2223-93-0Relevant articles and documents
Thermal Behavior of Langmuir-Blodgett Films. 1. Electron Diffraction Studies on Monolayers of Cadmium Stearate, Arachidate, and Behenate
Riegler, Johann E.
, p. 6475 - 6480 (1989)
Electron diffraction patterns of monolayers of several cadmium fatty acid salts were studied as a function of the sample temperature.A sharp decrease of the diffraction peak intensities at temperatures well below the main melting temperature of the headgroup lattice indicates a pretransitional disordering.It depends on the chain length and starts at ca. 35 deg C for cadmium stearate, at ca. 55 deg C for cadmium arachidate, and at ca. 75 deg C for cadmium behenate.The hexagonal geometry of the diffraction patterns does not change with temperature, and the radial and angular full width at half-maximum increase only slightly compared to the pronounced decrease of the intensity.This indicates that the overall bond orientational and traslational order of the molecules is preserved and that the intesity decrease is caused by thermally induced random tilt orientational disorder or bending of the chains.
Thioalkanoates as site-directing nucleating centers for the preparation of patterns of CdS nanoparticles within 3-D crystals and LB films of Cd alkanoates
Guo, Shouwu,Konopny, Leandro,Popovitz-Biro, Ronit,Cohen, Hagai,Porteanu, Horia,Lifshitz, Efrat,Lahav, Meir
, p. 9589 - 9598 (1999)
A method is described for the preparation of hybrid organic/inorganic structures where the inorganic component comprises semiconductor nanoparticles aligned in periodic layers within three-dimensional (3-D) crystalline powders and Langmuir-Blodgett (LB) films. The preparation process comprises the organization of metal ions in the form of periodic arrays within 3-D crystals or the LB films, followed by a topotactic gas/solid reaction. The method is illustrated for the organization of CdS nanoparticles within alkanoic acids. The order of the nanoparticles is achieved by introducing site directing nucleation centers of Cd thioalkanoates within Cd alkanoates, in the form of solid solutions. The formed particles are attached to the organic matrix via -C(O)S-Cd-S- bonds. The structure of those supramolecular architectures has been characterized by a variety of complementary methods, including transmission electron microscopy (TEM) and electron diffraction (ED), X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and other spectroscopic measurements.
A solvothermal route to capped CdSe nanoparticles
Gautam,Rajamathi,Meldrum,Morgan,Seshadri
, p. 629 - 630 (2001)
We present a convenient and safe one-pot route to capped 3 nm CdSe nanoparticles making use of common starting materials and inexpensive, low-boiling solvents under solvothermal conditions; H2Se required for the reaction is generated in situ through the aromatization of tetralin by Se.
Effect of Substrates on the Infrared External Reflection Spectra of Langmuir-Blodgett Films
Hasegawa, Takeshi,Nishijo, Jujiro,Kobayashi, Yoshihiro,Umemura, Junzo
, p. 525 - 533 (1997)
The Fourier transform infrared (FTIR) polarized external reflection (ER) spectra of 9-monolayer cadmium stearate Langmuir-Blodgett (LB) films were measured on various kinds of materials (Ge, ZnSe, and GaAs) in order to investigate whether their spectra could be used for a quantitative analysis of the molecular orientation. The FTIR ER spectra on double-side-polished substrates with LB films on both sides would not fit in, even qualitatively, with the 5-layer system (IR//air/LB/substrate/LB/air) theoretical prediction. On the other hand, the ER spectra of a single-side-deposited LB film (IR//air/substrate/LB/air) were qualitatively explained by a simple 3-layer system (IR//substrate/LB/air) in which the reflection in the substrate was treated as a single reflection. This indicated that the output rays from the substrate in the conventional 5-layer system did not interfere sufficiently with each other. A 5-layer system calculation without any interference effect qualitatively explained the ER spectra of LB films on a double-side-polished substrate. It was eventually concluded that double-side-polished materials are not suitable for a precise analysis of ER spectra, since it is almost impossible to estimate the area ratio of interferential and non-interferential rays.
A strategy for the synthesis of nanocrystal films of metal chalcogenides and oxides by employing the liquid-liquid interface
Gautam, Ujjal K.,Ghosh, Moumita,Rao
, p. 1 - 6 (2003)
The interface between water and an organic liquid has been exploited to prepare nanocrystals of CdS. The technique involves introducing an appropriate precursor of cadmium in the organic layer and the sulfiding reagent in the aqueous layer. The size distribution of the nanocrystals formed at the interface can be controlled by varying parameters such as the reactant concentration, temperature, viscosity of the medium, reaction time and the choice of the reagents. The CdS nanocrystals have been characterized by TEM, electronic absorption and emission spectroscopy. Nanocrystaline γ-Fe 2O3 and ZnO can be prepared by taking cupferron complex of the metals in the organic layer and NaOH in the aqueous layer.
Crystal structure control of CdSe nanocrystals in growth and nucleation: Dominating effects of surface versus interior structure
Gao, Yuan,Peng, Xiaogang
, p. 6724 - 6732 (2014)
For the most studied nanocrystal system in the literature, experimental results in this paper revealed that formation of either zinc blende or wurtzite CdSe nanocrystals was dominated by the ligand-surface interaction, instead of the interior structure difference. This conclusion was considered to be reasonable, given the very small energy difference between wurtzite and zinc blende CdSe (only 1.4 meV per CdSe unit and about 1000 times smaller than the energy of a single cadmium-ligand bond). Cadmium carboxylate ligands in the form of cadmium fatty acid salts promoted formation of the zinc blende structure. Conversely, cadmium phosphonate ligands with a long hydrocarbon chain favored the formation of the wurtzite structure. The effects of either cadmium carboxylate or cadmium phosphonate ligands were found to play a determining role during both nucleation and growth. Different from our expectation, fatty amine was found to be only a secondary factor for crystal structure determination. With an appropriate choice of capping ligands, it was possible to achieve precise control of the crystal structure of the CdSe nanocrystals in both nucleation and growth for either the zinc blende or wurtzite structure.
Electron transmission through molecular layers
Naaman,Haran,Nitzan,Evans,Galperin
, p. 3658 - 3668 (1998)
This article discusses general issues associated with electron transmission through thin molecular films. On the experimental side, we emphasize recent investigations of photoemission through organized organic films adsorbed on metal surfaces. Theoretical and numerical approaches to transmission and tunneling through such films are discussed. We focus on the relation between the structure of the film and its transmission properties. In the experimental work, these are controlled by varying the organic layer, by changing its thickness and by inducing disorder via thermal heating and by depositing mixtures of two molecular types. In numerical simulations of simple model systems, we consider the dimensionality of the process, effect of molecular ordering, and relation between electronic band structure in the film and its transmission properties. It is shown that electron transmission through thin molecular layers constitutes a sensitive tool for investigating molecular film properties in addition to providing a convenient prototype system for the study of electron transport in molecular electronic devices.
A low temperature phase transition in Langmuir-Blodgett films
Johansson, Thomas P.,Leach, Gary W.
, p. 13823 - 13833 (2008)
The influences of temperature on the SFG spectra of Langmuir-Blodgett films of cadmium steì?arate, ferric stearate, stearic acid and octadecanamide are reported. Upon cooling, all films display reversible discontinuous shifts of a??8 cm-1 in the r+, r- and r fermi modes of the terminal methyl groups at a??150 K. Reversible changes in the relative intensities of these methyl group peaks, most pronounced in the PPP spectra, are also observed and attributed to a change in the environment of the methyl group that accompanies a discontinuous transition in the ordering of their alkyl chains. The onset of new spectral features at higher frequency is attributed to the observation of ordered water molecules contained within the films. The correlation between the onset of the water features and the onset of the reversible, discontinuous, spectroscopic changes of the amphiphiles argues for a causal connection between the two. In addition to the discontinuous behavior upon cooling, monolayer films of stearic acid and octadecanamide display activity of methylene modes upon exposure to vacuum. Films displaying SFG-active methylene groups at room temperature had them gradually become completely SFG-inactive by 100 K. Heating the films to room temperature revealed that the methylene group activity was reversible. Monolayer films of cadmium ste;arate and ferric stearate do not display this methylene activity upon exposure to vacuum, suggesting that this behavior may be linked to solvation of the amphiphile's headgroup. These observations suggest that water plays a key role in the stability and structure of LB supported monolayers, and have important implications to those interested in low temperature (cryogenic) effects of biological systems. ? 2008 American Chemical Society.
Molecular-orientation change in Langmuir films of stearic acid and cadmium stearate upon surface compression, as studied by infrared external-reflection spectroscopy
Sakai, Hiroshi,Umemura, Junzo
, p. 1027 - 1032 (1997)
For interpretating the various phases appearing in a two-dimensional system, we have recorded in situ polarized FT-IR external reflection spectra of Langmuir films of stearic acid and cadmium stearate on the water surface at various surface areas, and evaluated the molecular orientation angles quantitatively. In the stearic acid monolayer, the orientation angle of the hydrocarbon chain from the surface normal decreased from 20° to almost 0° upon monolayer compression. In the cadmium stearate monolayer, on the other hand, the orientation angle (near 0°) did not change upon monolayer compression, though it was widely scattered at large surface areas, because of the formation of a rigid crystalline island. These results correspond well to the π-A isotherms.
Charge and energy transfer between CdSe quantum dots and polyaniline
Xu, Liang,Huang, Xingbin,Dai, Wenjiang,Sun, Punan,Chen, Xuanlin,An, Limin
, p. 3909 - 3913 (2016)
CdSe quantum dots (QDs) and polyaniline (PAni) were mixed to prepare CdSe QDs/PAni complex. PAni can quench the fluorescence of CdSe QDs. Fluorescence intensity of CdSe QDs/PAni complex is related to the size of CdSe QDs and the concentration of PAni. UV-
