Professor of Physics
| Office Phone: | (503) 725 - 3818 |
| Office: | SRTC Room B1-50 |
| E-Mail: | <hopl@pdx.edu> |
then...
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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
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 among the full time faculty 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!
HIGHLIGHT OF RESEARCH FINDINGS
Most of the publications below appeared in journals from the following societies/publishers :
American Chemical SocietyFor my publications in Physical Review and Physical Review
Letters, please click here
For more details, see my complete c.v.
Courses taught at
PSU (1988-2023)
Graduate
students supervised at PSU
P. T. Leung, C. W. Chen and H. P. Chiang, 2024, "
Electric response of a composite of topological insulator
nanoparticles " Chin. J. Phys. 89: 1883-1889 pdf
R. Chang, H. Y. Xie and P. T.
Leung, 2023, " Electromagnetic radiation from a
spherical static
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."
(I) 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. (I) 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. (III) 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. (II)
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. (III)
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." (III)
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. (I) 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. (II) 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. (I) 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. (II) 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. (II) 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. (II) 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." (III)
pdf
Leung P. T., Ni G. J., 2006
" On the singularities of the electrostatic and magnetostatic
dipole fields"
Eur. J. Phys. 27: N1-N3. (III) 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." (I) 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. (II)
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. (I) 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. (II) 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. (I) 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. (II) pdf
Leung P. T. 2004 " A note on the 'system-free' expressions of Maxwell's equations " Eur. J. Phys. 25: N1-N4. (III) 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. (II) 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. (II) 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." (II) 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. (II)
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." (II) 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. (II) 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." (II)
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. (II) 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. (II) 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." (III)
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." (III) 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. (II) 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." (III) 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. (II) 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." (II)
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). (II) 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. (II) 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. (II) pdf
Leung, P. T. 1995. " Magnetic monopole and
Poynting's theorem " Euro. J. Phys. 16: 43-44. (III) 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. (II) 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. (II) 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. (II) 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. (II) pdf AIPpage
Bodegom E. and Leung, P. T. 1993. " A surprising twist to
a simple capacitor problem " Euro. J. Phys. 14:
57-58. (III) 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.
(II) 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. (II) 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. (II) 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. (II) 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. (II) 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." (II)
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." (III)
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. (II) 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. (II) 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." (II) pdf