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.
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.
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.
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.
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.
Symmetry-Breaking for Formation of Rectangular CdSe Two-Dimensional Nanocrystals in Zinc-Blende Structure
Chen, Yiya,Chen, Dongdong,Li, Zheng,Peng, Xiaogang
, p. 10009 - 10019 (2017)
Formation of CdSe nanocrystals with two-dimensional quantum confinement (CdSe 2D nanocrystals) was studied with preformed CdSe nanocrystals in the size range between 1.7 and 2.2 nm as seeds. Specifically, the 2D CdSe nanocrystals were encased with six {100} facets of the zinc-blende (face-center-cubic) structure, that is, 1.5 nm in thickness with quite large atomically flat {100} basal planes (～8 nm width and X ≈ 45 nm length). Symmetry breaking between the thickness and lateral directions occurred in the early stage by rapid formation of single-dot intermediates with flat yet polar {100} basal planes and the desired thickness from the seeds through intraparticle ripening. Two single-dot intermediates fused together through their reactive side facets - mostly the nonpolar {110} ones - to form 2D embryos with the same thickness. Such oriented attachment continued selectively onto the reactive side facets of the 2D embryos. Simultaneously, intraparticle ripening occurred slowly on the side facets of the 2D nanocrystals, which converted unstable side facets gradually to four stable {100} ones. When ～3 stable {100} side facets were developed, oriented attachment would continue on the remaining active one, which would result in the second symmetry breaking between two lateral directions. Cadmium acetate assisted both formation of single-dot intermediates and oriented attachment. Cadmium alkanoates with a long hydrocarbon chain selectively stabilized polar {100} facets on the nanocrystals including single-dot intermediates and shuttled insoluble acetate to the reactive surface of the nanocrystals.
A solvothermal route to CdS nanocrystals
Gautam, Ujjal K.,Seshadri, Ram,Rao
, p. 560 - 564 (2003)
A novel solvothermal route for the preparation of organic soluble CdS nanocrystals, involving the reaction of cadmium stearate with sulfur in the presence of tetralin has been described. Tetralin in the presence of S gives H2S, getting aromatized to naphthalene. By using trioctylphosphineoxide as the capping agent, nanocrystals of 4 nm are obtained. Use of dodecanethiol cap results in 5 nm as well as 10 nm nanocrystals which can be separated readily. The nanocrystals have the cubic zinc blende structure and exhibit blue shifts of the absorption maximum.
Characterisation of metal carboxylates by Raman and infrared spectroscopy in works of art
Otero, Vanessa,Sanches, Diogo,Montagner, Cristina,Vilarigues, Mrcia,Carlyle, Leslie,Lopes, Joo A.,Melo, Maria J.
, p. 1197 - 1206 (2015/02/19)
This work introduces the complementary use of μ-Raman and μ-Fourier transform infrared (IR) spectroscopy for the detection of specific carbon chains and cations for the identification of metal carboxylates within oil paint microsamples. Metal carboxylates (metal soaps) form naturally when free fatty acids react with metal cations and may also be found as additives or degradation products. Twenty-two metal carboxylates were synthesised, and their spectra assembled in a reference database. Metal salts of cations commonly present in oil paintings were used, including lead, zinc, calcium, cadmium, copper and manganese. The fatty acids selected were the saturated acids palmitic (C1 6:0) and stearic (C18:0) and the polyunsaturated oleic acid (C1 8:1). Azelaic acid (C9 diacid), a product resulting from autoxidation of polyunsaturated acids, was also included. Metal carboxylates were characterised by Raman and IR spectroscopy, and their structures were confirmed by X-ray diffraction. Raman and IR spectroscopy proved to be complementary techniques for a full identification of the metal carboxylates in complex aged paint. Raman enables the differentiation of the carbon chain length in the C-C stretching region (1120-1040 cm-1), and IR distinguishes the metal cation in the COO- stretching absorption region (1650-1380cm-1). Principal component analysis was applied to the spectra in order to facilitate a fast and accurate method to discriminate between the different metal carboxylates and to aide in their identification. Finally, spectra from case studies were successfully projected in the principal component analysis models built, enabling a higher confidence level for the identification of copper palmitate and copper azelate in two 19th-century Portuguese oil paintings.
