The synthesis of self-assembled ZnO nanostructures at room temperature using a microphase separated diblock copolymer as a template is reported. Poly(norbornene) / poly(norbornene-dicarboxylic acid) diblock copolymers were synthesized using Ring Opening Metathesis Polymerization (ROMP). The polymers were dissolved and the solutions were doped with ZnCl2. Films were formed from this solution, and subsequently reacted with NH4OH. This converted the ZnCl2 into ZnO contained within the microphase-separated nanodomains of the block copolymer. Fourier Transform Infrared Spectroscopy verified the association of the metal to the second block of the polymer, and X-ray Photoelectron Spectroscopy verified the conversion of the salt to ZnO nanoclusters. The development of such ZnO - block copolymer nanocomposites is targeting the functionalization of nanostructures into device technologies.

Bio-assembly strategies may allow formation of high-density nano-electronic architectures possessing unique electronic properties. These bio-nanomaterial hybrids should exhibit bio- compatibility and bio-viability. Therefore, contingencies of maintaining tertiary structure in the presence of nanometer-sized particles are a potential fatal flaw in bio-scaffolded assemblies. In this manuscript we investigate the assembly of bio-scaffolded nanomaterial constructs, specifically polypeptides, while probing the issue of bio-compatibility and viability by TEM imaging.

The experimental and theoretical results of the electronic structure of self-assembled InAs/GaAs quantum dots are presented. We have performed analytical calculations to obtain the spatial strain distribution in truncated pyramidally-shaped InAs quantum dots grown on (001) GaAs substrates by molecular beam epitaxy. The model reproduces our cross sectional high- resolution transmission electron microscopy observations very well. We further take into account the microscopic effects of the spatial strain distribution on carrier confinement potentials. The effects of piezoelectricity have been neglected in our calculations since they minimally affect the energy levels involved in optical transition. The dots considered here are assumed to be in the strong confinement regime; so Coulomb interaction is neglected. Our calculations of the peak luminescence energies are in good agreement with our experimental results and those of others. The calculated energy separation between the ground and the excited states for electrons and for heavy-holes is in very good agreement with the available photoluminescence, capacitance and far- infrared absorption data.

It is found that the performance of self-assembled In0.5Ga0.5As/GaAs multi-stack quantum dot lasers is sensitive to the GaAs spacer thickness between the dots. Reducing the spacer thickness from 30 nm to 10 nm leads to narrow photoluminescence linewidth, low threshold current, high characteristic temperature and high internal quantum efficiency. This behavior is attributed to inhomogeneous broadening caused by dot size fluctuation related to spacer thickness.

We present quasi-steady-state photoinduced absorption measurements on thin films of colloidal CdSe nanocrystals. We observe an intense, size-dependent absorption peaking in the mid-infrared when the samples are irradiated with visible light. The absorption is accompanied by a bleach in the visible near the position of the first excitonic absorption and persists with a lifetime of milliseconds at room temperature. We characterize the lifetime of the electron state and its cross-section. We attribute this feature to the 1S-1P transition of a delocalized electron. We report a bleaching of the first excitonic transition in electrically excited nanocrystal-based diode structures, and attribute it to charging of the 1S electron state.

Colloidal semiconductor quantum dots (QDs) are luminescent nanoparticles with size- dependent emission spectra spanning a wide range of wavelengths in the visible and near IR. This property, as well as their higher resistance to photo-degradation compared to organic dye labels, makes QDs potentially suitable for certain biomolecule tagging and multiplexing applications. We describe an electrostatic self-assembly approach for conjugating highly luminescent colloidal CdSe-ZnS core-shell QDs with engineered two-domain recombinant proteins to form conjugates for sensing and imaging applications. The design, preparation, and characterization of high quantum yield IgG antibody-binding protein G bioconjugates using luminescence, electrophoretic gel shift, and affinity assays is reported.

We study the properties of the charge distribution (polarization) of a 4-quantum dot square cell with two electrons, induced or modified by the coupling to a single quantized mode field. The effect of the relevant parameters (tunneling between dots, the amplitude of the electron-cavity interaction, cavity frequency) is investigated in the properties of polarization of the two-electron fundamental states. We further investigate the effects of asymmetry in the electron-cavity interaction in each dot and evaluate the modification to the dynamic evolution of the polarization. We find that there is a range of values of the asymmetry for which the polarization is improved. This suggests that an optimization of the coupling of the quantum dot cell with its environment may yield more reliable and stable operation.

We observed the surface topography of CdSe colloidal nano-dot film by cyclic contact mode atomic force microscopy. The observed structure changes with cantilever oscillation amplitude, and non-uniform images with long-range corrugations are obtained with relatively large oscillation amplitude while fine structures are revealed with smaller oscillation amplitude. When the amplitude is larger and the surface is weakly ‘tapped’, the topography of the soft organic matrix of the film dominates, and when the tapping force is increased, the hard CdSe dots begin to reveal.

We have evaluated the photoluminescence (PL) properties of quantum dots (QDs) embedded in a p-n junction on GaAs(311)B and were compared with the identical structure grown on GaAs(001). The QDs on these two surfaces were fabricated with a similar size and density by optimizing the growth conditions. The PL emission from the QDs grown on GaAs(001) rapidly disappeared when the excitation power was decreased below 0.4W/cm2, while that from on GaAs(311)B was clearly observable even at a lower excitation power of 0.1W/cm2. From the measurements of PL intensity dependence on temperature and applied electric field, it was found that there are clear differences between the QDs grown on (001) and the QDs grown on (311)B in the recombination rates through non-radiative processes and/or the escape rates of carriers out of QDs to the GaAs host through a tunneling process.

Wurtzite structure monodisperse ZnS quantum dots (QDs) of 1 to 5 nm diameter, synthesized by colloidal chemical method, were confirmed by transmission electron microscopy (TEM) images and electron diffraction (ED) patterns. Enhanced blue shifted band edge emission from Zn(OH)2 capped ZnS QDs with decreasing size has been observed, which indicates the role of inorganic surface passivation and hence supports the quantum size effect. Detectable far-red shifted emission from bare ZnS QDs has been observed when QDs precursors and stabilizer dispersed in solvents with different polarities. This emission is attributed to the surface trap states of different energies.

The minimum energy atomic configurations of stacked GaAs/InAs/GaAs quantum dot structures are calculated by using the conjugate gradient energy minimization with the Stillinger-Weber potentials. The islands are assumed to be either of pyramidal shape or of trapezoidal shape. The numerical results for the five-layer stacked structures show that the normal strains exhibit stepwise up-and-down profiles through the vertical centerlines of the islands and intermediate layers. Next, the molecular dynamics method with the Tersoff potential is applied to single Ge/Si and Si/Ge/Si structures with pyramidal islands in order to investigate the effect of temperature. It is found that there is a considerable difference between the normal strain in the direction perpendicular to the island base obtained by the conjugate gradient minimization with the Stillinger-Weber potential and that obtained by the molecular dynamics method at 800 K.

A simple and versatile numerical method for electronic structure calculations in InAs pyramidal dots is presented, and its predictions compared with both theoretical and experimental data. The calculated ground state energy eigenvalues agree well with those of more sophisticated treatments which take into account band mixing and the microscopic effects of the strain distribution. The number of electron bound states predicted is in excellent agreement with very recent calculations for strained quantum dots performed in the framework of the 8-band k · p theory. Very good agreement is obtained with both the number and the energy of the peaks in several experimental photoluminescence spectra. Furthermore our ca agreement with that deduced from capacitance and photoluminescence measurements.

Quantum confinement and photoluminescence properties of self-assembled InAs quantum dot arrays on GaAs substrates are studied theoretically using a coupled morphology/electronic structure finite element approach. Simulations of island evolution due to strain energy driven diffusive mass transport are first used to generate realistic island arrays. The resulting finite element meshes are input to a continuum, single charge-carrier model in which band structure properties are prescribed using a k•p Hamiltonian formulation. The results of the electronic properties analysis are spectra of electron and hole energies and corresponding wave functions. The electron and hole states have characteristics unique to arrays, the most prominent of which are the energy separations due to size and shape variations among dots in the array. This feature is shown to lead directly to inhomogeneous broadening in the photoemission spectra. Other phenomena observed here include the onset of a discrete density of states at the point of island formation during growth; the presence of states with wave functions coupling multiple dots in the array; and the nature of wetting layer states in the system.

An In(Ga)As-based self-assembled quantum dot laser test structure grown on strain-relief Al0.5Ga0.5As1-ySby strain-relief buffer layers (0≤y ≤ 0.24) on a GaAs substrate is investigated in an effort to increase dot size and therefore extend the emission wavelength over conventional InAs quantum dots on GaAs platforms. Cross-section transmission electron microscopy, and high-resolution x-ray diffraction are used to monitor the dislocation filtering process and morphology in the buffer layers. Results show that the buffer layers act as an efficient dislocation filter by drastically reducing threading dislocations, thus providing a relaxed, low dislocation, compositionally modulated Al0.5Ga0.5Sb0.24As0.76 substrate for large (500Å height x 300Å width) defect -free InAs quantum dots. Photoluminescence shows a ground-state emission of the InAs quantum dots at 1.45 μm.

We study the dynamics of the charge distribution (polarization) in an array of four quantum dots located at the corners of a square. The array has two extra electrons in a neutralizing background. We take into account electron-phonon interaction effects using a quantum Markovian master equation approach. Results show that dissipative effects are determinant in the dynamical response of a quantum-dot cell close to a nearby driver cell with prescribed polarization varying with time. The response is shown to depend strongly on temperature.