4,238 research outputs found
Nano-Materials and Nano-Technology
Nano, a Greek word , means dwarf. Science has, however, given this dwarf a numerical value of "one billionth". A nanometer is thus one billionth of a meter, or 10A°.As a very general definition , materials/structures with one or more physical dimensions having the size of some nano-meters are now called nano-materials/ nano-structures. The processes utilized to create such materials/structures, and technologies to exploit these to fabricate devices with/ without integration with suitable micro/ macro dimension materials/ structures /devices are termed as nanotechnologies. With increasing use of the word NANO in popular science and consumer applications, sub-micron size materials and devices arealso loosely included in the nano-categories.
Nano-materials are low dimensional materials which are classified by physicists as zero, one, or two dimensional, depending on whether three, two, or one dimensions are small enough in size (which is of course relative to the size of the probe entities) so that classical laws of
physics are not applicable with confidence. Some typical examples of low dimensional materials and devices are listed in the following
Transmission Electron Microscope Studies of Thin Films of CdSe Vacuum Evaporated from Knudsen-Type Source
A Knudsen-type evaporation source was used for the vacuum deposition of thin films of CdSe to study their growth and microstructure on to air-cleaved KCI and mica substrates under different rates of evaporation and substrate temperatures. The conditions for the growth of epitaxial films of this material onto mica have also been established and their photoconducting properties evaluated. CdSe films prepared by this source retain their stoichiometry and compare well with those prepared by other sources of vacuum evaporation
Noninvasive Embedding of Single Co Atoms in Ge(111)2x1 Surfaces
We report on a combined scanning tunneling microscopy (STM) and density
functional theory (DFT) based investigation of Co atoms on Ge(111)2x1 surfaces.
When deposited on cold surfaces, individual Co atoms have a limited diffusivity
on the atomically flat areas and apparently reside on top of the upper
pi-bonded chain rows exclusively. Voltage-dependent STM imaging reveals a
highly anisotropic electronic perturbation of the Ge surface surrounding these
Co atoms and pronounced one-dimensional confinement along the pi-bonded chains.
DFT calculations reveal that the individual Co atoms are in fact embedded in
the Ge surface, where they occupy a quasi-stationary position within the big
7-member Ge ring in between the 3rd and 4th atomic Ge layer. The energy needed
for the Co atoms to overcome the potential barrier for penetration in the Ge
surface is provided by the kinetic energy resulting from the deposition
process. DFT calculations further demonstrate that the embedded Co atoms form
four covalent Co-Ge bonds, resulting in a Co4+ valence state and a 3d5
electronic configuration. Calculated STM images are in perfect agreement with
the experimental atomic resolution STM images for the broad range of applied
tunneling voltages.Comment: 19 pages, 15 figures, 3 table
Discrimination between two mechanisms of surface-scattering in a single-mode waveguide
Transport properties of a single-mode waveguide with rough boundary are
studied by discrimination between two mechanisms of surface scattering, the
amplitude and square-gradient ones. Although these mechanisms are generically
mixed, we show that for some profiles they can separately operate within
non-overlapping intervals of wave numbers of scattering waves. This effect may
be important in realistic situations due to inevitable long-range correlations
in scattering profiles.Comment: 5 pages, 3 figure
Early Results from the Wisconsin H-Alpha Mapper Southern Sky Survey
After a successful eleven-year campaign at Kitt Peak, we moved the Wisconsin
H-Alpha Mapper (WHAM) to Cerro Tololo in early 2009. Here we present some of
the early data after a few months under southern skies. These maps begin to
complete the first all-sky, kinematic survey of the diffuse H-alpha emission
from the Milky Way. Much of this emission arises from the Warm Ionized Medium
(WIM), a significant component of the ISM that extends a few kiloparsecs above
the Galactic disk. While this first look at the data focuses on the H-alpha
survey, WHAM is also capable of observing many other optical emission lines,
revealing fascinating trends in the temperature and ionization state of the
WIM. Our ongoing studies of the physical conditions of diffuse ionized gas will
continue from the southern hemisphere following the H-alpha survey. In
addition, future observations will cover the full velocity range of the
Magellanic Stream, Bridge, and Clouds to trace the ionized gas associated with
these neighboring systems.Comment: 4 pages, 2 figures. To appear in "The Dynamic ISM: A celebration of
the Canadian Galactic Plane Survey," ASP Conference Serie
Distribution of fatty acids during germination of soybean seeds
Gas chromatographic determination of the fatty acids in the seeds of soybean (Glycine max) showed mainly linoleic, oleic and palmitic acids with linoleic acid being the major component. Changes in the distribution of fatty acids were measured during germination in the cotyledons and roots. A decrease in palmitic and oleic acids was observed in the cotyledons from 6 to 12 days, while linoleic acid increased during the same period. In roots also, the major fatty acid was linoleic acid, while palmitic and linolenic acids were higher in roots in comparison with the cotyledons. During the 3-12 days of germination period, no major changes in the distribution pattern of fatty acids were observed in the roots. The possible significance of these changes is discussed
Cobalt oxide-iron oxide selective coatings for high temperature applications
Cobalt oxide-iron oxide coatings on stainless steel have been prepared by spray pyrolysis technique. These coatings have absorptance (α) = 0.94 and emittance (ε100) = 0.20 which are much better values than for cobalt oxide or iron oxide alone on stainless steel substrates. The coatings have been found to be stable for temperatures upto 400° C
Optically selective coatings
The natural optical selectivity of a material exhibited in the form of its reflectance, transmittance, or emittance spectra can be modified and tailored to yield any desired profile by applying surface coatings in the form of multilayers of suitable materials, or composite materials having an appropriate graded composition. This paper reviews the modes of selectivity, design and modelling of some technologically important optically selective coatings
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