NEVER-BEFORE-MADE MATERIAL SIMILAR TO
DIAMONDS AND ICE, SAYS UH PROF
New Form of Germanium Synthesized Has Rare
Properties with Major Technological Potential
HOUSTON, Nov. 27, 2006 – Not since the use of germanium
in the first transistor radios and the discovery of its crucial
role in semiconductor research more than 50 years ago has the study
of this element garnered so much attention.
This half-century rebound in popularity is thanks to a University
of Houston scientist and his team’s research into a first-time,
low-density synthetic form of this chemical element. Led by Arnold
Guloy, a UH chemistry professor, and a team of researchers from
UH and the Max Planck Institute for Chemical Physics of Solids in
Dresden, Germany, where Guloy is also a guest scientist, the findings
are described in a paper titled “A Guest-free Germanium Clathrate”
published in Nature magazine, a scientific journal for biological
and physical sciences research.
The usual form of germanium has the same structure as a diamond,
and this new form has a beautiful and unique “cage”
structure. That is, it has a crystal structure with an open framework
having empty cages or cavities. Additionally, this new solid form
of germanium is less dense and has the uncommon property of ice
in that it floats in its own liquid.
“There is a high interest in clathrate or open-framework
semiconductors as a general class of high-tech materials,”
Guloy said. “These materials have lower densities and larger
band gaps than the usual forms of semiconductors due to their rather
open or ‘porous’ structures. Until our report, there
was no scalable and high-yield preparative technique to produce
these materials – particularly the silicon- and germanium-based
clathrate semiconductors.”
As an important semiconductor material, germanium has thousands
of applications that range from use in fiber optics communication
networks to infrared night vision systems. Anything that is computerized
or uses radio waves uses semiconductors.
“The synthesis of this new form of germanium should allow
for new avenues of research in the germanium semiconductor,”
said John Bear, dean of UH’s College of Natural Sciences and
Mathematics. “Clathrate semiconductors have significant technological
potential because they exhibit a very wide variety of materials
properties.”
Silicon (which replaced germanium in transistor radios) and germanium
form the most important semiconductors for electronic devices. However,
their classical forms exhibit small and indirect band gaps that
are not suitable for many possible optoelectronic applications that
combine light and electronics technology. This new caged form of
germanium will provide scientists useful information to design high-efficiency
thermoelectrics, gain a better understanding of superconductivity
in this class of materials and create more new materials based on
Guloy’s synthetic technique, as well as point to “the
possibility of making silicon and carbon analogs that would be even
more spectacular,” he said.
“This breakthrough has resulted in a form of germanium with
a low-density, open-caged structure and the potential to emit light,”
Guloy said. “Furthermore one cannot make this empty germanium
clathrate or ‘cage’ compound by any other means. Our
method is done at relatively mild temperatures – 300 degrees
Celsius – and being a solution technique it can easily be
scaled to prepare thin films and its other functional forms. We
have created a low-density, metastable form of germanium that has
lots of holes in it – a cage structure – and this has
been predicted to have unusual thermoelectric and optoelectronic
properties, such as the potential to emit light. All previously
known compounds with clathrate structures have something in the
cages to keep them from collapsing. It’s amazing that our
new germanium structure can be constructed even though its cages
are empty.”
This research was funded in part by the Welch Foundation and the
Petroleum Research fund. Current supporters include the National
Science Foundation, the Texas Center for Superconductivity at the
University of Houston and the Max Planck Institute for Chemical
Physics of Solids.
“It is always novel and scientifically important to find
a new form of an element that is not made naturally,” Guloy
said. “Since the material has never been made before, there
is really no designed or direct application for it yet. The synthesis
of this unusual material and the predicted properties open many
possibilities. This is similar to the preparation of the buckyball
in 1985, where researchers initially did not know what they were
good for until they were made in bulk quantities that led to subsequent
research, discovering many applications for the now-famous material.”
Bear adds that this particular synthesis of germanium allows for
the preparation of bulk material, and the scalability of the solution
method offers excellent prospects of processing clathrate semiconductors.
About the University of Houston
The University of Houston, Texas’ premier metropolitan research
and teaching institution, is home to more than 40 research centers
and institutes and sponsors more than 300 partnerships with corporate,
civic and governmental entities. UH, the most diverse research university
in the country, stands at the forefront of education, research and
service with more than 35,000 students.
About the College of Natural Sciences and Mathematics
The UH College of Natural Sciences and Mathematics, with nearly
400 faculty members and approximately 4,000 students, offers bachelors,
masters and doctoral degrees in the natural sciences, computational
sciences and mathematics. Faculty members in the departments of
biology and biochemistry, chemistry, computer science, geosciences,
mathematics and physics have internationally recognized collaborative
research programs in association with UH interdisciplinary research
centers, Texas Medical Center institutions and national laboratories.
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