Inorganic Solids with Remarkable
Electronic Properties
by John Emsley
Chemistry
Top Ten Papers
Rank
Papers
Cites
May-Jun 08
Rank
Mar-Apr 08
1
S. Stankovich, et al.,
"Graphene-based composite materials,"
Nature, 442(7100): 282-6, 20
July 2006. [Northwestern U., Evanston,
IL; Purdue U., West Lafayette, IN]
*064WT
21
3
2
Y. Kamihara, et al.,
"Iron-based layered superconductor
La[O1-xFx]FeAs (x
= 0.05-0.12) with Tc = 26
K," J. Am. Chem. Soc.,
130(11): 3296-7, 19 March 2008. [Tokyo
Inst. Technol., Yokohama, Japan] *273SL
20
†
3
X.D. Wang, et al.,
"Direct-current nanogenerator driven by
ultrasonic waves," Science,
316(5821): 102-5, 6 April 2007.
[Georgia Inst. Tech., Atlanta] *153XD
16
†
4
J.G. Hill, J.A. Platts, H.J. Werner,
"Calculation of intermolecular
interactions in the benzene dimer using
coupled-cluster and local electron
correlation methods," Phys. Chem.
Chem. Phys., 8(35): 4072-8, 21
September 2006. [Cardiff U., U.K.; U.
Stuttgart, Germany] *078NA
15
†
5
J.E. Green, et al., "A
160-kilobit molecular electronic memory
patterned at 1011 bits per
square centimetre," Nature,
445(7126): 414-7, 25 January 2007.
[Caltech, Pasadena; U. Calif., Los
Angeles; Ohio St. U., Columbus] *128WD
13
10
6
M. Dinca, et al., "Hydrogen
storage in a microporous metal-organic
framework with exposed Mn2+
coordination sites," J. Am. Chem.
Soc., 128(51): 16876-83, 27
December 2007. [6 U.S. institutions]
*118KQ
13
†
7
L. Venkataraman, et al.,
"Dependence of single-molecule junction
conductance on molecular conformation,"
Nature, 442(7105): 904-7, 24
August 2006. [Columbia U., New York,
NY] *076LT
12
2
8
N.J.A. Martin, B. List, "Highly
enantioselective transfer hydrogenation
of a,ß-unsaturated ketones,"
J. Am. Chem. Soc., 128(41):
13368-9, 18 October 2006. [Max Planck
Inst. Coal Res., Mulheim, Germany]
*093GZ
12
†
9
S. Hoffmann, M. Nicoletti, B. List,
"Catalytic asymmetric reductive
amination of aldehydes via dynamic
kinetic resolution," J. Am. Chem.
Soc., 128(40): 13074-5, 11 October
2006. [Max Planck Inst. Coal Res.,
Mulheim, Germany] *091LP
12
†
10
P. Jurecka, et al., "Density
functional theory augmented with an
empirical dispersion term. Interaction
energies and geometries of 80
noncovalent complexes compared with
ab initio quantum mechanics
calculations," J. Comput.
Chem., 28(2): 555-69, 30 January
2007. [U. Calgary, Canada; Acad. Sci.
Czech Rep., Prague] *122PK
Hot chemistry papers #2 and #3 reveal unexpected features in two kinds of
inorganic materials. Paper #2 shows that lanthanum oxide iron arsenide
(LaOFeAs) is a remarkable superconductor, overturning a misconception that
iron was an element to be avoided in making such materials. Paper #3
reports how the electricity for a nanogenerator can be produced from
ultrasonic waves. Humans dissipate energy in many forms, and the author of
#3 believes that we might one day garner this to power nanodevices.
Paper #2 is a collaborative effort by a group at the Tokyo Institute of
Technology headed by Yoichi Kamihara. Their LaOFeAs was prepared by heating
pure samples of lanthanum and iron arsenides with lanthanum(III) oxide at
1200° C for 40 hours in a silicon tube under an atmosphere of argon
gas. A fluoride-doped version was also made, and it is this which has an
increased superconductivity, displaying this property at temperatures as
high as 26K. Samples of calcium-doped material were also produced, and
while this element adds "holes" to the structure it does not produce a
superconductor, and clearly it is the fluoride’s extra electron which
is the source of the observed superconductivity.
Just below the Hot Ten list is paper #12, also from the same stable as #2
(Y. Kamihara, et al., J. Am. Chem. Soc., 128[31]:
10012-3, 2006; 12 citations this period). This was an earlier paper and
concerned LaOFeP and its fluoride-doped version, although this was only
superconducting below 3K. Replacing phosphorus with arsenic has transformed
its ability to act this way.
Equally fascinating is the discovery reported in paper #3. This work comes
from a group led by Zhong Lin Wang of the Georgia Institute of Technology.
Wang is no stranger to the pages of Science Watch; his zinc oxide
"nanowindmills" were featured in the edition for
July/August 2003 (14[4]: 7, 2003). The new highly
cited paper reports a device that responds to ultrasound by generating
electricity and which in theory could power devices such as in
vivo biosensors and nano-robots without the need for a battery.
The new device consists of an array of zinc oxide nanowires grown from a
thin layer of zinc oxide on the surface of gallium nitride. Positioned
above them was a "zigzag" electrode, consisting of parallel trenches etched
onto a silicon wafer and which was then covered with a thin layer of
platinum. The gap between the nanowires and the zigzag electrode was
adjusted so that some wires were in contact and some are able to make
contact when they are caused to bend or vibrate by ultrasound. As they
brush against the electrode they generated a current of around 0.15 nA with
a voltage of 0.7 mV, although Wang says they have recently increased output
to 600 nA at 12 mV. The current was stable for more than an hour and could
be switched on and off as required. Modifications to the device, in the
form of a flat electrode in place of the zigzag one, or replacing the zinc
oxide nanowires with carbon nanowires, resulted in no current generation.
One day it might be possible for nanogenerators to glean energy from their
surroundings, from the sound of footsteps, or a beating heart, or even the
rustle of clothes, and turn this into electrical energy. Says Wang: "It is
important to explore innovative technologies that work at low frequency
range (such as < 10 Hz) and are based on flexible soft materials."
A step in this direction is Wang’s fiber-based nanogenerator reported
in Nature, 451(7180): 809-13, 2008. This paper demonstrates how to
convert low-frequency vibration/friction energy into electricity using
piezoelectric ZnO nanowires grown on textile fibers. As the nanorods brush
against the fibers the mechanical energy is converted into electricity via
a piezoelectric-semiconductor process.
Wang tells Science Watch that he is now trying to optimize the
growth of the nanowire arrays in a way that will maximize the generation of
electricity. The object is to raise the output voltage to more than 0.5 V
so that it can be used for practical applications. "My research goal is to
make self-powered nanosystems which can operate wirelessly, independently,
and sustainably, while harvesting their energy from the environment."
What might once have seemed an impossible dream could well become a reality
is a few years’ time.
Dr. John Emsley is based at the Department of Chemistry, Cambridge
University, U.K.
Keywords: carbon nanotubes, Olgica Bakajin, Aleksandr Noy, carbon nanotube
pores, water desalination, fast mass transport.