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<P><SPAN class=head2><A
href="http://nanotechweb.org/articles/news/2/12/13/1">http://nanotechweb.org/articles/news/2/12/13/1</A></SPAN></P>
<P><SPAN class=head2>Beetle perfects artificial opal growth</SPAN> <BR><FONT
size=2><SMALL>22 December 2003</SMALL> </FONT></P>
<P><B>Researchers at the University of Oxford, UK, have discovered what they say
is the first example of an opal-type photonic crystal structure in an animal.
The intricate three-dimensional structure occurs in a small beetle just a few
centimetres long. If the beetle’s self-assembly process can be emulated, the
team says it could lead to a simpler and cheaper way of producing artificial
opals (<I>Nature</I> 426 786).</B></P>
<P>“The interesting thing is that this has been found in a living organism,”
said researcher Andrew Parker. “This means that the beetle must have cells that
are making the structure, which gives us something to copy. There is a whole
manufacturing process going on which starts with a series of chemicals and ends
with a perfect opal structure.” </P>
<P>The opal-making animal is the weevil <I>Pachyrhynchus argus</I>, a small
beetle found in forests in north-eastern Australia. Its body appears a metallic
green colour from all angles thanks to a photonic crystal structure that
resembles opal. </P>
<P>The vivid colour comes courtesy of thin, flat scales which occur in patches
over the beetle’s body. The scales consist of an outer shell and an inner
structure that contains layers of 250 nm diameter transparent spheres. </P>
<P>“The spheres are arranged in hexagonal-close packing order,” explained
Parker. “The scales contain the opal structure. There are tens of layers packed
on top of each other in a single scale.” </P>
<P>The scales produce the green colour by thin-film reflection. “Because we have
stacks of spheres instead of flat layers, we have a three-dimensional structure
where you can effectively form layers in many directions,” he said. “The
reflections from each of these layers are superimposed and you get a
colour-averaging effect which appears green.”</P>
<P style="FONT-WEIGHT: bold"><A name=author>About the author</A></P>
<P>Jacqueline Hewett is an award-winning news reporter on <I>Optics.org</I> and
<I>Opto & Laser Europe</I> magazine.</P></FONT></DIV></BODY></HTML>