PHYS. REV. B: "Growth of Pentacene on Clean and Modified Gold Surfaces" D. Käfer, L. Ruppel, G. Witte Physical Review B 75 (8), 085309 (2007), DOI: 10.1103/PhysRevB.75.085309
TH. SOL. FILMS: "Energy-dispersive X-ray reflectivity and GID for Real-time Growth Studies of Pentacene Films" S. Kowarik, A. Gerlach, W. Leitenberger, J. Hua, G. Witte, C. Wöll, U. Pietsch, F. Schreiber Thin Solid Films 515 (14), 5606-5610 (2007), DOI: 10.1016/j.tsf.2006.12.020
AIP CONF. PROCEED.: "Reduced Sheet Resistance In Pentacene Field-Effect Transistors Using Thiol-Modified Electrodes" D. V. Pham, Y. Gravenstein, C. Bock, U. Kunze, D. Käfer, G. Witte, Ch. Wöll AIP Conference Proceedings 893 (1), 363-364 (2007), DOI: 10.1063/1.2729917
J. PHYS. CHEM. C: "Interplay of Anchoring and Ordering in aromatic Self-Assembled Monolayers" D. Käfer, A. Bashir, G. Witte Journal of Physical Chemistry C 111 (28), 10546-10551 (2007), DOI: 10.1021/jp073010w
CHEM. PHYS. LET.: "Evolution of Pentacene Films on Ag(111): growth beyond the first monolayer" D. Käfer and G. Witte Chemical Physics Letters 442 (4-6), 376-383 (2007), DOI: 10.1016/j.cplett.2007.06.006
CHEM. MAT.: "Molecules Coining Patterns into a Metal: The Hard Core of Soft Matter" G. Witte, K. Hänel, C. Busse, A. Birkner, Ch. Wöll Chemistry of Materials 19 (17), 4228-4233 (2007), DOI: 10.1021/cm071054b
APPL. PHYS. LET.: "Influence of anthracene-2-thiol treatment on the device parameters of pentacene bottom-contact transistors" C. Bock, D. V. Pham, U. Kunze, D. Käfer, G. Witte, A. Terfort Applied Physics Letters 91 (5), 052110 (2007), DOI: 10.1063/1.2767235
J. APPL. PHYS.: "A defect-free thin film pentacene diode: Interplay between transport and scanning tunneling microscope tip tunneling injection" L. Ruppel, A. Birkner, G. Witte, C. Busse, T. Lindner, G. Paasch, Ch. Wöll Journal of Applied Physics 102 (3), 033708 (2007), DOI: 10.1063/1.2764027
J. PHYS. CHEM. C: "Influence of Molecular Structure on Phase Transitions: A Study of Self-Assembled Monolayers of 2-(Aryl)-ethane Thiols" P. Cyganik, M. Buck, Th. Strunskus, A. Shaporenko, G. Witte, M. Zharnikov, Ch. Wöll Journal of Physical Chemistry C 111 (45), 16909-16919 (2007), DOI: 10.1021/jp073979k
2006
APPL. PHYS. A: "Growth and morphology of thin films of aromatic molecules on metals: the case of perylene" G. Witte, K. Hänel, S. Söhnchen, Ch. Wöll (invited paper) Applied Physics A 82 (3), 447-455 (2006), DOI: 10.1007/s00339-005-3367-1
ACS: "A Comprehensive Study of Self-Assembled Monolayers of Anthracenethiol on Gold: Solvent Effects, Structure, and Stability" D. Käfer, G. Witte, P. Cyganik, A. Terfort, Ch.Wöll Journal of the American Chemical Society 128 (5), 1723-1732 (2006), DOI: 10.1021/ja0571592
J. APPL. PHYS.: "Improved morphology and charge carrier injection in pentacene field-effect transistors with thiol treated electrodes." C. Bock, D. V. Pham, U. Kunze, D. Käfer, G. Witte, Ch. Wöll Journal of Applied Physics 100 (11), 114517 (2006), DOI: 10.1063/1.2400507
2005
CHEM. MATER.: "Metal−Organic Chemical Vapor Deposition of Palladium: Spectroscopic Study of Cyclopentadienyl-allyl-palladium Deposition on a Palladium Substrate" A. Niklewski, Th. Strunskus, G. Witte, Ch. Wöll Chemistry of Materials 17 (4), 861-868 (2005), DOI: 10.1021/cm048798z
PHYS. CHEM. CHEM. PHYS.: "Growth of crystalline Rubrene films with enhanced stability" D. Käfer and G. Witte Physical Chemistry Chemical Physics 7 (15), 2850-2853 (2005), DOI: 10.1039/B507620J
CHEM. VAP. DEP.: "Deposition of palladium from cyclopentadienyl-allyl-palladium precurser on differently pretreated Sibased substrates: The role of surface Si-OH and Si-H species studied by x-ray photoelectron spectroscopy" Q.-H. Wu, M. Gunia, Th. Strunskus, G. Witte, M. Muhler, Ch. Wöll Chemical Vapor Deposition 11 (8-9), 355-361 (2005), DOI: 10.1002/cvde.200506390
CHEM. MATER.: "Molecular beam deposition of perylene on copper: formation of ordered phases" S. Söhnchen, K. Hänel, A. Birkner, G. Witte, Ch. Wöll Chemistry of Materials 17 (21), 5297-5304 (2005), DOI: 10.1021/cm051183x
PHYS REV. LET.: "Role of Molecular Conformations in Rubrene Thin Film Growth" D. Käfer, L. Ruppel, G. Witte, Ch. Wöll Physical Review Letters 95 (16), 166602 (2005), DOI: 10.1103/PhysRevLett.95.166602
APPL. PHYS. LET.: "Vacuum level alignment at organic/metal junctions: The “cushion” effect and the interface dipole" G. Witte, S. Lukas, P. Bagus, Ch. Wöll Applied Physics Letters 87 (26), 263502 (2005), DOI: 10.1063/1.2151253
2004
COMP. MATER. SCI.: "Structural and electronic properties of pentacene molecule and molecular pentacene solid" R. G. Endres, C. Y. Fong, L. H. Yang, G. Witte, Ch. Wöll Computational Materials Science 29 (3), 362-370 (2004), DOI: 10.1016/j.commatsci.2003.09.006
CHEMPHYSCHEM: "Epitaxial Growth of Pentacene Films on Metal Surfaces" S. Lukas, S. Söhnchen, G. Witte, Ch. Wöll ChemPhysChem 5 (2), 266-270 (2004) • DOI: 10.1002/cphc.200300892
J. CHEM. PHYS.: "Epitaxial growth of Pentacene films on Cu(110)" S. Söhnchen, S. Lukas, G. Witte Journal of Chemical Physics 121 (1), 525-534 (2004), DOI: 10.1063/1.1760076
J. MATER. RES.: "Organic molecular beam epitaxy of perylene on Cu(110): Results from NEXAFS, XPS and AFM" K. Hänel, S. Söhnchen, S. Lukas, G. Beernink, A. Birkner, Th. Strunskus, G. Witte, Ch. Wöll Journal of Materials Research 19 (7), 2049-2056 (2004), DOI: 10.1557/JMR.2004.0256
J. MATER. RES.: "Growth of aromatic molecules on solid substrates for applications in organic electronics" G. Witte and Ch. Wöll Journal of Materials Research 19 (7), 1889-1916 (2004) • DOI: 10.1557/JMR.2004.0251
J. PHYS. COND. MATER.: "Probing metallization transitions by metastable He-atom scattering." G. Witte Journal of Physics: Condensed Matter 16 (29), S2937-S2952 (2004), DOI: 10.1088/0953-8984/16/29/009
APPL. PHYS. LET.: "Importance of dewetting in organic molecular beam deposition: Pentacene on gold" G. Beernink, Th. Strunskus, G. Witte, Ch. Wöll Applied Physics Letters 85 (3), 398-400 (2004), DOI: 10.1063/1.1775040
2003
PH. TRANS.: "Organic Surface Science: Creating order and complexity using self-assembly." G. Witte and Ch. Wöll Phase Transitions 76 (4), 291-305 (2003), DOI: 10.1080/0141159021000051488
LANGMUIR: "Pronounced Odd−Even Changes in the Molecular Arrangement and Packing Density of Biphenyl-Based Thiol SAMs: A Combined STM and LEED Study" W. Azzam, P. Cyganik, G. Witte, M. Buck, Ch. Wöll Langmuir 19 (20), 8262-8270 (2003), DOI: 10.1021/la030165w
2002
PHYS. REV. LET.: "Novel Mechanism for Molecular Self-Assembly on Metal Substrates: Unidirectional Rows of Pentacene on Cu(110) Produced by a Substrate-Mediated Repulsion" S. Lukas, G. Witte, Ch. Wöll Physical Review Letters 88 (2), 028301 (2002), DOI: 10.1103/PhysRevLett.88.028301
SURF. SCI.: "Low frequency vibrational modes of adsorbates" G. Witte Surface Science 502-503, 405-416 (2002), DOI: 10.1016/S0039-6028(01)01986-0
PHYS. REV. B: "Microstructure of the a-Al2O3(112-0) surface" Th. Becker, A. Birkner, G. Witte, Ch. Wöll Physical Review B 65 (11), 115401 (2002), DOI: 10.1103/PhysRevB.65.115401
LANGMUIR: "Adsorption of Dodecanethiol on Cu(110): Structural Ordering upon Thiolate Formation" A. Kühnle, S. Vollmer, T. R. Linderoth, G. Witte, Ch. Wöll, F. Besenbacher Langmuir 18 (14), 5558-5565 (2002), DOI: 10.1021/la025661j
PHYS. REV. B: "Structural, chemical, and magnetic properties of Fe films grown on InAs(100)." L. Ruppel, G. Witte, Ch. Wöll, T. Last, S. F. Fischer, U. Kunze Physical Review B 66 (24), 245307 (2002) • DOI: 10.1103/PhysRevB.66.245307
2001
SURF. SCI.: "Growth and dynamics of ultrathin barium films on Cu(100)" S. Bartholmei, P. Fouquet, G. Witte Surface Science 473 (3), 227-235 (2001) • DOI: 10.1016/S0039-6028(00)00973-0
J. CHEM. PHYS.: "Adsorption of acenes on flat and vicinal Cu(111) surfaces: Step induced formation of lateral order" S. Lukas, S. Vollmer, G. Witte, Ch. Wöll Journal of Chemical Physics 114 (22), 10123-10130 (2001), DOI: 10.1063/1.1370936
LANGMUIR: "Structural Characterization of Organothiolate Adlayers on Gold: The Case of Rigid, Aromatic Backbones" C. Fuxen, W. Azzam, R. Arnold, G. Witte, A. Terfort, Ch. Wöll Langmuir 17 (12), 3689-3695 (2001), DOI: 10.1021/la0018033
J. CHEM. PHYS.: "Low Energy Dynamics of NO and CO chemisorbed on Rh(111)" G. Witte Journal of Chemical Physics 115 (6), 2757-2767 (2001), DOI: 10.1063/1.1386434
APPL. SURF. SCI.: "Metallization and demetallization of clean and oxygen covered ultrathin alkali metal films on GaAs(100)" P. Fouquet and G. Witte Applied Surface Science 180 (3-4), 286-292 (2001), DOI: 10.1016/S0169-4332(01)00368-3
LANGMUIR: "Structural Analysis of Saturated Alkanethiolate Monolayers on Cu(100): Coexistence of Thiolate and Sulfide Species" S. Vollmer, G. Witte, Ch. Wöll Langmuir 17 (24), 7560-7565 (2001), DOI: 10.1021/la0107852
CAT. LET.: "Determination of Site Specific Adsorption Energies of CO on Copper" S. Vollmer, G. Witte, Ch. Wöll Catalysis Letters 77 (1-3), 97-101 (2001), DOI: 10.1023/A:1012755616064
2000
SURF. SCI.: "Monitoring of electronic poisoning of ultrathin alkali metal films by oxygen and carbon monoxide adsorption" P. Fouquet and G. Witte Surface Science 454-456, 256-261 (2000), DOI: 10.1016/S0039-6028(00)00169-2
J. CHEM. PHYS.: "A helium atom scattering study of the adsorption of NO on Pt(111)" P. Fouquet, A. P. Graham, G. Witte Journal of Chemical Physics 112 (17), 7600-7605 (2000), DOI: 10.1063/1.481354
APPL. PHYS. LET.: "Nanopatterning of copper (111) vicinal surfaces by oxygen-induced mesoscopic faceting" S. Vollmer, A. Birkner, S. Lukas, G. Witte, Ch. Wöll Applied Physics Letters 76 (19), 2686-2688 (2000), DOI: 10.1063/1.126444
J. VAC. SCI. TEC.: "Variable temperature and ex situ spin-polarized low-energy electron microscope (SPLEEM)" E. D. Tober, G. Witte, H. Poppa Journal of Vacuum Science & Technology A 18 (4), 1845-1847 (2000), DOI: 10.1116/1.582433
SURF. SCI.: "Low-energy vibrational dynamics of ultrathin organic adlayers: alkanethiols adsorbed on copper." S. Vollmer, P. Fouquet, G. Witte, Ch. Boas, M. Kunat, U. Burghaus, Ch. Wöll Surface Science 462 (1-3), 135-142 (2000), DOI: 10.1016/S0039-6028(00)00590-2
MAT.-SCI & ENG.-TEC.: "Nanostrukturierung von Kupferoberflächen durch Sauerstoff-induzierte Rekonstruktionen" S. Vollmer, A. Birkner, S. Lukas, G. Witte, Ch. Wöll Materials Science & Engineering Technology 31 (9), 845-849 (2000), DOI: 10.1002/1521-4052(200009)31:9<845::AID-MAWE845>3.0.CO;2-X
PHYS. REV. B: "Phonons in a quasi-two-dimensional solid: Cesium monolayer on Cu(001)" G. Witte and J. P. Toennies Physical Review B 62 (12), R7771-R7774 (2000), DOI: 10.1103/PhysRevB.62.R7771
1999
CHEM. PHYS. LET.: "Low-frequency vibrations of alkali atoms on Cu(001)" P. Senet, J. P. Toennies, G.Witte Chemical Physics Letters 299 (5), 389-394 (1999), DOI: 10.1016/S0009-2614(98)01314-1
SURF. REV. LET.: "Metastable (23S) Helium Atom Scattering From NiO(100) and Cu(100) Surfaces" P. Fouquet and G. Witte Surface Review and Letters 6 (1), 103-107 (1999), DOI: 10.1142/S0218625X99000123
PHYS. REV. B.: "Low-frequency adsorbate vibrational relaxation and sliding friction" B. N. J. Persson, E. Tosatti, D. Fuhrmann, G. Witte, Ch. Wöll Physical Review B 59 (18), 11777-11791 (1999), DOI: 10.1103/PhysRevB.59.11777
LANGMUIR: "Adsorption of Heptanethiol on Cu(110)" G. Loepp, S. Vollmer, G. Witte, Ch. Wöll Langmuir 15 (11), 3767-3772 (1999), DOI: 10.1021/la981510y
PHYS. REV. LET.: "Observation of Metallization Transition of 2D Alkali Metal Films" P. Fouquet and G. Witte Physical Review Letters 83 (2), 360-363 (1999), DOI: 10.1103/PhysRevLett.83.360
1998
PHYS. REV. LET.: "Damping of Molecular Motion on a Solid Substrate: Evidence for Electron-Hole Pair Creation" G. Witte, K. Weiss, P. Jakob, J. Braun, K. L. Kostov, Ch. Wöll Physical Review Letters 80 (1), 121-124 (1998), DOI: 10.1103/PhysRevLett.80.121
SURF. SCI.: "Metastable (23S) helium atom scattering from NiO(100) and Cu(100) surfaces" P. Fouquet, P. K. Day, G. Witte Surface Science 400 (1-3), 140-154 (1998), DOI: 10.1016/S0039-6028(97)00857-1
SURF. SCI.: "Second-harmonic generation from sodium covered Si(111)7×7 surfaces" J. Boness, G. Marowsky, J. Braun, G. Witte, H.-G. Rubahn Surface Science 402-404, 513-517 (1998), DOI: 10.1016/S0039-6028(97)00959-X
PHYS. REV. LET.: "Self-Assembled Lateral Multilayers from Thin Film Alloys of Immiscible Metals" E. D. Tober, R. F. C. Farrow, R. F. Marks, G. Witte, K. Kalki, D. D. Chambliss Physical Review Letters 81 (9), 1897-1900 (1998), DOI: 10.1103/PhysRevLett.81.1897
PHYS. REV. B: "Oxygen-induced reconstructions on Cu(211)" G. Witte, J. Braun, D. Nowack, L. Bartels, B. Neu, G. Meyer Physical Review B 58 (19), 13224-13232 (1998), DOI: 10.1103/PhysRevB.58.13224
PHYS. REV. B: "Helium-atom-scattering study of the structure and phonons of the NiO(100) and CoO(100) surfaces" G. Witte, P. Senet, J. P. Toennies Physical Review B 58 (19), 13264-13274 (1998), DOI: 10.1103/PhysRevB.58.13264
1997
PHYS. REV. B: "Lattice dynamics of the Ni(977) surface" G. Witte and J. P. Toennies Physical Review B 55 (3), 1395-1397 (1997), DOI: 10.1103/PhysRevB.55.1395
SURF. SCI.: "Surface phonon dispersion curves for a hexagonally close packed metal surface: Ru(0001)" J. Braun, K. L. Kostov, G. Witte, L. Surnev, J. G. Skofronick, S. A. Safron, Ch. Wöll Surface Science 372 (1-3), 132-144 (1997), DOI: 10.1016/S0039-6028(96)01108-9
CHEM. PHYS. LET.: "Low-energy molecular vibrations investigated by inelastic scattering of He atoms" G. Witte, D. Fuhrmann, Ch. Wöll Chemical Physics Letters 265 (3-5), 347-352 (1997), DOI: 10.1016/S0009-2614(96)01457-1
J. CHEM. PHYS.: "CO overlayers on Ru(0001) studied by helium atom scattering: Structure, dynamics, and the influence of coadsorbed H and O" J. Braun, K. L. Kostov, G. Witte, Ch. Wöll Journal of Chemical Physics 106 (19), 8262-8273 (1997), DOI: 10.1063/1.473828
REV. SCI. Instr.: "Micrometer-sized nozzles and skimmers for the production of supersonic He atom beams" J. Braun, P. K. Day, J. P. Toennies, G. Witte, E. Neher Review of Scientific Instruments 68 (8), 3001-3009 (1997), DOI: 10.1063/1.1148233
SURF. SCI. LET.: "A He atom scattering study of the low energy vibrations of CO adsorbed on Ni(110)" Massimo F. Bertino and Gregor Witte Surface Science Letters 385 (2-3), L984-L989 (1997), DOI: 10.1016/S0039-6028(97)00430-5
1996
APPL. PHYS. A: "The low-energy thermal excitation spectrum of nitrogen molecules adsorbed on Ni(110): Implications for molecular adsorption sites" M. Bertino, W. Steinhögl, H. Range, F. Hofmann, G. Witte, E. Hulpke, Ch. Wöll Applied Physics A 62 (2), 95-101 (1996), DOI: 10.1007/BF01575707
J. CHEM. PHYS.: "A He-atom scattering study of the frustrated translational mode of CO chemisorbed on defects on copper surfaces" J. Braun, A. P. Graham, F. Hofmann, W. Silvestri, J. P. Toennies, G. Witte Journal of Chemical Physics 105 (8), 3258-3263 (1996), DOI: 10.1063/1.471841
PHYS. REV. B: "Surface-scattering study of the interaction potential of He atoms with the step edges of the Cu(211) and Cu(511) vicinal surfaces" S. Miret-Artes, J. P. Toennies, G. Witte Physical Review B 54 (8), 5881-5892 (1996), DOI: 10.1103/PhysRevB.54.5881
1995
SURF. SCI.: "Comparison of surface phonon dispersion curves for clean and hydrogen covered Rh(111) surfaces" G. Witte, J. P. Toennies, Ch. Wöll Surface Science 323 (3), 228-240 (1995), DOI: 10.1016/0039-6028(94)00593-1
J. CHEM. PHYS.: "Helium atom scattering study of the frustrated translation mode of CO adsorbed on the Cu(001) surface" J. Ellis, J. P. Toennies, G. Witte Journal of Chemical Physics 102 (12), 5059-5070 (1995), DOI: 10.1063/1.469555
PHYS. REV. B.: "Helium-atom-scattering study of the dispersion curves of step-localized phonons on Cu(211) and Cu(511)" G. Witte, J. Braun, A. Lock, J. P. Toennies Physical Review B 52 (3), 2165-2176 (1995), DOI: 10.1103/PhysRevB.52.2165
J. CHEM. PHYS.: "External vibrations of hydrocarbons on Cu(100)" G. Witte, Ch. Wöll Journal of Chemical Physics (Letters to the Editor) 103 (13), 5860-5863 (1995), DOI: 10.1063/1.470465
A SPALEED structural study of cesium adsorption on stepped copper surfaces Cu(211) and Cu(511)" J. Braun, J. P. Toennies, G. Witte Surface Science 340 (3), 265-280 (1995), DOI: 10.1016/0039-6028(95)00682-6
DISSERTATION: "Untersuchung der Dynamik und Struktur von sauberen und adsorbatbedeckten Oxid- und Metalloberflächen (Investigation of the dynamics and structure of clean and adsorbate-covered oxide and metal surfaces)" Gregor Witte Dissertation Georg-August Universität Göttingen (1995). Max-Planck-Institut für Strömungsforschung, Bericht 8/1995, ISSN 0436-1199
1994
PHYS. REV. B: "Surface-phonon dispersion curves and the longitudinal resonance in Ag(001) observed by helium-atom scattering" N. Bunjes, N. Luo, P. Ruggerone, J. P. Toennies, G. Witte Physical Review B 50 (12), 8897-8900 (1994), DOI: 10.1103/PhysRevB.50.8897
1993
PHYS. REV. LET.: "Observation of the low-energy external vibrations of benzene on Rh(111)" G. Witte, H. Range, J. P. Toennies, Ch. Wöll Physical Review Letters 71 (7), 1063-1066 (1993), DOI: 10.1103/PhysRevLett.71.1063
J. ELEC. SPEC. REL. PHEN.: "High resolution He-atom scattering on NiO(100)" J. P. Toennies, G. Witte, A. M. Shikin, K. H. Rieder Journal of Electron Spectroscopy and Related Phenomena 64-65, 677-682 (1993), DOI: 10.1016/0368-2048(93)80136-A
J. ELEC. SPEC. REL. PHEN.: "External vibrations of molecules on surfaces: The case of CO and benzene" G. Witte, H. Range, J. P. Toennies, Ch. Wöll Journal of Electron Spectroscopy and Related Phenomena 64-65, 715-723 (1993), DOI: 10.1016/0368-2048(93)80141-8
J. ELEC. SPEC. REL. PHEN.: "The observation of well defined two and three phonon bands in time of flight spectra of helium atoms scattered from the c(2 × 2) structure of CO on Cu(001)" J. Ellis, A. Reichmuth, J. P. Toennies, G. Witte Journal of Electron Spectroscopy and Related Phenomena 64-65, 725-731 (1993), DOI: 10.1016/0368-2048(93)80142-9
1991
PROC. ISSAC: "Application of computer algebra to surface lattice dynamics" R. Berndt, A. Lock, G. Witte, Ch. Wöll Proceedings of the 1991 international symposium on Symbolic and algebraic computation (ISSAC), pp. 433-438 (1991), DOI: 10.1145/120694.120763
PROC. SPIE: "ORFEUS alignment concept" R. Graue, D. Kampf, H. Rippel, G. Witte Proc. SPIE, Space Astronomical Telescopes and Instruments 1494, 377-385 (1991), DOI: 10.1117/12.46737
1990
J. ELEC. SPEC. REL. PHEN.: "Photoemission and He-atom scattering from Xe adsorbed on Al(332)" B. J. Hinch, A. Lock, H. H. Madden, J. P. Toennies, G. Witte Journal of Electron Spectroscopy and Related Phenomena 51, 673-688 (1990), DOI: 10.1016/0368-2048(90)80190-L
PHYS. REV. B: "Helium-atom scattering investigation of facetting of the Al stepped (332) surface" B. J. Hinch, A. Lock, H. H. Madden, J. P. Toennies, G. Witte Physical Review B 42 (3), 1547-1559 (1990), DOI: 10.1103/PhysRevB.42.1547
J. ELEC. SPEC. REL. PHEN.: "Surface phonons of stepped metal surfaces" A. Lock, J. P. Toennies, G. Witte Journal of Electron Spectroscopy and Related Phenomena 54-55, 309-316 (1990), DOI: 10.1016/0368-2048(90)80223-W
PROC.: "Lattice Dynamical Calculations for stepped Surfaces" A. Lock, J. P. Toennies, G. Witte Proceedings of the Third International Conference on Phonon Physics and Sixth International Conference on Condensed Matter,Heidelberg, 1989, pp.901-903 (World Scientific, Singapore, 1990)