Coupled quantum dots (CQDs) can provide a sensitive probe of the electric field within a device. With non-resonant excitation above the wetting layer (WL) energy, optical generation of an electric field within the CQD structure was observed. By alternating this non-resonant excitation the temporal response of the optically generated electric field was measured. Decay of this field was measured to be on the order of 110-140 μsec whereas the onset of the optically generated electric field was observed to be less than the temporal resolution of our experiment (7.5 μsec). This may provide a means for fast, non-contact, electric field modulation techniques.

Here, we report on the enhancement of photon conversion by integration of photonic crystal (PhC) and surface plasmon (SP) structures into thermophotovoltaic (TPV) cells. PhCs consisting of rods of air are incorporated into the base of semiconductor TPV cells to increase the duration of thermal photon absorption, thus significantly enhancing quantum and conversion efficiencies (QE and CE, respectively). The potential of PhCs to augment the CE of TPV cells for most IR wavelengths makes it a widely useful technology. The ability to turn waste heat into usable energy will improve efficiency in a variety of electrical and electromechanical systems.

Solution phase triangular silver nanoplate (TSNP) ensembles are herein presented as tunable, highly sensitive, LSPR sensors with excellent potential for versatile amply responsive biosensing applications. The recorded LSPR refractive index sensitivities for the highest aspect ratio TSNPs examined are amongst the highest reported to date for various other nanostructures. Calculations demonstrate that sensitivities of the TSNP sols, as high as the theoretical upper limit, are achievable by tuning the aspect ratio parameter, without any significant diminution observed due to ensemble averaging. Theoretical studies identify the aspect ratio of the nanoplates as a key parameter in controlling the LSPR sensitivity of the TSNPs.

The size dependence of the photoluminescence spectra from silver nanoparticles embedded in a silica host medium was observed. The quantum yield of the photoluminescence increased when the size of the nanoparticles was decreased. The quantum yield for 8 nm silver nanoparticle was estimated to be on the order of 10-2 which is 108 times higher than the one observed for bulk silver. The two photoluminescence bands observed from silver nanoparticles were rationalized as the radiative electron interband transitions and radiative decay of the surface plasmons in silver nanoparticles. The strong local electric field induced by the surface plasmon resonance in silver nanoparticles enhances the exciting and emitted photons and increases the quantum yield of the photoluminescence.

We present the results of an electrical injection study of spin polarized electrons from ferromagnetic Fe contacts into electronic shells of self-assembled InAs quantum dots (QDs) incorporated in GaAs/AlGaAs spin LED structures. The circular polarization of the emitted light was measured as function of current and magnetic field. The polarization of the EL spectra exhibits strong maxima at energies that do not coincide with the electroluminescence (EL) intensity peaks. The magnetic field dependence of the polarization maxima is consistent with spin injection from the ferromagnetic Fe contacts. The experimental results are compared with calculated emission spectra from multi-exciton complexes (N = 2 and N = 6) as function of electron spin polarization. The energies of the EL features as well as their polarization characteristics are understood in terms of energy shifts due to exchange interactions between spin-down electrons occupying adjacent shells.

We compare the turn-on voltage, P-I, and EL responses between the MISLEDs made by Si-rich SiNx and SiOx films. Active layer thickness enlarged from 120 to 360 nm is achieved by lengthening deposition time from 10 to 30 min, which inevitably increases the forward turn-on voltage from 3 to 41 V. We observe that the forward turn-on voltage of SiNx based MISLED is only 10.43 V and that of SiOx based one is 69 V with the same film thickness of 100 nm. The tunneling-based carrier transport mechanism is dominated due to the exponential like V-I behavior, while the tunneling probability is strongly dependent on the height of the barriers between metal/dielectric and dielectric/nc-Si matrices. The P-I slope of SiNx and SiOx based MISLEDs are 1.6 and 115.2 mW/A, respectively. The SiNx MISLED reveals threshold current and voltage of only 4 A and 12 V due to lower barrier height of both ITO/SiNx and SiNx/nc-Si, whereas the threshold current and voltage of SiOx based MISLED are 400 A and 78 V, respectively. In comparison, the higher tunneling current through the SiNx MISLED fails to promote the larger external quantum efficiency of the MISLED, indicating that such lower barriers are not beneficial to the confinement of tunneling carriers and the enhancement of light-emission efficiency.

Our ability to fabricate close-packed single crystal rutile TiO2 nanowire arrays with average inter-wire distances of 5-10 nm allows us to create and control FRET-induced coupling effects, which can occur in this distance regime, in this architecture. We explored the use of such coupling to boost the performance of nanowire excitonic solar cells. Using Ru complex triplet dye N719 as the energy acceptor and fluorescent tetra tert-butyl substituted zinc phthalocyanine as the energy donor (see Fig. 1 for molecular structures), we obtained up to a four fold improvement in the quantum yield for red photons in the 660-690 nm spectral range. Similarly, by using a carboxylated unsymmetrical squaraine dye as the energy acceptor and highly fluorescent Nile Red dye as the donor (see Fig. 1 for molecular structures), we obtained 60% increased external quantum yields for photons in the 480-580 nm spectral range. For both systems, the use of FRET broadened spectral coverage and improved light harvesting. In this report, we also develop fundamental design principles in choosing donor-acceptor combinations for high efficiency FRET-enhanced solar cells in nanowire array architectures.

By using a multi-color, multi-modal imaging platform, we look into the effects of exciton-plasmon coupling on optical properties of a semiconductor quantum dot (QD) that is coupled to a nearby gold NPs (AuNPs). By exciting this coupled material with laser excitation energies that are either strongly or weakly resonating with the plasmon resonance of the AuNP, the effects of plasmon-exciton coupling was studied in detail by analyzing the changes in the photoluminescence signal, the photoluminescence lifetime, and the blinking pattern of the QD.

In this article, an alternative strain-free growth mode is presented where GaAs coupled-quantum dots are grown on lattice matched AlGaAs. The coupled quantum dots were grown at 550 °C in a molecular beam epitaxy system. The GaAs quantum dots were characterized by using a photoluminescence technique and an atomic force microscope. The photodetector was fabricated into normal incident configuration and photoconductivity spectra were measured covering the mid-infrared spectrum of 2.0 – 8.0 micron (intersubband transitions) and the visible-near-infrared spectrum of 0.5 – 0.9 micron (interband or exciton transitions). The photoresponse spectra in mid-infrared spectral range were found to exist at temperatures lower than 80 K, while the photoresponse spectra in the visible-near-infrared range were observed at temperatures as high as 300 K.

One-dimensional grating with 400 nm pitch was fabricated on a SiO2 glass surface. The grating was applied for detection of fluorescence excited by the electric field of the grating-coupled surface plasmon resonance and highly sensitive observation of fluorescence image by optical microscope. 40-times of fluorescence enhancement was obtained under optimal condition after our systematically investigating depth and duty ratio dependent behavior.

We have proposed and fabricated a hybrid nanodots floating gate (FG), in which Si quantum dots (QDs) as charge injection/emission nodes and NiSi nanodots as charge storage nodes are stacked with an ultrathin SiO2 interlayer, to satisfy both large memory window and multivalued capability. In this study, Si-QDs with an areal density of ˜3×1011cm-2 were formed on ultrathin SiO2 layer by controlling SiH4 chemical vapor deposition (CVD) and NiSi nanodots were prepared by full-silicidation of Si-QDs promoted with remote H2-plasma exposure after Ni evaporation. From capacitance-voltage(C-V) characteristics of MOS capacitors with a NiSi nanodots/Si-QDs hybrid FG, stable storage of many charges in the deep potential well of each NiSi nanodot was confirmed. Also, by applying pulsed gate biases, stepwise charge injection to and emission from NiSi nanodots through discrete energy states in Si-QDs were demonstrated. In addition, by 1310nm (˜0.95eV) light irradiation, a distinct optical response in C-V characteristics was detected, which can be interpreted in terms of the shift of charge centroid in the hybrid FG stack due to transfer of photoexcited electrons from NiSi-nanodots to the Si-QDs.

We studied photoluminescent properties and luminescent decay dynamics in Si quantum dots (QDs) produced by Si implantation in SiO2, and their modification by the application of an implantation mask. Silicon quantum dots were prepared by ion implantation, followed by high temperature annealing leading to nanocrystal nucleation and growth. The mask was prepared by spin-coating silica microspheres to achieve laterally-selective implantation, to control QD size and separation. Transmission electron microscopy (TEM) images were obtained to verify the diameter of the quantum dots. We observe a noticeable peak shift and narrowing in the photoluminescence spectra with the application of the implantation mask. Observed maxima in the photoluminescence spectra are compared with a quantum field theoretical model using an infinite confining 1D potential for Si quantum dots. We comment on the role of excitation transfer by observing a change in the dispersion exponent of the luminescent decay dynamics due to the mask.