| Plasmons
on Separate Paths
C. R. Williams, M. Misra, S. R. Andrews, S. A. Maier,
S. Carretero-Palacios, S. G. Rodrigo, F. J. Garcia-Vidal,
and L. Martin-Moreno
Appl.
Phys. Lett. 2010,
96, 011101
Metamaterial
calculated dispersion curves and maps of the absolute
electric field strength at fc (TE 11) and fc (TEM)
In the quest for faster signal
processing speeds there are essentially two approaches:
shrink the size of the circuitry, or use light rather
than electronic current as the information carrier.
In the former approach, the operating frequency
faces a fundamental upper limit of several tens
of GHz due to the properties of the materials required
in the design of current-based devices. Light, in
contrast, offers the ultimate speed, but requires
circuit size to remain on the order of its roughly
micrometer-scale wavelength.
Surface plasmons— light-induced
electronic excitations near the surface of a metal/dielectric
interface—offer the possibility of exploiting
the speed and size virtues of the two approaches.
However, exciting the plasmons is usually a resonant
phenomenon, meaning that only one kind of plasmon
can be excited at a particular wave-length.
Williams et al. present a technique
based on a designed array of annular holes on a
textured copper surface that allows two tightly
bound THz-induced plasmon modes to propagate independently,
thus providing potential for a number of applications
in chemical and biological sensing, security screening,
and communications.
|
Non-Covalent
Immobilization of Enantioselective Catalysts
José M. Fraile, José
I. García and José A. Mayoral
Chem. Rev. 2009, 109,
360–417
The most convenient strategy
to prepare chiral heterogeneous catalysts is the
immobilization of chiral homogeneous catalysts,
and the most used method to immobilize chiral
complexes is the formation of a covalent bond
between the solid support and the chiral ligand.
One important drawback of this
method is the need for an additional functionalization
of the chiral ligand.
The objective of this review
is to bring together all the knowledge about methods
of immobilization applied to enantioselective
catalysts, that don’t require the covalent
link of the chiral ligand to a solid support,
either organic (polymeric) or inorganic.
These methods are quite underestimated,
but they offer several advantages: many of them
don’t require modification of the known,
commercially available, chiral ligands used in
solution chemistry; many of these methods are
simple and efficient, precluding any important
supplementary cost; and there exist possibilities
to control the stereochemical outcome of the catalytic
process due to the relative position of the complex
with respect to the support.
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