Chemistry Reference
In-Depth Information
From the linear relation between 1/C and
N
, the thickness was estimated to be 15 Å.
A small variation in bias voltage gave rise to a large modulation of AC, which has
been ascribed to the small thickness of the insulator and from the high resistivity (ca.
600 Ω cm) of the p-type silicon.
In other studies on MOS structures, the two types of hysteresis, normal and
abnormal, are suggested to arise from the ion displacement in the insulator and
to the trapping at the interface states. The presence of site-radiation-induced poly-
merization has been used to provide increased film stability and has been described
as an application for high-resolution electron beam lithography for the fabrication
of microcircuitry.
So far, only polymerizable sites have been described, and monomolecular layers
involving radiation-sites appear unreported. One approach to such a site is the inclu-
sion of a quaternary center and/or a heavy element in the chain to enhance electron
beam and x-ray cross section. The transfer rate of the dipalmitoyl lecithin (DPPC)
monolayer from aqueous phase to glass surface has been investigated. The change
in the contact angle of DPPC monolayer/glass interface, where DPPC was kept at a
fixed area/molecule, 134 Å5, was reported to be sigmoidally increased. These rates
were analyzed as first-order kinetics, and the transfer rate was found to be 2.59 10
−3
1/s. Synthesis and monolayer studies were reported for a geminally branched acid—
O,O-dimethyl-arachidic acid—in order to assess the feasibility of forming stabler
films in such a system, films that should possess enhanced radiation sensitivity.
Surprisingly, the quaternary center did not markedly disturb the formation of mono-
molecular films, and films formed and transferred to a solid surface were studied by
optical and x-ray photoelectron spectroscopic measurements.
The interactions between insoluble monolayers of ionic surfactants and ions dis-
solved in the subsolution have been the subject of continuing scientific interest since
the time of the pioneering investigations of Adam and Langmuir (Adamson and
Gast, 1997; Gaines, 1966; Birdi, 1989). This interest rests upon the desire to model
important natural and technological processes such as enzymatic activity, perme-
ability of cellular membranes, ion exchange processes in soils, adsorption in ion
exchange resins, ion flotation, and chromatography.
A recent report describes the radioactive labeled chromium (iii) ion adsorption on
stearic acid LB films. The adsorption of chromium (iii) on a stearic acid monolayer
on the surface of CrCl
3
was described. Stearic acid monomolecular films on 10
−3
M
CaCl
2
subsolutions were deposited in paraffin-coated microscope glass slides by the
LB technique (pH range 2-9).
The combination of the LB technique and the neutron activation method of analy-
sis was used to determine the stoichiometry of the interaction between fatty acid
(arachidic acid) and metal ions dissolved in the subphase. The experimental data
were used to estimate the stability constants of arachidic acid and bivalent metal ions
(Cd and Ba). The data were explained as an interaction between metal ions and the
monolayer as an adsorption process:
2 RCOO
−
+ Me
++
⇔ (RCOO)
2
Me
(4.38)
The equilibrium constant is given by the mass action law:
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