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Research Projects
Supported by HKU's High Performance Computing Facilities |
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Researcher: |
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Dr
Jian Wang, Department of Physics |
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Project Title: |
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initio Calculation on Transport Properties of Molecular and Nano Devices |
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Project Description: |
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In this project, we investigate
the current-voltage characteristics and the shot noise spectrum of various
molecular devices based on carbon nanotubes using the first principle
calculation. In the ac case, we investigate the photon assisted tunneling
through carbon nanotube based devices using the non-equilibrium Green’s
function approach. We also study the frequency dependent shot noise of
carbon nanotube based devices. Finally, the adiabatic quantum pumping and
photovoltaic effect is studied. |
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Project Duration: |
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Three years |
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Project
Significance: |
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Besides the interest from the
fundamental science, another driving force of nano science is the potential
device applications. We know that many of our daily electrical appliances
consist of transistors as basic components. The first transistor is made in
1941 whose size is about one cubic cm. Due to the advance of modern
technology, the size of transistor that one can make becomes smaller and
smaller. In 1991, a computer chip of size one cubic cm contains about three
million transistors. The dimension of the transistor in the computer chip
will reach 130 nm in the near future. In such a small length scale, previous
traditional technology of fabricating transistor can no longer be used. New
nano technology has to be developed. More importantly, new physical laws
will emerge in such a small dimension. Our project is aimed to investigate
new principles in transport related phenomena through molecular and nano
devices from the first principle calculation, i.e., ab initio calculation. |
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Results
Achieved: |
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We have studied spin-valve effect
for the carbon nanotube based magnetic tunnel device and found a large
magnetoconductance ratio up to 20% for metallic armchair tubes. The magnetic
tunnel junctions are found to have distinctly different transport behavior
depending on whether or not the length of the tubes is commensurate with a
3N+1 rule, with N the number of basic carbon repeat units along the nanotube
length. The dynamic conductance of carbon nanotubes was investigated for the
first time using the non-equilibrium Green’s function formalism. Because of
the induced displacement currents, the dynamic conductance of the nanotubes
differs significantly from the dc conductance displaying both capacitive and
inductive responses. We have calculated the ac response of an Al atomic wire
junction in the tunneling regime using non-equilibrium Green’s function
approach. The ac response is found to be determined by the average channel
transmission weighted by the corresponding density of states. |
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Remarks on the
Use of High Performance Computing Cluster: |
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The project involves very
demanding numerical calculations which is impossible to carry out without
high performance computer facilities. |
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Email Address: |
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jianwang@hkusub.hku.hk |
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