Pui-tak (Peter) Leung  Professor of Physics     Office Phone: (503) 725 - 3818  Office: Room 406 Science Building 2 E-Mail: <hopl@odin.pdx.edu>

In the study of SERS, the effects of substrate temperatures and microscopic dielectric properties have been accounted for. Recent experiment has been done leading to qualitative verification of our model on SERS as a function of substrate temperature (from 100 K to 300 K). In addition we have also studied these effects at cryogenic temperatures accounting for the effects of the Pauli exclusion principle.

As a continuing effort, modeling work on the molecular fluorescence at rough and other complicated surface structures has been carried on from time to time.  We have recently proposed a relatively powerful approach to the modeling of this phenomena using the Green dyadic formulation.  In a related project, we have also been working on the surface plasmon resonance (SPR) biosensor since the collaboration first started with the Amersham International research group in England in 1989.  Our particular interest is to study the effects of the physical (optical) factors on the sensitivity of the sensor. Our goal is to look for mechanisms to increase the sensitivity of this sensor to cover the range of about 10e-9 to 10e-15 molar in concentration of the biosamples to be detected (e.g., certain specific antibodies in serum).  To this end, we have studied the possible enhancement effects using a "particle (colloidal gold) linkage technique" and the effects on the sensitivity due to the variation of temperatures in the sensing environment.

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.

Besides surface physics, we have also engaged recently in the study of energy deposition of fast particles in matter.  For this, we have applied previous results worked out in relativistic quantum mechanics concerning atomic sum rules. This represents a continuation of work in an area I first studied as a graduate student.

Most of the publications below can be retrieved from journals published by the following academic societies:

American Chemical Society
 Optical Society of America
 American Physical Society
American Insitute of Physics

For more details, see my complete  c.v.
 

 Link to an essay written in memory of my mother (in Chinese)
 

Selected Publications
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Refereed Journals (since joining PSU, 1988-)

H. Sinky and P. T. Leung, 2006 " Relativistic corrections to a generalized sum rule"
Phys. Rev. A (in press).

Leung P. T., Ni G. J., 2006 " On the singularities of the electrostatic and magnetostatic dipole fields"
Eur. J. Phys. 27: N1-N3.

R. Chang and P. T. Leung, 2006 " Nonlocal effects on the optical and molecular interactions with
metallic nanoshells" Phys. Rev. B 73: 125438.

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.

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.

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.

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.

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.

Leung P. T. 2004 " A note on the 'system-free' expressions of Maxwell's equations " Eur. J. Phys. 25: N1-N4.

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.

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.

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.

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.

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.

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.

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.

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.

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.

Leung, P. T. 1999. "Addendum : ‘Bethe stopping-power theory for heavy target atoms’ " Phys. Rev. A
60: 2562-2564; 63: 069902 (E).

Cohen S. M. and Leung P. T. 1999.  " Comment on 'Relativistic correction of the generalized oscillator strength sum
rule " Phys. Rev. A 59: 4847.

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.

Cohen S. M. and Leung P. T.  1998.  " General formulation of the semirelativistic approach to atomic sum rules. "
Phys. Rev. A 57: 4994-4997.

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.

Blacke W. L. and Leung P. T. 1997.  " Molecular fluorescence at a rough surface : the orientation effects. "  Phys. Rev. B 56: 12625-12631.

 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).

 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.

 Leung, P.T., Hider, M.H., and Sanchez, E.J. 1996.  " Surface enhanced Raman scattering at elevated temperatures. "
Phys. Rev. B. 53: 12659-12662.

 Bian, R.X., Dunn, R.D., Xie, X.S., and Leung, P.T. 1995 . " Single molecule fluorescence characteristics probed by a near-field scanning optical microscope. " Phys. Rev. Letts. 75: 4772-4775.

 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.

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.

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.

Leung, P. T. 1995. " Magnetic monopole and Poynting's theorem " Euro. J. Phys. 16: 43-44.

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.

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.

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.

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.

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.

Bodegom and Leung, P. T. 1993. " A surprising twist to a simple capacitor problem "  Euro. J. Phys. 14: 57-58.

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.

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.

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.

 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.

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.

Hider M. H. and Leung, P. T. 1991. " Frequency shifts of molecules at rough metal surfaces " Phys. Rev. B 44:
3262-3265.

 Leung, P. T. 1990. " Decay of molecules at spherical surfaces: nonlocal effects " Phys. Rev. B 42: 7622-7625.

 Leung, P. T. 1989. " Bethe stopping power theory for heavy target atoms " Phys. Rev. A 40: 5417-5419.

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.

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.

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.

Leung, P. T. and George, T. F. 1989 " Molecular spectroscopy at corrugated metal surfaces " Spectroscopy 4: 35-41.