Thermal quenching of luminescence from buried and surface InGaAs self-assembled quantum dots with high sheet density

Variable-temperature photoluminescence (PL) spectra of Si-doped self-assembled InGaAs quantum dots (QDs) with and without GaAs cap layers were measured. Narrow and strong emission peak at 1075 nm and broad and weak peak at 1310 nm were observed for the buried and surface QDs at low temperature, respectively. As large as 210 meV redshift of the PL peak of the surface QDs with respect to that of the buried QDs is mainly due to the change of the strain around QDs before and after growth of the GaAs cap layer. Using the developed localized-state luminescence model, we quantitatively calculate the temperature dependence of PL peaks and integrated intensities of the two samples. The results reveal that there exists a large difference in microscopic mechanisms of PL thermal quenching between two samples. (c) 2005 American Institute of Physics.

Effect of growth temperature on luminescence and structure of self-assembled InAlAs/AlGaAs quantum dots

The effect of growth temperature on the optical properties of self-assembled In0.65Al0.35As/Al0.35Ga0.65As quantum dots is studied using photoluminescence and electroluminescence spectra. With the growth temperature increasing from 530 to 560 degreesC, the improvement of optical and structural quality has been observed. Furthermore, edge-emitting laser diodes with three stacked InAlAs quantum dot layers grown at different temperature are processed, respectively. For samples with quantum dots grown at 560 degreesC, the continuous wave operation is obtained up to 220 K, which is much higher than that of ones with InAlAs islands grown at 530 degreesC and that of the short-wavelength quantum-dot laser previously reported. (C) 2001 American Institute of Physics.

Different transfer paths for thermally activated electrons and holes in self-organized Ge/Si(001) islands in a multilayer structure

We investigated the temperature dependence (10-250 K) of the photoluminescence (PL) emission spectrum of self-organized Ge/Si(001) islands in a multilayer structure. With elevated temperature, we find that the thermally activated holes and electrons are gathered by the Ge islands in different ways. The holes drift from the wetting layer into the islands, while the electrons, confined in Si due to type-II band alignment, leak into the Ge islands by the electrostatic interaction with the holes accumulated there. It results in an increase of the integrated intensity of island-related PL at a certain temperature range and a reduction of the phonon energy in the phonon-assisted PL of the islands by involving a type-I transition into a type-II transition. (C) 2001 American Institute of Physics.

Synthesis of a novel electroactive ABA triblock copolymer and its spontaneous self-assembly in water

An electroactive triblock copolymer of poly(ethylene glycol) (PEG) and aniline pentamer (AP), PEG-block-AP-block-PEG (PAP), was synthesized via polycondensation in the presence of N,N'-dicyclohexylcarbodiimide (DCC). The UV-vis spectra and cyclic-voltammograms (CV) spectra exhibited an excellent electroactivity of the triblock copolymer. The amphiphilic triblock copolymer self-assembles spontaneously into uniform micellar aggregates when the triblock copolymer was added directly to the aqueous solution. The size of the aggregates can be changed with the oxidation state of the AP segment in the PAP copolymer and the aggregates were pH-sensitive to the surrounding water solution, which provides a potential application in controlled drug release.

Fabrication and characterization of self-doped poly (aniline-co-anthranilic acid) nanorods in bundles

Poly (aniline-co-anthranilic acid) (PANANA) nanorods in bundles was prepared successfully in an alcohol/aqueous media without assistance of an), other kinds of acids. Anthranilic acid played all roles of monomer, acid-media provider, and dopant in the reaction system, and ammonium persulfate (APS) served as the oxidant. The morphologies of PANANA nanorods in bundles were investigated by scanning electron microscopy (SEM). Influences of the monomer molar ratio on the resulting morphology were investigated. Moreover the formation mechanism of the nanostructured copolymer was proposed. FT-IR. UV-vis and X-ray diffraction (XRD) measurements were used to confirm the molecular and electrical structure of the self-doped PANANA. The intrinsic properties, such as conductivity, electrochemical redox activity and room-temperature solubility of the resulting copolymer were explored.

Syntheses of Ag, PbSe, and PbTe nanocrystals and their binary self-assembly exploration at low size-ratio

Nanocrystals of Ag, PbSe, and PbTe were prepared via a high-temperature organic solution approach, respectively. Using a size-selection technique, the size-distribution of each set of nanocrystals could be fine-tuned and finally monodisperse products were achieved. Superlattice structure of binary self-assemblies in low size-ratio were also explored and characterized by transmission electron microscopy. It is realized that a success of achieving binary self-assembly pattern is greatly dependent on several key factors including particle size-distributions, relative concentrations of both components, as well as the size-ratios between Ag and PbSe (or PbTe) nanocrystals.

Morphology and structures of self-assembled symmetric poly(di-n-alkylsilanes)

The self-assembly of poly(di-n-butylsilane) (PDBS) and poly(di-n-hexylsilane) (PDHS) on the surfaces of amorphous carbon and highly oriented pyrolytic graphite (HOPG) have been investigated, respectively. The morphology and structures of these self-assembled thin films were studied by using atomic force microscopy, transmission electronic microscopy, and wide-angle X-ray diffraction. In the case of weak van der Waals interactions between absorbed molecules and substrate, i.e., on amorphous carbon, the self-assembly process was driven by absorbate-absorbate intermolecular interactions. For PDBS with weak absorbate-absorbate intermolecular interactions, the thin film showed organization lacking any measurable preferred orientation on the surface of amorphous carbon. While for PDHS with rigid backbone and strong intermolecular interactions, flat-on lamellae with silicon backbones perpendicular to the surface of amorphous carbon were formed. However, in the case of strong van der Waals interactions between absorbed molecules and substrate, i.e., on HOPG, the self-assembly process was tailored by the balance of absorbate-absorbate intermolecular interactions and molecule-substrate interactions. Both PDHS and PDBS thin films grew into edge-on lamellae on the surface of HOPG, which aligned according to a Mold symmetry.

Preparation and characterization of self-assembled monolayers of trichlorogermanyl propanoic acid and its derivatives

Self-assembled monolayers(SAMs) of trichlorogermanyl propanoic acid derivatives on hydroxylated silicon substrates are prepared for the first time. Contact angle measurement, ellipsometry and X-ray photoelectron spectrometry(XPS) are used to characterize these SAMs, It is demonstrated that a quasi-2D network is formed on the surface of the substrate after molecules adsorbed on it. The molecular chains have certain tilt angles to the substrate surface, The wettabilities of the SAMs are various,because the molecules adsorbed and liquids used in the experiments are different. It can be concluded that trichlorogermanes have similar self-assembly behavior as trichlorosilanes, Four SAMs are studied together: they are acid, ethyl, butyl and hexyl surfaces whose results are of good consistency.

Electrochemical study of interactions between DNA and viologen-thiol self-assembled monolayers

We investigated the binding characteristics of double-stranded DNA to self-assembled monolayers (SAMs) containing viologen groups formed on the surface of gold electrodes via Au-S bonds. The positive charged and hydrophobic surfaces of the viologen SAMs modified gold electrodes are suitable to bind strongly dth DNA, whose interactions to solution DNA and adsorbed DNA both lead to positive shifts (22.5 mV and 65 mV, respectively) in the first redox potential ci viologen centers, indicating that the main interaction is from a hydrophobic interaction. Meanwhile, the binding of DNA strongly affects the kinetics of electron transfer of the viologen group so that the separation of anodic and cathodic peak potentials becomes larger and the heterogeneous electron transfer constant becomes smaller.

STRUCTURE AND PROPERTIES OF SELF-DOPED POLYANILINE

Sulfonated polyaniline(SPAn) with different sulfonation degree(SD) was prepared, its structure was studied by spectroelectrochemical method, some of its special properties were given.

Self-instability and bending behaviors of nano plates

This paper aims at investigating the size-dependent self-buckling and bending behaviors of nano plates through incorporating surface elasticity into the elasticity with residual stress fields. In the absence of external loading, positive surface tension induces a compressive residual stress field in the bulk of the nano plate and there may be self-equilibrium states corresponding to the plate self-buckling. The self-instability of nano plates is investigated and the critical self-instability size of simply supported rectangular nano plates is determined. In addition, the residual stress field in the bulk of the nano plate is usually neglected in the existing literatures, where the elastic response of the bulk is often described by the classical Hooke’s law. The present paper considered the effect of the residual stress in the bulk induced by surface tension and adopted the elasticity with residual stress fields to study the bending behaviors of nano plates without buckling. The present results show that the surface effects only modify the coefficients in corresponding equations of the classical Kirchhoff plate theory.

Photoluminescence in Si and Be directly doped self-organized InAs/GaAs quantum dots

We report on the photoluminescence in directly Si- and Be-doped self-organized InAs/GaAs quantum dots (QDs). When the doping level is low, a decrease in linewidth is observed. However, it will decrease the uniformity and photoluminescence peak intensity of QDs when the doping level is high. We relate this phenomenon to a model that takes the Si or Be atoms as the nucleation centers for the formation of QDs. (C) 2000 Elsevier Science B.V. All rights reserved.

Thermal annealing of Au nanorod self-assembled nanostructured materials: Morphology and optical properties

Three-dimensional Au nanorod and An nanoparticle nanostructured materials were prepared by layer-by-layer self-assembly. The plasmonic properties of the An nanorod and An nanoparticle self-assembled nanostructured materials (abbreviated as AuNR and AuNP SANMs) are tunable by the controlled self-assenibly process. The effect of thermal annealing at 180 and 500 degrees C to the morphologies, plasmonic properties and surface-enhanced Raman scattering (SERS) responses of these SANMs were investigated. According to the experimental results, these properties correlate with the structure of the SANMs.

PolydA and polyrA self-structured by a europium and amino acid complex

Different DNA selectivity was found for the newly synthesized europium-L-valine complex. Unexpected DNA and RNA selection results showed that europium-L-valine complex can cause single-stranded polydA and polyrA to self-structure. The sigmoidal melting curve profiles indicate the transition is cooperative, similar to the cooperative melting of a duplex DNA. This is different from another europium amino acid complex, europium-L-aspartic acid complex which can induce B-Z transition under the low salt condition. To our knowledge, there is no report to show that a metal-amino acid complex can cause the self-structuring of single-stranded DNA and RNA.