Professor of Physics
| Office Phone: | (503) 725 - 3818 |
| Office: | SRTC Room B1-50 |
| E-Mail: | <hopl@pdx.edu> |
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| Pui-Tak (Peter) Leung Professor of Physics
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On Research: when research cannot be measured with "the shock from a discovery"; "the excitement from a breakthrough"; "the realization of an imaginative idea"...; you measure it with money!
On Teaching: you can only become a successful teacher when you feel more joy in bringing up others than in bringing up yourself!
On Doing Physics: if I can survive in a Physics Department only by not doing physics, I'd rather become a patent officer!
We are at present the only
research group in theoretical physics among the full
time faculty in the department. It
is of interest to recall a survey conducted by the magazine “Physics
World” at the turn of the new century (http://physicsworld.com/cws/article/print/851)
for the nomination of the greatest physicists ever lived.
Among the top 10 greatest ones, only
Well, we are still in the game, doing (and enjoying) theoretical research in the following three areas: plasmonics, surface optics, and fundamental physics. In particular, our latest efforts have been focused on the optical properties of metallic nanostructures. Thus we have divided into the following research engagements:
Plasmonics: we have been
studying the possibly novel optical properties of metallic nanoparticles and
nanoshells. These properties originated mainly
from the localized collective excitation of the free electrons
at the particle surfaces (surface plasmon excitation). These excitations can lead to very strong
local evanescent fields which can be applied to various spectroscopy
and sensor technologies. Our interest
is mainly in the possible quantum effect on these excitations as
the metallic structure gets to ultra-small sizes (below ~ 10 nm). While such dimensions are small enough for one
to start worrying about possible quantum effects, they still require
huge amount of computation starting with the Schrodinger equation
for the system. To compromise, we have
adopted a phenomenological approach using the formulations from
nonlocal optics. We have also applied our
results to study possible novel spectroscopic features such as those
from surface enhanced Raman scattering (SERS) from metallic nanoshells. Our work is in collaboration with people at
the National Taiwan University (http://pnstl.phys.ntu.edu.tw/)
and the
Other novel optical phenomena at metallic surfaces have also been studied from time to time. One interesting discovery from our recent study is the possibility of observing very large backward lateral displacement of the incident beam (known as negative Goos-Hanchen shift) at a vacuum-metal interface. Possible application of this displacement to optical sensing was also explored.
Another collaboration took place in 1991 with the IBM (Almaden) group in the study of the laser cleaning technique of contaminated surfaces. In this technique, a liquid layer (microns thick) is deposited on the surface and exploded by the fast heating of an excimer laser pulse (~20 ns). This project has since been completed by the IBM group, although we still keep our interest alive on the study of optothermal effects from the interaction of a solid surface with a laser pulse.
Fundamental Physics: It will be extremely short-sighted if one ignores completely
fundamental studies simply because of the so-called "funding
opportunities" in the "applied fields". In my opinion,
both for educational purpose and from the lessons we have
learned by studying the various evolutions in science and developments
in technology, the prime significance of fundamental studies is
obvious. For example, without Faraday's fundamental studies,
no electrical power would have ever been generated; without Maxwell's
theory, no wireless EM technology would ever have been developed;
without J.J. Thomson's discovery of the electron, the whole
"electronics industry" would have never existed; without Dirac's study
on Relativitiy and QM, no PET would have ever been operated in any hospital;
without de Broglie's insight into the dual nature of matter, no electron
microscopy would have ever been possible; without Newton's fundamental
study of motion, people would have never landed the moon; without Einstein's
deep insight into the relativity of motion, the technology of nuclear
energy would have never been possible; without the development of QM,
more than half of the modern technologies would have never existed;
... ; without teaching students enough fundamentals, they will
be graduating just like many technicians trained from various vocational
schools! Thus to maintain the only study in fundamental physics
in our department, we have been active recently in various areas including:
reciprocity symmetry in optics and quantum mechanics; certain apparently
incompatible issues in relativity and QM (the relativistic sum rules);
the consequences of having a finite photon mass; and some fundamental
issues in the teaching of classical electromagnetism. It is a lot
of fun -- without the need of much fund!
For the importance of fundamental research, read also an article by Carl Sagan, as well as comments
by the Nobel chemist Ahmed Zewail.
Most of the publications below appeared in journals from the following societies/publishers :
American Chemical Society
Optical
Society of America
American
Physical Society
American
Insitute of Physics
Institute
of Physics
Elsevier
For my publications in Physical Review and Physical Review Letters, please
click here
For more details, see my complete c.v.
Graduate students
supervised at PSU
Link to a poem: The stock market and the structure
of matter
Link to an essay written in memory of
my mother (in Chinese)
Publications
H. Y. Chung,
G. Y. Guo, H. P. Chiang, D. P. Tsai, and P.
T. Leung, 2010 “ Accurate description of the
optical
response of a multilayered spherical
system in the long wavelength approximation ” Phys.
Rev. B 82: 165440
"Copyright
(2010) by the American Physical Society."pdf
H. Y. Chung,
P. T. Leung, and D. P. Tsai, 2010 “ Enhanced intermolecular energy
transfer in the vicinity of a
plasmonic nanorice ” Plasmonics 5: 363-368. pdf
H. Y. Xie, P. T. Leung and D. P. Tsai, 2009 " Clarification and extension of the
optical reciprocity
theorem " J. Math. Phys.
50: 072901. pdf AIPpage
H. Y. Xie, P. T. Leung
and D. P. Tsai, 2009 " Molecular
decay rates and emission frequencies in the
vicinity of an anisotropic metamaterial"
Solid
State Commun. 149: 625-629.
pdf
H. Y. Xie, P. T. Leung,
and D. P. Tsai, 2009 " General proof of optical reciprocity for
nonlocal electrodynamics "
J. Phys.
A .42: 045402. pdf
H. Y. Xie, P. T. Leung,
and D. P. Tsai, 2008 " General validity
of reciprocity in quantum mechanics"
Phys. Rev.
A 78: 064101 "Copyright
(2008) by the American Physical Society." pdf
C. W. Chen, H.-P. Chiang, P. T. Leung, and D. P. Tsai, 2008 " Temperature dependence of enhanced
optical absorption and Raman spectroscopy
from metallic nanoparticles " Solid State
Commun 148: 413-416. pdf
Z. E. Goude and P. T. Leung, 2007 " Surface Enhanced Raman Scattering
from
Metallic Nanoshells with Nonlocal
Dielectric Response" Solid State Commun 143:
416-420. pdf
C. W. Chen, C. H. Lin, H. P. Chiang, Y. -C. Liu, P. T. Leung and
W. S. Tse, 2007
"Temperature Dependence of the Sensitivity
of a Long-Range Surface Plasmon Optical
Sensor" Applied Phys
A 89: 377-380. pdf
C.-W. Chen, W.-C. Lin, L.-S. Liao, Z.-H. Lin, H.-P. Chiang, P. T. Leung,
E. Sijercic
and W. S. Tse, 2007 "Optical
Temperature Sensing Based on the Goos-Hanchen Effect"
Applied Optics 46:
5347-5351. pdf
P. T. Leung, C..W. Chen and H.-P. Chiang, 2007 "Large
negative Goos-Hanchen shift at
metal surfaces" Optics Commun
276: 206-208. pdf.
Experimental observation had verified this
effect two months after our paper
appeared. See experimental verification
H.P. Chiang, C. W. Chen, J. J. Wu, H. L. Li, T. Y. Lin , E. J. Sanchez
and P. T. Leung, 2007
"Effects of
temperature on the surface plasmon resonance at a metal-semiconductor
interface"
Thin Solid Films 515:
6953-6961. pdf
H. Sinky and P. T. Leung,
2006 " Relativistic corrections to a generalized
sum rule"
Phys.
Rev. A 74: 034703. "Copyright (2006)
by the American Physical Society." pdf
Leung P. T., Ni G. J., 2006 " On the
singularities of the electrostatic and magnetostatic dipole
fields"
Eur.
J. Phys. 27: N1-N3. pdf
R. Chang and P. T. Leung, 2006 " Nonlocal
effects on the optical and molecular interactions with
metallic nanoshells"
Phys. Rev. B 73: 125438; ibid
75:079901(E). "Copyright
(2006) by the American Physical Society." pdf
H. P. Chiang, J. L. Lin, R. Chang, Z. W. Chen and
P. T. Leung, 2005 " High resolution angular
measurement using
surface-plasmon-resonance
heterodyne interferometry at optimal incident wavelengths
" Proc. SPIE vol. 6002, 600218: 1-10. pdf
R. Chang and P. T. Leung, 2005 " Theoretical
study of nonloal effects in the optical response of
metallic nanoshells"
Proc. SPIE
vol. 6002, 60020V: 1-10. pdf
Chiang H. P., Lin J. L., R. Chang, Su S. Y. and
Leung P. T., 2005 " High resolution angular measurement using
surface-plasmon-resonance
via phase interrogation at optimal incident wavelengths
" Opt. Lett. 30: 2727-2729. pdf
Chang R, Chiang H. P., Leung P. T., Tsai
D. P. and Tse W. S., 2005 " Nonlocal effects in the optical
response of composite
materials with
metallic nanoparticles " Solid State Commun. 133:
315-320; ibid. 137: 343. pdf
Chiang H. P., Yeh H. T., Chen C. M., Wu J. C., Su
S. Y., Chang R., Wu Y. J., Tsai D. P., Jen S. U.,
and
Leung P.
T., 2004" Surface plasmon resonance monitoring
of temperature via phase measurement" Optics
Commun.
241: 409-418.
pdf
Leung P. T. 2004 " A note on the 'system-free' expressions of Maxwell's equations " Eur. J. Phys. 25: N1-N4. pdf
Chang R., Chiang H. P., Leung P. T., and
Tse W. S. 2003 " Nonlocal electrodynamic effects in the optical excitation
of the surface
plasmon resonance " Optics Commun. 225:
353-361. pdf
Chiang H. P., Wang Y. C., and Leung P. T. 2003 " Effect
of temperature on the incident angle-dependence of
the sensitivity for surface plasmon
resonance spectroscopy " Thin Solid Films,
425: 135-138. pdf
Hider M. H. and Leung P. T. 2002 "
Nonlocal electrodynamic modeling of fluorescence characteristics
for
molecules in
a spherical cavity " Phys. Rev. B, 66: 195106.
"Copyright
(2002) by the American Physical Society." pdf
Chiang H. P., La Rosa A. H., Leung P. T.,
Li K. P., and Tse W. S. 2002 " Optical spectroscopy
for
single-molecules
near a microstructure at varying substrate temperatures
" Optics Commun. 205: 343-350. pdf
Hartman R. L. and Leung P. T. 2001. " Dynamical theory for modeling
dipole-dipole interactions in
a microcavity: The Green dyadic
approach " Phys. Rev. B, 64: 193308. "Copyright
(2001) by the American Physical Society." pdf
Chiang H. P., Wang Y. C., Leung P. T. and Tse W. S. 2001
." A theoretical model for the temperature-
dependent sensitivity of the optical
sensor based on surface plasmon resonance " Optics
Commun. 188: 283-289. pdf
Chang R., Leung P. T., Lin S. H. and Tse W. S. 2000. " Surface-enhanced
Raman scattering at cryogenic substrate temperatures"
Phys. Rev. B 62: 5168-5173. "Copyright (2000)
by the American Physical Society." pdf
Hartman R. L., Leung P. T. and Cohen S. M. 2000. " Molecular
fluorescence in the vicinity of a gradient-index
medium " J. Opt. Soc. Am. A
17: 933-936. pdf
Chiang H. P., Leung P. T. and Tse W. S. 2000. " Remarks
on the substrate-temperature dependence of surface-enhanced Raman scattering
" J. Phys. Chem. B 104: 2348-2350.
pdf
Leung, P. T. 1999. "Addendum : ‘Bethe stopping-power theory
for heavy target atoms’ " Phys. Rev. A
60: 2562-2564; 63: 069902 (E). "Copyright
(1999) by the American Physical Society." pdf
Cohen S. M. and Leung P. T. 1999. " Comment on 'Relativistic
correction of the generalized oscillator strength sum
rule " Phys. Rev. A
59: 4847. "Copyright (1999)
by the American Physical Society." pdf
Hartman, R. L., Cohen S. M. and Leung P. T. 1999.
" A note on the Green dyadic calculation of the decay
rates for admolecules at multiple planar interfaces. " J.
Chem. Phys. 110: 2189-2194. pdf AIPpage
Cohen S. M. and Leung P. T. 1998. " General
formulation of the semirelativistic approach to atomic sum rules. "
Phys. Rev. A 57: 4994-4997.
"Copyright (1998)
by the American Physical Society." pdf
Chiang H. P., Leung P. T. and Tse W. S. 1998. " The surface
plasmon enhancement effect on adsorbed molecules at elevated
temperatures. " J. Chem. Phys. 108: 2659-2660.
pdf AIPpage
Blacke W. L. and Leung P. T. 1997. " Molecular fluorescence
at a rough surface : the orientation effects. "
Phys. Rev. B 56: 12625-12631.
"Copyright (1997) by
the American Physical Society." pdf
Leung, P.T. 1997. " Emission frequency of single molecules
at a metallic aperture: the applicability of the image
theory. "
Optics Commun. 136:
360-364; 139: 336 (E). pdf
Chiang, H.P., Leung, P. T. and Tse, W.S. 1997. “ Optical
properties of composite materials at high temperatures
”
Solid State Commun.
101: 45-50. pdf
Leung, P.T. and Tse, W.S. 1995. " Non-local electrodynamic
effect on the enhancement factor for surface enhanced Raman
scattering. " Solid State Commun.
95: 39-44. pdf
Xiong, T., Leung, P. T. and George, T. F. 1995. “ Modeling
of decay rates for molecules at an island surface ” J.
Chin. Chem. Soc. 42 : 249-254. pdf
Leung, P. T. and George, T. F. 1995 " Molecular Fluorescence
Spectroscopy in the Vicinity of a Microstructure." J.
de Chim. Phys. (France) 92: 226-247. pdf
Leung, P. T. 1995. " Magnetic monopole and Poynting's theorem
" Euro. J. Phys. 16: 43-44. pdf
Leung, P. T., Pollard-Knight, D., Malan, G. P. and Finlan,
M. F. 1994. " Modeling of particle-Enhancement Sensitivity
of the Surface-Plasmon-Resonance Biosensor. " Sensors
and Actuators B 22:175-180. pdf
Pliska, M. J., Sanzhez, E. D., Leung, P. T. and George, T. F. 1994.
" Effect of Particle-Clustering on Decay Rates of Admolecules
at the Interface of a Composite Material Substrate. " Solid
State Common. 89: 397-401. pdf
Do, N., Klees, L., Tam, A. C., Leung, P. T. and Leung, W. P. 1993.
" Photodeflection Probing of the Explosion of a Liquid
Film in Contact with a Solid Heated by Pulsed Excimer Laser
Irradiation. " J. App. Phys. 74:1534-1538. pdf AIPpage
Park, H. K., Xu, X., Grigoropoulos, C. P., Do, N., Klees, L., Leung,
P. T. and Tam, A. C. 1993. " Transient optical
transmission measurement in excimer-laser irradiation of
amorphous silicon films " J. Heat Transfer 115:
178-183. pdf
Leung, P. T. and Hider, M. H. 1993. " Nonlocal Electrodynamic Modeling of Frequency Shifts of Molecules at Rough Metal Surfaces." J. Chem. Phys. 98:5019-5022. pdf AIPpage
Bodegom E. and Leung, P. T. 1993. " A surprising twist to a simple
capacitor problem " Euro. J. Phys. 14:
57-58. pdf
Yavas, O., Do, N., Tam, A. C., Leung, P. T., Leung, W. P., Park,
H. K., Grigoropoulos, C. P., Boneberg, J and Leiderer,
P. 1993. " Temperature dependence of optical properties
for amorphous silicon at wavelengths of 632.8 and 752 namometer
" Opt. Lett. 18: 540-542. pdf
Tam, A. C., Do, N, Klees, L., Leung, P. T. and Leung, W. P. 1992.
" Explosion of a liquid film in contact with a pulse-heated
solid surface detected by the probe-beam deflection method
" Opt. Lett. 17: 1809-1811. pdf
Leung, P. T., Do, N., Klees, L., Leung, W. P., Tong, F., Lam, L.,
Zapka, W. and Tam, A. C. " Transmission Studies of
Explosive Vaporization of a Transparent Liquid Film on an
Opaque Solid Surface Induced by Excimer-Laser-Pulsed Irradiation."
1992 J. Appl. Phys.72: 2256-2263. pdf AIPpage
Park, H. K., Xu, X, Grigoropoulos, C. P., Do, N, Klees, L, Leung,
P. T., and Tam, A C. 1992. " Temporal
profile of optical transmission probe for pulsed-laser heating
of amorphous silicon films " App. Phys. Lett.
61: 749-751. pdf AIPpage
Do, N., Klees, L, Leung, P. T., Tong, F, Leung, W. P. and Tam, A. C. 1992. " Temperature dependence of optical constants for amorphous silicon " App. Phys. Lett. 60: 2186-2188. pdf AIPpage
Hider M. H. and Leung, P. T. 1991. " Frequency shifts of molecules
at rough metal surfaces " Phys. Rev. B 44:
3262-3265.
"Copyright (1991) by
the American Physical Society." pdf
Leung, P. T. 1989. " Bethe stopping power theory for heavy
target atoms " Phys. Rev. A 40: 5417-5419.
"Copyright (1989) by
the American Physical Society." pdf For experimental
evidence, see experiment (1) experiment (2)
Leung, P. T., Kim, Y. S. and George, T. F. 1989 " Photochemistry
at corrugated thin metal films : a phenomenological
approach " SPIE Conference Proceeding 1056:
139-146. pdf
Leung, P. T., Kim, Y. S. and George, T. F. 1989 " Photoabsorption
of molecules at corrugated thin metal films."
J. Chem. Phys. 90:
7472-7477. pdf AIPpage
Leung, P. T., Kim, Y. S. and George, T. F. 1989 " Decay
of molecules at corrugated thin metal films "
Phys. Rev. B 39: 9888-9893.
"Copyright (1989)
by the American Physical Society." pdf
Leung, P. T. and George, T. F. 1989 " Molecular spectroscopy
at corrugated metal surfaces " Spectroscopy 4:
35-41. pdf