Essential Science IndicatorsSMfrom
Reuters, the paper currently ranked at #1 among
Materials Science papers published in the past decade
is "Room-temperature ultraviolet nanowire nanolasers"
(Huang, MH, et al., Science 292: 1897-9,
8 June 2001), with 2,849 citations to its credit up to
February 28, 2009.
The chief researcher behind this paper is Dr.
Peidong Yang. Dr. Yang's record in the database
includes 139 papers, mainly classified under either
Materials Science or Chemistry, cited a total of 18,814
times. He is also aHighly Cited Researcherin Materials Science. Dr. Yang is the Miller
Professor of Chemistry at the University of
California, Berkeley, where he heads up his own
research group. He is also an Associate Editor for
the Journal of the American Chemical Society.
In the interview below,
ScienceWatch.com talks with Dr. Yang about this paper
and its impact on the nanowire research
What factors led you to research room-temperature
Back in 1999, my research group at Berkeley initiated a research program
centered around semiconductor nanowires. This program was about developing
chemical processes for the rational synthesis and assembly of semiconductor
nanowires and exploring their fundamental physical properties. My first
postdoc fellow, Dr. Michael Huang (now a Chemistry Professor at National
Tsinghua University, Taiwan), developed a simple vapor condensation process
for the production of zinc oxide (ZnO) nanowires on substrates such as
silicon. This nanowire growth process was first published in Advanced
Materials in 2001 (Huang MH, et al., "Catalytic growth of
zinc oxide nanowires by vapor transport," 13: 113-6, 16 January 2001).
This paper is now also one of the highly cited papers in the nanowire
Having a research background in epitaxial oxide thin-film growth during my
Ph.D. training, a very natural next step was to examine the possibility of
growing ZnO nanowires on an epitaxial substrate such as sapphire. This
turned out to be a stunning success. Michael’s first trial on
nanowire growth on sapphire substrate yielded beautifully oriented,
high-density, uniform ZnO nanowire arrays.
These nanowires have a perfect hexagonal cylindrical shape with atomically
smooth side and end facets. The diameters of these nanowires are typically
in the range of 80-200 nm. At the time, we realized that these hexagonal
nanowires bear striking similarities to the conventional macroscopic laser
cavity—only in this case, it is a much smaller nanoscopic version.
This led to the first discovery of room-temperature UV nanowire nanolasers.
Would you sum up the paper—your methods, findings,
The 2001 Science paper on nanowire nanolasers reported the growth
of high-quality, uniform ZnO nanowire arrays by combining a typical
vapor-phase nanowire growth process with another common thin-film growth
technique: epitaxy. The resulting nanowires have a perfect hexagonal
cylindrical shape with atomically smooth side and end facets. The diameters
of these nanowires are typically in the range of 80-200 nm. Since ZnO is a
wide-bandgap material emitting in UV region and also has a relatively high
refractive index, we reasoned that it is very much likely that these
hexagonal nanoscopic cylinders could serve as a sub-wavelength laser cavity
in the UV region (below 400 nm).
We went ahead and tested the idea using an optical pumping approach. We
used the 4th harmonic output of a Nd:YAG laser (266 nm) as the
excitation source and have clearly demonstrated that these highly oriented
ZnO nanowire arrays indeed serve as an excellent nanoscopic laser cavity
with a lasing wavelength of 380 nm. This is the first report of using
semiconductor nanowires as a nanoscopic Fabry-Perot laser cavity.
How was the paper received by the community?
This paper has been very well received by the community, judging by the
large number of citations in the past decade. In retrospect, this work
could be considered as one of the milestones in the nanowire research
field. Back in 1999-2000, only very few research groups had concentrated
efforts on nanowire research. Since nanowire research was still at its
early stage, much of the research efforts at that time were targeted for
rational growth and assembly, not so much on functionalities.
The discovery of lasing in semiconductor nanowires led to a flurry of
research into photonic properties of nanowires. For example, the
nanowire lasing concept was later quickly adopted in many other nanowire
materials, including CdS and InSb, with lasing wavelengths spanning from
UV to IR. By now, nanowire photonics has become a very important
subfield within the nanowire research community.
You mention the potential applications in the
paper—have any of them been realized?
After our first discovery of UV lasing in ZnO nanowires, several other
research groups quickly demonstrated lasing in other material systems with
lasing wavelength from UV to IR. In addition, this research has further
evolved into a much larger research effort along the line of nanowire
photonics, with a purpose of miniaturizing optical devices using nanowires
as potential building blocks.
The development of these nanoscopic light sources could be very important
for applications such as data storage and optical computing, as well as
on-chip chemical/biological detection. At this point, the sensing
application seems to be most promising, part of which has already been
demonstrated in my lab (See Sirbuly DJ, et al., "Multifunctional
nanowire evanescent wave optical sensors,"
Adv. Mater. 19: 61+, 8
January 2007 and Sirbuly DJ, et al., "Optical routing and sensing
with nanowire assemblies," Proc. Nat.
Acad. Sci. 102: 7800-5, 31 May 2005).
Where have you taken this work since 2001, and where do
you hope to take it in the next several years?
"The discovery of lasing in
semiconductor nanowires led to a flurry of
research into photonic properties of
Since the first nanowire laser report in 2001, we have devoted significant
effort to understanding the optical processes at the single nanowire level.
This has led to several important pieces of work within the field,
including, for example, the demonstration of subwavelength waveguiding in a
single nanowire (See Law M, et al., "Nanoribbon waveguides for
subwavelength photonics integration," Science,
305: 1269-73, 27 August 2004); non-linear optical mixing within a
single nanowire (Nakayama Y, et al., "Tunable nanowire nonlinear
optical probe," Nature, 447: 1098-U8, 28 June 2007).
All of these studies represent important steps towards a functional,
integrated photonic system using our nanowire building blocks. I believe
that these subwavelength structures represent a new class of semiconductor
materials for investigating light generation, propagation, detection,
amplification, and modulation.
For the near future, I believe that there are two very important directions
for this research. First, these single crystalline oxide or nitride
nanowires could be used for the development of high-efficiency
light-emitting devices with different wavelengths, including white light
sources. Secondly, at the single-nanowire level, these nanoscopic light
sources could be used to probe individual living cells in a non-invasive
manner. Such single-cell endoscopy will rely on the use of these nanoscopic
light sources and allow us to monitor in-vivo biological processes
within single living cells with high spatial resolution.
Department of Chemistry
Department of Materials Science and Engineering
University of California, Berkeley
Berkeley, CA, USA
Peidong Yang is a Professor of Chemistry at the
University of California, Berkeley. In this podcast interview,
he discusses his lab’s interdisciplinary research in
semiconductor nanowires. Yang is a
Current Classics scientist (Mat. Sci.)
from Apr. 2008.