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Molecular orbital imaging


Dr. Xiaowei Fan getting ready to set up the new multiplex noncoplanar (e,2e) spectrometer.

Coplanar e-scattering of technological molecules


The newly improved coplanar electron coincidence spectrometer for "complete" e-molecule experiments.


Chief machinist Harmen Vander Heide (left) and Dr. Xiaowei Fan (right) began careful alignment of the redesigned spectrometer.


Magic angle.


Dr. Xiaowei Fan inspected the finished work.  Perfect.

Low energy ions and electron mediated processes on technological surfaces


Zhenhua He setting up to do an electron energy loss experiment.


Let's clean the Si(111) crystal first. Flashing the crystal.


Double flashing.

Nano-engineering of molecular electronic materials


Qiang Li is looking at the chemical processes of model organic olefins on Si(100).


Aligning the crystal for a TPD experiment.


Is the crystal close enough to the mass spectrometer?


Double-check the sample position.

Time-resolved FTIR studies of environment-sensitive industrial ultrathin films.


Sergey Mitlin putting on the finishing touch on the CAD drawings for the new TR-FTIR UHV chamber.


















































































The primary mission of the Laboratory is to conduct exploratory studies of radiation-matter interactions in molecular and condensed matter using new electron-impact (and photon-impact) coincidence techniques. A wide range of surface science and chemical physics experiments probing the fundamental aspects of polyatomic molecules, low-temperature plasmas, semiconductor surfaces, and technological thin films and their interactions with charged-particle beams are being conducted.


Momentum-space chemistry   Molecular orbital imaging of technological molecules by (e,2e) spectroscopy.   [Xiaowei Fan, K.T. Leung] [Position Available]

Coplanar electron scattering Radiation physics and cross-section measurement of "forbidden" molecular excitation, ionization and dissociation processes of  environment-relevant materials.  [Xiaowei Fan, and K.T. Leung] [Position Available]
[Bethe-II - recommissioned 99.01.  See Gallery]

Electron-molecules collision-controlled spectroscopies Time-of-flight ions spectrometry of common technological molecules. [Position Available]


Low energy ion and radical reactions of plasma gases on Si(111)7x7 A molecular approach to understanding low-temperature plasma enhanced CVD process.   [Zhenhua He, K.T. Leung]

UV-induced and thermal chemical processes of organic materials on Si(100)  Nanoscale engineering of a conductive polymer/semiconductor interface for molecular electronics applications.  [Qiang Li, K.T. Leung]

Time-resolved FTIR studies of surface chemistry of condensed molecular and catalytic industrial films.  [Sergey Mitlin, Hui Yu, K.T. Leung]

Momentum-resolved photoemission spectroscopy of "new" quantum superstructures for optoelectronics device fabrication.  [Position Available]


Photo-breakdown of  CFC-substitutes and VOCs by multiple photoion coincidence spectroscopy at the Advanced Light Source.  [K.T. Leung]


Project MPS:  Development of  the next-generation multi-technique portable spectrometer for "complete" surface electron spectroscopy.  [Position Available]

Time-resolved spectrochemical analysis with new imaging detector technology.  [Hui Yu, K.T. Leung]



Team Member Projects Contact
Dr. Hui Yu PDF
Surface Science
Mr. Zhenhua He Ph.D. Chemistry
Surface Science
Mr. Qiang Li Ph.D Chemistry
Surface Science
Dr. Xiaowei Fan PDF
Chemical Physics
Mr. Sergey Mitlin Ph.D. Chemistry
Materials Science



H. Yu and K.T. Leung, Surf. Sci. (1999). "Electronic and vibrational electron energy loss studies of the formation of SiO2 and carbonaceous layers on Si(111)7x7 by thermal and ion-assisted deposition techniques. - PDF file.

K.T. Leung, J. Electron Spectrosc. Relat. Phenom. (1999)Invited Contribution to celebrate Vol. 100. "Non dipole spectroscopy by angle-resolved electron scattering at high energy."  - PDF file.

K.T. Leung, Honorary Editor, Physics in Canada, Special Theme Issue on "Collaborative Research in Physics and Chemistry", CAP. - To appear in Sept/Oct 1999

K.T. Leung, Editor, "Electron-Matter Interactions: Introduction to Electron Scattering and its Applications", World Scientific, New York. - Work in progress



1.  D.L. Hansen, G.B Armen, M.E. Arrasate, J. Cotter, G.R. Fisher, K.T. Leung, J.C. Levin, R. Martin, P. Neill, R.C.C. Perera, I.A. Sellin, M. Simon, B. Vanderford, S.B. Whitfield, and D.W. Lindle, Phys. Rev. A 57, Rapid Comm. 4090-3 (1998). "Postcollision-interaction effects in HCl following photofragmentation near the chlorine K edge"

2.   D.L. Hansen, M.E. Arrasate, J. Cotter, G.R. Fisher, K.T. Leung, J.C. Levin, R. Martin, P. Neill, R.C.C. Perera, I.A. Sellin, M. Simon, B. Vanderford, S.B. Whitfield, and D.W. Lindle, Phys. Rev. A 57, 2608-11 (1998). "Neutral dissociation of hydrogen following photoexcitation of HCl at the chlorine K edge."

3.   K.T. Leung, "Novel Aspects of Electron-Molecule Scattering", K.H. Becker (ed.), World Scientific, London, 199-240 (1998). "Recent development of momentum density measurement of polyatomics by molecular (e,2e) spectroscopy." Invited Review

4.   H. Yu and K.T. Leung, Surf. Sci. 401, 269-81 (1998). "Generation of stabilized surface species by low-energy ion interactions of ethylene with O or N covered Cu(100) at room temperature."

5.    H. Yu and K.T. Leung, J. Vac. Sci. Tech. A 16, 30-4 (1998). "Interactions of low-energy (20-800 eV) nitrogen ions with Cu(100): A combined TPD and EELS study of chemisorption and entrapment states."

6.    H. Yu, D.Q. Hu and K.T. Leung, J. Vac. Sci. Tech. A 15, 2653-60 (1997). "Effects of low-energy electron and ion irradiation on CO/Cu(100): In situ production and coadsorbate-induced adsorption of CO above room temperature."

7.    K.T. Leung, Can. J. Chem. 75, 1295-309 (1997). The Noranda Lecture: "Chemical applications of electron-matter interactions: From probing low-temperature plasmas and atmospheric chemistry of Freon-substitutes to enhancing novel surface reactions on metals and semiconductors."iew

8.  C.D. MacPherson and K.T. Leung, Surf. Sci. Lett. 356, L399-402 (1996). "Observation of dehydrogenation of cyclohexane on Si(111)7x7."

9.  J.F. Ying and K.T. Leung, J. Chem. Phys. 105, 2188-98 (1996). "Electron-impact excitation of low-lying preionization-edge n s * and Rydberg transitions of CHF2Cl and CHFCl2.
Absolute generalized oscillator strength measurement."  This work shows, for the first time, that the adsorption of CO on Cu(100) (a "classic" model chemisorption system in surface science) can be achieved at room temperature by using simple low-energy electron and ion irradiation (EII) techniques. This work demonstrates the viability of using these EII techniques to induce novel surface chemistry for producing new materials and stable interfaces, and it sets the stage for our EII work on Si(111) and Si(100), currently in progress.  The main result reported in this work and reviewed recently in an invited lecture is featured on the front cover of the October 1997 issue of the Canadian Journal of Chemistry.

10.   H. Yu, D.Q. Hu and K.T. Leung, Surf. Sci. Lett. 355, L335-40 (1996). "Anomalous stabilization of CO adsorption on Cu(100) at room temperature by coadsorbed atomic oxygen."

11.  J.F. Ying and K.T. Leung, Phys. Rev. A 53, 1476-86 (1996). "Electron-impact excitation of low-lying preionization-edge electronic and Rydberg transitions of fluoroform and chloroform: Bethe surfaces and absolute generalized oscillator strengths."

12.  C.D. MacPherson and K.T. Leung, Phys. Rev. B 51, 17995-8 (1995). "Adsorption-state-specific C1s chemical shifts of thiophene on Si(111)7x7 by photoemission at 340 eV."

13.  D.Q. Hu and K.T. Leung, Rev. Sci. Instrum. 66, 2865-70 (1995). "A SIMION study of the fringing field effects in deflector-type electron energy analysers: A modified Jost correction scheme." 
This new correction scheme is drawing attentions from VG and other major electron optics manufacturers as a new innovation for the next-generation electron energy analysers.

14.  H. Yu, D.Q. Hu, and K.T. Leung, Prog. Surf. Sci. 50, 197-205 (1995). "Electron energy loss studies of room-temperature CO adsorption on Cu(100) induced by electron or ion irradiation." Invited Review

15.  C.D. MacPherson and K.T. Leung, Surf. Sci. 326, 141-9 (1995). "Toluene interactions with the 7x7 and sputtered Si surfaces: Evidence for CH3-induced and O-enhanced dissociation pathways."

16.  C.D. MacPherson and K.T. Leung, Surf. Sci. 324, 202-10 (1995). "Electron-induced chemistry of pyridine on Si(111)7x7: A LEED and TPD study."
The rapid dissociation of pyridine induced by electron irradiation is demonstrated and the implications to the formation of surface carbidic carbon are discussed.

17.  C.D. MacPherson, D.Q. Hu, and K.T. Leung, Surf. Sci. 322, 58-72 (1995). "Thermal surface chemistry of 1-, 3-, and 4-methyl-cyclohexene on Si(111)7x7: Dehydrogenation mechanism and the effects of methyl substitution."

18.   M.H. Chuaqui, L. Mei, C.P. Mathers, M. Allison, J.F. Ying, and K.T. Leung, J. Chem. Phys. 102, 90-103 (1995). "Momentum-space ionization spectroscopy of iso-dichloroethylene: A comparative (e,2e) study of orbital momentum distributions in iso-C2H2Cl2 and its cis and trans isomers." 
Dichloroethylene is an important electronic gas that provides an excellent testing ground for the application of (e,2e) spectroscopy to large molecules. We show that the momentum distributions of the HOMO and NHOMO, along with the momentum-specific ionization energy spectra of the satellite ionic states, can offer useful insight into isomeric effects on the electronic structure. The idea of using a complete energy-momentum map for diagnostic purposes of large molecules is proposed.

19.  J.F. Ying and K.T. Leung, J. Chem. Phys. 101, 8333-50 (1994). "Non-optical excited state spectroscopy of CF3Cl, CF2Cl2 and CFCl3: Bethe surfaces and absolute transition probability measurement of preionization-edge valence and Rydberg transitions by angle-resolved electron energy loss spectroscopy."

20.   J.F. Ying and K.T. Leung, J. Chem. Phys. 101, 7311-9 (1994). "Atomic-site-specific non-optical excitation spectroscopy of chlorofluoromethanes CF4-nCln (n=0-4): Absolute generalized oscillator strength measurement of below-edge electronic excitations of C 1s and S 2p shells."
Along with our earlier work on SF6, this work gives a comprehensive angle-resolved electron energy loss study of the inner-shell region in these technologically important electronic gases (Freons). It demonstrates that the momentum dependence of the GOS profiles for individual transitions can be used as a powerful means to characterize the nature of these states. These two inner-shell angle-resolved electron energy loss studies have generated a tremendous interest in this field, and led the way for the recent molecular inner-shell studies by  other groups.

21.  L. Mei, M. Chuaqui, C.P. Mathers, J.F. Ying, and K.T. Leung, Chem. Phys. 188, 347-65 (1994). "Experimental momentum-space orbital density study of valence-shell electronic structure and many-body effects of trans-dichloroethylene by symmetric noncoplanar (e,2e) spectroscopy."

22.  L. Mei, M. Chuaqui, C.P. Mathers, J.F. Ying, and K.T. Leung, J. Chem. Phys. 101, 3558-72 (1994). "Electron-momentum-specific valence-shell electronic structure of and many-body effects in cis-dichloroethylene: Ionic-state-resolved orientationally averaged electron momentum density measurement by symmetric noncoplanar (e,2e) spectroscopy."

23.  C.P. Mathers, B.N. Gover, J.F. Ying, H. Zhu, and K.T. Leung, J. Am. Chem. Soc. 116, 7250-7 (1994). "Experimental momentum-space chemistry of iso-butene: Isomeric effects on orbital-specific electron momentum distributions in iso-butene and its cis and trans isomers."

24.  C.K. Subramaniam, M. Coplan, J.A. Tossell, J.H. Moore, and K.T. Leung, Chem. Phys. 185, 237-250 (1994). "(e,2e) momentum spectroscopic study of the valence orbitals of hydrogen selenide."

25.  C.P. Mathers, J.F. Ying, B.N. Gover, and K.T. Leung, Chem. Phys. 184, 295-318 (1994). "Valence-shell electronic structures of cis- and trans-butene: Orientationally averaged momentum distributions by symmetric noncoplanar (e,2e) spectroscopy."

26.  C.D. MacPherson, D.Q. Hu, M. Doan, and K.T. Leung, Surf. Sci. 310, 231-42 (1994). "Catalytic dehydrogenation and thermal chemistry of cyclohexene and 1-methyl-1,4- cyclohexadiene on Si(111) 7x7 surfaces."
Despite the enormous amount of work on Si materials, this study illustrates, for the first time, the catalytic reforming properties of Si(111)7x7, which is generally believed to be relatively unreactive. In addition to the fundamental interests in Si organic chemistry, this result has enormous implications to Si device processing, particularly with respect to the nature and mechanisms of carbide formation on single-crystal and amorphous Si surfaces. We are currently extending our study to other novel surface reactions on Si(100)2x1 (a common technological surface).

27.  J.F. Ying, C.P. Mathers, and K.T. Leung, "Electron Scattering by Molecules, Clusters and Surfaces", H. Ehrhardt and L.A. Morgan (eds.), Plenum, New York, 141-150 (1994). "Valence and inner shell multiple electronic excitations of chlorofluorocarbons by momentum transfer resolved electron energy loss spectroscopy." Invited Review

28.  J.F. Ying and K.T. Leung, J. Chem. Phys. 100, 7120-34 (1994). "Absolute transition probability measurement of valence-shell electronic structure of CF4 and CCl4: Bethe surfaces, dipole-dominated pre-ionization-edge valence and Rydberg states."

29.  J.F. Ying and K.T. Leung, J. Chem. Phys. 100, 1011-20 (1994). "Non-optical excited state spectroscopy of CHF2Cl: Characterization of non-dipole n s * valence transitions by angle-resolved electron energy loss spectroscopy."
The GOS profiles of the HOMO-LUMO transitions for CF3Cl and its environment-safe substitute (CHF2Cl) are compared. This work provides strong evidence for the similarity in the dissociation pathways of these two molecules.

30.  J.F. Ying, C.P. Mathers, K.T. Leung, H.P. Pritchard, C. Winstead, and V. McKoy, Chem. Phys. Lett. 212, 289-97 (1993). "Observation of a "new" non-dipole transition at 7.7 eV in CF3Cl by momentum-transfer-resolved electron energy loss spectroscopy."

31.  J.F. Ying, T.A. Daniels, C.P. Mathers, H. Zhu, and K.T. Leung, J. Chem. Phys. 99, 3390-99 (1993). "Absolute transition probability measurement of non-dipole valence-shell (7-70 eV) electronic transitions of SF6 by angle-resolved electron energy loss spectroscopy."

32.  J.F. Ying and K.T. Leung, J.  Electron Spectrosc. Relat. Phenom. 63, 75-84 (1993). "Observation of many-body structure in valence photoelectron spectra of cis, trans and iso-C2H2Cl2 at 120 eV."

33.  J.F. Ying, H. Zhu, C.P. Mathers, B.N. Gover, M.P. Banjavcic, Y. Zheng, C.E. Brion, and K.T. Leung, J.  Chem. Phys. 98, 4512-19 (1993). "Electron momentum specific valence-shell electronic structures of cis-, trans- and iso-butene by symmetric noncoplanar (e,2e) spectroscopy."

34.  J.F. Ying, C.P. Mathers, T.A. Daniels, and K.T. Leung, Phys. Rev. A 47, Rapid Comm. 5-8 (1993). "Momentum-transfer dependence of S 2p excitations of SF6 by angle-resolved electron energy loss spectroscopy."
This work provides the first GOS measurement of a non-dipole inner-shell transition.


1.   K.T. Leung, C.E. Brion and P. Zetner, Guest Editors, Canadian Journal of Physics, Vol 74, No. 11-12 (1996). Proceedings of the 6th International Symposium on (e,2e), Double Photoionization and Related Topics - Vancouver (1995).

2.  K.T. Leung and W.K. Liu, Guest Editors, Progress in Surface Science, Vol. 50 (1995). Proceedings of the 15th Canadian Conference on Surface Science and Special Symposium to celebrate the 25th Anniversary of Progress in Surface Science - Waterloo (1995).