A stable droplet reactor for high temperature nanocrystal synthesis

We report a versatile capillary-based droplet reactor for the controlled synthesis of nanoparticles over a wide range of flow conditions and temperatures. The reactor tolerates large flow-rate differentials between individual reagent streams, and allows droplet composition to be varied independently of residence time and volume. The reactor was successfully applied to the synthesis of metal (Ag), metal-oxide (TiO(2)) and compound semiconductor (CdSe) nanoparticles, and in each case exhibited stable droplet flow over many hours of operation without fouling, even for reactions involving solid intermediates. For CdSe formed by the reaction of Cd oleate and Se, highly controlled growth could be achieved at temperatures of up to 250 °C, with emission spectra varying smoothly and reproducibly with temperature and flow-rate. The droplet reactor showed exceptional stability when operated under constant flow-rate and temperature conditions, yielding particles with well-defined band-edge emission spectra that did not vary over the course of a full day's continuous operation.     

A study of inclusive Λ polarization from hydrogen and other targets at 28 GeV

We report measurements of inclusive Λ polarization, produced by unpolarized protons incident at several momenta (20, 24, and 28.5 GeV/c) onto hydrogen, deuterium, and beryllium targets. A large polarization from hydrogen, P = ?0.34 ± 0.06 at pP_T = 1.2 GeV/c, establishes the fact that inclusive Λ polarization arises from p-p collisions.     

Neutron spectra coincident with discrete gamma rays in π− capture on 165Ho and 181Ta

Neutron spectra from π^?-capture in medium-heavy nuclei are presented in coincidence with discrete nuclear gamma rays to exhibit possible correlations of the spectra to neutron multiplicity and residual nuclear states. A discrete component in the pre-compound neutron spectra is resolved for the first time, and its correlation to the population of high spin nuclear states is observed.     

The phase diagram of (NH4I)x(KI)1−x

The χ,T phase diagram of (NH₄I)_x(KI)_1−x has been determined using neutron diffraction experiments and dielectric spectroscopy. At low temperatures and with decreasing χ, the sequence γ, β, ε and glass phase has been detected. The critical concentration χ_c≈0.55 separates the glassy phase with frozen-in orientational disorder from the ε phase which reveals long-range orientational order. Close to χ_c our experiments reveal evidence for two subsequent glass transitions.     

The determination of chain statistical parameters by light scattering measurements.

The effects of volume exclusion on polymer chain conformations can be determined from the study of the angular dependence of radiation scattered by chain molecules. It is found that useful information can be obtained only when the variable x is large, where x is the product of the square of the magnitude of the scattering vector and of the mean square radius of gyration. Hence, solutions of macromolecules of very high molecular weight are needed for these investigations. The theoretical treatment of the scattering function is based on several assumptions. The validity of these assumptions is examined by computing, using a Monte-Carlo technique, various moments of intramolecular separations and comparing the results so obtained, in the limit of a chain of infinite length, with the analytical results. The computations seem to verify the validity of the theoretical model. The scattering behavior of solutions of recently synthesized polystyrene of Mw = 4.4 X 10(7) in cyclohexane at various temperatures and in benzene at 40 degrees was investigated. From the log-log plots of the scattering function vs. x, a statistical parameter was calculated, whose value depends on the magnitude of long-range correlations between any pair of chain elements. It is found that above the theta temperature this parameter is practically independent of temperature and that its numerical value was found to agree well with the value obtained from Monte-Carlo calculations. In the neighborhood of the theta temperature, this parameter decreases rapidly with decreasing temperature, indicating a first-order transition in chain conformation.     

Analytic models for West Coast storm surges,with application to events of January 1976

Simple mathematical models describing wind-induced motion on a continental shelf are used to predict storm surges at the port of Milford Haven on the west coast of the British Isles. Attention is concentrated on surge events occurring during the stormy month of January 1976. It is demonstrated that useful first-order accuracies in prediction can be achieved. Oceanic influence on the coastal surge is shown to be small. Satisfactory results are obtained with wind input data coming either from the analysis of daily weather charts or from recorded values of wind speed and direction at a group of meteorological stations.     

ALD resist formed by vapor-deposited self-assembled monolayers

A new process of applying molecular resists to block HfO2 and Pt atomic layer deposition has been investigated. Monolayer films are formed from octadecyltrichlorosilane (ODTS) or tridecafluoro-1,1,2,2-tetrahydrooctyltrichlorosilane (FOTS) and water vapor on native silicon oxide surfaces and from 1-octadecene on hydrogen-passivated silicon surfaces through a low-pressure chemical vapor deposition process. X-ray photoelectron spectroscopy data indicates that surfaces blocked by these monolayer resists can prevent atomic layer deposition of both HfO2 and Pt successfully. Time-dependent studies show that the ODTS monolayers continue to improve in blocking ability for as long as 48 h of formation time, and infrared spectroscopy measurements confirm an evolution of packing order over these time scales.