We report systematic measurements of the lifetime of the 1.54 μm transition of erbium implanted at different energies in SiO2 films coated with titanium or chromium. The lifetime shows a strong reduction up to a factor of 20 with decreasing distance between the erbium and the metal coating. Our experiments combined with rigorous theoretical modeling demonstrate that a high degree of control over the radiative properties of erbium can be achieved in erbium-implanted materials.

Subwavelength cylindrical holes in optically thick metallic films always support a propagating HE11 mode near the surface plasmon frequency, regardless of how small the holes are. For holes filled with a uniform dielectric material, the bandwidth of the HE11 mode asymptotically approaches zero as the hole size is reduced to deep-subwavelength scales. We show that it is possible to create nano-scale propagating plasmonic modes with very large bandwidth in holes that are concentrically filled with two different dielectric materials, even when the hole radius goes to zero.

Room temperature near-infrared intersubband transitions were observed in MBE grown non-polar cubic GaN/AlN superlattice structures. The peak wavelengths of these transitions were observed in the spectral region of 1.5–2.0 μm and were theoretically supported using a transfer matrix approach. All samples were unintentionally doped and grown on 3C-SiC substrates with a 100 nm GaN buffer. Each structure consisted of a 20 periods of GaN/AlN superlattice capped with 100nm of GaN. The thickness of the AlN barrier was fixed at 1.35, while the thickness of the GaN well was varied between 1.6 and 2.1nm. Electrochemical Capacitance Voltage (ECV) measurements allowed direct measurement of the intrinsic carrier concentration in a thick unintentionally doped cubic GaN layer, which confirmed sufficient population of the ground state energy level.

Surface plasmon coupling technique was performed to enhanced green light emissions from InGaN/GaN quantum well. We found that photoluminescence intensities were increased by fabricated nano-grating structures on the gold layers and enhancement ratios depend on the grating periods. We also simulated the localized SP modes by 3D-finite difference time domain (FDTD) calculation. The experimental results were well correlated to the calculated results, and we found that the both exciton-SP coupling and light extraction process can be controlled by the nano-structures of the interfaces. This suggests that even more efficient emission should be obtainable by optimizing the nanostructure geometries.

The interband and intersubband transitions in self-assembled InAs and In0.3Ga0.7As quantum dots grown by molecular beam epitaxy have been investigated for their use in visible, near-, and mid-infrared detection applications. Devices based on InAs quantum dots embedded in an InxGa1−xAs (0 to 0.3) graded well and In0.3Ga0.7As quantum dots were fabricated in order to measure the temperature dependent (77 – 300 K) photoresponse. The dark current was measured in the temperature range of 77 to 300 K for the devices. Room temperature photoresponse ranging between 0.6 to 1.3 μm was observed for the InAs and In0.3Ga0.7As quantum dot photodetectors. Furthermore, a dual band photoresponse in the visible, near-, and mid-infrared spectral regions for both devices was observed at 77 K. Using a self-consistent solution of Schrödinger-Poisson equations, the peak position energies of the interband and intersubband transitions in the two multi-color quantum dot infrared photodetector structures was calculated.

We investigate the potential of a slit grating structure on a silver film embedded in a high index dielectric film, as a Plasmonic optical antenna in infrared region. Using FDTD calculations it is demonstrated that the transmission properties of the structure has strong dependence on the dimension of dielectric film. By tapering the height of output gratings directionality of the emitted beam has been improved. We propose the application of the Plasmonic antenna and examine its performance in axial injection of light from single mode fiber to photonic crystal waveguide.

Surface-enhanced Raman scattering (SERS) can enhance the intensity of Raman radiation by many orders of magnitude for molecules bound to metallic nanostructures. SERS is generally thought to have been a result of excitation of surface plasmons in nanostructured metal, which greatly enhances local electric field experienced by the molecule. Common SERS substrates fabricated using noble metal colloidal or electrochemically roughened thin films suffer from lack of homogeneity where only few hot spots yield high enhancement. We explore semiconducting nanowires and metallic nanorods as an economical, stable, and uniform SERS substrate for the detection of trace amount of chemicals and bio-species. We utilize bulk synthesized semiconducting nanowires as nano-scale structures that can be coated with noble metals or their colloidal forms to allow for excitation of surface plasmons over broad frequency range. The use of nanowires as SERS substrates has several advantages. The surface properties of these nanowires are highly reproducible and well defined as compared to other systems like colloidal aggregates, electrochemical roughening etc. The synthesized nanowires offer many unique features (sharp vertices, noncircular cross-sections, inter-wire coupling) that may lead to larger field enhancement factors. High density of nanowires means close interaction between adjacent nanowires, which enables SERS to manifest for a broad selection of excitation sources. We have synthesized germanium dioxide and zinc oxide nanowires using the vapor-liquid-solid growth mechanism utilizing a simple quartz tube furnace set up. The nanowires are grown either using thin gold film (5-15 nm) or colloidal gold (20 nm or 60 nm) as catalyst on substrates of silicon, quartz, and alumina. The resulting nanowires are dense (100-300 nm diameter, 10-40 μm long) and randomly distributed on the substrate. The nanowires are subsequently coated with thin films (10-15 nm) of gold that provide plasmons active surface. We have also investigated silver nanorods on glass formed by grazing angle deposition using e-beam evaporation. These nanorods have a diameter of ∼ 50-70 nm with lengths averaging 300-400 nm. These well aligned high aspect ratio and dense structures are ideal for excitation of surface plasmons. The synthesized structures have been characterized using SEM, TEM, and EDS. The SERS studies were conducted using EzRaman-L system from Enwave Optronics, Inc. Silver nanorods and gold-coated nanowires have been found to exhibit significant Raman enhancement for micro-molar concentrations of Rhodamine 6G and Nile blue, and are promising candidates for SERS applications.

Silicon nanocrystals (Si-nc) and amorphous silicon (a–Si) aggregates either produced by silicon implantation in fused silica have been studied by micro-Raman spectroscopy. Under certain experimental conditions, relevant information regarding both the dimension and the size distribution of Si-nc can be extracted from the energy shifts and the spectral distortion of the phonon excitation observed near 520 cm−1. Results are presented for different sample annealing times and ion fluences. These data agree with the direct observation by TEM of non-uniformly depth-distributed silicon nanocrystals. Moreover, measurements recorded for different Raman probing depths give evidence of chemical composition changes within the fused silica matrix. The depth evolution of the phonon peak associated with the Raman signature of a-Si near 470 cm−1 shows the presence of amorphous silicon, whose concentration is higher in the region where the large Si-nc are located.

Interaction of a highly focused beam of light with spherical nanoparticles is investigated for various incident field polarizations. First, an analytical solution is obtained to calculate the interaction of a highly focused beam of light with a spherical particle. To accurately express the incident electric field near the focus of an aplanatic lens, the technique established by Richards and Wolf is used. Using this analytical solution, electric field distributions of various spherical nanoparticles made of silver are investigated for highly focused linearly and radially polarized beams. The effect of the half angle of the focused beam is investigated. In addition a three-dimensional finite element method based solution is obtained and compared with the analytical solution for problems involving a highly focused beam of light interacting with a spherical particle.

Cones composed of noble metals with dimensions of the order of 100 nm, especially gold cones, are extremely well suited for optical near-field investigations using visible light. Their plasmon resonance frequency lies within the range of visible light frequencies, and upon illumination, strong electric field enhancement can be observed in the direct vicinity of the cone tip. For this purpose, a method to fabricate well-controlled nanocones with sharp tips is required. We present a top-down process in which arrays of cones are dry-etched from a metal stack on silicon. During the ion milling step, patterned hydrogen silsesquioxane resist is used as an etch mask. The resulting cones have tunable base diameters around 150 nm and tip radii down to less than 10 nm. Their optical characteristics are investigated by means of apertureless optical near-field microscopy, in which field enhancement at the cone tip is observed.