Correlated Nanoscale Analysis of the Emission from Wurtzite versus Zincblende (In,Ga)As/GaAs Nanowire Core-Shell Quantum Wells.

While the properties of wurtzite GaAs have been extensively studied during the past decade, little is known about the influence of the crystal polytype on ternary (In,Ga)As quantum well structures. We address this question with a unique combination of correlated, spatially resolved measurement techniques on core-shell nanowires that contain extended segments of both the zincblende and wurtzite polytypes. Cathodoluminescence hyperspectral imaging reveals a blue-shift of the quantum well emission energy by 75 ± 15 meV in the wurtzite polytype segment.

Excitonic Aharonov-Bohm Oscillations in Core-Shell Nanowires.

Phase coherence in nanostructures is at the heart of a wide range of quantum effects such as Josephson oscillations between exciton-polariton condensates in microcavities, conductance quantization in 1D ballistic transport, or the optical (excitonic) Aharonov-Bohm effect in semiconductor quantum rings. These effects only occur in structures of the highest perfection. The 2D semiconductor heterostructures required for the observation of Aharonov-Bohm oscillations have proved to be particularly demanding, since interface roughness or alloy fluctuations cause a loss of the spatial phase coherence of excitons, and ultimately induce exciton localization.

Impact of Shell Growth on Recombination Dynamics and Exciton-Phonon Interaction in CdSe-CdS Core-Shell Nanoplatelets.

We investigate the impact of shell growth on the carrier dynamics and exciton-phonon coupling in CdSe-CdS core-shell nanoplatelets with varying shell thickness. We observe that the recombination dynamics can be prolonged by more than one order of magnitude, and analyze the results in a global rate model as well as with simulations including strain and excitonic effects. We reveal that type I band alignment in the hetero platelets is maintained at least up to three monolayers of CdS, resulting in approximately constant radiative rates.

Crystal-Phase Quantum Wires: One-Dimensional Heterostructures with Atomically Flat Interfaces.

In semiconductor quantum-wire heterostructures, interface roughness leads to exciton localization and to a radiative decay rate much smaller than that expected for structures with flat interfaces. Here, we uncover the electronic and optical properties of the one-dimensional extended defects that form at the intersection between stacking faults and inversion domain boundaries in GaN nanowires. We show that they act as crystal-phase quantum wires, a novel one-dimensional quantum system with atomically flat interfaces.

Influence of strain relaxation in axial [Formula: see text] nanowire heterostructures on their electronic properties.

We present a systematic theoretical study of the influence of elastic strain relaxation on the built-in electrostatic potentials and the electronic properties of axial [Formula: see text] nanowire (NW) heterostructures. Our simulations reveal that for a sufficiently large ratio between the thickness of the [Formula: see text] disk and the diameter of the NW, the elastic relaxation leads to a significant reduction of the built-in electrostatic potential in comparison to a planar system of similar layer thickness and In content. In this case, the ground state transition energies approach constant values with increasing thickness of the disk and only depend on the In content, a behavior usually associated to that of a quantum well free of built-in electrostatic potentials.

Piezoelectric potential in axial (In,Ga)N/GaN nanowire heterostructures.

We derive analytic expressions for the built-in electrostatic potential arising from piezo- and pyroelectricity in a cylindrical axial In(x)Ga(1-x)N/GaN nanowire (NW) heterostructure. Our simulations show that, for sufficiently thin NWs, a significant reduction of the built-in potential is reached in comparison to the planar heterostructure of the same In content, thickness, and orientation. This specific feature of axial NW heterostructures makes the aspect ratio of the embedded In(x)Ga(1-x)N/GaN disks an important additional degree of freedom to control the recombination energies.

Impact of Random Dopant Fluctuations on the Electronic Properties of In(x)Ga(1-x)N/GaN Axial Nanowire Heterostructures.

We study the electronic properties of axial In(x)Ga(1-x)N/GaN nanowire heterostructures with randomly placed ionized donors. Our simulations are based on an eight-band k·p model and indicate large variations of both the ground state transition energy and the spatial distribution of the electron and hole charge density. We show that these variations are intrinsic to nanostructures containing ionized donors and that the presence of donors has important consequences for all nanowire-based light-emitting devices including single-photon emitters required for quantum computing and quantum cryptography.

Coaxial multishell (In,Ga)As/GaAs nanowires for near-infrared emission on Si substrates.

Efficient infrared light emitters integrated on the mature Si technology platform could lead to on-chip optical interconnects as deemed necessary for future generations of ultrafast processors as well as to nanoanalytical functionality. Toward this goal, we demonstrate the use of GaAs-based nanowires as building blocks for the emission of light with micrometer wavelength that are monolithically integrated on Si substrates. Free-standing (In,Ga)As/GaAs coaxial multishell nanowires were grown catalyst-free on Si(111) by molecular beam epitaxy.

Electronic properties of site-controlled (111)-oriented zinc-blende InGaAs/GaAs quantum dots calculated using a symmetry-adapted k·p Hamiltonian.

In this work, we present and evaluate a (111)-rotated eight-band k ⋅p Hamiltonian for the zinc-blende crystal lattice to investigate the electronic properties of site-controlled InGaAs/GaAs quantum dots grown along the [111] direction. We derive the rotated Hamiltonian including strain and piezoelectric potentials. In combination with our previously formulated (111)-oriented continuum elasticity model, we employ this approach to investigate the electronic properties of a realistic site-controlled (111)-grown InGaAs quantum dot.

Luminous efficiency of axial In(x)Ga(1-x)N/GaN nanowire heterostructures: interplay of polarization and surface potentials.

Using continuum elasticity theory and an eight-band k·p formalism, we study the electronic properties of GaN nanowires with axial InxGa1-xN insertions. The three-dimensional strain distribution in these insertions and the resulting distribution of the polarization fields are fully taken into account. In addition, we consider the presence of a surface potential originating from Fermi level pinning at the sidewall surfaces of the nanowires.

Structure and expression of the ornithine decarboxylase gene of Chlamydomonas reinhardtii.

A cDNA was cloned encoding ornithine decarboxylase (ODC) of the unicellular green alga Chlamydomonas reinhardtii. The polypeptide consists of 396 amino acid residues with 35-37% sequence identity to other eukaryotic ODCs. As indicated by the phylogenetic tree calculated by neighbour joining analysis, the Chlamydomonas ODC has the same evolutionary distances to the ODCs of higher plants and mammalians.

Establishment of a new bovine leukosis virus producing cell line.

Due to the prevalence of different bovine leukosis virus (BLV) species in the cattle population in Europe, problems may arise in the serological diagnosis of BLV infections. In addition, earlier investigations demonstrated that contamination of the BLV antigen-producing cell culture systems by bovine viral diarrhea virus (BVDV) may give rise to misinterpretation of serological test results after BVDV vaccination of cattle. By co-cultivation of peripheral leukocytes of a BLV-infected cow with a permanent sheep kidney cell line, a new BLV-producing cell line named PO714 was established.

A 14-3-3 protein of Chlamydomonas reinhardtii associated with the endoplasmic reticulum: nucleotide sequence of the cDNA and the corresponding gene and derived amino acid sequence.

Two major 14-3-3 proteins of the unicellular green alga Chlamydomonas reinhardtii were purified and partially sequenced. The obtained data show that the 30-kDa isoform predominant in the cytosol is encoded by a previously cloned and sequenced 14-3-3 cDNA whereas the 27-kDa isoform represents a new 14-3-3 protein which is largely associated with the endoplasmic reticulum (ER). Therefore, the corresponding cDNA was cloned and sequenced.

Differentiation of type A, Asia1 and O foot-and-mouth disease virus variants, amplified by the same system, by sequencing of the capsid protein genes.

A reverse transcription-dependent polymerase chain reaction (RT-PCR) is described that amplifies the genes encoding the capsid proteins VP1-3 of at least three evolutionary lineages each of the foot-and-mouth disease (FMD) virus types A, Asia1 and O. Most of these lineages are circulating at present in Asia and Africa. The method is not only suitable to confirm suspected outbreaks of FMD, but also describes the modulation of major and minor antigenic sites in the course of an epizootic by nucleotide sequence determination of the obtained RT-PCR products.

An outbreak of enzootic bovine leukosis in upper Egypt: clinical, laboratory and molecular-epidemiological studies.

In 1989, 220 Holstein Friesian cattle (212 heifers and eight bulls) were imported from Minnesota, USA, to form a closed dairy herd in Arab El-Aoumar, Assiut, Upper Egypt. In November 1996, some abnormal signs such as loss of weight, decreased milk yield, external lymphadenopathy and decreased appetite were observed on this farm. Serological screening by enzyme-linked immunosorbent assay revealed a seroprevalence of antibodies directed against bovine leukaemia virus (BLV) of 37.

Epidemiological implications of the molecular characterization of foot-and-mouth disease virus isolated between 1996 and 2000 in Bangladesh.

Foot-and-mouth disease virus was collected during two years throughout Bangladesh. Viral RNA from 40 samples was subjected to reverse transcription-dependent polymerase chain reactions that amplify parts of the capsid protein encoding genome region, and the products obtained were sequenced. This showed that all virus isolates up to January 1999 belonged to a genotype of serotype O, observed here already in 1987, 1996 and 1997, and elsewhere since 1990.

Identification of different BLV provirus isolates by PCR, RFLPA and DNA sequencing.

A first attempt for the investigation of molecular epidemiology of BLV was carried out. PCR amplicons of a part of the env gene of BLV isolated from 309 cattle of different geographical origin were compared with known BLV env sequences. Using RFLPA most of the PCR products can be assigned to the Australian, the Japanese or the Belgian subgroup.

Molecular epidemiology of serotype O foot-and-mouth disease virus with emphasis on West and South Africa.

Genetic relationships of serotype O foot-and-mouth disease (FMD) viruses recovered from outbreaks of the disease in the West African countries of Niger, Burkina Faso and, Ghana (1988-1993) and those from South Africa (2000) were determined by partial VP1 gene characterization. A 581-bp fragment, corresponding to the C-terminus half of the ID (VP1 gene) region was amplified and sequenced. An homologous region of 495 nucleotides was ultimately used to determine genetic relationships of serotype O viruses from the Middle East, Europe, South America, North Africa, East Africa, southern Africa and Asia.

Type-independent detection of foot-and-mouth disease virus by monoclonal antibodies that bind to amino-terminal residues of capsid protein VP2.

The characterization of monoclonal antibodies raised against the foot-and-mouth disease virus isolates A22 Iraq/1964, Asia1 Shamir-Israel/1989, and SAT1 Zimbabwe/1989 with regard to neutralizing activity and sensitivity of their epitopes for treatment with trypsin, resulted in the identification of one non-neutralizing antibody in each panel that binds to a trypsin-sensitive epitope. Furthermore, each of these antibodies recognized 27 isolates of different provenance, representative of six serotypes. These antibodies are recommended for type-independent antigen detection by ELISA.

Nucleotide sequence, genomic organization and cell-cycle-dependent expression of a Chlamydomonas 14-3-3 gene.

Members of the 14-3-3 protein family have been identified as regulatory elements in intracellular signalling pathways and cell cycle control. Previously we reported the nucleotide sequence of a 14-3-3 cDNA cloned from the unicellular green alga Chlamydomonas reinhardtii. In this communication, we describe the nucleotide sequence, the genomic organization and the cell-cycle-dependent expression of the corresponding gene.

A nucleotide deletion causing a translational stop in the protease reading frame of bovine leukaemia virus (BLV) results in modified protein expression and loss of infectivity.

Bovine leukaemia virus (BLV) is an oncogenic retrovirus that causes B-cell lymphocytosis and in the terminal stage of the disease lymphosarcoma. The comparison of the previously published BLV provirus sequence from Belgium, Australia and Japan showed that the protease gene (prt) of the Australian and the Japanese isolate contain a nucleotide deletion when compared to the Belgian isolate. Because all these proviruses were isolated from tumour tissue, the prt gene of functionally active and infectious proviruses from peripheral blood leucocytes (PBLs) of BLV-infected cattle and from BLV-infected fetal lamb kidney cells were sequenced.

Antigenic variation among foot-and-mouth disease virus type A field isolates of 1997-1999 from Iran.

The sequences of the antigenically relevant capsid proteins VP1-3 of 10 isolates obtained during an epizootic of serotype A foot-and-mouth disease virus in Iran, and collected within two and a half years, were found to be highly similar. However, each isolate differed by at least one amino acid from all others. This prompted us to analyze the immunological reactivity of the isolates.

Genetic and antigenic variance of foot-and-mouth disease virus type Asia1.

The capsid protein encoding genes of five recent type Asia1 foot-and-mouth disease virus isolates, representative of three genotypes, were sequenced. The deduced amino acid sequences were aligned to each other and to two published sequences. The sequence differences suggested different antigenic properties of the isolates.

Genetical and immunological analysis of recent Asian type A and O foot-and-mouth disease virus isolates.

This report extends the knowledge on the epizootical situation of foot-and-mouth disease in Asia. RNA from six samples of type A and five of type O virus, isolated between 1987 and 1997 in Bangladesh, Iran, Malaysia and Turkey, was subjected to reverse transcription-dependent polymerase chain reactions that amplify large parts of the capsid protein VP1 encoding genome region. The amplification products were sequenced, and the sequences aligned to each other and to published sequences.