plasmon resonance sensors, but also for nanoplasmonic and metamaterial-based devices.

Lossy gradient index metamaterial with sinusoidal periodicity of refractive index : case of constant impedance throughout the structure

We used an exact analytical approach to investigate the electromagnetic wave propagation across an isotropic metamaterial composite with i. a sinusoidally periodic gradient of the real parts of the effective permittivity and permeability, ii. spatially uniform imaginary parts of the effective permittivity and permeability, and iii. spatially uniform impedance. The real part of the effective refractive index can be positive and negative along the direction of nonhomogeneity. A remarkably simple direct solution for the field distribution was obtained.

Some theoretical and technological aspects of uncooled HgCdTe detectors: a review

Abstract This work analyses a relatively new type of Hg 1−x Cd x Te detector which is used for the detection of CO 2 laser radiation (10·6 μm) and which operates at room temperature. In the first part of the work basic parameters of this detector type are given (spectral responsivity, detectivity, time constant) as well as their dependence on starting material parameters (absorption coefficient, carrier concentration, lifetime). The second part describes the production technology of epitaxial Hg 1−x Cd x Te layers using the method of isothermal vapour phase epitaxy, as well as the methods of making the detector. Finally, in the third part of the work, experimental results are presented.

Plasmon modes on laminated nanomembrane-based waveguides

We studied the propagation of plasmonic modes along planar multilayer metal- dielectric structures with finite number of bi-layer unit cells. The dispersion relations for various investigated waveguide structures with the multilayer core and symmetric or asymmetric cladding have been analyzed. In the case of symmetric metallic cladding we have found both TE and TM modes within the light cone, while TM modes only exist outside the light cone. Both symmetric and asymmetric dielectric claddings support modes outside the light cone and of TM-polarization only. Formation of photonic bands and gaps, the structure of their edge lines, and the behavior of modes that cross the edge lines has been investigated. In the subwavelength regime, we have found ordinary surface plasmon polariton dispersion in the forbidden gap that is created via coalescence of the two modes that cross the neighboring band-gap edges. One of those modes can exhibit negative group velocity.

Nanomembrane-based plasmonics

This paper reviews the main properties and applications of nanomembrane-based plasmonic structures, including some results presented here for the first time. Artificial nanomembranes are a novel building block in micro- and nanosystems technologies. They represent quasi-two-dimensional (2D) freestanding structures thinner than 100 nm and with giant aspect ratios that often exceed 1,000,000. They may be fabricated as various quasi-2D metal-dielectric nanocomposites with tailorable properties; they are fully symmetric in an electromagnetic sense and support long-range surface plasmon polaritons. This makes nanomembranes a convenient platform for different plasmonic structures such as subwavelength plasmonic crystals and metamaterials and applications such as plasmon waveguides and ultrasensitive bio/chemical sensors. Among other advantages of nanomembrane plasmonics is the feasibility to fabricate flexible, transferable plasmonic guides applicable to different substrates and dynamically tunable through stretching. There are various approaches to multifunctionalization of nanomembranes for plasmonics, including the use of transparent conductive oxide nanoparticles, but also the incorporation of switchable ion channels. Since the natural counterpart of the artificial nanomembranes are cell membranes, the multifunctionalization of synthetic nanomembranes ensures the introduction of bionic principles into plasmonics, at the same time extending the toolbox of the available nanostructures, materials and functions.

Silicon UV flame detector utilizing photonic crystals

In this paper we propose a silicon UV flame detector for combustion systems. In gas burners the relative intensity of flame radiation is dominant in the UV region. In the visible and IR regions the relative intensity of radiation of the incandescent surfaces is several orders of magnitude greater than the gas flame radiation intensity. Therefore it is required that the flame detector has a much greater sensitivity in the UV region. The propose detector is formed on n-type silicon on isolator wafer. In order to suppress sensitivity in the visible and the IR regions, the absorption region of the detector is greatly reduced, and a UV filter utilizing photonic crystal is designed. The p-n junctions are formed by very shallow diffusion of impurities. The contacts are made after the deposition of a thin oxide layer. The UV filter is then sputtered on the detector surface. The filter consists of a thin silver film, and a 1D photonic crystal made of twelve pairs of NaF/Y2O3 layers. The photonic band gaps of the crystal should suppress the propagation of the light with wavelengths greater than 0.35 micrometers . For the detector active area of 5 mm2, the thickness of the silver layer of 0.13 micrometers and a dark current of 1 nA, the noise equivalent power at 0.32 micrometers is 4.23 10-13 W/Hz1/2. The calculated flame signal to total signal ratio is 0.52.