N. Ravishankar & Aditi
Halder talks with ScienceWatch.com and answers a
few questions about this month's Emerging Research Front
Paper in the field of Materials
Science.
Article: Ultrafine single-crystalline gold nanowire
arrays by oriented attachment
Authors: Halder,
A;Ravishankar,
N
Journal: ADVAN MATER, 19 (14): 1854-+ JUL 16 2007
Addresses: Indian Inst Sci, Mat Res Ctr, Bangalore 560012,
Karnataka, India.
Indian Inst Sci, Mat Res Ctr, Bangalore 560012, Karnataka,
India.
Why do you think your paper is highly
cited?
Our paper addresses a very fundamental problem in nanostructure growth
relating to the formation of single-crystalline wires of a high-symmetry
material. The problem is one of selecting one crystallographic
direction/facet for growth over several equivalent directions/facets in the
structure. This is what is technically called symmetry-breaking.
Although 1-D structures with twin defects that cause the symmetry breaking
had been synthesized earlier, we were the first ones to demonstrate a means
to achieve symmetry breaking to grow long, single-crystalline,
molecular-scale Au wires without using any template.
The mechanism that we demonstrated is general (not reagent-specific) and
can be extended to other systems. Importantly, it gives experimentalists
access to high-quality wires of molecular dimensions (< 2 nm diameter)
for the first time. These are absolutely fantastic model systems to test
out several important theoretical predictions, e.g., stability of and
transport through such wires and their possible use as interconnects for
nanoelectronics applications.
Does it describe a new discovery, methodology, or
synthesis of knowledge?
Coauthor
Aditi Halder
Our work describes the discovery of a new synthesis method and mechanism
that is general and widely applicable. It brings together a variety of
concepts relating to the interaction of capping agent with different
crystallographic facets in crystals, possibility of selective removal of
such capping agents using simple chemistry and the concept of sintering of
particles that ultimately provides the symmetry-breaking needed for the
growth of the wires.
Would you summarize the significance of your paper in
layman's terms?
We have a method to make the thinnest single-crystalline Au wires ever made
with a very high aspect ratio with relatively few defects. The best efforts
before that produced wires that were typically about five times thicker,
10-100 times shorter, and had a higher defect density.
To put it in perspective, if we were to scale our wires to a macroscopic
gold chain, approximately 2 mm thick, it would be about 2 meters long. The
reason this is interesting is that the wire is a single crystal with no
high-angle grain boundaries.
Theoretical studies predict high stability and exotic transport behavior
through such wires. Our synthesis method provides the first-time
opportunity to investigate the properties of such thin wires that also have
several potential applications in nanoelectronics, sensors, and catalysis,
to name a few.
How did you become involved in this research and were
any particular problems encountered along the way?
Our group has been interested in understanding the mechanisms of formation
of nanostructures as one of the major themes and particularly schemes to
induce symmetry breaking to produce anisotropic nanostructures. We have
been investigating templateless methods to synthesize nanowires and also
methods for synthesis of plate-shaped structures.
Our research effort has led to the development of morphology diagrams to
predict the conditions for formation of plate-shaped structures for the
first time (Nanotechnology, 2008; Biomaterials 2008;
J. Colloid Interface Sci., 2009; J. Phys. Chem. C, 2009) and,
in addition, symmetry-breaking schemes for the formation of wires. Our
approach has been to apply and combine principles available from other
related fields to understand mechanisms of nanostructure nucleation and
growth.
Where do you see your research leading in the
future?
We anticipate wide use of our method and also newer methods based on our
idea for the synthesis of ultrathin wires of Au and other metals/alloys.
The possibility of direct measurement of transport through such wires will
lead to critical evaluation of existing theories of electrical and thermal
transport through such wires and possibly even lead to some newer and
unexpected experimental observations.
On the application front, these wires could become the preferred
interconnects of the future, due to their higher stability against
electromigration, for instance. The possibility of formation of alloy wires
and hybrids will further multiply the areas in which these wires will find
applications.
Do you foresee any social or political implications for
your research?
We foresee advances in theoretical and experimental understanding of
transport behavior through molecular scale wires and the use of such wires
as fundamental building blocks for a variety of applications.
N. Ravishankar
Associate Professor
Materials Research Center
Indian Institute of Science
Bangalore, India Web
Aditi Halder
Ph.D. Student
Materials Research Center
Indian Institute of Science
Bangalore, India