Structural, optical and electrical studies of several hybrids of organic and inorganic nanostructures as well as core shell
nanocrystalline structures will be presented. The effects of thermal annealing on the morphological and photoconductive
properties of cadmium selenide quantum dots coreshell quantum dots together with indicate that there are collective
events happening due to annealing. Two different types of hybrid structures will be discussed. Optical and electrical
experimental results in semiconductor nanostructures in conductive polymers as well as those that were integrated into
the organic photosystem I (PS1), as part of an artificial light harvesting complex (LHC) will be presented.
Novel optoelectronic systems based on ensembles of semiconductor are described. We will present here the optical and electronic properties of organic-inorganic hybrid structures that enable integration of useful organic and inorganic characteristics for novel sensing applications. Several semiconductor nanostructures with both direct band gap and indirect band gap will be discussed in a few different polymer and biological matrices. A number of these colloidal
semiconductor quantum dots and related quantum-wire structures have been characterized using absorption, photoluminescence, and Raman measurements; these Raman measurements include those made on self-assembled monolayers of DNA molecules terminated on one end with a common substrate and on the other end with TiO2 quantum
dots. The electronic properties of these structures are modeled and compared with experiment. Devices fabricated with these materials as well as their potential for sensing will be discussed.
Nanoscale functionalization of semiconductor quantum dots (SQDs) with biomedical structures is promising for many
applications and novel studies of intrinsic properties of both constituent systems. Results of our study of structural
properties of the nanoscale functionalized SQDs such as CdS, and ZnS-capped CdSe SQDs, conjugated with
biomolecules such as short peptides and cells are presented. We study CdS SQDs functionalized with peptides specially
composed of the following amino acid chains: CGGGRGDS, CGGGRVDS, CGGIKVAV, and CGGGLDV, where R is
arginine, D - aspartic acid, S - serine, V - valine, K - lysine and L is Levine. As will be seen the cysteine (C) amino acid
links to CdS SQDs via the thiol link, the GGG sequences of glycine (G) amino acid, provide a spacer in the amino acid
chain. At the same time the RGDS, RVDS, IKAV, and LDV sequences have selective bonding affinities to specialized
transmembrane cellular structures known as integrins of neurons and MDA-MB-435 cancer cells, respectively. We found
that the quantum confinement and functionalizing in biomedical environments plays in altering and determining the
electronic, optical, and vibrational properties of these nanostructures as well as demonstrated the effectiveness to use
semiconductor quantum dots as integrin sensitive biotags.
Spontaneous polarizations of GaN nanostructures and quantum dots are calculated for different surface terminations. In
addition, dimensionally-confined phonons in GaN-based nanostructures are discussed. GaN-based nanostructures have
applications in a variety of systems and concepts including: non-charge-transfer-based devices and single-photon
detectors based on GaN-based double-barrier quantum-well injectors, conductive-polymer collectors, and colloidal
quantum dot recombination regions. In this paper, application of photodetectors is considered along with the related
application of using colloidal quantum-dot-based ensembles for solar cell applications.
Novel optoelectronic systems based on ensembles of semiconductor nanocrystals are addressed in this paper. Colloidal
semiconductor quantum dots and related quantum-wire structures have been characterized optically; these optical
measurements include those made on self-assembled monolayers of DNA molecules terminated on one end with a
common substrate and on the other end with TiO2 quantum dots. The electronic properties of these structures are
modeled and compared with experiment. The characterization and application of ensembles of colloidal quantum dots
with molecular interconnects are considered. The chemically-directed assembly of ensembles of colloidal quantum dots
with biomolecular interconnects is demonstrated with quantum dot densities in excess of 10+17 cm-3. A number of novel
photodetectors have been designed based on the combined use of double-barrier quantum-well injectors, colloidal
quantum dots, and conductive polymers. Optoelectronic devices including photodetectors and solar cells based on threedimensional
ensembles of quantum dots are considered along with underlying phenomena such as miniband formation
and the robustness of minibands to displacements of quantum dots in the ensemble.
This paper focuses on understanding the THz-phonon mediated transport of polarons in biomolecules, with particular attention on polaron transport in DNA. In order to exploit biology-based approaches to realizing new electronic systems, it is necessary to understand the electrical transport properties and THz-phonon interactions of biomolecules that portend applications both as electrically conductive wires and as structures that facilitate the chemically-directed assembly of massively integrated ensembles of nanoscale semiconducting elements into terascale integrated networks. Special attention is given to charge transport in biomolecules using indirect-bandgap colloidal nanocrystals linked with biomolecules.
A variety of colloidal semiconductor quantum dots and related quantum-wire structures are characterized using absorption and photoluminescence measurements. The electronic properties of these structures are modeled and compared with experiment. The characterization and application of ensembles of colloidal quantum dots with molecular interconnects are considered. The chemically-directed assembly of ensembles of colloidal quantum dots with biomolecular interconnects is demonstrated with quantum dot densities in excess of 10+17 cm-3. Non-charge transfer processes for switching based on dipole-dipole interactions - Forester interactions - are examined for colloidal quantum dots linked with biomolecules. Charge transport in biomolecules is studied using indirect-bandgap colloidal nanocrystals linked with biomolecules.
Self-assembled GaN quantum dots are characterized using Raman techniques. The electrical and optical properties of these GaN quantum dots are modeled in light of optoelectronic applications. Strain-induced changes in the phononic properties of these nanostructures are modeled and the strain-induced frequency shifts are compared with Raman measurements. Acoustic phonons in colloidal GaN quantum dots are modeled using a quantized elastic continuum model. Shifts observed in the Raman signatures for different excitation wavelengths provide evidence the Raman signatures of GaN quantum dots are observed.
Fundamental properties of phonons in III-V nitrides are examined with a view toward understanding processes important in the operation of III-V nitride devices. Firstly, confined, interface and propagating modes in wurtzite quantum wells are described in terms of Loudon's model for uniaxial semiconductors and the dielectric continuum model. Basic properties of the phonon modes and carrier-phonon interactions are considered in the basis of this treatment of dimensionally-confined phonons in wurtzite structures. A key feature of these phonon modes is their enhanced dispersion and its origin from the non-isotropic nature of the wurtzites. As will be discussed, this dispersion has important consequences for phonon propagation and phonon energy spectra. Secondly, the second-order phonon decay process of combined point defect scattering and anharmonic decay is examined as a means of estimating line broadening associated with the decay of phonons in III-V nitrides of wurtzite structure containing point defects. Thirdly, an analysis of Raman linewidths measured for AlN and GaN wurtzites is made to estimate phonon lifetimes.
An inexpensive and reliable process for the area-selective disordering of MQW structures is reported. The method relies on the diffusion, by rapid thermal annealing, of surface vacancies into the quantum wells thereby intermixing the Ga and Al atoms between the wells and barriers. A silicon oxide cap that is formed by curing a spun-on solution of glass forming compound acts as porous layer that enhances the formation of surface vacancies by allowing out-diffusion of Ga and Al atoms. This technique has been applied to the fabrication of two integrated optical devices. One is the nonlinear zero-gap directional coupler with disordered input and output branching waveguides, and the other is the symmetric nonlinear integrated Mach-Zehnder interferometer with one arm containing a non-intermixed MQW section. In both devices, the mechanism for the switching is the nonlinear refractive index that is caused by photo-generated carriers. Since this mechanism entails absorption of some of the pump beam, it is hence very important that the optical absorption be confined to the active sections only. Selective area disordering is shown to be very effective at defining regions of different bandgap energies. Hence it can be ensured that the energy of the pump laser beam is too low in comparison to the bandgap energy of the passive regions to be absorbed and the free carriers are only created in the non-intermixed active sections. The devices investigated using a pump-probe setup, exhibited strong all-optical switching behavior with a contrast ratio of better than 7:1. The controlled selective area intermixing of MQW structures will potentially play a significant role in the advancement of photonic integrated circuits.
Lateral carrier transport has been used to enhance the recovery time of bandgap resonant nonlinear transmission changes in multiple quantum well waveguide structures. Recovery times on the order of 90 ps have been measured in our samples. Such technique is applicable to all-optical and optoelectronic integrated optic switches.
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