30 research outputs found

    Effect of Trace Water on the Growth of Indium Phosphide Quantum Dots

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    We report that trace amounts of water impurities in indium myristate precursors can negatively impact indium phosphide nanoparticle growth by limiting its size tunability. Without water, the growth can be effectively tuned by growth temperature and time with the first absorption peak reaching 620 nm; with water, the growth presents a “focused” behavior with the first absorption peak remaining around 550 nm. The results imply that water impurities, either from indium acetate derived indium precursors or generated in situ during nanoparticle growth, may be the cause of the currently observed inhibited growth behavior of indium phosphide quantum dots. We use multistage microfluidic reactors to show that this inhibiting effect occurs at the late stage of particle growth, following precursor depletion. We extend our study by showing that trace amounts of free hydroxide can also inhibit nanoparticle growth. We attribute the inhibited growth behavior to the hydroxylation effect of water or free hydroxide

    Imaging Schottky Barriers and Ohmic Contacts in PbS Quantum Dot Devices

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    We fabricated planar PbS quantum dot devices with ohmic and Schottky type electrodes and characterized them using scanning photocurrent and photovoltage microscopies. The microscopy techniques used in this investigation allow for interrogation of the lateral depletion width and related photovoltaic properties in the planar Schottky type contacts. Titanium/QD contacts exhibited depletion widths that varied over a wide range as a function of bias voltage, while the gold/QD contacts showed ohmic behavior over the same voltage range

    Characterization of Indium Phosphide Quantum Dot Growth Intermediates Using MALDI-TOF Mass Spectrometry

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    Clusters have been identified as important growth intermediates during group III–V quantum dot (QD) formation. Here we report a one-solvent protocol that integrates synthesis, purification, and mass characterization of indium phosphide (InP) QD growth mixtures. The use of matrix-assisted laser desorption/ionization (MALDI) mass spectrometry (MS) successfully tracks the evolution of clusters and the formation of QDs throughout the synthesis. Similar clusters are observed during the formation of large particles, suggesting that these clusters serve as a reservoir for QD formation. Combining MALDI and NMR techniques further enables us to extract extinction coefficients and construct sizing curves for cluster-free InP QDs. The use of MALDI MS opens new opportunities for characterization and mechanistic studies of small-sized air-sensitive clusters or QDs