Biomedical subjects

Aarnoud L Roest

Publications and source records attributed to Aarnoud L Roest.

4 recordsLinked to original sources

PubMed2005

Increase of the photoluminescence intensity of InP nanowires by photoassisted surface passivation.

As-grown single-crystal InP nanowires, covered with a surface oxide, show a photoluminescence efficiency that strongly varies from wire to wire. We show that the luminescence efficiency of single-crystal InP nanowires can be improved by photoassisted wet chemical etching in a butanol solution containing HF and the indium-coordinating ligand trioctylphosphine oxide. Electron-hole photogeneration, electron scavenging, and oxidative dissolution combined with surface passivation by the indium-coordinating ligand are essential elements to improve the luminescence efficiency. Time traces of the luminescence of surface-passivated wires show strong oscillations resembling the on-off blinking observed with single quantum dots. These results reflect the strong influence of a single or a few nonradiative recombination center(s) on the luminescence properties of an entire wire.

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PubMed2005

Tunable supercurrent through semiconductor nanowires.

Nanoscale superconductor/semiconductor hybrid devices are assembled from indium arsenide semiconductor nanowires individually contacted by aluminum-based superconductor electrodes. Below 1 kelvin, the high transparency of the contacts gives rise to proximity-induced superconductivity. The nanowires form superconducting weak links operating as mesoscopic Josephson junctions with electrically tunable coupling. The supercurrent can be switched on/off by a gate voltage acting on the electron density in the nanowire. A variation in gate voltage induces universal fluctuations in the normal-state conductance, which are clearly correlated to critical current fluctuations. The alternating-current Josephson effect gives rise to Shapiro steps in the voltage-current characteristic under microwave irradiation.

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PubMed2004

Electron-conducting quantum-dot solids with ionic charge compensation.

Electron-conducting quantum-dot solids can be prepared on the basis of assemblies of colloidal insulating nanocrystals if electrons can be injected in the delocalized conduction orbitals. We discuss the energetics of electron injection in such an artificial solid consisting of weakly coupled quantum dots. We show that quantum confinement and electron electron repulsion determine the charging characteristics. The electron electron repulsion energy can be screened by three-dimensional charge compensation from trapped holes or positive inert ions inserted in the assembly. We present experimental results on the electron storage and long-range transport in assemblies of ZnO nanocrystals in which the electron charge is compensated by positive ions. The electron electron repulsion energy in assemblies permeated with an aqueous electrolyte solution is strongly screened. In contrast, the repulsion energy is about 100 meV in aprotic solvents; the repulsion energy strongly influences electron storage and the characteristics of long-range electron transport.

Journal Article↗

PubMed2003

Long-range transport in an assembly of ZnO quantum dots: the effects of quantum confinement, Coulomb repulsion and structural disorder.

We have studied the storage and long-range transport of electrons in a porous assembly of weakly coupled ZnO quantum dots permeated with an aqueous and a propylene carbonate electrolyte solution. The number of electrons per ZnO quantum dot is controlled by the electrochemical potential of the assembly; the charge of the electrons is compensated by ions present in the pores. We show with optical and electrical measurements that the injected electrons occupy the S, P, and D type conduction electron levels of the quantum dots; electron storage in surface states is not important. With this method of three-dimensional charge compensation, up to ten electrons per quantum-dot can be stored if the assembly is permeated with an aqueous electrolyte. The screening of the electron charge is less effective in the case of an assembly permeated with a propylene carbonate electrolyte solution. Long-range electron transport is studied with a transistor set-up. In the case of ZnO assemblies permeated with an aqueous electrolyte, two quantum regimes are observed corresponding to multiple tunnelling between the S orbitals (at a low occupation) and P orbitals (at a higher occupation). In a ZnO quantum-dot assembly permeated with a propylene carbonate electrolyte solution, there is a strong overlap between these two regimes.

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