Nanocrystals of degenerate semiconductors come in a variety of shapes, which have profound influence on the
localized surface plasmons which are supported. Ensembles of such nanocrystals are never perfect and will
always show a distribution of shapes. By embedding the Drude model into Mie scattering theory, the effect of
the shape inhomogeneity on the absorbance spectrum of a nanocrystal ensemble can be approximated for a few
common cases such as nanorods and nanodiscs as well as general ellipsoids. Using various distributions of aspect
ratios, broadening and shifting of the various plasmonic absorption peaks is observed for nanorod and nanodisc
ensembles. Similar behavior is also observed for ensembles of nearly spherical nanocrystals, which emphasizes
the importance of accounting for nanocrystal shape inhomogeneity when investigating broadening mechanisms
of nanocrystal plasmonic absorbance.
Amorphous and nanocrystalline Eu3+-doped ZnO thin films were synthesized by the sol–gel process. The films were spin-coated on glass substrates. The samples were annealed at 500°C for 1 hour to produce a nanocrystalline ZnO/Eu3+ films. The samples were characterized using UV-Vis absorption and infrared spectroscopy. A crystalline phase, wurtzite, was detected by X-ray diffraction. A spectroscopic study of the Eu3+ impurity in function of the heat treatment provided to the ZnO matrix was done. Results of emission and excitation studies at room temperature of Eu3+ inserted in the ZnO matrix are presented. For amorphous and nanocrystalline samples, the relative ratio of the 7F2/7F1 transitions was calculated. The evolution of this ratio was interpreted in terms of the Eu3+ symmetry site change when the nanocrystalline ZnO films. This fact was confirmed measuring the Eu3+ lifetimes.
Here we present an antenna-integrated QCL which can be actively and optically modulated using light in the near infrared, creating an optical nanocircuit – coupling two different frequency antennas with a nonlinear active switching element. For our design, we chose two cross-polarized bow-tie antennas with an aligned central spot. We have used detailed FDTD simulations to choose the length of each bow-tie. The larger bow-tie antenna is resonant with the QCL at 6.1 μm wavelength and is aligned perpendicular to the active region of the device because QCL emits TM polarized light. The smaller bow-tie is resonant with the incoming modulating light at 1550 nm and is aligned perpendicularly to the first bow-tie. There is a rectangular region of amorphous germanium below the smaller bow-tie which acts as an absorber at 1550 nm. When light at 1550 nm is incident upon the device, it is focused and enhanced by the smaller bowtie, creating a region of large absorption in the germanium rectangle below. Free carriers are generated, shorting the larger bow-tie which is already focusing and enhancing light from the QCL mode. When the bow-tie arms of the larger bow-tie are shorted by these free carriers, the focusing and enhancement of the light by the larger bow-tie of the QCL mode is severely diminished, affecting the entire laser output, even the far field. Simulation results, fabrication details, and finally experimental results are discussed. Such an all-optical switch could be useful for telecommunications, free space communications, or rangefinding applications.
Sensor technologies that can operate under extreme conditions including high temperatures, high pressures, highly
reducing and oxidizing environments, and corrosive gases are needed for process monitoring and control in
advanced fossil energy applications. Au nanoparticle incorporated metal oxide thin films have recently been
demonstrated to show a useful optical response to changing ambient gases at high temperatures as a result of
modifications to the localized surface plasmon resonance (LSPR) of the Au nanoparticles. Au nanoparticle
incorporated TiO2 films were prepared through sputter deposition techniques followed by high temperature oxidation treatments. Upon exposure to a 4% H2/N2 gas atmosphere at elevated temperatures, a shift of the absorption resonance associated with Au nanoparticles to shorter wavelengths is observed, as demonstrated in the literature previously. In this work, we also demonstrate that there is a shift of similar magnitude in the scattering resonance associated with Au. The LSPR absorption peak was monitored as a function of temperature up to 850oC demonstrating a broadening and a decrease in the maximum peak absorptance. Calculations performed in the quasistatic approximation are also presented to explain observed changes in LSPR as a function of temperature and to illustrate the effects on sensitivity of Au – based LSPR sensor materials for extreme temperature applications.
Perpendicular dual-grating (PDG) guided-mode resonance filters were constructed by placing two identical one-dimensional waveguide gratings close to and their grooves perpendicular to each other with a nano air gap between them. Multilayer waveguide theory was used to estimate the split of the resonant reflection peaks corresponding to the
TE and TM modes, and the rigorous coupled wave analysis (RCWA) was used to investigate the resonant wavelength, the linewidth of the resonant peaks, and electric field intensity distribution in the filter structures. The filters present identical spectral characteristics for normally incident wave with arbitrary polarization. The TM01 and the TM01 modes
are found displaying the greatest wavelength shift for the air gap variation between 0 and 100 nm, and 100 nm and 1000
nm，respectively. The coupling between the TE and TM modes is much greater in the g/w/a/w/g structure than that in the
w/g/a/g/w structure, since there is no space between the two waveguide layers in the former. The resonant peaks of the TM01 mode for the one-dimensional PDG g/w/a/w/g structure exhibit narrower width compared with those for the two-dimensional g/w/a/w/g structure. In addtion, the horizontal shift between the two gratings does not influence the
measured spectra, although it will certainly have great effect on the resonant peak width if the measurement were carried
out by the guided-mode filters where the two gratings are two dimensional.
Controlling the far field pattern of the electromagnetic (EM) waves has many applications including wireless
communications, radar detection, and industrial applications. The dynamic control of EM patterns is called beam
steering. Despite advantages in each technique, the speed, angular range, and spectral range of beam steering is limited
due to mechanical and optical properties of such systems. Here we present a beam steering method by means of an array
of optomechanical nanoantennas in which the generated optical force of each antenna results in changes to the antenna
response due to mechanical reconfiguration. As a result, the antenna far field phase is changed due to the mechanical
movement generated by the optical force. Depending on the mechanical properties of the movable component of the
antenna, the phase of the antenna can be tailored for a given optical source power. FDTD simulations are used to
calculate the optical response of antenna. A phase array of optomechanical nanoantennas is used to do beam steering.
The main far field lobe is steered by 0.5 degrees as a result of the mechanical reconfiguration of the phased array.
This work reports the synthesis of amorphous TiO2 matrix by sol-gel method at atmospheric
conditions. DA was encapsulated in a TiO2 matrix to reduce its chemical instability. To TiO2/DA sample
was added the 15C5 to diminish the oxidation process. The stabilization process was followed by
absorption spectra, colour change and infrared spectroscopy. Oxidation processes of the DA were
identified by the presence of DA-quinone and DA-chrome. The TiO2/DA complex retarded the oxidation
process for 30 days, while the TiO2/DA/15C5 complex this period was extended for 47 days.
Photoconductivity studies were performed on both kinds of samples to analyze their charge transports.
The experimental data were fitted with straight lines at darkness and under illumination at 320 nm, 400
nm, and 515 nm. This indicates an ohmic behavior. Transport parameters were calculated. The conductive
effect is stronger under darkness than under illumination at 320 nm because the oxidation process in the
darkness is less intense than under illumination.
A novel organic-inorganic hybrid material is presented containing a quenching moiety for improving the resolution of
Direct femtosecond Laser Writing by multi-photon polymerization. By exploiting the diffusion of the quencher molecule
for confining radical diffusion in the scanned area, sub-100nm resolution is achieved. 3D woodpile structures with rod
spacing of 400nm are successfully fabricated. We optically characterize these woodpiles structures and we show that
they exhibit well-ordered diffraction patterns and stopgaps down to near-infrared wavelengths.
Large area photonic crystal has been fabricated with monodisperse silica spheres
modified the surface with 3-(trimethoxysilyl) propylmethacrylate (TMSPM). The surface of
the spheres has been modified by hydrolysis and condensation reaction of TMSPM with base
catalyst and acid catalyst. The Fourier transform infrared (FTIR) spectra, field emission
scanning electron microscope (FESEM) images no evidence that the TMSPM is corporate on
the surface of the silica spheres for the base catalyst process. However, FTIR spectra and
FESEM images clearly presents the existence of hydrolyzed TMSPM on the surface of silica
spheres for the acid catalyst process. The FTIR absorption peak at 1714 cm-1 representing
C=O stretching vibration indicates that the hydrolyzed TMSPM is corporate on the surface of
the silica spheres. Although generally the colloidal photonic crystal has large number of
cracks, surface modification and photocross-linking process during the packing process can
be avoided the crack process of the photonic crystal.
The dichalcogenide MoS2, which is an indirect-gap semiconductor in its bulk form, was recently shown to become
an efficient emitter of photoluminescence as it is thinned to a single layer, indicating a transition to a direct-gap
semiconductor due to confinement effects. With its layered structure of weakly coupled, covalently bonded
two-dimensional sheets, it can be prepared, just as graphene, using mechanical exfoliation techniques. Here, we
present temperature-dependent and time-resolved photoluminescence (PL) studies of single-layer MoS2 flakes.
Some of the flakes are covered with oxide layers prepared by atomic layer deposition (ALD). At low temperatures,
we clearly see two PL peaks in the as-prepared flakes without oxide layers, which we may assign to bound and
free exciton transitions. The lower-energy, bound exciton PL peak is absent in the oxide-covered flakes. In
time-resolved PL measurements, we observe very fast photocarrier recombination on the few-ps timescale at low
temperatures, with increasing photocarrier lifetimes at higher temperatures due to exciton-phonon scattering.
Vertically oriented ZnO nanowires (NWs) are grown upon silicon substrates using a novel, modified vapor-solid
method. Electron-beam evaporation is then used to functionalize the sides of the ZnO NWs with MgO:Ag via glancing
angle deposition (GLAD). By varying the thickness of the deposited MgO insulating layer, it is possible to study the
underlying energetic mechanisms responsible for the quenching and enhancement of ZnO photoluminescence centers.
For the visible emission, strong quenching was observed to occur independently of the MgO thickness. In contrast, the
band-edge emission displayed an enhancement factor of 19 as the thickness of the MgO spacer was increased.
We report mechanical frequency and amplitude modulation of a quantum cascade laser (QCL) integrated with a
plasmonic antenna operating at ~6.1 μm. We have observed a shift in the lasing frequency by over 30 GHz and an
intensity modulation of ~74% when an atomic force microscope (AFM) tip approaches the hot spot of a metal-dielectricmetal
(MDM) bow-tie antenna integrated onto the facet of the laser. The tip diameter is ~λ/60 and in non-contact mode
its amplitude of motion is ~λ/120. We have presented a theoretical model based on the rate equations for a QCL which
affirms our experimental observations. Our experiment demonstrates the strong influence of the hot spot on the laser
cavity modes, despite the fact that the former is many orders of magnitude smaller than the latter. We have compared
our device to a previous mechanically frequency modulated QCL and calculated a figure of merit, change in frequency
divided by change in distance of the mechanical component (Δf/Δd), which is an order of magnitude higher, while our
design uses a volumetric change per λ3 that is five orders of magnitude smaller. Our device differs from optical gradient
force actuated devices in that our device is externally mechanically actuated while those devices are self actuated
through the optical force. This sensitivity of the laser cavity mode to the position of a nanometer-scale metallic absorber
opens up the opportunity for modulating large amount of optical power by changing the optical properties of a miniscule
volume in an integrated, chip-scale device.
Polydimethylsiloxane (PDMS) contains a large, flexible free space between weakly-bonded molecules, which allows
notable molecular diffusion. A toluene solution of diarylethene (photochromic dye) was mixed with a PDMS oil, and
then the mixture was cured in a glass vessel by adding a curing agent. Violet laser (405 nm wavelength) irradiation
induced an absorption band at around 530 nm, and consequently, the irradiated portion exhibited a red color. The colored
portion gradually expanded to the entire sample because of diffusion of the dye molecules. This diffusion characteristic
was used for improving an organic dye durability against a photo-induced degradation.
Amorphous and crystalline TiO2 and TiO2:Eu3+ thin films were synthesized by the sol–gel process at room temperature. The films were spin-coated on glass substrates. The samples were calcined at 400°C, 500°C for 2h to produce crystalline films. The films were characterized using X-ray diffraction, infrared spectroscopy, scanning
electron microscopy and transmission electronic microscopy and UV-Vis absorption spectroscopy. An anatase phase
was determined in the samples calcined at 500°C. Film thickness was calculated by SEM. Absorption peaks were
located between 293-298 nm which are due to the titania host. It can be observed that this peak position depends of
the calcination temperature. Band gap was calculated, and it indicates a non-linear behavior of the samples.
Photoconductivity studies were performed on amorphous and crystalline films. The experimental data were fitted with
curve lines to order square at darkness and under illumination (310 nm and 515 nm). This indicates a non-ohmic
behavior. Transport parameters, photovoltaic and photoconductive; were calculated for both samples.
Novel organic-inorganic hybrid materials were successfully synthesized by non-hydrolytic sol-gel processing. Crack-free
and thick films were produced with no remaining traces of solvents without high volume shrinkage. Adjusting the
chemical composition of the materials allows the precise tailoring of the optical properties of the materials, such as
optical loss, birefringence, refractive index, and thermo-optic coefficient. They can be fabricated into the step index
optical waveguide structures with well-defined and reproducible refractive index differences within 0.001. The
transmission performance of each waveguide channel was tested using a 10 Gbps data stream. The electrical output
signal from a photodetector, connected to a wide-band oscilloscope, displays a clear 10 Gbps eye pattern. We produced a
series of flexible optical waveguides from organic-inorganic hybrid materials by using soft-lithographic technique. The
optical losses of the flexible waveguide arrays bent over various curvatures were measured and the transmission
performance of each waveguide channel was also tested. The bending losses of a flexible waveguide array were
measured and found to yield no significant loss above 2 mm diameter curvature.
Utilizing thin photoresist imaging layers for successful pattern transfer has gained acceptance as a lithography process
of record, primarily due to the incorporation of silicon-containing hardmask (HM) layers for added etching resistance.
Our work includes understanding the impact of incorporating metal oxide (HfO2, ZrO2, ZnO, and TiZrO2) nanocrystal
additives supplied by Pixelligent Technologies into polymer-based spin-on HM coatings. The goal was to quantify
etch selectivity and analyze lithography process latitudes with the addition of nanocrystals into polymers. Results
indicate such additions provide substantial process window advantages with improvements in the depth of focus
(DOF) and overall pattern collapse margins.