Papers by David M . Schut
TechConnect Briefs, Jun 15, 2014
The colloidal synthesis of quantum dots occurs through either a kinetically dominated process whe... more The colloidal synthesis of quantum dots occurs through either a kinetically dominated process where nucleation proceeds rapidly followed by growth via coalescence of nucleates to form larger nanoparticles, or through a thermodynamically dominated process in which nucleation occurs at high temperatures followed by epitaxial growth of the nanoparticle at lower temperatures via step-wise addition of precursors to the surface of the nucleates. While either process may be utilized for the formation of binary quantum dots, problems arise when forming quantum dots of multinary compositions due to differences in thermodynamic or kinetic processes, or the rate of nucleation. We address this issue by using microwave irradiation to manipulate the reaction kinetics of the precursors in order to produce homogeneous materials.
Proceedings of SPIE, May 13, 2011
Materials Letters, Aug 1, 2014
Colloidal lead selenide nanoparticles (PbSe NPs) were synthesized using a microwave-assisted cont... more Colloidal lead selenide nanoparticles (PbSe NPs) were synthesized using a microwave-assisted continuous flow reactor. Rapid heating of precursors was performed in the microwave reaction zone to initiate nucleation and was followed by an oil bath growth zone. In this study we have evaluated the effect of the nucleation temperature on the PbSe NP size distributions, crystallographic structure, particle shape, and particle composition. The PbSe NP size could be varied from 11.2 to 13.9 nm by adjusting the microwave nucleation temperature between 124 to 159 °C. It was found that nucleation of Pb rich species occurred in the microwave reaction zone, while PbSe NPs form in the growth zone.
Crystal Growth & Design, Oct 16, 2014
Hot-injection techniques are currently the state-ofthe-art method for the synthesis of high-quali... more Hot-injection techniques are currently the state-ofthe-art method for the synthesis of high-quality colloidal nanocrystals (NCs) but have typically been limited to small batch reactors. The nature of this method leads to local fluctuations in temperature and concentration where inhomogeneity due to mixing makes precise control of reaction conditions very challenging at a large scale. Therefore, development of methods to produce high-quality colloidal NCs with highthroughput is necessary for many technological applications. Herein, we report a high-quality and high-throughput NC synthesis method via a continuous microwave-assisted flow reactor where separation of nucleation and growth is demonstrated. A significant issue of microwave heating in a single-phase continuous flow microwave reactor is the deposition of in situ generated NCs on the inner wall of the reactor in the microwave zone. This deposited material leads to significantly enhanced microwave absorption and rapid heating and can result in sparking in the reactor. A gas−liquid segmented flow is used to avoid this problem and also results in improved residence time distributions. The use of this system allows for finely tuned parameters to achieve a high level of control over the reaction by separating the nucleation and growth stages. C olloidal nanocrystals (NCs), exhibiting a wide range of size-and shape-dependent properties, have gained attention for a number of applications including light emitting diodes, 1,2 lasers, 3,4 and solar cells. 5−9 Each of these applications depends critically on the ability to synthesize "high-quality" NCs as judged by their uniformity in size, shape, composition, and crystal structure. 9,10 The development of a high-throughput method to produce colloidal NCs with the aforementioned properties is also a key step in the commercialization process. NCs are generally synthesized by thermal decomposition of precursors in a mixture of solvents and coordinating ligands. One of the key factors for synthesizing high-quality NCs is the temporal separation of nucleation and growth stages of the reaction which is most commonly accomplished using a hotinjection technique. 11 In a typical hot-injection reaction, a solution containing one or more precursors at lower temperature is rapidly injected into a hot (i.e., above nucleation temperature) solution containing the remaining precursor(s), resulting in burst nucleation. The mixed solution naturally decreases rapidly in temperature (thus confining nucleation to a short time period following injection) and is finally held at
Inorganic Chemistry, 1993
We report the synthesis of a new water-soluble phosphine for use in the study of aqueous organome... more We report the synthesis of a new water-soluble phosphine for use in the study of aqueous organometallic systems. Aqueous organometallic chemistry is receiving increased attention,l but a severe limitation is the small number of appropriate watersoluble ligands, chelating phosphines in particular. Commonly used water-soluble phosphines include I ((diphenylphosphin0)bmzcnesulfonate, "triphenylphosphinemonosulfonate~, TPPMS),IJ I1 (phosphinetriyltris(benzenesulfonate), "triphenylphosphinetrisulfonate", TPPTS),lJ and various sulfonated-derivatives of dppe (1,2-bis(diphenyIphosphino)ethane) and related chelating ligands (e.g., complex III).134 Unfortunately, the use of these \ ,CHzCHz P(CBHB)Z(CBHISO<) p(C~HiS03-)3 (-03SH4CdzP P(CBH~SO~-)Z
Advanced Functional Materials, Oct 15, 2007
Analytical Chemistry, Mar 31, 2007
We apply percolation theory to explain the operation of multiple-use gas sensors based on organic... more We apply percolation theory to explain the operation of multiple-use gas sensors based on organic field effect transistors (OFETs). For reversible operation, we predict that energetic disorder in the channel can obscure interactions with the analyte, because chemically induced traps are overwhelmed by the natural disorder. Consequently, the sensitivity of an energetically disordered OFET-based chemical sensor is significantly inferior to the ideal disorder-free case. Current modulation in disordered OFETs is predicted to rely on morphological alteration of percolation paths. The theory is compared to results from an array of metal phthalocyanine (MPC) transistors exposed to low concentrations of solvents. Despite the presence of very large adsorption fractions of solvent on the channel, the current modulation is small, consistent with theory. Chemical selectivity is possible, however, because the central metal atom of the MPC determines the strength of the solvent-MPC interaction, which in turn determines the amount of solvent adsorbed on the OFET channel. This work suggests that OFET-based sensors may be better suited to applications where the analyte binding energy exceeds the intrinsic energetic disorder of the organic semiconductor.
Proceedings of SPIE, May 13, 2011
Inorganica Chimica Acta, Dec 1, 1995
Journal of the American Chemical Society, Sep 1, 1995
An infrared spectroscopic method was devised for measuring 6 in 1 8 f 6 organometallic complexes ... more An infrared spectroscopic method was devised for measuring 6 in 1 8 f 6 organometallic complexes containing the chelating diphosphine ligand 2,3-bis(diphenylphosphino)maleic anhydride (L2) or 2,3-bis(diphe-nylphosphin0)-2-~yclopentene-1P-dione (L2'). (1 8 f 6 complexes are 19-electron complexes in which the unpaired 19th valence electron is primarily localized on a ligand; 6 represents the amount of the unpaired electron's charge on the metal.) 6 values for the Co(CO)3L2, Co(CO)3Li, Fe(CO)3L2-, and Fe(C0)3L2'-complexes fall in the range 0.01-0.25. The effects of the metal, the ligands, and the solvent on 6 were quantitatively evaluated. In addition, the effect of 6 on the reactivity was examined by studying the dissociative substitution reactions of Co(CO)3L2. The following principles emerged: (1) 6 is larger for complexes with a more electronegative metal center (e.g., Co(1) vs Fe(0)). (2) 6 is smaller for complexes containing the more electronegative L2 ligand than for those with the less electronegative L2'. (3) 6 increases with decreasing solvent polarity, but increases with increasing solvent donicity. (4) For those cases in which 6 is manipulated by changing the solvent, there is no simple correlation between 6 and the rate of a dissociative substitution reaction in an 18+6 complex. The latter two results are interpreted in terms of a model in which donor solvents increase the electronic population of the n* SOMO on the L2 ligand and acceptor solvents decrease the electron density in this orbital. Additional electron density in the n* orbital increases delocalization of the unpaired electron onto the Co fragment, causing 6 to increase and weakening the Co-CO bond. (The acceptor orbital on the Co fragment is Co-CO u antibonding.) There is no correlation between the rate constants and 6 because Asf effects are significant, especially in polar solvents. Nineteen-electron organometallic adducts, formed via the reactions of 17-electron radicals with 2-electron donors (eq l), are important intermediate's in many reactions.
Applied Physics Letters, Jan 31, 2005
An ultrahigh-density electron-beam-based data storage medium is described that consists of a diod... more An ultrahigh-density electron-beam-based data storage medium is described that consists of a diode formed by growing an InSe/GaSe phase-change bilayer film epitaxially on silicon. Bits are recorded as amorphous regions in the InSe layer and are detected via the current induced in the diode by a scanned electron beam. This signal current is modulated by differences in the electrical properties of the amorphous and crystalline states. The success of this recording scheme results from the remarkable ability of layered III-VI materials, such as InSe, to maintain useful electrical properties at their surfaces after repeated cycles of amorphization and recrystallization.
Organometallics, 1996
The ability of 18 + δ complexes to act as homogeneous catalysts was tested by studying the cycloo... more The ability of 18 + δ complexes to act as homogeneous catalysts was tested by studying the cyclooligomerization reactions of alkynes using the Co(CO) 3 L 2 complex as the catalyst (L 2) 2,3-bis(diphenylphosphino)maleic anhydride). Cyclotrimerization occurred for RCtCR, where R) Ph, CH 2 OSiMe 3 , and CO 2 Me. No reaction was observed for R) H, CH 3 , SiMe 3 , or CH 2 CH 2 CH 3. It is proposed that the alkynes need to be activated with electronwithdrawing groups to prevent the formation of high-energy 19-electron reaction intermediates. Although the mechanistic data are not conclusive, it is proposed that the reactions follow an odd-electron pathway involving the interconversion of 17-and 19-electron species. The 18 + δ complexes are labile to ligand dissociation, and it is this feature that makes them potentially good catalysts. The importance of ligand lability was demonstrated by comparing the activity of the Co(CO) 3 L 2 complex to that of its inert 18-electron counterpart, Co(CO) 3 L 2 + ; the 18-electron molecule was not catalytically active. The products of the reactions and the electrochemical potentials of the reactants are not consistent with an electron transfer-initiated pathway involving organic radicals.
A method for producing a metal oxide nanocrystals according to the embodiment of the present inve... more A method for producing a metal oxide nanocrystals according to the embodiment of the present invention comprises continuously flowing a nanocrystal precursor solution comprising a nanocrystal precursor into a continuous flow path and heating the nanocrystal precursor solution in the continuous flow path to create nanocrystals, comprising: providing a nanocrystal precursor solution supply unit that is connected to the continuous flow path and comprises a first vessel and a second vessel; delivering a nanocrystal precursor solution in the second vessel to the continuous low path; and creating a nanocrystal precursor solution in the first vessel as a different batch from the nanocrystal precursor solution in the second vessel.
L'invention concerne un reacteur a ecoulement continu pour une synthese efficace de nanoparti... more L'invention concerne un reacteur a ecoulement continu pour une synthese efficace de nanoparticules ayant un degre eleve de cristallinite, une taille de particule uniforme et une stœchiometrie homogene a travers le cristal. Les modes realisation divulgues comprennent un reacteur a ecoulement dote d'une source d'energie pour la nucleation rapide des procureurs suivie par une source de chauffage separee pour faire croitre les elements nuclees. L'ecoulement segmente permet de faciliter le melange et l'absorption uniforme d'energie des precurseurs, et le test de la qualite apres fabrication en communication avec un systeme de commande permet un reglage en temps reel automatique des parametres de production. La source d'energie de nucleation peut etre une energie hyperfrequence a frequence monomodale, multimodale ou multivariable et accordee pour permettre a differents precurseurs de se nucleer sensiblement en meme temps, ce qui conduit a des nanoparticules sen...
L'invention concerne des systemes et des procedes destines a former des modeles pour le depot... more L'invention concerne des systemes et des procedes destines a former des modeles pour le depot de circuit ou de trace. Plus particulierement, elle concerne un procede de formation d'un modele pour un depot de circuit ou de trace comprenant les etapes consistant a projeter une composition pouvant projeter de l'encre sur un substrat dans un motif predefini, cette composition comprenant un vehicule liquide et au moins un agent de couplage y etant disperse. Le substrat peut contenir des groupes fonctionnels interactifs avec l'agent de couplage, lorsque l'agent de couplage et le substrat entrent en contact apres l'etape de projection, l'agent de couplage etant fixe au substrat ou attire par celui-ci. Le procede peut egalement comprendre l'etape destinee a mettre en contact l'agent de couplage avec une composition contenant du metal de sorte qu'un metal de cette composition se fixe a l'agent de couplage ou soit attire par celui-ci.
Applied Physics Letters, 2005
An ultrahigh-density electron-beam-based data storage medium is described that consists of a diod... more An ultrahigh-density electron-beam-based data storage medium is described that consists of a diode formed by growing an InSe/GaSe phase-change bilayer film epitaxially on silicon. Bits are recorded as amorphous regions in the InSe layer and are detected via the current induced in the diode by a scanned electron beam. This signal current is modulated by differences in the electrical properties of the amorphous and crystalline states. The success of this recording scheme results from the remarkable ability of layered III-VI materials, such as InSe, to maintain useful electrical properties at their surfaces after repeated cycles of amorphization and recrystallization.
Materials Letters, 2014
Colloidal lead selenide nanoparticles (PbSe NPs) were synthesized using a microwave-assisted cont... more Colloidal lead selenide nanoparticles (PbSe NPs) were synthesized using a microwave-assisted continuous flow reactor. Rapid heating of precursors was performed in the microwave reaction zone to initiate nucleation and was followed by an oil bath growth zone. In this study we have evaluated the effect of the nucleation temperature on the PbSe NP size distributions, crystallographic structure, particle shape, and particle composition. The PbSe NP size could be varied from 11.2 to 13.9 nm by adjusting the microwave nucleation temperature between 124 to 159 °C. It was found that nucleation of Pb rich species occurred in the microwave reaction zone, while PbSe NPs form in the growth zone.
Uploads
Papers by David M . Schut