We demonstrate an effective method for depositing smooth silver (Ag) films on SiO(2)/Si(100) substrates using a thin seed layer of evaporated germanium (Ge). The deposited Ag films exhibit smaller root-mean-square surface roughness, narrower peak-to-valley surface topological height distribution, smaller grain-size distribution, and smaller sheet resistance in comparison to those of Ag films directly deposited on SiO(2)/Si(100) substrates. Optically thin ( approximately 10-20 nm) Ag films deposited with approximately 1-2 nm Ge nucleation layers show more than an order of magnitude improvement in the surface roughness. The presence of the thin layer of Ge changes the growth kinetics (nucleation and evolution) of the electron-beam-evaporated Ag, leading to Ag films with smooth surface morphology and high electrical conductivity. The demonstrated Ag thin films are very promising for large-scale applications as molecular anchors, optical metamaterials, plasmonic devices, and several areas of nanophotonics.

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We investigate thin film sensing capabilities of a terahertz (THz) metamaterial, which comprises of an array of single split gap ring resonators (SRRs). The top surface of the proposed metamaterial is covered with a thin layer of analyte in order to examine various sensing parameters. The sensitivity and corresponding figure of merit (FoM) of the odd and even resonant modes are analyzed with respect to different thicknesses of the coated analyte film. The sensing parameters of different resonance modes are elaborated and explained with appropriate physical explanations. We have also employed a semi-analytical transmission line model in order to validate our numerically simulated observations. Such study should be very useful for the development of metamaterials based sensing devices, bio-sensors etc in near future.

Shape dependent optical absorbance of Ag and Au loaded titania nanotubes.

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-Plasmon induced transparency (PIT) effect in a terahertz graphene metamaterial is numerically and theoretically analyzed. The proposed metamaterial comprises of a pair of graphene split ring resonators placed alternately on both sides of a graphene strip of nanometer scale. The PIT effect in the graphene metamaterial is studied for different vertical and horizontal configurations. Our results reveal that there is no PIT effect in the graphene metamaterial when the centers of both the split ring resonators and the graphene strip are collinear to each other. This is a noteworthy feature, as the PIT effect does not vanish for similar configuration in a metal-based metamaterial structure. We have further shown that the PIT effect can be tuned by varying the Fermi energy of graphene layer. A theoretical model using the three level plasmonic system is established in order to validate the numerical results. Our studies could be significant in designing graphene based frequency agile ultra-thin devices for terahertz applications.Introduction. -Electromagnetically induced transparency (EIT) is an interference effect that occurs in a three level atomic system. In EIT, an atom that absorbs a particular light signal is rendered transparent by shining another light signal having nearly the same resonance frequency [1]. In 2008, a novel study done by Zhang and his co-workers revealed that an EIT like phenomenon can occur in plasmonic metamaterials (MMs) [2]. The plasmonic analogue of this EIT effect is known as the Plasmon Induced Transparency (PIT) effect in MMs [2][3][4][5]. PIT usually occurs as a result of interference between the bright and dark plasmonic modes. The bright mode strongly couples with the incident light while the dark mode couples weakly with the incident light [6]. For the PIT effect to occur, both the bright and the dark modes should have similar resonant frequencies [2,7]. Then, the destructive interference of these modes induces a narrow transparency region in the otherwise absorptive spectrum. Since the detection of the PIT effect, a lot of theoretical as well as experimental studies have been done revealing its potential in various applications such as ultrafast sensing [8][9][10],

β-Ga 2 O 3 thin films were grown on n-type GaN substrates using the sol-gel method. The forward-biased temperature dependent current-voltage (I-V-T) characteristics of Ni/β-Ga 2 O 3 /GaN structure have been investigated in the temperature range of 298-473 K. The apparent barrier height (ap) increased while the ideality factor (n) decreased with the increase in temperature. Such a temperature dependent behavior of ap and n was explained by the inhomogeneity of ap , which obeyed Gaussian distribution with zero-bias mean barrier height (̄B 0) of 1.02 ± 0.02 eV and standard deviation (s0) of 153 ± 0.04 mV. Subsequently, ̄B 0 and Richardson constant A * were obtained from the slope and intercept of the modified Richardson plot as 0.99 ± 0.01 e V and 67.2 A cm −2 K −2 , respectively. The ̄B 0 obtained from the modified Richardson plot was in good agreement with the theoretical value calculated from the work function of Ni and electron affinity of β-Ga 2 O 3. The I-V-T characteristics of Ni/β-Ga 2 O 3 /GaN MOS structures can be successfully explained by the thermionic emission theory with a single Gaussian distribution of the barrier height.

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